Acrylic resin composition and resin film

Abstract

An acrylic resin composition for manufacturing a film based on a solution casting method, which comprises an acrylic polymer having as structural units 30 to 100 wt% of methyl methacrylate units and 0 to 70 wt% of other monomer units copolymerizable therewith, and an ionic emulsifier, the content of the aforementioned ionic emulsifier being 0.1 to 10 parts by weight per 100 parts by weight of the aforementioned acrylic polymer.

Description

Technical Field

[0001] This invention relates to an acrylic resin composition for manufacturing films by solution casting, and a resin film manufactured using the composition by solution casting. Background Technology

[0002] In recent years, with the increasing size and definition of screens, the problem of TAC (cellulose triacetate) used in the protective film of polarizers in liquid crystal displays causing panel warping and image quality degradation during transportation due to its high moisture permeability and water absorption has become increasingly apparent.

[0003] Acrylic resin films have excellent optical properties, low moisture permeability, and low water absorption, and therefore have attracted much attention as a substitute for TAC films.

[0004] Patent document 1 discloses the following technology: when manufacturing acrylic resin films by solution casting, by optimizing the residual solvent amount, temperature and other conditions in the drying process, the whitening of the resulting film and the bubbles generated in the film are suppressed.

[0005] In addition, Patent Document 2 discloses the following: using an acrylic polymer obtained by suspension polymerization in the presence of a suspension polymerization dispersant with a specific structure in a solution casting method, thereby obtaining a film with excellent optical properties, dimensional stability and adhesion.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2014-177089

[0009] Patent Document 2: Japanese Patent Publication No. 2019-533203 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] In the technology of Patent Document 1, complex manufacturing conditions such as solvent residue and temperature must be controlled. In the technology of Patent Document 2, a suspension polymerization dispersant with a special structure is required, leaving room for improvement. Furthermore, it has been clearly stated that, based on the aforementioned bubble problem in the film, and depending on the composition of the acrylic resin composition used in the solution casting method, there is a problem of deterioration in the transparency of the coating in the solution casting method.

[0012] In view of the above-mentioned situation, the present invention aims to provide an acrylic resin composition for use in manufacturing films by solution casting, wherein the transparency of coatings containing the composition is improved and foaming marks on the surface of acrylic resin films manufactured by solution casting are suppressed.

[0013] Solution for solving the problem

[0014] Through repeated and in-depth research, the inventors focused on the components in the acrylic resin composition other than the main polymer (the so-called by-products in the manufacture of the main polymer, known as inclusions), and discovered that by controlling their type and content, the transparency of the coating containing the acrylic resin composition can be improved, and at the same time, foaming marks during film drying are less likely to occur on the surface of the acrylic resin film manufactured by solution casting. Thus, the present invention was completed.

[0015] That is, the present invention relates to an acrylic resin composition for the manufacture of films based on solution casting, comprising an acrylic polymer and an ionic emulsifier, wherein the acrylic polymer is a structural unit comprising 30 to 100 wt% methyl methacrylate units and 0 to 70 wt% other monomer units that can copolymerize therewith, and the content of the aforementioned ionic emulsifier is 0.1 to 10 parts by weight relative to 100 parts by weight of the aforementioned acrylic polymer.

[0016] The aforementioned ionic emulsifier is preferably a sulfonate.

[0017] The aforementioned sulfonates preferably include at least one selected from the group consisting of lithium salts, sodium salts, and potassium salts.

[0018] The aforementioned sulfonate preferably comprises at least one selected from the group consisting of dialkyl sulfosuccinate, alkane sulfonate, α-olefin sulfonate, alkylbenzene sulfonate, naphthalene sulfonate-formaldehyde condensate, alkyl naphthalene sulfonate, and N-methyl-N-acyl taurate.

[0019] The other copolymerizable monomer units mentioned above preferably include (meth)acrylate units (excluding methyl methacrylate) and / or maleimide units with 1 to 20 carbon atoms in the ester site.

[0020] The content of the aforementioned copolymerizable monomer units is preferably 0.1% to 50% by weight of the total number of structural units of the aforementioned acrylic polymer.

[0021] The aforementioned acrylic resin composition may further comprise a graft copolymer having a core / shell structure in amounts of 1 to 50 parts by weight relative to 100 parts by weight of the aforementioned acrylic polymer.

[0022] The weight-average molecular weight of the aforementioned acrylic polymers is preferably 500,000 or higher.

[0023] The haze of a solution coating containing the aforementioned acrylic resin composition at a concentration of 5% by weight in a mixed solvent of 95% by weight dichloromethane and 5% by weight methanol is preferably 5% or less.

[0024] In addition, the present invention relates to a resin film formed by molding the aforementioned acrylic resin composition by solution casting.

[0025] The haze of the aforementioned resin film is preferably less than 2%.

[0026] The aforementioned resin film is preferably a film used for laminating and protecting the surface of other substrates.

[0027] The aforementioned resin film is preferably a protective film for polarizing components.

[0028] Furthermore, the present invention also relates to a polarizing plate formed by laminating a polarizing element with the aforementioned resin film, and to a display device comprising the aforementioned polarizing plate.

[0029] In addition, the present invention also relates to a manufacturing method for manufacturing the aforementioned acrylic resin composition, the method comprising the following steps: performing emulsion polymerization or suspension polymerization in the presence of an ionic emulsifier to obtain a mixture comprising the aforementioned acrylic polymer and water; and performing a drying operation on the aforementioned mixture without performing a washing operation.

[0030] In addition, the present invention also relates to a method for manufacturing a resin film, which includes a step of forming a coating comprising the aforementioned acrylic resin composition and solvent into a film by solution casting.

[0031] The aforementioned solvent preferably contains 1 to 25% by weight of an alcohol.

[0032] The aforementioned alcohols are preferably ethanol and / or methanol.

[0033] The effects of the invention

[0034] According to the present invention, an acrylic resin composition for manufacturing films by solution casting can be provided, wherein the transparency of coatings containing the composition is improved and foaming marks on the surface of acrylic resin films manufactured by solution casting can be suppressed.

[0035] Acrylic resin films manufactured using the acrylic resin composition described in this invention and by solution casting are films with excellent appearance and high transparency, exhibiting minimal foaming marks on the film surface during drying. These acrylic resin films have few optical defects and high light extraction efficiency, making them suitable for use as optical films for liquid crystal display components, especially as protective films for polarizers. Attached Figure Description

[0036] Figure 1 These are microscopic photographs taken of the surface of a film made using the resin composition obtained in Example 1 for the purpose of evaluating its foaming properties.

[0037] Figure 2 These are microscopic photographs taken of the surface of a film made using the resin composition obtained in Comparative Example 1 for evaluating its foaming properties. Detailed Implementation

[0038] The embodiments of the present invention will be described in detail below, but the present invention is not limited to these embodiments.

[0039] (Acrylic resin composition)

[0040] The acrylic resin composition of the present invention comprises at least an acrylic polymer and an ionic emulsifier. The acrylic polymer has 30-100% by weight of methyl methacrylate units and 0-70% by weight of other monomer units that can copolymerize with it as structural units. The content of the aforementioned ionic emulsifier is 0.1-10 parts by weight relative to 100 parts by weight of the aforementioned acrylic polymer. With this composition, when producing resin films using solution casting, films with high transparency that are less prone to foaming marks during the drying process can be obtained.

[0041] (Acrylic polymer)

[0042] The acrylic resin composition described in this embodiment contains an acrylic polymer with 30-100% by weight of methyl methacrylate units and 0-70% by weight of other monomer units that can be copolymerized with it as structural units.

[0043] From the viewpoints of appearance and weather resistance, the aforementioned acrylic polymer only needs to contain methyl methacrylate units of 30% or more by weight in the total amount of structural units of the polymer, preferably 50% or more by weight, more preferably 60% or more by weight, further preferably 70% or more by weight, and particularly preferably 80% or more by weight. Furthermore, from the viewpoints of optical properties and heat resistance, the upper limit is preferably 99.9% or less by weight, more preferably 99% or less by weight, further preferably 97% or less by weight, and particularly preferably 95% or less by weight. It should be noted that, from the viewpoints of processability and appearance, the aforementioned acrylic polymer preferably does not contain multifunctional monomer units having two or more polymerizable functional groups within the molecule.

[0044] In addition, other monomer units that can copolymerize with the methyl methacrylate unit include, for example, ethyl methacrylate, propyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, benzyl methacrylate, octyl methacrylate, stearyl methacrylate, glycidyl methacrylate, epoxycyclohexyl 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, epoxycyclohexyl methacrylate, and 2-hydroxyethyl methacrylate. (Meth)acrylate units with 1 to 20 carbon atoms in the ester site, such as methyl methacrylate and 2-hydroxypropyl acrylate (excluding methyl methacrylate); (meth)acrylamide units such as methacrylamide, N-hydroxymethylmethacrylamide, acrylamide, and N-hydroxymethylacrylamide; carboxylic acids such as methacrylic acid and acrylic acid and their salts; vinyl cyanide units such as acrylonitrile and methacrylonitrile; vinyl aromatic 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; halogenated vinyl compounds such as vinyl chloride, vinyl bromide, and chloroprene; vinyl esters such as vinyl formate, vinyl acetate, and vinyl propionate; and olefins such as ethylene, propylene, butene, butadiene, and isobutylene. Preferably, the ester site comprises (meth)acrylate units (excluding methyl methacrylate), vinyl aromatic units, and / or maleimide units having 1 to 20 carbon atoms, and particularly preferably (meth)acrylate units (excluding methyl methacrylate) and / or maleimide units having 1 to 20 carbon atoms at the ester site. These monomers may be used alone or in combination with two or more.

[0045] The acrylic resin composition described in this embodiment is used to manufacture acrylic resin films using a solution casting method. Therefore, as other copolymerizable monomer units, it is preferable to include drying-promoting comonomers that increase the solvent evaporation rate as structural units.

[0046] As a drying-promoting comonomer unit with good heat resistance and the ability to improve solvent evaporation rate, it is preferably selected from at least one of the following groups: maleimide unit, methacrylate unit with a primary, secondary, or aromatic hydrocarbon group having 2 to 8 carbon atoms in the ester site, methacrylate unit with a saturated hydrocarbon group having 7 to 16 carbon atoms in the ester site having a fused ring structure, methacrylate unit with a straight-chain or branched group containing an ether bond in the ester site, and vinyl aromatic unit. Using these drying-promoting comonomer units allows for both the excellent heat resistance of acrylic polymers and faster solvent evaporation from the cast film in solution casting.

[0047] Examples of maleimide units include N-phenylmaleimide, N-benzylmaleimide, N-cyclohexylmaleimide, and N-methylmaleimide, with N-phenylmaleimide, N-benzylmaleimide, and N-cyclohexylmaleimide being preferred.

[0048] Examples of methacrylate units whose ester sites are primary, secondary, or aromatic hydrocarbon groups having 2 to 8 carbon atoms include ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, phenyl methacrylate, and benzyl methacrylate. Among these, ethyl methacrylate, n-butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, and benzyl methacrylate are preferred.

[0049] The aforementioned ester site is a methacrylate unit with a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure, such as dicyclopentyl methacrylate and isobornyl methacrylate. The number of carbon atoms in the aforementioned saturated hydrocarbon group is preferably 8 to 14, more preferably 9 to 12. Furthermore, the fused ring structure is not particularly limited, but a structure obtained by condensing two five-membered rings through three consecutive carbon atoms is preferred.

[0050] The aforementioned ester site is a methacrylate unit containing a straight-chain group or a branched group with an ether bond, such as 2-methoxyethyl methacrylate.

[0051] Examples of vinyl aromatic units include styrene, α-methylstyrene, monochlorostyrene, and dichlorostyrene. Styrene is preferred.

[0052] The aforementioned acrylic polymer is not particularly limited as long as it contains 0 to 70% by weight of the aforementioned copolymerizable other monomer units in the total amount of structural units of the polymer. However, from the perspective of adjusting the optical properties and heat resistance of the resulting resin composition, the aforementioned acrylic polymer preferably contains 0.1% by weight or more of the aforementioned copolymerizable other monomer units, more preferably 1% by weight or more, further preferably 3% by weight or more, and particularly preferably 5% by weight or more. In addition, the upper limit is preferably 50% by weight or less, more preferably 40% by weight or less, further preferably 30% by weight or less, and particularly preferably 20% by weight or less.

[0053] To achieve excellent heat resistance, the aforementioned acrylic polymers preferably have a ring structure in their main chain. Examples of ring structures include glutarimide ring structures, lactone ring structures, structures derived from maleic anhydride, maleimide ring structures (including structures derived from N-substituted maleimides), and glutaric anhydride ring structures. Additionally, acrylic resins containing (meth)acrylic acid structural units in their molecules can also be listed. Specifically, examples include maleimide acrylic resins (acrylic resins copolymerized with unsubstituted or N-substituted maleimide compounds as copolymer components), glutarimide acrylic resins, acrylic resins containing lactone rings, acrylic resins containing hydroxyl and / or carboxyl groups, methacrylic resins, acrylic polymers containing partially hydrogenated styrene units obtained by partially hydrogenating the aromatic rings of styrene-containing acrylic polymers obtained by polymerizing styrene monomers and other copolymerizable monomers, and acrylic polymers with cyclic anhydride structures such as glutaric anhydride structures or structures derived from maleic anhydride.

[0054] Among these, glutarimide ring structures and maleimide ring structures are particularly preferred from the perspective of effectively improving the heat resistance and excellent balance between optical properties of acrylic resin films. They can be used in combination to impart optical properties, high thermal stability, and solvent resistance to acrylic polymers.

[0055] The weight-average molecular weight of the aforementioned acrylic polymer is not particularly limited. From the viewpoint that the resulting acrylic resin film becomes strong and exhibits a good balance with film-forming properties, a weight-average molecular weight of 400,000 to 4,000,000 is preferred, 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 can be 800,000 to 2,500,000, or 800,000 to 2,000,000.

[0056] Furthermore, when film formation is performed via melt extrusion, the acrylic polymer needs to be melted to reduce viscosity; therefore, the polymer's molecular weight needs to be relatively low. However, in this embodiment, since film formation is performed via solution casting, film formation can be easily achieved even with a high molecular weight polymer. From this perspective, the weight-average molecular weight of the aforementioned acrylic polymer can be 500,000 or higher.

[0057] Weight-average molecular weight can be calculated using gel permeation chromatography (GPC) and the standard polystyrene conversion method.

[0058] The aforementioned acrylic polymers preferably possess excellent heat resistance, and the glass transition temperature can be used as an indicator of heat resistance. The aforementioned acrylic polymers preferably exhibit 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.

[0059] (Manufacturing method of acrylic polymers)

[0060] The method for manufacturing acrylic polymers described in this embodiment is not particularly limited as long as it can demonstrate the inventive effect. From the viewpoint of structural design freedom, polymerization simplicity, and productivity of acrylic polymers, it is preferred to manufacture them by emulsion polymerization or suspension polymerization.

[0061] When manufacturing acrylic resin films by solution casting, from the viewpoint of minimizing foaming marks during film drying on the film surface and inside, and obtaining films with excellent appearance and high transparency, it is more preferable to manufacture them by emulsion polymerization in the presence of ionic emulsifiers.

[0062] In particular, there is a tendency for residual maleimide monomers in acrylic polymers whose main chain contains maleimide rings to hydrolyze, causing discoloration of the acrylic polymer. Since residual maleimide monomers can be effectively reduced, emulsion polymerization is preferred for manufacturing.

[0063] The acrylic resin composition described in this embodiment includes an ionic emulsifier. This ionic emulsifier, used in emulsion polymerization during the manufacture of the acrylic polymer, can remain in the acrylic polymer.

[0064] When recovering acrylic polymers from the reaction system after emulsion polymerization, the ionic emulsifiers are washed away when water and organic solvents are used for cleaning. Therefore, the recovered acrylic polymers do not actually contain ionic emulsifiers.

[0065] Therefore, when manufacturing the acrylic resin composition described in this embodiment, it is preferable to perform a drying operation on the reaction system only after the emulsion polymerization is completed, without performing a washing operation. Since the acrylic polymer recovered only through the drying operation contains an ionic emulsifier, the acrylic resin composition described in this embodiment can be formed.

[0066] From an energy cost and productivity perspective, it is desirable to avoid cleaning operations. Without cleaning, the ionic emulsifiers used in emulsion polymerization remain directly in the resulting acrylic polymer; therefore, the total amount of ionic emulsifiers used in emulsion polymerization is substantially equal to the amount of ionic emulsifiers in the acrylic resin composition. Furthermore, in emulsion polymerization, ionic emulsifiers can be added simultaneously or sequentially.

[0067] Although the acrylic resin composition described in this embodiment contains residual emulsifier, since the emulsifier is an ionic emulsifier, foaming marks on the film surface can be suppressed. On the other hand, when a nonionic emulsifier remains in the resin composition, foaming marks are more likely to occur on the film surface.

[0068] The aforementioned ionic emulsifier can be any of cationic, anionic, or amphoteric emulsifiers. Anionic emulsifiers are preferred. Nonionic emulsifiers are not included in the aforementioned ionic emulsifiers.

[0069] The type of ionic emulsifier mentioned above is not particularly limited as long as it is used to provide an acrylic resin composition that can exhibit the inventive effect; known types can be used. Examples include carboxylates, sulfonates, sulfate esters, and phosphate esters. Sulfonates are preferred from the perspective of significantly suppressing foaming marks during film drying and having excellent polymerization stability.

[0070] More specifically, examples include dialkyl sulfosuccinates, alkane sulfonates, α-olefin sulfonates, alkylbenzene sulfonates, naphthalene sulfonate-formaldehyde condensates, alkylnaphthalene sulfonates, N-methyl-N-acyl taurate, etc. Among these, dialkyl sulfosuccinates or alkylbenzene sulfonates are preferred.

[0071] These sulfonates are not particularly limited as long as they can exhibit the inventive effect, and can be lithium salts, sodium salts, potassium salts, calcium salts, magnesium salts, etc. In particular, from the viewpoint of effectively suppressing foaming marks, it is preferred to include at least one of the groups selected from lithium salts, sodium salts, and potassium salts. It can be considered that when the sulfonates exist in the form of their monovalent cationic salts, even if salts remain in the acrylic resin composition, the salts will dissolve in the alcohol component of the coating solvent, causing the salts to be microscopically and finely dispersed in the solution coating. Therefore, foaming can be suppressed to the microscopic level.

[0072] According to this embodiment, the amount of ionic emulsifier used during polymerization is less restricted, allowing for a wider range of polymerization designs. Furthermore, not only is cleaning time reduced, but polymer acquisition methods that do not require cleaning, such as spray drying and other granulation methods, can be used, thus significantly improving productivity in the manufacture of acrylic resins.

[0073] On the other hand, when the sulfonate is a salt formed by polyvalent cations such as calcium ion salt or magnesium salt, it tends to be insoluble in alcohol components. Therefore, from the viewpoint of suppressing foaming marks during film drying, it is preferable that it exists in a state in which, for example, after coagulating and heat-treating the polymer latex produced by emulsion polymerization with a coagulant, the resulting slurry particles are cleaned using a known cleaning method, thereby reducing the salt content contained in the acrylic resin composition to some extent.

[0074] The ionic emulsifier is preferably 0.1 to 10 parts by weight relative to 100 parts by weight of the acrylic polymer. From the viewpoint of achieving an excellent balance between suppressing foaming marks during film drying and polymerization stability, it is more preferably 0.3 to 7 parts by weight, further preferably 0.4 to 6 parts by weight, even more preferably 0.5 to 5 parts by weight, particularly preferably 0.8 to 3 parts by weight, and most preferably 1 to 3 parts by weight. When more than 10 parts by weight are included, the effect of suppressing foaming marks in the acrylic resin film is reduced, and the transparency of the acrylic resin film may decrease. In addition, there is a possibility that physical properties other than foaming characteristics, such as the thermal stability of the acrylic resin film, may decrease, or that salt may seep into the metal roller and contaminate the metal roller during film formation by solution casting.

[0075] As polymerization initiators for polymerizing the aforementioned acrylic polymers, known substances can be used, such as persulfates like potassium persulfate, sodium persulfate, and ammonium persulfate; organic peroxides such as tert-butyl hydroperoxide, tert-butyl peroxyisopropyl carbonate, cumene hydroperoxide, p-menthol hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, bis(8,5,5-trimethylhexanoyl) peroxide, dilauryl peroxide, and benzoyl peroxide.

[0076] These initiators can either crack the polymerization initiator, generate free radicals, and polymerize based solely on a thermal decomposition mechanism, or, as described in the embodiments of Japanese Patent No. 3960631, be used as redox initiators for initiating free radicals at low temperatures by combining an oxidizing agent such as ferrous sulfate with a reducing agent such as sodium formaldehyde sulfoxylate. Depending on the composition of the acrylic polymer, coloring can be suppressed by combining them.

[0077] In addition, to adjust the molecular weight of the aforementioned acrylic polymers, known chain transfer agents can be used during the polymerization of these acrylic polymers. Examples of chain transfer agents include thioglycolic acid esters such as alkyl thiols, alkyl sulfides, alkyl disulfides, and 2-ethylhexyl mercaptoacetate; α-methylstyrene dimers; mercapto acids such as β-mercaptopropionic acid; and aromatic thiols such as benzyl thiols, thiophenols, thiocresols, and thionaphthols.

[0078] (graft copolymer)

[0079] The acrylic resin composition described in this embodiment may further include a graft copolymer having a core / shell structure. Furthermore, when forming a coating using a solution casting method, the aforementioned acrylic resin composition and the graft copolymer having a core / shell structure can be added to the solvent, respectively. The graft copolymer having a core / shell structure can impart mechanical strength such as flexural strength and crack resistance to the acrylic resin film.

[0080] Graft copolymers with a core / shell structure are called multi-segment polymers, multilayer polymers, or core / shell polymers. These polymers are polymers with polymer layers (shells) obtained by polymerizing a monomer mixture in the presence of crosslinked polymer particles (core layers). The core and shell layers can each consist of one layer or two or more layers. There are no particular limitations on this type of graft copolymer, and known graft copolymers can be used appropriately. As an example, a graft copolymer can be obtained by polymerizing a monomer mixture with acrylate as the main component with a crosslinking agent to form an acrylate-based rubber-like polymer, and then polymerizing a monomer mixture with methacrylate as the main component in the presence of this acrylate-based rubber-like polymer.

[0081] The graft copolymer can be manufactured using known emulsifiers and through conventional emulsion polymerization. From the viewpoint of suppressing foaming marks during the drying of acrylic resin films, it is preferable to use alcohol-soluble ionic emulsifiers and manufacture it through emulsion polymerization.

[0082] Furthermore, when granulation of the graft copolymer is performed using coagulants such as calcium chloride or magnesium chloride, the aforementioned ionic emulsifier exists in the form of polyvalent cation salts. Therefore, from the viewpoint of suppressing foaming marks on the resin film, it is preferable to use a known cleaning method to clean the graft copolymer in advance to reduce the salt content in the graft copolymer.

[0083] The ratio of the acrylic polymer to the graft copolymer having a core / shell structure in the acrylic resin composition is preferably 1 to 50 parts by weight, more preferably 5 to 40 parts by weight, and particularly preferably 7 to 30 parts by weight relative to 100 parts by weight of the acrylic polymer.

[0084] If the proportion of graft copolymers with a core / shell structure is 1 part by weight or more, the strength can be improved by blending graft copolymers with a core / shell structure. Furthermore, if the proportion is 50 parts by weight or less, the acrylic resin film exhibits excellent heat resistance, elastic modulus, and good processability during film formation.

[0085] When dissolving and dispersing the aforementioned graft copolymer in a solvent used in a solution coating, it is preferable to use a solvent that does not easily swell. It can be considered that, for example, a graft copolymer with a high crosslinking density of the core layer crosslinked polymer inhibits solvent penetration into the core layer and suppresses swelling of the graft copolymer without reducing the density of the molecular chains in the shell layer, maintaining the steric repulsion effect between the particles. As a result, it exhibits good particle dispersibility.

[0086] The acrylic resin composition described in this embodiment contains an ionic emulsifier, thus suppressing the aggregation of graft copolymer particles with a core / shell structure and exhibiting good dispersion. Furthermore, it also contributes to improving the long-term stability of solution coatings (preventing aggregation even during long-term storage).

[0087] (Other ingredients)

[0088] When manufacturing acrylic resin films using solution casting, known additives such as light stabilizers, ultraviolet absorbers, heat stabilizers, antioxidants, matting agents, light diffusing agents, colorants, dyes, pigments, antistatic agents, heat reflective materials, lubricants, plasticizers, and fillers can be appropriately mixed into the aforementioned acrylic resin composition; or styrene-based resins such as acrylonitrile-styrene resin, methyl methacrylate-styrene resin, and styrene-maleic anhydride resin; polycarbonate resins; polyvinyl alcohol acetal resins; cellulose acylate resins; polyvinylidene fluoride; and poly(meth)acrylate fluorine... Alkyl ester resins and other fluorinated resins, organosilicon resins, polyolefin resins, polyethylene terephthalate resins, polybutylene terephthalate resins, and other resins. In addition, for the purpose of adjusting the orientation and birefringence of the formed film, inorganic microparticles with birefringence as described in Japanese Patent No. 3648201 and Japanese Patent No. 4336586, and low molecular weight compounds with birefringence and a molecular weight of 5000 or less, preferably 1000 or less as described in Japanese Patent No. 3696649, can be appropriately mixed to produce a solution coating.

[0089] (Solution casting method)

[0090] The acrylic resin composition described in this embodiment is used to manufacture resin films using a solution casting method. Specifically, a solution coating is prepared by making a so-called good solvent that dissolves well in the aforementioned acrylic resin composition. Then, the prepared coating is cast onto the surface of a support, and the solvent is evaporated, thereby manufacturing a resin film.

[0091] There are no particular limitations on the type of good solvent, as long as the aforementioned acrylic resin composition dissolves. Examples 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 these, dichloromethane is a suitable example, considering its ability to dissolve acrylic resin compositions well.

[0092] In solution coatings, it is preferable to add an alcohol, which is a poor solvent, along with a good solvent. As the aforementioned alcohol, examples include straight-chain or branched aliphatic alcohols having 1 to 4 carbon atoms. Ethanol and / or methanol are preferred.

[0093] By adding the aforementioned alcohol, the drying efficiency of the coating is increased. In addition, the evaporated alcohol creates multiple pores in the parts of the film, causing the film to become more porous. As a result, a film with excellent adhesion to other substrates such as polarizers can be obtained.

[0094] The amount of the aforementioned alcohol added is preferably 1 to 25% by weight of the total amount of solvent added to the coating, more preferably 2 to 20% by weight, and even more preferably 3 to 15% by weight.

[0095] Methods for producing solution coatings include: first, preparing granules containing an acrylic resin composition, and, depending on the case, other components such as graft copolymers; then mixing the granules with a solvent to produce a solution coating in which each component is dissolved and dispersed in the solvent; or, adding each component separately to a solvent and mixing them to produce a solution coating; or, preparing two or more coating preparation liquids and mixing them to produce a solution coating. From the viewpoint of ensuring uniform mixing / dispersion of the components in the solution coating, the preferred method is to prepare granules containing an acrylic resin composition, and, depending on the case, other components such as graft copolymers, and then mixing the granules with a solvent to produce a solution coating in which each component is dissolved and dispersed in the solvent.

[0096] The resulting solution coating has low levels of insoluble matter and excellent transparency during the solution coating stage, which is essential for obtaining highly transparent resin films that are less prone to foaming marks during film drying. The presence or absence of insoluble matter in the alcohol component, which can cause foaming marks, can be preventively detected by evaluating the transparency of the solution coating.

[0097] As one of the indicators for determining the transparency of solution coatings containing dissolved acrylic resin compositions, there is a method for measuring the haze of a solution coating prepared by dissolving an acrylic resin composition at a specified solids concentration in a solvent containing a specified good solvent / bad solvent alcohol.

[0098] Regarding the acrylic resin composition described in this embodiment, the haze of the coating obtained by dissolving the composition at a concentration of 5% by weight in a mixed solvent of 95% by weight dichloromethane and 5% by weight methanol is preferably 5% or less. When an acrylic resin composition capable of producing a solution coating with such low haze is used to produce a resin film by solution casting, foaming marks during film drying are less likely to occur on the film surface, resulting in a film with excellent appearance and high transparency.

[0099] The coating dissolution process can also be implemented by appropriately adjusting the temperature and pressure. After the dissolution process, the resulting coating solution can be filtered and degassed. Next, the aforementioned coating solution is transported to a pressure die using a pump, and the coating solution is cast from the slit of the pressure die onto the surface (mirror surface) of a support such as a metal or synthetic resin annular belt or rotating cylinder to form a coating film. The formed coating film is heated on the aforementioned support to evaporate the solvent and form a thin film. The temperature conditions for solvent evaporation can be appropriately determined according to the boiling point of the solvent used. The film obtained in this way is peeled off from the support. Subsequently, the resulting film can be subjected to drying, heating, stretching, and other processes as appropriate.

[0100] (Resin film)

[0101] The resin film described in this embodiment uses the aforementioned solution coating and is formed by solution casting. The thickness of the resin film is not particularly limited, but is preferably 5 to 200 μm, more preferably 5 to 100 μm. If the thickness of the resin film is 200 μm or less, the cooling after molding becomes more uniform, thus tending to result in uniform optical properties or faster drying speed. Furthermore, if the thickness of the resin film is 5 μm or more, the resin film tends to be easy to handle and has excellent function as a protective film.

[0102] When the aforementioned resin film is measured with a film thickness of 40 μm, the haze is preferably 2% or less, more preferably 1.5% or less, even more preferably 1% or less, further preferably 0.8% or less, even more preferably 0.6% or less, and particularly preferably 0.4% or less. When the haze meets this range, the transparency is high, and therefore, optical components requiring light transmittance can be suitably used.

[0103] Furthermore, the resin film formed by molding the acrylic resin composition described in this embodiment using the solution casting method is preferably used as a film for laminating and protecting the surface of other substrates, more preferably as an optical film, and particularly preferably as a protective film for polarizing components.

[0104] When used as a protective film for polarizing elements, low optical isotropy is preferable. It is particularly preferable that not only is the optical isotropy of the resin film low in the in-plane direction (length direction and width direction), but also in the thickness direction.

[0105] More specifically, the absolute value of the in-plane phase difference is preferably 10 nm or less, more preferably 5 nm or less, and particularly preferably 3 nm or less. Furthermore, the absolute value of the phase difference in the thickness direction 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. A resin film having this phase difference can be suitable as a protective film for the polarizing element in a polarizing plate of a liquid crystal display device.

[0106] Here, the phase difference is an index value calculated based on birefringence. The in-plane phase difference (Re) and the thickness direction phase difference (Rth) can be calculated using the following formulas. In an ideal molded body with perfect optical isotropy in three dimensions, both the in-plane phase difference (Re) and the thickness direction phase difference (Rth) are zero.

[0107] Re = (nx - ny) × d

[0108] Rth=((nx+ny) / 2-nz)×d

[0109] In the above formula, nx, ny, and nz represent the refractive indices along each axis when the in-plane extension direction (the orientation direction of the polymer chain) 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 molded body is set as the Z-axis. Additionally, d represents the thickness of the molded body. nx-ny represents orientation birefringence. It should be noted that when the MD direction of the molded body is set as the X-axis, in the case of a stretched molded body, the stretching direction is set as the X-axis.

[0110] The preferred orientation birefringence of the resin film formed by solution casting of the acrylic resin composition described in this embodiment is -2.6 × 10⁻⁶. -4 ~2.6×10 -4 More preferably -1.7×10 -4 ~1.7×10 -4 Further preferred value is -1.0×10 -4 ~1.0×10 -4 The preferred value is -0.5×10. -4 ~0.5×10 -4 The optimal value is -0.2×10 -4 ~0.2×10 -4 If the orientation birefringence is within the above range, birefringence will not occur during molding and processing, resulting in stable optical properties. Furthermore, it is also very suitable as an optical thin film for use in liquid crystal displays and the like.

[0111] The photoelastic constant of the resin film formed by molding the acrylic resin composition described in this embodiment using a solution casting method is preferably -6 × 10⁻⁶. -12 ~6×10 -12 Pa -1 More preferably -4×10 -12 ~4×10 -12 Pa -1 Further preferred is -2×10 -12 ~2×10 -12 Pa -1 A further preferred value is -1×10 -12 ~1×10-12 Pa -1 The preferred value is -0.5×10. -12 ~0.5×10 -12 Pa -1 The optimal value is -0.2×10 -12 ~0.2×10 -12 Pa -1 .

[0112] Here, photoelastic birefringence refers to the birefringence caused by the elastic deformation (deformation) of the polymer within a molded body under stress. In practice, the degree of photoelastic birefringence of the material can be evaluated by determining the inherent photoelastic constant of the polymer. First, stress is applied to the polymer material, and the birefringence during elastic deformation is measured. The proportionality constant of the obtained birefringence to stress is the photoelastic constant. By comparing this photoelastic constant, the birefringence of the polymer under stress can be evaluated. If the photoelastic constant is within the aforementioned range, birefringence will not occur even when the molded body is deformed due to stress, thus resulting in a molded body with low optical isotropy. For example, in applications using polarizer protective films, stable optical properties can be maintained even when panel deformation occurs during transportation due to moisture and temperature in the air, thus minimizing quality risks such as image degradation.

[0113] Example

[0114] The present invention will be specifically described below through examples, but the present invention is not limited to these examples. It should be noted that the test / evaluation methods for each physical property described in the examples and comparative examples are as follows.

[0115] (1) Weight-average molecular weight (Mw)

[0116] The weight-average molecular weight (Mw) of the acrylic polymers was calculated using the standard polystyrene conversion method of gel permeation chromatography (GPC). A column packed with polystyrene crosslinked gel (model: Shodex GPC K-806M, manufactured by Showa Denko Corporation) was used as the GPC column, and chloroform was used as the GPC solvent. The sample solution was prepared by dissolving 5 mg of the acrylic resin composition powder in 2 ml of chloroform, and the column temperature was set to 40 °C.

[0117] (2) Volume average particle size of polymeric latex

[0118] Using a Microtrac UPA150 (manufactured by Nikkiso Corporation), the volume average particle size of acrylic polymer latex was determined based on the principle of dynamic light scattering.

[0119] (3) Volume average particle size of bead-shaped particles

[0120] Using a Microtrac MT3300EXII (manufactured by Nikkiso Corporation), the volume average particle size of the bead-like particles was determined based on the principle of laser diffraction scattering.

[0121] (4) Glass transition temperature (Tg)

[0122] The glass transition temperature (Tg) of acrylic polymers was determined using a differential scanning calorimeter (DSC, model: Q1000, manufactured by TA Instruments). The sample was placed under a nitrogen gas flow and heated to 200°C at a heating rate of 10°C / min, then rapidly cooled to 40°C, and then heated again to 200°C at a heating rate of 10°C / min. The average of the heterodyne glass transition onset temperature and the heterodyne glass transition end temperature observed during the second heating was calculated and taken as the glass transition temperature (Tg).

[0123] (5) Methanol solubility test of surfactant

[0124] Measure 15 mg of the surfactant used to manufacture the acrylic polymer (for liquid substances, evaporate to dryness to obtain a dry powder) and add it to 10 ml of methanol. Confirm its solubility in methanol by visual inspection. The solubility parameters are shown below.

[0125] 〇 (soluble)

[0126] △ (Dissolution occurs, but takes time)

[0127] ×(insoluble)

[0128] "〇 (Soluble)" means that when the dry powder of the surfactant is added to methanol, it dissolves rapidly in methanol if shaken. On the other hand, "△ (Dissolves, but takes time)" means that when the dry powder of the surfactant is added to methanol, no change is observed immediately, but it slowly dissolves and eventually dissolves after continuous shaking for a while. "× (Insoluble)" means that it does not dissolve even with continuous shaking.

[0129] (6) Haze measurement of solution coatings

[0130] A mixed solvent of dichloromethane and methanol in a weight ratio of 95:5 was prepared. Powdered acrylic resin composition was added to this mixed solvent at a solids concentration of 5% by weight. The mixture was then stirred and mixed using a stirrer blade to produce a solution coating. After degassing the resulting solution coating, the haze was measured using a haze meter (NHK Denshoku Kogyo Co., Ltd., HAZE Meter NDH4000) with the mixed solvent of dichloromethane and methanol in a weight ratio of 95:5 as a standard sample, after zeroing the meter.

[0131] (7) Evaluation of foaming marks in acrylic resin films

[0132] An acrylic resin composition was added to a mixed solvent of dichloromethane and methanol in a weight ratio of 80:20, with the solids content set at 10% by weight. The mixture was then stirred and mixed using a stirrer blade to prepare a solution coating. Next, using a rod coater, the solution coating was deposited onto a glass plate to a thickness of 1.1 mm using a solution casting method and held for 10 minutes. The resulting film was then rapidly cut into 5.5 cm × 5.5 cm pieces, fixed in place with a 6 cm × 6 cm metal frame, and placed in a drying oven at 190°C for 10 minutes to dry.

[0133] After being removed from the drying oven, the surface of the film portion fixed by the metal frame was observed using an optical microscope. It should be noted that the high degree of film foaming indicates that the film portion directly exposed to hot air in the drying oven experiences turbidity (foaming), representing a harsh drying condition. On the other hand, the film portion fixed by the metal frame showed suppressed foaming even under harsh drying conditions, allowing for the detection of foaming traces with good accuracy through accelerated testing.

[0134] Based on the following indicators, the state of foaming traces on the surface of a thin film observed by an optical microscope is functionally evaluated through five stages, ranging from 1 (poor) to 5 (good) by visual inspection.

[0135] 1 (Foaming marks were observed throughout the surface)

[0136] 2 (Although not the entire surface, foaming marks were observed, and there were many of them.)

[0137] 3 (Foaming marks were observed on the surface, but in small quantities)

[0138] 4 (Slight foaming marks are observed on the surface, which is generally an aesthetically pleasing surface)

[0139] 5. (The surface has no foaming marks, making it a very aesthetically pleasing surface.)

[0140] (8) Haze measurement of acrylic resin films

[0141] A solvent was prepared by mixing dichloromethane and methanol in a weight ratio of 80:20. An acrylic resin composition was added to this solvent at a solids concentration of 10% by weight. The mixture was then stirred and mixed using a stirrer blade to prepare a solution coating. Next, using a rod coater, the solution coating was deposited onto a glass plate to a thickness of 1.1 mm using a solution casting method and held for 10 minutes. When the film was peeled off the glass plate and its thickness was measured, the average film thickness was found to be 40 μm. The haze of the resulting film was measured using a haze meter (Suga Test Instruments HZ-V3) according to the method described in JIS K7105.

[0142] The embodiments are described in detail below, but unless otherwise specified, "parts" and "%" mean "parts by weight" and "% by weight". In addition, the abbreviations refer to the following substances respectively.

[0143] MMA: Methyl methacrylate

[0144] BMA: n-Butyl methacrylate

[0145] 2-EHMA: 2-Ethylhexyl methacrylate

[0146] PhMI: N-Phenylonmaleimide

[0147] DSS: Sodium dioctylsulfosuccinate

[0148] DBS: Sodium dodecylbenzenesulfonate

[0149] NPS: Sodium persulfate

[0150] NDS: Sodium metabisulfite

[0151] SFS: Sodium hyposulfite-formaldehyde

[0152] ED: Disodium ethylenediaminetetraacetate

[0153] FeSO4: Ferrous sulfate heptahydrate

[0154] 2-EHTG: 2-Ethylhexyl mercaptoacetic acid

[0155] LPO: lauroyl peroxide

[0156] t-BHP: tert-butyl hydroperoxide

[0157] PSF: Semi-solidified potassium taurine

[0158] HPMC: Hydroxypropyl methylcellulose

[0159] (Example 1: Manufacturing of acrylic polymer A)

[0160] 143 parts deionized water, 0.01 parts sodium hydroxide, and 0.005 parts DSS were added to an 8-liter glass reactor equipped with a paddle mixer. The reactor was then stirred at 175 rpm while purging with nitrogen and heating to 80°C. Once 80°C was reached, 0.03 parts NPS and 0.001 parts NDS were added. Subsequently, a monomer mixture containing 90 parts MMA, 10 parts BMA, and 0.015 parts 2-EHTG was continuously added to the reactor over 80 minutes to allow the reaction to proceed. Additionally, 0.495 parts DSS were added dropwise to the reactor in sequence, starting 15 minutes after the monomer mixture was added. It should be noted that the stirring speed was increased to 200 rpm at 50 minutes and to 240 rpm at 70 minutes. After the addition of the monomer mixture was completed, the reaction was continued for 60 minutes to terminate the polymerization and obtain the polymerized latex. The polymerization conversion rate was 99.5%, and the average particle size was [missing information]. Next, the obtained polymeric latex was evaporated and dried in a drying oven at 75°C for 12 hours to obtain a white powdery resin composition containing acrylic polymer A. Acrylic polymer A has a weight-average molecular weight of 1 million, and the methanol solubility of the DSS used in the polymerization is zero (soluble). The resin composition containing acrylic polymer A contains 0.5 parts by weight of DSS relative to 100 parts by weight of acrylic polymer A.

[0161] Furthermore, the haze of the solution coating obtained using the white powder of the resin composition containing acrylic polymer A was 0.7%, and the visual evaluation of the foaming property of the acrylic resin film prepared by solution casting using the white powder of the resin composition containing acrylic polymer A was 5 points, with a haze of 0.22%. The results are shown in Table 1. Additionally, microscopic photographs of the film surface of the evaluated object taken during the foaming property evaluation are shown below. Figure 1 .

[0162] (Example 2: Manufacturing of acrylic polymer B)

[0163] The amount of DSS continuously added to the reactor was changed to 4.995 parts, and polymerization was carried out using the same method as in Example 1 to obtain a polymerized latex. The polymerization conversion rate was 99.7%, and the average particle size was [missing information]. Using the obtained polymeric latex, a white powdery resin composition containing acrylic polymer B was obtained using the same method as in Example 1. The acrylic polymer B has a weight-average molecular weight of 1.1 million. The resin composition containing acrylic polymer B contains 5.0 parts by weight of DSS relative to 100 parts by weight of acrylic polymer B. The methanol solubility of the surfactant, the haze of the solution coating, the foaming properties of the film, and the haze of the film were evaluated as in Example 1. The results are shown in Table 1.

[0164] (Example 3: Manufacturing of acrylic polymer C)

[0165] The DSS was replaced with DBS, and polymerization was carried out using the same method as in Example 2 to obtain a polymeric latex. Using the obtained polymeric latex, a white powdery resin composition containing acrylic polymer C was obtained using the same method as in Example 2. The weight-average molecular weight of acrylic polymer C was 900,000. The resin composition containing acrylic polymer C contained 5.0 parts by weight of DBS relative to 100 parts by weight of acrylic polymer C. The methanol solubility of the surfactant, the haze of the solution coating, the foaming properties of the film, and the haze of the film were evaluated as in Example 1. The results are shown in Table 1.

[0166] (Example 4: Manufacturing of acrylic polymer D)

[0167] Deionized water (143 parts), sodium hydroxide (0.01 parts), and DSS (0.15 parts) were added to an 8-liter glass reactor equipped with a paddle mixer. The reactor was then stirred at 175 rpm while purging with nitrogen and heating to 85°C. Once 85°C was reached, NPS (0.022 parts) and SFS (0.0005 parts) were added. Subsequently, a monomer mixture containing MMA (85 parts), 2-EHMA (5 parts), and PhMI (10 parts) was continuously added to the reactor over 80 minutes to initiate the reaction. Additionally, DSS (0.55 parts) was added dropwise to the reactor continuously, following the addition of the monomer mixture, starting at the 15-minute mark. It should be noted that the stirring speed was increased to 200 rpm at the 55-minute mark and to 240 rpm at the 70-minute mark. After the monomer mixture was added, a mixed aqueous solution of ED (0.0055 parts), FeSO4 (0.0015 parts), SFS (0.03 parts), DSS (0.3 parts), and t-BHP (0.03 parts) was sequentially added to the reactor. The reaction was then continued for 60 minutes to complete the polymerization and obtain the polymerized latex. The polymerization conversion rate was 99.9%, and the average particle size was [missing information]. Next, the obtained polymeric latex was evaporated and dried in a drying oven at 75°C for 12 hours to obtain a white powdery resin composition containing acrylic polymer D. The weight-average molecular weight of acrylic polymer D is 1.75 million. The resin composition containing acrylic polymer D contains 1.0 part by weight of DSS relative to 100 parts by weight of acrylic polymer D. Following the same procedure as in Example 1, the methanol solubility of the surfactant, the haze of the solution coating, the foaming properties of the film, and the haze of the film were evaluated. The results are shown in Table 1.

[0168] (Example 5: Manufacturing of acrylic polymer E)

[0169] The DSS was replaced with PSF, and polymerization was carried out using the same method as in Example 2 to obtain a polymeric latex. Using the obtained polymeric latex, a white powdery resin composition containing acrylic polymer E was obtained using the same method as in Example 2. The weight-average molecular weight of acrylic polymer E was 1 million. The resin composition containing acrylic polymer E contained 5.0 parts by weight of PSF relative to 100 parts by weight of acrylic polymer E. The methanol solubility of the surfactant, the haze of the solution coating, the foaming of the film, and the haze of the film were evaluated as in Example 1. The results are shown in Table 1.

[0170] (Comparative Example 1: Manufacturing of acrylic polymer F)

[0171] 170 parts deionized water and 0.1 parts anhydrous disodium hydrogen phosphate were added to an 8-liter glass reactor equipped with a paddle mixer. The reactor was then stirred at 300 rpm while purging with nitrogen and heating to 40°C. After adding 0.3 parts LPO, a monomer mixture containing 90 parts MMA, 10 parts BMA, and 0.02 parts 2-EHTG was continuously added over 30 minutes. 30 minutes after the addition of the monomer mixture, 0.4 parts HPMC (METOLOSE 60SH50: manufactured by Shin-Etsu Chemical Co., Ltd.) was continuously added over 30 minutes. After 30 minutes, the reactor temperature was raised, and the reaction began when the internal temperature reached 65°C. At the 100-minute mark of the reaction, the internal temperature of the reactor reached a maximum of 85°C, after which it gradually decreased. The internal temperature was then raised to 95°C and maintained for 60 minutes to complete the polymerization. The volume average particle size of the obtained bead-like particles was 50 μm. The suspension containing the bead-like particles was evaporated and dried in a drying oven at 50°C for 24 hours to obtain a resin composition containing acrylic polymer F. The weight average molecular weight of acrylic polymer F was 1 million. The resin composition containing acrylic polymer F contained 0.4 parts by weight of HPMC relative to 100 parts by weight of acrylic polymer F. HPMC is a nonionic surfactant and not an ionic emulsifier. Following the same procedure as in Example 1, the methanol solubility of the surfactant, the haze of the solution coating, the foaming properties of the film, and the haze of the film were evaluated. The results are shown in Table 1. Additionally, microscopic photographs of the film surface of the evaluated object during the foaming property evaluation are shown in Table 1. Figure 2 .

[0172] [Table 1]

[0173]

[0174] As shown in Table 1, the solution coatings containing acrylic polymers A to E in Examples 1-5 have a haze of 5% or less. The acrylic resin films obtained by casting these compositions using a solution casting method exhibit excellent foaming properties, resulting in films with a beautiful appearance. Furthermore, the aforementioned acrylic resin films have a haze of 2% or less, yielding films with high transparency. These aesthetically pleasing and highly transparent acrylic resin films are suitable for use in optical films such as polarizer protective films.

[0175] On the other hand, in Comparative Example 1, which contains an acrylic polymer F but not an ionic emulsifier, the haze of the solution coating exceeds 5%, and the foaming property of the acrylic resin film obtained by casting the composition using the solution casting method is rated as low, making it impossible to obtain a film with a beautiful appearance.

Claims

1. A resin film formed by solution casting of an acrylic resin composition, said acrylic resin composition being used for film manufacturing based on solution casting, comprising an acrylic polymer and an ionic emulsifier, said acrylic polymer having 30-99.9% by weight of methyl methacrylate units and 0.1-70% by weight of other copolymerizable monomer units as structural units. The content of the ionic emulsifier is 0.1 to 10 parts by weight relative to 100 parts by weight of the acrylic polymer. The acrylic polymer has a weight-average molecular weight of 800,000 or more, and a glass transition temperature of 110°C or more. The other copolymerizable monomer units include at least one selected from the group consisting of maleimide units, methacrylate units with a primary, secondary, or aromatic hydrocarbon group having 2 to 8 carbon atoms at the ester site, methacrylate units with a saturated hydrocarbon group having 7 to 16 carbon atoms at the ester site having a fused ring structure, methacrylate units with a straight-chain or branched group containing an ether bond at the ester site, and vinyl aromatic units. The ionic emulsifier is a sulfonate and includes dialkyl sulfosuccinate.

2. The resin film according to claim 1, wherein, The dialkyl sulfosuccinate comprises at least one salt selected from the group consisting of lithium, sodium, and potassium salts.

3. The resin film according to claim 1 or 2, wherein, The other copolymerizable monomer units comprise (meth)acrylate units and / or maleimide units having 1 to 20 carbon atoms in the ester site, wherein the (meth)acrylate units do not include methyl methacrylate.

4. The resin film according to claim 1 or 2, wherein, The content of the other copolymerizable monomer units is 0.1% to 50% by weight of the total number of structural units of the acrylic polymer.

5. The resin film according to claim 1 or 2, further comprising a graft copolymer having a core / shell structure in an amount of 1 to 50 parts by weight relative to 100 parts by weight of the acrylic polymer.

6. The resin film according to claim 1 or 2, wherein, The haze of a solution coating containing the acrylic resin composition at a concentration of 5% by weight in a mixed solvent of 95% by weight dichloromethane and 5% by weight methanol is less than 5%.

7. The resin film according to claim 1 or 2, wherein, The haze of the resin film is below 2%.

8. The resin film according to claim 1 or 2, wherein, The resin film is a film used for laminating and protecting the surface of other substrates.

9. The resin film according to claim 1 or 2, wherein, The resin film is a protective film for polarizing components.

10. A polarizing plate, which is formed by laminating a polarizing element with the resin film of claim 9.

11. A display device comprising the polarizing plate of claim 10.

12. A method for manufacturing a resin film according to any one of claims 1 to 9, comprising a step of forming a film from the acrylic resin composition and the solvent coating by solution casting.

13. The method for manufacturing a resin film according to claim 12, wherein, The solvent contains 1 to 25% by weight of alcohol.

14. The method for manufacturing a resin film according to claim 13, wherein, The alcohol is ethanol and / or methanol.

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