CN110050208B

CN110050208B - Liquid crystal display device, polarizing plate and polarizer protective film

Info

Publication number: CN110050208B
Application number: CN201780075986.0A
Authority: CN
Inventors: 早川章太; 阿部尭永; 村田浩一; 向山幸伸
Original assignee: Toyobo Co Ltd
Current assignee: Toyobo Co Ltd
Priority date: 2016-12-14
Filing date: 2017-12-14
Publication date: 2021-09-28
Anticipated expiration: 2037-12-14
Also published as: JPWO2018110625A1; KR102216520B1; TW202208525A; JP2022153484A; TWI750280B; JP7156034B2; KR20190087619A; TWI795086B; CN113912994A; WO2018110625A1; JP7396402B2; TW201831554A; CN110050208A

Abstract

Providing: a liquid crystal display device, a polarizing plate and a polarizer protective film, which can suppress the occurrence of rainbow unevenness and improve visibility even when a polyethylene terephthalate resin film as a polarizer protective film which is a constituent member of a polarizing plate is used for a liquid crystal display device which can cope with a wide color gamut or when the film is made thin. A polarizer protective film comprising a polyethylene terephthalate resin film, wherein the polyethylene terephthalate resin film satisfies the following (1) and (2). (1) The polyethylene terephthalate resin film has a retardation of 3000 to 30000nm, and (2) the degree of orientation of the (100) plane of the crystal relative to the film plane is 0.70 or less as measured by X-ray diffraction.

Description

Liquid crystal display device, polarizing plate and polarizer protective film

Technical Field

The invention relates to a liquid crystal display device, a polarizing plate and a polarizer protective film.

Background

A polarizing plate used in a Liquid Crystal Display (LCD) is generally configured by sandwiching a polarizing plate obtained by dyeing iodine on polyvinyl alcohol (PVA) or the like with 2 sheets of a polarizing plate protective film, and as the polarizing plate protective film, a Triacetylcellulose (TAC) film is mainly used. In recent years, with the thinning of LCDs, the polarizing plate has been required to be thinner. However, if the thickness of the TAC film used as the protective film is reduced for this purpose, a sufficient mechanical strength cannot be obtained, and the moisture permeability deteriorates. In addition, TAC films are very expensive, and polyester films have been proposed as an inexpensive alternative material (patent documents 1to 3), but there is a problem in that iridescent unevenness is observed.

When an oriented polyester film having birefringence is disposed on one side of a polarizing plate, the polarization state of linearly polarized light emitted from a backlight unit or the polarizing plate changes when the linearly polarized light passes through the polyester film. The transmitted light exhibits a characteristic interference color depending on the retardation amount, which is the product of the birefringence and the thickness of the oriented polyester film. Therefore, when discontinuous emission spectra such as cold cathode tubes and hot cathode tubes are used as light sources, the light sources exhibit different transmission light intensities depending on the wavelengths, and form iridescent color spots (see the 15 th Microoptics Commission, items 30 to 31).

As a method for solving the above-mentioned problems, it has been proposed to use a white light source having a continuous and wide emission spectrum, such as a white light emitting diode, as a backlight light source, and further use an oriented polyester film having a constant retardation amount as a polarizer protective film (patent document 4). For a white light emitting diode, there is a continuous and broad emission spectrum in the visible light region. Therefore, focusing on the shape of the envelope of the interference color spectrum of light transmitted through the birefringent body, by controlling the retardation amount of the oriented polyester film, a spectrum similar to the emission spectrum of the light source can be obtained, and thereby, the rainbow unevenness can be suppressed.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2002-116320

Patent document 2: japanese patent laid-open publication No. 2004-219620

Patent document 3: japanese patent laid-open publication No. 2004-205773

Patent document 4: WO2011/162198

Disclosure of Invention

Problems to be solved by the invention

As a backlight source of a liquid crystal display device, a white light emitting diode (white LED) formed of a light emitting element in which a blue light emitting diode and an yttrium-aluminum garnet-based yellow phosphor (YAG-based yellow phosphor) are combined has been widely used. The white light source has an emission spectrum having a wide spectrum in a visible light region and is excellent in light emission efficiency, and therefore, is commonly used as a backlight light source. However, in a liquid crystal display device using the white LED as a backlight light source, only about 20% of the spectrum recognizable to the human eye can be reproduced.

On the other hand, since the demand for color gamut expansion has increased in recent years, liquid crystal display devices have been developed which are adapted to a wider color gamut as follows: the emission spectrum of the white light source has clear peak shapes in the respective wavelength regions of R (red), G (green), and B (blue). For example, liquid crystal display devices have been developed which can cope with a wide color gamut as follows: it uses a white light source using quantum dot technology; a white LED light source of a phosphor system using a phosphor having clear emission peaks in R (red) and G (green) regions by excitation light and a blue LED; and various types of light sources such as 3-wavelength white LED light sources. In the case of a liquid crystal display device using a white light source using quantum dot technology as a backlight light source, it is said that 60% or more of the spectrum recognizable by human eyes can be reproduced.

These white light sources have a narrower peak half-value width than a conventional light source including a white light emitting diode using a YAG-based yellow phosphor, and when a polyethylene terephthalate resin film having a retardation is used as a polarizer protective film which is a constituent member of a polarizing plate, it has been newly found that a rainbow unevenness may occur depending on the type of the light source.

In addition, there is a strong demand for further reduction in the thickness of the polarizer protective film, and in such a case, there is also a demand for providing a polyethylene terephthalate resin film (polarizer protective film) which can further suppress the occurrence of rainbow unevenness when the display screen is viewed from an oblique direction.

That is, an object of the present invention is to provide: a polarizing plate protective film, a polarizing plate comprising the same, and a liquid crystal display device, wherein the occurrence of rainbow unevenness can be suppressed both when a polyethylene terephthalate resin film is used as a polarizing plate protective film for a liquid crystal display device that is compatible with a wide color gamut and when the polarizing plate protective film is made thin.

Means for solving the problems

The present inventors have intensively studied and found that: the polyethylene terephthalate resin film has a retardation in a specific range, and the lower the degree of orientation of the (100) plane of the crystal relative to the film plane as measured by X-ray diffraction, the more effectively the iridescence is suppressed.

Representative invention is described below.

Item 1.

A polarizer protective film comprising a polyethylene terephthalate resin film,

the polyethylene terephthalate resin film satisfies the following (1) and (2).

(1) The polyethylene terephthalate resin film has a retardation of 3000nm to 30000nm

(2) The degree of orientation of the (100) plane of the crystal relative to the film plane is 0.70 or less as measured by X-ray diffraction

Item 2.

The polarizer protective film according to item 1, wherein the polyethylene terephthalate resin film has a crystallite size of a (-105) plane of crystals measured in a slow axis direction of the film

The above.

Item 3.

A polarizing plate obtained by laminating the polarizer protective film according to claim 1 or 2 on at least one surface of a polarizer.

Item 4.

A liquid crystal display device has: a backlight source, 2 polarizing plates, and a liquid crystal cell disposed between the 2 polarizing plates,

at least one of the 2 polarizing plates is the polarizing plate of item 3.

ADVANTAGEOUS EFFECTS OF INVENTION

In the case of the liquid crystal display device, the polarizing plate and the polarizer protective film of the present invention, when the polyethylene terephthalate resin film as the polarizer protective film is used for a liquid crystal display device that can cope with a wide color gamut or when the film is made thin, the occurrence of rainbow unevenness on the display screen can be suppressed.

Detailed Description

1. Polarizer protective film

The polyethylene terephthalate resin film used in the polarizer protective film of the present invention preferably has a retardation (Re, in-plane retardation) of 3000nm to 30000 nm. When the retardation is less than 3000nm, a strong interference color appears when the polarizing plate is used as a polarizing plate protective film, and good visibility cannot be ensured. The lower limit of the retardation is preferably 4000nm, more preferably 5000nm, and still more preferably 6000 nm.

On the other hand, the upper limit of the retardation amount is preferably 30000nm, and more preferably 10000 nm. If the particle size is significantly larger than the upper limit of 30000nm, not only a further improvement effect of visibility is not substantially obtained, but also the film thickness becomes considerably thick, and the workability as an industrial material is lowered, which is not preferable.

The refractive index difference in the film plane (refractive index in the slow axis direction — refractive index in the fast axis direction) is preferably 0.08 or more, more preferably 0.09 or more, and still more preferably 0.10 or more. The upper limit of the difference in refractive index is preferably 0.15 or less. From the viewpoint of further suppressing the rainbow unevenness, it is preferable that the film is strongly stretched in the unidirectional direction, and the refractive index difference in the film plane is large.

The retardation of the present invention can be determined by measuring the refractive index in the 2-axis direction in the film plane and the film thickness, or by using a commercially available automatic birefringence measurement device such as KOBRA-21ADH (Oji Scientific Instruments co., Ltd.). The refractive index in the 2-axis direction in the film plane was determined by an Abbe refractometer (manufactured by ATAGO Inc., NAR-4T, measurement wavelength 589 nm).

The polyethylene terephthalate resin film used in the polarizer protective film of the present invention preferably has a retardation in a specific range and has a degree of orientation of the (100) plane of the crystal to the film plane as measured by X-ray diffraction of 0.70 or less, from the viewpoint of suppressing rainbow unevenness observed from an oblique direction. The degree of orientation of the (100) plane of the crystals of the polyethylene terephthalate resin film with respect to the film plane is preferably 0.70 or less, more preferably 0.65 or less, more preferably 0.60 or less, more preferably 0.59 or less, and even more preferably 0.58 or less. The lower limit is preferably 0.40. The degree of orientation of the (100) plane of the crystal with respect to the film plane is an index indicating the orientation around the molecular chain direction (c-axis) of the crystal of the polyethylene terephthalate resin film, and the lower the value, the more random the orientation around the c-axis. The more random the orientation around the c-axis, the more the rainbow unevenness observed from the oblique direction is suppressed.

The degree of orientation of the (100) plane of the crystal relative to the film plane is a parameter as follows: using an X-ray diffraction apparatus (manufactured by Rigaku Corporation, RINT2100PC), the half-value width with the slow axis direction of the diffraction intensity measured through the pole as the axis was defined as (180-half-value width)/180. Where the unit of half-value width is degrees. The slow axis direction of the film can be determined using a molecular orientation meter (an Oji scientific instruments co., ltd., MOA-6004 type molecular orientation meter). The details of the measurement of the degree of orientation are as described later in examples.

Further, the polyethylene terephthalate resin film preferably has a crystallite size of a (-105) plane of crystals measured in a slow axis direction by X-ray diffraction

(angstrom) or more. The crystallite size of the (-105 planes) of the aforementioned crystals is preferably

The above, more preferred

The above, further preferred

The above. The upper limit is preferably

But do not

The left and right are sufficient.

It is considered that the molecular chain direction (c-axis direction) of the crystals of the polyethylene terephthalate resin film is oriented in the slow axis direction of the film, the crystallite size in the molecular chain direction (c-axis direction) of the crystals is larger than a specific value, and the orientation around the molecular chain direction axis (c-axis) of the crystals is reduced, so that the generation of iridescent unevenness is further reduced. The crystallite size in the molecular chain axis direction of the crystal can be measured as the apparent crystallite size of the (-105) plane of the crystal as follows.

The crystallite size of the (-105) plane of the crystal measured in the slow axis direction can be calculated as follows: the diffraction position of the (-105) plane of the crystal and the actually measured half-value width (B) were read from the diffraction intensity curve of θ/2 θ measured in the slow axis direction using an X-ray diffraction device (manufactured by Rigaku Corporation, RINT2500), and the diffraction position and the actually measured half-value width (B) were calculated as an Apparent Crystallite Size (ACS) using the following formula (scherrer formula). The X-ray used in the measurement is Cu-Kalpha ray with a wavelength of

In the present invention, the crystallite size of the (-105) plane of the crystal measured in the slow axis direction means an apparent crystallite size. (ACS 0.9 λ/(β cos θ)). Where λ is the wavelength of the X-rays

Beta is the measured half-value width (B) and the constant (B) for correction, and²-b²)^1/2calculated half-value width. The constant (b) used for calibration is the half-value width of the silicon powder NIST640b measured under the same conditions. β, B, b are both values in radian units.

The degree of in-plane orientation of the (-105) plane of the crystal is preferably 0.6 or more, more preferably 0.7 or more, and still more preferably 0.8 or more. The degree of in-plane orientation of the (-105) plane of the crystal can be measured using an X-ray diffraction apparatus (RIGAKU Corporation, RINT 2500). The assay was as follows: the sample holder for azimuth measurement was used to fix θ/2 θ, and the sample was rotated by 360 ° to obtain the circumferential distribution of diffraction intensity of the (-105) plane of the crystal. From the half-value width of the obtained distribution, a parameter defined by (180-half-value width)/180 was taken as the in-plane orientation degree. The unit of half-value width is here expressed in degrees.

In order to uniaxially orient the molecular chain of the crystal, the film is preferably stretched in a single direction. In general, in order to increase the degree of orientation in the stretching direction, there are: a method of increasing the stretch ratio or decreasing the stretching temperature. When a film-like material is uniaxially stretched, the stress generated inside may be different in the stretching direction, the direction perpendicular to the stretching direction in the film plane, and the thickness direction. It is generally known that, when the dimension in the direction perpendicular to the stretching direction is made free or fixed, as in what is called free-end uniaxial stretching or fixed-end uniaxial stretching, the internal stress greatly differs. This is because the difference in poisson contraction generated during stretching is made free or suppressed in the direction perpendicular to the stretching direction. In the case of transverse stretching in a typical tenter, since the ends are held by clips, poisson shrinkage in the film flow direction (MD) during transverse stretching is limited. Therefore, the transverse stretching direction (TD) naturally also generates stress in the flow direction. Since there is no limitation in the thickness direction, it is considered that stress is not generated. That is, it is considered that the stress distribution around the molecular chain axis oriented in the stretching direction is different in the flow direction and the thickness direction, and the orientation of the benzene ring face of the crystal advances. Thus, in order to reduce the orientation around the molecular chain direction axis (c-axis) of the crystal, it is preferable to equalize the stress around the orientation axis while maintaining the stress and strain in the stretching direction. Since stress does not substantially act in the thickness direction, it is preferable to reduce stress in a direction (flow direction) perpendicular to the stretching direction.

The polyethylene terephthalate resin film as the protective film of the present invention can be produced by a usual method for producing a polyester film. For example, the following methods may be mentioned: the non-oriented polyethylene terephthalate resin obtained is stretched in the longitudinal direction at a temperature equal to or higher than the glass transition temperature by the speed difference of rolls, and then stretched in the transverse direction by a tenter, and heat-treated.

When the conditions for forming the polyethylene terephthalate resin film are specifically described, the longitudinal stretching temperature and the transverse stretching temperature are preferably 100 to 130 ℃, and particularly preferably 110 to 125 ℃.

When a film having a slow axis in the film width direction (TD direction) is produced, the longitudinal stretching ratio is preferably 0.7 to 1.0. The transverse stretching magnification is preferably 4.0 to 6.0 times, more preferably 4.0 to 5.5 times, and most preferably 4.5 to 5.5 times.

On the other hand, in the case of producing a film having a slow axis in the film longitudinal direction (MD direction), the stretching ratio in the transverse direction is preferably 1.0 to 3.0 times, more preferably 1.5 to 3.0 times, and still more preferably 2.0 to 3.0 times. The longitudinal stretching magnification is preferably 4.0 to 6.5 times, and more preferably 5.0 to 6.0 times. In the case of producing a film having a slow axis in the film longitudinal direction, it is preferable to perform stretching in the transverse direction and then stretching in the longitudinal direction from the viewpoint of reducing the degree of orientation of the (100) plane of the crystal with respect to the film plane.

In order to control the retardation to the above range, it is preferable to control the ratio of the longitudinal stretching magnification to the transverse stretching magnification, the stretching temperature, and the thickness of the film. If the difference in the longitudinal and lateral draw ratios is too small, it becomes difficult to increase the retardation, which is not preferable.

In order to increase the crystallite size of the (-105) plane of the crystal or decrease the degree of orientation of the (100) plane of the crystal with respect to the film plane, it is preferable to increase the stretch ratio for the unidirectional; the stretching temperature is set to be high, and at this time, the wind speed of the hot air is appropriately adjusted so as to apply sufficient heat to the film. The wind speed of the hot wind is preferably 6 to 15 m/sec, more preferably 8 to 12 m/sec. The film is stretched in one direction at a high magnification while applying sufficient heat, whereby the stress and strain in the stretching direction can be maintained, the stress around the orientation axis can be equalized, the crystallite size of the (-105) plane of the crystal can be increased, or the degree of orientation of the (100) plane of the crystal with respect to the film plane can be decreased.

In the subsequent heat treatment, the treatment temperature is preferably 150 to 250 ℃, particularly preferably 180 to 220 ℃. From the viewpoint of reducing the degree of orientation of the (100) plane of the crystal with respect to the film plane, a lower treatment temperature for the heat treatment is more preferable. On the other hand, from the viewpoint of increasing the crystallite size of the (-105) plane of the crystal, the higher the treatment temperature of the heat treatment, the higher the treatment temperature, and therefore, the adjustment is preferable in view of the balance between both.

The polyethylene terephthalate resin constituting the polyethylene terephthalate resin film preferably contains ethylene terephthalate in an amount of 85 mol% or more of the monomer units. The ethylene terephthalate unit is preferably 90 mol% or more, more preferably 95 mol% or more. The copolymerization component may contain a known acid component or glycol component. As the polyethylene terephthalate resin, polyethylene terephthalate as a homopolymer is particularly preferable. The ratio of the monomer units may be determined by¹H-NMR measurement.

These resins are excellent in transparency, thermal properties and mechanical properties, and the retardation can be easily controlled by drawing. Polyethylene terephthalate has a large intrinsic birefringence, and even if the film has a small thickness, a large retardation can be easily obtained, and it is an optimum material.

In addition, for the purpose of suppressing deterioration of an optically functional dye such as an iodine dye, the protective film of the present invention preferably has a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance at 380nm is more preferably 15% or less, still more preferably 10% or less, and particularly preferably 5% or less. When the light transmittance is 20% or less, the deterioration of the optically functional dye by ultraviolet rays can be suppressed. The light transmittance in the present invention is measured in a direction perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, hitachi U-3500 type).

In order to make the protective film of the present invention have a light transmittance of 20% or less at a wavelength of 380nm, it is desirable to appropriately adjust the type and concentration of the ultraviolet absorber and the thickness of the film. The ultraviolet absorber used in the present invention is a known one. Examples of the ultraviolet absorber include an organic ultraviolet absorber and an inorganic ultraviolet absorber, and from the viewpoint of transparency, an organic ultraviolet absorber is preferable. Examples of the organic ultraviolet absorber include benzotriazole-based, benzophenone-based, cyclic imino ester-based, and combinations thereof, but the range of absorbance defined in the present invention is not particularly limited. However, benzotriazole-based and cyclic imino ester-based compounds are particularly preferable from the viewpoint of durability. When 2 or more ultraviolet absorbers are used in combination, ultraviolet rays of respective wavelengths can be absorbed simultaneously, and therefore, the ultraviolet absorption effect can be further improved.

Examples of the benzophenone-based ultraviolet absorber, benzotriazole-based ultraviolet absorber and acrylonitrile-based ultraviolet absorber include 2- [2 '-hydroxy-5' - (methacryloyloxymethyl) phenyl ] -2H-benzotriazole, 2- [2 '-hydroxy-5' - (methacryloyloxyethyl) phenyl ] -2H-benzotriazole, 2- [2 '-hydroxy-5' - (methacryloyloxypropyl) phenyl ] -2H-benzotriazole, 2 '-dihydroxy-4, 4' -dimethoxybenzophenone, 2',4,4' -tetrahydroxybenzophenone, 2, 4-di-tert-butyl-6- (5-chlorobenzotriazol-2-yl) phenol, and mixtures thereof, Examples of the cyclic imino ester ultraviolet absorbers include 2- (2' -hydroxy-3 ' -tert-butyl-5 ' -methylphenyl) -5-chlorobenzotriazole, 2- (5-chloro (2H) -benzotriazol-2-yl) -4-methyl-6- (tert-butyl) phenol, 2' -methylenebis (4- (1,1,3, 3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, 2' - (1, 4-phenylene) bis (4H-3, 1-benzoxazin-4-one), 2-methyl-3, 1-benzoxazin-4-one, and the like, 2-butyl-3, 1-benzoxazin-4-one, 2-phenyl-3, 1-benzoxazin-4-one, and the like. However, the present invention is not particularly limited thereto.

It is also preferable to contain various additives other than the catalyst in addition to the ultraviolet absorber within a range not to impair the effects of the present invention. Examples of the additives include inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light-resistant agents, flame retardants, heat stabilizers, antioxidants, antigelling agents, and surfactants. In order to exhibit high transparency, it is also preferable that the polyethylene terephthalate resin film contains substantially no particles. "substantially no particles" means, for example, a content of 50ppm or less, preferably 10ppm or less, and particularly preferably a content of detection limit or less in the case of inorganic particles and in the case of quantitative determination of inorganic elements by fluorescent X-ray analysis.

The method of blending the ultraviolet absorber into the polyethylene terephthalate resin film of the present invention may be combined with known methods, and for example, the ultraviolet absorber and the polymer raw material may be blended in advance using a kneading extruder to prepare a master batch, and the master batch and the polymer raw material may be mixed in a predetermined manner at the time of film formation.

In order to uniformly disperse the ultraviolet absorber and economically mix the ultraviolet absorber, the ultraviolet absorber concentration of the master batch is preferably 5 to 30 mass%. The master batch is preferably prepared by extruding the raw material of the polyethylene terephthalate resin at an extrusion temperature of not lower than the melting point of the raw material and not higher than 290 ℃ for 1to 15 minutes using a kneading extruder. When the temperature is 290 ℃ or higher, the weight loss of the ultraviolet absorber is large, and the viscosity of the master batch is reduced greatly. When the extrusion time is 1 minute or less, it becomes difficult to uniformly mix the ultraviolet absorber. In this case, a stabilizer, a color tone adjuster, and an antistatic agent may be added as needed.

In the present invention, it is preferable that the film has a multilayer structure of at least 3 layers and that an ultraviolet absorber is added to an intermediate layer of the film. The film having a 3-layer structure in which the ultraviolet absorber is contained in the intermediate layer can be specifically produced as follows. Pellets of a polyethylene terephthalate resin for an outer layer were individually mixed, and a master batch containing an ultraviolet absorber for an intermediate layer and pellets of a polyethylene terephthalate resin were mixed at a predetermined ratio, dried, supplied to a known melt lamination extruder, extruded from a slit die into a sheet, and cooled and solidified on a casting roll to prepare an undrawn film. That is, using 2 or more extruders, a 3-layer manifold or a confluence block (for example, a confluence block having an angular confluence section), film layers constituting both outer layers and a middle layer were laminated, 3-layer sheets were extruded from a nozzle, and cooled on a casting roll to prepare an unstretched film. In the present invention, in order to remove foreign matters contained in the polyethylene terephthalate resin as a raw material, which causes optical defect, it is preferable to perform high-precision filtration at the time of melt extrusion. The filter medium used for high-precision filtration of the molten resin preferably has a filter particle size (initial filtration efficiency 95%) of 15 μm or less. If the filter particle size exceeds 15 μm, removal of foreign matter of 20 μm or more tends to be insufficient.

Further, the polyethylene terephthalate resin film of the present invention may be subjected to corona treatment, coating treatment, flame treatment, or the like in order to improve adhesiveness to a polarizing plate.

In the present invention, in order to improve the adhesiveness to the polarizing plate, it is preferable that at least one surface (preferably the surface in contact with the polarizing plate) of the film of the present invention is provided with an easy-adhesion layer containing at least 1 of a polyester resin, a polyurethane resin, or a polyacrylic resin as a main component. Here, the "main component" means a component of 50 mass% or more of the solid component constituting the easy adhesion layer. The coating liquid used for forming the easy adhesion layer of the present invention is preferably an aqueous coating liquid containing at least 1 kind of water-soluble or water-dispersible copolymerized polyester resin, acrylic resin, and urethane resin. Examples of such coating liquids include water-soluble or water-dispersible copolyester resin solutions, acrylic resin solutions, and urethane resin solutions disclosed in japanese patent No. 3567927, 3589232, 3589233, 3900191, 4150982, and the like.

The easy adhesion layer can be obtained as follows: the coating liquid is applied to one or both surfaces of an unstretched film or a longitudinally uniaxially stretched film, dried at 100 to 150 ℃, and stretched in the transverse direction. The coating weight of the final easy-bonding layer is preferably controlled to be 0.05-0.20 g/m². If the coating weight is less than 0.05g/m²The adhesiveness to the polarizing plate obtained may be insufficient. On the other hand, if the coating weight exceeds 0.20g/m²The blocking resistance is sometimes reduced. When the easy-adhesion layers are provided on both surfaces of the polyethylene terephthalate resin film, the amounts of the easy-adhesion layers on both surfaces may be the same or different, and may be set independently within the above ranges.

In order to impart slipperiness to the easy-adhesion layer, it is preferable to add particles. It is preferable to use particles having an average particle diameter of 2 μm or less. If the average particle diameter of the particles exceeds 2 μm, the particles are easily detached from the coating layer. Examples of the particles contained in the easy adhesion layer include inorganic particles such as titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconium oxide, tungsten oxide, lithium fluoride, and calcium fluoride, and organic polymer-based particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. These may be added alone to the easy-adhesion layer or in combination of 2 or more.

As a method for applying the coating liquid, a known method can be used. Examples of the method include a reverse roll coating method, a gravure coating method, a lip coating method, a roll brush method, a spray coating method, an air knife coating method, a wire bar coating method, and a tube doctor blade method, and these methods may be performed alone or in combination.

The average particle size of the particles was measured by the following method. The particles are photographed by a Scanning Electron Microscope (SEM), the maximum diameter (distance between the most distant 2 points) of 300 to 500 particles is measured at a magnification of 2 to 5mm for 1 particle which is the smallest particle, and the average value is defined as the average particle diameter.

The thickness of the polyethylene terephthalate resin film of the present invention is arbitrary, but it is preferably in the range of 30 to 300. mu.m. Even if the thickness is less than 30 μm, a retardation of 3000nm or more can be obtained in principle. However, in the above case, the anisotropy of the mechanical properties of the film becomes remarkable, and breakage, and the like are likely to occur, and the utility as an industrial material is remarkably lowered. The lower limit of the thickness is preferably 40 μm, and the lower limit of the thickness is particularly preferably 45 μm. On the other hand, if the upper limit of the thickness of the polarizer protective film exceeds 300 μm, the thickness of the polarizer becomes too thick, which is not preferable. From the viewpoint of practical use as a polarizer protective film, the upper limit of the thickness is preferably 200 μm, preferably 120 μm, more preferably 100 μm or less, further more preferably 80 μm or less, further more preferably 65 μm or less, further more preferably 60 μm or less, further more preferably 55 μm or less.

In order to suppress variation in retardation amount, it is preferable that the thickness unevenness of the thin film is small. Since the stretching temperature and stretching ratio greatly affect the thickness unevenness of the film, the film forming conditions are preferably optimized from the viewpoint of the thickness unevenness. In particular, when the longitudinal stretching magnification is reduced in order to increase the retardation, the longitudinal thickness unevenness may be deteriorated. Since the longitudinal thickness unevenness is present in a region where the longitudinal thickness unevenness becomes very poor within a certain specific range of the stretching magnification, it is desirable to set the film forming conditions outside this range.

The thickness variation of the film of the present invention is preferably 5.0% or less, more preferably 4.5% or less, still more preferably 4.0% or less, and particularly preferably 3.0% or less.

The ratio (Re/Rth) of the retardation (Re) to the retardation (Rth) in the thickness direction of the polyethylene terephthalate resin film is preferably 0.2 or more, more preferably 0.5 or more, and still more preferably 0.6 or more. From the viewpoint of suppressing rainbow unevenness when viewed from an oblique direction, the larger the ratio (Re/Rth) is, the more preferable. The upper limit of the ratio (Re/Rth) is preferably 2.0 or less, more preferably 1.8 or less. On the other hand, from the viewpoint of thickness unevenness and planarity, the upper limit of the above ratio (Re/Rth) is preferably less than 1.0. The retardation in the thickness direction is a parameter representing an average of 2 birefringence values Δ Nxz (═ nx-nz |) and Δ Nyz (═ ny-nz |) obtained by multiplying the respective retardation values by the film thickness d when viewed from a cross section in the thickness direction of the film. The thickness direction retardation (Rth) can be determined by calculating nx, ny, nz and the film thickness d (nm), and calculating the average value of (. DELTA. Nxz X d) and (. DELTA. Nyz X d). Nx, ny, and nz can be determined by an Abbe refractometer (manufactured by ATAGO Inc., NAR-4T, measurement wavelength 589 nm).

2. Polarizing plate

The polarizing plate of the present invention has a structure in which a polarizer protective film is attached to at least one surface of a polarizer obtained by dyeing polyvinyl alcohol (PVA) or the like with iodine, and any polarizer protective film is preferably the polarizer protective film of the present invention. As the other polarizer protective film, a film free from birefringence, such as a TAC film, an acrylic film, or a norbornene film, is preferably used. Or the other may be absent. In the polarizing plate used in the present invention, it is also preferable to coat various hard coatings on the surface for the purpose of preventing reflection, suppressing glare, suppressing scratches, and the like.

3. Liquid crystal display device having a plurality of pixel electrodes

In general, a liquid crystal panel is composed of a rear module, a liquid crystal cell, and a front module in this order from a side opposite to a backlight light source to a side (visible side) where an image is displayed. The rear module and the front module are generally composed of a transparent substrate, a transparent conductive film formed on the liquid crystal cell side surface, and a polarizing plate disposed on the opposite side. Here, the polarizing plate is disposed on the side of the rear module facing the backlight light source, and on the side of the front module (visible side) where an image is displayed.

The liquid crystal display device of the present invention has at least a backlight source and a liquid crystal cell disposed between 2 polarizing plates as constituent members. Other structures than these, for example, a color filter, a lens film, a diffusion sheet, an antireflection film, and the like may be appropriately provided. Preferably, at least one of the 2 polarizing plates is the polarizing plate of the present invention.

The backlight may be of a side-light type in which a light guide plate, a reflection plate, or the like is used as a constituent member, or of a direct-type.

The backlight source of the liquid crystal display device is not particularly limited. For example, the backlight light source may be a phosphor type white LED (i.e., an element that emits white light by using a combination of a light emitting diode that emits blue light or ultraviolet light using a compound semiconductor and a phosphor). As the phosphor, there are: yttrium-aluminum-garnet yellow phosphor, terbium-aluminum-garnet yellow phosphor, and the like.

In one embodiment, the backlight light source is preferably a white light source having a peak of an emission spectrum in each of wavelength regions of 400nm or more and less than 495nm, 495nm or more and less than 600nm, and 600nm or more and 780 nm. Examples thereof include: a white light source using quantum dot technology; a white LED light source of a phosphor system using a phosphor having emission peaks in R (red) and G (green) regions by excitation light and a blue LED; a 3-wavelength white LED light source; a white LED light source combined with a red laser; and for example using a composition formula of K₂SiF₆：Mn⁴⁺A fluoride phosphor (also referred to as "KSF") of (b), a white LED light source of a blue LED, and the like. They are attracting attention as backlight light sources for liquid crystal display devices coping with wide color gamut.

The polarizer protective film of the present invention having a specific retardation is not particularly limited in arrangement in a liquid crystal display device, and in the case of a liquid crystal display device provided with a polarizing plate arranged on the incident light side (light source side), a liquid crystal cell, and a polarizing plate arranged on the emergent light side (visible side), it is preferable that the polarizer protective film arranged on the incident light side of the polarizing plate on the incident light side and/or the polarizer protective film arranged on the emergent light side of the polarizing plate on the emergent light side is a polarizer protective film formed of the polyethylene terephthalate resin film having a specific retardation. Particularly preferred is the following: the polarizing plate protective film on the light-emitting side of the polarizing plate disposed on the light-emitting side was made of the polyethylene terephthalate resin film having a specific retardation. When the polyethylene terephthalate resin film is disposed at a position other than the above position, the polarization of the liquid crystal cell may be changed. The polymer film of the present invention is not preferably used in a portion where polarization is required, and therefore, it is preferably used as a protective film for a polarizing plate at such a specific position.

Examples

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to the following examples, and can be carried out by appropriately changing the examples within a range that can meet the gist of the present invention, and these examples are included in the scope of protection of the present invention. The evaluation methods of the physical properties in the following examples are as follows.

(1) Retardation (Re)

The retardation is a parameter defined by the product (Δ Nxy × d) of the refractive index anisotropy (Δ Nxy ═ Nx-Ny |) of the orthogonal biaxial refractive indices on the film and the film thickness d (nm), and is a standard indicating optical isotropy and anisotropy. The biaxial refractive index anisotropy (Δ Nxy) was obtained by the following method. The slow axis direction of the film was determined using a molecular orientation meter (MOA-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments co., ltd.) and a rectangle of 4cm × 2cm was cut out as a measurement sample so that the slow axis direction was parallel to the long side of the measurement sample. For this sample, refractive indices (a refractive index in the slow axis direction: ny, a refractive index in the direction orthogonal to the slow axis direction: nx) and a refractive index in the thickness direction (nz) of the biaxial perpendicular to each other were obtained by an Abbe refractometer (manufactured by ATAGO Inc., NAR-4T, measurement wavelength 589nm), and the absolute value of the difference in refractive indices of the biaxial (i.e., | nx-ny |) was used as the anisotropy of refractive index (Δ Nxy). The thickness D (nm) of the film was measured by using an electrical micrometer (Fine Liu off Co., Ltd., Miritoron 1245D), and the unit was converted to nm. The retardation (Re) is determined from the product (Δ Nxy × d) of the anisotropy of the refractive index (Δ Nxy) and the thickness d (nm) of the thin film.

(2) Retardation in thickness direction (Rth)

The retardation in the thickness direction is a parameter representing an average of 2 birefringence values Δ Nxz (═ nx-nz |), (| ny-nz |) and Δ Nyz (═ ny-nz |) obtained by multiplying the respective retardation values by the film thickness d when viewed from a cross section in the thickness direction of the film. Nx, ny, nz and the film thickness d (nm) were determined by the same method as the measurement of the retardation, and the retardation in the thickness direction (Rth) was determined by calculating the average value of (Δ Nxz × d) and (Δ Nyz × d).

(3) Degree of orientation of (100) plane of crystal with respect to film plane

The degree of orientation of the (100) plane of the crystal relative to the film plane is a parameter as follows: an X-ray diffraction apparatus (manufactured by Rigaku Corporation, RINT2100PC) was used, and defined as (180-half width)/180 in terms of the half width of the axis, which is the slow axis direction of the diffraction intensity measured by the pole. The X-ray used in the measurement is Cu-Kalpha ray with a wavelength of

Pole determination was performed as follows: the installation of a RINT2000 goniometer and pole, which can be mounted on RINT2100PC, was carried out with a multi-purpose sample table, using the schultz reflex method. The sample was cut into a circle having a diameter of 5cm, and mounted on a sample table so that the slow axis direction coincides with the direction of β 90 degrees and 270 degrees. The slow axis direction of the sample was determined using a molecular orientation meter (an Oji Scientific Instruments co., ltd., MOA-6004 type molecular orientation meter). The details of the measurement conditions are as follows: the tube voltage was set to 40kV, the tube current was set to 40mA, the 2 θ fixed angle was set to 25.830 degrees, the longitudinal divergence limit was set to 1.2mm, the divergence slit was set to 1 degree, the scattering slit was set to 7mm, and the receiving slit was set to 7 mm. In the transmission measurement, α start angle is 0 degree, α end angle is 35 degrees, and α step angle is 5 degrees. In the reflection measurement, the α start angle is 25 degrees, the α end angle is 90 degrees, and the α step angle is 5 degrees. The scanning method comprises the following steps: along concentric circles betaThe start angle is 0 degrees, the beta end angle is 360 degrees, and the beta step angle is 5 degrees.

Hereinafter, a method of calculating the degree of orientation of the (100) plane of the crystal with respect to the film plane will be described. The reflection diffraction intensity curves obtained in the measurement of β ═ 0 degrees and β ═ 180 degrees are represented as I (α) (25 ≦ α ≦ 90). By connecting the diffraction intensity curves at β ═ 0 degrees and 180 degrees with the abscissa axis being α ' (α ' ═ α when β ═ 0 degrees, and α ' ═ 180- α when β ═ 180 degrees), the diffraction intensity curves at β ═ 0 degrees and 180 degrees are connected, and a diffraction intensity curve I (α ') (25 ≦ α ' ≦ 155) can be obtained. In this case, the diffraction intensity at α' 90 degrees is an average value of β 0 degrees and β 180 degrees. The degree of orientation of the (100) plane of the crystal with respect to the film plane was calculated from the obtained diffraction intensity curve using the half-value width by subtracting the line connecting the diffraction intensities at α' ═ 25 degrees and 155 degrees as a base line, and from (180-half-value width)/180. The unit of half-value width is degrees.

(4) Crystallite size of the (-105) plane of the crystal

The crystallite size of the (-105) plane of the crystal in the slow axis direction of the film was calculated as follows: the actual half-value width (B) of the diffraction peak at the diffraction position (2 θ: 42.7 degrees) of the (-105) plane of the crystal was read from the diffraction intensity curve of θ/2 θ measured in the slow axis direction using an X-ray diffraction apparatus (manufactured by Rigaku Corporation, RINT2500), and calculated as an Apparent Crystallite Size (ACS) using the following formula (scherrer formula). The X-ray used in the measurement is Cu-Kalpha ray with a wavelength of

The base line is set as: a line connecting 2 points, which are a point where the diffraction intensity is the smallest between 30 degrees and 42.7 degrees in 2 theta, and a point where the diffraction intensity is the smallest between 42.7 degrees and 50 degrees in 2 theta, with a straight line. (ACS 0.9 λ/(β cos θ)). Where λ is the wavelength of the X-rays

Beta is the measured half-value width (B) and the constant (B) for correction, and²-b²)^1/2calculated half-value width. To be explainedThe constant (b) used for the calibration is the half-value width of the silicon powder NIST640b measured under the same conditions. Here, β and B, b are both values in radian units. The slow axis direction of the sample was determined using a molecular orientation meter (an Oji Scientific Instruments co., ltd., MOA-6004 type molecular orientation meter).

(5) Iridescent speckle Observation

A polyethylene terephthalate film prepared in the following manner was attached to one side of a polarizing plate made of PVA and iodine so that the absorption axis of the polarizing plate was perpendicular to the main axis of orientation of the film, and a commercially available TAC film was attached to the opposite surface of the polarizing plate, thereby producing a polarizing plate made of polyethylene terephthalate film/polarizing plate/TAC film. The polarizing plate originally present on the light-emitting side of a commercially available liquid crystal display device (BRAVIA KDL-40W920A manufactured by SONY corporation) was replaced with the polarizing plate thus obtained. The polarizing plate was replaced with a polyethylene terephthalate film so that the absorption axis of the polarizing plate and the absorption axis of the polarizing plate originally attached to the liquid crystal display device were aligned and the polyethylene terephthalate film was on the visible side. The liquid crystal display device includes a backlight light source including a light source for emitting excitation light and quantum dots. The emission spectrum of the backlight light source of the liquid crystal display device was measured by using a multichannel spectrometer PMA-12 manufactured by Hamamatsu Photonics K.K., and as a result, emission spectra having peaks were observed at around 450nm, 528nm, and 630nm, and the half-value width of each peak was 16nm to 34 nm. The exposure time during the spectrometry was set to 20 msec.

The liquid crystal display device thus produced was caused to display a white image, and the occurrence of rainbow-like spots was judged by the following criteria, by visual observation from the front and oblique directions of the display. The observation angles are: an angle formed by a line drawn from the center of the screen of the display in the normal direction (vertical direction) and a straight line connecting the center of the display and the position of the eye when viewed.

Very good: no rainbow spots were observed within the range of observation angles of 0 to 65 degrees.

O: in the range of the observation angle of 0-65 degrees, a little rainbow spots were observed.

X: in the range of the observation angle of 0-65 degrees, rainbow spots are observed.

Production example 1 polyester A

The esterification reaction tank was heated, and when the temperature reached 200 ℃, 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were added, and 0.017 parts by mass of antimony trioxide as a catalyst, 0.064 parts by mass of magnesium acetate tetrahydrate, and 0.16 parts by mass of triethylamine were added while stirring. Subsequently, the esterification reaction was carried out under a pressure and temperature rise condition, and after the pressure esterification reaction was carried out under a gage pressure of 0.34MPa at 240 ℃, the esterification reaction tank was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Further, the temperature was raised to 260 ℃ over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. After 15 minutes, the resulting mixture was dispersed by a high-pressure disperser, and after 15 minutes, the esterification reaction product was transferred to a polycondensation reaction tank and subjected to polycondensation reaction at 280 ℃ under reduced pressure.

After the completion of the polycondensation reaction, the reaction mixture was filtered through a NASLON filter having a 95% cutoff diameter of 5 μm, extruded from a nozzle into a strand form, cooled and solidified with cooling water having been subjected to a filtration treatment (pore diameter: 1 μm or less), and cut into pellets. The resulting polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62dl/g and was substantially free of inactive particles and internally precipitated particles. (hereinafter abbreviated as PET (A))

Production example 2 polyester B

10 parts by mass of dried ultraviolet absorber (2, 2' - (1, 4-phenylene) bis (4H-3, 1-benzoxazin-4-one) and 90 parts by mass of PET (A) (intrinsic viscosity 0.62dl/g) substantially not containing particles were mixed, and a kneading extruder was used to obtain a polyethylene terephthalate resin (B) containing an ultraviolet absorber (hereinafter abbreviated as PET (B))

Production example 3 preparation of coating liquid for adhesive Property modification

The ester exchange reaction and the polycondensation reaction were carried out by a conventional method to prepare a water-dispersible metal sulfonate group-containing copolyester resin having a composition of a dicarboxylic acid component (with respect to the whole dicarboxylic acid component) 46 mol% of terephthalic acid, 46 mol% of isophthalic acid, and 8 mol% of sodium 5-sulfoisophthalate, and a diol component (with respect to the whole diol component) 50 mol% of ethylene glycol, and 50 mol% of neopentyl glycol. Subsequently, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 part by mass of a nonionic surfactant were mixed, and then heated and stirred to 77 ℃. Further, after dispersing 3 parts by mass of aggregate silica particles (silji SILYSIACHEMICAL ltd. product, SILYSIA 310) in 50 parts by mass of water, 0.54 part by mass of an aqueous dispersion of SILYSIA 310 was added to 99.46 parts by mass of the above-mentioned water-dispersible copolyester resin solution, and 20 parts by mass of water was added thereto with stirring to obtain an adhesion modifying coating solution.

(example 1)

90 parts by mass of PET (A) resin pellets containing no particles as a raw material for an intermediate layer of a base film and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber were dried under reduced pressure at 135 ℃ for 6 hours (1Torr), and then supplied to an extruder 2 (for an intermediate layer II), and further, PET (A) was dried by a conventional method and supplied to the extruder 1 (for outer layers I and III), respectively, and dissolved at 285 ℃. The 2 kinds of polymers were each filtered with a filter medium of a stainless steel sintered body (nominal filtration accuracy 10 μm particle 95% cutoff), laminated with 2 kinds of 3-layer flow blocks, and extruded from a nozzle into a sheet shape. Winding the film on a casting drum (casting drum) with the surface temperature of 30 ℃ by using an electrostatic casting method for cooling and solidifying to prepare an unstretched film. In this case, the ratio of the thicknesses of the layers I, II, and III is 10: 80: the discharge amount of each extruder was adjusted in the manner of 10.

Then, the coating weight after drying was set to 0.08g/m by the reverse roll method²The coating liquid for modifying adhesiveness was applied to both surfaces of the non-stretched PET film, and then dried at 80 ℃ for 20 seconds.

The unstretched film on which the coating layer was formed was introduced into a tenter stretcher, and while holding the ends of the film with clips, the film was stretched so as to be 4.0 times in the width direction (TD) and 0.7 times in the film flow direction (MD) in a hot air zone having a hot air outlet with a wind speed of 12 m/sec at a temperature of 110 ℃. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 200 ℃ in a hot air zone having an air velocity of 10 m/sec from a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, to obtain a uniaxially oriented PET film having a film thickness of about 50 μm.

(example 2)

An unstretched film produced in the same manner as in example 1 was introduced into a tenter stretcher, and while holding the ends of the film with clips, the film was introduced into a hot air zone having an air speed of 10 m/sec at a hot air outlet at a temperature of 125 ℃ and stretched so as to be 4.5 times in the width direction. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 200 ℃ in a hot air zone having an air velocity of 10 m/sec from a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, to obtain a uniaxially oriented PET film having a film thickness of about 80 μm.

(example 3)

An unstretched film produced in the same manner as in example 1 was introduced into a tenter stretcher, and while holding the ends of the film with clips, the film was stretched so as to be 4.5 times in the width direction in a hot air zone at a temperature of 120 ℃ and at an air speed of 12 m/sec introduced into a hot air outlet. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 200 ℃ in a hot air zone having an air velocity of 10 m/sec from a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, to obtain a uniaxially oriented PET film having a film thickness of about 100. mu.m.

(example 4)

An unstretched film produced in the same manner as in example 1 was introduced into a tenter stretcher, and while holding the ends of the film with clips, the film was stretched at a temperature of 130 ℃ in a hot air zone having an air speed of 9 m/sec at a hot air outlet so as to be 5.5 times as high in the width direction. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 200 ℃ in a hot air zone having an air velocity of 10 m/sec from a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, to obtain a uniaxially oriented PET film having a film thickness of about 60 μm.

(example 5)

An unstretched film produced in the same manner as in example 1 was introduced into a tenter stretcher, and while holding the ends of the film with clips, the film was introduced into a hot air zone having an air speed of 10 m/sec at a hot air outlet at a temperature of 125 ℃ and stretched so as to be 5.0 times in the width direction and 0.9 times in the flow direction. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 200 ℃ in a hot air zone having an air velocity of 10 m/sec from a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, to obtain a uniaxially oriented PET film having a film thickness of about 60 μm.

(example 6)

An unstretched film produced in the same manner as in example 1 was introduced into a tenter stretcher, and while holding the ends of the film with clips, the film was stretched at a temperature of 120 ℃ in a hot air zone having an air speed of 10 m/sec at a hot air outlet so as to be 5.0 times as high in the width direction. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 200 ℃ in a hot air zone having an air velocity of 10 m/sec from a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, to obtain a uniaxially oriented PET film having a film thickness of about 40 μm.

(example 7)

An unstretched film produced in the same manner as in example 1 was introduced into a tenter stretcher, and while holding the ends of the film with clips, the film was stretched so as to be 4.5 times in the width direction in a hot air zone at a temperature of 110 ℃ and at an air speed of 12 m/sec introduced into a hot air outlet. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 200 ℃ in a hot air zone having an air velocity of 10 m/sec from a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, thereby obtaining a uniaxially oriented PET film having a film thickness of about 125. mu.m.

(example 8)

An unstretched film produced in the same manner as in example 1 was introduced into a tenter stretcher, and while holding the ends of the film with clips, the film was stretched so as to be 4.5 times in the width direction in a hot air zone having a temperature of 115 ℃ and a wind speed of 10 m/sec introduced into a hot air outlet. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 200 ℃ in a hot air zone having an air velocity of 10 m/sec from a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, to obtain a uniaxially oriented PET film having a film thickness of about 60 μm.

(example 9)

An unstretched film produced in the same manner as in example 1 was introduced into a tenter stretcher, and while holding the ends of the film with clips, the film was stretched in a width direction at a temperature of 120 ℃ in a hot air zone with an air speed of 12 m/sec at a hot air outlet, so as to be 5.0 times as high. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 130 ℃ in a hot air zone having an air velocity of 10 m/sec from a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, to obtain a uniaxially oriented PET film having a film thickness of about 50 μm.

Comparative example 1

An unstretched film produced in the same manner as in example 1 was introduced into a tenter stretcher, and while holding the ends of the film with clips, the film was stretched so as to be 4.0 times in the width direction in a hot air zone at a temperature of 125 ℃ and at an air speed of 5 m/sec introduced into a hot air outlet. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 225 ℃ in a hot air zone having an air velocity of 5 m/sec from a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, to obtain a uniaxially oriented PET film having a film thickness of about 50 μm.

Comparative example 2

An unstretched film produced in the same manner as in example 1 was introduced into a tenter stretcher, and while holding the ends of the film with clips, the film was stretched so as to be 4.0 times in the width direction in a hot air zone at a temperature of 95 ℃ and at an air speed of 10 m/sec introduced into a hot air outlet. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 150 ℃ in a hot air zone having an air velocity of 10 m/sec at a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, to obtain a uniaxially oriented PET film having a film thickness of about 60 μm.

Comparative example 3

An unstretched film produced in the same manner as in example 1 was heated to 105 ℃ by a heated roll stack and an infrared heater, then stretched 1.5 times in the traveling direction by the roll stack having a peripheral speed difference, and then stretched 4.0 times in the width direction at a temperature of 100 ℃ in a hot air zone having an air velocity of 10 m/sec introduced into a hot air outlet. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 200 ℃ in a hot air zone having an air velocity of 10 m/sec at a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, to obtain a biaxially oriented PET film having a film thickness of about 50 μm.

Comparative example 4

An unstretched film produced in the same manner as in example 1 was introduced into a tenter stretcher, and while holding the ends of the film with clips, the film was stretched so as to be 4.0 times in the width direction in a hot air zone at a temperature of 90 ℃ and at an air speed of 10 m/sec introduced into a hot air outlet. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 200 ℃ in a hot air zone having an air velocity of 10 m/sec from a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, to obtain a uniaxially oriented PET film having a film thickness of about 50 μm.

Comparative example 5

An unstretched film produced in the same manner as in example 1 was heated to 105 ℃ by a heated roll stack and an infrared heater, then stretched 3.5 times in the running direction by the roll stack having a peripheral speed difference, and then introduced into a tenter stretcher, while holding the end of the film with a clip, the film was stretched 4.0 times in the width direction in a hot air zone having a temperature of 130 ℃ and a wind speed of 10 m/sec at a hot air outlet. Subsequently, while maintaining the stretching width in the width direction, heat treatment was performed at a temperature of 220 ℃ in a hot air zone having an air velocity of 10 m/sec at a hot air outlet, and further relaxation treatment was performed by 3% in the width direction, to obtain a biaxially oriented PET film having a film thickness of about 100. mu.m.

The results of X-ray structural analysis and rainbow unevenness observation of the physical properties of the PET films of examples 1to 9 and comparative examples 1to 5 are shown in table 1 below. The PET films obtained in examples 2 to 4 and 6 to 9 had an Re/Rth of less than 1 and excellent film flatness.

[ Table 1]

Industrial applicability

In the liquid crystal display device, the polarizing plate and the polarizer protective film of the present invention, when the polyethylene terephthalate resin film as the polarizer protective film is used for a liquid crystal display device that can cope with a wide color gamut or when the film is made thin, occurrence of rainbow unevenness observed on a display screen can be suppressed.

Claims

1. A polarizer protective film comprising a polyethylene terephthalate resin film,

the polyethylene terephthalate resin film satisfies the following (1) and (2),

(1) the polyethylene terephthalate resin film has a retardation of 3000nm to 30000 nm;

(2) the degree of orientation of the (100) plane of the crystal relative to the film plane as measured by X-ray diffraction is 0.70 or less.

2. The polarizer protective film according to claim 1, wherein, with respect to the polyethylene terephthalate resin film, a crystallite size of a (-105) plane of crystals measured in a slow axis direction is

The above.

3. A polarizing plate obtained by laminating the polarizer protective film according to claim 1 or 2 on at least one surface of a polarizer.

4. A liquid crystal display device has: a backlight source, 2 polarizing plates, and a liquid crystal cell disposed between the 2 polarizing plates,

at least one of the 2 polarizing plates is the polarizing plate of claim 3.