Hard coat film, method for producing same, and display

Abstract

The hard coat film (11) is provided with a hard coat layer (3) on a second main surface of a transparent resin film (1) having a first main surface (1A) and a second main surface (1B). The transparent resin film has a thickness of 26 [mu] m or more and contains a polyimide-based resin and a solvent-soluble resin other than the polyimide-based resin. The first main surface of the transparent resin film is not provided with the hard coating layer. The arithmetic mean roughness Sa of the first main surface of the transparent resin film is 1 nm or less. The maximum height Sz of the first main surface of the transparent resin film may be 70 nm or less.

Description

Technical Field

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

[0002] Films made of transparent polyimide have excellent mechanical strength and are expected to be used as cover windows for displays. Patent Document 1 proposes using a hard coat film having a hard coat layer on the surface of a transparent polyimide film for cover windows.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-217647 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] Polyimide has a high refractive index, resulting in high light reflection (high reflectivity) due to differences in refractive index between the air interface and the interface with other components, resulting in low total light transmittance. Therefore, its use as a cover window material can be a major factor in reducing display brightness. Furthermore, in order to use a transparent polyimide film as a cover window material, it must be thicker. However, when observing a thick transparent polyimide film from an oblique angle, the entire film surface appears whitish, and variations in whiteness are observed as unevenness (hereinafter referred to as "whitening unevenness"), which can sometimes reduce display visibility.

[0008] In view of the above circumstances, an object of the present invention is to provide a hard coat film having a large thickness, excellent mechanical strength, high transparency, and little visible whitening unevenness.

[0009] Solutions for solving problems

[0010] The hard-coated film of the present invention comprises a hard coating layer on the second principal surface of a transparent resin film having a first principal surface and a second principal surface. The transparent resin film has a thickness of 26 μm or greater and comprises a polyimide resin and a solvent-soluble resin other than the polyimide resin. No hard coating layer is provided on the first principal surface of the transparent resin film. The arithmetic mean roughness Sa of the first principal surface of the transparent resin film is 1 nm or less. The maximum height Sz of the first principal surface of the transparent resin film can be 70 nm or less.

[0011] The arithmetic mean roughness Sa of the second main surface of the transparent resin film may be greater than that of the first main surface, and the maximum height Sz of the second main surface may be greater than that of the first main surface. The arithmetic mean roughness Sa of the second main surface of the transparent resin film may be greater than 1.5 nm.

[0012] The transparent resin film may be a stretched film. The solvent-soluble resin contained in the transparent resin film is preferably an acrylic resin, and among these, a resin containing methyl methacrylate as a main component is preferably. The polyimide resin contained in the transparent resin film is a polyimide or polyamide-imide, and includes a structure derived from tetracarboxylic dianhydride and a structure derived from diamine. The polyimide resin preferably includes fluorinated aromatic tetracarboxylic dianhydride and alicyclic tetracarboxylic dianhydride as the tetracarboxylic dianhydride, and includes a fluorinated diamine as the diamine.

[0013] Examples of the material of the hard coat layer include acrylic hard coat materials and silicone hard coat materials. The thickness of the hard coat layer may be 1 to 50 μm.

[0014] The transparent resin film can be produced by applying a resin solution prepared by dissolving a polyimide resin and a solvent-soluble resin in a solvent onto a support, and then heating the solution on the support to dry and remove the solvent.

[0015] The surface of the support on which the resin solution is applied 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.

[0016] The hard coat 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 the hard coat layer is formed on this surface.

[0017] Effects of the Invention

[0018] The hard coat film of the present invention has excellent mechanical strength due to the large thickness of the transparent resin film. In addition, the hard coat film has high transparency and is less likely to show whitening unevenness, making it suitable for use as a cover window material for displays. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a cross-sectional view of a hard coating film according to one embodiment. DETAILED DESCRIPTION

[0020] Figure 1 This is a cross-sectional view of a hard coat film according to one embodiment of the present invention. Hard coat film 11 includes a hard coat layer 3 on second principal surface 1B of a transparent resin film 1 having first principal surface 1A and second principal surface 1B. Hard coat film 11 includes a hard coat layer only on second principal surface 1B of transparent resin film 1; no hard coat layer is provided on first principal surface 1A of transparent resin film 1.

[0021] [Transparent resin film]

[0022] The transparent resin film 1 is a substrate that serves as a base for forming the hard coat layer 3. The transparent resin film 1 has a thickness of 26 μm or greater, and a first main surface 1A (the surface not provided with the hard coat layer 3) of the transparent resin film 1 has an arithmetic mean roughness Sa of 1 nm or less.

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

[0024] <Polyimide resin>

[0025] Polyimide can be obtained by dehydrating and cyclizing the polyamic acid obtained by the reaction of tetracarboxylic dianhydride (hereinafter sometimes described as " acid dianhydride ") and diamine. By replacing a part of the tetracarboxylic dianhydride of polyimide with dicarboxylic acid derivatives such as dicarboxylic acid dichlorides, polyamide-imide can be obtained. As polyimide-based resin, polyimide and polyamide-imide can be used in combination. From the viewpoints such as compatibility with other resins, it is sometimes preferred that polyimide is used as polyimide-based resin.

[0026] (Tetracarboxylic dianhydride)

[0027] The polyimide resin used in the embodiment of the present invention preferably contains alicyclic tetracarboxylic dianhydride as the acid dianhydride component. By making the acid dianhydride component have an alicyclic structure, there is a tendency for the compatibility of the polyimide resin with other resins such as acrylic resin to be improved. As long as the alicyclic tetracarboxylic dianhydride has at least one alicyclic structure, it can have both an alicyclic ring and an aromatic ring in one molecule. The alicyclic ring can be polycyclic or have a spirocyclic structure.

[0028] 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, 1,2,3,4-butanetetracarboxylic dianhydride, meso-butane-1,2,3,4-tetracarboxylic dianhydride, 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic dianhydride, and norbornene. 2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic dianhydride, 2,2'-bisnorbornane-5,5',6,6'tetracarboxylic 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 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-dihydrobenzofuran-5-carboxylate), 5-(2,5-dioxotetrahydrofuranyl)-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-dioxo-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-dimethylnaphthalene-2,3,6,7-tetracarboxylic dianhydride, tricyclo[6.4.0.0(2,7)]dodecane-1,8:2,7-tetracarboxylic dianhydride, octahydro-1H,3H,8H,10H-biphenyl[4a,4bc:8a,8b-c']difuran-1,3,8,10-tetraone, ethylene glycol bis(hydrogenated trimellitic anhydride), decahydro[2]benzopyrano[6,5,4,-def][2]benzopyran-1,3,6,8-tetraone, etc.

[0029] Among the alicyclic tetracarboxylic dianhydrides, from the viewpoint of transparency and mechanical strength of the polyimide-based resin, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (H-PMDA), or 1,1′-bicyclohexane-3,3′,4,4′-tetracarboxylic dianhydride (H-BPDA) is preferred, and 1,2,3,4-cyclobutanetetracarboxylic dianhydride is particularly preferred.

[0030] From the perspective of improving the compatibility of the polyimide resin with other resins, the content of alicyclic tetracarboxylic dianhydride is preferably 1 mol% or more, more preferably 3 mol% or more, further preferably 5 mol% or more, relative to 100 mol% of the total amount of the acid dianhydride component, and can be 6 mol% or more, 7 mol% or more, 8 mol% or more, 9 mol% or more, 10 mol% or more, 12 mol% or more, or 15 mol% or more. The amount of alicyclic tetracarboxylic dianhydride required for compatibility with other resins sometimes varies depending on the type of other resins, the type of alicyclic tetracarboxylic dianhydride amount, etc. For example, when the alicyclic tetracarboxylic dianhydride is 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), the content of CBDA is preferably 6 mol% or more, more preferably 8 mol% or more, and further preferably 10 mol% or more, relative to 100 mol% of the total amount of the acid dianhydride component.

[0031] From the perspective of ensuring the solubility of the polyimide resin in an organic solvent, the content of alicyclic tetracarboxylic dianhydride relative to 100 mol% of the total amount of the acid dianhydride component is preferably 80 mol% or less, more preferably 78 mol% or less, further preferably 76 mol% or less, and can be 74 mol% or less, 72 mol% or less, 70 mol% or less, 65 mol% or less, 60 mol% or less, 55 mol% or less, or 50 mol% or less. In order to make the polyimide resin soluble in a low-boiling-point halogen-based solvent such as dichloromethane, the content of alicyclic tetracarboxylic dianhydride is preferably 45 mol% or less, more preferably 40 mol% or less, and can also be 35 mol% or less.

[0032] From the viewpoint of making the polyimide resin soluble in an organic solvent, the acid dianhydride component preferably contains a fluorinated aromatic tetracarboxylic dianhydride and / or a bis(trimellitic anhydride) ester in addition to alicyclic tetracarboxylic dianhydride.

[0033] Examples of the fluorinated aromatic tetracarboxylic dianhydride include 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride and 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}-1,1,1,3,3,3-hexafluoropropane dianhydride.

[0034] Examples of the bis(trimellitic anhydride) ester include bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2′,3,3′,5,5′-hexamethylbiphenyl-4,4′-diester (abbreviation: TahmbP).

[0035] From the viewpoint of making polyimide-based resin soluble in organic solvent, relative to acid dianhydride component total amount 100 mol%, the total of the content of fluorinated aromatic tetracarboxylic dianhydride and bis(trimellitic anhydride) ester is preferably 15 mol% or more, more preferably 20 mol% or more, further preferably 25 mol% or more, can be 30 mol% or more, 35 mol% or more, 40 mol% or more, 45 mol% or more or 50 mol% or more.Relative to acid dianhydride component total amount 100 mol%, the total of the content of fluorinated aromatic tetracarboxylic dianhydride and bis(trimellitic anhydride) ester is preferably 99 mol% or less, more preferably 95 mol% or less, further preferably 90 mol% or less, can be 85 mol% or less, 80 mol% or less, 75 mol% or less or 70 mol% or less.

[0036] From the viewpoint of obtaining a polyimide-based resin having both solubility in an organic solvent and compatibility with other resins, the total content of alicyclic tetracarboxylic dianhydride, fluorinated aromatic tetracarboxylic dianhydride, and bis(trimellitic anhydride) ester relative to 100 mol% of the total amount of the acid dianhydride component is preferably 50 mol% or more, more preferably 60 mol% or more, further preferably 65 mol% or more, and can be 70 mol% or more, 75 mol% or more, 80 mol% or more, 85 mol% or more, 90 mol% or more, or 95 mol% or more.

[0037] The polyimide resin may contain an acid dianhydride other than alicyclic tetracarboxylic dianhydride, fluorinated aromatic tetracarboxylic dianhydride and bis(trimellitic anhydride) ester as an acid dianhydride component. Examples of acid dianhydrides other than the above include ethylene tetracarboxylic dianhydride, butane tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-biphenyl tetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl) propane dianhydride, bis(3,4-dicarboxyphenyl) ether dianhydride, bis(3,4-dicarboxyphenyl) sulfone dianhydride, 1,1-bis(2,3-dicarboxyphenyl) benzophenone tetracarboxylic ... 1,3-bis[(3,4-dicarboxy)benzoyl]phthalic dianhydride, 1,4-bis[(3,4-dicarboxy)benzoyl]phthalic dianhydride, 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride, 2,2-bis{4-[4-(3,4-dicarboxy)phenoxy]phenyl}propane dianhydride, 2,2-bis{4-[4-(3,4-dicarboxy)phenoxy]phenyl}propane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride), 1,3-bis[(3,4-dicarboxy)benzoyl]phthalic dianhydride, 1,4-bis[(3,4-dicarboxy)benzoyl]phthalic dianhydride, {4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, 4,4'-bis[4-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, 4,4'-bis[3-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl} ]phenyl}sulfone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,3,4-pyromellitic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylic acid)-1,4-phenylene ester.

[0038] (Dicarboxylic acid)

[0039] As described above, the polyimide resin may be a polyamide-imide obtained by replacing a portion of the tetracarboxylic dianhydride component with a dicarboxylic acid derivative. 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 bis(cyclohexyl)-4,4'-dicarboxylic acid; and heterocyclic dicarboxylic acids such as 2,5-thiophenedicarboxylic acid and 2,5-furandicarboxylic acid.

[0040] From the perspective of solubility of polyamide-imide and compatibility with other resins, aromatic dicarboxylic acids and alicyclic dicarboxylic acids are preferred as dicarboxylic acids, with aromatic dicarboxylic acids being particularly preferred. Among aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, 4,4'-biphenyldicarboxylic acid, and 4,4'-oxybisbenzoic acid are preferred. Among these, terephthalic acid and isophthalic acid are preferred, with terephthalic acid being particularly preferred.

[0041] As the dicarboxylic acid derivative used as a raw material monomer for polyamide-imide, dicarboxylic acid dichloride, dicarboxylic acid ester, dicarboxylic acid anhydride and the like can be used. Among them, dicarboxylic acid dichloride is preferred due to its high reactivity.

[0042] From the perspective of the solubility of the polyamide-imide and its compatibility with other resins, the ratio of the dicarboxylic acid derivative to the total of the tetracarboxylic dianhydride and the dicarboxylic 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).

[0043] (Diamine)

[0044] The diamine component of the polyimide resin used in the embodiments of the present invention is not particularly limited. From the perspective of solubility, the diamine in the polyimide resin preferably has one or more selected from the group consisting of a fluoro group, a trifluoromethyl group, a sulfo group, a fluorene structure, and an alicyclic structure. Specifically, from the perspective of balancing the solubility and transparency of the polyimide resin, the polyimide resin preferably contains a fluorine-containing diamine such as a fluoroalkyl-substituted benzidine as the diamine component.

[0045] Examples of fluoroalkyl-substituted benzidines of fluorinated diamines include 2-(trifluoromethyl)benzidine, 3-(trifluoromethyl)benzidine, 2,3-bis(trifluoromethyl)benzidine, 2,5-bis(trifluoromethyl)benzidine, 2,6-bis(trifluoromethyl)benzidine, 2,3,5-tris(trifluoromethyl)benzidine, 2,3,6-tris(trifluoromethyl)benzidine, 2,3,5,6-tetrakis(trifluoromethyl)benzidine, 2,2'-bis(trifluoromethyl)benzidine, 3,3'-bis(trifluoromethyl)benzidine, 2,3'-bis(trifluoromethyl)benzidine, , 2,2',3-bis(trifluoromethyl)benzidine, 2,3,3'-tris(trifluoromethyl)benzidine, 2,2',5-tris(trifluoromethyl)benzidine, 2,2',6-tris(trifluoromethyl)benzidine, 2,3',5-tris(trifluoromethyl)benzidine, 2,3',6-tris(trifluoromethyl)benzidine, 2,2',3,3'-tetrakis(trifluoromethyl)benzidine, 2,2',5,5'-tetrakis(trifluoromethyl)benzidine, 2,2',6,6'-tetrakis(trifluoromethyl)benzidine, and the like.

[0046] Among these, fluoroalkyl-substituted benzidines having a fluoroalkyl group at the 2-position of biphenyl are preferred, with 2,2'-bis(trifluoromethyl)benzidine (hereinafter referred to as "TFMB") being particularly preferred. The presence of fluoroalkyl groups at the 2- and 2'-positions of biphenyl reduces the π electron density due to the electron-withdrawing properties of the fluoroalkyl groups. Furthermore, the steric hindrance of the fluoroalkyl groups distorts the bond between the two benzene rings of biphenyl, reducing the planarity of the π conjugation. This shifts the absorption edge wavelength to a shorter wavelength, thus reducing coloration of the polyimide resin.

[0047] The content of the fluoroalkyl-substituted benzidine relative to 100 mol% of the total diamine component is preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, and can be 80 mol% or more, 85 mol% or more, or 90 mol% or more. A high content of the fluoroalkyl-substituted benzidine tends to suppress film coloring and increase mechanical strength, such as pencil hardness and elastic modulus.

[0048] The polyimide resin may contain a diamine other than fluoroalkyl-substituted benzidine as a diamine component. Examples of diamines other than fluoroalkyl-substituted benzidine include p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 9,9-bis(4-aminophenyl)fluorene, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3 ... '-Diaminodiphenylmethane, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 2-(3-aminophenyl)-2-(4-aminophenyl)propane, 1,1-bis(3-aminophenyl)-1-phenylethane, 1,1-bis(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-aminophenoxy)benzene (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-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]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'-diaminophenoxy 1,1'-spirobiiindane, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiiindane, 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)-1,1'-spirobiiindane, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisilox ...butyl)tetramethyldisiloxane, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, 1,3-bis(3-aminobutyl)tetramethyldisiloxane, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, 1,3-bis(3-aminobutyl)tetramethyldisiloxane, 1,3-bis(3-aminobutyl)tetramethyldisiloxane, ether, bis(2-aminoethyl) ether, bis(3-aminopropyl) ether, bis(2-aminomethoxy)ethyl] ether, bis[2-(2-aminoethoxy)ethyl] ether, bis[2-(3-aminopropoxy)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, cyclohexane, 1,3-bis(2-aminoethyl)cyclohexane, 1,4-bis(2-aminoethyl)cyclohexane, bis(4-aminocyclohexyl)methane, 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane, 2,5-bis(aminomethyl)bicyclo[2.2.1]heptane (Aminomethyl)bicyclo[2.2.1]heptane, 1,4-diamino-2-fluorobenzene, 1,4-diamino-2,3-difluorobenzene, 1,4-diamino-2,5-difluorobenzene, 1,4-diamino-2,6-difluorobenzene, 1,4-diamino-2,3,5-trifluorobenzene, 1,4-diamino-2,3,5,6-tetrafluorobenzene, 1,4-diamino-2-(trifluoromethyl)benzene, 1,4-diamino-2,3-bis(trifluoromethyl)benzene, 1,4-diamino-2,5-bis(trifluoromethyl)benzene, 1,4-diamino-2,6-bis(trifluoromethyl)benzene, 1,4-diamino-2,3,5-tris(trifluoromethyl)benzene, 1,4-diamino-2,3,5,6-tetra(trifluoromethyl)benzene, 2,2'-dimethylbenzidine, 2-fluorobenzidine, 3-fluorobenzidine, 2,3-difluorobenzidine, 2,5-difluorobenzidine, 2,6-difluorobenzidine, 2,3,5-trifluorobenzidine, 2,3,6-trifluorobenzidine, 2,3,5,6-tetrafluorobenzidine, 2,2'-difluorobenzidine, 3,3'-difluorobenzidine, 2,3'-difluorobenzidine, 2,2',3-trifluorobenzidine, 2,3,3'-trifluorobiphenyl Amine, 2,2',5-trifluorobenzidine, 2,2',6-trifluorobenzidine, 2,3',5-trifluorobenzidine, 2,3',6-trifluorobenzidine, 2,2',3,3'-tetrafluorobenzidine, 2,2',5,5'-tetrafluorobenzidine, 2,2',6,6'-tetrafluorobenzidine, 2,2',3,3',6,6'-hexafluorobenzidine, 2,2',3,3',5,5'6,,6'-octafluorobenzidine.

[0049] For example, by using diaminodiphenyl sulfone in addition to fluoroalkyl-substituted benzidine as a diamine, the solubility and transparency of the polyimide resin in the solvent may be improved. Among diaminodiphenyl sulfones, 3,3'-diaminodiphenyl sulfone (3,3'-DDS) and 4,4'-diaminodiphenyl sulfone (4,4'-DDS) are preferred. 3,3'-DDS and 4,4'-DDS may also be used in combination. The content of diaminodiphenyl sulfone can be 1 to 40 mol%, 3 to 30 mol%, or 5 to 25 mol% relative to 100 mol% of the total diamine content.

[0050] (Preparation of polyimide resin)

[0051] The polyamic acid as a polyimide precursor is obtained by the reaction of an acid dianhydride and a diamine, and the polyimide is obtained by dehydration cyclization (imidization) of the polyamic acid. The preparation method of the polyamic acid is not particularly limited, and all known methods can be applied. For example, diamine and tetracarboxylic dianhydride are dissolved in an organic solvent with approximately equimolar amounts (a molar ratio of 90:100 to 110:100) and stirred to obtain a polyamic acid solution.

[0052] In the preparation of polyamide-imide, in addition to diamine and tetracarboxylic dianhydride, dicarboxylic acid or its derivatives (dicarboxylic acid dichloride, dicarboxylic acid anhydride, etc.) can also be used as monomers. In this case, the amount of each monomer can be adjusted so that the total amount of tetracarboxylic dianhydride and dicarboxylic acid or its derivative is approximately equimolar to that of the diamine.

[0053] As described above, by adjusting the composition of the polyimide resin, that is, the types and ratios of the acid dianhydride and the diamine, the polyimide resin has transparency and solubility in organic solvents and exhibits compatibility with other resins.

[0054] The concentration of the polyamic acid solution is generally 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.

[0055] During the polymerization of polyamic acid, in order to suppress the ring-opening of acid dianhydride, it is preferred to add acid dianhydride to diamine. When adding multiple diamines or multiple acid dianhydrides, they can be added at one time or in multiple times. By adjusting the order of addition of monomers, the various physical properties of the polyimide resin can also be controlled.

[0056] The organic solvent used in the polymerization of polyamic acid is not particularly limited as long as it is a solvent that does not react with diamine and acid dianhydride, that polyamic acid can be dissolved. As organic solvent, methylurea, N, the urea solvents such as N-dimethylethylurea, dimethyl sulfoxide, diphenyl sulfone, tetramethyl sulfone, sulfoxide or sulfone solvents, N, N-dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), N, N'-diethylacetamide, N-methyl-2-pyrrolidone (NMP), gamma-butyrolactone, hexamethylphosphoric acid triamide, chloroform, the halogenated alkyl solvents such as dichloromethane, benzene, the aromatic hydrocarbon solvents such as toluene, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, p-cresol methyl ether, etc. are listed. Usually these solvents are used alone or two or more are suitably used in combination as needed. From the viewpoint of the solubility and polymerization reactivity of polyamic acid, preferably DMAc, DMF, NMP etc. are used.

[0057] Obtain polyimide resin by the dehydration cyclization of polyamic acid.As the method for preparing polyimide resin by polyamic acid solution, can enumerate in polyamic acid solution, add dehydrating agent, imidization catalyst etc., the method for carrying out imidization in solution.In order to promote the progress of imidization, polyamic acid solution can be heated. The solution of the polyimide resin generated by the imidization of polyamic acid is mixed with a poor solvent, and thus polyimide resin is separated out as a solid. By separating the polyimide resin as a solid, impurities, residual dehydrating agent and imidization catalyst etc. generated when the synthesis of polyamic acid can be cleaned and removed by a poor solvent, and the coloring of polyimide resin, the rising of yellowness can be prevented. In addition, by separating the polyimide resin as a solid, thus when the preparation is used to make the solution of film, solvents suitable for filmization such as low boiling point solvents can be applied.

[0058] The molecular weight of the polyimide resin (weight average molecular weight in terms of polyethylene oxide as measured by gel filtration chromatography (GPC)) is preferably 10,000 to 300,000, more preferably 20,000 to 250,000, and even more preferably 40,000 to 200,000. If the molecular weight is too low, the film strength may be insufficient. If the molecular weight is too high, the compatibility with other resins may be poor.

[0059] The polyimide resin is preferably soluble in a low-boiling-point solvent such as a ketone solvent or a haloalkyl solvent. The polyimide resin showing solubility in a solvent means dissolving at a concentration of 5% by weight or more. In one embodiment, the polyimide resin shows solubility in dichloromethane. Dichloromethane has a low boiling point and is easy to remove residual solvent during film production. Therefore, by using a polyimide resin soluble in dichloromethane, it is expected that the productivity of the film can be improved.

[0060] From the viewpoint of thermal stability and light stability of the transparent resin film, the polyimide resin preferably 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 further preferably 0.2 mmol / g or less. The acid value of the polyimide can 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, the polyimide resin preferably has a high imidization rate. By making the acid value small, there is a tendency for the stability of the polyimide resin to improve and for its compatibility with other resins to improve.

[0061] <Other resins>

[0062] As described above, the transparent resin film 1 includes, in addition to the polyimide resin, a resin other than the polyimide resin ("other resin"). As other resins, there is no particular limitation as long as they are soluble in organic solvents and can be mixed with the polyimide resin to form a transparent film. Examples include resins that are compatible with the polyimide resin, and resins that form microphase separation structures such as sea island structures, tubular structures, and layered structures. Among them, other resins are preferably resins that are compatible with the polyimide resin. When the polyimide resin is compatible with the other resins, regardless of the processing conditions of the film, there is a tendency for the film to have high transparency and excellent mechanical properties such as elastic modulus and pencil hardness.

[0063] The other resin is preferably a transparent resin having a lower refractive index than the polyimide resin. The refractive index of the other resin is preferably 1.600 or less, more preferably 1.550 or less, further preferably 1.520 or less, and particularly preferably 1.500 or less. By making the other resin have a lower refractive index than the polyimide resin, the blended resin film comprising the polyimide resin and the other resin has a lower refractive index than a film made of a single polyimide resin, and the reflection at the interface is small, so there is a tendency for the total light transmittance to increase.

[0064] Examples of other resins include acrylic resins, polycarbonate resins, polyester resins, polyamide resins, polyether resins, cellulose resins, silicone resins, and cyclic olefin resins. A variety of these resins may also be used. From the perspective of high compatibility with polyimide resins, acrylic resins, polycarbonate resins, and polyester resins having a fluorene structure are preferred as other resins. Among these, acrylic resins are particularly preferred from the perspective of high compatibility with polyimide resins, low refractive index, and ease of forming a high-hardness film.

[0065] Examples of acrylic resins include poly(meth)acrylates 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, and methyl (meth)acrylate-styrene copolymers. Acrylic resins can be modified to introduce glutarimide structural units or lactone ring structural units.

[0066] From the perspectives of transparency, compatibility with polyimide resins, and mechanical strength, acrylic resins preferably contain methyl methacrylate as their primary structural unit. The amount of methyl methacrylate relative to the total monomeric components of the acrylic resin is preferably 60% by weight or greater, and can be 70% by weight or greater, 80% by weight or greater, 85% by weight or greater, 90% by weight or greater, or 95% by weight or greater. The acrylic resin can be a homopolymer of methyl methacrylate. Alternatively, the acrylic resin can be a resin in which a glutarimide structure or a lactone ring structure is introduced into an acrylic polymer having a methyl methacrylate content within the aforementioned range.

[0067] 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.

[0068] 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, and even more preferably 15,000 to 200,000, from the viewpoints of solubility in organic solvents, compatibility with polyimide resins, and film strength.

[0069] From the viewpoint of thermal stability and light stability of the film, the acrylic resin preferably has a low content of reactive functional groups such as ethylenically unsaturated groups and carboxyl groups. The iodine value of the acrylic resin is preferably 10.16g / 100g (0.4mmol / g) or less, more preferably 7.62g / 100g (0.3mmol / g) or less, and further preferably 5.08g / 100g (0.2mmol / g) or less. The iodine value of the acrylic resin can be 2.54g / 100g (0.1mmol / g) or less or 1.27g / 100g (0.05mmol / g) or less. The acid value of the acrylic resin is preferably 0.4mmol / g or less, more preferably 0.3mmol / g or less, and further preferably 0.2mmol / g or less. The acid value of the acrylic resin can be 0.1mmol / g or less, 0.05mmol / g or less or 0.03mmol / g or less. When the acid value is reduced, the stability of the acrylic resin tends to be improved, and the compatibility with the polyimide resin tends to be improved.

[0070] <Composition of Transparent Resin Film>

[0071] As described above, the transparent resin film 1 is a blended resin film containing a polyimide resin and other resins as resin components. The ratio of the polyimide resin to the other resins in the transparent resin film is not particularly limited. The mixing ratio (weight ratio) of the polyimide resin to the other resins can 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 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 resins, the less coloring of the film, the higher the total light transmittance, the lower the yellowness (YI), and the higher the transparency.

[0072] In order to fully exert the effect of improving transparency brought about by mixing the polyimide resin with other resins, the ratio of other resins to the total of the polyimide resin and other resins is preferably 10 to 90 weight%, more preferably 15 to 85 weight%, further preferably 20 to 80 weight%, and can be 30 to 70 weight%, 35 to 65 weight% or 40 to 60 weight%.

[0073] In addition to the above resin components, the transparent resin film may also contain organic or inorganic low molecular weight compounds, etc. The transparent resin film may contain blueing agents, ultraviolet absorbers, flame retardants, stabilizers, crosslinking agents, surfactants, leveling agents, plasticizers, fine particles and the like as additives.

[0074] For the purposes such as improving anti-blocking property and adjusting refractive index, transparent resin film can include inorganic particles such as organic particles such as polystyrene, cross-linked acrylic resin, silicon dioxide, layered silicate. However, when compounding particles, it may become the reason that the transmittance of film decreases and haze rises. Although silicon oxides such as silicon dioxide are particularly useful for the low refractive index of film, they are easily poorly dispersed in the resin matrix and are easily the reason that transparency, mechanical strength and bending resistance are reduced. Therefore, relative to 100 parts by weight of the total of resin component, the content of silicon oxide is preferably below 5 parts by weight, preferably below 1 part by weight, more preferably below 0.5 part by weight, can be below 0.1 part by weight, or can be 0.

[0075] <Production of Transparent Resin Film>

[0076] The transparent resin film 1 is produced 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 removed by drying.

[0077] The solvent is not particularly limited as long as it exhibits solubility in both the polyimide resin and the other resin. Examples of solvents include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; ether solvents such as tetrahydrofuran and 1,4-dioxane; ketone solvents such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diethyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone; and haloalkyl solvents such as chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene, dichlorobenzene, and dichloromethane. Ketone solvents and haloalkyl solvents are preferred because they have excellent solubility in polyimide resins and the like, have low boiling points, and facilitate removal of residual solvent during film formation.

[0078] As a method for applying the resin solution to a support, a known method using a rod coater or a comma coater can be applied. As the support, a glass substrate, a metal substrate such as SUS, a metal roller, a metal belt, a plastic film, etc. can be used. From the viewpoint of improving productivity, as the support, an annular support such as a metal roller, a metal belt, or a long plastic film is preferably used, and a film is manufactured by roll-to-roll. When a plastic film is used as the support, a material that is insoluble in the solvent of the resin solution (dope) can be appropriately selected.

[0079] It is preferred to heat the film during the drying of the solvent. The heating temperature is not particularly limited as long as it is a temperature that can remove the solvent and suppress the coloring of the obtained film. It can be appropriately set at room temperature to about 250°C, preferably 50°C to 220°C. The heating temperature can be increased in stages. In order to improve the efficiency of solvent removal, the resin film can be peeled off from the support and dried after drying to a certain extent. Drying can be carried out in an air atmosphere or a nitrogen atmosphere. In order to promote the removal of the solvent, heating can be carried out under reduced pressure.

[0080] The film may be stretched in one or more directions to improve its mechanical strength, etc. When the film is stretched, the polymer chains are oriented in the stretching direction, thereby increasing the film's in-plane strength and suppressing film breakage and cracking.

[0081] Films made of acrylic resins alone sometimes have low toughness, but using a compatibilized system of polyimide-acrylic resins can sometimes improve film strength. Furthermore, when a film made of a compatibilized system of polyimide-acrylic resins is stretched, the polymer chains align in the stretching direction, increasing the tensile modulus in the stretching direction and, consequently, tending to improve flex resistance.

[0082] For example, films used as cover windows or substrates for foldable displays are repeatedly bent along a bending axis at the same location, requiring high mechanical strength in a direction perpendicular to the bending axis. Therefore, by arranging the film so that its stretching direction is perpendicular to the bending axis, the film is less likely to break or crack at the folded area even after repeated bending, resulting in a device with high bending resistance.

[0083] The film stretching conditions are not particularly limited. For example, the stretching temperature is approximately ±40°C of the film's glass transition temperature, and may be 120-300°C, 150-250°C, or 180-230°C. The stretching ratio is approximately 30-200%, and may be 50-150%, 80-120%, or 80-100%. The greater the stretching ratio, the greater the tensile modulus in the stretching direction. On the other hand, excessively high stretching ratios tend to reduce the mechanical strength in a direction perpendicular to the stretching direction, sometimes resulting in reduced handleability of the film.

[0084] From the perspective of increasing the strength in any direction within the plane, the film can be biaxially stretched. Biaxial stretching can be simultaneous biaxial stretching or sequential biaxial stretching. In biaxial stretching, the stretch ratio in one direction can be the same as or different from the stretch ratio in the orthogonal direction. If a difference is set in the stretch ratio, there is a tendency for the mechanical strength in the direction with a larger stretch ratio to be relatively larger. When a biaxially stretched film with anisotropic stretch ratio is used in a foldable device, it is preferably arranged so that the direction with a larger stretch ratio is orthogonal to the bending axis.

[0085] To ensure self-supporting properties and strength suitable for use as a cover window material, the thickness of the transparent resin film 1 is 26 μm or greater, and may be 30 μm or greater, 35 μm or greater, or 40 μm or greater. To ensure bendability (flexibility) suitable for 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.

[0086] 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.

[0087] The arithmetic mean roughness Sa of at least one main surface of the transparent resin film 1 is 1 nm or less, and may be 0.5 nm or less. The maximum height Sz of at least one main surface of the transparent resin film 1 is preferably 70 nm or less, more preferably 50 nm or less, further preferably 30 nm or less, and particularly preferably 10 nm or less.

[0088] When the surface roughness of one principal surface (first principal surface) of the transparent resin film 1 is small and Sa and Sz are within the above-mentioned ranges, even if Sa and Sz of the other principal surface (second principal surface) are large, the hard coating layer 3 formed on the principal surface with relatively large surface roughness fills the surface irregularities of the transparent resin film, thereby suppressing uneven whitening. Therefore, the arithmetic mean roughness Sa and maximum height Sz of the other principal surface (second principal surface) of the transparent resin film 1 can be greater than Sa and Sz of the above-mentioned one principal surface (first principal surface).

[0089] 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 too large, uneven whitening may not be sufficiently suppressed even after forming a hard coat layer. 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.

[0090] The maximum height Sz of the second main surface 1B of the transparent resin film 1 may be greater than 10 nm, and may be 30 nm or greater, 50 nm or greater, 70 nm or greater, or 72 nm or greater. 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.

[0091] Sa and Sz are the arithmetic mean roughness (arithmetic mean height) Sa and maximum height Sz of the profile surface specified in ISO 25178-2 (JIS B0681-2:2018), and are indicators of surface roughness. Sa and Sz are determined using an interferometric non-contact three-dimensional roughness meter. The three-dimensional surface shape of a 0.28 mm x 0.21 mm area is measured using vertical scanning low-coherence interferometry in accordance with ISO 25178-604, and filtered to remove the effects of undulations and thickness variations.

[0092] The film obtained by applying a resin solution to a support and drying to remove the solvent transfers the surface irregularities of the support onto the peeled surface (side B) of the support. If the support is a plastic film, the surface irregularities are present to ensure smoothness during film transport and prevent sticking when wound into a roll. If the support is an endless belt, the surface irregularities may be caused by the surface irregularities of the belt's material, peeling residues from repeated use of the belt, and scratches.

[0093] The surface roughness of the support is transferred onto the B surface of the transparent resin film 1, so in most cases the arithmetic mean roughness Sa is greater than 1 nm. On the other hand, the surface opposite the support during film formation, that is, the air surface (A surface), is not affected by the surface roughness of the support and is therefore smoother than the B surface, and the arithmetic mean roughness Sa is easily less than 1 nm.

[0094] <Uneven Whitening of Transparent Resin Film>

[0095] When observing a transparent resin film with a thickness of 26 μm or greater produced by a solution method from an oblique direction (a direction away from the normal to the film surface), the entire film surface may appear white, with variations in whiteness observed as uneven whitening. Uneven whitening is particularly noticeable when one surface of the transparent resin film has a high surface roughness.

[0096] The thickness of a film tends to increase with thickness, and this tendency is particularly pronounced when converting a composition containing a polyimide resin into a thin film using a solution method. This is believed to be due to the strong intermolecular interactions of polyimide, which cause aggregation of polymer molecules during the drying process. The migration of substances associated with this aggregation can easily lead to thickness variations within the film surface.

[0097] The thickness variation of the film before stretching can range from -20 μm to +20 μm, -10 μm to +10 μm, -5 μm to +5 μm, -3 μm to +3 μm, or -1 μm to +1 μm relative to the average thickness. While stretching tends to reduce the thickness variation, the pattern of thickness variation remains unchanged. When the thickness of the film after stretching is 26 μm or greater, the thickness variation remains large, and whitening unevenness is easily observed.

[0098] When the arithmetic mean roughness Sa of film surface is greater than 1nm, the scattering of transmitted light can occur, therefore sometimes observe that the whole face of film is slightly whitish, but if only in this case, then can not observe in uneven form.Think that except the surface roughness of film, when the thickness of film is unevenly large, the incident angle of transmitted light produces deviation in the plane, so the scattering intensity of light produces deviation, when observing from the oblique direction, there is strongly observed scattered light and the part that looks whitish, there is the deviation (shades) of whiteness in the film face, therefore is identified as bleaching uneven.As described later, by arranging hard coat 3 at the relatively large principal face (usually B face) of the surface roughness of transparent resin film 1, thus there is the tendency that surface concavo-convex is buried, bleaching uneven becomes difficult to observe.

[0099] <Characteristics of Transparent Resin Film>

[0100] The transparent resin film preferably has a single glass transition temperature in differential scanning calorimetry (DSC) and / or dynamic viscoelasticity measurement (DMA). When the polyimide resin contained in the transparent resin film is compatible with other resins, it exhibits a single glass transition temperature.

[0101] The haze of the transparent resin film is preferably 10% or less, more preferably 5% or less, and even more preferably 4% or less. It can 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 resin and another resin, low haze can be achieved by using a resin with high compatibility with the polyimide resin, such as an acrylic resin, as the other resin.

[0102] The total light transmittance of a transparent resin film is preferably 90.3% or higher, more preferably 90.5% or higher, even more preferably 91.0% or higher, and particularly preferably 91.5% or higher. A higher total light transmittance results in a higher white brightness of the display and better visibility. As described above, by mixing a polyimide resin with other resins, the refractive index tends to be lower and the total light transmittance higher than when the polyimide resin is used alone.

[0103] 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 greater, more preferably -2.0 or greater, and even more preferably -1.0 or greater. By mixing a polyimide resin with another resin such as an acrylic resin, a film with less coloration and a smaller absolute value of YI can be obtained compared to when using the polyimide resin alone.

[0104] The refractive index of the transparent resin film is preferably 1.600 or less. The refractive index of a film is the average of the maximum refractive index and the minimum refractive index within the film plane. The refractive index of the transparent resin film is more preferably 1.580 or less, further preferably 1.560 or less, particularly preferably 1.540 or less, and may also be 1.520 or less.

[0105] The refractive index of the film that only comprises polyimide-based resin as resin component is usually higher than 1.600, and the reflection of light caused by the refractive index difference in the air interface and the interface with other components is many (reflectivity is high), so transmittance is small. The mixed resin system of polyimide-based resin and other resins is low in refractive index compared with the situation that polyimide-based resin is independent, so the light reflection at the interface is reduced, and total light transmittance rises. Particularly because the refractive index of acrylic resin is low, if acrylic resin is used as other resins, then there is the tendency that film is low in refractive index, total light transmittance rises.

[0106] The tensile modulus of the transparent resin film is preferably 3.0 GPa or more, more preferably 3.5 GPa or more, further preferably 4.5 GPa or more, and can be 5.0 GPa or more, 5.5 GPa or more, or 6.0 GPa or more. A larger tensile modulus tends to result in better mechanical strength, such as hardness and bending resistance.

[0107] The tensile modulus of the transparent resin film may have in-plane anisotropy. When the transparent resin film is a stretched film, there is a tendency for the tensile modulus in the stretching direction to be greater than the tensile modulus in a direction orthogonal to the stretching direction. When the transparent resin film is a biaxially stretched film or a film uniaxially stretched at a fixed end, the tensile modulus in all directions in the plane may be greater than that before stretching. When the transparent resin film has in-plane anisotropy in the tensile modulus, the maximum in-plane tensile modulus (usually the tensile modulus in the stretching direction) is preferably within the above range.

[0108] [Hard Coating]

[0109] The hard coat film of the present invention includes a hard coat layer 3 on one surface of a transparent resin film 1. Providing the hard coat layer 3 on the surface of the transparent resin film 1 improves scratch resistance and hardness. Providing the hard coat layer 3 on the main surface of the transparent resin film 1, which has a relatively high surface roughness, can suppress uneven whitening.

[0110] The material constituting the hard coat layer is not particularly limited as long as it has a function of preventing scratches, and examples thereof include polyester, acrylic, urethane, amide, silicone, and epoxy resins. Among them, from the viewpoint of preventing scratches, acrylic hard coat layers that are cured products of acrylic hard coat resin compositions, and silicone hard coat layers that are cured products of silicone hard coat resin compositions are preferred.

[0111] <Acrylic Hard Coat Material>

[0112] Acrylic hard coating materials contain monomers or oligomers containing (meth)acryloyl groups within the molecule as curable resin components. The molecular weight of acrylic monomers or oligomers is, for example, approximately 200 to 10,000. Acrylic hard coating materials can control hardness, scratch resistance, bending resistance, optical properties, and the like by combining multiple monomers or oligomers containing (meth)acryloyl groups. From the perspective of curability based on photoradical polymerization, the hard coating material preferably contains an acryloyl group.

[0113] Specific examples of oligomers having a (meth)acryloyl group include urethane (meth)acrylate, polyester (meth)acrylate, epoxy (meth)acrylate, etc. 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.

[0114] Examples of acrylic monomers include compounds having one (meth)acryloyl group, such as methyl (meth)acrylate and 2-ethylhexyl (meth)acrylate; 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-butanediol di(meth)acrylate, and 1,6-hexanediol di(meth)acrylate; and compounds having three or more (meth)acryloyl groups in one molecule, such as glycerol 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.

[0115] To improve the scratch resistance of the hard coat layer, acrylic hard coat materials preferably contain trifunctional or higher-functional (meth)acrylates. The functional group equivalent weight of the (meth)acryloyl group in the multifunctional (meth)acrylate, i.e., the molecular weight per (meth)acryloyl group, is preferably 80 to 150 g / eq. Of the multifunctional (meth)acrylates exemplified above, dipentaerythritol hexa(meth)acrylate is particularly preferred.

[0116] <Siloxane-based hard coating material>

[0117] Siloxane-based hard coating materials contain a curable compound having a siloxane bond as a curable resin component. From the perspective of damage resistance, siloxane-based curable compounds preferably have an epoxy group as a polymerizable functional group, and polyorganosiloxane compounds containing an alicyclic epoxy group are particularly preferred. Such siloxane-based hard coating materials are disclosed in WO2014 / 204010, WO2018 / 096729, WO2020 / 040209, and other publications, which can be referenced / cited.

[0118] Since the siloxane-based hard coating material having an alicyclic epoxy group as a polymerizable functional group has a small cure shrinkage during curing, curling and cracking are less likely to occur even if the thickness of the hard coating layer is increased.

[0119] The polyorganosiloxane compound having an alicyclic epoxy group is obtained by condensing a silane compound represented by the general formula (1).

[0120] [Y-Si(OR 1 ) x R 2 3-x ](1)

[0121] In the general formula (1), R 1 It is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. Specific examples of the alkyl group include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, isopropyl, isobutyl, cyclohexyl, and ethylhexyl.

[0122] The silane compound represented by the general formula (1) has two or three (-OR 1 ). Due to Si-OR 1 Since it is hydrolyzable, polyorganosiloxane compounds can be obtained by condensation of silane compounds. 1 The number of carbon atoms is preferably 3 or less, and R 1 It is a methyl group.

[0123] In the general formula (1), R 2 is a hydrogen atom or a monovalent hydrocarbon group selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, and an aralkyl group 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.

[0124] In the general formula (1), x is 2 or 3. In the case of x=3 (i.e., three alkoxy (or hydroxy) groups -OR 1 In the case of silane compounds, the silane compound does not have R 2 From the viewpoint of forming a network-like polyorganosiloxane compound and increasing the number of epoxy groups contained in the polyorganosiloxane compound to improve the hardness of the cured film, in general formula (1), x=3 is preferred. A silane compound in which x=2 and a silane compound in which x=3 may be used in combination. In addition, in order to adjust 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.

[0125] In general formula (1), 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 bending resistance, an alkyl group having an alicyclic epoxy group as a substituent is preferred.

[0126] Specific examples of the alkyl group having an alicyclic epoxy group as a substituent include (3,4-epoxycyclohexyl)methyl, 2-(3,4-epoxycyclohexyl)ethyl, 3-(3,4-epoxycyclohexyl)propyl, 4-(3,4-epoxycyclohexyl)butyl, 5-(3,4-epoxycyclohexyl)pentyl, 6-(3,4-epoxycyclohexyl)hexyl, 7-(3,4-epoxycyclohexyl)heptyl, 8-(3,4-epoxycyclohexyl)octyl, 9-(3,4-epoxycyclohexyl)nonyl, 10-(3,4-epoxycyclohexyl)decyl, 11-(3,4-epoxycyclohexyl)undecyl, and 12-(3,4-epoxycyclohexyl)dodecyl.

[0127] Specific examples of the silane compound represented by the general formula (1) 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} {(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 them, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane is preferred from the viewpoint of ease of condensation reaction and hardness of the cured product.

[0128] The polyorganosiloxane compound as a condensate of a silane compound may be a condensate of the silane compound of the general formula (1) and another silane compound.

[0129] By reacting the above silane compound with water, the Si-OR 1 The hydrolyzate is partially hydrolyzed and condensed to form Si—O—Si bonds, thereby generating a condensate of the silane compound having an alicyclic epoxy group (polyorganosiloxane compound).

[0130] From the perspective of increasing the hardness of the cured film (hard coat), the weight-average molecular weight of the polyorganosiloxane compound is preferably 500 or greater. Furthermore, from the perspective of suppressing volatilization, the weight-average molecular weight of the polyorganosiloxane compound is also preferably 500 or greater. On the other hand, excessively high molecular weight may cause turbidity due to reduced compatibility with other components in the composition. Therefore, the weight-average molecular weight of the polyorganosiloxane compound is preferably 20,000 or less.

[0131] <Polymerization Initiator>

[0132] The hard coat composition preferably contains a polymerization initiator in addition to the aforementioned curable resin component. A photopolymerization initiator is preferred as the polymerization initiator. Acrylic hard coat compositions containing a compound having a (meth)acryloyl group as a curable resin component preferably contain a photoradical polymerization initiator that generates free radicals in response to light. Siloxane hard coat compositions containing a polyorganosiloxane compound having an epoxy group as a curable resin component preferably contain a photoacid generator (photocationic polymerization initiator) that generates acid in response to light.

[0133] 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, benzyl dimethyl ketal, N,N,N',N'-tetramethyl-4,4'-diaminobenzophenone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one, and other thioxanthone compounds.

[0134] Examples of the photoacid generator include onium salts formed by combining 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-allene complexes; silanol-metal chelates; sulfonic acid derivatives such as disulfones, disulfonyldiazomethanes, disulfonylmethanes, sulfonylbenzoylmethanes, imidesulfonates, and benzoinsulfonates; and organic halogen compounds.

[0135] <Other Components Constituting the Hard Coat Composition>

[0136] The hard coat composition used to form the hard coat layer may contain, in addition to a curable resin component and a polymerization initiator, a solvent and various additives. Examples of additives include fluorine-based or silicone-based leveling agents, sensitizers, reactive diluents, fine particles, fillers, dispersants, plasticizers, ultraviolet absorbers, surfactants, antioxidants, colorants, and viscosity modifiers.

[0137] <Formation of Hard Coat Layer>

[0138] A hard coating composition is applied to the second main surface 1B of the transparent resin film 1, and after the solvent is dried and removed as needed, it is cured to form a hard coating layer 3. When the surface roughness of the front and back surfaces of the transparent resin film 1 is different, the side with relatively larger surface roughness (the side with larger Sa) is the second main surface. When the transparent resin film 1 is produced by a solution method, the surface in contact with the support (B surface) is the second main surface, and the air surface (A surface) is the first main surface. By forming a hard coating layer 3 on the second main surface 1B with large surface roughness, the surface unevenness of the transparent resin film is buried and becomes less obvious, and the overall whiteness of the surface caused by the surface unevenness becomes difficult to observe, so that the uneven whitening is suppressed.

[0139] Examples of methods for applying the hard coating composition to the transparent resin film include roller coating such as rod coating, gravure coating, and comma coating, die coating such as slot die coating and fountain die coating, spin coating, spray coating, and dip coating. Prior to 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 adhesive layer or the like may be provided on the surface of the transparent resin film.

[0140] By irradiating the hard coating composition with active energy rays or heating it, active species such as acid and free radicals are generated from the photopolymerization initiator, and the curable resin component of the hard coating composition is cured. From the viewpoint of curing reactivity, it is preferred 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 rays, infrared rays, X-rays, α rays, β rays, γ rays, electron beams, and the like. From the perspective of high curing reaction speed and excellent energy efficiency, ultraviolet rays are preferred as active energy rays. The cumulative irradiation amount of active energy rays is, for example, 50 to 10,000 mJ / cm 2 The curing temperature may be set according to 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.

[0141] The thickness of the hard coat layer 3 is 1 to 50 μm, preferably 3 μm or greater, and more preferably 5 μm or greater. The thicker the hard coat layer, the higher the pencil hardness and scratch resistance tend to be. On the other hand, excessively thick hard coat layers can reduce flex resistance. Therefore, 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.

[0142] [Hard Coat Film]

[0143] The thickness of the hard coating film 11 (the total thickness of the transparent resin film 1 and the hard coating layer 3) is not particularly limited. From the perspective of mechanical strength, it is preferably 30 μm or more, more preferably 40 μm or more, and can be 50 μm or more. From the perspective of flexibility, it is preferably 200 μm or less, more preferably 100 μm or less, further preferably 80 μm or less, and particularly preferably 70 μm or less.

[0144] The arithmetic mean roughness Sa of the hard-coat-free surface 1A (the first main surface of the transparent resin film 1) of the hard-coat film 11 is 1 nm or less, and may be 0.5 nm or less. The maximum height Sz of the hard-coat-free surface 1A is preferably 70 nm or less, more preferably 50 nm or less, further 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 result in periodic surface shape changes such as undulations of the film. However, since Sa and Sz are obtained from a contour surface that has been filtered to remove the influence of these periodic surface shapes, Sa and Sz of the hard-coat-free surface 1A barely change before and after the formation of the hard-coat layer.

[0145] As described above, hard coat layer 3 is formed on second main surface 1B having relatively large surface roughness to fill surface irregularities. Since first main surface 1A of transparent resin film 1 has a small arithmetic mean roughness Sa, whitening unevenness is less likely to be observed in hard coat film 11.

[0146] 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. Using a resin compatible with the polyimide resin as the other resin constituting the transparent resin film can reduce haze. It should be noted that the polyimide resin does not necessarily need to be completely compatible with the other resins and can have a microphase separation structure small enough not to affect optical properties.

[0147] The total light transmittance of a hard coat film is preferably 90.3% or higher, more preferably 90.5% or higher, and even more preferably 91.0% or higher. Polyimide resins have a high refractive index and high reflectivity at the film-air interface and the film-hard coat interface, resulting in low total light transmittance for transparent polyimide resin films. By blending polyimide resins with other resins, such as acrylic resins, the refractive index is lowered, reducing reflectivity at the interface, thereby increasing total light transmittance.

[0148] 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 preferred for improving the visual visibility of the display and achieving a good color tone. Transparent polyimide is slightly colored yellow, so polyimide-based transparent resin films tend to have a large YI. By using a blend system of a polyimide-based resin and other resins such as an acrylic resin as the transparent resin film 1, coloration can be reduced, thereby reducing the YI of the hard coat film 11.

[0149] The pencil hardness of the surface of the hard coating layer of the hard coating film is preferably 3H or more, more preferably 4H or more, and may be 5H or more. The higher the pencil hardness, the more difficult it is to produce damage or depression caused by external force. The higher the pencil hardness, the better the scratch resistance, and it can also be suitable for use in applications such as cover windows arranged on the outermost surface of a display. In the case where the hard coating film is used as a material for a foldable display, it is preferred that the hard coating film has excellent bending resistance, and preferably can be repeatedly bent at a radius of 1.5 mm for more than 100,000 times.

[0150] The hard coat film of the present invention has excellent mechanical strength and bending resistance, high transparency, and less noticeable whitening unevenness, resulting in excellent appearance characteristics. Therefore, it can be suitably used as a cover window disposed on the surface of an image display panel.

[0151] Example

[0152] The present invention will be described in more detail below based on Examples and Comparative Examples, but the present invention is not limited to the following Examples. Hereinafter, the flow direction during coating is referred to as the MD direction, and the direction perpendicular to the MD direction is referred to as the TD direction.

[0153] [Preparation of polyimide resin]

[0154] Dimethylformamide (DMF) was placed in a separable flask and stirred under a nitrogen atmosphere. Diamine and tetracarboxylic dianhydride were added at the ratio (mol %) shown in Table 1 and stirred under a nitrogen atmosphere for 5 to 10 hours to allow the mixture to react, thereby obtaining a polyamic acid solution having a solid content concentration of 18% by weight.

[0155] In 100g of polyamic acid solution, 5.5g of pyridine as an imidization catalyst was added and completely dispersed. Then, 8g of acetic anhydride was added and stirred at 90°C for 3 hours. After cooling to room temperature, 100g of 2-propanol (IPA) was added at a rate of 2 to 3 drops per second while stirring the solution to precipitate polyimide. IPA150g was further added, and after stirring for about 30 minutes, suction filtration was performed using a Kiriyama funnel. After washing the obtained solid with IPA, it was dried in a vacuum oven set at 120°C for 12 hours to obtain polyimide resins 1 and 2 (PI1 and PI2).

[0156] In Table 1, the compounds are described by the following abbreviations.

[0157] <Tetracarboxylic Dianhydride>

[0158] CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride

[0159] 6FDA: 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride

[0160] TAHMBP: Bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diester

[0161] ODPA: 4,4'-oxydiphthalic dianhydride

[0162] <Diamine>

[0163] TFMB: 2,2'-bis(trifluoromethyl)benzidine

[0164] DDS: 3,3'-diaminodiphenyl sulfone

[0165] [Table 1]

[0166]

[0167] [Production of transparent resin film]

[0168] <Film 1>

[0169] Polyimide resin 1 (PI1) and a commercially available acrylic resin ("Parapet G" manufactured by Kuraray Co., Ltd.; a copolymer of methyl methacrylate / methyl acrylate (monomer ratio 87 / 13), glass transition temperature 109°C, acid value 0.0 mmol / g; hereinafter referred to as "acrylic resin" (Ac)) were dissolved in dichloromethane at a weight ratio of PI1 / Ac1 = 55 / 45. To a total of 100 parts by weight of the resins, 5.6 parts by weight of a triazine-based ultraviolet absorber ("Adekastab LA-31RG" manufactured by ADEKA Corporation) was added to prepare a solution having a solid content concentration of 15% by weight.

[0170] This solution was applied to a PET film ("Lumirror U40" manufactured by Toray Industries, Inc.; surface arithmetic mean roughness Sa: 1 nm, maximum height Sz: 41 nm) as a support using a roll-to-roll coating and drying machine. The film was then passed through a drying oven set to gradually increase the temperature from 30°C to 45°C, yielding a primary dried film with a residual solvent content of 10-15% by weight. Hereinafter, the air-exposed surface during the primary film production will be referred to as "side A," and the surface in contact with the support will be referred to as "side B."

[0171] The primary dried film was peeled from the support (PET film) and secondary dried by passing it through a drying oven set at a temperature gradually increased from 90°C to 150°C. This yielded a film having a residual solvent content of approximately 1% by weight and a thickness of 110 μm. The film thickness was measured using a contact thickness gauge.

[0172] Using a stretching machine with a heating oven, the TD direction was used as the stretching direction at a temperature of 215°C, and the obtained film was fixed-end uniaxially stretched at a stretching ratio of 120% (the length of TD was 2.20 times that of the film before stretching) to obtain a stretched film with a thickness of 50 μm.

[0173] <Film 2>

[0174] A 25 μm-thick stretched film was produced using the same solution as used for Film 1. The coating thickness was changed, the primary film production temperature range was changed from 30°C to 60°C, the secondary drying temperature range was changed from 80°C to 130°C, the stretching temperature was changed to 205°C, and the stretch ratio was changed to 115%. The same procedures as for Film 1 were followed except for these changes.

[0175] <Film 3>

[0176] 100 parts by weight of polyimide resin 2 (PI2), 2.4 parts by weight of a triazine ultraviolet absorber ("Tinuvin 477" manufactured by BASF), and 0.0065 parts by weight of a bluing agent ("Plast Blue 8590" manufactured by Arimoto Chemical Co., Ltd.) were dissolved in dichloromethane to prepare a solution having a solid content concentration of 7% by weight.

[0177] This solution was applied to a PET film ("Lumirror U40" manufactured by Toray Industries, Inc.) serving as a support using a roll-to-roll coating and drying system. The film was then passed through a drying oven set at a temperature gradually increasing from 30°C to 60°C, yielding a primary dried film having a residual solvent content of 5 to 15% by weight. The primary dried film was then peeled from the support and secondary dried by passing through a drying oven set at a temperature gradually increasing from 60°C to 200°C, yielding a film with a residual solvent content of approximately 1% by weight and a thickness of 50 μm.

[0178] [Evaluation of transparent resin film]

[0179] Films 1 to 3 were subjected to the following evaluations.

[0180] <Tensile elastic modulus>

[0181] The film was cut into 10 mm wide strips and allowed to stand for one day at 23°C / 55% RH for humidity control. Tensile tests were then conducted using a Shimadzu Corporation "Autograph AGS-X" tensile testing machine under the following conditions to calculate the tensile modulus. Tensile tests were conducted in both the MD and TD directions.

[0182] Distance between fixtures: 100mm

[0183] Tensile speed: 20.0 mm / min

[0184] Measurement temperature: 23°C

[0185] <Arithmetic mean roughness Sa and maximum height Sz>

[0186] The three-dimensional surface shape of the film's A and B surfaces was measured using a white interference microscope (ZYGO NEWVIEW 7300) with a 50x objective lens. The measurement area was 0.28 mm x 0.21 mm, with the entire area serving as the reference area. To eliminate the influence of periodic surface features such as undulations across the film, the following filtering conditions were applied to calculate the arithmetic mean roughness Sa and maximum height Sz. The maximum height Sz is the value indicated as PV in the software included with the instrument.

[0187] Filter: High Pass

[0188] Filter Type: Gauss Spline

[0189] Filter Low Wavelength: 30.00000μm

[0190] Filter High Wavelength: No setting

[0191] Table 2 shows the materials and thicknesses of films 1 to 3, and the evaluation results.

[0192] [Table 2]

[0193]

[0194] [Preparation of Hard Coat Composition]

[0195] <Preparation of Acrylic Hard Coat Composition>

[0196] To 100 parts by weight of dipentaerythritol hexaacrylate ("Aronix M-403" manufactured by Toagosei 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 leveling agent ("BYK-300" manufactured by BYK) were added, and propylene glycol monomethyl ether was added as a diluent to obtain an acrylic hard coat composition having a solid content concentration of 50% by weight.

[0197] <Silicone-based hard coat composition>

[0198] 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 added to a reaction vessel equipped with a thermometer, a stirring device, and a reflux cooling tube and stirred evenly. A solution prepared by dissolving 0.039 g (0.405 mmol) of magnesium chloride as a catalyst in a mixture of 9.7 g (539 mmol) of water and 5.8 g of methanol was added dropwise to the mixture over a period of 5 minutes and stirred until uniform. The mixture was then heated to 80°C and subjected to a polycondensation reaction for 6 hours while stirring. After the reaction was completed, the solvent and water were distilled off using a rotary evaporator to obtain a condensate of the silane compound (polyorganosiloxane compound).

[0199] The GPC apparatus "HLC-8220GPC" manufactured by Tosoh Corporation (chromatographic column: TSKgel GMH XL ×2 pieces, TSKgel G3000H XL ,TSKgel G2000H XL The weight average molecular weight of the polystyrene conversion measured by ) was 3000. The 400 MHz-NMR manufactured by Bruker was used, and the 3-D acetone was used as the solvent. 1 The residual rate of epoxy groups calculated from the H-NMR spectrum was 95% or more.

[0200] To 100 parts by weight of the above-mentioned polyorganosiloxane compound, 2 parts by weight of a sulfonium photoacid generator ("CPI-101A" manufactured by San-Apro) and 0.25 parts by weight of a polyether-modified silicone leveling agent ("BYK-300" manufactured by BYK) were added, and propylene glycol monomethyl ether was added as a diluent to obtain a silicone hard coat composition having a solid content concentration of 50% by weight.

[0201] [Production of hard coating film]

[0202] <Example 1>

[0203] The acrylic hard coating composition was applied to the B surface of the film 1 using a coater to a dry film thickness of 5 μm, and the solvent was removed at 120° C. Then, a high-pressure mercury lamp was used in a nitrogen atmosphere at a cumulative light intensity of 1950 mJ / cm 2 The hard coating resin composition was cured by irradiating with ultraviolet light in a manner to obtain a hard coating film having an acrylic hard coating layer having a thickness of 5 μm. The thickness of the hard coating layer is the difference between the thickness of the hard coating film measured using a contact thickness gauge and the thickness of the film before the hard coating layer is formed.

[0204] <Example 2>

[0205] The silicone hard coating composition was applied to the B surface of the film 1 using a coater to a dry film thickness of 20 μm, and the solvent was removed at 120° C. Then, a high-pressure mercury lamp was used in an air atmosphere at a cumulative light intensity of 1950 mJ / cm 2 The hard coating resin composition was cured by irradiating ultraviolet rays in a manner of 100 μm to obtain a hard coating film having a silicone hard coating layer with a thickness of 20 μm.

[0206] Comparative Examples 1 and 2

[0207] A hard coat film was obtained in the same manner as in Examples 1 and 2 except that the hard coat layer forming surface (the hard coat composition coating surface) was changed to surface A of the film 1 .

[0208] <Comparative Example 3>

[0209] Instead of Film 1, an acrylic hard coat layer having a thickness of 5 μm was formed on the A surface of Film 3 in the same manner as in Comparative Example 1 to obtain a hard coat film.

[0210] [Evaluation of Hard Coat Film]

[0211] <Total Light Transmittance and Haze>

[0212] The total light transmittance and haze were measured using a haze meter "HZ-V3" manufactured by Suga Test Instruments Co., Ltd. according to the methods described in JIS K7361-1: 1999 and JIS K7136: 2000. A D65 light source was used for the measurement.

[0213] <Pencil Hardness>

[0214] The pencil hardness of the hard coat surface was evaluated under a load of 750 g according to JIS K5600. A scratch test (moving a pencil) in the MD direction and a scratch test in the TD direction were performed, and the higher hardness was determined as the pencil hardness of the hard coat film.

[0215] <Repeated bending test>

[0216] 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 sample was placed in a U-shaped bending durability tester (DMLHB) manufactured by Yuasa System Co., Ltd. and subjected to a repeated bending test 100,000 times with a bend radius of 1.5 mm, a bend angle of 180°, and a rate of 1 bend / second, with the hard-coated layer facing inward and the MD direction as the bending axis. The test was conducted in a constant temperature and humidity environment set at 23°C and 55% humidity. The hard-coated films of Examples 1 and 2 and Comparative Examples 1-3 showed no cracks or breaks after the test, demonstrating excellent flex resistance.

[0217] <Appearance (uneven whitening)>

[0218] A hard-coated film was cut into a 300 mm x 210 mm rectangle with its long side in the MD direction. The four sides were fixed to a plastic corrugated cardboard frame to form a flat surface. In a darkroom, the hard-coated film was illuminated with light from a three-wavelength fluorescent lamp, and the transmitted light was visually observed. The incident angle of the transmitted light was within the range of 60° to 89° relative to the normal to the film surface. Specifically, the hard-coated film was placed between the fluorescent lamp and the observer, tilted within the range of 60° to 89° with either the MD or TD direction as the tilt axis, and the fluorescent light transmitted through the hard-coated film was observed. If uneven whitening was observed within the surface of the hard-coated film at any angle between 60° and 89°, the film was considered "present." If no uneven whitening was observed in either the MD or TD directions, the film was considered "absent."

[0219] Table 3 shows the composition and evaluation results of the hard coat films of Examples and Comparative Examples. Table 3 also shows the evaluation results (presence or absence of whitening unevenness) of films 1 and 2 without a hard coat layer as Reference Examples 1 and 2. For Reference Examples 1 and 2, the surface profile of the surface without a hard coat layer (HC non-formed surface) is reported as the roughness of surface A (nm) / the roughness of surface B (nm).

[0220] [Table 3]

[0221]

[0222] No whitening unevenness was observed in the 25 μm-thick film 2 (Reference Example 2), whereas whitening unevenness was observed in the 50 μm-thick film 1 (Reference Example 1). These results show that whitening unevenness is more likely to occur when the film thickness is large.

[0223] In Comparative Examples 1 and 2, in which a hard coating layer was formed on surface A of Film 1 (Sa = 0 nm, Sz = 5 nm), whitening unevenness was observed similarly to Film 1. Whitening unevenness was also observed in Comparative Example 3, in which a hard coating layer was formed on surface A of Film 3 (Sa = 1 nm, Sz = 38 nm). On the other hand, in Examples 1 and 2, in which a hard coating layer was formed on surface B of Film 1 (Sa = 2 nm, Sz = 77 nm), no whitening unevenness was observed.

[0224] Based on these results, it can be seen that in the hard coating films of Examples 1 and 2, by forming a hard coating layer on the B side with relatively large surface roughness, the unevenness on the surface of the film is filled, and the A side with relatively small surface roughness (Sa=0nm, Sz=5nm) is exposed on the surface, thereby eliminating the uneven whitening.

[0225] The hard-coated films of Examples 1 and 2, which had a hard coat layer formed on the surface of a blended resin film of a polyimide resin and an acrylic resin, not only eliminated uneven whitening but also exhibited higher total light transmittance and superior transparency compared to Comparative Example 3, which had a hard coat layer formed on the surface of a film 3 made solely of a polyimide resin. Furthermore, the hard-coated films of Examples 1 and 2 had high pencil hardness and excellent flex resistance, making them suitable for use as cover windows for foldable displays.

[0226] Description of Reference Numerals

[0227] 1Transparent resin film

[0228] 1A First main surface (hard coating non-formed surface)

[0229] 1B Second main surface (hard coating layer forming surface)

[0230] 3Hard coating

[0231] 11Hard coating 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. The transparent resin film has a thickness of 26 μm or more and contains a polyimide resin and a solvent-soluble resin other than the polyimide resin. No hard coating layer is provided on the first main surface of the transparent resin film, The arithmetic mean roughness Sa of the first main surface of the transparent resin film is 1 nm or less.

2. The hard coating film according to claim 1, wherein In the transparent resin film, the arithmetic mean roughness Sa of the second main surface is greater than the arithmetic mean roughness Sa of the first main surface.

3. The hard coating film according to claim 1, wherein The second main surface of the transparent resin film has an arithmetic mean roughness Sa of 1.5 nm or more.

4. The hard coating film according to claim 1, wherein The maximum height Sz of the first main surface of the transparent resin film is 70 nm or less.

5. The hard coating film according to claim 4, wherein In the transparent resin film, a maximum height Sz of the second main surface is greater than a maximum height Sz of the first main surface.

6. The hard coating film according to claim 1, wherein The solvent-soluble resin is an acrylic resin.

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

8. The hard coating film according to claim 1, wherein The polyimide resin is a polyimide containing a structure derived from tetracarboxylic dianhydride and a structure derived from diamine. The tetracarboxylic dianhydride includes fluorine-containing aromatic tetracarboxylic dianhydride and alicyclic tetracarboxylic dianhydride. The diamine includes fluorine-containing diamine.

9. The hard coating film according to claim 1, wherein The transparent resin film is a stretched film.

10. The hard coating film according to claim 1, wherein The hard coating layer is an acrylic hard coating layer.

11. The hard coating film according to claim 1, wherein The hard coating layer is a silicone hard coating layer.

12. The hard coating film according to claim 1, wherein The hard coating layer has a thickness of 1 to 50 μm.

13. A method for producing a hard coating film, the method comprising: A resin solution in which a polyimide resin and a solvent-soluble resin other than the polyimide resin are dissolved in a solvent is applied onto a support. The solution is heated on the support to dry and remove the solvent, thereby producing a transparent resin film. peeling the transparent resin film from the support, A hard coat layer is formed on the release surface of the transparent resin film to be released from the support.

14. The method for producing a hard coating film according to claim 13, wherein: In the support, the surface on which the resin solution is applied has an arithmetic mean roughness Sa of 0.5 nm or more.

15. The method for producing a hard coating film according to claim 13, wherein: In the support, a maximum height Sz of a surface on which the resin solution is applied is 10 nm or more.

16. The method for producing a hard coating film according to claim 13, wherein: The supporting body is a plastic film.

17. A display comprising the hard coating film according to any one of claims 1 to 12.

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