Graft copolymer and resin film

Abstract

A graft copolymer according to the present invention contains: crosslinked (meth)acrylic polymer particles (a) that have an average particle size of 150 nm or smaller and a glass transition temperature of -10°C or lower; and a non-crosslinked methacrylic polymer component (b) that has a weight average molecular weight of 250,000 or higher. At least a part of the non-crosslinked polymer component (b) is grafted to the crosslinked polymer particles (a), and the crosslinked polymer particles (a) constitute at least 1 wt% but less than 50 wt% of the total weight of the crosslinked polymer particles (a) and the non-crosslinked polymer component (b).

Description

Graft copolymer and resin film

[0001] The present invention relates to a graft copolymer capable of forming a resin film, a resin composition for producing a film containing the copolymer, a dope, and a resin film.

[0002] Methacrylic resins are excellent polymers that are used in large quantities in various industrial fields due to their excellent transparency, color tone, appearance, weather resistance, gloss, and processability. In particular, resin films molded from methacrylic resins are used in various applications, taking advantage of their excellent transparency, appearance, and weather resistance, such as automotive interior and exterior materials, exterior materials for electrical appliances such as mobile phones and smartphones, and interior and exterior materials for civil engineering and construction such as floors, windows, interior and exterior walls, lighting sections, and road signs. In recent years, methacrylic resins have also been used in optical components for liquid crystal displays, organic EL displays, and the like, taking advantage of their excellent optical properties.

[0003] However, resin films made from general methacrylic resins have the drawback of low impact resistance, so a widely used method for improving impact resistance is to blend a graft copolymer containing a rubber component into the methacrylic resin.

[0004] Known examples of such rubber-containing graft copolymers include core-shell graft copolymers having a core layer made of rubber and a shell layer that improves compatibility with methacrylic resins (see, for example, Patent Document 1).

[0005] International Publication No. 99 / 055779

[0006] Although the strength of a methacrylic resin can be improved by blending a conventional core-shell graft copolymer, the core-shell graft copolymer tends to aggregate due to the rubber component contained therein, resulting in poor storage stability. Furthermore, when a resin film is produced by a solution casting method, after a dope is produced by dissolving a conventional core-shell graft copolymer together with a methacrylic resin in a solvent, the dope tends to become cloudy, especially over time, and the haze of a resin film produced from the dope is reduced.

[0007] In view of the above-described current situation, the present invention aims to provide a graft copolymer that has excellent heat resistance, is capable of forming a high-strength, low-haze film, and has good storage stability, and a resin film formed from the graft copolymer.

[0008] As a result of extensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by a graft copolymer containing specific crosslinked (meth)acrylic polymer particles and a specific non-crosslinked methacrylic polymer component in a specific ratio, in which the non-crosslinked methacrylic polymer component is graft-bonded to the crosslinked (meth)acrylic polymer particles, thereby completing the present invention.

[0009] Specifically, the present invention relates to a graft copolymer comprising crosslinked (meth)acrylic polymer particles (a) having an average particle size of 150 nm or less and a glass transition temperature of -10°C or less, and a non-crosslinked methacrylic polymer component (b) having a weight-average molecular weight of 250,000 or more, wherein at least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a), and the proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is 1% by weight or more but less than 50% by weight. Preferably, the non-crosslinked methacrylic polymer component (b) contains 70% by weight or more but less than 99% by weight of methyl methacrylate units. Preferably, the non-crosslinked methacrylic polymer component (b) further comprises at least one selected from the group consisting of N-substituted maleimide monomer units, methacrylic acid ester units in which the ester moiety is a primary or secondary hydrocarbon group or an aromatic hydrocarbon group having 2 to 20 carbon atoms, methacrylic acid ester units in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure, methacrylic acid ester units in which the ester moiety is a linear or branched group containing an ether bond, and styrene monomer units. Preferably, the non-crosslinked methacrylic polymer component (b) further comprises at least one of N-substituted maleimide monomer units and methacrylic acid ester units in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure. Preferably, the non-crosslinked methacrylic polymer component (b) has a glass transition temperature of 118°C or higher. Preferably, the crosslinked (meth)acrylic polymer particles (a) contain, among the monomer components excluding the polyfunctional monomer, 90% by weight or more and 100% by weight or less of an acrylic acid alkyl ester in which the alkyl group has a carbon number of 1 to 8. Preferably, the crosslinked (meth)acrylic polymer particles (a) are formed from 100 parts by weight of the monomer components excluding the polyfunctional monomer and 0.1 to 2.0 parts by weight of the polyfunctional monomer.The present invention also relates to a resin composition for film production by a solution casting method, which contains the graft copolymer; a dope containing the resin composition for film production and a solvent; a method for producing a resin film, which includes a step of casting the dope on a support surface and then evaporating the solvent; or a resin film formed from the resin composition for film production by a solution casting method. Preferably, the resin film has a thickness of 1 to 500 μm. Preferably, the resin film is a film for protecting a laminate on the surface of another substrate. Preferably, the resin film is an optical film. Preferably, the optical film is a polarizer protective film. The present invention also relates to a polarizing plate formed by laminating a polarizer and the resin film; and a display device including the polarizing plate.

[0010] According to the present invention, it is possible to provide a graft copolymer having excellent heat resistance, capable of forming a high-strength, low-haze film, and good storage stability, and a resin film formed from the polymer. The graft copolymer of the present invention can form a high-strength resin film even when the resin component is the copolymer alone. Furthermore, since it is not necessary to blend and disperse a core-shell graft copolymer in a methacrylic resin as in the conventional method, a low-haze resin film can be easily formed. Furthermore, despite containing a rubber component, the graft copolymer has good storage stability and also has the advantage that when the dope is prepared by dissolving the graft copolymer in a solvent, the dope is less likely to become cloudy. As a result, the haze of a resin film produced by a solution casting method using the dope can be reduced.

[0011] Embodiments of the present invention will be described in detail below, but the present invention is not limited to these embodiments. (Graft Copolymer) The graft copolymer according to this embodiment contains crosslinked (meth)acrylic polymer particles (a) and a non-crosslinked methacrylic polymer component (b). The crosslinked (meth)acrylic polymer particles (a) are a rubber component and can contribute to improving strength. Furthermore, the non-crosslinked methacrylic polymer component (b) can achieve excellent heat resistance. Compared to a conventional system in which a core-shell graft copolymer is blended with a methacrylic resin, the crosslinked (meth)acrylic polymer particles (a) can correspond to the core rubber component in the core-shell graft copolymer, and the non-crosslinked methacrylic polymer component (b) can correspond to the methacrylic resin that is the matrix.

[0012] At least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a). This graft-bonding can be achieved by producing a graft copolymer by emulsion polymerization, as described below. Due to this production method, the graft copolymer may also contain non-crosslinked methacrylic polymer component (b) that is not graft-bonded to the crosslinked (meth)acrylic polymer particles (a).

[0013] The graft copolymer according to this embodiment can have a configuration in which small-sized crosslinked (meth)acrylic polymer particles (a) are dispersed in a high-molecular-weight non-crosslinked methacrylic polymer component (b), and therefore aggregation of the crosslinked (meth)acrylic polymer particles (a) in the graft copolymer is less likely to proceed. As a result, the graft copolymer according to this embodiment has good stability whether it is stored in powder form or as a dope dissolved in a solvent. Furthermore, since aggregation of the crosslinked (meth)acrylic polymer particles (a) is suppressed, the graft copolymer according to this embodiment has the advantage of being easily soluble in a solvent.

[0014] (Crosslinked (meth)acrylic polymer particles (a)) The crosslinked (meth)acrylic polymer particles (a) are (meth)acrylic rubber particles. By including the crosslinked (meth)acrylic polymer particles (a), the graft copolymer according to this embodiment can achieve high strength, for example, when formed into a film.

[0015] The crosslinked (meth)acrylic polymer particles (a) have a relatively small particle size, specifically an average particle size of 150 nm or less. By using crosslinked (meth)acrylic polymer particles with such a small particle size, low haze can be achieved when the graft copolymer according to this embodiment is formed into a film, for example. Furthermore, by reducing the size of the crosslinked (meth)acrylic polymer particles, it is no longer necessary to match the refractive index of the crosslinked (meth)acrylic polymer particles (a) with that of the non-crosslinked methacrylic polymer component (b). As a result, a monomer composition that lowers the glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) can be adopted without considering the refractive index, thereby achieving high strength when the graft copolymer is formed into a film, for example.

[0016] From the viewpoint of low haze, the average particle diameter is preferably 130 nm or less, more preferably 120 nm or less, even more preferably 110 nm or less, and even more preferably 100 nm or less. The lower limit of the average particle diameter is not particularly limited, but from the viewpoint of film strength or ease of particle production, it is preferably 30 nm or more, more preferably 50 nm or more, and even more preferably 60 nm or more. The average particle diameter is a volume average particle diameter and can be measured as described in the Examples section. The average particle diameter can also be controlled by adjusting the conditions during particle production (specifically, the type and amount of emulsifier, the stirring conditions during emulsion polymerization, etc.).

[0017] The crosslinked (meth)acrylic polymer particles (a) have a glass transition temperature of −10° C. or lower. By using crosslinked (meth)acrylic polymer particles having such a low glass transition temperature, high strength can be achieved when the graft copolymer is formed into, for example, a film. The glass transition temperature can be controlled by adjusting the types and ratios of the monomers constituting the crosslinked (meth)acrylic polymer particles (a).

[0018] The glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) is preferably −20° C. or lower, more preferably −30° C. or lower, even more preferably −40° C. or lower, and particularly preferably −45° C. or lower. There are no particular restrictions on the lower limit of the glass transition temperature, but for example, it is preferably −130° C. or higher, more preferably −110° C. or higher, even more preferably −100° C. or higher, even more preferably −80° C. or higher, and particularly preferably −70° C. or higher. The glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) is a value calculated using the Fox formula using values ​​described in the Polymer Handbook (J. Brandrup, Interscience 1989) (for example, the glass transition temperature for poly(n-butyl acrylate) is −54° C.).

[0019] The crosslinked (meth)acrylic polymer particles (a) are particles formed from a crosslinked (meth)acrylic polymer obtained by polymerizing a monomer component containing a (meth)acrylic monomer and a polyfunctional monomer. The monomer component excluding the polyfunctional monomer contains an acrylic monomer and / or a methacrylic monomer, and preferably contains at least an acrylic monomer.

[0020] The acrylic monomer contained in the crosslinked (meth)acrylic polymer particles (a) is preferably an acrylic acid alkyl ester having an alkyl group having 1 to 8 carbon atoms. Specific examples include ethyl acrylate, n-butyl acrylate, n-octyl acrylate, and 2-ethylhexyl acrylate. The acrylic acid alkyl ester may be used alone or in combination of two or more. Of these, n-butyl acrylate is preferred.

[0021] As the optional methacrylic monomer that can be contained in the crosslinked (meth)acrylic polymer particles (a), methacrylic acid alkyl esters having an alkyl group with 1 to 8 carbon atoms are preferred. Specific examples include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, and octyl methacrylate. The methacrylic acid alkyl esters may be used alone or in combination of two or more. Among these, methacrylic acid alkyl esters having an alkyl group with 1 to 4 carbon atoms are preferred. Methyl methacrylate is particularly preferred.

[0022] In the crosslinked (meth)acrylic polymer particles (a), monomers other than the above-mentioned alkyl acrylates and alkyl methacrylates may be used. Examples of such monomers include acrylic esters other than the above-mentioned alkyl acrylates, methacrylic esters other than the above-mentioned alkyl methacrylates, aromatic vinyl monomers, and other copolymerizable vinyl monomers. Examples of acrylic esters other than the alkyl acrylates include phenyl acrylate, benzyl acrylate, cyclohexyl acrylate, and isobornyl acrylate. Examples of methacrylic esters other than the alkyl methacrylates include phenyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, and isobornyl methacrylate. Examples of the aromatic vinyl monomers include styrene, α-methylstyrene, chlorostyrene, and other styrene derivatives. Examples of the other copolymerizable vinyl monomers include unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile, α,β-unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, olefin monomers such as vinyl acetate, ethylene, and propylene, halogenated vinyl monomers such as vinyl chloride, vinylidene chloride, and vinylidene fluoride, and maleimide monomers such as N-ethylmaleimide, N-propylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, and N-o-chlorophenylmaleimide. These may be used alone or in combination of two or more.

[0023] From the viewpoint of strength and heat resistance, the monomer components constituting the crosslinked (meth)acrylic polymer particles (a) preferably contain 70% by weight or more and 100% by weight or less, more preferably 80% by weight or more and 100% by weight or less, even more preferably 90% by weight or more and 100% by weight or less, and particularly preferably 95% by weight or more and 100% by weight or less, of acrylic acid esters (particularly acrylic acid alkyl esters having an alkyl group with 1 to 8 carbon atoms) among the monomer components excluding polyfunctional monomers.

[0024] The crosslinked (meth)acrylic polymer particles (a) are formed by polymerizing the above-mentioned monomer components in the presence of a polyfunctional monomer. The polyfunctional monomer, also known as a crosslinking agent or crosslinkable monomer, is a compound having two or more unsaturated bonds in one molecule that are copolymerizable with the (meth)acrylic monomer. Specific examples include allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate, diallyl itaconate, monoallyl maleate, monoallyl fumarate, butadiene, divinylbenzene, triallyl isocyanurate, alkylene glycol dimethacrylate, and alkylene glycol diacrylate. These may be used alone or in combination of two or more. Allyl methacrylate is preferred.

[0025] The amount of the polyfunctional monomer used can be appropriately set from the viewpoint of strength, and specifically, it may be about 0.1 to 5.0 parts by weight per 100 parts by weight of the monomer components (excluding the polyfunctional monomer) constituting the crosslinked (meth)acrylic polymer particles (a). However, from the viewpoint of the strength of the graft copolymer, the amount of the polyfunctional monomer used is preferably 0.2 to 3.5 parts by weight, more preferably 0.2 to 3.0 parts by weight, even more preferably 0.3 to 2.0 parts by weight, and particularly preferably 0.4 to 1.5 parts by weight.

[0026] (Non-crosslinked methacrylic polymer component (b)) The non-crosslinked methacrylic polymer component (b) is a polymer that is mainly formed by polymerizing methacrylic monomers and does not have a crosslinked structure (i.e., obtained by polymerization without using a polyfunctional monomer). At least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a). This makes the crosslinked (meth)acrylic polymer particles (a) less likely to aggregate, and the graft copolymer according to this embodiment has good storage stability and can achieve low haze when formed into a film.

[0027] The non-crosslinked methacrylic polymer component (b) is a high-molecular-weight polymer, specifically one having a weight-average molecular weight of 250,000 or more. The high molecular weight of the non-crosslinked methacrylic polymer component (b) enables the graft copolymer of this embodiment to achieve high heat resistance and to be formed into a film by solution casting. From the viewpoint of facilitating film formation by solution casting, the weight-average molecular weight is preferably 300,000 or more, more preferably 350,000 or more, even more preferably 400,000 or more, and particularly preferably 450,000 or more. The upper limit of the weight-average molecular weight is not particularly limited, but from the viewpoint of facilitating film formation by solution casting, it is preferably 1,000,000 or less, more preferably 900,000 or less. The weight-average molecular weight of the non-crosslinked methacrylic polymer component (b) can be measured as described in the Examples section.

[0028] From the viewpoint of the heat resistance of the graft copolymer, the non-crosslinked methacrylic polymer component (b) preferably exhibits a glass transition temperature of 115°C or higher, more preferably 118°C or higher, and even more preferably 120°C or higher. The upper limit of the glass transition temperature is not particularly limited, but may be, for example, 160°C or lower, or 150°C or lower. The glass transition temperature can be controlled by adjusting the type and ratio of the monomers constituting the non-crosslinked methacrylic polymer component (b). The glass transition temperature of the non-crosslinked methacrylic polymer component (b) can be measured as described in the Examples section, but it can also be calculated using the Fox formula using values ​​described in the Polymer Handbook (J. Brandrup, Interscience 1989) (for example, the glass transition temperature for polymethyl methacrylate is 105°C).

[0029] The non-crosslinked methacrylic polymer component (b) is a polymer mainly composed of methacrylic monomer units. From the viewpoint of the heat resistance and film-forming ability of the graft copolymer, methyl methacrylate units are preferred as the methacrylic monomer units. In particular, it is preferred that the monomer components constituting the non-crosslinked methacrylic polymer component (b) contain 70% by weight or more and 99% by weight or less of methyl methacrylate units. This improves heat resistance and makes it easier to form a film by solution casting. The content of methyl methacrylate units is more preferably 75 to 98% by weight, even more preferably 80 to 97% by weight, even more preferably 85 to 96% by weight, even more preferably 88 to 95% by weight, and particularly preferably 90 to 95% by weight.

[0030] The non-crosslinked methacrylic polymer component (b) preferably contains, as a monomer unit other than methyl methacrylate units, at least one selected from the group consisting of N-substituted maleimide monomer units, methacrylic acid ester units in which the ester moiety is a primary or secondary hydrocarbon group or an aromatic hydrocarbon group having 2 to 20 carbon atoms, methacrylic acid ester units in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure, methacrylic acid ester units in which the ester moiety is a linear or branched group containing an ether bond, and styrene monomer units. The inclusion of such a monomer unit makes it possible to increase the evaporation rate of the solvent from the cast film during film production by a solution casting method without significantly reducing the heat resistance of the graft copolymer. Hereinafter, the above-mentioned monomer unit will also be referred to as a "drying-accelerating comonomer unit."

[0031] Examples of the N-substituted maleimide monomer include N-phenylmaleimide, N-benzylmaleimide, N-cyclohexylmaleimide, N-methylmaleimide, etc. Among these, maleimide monomer units having a cyclic substituent on the N atom are preferred, that is, N-phenylmaleimide, N-benzylmaleimide, and N-cyclohexylmaleimide are preferred.

[0032] Examples of methacrylic acid esters in which the ester moiety is a primary or secondary hydrocarbon group or an aromatic hydrocarbon group having 2 to 20 carbon atoms include ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, stearyl methacrylate, phenyl methacrylate, benzyl methacrylate, etc. Of these, ethyl methacrylate, n-butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, and benzyl methacrylate are preferred.

[0033] Examples of methacrylic acid esters in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure include dicyclopentanyl methacrylate and isobornyl methacrylate. The saturated hydrocarbon group preferably has 8 to 14 carbon atoms, more preferably 9 to 12. The fused ring structure is not particularly limited, but is preferably a structure in which two five-membered rings are fused together by three consecutive carbon atoms.

[0034] Examples of the methacrylic acid ester in which the ester moiety is a linear or branched group containing an ether bond include 2-methoxyethyl methacrylate.

[0035] Examples of the styrene-based monomer include styrene, α-methylstyrene, monochlorostyrene, dichlorostyrene, etc. Among these, styrene is preferred.

[0036] The drying-accelerating comonomer unit preferably includes at least one of an N-substituted maleimide monomer unit and a methacrylic acid ester unit, the ester moiety of which is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure, because the drying-accelerating comonomer unit can increase the evaporation rate of the solvent from the casting film in the solution casting method and further increase the heat resistance of the graft copolymer.

[0037] In this case, the drying-accelerating comonomer unit may be at least one of an N-substituted maleimide monomer unit and a methacrylic acid ester unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure, or may be a combination of at least one of an N-substituted maleimide monomer unit and a methacrylic acid ester unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure, with a drying-accelerating comonomer unit other than these. By using such a combination, it is possible to adjust the heat resistance of the graft copolymer and the evaporation rate of the solvent, thereby improving both in a balanced manner.

[0038] The drying-accelerating comonomer unit other than the N-substituted maleimide monomer unit and the methacrylic acid ester unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure may be at least one selected from the group consisting of the above-mentioned methacrylic acid ester unit in which the ester moiety is a primary or secondary hydrocarbon group or an aromatic hydrocarbon group having 2 to 20 carbon atoms, the methacrylic acid ester unit in which the ester moiety is a linear or branched group containing an ether bond, and the styrene monomer unit.

[0039] Among the monomer components constituting the non-crosslinked methacrylic polymer component (b), the proportion of the drying-accelerating comonomer unit is preferably 1% by weight or more and 30% by weight or less, more preferably 2 to 25% by weight, even more preferably 3 to 20% by weight, even more preferably 4 to 18% by weight, even more preferably 4 to 15% by weight, even more preferably 4 to 12% by weight, and particularly preferably 5 to 10% by weight. When two or more types of drying-accelerating comonomer units are contained, the proportion of the drying-accelerating comonomer units refers to the proportion of the total amount of all the drying-accelerating comonomer units contained in the total monomer units. By achieving such a weight proportion, the graft copolymer can have excellent heat resistance while accelerating the solvent evaporation rate in the solution casting method. The weight proportion of each of these units can be determined by proton nuclear magnetic resonance spectroscopy.

[0040] The non-crosslinked methacrylic polymer component (b) may be a copolymer that does not contain other comonomer units that do not fall under the category of drying-accelerating comonomer units, or may be a copolymer that contains other comonomer units that do not fall under the category of drying-accelerating comonomer units. Examples of such other comonomers include methacrylic acid esters such as glycidyl methacrylate, epoxycyclohexylmethyl methacrylate, dimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,2-trichloroethyl methacrylate, methacrylamide, and N-methylolmethacrylamide; methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, benzyl acrylate, octyl acrylate, glycidyl acrylate; Examples of suitable comonomer units include acrylic esters such as epoxycyclohexylmethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, acrylamide, and N-methylol acrylamide; carboxylic acids such as methacrylic acid and acrylic acid and their salts; vinyl cyanides such as acrylonitrile and methacrylonitrile; maleic acid, fumaric acid, and their esters; vinyl halides such as vinyl chloride, vinyl bromide, and chloroprene; vinyl esters such as vinyl formate, vinyl acetate, and vinyl propionate; and alkenes such as ethylene, propylene, butylene, butadiene, and isobutylene. The proportion of such other comonomer units in the monomer components constituting the non-crosslinked methacrylic polymer component (b) is preferably 10% by weight or less, more preferably 8% by weight or less, and even more preferably 5% by weight or less.

[0041] In the graft copolymer according to this embodiment, the proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is 1% by weight or more and less than 50% by weight, and the proportion of the non-crosslinked methacrylic polymer component (b) is 99% by weight or less and more than 50% by weight. By containing such a high proportion of the non-crosslinked methacrylic polymer component (b), the graft copolymer according to this embodiment is less susceptible to aggregation, making it possible to form a film with high strength and low haze, and also improving the storage stability of the graft copolymer or a dope thereof. The proportion of the crosslinked (meth)acrylic polymer particles (a) is preferably 3% by weight or more and 45% by weight or less, more preferably 4 to 40% by weight, even more preferably 5 to 35% by weight, and particularly preferably 6 to 30% by weight.

[0042] Furthermore, from the viewpoint of the bending resistance of the resulting film, the proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is preferably 5% by weight or more, more preferably 6% by weight or more, and even more preferably 7% by weight or more. From the viewpoint of moisture permeability and elastic modulus, the upper limit of this proportion is preferably 25% by weight or less, more preferably 20% by weight or less, even more preferably 15% by weight or less, even more preferably 12% by weight or less, and particularly preferably 10% by weight or less. From the viewpoint of the balance between moisture permeability, elastic modulus, and bending resistance, it is preferably 6% by weight or more, more preferably 7% by weight or more, and also preferably 20% by weight or less, more preferably 15% by weight or less, even more preferably 12% by weight or less, and particularly preferably 10% by weight or less.

[0043] (Method for Producing Graft Copolymer) The graft copolymer according to this embodiment can be produced by conventional emulsion polymerization using an emulsifier and a polymerization initiator. Specifically, after forming crosslinked (meth)acrylic polymer particles (a) by emulsion polymerization, a monomer component constituting a non-crosslinked methacrylic polymer component (b) is added to the polymerization system, followed by emulsion polymerization to form the non-crosslinked methacrylic polymer component (b). This allows for the production of a graft copolymer in which at least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a). By producing the graft copolymer by the above method, it is possible to achieve a configuration in which the crosslinked (meth)acrylic polymer particles (a) are sufficiently dispersed in the non-crosslinked methacrylic polymer component (b).

[0044] The emulsifier is not particularly limited, and examples thereof include anionic surfactants such as sodium alkyl sulfonate, sodium alkylbenzene sulfonate, sodium dioctyl sulfosuccinate (di(2-ethylhexyl)sodium sulfosuccinate), sodium lauryl sulfate, sodium fatty acid, and phosphate ester salts such as polyoxyethylene lauryl ether sodium phosphate, as well as nonionic surfactants. These surfactants may be used alone or in combination of two or more. From the viewpoint of improving the thermal stability of a film formed from the graft copolymer, polymerization is preferably carried out using a phosphate ester salt (alkali metal or alkaline earth metal) such as dioctyl sulfosuccinate (di(2-ethylhexyl)sodium sulfosuccinate) or polyoxyethylene lauryl ether sodium phosphate, and particularly preferably using a phosphate ester salt (alkali metal or alkaline earth metal) such as polyoxyethylene lauryl ether sodium phosphate.

[0045] The polymerization initiator is not particularly limited, but from the viewpoint of improving the thermal stability of the film, a polymerization initiator having a 10-hour half-life temperature of 100° C. or less is preferred. The polymerization initiator is not particularly limited, but a persulfate is preferred. Specific examples include potassium persulfate, sodium persulfate, and ammonium persulfate.

[0046] The polymerization initiator is preferably added at least in the step of forming the crosslinked (meth)acrylic polymer particles (a), and may be additionally added in the step of forming the non-crosslinked methacrylic polymer component (b).

[0047] In the step of forming the non-crosslinked methacrylic polymer component (b), polymerization may be carried out in the presence of a chain transfer agent in order to control the molecular weight of the polymer component (b). The chain transfer agent that can be used in this step is not particularly limited, but examples thereof include primary alkyl mercaptan chain transfer agents such as n-butyl mercaptan, n-octyl mercaptan, n-hexadecyl mercaptan, n-dodecyl mercaptan, and n-tetradecyl mercaptan; secondary alkyl mercaptan chain transfer agents such as s-butyl mercaptan and s-dodecyl mercaptan; tertiary alkyl mercaptan chain transfer agents such as t-dodecyl mercaptan and t-tetradecyl mercaptan; thioglycolic acid esters such as ethylhexyl thioglycolate, ethylene glycol dithioglycolate, trimethylolpropane tris(thioglycolate), and pentaerythritol tetrakis(thioglycolate), thiophenol, tetraethylthiuram disulfide, pentanephenylethane, acrolein, methacrolein, allyl alcohol, carbon tetrachloride, ethylene bromide, styrene oligomers such as α-methylstyrene dimer, and terpinolene. These may be used alone or in combination of two or more.

[0048] The graft copolymer latex obtained by the emulsion polymerization can be subjected to heat drying or spray drying, or to a known method such as coagulating the latex by adding a water-soluble electrolyte such as a salt or an acid, followed by heat treatment, separating the resin component from the aqueous phase, and drying, to obtain a solid or powdery graft copolymer. Among these, the method of coagulating using a salt is preferred. The salt is not particularly limited, but divalent salts are preferred, and specific examples include calcium salts such as calcium chloride and calcium acetate, and magnesium salts such as magnesium chloride and magnesium sulfate. Among these, magnesium salts such as magnesium chloride and magnesium sulfate are preferred. During coagulation, commonly added additives such as antioxidants and ultraviolet absorbers may be added.

[0049] Before the coagulation operation, it is preferable to filter the latex with a filter, a mesh or the like to remove fine polymerization scales. This can reduce fish eyes and foreign matters caused by the fine polymerization scales, and can also reduce coarse particles in the dope.

[0050] (Resin Composition) The graft copolymer according to this embodiment can be used to form a resin composition for film production by a solution casting method. The resin composition may contain only the graft copolymer according to this embodiment as a resin component, or may contain other resins in addition to the graft copolymer according to this embodiment. Examples of such resins include, but are not limited to, styrene-based resins such as methacrylic resins, acrylonitrile-styrene resins, and styrene-maleic anhydride resins; polycarbonate resins; polyvinyl acetal resins; cellulose acylate resins; fluorine-based resins such as polyvinylidene fluoride and polyfluorinated alkyl (meth)acrylate resins; silicone-based resins; polyolefin-based resins; polyethylene terephthalate resins; and polybutylene terephthalate resins. The content of the other resins is not particularly limited, but may be, for example, approximately 0 to 50 parts by weight per 100 parts by weight of the graft copolymer according to this embodiment. Furthermore, the content may be 0 to 30 parts by weight, 0 to 10 parts by weight, 0 to 5 parts by weight, or 0 to 1 part by weight.

[0051] The resin composition for producing a film may further contain known additives such as a light stabilizer, an ultraviolet absorber, a heat stabilizer, a matting agent, a light diffusing agent, a colorant, a dye, a pigment, an antistatic agent, a heat ray reflecting material, a lubricant, a plasticizer, an ultraviolet absorber, a stabilizer, a filler, etc. The resin composition may also contain a conventionally known core-shell type graft copolymer.

[0052] (Dope) The resin composition for producing a film can be dissolved or dispersed in a solvent to form a dope used when producing a resin film by a solution casting method.

[0053] The solvent is a solvent capable of dissolving or dispersing the resin composition for film production, and is not particularly limited. It is preferable to use a solvent (c-1) having a hydrogen bond parameter δH of 1 or more and 12 or less in the Hansen solubility parameter. By using such a solvent to prepare a dope, the graft copolymer according to the present embodiment can be made to have good solubility or dispersibility in the solvent. Solvents having a hydrogen bond parameter δH of 3 or more and 10 or less are preferred, and solvents having a hydrogen bond parameter δH of 5 or more and 8 or less are more preferred.

[0054] The solubility parameter (SP value) has traditionally been known as an index of a substance's solubility. The Hansen solubility parameter (HSP) has been proposed, in which the cohesive energy term of the SP value is divided according to the type of intermolecular interaction energy (London dispersion force, dipole-dipole force, hydrogen bonding force), and each of these is expressed as a London dispersion force term, a dipole-dipole force term, and a hydrogen bonding force term. The hydrogen bonding term δH of the Hansen solubility parameter is used as an index of the solubility of a graft copolymer when dissolved in a solvent. For details of the hydrogen bonding term δH, see, for example, Hideki Yamamoto, "Special Feature: Polymer Compatibilization Design 1. Solubility Evaluation Using the Hansen Solubility Parameter (HSP Value)," Adhesion Technology, Vol. 34, No. 3 (2014), Vol. 116, pp. 1-8.

[0055] Examples of solvents (c-1) having a hydrogen bond parameter δH of 1 or more and 12 or less include 1,4-dioxane (9.0), 2-phenylethanol (11.2), acetone (7.0), acetonitrile (6.1), chloroform (5.7), dibasic acid ester (8.4), diacetone alcohol (10.8), N,N-dimethylformamide (11.3), dimethyl sulfoxide (10.2), ethyl acetate (7.2), γ-butyrolactone (7.4), methyl ethyl ketone (5.1), methyl isobutyl ketone (4.1), methylene chloride (7.1), n-butyl acetate (6.3), N-methyl-2-pyrrolidone (7.2), propylene carbonate (4.1), 1,1,2,2-tetrachloroethane (5.3), tetrahydrofuran (8.0), and toluene (2.0). The numbers in parentheses indicate the hydrogen bond parameter δH. These solvents may be used alone or in combination of two or more.

[0056] Among these solvents, methyl ethyl ketone, chloroform, and methylene chloride are preferred, and methylene chloride is more preferred, because they have excellent solubility for the graft copolymer according to this embodiment and a fast evaporation rate.

[0057] The solvent contained in the dope may be composed only of the solvent (c-1) having the hydrogen bond parameter δH of 1 to 12. However, in consideration of the film-forming property during solution casting, the releasability of the film, and the handling property, it is preferable that the dope contains the solvent (c-1) having the hydrogen bond parameter δH of 1 to 12 and the solvent (c-2) having the δH of 14 to 24.

[0058] Examples of the solvent (c-2) having a δH of 14 or more and 24 or less include methanol (22.3), ethanol (19.4), isopropanol (16.4), butanol (15.8), ethylene glycol monoethyl ether (14.3), etc. These solvents may be used alone or in combination of two or more.

[0059] When the solvent (c-1) having a δH of 14 to 24 is used in combination with the solvent (c-2), the content of the solvent (c-1) having a hydrogen bond parameter δH of 1 to 12 is preferably 55% by weight to 95% by weight, more preferably 60% by weight to 90% by weight, even more preferably 65% ​​by weight to 85% by weight, and still more preferably 70% by weight to 85% by weight.

[0060] The proportion of the graft copolymer in the dope is not particularly limited and can be appropriately determined in consideration of the solubility or dispersibility of the graft copolymer in the solvent used, the conditions for carrying out the solution casting method, etc., but is preferably 5 to 50% by weight, more preferably 10 to 45% by weight, and even more preferably 15 to 40% by weight.

[0061] (Solution Casting Method) The dope is used to produce a resin film by a solution casting method. Specifically, the dope is cast on a support surface, and then the solvent is evaporated to produce a resin film.

[0062] The following describes an embodiment of the solution casting method, but the method is not limited thereto. First, pellets containing the graft copolymer according to this embodiment and, if necessary, other components are prepared, and then the pellets are mixed with a solvent to prepare a dope in which each component is dissolved or dispersed in the solvent. Alternatively, without preparing pellets, the graft copolymer according to this embodiment and other components are simultaneously or sequentially mixed with a solvent to prepare a dope in which each component is dissolved or dispersed in the solvent. The dissolving or dispersing step can be carried out by appropriately adjusting the temperature and pressure. After the dissolving or dispersing step, the obtained dope can be filtered or degassed.

[0063] Next, the dope is sent to a pressure die by a liquid feed pump, and the dope is cast from a slit in the pressure die onto the surface (mirror surface) of a support such as an endless belt or drum made of metal or synthetic resin to form a dope film.

[0064] The doped film is heated on the support to evaporate the solvent, forming a film. The conditions for evaporating the solvent can be determined appropriately depending on the boiling point of the solvent used.

[0065] The film thus obtained is peeled off from the surface of the support, and may then be subjected to a drying step, a heating step, a stretching step, or the like, as appropriate.

[0066] (Resin Film) The resin film according to this embodiment is made of the resin composition for film production and can be formed by the dope solution casting method described above. The thickness of the resin film is not particularly limited, but is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. It is also preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and particularly preferably 30 μm or more.

[0067] The resin film according to this embodiment preferably has a total light transmittance of 85% or more, more preferably 88% or more, and even more preferably 90% or more, when measured at a film thickness of 80 μm. If the total light transmittance is within the above range, the resin film can be suitably used for optical components, decorative applications, interior applications, and vacuum forming applications, which require light transmittance.

[0068] From the viewpoint of heat resistance, the resin film according to this embodiment preferably has a glass transition temperature of 100°C or higher, more preferably 105°C or higher, even more preferably 110°C or higher, still more preferably 115°C or higher, still more preferably 120°C or higher, particularly preferably 124°C or higher, and most preferably 125°C or higher.

[0069] The resin film according to this embodiment preferably has a haze of 0.8% or less, more preferably 0.6% or less, even more preferably 0.5% or less, even more preferably 0.4% or less, and particularly preferably 0.3% or less, when measured at a thickness of 50 μm. Furthermore, the internal haze of the resin film, when measured at a thickness of 50 μm, is preferably 0.5% or less, more preferably 0.4% or less, even more preferably 0.3% or less, and particularly preferably 0.2% or less. If the haze and internal haze are within the above-mentioned ranges, the resin film can be suitably used for optical components, decorative applications, interior applications, and vacuum molding applications that require light transparency. The haze consists of the haze inside the film and the haze on the film surface (external), and these are referred to as internal haze and external haze, respectively.

[0070] The resin film according to this embodiment can be used as an optical film. When used as a polarizer protective film, it is preferable that the optical anisotropy is small. In particular, it is preferable that the optical anisotropy in the thickness direction as well as the optical anisotropy in the in-plane direction (length direction and width direction) of the film is small. That is, it is preferable that the absolute values ​​of the in-plane retardation and the thickness direction retardation are both small. More specifically, the absolute value of the in-plane retardation is preferably 30 nm or less, more preferably 20 nm or less, even more preferably 15 nm or less, even more preferably 13 nm or less, particularly preferably 12 nm or less, and most preferably 10 nm or less. Furthermore, the absolute value of the thickness direction retardation is preferably 50 nm or less, more preferably 20 nm or less, even more preferably 15 nm or less, even more preferably 10 nm or less, particularly preferably 8 nm or less, and most preferably 5 nm or less. Resin films with such small retardation can be suitably used as polarizer protective films included in polarizing plates of liquid crystal display devices.

[0071] The retardation is an index value calculated based on birefringence, and the in-plane retardation (Re) and thickness direction retardation (Rth) can be calculated by the following formulas: In an ideal film that is completely optically isotropic in three-dimensional directions, both the in-plane retardation Re and the thickness direction retardation Rth are 0.

[0072] Re = (nx - ny) x d Rth = ((nx + ny) / 2 - nz) x d In each formula, nx, ny, and nz represent the refractive index in the direction of in-plane stretching (direction of orientation of polymer chains) as the X axis, the direction perpendicular to the X axis as the Y axis, and the thickness direction of the film as the Z axis. Also, d represents the thickness of the film, and nx - ny represents the orientation birefringence. Note that the MD direction of the film is the X axis, but in the case of a stretched film, the stretching direction is the X axis.

[0073] (Stretching) The resin film according to the present embodiment has high toughness and flexibility, and may be an unstretched film or a stretched film. Stretching the resin film can improve the mechanical strength and thickness accuracy of the resin film.

[0074] When stretching the resin film according to the present embodiment, a stretched film (uniaxially stretched film or biaxially stretched film) can be produced by producing an unstretched film and then uniaxially stretching or biaxially stretching the film, or by appropriately adding a stretching operation during film formation as the film formation and solvent degassing processes progress. Stretching during film formation and stretching after film formation may also be appropriately combined.

[0075] The stretching ratio of the stretched film is not particularly limited and may be determined depending on the mechanical strength, surface properties, thickness accuracy, etc. of the stretched film to be produced. Although it also depends on the stretching temperature, the stretching ratio is generally preferably selected from the range of 1.1 to 5, more preferably from 1.3 to 4, and even more preferably from 1.5 to 3. If the stretching ratio is within the above range, the mechanical properties of the film, such as elongation, tear propagation strength, and flexural fatigue resistance, can be significantly improved.

[0076] (Uses) The resin film according to this embodiment can be used to reduce the gloss of the film surface, if necessary, by a known method. Examples of such methods include adding an inorganic filler or crosslinkable polymer particles. Furthermore, by embossing the resulting film, it is possible to form a surface irregularity layer such as a prism shape, pattern, design, or knurling, or to reduce the gloss of the film surface.

[0077] The resin film according to the present embodiment can be used by laminating another film thereon using a dry lamination method and / or a thermal lamination method using a pressure-sensitive adhesive, adhesive, or the like, as needed, or by forming a functional layer such as a hard coat layer, an anti-reflection layer, an anti-fouling layer, an anti-static layer, a printed decorative layer, a metallic gloss layer, a surface irregularity layer, or a matte layer on the front or back surface of the film.

[0078] The resin film according to the present embodiment can be used in various applications by utilizing properties such as heat resistance, transparency, flexibility, etc. For example, it can be used in the following applications: automobile interior / exterior, personal computer interior / exterior, mobile phone interior / exterior, solar cell interior / exterior, solar cell backsheet; imaging fields such as photographic lenses, viewfinders, filters, prisms, Fresnel lenses, and lens covers for cameras, VTRs, and projectors; lens fields such as pickup lenses for optical discs in CD players, DVD players, and MD players; optical recording fields for optical discs such as CDs, DVDs, and MDs; organic EL films, light guide plates for liquid crystal displays, diffusion plates, backsheets, reflective sheets, polarizer protective films, polarizing film transparent resin sheets, retardation films, light diffusion films, and prism sheets. It can be used in information equipment such as LCD films and surface protection films, optical communications such as optical fibers, optical switches, and optical connectors, automotive headlights, taillight lenses, inner lenses, instrument covers, and sunroofs, medical equipment such as eyeglasses, contact lenses, endoscope lenses, and medical supplies that require sterilization, construction and building materials such as road signs, bathroom equipment, flooring, road translucent panels, double-glazed lenses, skylights, carports, lighting lenses, lighting covers, and building sizing, microwave cooking containers (tableware), home appliance housings, toys, sunglasses, stationery, etc. It can also be used as a replacement for molded products using transfer foil sheets.

[0079] The resin film according to this embodiment can be used by laminating it to a substrate such as a metal, a plastic, etc. Examples of methods for laminating the resin film include lamination molding, wet lamination in which an adhesive is applied to a metal plate such as a steel plate, and then a film is placed on the metal plate and dried to bond them together, dry lamination, extrusion lamination, hot melt lamination, etc.

[0080] Methods for laminating a film onto a plastic part include insert molding or laminate injection press molding, in which the film is placed in a mold and then filled with resin by injection molding, and in-mold molding, in which a preformed film is placed in a mold and then filled with resin by injection molding.

[0081] The resin film laminate according to this embodiment can be used as a paint replacement for automobile interior materials, automobile exterior materials, and the like; civil engineering and construction materials such as window frames, bathroom equipment, wallpaper, flooring materials, lighting and light control materials, soundproof walls, and road signs; daily goods; housings for furniture and electronic and electrical devices; housings for office automation equipment such as facsimiles, laptops, and copiers; front panels for LCD screens of terminals such as mobile phones, smartphones, and tablets; optical materials such as lighting lenses, automobile headlights, optical lenses, optical fibers, optical disks, and LCD light guide plates; optical elements; parts for electric or electronic devices; medical supplies requiring sterilization; toys or recreational items; and fiber-reinforced resin composite materials.

[0082] In particular, the resin film according to the present embodiment is suitable for optical films because of its excellent heat resistance and optical properties, and can be used for various optical members. For example, the resin film according to the present embodiment can be used for known optical applications such as front panels of liquid crystal screens of terminals such as mobile phones, smartphones, and tablets, lighting lenses, automobile headlights, optical lenses, optical fibers, optical disks, light guide plates for liquid crystal displays, diffusion plates, backsheets, reflective sheets, polarizing films, transparent resin sheets, retardation films, light diffusion films, prism sheets, surface protective films, optically isotropic films, polarizer protective films, and transparent conductive films in the fields of liquid crystal display devices, organic EL devices, and optical communications.

[0083] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following, "parts" and "%" mean "parts by weight" and "% by weight" unless otherwise specified.

[0084] Example 1 Production of Graft Copolymer (A1) The following substances were charged into an 8-L polymerization apparatus equipped with a stirrer: 133 parts deionized water; 0.004 parts sodium hydroxide; 0.2 parts di(2-ethylhexyl)sodium sulfosuccinate. After thoroughly purging the atmosphere inside the polymerization apparatus with nitrogen gas, the internal temperature was raised to 80°C, and 0.03 parts sodium persulfate and 0.001 parts sodium pyrosulfite were added as a 0.5% aqueous solution. Next, 40 parts of a monomer (a) for crosslinked (meth)acrylic polymer particles shown in Table 1 were continuously added at a rate of 0.523 parts / min. Polymerization was continued for an additional 30 minutes to obtain crosslinked (meth)acrylic polymer particles (a). The polymerization conversion rate was 99.5%. The average particle size is shown in Table 2. Thereafter, 60 parts of a monomer (b) for non-crosslinked methacrylic polymer components shown in Table 1 were continuously added at a rate of 1.353 parts / min. Simultaneously with the start of addition of monomer (b), 0.4 parts of sodium di(2-ethylhexyl) sulfosuccinate was continuously added as a 5% aqueous solution over the same time period as that of monomer (b). After completion of the addition, polymerization was continued for 60 minutes to obtain a graft copolymer latex. The polymerization conversion rate was 100.0%. The average particle size is shown in Table 2. The obtained latex was dried at 75°C for 12 hours to obtain a white powdery graft copolymer (A1).

[0085] Examples 2 to 8 and Comparative Example 1 Graft copolymers (A2) to (A9) were produced in the same manner as in Example 1, except that the types and amounts of raw materials used were changed as shown in Table 1.

[0086]

[0087] (Polymerization Conversion Rate) The polymerization conversion rate of the polymer obtained by polymerization was determined by the following method. Approximately 2 g of latex containing the polymer was collected from the polymerization system and precisely weighed, and then dried in a hot air dryer at 120°C for 1 hour. The weight after drying was precisely weighed as the solid content. Next, the ratio of the weighing results before and after drying was determined as the solid content ratio in the sample. Finally, using this solid content ratio, the polymerization conversion rate was calculated by the following calculation formula. In this calculation formula, the polyfunctional monomer and the chain transfer agent were treated as charged monomers. Polymerization Conversion Rate (%) = {(Total Weight of Charged Raw Materials x Solid Content Ratio - Total Weight of Raw Materials Other Than Water and Monomers) / Weight of Charged Monomer} x 100

[0088] (Weight-Average Molecular Weight of Non-Crosslinked Methacrylic Polymer Component (b)) Of the graft copolymers obtained by polymerization, the weight-average molecular weight of the non-crosslinked methacrylic polymer component (b) was calculated by a standard polystyrene conversion method using gel permeation chromatography (GPC) and is shown in Table 2. The GPC column used was one packed with crosslinked polystyrene gel (model: TSKgel Super HZM-H, manufactured by Tosoh Corporation), and tetrahydrofuran (THF) was used as the GPC solvent. The sample solution used was a clear supernatant obtained by centrifuging a polymer solution consisting of 20 mg of graft copolymer powder and 10 ml of THF at 43,000 G for 30 minutes. The GPC column temperature was set to 40°C.

[0089] (Average particle diameter of crosslinked (meth)acrylic polymer particles (a) and graft copolymers (A1) to (A9)) The average particle diameter is the volume average particle diameter measured in the state of each latex obtained at the completion of polymerization of the crosslinked (meth)acrylic polymer particles (a) and the graft copolymers (A1) to (A9). The measurement was performed using a Microtrac UPA150 manufactured by Nikkiso Co., Ltd., and the volume average particle diameter measured is shown in Table 2 as the average particle diameter. The measurement was performed at room temperature, and the refractive index of the measured particles was the weight average value of the refractive index of a homopolymer made of the monomers used in the polymerization. The refractive index of the homopolymer was the value listed in the Polymer Handbook [Polymer Hand Book (J. Brandrup, Interscience 1989)].

[0090] (Comparative Example 3) 200 parts of deionized water and 0.5 parts of disodium hydrogen phosphate as a suspension aid were charged into an 8-liter glass reactor equipped with a stirrer. Next, while stirring at 300 rpm, a monomer mixture consisting of 91 parts of MMA in which 0.3 parts of lauroyl peroxide had been dissolved, 9 parts of BMA, and 0.018 parts of 2-ethylhexyl thioglycolate (2-EHTG) as a chain transfer agent was added to the reactor, and the reactor was heated to 60 ° C. while purging with nitrogen to initiate polymerization. 50 minutes after reaching 60 ° C., 0.15 parts of Adeka Pluronic F-68 (manufactured by ADEKA Corporation, polyoxyethylene-polyoxypropylene block copolymer), a nonionic water-soluble polymer, was added as a suspension stabilizer. After that, the mixture was allowed to react for another 200 minutes at 60 ° C., and then heated to 80 ° C. and stirred for 3 hours to complete the polymerization. The obtained polymer was washed four times with deionized water in an amount three times the amount of the resin, and then dried to obtain a suspension polymer (A10) in the form of beads (weight average molecular weight: 970,000).

[0091] (Weight Average Molecular Weight of Suspension Polymer) The weight average molecular weight of the suspension polymer was calculated in the same manner as for the weight average molecular weight of the non-crosslinked methacrylic polymer component (b) except that a polymer solution consisting of 20 mg of suspension polymer beads and 10 ml of THF was used as the sample solution.

[0092] Comparative Example 4 The following substances were charged into an 8-L polymerization apparatus equipped with a stirrer: 175 parts deionized water, 0.002 parts polyoxyethylene lauryl ether sodium phosphate, and 0.04725 parts sodium carbonate. After thoroughly purging the atmosphere inside the polymerization apparatus with nitrogen gas, the internal temperature was raised to 80°C, and 0.03 parts potassium persulfate was added as a 2% aqueous solution. Subsequently, mixture (I) (25.2 parts MMA, 1.6 parts BA, 0.2 parts St, 0.135 parts ALMA, 0.3 parts n-OM, and 0.1 parts polyoxyethylene lauryl ether sodium phosphate) was continuously added over 81 minutes. Polymerization was continued for an additional 60 minutes to obtain a polymer (I). The polymerization conversion was 99.5%. Subsequently, 0.08 parts of potassium persulfate was added as a 2% aqueous solution, followed by continuous addition of mixture (II) (41 parts of BA, 9 parts of St, 0.75 parts of ALMA, and 0.2 parts of sodium polyoxyethylene lauryl ether phosphate) over 150 minutes. After completion of the addition, 0.015 parts of pure potassium persulfate was added as a 2% aqueous solution, and polymerization was continued for 120 minutes to obtain a polymer (II). The polymerization conversion rate was 99.7%, and the average particle size was 220 nm. Subsequently, 0.023 parts of potassium persulfate was added as a 2% aqueous solution, followed by continuous addition of mixture (III) (18.4 parts of MMA, 4.6 parts of BA) over 70 minutes, and polymerization was continued for 60 minutes to obtain a core-shell graft copolymer particle latex. The polymerization conversion rate was 100.0%. The obtained latex was salted out with magnesium chloride, coagulated, washed with water, and dried to obtain a white powdery core-shell graft copolymer (A11), which is a typical example of a conventional core-shell graft copolymer.

[0093] (Average particle diameter of graft copolymer (A11) up to the intermediate rubber layer) The average particle diameter of graft copolymer (A11) up to the intermediate rubber layer was calculated in the same manner as the average particle diameter of graft copolymers (A1) to (A9) described above, except that it was measured in the state of the latex obtained by polymerization up to the polymerization stage (II).

[0094] (Weight Average Molecular Weight of Outermost Layer of Graft Copolymer (A11)) The weight average molecular weight of the outermost layer of graft copolymer (A11) was calculated in the same manner as the weight average molecular weight of the non-crosslinked methacrylic polymer component (b) except that graft copolymer (A11) was used.

[0095] (Preparation of Resin Dope) A resin dope having a solid content of 10% for each of the graft copolymers (A1) to (A9) alone and the suspension polymer (A10) alone was prepared by adding 4.5 g of powder or beads of each polymer to 41.5 g of a mixed solvent consisting of 92% methylene chloride and 8% ethanol, and stirring with a magnetic stirrer until completely dissolved.

[0096] In Comparative Example 2, a resin dope containing a suspension polymer (A10) and a graft copolymer (A11) and having a solids concentration of 10% was prepared by adding 0.68 g of graft copolymer (A11) powder to 41.5 g of the mixed solvent and stirring with a magnetic stirrer until uniform, and then dispersing the resulting dispersion in an ultrasonic bath (Branson Nick 1510J, manufactured by Yamato Scientific Co., Ltd.) for an additional 15 minutes. Then, 3.82 g of suspension polymer (A10) beads were gradually added to the dispersion and stirred until completely dissolved.

[0097] (Preparation of Cast Film) The resin dope was cast onto a PET film (Cosmoshine A4100, manufactured by Toyobo Co., Ltd.) and applied to form a uniform film using an applicator. The clearance was adjusted so that the thickness after drying would be approximately 70 μm. The coating film was dried in a dry atmosphere at 40°C for 1 hour and then peeled off from the PET film. The resulting film was fixed to a stainless steel frame and dried in a dry atmosphere at 140°C for 90 minutes to remove residual solvent, yielding a cast film.

[0098] (Preparation of uniaxially stretched film) A 16 cm square test piece was cut out from an unstretched cast film and subjected to fixed-width uniaxial stretching at 135° C. The stretching ratio was 1.4 times and the stretching speed was 150 mm / min.

[0099] (Film Thickness) The film thickness was measured using a Digimatic Indicator (manufactured by Mitutoyo Corporation).

[0100] (MIT) The repeated bending strength of uniaxially stretched films was measured using an MIT-DA type MIT testing machine manufactured by Toyo Seiki Seisakusho, Ltd. Test pieces were cut out to a width of 1.5 cm, and a load of 200 g was applied under conditions of a bending radius of 0.4 mm and a bending angle of 135°, and the test was carried out in the direction in which a crease was formed perpendicular to the stretching direction. The test was carried out three times, and the average values ​​are shown in Table 2.

[0101] (Trimming test) A uniaxially stretched film was quickly cut with a cutter blade (Quick Knife Q-100P manufactured by NT Cutter) in a direction parallel to the stretching direction against a ruler, and the appearance of the cut surface was evaluated on a 5-point scale according to the following criteria. The test was performed five times for each sheet of uniaxially stretched film, and the average of the five evaluation scores is shown in Table 2. An average of 3 points or more for the five evaluation scores can be evaluated as having good trimmability.

[0102] 1: The cut surface was not smooth for more than half the length, and in addition, cracks or chips of 5 mm or more, or film breakage occurred. 2: The cut surface was not smooth for more than half the length, and in addition, cracks or chips of less than 5 mm occurred, but no film breakage occurred. 3: The cut surface was not smooth for more than half the length, but no cracks, chips, or film breakage occurred. 4: The cut surface was smooth for more than half the length, and no cracks, chips, or film breakage occurred. 5: All cut surfaces were smooth.

[0103] (Haze) The overall haze of the unstretched film was measured using a haze meter (HZ-V3 manufactured by Suga Test Instruments Co., Ltd.) according to the method described in JIS K7105. On the other hand, the unstretched film was sandwiched between glycerin and then glass on both sides, and the same measurement was carried out, and the obtained value was taken as the internal haze. The obtained results were converted to a film thickness equivalent to 50 μm and are shown in Table 2.

[0104] (In-plane retardation and thickness direction retardation of uniaxially stretched film) A test specimen was cut out from the center of the stretched film. The in-plane retardation of this test specimen was measured at a wavelength of 590 nm and an incident angle of 0° using an automatic birefringence meter (KOBRA-WR manufactured by Oji Measurement Co., Ltd.). Measurement was also performed at an incident angle of 40°, and the thickness direction retardation was also calculated. The measurement was performed three times while moving the test specimen to change the measurement location, and the average value was converted to a film thickness equivalent to 50 μm and is shown in Table 2.

[0105] (Glass Transition Temperature) The glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) was calculated using the Fox formula using values ​​listed in the Polymer Hand Book (J. Brandrup, Interscience 1989).

[0106] The glass transition temperature of the non-crosslinked methacrylic polymer component (b) or suspension polymer beads was measured using a differential scanning calorimeter DSC7000X manufactured by Hitachi High-Tech Science Corporation. The sample graft copolymer powder or suspension polymer beads was placed under a nitrogen stream and heated to 190°C at a heating rate of 10°C / min, held at 190°C for 3 minutes, then rapidly cooled to 40°C, and heated again to 190°C at a heating rate of 10°C / min. The glass transition observed during the second heating was averaged between the extrapolated glass transition onset temperature and the extrapolated glass transition end temperature, and this value was taken as the glass transition temperature. The results are shown in Table 2.

[0107] The glass transition temperature of the film was determined in the same manner as for the glass transition temperature of the non-crosslinked methacrylic polymer component (b) or suspension polymer beads, except that the cast film, which had been dried at 140° C., was further dried at 175° C. for 1 hour, and then used as a sample for measurement. The results are shown in Table 2.

[0108] (Storage Stability of Graft Copolymer Powder) The storage stability of the graft copolymer in powder form was evaluated by measuring the change in particle size distribution over time using a laser diffraction particle size distribution analyzer (Malvern Instruments Mastersizer 3000). A mixed solvent consisting of 92% methylene chloride and 8% ethanol was used as the dispersion medium for particle size distribution measurement. A resin dope with a solids concentration of 10% was prepared from the powder and the mixed solvent immediately before measurement. The resin dope was added dropwise while circulating the dispersion medium within the apparatus, and measurements were performed so that the laser scattering intensity was 0.5 to 2.0%. The graft copolymer powder was stored under conditions of 50°C and 95% RH, and the above measurements were performed on the powder on days 0, 3, and 14 of storage. The volume percentage of particles 1 μm or larger relative to the total particles is shown in Table 2.

[0109] (Storage Stability of Resin Dope Containing Graft Copolymer) The storage stability of the resin dope containing the graft copolymer was evaluated in the same manner as the storage stability of the graft copolymer powder. A mixed solvent consisting of 82% methylene chloride and 18% methanol, or a mixed solvent consisting of 92% methylene chloride and 8% ethanol, was used to prepare the resin dope. Resin dopes prepared with a solids concentration of 10% were stored at room temperature, and measurements were performed on the resin dopes 0, 3, and 14 days after the start of storage using a mixed solvent with the same composition as the resin dope as a dispersion medium. The volume percentage of particles 1 μm or larger relative to the total particles is shown in Table 2.

[0110]

[0111] Table 2 reveals the following: In Examples 1 to 8, resin films having high bending resistance, trimming resistance, and heat resistance and low haze could be molded from the graft copolymer alone. In addition, the storage stability of the graft copolymer powder and the graft copolymer-containing dope was good.

[0112] On the other hand, in Comparative Example 1, in which a graft copolymer with a low weight-average molecular weight of less than 250,000 was used, the resin film produced had a low glass transition temperature and poor heat resistance. In Comparative Example 2, in which a resin film was produced by blending a core-shell graft copolymer with a methacrylic resin as in the past, the haze of the resin film was high, and the content of coarse particles increased over time in both the core-shell graft copolymer powder and the core-shell graft copolymer-containing dope, resulting in poor storage stability. The resin film of Comparative Example 3, produced solely from a typical methacrylic resin, had insufficient bending resistance and trimming resistance. Furthermore, as shown in Comparative Example 4, a resin film could not be produced solely from a conventional core-shell graft copolymer.

[0113] The elastic modulus and moisture permeability of the graft copolymers obtained in Examples 4 and 6-8 were measured according to the following methods. The results are shown in Table 3.

[0114] (Elastic Modulus) The resin films used for measurement were prepared according to the following procedure. First, 2 g of each graft copolymer was added and dissolved in 18 g of a mixed solvent consisting of 92% methylene chloride and 8% ethanol to prepare a dope with a solids concentration of 10%. This dope was applied to a PET film (product name: Cosmoshine A4100, manufactured by Toyobo Co., Ltd.) to a wet film thickness of 0.6 mm, quickly covered with a tray, dried at room temperature for 30 minutes, and then dried in a hot air dryer at 40°C for 60 minutes to prepare an undried film. This undried film was peeled from the PET film, fixed to a metal frame, and dried in a hot air dryer at 140°C for 1 hour to prepare a film with a thickness of 40 μm. The obtained film was cut into strips with a width of 10 mm and a length of 130 mm. A tensile test was performed under conditions of a chuck distance of 100 mm and a tensile speed of 13 mm / min, and the elastic modulus was calculated in the range of 3 to 12 mm. The calculation results were calculated as the average value of n=7.

[0115] (Moisture Permeability) The resin films used for measurement were prepared according to the following procedure. First, 2 g of each graft copolymer was added and dissolved in 18 g of a mixed solvent consisting of 82% methylene chloride and 18% methanol to prepare a dope with a solids concentration of 10%. This dope was applied to a PET film (product name: Cosmoshine A4100, manufactured by Toyobo Co., Ltd.) to a wet film thickness of 0.5 mm and immediately dried in a hot air dryer at 40°C for 10 minutes to prepare an undried film. This undried film was peeled from the PET film, fixed to a metal frame of an appropriate size, and further dried in a hot air dryer at 140°C for 1 hour to prepare a film with a thickness of 50 μm. The moisture permeability was measured using the cup method in accordance with JIS Z 0208-1976. A circular film with a thickness of 50 μm and a measurement area of ​​28.3 cm was used. ２ A sample prepared using a cup (manufactured by Tester Sangyo Co., Ltd.) and 8 g of calcium chloride for moisture measurement (Wako) was placed in a thermo-hygrostat (model: LH33-13P, manufactured by Nagano Science Co., Ltd.) and measured at 40°C and 90% RH.

[0116]

[0117] The following can be seen from Table 3. In Examples 4 and 6 to 8, resin films having good moisture permeability and elastic modulus in addition to the above-mentioned bending resistance and trimming resistance could be molded from the graft copolymer alone. In particular, the resin films obtained in Examples 6 and 7 had a good balance between moisture permeability and elastic modulus.

Claims

1. Crosslinked (meth)acrylic polymer particles (a) having an average particle size of 150 nm or less and a glass transition temperature of −10° C. or less; A non-crosslinked methacrylic polymer component (b) having a weight average molecular weight of 300,000 or more; At least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a); A graft copolymer, in which the proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is 1% by weight or more and less than 50% by weight.

2. A graft copolymer as described in claim 1, wherein the weight average molecular weight of the non-crosslinked methacrylic polymer component (b) is 350,000 or more.

3. 3. The graft copolymer according to claim 1, wherein the non-crosslinked methacrylic polymer component (b) contains 70% by weight or more and 99% by weight or less of methyl methacrylate units.

4. The graft copolymer according to claim 3, wherein the non-crosslinked methacrylic polymer component (b) further comprises at least one selected from the group consisting of N-substituted maleimide monomer units, methacrylic ester units in which the ester moiety is a primary or secondary hydrocarbon group having 2 to 20 carbon atoms or an aromatic hydrocarbon group, methacrylic ester units in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and having a condensed ring structure, methacrylic ester units in which the ester moiety is a linear or branched group containing an ether bond, and styrene monomer units.

5. The graft copolymer according to claim 3, wherein the non-crosslinked methacrylic polymer component (b) further comprises at least one of an N-substituted maleimide monomer unit and a methacrylic acid ester unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a condensed ring structure.

6. 6. The graft copolymer according to claim 1, wherein the non-crosslinked methacrylic polymer component (b) has a glass transition temperature of 118° C. or higher.

7. A graft copolymer as described in claim 6, wherein the non-crosslinked methacrylic polymer component (b) has a glass transition temperature of 120°C or higher.

8. The graft copolymer according to any one of claims 1 to 7, wherein the crosslinked (meth)acrylic polymer particles (a) contain 90% by weight or more and 100% by weight or less of an acrylic acid alkyl ester having an alkyl group having 1 to 8 carbon atoms among monomer components excluding polyfunctional monomers.

9. The crosslinked (meth)acrylic polymer particles (a) are formed from 100 parts by weight of monomer components excluding the polyfunctional monomer and 0.1 to 2.0 parts by weight of the polyfunctional monomer, the graft copolymer according to any one of claims 1 to 8.

10. A resin composition for producing a film by a solution casting method, comprising the graft copolymer according to any one of claims 1 to 9.

11. A dope comprising the resin composition for producing a film according to claim 10 and a solvent.

12. A method for producing a resin film, comprising the steps of casting the dope according to claim 11 on a surface of a support and then evaporating the solvent.

13. A resin film formed from the resin composition for film production according to claim 10 by a solution casting method.

14. The resin film according to claim 13, wherein the resin film has a thickness of 1 to 500 μm.

15. The resin film according to claim 13 or 14, which is a film for laminating and protecting a surface of another substrate.

16. The resin film according to any one of claims 13 to 15, which is an optical film.

17. The resin film according to claim 16 , wherein the optical film is a polarizer protective film.

18. A polarizing plate comprising a polarizer and the resin film according to claim 17 laminated together.

19. A display device comprising the polarizer of claim 18.