Hard coat film and method for producing same, and display

Abstract

A hard coat film (11) is provided with a hard coat layer (3) on a second main surface (1B) of a transparent resin film (1) having a thickness of 26 μm or more. The transparent resin film comprises a polyimide-based resin and a solvent-soluble resin that is different from a polyimide-based resin. The polyimide-based resin contains: a diamine component that comprises a diamine having at least one structure selected from among CF3-O-, -(CF2-O)n-, and -O-(CF2-CF2-O)n- (wherein n is an integer of 1-20); and a tetracarboxylic acid dianhydride component that comprises at least one tetracarboxylic acid dianhydride selected from the group consisting of tetracarboxylic acid dianhydrides each having an ether bond, tetracarboxylic acid dianhydrides each having a fluorene structure, tetracarboxylic acid dianhydrides each having a xanthene structure, and bis(trimellitic anhydride) esters.

Description

Hard-coated film, manufacturing method thereof, and display

[0001] The present invention relates to a hard coat film, a method for producing the same, and a display including the hard coat film.

[0002] Films containing transparent polyimides have excellent mechanical strength and are expected to be used as cover windows for displays.

[0003] As a method for producing a transparent polyimide film, a method using a polyimide resin that is soluble in an organic solvent and does not require high-temperature imidization after film formation has been proposed. For example, Patent Document 1 discloses a soluble polyimide that uses a fluoroalkyl-substituted benzidine such as 2,2'-bis(trifluoromethyl)benzidine (TFMB) as a diamine. Patent Document 2 describes that the transparency and other properties of a transparent polyimide film can be improved by mixing a soluble polyimide with an acrylic resin.

[0004] Patent Document 3 proposes applying a hard coat film having a hard coat layer on the surface of a transparent polyimide film to a cover window.

[0005] International Publication No. 2020 / 004236 International Publication No. 2023 / 026982 Japanese Patent Application Laid-Open No. 2019-217647

[0006] In recent years, the environmental persistence of organic fluorine compounds (PFAS) has become a problem. In general, the bond energy of the carbon-fluorine bond contained in organic fluorine compounds is high, making them difficult to decompose in the environment. In particular, the structure in which a trifluoromethyl group is bonded to a carbon atom (-C-CF ３ ), or a structure in which carbon atoms are bonded to both sides of a difluoromethylene group (—C—CF ２ Organic fluorine compounds containing fluorine atoms (C) have low decomposition properties in the environment and have been reported to have adverse effects on the human body.

[0007] In view of the above, an object of the present invention is to provide a hard coat film using a film substrate that is excellent in environmental safety.

[0008] The present invention relates to a hard coat film comprising a transparent resin film having a first main surface and a second main surface and a hard coat layer on the second main surface. The transparent resin film has a thickness of 26 μm or more. The transparent resin film contains a polyimide resin and a solvent-soluble resin other than the polyimide resin.

[0009] The polyimide resin has a tetracarboxylic dianhydride-derived structure and a diamine-derived structure, and the diamine is CF ３ -O-, -(CF ２ -O) ｎ -, and -O-(CF ２ -CF ２ -O) ｎ -(CF), and the tetracarboxylic dianhydride contains one or more tetracarboxylic dianhydrides (specific acid dianhydrides) selected from the group consisting of tetracarboxylic dianhydrides having an ether bond, tetracarboxylic dianhydrides having a fluorene structure, tetracarboxylic dianhydrides having a xanthene structure, and bis(trimellitic anhydride) esters. ２ -O) ｎ -, and -O-(CF ２ -CF ２ -O) ｎ In the -, n is an integer of 1 to 20.

[0010] Preferred examples of the specific diamine that is a fluorine atom-containing diamine include 2,2'-bis(trifluoromethoxy)benzidine, 3,3'-bis(trifluoromethoxy)benzidine, and 2,3'-bis(trifluoromethoxy)benzidine.

[0011] The polyimide-based resin may contain a diamine other than the specific diamine as the diamine component, and may contain a tetracarboxylic acid dianhydride other than the specific acid dianhydride as the tetracarboxylic acid dianhydride component. The tetracarboxylic acid dianhydride other than the specific acid dianhydride may be an alicyclic tetracarboxylic acid dianhydride. The amount of the alicyclic tetracarboxylic acid dianhydride relative to the total amount of tetracarboxylic acid dianhydrides in the polyimide-based resin may be 1 to 80 mol %.

[0012] Polyimide resins are made by adding CF to the carbon atoms of the aromatic ring relative to the total amount of diamine. ３ - or -C(CF ３ ) ２ The amount of diamine having a structure in which - is directly bonded is less than 0.5 mol %, and the amount of CF ３ - or -C(CF ３ ) ２ The amount of tetracarboxylic dianhydride having a structure in which - is directly bonded is preferably less than 0.5 mol %.

[0013] As the solvent-soluble resin other than the polyimide resin contained in the transparent resin film, an acrylic resin and a polyester resin are preferred.

[0014] The hard coat film may have a hard coat layer only on the second main surface of the transparent resin film, and no hard coat layer on the first main surface of the transparent resin film. In this embodiment, the arithmetic mean roughness Sa of the first main surface of the transparent resin film is preferably 1 nm or less. The maximum height Sz of the first main surface of the transparent resin film may be 60 nm or less.

[0015] The transparent resin film may have a second main surface having a larger arithmetic mean roughness Sa than the first main surface, and a second main surface having a larger maximum height Sz than the first main surface. The second main surface of the transparent resin film may have an arithmetic mean roughness Sa of 1.5 nm or more.

[0016] The thickness of the hard coat layer may be from 1 to 50 μm.

[0017] The transparent resin film can be produced by applying a resin solution containing a polyimide resin and a solvent-soluble resin dissolved in a solvent onto a support, heating the solution on the support, and drying and removing the solvent. The hard-coated film is obtained by peeling the transparent resin film from the support and forming a hard-coat layer on one main surface of the transparent resin film. In one embodiment, the surface of the transparent resin film peeled from the support is used as the second main surface, and a hard-coat layer is formed on this surface.

[0018] The surface of the support to be coated with the resin solution may have an arithmetic mean roughness Sa of 0.5 nm or more and a maximum height Sz of 10 nm or more. The support may be a plastic film.

[0019] The hard coat film of the present invention is excellent in mechanical strength and transparency, and is also excellent in environmental safety because the polyimide resin contained in the transparent resin film contains a specific diamine as a diamine component.

[0020] FIG. 1 is a cross-sectional view of a hard coat film according to an embodiment.

[0021] 1 is a cross-sectional view of a hard coat film according to one embodiment of the present invention. The hard coat film 11 includes a transparent resin film 1 having a first main surface 1A and a second main surface 1B, and a hard coat layer 3 on the second main surface 1B.

[0022] [Transparent Resin Film] The transparent resin film 1 is a substrate that serves as a base when forming the hard coat layer 3. The transparent resin film 1 has a thickness of 26 μm or more.

[0023] The transparent resin film 1 is a blend resin film containing one or more polyimide-based resins selected from the group consisting of polyimides and polyamideimides, and a solvent-soluble resin other than the polyimide-based resin (hereinafter, sometimes referred to as "other resin"). By containing the polyimide-based resin and the other resin, the transparency of the transparent resin film 1 tends to be improved.

[0024] <Polyimide-based resin> Polyimide is obtained by dehydrating and cyclizing polyamic acid obtained by reacting tetracarboxylic dianhydride (hereinafter sometimes referred to as "acid dianhydride") with diamine. Polyamideimide is obtained by replacing a part of the tetracarboxylic dianhydride of polyimide with a polybasic acid derivative such as dicarboxylic acid dichloride. Polyimide and polyamideimide may be used in combination as the polyimide-based resin.

[0025] (Diamine) The polyimide resin contained in the transparent resin film contains CF as a diamine component. ３ -O-, -(CF ２ -O)ｎ -, and -O-(CF ２ -CF ２ -O) ｎ -, wherein n is an integer of 1 to 20. Hereinafter, these diamines will be referred to as "specific diamines."

[0026] In certain diamines, a trifluoromethyl group (-CF ３ ) or a difluoromethylene group (—CF ２ The carbon atom of the fluorine-containing alkyl group (-C-CF) is bonded to an oxygen atom. This structure is different from the structure in which a trifluoromethyl group is bonded to a carbon atom (-C-CF ３ ) and a structure in which carbon atoms are bonded to both ends of a difluoromethylene group (—C—CF ２ As a result, polyimide resins containing specific diamines as diamine components are superior in environmental safety to conventional soluble polyimide resins containing organic fluorine compounds such as fluoroalkyl-substituted benzidine as diamine components.

[0027] Among the specific diamines, CF does not fall under the category of "specific fluorine structure" described below. ３ -O-, or -(CF ２ -O) ｎ From the viewpoint of the polymerizability and mechanical strength of the polyimide resin, it is preferable to use a trifluoromethoxy group (CF ３ -O-) is preferred, and among them, diamines in which the oxygen atom of the trifluoromethoxy group is bonded to a carbon atom of an aromatic ring are preferred. From the viewpoint of reactivity, diamines in which a trifluoromethoxy group is bonded to a carbon atom of an aromatic ring are preferably those which do not have a fluorine atom directly bonded to the aromatic ring to which the trifluoromethoxy group is bonded, and particularly preferred are those which do not contain fluorine atoms other than the trifluoromethoxy group. Examples of specific diamines in which a trifluoromethoxy group is bonded to a carbon atom of an aromatic ring include trifluoromethoxy-substituted benzidine and trifluoromethoxy-substituted phenylenediamine.

[0028] Examples of trifluoromethoxy-substituted benzidines include 2-(trifluoromethoxy)benzidine, 3-(trifluoromethoxy)benzidine, 2,3-bis(trifluoromethoxy)benzidine, 2,5-bis(trifluoromethoxy)benzidine, 2,6-bis(trifluoromethoxy)benzidine, 2,3,5-tris(trifluoromethoxy)benzidine, 2,3,6-tris(trifluoromethoxy)benzidine, 2,3,5,6-tetrakis(trifluoromethoxy)benzidine, 2,2'-bis(trifluoromethoxy)benzidine (TFMOB), 3,3'-bis(trifluoromethoxy)benzidine, 2,3'-bis(trifluoromethoxy)benzidine, 2,2',3-tris(trifluoromethoxy)benzidine, 2,3,3'-tris(trifluoromethoxy)benzidine, 2,2',5-tris(trifluoromethoxy)benzidine, 2,2',6-tris(trifluoromethoxy)benzidine, 2,3',5-tris(trifluoromethoxy)benzidine, 2,3',6-tris(trifluoromethoxy)benzidine, 2,2',3,3'-tetrakis(trifluoromethoxy)benzidine, 2,2',5,5'-tetrakis(trifluoromethoxy)benzidine, and 2,2',6,6'-tetrakis(trifluoromethoxy)benzidine.

[0029] Examples of trifluoromethoxy-substituted phenylenediamines include 1,2-diamino-4-(trifluoromethoxy)benzene, 1,3-diamino-4-(trifluoromethoxy)benzene, 1,4-diamino-2-(trifluoromethoxy)benzene, 1,4-diamino-2,3-bis(trifluoromethoxy)benzene, 1,4-diamino-2,5-bis(trifluoromethoxy)benzene, 1,4-diamino-2,6-bis(trifluoromethoxy)benzene, 1,4-diamino-2,3,5-tris(trifluoromethoxy)benzene, and 1,4-diamino-2,3,5,6-tetrakis(trifluoromethoxy)benzene.

[0030] From the viewpoint of the polymerizability of the polyimide resin and compatibility with polyester, trifluoromethoxy-substituted benzidine is preferred as the specific diamine. Among them, from the viewpoint of the solubility of the polyimide resin in organic solvents and compatibility with other resins, those having a trifluoromethoxy group at the 2- or 3-position of the biphenyl are preferred, with 2,2'-bis(trifluoromethoxy)benzidine (hereinafter referred to as "TFMOB"), 3,3'-bis(trifluoromethoxy)benzidine, and 2,3'-bis(trifluoromethoxy)benzidine being more preferred, and TFMOB being particularly preferred. By having a trifluoromethoxy group at the 2- or 3-position of the biphenyl, in addition to a decrease in π electron density due to the electron-withdrawing properties of the trifluoromethoxy group, the steric hindrance of the trifluoromethoxy group inhibits π-π stacking between benzene rings, thereby shifting the absorption edge wavelength to shorter wavelengths and reducing coloration of the polyimide resin. Furthermore, in the case of TFMOB, the steric hindrance between the trifluoromethoxy groups at the 2- and 2'-positions of the biphenyl causes the bond between the two benzene rings of the biphenyl to twist, reducing the planarity of the π-conjugation, thereby shifting the absorption edge wavelength to shorter wavelengths and reducing the coloration of the polyimide resin.

[0031] The amount of the specific diamine relative to the total amount of the diamine components of the polyimide resin is preferably 10 mol% or more, more preferably 30 mol% or more, even more preferably 50 mol% or more, and may be 60 mol% or more, 70 mol% or more, 80 mol% or more, or 90 mol% or more, or even 100 mol%. Among these, the amount of the trifluoromethoxy group-containing diamine is preferably within this range, and the amount of the trifluoromethoxy-substituted benzidine is particularly preferably within this range. The higher the ratio of the specific diamine, the more suppressed the coloring and the mechanical strength of the film, such as pencil hardness, elastic modulus, breaking strength, and breaking elongation, may be improved.

[0032] The polyimide resin may contain a diamine other than the specific diamine as a diamine component. ３ and -C-CF ２ Those which do not contain —C— are preferred, and those which do not contain a fluorine atom are particularly preferred.

[0033] Examples of diamines not containing fluorine atoms include 2,2'-dimethylbenzidine, 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, and 3,4'-diaminodiphenyl sulfone. sulfone, 4,4'-diaminodiphenyl sulfone, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-di(3-amino phenyl)propane, 2,2-di(4-aminophenyl)propane, 2-(3-aminophenyl)-2-(4-aminophenyl)propane, 1,1-di(3-aminophenyl)-1-phenylethane, 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, 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-amino 2,2-bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 2,2-bis[4-(3-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]benz 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-dimethylbenzyl]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'-diviphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-biphenoxybenzophenone, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane, 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane, 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, 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, isophoronediamine, 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane, 2,5-bis(aminomethyl)bicyclo[2.2.1]heptane, and the like.

[0034] The use of diaminodiphenyl sulfone as the diamine in addition to the specific diamine may improve the solubility in solvents and transparency of the polyimide resin. Among diaminodiphenyl sulfones, 3,3'-diaminodiphenyl sulfone (3,3'-DDS) and 4,4'-diaminodiphenyl sulfone (4,4'-DDS) are preferred, and these may be used in combination.

[0035] When diaminodiphenyl sulfone is used in addition to the specific diamine, the amount of diaminodiphenyl sulfone relative to the total amount of the diamine components may be 1 to 40 mol %, 3 to 30 mol %, or 5 to 25 mol %.

[0036] The use of a diamine having a fluorene structure in addition to the specific diamine as the diamine may improve the solubility in solvents, transparency, and mechanical strength of the polyimide resin. Preferred fluorene-containing diamines are 9,9-bis(4-aminophenyl)fluorene, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene, and 9,9-bis(4-amino-3-methylphenyl)fluorene, and these may be used in combination.

[0037] When a diamine having a fluorene structure is used in addition to the specific diamine, the amount of the diamine having a fluorene structure relative to the total amount of the diamine components may be 1 to 40 mol %, 3 to 30 mol %, or 5 to 25 mol %.

[0038] Among fluorine atom-containing diamines, the structure in which a trifluoromethyl group is bonded to a carbon atom (—C—CF ３ ) and / or a structure in which carbon atoms are bonded to both ends of a difluoromethylene group (—C—CF ２ In order to improve the transparency and solubility in solvents of polyimide resins, general soluble polyimide resins contain CF4 as a diamine component on the carbon atom of the aromatic ring. ３ - or -C(CF ３ ) ２ Although the polyimide resin contains diamines having a structure in which a CF group is directly bonded (for example, trifluoromethoxy-substituted benzidines such as 2,2'-bis(trifluoromethyl)benzidine, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane), from the viewpoint of environmental safety of the polyimide resin, it is preferable that the polyimide resin does not substantially contain these diamines. ３ - or -C(CF３ ) ２ The amount of diamine to which - is directly bonded is preferably less than 0.5 mol %, and may be 0.3 mol % or less, 0.1 mol % or less, or 0.05 mol % or less, or may be 0.

[0039] (Tetracarboxylic acid dianhydride) The polyimide resin contained in the transparent resin film contains, as an acid dianhydride component, one or more acid dianhydrides selected from the group consisting of acid dianhydrides having an ether bond, bis(trimellitic anhydride) esters, acid dianhydrides having a fluorene structure, and acid dianhydrides having a xanthene structure. Hereinafter, these acid dianhydrides will be referred to as "specific acid dianhydrides."

[0040] Examples of acid dianhydrides having an ether bond include 3,4'-oxydiphthalic anhydride (a-ODPA), 4,4'-oxydiphthalic anhydride (s-ODPA), 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride (BPADA), etc. From the viewpoints of solubility in polyimide resins and compatibility with other resins, BPADA is particularly preferred.

[0041] The bis(trimellitic anhydride) ester is represented by the following general formula (1).

[0042]

[0043] In general formula (1), X is any divalent organic group, and at both ends of X, a carboxy group and a carbon atom of X are bonded. The carbon atoms bonded to the carboxy group may form a ring structure. Specific examples of the divalent organic group X include the following (A) to (K).

[0044]

[0045] R in formula (A) １represents a fluorine atom or an alkyl group having 1 to 20 carbon atoms, and m is an integer of 1 to 4. The group represented by formula (A) is a group obtained by removing two hydroxyl groups from a hydroquinone derivative having a substituent on the benzene ring. Examples of hydroquinones having a substituent on the benzene ring include tert-butylhydroquinone, 2,5-di-tert-butylhydroquinone, and 2,5-di-tert-amylhydroquinone.

[0046] R in formula (B) ２ represents a fluorine atom or an alkyl group having 1 to 20 carbon atoms, and n is an integer of 0 to 4. The group represented by formula (B) is a group obtained by removing two hydroxyl groups from a biphenol which may have a substituent on the benzene ring. Examples of biphenol derivatives having a substituent on the benzene ring include 2,2'-dimethylbiphenyl-4,4'-diol, 3,3'-dimethylbiphenyl-4,4'-diol, 3,3',5,5'-tetramethylbiphenyl-4,4'-diol, and 2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diol.

[0047] The group represented by formula (C) is a group obtained by removing two hydroxyl groups from 4,4'-isopropylidenediphenol (bisphenol A). The group represented by formula (D) is a group obtained by removing two hydroxyl groups from resorcinol.

[0048] In formula (E), p is an integer of 1 to 10. The group represented by formula (E) is a group obtained by removing two hydroxyl groups from a linear diol having 1 to 10 carbon atoms. Examples of the linear diol having 1 to 10 carbon atoms include ethylene glycol and 1,4-butanediol.

[0049] The group represented by formula (F) is a group obtained by removing two hydroxyl groups from 1,4-cyclohexanedimethanol.

[0050] R in formula (G) ３is a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 20 carbon atoms, and q is an integer from 0 to 4. The group represented by formula (G) is a group obtained by removing two hydroxyl groups from bisphenolfluorene, which may have a substituent on the benzene ring having a phenolic hydroxyl group. Examples of bisphenolfluorene derivatives having a substituent on the benzene ring having a phenolic hydroxyl group include biscresolfluorene. When the compound has the structure of formula (G), it corresponds to both an acid dianhydride having a fluorene structure and a bis(trimellitic anhydride) ester, but in the present invention, it corresponds to a bis(trimellitic anhydride) ester.

[0051] The bis(trimellitic anhydride) ester is preferably an aromatic ester. Of the above (A) to (K), (A), (B), (C), (D), (G), (H), and (I) are preferred for X. Of these, (A) to (D) are preferred, with (B) being the group having a biphenyl skeleton being particularly preferred. When X is a group represented by general formula (B), from the viewpoint of the solubility of the polyimide resin, X is preferably 2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diyl represented by the following formula (B1):

[0052]

[0053] The acid dianhydride in which X is a group represented by formula (B1) in general formula (1) is bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'diyl (abbreviation: TAHMBP) represented by the following formula (3):

[0054]

[0055] As the bis(trimellitic anhydride) ester in which X in the general formula (1) is a structure other than that of formula (B), p-phenylenebis(trimellitic acid monoester anhydride) (TMHQ), bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-biphenyl-4,4'-diyl (OCBP-TME), 5,5'-(3,3'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate) (BP-TME), tert-butylhydroquinone bis(trimellitate anhydride) (TA.BHQ), trimethylhydroquinone bis(trimellitate anhydride) (TA.TMHQ), are preferred.

[0056] From the viewpoint of the solubility of the polyimide resin, TMHQ, TAHMBP, and OCBP-TME are particularly preferred as the bis(trimellitic anhydride) ester.

[0057] Examples of acid dianhydrides having a fluorene structure include 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF), 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride (BPF-PA), N,N'-(9H-fluoren-9-ylidene-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxamide] ( FDA-ATA), 5,5'-(9H-fluoren-9-ylidenebis(2-methyl-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate] (TBIS.MPN), and the like. From the viewpoint of the solubility of the polyimide resin, BPAF, BPF-PA, or TBIS.MPN are preferred, and among these, BPAF or BPF-PA is particularly preferred.

[0058] Examples of acid dianhydrides having a xanthene structure include 5,5'-spiro[9H-fluorene-9,9'-[9H]xanthene]-3',6'-diylbis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate (TBIS.RXN) and spiro[fluorene-9,9'xanthene]-2',3',6',7'-tetracarboxylic dianhydride (SFDA). These exemplary compounds contain a xanthene structure and a fluorene structure, but are classified as acid dianhydrides having a xanthene structure.

[0059] Among the specific acid dianhydrides, from the viewpoint of the solubility in organic solvents and transparency of polyimide resins, 4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride (BPADA), 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF), 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride (BPF-PA), 5,5'-(9H-fluoren-9-ylidenebis(2-methyl-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate] (TBIS.MPN), p-phenylenebis(trimellitic acid monoester anhydride) (TMHQ), 5,5'-(3,3'-dimethyl[1,1'-biphenyl]-4 ,4'-diyl)bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate) (BP-TME), bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-biphenyl-4,4'-diyl (OCBP-TME), bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diyl (TAHMBP), tert-butylhydroquinone bis(trimellitate anhydride) (TA.BHQ), and trimethylhydroquinone bis(trimellitate anhydride) (TA.TMHQ) are preferred. Among these, BPAF, BPF-PPA, and TBIS.MPN, which have a fluorene structure, are particularly preferred.

[0060] Among the specific acid dianhydrides, acid dianhydrides having an ether bond, acid dianhydrides having a fluorene structure, and acid dianhydrides having a xanthene structure are preferred from the viewpoint of UV resistance of the polyimide resin. From the viewpoint of solubility in solvents and mechanical strength, BPADA, 3,4'-oxydiphthalic anhydride (a-ODPA), 4,4'-oxydiphthalic anhydride (s-ODPA), BPAF, BPF-PA, and spiro[fluorene-9,9'xanthene]-2',3',6',7'-tetracarboxylic dianhydride (SFDA) are particularly preferred. These acid dianhydrides do not have an ester bond and do not undergo Friess transition due to UV light, so that the polyimide resin is less likely to discolor when exposed to UV light.

[0061] From the viewpoint of making the polyimide-based resin soluble in an organic solvent, the total amount of the specific acid dianhydride relative to the total amount of the acid dianhydride components is preferably 15 mol% or more, more preferably 20 mol% or more, even more preferably 25 mol% or more, and may be 30 mol% or more, 35 mol% or more, 40 mol% or more, 45 mol% or more, or 50 mol% or more. The total amount of the specific acid dianhydride relative to the total amount of the acid dianhydride components may be 100 mol%, or may be 95 mol% or less, 90 mol% or less, 85 mol% or less, 80 mol% or less, 75 mol% or less, or 70 mol% or less.

[0062] The polyimide resin may contain an acid dianhydride other than the specific acid dianhydride as the acid dianhydride component. Examples of such an acid dianhydride include alicyclic tetracarboxylic acid dianhydrides and aromatic tetracarboxylic acid dianhydrides. From the viewpoint of environmental safety of the polyimide resin, -C-CF ３ and -C-CF ２ Those which do not contain —C— are preferred, and those which do not contain a fluorine atom are particularly preferred.

[0063] The alicyclic tetracarboxylic dianhydride may have at least one alicyclic structure, and may have both an alicyclic ring and an aromatic ring in one molecule. The alicyclic ring may be polycyclic or may have a spiro structure. Examples of the alicyclic tetracarboxylic dianhydride include 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic acid-3,4:3',4'-dianhydride, and 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic acid-3,4:3',4'-dianhydride. hydrate, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic acid dianhydride, 2,2'-binorbornane-5,5',6,6'tetracarboxylic acid dianhydride, 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic acid-1,4:2,3-dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4- Tetrahydronaphthalene-1,2-dicarboxylic anhydride, cyclohexane-1,4-diylbis(methylene)bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate), 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 5,5'-[cyclohexylidenebis(4,1-phenyleneoxy)]bis-1,3-isobenzofurandione, 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-di Oxo-,5,5'-[1,4-cyclohexanediylbis(methylene)]ester, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, 3,5,6-tricarboxynorbornane-2-acetic acid 2,3:5,6-dianhydride, decahydro-1,4,5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic dianhydride, tricyclo[6.4.0.0(2,7)]dodecane-1,8:2,Examples of suitable dianhydrides include 7-tetracarboxylic acid dianhydride, octahydro-1H,3H,8H,10H-biphenyleno[4a,4b-c:8a,8b-c']difuran-1,3,8,10-tetraone, ethylene glycol bis(hydrogenated trimellitic anhydride) ester, and decahydro[2]benzopyrano[6,5,4,-def][2]benzopyran-1,3,6,8-tetraone. By including an alicyclic tetracarboxylic acid dianhydride in addition to a specific dianhydride as the dianhydride component, the mechanical strength of the polyimide resin tends to be improved. Furthermore, by including an alicyclic tetracarboxylic acid dianhydride as the dianhydride component in the polyimide resin, the compatibility of the polyimide resin with other resins tends to be enhanced.

[0064] Among alicyclic tetracarboxylic dianhydrides, from the viewpoint of transparency and mechanical strength of polyimide resins, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (H-PMDA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetracarboxylic dianhydride, and 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetracarboxylic dianhydride are preferred. Tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA-100), bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BEDA), bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride (BODA), and 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic acid-3,4:3',4'-dianhydride (H-BPDA) are preferred. Among these, from the viewpoint of mechanical strength, tetracarboxylic anhydrides in which two acid anhydride groups are bonded to one alicyclic ring are preferred, and CBDA is particularly preferred.

[0065] When an alicyclic tetracarboxylic dianhydride is used in addition to the specific acid dianhydride, the amount of the alicyclic tetracarboxylic dianhydride relative to the total amount of the acid dianhydride components may be 1 mol% or more, 3 mol% or more, 5 mol% or more, 10 mol% or more, 12 mol% or more, or 15 mol% or more. The greater the amount of alicyclic tetracarboxylic dianhydride, the higher the mechanical strength tends to be. From the viewpoint of ensuring the solubility of the polyimide-based resin in organic solvents, the amount of the alicyclic tetracarboxylic dianhydride relative to the total amount of the acid dianhydride components is preferably 80 mol% or less, more preferably 60 mol% or less, and even more preferably 50 mol% or less, and may be 40 mol% or less, 30 mol% or less, or 20 mol% or less. Furthermore, polyimide-based resins containing an alicyclic tetracarboxylic dianhydride within the above range as an acid dianhydride component tend to have excellent compatibility with other resins.

[0066] Examples of aromatic tetracarboxylic dianhydrides other than the specific acid dianhydrides include pyromellitic dianhydride (PMDA), 1,2,3,4-benzenetetracarboxylic dianhydride (MPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4' 2,3,3',4'-biphenyltetracarboxylic dianhydride (s-BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA), 2,2',3,3',-biphenyltetracarboxylic dianhydride (i-BPDA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 5,5'-dimethylmethylenebis(phthalic anhydride), 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, terphenyltetracarboxylic dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, and bis(3,4-dicarboxyphenyl)sulfone dianhydride. Among these aromatic tetracarboxylic dianhydrides, a-BPDA, s-BPDA, i-BPDA, PMDA, MPDA, and DSDA are preferred from the viewpoint of improving mechanical strength.

[0067] When an aromatic tetracarboxylic dianhydride other than the specific acid dianhydride is used in addition to the specific acid dianhydride, the amount of the aromatic tetracarboxylic dianhydride other than the specific acid dianhydride relative to the total amount of the acid dianhydride components may be 1 mol% or more, 3 mol% or more, 5 mol% or more, 10 mol% or more, 12 mol% or more, or 15 mol% or more. From the viewpoint of ensuring the solubility of the polyimide resin in organic solvents, the amount of the aromatic tetracarboxylic dianhydride other than the specific acid dianhydride relative to the total amount of the acid dianhydride components is preferably 80 mol% or less, more preferably 60 mol% or less, and even more preferably 50 mol% or less, and may be 40 mol% or less, 30 mol% or less, or 20 mol% or less.

[0068] The polyimide resin may contain, as an acid dianhydride component, a chain aliphatic tetracarboxylic dianhydride such as ethylene tetracarboxylic dianhydride, 1,2,3,4-butane tetracarboxylic dianhydride, or meso-butane-1,2,3,4-tetracarboxylic dianhydride.

[0069] The amount of the fluorine atom-containing acid dianhydride relative to the total amount of the acid dianhydride components in the polyimide resin is preferably 30 mol% or less, more preferably 20 mol% or less, and even more preferably 10 mol% or less, and may be 5 mol% or less, 1 mol% or less, or 0.5 mol% or less. The polyimide resin may not contain a fluorine atom-containing acid dianhydride as an acid dianhydride component.

[0070] Among fluorine atom-containing acid dianhydrides, the structure in which a trifluoromethyl group is bonded to a carbon atom (-C-CF ３ ) and / or a structure in which carbon atoms are bonded to both ends of a difluoromethylene group (—C—CF ２ -C-) has low decomposition properties and is a concern for environmental safety. ３ - or -C(CF ３ ) ２Acid dianhydrides having a structure in which - is directly bonded (for example, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 9,9-bis(trifluoromethyl)xanthenetetracarboxylic dianhydride, 9-trifluoromethylxanthenetetracarboxylic dianhydride) are poorly degradable in the environment, and therefore, from the viewpoint of environmental safety of polyimide-based resins, it is preferable that these acid dianhydrides are substantially not contained. ３ - or -C(CF ３ ) ２ The amount of acid dianhydride to which - is directly bonded is preferably less than 0.5 mol %, and may be 0.3 mol % or less, 0.1 mol % or less, or 0.05 mol % or less, or may be 0.

[0071] (Polybasic Acid) As described above, the polyimide resin may be a polyamideimide in which a part of the tetracarboxylic dianhydride component is replaced with a polybasic acid derivative. Examples of the polybasic acid include dicarboxylic acid and tricarboxylic acid anhydrides.

[0072] Examples of dicarboxylic acids include aliphatic dicarboxylic acids such as adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-oxybisbenzoic acid, 4,4'-biphenyldicarboxylic acid, and 2-fluoroterephthalic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-hexahydroterephthalic acid, hexahydroisophthalic acid, 1,3-cyclopentanedicarboxylic acid, and bi(cyclohexyl)-4,4'-dicarboxylic acid; and heterocyclic dicarboxylic acids such as 2,5-thiophenedicarboxylic acid and 2,5-furandicarboxylic acid.

[0073] Examples of tricarboxylic acids include trimellitic anhydride derivatives such as trimellitic anhydride, 2-fluorotrimellitic anhydride, 5-fluorotrimellitic anhydride, 6-fluorotrimellitic anhydride, 2,5-difluorotrimellitic anhydride, 2,6-difluorotrimellitic anhydride, 5,6-difluorotrimellitic anhydride, and 2,5,6-trifluorotrimellitic anhydride.

[0074] From the viewpoint of the solubility of the polyamideimide, the polybasic acid is preferably an aromatic dicarboxylic acid, an alicyclic dicarboxylic acid, or trimellitic anhydride, and particularly preferably an aromatic dicarboxylic acid. Among the aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, 4,4'-biphenyldicarboxylic acid, and 4,4'-oxybisbenzoic acid are preferred, with terephthalic acid and isophthalic acid being preferred, and terephthalic acid being particularly preferred.

[0075] In preparing polyamide-imide and its precursor, polyamic acid, a polybasic acid derivative is used. Examples of the polybasic acid derivative include dicarboxylic acid dichlorides, dicarboxylic acid esters, dicarboxylic acid anhydrides, and tricarboxylic acid anhydride chlorides. Among these, dicarboxylic acid dichlorides and tricarboxylic acid anhydride chlorides are preferred due to their high reactivity.

[0076] From the viewpoint of the solubility of the polyamideimide and its compatibility with other resins, the ratio of the polybasic acid derivative to the total of the tetracarboxylic dianhydride and the polybasic acid derivative is preferably 40 mol % or less, more preferably 35 mol % or less, and even more preferably 30 mol % or less. The polyimide resin may be a polyimide in which the ratio of the dicarboxylic acid derivative is 0 (i.e., does not contain a structure derived from a dicarboxylic acid derivative).

[0077] (Content of specific fluorine structure in polyimide resin) As described above, the diamine component is CF ３ -O-, -(CF ２ -O) ｎ -, and -O-(CF ２ -CF ２ -O) ｎand a polyimide-based resin containing, as an acid dianhydride component, one or more acid dianhydrides (specific acid dianhydrides) selected from the group consisting of acid dianhydrides having an ether bond, bis(trimellitic anhydride) esters, acid dianhydrides having a fluorene structure, and acid dianhydrides having a xanthene structure, is -C-CF ３ , -C-CF ２ It is substantially free of structures such as —C— and exhibits solubility in organic solvents.

[0078] In order to reduce the environmental persistence of fluorine-containing compounds, it is preferable that the polyimide resin contains a small amount of monomers having a specific fluorine structure. The specific fluorine structure is a monomer having at least one completely fluorinated methyl group (CF ３ -) or methylene (-CF ２ -) A structure containing a carbon atom (not bonded to any of H, Cl, Br, or I) excluding those having only the components of the following structural formula (i) or (ii): CF ３ -X (i) X-CF ２ -X' (ii)

[0079] X in formula (i) and (ii) is —OR or —NRR′, and X′ in formula (ii) is —CH ３ , -CH ２ R, R', R'' and R''' are each independently -H, -CH ３ , -CH ２ -, aromatic, or -C(O)-.

[0080] From the viewpoint of improving environmental degradability, the amount of fluorine atoms contained in the specific fluorine structure per 1 kg of the polyimide resin is preferably less than 500 mg, more preferably less than 300 mg, even more preferably less than 100 mg, and particularly preferably less than 50 mg.

[0081] (Preparation of Polyimide Resin) Polyamic acid as a polyimide precursor is obtained by the reaction of an acid dianhydride with a diamine, and polyimide is obtained by cyclodehydration (imidization) of the polyamic acid. The method for preparing polyamic acid is not particularly limited, and any known method can be used. For example, a polyamic acid solution can be obtained by dissolving diamine and tetracarboxylic dianhydride in approximately equimolar amounts (molar ratio of 90:100 to 110:100) in an organic solvent and stirring the mixture.

[0082] When preparing polyamide-imide, in addition to a diamine and a tetracarboxylic dianhydride, a polybasic acid derivative such as a dicarboxylic dichloride may be used as a monomer. In this case, the amounts of the respective monomers may be adjusted so that the total amount of the tetracarboxylic dianhydride and the polybasic acid derivative is approximately equimolar to the diamine.

[0083] As described above, by adjusting the composition of the polyimide resin, i.e., the types and ratios of the acid dianhydrides and diamines, the polyimide resin has transparency and solubility in organic solvents, and also exhibits compatibility with other resins.

[0084] The concentration of the polyamic acid solution is usually 5 to 35% by weight, preferably 10 to 30% by weight. When the concentration is within this range, the polyamic acid obtained by polymerization has an appropriate molecular weight, and the polyamic acid solution has an appropriate viscosity.

[0085] In the polymerization of polyamic acid, it is preferable to add the acid dianhydride to the diamine in order to suppress ring-opening of the acid dianhydride. When adding multiple types of diamines or multiple types of acid dianhydrides, they may be added all at once or in multiple portions. The physical properties of the polyimide resin can also be controlled by adjusting the order of addition of the monomers.

[0086] The organic solvent used in the polymerization of polyamic acid is not particularly limited, as long as it does not react with the diamine and the acid dianhydride and can dissolve the polyamic acid. Examples of organic solvents include urea solvents such as methylurea and N,N-dimethylethylurea; sulfoxide or sulfone solvents such as dimethyl sulfoxide, diphenyl sulfone, and tetramethyl sulfone; amide solvents such as N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N,N'-diethylacetamide, N-methyl-2-pyrrolidone (NMP), γ-butyrolactone, and hexamethylphosphoric triamide; alkyl halide solvents such as chloroform and methylene chloride; aromatic hydrocarbon solvents such as benzene and toluene; and ether solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, and p-cresol methyl ether. These solvents are typically used alone or in combination as needed. From the viewpoint of the solubility and polymerization reactivity of polyamic acid, DMAc, DMF, NMP, etc. are preferably used.

[0087] Polyimide resins are obtained by dehydration cyclization of polyamic acid. One method for preparing polyimide resins from polyamic acid solutions is to add a dehydrating agent, an imidization catalyst, etc. to the polyamic acid solution and allow imidization to proceed in the solution. To accelerate the imidization process, the polyamic acid solution may be heated. Mixing a solution containing the polyimide resin produced by imidization of polyamic acid with a poor solvent results in the polyimide resin being precipitated as a solid. Isolating the polyimide resin as a solid allows impurities generated during the synthesis of the polyamic acid, as well as residual dehydrating agents and imidization catalysts, to be washed and removed with the poor solvent, preventing discoloration and increased yellowness of the polyimide resin. Furthermore, isolating the polyimide resin as a solid allows the use of solvents suitable for film formation, such as low-boiling point solvents, when preparing a solution for film production.

[0088] The molecular weight of the polyimide resin (weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC)) is preferably 90,000 to 500,000, more preferably 100,000 to 400,000, still more preferably 100,000 to 300,000, and particularly preferably 150,000 to 300,000. If the molecular weight is too small, the strength of the film may be insufficient. If the molecular weight is too large, the compatibility with other resins may be poor.

[0089] The polyimide resin is preferably soluble in a low-boiling point solvent such as a ketone solvent or an alkyl halide solvent. The solubility of a polyimide resin in a solvent means that the polyimide resin is soluble in a concentration of 5% by weight or more. In one embodiment, the polyimide resin is soluble in methylene chloride. Methylene chloride has a low boiling point and allows easy removal of residual solvent during film production. Therefore, by using a polyimide resin soluble in methylene chloride, improved film productivity can be expected.

[0090] From the viewpoint of the thermal stability and light stability of the transparent resin film, it is preferable that the polyimide resin has low reactivity. The acid value of the polyimide resin is preferably 0.4 mmol / g or less, more preferably 0.3 mmol / g or less, and even more preferably 0.2 mmol / g or less. The acid value of the polyimide resin may be 0.1 mmol / g or less, 0.05 mmol / g or less, or 0.03 mmol / g or less. From the viewpoint of reducing the acid value, it is preferable that the polyimide resin has a high imidization rate. A low acid value tends to increase the stability of the polyimide resin and improve its compatibility with other resins.

[0091] <Other Resins> As described above, the transparent resin film 1 contains, in addition to the polyimide-based resin, a resin other than the polyimide-based resin ("other resin"). The other resin is not particularly limited as long as it is soluble in an organic solvent and can be mixed with the polyimide-based resin to form a transparent film, and examples include resins that are compatible with the polyimide-based resin and resins that form a microphase-separated structure such as a sea-island structure, a cylindrical structure, or a lamellar structure. Among these, the other resin is preferably one that is compatible with the polyimide-based resin. When the polyimide-based resin and the other resin are compatible with each other, the film tends to have high transparency and excellent mechanical properties such as elastic modulus and pencil hardness, regardless of the processing conditions.

[0092] Examples of the other resin include acrylic resins, polycarbonate resins, polyester resins, polyamide resins, polyether resins, cellulose resins, silicone resins, and cyclic olefin resins. A plurality of these resins may be used. Because of their high compatibility with polyimide resins containing specific diamines and specific acid dianhydrides, acrylic resins and polyester resins are particularly preferred as the other resin.

[0093] (Acrylic Resin) Examples of the acrylic resin include poly(meth)acrylic acid esters such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymers, methyl methacrylate-(meth)acrylic acid ester copolymers, methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymers, methyl (meth)acrylate-styrene copolymers, and copolymers of methyl (meth)acrylate with a monomer having a benzotriazole skeleton or a benzophenone skeleton. The stereoregularity of the polymer is not particularly limited, and may be any of isotactic, syndiotactic, and atactic.

[0094] From the viewpoints of transparency, compatibility with polyimide resins, and mechanical strength of molded articles such as films, the acrylic resin is preferably one having methyl methacrylate as a main structural unit. The amount of methyl methacrylate relative to the total amount of monomer components in the acrylic resin is preferably 60% by weight or more, and may be 70% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. The acrylic resin may be a homopolymer of methyl methacrylate.

[0095] The acrylic resin may be modified by introducing an imide structure or a lactone ring structure. Such modified polymers are preferably those obtained by introducing an imide structure or a lactone ring structure into an acrylic polymer having a methyl methacrylate content within the above range. That is, in the acrylic resin modified by introducing an imide structure or a lactone ring structure, the total amount of methyl methacrylate and the modified structure of methyl methacrylate is preferably 60% by weight or more, and may be 70% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. The modified polymer may be a methyl methacrylate homopolymer into which an imide structure or a lactone ring structure has been introduced.

[0096] Introducing an imide structure into an acrylic polymer such as methyl methacrylate tends to increase the glass transition temperature of the acrylic resin, and the imide structure of the acrylic resin may improve its compatibility with polyimide resins.

[0097] From the viewpoint of heat resistance of the transparent resin film, the glass transition temperature of the acrylic resin is preferably 100°C or higher, more preferably 110°C or higher, and may be 115°C or higher or 120°C or higher.

[0098] From the viewpoints of solubility in organic solvents, compatibility with polyimide resins, and film strength, the weight average molecular weight (polystyrene equivalent) of the acrylic resin is preferably 5,000 to 500,000, more preferably 10,000 to 300,000, still more preferably 15,000 to 200,000, and particularly preferably 50,000 to 150,000.

[0099] From the viewpoint of the thermal stability and light stability of the film, it is preferable that the acrylic resin have a low content of reactive functional groups such as ethylenically unsaturated groups and carboxyl groups. The iodine value of the acrylic resin is preferably 10.16 g / 100 g (0.4 mmol / g) or less, more preferably 7.62 g / 100 g (0.3 mmol / g) or less, and even more preferably 5.08 g / 100 g (0.2 mmol / g) or less. The iodine value of the acrylic resin may be 2.54 g / 100 g (0.1 mmol / g) or less or 1.27 g / 100 g (0.05 mmol / g) or less. The acid value of the acrylic resin is preferably 0.4 mmol / g or less, more preferably 0.3 mmol / g or less, and even more preferably 0.2 mmol / g or less. The acid value of the acrylic resin may be 0.1 mmol / g or less, 0.05 mmol / g or less, or 0.03 mmol / g or less. A small acid value tends to increase the stability of the acrylic resin and improve the compatibility with the polyimide resin.

[0100] Since acrylic resins generally have a lower refractive index than polyimide resins, transparent resin films containing polyimide resins and acrylic resins tend to have a lower refractive index and less reflection at the interface than films made of polyimide resin alone, resulting in a higher total light transmittance. From the viewpoint of reducing the refractive index of the film, the refractive index of the acrylic resin is preferably 1.550 or less, more preferably 1.520 or less, and even more preferably 1.500 or less.

[0101] (Polyester Resin) Polyester is a condensation product of dicarboxylic acid and diol, and has a structure derived from dicarboxylic acid and a structure derived from diol. The dicarboxylic acid component and diol component of polyester are not particularly limited, but from the viewpoint of solubility in organic solvents, they are preferably amorphous. Polyethylene terephthalate (PET), a typical polyester, is a condensation product of ethylene glycol and terephthalic acid, and has high crystallinity and low solubility in organic solvents, whereas amorphous polyester is soluble in organic solvents and exhibits high compatibility with the above-mentioned polyimide resin. Transparent resin films containing polyimide resin and polyester resin tend to have excellent flex resistance.

[0102] From the viewpoint of imparting solubility to the polyester resin in organic solvents, the diol component of the polyester resin is preferably a diol having a chain alkylene group having 3 or more carbon atoms which may be branched, a diol having a chain alkenylene group having 3 or more carbon atoms which may be branched, a polyalkylene glycol, or a diol having a cyclic structure. Hereinafter, these diols will be referred to as "specific diols."

[0103] Examples of diols having a chain alkylene structure of 3 or more carbon atoms which may have a branch include propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, etc. Among these, diols having a chain alkylene structure of 5 or more carbon atoms are preferred, and diols having an alkylene group with a branched structure such as neopentyl glycol are particularly preferred. Examples of diols having a chain alkenylene group of 3 or more carbon atoms which may have a branch include 2-butene-1,4-diol, etc.

[0104] Examples of polyalkylene glycols include diethylene glycol, triethylene glycol, dipropylene glycol, and polytetramethylene ether glycol.

[0105] Examples of diols having a cyclic structure include diols having a cycloalkylene structure such as 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol; diols having a cyclic ether structure such as isosorbide; diols having a fluorene structure; and diols having a bisphenol derivative structure.

[0106] Among these, butanediol, neopentyl glycol, polytetramethylene ether glycol, diols having a fluorene structure, and diols having a bisphenol derivative structure are preferred from the viewpoint of solubility of polyester resins and compatibility with polyimide resins.

[0107] Specific examples of diols having a fluorene structure include 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 9,9-bis[4-(2-hydroxypropoxy)phenyl]fluorene, 9,9-bis[4-[2-(2-hydroxyethoxy)ethoxy]phenyl]-9H-fluorene, 2,2'-[(9H-fluorene-9,9-diyl)bis(naphthalene-6,2-diyloxy)]diethanol, 9,9-bis[4-(2-hydroxyethoxy)-3-phenylphenyl]fluorene, 9,9-bis[4-(2-hydroxypropoxy)-3-phenylphenyl]fluorene, and 9,9-bis{4-[2-(2-hydroxyethoxy)ethoxy]-3-phenylphenyl}fluorene. Among these, from the viewpoint of improving heat resistance, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 9,9-bis[4-(2-hydroxypropoxy)phenyl]fluorene, and 9,9-bis[4-(2-hydroxyethoxy)-3-phenylphenyl]fluorene are preferred.

[0108] The diol having bisphenol derivative structure is the one in which alkylene oxide is added to two phenolic hydroxyl groups of bisphenol (bisphenol alkylene oxide adduct), and preferably the ethylene oxide (EO) adduct and propylene oxide (PO) adduct of bisphenol.In addition, the diol having fluorene structure includes the diol having bisphenol derivative structure, but the diol having fluorene structure is treated as the diol having fluorene structure even if it has bisphenol derivative structure.

[0109] Examples of bisphenols that do not have a fluorene structure include 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 1,1-bis(4-hydroxyphenyl)-1-phenylethane (bisphenol AP), 2,2-bis(4-hydroxyphenyl)butane (bisphenol B), bis(4-hydroxyphenyl)diphenylmethane (bisphenol BP), 2,2-bis(3-methyl-4-hydroxyphenyl)propane (bisphenol C), 1,1-bis(4-hydroxyphenyl)ethane (bisphenol E), bis(4-hydroxyphenyl)methane (bisphenol F), and 2,2-bis(4-hydroxy-3-isopropyl bisphenol G), 1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene (bisphenol M), bis(4-hydroxyphenyl)sulfone (bisphenol S), 1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene (bisphenol P), 5,5'-(1-methylethylidene)-bis[1,1'(bisphenyl)-2-ol]propane (bisphenol PH), 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (bisphenol TMC), 1,1-bis(4-hydroxyphenyl)cyclohexane (bisphenol Z), and the like.

[0110] Among the bisphenol alkylene oxide adducts, from the viewpoint of solubility in polyester, ethylene oxide adducts of bisphenol A, ethylene oxide adducts of bisphenol S, and ethylene oxide adducts of bisphenol Z are preferred.

[0111] The polyester may contain a diol other than the above-mentioned specific diol as a diol component. An example of a diol other than the specific diol is ethylene glycol. When the specific diol and ethylene glycol are used in combination, from the viewpoint of compatibility between the polyester and the polyimide resin, the molar ratio of the specific diol to ethylene glycol is preferably 90:10 to 10:90, and may be 80:20 to 20:80, or 60:40 to 40:60. In other words, the amount of the specific diol relative to the total amount of the diol component is preferably 10 mol% or more, and may be 20 mol% or more, or 40 mol% or more.

[0112] The dicarboxylic acid component of the polyester resin is not particularly limited, and various aromatic dicarboxylic acids and aliphatic dicarboxylic acids can be used. As the dicarboxylic acid, an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid can be used in combination.

[0113] Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, and biphenyldicarboxylic acid.Further examples of aromatic dicarboxylic acids include dicarboxylic acids having a fluorene skeleton, such as 9,9-bis(carboxymethyl)fluorene and 9,9-bis(2-carboxyethyl)fluorene.

[0114] From the viewpoint of improving the solubility and mechanical strength of the polyester resin, terephthalic acid and isophthalic acid are preferred as aromatic dicarboxylic acids. Terephthalic acid and isophthalic acid may be used alone or in combination. When terephthalic acid and isophthalic acid are used in combination, from the viewpoint of the solubility of the polyester, the molar ratio of terephthalic acid to isophthalic acid is preferably 90:10 to 10:90, and may be 25:75 to 75:25 or 60:40 to 40:60. From the viewpoint of the solubility and mechanical strength of the polyester, the total amount of terephthalic acid and isophthalic acid relative to the total amount of dicarboxylic acid components of the polyester is preferably 30 mol% or more, more preferably 40 mol% or more, even more preferably 60 mol% or more, and may be 80 mol% or more.

[0115] Examples of aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, fumaric acid, maleic acid, itaconic acid, citraconic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, and tetrahydrophthalic acid.

[0116] Inclusion of an aliphatic dicarboxylic acid as the dicarboxylic acid component of a polyester resin may improve the compatibility between the polyester resin and the polyimide resin. From the viewpoint of improving compatibility with the polyimide resin, the aliphatic dicarboxylic acid is preferably a dicarboxylic acid having 6 to 12 carbon atoms, particularly 6 to 10 carbon atoms, and among these, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid are preferred because they can also contribute to improving the solubility of the polyester resin.

[0117] Monomers other than diols and dicarboxylic acids may be used as monomer components constituting the polyester resin, as long as the effects of the present invention are not impaired. Examples of monomers other than diols and dicarboxylic acids include polyols having three or more hydroxy groups (e.g., trimethylolpropane, glycerin), monoalcohols (e.g., octyl alcohol, decyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, 2-phenoxyethanol), polycarboxylic acids having three or more carboxy groups (e.g., 1,3,4-benzenetricarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid, pyromellitic acid, trimellitic acid, tetrahydrophthalic acid), monocarboxylic acids (e.g., lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, p-tert-butylbenzoic acid, cyclohexanoic acid), and hydroxycarboxylic acids (e.g., methyl methyl esters). Examples of such an acid include compounds having one or more hydroxy groups and / or one or more carboxy groups, such as lactic acid, glycolic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxyisobutyric acid, 2-hydroxy-2-methylbutyric acid, 2-hydroxyvaleric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxycaproic acid, 10-hydroxystearic acid, 4-hydroxyphenylstearic acid, and 4-(β-hydroxy)ethoxybenzoic acid), lactones (e.g., β-propiolactone, β-butyrolactone, γ-butyrolactone, δ-valerolactone, and ε-caprolactone), and oxiranes (e.g., ethylene oxide), as well as compounds that generate one or more hydroxy groups and / or one or more carboxy groups upon hydrolysis.

[0118] The polymerization method for the polyester resin is not particularly limited, and various known methods can be used, such as a method in which an oligomer is obtained by a transesterification method or a direct esterification method, and then melt polymerization or solid-phase polymerization is performed. In the polymerization of the polyester resin, a dicarboxylic acid derivative such as an acid anhydride may be used as the dicarboxylic acid component.

[0119] From the viewpoint of ensuring the mechanical strength of the film, the weight-average molecular weight of the polyester resin is preferably greater than 10,000, more preferably 15,000 or more, even more preferably 20,000 or more, and may be 30,000 or more. From the viewpoint of ensuring compatibility with the polyimide resin and formability into a film, the weight-average molecular weight of the polyester resin is preferably 200,000 or less, more preferably 150,000 or less, even more preferably 100,000 or less, and may be 80,000 or less.

[0120] From the viewpoint of heat resistance and formability of the film, the glass transition temperature (Tg) of the polyester resin is preferably −25 to 200° C., more preferably 15 to 180° C., even more preferably 40 to 150° C., and may be about 60 to 130° C.

[0121] Commercially available polyester resins may be used. Examples of commercially available polyester resins containing a specific diol as a diol component include OKP4HT (manufactured by Osaka Gas Chemicals, Mw: 38,000, Tg: 142°C), OKP4 (manufactured by Osaka Gas Chemicals, Mw: 40,000, Tg: 121°C), Elitel UE3200G (manufactured by Unitika, Mw: 43,000, Tg: 65°C), Elitel UE3210 (manufactured by Unitika, Mw: 62,000, Tg: 45°C), Elitel UE3240 (manufactured by Unitika, Mw: 50,000, Tg: 40°C), Elitel UE3500 (manufactured by Unitika, Mw: 83,000, Tg: 15°C), Elitel UE3510 (manufactured by Unitika, Mw: 63,000, Tg: -25°C), Elitel UE3 600 (manufactured by Unitika, Mw: 60,000, Tg: 75°C), Elitel UE3690 (manufactured by Unitika, Mw: 46,000, Tg: 90°C), Elitel UE9100 (manufactured by Unitika, Mw: 77,000, Tg: 19°C), Elitel UE9200 (manufactured by Unitika, Mw: 39,000, Tg: 65°C), Elitel UE980 ...800 (manufactured by Unitika, Mw: 46,000, Tg: 90°C), Elitel UE9800 (manufactured by Unitika, Mw: 46,000, Tg: 90°C), Elitel UE9800 (manufactured by Unitika, Mw: Examples of such copolymers include Vylon 200 (manufactured by Nichika, Mw: 40,000, Tg: 85°C), Vylon 200 (manufactured by Toyobo, Mw: 42,000, Tg: 67°C), Vylon 240 (manufactured by Toyobo, Mw: 35,000, Tg: 60°C), Vylon 290 (manufactured by Toyobo, Mw: 61,000, Tg: 72°C), and Vylon 600 (manufactured by Toyobo, Mw: 38,000, Tg: 47°C).

[0122] <Composition of Transparent Resin Film> As described above, the transparent resin film 1 is a blend resin film containing a polyimide-based resin and other resins as resin components. The ratio of the polyimide-based resin to the other resins in the transparent resin film is not particularly limited. The mixing ratio (weight ratio) of the polyimide-based resin to the other resins may be 98:2 to 2:98, 95:5 to 10:90, 90:10 to 15:85, or 65:35 to 50:50. The higher the ratio of the polyimide-based resin, the higher the elastic modulus and pencil hardness of the film, and the better the mechanical strength. The higher the ratio of the other resin, the less coloring of the film, the higher the total light transmittance, the lower the yellowness index (YI), and the higher the transparency.

[0123] In order to fully exert the effect of improving transparency by mixing the polyimide-based resin with the other resin, the ratio of the other resin to the total of the polyimide-based resin and the other resin is preferably 10 to 90% by weight, more preferably 15 to 85% by weight, and even more preferably 20 to 80% by weight, and may be 30 to 70% by weight, 35 to 65% by weight, or 40 to 60% by weight.

[0124] In addition to the above resin components, the transparent resin film may contain organic or inorganic low-molecular-weight compounds, etc. The transparent resin film may also contain additives such as bluing agents, ultraviolet absorbers, flame retardants, stabilizers, crosslinking agents, surfactants, leveling agents, plasticizers, and fine particles.

[0125] The transparent resin film may contain organic fine particles such as polystyrene or crosslinked acrylic resin, or inorganic fine particles such as silica or layered silicate, for the purpose of improving blocking resistance or adjusting the refractive index. However, the incorporation of fine particles can cause a decrease in the transmittance of the film or an increase in haze. In particular, silicon oxides such as silica are useful for lowering the refractive index of the film, but they tend to be poorly dispersed in the resin matrix, which can cause a decrease in transparency, mechanical strength, and flex resistance. Therefore, the content of silicon oxide is preferably 5 parts by weight or less, more preferably 1 part by weight or less, more preferably 0.5 parts by weight or less, and may even be 0.1 parts by weight or less, per 100 parts by weight of the total resin components.

[0126] <Preparation of Transparent Resin Film> The transparent resin film 1 is prepared by a solution method in which a solution containing the above-mentioned polyimide resin and other resins is applied onto a support, and the solvent is then dried and removed.

[0127] The solvent is not particularly limited as long as it exhibits solubility in both polyimide-based resins and other resins. Examples of solvents include amide-based solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; ether-based solvents such as tetrahydrofuran and 1,4-dioxane; ketone-based solvents such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diethyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone; and alkyl halide solvents such as chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene, dichlorobenzene, and methylene chloride. Among these, ketone-based solvents and alkyl halide solvents are preferred because they have excellent solubility in polyimide-based resins and the like, have low boiling points, and allow for easy removal of residual solvent during film production.

[0128] As a method for applying the resin solution onto a support, a known method using a bar coater, a comma coater, or the like can be applied. As the support, a glass substrate, a metal substrate such as SUS, a metal drum, a metal belt, a plastic film, or the like can be used. 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, or the like, as the support, and produce the film by a roll-to-roll method. When using a plastic film as the support, it is only necessary to appropriately select a material that is insoluble in the solvent of the resin solution (dope).

[0129] The arithmetic mean roughness Sa and maximum height Sz of the support surface are not particularly limited. When the support is a plastic film, the arithmetic mean roughness Sa may be 0.5 nm or more or 1.0 nm or more, and the maximum height Sz may be 10 nm or more or 20 nm or more, from the viewpoint of ensuring smoothness during transport and preventing blocking when wound into a roll. If the arithmetic mean roughness Sa and maximum height Sz of the support surface are large, the surface irregularities of the support may be transferred to the surface of the transparent resin film, causing whitening unevenness. However, as described below, by forming a hard coat layer on the surface (side B) that was in contact with the support during film formation of the transparent resin film, the whitening unevenness can be suppressed.

[0130] It is preferable to heat the film when drying the solvent. The heating temperature is not particularly limited as long as it can remove the solvent and prevent the resulting film from becoming discolored, and is appropriately set between room temperature and about 250°C, with 50°C to 220°C being preferred. The heating temperature may be increased in stages. To increase the efficiency of solvent removal, the resin film may be peeled off from the support and dried after drying has progressed to a certain extent. Drying may be carried out in air or nitrogen. Heating may be carried out under reduced pressure to promote solvent removal.

[0131] The film may be stretched in one or more directions for the purpose of improving the mechanical strength, etc. When the film is stretched, the polymer chains are oriented in the stretching direction, which tends to improve the strength of the film in the in-plane direction and suppress the occurrence of breakage or cracks in the film.

[0132] Although films made solely of acrylic resins may have low toughness, the use of a compatible system of polyimide resins and acrylic resins may improve the strength of the film. Furthermore, when a film made of a compatible system of polyimide resins and other resins is stretched, the polymer chains are oriented in the stretching direction, increasing the tensile modulus in the stretching direction, which tends to improve flex resistance.

[0133] For example, films used as cover windows or substrate materials for foldable displays are repeatedly folded along the folding axis at the same location, and therefore are required to have high mechanical strength in a direction perpendicular to the folding axis. Therefore, by arranging the film so that the stretching direction is perpendicular to the folding axis, even when the film is repeatedly folded, breakage or cracking of the film at the folding location is unlikely to occur, and a device with high bending resistance can be provided.

[0134] The conditions for stretching the film are not particularly limited. For example, the stretching temperature is about ±40°C of the glass transition temperature of the film, and may be about 120 to 300°C, 150 to 250°C, or 180 to 230°C. The stretching ratio is about 30 to 200%, and may be 50 to 150%, 80 to 120%, or 80 to 100%. The higher the stretching ratio, the higher the tensile modulus in the stretching direction tends to be. On the other hand, if the stretching ratio is excessively high, the mechanical strength in the direction perpendicular to the stretching direction tends to decrease, and the handleability of the film may be reduced.

[0135] The film may be biaxially stretched to increase the strength in any in-plane direction. The biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. In biaxial stretching, the stretching ratio in one direction and the stretching ratio in the perpendicular direction may be the same or different. When a difference in stretching ratio is made, the mechanical strength in the direction with the larger stretching ratio tends to be relatively larger. When a biaxially stretched film with anisotropic stretching ratio is used in a foldable device, it is preferable to arrange it so that the direction with the larger stretching ratio is perpendicular to the folding axis.

[0136] From the viewpoint of imparting self-supporting properties to the film and imparting strength applicable as a cover window material, the thickness of the transparent resin film 1 is 26 μm or more, and may be 30 μm or more, 35 μm or more, or 40 μm or more. From the viewpoint of ensuring bendability (flexibility) applicable to foldable devices, the thickness of the transparent resin film 1 is preferably 100 μm or less, more preferably 80 μm or less, and may be 70 μm or less, 60 μm or less, or 50 μm or less.

[0137] When the transparent resin film 1 is a stretched film, the thickness after stretching is preferably within the above range. The thickness of the film before stretching may be 50 μm or more, 80 μm or more, 100 μm or more, or 120 μm or more.

[0138] <Characteristics of Transparent Resin Film> The transparent resin film preferably has a single glass transition temperature in differential scanning calorimetry (DSC) and / or dynamic mechanical analysis (DMA). When the polyimide resin contained in the transparent resin film is compatible with other resins, the transparent resin film exhibits a single glass transition temperature.

[0139] The haze of the transparent resin film is preferably 10% or less, more preferably 5% or less, and even more preferably 4% or less, and may be 3.5% or less, 3% or less, 2% or less, 1% or less, or 0.5% or less. When the transparent resin film contains a polyimide-based resin and another resin, a low haze can be achieved by using, as the other resin, an acrylic-based resin, a polyester-based resin, or the like that has high compatibility with the polyimide-based resin.

[0140] The total light transmittance of the transparent resin film is preferably 88.0% or more, more preferably 89.0% or more, even more preferably 90.0% or more, and may be 90.5% or more, 910% or more, or 91.2% or more. The higher the total light transmittance, the higher the white brightness of the display and the more excellent the visibility. As mentioned above, by mixing a polyimide-based resin with another resin, the refractive index tends to be lower and the total light transmittance tends to be higher compared to when the polyimide-based resin is used alone.

[0141] The yellowness index (YI) of the transparent resin film is preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.0 or less. The yellowness index (YI) of the transparent resin film is preferably −3.0 or more, more preferably −2.0 or more, and even more preferably −1.0 or more. By mixing a polyimide-based resin with another resin such as an acrylic-based resin or a polyester-based resin, the coloring of the film tends to be less and the absolute value of YI tends to be smaller than when a polyimide-based resin is used alone.

[0142] The refractive index of the transparent resin film is not particularly limited, but is preferably 1.600 or less from the viewpoint of improving total light transmittance. The refractive index of the transparent resin film is more preferably 1.580 or less, and even more preferably 1.560 or less. The refractive index of the transparent resin film is generally 1.400 or more, and may be 1.500 or more, 1.530 or more, or 1.540 or more.

[0143] The refractive index of a film containing only polyimide resin as a resin component is generally higher than 1.600, resulting in a large amount of light reflection (high reflectance) due to the difference in refractive index at the air interface and at the interface with other components, resulting in a low light transmittance. A mixed resin system of a polyimide resin and another resin with a lower refractive index than the polyimide resin has a lower refractive index than the polyimide resin alone, reducing light reflection at the interface and increasing the total light transmittance. In particular, since acrylic resins have a low refractive index, using an acrylic resin as the other resin tends to lower the refractive index of the transparent resin film and increase the total light transmittance.

[0144] The tensile modulus of the transparent resin film is preferably 3.0 GPa or more, more preferably 3.5 GPa or more, even more preferably 4.5 GPa or more, and may be 5.0 GPa or more, 5.5 GPa or more, or 6.0 GPa or more. The higher the tensile modulus, the more excellent the mechanical strength such as hardness and flex resistance tends to be.

[0145] The transparent resin film may have anisotropy in the tensile modulus in the plane. When the transparent resin film is a stretched film, the tensile modulus in the stretching direction tends to be greater than the tensile modulus in the direction perpendicular to the stretching direction. When the transparent resin film is a biaxially stretched film or a fixed-end uniaxially stretched film, the tensile modulus in all directions in the plane may be greater than before stretching. When the transparent resin film has an in-plane anisotropy in the tensile modulus, it is preferable that the maximum in-plane tensile modulus (generally the tensile modulus in the stretching direction) is within the above range.

[0146] The transparent resin film 1 has an arithmetic mean roughness Sa of preferably 1 nm or less, more preferably 0.5 nm or less, of at least one main surface. The transparent resin film 1 has a maximum height Sz of preferably 70 nm or less, more preferably 60 nm or less, even more preferably 50 nm or less, and may be 40 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less, of at least one main surface.

[0147] The arithmetic mean roughness Sa and maximum height Sz are the arithmetic mean roughness (arithmetic mean height) Sa and maximum height Sz of a contoured surface as defined in ISO 25178-2 (JIS B0681-2:2018), and are indices that represent surface roughness. Sa and Sz are determined from the contoured surface from which the effects of waviness and thickness unevenness have been removed by filtering a 0.28 mm x 0.21 mm area of ​​the three-dimensional surface profile measured using a non-contact interferometric three-dimensional roughness meter and vertical scanning low-coherence interferometry in accordance with ISO 25178-604.

[0148] When a transparent resin film produced by a solution method is viewed from an oblique direction (a direction deviating from the normal direction of the film surface), the entire film surface appears whitish, and variations in the shade of whiteness appear as unevenness (hereinafter, this phenomenon will be referred to as "whitening unevenness"), which may reduce the visibility of the display.

[0149] When the arithmetic mean roughness Sa of the film surface is greater than 1 nm, scattering of transmitted light is likely to occur, and the entire film may appear slightly whitish, but this alone is not visually noticeable as unevenness. When the film has large thickness unevenness in addition to surface roughness, the incident angle of transmitted light varies within the plane, causing variations in the intensity of scattered light. When viewed from an oblique direction, there are areas where the scattered light is strongly visible and appears white, and this variation in whiteness (shading) within the film plane is thought to be recognized as white unevenness.

[0150] The thicker the film, the greater the thickness unevenness tends to be, and this tendency is particularly pronounced when a composition containing a polyimide resin is formed into a film by a solution method. Transparent resin films with a thickness of 26 μm or more are prone to visible whitening unevenness due to the influence of thickness unevenness and surface roughness. If the surface roughness of one main surface (first main surface) of the transparent resin film 1 is small and Sa and Sz are within the above ranges, even if Sa and Sz of the other main surface (second main surface) are large, by forming a hard coat layer 3 on the main surface with the relatively larger surface roughness, the surface unevenness of the transparent resin film is filled in, and whitening unevenness can be suppressed.

[0151] The other main surface (second main surface) of the transparent resin film 1 may have an arithmetic mean roughness Sa and a maximum height Sz greater than those of the one main surface (first main surface). The arithmetic mean roughness Sa of the second main surface 1B of the transparent resin film 1 may be greater than 1 nm or may be 1.5 nm or greater. If the arithmetic mean roughness Sa of the second main surface 1B of the transparent resin film 1 is excessively large, even if a hard coat layer is formed, whitening unevenness may not be sufficiently suppressed. Therefore, the arithmetic mean roughness Sa of the second main surface 1B of the transparent resin film 1 is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 20 nm or less.

[0152] The maximum height Sz of the second main surface 1B of the transparent resin film 1 may be greater than 10 nm, or may be 30 nm or more, 50 nm or more, 60 nm or more, or 70 nm or more. The maximum height Sz of the second main surface 1B of the transparent resin film 1 is preferably 1000 nm or less, more preferably 500 nm or less, and may be 300 nm or less, 200 nm or less, or 100 nm or less.

[0153] A film obtained by applying a resin solution onto a support and drying and removing the solvent has the surface irregularities of the support transferred to the release surface (side B) from the support. When the support is a plastic film, the plastic film has surface irregularities to ensure slippage during film transport and to prevent blocking when wound into a roll. When the support is an endless belt, the support has surface irregularities due to the surface irregularities of the metal material constituting the belt, or due to residual peeling or scratches caused by repeated use of the belt.

[0154] Since the surface irregularities of the support are transferred to side B of the transparent resin film 1, the arithmetic mean roughness Sa is often greater than 1 nm. In particular, when the support is a plastic film, the surface irregularities of the support tend to be greater than when the support is a metal endless belt, and the transfer of the irregularities to side B of the transparent resin film tends to increase Sa and Sz. On the other hand, the air side (side A), which is the side opposite the support during film formation, is not affected by the surface irregularities of the support, so is smoother than side B and tends to have an arithmetic mean roughness Sa of 1 nm or less.

[0155] [Hard Coat Layer] The hard coat film of the present invention has a hard coat layer 3 on one surface of a transparent resin film 1. By providing the hard coat layer 3 on the surface of the transparent resin film 1, scratch resistance and hardness are improved. By providing the hard coat layer 3 on the main surface of the transparent resin film 1 that has a relatively greater surface roughness, the surface irregularities of the transparent resin film 1 are filled in, and whitening unevenness tends to become less visible.

[0156] <Hard Coating Material> The material constituting the hard coating layer is not particularly limited as long as it has the function of preventing the occurrence of scratches, and examples thereof include polyester-based, acrylic-based, urethane-based, amide-based, siloxane-based, and epoxy-based resins. Among these, an acrylic hard coating layer which is a cured product of an acrylic hard coating resin composition, or a siloxane hard coating layer which is a cured product of a siloxane hard coating resin composition is preferred from the viewpoint of preventing the occurrence of scratches.

[0157] (Acrylic Hard Coat Material) The acrylic hard coat material contains a monomer or oligomer having a (meth)acryloyl group in the molecule as a curable resin component. The molecular weight of the acrylic monomer or oligomer is, for example, about 200 to 10,000. The acrylic hard coat material can control hardness, scratch resistance, bending resistance, optical properties, etc. by combining multiple types of monomers or oligomers having a (meth)acryloyl group. From the viewpoint of curability by photoradical polymerization, it is preferable that the hard coat material have an acryloyl group.

[0158] Specific examples of oligomers having a (meth)acryloyl group include urethane (meth)acrylate, polyester (meth)acrylate, and epoxy (meth)acrylate. The oligomer may have two or more (meth)acryloyl groups in one molecule. The molecular weight of the oligomer is preferably 10,000 or less.

[0159] Examples of acrylic monomers include compounds having one (meth)acryloyl group, such as methyl (meth)acrylate and 2-ethylhexyl (meth)acrylate; and compounds having two (meth)acryloyl groups in one molecule, such as ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, and 1,6-hexanediol di(meth)acrylate. Compounds having (meth)acryloyl groups include compounds having three or more (meth)acryloyl groups in one molecule, such as glycerin tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0160] From the viewpoint of enhancing the scratch resistance of the hard coat layer, the acrylic hard coat material preferably contains a trifunctional or higher polyfunctional (meth)acrylate. The functional group equivalent of the (meth)acryloyl group of the polyfunctional (meth)acrylate, i.e., the molecular weight per (meth)acryloyl group, is preferably 80 to 150 g / eq. Among the above-exemplified polyfunctional (meth)acrylates, dipentaerythritol hexa(meth)acrylate is particularly preferred.

[0161] (Siloxane-based hard coat material) The siloxane-based hard coat material contains a curable compound having a siloxane bond as a curable resin component. From the viewpoint of scratch resistance, the siloxane-based curable compound preferably has an epoxy group as a polymerizable functional group, and among them, a polyorganosiloxane compound containing an alicyclic epoxy group is preferred. Such siloxane-based hard coat materials are disclosed in WO2014 / 204010, WO2018 / 096729, WO2020 / 040209, etc., and these descriptions can be used for reference.

[0162] Siloxane-based hard coat materials having alicyclic epoxy groups as polymerizable functional groups have little shrinkage upon curing, so curling and cracking are unlikely to occur even if the hard coat layer is made thick.

[0163] The polyorganosiloxane compound having an alicyclic epoxy group can be obtained by condensation of a silane compound represented by the general formula (5): [Y-Si(OR １ ) ｘ R ２ ３－ｘ ] (5)

[0164] In general formula (5), R １ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an isopropyl group, an isobutyl group, a cyclohexyl group, and an ethylhexyl group.

[0165] The silane compound represented by the general formula (5) has two or three (—OR１ ) Si—OR １ Since R is hydrolyzable, a polyorganosiloxane compound can be obtained by condensation of the silane compound. １ The number of carbon atoms in R is preferably 3 or less, １ is particularly preferably a methyl group.

[0166] In general formula (5), R ２ is a hydrogen atom or a monovalent hydrocarbon group selected from the group consisting of alkyl groups having 1 to 10 carbon atoms, aryl groups having 6 to 25 carbon atoms, and aralkyl groups having 7 to 12 carbon atoms. Specific examples of the hydrocarbon group include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, isopropyl, isobutyl, cyclohexyl, ethylhexyl, benzyl, phenyl, tolyl, xylyl, naphthyl, and phenethyl groups.

[0167] In the general formula (5), x is 2 or 3. When x=3 (i.e., three alkoxy groups (or hydroxy groups) -OR １ is bonded), the silane compound is ２ It does not have. From the viewpoint of forming a network-like polyorganosiloxane compound and increasing the number of epoxy groups contained in the polyorganosiloxane compound to increase the hardness of the cured film, it is preferable that x = 3 in the general formula (5). A silane compound in which x = 2 and a silane compound in which x = 3 may be used in combination. Furthermore, for the purpose of adjusting the molecular weight of the polyorganosiloxane compound obtained by condensation, a silane compound in which x is 1 may be used in addition to a silane compound in which x is 2 or 3.

[0168] In general formula (5), Y is a monovalent organic group containing an alicyclic epoxy group. Examples of Y include an alicyclic epoxy group, an alkyl group having an alicyclic epoxy group as a substituent, and an alkylene glycol group having an alicyclic epoxy group as a substituent. From the viewpoint of heat resistance and flex resistance, an alkyl group having an alicyclic epoxy group as a substituent is preferred.

[0169] Specific examples of alkyl groups having an alicyclic epoxy group as a substituent include a (3,4-epoxycyclohexyl)methyl group, a 2-(3,4-epoxycyclohexyl)ethyl group, a 3-(3,4-epoxycyclohexyl)propyl group, a 4-(3,4-epoxycyclohexyl)butyl group, a 5-(3,4-epoxycyclohexyl)pentyl group, a 6-(3,4-epoxycyclohexyl)hexyl group, a 7-(3,4-epoxycyclohexyl)heptyl group, an 8-(3,4-epoxycyclohexyl)octyl group, a 9-(3,4-epoxycyclohexyl)nonyl group, a 10-(3,4-epoxycyclohexyl)decyl group, an 11-(3,4-epoxycyclohexyl)undecyl group, and a 12-(3,4-epoxycyclohexyl)dodecyl group.

[0170] Specific examples of the silane compound represented by general formula (5) include (3,4-epoxycyclohexyl)trimethoxysilane, (3,4-epoxycyclohexyl)methyldimethoxysilane, (3,4-epoxycyclohexyl)dimethylmethoxysilane, (3,4-epoxycyclohexyl)triethoxysilane, (3,4-epoxycyclohexyl)methyldiethoxysilane, (3,4-epoxycyclohexyl)dimethylethoxysilane, {(3,4-epoxycyclohexyl)methyl}trimethoxysilane, {(3,4-epoxycyclohexyl)methyl}methyldimethoxysilane, {(3,4-epoxycyclohexyl)methyl}dimethylmethoxysilane, {(3,4-epoxycyclohexyl)methyl}dimethylmethoxysilane, {(3,4-epoxycyclohexyl)methyl}triethoxysilane, {(3,4-epoxycyclohexyl)methyl}methyldiethoxysilane, {(3,4-epoxycyclohexyl)methyl}dimethylethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}trimethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}methyldimethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}dimethylmethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}triethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}methyldiethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}dimethylethoxysilane, etc. Among these, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane is preferred from the viewpoints of ease of condensation reaction and hardness of the cured product.

[0171] The polyorganosiloxane compound as the condensate of the silane compound may be a condensate of the silane compound of the general formula (5) with another silane compound.

[0172] The silane compound is reacted with water to form a Si—OR １ The part is hydrolyzed, and the hydrolyzate is condensed to form an Si—O—Si bond, producing a condensate of the silane compound having an alicyclic epoxy group (a polyorganosiloxane compound).

[0173] From the viewpoint of increasing the hardness of the cured film (hard coat layer), the weight average molecular weight of the polyorganosiloxane compound is preferably 500 or more. Also, from the viewpoint of suppressing volatilization, the weight average molecular weight of the polyorganosiloxane compound is preferably 500 or more. On the other hand, if the molecular weight is excessively large, cloudiness may occur due to a decrease in compatibility with other components in the composition. Therefore, the weight average molecular weight of the polyorganosiloxane compound is preferably 20,000 or less.

[0174] <Polymerization initiator> The hard coat composition preferably contains a polymerization initiator in addition to the above-mentioned curable resin component. As the polymerization initiator, a photopolymerization initiator is preferable. An acrylic hard coat composition containing a compound having a (meth)acryloyl group as a curable resin component preferably contains a photoradical polymerization initiator that generates radicals by light. A siloxane hard coat composition containing a polyorganosiloxane compound having an epoxy group as a curable resin component preferably contains a photoacid generator (photocationic polymerization initiator) that generates acid by light.

[0175] Examples of the photoradical polymerization initiator include 2,2-dimethoxy-2-phenylacetophenone, acetophenone, benzophenone, xanthone, 3-methylacetophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, benzoin propyl ether, benzil dimethyl ketal, N,N,N',N'-tetramethyl-4,4'-diaminobenzophenone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, and other thioxanthan-based compounds.

[0176] Examples of the photoacid generator include onium salts which combine anions (strong acids) such as antimony hexafluoride, boron tetrafluoride, phosphorus hexafluoride, fluoroalkyl phosphorus fluoride, and fluoroalkyl gallium fluoride with cations such as sulfonium, ammonium, phosphonium, iodonium, and selenium; iron-arene complexes; silanol-metal chelate complexes; sulfonic acid derivatives such as disulfones, disulfonyldiazomethanes, disulfonylmethanes, sulfonylbenzoylmethanes, imide sulfonates, and benzoin sulfonates; and organic halogen compounds.

[0177] <Other Components Constituting the Hard Coat Composition> The hard coat composition for forming the hard coat layer may contain, in addition to the curable resin component and the polymerization initiator, a solvent and various additives. Examples of the additives include a fluorine-based or silicone-based leveling agent, a sensitizer, a reactive diluent, fine particles, a filler, a dispersant, a plasticizer, an ultraviolet absorber, a surfactant, an antioxidant, a colorant, and a viscosity modifier.

[0178] <Formation of Hard Coat Layer> A hard coat composition is applied to one main surface of the transparent resin film 1, and if necessary, the solvent is dried and removed, followed by curing to form the hard coat layer 3. When the surface roughness of the front and back of the transparent resin film 1 differs, by forming the hard coat layer 3 on the main surface with the relatively larger surface roughness (the surface with the larger Sa), the surface irregularities of the transparent resin film are filled in and become less noticeable, and whitening unevenness tends to be suppressed.

[0179] As described above, in films produced by the solution method, the surface to be peeled from the support (side B) generally has greater surface irregularities than the air side (side A). Therefore, from the viewpoint of suppressing whitening unevenness, it is preferable to form a hard coat layer 3 on side B of the transparent resin film 1.

[0180] Examples of methods for applying the hard coat composition onto a transparent resin film include roll coating such as bar coating, gravure coating, and comma coating, die coating such as slot die coating and fountain die coating, spin coating, spray coating, and dip coating. Before applying the curable resin composition, the surface of the transparent resin film may be subjected to a surface treatment such as corona treatment or plasma treatment. Furthermore, an easy-adhesion layer or the like may be provided on the surface of the transparent resin film.

[0181] When the hard coat composition is irradiated with active energy rays or heated, active species such as acids and radicals are generated from the photopolymerization initiator, and the curable resin component of the hard coat composition is cured. From the viewpoint of curing reactivity, it is preferable that the curable resin composition contains a photopolymerization initiator and is cured by irradiation with active energy rays. Examples of active energy rays irradiated during photocuring include visible light, ultraviolet light, infrared light, X-rays, α-rays, β-rays, γ-rays, and electron beams. Ultraviolet light is preferred as the active energy ray because of its high curing reaction rate and excellent energy efficiency. The cumulative irradiation dose of the active energy ray is, for example, 50 to 10,000 mJ / cm. ２ The curing temperature is about 150° C., and may be set depending on the type and amount of the photocationic polymerization initiator, the thickness of the hard coat layer, etc. The curing temperature is not particularly limited, but is usually 150° C. or lower.

[0182] The thickness of the hard coat layer 3 is 1 to 50 μm, preferably 3 μm or more, and more preferably 5 μm or more. The thicker the hard coat layer, the more improved the pencil hardness and scratch resistance tend to be. On the other hand, if the hard coat layer is too thick, the flex resistance decreases, so the thickness of the hard coat layer is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less.

[0183] [Hard Coat Film] The thickness of the hard coat film 11 (total thickness of the transparent resin film 1 and the hard coat layer 3) is not particularly limited, but from the viewpoint of mechanical strength, it is preferably 30 μm or more, more preferably 40 μm or more, and may be 50 μm or more, and from the viewpoint of flexibility, it is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, and particularly preferably 70 μm or less.

[0184] The arithmetic mean roughness Sa of the non-hard coat layer surface 1A of the hard coat film 11 (the first main surface of the transparent resin film 1) is preferably 1 nm or less, and may be 0.5 nm or less. The maximum height Sz of the non-hard coat layer surface 1A is preferably 70 nm or less, more preferably 50 nm or less, even more preferably 30 nm or less, and particularly preferably 10 nm or less. Forming the hard coat layer 3 on the second main surface 1B of the transparent resin film 1 may change the periodic surface shape of the film, such as waviness. However, since Sa and Sz are determined from the contour curved surface from which the influence of these periodic surface shapes has been removed by filtering, Sa and Sz of the non-hard coat layer surface 1A hardly change before and after the formation of the hard coat layer.

[0185] As described above, if the hard coat layer 3 is formed on the second main surface 1B, which has a relatively large surface roughness, the surface irregularities of the second main surface 1B are filled with the hard coat layer. If the arithmetic mean roughness Sa of the first main surface 1A (the surface on which the hard coat layer is not formed) of the transparent resin film 1 is small, whitening unevenness in the hard coat film 11 is less likely to be visually recognized.

[0186] The haze of the hard coat film is preferably 1% or less, more preferably 0.7% or less, and even more preferably 0.5% or less. The haze can be reduced by using a resin compatible with the polyimide resin as the other resin constituting the transparent resin film. Note that the polyimide resin and the other resin do not necessarily need to be completely compatible with each other, and may have a microphase separation structure small enough not to affect the optical properties.

[0187] The total light transmittance of the hard coat film is preferably 89.0% or more, more preferably 90.0% or more, even more preferably 90.3% or more, and may be 90.5% or more or 91.0% or more. Polyimide resins have a high refractive index and high reflectance at the interface between the film and air and the interface between the film and the hard coat layer, so polyimide transparent resin films have low total light transmittance. Blending a polyimide resin with a resin (such as an acrylic resin) that has a lower refractive index than the polyimide resin reduces the refractive index, reducing the reflectance at the interface, and thereby increasing the total light transmittance.

[0188] The yellowness index (YI) of the hard coat film is preferably -3.0 to 3.0, more preferably -2.0 to 2.0, and even more preferably -1.0 to 1.0. A small absolute value of YI is preferable in terms of improving the visibility of the display and improving the color tone. Transparent polyimide is slightly colored yellow, so polyimide-based transparent resin films tend to have a high YI. By using a blend of a polyimide-based resin with other resins such as an acrylic resin or a polyester-based resin as the transparent resin film 1, it is possible to reduce coloration and decrease the YI of the hard coat film 11.

[0189] The pencil hardness of the surface of the hard coat layer of the hard coat film is preferably H or higher, more preferably 2H or higher, even more preferably 3H or higher, and may be 4H or higher or 5H or higher. The higher the pencil hardness, the less likely scratches or dents will occur due to external forces. The higher the pencil hardness, the better the scratch resistance, making it suitable for use in applications such as cover windows placed on the outermost surface of displays. When the hard coat film is used as a material for a foldable display, it is preferable that the hard coat film has excellent bending resistance and can be repeatedly bent at a radius of 1.5 mm or more 100,000 times.

[0190] The hard coat film of the present invention has excellent mechanical strength and flex resistance, and is highly transparent, and therefore can be suitably used as a cover window to be placed on the surface of an image display panel. The hard coat film of the present invention has high degradability and excellent environmental safety because the polyimide resin contained in the transparent resin film is substantially free of a specific fluorine structure.

[0191] The present invention will be described in more detail below with reference to examples, but is not limited to the following examples. In the following, the flow direction during coating is defined as the MD direction, and the direction perpendicular to the MD direction is defined as the TD direction.

[0192] [Preparation of Polyimide Resin] Dimethylformamide (DMF) was placed in a separable flask and stirred under a nitrogen atmosphere. Diamine and tetracarboxylic dianhydride were added in the ratios (mol %) shown in Table 1, and the mixture was stirred under a nitrogen atmosphere for 5 to 10 hours to react, yielding a polyamic acid solution with a solids concentration of 18 wt %.

[0193] To 100 g of polyamic acid solution, 5.5 g of pyridine was added as an imidization catalyst. After complete dispersion, 8 g of acetic anhydride was added and the mixture was stirred at 90°C for 3 hours. After cooling to room temperature, 100 g of 2-propyl alcohol (IPA) was added at a rate of 2-3 drops / second while stirring the solution, causing polyimide to precipitate. An additional 150 g of IPA was added, and the mixture was stirred for approximately 30 minutes. After that, the mixture was subjected to suction filtration using a Kiriyama funnel. The resulting solid was washed with IPA and then dried for 12 hours in a vacuum oven set at 120°C to obtain polyimide resins 1, 2, and 3 (PI1, PI2, and PI3).

[0194] The compositions of the polyimide resins and their weight-average molecular weights (Mw) in terms of polystyrene measured by GPC are shown in Table 1. The polyimide compositions (amounts of diamine and tetracarboxylic dianhydride) are shown as molar ratios, with the total amount of diamine taken as 100 parts by mole, and the compounds are abbreviated as follows:

[0195] <Tetracarboxylic acid dianhydrides> BPAF: 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride 6FDA: 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride CBDA: 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride

[0196] <Diamine> TFMOB: 2,2'-bis(trifluoromethoxy)benzidine TFMB: 2,2'-bis(trifluoromethyl)benzidine

[0197]

[0198] [Preparation of Transparent Resin Film] <Film 1> Polyimide resin 1 (PI1) and a commercially available acrylic resin ("Parapet G" manufactured by Kuraray; a copolymer of methyl methacrylate / methyl acrylate (monomer ratio 87 / 13), glass transition temperature 109°C, acid value 0.0 mmol / g, molecular weight 100,000; hereinafter referred to as "acrylic resin" (Ac)) were dissolved in methylene chloride at a weight ratio of PI1 / Ac = 50 / 50, and 5.6 parts by weight of a triazine-based ultraviolet absorber ("ADK STAB LA-31RG" manufactured by ADEKA Corporation) and 0.018 parts by weight of a phthalocyanine-based bluing agent ("ET 4B403" manufactured by Dainichiseika Chemicals & Chemicals Co., Ltd.) were added relative to a total of 100 parts by weight of the resins to prepare a solution with a solids concentration of 15% by weight.

[0199] This solution was applied to a PET film support ("Lumirror U40" manufactured by Toray Industries, Inc.: arithmetic mean surface roughness Sa of 1 nm, maximum height Sz of 41 nm) using a roll-to-roll coating and drying facility, and the film was passed through a drying oven set to increase the temperature stepwise from 30°C to 45°C to obtain a primary dried film with a residual solvent content of 10 to 15 wt %. Hereinafter, the air side during primary film production will be referred to as "side A," and the side in contact with the support will be referred to as "side B."

[0200] The primary dried film was peeled from the support (PET film) and subjected to secondary drying in a drying oven set to gradually increase the temperature from 90° C. to 150° C. to obtain a film with a residual solvent content of approximately 1 wt % and a thickness of 105 μm. The film thickness was measured using a contact thickness meter.

[0201] The obtained film was subjected to fixed-end uniaxial stretching using a stretching machine equipped with a heating oven at a temperature of 215°C with the TD direction as the stretching direction and a stretch ratio of 115% (the TD length was 2.15 times that of the film before stretching) to obtain a stretched film with a thickness of 50 μm.

[0202] <Film 2> Polyimide resin 1 (PI1) and a commercially available polyester resin ("Elitel UE3600" manufactured by Unitika Co., Ltd.; polyester containing a bisphenol alkylene oxide adduct as a diol component, weight average molecular weight 60,000, glass transition temperature 75°C; hereinafter referred to as "polyester resin" (PEs)) were dissolved in methylene chloride at a weight ratio of PI1 / PEs = 50 / 50, and 5.6 parts by weight of a triazine-based ultraviolet absorber ("ADK STAB LA-31RG" manufactured by ADEKA Corporation) and 0.018 parts by weight of a phthalocyanine-based bluing agent ("ET 4B403" manufactured by Dainichiseika Chemicals Co., Ltd.) were added per 100 parts by weight of the total resins to prepare a solution with a solids concentration of 10% by weight.

[0203] This solution was applied to a PET film ("PJ-101" manufactured by Toray Industries, Inc.: arithmetic mean surface roughness Sa of 3 nm, maximum height Sz of 79 nm) as a support using a roll-to-roll coating and drying facility, and the film was passed through a drying oven set to gradually increase the temperature from 30°C to 45°C to obtain a primary dried film with a residual solvent content of 10 to 15 wt%. The primary dried film was peeled from the support, and the primary dried film was dried by heating in an air atmosphere for 15 minutes at 40°C, 15 minutes at 60°C, 15 minutes at 90°C, 15 minutes at 120°C, 15 minutes at 150°C, and 15 minutes at 200°C to obtain a film with a thickness of 105 μm.

[0204] The obtained film was uniaxially stretched with fixed ends at a stretching ratio of 115% in the TD direction at a temperature of 170° C. using a stretching machine equipped with a heating oven to obtain a stretched film with a thickness of 50 μm.

[0205] <Film 3> Polyimide resin 2 (PI2) and a commercially available acrylic resin (Ac) were dissolved in methylene chloride at a weight ratio of PI2 / Ac = 55 / 45, and 5.6 parts by weight of a triazine-based ultraviolet absorber ("ADEKA STAB LA-31RG" manufactured by ADEKA Corporation) was added per 100 parts by weight of the resins in total to prepare a solution with a solids concentration of 15% by weight.

[0206] This solution was applied to a PET film and subjected to primary and secondary drying in the same manner as in the production of Film 1, to obtain a film having a thickness of 63 μm and a residual solvent content of approximately 1 wt %. The obtained film was subjected to fixed-end uniaxial stretching at a temperature of 205°C and a stretch ratio of 115% in the TD direction using a stretching machine equipped with a heating oven, to obtain a stretched film having a thickness of 25 μm.

[0207] <Film 4> Polyimide resin 2 (PI2) and a commercially available acrylic resin (Ac) were dissolved in methylene chloride at a weight ratio of PI2 / Ac = 55 / 45, and 5.6 parts by weight of a triazine-based ultraviolet absorber ("ADEKA STAB LA-31RG" manufactured by ADEKA Corporation) was added per 100 parts by weight of the resins in total to prepare a solution with a solids concentration of 15% by weight.

[0208] This solution was applied to a PET film and subjected to primary and secondary drying in the same manner as in the production of Film 1, to obtain a film having a thickness of 110 μm and a residual solvent content of approximately 1 wt %. The obtained film was subjected to fixed-end uniaxial stretching at a stretch ratio of 120% in the TD direction at a temperature of 215°C using a stretching machine equipped with a heating oven, to obtain a stretched film having a thickness of 50 μm.

[0209] [Evaluation of Transparent Resin Films] Films 1 and 2 were measured for the tensile modulus as described below, and films 1 to 4 were measured for the arithmetic mean roughness Sa and maximum height Sz as described below.

[0210] <Tensile modulus> The film was cut into strips with a width of 10 mm, and after standing at 23°C / 55% RH for one day to condition the humidity, a tensile test was carried out using a tensile tester "AUTOGRAPH AGS-X" manufactured by Shimadzu Corporation under the following conditions to calculate the tensile modulus. The tensile test was carried out in both the MD and TD directions. Grip distance: 100 mm, Pulling speed: 20.0 mm / min, Measurement temperature: 23°C

[0211] <Arithmetic mean roughness Sa and maximum height Sz> Using a white light interference microscope (ZYGO NEWVIEW7300 manufactured by ZYGO), the three-dimensional surface shape of sides A and B of the film was measured with a 50x objective lens. The measurement range was 0.28 mm x 0.21 mm, and the entire area was used as the reference area. In order to eliminate the influence of periodic surface shapes such as waviness of the entire film, the following filter conditions were applied to calculate the arithmetic mean roughness Sa and maximum height Sz. The maximum height Sz is a value expressed as PV in the software provided with the device. Filter: High Pass Filter Type: Gauss Spline Filter Low Wavelength: 30.00000 μm Filter High Wavelength: Not set

[0212] The materials and thicknesses of films 1 to 4, as well as the evaluation results, are shown in Table 2.

[0213]

[0214] [Preparation of Hard Coat Composition] <Preparation of Acrylic Hard Coat Composition> To 100 parts by weight of dipentaerythritol hexaacrylate ("Aronix M-403" manufactured by Toa Gosei Co., Ltd.), 2 parts by weight of a photoradical polymerization initiator ("Omnirad 184" manufactured by IGM Resins) and 0.25 parts by weight of a polyether-modified silicone-based leveling agent ("BYK-300" manufactured by BYK) were added, and propylene glycol monomethyl ether was added as a dilution solvent to obtain an acrylic hard coat composition with a solids concentration of 50% by weight.

[0215] <Preparation of Siloxane-Based Hard Coat Composition> 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) were charged into a reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser, and the mixture was stirred uniformly. A solution of 0.039 g (0.405 mmol) of magnesium chloride as a catalyst dissolved in a mixture of 9.7 g (539 mmol) of water and 5.8 g of methanol was added dropwise to this mixture over 5 minutes and stirred until uniform. The mixture was then heated to 80°C, and a polycondensation reaction was carried out for 6 hours with stirring. After completion of the reaction, the solvent and water were removed using a rotary evaporator to obtain a condensate of the silane compound (polyorganosiloxane compound).

[0216] Tosoh GPC equipment "HLC-8220GPC" (column: TSKgel GMH Ｘ L x 2, TSKgel G3000H ＸＬ ,TSKgel G2000H ＸＬ The weight average molecular weight of the polymer measured by NMR spectroscopy was 3,000 in terms of polystyrene. １ The residual rate of epoxy groups calculated from the H-NMR spectrum was 95% or more.

[0217] To 100 parts by weight of the above polyorganosiloxane compound, 2 parts by weight of a sulfonium-based photoacid generator ("CPI-101A" manufactured by San-Apro) and 0.25 parts by weight of a polyether-modified silicone-based leveling agent ("BYK-300" manufactured by BYK) were added, and propylene glycol monomethyl ether was added as a dilution solvent to obtain a siloxane-based hard coat composition with a solids concentration of 50% by weight.

[0218] [Preparation of Hard Coat Film] Example 1 An acrylic hard coat composition was applied to side B of film 1 using a coater so that the dry film thickness was 5 μm, and the solvent was removed at 120° C. Thereafter, in a nitrogen atmosphere, a high-pressure mercury lamp was used to apply an integrated light dose of 1950 mJ / cm ２The hard coat resin composition was cured by irradiating with ultraviolet light so that the hard coat resin composition became 5 μm thick, thereby obtaining a hard coat film having an acrylic hard coat layer. The thickness of the hard coat layer is the difference between the thickness of the hard coat film measured using a contact thickness meter and the thickness of the film before the hard coat layer was formed.

[0219] Example 2 A siloxane-based hard coat composition was applied to side B of film 1 using a coater so that the dry film thickness was 20 μm, and the solvent was removed at 120° C. Thereafter, the film was irradiated with a high-pressure mercury lamp in an atmospheric atmosphere with an integrated light intensity of 1950 mJ / cm ２ The hard coat resin composition was cured by irradiating it with ultraviolet light so that the hard coat resin composition became 20 μm thick, thereby obtaining a hard coat film having a siloxane-based hard coat layer.

[0220] Example 3 A hard-coated film having a 5 μm-thick acrylic hard-coat layer on side B of Film 2 was obtained in the same manner as in Example 1, except that Film 2 was used instead of Film 1.

[0221] Example 4 A hard-coated film having a 20 μm-thick siloxane-based hard-coat layer on side B of Film 2 was obtained in the same manner as in Example 2, except that Film 2 was used instead of Film 1.

[0222] Examples 5 and 6 Hard coat films were obtained in the same manner as in Examples 1 and 3, except that the surface on which the hard coat layer was formed (the surface on which the hard coat composition was applied) was changed to side A of Films 1 and 2.

[0223] [Evaluation of Hard Coat Film] <Total Light Transmittance and Haze> Using a haze meter "HZ-V3" manufactured by Suga Test Instruments, the total light transmittance and haze were measured according to the methods described in JIS K7361-1: 1999 and JIS K7136: 2000. A D65 light source was used for the measurement.

[0224] <Pencil Hardness> The pencil hardness of the hard coat layer surface was evaluated under a load of 750 g in accordance with JIS K 5600. A scratch test (moving a pencil) along the MD direction and a scratch test along the TD direction were performed, and the higher hardness was determined as the pencil hardness of the hard coat film.

[0225] <Repeated Bending Test> The hard-coated film was cut into a 20 mm x 150 mm rectangle with the long side in the TD direction to prepare an evaluation sample. The evaluation sample was set in a Yuasa System Co., Ltd. U-shaped bending durability tester DMLHB, and a repeated bending test was performed 100,000 times with a bending radius of 1.5 mm, a bending angle of 180°, and a rate of 1 bending / second, with the MD direction as the bending axis so that the hard-coated layer was on the inside. The test was performed in a constant temperature and humidity environment set at a temperature of 23°C and a humidity of 55%. None of the hard-coated films of Examples 1 to 6 showed cracks or breaks after the test, demonstrating good bending resistance.

[0226] <Appearance (Whitening Unevenness)> A hard-coated film was cut into a 300 mm x 210 mm rectangle with the long side in the MD direction, and the four sides were fixed flat in a plastic cardboard frame. In a darkroom, light from a three-wavelength fluorescent lamp was irradiated onto the hard-coated film, and the transmitted light was visually observed. The incident angle of the transmitted light was in the range of 60 to 89° with respect to the normal to the film surface. That is, the hard-coated film was placed between the fluorescent lamp and the observer, and the hard-coated film was tilted in the range of 60 to 89° with the MD or TD direction as the tilt axis, and the fluorescent light transmitted through the hard-coated film was observed. If white and non-white areas were distributed within the surface of the hard-coated film at any angle between 60 and 89° and were visually recognized as unevenness, whitening unevenness was scored as "present." When no unevenness was visible in either the case where the MD direction was tilted within a range of 60 to 89° with the slant axis as the inclination axis, or the case where the TD direction was tilted within a range of 60 to 89°, the whitening unevenness was judged to be "absent."

[0227] The structures and evaluation results of the hard coat films of Examples 1 to 6 are shown in Table 3. Table 3 also shows the evaluation results (presence or absence of whitening unevenness) of Films 1 to 4, which do not have a hard coat layer, as Reference Examples 1 to 4. For Reference Examples 1 to 4, the surface shape of the side without a hard coat layer (HC non-formed side) is shown in the format of roughness of side A (nm) / roughness of side B (nm).

[0228]

[0229] The hard-coated films of Examples 1 to 6 all had high total light transmittance and excellent transparency. In particular, Examples 1, 2, and 5, which used Film 1 containing a polyimide resin and an acrylic resin, exhibited high total light transmittance of 90% or more. Furthermore, the hard-coated films of Examples 1 to 6 had pencil hardnesses of H or higher and excellent scratch resistance. In particular, the hard-coated films of Examples 1, 2, 4, and 5 had pencil hardnesses of 3H or higher and high scratch resistance.

[0230] The hard-coated films of Examples 1 to 6 all have high total light transmittance, high hardness, excellent scratch resistance, and excellent bending resistance, making them suitable for use as cover windows for foldable displays. Furthermore, the hard-coated films of Examples 1 to 6 use a specific diamine that does not contain a specific fluorine structure as the diamine component of the polyimide resin, making them excellent in terms of environmental safety.

[0231] No whitening unevenness was observed in Film 3 (Reference Example 3) having a thickness of 25 μm, whereas whitening unevenness was observed in Film 4 having a thickness of 50 μm, and whitening unevenness was also observed in Films 1 and 2 having a thickness of 50 μm, similar to Film 4. These results show that films containing polyimide resins are prone to whitening unevenness when they are thick.

[0232] In Examples 5 and 6, in which a hard coat layer was formed on side A of Film 1 (Sa = 0 nm, Sz = 9 nm) and side A of Film 2 (Sa = 0 nm, Sz = 23 nm), whitening unevenness was observed similarly to Reference Examples 1 and 2. On the other hand, in Examples 1 to 4, in which a hard coat layer was formed on side B of Film 1 (Sa = 2 nm, Sz = 62 nm) and side B of Film 2 (Sa = 2 nm, Sz = 96 nm), no whitening unevenness was observed.

[0233] From these results, it is believed that in the hard-coated films of Examples 1 to 4, by forming a hard-coat layer on side B, which has a relatively high surface roughness, the irregularities on the film surface are filled in, and side A, which has a relatively low surface roughness, is exposed to the surface, thereby eliminating uneven whitening.

[0234] 1 transparent resin film 1A first main surface (surface on which hard coat layer is not formed) 1B second main surface (surface on which hard coat layer is formed) 3 hard coat layer 11 hard coat film

Claims

1. A hard coat film comprising a transparent resin film having a first main surface and a second main surface, and a hard coat layer provided on the second main surface of the transparent resin film, wherein the transparent resin film has a thickness of 26 μm or more and contains a polyimide resin and a solvent-soluble resin other than a polyimide resin, the polyimide resin has a tetracarboxylic dianhydride-derived structure and a diamine-derived structure, and the diamine is selected from the group consisting of CF ３ -O-, -(CF ２ -O) ｎ -, and -O-(CF ２ -CF ２ -O) ｎ - (where n is an integer of 1 to 20), and the tetracarboxylic dianhydride is one or more tetracarboxylic dianhydrides selected from the group consisting of tetracarboxylic dianhydrides having an ether bond, tetracarboxylic dianhydrides having a fluorene structure, tetracarboxylic dianhydrides having a xanthene structure, and bis(trimellitic anhydride) esters.

2. The hard coat film according to claim 1, wherein the fluorine atom-containing diamine is 2,2'-bis(trifluoromethoxy)benzidine, 3,3'-bis(trifluoromethoxy)benzidine, or 2,3'-bis(trifluoromethoxy)benzidine.

3. The hard coat film according to claim 1, wherein the polyimide resin further contains a structure derived from an alicyclic tetracarboxylic dianhydride as the tetracarboxylic dianhydride, and the amount of the alicyclic tetracarboxylic dianhydride relative to the total amount of the tetracarboxylic dianhydride is 1 to 80 mol %.

4. The polyimide resin contains CF3 at the carbon atom of the aromatic ring relative to the total amount of diamine. ３ - or -C(CF ３ ) ２ the amount of diamine having a structure in which - is directly bonded is less than 0.5 mol %, and the amount of CF bonded to a carbon atom of an aromatic ring is less than 0.5 mol % relative to the total amount of tetracarboxylic dianhydride ３ - or -C(CF ３ ) ２ 2. The hard coat film according to claim 1, wherein the amount of the tetracarboxylic dianhydride having a structure in which - is directly bonded is less than 0.5 mol %.

5. The hard coat film according to claim 1, wherein the solvent-soluble resin is an acrylic resin.

6. The hard coat film according to claim 5, wherein the acrylic resin is an acrylic resin containing methyl methacrylate as a main component.

7. The hard coat film according to claim 1, wherein the solvent-soluble resin is a polyester resin.

8. The hard coat film according to claim 7, wherein the polyester has a structure derived from a dicarboxylic acid and a structure derived from a diol, and the diol comprises at least one selected from the group consisting of diols having an optionally branched chain alkylene group having 3 or more carbon atoms, diols having an optionally branched chain alkenylene group having 3 or more carbon atoms, polyalkylene glycol, and diols having a cyclic structure.

9. The hard coat film according to claim 7, wherein the polyester has a structure derived from a dicarboxylic acid and a structure derived from a diol, and the diol contains at least one selected from the group consisting of diols having a fluorene structure and diols having a bisphenol derivative structure.

10. The hard coat film according to claim 1, wherein a hard coat layer is not provided on a first main surface of the transparent resin film, and the arithmetic mean roughness Sa of the first main surface of the transparent resin film is 1 nm or less.

11. The hard coat film according to claim 10, wherein the transparent resin film has a second main surface having an arithmetic mean roughness Sa greater than the arithmetic mean roughness Sa of the first main surface.

12. The hard coat film according to claim 10, wherein the second main surface of the transparent resin film has an arithmetic mean roughness Sa of 1.5 nm or more.

13. The hard coat film according to claim 10, wherein the maximum height Sz of the first main surface of the transparent resin film is 60 nm or less.

14. The hard coat film according to claim 10, wherein the maximum height Sz of the second main surface of the transparent resin film is greater than the maximum height Sz of the first main surface.

15. The hard coat film according to claim 1, wherein the hard coat layer has a thickness of 1 to 50 μm.

16. A method for producing a hard coat film according to any one of claims 1 to 15, comprising: applying a resin solution, in which a polyimide resin and a solvent-soluble resin other than a polyimide resin are dissolved in a solvent, onto a support; heating the solution on the support to dry and remove the solvent, thereby producing a transparent resin film; peeling the transparent resin film from the support; and forming a hard coat layer on one main surface of the transparent resin film.

17. The method for producing a hard coat film according to claim 16, wherein the hard coat layer is formed on the surface of the transparent resin film that has been peeled off from the support.

18. The method for producing a hard coat film according to claim 17, wherein the surface of the support to which the resin solution is applied has an arithmetic mean roughness Sa of 0.5 nm or more.

19. The method for producing a hard coat film according to claim 18, wherein the maximum height Sz of the surface of the support to which the resin solution is applied is 10 nm or more.

20. A display comprising the hard coat film according to any one of claims 1 to 15.

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