JP7598285B2 - (Meth)acrylic resin film - Google Patents

Description

The present invention relates to a (meth)acrylic resin film.

2. Description of the Related Art Since (meth)acrylic resin films have excellent transparency, heat processability, weather resistance, and chemical resistance, they 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.
Moreover, in recent years, (meth)acrylic resin films have been used as optical films because of their excellent transparency, weather resistance, and the like.

Conventionally, the method of producing (meth)acrylic resin films (PMMA films) made of polymethyl methacrylate (PMMA) resin has been to form films from PMMA resin by melt extrusion, because this method has high productivity.

For example, Patent Document 1 discloses an acrylic resin film that can be suitably used for components that integrate an acrylic resin film with a molded resin, and in particular, an acrylic resin film that is a paint-substitute suitable for forming a surface protective layer. The acrylic resin film according to the invention described in Patent Document 1 combines specific types of ultraviolet absorbers and lubricants to be added to the acrylic resin film, and these components are contained in specific amounts. For this reason, Patent Document 1 claims that the film can be suitably used as a paint-substitute acrylic resin film for forming a surface protective layer.

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

JP 2009-286960 A International Publication No. 2016/139927

Incidentally, the acrylic resin film according to the invention described in Patent Document 1 is produced by kneading a mixture of an acrylic resin composition containing a thermoplastic polymer in a degassing twin-screw extruder to obtain pellets of the acrylic resin composition, and then extruding the molten resin composition in a melt extruder into a T-die to produce an acrylic resin film by a melt extrusion method. In addition, in Examples 1 to 6 described in Patent Document 1, acrylic resin films with thicknesses of 50 to 125 μm are obtained. However, since the acrylic resin film according to the invention described in Patent Document 1 is a resin film produced by the melt extrusion method, there is a problem in that it is difficult to obtain a thin resin film with a thickness of 10 μm or less.

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 to four graft polymerization reactions. In addition, 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 film obtained without stretching was 80 μm, and the thickness of the acrylic resin film obtained by stretching was 40 μm, and a thin resin film with a thickness of 10 μm or less was not obtained.

In this situation, there was a demand for a method of forming PMMA resin films using a solution casting method, which is a simpler resin film formation method compared to the melt extrusion method and has the advantage of being able to produce thin films. Furthermore, in the optical and display applications in which PMMA resin is used, the demand for thinner films is increasing day by day, and thin films that meet these demands are now in a range that cannot be formed using the melt extrusion method.

The present inventors have thoroughly investigated a method for forming a PMMA resin film by a solution casting method. As a result, they have found that by using a specific PMMA resin composition, it is possible to produce a thin PMMA resin film with a thickness of 10 μm or less that has excellent physical properties equal to or greater than those of a film formed by a melt extrusion method, even when the film is formed by a solution casting method, and thus have been able to complete the present invention.

In the case of a method for forming a (meth)acrylic resin film by a conventional melt extrusion method, it was difficult to thin the film to a thickness of 10 μm or less. On the other hand, in the case of a method for forming a (meth)acrylic resin film by a solution casting method, it was possible to thin the film to a thickness of 10 μm or less, but there was a problem that it was difficult to improve the solvent resistance performance as a physical property of the obtained (meth)acrylic resin film. In addition, in the solution casting method, the weight average molecular weight of the uncrosslinked PMMA resin contained in the (meth)acrylic resin composition needs to be a large value of 1 million or more, so there was a problem that the solution of the (meth)acrylic resin composition had a high viscosity, and the workability in the film formation process was poor.

An object of the present invention is to provide a (meth)acrylic resin film that is excellent in folding resistance, cut resistance, elongation and solvent resistance even when it has a thin thickness.
Various physical properties of the formed (meth)acrylic resin film can be determined, for example, by measuring the "number of folding times" for "folding resistance", by measuring the "tensile breaking strength" for "cut resistance", by measuring the "breaking elongation" for "extensibility", by measuring the "breaking elongation" for "elongation", and by measuring the "gel fraction" for "solvent resistance".

As a result of intensive research into solving the above problems, the present inventors have discovered that a (meth)acrylic resin film obtained by a solution casting method using a (meth)acrylic resin composition containing a (meth)acrylic polymer, a rubber compound, a crosslinking agent, and an antioxidant, the (meth)acrylic polymer being a copolymer obtained by copolymerizing, in a specific ratio, MMA (methyl methacrylate), an alkyl (meth)acrylate other than the MMA, the homopolymer of which has a Tg of 0°C or higher and in which the alkyl group has a carbon number of C1 to C14, and at least one copolymerizable monomer having a functional group, has excellent folding resistance, cut resistance, elongation, and solvent resistance, and is particularly significantly improved in folding resistance and elongation, thereby completing the present invention. That is, the technical idea of the present invention is to obtain, by a solution casting method, a (meth)acrylic resin film consisting of a resin layer crosslinked from a (meth)acrylic resin composition containing a specific (meth)acrylic polymer, a rubber compound, a crosslinking agent, and an antioxidant.

In order to solve the above-mentioned problems, the present invention provides a (meth)acrylic resin film, which is a resin layer formed by crosslinking a (meth)acrylic resin composition containing a (meth)acrylic polymer, a rubber compound, a crosslinking agent, and an antioxidant, wherein the (meth)acrylic polymer is a resin film containing 80 parts by weight or more of (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 more and the alkyl group has a carbon number of C1 to C14, in a total amount of 10 parts by weight or more. 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, which is obtained by copolymerizing (A) 0 parts by weight and (B) 1.0 to 20.0 parts by weight of at least one or more copolymerizable monomers having a functional group capable of reacting with the crosslinking agent, and the (meth)acrylic resin composition contains 1.0 to 25.0 parts by weight of the rubber compound per 100 parts by weight of (A), and the thickness of the resin layer is 10 μm or less.

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 (A) 80 parts by weight or more of methyl methacrylate, 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 more and the alkyl group has a carbon number of C1 to C14, and (B) 1.0 to 20.0 parts by weight of at least one monomer selected from a monomer group consisting of a copolymerizable monomer having a hydroxyl group and a copolymerizable monomer having a carboxyl group, and the antioxidant preferably contains a total of at least one selected from a phenol-based antioxidant, a thioether-based antioxidant, a phosphite-based antioxidant, and a hindered amine-based antioxidant in an amount of 0.01 to 0.5 parts by weight per 100 parts by weight of the total of (A).

It is preferable that the crosslinking agent is one or more selected from the group consisting of epoxy compounds, aziridine compounds, and isocyanate compounds.

The rubber compound is a core-shell particle formed of a rubber layer mainly made of SBR or butadiene in the core portion and an acrylic layer mainly made of methyl methacrylate in the shell portion, and it is preferable that the volume-based average particle size of the core-shell particle is 0.1 to 0.3 μm.

It is preferable that the (B) copolymerizable monomer having a hydroxyl group is at least one selected from 8-hydroxyoctyl methacrylate, 6-hydroxyhexyl methacrylate, 4-hydroxybutyl methacrylate, and 2-hydroxyethyl methacrylate.

The (meth)acrylic resin film preferably has a resin layer thickness of 0.1 to 9 μm.

The (meth)acrylic resin film preferably has an in-plane retardation Re of 1.0 nm or less and a haze value of 3.0% or less.

The (meth)acrylic resin film preferably has a gel fraction of 90% or more as a solvent resistance, a folding endurance of 200 or more times (JIS P8115) as a folding endurance, and a breaking elongation of 20% or more as a folding endurance.

The present invention also provides an adhesive sheet having an adhesive layer formed on one or both sides of the (meth)acrylic resin film.

The present invention also provides a polarizing film having the above-mentioned (meth)acrylic resin film formed on one or both sides of a polarizer and having a total thickness of 80 μm or less.

According to the present invention, it is possible to provide a (meth)acrylic resin film that is excellent in folding resistance, cut resistance, elongation, and solvent resistance even when it has a thin film thickness. In the present invention, the solvent resistance was tested by immersing a test piece of the (meth)acrylic resin film in a solvent liquid 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 portion (residue) (so-called gel fraction).

In addition, when a (meth)acrylic resin film is produced by the melt extrusion method of the prior art, it is impossible to obtain a film thickness of 10 μm or less unless the resin film is subjected to uniaxial or biaxial stretching after production. 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 10 μm or less, or even 9 μm or less, can be produced using only the solution casting method, which simplifies the production process and reduces the cost of the production equipment.

In addition, according to the present invention, by using an antioxidant in combination with the (meth)acrylic resin composition, the antioxidant can be easily incorporated even if the (meth)acrylic resin film is thin. By incorporating an antioxidant, changes in the appearance of the (meth)acrylic resin film can be suppressed.

The present invention will be described below based on a preferred embodiment.

The (meth)acrylic resin film of this embodiment is a (meth)acrylic resin film that is a resin layer formed by crosslinking a (meth)acrylic resin composition containing a (meth)acrylic polymer, a rubber compound, a crosslinking agent, and an antioxidant, and the (meth)acrylic polymer is a (meth)acrylic resin film that is a resin layer formed by crosslinking a (meth)acrylic resin composition containing a (meth)acrylic polymer, a rubber compound, a crosslinking agent, and an antioxidant, and the (meth)acrylic polymer is a (meth)acrylic polymer that ... (A) 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 (A) a total of 100 parts by weight of at least one type of copolymerizable monomer having a functional group capable of reacting with the crosslinking agent and (B) 1.0 to 20.0 parts by weight of at least one type of copolymerizable monomer having a functional group capable of reacting with the crosslinking agent, and the (meth)acrylic resin composition contains 1.0 to 25.0 parts by weight of the rubber compound per 100 parts by weight of (A), and the thickness of the resin layer is 10 μm or less.

The (meth)acrylic polymer used in the (meth)acrylic resin film of this embodiment is preferably a (meth)acrylic polymer mainly composed of an alkyl (meth)acrylate having an alkyl group with a carbon number of C1 to C14, and particularly preferably composed of methyl methacrylate (MMA). The alkyl group of the alkyl (meth)acrylate may be either acyclic (straight-chain, branched) or cyclic (monocyclic, polycyclic). The (meth)acrylic polymer is preferably a copolymer containing at least two or more 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 or more alkyl (meth)acrylates having an alkyl group with a carbon number of C1 to C14. Here, the main component of the (meth)acrylic polymer means a compound that accounts for 50% by weight or more of the (meth)acrylic polymer, or a group of compounds that account for 50% by weight or more of the (meth)acrylic polymer in total of two or more kinds. In other words, the main component accounts for 50 parts by weight or more of 100 parts by weight of the (meth)acrylic polymer. In the following explanation, when the Tg of a monomer is simply mentioned, it may refer to the Tg of the homopolymer.

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 means at least one of acrylate and methacrylate.

In the (meth)acrylic polymer, the Tg of the homopolymer is 0°C or higher, and the alkyl (meth)acrylate has an alkyl group with carbon number of C1 to C14. The alkyl (meth)acrylate has an alkyl group with carbon number of C1 to C6, and more preferably has an alkyl group with carbon number of C1 to C4. In addition, among the alkyl (meth)acrylates having an alkyl group with carbon number of C1 to C4 other than methyl methacrylate, it is particularly preferable to use 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.

In the (meth)acrylic polymer, out of 100 parts by weight of (A) methyl methacrylate and at least one alkyl (meth)acrylate other than the methyl methacrylate, the homopolymer Tg of which is 0°C or higher and the alkyl group has a carbon number of C1 to C14, 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, the homopolymer Tg of which is 0°C or higher and the alkyl group has a carbon number of C1 to C14 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, the homopolymer Tg of which is 0°C or higher and the alkyl group has a carbon number of C1 to C14 is 1 to 20 parts by weight.

The (meth)acrylic polymer preferably contains 1.0 to 20.0 parts by weight of at least one copolymerizable monomer having a functional group capable of reacting with the (B) crosslinking agent, more preferably 1.0 to 12.0 parts by weight, and particularly preferably 1.0 to 9.0 parts by weight, per 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.

The copolymerizable monomer having a functional group capable of reacting with the (B) crosslinking agent may be 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. The (B) copolymerizable monomer having a functional group capable of reacting with the crosslinking agent may be only a copolymerizable monomer having a hydroxyl group, may be 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.

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

It is also preferable that the copolymerizable monomer having a hydroxyl group is at least one selected from 8-hydroxyoctyl methacrylate, 6-hydroxyhexyl methacrylate, 4-hydroxybutyl methacrylate, and 2-hydroxyethyl methacrylate.

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 hexahydrophthalic acid, 2-(meth)acryloyloxypropyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl maleic acid, carboxypolycaprolactone mono(meth)acrylate, 2-(meth)acryloyloxyethyl tetrahydrophthalic acid, etc.

The 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 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 (B), per 100 parts by weight of the total 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.

The method for producing the acrylic polymer is not particularly limited, and any known polymerization method such as solution polymerization or emulsion polymerization can be used. 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 is difficult to obtain a molded product such as a (meth)acrylic resin film having excellent physical properties even if the (meth)acrylic resin composition is crosslinked. If the weight average molecular weight of the acrylic polymer is more than 1,000,000, the solution of the (meth)acrylic resin composition becomes highly viscous, and the workability of the film formation process is poor.

The crosslinking agent may be a compound having a crosslinkable functional group capable of undergoing a crosslinking reaction with the functional group of the (meth)acrylic polymer. From the viewpoint of storage stability of the (meth)acrylic resin composition, the crosslinking agent is preferably a compound that does not easily 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.

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

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 epoxy compound, but examples thereof include at least one selected from the group of compounds consisting of polyglycidyl ethers of polyols (including diols, glycols, and bisphenols), diglycidyl esters of dicarboxylic acids, diglycidyl-substituted amines, and tetraglycidyl-substituted diamines.

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.
Examples of tetraglycidyl-substituted diamines include 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane and N,N,N',N'-tetraglycidyl-m-xylylenediamine.

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(CH ₂ ) 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 (1) to (2) addition products of a polyisocyanate compound and aziridine, the following (3) to (4) addition products of a polyol polyacrylate compound and aziridine, and the following (5) to (7) other polyacridine compounds.

(1) 4,4'-bis[(1-aziridinyl)carbonylamino]diphenylmethane (CH ₂ ) ₂ NCONH-C ₆ H ₄ CH ₂ C ₆ H ₄ -NHCON(CH ₂ ) ₂
(2) 1,6-bis[(1-aziridinyl)carbonylamino]hexane (CH ₂ ) ₂ NCONH-(CH ₂ ) ₆ -NHCON(CH ₂ ) ₂
(3) Trimethylolpropane-tris[2-(1-aziridinyl)propionate]
CH ₃ CH ₂ C[CH ₂ O-COCH ₂ CH ₂ N(CH ₂ ) ₂ ] ₃
(4) Tetramethylolmethane-tris[2-(1-aziridinyl)propionate]
HOCH ₂ C[CH ₂ O-COCH ₂ CH ₂ N(CH ₂ ) ₂ ] ₃
(5) Tris(1-aziridinyl)phosphine oxide O=P[N( _CH2 ) ₂ ] ₃
(6) Tris(1-aziridinyl)phosphine sulfide S=P[N(CH ₂ ) ₂ ] ₃
(7) 2,4,6-tris(1-aziridinyl)-1,3,5-triazine (C ₃ N ₃ ) [N (CH ₂ ) ₂ ] ₃

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

The (meth)acrylic resin composition contains a (meth)acrylic polymer, a crosslinking agent that crosslinks the (meth)acrylic polymer, and a rubber compound and an antioxidant as essential components.

The (meth)acrylic resin composition preferably contains 1.0 to 25.0 parts by weight of the rubber compound per 100 parts by weight of the total 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, and more preferably contains 3.0 to 20.0 parts by weight of the rubber compound.

The rubber compound is not particularly limited as long as it is a polymer that exhibits rubber-like elasticity, but a rubber compound that has excellent dispersibility or miscibility with the (meth)acrylic polymer is preferred. For example, a rubber compound made of a vinyl polymer such as an olefin elastomer, a styrene elastomer, an acrylic elastomer, an acrylic rubber, a nitrile rubber, a butadiene rubber, a polyisoprene rubber, or a natural rubber is preferred. The rubber compound may be a copolymer made of a hard segment and a soft segment, and may be a block copolymer having at least three blocks, such as (hard segment)-(soft segment)-(hard segment).

The rubber compound is preferably crosslinked by physical or chemical crosslinking.
The physical crosslink is not particularly limited as long as it is a crosslink caused by an interaction not based on a covalent bond, and is not limited to, for example, a hydrogen bond, a hydrophobic bond, etc. In the case of a physical crosslink, the crosslinking point is fixed at room temperature, and the bond is dissociated at a high temperature, so that the rubber compound can exhibit thermoplasticity.
For chemical crosslinking, a compound having a functional group such as a vinyl group, an epoxy group, or an isocyanate group is used as a crosslinking monomer or a crosslinking agent. A crosslinking polymer may be synthesized by copolymerizing a crosslinking monomer with a non-crosslinking monomer. A crosslinking polymer may be synthesized by reacting a crosslinking agent with a non-crosslinking polymer obtained from a non-crosslinking monomer. Crosslinking of a non-crosslinking polymer can also be performed by introducing a covalent bond into the polymer using a radical generator such as a peroxide, an energy ray such as ultraviolet light, or the like.

Examples of the olefin-based elastomer include copolymers of aliphatic olefins such as propylene-ethylene copolymers, ethylene-1-butene copolymers, ethylene-1-hexene copolymers, ethylene-1-octene copolymers, propylene-ethylene-1-butene copolymers, and propylene-1-butene copolymers.
Examples of the styrene-based elastomer include styrene-butadiene copolymers such as styrene-butadiene rubber (SBR), aromatic olefin-aliphatic olefin copolymers such as styrene-isoprene copolymers and styrene-ethylene copolymers.
Examples of the acrylic elastomer include a (meth)acrylic acid ester-acrylonitrile copolymer, a (meth)acrylic acid ester-ethylene copolymer, and an acrylic acid ester-methacrylic acid ester block copolymer.

Examples of the acrylic rubber include an acrylic acid ester-acrylonitrile copolymer and an acrylic acid ester-chloroethyl vinyl ether copolymer.
Examples of the nitrile rubber include acrylonitrile-butadiene copolymers and acrylonitrile-isoprene copolymers.
Examples of the butadiene rubber include polybutadiene, acrylonitrile-butadiene-styrene copolymer, and methyl methacrylate-butadiene-styrene copolymer.
The rubber compound may be a crosslinked rubber obtained by copolymerizing an acrylic acid ester as a main component with a crosslinkable monomer such as alkylene glycol di(meth)acrylate, polyalkylene glycol di(meth)acrylate, or allyl (meth)acrylate.

The rubber compound is preferably a core-shell particle formed of a rubber layer of the core portion and an acrylic layer of the shell portion. This can improve the compatibility and dispersibility of the rubber compound with the (meth)acrylic polymer. The various rubber compounds described above can be used as the material for the rubber layer that forms the core portion. The rubber compound may be a copolymer containing a conjugated diene such as butadiene or isoprene.

Examples of the acrylic material forming the acrylic layer of the shell portion include (meth)acrylic polymers containing at least one of (meth)acrylic acid esters, (meth)acrylic acid, (meth)acrylonitrile, etc. as monomers. The acrylic material may be a methyl methacrylate copolymer or a methyl methacrylate homopolymer containing methyl methacrylate (MMA). The (meth)acrylic polymer may be a (meth)acrylic copolymer obtained by copolymerizing olefins such as ethylene, propylene, butadiene, isoprene, and styrene. The acrylic material may be a (meth)acrylic copolymer obtained by copolymerizing a monomer having a functional group such as a hydroxyl group, a carboxyl group, or a vinyl group.

The core-shell particles may have a structure in which the shell completely covers the periphery of the core, or a structure in which the shell partially covers the periphery of the core. The shell may be formed around the core by coating and curing a resin, for example.
The core-shell particle may have an intermediate layer between the core and shell. The intermediate layer may be omitted and the shell layer may be formed in contact with the core. The intermediate layer may have a transitional composition in which a rubber compound forming the core and an acrylic layer forming the shell layer are mixed. An adhesive layer between the core and shell may be laminated as the intermediate layer.

In the core-shell particles, the core and shell may be bonded via a chemical bond. For example, the resin forming the shell may be graft-polymerized onto the core by polymerizing a monomer forming the shell in the presence of particles of a rubber compound forming the core. The core and shell may form an integral graft copolymer.

The method for producing the core-shell particles is not particularly limited. For example, by emulsion polymerization of the core portion, polymerization of the core portion is allowed to proceed until the desired diameter of the core portion is reached, thereby forming a particulate core portion having a high uniformity in shape, size, etc. Furthermore, by emulsion polymerization of the shell portion, polymerization of the shell portion is allowed to proceed until the desired diameter of the shell portion is reached, thereby forming a particulate shell portion having a high uniformity in shape, size, etc. When the core portion and the shell portion are bonded by graft polymerization, the core portion and the shell portion are firmly integrated via a chemical bond, thereby suppressing peeling of the shell layer.

The rubber compound is preferably particulate in the (meth)acrylic resin composition. When the (meth)acrylic resin composition is heated and molded, the rubber compound may maintain the shape of the particles, or the rubber compound may be melted and dispersed in the (meth)acrylic resin composition. The type of particle size of the rubber compound includes a volume-based average particle size that can be measured by a laser diffraction method or the like. The volume-based average particle size of the rubber compound is, for example, preferably 0.05 to 2.0 μm, more preferably 0.05 to 1.0 μm, and even more preferably 0.1 to 0.3 μm. When the rubber compound is a core-shell particle, the particle size of the core-shell particle also includes the range of the shell portion.

The rubber compound is preferably a core-shell particle formed of a rubber layer mainly made of styrene-butadiene rubber (SBR) or butadiene in the core portion and an acrylic layer mainly made of methyl methacrylate (MMA) in the shell portion, and the volume-based average particle size of the core-shell particle is preferably 0.05 to 2.0 μm, more preferably 0.05 to 1.0 μm, and even more preferably 0.1 to 0.3 μm.

The antioxidant is not particularly limited as long as it is a compound suitable for incorporation into the (meth)acrylic resin composition and the (meth)acrylic resin film, and may be appropriately selected from known antioxidants. The antioxidant is preferably an organic antioxidant. For example, at least one selected from phenol-based antioxidants, thioether-based antioxidants, phosphite-based antioxidants, and hindered amine-based antioxidants may be used.

When the (meth)acrylic resin composition and (meth)acrylic resin film are used as resin materials for optical applications, display applications, etc., it is preferable that the antioxidant does not affect the optical properties of the resin material. For example, it is preferable to use an antioxidant of a material and concentration that allows the (meth)acrylic resin composition or (meth)acrylic resin film to which the antioxidant has been added to remain colorless and transparent.

The (meth)acrylic resin composition preferably contains 0.01 to 0.5 parts by weight, and more preferably 0.05 to 0.4 parts by weight, of the antioxidant per 100 parts by weight of the total 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.

Phenol-based antioxidants are not particularly limited, but specific examples include pentaerythritol-tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), N,N'-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2,6-di-tert-butyl-p-cresol, and 2,5-di-tert-butylhydroquinone.

Thioether-based antioxidants are not particularly limited, but specific examples include didodecyl-3,3'-thiodipropionate, ditridecyl-3,3'-thiodipropionate, ditetradecyl-3,3'-thiodipropionate, dioctadecyl-3,3'-thiodipropionate, pentaerythritol-tetrakis (3-dodecylthiopropionate), pentaerythritol-tetrakis (3-tetradecylthiopropionate), pentaerythritol-tetrakis (3-octadecylthiopropionate), etc.

Phosphite-based antioxidants are not particularly limited, but specific examples include tris(2,4-di-tert-butylphenyl)phosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite, etc.

Hindered amine antioxidants are not particularly limited, but specific examples include bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate, methyl(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate, bis(2,2,6,6-tetramethyl-1-octyloxy-4-piperidinyl)sebacate, bis(2,2,6,6-tetramethyl-1-octyloxy-4-piperidinyl)dodecanedioate, and the like.

The (meth)acrylic resin composition may contain, in addition to the additives described above, known additives such as surfactants, curing accelerators, curing retarders, plasticizers, fillers, lubricants, processing aids, antioxidants, heat stabilizers, light stabilizers, antistatic agents, colorants, ultraviolet absorbers, and infrared absorbers. These additives may be used alone or in combination of two or more.

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.

When the crosslinking agent contained in the (meth)acrylic resin composition is a thermal crosslinking agent that initiates a crosslinking reaction by heating, it is preferable to fluidize the acrylic polymer as a solution of the (meth)acrylic resin composition rather than heating and melting it to fluidize it during molding of the molded product. The solvent for obtaining the solution of the (meth)acrylic resin composition is not particularly limited as long as it can dissolve the acrylic polymer without impairing the functional groups of the acrylic polymer and the reactivity of 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 a solution polymerization method, at least a part of the solvent used in polymerization may be at least a part of the solvent of the (meth)acrylic resin composition.

The (meth)acrylic resin film of this embodiment is characterized in that the resin layer is formed by crosslinking the (meth)acrylic resin composition, and the thickness of the resin layer is 10 μm or less. 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 thin 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, a drum, and the like. The surface property of the substrate is preferably a smooth surface, but it is also possible to transfer the unevenness to the surface of the (meth)acrylic resin film obtained by providing a predetermined unevenness on the substrate.

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 be left unstretched. When it is necessary to reduce anisotropy in the use of an optical film, 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 the anisotropy of 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, optical film, surface protection film, process film, etc., or when it is transported in the longitudinal direction, unwound from a roll, wound up on a roll, etc., it is preferable that the film has a high number of folding cycles as folding resistance, a high tensile breaking strength as cut resistance, and an appropriate breaking elongation as extensibility so that it can conform to the adherend, etc.

The gel fraction of the resin layer that constitutes the (meth)acrylic resin film and is formed 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.

The (meth)acrylic resin film preferably has a thickness of 10 μm or less, more preferably less than 10 μm, and particularly preferably 0.1 to 9 μm. When other materials are laminated on one or both sides of the (meth)acrylic resin film, the film may be subjected to a surface modification by corona discharge or an easy-adhesion treatment such as application of an anchor coating agent, if necessary.

The (meth)acrylic resin film can improve bending resistance because the (meth)acrylic resin composition contains a rubber compound. When the (meth)acrylic resin film is measured in accordance with JIS P8115 (Paper and cardboard - Folding endurance test method - MIT tester method), the number of folding times as folding resistance is preferably 100 or more, and more preferably 200 or more. Typical conditions for measuring the number of folding times include a method in which a test piece having a width of 15.0±0.1 mm and a length of about 110 mm is repeatedly folded back and forth at a load of 9.8 N at a speed of 175±10 times per minute. The number of folding times until the test piece breaks is measured as the number of folding times.

The (meth)acrylic resin film can improve deformability because the (meth)acrylic resin composition contains a rubber compound. The (meth)acrylic resin film has a breaking elongation percentage as an extensibility of preferably 10% or more, more preferably 20% or more. The breaking elongation percentage of films can be measured in accordance with standards such as JIS K7161 (Plastics - Determination of tensile properties) and JIS K7127 (Plastics - Test method for tensile properties).

The (meth)acrylic resin film may be used as a substrate for an optical film. Examples of optical films include polarizing films, retardation films, anti-reflection films, anti-glare 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.

It is preferable that the in-plane retardation Re of the (meth)acrylic resin film is 1.0 nm or less. The smaller the in-plane retardation Re, the more optically isotropic the (meth)acrylic resin film becomes, and the more the change in color tone can be suppressed when the (meth)acrylic resin film is attached to an optical device or used for optical inspection.

The haze value of the (meth)acrylic resin film is preferably 3.0% or less. The lower the haze value, the less light is scattered when passing through the (meth)acrylic resin film. For example, when the (meth)acrylic resin film is incorporated into an optical device such as a display, light leakage due to scattered light can be suppressed.

When measuring optical properties such as in-plane retardation Re and haze value for the purpose of comparing the optical properties of the (meth)acrylic resin compositions, the thickness of the (meth)acrylic resin film used for the measurement may be different from the thickness of the (meth)acrylic resin film to be manufactured. The thickness of the (meth)acrylic resin film when used as the standard for in-plane retardation Re and haze value may be, for example, 20 to 30 μm, and more specifically, 25 μm.

The (meth)acrylic resin film preferably contains an antioxidant to suppress changes in appearance such as yellowing. For example, it is preferable that the (meth)acrylic resin film does not change in appearance even after being stored at 70°C for 30 days.

One or more layers such as a hard coat layer, an antistatic layer, an anti-reflection layer, an antifouling layer, an anti-glare 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. In addition to fluorinated monomers, the fluorine-containing copolymers may also be copolymerized with non-fluorinated monomers such as olefins, vinyl ethers, and (meth)acrylates. The low refractive index layer may be combined with a high refractive index layer to form an anti-reflection layer.

The adhesive sheet of this embodiment is characterized in that an adhesive layer is 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 adhesive layer is preferably an adhesive layer made of a (meth)acrylic adhesive. The 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.

The adhesive sheet may be an optical film with an adhesive layer, which is formed by laminating an adhesive layer on at least one surface of an optical film having the (meth)acrylic resin film as a base material. The optical film with an adhesive layer can be used for bonding optical films in various display devices such as liquid crystal display devices, touch panels, electronic paper, and organic EL. The adhesive surface of the adhesive layer used for bonding the optical film may be protected by 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 is to be joined to the adhesive surface of the adhesive layer.

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 component. 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.

The (meth)acrylic resin film can be made very thin, with a thickness of 10 μm or less, or even 0.1 to 9 μm, allowing the total thickness of the adhesive film to be thin. Even when a double-sided adhesive film is produced in which adhesive layers are formed on both sides of the (meth)acrylic resin film, it is possible to achieve a thin film comparable to that of a double-sided adhesive film having a single adhesive layer.

The polarizing film of this embodiment is characterized in that the (meth)acrylic resin film, which is a resin layer formed by crosslinking the (meth)acrylic resin composition, is formed on one or both sides of a polarizer.

The (meth)acrylic resin film can be made very thin, with a thickness of 10 μm or less, or even 0.1 to 9 μm, so that the total thickness of the polarizing film can be made thin. The total thickness of the polarizing film is preferably 150 μm or less, and more preferably 80 μm or less. The polarizer of the polarizing film used in a liquid crystal display or the like is not particularly limited, but may be, for example, a polyvinyl alcohol (PVA) layer containing iodine molecules (I ₂ ).

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.

Examples of the protective layer of the polarizer include triacetyl cellulose (TAC), acrylic resins such as polymethyl methacrylate (PMMA), polyester resins such as polyethylene terephthalate (PET), cyclic olefin polymers, polycarbonates, and the like. The (meth)acrylic resin film may be attached to the protective layer of the polarizer via the adhesive layer of the adhesive sheet. The (meth)acrylic resin film of this embodiment may also be used as the protective layer of the polarizer.

The present invention will now be described in detail with reference to examples.

<Production of (meth)acrylic polymer and (meth)acrylic resin composition>
[Example 1]
Nitrogen gas was introduced into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, and the air in the reactor was replaced with nitrogen gas. Then, 95 parts by weight of methyl methacrylate, 5 parts by weight of methyl acrylate, 3.0 parts by weight of 8-hydroxyoctyl methacrylate, and a solvent (ethyl acetate) were added to the reactor. Then, 0.1 parts by weight of azobisisobutyronitrile was dropped as a polymerization initiator, 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. To the (meth)acrylic polymer solution of Example 1, 10 parts by weight of Kane Ace (registered trademark) M-230 as a rubber compound, 3.0 parts by weight of Coronate (registered trademark) HX as a crosslinking agent, and 0.1 parts by weight of Irganox (registered trademark) 1010 as an antioxidant were added and mixed with stirring to obtain a (meth)acrylic resin composition of Example 1.

[Examples 2 to 6 and Comparative Examples 1 to 4]
The (meth)acrylic polymers and (meth)acrylic resin compositions of Examples 2 to 6 and Comparative Examples 1 to 4 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 6 and Comparative Examples 1 to 4 were as shown in Table 1.

[Comparative Example 5]
A commercially available PMMA film (thickness: 80 μm) produced by a melt extrusion method 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 and found to be 300,000.

In Table 1, the value in parts by weight calculated assuming the total of the monomers in group (A) to be 100 parts by weight is shown next to the abbreviation corresponding to the compound name.
The meanings of the abbreviations (compound names, etc.) used in Table 1 are as follows:

[Monomers of Group (A)]
"MMA": methyl methacrylate, "MA": methyl acrylate, "TBA": t-butyl acrylate, "BMA": n-butyl methacrylate, "EMA": ethyl methacrylate, "IBMA": isobutyl methacrylate

[Monomers of group (B)]
"8HOA": 8-hydroxyoctyl acrylate, "8HOMA": 8-hydroxyoctyl methacrylate, "6HHA": 6-hydroxyhexyl acrylate, "6HHMA": 6-hydroxyhexyl methacrylate, "4HBMA": 4-hydroxybutyl methacrylate, "HEA": 2-hydroxyethyl acrylate, "HEMA": 2-hydroxyethyl methacrylate, "Aac": acrylic acid

[Rubber compounds]
The particle sizes shown below are all volume-based average particle sizes.
"M-230": Kane Ace (registered trademark) M-230 (core-shell particle, particle size: 0.1 μm, core part: SBR, shell part: MMA, product name of Kaneka Corporation)
"M-210": Kane Ace (registered trademark) M-210 (core-shell particle, particle size: 0.2 μm, core part: SBR, shell part: MMA, product name of Kaneka Corporation)
"B-513": Kane Ace (registered trademark) B-513 (core-shell particle, particle size: 0.2 μm, core part: butadiene, shell part: MMA, product name of Kaneka Corporation)
"LP-4100": Metablen (registered trademark) LP-4100 (acrylic rubber particles, particle size: 1 μm, product name of Mitsubishi Chemical Corporation)

[Crosslinking agent]
"HX": Coronate (registered trademark) HX (HDI isocyanurate, trade name of Tosoh Corporation)
"HL": Coronate (registered trademark) HL (HDI adduct, trade name of Tosoh Corporation)
"D-140N": Takenate (registered trademark) D-140N (IPDI adduct, product name of Mitsui Chemicals, Inc.)
"T-X": TETRAD (registered trademark)-X (tetrafunctional epoxy compound, trade name of Mitsubishi Gas Chemical Company, Inc.)

[Antioxidants]
"E-1": Irganox (registered trademark) 1010 (phenolic antioxidant, trade name of BASF Corporation)
"E-2": Tinuvin (registered trademark) 292 (hindered amine antioxidant, trade name of BASF Corporation)
"E-3": Irgafos (registered trademark) 168 (phosphite antioxidant, trade name of BASF Corporation)
"E-4": Irganox (registered trademark) PS822FL (thioether-based antioxidant, trade name of BASF Corporation)

<Preparation of (meth)acrylic resin film>
The (meth)acrylic resin compositions of Examples 1 to 6 and Comparative Examples 1 to 4 were formed into resin films by a solution casting method, and the films were dried by heating and crosslinked under temperature conditions suitable for drying the solvent and curing the crosslinking agent, to obtain the (meth)acrylic resin films of Examples 1 to 6 and Comparative Examples 1 to 4. The thickness (μm) of each film is shown in the "Thickness" column of Table 2.
As the (meth)acrylic resin film of Comparative Example 5, a commercially available PMMA film (thickness: 80 μm) produced by the melt extrusion method was used as described above.

<Preparation of Polarizing Film>
A polarizing film was produced using a (meth)acrylic resin film having a "thickness" shown in Table 2 as a surface substrate. A polyvinyl alcohol (PVA) layer having a thickness of 30 μm was used as a polarizer. A triacetyl cellulose (TAC) film having a thickness of 30 μm was used as a substrate used on the opposite side to the surface substrate. The total thickness of the obtained polarizing film is shown in "Total Thickness" in Table 2.

<Test methods and evaluation of (meth)acrylic resin films>
The (meth)acrylic resin films of Examples 1 to 6 and Comparative Examples 1 to 5 were evaluated by the following test methods.

<Haze value>
Test pieces were prepared from the (meth)acrylic resin films of Examples 1 to 6 and Comparative Examples 1 to 5, and the haze value (%) was measured using a haze meter (manufacturer: Nippon Denshoku Co., Ltd., model: Haze Meter, NDH2000).

<Appearance Changes>
Test pieces were prepared from the (meth)acrylic resin films of Examples 1 to 6 and Comparative Examples 1 to 5, and after standing at 70° C. for 30 days, the changes in the appearance of the films were visually judged. Comparing the appearance of the films before standing at 70° C. for 30 days (or films that can be assumed to have no change in appearance after standing at 23° C. for the same period), the films were rated as "○" when there was no change in appearance at all, "△" when there was a partial change in color in the appearance, and "×" when there was a change in appearance and yellowing.

<Number of times of folding as folding durability>
Test pieces were prepared from the (meth)acrylic resin films of Examples 1 to 6 and Comparative Examples 1 to 5, and then a folding endurance test was performed using a folding endurance tester (manufacturer: Tester Sangyo Co., Ltd., model: MIT folding endurance tester BE-201) in accordance with JIS P8115 (paper and paperboard--folding endurance test method--MIT tester method), and the number of reciprocating folds (fold endurance number) until the test piece broke was measured.

<Gel Fraction as Solvent Resistance>
As a method for testing solvent resistance, a test piece of a (meth)acrylic resin film was immersed in a solvent liquid 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 portion (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 6 and Comparative Examples 1 to 5, the masses of the test pieces were accurately measured, and the test pieces were immersed in methyl ethyl ketone (MEK) for 24 hours, and then filtered through a 200-mesh wire screen. The filtered material was then dried at a temperature of 100° C. for 1 hour, and the mass of the resulting residue was accurately measured, and the gel fraction (%) due to immersion in a solvent was measured as a method for testing solvent resistance according to the following formula:
Gel fraction (%)=insoluble matter (residue) mass (g)/film (test piece) mass (g)×100

<Tensile breaking strength as cut resistance, and breaking elongation as extensibility>
Test pieces were prepared from the (meth)acrylic resin films of Examples 1 to 6 and Comparative Examples 1 to 5, and were measured using a tensile testing device (manufacturer: Shimadzu Corporation, model: AGS-X) to determine the tensile breaking strength (MPa) as the cut resistance until the test piece broke, and the breaking elongation (%) as the extensibility.

<Retardation (in-plane retardation Re value)>
The in-plane retardation (Re) values (nm) of the (meth)acrylic resin films of Examples 1 to 6 and Comparative Examples 1 to 5 were measured using a retardation measuring device (manufacturer: Oji Scientific Instruments Co., Ltd., model: KOBRA-HBPR/SPC). The wavelength for measuring the retardation can be appropriately selected from the visible region, such as 450 to 550 nm. The Re value is calculated from the refractive index n x in the x-axis direction, the refractive index n _y in the y-axis direction, and the film thickness d of the film, using the following formula, 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 ).
In-plane phase difference Re = (n _x - n _y ) x d
Here, the film thickness d of the film is expressed in nm units like the in-plane retardation Re, and is 1000 times the film thickness (μm).

Table 2 shows the evaluation results for the (meth)acrylic resin films of Examples 1 to 6 and Comparative Examples 1 to 5.

The (meth)acrylic resin films of Examples 1 to 5 were formed into thin films with a thickness of 10 μm or less, and could be used to produce polarizing films with a total thickness of 80 μm or less. The (meth)acrylic resin films of Examples 1 to 5 also had a haze value of 3.0% or less, folding resistance of 200 or more folding cycles, solvent resistance of 90% or more gel fraction, cut resistance of tensile breaking strength of 40 MPa or more (approximately 50 MPa or more), elongation at break of 20% or more, and in-plane retardation Re of 1.0 nm or less. Thus, the (meth)acrylic resin films of Examples 1 to 5 were excellent in all physical properties. The (meth)acrylic resin films of Examples 1 to 5 also contained an antioxidant, and showed no change in appearance even after 30 days at 70°C.

The (meth)acrylic resin film of Example 6 was formed into a thin film having a thickness of 10 μm or less, and could be used to produce a polarizing film having a total thickness of 80 μm or less. Although the (meth)acrylic resin film of Example 6 had a slightly high haze value, it had a folding resistance of 200 or more folding times, a solvent resistance of 90% or more gel fraction, a cut resistance of 50 MPa or more tensile breaking strength, an extensibility of 20% or more breaking elongation, and an in-plane retardation Re of 1.0 nm or less. Thus, the (meth)acrylic resin film of Example 6 was excellent in all physical properties. The (meth)acrylic resin film of Example 6 also contained an antioxidant, and showed no change in appearance even after 30 days at 70°C.

In this way, it has been demonstrated that the (meth)acrylic resin films of Examples 1 to 6 can solve the problems of the present invention.

The (meth)acrylic resin film of Comparative Example 1 had a low number of folding cycles, possibly because the (meth)acrylic resin composition did not contain a rubber compound. In addition, the (meth)acrylic resin film of Comparative Example 1 changed in appearance (yellowing) after 30 days at 70°C, possibly because it did not contain an antioxidant.

The (meth)acrylic resin film of Comparative Example 2 had a high haze value, possibly due to its thick film. In addition, the (meth)acrylic resin film of Comparative Example 2 showed a change in appearance (precipitation) after 30 days at 70°C.

The (meth)acrylic resin film of Comparative Example 3 is a (meth)acrylic polymer in which only MMA is copolymerized as an alkyl (meth)acrylate with an alkyl group having a carbon number of C1 to C14. The homopolymer Tg is 0°C or higher, and no alkyl (meth)acrylate with an alkyl group having a carbon number of C1 to C14 is copolymerized. This is probably because the film had a low number of folding cycles as a folding resistance and an extremely low breaking elongation as a stretchability. In addition, the (meth)acrylic resin film of Comparative Example 3 showed a change in appearance (yellowing) after 30 days at 70°C, possibly because it did not contain an antioxidant.

The (meth)acrylic resin film of Comparative Example 4 had a low number of folding cycles as a measure of folding resistance, and an extremely low gel fraction as a measure of solvent resistance, possibly because the (meth)acrylic resin composition did not contain a rubber compound or a crosslinking agent. The extremely low gel fraction as a measure of solvent resistance is believed to be due to the (meth)acrylic resin composition not being crosslinked by a crosslinking agent.

The (meth)acrylic resin film of Comparative Example 5 was a resin film produced by melt extrusion, but had a low number of folding cycles as a measure of folding resistance, an extremely low gel fraction as a measure of solvent resistance, and a large in-plane retardation Re. The extremely low gel fraction as a measure of solvent resistance is thought to be due to the fact that the resin film produced by melt extrusion was not crosslinked by a crosslinking agent.

As described above, the (meth)acrylic resin films of Comparative Examples 1 to 5 were unable to achieve the objective of the present invention, which is to provide a (meth)acrylic resin film that is excellent in folding resistance, cut resistance, elongation, and solvent resistance even when it has a thin film thickness.

Compared to (meth)acrylic resin films obtained by conventional melt extrusion methods, the (meth)acrylic resin film of the present invention has excellent physical properties, particularly in terms of thinning, folding resistance, and solvent resistance, and is therefore expected to be effective in making various optical devices such as displays thinner and improving their durability, making it of great industrial value.

Claims (10)

A (meth)acrylic resin film which is a resin layer obtained by crosslinking a (meth)acrylic resin composition containing a (meth)acrylic polymer, a rubber compound, a crosslinking agent, and an antioxidant,
The (meth)acrylic polymer is
(A) 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 more and the alkyl group has a carbon number of C1 to C14;
(B) 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;
and having a weight average molecular weight of more than 100,000 and not more than 1,000,000,
The (meth)acrylic resin composition contains the rubber compound in an amount of 1.0 to 25.0 parts by weight per 100 parts by weight of the (A),
The (meth)acrylic resin film, wherein the resin layer has a thickness of 10 μm or less. The (meth)acrylic polymer is
(A) 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 more and the alkyl group has a carbon number of C1 to C14;
(B) 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 1.0 to 20.0 parts by weight of at least one monomer selected from a monomer group consisting of copolymerizable monomers having a hydroxyl group and copolymerizable monomers having a carboxyl group;
The (meth)acrylic resin film according to claim 1, characterized in that the antioxidant contains at least one selected from the group consisting of a phenol-based antioxidant, a thioether-based antioxidant, a phosphite-based antioxidant, and a hindered amine-based antioxidant in an amount of 0.01 to 0.5 parts by weight per 100 parts by weight of the (A). The (meth)acrylic resin film according to claim 1 or 2, characterized in that the crosslinking agent is one or more selected from the group of compounds consisting of epoxy compounds, aziridine compounds, and isocyanate compounds. The (meth)acrylic resin film according to any one of claims 1 to 3, characterized in that the rubber compound is a core-shell particle formed of a rubber layer mainly made of SBR or butadiene in the core portion and an acrylic layer mainly made of methyl methacrylate in the shell portion, and the volume-based average particle diameter of the core-shell particles is 0.1 to 0.3 μm. The (meth)acrylic resin film according to claim 2, characterized in that the (B) copolymerizable monomer having a hydroxyl group is at least one selected from 8-hydroxyoctyl methacrylate, 6-hydroxyhexyl methacrylate, 4-hydroxybutyl methacrylate, and 2-hydroxyethyl methacrylate. The (meth)acrylic resin film according to any one of claims 1 to 5, wherein the resin layer has a thickness of 0.1 to 9 μm. The (meth)acrylic resin film according to any one of claims 1 to 6, characterized in that the in-plane retardation Re is 1.0 nm or less and the haze value is 3.0% or less. The (meth)acrylic resin film according to any one of claims 1 to 7, characterized in that the gel fraction as a solvent resistance is 90% or more, the number of folding times as a folding resistance (JIS P8115) is 200 or more, and the breaking elongation is 20% or more. An adhesive sheet comprising an adhesive layer formed on one or both sides of the (meth)acrylic resin film according to any one of claims 1 to 8. A polarizing film having a total thickness of 80 μm or less, the polarizing film being formed by forming the (meth)acrylic resin film according to any one of claims 1 to 8 on one or both sides of a polarizer.