Laminate and display

Abstract

A laminate (10) comprises a transparent resin film (1) which is affixed to one main surface of thin glass (7) having a thickness not more than 100 μm. A hard coat layer (3) may be provided to a main surface of the transparent resin film on the opposite side from the thin glass. The transparent resin film includes a polyimide resin and a solvent-soluble resin other than a polyimide resin. The polyimide resin contains: as a diamine component, a diamine having one or more structures selected from among CF3-O-, -(CF2-O)n-, and -O-(CF2-CF2-O)n- (where n is an integer of 1-20); and, as a tetracarboxylic dianhydride component, one or more tetracarboxylic dianhydrides selected from the group consisting of tetracarboxylic dianhydrides having a fluorene structure, tetracarboxylic dianhydrides having an ether bond, and bis(trimellitic anhydride) ester.

Description

Laminate and display

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

[0002] Thin, bendable glass is used as the cover window material for the surface of flexible displays. While glass has high optical transparency and can improve the visibility of display devices, concerns remain about the fragility of thin glass due to its thin thickness, which can be easily broken by strong impacts or cracks at the edges.

[0003] For the purpose of improving impact resistance and preventing glass shattering, it has been proposed to use a laminate formed by laminating a transparent resin film to the surface of thin glass as a cover window material. For example, Patent Document 1 proposes using a laminate formed by laminating thin glass and a transparent polyimide film with a hard coat as a cover window material for a flexible display. Because the transparent polyimide film has good mechanical properties, a laminate formed by laminating thin glass and a transparent polyimide film has excellent impact resistance and a function of preventing glass shattering, thereby providing high protection for the display.

[0004] International Publication No. 2021 / 177288

[0005] Although transparent polyimide films have excellent mechanical strength, laminates formed by bonding thin glass and transparent polyimide films can develop dents due to pressure or sliding caused by fingernails, touch pens, etc., and therefore there is a demand for improved dent resistance.

[0006] Furthermore, in recent years, the environmental persistence of organic fluorine compounds (PFAS) has become a problem. In general, the bond energy of the carbon-fluorine bond contained in organic fluorine compounds is high, making them difficult to decompose in the environment. In Patent Document 1, a transparent polyimide containing 2,2'-bis(trifluoromethyl)benzidine (TFMB) is used as a diamine component, but the structure in which the trifluoromethyl group is bonded to a carbon atom (-C-CF ３ ), or a structure in which carbon atoms are bonded to both sides of a difluoromethylene group (—C—CF ２Organic fluorine compounds containing fluorine atoms (C) have low decomposition properties in the environment and have been reported to have adverse effects on the human body.

[0007] In view of the above, an object of the present invention is to provide a laminate as a cover window material that uses a transparent resin film that is excellent in environmental safety and has excellent dent resistance.

[0008] The present invention relates to a laminate in which a transparent resin film is laminated to one main surface of a thin glass sheet having a thickness of 100 μm or less. The transparent resin film contains a polyimide resin and a solvent-soluble resin other than a polyimide resin.

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

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

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

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

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

[0014] The laminate may have a hard coat layer on the main surface of the transparent resin film opposite to the thin glass, and the thickness of the hard coat layer is, for example, 1 to 50 μm.

[0015] The laminate of the present invention has excellent transparency and dent resistance. In addition, since the polyimide resin contained in the transparent resin film contains a specific diamine as a diamine component, it has excellent environmental safety.

[0016] FIG. 2 is a cross-sectional view of a laminate according to one embodiment.

[0017] 1 is a cross-sectional view of a laminate according to one embodiment of the present invention. The laminate 10 includes a transparent film 5 on one main surface of a thin glass sheet 7. The thin glass sheet 7 and the transparent film 5 may be in direct contact with each other, or may be bonded together via an appropriate transparent adhesive layer 9. The transparent film 5 includes a transparent resin film 1. The transparent film 5 may be a hard coat film having a hard coat layer 3 on the main surface of the transparent resin film 1 opposite the thin glass sheet 7.

[0018] [Thin Glass] The thin glass 7 is a glass substrate (glass film) having a thickness of 100 μm or less. It has excellent mechanical strength and transparency characteristic of glass, while being flexible due to its small thickness. The glass material constituting the thin glass is not particularly limited, but chemically strengthened glass is preferred. Examples of glass constituting the chemically strengthened glass include aluminosilicate glass, soda-lime glass, borosilicate glass, lead glass, alkali barium glass, and aluminoborosilicate glass.

[0019] Chemically strengthened glass is glass whose mechanical strength is improved by partially exchanging the ionic species that make up the glass near the surface of the glass. By exchanging the ionic species, a strengthened layer with compressive stress is formed near the surface of the glass, resulting in thin glass that is less likely to break and has excellent mechanical properties. From the perspective of less likely to break, it is preferable that chemical strengthening be performed not only on the surface of the thin glass but also on the edge.

[0020] From the viewpoint of imparting flexibility (bendability), the thickness of the thin glass is 100 μm or less, preferably 60 μm or less, more preferably 55 μm or less, even more preferably 50 μm or less, and may be 40 μm or less, 35 μm or less, or 30 μm or less, from the viewpoint of ensuring bending resistance. From the viewpoint of ensuring mechanical properties, the thickness of the thin glass is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 15 μm or more, and may be 20 μm or more or 25 μm or more.

[0021] 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 be improved.

[0022] [Transparent Film] The transparent film 5 to be laminated onto the thin glass 7 includes a transparent resin film 1. The transparent film 5 may be made of the transparent resin film 1, or may have a functional layer such as a hard coat layer 3 on the transparent resin film 1 (the main surface opposite to the thin glass).

[0023] [Transparent Resin Film] The transparent resin film 1 contains one or more polyimide-based resins selected from the group consisting of polyimides and polyamideimides, and a solvent-soluble resin other than the polyimide-based resin (hereinafter, sometimes referred to as "other resin"). When the transparent resin film 1 contains the polyimide-based resin and the other resin, the transparency and dent resistance tend to be improved.

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

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

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

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

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

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

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

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

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

[0033] Examples of diamines not containing fluorine atoms include 2,2'-dimethylbenzidine, p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, and 3,4'-diaminodiphenyl sulfone. sulfone, 4,4'-diaminodiphenyl sulfone, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-di(3-amino phenyl)propane, 2,2-di(4-aminophenyl)propane, 2-(3-aminophenyl)-2-(4-aminophenyl)propane, 1,1-di(3-aminophenyl)-1-phenylethane, 1,1-di(4-aminophenyl)-1-phenylethane, 1-(3-aminophenyl)-1-(4-aminophenyl)-1-phenylethane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene , 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminobenzoyl)benzene, 1,3-bis(4-aminobenzoyl)benzene, 1,4-bis(3-aminobenzoyl)benzene, 1,4-bis(4-aminobenzoyl)benzene, 1,3-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(4-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(4-amino-α,α-dimethylbenzyl)benzene, 2,6-bis(3-aminophenoxy)benzonitrile, 2,6-bis(3-aminophenoxy)pyridine, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-amino 2,2-bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(3-aminophenoxy)benzoyl]benz benzene, 1,4-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 4 ,4'-bis[4-(4-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenyl sulfone, 4,4'-bis[4-(4-aminophenoxy)phenoxy]diphenyl sulfone, 3,3'-diamino-4,4'-diphenoxybenzophenone, 3,3 '-Diamino-4,4'-diviphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-biphenoxybenzophenone, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane, 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, α,ω-bis(3-aminopropyl)polydimethylsiloxane, α,ω-bis(3-aminobutyl)polydimethylsiloxane, bis(aminomethyl)ether, bis(2-aminoethyl)ether, bis(3-aminopropyl)ether, bis(2-aminomethoxy)ethyl]ether, bis[2-(2-aminoethoxy)ethyl]ether, bis[2-(3-aminoprotoxy)ethyl]ether, 1,2-bis(aminomethoxy)ethane, 1,2-bis(2-aminoethoxy)ethane, 1,2-bis[2-(aminomethoxy)ethoxy]ethane, 1,2-bis[2-(2-aminoethoxy)ethoxy]ethane, ethylene glycol bis(3-aminopropyl)ether, diethylene glycol bis(3-aminopropyl)ether, triethylene glycol bis(3-aminopropyl)ether, ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, trans 1,4-diaminocyclohexane, 1,2-di(2-aminoethyl)cyclohexane, 1,3-di(2-aminoethyl)cyclohexane, 1,4-di(2-aminoethyl)cyclohexane, bis(4-aminocyclohexyl)methane, isophoronediamine, 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane, 2,5-bis(aminomethyl)bicyclo[2.2.1]heptane, and the like.

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

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

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

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

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

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

[0040] The acid dianhydride having a fluorene structure is sufficient as long as it has at least one fluorene structure, and may have a fluorene structure and an aromatic ring other than fluorene, an alicyclic ring, or a chain structure in one molecule. When the polyimide resin contains a tetracarboxylic dianhydride having a fluorene structure as an acid dianhydride component, the dent resistance of the laminate tends to be improved.

[0041] Specific examples of acid dianhydrides having a fluorene structure include 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF), 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride (BPF-PA), N,N'-(9H-fluoren-9-ylidene-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxamide] (FDA-ATA), 5,5'-(9H-fluoren-9-ylidenebis(2-methyl-4,1-phenylene)bis[1,3-dihydro- bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate) (TBIS.MPN), 5,5'-spiro[9H-fluorene-9,9'-[9H]xanthene]-3',6'-diylbis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate (TBIS.RXN), spiro[fluorene-9,9'xanthene]-2',3',6',7'-tetracarboxylic dianhydride (SFDA), and the like. From the viewpoint of solubility in polyimide resins and compatibility with other resins, BPAF or BPF-PA is particularly preferred.

[0042] Examples of acid dianhydrides having an ether bond include 3,4'-oxydiphthalic anhydride (a-ODPA), 4,4'-oxydiphthalic anhydride (s-ODPA), 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride (BPADA), etc. From the viewpoints of solubility in polyimide resins and compatibility with other resins, BPADA is particularly preferred.

[0043] The bis(trimellitic anhydride) ester is represented by the following general formula (1).

[0044]

[0045] X in general formula (1) is any divalent organic group, and carboxy groups are bonded to carbon atoms of X at both ends of X. The carbon atoms bonded to the carboxy groups may form a ring structure.

[0046] Specific examples of bis(trimellitic anhydride) esters include bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'diyl (TAHMBP), p-phenylenebis(trimellitic acid monoester anhydride) (TMHQ), and bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-biphenyl. Examples of suitable bis(trimellitic anhydride) esters include TAHMBP, TMHQ, and OCBP-TME, and 5,5'-(3,3'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate) (BP-TME), tert-butylhydroquinone bis(trimellitate anhydride) (TA.BHQ), and trimethylhydroquinone bis(trimellitate anhydride) (TA.TMHQ). From the viewpoint of solubility of polyimide resins, preferred bis(trimellitic anhydride) esters are TAHMBP, TMHQ, and OCBP-TME, with TAHMBP being particularly preferred.

[0047] From the viewpoint of UV resistance of the polyimide-based resin, among the specific acid dianhydrides, acid dianhydrides having a fluorene structure and acid dianhydrides having an ether bond are preferred, and from the viewpoint of improving dent resistance, acid dianhydrides having a fluorene structure are particularly preferred.

[0048] From the viewpoint of making the polyimide resin soluble in organic solvents, the total amount of specific acid dianhydrides relative to the total amount of acid dianhydride components is preferably 15 mol% or more, more preferably 20 mol% or more, even more preferably 25 mol% or more, and may be 30 mol% or more, 35 mol% or more, 40 mol% or more, 45 mol% or more, or 50 mol% or more.The total amount of specific acid dianhydrides relative to the total amount of acid dianhydride components may be 100 mol%, or may be 95 mol% or less, 90 mol% or less, 85 mol% or less, 80 mol% or less, 75 mol% or less, or 70 mol% or less.From the viewpoint of improving dent resistance, it is preferable that the content of acid dianhydrides having a fluorene structure is within the above range.

[0049] The polyimide resin may contain an acid dianhydride other than the specific acid dianhydride as the acid dianhydride component. Examples of such an acid dianhydride include alicyclic tetracarboxylic acid dianhydrides and aromatic tetracarboxylic acid dianhydrides. From the viewpoint of environmental safety of the polyimide resin, -C-CF ３ and -C-CF ２ Those which do not contain —C— are preferred, and those which do not contain a fluorine atom are particularly preferred.

[0050] The alicyclic tetracarboxylic dianhydride may have at least one alicyclic structure, and may have both an alicyclic ring and an aromatic ring in one molecule. The alicyclic ring may be polycyclic or may have a spiro structure. Examples of the alicyclic tetracarboxylic dianhydride include 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic acid-3,4:3',4'-dianhydride, and 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic acid-3,4:3',4'-dianhydride. hydrate, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic acid dianhydride, 2,2'-binorbornane-5,5',6,6'tetracarboxylic acid dianhydride, 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic acid-1,4:2,3-dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4- Tetrahydronaphthalene-1,2-dicarboxylic anhydride, cyclohexane-1,4-diylbis(methylene)bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate), 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 5,5'-[cyclohexylidenebis(4,1-phenyleneoxy)]bis-1,3-isobenzofurandione, 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-di Oxo-,5,5'-[1,4-cyclohexanediylbis(methylene)]ester, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, 3,5,6-tricarboxynorbornane-2-acetic acid 2,3:5,6-dianhydride, decahydro-1,4,5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic dianhydride, tricyclo[6.4.0.0(2,7)]dodecane-1,8:2,Examples of suitable dianhydrides include 7-tetracarboxylic acid dianhydride, octahydro-1H,3H,8H,10H-biphenyleno[4a,4b-c:8a,8b-c']difuran-1,3,8,10-tetraone, ethylene glycol bis(hydrogenated trimellitic anhydride) ester, and decahydro[2]benzopyrano[6,5,4,-def][2]benzopyran-1,3,6,8-tetraone. By including an alicyclic tetracarboxylic acid dianhydride in addition to a specific dianhydride as the dianhydride component, the mechanical strength of the polyimide resin tends to be improved. Furthermore, by including an alicyclic tetracarboxylic acid dianhydride as the dianhydride component in the polyimide resin, the compatibility of the polyimide resin with other resins tends to be enhanced.

[0051] Among alicyclic tetracarboxylic dianhydrides, from the viewpoint of transparency and mechanical strength of polyimide resins, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (H-PMDA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetracarboxylic dianhydride, and 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetracarboxylic dianhydride are preferred. Tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA-100), bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BEDA), bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride (BODA), and 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic acid-3,4:3',4'-dianhydride (H-BPDA) are preferred. Among these, from the viewpoint of mechanical strength, tetracarboxylic anhydrides in which two acid anhydride groups are bonded to one alicyclic ring are preferred, and CBDA is particularly preferred.

[0052] When an alicyclic tetracarboxylic dianhydride is used in addition to the specific acid dianhydride, the amount of the alicyclic tetracarboxylic dianhydride relative to the total amount of the acid dianhydride components may be 1 mol% or more, 3 mol% or more, 5 mol% or more, 10 mol% or more, 12 mol% or more, or 15 mol% or more. The greater the amount of alicyclic tetracarboxylic dianhydride, the higher the mechanical strength tends to be. From the viewpoint of ensuring the solubility of the polyimide-based resin in organic solvents, the amount of the alicyclic tetracarboxylic dianhydride relative to the total amount of the acid dianhydride components is preferably 80 mol% or less, more preferably 60 mol% or less, and even more preferably 50 mol% or less, and may be 40 mol% or less, 30 mol% or less, or 20 mol% or less. Furthermore, polyimide-based resins containing an alicyclic tetracarboxylic dianhydride within the above range as an acid dianhydride component tend to have excellent compatibility with other resins.

[0053] Examples of aromatic tetracarboxylic dianhydrides other than the specific acid dianhydrides include pyromellitic dianhydride (PMDA), 1,2,3,4-benzenetetracarboxylic dianhydride (MPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4' 2,3,3',4'-biphenyltetracarboxylic dianhydride (s-BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA), 2,2',3,3',-biphenyltetracarboxylic dianhydride (i-BPDA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 5,5'-dimethylmethylenebis(phthalic anhydride), 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, terphenyltetracarboxylic dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, and bis(3,4-dicarboxyphenyl)sulfone dianhydride. Among these aromatic tetracarboxylic dianhydrides, a-BPDA, s-BPDA, i-BPDA, PMDA, MPDA, and DSDA are preferred from the viewpoint of improving mechanical strength.

[0054] When an aromatic tetracarboxylic dianhydride other than the specific acid dianhydride is used in addition to the specific acid dianhydride, the amount of the aromatic tetracarboxylic dianhydride other than the specific acid dianhydride relative to the total amount of the acid dianhydride components may be 1 mol% or more, 3 mol% or more, 5 mol% or more, 10 mol% or more, 12 mol% or more, or 15 mol% or more. From the viewpoint of ensuring the solubility of the polyimide resin in organic solvents, the amount of the aromatic tetracarboxylic dianhydride other than the specific acid dianhydride relative to the total amount of the acid dianhydride components is preferably 80 mol% or less, more preferably 60 mol% or less, and even more preferably 50 mol% or less, and may be 40 mol% or less, 30 mol% or less, or 20 mol% or less.

[0055] The polyimide resin may contain, as an acid dianhydride component, a chain aliphatic tetracarboxylic dianhydride such as ethylene tetracarboxylic dianhydride, 1,2,3,4-butane tetracarboxylic dianhydride, or meso-butane-1,2,3,4-tetracarboxylic dianhydride.

[0056] The amount of the fluorine atom-containing acid dianhydride relative to the total amount of the acid dianhydride components in the polyimide resin is preferably 30 mol% or less, more preferably 20 mol% or less, and even more preferably 10 mol% or less, and may be 5 mol% or less, 1 mol% or less, or 0.5 mol% or less. The polyimide resin may not contain a fluorine atom-containing acid dianhydride as an acid dianhydride component.

[0057] Among fluorine atom-containing acid dianhydrides, the structure in which a trifluoromethyl group is bonded to a carbon atom (-C-CF ３ ) and / or a structure in which carbon atoms are bonded to both ends of a difluoromethylene group (—C—CF ２ -C-) has low decomposition properties and is a concern for environmental safety. ３ - or -C(CF ３ ) ２Acid dianhydrides having a structure in which - is directly bonded (for example, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 9,9-bis(trifluoromethyl)xanthenetetracarboxylic dianhydride, 9-trifluoromethylxanthenetetracarboxylic dianhydride) are poorly degradable in the environment, and therefore, from the viewpoint of environmental safety of polyimide-based resins, it is preferable that these acid dianhydrides are substantially not contained. ３ - or -C(CF ３ ) ２ The amount of acid dianhydride to which - is directly bonded is preferably less than 0.5 mol %, and may be 0.3 mol % or less, 0.1 mol % or less, or 0.05 mol % or less, or may be 0.

[0058] (Polybasic Acid) As described above, the polyimide resin may be a polyamideimide in which a part of the tetracarboxylic dianhydride component is replaced with a polybasic acid derivative. Examples of the polybasic acid include dicarboxylic acid and tricarboxylic acid anhydrides.

[0059] Examples of dicarboxylic acids include aliphatic dicarboxylic acids such as adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-oxybisbenzoic acid, 4,4'-biphenyldicarboxylic acid, and 2-fluoroterephthalic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-hexahydroterephthalic acid, hexahydroisophthalic acid, 1,3-cyclopentanedicarboxylic acid, and bi(cyclohexyl)-4,4'-dicarboxylic acid; and heterocyclic dicarboxylic acids such as 2,5-thiophenedicarboxylic acid and 2,5-furandicarboxylic acid.

[0060] Examples of tricarboxylic acids include trimellitic anhydride derivatives such as trimellitic anhydride, 2-fluorotrimellitic anhydride, 5-fluorotrimellitic anhydride, 6-fluorotrimellitic anhydride, 2,5-difluorotrimellitic anhydride, 2,6-difluorotrimellitic anhydride, 5,6-difluorotrimellitic anhydride, and 2,5,6-trifluorotrimellitic anhydride.

[0061] From the viewpoint of the solubility of the polyamideimide, the polybasic acid is preferably an aromatic dicarboxylic acid, an alicyclic dicarboxylic acid, or trimellitic anhydride, and particularly preferably an aromatic dicarboxylic acid. Among the aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, 4,4'-biphenyldicarboxylic acid, and 4,4'-oxybisbenzoic acid are preferred, with terephthalic acid and isophthalic acid being preferred, and terephthalic acid being particularly preferred.

[0062] In preparing polyamide-imide and its precursor, polyamic acid, a polybasic acid derivative is used. Examples of the polybasic acid derivative include dicarboxylic acid dichlorides, dicarboxylic acid esters, dicarboxylic acid anhydrides, and tricarboxylic acid anhydride chlorides. Among these, dicarboxylic acid dichlorides and tricarboxylic acid anhydride chlorides are preferred due to their high reactivity.

[0063] From the viewpoint of the solubility of the polyamideimide and its compatibility with other resins, the ratio of the polybasic acid derivative to the total of the tetracarboxylic dianhydride and the polybasic acid derivative is preferably 40 mol % or less, more preferably 35 mol % or less, and even more preferably 30 mol % or less. The polyimide resin may be a polyimide in which the ratio of the dicarboxylic acid derivative is 0 (i.e., does not contain a structure derived from a dicarboxylic acid derivative).

[0064] (Content of specific fluorine structure in polyimide resin) As described above, the diamine component is CF ３ -O-, -(CF ２ -O) ｎ -, and -O-(CF ２ -CF ２ -O) ｎ-, and containing, as an acid dianhydride component, one or more acid dianhydrides (specific acid dianhydrides) selected from the group consisting of acid dianhydrides having a fluorene structure, acid dianhydrides having an ether bond, and bis(trimellitic anhydride) esters, -C-CF ３ , -C-CF ２ It is substantially free of structures such as —C— and exhibits solubility in organic solvents.

[0065] In order to reduce the environmental persistence of fluorine-containing compounds, it is preferable that the polyimide resin contains a small amount of monomers having a specific fluorine structure. The specific fluorine structure is a monomer having at least one completely fluorinated methyl group (CF ３ -) or methylene (-CF ２ -) A structure containing a carbon atom (not bonded to any of H, Cl, Br, or I) excluding those having only the components of the following structural formula (i) or (ii): CF ３ -X (i) X-CF ２ -X' (ii)

[0066] X in formula (i) and (ii) is —OR or —NRR′, and X′ in formula (ii) is —CH ３ , -CH ２ R, R', R'' and R''' are each independently -H, -CH ３ , -CH ２ -, aromatic, or -C(O)-.

[0067] From the viewpoint of improving environmental degradability, the amount of fluorine atoms contained in the specific fluorine structure per 1 kg of the polyimide resin is preferably less than 500 mg, more preferably less than 300 mg, even more preferably less than 100 mg, and particularly preferably less than 50 mg.

[0068] (Preparation of Polyimide Resin) Polyamic acid as a polyimide precursor is obtained by the reaction of an acid dianhydride with a diamine, and polyimide is obtained by cyclodehydration (imidization) of the polyamic acid. The method for preparing polyamic acid is not particularly limited, and any known method can be used. For example, a polyamic acid solution can be obtained by dissolving diamine and tetracarboxylic dianhydride in approximately equimolar amounts (molar ratio of 90:100 to 110:100) in an organic solvent and stirring the mixture.

[0069] When preparing polyamide-imide, in addition to a diamine and a tetracarboxylic dianhydride, a polybasic acid derivative such as a dicarboxylic dichloride may be used as a monomer. In this case, the amounts of the respective monomers may be adjusted so that the total amount of the tetracarboxylic dianhydride and the polybasic acid derivative is approximately equimolar to the diamine.

[0070] As described above, by adjusting the composition of the polyimide resin, i.e., the types and ratios of the acid dianhydrides and diamines, the polyimide resin has transparency and solubility in organic solvents, and also exhibits compatibility with other resins.

[0071] The concentration of the polyamic acid solution is usually 5 to 35% by weight, preferably 10 to 30% by weight. When the concentration is within this range, the polyamic acid obtained by polymerization has an appropriate molecular weight, and the polyamic acid solution has an appropriate viscosity.

[0072] In the polymerization of polyamic acid, it is preferable to add the acid dianhydride to the diamine in order to suppress ring-opening of the acid dianhydride. When adding multiple types of diamines or multiple types of acid dianhydrides, they may be added all at once or in multiple portions. The physical properties of the polyimide resin can also be controlled by adjusting the order of addition of the monomers.

[0073] The organic solvent used in the polymerization of polyamic acid is not particularly limited, as long as it does not react with the diamine and the acid dianhydride and can dissolve the polyamic acid. Examples of organic solvents include urea solvents such as methylurea and N,N-dimethylethylurea; sulfoxide or sulfone solvents such as dimethyl sulfoxide, diphenyl sulfone, and tetramethyl sulfone; amide solvents such as N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N,N'-diethylacetamide, N-methyl-2-pyrrolidone (NMP), γ-butyrolactone, and hexamethylphosphoric triamide; alkyl halide solvents such as chloroform and methylene chloride; aromatic hydrocarbon solvents such as benzene and toluene; and ether solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, and p-cresol methyl ether. These solvents are typically used alone or in combination as needed. From the viewpoint of the solubility and polymerization reactivity of polyamic acid, DMAc, DMF, NMP, etc. are preferably used.

[0074] Polyimide resins are obtained by dehydration cyclization of polyamic acid. One method for preparing polyimide resins from polyamic acid solutions is to add a dehydrating agent, an imidization catalyst, etc. to the polyamic acid solution and allow imidization to proceed in the solution. To accelerate the imidization process, the polyamic acid solution may be heated. Mixing a solution containing the polyimide resin produced by imidization of polyamic acid with a poor solvent results in the polyimide resin being precipitated as a solid. Isolating the polyimide resin as a solid allows impurities generated during the synthesis of the polyamic acid, as well as residual dehydrating agents and imidization catalysts, to be washed and removed with the poor solvent, preventing discoloration and increased yellowness of the polyimide resin. Furthermore, isolating the polyimide resin as a solid allows the use of solvents suitable for film formation, such as low-boiling point solvents, when preparing a solution for film production.

[0075] The molecular weight of the polyimide resin (weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC)) is preferably 10,000 to 500,000, more preferably 100,000 to 400,000, still more preferably 100,000 to 300,000, and particularly preferably 150,000 to 300,000. If the molecular weight is too small, the strength of the film may be insufficient. If the molecular weight is too large, the compatibility with other resins may be poor.

[0076] The polyimide resin is preferably soluble in a low-boiling point solvent such as a ketone solvent or an alkyl halide solvent. The solubility of a polyimide resin in a solvent means that the polyimide resin is soluble in a concentration of 5% by weight or more. In one embodiment, the polyimide resin is soluble in methylene chloride. Methylene chloride has a low boiling point and allows easy removal of residual solvent during film production. Therefore, by using a polyimide resin soluble in methylene chloride, improved film productivity can be expected.

[0077] From the viewpoint of the thermal stability and light stability of the transparent resin film, it is preferable that the polyimide resin has low reactivity. The acid value of the polyimide resin is preferably 0.4 mmol / g or less, more preferably 0.3 mmol / g or less, and even more preferably 0.2 mmol / g or less. The acid value of the polyimide resin may be 0.1 mmol / g or less, 0.05 mmol / g or less, or 0.03 mmol / g or less. From the viewpoint of reducing the acid value, it is preferable that the polyimide resin has a high imidization rate. A low acid value tends to increase the stability of the polyimide resin and improve its compatibility with other resins.

[0078] <Other Resins> As described above, the transparent resin film 1 contains, in addition to the polyimide-based resin, a resin other than the polyimide-based resin ("other resin"). The other resin is not particularly limited as long as it is soluble in an organic solvent and can be mixed with the polyimide-based resin to form a transparent film, and examples include resins that are compatible with the polyimide-based resin and resins that form a microphase-separated structure such as a sea-island structure, a cylindrical structure, or a lamellar structure. Among these, the other resin is preferably one that is compatible with the polyimide-based resin. When the polyimide-based resin and the other resin are compatible with each other, the film tends to have high transparency and excellent mechanical properties such as elastic modulus and pencil hardness, regardless of the processing conditions.

[0079] Examples of the other resin include acrylic resins, polycarbonate resins, polyester resins, polyamide resins, polyether resins, cellulose resins, silicone resins, and cyclic olefin resins. A plurality of these resins may be used. Because of their high compatibility with polyimide resins, acrylic resins, polycarbonate resins, and polyester resins are preferred as the other resin. Among these, acrylic resins are particularly preferred because of their high compatibility with polyimide resins, low refractive index, and ease of forming a high-hardness film.

[0080] (Acrylic Resin) Examples of the acrylic resin include poly(meth)acrylic acid esters such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymers, methyl methacrylate-(meth)acrylic acid ester copolymers, methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymers, methyl (meth)acrylate-styrene copolymers, copolymers of methyl (meth)acrylate with a monomer having a benzotriazole skeleton or a benzophenone skeleton, etc. The acrylic resin may be modified to introduce a glutarimide structural unit or a lactone ring structural unit.

[0081] From the viewpoints of transparency, compatibility with polyimide resins, and mechanical strength of molded articles such as films, it is preferable that the acrylic resin has methyl methacrylate as its main structural unit. The amount of methyl methacrylate relative to the total amount of monomer components in the acrylic resin is preferably 60% by weight or more, and may be 70% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. The acrylic resin may be a homopolymer of methyl methacrylate. From the viewpoints of transparency and light resistance, the ratio of aromatic ring-containing monomers relative to the total amount of monomer components in the acrylic resin is preferably 5 mol% or less, and may be 3 mol% or less, or 1 mol% or less. The acrylic resin may not contain aromatic ring-containing monomers.

[0082] The acrylic resin may be modified by introducing an imide structure or a lactone ring structure. Such modified polymers are preferably those obtained by introducing an imide structure or a lactone ring structure into an acrylic polymer having a methyl methacrylate content within the above range. That is, in the acrylic resin modified by introducing an imide structure or a lactone ring structure, the total amount of methyl methacrylate and the modified structure of methyl methacrylate is preferably 60% by weight or more, and may be 70% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. The modified polymer may be a methyl methacrylate homopolymer into which an imide structure or a lactone ring structure has been introduced.

[0083] 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.

[0084] From the viewpoints of solubility in organic solvents, compatibility with polyimide resins, and film strength, the weight average molecular weight (polystyrene equivalent) of the acrylic resin is preferably 5,000 to 500,000, more preferably 10,000 to 300,000, and even more preferably 15,000 to 200,000.

[0085] From the viewpoint of the thermal stability and light stability of the film, it is preferable that the acrylic resin have a low content of reactive functional groups such as ethylenically unsaturated groups and carboxyl groups. The iodine value of the acrylic resin is preferably 10.16 g / 100 g (0.4 mmol / g) or less, more preferably 7.62 g / 100 g (0.3 mmol / g) or less, and even more preferably 5.08 g / 100 g (0.2 mmol / g) or less. The iodine value of the acrylic resin may be 2.54 g / 100 g (0.1 mmol / g) or less or 1.27 g / 100 g (0.05 mmol / g) or less. The acid value of the acrylic resin is preferably 0.4 mmol / g or less, more preferably 0.3 mmol / g or less, and even more preferably 0.2 mmol / g or less. The acid value of the acrylic resin may be 0.1 mmol / g or less, 0.05 mmol / g or less, or 0.03 mmol / g or less. A small acid value tends to increase the stability of the acrylic resin and improve the compatibility with the polyimide resin.

[0086] Since acrylic resins generally have a lower refractive index than polyimide resins, transparent resin films containing polyimide resins and acrylic resins tend to have a lower refractive index and less reflection at the interface than films made of polyimide resin alone, resulting in a higher total light transmittance. From the viewpoint of reducing the refractive index of the film, the refractive index of the acrylic resin is preferably 1.550 or less, more preferably 1.520 or less, and even more preferably 1.500 or less.

[0087] (Polyester Resin) Polyester is a condensation product of dicarboxylic acid and diol, and has a structure derived from dicarboxylic acid and a structure derived from diol. The dicarboxylic acid component and diol component of polyester are not particularly limited, but from the viewpoint of solubility in organic solvents, amorphous polyesters are preferred. Polyethylene terephthalate (PET), a typical polyester, is a condensation product of ethylene glycol and terephthalic acid, and has high crystallinity and low solubility in organic solvents, whereas amorphous polyesters are soluble in organic solvents and exhibit high compatibility with the above-mentioned polyimide resins. Transparent resin films containing polyimide resins and polyester resins tend to have excellent bending resistance and, when laminated with thin glass, have excellent dent resistance.

[0088] From the viewpoint of imparting solubility to the polyester resin in organic solvents, the diol component of the polyester resin is preferably a diol having a chain alkylene group having 3 or more carbon atoms which may be branched, a diol having a chain alkenylene group having 3 or more carbon atoms which may be branched, a polyalkylene glycol, or a diol having a cyclic structure. Hereinafter, these diols will be referred to as "specific diols."

[0089] Examples of diols having a chain alkylene structure of 3 or more carbon atoms which may have a branch include propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, etc. Among these, diols having a chain alkylene structure of 5 or more carbon atoms are preferred, and diols having an alkylene group with a branched structure such as neopentyl glycol are particularly preferred. Examples of diols having a chain alkenylene group of 3 or more carbon atoms which may have a branch include 2-butene-1,4-diol, etc.

[0090] Examples of polyalkylene glycols include diethylene glycol, triethylene glycol, dipropylene glycol, and polytetramethylene ether glycol.

[0091] Examples of diols having a cyclic structure include diols having a cycloalkylene structure such as 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol; diols having a cyclic ether structure such as isosorbide; diols having a fluorene structure; and diols having a bisphenol derivative structure.

[0092] Among these, butanediol, neopentyl glycol, polytetramethylene ether glycol, diols having a fluorene structure, and diols having a bisphenol derivative structure are preferred from the viewpoint of solubility of polyester resins and compatibility with polyimide resins.

[0093] Specific examples of diols having a fluorene structure include 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 9,9-bis[4-(2-hydroxypropoxy)phenyl]fluorene, 9,9-bis[4-[2-(2-hydroxyethoxy)ethoxy]phenyl]-9H-fluorene, 2,2'-[(9H-fluorene-9,9-diyl)bis(naphthalene-6,2-diyloxy)]diethanol, 9,9-bis[4-(2-hydroxyethoxy)-3-phenylphenyl]fluorene, 9,9-bis[4-(2-hydroxypropoxy)-3-phenylphenyl]fluorene, and 9,9-bis{4-[2-(2-hydroxyethoxy)ethoxy]-3-phenylphenyl}fluorene. Among these, from the viewpoint of improving heat resistance, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 9,9-bis[4-(2-hydroxypropoxy)phenyl]fluorene, and 9,9-bis[4-(2-hydroxyethoxy)-3-phenylphenyl]fluorene are preferred.

[0094] The diol having bisphenol derivative structure is the one in which alkylene oxide is added to two phenolic hydroxyl groups of bisphenol (bisphenol alkylene oxide adduct), and preferably the ethylene oxide (EO) adduct and propylene oxide (PO) adduct of bisphenol.In addition, the diol having fluorene structure includes the diol having bisphenol derivative structure, but the diol having fluorene structure is treated as the diol having fluorene structure even if it has bisphenol derivative structure.

[0095] Examples of bisphenols that do not have a fluorene structure include 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 1,1-bis(4-hydroxyphenyl)-1-phenylethane (bisphenol AP), 2,2-bis(4-hydroxyphenyl)butane (bisphenol B), bis(4-hydroxyphenyl)diphenylmethane (bisphenol BP), 2,2-bis(3-methyl-4-hydroxyphenyl)propane (bisphenol C), 1,1-bis(4-hydroxyphenyl)ethane (bisphenol E), bis(4-hydroxyphenyl)methane (bisphenol F), and 2,2-bis(4-hydroxy-3-isopropyl bisphenol G), 1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene (bisphenol M), bis(4-hydroxyphenyl)sulfone (bisphenol S), 1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene (bisphenol P), 5,5'-(1-methylethylidene)-bis[1,1'(bisphenyl)-2-ol]propane (bisphenol PH), 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (bisphenol TMC), 1,1-bis(4-hydroxyphenyl)cyclohexane (bisphenol Z), and the like.

[0096] Among the bisphenol alkylene oxide adducts, from the viewpoint of solubility in polyester, ethylene oxide adducts of bisphenol A, ethylene oxide adducts of bisphenol S, and ethylene oxide adducts of bisphenol Z are preferred.

[0097] The polyester may contain a diol other than the above-mentioned specific diol as a diol component. An example of a diol other than the specific diol is ethylene glycol. When the specific diol and ethylene glycol are used in combination, from the viewpoint of compatibility between the polyester and the polyimide resin, the molar ratio of the specific diol to ethylene glycol is preferably 90:10 to 10:90, and may be 80:20 to 20:80, or 60:40 to 40:60. In other words, the amount of the specific diol relative to the total amount of the diol component is preferably 10 mol% or more, and may be 20 mol% or more, or 40 mol% or more.

[0098] The dicarboxylic acid component of the polyester resin is not particularly limited, and various aromatic dicarboxylic acids and aliphatic dicarboxylic acids can be used. As the dicarboxylic acid, an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid can be used in combination.

[0099] Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, and biphenyldicarboxylic acid.Further examples of aromatic dicarboxylic acids include dicarboxylic acids having a fluorene skeleton, such as 9,9-bis(carboxymethyl)fluorene and 9,9-bis(2-carboxyethyl)fluorene.

[0100] From the viewpoint of improving the solubility and mechanical strength of the polyester resin, terephthalic acid and isophthalic acid are preferred as aromatic dicarboxylic acids. Terephthalic acid and isophthalic acid may be used alone or in combination. When terephthalic acid and isophthalic acid are used in combination, from the viewpoint of the solubility of the polyester, the molar ratio of terephthalic acid to isophthalic acid is preferably 90:10 to 10:90, and may be 25:75 to 75:25 or 60:40 to 40:60. From the viewpoint of the solubility and mechanical strength of the polyester, the total amount of terephthalic acid and isophthalic acid relative to the total amount of dicarboxylic acid components of the polyester is preferably 30 mol% or more, more preferably 40 mol% or more, even more preferably 60 mol% or more, and may be 80 mol% or more.

[0101] Examples of aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, fumaric acid, maleic acid, itaconic acid, citraconic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, and tetrahydrophthalic acid.

[0102] Inclusion of an aliphatic dicarboxylic acid as the dicarboxylic acid component of a polyester resin may improve the compatibility between the polyester resin and the polyimide resin. From the viewpoint of improving compatibility with the polyimide resin, the aliphatic dicarboxylic acid is preferably a dicarboxylic acid having 6 to 12 carbon atoms, particularly 6 to 10 carbon atoms, and among these, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid are preferred because they can also contribute to improving the solubility of the polyester resin.

[0103] Monomers other than diols and dicarboxylic acids may be used as monomer components constituting the polyester resin, as long as the effects of the present invention are not impaired. Examples of monomers other than diols and dicarboxylic acids include polyols having three or more hydroxy groups (e.g., trimethylolpropane, glycerin), monoalcohols (e.g., octyl alcohol, decyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, 2-phenoxyethanol), polycarboxylic acids having three or more carboxy groups (e.g., 1,3,4-benzenetricarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid, pyromellitic acid, trimellitic acid, tetrahydrophthalic acid), monocarboxylic acids (e.g., lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, p-tert-butylbenzoic acid, cyclohexanoic acid), and hydroxycarboxylic acids (e.g., methyl methyl esters). Examples of such an acid include compounds having one or more hydroxy groups and / or one or more carboxy groups, such as lactic acid, glycolic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxyisobutyric acid, 2-hydroxy-2-methylbutyric acid, 2-hydroxyvaleric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxycaproic acid, 10-hydroxystearic acid, 4-hydroxyphenylstearic acid, and 4-(β-hydroxy)ethoxybenzoic acid), lactones (e.g., β-propiolactone, β-butyrolactone, γ-butyrolactone, δ-valerolactone, and ε-caprolactone), and oxiranes (e.g., ethylene oxide), as well as compounds that generate one or more hydroxy groups and / or one or more carboxy groups upon hydrolysis.

[0104] The polymerization method for the polyester resin is not particularly limited, and various known methods can be used, such as a method in which an oligomer is obtained by a transesterification method or a direct esterification method, and then melt polymerization or solid-phase polymerization is performed. In the polymerization of the polyester resin, a dicarboxylic acid derivative such as an acid anhydride may be used as the dicarboxylic acid component.

[0105] From the viewpoint of ensuring the mechanical strength of the film, the weight-average molecular weight of the polyester resin is preferably greater than 10,000, more preferably 15,000 or more, even more preferably 20,000 or more, and may be 30,000 or more. From the viewpoint of ensuring compatibility with the polyimide resin and formability into a film, the weight-average molecular weight of the polyester resin is preferably 200,000 or less, more preferably 150,000 or less, even more preferably 100,000 or less, and may be 80,000 or less.

[0106] From the viewpoint of heat resistance and formability of the film, the glass transition temperature (Tg) of the polyester resin is preferably −25 to 200° C., more preferably 15 to 180° C., even more preferably 40 to 150° C., and may be about 60 to 130° C.

[0107] Commercially available polyester resins may be used. Examples of commercially available polyester resins containing a specific diol as a diol component include OKP4HT (manufactured by Osaka Gas Chemicals, Mw: 38,000, Tg: 142°C), OKP4 (manufactured by Osaka Gas Chemicals, Mw: 40,000, Tg: 121°C), Elitel UE3200G (manufactured by Unitika, Mw: 43,000, Tg: 65°C), Elitel UE3210 (manufactured by Unitika, Mw: 62,000, Tg: 45°C), Elitel UE3240 (manufactured by Unitika, Mw: 50,000, Tg: 40°C), Elitel UE3500 (manufactured by Unitika, Mw: 83,000, Tg: 15°C), Elitel UE3510 (manufactured by Unitika, Mw: 63,000, Tg: -25°C), Elitel UE3 600 (manufactured by Unitika, Mw: 60,000, Tg: 75°C), Elitel UE3690 (manufactured by Unitika, Mw: 46,000, Tg: 90°C), Elitel UE9100 (manufactured by Unitika, Mw: 77,000, Tg: 19°C), Elitel UE9200 (manufactured by Unitika, Mw: 39,000, Tg: 65°C), Elitel UE980 ...800 (manufactured by Unitika, Mw: 46,000, Tg: 90°C), Elitel UE9800 (manufactured by Unitika, Mw: 46,000, Tg: 90°C), Elitel UE9800 (manufactured by Unitika, Mw: Examples of such copolymers include Vylon 200 (manufactured by Nichika, Mw: 40,000, Tg: 85°C), Vylon 200 (manufactured by Toyobo, Mw: 42,000, Tg: 67°C), Vylon 240 (manufactured by Toyobo, Mw: 35,000, Tg: 60°C), Vylon 290 (manufactured by Toyobo, Mw: 61,000, Tg: 72°C), and Vylon 600 (manufactured by Toyobo, Mw: 38,000, Tg: 47°C).

[0108] <Composition of Transparent Resin Film> As described above, the transparent resin film contains a polyimide-based resin and other resins as resin components. The ratio of the polyimide-based resin to the other resins in the transparent resin film is not particularly limited. The mixing ratio (weight ratio) of the polyimide-based resin to the other resins may be 98:2 to 2:98, 95:5 to 10:90, 90:10 to 15:85, or 65:35 to 50:50. The higher the ratio of the polyimide-based resin, the higher the elastic modulus and pencil hardness of the film, and the more excellent the mechanical strength. The higher the ratio of the other resin, the less coloring of the film, the higher the total light transmittance, the smaller the yellowness index (YI), and the more transparent the film tends to be.

[0109] In order to fully exert the effect of improving transparency by mixing the polyimide-based resin with the other resin, the ratio of the other resin to the total of the polyimide-based resin and the other resin is preferably 10 to 90% by weight, more preferably 15 to 85% by weight, and even more preferably 20 to 80% by weight, and may be 30 to 70% by weight, 35 to 65% by weight, or 40 to 60% by weight.

[0110] In addition to the above resin components, the transparent resin film may contain organic or inorganic low-molecular-weight compounds, etc. The transparent resin film may also contain additives such as bluing agents, ultraviolet absorbers, flame retardants, stabilizers, crosslinking agents, surfactants, leveling agents, plasticizers, and fine particles.

[0111] The transparent resin film may contain organic fine particles such as polystyrene or crosslinked acrylic resin, or inorganic fine particles such as silica or layered silicate, for the purpose of improving blocking resistance or adjusting the refractive index. However, the incorporation of fine particles can cause a decrease in the transmittance of the film or an increase in haze. In particular, silicon oxides such as silica are useful for lowering the refractive index of the film, but they tend to be poorly dispersed in the resin matrix, which can cause a decrease in transparency, mechanical strength, and flex resistance. Therefore, the content of silicon oxide is preferably 5 parts by weight or less, more preferably 1 part by weight or less, more preferably 0.5 parts by weight or less, and may even be 0.1 parts by weight or less, per 100 parts by weight of the total resin components.

[0112] <Preparation of Transparent Resin Film> The method for forming the transparent resin film is not particularly limited, but a solution method in which a solution containing the above-mentioned polyimide resin and other resins is applied to a support and the solvent is then dried and removed is preferred.

[0113] The solvent is not particularly limited as long as it exhibits solubility in both polyimide resins and other resins. 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 alkyl halide solvents such as chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene, dichlorobenzene, and methylene chloride. Among these, ketone solvents and alkyl halide solvents are preferred because they have excellent solubility in polyimide resins and the like, have low boiling points, and allow for easy removal of residual solvent during film production.

[0114] As a method for applying the resin solution onto a support, a known method using a bar coater, a comma coater, or the like can be applied. As the support, a glass substrate, a metal substrate such as SUS, a metal drum, a metal belt, a plastic film, or the like can be used. From the viewpoint of improving productivity, it is preferable to use an endless support such as a metal drum or a metal belt, or a long plastic film, or the like, as the support, and produce the film by a roll-to-roll method. When using a plastic film as the support, it is only necessary to appropriately select a material that is insoluble in the solvent of the resin solution (dope).

[0115] It is preferable to heat the film when drying the solvent. The heating temperature is not particularly limited as long as it can remove the solvent and prevent the resulting film from becoming discolored, and is appropriately set between room temperature and about 250°C, with 50°C to 220°C being preferred. The heating temperature may be increased in stages. To increase the efficiency of solvent removal, the resin film may be peeled off from the support and dried after drying has progressed to a certain extent. Drying may be carried out in air or nitrogen. Heating may be carried out under reduced pressure to promote solvent removal.

[0116] The film may be stretched in one or more directions for the purpose of improving the mechanical strength, etc. Stretching the film orients the polymer chains in the stretching direction, which tends to improve the strength of the film in the in-plane direction, suppress the occurrence of breakage or cracking in the film, and improve dent resistance.

[0117] Although films made solely of acrylic resins may have low toughness, the strength of the film may be improved by using a compatible system of polyimide resin and acrylic resin. Furthermore, when a film made of a compatible system of polyimide resin and other resin is stretched, the tensile modulus in the stretching direction tends to increase, and as a result, the flex resistance tends to improve.

[0118] For example, films used as cover windows or substrate materials for foldable displays are repeatedly folded along the folding axis at the same location, and therefore are required to have high mechanical strength in a direction perpendicular to the folding axis. Therefore, by arranging the film so that the stretching direction is perpendicular to the folding axis, even when the film is repeatedly folded, breakage or cracking of the film at the folding location is unlikely to occur, and a device with high bending resistance can be provided.

[0119] The conditions for stretching the film are not particularly limited. For example, the stretching temperature is about ±40°C of the glass transition temperature of the film, and may be about 120 to 300°C, 150 to 250°C, or 180 to 230°C. The stretching ratio is about 1 to 200%, and may be 5 to 150%, 10 to 120%, or 20 to 100%. The higher the stretching ratio, the higher the tensile modulus in the stretching direction tends to be. On the other hand, if the stretching ratio is excessively high, the mechanical strength in the direction perpendicular to the stretching direction tends to decrease, and the handleability of the film may be reduced.

[0120] The film may be biaxially stretched to increase the strength in any in-plane direction. The biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. In biaxial stretching, the stretching ratio in one direction and the stretching ratio in the perpendicular direction may be the same or different. When a difference in stretching ratio is made, the mechanical strength in the direction with the larger stretching ratio tends to be relatively larger. When a biaxially stretched film with anisotropic stretching ratio is used in a foldable device, it is preferable to arrange it so that the direction with the larger stretching ratio is perpendicular to the folding axis.

[0121] The thickness of the transparent resin film is not particularly limited and may be appropriately set depending on the application. The thickness of the transparent resin film is, for example, 5 to 300 μm. From the viewpoint of achieving both self-supporting properties and flexibility and providing a highly transparent film, the thickness of the transparent resin film is preferably 10 to 100 μm, and may also 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.

[0122] <Characteristics of Transparent Resin Film> The transparent resin film preferably has a single glass transition temperature in differential scanning calorimetry (DSC) and / or dynamic mechanical analysis (DMA). When the polyimide resin contained in the transparent resin film is compatible with other resins, the transparent resin film exhibits a single glass transition temperature.

[0123] The haze of the transparent resin film is preferably 10% or less, more preferably 5% or less, and even more preferably 4% or less, and may be 3.5% or less, 3% or less, 2% or less, 1% or less, or 0.5% or less. When the transparent resin film contains a polyimide-based resin and another resin, a low haze can be achieved by using, as the other resin, an acrylic-based resin, a polyester-based resin, or the like that has high compatibility with the polyimide-based resin.

[0124] The total light transmittance of the transparent resin film is preferably 88.0% or more, more preferably 89.0% or more, even more preferably 90.0% or more, and may be 90.5% or more, 91.0% or more, or 91.2% or more. The higher the total light transmittance, the higher the white brightness of the display and the more excellent the visibility. As mentioned above, by mixing a polyimide-based resin with another resin, the refractive index tends to be lower and the total light transmittance tends to be higher compared to when the polyimide-based resin is used alone.

[0125] The yellowness index (YI) of the transparent resin film is preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.0 or less. The yellowness index (YI) of the transparent resin film is preferably −3.0 or more, more preferably −2.0 or more, and even more preferably −1.0 or more. By mixing a polyimide-based resin with another resin such as an acrylic-based resin or a polyester-based resin, the coloring of the film tends to be less and the absolute value of YI tends to be smaller than when a polyimide-based resin is used alone.

[0126] The refractive index of the transparent resin film is not particularly limited, but is preferably 1.600 or less from the viewpoint of improving total light transmittance. The refractive index of the transparent resin film is more preferably 1.580 or less, and even more preferably 1.560 or less. The refractive index of the transparent resin film is generally 1.400 or more, and may be 1.500 or more, 1.530 or more, or 1.540 or more.

[0127] The refractive index of a film containing only polyimide resin as a resin component is generally higher than 1.600, resulting in a large amount of light reflection (high reflectance) due to the difference in refractive index at the air interface and at the interface with other components, resulting in a low light transmittance. A mixed resin system of a polyimide resin and another resin with a lower refractive index than the polyimide resin has a lower refractive index than the polyimide resin alone, reducing light reflection at the interface and increasing the total light transmittance. In particular, since acrylic resins have a low refractive index, using an acrylic resin as the other resin tends to lower the refractive index of the transparent resin film and increase the total light transmittance.

[0128] Since a stretched film tends to have a large refractive index in the stretching direction (the orientation direction of the polymer chain), when the transparent resin film is a stretched film, it may have in-plane refractive index anisotropy. The in-plane refractive index difference of the transparent resin film (the difference between the maximum and minimum in-plane refractive index) may be 0.005 or more, 0.010 or more, 0.020 or more, or 0.030 or more. When the transparent resin film has refractive index anisotropy, it is preferable that the average value of the maximum in-plane refractive index (generally the refractive index in the stretching direction) and the minimum in-plane refractive index is within the above range.

[0129] The tensile modulus of the transparent resin film is preferably 3.0 GPa or more, more preferably 3.5 GPa or more, even more preferably 4.5 GPa or more, and may be 5.0 GPa or more, 5.5 GPa or more, or 6.0 GPa or more. The higher the tensile modulus, the more excellent the mechanical strength such as hardness and flex resistance tends to be.

[0130] The transparent resin film may have anisotropy in the tensile modulus in the plane. When the transparent resin film is a stretched film, the tensile modulus in the stretching direction tends to be greater than the tensile modulus in the direction perpendicular to the stretching direction. When the transparent resin film is a biaxially stretched film or a fixed-end uniaxially stretched film, the tensile modulus in all directions in the plane may be greater than before stretching. When the transparent resin film has an in-plane anisotropy in the tensile modulus, it is preferable that the maximum in-plane tensile modulus (generally the tensile modulus in the stretching direction) is within the above range.

[0131] When the transparent resin film has anisotropy in tensile modulus, the tensile modulus in the direction in which the tensile modulus is greatest (generally the direction in which the stretching ratio is large) may be 4.0 GPa or more, 4.5 GPa or more, or 5.0 GPa or more. The difference between the maximum and minimum in-plane tensile modulus may be 0.5 GPa or more, 1.0 GPa or more, or 1.3 GPa or more. The greater the difference between the maximum and minimum in-plane tensile modulus, the more excellent the dent resistance may be.

[0132] [Hard Coat Layer] The transparent film 5 may consist of only the transparent resin film 1, or may be provided as a laminate having various functional layers on one or both main surfaces. Examples of functional layers include a hard coat layer, an ultraviolet absorbing layer, an adhesive layer, a refractive index adjusting layer, and an easy-adhesion layer. When a laminate of thin glass and a 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. By providing a hard coat layer on the surface of the transparent resin film, the scratch resistance and hardness of the laminate are improved.

[0133] <Hard Coating Material> The material constituting the hard coating layer is not particularly limited as long as it has the function of preventing the occurrence of scratches, and examples thereof include polyester-based, acrylic-based, urethane-based, amide-based, siloxane-based, and epoxy-based resins. Among these, an acrylic hard coating layer which is a cured product of an acrylic hard coating resin composition, or a siloxane hard coating layer which is a cured product of a siloxane hard coating resin composition is preferred from the viewpoint of preventing the occurrence of scratches.

[0134] (Acrylic Hard Coat Material) The acrylic hard coat material contains a monomer or oligomer having a (meth)acryloyl group in the molecule as a curable resin component. The molecular weight of the acrylic monomer or oligomer is, for example, about 200 to 10,000. The acrylic hard coat material can control hardness, scratch resistance, bending resistance, optical properties, etc. by combining multiple types of monomers or oligomers having a (meth)acryloyl group. From the viewpoint of curability by photoradical polymerization, it is preferable that the hard coat material have an acryloyl group.

[0135] Specific examples of oligomers having a (meth)acryloyl group include urethane (meth)acrylate, polyester (meth)acrylate, and epoxy (meth)acrylate. The oligomer may have two or more (meth)acryloyl groups in one molecule. The molecular weight of the oligomer is preferably 10,000 or less.

[0136] Examples of acrylic monomers include compounds having one (meth)acryloyl group, such as methyl (meth)acrylate and 2-ethylhexyl (meth)acrylate; and compounds having two (meth)acryloyl groups in one molecule, such as ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, and 1,6-hexanediol di(meth)acrylate. Compounds having (meth)acryloyl groups include compounds having three or more (meth)acryloyl groups in one molecule, such as glycerin tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0137] From the viewpoint of enhancing the scratch resistance of the hard coat layer, the acrylic hard coat material preferably contains a trifunctional or higher polyfunctional (meth)acrylate. The functional group equivalent of the (meth)acryloyl group of the polyfunctional (meth)acrylate, i.e., the molecular weight per (meth)acryloyl group, is preferably 80 to 150 g / eq. Among the above-exemplified polyfunctional (meth)acrylates, dipentaerythritol hexa(meth)acrylate is particularly preferred.

[0138] (Siloxane-based hard coat material) The siloxane-based hard coat material contains a curable compound having a siloxane bond as a curable resin component. From the viewpoint of scratch resistance, the siloxane-based curable compound preferably has an epoxy group as a polymerizable functional group, and among them, a polyorganosiloxane compound containing an alicyclic epoxy group is preferred. Such siloxane-based hard coat materials are disclosed in WO2014 / 204010, WO2018 / 096729, WO2020 / 040209, etc., and these descriptions can be used for reference.

[0139] Siloxane-based hard coat materials having alicyclic epoxy groups as polymerizable functional groups have little shrinkage upon curing, so curling and cracking are unlikely to occur even if the hard coat layer is made thick.

[0140] The polyorganosiloxane compound having an alicyclic epoxy group can be obtained by condensation of a silane compound represented by the general formula (4): [Y-Si(OR １ ) ｘ R ２ ３－ｘ ] (4)

[0141] In general formula (4), R １ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an isopropyl group, an isobutyl group, a cyclohexyl group, and an ethylhexyl group.

[0142] The silane compound represented by the general formula (4) has two or three (—OR１ ) Si—OR １ Since R is hydrolyzable, a polyorganosiloxane compound can be obtained by condensation of the silane compound. １ The number of carbon atoms in R is preferably 3 or less, １ is particularly preferably a methyl group.

[0143] In general formula (4), R ２ is a hydrogen atom or a monovalent hydrocarbon group selected from the group consisting of alkyl groups having 1 to 10 carbon atoms, aryl groups having 6 to 25 carbon atoms, and aralkyl groups having 7 to 12 carbon atoms. Specific examples of the hydrocarbon group include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, isopropyl, isobutyl, cyclohexyl, ethylhexyl, benzyl, phenyl, tolyl, xylyl, naphthyl, and phenethyl groups.

[0144] In the general formula (4), x is 2 or 3. When x=3 (i.e., three alkoxy groups (or hydroxy groups) -OR １ is bonded), the silane compound is ２ It does not have. From the viewpoint of forming a network-like polyorganosiloxane compound and increasing the number of epoxy groups contained in the polyorganosiloxane compound to increase the hardness of the cured film, it is preferable that x = 3 in the general formula (4). A silane compound where x = 2 and a silane compound where x = 3 may be used in combination. Furthermore, for the purpose of adjusting the molecular weight of the polyorganosiloxane compound obtained by condensation, a silane compound where x is 1 may be used in addition to a silane compound where x is 2 or 3.

[0145] In general formula (4), Y is a monovalent organic group containing an alicyclic epoxy group. Examples of Y include an alicyclic epoxy group, an alkyl group having an alicyclic epoxy group as a substituent, and an alkylene glycol group having an alicyclic epoxy group as a substituent. From the viewpoint of heat resistance and flex resistance, an alkyl group having an alicyclic epoxy group as a substituent is preferred.

[0146] Specific examples of alkyl groups having an alicyclic epoxy group as a substituent include a (3,4-epoxycyclohexyl)methyl group, a 2-(3,4-epoxycyclohexyl)ethyl group, a 3-(3,4-epoxycyclohexyl)propyl group, a 4-(3,4-epoxycyclohexyl)butyl group, a 5-(3,4-epoxycyclohexyl)pentyl group, a 6-(3,4-epoxycyclohexyl)hexyl group, a 7-(3,4-epoxycyclohexyl)heptyl group, an 8-(3,4-epoxycyclohexyl)octyl group, a 9-(3,4-epoxycyclohexyl)nonyl group, a 10-(3,4-epoxycyclohexyl)decyl group, an 11-(3,4-epoxycyclohexyl)undecyl group, and a 12-(3,4-epoxycyclohexyl)dodecyl group.

[0147] Specific examples of the silane compound represented by general formula (4) include (3,4-epoxycyclohexyl)trimethoxysilane, (3,4-epoxycyclohexyl)methyldimethoxysilane, (3,4-epoxycyclohexyl)dimethylmethoxysilane, (3,4-epoxycyclohexyl)triethoxysilane, (3,4-epoxycyclohexyl)methyldiethoxysilane, (3,4-epoxycyclohexyl)dimethylethoxysilane, {(3,4-epoxycyclohexyl)methyl}trimethoxysilane, {(3,4-epoxycyclohexyl)methyl}methyldimethoxysilane, {(3,4-epoxycyclohexyl)methyl}dimethylmethoxysilane, {(3,4-epoxycyclohexyl)methyl}dimethylmethoxysilane, {(3,4-epoxycyclohexyl)methyl}triethoxysilane, {(3,4-epoxycyclohexyl)methyl}methyldiethoxysilane, {(3,4-epoxycyclohexyl)methyl}dimethylethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}trimethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}methyldimethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}dimethylmethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}triethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}methyldiethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}dimethylethoxysilane, etc. Among these, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane is preferred from the viewpoints of ease of condensation reaction and hardness of the cured product.

[0148] The polyorganosiloxane compound as the condensate of the silane compound may be a condensate of the silane compound of the general formula (4) with another silane compound.

[0149] The silane compound is reacted with water to form a Si—OR １ The part is hydrolyzed, and the hydrolyzate is condensed to form an Si—O—Si bond, producing a condensate of the silane compound having an alicyclic epoxy group (a polyorganosiloxane compound).

[0150] From the viewpoint of increasing the hardness of the cured film (hard coat layer), the weight average molecular weight of the polyorganosiloxane compound is preferably 500 or more. Also, from the viewpoint of suppressing volatilization, the weight average molecular weight of the polyorganosiloxane compound is preferably 500 or more. On the other hand, if the molecular weight is excessively large, cloudiness may occur due to a decrease in compatibility with other components in the composition. Therefore, the weight average molecular weight of the polyorganosiloxane compound is preferably 20,000 or less.

[0151] <Polymerization initiator> The hard coat composition preferably contains a polymerization initiator in addition to the above-mentioned curable resin component. As the polymerization initiator, a photopolymerization initiator is preferable. An acrylic hard coat composition containing a compound having a (meth)acryloyl group as a curable resin component preferably contains a photoradical polymerization initiator that generates radicals by light. A siloxane hard coat composition containing a polyorganosiloxane compound having an epoxy group as a curable resin component preferably contains a photoacid generator (photocationic polymerization initiator) that generates acid by light.

[0152] Examples of the photoradical polymerization initiator include 2,2-dimethoxy-2-phenylacetophenone, acetophenone, benzophenone, xanthone, 3-methylacetophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, benzoin propyl ether, benzil dimethyl ketal, N,N,N',N'-tetramethyl-4,4'-diaminobenzophenone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, and other thioxanthan-based compounds.

[0153] Examples of the photoacid generator include onium salts which combine anions (strong acids) such as antimony hexafluoride, boron tetrafluoride, phosphorus hexafluoride, fluoroalkyl phosphorus fluoride, and fluoroalkyl gallium fluoride with cations such as sulfonium, ammonium, phosphonium, iodonium, and selenium; iron-arene complexes; silanol-metal chelate complexes; sulfonic acid derivatives such as disulfones, disulfonyldiazomethanes, disulfonylmethanes, sulfonylbenzoylmethanes, imide sulfonates, and benzoin sulfonates; and organic halogen compounds.

[0154] <Other Components Constituting the Hard Coat Composition> The hard coat composition for forming the hard coat layer may contain, in addition to the curable resin component and the polymerization initiator, a solvent and various additives. Examples of the additives include a fluorine-based or silicone-based leveling agent, a sensitizer, a reactive diluent, fine particles, a filler, a dispersant, a plasticizer, an ultraviolet absorber, a surfactant, an antioxidant, a colorant, and a viscosity modifier.

[0155] <Formation of Hard Coat Layer> A hard coat composition is applied to a transparent resin film 1, and the solvent is dried and removed as necessary, followed by curing to form a hard coat layer 3. Methods for applying the hard coat composition include roll coating such as bar coating, gravure coating, and comma coating, die coating such as slot die coating and fountain die coating, spin coating, spray coating, and dip coating. Before applying the curable resin composition, the surface of the transparent resin film may be subjected to a surface treatment such as corona treatment or plasma treatment. Furthermore, an easy-adhesion layer or the like may be provided on the surface of the transparent resin film.

[0156] When the hard coat composition is irradiated with active energy rays or heated, active species such as acids and radicals are generated from the photopolymerization initiator, and the curable resin component of the hard coat composition is cured. From the viewpoint of curing reactivity, it is preferable that the curable resin composition contains a photopolymerization initiator and is cured by irradiation with active energy rays. Examples of active energy rays irradiated during photocuring include visible light, ultraviolet light, infrared light, X-rays, α-rays, β-rays, γ-rays, and electron beams. Ultraviolet light is preferred as the active energy ray because of its high curing reaction rate and excellent energy efficiency. The cumulative irradiation dose of the active energy ray is, for example, 50 to 10,000 mJ / cm. ２ The curing temperature is about 150° C., and may be set depending on the type and amount of the photocationic polymerization initiator, the thickness of the hard coat layer, etc. The curing temperature is not particularly limited, but is usually 150° C. or lower.

[0157] The thickness of the hard coat layer 3 is 1 to 50 μm, preferably 3 μm or more, and more preferably 5 μm or more. The thicker the hard coat layer, the more improved the pencil hardness and scratch resistance tend to be. On the other hand, if the hard coat layer is too thick, the flex resistance decreases, so the thickness of the hard coat layer is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less.

[0158] [Transparent Adhesive Layer] In the laminate 10 having a transparent film 5 on a thin glass sheet 7, the thin glass sheet 7 and the transparent film 5 (transparent resin film 1) may be in direct contact with each other, or the thin glass sheet 7 and the transparent film 5 may be bonded together via an appropriate transparent adhesive layer 9. When the thin glass sheet 7 and the transparent film 5 are bonded together via the transparent adhesive layer 9, the stress relaxation effect of the transparent adhesive layer 9 tends to improve the bending resistance and flexibility of the laminate 10 when it is bent.

[0159] 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 adhesives include solvent-type adhesives, reactive adhesives that react and harden with heat or active energy rays, and hot-melt adhesives. Examples of adhesive materials 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.

[0160] Since the thickness between the transparent film 5 and the thin glass 7 can be kept constant, a pressure-sensitive adhesive layer in which an adhesive or pressure-sensitive adhesive is pre-formed into a film shape is preferred as the transparent adhesive layer 9. Among these, a double-sided pressure-sensitive adhesive sheet is preferred because it can be attached as is without the need for a curing reaction. The double-sided pressure-sensitive adhesive sheet may be a substrate-attached pressure-sensitive adhesive sheet in which pressure-sensitive adhesive layers are provided on both sides of a transparent substrate film, or a substrate-less pressure-sensitive adhesive sheet consisting only of a pressure-sensitive adhesive layer. From the viewpoints of transparency and thinness, a substrate-less pressure-sensitive adhesive sheet is preferred. An example of a substrate-less pressure-sensitive adhesive sheet is an optically transparent adhesive tape called OCA (Optical Clear Adhesive).

[0161] The thickness of the transparent adhesive layer is preferably 5 μm or more, more preferably 10 μm or more, and more preferably 20 μm or more, and is preferably 500 μm or less, more preferably 100 μm or less, and more 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 providing stress relaxation performance when the laminate is bent, the storage modulus of the transparent adhesive layer at a temperature of 25° C. and a frequency of 1 Hz is 1×10 ４ Pa or less is preferable, and 5 × 10 ５ Pa or less is more preferable.

[0162] [Laminate] In the laminate 10 in which the transparent film 5 is bonded onto the thin glass 7, the transparent film 5 has the function of preventing glass fragments from scattering if the thin glass 7 is broken. Furthermore, the transparent film 5 (transparent resin film 1) has superior bending resistance compared to glass.

[0163] 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, but from the viewpoint of improving impact resistance and dent resistance, it is preferably 50 μm or more, more preferably 80 μm or more, even more preferably 90 μm or more, and may be 100 μm or more or 110 μm or more. From the viewpoint of bendability, the total thickness of the laminate 10 is preferably 200 μm or less, more preferably 180 μm or less.

[0164] 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 preferable in terms of improving the visibility of the display and improving the color tone.

[0165] The haze of the laminate 10 is preferably 1.5% or less, more preferably 1% or less, even more preferably 0.7% or less, and may be 0.5% or less. The total light transmittance of the laminate 10 is preferably 89.0% or more, more preferably 89.5% or more, even more preferably 90.0% or more, and may be 90.5% or more, 90.8% or more, 91.0% or more, 91.2% or more, or 91.5% or more.

[0166] Polyimide-based transparent resin films have higher mechanical strength than transparent resin films such as polyethylene terephthalate, so laminates comprising a polyimide-based transparent resin film on thin glass have excellent impact resistance. On the other hand, transparent polyimide is slightly yellow-colored, 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, it is possible to reduce coloration and lower the YI.

[0167] In addition, polyimide-based transparent resin films have a low total light transmittance because polyimide-based resins have a high refractive index and high reflectance at the interface between the film and air and at the interface between the film and the hard coat layer. Blending polyimide-based resins with other resins such as acrylic resins reduces the refractive index and reduces the reflectance at the interface, thereby increasing the total light transmittance.

[0168] The laminate 10, in which the transparent film 5 is bonded to the thin glass 7, preferably has a property (dent resistance) that makes it difficult for dents to form on the surface of the transparent film 5 due to external forces. The dent resistance is evaluated by determining whether a dent is present immediately after scratching the transparent film side surface of the laminate using a pencil of a predetermined hardness used in pencil hardness testing under conditions of a load of 750 gf and a speed of 60 mm / min. The lowest hardness at which no dent is present is the evaluation value for dent resistance. The dent resistance (pencil hardness) of the laminate 10 is preferably 6B or higher, more preferably 5B or higher, and may be 4B or higher or 3B or higher.

[0169] A laminate 10 has high dent resistance, and is formed by laminating a transparent resin film 1 containing a polyimide resin containing a specific diamine and a specific acid dianhydride and another resin onto a thin glass 7. Furthermore, the transparent film 5 has a tendency to have improved dent resistance by providing a hard coat layer 3 on the transparent resin film 1.

[0170] In blends of polyimide resins with other resins, it is believed that the other resins provide a moderate degree of flexibility, and that the intermolecular interactions between the polyimide resin and the other resins allow the absorption of external forces, thereby contributing to improved dent resistance.

[0171] In particular, when the polyimide resin contains an acid dianhydride having a fluorene structure as the specific acid dianhydride, dent resistance tends to be improved. Polyimide resins have strong intermolecular interactions, and imide rings tend to be oriented parallel to the in-plane direction of the film. On the other hand, polyimide resins having a structure derived from an acid dianhydride having a fluorene structure tend to have fluorene rings oriented in a plane perpendicular to the orientation direction of the polymer main chain. Therefore, polyimide resins having a fluorene structure have high strength not only in the film plane but also in the film thickness direction, and have high resistance to deformation when an external force is applied to the laminate, which is thought to result in excellent dent resistance. When the transparent resin film is a stretched film, the above orientation is enhanced, and therefore dent resistance is thought to be further improved.

[0172] The laminate 10 preferably has flex resistance and is resistant to breakage or cracking due to bending. It is preferable that the laminate 10 is free from breakage or cracking after being folded 180° at a radius of 10 mm with the transparent film 5 facing inward and then returned to its original flat state.

[0173] The laminate of the present invention has excellent transparency and flex resistance, and further has dent resistance, so that it can be suitably used as a cover window to be placed on the surface of an image display panel. The laminate of the present invention has high degradability and excellent environmental safety because the polyimide resin contained in the transparent resin film is substantially free of a specific fluorine structure.

[0174] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following, the flow direction during coating is defined as the MD direction, and the direction perpendicular to the MD direction is defined as the TD direction.

[0175] [Preparation of Polyimide Resin] Dimethylformamide (DMF) was placed in a separable flask and stirred under a nitrogen atmosphere. Diamine and tetracarboxylic dianhydride were added in the ratios (mol %) shown in Table 1, and the mixture was stirred under a nitrogen atmosphere for 5 to 10 hours to react, yielding a polyamic acid solution with a solids concentration of 18 wt %.

[0176] To 100 g of polyamic acid solution, 5.5 g of pyridine was added as an imidization catalyst. After complete dispersion, 8 g of acetic anhydride was added and the mixture was stirred at 90°C for 3 hours. After cooling to room temperature, 100 g of 2-propyl alcohol (IPA) was added at a rate of 2-3 drops / second while stirring the solution, resulting in the precipitation of polyimide. An additional 150 g of IPA was added, and the mixture was stirred for approximately 30 minutes. Afterwards, the mixture was subjected to suction filtration using a Kiriyama funnel. The resulting solid was washed with IPA and then dried for 12 hours in a vacuum oven set at 120°C to obtain polyimide resins 1, 2, and 3 (PI1, PI2, and PI3). The weight-average molecular weight of PI1 was 290,000.

[0177] In Table 1, the compounds are described by the following abbreviations. <Diamines> TFMOB: 2,2'-bis(trifluoromethoxy)benzidine TFMB: 2,2'-bis(trifluoromethyl)benzidine DDS: 3,3'-diaminodiphenyl sulfone <Tetracarboxylic acid dianhydrides> BPAF: 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride TAHMBP: bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'diyl 6FDA: 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride CBDA: 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride ODPA: 4,4'-oxydiphthalic dianhydride

[0178]

[0179] [Preparation of Transparent Resin Film] <Film 1> Polyimide resin 1 (PI1) and a commercially available acrylic resin ("Parapet G" manufactured by Kuraray; a copolymer of methyl methacrylate / methyl acrylate (monomer ratio 87 / 13), glass transition temperature 109°C, acid value 0.0 mmol / g, molecular weight 100,000; hereinafter referred to as "acrylic resin" (Ac)) were dissolved in methylene chloride at a weight ratio of PI1 / Ac = 50 / 50, and 5.6 parts by weight of a triazine-based ultraviolet absorber ("ADK STAB LA-31RG" manufactured by ADEKA Corporation) and 0.018 parts by weight of a phthalocyanine-based bluing agent ("ET 4B403" manufactured by Dainichiseika Chemicals & Chemicals Co., Ltd.) were added and dissolved per 100 parts by weight of the solids content (total of PI1 and Ac) to prepare a solution with a solids concentration of 11% by weight. This solution was applied to a non-alkali glass plate and dried by heating in an atmospheric 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 blend resin film having a thickness of approximately 105 μm.

[0180] The obtained film was subjected to fixed-end uniaxial stretching using a stretching machine equipped with a heating oven at a temperature of 215°C with the TD direction as the stretching direction and a stretch ratio of 115% (the TD length was 2.15 times that of the film before stretching) to obtain a stretched film with a thickness of 50 μm.

[0181] <Film 2> A solution was prepared in the same manner as in the production of Film 1, except that a commercially available polyester resin ("Elitel UE3600" manufactured by Unitika Co., Ltd.; polyester containing a bisphenol alkylene oxide adduct as a diol component, weight average molecular weight 60,000, glass transition temperature 75°C; hereinafter referred to as "polyester resin" (PEs)) was used instead of the acrylic resin in the preparation of the solution, and the solid content concentration was set to 10 wt%. The solution was then coated and dried to obtain a blend resin film with a thickness of 105 µm. A stretched film with a thickness of 50 µm was obtained in the same manner as in the production of Film 1, except that the stretching temperature was changed to 170°C.

[0182] <Film 3> Except for changing the polyimide resin to PI2 and not adding the ultraviolet absorber or bluing agent in the solution preparation, a solution with a solids concentration of 11 wt % was prepared in the same manner as in the production of Film 1. Using this solution, a stretched film with a thickness of 50 μm was obtained in the same manner as in the production of Film 1, except for changing the coating thickness so that the thickness after drying would be approximately 90 μm, and changing the stretching conditions to a stretching temperature of 205° C. and a stretching ratio of 80%.

[0183] <Film 4> 100 parts by weight of polyimide resin 3 (PI3), 2.4 parts by weight of a triazine-based ultraviolet absorber (BASF's "Tinuvin 477"), and 0.0065 parts by weight of an anthraquinone-based bluing agent (Arimoto Chemical Industry's "Plast Blue 8590") were dissolved in methylene chloride to prepare a solution with a solids concentration of 10 wt%. This solution was applied to an alkali-free glass plate and dried by heating in an atmospheric 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 with a thickness of 50 μm.

[0184] [Production of Laminate] Example 1 (Preparation of Acrylic Hard Coat Composition) To 100 parts by weight of dipentaerythritol hexaacrylate ("Aronix M-403" manufactured by Toa Gosei Co., Ltd.), 2 parts by weight of a photoradical polymerization initiator ("Omnirad 184" manufactured by IGM Resins) and 0.25 parts by weight of a polyether-modified silicone leveling agent ("BYK-300" manufactured by BYK) were added, and propylene glycol monomethyl ether was added as a dilution solvent to obtain an acrylic hard coat composition with a solids concentration of 50% by weight.

[0185] (Formation of Hard Coat Layer) An acrylic hard coat composition was applied to one surface of Film 1 using a coater so that the dry film thickness was 10 μm, and the solvent was removed at 120° C. Thereafter, in a nitrogen atmosphere, a high-pressure mercury lamp was used to apply an integrated light dose of 1950 mJ / cm ２ The hard coat resin composition was cured by irradiating it with ultraviolet light so that the hard coat resin composition became cured, thereby obtaining a hard coat film having an acrylic hard coat layer with a thickness of 10 μm.

[0186] (Preparation of Laminate) A 25 μm thick transparent adhesive sheet (3M "8146-1", storage modulus of 1.2 × 10 at 25 °C and 1 Hz) was attached to one side of a 32 μm thick thin glass (Nippon Electric Glass "Dinorex UTG T2X-1", elastic modulus 70 GPa). ５ Pa) was laminated onto the glass substrate, and the surface of the hard coat film on which the hard coat layer was not formed was placed on top of the glass substrate, and the resulting mixture was pressed with a rubber roller to prepare a laminate of the thin glass and the hard coat film.

[0187] Example 2 A laminate of thin glass and a hard coat film was obtained in the same manner as in Example 1, except that Film 2 was used instead of Film 1.

[0188] Comparative Example 1 A laminate of thin glass and a hard coat film was obtained in the same manner as in Example 1, except that Film 3 was used instead of Film 1.

[0189] Comparative Example 2 A laminate of thin glass and a hard coat film was produced in the same manner as in Comparative Example 1, except that the thickness of the acrylic hard coat layer was changed to 5 μm.

[0190] Comparative Example 3 A laminate of thin glass and a hard coat film was produced in the same manner as in Example 1, except that Film 4 was used instead of Film 1.

[0191] [Evaluation of Transparent Resin Films] Films 1 to 4 were evaluated as follows.

[0192] <Tensile modulus> The film was cut into strips with a width of 10 mm, and after standing at 23°C / 55% RH for one day to condition the humidity, a tensile test was carried out using a tensile tester "AUTOGRAPH AGS-X" manufactured by Shimadzu Corporation under the following conditions to calculate the tensile modulus. The tensile test was carried out in both the MD and TD directions. Grip distance: 100 mm, Pulling speed: 20.0 mm / min, Measurement temperature: 23°C

[0193] <Refractive Index> The film was cut into 3 cm squares, and the orientation angle was measured using a retardation measurement device (OPTIPRO 21-255MA manufactured by Shintech) to determine the direction in which the refractive index was maximum. Films 1, 2, and 4 had the maximum refractive index in the TD direction, and Film 3 had the maximum refractive index in the MD direction. Using a prism coupler (Metricon's 2010 / M), the refractive index nx in the direction in which the refractive index was maximum and the refractive index ny in the direction perpendicular thereto were measured. The refractive index at a wavelength of 589 nm, obtained by Cauchy dispersion fitting of the measurements at wavelengths of 404 nm, 594 nm, and 827 nm, was taken as the refractive index of the film. From the refractive indices thus determined, the average in-plane refractive index n ａｖｅ = (nx + ny) / 2, and the in-plane birefringence Δn = nx - ny was calculated.

[0194] [Evaluation of Laminates] The laminates of the Examples and Comparative Examples were evaluated as follows.

[0195] <Total Light Transmittance and Haze> Using a haze meter "HZ-V3" manufactured by Suga Test Instruments, total light transmittance (TT) and haze were measured according to the methods described in JIS K7361-1: 1999 and JIS K7136: 2000. A D65 light source was used for the measurement.

[0196] <Yellowness Index> Yellowness index (YI) was measured according to JIS K7373 using a spectrophotometer SC-P manufactured by Suga Test Instruments Co., Ltd.

[0197] <Dent Resistance> According to JIS K5600, a pencil hardness test was carried out by scratching the surface of the hard coat layer of the laminate with a pencil under the conditions of a load of 750 gf and a speed of 60 mm / min, and the presence or absence of dents in the film was observed. Seventeen types of pencils, from 6B to 9H, were used, and the scratching direction of the pencil was the TD direction of the transparent resin film. The presence or absence of dents was visually observed under the illumination of a straight-tube three-wavelength fluorescent lamp, with the transmitted light and reflected light of the lamp, and if the fluorescent lamp appeared distorted at the scratched area, it was considered that there was a dent.

[0198] The scratch test was carried out five times (at five locations) using a pencil of each hardness, and if no dents were observed in four or more locations (if dents were observed in one location or less), it was determined that the sample had dent resistance for that pencil hardness. In Comparative Examples 1 to 3, dents were observed in two or more locations when scratched with a 6B pencil, so the dent resistance (dents immediately after the test) was rated as "6B>" (less than 6B).

[0199] <Bending test (bending resistance)> The laminate was wrapped around a cylindrical rod with a radius of 10 mm at an angle of 180° with the thin glass side of the laminate facing outward and the film side facing inward, and the laminate was bent, then returned to its extended state and visually inspected. No cracks or breaks were observed in any of the laminates of the Examples and Comparative Examples, and they had good bending resistance.

[0200] Table 2 shows the configurations of the transparent resin films and hard coat layers in the laminates of the Examples and Comparative Examples, as well as the evaluation results of the transparent resin films and laminates.

[0201]

[0202] The laminates of Examples 1 and 2 had superior dent resistance compared to the laminates of Comparative Examples 1 to 3. The laminates of Examples 1 and 2 have high transparency and excellent bending resistance, making them suitable for use as cover windows for foldable displays. In addition, in Examples 1 and 2, the polyimide resin constituting the transparent resin film uses a specific diamine that does not contain a specific fluorine structure as a diamine component, making them excellent in terms of environmental safety.

[0203] REFERENCE SIGNS LIST 1 transparent resin film 3 hard coat layer 5 transparent film (hard coat film) 7 thin glass 9 transparent adhesive layer 10 laminate

Claims

A laminate comprising a thin glass sheet having a thickness of 100 μm or less and a transparent resin film bonded to one main surface of the thin glass sheet, the transparent resin film contains a polyimide-based resin and a solvent-soluble resin other than a polyimide-based resin, the polyimide resin has a tetracarboxylic dianhydride-derived structure and a diamine-derived structure, The diamine may be CF ３ -O-, -(CF ２ -O) ｎ -, and -O-(CF ２ -CF ２ -O) ｎ - (where n is an integer of 1 to 20), The tetracarboxylic dianhydride includes one or more tetracarboxylic dianhydrides selected from the group consisting of tetracarboxylic dianhydrides having a fluorene structure, tetracarboxylic dianhydrides having an ether bond, and bis(trimellitic anhydride) esters, Laminate.

2. The laminate according to claim 1, wherein the fluorine atom-containing diamine is 2,2'-bis(trifluoromethoxy)benzidine, 3,3'-bis(trifluoromethoxy)benzidine, or 2,3'-bis(trifluoromethoxy)benzidine. 　 The polyimide resin may contain, as the tetracarboxylic dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride, N,N'-(9H-fluoren-9-ylidene-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxamide], 5,5'-(9H-fluoren-9-ylidenebis(2-methyl ...

2. The laminate according to claim 1, comprising one or more tetracarboxylic acid dianhydrides having a fluorene structure selected from the group consisting of 5,5'-spiro[9H-fluorene-9,9'-[9H]xanthene]-3',6'-diylbis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate), 5,5'-spiro[9H-fluorene-9,9'-[9H]xanthene]-3',6'-diylbis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate), and spiro[11H-difuro[3,4-b:3',4'-i]xanthene-11,9'-[9H]fluorene]-1,3,7,9-tetrone.

2. The laminate according to claim 1, wherein the polyimide resin contains 15 to 100 mol % of the tetracarboxylic dianhydride having a fluorene structure relative to the total amount of the tetracarboxylic dianhydride. 　 the polyimide-based resin further contains a structure derived from an alicyclic tetracarboxylic dianhydride as the tetracarboxylic dianhydride, 2. The laminate according to claim 1, wherein the amount of the alicyclic tetracarboxylic dianhydride relative to the total amount of the tetracarboxylic dianhydride is 1 to 80 mol %. 　 The polyimide resin is The amount of CF on the carbon atoms of the aromatic ring relative to the total amount of diamine ３ - or -C(CF ３ ) ２ the amount of diamine having a structure in which - is directly bonded is less than 0.5 mol %, The amount of CF on the carbon atoms of the aromatic ring relative to the total amount of tetracarboxylic dianhydride ３ - or -C(CF ３ ) ２ the amount of tetracarboxylic dianhydride having a structure in which - is directly bonded is less than 0.5 mol %; The laminate according to claim 1 . 　 The laminate according to claim 1 , wherein the solvent-soluble resin is an acrylic resin. 　 The laminate according to claim 7 , wherein the acrylic resin is an acrylic resin containing methyl methacrylate as a main component. 　 The laminate according to claim 1 , wherein the solvent-soluble resin is a polyester resin. 　 the polyester has a structure derived from a dicarboxylic acid and a structure derived from a diol, The diol includes at least one selected from the group consisting of diols having a chain alkylene group having 3 or more carbon atoms which may be branched, diols having a chain alkenylene group having 3 or more carbon atoms which may be branched, polyalkylene glycols, and diols having a cyclic structure; The laminate according to claim 9. 　 the polyester has a structure derived from a dicarboxylic acid and a structure derived from a diol, The diol includes at least one selected from the group consisting of diols having a fluorene structure and diols having a bisphenol derivative structure. The laminate according to claim 9. 　 The laminate according to any one of claims 1 to 11, wherein the transparent resin film is a stretched film. 　 The laminate according to any one of claims 1 to 11, wherein the refractive index of the transparent resin film is 1.600 or less. 　 The laminate according to any one of claims 1 to 11, wherein the transparent resin film has a thickness of 20 to 55 µm. 　 The laminate according to any one of claims 1 to 11, wherein the transparent resin film has a total light transmittance of 90.5% or more. 　 The laminate according to any one of claims 1 to 11, further comprising a hard coat layer on the main surface of the transparent resin film opposite to the thin glass. 　 The laminate according to claim 16, wherein the hard coat layer has a thickness of 1 to 50 μm. 　 A display comprising the laminate according to any one of claims 1 to 11.

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