Hard coated film and display

Abstract

The hard coat film (11) is provided with a hard coat layer (3) on at least one surface of a transparent film (1). The transparent film contains a polyimide-based resin and a solvent-soluble resin other than the polyimide-based resin. The solvent-soluble resin is preferably an acrylic resin. The hard coat film preferably has a recess recovery property. The indentation hardness of the transparent film is preferably 300 N / mm2 or more, and the stress relaxation amount is preferably 1.50% or more. The hard coat film can be suitably used as a cover window material for a display.

Description

Technical Field

[0001] The present invention relates to a hard coating film and a display including the hard coating film. Background Art

[0002] Curved displays and foldable displays (foldable displays) have been developed, and research is underway to use plastic film materials with excellent flexibility in display cover windows, substrates, and the like. For cover windows of flexible displays, such as foldable displays, in addition to transparency and hardness, bending resistance is also required. Patent document 1 proposes using a hard-coated film having a hard coating on the surface of a transparent film as a cover window, wherein the transparent film is formed of a resin material such as triacetyl cellulose, transparent polyimide, and polyethylene naphthalate.

[0003] Most mobile displays such as smartphones and small PCs equipped with foldable displays can be operated by touch panels, and the cover window is required to be less likely to be dented by the pressure and sliding caused by the operator's nails or stylus (stylus). Patent document 2 discloses that by making the resin film of the hard coating film contain elastomer particles, it is possible to suppress the denting of the hard coating film caused by keystrokes.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2018 / 096729

[0007] Patent Document 2: International Publication No. 2019 / 078196 Summary of the invention

[0008] Problem that the invention aims to solve

[0009] Although hard coating films using resin films with high mechanical strength such as polyimide are not easily dented by pressure or sliding caused by nails, styluses, etc., once dented, it is difficult to recover over time and remains, which has a negative impact on the visual recognition of the display. As disclosed in Patent Document 2, although the film can be made to contain an elastomer to give the dent recovery, it contains a soft material and therefore has problems such as insufficient hardness.

[0010] In view of the above circumstances, an object of the present invention is to provide a hard coating film which is less likely to be dented by an external force and has excellent recovery properties from dents that are dented.

[0011] Solutions for solving problems

[0012] The hard coating film has a hard coating layer on at least one surface of the transparent film. The transparent film contains a polyimide resin and a solvent-soluble resin other than the polyimide resin. The hard coating film preferably exhibits a dent recovery property in a dent test described in the examples described below.

[0013] As the solvent-soluble resin, an acrylic resin is preferred, and among them, a resin containing methyl methacrylate as a main component is preferred.

[0014] The polyimide resin is polyimide or polyamideimide, and includes a structure derived from tetracarboxylic dianhydride and a structure derived from diamine. The polyimide resin is preferably polyimide.

[0015] The polyimide resin preferably contains alicyclic tetracarboxylic dianhydride as tetracarboxylic dianhydride and further contains fluorine-containing aromatic tetracarboxylic dianhydride and / or bis(trimellitic anhydride) ester. The polyimide resin preferably contains fluorine-containing diamine as diamine.

[0016] The indentation hardness of the transparent film is preferably 300N / mm 2 The stress relaxation amount of the transparent film when a triangular pyramid indenter is applied with a load of 100 mN for 2 seconds in a nanoindentation method is preferably 1.50% or more.

[0017] The transparent film may be a stretched film. In the case where the transparent film is a stretched film, the difference between the direction of the maximum tensile elastic modulus in the film surface and the tensile elastic modulus in the orthogonal direction thereof may be 1.3 GPa or more. The tensile elastic modulus in the direction of the maximum tensile elastic modulus in the surface of the transparent film may be 5.0 GPa or more.

[0018] The thickness of the transparent film can be 20 to 60 μm.

[0019] Examples of the material of the hard coat layer include acrylic hard coat materials and silicone hard coat materials.

[0020] The pencil hardness of the hard coating film may be 3H or higher. The thickness of the hard coating layer may be 1 to 50 μm.

[0021] Effects of the Invention

[0022] The hard coating film of the present invention is unlikely to be dented by external force and has excellent recovery properties from dents that are generated, and can be suitably used for cover windows of displays and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a cross-sectional view of a hard coating film according to one embodiment. DETAILED DESCRIPTION

[0024] Figure 11 is a cross-sectional view of a hard coating film according to an embodiment of the present invention. The hard coating film 11 includes a hard coating layer 3 on a transparent film 1 .

[0025] [Transparent film]

[0026] The transparent film 1 is a substrate that serves as a base when forming the hard coat layer 3. The total light transmittance of the transparent film is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0027] In the hard coating film of the present invention, the transparent film 1 contains one or more polyimide resins selected from the group consisting of polyimide and polyamide-imide, and a solvent-soluble resin other than the polyimide resin. Since the transparent film 1 contains the polyimide resin and the solvent-soluble resin, the hard coating film 11 having the hard coating layer 3 formed on the transparent film 1 is not easily dented by external force, and even if dented, it has dent recovery properties.

[0028] <Polyimide resin>

[0029] Polyimide can be obtained by dehydration cyclization of polyamic acid obtained by the reaction of tetracarboxylic dianhydride (hereinafter sometimes referred to as "acid dianhydride") and diamine. Polyamide-imide is obtained by substituting a part of the tetracarboxylic dianhydride of polyimide with dicarboxylic acid derivatives such as dicarboxylic acid dichlorides. As polyimide-based resins, polyimide and polyamide-imide can be used in combination. From the viewpoints of compatibility with solvent-soluble resins described later, as polyimide-based resins, polyimide is sometimes preferred.

[0030] (Tetracarboxylic dianhydride)

[0031] In the polyimide resin used in the present embodiment, as the acid dianhydride component, it is preferred to include alicyclic tetracarboxylic dianhydride. By making the acid dianhydride component have an alicyclic structure, there is a tendency to improve the compatibility of the polyimide resin with solvent-soluble resins such as acrylic resins. 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 a condensed ring or a spiro structure.

[0032] 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 acid-3,4:3',4'-dianhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic dianhydride, 2,2' -Norbornane-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-dihydroisobenzofuran-5-carboxylate), 5-(2,5-dioxotetrahydrofuranyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 5,5'-[cyclohexylidenebis(4,1-phenyleneoxy)]bis-1,3-isobenzofuran dicarboxylate ketone, 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-biphenylene[4a,4bc:8a,8b-c']difuran-1,3 ,8,10-tetraketone, ethylene glycol bis(hydrogenated trimellitic anhydride), decahydro[2]benzopyrano[6,5,4,-def][2]benzopyran-1,3,6,8-tetraketone, etc. Among the alicyclic tetracarboxylic dianhydrides, from the viewpoint of transparency and mechanical strength of the polyimide 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 acid-3,4:3',4'-dianhydride (H-BPDA) is preferred, and 1,2,3,4-cyclobutanetetracarboxylic dianhydride is particularly preferred.

[0033] From the viewpoint of improving the compatibility of polyimide resin and solvent-soluble resin, the content of alicyclic tetracarboxylic dianhydride relative to 100 mol% of the total amount of acid dianhydride components is preferably 1 mol% or more, more preferably 3 mol% or more, and further preferably 5 mol% or more, 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 to make it compatible with solvent-soluble resins sometimes varies depending on the type of solvent-soluble resin, the amount of alicyclic tetracarboxylic dianhydride, etc. For example, in the case where the alicyclic tetracarboxylic dianhydride is 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), the content of CBDA relative to 100 mol% of the total amount of acid dianhydride components is preferably 6 mol% or more, more preferably 8 mol% or more, and further preferably 10 mol% or more.

[0034] From the viewpoint of ensuring the solubility of polyimide resin in organic solvent, the content of alicyclic tetracarboxylic dianhydride relative to the total amount of acid dianhydride component 100 mol% is preferably 80 mol% or less, more preferably 78 mol% or less, further preferably 76 mol% or less, 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 polyimide resin soluble in low boiling point halogen solvents such as dichloromethane, the content of alicyclic tetracarboxylic dianhydride is preferably 45 mol% or less, more preferably 40 mol% or less, can be 35 mol% or less.

[0035] From the viewpoint of making the polyimide resin soluble in an organic solvent, it is preferred that, as the acid dianhydride component, in addition to the alicyclic tetracarboxylic dianhydride, a fluorine-containing aromatic tetracarboxylic dianhydride or / and a bis(trimellitic anhydride) ester are included. As the fluorine-containing aromatic tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}-1,1,1,3,3,3-hexafluoropropane dianhydride, etc. can be listed. As the bis(trimellitic anhydride) ester, bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'diyl (abbreviated as: TAMBP) and the like can be listed.

[0036] From the viewpoint of making the polyimide resin soluble in an organic solvent, the total content of fluorinated aromatic tetracarboxylic dianhydride and bis(trimellitic anhydride) ester is preferably 15 mol% or more relative to the total amount of the acid dianhydride component 100 mol%, more preferably 20 mol% or more, further preferably 25 mol% or more, and can be 30 mol% or more, 35 mol% or more, 40 mol% or more, 45 mol% or more or 50 mol% or more. The total content of fluorinated aromatic tetracarboxylic dianhydride and bis(trimellitic anhydride) ester is preferably 99 mol% or less relative to the total amount of the acid dianhydride component 100 mol%, more preferably 95 mol% or less, further preferably 90 mol% or less, and can be 85 mol% or less, 80 mol% or less, 75 mol% or less or 70 mol% or less.

[0037] From the viewpoint of obtaining a polyimide-based resin having both solubility in an organic solvent and compatibility with a solvent-soluble resin, the total content of alicyclic tetracarboxylic dianhydride, fluorinated aromatic tetracarboxylic dianhydride and bis(trimellitic anhydride) ester is preferably 50 mol% or more, more preferably 60 mol% or more, further preferably 65 mol% or more, relative to 100 mol% of the total amount of the acid dianhydride component. It 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.

[0038] In the polyimide resin, as an acid dianhydride component, an acid dianhydride other than alicyclic tetracarboxylic dianhydride, fluorine-containing aromatic tetracarboxylic dianhydride and bis(trimellitic anhydride) ester may be included. 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) phenyl)ethane 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 anhydride, 1,4-bis[(3,4-dicarboxy)benzoyl]phthalic anhydride, 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride, 2,2-bis{4-[4-(3,4-dicarboxy)phenoxy]phenyl}propane dianhydride, bis(4-[3-(1,2-dicarboxy)phenoxy]phenyl}propane 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-benzenetetracarboxylic 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.

[0039] (Dicarboxylic Acid)

[0040] As described above, the polyimide resin may be a polyamideimide 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 bi(cyclohexyl)-4,4'-dicarboxylic acid; and heterocyclic dicarboxylic acids such as 2,5-thiophenedicarboxylic acid and 2,5-furandicarboxylic acid.

[0041] From the viewpoint of solubility of polyamide-imide and compatibility with solvent-soluble resin, the dicarboxylic acid is preferably an aromatic dicarboxylic acid and an alicyclic dicarboxylic acid, and particularly preferably an aromatic dicarboxylic acid. Among the aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, 4,4'-biphenyl dicarboxylic acid, and 4,4'-oxybisbenzoic acid are preferred, among which terephthalic acid and isophthalic acid are preferred, and terephthalic acid is particularly preferred.

[0042] As the dicarboxylic acid derivative used as the raw material monomer of the polyamideimide, dicarboxylic acid dichloride, dicarboxylic acid ester, dicarboxylic acid anhydride and the like can be used. Among them, dicarboxylic acid dichloride is preferred because of its high reactivity.

[0043] From the viewpoint of solubility of polyamide-imide and compatibility with solvent-soluble resin, the ratio of dicarboxylic acid derivatives to the total of tetracarboxylic dianhydride and dicarboxylic acid derivatives is preferably 40 mol% or less, more preferably 35 mol% or less, and further preferably 30 mol% or less. The polyimide-based resin may be a polyimide in which the ratio of dicarboxylic acid derivatives is 0 (i.e., does not contain a structure derived from a dicarboxylic acid derivative).

[0044] (Diamine)

[0045] The diamine component of the polyimide resin used in the present embodiment is not particularly limited. From the viewpoint of solubility, the diamine as the polyimide resin preferably has one or more selected from the group consisting of a fluorine group, a trifluoromethyl group, a sulfone group, a fluorene structure and an alicyclic structure. Among them, from the viewpoint of taking into account 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.

[0046] Examples of the fluoroalkyl-substituted benzidine as the fluorinated diamine 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.

[0047] Among them, fluoroalkyl-substituted benzidine having a fluoroalkyl group at the 2-position of the biphenyl group is preferred, and 2,2'-bis(trifluoromethyl)benzidine (hereinafter referred to as "TFMB") is particularly preferred. By having fluoroalkyl groups at the 2-position and 2'-position of the biphenyl group, the π electron density is reduced due to the electron-withdrawing property of the fluoroalkyl group, and the bond between the two benzene rings of the biphenyl group is twisted due to the steric hindrance of the fluoroalkyl group, and the planarity of the π conjugation is reduced. Therefore, the absorption end wavelength is shifted to a shorter wavelength, and the coloring of the polyimide resin can be reduced.

[0048] The content of the fluoroalkyl-substituted benzidine relative to 100 mol% of the total amount of the diamine component is preferably 50 mol% or more, more preferably 60 mol% or more, further preferably 70 mol% or more, and may be 80 mol% or more, 85 mol% or more, or 90 mol% or more. When the content of the fluoroalkyl-substituted benzidine is large, coloring of the film is suppressed and mechanical strength such as pencil hardness and elastic modulus tends to increase.

[0049] 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, 3,4 '-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 4,4'-diphenoxybenzophenone, 3,3'-diamino-4,4'-diphenyloxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-phenyloxybenzophenone, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane, 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, α,ω-bis(3-aminopropyl)polydimethylsiloxane, α,ω-bis(3-aminobutyl)polydimethylsiloxane, bis(aminomethyl 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. For example, as a diamine, by using diaminodiphenyl sulfone in addition to fluoroalkyl-substituted benzidine, the solubility and transparency of the polyimide resin in the solvent may be improved. Among the 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 be used in combination. The content of diaminodiphenyl sulfone relative to 100 mol% of the total amount of diamine may be 1 to 40 mol%, 3 to 30 mol%, or 5 to 25 mol%.

[0050] (Preparation of polyimide resin)

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

[0052] When preparing polyamide-imide, dicarboxylic acid or its derivative (dicarboxylic acid dichloride, dicarboxylic acid anhydride, etc.) may be used as a monomer in addition to diamine and tetracarboxylic dianhydride. In this case, the amount of each monomer may be adjusted so that the total amount of tetracarboxylic dianhydride and dicarboxylic acid or its derivative is substantially equal to the molar amount of 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 an organic solvent and exhibits compatibility with a solvent-soluble resin.

[0054] The concentration of the polyamic acid solution is usually 5 to 35% by weight, preferably 10 to 30% by weight. When the concentration is within this range, the polyamic acid obtained by polymerization has an appropriate molecular weight, and the polyamic acid solution has an appropriate viscosity.

[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. In the case of adding multiple diamines and multiple acid dianhydrides, it can be added once or in multiple times. By adjusting the order of adding monomers, it is also possible to control the various physical properties of polyimide resins.

[0056] The organic solvent used in the polymerization of polyamic acid is not particularly limited as long as it is a solvent that can dissolve polyamic acid without reacting with diamine and acid dianhydride. As an organic solvent, urea solvents such as methyl urea and N, N-dimethylethyl urea can be listed; sulfoxide or sulfone solvents such as dimethyl sulfoxide, diphenyl sulfone, and tetramethyl sulfone; amide solvents such as N, N-dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), N, N'-diethylacetamide, N-methyl-2-pyrrolidone (NMP), γ-butyrolactone, and hexamethylphosphorus triamide; halogenated alkane solvents such as chloroform and dichloromethane; aromatic hydrocarbon solvents such as benzene and toluene; ether solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, and p-cresol methyl ether. Usually, these solvents are used alone or in combination as needed. From the viewpoint of the solubility and polymerization reactivity of polyamic acid, DMAc, DMF, NMP, etc. are preferably used.

[0057] The polyimide resin is obtained by the dehydration cyclization of polyamic acid. As a method for preparing polyimide resin from polyamic acid solution, a method for imidizing in solution by adding a dehydrating agent, an imidization catalyst, etc. to the polyamic acid solution can be cited. In order to promote the progress of imidization, the polyamic acid solution can be heated. By mixing the solution containing the polyimide resin generated by the imidization of polyamic acid with a poor solvent, the polyimide resin is precipitated in the form of a solid. By separating the polyimide resin in the form of a solid, the impurities, residual dehydrating agent and imidization catalyst generated when synthesizing polyamic acid can be cleaned / removed using a poor solvent, and the coloring of the polyimide resin, the rise of yellowness, etc. can be prevented. In addition, by separating the polyimide resin in the form of a solid, when preparing a solution for making a film, a solvent suitable for filmization such as a low boiling point solvent can be applied.

[0058] The molecular weight of the polyimide resin (weight average molecular weight measured by gel filtration chromatography (GPC) in terms of polyethylene oxide) is preferably 10,000 to 300,000, more preferably 20,000 to 250,000, and further preferably 40,000 to 200,000. When the molecular weight is too small, the strength of the film is sometimes insufficient. When the molecular weight is too large, the compatibility with the solvent-soluble resin is sometimes poor.

[0059] The polyimide resin is preferably soluble in a low boiling point solvent such as a ketone solvent or a haloalkane 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 solvents during film production. Therefore, by using a polyimide resin soluble in dichloromethane, it is expected that the productivity of the film will be improved.

[0060] From the viewpoint of thermal stability and light stability of transparent film, polyimide resin preferably has low reactivity. The acid value of polyimide 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 polyimide can be 0.1mmol / g or less, 0.05mmol / g or less or 0.03mmol / g or less. From the viewpoint of reducing acid value, polyimide resin preferably has high imidization rate. By making acid value small, there is a tendency that the stability of polyimide resin can be improved and the compatibility with solvent-soluble resin can be improved.

[0061] <Solvent-soluble resin>

[0062] As mentioned above, the transparent film 1 includes, in addition to the polyimide resin, a solvent-soluble resin other than the polyimide resin. As the solvent-soluble resin, there is no particular limitation as long as it has solvent solubility, is compatible with the polyimide resin, and shows transparency when blended. As the solvent-soluble resin showing compatibility with the polyimide resin, acrylic resin, polycarbonate resin, polyester resin, polyamide resin, polyether resin, cellulose resin, silicone resin, cyclic olefin resin, etc. can be listed. As the solvent-soluble resin, a variety of these resins can be used.

[0063] As the solvent-soluble resin, acrylic resin, polycarbonate resin, and polyester resin having a fluorene structure are preferred from the viewpoint of high compatibility with polyimide resin. Among them, acrylic resin is particularly preferred from the viewpoint of high compatibility with polyimide resin and easy formation of a film having high transmittance, low haze, and high hardness.

[0064] 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, methyl (meth)acrylate-styrene copolymers, etc. Acrylic resins may be modified to introduce glutarimide structural units and lactone ring structural units.

[0065] From the viewpoints of transparency, compatibility with polyimide and mechanical strength, the acrylic resin preferably has methyl methacrylate as the main structural unit. The amount of methyl methacrylate in the acrylic resin relative to the total amount of monomer components is preferably 60% by weight or more, and can be 70% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. The acrylic resin can be a homopolymer of methyl methacrylate. In addition, the acrylic resin can be a resin obtained by introducing a glutarimide structure or a lactone ring structure into an acrylic polymer having a methyl methacrylate content within the above range.

[0066] From the viewpoint of heat resistance of the transparent 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.

[0067] 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 viewpoint of solubility in an organic solvent, compatibility with a polyimide resin, and film strength.

[0068] From the viewpoint of thermal stability and light stability of resin composition and film, acrylic resin preferably has less content of reactive functional groups such as ethylenically unsaturated groups and carboxyl groups. The iodine value of acrylic resin is preferably less than 10.16g / 100g (0.4mmol / g), more preferably less than 7.62g / 100g (0.3mmol / g), and further preferably less than 5.08g / 100g (0.2mmol / g). The iodine value of acrylic resin can be less than 2.54g / 100g (0.1mmol / g) or less than 1.27g / 100g (0.05mmol / g). The acid value of acrylic resin is preferably less than 0.4mmol / g, more preferably less than 0.3mmol / g, and further preferably less than 0.2mmol / g. The acid value of acrylic resin can be less than 0.1mmol / g, less than 0.05mmol / g or less than 0.03mmol / g. When the acid value is reduced, the stability of the acrylic resin is improved and the compatibility with the polyimide resin tends to be improved.

[0069] <Production of transparent film>

[0070] The method for forming the transparent film is not particularly limited, but a solution method is preferably used in which a solution containing the polyimide resin and a solvent-soluble resin is applied onto a support and the solvent is removed by drying.

[0071] The above-mentioned polyimide resin and solvent-soluble resin can show compatibility in any ratio, therefore, the ratio of the polyimide resin to the solvent-soluble resin in the resin composition is not particularly limited. The mixing ratio (weight ratio) of the polyimide resin and the solvent-soluble resin can be 98:2 to 2:98, 95:5 to 10:90, 90:10 to 15:85 or 65:35 to 50:50. There is a tendency that 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. There is a tendency that the higher the ratio of the solvent-soluble resin, the less coloring of the film and the higher the transparency.

[0072] From the viewpoint of fully exerting the effect of improving transparency by mixing the polyimide resin and the solvent-soluble resin and providing the hard coat film with dent recovery properties, the ratio of the solvent-soluble resin to the total of the polyimide resin and the solvent-soluble resin is preferably 10 to 90 wt %, more preferably 15 to 85 wt %, further preferably 20 to 80 wt %, and may be 30 to 70 wt %, 35 to 65 wt % or 40 to 60 wt %.

[0073] The solvent is not particularly limited as long as it shows solubility in both the polyimide resin and the solvent-soluble 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 halogenated alkane solvents such as chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene, dichlorobenzene, and dichloromethane. Among them, ketone solvents and halogenated alkane solvents are preferred because they have excellent solubility in both polyimide resins and solvent-soluble resins such as acrylic resins, and have low boiling points and are easy to remove residual solvents when making thin films.

[0074] The resin solution may contain, in addition to the polyimide resin and the solvent-soluble resin, an organic or inorganic low molecular compound, a high molecular compound (e.g., epoxy resin), etc. The resin solution may contain additives such as flame retardants, ultraviolet absorbers, stabilizers, crosslinking agents, dyes, pigments, surfactants, leveling agents, plasticizers, and microparticles.

[0075] As a method for coating the resin solution on the support, a known method using a bar coater, a comma coater, etc. can be applied. As the support, a glass substrate, a metal substrate such as SUS, a metal cylinder, a metal belt, a plastic film, etc. can be used.

[0076] When drying the solvent, it is preferred to heat. 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, and is appropriately set at about room temperature to 250°C, preferably 50°C to 220°C. The heating temperature can be increased in stages. In order to improve the removal efficiency of the solvent, the resin film can be peeled off from the support and dried after drying to a certain extent. In order to promote the removal of the solvent, heating can be performed under reduced pressure.

[0077] The film may be stretched in one direction or in multiple directions for the purpose of improving the mechanical strength of the film. When the film is stretched, the polymer chains are oriented in the stretching direction, so there is a tendency that the film's in-plane strength is improved, the film's rupture and cracking are suppressed, and the dent resistance and dent recovery are improved.

[0078] Films made of acrylic resins, which are examples of solvent-soluble resins, may have low toughness, but the strength of the film may be improved by using a compatibility system of polyimide resins and acrylic resins. In addition, when a film made of a compatibility system of polyimide resins and acrylic resins is stretched, the tensile modulus in the stretching direction increases, and accordingly, there is a tendency for the bending resistance to be improved.

[0079] For example, a film used as a cover film or substrate material of a foldable display device (foldable display) is repeatedly bent along a bending axis at the same location, and therefore requires high mechanical strength in a direction orthogonal to the bending axis. Therefore, by arranging the film so that the stretching direction of the film is orthogonal to the bending axis, the film is unlikely to break or crack at the bending location even if it is repeatedly bent, and a device with high bending resistance can be provided.

[0080] The stretching conditions of the film are not particularly limited. For example, the stretching temperature is about ±40°C of the glass transition temperature of the film, and can be about 120 to 300°C, 150 to 250°C, or 180 to 230°C. The stretching ratio is about 1 to 200%, and can be 5 to 150%, 10 to 120%, or 20 to 100%. There is a tendency that the larger the stretching ratio, the larger the tensile elastic modulus in the stretching direction. On the other hand, when the stretching ratio is too large, there is a tendency that the mechanical strength in the direction orthogonal to the stretching direction decreases, and sometimes the operability of the film decreases.

[0081] From the viewpoint of improving 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 stretching ratio in one direction may be the same as or different from the stretching ratio in the orthogonal direction. If a difference is set in the stretching ratio, there is a tendency for the mechanical strength in the direction with a large stretching ratio to become relatively large. In the case of using a biaxially stretched film with anisotropy in the stretching ratio for a foldable device, it is preferably configured in a manner that the direction with a large stretching ratio is orthogonal to the bending axis.

[0082] The thickness of the transparent film is not particularly limited, as long as it is appropriately set according to the purpose. The thickness of the film is, for example, 5 to 300 μm. From the viewpoint of making a film that takes into account both self-supporting properties and flexibility and high transparency, the thickness of the transparent film is preferably 20 μm to 100 μm, and can be 25 μm to 80 μm, 30 to 70 μm or 35 to 65 μm. From the viewpoint of improving the bending resistance of the hard coating film, the thickness of the transparent film is preferably 60 μm or less, and more preferably 55 μm or less. When the film is stretched, the thickness after stretching is preferably within the above range.

[0083] The transparent 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 film is compatible with the solvent-soluble resin, it shows a single glass transition temperature.

[0084] The transparent film can be a single layer or a multilayer structure. For example, the transparent film can be a film having functional layers such as an easy adhesion layer, an antistatic layer, and an antireflection layer on the film surface (the hard coating forming surface and / or the hard coating non-forming surface).

[0085] The haze of the transparent film is preferably 1% or less, more preferably 0.7% or less, and further preferably 0.5% or less. As described above, among solvent-soluble resins, acrylic resins show high compatibility with polyimide resins. Therefore, the film containing polyimide resin and acrylic resin as a solvent-soluble resin has low haze and high transparency.

[0086] The yellowness index (YI) of the transparent film is preferably 4.0 or less, more preferably 3.0 or less, and further preferably 2.5 or less. By mixing the polyimide resin with a solvent-soluble resin such as an acrylic resin, a film with less coloration and a lower YI can be obtained compared to the case of using the polyimide resin alone.

[0087] The indentation hardness of the transparent film measured by nanoindentation is preferably 300 N / mm 2 The indentation hardness of the transparent film is more preferably 310 N / mm 2 More than 320 N / mm 2 Above, more preferably 330N / mm 2 Above, it can be 340N / mm 2 Above, 350N / mm 2 Above or 360N / mm 2 By making the indentation hardness 300N / mm 2 As described above, the generation of deep depressions in the hard coating film due to external force is suppressed, and therefore, even when depressions are generated, the depressions are easily restored over time.

[0088] When the indentation hardness of the transparent film is too large, the generation of dents is suppressed, but there is a tendency that the stress relaxation property is small and the dent recovery property is reduced. The indentation hardness of the transparent film is preferably 420 N / mm 2 Below, more preferably 410N / mm 2 Below, it can be 405N / mm 2 Below or 400N / mm 2 the following.

[0089] The stress relaxation amount (creep rate) of the transparent film when a triangular pyramid indenter (Bosch indenter) is applied with a load of 100 mN for 2 seconds in the nanoindentation method is preferably 1.50% or more. The stress relaxation amount is more preferably 1.80% or more, further preferably 1.90% or more, and can be 1.95% or more or 2.00% or more. If the stress relaxation amount is 1.50% or more, it is not easy to produce deep depressions due to the concentration of local pressing force. Therefore, even if the hard coating film is depressed, the depression is easy to recover over time.

[0090] When the stress relaxation amount of the transparent film is too large, there is a tendency for the dent recovery property to decrease. The stress relaxation amount of the transparent film is preferably 2.90% or less, more preferably 2.80% or less, further preferably 2.70% or less, and may be 2.60% or less, 2.50% or less, 2.40% or less, or 2.30% or less.

[0091] The indentation hardness and the stress relaxation amount were measured by the following indentation test.

[0092] (1) Press the film surface with a triangular pyramid indenter (Bosch indenter) at a speed of 6.667 mN / s for 15 seconds until the load reaches 100 mN;

[0093] (2) After holding the load of 100 mN for 2 seconds;

[0094] (3) Gradually unload the load at a rate of 6.667 mN / s, taking 15 s to reach 0 mN.

[0095] When a hard-coated film having a hard-coated layer formed on one side of a transparent film is used as the measurement object, the test is carried out with the side without the hard-coated layer formed as the pressing side. When hard-coated layers are formed on both sides of a transparent film, or when an adhesive layer is provided on the side without the hard-coated layer, the transparent film is exposed by grinding or the like, and the test is carried out.

[0096] The indentation hardness is calculated according to the following formula based on the unloading curve obtained by plotting the displacement during unloading of the above (3) as the horizontal axis and the load as the vertical axis: Fmax is the maximum load of the unloading curve, A is the contact projection area, hc is the contact depth, hmax is the maximum displacement, and S is the slope of the unloading curve.

[0097] Indentation hardness (N / mm 2 )=Fmax / A

[0098] A=24.56×(hc) 2

[0099] hc=hmax-0.75×Fmax / S

[0100] The unloading curve was fitted with a sixth-order polynomial, and the slope of the straight line connecting the unloading starting point and the point where the displacement was reduced by 0.5% from the unloading starting point was defined as the slope S of the unloading curve (this method was defined as "A method").

[0101] In the general nanoindentation method, the slope of the straight line connecting the point where the displacement is reduced by 70% and the point where the displacement is reduced by 90% from the unloading start point is defined as the slope S of the unloading curve, and the indentation hardness H is calculated. IT There are many cases (this method is called "B method").

[0102] In the B method, most of the load caused by the indentation of the indenter is unloaded, and the behavior in the stage where the indentation amount of the indenter becomes smaller is evaluated. In contrast, in the A method, the behavior is evaluated in the state where the indentation amount is large and the load is large. Regarding the recovery of the depression, the contribution of the film hardness under the deeper indentation (large depression) is large, so the A method is used in this specification. It should be noted that, as shown in the examples described later (see Tables 3 to 5), the indentation hardness calculated by the A method has a high correlation with the indentation hardness calculated by the B method.

[0103] The stress relaxation amount was calculated from the displacement while the load of (2) was maintained using the following equation: h0 is the displacement when the load reached 100 mN, and h1 is the displacement after the load of 100 mN was maintained for 2 seconds (just before unloading).

[0104] Stress relaxation (%) = 100 × (h1-h0) / h0

[0105] The amount of stress relaxation indicates the degree to which the shape of the film surface follows the pressed indenter. It is believed that the greater the amount of stress relaxation, the easier it is to disperse the pressure during indentation, and the better the time-dependent recovery of the depression after unloading.

[0106] The tensile modulus of the transparent film is preferably 2.8 GPa or more, more preferably 3.0 GPa or more, further preferably 3.2 GPa or more, and may be 3.4 GPa or more or 3.5 GPa or more. When the tensile modulus is small, the mechanical strength is low and depressions tend to occur easily.

[0107] The transparent film may have anisotropy of the stretching elastic modulus. As described above, if the film is stretched, there is a tendency for the stretching elastic modulus in the stretching direction to become larger. When the transparent film has anisotropy of the stretching elastic modulus, the stretching elastic modulus in the direction where the stretching elastic modulus reaches the maximum (usually the direction with a large stretching ratio) may be 4.0 GPa or more, 5.0 GPa or more, 6.0 GPa or more, or 7.0 GPa or more. The difference between the maximum and minimum values ​​of the stretching elastic modulus in the plane may be 1.3 GPa or more, 1.7 GPa or more, or 2.0 GPa or more.

[0108] The tensile modulus has anisotropy, and sometimes the greater the difference between the maximum and minimum values ​​of the tensile modulus in a plane, the better the dent recovery. As a presumed reason why the dent recovery is improved due to the large anisotropy of the tensile modulus, it can be considered that the dent recovery is provided by balancing the dent resistance performance brought about by the high elastic modulus and the flexibility brought about by the relatively low elastic modulus in the direction orthogonal thereto.

[0109] [Hard coating]

[0110] The hard coating film 11 has a hard coating layer 3 on a transparent film 1. The hard coating layer has a function of preventing damage due to external force applied from a stylus pen, a nail, etc. In addition, by forming a hard coating layer, there is a tendency that a dent is less likely to occur and an dent that occurs tends to recover easily.

[0111] 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, siloxane, and epoxy resins, etc. Among them, from the viewpoint of preventing scratches, a cured product of an acrylic hard coat resin composition, i.e., an acrylic hard coat layer, or a cured product of a siloxane hard coat resin composition, i.e., a siloxane hard coat layer, is preferred.

[0112] <Acrylic hard coating material>

[0113] The acrylic hard coating material contains a monomer or oligomer having a (meth)acryloyl group in the molecule as a curable resin component. The molecular weight of the acrylic monomer or oligomer is, for example, about 200 to 10,000. The acrylic hard coating material can control hardness, scratch resistance, bending resistance, optical properties, etc. by combining a variety of monomers or oligomers having a (meth)acryloyl group. From the perspective of curability based on photoradical polymerization, the hard coating material preferably has an acryloyl group.

[0114] Specific examples of the oligomer 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.

[0115] Examples of acrylic monomers include compounds having one (meth)acryloyl group, such as methyl (meth)acrylate and 2-ethylhexyl (meth)acrylate; 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, 1,6-hexanediol di(meth)acrylate, and the like. A compound having two (meth)acryloyl groups in one molecule; a compound 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.

[0116] From the viewpoint of improving the scratch resistance of the hard coating layer, the acrylic hard coating material preferably contains a trifunctional or higher multifunctional (meth)acrylate. The functional group equivalent of the (meth)acryloyl group of the multifunctional (meth)acrylate, that is, the molecular weight per one (meth)acryloyl group is preferably 80 to 150 g / eq. Among the multifunctional (meth)acrylates exemplified above, dipentaerythritol hexa(meth)acrylate is particularly preferred.

[0117] <Siloxane-based hard coating material>

[0118] The siloxane-based hard coating material includes a curable compound having a siloxane bond as a curable resin component. From the perspective of damage resistance, the siloxane-based curable compound preferably has an epoxy group as a polymerizable functional group, and preferably a polyorganosiloxane compound containing an alicyclic epoxy group. Such siloxane-based hard coating materials are disclosed in WO2014 / 204010, WO2018 / 096729, WO2020 / 040209, etc., and these records can be referenced / cited.

[0119] Siloxane-based hard coating materials having alicyclic epoxy groups as polymerizable functional groups have small curing shrinkage during curing, so even if the thickness of the hard coating layer is increased, warping and cracking are not easily generated. Since the thickness of the hard coating layer can be increased, it is advantageous for improving dent resistance and dent recovery.

[0120] The polyorganosiloxane compound having an alicyclic epoxy group is obtained by condensing a silane compound represented by the general formula (1).

[0121] [Y-Si(OR 1 ) x R 2 3-x ](1)

[0122] 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.

[0123] The silane compound represented by the general formula (1) has two or three (-OR 1 ). Due to Si-OR 1 Since it is hydrolyzable, a polyorganosiloxane compound can be obtained by condensation of the silane compound. 1 The number of carbon atoms is preferably 3 or less, R 1 A methyl group is particularly preferred.

[0124] In the general formula (1), R 2 It 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.

[0125] In the general formula (1), x is 2 or 3. When x=3 (i.e., three alkoxy (or hydroxyl) groups -OR are bonded to the Si atom), 1 When the silane compound does not have R 2 . From the viewpoint of forming a grid-like polyorganosiloxane compound and increasing the number of epoxy groups contained in the polyorganosiloxane compound to improve the hardness of the cured film, in the general formula (1), x=3 is preferred. A silane compound in which x=2 and a silane compound in which x=3 can be used in combination. In addition, in order to adjust the molecular weight of the polyorganosiloxane compound obtained by condensation, in addition to using a silane compound in which x is 2 or 3, a silane compound in which x is 1 can also be used.

[0126] In the 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.

[0127] 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.

[0128] 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 these, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane is preferred from the viewpoint of the ease of condensation reaction and the hardness of the cured product.

[0129] The polyorganosiloxane compound as the condensate of the silane compound may be a condensate of the silane compound of the general formula (1) and other silane compounds. Examples of other silane compounds, that is, silane compounds not containing an alicyclic epoxy group include silane compounds represented by the general formula (2).

[0130] R 3 -(Si(OR 1 ) x R 2 3-x )(2)

[0131] In the general formula (2), R 1 , R 2 and x are the same as in general formula (1). In general formula (2), R 3 is a monovalent organic group not containing an alicyclic epoxy group. 3 Examples of the present invention include substituted or unsubstituted groups containing double bonds, substituted or unsubstituted groups containing cycloalkyl groups, substituted or unsubstituted groups containing aromatic rings, substituted or unsubstituted alkyl groups, groups having glycidyl groups, groups having oxetanyl groups, and hydrogen atoms. Among these, groups having glycidyl groups are sometimes preferred from the viewpoints of reactivity with the silane compound represented by the general formula (1), adhesion with the transparent film, and hardness of the hard coating layer.

[0132] By reacting the above silane compound with water, the Si-OR 1 The hydrolysis is partially carried out, and the hydrolyzate is condensed to form Si-O-Si bonds, thereby generating a condensate of the silane compound having an alicyclic epoxy group (polyorganosiloxane compound).

[0133] From the viewpoint of improving the hardness of the cured film (hard coat), the weight average molecular weight of the polyorganosiloxane compound is preferably 500 or more. In addition, from the viewpoint of suppressing volatilization, the weight average molecular weight of the polyorganosiloxane compound is also preferably 500 or more. On the other hand, if the molecular weight is too large, white turbidity may occur 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.

[0134] <Polymerization Initiator>

[0135] The hard coating composition preferably contains a polymerization initiator in addition to the above-mentioned curable resin component. As the polymerization initiator, a photopolymerization initiator is preferred. The acrylic hard coating composition containing a compound having a (meth)acryloyl group as a curable resin component preferably contains a photoradical polymerization initiator that generates free radicals by light. The siloxane hard coating composition containing a polyorganosiloxane compound having an epoxy group as a curable resin component contains a photoacid generator (photocationic polymerization initiator) that generates acid by light.

[0136] 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.

[0137] Examples of the photoacid generator include onium salts obtained 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 coordination compounds; silanol-metal chelate complexes; sulfonic acid derivatives such as disulfones, disulfonyldiazomethanes, disulfonylmethanes, sulfonylbenzoylmethanes, imidesulfonates, and benzoinsulfonates; and organic halides.

[0138] <Other Components Constituting the Hard Coat Composition>

[0139] The hard coating composition for forming the hard coating layer may contain a solvent and various additives in addition to the curable resin component and the polymerization initiator. Examples of the additives include fluorine-based or silicone-based leveling agents, sensitizers, reactive diluents, microparticles, fillers, dispersants, plasticizers, ultraviolet absorbers, surfactants, antioxidants, colorants, viscosity modifiers, and the like.

[0140] <Formation of Hard Coat Layer>

[0141] The hard coating composition is applied to the transparent film 1, and after drying and removing the solvent as needed, the hard coating layer 3 is cured. Examples of the method for applying the hard coating composition include roller coating such as bar coating, gravure coating, and comma coating, die coating such as slit die coating, and spray die coating, spin coating, spray coating, and dip coating. Before applying the curable resin composition, the surface of the transparent film 1 may be subjected to a surface treatment such as a corona treatment or a plasma treatment. In addition, an easy-adhesion layer or the like may be provided on the surface of the transparent film 1.

[0142] By irradiating the hard coating composition with active energy rays or heating, active species such as acids and free radicals are generated from the photopolymerization initiator, so that 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 irradiating with active energy rays. As active energy rays irradiated during photocuring, there can be listed visible light, ultraviolet rays, infrared rays, X-rays, α rays, β rays, γ rays, electron rays, etc. 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 10000 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.

[0143] The thickness of the hard coating layer 3 is 1 to 100 μm, preferably 5 μm or more, more preferably 10 μm or more, and further preferably 15 μm or more. There is a tendency that the greater the thickness of the hard coating layer, the higher the dent resistance and dent recovery. On the other hand, if the thickness of the hard coating layer is too large, it will lead to a decrease in bending resistance, warping of the hard coating film, and the generation of cracks in the hard coating layer. Therefore, the thickness of the hard coating layer is preferably 50 μm or less, more preferably 40 μm or less, further preferably 30 μm or less, and particularly preferably 25 μm or less.

[0144] The total thickness of the transparent film 1 and the thickness of the hard coating layer 3 is not particularly limited, but is preferably 10 μm or more, more preferably 30 μm or more, further preferably 40 μm or more, preferably 500 μm or less, more preferably 200 μm or less, further preferably 100 μm or less, and particularly preferably 80 μm or less. The ratio of the thickness of the hard coating layer 3 to the thickness of the transparent film 1 (thickness of the hard coating layer / thickness of the transparent film) is preferably 2 / 100 to 100 / 20.

[0145] [Characteristics of hard coating films]

[0146] <Depression recovery>

[0147] The hard coating film preferably has a property that the depression caused by external force becomes shallower over time and the depression is no longer observed (depression recovery). The depression recovery can be measured by the following depression test.

[0148] In the depression test, 17 types of pencils from 6B to 9H used in the pencil hardness test were used. As shown in Table 1, scores were given to these 17 types of pencils so that the higher the hardness, the higher the score.

[0149] [Table 1]

[0150] hardness Score 9H 9 8H 8 7H 7 6H 6 5H 5 4H 4 3H 3 2H 2 H 1 F 0 HB -1 B -2 2B -3 3B -4 4B -5 5B -6 6B -7

[0151] The surface of the hard coating layer 3 of the hard coating film 11 was scratched at a speed of 60 mm / min under a load of 750 g using the 17 pencils described above, and the presence or absence of dents in the hard coating film was observed immediately after the test and one week after the test. If dents were observed immediately after the test but were no longer observed one week later, the hard coating film was judged to have dent recovery properties.

[0152] Regarding the scratch test with a pencil, the direction with the largest tensile elastic modulus in the film surface (usually the MD direction or TD direction, the stretching direction of the stretched film) and its orthogonal direction are each performed 5 times. The situation where depression occurs more than 2 times out of 5 times is judged as "there is depression". The situation where no depression occurs just after the test is set as the depression score just after the test. For example, after the test is just over, there is no depression when using a 3H pencil (the situation where depression occurs 1 time or 0 times among 5 times), and there is depression when using a 4H pencil (the situation where depression occurs more than 2 times among 5 times), the depression score just after the test is "3". The average value of the depression score in the direction with the largest tensile elastic modulus and the direction with the smallest tensile elastic modulus is set as the depression score just after the test. When the depression scores in the two directions are different, the depression score calculated by its average value sometimes becomes a decimal of 0.5 on the scale.

[0153] The case with the lowest hardness among the cases where no depression remains after one week from scratching is set as the depression score after one week. For example, the depression score immediately after the test is 3 (no depression when using a 3H pencil, depression when using a 4H pencil), and after one week, when no depression is confirmed in the object scratched with a 4H or 5H pencil (the depression is restored), and the object scratched with a 6H pencil has a residual depression, the depression score after one week is "5". The average of the depression scores in the direction with the largest tensile elastic modulus and the direction with the smallest tensile elastic modulus is set as the depression score after one week.

[0154] The difference between the depression score after 1 week and the depression score immediately after the test is defined as the depression recovery amount of the hard coating film. When the depression recovery amount is 0, there is no depression recovery property, and the larger the depression recovery amount, the higher the recovery property. The depression recovery amount is preferably 0.5 or more, more preferably 1 or more, further preferably 1.5 or more, and particularly preferably 2 or more.

[0155] Even if the hard coating film having dent recovery properties was dented immediately after the test, no dents were observed one week after the test, and the visibility of the display was no longer affected. Therefore, it can be said that the hard coating film has excellent durability for long-term use.

[0156] As described above, in the present invention, the transparent film contains a solvent-soluble resin such as a polyimide resin and an acrylic resin, so that the dent recovery tends to be improved. In addition, the greater the indentation hardness and stress relaxation amount of the transparent film, the higher the dent recovery tends to be.

[0157] <Pencil Hardness>

[0158] The pencil hardness of the hard coating film is preferably 3H or more, more preferably 4H or more, and may be 5H or more or 6H or more. The higher the pencil hardness, the less likely it is to be damaged or dented by an external force. A hard coating film having a high pencil hardness and dent recovery is not likely to be damaged or dented by an external force, and even if a dent is caused by a large external force, it will recover in about 1 week, and therefore is excellent from the viewpoint of long-term use.

[0159] <Bending resistance>

[0160] The hard coating film can be bent repeatedly at a radius of 1.5 mm for more than 100,000 times with the hard coating layer inside, and no cracks in the hard coating layer or breakage of the film occur during repeated bending. It is preferably used in foldable displays that are repeatedly bent and stretched at the same location.

[0161] <Transparency>

[0162] The yellowness (YI) of the hard coating film is preferably 4.0 or less, more preferably 3.0 or less, and further preferably 2.5 or less. A low YI is preferred in terms of improving the visual recognition of the display and making the color tone good. Although the polyimide resin film is slightly colored yellow, by adopting a blending system with a solvent-soluble resin such as an acrylic resin, the coloring can be reduced and the YI can be reduced.

[0163] The total light transmittance of the hard coating film is preferably 88.0% or more, more preferably 90.0% or more, further preferably 91.0% or more, and can be 91.5% or more. As described above, by adopting a blending system of a polyimide resin and a solvent-soluble resin such as an acrylic resin, coloring is reduced, so there is a tendency for the total light transmittance to increase.

[0164] Generally speaking, polyimide resins have a high refractive index, and the reflectivity at the interface between the film and air and the interface between the film and the hard coating is high, so the total light transmittance is small. By blending polyimide resins with solvent-soluble resins such as acrylic resins, the refractive index is reduced, and the reflectivity at the interface becomes small, so the total light transmittance can be increased.

[0165] The haze of the hard coating film is preferably 1% or less, more preferably 0.7% or less, and further preferably 0.5% or less. As the resin material of the transparent film, the haze can be reduced by using a solvent-soluble resin that is compatible with the polyimide resin. It should be noted that the polyimide resin and the solvent-soluble resin do not necessarily need to be completely compatible, and may have a microphase separation structure that is so small as not to affect the optical properties.

[0166] [Application of hard coating film]

[0167] The hard coating film may have various functional layers on the hard coating layer or on the non-hard coating layer forming surface of the transparent film. As the functional layer, anti-reflection layer, anti-glare layer, antistatic layer, transparent electrode, scratch-resistant layer, antifouling layer, etc. may be listed. The hard coating film may be provided with a transparent adhesive layer.

[0168] The hard coating film of the present invention has excellent transparency and bending resistance, and has both dent resistance and dent recovery properties against external forces, and therefore can be suitably used for cover windows, transparent substrates for displays, transparent substrates for touch panels, and substrates for solar cells, etc., which are provided on the surface of image display panels. It can be particularly suitably used as a cover window or substrate film for curved displays, flexible displays, etc., and since the dents have recovery properties, it can be suitably used as a cover window arranged on the outermost surface of the device.

[0169] Example

[0170] Hereinafter, the present invention will be described in more detail 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 orthogonal to the MD direction is referred to as the TD direction.

[0171] [Preparation of polyimide resin]

[0172] Dimethylformamide (DMF) was added to a separable flask and stirred under a nitrogen atmosphere. Diamine and tetracarboxylic dianhydride were added at the ratio (mol %) shown in Table 2 and stirred for 5 to 10 hours under a nitrogen atmosphere to react to obtain a polyamic acid solution having a solid content concentration of 18 wt %.

[0173] To 100g of the polyamic acid solution, 5.5g of pyridine as an imidization catalyst was added to completely disperse it, and 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 the polyimide. 150g of IPA was further added, and after stirring for about 30 minutes, suction was filtered using a Kiriyama funnel. After washing the obtained solid with IPA, it was dried in a vacuum oven set to 120°C for 12 hours to obtain polyimide resins 1 to 5 (PI1 to PI5).

[0174] [Preparation of polyamide-imide resin]

[0175] Dimethylacetamide (DMAc) was added to a separable flask and stirred under a nitrogen atmosphere. Diamine, tetracarboxylic dianhydride and diformyl chloride were added thereto at the ratio (mol %) shown in Table 2, and stirred for 5 to 10 hours under a nitrogen atmosphere to react to obtain a polyamic acid solution having a solid content concentration of 9 wt %. Thereafter, imidization, resin precipitation, washing and drying were performed in the same manner as in the preparation of polyimide resin to obtain polyamide-imide resin 6 (PAI6).

[0176] In Table 2, the compounds are described using the following abbreviations.

[0177] <Tetracarboxylic dianhydride>

[0178] CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride

[0179] H-PMDA: 1,2,4,5-cyclohexanetetracarboxylic dianhydride

[0180] 6FDA: 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride

[0181] TAAHBP: Bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diyl

[0182] ODPA: 4,4'-oxydiphthalic anhydride

[0183] <Diformyl chloride>

[0184] TPC: Terephthaloyl chloride

[0185] <Diamine>

[0186] TFMB: 2,2'-bis(trifluoromethyl)benzidine

[0187] DDS: 3,3'-Diaminodiphenyl sulfone

[0188] [Table 2]

[0189]

[0190] [Production of transparent film]

[0191] <Film 1A>

[0192] 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 of 87 / 13), glass transition temperature of 109°C, acid value of 0.0 mmol / g; hereinafter referred to as "acrylic resin 1" (Ac1)) were dissolved in dichloromethane at a weight ratio of PI1 / Ac1=55 / 45 to prepare a solution having a solid content concentration of 11% by weight. The solution was applied on an alkali-free glass plate and heated and dried in an air atmosphere at 60°C for 20 minutes, 70°C for 15 minutes, 120°C for 15 minutes, and 150°C for 15 minutes to obtain a film having a thickness of about 50 μm.

[0193] <Film 1B~1F>

[0194] A dichloromethane solution with a weight ratio of PI1 / Ac1=55 / 45 was applied on an alkali-free glass plate, and heated and dried in an atmosphere at 60°C for 15 minutes, 90°C for 15 minutes, 120°C for 15 minutes, 150°C for 15 minutes, 180°C for 15 minutes, and 200°C for 15 minutes to produce a film with a thickness of about 90 μm. A stretching machine with a heating oven was used, and the TD direction was set as the stretching direction. The obtained film was subjected to fixed-end uniaxial stretching at the temperature and stretching ratio described in Table 3 to obtain films 1B to 1F. It should be noted that the stretching ratios of 80%, 115%, and 150% refer to stretching in a manner that is 1.80 times, 2.15 times, and 2.50 times the length of the film before stretching.

[0195] <Film 2>

[0196] Polyimide resin 1 (PI1) and commercially available polymethyl methacrylate resin ("PARAPET HM1000" manufactured by Kuraray Co., Ltd., glass transition temperature of 120°C, acid value of 0.0 mmol / g; hereinafter referred to as "acrylic resin 2" (Ac2)) were dissolved in dichloromethane at a weight ratio of PI1 / Ac2 = 10 / 90 to prepare a solution having a solid content concentration of 20% by weight. The solution was applied on an alkali-free glass plate, and heated and dried in an air atmosphere at 40°C for 15 minutes, 60°C for 15 minutes, 80°C for 15 minutes, 100°C for 15 minutes, 120°C for 15 minutes, and 150°C for 15 minutes. The MD direction was set as the stretching direction, and the obtained film was fixed-end uniaxially stretched at the temperature and stretching ratio described in Table 4 to obtain Film 2.

[0197] <Film 3>

[0198] A dichloromethane solution (solid content concentration of 12.5%) with a weight ratio of PI1 / Ac2=30 / 70 was applied on an alkali-free glass plate, and heated and dried in an atmospheric atmosphere at 60°C for 20 minutes, 70°C for 15 minutes, 120°C for 15 minutes, and 150°C for 15 minutes. The MD direction was set as the stretching direction, and the obtained film was fixed-end uniaxially stretched at the temperature and stretching ratio described in Table 4 to obtain Film 3.

[0199] <Film 4>

[0200] A DMF solution (solid content concentration of 12%) with a weight ratio of PI2 / Ac2=55 / 45 was applied on an alkali-free glass plate, and heated and dried in an atmospheric atmosphere at 60°C for 30 minutes, 90°C for 30 minutes, 120°C for 30 minutes, 150°C for 15 minutes, and 180°C for 15 minutes. The MD direction was set as the stretching direction, and the obtained film was fixed-end uniaxially stretched at the temperature and stretching ratio listed in Table 4 to obtain Film 4.

[0201] <Film 5>

[0202] A dichloromethane solution (solid content concentration of 12.5%) with a weight ratio of PI3 / Ac2=55 / 45 was applied on an alkali-free glass plate, and heated and dried in an atmospheric atmosphere at 60°C for 20 minutes, 70°C for 15 minutes, 120°C for 15 minutes, and 150°C for 15 minutes. The MD direction was set as the stretching direction, and the obtained film was fixed-end uniaxially stretched at the temperature and stretching ratio described in Table 4 to obtain Film 5.

[0203] <Film 6>

[0204] A dichloromethane solution (solid content concentration is 10%) with a weight ratio of PI4 / Ac2=55 / 45 is applied on an alkali-free glass plate, and heated and dried in an atmospheric atmosphere at 60°C for 20 minutes, 70°C for 15 minutes, 120°C for 15 minutes, and 150°C for 15 minutes. The MD direction is set as the stretching direction, and the obtained film is fixed-end uniaxially stretched at the temperature and stretching ratio described in Table 4 to obtain Film 6.

[0205] <Film 7>

[0206] A dichloromethane solution (solid content concentration is 20%) with a weight ratio of PI5 / Ac2=55 / 45 is applied on an alkali-free glass plate, and heated and dried in an atmospheric atmosphere at 60°C for 20 minutes, 70°C for 15 minutes, 120°C for 15 minutes, and 150°C for 15 minutes. The MD direction is set as the stretching direction, and the obtained film is fixed-end uniaxially stretched at the temperature and stretching ratio described in Table 4 to obtain Film 7.

[0207] <Film 8>

[0208] A DMF solution (solid content concentration of 20%) with a weight ratio of PAI6 / Ac2=55 / 45 was applied on an alkali-free glass plate and heated and dried in an atmospheric atmosphere at 60°C for 30 minutes, 90°C for 30 minutes, 120°C for 30 minutes, 150°C for 15 minutes, and 180°C for 15 minutes. The MD direction was set as the stretching direction, and the obtained film was fixed-end uniaxially stretched at the temperature and stretching ratio listed in Table 4 to obtain Film 8.

[0209] <Film 11>

[0210] 100 parts by weight of polyimide resin 2 (PI2), 2.4 parts by weight of "Tinuvin 477" manufactured by BASF as an ultraviolet absorber, and 0.0065 parts by weight of "Plast Blue 8590" manufactured by Arimoto Chemical Industry Co., Ltd. as a toner were dissolved in dichloromethane to prepare a solution having a solid content concentration of 10% by weight. The solution was applied on an alkali-free glass plate and heated and dried in an air atmosphere under conditions of 40° C. for 60 minutes, 80° C. for 30 minutes, 150° C. for 30 minutes, 170° C. for 30 minutes, and 200° C. for 60 minutes to obtain a film 11 having a thickness of 50 μm.

[0211] <Film 12>

[0212] In the preparation of the film 11, the ultraviolet absorber was changed to 2 parts by weight of "ADEKASTAB LA-31RG" and 0.8 parts by weight of "ADEKASTAB LA-F70" manufactured by ADEKA, and the amount of the toner was changed to 0.004 parts by weight. A film 12 having a thickness of 50 μm was obtained in the same manner as above.

[0213] <Film 13>

[0214] A dichloromethane solution (solid content concentration is 30%) of acrylic resin 2 (Ac2) is applied on an alkali-free glass plate and heated and dried in an atmospheric atmosphere at 40°C for 15 minutes, 60°C for 15 minutes, 80°C for 15 minutes, 100°C for 15 minutes, 120°C for 15 minutes and 150°C for 15 minutes. The MD direction is set as the stretching direction, and the obtained film is fixed-end uniaxially stretched at the temperature and stretching ratio described in Table 5 to obtain Film 13.

[0215] <Film 14>

[0216] As the film 14 , a biaxially stretched polyethylene terephthalate film having a thickness of 50 μm (“Lumirror U48” manufactured by Toray Industries, Inc.) was used.

[0217] [Preparation of hard coating composition]

[0218] <Hard Coat Composition A: Siloxane Hard Coat Composition>

[0219] 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 condenser, and stirred evenly. A solution obtained by dissolving 0.039 g (0.405 mmol) of magnesium chloride as a catalyst in a mixed solution of 9.7 g (539 mmol) of water and 5.8 g of methanol was added dropwise to the mixed solution over 5 minutes, and stirred until uniform. The temperature was then raised to 80°C, and a polycondensation reaction was carried out for 6 hours while stirring. After the reaction was completed, a rotary evaporator was used to distill off the solvent and water to obtain a condensate of the silane compound (polyorganosiloxane compound).

[0220] The GPC apparatus "HLC-8220GPC" manufactured by Tosoh Corporation (column: TSKgel GMH XL ×2, TSKgelG3000H XL 、TSKgel G2000H XL ) and the weight average molecular weight in terms of polystyrene was 3000. Using a 400 MHz-NMR manufactured by Bruker, the 1 The residual rate of epoxy groups calculated from the H-NMR spectrum was 95% or more.

[0221] 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 coating composition A having a solid content concentration of 50% by weight.

[0222] <Hard Coat Composition B: Acrylic Hard Coat Composition>

[0223] 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 Co., Ltd.) and 0.25 parts by weight of a polyether-modified silicone leveling agent ("BYK-300" manufactured by BYK Co., Ltd.) were added, and propylene glycol monomethyl ether was added as a diluent to obtain an acrylic hard coating composition B having a solid content concentration of 50% by weight.

[0224] [Production of hard coating film]

[0225] <Example 1>

[0226] The hard coating composition B was applied to the film 1A by a coater to a dry film thickness of 10 μm, and the solvent was removed at 120° C. Thereafter, 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 ultraviolet rays in a manner of 10 μm to obtain a hard coating film having an acrylic hard coating layer with a thickness of 10 μm on one surface of the film 1A.

[0227] <Example 2>

[0228] A hard coat film having a 10 μm-thick siloxane hard coat layer on one surface of the film 1A was obtained in the same manner as in Example 1 except that the hard coat composition A was used instead of the hard coat composition B.

[0229] <Examples 3 to 21 and Comparative Examples 1 to 7>

[0230] The type of transparent film, the type of hard coating composition and the thickness of the hard coating layer were changed as shown in Tables 3 to 5, and the same operation as in Examples 1 and 2 was performed to obtain a hard coating film having a hard coating layer on a transparent film.

[0231] [Evaluation of transparent film]

[0232] <Tensile elastic modulus>

[0233] The film was cut into 10 mm wide strips, left to stand for 1 day at 23°C / 55%RH for humidity conditioning, and then subjected to a tensile test using a tensile tester "AUTOGRAPH AGS-X" manufactured by Shimadzu Corporation under the following conditions to calculate the tensile modulus. The tensile test was performed in both the MD and TD directions.

[0234] Distance between fixtures: 100mm

[0235] Stretching speed: 12.5 mm / min

[0236] Measurement temperature: 23°C

[0237] <Indentation hardness and stress relaxation>

[0238] The indentation test was performed using a nanoindentation tester (ELIONIX "ENT-2100"). A triangular pyramid indenter (Bosch indenter) with a ridgeline of 115° was gradually loaded (applied) at a rate of 6.667 mN / sec to the film surface, from 0 mN to 100 mN in 15 seconds, and the load was maintained at 100 mN for 2 seconds. Thereafter, the load was gradually unloaded at a rate of 6.667 mN / sec, from 100 mN to 0 mN in 15 seconds.

[0239] (Indentation hardness)

[0240] The indentation hardness is calculated from the unloading curve based on the following formula: Fmax is the maximum load of the unloading curve, A is the contact projection area, hc is the contact depth, hmax is the maximum displacement, and S is the slope of the unloading curve.

[0241] Indentation hardness (N / mm 2 )=Fmax / A

[0242] A=24.56×(hc) 2

[0243] hc=hmax-0.75×Fmax / S

[0244] The slope S of the unloading curve is calculated by using the following two methods: method A and method B, and the indentation hardness is calculated according to each method.

[0245] Method A:

[0246] The curve obtained by fitting the displacement (horizontal axis) and load (vertical axis) data during unloading using the spreadsheet software "Excel" of Microsoft Corporation is set as the unloading curve. The coefficients of the polynomial are set to 30 significant figures. The slope of the straight line obtained by connecting the unloading starting point of the unloading curve obtained by polynomial fitting and the point when the displacement is reduced by 0.5% from the unloading starting point is set as the slope S of the unloading curve.

[0247] Method B:

[0248] The indentation test results were analyzed using the analysis software "ENT-2100Ver7.5" that comes with the device, and the indentation hardness was calculated. In this method, the tip of the indenter is corrected using the Tanaka equation, and the slope of the straight line connecting the point where the displacement is reduced by 70% from the unloading start point and the point where the displacement is reduced by 90% is set as the slope S of the unloading curve, and the indentation hardness H is calculated. IT .

[0249] (Stress relaxation amount)

[0250] The stress relaxation amount was calculated by the following formula from the displacement h0 when the load reached 100 mN and the displacement h1 after the load of 100 mN was maintained for 2 seconds (immediately before the load was unloaded).

[0251] Stress relaxation (%) = 100 × (h1-h0) / h0

[0252] [Evaluation of hard coating film]

[0253] <Total Light Transmittance and Haze>

[0254] The haze was measured using a haze meter HZ-V3 manufactured by Suga Test Instruments according to the method described in JIS K7361-1: 1999 and JIS K7136: 2000. The measurement was performed using a D65 light source.

[0255] <Pencil Hardness>

[0256] The pencil hardness of the hard coat surface was evaluated at 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 defined as the pencil hardness of the hard coat film.

[0257] <Sunk Test>

[0258] The surface of the hard coating layer of the hard coating film was scratched at a speed of 60 mm / min under a load of 750 g using 17 pencils from 6B to 9H (see Table 1). Immediately after the test and one week after the test, the hard coating film was observed for depression. The scratching with the pencil was performed by placing the hard coating film directly above a horizontal glass plate. The presence or absence of depression was determined by visually observing the transmitted light and reflected light of the illumination under the illumination of a straight tube three-wavelength fluorescent lamp. If the fluorescent lamp looked distorted at the scratched part, it was considered that there was a depression.

[0259] The scratch test was performed 5 times with pencils of various hardnesses, and the presence of depression was judged to be present when depression occurred in 2 or more of the 5 times. The scratch test was performed in both the MD direction and the TD direction, and the score corresponding to the pencil with the lowest hardness (smallest score) in the case where depression did not occur immediately after the test was set as the depression score.

[0260] The presence of depression was checked again one week after the scratch test, and the case with the lowest hardness among the cases where no depression remained was set as the depression score after one week. The average values ​​of the cases where the scratching direction was in the MD direction and the TD direction were calculated for the cases immediately after the test and one week after the test, and the difference between the depression score after one week and the depression score immediately after the test was set as the depression recovery amount of the hard coating film.

[0261] <Bending resistance (repeated bending test)>

[0262] The hard coating film was placed in a U-shaped bending durability tester DMLHB manufactured by YUASA SYSTEM, and a repeated bending test was performed 100,000 times with the hard coating layer on the inside under the conditions of a bending radius of 1.5 mm, a bending angle of 180°, and a speed of 1 time / second. In Examples 1 to 13, the bending was performed in a manner that the bending axis was parallel to the MD direction, and in Examples 14 to 21 and Comparative Examples 1 to 7, the bending was performed in a manner that the bending axis was parallel to the TD direction. The test was performed in a constant temperature and humidity environment with the temperature set to 23°C and the humidity set to 55%. After the test, the case where no cracks or ruptures of the hard coating layer were observed was set to 0, and the case where cracks or ruptures occurred in the hard coating layer was set to ×.

[0263] [Evaluation results]

[0264] For the hard-coated films of the examples and comparative examples, the types (composition, stretching conditions, thickness) and physical properties (indentation hardness, stress relaxation amount) of the transparent films, the types (composition, thickness) of the hard-coated films, and the evaluation results of the hard-coated films are shown in Tables 3 to 5. In Tables 3 to 5, regarding the tensile elastic modulus, the stretching direction is referred to as "Elastic modulus 1", and the direction orthogonal to the stretching direction is referred to as "Elastic modulus 2". For the unstretched films (film 1A, film 11, and film 12) and the biaxially stretched PET film (film 14), the MD direction is referred to as "Elastic modulus 1", and the TD direction is referred to as "Elastic modulus 2".

[0265] [Table 3]

[0266]

[0267] [Table 4]

[0268]

[0269] [Table 5]

[0270]

[0271] The hard coating films of Comparative Examples 1 to 5, in which a hard coating layer was formed on a film of a single polyimide resin 2, had a dent recovery amount of 0 and had no recovery property. The same was true for Comparative Example 6 obtained using a film of a single acrylic resin 2 and Comparative Example 7 obtained using a stretched PET film. In contrast, Examples 1 to 21, in which a hard coating layer was formed on a film containing a polyimide resin and an acrylic resin, all showed dent recovery property.

[0272] Comparative Examples 1 to 4 (film 11) and Comparative Example 5 (film 12) of the polyimide resin 2 alone have large indentation hardness but small stress relaxation, and Comparative Example 6 (film 13) of the acrylic resin 2 alone has large stress relaxation but small indentation hardness. In contrast, Examples 1 to 21 (films 1 to 8) have large stress relaxation compared to Film 11 and Film 12, and show large indentation hardness compared to Film 13.

[0273] In Example 14 (film 2) in which the acrylic resin ratio is 90%, the indentation hardness is smaller and the stress relaxation amount is larger than in other examples. In Examples 15 and 16 (film 3) in which the acrylic resin ratio is 30%, the indentation hardness is larger and the stress relaxation amount is smaller than in other examples.

[0274] From these results, it is believed that in the blend system of polyimide resin and acrylic resin, the indentation hardness is lower than that of the single polyimide resin, while the stress relaxation amount is increased, and the dent recovery property is exerted by the balance between hardness and stress relaxation.

[0275] It can be seen that Examples 1 to 21 show a high total light transmittance compared to Comparative Examples 1 to 5 of a single polyimide resin, and that in a blend of a polyimide resin and an acrylic resin, the optical properties are more excellent than in the case of a single polyimide resin. Comparison of Example 14 with Examples 15 and 16 shows that there is a tendency that the higher the ratio of the acrylic resin, the higher the total light transmittance.

[0276] Comparative Example 5 of acrylic resin 2 alone has poor bending resistance, whereas the hard-coated film of the embodiment in which a hard-coated layer is formed on a transparent film of a blend system of polyimide resin and acrylic resin shows excellent bending resistance of more than 100,000 times. It should be noted that Example 14 has a high ratio of acrylic resin and a low ratio of polyimide film, so it is considered that the bending resistance is poor as in Comparative Example 6. It is considered that the large thickness of the transparent films (films 5 and 6) of Examples 18 and 19 is the cause of the reduced bending resistance.

[0277] According to the comparison between Examples 1 and 2 and Examples 3 to 13, it can be seen that the stretched film tends to have higher mechanical strength and excellent dent recovery compared to the unstretched film. In Examples 3 to 13 (Films 1B to 1F), the tensile elastic modulus in the TD direction, which is the stretching direction, is greatly increased compared to Examples 1 and 2 (Film 1A), and the tensile elastic modulus in the MD direction is also increased. Examples 15 to 19 (Films 3 to 6) also show high tensile elastic modulus by stretching, and the same is true for Example 21 (Film 8) which is a blend system of polyamide-imide and acrylic resin. Based on these results, it can be considered that increasing the tensile elastic modulus (mechanical strength) by stretching helps to improve dent recovery.

[0278] From the comparison between Example 1 and Example 2 and from the comparison between Example 15 and Example 16, it can be seen that compared with the acrylic hard coating, the silicone hard coating has a tendency to be less likely to be dented immediately after the dent test (scratch test) and also has excellent dent recovery. From the comparison between Examples 3 to 6 and Examples 10 to 12, it can be seen that the thicker the hard coating, the higher the pencil hardness, the higher the dent score immediately after the dent test, and the less likely it is to be dented.

[0279] According to the comparison between the above embodiments and comparative examples, the hard coating film having a hard coating layer on a blended film of polyimide resin and acrylic resin has excellent dent recovery, hardness, transparency and bending resistance, and is suitable for cover window materials of flexible displays.

Claims

1. A hard coating film comprising a transparent film and a hard coating layer, wherein the hard coating layer is disposed on at least one surface of the transparent film. In the hard coating film, the transparent film contains a polyimide-based resin and a solvent-soluble resin other than the polyimide-based resin. 2 . The hard coating film according to claim 1 , which has a dent recovery property.

3. The hard coating film according to claim 1, wherein The indentation hardness of the transparent film is 300N / mm 2 above, In the nanoindentation method, the amount of stress relaxation when a triangular pyramid indenter is applied with a load of 100 mN for 2 seconds is 1.50% or more.

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

5. The hard coating film according to claim 4, wherein The acrylic resin is an acrylic resin containing methyl methacrylate as a main component.

6. The hard coating film according to claim 1, wherein The polyimide resin is a polyimide including a structure derived from tetracarboxylic dianhydride and a structure derived from diamine. The tetracarboxylic dianhydride includes one or more selected from the group consisting of fluorine-containing aromatic tetracarboxylic dianhydrides and bis(trimellitic anhydride) esters, and alicyclic tetracarboxylic dianhydride. The diamine includes fluorine-containing diamine.

7. The hard coating film according to any one of claims 1 to 6, wherein The transparent film is a stretched film.

8. The hard coating film according to claim 7, wherein: The transparent film has a difference in tensile elastic modulus between a direction in which the maximum tensile elastic modulus is present in a plane and a direction orthogonal thereto of 1.3 GPa or more.

9. The hard coating film according to any one of claims 1 to 6, wherein The transparent film has a tensile modulus of 5.0 GPa or more in a direction in which the maximum tensile modulus is exhibited in a plane.

10. The hard coating film according to any one of claims 1 to 6, wherein The thickness of the transparent film is 20-60 μm.

11. The hard coating film according to any one of claims 1 to 6, wherein The hard coating layer is an acrylic hard coating layer.

12. The hard coating film according to any one of claims 1 to 6, wherein The hard coating layer is a silicone-based hard coating layer. 13 . The hard coating film according to claim 1 , which has a pencil hardness of 3H or more.

14. The hard coating film according to any one of claims 1 to 6, wherein The hard coating layer has a thickness of 1 to 50 μm.

15. A display comprising the hard coating film according to any one of claims 1 to 6.

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