Resin film manufacturing method

Abstract

To provide a method for producing a resin film having a low haze and suppressed foaming by a solution casting method using a solidified product of a (meth)acrylic polymer synthesized by emulsion polymerization.SOLUTION: There is provided a method for producing a resin film which comprises: a step of obtaining a latex of a (meth)acrylic polymer by emulsion polymerization; a step of coagulating the (meth)acrylic polymer by adding a coagulant to the latex, followed by separating the (meth)acrylic polymer from the water phase; a step of mixing the separated (meth)acrylic polymer with a solvent containing ethanol to form a dope; and a step of casting the dope on a support surface, followed by evaporating the solvent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a resin film by a solution casting method. [Background technology]

[0002] TAC (triacetyl cellulose), which is used in polarizer protective films for LCD displays, has recently become a problem due to the increasing size and high definition of screens. This is due to its high moisture permeability and water absorption, which can cause panels to warp during transportation, resulting in a deterioration in image quality.

[0003] Acrylic resin films have been attracting attention as an alternative to TAC films because they have excellent optical properties, low moisture permeability, and low water absorption.

[0004] Patent Document 1 discloses a technology for suppressing whitening of the resulting film and the generation of bubbles in the film by optimizing conditions such as the amount of residual solvent and temperature during the drying process when forming a film from an acrylic resin using a solution casting method.

[0005] Furthermore, Patent Document 2 discloses that a film having excellent optical properties, dimensional stability, and adhesiveness can be obtained by using an acrylic polymer obtained by suspension polymerization in the presence of a suspension polymerization dispersant having a specific structure in a solution casting method.

[0006] On the other hand, emulsion polymerization is known as one of the polymerization methods for producing a (meth)acrylic polymer, which is the main component of an acrylic resin film. As a method for separating the polymer from the latex obtained by emulsion polymerization, it is conceivable to apply a drying method such as heat drying or spray drying to the latex, but such a drying method requires a large amount of energy. A method that can reduce energy consumption compared to the drying method is known in which a coagulant is added to the latex after emulsion polymerization to coagulate the resin component, and then the resin component is separated from the aqueous phase (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-177089 [Patent Document 2] Special Publication No. 2019-533203 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-124282 Summary of the Invention [Problem to be solved by the invention]

[0008] It has been found that when a resin film is produced by a solution casting method using a coagulated product of a (meth)acrylic polymer separated from the aqueous phase using a coagulant after emulsion polymerization, the haze of the resulting resin film may deteriorate or the film may contain fine bubbles.

[0009] In view of the above-described current situation, the present invention aims to provide a method for producing a resin film having low haze and suppressed foaming by a solution casting method using a coagulated product of a (meth)acrylic polymer synthesized by emulsion polymerization. [Means for solving the problem]

[0010] As a result of extensive research, the present inventors have found that when a resin film is produced by a solution casting method using a coagulated product of a (meth)acrylic polymer synthesized by emulsion polymerization, the use of at least ethanol as a solvent for a dope in the solution casting method results in a resin film with low haze and foaming can be suppressed, and have completed the present invention.

[0011] That is, the present invention provides a process for obtaining a latex of a (meth)acrylic polymer by emulsion polymerization; a step of adding a coagulant to the latex to coagulate the (meth)acrylic polymer, and then separating the (meth)acrylic polymer from the aqueous phase; A step of mixing the separated (meth)acrylic polymer with a solvent containing ethanol to form a dope; and The present invention relates to a method for producing a resin film, which comprises a step of casting the dope onto a support surface and then evaporating the solvent. Preferably, the coagulant is an inorganic salt or an acid. Preferably, the inorganic salt is a calcium salt or a magnesium salt. Preferably, the content of ethanol in the solvent is 1 to 25% by weight. Preferably, the solvent further comprises methylene chloride. Preferably, the (meth)acrylic polymer is a polymer having 30 to 100% by weight of methyl methacrylate units and 0 to 70% by weight of other monomer units copolymerizable therewith as constituent units. Preferably, the other copolymerizable monomer units include (meth)acrylic acid ester units (excluding methyl methacrylate units) having 1 to 20 carbon atoms in the ester moiety, and / or substituted or unsubstituted maleimide units. Preferably, the (meth)acrylic polymer is a graft copolymer containing crosslinked (meth)acrylic polymer particles (a) and a non-crosslinked methacrylic polymer component (b), and the proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is 1% by weight or more and less than 50% by weight. Preferably, the non-crosslinked methacrylic polymer component (b) contains 70% by weight or more and 99% by weight or less of methyl methacrylate units. Preferably, the non-crosslinked methacrylic polymer component (b) contains at least one of a substituted or unsubstituted maleimide 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. The present invention also relates to a dope containing a coagulated product of a (meth)acrylic polymer synthesized by emulsion polymerization and a solvent containing ethanol. The present invention also relates to a method for producing a resin film, which comprises a step of casting the dope on a surface of a support and then evaporating the solvent. [Effects of the Invention]

[0012] According to the present invention, a method for producing a resin film having low haze and suppressed foaming by a solution casting method using a coagulated product of a (meth)acrylic polymer synthesized by emulsion polymerization can be provided. The resin film obtained by the present invention has reduced fine bubbles contained therein, and can be a film with excellent appearance and high transparency. Such a resin film has few optical defects and high light extraction efficiency, and therefore can be suitably used as an optical film for liquid crystal display components, in particular, as a polarizer protective film. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to these embodiments. The method for producing a resin film according to this embodiment involves obtaining a latex of a (meth)acrylic polymer by emulsion polymerization, adding a coagulant to the latex to coagulate the (meth)acrylic polymer, separating the polymer from the aqueous phase, mixing the polymer with a solvent containing ethanol to form a dope, casting the dope on a support surface, and then evaporating the solvent to produce a resin film.

[0014] ((Meth)acrylic polymer) First, two types of embodiments of the (meth)acrylic polymer in this embodiment will be described. Note that "(meth)acrylic" collectively denotes acrylic and methacrylic, and means acrylic and / or methacrylic.

[0015] <(Meth)acrylic polymer related to the first aspect> The (meth)acrylic polymer according to the first aspect may be a polymer having 30 to 100% by weight of methyl methacrylate units and 0 to 70% by weight of other monomer units copolymerizable therewith as constituent units. The (meth)acrylic polymer is preferably a polymer having no crosslinked structure.

[0016] From the viewpoints of appearance and weather resistance, the (meth)acrylic polymer according to the first aspect may contain methyl methacrylate units in an amount of 30% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more, even more preferably 70% by weight or more, and particularly preferably 80% by weight or more, of the total amount of structural units of the polymer. Furthermore, from the viewpoints of optical properties and heat resistance, the upper limit is preferably 99.9% by weight or less, more preferably 99% by weight or less, even more preferably 97% by weight or less, and particularly preferably 95% by weight or less. From the viewpoints of processability and appearance, the (meth)acrylic polymer preferably does not contain a polyfunctional monomer unit having two or more polymerizable functional groups in the molecule.

[0017] Examples of other monomer units copolymerizable with the methyl methacrylate unit include ethyl methacrylate, propyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, benzyl methacrylate, octyl methacrylate, stearyl methacrylate, glycidyl methacrylate, epoxycyclohexylmethyl methacrylate, dimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, dicyclopentanyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,2-trichloroethyl methacrylate, isobornyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, glycidyl acrylate, epoxycyclohexylmethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, Examples of suitable monomers include (meth)acrylic acid ester units having 1 to 20 carbon atoms in the ester moiety, such as hydroxypropyl (excluding methyl methacrylate); (meth)acrylamide units such as methacrylamide, N-methylolmethacrylamide, acrylamide, and N-methylolacrylamide; carboxylic acids such as methacrylic acid and acrylic acid and their salts; vinyl cyanide units such as acrylonitrile and methacrylonitrile; vinyl arene units such as styrene, α-methylstyrene, monochlorostyrene, and dichlorostyrene; maleimide units such as N-phenylmaleimide, N-cyclohexylmaleimide, and N-methylmaleimide; 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. These monomers can be used alone or in combination.

[0018] Among these, (meth)acrylic acid ester units (excluding methyl methacrylate) having 1 to 20 carbon atoms in the ester moiety, vinylarene units, and / or substituted or unsubstituted maleimide units are preferred, and (meth)acrylic acid ester units (excluding methyl methacrylate) having 1 to 20 carbon atoms in the ester moiety, and / or substituted or unsubstituted maleimide units are particularly preferred.

[0019] The (meth)acrylic polymer is used to produce a resin film by a solution casting method, and therefore preferably contains, as a structural unit, a drying-accelerating comonomer that increases the evaporation rate of a solvent, as the copolymerizable other monomer unit.

[0020] The drying-accelerating comonomer unit having good heat resistance and capable of increasing the evaporation rate of the solvent is preferably at least one selected from the group consisting of a substituted or unsubstituted maleimide unit, a methacrylate unit in which the ester moiety is a primary or secondary hydrocarbon group having 2 to 8 carbon atoms or an aromatic hydrocarbon group, a methacrylate unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and having a fused ring structure, a methacrylate unit in which the ester moiety is a linear or branched group containing an ether bond, and a vinylarene unit. The use of such a drying-accelerating comonomer unit enables the (meth)acrylic polymer to have excellent heat resistance while increasing the evaporation rate of the solvent from the cast film in the solution casting method.

[0021] Examples of the maleimide unit include N-phenylmaleimide, N-benzylmaleimide, N-cyclohexylmaleimide, and N-methylmaleimide, and N-phenylmaleimide, N-benzylmaleimide, and N-cyclohexylmaleimide are preferred.

[0022] Examples of the methacrylic acid ester unit in which the ester moiety is a primary or secondary hydrocarbon group having 2 to 8 carbon atoms or an aromatic hydrocarbon group include ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, phenyl methacrylate, benzyl methacrylate, etc. Among these, ethyl methacrylate, n-butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, and benzyl methacrylate are preferred.

[0023] Examples of the methacrylic acid ester unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure include dicyclopentanyl methacrylate and isobornyl methacrylate. The saturated hydrocarbon group preferably has 8 to 14 carbon atoms, more preferably 9 to 12. The fused ring structure is not particularly limited, but is preferably a structure in which two five-membered rings are fused together by three consecutive carbon atoms.

[0024] Examples of the methacrylic acid ester unit in which the ester moiety is a linear or branched group containing an ether bond include 2-methoxyethyl methacrylate.

[0025] Examples of the vinylarene unit include styrene, α-methylstyrene, monochlorostyrene, dichlorostyrene, etc. Among these, styrene is preferred.

[0026] The (meth)acrylic polymer according to the first aspect may contain 0 to 70% by weight of the other copolymerizable monomer units relative to the total amount of the constituent units of the polymer. However, in order to adjust the optical properties and heat resistance, the (meth)acrylic polymer preferably contains 0.1% by weight or more of the other copolymerizable monomer units, more preferably 1% by weight or more, even more preferably 3% by weight or more, and particularly preferably 5% by weight or more. The upper limit is preferably 50% by weight or less, more preferably 40% by weight or less, even more preferably 30% by weight or less, and particularly preferably 20% by weight or less.

[0027] The (meth)acrylic polymer according to the first aspect preferably has a ring structure in the main chain because it has excellent heat resistance. Examples of the ring structure include a glutarimide ring structure, a lactone ring structure, a maleic anhydride-derived structure, a substituted or unsubstituted maleimide ring structure, and a glutaric anhydride ring structure. Also included are acrylic resins containing (meth)acrylic acid structural units in the molecule. Specific examples include maleimide acrylic resins (acrylic resins in which an unsubstituted or N-substituted maleimide compound is copolymerized as a copolymerization component), glutarimide acrylic resins, lactone ring-containing acrylic resins, acrylic or methacrylic resins containing hydroxyl and / or carboxyl groups, partially hydrogenated styrene unit-containing (meth)acrylic polymers obtained by partially hydrogenating the aromatic ring of a styrene-containing (meth)acrylic polymer obtained by polymerizing a styrene monomer and another monomer copolymerizable therewith, and (meth)acrylic polymers having a cyclic acid anhydride structure such as a glutaric anhydride structure or a maleic anhydride-derived structure.

[0028] Among these, a glutarimide ring structure and a substituted or unsubstituted maleimide ring structure are particularly preferred because they can effectively improve the heat resistance of the resin film and have an excellent balance with the optical properties. These may be used in combination to impart optical properties, high thermal stability, and solvent resistance to the (meth)acrylic polymer.

[0029] The weight-average molecular weight of the (meth)acrylic polymer according to the first aspect is not particularly limited, but from the viewpoint of achieving a balance between the toughness of the resulting resin film and good film-forming properties, it is preferably 400,000 to 4,000,000, more preferably 800,000 to 3,500,000, even more preferably 800,000 to 3,000,000, and particularly preferably 1,000,000 to 3,000,000. The weight-average molecular weight may be 800,000 to 2,500,000 or 800,000 to 2,000,000.

[0030] Furthermore, when forming a film by melt extrusion, it is necessary to melt the (meth)acrylic polymer to reduce the viscosity, and therefore the molecular weight of the polymer must be relatively low. However, in this embodiment, since the film is formed by the solution casting method, it is possible to easily form a film even if the polymer has a high molecular weight. From this viewpoint, the weight average molecular weight of the (meth)acrylic polymer may be 500,000 or more. The weight average molecular weight can be calculated by gel permeation chromatography (GPC) using a standard polystyrene conversion method.

[0031] The (meth)acrylic polymer according to the first aspect preferably has excellent heat resistance, and the glass transition temperature can be used as an index of heat resistance. The (meth)acrylic polymer preferably has a glass transition temperature of 110°C or higher, more preferably 114°C or higher, even more preferably 115°C or higher, even more preferably 119°C or higher, particularly preferably 122°C or higher, and most preferably 125°C or higher.

[0032] <(Meth)acrylic polymer according to the second aspect> The (meth)acrylic polymer according to the second aspect may be a graft copolymer containing crosslinked (meth)acrylic polymer particles (a) and a non-crosslinked methacrylic polymer component (b). Hereinafter, the (meth)acrylic polymer according to the second aspect will also be referred to as a graft copolymer.

[0033] The crosslinked (meth)acrylic polymer particles (a) are a rubber component, which can contribute to improving strength. Furthermore, the non-crosslinked methacrylic polymer component (b) can achieve excellent heat resistance. In comparison with a system in which a core-shell graft copolymer is mixed with a methacrylic resin, the crosslinked (meth)acrylic polymer particles (a) can correspond to the core rubber component in the core-shell graft copolymer, and the non-crosslinked methacrylic polymer component (b) can correspond to the methacrylic resin matrix.

[0034] At least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a). This graft-bonding can be achieved by producing a graft copolymer by emulsion polymerization, as described below. Due to this production method, the graft copolymer may also contain non-crosslinked methacrylic polymer component (b) that is not graft-bonded to the crosslinked (meth)acrylic polymer particles (a).

[0035] The graft copolymer according to the second embodiment can have a configuration in which small-sized crosslinked (meth)acrylic polymer particles (a) are dispersed in a high-molecular-weight non-crosslinked methacrylic polymer component (b), and therefore aggregation of the crosslinked (meth)acrylic polymer particles (a) in the graft copolymer is less likely to proceed. As a result, the graft copolymer according to the second embodiment has good stability whether 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 the second embodiment has the advantage of being easily soluble in a solvent.

[0036] (Crosslinked (meth)acrylic polymer particles (a)) The crosslinked (meth)acrylic polymer particles (a) are (meth)acrylic rubber particles. The graft copolymer according to the second embodiment contains the crosslinked (meth)acrylic polymer particles (a), and thus can achieve high strength when formed into a film, for example.

[0037] The crosslinked (meth)acrylic polymer particles (a) preferably have a relatively small particle size, specifically, an average particle size of 150 nm or less. By using crosslinked (meth)acrylic polymer particles with such a small particle size, low haze can be achieved when the graft copolymer according to the second embodiment is formed into, for example, a film. Furthermore, by reducing the size of the crosslinked (meth)acrylic polymer particles, it is not necessary to match the refractive index of the crosslinked (meth)acrylic polymer particles (a) with that of the non-crosslinked methacrylic polymer component (b). As a result, a monomer composition that lowers the glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) can be adopted without considering the refractive index, thereby achieving high strength when the graft copolymer is formed into, for example, a film.

[0038] From the viewpoint of low haze, the average particle size is more preferably 130 nm or less, even more preferably 120 nm or less, even more preferably 110 nm or less, and particularly preferably 100 nm or less. The lower limit of the average particle size is not particularly limited, but from the viewpoint of film strength or ease of particle production, it is preferably 30 nm or more, more preferably 50 nm or more, and even more preferably 60 nm or more. The average particle size is a volume-average particle size, and can be measured in the latex state of the crosslinked (meth)acrylic polymer particles (a) using a commercially available measuring device (e.g., Microtrac UPA150 manufactured by Nikkiso Co., Ltd.). The average particle size can also be controlled by adjusting the conditions during particle production (specifically, the type and amount of emulsifier, the stirring conditions during emulsion polymerization, etc.).

[0039] The crosslinked (meth)acrylic polymer particles (a) preferably 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 the graft copolymer is formed into a film, for example. The glass transition temperature can be controlled by adjusting the type and ratio of the monomers constituting the crosslinked (meth)acrylic polymer particles (a).

[0040] The glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) is more preferably -20°C or lower, even more preferably -30°C or lower, even more preferably -40°C or lower, and particularly preferably -45°C or lower. There are no particular restrictions on the lower limit of the glass transition temperature, but for example, it is preferably -130°C or higher, more preferably -110°C or higher, even more preferably -100°C or higher, even more preferably -80°C or higher, and particularly preferably -70°C or higher. The glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) is a value calculated using the Fox formula using values ​​listed in the Polymer Handbook (J. Brandrup, Interscience 1989) (for example, the glass transition temperature for poly(n-butyl acrylate) is -54°C).

[0041] The crosslinked (meth)acrylic polymer particles (a) are particles formed from a crosslinked (meth)acrylic polymer obtained by polymerizing a monomer component containing a (meth)acrylic monomer and a polyfunctional monomer. The monomer component excluding the polyfunctional monomer contains an acrylic monomer and / or a methacrylic monomer, and preferably contains at least an acrylic monomer.

[0042] The acrylic monomer contained in the crosslinked (meth)acrylic polymer particles (a) is preferably an acrylic acid alkyl ester having an alkyl group with 1 to 8 carbon atoms. Specific examples include ethyl acrylate, n-butyl acrylate, n-octyl acrylate, and 2-ethylhexyl acrylate. The acrylic acid alkyl ester may be used alone or in combination of two or more. Of these, n-butyl acrylate is preferred.

[0043] As the optional methacrylic monomer that can be contained in the crosslinked (meth)acrylic polymer particles (a), a methacrylic acid alkyl ester having an alkyl group with 1 to 8 carbon atoms is preferred. Specific examples include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, and octyl methacrylate. The methacrylic acid alkyl ester may be used alone or in combination of two or more. Among these, a methacrylic acid alkyl ester having an alkyl group with 1 to 4 carbon atoms is preferred. Methyl methacrylate is particularly preferred.

[0044] The crosslinked (meth)acrylic polymer particles (a) may contain monomers other than the alkyl acrylates and alkyl methacrylates described above. 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 the aromatic vinyl monomers include styrene, α-methylstyrene, chlorostyrene, and other styrene derivatives. Examples of the other copolymerizable vinyl monomers include unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile, α,β-unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, olefin monomers such as vinyl acetate, ethylene, and propylene, halogenated vinyl monomers such as vinyl chloride, vinylidene chloride, and vinylidene fluoride, and maleimide monomers such as N-ethylmaleimide, N-propylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, and No-chlorophenylmaleimide. These may be used alone or in combination of two or more.

[0045] From the viewpoint of strength and heat resistance, the monomer components constituting the crosslinked (meth)acrylic polymer particles (a) preferably contain 70% by weight or more and 100% by weight or less, more preferably 80% by weight or more and 100% by weight or less, even more preferably 90% by weight or more and 100% by weight or less, and particularly preferably 95% by weight or more and 100% by weight or less, of acrylic acid esters (particularly acrylic acid alkyl esters having an alkyl group with 1 to 8 carbon atoms) among the monomer components excluding polyfunctional monomers.

[0046] The crosslinked (meth)acrylic polymer particles (a) can be formed by polymerizing the above-mentioned monomer components in the presence of a polyfunctional monomer. The polyfunctional monomer, also known as a crosslinking agent or crosslinkable monomer, is a compound having two or more unsaturated bonds in one molecule that are copolymerizable with the (meth)acrylic monomer. Specific examples include allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate, diallyl itaconate, monoallyl maleate, monoallyl fumarate, butadiene, divinylbenzene, triallyl isocyanurate, alkylene glycol dimethacrylate, and alkylene glycol diacrylate. These may be used alone or in combination of two or more. Allyl methacrylate is preferred.

[0047] The amount of the polyfunctional monomer used can be appropriately set from the viewpoint of strength, and specifically, it may be about 0.1 to 5.0 parts by weight per 100 parts by weight of the monomer components (excluding the polyfunctional monomer) constituting the crosslinked (meth)acrylic polymer particles (a). However, from the viewpoint of the strength of the graft copolymer, the amount of the polyfunctional monomer used is preferably 0.2 to 3.5 parts by weight, more preferably 0.2 to 3.0 parts by weight, even more preferably 0.3 to 2.0 parts by weight, and particularly preferably 0.4 to 1.5 parts by weight.

[0048] (Non-crosslinked methacrylic polymer component (b)) The non-crosslinked methacrylic polymer component (b) is a polymer mainly composed of methacrylic monomers polymerized and does not have a crosslinked structure (i.e., obtained by polymerization without using a polyfunctional monomer). At least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a). This makes the crosslinked (meth)acrylic polymer particles (a) less likely to aggregate, improves the storage stability of the graft copolymer according to the second embodiment, and enables low haze to be achieved when formed into a film.

[0049] The non-crosslinked methacrylic polymer component (b) is preferably a polymer with a high molecular weight, specifically, preferably exhibiting 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 the second 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 more preferably 300,000 or more, even more preferably 350,000 or more, even more preferably 400,000 or more, and particularly preferably 450,000 or more. There are no particular limitations on the upper limit of the weight-average molecular weight, but from the viewpoint of facilitating film formation by solution casting, it is preferably 1,000,000 or less, more preferably 900,000 or less.

[0050] From the viewpoint of the heat resistance of the graft copolymer, the non-crosslinked methacrylic polymer component (b) preferably exhibits a glass transition temperature of 115°C or higher, more preferably 118°C or higher, and even more preferably 120°C or higher. The upper limit of the glass transition temperature is not particularly limited, but may be, for example, 160°C or lower, or 150°C or lower. The glass transition temperature can be controlled by adjusting the type and ratio of the monomers constituting the non-crosslinked methacrylic polymer component (b). The glass transition temperature of the non-crosslinked methacrylic polymer component (b) can also be calculated using the Fox formula using values ​​listed in the Polymer Handbook (J. Brandrup, Interscience 1989) (for example, the glass transition temperature for polymethyl methacrylate is 105°C).

[0051] The non-crosslinked methacrylic polymer component (b) is a polymer mainly composed of methacrylic monomer units. From the viewpoint of the heat resistance and film-forming ability of the graft copolymer, methyl methacrylate units are preferred as the methacrylic monomer units. In particular, it is preferred that the monomer components constituting the non-crosslinked methacrylic polymer component (b) contain 70 to 99% by weight of methyl methacrylate units. This improves heat resistance and makes it easier to form a film by solution casting. The content of methyl methacrylate units is more preferably 75 to 98% by weight, even more preferably 80 to 97% by weight, even more preferably 85 to 96% by weight, even more preferably 88 to 95% by weight, and particularly preferably 90 to 95% by weight.

[0052] The non-crosslinked methacrylic polymer component (b) preferably contains, as a structural unit, the drying-accelerating comonomer described in relation to the (meth)acrylic polymer according to the first embodiment as a monomer unit other than the methyl methacrylate unit. By including such a monomer unit, it becomes possible to increase the evaporation rate of the solvent when evaporating the solvent from the casting film when producing a film by a solution casting method, without significantly reducing the heat resistance of the graft copolymer. Specific types of drying-accelerating comonomers are the same as those described above in relation to the (meth)acrylic polymer according to the first embodiment, and therefore will not be described here.

[0053] In addition to accelerating the evaporation rate of the solvent from the casting film in the solution casting method, the heat resistance of the graft copolymer can be further improved. For this reason, it is preferable that the non-crosslinked methacrylic polymer component (b) contains, as the drying-accelerating comonomer unit, at least one of a substituted or unsubstituted maleimide unit and a methacrylic acid ester unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure.

[0054] In this case, the drying-accelerating comonomer unit may be at least one of a substituted or unsubstituted maleimide unit and a methacrylic acid ester unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure, or a combination of at least one of a substituted or unsubstituted maleimide unit and a methacrylic acid ester unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure with a drying-accelerating comonomer unit other than these. By using such a combination, it is possible to adjust the heat resistance of the graft copolymer and the evaporation rate of the solvent, thereby improving both in a balanced manner.

[0055] The drying-accelerating comonomer units other than the substituted or unsubstituted maleimide units and the methacrylic acid ester units in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure 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 an aromatic hydrocarbon group having 2 to 8 carbon atoms, as described above, methacrylic acid ester units in which the ester moiety is a linear or branched group containing an ether bond, and vinylarene units.

[0056] Among the monomer components constituting the non-crosslinked methacrylic polymer component (b), the proportion of the drying-accelerating comonomer unit is preferably 1% by weight or more and 30% by weight or less, more preferably 2-25% by weight, even more preferably 3-20% by weight, even more preferably 4-18% by weight, even more preferably 4-15% by weight, even more preferably 4-12% by weight, and particularly preferably 5-10% by weight. When two or more types of drying-accelerating comonomer units are contained, the proportion of the drying-accelerating comonomer units refers to the proportion of the total amount of all the drying-accelerating comonomer units contained in the total monomer units. By achieving such a weight proportion, the graft copolymer can have excellent heat resistance while accelerating the solvent evaporation rate in the solution casting method. The weight proportion of each of these units can be determined by proton nuclear magnetic resonance spectroscopy.

[0057] The non-crosslinked methacrylic polymer component (b) may be a copolymer that does not contain other comonomer units that do not fall under the category of drying-accelerating comonomer units, or may be a copolymer that contains other comonomer units that do not fall under the category of drying-accelerating comonomer units. Examples of such other comonomers include methacrylic acid esters such as glycidyl methacrylate, epoxycyclohexylmethyl methacrylate, dimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,2-trichloroethyl methacrylate, methacrylamide, and N-methylolmethacrylamide; methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, benzyl acrylate, octyl acrylate, glycidyl acrylate; Examples of suitable comonomer units include acrylic esters such as epoxycyclohexylmethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, acrylamide, and N-methylol acrylamide; carboxylic acids such as methacrylic acid and acrylic acid and their salts; vinyl cyanides such as acrylonitrile and methacrylonitrile; maleic acid, fumaric acid, and their esters; vinyl halides such as vinyl chloride, vinyl bromide, and chloroprene; vinyl esters such as vinyl formate, vinyl acetate, and vinyl propionate; and alkenes such as ethylene, propylene, butylene, butadiene, and isobutylene. The proportion of such other comonomer units in the monomer components constituting the non-crosslinked methacrylic polymer component (b) is preferably 10% by weight or less, more preferably 8% by weight or less, and even more preferably 5% by weight or less.

[0058] In the graft copolymer according to the second embodiment, the proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is preferably 1% by weight or more but less than 50% by weight, and the proportion of the non-crosslinked methacrylic polymer component (b) is preferably 99% by weight or less but more than 50% by weight. By containing a high proportion of the non-crosslinked methacrylic polymer component (b) in the graft copolymer according to the second embodiment, the crosslinked (meth)acrylic polymer particles (a) are less likely to aggregate, making it possible to form a high-strength, low-haze film, and improving the storage stability of the graft copolymer or a dope thereof. The proportion of the crosslinked (meth)acrylic polymer particles (a) is preferably 3% by weight or more but less than 45% by weight, more preferably 4 to 40% by weight, even more preferably 5 to 35% by weight, and particularly preferably 6 to 30% by weight.

[0059] Furthermore, from the viewpoint of the bending resistance of the resulting film, the proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is preferably 5% by weight or more, more preferably 6% by weight or more, and even more preferably 7% by weight or more. From the viewpoint of moisture permeability and elastic modulus, the upper limit of this proportion is preferably 25% by weight or less, more preferably 20% by weight or less, even more preferably 15% by weight or less, even more preferably 12% by weight or less, and particularly preferably 10% by weight or less. From the viewpoint of the balance between moisture permeability, elastic modulus, and bending resistance, it is preferably 6% by weight or more, more preferably 7% by weight or more, and 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.

[0060] (emulsion polymerization) In this embodiment, the (meth)acrylic polymer can be formed by conventional emulsion polymerization using an emulsifier and a polymerization initiator. By carrying out emulsion polymerization, a latex of the (meth)acrylic polymer can be obtained.

[0061] In particular, when producing the graft copolymer according to the second embodiment, crosslinked (meth)acrylic polymer particles (a) are formed by emulsion polymerization, and then the monomer components constituting the non-crosslinked methacrylic polymer component (b) are added to the polymerization system, followed by emulsion polymerization to form the non-crosslinked methacrylic polymer component (b). This allows the production of a graft copolymer in which at least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a). This allows the crosslinked (meth)acrylic polymer particles (a) to be sufficiently dispersed in the non-crosslinked methacrylic polymer component (b).

[0062] The emulsifier is not particularly limited, and examples thereof include anionic surfactants such as sodium alkylsulfonate, sodium alkylbenzenesulfonate, dioctyl sodium sulfosuccinate (sodium di(2-ethylhexyl)sulfosuccinate), sodium lauryl sulfate, sodium fatty acid, and phosphate ester salts such as sodium polyoxyethylene lauryl ether phosphate, as well as nonionic surfactants. These surfactants may be used alone or in combination of two or more.

[0063] Sulfonates are preferred as the emulsifier because they can highly suppress foaming marks during film drying and also have excellent polymerization stability. Examples of sulfonates include dialkyl sulfosuccinates, alkane sulfonates, alpha-olefin sulfonates, alkyl benzene sulfonates, naphthalene sulfonate-formaldehyde condensates, alkyl naphthalene sulfonates, and N-methyl-N-acyltaurate salts. Among these, dialkyl sulfosuccinates or alkyl benzene sulfonates are preferred.

[0064] The sulfonate is not particularly limited, and may be a lithium salt, a sodium salt, a potassium salt, a calcium salt, a magnesium salt, or the like. In particular, from the viewpoint of effectively suppressing foaming marks, it is preferable to include at least one selected from the group consisting of a lithium salt, a sodium salt, and a potassium salt. When the sulfonate exists as a salt of such a monovalent cation, even if the salt remains in the (meth)acrylic polymer, it is believed that the salt dissolves in ethanol in the dope solvent and is micro-dispersed in the solution dope, thereby suppressing foaming during film formation and drying.

[0065] As the polymerization initiator, known ones can be used, and examples thereof include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; and organic peroxides such as tert-butyl hydroperoxide, tert-butylperoxyisopropyl carbonate, cumene hydroperoxide, paramenthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, di-8,5,5-trimethylhexanoyl peroxide, dilauroyl peroxide, and benzoyl peroxide. From the viewpoint of improving the thermal stability of the resulting resin film, it is preferable to use a polymerization initiator having a 10-hour half-life temperature of 100° C. or less. Such a polymerization initiator is not particularly limited, but a persulfate is preferable.

[0066] The polymerization initiator may be polymerized by cleaving the polymerization initiator solely by a thermal decomposition mechanism to generate radicals, or may be used as a redox initiator that generates radicals at low temperatures by combining the polymerization initiator with an oxidizing agent such as ferrous sulfate and a reducing agent such as sodium formaldehyde sulfoxylate, as described in the examples of Japanese Patent No. 3,960,631.

[0067] In order to adjust the molecular weight of the (meth)acrylic polymer, a known chain transfer agent may be used during emulsion polymerization. In particular, when producing the graft copolymer according to the second embodiment, a chain transfer agent may be used in the step of forming the non-crosslinked methacrylic polymer component (b) to control the molecular weight of the polymer component (b).

[0068] The chain transfer agent is not particularly limited, and examples thereof include primary alkyl mercaptan chain transfer agents such as n-butyl mercaptan, n-octyl mercaptan, n-hexadecyl mercaptan, n-dodecyl mercaptan, and n-tetradecyl mercaptan; secondary alkyl mercaptan chain transfer agents such as s-butyl mercaptan and s-dodecyl mercaptan; tertiary alkyl mercaptan chain transfer agents such as t-dodecyl mercaptan and t-tetradecyl mercaptan; thioglycolic acid esters such as 2-ethylhexyl thioglycolate, ethylene glycol dithioglycolate, trimethylolpropane tris(thioglycolate), and pentaerythritol tetrakis(thioglycolate); thiophenol, tetraethylthiuram disulfide, pentanephenylethane, acrolein, methacrolein, allyl alcohol, carbon tetrachloride, ethylene bromide, styrene oligomers such as α-methylstyrene dimer, and terpinolene. These may be used alone or in combination of two or more.

[0069] (coagulation) The (meth)acrylic polymer latex obtained by the emulsion polymerization can be coagulated by adding a coagulant to the (meth)acrylic polymer. After that, if necessary, heat treatment is performed, and the coagulated polymer is separated from the aqueous phase and dried, or other known methods are used to obtain a solid or powdery coagulated (meth)acrylic polymer product.

[0070] The coagulant is not particularly limited and any known coagulant can be used, but is preferably an inorganic salt or an acid. The coagulant may be in the form of an aqueous solution.

[0071] Examples of inorganic salts include alkali metal halides such as sodium chloride, potassium chloride, lithium chloride, sodium bromide, potassium bromide, lithium bromide, potassium iodide, and sodium iodide; alkali metal sulfides such as potassium sulfate and sodium sulfate; ammonium sulfate; ammonium chloride; alkali metal nitrates such as sodium nitrate and potassium nitrate; calcium chloride, ferrous sulfate, magnesium sulfate, zinc sulfate, copper sulfate, barium chloride, ferrous chloride, ferric chloride, magnesium chloride, ferric sulfate, aluminum sulfate, potassium alum, and iron alum. Examples of acids include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and organic acids such as acetic acid and formic acid. Only one type of coagulant may be used, or two or more types may be used in combination.

[0072] As the coagulant, inorganic salts are preferred, and among them, calcium salts or magnesium salts are preferred, and calcium chloride or magnesium chloride is more preferred.

[0073] The amount of coagulant used is not particularly limited, but may be, for example, about 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, per 100 parts by weight of the total amount of the (meth)acrylic polymer contained in the latex.

[0074] Before adding the coagulant, it is preferable to filter the (meth)acrylic polymer latex with a filter, mesh, etc. to remove fine polymerization scales in advance, thereby reducing fish eyes and foreign matter caused by fine polymerization scales.

[0075] After adding the coagulant to the latex, the latex may be heated for heat treatment to promote aggregation of the polymer particles. The heating temperature during the heat treatment is not particularly limited, but may be, for example, 60 to 130°C, preferably 70 to 120°C, more preferably 70 to 100°C, and even more preferably 70 to 98°C. The heating time is also not particularly limited, but may be, for example, about 1 minute to 1 hour, preferably 3 to 30 minutes. Furthermore, by performing the heat treatment under pressure as needed, even resins with high glass transition temperatures can be coagulated.

[0076] After adding a coagulant to coagulate the (meth)acrylic polymer, dehydration is carried out. After this dehydration, the resin is washed with, for example, 10 times the weight of the solid resin content, and then dehydrated again, thereby reducing the amount of impurities remaining in the system that could be a source of foaming. Although impurities may remain in the system even after this operation, foaming in the resin film can be suppressed by using a specific solvent in a solution casting method, as described below. The resulting dehydrated resin is dried, for example, at 100°C, to obtain the (meth)acrylic polymer.

[0077] (Dope) The solidified product of the (meth)acrylic polymer obtained by separating it from the aqueous phase as described above can be mixed with a solvent and dissolved or dispersed in the solvent to form a dope.

[0078] In this embodiment, at least ethanol is used as the solvent. By using a dope containing ethanol, the resin film obtained by the solution casting method has low haze and can suppress the generation of fine bubbles. In contrast, when a dope containing no ethanol or a dope containing methanol instead of ethanol is used, the resin film obtained by the solution casting method has high haze and contains many fine bubbles.

[0079] The reason why using ethanol as a solvent can achieve low haze and suppress foaming in the resin film is unclear, but it is thought that this is because salts derived from the emulsifier and / or coagulant used in emulsion polymerization remain in the (meth)acrylic polymer, and these dissolve in ethanol, making foaming less likely to occur during film formation and drying. On the other hand, if ethanol is not used, the emulsifier and / or salt are less soluble in the solvent and act as foaming nuclei, which may cause numerous bubbles to form during film formation and drying. However, the present invention is not limited by the above description.

[0080] Furthermore, by using ethanol as a solvent, it is possible to improve film-forming properties during solution casting, as well as the releasability and handling properties of the film.

[0081] The content ratio of ethanol to the total amount of solvent contained in the dope is preferably 1 to 25% by weight, more preferably 3 to 20% by weight, even more preferably 5 to 15% by weight, and particularly preferably 5 to 10% by weight, from the viewpoint of realizing good solubility or dispersibility of the (meth)acrylic polymer in the solvent while achieving the above-mentioned low haze and foaming suppression.

[0082] As the solvent contained in the dope, it is preferable to use, in addition to ethanol, a so-called good solvent that has high solubility for the (meth)acrylic polymer. The type of good solvent is not particularly limited, but examples thereof include 1,4-dioxane, 2-phenylethanol, acetone, acetonitrile, chloroform, dibasic acid esters, diacetone alcohol, N,N-dimethylformamide, dimethyl sulfoxide, methyl acetate, ethyl acetate, γ-butyrolactone, methyl ethyl ketone, methyl isobutyl ketone, methylene chloride, n-butyl acetate, N-methyl-2-pyrrolidone, propylene carbonate, 1,1,2,2-tetrachloroethane, tetrahydrofuran, and toluene. These good solvents may be used alone or in combination.

[0083] Among the good solvents, methyl ethyl ketone, chloroform and methylene chloride are preferred, and methylene chloride is more preferred, because they have excellent solubility for the (meth)acrylic polymer and a fast evaporation rate.

[0084] The content ratio of the good solvent to the total amount of solvent contained in the dope is preferably 75 to 99% by weight, more preferably 80 to 97% by weight, even more preferably 85 to 95% by weight, and particularly preferably 90 to 95% by weight, from the viewpoint of realizing good solubility or dispersibility of the (meth)acrylic polymer in the solvent while achieving the above-mentioned low haze and foaming suppression.

[0085] The dope may or may not contain a solvent other than ethanol and the good solvent. Examples of such other solvents include methanol, isopropanol, butanol, and ethylene glycol monoethyl ether. The content of the other solvents relative to the total amount of solvents contained in the dope may be, for example, about 0 to 5% by weight, 0 to 3% by weight, or 0 to 1% by weight.

[0086] The concentration of the (meth)acrylic polymer in the dope is not particularly limited and can be appropriately determined taking into consideration the solubility or dispersibility of the (meth)acrylic polymer in the solvent used, the conditions under which the solution casting method is carried out, and the like. However, the concentration is preferably 5 to 50% by weight, more preferably 7 to 45% by weight, even more preferably 10 to 40% by weight, even more preferably 12 to 35% by weight, particularly preferably 15 to 30% by weight, and most preferably 15 to 20% by weight.

[0087] An example of the procedure for preparing the dope is described below. First, pellets containing the (meth)acrylic polymer and, if necessary, other components are prepared, and then the pellets are mixed with a solvent to prepare a dope in which each component is dissolved or dispersed in the solvent. Alternatively, without preparing pellets, the (meth)acrylic polymer and other components are simultaneously or sequentially mixed in a solvent to prepare a dope in which each component is dissolved or dispersed in the solvent. The dissolving or dispersing step can be carried out by appropriately adjusting the temperature and pressure. After the dissolving or dispersing step, the obtained dope may be filtered or degassed.

[0088] (Other ingredients) The dope may contain only the (meth)acrylic polymer as a resin component, or may contain other resins in addition to the (meth)acrylic polymer. The other resin is not particularly limited, and examples thereof include styrene-based resins such as acrylonitrile-styrene resin, methyl methacrylate-styrene resin, and styrene-maleic anhydride resin; polycarbonate resin, polyvinyl acetal resin, cellulose acylate resin; fluorine-based resins such as polyvinylidene fluoride and polyfluorinated alkyl (meth)acrylate resin; silicone-based resin, polyolefin-based resin, polyethylene terephthalate resin, and polybutylene terephthalate resin.

[0089] The content of the other resin is not particularly limited, but may be, for example, about 0 to 50 parts by weight relative to 100 parts by weight of the (meth)acrylic polymer, or 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.

[0090] The dope may further contain known additives such as a light stabilizer, an ultraviolet absorber, a heat stabilizer, an antioxidant, a matting agent, a light diffusing agent, a colorant, a dye, a pigment, an antistatic agent, a heat ray reflecting material, a lubricant, a plasticizer, and a filler.

[0091] The dope may further contain a graft copolymer having a core-shell structure, which does not fall under the graft copolymer according to the second embodiment. By blending the graft copolymer having a core-shell structure, mechanical strength such as bending resistance and crack resistance can be imparted to the resin film.

[0092] The graft copolymer having a core-shell structure is also called a multistage polymer, a multilayer structure polymer, or a core-shell polymer. These polymers have a polymer layer (shell layer) obtained by polymerizing a monomer mixture in the presence of crosslinked polymer particles (core layer). The core layer and the shell layer may each consist of one layer or two or more layers. Such graft copolymers are not particularly limited, and known graft copolymers can be used as appropriate. One example is a graft copolymer obtained by polymerizing a monomer mixture containing an acrylic acid ester as the main component with a crosslinking agent to form an acrylic acid ester-based rubber-like polymer, and then polymerizing a monomer mixture containing a methacrylic acid ester as the main component in the presence of the acrylic acid ester-based rubber-like polymer.

[0093] When the graft copolymer having a core-shell structure is used, the blending ratio of the (meth)acrylic polymer to the graft copolymer having a core-shell structure may be, for example, 1 to 50 parts by weight, preferably 5 to 40 parts by weight, and more preferably 7 to 30 parts by weight, per 100 parts by weight of the (meth)acrylic polymer.

[0094] (Solution casting method) The dope obtained as described above is used to form a resin film by a solution casting method. Specifically, the dope is cast on the surface of a support, and then the solvent is evaporated to produce a resin film.

[0095] The solution casting method is described below, but is not limited thereto: The dope is sent to a pressure die by a liquid feed pump, and the dope is cast from a slit in the pressure die onto the surface (mirror surface) of a support such as an endless belt or drum made of metal or synthetic resin to form a casting film.

[0096] The cast membrane is heated on the support to evaporate the solvent, forming a film. The conditions for evaporating the solvent can be appropriately determined depending on the boiling point of the solvent used.

[0097] The resin film thus obtained is peeled off from the surface of the support, and may then be subjected to a drying step, a heating step, a stretching step, or the like, as appropriate.

[0098] (resin film) The thickness of the resin film produced by this embodiment is not particularly limited, but is preferably 5 to 200 μm, and more preferably 5 to 100 μm. If the resin film is 200 μm or less in thickness, cooling after molding becomes uniform, which tends to result in uniform optical properties and a faster drying rate. Furthermore, if the resin film is 5 μm or more in thickness, the resin film becomes easier to handle and tends to function better as a protective film.

[0099] The resin film preferably has a haze of 2% or less, more preferably 1.5% or less, more preferably 1% or less, even more preferably 0.8% or less, even more preferably 0.6% or less, and particularly preferably 0.4% or less, when measured at a film thickness of 40 μm. When the haze satisfies this range, the film has high transparency and can therefore be suitably used for optical components that require light transmittance.

[0100] The resin film can be preferably used as a film for protecting a laminate on the surface of another substrate, more preferably as an optical film, and particularly preferably as a polarizer protective film.

[0101] When used as a polarizer protective film, it is preferable that the optical isotropy is small. In particular, it is preferable that the optical isotropy is small not only in the in-plane directions (length direction and width direction) of the resin film but also in the thickness direction.

[0102] More specifically, the absolute value of the in-plane retardation is preferably 10 nm or less, more preferably 5 nm or less, and particularly preferably 3 nm or less. The absolute value of the thickness direction retardation is preferably 50 nm or less, more preferably 20 nm or less, even more preferably 10 nm or less, and particularly preferably 5 nm or less. A resin film having such a retardation can be suitably used as a polarizer protective film included in a polarizing plate of a liquid crystal display device.

[0103] Here, the retardation is an index value calculated based on birefringence, and the in-plane retardation (Re) and thickness direction retardation (Rth) can be calculated using the following formulas: In an ideal molded body that is completely optically isotropic in three dimensional directions, both the in-plane retardation (Re) and thickness direction retardation (Rth) are zero. Re=(nx-ny)×d Rth=((nx+ny) / 2-nz)×d In the above formula, nx, ny, and nz represent the refractive index in the direction of in-plane stretching (the orientation direction of the polymer chain) as the X axis, the direction perpendicular to the X axis as the Y axis, and the thickness direction of the molded product as the Z axis. Also, d represents the thickness of the molded product, and nx-ny represents the orientation birefringence. The MD direction of the molded product is the X axis, but in the case of a stretched molded product, the stretching direction is the X axis.

[0104] The resin film produced by this embodiment has an orientation birefringence of −2.6×10 -4 ~2.6×10 -4 is preferably -1.7 x 10 -4 ~1.7×10 -4 It is more preferable that the -4 ~1.0×10 -4 More preferably, it is -0.5 × 10-4 ~0.5×10 -4 It is particularly preferable that -4 ~0.2×10 -4 When the orientation birefringence is within the above range, birefringence does not occur during molding and stable optical properties can be obtained. In addition, the film is very suitable as an optical film for use in liquid crystal displays and the like.

[0105] The resin film has a photoelastic constant of −6×10 -12 ~6×10 -12 Pa -1 is preferably -4 x 10 -12 ~4×10 -12 Pa -1 It is more preferable that -12 ~2×10 -12 Pa -1 More preferably, it is -1 × 10 -12 ~1×10 -12 Pa -1 It is especially preferable that -12 ~0.5×10 -12 Pa -1 It is particularly preferable that -12 ~0.2×10 -12 Pa -1 It is most preferable that:

[0106] Photoelastic birefringence is the birefringence caused by elastic deformation (strain) of the polymer in a molded body when stress is applied to the molded body. In practice, the degree of photoelastic birefringence of a material can be evaluated by determining the polymer's inherent photoelastic constant. First, stress is applied to the polymer material, and the birefringence is measured when elastic strain occurs. The proportional constant between the obtained birefringence and stress is the photoelastic constant. By comparing these photoelastic constants, the birefringence of the polymer when stress is applied can be evaluated. If the photoelastic constant is within the above range, birefringence does not occur even when the molded body is deformed by stress, allowing for the production of molded bodies with low optical isotropy. For example, in polarizer protective film applications, stable optical properties are maintained even if the panel is deformed during transportation due to the influence of moisture or temperature in the air, thereby minimizing quality risks such as image quality degradation.

[0107] (Stretching) The resin film produced by this embodiment has high toughness and is highly flexible, and may be an unstretched film or a stretched film. Stretching the resin film can improve the mechanical strength and thickness accuracy of the resin film.

[0108] When the resin film is stretched, a stretched film (uniaxially stretched film or biaxially stretched film) can be produced by producing an unstretched film and then uniaxially stretching or biaxially stretching the film, or by appropriately adding a stretching operation during film formation as the film formation and solvent degassing processes progress. Stretching during film formation and stretching after film formation may also be appropriately combined.

[0109] The stretching ratio of the stretched film is not particularly limited and may be determined depending on the mechanical strength, surface properties, thickness accuracy, etc. of the stretched film to be produced. Although it also depends on the stretching temperature, the stretching ratio is generally preferably selected from the range of 1.1 to 5, more preferably from 1.3 to 4, and even more preferably from 1.5 to 3. If the stretching ratio is within the above range, the mechanical properties of the film, such as elongation, tear propagation strength, and flexural fatigue resistance, can be significantly improved.

[0110] (Application) The resin film produced by this embodiment can be reduced in surface gloss by known methods, if necessary. Examples of such methods include adding inorganic fillers or crosslinkable polymer particles. Furthermore, the resulting film can be embossed to form a surface irregularity layer, such as a prism shape, pattern, design, or knurling, or to reduce the surface gloss.

[0111] If necessary, the resin film can be laminated with another film using a dry lamination method and / or a thermal lamination method using a pressure-sensitive adhesive, adhesive, etc., or a functional layer such as a hard coat layer, an anti-reflection layer, an anti-fouling layer, an anti-static layer, a printed decorative layer, a metallic gloss layer, a surface uneven layer, or a matte layer can be formed on the front or back surface of the film.

[0112] The resin film can be used in various applications, taking advantage of its properties such as heat resistance, transparency, flexibility, etc. Examples of applications include the interior and exterior of automobiles, the interior and exterior of personal computers, the interior and exterior of mobile phones, the interior and exterior of solar cells, solar cell backsheets; imaging fields such as photographic lenses, viewfinders, filters, prisms, Fresnel lenses, and lens covers for cameras, VTRs, and projectors; lens fields such as pickup lenses for optical discs in CD players, DVD players, and MD players; optical recording fields for optical discs such as CDs, DVDs, and MDs; organic EL films, light guide plates for liquid crystal displays, diffusion plates, backsheets, reflective sheets, polarizer protective films, polarizing films, transparent resin sheets, retardation films, light diffusion films, and prism sheets. It can be used in information equipment such as LCD film and surface protection film, optical communications such as optical fiber, optical switches, and optical connectors, automotive headlights, tail lamp lenses, inner lenses, instrument covers, and sunroofs, medical equipment such as eyeglasses, contact lenses, endoscope lenses, and medical supplies that require sterilization, construction and building materials such as road signs, bathroom equipment, flooring, road translucent panels, double-glazed lenses, skylights, carports, lighting lenses, lighting covers, and building sizing, microwave cooking containers (tableware), home appliance housings, toys, sunglasses, stationery, etc. It can also be used as a replacement for molded products using transfer foil sheets.

[0113] The resin film can be used by being laminated on a substrate such as a metal, a plastic, etc. Examples of methods for laminating the resin film include lamination molding, wet lamination in which an adhesive is applied to a metal plate such as a steel plate, and then a film is placed on the metal plate and dried to bond them together, dry lamination, extrusion lamination, hot melt lamination, etc.

[0114] Methods for laminating a film onto a plastic part include insert molding or laminate injection press molding, in which the film is placed in a mold and then filled with resin by injection molding, and in-mold molding, in which a preformed film is placed in a mold and then filled with resin by injection molding.

[0115] The resin film laminate can be used as a paint replacement for automobile interior materials, automobile exterior materials, etc.; civil engineering and construction materials such as window frames, bathroom equipment, wallpaper, flooring materials, lighting and light control materials, soundproof walls, and road signs; daily goods; housings for furniture and electronic and electrical devices; housings for office automation equipment such as facsimiles, laptops, and copiers; front panels for LCD screens of terminals such as mobile phones, smartphones, and tablets; optical materials such as lighting lenses, automobile headlights, optical lenses, optical fibers, optical disks, and LCD light guide plates; optical elements; parts for electric or electronic devices; medical supplies requiring sterilization; toys or recreational items; and fiber-reinforced resin composite materials.

[0116] In particular, the resin film is suitable for optical films in terms of excellent heat resistance and optical properties, and can be used for various optical members. For example, the resin film can be used for known optical applications such as front panels of liquid crystal screens of terminals such as mobile phones, smartphones, and tablets, lighting lenses, automobile headlights, optical lenses, optical fibers, optical disks, light guide plates for liquid crystal displays, diffusion plates, backsheets, reflective sheets, polarizing films, transparent resin sheets, retardation films, light diffusion films, prism sheets, surface protective films, optically isotropic films, polarizer protective films, and transparent conductive films in the fields of liquid crystal display devices, organic EL devices, and optical communications. [Example]

[0117] 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" unless otherwise specified. The abbreviations used represent the following substances. BA: butyl acrylate MMA: methyl methacrylate BMA: butyl methacrylate PhMI: Phenylmaleimide 2-EHMA: 2-ethylhexyl methacrylate ALMA: Allyl methacrylate 2-EHTG: 2-ethylhexyl thioglycolate DSS: Dioctyl sodium sulfosuccinate NPS: Sodium persulfate NDS: Sodium pyrosulfite SFS: Sodium sulfoxylate formaldehyde ED: Ethylenediaminetetraacetic acid disodium salt FeSO4: Ferrous sulfate heptahydrate t-BHP: t-butyl hydroperoxide

[0118] (Production Example 1) Production of (meth)acrylic polymer A An 8-liter polymerization reactor equipped with a stirrer was charged with 133 parts of deionized water, 0.004 parts of sodium hydroxide, and 0.2 parts of di(2-ethylhexyl)sodium sulfosuccinate. After thoroughly purging the interior of the polymerization reactor with nitrogen gas, the internal temperature was raised to 80°C, and 0.03 parts of NPS and 0.001 parts of NDS were added as a 0.5% aqueous solution. Next, 8.5 parts of the monomer (a) for crosslinked (meth)acrylic polymer particles listed in Table 1 were added continuously at a rate of 0.523 parts / min. Polymerization was continued for an additional 30 minutes to obtain crosslinked (meth)acrylic polymer particles (a). The volume average particle size was 60 nm, and the polymerization conversion rate was 99.5%. Then, 91.5 parts of monomer (b) for the non-crosslinked methacrylic polymer component shown in Table 1 was continuously added at a rate of 1.353 parts / min. Simultaneously with the start of the addition of monomer (b), 0.4 parts of sodium di(2-ethylhexyl) sulfosuccinate was added continuously as a 5% aqueous solution over the same time period as monomer (b). After the addition was completed, polymerization was continued for 60 minutes to obtain a graft copolymer latex. The polymerization conversion rate was 100.0%. Next, 3.0 parts of a coagulant (calcium chloride or magnesium chloride) was added in the form of an aqueous solution to the solids content of the resulting polymerized latex to achieve a solids concentration of 15%, and the mixture was stirred at 95°C for 5 minutes to salt out and coagulate. The resulting coagulated solution was dehydrated by a Nutsche dehydration method and reslurried with 10 times the amount of water relative to the solids content. It was then further dehydrated by a Nutsche dehydration method and dried in a drying oven at 75°C for 12 hours to obtain a white powdery (meth)acrylic polymer A [a graft copolymer containing crosslinked (meth)acrylic polymer particles (a) and a non-crosslinked methacrylic polymer component (b)]. The volume-average particle diameter was 131 nm and the weight-average molecular weight was 683,496.

[0119] [Table 1]

[0120] (polymerization conversion rate) The polymerization conversion rate of the polymer obtained by polymerization was determined using the following method. Approximately 2 g of latex containing the polymer was collected from the polymerization system and precisely weighed. It was then dried in a hot air dryer at 120°C for 1 hour, and the weight after drying was precisely weighed as the solid content. Next, the ratio of the weighing results before and after drying was calculated as the solid content ratio in the sample. Finally, the polymerization conversion rate was calculated using this solid content ratio using the following formula. In this formula, the multifunctional monomer and chain transfer agent were treated as charged monomers. Polymerization conversion rate (%) = {(total weight of raw materials charged × solid content ratio - total weight of raw materials other than water and monomers) / weight of charged monomer} × 100

[0121] (Production Example 2) Production of (meth)acrylic polymer B An 8-L glass reactor equipped with a paddle stirrer was charged with 143 parts of deionized water, 0.01 parts of sodium hydroxide, and 0.15 parts of DSS. The contents were then stirred at 175 rpm and the reactor was heated to 85°C while purging with nitrogen. After reaching 85°C, 0.022 parts of NPS and 0.0005 parts of SFS were added. A monomer mixture consisting of 85 parts of MMA, 5 parts of 2-EHMA, and 10 parts of PhMI was then continuously added to the reactor over 80 minutes, and the reaction was carried out. At 15 minutes after the addition of the monomer mixture, 0.55 parts of DSS was added dropwise and continuously added to the reactor. The stirring speed was increased to 200 rpm 55 minutes after the start of the monomer mixture addition and to 240 rpm at 70 minutes. After the addition of the monomer mixture was completed, a mixed aqueous solution of 0.0055 parts of ED and 0.0015 parts of FeSO4, 0.03 parts of SFS, 0.3 parts of DSS, and 0.03 parts of t-BHP were added to the reactor in this order. The reaction was then continued for 60 minutes to complete the polymerization, yielding a polymerized latex. The polymerization conversion was 99.9%. Next, 3.0 parts of a coagulant (calcium chloride or magnesium chloride) based on the solid content of the obtained polymerized latex was added in the form of an aqueous solution so that the solid content concentration of the latex solution was 15%, and then the mixture was stirred at 95°C for 5 minutes to salt out and coagulate. The obtained coagulated liquid was dehydrated by a Nutsche dehydration method and reslurried with 10 times the amount of water based on the solid content, then further dehydrated by a Nutsche dehydration method and dried in a drying oven at 75°C for 12 hours to obtain a white powdery (meth)acrylic polymer B. The volume average particle size was 196 nm and the weight average molecular weight was 1,600,000.

[0122] (Examples 1 to 4 and Comparative Examples 1 to 5) Production of Resin Films According to the description in Table 2, a resin film was produced using the (meth)acrylic polymer A or B obtained in Production Example 1 or 2 in the following procedure. Methylene chloride (MC), a mixed solvent of methylene chloride / methanol (MC / MeOH), or a mixed solvent of methylene chloride / ethanol (MC / EtOH) was prepared, and the (meth)acrylic polymer A or B was added to the solvent so that the solid content was 20 wt %, followed by stirring and mixing with a stirrer tip to prepare a dope. The content of alcohol (methanol or ethanol) in the mixed solvent is as shown in Table 2. This dope was applied to a glass plate using a bar coater to a wet film thickness of 0.25 mm, and left to stand at room temperature in a place not exposed to wind for 8 minutes to prepare a semi-dried film. After peeling the semi-dried film from the glass plate, it was quickly fixed to a metal frame of an appropriate size using heat-resistant tape and clips, and dried in a hot air dryer at 160°C for 15 minutes. After drying, it was removed from the metal frame to obtain each resin film.

[0123] (Haze measurement of resin film) The haze of each resin film was measured using a HZ-V3 haze meter manufactured by Suga Test Instruments Co., Ltd. in accordance with JIS-K7105. On the other hand, both sides of each resin film were sandwiched between glycerin and then glass, and the same measurement was carried out, and the obtained value was taken as the internal haze.

[0124] (YI measurement of resin film) The YI of each resin film was measured using an SC-P spectrophotometer manufactured by Suga Test Instruments Co., Ltd.

[0125] (Measurement of the number of foam marks on the resin film) The surface of each resin film was observed using a BX51 polarizing microscope manufactured by Olympus Corporation, and the number of bubble marks with a diameter of 30 μm or less was counted within a square with a side length of 100 μm in the enlarged micrograph. Based on the number, evaluation was performed according to the following criteria. 1: 0 to 2 bubble marks 2: 3 to 5 bubble marks 3: 6 to 10 bubble marks 4: 10 to 20 bubble marks 5: 20 or more bubble marks The results of the above measurements are shown in Table 2. [Table 2]

[0126] Table 2 shows that in Examples 1 to 3, in which resin films were formed from a dope containing a coagulated product of (meth)acrylic polymer A synthesized by emulsion polymerization and ethanol, the haze was lower and the number of bubble marks was reduced compared to Comparative Examples 1 to 3, in which dopes containing no ethanol were used. The same is true for Example 4, in which a resin film was formed from a dope containing a coagulated product of (meth)acrylic polymer B synthesized by emulsion polymerization and ethanol, and it can be seen that the haze was lower and the number of bubble marks was reduced compared to Comparative Examples 4 and 5, in which dopes not containing ethanol were used.

Claims

1. a step of obtaining a latex of a (meth)acrylic polymer by emulsion polymerization; a step of adding a coagulant to the latex to coagulate the (meth)acrylic polymer, and then separating the (meth)acrylic polymer from the aqueous phase; A step of mixing the separated (meth)acrylic polymer with a solvent containing ethanol to form a dope; and a step of casting the dope onto a surface of a support and then evaporating the solvent; the (meth)acrylic polymer is a graft copolymer containing crosslinked (meth)acrylic polymer particles (a) and a non-crosslinked methacrylic polymer component (b), A method for producing a resin film, wherein the crosslinked (meth)acrylic polymer particles (a) account for 1% by weight or more and less than 50% by weight of the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b).

2. The method for producing a resin film according to claim 1 , wherein the coagulant is an inorganic salt or an acid.

3. The method for producing a resin film according to claim 2 , wherein the inorganic salt is a calcium salt or a magnesium salt.

4. The method for producing a resin film according to any one of claims 1 to 3, wherein the content of ethanol in the solvent is 1 to 25% by weight.

5. The method for producing a resin film according to any one of claims 1 to 4, wherein the solvent further contains methylene chloride.

6. The method for producing a resin film according to any one of claims 1 to 5, wherein the non-crosslinked methacrylic polymer component (b) contains 70% by weight or more and 99% by weight or less of methyl methacrylate units.

7. The method for producing a resin film according to any one of claims 1 to 6, wherein the non-crosslinked methacrylic polymer component (b) contains at least one of a substituted or unsubstituted maleimide unit and a methacrylic acid ester unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure.

8. A solidified product of a (meth)acrylic polymer synthesized by emulsion polymerization, and a solvent comprising ethanol; the (meth)acrylic polymer is a graft copolymer containing crosslinked (meth)acrylic polymer particles (a) and a non-crosslinked methacrylic polymer component (b), A dope in which 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.

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

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