(Meth)acrylic resin composition and (meth)acrylic resin film

Abstract

To provide a (meth)acrylic resin composition that can be used in a solution casting method for obtaining a resin film having a thin film-thickness and is excellent in folding endurance, cut resistance (tensile breaking strength), breaking elongation and solvent resistance (gel fraction) and to provide a (meth)acrylic resin film.SOLUTION: The (meth)acrylic resin composition contains a (meth)acrylic polymer and a crosslinking agent. The (meth)acrylic polymer is a (meth)acrylic polymer comprising a copolymer having a weight average molecular weight of more than 100,000 to 1,000,000 produced by copolymerizing 100 pts.wt. of the total of 80 pts.wt. or more of methyl methacrylate and at least one kind of alkyl (meth)acrylate other than the methyl methacrylate in which the homopolymer has a Tg of 0°C or higher and the carbon number of the alkyl group is C1 to C14 and 1.0 to 20.0 pts.wt of the total of at least one kind of copolymerizable monomer having a functional group capable of reacting with the crosslinking agent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a (meth)acrylic resin composition that is suitably used for forming a (meth)acrylic resin film, etc., and a (meth)acrylic resin film using the same. [Background technology]

[0002] BACKGROUND ART (Meth)acrylic resin films have been used as resin films for surface coating of various equipment parts such as electronic devices, home appliances, automobile interior / exterior parts, and building materials because of their high transparency, heat processability, weather resistance, and chemical resistance. In recent years, (meth)acrylic resin films have been used as optical films due to their excellent transparency and weather resistance.

[0003] Conventionally, the method of producing a (meth)acrylic resin film (PMMA film) made of polymethyl methacrylate (PMMA) resin has been to form a film by melt extrusion of PMMA resin because of its high productivity.

[0004] For example, Patent Document 1 discloses an acrylic resin film suitable for use in components that integrate an acrylic resin film with a molded resin, and in particular, an acrylic resin film suitable as a paint replacement for forming a surface protective layer. The acrylic resin film according to the invention described in Patent Document 1 is made by adding a specific combination of ultraviolet absorbers and lubricants to the acrylic resin film, and these components are added in specific amounts. For this reason, Patent Document 1 states that the film can be used as a paint replacement acrylic resin film for forming a surface protective layer.

[0005] Furthermore, Patent Document 2 discloses a method for improving the impact resistance, an essential drawback of acrylic resins, without incorporating a rubber-containing graft copolymer, which causes a loss of the unique beautiful color and transparency that are advantages of acrylic resins. The acrylic resin composition according to the invention described in Patent Document 2 is said to be able to solve the problem that, when the melt extrusion temperature is increased during the melt extrusion process of forming the resin composition into a film, the decomposition gas or bleed-out material generated by the thermal decomposition of the graft copolymer contaminates cooling rolls such as casting rolls, resulting in reduced productivity. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-286960 [Patent Document 2] International Publication No. 2016 / 139927 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-291114 [Patent Document 4] Japanese Patent Application Laid-Open No. 2010-126633 Summary of the Invention [Problem to be solved by the invention]

[0007] The acrylic resin film according to the invention described in Patent Document 1 is produced by a melt extrusion method in which a mixture of an acrylic resin composition containing a thermoplastic polymer is kneaded in a degassing twin-screw extruder to obtain pellets of the acrylic resin composition, and then the molten resin composition is extruded through a T-die in a melt extruder. Furthermore, in Examples 1 to 6 described in Patent Document 1, acrylic resin films with thicknesses of 50 to 125 μm are obtained. However, because the acrylic resin film according to the invention described in Patent Document 1 is a resin film produced by the melt extrusion method, it has the problem of difficulty in producing a thin resin film with a thickness of 40 μm or less.

[0008] Furthermore, the acrylic resin composition according to the invention described in Patent Document 2 has the problem that the process for obtaining the graft copolymer requires a long time because the graft copolymer is gradually completed through three or four graft polymerization reactions. Furthermore, in Examples 6 to 8 of Patent Document 2, in which acrylic resin films were produced by melt extrusion, the thickness of the acrylic resin films obtained without stretching was 80 μm, and thin resin films with thicknesses of 40 μm or less were not obtained without stretching.

[0009] In this context, there has been a demand for a method for forming a PMMA resin film by solution casting, which is a simpler method for forming resin films than melt extrusion and has the advantage of being able to produce thin films. The present inventors have conducted extensive research into methods for forming PMMA resin films by solution casting. As a result, they have found that by using a specific PMMA resin composition, PMMA resin films formed by solution casting can be obtained that have excellent physical properties equal to or better than those formed by melt extrusion, thereby completing the present invention.

[0010] In the case of a conventional method for forming a (meth)acrylic resin film using a melt extrusion method, it was difficult to thin the film to a thickness of 40 μm or less. On the other hand, in the case of a method for forming a (meth)acrylic resin film using a solution casting method, it was possible to thin the film to a thickness of 40 μm or less, but there was a problem in that it was difficult to improve the solvent resistance performance as a physical property of the obtained (meth)acrylic resin film. Furthermore, in the solution casting method, the weight-average molecular weight of the uncrosslinked PMMA resin contained in the (meth)acrylic resin composition must be a large value of 1 million or more, and therefore the solution of the (meth)acrylic resin composition is highly viscous, which has the problem of poor workability in the film formation process.

[0011] An object of the present invention is to provide a (meth)acrylic resin composition that can be used in a solution casting method for obtaining a thin resin film, and to provide a molded article such as a resin film that is excellent in folding resistance, cut resistance (tensile breaking strength), elongation at break, and solvent resistance (gel fraction), and a (meth)acrylic resin film. [Means for solving the problem]

[0012] The present inventors conducted extensive research to solve the above-mentioned problems and discovered that a (meth)acrylic resin composition containing a (meth)acrylic polymer and a crosslinking agent, wherein the (meth)acrylic polymer is a copolymer of MMA (methyl methacrylate), an alkyl (meth)acrylate other than MMA, the alkyl group of which has a carbon number of C1 to C14 and a homopolymer Tg of 0°C or higher, and at least one copolymerizable monomer having a functional group, copolymerized in specific ratios, results in a (meth)acrylic resin film obtained by solution casting using such a (meth)acrylic resin composition, which exhibits excellent folding endurance, cut resistance (tensile break strength), elongation at break, and solvent resistance (gel fraction), thereby completing the present invention. Specifically, the technical concept of the present invention is to obtain a (meth)acrylic resin film comprising a resin layer crosslinked from a (meth)acrylic resin composition containing a specific (meth)acrylic polymer and a crosslinking agent. The statement "(meth)acrylic resin composition (excluding photocurable compositions containing a reactive diluent having a photopolymerizable functional group, and excluding resin compositions containing a prepolymer having three or more acryloyl groups or methacryloyl groups in one molecule)" excludes the matters stated in Patent Documents 3 and 4, while claim 1 of Patent Document 3 (JP 2006-291114 A) states "a photocurable composition containing a polymer having a glass transition temperature of 80°C or higher and a reactive diluent having a photopolymerizable functional group," and claim 1 of Patent Document 4 (JP 2010-126633 A) states "a resin composition containing a prepolymer (C) having three or more acryloyl groups or methacryloyl groups in one molecule."

[0013] In order to solve the above-mentioned problems, the present invention provides a (meth)acrylic resin composition containing a (meth)acrylic polymer and a crosslinking agent, wherein the (meth)acrylic polymer is a (meth)acrylic polymer consisting of a copolymer having a weight-average molecular weight of more than 100,000 and not more than 1,000,000, obtained by copolymerizing 80 parts by weight or more of methyl methacrylate, 100 parts by weight in total of at least one alkyl (meth)acrylate other than the methyl methacrylate, the homopolymer of which has a Tg of 0°C or higher and the alkyl group has carbon atoms of C1 to C14, and 1.0 to 20.0 parts by weight in total of at least one copolymerizable monomer having a functional group capable of reacting with the crosslinking agent.

[0014] The (meth)acrylic polymer is preferably a (meth)acrylic polymer consisting of a copolymer having a weight-average molecular weight of more than 100,000 and not more than 1,000,000, obtained by copolymerizing 80 to 99 parts by weight of (A) methyl methacrylate, 1 to 20 parts by weight of at least one alkyl (meth)acrylate other than the methyl methacrylate, the homopolymer of which has a Tg of 0°C or higher and the alkyl group has a carbon number of C1 to C14, to a total of 100 parts by weight, and 1.0 to 20.0 parts by weight of (B) at least one monomer selected from the group of monomers consisting of copolymerizable monomers having a hydroxyl group and copolymerizable monomers having a carboxyl group, as a copolymerizable monomer having a functional group capable of reacting with the crosslinking agent.

[0015] The crosslinking agent is preferably one or more compounds selected from the group consisting of epoxy compounds, aziridine compounds, and isocyanate compounds.

[0016] The present invention also provides a (meth)acrylic resin film, characterized in that the resin layer is formed by crosslinking the (meth)acrylic resin composition.

[0017] The present invention also provides a pressure-sensitive adhesive sheet, characterized in that it comprises a (meth)acrylic resin film, which is a resin layer formed by crosslinking the (meth)acrylic resin composition, and an adhesive layer formed on one or both sides of the (meth)acrylic resin film.

[0018] The present invention also provides a polarizing film, characterized in that a (meth)acrylic resin film, which is a resin layer obtained by crosslinking the (meth)acrylic resin composition, is formed on one or both sides of a polarizer. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a (meth)acrylic resin composition that can be used in a solution casting method for obtaining a thin resin film, and a (meth)acrylic resin film from which a molded article such as a resin film obtained has excellent folding resistance, cut resistance (tensile breaking strength), elongation at break, and solvent resistance (gel fraction). In the present invention, the solvent resistance was tested by immersing a test piece of a (meth)acrylic resin film in a solvent solution for a predetermined time, and then measuring the proportion of the (meth)acrylic resin film that was not dissolved in the solvent and remained as an insoluble component (residue) (so-called gel fraction). Furthermore, when a (meth)acrylic resin film is formed by the conventional melt extrusion method, it is impossible to achieve a film thickness of 40 μm or less unless the formed resin film is subjected to uniaxial or biaxial stretching. On the other hand, by using the (meth)acrylic resin composition of the present invention, a thin (meth)acrylic resin film having a film thickness of 40 μm or less can be produced using only a solution casting method, which simplifies the production process and reduces the cost of the production equipment. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be described below based on preferred embodiments. The (meth)acrylic resin composition of the present embodiment is a (meth)acrylic resin composition containing a (meth)acrylic polymer and a crosslinking agent, characterized in that the (meth)acrylic polymer is a (meth)acrylic polymer consisting of a copolymer having a weight-average molecular weight of more than 100,000 and not more than 1,000,000, obtained by copolymerizing 80 parts by weight or more of methyl methacrylate, 100 parts by weight in total of at least one alkyl (meth)acrylate other than the methyl methacrylate, the homopolymer of which has a Tg of 0°C or higher and the alkyl group has carbon atoms of C1 to C14, and 1.0 to 20.0 parts by weight in total of at least one copolymerizable monomer having a functional group capable of reacting with the crosslinking agent.

[0021] The (meth)acrylic polymer used in the (meth)acrylic resin composition of this embodiment is preferably a (meth)acrylic polymer primarily composed of an alkyl (meth)acrylate having an alkyl group with a carbon number of C1 to C14, particularly methyl methacrylate (MMA). The alkyl group of the alkyl (meth)acrylate may be acyclic (straight-chain or branched) or cyclic (monocyclic or polycyclic). The (meth)acrylic polymer is preferably a copolymer containing at least two alkyl (meth)acrylates having an alkyl group with a carbon number of C1 to C14. The (meth)acrylic polymer is preferably a copolymer having a homopolymer Tg of 0°C or higher and copolymerized with at least one alkyl (meth)acrylate having an alkyl group with a carbon number of C1 to C14. Here, the term "major component of the (meth)acrylic polymer" refers to a compound that accounts for 50% by weight or more of the (meth)acrylic polymer, or a group of two or more compounds that together account for 50% by weight or more of the (meth)acrylic polymer. That is, the main component accounts for 50 parts by weight or more of 100 parts by weight of the (meth)acrylic polymer. In the following description, when simply referring to the Tg of a monomer, this may refer to the Tg of the homopolymer.

[0022] In the (meth)acrylic polymer, examples of the alkyl (meth)acrylate having a homopolymer Tg of 0°C or higher and an alkyl group having a carbon number of C1 to C14 include one or more selected from the group consisting of methyl (meth)acrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, s-butyl methacrylate, t-butyl (meth)acrylate, n-pentyl methacrylate, isopentyl methacrylate, n-hexyl methacrylate, isohexyl methacrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate. Here, (meth)acrylate refers to at least one of acrylate and methacrylate.

[0023] In the (meth)acrylic polymer, the alkyl(meth)acrylate having a homopolymer Tg of 0°C or higher and an alkyl group having C1 to C14 carbon atoms is preferably an alkyl(meth)acrylate having C1 to C6 carbon atoms, and more preferably an alkyl(meth)acrylate having C1 to C4 carbon atoms. Furthermore, among the alkyl(meth)acrylates having C1 to C4 carbon atoms in the alkyl group other than methyl methacrylate, one or more selected from the group consisting of methyl acrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, s-butyl methacrylate, t-butyl acrylate, and t-butyl methacrylate are particularly preferred.

[0024] Furthermore, in the (meth)acrylic polymer, out of 100 parts by weight of the total of (A) methyl methacrylate and at least one alkyl (meth)acrylate other than the methyl methacrylate, which has a homopolymer Tg of 0°C or higher and has a carbon number of C1 to C14 in the alkyl group, it is preferable that the total of 80 parts by weight or more of methyl methacrylate and at least one alkyl (meth)acrylate other than the methyl methacrylate, which has a homopolymer Tg of 0°C or higher and has a carbon number of C1 to C14 in the alkyl group is 20 parts by weight or less, and it is more preferable that the total of 80 to 99 parts by weight of methyl methacrylate and at least one alkyl (meth)acrylate other than the methyl methacrylate, which has a homopolymer Tg of 0°C or higher and has a carbon number of C1 to C14 in the alkyl group is 1 to 20 parts by weight.

[0025] The (meth)acrylic polymer preferably contains 1.0 to 20.0 parts by weight, more preferably 1.0 to 12.0 parts by weight, and particularly preferably 1.0 to 9.0 parts by weight of at least one copolymerizable monomer having a functional group capable of reacting with the crosslinking agent, relative to 100 parts by weight of the (A) methyl methacrylate and at least one alkyl (meth)acrylate other than the methyl methacrylate, the homopolymer of which has a Tg of 0°C or higher and the alkyl group has a carbon number of C1 to C14.

[0026] The copolymerizable monomer having a functional group capable of reacting with the crosslinking agent may be at least one monomer selected from the group consisting of (B) copolymerizable monomers having a hydroxyl group and copolymerizable monomers having a carboxyl group. The copolymerizable monomer having a functional group capable of reacting with the crosslinking agent may be only a copolymerizable monomer having a hydroxyl group, or only a copolymerizable monomer having a carboxyl group, or may be a combination of both a copolymerizable monomer having a hydroxyl group and a copolymerizable monomer having a carboxyl group.

[0027] The copolymerizable monomer having a hydroxyl group is preferably at least one selected from the group consisting of hydroxyalkyl (meth)acrylates such as 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate, and hydroxyl group-containing (meth)acrylamides such as N-hydroxy(meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide.

[0028] The copolymerizable monomer having a carboxyl group is preferably at least one selected from the group consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxypropyl hexahydrophthalate, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl maleate, carboxypolycaprolactone mono(meth)acrylate, 2-(meth)acryloyloxyethyl tetrahydrophthalate, and the like.

[0029] The acrylic polymer preferably contains 1.0 to 20.0 parts by weight of at least one monomer selected from the group of monomers (B) consisting of copolymerizable monomers having a hydroxyl group and copolymerizable monomers having a carboxyl group, relative to 100 parts by weight of the total of (A) methyl methacrylate and at least one alkyl (meth)acrylate other than methyl methacrylate, the homopolymer of which has a Tg of 0°C or higher and the alkyl group has a carbon number of C1 to C14.

[0030] The method for producing the acrylic polymer is not particularly limited, and known polymerization methods such as solution polymerization and emulsion polymerization can be used as appropriate. The acrylic polymer is preferably a copolymer having a weight-average molecular weight of more than 100,000 and not more than 1,000,000, more preferably a copolymer having a weight-average molecular weight of more than 100,000 and not more than 950,000, and particularly preferably a copolymer having a weight-average molecular weight of more than 100,000 and not more than 900,000. If the weight-average molecular weight of the acrylic polymer is 100,000 or less, it becomes difficult to obtain a molded product such as a (meth)acrylic resin film having excellent physical properties even when the (meth)acrylic resin composition is crosslinked. If the weight-average molecular weight of the acrylic polymer is greater than 1,000,000, the solution of the (meth)acrylic resin composition becomes highly viscous, resulting in poor workability in the film-forming process.

[0031] The crosslinking agent may be a compound having a crosslinkable functional group capable of undergoing a crosslinking reaction with a functional group of the (meth)acrylic polymer. From the viewpoint of the storage stability of the (meth)acrylic resin composition, the crosslinking agent is preferably a compound that does not readily undergo a crosslinking reaction at room temperature (generally 5 to 35°C) but initiates a crosslinking reaction when heated to a predetermined temperature or higher.

[0032] The crosslinking agent is preferably one or more selected from the group consisting of epoxy compounds, aziridine compounds, and isocyanate compounds. The (meth)acrylic resin composition of this embodiment preferably contains 0.01 to 10 parts by weight of the crosslinking agent relative to 100 parts by weight of the total of (A) methyl methacrylate and at least one alkyl (meth)acrylate other than methyl methacrylate, the homopolymer of which has a Tg of 0°C or higher and the alkyl group has a carbon number of C1 to C14.

[0033] The crosslinking agent (epoxy-based crosslinking agent) made of the epoxy compound is not particularly limited as long as it is a bifunctional or higher functional epoxy compound, and examples thereof include at least one selected from the group consisting of polyglycidyl ethers of polyols (including diols, glycols, and bisphenols), diglycidyl esters of dicarboxylic acids, diglycidyl-substituted amines, and tetraglycidyl-substituted diamines.

[0034] Among the epoxy-based crosslinking agents, examples of polyglycidyl ethers of polyols include ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, resorcinol diglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, and sorbitol polyglycidyl ether. Examples of diglycidyl esters of dicarboxylic acids include diglycidyl adipic acid ester and diglycidyl phthalate ester. Examples of diglycidyl-substituted amines include N,N-diglycidylaniline and N,N-diglycidyltoluidine. Furthermore, examples of tetraglycidyl-substituted diamines include 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane and N,N,N',N'-tetraglycidyl-m-xylylenediamine.

[0035] The crosslinking agent (aziridine crosslinking agent) made of the aziridine compound is not particularly limited as long as it is a bifunctional or higher functional aziridine compound or a compound having two or more aziridine functional groups in one molecule. Examples of the aziridine functional group include a 1-aziridinyl group [-N(CH2)2], a 2-aziridinyl group, and a substituted aziridinyl group having a substituent such as a methyl group. Specific examples of the aziridine crosslinking agent include the following addition products of polyisocyanate compounds and aziridine, such as those shown in (1) and (2), the following addition products of polyol polyacrylate compounds and aziridine, such as those shown in (3) and (4), and other polyacridine compounds, such as those shown in (5) to (7).

[0036] (1) 4,4'-bis[(1-aziridinyl)carbonylamino]diphenylmethane (CH2)2NCONH-C6H4CH2C6H4-NHCON(CH2)2 (2) 1,6-bis[(1-aziridinyl)carbonylamino]hexane (CH2)2NCONH-(CH2)6-NHCON(CH2)2 (3) Trimethylolpropane-tris[2-(1-aziridinyl)propionate] CH3CH2C[CH2O-COCH2CH2N(CH2)2]3 (4) Tetramethylolmethane-tris[2-(1-aziridinyl)propionate] HOCH2C[CH2O-COCH2CH2N(CH2)2]3 (5) Tris(1-aziridinyl)phosphine oxide O=P[N(CH2)2]3 (6) Tris(1-aziridinyl)phosphine sulfide S=P[N(CH2)2]3 (7) 2,4,6-tris(1-aziridinyl)-1,3,5-triazine (C3N3)[N(CH2)2]3

[0037] Examples of the crosslinking agent (isocyanate-based crosslinking agent) made of an isocyanate compound include at least one selected from the group consisting of bifunctional isocyanates (diisocyanate compounds) such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), and xylylene diisocyanate (XDI), as well as trifunctional or higher polyisocyanate compounds such as biuret-modified products, isocyanurate-modified products, and adducts thereof. Examples of trifunctional or higher adducts include adducts of diisocyanate compounds with trivalent or higher polyols such as trimethylolpropane and glycerin.

[0038] The (meth)acrylic resin composition may contain, as appropriate, known additives such as, but not limited to, surfactants, curing accelerators, curing retarders, plasticizers, fillers, lubricants, processing aids, antioxidants, heat stabilizers, light stabilizers, antioxidants, antistatic agents, colorants, ultraviolet absorbers, infrared absorbers, etc. These additives may be used alone or in combination of two or more.

[0039] The (meth)acrylic resin composition can be cured by reacting the (meth)acrylic polymer with the crosslinking agent after molding or coating into a predetermined shape. Molded articles obtained from the (meth)acrylic resin composition include, but are not limited to, films, plates (sheets), rods, fibers, and the like. The molding method for the molded articles includes, but is not limited to, cast molding, laminate molding, extrusion molding, and the like. When the (meth)acrylic resin composition is applied to a substrate, a resin film can be formed on the substrate by, for example, solution coating. Examples of the substrate include, but are not limited to, resin films, release films, paper substrates, metal foils, laminates, and the like.

[0040] When the crosslinking agent contained in the (meth)acrylic resin composition is a thermal crosslinking agent that initiates a crosslinking reaction upon heating, it is preferable to fluidize the acrylic polymer as a solution of the (meth)acrylic resin composition during molding of the molded article, rather than by heating and melting it to fluidize it. The solvent used to obtain the solution of the (meth)acrylic resin composition is not particularly limited as long as it can dissolve the acrylic polymer without impairing the reactivity of the functional groups of the acrylic polymer and the crosslinking agent. Examples of the solvent include hydrocarbon solvents such as toluene, alcohol solvents such as ethanol and isopropyl alcohol, ether solvents such as diethyl ether and tetrahydrofuran, ketone solvents such as acetone and methyl ethyl ketone (MEK), and ester solvents such as ethyl acetate. When the acrylic polymer is produced by solution polymerization, at least a portion of the solvent used in the polymerization may serve as at least a portion of the solvent for the (meth)acrylic resin composition.

[0041] The (meth)acrylic resin film of this embodiment is characterized in that it is a resin layer formed by crosslinking the (meth)acrylic resin composition. The (meth)acrylic resin film can be produced, for example, by using a solution casting method to apply a solution of the (meth)acrylic resin composition to a predetermined substrate to form a thin film, and then heating and drying the thin film to volatilize the solvent and crosslink the film. The substrate is not limited to a fixed flat surface, and examples include a resin film unwound from a roll of resin film, a movable belt, and a drum. The surface of the substrate is preferably smooth, but it is also possible to provide a predetermined unevenness on the substrate so that the unevenness can be transferred to the surface of the resulting (meth)acrylic resin film.

[0042] The (meth)acrylic resin film obtained by the solution casting method may be stretched in a predetermined direction such as the longitudinal direction or the width direction, or may remain unstretched. When it is necessary to reduce anisotropy in applications as optical films, it is preferable to make the (meth)acrylic resin film an unstretched film. The (meth)acrylic resin film may be processed into a biaxially stretched film by stretching it in the longitudinal direction and the width direction. The anisotropy of the film is not limited to anisotropy in mechanical properties such as "elongation at break," but also includes optical anisotropy such as "birefringence." The mechanical properties of the (meth)acrylic resin film depend on the application, but when it is used as an adhesive sheet, an optical film, a surface protection film, a process film, etc., or when it is transported in the longitudinal direction, unwound from a roll, wound onto a roll, etc., it is preferable that the (meth)acrylic resin film has a moderate breaking elongation in addition to high folding resistance and cut resistance (tensile breaking strength) so as to obtain conformability to an adherend, etc.

[0043] The gel fraction of the resin layer constituting the (meth)acrylic resin film, which is obtained by crosslinking the (meth)acrylic resin composition, is preferably 50% or more, more preferably 70% or more, even more preferably 90 to 100%, and particularly preferably 93 to 100%. Such a high gel fraction of the resin layer can improve the solvent resistance, which is a required physical property of the (meth)acrylic resin film.

[0044] The thickness of the (meth)acrylic resin film is not particularly limited, but for example, in the case of an optical film, the thickness is preferably about 10 to 200 μm, more preferably 10 to 50 μm, and particularly preferably 10 to 40 μm, and the film can also be made thin with a thickness of 40 μm or less. When another material is laminated on one or both sides of the (meth)acrylic resin film, the film may be subjected to a surface modification by corona discharge, an adhesion-enhancing treatment such as application of an anchor coating agent, etc., as needed.

[0045] The (meth)acrylic resin film may be used as a substrate for an optical film. Examples of optical films include polarizing films, retardation films, antireflection films, antiglare films, ultraviolet absorbing films, infrared absorbing films, optical compensation films, and brightness enhancing films. Examples of devices to which optical members are applied include liquid crystal panels, organic EL panels, and touch panels. When the (meth)acrylic resin film is used as an optical film, it is preferably colorless and transparent.

[0046] One or more layers such as a hard coat layer, an antistatic layer, an antireflection layer, an antifouling layer, an antiglare layer, a low refractive index layer, an adhesive layer, and a release layer may be laminated on one or both sides of the (meth)acrylic resin film. Examples of fluorine compounds used in the composition for forming the low refractive index layer include fluorine-containing copolymers, which are polymers of one or more of fluorinated olefins, fluorinated vinyl ethers, and fluorinated alkyl (meth)acrylates, and condensates of fluorinated alkyl group-containing silane compounds. The fluorine-containing copolymer may be copolymerized with a fluorinated monomer and a non-fluorinated monomer such as an olefin, a vinyl ether, or a (meth)acrylate. The low refractive index layer may be combined with a high refractive index layer to form an antireflection layer.

[0047] The pressure-sensitive adhesive sheet of this embodiment is characterized in that it comprises a pressure-sensitive adhesive layer formed on one or both sides of the (meth)acrylic resin film, which is a resin layer formed by crosslinking the (meth)acrylic resin composition. The pressure-sensitive adhesive layer is preferably a pressure-sensitive adhesive layer made of a (meth)acrylic pressure-sensitive adhesive. The pressure-sensitive adhesive layer may be formed on the (meth)acrylic resin film by a known method. Specifically, known coating methods such as reverse coating, comma coating, gravure coating, slot die coating, Mayer bar coating, and air knife coating can be used.

[0048] The pressure-sensitive adhesive sheet may be an optical film with a pressure-sensitive adhesive layer, which is formed by laminating a pressure-sensitive adhesive layer on at least one surface of an optical film made of the (meth)acrylic resin film as a base material. The optical film with a pressure-sensitive adhesive layer can be used to bond optical films to various display devices such as liquid crystal displays, touch panels, electronic paper, and organic EL displays. The adhesive surface of the pressure-sensitive adhesive layer used to bond the optical film may be protected with a release film. The release film may be subjected to a release treatment with a silicone-based or fluorine-based release agent on the surface that faces the adhesive surface of the pressure-sensitive adhesive layer.

[0049] The pressure-sensitive adhesive sheet may constitute a surface protection film that is attached via the pressure-sensitive adhesive layer to protect the surface of an adherend such as glass, an optical film, or an optical member. With the surface protection film attached to the adherend, the optical properties of the adherend, the presence or absence of foreign matter, etc. can be optically inspected. Furthermore, when the adherend is incorporated into a product, the surface protection film can be peeled off and removed from the adherend.

[0050] The polarizing film of this embodiment is characterized in that the (meth)acrylic resin film, which is a resin layer obtained by crosslinking the (meth)acrylic resin composition, is formed on one or both sides of a polarizer. The surface treatment applied to the surface of the protective layer of the polarizer may be at least one selected from the group consisting of untreated, AG treatment, LR treatment, AR treatment, AG-LR treatment, and AG-AR treatment. Here, AG stands for anti-glare, LR stands for low reflection, and AR stands for anti-reflection. [Example]

[0051] The present invention will be specifically described below with reference to examples.

[0052] <Production of (meth)acrylic polymer and (meth)acrylic resin composition> [Example 1] Nitrogen gas was introduced into a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube, and the air in the reactor was replaced with nitrogen gas. Subsequently, 95 parts by weight of methyl methacrylate, 5 parts by weight of methyl acrylate, 3.0 parts by weight of 8-hydroxyoctyl acrylate, and a solvent (ethyl acetate) were added to the reactor. 0.1 parts by weight of azobisisobutyronitrile as a polymerization initiator was then added dropwise, and the mixture was heated to 65°C and reacted for a predetermined time to obtain a (meth)acrylic polymer solution of Example 1. The weight-average molecular weight (Mw) of the (meth)acrylic polymer contained in this (meth)acrylic polymer solution was measured and found to be 200,000. 3.0 parts by weight of Coronate HX (an isocyanurate derivative of a hexamethylene diisocyanate compound) was added to the (meth)acrylic polymer solution of Example 1, and the mixture was stirred and mixed to obtain a (meth)acrylic resin composition of Example 1.

[0053] [Examples 2 to 5 and Comparative Examples 1 and 2] The (meth)acrylic polymers and (meth)acrylic resin compositions of Examples 2 to 5 and Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the compositions of the (meth)acrylic polymer and (meth)acrylic resin composition of Example 1 were respectively as shown in Table 1. The weight average molecular weights (Mw) of the (meth)acrylic polymers of Examples 2 to 5 and Comparative Examples 1 and 2 were as shown in Table 1.

[0054] Comparative Example 3 A commercially available PMMA film (thickness: 80 μm) produced by melt extrusion was dissolved in methyl ethyl ketone (MEK) as a solvent, and the weight average molecular weight (Mw) of the polymer contained in the PMMA film was measured, which was found to be 300,000.

[0055] [Table 1]

[0056] The compound names of the abbreviations of the components (A) to (C) used in Table 1 are shown in Table 2. Among the crosslinking agents in group (C), Coronate (registered trademark) HX and Coronate HL are trade names of Tosoh Corporation, Takenate (registered trademark) D-140N is a trade name of Mitsui Chemicals, Inc., and TETRAD (registered trademark)-X is a trade name of Mitsubishi Gas Chemical Company, Inc.

[0057] [Table 2]

[0058] <Preparation of (meth)acrylic resin film> The (meth)acrylic resin compositions of Examples 1 to 5 and Comparative Examples 1 and 2 were formed into resin films by solution casting, and then heated and dried under temperature conditions suitable for drying the solvent and curing the crosslinking agent, followed by crosslinking to obtain the (meth)acrylic resin films of Examples 1 to 5 and Comparative Examples 1 and 2. The thicknesses of the films are shown in Table 3. As the (meth)acrylic resin film of Comparative Example 3, a commercially available PMMA film (thickness: 80 μm) produced by melt extrusion was used as described above.

[0059] <Test methods and evaluation of (meth)acrylic resin films> The (meth)acrylic resin films of Examples 1 to 5 and Comparative Examples 1 to 3 were evaluated by the following test methods.

[0060] <Bending resistance> Test pieces were prepared from the (meth)acrylic resin films of Examples 1 to 5 and Comparative Examples 1 to 3, and then subjected to a folding endurance test using a folding endurance tester (manufacturer: Tester Sangyo Co., Ltd., model: MIT folding endurance tester BE-201) in accordance with JIS P8115 (Paper and cardboard - Folding endurance test method - MIT testing machine method), and the number of times the test piece could be folded back and forth until it broke (folding endurance number) was measured.

[0061] <Solvent resistance (gel fraction)> As a method for testing solvent resistance, a test piece of a (meth)acrylic resin film was immersed in a solvent solution for a predetermined time as described below, and then the proportion of the (meth)acrylic resin film that was not dissolved in the solvent and remained as an insoluble component (residue) (so-called gel fraction) was measured to test the solvent resistance. Test pieces were prepared from the (meth)acrylic resin films of Examples 1 to 5 and Comparative Examples 1 to 3, and the masses of the test pieces were accurately measured. They were then immersed in methyl ethyl ketone (MEK) for 24 hours and filtered through a 200-mesh wire net. The filtered material was then dried at 100°C for 1 hour, and the mass of the resulting residue was accurately measured. The gel fraction (%) due to immersion in a solvent was measured using the following formula as a method for testing solvent resistance. Gel fraction (%) = insoluble matter (residue) mass (g) / film (test piece) mass (g) × 100

[0062] <Cut resistance (tensile breaking strength), breaking elongation> Test pieces were prepared from the (meth)acrylic resin films of Examples 1 to 5 and Comparative Examples 1 to 3, and measurements were performed using a tensile testing device (manufacturer: Shimadzu Corporation, model: AGS-X) to determine the cut resistance (tensile breaking strength (MPa)) and breaking elongation (%) until the test pieces broke.

[0063] <Phase difference> The in-plane retardation (Re) values ​​(nm) of the (meth)acrylic resin films of Examples 1 to 5 and Comparative Examples 1 to 3 were measured using a retardation measurement device (manufacturer: Oji Scientific Instruments Co., Ltd., model: KOBRA-HBPR / SPC). The wavelength for measuring the retardation can be appropriately selected from the visible range, for example, 450 to 550 nm. The Re value is calculated by dividing the refractive index n in the x-axis direction by the refractive index in the x-axis direction, where the direction in which the in-plane refractive index is maximum is the x-axis (slow axis) and the direction perpendicular to this is the y-axis (fast axis). x and the refractive index in the y-axis direction, n y and the film thickness d, it is calculated by the following formula. In-plane phase difference Re=(n x -n y )×d Here, the film thickness d of the film is expressed in nm units, just like the in-plane retardation Re, and is therefore 1000 times the film thickness (μm).

[0064] Table 3 shows the evaluation results for the (meth)acrylic resin films of Examples 1 to 5 and Comparative Examples 1 to 3.

[0065] [Table 3]

[0066] The (meth)acrylic resin films of Examples 1 to 5 were formed into thin films having a thickness of 40 μm or less, and had excellent properties in all respects, including folding resistance of 50 times or more, cut resistance (tensile breaking strength) of 50 MPa or more, elongation at break of 9 to 12%, and solvent resistance (gel fraction) of 93% or more. As described above, it has been demonstrated that the (meth)acrylic resin films of Examples 1 to 5 can solve the problems of the present invention.

[0067] The (meth)acrylic resin film of Comparative Example 1 was a (meth)acrylic polymer in which only MMA was copolymerized as an alkyl (meth)acrylate having a carbon number of C1 to C14 in the alkyl group. The Tg of the homopolymer was 0°C or higher, and no alkyl (meth)acrylate having a carbon number of C1 to C14 in the alkyl group was copolymerized, possibly because no other alkyl (meth)acrylate was copolymerized. The film had extremely low folding endurance and low elongation at break. The (meth)acrylic resin film of Comparative Example 2 had extremely low folding resistance and solvent resistance (gel fraction), possibly because the (meth)acrylic resin composition did not contain a crosslinking agent.

[0068] The (meth)acrylic resin film of Comparative Example 3 was a resin film produced by melt extrusion, but it was found that its folding resistance and solvent resistance (gel fraction) were extremely low compared to the (meth)acrylic resin films of Examples 1 to 5. Assuming that the thickness of the (meth)acrylic resin film of Comparative Example 3 is 20 μm, the Re value is 1 / 4 in accordance with the thickness ratio (20 / 80). However, since the Re value is still large, the birefringence (n x -n y ) itself is considered to be large.

[0069] As described above, the (meth)acrylic resin films of Comparative Examples 1 to 3 were unable to achieve the object of the present invention of providing a (meth)acrylic resin film that is excellent in folding resistance, cut resistance (tensile breaking strength), elongation at break, and solvent resistance (gel fraction). [Industrial Applicability]

[0070] The (meth)acrylic resin composition of the present invention and the (meth)acrylic resin film using the same have excellent properties, particularly in terms of thinning, folding resistance, and solvent resistance (gel fraction), compared with (meth)acrylic resin films obtained by conventional melt extrusion methods. Therefore, they are expected to be effective in reducing the thickness and improving the durability of various optical devices such as displays, and are therefore of great industrial utility value.

Claims

1. A (meth)acrylic resin composition (excluding photocurable compositions containing a reactive diluent having a photopolymerizable functional group, and excluding resin compositions containing a prepolymer having three or more acryloyl groups or methacryloyl groups in one molecule) containing a (meth)acrylic polymer (excluding vinyl polymers having an acetone soluble content of 2% by mass or more and 35% by mass or less) and a crosslinking agent, The (meth)acrylic polymer a total of 80 parts by weight or more of methyl methacrylate and 100 parts by weight of at least one alkyl (meth)acrylate other than the methyl methacrylate, the homopolymer of which has a Tg of 0°C or higher and the alkyl group has a carbon number of C1 to C14; a total of 1.0 to 20.0 parts by weight of at least one copolymerizable monomer having a functional group capable of reacting with the crosslinking agent; 1. A (meth)acrylic resin composition comprising a (meth)acrylic polymer comprising a copolymer having a weight average molecular weight of more than 100,000 and not more than 1,000,000, obtained by copolymerizing the above.

2. The (meth)acrylic polymer (A) 80 to 99 parts by weight of methyl methacrylate and 1 to 20 parts by weight of at least one alkyl (meth)acrylate other than the methyl methacrylate, the homopolymer of which has a Tg of 0°C or higher and the alkyl group has a carbon number of C1 to C14, totaling 100 parts by weight; (B) 1.0 to 20.0 parts by weight of at least one or more monomers selected from the group consisting of copolymerizable monomers having a hydroxyl group and copolymerizable monomers having a carboxyl group, as copolymerizable monomers having a functional group capable of reacting with the crosslinking agent; 2. The (meth)acrylic resin composition according to claim 1, wherein the (meth)acrylic polymer is a copolymer having a weight average molecular weight of more than 100,000 and not more than 1,000,000, obtained by copolymerizing

3. 3. The (meth)acrylic resin composition according to claim 1, wherein the crosslinking agent is at least one selected from the group consisting of epoxy compounds, aziridine compounds, and isocyanate compounds.

4. A (meth)acrylic resin film, characterized in that it has a resin layer obtained by crosslinking the (meth)acrylic resin composition according to any one of claims 1 to 3.

5. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed on one or both sides of a (meth)acrylic resin film, which is a resin layer obtained by crosslinking the (meth)acrylic resin composition according to any one of claims 1 to 3.

6. A polarizing film comprising a (meth)acrylic resin film, which is a resin layer obtained by crosslinking the (meth)acrylic resin composition according to any one of claims 1 to 3, formed on one or both sides of a polarizer.

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