Graft copolymers and resin films

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

Technical Field

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

Background Art

[0002] Methacrylic resins are excellent polymers that are widely used industrially in various fields because they have excellent transparency, color tone, appearance, weather resistance, gloss, and processability. In particular, resin films formed from methacrylic resins utilize their excellent transparency, appearance, and weather resistance, and are used in various applications such as interior and exterior automotive materials, exterior materials for electrical appliances such as mobile phones and smartphones, and interior and exterior civil engineering and architectural materials such as floors, windows, interior and exterior walls, lighting sections, and road signs. In recent years, methacrylic resins have been applied to optical members such as liquid crystal display devices and organic EL display devices by taking advantage of their excellent optical properties.

[0003] However, resin films formed from general methacrylic resins have the drawback of low impact resistance. Therefore, a method of blending a graft copolymer containing a rubber component with a methacrylic resin has been widely used for the purpose of improving impact resistance.

[0004] As such a rubber-containing graft copolymer, a core-shell type graft copolymer having a core layer made of rubber and a shell layer for improving the compatibility with a methacrylic resin is known (see, for example, Patent Document 1).

Prior Art Documents

[0007] In view of the above situation, the present invention aims to provide a graft copolymer that has excellent heat resistance, can form a high-strength and low-haze film, has good storage stability, and a resin film formed from the graft copolymer. [Means for solving the problem]

[0008] As a result of diligent research to solve the above problems, the present inventors have found that the above problems can be solved by a graft copolymer containing specific crosslinked (meth)acrylic polymer particles and specific non-crosslinked methacrylic polymer components in specific ratios, wherein the non-crosslinked methacrylic polymer components are graft-bonded to the crosslinked (meth)acrylic polymer particles, leading to the present invention.

[0009] In other words, the present invention relates to a graft copolymer comprising crosslinked (meth)acrylic polymer particles (a) having an average particle diameter 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) to 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. Preferably, the non-crosslinked methacrylate polymer component (b) contains 70% to 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 ester units whose ester moiety is a primary or secondary hydrocarbon group having 2 to 20 carbon atoms or an aromatic hydrocarbon group, methacrylic ester units whose ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms having a condensed ring structure, methacrylic ester units whose ester moiety is a linear or branched group containing an ether linkage, and styrene monomer units. Preferably, 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. 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 90% to 100% by weight of alkyl acrylates having 1 to 8 carbon atoms in the alkyl group, among the monomer components excluding the polyfunctional monomer. Preferably, the crosslinked (meth)acrylic polymer particles (a) are formed from 100 parts by weight of monomer components excluding polyfunctional monomers and 0.1 to 2.0 parts by weight of polyfunctional monomers. The present invention also relates to a resin composition for film production by solution casting, comprising the graft copolymer; a dope comprising the resin composition for film production and a solvent; a method for producing a resin film, comprising the step of casting the dope onto a support surface and then evaporating the solvent; or a resin film formed from the resin composition for film production by solution casting. Preferably, the resin film has a thickness of 1 to 500 μm. Preferably, the resin film is a protective film for lamination onto the surface of another substrate. Preferably, the resin film is an optical film. Preferably, the optical film is a polarizer protective film. Furthermore, the present invention relates to a polarizer and a polarizing plate formed by laminating the resin film; and the This also relates to display devices, including polarizing plates. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a graft copolymer that has excellent heat resistance, can form a high-strength and low-haze film, has good storage stability, and a resin film formed from the polymer. The graft copolymer according to the present invention can form a high-strength resin film even if the resin component consists solely of the copolymer. Furthermore, since it is not necessary to blend and disperse the core-shell type graft copolymer in a methacrylic resin as in the conventional method, a low-haze resin film can be easily formed. In addition, despite containing rubber components, the graft copolymer has good storage stability and also has the advantage of not causing turbidity when a dope is prepared by dissolving it in a solvent. As a result, the haze of the resin film produced by solution casting using this dope can be reduced. [Modes for carrying out the invention]

[0011] The 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 comprises crosslinked (meth)acrylic polymer particles (a) and a non-crosslinked methacrylic polymer component (b). Since the crosslinked (meth)acrylic polymer particles (a) are rubber components, they can contribute to improved strength. Furthermore, the non-crosslinked methacrylic polymer component (b) can achieve excellent heat resistance. Compared to a conventional system in which a core-shell type graft copolymer is blended with a methacrylic resin, the crosslinked (meth)acrylic polymer particles (a) correspond to the rubber component of the core in the core-shell type graft copolymer, and the non-crosslinked methacrylic polymer component (b) can correspond to the methacrylic resin which 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 the graft copolymer by emulsion polymerization, as described later. Due to this manufacturing 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 structure in which small-particle-size 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 occur. As a result, the graft copolymer according to this embodiment exhibits good stability whether it is stored in powder form or as a dope dissolved in a solvent. Furthermore, because aggregation of the crosslinked (meth)acrylic polymer particles (a) is suppressed, the graft copolymer according to this embodiment also has the advantage of being easily soluble in solvents.

[0014] (Cross-linked (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) in the graft copolymer according to this embodiment, high strength can be achieved, for example, when it is 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, when the graft copolymer according to this embodiment is formed into a film, for example, a low haze can be achieved. Also, by reducing the particle size of the crosslinked (meth)acrylic polymer particles, there is no need to match the refractive indices of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b). As a result, a monomer composition can be adopted such that the glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) is low without considering the refractive index. Thereby, when the graft copolymer is formed into a film, for example, high strength can be achieved.

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

[0017] The crosslinked (meth)acrylic polymer particles (a) exhibit a glass transition temperature of -10°C or lower. By using crosslinked (meth)acrylic polymer particles with such a low glass transition temperature, when the graft copolymer is formed into a film, for example, high strength can be achieved. The glass transition temperature can be controlled by adjusting the type and ratio 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, still more preferably -40°C or lower, and particularly preferably -45°C or lower. The lower limit of the glass transition temperature is not particularly limited. For example, it is preferably -130°C or higher, more preferably -110°C or higher, still more preferably -100°C or higher, even more preferably -80°C or higher, and particularly preferably -70°C or higher. Incidentally, the glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) is a value calculated using Fox's equation using the values described in Polymer Handbook [Polymer Hand Book (J. Brandrup, Interscience 1989)] (for example, poly(n-butyl acrylate) is -54°C).

[0019] The crosslinked (meth)acrylic polymer particles (a) are particles formed from a monomer component containing a (meth)acrylic monomer and a crosslinked (meth)acrylic polymer obtained by polymerizing 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] As the acrylic monomer contained in the crosslinked (meth)acrylic polymer particles (a), an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group is preferable. Specifically, ethyl acrylate, n-butyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, etc. can be mentioned. Only one kind of the alkyl acrylate may be used, or two or more kinds may be used in combination. Among them, n-butyl acrylate is preferable.

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

[0022] In the crosslinked (meth)acrylic polymer particles (a), monomers other than the alkyl acrylates and alkyl methacrylates described above may be used. Examples of such monomers include acrylic esters other than the alkyl acrylates, methacrylic esters other than the 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 aromatic vinyl monomers include styrene, α-methylstyrene, chlorostyrene, and other styrene derivatives. Examples of the aforementioned 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-ethyl maleimide, N-propyl maleimide, N-cyclohexyl maleimide, N-phenyl maleimide, and No-chlorophenyl maleimide. These may be used individually 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% to 100% by weight of acrylic acid esters (particularly alkyl acrylates with 1 to 8 carbon atoms in the alkyl group), more preferably 80% to 100% by weight, even more preferably 90% to 100% by weight, and particularly preferably 95% to 100% by weight.

[0024] The crosslinked (meth)acrylic polymer particles (a) are formed by polymerizing the monomer components in the presence of a polyfunctional monomer. This polyfunctional monomer is also known as a crosslinking agent or crosslinkable monomer, and is a compound having two or more unsaturated bonds in one molecule that can copolymerize with the (meth)acrylic monomer. Specifically, examples include allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate, diallyl itaconate, monoallyl maleate, monoallyl fumarate, butadiene, divinylbenzene, triallyl isocyanurate, alkylene glycol dimethacrylate, alkylene glycol diacrylate, etc. Only one of these may be used, or two or more may be used. Preferably, allyl methacrylate is used.

[0025] The amount of the polyfunctional monomer used can be appropriately set from the viewpoint of strength, but specifically, it may be about 0.1 parts by weight or more and 5.0 parts by weight or less per 100 parts by weight of monomer components constituting the crosslinked (meth)acrylic polymer particles (a) (excluding the polyfunctional monomer). 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 mainly composed of polymerized methacrylic monomers and is a polymer that does not have a crosslinked structure (i.e., obtained by polymerization without using polyfunctional monomers). At least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a), which makes the crosslinked (meth)acrylic polymer particles (a) less prone to aggregation. As a result, 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 with 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 according to 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. While there is no particular upper limit to the weight-average molecular weight, from the viewpoint of facilitating film formation by solution casting, it is preferably 1,000,000 or less, and more preferably 900,000 or less. The weight-average molecular weight of the non-crosslinked methacrylic polymer component (b) can be measured according to the description in the Examples section.

[0028] 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, from the viewpoint of the heat resistance of the graft copolymer. The upper limit of the glass transition temperature is not particularly limited, but for example, it may be 160°C or lower, or 150°C or lower. The glass transition temperature can be controlled by adjusting the type and ratio of 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 Fox's formula with values ​​listed in the Polymer Handbook [Polymer Hand Book (J. Brandrup, Interscience 1989)] (for example, 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 heat resistance and film formation of the graft copolymer, methyl methacrylate units are preferred as the methacrylic monomer units. In particular, it is preferable that the non-crosslinked methacrylic polymer component (b) contains 70% to 99% by weight of methyl methacrylate units among the monomer components constituting it. This improves heat resistance and makes film formation by solution casting easier. 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 at least one selected from the group consisting of N-substituted maleimide monomer units, methacrylic ester units whose ester moiety is a primary or secondary hydrocarbon group having 2 to 20 carbon atoms or an aromatic hydrocarbon group, methacrylic ester units whose ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms with a condensed ring structure, methacrylic ester units whose ester moiety is a linear or branched group containing an ether linkage, and styrene monomer units. Including such monomer units makes it possible to increase the rate of solvent evaporation when evaporating the solvent from the cast film during film production by solution casting without significantly reducing the heat resistance of the graft copolymer. The above-mentioned monomer units are also referred to as "drying-promoting comonomer units" below.

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

[0032] Examples of methacrylic acid esters in which the ester moiety is a primary or secondary hydrocarbon group or 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, and benzyl methacrylate. 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 number of carbon atoms in the saturated hydrocarbon group is preferably 8 to 14, and more preferably 9 to 12. The fused ring structure is not particularly limited, but it is preferably a structure in which two five-membered rings are fused by three consecutive carbon atoms.

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

[0035] Examples of the styrene monomers mentioned above include styrene, α-methylstyrene, monochlorostyrene, and dichlorostyrene. Of these, styrene is preferred.

[0036] In addition to increasing the rate of solvent evaporation from the cast film in the solution casting method, it is preferable that the drying-promoting comonomer unit contains at least one of the following: 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.

[0037] In this case, as the drying-promoting comonomer unit, only at least one of the following may be used: an N-substituted maleimide monomer unit and a methacrylic acid ester unit, which is a saturated hydrocarbon group having 7 to 16 carbon atoms with a condensed ring structure at the ester moiety. Alternatively, at least one of the following may be used in combination with other drying-promoting comonomer units: an N-substituted maleimide monomer unit and a methacrylic acid ester unit, which is a saturated hydrocarbon group having 7 to 16 carbon atoms with a condensed ring structure at the ester moiety. This combination makes it 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] Other drying-promoting comonomer units, besides 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 condensed 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 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 linkage, and styrene monomer units.

[0039] Of the monomer components constituting the non-crosslinked methacrylic polymer component (b), the proportion of the drying-promoting comonomer units 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-promoting comonomer units are included, the proportion of drying-promoting comonomer units refers to the proportion of the total amount of all included drying-promoting comonomer units to the total number of monomer units. By using such weight proportions, the graft copolymer can have excellent heat resistance while accelerating the evaporation rate of the solvent in the solution casting method. The weight proportions of each of these units can be determined by proton nuclear magnetic resonance spectroscopy.

[0040] The non-crosslinked methacrylate polymer component (b) may be a copolymer that does not contain other comonomer units that do not correspond to drying-promoting comonomer units, or it may be a copolymer that contains other comonomer units that do not correspond to drying-promoting 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, N-methylolmethacrylamide; methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, benzyl acrylate, octyl acrylate, glycidyl acrylate, and Examples include acrylic acid esters such as epoxycyclohexylmethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, acrylamide, and N-methylolacrylamide; carboxylic acids and their salts such as methacrylic acid and acrylic acid; vinyl cyanides such as acrylonitonyl 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 crosslinked (meth)acrylic polymer particles (a) to the total of crosslinked (meth)acrylic polymer particles (a) and non-crosslinked methacrylic polymer components (b) is 1% by weight or more and less than 50% by weight, and the proportion of non-crosslinked methacrylic polymer components (b) is 99% by weight or less and more than 50% by weight. By containing a high proportion of non-crosslinked methacrylic polymer components (b) in this embodiment, the crosslinked (meth)acrylic polymer particles (a) are less likely to aggregate, enabling the formation of a high-strength and low-haze film, and furthermore, the storage stability of the graft copolymer or its dope can be improved. The proportion of 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 crosslinked (meth)acrylic polymer particles (a) in the total of crosslinked (meth)acrylic polymer particles (a) and non-crosslinked methacrylic polymer components (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 modulus of elasticity, the upper limit of the above 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 balancing moisture permeability, modulus of elasticity 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 manufacturing graft copolymers) 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, monomer components constituting the non-crosslinked methacrylic polymer component (b) are added to the polymerization system and emulsion polymerization is continued to form the non-crosslinked methacrylic polymer component (b). This makes it possible to produce 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 obtain a structure 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, but examples include anionic surfactants such as sodium alkylsulfonate, sodium alkylbenzenesulfonate, sodium dioctylsulfosuccinate (sodium di(2-ethylhexyl)sulfosuccinate), sodium lauryl sulfate, sodium fatty acid, and sodium polyoxyethylene lauryl ether 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 the film formed from the graft copolymer, polymerization is preferably carried out using phosphate ester salts (alkali metal or alkaline earth metal) such as sodium dioctylsulfosuccinate (sodium di(2-ethylhexyl)sulfosuccinate) and sodium polyoxyethylene lauryl ether phosphate, and is particularly preferable to polymerize using phosphate ester salts (alkali metal or alkaline earth metal) such as sodium polyoxyethylene lauryl ether phosphate.

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

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

[0047] In the step of forming the non-crosslinked methacrylate 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 is not particularly limited, but examples 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; and tertiary alkyl mercaptan chain transfer agents such as t-dodecyl mercaptan and t-tetradecyl mercaptan. Examples include thioglycolic acid esters such as ethylhexyl thioglycolate, ethylene glycol dithioglycolate, trimethylolpropane tris(thioglycolate), and pentaerythritol tetrakis(thioglycolate); thiophenol, tetraethyl thiuram disulfide, pentanephenylethane, acrolein, methacrolein, allyl alcohol, carbon tetrachloride, ethylene bromide, styrene oligomers such as α-methylstyrene dimer, and terpinolenes. These may be used individually or in combination of two or more.

[0048] Solid or powdered graft copolymers can be obtained by subjecting the latex of the graft copolymer obtained by the emulsion polymerization to heat drying or spray drying, or by subjecting it to known methods such as adding a water-soluble electrolyte such as a salt or acid to coagulate it, then performing heat treatment and separating the resin component from the aqueous phase and drying it. Among these, the method of coagulation using a salt is preferred. The salt is not particularly limited, but divalent salts are preferred, and specifically, calcium salts such as calcium chloride and calcium acetate, and magnesium salts such as magnesium chloride and magnesium sulfate are examples. 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 process, it is preferable to filter the latex using a filter, mesh, or the like to remove fine polymerization scale. This reduces fish eyes and foreign matter caused by fine polymerization scale, and also reduces coarse particles in the dope.

[0050] (Resin composition) The graft copolymer according to this embodiment can constitute a resin composition for film production by solution casting. The resin composition may contain only the graft copolymer according to this embodiment as a resin component, or it may contain other resins in addition to the graft copolymer according to this embodiment. Such resins are not particularly limited and include, for example, methacrylic resins, styrene resins such as acrylonitrile styrene resin and styrene maleic anhydride resin, polycarbonate resins, polyvinyl acetal resins, cellulose acylate resins, fluorine resins such as polyvinylidene fluoride and polyalkyl (meth)acrylate resins, silicone resins, polyolefin resins, polyethylene terephthalate resins, and polybutylene terephthalate resins. The content of the other resins is not particularly limited, but for example, it may be about 0 to 50 parts by weight per 100 parts by weight of the graft copolymer according to this embodiment. Furthermore, it 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] Furthermore, the resin composition for film manufacturing may further contain known additives such as light stabilizers, ultraviolet absorbers, heat stabilizers, matting agents, light diffusing agents, colorants, dyes, pigments, antistatic agents, heat reflectors, lubricants, plasticizers, ultraviolet absorbers, stabilizers, and fillers. It may also further contain conventionally known core-shell type graft copolymers.

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

[0053] The solvent is a solvent capable of dissolving or dispersing the resin composition for film production, and is not particularly limited, but preferably includes a solvent (c-1) in which the hydrogen bonding term δH in the Hansen solubility parameter is 1 or more and 12 or less. By constructing the dope using such a solvent, good solubility or dispersibility of the graft copolymer in the solvent according to this embodiment can be achieved. A solvent showing a hydrogen bonding term δH of 3 or more and 10 or less is preferred, and a solvent showing δH of 5 or more and 8 or less is more preferred.

[0054] Conventionally, solubility parameters (SP values) have been known as indicators of the solubility of substances. The Hansen solubility parameter has been proposed in which the cohesive energy term of the SP value is divided according to the type of interaction energy acting between molecules (London dispersion force, dipole force, hydrogen bonding force), and expressed as the London dispersion force term, dipole force term, and hydrogen bonding force term, respectively. The hydrogen bonding term δH of this Hansen solubility parameter is used as an indicator of the solubility when graft copolymers dissolve in solvents. For details of the hydrogen bonding term δH, see, for example, Hideki Yamamoto, "Special Feature: Polymer Compatibilization Design 1. Solubility Evaluation Using Hansen Solubility Parameters (HSP Values)," Adhesion Technology, Vol. 34 No. 3 (2014), Issue 116, pp. 1-8.

[0055] Examples of solvents (c-1) having a hydrogen bonding term 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 esters (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), toluene (2.0), and the like. The numbers in parentheses indicate the hydrogen bond term δH. These solvents may be used individually or in mixtures of two or more.

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

[0057] The solvent contained in the dope may consist only of a solvent (c-1) having a hydrogen bonding term δH of 1 or more and 12 or less. However, considering improvements in film formation during solution casting, film release properties, and handling properties, it is preferable to include a solvent (c-1) having a hydrogen bonding term δH of 1 or more and 12 or less, and a solvent (c-2) having a δH of 14 or more and 24 or less.

[0058] Examples of solvents (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), and ethylene glycol monoethyl ether (14.3). These solvents may be used individually or in mixtures of two or more.

[0059] When used in combination with solvent (c-2) having a δH of 14 or more and 24 or less, the content of solvent (c-1) having a hydrogen bonding term δH of 1 or more and 12 or less is preferably 55% by weight or more and 95% by weight or less, more preferably 60% by weight or more and 90% by weight or less, even more preferably 65% ​​by weight or more and 85% by weight or less, and even more preferably 70% by weight or more and 85% by weight or less, relative to the total amount of solvent contained in the dope.

[0060] The proportion of the graft copolymer in the dope is not particularly limited and can be appropriately determined considering the solubility or dispersibility of the graft copolymer in the solvent used and the conditions for implementing the solution casting method, but it 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 manufacture a resin film by solution casting. Specifically, the resin film can be manufactured by casting the dope onto a support surface and then evaporating the solvent.

[0062] Embodiments of the solution casting method described above are described below, but are not limited thereto. First, pellets containing the graft copolymer according to this embodiment, and optionally other components, are prepared. These pellets are then 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 mixed with a solvent simultaneously or sequentially to prepare a dope in which each component is dissolved or dispersed in the solvent. The dissolution or dispersion step can be carried out by appropriately adjusting the temperature and pressure. After the above dissolution or dispersion step, the obtained dope can be filtered or degassed.

[0063] Next, the dope is supplied to a pressurized die by a liquid transfer pump, and the dope is cast from the slits of the pressurized 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 doped film.

[0064] The formed doped film is heated on the support to evaporate the solvent and form a film. The conditions for evaporating the solvent can be appropriately determined according to the boiling point of the solvent used.

[0065] The film obtained in this way is peeled off the support surface. The obtained film may then be subjected to drying, heating, stretching, or other processes as appropriate.

[0066] (Resin film) The resin film according to this embodiment is composed of the resin composition for film manufacturing and can be formed by the solution casting method of the dope 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 requiring light transmittance, decorative applications, interior applications, and vacuum forming applications.

[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, even more preferably 115°C or higher, even more preferably 120°C or higher, particularly preferably 124°C or higher, and most preferably 125°C or higher.

[0069] In this embodiment, the resin film 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 film thickness of 50 μm. Furthermore, the internal haze of the resin film preferably has a haze of 0.5% or less, more preferably 0.4% or less, even more preferably 0.3% or less, and particularly preferably 0.2% or less when measured at a film thickness of 50 μm. If the haze and internal haze are within the above ranges, the resin film can be suitably used for optical components requiring light transmittance, decorative applications, interior applications, and vacuum forming applications. Note that the haze consists of haze inside the film and haze on the film surface (outside), 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 is small not only in the in-plane direction (length direction and width direction) of the film, but also in the thickness direction. That is, it is preferable that both the absolute values ​​of the in-plane phase difference and the thickness direction phase difference are small. More specifically, the absolute value of the in-plane phase difference 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. Also, the absolute value of the thickness direction phase difference 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. A resin film with such small phase difference can be suitably used as a polarizer protective film for a polarizer plate of a liquid crystal display device.

[0071] Phase difference is an index value calculated based on birefringence, and the in-plane phase difference (Re) and the thickness-direction phase difference (Rth) can be calculated using the following formulas, respectively. In an ideal film that is perfectly optically isotropic in three dimensions, both the in-plane phase difference Re and the thickness-direction phase difference Rth are 0.

[0072] Re=(nx-ny)×d Rth = ((nx + ny) / 2 - nz) × d In each formula, nx, ny, and nz represent the refractive indices in the respective axial directions, with the stretching direction (orientation direction of polymer chains) being the X-axis, the direction perpendicular to the X-axis being the Y-axis, and the film thickness direction being the Z-axis, respectively. d represents the film thickness, and nx-ny represents the orientational birefringence. Note that the MD direction of the film is considered the X-axis, but in the case of a stretched film, the stretching direction is considered the X-axis.

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

[0074] When stretching the resin film according to this embodiment, a stretched film (uniaxially oriented film or biaxially oriented film) can be produced by first manufacturing an unstretched film and then performing uniaxial or biaxial stretching, or by appropriately adding stretching operations during film molding as the film formation and solvent degassing processes progress. Furthermore, stretching during film molding and stretching after film molding may be appropriately combined.

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

[0076] (Application) The resin film according to this embodiment can have its surface gloss reduced by known methods as needed. Such methods include, for example, adding inorganic fillers or crosslinkable polymer particles. Furthermore, by embossing the resulting film, it is possible to form surface irregularities such as prism shapes, patterns, designs, or knurling, or to reduce the surface gloss of the film.

[0077] The resin film according to this embodiment can be used by laminating another film with it using a dry lamination method and / or a thermal lamination method with an adhesive, or by forming a functional layer such as a hard coat layer, anti-reflective layer, anti-fouling layer, anti-static layer, printed decorative layer, metallic gloss layer, surface texture layer, or matte layer on the surface or back of the film, as needed.

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

[0079] The resin film according to this embodiment can be used by laminating it onto a substrate such as metal or plastic. Methods for laminating the resin film include lamination molding, wet lamination (where an adhesive is applied to a metal plate such as a steel plate, and then the film is placed on the metal plate and dried to bond it), dry lamination, extrusion lamination, and hot melt lamination.

[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 the film is pre-molded and then 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 substitute for paint in automotive interior materials and automotive exterior materials, as well as in civil engineering and construction materials such as window frames, bathroom fixtures, wallpaper, flooring, lighting and dimming components, soundproof walls, and road signs, as well as in daily necessities, housings for furniture and electronic equipment, housings for office automation equipment such as facsimile machines, laptops, and copiers, front panels for liquid crystal screens of terminals such as mobile phones, smartphones, and tablets, as well as optical components such as lighting lenses, automotive headlights, optical lenses, optical fibers, optical discs, and liquid crystal light guide plates, optical elements, components for electrical 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 this embodiment is suitable for optical films due to its excellent heat resistance and optical properties, and can be used in various optical components. For example, it can be applied to known optical applications such as the front panel of liquid crystal screens in terminals such as mobile phones, smartphones, and tablets, illumination lenses, automobile headlights, optical lenses, optical fibers, optical discs, liquid crystal light guide plates, diffusers, back sheets, reflective sheets, polarizing films, transparent resin sheets, phase difference films, light diffusion films, prism sheets, surface protection films, optical isotropic films, polarizer protection films, and transparent conductive films, as well as around liquid crystal display devices, around organic EL devices, and in the field of optical communication. [Examples]

[0083] The present invention will be described in 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" respectively, unless otherwise specified.

[0084] (Example 1) <Production of graft copolymer (A1)> The following substances were charged into an 8L polymerization apparatus equipped with a stirrer. Deionized water 133 parts Sodium hydroxide 0.004 parts 0.2 parts of sodium di(2-ethylhexyl) sulfosuccinate After thoroughly purging the polymer chamber with nitrogen gas, the internal temperature was set to 80°C. 0.03 parts of sodium persulfate and 0.001 parts of sodium pyrosulfite were added in a 0.5% aqueous solution. Then, 40 parts of monomer (a) for crosslinked (meth)acrylic polymer particles, as described in Table 1, were continuously added at a rate of 0.523 parts / min. Polymerization was continued for another 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. Subsequently, 60 parts of monomer (b) for the non-crosslinked methacrylic polymer component, as listed in Table 1, were continuously added at a rate of 1.353 parts / minute. Simultaneously with the start of monomer (b) addition, 0.4 parts of di(2-ethylhexyl) sodium sulfosuccinate in a 5% aqueous solution were continuously added over the same time as monomer (b). After the addition was completed, polymerization was continued for 60 minutes to obtain 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 2-8 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] [Table 1]

[0087] (polymerization 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 taken from the polymerization system and accurately weighed. It was dried in a hot air dryer at 120°C for 1 hour, and the weight after drying was accurately 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, the polymerization conversion rate was calculated using this solid content ratio with the following formula. In this formula, the polyfunctional monomer and chain transfer agent were treated as input monomers. Polymerization conversion rate (%) = {(Total weight of raw materials × Solid content ratio - Total weight of raw materials other than water and monomers) / Weight of monomers} × 100

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

[0089] (Average particle size of cross-linked (meth)acrylic polymer particles (a) and graft copolymers (A1) to (A9)) The average particle diameter is the volume-average particle diameter measured in the latex state obtained at the completion of polymerization of the cross-linked (meth)acrylic polymer particles (a) and graft copolymers (A1) to (A9). A Microtrac UPA150 from Nikkiso Co., Ltd. was used as the measuring device, and the measured volume-average particle diameter is listed as the average particle diameter in Table 2. The measurements were performed at room temperature, and the refractive index of the measured particles was the weight-average value of the refractive index of the homopolymer composed of the monomers used in 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, 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 (containing 0.3 parts of lauroyl peroxide), 9 parts of BMA, and 0.018 parts of 2-ethylhexyl thioglycolate (2-EHTG), a chain transfer agent, was added to the reactor. Polymerization was started by raising the temperature to 60°C while purging the reactor with nitrogen. 50 minutes after reaching 60°C, 0.15 parts of ADEKA Pluronic F-68 (a nonionic water-soluble polymer, manufactured by ADEKA Corporation, a polyoxyethylene-polyoxypropylene block copolymer) was added as a suspension stabilizer. The reaction was then continued at 60°C for a further 200 minutes, after which the temperature was raised 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 that of the resin, and then dried to obtain a bead-shaped suspension polymer (A10) (weight-average molecular weight 970,000).

[0091] (Weight-average molecular weight of suspended polymers) The weight-average molecular weight of the suspension polymer was calculated in the same manner as the weight-average molecular weight of the non-crosslinked methacrylic polymer component (b) described above, 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 8L polymerization apparatus equipped with a stirrer. Deionized water 175 parts Sodium polyoxyethylene lauryl ether phosphate 0.002 parts Sodium carbonate 0.04725 parts After thoroughly purging the polymer chamber with nitrogen gas, the internal temperature was set to 80°C, and 0.03 parts of potassium persulfate were added in a 2% aqueous solution. Then, mixture (I) (25.2 parts MMA, 1.6 parts BA, 0.2 parts St, 0.135 parts ALMA, 0.3 parts n-OM, 0.1 part sodium polyoxyethylene lauryl ether phosphate) was continuously added over 81 minutes. Polymerization was continued for another 60 minutes to obtain polymer (I). The polymerization conversion rate was 99.5%. Subsequently, 0.08 parts of potassium persulfate were added in a 2% aqueous solution, and then mixture (II) (41 parts BA, 9 parts St, 0.75 parts ALMA, 0.2 parts sodium polyoxyethylene lauryl ether phosphate) was continuously added over 150 minutes. After the addition was complete, 0.015 parts of pure potassium persulfate were added in a 2% aqueous solution, and polymerization was continued for 120 minutes to obtain polymer (II). The polymerization conversion rate was 99.7%, and the average particle size was 220 nm. Subsequently, 0.023 parts of potassium persulfate were added in a 2% aqueous solution, followed by the continuous addition of mixture (III) (18.4 parts MMA, 4.6 parts BA) over 70 minutes, and polymerization was continued for 60 minutes to obtain core-shell type 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 type graft copolymer (A11). (A11) is a representative example of a conventional core-shell type graft copolymer.

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

[0094] (Weight-average molecular weight of the outermost layer of the graft copolymer (A11)) The weight-average molecular weight of the outermost layer of the graft copolymer (A11) was calculated in the same manner as the weight-average molecular weight of the non-crosslinked methacrylic polymer component (b) described above, except that graft copolymer (A11) was used.

[0095] (Preparation of resin dope) Resin dopes with a solid content of 10% were prepared by adding 4.5 g of the 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 with a solid content of 10% containing suspension polymer (A10) and graft copolymer (A11) 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 homogeneous. The resulting dispersion was then dispersed in an ultrasonic bath (Bransonnick 1510J, Yamato Scientific Co., Ltd.) for a further 15 minutes. Finally, 3.82 g of suspension polymer (A10) beads were gradually added to the dispersion and stirred until completely dissolved.

[0097] (Cast film production) The aforementioned resin dope was cast onto a PET film (Cosmoshine A4100, manufactured by Toyobo) and applied to form a uniform film using an applicator. The clearance was adjusted so that the thickness after drying was approximately 70 μm. After drying the coating film in a 40°C dry atmosphere for 1 hour, it was peeled off the PET film. The obtained film was fixed to a stainless steel frame and dried in a 140°C dry atmosphere for 90 minutes to remove any remaining solvent, thereby obtaining a cast film.

[0098] (Preparation of uniaxially oriented film) A 16cm square test piece was cut from an unstretched cast film and subjected to uniaxial stretching at a fixed width 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 oriented film was measured using an MIT-DA type MIT testing machine manufactured by Toyo Seiki Co., Ltd. Test specimens were cut to a width of 1.5 cm, and tested under conditions of a bending radius of 0.4 mm and a bending angle of 135°, with a load of 200 g applied, in a direction perpendicular to the stretching direction. Each test was performed three times, and the average values ​​are shown in Table 2.

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

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

[0103] (Hayes) 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. Meanwhile, the internal haze was defined as the value obtained by sandwiching both sides of the unstretched film with glycerin, followed by glass, in the same manner. The results obtained are shown in Table 2, converted to the equivalent of a 50 μm film thickness.

[0104] (In-plane phase difference and thickness-direction phase difference of uniaxially oriented film) A test specimen was cut from the center of the stretched film. The in-plane phase difference of this specimen was measured using an automatic birefringent (KOBRA-WR, manufactured by Oji Instruments Co., Ltd.) at a wavelength of 590 nm and an incident angle of 0°. Measurements were also taken at an incident angle of 40°, and the phase difference in the thickness direction was calculated. Measurements were performed three times for each measurement point, moving the specimen, and the average value was converted to the equivalent of a 50 μm film thickness 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 Fox's formula, with values ​​listed in the Polymer Handbook [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 graft copolymer powder or suspension polymer beads, which were the samples, were placed under a nitrogen stream and heated to 190°C at a heating rate of 10°C / min. After being held at 190°C for 3 minutes, they were rapidly cooled to 40°C and then heated again to 190°C at a heating rate of 10°C / min. For the glass transition observed during the second heating cycle, the average of the extrapolation glass transition start temperature and the extrapolation glass transition end temperature was calculated, and this value was defined 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 the glass transition temperature of the non-crosslinked methacrylic polymer component (b) or suspension polymer beads described above, except that the sample used was a cast film dried at 140°C and then further dried at 175°C for 1 hour. 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 the change in particle size distribution over time using a laser diffraction particle size analyzer (Malvern 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 solid content of 10%, which served as the measurement sample, was prepared from the powder and the mixed solvent immediately before measurement. The resin dope was added dropwise while circulating the dispersion medium in the apparatus, and the measurement was performed so that the laser scattering intensity was 0.5 to 2.0%. The graft copolymer powder was stored at 50°C and 95% RH, and the above measurements were performed on the powder at 0, 3, and 14 days after the start of storage. The volume % occupied by particles of 1 μm or larger relative to the total particle size is shown in Table 2.

[0109] (Storage stability of resin-doped graft copolymers) The storage stability of resin dopes containing graft copolymers was evaluated in the same manner as the storage stability of the graft copolymer powder described above. For the preparation of the resin dopes, 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. Resin dopes prepared with a solid content concentration of 10% were stored at room temperature, and measurements were taken for each resin dope at 0, 3, and 14 days after the start of storage, using a mixed solvent of the same composition as the resin dope as the dispersion medium. The volume percentage of particles larger than 1 μm relative to the total particle size is shown in Table 2.

[0110] [Table 2]

[0111] The following can be seen from Table 2. In Examples 1 to 8, resin films with high bending resistance, trimming resistance, and heat resistance, as well as low haze, were successfully molded from the graft copolymer alone. Furthermore, 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, which used a graft copolymer with a low weight-average molecular weight of less than 250,000 for the non-crosslinked methacrylic polymer component, the glass transition temperature of the produced resin film was low, resulting in poor heat resistance. In Comparative Example 2, where a resin film was prepared by blending a core-shell type graft copolymer with a methacrylic resin as in the conventional method, the resin film exhibited significant haze, and both the core-shell type graft copolymer powder and the core-shell type graft copolymer-containing dope showed an increase in coarse particle content over time, resulting in poor storage stability. The resin film of Comparative Example 3, made solely from a general methacrylic resin, had insufficient bending resistance and trimming resistance. Furthermore, as shown in Comparative Example 4, it was not possible to produce a resin film solely from the conventional core-shell type graft copolymer.

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

[0114] (modulus of elasticity) The resin films used for measurement were prepared using the following procedure. First, 2 g of each graft copolymer was added to 18 g of a mixed solvent consisting of 92% methylene chloride and 8% ethanol and dissolved to prepare a dope with a solid content of 10%. This dope was coated onto a PET film (product name: Cosmoshine A4100, manufactured by Toyobo Co., Ltd.) to a wet film thickness of 0.6 mm, and immediately covered with a tray. After drying at room temperature for 30 minutes, it was dried in a hot air dryer at 40°C for 60 minutes to produce a partially dried film. After peeling this partially dried film from the PET film, it was fixed to a metal frame and dried in a hot air dryer at 140°C for 1 hour to produce a film with a thickness of 40 μm. The obtained film was cut into strips 10 mm wide and 130 mm long, and a tensile test was performed under the conditions of a chuck distance of 100 mm and a tensile speed of 13 mm / min. The modulus of elasticity was calculated in the range of 3 to 12 mm. The calculation results were obtained as the average value for n=7.

[0115] (moisture permeability) The resin films used for measurement were prepared using the following procedure. First, 2 g of each graft copolymer was added to 18 g of a mixed solvent consisting of 82% methylene chloride and 18% methanol and dissolved to prepare a dope with a solid content of 10%. This dope was coated onto a PET film (product name: Cosmoshine A4100, manufactured by Toyobo Co., Ltd.) to a wet film thickness of 0.5 mm and quickly dried in a hot air dryer at 40°C for 10 minutes to produce a semi-dried film. After peeling this semi-dried film from the PET film, it was fixed to a metal frame of a suitable size and further dried in a hot air dryer at 140°C for 1 hour to produce a film with a thickness of 50 μm. Water vapor permeability was measured using the cup method in accordance with JIS Z 0208-1976. A circular film with a thickness of 50 μm was used, and the measurement area was 28.3 cm². 2 Samples prepared using a measuring cup (manufactured by Tester Industries Co., Ltd.) and 8g of calcium chloride (Wako) for moisture measurement were placed in a constant temperature and humidity chamber (model: LH33-13P, manufactured by Nagano Science Co., Ltd.) and measured at 40°C and 90%RH.

[0116] [Table 3]

[0117] Table 3 shows the following: In Examples 4, 6-8, resin films with good moisture permeability and elastic modulus, in addition to the aforementioned bending resistance and trimming resistance, were formed 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, It contains a non-crosslinked methacrylic polymer component (b) having a weight-average molecular weight of 300,000 or more and a glass transition temperature of 118°C or higher. At least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a), The proportion of crosslinked (meth)acrylic polymer particles (a) to the total of crosslinked (meth)acrylic polymer particles (a) and non-crosslinked methacrylic polymer components (b) is 1% by weight or more and less than 50% by weight. The non-crosslinked methacrylic polymer component (b) is a graft copolymer containing 70% to 99% by weight of methyl methacrylate units, and further comprising at least one of N-substituted maleimide monomer units and methacrylic ester units in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a condensed ring structure.

2. The graft copolymer according to claim 1, wherein the weight-average molecular weight of the non-crosslinked methacrylic polymer component (b) is 350,000 or more.

3. The graft copolymer according to claim 1 or 2, wherein the non-crosslinked methacrylic polymer component (b) has a glass transition temperature of 120°C or higher.

4. The graft copolymer according to any one of claims 1 to 3, wherein the crosslinked (meth)acrylic polymer particles (a) contain 90% to 100% by weight of alkyl acrylate esters having 1 to 8 carbon atoms in the alkyl group, among the monomer components excluding the polyfunctional monomer.

5. The graft copolymer according to any one of claims 1 to 4, wherein the crosslinked (meth)acrylic polymer particles (a) are formed from 100 parts by weight of monomer components excluding polyfunctional monomers and 0.1 to 2.0 parts by weight of polyfunctional monomers.

6. A resin composition for film production by solution casting, comprising a graft copolymer according to any one of claims 1 to 5.

7. A dope comprising the resin composition for film manufacturing according to claim 6, and a solvent.

8. A method for producing a resin film, comprising the step of casting the dope described in claim 7 onto a support surface, and then evaporating the solvent.

9. A resin film formed by solution casting from the resin composition for film manufacturing described in claim 6.

10. The resin film according to claim 9, wherein the resin film has a thickness of 1 to 500 μm.

11. The resin film according to claim 9 or 10, wherein the resin film is a laminated protective film for the surface of another substrate.

12. The resin film is an optical film, as described in any one of claims 9 to 11.

13. The resin film according to claim 12, wherein the optical film is a polarizer protective film.

14. A polarizing plate comprising a polarizer and a resin film according to claim 13, laminated together.

15. A display device comprising a polarizing plate as described in claim 14.

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