JP2024115450A - Resin composition, molded article, resin film, and method for producing resin film - Google Patents

Abstract

[Problem] The present invention aims to provide a resin composition, molded article, and resin film that have suitable transparency, a fast solvent drying rate when formed into a film by a solution casting method, and good appearance unevenness, as well as a method for manufacturing a resin film. [Solution] The above problem can be solved by a resin composition, molded article, and resin film, as well as a method for manufacturing a resin film, which comprises an acrylic resin and a polyimide resin, the polyimide resin having a specific diamine-derived structure and a specific tetracarboxylic dianhydride-derived structure, the polyimide resin being contained in the resin composition in an amount of 5% by weight or more and less than 20% by weight based on the total of the acrylic resin and the polyimide resin, and the acrylic resin and the polyimide resin being compatible in a solvent. [Selected Figure] None

Description

The present invention relates to a resin composition, a molded body, a resin film, and a method for producing a resin film.

Acrylic films made from acrylic resins such as polymethyl methacrylate (hereinafter sometimes abbreviated as "PMMA") are ideal for use in optical films due to their excellent transparency, dimensional stability, low moisture absorption, etc.

Acrylic films are sometimes produced by a solution casting method in which acrylic resin dissolved in a solvent such as methylene chloride is cast into a film. For example, Patent Document 1 describes a manufacturing method in which acrylic resin with a mass average molecular weight of 80,000 to 150,000 is turned into a film using a solution casting method, in which the solvent is dried until the acrylic film has self-supporting properties, and then the PET is peeled off and removed.

JP2007-118266

However, when acrylic resin is used to form a film by the solution casting method as described above, the drying of the solvent takes a long time, resulting in poor productivity and the resulting acrylic film having problems such as uneven thickness and uneven appearance. In view of these problems, the present invention aims to provide a resin composition, molded body, and resin film that have suitable transparency for an optical film, while having a fast drying rate of the solvent when formed into a film by the solution casting method, and that have good uneven thickness and uneven appearance, as well as a method for producing the resin film.

After extensive research, the inventors discovered that the above problem can be solved by using the following configuration.

1) A resin composition containing an acrylic resin and a polyimide resin, the polyimide resin has a diamine-derived structure represented by general formula (IIa) and a tetracarboxylic dianhydride-derived structure represented by general formula (IIIa), Y is a diamine residue which is a divalent organic group, and X is a tetracarboxylic dianhydride residue which is a tetravalent organic group, the polyimide resin is contained in the resin composition in an amount of 5% by weight or more and less than 20% by weight based on the total weight of the acrylic resin and the polyimide resin, and the acrylic resin and the polyimide resin are compatible in a solvent.

2) The resin composition according to 1), characterized in that the acrylic resin is an acrylic resin whose main component is methyl methacrylate.

3) The resin composition according to 1) or 2), in which the diamine-derived structure has a fluoroalkyl group and the tetracarboxylic acid dianhydride-derived structure contains an alicyclic tetracarboxylic acid dianhydride.

4) The resin composition according to 1) to 3), in which the diamine having a fluoroalkyl group includes a fluoroalkyl-substituted benzidine.

5) The resin composition according to 4), in which the fluoroalkyl-substituted benzidine is 2,2'-bis(trifluoromethyl)benzidine.

6) The resin composition according to any one of 3) to 5), wherein the polyimide has a ratio of structures derived from diamines having fluoroalkyl groups to the total amount of structures derived from diamines of 20 mol % or more.

7) The resin composition according to any one of 1) to 6), characterized in that the tetracarboxylic dianhydride is one or more alicyclic tetracarboxylic dianhydrides selected from the group consisting of 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic-3,4:3',4'-dianhydride.

8) The resin composition according to 7), in which the polyimide further contains a fluorine-containing aromatic tetracarboxylic dianhydride as a tetracarboxylic dianhydride component.

9) The resin composition according to either 7) or 8), in which the amount of alicyclic tetracarboxylic dianhydride relative to the total amount of the acid dianhydride components of the polyimide is 1 to 80 mol %.

10) A molded article comprising the resin composition described in any one of 1) to 9).

11) A film comprising the resin composition described in any one of 1) to 9).

12) The film described in 11) has a total light transmittance of 90% or more, a haze of 1% or less, and a yellowness index of 1.0 or less.

13) A method for producing a resin film, comprising: a dissolving step of dissolving the resin composition according to any one of 1) to 9) in a solvent to prepare a resin solution; a coating step of applying the resin solution onto a support to form a coating film; a drying step of drying the coating film so that the residual solvent is 5 to 20% by weight; and a peeling step of peeling the dried coating film from the support to obtain a green sheet.

The present invention provides a resin composition, molded article, and resin film that have suitable transparency for an optical film, while having a fast solvent drying rate when formed into a film by a solution casting method, and has good thickness unevenness and appearance unevenness, as well as a method for producing the resin film.

[Resin composition and film containing resin composition]
One embodiment of the present invention is a resin composition containing an acrylic resin and a polyimide resin, the polyimide resin having a diamine-derived structure represented by general formula (IIa) and a tetracarboxylic dianhydride-derived structure represented by general formula (IIIa), Y is a diamine residue which is a divalent organic group, and X is a tetracarboxylic dianhydride residue which is a tetravalent organic group, the polyimide resin is contained in the resin composition in an amount of 5% by weight or more and less than 20% by weight with respect to the total weight of the acrylic resin and the polyimide resin, and the acrylic resin and the polyimide resin are compatible in a solvent.

<Acrylic resin>
The acrylic resin is a polymer of an acrylic acid ester or a methacrylic acid ester. The acrylic resin is not limited as long as it shows transparency when blended with a polyimide resin, but it is preferably a solvent-soluble resin. Being a solvent-soluble resin is preferable in that it is easy to obtain a uniform mixed state with polyimide by mixing in a solvent. In the present application, the solvent may be referred to as a solvent. The acrylic resin may be a copolymer of an acrylic acid ester, a methacrylic acid ester, acrylic acid, or methacrylic acid, or may be a copolymer of another resin such as styrene.

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, and methyl (meth)acrylate-styrene copolymers. The acrylic resins may be modified to introduce glutarimide structural units or lactone ring structural units.

From the viewpoints of transparency, compatibility with polyimide resin, and mechanical strength of molded bodies such as resin films, it is preferable that the acrylic resin has methyl methacrylate as the 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. The acrylic resin may also be an acrylic polymer having a methyl methacrylate content in the above range, into which a glutarimide structure or a lactone ring structure has been introduced.

From the viewpoint of the heat resistance of the resin composition, molded body, and resin film of the present invention, 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.

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

From the viewpoint of the thermal stability and light stability of the resin composition, molded body, and resin film of the present invention, it is preferable that the acrylic resin has a small content of reactive functional groups such as ethylenically unsaturated groups and carboxy 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 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. A small acid value tends to increase the stability of the acrylic resin and improve its compatibility with polyimide resins.

An example of an acrylic resin is Parapet G (Kuraray Co., Ltd., weight average molecular weight 100,000, Tg: 101°C).

<Polyimide>
Polyimide is a polymer having a structural unit represented by the general formula (I), and is obtained by dehydrating and cyclizing a polyamic acid obtained by addition polymerization of a tetracarboxylic dianhydride (hereinafter, sometimes referred to as "acid dianhydride") and a diamine. That is, polyimide is a polycondensation product of a tetracarboxylic dianhydride and a diamine, and has a tetracarboxylic dianhydride-derived structure (acid dianhydride component) and a diamine-derived structure (diamine component). In addition, polyimide may be a polyamideimide in which a part of the acid dianhydride-derived structure (acid dianhydride component) is replaced with a structure derived from a diacid halide such as terephthalic acid chloride. In the present invention, either polyimide or polyamideimide can be selected, but polyimide may be preferred in terms of compatibility with acrylic resins. Polyimide and polyamideimide can also be used in combination. Hereinafter, polyimide and polyamideimide are also referred to as polyimide-based resins. In addition, polyimide-based resins can also be synthesized by condensation by decarbonation of a diisocyanate and a tetracarboxylic dianhydride.

In general formula (I), Y is a divalent organic group, and X is a tetravalent organic group. Y is a diamine residue, which is an organic group obtained by removing two amino groups from a diamine represented by the following general formula (II). When a diisocyanate is used to synthesize a polyimide resin, Y is a diisocyanate residue, which is an organic group obtained by removing two isocyanate groups from a diisocyanate compound. X is a tetracarboxylic dianhydride residue, which is an organic group obtained by removing two carboxy anhydride groups from a tetracarboxylic dianhydride represented by the following general formula (III).

In other words, the polyimide resin contains a structural unit represented by the following general formula (IIa) and a structural unit represented by the following general formula (IIIa), and has a structural unit represented by general formula (I) by forming an imide bond between the diamine-derived structure (IIa) and the tetracarboxylic dianhydride-derived structure (IIIa).

(Diamine)
The diamine component of the polyimide resin used in this embodiment is not particularly limited. From the viewpoint of solubility, the diamine of the polyimide resin is preferably one or more selected from the group consisting of a fluoroalkyl group, a fluorine group, an alicyclic structure, a fluorene structure, and a sulfone group. Among them, from the viewpoint of achieving both the solubility and transparency of the polyimide resin, it is preferable that the polyimide resin contains a fluorine-containing diamine as a diamine component, especially a diamine having a fluoroalkyl group such as fluoroalkyl-substituted benzidine.

It is particularly preferred that the diamine-derived structure has a fluoroalkyl group and the tetracarboxylic acid dianhydride-derived structure contains an alicyclic tetracarboxylic acid dianhydride as described below.

Fluorine-containing diamines include diamines having a fluoroalkyl group, such as fluoroalkyl-substituted benzidines. Specific examples of fluoroalkyl-substituted benzidines include 2-(trifluoromethyl)benzidine, 3-(trifluoromethyl)benzidine, 2,3-bis(trifluoromethyl)benzidine, 2,5-bis(trifluoromethyl)benzidine, 2,6-bis(trifluoromethyl)benzidine, 2,3,5-tris(trifluoromethyl)benzidine, 2,3,6-tris(trifluoromethyl)benzidine, 2,3,5,6-tetrakis(trifluoromethyl)benzidine, 2,2'-bis(trifluoromethyl)benzidine, 3,3'-bis(trifluoromethyl)benzidine, 2,3'-bis(trifluoromethyl)benzidine, methyl)benzidine, 2,2',3-bis(trifluoromethyl)benzidine, 2,3,3'-tris(trifluoromethyl)benzidine, 2,2',5-tris(trifluoromethyl)benzidine, 2,2',6-tris(trifluoromethyl)benzidine, 2,3',5-tris(trifluoromethyl)benzidine, 2,3',6-tris(trifluoromethyl)benzidine, 2,2',3,3'-tetrakis(trifluoromethyl)benzidine, 2,2',5,5'-tetrakis(trifluoromethyl)benzidine, 2,2',6,6'-tetrakis(trifluoromethyl)benzidine, etc.

Among these, fluoroalkyl-substituted benzidines having a fluoroalkyl group at the 2-position of the biphenyl are preferred, and 2,2'-bis(trifluoromethyl)benzidine (hereinafter referred to as "TFMB") is particularly preferred. By having fluoroalkyl groups at the 2- and 2'-positions of the biphenyl, in addition to the decrease in π electron density due to the electron-withdrawing properties of the fluoroalkyl group, the bond between the two benzene rings of the biphenyl is twisted due to the steric hindrance of the fluoroalkyl group, decreasing the planarity of the π conjugation, so that the absorption edge wavelength shifts to shorter wavelengths, reducing coloration of the polyimide resin and tending to increase solubility in organic solvents.

The content of diamines having fluoroalkyl groups, such as fluoroalkyl-substituted benzidine, relative to the total amount of the diamine-derived structure is preferably 20 mol% or more, more preferably 50 mol% or more, even more preferably 70 mol% or more, and may be 80 mol% or more, 85 mol% or more, or 90 mol% or more. A high content of fluoroalkyl-substituted benzidine suppresses coloration of the polyimide resin and tends to increase mechanical strength, such as pencil hardness and elastic modulus.

Other than fluoroalkyl-substituted benzidine, diamines having a fluoroalkyl group include diamines having an aromatic ring to which a fluoroalkyl group is bonded, such as 1,4-diamino-2-(trifluoromethyl)benzene, 1,4-diamino-2,3-bis(trifluoromethyl)benzene, 1,4-diamino-2,5-bis(trifluoromethyl)benzene, 1,4-diamino-2,6-bis(trifluoromethyl)benzene, 1,4-diamino-2,3,5-tris(trifluoromethyl)benzene, 1,4-diamino, 2,3,5,6-tetrakis(trifluoromethyl)benzene, and diamines having a fluoroalkyl group that is not directly bonded to an aromatic ring, such as 2,2-bis(4-aminophenyl)hexafluoropropane, 2,2-bis(3-aminophenyl)hexafluoropropane, and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane.

In addition, examples of diamines having a fluorine-containing group other than a fluoroalkyl group include 2-fluorobenzidine, 3-fluorobenzidine, 2,3-difluorobenzidine, 2,5-difluorobenzidine, 2,6-difluorobenzidine, 2,3,5-trifluorobenzidine, 2,3,6-trifluorobenzidine, 2,3,5,6-tetrafluorobenzidine, 2,2'-difluorobenzidine, 3,3'-difluorobenzidine, 2,3'-difluorobenzidine, 2,2',3-trifluorobenzidine, 2,3,3'-trifluorobenzidine, 2,2',5-trifluorobenzidine, 2,2',6-trifluorobenzidine, 2,3',5-trifluorobenzidine, 2,3',6 -trifluorobenzidine, 2,2',3,3'-tetrafluorobenzidine, 2,2',5,5'-tetrafluorobenzidine, 2,2',6,6'-tetrafluorobenzidine, 2,2',3,3',6,6'-hexafluorobenzidine, 2,2',3,3',5,5',6,6'-octafluorobenzidine, 1,4-diamino-2-fluorobenzene, 1,4-diamino-2,3-difluorobenzene, 1,4-diamino-2,5-difluorobenzene, 1,4-diamino-2,6-difluorobenzene, 1,4-diamino-2,3,5-trifluorobenzene, 1,4-diamino-2,3,5,6-tetrafluorobenzene, 2,2'-dimethylbenzidine, etc. By using a fluorine-containing diamine, a molded product of a polyimide resin having excellent transmittance can be obtained.

The polyimide resin may contain a diamine that does not contain fluorine as a diamine component. Examples of diamine components that do not contain fluorine and have excellent compatibility with resins other than polyimide include diamines with alicyclic structures, diamines with fluorene structures, and diamines with sulfone groups.

Examples of diamines having an alicyclic structure include isophorone diamine, 1,2-cyclohexane diamine, 1,3-cyclohexane diamine, 1,4-cyclohexane diamine, 1,2-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, bis(aminomethyl)norbornene, 4,4'-methylenebis(cyclohexylamine), bis(4-aminocyclohexyl)methane, 4,4'-methylenebis(2-methylcyclohexylamine), adamantane-1,3-diamine, 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane, 2,5-bis(aminomethyl)bicyclo[2.2.1]heptane, and 1,1-bis(4-aminophenyl)cyclohexane. By using diamines having an alicyclic structure, molded products having excellent elastic modulus, transmittance, and mechanical strength can be obtained.

An example of a diamine with a fluorene structure is 9,9-bis(4-aminophenyl)fluorene. By using a diamine with a fluorene structure, it is possible to obtain a molded product with excellent elastic modulus and mechanical strength.

Examples of diamines having a sulfone group include 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenyl sulfone, and 4,4'-bis[4-(4-aminophenoxy)phenoxy]diphenyl sulfone. By using a diamine having a sulfone group, the solubility and transparency of the polyimide in a solvent may be improved, and mechanical properties such as elastic modulus and toughness may be improved. Among diaminodiphenyl sulfones, 3,3'-diaminodiphenyl sulfone (3,3'-DDS) and 4,4'-diaminodiphenyl sulfone (4,4'-DDS) are preferred. 3,3'-DDS and 4,4'-DDS may be used in combination. By using a diamine with a sulfone group, a molded product with excellent elastic modulus and mechanical strength can be obtained.

Examples of diamines other than those mentioned above include p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, p-xylylenediamine, m-xylylenediamine, o-xylylenediamine, 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'-diaminobenzyl Zofenone, 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)-2-(4-aminophenyl)propane, 1,1-di(3-aminophenyl)-1-phenylethane, 1,1-di(4-aminophenyl)-1 -phenylethane, 1-(3-aminophenyl)-1-(4-aminophenyl)-1-phenylethane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminobenzoyl)benzene, 1,3-bis(4-aminobenzoyl)benzene, 1,4-bis(3-aminobenzoyl)benzene, 1,4- Bis(4-aminobenzoyl)benzene, 1,3-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(4-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(4-amino-α,α-dimethylbenzyl)benzene, 2,6-bis(3-aminophenoxy)benzonitrile, 2,6-bis(3-aminophenoxy)pyridine, 4,4'-bis(3-aminophenoxy)biphenyl phenyl, 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]ether, bis[4-(4-aminophenoxy)phenyl]ether, 2,2-bis[4-(3-aminophenoxy) phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,3- Bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 4,4'-bis[4-(4-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 3,3'-diamino-4,4'- Examples of aromatic diamines include 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'-spirobiindane, and 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane.

Diamines include 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, and triethylene glycol. Chain diamines such as bis(3-aminopropyl)ether, ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, α,ω-bis(3-aminopropyl)polydimethylsiloxane, and α,ω-bis(3-aminobutyl)polydimethylsiloxane can also be used.

(Tetracarboxylic acid dianhydride)
The acid dianhydride component of the polyimide resin used in this embodiment is not particularly limited. From the viewpoint of compatibility between the polyimide resin and the acrylic resin, it is preferable that the acid dianhydride component of the polyimide resin contains an alicyclic tetracarboxylic acid dianhydride. The alicyclic tetracarboxylic acid dianhydride has at least one alicyclic structure, and may have both an alicyclic ring and an aromatic ring in one molecule. The alicyclic ring may be polycyclic or may have a spiro structure.

Alicyclic tetracarboxylic dianhydrides include 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,3,4-cyclopentane tetracarboxylic dianhydride, 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride, 1,2,3,4-butane tetracarboxylic dianhydride, meso-butane-1,2,3,4-tetracarboxylic dianhydride, 1,1'-bicyclohexane-3,3',4,4' tetracarboxylic acid-3,4:3',4'-dianhydride, Norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic dianhydride, 2,2'-binorbornane-5,5',6,6'tetracarboxylic dianhydride, 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, cyclohexane-1,4-diylbis(methylene)bis(1,3-dioxo so-1,3-dihydroisobenzofuran-5-carboxylate), 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 5,5'-[cyclohexylidenebis(4,1-phenyleneoxy)]bis-1,3-isobenzofurandione, 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-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[6.4.0.0(2,7)]dodecane-1,8:2,7-tetracarboxylic dianhydride, 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, decahydro[2]benzopyrano[6,5,4,-def][2]benzopyran-1,3,6,8-tetrone, and the like.

Among alicyclic tetracarboxylic dianhydrides, from the viewpoint of the transparency and mechanical strength of the polyimide, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (H-PMDA) or 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic acid-3,4:3',4'-dianhydride (H-BPDA) are preferred, with 1,2,3,4-cyclobutanetetracarboxylic dianhydride being particularly preferred.

From the viewpoint of enhancing the compatibility between the acrylic resin and the polyimide resin, the content of the alicyclic tetracarboxylic dianhydride relative to 100 mol% of the total amount of the acid dianhydride components is preferably 1 mol% or more, more preferably 3 mol% or more, and even more preferably 5 mol% or more, and may be 6 mol% or more, 7 mol% or more, 8 mol% or more, 9 mol% or more, 10 mol% or more, 12 mol% or more, or 15 mol% or more. The amount of the alicyclic tetracarboxylic dianhydride required to provide compatibility with the acrylic resin may vary depending on the type of acrylic resin and the amount of the alicyclic tetracarboxylic dianhydride. For example, when the alicyclic tetracarboxylic dianhydride is 1,2,3,4-cyclobutane tetracarboxylic dianhydride (CBDA), the content of CBDA relative to 100 mol% of the total amount of the acid dianhydride components is preferably 6 mol% or more, more preferably 8 mol% or more, and even more preferably 10 mol% or more.

From the viewpoint of ensuring the solubility of the polyimide resin in an organic solvent, 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 78 mol% or less, and even more preferably 76 mol% or less, and may be 74 mol% or less, 72 mol% or less, 70 mol% or less, 65 mol% or less, 60 mol% or less, 55 mol% or less, or 50 mol% or less. In order to make the polyimide resin soluble in a low-boiling halogen-based solvent such as methylene chloride, the content of the alicyclic tetracarboxylic dianhydride is preferably 45 mol% or less, more preferably 40 mol% or less, and may be 35 mol% or less.

From the viewpoint of making the polyimide-based resin soluble in an organic solvent, it is preferable that the acid dianhydride component contains a fluorine-containing aromatic tetracarboxylic acid dianhydride in addition to an alicyclic tetracarboxylic acid dianhydride.

Fluorine-containing aromatic tetracarboxylic acid dianhydrides include 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}-1,1,1,3,3,3-hexafluoropropane dianhydride, 1,4-bis(trifluoromethyl)pyromellitic dianhydride, and 4-trifluoromethylpyromellitic dianhydride. , 3,6-di[3',5'-bis(trifluoromethyl)phenyl]pyromellitic dianhydride, 1-[3',5'-bis(trifluoromethyl)phenyl]pyromellitic dianhydride, N,N'-[[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bis(6-hydroxy-3,1-phenylene)]bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxamide], etc. Among them, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride (hereinafter referred to as "6FDA") is particularly preferred.

From the viewpoint of making the polyimide-based resin soluble in an organic solvent, the content of the fluorine-containing aromatic tetracarboxylic acid dianhydride 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 content of the fluorine-containing aromatic tetracarboxylic acid dianhydride relative to 100 mol% of the total amount of the acid dianhydride components is preferably 99 mol% or less, more preferably 95 mol% or less, even more preferably 90 mol% or less, and may be 85 mol% or less, 80 mol% or less, 75 mol% or less, or 70 mol% or less.

From the viewpoint of obtaining a polyimide-based resin that is both soluble in organic solvents and compatible with resins other than polyimide, the total content of the alicyclic tetracarboxylic acid dianhydride and the fluorine-containing aromatic tetracarboxylic acid dianhydride relative to the total amount of the acid dianhydride components (100 mol%) is preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 65 mol% or more, and may be 70 mol% or more, 75 mol% or more, 80 mol% or more, 85 mol% or more, 90 mol% or more, or 95 mol% or more.

The polyimide resin may contain a tetracarboxylic acid dianhydride other than the alicyclic tetracarboxylic acid dianhydride and the fluorine-containing aromatic tetracarboxylic acid dianhydride as the acid dianhydride component. Among the tetracarboxylic acid dianhydrides other than those mentioned above, examples that enhance compatibility with resins other than polyimides include tetracarboxylic acid dianhydrides having an ester structure, tetracarboxylic acid dianhydrides having an ether bond, and aromatic tetracarboxylic acid dianhydrides.

As a tetracarboxylic dianhydride having an ester structure, a bis(trimellitic anhydride) ester is represented by the following general formula (1).

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

In formula (A), R ¹ is a fluorine atom, an alkyl group having 1 to 20 carbon atoms, or a fluoroalkyl group having 1 to 20 carbon atoms, and m is an integer from 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. When R ¹ is a fluoroalkyl group having 1 to 20 carbon atoms, the bis(trimellitic anhydride) ester corresponds to a tetracarboxylic dianhydride having a fluoroalkyl group.

In formula (B), R ² is a fluorine atom, an alkyl group having 1 to 20 carbon atoms, or a fluoroalkyl 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. When R ² is a fluoroalkyl group having 1 to 20 carbon atoms, the bis(trimellitic anhydride) ester corresponds to a tetracarboxylic dianhydride having a fluoroalkyl group.

The group represented by formula (C) is a group in which two hydroxyl groups have been removed from 4,4'-isopropylidenediphenol (bisphenol A). The group represented by formula (D) is a group in which two hydroxyl groups have been removed from resorcinol.

In formula (E), p is an integer from 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.

The group represented by formula (F) is a group obtained by removing two hydroxyl groups from 1,4-cyclohexanedimethanol.

In formula (G), R ³ is a hydrogen atom, a fluorine atom, an alkyl group having 1 to 20 carbon atoms, or a fluoroalkyl 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 R ³ is a fluoroalkyl group having 1 to 20 carbon atoms, the bis(trimellitic anhydride) ester corresponds to a tetracarboxylic dianhydride having a fluoroalkyl group.

The bis(trimellitic anhydride) ester is preferably an aromatic ester, and among the above (A) to (K), Q is preferably (A), (B), (C), (D), (G), (H), or (I). Among these, (A) to (D) are preferred, with (B) and (C) being particularly preferred. When Q is a group represented by general formula (B), from the viewpoint of the solubility of the polyimide, Q is preferably 2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diyl represented by the following formula (B1).

In general formula (1), the acid dianhydride in which Q is a group represented by formula (B1) 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 (2).

Examples of tetracarboxylic dianhydrides having an ether bond include 3,4'-oxydiphthalic anhydride, 4,4'-oxydiphthalic anhydride, 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride, etc. Among the acid dianhydrides having an ether bond, 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride is preferred from the viewpoint of compatibility with acrylic resins.

Aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, mellophanic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-biphenyl tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 5,5'-dimethylmethylenebis(phthalic anhydride), 2,3,6,7-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, terphenyl tetracarboxylic dianhydride, 9,9- Examples include bis(3,4-dicarboxyphenyl)fluorene dianhydride, N,N'-(9H-fluoren-9-ylidene di-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxamide], 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 2,2-bis(4-hydroxyphenyl)propane dibenzoate-3,3',4,4'-tetracarboxylic dianhydride, 11,11-dimethyl-1H-difuro[3,4-b:3',4'-i]xanthene-1,3,7,9(11H)-tetrone, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic dianhydride, and the like.

Examples of aromatic acid dianhydrides other than those mentioned above include 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 1,3-bis[(3,4-dicarboxy)benzoyl]benzamide dianhydride, and bis(3,4-dicarboxyphenyl)methane dianhydride. benzene dianhydride, 1,4-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride, 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride, 2,2-bis{4-[4-(3,4-dicarboxy)phenoxy]phenyl}propane dianhydride, 2,2-bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl} Ketone dianhydride, 4,4'-bis[4-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, 4,4'-bis[3-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis Examples of the dianhydride include {4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, and bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylic acid)-1,4-phenylene ester. As the dianhydride, a chain aliphatic dianhydride such as ethylenetetracarboxylic dianhydride or butanetetracarboxylic dianhydride may be used.

Among aromatic tetracarboxylic dianhydrides, pyromellitic dianhydride and mellophanic dianhydride are particularly preferred from the viewpoint of compatibility between polyimide resins and resins other than polyimide.

The polyimide resin may be a polyamideimide in which a portion of the acid dianhydride component is replaced with a structure derived from a diacid halide such as terephthalic acid chloride. The ratio of the diacid halide-derived component to the total amount of the acid dianhydride components (100 mol%) is preferably 40 mol% or less, more preferably 35 mol% or less, even more preferably 30 mol% or less, and may be 0 mol%. If the diacid halide-derived structure exceeds 40 mol%, the solvent solubility may decrease.

(Preparation of polyimide resin)
A polyamic acid is obtained as a polyimide precursor by the reaction of a tetracarboxylic dianhydride with a diamine, and a polyimide is obtained by dehydrating and cyclizing (imidizing) the polyamic acid. The method for preparing the polyamic acid is not particularly limited, and any known method can be applied. For example, a polyamic acid solution is obtained by dissolving a diamine and a tetracarboxylic dianhydride in approximately equimolar amounts (molar ratio of 90:100 to 110:100) in an organic solvent and stirring the mixture.

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.

When polymerizing polyamic acid, it is preferable to add tetracarboxylic dianhydride to diamine in order to suppress ring opening of tetracarboxylic dianhydride. When adding multiple types of diamine or multiple types of tetracarboxylic dianhydride, they may be added at once or in multiple portions. By adjusting the order of addition of the monomers, it is also possible to control the various physical properties of the polyimide resin.

The organic solvent used in the polymerization of polyamic acid is not particularly limited as long as it does not react with diamines and tetracarboxylic dianhydrides and can dissolve polyamic acid. Examples of organic solvents include urea solvents such as methylurea and N,N-dimethylethylurea, sulfoxide or sulfone solvents such as dimethyl sulfoxide, diphenyl sulfone, and tetramethyl sulfone, amide solvents such as N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N,N'-diethylacetamide, N-methyl-2-pyrrolidone (NMP), γ-butyrolactone, and hexamethylphosphoric acid triamide, halogenated alkyl solvents such as chloroform and dichloromethane, aromatic hydrocarbon solvents such as benzene and toluene, and ether solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, and p-cresol methyl ether. These solvents are usually used alone or in appropriate combinations of two or more as necessary. From the viewpoint of the solubility and polymerization reactivity of polyamic acid, DMAc, DMF, NMP, etc. are preferably used.

Polyimide is obtained by dehydration cyclization of polyamic acid. One method for preparing polyimide from a polyamic acid solution is to add a dehydrating agent, an imidization catalyst, etc. to the polyamic acid solution and allow the imidization to proceed in the solution. The polyamic acid solution may be heated to promote the imidization. By mixing a solution containing the polyimide produced by the imidization of polyamic acid with a poor solvent, the polyimide precipitates as a solid. By isolating the polyimide as a solid, impurities generated during the synthesis of the polyamic acid, residual dehydrating agents, imidization catalysts, etc. can be washed and removed with the poor solvent, and coloring of the polyimide and an increase in yellowness can be prevented. In addition, by isolating the polyimide as a solid, a solvent suitable for film formation, such as a low-boiling point solvent, can be used when preparing a solution for producing a molded body such as a film.

The molecular weight of the polyimide (weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC)) is preferably 10,000 to 500,000, more preferably 20,000 to 400,000, and even more preferably 40,000 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 resins other than polyimide may be poor, and the film formability may be poor.

The polyimide resin is preferably soluble in a low-boiling point solvent such as a ketone solvent or an alkyl halide solvent. When a polyimide resin is soluble in a solvent, it means that it is soluble at a concentration of 5% by weight or more. In one embodiment, the polyimide resin is soluble in methylene chloride. Since methylene chloride has a low boiling point and the remaining solvent during film production can be easily removed, the use of a polyimide resin soluble in methylene chloride is expected to improve the productivity of resin films.

From the viewpoint of the thermal stability and light stability of the resin composition and the film, it is preferable that the polyimide has low reactivity. The acid value of the polyimide 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 has a high imidization rate. A small acid value increases the stability of the polyimide and tends to improve the compatibility with resins other than polyimide.

<Ultraviolet absorbing agent>
The resin film of the present invention may contain an ultraviolet absorbing agent for the purpose of improving light resistance. The ultraviolet absorbing agent is a compound that mainly absorbs light having wavelengths in the ultraviolet region, and serves to prevent deterioration of the resin due to ultraviolet rays.

Since the resin film of the present invention contains a polyimide resin and an acrylic resin, the ratio of polyimide resin in the resin composition is small, and the polyimide resin is less likely to decompose due to coloration caused by light, and the film has good light resistance even without containing an ultraviolet absorber. It is preferable to contain an ultraviolet absorber in order to achieve even better light resistance, such as a change in yellowness index (YI) of the resin film before and after a light resistance test of 10.0 or less.

The content of the ultraviolet absorber relative to 100 parts by weight of the resin constituting the resin film is preferably 0.1 parts by weight or more, more preferably 1.0 parts by weight or more, even more preferably 3.0 parts by weight or more, and particularly preferably 5.0 parts by weight or more. The content of the ultraviolet absorber is preferably 10.0 parts by weight or less, more preferably 8.0 parts by weight or less, and particularly preferably 6.0 parts by weight or less. If the content of the ultraviolet absorber is less than 0.1 parts by weight, the light resistance tends to be low, and if the content is more than 10.0 parts by weight, the yellowness index (YI) of the resin film tends to be high due to the absorption of light on the short wavelength side of the visible light range indicated by the ultraviolet absorber, which may be undesirable.

Examples of ultraviolet absorbers include triazine-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, and hydroxybenzoate-based ultraviolet absorbers. Among these ultraviolet absorbers, triazine-based ultraviolet absorbers and benzotriazole-based ultraviolet absorbers are preferred from the viewpoint of obtaining good light resistance, and benzotriazole-based ultraviolet absorbers are particularly preferred from the viewpoint of less coloring of the resin film. Only one type of ultraviolet absorber may be used, or multiple types may be used in combination.

As the triazine-based UV absorber, commercially available triazine-based UV absorbers can be used. Examples of commercially available triazine-based UV absorbers include those with the trade names "Tinuvin 477", "Tinuvin 460", and "Tinuvin 1600" (all manufactured by BASF), "Adeka STAB LA-46" and "Adeka STAB LA-F70" (all manufactured by ADEKA Corporation), and "Kemisorb 102" (manufactured by Chemipro Chemicals).

As the benzotriazole-based UV absorber, commercially available benzotriazole-based UV absorbers can be used. Examples of commercially available benzotriazole-based UV absorbers include those sold under the trade names "Tinuvin 326" and "Tinuvin 360" (both manufactured by BASF), "Kemisorb 279" (manufactured by Chemipro Chemicals), "ADK STAB LA-24", "ADK STAB LA-29", "ADK STAB LA-31RG", "ADK STAB LA-32", and "ADK STAB LA-36" (all manufactured by ADEKA Corporation).

As the benzophenone-based UV absorber, commercially available benzophenone-based UV absorbers can be used. Examples of commercially available benzophenone-based UV absorbers include those sold under the trade names "seesorb 101" (manufactured by Shipro Chemicals Co., Ltd.) and "Adekastab 1413" (manufactured by ADEKA Corporation).

When the polyimide resin has an alkyl group or a fluoroalkyl group having 1 to 20 carbon atoms on the benzene ring, particularly when the polyimide resin has a fluoroalkylalkyl group having 1 to 20 carbon atoms on the benzene ring, a combination with a triazine-based UV absorber or a benzotriazole-based UV absorber is more preferable because good light resistance can be obtained.

In addition, when the polyimide resin has a skeleton with distortion such as a cyclobutane structure, a combination with a triazine-based UV absorber or a benzotriazole-based UV absorber is more preferable because good light resistance can be obtained.

When the resin film is a resin film obtained by a solution casting method in which a solution of a resin composition containing at least an acrylic resin, a polyimide resin, an ultraviolet absorber, and a solvent is applied onto a support and the solvent is removed, the ultraviolet absorber tends to be unevenly distributed on the surface in contact with the support. Therefore, in a light resistance test, the degree of yellowing when irradiated with light from the side in contact with the support tends to be smaller than the degree of yellowing when irradiated with light from the side not in contact with the support, which is preferable. The light resistance test can be performed by a known method, for example, a xenon weather test for 200 hours at a black panel temperature of 80° C. and an irradiance of 180 W/m ² at a wavelength of 300 nm to 400 nm.

<Bluing agent>
The resin film may contain a bluing agent. The bluing agent is an additive (dye, pigment) that absorbs light such as red, orange, and yellow, which are relatively long wavelengths in the visible light region, and adjusts the color. Examples of the bluing agent include organic pigments such as phthalocyanine blue, inorganic pigments such as ultramarine, Prussian blue, and cobalt blue, and organic dyes such as anthraquinone derivatives, indigo compounds, and methylene blue. Among these, phthalocyanine blue, ultramarine blue, anthraquinone derivatives, and indigo compounds are preferred from the viewpoint of solubility and dispersibility in resins and solvents, and phthalocyanine blue and ultramarine blue are particularly preferred from the viewpoint of heat resistance and light resistance. The bluing agent may be used alone or in combination of two or more types.

From the viewpoint of moldability of the resin film, it is preferable that the heat resistance of the bluing agent is high. The 1% weight loss temperature is preferably 200°C or higher, more preferably 220°C or higher, and particularly preferably 240°C or higher.

The resin film of the present invention does not need to contain a bluing agent because it has little coloring and is suitable for use as a display film even if it does not contain a bluing agent. In order to make the resin film of the present invention suitable for use as a cover film for displays and the like, with a yellowness index (YI) in the range of -1.0 to 1.0, the total amount of bluing agent contained in the resin film can be appropriately adjusted depending on the yellowness index (YI) required for the resin film, but in order to uniformly tone the resin film, it is preferable for the amount to be 10 ppm by weight or more, and particularly preferable for the amount to be 20 ppm by weight or more, per 100 parts by weight of the resin constituting the resin film.

As the bluing agent, any known agent can be used as appropriate. For example, examples of anthraquinone-based bluing agents include Plast Blue 8510, Plast Blue 8514, Plast Blue 8516, Plast Blue 8520, Plast Blue 8540, Plast Blue 8580, and Plast Blue 8590 (all manufactured by Arimoto Chemical Industry Co., Ltd.), examples of phthalocyanine blue-based bluing agents include ET 4B403 (manufactured by Dainichiseika Color & Chemicals Co., Ltd.) and BL-G207 (manufactured by Sanyo Pigment Co., Ltd.), and examples of ultramarine blue-based bluing agents include Ultramarine Blue 51 (manufactured by Holliday Pigments Co., Ltd.).

It is preferable that the bluing agent contained in the resin film does not change in quality due to light irradiation. In a 200-hour xenon weather test at a black panel temperature of 80° C. and an irradiance of 180 W/m ² at a wavelength of 300 nm to 400 nm, the change in transmittance before and after the test at the maximum wavelength (λmax) at which the absorption of the bluing agent in the range of 500 nm to 700 nm of the resin film is maximized is preferably less than 0.4%, more preferably 0.3% or less, and even more preferably 0.2% or less.

<Preparation of Resin Composition (Blend Resin)>
The acrylic resin and the polyimide resin are mixed to prepare a resin composition. The acrylic resin and the polyimide resin are compatible at any ratio, but the resin film of the present invention contains the polyimide resin in a range of 5% by weight or more and less than 20% by weight relative to the total of the acrylic resin and the polyimide resin, and the ratio of the acrylic resin and the polyimide resin is not particularly limited as long as it is within this range. The higher the ratio of the acrylic resin, the higher the total light transmittance of the resin film, the lower the yellowness index (YI), and the better the optical properties tend to be. The higher the ratio of the polyimide resin, the faster the drying speed of the solvent when the film is formed by the solution casting method, and the resin film with good thickness unevenness and appearance unevenness is obtained, and the elastic modulus and pencil hardness of the resin film tend to be high, and the mechanical strength tends to be excellent. From the viewpoint of the balance between thickness unevenness, appearance unevenness, and optical properties, the ratio of the polyimide resin to the total of the acrylic resin and the polyimide resin is preferably 5% by weight or more and less than 20% by weight, and more preferably 7% by weight or more and 15% by weight or less.

Polyimide resins are polymers with a special molecular structure, and generally have low solubility in organic solvents and are not compatible with other polymers. In this embodiment, the polyimide resin contains an alicyclic tetracarboxylic dianhydride as an acid anhydride component, and thus exhibits high solubility in organic solvents and compatibility with acrylic resins. Whether or not the acrylic resin and the polyimide resin are compatible is confirmed by dissolving the resin composition in a solvent that exhibits solubility in both polyimide resins and resins other than polyimide, such as N,N-dimethylformamide (DMF) or methylene chloride, so that the solid content concentration is 10% by weight. If the resin solution is not phase-separated and is transparent, it is determined that the acrylic resin and the polyimide resin are compatible in the resin composition, and if the resin solution is separated into two or more phases or is cloudy, it is determined that the acrylic resin and the polyimide resin are not compatible. The haze of a solution containing an acrylic resin and a polyimide resin, measured with an optical path length of 1 cm, is preferably 10% or less, more preferably 5% or less, even more preferably 2% or less, and particularly preferably 1% or less.

The resin composition may be a mixed solution containing an acrylic resin and a polyimide resin. The method for mixing the resins is not particularly limited, and the resins may be mixed in a solid state or in a liquid state to form a mixed solution. An acrylic resin solution and a polyimide resin solution may be prepared separately, and the two may be mixed to prepare a mixed solution of acrylic resin and polyimide resin.

The solvent for the solution containing the acrylic resin and the polyimide resin is not particularly limited as long as it shows solubility in both the acrylic resin and the polyimide resin. Examples of the solvent include amide-based solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; ether-based solvents such as tetrahydrofuran and 1,4-dioxane; ketone-based solvents such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diethyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone; and halogenated alkyl solvents such as chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene, dichlorobenzene, and methylene chloride. Among them, ketone-based solvents and halogenated alkyl solvents are preferred because they have excellent solubility in both the acrylic resin and the polyimide resin, have a low boiling point, and are easy to remove the remaining solvent during film production.

In general, polyimides have low solubility in solvents, and in many cases dissolve only in highly polar solvents. For this reason, amide-based solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone are more preferable as solvents. By using these solvents, the compatibility between acrylic resins and polyimide-based resins may be improved. In addition, by using solvents in which these polyimides are easily soluble, the viscosity of the resulting solution may be reduced, which may result in improved handleability and less occurrence of appearance defects such as unevenness when producing molded products by film formation, etc.

For the purpose of improving the workability of the film and imparting various functions, the resin composition (solution) may contain organic or inorganic low molecular weight compounds, polymeric compounds (e.g., epoxy resins), etc. The resin composition may contain dyes and pigments including bluing agents, ultraviolet absorbers, flame retardants, crosslinking agents, surfactants, leveling agents, plasticizers, fine particles, etc. The fine particles include organic fine particles such as polystyrene and crosslinked acrylic resins, and inorganic fine particles such as silica and layered silicates, and may have a porous or hollow structure.

[Forming of resin film and film characteristics]
The resin film of the present invention is obtained by forming a resin composition containing an acrylic resin and a polyimide resin into a film. Examples of the forming method include melting methods such as injection molding, transfer molding, press molding, blow molding, inflation molding, calendar molding, and melt extrusion molding. Although polyimide resins have high melting points and glass transition temperatures, resin compositions containing acrylic resins and polyimide resins tend to have lower melt viscosities than polyimide resins, and are excellent in formability such as injection molding, transfer molding, press molding, and melt extrusion molding. In addition to the melting method, a solution casting method can also be selected in which a composition containing an acrylic resin and a polyimide resin is applied in a solution state in which it is dissolved in a solvent, and the solvent is dried.

In one embodiment, the molded article is a film. The film may be molded by either the melting method or the solution casting method, but the solution casting method is preferred from the viewpoint of producing a film with excellent transparency and uniformity. In the solution casting method, a solution containing the above-mentioned acrylic resin and polyimide resin is applied onto a support, and the solvent is dried and removed to obtain a resin film.

The resin film of the present invention includes a dissolving process in which a resin composition containing an acrylic resin and a polyimide resin is dissolved in a solvent to prepare a resin solution, a coating process in which the resin solution is applied onto a support to form a coating film, a drying process in which the coating film is dried so that the residual solvent is 5 to 20% by weight, and a peeling process in which the dried coating film is peeled off from the support to obtain a green sheet, thereby obtaining a resin film with good unevenness in appearance and thickness.

Each step will be described below.
(Dissolving process)
The solvent for dissolving the resin composition containing the acrylic resin and the polyimide resin is not particularly limited as long as it shows solubility in both the acrylic resin and the polyimide resin, and examples thereof include amide-based solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; ether-based solvents such as tetrahydrofuran and 1,4-dioxane; ketone-based solvents such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diethyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone; and halogenated alkyl solvents such as chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene, dichlorobenzene, and methylene chloride. Among these, ketone-based solvents and halogenated alkyl solvents are preferred because they have excellent solubility in both the acrylic resin and the polyimide resin, have a low boiling point, and are easy to remove the remaining solvent during film production. These may be used alone or in combination.

The solids concentration of the solution of the resin composition containing the acrylic resin and the polyimide resin (resin solution) may be appropriately set depending on the molecular weight of the acrylic resin and the polyimide resin, the thickness of the resin film, the film-forming environment, etc. The solids concentration is preferably 5 to 30% by weight, more preferably 8 to 20% by weight. The resin solution may contain resin components and additives other than the resin composition. Examples of additives include ultraviolet absorbers, bluing agents, crosslinking agents, dyes, surfactants, leveling agents, plasticizers, fine particles, etc.

A solution of a resin composition containing an acrylic resin and a polyimide resin tends to have a lower solution viscosity than a solution of a polyimide resin with the same solid content concentration. This makes the resin solution easier to handle, such as when transporting it, and has high coatability, which is advantageous in reducing unevenness in film thickness.

(Coating process)
As a method for applying the resin solution onto the support, a known method using a bar coater or a comma coater can be applied. As the support, a glass substrate, a metal substrate such as SUS, a metal drum, a metal belt, a plastic film, etc. can be used. From the viewpoint of improving productivity, it is preferable to use an endless support such as a metal drum or a metal belt, or a long plastic film, etc. as the support and produce the film by roll-to-roll. When using a plastic film as the support, a material that is not dissolved in the solvent of the resin solution (dope) may be appropriately selected. Examples of the plastic material include films made of polymers such as polyester-based polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose-based polymers such as diacetyl cellulose and triacetyl cellulose, or acrylic polymers such as polycarbonate-based polymers and polymethyl methacrylate.

(Drying process)
After applying the resin solution to the substrate, the solvent is dried to prepare a coating film of the resin composition. The drying temperature and drying time are not particularly limited, but it is preferable to dry the coating film so that the residual solvent is 5% by weight or more and 20% by weight or less, and more preferably 10% by weight or more and 15% by weight or less. By setting the residual solvent amount within the above range, a self-supporting coating film can be obtained without excessively stretching the coating film or breaking the coating film during peeling in the subsequent peeling step. However, the residual solvent in the coating film indicates the amount of solvent contained in the coating film, and may be quantified by an analytical instrument such as a gas chromatograph device by dissolving the coating film in a solvent, or may be determined by the weight change before and after heating the coating film to remove the solvent.

(Peeling process)
By peeling and removing the substrate from the coating film of the resin composition containing the acrylic resin and the polyimide resin, a resin sheet (hereinafter referred to as a green sheet) having a residual solvent content of 5 to 20% by weight can be produced. A peeling roll may be used to peel and remove the substrate.

It is preferable to heat the green sheet of the resin composition containing the acrylic resin and the polyimide resin to further dry the solvent. The heating temperature is not particularly limited as long as it can remove the solvent and suppress coloration of the resulting film, and is appropriately set between room temperature and about 250°C, with 50°C to 220°C being preferred. The heating temperature may be increased in stages. In order to increase the efficiency of removing the solvent, the resin film may be peeled off from the support and dried after a certain degree of drying has progressed. In order to promote the removal of the solvent, heating may be performed under reduced pressure. If the temperature is below the decomposition temperature of the solvent-soluble resin, high-boiling point solvents such as amide solvents such as N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc) can also be dried under a nitrogen atmosphere.

Although acrylic resin films may have low toughness, the strength of the film may be improved by adopting a compatible system of acrylic resin and polyimide resin. A compatible system of acrylic resin and polyimide resin also has the effect of improving mechanical properties such as elastic modulus, bending resistance, and pencil hardness compared to acrylic resin alone. For the purpose of improving the mechanical strength of the film and imparting optical anisotropy, the resin film of the present invention may be stretched in one or more directions using any stretching method and stretching conditions. When the film is stretched, the polymer chains are oriented in the stretching direction, so that a phase difference is generated, and the strength of the film in the in-plane direction is improved, and the occurrence of breakage and cracks in the film tends to be suppressed.

In particular, in a compatible system of acrylic resin and polyimide, the tensile modulus in the stretching direction tends to increase, and as a result, the flex resistance tends to improve. The higher the ratio of methyl methacrylate in the monomer components of the acrylic resin, the more pronounced the tendency for the tensile modulus in the stretching direction to increase.

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

The film stretching method is not particularly limited. Various stretching methods such as free end stretching, fixed end stretching, free end shrinkage, and fixed end shrinkage are used. Among them, from the viewpoint of orienting the molecules in the film in one direction, it is preferable to use free end stretching, which is typified by a method in which the film is stretched in the conveying direction by the difference in peripheral speed between nip rolls in front of and behind the film (so-called longitudinal stretching), or fixed end stretching, which is typified by a method in which the film is stretched in the direction perpendicular to the conveying direction using a tenter clip device (so-called transverse stretching).

The film stretching conditions (e.g., stretching direction, stretching temperature, stretching ratio) are not particularly limited. Stretching can be performed in various directions, such as the length direction, width direction, thickness direction, and diagonal direction. The stretching temperature is not particularly limited, but is about the glass transition temperature of the film ±40°C, and may be about 120 to 300°C, 150 to 250°C, or 180 to 230°C. The stretching ratio is not particularly limited, but is about 1 to 200%, and may be 5 to 150%, 10 to 120%, or 20 to 100%. The larger the stretching ratio, the higher the tensile modulus in the stretching direction tends to be. On the other hand, if the stretching ratio is excessively large, the mechanical strength in the direction perpendicular to the stretching direction tends to decrease, and the handling properties of the film may decrease.

The film may be biaxially stretched to increase the strength in any direction in the plane. 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. If there is a difference in the stretching ratio, the mechanical strength in the direction with the larger stretching ratio tends to be relatively large. When a biaxially stretched film with anisotropic stretching ratio is used for a foldable device, it is preferable to arrange it so that the direction with the larger stretching ratio is perpendicular to the folding axis.

The thickness of the resin film is not particularly limited and may be set appropriately depending on the application. The thickness of the film is, for example, 5 to 300 μm. From the viewpoint of obtaining a film that is both self-supporting and flexible and has high transparency, the thickness of the film is preferably 20 μm to 100 μm, and may be 25 μm to 80 μm or 25 μm to 50 μm. The thickness of the 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.

The total light transmittance of the resin film is preferably 90.0% or more, more preferably 91.0% or more, even more preferably 91.5% or more, and particularly preferably 92.0% or more. A high total light transmittance is preferable because it increases the brightness of the display when the resin film is used as a display film. As described above, by mixing a polyimide resin with an acrylic resin, a film with a high total light transmittance can be obtained compared to the case where polyimide or polyamideimide is used alone.

The yellowness index (YI) of the resin film is preferably 3.0 or less, more preferably 2.0 or less, 1.0 or less, and even more preferably 0.5 or less. If the yellowness index (YI) is greater than 3.0, the display will be yellowish when the resin film is used as a display film, and the color reproducibility of the display will decrease. The yellowness index (YI) of the film is preferably -3.0 or more, more preferably -2.0 or -1.0 or more, and even more preferably -0.5 or more. If the yellowness index (YI) is less than -3.0, the display will be bluish when the resin film is used as a display film, and the color reproducibility of the display will decrease. As described above, by mixing the polyimide resin and the acrylic resin, a film with less coloring and a smaller absolute value of the yellowness index (YI) can be obtained compared to the case where the polyimide resin is used alone.

The haze of the resin film is preferably 10% or less, more preferably 1% or less, even more preferably 0.5% or less, and particularly preferably 0.3% or less. The lower the haze of the resin film, the less the image resolution is hindered when the resin film is used as a display film, which is preferable. As described above, resins made by mixing polyimide resin and acrylic resin show particularly high compatibility, so that films with low haze and high transparency can be obtained. It is preferable that the haze of the resin composition made by mixing polyimide resin and polyacrylic resin is 1% or less when a film with a thickness of 50 μm is produced.

The refractive index of the resin film is preferably such that the maximum in-plane refractive index is 1.60 or less. A low refractive index leads to a high total light transmittance. The refractive index is determined by the composition of the resin composition and the orientation state of the polymer chain. Since a resin composition consisting of polyimide and acrylic resin tends to have a high refractive index in the orientation direction of the polymer chain, the maximum in-plane refractive index direction tends to be the stretching direction. In the case of biaxial stretching, it tends to be either the first stretching direction or the second stretching direction. The maximum in-plane refractive index is more preferably 1.58 or less, even more preferably 1.56 or less, and particularly preferably 1.54 or less. It may be 1.52 or less, or 1.51 or less. A low refractive index and a high total light transmittance are preferable because they improve the visibility of the display. As described above, by mixing a polyimide resin and an acrylic resin, a film with a low refractive index can be obtained compared to the case of using polyimide or polyamideimide alone. However, when the refractive index is high due to the orientation of the polymer chain, the orientation of the polymer chain 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.

In some cases, it is preferable that the difference between the maximum and minimum in-plane refractive index of the resin film is 0.001 or more. In particular, in a uniaxially stretched film, the mechanical properties may be improved if the difference between the maximum and minimum in-plane refractive index is large. The difference between the maximum and minimum in-plane refractive index is determined by the orientation state of the polymer chain. Since a resin composition consisting of polyimide and acrylic resin tends to have a high refractive index in the orientation direction of the polymer chain, the direction in which the difference between the maximum and minimum in-plane refractive index is large is the stretching direction and the direction perpendicular thereto. The difference between the maximum and minimum in-plane refractive index is more preferably 0.01 or more, even more preferably 0.02 or more, and in some cases, 0.03 or more is particularly preferable. If the difference between the maximum and minimum in-plane refractive index is large, mechanical properties such as bending resistance and pencil hardness tend to be improved, which is preferable. However, in the case of a biaxially stretched film, the difference between the maximum and minimum in-plane refractive index does not become large, but the orientation of the polymer molecular chain occurs due to stretching, so the mechanical properties tend to be excellent.

The elastic modulus of the resin film is preferably 2.5 GPa or more. A high elastic modulus tends to improve mechanical properties such as pencil hardness and bending resistance. The elastic modulus is more preferably 2.5 GPa or more, even more preferably 3.0 GPa or more, particularly preferably 3.5 GPa or more, and may be 4.0 GPa or more. The elastic modulus of the film means the maximum elastic modulus in the plane. The elastic modulus is determined by the composition of the resin composition and the orientation state of the polymer chain. Since a resin composition consisting of polyimide and acrylic resin tends to have a high elastic modulus in the orientation direction of the polymer chain, the maximum elastic modulus in the plane is the stretching direction. In the case of biaxial stretching, it tends to be either the first stretching direction or the second stretching direction.

It is preferable that the resin film has excellent bending resistance. If the resin film has excellent bending resistance, it can be suitably used as a film for flexible displays. In the present invention, excellent bending resistance means that the resin film has no cracks or breaks after an unfolded flat resin film is folded 180° with a bending radius of 1.0 mm and then returned to its original flat state 100,000 times at a speed of 1 time per second. Such a test can be performed using a commercially available repeated bending tester, for example, a U-shaped bending durability tester manufactured by Yuasa System Co., Ltd.

The resin film preferably has a hardness of HB or more in a pencil hardness test conforming to JIS-K5600. The pencil hardness is more preferably H or more, even more preferably 2H or more, and particularly preferably 3H or more. If the pencil hardness is HB or more, the film can be suitably used as a cover window for a display.

The light resistance of the resin film is preferably such that the change in yellowness index (YI) in the light resistance test is 10.0 or less. A small change in yellowness index (YI) is preferable because it tends to cause small changes in color tone and small changes in visibility of the display even when used in an environment with a large amount of ultraviolet exposure, such as outdoors. The change in yellowness index (YI) is more preferably 4.0 or less, even more preferably 2.0 or less, and particularly preferably 1.5 or less. The light resistance test is a test in which the film is exposed for 200 hours under conditions of irradiance of 180 W/m ² at a wavelength of 300 nm to 400 nm using a xenon light source, a black panel temperature of 80° C., and no rain, and the change in yellowness index (YI) ΔYI (YI after test-YI before test) can be obtained by measuring the yellowness index (YI) before and after the test.

<Laminate>
The present invention includes a laminate in which a resin film and a functional layer are laminated. That is, another embodiment of the present invention is a laminate including at least a resin film and a functional layer. Examples of the functional layer include layers having various functions such as a hard coat layer, an ultraviolet absorbing layer, an adhesive layer, a refractive index adjustment layer, and an easy-adhesion layer. These functional layers may contain a bluing agent for the purpose of adjusting the color tone. These functional layers may contain an ultraviolet absorber for the purpose of improving light resistance. In particular, when additives such as a bluing agent or an ultraviolet absorber cannot be blended into the resin film layer from the viewpoint of compatibility or heat resistance, the color tone of the laminate can be adjusted or the light resistance of the laminate can be improved by adding an additive to the functional layer. As these functional layers, a hard coat layer that can impart scratch resistance, which is a function required for a flexible display, an adhesive layer that can impart adhesion, and an easy-adhesion layer that can impart adhesion to other layers such as a hard coat layer are more preferable.

The thickness of the functional layer can be set appropriately depending on the desired characteristics. There may be only one type of functional layer, or multiple or more types of functional layers. In addition, the functional layer may be formed on only one side of the resin film, or on both sides.

Among the functional layers, a hard coat layer is particularly preferred as a functional layer that imparts the scratch resistance required for a cover window. 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 the occurrence of scratches, an acrylic hard coat layer that is a cured product of an acrylic hard coat resin composition or a siloxane hard coat layer that is a cured product of a siloxane hard coat resin composition is preferred.

The hard coat resin composition may also contain additives. Examples of additives include fluorine-based or silicone-based leveling agents, fine particles, fillers, dispersants, plasticizers, UV absorbers, color adjusters such as bluing agents, surfactants, antioxidants, viscosity adjusters, and solvents.

[Forming of hard coat layer and laminate properties, and application of laminate to displays]
The hard coat layer of the laminate of the present invention is obtained by applying a curable composition (hard coat composition) onto a resin film (a step of forming a hard coat layer by coating), drying and removing the solvent as necessary, and then irradiating with active energy rays (a step of irradiating with active energy rays) to cure the curable composition. Among them, a method including a step of applying a composition containing a curable resin composition and a photoinitiator onto a resin film and then a step of irradiating with active energy rays is preferred from the viewpoint of productivity. The method of applying the hard coat composition is not particularly limited, and existing application 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.

The thickness of the hard coat layer of the present invention is 1 to 50 μm, preferably 1 to 30 μm. It can be appropriately selected from this range, and is preferably 3 μm or more, more preferably 5 μm or more, more preferably 40 μm or less, even more preferably 30 μm or less, and particularly preferably 25 μm or less. If the hard coat layer is thick, the hardness and impact resistance tend to be good, and if it is thinner than 1 μm, the hardness is insufficient. If the hard coat layer is thin, the bending resistance tends to be good, and if it is thicker than 50 μm, the bending resistance is insufficient.

The total thickness of the laminate of the present invention (the sum of the thickness of the functional layer and the thickness of the resin 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, 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.

When the functional layer of the laminate of the present invention is a hard coat layer, the laminate has excellent optical properties and mechanical properties derived from the resin film, as well as high scratch resistance derived from the hard coat layer. The cover window of a flexible display is required to have excellent optical properties to display images beautifully, as well as to prevent scratches and dents due to contact with various objects. Therefore, the laminate of the present invention can be suitably used for the cover window of a flexible display.

In the present invention, "excellent bending resistance" means that an unfolded flat resin film or laminate is bent 180 degrees with a bending radius of 1.5 mm or less, and then returned to its original flat state 200,000 times at a speed of 1 time per second, after which the film or laminate shows no cracks or breaks. Such a test can be performed using a commercially available repeated bending tester, such as a U-shaped bending durability tester manufactured by Yuasa System Co., Ltd.

The laminate of the present invention preferably has a hardness of H or more in a pencil hardness test conforming to JIS-K5600. The pencil hardness is more preferably 3H or more, even more preferably 4H or more, and particularly preferably 5H or more.

The laminate of the present invention preferably has a haze of 1% or less. A low haze can improve the visibility of the 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.

The laminate of the present invention preferably has a total light transmittance of 90.0% or more. A high total light transmittance can improve the visibility of the display and reduce power consumption. A total light transmittance of 90.5% or more is more preferable, 91.0% or more is more preferable, and 91.5% or more is particularly preferable.

The laminate of the present invention preferably has a yellowness index (YI) of -3.0 to 3.0. Having a yellowness index (YI) in the above range makes it possible to improve the visibility of the display and improve the color tone. The yellowness index (YI) is more preferably -2.0 to 2.0, and even more preferably -1.0 to 1.0.

The following provides a more detailed explanation of the embodiments of the present invention by showing examples. Note that the present invention is not limited to the following examples.

[Preparation of polyimide resin]
75.2 g of 2,2'-bis(trifluoromethyl)benzidine (TFMB) and 620 g of N,N-dimethylformamide were added to a separable flask and stirred under a nitrogen atmosphere to obtain a diamine solution. 13.8 g of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) and 72.8 g of 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride (6FDA) were added thereto and stirred for 12 hours under a nitrogen atmosphere to obtain a polyamic acid solution with a solid content concentration of 18%. Pyridine was added as an imidization catalyst to the polyamic acid solution, and after complete dispersion, acetic anhydride was added and stirred at 90°C for 3 hours. After cooling to room temperature, 2-propyl alcohol was dropped while stirring the solution to precipitate a polyimide resin. IPA was further added, and after stirring for about 30 minutes, suction filtration was performed using a Kiriyama funnel. The obtained solid was washed with IPA and then dried in a vacuum oven set at 120° C. for 12 hours to obtain a polyimide resin.

<Examples 1 to 4: Resin compositions containing acrylic resin and polyimide resin>
[Preparation of solution containing resin composition]
The above-mentioned polyimide resin and a commercially available polymethyl methacrylate resin (a copolymer of methyl methacrylate/methyl acrylate (monomer ratio 87/13), glass transition temperature 101° C., acid value 0.0 mmol/g) as an acrylic resin were added to methylene chloride in the ratios shown in Table 1 to prepare a methylene chloride solution with a resin content of 20% by weight.

[Preparation of resin film]
A solution containing the above resin composition was applied to a 200 mm width on a non-alkali glass plate of 305 mm × 220 mm as a substrate, and the plate was dried by heating at 35°C to 180°C for 120 minutes in an air atmosphere. The non-alkali glass was then peeled off to produce a resin film containing an acrylic resin and a polyimide resin.

[Measurement of drying rate of coating film]
A solution containing the resin composition was applied to a 100 mm x 100 mm alkali-free glass plate as a substrate so that the film thickness after drying would be 50 ± 5μ, and then the weight of the coating film was measured every 30 seconds using an electronic balance "GH-300" manufactured by A&D Co., Ltd., and the time until the residual solvent in the coating film (hereinafter sometimes referred to as "residual solvent") became less than 60% and the time until it became less than 30% were measured. The residual solvent can be calculated from the following formula. (The bone-dry film in the formula refers to a coating film with a residual solvent content of less than 700 ppm, and can be obtained, for example, by drying a coating film with a residual solvent content of 25% or less at 70°C to 200°C for a total of 2 hours.)

Comparative Examples 1-2: Resin composition containing acrylic resin and polyimide resin
Except for using the acrylic resin and the polyimide resin in the ratio shown in Table 1, a resin film was prepared in the same manner as in the Examples, and the time until the residual solvent in the coating film became less than 60% and the time until the residual solvent became less than 30% were measured.

[evaluation]
<Haze and total light transmittance>
The haze and total light transmittance (TT:%) of the resin film were measured using a haze meter "HZ-V3" manufactured by Suga Test Instruments Co., Ltd. in accordance with JIS K7136 and JIS K7361-1. The measurement was performed using a D65 light source.

<Yellowness Index (YI)>
The yellowness index (YI) of the resin film was measured using a spectrophotometer "SC-P" manufactured by Suga Test Instruments Co., Ltd. in accordance with JIS K7373.

<Thickness Unevenness>
The thickness of the resin film was measured at intervals of 1 cm in the width direction using a length gauge "CT-2501" manufactured by Heidenhain Co., Ltd. The standard deviation of the measured thickness was calculated, and a standard deviation of less than 3 μm was judged as "good", and a standard deviation of 3 μm or more was judged as "poor".

<Appearance unevenness>
The resin film was visually observed by reflecting a fluorescent light on the film surface, and was judged as "good" if it was smooth, and "poor" if wrinkles or wind ripples were observed.

<Residual Solvent>
A resin composition containing an acrylic resin and a polyimide resin was dissolved in 1,3-dioxolane to prepare a measurement sample with a resin content of 1% by weight. This solution was measured using a Shimadzu gas chromatograph "GC-2025" to determine the weight ratio of the residual solvent contained in the resin composition from the peak area and the preparation concentration.

<Weight average molecular weight>
The resin was dissolved in the eluent shown in Table 2 so that the resin was 0.15 wt % in the solution, and then the weight average molecular weight was measured under the following conditions.

The resin films shown in Examples 1 to 3 were obtained with good thickness unevenness and appearance unevenness because the time until the residual amount became less than 60% and the time until the residual amount became less than 30% were both short. Therefore, they can be suitably used as optical films. On the other hand, in Comparative Example 1, the time until the residual amount became less than 60%, that is, the time until the surface of the coating film was dried in the initial stage of drying, was long, and during this time, appearance unevenness such as streaks and wind ripples occurred. In Comparative Example 2, the time until the residual amount became less than 30% was long, so productivity was poor, and further, as the solvent volatilized, the coffee ring phenomenon in which the resin solution moved to the periphery of the coating film occurred, and therefore the resin film had thickness unevenness and appearance unevenness.

Claims (13)

The resin composition includes an acrylic resin and a polyimide resin, the polyimide resin has a diamine-derived structure represented by general formula (IIa) and a tetracarboxylic dianhydride-derived structure represented by general formula (IIIa), Y is a diamine residue which is a divalent organic group, and X is a tetracarboxylic dianhydride residue which is a tetravalent organic group, the polyimide resin is contained in the resin composition in an amount of 5% by weight or more and less than 20% by weight with respect to the total weight of the acrylic resin and the polyimide resin, and the acrylic resin and the polyimide resin are compatible in a solvent.
The resin film according to claim 1, characterized in that the acrylic resin is an acrylic resin whose main component is methyl methacrylate. The resin composition according to claim 1, wherein the diamine-derived structure has a fluoroalkyl group, and the tetracarboxylic acid dianhydride-derived structure contains an alicyclic tetracarboxylic acid dianhydride. The resin composition according to claim 3, wherein the diamine having a fluoroalkyl group includes a fluoroalkyl-substituted benzidine. The resin composition according to claim 3, wherein the fluoroalkyl-substituted benzidine is 2,2'-bis(trifluoromethyl)benzidine. The resin composition according to claim 4, wherein the polyimide has a ratio of structures derived from diamines having fluoroalkyl groups to the total amount of structures derived from diamines of 20 mol % or more. The resin composition according to claim 1, characterized in that the tetracarboxylic dianhydride is one or more alicyclic tetracarboxylic dianhydrides selected from the group consisting of 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic-3,4:3',4'-dianhydride. The resin composition according to claim 7, wherein the polyimide further contains a fluorine-containing aromatic tetracarboxylic dianhydride as a tetracarboxylic dianhydride component. The resin composition according to claim 7, wherein the amount of alicyclic tetracarboxylic dianhydride relative to the total amount of the acid dianhydride components of the polyimide is 1 to 80 mol %. A molded article comprising the resin composition according to any one of claims 1 to 9. A resin film comprising the resin composition according to any one of claims 1 to 9. The resin film according to claim 11, having a total light transmittance of 90% or more, a haze of 1% or less, and a yellowness index of 1.0 or less. A method for producing a resin film, comprising a dissolving step of dissolving the resin composition according to any one of claims 1 to 9 in a solvent to prepare a resin solution, a coating step of applying the resin solution onto a support to form a coating film, a drying step of drying the coating film so that the residual solvent is 5 to 20% by weight, and a peeling step of peeling the dried coating film from the support to obtain a green sheet.