Graft copolymers and resin films

Abstract

A graft copolymer according to the present invention contains: crosslinked (meth)acrylic polymer particles (a) that include (meth)acrylic monomer units and styrene monomer units, and 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 includes methacrylic monomer units and styrene monomer units, and 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 of their 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 materials for automobiles, exterior materials for electrical appliances such as mobile phones and smartphones, and interior and exterior materials for civil engineering and architecture such as floors, windows, interior and exterior walls, lighting parts, and road signs. In recent years, methacrylic resins are also 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 is 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).

[0005] By the way, as one of the optical films used in liquid crystal displays, a retardation film for imparting optical anisotropy and compensating for viewing angle dependence is known.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] While the strength of methacrylic resins can be improved by incorporating conventional core-shell graft copolymers, these copolymers tend to aggregate due to the rubber components they contain, resulting in poor storage stability. Furthermore, when manufacturing resin films by solution casting, after preparing a dope by dissolving conventional core-shell graft copolymers together with methacrylic resin in a solvent, the dope tends to become cloudy, especially over time, and the resin film produced from this dope suffers from reduced haze. In addition, it was difficult to design resin films formed by compounding methacrylic resins with core-shell type graft copolymers that achieved both high strength and low haze while also increasing the phase difference.

[0008] In view of the above situation, the present invention aims to provide a graft copolymer that has excellent heat resistance, high strength, low haze, and can form a film with a large phase difference, and has good storage stability, as well as a resin film formed from the graft copolymer. [Means for solving the problem]

[0009] 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.

[0010] 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 containing (meth)acrylic monomer units and styrene monomer units, and a non-crosslinked methacrylic polymer component (b) having a weight-average molecular weight of 250,000 or more, and containing methacrylic monomer units and styrene monomer units, 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 methacrylic polymer component (b) contains 50% to 90% by weight of methyl methacrylate units and 10% to 50% by weight of styrene monomer 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 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 having a condensed ring structure, and methacrylic ester units in which the ester moiety is a linear or branched group containing an ether linkage. 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 110°C or higher. Preferably, the crosslinked (meth)acrylic polymer particles (a) contain 60% to 95% by weight of alkyl acrylate units having 1 to 8 carbon atoms in the alkyl group, and 5% to 40% by weight of styrene monomer units, 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 a graft copolymer; a dope comprising the film production resin composition 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 film production resin composition by solution casting. Preferably, the resin film has a thickness of 1 to 500 μm. Preferably, the resin film is a phase difference film. Furthermore, the present invention relates to a polarizing plate formed by laminating a polarizer and the resin film; and a display device including the polarizing plate. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a graft copolymer that has excellent heat resistance, high strength, low haze, and can form a film with a large phase difference, and has good storage stability, as well as 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]

[0012] 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.

[0013] 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).

[0014] 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.

[0015] (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.

[0016] 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 such small crosslinked (meth)acrylic polymer particles, low haze can be achieved when the graft copolymer according to this embodiment is formed into a film, for example. Furthermore, by making the crosslinked (meth)acrylic polymer particles small, it becomes unnecessary to strictly match the refractive index 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 that lowers the glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) without prioritizing refractive index, thereby achieving high strength when the graft copolymer is formed into a film, for example.

[0017] 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 40 nm or more, even more preferably 45 nm, and particularly preferably 50 nm or more. The average particle diameter is the volume average particle diameter and can be measured as described in the Examples section. Furthermore, the average particle diameter can be controlled by adjusting the conditions during particle production (specifically, the type and amount of emulsifier, stirring conditions during emulsion polymerization, etc.).

[0018] The crosslinked (meth)acrylic polymer particles (a) have a glass transition temperature of -10°C or lower. By using crosslinked (meth)acrylic polymer particles with such a low glass transition temperature, high strength can be achieved when, for example, the graft copolymer is formed into 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).

[0019] The glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) is preferably -20°C or lower, more preferably -25°C or lower. The lower limit of the glass transition temperature is not particularly limited, but for example, -130°C or higher is preferable, -110°C or higher is more preferable, -100°C or higher is further preferable, -80°C or higher is even more preferable, and -70°C or higher is particularly preferable. 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).

[0020] 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 styrenic monomer, and a polyfunctional monomer. By including a styrenic monomer in the crosslinked (meth)acrylic polymer particles (a), the phase difference can be increased when, for example, the graft copolymer is formed into a film. The monomer component excluding the polyfunctional monomer includes an acrylic monomer and / or a methacrylic monomer and a styrenic monomer, but preferably contains at least an acrylic monomer and a styrenic monomer.

[0021] The acrylic monomer contained in the crosslinked (meth)acrylic polymer particles (a) is preferably an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. Specifically, examples include ethyl acrylate, n-butyl acrylate, n-octyl acrylate, and 2-ethylhexyl acrylate. Only one of the alkyl acrylates may be used, or two or more may be used in combination. Among these, n-butyl acrylate is preferred.

[0022] 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.

[0023] Examples of styrene monomers contained in the crosslinked (meth)acrylic polymer particles (a) include styrene, α-methylstyrene, monochlorostyrene, and dichlorostyrene.

[0024] In the crosslinked (meth)acrylic polymer particles (a), monomers other than the alkyl acrylates, alkyl methacrylates, and styrene monomers mentioned above may be used. Examples of such monomers include acrylic esters other than the alkyl acrylates, methacrylic esters other than the alkyl methacrylates, 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 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.

[0025] From the viewpoint of strength and heat resistance, the monomer components constituting the crosslinked (meth)acrylic polymer particles (a) preferably contain 50% to 99% by weight of acrylic acid esters (particularly alkyl acrylates with 1 to 8 carbon atoms in the alkyl group), more preferably 55% to 97% by weight, even more preferably 60% to 95% by weight, and particularly preferably 65% ​​to 92% by weight, among the monomer components excluding polyfunctional monomers.

[0026] From the viewpoint of adjusting the refractive index between the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) to ensure transparency, and from the viewpoint of generating a phase difference, the monomer components constituting the crosslinked (meth)acrylic polymer particles (a) preferably contain 1% to 50% by weight of styrene monomers, more preferably 3% to 45% by weight, even more preferably 5% to 40% by weight, and particularly preferably 8% to 35% by weight, among the monomer components excluding polyfunctional monomers.

[0027] 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 (meth)acrylic monomers and styrene monomers. 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.

[0028] 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.

[0029] (Non-crosslinked methacrylic polymer component (b)) The non-crosslinked methacrylic polymer component (b) is a polymer composed of at least a methacrylic monomer and a styrene monomer, and does not have a crosslinked structure (i.e., obtained by polymerization without the use of 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), thereby making 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.

[0030] 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. There is no particular upper limit to the weight-average molecular weight, but for example, 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.

[0031] The non-crosslinked methacrylic polymer component (b) preferably exhibits a glass transition temperature of 105°C or higher, and more preferably 110°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 has a glass transition temperature of 105°C).

[0032] The non-crosslinked methacrylic polymer component (b) is a polymer composed of at least methacrylic monomer units and styrene 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 50% to 90% 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 53 to 85% by weight, even more preferably 55 to 80% by weight, even more preferably 58 to 75% by weight, and particularly preferably 60 to 70% by weight.

[0033] To achieve phase difference, the non-crosslinked methacrylic polymer component (b) contains styrene monomer units. From this viewpoint, it is preferable that the non-crosslinked methacrylic polymer component (b) contains 10% to 50% by weight of styrene monomer units, more preferably 15 to 45% by weight, even more preferably 20 to 40% by weight, and particularly preferably 25 to 35% by weight. Examples of styrene monomers include styrene, α-methylstyrene, monochlorostyrene, and dichlorostyrene, with styrene being preferred.

[0034] The non-crosslinked methacrylic polymer component (b) preferably includes 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 and a condensed ring structure, and methacrylic ester units whose ester moiety is a linear or branched group containing an ether linkage. 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] Examples of methacrylic acid esters in which the ester moiety is a linear or branched group containing an ether linkage include 2-methoxyethyl methacrylate.

[0039] 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.

[0040] 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.

[0041] 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 methacrylic acid ester units in which the ester moiety is a primary or secondary hydrocarbon group or aromatic hydrocarbon group having 2 to 20 carbon atoms, and methacrylic acid ester units in which the ester moiety is a linear or branched group containing an ether linkage.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] (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).

[0047] 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.

[0048] 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.

[0049] 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).

[0050] 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.

[0051] 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.

[0052] 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.

[0053] (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.

[0054] 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.

[0055] (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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] (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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] (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.

[0070] 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.

[0071] 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, and particularly preferably 115°C or higher.

[0072] 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.

[0073] The resin film according to this embodiment preferably has high optical anisotropy. In particular, it is preferable that the optical anisotropy is high not only in the in-plane direction (length direction and width direction) 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 large. More specifically, the absolute value of the in-plane phase difference is preferably 10 nm or more, more preferably 15 nm or more, even more preferably 20 nm or more, and particularly preferably 25 nm or more. Similarly, the absolute value of the thickness direction phase difference is preferably 15 nm or more, more preferably 20 nm or more, even more preferably 25 nm or more, and particularly preferably 30 nm or more. There is no particular upper limit, but for example it can be 150 nm or less. A resin film with such a large phase difference can be suitably used as a phase difference film for a polarizing plate in a liquid crystal display device.

[0074] 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.

[0075] 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.

[0076] (Stretching) The resin film according to this embodiment is highly tough and flexible, 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.

[0077] 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.

[0078] 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.

[0079] (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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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]

[0086] 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.

[0087] (Example 1) <Production of graft copolymer (A1)> The following substances were charged into an 8L polymerization apparatus equipped with a stirrer. Deionized water 142 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 0.0005 parts of sodium formaldehyde sulfoxylate were added in a 0.5% aqueous solution. Then, 10 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, 90 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, 0.7 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). The weight-average molecular weight of the non-crosslinked methacrylic polymer component (b) was 670,000.

[0088] (Examples 2-3 and Comparative Example 1) Graft copolymers (A2) to (A4) 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.

[0089] [Table 1]

[0090] (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

[0091] (Weight-average molecular weight of non-crosslinked methacrylic polymer component (b)) The weight-average molecular weight of the non-crosslinked methacrylic 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: TSK gel 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.

[0092] (Average particle size of cross-linked (meth)acrylic polymer particles (a) and graft copolymers (A1) to (A4)) 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 (A4). 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)].

[0093] (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-like suspension polymer (A5) (weight-average molecular weight 970,000).

[0094] (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.

[0095] (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 (A6). (A6) is a representative example of a conventional core-shell type graft copolymer.

[0096] (Average particle diameter up to the rubber interlayer of graft copolymer (A6)) The average particle size up to the rubber intermediate layer of the graft copolymer (A6) was calculated in the same manner as the average particle size of the graft copolymers (A1) to (A4), except that it was measured in the latex state obtained by polymerization up to the polymerization step (II).

[0097] (Weight-average molecular weight of the outermost layer of the graft copolymer (A6)) The weight-average molecular weight of the outermost layer of the graft copolymer (A6) was calculated in the same manner as the weight-average molecular weight of the non-crosslinked methacrylic polymer component (b), except that graft copolymer (A6) was used.

[0098] (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.

[0099] In Comparative Example 2, a resin dope with a solid content of 10% containing suspension polymer (A5) and graft copolymer (A6) was prepared by adding 0.68 g of graft copolymer (A6) 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 (A5) beads were gradually added to the dispersion and stirred until completely dissolved.

[0100] (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.

[0101] (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.

[0102] (film thickness) The film thickness was measured using a Digimatic Indicator (manufactured by Mitutoyo Corporation).

[0103] (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.

[0104] (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.

[0105] 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.

[0106] (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.

[0107] (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.

[0108] (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)].

[0109] 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.

[0110] 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.

[0111] (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.

[0112] (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.

[0113] [Table 2]

[0114] The following can be seen from Table 2. In Examples 1 to 3, resin films with high bending resistance, trimming resistance, and heat resistance, low haze, and large phase difference were formed from the graft copolymer alone. In addition, the storage stability of the graft copolymer powder and the graft copolymer-containing dope was good.

[0115] On the other hand, in Comparative Example 1, where the weight-average molecular weight of the non-crosslinked methacrylic polymer component was set low at less than 250,000 and a graft copolymer containing crosslinked (meth)acrylic polymer particles and a non-crosslinked methacrylic polymer component without styrene was used, the resulting resin film had a low glass transition temperature and poor heat resistance, as well as a small phase difference. 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 large haze and a small phase difference. Furthermore, 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, prepared solely from a general methacrylic resin, had insufficient bending resistance and trimming resistance, and a small phase difference. Also, as shown in Comparative Example 4, a resin film could not be prepared solely from the conventional core-shell type graft copolymer.

Claims

1. A resin composition for film production by solution casting, comprising a graft copolymer, The graft copolymer has an average particle size of 150 nm or less and a glass transition temperature of -10°C or less, and comprises crosslinked (meth)acrylic polymer particles (a) containing (meth)acrylic monomer units and styrene monomer units, The weight-average molecular weight is 300,000 or more, the glass transition temperature is 110°C or higher, and it contains a non-crosslinked methacrylic polymer component (b) which includes methacrylic monomer units and styrene monomer units. 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. A resin composition for film production by solution casting, wherein the content of resins other than the graft copolymer is 0 to 30 parts by weight per 100 parts by weight of the graft copolymer.

2. The resin composition for film production according to claim 1, wherein 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 6% by weight or more and 30% by weight or less.

3. The non-crosslinked methacrylic polymer component (b) contains 50% to 90% by weight of methyl methacrylate units and 10% to 50% by weight of styrene monomer units, wherein the resin composition for film production according to claim 1 or 2.

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

5. 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, according to claim 3, for the production of a film resin composition.

6. The film manufacturing resin composition according to any one of claims 1 to 5, wherein the crosslinked (meth)acrylic polymer particles (a) contain 60% by weight or more and 95% by weight or less of alkyl acrylate units having 1 to 8 carbon atoms in the alkyl group, and 5% by weight or more and 40% by weight or less of styrene monomer units among the monomer components excluding the polyfunctional monomer.

7. The film manufacturing resin composition according to any one of claims 1 to 6, 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.

8. A dope comprising a resin composition for film manufacturing according to any one of claims 1 to 7, and a solvent.

9. A dope comprising a graft copolymer and a solvent, The graft copolymer has an average particle size of 150 nm or less and a glass transition temperature of -10°C or less, and comprises crosslinked (meth)acrylic polymer particles (a) containing (meth)acrylic monomer units and styrene monomer units, The weight-average molecular weight is 300,000 or more, the glass transition temperature is 110°C or higher, and it contains a non-crosslinked methacrylic polymer component (b) which includes methacrylic monomer units and styrene monomer units. 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 content of resins other than the graft copolymer is 0 to 30 parts by weight per 100 parts by weight of the graft copolymer, in a dope.

10. A method for producing a resin film, comprising the step of casting the dope according to claim 8 or 9 onto a support surface, and then evaporating the solvent.

11. A resin film formed by solution casting from a resin composition for film manufacturing according to any one of claims 1 to 7 or a dope according to claim 9.

12. The resin film according to claim 11, wherein the resin film has a thickness of 1 to 500 μm.

13. The resin film according to claim 11 or 12, wherein the resin film is a phase difference film.

14. A polarizing plate comprising a polarizer and a resin film according to any one of claims 11 to 13.

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

16. A resin composition for manufacturing a film according to any one of claims 1 to 7, wherein the haze value of a resin film with a thickness of 50 μm made from the resin composition is 0.3% or less.

17. The resin composition for film production according to any one of claims 1 to 7, wherein the content of the resin other than the graft copolymer is 0 to 10 parts by weight per 100 parts by weight of the graft copolymer.

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