CN113811562A

CN113811562A - Varnish, optical film, and method for producing optical film

Info

Publication number: CN113811562A
Application number: CN202080033043.3A
Authority: CN
Inventors: 杉山纮子; 塚田洋行; 池内淳一
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2019-05-10
Filing date: 2020-05-01
Publication date: 2021-12-17
Also published as: TW202106823A; KR20220007101A; JP2020186369A; WO2020230663A1

Abstract

The present invention provides a varnish which can effectively prevent yellowing of a polyimide polymer film even when the film is produced after being stored in a varnish state for a long period of time. A varnish comprising a polyimide-based polymer and a solvent comprising gamma-butyrolactone which is: gamma-butyrolactone with a light transmittance at a wavelength of 275nm of 88% or more; or, in a capillary gas chromatography using polyethylene glycol as a stationary phase, when a sample is injected while the column temperature is maintained at 120 ℃, the temperature is maintained at 120 ℃ for 1 minute, the temperature is raised to 240 ℃ at a rate of 10 ℃/minute, and the temperature is maintained at 240 ℃ for 7 minutes, the area ratio of the component detected at a relative retention time of 1.05 to 1.50 based on the peak of γ -butyrolactone is 260ppm or less.

Description

Varnish, optical film, and method for producing optical film

Technical Field

The present invention relates to a varnish containing γ -butyrolactone (hereinafter, may be abbreviated as GBL) and a polyimide-based polymer, an optical film formed from the varnish, and a method for producing the optical film.

Background

Currently, image display devices such as liquid crystal display devices and organic EL display devices are widely and effectively used for various applications such as mobile phones and smartwatches, as well as television sets. With such expansion of applications, an image display device (flexible display) having flexible characteristics is required. The image display device includes a display element such as a liquid crystal display element or an organic EL display element, and components such as a polarizing plate, a retardation plate, and a front panel. In order to realize a flexible display, all of the above-described constituent members need to have flexibility.

Glass has been used as a front panel. Glass has high transparency and can exhibit high hardness depending on the kind of glass, but on the other hand, it is very rigid and easily broken, and thus it is difficult to use it as a front panel material for a flexible display. Therefore, as one of materials that can replace glass, there is a polyimide-based resin, and an optical film using the polyimide-based resin has been studied (for example, patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2017-203984

Disclosure of Invention

Problems to be solved by the invention

Such an optical film is produced, for example, by a casting method in which a resin composition called a varnish prepared by dissolving a polyimide-based polymer in a solvent is applied to a support and then dried. The inventors of the present application have found that, particularly in the case of producing an optical film to be used as a front panel of an image display device or the like, a varnish containing GBL is preferable from the viewpoint of good compatibility with a polyimide-based polymer and easy improvement in optical characteristics of the optical film to be obtained.

Here, when an optical film is produced by a casting method, the solvent itself contained in the varnish is a component distilled off by drying, and hardly remains in the obtained optical film. Therefore, when an optical film is produced by forming and drying a varnish immediately after the preparation of the varnish, no phenomenon such as a decrease in YI value, which is an index of the yellow index of the optical film, is observed. However, it is known that when GBL is used as a solvent for at least a part of varnish containing polyimide-based polymers, the polyimide-based polymers in varnish having improved reactivity in a state of being dissolved in the solvent react with impurities in γ -butyrolactone, and as a result, the following may occur: as the storage time in the varnish state becomes longer, the YI value of the obtained optical film increases and the optical characteristics deteriorate.

Accordingly, an object of the present invention is to provide a varnish in which a polyimide polymer is dissolved in GBL, and which can effectively prevent yellowing of a polyimide polymer film even when the film is produced after being stored in a varnish state for a long period of time.

Means for solving the problems

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by using a varnish containing at least a polyimide-based polymer and a solvent containing GBL having a light transmittance of 88% or more at a wavelength of 275nm and/or GBL having an area ratio of a component detected in a gas chromatography under a predetermined condition within a predetermined range with respect to a peak of GBL of a predetermined value or less.

That is, the present invention includes the following preferred embodiments.

[ 1] A varnish comprising:

a solvent containing gamma-butyrolactone having a light transmittance of 88% or more at a wavelength of 275 nm; and

a polyimide polymer.

[ 2] A varnish comprising at least a polyimide-based polymer and a solvent containing gamma-butyrolactone in which the area ratio of a component detected at a column temperature of 120 ℃ in a capillary gas chromatography analysis using polyethylene glycol as a stationary phase is 260ppm or less, when the sample is injected, the temperature is maintained at 120 ℃ for 1 minute, the temperature is raised to 240 ℃ at a rate of 10 ℃/minute, and the temperature is maintained at 240 ℃ for 7 minutes, and the peak of gamma-butyrolactone is used as a reference, the relative retention time is 1.05 to 1.50.

[ 3] the varnish according to the above [ 2], wherein the column in the capillary gas chromatography is DB-WAX (30 m.times.0.32 mm I.D., d.) manufactured by Agilent Technologies_f0.50μm)。

The varnish according to any one of [ 1] to [ 3] above, wherein the content of γ -butyrolactone is 30 to 100% by mass based on the total amount of solvent contained in the varnish.

The varnish according to any one of [ 1] to [ 4] above, wherein the solvent is contained in an amount of 75 to 99% by mass based on the total amount of the varnish.

The varnish according to any one of [ 1] to [ 5] above, wherein the content of the polyimide-based polymer is 1 to 25% by mass based on the total amount of the varnish.

[ 7] the varnish according to any one of [ 1] to [ 6] above, which is based on L^＊a^＊b^＊In the color difference measurement of the color system, L is satisfied^＊≥80、-10≤a^＊B is not more than 10, and-10 is not more than b^＊≤10。

The varnish according to any one of [ 1] to [ 7] above, wherein the weight average molecular weight of the polyimide-based polymer in terms of polystyrene is 200,000 or more.

The varnish according to any one of [ 1] to [ 8] above, wherein the polyimide-based polymer is polyamideimide.

An optical film comprising the varnish according to any one of [ 1] to [ 9] above.

The method for producing an optical film includes at least the steps of:

(a) a step of applying the varnish according to any one of [ 1] to [ 9] above to a support to form a coating film; and a process for the preparation of a coating,

(b) and drying the coating film at a temperature of 100 ℃ to 240 ℃ to obtain the optical film.

A flexible display device comprising the optical film according to [ 10 ].

[ 13] the flexible display device according to [ 12], further comprising a touch sensor.

[ 14] the flexible display device according to [ 12] or [ 13], which further comprises a polarizing plate.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide a varnish which can effectively prevent yellowing of a polyimide-based polymer film even when the film is produced after being stored in a varnish state for a long period of time.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail. The scope of the present invention is not limited to the embodiments described herein, and various modifications can be made without departing from the scope of the present invention.

The varnish of the present invention comprises a polyimide-based polymer and a solvent containing GBL: GBL having a light transmittance of 88% or more at a wavelength of 275 nm; and/or, in a capillary gas chromatography using polyethylene glycol as a stationary phase, when a sample is injected while a column temperature is maintained at 120 ℃, the temperature is maintained at 120 ℃ for 1 minute, the temperature is increased to 240 ℃ at a rate of 10 ℃/minute, and the temperature is maintained at 240 ℃ for 7 minutes, an area ratio of a component detected at a relative retention time within a predetermined range (1.02 to 1.50, or 1.05 to 1.50) based on a peak of GBL is a predetermined value or less (300ppm or less or 260ppm or less)) The GBL of (1). The stationary phase in the capillary gas chromatography is polyethylene glycol, and preferable examples of the column include DB-WAX manufactured by Agilent Technologies, Heliflex AT-WAX manufactured by Analitic Columns, and TC-WAX manufactured by GL Sciences, and more preferably DB-WAX manufactured by Agilent Technologies (30 m.times.0.32 mm I.D., d._f0.50 μm). In the case of using a column other than the above, the measurement conditions can be adjusted in advance so as to quantify the target component, and the same can be performed.

In the case of preparing a varnish by dissolving a polyimide-based polymer in a solvent, it is considered that GBL having high compatibility with the polyimide-based polymer is preferably used from the viewpoint of easily improving the optical characteristics of the optical film to be obtained. However, when GBL is used as at least a part of the solvent, it is considered that the polyimide-based polymer dissolved in GBL is likely to react because of its high reactivity and because GBL used as the solvent may contain a small amount of impurities. In particular, when an optical film is produced on an industrial production scale, the optical film may be produced by temporarily storing the prepared varnish and then applying the varnish to a support. However, it is known that an optical film obtained from a varnish after long-term storage has a high YI value and thus has deteriorated optical properties. The varnish of the present invention is a varnish for producing an optical film such as a front panel of a display device, and contains GBL having the above-described specific characteristics as a solvent, whereby yellowing of the film can be effectively prevented even when a polyimide-based polymer film is produced after the film is stored in the varnish for a long period of time.

Although the reason why yellowing of the obtained optical film can be suppressed by using a solvent containing GBL having the above-described specific characteristics is not clear, it is considered that a component having an absorption at a wavelength of 275nm, a component detected at a relative retention time of 1.02 to 1.50 based on a peak of GBL, and/or a component detected at a relative retention time of 1.05 to 1.50 based on a peak of GBL and a polyimide-based polymer in a state of being dissolved in GBL undergo some interaction, and the varnish undergoes yellowing with time. Therefore, it is considered that the yellowing of the polyimide resin in a state of being dissolved in the varnish is suppressed by reducing the amounts of these components, and the yellowing of the film can be prevented even in the case of producing a polyimide polymer film after long-term storage in a state of the varnish. Hereinafter, GBL having a light transmittance of 88% or more at a wavelength of 275nm is referred to as GBL (A), and GBL having an area ratio of component B1 detected at a relative retention time of 1.02 to 1.50 based on the peak of GBL of 300ppm or less is referred to as GBL (B1). In addition, GBL (B1) in which the area ratio of component B2 detected in GBL (B1) at a relative retention time of 1.05 to 1.50 based on the peak of GBL is 260ppm or less is also referred to as GBL (B2). GBL (B2) is included in GBL (B1), and is also collectively referred to as GBL (B).

The GBL contained as a solvent in the varnish of the present invention may be a solvent corresponding to GBL (a), and/or a solvent corresponding to GBL (b), or may be a solvent corresponding to both GBL (a) and GBL (b). The varnish of the present invention may further contain a solvent other than GBL. The proportion of GBL contained as a solvent in the varnish of the present invention is preferably 30 to 100 mass%, more preferably 50 to 100 mass%, even more preferably 60 to 100 mass%, even more preferably 70 to 100 mass%, even more preferably 80 to 100 mass%, even more preferably 90 to 100 mass%, based on the total amount of solvents contained in the varnish. When the content of GBL is within the above range, even in the case of producing a polyimide-based polymer film after long-term storage in the state of varnish, yellowing of the obtained film is easily prevented, and moreover, the viscosity is easily the most suitable for cast film formation of varnish, so that the handling property is good and the visibility of the obtained optical film is easily improved. The above ratio may be a charging ratio of the solvent used in the production of the varnish. Here, GBL used for producing the varnish of the present invention may be a solvent belonging to at least one of GBL (a), GBL (B1) and GBL (B2), or may be a solvent belonging to both GBL (a) and GBL (B).

From the viewpoint of easily suppressing discoloration of the varnish during long-term storage, the light transmittance at a wavelength of 275nm of GBL is preferably 89% or more, more preferably 93% or more, and still more preferably 95% or more.

From the viewpoint of easily suppressing discoloration of the varnish during long-term storage, the area ratio of the component detected at a relative retention time of 1.02 to 1.50 is preferably 270ppm or less, more preferably 260ppm or less, further preferably 200ppm or less, and particularly preferably 100ppm or less.

From the viewpoint of easily suppressing discoloration of the varnish during long-term storage, the area ratio of the component detected at a relative retention time of 1.05 to 1.50 is preferably 250ppm or less, more preferably 210ppm or less, still more preferably 150ppm or less, particularly preferably 100ppm or less, and most preferably 50ppm or less.

The method of making the light transmittance at 275nm in GBL 88% or more and the method of making the area ratio of the components detected in GBL within a predetermined range of the relative retention time within a predetermined range (1.02 to 1.50, or 1.05 to 1.50) in gas chromatography under the above conditions within a predetermined range are not particularly limited as long as GBL (a) or GBL (b) having the above characteristics can be obtained, and examples thereof include: a method for purifying GBL using a distillation column; a method of purifying GBL by an adsorption method such as a metal ion adsorption method; a method of distillation after contacting with an acidic ion exchange resin; a method combining liquid-liquid extraction with distillation; and so on.

When GBL having the above characteristics is produced using a distillation column, the operating conditions are not particularly limited as long as GBL having the above characteristics can be obtained. The temperature at the top of the column is, for example, 50 to 150 ℃, preferably 60 to 140 ℃, more preferably 70 to 130 ℃, and still more preferably 75 to 120 ℃. In addition, the temperature of the bottom of the column is, for example, 70 to 170 ℃, preferably 80 to 160 ℃, more preferably 90 to 150 ℃, and still more preferably 100 to 140 ℃. The temperature at the bottom of the tower is preferably higher than the temperature at the top of the tower by about 5-50 ℃. By controlling the column top temperature and the column bottom temperature within the above ranges, the light transmittance of GBL at a wavelength of 275nm can be easily made 88% or more, and the area ratio of the components detected at a relative retention time within a predetermined range in the gas chromatography under the above conditions can be easily made within the above range. The pressure during distillation may be set so that the column top temperature falls within the above range.

Examples of the type of the distillation column include a regular packed column, an irregular packed column, a plate column, an oldershaw type distillation column, and a distiller equipped with a Widmer rectifier. The number of plates is usually 1 to 100 plates, preferably 5 to 90 plates, and more preferably 10 to 80 plates. The circulation ratio is usually in the range of 0.1 to 100, preferably 0.5 to 80, and more preferably 1 to 60. The extraction temperature of the GBL used in the varnish of the present invention is not particularly limited, and is preferably 90 to 140 ℃, and more preferably 100 to 130 ℃ from the viewpoint of easily obtaining GBL having the above-described characteristics. Further, the extraction temperature can be adjusted while observing the light transmittance of the GBL at a wavelength of 275nm and the results of gas chromatography. The distillation may be continuous or batch.

For example, when an oldham distillation column is used, the combination of the column top temperature, the column bottom temperature, and the extraction temperature includes, for example: the temperature at the top of the column is 100 ℃, the temperature at the bottom of the column is 112 ℃, and the extraction temperature is 108 ℃; the temperature at the top of the column is 75 ℃, the temperature at the bottom of the column is 120 ℃, and the extraction temperature is 112 ℃; the temperature at the top of the column is 110 ℃, the temperature at the bottom of the column is 131 ℃, and the extraction temperature is 125 ℃.

GBL (A) or GBL (B) having the above-mentioned characteristics can be produced by: for example, the extraction temperature is set so that GBL satisfying the above characteristics can be obtained by distilling GBL with a distillation column by the method described in japanese patent No. 4154897, japanese patent No. 4348890, japanese patent No. 5392937, and the like.

It is also known to add an epoxy compound or the like when purifying GBL, but when producing a varnish containing a polyimide-based polymer using GBL obtained by this method, the optical properties of the optical film may not be sufficiently improved. Therefore, this method is considered to be unsuitable as a method for producing GBL for obtaining the varnish of the present invention.

The content of the solvent in the varnish of the present invention is preferably 75 to 99% by mass, more preferably 78 to 95% by mass, and still more preferably 80 to 90% by mass, based on the total amount of the varnish. When the content of the solvent is within the above range, even in the case of producing a polyimide-based polymer film after long-term storage in a varnish state, the resultant film is easily prevented from yellowing, and the viscosity is easily the most suitable for cast film formation of the varnish, so that the handling property is improved and the visibility of the resultant optical film is easily improved.

The content of the polyimide-based polymer in the varnish of the present invention is preferably 1 to 25% by mass, more preferably 5 to 22% by mass, and still more preferably 10 to 20% by mass, based on the total amount of the varnish. When the content of the polyimide-based polymer is within the above range, even in the case of producing a polyimide-based polymer film after long-term storage in a varnish state, yellowing of the obtained film is easily prevented, and moreover, the viscosity is easily the most suitable for cast film formation of the varnish, so that the handling property is good, and the visibility of the obtained optical film is easily improved.

The varnish of the invention is based on L^＊a^＊b^＊In the measurement of color difference in a colorimetric system, it is preferable that L is satisfied^＊≥80、-10≤a^＊B is not more than 10, and-10 is not more than b^＊Less than or equal to 10. L in the above-mentioned measurement of chromatic aberration is considered to be easy to improve the transparency and visibility of the polymer material finally obtained^＊Preferably 90 or more, more preferably 93 or more, and still more preferably 95 or more. L is^＊The upper limit of (b) is not particularly limited, and may be 100 or less. A in the above-mentioned measurement of chromatic aberration^＊The index indicating red is preferably-10 to 10, more preferably-7 to 7, and still more preferably-5 to 5, from the viewpoint of easily improving the visibility of the polymer material finally obtained. B in the measurement of chromatic aberration^＊The index indicating blue color is preferably from-10 to 10, more preferably from-5 to 10, and still more preferably from-3 to 7, from the viewpoint of easily improving the visibility of the polymer material finally obtained. The color difference can be measured using a color difference meter, and can be measured, for example, by the method described in examples.

< polyimide-based resin >

The polyimide resin contained in the varnish of the present invention is a polyimide resin, a polyamideimide resin, or a polyamic acid resin which is a precursor of the polyimide resin and the polyamideimide resin. The varnish of the present invention may contain one kind of polyimide resin, or may contain two or more kinds of polyimide resins. From the viewpoint of film formability, the polyimide-based resin is preferably a polyimide resin or a polyamideimide resin, and more preferably a polyamideimide resin.

The polyimide-based resin contained in the varnish of the present invention has a polystyrene-equivalent weight average molecular weight of preferably 200,000 or more, more preferably 250,000 or more, and still more preferably 300,000 or more. The polyimide resin preferably has a weight average molecular weight in terms of polystyrene of 800,000 or less, more preferably 600,000 or less, even more preferably 500,000 or less, and even more preferably 450,000 or less, from the viewpoints of ease of production of varnish and film forming property in the production of polymer material. The above weight average molecular weight is measured by Gel Permeation Chromatography (GPC) measurement. The measurement conditions used may be the conditions described in the examples.

In one embodiment of the present invention, the polyimide-based resin is preferably a polyimide resin having a structural unit represented by formula (1), or a polyamideimide resin having a structural unit represented by formula (1) and a structural unit represented by formula (2). From the viewpoint of transparency and bendability, the polyimide-based resin is more preferably a polyamideimide resin having a structural unit represented by formula (1) and a structural unit represented by formula (2). Hereinafter, the formula (1) and the formula (2) will be described, the description of the formula (1) will be directed to both the polyimide resin and the polyamideimide resin, and the description of the formula (2) will be directed to the polyamideimide resin.

[ chemical formula 1]

The structural unit represented by formula (1) is a structural unit formed by reacting a tetracarboxylic acid compound with a diamine compound, and the structural unit represented by formula (2) is a structural unit formed by reacting a dicarboxylic acid compound with a diamine compound.

In one embodiment of the present invention in which the polyimide resin is a polyimide resin having a structural unit represented by formula (1) or a polyamideimide resin having a structural unit represented by formula (1) and a structural unit represented by formula (2), Y in formula (1) independently represents a tetravalent organic group, preferably a tetravalent organic group having 4 to 40 carbon atoms. The organic group is an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, and in this case, the number of carbon atoms in the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably 1 to 8. The polyimide-based resin according to one embodiment of the present invention may contain a plurality of kinds of Y, and the plurality of kinds of Y may be the same or different from each other. As Y, there can be exemplified: a group represented by formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28) or formula (29); a group in which a hydrogen atom in the group represented by the formulae (20) to (29) is substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group; and a tetravalent chain hydrocarbon group having 6 or less carbon atoms.

[ chemical formula 2]

[ formula (20) to formula (29),

it represents a connecting bond,

W¹represents a single bond, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-Ar-、-SO₂-、-CO-、-O-Ar-O-、-Ar-O-Ar-、-Ar-CH₂-Ar-、-Ar-C(CH₃)₂-Ar-or-Ar-SO₂-Ar-. Ar represents an arylene group having 6 to 20 carbon atoms in which a hydrogen atom may be substituted with a fluorine atom, and specific examples thereof include phenylene groups.]

The group represented by the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25), the formula (26), the formula (27), the formula (28) and the formula (29) is obtained by including the polyimide resinFrom the viewpoint of surface hardness and flexibility of the optical member of (1), a group represented by formula (26), formula (28) or formula (29) is preferable, and a group represented by formula (26) is more preferable. In addition, from the viewpoint of surface hardness and flexibility of an optical member comprising the polyimide resin, W is¹Independently of one another, are preferably single bonds, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-or-C (CF)₃)₂-, more preferably a single bond, -O-, -CH₂-、-CH(CH₃)-、-C(CH₃)₂-or-C (CF)₃)₂-, more preferably a single bond, -O-, -C (CH)₃)₂-or-C (CF)₃)₂-O-or-C (CF) is more preferable₃)₂-。

In the above aspect, at least a part of Y in formula (1) is preferably a constitutional unit represented by formula (5). When at least a part of the plurality of Y in formula (1) is a group represented by formula (5), the obtained optical member tends to exhibit high transparency. Further, the polyimide resin has improved solubility in a solvent due to the high bendability skeleton, and the viscosity of a varnish containing the polyimide resin can be suppressed to be low, and the optical member can be easily processed.

[ chemical formula 3]

[ in the formula (5), R¹⁸～R²⁵Independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, R¹⁸～R²⁵The hydrogen atoms contained in (a) may be substituted independently of each other by halogen atoms,

it represents a connecting bond. ]

In the formula (5), R¹⁸、R¹⁹、R²⁰、R²¹、R²²、R²³、R²⁴、R²⁵Independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, preferably a hydrogen atomOr an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms and the aryl group having 6 to 12 carbon atoms include those mentioned later as the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms or the aryl group having 6 to 12 carbon atoms in the formula (3). Here, R¹⁸～R²⁵The hydrogen atoms contained in (a) may be substituted independently of each other by halogen atoms. R is a group represented by formula (I) in view of surface hardness and flexibility of an optical member comprising the polyimide resin¹⁸～R²⁵Further preferred are, independently of one another, a hydrogen atom, a methyl group, a fluoro group, a chloro group or a trifluoromethyl group, and particularly preferred is a hydrogen atom or a trifluoromethyl group.

In a preferred embodiment of the present invention, the structural unit represented by formula (5) is a group represented by formula (5 '), that is, at least a part of the plurality of Y is a structural unit represented by formula (5'). In this case, an optical member including the polyimide resin can have high transparency.

[ chemical formula 4]

[ in the formula (5'), the symbol represents a connecting bond ]

In a preferred embodiment of the present invention, preferably 50 mol% or more, more preferably 60 mol% or more, and still more preferably 70 mol% or more of Y in the polyimide-based resin is represented by formula (5), particularly formula (5'). When Y in the above range in the polyimide-based resin is represented by formula (5), particularly formula (5'), the optical member comprising the polyimide-based resin can have high transparency, and the solubility of the polyimide-based resin in a solvent is improved by the fluorine element-containing skeleton, so that the viscosity of a varnish comprising the polyimide-based resin can be suppressed to be low, and the optical member can be easily produced. Preferably, 100 mol% or less of Y in the polyimide-based resin is represented by formula (5), particularly formula (5'). Y in the above polyimide resinMay be of formula (5), especially of formula (5'). The content of the structural unit represented by formula (5) of Y in the polyimide resin can be, for example, used¹H-NMR was measured, or it was calculated from the feed ratio of the raw materials.

In one embodiment of the present invention in which the polyimide-based resin is a polyamideimide resin having a structural unit represented by formula (1) and a structural unit represented by formula (2), Z in formula (2) independently represents a divalent organic group. In one embodiment of the present invention, the polyamideimide resin may include a plurality of kinds of Z, and the plurality of kinds of Z may be the same as or different from each other. The divalent organic group preferably represents a divalent organic group having 4 to 40 carbon atoms. The organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, and in this case, the number of carbon atoms of the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably 1 to 8. As the organic group of Z, there can be exemplified: a group in which two of the bonds of the group represented by formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28) or formula (29) that are not adjacent to each other are replaced with a hydrogen atom; and a divalent chain hydrocarbon group having 6 or less carbon atoms. From the viewpoint of improving the optical characteristics of the optical member, for example, easily lowering the YI value, a group represented by a group in which two non-adjacent bonds of the groups represented by formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28), or formula (29) are replaced with hydrogen atoms is preferable. In one embodiment of the present invention, the polyamideimide resin may include one kind of organic group as Z, or may include two or more kinds of organic groups as Z.

As the organic group of Z, divalent organic groups represented by formula (20 '), formula (21'), formula (22 '), formula (23'), formula (24 '), formula (25'), formula (26 '), formula (27'), formula (28 ') and formula (29') are more preferable,

[ chemical formula 5]

In [ formulae (20 ') to (29'), W¹And, of the formula20) Defined in formula (29)]。

The hydrogen atoms on the ring in the formulae (20) to (29) and (20 ') to (29') may be substituted by a hydrocarbon group having 1 to 8 carbon atoms, a hydrocarbon group having 1 to 8 carbon atoms substituted with fluorine, an alkoxy group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms substituted with fluorine.

In the case where the polyamideimide resin has a structural unit wherein Z in the formula (2) is represented by any one of the above-mentioned formulae (20 ') to (29'), it is preferable that the polyamideimide resin contains a structural unit derived from a carboxylic acid represented by the following formula (d1) in addition to the structural unit, from the viewpoints of easily lowering the viscosity of the varnish, easily improving the film formability of the varnish, and easily improving the uniformity of the optical film to be obtained:

[ chemical formula 6]

[ in the formula (d1), R²⁴Independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, R²⁵Represents R²⁴or-C (═ O) -, represents a connecting bond]。

R²⁴In the above formula (3), examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms and the aryl group having 6 to 12 carbon atoms include R¹～R⁸But are exemplary groups. Specific examples of the structural unit (d1) include R²⁴And R²⁵Structural units each of which is a hydrogen atom (structural units derived from a dicarboxylic acid compound), R²⁴Are all hydrogen atoms and R²⁵A structural unit (structural unit derived from a tricarboxylic acid compound) representing — C (═ O) -, and the like.

In one embodiment of the present invention, the polyamideimide resin may include a plurality of kinds of Z, and the plurality of kinds of Z may be the same as or different from each other. In particular, from the viewpoint of easily improving the surface hardness and optical properties of the obtained film, it is preferable that at least a part of Z is represented by formula (3 a):

[ chemical formula 7]

[ in the formula (3a), R^gAnd R^hIndependently represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, R^gAnd R^hWherein the hydrogen atoms contained in (A) may be independently substituted with halogen atoms, A, m and r are the same as A, m and r in the formula (3), and t and u are independently an integer of 0 to 4]

More preferably represented by formula (3):

[ chemical formula 8]

[ in the formula (3), R¹～R⁸Independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, R¹～R⁸The hydrogen atoms contained in (a) may be substituted independently of each other by halogen atoms,

a independently of one another represents a single bond, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-, -S-, -CO-or-N (R)⁹)-，R⁹Represents a hydrogen atom, a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom,

m is an integer of 0 to 4,

it represents a bond.

In the formulae (3) and (3a), A independently represents a single bond, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-, -S-, -CO-or-N (R)⁹) From the viewpoint of the bending resistance of the resulting film, it preferably represents-O-or-S-, and more preferably represents-O-.

R¹、R²、R³、R⁴、R⁵、R⁶、R⁷And R⁸Independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. R^gAnd R^hIndependently represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 2-ethylpropyl group, and an n-hexyl group. Examples of the alkoxy group having 1 to 6 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group, a cyclohexyloxy group and the like. Examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a biphenyl group. From the viewpoint of surface hardness and flexibility of a film obtained from the varnish, R¹～R⁸Independently of each other, the alkyl group preferably represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and still more preferably represents a hydrogen atom. Here, R¹～R⁸、R^gAnd R^hThe hydrogen atoms contained in (a) may be substituted independently of each other by halogen atoms.

R⁹Represents a hydrogen atom, a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 2-ethylpropyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, a tert-octyl group, an n-nonyl group, an n-decyl group, and the like, and these may be substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom and the like. The polyimide-based resin may contain a plurality of kinds of a, and the plurality of kinds of a may be the same as or different from each other.

T and u in formula (3a) are each independently an integer of 0 to 4, preferably an integer of 0 to 2, more preferably 0 or 1, and still more preferably 0.

In the formulae (3) and (3a), when m is an integer in the range of 0 to 4, and m is within this range, the stability of the varnish, and the bending resistance and elastic modulus of the film obtained from the varnish tend to be good. In the formulae (3) and (3a), m is preferably an integer in the range of 0 to 3, more preferably an integer in the range of 0 to 2, still more preferably 0 or 1, and still more preferably 0. When m is within this range, the film tends to have improved bending resistance and modulus of elasticity. Z may contain one or more kinds of structural units represented by formula (3) or formula (3a), and in particular, two or more kinds of structural units having different values of m, preferably two or three kinds of structural units having different values of m, may be contained from the viewpoint of improving the elastic modulus and the bending resistance of the optical film and reducing the YI value. In this case, from the viewpoint that a film obtained from the varnish is likely to exhibit a high elastic modulus, a high bending resistance, and a low YI value, it is preferable that the resin contains a structural unit represented by formula (3) or formula (3a) in which m is 0 in Z, and more preferably contains a structural unit represented by formula (3) or formula (3a) in which m is 1 in addition to the structural unit. It is also preferable that the structural element represented by the above formula (d1) is contained in addition to the structural element represented by the formula (2) (which includes Z represented by the formula (3) in which m is 0).

In a preferred embodiment of the present invention, the resin has m ═ 0 and R⁵～R⁸The structural unit which is a hydrogen atom is a structural unit represented by formula (3). In a more preferred embodiment of the present invention, the resin has m ═ 0 and R⁵～R⁸A structural unit which is a hydrogen atom and a structural unit represented by formula (3') as a structural unit represented by formula (3),

[ chemical formula 9]

In this case, the surface hardness and the bending resistance of the film obtained from the varnish are easily improved, and the YI value is easily reduced.

In a preferred embodiment of the present invention, the proportion of the structural unit represented by formula (3) or formula (3a) is preferably 20 mol% or more, more preferably 30 mol% or more, further preferably 40 mol% or more, further preferably 50 mol% or more, particularly preferably 60 mol% or more, preferably 90 mol% or less, more preferably 85 mol% or less, and further preferably 80 mol% or less, when the total of the structural unit represented by formula (1) and the structural unit represented by formula (2) in the polyamide imide resin is 100 mol%. When the proportion of the structural unit represented by formula (3) or formula (3a) is not less than the above lower limit, the surface hardness of the film obtained from the varnish is easily increased, and the bending resistance and the elastic modulus are easily increased. When the proportion of the structural unit represented by formula (3) or formula (3a) is not more than the above upper limit, the viscosity of the varnish containing the resin is easily inhibited from increasing due to hydrogen bonding between amide bonds derived from formula (3) or formula (3a), and the processability of the film is improved.

In the case where the polyamideimide resin has the structural unit of the formula (3) or the formula (3a) in which m is 1 to 4, the proportion of the structural unit of the formula (3) or the formula (3a) in which m is 1 to 4 is preferably 2 mol% or more, more preferably 4 mol% or more, further preferably 6 mol% or more, further preferably 8 mol% or more, preferably 70 mol% or less, more preferably 50 mol% or less, further preferably 30 mol% or less, further preferably 15 mol% or less, more preferably 12 mol% or less, when the total of the structural unit of the formula (1) and the structural unit of the formula (2) in the polyamideimide resin is 100 mol%. When the ratio of the structural unit of the formula (3) or the formula (3a) in which m is 1 to 4 is not less than the above lower limit, the surface hardness and the bending resistance of the film obtained from the varnish are easily improved. When the proportion of the structural unit of formula (3) or formula (3a) in which m is 1 to 4 is not more than the upper limit, the viscosity increase of the varnish containing the resin due to hydrogen bonds between amide bonds derived from formula (3) or formula (3a) is easily suppressed, and the film processability is easily improved. The content of the structural unit represented by the formula (1), the formula (2), the formula (3) or the formula (3a) may be, for example, the content¹H-NMR was measured, or it was calculated from the feed ratio of the raw materials.

In a preferred embodiment of the present invention, the polyamideimide tree is used as the polyamide-imide resinPreferably 30 mol% or more, more preferably 40 mol% or more, further preferably 45 mol% or more, further preferably 50 mol% or more, and particularly preferably 70 mol% or more of Z in the lipid is a structural unit represented by formula (3) or formula (3a) in which m is 0 to 4. When the lower limit of Z is a structural unit represented by formula (3) or formula (3a) where m is 0 to 4, the surface hardness of the film obtained from the varnish is easily increased, and the bending resistance and the elastic modulus are also easily increased. In addition, the polyamide-imide resin may contain 100 mol% or less of Z as a structural unit represented by formula (3) or formula (3a) wherein m is 0 to 4. The proportion of the structural unit represented by the formula (3) or the formula (3a) wherein m is 0 to 4 in the resin can be, for example, used¹H-NMR was measured, or it was calculated from the feed ratio of the raw materials.

In a preferred embodiment of the present invention, preferably 5 mol% or more, more preferably 8 mol% or more, still more preferably 10 mol% or more, and still more preferably 12 mol% or more of Z in the polyamideimide resin is represented by formula (3) or formula (3a) wherein m is 1 to 4. When the lower limit of Z of the polyamideimide resin is represented by formula (3) or formula (3a) wherein m is 1 to 4, the surface hardness of the film obtained from the varnish is easily increased, and the bending resistance and the elastic modulus are easily increased. In addition, preferably 90 mol% or less, more preferably 70 mol% or less, still more preferably 50 mol% or less, and still more preferably 30 mol% or less of Z is represented by formula (3) or formula (3a) in which m is 1 to 4. When the upper limit of Z is represented by formula (3) or formula (3a) where m is 1 to 4, the viscosity of the varnish containing the resin is easily prevented from increasing due to hydrogen bonds between amide bonds derived from formula (3) or formula (3a) where m is 1 to 4, and the processability of the film is improved. The proportion of the structural unit represented by the formula (3) or the formula (3a) wherein m is 1 to 4 in the resin can be, for example, used¹H-NMR was measured, or it was calculated from the feed ratio of the raw materials.

In the formulas (1) and (2), X independently represents a divalent organic group, preferably represents a divalent organic group having 4 to 40 carbon atoms, and more preferably represents a divalent organic group having 4 to 40 carbon atoms and having a cyclic structure. Examples of the cyclic structure include alicyclic, aromatic ring, and heterocyclic structure. In the above organic group, the hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, and in this case, the number of carbon atoms of the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably 1 to 8. In one embodiment of the present invention, the polyimide resin or polyamideimide resin may contain a plurality of kinds of X, and the plurality of kinds of X may be the same as or different from each other. Examples of X may include groups represented by formula (10), formula (11), formula (12), formula (13), formula (14), formula (15), formula (16), formula (17) and formula (18); a group in which a hydrogen atom in the group represented by the formulae (10) to (18) is substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group; and a chain hydrocarbon group having 6 or less carbon atoms.

[ chemical formula 10]

In the formulae (10) to (18), the bond is represented by,

V¹、V²and V³Independently of one another, represents a single bond, -O-, -S-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-, -CO-or-N (Q) -. Wherein Q represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms include those for R⁹But the groups described hereinbefore.

An example is: v¹And V³Is a single bond, -O-or-S-, and V²is-CH₂-、-C(CH₃)₂-、-C(CF₃)₂-or-SO₂-。V¹And V²Bonding position with respect to each ring, and V²And V³The bonding positions to each ring are independently preferably meta or para to each ring, more preferably para.

Among the groups represented by the formulae (10) to (18), the surface hardness and bending resistance of the film obtained from the varnish can be easily improvedIn view of this point, preferred are groups represented by formula (13), formula (14), formula (15), formula (16) and formula (17), and more preferred are groups represented by formula (14), formula (15) and formula (16). In addition, from the viewpoint of easily improving the surface hardness and flexibility of the film obtained from the varnish of the present invention, V¹、V²And V³Independently of one another, are preferably single bonds, -O-or-S-, more preferably single bonds or-O-.

In a preferred embodiment of the present invention, at least a part of X in the formulae (1) and (2) is a structural unit represented by the formula (4),

[ chemical formula 11]

[ in the formula (4), R¹⁰～R¹⁷Independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, R¹⁰～R¹⁷In which the hydrogen atoms may be substituted independently of one another by halogen atoms, represent a connecting bond]。

When at least a part of the plurality of xs in the formulae (1) and (2) is a group represented by the formula (4), the surface hardness and transparency of the film obtained from the varnish are easily improved.

In the formula (4), R¹⁰、R¹¹、R¹²、R¹³、R¹⁴、R¹⁵、R¹⁶And R¹⁷Independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, or the aryl group having 6 to 12 carbon atoms include alkyl groups having 1 to 6 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, or aryl groups having 6 to 12 carbon atoms in the formula (3). R¹⁰～R¹⁷Independently of each other, preferably represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, wherein R¹⁰～R¹⁷The hydrogen atoms contained in (a) may be substituted independently of each other by halogen atoms. As halogen atoms, e.g.Examples thereof include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. From the viewpoint of surface hardness, transparency and bending resistance of the optical film, R¹⁰～R¹⁷Independently of one another, further preferably represents a hydrogen atom, a methyl group, a fluoro group, a chloro group or a trifluoromethyl group, and further preferably R¹⁰、R¹²、R¹³、R¹⁴、R¹⁵And R¹⁶Represents a hydrogen atom, and R¹¹And R¹⁷Represents a hydrogen atom, a methyl group, a fluoro group, a chloro group or a trifluoromethyl group (particularly preferably R)¹¹And R¹⁷Represents a methyl group or a trifluoromethyl group).

In a preferred embodiment of the present invention, the structural unit represented by formula (4) is a structural unit represented by formula (4'):

[ chemical formula 12]

That is, at least a part of X among the structural units represented by formulas (1) and (2) is a structural unit represented by formula (4'). In this case, the solubility of the polyimide-based resin in the solvent can be easily improved by the skeleton containing the fluorine element. In addition, the viscosity of the varnish is easily reduced, and the processability of the optical film is easily improved. Further, the optical properties of the film obtained from the varnish are easily improved by the skeleton containing the fluorine element.

In a preferred embodiment of the present invention, preferably 30 mol% or more, more preferably 50 mol% or more, and still more preferably 70 mol% or more of X in the polyimide-based resin is represented by formula (4), particularly formula (4'). When X in the above range in the polyimide-based resin is represented by formula (4), particularly formula (4'), the solubility of the polyimide-based resin in a solvent is easily improved by the skeleton containing a fluorine element. In addition, the viscosity of the varnish is easily reduced, and the processability of a film obtained from the varnish is easily improved. Further, the optical properties of the film obtained from the varnish can be easily improved by the skeleton containing the fluorine element. Preferably, 100 mol% or less of X in the polyimide-based resin is represented by the formula (4)) In particular, formula (4'). The X in the above polyamideimide resin may be formula (4), especially formula (4'). The proportion of the structural unit represented by formula (4) of X in the above resin can be used, for example¹H-NMR was measured, or it was calculated from the feed ratio of the raw materials.

The polyimide-based resin may contain a structural unit represented by formula (30) and/or a structural unit represented by formula (31), or may contain a structural unit represented by formula (30) and/or a structural unit represented by formula (31) in addition to the structural units represented by formulae (1) and (2).

[ chemical formula 13]

In the formula (30), Y¹Independently of one another, a tetravalent organic group, preferably an organic group in which the hydrogen atoms of the organic group may be replaced by a hydrocarbon group or a fluorine-substituted hydrocarbon group. As Y¹Examples thereof include: a group represented by formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28) or formula (29); a group represented by the above formulae (20) to (29) wherein a hydrogen atom is substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group; and a chain hydrocarbon group having a valence of 4 and a carbon number of 6 or less. In one embodiment of the present invention, the polyimide-based resin may contain a plurality of kinds of Y¹Plural kinds of Y¹May be the same as or different from each other.

In the formula (31), Y²Is a trivalent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a hydrocarbon group substituted with fluorine. As Y²Examples thereof include: a group in which any one of the connecting bonds of the groups represented by the above-mentioned formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28) and formula (29) is replaced with a hydrogen atom; and a chain hydrocarbon group having 3-valent carbon atoms of 6 or less. In one embodiment of the present invention, the polyimide-based resin may contain a plurality of kinds of Y²Plural kinds of Y²May be the same as or different from each other.

In the formulae (30) and (31), X¹And X²Independently of one another, are divalent organic groups, preferably organic groups in which the hydrogen atoms of the organic group may be replaced by hydrocarbon groups or fluorine-substituted hydrocarbon groups. As X¹And X²Examples thereof include: groups represented by the above-mentioned formula (10), formula (11), formula (12), formula (13), formula (14), formula (15), formula (16), formula (17) and formula (18); a group in which a hydrogen atom in the group represented by the above formula (10) to formula (18) is substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group; and a chain hydrocarbon group having 6 or less carbon atoms.

In one embodiment of the present invention, the polyimide-based resin includes a structural unit represented by formula (1) and/or formula (2), and a structural unit represented by formula (30) and/or formula (31) which is contained as the case may be. In the polyimide-based resin, the structural unit represented by formula (1) and formula (2) is preferably 80 mol% or more, more preferably 90 mol% or more, and even more preferably 95 mol% or more based on all the structural units represented by formula (1) and formula (2) and, if necessary, formula (30) and formula (31) contained in the polyimide-based resin, from the viewpoint of optical characteristics, surface hardness, and bending resistance of the film obtained from the varnish. In the polyimide-based resin, the structural units represented by the formulae (1) and (2) are usually 100% or less based on all the structural units represented by the formulae (1) and (2) and, if necessary, the formulae (30) and/or (31). The above ratio can be used, for example¹H-NMR was measured, or it was calculated from the feed ratio of the raw materials.

In one embodiment of the present invention, the content of the polyimide-based resin in the film obtained from the varnish is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, further preferably 50 parts by mass or more, preferably 99.5 parts by mass or less, and more preferably 95 parts by mass or less, per 100 parts by mass of the film. When the content of the polyimide-based resin is within the above range, the optical properties and the elastic modulus of the film obtained from the varnish are easily improved.

In the polyamide-imide resin, the content of the structural unit represented by formula (2) is preferably 0.1 mol or more, more preferably 0.5 mol or more, further preferably 1.0 mol or more, further preferably 1.5 mol or more, preferably 6.0 mol or less, more preferably 5.0 mol or less, and further preferably 4.5 mol or less, relative to 1 mol of the structural unit represented by formula (1). When the content of the structural unit represented by formula (2) is not less than the above lower limit, the surface hardness of the optical film obtained from the varnish is easily increased. When the content of the structural unit represented by formula (2) is not more than the upper limit, the thickening due to the hydrogen bond between the amide bonds in formula (2) is easily suppressed, and the processability of the optical film is improved.

In a preferred embodiment of the present invention, the polyimide-based resin may contain a halogen atom such as a fluorine atom, which may be introduced through the above-mentioned fluorine-containing substituent or the like. When the polyimide resin contains a halogen atom, the elastic modulus of a film containing the polyimide resin is easily improved, and the YI value is easily reduced. When the elastic modulus of the film is high, when the film is used in, for example, a flexible display device, generation of damage, wrinkles, or the like in the film is easily suppressed. Further, when the YI value of the film is low, the transparency and visibility of the film are easily improved. The halogen atom is preferably a fluorine atom. Examples of the preferable fluorine-containing substituent for making the polyimide resin contain a fluorine atom include a fluorine group and a trifluoromethyl group.

The content of the halogen atom in the polyimide resin is preferably 1 to 40% by mass, more preferably 5 to 40% by mass, and still more preferably 5 to 30% by mass, based on the mass of the polyimide resin. When the content of the halogen atom is not less than the lower limit, it is easy to further increase the elastic modulus of the film containing the polyimide-based resin, to reduce the water absorption, to further reduce the YI value, and to further improve the transparency and the visibility. When the content of the halogen atom is not more than the upper limit, the synthesis of the resin becomes easy.

The imidization ratio of the polyimide resin is preferably 90% or more, more preferably 93% or more, and still more preferably 96% or more. The imidization rate is preferably not less than the above-described lower limit from the viewpoint of easily improving the optical homogeneity of a film containing the polyimide-based resin. The upper limit of the imidization rate is 100% or less. The imidization ratio indicates a ratio of a molar amount of imide bonds in the polyimide-based resin to a value 2 times a molar amount of structural units derived from a tetracarboxylic acid compound in the polyimide-based resin. When the polyimide resin contains a tricarboxylic acid compound, the imidization ratio represents a ratio of a molar amount of imide bonds in the polyimide resin and the polyamideimide resin to a total of a value 2 times as large as a molar amount of a structural unit derived from a tetracarboxylic acid compound in the polyimide resin and a molar amount of a structural unit derived from a tricarboxylic acid compound. The imidization ratio can be determined by an IR method, an NMR method, or the like, and for example, in the NMR method, it can be measured by the method described in examples.

Commercially available polyimide resins can be used. Examples of commercially available products of polyimide resins include Neopulim (registered trademark) manufactured by Mitsubishi gas chemical corporation and KPI-MX300F manufactured by Fumura industries, Ltd.

< method for producing polyimide resin >

The polyimide resin can be produced using, for example, a tetracarboxylic acid compound and a diamine compound as main raw materials, and the polyamideimide resin can be produced using, for example, a tetracarboxylic acid compound, a dicarboxylic acid compound and a diamine compound as main raw materials. Here, the dicarboxylic acid compound preferably contains at least a compound represented by the formula (3 ").

[ chemical formula 14]

[ formula (3) ], R¹～R⁸Independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, R¹～R⁸The hydrogen atoms contained in (a) may be substituted independently of each other by halogen atoms,

a represents a single bond, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-, -S-, -CO-or-N (R)⁹)-，

R⁹Represents a hydrogen atom, a monovalent hydrocarbon group of 1 to 12 carbon atoms which may be substituted with a halogen atom, m is an integer of 0 to 4,

R³¹and R³²Independently of one another, represents a hydroxyl group, a methoxy group, an ethoxy group, a n-propoxy group, an isopropoxy group, a n-butoxy group, a sec-butoxy group, a tert-butoxy group or a chlorine atom.]

In a preferred embodiment of the present invention, the dicarboxylic acid compound is a compound represented by formula (3 ") wherein m is 0. As the dicarboxylic acid compound, it is more preferable to use a compound represented by the formula (3 ") in which a is an oxygen atom in addition to the compound represented by the formula (3") in which m is 0. In another preferred embodiment, the dicarboxylic acid compound is represented by R³¹And R³²A compound represented by the formula (3') which is a chlorine atom. In addition, a diisocyanate compound may be used instead of the diamine compound.

Examples of the diamine compound used for producing the resin include aliphatic diamines, aromatic diamines, and mixtures thereof. In the present embodiment, the "aromatic diamine" refers to a diamine in which an amino group is directly bonded to an aromatic ring, and may include an aliphatic group or other substituent in a part of the structure. The aromatic ring may be a monocyclic ring or a fused ring, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring, but are not limited thereto. Among these, benzene rings are preferred. The "aliphatic diamine" refers to a diamine in which an amino group is directly bonded to an aliphatic group, and may contain an aromatic ring or other substituent in a part of the structure.

Examples of the aliphatic diamine include acyclic aliphatic diamines such as hexamethylenediamine and cyclic aliphatic diamines such as 1, 3-bis (aminomethyl) cyclohexane, 1, 4-bis (aminomethyl) cyclohexane, norbornanediamine and 4, 4' -diaminodicyclohexylmethane. These may be used alone or in combination of two or more.

Examples of the aromatic diamine include: aromatic diamines having one aromatic ring, such as p-phenylenediamine, m-phenylenediamine, 2, 4-tolylenediamine, m-xylylenediamine, p-xylylenediamine, 1, 5-diaminonaphthalene, and 2, 6-diaminonaphthalene; 4,4 '-diaminodiphenylmethane, 4' -diaminodiphenylpropane, 4 '-diaminodiphenyl ether, 3' -diaminodiphenyl ether, 4 '-diaminodiphenyl sulfone, 3' -diaminodiphenyl sulfone, 1, 4-bis (4-aminophenoxy) benzene, 1, 3-bis (4-aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl ] sulfone, bis [4- (3-aminophenoxy) phenyl ] sulfone, 2-bis [4- (4-aminophenoxy) phenyl ] propane, 2-bis [4- (3-aminophenoxy) phenyl ] propane, 3,4 '-diaminodiphenyl ether, 3' -diaminodiphenyl ether, 3-bis (4-aminophenoxy) benzene, 1, 3-bis (4-aminophenoxy) benzene, bis (4-aminophenoxy) phenyl) sulfone, bis (4-aminophenoxy) phenyl) propane, 2-bis (4-phenoxy) phenyl) propane, 2-bis (4-aminophenoxy) phenyl) propane, 2,3, or a, 3, or a, 2, or a, 2, or a, 2, or a, 2, Aromatic diamines having two or more aromatic rings, such as 2,2 '-dimethylbenzidine, 2' -bis (trifluoromethyl) -4,4 '-diaminobiphenyl (may be referred to as TFMB), 4' -bis (4-aminophenoxy) biphenyl, 9-bis (4-aminophenyl) fluorene, 9-bis (4-amino-3-methylphenyl) fluorene, 9-bis (4-amino-3-chlorophenyl) fluorene, and 9, 9-bis (4-amino-3-fluorophenyl) fluorene. These may be used alone or in combination of two or more.

The aromatic diamine is preferably 4,4 ' -diaminodiphenylmethane, 4 ' -diaminodiphenylpropane, 4 ' -diaminodiphenylether, 3 ' -diaminodiphenylether, 4 ' -diaminodiphenylsulfone, 3 ' -diaminodiphenylsulfone, 1, 4-bis (4-aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl ] sulfone, bis [4- (3-aminophenoxy) phenyl ] sulfone, 2-bis [4- (4-aminophenoxy) phenyl ] propane, 2-bis [4- (3-aminophenoxy) phenyl ] propane, 2 ' -dimethylbenzidine, 2 ' -bis (trifluoromethyl) -4,4 ' -diaminobiphenyl (TFMB), 4,4 ' -bis (4-aminophenoxy) biphenyl, more preferably 4,4 ' -diaminodiphenylmethane, 4 ' -diaminodiphenylpropane, 4 ' -diaminodiphenyl ether, 4 ' -diaminodiphenylsulfone, 1, 4-bis (4-aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl ] sulfone, 2-bis [4- (4-aminophenoxy) phenyl ] propane, 2 ' -dimethylbenzidine, 2 ' -bis (trifluoromethyl) -4,4 ' -diaminobiphenyl (TFMB), 4 ' -bis (4-aminophenoxy) biphenyl. These may be used alone or in combination of two or more.

Among the above diamine compounds, one or more selected from the group consisting of aromatic diamines having a biphenyl structure are preferably used from the viewpoints of high surface hardness, high transparency, high flexibility, high bending resistance, and low coloring of the optical film. More preferably, at least one selected from the group consisting of 2,2 '-dimethylbenzidine, 2' -bis (trifluoromethyl) benzidine, 4 '-bis (4-aminophenoxy) biphenyl, and 4, 4' -diaminodiphenyl ether is used, and still more preferably, 2 '-bis (trifluoromethyl) -4, 4' -diaminobiphenyl (TFMB) is used.

Examples of the tetracarboxylic acid compound used for producing the resin include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic dianhydride; and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic dianhydride. The tetracarboxylic acid compound may be used alone or in combination of two or more. The tetracarboxylic acid compound may be a tetracarboxylic acid compound analog such as an acid chloride compound, in addition to the dianhydride.

Specific examples of the aromatic tetracarboxylic acid dianhydride include non-condensed polycyclic aromatic tetracarboxylic acid dianhydride, monocyclic aromatic tetracarboxylic acid dianhydride, and condensed polycyclic aromatic tetracarboxylic acid dianhydride. Examples of the non-condensed polycyclic aromatic tetracarboxylic acid dianhydride include 4,4 '-oxydiphthalic dianhydride, 3, 3', 4,4 '-benzophenonetetracarboxylic acid dianhydride, 2', 3,3 '-benzophenonetetracarboxylic acid dianhydride, 3, 3', 4,4 '-biphenyltetracarboxylic acid dianhydride, 2', 3,3 '-biphenyltetracarboxylic acid dianhydride, 3, 3', 4,4 '-diphenylsulfonetetracarboxylic acid dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 2-bis (2, 3-dicarboxyphenyl) propane dianhydride, 2-bis (3, 4-dicarboxyphenoxyphenyl) propane dianhydride, 4, 4' - (hexafluoroisopropylidene) diphthalic acid dianhydride (sometimes referred to as 6FDA), 1, 2-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1, 2-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, 4 '- (p-phenylenedioxy) diphthalic dianhydride, 4' - (m-phenylenedioxy) diphthalic dianhydride. Examples of the monocyclic aromatic tetracarboxylic acid dianhydride include 1,2,4, 5-benzenetetracarboxylic acid dianhydride, and examples of the condensed polycyclic aromatic tetracarboxylic acid dianhydride include 2,3,6, 7-naphthalenetetracarboxylic acid dianhydride.

Among these, preferred examples include 4,4 '-oxydiphthalic dianhydride, 3, 3', 4,4 '-benzophenonetetracarboxylic dianhydride, 2', 3,3 '-benzophenonetetracarboxylic dianhydride, 3, 3', 4,4 '-biphenyltetracarboxylic dianhydride, 2', 3,3 '-biphenyltetracarboxylic dianhydride, 3, 3', 4,4 '-diphenylsulfonetetracarboxylic dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 2-bis (2, 3-dicarboxyphenyl) propane dianhydride, 2-bis (3, 4-dicarboxyphenoxyphenyl) propane dianhydride, 4, 4' - (hexafluoroisopropylidene) diphthalic dianhydride (6FDA), 1, 2-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1, 1-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1, 2-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, 4,4 '- (terephthalic acid) diphthalic dianhydride and 4, 4' - (isophthalic acid) diphthalic dianhydride, more preferably 4,4 '-oxybisphthalic acid dianhydride, 3, 3', 4,4 '-biphenyltetracarboxylic acid dianhydride, 2', 3,3 '-biphenyltetracarboxylic acid dianhydride, 4, 4' - (hexafluoroisopropylidene) diphthalic acid dianhydride (6FDA), bis (3, 4-dicarboxyphenyl) methane dianhydride and 4, 4' - (p-phenylenedioxy) diphthalic dianhydride. These may be used alone or in combination of two or more.

Examples of the aliphatic tetracarboxylic dianhydride include cyclic and acyclic aliphatic tetracarboxylic dianhydrides. The cyclic aliphatic tetracarboxylic dianhydride is a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure, and specific examples thereof include cycloalkanetetracarboxylic dianhydrides such as 1,2,4, 5-cyclohexanetetracarboxylic dianhydride, 1,2,3, 4-cyclobutanetetracarboxylic dianhydride and 1,2,3, 4-cyclopentanetetracarboxylic dianhydride, bicyclo [2.2.2] oct-7-ene-2, 3,5, 6-tetracarboxylic dianhydride, dicyclohexyl-3, 3 ', 4, 4' -tetracarboxylic dianhydride and positional isomers thereof. These may be used alone or in combination of two or more. Specific examples of the acyclic aliphatic tetracarboxylic acid dianhydride include 1,2,3, 4-butanetetracarboxylic acid dianhydride, and 1,2,3, 4-pentanedicarboxylic acid dianhydride, and these can be used alone or in combination of two or more. In addition, a cyclic aliphatic tetracarboxylic dianhydride and an acyclic aliphatic tetracarboxylic dianhydride may be used in combination.

Among the tetracarboxylic dianhydrides, from the viewpoint of high surface hardness, high transparency, high flexibility, high bending resistance, and low coloring property of the optical film, 4,4 ' -oxydiphthalic dianhydride, 3,3 ', 4,4 ' -benzophenone tetracarboxylic dianhydride, 3,3 ', 4,4 ' -biphenyl tetracarboxylic dianhydride, 2 ', 3,3 ' -biphenyl tetracarboxylic dianhydride, 3,3 ', 4,4 ' -diphenylsulfone tetracarboxylic dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 4,4 ' - (hexafluoroisopropylidene) diphthalic dianhydride, and mixtures thereof are preferable, and 3,3 ', 4,4 ' -biphenyl tetracarboxylic dianhydride and 4,4 ' - (hexafluoroisopropylidene) diphthalic dianhydride, and mixtures thereof are more preferable, further preferably 4, 4' - (hexafluoroisopropylidene) diphthalic dianhydride (6 FDA).

As the dicarboxylic acid compound used for producing the resin, terephthalic acid, 4' -oxybenzoic acid or an acid chloride compound thereof is preferably used. In addition to terephthalic acid, 4' -oxybis-benzoic acid or their acid chloride compounds, other dicarboxylic acid compounds may also be used. Examples of the other dicarboxylic acid compound include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and acid chloride compounds and acid anhydrides which are analogues thereof, and two or more of them may be used in combination. Specific examples thereof include isophthalic acid; naphthalenedicarboxylic acid; 4, 4' -biphenyldicarboxylic acid; 3, 3' -biphenyldicarboxylic acid; a dicarboxylic acid compound of chain hydrocarbon having 8 or less carbon atoms and 2 benzoic acids via a single bond, -CH₂-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-or phenylene group-linked compounds and their acid chloride compounds. Specifically, 4 '-oxybis (benzoyl chloride) and terephthaloyl chloride are preferable, and a combination of 4, 4' -oxybis (benzoyl chloride) and terephthaloyl chloride is more preferable.

The polyimide resin may be obtained by reacting tetracarboxylic acid, tricarboxylic acid, and their anhydrides and derivatives in addition to the tetracarboxylic acid compound, as long as the physical properties of the optical member are not impaired.

Examples of the tetracarboxylic acid include water adducts of anhydrides of the above tetracarboxylic acid compounds.

Examples of the tricarboxylic acid compound include aromatic tricarboxylic acids, aliphatic tricarboxylic acids, and acid chloride compounds and acid anhydrides which are analogues thereof, and two or more of them may be used in combination. Specific examples thereof include: anhydride of 1,2, 4-benzenetricarboxylic acid; acid chloride compounds of 1,3, 5-benzenetricarboxylic acid; 2,3, 6-naphthalene tricarboxylic acid-2, 3-anhydride; phthalic anhydride and benzoic acid through single bond, -O-, -CH₂-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-or phenylene groups.

In the production of the resin, the amount of the diamine compound, the tetracarboxylic acid compound and/or the dicarboxylic acid compound to be used may be appropriately selected depending on the ratio of each constituent unit of the desired polyimide-based resin.

In the production of the resin, the reaction temperature of the diamine compound, the tetracarboxylic acid compound and the dicarboxylic acid compound is not particularly limited, and is, for example, 5 to 350 ℃, preferably 20 to 200 ℃, and more preferably 25 to 100 ℃. The reaction time is also not particularly limited, and is, for example, about 30 minutes to 10 hours. The reaction may be carried out in an inert atmosphere or under reduced pressure as required. In a preferred embodiment, the reaction is carried out under normal pressure and/or in an inert gas atmosphere while stirring. In addition, the reaction is preferably carried out in a solvent inert to the reaction. The solvent is not particularly limited as long as it does not affect the reaction, and examples thereof include alcohol solvents such as water, methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, 1-methoxy-2-propanol, 2-butoxyethanol, and propylene glycol monomethyl ether; ester solvents such as ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, GBL, γ -valerolactone, propylene glycol methyl ether acetate, and ethyl lactate; ketone solvents such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, 2-heptanone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; alicyclic hydrocarbon solvents such as ethylcyclohexane; aromatic hydrocarbon solvents such as toluene and xylene; nitrile solvents such as acetonitrile; ether solvents such as tetrahydrofuran and dimethoxyethane; chlorine-containing solvents such as chloroform and chlorobenzene; amide solvents such as N, N-dimethylacetamide and N, N-dimethylformamide; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide and sulfolane; carbonate solvents such as ethylene carbonate and propylene carbonate; combinations thereof, and the like. Among these, an amide solvent is preferably used from the viewpoint of solubility.

In the imidization step in the production of the polyimide-based resin, imidization may be performed in the presence of an imidization catalyst. Examples of the imidization catalyst include aliphatic amines such as tripropylamine, dibutylpropylamine, and ethyldibutylamine; alicyclic amines (monocyclic type) such as N-ethylpiperidine, N-propylpiperidine, N-butylpyrrolidine, N-butylpiperidine and N-propylhexahydroazepine; alicyclic amines (polycyclic type) such as azabicyclo [2.2.1] heptane, azabicyclo [3.2.1] octane, azabicyclo [2.2.2] octane and azabicyclo [3.2.2] nonane; and aromatic amines such as pyridine, 2-methylpyridine (2-picoline), 3-methylpyridine (3-picoline), 4-methylpyridine (4-picoline), 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2, 4-dimethylpyridine, 2,4, 6-trimethylpyridine, 3, 4-cyclopentenopyridine, 5,6,7, 8-tetrahydroisoquinoline, and isoquinoline. In addition, from the viewpoint of facilitating the imidization reaction, it is preferable to use an acid anhydride together with an imidization catalyst. Examples of the acid anhydride include conventional acid anhydrides used in the imidization reaction, and specific examples thereof include aliphatic acid anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride, and aromatic acid anhydrides such as phthalic anhydride.

The polyimide-based resin can be isolated (separated and purified) by a conventional method, for example, separation means such as filtration, concentration, extraction, crystallization, recrystallization, column chromatography, or a combination thereof, and in a preferred embodiment, the resin is precipitated by adding a large amount of an alcohol such as methanol to a reaction solution containing the transparent polyamideimide resin, and the resin is concentrated, filtered, dried, or the like.

The present invention also provides an optical film formed from the varnish of the present invention. The optical film of the present invention can be produced by casting the varnish of the present invention to form a film. The optical film is excellent in flexibility, bending resistance and surface hardness, and therefore is suitable as a front panel of an image display device, particularly a front panel (window film) of a flexible display. The optical film may be a single layer or a multilayer. When the optical film is a multilayer, each layer may have the same composition or different compositions.

When an optical film is obtained by casting film formation of the varnish of the present invention, the content of the polyimide-based resin in the optical member is preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 70% by mass or more, particularly preferably 80% by mass or more, and very preferably 90% by mass or more, based on the total mass of the optical member. When the content of the polyimide resin is not less than the lower limit, the optical member has good bending resistance. The content of the polyimide-based resin in the optical member is usually 100 mass% or less with respect to the total mass of the optical member.

(Filler)

The varnish of the present invention may contain a filler. Examples of the filler include organic particles and inorganic particles, and preferably inorganic particles. The inorganic particles include silica, zirconia, alumina, titania, zinc oxide, germanium oxide, indium oxide, tin oxide, Indium Tin Oxide (ITO), metal oxide particles such as antimony oxide and cerium oxide, and metal fluoride particles such as magnesium fluoride and sodium fluoride, among which silica particles, zirconia particles and alumina particles are preferable, and silica particles are more preferable from the viewpoint of easily improving the impact resistance of the optical film to be obtained. These fillers may be used alone or in combination of two or more.

The average primary particle diameter of the filler (preferably silica particles) is preferably 10nm or more, more preferably 15nm or more, further preferably 20nm or more, preferably 100nm or less, more preferably 90nm or less, further preferably 80nm or less, further preferably 70nm or less, particularly preferably 60nm or less, particularly preferably 50nm or less, and particularly preferably 40nm or less. When the average primary particle size of the silica particles is within the above range, aggregation of the silica particles is easily suppressed, and the optical properties of the obtained optical film are improved. The average primary particle diameter of the filler can be measured by the BET method. The primary particle size (average primary particle size) may be measured by image analysis using a Transmission Electron Microscope (TEM) or a Scanning Electron Microscope (SEM).

When the varnish of the present invention contains a filler (preferably silica particles), the content of the filler (preferably silica particles) is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 5% by mass or more, further preferably 10% by mass or more, further preferably 20% by mass or more, particularly preferably 30% by mass or more, and preferably 60% by mass or less, relative to the solid content in the varnish. When the content of the filler is not less than the above lower limit, the elastic modulus of the optical film to be obtained is easily increased. When the content of the filler is not more than the above upper limit, the storage stability of the varnish is easily improved, and the optical properties of the obtained optical film are easily improved.

(ultraviolet absorber)

The varnish of the present invention may contain one or more ultraviolet absorbers. The ultraviolet absorber can be appropriately selected from those commonly used as ultraviolet absorbers in the field of resin materials. The ultraviolet absorber may contain a compound that absorbs light having a wavelength of 400nm or less. Examples of the ultraviolet absorber include at least one compound selected from the group consisting of benzophenone-based compounds, salicylate-based compounds, benzotriazole-based compounds, and triazine-based compounds. By incorporating an ultraviolet absorber into an optical member obtained from the varnish of the present invention, deterioration of the polyimide resin can be suppressed, and thus visibility of the optical member can be improved.

In the present specification, the term "related compound" refers to a derivative of a compound to which the "related compound" is attached. For example, the "benzophenone-based compound" refers to a compound having benzophenone as a matrix skeleton and a substituent bonded to benzophenone.

When the varnish of the present invention contains an ultraviolet absorber, the content of the ultraviolet absorber is preferably 1% by mass or more, more preferably 2% by mass or more, further preferably 3% by mass or more, preferably 10% by mass or less, more preferably 8% by mass or less, and further preferably 6% by mass or less, relative to the solid content of the varnish. The appropriate content varies depending on the ultraviolet absorber used, and when the content of the ultraviolet absorber is adjusted so that the light transmittance at 400nm becomes about 20 to 60%, the light resistance of the optical member is improved, and an optical member having high transparency can be obtained.

(other additives)

The varnish of the invention may also contain other additives. Examples of the other components include an antioxidant, a release agent, a stabilizer, a bluing agent, a flame retardant, a pH adjuster, a silica dispersant, a lubricant, a thickener, and a leveling agent.

When other additives are contained, the content thereof is preferably 0.01 to 20 mass%, more preferably 0.01 to 10 mass%, based on the solid content of the varnish.

[ optical film ]

The present invention also provides an optical film formed from the varnish of the present invention, particularly an optical film obtained by casting the varnish of the present invention to form a film. The optical film of the present invention is formed from a varnish that can effectively suppress or prevent the denaturation of the polyimide resin even after the varnish is stored for a long period of time, and therefore can have excellent optical characteristics such as high total light transmittance, low YI value, and low haze. In the present specification, the term "optical properties" refers to properties that can be evaluated optically, including, for example, total light transmittance, YI value, and haze, and the term "improvement in optical properties" refers to improvement in total light transmittance, reduction in YI value, reduction in haze, and the like.

The thickness of the optical member, particularly the optical film, obtained from the varnish of the present invention can be suitably adjusted depending on the application, and is usually 10 to 1,000. mu.m, preferably 15 to 500. mu.m, more preferably 20 to 400. mu.m, and still more preferably 25 to 300. mu.m. In the present invention, the thickness can be measured by a contact-type digital indicator.

The optical member obtained from the varnish of the present invention has a total light transmittance Tt of preferably 70% or more, more preferably 80% or more, still more preferably 85% or more, and still more preferably 90% or more. When the total light transmittance Tt of the optical member is not less than the above-described lower limit, sufficient visibility is easily ensured when the optical member is incorporated into an image display device. The upper limit of the total light transmittance Tt of the optical member is usually 100% or less. The total light transmittance may be, for example, in accordance with JIS K7361-1: 1997. measured using a haze meter. The Haze (Haze) of the optical member is preferably 3.0% or less, more preferably 2.0% or less, still more preferably 1.0% or less, yet more preferably 0.8% or less, particularly preferably 0.5% or less, and particularly preferably 0.3% or less. When the haze of the optical member is not more than the above upper limit, sufficient visibility can be easily ensured when the optical member is incorporated into a flexible electronic device such as an image display device. The lower limit of the haze is not particularly limited, and may be 0% or more. The haze may be measured in accordance with JIS K7105: 1981. measured using a haze meter.

The YI value of the optical film obtained from the varnish of the present invention is preferably 8 or less, more preferably 5 or less, still more preferably 3 or less, and still more preferably 2 or less. When the YI value of the optical film is equal to or less than the upper limit, the transparency becomes good, and it can contribute to obtaining high visibility when used for, for example, a front panel of an image display device. The YI value is usually-5 or more, preferably-2 or more. The YI value can be calculated based on the formula of YI × (1.2769X-1.0592Z)/Y by measuring the transmittance of light of 300 to 800nm using an ultraviolet-visible near-infrared spectrophotometer to obtain the tristimulus value (X, Y, Z). For example, the measurement can be carried out by the method described in examples.

In the case of producing an optical film from the varnish of the present invention, the total light transmittance, the haze and the YI value may be those of an optical film formed from the varnish after storage because the varnish exhibits excellent optical characteristics even after storage for a long time.

(method of manufacturing optical Member)

The varnish of the present invention can be used to produce an optical member such as an optical film. The production method is not particularly limited. The optical member can be manufactured, for example, by a manufacturing method including the steps of:

(a) a step (coating step) of coating the varnish of the present invention on a support to form a coating film; and

(b) and a step (forming step) of drying the applied liquid (varnish of the polyimide resin) to form an optical member, particularly an optical film (polyimide resin film).

Usually, the steps (a) and (b) may be performed sequentially.

In the coating step, the varnish of the present invention is prepared by dissolving the polyimide resin powder in a solvent, adding the above-mentioned ultraviolet absorber and other additives as needed, and stirring.

As the solvent used in the preparation of the varnish, other solvents may be used in combination in addition to GBL described above. Examples of other solvents include: amide solvents such as N, N-dimethylacetamide and N, N-dimethylformamide; lactone solvents such as γ -valerolactone; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide and sulfolane; carbonate solvents such as ethylene carbonate and propylene carbonate; and combinations thereof. Among these solvents, an amide solvent or a lactone solvent is preferable. The varnish may contain water, an alcohol solvent, a ketone solvent, an acyclic ester solvent, an ether solvent, and the like.

Next, a coating film can be formed on a support such as a resin substrate, SUS band, or glass substrate by casting or the like using a varnish of a polyimide resin by a known roll-to-roll or batch method.

In the forming step, the coating film is dried and peeled from the substrate, whereby an optical member can be formed. After the peeling, a drying step of drying the optical member may be further performed. The drying of the coating film may be carried out at a temperature of 50 to 350 ℃. If necessary, the coating film may be dried in an inert atmosphere or under reduced pressure.

The surface treatment step of performing surface treatment on at least one surface of the optical member may be performed. Examples of the surface treatment include UV ozone treatment, plasma treatment, and corona discharge treatment.

Examples of the resin substrate include a metal tape such as SUS, a PET film, a PEN film, a polyimide film, and a polyamideimide film. Among them, a PET film, a PEN film, a polyimide film, and other polyamide-imide films are preferable from the viewpoint of excellent heat resistance. Further, from the viewpoint of adhesion to an optical member and cost, a PET film is more preferable.

From the viewpoint of facilitating the production of an optical member (for example, an optical film) having a reduced YI, it is preferable to produce the optical member by a production method including at least the following steps: (a) a step of applying the varnish of the present invention to a support to form a coating film; and (b) drying the coating film at a temperature of 100 ℃ to 240 ℃ to obtain an optical film. The drying temperature of the coating is preferably 100-240 ℃, more preferably 120-220 ℃, and further preferably 150-220 ℃.

Optical parts that can be produced using the varnish of the present invention have high elastic modulus and flexibility. In a preferred embodiment of the present invention, the elastic modulus of the optical member is preferably 3.0GPa or more, more preferably 4.0GPa or more, further preferably 5.0GPa or more, particularly preferably 6.0GPa or more, preferably 10.0GPa or less, more preferably 8.0GPa or less, further preferably 7.0GPa or less. When the elastic modulus of the optical member is not more than the upper limit, damage to other members caused by the optical member can be suppressed when the flexible display is bent. The elastic modulus can be measured by measuring the S-S curve of a test piece having a width of 10mm under the conditions of an inter-chuck distance of 50mm and a tensile rate of 20 mm/min using, for example, Autograph AG-IS manufactured by Shimadzu corporation, and measuring the slope thereof.

The optical member, particularly the optical film, has excellent bending resistance. In a preferred embodiment of the present invention, when the optical member is measured at a rate of 175cpm under a load of 0.75kgf at a rate of 135 ° with R1 mm, the number of times of repeated bending until breakage is preferably 10,000 or more, more preferably 20,000 or more, further preferably 30,000 or more, further preferably 40,000 or more, and particularly preferably 50,000 or more.

When the number of times of repeated bending of the optical member is equal to or more than the lower limit, wrinkles that may occur when the optical member is bent can be further suppressed. The number of times of bending the optical member is repeated is not limited, and it is generally sufficient to bend the optical member 1,000,000 times. The number of times of repeated bending can be determined, for example, by using an MIT bending fatigue tester (model 0530) manufactured by Toyo Seiki Seisaku-Sho K.K., using a test piece (optical component) having a thickness of 50 μm and a width of 10 mm.

The optical member can exhibit excellent transparency. Therefore, the optical member is very useful as a front panel (window film) of an image display device, particularly a flexible display. In a preferred embodiment of the present invention, the optical member is a member according to JIS K7373: the YI value measured by 2006 is preferably 5 or less, more preferably 3 or less, further preferably 2.5 or less, and further preferably 2.0 or less. An optical member having a YI value of not more than the above upper limit can contribute to high visibility of a display device or the like. The YI value of the optical member is preferably 0 or more.

[ optical laminate ]

The optical film of the present invention may be an optical laminate formed by laminating 1 or more functional layers on at least one surface. Examples of the functional layer include an ultraviolet absorbing layer, a hard coat layer, an undercoat layer, a gas barrier layer, an adhesive layer, a color tone adjusting layer, and a refractive index adjusting layer. The functional layers may be used alone or in combination of two or more.

The ultraviolet absorbing layer is a layer having a function of absorbing ultraviolet rays, and is composed of a main material selected from an ultraviolet-curable transparent resin, an electron beam-curable transparent resin, and a thermosetting transparent resin, and an ultraviolet absorber dispersed in the main material, for example.

A hard coat layer may be provided on at least one side of the optical film of the present invention. The thickness of the hard coat layer is not particularly limited, and may be, for example, 2 to 100 μm. When the thickness of the hard coat layer is within the above range, the impact resistance is easily improved. The hard coat layer may be formed by curing a hard coat layer composition containing a reactive material capable of forming a cross-linked structure by irradiation with active energy rays or application of thermal energy, and is preferably a layer based on irradiation with active energy rays. The active energy ray is defined as an energy ray that can decompose a compound that generates an active species to generate an active species, and examples thereof include visible light, ultraviolet ray, infrared ray, X-ray, α -ray, β -ray, γ -ray, and electron ray, and preferable examples thereof include ultraviolet ray. The hard coat composition contains at least one polymer selected from a radical polymerizable compound and a cation polymerizable compound.

The radical polymerizable compound is a compound having a radical polymerizable group. The radical polymerizable group of the radical polymerizable compound may be a functional group capable of undergoing a radical polymerization reaction, and examples thereof include a group containing a carbon-carbon unsaturated double bond, specifically, a vinyl group and a (meth) acryloyl group. When the radical polymerizable compound has 2 or more radical polymerizable groups, the radical polymerizable groups may be the same or different. The number of the radical polymerizable groups contained in 1 molecule of the radical polymerizable compound is preferably 2 or more in terms of increasing the hardness of the hard coat layer. The radical polymerizable compound is preferably a compound having a (meth) acryloyl group in view of high reactivity, and specifically, a compound called a multifunctional acrylate monomer having 2 to 6 (meth) acryloyl groups in 1 molecule; oligomers having a molecular weight of several hundred to several thousand and having several (meth) acryloyl groups in the molecule, which are called epoxy (meth) acrylate, urethane (meth) acrylate, and polyester (meth) acrylate, preferably include one or more selected from epoxy (meth) acrylate, urethane (meth) acrylate, and polyester (meth) acrylate.

The cationically polymerizable compound is a compound having a cationically polymerizable group such as an epoxy group, an oxetane group, or a vinyl ether group. The number of the cationically polymerizable groups contained in 1 molecule of the cationically polymerizable compound is preferably 2 or more, and more preferably 3 or more, from the viewpoint of improving the hardness of the hard coat layer.

Among the above cationically polymerizable compounds, preferred are compounds having at least one of an epoxy group and an oxetane group as a cationically polymerizable group. From the viewpoint of reducing shrinkage accompanying the polymerization reaction, a cyclic ether group such as an epoxy group or an oxetane group is preferable. In addition, the compound having an epoxy group in a cyclic ether group has the following advantages: compounds with various structures are easily obtained; the durability of the obtained hard coating is not adversely affected; the compatibility with the radical polymerizable compound can be easily controlled. In addition, the oxetanyl group in the cyclic ether group has the following advantages as compared with the epoxy group: the polymerization degree is easy to be improved; the toxicity is low; accelerating the network formation rate obtained from the cationic polymerizable compound of the obtained hard coat layer; forming an independent network so that an unreacted monomer does not remain in the film even in a region where the radical polymerizable compound is present in a mixed state; and so on.

Examples of the cationically polymerizable compound having an epoxy group include: an alicyclic epoxy resin obtained by epoxidizing a polyglycidyl ether of a polyhydric alcohol having an alicyclic ring or a compound containing a cyclohexene ring or a cyclopentene ring with an appropriate oxidizing agent such as hydrogen peroxide or a peroxy acid; aliphatic epoxy resins such as polyglycidyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof, polyglycidyl esters of aliphatic long-chain polybasic acids, homopolymers and copolymers of glycidyl (meth) acrylate; glycidyl ethers produced by the reaction of epichlorohydrin with phenols such as bisphenol a, bisphenol F, hydrogenated bisphenol a, and derivatives such as alkylene oxide adducts and caprolactone adducts of these phenols, and glycidyl ether-type epoxy resins derived from bisphenols such as Novolac epoxy resins; and so on.

The above hard coating composition may further comprise a polymerization initiator. Examples of the polymerization initiator include a radical polymerization initiator, a cationic polymerization initiator, a radical and cationic polymerization initiator, and they can be appropriately selected and used. These polymerization initiators are decomposed by at least one of irradiation with active energy rays and heating to generate radicals or cations, and radical polymerization and cationic polymerization are performed.

The radical polymerization initiator may be one that can release a substance that causes radical polymerization by at least one of irradiation with active energy rays and heating. Examples of the thermal radical polymerization initiator include organic peroxides such as hydrogen peroxide and perbenzoic acid, and azo compounds such as azobisisobutyronitrile.

The active energy ray radical polymerization initiator includes a Type1 radical polymerization initiator which generates radicals by decomposition of molecules and a Type2 radical polymerization initiator which generates radicals by hydrogen abstraction reaction in the coexistence of a tertiary amine, and they can be used alone or in combination.

The cationic polymerization initiator may be a substance capable of releasing cationic polymerization initiated by at least one of irradiation with active energy rays and heating. As the cationic polymerization initiator, aromatic iodonium salts, aromatic sulfonium salts, cyclopentadienyl iron (II) complexes, and the like can be used. In the case of these cationic polymerization initiators, cationic polymerization can be initiated by either or both of irradiation with active energy rays or heating, depending on the structure.

The polymerization initiator may be contained in an amount of preferably 0.1 to 10% by mass based on 100% by mass of the entire hard coat composition. When the content of the polymerization initiator is within the above range, the curing can be sufficiently performed, the mechanical properties and the adhesion of the finally obtained coating film can be in a favorable range, and poor adhesion, a crack phenomenon, and a curl phenomenon due to curing shrinkage tend to be less likely to occur.

The hard coating composition may further include one or more selected from the group consisting of a solvent and an additive.

The solvent may be any solvent that can dissolve or disperse the polymerizable compound and the polymerization initiator and is known as a solvent for a hard coat composition in the art, and may be used within a range that does not impair the effects of the present invention.

The additives may further include inorganic particles, leveling agents, stabilizers, surfactants, antistatic agents, lubricants, antifouling agents, and the like.

The pressure-sensitive adhesive layer is a layer having a pressure-sensitive adhesive function and has a function of bonding the optical film to another member. As a material for forming the adhesive layer, a generally known material can be used. For example, a thermosetting resin composition or a photocurable resin composition may be used. In this case, the resin composition can be polymerized and cured by supplying energy afterwards.

The Pressure-Sensitive Adhesive layer may be a layer called a Pressure-Sensitive Adhesive (PSA) that is pressed and attached to an object. The pressure-sensitive adhesive may be a capsule adhesive as "a substance having adhesiveness at normal temperature and adhering to an adherend under light pressure" (JIS K6800), or as "an adhesive which contains a specific component in a protective film (microcapsule) and can maintain stability until the film is broken by an appropriate means (pressure, heat, etc.)" (JIS K6800).

The color tone adjusting layer is a layer having a function of adjusting color tone, and is a layer capable of adjusting the optical layered body to a target color tone. The color tone adjusting layer is, for example, a layer containing a resin and a colorant. Examples of the colorant include inorganic pigments such as titanium oxide, zinc oxide, red iron oxide, titanium oxide-based calcined pigments, ultramarine blue, cobalt aluminate, and carbon black; organic pigments such as azo-based compounds, quinacridone-based compounds, anthraquinone-based compounds, perylene-based compounds, isoindolinone-based compounds, phthalocyanine-based compounds, quinophthalone-based compounds, threne-based compounds, and diketopyrrolopyrrole-based compounds; bulk pigments such as barium sulfate and calcium carbonate; and basic dyes, acid dyes, mordant dyes and the like.

The refractive index adjustment layer is a layer having a function of adjusting the refractive index, and is, for example, a layer having a refractive index different from that of the optical film and capable of providing a predetermined refractive index to the optical laminate. The refractive index adjusting layer may be, for example, a resin layer containing an appropriately selected resin and, in some cases, a pigment, or may be a metal thin film. Examples of the pigment for adjusting the refractive index include silicon oxide, aluminum oxide, antimony oxide, tin oxide, titanium oxide, zirconium oxide, and tantalum oxide. The average primary particle diameter of the pigment may be 0.1 μm or less. By setting the average primary particle diameter of the pigment to 0.1 μm or less, diffuse reflection of light transmitted through the refractive index adjustment layer can be prevented, and a decrease in transparency can be prevented. Examples of the metal used for the refractive index adjustment layer include metal oxides and metal nitrides such as titanium oxide, tantalum oxide, zirconium oxide, zinc oxide, tin oxide, silicon oxide, indium oxide, titanium oxynitride, titanium nitride, silicon oxynitride, and silicon nitride.

The optical stack may further include a protective film. The protective film may be laminated on one or both sides of the optical film. When one surface of the optical film has a functional layer, the protective film may be laminated on the surface of the optical film or the surface of the functional layer, or may be laminated on both the optical film and the functional layer. When the optical film has functional layers on both surfaces thereof, the protective film may be laminated on the surface of one functional layer side, or may be laminated on the surfaces of both functional layers. The protective film is a film for temporarily protecting the surface of the optical film or the functional layer, and is not particularly limited as long as it is a peelable film capable of protecting the surface of the optical film or the functional layer. Examples of the protective film include polyester resin films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; the resin film is preferably selected from the group consisting of polyolefin resin films, polyethylene, polypropylene films and the like, and acrylic resin films. When the optical laminate includes 2 protective films, the protective films may be the same or different.

The thickness of the protective film is not particularly limited, but is usually 10 to 100 μm, preferably 10 to 80 μm, and more preferably 10 to 50 μm. When the optical laminate includes 2 protective films, the thicknesses of the protective films may be the same or different.

In one embodiment of the present invention, the optical laminate may be wound around a winding core in a roll shape, and this form is referred to as a laminate film roll. Examples of the material constituting the core include synthetic resins such as polyethylene resin, polypropylene resin, polyvinyl chloride resin, polyester resin, epoxy resin, phenol resin, melamine resin, silicone resin, polyurethane resin, polycarbonate resin, and ABS resin; metals such as aluminum; fiber-reinforced plastics (FRP: a composite material having increased strength obtained by incorporating fibers such as glass fibers into plastics); and so on. The winding core is cylindrical or columnar, and has a diameter of, for example, 80 to 170 mm. The diameter of the laminate film roll (diameter after winding) is not particularly limited, and is usually 200 to 800 mm. In one embodiment of the present invention, in the laminate film roll, the support is not peeled off from the optical film in the optical film production process, and the laminate having the support, the optical film, and optionally the functional layer and the protective film may be wound around the core in a roll form. In the case of a laminate film roll, the laminate is often temporarily stored in the form of a film roll due to space limitations or the like in continuous production, and in the case of a laminate film roll, the laminate is tightly wound, and therefore, the substance responsible for cloudiness on the support is easily transferred to the optical film. However, when a support having a predetermined water contact angle is used, the white turbidity substance from the support is not easily transferred to the optical film, and even if the support is wound up in the form of a roll of the laminate film, white turbidity is not easily generated.

The optical member may include functional layers such as an ultraviolet absorbing layer, an adhesive layer, a color tone adjusting layer, and a refractive index adjusting layer, and a hard coat layer.

An optical member (for example, an optical film) produced using the varnish of the present invention is useful as a front panel of an image display device, particularly a front panel of a flexible display, particularly a front panel (window film) of a rollable display or a foldable display. The optical member can be disposed as a front panel on a viewing side surface of an image display device, particularly a flexible display. The front panel has a function of protecting the image display elements within the flexible display. The image display device provided with the optical member has high flexibility and bending resistance, and also has high surface hardness, so that other members are not damaged during bending, and the optical member itself is not easily wrinkled, and further damage to the surface can be favorably suppressed.

[ image display device ]

The optical film of the present invention is formed from the varnish of the present invention, has excellent optical characteristics, and thus can be suitably used as a front panel (window film) of an image display device. The optical film of the present invention can be disposed as a front panel on the viewing-side surface of an image display device, particularly a flexible display. The front panel has a function of protecting the image display elements within the flexible display. Examples of the image display device include wearable devices such as a television, a smartphone, a mobile phone, a navigator, a tablet PC, a portable game machine, electronic paper, a pointer, a signboard, a clock, and a smart watch. Examples of the flexible display include an image display device having a flexible property, such as a television, a smart phone, a mobile phone, and a smart watch.

In one embodiment of the present invention, an image display device may include the optical film of the present invention and at least 1 selected from the group consisting of a polarizing plate, a touch sensor, and a display panel. For example, the image display device may be one in which a polarizing plate, a touch sensor, and a display panel are laminated on one surface of the optical film with or without a transparent adhesive or a transparent pressure-sensitive adhesive. The optical film of the present invention may be incorporated in an image display device in the form of the above optical laminate, and the optical film included in the image display device may be the above optical laminate.

In one embodiment of the present invention, the image display device may include a colored light-shielding pattern printed so as to surround the frame on at least one surface of the optical film or the polarizing plate, and the light-shielding pattern may be in the form of a single layer or a plurality of layers. The polarizing plate may be a general polarizing plate which continuously extends to the non-display region or the frame (bezel) portion, and may include a polyvinyl alcohol-based polarizer and a protective layer laminated (or attached) on at least one surface of the polyvinyl alcohol-based polarizer.

In one embodiment of the present invention, in the structure in which the polarizing plate and the touch sensor are integrated on one surface of the optical film, the order of arrangement of the polarizing plate and the touch sensor is not limited, and the polarizing plate, the touch sensor, and the display panel may be arranged in the order of the optical film, the polarizing plate, the touch sensor, and the display panel, or the optical film, the touch sensor, the polarizing plate, and the display panel may be arranged in the order of the optical film, the touch sensor, and the display panel. When the optical film, the polarizing plate, the touch sensor, and the display panel are arranged in this order, the touch sensor is present below the polarizing plate when the image display device is viewed from the viewing side, and thus the pattern of the touch sensor is not easily visible. In this case, the front phase difference of the substrate of the touch sensor is preferably ± 2.5nm or less. As a material of the substrate, for example, a film of 1 or more kinds of materials selected from the group consisting of triacetyl cellulose, cycloolefin copolymer, polynorbornene copolymer, and the like can be used as an unstretched film. On the other hand, a structure may be employed in which a pattern is transferred only to the optical film and the polarizing plate without using a substrate having a touch sensor.

The polarizing plate and the touch sensor may be disposed between the optical film and the display panel via a transparent adhesive layer or a transparent adhesive layer, and the transparent adhesive layer is preferable. In the case where the optical film, the polarizing plate, the touch sensor, and the display panel are disposed in this order, the transparent adhesive layer may be located between the optical film and the polarizing plate, and between the touch sensor and the display panel. In the case where the optical film, the touch sensor, the polarizing plate, and the display panel are arranged in this order, the transparent adhesive layer may be arranged between the optical film and the touch sensor, between the touch sensor and the polarizing plate, and between the polarizing plate and the display panel.

The thickness of the transparent adhesive layer is not particularly limited, and may be, for example, 1 to 100 μm. In the transparent pressure-sensitive adhesive layer, the thickness of the transparent pressure-sensitive adhesive layer on the lower side (display panel side) is preferably not less than the thickness of the transparent pressure-sensitive adhesive layer on the upper side (optical film side), and the viscoelasticity is preferably 0.2MPa or less at-20 to 80 ℃. In this case, noise generated by interference between the touch sensor and the display panel can be reduced, and the interface stress at the time of bending can be relaxed, thereby suppressing the destruction of the upper and lower members. The viscoelasticity may be more preferably 0.01 to 0.15MPa from the viewpoint of suppressing aggregation breakdown of the transparent adhesive and relaxing the interfacial stress.

< polarizing plate >

The polarizing plate may include, for example, a polarizer and, if necessary, at least 1 selected from the group consisting of a support, an alignment film, a retardation coating layer, an adhesive layer and a protective layer. The thickness of the polarizer is not particularly limited, and may be, for example, 100 μm or less. When the thickness is 100 μm or less, the flexibility is less likely to be lowered. Within the above range, for example, the thickness may be 5 to 100 μm.

The polarizer may be a film-type polarizer generally used in the art, which is manufactured by a process including steps of swelling, dyeing, crosslinking, stretching, washing with water, drying, etc. of a polyvinyl alcohol-based film, or a coating-type polarizer (sometimes referred to as a polarizing coating) formed by coating a polarizing coating forming composition containing a polymerizable liquid crystal and a dichroic dye. The above-mentioned polarizing coating layer (sometimes simply referred to as polarizing layer) can be produced, for example, by: an alignment film-forming composition is applied to a support to impart alignment properties to the support to form an alignment film, and a polarizing coating layer-forming composition containing a polymerizable liquid crystal compound and a dichroic dye is applied to the alignment film to form a liquid crystal coating layer. Such a polarizing coating can be formed to have a smaller thickness than a polarizing plate including protective layers attached to both surfaces of a film-type polarizer by an adhesive. The thickness of the polarizing coating layer may be 0.5 to 10 μm, preferably 2 to 4 μm. As the support, the polymer film exemplified above as the protective film can be used.

(alignment film)

The alignment film can be formed by coating an alignment film-forming composition. The alignment film-forming composition may contain an alignment agent, a photopolymerization initiator, and a solvent, which are generally used in the art. As the above-mentioned aligning agent, an aligning agent generally used in this field can be used without particular limitation. For example, a polyacrylate-based polymer, a polyamic acid, a polyimide-based polymer, or a cinnamate-group-containing polymer can be used as the alignment agent, and in the case where photo-alignment is applied, a cinnamate-group-containing polymer is preferably used. Examples of the solvent include alcohol solvents such as methanol, ethanol, ethylene glycol, isopropanol, propylene glycol, methyl cellosolve, butyl cellosolve, and propylene glycol monomethyl ether, ester solvents such as ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, GBL, propylene glycol methyl ether acetate, and ethyl lactate, ketone solvents such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, methyl amyl ketone, and methyl isobutyl ketone, aliphatic hydrocarbon solvents such as pentane, hexane, and heptane, aromatic hydrocarbon solvents such as toluene and xylene, nitrile solvents such as acetonitrile, ether solvents such as tetrahydrofuran and dimethoxyethane, and chlorinated hydrocarbon solvents such as chloroform and chlorobenzene. The solvent may be used alone or in combination of two or more.

Examples of the coating of the alignment film forming composition include spin coating, extrusion molding, dip coating, flow coating, spray coating, roll coating, gravure coating, and microgravure coating, and an in-line coating method is preferably used. The above-described alignment film-forming composition is applied and, if necessary, dried, and then subjected to an alignment treatment. The alignment treatment may be performed by any of various methods known in the art without particular limitation, and preferably, a photo-alignment film may be used. The photo alignment film can be generally obtained by applying a composition for forming a photo alignment film, which includes a polymer or monomer having a photoreactive group and a solvent, onto a support and irradiating polarized light (preferably polarized UV light). The photo-alignment film is further preferable in that the direction of the alignment regulating force can be arbitrarily controlled by selecting the polarization direction of the irradiated polarized light.

The thickness of the photo-alignment layer is usually 10 to 10,000nm, preferably 10 to 1,000nm, and more preferably 10 to 500 nm. When the thickness of the photo-alignment film is within the above range, the alignment regulating force can be sufficiently exhibited.

(polarizing coating)

The polarizing coating layer may be formed by applying a polarizing coating layer-forming composition. Specifically, the polarizing coating layer-forming composition is a polymerizable liquid crystal composition (hereinafter, sometimes referred to as a polymerizable liquid crystal composition B) containing 1 or more kinds of polymerizable liquid crystals (hereinafter, sometimes referred to as a polymerizable liquid crystal (B)) as a host compound in addition to a dichroic dye.

The "dichroic dye" refers to a dye having a property that the absorbance of a molecule in the major axis direction is different from the absorbance of a molecule in the minor axis direction. The dichroic dye is not limited as long as it has such properties, and may be a dye or a pigment. More than 2 dyes may be used in combination, more than 2 pigments may be used in combination, or a combination of a dye and a pigment may be used.

The dichroic dye preferably has a maximum absorption wavelength (lambda) in the range of 300 to 700nm_MAX). Examples of such dichroic pigments include acridine pigments, oxazine pigments, phthalocyanine pigments, naphthalene pigments, azo pigments, and anthraquinone pigments, and preferably include azo pigments. The azo dyes include monoazo dyes, disazo dyes, trisazo dyes, tetraazo dyes, and stilbene azo dyes, and preferably disazo dyes and trisazo dyes.

The liquid crystal state exhibited by the polymerizable liquid crystal (B) is preferably a smectic phase, and more preferably a higher order smectic phase, from the viewpoint of enabling the production of a polarizing layer having a high degree of orientational order. The polymerizable liquid crystal (B) exhibiting a smectic phase is referred to as a polymerizable smectic liquid crystal compound. The polymerizable liquid crystal (B) may be used alone or in combination. When 2 or more kinds of polymerizable liquid crystals are combined, at least 1 kind is preferably the polymerizable liquid crystal (B), and more preferably 2 or more kinds are the polymerizable liquid crystal (B). By combining these, the liquid crystal properties can be temporarily maintained even at a temperature not higher than the liquid crystal-to-crystalline phase transition temperature in some cases. The polymerizable liquid crystal (B) can be produced by a known method described in Lub et al, Recl.Trav.Chim.Pays-Bas, 115, 321-328(1996), Japanese patent No. 4719156, or the like. The content of the dichroic dye in the polymerizable liquid crystal composition B may be appropriately adjusted depending on the kind of the dichroic dye, and is preferably 0.1 to 50 parts by mass, more preferably 0.1 to 20 parts by mass, and still more preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the polymerizable liquid crystal (B). When the content of the dichroic dye is within the above range, polymerization can be performed without disturbing the orientation of the polymerizable liquid crystal (B), and the tendency of inhibiting the orientation of the polymerizable liquid crystal (B) is small.

The polymerizable liquid crystal composition B preferably contains a solvent. In general, a polymerizable liquid crystal composition containing a solvent is easily applied because of high viscosity of a smectic liquid crystal compound, and as a result, a polarizing film is often easily formed. The solvent may be the same as the solvent contained in the alignment polymer composition, and may be appropriately selected depending on the solubility of the polymerizable liquid crystal (B) and the dichroic dye. The content of the solvent is preferably 50 to 98% by mass based on the total amount of the polymerizable liquid crystal composition B. In other words, the solid content in the polymerizable liquid crystal composition B is preferably 2 to 50% by mass based on the total amount of the polymerizable liquid crystal composition B.

The polymerizable liquid crystal composition B preferably contains one or more leveling agents. The leveling agent has a function of adjusting the fluidity of the composition B to flatten a coating film obtained by coating the polymerizable liquid crystal composition B, and specifically includes a surfactant. When the polymerizable liquid crystal composition B contains the leveling agent, the content thereof is preferably 0.05 to 0.05 parts by mass, and more preferably 0.05 to 3 parts by mass, based on 100 parts by mass of the polymerizable liquid crystal. When the content of the leveling agent is within the above range, the polymerizable liquid crystal is easily aligned horizontally, and the obtained polarizing layer tends to be smoother. When the content of the leveling agent with respect to the polymerizable liquid crystal is within the above range, unevenness tends not to be generated in the obtained polarizing layer.

The polymerizable liquid crystal composition B preferably contains one or more polymerization initiators. The polymerization initiator is a compound capable of initiating the polymerization reaction of the polymerizable liquid crystal (B), and is preferably a photopolymerization initiator in that the polymerization reaction can be initiated at a relatively low temperature. Specifically, a photopolymerization initiator which can generate an active radical or an acid by the action of light is exemplified, and among them, a photopolymerization initiator which can generate a radical by the action of light is preferable. Examples of the polymerization initiator include benzoin compounds, benzophenone compounds, alkylphenone compounds, acylphosphine oxide compounds, triazine compounds, iodonium salts, and sulfonium salts.

When the polymerizable liquid crystal composition B contains a polymerization initiator, the content thereof may be appropriately adjusted depending on the kind and amount of the polymerizable liquid crystal contained in the polymerizable liquid crystal composition, and is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 10 parts by mass, and still more preferably 0.5 to 8 parts by mass, based on 100 parts by mass of the polymerizable liquid crystal. When the content of the polymerization initiator is within the above range, polymerization can be performed without disturbing the orientation of the polymerizable liquid crystal (B). When the polymerizable liquid crystal composition B contains a photopolymerization initiator, the polymerizable liquid crystal composition may further contain a photosensitizer. When the polymerizable liquid crystal composition B contains a photopolymerization initiator and a photosensitizer, the polymerization reaction of the polymerizable liquid crystal contained in the polymerizable liquid crystal composition can be further promoted. The amount of the photosensitizer to be used may be appropriately adjusted depending on the kind and amount of the photopolymerization initiator and the polymerizable liquid crystal, and is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 10 parts by mass, and still more preferably 0.5 to 8 parts by mass, per 100 parts by mass of the polymerizable liquid crystal.

In order to more stably perform the polymerization reaction of the polymerizable liquid crystal, the polymerizable liquid crystal composition B may contain an appropriate amount of a polymerization inhibitor, and thus the degree of progress of the polymerization reaction of the polymerizable liquid crystal can be easily controlled. When the polymerizable liquid crystal composition B contains a polymerization inhibitor, the content thereof may be appropriately adjusted depending on the kind and amount of the polymerizable liquid crystal, the amount of the photosensitizer used, and the like, and is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 10 parts by mass, and still more preferably 0.5 to 8 parts by mass, based on 100 parts by mass of the polymerizable liquid crystal. When the content of the polymerization inhibitor is within the above range, polymerization can be carried out without disturbing the orientation of the polymerizable liquid crystal.

The polarizing coating layer can be usually formed by applying a polarizing coating layer-forming composition to a support subjected to an alignment treatment and polymerizing polymerizable liquid crystals in the resultant coating film. The method of applying the above-described polarizing coating layer-forming composition is not limited. Examples of the orientation treatment include the above-mentioned orientation treatment. The composition for forming a polarizing coating is applied, and the solvent is dried and removed under the condition that the polymerizable liquid crystal contained in the obtained coating film is not polymerized, thereby forming a dry coating film. Examples of the drying method include a natural drying method, a forced air drying method, a heat drying method, and a reduced pressure drying method. When the polymerizable liquid crystal is a polymerizable smectic liquid crystal compound, it is preferable that the liquid crystal state of the polymerizable smectic liquid crystal compound contained in the dry film is changed to a nematic phase (nematic liquid crystal state) and then the liquid crystal is changed to a smectic phase. In order to form a smectic phase via a nematic phase, for example, the following method can be employed: the dried film is heated to a temperature at which the polymerizable smectic liquid crystal compound contained in the dried film is phase-changed to a nematic liquid crystal state or higher, and then cooled to a temperature at which the polymerizable smectic liquid crystal compound assumes a smectic liquid crystal state. Next, a method of photopolymerizing the polymerizable liquid crystal while keeping the liquid crystal state of the smectic phase unchanged after the liquid crystal state of the polymerizable liquid crystal in the dry film is brought into the smectic phase will be described. In photopolymerization, the light to be irradiated to the dry film may be appropriately selected depending on the kind of the photopolymerization initiator contained in the dry film, the kind of the polymerizable liquid crystal (particularly, the kind of the photopolymerizable group of the polymerizable liquid crystal) and the amount thereof, and specific examples thereof include active energy rays selected from the group consisting of visible light, ultraviolet light, and laser light. Among these, ultraviolet light is preferable because the progress of the polymerization reaction can be easily controlled and a photopolymerization device widely used in the art can be used as the photopolymerization device. By photopolymerization, the polymerizable liquid crystal is polymerized while maintaining a liquid crystal state of a smectic phase, preferably a higher order smectic phase, to form a polarizing layer.

(phase difference coating)

The polarizing plate may include a retardation coating layer (sometimes simply referred to as a retardation layer). The retardation coating layer is collectively referred to as a λ/2 layer, a λ/4 layer, a positive C layer, and the like, in terms of optical characteristics. The phase difference coating layer can be formed, for example, by the following method, but is not limited thereto: the liquid crystal coating layer is formed by applying a phase difference coating layer forming composition containing a liquid crystal compound on an alignment film of a support having the alignment film formed on the surface thereof, and then the liquid crystal coating layer is bonded to a polarizing layer via an adhesive layer, and then the support is peeled off. As the support, the polymer film exemplified above as the protective film can be used, and the surface of the support on the side where the alignment film and the retardation layer are formed can be subjected to surface treatment before the formation of the alignment film. The alignment film-forming composition and the coating and drying methods thereof are the same as those described for the polarizing coating layer. The composition of the retardation coating layer-forming composition is the same as that described in the above-mentioned polarizing coating layer, except that the composition does not contain a dichroic dye. The methods of applying, drying, and curing the retardation coating layer-forming composition are the same as those described above for the polarizing coating layer.

The thickness of the phase difference coating layer may preferably be 0.5 to 10 μm, more preferably 1 to 4 μm.

In one embodiment of the present invention, the optical characteristics of the retardation coating layer can be adjusted by the thickness of the coating layer, the alignment state of the polymerizable liquid crystal compound, and the like. By adjusting the thickness of the retardation layer, a retardation layer that imparts a desired in-plane retardation can be produced. The in-plane phase difference value (in-plane retardation value, Re) is a value defined by the equation (1), and Δ n and the thickness (d) can be adjusted to obtain a desired Re.

Re × Δ n (λ) · · mathematical formula (1) (here, Δ n ═ nx-ny)

(in the formula (1), Re represents an in-plane retardation value, d represents a thickness of a coating layer, and Δ n represents a birefringence index. in consideration of a refractive index ellipsoid formed by orientation of a polymerizable liquid crystal compound, 3 directions of refractive indices, that is, nx, ny, and nz. nx represent main refractive indices in a direction parallel to a plane of the retardation layer in the refractive index ellipsoid formed by the retardation layer, ny represents a refractive index in a direction parallel to the plane of the retardation layer and orthogonal to the direction of nx in the refractive index ellipsoid formed by the retardation layer, nz represents a refractive index in a direction perpendicular to the plane of the retardation layer in the refractive index ellipsoid formed by the retardation layer, and when the retardation layer is a λ/4 layer, the in-plane retardation value Re (550) is usually in the range of 113 to 163nm, preferably 130 to 150 nm. when the retardation layer is a λ/2 layer, re (550) is usually in the range of 250 to 300nm, preferably 250 to 300 nm.

Further, depending on the alignment state of the polymerizable liquid crystal compound, a retardation layer exhibiting a retardation in the thickness direction can be produced. The expression of the retardation in the thickness direction means that the retardation value Rth in the thickness direction is negative in the formula (2).

Rth [ (nx + ny)/2-nz ] x d · · math figure (2)

(in the numerical formula (2), nx, ny, nz and d are as defined above)

The in-plane retardation Re (550) of the positive C layer is usually in the range of 0 to 10nm, preferably 0 to 5nm, and the retardation value Rth in the thickness direction is usually in the range of-10 to-300 nm, preferably-20 to-200 nm. The polarizing plate may have 2 or more retardation coatings, and when having 2 retardation coatings, the following may be the case: the 1 st phase difference coating is a lambda/4 layer for making circularly polarized light, and the 2 nd phase difference coating is a positive C layer for improving the color viewed from an oblique direction. Further, the following case may be adopted: the 1 st phase difference coating is a positive C layer for improving the color viewed from an oblique direction, and the 2 nd phase difference coating is a λ/4 layer for making circularly polarized light.

(adhesive layer and pressure-sensitive adhesive layer)

The polarizing plate may include an adhesive layer and/or an adhesive layer. In one embodiment of the present invention, the polarizing coating layer and the 1 st retardation coating layer or the 1 st retardation coating layer and the 2 nd retardation coating layer may be bonded via an adhesive or an adhesive. As the adhesive for forming the adhesive layer, an aqueous adhesive, an active energy ray-curable adhesive, or a thermosetting adhesive can be used, and an aqueous adhesive or an active energy ray-curable adhesive is preferable. As the pressure-sensitive adhesive layer, a pressure-sensitive adhesive layer described later can be used.

Examples of the aqueous adhesive include an adhesive comprising a polyvinyl alcohol resin aqueous solution, and an aqueous two-pack type urethane emulsion adhesive. Among them, an aqueous adhesive comprising a polyvinyl alcohol resin aqueous solution can be preferably used. As the polyvinyl alcohol resin, in addition to a vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate which is a homopolymer of vinyl acetate, a polyvinyl alcohol copolymer obtained by saponifying a copolymer of vinyl acetate and another monomer copolymerizable therewith, a modified polyvinyl alcohol polymer obtained by partially modifying hydroxyl groups thereof, and the like can be used. The aqueous adhesive may contain a crosslinking agent such as an aldehyde compound (e.g., glyoxal), an epoxy compound, a melamine compound, a methylol compound, an isocyanate compound, an amine compound, or a polyvalent metal salt.

When an aqueous adhesive is used, it is preferable to perform a drying step for removing water contained in the aqueous adhesive after the coating layer is attached.

The active energy ray-curable adhesive is an adhesive containing a curable compound that is cured by irradiation with an active energy ray such as an ultraviolet ray, a visible light, an electron beam, or an X-ray, and is preferably an ultraviolet ray-curable adhesive.

The curable compound may be a cationically polymerizable curable compound or a radically polymerizable curable compound. Examples of the cationically polymerizable curable compound include an epoxy compound (a compound having 1 or 2 or more epoxy groups in a molecule), an oxetane compound (a compound having 1 or 2 or more oxetane rings in a molecule), and a combination thereof. Examples of the radically polymerizable curable compound include a (meth) acrylic compound (a compound having 1 or 2 or more (meth) acryloyloxy groups in the molecule), another vinyl compound having a radically polymerizable double bond, and a combination thereof. The cationically polymerizable curable compound may be used in combination with the radically polymerizable curable compound. The active energy ray-curable adhesive usually further contains a cationic polymerization initiator and/or a radical polymerization initiator for initiating a curing reaction of the curable compound.

In order to improve the adhesiveness when the coating layer is bonded, a surface activation treatment may be applied to at least one of the surfaces to be bonded. Examples of the surface activation treatment include dry treatments such as corona treatment, plasma treatment, discharge treatment (glow discharge treatment, etc.), flame treatment, ozone treatment, UV ozone treatment, and ionizing active ray treatment (ultraviolet treatment, electron beam treatment, etc.); a wet treatment such as an ultrasonic treatment, a saponification treatment, and an anchor coat treatment using a solvent such as water or acetone. These surface activation treatments may be carried out alone or in combination of 2 or more.

The thickness of the adhesive layer can be adjusted according to the adhesive strength, and is preferably 0.1 to 10 μm, more preferably 1 to 5 μm. In one embodiment of the present invention, in the case of a structure using a plurality of the above adhesive layers, the adhesive layers may be made of the same material or different materials, and may have the same thickness or different thicknesses.

The pressure-sensitive adhesive layer may be composed of a pressure-sensitive adhesive composition containing a resin as a main component, such as a (meth) acrylic resin, a rubber-based resin, a polyurethane-based resin, a polyester-based resin, a silicone-based resin, or a polyvinyl ether-based resin. Among them, preferred are adhesive compositions containing a polyester resin or a (meth) acrylic resin as a base polymer, which are excellent in transparency, weather resistance, heat resistance, and the like. The adhesive composition may be an active energy ray-curable type or a thermosetting type.

As the binder resin used in the present invention, a binder resin having a weight average molecular weight of 30 to 400 ten thousand is generally used. In view of durability, particularly heat resistance, the weight average molecular weight thereof is preferably 50 to 300 ten thousand, more preferably 65 to 200 ten thousand. When the weight average molecular weight is more than 30 ten thousand, it is preferable from the viewpoint of heat resistance, and when the weight average molecular weight is less than 400 ten thousand, it is also preferable from the viewpoint of reduced adhesiveness and adhesive force. The weight average molecular weight is a value calculated by measuring with GPC (gel permeation chromatography) and converting into polystyrene.

In addition, a crosslinking agent may be contained in the adhesive composition. As the crosslinking agent, an organic crosslinking agent or a polyfunctional metal chelate compound can be used. Examples of the organic crosslinking agent include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, and imine crosslinking agents. The polyfunctional metal chelate compound is a product in which a polyvalent metal is bonded to an organic compound by a covalent bond or a coordinate bond. Examples of the polyvalent metal atom include Al, Cr, Zr, Co, Cu, Fe, Ni, V, Zn, In, Ca, Mg, Mn, Y, Ce, Sr, Ba, Mo, La, Sn, Ti and the like. Examples of the atom in the organic compound bonded by a covalent bond or a coordinate bond include an oxygen atom, and examples of the organic compound include an alkyl ester, an alcohol compound, a carboxylic acid compound, an ether compound, and a ketone compound.

When the crosslinking agent is contained, the amount of the crosslinking agent is preferably 0.01 to 20 parts by mass, more preferably 0.03 to 10 parts by mass, per 100 parts by mass of the binder resin. When the amount of the crosslinking agent is more than 0.01 parts by mass, the cohesive force of the pressure-sensitive adhesive layer tends not to be insufficient, and foaming is less likely to occur during heating, while when the amount is less than 20 parts by mass, moisture resistance is sufficient, and peeling is less likely to occur in a reliability test or the like.

The adhesive composition preferably contains a silane coupling agent as an additive. Examples of the silane coupling agent include silicon compounds having an epoxy group structure such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane and 2- (3, 4-epoxycyclohexyl) ethyltrimethoxysilane; amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) 3-aminopropyltrimethoxysilane and N- (2-aminoethyl) 3-aminopropylmethyldimethoxysilane; 3-chloropropyltrimethoxysilane; (meth) acrylic group-containing silane coupling agents such as acetoacetyl group-containing trimethoxysilane, 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane; and isocyanate group-containing silane coupling agents such as 3-isocyanatopropyltriethoxysilane. The silane coupling agent can impart durability, particularly, an effect of suppressing peeling in a humidified environment. The amount of the silane coupling agent used is preferably 1 part by mass or less, more preferably 0.01 to 1 part by mass, and still more preferably 0.02 to 0.6 part by mass, per 100 parts by mass of the binder resin.

The pressure-sensitive adhesive composition may contain other known additives, and for example, powders such as colorants and pigments, dyes, surfactants, plasticizers, adhesion imparting agents, surface lubricants, leveling agents, softeners, antioxidants, antiaging agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, inorganic or organic fillers, metal powders, particles, foils, and the like may be added to the pressure-sensitive adhesive composition as appropriate depending on the application. In addition, a redox system in which a reducing agent is added may be used within a controllable range.

The thickness of the adhesive layer is not particularly limited, and is, for example, about 1 to 100. mu.m, preferably 2 to 50 μm, and more preferably 3 to 30 μm.

(protective layer)

The polarizing plate may include a protective layer. In one embodiment of the present invention, the polarizing plate may have at least one protective layer, and may be located on one surface of a polarizer formed as the polarizing plate, or may be located on the opposite surface of a retardation layer from the polarizer in the case where the polarizer has the retardation layer.

The protective layer is not particularly limited, and may be a film excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, isotropy, and the like. Specific examples thereof include polyester films such as polyethylene terephthalate, polyethylene isophthalate, and polybutylene terephthalate; cellulose films such as diacetylcellulose and triacetylcellulose; a polycarbonate-based film; acrylic films such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; styrene-based films such as polystyrene and acrylonitrile-styrene copolymer; polyolefin-based films such as cycloolefin, cycloolefin copolymer, polynorbornene, polypropylene, polyethylene, and ethylene-propylene copolymer; a vinyl chloride film; polyamide films such as nylon and aromatic polyamide; an imide-based film; a sulfone-based membrane; a polyether ketone film; a polyphenylene sulfide-based film; a vinyl alcohol film; a vinylidene chloride film; a vinyl butyral based film; an arylate-based film; a polyoxymethylene film; a urethane film; an epoxy film; silicone-based films, and the like. Among these, cellulose-based films having a surface saponified with an alkali or the like are particularly preferable in view of polarization characteristics and durability. The protective layer may have an optical compensation function such as a retardation function.

The protective layer may be a layer to which an easy adhesion treatment for improving adhesion is applied to a surface to be adhered to the polarizer or the retardation coating layer. The easy adhesion treatment is not particularly limited as long as it is a treatment capable of improving the adhesion, and examples thereof include a dry treatment such as a primer treatment, a plasma treatment, and a corona treatment; chemical treatments such as alkali treatment (saponification treatment); low pressure UV treatment, etc.

< touch sensor >

The image display device may include a touch sensor. The touch sensor includes a support, a lower electrode provided on the support, an upper electrode facing the lower electrode, and an insulating layer sandwiched between the lower electrode and the upper electrode.

As the support, various supports can be used as long as they are a flexible resin film having light transmittance. Examples of the support include the films described above as the protective layer.

The lower electrode has a plurality of small electrodes in a square shape in plan view, for example. A plurality of small electrodes are arranged in a matrix.

In addition, the plurality of small electrodes are connected to each other in one diagonal direction of the small electrodes to form a plurality of electrode columns. The plurality of electrode columns are connected to each other at end portions, and a capacitance between adjacent electrode columns can be detected.

The upper electrode has, for example, a plurality of small electrodes in a square shape in a plan view. The plurality of small electrodes are arranged in a complementary matrix at positions where the lower electrodes are not arranged in a plan view. That is, the upper electrode and the lower electrode are arranged without a gap in a plan view.

In addition, the plurality of small electrodes are connected to each other in the other diagonal direction of the small electrodes to form a plurality of electrode columns. The plurality of electrode columns are connected to each other at end portions, and a capacitance between adjacent electrode columns can be detected.

The insulating layer insulates the lower electrode from the upper electrode. As a material for forming the insulating layer, a material generally known as a material of an insulating layer of a touch sensor can be used.

In the present embodiment, a case where the touch sensor is a so-called projected capacitive touch sensor is described, but a touch sensor of another type such as a thin film resistance type may be employed within a range not impairing the effects of the present invention.

[ Flexible display device ]

The present invention also provides a flexible display device provided with the optical film of the present invention. The optical film of the present invention is preferably used as a front panel in a flexible display device, which is sometimes referred to as a window film. The flexible display device includes a laminate for flexible display device and an organic EL display panel, and the laminate for flexible display device is disposed on the viewing side of the organic EL display panel and is configured to be bendable. The laminate for a flexible display device may contain the optical film (window film), circularly polarizing plate, and touch sensor of the present invention in any order of lamination, but it is preferable to laminate the window film, circularly polarizing plate, and touch sensor in this order, or the window film, touch sensor, and circularly polarizing plate in this order from the viewing side. When the circularly polarizing plate is present on the viewing side of the touch sensor, the pattern of the touch sensor is not easily recognized, and visibility of the display image is improved, which is preferable. The members may be laminated using an adhesive, a bonding agent, or the like. The touch panel may further include a light-shielding pattern formed on at least one surface of any one of the window film, the circularly polarizing plate, and the touch sensor.

[ polarizing plate ]

The flexible display device of the present invention may further include a polarizing plate, preferably a circular polarizing plate. The circularly polarizing plate is a functional layer having a function of transmitting only a right-handed circularly polarized light component or a left-handed circularly polarized light component by laminating a λ/4 phase difference plate on a linearly polarizing plate. For example, can be used for: the external light is converted into right-handed circularly polarized light, the external light which is reflected by the organic EL panel and becomes left-handed circularly polarized light is blocked, and only the light emitting component of the organic EL is transmitted, thereby suppressing the influence of the reflected light and making it easy to view an image. In order to realize the circularly polarized light function, the absorption axis of the linear polarizer and the slow axis of the λ/4 phase difference plate must be 45 ° in theory, but in practical use, 45 ± 10 °. The linear polarizing plate and the λ/4 phase difference plate do not necessarily have to be stacked adjacent to each other as long as the relationship between the absorption axis and the slow axis satisfies the above range. It is preferable to realize completely circularly polarized light at the full wavelength, but this is not necessarily required in practical use, and thus the circularly polarizing plate in the present invention also includes an elliptically polarizing plate. It is also preferable to further laminate a λ/4 retardation film on the viewing side of the linear polarizing plate to convert the emitted light into circularly polarized light, thereby improving visibility in a state where the polarized sunglasses are worn.

The linear polarizing plate is a functional layer having the following functions: light vibrating in the direction of the transmission axis passes through but polarized light of the vibration component perpendicular thereto is blocked. The linear polarizing plate may be a single linear polarizer or a linear polarizer and a protective film attached to at least one surface of the linear polarizer. The thickness of the linearly polarizing plate may be 200 μm or less, and preferably 0.5 to 100 μm. When the thickness is within the above range, the flexibility tends not to be easily lowered.

The linear polarizer may be a film type polarizer manufactured by dyeing and stretching a polyvinyl alcohol (PVA) film. The polarizing performance can be exhibited by adsorbing a dichroic dye such as iodine onto a PVA-based film that has been stretched and oriented, or by stretching the film in a state where the dichroic dye is adsorbed onto PVA to orient the dichroic dye. The film-type polarizer may be produced by steps such as swelling, crosslinking with boric acid, washing with an aqueous solution, and drying. The stretching and dyeing step may be performed by a PVA film alone, or may be performed in a state of being laminated with another film such as polyethylene terephthalate. The thickness of the PVA film to be used is preferably 10 to 100 μm, and the stretch ratio is preferably 2 to 10 times.

In addition, as another example of the polarizer, a liquid crystal coating type polarizer formed by coating a liquid crystal polarizing composition may be used. The liquid crystal polarizing composition may include a liquid crystal compound and a dichroic pigment compound. The liquid crystalline compound is preferably used as long as it has a property of exhibiting a liquid crystal state, and particularly, it can exhibit high polarizing performance when it has a high-order alignment state such as smectic state. Further, it is also preferable that the liquid crystalline compound has a polymerizable functional group.

The dichroic pigment is a pigment which exhibits dichroism by being aligned with the liquid crystal compound, and the dichroic pigment itself may have liquid crystallinity or may have a polymerizable functional group. Any of the compounds in the liquid crystal polarizing composition has a polymerizable functional group.

The liquid crystal polarizing composition may further include an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, and the like.

The liquid crystal polarizing layer is manufactured by the following method: the liquid crystal polarizing composition is coated on an alignment film to form a liquid crystal polarizing layer.

The liquid crystal polarizing layer can be formed to a thin thickness as compared to a film type polarizer. The thickness of the liquid crystal polarizing layer may be preferably 0.5 to 10 μm, and more preferably 1 to 5 μm.

The alignment film can be produced, for example, by: the alignment film-forming composition is applied to a substrate and is imparted with alignment properties by rubbing, polarized light irradiation, or the like. The alignment film-forming composition may contain a solvent, a crosslinking agent, an initiator, a dispersant, a leveling agent, a silane coupling agent, and the like in addition to the alignment agent. Examples of the orientation agent include polyvinyl alcohols, polyacrylates, polyamide acids, and polyimides. In the case of applying photo-alignment, an alignment agent containing a cinnamate group (cinnamate group) is preferably used. The weight average molecular weight of the polymer used as the orientation agent may be about 10,000 to 1,000,000. The thickness of the alignment film is preferably 5 to 10,000nm, more preferably 10 to 500nm, from the viewpoint of alignment control force. The liquid crystal polarizing layer may be separated from the substrate and then transferred to be laminated, or the substrate may be directly laminated. The substrate preferably functions as a transparent substrate for a protective film, a retardation plate, and a window film.

The protective film may be a transparent polymer film, and specifically, the polymer film to be used includes films of: polyolefins such as polyethylene, polypropylene, polymethylpentene, and cycloolefin derivatives having a monomer unit containing norbornene or cycloolefin; (modified) celluloses such as diacetyl cellulose, triacetyl cellulose, and propionyl cellulose; acrylic acids such as methyl methacrylate (co) polymers; polystyrenes such as styrene (co) polymers; acrylonitrile-butadiene-styrene copolymers; acrylonitrile-styrene copolymers; ethylene-vinyl acetate copolymers; polyvinyl chloride-based; polyvinylidene chlorides; polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, and polyarylate; polyamides such as nylon; polyimides; polyamide imides; polyether imides; polyether sulfones; polysulfones; polyvinyl alcohols; polyvinyl acetals; polyurethanes; epoxy resins; and the like, and preferably includes polyamide, polyamideimide, polyimide, polyester, olefin, acrylic or cellulose films in view of excellent transparency and heat resistance. These polymers may be used alone or in combination of two or more. These films may be used in an unstretched state or in the form of uniaxially or biaxially stretched films. Cellulose-based films, olefin-based films, acrylic films, and polyester films are preferable. The coating-type protective film may be one obtained by applying and curing a cationically curable composition such as an epoxy resin or a radically curable composition such as an acrylate. If necessary, a plasticizer, an ultraviolet absorber, an infrared absorber, a pigment, a colorant such as a dye, a fluorescent brightener, a dispersant, a heat stabilizer, a light stabilizer, an antistatic agent, an antioxidant, a lubricant, a solvent, and the like may be included. The thickness of the protective film may be 200 μm or less, preferably 1 to 100 μm. When the thickness of the protective film is within the above range, the flexibility of the protective film is not easily reduced.

The λ/4 phase difference plate is a film that imparts a phase difference of λ/4 in a direction orthogonal to the traveling direction of incident light (in other words, in the in-plane direction of the film). The λ/4 retardation plate may be a stretched retardation plate produced by stretching a polymer film such as a cellulose film, an olefin film, or a polycarbonate film. If necessary, a retardation adjuster, a plasticizer, an ultraviolet absorber, an infrared absorber, a colorant (such as a pigment or a dye), a fluorescent brightener, a dispersant, a heat stabilizer, a light stabilizer, an antistatic agent, an antioxidant, a lubricant, a solvent, or the like may be contained. The thickness of the stretched retardation film may be 200 μm or less, preferably 1 to 100 μm. When the thickness is within the above range, the flexibility of the film tends not to be easily reduced.

Further, another example of the λ/4 retardation plate may be a liquid crystal coating type retardation plate formed by coating a liquid crystal composition. The liquid crystal composition comprises a liquid crystalline compound having the following properties: showing nematic, cholesteric, smectic, and the like liquid crystal states. Any compound including a liquid crystalline compound in the liquid crystal composition has a polymerizable functional group. The liquid crystal coating type retardation plate may further contain an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, and the like. The liquid crystal coating type retardation plate can be produced by: similarly to the above-mentioned liquid crystal polarizing layer, a liquid crystal composition is applied onto an alignment film and cured to form a liquid crystal retardation layer. The liquid crystal coating type retardation plate can be formed to a smaller thickness than the stretching type retardation plate. The thickness of the liquid crystal polarizing layer may be usually 0.5 to 10 μm, preferably 1 to 5 μm. The liquid crystal-coated retardation plate may be peeled from the substrate and transferred to be laminated, or the substrate may be directly laminated. The substrate preferably functions as a transparent substrate for a protective film, a retardation plate, and a window film.

Generally, the following materials are more: the shorter the wavelength, the greater the birefringence; the longer the wavelength, the less birefringence is exhibited. In this case, since a phase difference of λ/4 cannot be realized in all visible light regions, it is often designed as follows: the in-plane retardation is 100 to 180nm (preferably 130 to 150nm) such as λ/4 in the vicinity of 560nm, which is high in visibility. The use of an inverse dispersion λ/4 phase difference plate using a material having a birefringence wavelength dispersion characteristic opposite to that of the usual one is preferable because it can improve visibility. As such a material, the material described in japanese patent application laid-open No. 2007-232873 and the like is preferably used also in the case of a stretched phase difference plate, and the material described in japanese patent application laid-open No. 2010-30979 is preferably used also in the case of a liquid crystal coated phase difference plate.

As another method, a technique is also known in which a broadband λ/4 phase difference plate is obtained by combining a λ/2 phase difference plate (japanese patent application laid-open No. h 10-90521). The λ/2 phase difference plate is also manufactured by the same material and method as the λ/4 phase difference plate. The combination of the stretching type retardation plate and the liquid crystal coating type retardation plate is arbitrary, and the use of the liquid crystal coating type retardation plate is preferable because the thickness can be reduced.

For the circularly polarizing plate, a method of laminating a positive C plate is also known in order to improve visibility in an oblique direction (japanese patent application laid-open No. 2014-224837). The positive C plate may be a liquid crystal coated retardation plate or a stretched retardation plate. The phase difference in the thickness direction is usually from-200 to-20 nm, preferably from-140 to-40 nm.

[ touch sensor ]

The flexible display device of the present invention may further include a touch sensor. The touch sensor serves as an input means. As the touch sensor, various types such as a resistive film type, a surface acoustic wave type, an infrared ray type, an electromagnetic induction type, and a capacitance type have been proposed, and any type may be used. Among them, the electrostatic capacitance system is preferable. The capacitive touch sensor is divided into an active region and an inactive region located at an outer peripheral portion of the active region. The active region is a region corresponding to a region (display portion) on the display panel where a screen is displayed, and is a region where a user's touch is sensed, and the inactive region is a region corresponding to a region (non-display portion) on the display device where a screen is not displayed. The touch sensor may include: a substrate having flexible properties; a sensing pattern formed in an active region of the substrate; and each sensing line formed in the inactive region of the substrate and used for connecting the sensing pattern with an external driving circuit through a pad (pad) part. As the substrate having a flexible property, the same material as the polymer film can be used. The substrate of the touch sensor preferably has a toughness of 2,000 MPa% or more in terms of suppressing cracks in the touch sensor. The toughness may be more preferably 2,000 to 30,000 MPa%. Here, toughness is defined as: the area of the lower portion of the Stress (MPa) -strain (%) curve (Stress-strain curve) obtained by the tensile test of the polymer material up to the failure point is shown.

The sensing pattern may include a 1 st pattern formed in a 1 st direction and a 2 nd pattern formed in a 2 nd direction. The 1 st pattern and the 2 nd pattern are arranged in different directions from each other. The 1 st pattern and the 2 nd pattern are formed in the same layer, and in order to sense the touch position, the patterns must be electrically connected. The 1 st pattern is a form in which the unit patterns are connected to each other via a terminal, but the 2 nd pattern has a structure in which the unit patterns are separated from each other in an island form, and therefore, in order to electrically connect the 2 nd pattern, a separate bridge electrode is required. The sensing pattern may use a known transparent electrode material. Examples thereof include Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), zinc oxide (ZnO), Indium Zinc Tin Oxide (IZTO), Indium Gallium Zinc Oxide (IGZO), Cadmium Tin Oxide (CTO), PEDOT (poly (3, 4-ethylenedioxythiophene)), Carbon Nanotubes (CNTs), graphene, and metal wires, and these may be used alone or in a mixture of two or more. ITO may be preferably used. The metal used for the metal wire is not particularly limited, and examples thereof include silver, gold, aluminum, copper, iron, nickel, titanium, selenium, and chromium. These may be used alone or in combination of two or more.

The bridge electrode may be formed on the insulating layer with an insulating layer interposed therebetween on the sensing pattern, and the bridge electrode may be formed on the substrate, on which the insulating layer and the sensing pattern may be formed. The bridge electrode may be formed of the same material as the sensor pattern, or may be formed of a metal such as molybdenum, silver, aluminum, copper, palladium, gold, platinum, zinc, tin, titanium, or an alloy of two or more of these metals. Since the 1 st pattern and the 2 nd pattern must be electrically insulated, an insulating layer is formed between the sensing pattern and the bridge electrode. The insulating layer may be formed only between the contact of the 1 st pattern and the bridge electrode, or may be formed in a structure of a layer covering the sensing pattern. In the latter case, the bridge electrode may be connected with the 2 nd pattern via a contact hole formed in the insulating layer. In the touch sensor, as means for appropriately compensating for a difference in transmittance between a pattern region where a pattern is formed and a non-pattern region where no pattern is formed (specifically, a difference in transmittance due to a difference in refractive index in these regions), an optical adjustment layer may be further included between the substrate and the electrode, and the optical adjustment layer may include an inorganic insulating substance or an organic insulating substance. The optical adjustment layer can be formed by applying a photocurable composition containing a photocurable organic binder and a solvent onto a substrate. The above-mentioned photocurable composition may further comprise inorganic particles. The refractive index of the optical adjustment layer can be increased by the inorganic particles.

The photocurable organic binder may include a copolymer of monomers such as an acrylate monomer, a styrene monomer, and a carboxylic acid monomer. The photocurable organic binder may be a copolymer containing different repeating units such as an epoxy group-containing repeating unit, an acrylate repeating unit, and a carboxylic acid repeating unit.

The inorganic particles may include, for example, zirconia particles, titania particles, alumina particles, and the like. The photocurable composition may further contain various additives such as a photopolymerization initiator, a polymerizable monomer, and a curing assistant.

[ adhesive layer ]

Each layer (a window film, a polarizing plate, a touch sensor, and the like) and a film member (a linear polarizing plate, a λ/4 retardation plate, and the like) constituting each layer forming the laminate for a flexible display device may be bonded with an adhesive. As the adhesive, a commonly used adhesive such as an aqueous adhesive, an organic solvent adhesive, a solventless adhesive, a solid adhesive, a solvent volatile adhesive, a moisture curable adhesive, a heat curable adhesive, an anaerobic curable adhesive, an aqueous solvent volatile adhesive, an active energy ray curable adhesive, a curing agent hybrid adhesive, a hot melt adhesive, a pressure sensitive adhesive (adhesive), a rewetting adhesive, or the like can be used. Among them, an aqueous solvent-volatile adhesive, an active energy ray-curable adhesive, and a pressure-sensitive adhesive are preferably used. The thickness of the adhesive layer can be adjusted as appropriate according to the required adhesive strength, and is, for example, 0.01 to 500. mu.m, preferably 0.1 to 300. mu.m. The laminate for a flexible image display device may have a plurality of adhesive layers, and the thickness of each adhesive layer and the type of adhesive used may be the same or different.

The aqueous solvent-volatile adhesive may be a polyvinyl alcohol polymer, a water-soluble polymer such as starch, or a water-dispersed polymer such as an ethylene-vinyl acetate emulsion or a styrene-butadiene emulsion. In addition to water and the main agent polymer, a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, a dye, a pigment, an inorganic filler, an organic solvent, and the like may be added. In the case of bonding with the aqueous solvent volatile adhesive, adhesiveness can be provided by injecting the aqueous solvent volatile adhesive between the layers to be bonded, bonding the layers to be bonded, and then drying the layers. The thickness of the adhesive layer when the aqueous solvent-volatile adhesive is used may be 0.01 to 10 μm, preferably 0.1 to 1 μm. When the aqueous solvent volatile adhesive is used for forming a plurality of layers, the thickness of each layer and the type of the adhesive may be the same or different.

The active energy ray-curable adhesive can be formed by curing an active energy ray-curable composition containing a reactive material capable of forming an adhesive layer by irradiation with an active energy ray. The active energy ray-curable composition may contain at least one polymer selected from the group consisting of a radically polymerizable compound and a cationically polymerizable compound, as in the case of the hard coat composition. The radical polymerizable compound may be the same kind of compound as the hard coat composition, as the hard coat composition. The radical polymerizable compound used in the adhesive layer is preferably a compound having an acryloyl group. In order to reduce the viscosity of the adhesive composition, it is also preferable to include a monofunctional compound.

The cationic polymerizable compound may be the same kind of compound as used in the hard coat composition, as used in the hard coat composition. The cationic polymerizable compound used in the active energy ray-curable composition is particularly preferably an epoxy compound. To reduce the viscosity of the adhesive composition, it is also preferable to include a monofunctional compound as a reactive diluent.

The active energy ray composition may further contain a polymerization initiator. The polymerization initiator may be a radical polymerization initiator, a cationic polymerization initiator, a radical or cationic polymerization initiator, and the like, and may be appropriately selected and used. These polymerization initiators are decomposed by at least one of irradiation with active energy rays and heating to generate radicals or cations, and radical polymerization and cationic polymerization are carried out. An initiator capable of initiating at least either of radical polymerization and cationic polymerization by irradiation with active energy rays, which are described in the description of the hard coating composition, can be used.

The active energy ray-curable composition may further contain an ion scavenger, an antioxidant, a chain transfer agent, an adhesion-imparting agent, a thermoplastic resin, a filler, a flow viscosity modifier, a plasticizer, an antifoaming agent, an additive, and a solvent. When the bonding is performed by the active energy ray-curable adhesive, the bonding may be performed by: the active energy ray-curable composition is applied to either or both of the adhesive layers, and then the adhesive layers are bonded to each other, and either or both of the adhesive layers are cured by irradiation with active energy rays. The thickness of the adhesive layer when the active energy ray-curable adhesive is used may be usually 0.01 to 20 μm, preferably 0.1 to 10 μm. When the active energy ray-curable adhesive is used for forming a plurality of layers, the thickness of each layer and the type of the adhesive used may be the same or different.

The adhesive may be classified into an acrylic adhesive, a urethane adhesive, a rubber adhesive, a silicone adhesive, and the like, depending on the base polymer. The binder may contain a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, an adhesion-imparting agent, a plasticizer, a dye, a pigment, an inorganic filler, and the like in addition to the main polymer. The adhesive layer (adhesive layer) is formed by dissolving and dispersing the components constituting the adhesive in a solvent to obtain an adhesive composition, applying the adhesive composition to a substrate, and then drying the adhesive composition. The adhesive layer may be formed directly or by transferring an adhesive layer formed on another substrate. A release film is also preferably used to cover the pressure-sensitive adhesive surface before bonding. The thickness of the adhesive layer when the adhesive is used may be usually 1 to 500. mu.m, preferably 2 to 300. mu.m. When the above-mentioned adhesive is used for forming a plurality of layers, the thickness of each layer and the kind of the adhesive used may be the same or different.

< light-shielding pattern >

The light blocking pattern may be at least a portion of a bezel or a housing of the optical film or a display device to which the optical film is applied. For example, the respective wirings of the display device may be hidden by a light-shielding pattern and may not be easily visible to a user. The color and/or material of the light-shielding pattern is not particularly limited, and may be formed of a resin material having a plurality of colors such as black, white, gold, and the like. For example, the light-shielding pattern may be formed of a resin substance such as an acrylic resin, an ester resin, an epoxy resin, polyurethane, or polysiloxane mixed with a pigment for color. The material and thickness of the light blocking pattern may be determined in consideration of the protection and flexibility characteristics of the optical film or the display device. Further, they may be used alone or in the form of a mixture of 2 or more. The light-shielding pattern can be formed by various methods such as printing, photolithography, and inkjet. The thickness of the light-shielding pattern is usually 1 to 100 μm, preferably 2 to 50 μm. Further, it is also preferable to provide a shape such as an inclination in the thickness direction of the light-shielding pattern.

Examples

The present invention will be described in more detail below with reference to examples. Unless otherwise specified, "%" and "parts" in the examples mean mass% and parts by mass. First, the evaluation method will be explained.

[ measurement of weight average molecular weight in terms of polystyrene ]

Gel Permeation Chromatography (GPC) measurement

(1) Pretreatment method

The sample was dissolved in GBL to prepare a 20% solution, which was diluted 100-fold with DMF eluent, and the solution was filtered through a 0.45 μm membrane filter to obtain a measurement solution.

(2) Measurement conditions

Column: TSKgel SuperAWM-H.times.2 + SuperAW 2500X 1(6.0mm I.D.. times.150 mm. times.3)

Eluent: DMF solution containing 10mmol/L lithium bromide

Flow rate: 0.6 mL/min

A detector: RI detector

Column temperature: 40 deg.C

Sample introduction amount: 20 μ L

Molecular weight standard: standard polystyrene

[ light transmittance at a wavelength of 275nm of GBL ]

GBL was measured using an ultraviolet-visible near-infrared spectrophotometer ("V-670" manufactured by Nippon Kabushiki Kaisha). First, MilliQ water was put into a quartz cell having an optical path length of 1cm, and the quartz cell was set in an ultraviolet-visible near-infrared spectrophotometer to perform blank measurement. Next, the GBL was placed in a quartz cell having an optical path length of 1cm, and the quartz cell was set in the spectrophotometer. A white light having a wavelength of 300 to 800nm is irradiated, and transmittance measurement is performed, whereby a transmittance having a wavelength of 275nm is obtained.

[ gas chromatography measurement of GBL ]

The peaks of impurities contained in GBL were determined using gas chromatography.

(1) Measurement conditions

The device comprises the following steps: GC-2025 manufactured by Shimadzu corporation

Column: agilent Technologies DB-WAX (30m × 0.32mm I.D., d)_f 0.50μm)

A detector: FID

H₂40 mL/min, Air 400 mL/min

Make-up gas (N)₂)25 mL/min

Sample inlet temperature: 250 deg.C

Detector temperature: 250 deg.C

Sample introduction amount: 1 μ L

The split ratio is as follows: 1: 50

Column temperature conditions: initial temperature 120 deg.C (hold for 1 minute), ramp to 240 deg.C at a rate of 10 deg.C/minute (hold for 7 minutes)

Carrier gas: he (He)

Carrier gas flow: 23.3 cm/sec

(2) Method for calculating integral value

The area percentage in the above-mentioned gas chromatography, that is, the area percentage of each impurity peak with respect to the total peak area value in the analysis result of the gas chromatography, is shown. The relative retention time (Rrt) of each peak was calculated as (retention time of peak) ÷ (retention time of GBL).

[ measurement of thickness ]

The thickness of the polyimide polymer film was measured using a digital display universal thickness gauge ("model 547-401" manufactured by Mitutoyo Co., Ltd.).

[ measurement of Total light transmittance (Tt) and Haze ]

In compliance with JIS K7105: 1981, the total light transmittance Tt of the transparent polyimide polymer films obtained in the examples and comparative examples was measured by a haze meter (a fully automatic direct reading haze meter HGM-2DP, manufactured by Suga Test Instruments).

[ L of varnish^＊、a^＊、b^＊Method of measurement of]

(1) Measurement of optical Properties of varnish

The varnishes obtained in examples and comparative examples and having a solid content concentration of 7.5% by mass were subjected to an ultraviolet-visible near-infrared spectrophotometer ("V-670" manufactured by Nippon Kasei corporation)^＊、a^＊、b^＊And (4) carrying out measurement. MilliQ water was charged into a quartz cell having an optical path length of 1cm, and the quartz cell was set in the spectrophotometer described above to perform blank measurement. Subsequently, the varnish was charged into a quartz cell having an optical path length of 1cm, and the quartz cell was set in the spectrophotometer. Irradiating white light with a wavelength of 300 to 800nm, and measuring transmittance to obtain L^＊、a^＊、b^＊The value is obtained. In addition, b to be obtained^＊As initial b^＊(before storage b)^＊)。

(2) Varnish storage test: Δ b^＊Is calculated by

The varnishes obtained in examples 1 to 3 and comparative examples 1 to 2 were stored at 50 ℃ for 1 week. For preserved varnish b^＊Measuring to obtain b after storage^＊. According to the initial b^＊And b after storage^＊To obtain a difference value (Δ b)^＊)。

[ method for measuring YI of film ]

(1) Calculation of YI value of film

The YI value (Yellow Index) of each of the transparent polyimide polymer films obtained in examples and comparative examples was measured using the spectrophotometer described above ("V-670", manufactured by japan spectro-corporation). After the background measurement was performed in the state where no sample was present, the polyimide film was placed on a sample holder, and transmittance measurement was performed with respect to light having a wavelength of 300 to 800nm to obtain a tristimulus value (X, Y, Z). From the tristimulus values, the YI value was calculated based on the following formula. The obtained YI value was set as an initial YI value (YI value before storage).

YI＝100×(1.2769X-1.0592Z)/Y

(2) Varnish storage test: calculation of the Δ YI value

The varnishes obtained in examples 1 to 3 and comparative examples 1 to 2 were stored at 50 ℃ for 1 week. The stored varnish was formed into a film, and the YI value of the obtained film was measured by the same method as the initial YI value to obtain the YI value after storage. The difference (Δ YI) is obtained from the initial YI value and the saved YI value.

Synthetic example 1: production of Polyamide-imide resin (1)

A fully dried reaction vessel equipped with a stirrer and a thermometer was purged with nitrogen, and the inside of the vessel was replaced with nitrogen. 3,815 parts by mass of dimethylacetamide (DMAc) was charged into the reaction vessel, and 111.94 parts by mass of 2,2 '-bis (trifluoromethyl) benzidine (TFMB) and 46.82 parts by mass of 4, 4' - (hexafluoroisopropylidene) diphthalic dianhydride (6FDA) were added and reacted.

Subsequently, 10.37 parts by mass of 4, 4' -oxybis (benzoyl chloride) (OBBC) and 42.82 parts by mass of terephthaloyl chloride (TPC) were added and reacted.

Next, 75.33 parts by mass of acetic anhydride was added, and after stirring for 15 minutes, 22.90 parts by mass of 4-methylpyridine was added, and the reaction vessel was heated to 70 ℃ and further stirred for 3 hours to obtain a reaction solution.

The reaction solution was cooled, 3794.5 parts by mass of methanol was added, and 2861 parts by mass of ion-exchanged water was added dropwise to precipitate a white solid. The precipitated white solid was captured by centrifugal filtration and washed with methanol to obtain a wet cake containing a polyamideimide resin. The obtained wet cake was dried at 78 ℃ under reduced pressure, thereby obtaining a powder of a polyamideimide resin. The weight average molecular weight of the obtained polyamideimide resin (1) was 466,000.

[ Synthesis example 2: production of Polyamide-imide resin (2)

A fully dried reaction vessel equipped with a stirrer and a thermometer was purged with nitrogen, and the inside of the vessel was replaced with nitrogen. 276.2 parts by mass of DMAc was added to the reaction vessel, and 14.64 parts by mass of TFMB was added thereto and stirred for 1 hour. 6.14 parts by mass of 6FDA and 1.36 parts by mass of 3,3 ', 4, 4' -biphenyltetracarboxylic dianhydride (BPDA) were further added thereto and reacted for 16 hours.

Next, 2.53 parts by mass of TPC was added and stirred for 15 minutes, and further 2.53 parts by mass of TPC was added and stirred for 20 minutes. Further, 250.0 parts by mass of DMAc was added thereto, and after stirring for 10 minutes, 0.56 parts by mass of TPC was added thereto, and the mixture was stirred for 2 hours.

Then, 13.21 parts by mass of acetic anhydride was added thereto, and after stirring for 15 minutes, 2.59 parts by mass of 4-methylpyridine was added thereto, and the reaction vessel was heated to 70 ℃ and further stirred for 3 hours to obtain a reaction solution.

The reaction solution was cooled, 890.4 parts by mass of methanol was added thereto, and 344.6 parts by mass of ion-exchanged water was added dropwise thereto, thereby precipitating a white solid. The precipitated white solid was captured by centrifugal filtration and washed with methanol to obtain a wet cake containing a polyamideimide resin. The obtained wet cake was dried at 75 ℃ under reduced pressure, thereby obtaining a powder of a polyamideimide resin. The weight average molecular weight of the obtained polyamideimide resin (2) was 241,000.

[ purification of GBL ]

Purified GBL-2 was obtained by distilling GBL (manufactured by BASF) as a raw material by the method described in Japanese patent No. 4348890. Purification of GBL-1 GBL (unpurified) from BASF corporation and purified GBL-2 were mixed in a ratio of 1: 1 in a mass ratio of 1. In fact, by optimizing the distillation conditions, GBL of different purity can be obtained. For each GBL, transmittance measurement at λ 275nm and gas chromatography analysis were performed to calculate the area percentage of high-boiling components (components detected at Rrt 1.02 to 1.50 and Rrt 1.05 to 1.50). The obtained results are shown in table 1.

[ Table 1]

The purified GBL-1 and the purified GBL-2 have a transmittance of 88% or more at λ 275 nm. On the other hand, GBL manufactured by unpurified BASF corporation has a transmittance of less than 88% at λ 275 nm.

In addition, the amount of components detected by GC analysis at Rrt 1.02 to 1.50 is 300ppm or less in both purified GBL-1 and purified GBL-2. On the other hand, GBL manufactured by BASF corporation, which was not purified, the amount of the component detected at the above retention time was 455 ppm. The amount of a component detected by GC analysis at an Rrt of 1.05 to 1.50 is 260ppm or less in both of purified GBL-1 and purified GBL-2. On the other hand, GBL manufactured by BASF corporation, which was not purified, the amount of the component detected at the above retention time was 382 ppm.

Comparative example 1

(preparation of varnish)

The polyamideimide resin (1) was dissolved in unpurified GBL (manufactured by BASF) so that the mass of the polyamideimide resin was 7.5 mass% based on the mass of the varnish to prepare a polyamideimide varnish.

(production of optical film)

The polyamideimide varnish was applied to a smooth surface of a polyester substrate (support) (product of Toyo Boseki Kagaku K.K., trade name "A4100") using an applicator so that the average thickness of the self-supporting film became 52 μm, and the film was dried at 50 ℃ for 30 minutes and then at 140 ℃ for 15 minutes to obtain a self-supporting film. The self-supporting film was fixed to a metal frame of A4 size, heated to 200 ℃ over 40 minutes, and dried at 200 ℃ for 20 minutes to obtain an optical film having a thickness of 50 μm.

[ example 1]

(production of varnish and optical film)

The polyamideimide resin (1) was dissolved in purified GBL-1 so that the mass of the polyamideimide resin was 7.5 mass% based on the mass of the varnish to prepare a polyamideimide varnish. Then, an optical film having a thickness of 50 μm was obtained in the same manner as in comparative example 1 using the above polyamide imide varnish.

[ example 2]

(production of varnish and optical film)

The polyamideimide resin (1) was dissolved in purified GBL-2 so that the mass of the polyamideimide resin was 7.5 mass% based on the mass of the varnish to prepare a polyamideimide varnish. Then, an optical film having a thickness of 50 μm was obtained in the same manner as in comparative example 1 using the above polyamide imide varnish.

Comparative example 2

(preparation of varnish)

The polyamideimide resin (2) was dissolved in GBL (product of BASF corporation) without purification so that the mass of the polyamideimide resin was 7.5 mass% based on the mass of the varnish to prepare a polyamideimide varnish (1).

Comparative example 3

(preparation of varnish)

The polyamideimide resin (2) was dissolved in GBL (product of BASF corporation) without purification so that the mass of the polyamideimide resin (2) was 8.1 mass% based on the mass of the varnish to prepare a polyamideimide varnish (2).

(production of optical film)

Using the above polyamideimide varnish (2), a self-supporting film was obtained by coating the smooth surface of a polyester substrate (manufactured by Toyo Boseki K.K., trade name "A4100") with an applicator so that the average thickness of the self-supporting film became 52 μm, drying the coating at 50 ℃ for 30 minutes, and then drying the coating at 140 ℃ for 15 minutes. The self-supporting film was fixed to a metal frame of A4 size, heated to 200 ℃ over 40 minutes, and dried at 200 ℃ for 20 minutes to obtain an optical film having a thickness of 50 μm.

[ example 3]

(preparation of varnish)

The polyamideimide resin (2) was dissolved in purified GBL-2 so that the mass of the polyamideimide resin was 7.5 mass% based on the mass of the varnish to prepare a polyamideimide varnish (3).

[ example 4]

(preparation of varnish)

The polyamideimide resin (2) was dissolved in purified GBL-2 so that the mass of the polyamideimide resin was 8.1 mass% based on the mass of the varnish to prepare a polyamideimide varnish (4).

(production of optical film)

Using the above polyamideimide varnish (4), an optical film having a thickness of 50 μm was obtained in the same manner as in comparative example 3.

The varnishes of examples 1 to 3 and comparative examples 1 and 2 obtained in the above manner were subjected to the above-described method for L^＊、a^＊、b^＊The measurements were carried out and are shown in Table 2. The total light transmittance (Tt), haze and YI of the optical films of examples 1,2 and 4 and comparative examples 1 and 3 obtained as described above were measured by the above-described methods. The obtained results are shown in table 3.

(varnish storage test)

The polyamideimide varnish obtained in examples 1 to 3 and comparative examples 1 and 2, in which the mass of the resin was 7.5% by mass relative to the mass of the varnish, was stored at 50 ℃ for 1 week.

Using and initiating b^＊In the same manner, b of the varnish after storage (in all of examples and comparative examples, the mass of the resin was 7.5 mass% based on the mass of the varnish) was measured^＊Is measured as b after storage^＊The value is obtained. From storage of the varnish b^＊Minus the initial b^＊The obtained value is referred to as Δ b^＊。

(evaluation of film after varnish storage test)

The polyamideimide varnish obtained in examples 1,2 and 4 and comparative examples 1 and 3, in which the mass of the resin was 8.1% by mass relative to the mass of the varnish, was stored at 50 ℃ for 1 week. The YI value of a film obtained by forming a varnish after storage (in examples 1 and 2 and comparative example 1, the mass of the resin was 7.5 mass% with respect to the mass of the varnish, and in example 4 and comparative example 3, the mass of the resin was 8.1 mass% with respect to the mass of the varnish) was measured as the YI value after storage in the same manner as the initial YI value. The initial YI value is subtracted from the stored YI value, and the obtained value is defined as Δ YI. The obtained results are shown in table 3.

[ Table 2]

[ Table 3]

The varnishes of examples 1 to 4 each contained a transparent polyimide polymer and GBL. GBL used in examples 1 to 4 had a transmittance of 88% or more at λ 275nm, and impurities of less than 300ppm were detected at Rrt 1.02 to 1.50 and less than 260ppm were detected at Rrt 1.05 to 1.50 based on GC analysis. Delta b of the varnishes of examples 1 to 3 (the mass of the resin relative to the mass of the varnish was 7.5 mass% in all examples)^＊All are 0.27 or less.

The Δ YI of the polyamideimide films produced from the varnishes of examples 1,2 and 4 (in examples 1 and 2, the mass of the resin was 7.5 mass% relative to the mass of the varnish, and in example 4, the mass of the resin was 8.1 mass% relative to the mass of the varnish) was 0.1 or less.

The varnishes of comparative examples 1 to 3 each contained a transparent polyimide polymer and GBL. GBL used in comparative examples 1 to 3 at λ 275nmHas a transmittance of less than 88%, and has an impurity content of 300ppm or more detected at an Rrt of 1.02 to 1.50 and an impurity content of 260ppm or more detected at an Rrt of 1.05 to 1.50, respectively, by gas chromatography. Delta b of the varnishes of comparative examples 1 to 2 (the mass of the resin relative to the mass of the varnish was 7.5 mass% in all comparative examples)^＊All of them are 0.33 or more.

The Δ YI of the polyamideimide film produced from the varnishes of comparative examples 1 and 3 (in comparative example 1, the mass of the resin is 7.5 mass% with respect to the mass of the varnish, and in comparative example 3, the mass of the resin is 8.1 mass% with respect to the mass of the varnish) is 0.5 or more.

As is clear from the above, the varnishes of examples 1 to 3 had Δ b values higher than those of comparative examples 1 to 2^＊The varnish is small in size, inhibited from discoloration due to long-term storage, and high in transparency. In addition, it is clear that the Δ YI of the films produced using the varnishes of examples 1,2 and 4 is smaller than that of comparative examples 1 and 3, and therefore the YI value is low and the optical properties are excellent even in the optical film obtained from the varnish after long-term storage.

Claims

1. A varnish, comprising:

a solvent containing gamma-butyrolactone having a light transmittance of 88% or more at a wavelength of 275 nm; and a process for the preparation of a coating,

a polyimide polymer.

2. A varnish comprising at least a polyimide-based polymer and a solvent containing gamma-butyrolactone in which the area ratio of a component detected in a capillary gas chromatography analysis using polyethylene glycol as a stationary phase is 260ppm or less, when a sample is injected while the column temperature is maintained at 120 ℃, the temperature is maintained at 120 ℃ for 1 minute, the temperature is raised to 240 ℃ at a rate of 10 ℃/minute, and the temperature is maintained at 240 ℃ for 7 minutes, the relative retention time based on the peak of gamma-butyrolactone is 1.05 to 1.50.

3. The varnish of claim 2 wherein the capillary gas chromatographyThe column under analysis was DB-WAX (30 m.times.0.32 mm I.D., d.) manufactured by Agilent Technologies_f0.50μm)。

4. The varnish according to any one of claims 1 to 3, wherein the content of γ -butyrolactone is 30 to 100 mass% based on the total amount of solvent contained in the varnish.

5. The varnish according to any one of claims 1 to 4, wherein the solvent is contained in an amount of 75 to 99 mass% based on the total amount of the varnish.

6. The varnish according to any one of claims 1 to 5, wherein the content of the polyimide-based polymer is 1 to 25% by mass based on the total amount of the varnish.

7. The varnish of any one of claims 1 to 6 when based on L^＊a^＊b^＊In the color difference measurement of the color system, L is satisfied^＊≥80、-10≤a^＊B is not more than 10, and-10 is not more than b^＊≤10。

8. The varnish according to any one of claims 1 to 7, wherein the weight average molecular weight of the polyimide-based polymer in terms of polystyrene is 200,000 or more.

9. The varnish according to any one of claims 1 to 8 wherein the polyimide-based polymer is polyamideimide.

10. An optical film formed from the varnish recited in any one of claims 1 to 9.

11. A method for producing an optical film, comprising at least the steps of:

(a) a step of applying the varnish according to any one of claims 1 to 9 to a support to form a coating film; and a process for the preparation of a coating,

12. A flexible display device provided with the optical film according to claim 10.

13. The flexible display device of claim 12, further provided with a touch sensor.

14. The flexible display device according to claim 12 or 13, further comprising a polarizing plate.