Laminate and display

Abstract

An object of the present invention is to provide a laminate having good interference unevenness and total light transmittance, excellent visibility, and excellent environmental safety, hardness, and bending resistance without providing a refractive index adjusting layer.SOLUTION: A hard coat film comprising a transparent film and a hard coat layer, wherein the transparent film is a polymer composition comprising a polyimide polymer and a solvent-soluble polymer and having an index of refraction of 1.600 or less, and the polyimide polymer comprises, as a diamine-derived structure, a diamine-derived structure having a structure selected from CF3 - O -, - (CF2 - O) n -, and - O - (CF2 - CF2 - O) n - (where n is an integer of 1 to 20), and, as a tetracarboxylic dianhydride-derived structure, An acid dianhydride-derived structure selected from a tetracarboxylic acid dianhydride having an ether bond, a tetracarboxylic acid dianhydride having a fluorene structure, a tetracarboxylic acid dianhydride having a xanthene structure, and a bis (trimellitic anhydride) ester.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a laminate and to a display including the laminate. [Background technology]

[0002] Laminates containing transparent polyimide films and hard coat layers are used as cover window films for displays because of their excellent hardness, transparency, and flex resistance. However, because the refractive index of the transparent polyimide film is high, the total light transmittance of the laminate is low, and there is significant interference, which is color unevenness caused by reflected light, resulting in insufficient visibility of the display.

[0003] Patent Document 1 proposes a method of reducing interference unevenness by providing a refractive index adjustment layer between a transparent polyimide film and a hard coat layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6307205 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a refractive index adjustment layer is provided as in Patent Document 1, problems such as an increase in manufacturing costs and insufficient adhesion to the refractive index adjustment layer may arise.

[0006] Furthermore, in recent years, the environmental persistence of fluorocarbon compounds (PFAS) has become a problem. In general, the carbon-fluorine bonds contained in fluorocarbon compounds have high bond energy, making them difficult to decompose in the environment, leading to their accumulation in water and other environments, and their toxicity to humans has also been noted. Many transparent polyimide resins have a structure within their molecules that makes them difficult to decompose in the environment, and there has been a demand for cover window materials containing polyimide resins made from fluorine compounds that have low environmental persistence and are highly environmentally safe.

[0007] In view of the above, an object of the present invention is to provide a laminate that does not require a refractive index-adjusting layer, has good interference unevenness and total light transmittance, has excellent visibility, and is also excellent in environmental safety, hardness, and flex resistance, and also provides a display including the laminate. [Means for solving the problem]

[0008] In view of the above, the present invention has been conducted with great effort and has found that, according to the following configuration, it is possible to provide a laminate that has good interference unevenness and total light transmittance, excellent visibility, environmental safety, hardness, and bending resistance, without providing a refractive index-adjusting layer.

[0009] 1) A laminate including a transparent film and a hard coat layer, the transparent film is a resin composition containing at least a polyimide resin and a solvent-soluble resin other than a polyimide resin, and having a refractive index of 1.600 or less; the polyimide-based resin contains a tetracarboxylic dianhydride-derived structure and a diamine-derived structure, Diamine-derived structures include CF3-O- and -(CF2-O) n -, -O-(CF2-CF2-O) n - a diamine-derived structure having any structure selected from the following (wherein n is an integer of 1 to 20); A laminate characterized by comprising, as a tetracarboxylic dianhydride-derived structure, any one of a tetracarboxylic dianhydride-derived structure selected from a tetracarboxylic dianhydride having an ether bond, a tetracarboxylic dianhydride having a fluorene structure, a tetracarboxylic dianhydride having a xanthene structure, and a bis(trimellitic anhydride) ester.

[0010] 2) The polyimide resin has a content of a tetracarboxylic dianhydride-derived structure having a CF3- group directly bonded to an aromatic ring or a -C(CF3)2- group directly bonded to an aromatic ring of less than 0.5 mol% of all tetracarboxylic dianhydride-derived structures, The laminate according to 1), characterized in that the content of diamine-derived structures having a CF3- group directly bonded to an aromatic ring or a -C(CF3)2- group directly bonded to an aromatic ring is less than 0.5 mol% of all diamine-derived structures.

[0011] 3) The laminate according to 1) or 2), wherein the polyimide resin contains an alicyclic tetracarboxylic dianhydride-derived structure as the tetracarboxylic dianhydride-derived structure, and the amount of the alicyclic tetracarboxylic dianhydride relative to the total amount of tetracarboxylic dianhydride is 1 to 80 mol%.

[0012] 4) The laminate according to 3), wherein the alicyclic tetracarboxylic dianhydride is any one of 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-butanetetracarboxylic dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, and 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic-3,4:3',4'-dianhydride.

[0013] 5) The CF3-O-, -(CF2-O) n -, -O-(CF2-CF2-O) n - (wherein n is an integer of 1 to 20) is a diamine selected from 2,2'-bis(trifluoromethoxy)benzidine, 3,3'-bis(trifluoromethoxy)benzidine, and 2,3'-bis(trifluoromethoxy)benzidine.

[0014] 6) The laminate according to any one of 1) to 5), wherein the aromatic acid dianhydride other than any acid dianhydride selected from the group consisting of an acid dianhydride having an ether bond, an acid dianhydride having a fluorene structure, an acid dianhydride having a xanthene structure, and a bis(trimellitic anhydride) ester includes at least one of 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, and 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride.

[0015] 7) The laminate according to any one of 1) to 6), wherein the polyimide resin has a weight-average molecular weight of 90,000 to 500,000.

[0016] 8) The laminate according to any one of 1) to 7), wherein the absolute value of the difference between the refractive index of the transparent film and the refractive index of the hard coat layer is 0.090 or less.

[0017] 9) The laminate according to any one of items 1) to 8), which has a total light transmittance of 90.3% or more.

[0018] 10) The laminate according to any one of items 1) to 9), which has a pencil hardness of H or more.

[0019] 11) The laminate according to any one of 1) to 10), wherein the amplitude, which is the difference between the maximum and minimum values ​​of light transmittance (%) at wavelengths of 700 to 800 nm, is 0.25 (%) or less.

[0020] 12) The laminate according to any one of 1) to 11), wherein the thickness of the hard coat layer is 9 μm or less.

[0021] 13) The laminate according to any one of 1) to 12), wherein the solvent-soluble resin other than the polyimide resin is an acrylic resin.

[0022] 14) The laminate according to 13), wherein the acrylic resin is an acrylic resin containing methyl methacrylate as a main component.

[0023] 15) The laminate according to any one of items 1) to 14), wherein the hard coat layer is an acrylic hard coat layer.

[0024] 16) The laminate according to 15), wherein the acrylic hard coat layer is a cured product of a curable composition containing dipentaerythritol hexaacrylate.

[0025] 17) The laminate according to any one of items 1) to 14), wherein the hard coat layer is a siloxane-based hard coat layer.

[0026] 18) The laminate according to 17), wherein the siloxane-based hard coat layer comprises a cured product of a curable composition containing a condensate of a silane compound having an alicyclic epoxy group in the molecule, represented by the following general formula (4): (wherein, in formula (4), R 1 is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R 2 is a hydrogen atom or a monovalent hydrocarbon group selected from an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms, x is 2 or 3, and Y is an alicyclic epoxy group. [ka]

[0027] 19) The laminate according to any one of 1) to 18), wherein the difference between the maximum refractive index and the minimum refractive index in the plane of the transparent film is 0.005 or more.

[0028] 20) The laminate according to any one of 1) to 19), wherein the transparent film has a thickness of 20 to 100 μm.

[0029] 21) The laminate according to any one of 1) to 20) above, wherein the transparent film has a tensile modulus of elasticity of 5.0 GPa or more.

[0030] 22) A display comprising the laminate according to any one of 1) to 21). [Effects of the Invention]

[0031] According to the present invention, it is possible to provide a laminate that has good interference unevenness and total light transmittance, excellent visibility, and also excellent environmental safety, hardness, and bending resistance, without providing a refractive index adjustment layer, and a display that includes the laminate. DETAILED DESCRIPTION OF THE INVENTION

[0032] The laminate of the present invention is a laminate including a transparent film and a hard coat layer, wherein the transparent film is a resin composition containing at least a polyimide resin and a solvent-soluble resin other than a polyimide resin, and has a refractive index of 1.600 or less, and the polyimide resin contains a tetracarboxylic dianhydride-derived structure and a diamine-derived structure, and the diamine-derived structure is selected from the group consisting of CF3-O-, -(CF2-O) n -, -O-(CF2-CF2-O) n- (where n is an integer of 1 to 20), and the tetracarboxylic dianhydride-derived structure is an acid dianhydride-derived structure selected from tetracarboxylic dianhydride having an ether bond, tetracarboxylic dianhydride having a fluorene structure, tetracarboxylic dianhydride having a xanthene structure, and bis(trimellitic anhydride) ester. The laminate of the present invention has excellent visibility with good interference unevenness and total light transmittance, and is also excellent in environmental safety, hardness, and flex resistance. The mechanism by which these excellent properties are exhibited will be described.

[0033] <Mechanism for reducing interference unevenness> The excellent interference unevenness (the characteristic of less visible interference unevenness), which is an effect of the present invention, is mainly achieved by a blend resin containing a polyimide-based resin constituting the transparent film and a solvent-soluble resin other than polyimide-based resin. In blend resins obtained by blending a polyimide-based resin and a solvent-soluble resin other than polyimide-based resin, the high refractive index of the polyimide-based resin is reduced by the inclusion of the solvent-soluble resin, thereby lowering the refractive index of the entire transparent film. Since the refractive index of a hard coat layer is generally lower than that of the polyimide-based resin, a lower refractive index of the transparent film reduces the refractive index difference between the hard coat layer and the transparent film, making interference unevenness less likely to occur. The absence of interference unevenness is preferable because it improves the visibility of displays. It is preferable that the refractive index of the blend resin composed of a polyimide-based resin and a solvent-soluble resin other than polyimide-based resin constituting the transparent film be 1.600 or less, from the viewpoint of making interference unevenness less visible. Furthermore, it may be preferable that the absolute value of the difference between the refractive index of the transparent film and the refractive index of the hard coat layer be 0.090 or less, from the viewpoint of making interference unevenness less visible. From the viewpoint of controlling the refractive index of the transparent film to 1.600 or less, the refractive index of the solvent-soluble resin other than the polyimide resin is preferably 1.600 or less.

[0034] Interference unevenness occurs when light is incident on a laminate, whether it is transmitted light or reflected light, but tends to be particularly visible with reflected light. Of the light incident on the laminate, light reflected from the surface of the hard coat layer and light reflected from the surface of the transparent film (the interface between the hard coat layer and the transparent film) strengthen or weaken each other at each wavelength, causing a change in the color of the light (wavelength of light) as perceived by the human eye, resulting in color unevenness called interference unevenness. The reflectance tends to increase as the difference in refractive index between the materials that form the interface increases. Therefore, by reducing the difference in refractive index between the materials that form the interface (between the hard coat layer and the transparent film), reflected light is reduced, and interference unevenness is reduced.

[0035] In a laminate that transmits light, there is a close relationship between the reflectance and transmittance of light. When the reflectance of light is high, the transmittance is low, and when the reflectance is low, the transmittance is high. Therefore, the state of light interference can be quantified by measuring the transmittance spectrum or reflectance spectrum. Specifically, when the amplitude of the transmittance spectrum (the difference between the maximum and minimum transmittance values) in a specified wavelength range is large, interference unevenness becomes stronger and the interference unevenness becomes more visible. It is preferable that the amplitude of the transmittance spectrum (the difference between the maximum and minimum transmittance values) is 0.25% or less, as this makes interference unevenness less visible. Similarly, in the case of reflectance, when the amplitude of the reflection spectrum (the difference between the maximum and minimum reflectance values) in a specified wavelength range is large, interference unevenness becomes stronger.

[0036] Generally, polyimide resins are difficult to blend with other resins because of the strong interactions between polymer molecules due to the imide structure, making them difficult to mix uniformly with other resins. However, the polyimide resin of the present application, which has a specific structure, can be uniformly mixed with other resins, enabling blending while exhibiting excellent optical and mechanical properties. One method for lowering the refractive index of a resin composition involves dispersing particles of a low-refractive-index material, such as silica, in the resin composition, but this method can sometimes cause problems due to poor dispersion of the low-refractive-index material. The polyimide resin of the present application and solvent-soluble resins other than polyimide resins can stably achieve a good mixed state, which has the advantage of preventing the deterioration of optical and mechanical properties due to poor dispersion of the low-refractive-index material, which occurs when a low-refractive-index material, such as silica, is dispersed in a polyimide resin to reduce reflectance or suppress interference unevenness.

[0037] In a laminate consisting of a transparent film and a hard coat layer, if the refractive index of the transparent film is high, a method of increasing the refractive index of the hard coat layer by incorporating high-refractive-index metal oxide particles into the hard coat layer may be employed. However, this method may result in deterioration of mechanical properties such as bending resistance of the laminate, and optical properties such as haze, YI, and transmittance due to the particles. The present invention is also preferable in that it can suppress interference unevenness without incorporating a high-refractive-index material into the hard coat layer.

[0038] <Mechanism for improving total light transmittance> The high total light transmittance, which is an effect of the present invention, is mainly achieved by a blend resin composed of a polyimide-based resin and a solvent-soluble resin other than polyimide-based resin that constitutes the transparent film. The blend resin obtained by blending a polyimide-based resin and a solvent-soluble resin other than polyimide-based resin reduces the high refractive index of the polyimide-based resin by blending the solvent-soluble resin other than polyimide-based resin, thereby lowering the refractive index of the entire transparent film, thereby increasing the total light transmittance of the transparent film. By improving the total light transmittance of the transparent film, the total light transmittance of the laminate including the hard coat layer also improves. A total light transmittance of 90.3% or more for the laminate is preferable because it improves the visibility of the display.

[0039] [Materials Constituting the Present Invention] The laminate of the present invention is a laminate including a transparent film and a hard coat layer, wherein the transparent film is a resin composition containing at least a polyimide resin and a solvent-soluble resin other than a polyimide resin and having a refractive index of 1.600 or less, and the polyimide resin contains a tetracarboxylic dianhydride-derived structure and a diamine-derived structure, and the diamine-derived structure is selected from the group consisting of CF3-O-, -(CF2-O) n -, -O-(CF2-CF2-O) n - (where n is an integer of 1 to 20), and a tetracarboxylic dianhydride-derived structure, which is any acid dianhydride-derived structure selected from tetracarboxylic dianhydride having an ether bond, tetracarboxylic dianhydride having a fluorene structure, tetracarboxylic dianhydride having a xanthene structure, and bis(trimellitic anhydride) ester. The transparent film, hard coat layer, and laminate constituting the present invention will be described below.

[0040] <Transparent film> The transparent film is a blend resin film containing one or more polyimide-based resins selected from the group consisting of polyimides and polyamideimides, and a solvent-soluble resin other than the polyimide-based resin (hereinafter sometimes referred to as "other resin").

[0041] The transparent film contains at least a polyimide or polyamideimide and a solvent-soluble resin. In addition, it may contain other components such as other resins or particles, flame retardants, UV absorbers, stabilizers, crosslinkers, dyes, pigments, surfactants, plasticizers, and lubricants. For example, it may contain UV absorbers for imparting weather resistance and light resistance, stabilizers such as radical trapping agents, and dyes or pigments such as bluing agents for adjusting color tone.

[0042] However, the particles are preferably contained in an amount of 5 parts by weight or less per 100 parts by weight of the resin composition constituting the transparent film. In particular, silicon oxides such as silica, which are blended to reduce the refractive index, tend to be poorly dispersed in the resin composition, causing a decrease in the transparency of the transparent film, an increase in haze and YI, as well as a decrease in tensile elongation and flexural resistance, which may be undesirable. The silicon oxide content 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 even more preferably 0.1 parts by weight or less. Silicon oxide may not be present. Particles containing silicon oxide tend to improve the blocking resistance of the transparent film, and in some cases it may be preferable to contain 5 parts by weight or less.

[0043] The resin composition contained in the transparent film, which contains at least a polyimide resin and a solvent-soluble resin other than a polyimide resin, is not particularly limited as long as it is a blend resin that exhibits transparency, and may be compatible with each other or may form a microlayer-separated structure such as a sea-island structure, a cylindrical structure, or a lamellar structure. Among these, it is preferable that the polyimide resin and the solvent-soluble resin other than a polyimide resin are compatible with each other. This compatibility improves transparency regardless of the processing conditions of the film, and also facilitates improvements in mechanical properties such as elastic modulus and pencil hardness.

[0044] <Polyimide resin> Polyimides are obtained by dehydrating and cyclizing polyamic acids obtained by addition polymerization of tetracarboxylic dianhydrides (hereinafter sometimes referred to as "acid dianhydrides") and diamines. That is, polyimides are polycondensates of tetracarboxylic dianhydrides and diamines, and have a structure derived from the acid dianhydride (acid dianhydride component) and a structure derived from the diamine (diamine component). Polyamideimides are obtained by substituting a portion of the acid dianhydride-derived structure (acid dianhydride component) with a structure derived from a dicarboxylic acid such as terephthalic acid chloride. In the present invention, either polyimides or polyamideimides can be selected, but polyimides may be preferred in terms of compatibility with solvent-soluble resins. Polyimides and polyamideimides can also be used in combination. Hereinafter, polyimides and polyamideimides will also be referred to as polyimide-based resins.

[0045] (Tetracarboxylic acid dianhydride) The polyimide resin of the present invention is characterized by containing any one of the acid dianhydrides selected from the group consisting of an acid dianhydride having an ether bond, an acid dianhydride having a fluorene structure, an acid dianhydride having a xanthene structure, and a bis(trimellitic anhydride) ester. The inclusion of these acid dianhydride components makes it possible to improve the solubility of the polyimide resin in solvents, improve the compatibility of the polyimide resin with resins other than the polyimide resin (particularly with acrylic resins), and obtain a molded product with an excellent balance of transparency and mechanical strength.

[0046] From the viewpoint of making the polyimide-based resin soluble in an organic solvent, the total content of any acid dianhydride selected from acid dianhydrides having an ether bond, acid dianhydrides having a fluorene structure, acid dianhydrides having a xanthene structure, and bis(trimellitic anhydride) esters, relative to 100 mol% of the total amount of the acid dianhydride components, is preferably 15 mol% or more, more preferably 20 mol% or more, even more preferably 25 mol% or more, and may be 30 mol% or more, 35 mol% or more, 40 mol% or more, 45 mol% or more, or 50 mol% or more. The total content of any acid dianhydrides selected from acid dianhydrides having an ether bond, acid dianhydrides having a fluorene structure, acid dianhydrides having a xanthene structure, and / or bis(trimellitic anhydride) esters, relative to 100 mol% of the total amount of the acid dianhydride components, may be 100 mol%, or may be 95 mol% or less, 90 mol% or less, 85 mol% or less, 80 mol% or less, 75 mol% or less, or 70 mol% or less.

[0047] Examples of acid dianhydrides having an ether bond include 3,4'-oxydiphthalic anhydride (a-ODPA), 4,4'-oxydiphthalic anhydride (s-ODPA), and 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride (BPADA). From the viewpoints of the solubility of polyimide resins and compatibility with resins other than polyimide resins, 4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride (BPADA) is particularly preferred. The use of an acid dianhydride having an ether bond tends to improve the solubility of polyimide resins in solvents and the compatibility of polyimide resins with resins other than polyimide resins.

[0048] 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-PPA), 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- Examples of suitable dianhydrides include bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate] (TBIS.MPN), bis[1,3-dihydro-4,1-phenylene]bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate] (TBIS.MPN), and the like. From the viewpoint of the solubility of polyimide resins and compatibility with resins other than polyimide resins, BPAF or BPF-PPA is particularly preferred. The use of an acid dianhydride having a fluorene structure tends to improve the solubility of polyimide resins in solvents and the compatibility of polyimide resins with resins other than polyimide resins.

[0049] Examples of acid dianhydrides having a xanthene structure include 5,5'-spiro[9H-fluorene-9,9'-[9H]xanthene]-3',6'-diylbis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate (TBIS.RXN) and spiro[11H-difuro[3,4-b:3',4'-i]xanthene-11,9'-[9H]fluorene]-1,3,7,9-tetrone (SFDA). The use of acid dianhydrides having a xanthene structure tends to improve the solubility of polyimide resins in solvents and the compatibility of polyimide resins with resins other than polyimide resins. Although the aforementioned TBIS.RXN and SFDA have both a xanthene structure and a fluorene skeleton, for convenience they are classified as acid dianhydrides having a xanthene structure.

[0050] The bis(trimellitic anhydride) ester is represented by the following general formula (1).

[0051] [ka]

[0052] In general formula (1), X is any divalent organic group, and at both ends of X, a carboxy group and a carbon atom of X are bonded. The carbon atoms bonded to the carboxy group may form a ring structure. Specific examples of the divalent organic group X include the following (A) to (K).

[0053] [ka]

[0054] R in formula (A) 1represents a fluorine atom or an alkyl group having 1 to 20 carbon atoms, and m is an integer of 1 to 4. The group represented by formula (A) is a group obtained by removing two hydroxyl groups from a hydroquinone derivative having a substituent on the benzene ring. Examples of hydroquinones having a substituent on the benzene ring include tert-butylhydroquinone, 2,5-di-tert-butylhydroquinone, and 2,5-di-tert-amylhydroquinone.

[0055] R in formula (B) 2 represents a fluorine atom or an alkyl group having 1 to 20 carbon atoms, and n is an integer of 0 to 4. The group represented by formula (B) is a group obtained by removing two hydroxyl groups from a biphenol which may have a substituent on the benzene ring. Examples of biphenol derivatives having a substituent on the benzene ring include 2,2'-dimethylbiphenyl-4,4'-diol, 3,3'-dimethylbiphenyl-4,4'-diol, 3,3',5,5'-tetramethylbiphenyl-4,4'-diol, and 2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diol.

[0056] The group represented by formula (C) is a group obtained by removing two hydroxyl groups from 4,4'-isopropylidenediphenol (bisphenol A). The group represented by formula (D) is a group obtained by removing two hydroxyl groups from resorcinol.

[0057] In formula (E), p is an integer of 1 to 10. The group represented by formula (E) is a group obtained by removing two hydroxyl groups from a linear diol having 1 to 10 carbon atoms. Examples of linear diols having 1 to 10 carbon atoms include ethylene glycol and 1,4-butanediol.

[0058] The group represented by formula (F) is a group in which two hydroxyl groups have been removed from 1,4-cyclohexanedimethanol.

[0059] R in formula (G) 3is a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 20 carbon atoms, and q is an integer of 0 to 4. The group represented by formula (G) is a group obtained by removing two hydroxyl groups from bisphenolfluorene, which may have a substituent on the benzene ring having a phenolic hydroxyl group. Examples of bisphenolfluorene derivatives having a substituent on the benzene ring having a phenolic hydroxyl group include biscresolfluorene. When the compound has the structure of formula (G), it corresponds to both an acid dianhydride having a fluorene structure and a bis(trimellitic anhydride) ester, but in the present invention, it corresponds to a bis(trimellitic anhydride) ester.

[0060] The bis(trimellitic anhydride) ester is preferably an aromatic ester. Of the above (A) to (K), (A), (B), (C), (D), (G), (H), and (I) are preferred for X. Among these, (A) to (D) are preferred, and the group having a biphenyl skeleton of (B) is particularly preferred. When X is a group represented by general formula (B), from the viewpoint of the solubility of the polyimide resin, X is preferably 2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diyl represented by the following formula (B1).

[0061] [ka]

[0062] The acid dianhydride in which X is a group represented by formula (B1) in general formula (1) is bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'diyl (abbreviation: TAHMBP) represented by the following formula (3).

[0063] [ka]

[0064] Among acid dianhydrides having an ether bond, acid dianhydrides having a fluorene structure, acid dianhydrides having a xanthene structure, and bis(trimellitic anhydride) esters, from the viewpoint of UV resistance of the resulting polyimide resin, acid dianhydrides having an ether bond, acid dianhydrides having a fluorene structure, and acid dianhydrides having a xanthene structure are preferred, and from the viewpoint of solubility in solvents and mechanical strength, BPADA, a-ODPA, s-ODPA, BPAF, BPF-PPA, and SFDA structures are particularly preferred. If there is no ester bond, the Friess transition due to UV light does not occur, and the resulting polyimide resin tends to be less likely to discolor when exposed to UV light.

[0065] Among the acid dianhydrides having an ether bond, the acid dianhydrides having a fluorene structure, the acid dianhydrides having a xanthene structure, and the bis(trimellitic anhydride) esters, from the viewpoint of solubility of the resulting polyimide resin in non-amide solvents, the acid dianhydrides having an ether bond, the acid dianhydrides having a fluorene structure, and the bis(trimellitic anhydride) esters are preferred, and BPADA, BPAF, BPF-PPA, TBIS.MPN, p-phenylenebis(trimellitate anhydride) (TAHQ), 5,5'-(3,3'-diphenyl methacrylate) (PA ... Methyl [1,1'-biphenyl]-4,4'-diyl)bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate) (BP-TME), p-biphenylene bis(trimellitate anhydride) (OCBP-TME), tert-butylhydroquinone bis(trimellitate anhydride) (TA.BHQ), trimethylhydroquinone bis(trimellitate anhydride) (TA.TMHQ), and TAHMBP are more preferred, and BPAF, BPF-PPA, and TBIS.MPN, which have a fluorene structure, are even more preferred.

[0066] The polyimide resin used in the present invention may contain, as an acid dianhydride component, an acid dianhydride component other than any one selected from the group consisting of the acid dianhydrides having an ether bond, the acid dianhydrides having a fluorene structure, and the acid dianhydride bis(trimellitic anhydride) esters having a xanthene structure. Examples of such acid dianhydride components include alicyclic tetracarboxylic acid dianhydrides, aromatic acid dianhydrides, and / or other acid dianhydrides.

[0067] Examples of alicyclic tetracarboxylic dianhydrides include 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-butanetetracarboxylic dianhydride, meso-butane-1,2,3,4-tetracarboxylic dianhydride, 1,1'-Bicyclohexane-3,3',4,4'tetracarboxylic acid-3,4:3',4'-dianhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic 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 acid 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 acid anhydride, 5,5'-[cyclohexylidenebis(4,1-phenyleneoxy)]bis-1,3-isobenzofurandione, 5-isobenzyl Benzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-,5,5'-[1,4-cyclohexanediylbis(methylene)] ester, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, 3,5,6-tricarboxynorbornane-2-acetic acid 2,3:5,6-dianhydride, decahydro-1,4,5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic dianhydride, tricyclo[6.4.0.Examples of suitable dianhydrides include octahydro-1H,3H,8H,10H-biphenyleno[4a,4b-c:8a,8b-c']difuran-1,3,8,10-tetrone, ethylene glycol bis(hydrogenated trimellitic anhydride) ester, and decahydro[2]benzopyrano[6,5,4,-def][2]benzopyran-1,3,6,8-tetrone. The alicyclic structure of the dianhydride component tends to improve the compatibility of polyimide resins with other resins (especially acrylic resins). Alicyclic tetracarboxylic dianhydrides need only have at least one alicyclic structure, and may contain both an alicyclic ring and an aromatic ring in one molecule. The alicyclic ring may be polycyclic or have a spiro structure.

[0068] Among alicyclic tetracarboxylic dianhydrides, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (H-PMDA), 1,2,3,4-butanetetracarboxylic dianhydride (BT-100), 4-(2,5-dioxotetrahydrofuran- Preferred are 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). Among these, from the viewpoint of mechanical strength, tetracarboxylic acid anhydrides in which two acid anhydride groups are bonded to one alicyclic ring are preferred, and 1,2,3,4-cyclobutanetetracarboxylic dianhydride is particularly preferred.

[0069] When an alicyclic tetracarboxylic dianhydride is used, from the viewpoint of improving compatibility between the polyimide resin and resins other than the polyimide resin and from the viewpoint of mechanical strength, the content of the alicyclic tetracarboxylic dianhydride relative to the total amount of the dianhydride components (100 mol %) is preferably 1 mol % or more, more preferably 3 mol % or more, even more preferably 5 mol % or more, and may be 10 mol % or more, 12 mol % or more, or 15 mol % or more. The amount of alicyclic tetracarboxylic dianhydride required to ensure compatibility with resins other than the polyimide resin may vary depending on the type of resin other than the polyimide resin, the amount of alicyclic tetracarboxylic dianhydride, etc.

[0070] From the viewpoint of ensuring the solubility of the polyimide resin in organic solvents, the content of the alicyclic tetracarboxylic dianhydride relative to the total amount of the acid dianhydride components (100 mol%) is preferably 80 mol% or less, more preferably 60 mol% or less, and may be 50 mol% or less, 30 mol% or less, or may not be present. In order to make the polyimide resin compatible with resins other than the polyimide resin even in a low-boiling non-amide solvent (e.g., a halogen-based solvent such as methylene chloride), the content of the alicyclic tetracarboxylic dianhydride is preferably 60 mol% or less, more preferably 40 mol% or less, and may be 20 mol% or less, or may not be present.

[0071] Aromatic 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'-biphenyltetracarboxylic dianhydride (s-BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA), 2,2',3,3'-biphenyltetracarboxylic dianhydride, Examples of suitable dianhydrides include carboxylic 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 acid dianhydrides, from the viewpoint of improving mechanical strength, it is preferable to include at least one of 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, and 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride.

[0072] From the viewpoint of ensuring the solubility of the polyimide resin in organic solvents, the content of aromatic acid dianhydride relative to the total amount of acid dianhydride components (100 mol%) is preferably 80 mol% or less, more preferably 60 mol% or less, and may be 50 mol% or less, 30 mol% or less, or may not be present. In order to make the polyimide resin compatible with resins other than the polyimide resin even in a low-boiling non-amide solvent (e.g., a halogen-based solvent such as methylene chloride), the content of aromatic acid dianhydride is preferably 60 mol% or less, more preferably 40 mol% or less, and may be 20 mol% or less, or may not be present.

[0073] As other acid dianhydrides, chain aliphatic acid dianhydrides such as ethylene tetracarboxylic dianhydride and butane tetracarboxylic dianhydride may be used.

[0074] (dicarboxylic acid) As mentioned above, the polyimide resin may be a polyamide-imide in which a portion of the tetracarboxylic dianhydride component is replaced with a dicarboxylic acid derivative. Examples of dicarboxylic acids include aliphatic dicarboxylic acids such as adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-oxybisbenzoic acid, 4,4'-biphenyldicarboxylic acid, and 2-fluoroterephthalic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-hexahydroterephthalic acid, hexahydroisophthalic acid, 1,3-cyclopentanedicarboxylic acid, and bi(cyclohexyl)-4,4'-dicarboxylic acid; and heterocyclic dicarboxylic acids such as 2,5-thiophenedicarboxylic acid and 2,5-furandicarboxylic acid.

[0075] From the viewpoint of the solubility of polyamideimide and compatibility with other resins, aromatic dicarboxylic acids and alicyclic dicarboxylic acids are preferred, with aromatic dicarboxylic acids being particularly preferred. Among aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, 4,4'-biphenyldicarboxylic acid, and 4,4'-oxybisbenzoic acid are preferred, with terephthalic acid and isophthalic acid being particularly preferred, with terephthalic acid being particularly preferred.

[0076] As the dicarboxylic acid derivative used as a raw material monomer for polyamideimide, dicarboxylic acid dichlorides, dicarboxylic acid esters, dicarboxylic acid anhydrides, etc. are used. Among them, dicarboxylic acid dichlorides are preferred because of their high reactivity.

[0077] From the viewpoint of the solubility of the polyamideimide and its compatibility with other resins, the ratio of the dicarboxylic acid derivative to the total of the tetracarboxylic dianhydride and the dicarboxylic acid derivative is preferably 40 mol % or less, more preferably 35 mol % or less, and even more preferably 30 mol % or less. The polyimide resin may be a polyimide in which the ratio of the dicarboxylic acid derivative is 0 (i.e., does not contain a structure derived from the dicarboxylic acid derivative).

[0078] (diamine) The diamine component of the polyimide resin used in the present invention is CF3-O-, -(CF2-O) n -, -O-(CF2-CF2-O) n - (where n is an integer of 1 to 20). By having such a structure in which a fluorinated methyl structure or a fluorinated methylene structure is directly bonded to an oxygen atom, it is expected that the decomposition property of the fluorine-containing compound in the environment will be improved and the environmental persistence of the fluorine-containing compound will be significantly reduced.

[0079] CF3-O-, -(CF2-O) n -, -O-(CF2-CF2-O) n- (where n is an integer of 1 to 20) includes perfluoroalkoxy-substituted benzidines. Examples of perfluoroalkoxy-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, 3,3'-bis(trifluoromethoxy)benzidine, 2,3'-bis(trifluoro methoxy)benzidine, 2,2',3-tris(trifluoromethoxy)benzidine, 2,3,3'-tris(trifluoromethoxyl)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, 2,2',6,6'-tetrakis(trifluoromethoxy)benzidine, and the like.

[0080] CF3-O-, -(CF2-O) n -, -O-(CF2-CF2-O) n- (where n is an integer of 1 to 20), other examples of diamines having any structure selected from the above include phenylenediamines having perfluoroalkoxy substitutions, such as 1,2-diamino-4-(trifluoromethoxy)benzene (TFMOBzo), 1,3-diamino-4-(trifluoromethoxy)benzene (TFMOBzm), 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.

[0081] From the viewpoints of mechanical strength and polymerizability, perfluoroalkoxy-substituted benzidines are preferred. Among them, from the viewpoints of the solubility of polyimide resins in organic solvents and compatibility with resins other than polyimide resins, perfluoroalkoxy-substituted benzidines having a perfluoroalkoxy group at the 2- or 3-position of 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, with TFMOB being particularly preferred. By having a trifluoromethoxy group at the 2- or 3-position of biphenyl, not only is the electron-withdrawing property of the trifluoromethoxy group reduced in π electron density, but the steric hindrance of the trifluoromethoxy group inhibits π-π stacking between benzene rings, shifting the absorption edge wavelength to shorter wavelengths and reducing coloration of the polyimide resin. Furthermore, by having trifluoromethoxy groups at the 2- and 2'-positions, the steric hindrance of the trifluoromethoxy groups twists the bond between the two benzene rings of the biphenyl, reducing the planarity of the π-conjugation, thereby shifting the absorption edge wavelength to shorter wavelengths and reducing the coloration of the polyimide resin.

[0082] CF3-O-, -(CF2-O) relative to 100 mol% of the total amount of diamine components n-, -O-(CF2-CF2-O) n The content of the diamine having any structure selected from -CF3-O-, -(CF2-O) (where n is an integer of 1 to 20) is preferably 10 mol% or more, more preferably 30 mol% or more, and even more preferably 50 mol% or more, and may be 60 mol% or more, 70 mol% or more, or 80 mol% or more, or even 100 mol%. n -, -O-(CF2-CF2-O) n - (where n is an integer of 1 to 20), coloration of the film is suppressed, and mechanical strength such as pencil hardness, elastic modulus, breaking strength, and breaking elongation may be improved.

[0083] Polyimide resins contain diamine components such as CF3-O- and -(CF2-O) n -, -O-(CF2-CF2-O) n -CF3-O-, -(CF2-O) (where n is an integer of 1 to 20) may be contained. n -, -O-(CF2-CF2-O) n- (where n is an integer of 1 to 20), examples of diamines that do not have any structure selected from the group consisting of p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, and 4,4'-diaminodiphenyl Phenyl 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-aminophenyl)propane, 2,2-di(4-aminophenyl)propane, 2-(3-aminophenyl) 1,1-di(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 Zene, 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-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 2,2-bis[4-( 1,3-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)-α,α-dimethyl benzyl]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'-dibiphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-biphenoxybenzophenone, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindan, 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindan, 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-amino propyl 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, 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane, 2,5-bis(aminomethyl)bicyclo[2.2.1]heptane, and the like. ,

[0084] For example, diamines include CF3-O-, -(CF2-O) n -, -O-(CF2-CF2-O) nThe use of diaminodiphenyl sulfone in addition to a diamine having any of the structures selected from the group consisting of - (where n is an integer of 1 to 20) 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. 3,3'-DDS and 4,4'-DDS may be used in combination.

[0085] The content of diaminodiphenylsulfone relative to 100 mol % of the total amount of diamines may be 1 to 40 mol %, 3 to 30 mol %, or 5 to 25 mol %.

[0086] For example, diamines include CF3-O-, -(CF2-O) n -, -O-(CF2-CF2-O) n - (where n is an integer of 1 to 20), the use of a fluorene-containing diamine in addition to a diamine having any structure selected from the group consisting of - may improve the solubility of the polyimide resin in solvents, the compatibility with resins other than the polyimide resin (especially acrylic resins), transparency, and mechanical strength. 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.

[0087] The content of the fluorene-containing diamine relative to 100 mol % of the total amount of diamines may be 1 to 40 mol %, 3 to 30 mol %, or 5 to 25 mol %.

[0088] To obtain a polyimide resin in which the environmental degradability of fluorine-containing compounds is improved and the environmental persistence of fluorine-containing compounds is significantly reduced, the total content of the acid dianhydride having a specific fluorine structure and the diamine having a specific fluorine structure is preferably less than 500 mg, more preferably less than 300 mg, even more preferably less than 100 mg, and still more preferably less than 50 mg per kg of polyimide resin. Here, the diamine having a specific fluorine structure refers to acid dianhydrides having a fully fluorinated methyl group (CF3-) or methylene group (-CF2-), and diamines having a fully fluorinated methyl group (CF3-) or methylene group (-CF2-), excluding substances containing only the structural elements of the following structural formula (A) or (B): CF3-X (A) X-CF2-X' (B) (wherein X is an -OR or -NRR' structure, X' is any one of -H, -CH3, aromatic, -C(O)-, -OR'', -SR'', and NR''R''', and R, R', R'', and R''' are any one of -H, -CH3, -CH2-, aromatic, and -C(O)-)

[0089] More preferably, the content of tetracarboxylic dianhydride components having a CF3- group directly bonded to an aromatic ring or a -C(CF3)2- group directly bonded to an aromatic ring is less than 0.5 mol % of all tetracarboxylic dianhydride components, and the content of diamine components having a CF3- group directly bonded to an aromatic ring or a -C(CF3)2- group directly bonded to an aromatic ring is less than 0.5 mol % of all diamine components. Examples of acid dianhydrides and diamines having a CF3- group directly bonded to an aromatic ring or a -C(CF3)2- group directly bonded to an aromatic ring include 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 9,9-bis(trifluoromethyl)xanthenetetracarboxylic dianhydride, 9-bis(trifluoromethyl)xanthenetetracarboxylic dianhydride, 2,2'-bis(trifluoromethyl)benzidine, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane.

[0090] (Preparation of polyimide resin) Polyamic acid is obtained as a polyimide precursor 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.

[0091] When preparing polyamideimide, in addition to diamine and tetracarboxylic dianhydride, dicarboxylic acid or its derivative (dicarboxylic acid dichloride, dicarboxylic acid anhydride, etc.) may be used as a monomer. In this case, the amount of each monomer may be adjusted so that the total amount of tetracarboxylic dianhydride and dicarboxylic acid or its derivative is approximately equimolar to the diamine.

[0092] 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.

[0093] The concentration of the polyamic acid solution is usually 5 to 35% by weight, and 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.

[0094] 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.

[0095] The organic solvent used in the polymerization of polyamic acid is not particularly limited as long as it does not react with diamines and dianhydrides and can dissolve polyamic acid. Examples of organic solvents include urea-based solvents such as methylurea and N,N-dimethylethylurea; sulfoxide or sulfone-based solvents such as dimethyl sulfoxide, diphenyl sulfone, and tetramethyl sulfone; amide-based 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-based 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.

[0096] 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. Heating the polyamic acid solution can also be used to accelerate the imidization process. 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 polyamic acid synthesis, as well as residual dehydrating agents and imidization catalysts, to be washed away 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.

[0097] The molecular weight of the polyimide resin (weight average molecular weight in terms of polyethylene oxide measured by gel permeation chromatography (GPC)) is preferably 90,000 to 500,000, more preferably 100,000 to 400,000, still more preferably 100,000 to 300,000, and particularly preferably 150,000 to 300,000. If the molecular weight is too small, the strength of the film may be insufficient. If the molecular weight is too large, the compatibility with other resins may be poor.

[0098] The polyimide resin is preferably soluble in a low-boiling solvent such as a ketone solvent or an alkyl halide solvent. The term "solubility of a polyimide resin in a solvent" means that the polyimide resin is soluble in a solvent at 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, making it easy to remove residual solvent during film production. Therefore, the use of a polyimide resin soluble in methylene chloride is expected to improve film productivity.

[0099] From the viewpoint of the thermal stability and light stability of the transparent resin film, it is preferable that the polyimide-based resin has low reactivity. The acid value of the polyimide-based 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 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-based resin has a high imidization rate. A low acid value tends to increase the stability of the polyimide-based resin and improve its compatibility with other resins.

[0100] <Other resins> As mentioned above, the transparent film contains, in addition to the polyimide resin, a resin other than the polyimide 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 resin to form a transparent film, and examples include resins that are compatible with the polyimide 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 compatible with the polyimide resin. When the polyimide 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.

[0101] The other resin is preferably a transparent resin having a refractive index lower than that of the polyimide-based resin. The refractive index of the other resin is preferably 1.600 or less, more preferably 1.550 or less, even more preferably 1.520 or less, and particularly preferably 1.500 or less. Since the other resin has a refractive index lower than that of the polyimide-based resin, a transparent resin film containing a polyimide-based resin and another resin has a lower refractive index than a film containing only the polyimide-based resin, and therefore has less reflection at the interface, and therefore tends to have a higher total light transmittance.

[0102] 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 having a fluorene structure 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 high-hardness films.

[0103] Examples of acrylic resins include poly(meth)acrylic acid esters such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymers, methyl methacrylate-(meth)acrylic acid ester copolymers, methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymers, methyl (meth)acrylate-styrene copolymers, and copolymers of methyl (meth)acrylate with a monomer having a benzotriazole skeleton or a benzophenone skeleton. The acrylic resin may be modified to incorporate a glutarimide structural unit or a lactone ring structural unit. The stereoregularity of the polymer is not particularly limited, and may be any of isotactic, syndiotactic, and atactic.

[0104] Introducing a glutarimide structure into an acrylic polymer such as methyl methacrylate tends to increase the glass transition temperature of the acrylic resin. Furthermore, since the acrylic resin contains an imide structure, compatibility with polyimide resins may be improved. For example, even if a specific polyimide resin is not compatible with polymethyl methacrylate, it may be compatible with an acrylic resin having a glutarimide structure. Acrylic resins having a glutarimide structure can be obtained by heating and melting polymethyl methacrylate resin and treating it with an imidizing agent, as described in JP 2010-261025 A, for example.

[0105] When the acrylic polymer has a glutarimide structure, the glutarimide content may be 3% by weight or more, 10% by weight or more, 20% by weight or more, 30% by weight or more, or 50% by weight or more. The glutarimide content can be calculated by determining the imidization ratio Im = B / (A + B) from the H-NMR spectrum of the acrylic resin, where A is the area of ​​the peak derived from the O-CH3 proton of methyl methacrylate and B is the area of ​​the peak derived from the N-CH3 proton of glutarimide, and then converting the imidization ratio into weight. Introducing a glutarimide structure into the acrylic resin is expected to improve compatibility with polyimide resins and the elastic modulus of the resulting molded product.

[0106] Among these, from the viewpoints of the yellowness index (YI) of the acrylic resin, color change such as yellowing after ultraviolet irradiation, and light resistance, it may be preferable that the proportion of aromatic ring-containing monomers be 5 mol% or less out of 100 mol% of the monomers constituting the acrylic resin. The proportion of aromatic ring-containing monomers may be 3% or less, or 1% or less, or the acrylic resin may not contain any aromatic ring-containing monomers. The aromatic ring-containing monomer is not particularly limited, but examples include styrene copolymers and monomers having a benzotriazole skeleton or a benzophenone skeleton.

[0107] From the viewpoints of transparency, compatibility with polyimide resins, and mechanical strength, the acrylic resin preferably 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. Alternatively, the acrylic resin may be an acrylic polymer having a methyl methacrylate content within the above range, into which a glutarimide structure or a lactone ring structure has been introduced.

[0108] 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.

[0109] From the viewpoints of solubility in organic solvents, compatibility with polyimide resins, and film strength, the weight average molecular weight (polystyrene equivalent) of the acrylic resin is preferably 5,000 to 500,000, more preferably 10,000 to 300,000, still more preferably 15,000 to 200,000, and particularly preferably 50,000 to 150,000.

[0110] 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 compatibility with polyimide resins.

[0111] <Composition of transparent film> As described above, the transparent film contains a polyimide resin and other resins as resin components. The ratio of the polyimide resin to the other resins in the transparent film is not particularly limited. The mixing ratio (weight ratio) of the polyimide 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 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 the film will have, the higher the total light transmittance, the lower the yellowness index (YI), and the more transparent it will be.

[0112] In order to fully achieve the effect of improving transparency by mixing the polyimide resin with the other resin, the ratio of the other resin to the total of the polyimide resin and the other resin is preferably 10 to 90% by weight, more preferably 15 to 85% by weight, 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.

[0113] The distribution of the polyimide resin and other resins in the thickness direction of the transparent film is not particularly limited, but from the viewpoint of optical properties, it may be preferable that the distribution is uniform in the thickness direction or that resins other than the polyimide resin are unevenly distributed on the surface side, and it may be more preferable that the distribution is uniform in the thickness direction. If the polyimide resin is unevenly distributed on the surface, the refractive index of the film surface may become high and the transmittance may become low.

[0114] In addition to the resin components, the transparent film may contain organic or inorganic low-molecular-weight compounds, etc. The transparent film may also contain additives such as bluing agents, ultraviolet absorbers, flame retardants, stabilizers, crosslinking agents, surfactants, leveling agents, plasticizers, and fine particles.

[0115] The transparent film may contain organic fine particles such as polystyrene or cross-linked acrylic resin, or inorganic fine particles such as silica or layered silicate, for the purposes of improving blocking resistance and adjusting the refractive index. However, the incorporation of fine particles can cause a decrease in the transmittance of the film and 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.

[0116] <Preparation of transparent film> The transparent film is produced by applying a resin solution, in which a polyimide resin and a solvent-soluble resin other than a polyimide resin are dissolved in a solvent, onto a support, and then heating the solution on the support to dry and remove the solvent.

[0117] The solvent is not particularly limited as long as it dissolves 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 for polyimide resins and other resins, have low boiling points, and allow for easy removal of residual solvent during film production.

[0118] As a method for applying the resin solution onto a support, known methods using a bar coater, a comma coater, or the like can be applied. Examples of the support that can be used include a glass substrate, a metal substrate such as SUS, a metal drum, a metal belt, and a plastic film. 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 as the support, and produce the film by a roll-to-roll method. When using a plastic film as the support, it is sufficient to appropriately select a material that is insoluble in the solvent of the resin solution (dope). Among these, a plastic film may be preferred as the support from the viewpoints of availability and the fact that it can be used without the assumption of repeated use, thereby reducing the risk of changes in surface roughness during repeated use.

[0119] 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, preferably between 50°C and 220°C. 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 atmosphere. Heating may be carried out under reduced pressure to promote solvent removal.

[0120] The film may be stretched in one or more directions for the purpose of improving the mechanical strength, etc. When the film is stretched, the polymer chains are oriented in the stretching direction, which tends to improve the strength of the film in the in-plane direction and suppress the occurrence of breakage or cracks in the film.

[0121] Although films made solely of acrylic resins may have low toughness, the use of a compatible system of polyimide resins and acrylic resins may improve the strength of the film. Furthermore, when a film made of a compatible system of polyimide resins and acrylic resins is stretched, the polymer chains are oriented in the stretching direction, which increases the tensile modulus in the stretching direction, and this tends to improve the flex resistance.

[0122] 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.

[0123] The conditions for stretching the film are not particularly limited. For example, the stretching temperature is about ±40°C of the glass transition temperature of the film, and may be about 120 to 300°C, 150 to 250°C, or 180 to 230°C. The stretching ratio is about 30 to 200%, and may be 50 to 150%, 80 to 120%, or 80 to 100%. The higher the stretching ratio, the higher the tensile modulus in the stretching direction tends to be. On the other hand, if the stretching ratio is too high, the mechanical strength in the direction perpendicular to the stretching direction tends to decrease, and the handleability of the film may be reduced.

[0124] 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.

[0125] The thickness of the transparent film is not particularly limited and may be appropriately set depending on the application. The film thickness is, for example, 5 to 300 μm. From the viewpoint of achieving both self-supporting properties and flexibility and also providing a highly transparent film, the film thickness is preferably 20 μm to 100 μm, and may be 25 μm to 80 μm, or 25 μm to 50 μm. The thickness of a film used as a cover window for a display is preferably 20 μm or more. When the film is stretched, the thickness after stretching is preferably within the above range.

[0126] <Transparent film characteristics> The transparent 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 film is compatible with other resins, the transparent film exhibits a single glass transition temperature.

[0127] The total light transmittance of the transparent film is preferably 90.3% or more, more preferably 90.5% or more, even more preferably 91.0% or more, and particularly preferably 91.5% or more. A high total light transmittance is preferable because it improves the visibility of the display. As described above, by mixing a polyimide resin with a solvent-soluble resin, a film with a higher total light transmittance can be obtained compared to when polyimide or polyamideimide is used alone.

[0128] The yellowness index (YI) of the transparent 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 film is preferably -3.0 or more, more preferably -2.0 or more, and even more preferably -1.0 or more. A YI in the range of -3.0 to 3.0 is preferred because it results in less coloration and improves the visibility of the display. A YI in the range of -1.0 to 3.0 is particularly preferred. As described above, by mixing a polyimide-based resin with a solvent-soluble resin, a film with less coloration and a smaller absolute value of YI can be obtained compared to when a polyimide-based resin is used alone.

[0129] The haze of the transparent film is preferably 10% or less, more preferably 5% or less, 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. The lower the haze of the film, the better. As described above, among blended resins of polyimide-based resins and solvent-soluble resins, those using acrylic resins as the solvent-soluble resin exhibit particularly high compatibility, resulting in films with low haze and high transparency. It is preferable that the haze of a resin composition obtained by mixing a polyimide-based resin and a solvent-soluble resin is 10% or less when a film with a thickness of 50 μm is produced.

[0130] The refractive index of the transparent film is preferably 1.600 or less, which is the average of the maximum and minimum in-plane refractive indices. A low refractive index reduces interference unevenness and increases total light transmittance. Among solvent-soluble resins, acrylic resins have a low refractive index, which makes the blended resins also low in refractive index, making them preferable. The refractive index is determined by the composition of the resin composition and the orientation state of the polymer chains. Resin compositions consisting of polyimide resins and acrylic resins tend to have a high refractive index in the orientation direction of the polymer chains, so the maximum in-plane refractive index direction tends to be the stretching direction. In the case of biaxial stretching, this tends to be either the first stretching direction or the second stretching direction. The in-plane average refractive index is more preferably 1.580 or less, even more preferably 1.570 or less, and may be 1.560 or less, or 1.550 or less. A low refractive index, reduced interference unevenness, and high total light transmittance are preferable because they improve the visibility of the display. As described above, by mixing a polyimide resin with a solvent-soluble resin, a film with a lower refractive index can be obtained compared to when polyimide or polyamideimide is used alone. However, when the refractive index is high due to the orientation of the polymer chains, the orientation of the polymer chains can be expected to improve the mechanical properties. Therefore, the maximum in-plane refractive index can be set to any value taking into account the balance with the mechanical properties.

[0131] Regarding the refractive index of a transparent film, it is sometimes preferable that the absolute value of the difference between the maximum and minimum in-plane refractive indexes is 0.005 or more. In particular, in uniaxially stretched films, a large absolute value of the difference between the maximum and minimum in-plane refractive indexes can improve mechanical properties. The absolute value of the difference between the maximum and minimum in-plane refractive indexes is determined by the orientation state of the polymer chains. Since resin compositions consisting of polyimide and acrylic resins tend to have a high refractive index in the orientation direction of the polymer chains, the direction in which the absolute value of the difference between the maximum and minimum in-plane refractive indexes increases is the stretching direction and the direction perpendicular thereto. The absolute value of the difference between the maximum and minimum in-plane refractive indexes is more preferably 0.007 or more, even more preferably 0.008 or more, and in some cases, 0.009 or more is particularly preferable. A large absolute value of the difference between the maximum and minimum in-plane refractive indexes tends to improve mechanical properties such as bending resistance and pencil hardness, and is therefore preferable. However, in the case of biaxially stretched films, although the absolute value of the difference between the maximum and minimum in-plane refractive indexes does not increase, the orientation of the polymer molecular chains occurs due to stretching, and therefore mechanical properties tend to be excellent.

[0132] The tensile modulus of the transparent film is preferably 3.0 GPa or more. A high tensile modulus tends to improve mechanical properties such as pencil hardness and bending resistance. The tensile modulus is more preferably 3.5 GPa or more, even more preferably 5.0 GPa or more, particularly preferably 5.5 GPa or more, and may be 6.0 GPa or more. The tensile modulus of the film refers to the maximum in-plane modulus of elasticity. The modulus of elasticity is determined by the composition of the resin composition and the orientation state of the polymer chains. Since resin compositions consisting of polyimide resins and acrylic resins tend to have a high modulus of elasticity in the orientation direction of the polymer chains, the direction of the maximum in-plane modulus of elasticity is the stretching direction. In the case of biaxial stretching, this tends to be either the first stretching direction or the second stretching direction.

[0133] The transparent film may have in-plane anisotropy in tensile modulus. 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 in-plane directions may be greater than that before stretching. When the transparent film has in-plane anisotropy in 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.

[0134] Regarding the lightfastness of a transparent film, it is sometimes preferable that the YI change in a lightfastness test be 10.0 or less. A small YI change is preferable because it tends to result in small changes in color tone and small changes in display visibility even when used in an environment with high UV exposure, such as outdoors. The YI change is more preferably 4.0 or less, even more preferably 2.0 or less, and particularly preferably 1.0 or less. The lightfastness test is performed using an ultraviolet carbon arc light source with an irradiation intensity of 500 W / m 2 The test involves exposure for 48 hours at a black panel temperature of 63°C in the absence of rain. By measuring the YI before and after the test, the change in YI, ΔYI (YI after the test - YI before the test), can be calculated.

[0135] The indentation hardness of the transparent film is 300N / mm 2 The above is preferable. High indentation hardness tends to improve pencil hardness.

[0136] Indentation hardness is measured using the nanoindentation method. A triangular pyramidal indenter (Berkovich indenter) is loaded (applied) to the film surface at a rate of 6.667 mN / s, from 0 mN to 100 mN over 15 seconds, and held there for 2 seconds. After 2 seconds, the load is released at a rate of 6.667 mN / s, from 100 mN to 0 mN over 15 seconds. The unloading curve data for the horizontal axis displacement and vertical axis load during unloading is used to calculate the indentation hardness. For the calculation, an unloading curve obtained by performing a sixth-order polynomial approximation on the unloading curve data obtained from the measurement using Microsoft Excel spreadsheet software is used. The coefficients of the approximation curve in this case are 30 digits. Indentation hardness is calculated using the following formula. Indentation hardness (N / mm 2 ) = Maximum load Fmax / contact projected area A Contact projection area A = 24.56 × contact depth hc 2 Contact depth hc = maximum displacement hmax - 0.75 × maximum load Fmax / inclination at the start of unloading Here, the slope at the start of unloading is the slope of the line connecting the start point of unloading and the point at which the displacement has decreased by 0.5% from the start point of unloading.

[0137] Indentation hardness is 300N / mm 2 More than 350N / mm is preferable. 2 More preferably, 360N / mm 2 The above is particularly preferable. Indentation hardness is 300N / mm 2 If it is less than this, the pencil hardness may be insufficient.

[0138] <Laminate> The present invention is a laminate including a transparent film and a hard coat layer. The laminate of the present invention may include a functional layer other than the hard coat layer. Examples of functional layers include layers having various functions such as an ultraviolet absorbing layer, an adhesive layer, an easy-adhesion layer, a refractive index adjustment layer, and an anti-reflection layer. The laminate of the present invention may include a refractive index adjustment layer, but a transparent film made of a blend resin containing at least polyimide or polyamideimide and a solvent-soluble resin has a low refractive index, so it has the advantage of being able to reduce interference unevenness even without including a refractive index adjustment layer. Therefore, the laminate of the present invention may not include a refractive index adjustment layer, and in some cases it may be preferable not to include a refractive index adjustment layer from the standpoint of cost and adhesion to the refractive index adjustment layer.

[0139] The hard coat layer and the functional layer may contain a bluing agent for the purpose of adjusting the color tone. These hard coat layers and functional layers may contain an ultraviolet absorber for the purpose of improving light resistance. In particular, when additives such as bluing agents or ultraviolet absorbers cannot be incorporated into the transparent film due to compatibility or heat resistance considerations, adding additives to the hard coat layer and functional layer can adjust the color tone of the laminate or improve the light resistance of the laminate. As the functional layer, an adhesive layer that can impart adhesiveness, a function required for flexible displays, or an easy-adhesion layer that can impart adhesion to other layers such as the hard coat layer is more preferred. When the functional layer is made of a material that can be cured by active energy rays such as ultraviolet rays, containing an ultraviolet absorber in the functional layer may cause curing inhibition.

[0140] The thickness of the hard coat layer and the functional layer can be appropriately set depending on the desired properties. However, there is a preferred range for the thickness of the hard coat layer, which is described below. The hard coat layer and the functional layer may be of one type, or multiple or more types may be formed. Furthermore, the hard coat layer and the functional layer may be formed on only one side of the transparent film, or on both sides.

[0141] The material constituting the hard coat 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. From the viewpoint of preventing scratches, however, an acrylic hard coat layer which is a cured product of an acrylic hard coat resin composition or a siloxane hard coat layer which is a cured product of a siloxane hard coat resin composition is preferred.

[0142] <Acrylic hard coating materials> Acrylic hard coat materials contain, as a curable resin component, a monomer or oligomer having a (meth)acryloyl group in the molecule. The molecular weight of the acrylic monomer or oligomer is, for example, about 200 to 10,000. By combining multiple types of monomers or oligomers having a (meth)acryloyl group, the hardness, scratch resistance, bending resistance, optical properties, etc. of the acrylic hard coat material can be controlled. From the viewpoint of curability by photoradical polymerization, hard coat materials having an acryloyl group are preferred.

[0143] 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.

[0144] 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 a (meth)acryloyl group: examples thereof 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.

[0145] From the viewpoint of improving the scratch resistance of the hard coat layer, the acrylic hard coat material preferably contains a polyfunctional (meth)acrylate having three or more functional groups. 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.

[0146] <Siloxane-based hard coating materials> 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 these, 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 the descriptions therein are incorporated by reference.

[0147] 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.

[0148] The polyorganosiloxane compound having an alicyclic epoxy group can be obtained by condensation of a silane compound represented by general formula (4). [ka]

[0149] 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.

[0150] The silane compound represented by the general formula (4) has two or three (-OR 1 ) 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.

[0151] In general formula (4), R2 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.

[0152] 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 In order to form a network-like polyorganosiloxane compound and to increase 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 general formula (1). A silane compound in which x = 2 and a silane compound in which x = 3 may be used in combination. Furthermore, in order to adjust the molecular weight of the polyorganosiloxane compound obtained by condensation, a silane compound in which x = 1 may be used in addition to a silane compound in which x = 2 or 3.

[0153] 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 viewpoints of heat resistance and flex resistance, an alkyl group having an alicyclic epoxy group as a substituent is preferred.

[0154] 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.

[0155] 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}dimethyl {(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.

[0156] 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.

[0157] The above silane compound is reacted with water to form the 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).

[0158] 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.

[0159] <Polymerization initiator> The hard coat composition preferably contains a polymerization initiator in addition to the above-mentioned curable resin component. The polymerization initiator is preferably a photopolymerization initiator. 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 when exposed to 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 when exposed to light.

[0160] 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.

[0161] Examples of photoacid generators include onium salts that 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.

[0162] <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, such as 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.

[0163] [Hard coat layer formation and laminate properties, and application of laminates to displays] The method for producing the laminate of the present invention is not particularly limited, but a preferred production example is a method in which a curable composition (hard coat composition) is applied to a transparent film (a step of forming a hard coat layer by coating), and if necessary, the solvent is dried and removed, followed by irradiating with active energy rays (a step of irradiating with active energy rays) to cure the curable composition, thereby obtaining a laminate. Among these, a method including a step of applying a composition containing a curable resin composition and a photoinitiator to a transparent film, followed by a step of irradiating with active energy rays, is preferred from the standpoint of productivity. The method for applying the hard coat composition is not particularly limited, and existing coating methods such as 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 can be used.

[0164] The thickness of the hard coat layer in the laminate of the present invention can be appropriately set within the range of 1 to 50 μm, preferably 0.1 to 9 μm, more preferably 0.5 to 6 μm, and even more preferably 1 to 5 μm. When the hard coat layer is 9 μm or less, interference unevenness is likely to occur. However, the laminate of the present invention is excellent in preventing interference unevenness, and is therefore characterized by the fact that good visibility can be obtained even when the hard coat layer is 9 μm or less in thickness. A thick hard coat layer tends to have good pencil hardness and impact resistance, while a thickness of less than 0.1 μm results in insufficient hardness. A thin hard coat layer tends to have good flex resistance, while a thickness of more than 50 μm results in insufficient flex resistance.

[0165] The total thickness of the laminate of the present invention (the sum of the thickness of the hard coat layer and the thickness of the transparent film) is not particularly limited, but is preferably 10 μm or more, more preferably 30 μm or more, even more preferably 40 μm or more, and is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, and particularly preferably 60 μm or less. If the total thickness is less than 10 μm, the hardness may be insufficient. If the total thickness exceeds 200 μm, the bending resistance may be insufficient.

[0166] The laminate of the present invention has excellent optical properties and mechanical properties derived from the transparent film, as well as high scratch resistance derived from the hard coat layer. Cover windows for flexible displays are required to have excellent optical properties for beautifully displaying images on the display, as well as to be resistant to scratches and dents caused by contact with various objects. Therefore, the laminate of the present invention can be suitably used for cover windows of flexible displays.

[0167] "Excellent flex resistance" as used herein means that the laminate does not crack or break after the process of bending an unfolded flat laminate 180° at a bending radius of 1.5 mm or less and then returning it to its original flat state 10 times. It is preferable that the laminate of the present invention does not crack or break even when bent 10 times at a bending radius of 1.5 mm with the hard coat layer facing inner surface.

[0168] The laminate of the present invention preferably has a hardness of H or more in a pencil hardness test in accordance with JIS-K5600, more preferably 2H or more, and even more preferably 3H or more.

[0169] The laminate of the present invention preferably has a haze of 1% or less. A low haze can improve the visibility of a display and reduce power consumption. A haze of 0.7% or less is more preferable, and a haze of 0.5% or less is even more preferable.

[0170] The laminate of the present invention has a total light transmittance of 90.3% or more. A high total light transmittance can improve the visibility of a display and reduce power consumption. The total light transmittance is more preferably 90.5% or more, and even more preferably 91.0% or more.

[0171] The laminate of the present invention preferably has a YI of -3.0 to 3.0. When the YI is within the above range, it is possible to improve the visibility of the display and improve the color tone. The YI is more preferably -2.0 to 2.0, and even more preferably -1.0 to 1.0.

[0172] In the laminate of the present invention, the absolute value of the difference between the refractive index of the transparent film and the refractive index of the hard coat layer is preferably 0.090 or less. A small absolute value of the refractive index difference is preferable because interference unevenness is less likely to occur due to the mechanism described above. The absolute value of the refractive index difference is preferably 0.090 or less, more preferably 0.050 or less, even more preferably 0.040 or less, and may be 0.020 or less, or even 0.000.

[0173] The laminate of the present invention preferably has an amplitude, which is the difference between the maximum and minimum values ​​of light transmittance (%) at wavelengths of 700 to 800 nm, of 0.25% or less. As mentioned above, interference unevenness can be quantified using a transmittance spectrum, and the larger the difference (amplitude) between the maximum and minimum light transmittance in the transmittance spectrum, the stronger the interference unevenness becomes, as light of specific wavelengths strengthens or weakens each other, making it easier to see as a color difference. From the viewpoint of preventing interference unevenness from occurring, the amplitude, which is the difference between the maximum and minimum values, is preferably 0.25% or less, and more preferably 0.20% or less. The amplitude, which is the difference between the maximum and minimum values, may be 0.00%.

[0174] In order to determine the amplitude, which is the difference between the maximum and minimum values ​​of the light transmittance (%) at wavelengths of 700 to 800 nm, the transmittance spectrum data, which is the transmittance for each wavelength, is smoothed by a five-term moving average process to prevent sudden maximum or minimum values ​​from occurring, and then the difference between the maximum and minimum values ​​of the light transmittance (%) at wavelengths of 700 to 800 nm is taken as the amplitude. The transmittance data at the nth wavelength is then calculated as C n In this case, the five-term moving average value of transmittance is calculated by the following formula:

number

[0175] The laminate of the present invention preferably has no or only weak interference unevenness. The strength of interference unevenness can be determined by laminating the transparent film surface of the laminate to a black PET film with adhesive, and then observing the laminate from the hard coat layer side under three-wavelength fluorescent light illumination. By laminating the black PET film, it is possible to reproduce the situation in which interference unevenness is most easily visible when the display is set to black. From the viewpoint of display visibility, it is preferable that interference unevenness is absent or very weak in this state.

[0176] The laminate of the present invention has good interference unevenness due to the low refractive index of the transparent film, high total light transmittance, and good visibility and optical properties required for displays. Furthermore, the combination of the transparent film and the hard coat layer provides good scratch resistance, resulting in high pencil hardness and the good scratch resistance required for display cover windows. Furthermore, the laminate has excellent bending resistance (resistance to repeated bending tests), and can be suitably used as a cover window for flexible displays and foldable displays that require flexibility, by being disposed on the surface side of display devices such as liquid crystal displays and organic electroluminescence displays. In particular, the laminate can be suitably used as a cover window for organic electroluminescence displays, which have excellent flexibility. [Example]

[0177] 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 these examples. In these examples, the MD direction is the flow direction during coating, and the TD direction is the direction perpendicular to the MD direction.

[0178] [Example of polyimide resin production] Dimethylformamide was placed in a separable flask and stirred under a nitrogen atmosphere. Diamine and acid dianhydride were then 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 %.

[0179] 5.5 g of pyridine was added as an imidization catalyst to 100 g of polyamic acid solution. 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 (hereinafter referred to as IPA) was added at a rate of 2-3 drops per second while stirring the solution, resulting in the precipitation of polyimide. 150 g of IPA was then added, and the mixture was stirred for approximately 30 minutes. Afterwards, the mixture was suction filtered 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 the polyimide resins polyimide 1 (PI1), polyimide 2 (PI2), and polyimide 3 (PI3). The molecular weights of the polyimide resins were 290,000 for PI1, 270,000 for PI2, and 180,000 for PI3.

[0180] In Table 1, the compounds are described by the following abbreviations. <Tetracarboxylic acid dianhydride> BPAF: 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride 6FDA: 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride TAHMBP: bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diyl ODPA: 4,4'-oxydiphthalic dianhydride

[0181] <Diamine> TFMOB: 2,2'-bis(trifluoromethoxy)benzidine TFMB: 2,2'-bis(trifluoromethyl)benzidine DDS: 3,3'-diaminodiphenyl sulfone [Table 1]

[0182] [Creating transparent film] <Blend resin film 1> Polyimide resin (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; hereafter referred to as "acrylic resin" (Ac)) were mixed in the ratios shown in Table 2 to prepare a methylene chloride solution with a resin content of 11 wt%. This solution was applied to an alkali-free glass substrate and dried by heating in the air 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 of the specified thickness.

[0183] The obtained film was uniaxially stretched at a fixed end using a stretching machine equipped with a heating oven at a temperature of 220°C with the TD direction as the stretching direction at a stretch ratio of 75% (the TD length was 1.75 times that of the film before stretching), to obtain a stretched film with a thickness of 50 μm. The refractive index measurement results are shown in Table 4. The maximum in-plane refractive index was in the TD direction, and the minimum in the MD direction.

[0184] [Table 2]

[0185] <Blend resin film 2> A blend resin film of a predetermined thickness was obtained in the same manner as described in <Blend Resin Film 1>, except that the polyimide resin in the solution preparation was changed to PI2. Subsequently, a blend resin film 2 of a thickness of 50 μm was obtained in the same manner as described in <Blend Resin Film 1>, except that the stretching conditions were changed to a stretching temperature of 205°C and a stretch ratio of 80%. The results of refractive index measurement are shown in Table 4. The direction of maximum in-plane refractive index was the TD direction, and the direction of minimum in-plane refractive index was the MD direction.

[0186] <Blend resin film 3> Blend resin film 3 having a thickness of 50 μm was obtained in the same manner as described in <Blend resin film 2>, except that the stretching conditions were changed to a stretching temperature of 215° C. The refractive index measurement results are shown in Table 4. The direction in which the in-plane refractive index was maximum was the TD direction, and the direction in which the refractive index was minimum was the MD direction.

[0187] [Example of polyimide film production] PI3 was used as the polyimide resin, and Tinuvin 477 (BASF Japan) as a triazine-based UV absorber and Plas Blue 8590 (Arimoto Chemical Industry Co., Ltd.) as an anthraquinone-based bluing agent were dissolved in methylene chloride in the ratios (parts by weight) shown in Table 2 to obtain a methylene chloride solution with a solids concentration of 10 wt%. This solution was applied to an alkali-free glass substrate and heated in air 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 remove the solvent, yielding a 50 μm-thick transparent polyimide film. The refractive index measurement results are shown in Table 4. The maximum in-plane refractive index was measured in the MD direction, and the minimum in the TD direction.

[0188] [Example of laminate production] An example of producing a laminate will be described below.

[0189] [Synthesis example of silane compound condensation product] A 200 mL flask reaction vessel equipped with a thermometer, stirrer, and reflux condenser was charged with 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (SILQUEST A-186, Momentive Performance Materials) (66.5 g; 270 mmol) and 1-methoxy-2-propanol (PGME) (16.5 g) and stirred until homogeneous. A solution of magnesium chloride (0.039 g; 0.405 mmol) dissolved in a mixture of water (9.7 g; 539 mmol) and methanol (5.8 g) was added dropwise to the mixture over 5 minutes and stirred until homogeneous. The mixture was then heated to 80°C and stirred for 6 hours. After completion of the reaction, the mixture was devolatilized and concentrated under reduced pressure using a rotary evaporator to remove the methanol and water from the condensate. Analysis of the resulting condensate revealed that it had a weight average molecular weight Mw of 1700. The content of magnesium chloride (neutral salt catalyst) calculated based on the above-mentioned charged weight was 814 ppm.

[0190] The condensates of the silane compounds obtained in the above synthesis examples were evaluated as follows. <Measurement of weight average molecular weight Mw> The weight average molecular weight of the condensation product of the silane compound was measured by GPC. The GPC apparatus used was a Tosoh HLC-8220GPC (column: TSKgel GMH XL x 2, TSKgel G3000H XL ,TSKgel G2000H XL ) and THF was used as the solvent, and the values ​​were calculated in terms of polystyrene.

[0191] The method for preparing the hard coat composition and the method for producing the laminate having the hard coat layer are as follows.

[0192] [Preparation of hard coat composition and production of laminate having hard coat layer] (Preparation of Hard Coat Composition) Dipentaerythritol hexaacrylate (Aronix M-403, manufactured by Toagosei Co., Ltd.), the silane compound condensate obtained in the synthesis example, 1-hydroxycyclohexyl phenyl ketone (Irgacure 184, manufactured by BASF Japan Ltd.) as a photoinitiator, a sulfonium-based photoacid generator (CPI-101A, manufactured by San-Apro Co., Ltd.), and a polyether-modified silicone leveling agent (BYK-300, manufactured by BYK Japan Ltd.) as a leveling agent were mixed in the weight parts shown in Table 3 in terms of solid content to obtain a curable resin composition. Propylene glycol monomethyl ether was used as a dilution solvent, and the solid content concentration was set to 50%.

[0193] [Table 3]

[0194] (Example 1: Preparation of a laminate of an acrylic hard coat layer and a Friend resin film 1) The acrylic hard coat composition shown in Table 3 was applied to the main surface of a 50 μm-thick blend resin film 1 obtained under the composition and conditions shown in Table 2 using a bar coater to a dry film thickness of 5 μm, and the solvent was removed at 120° C. Thereafter, the film was irradiated with a high-pressure mercury lamp under a nitrogen atmosphere with 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 layer was formed. Thus, a laminate having a hard coat layer was obtained.

[0195] (Example 2: Preparation of a laminate of a siloxane-based hard coat layer and Friend Resin Film 1) The siloxane-based hard coat composition shown in Table 3 was applied to the main surface of a 50 μm-thick blend resin film 1 obtained under the composition and conditions shown in Table 2 using a bar coater to a dry film thickness of 5 μm, and the solvent was removed at 120° C. Thereafter, the film was irradiated with a high-pressure mercury lamp under atmospheric pressure with 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 layer was formed. Thus, a laminate having a hard coat layer was obtained.

[0196] (Comparative Example 1: Preparation of a Laminate of Acrylic Hard Coat Layer and Friend Resin Film 2) A laminate having a hard coat layer was obtained in the same manner as in Example 1, except that Blend Resin Film 2 was used.

[0197] (Comparative Example 2: Preparation of a Laminate of Siloxane-Based Hard Coat Layer and Friend Resin Film 3) A laminate having a hard coat layer was obtained in the same manner as in Example 2, except that Blend Resin Film 3 was used.

[0198] (Comparative Example 3: Preparation of a Laminate of Acrylic Hard Coat Layer and Polyimide Film) A laminate having a hard coat layer was obtained in the same manner as in Example 1, except that a polyimide film having a thickness of 50 μm and obtained under the composition and conditions shown in Table 2 was used.

[0199] The transparent films and laminates obtained in the above production examples were evaluated as follows.

[0200] <Total light transmittance and haze> Measurements were made using a haze meter HZ-V3 manufactured by Suga Test Instruments in accordance with the methods described in JIS K7361-1:1999 and JIS K7136:2000. The measurement was made using a D65 light source. A higher transmittance indicates better transparency.

[0201] <Elastic modulus> The transparent film was cut into 10 mm wide strips and left to stand at 23°C / 55% RH for one day to condition the humidity. Then, the tensile modulus was measured under the following conditions using a Shimadzu tensile testing machine, "AUTOGRAPH AGS-X." A high modulus indicates excellent mechanical properties. Grip distance: 100 mm Tensile speed: 20.0 mm / min Measurement temperature: 23℃

[0202] <Thickness measurement> The thicknesses of the transparent film and the laminate were measured using a contact thickness meter (manufactured by Mitutoyo Corporation). The thickness of the hard coat layer was determined by subtracting the thickness of the transparent film (substrate film) from the thickness of the laminate.

[0203] <Checking the maximum refractive index direction and measuring the refractive index> The orientation angle of the transparent film was measured using a retardation measuring device OPTIPRO (MODEL 21-255MA) manufactured by Shintech Co., Ltd., and the direction in which the refractive index was maximum was determined. For the stretched films of the Examples and Comparative Examples, the stretching direction was the maximum refractive index direction, and the perpendicular direction was the minimum refractive index direction. For the polyimide film, the MD direction was the maximum refractive index direction, and the perpendicular direction was the minimum refractive index direction (here, the coating direction during film production was defined as MD, and the direction perpendicular to MD was defined as TD).

[0204] Next, the refractive index in the maximum refractive index direction and the perpendicular direction was measured using a Metricon prism coupler "Model 2010 / M." The refractive index values ​​were measured at 404 nm, 594 nm, and 827 nm, and the value at 589 nm obtained by Cauchy dispersion fitting was used. The refractive index of the hard coat layer was measured by pressing the hard coat layer of the laminate against the prism of the prism coupler. There was no refractive index anisotropy in the plane of the hard coat layer.

[0205] <Pencil hardness> In accordance with JIS K5600, the pencil hardness of the hard coat layer-formed surface of the laminate was measured with a load of 750 g to evaluate the surface hardness. Both pencil scratch tests in the MD and TD directions were performed, and the higher hardness value was used. Higher hardness indicates better scratch resistance. (Here, the coating direction during film production was defined as MD, and the direction perpendicular to MD was defined as TD.)

[0206] <Repeated bending test (bending resistance)> The laminate was wrapped 180° around a cylindrical rod with a radius of 1.5 mm with the hard coat side facing inward and the film side facing outward, and the laminate was bent and then returned to the extended state. This test was repeated 10 times, and the presence or absence of cracks or breaks near the bent portion was visually confirmed. Those without cracks or breaks were evaluated as ◯, and those with cracks or breaks were evaluated as ×. None of the laminates of the Examples and Comparative Examples showed cracks or breaks and had good bending resistance.

[0207] <Amplitude, which is the difference between the maximum and minimum values ​​of light transmittance at wavelengths of 700 to 800 nm> The transmittance was measured at wavelengths of 700 to 800 nm using a UV-visible spectrophotometer (JASCO Corporation: Model V-770). The obtained transmittance spectrum data was smoothed using a five-term moving average process, and the difference between the maximum and minimum transmittance (%) values ​​at wavelengths of 700 to 800 nm was taken as the amplitude.

[0208] <Interference unevenness> The transparent film surface of the laminate was attached to a black PET film with adhesive (Kukkiri Mieru, manufactured by Tomoegawa Paper Co., Ltd.) The laminate with the black PET attached was visually observed from the hard coat layer side under a three-wavelength fluorescent lamp, and the intensity of interference unevenness was judged according to the following criteria. ◯: A very slight color change (interference unevenness) is observed. Relatively good, and at a practically preferable level. △: A strong color change (interference unevenness) is observed, which is at a level that is not suitable for practical use. [Table 4]

[0209] In the laminates of the transparent film and hard coat layer made of the blend resins of Examples 1 and 2, the refractive index of the transparent film was low, so the difference in refractive index between the hard coat layer and the transparent film layer was small, and the amplitude of the transmittance was small. As a result, interference unevenness was good and the total light transmittance was high. In addition, the pencil hardness was high and the bending resistance (repeated bending test) was also excellent. Therefore, the laminates can be suitably used as cover windows for flexible displays. In particular, despite containing polyimide resin, interference unevenness was very weak, the total light transmittance was very high at 91.1% or more, and the pencil hardness was good at 3H or more.

[0210] Furthermore, the constituent components of the transparent films of the blend resins of Examples 1 and 2 do not contain fluorine atoms other than those in which the fluorinated methyl structure derived from TFMOB is directly bonded to an oxygen atom, and therefore, compared to the laminates of Comparative Examples 1 to 3, it is expected that the environmental decomposition properties of fluorine-containing compounds will be improved and the environmental persistence of fluorine-containing compounds will be significantly reduced.

[0211] The laminate of the transparent film made of polyimide alone and the hard coat layer in Comparative Example 3 had a refractive index of 1.619 and a transmittance amplitude of 0.28%, which were higher than those of Examples 1 and 2, a total light transmittance of 88.9%, which was poor, and the interference unevenness was also poor.

Claims

1. A laminate including a transparent film and a hard coat layer, the transparent film is a resin composition containing at least a polyimide resin and a solvent-soluble resin other than a polyimide resin, and having a refractive index of 1.600 or less; the polyimide-based resin contains a tetracarboxylic dianhydride-derived structure and a diamine-derived structure, As a diamine-derived structure, CF ３ -O-, -(CF ２ -O) ｎ -, -O-(CF ２ -CF ２ -O) ｎ - a diamine-derived structure having any structure selected from the following (wherein n is an integer of 1 to 20): A laminate comprising, as a tetracarboxylic dianhydride-derived structure, any one of a tetracarboxylic dianhydride-derived structure selected from the group consisting of a tetracarboxylic dianhydride having an ether bond, a tetracarboxylic dianhydride having a fluorene structure, a tetracarboxylic dianhydride having a xanthene structure, and a bis(trimellitic anhydride) ester.

2. The polyimide resin is a CF directly bonded to an aromatic ring. ３ - group or -C(CF ３ ) ２ the content of tetracarboxylic dianhydride-derived structures having - is less than 0.5 mol % in all tetracarboxylic dianhydride-derived structures, CF directly attached to aromatic ring ３ - group or -C(CF ３ ) ２ 2. The laminate according to claim 1, wherein the content of the diamine-derived structure having - is less than 0.5 mol % of all diamine-derived structures.

3. 2. The laminate according to claim 1, wherein the polyimide resin contains an alicyclic tetracarboxylic dianhydride-derived structure as the tetracarboxylic dianhydride-derived structure, and the amount of the alicyclic tetracarboxylic dianhydride relative to the total amount of the tetracarboxylic dianhydride is 1 to 80 mol %.

4. The laminate according to claim 3, wherein the alicyclic tetracarboxylic dianhydride is any one of 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-butanetetracarboxylic dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, and 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic acid-3,4:3',4'-dianhydride.

5. The CF ３ -O-, -(CF ２ -O) ｎ -, -O-(CF ２ -CF ２ -O) ｎ - (wherein n is an integer of 1 to 20) is any diamine selected from 2,2'-bis(trifluoromethoxy)benzidine, 3,3'-bis(trifluoromethoxy)benzidine, and 2,3'-bis(trifluoromethoxy)benzidine.

6. The aromatic acid dianhydride other than any one acid dianhydride selected from the acid dianhydrides having an ether bond, the acid dianhydride having a fluorene structure, the acid dianhydride having a xanthene structure, and the bis(trimellitic anhydride) ester, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 2,2',3,3', -biphenyltetracarboxylic acid dianhydride, pyromellitic acid dianhydride, 1,2,3,4-benzenetetracarboxylic acid dianhydride, and 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride, the laminate according to claim 1, comprising at least one of the following.

7. 2. The laminate according to claim 1, wherein the polyimide resin has a weight average molecular weight of 90,000 to 500,000.

8. 2. The laminate according to claim 1, wherein the absolute value of the difference between the refractive index of the transparent film and the refractive index of the hard coat layer is 0.090 or less.

9. 2. The laminate according to claim 1, wherein the total light transmittance is 90.3% or more.

10. 2. The laminate according to claim 1, wherein the pencil hardness is H or more.

11. 2. The laminate according to claim 1, wherein the amplitude, which is the difference between the maximum and minimum values ​​of light transmittance (%) in the wavelength range of 700 to 800 nm, is 0.25 (%) or less.

12. 2. The laminate according to claim 1, wherein the thickness of the hard coat layer is 9 μm or less.

13. 2. The laminate according to claim 1, wherein the solvent-soluble resin other than the polyimide resin is an acrylic resin.

14. 14. The laminate according to claim 13, wherein the acrylic resin is an acrylic resin containing methyl methacrylate as a main component.

15. 2. The laminate according to claim 1, wherein the hard coat layer is an acrylic hard coat layer.

16. 16. The laminate according to claim 15, wherein the acrylic hard coat layer is a cured product of a curable composition containing dipentaerythritol hexaacrylate.

17. 2. The laminate according to claim 1, wherein the hard coat layer is a siloxane-based hard coat layer.

18. The laminate according to claim 17, wherein the siloxane-based hard coat layer comprises a cured product of a curable composition containing a condensate of a silane compound having an alicyclic epoxy group in the molecule, represented by the following general formula (4): (wherein, in formula (4), R １ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ２ is a hydrogen atom or a monovalent hydrocarbon group selected from an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms, x is 2 or 3, and Y is an alicyclic epoxy group. 【Chemistry 1】

19. 2. The laminate according to claim 1, wherein the difference between the maximum refractive index and the minimum refractive index in the plane of the transparent film is 0.005 or more.

20. 2. The laminate according to claim 1, wherein the transparent film has a thickness of 20 to 100 μm.

21. 2. The laminate according to claim 1, wherein the transparent film has a tensile modulus of elasticity of 5.0 GPa or more.

22. A display comprising the laminate according to any one of claims 1 to 21.

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