Acrylic resin powder and film

Abstract

The present invention provides acrylic resin particles in which an aqueous solution obtained by mixing the acrylic resin particles and ultrapure water at a weight ratio of 1: 10, placing the mixture in a pressure container, heating the mixture at 100 DEG C for 20 hours, and then filtering the mixture, has an electrical conductivity of 300 [mu] S / cm or less at 23 DEG C and 50% RH, and in which the content of volatile components in the acrylic resin particles is less than 1.0 wt%.

Description

Technical Field

[0001] The present invention relates to an acrylic resin powder, a coating solution, a method for producing a coating solution, a film, and a method for producing a film. Background Art

[0002] Conventionally, as a polarizer protection film for a liquid crystal display, a triacetyl cellulose (TAC) film has been used. However, since the TAC film has high hygroscopicity, with the increase in the size and high definition of the screen, problems such as warping of the liquid crystal panel and deterioration of image quality during transportation have become increasingly obvious.

[0003] On the other hand, acrylic resin films have attracted attention as alternative films to TAC films because of their excellent optical properties and low hygroscopicity.

[0004] In Patent Document 1, as an acrylic resin powder for film production based on the solution casting method, a powder is described that contains: an acrylic polymer having methyl methacrylate units in an amount of 30 to 100% by weight and other monomer units copolymerizable therewith in an amount of 0 to 70% by weight as structural units; and an ionic emulsifier. Among them, the content of the ionic emulsifier is 0.1 part by weight to 10 parts by weight with respect to 100 parts by weight of the acrylic polymer.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: WO 2022 / 124402 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, the acrylic resin powder contains hygroscopic substances used during polymerization (for example, ferrous sulfate heptahydrate, sodium formaldehyde sulfoxylate, sodium persulfate, sodium hydroxide, disodium ethylenediaminetetraacetate, anhydrous disodium hydrogen phosphate, etc.). Therefore, when producing a film, after the solvent volatilizes from the coating solution cast on the surface of the support, polar substances such as moisture adsorbed by the hygroscopic substances sometimes volatilize, resulting in foaming, that is, foaming marks are generated in the film. In addition, if the film is stored in a high-temperature and high-humidity environment for a long time, the hygroscopic substances contained in the film will absorb moisture, sometimes resulting in a decrease in the transparency of the film.

[0010] An object of the present invention is to provide an acrylic resin powder that can suppress foaming marks in the film and a decrease in transparency in a high-temperature and high-humidity environment.

[0011] Solutions to the Problems

[0012] (1) An acrylic resin powder, wherein an aqueous solution obtained by mixing the acrylic resin powder and ultrapure water at a weight ratio of 1:10, placing the mixture in a pressure-resistant container, heating at 100 °C for 20 hours, and then filtering has a conductivity of 300 μS / cm or less at 23 °C and 50% RH, and the content of volatile components in the acrylic resin powder is less than 1.0% by weight.

[0013] (2) The acrylic resin powder according to (1), having a glass transition temperature of 110 °C or higher.

[0014] (3) The acrylic resin powder according to (1) or (2), wherein the acrylic resin contained in the acrylic resin powder has a structural unit containing a heterocycle in the main chain.

[0015] (4) The acrylic resin powder according to (3), wherein the acrylic resin has a structural unit derived from N-substituted maleimide.

[0016] (5) The acrylic resin powder according to (4), wherein the N-substituted maleimide is N-cyclohexyl maleimide or N-phenyl maleimide.

[0017] (6) The acrylic resin powder according to (4) or (5), wherein the content of sulfate ions in the aqueous solution is 350 ppm or less.

[0018] (7) The acrylic resin powder according to any one of (1) to (6), having a weight average molecular weight of 400,000 or more and 4,000,000 or less.

[0019] (8) The acrylic resin powder according to any one of (1) to (7), which is used for manufacturing a film based on the solution casting method.

[0020] (9) A coating solution, which dissolves the acrylic resin powder according to any one of (1) to (8) in a solvent.

[0021] (10) A method for manufacturing a coating solution, wherein the acrylic resin powder according to any one of (1) to (8) is dissolved in a solvent to manufacture a coating solution.

[0022] (11) A film, which is manufactured by casting the coating solution according to (9) onto the surface of a support and then volatilizing the solvent.

[0023] (12) A method for manufacturing a film, wherein the coating solution according to (9) is cast onto the surface of a support and then the solvent is volatilized to manufacture a film.

[0024] (13) A film comprising an acrylic resin, wherein the acrylic resin has a structural unit containing a heterocycle in the main chain, a glass transition temperature of 110 °C or higher, a weight average molecular weight of 400,000 or higher and 4,000,000 or lower, and the change ΔHz in haze before and after storage for 96 hours under the conditions of 85 °C and 95% RH is 2.5% or lower when the thickness of the film is 40 μm, and the change ΔYI in yellowness before and after storage for 96 hours under the conditions of 85 °C and 95% RH is 3.5 or lower when the thickness of the film is 40 μm.

[0025] (14) The film according to (13), wherein the haze Hz when the thickness is 40 μm is 2% or lower, and the yellowness YI when the thickness is 40 μm is 2.0 or lower.

[0026] (15) The film according to (13) or (14), wherein the acrylic resin has a structural unit derived from N-substituted maleimide.

[0027] (16) The film according to (15), wherein the N-substituted maleimide is N-cyclohexyl maleimide or N-phenyl maleimide.

[0028] Effects of the Invention

[0029] According to the present invention, an acrylic resin powder can be provided, which can suppress the foaming marks of the film and the decrease in transparency under high temperature and high humidity environments. Detailed Embodiments

[0030] Hereinafter, embodiments of the present invention will be described.

[0031] (Acrylic Resin Powder)

[0032] The acrylic resin powder of the present embodiment is used, for example, in the production of films based on the solution casting method, and the content of volatile components is less than 1.0% by weight. Among them, the content of volatile components is preferably less than 0.5% by weight. The conductivity of the aqueous solution obtained by mixing the acrylic resin powder of the present embodiment and ultrapure water at a weight ratio of 1:10, placing them in a pressure-resistant container, heating at 100°C for 20 hours, and then filtering is 300 μS / cm or less at 23°C and 50% RH. When the conductivity of the above aqueous solution is 300 μS / cm or less at 23°C and 50% RH, the content of hygroscopic substances in the acrylic resin powder of the present embodiment will decrease, so that the foaming marks of the film and the decrease in transparency in a high-temperature and high-humidity environment can be suppressed. From the viewpoint of further suppressing the foaming marks of the film and the decrease in transparency in a high-temperature and high-humidity environment, the conductivity of the above aqueous solution is preferably less than 300 μS / cm at 23°C and 50% RH, more preferably 290 μS / cm or less, further preferably 280 μS / cm or less, and particularly preferably 260 μS / cm or less.

[0033] In this specification and claims, the acrylic resin refers to a polymer of a monomer having an acryloyl group and / or a monomer having a methacryloyl group. At this time, the acrylic resin can be either a homopolymer or a copolymer. In the case where the acrylic resin is a copolymer, the acrylic resin can be a copolymer of a monomer not having an acryloyl group or a methacryloyl group.

[0034] In addition, the powder or granule refers to a powder having a volume average particle size of 0.01 mm or more and less than 0.1 mm and / or a granule having a volume average particle size of 0.1 mm or more and less than 10 mm.

[0035] From the viewpoint of the heat resistance of the film, the glass transition temperature of the acrylic resin powder of the present embodiment is preferably 110°C or higher, more preferably 114°C or higher, further preferably 115°C or higher, still further preferably 117°C or higher, still further preferably 119°C or higher, still further preferably 120°C or higher, still further preferably 121°C or higher, still further preferably 122°C or higher, particularly preferably 125°C or higher, and most preferably 126°C or higher.

[0036] From the viewpoints of the toughness and film-forming property of the film, the weight-average molecular weight of the acrylic resin powder particles of the present embodiment is preferably 400,000 or more and 4,000,000 or less, more preferably 500,000 or more and 3,500,000 or less, still more preferably 500,000 or more and 3,000,000 or less, and particularly preferably 600,000 or more and 3,000,000 or less. In addition, the weight-average molecular weight of the acrylic resin powder particles of the present embodiment may be 500,000 or more and 2,500,000 or less, or may be 500,000 or more and 2,000,000 or less. Further, the weight-average molecular weight of the acrylic resin powder particles of the present embodiment may be 700,000 or more, or may be 800,000 or more.

[0037] From the viewpoint of suppressing the foaming marks on the film, the acrylic resin powder particles of the present embodiment preferably contain an ionic emulsifier.

[0038] (Acrylic resin)

[0039] In the acrylic resin constituting the acrylic resin powder particles of the present embodiment, for example, the content of the structural unit derived from methyl methacrylate is 30% by weight or more, and the content of the structural unit derived from other monomers copolymerizable with methyl methacrylate (hereinafter referred to as other monomers) is 70% by weight or less.

[0040] From the viewpoints of the appearance and weather resistance of the film, the content of the structural unit derived from methyl methacrylate in the acrylic resin is preferably 50% by weight or more, more preferably 60% by weight or more, still more preferably 70% by weight or more, and particularly preferably 80% by weight or more. In addition, from the viewpoints of the optical properties and heat resistance of the film, the content of the structural unit derived from methyl methacrylate in the acrylic resin is preferably 99.9% by weight or less, more preferably 99% by weight or less, still more preferably 97% by weight or less, and particularly preferably 95% by weight or less.

[0041] It should be noted that the acrylic resin may contain a structural unit derived from a polyfunctional monomer having two or more polymerizable functional groups in the molecule.

[0042] Examples of other monomers include (meth)acrylate esters having 1 to 20 carbon atoms in the ester moiety (excluding methyl methacrylate), such as ethyl methacrylate, propyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, benzyl methacrylate, octyl methacrylate, stearyl methacrylate, glycidyl methacrylate, cyclohexylmethyl glycidyl methacrylate, dimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, dicyclopentyl 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, cyclohexylmethyl glycidyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate; (meth)acrylamides such as methacrylamide, N-hydroxymethylmethacrylamide, acrylamide, N-hydroxymethylacrylamide; carboxylic acids such as methacrylic acid and acrylic acid and their salts; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl aromatics such as styrene, α-methylstyrene, monochlorostyrene, and dichlorostyrene; N-substituted maleimides 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; olefins such as ethylene, propylene, butene, butadiene, and isobutene. Two or more of them can be used in combination. Among them, (meth)acrylate esters having 1 to 20 carbon atoms in the ester moiety (excluding methyl methacrylate), vinyl aromatics, and N-substituted maleimides are preferred, and (meth)acrylate esters having 1 to 20 carbon atoms in the ester moiety (excluding methyl methacrylate) and N-substituted maleimides are particularly preferred.

[0043] Here, when an N-substituted maleimide is used as other monomer, if a persulfate is used as a polymerization initiator, the yellowness change of the film may become large. Therefore, the sulfate ion content in the aqueous solution used in the measurement of the conductivity at 23 °C and 50% RH is preferably 350 ppm or less, more preferably 150 ppm or less, and particularly preferably 100 ppm or less. Here, the sulfate ion is generated by the hydrolysis of the persulfate.

[0044] Since the acrylic resin powder of the present embodiment is used for film production based on the solution casting method, other monomers preferably include drying-promoting comonomers that can increase the solvent evaporation rate.

[0045] Examples of the drying-promoting comonomer include N-substituted maleimides, methacrylates in which the ester moiety is a primary or secondary hydrocarbon group having 2 to 8 carbon atoms or an aromatic hydrocarbon group, methacrylates in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms with a condensed ring structure, methacrylates in which the ester moiety is a linear or branched group containing an ether bond, vinyl aromatics, etc. Two or more of them can also be used in combination. When using the drying-promoting comonomer, the heat resistance of the acrylic resin becomes higher, and when manufacturing a film, the rate at which the solvent volatilizes from the coating solution cast on the surface of the support becomes faster.

[0046] Examples of the N-substituted maleimide include N-phenylmaleimide, N-benzylmaleimide, N-cyclohexylmaleimide, N-methylmaleimide, etc. Among them, N-phenylmaleimide and N-cyclohexylmaleimide are preferred.

[0047] Examples of the methacrylate 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 them, ethyl methacrylate, n-butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, and benzyl methacrylate are preferred.

[0048] Examples of the methacrylate in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms with a condensed ring structure include dicyclopentyl methacrylate, isobornyl methacrylate, etc. The number of carbon atoms of the saturated hydrocarbon group is preferably 8 to 14, more preferably 9 to 12. In addition, the condensed ring structure is preferably a structure obtained by condensing two five-membered rings through three consecutive carbon atoms.

[0049] Examples of the methacrylate in which the ester moiety is a linear or branched group containing an ether bond include 2-methoxyethyl methacrylate, etc.

[0050] Examples of the vinyl aromatic include styrene, α-methylstyrene, monochlorostyrene, dichlorostyrene, etc. Among them, styrene is preferred.

[0051] The content ratio of structural units derived from other monomers in the acrylic resin is preferably 50% by weight or less, more preferably 40% by weight or less, still more preferably 30% by weight or less, and particularly preferably 20% by weight or less. On the other hand, from the aspect of being able to adjust the optical properties and heat resistance of the film, the content ratio of structural units derived from other monomers in the acrylic resin is preferably 0.1% by weight or more, more preferably 1% by weight or more, still more preferably 3% by weight or more, and particularly preferably 5% by weight or more.

[0052] From the viewpoint of the heat resistance of the film, the acrylic resin preferably has a structural unit containing a heterocycle in the main chain. Examples of the heterocycle include, for example, a glutarimide ring, a lactone ring, a maleic anhydride ring, a maleimide ring, a glutaric anhydride ring, etc., and two or more thereof can also be used in combination. Among them, from the viewpoints of the heat resistance and optical properties of the film, a glutarimide ring, a lactone ring, and a maleimide ring are preferred.

[0053] (Polymerization method of acrylic resin)

[0054] The polymerization method of the monomer constituting the acrylic resin is not particularly limited. From the viewpoints of the degree of freedom in designing the acrylic resin structure, the simplicity of polymerization, productivity, etc., emulsion polymerization and suspension polymerization are preferred. Here, when N-substituted maleimide is used as other monomers, there is a tendency that the unreacted remaining N-substituted maleimide hydrolyzes and causes the acrylic resin to be colored. From the viewpoint of reducing the residual amount of N-substituted maleimide, emulsion polymerization is preferred. At this time, N-substituted maleimide and monomers other than N-substituted maleimide constituting the acrylic resin can be pre-dissolved and mixed, and the obtained mixture can be supplied to a reactor for reaction. Alternatively, N-substituted maleimide can be directly supplied to a reactor containing monomers other than N-substituted maleimide constituting the acrylic resin, and dissolved and mixed in the reactor for reaction. Here, the mixture formed by dissolving and mixing N-substituted maleimide and monomers other than N-substituted maleimide constituting the acrylic resin can be directly supplied to a reactor for reaction. Among them, for example, when the polymerization reactivity of N-substituted maleimide and monomers other than N-substituted maleimide constituting the acrylic resin is low, there is a tendency that N-substituted maleimide easily remains. Therefore, after supplying the mixture to the reactor for reaction, monomers other than N-substituted maleimide constituting the acrylic resin are further supplied for reaction, whereby N-substituted maleimide can be effectively polymerized, and the residual amount of N-substituted maleimide that causes the acrylic resin to be colored can be reduced.

[0055] From the viewpoint of suppressing the foaming marks on the film, the acrylic resin is preferably produced by emulsion polymerization of monomers in the presence of an ionic emulsifier. At this time, the ionic emulsifier can be added all at once or sequentially. For example, when the latex obtained by emulsion polymerization of monomers in the presence of an ionic emulsifier is dried without washing, an acrylic resin powder containing the ionic emulsifier can be obtained.

[0056] The ionic emulsifier can be any one of a cationic emulsifier, an anionic emulsifier, and an amphoteric emulsifier, and an anionic emulsifier is preferred.

[0057] Examples of the anionic emulsifier include dialkyl sulfosuccinates, alkane sulfonates, α-olefin sulfonates, alkylbenzene sulfonates, naphthalene sulfonate-formaldehyde condensates, alkylnaphthalene sulfonates, N-methyl-N-acyl taurates, etc. Among them, from the viewpoints of suppressing the foaming marks on the film and the polymerization stability of emulsion polymerization, dialkyl sulfosuccinates and alkylbenzene sulfonates are preferred.

[0058] Examples of the anionic emulsifier include lithium salts, sodium salts, potassium salts, calcium salts, magnesium salts, etc. Among them, from the viewpoint of the foaming marks on the film, lithium salts, sodium salts, and potassium salts are preferred.

[0059] The weight ratio of the ionic emulsifier to the monomer is preferably 0.1% or more and 10% or less, more preferably 0.3% or more and 7% or less, further preferably 0.4% or more and 6% or less, still further preferably 0.5% or more and 5% or less, particularly preferably 0.8% or more and 3% or less, and most preferably 1% or more and 3% or less. When the weight ratio of the ionic emulsifier to the monomer is 10% or less, the foaming marks on the film are suppressed, and when it is 10% or less, the polymerization stability of emulsion polymerization is improved.

[0060] When polymerizing the monomers, a polymerization initiator can be used. Examples of the polymerization initiator include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; organic peroxides such as tert-butyl hydroperoxide, tert-butyl peroxyisopropyl carbonate, cumene hydroperoxide, p-menthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, bis(3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, and benzoyl peroxide.

[0061] When using an organic peroxide as a polymerization initiator, the organic peroxide can be decomposed thermally to generate free radicals, thereby polymerizing the monomers. Additionally, an oxidizing agent such as ferrous sulfate and a reducing agent such as sodium formaldehyde sulfoxylate can be combined with the organic peroxide to generate free radicals at low temperatures, enabling redox polymerization of the monomers (for example, see Japanese Patent No. 3960631).

[0062] When polymerizing monomers, a chain transfer agent can be used to adjust the molecular weight of the acrylic resin. Examples of the chain transfer agent include alkyl mercaptans, alkyl sulfides, alkyl disulfides, mercaptoacetates such as 2-ethylhexyl mercaptoacetate; mercapto acids such as α-methylstyrene dimer and β-mercaptopropionic acid; aromatic mercaptans such as benzyl mercaptan, thiophenol, thio-p-cresol, and thionaphthol.

[0063] (Graft copolymer)

[0064] The acrylic resin constituting the acrylic resin powder of the present embodiment can be a graft copolymer having a core / shell structure. Thereby, mechanical strengths such as the bending resistance and crack resistance of the film are improved.

[0065] A graft copolymer having a core / shell structure can be obtained, for example, by polymerizing a monomer composition in the presence of crosslinked polymer particles (core layer) to form a shell layer. The core layer and the shell layer can each be composed of one layer or two or more layers. As a method for producing a graft copolymer having a core / shell structure, there is no particular limitation, and examples thereof include the following method: polymerizing a monomer composition mainly composed of an acrylate in the presence of a crosslinking agent to form rubber-like polymer particles, and then polymerizing a monomer composition mainly composed of a methacrylate.

[0066] A graft copolymer having a core / shell structure can be obtained, for example, by subjecting a monomer composition to emulsion polymerization. From the viewpoint of suppressing the foaming marks on the film, it is preferable to subject the monomer composition to emulsion polymerization in the presence of an ionic emulsifier. Thereby, the mutual aggregation of the graft copolymer particles having a core / shell structure is suppressed, and thus, on the basis of good dispersion, the stability of the coating solution over time is improved.

[0067] (Coating solution)

[0068] The coating solution of the present embodiment dissolves the acrylic resin powder of the present embodiment in a solvent. As the solvent, as long as it is a good solvent for the acrylic resin powder of the present embodiment, there is no particular limitation, and examples thereof include chlorinated organic solvents such as dichloromethane, and non-chlorinated organic solvents such as methyl acetate, ethyl acetate, acetone, methyl ethyl ketone, and tetrahydrofuran. Among them, from the viewpoint of the solubility of the acrylic resin powder of the present embodiment, dichloromethane is preferred.

[0069] The solvent preferably contains an alcohol. Although the alcohol is a poor solvent for the acrylic resin powder particles of the present embodiment, it not only improves the drying efficiency of the coating solution of the present embodiment, but also improves the adhesion between the film and other substrates such as polarizers. The alcohol is not particularly limited, and examples thereof include linear or branched aliphatic alcohols having 1 to 4 carbon atoms. Among them, ethanol and methanol are preferred.

[0070] The content of the alcohol in the solvent is preferably 1% by weight or more and 25% by weight or less, more preferably 2% by weight or more and 20% by weight or less, and still more preferably 3% by weight or more and 15% by weight or less.

[0071] The coating solution of the present embodiment may further contain, as needed, known additives such as light stabilizers, ultraviolet absorbers, heat stabilizers, antioxidants, matting agents, light diffusing agents, colorants, dyes, pigments, antistatic agents, heat ray reflecting materials, lubricants, plasticizers, fillers, etc., styrene resins such as acrylonitrile-styrene resins and styrene-maleic anhydride resins, polycarbonate resins, polyvinyl acetal resins, cellulose acylate resins, fluororesins such as polyvinylidene fluoride and poly(fluoroalkyl) (meth)acrylate resins, silicone resins, polyolefin resins, polyethylene terephthalate resins, polybutylene terephthalate resins, and other resins. In addition, it may also contain inorganic fine particles having birefringence (see Japanese Patent No. 3648201 and Japanese Patent No. 4336586), low molecular weight compounds having birefringence and a molecular weight of 5000 or less, preferably 1000 or less (see Japanese Patent No. 3696649), etc.

[0072] The coating solution of the present embodiment is produced by dissolving the acrylic resin powder particles of the present embodiment in a solvent. When dissolving the acrylic resin powder particles of the present embodiment in a solvent, the temperature and pressure can be appropriately adjusted. After dissolving the acrylic resin powder particles of the present embodiment in a solvent, post-treatments such as filtration and defoaming can be carried out as needed.

[0073] (Film)

[0074] The thin film of the present embodiment is manufactured by casting the coating solution of the present embodiment onto the surface of a support and then volatilizing the solvent. For example, first, the coating solution of the present embodiment pumped by a liquid delivery pump is cast from the slit of a pressure die onto the surface (mirror surface) of a support such as an annular belt or a drum made of metal or synthetic resin to form a cast film. Then, the cast film is heated on the support to volatilize the solvent, thereby manufacturing the thin film of the present embodiment. The support is not particularly limited, and examples thereof include a PET film and a glass plate. The temperature conditions for volatilizing the solvent can be appropriately determined according to the boiling point of the solvent used. Then, the thin film is peeled off from the support, and post-treatments such as drying, heating, and stretching can be further performed as needed.

[0075] The thickness of the thin film of the present embodiment is preferably 5 μm or more and 200 μm or less, more preferably 5 μm or more and 100 μm or less, and particularly preferably 10 μm or more and 80 μm or less. When the thickness of the thin film of the present embodiment is 5 μm or more, the operability and the function as a protective film are enhanced. When it is 200 μm or less, the uniformity of optical properties and the drying speed are improved.

[0076] The thin film of the present embodiment contains an acrylic resin. The acrylic resin has a structural unit containing a heterocycle in the main chain, a glass transition temperature of 110 °C or more, and a weight average molecular weight of 400,000 or more and 4,000,000 or less.

[0077] Here, when the thickness of the thin film of the present embodiment is 40 μm, the change ΔHz in haze before and after storage for 96 hours under the conditions of 85 °C and 95% RH is 2.5% or less, preferably 2% or less, and more preferably 1.5% or less. When ΔHz is 2.5% or less, the thin film of the present embodiment can be suitably applied to optical members that require light transmittance.

[0078] At this time, the haze Hz of the thin film of the present embodiment when the thickness is 40 μm is preferably 2% or less, more preferably 1.5% or less, still more preferably 1% or less, further preferably 0.8% or less, still further preferably 0.6% or less, and particularly preferably 0.4% or less. When Hz is 2% or less, the thin film of the present embodiment can be suitably applied to optical members that require light transmittance.

[0079] In addition, when the thickness of the thin film of the present embodiment is 40 μm, the change ΔYI in yellowness index before and after storage for 96 hours under the conditions of 85 °C and 95% RH is 3.5 or less, preferably 3.0 or less, and more preferably 2.0 or less. When ΔYI is 3.5 or less, the thin film of the present embodiment can be suitably applied to optical members that require light transmittance.

[0080] At this time, when the thickness of the film of the present embodiment is 40 μm, the yellowness index YI is preferably 2.0 or less, more preferably 1.5 or less, still more preferably 1.0 or less, further preferably 0.8 or less, and even more preferably 0.65% or less, and particularly preferably 0.5% or less. When YI is 2.0 or less, the film of the present embodiment can be suitably applied to an optical member that requires translucency.

[0081] The film of the present embodiment can be suitably used as an optical film for a display, for example. Examples of the optical film for a display include protective films such as a polarizer protective film.

[0082] When the film of the present embodiment is used as a polarizer protective film, the film of the present embodiment preferably has small optical isotropy. In particular, the film of the present embodiment preferably has small optical isotropy not only in the in-plane direction (length direction, width direction) but also in the thickness direction. Specifically, the absolute value of the in-plane retardation of the film of the present embodiment is preferably 10 nm or less, more preferably 5 nm or less, and particularly preferably 3 nm or less. In addition, the absolute value of the retardation in the thickness direction of the film of the present embodiment is preferably 50 nm or less, more preferably 20 nm or less, further preferably 10 nm or less, and particularly preferably 5 nm or less.

[0083] Here, the retardation is an index value calculated based on birefringence, and the in-plane retardation (Re) and the retardation in the thickness direction (Rth) can be calculated by the following formulas, respectively.

[0084] Re = (nx - ny) × d

[0085] Rth = ((nx + ny) / 2 - nz) × d

[0086] (In the formulas, nx, ny, and nz represent the refractive indices in the respective axial directions when the in-plane extension direction (orientation direction of the polymer chain) of the molded body is set as the X axis, the direction perpendicular to the X axis is set as the Y axis, and the thickness direction of the film is set as the Z axis, d is the thickness of the molded body, and nx - ny is the orientation birefringence.)

[0087] In an ideal molded body having complete optical isotropy, the in-plane retardation (Re) and the retardation in the thickness direction (Rth) are 0. It should be noted that the MD direction of the molded body is set as the X axis, but in the case of a stretched molded body, the stretching direction is set as the X axis.

[0088] The orientation birefringence of the film of the present embodiment is preferably -2.6×10 -4 or more and 2.6×10 -4 or less, more preferably -1.7×10 -4 or more and 1.7×10 -4Hereinafter, it is further preferably -1.0×10 -4 or more and 1.0×10 -4 or less, particularly preferably -0.5×10 -4 or more and 0.5×10 -4 or less, and most preferably -0.2×10 -4 or more and 0.2×10 -4 or less. When the orientation birefringence of the film of the present embodiment is -2.6×10 -4 or more and 2.6×10 -4 or less, the birefringence during the molding process of the film of the present embodiment is suppressed, and the optical properties are stable. Therefore, the film of the present embodiment can be used as an optical film used in a liquid crystal display or the like.

[0089] The photoelastic constant of the film of the present embodiment is preferably -6×10 -12 Pa -1 or more and 6×10 -12 Pa -1 or less, more preferably -4×10 -12 Pa -1 or more and 4×10 -12 Pa -1 or less, further preferably -2×10 -12 Pa -1 or more and 2×10 - 12 Pa -1 or less, further preferably -1×10 -12 Pa -1 or more and 1×10 -12 Pa -1 or less, particularly preferably -0.5×10 -12 Pa -1 or more and 0.5×10 -12 Pa -1 or less, and most preferably -0.2×10 -12 Pa -1 or more and 0.2×10 -12 Pa -1 or less. When the photoelastic constant of the film of the present embodiment is -6×10 -12 Pa -1 or more and 6×10 -12 Pa -1 or less, even if the film of the present embodiment is stressed and deformed, the birefringence is suppressed, so the optical isotropy becomes smaller. For example, when the film of the present embodiment is used as a polarizer protection film, even if the liquid crystal panel is deformed during transportation due to the influence of moisture and temperature in the air, the optical properties are maintained, so the image quality is not easily degraded.

[0090] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and the above embodiments can be appropriately changed within the scope of the gist of the present invention.

[0091] Example

[0092] The following describes the examples of the present invention. However, the present invention is not limited to the examples. It should be noted that the following abbreviations represent the following substances respectively. In addition, the amounts of each substance are based on weight and represent pure components (solid components).

[0093] Monomer

[0094] BA: Butyl acrylate

[0095] ALMA: Allyl methacrylate

[0096] MMA: Methyl methacrylate

[0097] n-BMA: n-Butyl methacrylate

[0098] PhMI: N-Phenylmaleimide

[0099] ChMI: N-Cyclohexylmaleimide

[0100] 2-EHMA: 2-Ethylhexyl methacrylate

[0101] Anionic emulsifier

[0102] SDSS: Dioctyl sulfosuccinate

[0103] Polymerization initiator

[0104] t-BHP: tert-Butyl hydroperoxide

[0105] FeSO4: Ferrous sulfate heptahydrate

[0106] SFS: Sodium formaldehyde sulfoxylate

[0107] NPS: Sodium persulfate

[0108] LPO: Lauroyl peroxide

[0109] Chain transfer agent

[0110] 2-EHTG: 2-Ethylhexyl thioglycolate

[0111] Suspending agent

[0112] HPMC: Hydroxypropyl methylcellulose; METOLOSE 60SH50 (manufactured by Shin-Etsu Chemical Co., Ltd.)

[0113] Others

[0114] EDTA: Disodium Ethylenediaminetetraacetate

[0115] DSHP: Disodium Hydrogen Phosphate Anhydrous

[0116] (Example 1)

[0117] Deionized water (110 parts), sodium hydroxide (0.004 parts), and SDSS (0.6 parts) were charged into an 8 L glass reactor equipped with a paddle stirrer, and the mixture was stirred at a rotation speed of 175 rpm while the inside of the reactor was purged with nitrogen and heated to 60°C. Then, a mixture of BA (8.5 parts) and ALMA (0.043 parts) was added to the reactor, and then t-BHP (0.006 parts), EDTA (0.0055 parts), FeSO4 (0.0015 parts), and SFS (0.005 parts) were successively added to the reactor to carry out emulsion polymerization of BA and ALMA, obtaining a latex containing crosslinked polymer particles (core). Here, after the addition of the mixture was completed, emulsion polymerization of BA and ALMA was carried out for 30 minutes. At this time, the polymerization conversion rate was 99.5%, and the volume average particle size was Then, a mixture of MMA (83.5 parts), n-BMA (1 part), PhMI (7 parts), and 2-EHTG (0.037 parts) was continuously added to the reactor over 70 minutes to carry out emulsion polymerization of MMA, n-BMA, and PhMI to form a shell layer. At this time, SDSS (0.3 parts) was continuously added to the reactor in a form linked to the addition of the mixture. In addition, the rotation speed was adjusted to 200 rpm at the start of the addition of the mixture, adjusted to 235 rpm 10 minutes after the start of the addition, adjusted to 260 rpm 20 minutes after the start, adjusted to 300 rpm 35 minutes after the start, and adjusted to 325 rpm 50 minutes after the start. Then, SFS (0.0052 parts), SDSS (0.2 parts), and t-BHP (0.005 parts) were successively added to the reactor, and after heating to 90°C, the reaction was carried out for 120 minutes to complete the polymerization, obtaining a latex containing a graft copolymer having a core / shell structure. At this time, the polymerization conversion rate was 99.9%, and the volume average particle size was Then, the latex was evaporated to dryness in a hot air oven at 50°C for 24 hours to obtain white acrylic resin powder particles with a volume average particle size of 120 μm. The content of volatile components in the acrylic resin powder particles was less than 0.5% by weight. The weight average molecular weight of the acrylic resin powder particles was 791,000.

[0118] (Example 2)

[0119] Except for changing PhMI to ChMI in Example 1, white acrylic resin powder particles with a volume average particle diameter of 120 μm were obtained in the same manner as in Example 1. The content rate of volatile components in the acrylic resin powder particles was less than 0.5% by weight. The weight average molecular weight of the acrylic resin powder particles was 869,000.

[0120] It should be noted that the polymerization conversion rate of the latex containing crosslinked polymer particles (core) was 97.0%, and the volume average particle diameter was In addition, the polymerization conversion rate of the latex containing a graft copolymer having a core / shell structure was 99.9%, and the volume average particle diameter was

[0121] (Example 3)

[0122] Deionized water (110 parts), sodium hydroxide (0.004 parts), and SDSS (0.3 parts) were charged into an 8 L glass reactor equipped with a paddle stirrer, and then stirred at a rotation speed of 175 rpm. While purging the inside of the reactor with nitrogen, the temperature was raised to 60°C. Next, a mixture of BA (8.5 parts) and ALMA (0.043 parts) was added to the reactor, and then t-BHP (0.009 parts), EDTA (0.0055 parts), FeSO4 (0.0015 parts), and SFS (0.0076 parts) were successively added to the reactor to carry out emulsion polymerization of BA and ALMA, obtaining a latex containing crosslinked polymer particles (core). Here, after the addition of the mixture was completed, emulsion polymerization of BA and ALMA was carried out for 30 minutes. At this time, the polymerization conversion rate was 99.1%, and the volume average particle diameter was Next, a mixture of MMA (80.6 parts), n-BMA (1 part), PhMI (5 parts), and 2-EHTG (0.029 parts) was continuously added to the reactor over 135 minutes to carry out emulsion polymerization of MMA, n-BMA, and PhMI to form a shell layer. At this time, SDSS (0.6 parts) was continuously added to the reactor in a form linked to the addition of the mixture. In addition, the rotation speed was adjusted to 200 rpm at the start of the addition of the mixture, adjusted to 235 rpm 10 minutes after the start of the addition, adjusted to 260 rpm 20 minutes after the start of the addition, adjusted to 300 rpm 35 minutes after the start of the addition, and adjusted to 325 rpm 50 minutes after the start of the addition. Then, 15 minutes after the addition of the mixture was completed, MMA (5 parts) was continuously added to the reactor over 5 minutes, and the reaction was carried out for 30 minutes to cause the PhMI in the shell layer to react. Next, SFS (0.0026 parts) and t-BHP (0.005 parts) were successively added to the reactor, and after raising the temperature to 80°C, the reaction was carried out for 120 minutes to complete the polymerization, obtaining a latex containing a graft copolymer having a core / shell structure. At this time, the polymerization conversion rate was 100.0%, and the volume average particle diameter was Next, the latex was evaporated and dried in a hot air oven at 50°C for 24 hours to obtain white acrylic resin powder particles with a volume average particle diameter of 120 μm. The content rate of volatile components in the acrylic resin powder particles was less than 0.5% by weight. The weight average molecular weight of the acrylic resin powder particles was 770,000.

[0123] (Example 4)

[0124] Deionized water (110 parts), sodium hydroxide (0.004 parts), and SDSS (0.15 parts) were charged into an 8 L glass reactor equipped with a paddle stirrer, and then stirred at a rotation speed of 175 rpm. While purging the inside of the reactor with nitrogen, the temperature was raised to 60°C. Next, t-BHP (0.024 parts), EDTA (0.0055 parts), FeSO4 (0.0015 parts), and SFS (0.02 parts) were sequentially added to the reactor, and then a mixture of BA (8.5 parts) and ALMA (0.043 parts) was continuously added to the reactor over 20 minutes to carry out emulsion polymerization of BA and ALMA, obtaining a latex containing crosslinked polymer particles (core). Here, after the addition of the mixture was completed, emulsion polymerization of BA and ALMA was carried out for 30 minutes. At this time, the polymerization conversion rate was 99.9%, and the volume average particle diameter was Next, a mixture of MMA (83.5 parts), n-BMA (1 part), PhMI (7 parts), and 2-EHTG (0.02 parts) was continuously added to the reactor over 70 minutes to carry out emulsion polymerization of MMA, n-BMA, and PhMI to form a shell layer. At this time, SDSS (0.75 parts) was continuously added to the reactor in a form linked to the addition of the mixture. In addition, the rotation speed was adjusted to 200 rpm at the start of the addition of the mixture, adjusted to 235 rpm 10 minutes after the start of the addition, adjusted to 260 rpm 20 minutes after the start of the addition, adjusted to 300 rpm 35 minutes after the start of the addition, and adjusted to 325 rpm 50 minutes after the start of the addition. Next, SFS (0.01 parts), SDSS (0.2 parts), and t-BHP (0.01 parts) were sequentially added to the reactor, and after raising the temperature to 90°C, the reaction was carried out for 120 minutes to complete the polymerization, obtaining a latex containing a graft copolymer having a core / shell structure. At this time, the polymerization conversion rate was 100.0%, and the volume average particle diameter was Next, the latex was evaporated and dried in a hot air oven at 50°C for 24 hours to obtain white acrylic resin powder particles with a volume average particle diameter of 120 μm. The content rate of volatile components in the acrylic resin powder particles was less than 0.5% by weight. The weight average molecular weight of the acrylic resin powder particles was 753,000.

[0125] (Example 5)

[0126] Deionized water (110 parts), sodium hydroxide (0.004 parts), and SDSS (0.2 parts) were charged into an 8 L glass reactor equipped with a paddle-type stirrer, and the mixture was stirred at 175 rpm while purging the inside of the reactor with nitrogen and heating to 80 °C. Then, NPS (0.0321 parts) and SFS (0.0005 parts) were successively added to the reactor, and then a mixture of BA (8.5 parts) and ALMA (0.043 parts) was continuously added to the reactor over 20 minutes to carry out emulsion polymerization of BA and ALMA, obtaining a latex containing crosslinked polymer particles (core). Here, after the addition of the mixture was completed, emulsion polymerization of BA and ALMA was carried out for 30 minutes. At this time, the polymerization conversion rate was 99.2%, and the volume average particle size was Then, a mixture of MMA (83.5 parts), n-BMA (1 part), PhMI (7 parts), and 2-EHTG (0.0235 parts) was continuously added to the reactor over 70 minutes to carry out emulsion polymerization of MMA, n-BMA, and PhMI to form a shell layer. At this time, SDSS (0.7 parts) was continuously added to the reactor in a form linked to the addition of the mixture. In addition, the rotation speed was adjusted to 200 rpm at the start of the addition of the mixture, to 235 rpm 10 minutes after the start of the addition, to 260 rpm 20 minutes after the start, to 300 rpm 35 minutes after the start, and to 325 rpm 50 minutes after the start. Then, EDTA (0.0055 parts), FeSO4 (0.0015 parts), SFS (0.0077 parts), SDSS (0.2 parts), and t-BHP (0.015 parts) were successively added to the reactor, and after heating to 90 °C, the reaction was carried out for 120 minutes to complete the polymerization, obtaining a latex containing a graft copolymer having a core / shell structure. At this time, the polymerization conversion rate was 100.0%, and the volume average particle size was Then, the latex was evaporated and dried in a hot air oven at 50 °C for 24 hours to obtain white acrylic resin powder particles with a volume average particle size of 120 μm. The content of volatile components in the acrylic resin powder particles was less than 0.5% by weight. The weight average molecular weight of the acrylic resin powder particles was 692,000.

[0127] (Comparative Example 1)

[0128] Deionized water (110 parts), sodium hydroxide (0.004 parts), and SDSS (0.2 parts) were charged into an 8 L glass reactor equipped with a paddle-type stirrer, and then stirred at a rotation speed of 175 rpm while purging the inside of the reactor with nitrogen and heating to 80 °C. Next, NPS (0.0321 parts) and SFS (0.0005 parts) were sequentially added to the reactor, and then a mixture of BA (8.5 parts) and ALMA (0.043 parts) was continuously added to the reactor over 20 minutes to carry out emulsion polymerization of BA and ALMA, obtaining a latex containing crosslinked polymer particles (core). Here, after the addition of the mixture was completed, emulsion polymerization of BA and ALMA was carried out for 30 minutes. At this time, the polymerization conversion rate was 99.5%, and the volume average particle size was Next, a mixture of MMA (83.5 parts), n-BMA (1 part), PhMI (7 parts), and 2-EHTG (0.02 parts) was continuously added to the reactor over 70 minutes to carry out emulsion polymerization of MMA, n-BMA, and PhMI to form a shell layer. At this time, SDSS (0.7 parts) was continuously added to the reactor in a form linked to the addition of the mixture. In addition, the rotation speed was adjusted to 200 rpm at the start of the addition of the mixture, adjusted to 235 rpm 10 minutes after the start of the addition, adjusted to 260 rpm 20 minutes after the start of the addition, adjusted to 300 rpm 35 minutes after the start of the addition, and adjusted to 325 rpm 50 minutes after the start of the addition. Next, EDTA (0.0055 parts), FeSO4 (0.0015 parts), SFS (0.0616 parts), SDSS (0.2 parts), and t-BHP (0.06 parts) were sequentially added to the reactor, and then the reaction was carried out for 60 minutes to complete the polymerization, obtaining a latex containing a graft copolymer having a core / shell structure. At this time, the polymerization conversion rate was 99.8%, and the volume average particle size was Next, the latex was evaporated to dryness in a hot air oven at 50 °C for 24 hours to obtain white acrylic resin powder particles with a volume average particle size of 120 μm. The content rate of volatile components in the acrylic resin powder particles was less than 0.5% by weight. The weight average molecular weight of the acrylic resin powder particles was 683,000.

[0129] (Comparative Example 2)

[0130] Except that after cooling the latex containing the graft copolymer having a core / shell structure to 50 °C in Comparative Example 1, EDTA (0.025 parts) and sodium hydroxide (0.04 parts) were sequentially added to the reactor, in the same manner as in Comparative Example 1, white acrylic resin powder particles with a volume average particle size of 120 μm were obtained. The content rate of volatile components in the acrylic resin powder particles was less than 0.5% by weight. The weight average molecular weight of the acrylic resin powder particles was 683,000.

[0131] (Comparative Example 3)

[0132] Except for changing PhMI to ChMI in Comparative Example 1, white acrylic resin powder particles with a volume average particle diameter of 120 μm were obtained in the same manner as in Comparative Example 1. The content rate of volatile components in the acrylic resin powder particles was less than 0.5% by weight. The weight average molecular weight of the acrylic resin powder particles was 645,000.

[0133] It should be noted that the polymerization conversion rate of the latex containing crosslinked polymer particles (core) was 93.5%, and the volume average particle diameter was In addition, the polymerization conversion rate of the latex containing a graft copolymer having a core / shell structure was 100.0%, and the volume average particle diameter was

[0134] (Comparative Example 4)

[0135] Deionized water (170 parts) and DSHP (0.1 part) were put into an 8 L glass reactor equipped with a paddle stirrer, and then stirred at a rotation speed of 300 rpm. While purging the inside of the reactor with nitrogen, the temperature was raised to 40°C. Then, LPO (0.3 part) was added to the reactor, and then a mixture of MMA (85 parts), 2-EHMA (5 parts), and PhMI (10 parts) was continuously added to the reactor over 30 minutes. Here, after the addition of the mixture was completed, stirring was carried out for 30 minutes. Then, HPMC (0.375 part) was continuously added to the reactor over 30 minutes, and then stirring was carried out for 30 minutes. Then, the temperature of the reactor was raised to 65°C to carry out suspension polymerization of MMA, 2-EHMA, and PhMI. At this time, the temperature reached 85°C 100 minutes after the temperature of the reactor was raised to 65°C, and then it was slowly cooled. Then, after the temperature of the reactor was raised to 95°C, it was maintained for 60 minutes to complete the polymerization, and a slurry containing bead-like particles was obtained. At this time, the polymerization conversion rate was 99.5%, and the volume average particle diameter was 50 μm. Then, the slurry was evaporated to dryness in a hot air oven at 50°C for 24 hours to obtain white acrylic resin powder particles with a volume average particle diameter of 55 μm. The content rate of volatile components in the acrylic resin powder particles was less than 0.5% by weight. The weight average molecular weight of the acrylic resin powder particles was 1,900,000.

[0136] <Test Method>

[0137] (Polymerization Conversion Rate)

[0138] Take about 2 g of the sample (latex or slurry), and then accurately weigh the weight of the sample. Next, dry the sample in a hot air oven at 120 °C for 1 hour, and then accurately weigh the weight of the dried sample as the weight of the solid component. Then, find the ratio of the weight of the sample before and after drying as the solid component ratio in the sample. Finally, calculate the polymerization conversion rate by the following formula. It should be noted that polyfunctional monomers and chain transfer agents are treated as input monomers.

[0139] {(Total weight of input raw materials × solid component ratio - total weight of raw materials other than water and monomers) / weight of input monomers} × 100

[0140] (Volume average particle size of latex)

[0141] Use Microtrac UPA150 (manufactured by Nikkiso Co., Ltd.) to measure the volume average particle size of latex by dynamic light scattering method.

[0142] (Volume average particle size of slurry)

[0143] Use Microtrac MT3300EXII (manufactured by Nikkiso Co., Ltd.) to measure the volume average particle size of slurry by laser diffraction scattering method.

[0144] (Volume average particle size of acrylic resin powder)

[0145] Disperse the acrylic resin powder into water containing surfactant at a specified concentration, and then use Microtrac MT3300EXII (manufactured by Nikkiso Co., Ltd.) to measure the volume average particle size of acrylic resin powder by laser diffraction scattering method.

[0146] (Content rate of volatile components)

[0147] Use a heating drying type moisture meter MX-50 (manufactured by A&D) equipped with a straight tube type halogen lamp to measure the content rate of volatile components of acrylic resin powder. Specifically, use 5 g of acrylic resin powder and measure the content rate of volatile components of acrylic resin powder under the conditions of a maximum temperature of 130 °C and a measurement accuracy of MID (minimum display 0.01%, 0.05% / min).

[0148] (Weight average molecular weight)

[0149] Using gel permeation chromatography (GPC), the weight-average molecular weight of the acrylic resin powder was calculated by the standard polystyrene conversion method. At this time, as the GPC column, TSK gel Super HZM-H (manufactured by Tosoh Corporation) filled with polystyrene cross-linked gel was used, and as the GPC solvent, tetrahydrofuran (THF) was used. In addition, as the sample solution, a solution obtained by dissolving 20 mg of the acrylic resin powder in 10 ml of THF and then filtering it through a membrane filter with a pore size of 0.2 μm was used, and the column temperature of the GPC was set at 40°C.

[0150] (Conductivity)

[0151] Weigh 8 g of the acrylic resin powder and 80 g of ultrapure water in a Teflon (registered trademark) container, then place the Teflon (registered trademark) container in a pressure-resistant container and close and seal the outer lid with a special tool. Then, gently shake the pressure-resistant container to mix the acrylic resin powder and ultrapure water, and then place the pressure-resistant container in a hot air oven at 100°C and heat for 20 hours. Then, after allowing the pressure-resistant container to cool completely, open the outer lid with a special tool and take out the Teflon (registered trademark) container. Then, suck out the liquid in the Teflon (registered trademark) container and filter it through a membrane filter with a pore size of 0.2 μm to obtain an aqueous solution (filtrate). Then, after storing the aqueous solution in a constant temperature room at 23°C and 50% RH for 24 hours, use a small conductivity meter LAQUAtwin EC-33B (manufactured by HORIBA) to measure the conductivity of the aqueous solution.

[0152] It should be noted that if the volume average particle diameter of the acrylic resin powder is greater than 250 μm, the acrylic resin powder is pulverized until the volume average particle diameter is 100 μm or more and 250 μm or less, and then the conductivity of the aqueous solution is measured in the same manner as above. Here, the method for measuring the volume average particle diameter of the acrylic resin powder is the same as described above. In addition, as the device for pulverizing the acrylic resin powder, a mortar, a food cutter, etc. can be cited.

[0153] (Content rate of sulfate ion)

[0154] Using an ion chromatograph (manufactured by SHIMADZU), the content rate of sulfate ions in the aqueous solution used for conductivity measurement was measured under the following measurement conditions. Specifically, the peak area of sulfate ions derived from the aqueous solution was measured, and then the content rate of sulfate ions (SO4 2- ) was obtained by the ratio of the peak area of sulfate ions in the aqueous solution to the peak area of sulfate ions in a standard solution with a known content rate of sulfate ions measured in advance.

[0155] <Measurement conditions>

[0156] Conductivity Detector: CDD-10AVP (manufactured by SHIMADZU)

[0157] Analytical Column: Shim-pack IC-SA2 (manufactured by SHIMADZU) with an inner diameter of 4 mm and a length of 250 mm

[0158] Guard Column: Shim-pack IC-SA2(G) (manufactured by SHIMADZU) with an inner diameter of 4.6 mm and a length of 10 mm

[0159] Eluent: Aqueous solution of 0.6 mmol of Na2CO3 and 12 mmol of NaHCO3

[0160] Flow Rate of Eluent: 1.0 mL / min

[0161] (Foaming Traces on the Film)

[0162] Acrylic resin powder was added to a mixed solvent of dichloromethane and methanol (weight ratio 8:2) to a concentration of 10% by weight, and then stirred and mixed using a magnetic stirrer to prepare a transparent coating solution. Next, using a bar coater, the coating solution was cast onto a glass plate serving as a support at a thickness of 1.1 mm. Then, the glass plate coated with the coating solution was dried at room temperature for 10 minutes, and the semi-dry film was peeled off from the glass plate. Next, the semi-dry film was cut into a size of 5.5 cm × 5.5 cm, and then dried in a drying oven at 175 °C for 7 minutes while fixed to a 6 cm × 6 cm metal frame to obtain a film for evaluating foaming traces. Next, using an optical microscope, the surface of the film for evaluating foaming traces was observed to evaluate the foaming traces. It should be noted that according to the following criteria, the state of the foaming traces was evaluated by sensory evaluation on a scale of 1 (good) to 5 (poor).

[0163] 1: There are no foaming traces on the surface of the film, and it is a very beautiful surface

[0164] 2: Slight foaming traces are observed on the surface of the film, and it is a generally beautiful surface

[0165] 3: Although foaming traces are observed on the surface of the film, the number of foaming traces is small

[0166] 4: Although not on the entire surface of the film, foaming traces are observed and the number of foaming traces is large

[0167] 5: Foaming traces are observed on the entire surface of the film

[0168] (Film for Temperature and Humidity Constant Test)

[0169] Add acrylic resin powder to a mixed solvent of dichloromethane and methanol (weight ratio 8:2) to a concentration of 20% by weight, and then stir and mix using a magnetic stirrer to prepare a transparent coating solution. Next, let the coating solution stand for 24 hours, defoam it, and then cast it onto a transparent glass plate as a support. At this time, use a spreader to coat it into a uniform film, and adjust the gap so that the thickness of the film for the temperature and humidity test is 40 μm. Next, dry the transparent glass plate with the coating solution cast on it at room temperature for 8 minutes, and then peel off the semi-dry film from the transparent glass plate. Then, fix the semi-dry film to a stainless steel frame, and then dry it in a hot air oven at 160 °C for 15 minutes to obtain a film for the temperature and humidity test.

[0170] (Temperature and Humidity Test)

[0171] Cut out a 4 cm × 4 cm test piece from the film for the temperature and humidity test with a thickness of 40 μm, and then use a temperature and humidity test device LHU-123 (manufactured by ESPEC) to conduct the temperature and humidity test on the test piece under the conditions of 85 °C and 95% RH. It should be noted that in the temperature and humidity test, the haze (Hz), internal haze (internal Hz), and yellowness index (YI) of the test piece before being put into the temperature and humidity test device (initial value) and after 96 hours of being put in are measured. In addition, calculate the difference between the value after 96 hours of being put into the temperature and humidity test device and the initial value, and also obtain Δ haze (ΔHz), Δ internal haze (Δ internal Hz), and Δ yellowness index (ΔYI).

[0172] (Haze (Hz))

[0173] Use a haze meter HZ-V3 (manufactured by SUGA Test Instruments) to measure the haze (Hz) of the test piece by the method described in JIS K7105.

[0174] (Internal Haze (Internal Hz))

[0175] Measure the internal haze of the test piece by measuring the haze of the test piece in a state where the influence of surface scattering of the test piece is eliminated. Specifically, first drop glycerin with a refractive index close to that of the acrylic resin powder on both sides of the test piece, and then clamp it with a glass plate so that the interface between the test piece and the glass plate is filled with glycerin. After measuring the haze in this state by the above-mentioned method, subtract the haze of only the glass plate measured in advance to obtain the internal haze (internal Hz) of the test piece.

[0176] (Yellowness Index (YI))

[0177] Use a color difference meter SC-P (manufactured by SUGA Test Instruments) to measure the yellowness index (YI) of the test piece in the transmission mode by the method described in JIS K7373.

[0178] (Thin film for phase difference measurement)

[0179] Add acrylic resin powder to a mixed solvent of dichloromethane and ethanol (weight ratio 9:1) to make the concentration 10% by weight, and then stir and mix using a magnetic stirrer to prepare a transparent coating solution. Next, let the coating solution stand for 24 hours, defoam it, and then cast it onto a PET film as a support. At this time, use a spreader to coat it into a uniform film, and adjust the gap so that the thickness of the dried film is about 60 μm. In addition, as the PET film, use Cosmo Shine A4100 (manufactured by Toyobo). Then, after drying the PET film with the coating solution cast on it in a drying atmosphere at 40 °C for 1 hour, peel off the semi-dry film from the PET film. Next, fix the semi-dry film to a stainless steel frame, and then dry it in a drying atmosphere at 140 °C for 60 minutes to obtain a dried film.

[0180] Using a stretcher with a hot air oven function, preheat the dried film for 5 minutes at a temperature condition 10 °C higher than the glass transition temperature of the dried film, and then under the conditions of a stretching speed of 100 mm / min and a stretching ratio of 1.4 times, fix the width and perform uniaxial stretching on the dried film to obtain a thin film for phase difference measurement with a thickness of 40 μm.

[0181] (Phase difference)

[0182] After cutting out a test piece from the central part of the thin film for phase difference measurement, use an automatic birefringence meter KOBRA-WR (manufactured by Oji Scientific Instruments) to measure the in-plane phase difference Re of the test piece under the conditions of a wavelength of 590 nm and an incident angle of 0°. At this time, under the condition of an incident angle of 40°, also measure the thickness direction phase difference Rth of the test piece. It should be noted that by moving the test piece, change the measurement position and measure the phase difference 3 times respectively, and calculate the average value.

[0183] (Thin film for glass transition temperature measurement)

[0184] Fix the obtained dried film to a stainless steel frame in the same manner as the thin film for phase difference measurement, and dry it in a hot air oven at 175 °C for 10 minutes to obtain a thin film for glass transition temperature measurement.

[0185] (Glass transition temperature (Tg))

[0186] Using a differential scanning calorimeter (DSC) Q1000 (manufactured by TA Instruments), the Tg of the film for measuring the glass transition temperature was measured. Specifically, in a nitrogen gas stream, the film for measuring the glass transition temperature was heated to 200°C at a heating rate of 10°C / minute, then rapidly cooled to 40°C, and then heated to 200°C again at a heating rate of 10°C / minute. For the glass transition observed during the second heating, the average value of the extrapolated glass transition start temperature and the extrapolated glass transition end temperature was determined as Tg.

[0187] Table 1 shows the evaluation results of the conductivity, Tg, foaming marks on the film, Hz, internal Hz, and phase difference of the acrylic resin powder.

[0188] [Table 1]

[0189]

[0190] As can be seen from Table 1, when the acrylic resin powder of Examples 1 to 5 was used, the foaming marks on the film and the decrease in transparency in a high-temperature and high-humidity environment were suppressed. In contrast, for the acrylic resin powder of Comparative Examples 1 to 4, since the conductivity was 325 to 386 μS / cm, the foaming marks on the film were more, or the transparency decreased in a high-temperature and high-humidity environment.

Claims

1. An acrylic resin powder, wherein, the aqueous solution obtained by mixing the acrylic resin powder and ultrapure water at a weight ratio of 1:10, putting them into a pressure-resistant container, heating at 100 °C for 20 hours, and then filtering has a conductivity of 300 μS / cm or less at 23 °C and 50% RH, the content rate of volatile components of the acrylic resin powder is less than 1.0% by weight.

2. The acrylic resin powder according to claim 1, having a glass transition temperature of 110 °C or higher.

3. The acrylic resin powder according to claim 1, wherein, The acrylic resin contained in the acrylic resin powder has a structural unit containing a heterocycle in the main chain.

4. The acrylic resin powder according to claim 3, wherein, The acrylic resin has a structural unit derived from N-substituted maleimide.

5. The acrylic resin powder according to claim 4, wherein, The N-substituted maleimide is N-cyclohexyl maleimide or N-phenyl maleimide.

6. The acrylic resin powder according to claim 4, wherein, The content rate of sulfate ions in the aqueous solution is 350 ppm or less.

7. The acrylic resin powder according to claim 1, having a weight average molecular weight of 400,000 or more and 4,000,000 or less.

8. The acrylic resin powder according to claim 1, which is used for manufacturing a film based on the solution casting method.

9. A coating solution, which dissolves the acrylic resin powder according to any one of claims 1 to 8 in a solvent.

10. A method for manufacturing a coating solution, wherein, The acrylic resin powder according to any one of claims 1 to 8 is dissolved in a solvent to manufacture a coating solution.

11. A film, which is manufactured by casting the coating solution according to claim 9 onto the surface of a support and then volatilizing the solvent.

12. A method for manufacturing a thin film, wherein, The coating solution according to claim 9 is cast onto the surface of a support and then the solvent is volatilized to manufacture a film.

13. A film, which contains an acrylic resin, the acrylic resin has a structural unit containing a heterocycle in the main chain, a glass transition temperature of 110 °C or higher, and a weight average molecular weight of 400,000 or more and 4,000,000 or less, when the thickness of the film is 40 μm, the change ΔHz in haze before and after storage for 96 hours under the conditions of 85 °C and 95% RH is 2.5% or less, when the thickness is 40 μm, the change ΔYI in yellowness before and after storage for 96 hours under the conditions of 85 °C and 95% RH is 3.5 or less.

14. The film according to claim 13, having a haze Hz of 2% or less when the thickness is 40 μm, and a yellowness YI of 2.0 or less when the thickness is 40 μm.

15. The thin film according to claim 13 or 14, wherein, The acrylic resin has a structural unit derived from N-substituted maleimide.

16. The thin film according to claim 15, wherein, The N-substituted maleimide is N-cyclohexyl maleimide or N-phenyl maleimide.

Images