Laminate and display

Abstract

A laminate (10) is provided with a thin glass (7) having a thickness of 100 [mu] m or less, and a transparent resin film (1) bonded to one main surface of the thin glass. A hard coat layer (3) may be provided on one main surface of the transparent resin film. The transparent resin 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 laminate has excellent transparency and depression recovery, and is suitable for use as a cover window material for a display.

Description

Technical Field

[0001] The present invention relates to a laminated body in which thin glass and a transparent resin film are laminated together, and a display including the laminated body. Background Art

[0002] Thin, bendable glass is used as the cover window material for flexible displays. Glass has high optical transparency, improving the visibility of displays. However, thin glass with a small thickness is prone to breakage due to strong impact or cracks at the edges.

[0003] To improve impact resistance and prevent glass scattering, a laminated product consisting of a transparent resin film laminated to the surface of thin glass has been proposed as a cover window material. For example, Patent Document 1 proposes the use of a laminated product consisting of thin glass laminated to a transparent polyimide film with a hard coating as a cover window material for a flexible display. Transparent polyimide film has excellent mechanical properties, so a laminated product consisting of thin glass laminated to a transparent polyimide film exhibits excellent impact resistance and prevents glass scattering, providing high protection for the display.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: WO2021 / 177288 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] Polyimide has a high refractive index, and the refractive index difference between it and air and other components causes high light reflection (high reflectivity), resulting in low total light transmittance. Therefore, using a laminate composed of thin glass and transparent polyimide film as a cover window material can cause a decrease in display brightness. Furthermore, transparent polyimide has a slight yellow tint due to its absorption band overlapping with the short-wavelength region of visible light, which can affect the hue (color tone) of the display.

[0009] Transparent polyimide film has excellent mechanical strength, and laminates formed by laminating thin glass and transparent polyimide film are less susceptible to indentation caused by pressure from fingernails, styluses, and other factors, or by sliding. However, once indentation occurs, it is difficult to recover over time and remains, negatively impacting display visibility. Therefore, there is a need for a cover window material that can recover over time even when indented by external forces.

[0010] In view of the above circumstances, an object of the present invention is to provide a cover window material having excellent transparency and sag recovery properties.

[0011] Solutions for solving problems

[0012] The laminate of the present invention comprises thin glass having a thickness of 100 μm or less and a transparent resin film bonded to one principal surface of the thin glass. The transparent resin film comprises a polyimide resin and a solvent-soluble resin other than the polyimide resin. The refractive index of the transparent resin film is preferably 1.600 or less.

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

[0014] The polyimide resin is a polyimide or polyamide-imide, and includes a structure derived from a tetracarboxylic dianhydride and a structure derived from a diamine. The polyimide resin is preferably a polyimide. The polyimide resin preferably includes fluorinated aromatic tetracarboxylic dianhydride and alicyclic tetracarboxylic dianhydride as the tetracarboxylic dianhydride, and includes a fluorinated diamine as the diamine.

[0015] The transparent resin film may be a stretched film, may have a thickness of 20 to 55 μm, and may have a total light transmittance of 90.5% or more.

[0016] A hard coat layer may be provided on the main surface of the transparent resin film. Specifically, the laminate of the present invention may be a laminate formed by laminating a transparent film (hard coat film) having a hard coat layer on the main surface of the transparent resin film to thin glass. Examples of materials for the hard coat layer include acrylic hard coat materials and silicone hard coat materials. The hard coat layer may have a thickness of 1 to 50 μm.

[0017] Effects of the Invention

[0018] The laminate of the present invention has high total light transmittance and good sag recovery properties, and is therefore suitable for use as a cover window material for a display. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0020] Figure 1 This is a cross-sectional view of a laminated body according to one embodiment of the present invention. Laminated body 10 includes a transparent film 5 on one main surface of thin glass 7. Thin glass 7 and transparent film 5 may be in direct contact or bonded together via an appropriate transparent adhesive layer 9. Transparent film 5 comprises a transparent resin film 1. Transparent film 5 may be a hard coat film having a hard coat layer 3 on one surface of transparent resin film 1.

[0021] [Thin Glass]

[0022] Thin glass 7 is a glass substrate (glass film) with a thickness of 100 μm or less. It possesses the excellent mechanical strength and transparency unique to glass, and its small thickness allows for flexibility. The glass material constituting thin glass is not particularly limited, but chemically strengthened glass is preferred. Examples of chemically strengthened glass include aluminosilicate glass, soda-lime glass, borosilicate glass, lead glass, alkali-barium glass, and aluminoborosilicate glass.

[0023] Chemically strengthened glass is a glass whose mechanical strength is enhanced by partially exchanging the ions that make up the glass near its surface. This ion exchange forms a strengthening layer near the surface that exhibits compressive stress, resulting in thin glass that is resistant to breakage and exhibits excellent mechanical properties. To improve breakage resistance, chemical strengthening is preferably performed not only on the surface of thin glass but also on its end faces.

[0024] From the perspective of bendability, the thickness of thin glass is 100 μm or less, preferably 60 μm or less, more preferably 55 μm or less, and even more preferably 50 μm or less, and can be 40 μm or less, 35 μm or less, or 30 μm or less. From the perspective of ensuring mechanical properties, the thickness of thin glass is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 15 μm or more, and can be 20 μm or more or 25 μm or more.

[0025] The elastic modulus of the thin glass is preferably 50 GPa or more, more preferably 60 GPa or more, and even more preferably 70 GPa or more. When the elastic modulus of the thin glass is high, the impact resistance of the laminate tends to improve.

[0026] [Transparent film]

[0027] The transparent film 5 bonded to the thin glass 7 includes a transparent resin film 1. The transparent film 5 may be formed of the transparent resin film 1, or may include a functional layer such as a hard coat layer 3 on the transparent resin film 1.

[0028] [Transparent resin film]

[0029] The transparent resin 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 (hereinafter sometimes referred to as "other resin"). By making the transparent resin film 1 contain the polyimide resin and other resins, there is a tendency for transparency and sag recovery to be improved.

[0030] <Polyimide resin>

[0031] Polyimide can be obtained by dehydrating and cyclizing the polyamic acid obtained by the reaction of tetracarboxylic dianhydride (hereinafter sometimes described as "acid dianhydride") and diamine. By replacing a part of the tetracarboxylic dianhydride of polyimide with dicarboxylic acid derivatives such as dicarboxylic acid dichloride, polyamide-imide can be obtained. As polyimide-based resin, polyimide and polyamide-imide can be used in combination. From the viewpoints such as compatibility with other resins, it is sometimes preferred that polyimide is used as polyimide-based resin.

[0032] (Tetracarboxylic dianhydride)

[0033] In the present embodiment, the polyimide resin used is preferably an acid dianhydride component, which includes alicyclic tetracarboxylic dianhydride. By making the acid dianhydride component have an alicyclic structure, there is a tendency for the compatibility of polyimide resins with other resins such as acrylic resins to improve. As long as the alicyclic tetracarboxylic dianhydride has at least one alicyclic structure, it can have both an alicyclic ring and an aromatic ring in one molecule. The alicyclic ring can be polycyclic or have a spirocyclic structure.

[0034] Examples of the alicyclic tetracarboxylic dianhydride include 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-butanetetracarboxylic dianhydride, meso-butane-1,2,3,4-tetracarboxylic dianhydride, 1,1'-bicyclohexane-3,3',4,4'-tetracarboxylic dianhydride, and norbornene. 2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic dianhydride, 2,2'-bisnorbornane-5,5',6,6'-tetracarboxylic dianhydride, 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, cyclohexane-1,4-diylbis(methylene)bis(1,3-dioxo-1,3 -dihydrobenzofuran-5-carboxylate), 5-(2,5-dioxotetrahydrofuranyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 5,5'-[cyclohexylidenebis(4,1-phenyleneoxy)]bis-1,3-isobenzofurandione, 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-, 5,5'-[1,4-cyclohexanediylbis(methylene)] ester, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, 3,5,6- Tricarboxynorbornane-2-acetic acid 2,3:5,6-dianhydride, decahydro-1,4,5,8-dimethylnaphthalene-2,3,6,7-tetracarboxylic dianhydride, tricyclo[6.4.0.0(2,7)]dodecane-1,8:2,7-tetracarboxylic dianhydride, octahydro-1H,3H,8H,10H-biphenylene[4a,4bc:8a,8b-c']difuran-1,3,8,10-tetraone, ethylene glycol bis(hydrogenated trimellitic anhydride), decahydro[2]benzopyrano[6,5,4,-def][2]benzopyran-1,3,6,8-tetraone, etc.

[0035] Among the alicyclic tetracarboxylic dianhydrides, from the viewpoint of transparency and mechanical strength of the polyimide-based resin, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (H-PMDA), or 1,1′-bicyclohexane-3,3′,4,4′-tetracarboxylic dianhydride (H-BPDA) is preferred, and 1,2,3,4-cyclobutanetetracarboxylic dianhydride is particularly preferred.

[0036] From the perspective of improving the compatibility of the polyimide resin with other resins, the content of alicyclic tetracarboxylic dianhydride is preferably 1 mol% or more, more preferably 3 mol% or more, further preferably 5 mol% or more, relative to 100 mol% of the total amount of the acid dianhydride component, and can be 6 mol% or more, 7 mol% or more, 8 mol% or more, 9 mol% or more, 10 mol% or more, 12 mol% or more, or 15 mol% or more. The amount of alicyclic tetracarboxylic dianhydride required for compatibility with other resins sometimes varies depending on the type of other resins, the type of alicyclic tetracarboxylic dianhydride amount, etc. For example, when the alicyclic tetracarboxylic dianhydride is 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), the content of CBDA is preferably 6 mol% or more, more preferably 8 mol% or more, and further preferably 10 mol% or more, relative to 100 mol% of the total amount of the acid dianhydride component.

[0037] From the perspective of ensuring the solubility of the polyimide resin in an organic solvent, the content of alicyclic tetracarboxylic dianhydride relative to 100 mol% of the total amount of the acid dianhydride component is preferably 80 mol% or less, more preferably 78 mol% or less, further preferably 76 mol% or less, and can be 74 mol% or less, 72 mol% or less, 70 mol% or less, 65 mol% or less, 60 mol% or less, 55 mol% or less, or 50 mol% or less. In order to make the polyimide resin soluble in a low-boiling-point halogen-based solvent such as dichloromethane, the content of alicyclic tetracarboxylic dianhydride is preferably 45 mol% or less, more preferably 40 mol% or less, and can also be 35 mol% or less.

[0038] From the viewpoint of making the polyimide resin soluble in an organic solvent, the acid dianhydride component preferably contains a fluorinated aromatic tetracarboxylic dianhydride and / or a bis(trimellitic anhydride) ester in addition to the alicyclic tetracarboxylic dianhydride.

[0039] Examples of the fluorinated aromatic tetracarboxylic dianhydride include 2,2-bis(3,4-dicarboxyphenyl)

[0040] -1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis{4-[4-(1,2-dicarboxyl)phenoxy]phenyl}-1,1,1,3,3,3-hexafluoropropane dianhydride, and the like.

[0041] Examples of the bis(trimellitic anhydride) ester include bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2′,3,3′,5,5′-hexamethylbiphenyl-4,4′-diester (abbreviation: TahmbP).

[0042] From the viewpoint of making polyimide-based resin soluble in organic solvent, relative to acid dianhydride component total amount 100 mol%, the total of the content of fluorinated aromatic tetracarboxylic dianhydride and bis(trimellitic anhydride) ester is preferably 15 mol% or more, more preferably 20 mol% or more, further preferably 25 mol% or more, can be 30 mol% or more, 35 mol% or more, 40 mol% or more, 45 mol% or more or 50 mol% or more.Relative to acid dianhydride component total amount 100 mol%, the total of the content of fluorinated aromatic tetracarboxylic dianhydride and bis(trimellitic anhydride) ester is preferably 99 mol% or less, more preferably 95 mol% or less, further preferably 90 mol% or less, can be 85 mol% or less, 80 mol% or less, 75 mol% or less or 70 mol% or less.

[0043] From the viewpoint of obtaining a polyimide-based resin having both solubility in an organic solvent and compatibility with other resins, the total content of alicyclic tetracarboxylic dianhydride, fluorinated aromatic tetracarboxylic dianhydride, and bis(trimellitic anhydride) ester relative to 100 mol% of the total amount of the acid dianhydride component is preferably 50 mol% or more, more preferably 60 mol% or more, further preferably 65 mol% or more, and can be 70 mol% or more, 75 mol% or more, 80 mol% or more, 85 mol% or more, 90 mol% or more, or 95 mol% or more.

[0044] For polyimide resins, as acid dianhydride components, acid dianhydrides other than alicyclic tetracarboxylic dianhydride, fluorinated aromatic tetracarboxylic dianhydride and bis(trimellitic anhydride) esters 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) 1,3-bis[(3,4-dicarboxy)benzoyl]phthalic dianhydride, 1,4-bis[(3,4-dicarboxy)benzoyl]phthalic dianhydride, 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride, 2,2-bis{4-[4-(3,4-dicarboxy)phenoxy]phenyl}propane dianhydride, 2,2-bis{4-[4-(3,4-dicarboxy)phenoxy]phenyl}propane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride), 1,3-bis[(3,4-dicarboxy)benzoyl]phthalic dianhydride, 1,4-bis[(3,4-dicarboxy)benzoyl]phthalic dianhydride, {4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, 4,4'-bis[4-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, 4,4'-bis[3-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl} ]phenyl}sulfone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,3,4-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.

[0045] (Dicarboxylic acid)

[0046] As described above, the polyimide resin may be a polyamide-imide obtained by replacing a portion of the tetracarboxylic dianhydride component with a dicarboxylic acid derivative. Examples of dicarboxylic acids include aliphatic dicarboxylic acids such as adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-oxybisbenzoic acid, 4,4'-biphenyldicarboxylic acid, and 2-fluoroterephthalic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-hexahydroterephthalic acid, hexahydroisophthalic acid, 1,3-cyclopentanedicarboxylic acid, and bis(cyclohexyl)-4,4'-dicarboxylic acid; and heterocyclic dicarboxylic acids such as 2,5-thiophenedicarboxylic acid and 2,5-furandicarboxylic acid.

[0047] From the perspective of solubility of polyamide-imide and compatibility with other resins, aromatic dicarboxylic acids and alicyclic dicarboxylic acids are preferred as dicarboxylic acids, with aromatic dicarboxylic acids being particularly preferred. Among aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, 4,4'-biphenyldicarboxylic acid, and 4,4'-oxybisbenzoic acid are preferred. Among these, terephthalic acid and isophthalic acid are preferred, with terephthalic acid being particularly preferred.

[0048] As the dicarboxylic acid derivative used as a raw material monomer for polyamide-imide, dicarboxylic acid dichloride, dicarboxylic acid ester, dicarboxylic acid anhydride and the like can be used. Among them, dicarboxylic acid dichloride is preferred due to its high reactivity.

[0049] From the perspective of the solubility of the polyamide-imide and its compatibility with other resins, the ratio of the dicarboxylic acid derivative to the total of the tetracarboxylic dianhydride and the dicarboxylic acid derivative is preferably 40 mol% or less, more preferably 35 mol% or less, and even more preferably 30 mol% or less. The polyimide resin may be a polyimide in which the ratio of the dicarboxylic acid derivative is 0 (i.e., does not contain a structure derived from a dicarboxylic acid derivative).

[0050] (Diamine)

[0051] The diamine component of the polyimide resin used in this embodiment is not particularly limited. From the perspective of solubility, the diamine of the polyimide resin preferably has one or more selected from the group consisting of a fluoro group, a trifluoromethyl group, a sulfo group, a fluorene structure, and an alicyclic structure. From the perspective of balancing the solubility and transparency of the polyimide resin, the polyimide resin preferably contains a fluorine-containing diamine such as a fluoroalkyl-substituted benzidine as the diamine component.

[0052] Examples of fluoroalkyl-substituted benzidines of fluorinated diamines include 2-(trifluoromethyl)benzidine, 3-(trifluoromethyl)benzidine, 2,3-bis(trifluoromethyl)benzidine, 2,5-bis(trifluoromethyl)benzidine, 2,6-bis(trifluoromethyl)benzidine, 2,3,5-tris(trifluoromethyl)benzidine, 2,3,6-tris(trifluoromethyl)benzidine, 2,3,5,6-tetrakis(trifluoromethyl)benzidine, 2,2'-bis(trifluoromethyl)benzidine, 3,3'-bis(trifluoromethyl)benzidine, 2,3'-bis(trifluoromethyl)benzidine, , 2,2',3-bis(trifluoromethyl)benzidine, 2,3,3'-tris(trifluoromethyl)benzidine, 2,2',5-tris(trifluoromethyl)benzidine, 2,2',6-tris(trifluoromethyl)benzidine, 2,3',5-tris(trifluoromethyl)benzidine, 2,3',6-tris(trifluoromethyl)benzidine, 2,2',3,3'-tetrakis(trifluoromethyl)benzidine, 2,2',5,5'-tetrakis(trifluoromethyl)benzidine, 2,2',6,6'-tetrakis(trifluoromethyl)benzidine, and the like.

[0053] Among these, fluoroalkyl-substituted benzidines having a fluoroalkyl group at the 2-position of biphenyl are preferred, with 2,2'-bis(trifluoromethyl)benzidine (hereinafter referred to as "TFMB") being particularly preferred. The presence of fluoroalkyl groups at the 2- and 2'-positions of biphenyl reduces the π electron density due to the electron-withdrawing properties of the fluoroalkyl groups. Furthermore, the steric hindrance of the fluoroalkyl groups distorts the bond between the two benzene rings of biphenyl, reducing the planarity of the π conjugation. This shifts the absorption edge wavelength to a shorter wavelength, thus reducing coloration of the polyimide resin.

[0054] The content of the fluoroalkyl-substituted benzidine relative to 100 mol% of the total diamine component is preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, and can be 80 mol% or more, 85 mol% or more, or 90 mol% or more. A high content of the fluoroalkyl-substituted benzidine tends to suppress film coloring and increase mechanical strength, such as pencil hardness and elastic modulus.

[0055] The polyimide resin may contain a diamine other than fluoroalkyl-substituted benzidine as a diamine component. Examples of diamines other than fluoroalkyl-substituted benzidine include p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 9,9-bis(4-aminophenyl)fluorene, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3 ... '-Diaminodiphenylmethane, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 2-(3-aminophenyl)-2-(4-aminophenyl)propane, 1,1-bis(3-aminophenyl)-1-phenylethane, 1,1-bis(4-aminophenyl)-1-phenylethane, 1-(3-aminophenyl)-1-(4-aminophenyl)-1-phenylethane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminobenzoyl)benzene, 1,3-bis(4-aminobenzoyl)benzene, 1,4-bis(3-aminophenoxy)benzene (3-Aminobenzoyl)benzene, 1,4-bis(4-aminobenzoyl)benzene, 1,3-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(4-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(4-amino-α,α-dimethylbenzyl)benzene, 2,6-bis(3-aminophenoxy)benzonitrile, 2,6-bis(3-aminophenoxy)pyridine, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy) phenyl] sulfide, bis[4-(4-aminophenoxy)phenyl] sulfide, bis[4-(3-aminophenoxy)phenyl] sulfone, bis[4-(4-aminophenoxy)phenyl] sulfone, bis[4-(3-aminophenoxy)phenyl] ether, bis[4-(4-aminophenoxy)phenyl] ether, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 4,4'-bis[4-(4-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenyl sulfone, 4,4'-bis[4-(4-aminophenoxy)phenoxy]diphenyl sulfone, 3,3'-diaminophenoxy 1,1'-spirobiiindane, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiiindane, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, α,ω-bis(3-aminopropyl)polydimethylsiloxane, α,ω-bis(3-aminobutyl)polydimethylsiloxane, bis(aminomethyl)-1,1'-spirobiiindane, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisilox ...butyl)tetramethyldisiloxane, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, 1,3-bis(3-aminobutyl)tetramethyldisiloxane, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, 1,3-bis(3-aminobutyl)tetramethyldisiloxane, 1,3-bis(3-aminobutyl)tetramethyldisiloxane, ether, bis(2-aminoethyl) ether, bis(3-aminopropyl) ether, bis(2-aminomethoxy)ethyl] ether, bis[2-(2-aminoethoxy)ethyl] ether, bis[2-(3-aminopropoxy)ethyl] ether, 1,2-bis(aminomethoxy)ethane, 1,2-bis(2-aminoethoxy)ethane, 1,2-bis[2-(aminomethoxy)ethoxy]ethane, 1,2-bis[2-(2-aminoethoxy)ethoxy]ethane, ethylene glycol bis(3-aminopropyl) ether, cyclohexane, 1,3-bis(2-aminoethyl)cyclohexane, 1,4-bis(2-aminoethyl)cyclohexane, bis(4-aminocyclohexyl)methane, 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane, 2,5-bis(aminomethyl)bicyclo[2.2.1]heptane (Aminomethyl)bicyclo[2.2.1]heptane, 1,4-diamino-2-fluorobenzene, 1,4-diamino-2,3-difluorobenzene, 1,4-diamino-2,5-difluorobenzene, 1,4-diamino-2,6-difluorobenzene, 1,4-diamino-2,3,5-trifluorobenzene, 1,4-diamino-2,3,5,6-tetrafluorobenzene, 1,4-diamino-2-(trifluoromethyl)benzene, 1,4-diamino-2,3-bis(trifluoromethyl)benzene, 1,4-diamino-2,5-bis(trifluoromethyl)benzene, 1,4-diamino-2,6-bis(trifluoromethyl)benzene, 1,4-diamino-2,3,5-tris(trifluoromethyl)benzene, 1,4-diamino-2,3,5,6-tetra(trifluoromethyl)benzene, 2,2'-dimethylbenzidine, 2-fluorobenzidine, 3-fluorobenzidine, 2,3-difluorobenzidine, 2,5-difluorobenzidine, 2,6-difluorobenzidine, 2,3,5-trifluorobenzidine, 2,3,6-trifluorobenzidine, 2,3,5,6-tetrafluorobenzidine, 2,2'-difluorobenzidine, 3,3'-difluorobenzidine, 2,3'-difluorobenzidine, 2,2',3-trifluorobenzidine, 2,3,3'-trifluorobiphenyl Amine, 2,2',5-trifluorobenzidine, 2,2',6-trifluorobenzidine, 2,3',5-trifluorobenzidine, 2,3',6-trifluorobenzidine, 2,2',3,3'-tetrafluorobenzidine, 2,2',5,5'-tetrafluorobenzidine, 2,2',6,6'-tetrafluorobenzidine, 2,2',3,3',6,6'-hexafluorobenzidine, 2,2',3,3',5,5'6,,6'-octafluorobenzidine.

[0056] For example, using diaminodiphenyl sulfone in addition to fluoroalkyl-substituted benzidine as a diamine may improve the solubility and transparency of the polyimide resin in the solvent. Among diaminodiphenyl sulfones, 3,3'-diaminodiphenyl sulfone (3,3'-DDS) and 4,4'-diaminodiphenyl sulfone (4,4'-DDS) are preferred. 3,3'-DDS and 4,4'-DDS may also be used in combination. The content of diaminodiphenyl sulfone can be 1 to 40 mol%, 3 to 30 mol%, or 5 to 25 mol% relative to 100 mol% of the total diamine content.

[0057] (Preparation of polyimide resin)

[0058] The polyamic acid as a polyimide precursor is obtained by the reaction of an acid dianhydride and a diamine, and the polyimide is obtained by dehydration cyclization (imidization) of the polyamic acid. The preparation method of the polyamic acid is not particularly limited, and all known methods can be applied. For example, diamine and tetracarboxylic dianhydride are dissolved in an organic solvent with approximately equimolar amounts (a molar ratio of 90:100 to 110:100) and stirred to obtain a polyamic acid solution.

[0059] In the preparation of polyamide-imide, in addition to diamine and tetracarboxylic dianhydride, dicarboxylic acid or its derivatives (dicarboxylic acid dichloride, dicarboxylic acid anhydride, etc.) can also be used as monomers. In this case, the amount of each monomer can be adjusted so that the total amount of tetracarboxylic dianhydride and dicarboxylic acid or its derivative is approximately equimolar to that of the diamine.

[0060] As described above, by adjusting the composition of the polyimide resin, that is, the types and ratios of the acid dianhydride and the diamine, the polyimide resin has transparency and solubility in organic solvents and exhibits compatibility with other resins.

[0061] The concentration of the polyamic acid solution is generally 5 to 35% by weight, preferably 10 to 30% by weight. When the concentration is within this range, the polyamic acid obtained by polymerization has an appropriate molecular weight, and the polyamic acid solution has an appropriate viscosity.

[0062] During the polymerization of polyamic acid, in order to suppress the ring-opening of acid dianhydride, it is preferred to add acid dianhydride to diamine. When adding multiple diamines or multiple acid dianhydrides, they can be added at one time or in multiple times. By adjusting the order of addition of monomers, the various physical properties of the polyimide resin can also be controlled.

[0063] The organic solvent used in the polymerization of polyamic acid is not particularly limited as long as it is a solvent that does not react with diamine and acid dianhydride, that polyamic acid can be dissolved. As organic solvent, methylurea, N, the urea solvents such as N-dimethylethylurea, dimethyl sulfoxide, diphenyl sulfone, tetramethyl sulfone, sulfoxide or sulfone solvents, N, N-dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), N, N'-diethylacetamide, N-methyl-2-pyrrolidone (NMP), gamma-butyrolactone, hexamethylphosphoric acid triamide, chloroform, the halogenated alkyl solvents such as dichloromethane, benzene, the aromatic hydrocarbon solvents such as toluene, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, p-cresol methyl ether, etc. are listed. Usually these solvents are used alone or two or more are suitably used in combination as needed. From the viewpoint of the solubility and polymerization reactivity of polyamic acid, preferably DMAc, DMF, NMP etc. are used.

[0064] Obtain polyimide resin by the dehydration cyclization of polyamic acid.As the method for preparing polyimide resin by polyamic acid solution, can enumerate in polyamic acid solution, add dehydrating agent, imidization catalyst etc., the method for carrying out imidization in solution.In order to promote the progress of imidization, polyamic acid solution can be heated. The solution of the polyimide resin generated by the imidization of polyamic acid is mixed with a poor solvent, and thus polyimide resin is separated out as a solid. By separating the polyimide resin as a solid, impurities, residual dehydrating agent and imidization catalyst etc. generated when the synthesis of polyamic acid can be cleaned and removed by a poor solvent, and the coloring of polyimide resin, the rising of yellowness can be prevented. In addition, by separating the polyimide resin as a solid, thus when the preparation is used to make the solution of film, solvents suitable for filmization such as low boiling point solvents can be applied.

[0065] The molecular weight of the polyimide resin (weight average molecular weight in terms of polyethylene oxide as measured by gel filtration chromatography (GPC)) is preferably 10,000 to 300,000, more preferably 20,000 to 250,000, and even more preferably 40,000 to 200,000. If the molecular weight is too low, the film strength may be insufficient. If the molecular weight is too high, the compatibility with other resins may be poor.

[0066] The polyimide resin is preferably soluble in a low-boiling-point solvent such as a ketone solvent or a haloalkyl solvent. The polyimide resin showing solubility in a solvent means dissolving at a concentration of 5% by weight or more. In one embodiment, the polyimide resin shows solubility in dichloromethane. Dichloromethane has a low boiling point and is easy to remove residual solvent during film production. Therefore, by using a polyimide resin soluble in dichloromethane, it is expected that the productivity of the film will be improved.

[0067] From the viewpoint of thermal stability and light stability of the transparent resin film, the polyimide resin preferably has low reactivity. The acid value of the polyimide resin is preferably 0.4 mmol / g or less, more preferably 0.3 mmol / g or less, and further preferably 0.2 mmol / g or less. The acid value of the polyimide can be 0.1 mmol / g or less, 0.05 mmol / g or less, or 0.03 mmol / g or less. From the viewpoint of reducing the acid value, the polyimide resin preferably has a high imidization rate. By making the acid value small, there is a tendency for the stability of the polyimide resin to improve and for its compatibility with other resins to improve.

[0068] <Other resins>

[0069] As described above, the transparent resin film 1 includes, in addition to the polyimide resin, a resin other than the polyimide resin ("other resin"). As other resins, there is no particular limitation as long as they are soluble in organic solvents and can be mixed with the polyimide resin to form a transparent film. Examples include resins that are compatible with the polyimide resin, and resins that form microphase separation structures such as island structures, cylinder structures, and layered structures. Among them, other resins are preferably resins that are compatible with the polyimide resin. When the polyimide resin is compatible with the other resins, regardless of the processing conditions of the film, there is a tendency for the film to have high transparency and excellent mechanical properties such as elastic modulus and pencil hardness.

[0070] The other resin is preferably a transparent resin having a lower refractive index than the polyimide resin. The refractive index of the other resin is preferably 1.600 or less, more preferably 1.550 or less, further preferably 1.520 or less, and particularly preferably 1.500 or less. By making the other resin have a lower refractive index than the polyimide resin, the transparent resin film containing the polyimide resin and the other resin has a lower refractive index than the film of the polyimide resin alone, and the reflection at the interface is small, so there is a tendency for the total light transmittance to increase.

[0071] Examples of other resins include acrylic resins, polycarbonate resins, polyester resins, polyamide resins, polyether resins, cellulose resins, silicone resins, and cyclic olefin resins. A variety of these resins may also be used. From the perspective of high compatibility with polyimide resins, acrylic resins, polycarbonate resins, and polyester resins having a fluorene structure are preferred as other resins. Among these, acrylic resins are particularly preferred from the perspective of high compatibility with polyimide resins, low refractive index, and ease of forming a high-hardness film.

[0072] Examples of acrylic resins include poly(meth)acrylates such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymers, methyl methacrylate-(meth)acrylic acid ester copolymers, methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymers, and methyl (meth)acrylate-styrene copolymers. Acrylic resins can be modified to introduce glutarimide structural units or lactone ring structural units.

[0073] From the perspectives of transparency, compatibility with polyimide resins, and mechanical strength, acrylic resins preferably contain methyl methacrylate as their primary structural unit. The amount of methyl methacrylate relative to the total monomeric components of the acrylic resin is preferably 60% by weight or greater, and can be 70% by weight or greater, 80% by weight or greater, 85% by weight or greater, 90% by weight or greater, or 95% by weight or greater. The acrylic resin can be a homopolymer of methyl methacrylate. Alternatively, the acrylic resin can be a resin in which a glutarimide structure or a lactone ring structure is introduced into an acrylic polymer having a methyl methacrylate content within the aforementioned range.

[0074] From the viewpoint of heat resistance of the transparent resin film, the glass transition temperature of the acrylic resin is preferably 100° C. or higher, more preferably 110° C. or higher, and may be 115° C. or higher or 120° C. or higher.

[0075] The weight average molecular weight (polystyrene equivalent) of the acrylic resin is preferably 5,000 to 500,000, more preferably 10,000 to 300,000, and even more preferably 15,000 to 200,000, from the viewpoints of solubility in organic solvents, compatibility with polyimide resins, and film strength.

[0076] From the viewpoint of thermal stability and light stability of the film, the acrylic resin preferably has a low content of reactive functional groups such as ethylenically unsaturated groups and carboxyl groups. The iodine value of the acrylic resin is preferably 10.16g / 100g (0.4mmol / g) or less, more preferably 7.62g / 100g (0.3mmol / g) or less, and further preferably 5.08g / 100g (0.2mmol / g) or less. The iodine value of the acrylic resin can be 2.54g / 100g (0.1mmol / g) or less or 1.27g / 100g (0.05mmol / g) or less. The acid value of the acrylic resin is preferably 0.4mmol / g or less, more preferably 0.3mmol / g or less, and further preferably 0.2mmol / g or less. The acid value of the acrylic resin can be 0.1mmol / g or less, 0.05mmol / g or less or 0.03mmol / g or less. When the acid value is reduced, the stability of the acrylic resin tends to be improved, and the compatibility with the polyimide resin tends to be improved.

[0077] <Composition of Transparent Resin Film>

[0078] As described above, the transparent resin film contains a polyimide resin and other resins as resin components. The ratio of the polyimide resin to the other resins in the transparent resin film is not particularly limited. The mixing ratio (weight ratio) of the polyimide resin to the other resins can be 98:2 to 2:98, 95:5 to 10:90, 90:10 to 15:85, or 65:35 to 50:50. The higher the ratio of the polyimide resin, the higher the elastic modulus and pencil hardness of the film, and the better the mechanical strength. The higher the ratio of other resins, the less coloring of the film, the higher the total light transmittance, the lower the yellowness (YI), and the higher the transparency.

[0079] In order to fully exert the effect of improving transparency brought about by mixing the polyimide resin with other resins, the ratio of other resins to the total of the polyimide resin and other resins is preferably 10 to 90 weight%, more preferably 15 to 85 weight%, further preferably 20 to 80 weight%, and can be 30 to 70 weight%, 35 to 65 weight% or 40 to 60 weight%.

[0080] In addition to the above resin components, the transparent resin film may also contain organic or inorganic low molecular weight compounds, etc. The transparent resin film may contain blueing agents, ultraviolet absorbers, flame retardants, stabilizers, crosslinking agents, surfactants, leveling agents, plasticizers, fine particles and the like as additives.

[0081] For the purposes such as improving anti-blocking property and adjusting refractive index, transparent resin film can include inorganic particles such as organic particles such as polystyrene, cross-linked acrylic resin, silicon dioxide, layered silicate. However, when compounding particles, it may become the reason that the transmittance of film decreases and haze rises. Although silicon oxides such as silicon dioxide are particularly useful for the low refractive index of film, they are easily poorly dispersed in the resin matrix and are easily the reason that transparency, mechanical strength and bending resistance are reduced. Therefore, relative to 100 parts by weight of the total of resin component, the content of silicon oxide is preferably less than 5 parts by weight, preferably less than 1 part by weight, more preferably less than 0.5 part by weight, can be less than 0.1 part by weight, or can be 0.

[0082] <Production of Transparent Resin Film>

[0083] The method for forming the transparent resin film is not particularly limited, but a solution method is preferred in which a solution containing the polyimide resin and other resins is applied onto a support and then dried to remove the solvent.

[0084] The solvent is not particularly limited as long as it exhibits solubility in both the polyimide resin and the other resin. Examples of solvents include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; ether solvents such as tetrahydrofuran and 1,4-dioxane; ketone solvents such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diethyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone; and haloalkyl solvents such as chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene, dichlorobenzene, and dichloromethane. Ketone solvents and haloalkyl solvents are preferred because they have excellent solubility in polyimide resins and the like, have low boiling points, and can easily remove residual solvent during film formation.

[0085] As a method for coating the resin solution on a support, a known method using a rod coater, a comma coater, or the like can be applied. As the support, a glass substrate, a metal substrate such as SUS, a metal roller, a metal belt, a plastic film, or the like can be used. From the perspective of improving productivity, it is preferred to use an endless support such as a metal roller or metal belt, or a long plastic film, as the support, and to produce the film by roll-to-roll method. When using a plastic film as the support, a material that is insoluble in the solvent of the resin solution (dope) can be appropriately selected.

[0086] It is preferred to heat the film during the drying of the solvent. The heating temperature is not particularly limited as long as it is a temperature that can remove the solvent and suppress the coloring of the obtained film. It can be appropriately set at room temperature to about 250°C, preferably 50°C to 220°C. The heating temperature can be increased in stages. In order to improve the efficiency of solvent removal, the resin film can be peeled off from the support and dried after drying to a certain extent. Drying can be carried out in an air atmosphere or a nitrogen atmosphere. In order to promote the removal of the solvent, heating can be carried out under reduced pressure.

[0087] The film may be stretched in one or more directions to improve its mechanical strength, etc. Stretching the film orients the polymer chains in the stretching direction, thereby increasing the film's in-plane strength, suppressing breakage or cracking, and improving dent recovery.

[0088] Films made of acrylic resins alone sometimes have low toughness, but using a compatibilized system of polyimide-acrylic resins can sometimes improve film strength. Furthermore, when films made of a compatibilized system of polyimide-acrylic resins are stretched, the tensile modulus in the stretching direction increases, which tends to improve flex resistance.

[0089] For example, films used as cover windows or substrates for foldable displays are repeatedly bent along a bending axis at the same location, requiring high mechanical strength in a direction perpendicular to the bending axis. Therefore, by arranging the film so that its stretching direction is perpendicular to the bending axis, the film is less likely to break or crack at the bent portion even after repeated bending, resulting in a device with high bending resistance.

[0090] The film stretching conditions are not particularly limited. For example, the stretching temperature is approximately ±40°C of the film's glass transition temperature, and may be 120-300°C, 150-250°C, or 180-230°C. The stretching ratio is approximately 1-200%, and may be 5-150%, 10-120%, or 20-100%. The greater the stretching ratio, the greater the tensile modulus in the stretching direction. On the other hand, excessively high stretching ratios tend to reduce the mechanical strength in a direction perpendicular to the stretching direction, sometimes resulting in reduced handleability of the film.

[0091] From the perspective of increasing the strength in any direction within the plane, the film can be biaxially stretched. Biaxial stretching can be simultaneous biaxial stretching or sequential biaxial stretching. In biaxial stretching, the stretch ratio in one direction can be the same as or different from the stretch ratio in the orthogonal direction. If a difference is set in the stretch ratio, there is a tendency for the mechanical strength in the direction with a larger stretch ratio to be relatively larger. When a biaxially stretched film with anisotropic stretch ratio is used in a foldable device, it is preferably arranged so that the direction with a larger stretch ratio is orthogonal to the bending axis.

[0092] The thickness of the transparent resin film is not particularly limited and can be appropriately set depending on the intended use. The thickness of the transparent resin film is, for example, 5 to 300 μm. From the perspective of achieving a film that is both self-supporting and flexible while also being highly transparent, the thickness of the transparent resin film is preferably 10 to 100 μm, and may be 15 to 80 μm, 20 to 55 μm, or 25 to 55 μm. When the film is stretched, the thickness after stretching is preferably within the above range.

[0093] <Characteristics of Transparent Resin Film>

[0094] The transparent resin film preferably has a single glass transition temperature in differential scanning calorimetry (DSC) and / or dynamic viscoelasticity measurement (DMA). When the polyimide resin contained in the transparent resin film is compatible with other resins, it exhibits a single glass transition temperature.

[0095] The haze of the transparent resin film is preferably 10% or less, more preferably 5% or less, and even more preferably 4% or less. It can be 3.5% or less, 3% or less, 2% or less, 1% or less, or 0.5% or less. When the transparent resin film contains a polyimide resin and another resin, low haze can be achieved by using a resin with high compatibility with the polyimide resin, such as an acrylic resin, as the other resin.

[0096] The total light transmittance of the transparent resin film is preferably 90.0% or higher, more preferably 90.5% or higher, even more preferably 91.0% or higher, and may be 91.5% or higher. The higher the total light transmittance, the higher the white brightness of the display and the better the visual recognition. As described above, by mixing a polyimide resin with other resins, there is a tendency for the refractive index to be lower and the total light transmittance to be higher compared to the case of the polyimide resin alone.

[0097] The yellowness index (YI) of the transparent resin film is preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.0 or less. The yellowness index (YI) of the transparent resin film is preferably -3.0 or greater, more preferably -2.0 or greater, and even more preferably -1.0 or greater. By mixing a polyimide resin with another resin such as an acrylic resin, a film with less coloration and a smaller absolute value of YI can be obtained compared to when using the polyimide resin alone.

[0098] The refractive index of transparent resin film is preferably below 1.600. The refractive index of transparent resin film is more preferably below 1.580, further preferably below 1.560, particularly preferably below 1.540, and can also be below 1.520. The refractive index of the film that only comprises polyimide-based resin as resin component is usually higher than 1.600, and the reflection of light caused by the refractive index difference of the interface with air and other components is many (reflectivity is high), so transmittance is small. The mixed resin system of polyimide-based resin and other resins has low refractive index compared with the situation that polyimide-based resin is independent, so the light reflection at interface reduces, and total light transmittance rises. Particularly because the refractive index of acrylic resin is low, if acrylic resin is used as other resins, then there is the tendency that transparent resin film is low in refractive index, total light transmittance rises.

[0099] Stretched films have a tendency to have a greater refractive index in the stretching direction (the orientation direction of the polymer chains). Therefore, when the transparent resin film is a stretched film, it can have an in-plane refractive index anisotropy. The in-plane refractive index difference of the transparent resin film (the difference between the maximum refractive index and the minimum refractive index in the plane) can be 0.005 or more, 0.010 or more, 0.020 or more, or 0.030 or more. When the transparent resin film has an in-plane refractive index anisotropy, the average value of the maximum refractive index in the plane (usually the refractive index in the stretching direction) and the minimum refractive index in the plane is preferably within the above range.

[0100] The tensile modulus of the transparent resin film is preferably 3.0 GPa or more, more preferably 3.5 GPa or more, further preferably 4.5 GPa or more, and can be 5.0 GPa or more, 5.5 GPa or more, or 6.0 GPa or more. A larger tensile modulus tends to result in better mechanical strength, such as hardness and bending resistance.

[0101] The tensile modulus of a transparent resin film may have in-plane anisotropy. When the transparent resin film is a stretched film, there is a tendency for the tensile modulus in the stretching direction to be greater than the tensile modulus in a direction orthogonal to the stretching direction. When the transparent resin film is a biaxially stretched film or a film uniaxially stretched at a fixed end, the tensile modulus in all directions in the plane may be greater than that before stretching. When the transparent resin film has in-plane anisotropy in the tensile modulus, the maximum in-plane tensile modulus (usually the tensile modulus in the stretching direction) is preferably within the above range.

[0102] When the transparent resin film has anisotropy of tensile modulus, the tensile modulus in the direction where the tensile modulus is the largest (usually the direction with a large stretching ratio) can be 4.0 GPa or more, 4.5 GPa or more, or 5.0 GPa or more. The difference between the maximum and minimum values ​​of the tensile modulus in the plane can be 0.5 GPa or more, 1.0 GPa or more, or 1.3 GPa or more. The transparent resin film has anisotropy of tensile modulus, and the greater the difference between the maximum and minimum values ​​of the tensile modulus in the plane, the better the sag recovery. As an estimated factor for improving sag recovery by the large anisotropy of the tensile modulus, it is considered to impart recovery to sag by balancing the resistance to sag caused by the high elastic modulus and the flexibility caused by the relatively low elastic modulus in the direction orthogonal thereto.

[0103] [Hard Coating]

[0104] The transparent film 5 may be composed solely of the transparent resin film 1, or may be provided as a laminate having various functional layers on one or both principal surfaces. Examples of the functional layers include a hard coat layer, an ultraviolet absorbing layer, an adhesive layer, a refractive index adjusting layer, and an adhesion-facilitating layer. When the laminate of thin glass and transparent film is used as a cover window material for a display, the transparent film 5 preferably has a hard coat layer 3 on the surface of the transparent resin film 1 opposite the thin glass 7. Providing a hard coat layer on the surface of the transparent resin film improves the scratch resistance and hardness of the laminate.

[0105] The material constituting the hard coat layer is not particularly limited as long as it has a function of preventing scratches, and examples thereof include polyester, acrylic, urethane, amide, silicone, and epoxy resins. Among them, from the viewpoint of preventing scratches, acrylic hard coat layers that are cured products of acrylic hard coat resin compositions, and silicone hard coat layers that are cured products of silicone hard coat resin compositions are preferred.

[0106] <Acrylic Hard Coat Material>

[0107] Acrylic hard coating materials contain monomers or oligomers having (meth)acryloyl groups in their molecules as curable resin components. The molecular weight of acrylic monomers or oligomers is, for example, approximately 200 to 10,000. Acrylic hard coating materials can control hardness, scratch resistance, bending resistance, optical properties, etc. by combining various monomers or oligomers having (meth)acryloyl groups. From the perspective of curability based on photoradical polymerization, the hard coating material preferably contains an acryloyl group.

[0108] Specific examples of oligomers having a (meth)acryloyl group include urethane (meth)acrylate, polyester (meth)acrylate, epoxy (meth)acrylate, etc. The oligomer may have two or more (meth)acryloyl groups in one molecule. The molecular weight of the oligomer is preferably 10,000 or less.

[0109] Examples of acrylic monomers include compounds having one (meth)acryloyl group, such as methyl (meth)acrylate and 2-ethylhexyl (meth)acrylate; compounds having two (meth)acryloyl groups in one molecule, such as ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, and 1,6-hexanediol di(meth)acrylate; and compounds having three or more (meth)acryloyl groups in one molecule, such as glycerol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0110] To improve the scratch resistance of the hard coat layer, acrylic hard coat materials preferably contain trifunctional or higher-functional (meth)acrylates. The functional group equivalent weight of the (meth)acryloyl group in the multifunctional (meth)acrylate, i.e., the molecular weight per (meth)acryloyl group, is preferably 80 to 150 g / eq. Among the multifunctional (meth)acrylates exemplified above, dipentaerythritol hexa(meth)acrylate is particularly preferred.

[0111] <Siloxane-based hard coating material>

[0112] Siloxane-based hard coating materials contain a curable compound having a siloxane bond as a curable resin component. From the perspective of damage resistance, siloxane-based curable compounds preferably have an epoxy group as a polymerizable functional group, and polyorganosiloxane compounds containing an alicyclic epoxy group are particularly preferred. Such siloxane-based hard coating materials are disclosed in WO2014 / 204010, WO2018 / 096729, WO2020 / 040209, and other publications, which can be referenced / cited.

[0113] Siloxane-based hard coat materials containing alicyclic epoxy groups as polymerizable functional groups exhibit minimal shrinkage during curing, making them less susceptible to curling and cracking even when the hard coat thickness is increased. This increased hard coat thickness contributes to improved dent resistance and dent recovery properties.

[0114] The polyorganosiloxane compound having an alicyclic epoxy group is obtained by condensing a silane compound represented by the general formula (1).

[0115] [Y-Si(OR 1 ) x R 2 3-x ](1)

[0116] 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.

[0117] The silane compound represented by the general formula (1) has two or three (-OR 1 ). Due to Si-OR 1 Since it is hydrolyzable, polyorganosiloxane compounds can be obtained by condensation of silane compounds. 1 The number of carbon atoms is preferably 3 or less, and R 1 It is a methyl group.

[0118] In the general formula (1), R 2 is a hydrogen atom or a monovalent hydrocarbon group selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms. Specific examples of the hydrocarbon group include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, isopropyl, isobutyl, cyclohexyl, ethylhexyl, benzyl, phenyl, tolyl, xylyl, naphthyl, and phenethyl.

[0119] In the general formula (1), x is 2 or 3. In the case of x=3 (i.e., three alkoxy (or hydroxy) groups -OR 1 In the case of silane compounds, the silane compound does not have R 2 From the viewpoint of forming a network-like polyorganosiloxane compound and increasing the number of epoxy groups contained in the polyorganosiloxane compound to improve the hardness of the cured film, in general formula (1), x=3 is preferred. A silane compound in which x=2 and a silane compound in which x=3 may be used in combination. In addition, for the purpose of adjusting the molecular weight of the polyorganosiloxane compound obtained by condensation, a silane compound in which x is 1 may be used in addition to a silane compound in which x is 2 or 3.

[0120] In general formula (1), Y is a monovalent organic group containing an alicyclic epoxy group. Examples of Y include an alicyclic epoxy group, an alkyl group having an alicyclic epoxy group as a substituent, and an alkylene glycol group having an alicyclic epoxy group as a substituent. From the viewpoint of heat resistance and bending resistance, an alkyl group having an alicyclic epoxy group as a substituent is preferred.

[0121] 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.

[0122] Specific examples of the silane compound represented by the general formula (1) include (3,4-epoxycyclohexyl)trimethoxysilane, (3,4-epoxycyclohexyl)methyldimethoxysilane, (3,4-epoxycyclohexyl)dimethylmethoxysilane, (3,4-epoxycyclohexyl)triethoxysilane, (3,4-epoxycyclohexyl)methyldiethoxysilane, (3,4-epoxycyclohexyl)dimethylethoxysilane, {(3,4-epoxycyclohexyl)methyl}trimethoxysilane, {(3,4-epoxycyclohexyl)methyl}methyldimethoxysilane, {(3,4-epoxycyclohexyl)methyl}dimethylmethoxysilane, {(3,4-epoxycyclohexyl)methyl} {(3,4-epoxycyclohexyl)methyl}triethoxysilane, {(3,4-epoxycyclohexyl)methyl}methyldiethoxysilane, {(3,4-epoxycyclohexyl)methyl}dimethylethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}trimethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}methyldimethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}dimethylmethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}triethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}methyldiethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}dimethylethoxysilane, etc. Among them, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane is preferred from the viewpoint of ease of condensation reaction and hardness of cured product.

[0123] The polyorganosiloxane compound as a condensate of a silane compound may be a condensate of the silane compound of the general formula (1) and another silane compound.

[0124] By reacting the above silane compound with water, the Si-OR 1 The hydrolyzate is partially hydrolyzed and condensed to form Si—O—Si bonds, thereby generating a condensate of the silane compound having an alicyclic epoxy group (polyorganosiloxane compound).

[0125] From the perspective of increasing the hardness of the cured film (hard coat), the weight-average molecular weight of the polyorganosiloxane compound is preferably 500 or greater. Furthermore, from the perspective of suppressing volatilization, the weight-average molecular weight of the polyorganosiloxane compound is also preferably 500 or greater. On the other hand, excessively high molecular weight may cause turbidity due to reduced compatibility with other components in the composition. Therefore, the weight-average molecular weight of the polyorganosiloxane compound is preferably 20,000 or less.

[0126] <Polymerization Initiator>

[0127] The hard coat composition preferably contains a polymerization initiator in addition to the aforementioned curable resin component. A photopolymerization initiator is preferred as the polymerization initiator. Acrylic hard coat compositions containing a compound having a (meth)acryloyl group as a curable resin component preferably contain a photoradical polymerization initiator that generates free radicals in response to light. Siloxane hard coat compositions containing a polyorganosiloxane compound having an epoxy group as a curable resin component preferably contain a photoacid generator (photocationic polymerization initiator) that generates acid in response to light.

[0128] 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.

[0129] Examples of photoacid generators include: onium salts formed by combining anions (strong acids) such as antimony hexafluoride, boron tetrafluoride, phosphorus hexafluoride, fluoroalkyl phosphorus fluoride, and fluoroalkyl gallium fluoride with cations such as sulfonium, ammonium, phosphonium, iodonium, and selenium; iron-allene complexes; silanol-metal chelates; sulfonic acid derivatives such as disulfones, disulfonyldiazomethanes, disulfonylmethanes, sulfonylbenzoylmethanes, imidesulfonates, and benzoinsulfonates; and organic halogen compounds.

[0130] <Other Components Constituting the Hard Coat Composition>

[0131] The hard coat composition used to form the hard coat layer may contain, in addition to a curable resin component and a polymerization initiator, a solvent and various additives. Examples of additives include fluorine-based or silicone-based leveling agents, sensitizers, reactive diluents, fine particles, fillers, dispersants, plasticizers, ultraviolet absorbers, surfactants, antioxidants, colorants, and viscosity modifiers.

[0132] <Formation of Hard Coat Layer>

[0133] A hard coating composition is applied to the transparent resin film 1, and after drying and removing the solvent as needed, the hard coating composition is cured to form a hard coating layer 3. Examples of methods for applying the hard coating composition include roller coating such as rod coating, gravure coating, and comma coating, die coating such as slot die coating and injection die coating, spin coating, spray coating, and dip coating. Prior to applying the curable resin composition, the surface of the transparent resin film 1 may be subjected to a surface treatment such as a corona treatment or a plasma treatment. Furthermore, an adhesive layer or the like may be provided on the surface of the transparent resin film 1.

[0134] By irradiating the hard coating composition with active energy rays or heating it, active species such as acid and free radicals are generated from the photopolymerization initiator, and the curable resin component of the hard coating composition is cured. From the viewpoint of curing reactivity, it is preferred that the curable resin composition contains a photopolymerization initiator and is cured by irradiation with active energy rays. Examples of active energy rays irradiated during photocuring include visible light, ultraviolet rays, infrared rays, X-rays, α rays, β rays, γ rays, electron beams, and the like. From the perspective of high curing reaction speed and excellent energy efficiency, ultraviolet rays are preferred as active energy rays. The cumulative irradiation amount of active energy rays is, for example, 50 to 10,000 mJ / cm 2 The curing temperature may be set according to the type and amount of the photocationic polymerization initiator, the thickness of the hard coat layer, etc. The curing temperature is not particularly limited, but is usually 150° C. or lower.

[0135] The thickness of the hard coat layer 3 is 1 to 50 μm, preferably 3 μm or greater, and more preferably 5 μm or greater. The thicker the hard coat layer, the higher the pencil hardness, dent recovery, and scratch resistance. On the other hand, excessively thick hard coat layers can reduce flex resistance. Therefore, the thickness of the hard coat layer is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less.

[0136] [Transparent adhesive layer]

[0137] The laminate 10 having the transparent film 5 on the thin glass 7 may be formed by direct contact between the thin glass 7 and the transparent film 5 (transparent resin film 1), or the thin glass 7 and the transparent film 5 may be bonded together via an appropriate transparent adhesive layer 9. When the thin glass 7 and the transparent film 5 are bonded together via the transparent adhesive layer 9, the stress of the transparent adhesive layer 9 is relaxed, and thus the bending resistance and flexibility of the laminate 10 when bent tend to be improved.

[0138] The material constituting the transparent adhesive layer 9 is not particularly limited as long as it is transparent, and various adhesives and pressure-sensitive adhesives (pressure-sensitive adhesives) can be used. Examples of the adhesive include solvent-based adhesives, reactive adhesives that react and cure by heat or active energy rays, hot-melt adhesives, and the like. Examples of the adhesive material include (meth) acrylic resins, urethane resins, silicone resins, cross-linked rubbers, and thermoplastic elastomers. Among these, (meth) acrylic resins are preferred from the viewpoints of transparency and weather resistance.

[0139] From the perspective of maintaining the thickness between the transparent film 5 and the thin glass 7 at a certain level, as the transparent adhesive layer 9, it is preferred that an adhesive or a bonding agent be pre-formed into an adhesive layer in the shape of a film. Wherein, from the perspective of not requiring a curing reaction and being able to directly adhere, a double-sided adhesive sheet is preferred. The double-sided adhesive sheet can be an adhesive sheet with a base material provided with an adhesive layer on both sides of a transparent base film, or it can be an adhesive sheet without a base material consisting only of an adhesive layer. From the perspective of transparency and thinning, an adhesive sheet without a base material is preferred. As the adhesive sheet without a base material, an optical transparent adhesive tape called OCA (Optical Clear Adhesive) can be exemplified.

[0140] The thickness of the transparent adhesive layer is preferably 5 μm or more, preferably 10 μm or more, preferably 20 μm or more, preferably 500 μm or less, preferably 100 μm or less, and preferably 50 μm or less. If the thickness is too thin, the adhesiveness may be insufficient, and if the thickness is too thick, the bending resistance and flexibility of the laminate may be insufficient. From the viewpoint of having stress relaxation performance when the laminate is bent, the storage elastic modulus of the transparent adhesive layer at a temperature of 25°C and a frequency of 1 Hz is preferably 1×10 4 Pa or less, more preferably 5×10 5 Below Pa.

[0141] [Laminated body]

[0142] The laminate 10 in which the transparent film 5 is bonded to the thin glass 7 has the function of preventing glass pieces from scattering when the thin glass 7 is broken. In addition, the transparent film 5 (transparent resin film 1) has superior bending resistance compared to glass.

[0143] The total thickness of the laminate 10 (the sum of the thicknesses of the thin glass 7, the transparent adhesive layer 9, and the transparent film 5) is not particularly limited. From the perspective of improving impact resistance and dent recovery, it is preferably 50 μm or greater, more preferably 80 μm or greater, and even more preferably 90 μm or greater. It can be 100 μm or greater or 110 μm or greater. From the perspective of bendability, the total thickness of the laminate 10 is preferably 200 μm or less, and more preferably 180 μm or less.

[0144] The yellowness index (YI) of the laminate 10 is preferably -3.0 to 3.0, more preferably -2.0 to 2.0, and even more preferably -1.0 to 1.0. A small absolute value of YI is preferred in terms of improving the visibility of the display and achieving a good color tone.

[0145] The haze of the laminate 10 is preferably 1% or less, more preferably 0.7% or less, and further preferably 0.5% or less. The total light transmittance of the laminate 10 is preferably 90.5% or more, more preferably 90.8% or more, further preferably 91.0% or more, and may be 91.5% or more.

[0146] Polyimide-based transparent resin films have higher mechanical strength than transparent resin films such as polyethylene terephthalate. Therefore, laminates comprising polyimide-based transparent resin films on thin glass exhibit excellent impact resistance and dent recovery. On the other hand, transparent polyimide exhibits a slight yellowish coloration, so polyimide-based transparent resin films tend to have a high YI. By using a blend of a polyimide-based resin and another resin, such as an acrylic resin, as the transparent resin film 1, coloration can be reduced, thereby lowering the YI.

[0147] Furthermore, polyimide resins have a high refractive index, resulting in high reflectivity at the film-air interface and the film-hard coat interface. Consequently, polyimide-based transparent resin films have a low total light transmittance. Blending polyimide resins with other resins, such as acrylic resins, lowers the refractive index and reduces reflectivity at the interfaces, thereby improving total light transmittance.

[0148] The laminate 10 having the transparent film 5 bonded to the thin glass 7 preferably has the following characteristics (depression recovery): the depression caused by the external force on the surface of the transparent film 5 becomes shallower over time, the depression is no longer visible, and the laminate returns to its original shape. Depression recovery is evaluated as follows: using a pencil of a specified hardness used in a pencil hardness test, under the conditions of a load of 750gf and a speed of 60mm / min, the surface of the transparent film side of the laminate is scratched to produce a depression, and the evaluation is performed by whether the depression disappears after 24 hours. If a sample in which depression is observed immediately after the test does not show depression after 24 hours, it is judged to have depression recovery for that hardness. The pencil hardness of the laminate 10 having depression recovery is preferably H or higher, more preferably 2H or higher, and can be 3H or higher or 4H or higher.

[0149] Since the transparent resin film 1 constituting the transparent film 5 comprises a polyimide resin, the laminate 10 in which the transparent film 5 is bonded to the thin glass 7 has high dent recovery due to the excellent mechanical strength derived from the polyimide. Furthermore, the transparent film 5 tends to have improved dent recovery due to the hard coat layer 3 on the transparent resin film 1.

[0150] When the transparent resin film 1 is a blended resin film of a polyimide resin and another resin such as an acrylic resin, it tends to have superior sag recovery properties compared to a transparent resin film made solely of a polyimide resin. It is believed that in a blend of a polyimide resin and another resin, the other resin imparts moderate flexibility, and the intermolecular interaction between the polyimide resin and the other resin polymers absorbs external forces, which contribute to improved sag recovery properties.

[0151] The laminate 10 preferably has bending resistance and is not susceptible to breakage or cracking caused by bending. The laminate 10 preferably does not break or crack after being bent 180° with a radius of 10 mm with the transparent film 5 on the inside and then restored to its original flat state.

[0152] The laminate of the present invention exhibits excellent transparency and bending resistance, and is also resilient to dents caused by external forces, making it suitable for use as a cover window disposed on the surface of an image display panel. In flexible display devices with touch sensors, cover windows with excellent dent recovery easily recover from deformation such as dents caused by pressure from fingernails, styluses, and the like, thereby improving the display's visual visibility and enhancing its product value.

[0153] Example

[0154] The present invention will be described in more detail below based on Examples and Comparative Examples, but the present invention is not limited to the following Examples. Hereinafter, the flow direction during coating is referred to as the MD direction, and the direction perpendicular to the MD direction is referred to as the TD direction.

[0155] [Preparation of polyimide resin]

[0156] Dimethylformamide (DMF) was placed in a separable flask and stirred under a nitrogen atmosphere. Diamine and tetracarboxylic dianhydride were added at the ratio (mol %) shown in Table 1 and stirred under a nitrogen atmosphere for 5 to 10 hours to allow the mixture to react, thereby obtaining a polyamic acid solution having a solid content concentration of 18% by weight.

[0157] In 100g of polyamic acid solution, 5.5g of pyridine as an imidization catalyst was added and completely dispersed. Then, 8g of acetic anhydride was added and stirred at 90°C for 3 hours. After cooling to room temperature, 100g of 2-propanol (IPA) was added at a rate of 2 to 3 drops per second while stirring the solution to precipitate polyimide. IPA150g was further added, and after stirring for about 30 minutes, suction filtration was performed using a Kiriyama funnel. After washing the obtained solid with IPA, it was dried in a vacuum oven set at 120°C for 12 hours to obtain polyimide resins 1 and 2 (PI1 and PI2).

[0158] In Table 1, the compounds are described by the following abbreviations.

[0159] <Tetracarboxylic Dianhydride>

[0160] CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride

[0161] 6FDA: 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride

[0162] TAHMBP: Bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diester

[0163] ODPA: 4,4'-oxydiphthalic dianhydride

[0164] <Diamine>

[0165] TFMB: 2,2'-bis(trifluoromethyl)benzidine

[0166] DDS: 3,3'-diaminodiphenyl sulfone

[0167] [Table 1]

[0168]

[0169] [Production of transparent resin film]

[0170] <Film 1>

[0171] Polyimide resin 1 (PI1) and a commercially available acrylic resin ("Parapet G" manufactured by Kuraray Co., Ltd.; a copolymer of methyl methacrylate / methyl acrylate (monomer ratio 87 / 13), glass transition temperature 109°C, acid value 0.0 mmol / g; hereinafter referred to as "acrylic resin" (Ac)) were dissolved in dichloromethane at a weight ratio of PI1 / Ac1 = 55 / 45 to prepare a solution having a solids concentration of 11% by weight. This solution was applied to an alkali-free glass plate and heat-dried in an air atmosphere at 60°C for 15 minutes, 90°C for 15 minutes, 120°C for 15 minutes, 150°C for 15 minutes, and 180°C for 15 minutes to obtain a blended resin film having a thickness of approximately 90 μm.

[0172] Using a stretching machine with a heating oven, the TD direction was used as the stretching direction at a temperature of 205°C, and the obtained film was fixed-end uniaxially stretched with a stretching ratio of 80% (the length of TD was 1.80 times that of the film before stretching) to obtain a stretched film with a thickness of 50 μm.

[0173] <Film 2>

[0174] In preparing the solution, 5.6 parts by weight of a triazine-based UV absorber ("ADK STAB LA-31RG" manufactured by ADEKA CORPORATION) and 0.002 parts by weight of an anthraquinone-based bluing agent ("Plast Blue 8590" manufactured by ARIMOTO CHEMICAL CO., LTD.) were added to a total of 100 parts by weight of the polyimide resin and acrylic resin. The coating thickness was adjusted to achieve a thickness of approximately 55 μm after drying, and the stretching conditions were changed to a stretching temperature of 215°C and a stretch ratio of 115%. A stretched film having a thickness of 25 μm was obtained by following the same procedures as for the preparation of Film 1, except for these changes.

[0175] <Film 3>

[0176] 100 parts by weight of polyimide resin 2 (PI2), 2.4 parts by weight of a triazine-based UV absorber ("Tinuvin 477" manufactured by BASF), and 0.0065 parts by weight of an anthraquinone-based bluing agent ("Plast Blue 8590" manufactured by Arimoto Chemical Co., Ltd.) were dissolved in dichloromethane to prepare a solution having a solids concentration of 10% by weight. This solution was applied to an alkali-free glass plate and heat-dried in an atmosphere at 40°C for 60 minutes, 80°C for 30 minutes, 150°C for 30 minutes, 170°C for 30 minutes, and 200°C for 60 minutes to obtain a transparent polyimide film having a thickness of 50 μm.

[0177] <Film 4>

[0178] As the film 4 , a commercially available biaxially stretched PET film having a thickness of 50 μm (“Lumirror U48” manufactured by Toray Industries, Ltd.) was used.

[0179] [Preparation of Hard Coat Composition]

[0180] <Preparation of Acrylic Hard Coat Composition>

[0181] To 100 parts by weight of dipentaerythritol hexaacrylate ("Aronix M-403" manufactured by Toagosei Co., Ltd.), 2 parts by weight of a photoradical polymerization initiator ("Omnirad 184" manufactured by IGM Resins) and 0.25 parts by weight of a polyether-modified silicone leveling agent ("BYK-300" manufactured by BYK) were added, and propylene glycol monomethyl ether was added as a diluent to obtain an acrylic hard coat composition having a solid content concentration of 50% by weight.

[0182] <Silicone-based hard coat composition>

[0183] 66.5 g (270 mmol) of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane ("SILQUEST A-186" manufactured by Momentive Performance Materials) and 16.5 g of 1-methoxy-2-propanol (PGME) were added to a reaction vessel equipped with a thermometer, a stirring device, and a reflux cooling tube and stirred evenly. A solution prepared by dissolving 0.039 g (0.405 mmol) of magnesium chloride as a catalyst in a mixture of 9.7 g (539 mmol) of water and 5.8 g of methanol was added dropwise to the mixture over a period of 5 minutes and stirred until uniform. The mixture was then heated to 80°C and subjected to a polycondensation reaction for 6 hours while stirring. After the reaction was completed, the solvent and water were distilled off using a rotary evaporator to obtain a condensate of the silane compound (polyorganosiloxane compound).

[0184] The GPC apparatus "HLC-8220GPC" manufactured by Tosoh Corporation (chromatographic column: TSKgel GMH XL ×2 pieces, TSKgel G3000H XL ,TSKgel G2000H XL The weight average molecular weight of the polystyrene conversion measured by ) was 3000. The 400 MHz-NMR manufactured by Bruker was used, and the 3-D acetone was used as the solvent. 1 The residual rate of epoxy groups calculated from H-NMR spectroscopy was 95% or more.

[0185] To 100 parts by weight of the above-mentioned polyorganosiloxane compound, 2 parts by weight of a sulfonium photoacid generator ("CPI-101A" manufactured by San-Apro) and 0.25 parts by weight of a polyether-modified silicone leveling agent ("BYK-300" manufactured by BYK) were added, and propylene glycol monomethyl ether was added as a diluent to obtain a silicone hard coat composition having a solid content concentration of 50% by weight.

[0186] [Production of Laminated Body]

[0187] <Example 1>

[0188] A 25 μm thick transparent adhesive sheet (“8146-1” manufactured by 3M, storage elastic modulus at 25°C and 1 Hz of 1.2×10 5 Pa) and the above-mentioned film 1 are pressed together with a rubber roller to produce a laminate of thin glass and film 1.

[0189] <Example 2>

[0190] The acrylic hard coating composition was applied to one side of the film 1 using a coater to a dry film thickness of 5 μm, and the solvent was removed at 120° C. Then, a high pressure mercury lamp was used in a nitrogen atmosphere at a cumulative light intensity of 1950 mJ / cm 2 The hard coating resin composition was cured by irradiating ultraviolet rays in a manner of 5 μm to obtain a hard coating film having an acrylic hard coating layer with a thickness of 5 μm.

[0191] A laminate of thin glass and hard coat film was produced in the same manner as in Example 1 except that the hard coat film was used instead of Film 1. The surface of the hard coat film not having the hard coat layer formed thereon was bonded to the thin glass.

[0192] <Example 3>

[0193] A laminate of thin glass and a hard coat film was produced in the same manner as in Example 2 except that the thickness of the acrylic hard coat layer was changed to 10 μm.

[0194] <Example 4>

[0195] A laminate of thin glass and a hard coat film was produced in the same manner as in Example 3, except that Film 2 was used instead of Film 1 in the production of the hard coat film.

[0196] <Example 5>

[0197] The silicone hard coating composition was applied to one side of the film 1 using a coater to a dry film thickness of 20 μm, and the solvent was removed at 120° C. Then, a high-pressure mercury lamp was used in a nitrogen atmosphere at a cumulative light intensity of 1950 mJ / cm 2 The hard coating resin composition was cured by irradiating with ultraviolet light to obtain a hard coating film having a 20 μm thick silicone hard coating layer. The hard coating film was laminated to thin glass in the same manner as in Example 2 to produce a laminate of thin glass and hard coating film.

[0198] <Comparative Example 1>

[0199] A laminate of thin glass and film 4 was produced in the same manner as in Example 1 except that film 4 (PET film) was used instead of film 1.

[0200] <Comparative Example 2>

[0201] A laminate of thin glass and a hard coat film was produced in the same manner as in Example 2, except that Film 4 was used instead of Film 1 in the production of the hard coat film.

[0202] <Comparative Example 3>

[0203] A laminate of thin glass and a hard coat film was produced in the same manner as in Example 2, except that Film 3 was used instead of Film 1 in the production of the hard coat film.

[0204] [Evaluation of transparent resin film]

[0205] Films 1 to 4 were subjected to the following evaluations.

[0206] <Tensile elastic modulus>

[0207] The film was cut into 10 mm wide strips and allowed to stand for one day at 23°C / 55% RH for humidity control. Tensile tests were then conducted using a Shimadzu Corporation "Autograph AGS-X" tensile testing machine under the following conditions to calculate the tensile modulus. Tensile tests were conducted in both the MD and TD directions.

[0208] Distance between fixtures: 100mm

[0209] Tensile speed: 20.0 mm / min

[0210] Measurement temperature: 23°C

[0211] <Refractive Index>

[0212] The film was cut into 3 cm squares, and the orientation angle was measured using a phase difference measuring device ("OPTIPRO 21-255MA" manufactured by Shintech Co., Ltd.) to determine the direction in which the refractive index is the largest. The refractive index in the TD direction of films 1, 2, and 4 is the largest, and the refractive index in the MD direction of film 3 is the largest. The refractive index nx in the direction with the largest refractive index and the refractive index ny in the direction orthogonal to it were measured using a prism coupler ("2010 / M" manufactured by Metricon). The refractive index at a wavelength of 589 nm obtained by Cauchy dispersion fitting the measured values ​​at wavelengths of 404 nm, 594 nm, and 827 nm was used as the refractive index of the film. Based on the refractive index obtained, the average refractive index n within the surface was calculated. ave =(nx+ny) / 2, and in-plane birefringence Δn=nx-ny.

[0213] [Evaluation of Laminated Body]

[0214] The following evaluations were performed on the laminated bodies of Examples and Comparative Examples.

[0215] <Total Light Transmittance and Haze>

[0216] The total light transmittance (TT) and haze were measured using a haze meter "HZ-V3" manufactured by Suga Test Instruments Co., Ltd. according to the method described in JIS K7361-1: 1999 and JIS K7136: 2000. A D65 light source was used for the measurement.

[0217] <Yellowness>

[0218] The yellowness (YI) was measured using a spectrocolorimeter SC-P manufactured by Suga Test Instruments Co., Ltd. in accordance with JIS K7373.

[0219] <Depression recovery>

[0220] According to JIS K5600, a pencil hardness test was conducted by scratching the film surface (in the case of a hard-coated film, the hard-coat surface) of the laminate with a pencil under a load of 750 gf and a speed of 60 mm / min. The film was observed for the presence of dents immediately after the test and 24 hours after the test. Seventeen types of pencils, ranging from 6B to 9H, were used, and the scratching direction was in the TD direction of the transparent resin film. The presence of dents was determined by visual observation of the transmitted and reflected light under illumination with a straight-tube three-wavelength fluorescent lamp. Deformation of the fluorescent lamp at the scratched area was considered to be present.

[0221] The scratch test was performed five times (at five locations) with a pencil of each hardness. If no indentation was observed at four or more locations (or if indentation was observed at one or less), the sample was judged to have indentation resistance appropriate to the pencil hardness. In Examples 1 to 3 and 5 and Comparative Examples 1 to 3, indentations were observed at two or more locations when scratched with a 6B pencil, and thus the indentation resistance (indentation immediately after the test) was designated "6B>" (less than 6B). In Example 4, indentation was observed at one or less locations when scratched with a 3B pencil, and at two or more locations when scratched with a 2B pencil, and thus the indentation immediately after the test was designated "3B."

[0222] For samples where dents were observed in more than two places, the presence or absence of dents was reconfirmed 24 hours after the scratch test, and samples with dents in one place or less were judged to have recovered from the dents. The highest pencil hardness at which the dents recovered was taken as the dents after 24 hours. In Comparative Examples 1 and 2, the dents were not recovered for those scratched with a 6B pencil, so the dents after 24 hours were set to "6B>". For the others, the highest hardness at which the dents recovered was taken as the dents after 24 hours. In Example 1, the dents recovered in the samples scratched with 2H to 6B pencils, but damage was observed on the film surface in any of the samples. In Examples 2 to 5 and Comparative Example 3, no damage was observed on the film surface (hard coating) for those where the dents recovered.

[0223] <Bending Test (Bending Resistance)>

[0224] The laminate was bent 180° around a cylindrical rod with a radius of 10 mm, with the thin glass side of the laminate as the outer surface and the film side as the inner surface. The laminate was then visually inspected to confirm its return to the stretched state. No cracks or breaks were observed in the laminates of the Examples and Comparative Examples, indicating good bending resistance.

[0225] Table 2 shows the configurations of the transparent resin films and the hard coat layers in the laminates of Examples and Comparative Examples, and the evaluation results of the transparent resin films and the laminates.

[0226] [Table 2]

[0227]

[0228] The laminates of the transparent resin films comprising the blended resins of Examples 1 to 5 had high total light transmittance, low haze and low YI, and excellent transparency, and also had good recovery from scratches caused by pencils with a hardness of 2H or higher.

[0229] Comparative Example 1 using a PET film as the transparent resin film also showed poor dent recovery even after scratching with a pencil having a hardness of 6B. The same was true for Comparative Example 2 using a hard coat film having a hard coat layer on a PET film.

[0230] The laminate of Comparative Example 3, which used a hard-coated film having a hard-coated layer on a transparent polyimide film, exhibited superior sag recovery compared to Comparative Examples 1 and 2, but inferior sag recovery compared to Examples 1 to 5, which used blended resin films of transparent polyimide and acrylic resin. Although Films 1 and 2 used in Examples 1 to 5 had lower tensile moduli than Film 3 used in Comparative Example 3, the laminates of Examples 1 to 5 exhibited superior sag recovery, suggesting that blending of transparent polyimide and acrylic resin tends to improve sag recovery.

[0231] A comparison between Example 2 and Examples 3 and 4, which used hard-coated films having a thicker hard-coat layer than Example 2, reveals that the thicker the hard-coat layer, the better the sag recovery performance. On the other hand, Example 1, which did not have a hard-coat layer on the transparent resin film, exhibited sag recovery performance comparable to that of Example 2, and Example 1 exhibited superior sag recovery performance compared to Comparative Examples 2 and 3, which had a hard-coat layer. This suggests that the fact that the transparent resin film constituting the laminate was a blended resin film significantly contributed to the improved sag recovery performance.

[0232] Comparison between Example 3 and Example 5 shows that the thicker the transparent resin film is, the better the dent recovery property tends to be.

[0233] The total light transmittance of the laminates of Examples 1 to 5, which used transparent polyimide and acrylic resin blended resin films, was 91.7% or higher, superior to the laminates of Comparative Examples 1 to 3. It is believed that the films 1 and 2 used in Examples 1 to 5 had a lower refractive index due to the blending of polyimide and acrylic resin, which reduced light reflection at the interface and thus improved the total light transmittance.

[0234] Description of Reference Numerals

[0235] 1 Transparent resin film

[0236] 3 Hard coating

[0237] 5. Transparent film (hard coating film)

[0238] 7 Thin Glass

[0239] 9 Transparent adhesive layer

[0240] 10 laminate

Claims

1. A laminate comprising a thin glass having a thickness of 100 μm or less and a transparent resin film bonded to one main surface of the thin glass. The transparent resin film includes a polyimide-based resin and a solvent-soluble resin other than the polyimide-based resin.

2. The laminate according to claim 1, wherein The refractive index of the transparent resin film is 1.600 or less.

3. The laminate according to claim 1 or 2, wherein The solvent-soluble resin is an acrylic resin. The laminate according to claim 3 , wherein: The acrylic resin is an acrylic resin containing methyl methacrylate as a main component.

5. The laminate according to claim 1 or 2, wherein The polyimide resin is a polyimide containing a structure derived from tetracarboxylic dianhydride and a structure derived from diamine. The tetracarboxylic dianhydride includes fluorine-containing aromatic tetracarboxylic dianhydride and alicyclic tetracarboxylic dianhydride. The diamine includes fluorine-containing diamine.

6. The laminate according to claim 1 or 2, wherein The transparent resin film is a stretched film.

7. The laminate according to claim 1 or 2, wherein The thickness of the transparent resin film is 20 to 55 μm.

8. The laminate according to claim 1 or 2, wherein The total light transmittance of the transparent resin film is above 90.5%. 9 . The laminate according to claim 1 , further comprising a hard coating layer on one main surface of the transparent resin film.

10. The laminate according to claim 9, wherein The hard coating layer is an acrylic hard coating layer.

11. The laminate according to claim 9, wherein The hard coating layer is a silicone hard coating layer.

12. The laminate according to claim 9, wherein The hard coating layer has a thickness of 1 to 50 μm. 13 . A display comprising the laminate according to claim 1 .

Images