WO2021215349A1 - ポリエステルフィルムとその用途 - Google Patents
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- WO2021215349A1 WO2021215349A1 PCT/JP2021/015609 JP2021015609W WO2021215349A1 WO 2021215349 A1 WO2021215349 A1 WO 2021215349A1 JP 2021015609 W JP2021015609 W JP 2021015609W WO 2021215349 A1 WO2021215349 A1 WO 2021215349A1
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
- C08J7/04—Coating
- C08J7/042—Coating with two or more layers, where at least one layer of a composition contains a polymer binder
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
- C08J7/04—Coating
- C08J7/0427—Coating with only one layer of a composition containing a polymer binder
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
- C08J7/04—Coating
- C08J7/043—Improving the adhesiveness of the coatings per se, e.g. forming primers
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
- C08J7/04—Coating
- C08J7/046—Forming abrasion-resistant coatings; Forming surface-hardening coatings
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
- C08L67/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
- G02B1/10—Optical coatings produced by application to, or surface treatment of, optical elements
- G02B1/14—Protective coatings, e.g. hard coatings
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F1/00—Details not covered by groups G06F3/00 - G06F13/00 and G06F21/00
- G06F1/16—Constructional details or arrangements
- G06F1/1613—Constructional details or arrangements for portable computers
- G06F1/1633—Constructional details or arrangements of portable computers not specific to the type of enclosures covered by groups G06F1/1615 - G06F1/1626
- G06F1/1637—Details related to the display arrangement, including those related to the mounting of the display in the housing
- G06F1/1652—Details related to the display arrangement, including those related to the mounting of the display in the housing the display being flexible, e.g. mimicking a sheet of paper, or rollable
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
- G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
- G09F9/30—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements
- G09F9/301—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements flexible foldable or roll-able electronic displays, e.g. thin LCD, OLED
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/02—Constructional features of telephone sets
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
- C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
- C08J2367/03—Polyesters derived from dicarboxylic acids and dihydroxy compounds the dicarboxylic acids and dihydroxy compounds having the hydroxy and the carboxyl groups directly linked to aromatic rings
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/02—Constructional features of telephone sets
- H04M1/0202—Portable telephone sets, e.g. cordless phones, mobile phones or bar type handsets
- H04M1/0206—Portable telephones comprising a plurality of mechanically joined movable body parts, e.g. hinged housings
- H04M1/0208—Portable telephones comprising a plurality of mechanically joined movable body parts, e.g. hinged housings characterized by the relative motions of the body parts
- H04M1/0214—Foldable telephones, i.e. with body parts pivoting to an open position around an axis parallel to the plane they define in closed position
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/02—Constructional features of telephone sets
- H04M1/0202—Portable telephone sets, e.g. cordless phones, mobile phones or bar type handsets
- H04M1/026—Details of the structure or mounting of specific components
- H04M1/0266—Details of the structure or mounting of specific components for a display module assembly
- H04M1/0268—Details of the structure or mounting of specific components for a display module assembly including a flexible display panel
Definitions
- the present invention relates to a polyester film for a foldable display, a hard coat film for a foldable display, a foldable display, and a portable terminal device. And the above-mentioned polyester film for a foldable display.
- mobile terminal devices such as smartphones have become widespread. While mobile terminal devices are required to have various functions, they are also required to be convenient. For this reason, popular mobile terminal devices need to have a small screen size of about 6 inches because they can be easily operated with one hand and are supposed to be stored in a pocket of clothes.
- tablet terminals with a screen size of 7 inches to 10 inches are expected to be used not only for video content and music, but also for business use, drawing use, reading, etc., and have high functionality. However, it cannot be operated with one hand, is inferior in portability, and has a problem in convenience.
- Patent Document 1 a method of making it compact by connecting a plurality of displays has been proposed (see Patent Document 1).
- the invention of Patent Document 1 is not widely used because the bezel portion remains, so that the image is cut off and the visibility is deteriorated.
- the surface of the display can be protected with a non-flexible material such as glass.
- a foldable display when a one-sided display is formed through a foldable portion, it is necessary to use a hard coat film or the like that is flexible and can protect the surface.
- the foldable display since the portion corresponding to a certain foldable portion is repeatedly folded, there is a problem that the film at the portion is deformed with time and the image displayed on the display is distorted.
- the foldable display uses films for various parts such as polarizing plates, retardation plates, touch panel base materials, base materials for display cells such as organic EL, and protective members on the back surface. , These films were also required to have durability against repeated folding.
- Patent Document 2 a method of partially changing the film thickness has also been proposed.
- Patent Document 2 there is a problem that the manufacturing process becomes complicated because the film thickness is changed, and the mass productivity is poor.
- the present invention is intended to solve the problems of conventional display members as described above, is excellent in mass productivity, and does not cause distortion in the image displayed in the folded portion after being repeatedly folded.
- a foldable display and a polyester film for a foldable display which makes it possible to provide a portable terminal device equipped with such a foldable display.
- the present invention is intended to provide a polyester film for a foldable display in which creases do not occur in the foldable portion in a high temperature range.
- the present invention has the following configuration.
- 1. A polyester film having a thickness of 10 ⁇ m or more and 125 ⁇ m or less and having a high-temperature hold angle in the bending direction of 70 ° or more for a foldable display.
- the high-temperature hold angle refers to the angle formed after bending after being fixed at 85 ° C. for 18 hours so that 1.7% of strain is applied to both surfaces of the bent portion. Refers to the direction orthogonal to the folding part
- the first polyester film for a foldable display having a density of 1.349 g / cm 3 or more.
- 3. The polyester film for a foldable display according to the first or second, wherein the polyester is polyethylene naphthalate. 4.
- the polyester film for a foldable display according to any one of 1 to 3 above which has an easy-adhesion layer on at least one side of the polyester film.
- the polyester film for a foldable display according to any one of the above 1 to 4 is a foldable display arranged as a back surface protective film, and is a single polyester film continuous via a foldable portion of the foldable display. Folding display with. 6.
- the foldable display using the polyester film for a foldable display of the present invention maintains mass productivity, and the polyester film does not cause deformation after being repeatedly folded even in a high temperature region, and an image at the folded portion of the display. It does not cause any disturbance.
- a mobile terminal device equipped with a foldable display using a polyester film as described above provides a beautiful image, is rich in functionality, and is excellent in convenience such as portability.
- the display referred to in the present invention generally refers to a display device, and the types of displays include LCD, organic EL display, inorganic EL display, LED, and FED.
- LCDs, organic ELs, and inorganic ELs having a bendable structure are preferable.
- organic EL and inorganic EL that can reduce the layer structure are particularly preferable, and organic EL having a wide color gamut is further preferable.
- the foldable display is a display in which one continuous display can be folded in half when carried. By folding, the size can be halved and portability can be improved.
- the bending radius of the foldable display is preferably 5 mm or less, more preferably 3 mm or less. If the bending radius is 5 mm or less, the thickness can be reduced in the folded state. It can be said that the smaller the bending radius, the better. According to the present invention, creases can be suppressed even with such a bending radius.
- the bending radius is preferably 0.1 mm or more, and may be 0.5 mm or more, or 1 mm or more. Even if the bending radius is 0.1 mm, it is possible to achieve a practically sufficient thinning when carrying.
- the bending radius when folded is a value measured at the portion of the foldable display 1 in the schematic view of FIG. 1 at reference numeral 11, and means the radius inside the folded portion when folded.
- the surface protective film described later may be located on the folded outer side or the inner side of the foldable display.
- the foldable display may be folded in three, folded in four, or further, and may be a retractable type called rollable, all of which fall within the scope of the foldable display according to the present invention.
- the polyester film of the present invention can be bent not only in the longitudinal direction as shown in FIG. 1 but also in the width direction.
- the polyester film for a foldable display of the present invention may be used for any part as long as it is a constituent member of the foldable display.
- a typical configuration of a foldable display and a portion where the polyester film of the present invention can be used will be described by taking an organic EL display as an example.
- the polyester film for a folding display of the present invention may be simply referred to as the polyester film of the present invention.
- An essential configuration of the foldable organic EL display is an organic EL module, but if necessary, a circularly polarizing plate, a touch panel module, a front surface protective film, a back surface protective film, and the like are provided.
- Organic EL module The general configuration of an organic EL module consists of an electrode / electron transport layer / light emitting layer / hole transport layer / transparent electrode.
- the polyester film of the present invention can be used as a base material on which an electrode is provided and an electron transport layer, a light emitting layer, and a hole transport layer are further provided. In particular, it can be preferably used as a base material for a transparent electrode.
- the polyester film of the present invention is provided with a barrier layer such as a metal oxide layer.
- a barrier layer such as a metal oxide layer.
- a plurality of barrier layers may be provided, or a plurality of polyester films provided with the barrier layer may be used.
- the mobile terminal device has a touch panel.
- the touch panel module is arranged on the upper part of the organic EL display or between the organic EL module / circularly polarizing plate.
- the touch panel module has a transparent base material such as a film and a transparent electrode arranged on the transparent base material.
- the polyester film of the present invention can be used as this transparent base material.
- the circularly polarizing plate suppresses deterioration of image quality due to reflection of external light by a member inside the display.
- the circular polarizing plate has a linear polarizing plate and a retardation plate.
- the linear polarizing plate has a protective film on at least the surface of the polarizer on the visible side.
- a protective film may be provided on the surface opposite to the viewing side of the polarizer, or a retardation plate may be directly laminated on the polarizer.
- the retardation plate a resin film having a retardation such as polycarbonate or cyclic olefin or a resin film provided with a retardation layer made of a liquid crystal compound is used.
- the polyester film of the present invention can be used as a polarizer protective film or a resin film for a retardation plate.
- the slow axis direction of the polyester film is parallel or orthogonal to the absorption axis direction of the polarizer. A deviation of up to 10 degrees, preferably up to 5 degrees, is allowed with respect to this parallelism or orthogonality.
- a surface protective film is provided.
- the polyester film of the present invention is used as this surface protective film.
- the surface protective film includes a cover window built into the outermost surface of the display and a replaceable after-sale film that can be attached and detached by the user himself. In either case, the polyester of the present invention is used. Film is used.
- a hard coat layer is laminated on at least the surface side of the polyester film. It is provided on the surface of a foldable display with the hard coat layer on the visual side. The hard coat layer may be provided on both sides.
- a protective film is also provided on the back surface side of the display. Specifically, an adhesive layer is provided on the non-visual side of the organic EL module, and the modules are bonded together.
- the polyester film of the present invention can be used as a protective film on the back surface side.
- the polyester film of the present invention can be used for applications other than the above as long as it is used in a foldable portion of a foldable display component.
- the polyester film of the present invention is preferably used for the cover window surface protective film, the after surface protective film, the base film of the touch panel module, and the back surface protective film. Furthermore, it is preferably used for the cover window surface protective film and the after surface protective film.
- a foldable display it is not necessary to use the polyester film of the present invention for all of the above.
- a polyimide film, a polyamide film, a polyamideimide film, a polyester film that is not the polyester film of the present invention a polycarbonate film, an acrylic film, a triacetyl cellulose film, a cycloolefin polymer film, A polyphenylene sulfide film, a polymethylpentene film, or the like can be appropriately used according to suitability.
- the polyester film of the present invention may be a single-layer film made of one or more types of polyester resins, or when two or more types of polyesters are used, it may be a multilayer film or a repeating supermultilayer laminated film. ..
- polyester resin used for the polyester film examples include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, for example, polyethylene-2,6-naphthalate, or a copolymer containing components of these resins as main components.
- Polyester film can be mentioned.
- a polyethylene naphthalate film, particularly a stretched polyethylene naphthalate film, is preferable from the viewpoint of mechanical properties, heat resistance, transparency and the like.
- the amount of the other polyester resin may be 40% by weight or less with respect to 100% by weight of the resin in the polyester film, for example, 10.
- the polyethylene naphthalate resin may be 60% by weight or more, 90% by weight or more, 95% by weight or more, for example, more than 95% by weight, based on 100% by weight of the resin in the polyester film. It is preferable that it is contained in.
- the other polyester resin is less than 5% by weight, the crystallinity of the polyester film can be kept high and the high temperature holding angle can be held satisfactorily.
- the proportion of polyethylene naphthalate in the raw material ratio of the polyester film is 100% by weight.
- the polyester film may contain a plurality of types of polyethylene naphthalates having different characteristics.
- the polyester film does not deform after being repeatedly folded even in a high temperature region, and it is possible to suppress image distortion in the folded portion of the display. Further, the portable terminal device equipped with the foldable display using the polyester film of the present invention provides a beautiful image, is rich in functionality, and is excellent in convenience such as portability.
- the dicarboxylic acid component of the polyester is, for example, an aliphatic dicarboxylic acid such as adipic acid or sebacic acid; terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid.
- Aromatic dicarboxylic acids such as; polyfunctional carboxylic acids such as trimellitic acid and pyromellitic acid.
- glycol component examples include fatty acid glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol, propylene glycol, and neopentyl glycol; aromatic glycols such as p-xylene glycol; 1,4-cyclohexanedimethanol, and the like. Alicyclic glycols; polyethylene glycols having an average molecular weight of 150 to 20,000.
- the mass ratio of the copolymerization component of the preferred copolymer is less than 3% by mass. When it is less than 3% by mass, the film strength, transparency and heat resistance are maintained, which is preferable.
- the ultimate viscosity of at least one type of resin pellet is preferably in the range of 0.40 to 1.0 dl / g.
- the ultimate viscosity is 0.40 dl / g or more, the impact resistance of the obtained film is improved, and it is preferable that the internal circuit of the display is less likely to be broken due to an external impact.
- the ultimate viscosity is 1.00 dl / g or less, the filter pressure increase of the molten fluid does not become too large, and it is preferable that the film production can be operated stably.
- the ultimate viscosity of at least one type of resin pellet may be 0.40 to 0.8 dl / g, and the ultimate viscosity may be 0.40 to 0.7 dl / g.
- the thickness of the polyester film is 10 ⁇ m or more and 125 ⁇ m, and more preferably 25 ⁇ m or more and 100 ⁇ m or less, for example.
- the thickness is 10 ⁇ m or more, the pencil hardness improving effect and the impact resistance improving effect are observed, and when the thickness is 125 ⁇ m or less, it is advantageous for weight reduction and also excellent in flexibility, workability and handleability.
- the surface of the polyester film of the present invention may be smooth or may have irregularities. When used as a surface cover application for displays, it is preferable to have a smooth film surface.
- the haze is preferably 3% or less, more preferably 2% or less, and particularly preferably 1% or less. When the haze is 3% or less, the visibility of the image can be improved. The smaller the lower limit of the haze is, the better, but from the viewpoint of stable production, 0.1% or more is preferable, and 0.3% or more may be used.
- the unevenness of the film surface is not so large for the purpose of reducing the haze, but the unevenness may be provided in order to give a certain degree of slipperiness from the viewpoint of handling.
- a method for forming surface irregularities it can be formed by blending particles into a polyester resin layer on the surface layer, or by coating a coat layer containing particles in the middle of film formation.
- a known method can be adopted. For example, it can be added at any stage in the production of polyester, but is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or at the stage after the completion of the transesterification reaction and before the start of the polycondensation reaction. Then, the polycondensation reaction may proceed. Further, a method of blending a slurry of particles dispersed in ethylene glycol or water with a polyester raw material using a kneading extruder with a vent, or a method of blending dried particles with a polyester raw material using a kneading extruder. It can be done by such as.
- the aggregate inorganic particles are homogeneously dispersed in a monomer solution that is a part of the polyester raw material, and then filtered, and the residue of the polyester raw material before the esterification reaction, during the esterification reaction, or after the esterification reaction is used.
- the method of addition is preferable. According to this method, since the monomer liquid has a low viscosity, uniform dispersion of particles and high-precision filtration of the slurry can be easily performed, and when added to the rest of the raw material, the dispersibility of the particles is good, which is new. Aggregates are also unlikely to occur. From this point of view, it is particularly preferable to add it to the balance of the raw material in a low temperature state before the esterification reaction.
- the number of protrusions on the film surface can be further reduced by a method (masterbatch method) in which the polyester containing particles is obtained in advance and then the pellets and the pellets containing no particles are kneaded and extruded.
- the polyester film may contain various additives within a range that maintains a preferable range of total light transmittance.
- the additive include an antistatic agent, a UV absorber, and a stabilizer.
- the total light transmittance of the polyester film is preferably 85% or more, more preferably 87% or more. If the transmittance is 85% or more, sufficient visibility can be ensured. It can be said that the higher the total light transmittance of the polyester film, the better, but from the viewpoint of stable production, 99% or less is preferable, and 97% or less may be used.
- the maximum heat shrinkage of the polyester film after heat treatment at 150 ° C. for 30 minutes is preferably 2% or less, more preferably 1.5% or less, for example, 1.2% or less. If the heat shrinkage rate is 2% or less, the dimensional change due to heat generation of the organic EL display itself can be suppressed. It can be said that the lower the heat shrinkage rate is, the better, but it is preferably -1% or more, and preferably 0% or more. A minus here means that it has expanded after heating, and even if it is less than -1%, a flat surface may be defective.
- the surface of the polyester film of the present invention can be treated to improve the adhesion with the resin forming the hard coat layer or the like.
- Examples of the surface treatment method include sand blast treatment, uneven treatment by solvent treatment, corona discharge treatment, electron beam irradiation treatment, plasma treatment, ozone / ultraviolet irradiation treatment, flame treatment, chromic acid treatment, hot air treatment, and the like. Oxidation treatment and the like can be mentioned and can be used without particular limitation.
- the adhesiveness can be improved by an adhesiveness improving layer such as an easy adhesive layer.
- an adhesiveness improving layer such as an easy adhesive layer.
- an acrylic resin, a polyester resin, a polyurethane resin, a polyether resin or the like can be used without particular limitation, and can be formed by a general coating method, preferably a so-called in-line coating formulation.
- the above-mentioned polyester film is obtained by, for example, a polymerization step in which inorganic particles are homogeneously dispersed in a monomer solution that is a part of a polyester raw material, filtered, and then added to the rest of the polyester raw material to polymerize the polyester, and the polyester thereof. It can be produced through a film forming step of forming a base film by melting and extruding it into a sheet through a filter, cooling it, and then stretching it.
- PET polyethylene terephthalate
- the number of layers is not limited, such as a single-layer structure or a multi-layer structure.
- PEN polyethylene naphthalate
- the PET pellets are mixed and dried at a predetermined ratio, they are supplied to a known hot-dip laminating extruder, extruded into a sheet from a slit-shaped die, and cooled and solidified on a casting roll to form an unstretched film. ..
- a known hot-dip laminating extruder extruded into a sheet from a slit-shaped die, and cooled and solidified on a casting roll to form an unstretched film. ..
- one extruder is sufficient, but in the case of producing a multi-layer film, two or more extruders, two or more layers of manifolds or a merging block (for example, a merging having a square merging part).
- a block can be used to stack a plurality of film layers constituting each outermost layer, extrude two or more sheets from a base, and cool them with a casting roll to form an unstretched film.
- the filter medium used for high-precision filtration of the molten resin is not particularly limited, but the filter medium of the stainless sintered body is excellent in the removal performance of aggregates containing Si, Ti, Sb, Ge and Cu as main components and high melting point organic substances. Therefore, it is preferable.
- the filtered particle size (initial filtration efficiency 95%) of the filter medium is preferably 20 ⁇ m or less, and particularly preferably 15 ⁇ m or less. If the filtered particle size (initial filtration efficiency 95%) of the filter medium exceeds 20 ⁇ m, foreign matter having a size of 20 ⁇ m or more cannot be sufficiently removed. High-precision filtration of the molten resin using a filter medium having a filter medium size (initial filtration efficiency of 95%) of 20 ⁇ m or less may reduce productivity, but a film with few protrusions due to coarse particles can be obtained. Preferred above.
- the refractive index of the polyester film in at least one of the longitudinal direction (mechanical flow direction) and the width direction is preferably 1.610 or more and 1.750 or less, for example, 1.610 or more and 1.710. It is less than or equal to, and more preferably 1.630 or more and 1.680 or less.
- the refractive index of the polyester film in the longitudinal direction is 1.610 or more
- the crystallinity can be efficiently improved and the high temperature hold angle can be improved.
- it is 1.750 or less the stress at the time of bending can be reduced, and both the hold angle at room temperature and the high temperature hold angle can be improved.
- the refractive index in the width direction of the polyester film is within the above range, it is desirable that the refractive index in the longitudinal direction of the polyester film is higher than the refractive index in the width direction of the polyester film.
- the refractive index of the polyester film in the bending direction is preferably 1.610 or more and 1.750 or less, for example, 1.610 or more and 1.710 or less, and 1.630 or more and 1.680 or less. preferable.
- the bending direction refers to a direction orthogonal to the folding portion (reference numeral 21) assumed in the application of the foldable display, as shown by reference numeral 22 on the polyester film (reference numeral 2) of FIG.
- the refractive index in at least one of the longitudinal direction and the width direction is 1.610 or more and 1.750 or less, there is little deformation when repeatedly folded, and there is no risk of deteriorating the image quality of the foldable display, which is preferable.
- the refractive index of the polyester film in the bending direction is more preferably 1.630 to 1.680.
- the direction is preferably the above-mentioned bending direction.
- it is 1.610 or more, the crystallinity can be efficiently improved and the high temperature hold angle can be improved.
- it is 1.750 or less the stress at the time of bending can be reduced, and both the hold angle at room temperature and the high temperature hold angle can be improved.
- the refractive index of the polyester film can be effectively adjusted by adjusting the stretching ratio and the stretching temperature. Further, in order to adjust the refractive index, a relaxation step in the stretching direction and multi-step stretching may be used. When performing multi-stage stretching, it is preferable that the stretching ratio of the second and subsequent stages is higher than the stretching ratio of the first stage.
- the refractive index in at least one of the longitudinal direction (mechanical flow direction) and the width direction of the polyester film in the above range more preferably by controlling the refractive index in the bending direction in the above range, at the time of folding. Fatigue due to compressive stress applied to the inside of the folding can be reduced. Fatigue due to compressive stress is thought to occur mainly in the crystal part, and the smaller the number of crystals in the bending direction, the less likely it is to fatigue. Therefore, it is considered that the refractive index in the bending direction becomes smaller than the refractive index in the direction perpendicular to the bending direction, so that the amount of oriented crystals in the bending direction is reduced and compression fatigue is suppressed.
- the creep phenomenon caused by the tensile stress applied to the outside of the fold during folding can be suppressed by reducing the refractive index. Fatigue due to tensile stress is thought to occur mainly in the amorphous part, and the molecular chains are aligned and deformed due to the repeated stress. It can be inferred that the smaller the number of molecular chains aligned in the bending direction, the smaller the deformation due to alignment. Further, since fatigue due to tension can be suppressed when the number of amorphous portions is small, a high crystallinity, that is, a high density is preferable.
- the draw ratio of the unstretched polyester sheet in at least one of the longitudinal direction (mechanical flow direction) and the width direction is preferably 1.0 times or more and 3.4 times or less, preferably 1.4 times. More preferably 2.3 times or less.
- the stretching direction is preferably the bending direction. When the draw ratio is 3.4 times or less, uneven thickness of the film does not occur, which is preferable.
- the stretching temperature is preferably 120 ° C. or higher and 150 ° C. or lower, and more preferably 125 ° C. or higher and 145 ° C. or lower.
- conventionally known means such as a hot air heating method, a roll heating method, and an infrared heating method can be adopted. By setting the stretching temperature to 125 ° C. or higher and 145 ° C. or lower, it is possible to prevent large thickness unevenness due to stretching at the above stretching ratio.
- the refractive index of the polyester film in the direction orthogonal to the direction in which the refractive index is 1.610 or more and 1.750 or less is preferably 1.750 to 1.870. That is, it is preferable that the refractive index in the direction orthogonal to the bending direction (direction of the folded portion) is 1.750 or more and 1.870 or less. By setting it to 1.750 or more and 1.870 or less, it is possible to reduce the deformation when folded in the bending direction. By setting the value to 1.870 or less, it is possible to prevent cracks from entering in the direction of the folded portion, and further to prevent breakage. In addition, it is possible to suppress breakage in the winding process after stretching.
- the density can be increased and the high temperature hold angle can be improved.
- the direction orthogonal to the bending direction corresponds to the direction in which the width direction of the polyester film is orthogonal to the bending direction (the direction of the folding portion). ..
- the refractive index in the direction orthogonal to the bending direction is more preferably 1.770 to 1.830. Further, when the refractive index in the bending direction is compared with the refractive index in the direction orthogonal to the bending direction (the direction of the folded portion), it is desirable that the refractive index in the bending direction is low.
- the method for adjusting the refractive index in the direction orthogonal to the bending direction include stretching ratio, stretching preheating temperature, stretching temperature, multi-stage stretching, and film relaxation.
- the draw ratio is preferably 3.3 to 5.0 times, more preferably 3.5 to 4.5 times.
- the stretching preheating temperature in the direction orthogonal to the bending direction is preferably 125 to 145 ° C.
- the film may be relaxed by 0 to 10% in either the machine flow direction (longitudinal direction) or the vertical direction (width direction).
- the refractive index in the thickness direction is preferably 1.520 or less. It is more preferably 1.515 or less, further preferably 1.510 or less, particularly preferably 1.505 or less, and most preferably 1.500 or less.
- the refractive index in the thickness direction is preferably low, but 1.3 or more is preferable in terms of stable production, and it may be 1.4 or more. Especially preferably, it is 1.410 or more.
- the density of the polyester film is preferably 1.349 g / cm 3 or more. More preferably, it is 1.350 g / cm 3 or more.
- the high temperature hold angle can be improved by setting the temperature to 1.350 g / cm 3 or more.
- the polyester film of the present invention can be sufficiently crystallized and deformation at 85 ° C. can be suppressed.
- the bending direction of the polyester film corresponds to the longitudinal direction (machine flow direction). By doing so, it is easy to reduce the refractive index in the bending direction at the biaxial stretching, and it is easy to improve the flexibility. That is, it is preferable to stretch the unstretched polyester sheet at a stretching ratio of 1.0 to 2.3 times, more preferably 1.4 to 2.1 times in the longitudinal direction to obtain a polyester film. Then, in the width direction, it can be said that it is a preferable mode to stretch at a stretching ratio of 3.3 to 5.0 times, more preferably 3.5 to 4.5 times.
- the polyester film of the present invention has a high temperature hold angle of 70 ° or more in the bending direction.
- the high-temperature hold angle refers to the angle formed after the bending portion is fixed for 18 hours by heating at 85 ° C. so that 1.7% of the strain is applied to both surfaces of the bent portion.
- the bending direction refers to a direction orthogonal to the folded portion.
- the high temperature hold angle in the bending direction is 71 ° or more, for example, 72 ° or more. The higher the value, the better, and 180 ° is most preferable.
- the high temperature hold angle in the bending direction may be 180 ° or less, and for example, 170 ° or less has a sufficient function.
- the high temperature hold angle in the bending direction is within the above range, deformation at 85 ° C. can be suppressed.
- a mobile terminal device equipped with a foldable display using a polyester film provides a beautiful image, is rich in functionality, and is excellent in convenience such as portability.
- the method of measuring the high temperature hold angle in the bending direction will be illustrated in Examples.
- an easy-adhesion layer on at least one surface of the polyester film of the present invention.
- a coating liquid for forming the easy-adhesion layer is applied to one or both sides of an unstretched or longitudinally uniaxially stretched film, heat-treated and dried as necessary, and further unstretched in at least one direction. Can be obtained by stretching to. Heat treatment can be performed even after biaxial stretching.
- the final coating amount of the easy-adhesion layer is preferably controlled to 0.005 to 0.20 g / m 2. When the coating amount is 0.005 g / m 2 or more, adhesiveness is obtained, which is preferable. On the other hand, when the coating amount is 0.20 g / m 2 or less, blocking resistance is obtained, which is preferable.
- the resin contained in the coating liquid used for laminating the easy-adhesion layer is, for example, a polyester resin, a polyether polyurethane resin, a polyester polyurethane resin, a polycarbonate polyurethane resin, an acrylic resin, or the like, and can be used without particular limitation.
- the cross-linking agent contained in the coating liquid for forming an easy-adhesion layer include melamine compounds, isocyanate compounds, oxazoline compounds, epoxy compounds, and carbodiimide compounds. It is also possible to use a mixture of two or more of each. Due to the nature of the in-line coating, these are preferably coated with an aqueous coating liquid, and the above-mentioned resin or cross-linking agent is preferably a water-soluble or water-dispersible resin or compound.
- the average particle size of the fine particles is preferably 2 ⁇ m or less. When the average particle size of the particles exceeds 2 ⁇ m, the particles are likely to fall off from the easy-adhesion layer.
- the particles contained in the easy-adhesion layer include, for example, titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectrite, zirconia, tungsten oxide, lithium fluoride, etc.
- examples thereof include inorganic particles such as calcium fluoride and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. These may be added to the easy-adhesion layer alone, or may be added in combination of two or more.
- a known method can be used in the same manner as the above-mentioned coating layer.
- the reverse roll coating method, the gravure coating method, the kiss coating method, the roll brush method, the spray coating method, the air knife coating method, the wire bar coating method, the pipe doctor method, etc. can be mentioned, and these methods can be used alone. Alternatively, it can be performed in combination.
- the polyester film of the present invention When the polyester film of the present invention is used as a surface protective film for protecting a display by locating it on the surface of a foldable display, it is preferable to have a hard coat layer on at least one surface thereof.
- the hard coat layer is preferably located on the surface side of the display on the polyester film and used in the display.
- acrylic type, siloxane type, inorganic hybrid type, urethane acrylate type, polyester acrylate type, epoxy type and the like can be used without particular limitation. Further, two or more kinds of materials can be mixed and used, and particles such as an inorganic filler and an organic filler can be added.
- the film thickness of the hard coat layer is preferably 1 to 50 ⁇ m. When it is 1 ⁇ m or more, it is sufficiently cured and the pencil hardness becomes high, which is preferable. Further, by setting the thickness to 50 ⁇ m or less, curling due to curing shrinkage of the hard coat can be suppressed, and the handleability of the film can be improved.
- a Meyer bar, a gravure coater, a die coater, a knife coater and the like can be used without particular limitation, and can be appropriately selected according to the viscosity and the film thickness.
- a curing method of the hard coat layer energy rays such as ultraviolet rays and electron beams and a curing method by heat can be used, and in order to reduce damage to the film, a curing method using ultraviolet rays and electron beams is preferable.
- the pencil hardness of the hard coat layer is preferably 3H or higher, and more preferably 4H or higher. If the pencil has a hardness of 3H or more, it will not be easily scratched and the visibility will not be deteriorated. Generally, it is preferable that the pencil hardness of the hard coat layer is high, but it may be 9H or less, 8H or less, and 6H or less can be used without any problem in practical use.
- the hard coat layer in the present invention can be used for the purpose of increasing the pencil hardness of the surface as described above to protect the display, and preferably has a high transmittance.
- the total light transmittance of the hard coat film is preferably 87% or more, more preferably 88% or more. When the transmittance is 87% or more, sufficient visibility can be obtained.
- the haze of the hard coat film is generally preferably low, preferably 3% or less.
- the haze of the hard coat film is more preferably 2% or less, and most preferably 1% or less.
- the visibility of the image can be improved.
- 0.1% or more is preferable, and 0.3% or more may be used.
- the hard coat layer may have other functions added to it.
- the present invention also includes a hard coat layer having functionality such as an antiglare layer having a certain pencil hardness, an antiglare antireflection layer, an antireflection layer, a low reflection layer, and an antistatic layer as described above. Is preferably applied.
- a hard coat layer may also be provided when used as a base film for a touch panel module.
- an ITO layer is used as the transparent electrode layer of the touch panel module, it is preferable to provide a depression rate adjusting layer between the base film and the transparent electrode layer in order to make the electrode pattern difficult to see.
- the hard coat layer itself may also serve as the refractive index adjusting layer, and the refractive index adjusting may be separately laminated.
- the polyester film for a foldable display of the present invention can be used for a foldable display arranged as a back surface protective film.
- the polyester film for a foldable display of the present invention can be arranged on a single polyester film continuous through a foldable portion of the foldable display.
- a portable terminal device having the polyester foldable display of the present invention is provided.
- Density The density was measured according to a method (density gradient tube method) conforming to JIS K 7112: 1999. (Unit: g / cm 3 ).
- the sample film is cut and measured separately in both the bending direction and the folding direction so that the vertical and horizontal directions are different, and the data in the direction in which the measured value is large is defined as the maximum heat shrinkage rate (%).
- FIG. 3 is a schematic view for explaining a method of measuring the hold angle in the bending direction, and the sample film (reference numeral 3) was cut into a width direction of 10 mm and a flow direction of 50 mm.
- Two PTFE plates (reference numeral 31) were superposed, and in the case of a 50 ⁇ m sample film, a gap was created by sandwiching a 3 mm thick PTFE plate (reference numeral 32) as a spacer.
- FIG. 4 shows an enlarged schematic view of a sample film (reference numeral 3) sandwiched between two PTFE plates (reference numeral 31 in FIG.
- the neutral surface on which neither compressive stress nor tensile stress is applied is defined as the center in the thickness direction (broken line in the figure), and the difference between the neutral surface and both surfaces is defined as strain. That is, the strain applied to both surfaces can be expressed by the following equation.
- reference numeral 41 is the diameter of the outermost surface of the sample film
- reference numeral 42 is the diameter of the neutral surface of the sample film
- reference numeral 43 is the diameter of the innermost surface of the sample film.
- the strain (1.7%) can be expressed by the following method.
- Strain (1.7%) (
- the semicircle can be obtained by the following equations when the thickness t (mm) of the sample film and the bending diameter (diameter of the outermost surface), that is, the thickness of the spacer to be used is d (mm).
- Spacer thickness d (mm) film thickness (mm) x 60
- the diameter of the outermost surface (reference numeral 41) is the same as the thickness d of the spacer and is 3 mm.
- the diameter of the innermost surface (reference numeral 43) is 2.9 mm, and the diameter of the neutral surface (reference numeral 42) is 2.95 mm.
- the outermost semicircle and the innermost semicircle can be appropriately selected.
- reaction product was transferred to a polymerization reactor, the temperature was raised to 290 ° C., and a polycondensation reaction was carried out under a high vacuum of 27 Pa or less. Polyethylene-2,6-naphthalenedicarboxylate was obtained.
- the esterification reaction device a continuous esterification reaction device consisting of a three-stage complete mixing tank having a stirrer, a splitter, a raw material charging port and a product extraction port is used, the TPA is 2 tons / hr, and the EG is TPA1.
- the amount of antimony trioxide is 2 mol per mol
- the amount of Sb atom is 160 ppm with respect to the produced PET, and these slurries are continuously supplied to the first esterification reaction can of the esterification reaction apparatus at normal pressure.
- the reaction was carried out at 255 ° C. with an average residence time of 4 hours.
- the reaction product in the first esterification reaction can is continuously taken out of the system and supplied to the second esterification reaction can, and distilled from the first esterification reaction can in the second esterification reaction can.
- the EG to be produced is supplied in an amount of 8% by mass based on the produced polymer (produced PET), and further, an EG solution containing magnesium acetate in an amount of 65 ppm of Mg atoms with respect to the produced PET and 20 ppm of P atoms with respect to the produced PET.
- An EG solution containing an amount of TMPA was added, and the reaction was carried out at normal pressure at an average residence time of 1.5 hours and at 260 ° C.
- the reaction product in the second esterification reaction can is continuously taken out of the system and supplied to the third esterification reaction can, and further contains TMPA in an amount such that the P atom is 20 ppm with respect to the produced PET.
- An EG solution was added and the reaction was carried out at normal pressure at an average residence time of 0.5 hours and at 260 ° C.
- the esterification reaction product produced in the third esterification reaction can is continuously supplied to a three-stage continuous polycondensation reaction apparatus to carry out polycondensation, and further, a filter medium of a stainless sintered body (nominal filtration accuracy of 5 ⁇ m). The particles were filtered through 90% of the particles) to obtain polyethylene terephthalate pellets (a) having an ultimate viscosity of 0.58 dl / g.
- Example 1 Pellets of polyethylene naphthalate were fed to the extruder and melted at 310 ° C. This polymer is filtered through a stainless sintered filter medium (nominal filtration accuracy of 10 ⁇ m particles 95% cut), extruded into a sheet from the base, and then cast into a casting drum with a surface temperature of 60 ° C. using an electrostatic application casting method.
- the unstretched film was prepared by contacting and cooling and solidifying.
- the above coating liquid for forming an easy-adhesion layer was applied to both sides of the unstretched film by a roll coating method, and then dried at 80 ° C. for 20 seconds. The final (after biaxial stretching) coating amount after drying was adjusted to 0.06 g / m 2.
- Examples 2 to 6 After obtaining the unstretched film in the same manner as in Example 1, the unstretched film was uniformly heated to 120 ° C. using a heating roll and heated to 135 ° C. with a non-contact heater at the MD magnification shown in Table 1. Roll stretching (longitudinal stretching) was performed. A polyester film was obtained in the same manner as in Example 1 except that the stretching ratio in the longitudinal direction shown in Table 1 was changed.
- Example 7 After obtaining the unstretched film in the same manner as in Example 1, the unstretched film was uniformly heated to 120 ° C. using a heating roll and heated to 140 ° C. with a non-contact heater at the MD magnification shown in Table 1. Roll stretching (longitudinal stretching) was performed. A polyester film was obtained in the same manner as in Example 1 except that the stretching ratio in the longitudinal direction shown in Table 1 was changed.
- the above-mentioned coating liquid for forming an easy-adhesion layer was applied to both sides of the obtained uniaxially stretched film by a roll coating method, and then dried at 80 ° C. for 20 seconds.
- the final (after biaxial stretching) coating amount after drying was adjusted to 0.06 g / m 2. Then, it is guided to a tenter, preheated at 105 ° C., laterally stretched 4.0 times at 95 ° C., fixed in width, heat-fixed at 230 ° C. for 5 seconds, and further relaxed by 4% in the width direction at 180 ° C. To obtain a polyethylene terephthalate film having a thickness of 50 ⁇ m.
- Comparative Example 2 A polyester film was obtained in the same manner as in Comparative Example 1 except that the stretching ratio in the longitudinal direction was changed to 1.4 times as shown in Table 1.
- the polyester film is arranged on the non-visual side of one continuous display via a folding portion, and is attached to a polyimide film having a barrier layer which is an organic EL substrate.
- the one using the polyester film of each example satisfied the operation and visibility as a smartphone that can be folded in half at the center and carried. In addition, there was no problem in operation and visibility even at high temperatures.
- the foldable display in which the polyester film of each comparative example is used for the same purpose seems to have caused image distortion in the foldable portion of the display as the frequency of use at high temperature increases, which is not very preferable. rice field. In addition, some were dented on the surface and scratches were confirmed.
- the foldable display using the polyester film for a foldable display of the present invention maintains mass productivity, for example, because the polyester film located on the back surface of the foldable display does not deform after being repeatedly folded. , The image is not distorted in the folded part of the display.
- a mobile terminal device or an image display device equipped with a foldable display using the polyester film of the present invention as a back surface protective film provides beautiful images, is rich in functionality, is excellent in convenience such as portability, and is reliable. Is expensive.
- Folding display 11 Bending radius 2: Polyester film for surface protection film of folding display 21: Folding part 22: Bending direction (direction orthogonal to the folding part) 3: Sample film 31: PTFE plate 32: Spacer 33: Hold angle 41: Outermost surface diameter 42: Neutral surface diameter 43: Innermost surface diameter
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Abstract
Description
しかしながら、折りたたみ型ディスプレイでは、一定の折りたたみ部分に当たる箇所が繰り返し折り曲げられるため、当該箇所のフィルムが経時的に変形し、ディスプレイに表示される画像を歪める等の問題があった。また、表面保護フィルムだけでなく、折りたたみ型ディスプレイには、偏光板、位相差板、タッチパネル基材、有機ELなどの表示セルの基材、背面の保護部材など、様々な部位にフィルムが用いられ、これらのフィルムに対しても繰り返し折りたたみに対する耐久性が求められていた。
特許文献2の発明では、膜厚を変化させるために製造工程が複雑になり、量産性に乏しい問題がある。
更に、本発明は、高温度域で折りたたみ部に折り跡が発生することのない、折りたたみ型ディスプレイ用ポリエステルフィルムを提供しようとするものである。
1. 厚みが10μm以上125μm以下のポリエステルフィルムであって、屈曲方向の高温ホールド角が70°以上の折りたたみ型ディスプレイ用ポリエステルフィルム。
(ここで、高温ホールド角とは、屈曲部分の両表面にそれぞれ1.7%のひずみがかかるように85℃加熱化で18時間固定した後につく折れあとのなす角度を指す。また、屈曲方向とは、折りたたみ部と直交する方向を指す)
2.密度が1.349g/cm3以上の第1に記載の折りたたみ型ディスプレイ用ポリエステルフィルム。
3.ポリエステルがポリエチレンナフタレートである第1または2に記載の折りたたみ型ディスプレイ用ポリエステルフィルム。
4.前記ポリエステルフィルムの少なくとも片面に易接着層を有する上記第1から3のいずれか1に記載の折りたたみ型ディスプレイ用ポリエステルフィルム。
5.上記第1から4のいずれか1に記載の折りたたみ型ディスプレイ用ポリエステルフィルムが、裏面保護フィルムとして配置された折りたたみ型ディスプレイであって、折りたたみ型ディスプレイの折りたたみ部分を介して連続した単一のポリエステルフィルムが配されている折りたたみ型ディスプレイ。
6.上記第5に記載の折りたたみ型ディスプレイを有する携帯端末機器。
本発明で言うディスプレイとは、表示装置を全般に指すものであり、ディスプレイの種類としては、LCD、有機ELディスプレイ、無機ELディスプレイ、LED、FEDなどある。例えば、折曲げ可能な構造を有するLCD、有機EL、無機ELが好ましい。特に層構成を少なくすることができる有機EL、無機ELが特に好ましく、色域の広い有機ELがさらに好ましい。
折りたたみ型ディスプレイは、連続した1枚のディスプレイが、携帯時は2つ折りなどに折りたたむことができるものである。折りたたむことでサイズを半減させ、携帯性を向上させることができる。折りたたみ型ディスプレイの屈曲半径は5mm以下が好ましく、3mm以下がさらに好ましい。屈曲半径が5mm以下であれば、折りたたんだ状態での薄型化が可能となる。屈曲半径は小さいほど良いと言える。本発明であれば、このような屈曲半径であっても、折跡を抑制できる。
屈曲半径は0.1mm以上が好ましく、0.5mm以上であってもよく、1mm以上であってもよい。屈曲半径が0.1mmであっても、携帯時には実用的に十分な薄型化を達成することができる。
折りたたんだ際の屈曲半径とは、図1の模式図における、折りたたみ型ディスプレイ1のうち、符号11の箇所を測定した値であり、折りたたんだ際の折りたたみ部分の内側の半径を意味している。なお、後述する表面保護フィルムは、折りたたみ型ディスプレイの折りたたんだ外側に位置していてもよいし、内側に位置していてもよい。
また、折りたたみ型ディスプレイは3つ折り、4つ折りであってもよく、さらに、ローラブルといわれる巻き取り型であってもよく、これらいずれも本発明でいう折りたたみ型ディスプレイの範囲に入るものとする。
また、本発明のポリエステルフィルムであれば、図1に示すような長手方向での折り曲げだけでなく、幅方向での折り曲げも可能である。
折りたたみ型有機ELディスプレイの必須構成としては、有機ELモジュールであるが、さらに必要に応じて、円偏光板、タッチパネルモジュール、表面保護フィルム、裏面保護フィルムなどが設けられる。
(有機ELモジュール)
有機ELモジュールの一般的な構成は、電極/電子輸送層/発光層/ホール輸送層/透明電極からなる。電極を設け、さらに電子輸送層、発光層、ホール輸送層を設ける基材として、本発明のポリエステルフィルムを用いることができる。特に、透明電極の基材として好ましく用いることができる。この場合、基材フィルムは高い水蒸気や酸素のバリア性が求められるため、本発明のポリエステルフィルムには、金属酸化物層などのバリア層が設けられることが好ましい。バリア性を上げるため、バリア層は複数設けられていてもよく、バリア層が設けられたポリエステルフィルムを複数枚用いても良い。
携帯端末機器にはタッチパネルを有することが好ましい。有機ELディスプレイを用いた場合、有機ELディスプレイの上部、もしくは有機ELモジュール/円偏光板間にタッチパネルモジュールが配置されていることが好ましい。タッチパネルモジュールはフィルムなどの透明基材とその上に配置された透明電極を有する。本発明のポリエステルフィルムはこの透明基材として用いることができる。タッチパネルの透明基材として用いる場合、ポリエステルフィルムにはハードコート層や屈折率調整層を設けることが好ましい。
円偏光板は、ディスプレイ内部の部材によって外光が反射され、画質が低下することを抑制する。円偏光板は直線偏光板と位相差板を有する。直線偏光板は偏光子の少なくとも視認側の面に保護フィルムを有する。偏光子の視認側とは反対の面にも保護フィルムを有していてもよく、偏光子に位相差板が直接積層されていてもよい。位相差板はポリカーボネートや環状オレフィンなどの位相差を有する樹脂フィルムや樹脂フィルムに液晶化合物からなる位相差層が設けられたものが用いられる。本発明のポリエステルフィルムは、偏光子保護フィルムや位相差板の樹脂フィルムとして用いることができる。これらの場合、本発明のポリエステルフィルムはポリエステルフィルムの遅相軸方向が偏光子の吸収軸方向と平行または直交となることが好ましい。なお、この平行または直交に対して10度、好ましくは5度までのずれは許容される。
ディスプレイに上部から衝撃が加わると、有機ELモジュールやタッチパネルモジュールの回路が断線するおそれがあるため、多くの場合、表面保護フィルムが設けられている。本発明のポリエステルフィルムはこの表面保護フィルムとして用いられる。表面保護フィルムはディスプレイの最表面に組み込まれたカバーウインドウと呼ばれるものや、使用者自身で貼り合わせ、剥離ができ、交換可能なアフターと呼ばれるものがあるが、いずれであっても本発明のポリエステルフィルムが用いられる。本発明のポリエステルフィルムを表面保護フィルムとして用いる場合、ポリエステルフィルムの少なくとも表面側にはハードコート層が積層されたものであることが好ましい。ハードコート層を視認側にして折りたたみ型ディスプレイの表面に設けられる。なお、ハードコート層は両面に設けられていてもよい。
ディスプレイの裏面側にも保護フィルムが設けられることも好ましい。具体的には有機ELモジュールの非視認側に接着層を設け、貼り合せた構成となる。本発明のポリエステルフィルムはこの裏面側の保護フィルムとして用いることができる。
これらの中でも、本発明のポリエステルフィルムは、カバーウインドウ表面保護フィルム、アフター表面保護フィルム、タッチパネルモジュールの基材フィルム、裏面保護フィルムに用いられることが好ましい。さらには、カバーウインドウ表面保護フィルム、アフター表面保護フィルムに用いられることが好ましい。
ポリエチレンナフタレート樹脂を主成分とする態様であって、他のポリエステルを混合する場合、ポリエステルフィルムにおける樹脂100重量%に対して、他のポリエステル樹脂は、40重量%以下であってよく、例えば10重量%以下であり、5重量%以下であってよく、5重量%未満が好ましい。
一方、ポリエチレンナフタレート樹脂は、ポリエステルフィルムにおける樹脂100重量%に対して、60重量%以上であってよく、90重量%以上でよく、95重量%以上であってよく、例えば、95重量%超で含まれることが好ましい。
他のポリエステル樹脂が5重量%未満であることにより、ポリエステルフィルムの結晶性を高く保持でき、高温ホールド角を良好に保持できる。
一実施態様において、ポリエステルフィルムの原料比率におけるポリエチレンナフタレートの割合は、100重量%である。
なお、本発明において、ポリエステルフィルムは、特性の異なるポリエチレンナフタレートを複数種含んでもよい。
ポリエチレンナフタレートの割合を高くすることで、ポリエステルフィルムが、高温度領域でも繰り返し折りたたんだ後の変形を起こさず、ディスプレイの折りたたみ部分での画像の乱れを抑制できる。更に、本発明のポリエステルフィルム用いた折りたたみ型ディスプレイを搭載した携帯端末機器は、美しい画像を提供し、機能性に富み、携帯性等の利便性に優れたものとなる。
ましい。
例えば、少なくとも1種類以上の樹脂ペレットの極限粘度は、0.40~0.8dl/gであり、極限粘度は、0.40~0.7dl/gであってもよい。
ヘイズは、3%以下が好ましく、2%以下がさらに好ましく、1%以下が特に好ましい。ヘイズが3%以下であれば、画像の視認性を向上させることができる。ヘイズの下限は小さいほどよいが、安定した生産の面からは0.1%以上が好ましく、0.3%以上であってもよい。
表面凹凸を形成する方法としては、表層のポリエステル樹脂層に粒子を配合する方法で形成でき、また、粒子入りのコート層を製膜途中でコーティングすることで形成できる。
2%以下の熱収縮率あれば、有機ELディスプレイ自体の発熱による寸法変化を抑制することができる。熱収縮率は低いほどよいと言えるが、-1%以上であることが好ましく、0%以上であることが好ましい。ここでのマイナスは加熱後に膨張したことを意味し、-1%を下回る場合も平面不良となる場合がある。
なお、PETフィルムの代わりにポリエチレンナフタレート(PEN)フィルムを用いる態様においても、同様の方法で、本発明に係るポリエステルフィルムを製造できる。
本発明において、ポリエステルフィルムの長手方向(機械流れ方向)及び幅方向の少なくともいずれか一方向の屈折率は1.610以上1.750以下であることが好ましく、例えば、1.610以上1.710以下であり、更に好ましくは、1.630以上1.680以下である。
一態様において、ポリエステルフィルムの長手方向の屈折率が1.610以上であることにより、結晶化度を効率的に向上させることができ、高温ホールド角を向上させることができる。1.750以下であると屈曲時の応力を下げることができ、室温時のホールド角、高温ホールド角どちらも向上させることができる。
また、この態様とは逆に、ポリエステルフィルムの幅方向の屈折率が上記範囲内である場合、ポリエステルフィルムの長手方向の屈折率は、ポリエステルフィルムの幅方向の屈折率よりも高いことが望ましい。
ポリエステルフィルムの屈曲方向の屈折率は、1.610以上1.750以下であることが好ましく、例えば、1.610以上1.710以下であり、1.630以上1.680以下であることがより好ましい。
ここで、屈曲方向とは、図2のポリエステルフィルム(符号2)上の符号22に示すように、折りたたみ型ディスプレイの用途において想定される折りたたみ部(符号21)と直交する方向を指している。
長手方向及び幅方向の少なくともいずれか一方向の屈折率が1.610以上1.750以下であると、繰り返し折りたたんだ際の変形が少なく、折りたたみ型ディスプレイの画質を低下させるおそれがなく好ましい。
ポリエステルフィルムの屈曲方向の屈折率は、1.630~1.680であることがより好ましい。もちろん、その方向は前記の屈曲方向であることが好ましい。1.610以上であると結晶化度を効率的に向上させることができ高温ホールド角を向上させることができる。1.750以下であると屈曲時の応力を下げることができ、室温時のホールド角、高温ホールド角どちらも向上させることができる。
ポリエステルフィルムの屈折率は、延伸倍率、延伸温度を調節することで効果的に調節することができる。また、屈折率の調整のために延伸方向の緩和工程、多段延伸を用いても良い。多段延伸を行う場合には、1段目の延伸倍率よりも2段目以降の延伸倍率を高くすることが好ましい。
上記のポリエステルフィルムの屈折率が1.610以上1.750以下である方向と直交する方向の屈折率は、1.750~1.870であることが好ましい。即ち、屈曲方向と直交する方向(折りたたみ部の方向)の屈折率が1.750以上1.870以下であることが好ましい。1.750以上1.870以下にすることで屈曲方向に折りたたんだ際の変形を少なくすることができる。1.870以下にすることで折りたたみ部の方向にクラックが入ることを抑制でき、更に破断することを抑制できる。また、延伸後の巻取り工程における破断を抑制することができる。1.750以上にすることで密度を上げることができ、高温ホールド角を向上させることができる。
例えば、ポリエステルフィルムの長手方向が屈曲方向である場合、屈曲方向と直交する方向(折りたたみ部の方向)は、ポリエステルフィルムの幅方向が、屈曲方向と直交する方向(折りたたみ部の方向)に該当する。
屈曲方向と直交する方向の屈折率は、1.770~1.830がより好ましい。
また、屈曲方向の屈折率と、屈曲方向と直交する方向(折りたたみ部の方向)の屈折率とを比較した場合、屈曲方向の屈折率が低いことが望ましい。
この態様により、屈曲方向に折りたたんだ際の変形を少なくすることができる。また、折りたたみ部の方向にクラックが入ることを抑制でき、更に破断することを抑制できる。その上、延伸後の巻取り工程における破断を抑制することができる。加えて、密度を上げることができ、高温ホールド角を向上させることができる。
屈曲方向と直交する方向の屈折率を調整する方法として、延伸倍率、延伸予熱温度、延伸温度、多段延伸、フィルム弛緩が挙げられる。延伸倍率は3.3~5.0倍であることが好ましく、より好ましくは3.5~4.5倍である。また、屈曲方向と直交する方向の延伸予熱温度は125~145℃であることが好ましい。屈曲方向と直交する方向に多段延伸する場合、1段目より2段目以降の延伸倍率を高くする方が好ましい。フィルム弛緩は機械流れ方向(長手方向)、垂直方向(幅方向)に何れにおいても0~10%行っても良い。
厚み方向の屈折率は1.520以下であることが好ましい。より好ましくは1.515以下、更に好ましくは1.510以下、特に好ましくは1.505以下、最も好ましくは1.500以下である。厚み方向の屈折率は低いことが好ましいが、安定した生産の面で1.3以上が好ましく、さらには1.4以上であってもよい。特に好ましくは1.410以上である。
ポリエステルフィルムの密度は1.349g/cm3以上であることが好ましい。1.350g/cm3以上であることがより好ましい。1.350g/cm3以上にすることで高温ホールド角を向上させることができる。密度は高いほど好ましく、フィルム中の粒子の有無等によっても多少左右されるが、1.40g/cm3以下であることが好ましく、さらには1.395g/cm3以下がより好ましい。
ポリエステルフィルムの密度が1.349g/cm3以上であることで、本発明のポリエステルフィルムの結晶化を十分にでき、85℃での変形を抑制できる。また、熱収縮率が高くなることを抑制でき、デバイスの発熱による寸法変化を抑制できる。
製膜時の熱固定温度を210~270℃に設定することで結晶化を進行させ、上記範囲内で密度を効果的に増大させることができる。
屈曲方向の高温ホールド角は、71°以上、例えば、72°以上である。高ければ高いほうがよく、180°が最も好ましいが、屈曲方向の高温ホールド角は、180°以下であってよく、例えば170°以下でも十分な機能を有する。
屈曲方向の高温ホールド角が上記範囲内であることにより、85℃での変形を抑制できる。また、熱収縮率が高くなることを抑制でき、デバイスの発熱による寸法変化を抑制できる。このため、本発明であれば、高温度領域でも繰り返し折りたたんだ後の変形を起こさず、ディスプレイの折りたたみ部分での画像の乱れを抑えることができる。更に、ポリエステルフィルム用いた折りたたみ型ディスプレイを搭載した携帯端末機器は、美しい画像を提供し、機能性に富み、携帯性等の利便性に優れたものである。
なお、屈曲方向の高温ホールド角の測定方法は、実施例において例示する。
本発明において、ポリエステルフィルムとハードコート層などとの接着性を向上させるため、本発明のポリエステルフィルムの少なくとも片面に、易接着層を積層することも好ましい。易接着層は、易接着層形成のための塗布液を未延伸又は縦方向の1軸延伸フィルムの片面または両面に塗布した後、必要に応じて熱処理乾燥し、さらに延伸されていない少なくとも一方向に延伸して得ることができる。二軸延伸後にも熱処理することができる。最終的な易接着層の塗布量は、0.005~0.20g/m2に管理することが好ましい。塗布量が0.005g/m2以上であると、接着性が得られて好ましい。一方、塗布量が0.20g/m2以下であると、耐ブロッキング性が得られて好ましい。
本発明のポリエステルフィルムを折りたたみ型ディスプレイの表面に位置させてディスプレイを保護する表面保護フィルムとして用いる場合は、その少なくとも一方の表面にハードコート層を有していることが好ましい。ハードコート層は、ポリエステルフィルム上のディスプレイ表面側に位置させてディスプレイにおいて用いられることが好ましい。ハードコート層を形成する樹脂としては、アクリル系、シロキサン系、無機ハイブリッド系、ウレタンアクリレート系、ポリエステルアクリレート系、エポキシ系など特に限定なく使用できる。また、2種類以上の材料を混合して用いることもできるし、無機フィラーや有機フィラーなどの粒子を添加することもできる。
ハードコート層の膜厚としては、1~50μmが好ましい。1μm以上であると十分に硬化し、鉛筆硬度が高くなり好ましい。また厚みを50μm以下にすることで、ハードコートの硬化収縮によるカールを抑制し、フィルムのハンドリング性を向上させることができる。
ハードコート層の塗布方法としては、マイヤーバー、グラビアコーター、ダイコーター、ナイフコーターなど特に限定なく使用でき、粘度、膜厚に応じて適宜選択できる。
ハードコート層の硬化方法としては、紫外線、電子線などのエネルギー線や、熱による硬化方法など使用でき、フィルムへのダメージを軽減させるために、紫外線や電子線などによる硬化方法が好ましい。
ハードコート層の鉛筆硬度としては、3H以上が好ましく、4H以上が更に好ましい。3H以上の鉛筆硬度があれば、容易に傷がつくことはなく、視認性を低下させない。一般にハードコート層の鉛筆硬度は高い方が好ましいが9H以下で構わず、8H以下でも構わず、6H以下でも実用上は問題なく使用できる。
本発明におけるハードコート層は、上述のような表面の鉛筆硬度を高めてディスプレイの保護をする目的に使用できるものであり、透過率が高いことが好ましい。ハードコートフィルムの全光線透過率としては、87%以上が好ましく、88%以上がさらに好ましい。透過率が87%以上あれば、十分な視認性が得られる。ハードコートフィルムの全光線透過率は、一般的に高いほど好ましいが、安定した生産の面から99%以下が好ましく、97%以下であってもよい。また、ハードコートフィルムのヘイズは、一般的に低いことが好ましく、3%以下が好ましい。ハードコートフィルムのヘイズは2%以下がより好ましく、1%以下が最も好ましい。ヘイズが3%以下であれば、画像の視認性を向上させることができる。ヘイズは一般的には低いほどよいが、安定した生産の面から0.1%以上が好ましく、0.3%以上であってもよい。
フィルムまたはポリエステル樹脂を粉砕して乾燥した後、フェノール/テトラクロロエタン=60/40(質量比)の混合溶媒に溶解した。この溶液に遠心分離処理を施して無機粒子を取り除いた後に、ウベローデ粘度計を用いて、30℃で0.4(g/dl)の濃度の溶液の流下時間及び溶媒のみの流下時間を測定し、それらの時間比率から、Hugginsの式を用い、Hugginsの定数が0.38であると仮定して極限粘度を算出した。ポリエチレンテレフタレート(PET)、ポリエチレンナフタレート(PEN)のいずれにも同じ計算式を用いて評価した。
メトリコン社製レーザー屈折計(モデル2010プリズムカプラ-)を用いて、1枚のサンプルフィルムを内蔵圧力計40目盛の圧力で挟み、波長633nmのレーザー光にて測定を行い、スペクトラムチャートを得た。得られたスペクトラムチャート上で、検知器出力が急激に低下する点を読み取り、この値を屈折率とした。測定モードTEにて長手方向と幅方向の屈折率、TMにて厚み方向の屈折率を測定した。
ヘイズメーター(日本電色工業社製、NDH5000)を用いて測定した。
JIS K 7112:1999準拠の方法(密度勾配管法)に従って密度を測定した。(単位:g/cm3)。
試料フィルムをタテ10mm×ヨコ250mmにカットし、長辺を測定したい方向に合わせて、200mm間隔で印をつけ、5gの一定張力下で印の間隔Aを測った。続いて、試料フィルムを無荷重で150℃の雰囲気のオーブン中で30分間放置した後、オーブンから取り出し室温まで冷却した。その後、5gの一定張力下で印の間隔Bを求め、下記式により熱収縮率(%)を求めた。なお、上記熱収縮率は試料フィルムの幅方向に3等分した位置で測定し、3点の平均値を熱収縮率(%)とする
熱収縮率(%)=[(A-B)×100]/A
屈曲方向と折りたたみ方向の双方向についてそれぞれ別個に試料フィルムのタテ、ヨコが異なるようにカットして測定し、測定値が大きい方向のデータを最大熱収縮率(%)とする。
屈曲部分の両表面にそれぞれ1.7%のひずみがかかるよう固定したときにつく折れあとの強さを評価する。
図3は、屈曲方向のホールド角の測定方法を説明するための模式図であり、試料フィルム(符号3)を幅方向10mm、流れ方向50mmにカットした。PTFE板2枚(符号31)を重ね合わせ、50μmの試料フィルムの場合、スペーサーとして厚さ3mmのPTFE板(符号32)を間にはさむことですきまを作った。試料の両端に両面テープを貼り、屈曲させた状態でPTFE板の3mmのすきまにはさみ、両端を両面テープで固定した。85℃dry環境下に18時間置いた後、2枚のPTFE板(符号31)の間から取り出した後5分後にフィルムについた折れ痕のなす角度(符号33)を測定した。この角度を高温ホールド角とする。
ひずみを一定とするため、フィルムの厚みのよってスペーサーとして用いるPTFE板の厚み32を変更する。
図4に、2枚のPTFE板(図3の符号31)の間に挟まれた状態の試料フィルム(符号3)の拡大模式図を示す。上記の圧縮応力、引張応力ともにかからない中立面を厚み方向の中心(図中の破線)と定め、中立面と両表面の差をひずみとする。つまり両表面にかかるひずみは以下の式で表すことができる。
なお、図4において、符号41は、試料フィルムにおける最外面の直径であり、符号42は、試料フィルムにおける上記中立面の直径であり、符号43は、試料フィルムにおける最内面の直径を示す。
ひずみ(1.7%)
=(|最外面または最内面の半円周-中立面の半円周|/中立面の半円周)×100
ここで半円周は試料フィルムの厚みt(mm)、屈曲直径(最外面の直径)即ち、用いるスペーサーの厚みをd(mm)としたとき以下の式でそれぞれ求めることができる。
最外面の半円周=d×π/2
中立面の半円周=(d-t)×π/2
最内面の半円周=(d-2t)×π/2
以上より、ひずみ1.7%に定めるとき、試料フィルムの厚みt(mm)、屈曲直径つまり用いるスペーサーの厚みをd(mm)とし、用いるスペーサー(PTFE板)の厚みは以下の式より決定する。代表的なフィルム厚みに対するスペーサー厚みは、例えば、以下のように示される。
スペーサー厚みd(mm)=フィルム厚み(mm)×60
例えば、上記の厚みが50μmの試料フィルムの場合、最外面の直径(符号41)はスペーサーの厚みdと同一であって3mmである。最内面の直径(符号43)は2.9mmであり、中立面の直径(符号42)は、2.95mmである。ここで、上記ひずみを示す式において、最外面の半円周、最内面の半円周は適宜選択できる。
ナフタレン-2,6-ジカルボン酸ジメチル100部およびエチレングリコール60部を、エステル交換触媒として酢酸マンガン四水塩0.03部を使用し、150℃から238℃に徐々に昇温させながら120分間エステル交換反応を行った。途中、反応温度が170℃に達した時点でリン酸トリメチル(エチレングリコール中で135℃、5時間、0.11~0.16MPaの加圧下で加熱処理した溶液として添加:リン酸トリメチル換算量で0.023部)を添加し、エステル交換反応終了後、三酸化アンチモン0.024部を添加した。その後反応生成物を重合反応器に移し、290℃まで昇温し、27Pa以下の高真空下にて重縮合反応を行い、固有粘度が0.48dl/gの、実質的に粒子を含有しない、ポリエチレン-2,6-ナフタレンジカルボキシレートを得た。
エステル化反応装置として、攪拌装置、分縮器、原料仕込口および生成物取り出し口を有する3段の完全混合槽よりなる連続エステル化反応装置を用い、TPAを2トン/hrとし、EGをTPA1モルに対して2モルとし、三酸化アンチモンを生成PETに対してSb原子が160ppmとなる量とし、これらのスラリーをエステル化反応装置の第1エステル化反応缶に連続供給し、常圧にて平均滞留時間4時間で、255℃で反応させた。
次いで、上記第1エステル化反応缶内の反応生成物を連続的に系外に取り出して第2エステル化反応缶に供給し、第2エステル化反応缶内に第1エステル化反応缶から留去されるEGを生成ポリマー(生成PET)に対し8質量%供給し、さらに、生成PETに対してMg原子が65ppmとなる量の酢酸マグネシウムを含むEG溶液と、生成PETに対してP原子が20ppmのとなる量のTMPAを含むEG溶液を添加し、常圧にて平均滞留時間1.5時間で、260℃で反応させた。次いで、上記第2エステル化反応缶内の反応生成物を連続的に系外に取り出して第3エステル化反応缶に供給し、さらに生成PETに対してP原子が20ppmとなる量のTMPAを含むEG溶液を添加し、常圧にて平均滞留時間0.5時間で、260℃で反応させた。上記第3エステル化反応缶内で生成したエステル化反応生成物を3段の連続重縮合反応装置に連続的に供給して重縮合を行い、さらに、ステンレス焼結体の濾材(公称濾過精度5μm粒子90%カット)で濾過し、極限粘度0.58dl/gのポリエチレンテレフタレートペレット(a)を得た。
撹拌機、ジムロート冷却器、窒素導入管、シリカゲル乾燥管、及び温度計を備えた4つ口フラスコに、1,3-ビス(イソシアネートメチル)シクロヘキサン72.96質量部、ジメチロールプロピオン酸12.60質量部、ネオペンチルグリコール11.74質量部、数平均分子量2000のポリカーボネートジオール112.70質量部、及び溶剤としてアセトニトリル85.00質量部、N-メチルピロリドン5.00質量部を投入し、窒素雰囲気下、75℃において3時間撹拌し、反応液が所定のアミン当量に達したことを確認した。次に、この反応液を40℃にまで降温した後、トリエチルアミン9.03質量部を添加し、ポリウレタンプレポリマーD溶液を得た。次に、高速攪拌可能なホモディスパーを備えた反応容器に、水450gを添加して、25℃に調整して、2000min-1で攪拌混合しながら、イソシアネート基末端プレポリマーを添加して水分散した。その後、減圧下で、アセトニトリルおよび水の一部を除去することにより、固形分35質量%の水溶性ポリウレタン樹脂(A)を調製した。
温度計、窒素ガス導入管、還流冷却器、滴下ロート、および攪拌機を備えたフラスコにイソホロンジイソシアネート200質量部、カルボジイミド化触媒の3-メチル-1-フェニル-2-ホスホレン-1-オキシド4質量部を投入し、窒素雰囲気下、180℃において10時間撹拌し、イソシアネート末端イソホロンカルボジイミド(重合度=5)を得た。次いで、得られたカルボジイミド111.2g、ポリエチレングリコールモノメチルエーテル(分子量400)80gを100℃で24時間反応させた。これに水を50℃で徐々に加え、固形分40質量%の黄色透明な水溶性カルボジイミド化合物(B)を得た。
下記の塗剤を混合し、塗布液を作成した。
水 16.97質量部
イソプロパノール 21.96質量部
ポリウレタン樹脂(A) 3.27質量部
水溶性カルボジイミド化合物(B) 1.22質量部
粒子 0.51質量部
(平均粒径40nmのシリカゾル、固形分濃度40質量%)
界面活性剤 0.05質量部
(シリコーン系、固形分濃度100質量%)
ポリエチレンナフタレートのペレットを押出機に供給し、310℃で融解した。このポリマーを、ステンレス焼結体の濾材(公称濾過精度10μm粒子95%カット)で濾過し、口金よりシート状にして押し出した後、静電印加キャスト法を用いて表面温度60℃のキャスティングドラムに接触させ冷却固化し、未延伸フィルムを作った。未延伸フィルムに上記の易接着層形成用塗布液をロールコート法で両面に塗布した後、80℃で20秒間乾燥した。なお、最終(二軸延伸後)の乾燥後の塗布量が0.06g/m2になるように調整した。その後、テンターに導き140℃で予熱後、135℃で4.2倍に横延伸し、幅固定して240℃で5秒間の熱固定を施し、さらに180℃で幅方向に1%緩和させることにより、厚み50μmポリエチレンナフタレートフィルムを得た。評価結果を表1に示す。
実施例1と同様に未延伸フィルムを得た後、未延伸フィルムを、加熱ロールを用いて120℃に均一加熱し、非接触ヒーターで135℃に加熱して表1に記載のMD倍率でのロール延伸(縦延伸)を行った。表1に記載の長手方向の延伸倍率に変更した他は実施例1と同様にしてポリエステルフィルムを得た。
実施例1と同様に未延伸フィルムを得た後、未延伸フィルムを、加熱ロールを用いて120℃に均一加熱し、非接触ヒーターで140℃に加熱して表1に記載のMD倍率でのロール延伸(縦延伸)を行った。表1に記載の長手方向の延伸倍率に変更した他は実施例1と同様にしてポリエステルフィルムを得た。
ポリエチレンテレフタレートのペレットを押出機に供給し、285℃で融解した。このポリマーを、ステンレス焼結体の濾材(公称濾過精度10μm粒子95%カット)で濾過し、口金よりシート状にして押し出した後、静電印加キャスト法を用いて表面温度30℃のキャスティングドラムに接触させ冷却固化し、未延伸フィルムを作った。この未延伸フィルムを、加熱ロールを用いて75℃に均一加熱し、非接触ヒーターで85℃に加熱して1.4倍のロール延伸(縦延伸)を行った。
得られた一軸延伸フィルムに上記の易接着層形成用塗布液をロールコート法で両面に塗布した後、80℃で20秒間乾燥した。なお、最終(二軸延伸後)の乾燥後の塗布量が0.06g/m2になるように調整した。その後、テンターに導き105℃で予熱後、95℃で4.0倍に横延伸し、幅固定して230℃で5秒間の熱固定を施し、さらに180℃で幅方向に4%緩和させることにより、厚み50μmポリエチレンテレフタレートフィルムを得た。
表1のように長手方向の延伸倍率を1.4倍に変更した他は比較例1と同様にしてポリエステルフィルムを得た。
一方、各比較例のポリエステルフィルムを同じ用途で使用した折りたたみ型ディスプレイは、高温化での使用頻度が増えるに従って、ディスプレイの折りたたみ部で画像の歪を生じてきたように感じ、あまり好ましいものではなかった。また、表面に凹み、キズが確認されるものもあった。
11: 屈曲半径
2 : 折りたたみ型ディスプレイの表面保護フィルム用ポリエステルフィルム
21: 折りたたみ部
22: 屈曲方向(折りたたみ部と直交する方向)
3 : 試料フィルム
31: PTFE板
32: スペーサー
33: ホールド角
41: 最外面の直径
42: 中立面の直径
43: 最内面の直径
Claims (6)
- 厚みが10~125μmのポリエステルフィルムであって、屈曲方向の高温ホールド角が70°以上の折りたたみ型ディスプレイ用ポリエステルフィルム:
ここで、高温ホールド角とは、屈曲部分の両表面にそれぞれ1.7%のひずみがかかるように85℃加熱化で18時間固定した後につく折れあとのなす角度を指す。また、屈曲方向とは、折りたたみ部と直交する方向を指す。 - 密度が1.349g/cm3以上の請求項1に記載の折りたたみ型ディスプレイ用ポリエステルフィルム。
- ポリエステルがポリエチレンナフタレートである請求項1または2に記載の折りたたみ型ディスプレイ用ポリエステルフィルム。
- 前記ポリエステルフィルムの少なくとも片面に易接着層を有する請求項1から3のいずれか1項に記載の折りたたみ型ディスプレイ用ポリエステルフィルム。
- 請求項1から4のいずれか1項に記載の折りたたみ型ディスプレイ用ポリエステルフィルムが、裏面保護フィルムとして配置された折りたたみ型ディスプレイであって、
前記ポリエステルフィルムが、折りたたみ型ディスプレイの折りたたみ部分を介して連続した単一のポリエステルフィルムとして配置されている、折りたたみ型ディスプレイ。 - 請求項5に記載の折りたたみ型ディスプレイを有する携帯端末機器。
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