Hard-coated film, its manufacturing method, and image display device

Abstract

This hard coating film (10) is provided with a hard coating layer (2) on at least one surface of a base material film (1). The base material film is a polyimide film that contains a polyimide resin; and the hard coating layer is formed of a cured product of a photocurable resin composition. Since both of the hard coating layer and the polyimide film contain an ultraviolet absorbent, the hard coating film has high hardness and excellent light resistance. This hard coating film is applicable to a surface protective material that is arranged on the viewing-side surface of an image display panel, or the like.

Description

[Technical Field]

[0001] The present invention relates to a hard-coated film having a hard-coat layer on at least one surface of a transparent polyimide film, a method for producing the same, and an image display device having the hard-coated film. [Background technology]

[0002] As mobile devices become thinner and lighter, smartphones and other devices are becoming more and more popular. In recent years, flexible displays, particularly foldable mobile devices equipped with organic EL panels using flexible substrates, have been proposed as a way to achieve both larger screens and portability.

[0003] In flexible devices, not only the display substrate but also surface protection materials such as cover windows must be flexible, and the use of a hard coat film in which a hard coat layer is provided on the surface of a polyimide film that is excellent in transparency, surface hardness, and flexural durability has been proposed (for example, Patent Documents 1 and 2). Patent Document 1 discloses that the hard coat layer is formed using a photocurable resin composition containing a reactive urethane acrylate, a photoradical polymerization initiator, and an ultraviolet absorber. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-226712 [Patent Document 2] International Publication No. 2020 / 040209 Summary of the Invention [Problem to be solved by the invention]

[0005] Since the surface protective material of a display device is located as the outermost layer and is therefore easily exposed to external light, the hard coat film used as the surface protective material is required to have high light resistance and to show little change in optical properties and mechanical strength even when exposed to ultraviolet rays, etc. [Means for solving the problem]

[0006] One aspect of the present invention is a hard-coat film comprising a substrate film and a hard-coat layer provided on at least one surface thereof. The substrate film is a polyimide film containing a polyimide resin, and the hard-coat layer is made of a cured product of a photocurable resin composition. Each of the hard-coat layer and the polyimide film contains an ultraviolet absorber.

[0007] The ultraviolet absorber contained in the polyimide film and the hard coat layer is preferably a benzotriazole compound or a triazine compound. The content of the ultraviolet absorber in the polyimide film is preferably 0.1 to 4.5 wt %. The content of the ultraviolet absorber in the hard coat layer is preferably 0.1 to 4.5 wt %.

[0008] The hard coat layer has a thickness of, for example, 0.5 to 100 μm, and the polyimide film has a thickness of, for example, 5 to 100 μm.

[0009] The polyimide resin of the polyimide film is preferably soluble in dichloromethane. For example, a solution containing a dichloromethane-soluble polyimide resin and an ultraviolet absorber is applied to a substrate, and the solvent is removed to obtain a polyimide film containing an ultraviolet absorber. A photocurable resin composition (hard coat composition) containing a photocurable resin and a photopolymerization initiator is applied to the surface of this polyimide film, and the resulting composition is photocured to produce a hard coat film having a hard coat layer on the surface of the polyimide film.

[0010] The hard coat composition may be photocationically polymerizable. An example of a photocurable resin having photocationic polymerizability is a polysiloxane compound having an epoxy group. The hard coat composition contains, for example, a photocurable resin having photocationic polymerizability, a photocationic polymerization initiator (photoacid generator), and an ultraviolet absorber.

[0011] The hard coat film can be used, for example, as a surface protective material disposed on the viewer side surface of an image display panel in an image display device. The image display device may be foldable. [Effects of the Invention]

[0012] The hard coat film contains an ultraviolet absorber in both the polyimide film and the hard coat layer, which suppresses photodegradation of the polyimide. Therefore, even when exposed to ultraviolet rays, etc., there is little change in the optical properties and mechanical strength, and the film has excellent light resistance. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view showing an example of the configuration of a hard coat film. DETAILED DESCRIPTION OF THE INVENTION

[0014] 1 is a cross-sectional view of a hard coat film 10 having a hard coat layer 2 provided on one main surface of a polyimide film 1. A hard coat composition is applied to the main surface of the polyimide film 1 as a film substrate, and then cured to form the hard coat layer 2. The hard coat layer may be provided on only one main surface of the polyimide film, or on both surfaces of the polyimide film.

[0015] Both the polyimide film 1 and the hard coat layer 2 contain an ultraviolet absorber. When both the polyimide film and the hard coat layer contain an ultraviolet absorber, light resistance is improved, and yellowing of the hard coat film tends to be suppressed even after long-term exposure to ultraviolet light.

[0016] Examples of the ultraviolet absorber contained in the polyimide film and the hard coat layer include triazine-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, hydroxybenzoate-based ultraviolet absorbers, etc. Among these, benzotriazole-based ultraviolet absorbers and triazine-based ultraviolet absorbers are preferred because they have little absorption of visible light and can provide good light resistance.

[0017] Specific examples of benzotriazole-based ultraviolet absorbers include 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (ADEKA's "ADK STAB LA-24"), 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (ADEKA's "ADK STAB LA-29"), 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol] (ADEKA's "ADK STAB LA-31G" and "ADK STAB LA-31RG"), and 2-(2H-benzotriazol-2-yl)-p-cresol (ADEKA's "ADK STAB LA-31G"). LA-32"), 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol (BASF "TINUVIN 571"), 2-(2H-benzotriazol-2-yl)-p-cresol (BASF "TINUVIN P"), 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole (BASF "TINUVIN PS"), 2-(2H-benzotriazol-2-yl)-4-6-bis(1-methyl-1-phenylethyl)phenol (BASF "TINUVIN 234"), 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol (BASF "TINUVIN 326"), 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (BASF "TINUVIN 328"), 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (BASF "TINUVIN 329"), 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (BASF "TINUVIN 900"), 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (BASF "TINUVIN 928"), 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimido-methyl)-5-methylphenyl]benzotriazole (Sumitomo Chemical Co., Ltd., "Sumisorb 250"), etc.

[0018] Specific examples of triazine-based ultraviolet absorbers include 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]-phenol (ADEKA's "ADK STAB LA-46"), 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine (ADEKA's "ADK STAB LA-F70"), and the reaction product of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-hydroxyphenyl with [(alkyloxy)methyl]oxirane (BASF's "TINUVIN"). 400"), reaction products of 2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine with (2-ethylhexyl)-glycidic acid ester (BASF "TINUVIN 405"), (2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine (BASF "TINUVIN 460"), 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine (BASF "TINUVIN 479"), 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]-phenol (BASF "TINUVIN 577"), bisethylhexyloxyphenol methoxyphenyl triazine (BASF "Tinosorb S"), and the like.

[0019] Preferred embodiments of the polyimide film and the hard coat layer will be described below. Unless otherwise specified, the compounds exemplified in this specification may be used alone or in combination (coexistence) of two or more kinds.

[0020] [Polyimide film] <Polyimide composition> The polyimide film 1 contains a polyimide resin. Polyimides are generally obtained by cyclodehydration of polyamic acid, which is obtained by reacting a tetracarboxylic dianhydride (hereinafter sometimes simply referred to as "acid dianhydride") with a diamine. That is, polyimides have a structure derived from the acid dianhydride and a structure derived from the diamine.

[0021] In the production of transparent polyimide films, a method (solution casting method) is preferably used, in which a solution of a polyimide resin dissolved in an organic solvent is applied to a substrate and the solvent is dried and removed by heating. Therefore, it is preferable that the polyimide is not only transparent but also soluble in organic solvents. From the viewpoint of productivity of polyimide films, it is preferable to use a low-boiling solvent such as dichloromethane for the solution casting method. Therefore, it is preferable that the polyimide resin is soluble in dichloromethane.

[0022] An example of a polyimide soluble in dichloromethane is a polyimide containing, as an acid dianhydride component, a tetracarboxylic dianhydride represented by general formula (1) and a tetracarboxylic dianhydride having a cyclobutane structure, and containing, as a diamine component, a fluoroalkyl-substituted benzidine.

[0023] [ka]

[0024] In general formula (1), n ​​is 1 or 2. 1 ~R 4 are each independently a hydrogen atom, a fluorine atom, an alkyl group or a fluoroalkyl group having 1 to 20 carbon atoms, and R 1 ~R 4 At least one of them is an alkyl group or a fluoroalkyl group having 1 to 20 carbon atoms.

[0025] An example of the polyimide composition is one that contains 40 mol % to 100 mol % of fluoroalkyl-substituted benzidine relative to 100 mol % of the total diamine components, 40 mol % to 85 mol % of an acid dianhydride having an ester structure represented by formula (1) relative to 100 mol % of the total acid dianhydride components, and 15 mol % to 60 mol % of an acid dianhydride having a cyclobutane structure.

[0026] (Acid dianhydride with ester structure) The compound represented by the above general formula (1) is an acid dianhydride having an ester structure. 1 ~R 4 When is an alkyl group or a fluoroalkyl group, examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a cyclobutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a cyclopentyl group, an n-hexyl group, a cyclohexyl group, etc. Examples of the fluoroalkyl group include a monofluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a pentafluoroethyl group, etc.

[0027] Among the compounds represented by general formula (1), bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diyl (TAHMBP) represented by the following formula (2) is preferred because it can produce polyimides that exhibit high solubility in dichloromethane.

[0028] [ka]

[0029] (Cyclobutane-containing dianhydride) Specific examples of acid dianhydrides having a cyclobutane structure include 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,4-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dipropyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,4-dipropyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, cyclobutane-1,2:3,4-bis(tetramethylene)-1,2,3,4-tetracarboxylic dianhydride, etc. Among these, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) is preferred.

[0030] (Fluoroalkyl-substituted benzidine) Specific examples of fluoroalkyl-substituted benzidines include 2-fluorobenzidine, 3-fluorobenzidine, 2,3-difluorobenzidine, 2,5-difluorobenzidine, 2,6-difluorobenzidine, 2,3,5-trifluorobenzidine, 2,3,6-trifluorobenzidine, 2,3,5,6-tetrafluorobenzidine, 2,2'-difluorobenzidine, 3,3'-difluorobenzidine, 2,3'-difluorobenzidine, 2,2',3-trifluorobenzidine, 2,3,3'-trifluorobenzidine, 2,2',5 -Trifluorobenzidine, 2,2',6-trifluorobenzidine, 2,3',5-trifluorobenzidine, 2,3',6-trifluorobenzidine, 2,2',3,3'-tetrafluorobenzidine, 2,2',5,5'-tetrafluorobenzidine, 2,2',6,6'-tetrafluorobenzidine, 2,2',3,3',6,6'-hexafluorobenzidine, 2,2',3,3',5,5',6,6'-octafluorobenzidine, 2-(trifluoromethyl)benzidine, 3-(trifluoromethyl)benzidine, 2,3 -Bis(trifluoromethyl)benzidine, 2,5-bis(trifluoromethyl)benzidine, 2,6-bis(trifluoromethyl)benzidine, 2,3,5-tris(trifluoromethyl)benzidine, 2,3,6-tris(trifluoromethyl)benzidine, 2,3,5,6-tetrakis(trifluoromethyl)benzidine, 2,2'-bis(trifluoromethyl)benzidine, 3,3'-bis(trifluoromethyl)benzidine, 2,3'-bis(trifluoromethyl)benzidine, 2,2',3-bis(trifluoromethyl)benzidine bis(trifluoromethyl)benzidine, 2,3,3'-tris(trifluoromethyl)benzidine, 2,2',5-tris(trifluoromethyl)benzidine, 2,2',6-tris(trifluoromethyl)benzidine, 2,3',5-tris(trifluoromethyl)benzidine, 2,3',6-tris(trifluoromethyl)benzidine, 2,2',3,3'-tetrakis(trifluoromethyl)benzidine, 2,2',5,5'-tetrakis(trifluoromethyl)benzidine, 2,2',6,6'-tetrakis(trifluoromethyl)benzidine, and the like.

[0031] Among these, fluoroalkyl-substituted benzidines having a fluoroalkyl group at the 2-position of the biphenyl skeleton are preferred, and 2,2'-bis(trifluoromethyl)benzidine is more preferred. By having a fluoroalkyl group at the 2-position of the biphenyl skeleton, the aromatic ring of the biphenyl skeleton is twisted due to the steric hindrance of the fluoroalkyl group, and the electron-withdrawing properties of the fluoroalkyl group reduce coloration.

[0032] (Other acid dianhydrides and diamines) The polyimide may contain an acid dianhydride component and a diamine component other than those mentioned above, as long as the solubility in a low boiling point solvent such as dichloromethane is not impaired and the transparency and mechanical strength are not impaired.

[0033] Examples of acid dianhydride components that can be used in combination include pyromellitic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropanoic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, ethylene tetracarboxylic dianhydride, butane tetracarboxylic dianhydride, 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,3,4-cyclopentane tetracarboxylic dianhydride, 1,2,4,5-cyclohexa tetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 1,1'-bicyclohexane-3,3',4,4'-tetracarboxylic-3,4:3',4'-dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, bis(3,4-dicarboxyphenyl) ) sulfone dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 1,3-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride, 1,4-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride, 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride, 2,2-bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride Aqueous solution, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, 4,4'-bis[4-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, 4,4'-bis[3-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, 2,2-bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}-1,1,1,3,3,3- Examples of the dianhydride include propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, and 1,2,7,8-phenanthrenetetracarboxylic dianhydride.

[0034] Examples of diamines that can be used in combination include p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 9,9-bis(4-aminophenyl)fluorene, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-di(3-aminophenyl)propane, 2,2-di(4-aminophenyl)propane, 2-(3-aminophenyl)-2-(4-aminophenyl)propane, 1,1-di(3-aminophenyl)-1-phenylene ethane, 1,1-di(4-aminophenyl)-1-phenylethane, 1-(3-aminophenyl)-1-(4-aminophenyl)-1-phenylethane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminobenzoyl)benzene, 1,3-bis(4-aminobenzoyl)benzene, 1,4-bis(3-aminobenzoyl)benzene Zene, 1,4-bis(4-aminobenzoyl)benzene, 1,3-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(4-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(4-amino-α,α-dimethylbenzyl)benzene, 2,6-bis(3-aminophenoxy)benzonitrile, 2,6-bis(3-aminophenoxy)pyridine, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 2,2-bis[4-( 1,3-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)-α,α-dimethyl benzyl]benzene, 1,4-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 4,4'-bis[4-(4-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenyl sulfone, 4,4'-bis[4-(4-aminophenoxy)phenoxy]diphenyl sulfone, 3,3'-diamino-4,4'-diphenoxybenzophenone, 3,3'-diamino-4,4'-dibiphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-biphenoxybenzophenone, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindan, 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindan, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, α,ω-bis(3-aminopropyl)polydimethylsiloxane, α,ω-bis(3-aminobutyl)polydimethylsiloxane, bis(aminomethyl)ether, bis(2-aminoethyl)ether, bis(3-aminopropyl)ether, bis(2-aminomethoxy)ethyl]ether, bis[2-(2-aminoethoxy)ethyl]ether, bis[2-(3-aminoprotoxy)ethyl]ether, 1,2-bis(aminomethoxy)ethane, 1,2-bis(2-aminoethoxy)ethane, 1,2-bis[2-(aminomethoxy)ethoxy]ethane, 1,2-bis[2-(2-aminoethoxy)ethoxy]ethane, ethylene glycol bis(3-aminopropyl) ether, diethylene glycol bis(3-aminopropyl) ether, triethylene glycol bis(3-aminopropyl) ether, ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane cyclohexane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, trans-1,4-diaminocyclohexane, 1,2-di(2-aminoethyl)cyclohexane, 1,3-di(2-aminoethyl)cyclohexane, 1,4-di(2-aminoethyl)cyclohexane, bis(4-aminocyclohexyl)methane, 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane, 2,5-bis(aminomethyl)bicyclo[2.2.1]heptane butane, 1,4-diamino-2-fluorobenzene, 1,4-diamino-2,3-difluorobenzene, 1,4-diamino-2,5-difluorobenzene, 1,4-diamino-2,6-difluorobenzene, 1,4-diamino-2,3,5-trifluorobenzene, 1,4-diamino, 2,3,5,6-tetrafluorobenzene, 1,4-diamino-2-(trifluoromethyl)benzene, 1,4-diamino-2,3-bis(trifluoromethyl)benzene, 1,4-diamino-2,5-bis(trifluoromethyl)benzene, 1,4-diamino-2,Examples include 6-bis(trifluoromethyl)benzene, 1,4-diamino-2,3,5-tris(trifluoromethyl)benzene, and 1,4-diamino-2,3,5,6-tetrakis(trifluoromethyl)benzene.

[0035] (Specific example of polyimide composition) As described above, a polyimide according to one embodiment includes, as the acid dianhydride component, an acid dianhydride having an ester structure represented by general formula (1) and an acid dianhydride having a cyclobutane structure, and includes, as the diamine component, a fluoroalkyl-substituted benzidine.

[0036] The amount of the acid dianhydride represented by general formula (1) is preferably 40 to 85 mol%, more preferably 45 to 80 mol%, and even more preferably 50 to 70 mol%, based on 100 mol% of the total amount of the acid dianhydride components. By adjusting the amount within this range, a polyimide having high solubility in low-boiling point solvents such as dichloromethane and excellent mechanical strength can be obtained. As mentioned above, among the acid dianhydrides represented by general formula (1), TAHMBP represented by formula (2) is particularly preferred.

[0037] The amount of the acid dianhydride having a cyclobutane structure is preferably 15 to 60 mol%, more preferably 20 to 55 mol%, and even more preferably 25 to 50 mol%, based on 100 mol% of the total amount of the acid dianhydride components. By adjusting the amount within this range, a polyimide having solubility in low-boiling point solvents such as dichloromethane, little coloration, and excellent mechanical strength can be obtained. As mentioned above, among the acid dianhydrides having a cyclobutane structure, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) is particularly preferred.

[0038] When an acid dianhydride other than the acid dianhydride represented by general formula (1) and the acid dianhydride having a cyclobutane structure is used in combination, the amount thereof is preferably 45 mol % or less, more preferably 30 mol % or less, based on 100 mol % of the total amount of the acid dianhydride components. From the viewpoint of obtaining a polyimide having excellent solubility, transparency, and mechanical strength, preferred examples of the acid dianhydride to be used in combination include 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), 4,4'-oxydiphthalic dianhydride (s-ODPA), and 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride (6FDA).

[0039] The amount of fluoroalkyl-substituted benzidine is preferably 40 mol% or more, more preferably 60 mol% or more, and even more preferably 70 mol% or more, based on 100 mol% of the total amount of diamine components. By adjusting the amount within this range, polyimide with excellent transparency and solubility can be obtained without impairing mechanical strength. As mentioned above, among fluoroalkyl-substituted benzidines, 2,2'-bis(trifluoromethyl)benzidine (TFMB) is particularly preferred.

[0040] When a diamine other than a fluoroalkyl-substituted benzidine is used in combination, the amount is preferably 60 mol% or less, more preferably 40 mol% or less, and even more preferably 30 mol% or less, based on 100 mol% of the total amount of diamine components. From the viewpoint of transparency and solubility of the polyimide, it is preferable to use a fluoroalkyl-substituted benzidine such as TFMB in combination with 3,3'-diaminodiphenyl sulfone (3,3'-DDS) or 4,4'-diaminodiphenyl sulfone (3,3'-DDS). The amount of diaminodiphenyl sulfone based on 100 mol% of the total amount of diamine components is preferably 5 to 40 mol%, more preferably 10 to 30 mol%.

[0041] As described above, the polyimide preferably contains 40 to 85 mol% of TAHMBP and 15 to 60 mol% of CBDA as the acid dianhydride component, and 40 to 100 mol% of TFMB as the diamine component. Furthermore, from the viewpoint of improving solubility in solvents and transparency of the film, it preferably contains 5 to 40 mol% of diaminodiphenylsulfone (3,3'-DDS and / or 4,4'-DDS) as the diamine component, and may contain 6FDA, s-BPDA, s-ODPA, etc. as the acid dianhydride.

[0042] <Preparation of polyimide resin> Although the method for producing a polyimide resin is not particularly limited, a preferred method involves reacting a diamine with an acid dianhydride in a solvent to prepare a polyimide precursor, polyamic acid, and then cyclizing the polyamic acid to form an imidized polyimide. For example, an imidization catalyst and a dehydrating agent are added to a polyamic acid solution to dehydrate and cyclize the polyamic acid, thereby obtaining a polyimide solution. The polyimide solution is mixed with a poor solvent for the polyimide to precipitate a polyimide resin, which is then separated into solid and liquid to obtain the polyimide resin.

[0043] (Synthesis of polyamic acid) A polyamic acid solution is obtained by reacting an acid dianhydride with a diamine in a solvent. The acid dianhydride and the diamine are preferably used in substantially equimolar amounts. That is, the molar ratio of the acid dianhydride component to the diamine is preferably in the range of 95:105 to 105:95.

[0044] The organic solvents that can be used in the polymerization of an acid dianhydride and a diamine are not particularly limited, as long as they dissolve the acid dianhydride, the diamine, and the polymerization product, polyamic acid. Specific examples of organic solvents include urea-based solvents such as methylurea and N,N-dimethylethylurea; sulfone-based solvents such as dimethyl sulfoxide, diphenyl sulfone, and tetramethyl sulfone; amide-based solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N,N'-diethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, and hexamethylphosphoric acid triamide; alkyl halide solvents such as chloroform and dichloromethane; aromatic hydrocarbon solvents such as benzene and toluene; and ether-based solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, and p-cresol methyl ether. Among these, N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone are preferred due to their excellent polymerization reactivity and solubility of polyamic acid.

[0045] The reaction temperature for the polymerization of the acid dianhydride and the diamine is not particularly limited, but is preferably from 0° C. to 80° C., and more preferably from 20° C. to 45° C. A temperature of 0° C. or higher tends to prevent a decrease in the reaction rate, while a temperature of 80° C. or lower tends to prevent a decrease in the degree of polymerization due to ring-opening of the acid dianhydride.

[0046] (imidization) Polyimides are obtained by dehydration and cyclization of polyamic acid. For imidization in solution, a chemical imidization method is suitable, in which a dehydrating agent and an imidization catalyst are added to a polyamic acid solution. To accelerate the imidization process, the polyamic acid solution may be heated.

[0047] A tertiary amine is used as the imidization catalyst. A heterocyclic tertiary amine is preferred as the tertiary amine. Specific examples of heterocyclic tertiary amines include pyridine, picoline, quinoline, and isoquinoline. A carboxylic acid anhydride is used as the dehydrating agent, and specific examples include acetic anhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride, and trifluoroacetic anhydride.

[0048] The amount of the imidization catalyst added is preferably 0.5 to 5.0 molar equivalents, more preferably 0.7 to 2.5 molar equivalents, and even more preferably 0.8 to 2.0 molar equivalents, relative to the amide groups of the polyamic acid. The amount of the dehydrating agent added is preferably 0.5 to 10.0 molar equivalents, more preferably 0.7 to 5.0 molar equivalents, and even more preferably 0.8 to 3.0 molar equivalents, relative to the amide groups of the polyamic acid.

[0049] (Polyimide resin precipitation) It is preferable to precipitate a polyimide resin as a solid from a polyimide solution obtained by imidizing a polyamic acid. The polyimide resin is precipitated by mixing the polyimide solution with a poor solvent. The poor solvent is preferably a poor solvent for the polyimide resin that is miscible with the solvent dissolving the polyimide resin, and examples thereof include water and alcohols. Examples of alcohols include methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, triethylene glycol, 2-butyl alcohol, 2-hexyl alcohol, cyclopentyl alcohol, cyclohexyl alcohol, phenol, and t-butyl alcohol. Since ring opening of the polyimide is unlikely to occur, alcohols such as isopropyl alcohol, 2-butyl alcohol, 2-pentyl alcohol, phenol, cyclopentyl alcohol, cyclohexyl alcohol, and t-butyl alcohol are preferred, with isopropyl alcohol being particularly preferred.

[0050] <Preparation of polyimide film> A polyimide film can be produced by applying a polyimide solution (film-forming dope) prepared by dissolving a polyimide resin in an organic solvent onto a substrate and then drying and removing the solvent. The organic solvent used to dissolve the polyimide resin may be any solvent capable of dissolving the polyimide resin, and may be selected appropriately depending on the intended use of the polyimide resin. Low-boiling solvents such as dichloromethane, methyl acetate, tetrahydrofuran, acetone, and 1,3-dioxolane are preferred, with dichloromethane being particularly preferred due to its low boiling point and ease of drying and removal of the solvent. By adjusting the composition ratio of the acid dianhydride component and the diamine component as described above, polyimides exhibiting high solubility in low-boiling solvents such as dichloromethane can be obtained.

[0051] The solid content concentration of the polyimide solution may be appropriately set depending on the molecular weight of the polyimide, the thickness of the film, the film-forming environment, etc. The solid content concentration is preferably 5 to 30% by weight, more preferably 6 to 20% by weight.

[0052] (ultraviolet absorber) As described above, the polyimide film contains an ultraviolet absorber. In producing a polyimide containing an ultraviolet absorber, it is preferable to add the ultraviolet absorber to the polyimide solution. As described above, benzotriazole-based ultraviolet absorbers and triazine-based ultraviolet absorbers are preferred as ultraviolet absorbers because they have low visible light absorption and good light resistance. In particular, from the viewpoint of suppressing volatilization of the ultraviolet absorber due to heating during drying of the solvent, it is preferable that the polyimide solution contains a triazine-based ultraviolet absorber. The polyimide solution (and polyimide film) may contain a triazine-based ultraviolet absorber and a benzotriazole-based ultraviolet absorber.

[0053] The acid dianhydride of general formula (1), which is used as the acid dianhydride component of polyimide, is an ester of phenol and trimellitic anhydride, and is susceptible to photodegradation by ultraviolet light. This is presumably because its structure makes it susceptible to transition reactions such as the optical Fries transition. When the polyimide film contains an ultraviolet absorber, ultraviolet light incident on the polyimide film is absorbed by the ultraviolet absorber, making the polyimide less susceptible to ultraviolet light and tending to suppress coloration (yellowing) due to photodegradation.

[0054] From the viewpoint of suppressing photodegradation of polyimide, the amount of UV absorber in the polyimide solution is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and may be 0.5 parts by weight or more, 0.7 parts by weight or more, or 1 part by weight or more, per 100 parts by weight of the total solids content. The greater the amount of UV absorber, the more likely it is that photodegradation of polyimide will be suppressed. On the other hand, if the amount of UV absorber is excessively large, the UV absorber may not be sufficiently compatible with the polyimide, resulting in clouding of the polyimide film or bleeding of the UV absorber to the surface. Therefore, the amount of UV absorber in the polyimide solution is preferably 4.5 parts by weight or less, more preferably 4 parts by weight or less, and may be 3.5 parts by weight or less, or 3 parts by weight or less, per 100 parts by weight of the total solids content.

[0055] When a polyimide contains an acid dianhydride component represented by general formula (1), it is not easy to sufficiently suppress photodegradation of the polyimide while suppressing film clouding and bleed-out of the UV absorber. Therefore, as described below, it is preferable to impart UV-shielding properties to the hard coat layer 2 provided on the surface of the polyimide film 1 by incorporating a UV absorber, thereby reducing the amount of UV reaching the polyimide film 1.

[0056] (additives) The polyimide solution may contain resin components and additives other than the polyimide resin and UV absorber. Examples of additives include crosslinking agents, dyes, surfactants, leveling agents, plasticizers, and fine particles. The content of the polyimide resin per 100 parts by weight of the solid content of the polyimide resin composition is preferably 60 parts by weight or more, more preferably 70 parts by weight or more, and even more preferably 80 parts by weight or more.

[0057] Specific examples of the dye include anthraquinone compounds, phthalocyanine compounds, and indigo compounds. Among these, anthraquinone compounds are preferred from the viewpoint of heat resistance. The amount used is, for example, approximately 0.1 to 100 ppm, and may be 1 to 90 ppm, 10 to 80 ppm, or 20 to 70 ppm, based on the polyimide resin. The inclusion of a dye allows for the adjustment of the color tone of the polyimide film. Polyimides and ultraviolet absorbers are slightly yellow-colored due to their absorption of light in the short wavelength region of visible light. However, the hue can be neutralized by adding a dye that functions as a bluing agent. Known bluing agents can be used as appropriate, and commercially available products include "Macrolex Blue RR," "Sumiplast Violet B," "Sumiplast Violet OR," "Plast Blue 8580," "Plast Blue 8590," and "Plast Violet 8840."

[0058] (application and drying) The polyimide solution can be applied to the substrate by a known method, for example, using a bar coater or a comma coater. The substrate to which the polyimide solution is applied can be a glass substrate, a metal substrate such as SUS, a metal drum, a metal belt, a plastic film, or the like. From the viewpoint of improving productivity, it is preferable to use an endless support such as a metal drum or a metal belt, or a long plastic film as the support, and produce the film by a roll-to-roll method. When using a plastic film as the support, it is sufficient to select an appropriate material that is insoluble in the solvent of the film-forming dope. Examples of suitable plastic materials include polyethylene terephthalate, polycarbonate, polyacrylate, and polyethylene naphthalate.

[0059] Heating is preferably performed when drying the solvent. The heating temperature is not particularly limited, but is preferably 200°C or less, more preferably 180°C or less, from the viewpoint of suppressing coloration of the polyimide film and volatilization of the UV absorber. The heating temperature may be increased stepwise when drying the solvent. The solvent may also be dried under reduced pressure. By using a polyimide resin soluble in dichloromethane and preparing a polyimide solution using dichloromethane as the solvent, residual solvent can be easily reduced even when heated at 200°C or less, thereby suppressing coloration and volatilization of the UV absorber. The amount of residual solvent in the polyimide film (the mass of solvent contained in the film relative to the mass of the film) is preferably 1.5% or less, more preferably 1.0% or less. If the amount of residual solvent is within this range, the mechanical strength of the polyimide film tends to be improved.

[0060] The thickness of the polyimide film is not particularly limited and may be appropriately set depending on the application. The thickness of the polyimide film is, for example, about 5 to 100 μm. From the viewpoint of achieving both mechanical strength and transparency, the thickness of the polyimide film is preferably 30 μm or more, more preferably 35 μm or more, and even more preferably 40 μm or more. In particular, when used in applications requiring strength, such as display cover windows, the thickness of the polyimide film is preferably 40 μm or more. The thickness of the polyimide film is preferably 90 μm or less, more preferably 85 μm or less.

[0061] From the viewpoint of preventing scratches on the film due to contact with rolls during roll-to-roll transport or contact between films during winding, the pencil hardness of the polyimide film before forming the hard coat layer is preferably HB or higher, more preferably F or higher.

[0062] [Hard coat layer] A hard coat layer 2 is formed by applying a hard coat composition to a polyimide film 1 and photocuring the composition. The hard coat composition contains a photocurable resin and a photopolymerization initiator. That is, the hard coat layer is a cured resin layer made of a cured product of the hard coat composition, which is a photocurable resin composition. By adding an ultraviolet absorber to the hard coat composition, a hard coat layer containing the ultraviolet absorber is formed.

[0063] <Hard Coat Composition> The photocurable resin of the hard coat composition is a polyfunctional compound having two or more photopolymerizable functional groups. The polyfunctional compound may be a monomer or an oligomer. The photopolymerizable functional group may be radically polymerizable or cationic polymerizable. Examples of the radically polymerizable functional group include functional groups having an ethylenically unsaturated double bond, such as a vinyl group or a (meth)acryloyl group. Examples of the cationic polymerizable functional group include cyclic ether groups, such as an epoxy group or an oxetane group.

[0064] Among these, epoxy groups and oxetane groups are preferred as photopolymerizable functional groups of photocurable resins because they can be cured by photocationic polymerization and have little shrinkage on cure. Examples of photocationic polymerizable functional groups containing an epoxy group include glycidyl groups and alicyclic epoxy groups. Among these, alicyclic epoxy groups are preferred because of their high reactivity in photocationic polymerization.

[0065] As described above, since the hard coat composition contains an ultraviolet absorber, the ultraviolet light acting as excitation light is absorbed by the ultraviolet absorber during photocuring by ultraviolet irradiation, which may cause poor curing (curing inhibition). Since photoradicals, which are the active species in the photoradical polymerization reaction, have a short lifespan, continuous irradiation with ultraviolet light is required during the curing reaction, and the composition is susceptible to the influence of curing inhibition by the ultraviolet absorber.

[0066] On the other hand, the active species in the photocationic polymerization reaction is an acid generated by light irradiation, and the active species has a longer lifespan than photoradicals, allowing the curing reaction to proceed for a long period of time even after light irradiation. Therefore, photocationic polymerization is less susceptible to the influence of ultraviolet absorbers than photoradical polymerization, and curing defects are less likely to occur even when the hard coat composition contains an ultraviolet absorber. Therefore, the hard coat composition is preferably a photocationic polymerizable composition containing a photocurable resin having a photocationic polymerizable functional group such as an epoxy group, a photocationic polymerization initiator (photoacid generator), and an ultraviolet absorber.

[0067] Examples of photocationically polymerizable hard coat compositions include compositions containing a polysiloxane compound having an epoxy group, as disclosed in WO2018 / 096729, WO2014 / 204010, JP2017-8142A, and the like.

[0068] (Polysiloxane Compound as Photocurable Resin) The photocationically polymerizable polysiloxane compound has an epoxy group as a photocationically polymerizable functional group, which is preferably an alicyclic epoxy group, and more preferably a 3,4-epoxycyclohexyl group.

[0069] Polysiloxane compounds having alicyclic epoxy groups can be obtained, for example, by (A) condensation of a silane compound having an alicyclic epoxy group; or (B) hydrosilylation reaction of a compound having a carbon-carbon double bond reactive with SiH groups and an alicyclic epoxy group in one molecule (e.g., vinylcyclohexene oxide) with a polysiloxane compound having at least two SiH groups in one molecule. Since this produces a polysiloxane compound with a network structure having many alicyclic epoxy groups in one molecule, it is preferable to form the polysiloxane compound by the above method (A).

[0070] The silane compound used as a raw material for the condensation reaction of (A) above includes compounds represented by the following general formula (3). YR 5 -(Si(OR 6 ) x R 7 3-x ) …(3)

[0071] In general formula (3), Y is an alicyclic epoxy group, and R 5 is an alkylene group having 1 to 10 carbon atoms. 6 R is a monovalent hydrocarbon group selected from a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, and an alkyl group having 7 to 12 carbon atoms. 7 is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. x is an integer of 1 to 3. When x is 2 or more, multiple R 6 may be the same or different. When (3-x) is 2 or more, multiple R 7 may be the same or different.

[0072] As described above, the alicyclic epoxy group Y is preferably a 3,4-epoxycyclohexyl group. 5 may be linear or branched, but is preferably a linear alkylene group, more preferably a linear alkylene group having 1 to 5 carbon atoms, and particularly preferably ethylene. 5Preferably, - is β-(3,4-epoxycyclohexyl)ethyl.

[0073] R 6 Specific examples of R include a hydrogen atom, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, an octyl group, a nonyl group, a decyl group, a phenyl group, a tolyl group, a xylyl group, a naphthyl group, a benzyl group, and a phenethyl group. 6 is preferably an alkyl group having 1 to 4 carbon atoms, and particularly preferably an ethyl group or a propyl group.

[0074] R 7 Specific examples of R include a hydrogen atom, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, an octyl group, a nonyl group, and a decyl group. 7 is preferably an alkyl group having 1 to 3 carbon atoms, and particularly preferably a methyl group.

[0075] From the viewpoints of forming a network-like polysiloxane compound and increasing the number of alicyclic epoxy groups contained in the polysiloxane compound to increase the hardness of the cured film, x in general formula (3) is preferably 2 or 3. For the purpose of adjusting the molecular weight of the polysiloxane compound obtained by condensation, a silane compound in which x is 2 or 3 and a silane compound in which x is 1 may be used in combination.

[0076] Specific examples of the silane compound represented by general formula (3) include β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, β-(3,4-epoxycyclohexyl)ethyldimethylmethoxysilane, γ-(3,4-epoxycyclohexyl)propyltrimethoxysilane, γ-(3,4-epoxycyclohexyl)propylmethyldimethoxysilane, and γ-(3,4-epoxycyclohexyl)propyldimethylmethoxysilane.

[0077] The Si-OR compounds of the above silane compounds 6 The reaction of the two groups forms an Si-O-Si bond, producing a polysiloxane compound. Alicyclic epoxides such as epoxycyclohexyl groups have high electrophilic reactivity and low nucleophilic reactivity. Therefore, in order to prevent the ring-opening of the epoxy groups, it is preferable to carry out the reaction under neutral or basic conditions.

[0078] Examples of basic compounds used to make the reaction system basic include alkali metal or alkaline earth metal hydroxides such as sodium hydroxide, lithium hydroxide, and magnesium hydroxide, as well as amines. If a basic compound is present during the formation of a hard coat layer (photocuring reaction), the acid generated from the photocationic polymerization initiator (photoacid generator) may be quenched by the basic compound, inhibiting the photocationic polymerization reaction of the alicyclic epoxy group. Therefore, the basic compound used to form the polysiloxane compound is preferably one that can be removed by volatilization. Furthermore, from the viewpoint of suppressing ring-opening of the epoxy group in the polysiloxane compound, it is preferable that the basic compound has low nucleophilicity. Therefore, tertiary amines are preferred as basic compounds, and among these, tertiary amines with a boiling point of 30 to 160°C, such as triethylamine, diethylmethylamine, tripropylamine, methyldiisopropylamine, and diisopropylethylamine, are preferred.

[0079] From the viewpoint of increasing the hardness of the cured film, the weight-average molecular weight of the polysiloxane compound obtained by condensation of the silane compound is preferably 500 or more. Furthermore, from the viewpoint of suppressing the volatilization of the polysiloxane compound, the weight-average molecular weight of the polysiloxane compound is preferably 500 or more. On the other hand, if the molecular weight is excessively large, cloudiness may occur due to reduced compatibility with other compositions. Therefore, the weight-average molecular weight of the polysiloxane compound is preferably 20,000 or less. The weight-average molecular weight of the polysiloxane compound is more preferably 1,000 to 18,000, more preferably 1,500 to 16,000, even more preferably 2,000 to 14,000, and particularly preferably 2,800 to 12,000.

[0080] The polysiloxane compound preferably has multiple alicyclic epoxy groups in one molecule. The larger the number of alicyclic epoxy groups contained in one molecule of the polysiloxane compound, the higher the crosslinking density upon photocuring, and the more likely the cured film will have improved mechanical strength. The number of alicyclic epoxy groups in one molecule of the polysiloxane compound is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more. On the other hand, if the number of alicyclic epoxy groups contained in one molecule is excessively large, the proportion of functional groups that do not contribute to intermolecular crosslinking upon curing may increase. Therefore, the number of alicyclic epoxy groups in one molecule of the polysiloxane compound is preferably 100 or less, more preferably 80 or less, even more preferably 70 or less, and particularly preferably 60 or less.

[0081] From the viewpoint of increasing the crosslinking density and improving the hardness and scratch resistance of the cured product, it is preferable that the polysiloxane compound obtained by condensing the silane compound represented by general formula (3) has a high residual rate of alicyclic epoxy groups. The ratio of the number of moles of alicyclic epoxy groups in the condensate (polysiloxane compound) to the number of moles of alicyclic epoxy groups in the silane compound is preferably 20% or more, more preferably 40% or more, and even more preferably 60% or more.

[0082] From the viewpoint of suppressing side reactions during photo-curing and the hardness of the cured product, the amount of OR remaining per silane compound unit in the polysiloxane compound is 6 The number of OR groups per Si atom in the polysiloxane compound is preferably small. 6 The number of OR groups is 2 or less per Si atom. 6 The number of OR groups per Si atom in the polysiloxane compound is preferably 1.5 or less, more preferably 1.0 or less, on average. 6 The number of groups may be an average of 0.01 or more, 0.05 or more, or 0.3 or more.

[0083] When a polysiloxane compound is obtained by condensation of a silane compound, a silane compound not having an alicyclic epoxy group may be used in addition to a silane compound having an alicyclic epoxy group. The silane compound not having an alicyclic epoxy group is, for example, represented by the following general formula (4). R 8 -Si(OR 6 )3…(4)

[0084] R in general formula (4) 8 R is a monovalent group selected from the group consisting of substituted or unsubstituted alkyl groups, alkenyl groups, and substituted aryl groups having 1 to 10 carbon atoms, and does not have an alicyclic epoxy group. 8 When R is a substituted alkyl group, examples of the substituent include a glycidyl group, a thiol group, an amino group, a (meth)acryloyl group, a phenyl group, a cyclohexyl group, and a halogen atom. 6 is R in general formula (3) 6 is the same as:

[0085] As mentioned above, from the viewpoint of increasing the mechanical strength of the cured film, the larger the number of alicyclic epoxy groups contained in one molecule of the polysiloxane compound, the more preferable. Therefore, the polysiloxane compound obtained by the reaction of the silane compound is preferably a condensation product obtained under the condition that the molar ratio of the silane compound having an alicyclic epoxy group (compound represented by general formula (3)) to the silane compound not having an alicyclic epoxy group (compound represented by general formula (4)) is 2 or less. The molar ratio of the compound represented by general formula (4) to the compound represented by general formula (3) is preferably 1 or less, more preferably 0.6 or less, even more preferably 0.4 or less, and particularly preferably 0.2 or less. The molar ratio of the compound represented by general formula (4) to the compound represented by general formula (3) may be 0.

[0086] From the viewpoint of forming a hard coat layer having excellent mechanical strength, the content of the polysiloxane compound in the hard coat composition is preferably 40 parts by weight or more, more preferably 50 parts by weight or more, and even more preferably 60 parts by weight or more, per 100 parts by weight of the total solid content.

[0087] (Photocationic polymerization initiator) The photocationically polymerizable hard coat composition preferably contains a photocationic polymerization initiator. The photocationic polymerization initiator is a compound (photoacid generator) that generates an acid upon irradiation with active energy rays. The acid generated from the photoacid generator reacts with the alicyclic epoxy groups of the polysiloxane compound, forming intermolecular crosslinks and curing the hard coat material.

[0088] Examples of photoacid generators include strong acids such as toluenesulfonic acid and boron tetrafluoride; onium salts such as sulfonium salts, ammonium salts, phosphonium salts, iodonium salts, and selenium salts; iron-arene complexes; silanol-metal chelate complexes; sulfonic acid derivatives such as disulfones, disulfonyldiazomethanes, disulfonylmethanes, sulfonylbenzoylmethanes, imidosulfonates, and benzoin sulfonates; and organic halogen compounds.

[0089] Among the above photoacid generators, aromatic sulfonium salts or aromatic iodonium salts are preferred due to their high stability in hard coat compositions containing polysiloxane compounds with alicyclic epoxy groups. Among these, aromatic sulfonium salts or aromatic iodonium salts with a counter anion of fluorophosphate, fluoroantimonate, or fluoroborate are preferred due to their rapid photocuring and the ease with which a hard coat layer with excellent adhesion to polyimide films can be obtained. In particular, fluorophosphate or fluoroantimonate counter anions are preferred. Specific examples of such photoacid generators include diphenyl(4-phenylthiophenyl)sulfonium hexafluorophosphate, hexafluorophosphate derivatives in which some or all of the fluorine atoms of hexafluorophosphate are substituted with perfluoroalkyl groups, and diphenyl(4-phenylthiophenyl)sulfonium hexafluoroantimonate.

[0090] The content of the cationic photopolymerization initiator in the hard coat composition is preferably 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, relative to 100 parts by weight of the polysiloxane compound.

[0091] (ultraviolet absorber) By including an ultraviolet absorber in the hard coat composition, a hard coat layer containing the ultraviolet absorber is formed. As described above, benzotriazole-based ultraviolet absorbers and triazine-based ultraviolet absorbers are preferred as ultraviolet absorbers because they have low visible light absorption and good light resistance. In particular, benzotriazole-based ultraviolet absorbers have a large absorption coefficient in the UVA region (wavelength 320 to 400 nm) and can effectively suppress deterioration due to phototransition reactions of polyimides, so it is preferred that the hard coat layer (hard coat composition) contain a benzotriazole-based ultraviolet absorber.

[0092] As described above, the production of a polyimide film requires high-temperature heating for drying and removing the solvent, and therefore the polyimide film preferably contains a triazine-based UV absorber, which has excellent heat resistance. If a hard coat layer 2 containing a benzotriazole-based UV absorber is formed on a polyimide film 1 containing a triazine-based UV absorber, UV rays over a wide wavelength range are absorbed, thereby efficiently suppressing photodegradation of the polyimide.

[0093] From the viewpoint of enhancing the UV absorption (shielding) of the hard coat layer and reducing the amount of UV reaching the polyimide film, the amount of UV absorber in the hard coat composition is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and may be 0.5 parts by weight or more, 0.7 parts by weight or more, or 1 part by weight or more, per 100 parts by weight of the total solids content. The greater the amount of UV absorber, the greater the UV shielding ability of the hard coat layer tends to be. On the other hand, if the amount of UV absorber is excessively large, the amount of UV absorbed by the UV absorber during photocuring of the hard coat composition is large, and even in the case of a photocationically polymerizable hard coat composition, photocuring may be insufficient, resulting in insufficient mechanical strength (surface hardness) of the hard coat film. Therefore, the amount of UV absorber in the hard coat composition is preferably 4.5 parts by weight or less, more preferably 4 parts by weight or less, and may be 3.5 parts by weight or less, or 3 parts by weight or less, per 100 parts by weight of the total solids content.

[0094] (solvent) The hard coat composition may be solvent-free or may contain a solvent. If a solvent is contained, it is preferable that the solvent does not dissolve the polyimide film. On the other hand, by using a solvent that dissolves the polyimide film to such an extent that it swells, the adhesion between the polyimide film substrate 1 and the hard coat layer 2 may be improved. The amount of solvent in the hard coat composition is preferably 500 parts by weight or less, more preferably 300 parts by weight or less, and even more preferably 100 parts by weight or less, per 100 parts by weight of the curable resin (polysiloxane compound).

[0095] (reactive diluent) The hard coat composition may contain a reactive diluent. Examples of the reactive diluent include cationic polymerizable compounds other than the above-mentioned polysiloxane compounds. Examples of the reactive diluent for polymerization include compounds having functional groups such as epoxy groups, vinyl ether groups, oxetane groups, and alkoxysilyl groups.

[0096] (photosensitizer) The hard coat composition may contain a photosensitizer for the purpose of improving the photosensitivity of the photocationic polymerization initiator (photoacid generator). Photosensitizers that can absorb light in a wavelength range that the photoacid generator itself cannot absorb are more efficient, so it is preferable that the photosensitizer has little overlap with the absorption wavelength range of the photoacid generator. Examples of photosensitizers include anthracene derivatives, benzophenone derivatives, thioxanthone derivatives, anthraquinone derivatives, and benzoin derivatives.

[0097] (particle) The hard coat composition may contain particles for the purpose of adjusting film properties such as surface hardness and flex resistance, suppressing cure shrinkage, etc. Particles may be appropriately selected from organic particles, inorganic particles, organic-inorganic composite particles, etc. Examples of organic particle materials include poly(meth)acrylic acid alkyl esters, crosslinked poly(meth)acrylic acid alkyl esters, crosslinked styrene, nylon, silicone, crosslinked silicone, crosslinked urethane, and crosslinked butadiene. Examples of inorganic particle materials include metal oxides such as silica, titania, alumina, tin oxide, zirconia, zinc oxide, and antimony oxide; metal nitrides such as silicon nitride and boron nitride; and metal salts such as calcium carbonate, calcium hydrogen phosphate, calcium phosphate, and aluminum phosphate. Examples of organic-inorganic composite fillers include organic particles having an inorganic layer formed on the surface thereof, and inorganic particles having an organic layer or organic fine particles formed on the surface thereof.

[0098] The average particle size of the particles is, for example, about 5 nm to 10 μm. From the viewpoint of increasing the transparency of the hard coat layer, the average particle size is preferably 1000 nm or less, more preferably 500 nm or less, even more preferably 300 nm or less, and particularly preferably 100 nm or less. The particle size can be measured using a laser diffraction / scattering particle size distribution measuring device, and the volume-based median size is taken as the average particle size.

[0099] The particles may be surface-modified. By surface-modifying the particles, the dispersibility of the particles tends to be improved. In addition, when the particle surface is modified with a polymerizable functional group capable of reacting with an epoxy group, the functional group on the particle surface reacts with the epoxy group of the polysiloxane compound to form a chemical crosslink, which is expected to improve the film strength.

[0100] (additives) The hard coat composition may contain additives such as inorganic pigments, organic pigments, surface conditioners, surface modifiers, plasticizers, dispersants, wetting agents, thickeners, antifoaming agents, etc. The hard coat composition may also contain a thermoplastic, thermosetting, or photocurable resin material other than the above-mentioned polysiloxane compounds.

[0101] As described above, the hard coat composition contains a photopolymerization initiator and an ultraviolet absorber in addition to a polysiloxane compound as a curable resin, and may further contain a reactive diluent, a photosensitizer, particles, and other additives as solid contents (non-volatile contents). From the viewpoint of forming a hard coat layer excellent in mechanical strength, the content of the polysiloxane compound in the hard coat composition is preferably 40 parts by weight or more, more preferably 50 parts by weight or more, and even more preferably 60 parts by weight or more, per 100 parts by weight of the total solid contents.

[0102] <Formation of hard coat layer> A hard coat composition is applied onto a polyimide film, and the solvent is dried and removed as necessary. The hard coat composition is then cured by irradiating it with active energy rays such as ultraviolet rays, thereby obtaining a hard coat film having a hard coat layer 2 provided on a polyimide film 1.

[0103] The cumulative irradiation dose of active energy rays during photocuring is, for example, 50 to 10,000 mJ / cm 2 The curing temperature is about 100° C., and may be set depending on the type and amount of the polymerization initiator, the thickness of the hard coat layer, etc. The curing temperature is not particularly limited, but is usually 100° C. or lower.

[0104] The thickness of the hard coat layer is preferably 0.5 μm or more, more preferably 2 μm or more, even more preferably 3 μm or more, and most preferably 5 μm or more. The thickness of the hard coat layer is preferably 100 μm or less, more preferably 80 μm or less. If the thickness of the hard coat layer is less than 0.5 μm, mechanical properties such as surface hardness may not be sufficiently improved. On the other hand, if the thickness of the hard coat layer is more than 100 μm, transparency and flex resistance may be reduced.

[0105] [Hard coat film characteristics] The total light transmittance of the hard coat film is preferably 80% or more, more preferably 85% or more, and even more preferably 88% or more.The haze of the hard coat film is preferably 1.5% or less, more preferably 0.9% or less, even more preferably 0.7% or less, and particularly preferably 0.5% or less.

[0106] The yellowness index (YI) of the hard coat film is preferably 10 or less, more preferably 6 or less, even more preferably 5 or less, and may be 4 or less, 3.5 or less, 3.0 or less, or 2.5 or less.

[0107] As described above, the hard coat film of the present invention contains an ultraviolet absorber in both the polyimide film 1 and the hard coat layer 2. Therefore, when external light is incident from the hard coat layer 2 side, the ultraviolet light is absorbed (blocked) by the hard coat layer 2, reducing the amount of ultraviolet light that reaches the polyimide film 1, and the ultraviolet light that does reach the polyimide film 1 is absorbed by the ultraviolet absorber contained in the polyimide film 1. Therefore, the polyimide resin of the polyimide film 1 is less susceptible to the effects of ultraviolet light, and discoloration (increase in yellowness) due to photodegradation is suppressed.

[0108] The content of the ultraviolet absorber in the polyimide film is preferably 0.1 to 4.5 wt%, more preferably 0.3 to 4 wt%, even more preferably 0.5 to 3.5 wt%, and may be 0.7 to 3 wt% or 1.0 to 2.5 wt%. The content of the ultraviolet absorber in the hard coat layer is preferably 0.1 to 4.5 wt%, more preferably 0.3 to 4 wt%, even more preferably 0.5 to 3.5 wt%, and may be 0.7 to 3 wt% or 1.0 to 2.5 wt%.

[0109] Irradiance 500W / m from the hard coat layer forming surface 2 The increase in yellowness ΔYI of the hard coat film when irradiated with ultraviolet light for 48 hours under the condition of a black panel temperature of 63°C is preferably 6 or less, more preferably 5 or less, and may be 4.5 or less or 4.0 or less.

[0110] The pencil hardness of the surface of the hard coat film on which the hard coat layer is formed is preferably HB or higher, more preferably H or higher, even more preferably 2H or higher, particularly preferably 3H or higher, and may be 4H or higher. The tensile modulus of the hard coat film is preferably 3.5 GPa or higher, more preferably 4.0 GPa or higher, and even more preferably 5.0 GPa or higher.

[0111] [Applications of hard coated films] The hard coat film may have various functional layers provided on the hard coat layer 2 or on the surface of the polyimide film 1 on which the hard coat layer is not formed. Examples of functional layers include an antireflection layer, an antiglare layer, an antistatic layer, and a transparent electrode. The hard coat film may also have a transparent pressure-sensitive adhesive layer attached thereto.

[0112] The hard coat film of the present invention has high transparency and excellent mechanical strength, and is therefore suitable for use as a cover window disposed on the viewing side surface of an image display panel, a transparent substrate for a display, a transparent substrate for a touch panel, a substrate for a solar cell, etc. In addition to transparency and mechanical strength, the hard coat film of the present invention also has excellent flex resistance and high light resistance, and is therefore particularly suitable for use as a cover window disposed on the viewing side surface of a curved display or a foldable display. [Example]

[0113] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0114] [Preparation of transparent polyimide film] (Preparation of Polyimide Resin) A reaction vessel was charged with 44.2 g (138.1 mmol) of 2,2'-bis(trifluoromethyl)benzidine (TFMB) and 3.8 g (15.3 mmol) of 3,3'-diaminodiphenyl sulfone (3,3-DDS) as diamines, and bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethyl ... 47.4 g (76.7 mmol) of phenyl-4,4'-diyl ester (TAHMBP), 9.0 g (46.0 mmol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), and 9.5 g (30.7 mmol) of 4,4'-oxydiphthalic dianhydride (ODA), as well as 800 g of N,N-dimethylformamide as a solvent, were added and stirred for 12 hours under a nitrogen atmosphere to obtain a polyamic acid solution.

[0115] To the polyamic acid solution, 36.4 g (460 mmol) of pyridine and 7.0 g (460 mmol) of acetic anhydride were added as imidization catalysts and stirred at 90°C for 4 hours. The solution was cooled to room temperature, and 2000 g of 2-propyl alcohol (IPA) was added while stirring. The mixture was then suction filtered using a Kiriyama funnel. The resulting solid was washed six times with 1000 g of IPA and then dried in a vacuum oven set at 120°C for 8 hours to obtain a white polyimide resin. The monomer composition of this polyimide resin was TFMB / 3,3'-DDS / TAHMBP / CBDA / ODA = 90 / 10 / 50 / 30 / 20 (molar ratio).

[0116] (Preparation of polyimide film) 100 parts by weight of the above polyimide resin, an ultraviolet absorber (UVA) and a bluing agent ("PlastBlue 8590" manufactured by Arimoto Chemical Industry Co., Ltd.) shown in Table 1 were dissolved in dichloromethane to obtain a polyimide solution with a solids concentration of 10% by weight. In Comparative Examples 1, 5, and 6, no ultraviolet absorber was added. In Comparative Examples 4 and 6, no bluing agent was added.

[0117] The polyimide solution was applied to alkali-free glass using a bar coater and heated in an atmospheric environment at 40°C for 60 minutes, 80°C for 30 minutes, 150°C for 30 minutes, 170°C for 30 minutes, and 200°C for 60 minutes to remove the solvent, yielding a transparent polyimide film with a thickness of 50 μm.

[0118] [Preparation of hard-coated film] (Synthesis of silsesquioxane compounds) A reaction vessel equipped with a thermometer, stirrer, and reflux condenser was charged with 66.5 g (270 mmol) of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (SILQUEST A-186, manufactured by Momentive Performance Materials) and 16.5 g of 1-methoxy-2-propanol (PGME) and stirred until homogeneous. A solution of 0.039 g (0.405 mmol) of magnesium chloride dissolved in 9.7 g (539 mmol) of water and 5.8 g of methanol was added dropwise to the mixture over 5 minutes and stirred until homogeneous. The mixture was then heated to 80°C and stirred for 6 hours. After the reaction was complete, the mixture was concentrated under reduced pressure using a rotary evaporator to remove the methanol and water from the condensate, yielding a silsesquioxane compound.

[0119] (Preparation of Hard Coat Composition) A hard coat composition was prepared by adding a 50% propylene carbonate solution of diphenyl(4-phenylthiophenyl) SbF6 salt ("CPI-101A" manufactured by San-Apro) as a photoacid generator (photocationic polymerization initiator) and an ultraviolet absorber (UVA) to 100 parts by weight of the above silsesquioxane compound in the amounts shown in Table 1. In Comparative Examples 4 and 6, only the photoacid generator was added, and no ultraviolet absorber was added.

[0120] (Formation of hard coat layer) The hard coat composition was applied to the main surface of a 50 μm thick transparent polyimide substrate using a bar coater so that the thickness after curing would be 50 μm, and the coating was heated at 120° C. for 10 minutes. A high-pressure mercury lamp was used to apply an integrated light intensity of 1000 mJ / cm at a wavelength of 365 nm. 2 After irradiating with ultraviolet light so that the hard coat composition became uniform, the hard coat composition was cured by heating at 80°C for 2 hours to obtain a hard coat film having a hard coat (HC) layer on the polyimide film substrate. In Example 2, Comparative Examples 5 and 6, a hard coat (HC) layer having a thickness of 50 μm was formed on both sides of the transparent polyimide film substrate. In Comparative Examples 1 to 4, no hard coat layer was formed.

[0121] [Evaluation of hard-coated films] The hard coat films of the examples and comparative examples (Comparative Examples 1 to 4 are polyimide films without a hard coat layer) were evaluated as follows.

[0122] (exterior) Visual observation of the hard coat film revealed cloudiness in Comparative Example 4. The haze of the hard coat film of Comparative Example 4 was measured using a haze meter "HZ-V3" manufactured by Suga Test Instruments according to the method described in JIS K7361-1, and was found to be 41.0%. The haze of the hard coat films of Examples 1 to 8 was all less than 0.5%.

[0123] The hard coat films of Comparative Examples 8 and 9 had wrinkles on the film surface, and therefore, the following evaluations were not carried out for Comparative Examples 8 and 9.

[0124] (yellowness) The film was cut into 3 cm squares and the yellowness index (YI) was measured using a spectrophotometer (Suga Test Instruments "SC-P"). Then, a fade meter (Suga Test Instruments "U48-HB") was used to measure the yellowness index (YI) at an irradiance of 500 W / m 2 One side of the film (the side on which the hard coat layer was formed in Examples 1, 3 to 8 and Comparative Examples 7 to 9) was irradiated with ultraviolet light for 48 hours under the condition of a black panel temperature of 63°C. The yellowness of the film after ultraviolet irradiation was measured, and the change in yellowness before and after irradiation, ΔYI, was calculated from the yellowness before irradiation YI0 and the yellowness after irradiation YI1 according to the following formula: ΔYI=YI1-YI0

[0125] (Pencil hardness) The pencil hardness of the film was measured by a pencil scratch test according to JIS K-5600-5-4. In Examples 1 and 3 to 8 and Comparative Examples 7 to 9, the pencil hardness of the surface on which the hard coat layer was formed was evaluated.

[0126] Table 1 shows the types and contents of additives in the polyimide films, the surfaces on which the hard coat layers are formed, the amounts of photoacid generators added to the hard coat compositions, the types and contents of UV absorbers in the hard coat compositions, and the evaluation results of the films in the examples and comparative examples.

[0127] In Table 1, ultraviolet absorbers (UVA) are described by the following abbreviations. LA-31RG: ADEKA "ADEKA STAB LA-31RG": 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol] LA-F70: ADEKA "ADEKA STAB LA-F70": 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine Tin 326: "Tinvin 326" manufactured by BASF; 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol LA-29: ADEKA "ADEKA STAB LA-29"; 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol LA-32: ADEKA "ADEKA STAB LA-32"; 2-(2H-benzotriazol-2-yl)-p-cresol LA-24: ADEKA "ADEKA STAB LA-24"; 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol

[0128] [Table 1]

[0129] As shown in Table 1, the hard-coated film containing UV absorbers in both the polyimide film and the hard-coat layer exhibits high pencil hardness due to the hard-coat layer, and also exhibits a small ΔYI after light exposure in the fade test, demonstrating excellent light resistance.

[0130] Comparisons between Examples 3 and 4, Examples 5 and 6, and Examples 7 and 8 reveal that the greater the amount of UV absorber contained in the hard coat layer, the smaller the ΔYI tends to be. On the other hand, in Comparative Examples 8 and 9, in which 5 parts by weight of UV absorber was blended per 100 parts by weight of the resin content of the hard coat composition, wrinkles were observed on the surface of the hard coat layer after curing. This is thought to be due to insufficient curing due to the large amount of UV absorber.

[0131] In Comparative Examples 1 to 4, in which no hard coat layer was provided, the pencil hardness of the film was lower than that of the Examples, and the hardness was insufficient. Furthermore, ΔYI was large regardless of the presence or absence of an ultraviolet absorber in the polyimide film, and the light resistance was insufficient. In Comparative Example 4, in which 5 parts by weight of an ultraviolet absorber was blended with 100 parts by weight of polyimide resin, significant cloudiness was observed due to insufficient compatibility.

[0132] In Comparative Example 5, in which neither the polyimide film nor the hard coat layer contained an ultraviolet absorber, ΔYI was large and light resistance was insufficient. In Comparative Example 6, in which an ultraviolet absorber was blended only in the hard coat layer, and Comparative Example 7, in which an ultraviolet absorber was blended only in the polyimide film, ΔYI was smaller than in Comparative Example 5, but light resistance was insufficient.

[0133] From the above results, it is clear that by including an ultraviolet absorber in both the polyimide film and the hard coat layer, a hard coat film excellent in transparency, light resistance and surface hardness can be obtained. [Explanation of symbols]

[0134] 1 Polyimide film 2 Hard coat layer 10 Hard coat film

Claims

1. A hard coat film comprising a substrate film and a hard coat layer provided on at least one surface of the substrate film, the base film is a polyimide film containing a polyimide resin and having a thickness of 5 to 100 μm, the hard coat layer is made of a cured product of a photocurable resin composition containing a photocurable resin having two or more radically polymerizable or cationically polymerizable photopolymerizable functional groups and a photopolymerization initiator, and has a thickness of 0.5 to 100 μm; each of the hard coat layer and the polyimide film contains an ultraviolet absorber; the content of the ultraviolet absorber in the polyimide film is 0.1 to 4.5% by weight, and the content of the ultraviolet absorber in the hard coat layer is 0.1 to 4.5% by weight; Hard coat film.

2. The polyimide resin is The diamine component contains 40 mol% or more and 100 mol% or less of fluoroalkyl-substituted benzidine relative to 100 mol% of the total amount of diamines, As the tetracarboxylic dianhydride component, the tetracarboxylic dianhydride component contains 40 mol % or more and 85 mol % or less of an acid dianhydride having an ester structure represented by formula (1) and 15 mol % or more and 60 mol % or less of an acid dianhydride having a cyclobutane structure, relative to 100 mol % of the total amount of the tetracarboxylic dianhydride component; The hard coat film according to claim 1: 【Chemistry 1】 In formula (1), n ​​is 1 or 2, and R １ ~R ４ are each independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a fluoroalkyl group; R １ ~R ４ At least one of the groups is an alkyl group or a fluoroalkyl group having 1 to 20 carbon atoms.

3. 3. The hard coat film according to claim 1, wherein the hard coat layer comprises a cured product of a polysiloxane compound having an epoxy group.

4. 4. The hard coat film according to claim 1, wherein the ultraviolet absorber is a benzotriazole compound or a triazine compound.

5. A hard coat film described in any one of claims 1 to 4, wherein the content of the ultraviolet absorber in the hard coat layer is 0.7 to 3.5 wt%.

6. A method for producing the hard coat film according to any one of claims 1 to 5, a dichloromethane solution containing a polyimide resin and an ultraviolet absorber is applied to a substrate, and the solvent is removed to prepare a polyimide film containing the ultraviolet absorber; A method for producing a hard coat film, comprising: applying a photocurable resin composition containing a photocurable resin having two or more radically polymerizable or cationically polymerizable photopolymerizable functional groups and a photopolymerization initiator to the surface of the polyimide film; and photocuring the composition to form a hard coat layer.

7. 7. The method for producing a hard coat film according to claim 6, wherein the photocurable resin is a polysiloxane compound having an epoxy group, and the photopolymerization initiator is a cationic photopolymerization initiator.

8. An image display device comprising the hard coat film according to any one of claims 1 to 5 on a viewer-side surface of an image display panel.

9. The image display device according to claim 8, which is foldable.

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