Resin composition and method for producing same

Abstract

Provided is a resin composition containing: a methacrylic resin having a triad syndiotacticity of 55% or more and a weight average molecular weight (Mw) of 500,000 or more as measured by gel permeation chromatography (GPC); and acrylic crosslinked particles. Also provided are a method for producing the resin composition, a dope for producing a film containing the resin composition, a resin film containing the resin composition, and a polarizing plate and a display device using the resin film.

Description

Resin composition and method for producing same

[0001] The present invention relates to a resin composition and a method for producing the same.

[0002] Methacrylic resins are widely used in various fields due to their excellent transparency, weather resistance, processability, etc. In particular, resin films obtained by molding methacrylic resins are also used in optical applications such as display devices due to their excellent optical properties.

[0003] Known methods for producing resin films include melt extrusion using a T-die and solution casting, in which a dope prepared by dissolving a resin in a solvent is cast onto the surface of a support and then the solvent is evaporated to form a film. Among these methods, the solution casting method has the advantage that the physical stress applied to the resin film during film formation is small, making it difficult for polymer orientation to occur, resulting in isotropic strength and optical properties of the resulting resin film. Another advantage of the solution casting method is that the thickness precision of the resulting resin film is extremely high.

[0004] When producing a resin film by the solution casting method, a methacrylic resin having a high molecular weight is generally used. The use of a high molecular weight methacrylic resin not only makes the method suitable for the solution casting method, but also improves the mechanical properties of the resulting resin film.

[0005] International Publication No. 2019 / 167471

[0006] However, the inventors have conducted studies and found that there is room for improvement in the heat resistance and mechanical properties of resin films using such high molecular weight methacrylic resins.

[0007] An object of the present invention is to provide a resin composition containing a methacrylic resin that can be used to produce a molded article that is excellent in heat resistance and mechanical properties while maintaining transparency, and a method for producing the same.

[0008] Specific means for solving the above problems include the following embodiments. <1> A resin composition comprising: a methacrylic resin having a triad syndiotacticity of 55% or more and a weight-average molecular weight (Mw) of 500,000 or more as measured by gel permeation chromatography (GPC); and acrylic crosslinked particles. <2> The resin composition according to <1>, in which the mass ratio of the methacrylic resin to the acrylic crosslinked particles is 99.9:0.1 to 65:35. <3> The resin composition according to <1> or <2>, in which the methacrylic resin contains structural units derived from methyl methacrylate in a proportion of 99.5% by mass or more. <4> The resin composition according to <1> or <2>, in which the methacrylic resin has a ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of 1.6 to 2.8. <5> The resin composition according to any one of <1> to <4>, wherein the methacrylic resin has a terminal double bond ratio of less than 0.02 mol% to structural units derived from methyl methacrylate. <6> The resin composition according to any one of <1> to <5>, wherein the methacrylic resin includes a terminal structure represented by the following formula (1) derived from a polymerization initiator: (In the formula, R １ , R ２ , and R ３ each independently represents an alkyl group, a substituted alkyl group, an ester group, or an amide group. １ , R ２ , and R ３ At least one of R represents an ester group or an amide group. １ , R ２ , and R ３Two of the groups may be bonded to each other to form an alicyclic structure. * indicates a bond to a structural unit derived from a monomer.) <7> The resin composition according to any one of <1> to <6>, wherein the acrylic crosslinked particles are core-shell elastomers having a core layer made of a rubbery polymer and a shell layer made of a glassy polymer. <8> A dope for film production by a solution casting method, comprising the resin composition according to any one of <1> to <7> and a solvent, wherein the solvent comprises a first solvent having a hydrogen bond parameter δH of 1 to 12 in Hansen solubility parameters, and a second solvent having the hydrogen bond parameter δH of 14 to 24. <9> A resin film comprising the resin composition according to any one of <1> to <7>. <10> The resin film according to <9>, which has a glass transition temperature of 120°C or higher. <11> The resin film according to <9> or <10>, which has a flex cycle of 2,500 or more in an MIT flex endurance test. <12> The resin film according to any one of <9> to <11>, having an internal haze of 0.4% or less. <13> The resin film according to any one of <9> to <12>, having a b* value of 0.3 or less. <14> The method for producing a resin composition according to any one of <1> to <7>, comprising: a polymerization step of polymerizing a monomer mixture having a methyl methacrylate content of 99.5% by mass or more in the presence of a polymerization initiator and a chain transfer agent, wherein in the polymerization step, the polymerization temperature is less than 100°C until 90% or more of the methacrylic resin is produced, the amount of the chain transfer agent used is 0.03 mol% or less with respect to the total amount of the monomer mixture, and the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiators is 3.0 or less. <15> The method for producing a resin composition according to <14>, wherein the polymerization initiator is a non-nitrile azo polymerization initiator. <16> The method for producing a resin composition according to <14> or <15>, wherein the polymerization step is carried out in an aqueous system in the method for producing the methacrylic resin. <17> The resin film according to any one of <9> to <13>, wherein the resin film is an optical film.<18> The resin film according to any one of <9> to <13>, wherein the resin film is a polarizer protective film. <19> A polarizing plate obtained by laminating a polarizer and the resin film according to any one of <9> to <13>. <20> A display device comprising the polarizing plate according to <19>.

[0009] According to the present invention, it is possible to provide a resin composition that can produce a molded article that has excellent heat resistance and mechanical properties while maintaining transparency, a method for producing the same, and a resin film that includes the resin composition.

[0010] Specific embodiments of the present invention will be described in detail below. The symbol "to" indicating a range of values ​​is used to mean that the range includes both the lower and upper limits, unless otherwise specified.

[0011] <Methacrylic Resin> The methacrylic resin according to this embodiment has a syndiotacticity (rr) of 55% or more, preferably 56% or more, and more preferably 57% or more. When the syndiotacticity (rr) of 55% or more, the glass transition temperature (Tg) of the methacrylic resin increases, and the heat resistance tends to improve. The upper limit of the syndiotacticity (rr) is not particularly limited, but from the viewpoints of the molding temperature and the toughness and secondary processability of the molded body, it is preferably 67% or less, more preferably 65% ​​or less, and even more preferably 63% or less.

[0012] Syndiotacticity (rr) is the proportion of two chains (diads) in a chain of three consecutive structural units (triad) that are both racemo (rr). Chains (diads) of structural units in a polymer molecule that have the same configuration are called meso, and those with the opposite configuration are called racemo, and are represented by m and r, respectively.

[0013] As described in the Examples below, syndiotacticity (rr) was measured in deuterated chloroform at 22°C and 16 cycles. １A H-NMR spectrum is measured, and from the spectrum, the area (X) of the region from 0.60 to 0.95 ppm and the area (Y) of the region from 0.60 to 1.25 ppm when tetramethylsilane (TMS) is set to 0 ppm are measured, and the chromaticity can be calculated using the formula: (X / Y) × 100.

[0014] The methacrylic resin according to this embodiment preferably has a glass transition temperature (Tg) of 120° C. or higher, more preferably 122° C. or higher, and even more preferably 124° C. or higher. There is no particular upper limit to the glass transition temperature (Tg), but from the viewpoint of the molding temperature and secondary processability of the molded article, it is preferably 135° C. or lower, and may be 130° C. or lower.

[0015] The glass transition temperature (Tg) in this specification is the midpoint glass transition temperature determined from a DSC curve, and is measured by the method described in the examples below.

[0016] The syndiotacticity (rr) and glass transition temperature (Tg) of the methacrylic resin can be controlled by adjusting the polymerization temperature during synthesis of the methacrylic resin. For example, lowering the polymerization temperature is preferable for increasing the syndiotacticity (rr) of the methacrylic resin and increasing the glass transition temperature (Tg). The glass transition temperature (Tg) can also be controlled by adjusting the molecular weight of the methacrylic resin.

[0017] The methacrylic resin according to this embodiment has a weight-average molecular weight (Mw) of 500,000 or more. When the weight-average molecular weight (Mw) of the methacrylic resin is 500,000 or more, the mechanical properties of the resulting molded body tend to be improved, and for example, a resin film with excellent bending resistance can be obtained. The weight-average molecular weight (Mw) of the methacrylic resin is preferably 600,000 or more, more preferably 700,000 or more, and even more preferably 800,000 or more. The upper limit of the weight-average molecular weight (Mw) is not particularly limited, but from the viewpoint of moldability, it is preferably 4,000,000 or less, more preferably 3,500,000 or less, even more preferably 3,000,000 or less, even more preferably 2,000,000 or less, and particularly preferably 1,500,000 or less.

[0018] Furthermore, the methacrylic resin according to this embodiment preferably has a dispersity (Mw / Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), of 1.6 to 2.8, more preferably 1.7 to 2.5, even more preferably 1.7 to 2.4, and particularly preferably 1.7 to 2.3. When the dispersity (Mw / Mn) of the methacrylic resin is 1.6 or higher, the flowability of the methacrylic resin tends to be improved and it tends to be easier to mold, and when the dispersity (Mw / Mn) of the methacrylic resin is 2.8 or lower, the mechanical properties of the resulting molded article, such as impact resistance, toughness, and flex resistance, tend to be improved.

[0019] The weight average molecular weight (Mw) and number average molecular weight (Mn) in this specification are values ​​measured by gel permeation chromatography (GPC) in terms of standard polystyrene, and are measured by the method described in the examples below.

[0020] The weight average molecular weight (Mw) and number average molecular weight (Mn) of the methacrylic resin can be controlled by adjusting the types and amounts of the polymerization initiator and chain transfer agent used when synthesizing the methacrylic resin.

[0021] The methacrylic resin according to this embodiment preferably has a proportion of structural units derived from methyl methacrylate of 99.5% by mass or more and a proportion of structural units derived from monomers other than methyl methacrylate of 0.5% by mass or less. By making the proportion of structural units derived from methyl methacrylate 99.5% by mass or more, the transparency of the resin film formed from the resin composition according to this embodiment described below can be improved. Furthermore, since the content of methyl methacrylate is high, there are few impurities, which is also suitable from the viewpoint of recycling. The structural units derived from methyl methacrylate are represented by the following formula:

[0022]

[0023] Examples of monomers other than methyl methacrylate include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; aryl acrylates such as phenyl acrylate; cycloalkyl acrylates such as cyclohexyl acrylate and norbornenyl acrylate; alkyl methacrylates other than methyl methacrylate such as ethyl methacrylate, propyl methacrylate, and butyl methacrylate; aryl methacrylates such as phenyl methacrylate; cycloalkyl methacrylates such as cyclohexyl methacrylate and norbornenyl methacrylate; aromatic vinyl compounds such as styrene and α-methylstyrene; acrylamide; methacrylamide; acrylonitrile; and methacrylonitrile.

[0024] Furthermore, the methacrylic resin according to this embodiment preferably has a 5% weight loss temperature of 300° C. or higher, which allows it to have excellent thermal stability.

[0025] Generally, when producing a resin with a high molecular weight, a method is adopted in which the amount of chain transfer agent and / or polymerization initiator used is reduced. However, for example, when a thiol compound is used as a chain transfer agent, the proportion of propagating radicals terminated by hydrogen abstraction reactions from the chain transfer agent is reduced, and relatively more polymers with terminal double bonds are likely to be produced by disproportionation termination reactions between propagating radicals. Terminal double bonds are known to thermally decompose at a lower temperature than the main chain of the methacrylic resin (e.g., T. Kashiwagi, et al., Macromolecules, 1986, 19, pp. 2160-2168, etc.), which can cause the thermal stability of the resin to deteriorate. In this regard, in the methacrylic resin according to this embodiment, the proportion of terminal double bonds is reduced by adjusting the ratio of the amount of chain transfer agent to the amount of polymerization initiator during production to an appropriate range. As a result, the methacrylic resin according to this embodiment can achieve a 5% weight loss temperature of 300° C. or higher, despite having a high molecular weight of 500,000 or higher weight average molecular weight (Mw).

[0026] The 5% weight loss temperature in this specification is a temperature determined from a thermogravimetric curve, and is measured by the method described in the examples below.

[0027] In the methacrylic resin according to the present embodiment, from the viewpoint of setting the 5% weight loss temperature to 300°C or higher, the ratio of terminal double bonds to structural units derived from methyl methacrylate is preferably less than 0.02 mol%, more preferably less than 0.010 mol%, and even more preferably less than 0.006 mol%.

[0028] The methacrylic resin according to this embodiment can be produced by radical polymerization, as shown in the production method described below. The methacrylic resin produced by radical polymerization contains terminal double bonds generated by disproportionation termination reactions during polymerization, hydrogen abstraction reactions of monomers by a polymerization initiator, and the like. As described above, terminal double bonds affect the thermal stability of the resin, so a low proportion of terminal double bonds is preferable. The proportion of terminal double bonds is controlled by the method described below, and if it can be reduced to less than 0.015 mol%, the thermal stability of the methacrylic resin tends to be significantly improved. The lower limit of the proportion of terminal double bonds is preferably 0 mol%, but may be 0.0005 mol%.

[0029] The ratio of terminal double bonds to structural units derived from methyl methacrylate was determined by the following procedure, as described in the Examples below, under the conditions of 8,192 cycles of accumulation in deuterated chloroform at 20°C. １ A H-NMR spectrum is measured, and from the spectrum, the sum (X) of the areas of the peaks (5.47 to 5.52 ppm and 6.21 ppm) derived from the terminal double bonds of the methacrylic resin and the area (Y) of the peaks (0.5 to 1.25 ppm) derived from the α-methyl groups of the methacrylic resin are measured, and the % y can be calculated using the formula: [(3 × X) / (2 × Y)] × 100.

[0030] The proportion of terminal double bonds in the methacrylic resin can be controlled by adjusting the amounts of polymerization initiator and chain transfer agent used when synthesizing the methacrylic resin, the polymerization temperature, the polymerization time, etc. For example, it is preferable to reduce the amount of polymerization initiator used, increase the amount of chain transfer agent used, lower the polymerization temperature, and extend the polymerization time in order to reduce the proportion of terminal double bonds.

[0031] Furthermore, the methacrylic resin according to this embodiment preferably contains a terminal structure represented by the following formula (1) derived from a polymerization initiator.

[0032] (In the formula, R １ , R ２ , and R ３ each independently represents an alkyl group, a substituted alkyl group, an ester group, or an amide group. １ , R ２ , and R ３ At least one of R represents an ester group or an amide group. １ , R ２ , and R ３ Two of these may be bonded to each other to form an alicyclic structure. * indicates a bond to a structural unit derived from a monomer.)

[0033] Examples of the alkyl group include linear or branched alkyl groups having 1 to 6 carbon atoms. Examples of the substituent that the alkyl group may have include a hydroxy group, a carboxy group, an alkoxy group, and a halogen atom.

[0034] Examples of the ester group include -COOR ４ Examples of the group include a group represented by the following formula: ４ represents an alkyl group having 1 to 6 carbon atoms, which may have a substituent such as a hydroxy group, a carboxy group, an alkoxy group, or a halogen atom.

[0035] Examples of the amide group include —C(O)NR ５ Examples of the group include a group represented by the following formula: ５represents an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group, or an alkenyl group having 2 to 6 carbon atoms, which may have a substituent such as a hydroxy group, a carboxy group, an alkoxy group, or a halogen atom.

[0036] The terminal structure represented by the above formula (1) can be introduced into the molecule of the methacrylic resin by using a non-nitrile azo polymerization initiator represented by the following formula (2) when synthesizing the methacrylic resin. １ , R ２ , and R ３ is synonymous with the above formula (1). Use of such a non-nitrile azo polymerization initiator tends to improve the thermal stability of the resulting methacrylic resin compared to the use of a polymerization initiator other than a non-nitrile azo polymerization initiator (for example, a nitrile azo polymerization initiator). In addition, non-nitrile azo polymerization initiators are also preferred in that the toxicity of the initiator itself and decomposition products tends to be lower compared to nitrile azo polymerization initiators.

[0037]

[0038] Examples of non-nitrile azo polymerization initiators represented by the formula (2) include 2,2'-azobis(dimethyl isobutyrate), 1,1'-azobis(methyl cyclohexanecarboxylate), 2,2'-azobis[N-(2-propenyl)-2-methylpropionamide], 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis(N-cyclohexyl-2-methylpropionamide), 2,2'-azobis{2-methyl-N-[2-(1-hydroxyethyl)]propionamide}, 2,2'-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propionamide}, etc. Among these, from the viewpoints of half-life temperature, cost, etc., at least one selected from 2,2'-azobis(dimethyl isobutyrate) and 1,1'-azobis(methyl cyclohexanecarboxylate) is preferred.

[0039] In the methacrylic resin according to the present embodiment, the residual rate of the chain transfer agent is preferably 0.005% by mass or less, and more preferably substantially 0% by mass (i.e., below the detection limit). The residual rate of the chain transfer agent is measured by the method described in the Examples below.

[0040] The methacrylic resin according to this embodiment not only has excellent heat resistance and thermal stability, but is also expected to be suitable for reuse after disposal, i.e., recycling. Known methods for recycling methacrylic resin include chemical recycling (a method in which cracked oil is recovered as a cracked product by thermal decomposition and reused as a chemical raw material or fuel). Generally, to improve the heat resistance and thermal stability of methacrylic resin, a cyclic structure is introduced into the molecular structure of the methacrylic resin or a monomer having a rigid structure is copolymerized. However, these structures become impurities in chemical recycling and are undesirable. In this regard, the methacrylic resin according to this embodiment has a high proportion of structural units derived from methyl methacrylate, and the yield of monomers recovered as cracked oil is expected to be high, and the resin is expected to exhibit good chemical recyclability.

[0041] <Method for Producing Methacrylic Resin> The method for producing a methacrylic resin according to this embodiment includes a polymerization step in which a monomer mixture containing 99.5% by mass or more of methyl methacrylate is polymerized in the presence of a polymerization initiator and a chain transfer agent. In the polymerization step, the polymerization temperature is kept below 100°C until 90% or more of the resulting methacrylic resin is produced. Here, "until 90% or more of the resulting methacrylic resin is produced" means "until at least 90% conversion is reached" if the polymerization reaction is carried out to a conversion rate of 100%. For example, if the polymerization reaction is terminated at a conversion rate of 50%, it means "until at least 45% conversion is reached." After 90% or more of the resulting methacrylic resin is produced, the polymerization temperature may be raised to 100°C or higher for purposes such as reducing residual monomer components and deactivating residual polymerization initiators. As a method for producing a methacrylic resin, a conventionally known polymerization method can be employed, for example, a radical polymerization method such as continuous bulk polymerization, solution polymerization, emulsion polymerization, emulsifier-free (soap-free) emulsion polymerization, suspension polymerization, etc. Among these, from the viewpoints of the degree of freedom in structural design of the methacrylic resin, ease of polymerization, productivity, etc., a production method involving aqueous polymerization is preferred, suspension polymerization and emulsion polymerization are more preferred, and suspension polymerization is even more preferred.

[0042] [Suspension Polymerization Method] In the suspension polymerization method, a methacrylic resin is synthesized in an aqueous suspension containing a mixture of water, a monomer mixture, a dispersant, a polymerization initiator, a chain transfer agent, and optionally other additives. The order in which the components are mixed is not particularly limited. For example, the aqueous suspension may be prepared by simultaneously mixing the components. Alternatively, an aqueous suspension may be prepared by mixing water, a polymerization initiator, and optionally other additives to prepare an aqueous solution, followed by adding the monomer mixture and the chain transfer agent, and then adding the dispersant. The mass ratio of the resulting methacrylic resin to water (methacrylic resin / water) is preferably 1.0 / 0.6 to 1.0 / 3.0.

[0043] The monomer mixture preferably contains 99.5% by mass or more of methyl methacrylate.

[0044] Examples of dispersants include poorly water-soluble inorganic salts such as tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, and kaolin; and water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, and polyvinylpyrrolidone. When a poorly water-soluble inorganic salt is used as a dispersant, it is effective to use it in combination with an anionic surfactant such as sodium α-olefin sulfonate or sodium dodecylbenzene sulfonate. These dispersants may be added during the polymerization as needed.

[0045] As the polymerization initiator, known polymerization initiators such as azo polymerization initiators, peroxide polymerization initiators, etc. can be used. Among known polymerization initiators, azo polymerization initiators are preferred from the viewpoint of improving the thermal stability of the resulting methacrylic resin.

[0046] It is known that free radicals generated from polymerization initiators can not only undergo addition reactions with monomers, but also hydrogen abstraction reactions in the presence of substances that readily donate hydrogen. In this regard, azo polymerization initiators only generate alkyl radicals, and therefore have lower hydrogen abstraction capacity than peroxide polymerization initiators. Here, if the polymerization initiator has high hydrogen abstraction capacity, for example, when methyl methacrylate is used as the monomer, free radicals generated from the polymerization initiator abstract hydrogen from the α-methyl group of methyl methacrylate or the methyl group of the ester, and polymerization proceeds from the newly generated radicals on the α-methyl group or the methyl group of the ester, resulting in the production of a polymer with a terminal double bond derived from the monomer structure. Therefore, when a polymerization initiator with high hydrogen abstraction capacity is used, the resulting methacrylic resin tends to have insufficient thermal stability. Therefore, to obtain a methacrylic resin with high thermal stability, azo polymerization initiators are more suitable than peroxide polymerization initiators.

[0047] The hydrogen abstraction ability of the polymerization initiator can be measured, for example, by a radical trapping method using α-methylstyrene dimer (ie, α-methylstyrene dimer trapping method).

[0048] Furthermore, as a result of investigations conducted by the present inventors using various polymerization initiators, they found that methacrylic resins synthesized using non-nitrile azo polymerization initiators have terminal structures introduced into the molecules that are more thermally stable than methacrylic resins synthesized using polymerization initiators other than non-nitrile azo polymerization initiators (e.g., nitrile azo polymerization initiators). For this reason, among azo polymerization initiators, non-nitrile azo polymerization initiators are more preferred. Examples of non-nitrile azo polymerization initiators include those represented by the above formula (2). From the standpoints of half-life temperature, cost, and the like, at least one selected from 2,2'-azobis(isobutyrate)dimethyl and 1,1'-azobis(cyclohexanemethyl carboxylate) is preferred.

[0049] The amount of the polymerization initiator used is preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, and even more preferably 0.1 parts by mass or less, relative to 100 parts by mass of the total amount of the monomer mixture. There is no particular lower limit to the amount of the polymerization initiator used, but from the viewpoint of the polymerization rate, it is preferably 0.001 parts by mass or more, relative to 100 parts by mass of the total amount of the monomer mixture.

[0050] Examples of the chain transfer agent include primary alkyl mercaptan chain transfer agents such as n-butyl mercaptan, n-octyl mercaptan, n-hexadecyl mercaptan, n-dodecyl mercaptan, and n-tetradecyl mercaptan; secondary alkyl mercaptan chain transfer agents such as s-butyl mercaptan and s-dodecyl mercaptan; tertiary alkyl mercaptan chain transfer agents such as t-dodecyl mercaptan and t-tetradecyl mercaptan; thioglycolic acid esters such as 2-ethylhexyl thioglycolate, ethylene glycol dithioglycolate, trimethylolpropane tris(thioglycolate), and pentaerythritol tetrakis(thioglycolate); thiophenol, tetraethylthiuram disulfide, pentanephenylethane, acrolein, methacrolein, allyl alcohol, carbon tetrachloride, ethylene bromide, styrene oligomers (such as α-methylstyrene dimer), and terpinolene. These chain transfer agents may be used alone or in combination of two or more.

[0051] Among these chain transfer agents, alkyl mercaptan chain transfer agents and thioglycolic acid esters are preferred from the viewpoints of ease of handling, stability, and the thermal stability of the resulting methacrylic resin, and n-octyl mercaptan is more preferred as the alkyl mercaptan chain transfer agent, and 2-ethylhexyl thioglycolate is more preferred as the thioglycolic acid ester.

[0052] The amount of the chain transfer agent used is preferably 0.03 mol % or less, more preferably 0.025 mol % or less, based on the total amount of the monomer mixture. There is no particular lower limit to the amount of the chain transfer agent used, but it is preferably 0.0015 mol % or more, based on the total amount of the monomer mixture.

[0053] In order to obtain a methacrylic resin having a high weight-average molecular weight (Mw) and a small proportion of terminal double bonds, the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is preferably 3.0 or less, more preferably 2.6 or less, and even more preferably 2.0 or less. There is no particular lower limit to the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator, but it is preferably, for example, 0.1 or more.

[0054] The polymerization temperature during synthesis of the methacrylic resin is set to less than 100° C., preferably 20° C. or higher but less than 100° C., more preferably 30 to 95° C., even more preferably 50 to 90° C., and particularly preferably 60 to 85° C., from the viewpoints of controlling the syndiotacticity of the resulting methacrylic resin and productivity. After the main reaction is completed in the first-stage polymerization, post-polymerization may be carried out at a temperature higher than that of the first stage in order to reduce the residual monomer.

[0055] In addition, since polymerization can be initiated with a small amount of polymerization initiator, it is preferable to carry out the polymerization reaction with a low dissolved oxygen content. The amount of dissolved oxygen in the polymerization raw materials is preferably 10 ppm or less, more preferably 5 ppm or less, even more preferably 4 ppm or less, and particularly preferably 2 ppm or less. By setting the dissolved oxygen content within this range, the polymerization reaction proceeds smoothly and coloration of the methacrylic resin molded body tends to be suppressed. As a method for removing dissolved oxygen from the polymerization raw materials, for example, an inert gas such as nitrogen gas can be fed into the reaction vessel before, during, and after heating to a predetermined polymerization temperature. In order to remove dissolved oxygen from raw materials added during polymerization, it is preferable to separately ventilate these raw materials with an inert gas.

[0056] In order to ensure smooth progress of the polymerization reaction, when a polymerization inhibitor is contained in the monomer mixture, it is preferable to remove the polymerization inhibitor by distillation or alkali extraction, or by using an adsorbent such as alumina, silica gel, molecular sieve, activated carbon, ion exchange resin, zeolite, or acid clay.

[0057] The suspension containing the methacrylic resin obtained by suspension polymerization may be subjected to a washing operation such as acid washing, water washing, alkali washing, etc. in order to remove the dispersant. The number of times these washing operations are performed may be selected optimally in consideration of the working efficiency and the efficiency of removing the dispersant, and may be performed once or multiple times.

[0058] A conventionally known dehydration method can be used to separate the methacrylic resin from the suspension containing the methacrylic resin, such as a method using a centrifuge or a method of removing water by suction on a porous belt or a filter membrane.

[0059] The hydrous methacrylic resin obtained through the dehydration can be dried and recovered by a conventionally known method. Examples of drying methods include hot air drying, which involves blowing hot air into a tank from a hot air blower, blow heater, etc.; vacuum drying, which involves reducing the pressure in the system and then heating it as needed; barrel drying, which involves rotating the obtained methacrylic resin in a container to remove moisture; and spin drying, which involves drying using centrifugal force. These drying methods may be used alone or in combination of two or more.

[0060] [Emulsion Polymerization Method] In the emulsion polymerization method, a methacrylic resin is synthesized in an emulsion obtained by mixing water, a monomer mixture, an emulsifier, a polymerization initiator, a chain transfer agent, and optionally other additives.

[0061] The monomer mixture preferably contains 99.5% by mass or more of methyl methacrylate, and more preferably contains 100% by mass of methyl methacrylate.

[0062] Examples of emulsifiers include anionic surfactants such as alkyl sulfonates, alkyl benzene sulfonates, dialkyl sulfosuccinates, α-olefin sulfonates, naphthalene sulfonate-formaldehyde condensates, alkyl naphthalene sulfonates, N-methyl-N-acyltaurine salts, and phosphate ester salts (such as polyoxyethylene alkyl ether phosphates); nonionic surfactants; and the like. Examples of the above salts include lithium salts, sodium salts, potassium salts, calcium salts, and magnesium salts. These emulsifiers may be used alone or in combination of two or more. The emulsifier used in emulsion polymerization may remain in the final methacrylic resin.

[0063] When the pH of the emulsion deviates from neutral and becomes acidic or basic, a suitable pH adjuster can be used to prevent hydrolysis of the monomer methyl methacrylate or structural units derived from methyl methacrylate in the methacrylic resin obtained by polymerization. Examples of pH adjusters that can be used include boric acid-potassium chloride-potassium hydroxide, potassium dihydrogen phosphate-sodium hydrogen phosphate, boric acid-potassium chloride-potassium carbonate, citric acid-potassium hydrogen citrate, potassium dihydrogen phosphate-boric acid, and sodium dihydrogen phosphate-citric acid.

[0064] The polymerization initiator and chain transfer agent may be the same as those used in the suspension polymerization method. The polymerization initiator may be a redox initiator, if necessary.

[0065] In order to obtain a methacrylic resin having a high weight-average molecular weight (Mw) and a low proportion of terminal double bonds, the ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator is set to 3.0 or less. The ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator is preferably 2.6 or less, more preferably 2.0 or less. There is no particular lower limit to the ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator, but it is preferably, for example, 0.1 or more.

[0066] A solid or powdery methacrylic resin can be obtained by subjecting the methacrylic resin latex obtained by emulsion polymerization to heat drying or spray drying, or by coagulating the latex by adding a water-soluble electrolyte such as a salt or an acid, followed by heat treatment, separating the resin component from the aqueous phase, and then drying the coagulated latex. The salt is not particularly limited, but a divalent salt is preferred. Specific examples include calcium salts such as calcium chloride and calcium acetate; magnesium salts such as magnesium chloride and magnesium sulfate; and the like. Among these salts, magnesium salts such as magnesium chloride and magnesium sulfate are preferred. During coagulation, commonly added additives such as antioxidants and ultraviolet absorbers may be added.

[0067] Before the coagulation operation, it is preferable to filter the latex with a filter, a mesh, etc. to remove fine polymerization scales. This can reduce fish eyes, foreign matter, etc. caused by the fine polymerization scales when the methacrylic resin is molded into a molded article.

[0068] In this embodiment, the methacrylic resin obtained by aqueous polymerization may be in the form of a powder, granules, or a granular powder containing both powder and granules. Regarding the primary particles that make up the powder, granules, and granular powder, suspension polymerization is suitable for producing primary particles with an average particle size of about 10 to 1000 μm, while emulsion polymerization is suitable for producing primary particles with an average particle size of about 50 to 500 nm. The powder, granules, and granular powder may contain aggregates, which are aggregates of the primary particles.

[0069] After the polymerization is completed, the methacrylic resin may be purified as necessary. Examples of purification methods include dissolving the methacrylic resin in a solvent and dropping the solution into a poor solvent to cause precipitation; heating the methacrylic resin to volatilize and remove impurities; and the like. These methods may be appropriately selected depending on the application, and may be combined with each other.

[0070] <Crosslinked Acrylic Particles> By using a resin composition containing crosslinked acrylic particles, it is possible to obtain a resin film that is excellent in transparency and color tone, and further in mechanical strength such as bending resistance.

[0071] The acrylic crosslinked particles are not particularly limited, and a wide range of hard or soft crosslinked particles can be used, and may be single-layered or multi-layered. As the hard crosslinked particles, methacrylic acid esters such as methyl methacrylate and polyfunctional monomers having two or more non-conjugated double bonds can be used as raw materials, but as described below, they may also be in the form of core-shell polymers. In particular, core-shell elastomers having a core layer made of a rubber-like polymer with excellent thermal stability and a shell layer made of a glassy polymer are preferred.

[0072] The acrylic crosslinked particles can be formed, for example, from a multilayer structure polymer, a graft copolymer known as a core-shell polymer. The multilayer structure polymer is a polymer (core-shell polymer) having a polymer layer (shell layer) obtained by polymerizing a monomer mixture in the presence of polymer particles (core layer).

[0073] In the acrylic crosslinked particles, the average particle diameter of the core layer is preferably 125 to 400 nm. When the average particle diameter of the core layer is 125 nm or more, the strength of the produced resin film can be excellent. Furthermore, when the average particle diameter of the core layer is 400 nm or less, the produced resin film has excellent transparency, appearance, optical properties, etc. The average particle diameter of the core layer is more preferably 130 to 380 nm, and particularly preferably 200 to 260 nm. The average particle diameter of the core layer of the acrylic crosslinked particles of the present invention is calculated by measuring light scattering at a wavelength of 546 nm using a spectrophotometer in the state of the polymer latex of the core layer before polymerization of the shell layer.

[0074] It is preferable to use acrylic crosslinked particles that are easily swellable when dissolved and dispersed in a solvent used in the dope. The degree of swelling can be measured by the method described in International Publication No. WO2018 / 212227.

[0075] The acrylic crosslinked particles preferably have a gel fraction of 90% or less. The gel fraction is the mass ratio of components of the acrylic crosslinked particles that are insoluble in methyl ethyl ketone to the total mass of the acrylic crosslinked particles. If the gel fraction of the acrylic crosslinked particles is 90% or less, the acrylic crosslinked particles contain a considerable amount of components soluble in methyl ethyl ketone, and these soluble components tend to cause the primary particles of the acrylic crosslinked particles to break apart in the dope. The gel fraction is more preferably 87% or less, even more preferably 85% or less, even more preferably 83% or less, and particularly preferably 80% or less. Although the lower limit of the gel fraction is not particularly limited, if it is too low, mechanical properties such as bending resistance of the resin film, cracking during slitting, and cracking during punching may be reduced. Therefore, the gel fraction is preferably 65% ​​or more, more preferably 68% or more, even more preferably 70% or more, and most preferably 73% or more. The gel fraction can be measured by the method described below.

[0076] In a preferred embodiment, the core layer of the acrylic crosslinked particle comprises a rigid polymer (I) containing, as constituent units, 40 to 100 mass% of methacrylic acid ester units (a-1), 60 to 0 mass% of other monomer units (a-2) having a double bond copolymerizable therewith, and 0.01 to 10 mass parts of a polyfunctional monomer unit relative to a total of 100 mass parts of the (a-1) and (a-2); and 60 to 100 mass% of acrylic acid ester units (b-1), 0 to 40 mass% of other monomer units (b-2) having a double bond copolymerizable therewith, and 0.01 to 10 mass parts of a polyfunctional monomer unit relative to a total of 100 mass parts of the (b-1) and (b-2). and a flexible polymer (II) containing 0.1 to 5 parts by mass of a polyfunctional monomer unit as a structural unit, the flexible polymer (II) being bonded to the rigid polymer (I). The shell layer contains 60 to 100% by mass of methacrylic acid ester units (c-1), 40 to 0% by mass of other monomer units (c-2) having a double bond copolymerizable therewith, and a rigid polymer (III) containing 0 to 10 parts by mass of the polyfunctional monomer unit as a structural unit per 100 parts by mass of the total of (c-1) and (c-2), and the rigid polymer (III) is graft-bonded to the rigid polymer (I) and / or the flexible polymer (II).

[0077] In a preferred embodiment, the acrylic crosslinked particles can be obtained by the method described in International Publication No. WO 2018 / 212227. The polymer layer formed in the (I) polymerization step to the (II) polymerization step corresponds to the core layer, and the polymer layer formed after the (III) polymerization step corresponds to the shell layer.

[0078] (I) Polymerization Step In the (I) polymerization step, it is preferable to obtain a rigid polymer (I) by polymerizing 0.01 to 10 parts by mass of a polyfunctional monomer and 0.1 to 4.0 parts by mass of a chain transfer agent relative to a monomer mixture (a) consisting of 40 to 100% by mass of a methacrylic acid ester (a-1) and 60 to 0% by mass of another monomer (a-2) having a double bond copolymerizable therewith, and a total of 100 parts by mass of (a-1) and (a-2).

[0079] The other monomer having a copolymerizable double bond (hereinafter, also referred to as "copolymerizable monomer") is preferably an acrylic acid alkyl ester having an alkyl group with 1 to 12 carbon atoms and / or an aromatic vinyl monomer.

[0080] The monomer mixture (a) preferably comprises 40 to 100% by mass of a methacrylic acid ester, 0 to 35% by mass of an acrylic acid ester, 0 to 10% by mass of an aromatic vinyl monomer, and 0 to 15% by mass of another monomer having a copolymerizable double bond, and particularly preferably comprises 51 to 96.8% by mass of a methacrylic acid ester, 3.1 to 29% by mass of an acrylic acid ester, 0.1 to 10% by mass of an aromatic vinyl monomer, and 0 to 10% by mass of another monomer having a copolymerizable double bond. Within this range, zipping depolymerization under high temperature conditions is suppressed, improving thermal stability, and the resulting acrylic crosslinked particles can be incorporated into a methacrylic resin without impairing the optical properties, such as transparency and color tone, of the methacrylic resin.

[0081] Examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, isobornyl methacrylate, phenyl methacrylate, and benzyl methacrylate. Among these, methacrylic acid alkyl esters having an alkyl group of 1 to 4 carbon atoms are preferred, such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, and t-butyl methacrylate. These may be used alone or in combination of two or more, with methyl methacrylate being particularly preferred.

[0082] The other monomer having a copolymerizable double bond is preferably at least one selected from the group consisting of acrylic acid esters, aromatic vinyl monomers, and copolymerizable monomers other than (meth)acrylic acid esters and aromatic vinyl monomers, and more preferably one or more monomers selected from the group consisting of acrylic acid alkyl esters having an alkyl group with a carbon number of 1 to 12, aromatic vinyl monomers, and copolymerizable monomers other than (meth)acrylic acid esters and aromatic vinyl monomers. The other monomer having a copolymerizable double bond is preferably an acrylic acid alkyl ester having an alkyl group with a carbon number of 1 to 12 and / or an aromatic vinyl monomer.

[0083] The amount of the polyfunctional monomer used in the polymerization step (I) is preferably 0.01 to 10 parts by mass, more preferably 0.01 to 5 parts by mass, and most preferably 0.01 to 2 parts by mass, per 100 parts by mass of the total of (a-1) and (a-2). When the amount of the polyfunctional monomer used is 0.01 part by mass or more, the transparency of the obtained film is improved, and when it is 10 parts by mass or less, excellent mechanical properties can be imparted to the film.

[0084] As the polyfunctional monomer, any of those known as crosslinking agents or crosslinkable monomers can be used. As the crosslinkable monomer, it is more preferable to use allyl methacrylate alone or a combination of allyl methacrylate and another polyfunctional monomer.

[0085] In the polymerization step (I), it is preferable to polymerize the monomer mixture (a) and the mixture of polyfunctional monomers in the presence of a chain transfer agent to obtain the rigid polymer (I).

[0086] The amount of chain transfer agent used in the (I) polymerization step is preferably 0.1 to 4.0 parts by mass per 100 parts by mass of the total of (a-1) and (a-2). The lower limit is more preferably 0.20 parts by mass, and particularly preferably 0.50 parts by mass. The upper limit is more preferably 3.5 parts by mass, and particularly preferably 1.5 parts by mass. Since the chain transfer agent functions to increase the amount of low-molecular-weight free polymer, the use of a larger amount of chain transfer agent reduces the degree of crosslinking of the core layer, making the core layer more susceptible to solvent absorption, improving the swelling of the acrylic crosslinked particles, and making the primary particles of the acrylic crosslinked particles more susceptible to fragmentation, reducing the likelihood of dope turbidity. On the other hand, if an excessive amount of chain transfer agent is used, it may be difficult to obtain sufficient mechanical properties, such as bending resistance, cracking during slitting, and cracking during punching, of the resin film. However, using the chain transfer agent within the above range reduces the likelihood of dope turbidity and allows the production of acrylic crosslinked particles that can impart excellent mechanical properties to the resin film.

[0087] The chain transfer agent used in the polymerization step (I) is not particularly limited, and any chain transfer agent known in the art can be used. The chain transfer agents can be used alone or in combination of two or more.

[0088] Since the thermal stability of the acrylic crosslinked particles is improved when the chain transfer agent contains a sulfur component, alkyl mercaptan chain transfer agents and thiophenol are preferred, and alkyl mercaptan chain transfer agents are more preferred. Among them, n-octyl mercaptan and n-dodecyl mercaptan are preferred, and n-octyl mercaptan is particularly preferred.

[0089] The rigid polymer (I) obtained in the polymerization step (I) of the acrylic crosslinked particles preferably has alkylthio groups derived from an alkyl mercaptan chain transfer agent, and more preferably has primary and / or secondary alkylthio groups derived from a primary and / or secondary alkyl mercaptan chain transfer agent. The alkylthio group refers to a structure represented by the chemical formula RS- (R is an alkyl group), and the primary and / or secondary alkylthio group refers to a structure in which the R is a primary and / or secondary alkyl group.

[0090] (II) Polymerization Step In the (II) polymerization step, it is preferable to obtain a flexible polymer (II) by polymerizing 0.1 to 5 parts by mass of a polyfunctional monomer and 0 to 2.0 parts by mass of a chain transfer agent relative to a monomer mixture (b) consisting of 60 to 100% by mass of an acrylic acid ester (b-1) and 0 to 40% by mass of another monomer (b-2) having a double bond copolymerizable therewith, and a total of 100 parts by mass of (b-1) and (b-2).

[0091] The other monomer having a copolymerizable double bond is preferably at least one selected from the group consisting of methacrylic acid esters and other monomers having a copolymerizable double bond.

[0092] The acrylic acid ester is preferably an alkyl acrylate ester having an alkyl group containing 1 to 12 carbon atoms, such as ethyl acrylate, n-butyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate. These acrylic acid esters may be used alone or in combination of two or more. The alkyl acrylate ester is preferably n-butyl acrylate, and a combination of n-butyl acrylate and ethyl acrylate, or a combination of n-butyl acrylate and 2-ethylhexyl acrylate, is also preferred. In particular, the acrylic acid ester used in the (II) polymerization step preferably contains 50 to 100% by mass of n-butyl acrylate, and particularly preferably 80 to 100% by mass.

[0093] The methacrylic acid ester, other monomer having a copolymerizable double bond, polyfunctional monomer, and chain transfer agent used in the polymerization step (II) are the same as those described in the polymerization step (I). In the polymerization step (II), a chain transfer agent may or may not be used, but it is preferable not to use one.

[0094] (III) Polymerization Step In the (III) polymerization step, it is preferable to obtain a rigid polymer (III) by polymerizing a monomer mixture (c) consisting of 60 to 100 mass% of a methacrylic acid ester (c-1) and 40 to 0 mass% of another monomer (c-2) having a double bond copolymerizable therewith, and 0 to 10 parts by mass of a polyfunctional monomer and 0 to 6 parts by mass of a chain transfer agent per 100 parts by mass of the total of (c-1) and (c-2).

[0095] (III) In order to lower the glass transition temperature of the rigid polymer (III) formed by the polymerization step, the monomer mixture (c) preferably contains an acrylic acid ester. The amount of the acrylic acid ester used in the monomer mixture (c) is preferably 0 to 40% by mass, more preferably 10 to 40% by mass, and most preferably 20 to 30% by mass.

[0096] The acrylic crosslinked particles preferably have a structure in which the hard polymer (III) is grafted to the hard polymer (I) and / or the soft polymer (II). All of the hard polymer (III) may be grafted to the hard polymer (I) and / or the soft polymer (II), or a portion of the hard polymer (III) may be grafted to the hard polymer (I) and / or the soft polymer (II), with the remainder being present as a polymer component (free polymer) that is not grafted to either the hard polymer (I) or the soft polymer (II). The non-grafted polymer component also constitutes a part of the acrylic crosslinked particles.

[0097] The methacrylic acid ester, other monomer having a copolymerizable double bond, polyfunctional monomer, and chain transfer agent used in the polymerization step (III) are the same as those described in the polymerization step (I). In the polymerization step (III), polyfunctional monomers and / or chain transfer agents may or may not be used, but it is preferable not to use them.

[0098] (IV) Polymerization Stage The acrylic crosslinked particles may include a polymerization stage other than the polymerization stages (I) to (III).

[0099] In the polymerization step (IV), it is preferable to obtain a rigid polymer (IV) by polymerizing a monomer mixture (d) consisting of 40 to 100 mass% of a methacrylic acid ester (d-1), 0 to 60 mass% of an acrylic acid ester (d-2), and 0 to 5 mass% of another monomer (d-3) having a copolymerizable double bond, as well as 0 to 10 parts by mass of a polyfunctional monomer and 0 to 6 parts by mass of a chain transfer agent per 100 parts by mass of the total of (d-1), (d-2), and (d-3).

[0100] (IV) In order to lower the glass transition temperature of the rigid polymer (IV) formed by the polymerization step, the amount of the acrylic acid ester (d-2) used is preferably 0 to 55% by mass, particularly preferably 15 to 40% by mass, and most preferably 20 to 40% by mass.

[0101] The methacrylic acid ester, acrylic acid ester, other monomer having a copolymerizable double bond, polyfunctional monomer, and chain transfer agent used in the polymerization step (IV) are the same as those described in the above (I) to (III). In the polymerization step (IV), a polyfunctional monomer and / or a chain transfer agent may or may not be used, but it is preferable not to use them.

[0102] In the preferred embodiment of the acrylic crosslinked particles, the hard polymer (IV) may have a structure in which it is grafted to the hard polymer (I) and / or the soft polymer (II) and / or the hard polymer (III). All of the hard polymer (IV) may be grafted to the hard polymer (I) and / or the soft polymer (II) and / or the hard polymer (III), or a portion of the hard polymer (IV) may be grafted to the hard polymer (I) and / or the soft polymer (II) and / or the hard polymer (III), while the remainder may be present as a polymer component that is not grafted to any of the hard polymer (I), the soft polymer (II), and the hard polymer (III). The polymer component that is not grafted also constitutes a part of the acrylic crosslinked particles.

[0103] Acrylic crosslinked particles can be produced by conventional emulsion polymerization using a known emulsifier. The polymerization initiator used in the polymerization to obtain the acrylic crosslinked particles is preferably a polymerization initiator having a 10-hour half-life temperature of 100°C or less, from the viewpoint of improving the thermal stability of the resin film. The polymerization initiator is not particularly limited as long as it has a 10-hour half-life temperature of 100°C or less. However, the 10-hour half-life temperature of the polymerization initiator is preferably 100°C or less, more preferably 80°C or less, and particularly preferably 75°C or less. Persulfates are also preferred, such as potassium persulfate, sodium persulfate, and ammonium persulfate. Potassium persulfate is particularly preferred.

[0104] The polymerization initiator is preferably used in the polymerization step (I), more preferably in the polymerization step using a chain transfer agent, and particularly preferably in all polymerization steps of the acrylic crosslinked particles.

[0105] The total amount of polymerization initiator used is preferably 0.01 to 1.0 parts by mass relative to 100 parts by mass of the total amount of the monomer mixture constituting the acrylic crosslinked particles. When the acrylic crosslinked particles are obtained by three polymerization stages (I) to (III), when the monomer mixture in each of the polymerization stages (I) to (III) is taken as 100 parts by mass, the amount of each polymerization initiator used is preferably 0.01 to 1.85 parts by mass in the (I) polymerization stage, 0.01 to 0.6 parts by mass in the (II) polymerization stage, and 0.01 to 0.90 parts by mass in the (III) polymerization stage. Furthermore, the amount of polymerization initiator used in the (I) polymerization stage is preferably more than 1% by mass and not more than 29% by mass relative to the total amount of polymerization initiator used.

[0106] The core layer of the acrylic crosslinked particle refers to a crosslinked polymer obtained by carrying out polymerization up to the (II) polymerization stage (therefore, the outermost layer of the core layer is a soft polymer formed in the (II) polymerization stage), and the shell layer refers to a hard polymer obtained by carrying out polymerization after the (II) polymerization stage.

[0107] The acrylic crosslinked particle latex thus obtained is coagulated by spray drying or by adding a water-soluble electrolyte such as a salt or an acid, and then subjected to heat treatment, followed by separating the resin component from the aqueous phase, washing appropriately, and drying, to obtain solid or powdery acrylic crosslinked particles by a known method.

[0108] Here, "soft" means that the glass transition temperature of the polymer is less than 10°C. From the viewpoint of enhancing the impact resistance improving effect such as crack resistance, the glass transition temperature of the soft polymer is preferably less than 0°C, more preferably less than -20°C. Furthermore, "hard" means that the glass transition temperature of the polymer is 10°C or higher.

[0109] The hard polymer constituting the shell layer of the acrylic crosslinked particles (when the shell layer is multilayered, the layer with the highest glass transition temperature among the multilayered layers) preferably has a glass transition temperature of 10° C. or higher and 92° C. or lower. By setting the glass transition temperature of the hard polymer to 92° C. or lower, the bonding strength between polymer molecular chains in the shell layer is weakened, and the cohesive force between primary particles of the acrylic crosslinked particles is reduced, making the primary particles of the acrylic crosslinked particles more likely to break up, and making it difficult for the dope to become cloudy.

[0110] The glass transition temperatures of "soft" and "hard" polymers are calculated using the Fox equation using values ​​given in the Polymer Hand Book (J. Brandrup, Interscience 1989) (e.g., 105°C for polymethyl methacrylate and -54°C for polybutyl acrylate).

[0111] In a preferred embodiment, the polymer (I) obtained in the polymerization step (I) is a hard polymer, the polymer (II) obtained in the polymerization step (II) is a soft polymer, and the polymer (III) obtained in the polymerization step (III) is a hard polymer. Furthermore, the polymer (IV) obtained in the polymerization step (IV) is a hard polymer. Acrylic crosslinked particles having such a configuration have a well-balanced appearance, transparency, weather resistance, gloss, processability, thermal stability, etc. when blended with various methacrylic resins. This allows for the provision of films with excellent thermal stability, weather resistance, gloss, processability, etc., without impairing the excellent color tone, appearance, and transparency unique to the blended methacrylic resin.

[0112] <Resin Composition> The resin composition according to this embodiment contains the methacrylic resin according to this embodiment described above and acrylic crosslinked particles. In the resin composition according to this embodiment, the blending ratio of the methacrylic resin to the acrylic crosslinked particles varies depending on the application of the molded article, etc., but the mass ratio of the methacrylic resin to the acrylic crosslinked particles is preferably 99.9:0.1 to 65:35, and more preferably 99:1 to 65:35. When the acrylic crosslinked particles are core-shell type particles, the mass ratio of the methacrylic resin to the acrylic crosslinked particles is preferably 95:5 to 65:35, and even more preferably 90:10 to 60:40. When the blending amount of the methacrylic resin is 65 parts by mass or more per 100 parts by mass of the combined blending amount of both the methacrylic resin and the acrylic crosslinked particles, the properties of the methacrylic resin can be fully exhibited, and when the blending amount is 95 parts by mass or less, the mechanical strength of the methacrylic resin can be fully improved.

[0113] The resin composition may further contain known additives such as light stabilizers, ultraviolet absorbers, heat stabilizers, matting agents, light diffusing agents, colorants, dyes, pigments, antistatic agents, heat ray reflecting materials, lubricants, plasticizers, stabilizers, flame retardants, mold release agents, polymer processing aids, antioxidants, and fillers, as well as resins other than methacrylic resins. Examples of resins other than methacrylic resins include styrene-based resins such as acrylonitrile-styrene resins and styrene-maleic anhydride resins; polycarbonate resins; polyvinyl acetal resins; cellulose acylate resins; fluorine-based resins such as polyvinylidene fluoride and polyfluorinated alkyl (meth)acrylate resins; silicone-based resins; polyolefin-based resins; polyethylene terephthalate resins; and polybutylene terephthalate resins.

[0114] Furthermore, in order to adjust the orientation birefringence of the molded article, the resin composition according to this embodiment may contain inorganic fine particles having birefringence as described in Japanese Patent No. 3648201, Japanese Patent No. 4336586, etc., or a low molecular weight compound having birefringence and a molecular weight of 5,000 or less (preferably 1,000 or less) as described in Japanese Patent No. 3696649.

[0115] The form of the resin composition according to this embodiment is not particularly limited, and may be a powder, granules, a powder-granular material containing both powder and granules, or pellet-shaped.

[0116] <Dope> The dope used to produce a resin film by a solution casting method contains the resin composition according to the present embodiment described above and a solvent. The solvent preferably contains a first solvent having a hydrogen bond parameter δH of 1 to 12 in the Hansen solubility parameters and a second solvent having a hydrogen bond parameter δH of 14 to 24. The dope according to the present embodiment may further contain other components such as multilayer structure polymer particles, similar to the resin composition according to the present embodiment described above. Each component, such as the methacrylic resin and the multilayer structure polymer particles, is dissolved or dispersed in the solvent.

[0117] Examples of first solvents having a hydrogen bond parameter δH of 1 to 12 include those described in International Publication No. WO 2018 / 212227. These first solvents may be used singly or in combination of two or more. Among these first solvents, methyl ethyl ketone (5.1), chloroform (5.7), and methylene chloride (7.1) are preferred, with methylene chloride being more preferred, due to their excellent solubility for methacrylic resins and fast evaporation rate. The number in parentheses indicates the value of the hydrogen bond parameter δH.

[0118] Examples of second solvents having a hydrogen bond parameter δH of 14 to 24 include methanol (22.3), ethanol (19.4), isopropanol (16.4), butanol (15.8), and ethylene glycol monoethyl ether (14.3). The numbers in parentheses indicate the value of the hydrogen bond parameter δH. These second solvents may be used alone or in combination of two or more. Of these second solvents, methanol and ethanol are preferred, and ethanol is more preferred.

[0119] The proportion of the first solvent contained in the solvent is preferably 55 to 95% by mass, more preferably 60 to 95% by mass, and even more preferably 70 to 95% by mass.

[0120] The content of the methacrylic resin in the dope is not particularly limited and is appropriately determined in consideration of the solubility of the methacrylic resin in the solvent used, the conditions for carrying out the solution casting method, etc. The content of the methacrylic resin is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 15 to 40% by mass.

[0121] The viscosity of the dope can be adjusted appropriately by adjusting the content of the methacrylic resin and other components in the dope. From the viewpoint of coatability, filtration accuracy, etc., the viscosity of the dope is preferably 1,000 Poise (= 100 Pa s) or less, more preferably 500 Poise (= 50 Pa s) or less, and even more preferably 300 Poise (= 30 Pa s) or less. The viscosity of the dope is measured by the method described in the examples below.

[0122] The dope is used to produce a resin film by a solution casting method. When producing a resin film by the solution casting method, the dope according to this embodiment is first cast onto the surface of a support and coated with an applicator to form a uniform film to form a dope film. Alternatively, the dope may be cast onto the support using a pressure die. Next, the formed dope film is heated on the support to evaporate the solvent and form a resin film. The conditions for evaporating the solvent can be determined appropriately depending on the boiling point of the solvent used. The formed resin film is then peeled off from the surface of the support. The obtained resin film may be subjected to a drying process, a heating process, a stretching process, or the like, as appropriate.

[0123] <Resin Film> The resin film according to the present embodiment includes the resin composition according to the present embodiment described above. The resin film according to the present embodiment is produced, for example, by a solution casting method using the dope according to the present embodiment described above.

[0124] The thickness of the resin film according to this embodiment is, for example, preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. Furthermore, the thickness of the resin film according to this embodiment is, for example, preferably 10 μm or more, more preferably 30 μm or more, even more preferably 50 μm or more, and particularly preferably 60 μm or more. If the thickness of the resin film is within the above range, there is an advantage that the resin film is less likely to deform when vacuum forming is performed using the resin film, and breakage is less likely to occur at the deep drawing portion. Furthermore, there is also an advantage that a resin film with uniform optical properties and good transparency can be produced.

[0125] The total light transmittance of the resin film according to the present embodiment is preferably 85% or more, more preferably 88% or more, and even more preferably 91% or more. If the total light transmittance is within the above range, the transparency is high, and the film can be suitably used for optical applications that require light transmittance.

[0126] The glass transition temperature of the resin film according to this embodiment is preferably 120° C. or higher, more preferably 122° C. or higher, and even more preferably 124° C. or higher. If the glass transition temperature is within the above range, the resin film will have sufficient heat resistance.

[0127] Furthermore, the resin film according to this embodiment preferably has a 5% weight loss temperature of 300° C. or higher, and more preferably 305° C. or higher, thereby providing excellent thermal stability.

[0128] The haze of the resin film according to this embodiment is preferably 2.0% or less, more preferably 1.5% or less, even more preferably 1.3% or less, and particularly preferably 1.0% or less. The internal haze of the resin film is preferably 1.5% or less, more preferably 1.0% or less, even more preferably 0.5% or less, and particularly preferably 0.4% or less. When the haze and internal haze are within the above ranges, the film has high transparency and can be suitably used for optical applications requiring light transmittance. The haze consists of the haze inside the film and the haze on the film surface (external), which are referred to as internal haze and external haze, respectively.

[0129] The b* value of the resin film according to this embodiment is preferably 0.3 or less, more preferably 0.25 or less, and even more preferably 0.20 or less.

[0130] The yellow index (YI) of the resin film according to the present embodiment is preferably 1.2 or less, more preferably 1.0 or less, and even more preferably 0.5 or less. When the YI is in the above range, the transparency is high, and therefore the film can be suitably used for optical applications requiring light transmittance.

[0131] The resin film according to this embodiment preferably has excellent mechanical properties, for example, high bending resistance. The MIT bending resistance test and the clamshell bending test are known methods for evaluating bending resistance. For example, the resin film according to this embodiment preferably has a bending count of 2,500 or more, more preferably 3,000 or more, in the MIT bending resistance test. If the number of bendings until breakage is within the above range, the bending resistance of the resin film is sufficient. The number of bendings in the MIT bending resistance test is measured by the method described in the examples below.

[0132] The resin film according to this embodiment can be suitably used as an optical film such as a polarizer protective film. When the resin film according to this embodiment is used as a polarizer protective film, it is preferable that the optical anisotropy is small. In particular, it is preferable that not only the optical anisotropy in the in-plane direction (length direction, width direction) of the resin film but also the optical anisotropy in the thickness direction is small. In other words, it is preferable that the absolute values ​​of both the in-plane retardation and the thickness direction retardation are small. For example, when the measurement wavelength is 590 nm, the absolute value of the in-plane retardation is preferably 20 nm or less, more preferably 15 nm or less. Furthermore, the absolute value of the thickness direction retardation is preferably 50 nm or less, more preferably 20 nm or less, and even more preferably 15 nm or less.

[0133] The retardation is an index value calculated based on birefringence. The in-plane retardation (Re) and thickness direction retardation (Rth) can be calculated by the following formulas. In an ideal resin film that is completely optically isotropic in three-dimensional directions, the in-plane retardation Re and thickness direction retardation Rth are both 0.

[0134] Re = (nx - ny) x d Rth = [(nx + ny) / 2 - nz] x d In the above formulas, nx, ny, and nz represent the refractive index in the respective axial directions, where the in-plane stretching direction (polymer chain orientation direction) is the X axis, the direction perpendicular to the X axis is the Y axis, and the thickness direction of the resin film is the Z axis. Also, d represents the thickness of the resin film, and nx - ny represents the orientation birefringence. The MD direction of the film is the X axis, but in the case of a stretched film, the stretching direction is the X axis.

[0135] The resin film according to this embodiment preferably has an orientation birefringence value of −5.0×10 －４ ~5.0 x 10 －４ , more preferably −4.0×10 －４ ~4.0 x 10 －４ , and more preferably −3.8×10 －４ ~3.8 x 10 －４ If the orientation birefringence is within the above range, birefringence does not occur during molding and stable optical properties tend to be obtained.

[0136] (Stretching) The resin film according to this embodiment may be further stretched. Stretching the resin film can improve the mechanical strength and thickness accuracy of the resin film.

[0137] When stretching the resin film according to the present embodiment, an unstretched resin film is first formed from the dope according to the present embodiment, and then uniaxially or biaxially stretched. Alternatively, during the formation of the resin film, a stretching operation is appropriately performed as the film formation and solvent degassing processes progress. This allows the production of a stretched film (uniaxially or biaxially stretched film). Stretching during film formation and stretching after film formation may be appropriately combined.

[0138] The stretching ratio of the stretched film is not particularly limited and is determined appropriately depending on the mechanical strength, surface properties, thickness accuracy, etc. of the stretched film to be produced. Although it also depends on the stretching temperature, the stretching ratio is generally preferably selected from the range of 1.1 to 5, more preferably from 1.3 to 4, and even more preferably from 1.5 to 3. If the stretching ratio is within the above range, the mechanical properties of the film, such as elongation, tear propagation strength, and flexural fatigue resistance, tend to be significantly improved.

[0139] (Applications) The resin film according to this embodiment can be used in various applications such as transportation equipment, solar cell components, civil engineering and construction components, daily necessities, electrical and electronic devices, optical components, and medical supplies. In particular, the resin film according to this embodiment has excellent heat resistance and optical properties, and therefore can be suitably used for optical applications. Examples of optical applications include optical films such as front panels (cover windows) for various display devices, diffusers, polarizer protective films, polarizing plate protective films, retardation films, light diffusion films, and optically isotropic films.

[0140] Among these, the resin film according to the present embodiment can be suitably used as a polarizer protective film or a front panel (cover window) of a display device. When the resin film according to the present embodiment is used as a front panel (cover window) of various display devices, a functional coating layer such as a primer layer or a hard coat layer may be formed on at least one main surface of the resin film, as necessary. When the resin film according to the present embodiment is used as a polarizer protective film, the resin film according to the present embodiment is bonded to a polarizer to form a polarizing plate. The polarizer is not particularly limited, and any conventionally known polarizer can be used. This polarizing plate is used in display devices such as liquid crystal display devices and organic EL display devices.

[0141] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The methods for measuring various physical properties described in the examples and comparative examples are as follows.

[0142] (1) Polymerization Conversion Rate (Conversion Rate) The polymerization conversion rate was determined by a gravimetric method from the ratio of the weight of solid content remaining after drying to the weight of charged monomer. The weight of solid content was determined by drying resin beads in an oven heated to 150°C for 30 minutes. Conversion rate (%) = (weight of solid content / weight of charged monomer) x 100

[0143] (2) Average particle size of acrylic crosslinked particles The average particle size was measured in the form of latex using a Hitachi High-Technologies Corporation U-5100 ratio beam spectrophotometer and light scattering at a wavelength of 546 nm.

[0144] (3) Gel Fraction of Acrylic Crosslinked Particles 1 g of acrylic crosslinked particles was dissolved in 40 mL of methyl ethyl ketone, followed by centrifugation to separate the polymer component insoluble in methyl ethyl ketone (gel polymer) and the component soluble in methyl ethyl ketone. The resulting gel polymer was dried at 60°C and 5 torr for 10 hours to recover a dried gel polymer. The component soluble in methyl ethyl ketone was poured into 200 mL of methanol and reprecipitated to separate the component soluble in methanol and the component insoluble in methanol (free polymer). Drying was carried out under the same conditions as above to recover the dried free polymer and the dried methanol-soluble component. The gel fraction (%) was calculated from the weight of the dried gel polymer, the weight of the dried free polymer, and the weight of the dried methanol-soluble component using the following formula: (Gel Fraction) = (Weight of Gel Polymer After Drying) / (Weight of Gel Polymer After Drying + Weight of Free Polymer After Drying + Weight of Methanol-Soluble Components After Drying) × 100

[0145] (4) Triad syndiotacticity (rr) of methacrylic resin １ The H-NMR spectrum was measured using a nuclear magnetic resonance spectrometer (AVANCEIII 400 MHz, manufactured by Bruker) in a deuterated chloroform solution at 22°C with 16 accumulations. From the spectrum, the area (X) of the region from 0.60 to 0.95 ppm and the area (Y) of the region from 0.60 to 1.25 ppm, when tetramethylsilane (TMS) was set to 0 ppm, were measured, and the syndiotacticity (rr) expressed in triad form was then calculated using the formula: (X / Y) × 100.

[0146] (5) Average Molecular Weight, Molecular Weight Distribution The weight average molecular weight (Mw), number average molecular weight (Mn), and the ratio of weight average molecular weight to number average molecular weight (Mw / Mn), which is an index of molecular weight distribution, of the methacrylic resin were calculated by a standard polystyrene conversion method using gel permeation chromatography (GPC). Specifically, analysis was carried out using a sample solution prepared by dissolving 40 mg of methacrylic resin in 2 mL of chloroform, with the following equipment and conditions. Measuring instrument: HLC-8220GPC (Tosoh Corporation) Detector: RI detector Eluent: chloroform Guard column: KF-G 4A (manufactured by Resonac Corporation) Analytical column: KF-806M and KF-806L manufactured by Resonac Corporation connected in series Measurement temperature: 40°C Eluent flow rate: 1 mL / min Standard substance: standard polystyrene (Tosoh Corporation)

[0147] (6) Amount of Terminal Double Bonds As a pretreatment, the methacrylic resin was dissolved in methylene chloride, and the solution was dropped into methanol to precipitate and purify the resin. The precipitated resin was collected by suction filtration, dried, and then subjected to analysis. 20 mg of the dried methacrylic resin was dissolved in 0.6 to 0.7 mL of deuterated chloroform to prepare a solution, and the amount of terminal double bonds was measured using a nuclear magnetic resonance spectrometer (Bruker, AVANCE NEO 700 MHz). １ H-NMR was measured. The measurement temperature was 20°C, the number of accumulations was 8,192, and the measurement was performed while eliminating the peak derived from the methoxy group of the methacrylic resin (3.60 ppm, the value when the chemical shift of the solvent peak was set to 7.26 ppm) using the Excitation Sculpting (ES) method, which is a type of solvent elimination method. １ From the H-NMR spectrum, the total area (X) of the peaks (5.47 to 5.53 ppm and 6.21 ppm) derived from the terminal double bonds of the methacrylic resin and the area (Y) of the peaks (0.5 to 1.25 ppm) derived from the α-methyl groups of the methacrylic resin were measured, and then the proportion of the amount of terminal double bonds of the methacrylic resin was calculated using the formula: [(3 × X) / (2 × Y)] × 100.

[0148] (7) Residual Rate of Chain Transfer Agent The residual rate of chain transfer agent in the methacrylic resin was quantified using a gas chromatograph (Agilent Technologies, 7890B). A DB-1 analytical column (Agilent Technologies, 0.8 μm film thickness × 0.20 mm inner diameter × 30 m length) was used, with the inlet temperature set to 150°C and the detector temperature set to 320°C. The column temperature was raised from 35°C to 210°C at a heating rate of 30°C / min, then from 210°C to 260°C at a heating rate of 10°C / min, and further raised from 260°C to 320°C at a heating rate of 20°C / min, and held for 3 minutes. A calibration curve was prepared by the internal standard method using dichloromethane as the measurement solvent and chlorobenzene as the internal standard, and the residual rate of chain transfer agent in the methacrylic resin was calculated.

[0149] (8) Dope Viscosity A methacrylic resin was dissolved in a mixed solvent consisting of 93% by mass of methylene chloride and 7% by mass of ethanol to prepare dopes with solid content (SC) of 10% by mass (Examples 1 and 2), 12% by mass (Example 3), or 25% by mass (Comparative Examples 1 and 2). The dope viscosity was measured using a Brookfield viscometer (BMII, manufactured by Toki Sangyo Co., Ltd.). The temperature of the measurement sample was adjusted to 23°C, and the reading was read at 30 rpm (12 rpm for Examples 1 and 3) using a No. 2 rotor.

[0150] (9) Glass Transition Temperature (Tg) The glass transition temperature of the resin film was measured by the following method. As a pretreatment, the methacrylic resin was heat-treated using a thermogravimetric analyzer (STA7200, manufactured by Hitachi High-Tech Science Corporation) for the purpose of removing residual monomers and decomposition products of the polymerization initiator in the methacrylic resin. Specifically, the heat treatment was performed under the conditions of raising the temperature from 40°C to 190°C at a heating rate of 10°C / min under a nitrogen gas flow of 200 mL / min, and holding at 190°C for 2.0 to 2.5 minutes. The glass transition temperature (Tg) of the methacrylic resin after the heat treatment was measured using a differential scanning calorimeter (DSC; DSC7000X, manufactured by Hitachi High-Tech Science Corporation). First, under a nitrogen flow rate of 40 mL / min, a first temperature increase was performed from 40° C. to 160° C. at a temperature increase rate of 10° C. / min, followed by cooling to 40° C., and then a second temperature increase was performed at a temperature increase rate of 10° C. / min from 40° C. to 160° C. DSC measurement was performed under these conditions. Then, from the DSC curve measured during the second temperature increase, the midpoint glass transition temperature (the temperature at the point where the curve representing the stepwise change in the glass transition intersects with a line equidistant in the vertical direction from both a line obtained by extrapolating the baseline before the inflection point to the higher temperature side and a line obtained by extrapolating the baseline after the inflection point to the lower temperature side) was read.

[0151] (10) 5% Weight Loss Temperature (Td5) The 5% weight loss temperature (Td5) of the resin film and the acrylic crosslinked particle powder was measured using a thermogravimetric analyzer (STA7200, manufactured by Hitachi High-Tech Science Corporation). First, under a nitrogen flow of 200 mL / min, the sample was heated from 40°C to 190°C at a heating rate of 10°C / min for the first time, then cooled to 40°C, and then heated from 40°C to 500°C for the second time at a heating rate of 10°C / min. The temperature at which the weight of the sample decreased to 95% of the weight at the start of the second heating, as determined from the thermogravimetric (TG) curve measured during the second heating, was taken as the 5% weight loss temperature (Td5).

[0152] (11) Retention Heat Stability The retention heat stability of the resin film was evaluated using a thermogravimetric analyzer (STA7200, manufactured by Hitachi High-Tech Science Corporation). First, the sample was heated from 40°C to 190°C at a heating rate of 10°C / min under a nitrogen gas flow of 200 mL / min, and then heat-treated under the conditions of holding at 190°C for 2.0 to 2.5 minutes. Next, after cooling to 40°C, the sample was heated from 40°C to 280°C at a heating rate of 10°C / min, and held at 280°C for 30 minutes, and the mass change was recorded. The mass when the sample temperature reached 280°C was recorded as X ０ , the mass when kept at 280 ° C for 15 minutes is X １５ and the formula: [(X ０ -X １５ ) / X ０ ] × 100, the mass loss rate was calculated and the residence thermal stability was evaluated.

[0153] (12) Total Light Transmittance The total light transmittance of the stretched resin film was measured using a haze meter (HZ-V3, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K7361-1.

[0154] (13) Internal Haze The internal haze of the stretched resin film was measured using a haze meter (HZ-V3, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K7136. The measurement was carried out by sandwiching both sides of the resin film between glycerin and then glass. The obtained results were converted into a film thickness equivalent to 40 μm.

[0155] (14) Yellowness Index (YI) The yellowness index (YI) of the stretched resin film was measured using a spectrophotometer (SC-P, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K 7373. The obtained results were converted into a film thickness equivalent to 40 μm.

[0156] (15) b* Value The b* value of the stretched resin film was measured using a spectrophotometer (SC-P, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS Z8781-4.

[0157] (16) MIT Bending Resistance Test The stretched resin film was cut into a 15 mm wide strip, which was used as a test specimen. This test specimen was set in an MIT Fatigue Resistance Tester Model D manufactured by Toyo Seiki Co., Ltd., so that a crease was formed perpendicular to the stretching direction. Measurement was performed under a test load of 1.96 N, a speed of 175 times / min, a bending clamp curvature radius R of 0.38 mm, and a bending angle of 135° to the left and right, and the number of reciprocal bendings until the test specimen broke was determined. Five measurements were performed, and the arithmetic average value was used as the MIT reciprocal bending number.

[0158] <Production of Methacrylic Resin (Resin A)> A 5-liter glass reactor equipped with an H-shaped impeller stirrer was charged with 150 parts by mass of deionized water, 0.40 parts by mass of tribasic calcium phosphate (dispersant), 0.0075 parts by mass of sodium α-olefin sulfonate, and 0.30 parts by mass of sodium chloride. Under a nitrogen atmosphere, while stirring at 250 rpm, 100 parts by mass of methyl methacrylate (MMA), 0.02 parts by mass of n-octyl mercaptan (n-OM) (chain transfer agent), and 0.012 parts by mass of 2,2'-azobis(isobutyrate)dimethyl (V-601, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (polymerization initiator) were added to the reactor. The temperature of the liquid in the reactor was then raised to 75°C to initiate polymerization. Two hours after the start of polymerization, 0.10 parts by mass of tribasic calcium phosphate was added to the reaction solution. An exothermic peak associated with the gel effect was observed 4 hours and 35 minutes after the start of polymerization. The temperature was raised 5 hours and 30 minutes after the start of polymerization, and the temperature of the liquid in the reactor was raised to 95°C. The conversion rate was 94% 5 hours and 30 minutes after the start of polymerization. Three hours after reaching 95°C, the reactor was cooled to room temperature to terminate the polymerization. The conversion rate at the end of polymerization was 99%. The methacrylic resin bead dispersion obtained by the above polymerization was acid washed and washed with water using 0.1 times the amount of 1N hydrochloric acid by mass relative to the amount of charged monomer to remove dispersants, etc., and then dehydrated and dried to obtain bead-shaped methacrylic resin (resin A).

[0159] <Production of Acrylic Crosslinked Particles (1)> An 8-L polymerization reactor equipped with a stirrer was charged with 175 parts by mass of deionized water, 0.01 parts by mass of polyoxyethylene lauryl ether phosphate, 0.5 parts by mass of boric acid, and 0.05 parts by mass of sodium carbonate. After thoroughly purging the atmosphere inside the polymerization reactor with nitrogen gas, the internal temperature was raised to 80°C, and 26% of (I) shown in Table 1 was added all at once to the polymerization reactor. Subsequently, 0.06 parts by mass of sodium formaldehyde sulfoxylate, 0.006 parts by mass of 2-sodium ethylenediaminetetraacetate, 0.001 parts by mass of ferrous sulfate, and 0.02 parts by mass of t-butyl hydroperoxide were added. After 15 minutes, 0.03 parts by mass of t-butyl hydroperoxide was added, and polymerization was continued for another 15 minutes. Next, 0.01 parts by mass of sodium hydroxide was added as a 2% aqueous solution, 0.09 parts by mass of polyoxyethylene lauryl ether phosphate was added, and the remaining 74% of (I) was added continuously over 60 minutes. Thirty minutes after the completion of the addition, 0.07 parts by mass of t-butyl hydroperoxide was added, and polymerization was continued for another 30 minutes to obtain a polymer of (I). Subsequently, 0.03 parts by mass of sodium hydroxide as a 2% aqueous solution and 0.08 parts by mass of potassium persulfate as a 2% aqueous solution were added, followed by the continuous addition of (II) shown in Table 1 over 150 minutes. After the completion of the addition, 0.02 parts by mass of potassium persulfate as a 2% aqueous solution was added, and polymerization was continued for 120 minutes to obtain a polymer of (II). The average particle size was 225 nm. Subsequently, 0.02 parts by mass of potassium persulfate as a 2% aqueous solution was added, and (III-1) shown in Table 1 was added continuously over 45 minutes, and polymerization was continued for another 30 minutes. Thereafter, (III-2) shown in Table 1 was continuously added over 25 minutes, and polymerization was continued for another 60 minutes to obtain a latex of acrylic crosslinked particles (1). The obtained latex was salted out with magnesium chloride, coagulated, washed with water, and dried to obtain white powdery acrylic crosslinked particles (1). The Td5 of the acrylic crosslinked particles (1) was 294°C, and the gel fraction was 93.7%.

[0160] <Production of Acrylic Crosslinked Particles (2)> An 8-L polymerization apparatus equipped with a stirrer was charged with 180 parts by weight of deionized water, 0.003 parts by weight of polyoxyethylene lauryl ether phosphate, 0.5 parts by weight of boric acid, 0.05 parts by weight of sodium carbonate, and 0.01 parts by weight of sodium hydroxide. After thoroughly purging the atmosphere inside the polymerization apparatus with nitrogen gas, the internal temperature was raised to 80°C, and 0.03 parts by weight of potassium persulfate was added as a 2% aqueous solution. Then, (I) shown in Table 1 was continuously added over 81 minutes. Polymerization was continued for an additional 60 minutes to obtain a polymer of (I). Thereafter, 0.03 parts by weight of sodium hydroxide was added as a 2% aqueous solution, and 0.08 parts by weight of potassium persulfate was added as a 2% aqueous solution. Then, (II) shown in Table 1 was continuously added over 150 minutes. After completion of the addition, 0.02 parts by weight of pure potassium persulfate was added as a 2% aqueous solution, and polymerization was continued for 120 minutes to obtain a polymer of (II). The average particle size was 224 nm. Thereafter, 0.02 parts by mass of potassium persulfate was added as a 2% aqueous solution, and (III) shown in Table 1 was continuously added over 70 minutes. Polymerization was continued for another 60 minutes to obtain a latex of acrylic crosslinked particles (2). The obtained latex was salted out with magnesium chloride, coagulated, washed with water, and dried to obtain white powdery acrylic crosslinked particles (2). The Td5 of the acrylic crosslinked particles (2) was 338°C, and the gel fraction was 79.0%.

[0161]

[0162] Example 1: 93% by weight of methylene chloride was placed in a screw tube container. While stirring with a magnetic stirrer, 10 parts by weight of acrylic crosslinked particle (1) powder was gradually added. The resulting acrylic crosslinked particle dispersion was dispersed using a homogenizer (Ultra-Turrax T25, manufactured by IKA) at 8,000 rpm for 10 minutes, after which 7% by weight of ethanol was added to the dispersion. Subsequently, 90 parts by weight of methacrylic resin (resin A) was gradually added while stirring, and the mixture was stirred until completely dissolved to prepare a resin dope with a solids concentration of 12%. The dope was cast onto a glass substrate and coated with an applicator to form a uniform film. The clearance was adjusted so that the dried thickness was approximately 80 μm. After coating, the dope film was dried in an oven at 40°C for 1 hour, and the resulting resin film was peeled off from the glass substrate. The surface that had adhered to the glass substrate was designated as Side B, and the other side was designated as Side A. The resin film was then fixed to a stainless steel frame and dried in an oven at 140°C for 2 hours to remove residual solvent, yielding a resin film. The resulting resin film was then subjected to width-fixed uniaxial stretching at 145°C. The stretching ratio was set to 2, yielding a stretched resin film (stretched film). Table 2 shows the physical properties.

[0163] Example 2 A resin film and a stretched film were obtained in the same manner as in Example 1, except that 20 parts by mass of acrylic crosslinked particles (1) and 80 parts by mass of methacrylic resin (resin A) were used instead of 10 parts by mass of acrylic crosslinked particles (1) and 90 parts by mass of methacrylic resin (resin A) in Example 1. Table 2 shows the respective physical properties.

[0164] Example 3 A resin film and a stretched film were obtained in the same manner as in Example 1, except that 20 parts by mass of acrylic crosslinked particles (2) and 80 parts by mass of methacrylic resin (resin A) were used instead of 10 parts by mass of acrylic crosslinked particles (1) and 90 parts by mass of methacrylic resin (resin A) in Example 1. Table 2 shows the respective physical properties.

[0165] Comparative Example 1: A screw tube container was charged with 93% by weight of methylene chloride and 7% by weight of ethanol. While stirring with a magnetic stirrer, 100 parts by weight of methacrylic resin (Resin A) was gradually added and stirred until completely dissolved, producing a resin dope with a solids concentration of 12%. The dope was cast onto a glass substrate and coated with an applicator to form a uniform film. The clearance was adjusted so that the dried thickness would be approximately 80 μm. After coating, the dope film was dried in an oven at 40°C for 1 hour, and the resulting resin film was peeled off from the glass substrate. The resin film was then fixed to a stainless steel frame and dried in an oven at 140°C for 2 hours to remove residual solvent, yielding a resin film. The resulting resin film was then subjected to width-fixed uniaxial stretching at 145°C. The stretching ratio was set to 2x, yielding a stretched resin film (stretched film). Physical properties are shown in Table 2. Compared to Examples 1 to 3, the number of MIT back-and-forth bending cycles was low, resulting in poor flex resistance.

[0166] Comparative Example 2 A resin film and a stretched film were obtained in the same manner as in Comparative Example 1, except that a methacrylic resin (Resin B) (Parapet HR-F, manufactured by Kuraray Co., Ltd.) was used instead of the methacrylic resin (Resin A) in Comparative Example 1. The physical properties are shown in Table 2. Compared with Examples 1 to 3, the glass transition temperature was low, resulting in insufficient heat resistance, and the number of MIT reciprocating bending cycles was very small, resulting in very low flex resistance.

[0167] Comparative Example 3 A resin film and a stretched film were obtained in the same manner as in Example 1, except that 20 parts by mass of acrylic crosslinked particles (1) and 80 parts by mass of methacrylic resin (resin B) were used instead of 10 parts by mass of acrylic crosslinked particles (1) and 90 parts by mass of methacrylic resin (resin A) in Example 1. The physical properties are shown in Table 2. Compared with Examples 1 to 3, the glass transition temperature was low, resulting in insufficient heat resistance, the number of MIT back-and-forth bending tests was small, resulting in low bending resistance, and the total light transmittance was below 90%, resulting in low transparency.

[0168] Comparative Example 4 A resin film and a stretched film were obtained in the same manner as in Example 1, except that 20 parts by mass of acrylic crosslinked particles (1) and 80 parts by mass of methacrylic resin (resin C) (Parapet HR-S, manufactured by Kuraray Co., Ltd.) were used instead of 10 parts by mass of acrylic crosslinked particles (1) and 90 parts by mass of methacrylic resin (resin A) in Example 1. The physical properties are shown in Table 2. Compared with Examples 1 to 3, the glass transition temperature was low, resulting in insufficient heat resistance, and the total light transmittance was below 91%, resulting in low transparency.

[0169]

Claims

1. A resin composition comprising: a methacrylic resin having a triad syndiotacticity of 55% or more and a weight average molecular weight (Mw) of 500,000 or more as measured by gel permeation chromatography (GPC); and acrylic crosslinked particles.

2. The resin composition according to claim 1, wherein the mass ratio of the methacrylic resin to the acrylic crosslinked particles is 99.9:0.1 to 65:

35.

3. A resin composition according to claim 1 or 2, wherein the methacrylic resin has a proportion of structural units derived from methyl methacrylate of 99.5 mass% or more.

4. The resin composition according to claim 1 or 2, wherein the methacrylic resin has a ratio (Mw / Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) of 1.6 to 2.

8.

5. A resin composition according to claim 1 or 2, wherein the methacrylic resin has a ratio of terminal double bonds to structural units derived from methyl methacrylate of less than 0.02 mol %.

6. The resin composition according to claim 1 or 2, wherein the methacrylic resin contains a terminal structure represented by the following formula (1) derived from a polymerization initiator. (In the formula, R １ , R ２ , and R ３ each independently represents an alkyl group, a substituted alkyl group, an ester group, or an amide group. １ , R ２ , and R ３ At least one of R represents an ester group or an amide group. １ , R ２ , and R ３ Two of the above may be bonded to each other to form an alicyclic structure. * indicates a bond to a structural unit derived from a monomer.) 7. The resin composition according to claim 1 or 2, wherein the acrylic crosslinked particles are a core-shell type elastomer having a core layer made of a rubber-like polymer and a shell layer made of a glassy polymer.

8. A dope for film production by a solution casting method, comprising the resin composition according to claim 1 or 2 and a solvent, the solvent comprising a first solvent having a hydrogen bond term δH of 1 to 12 in the Hansen solubility parameters, and a second solvent having the hydrogen bond term δH of 14 to 24.

9. A resin film comprising the resin composition according to claim 1 or 2.

10. The resin film according to claim 9, having a glass transition temperature of 120° C. or higher.

11. The resin film according to claim 9, which can be bent 2,500 times or more in an MIT bending endurance test.

12. The resin film according to claim 9, having an internal haze of 0.4% or less.

13. The resin film according to claim 9, having a b* value of 0.3 or less.

14. A method for producing a resin composition according to claim 1 or 2, comprising a polymerization step of polymerizing a monomer mixture having a methyl methacrylate content of 99.5 mass% or more in the presence of a polymerization initiator and a chain transfer agent, wherein in the polymerization step, the polymerization temperature is set to less than 100°C until 90% or more of the methacrylic resin is produced, the amount of the chain transfer agent used is 0.03 mol% or less relative to the total amount of the monomer mixture, and the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is 3.0 or less.

15. The method for producing a resin composition according to claim 14, wherein in the method for producing the methacrylic resin, the polymerization initiator is a non-nitrile azo polymerization initiator.

16. The method for producing a resin composition according to claim 14, wherein in the method for producing the methacrylic resin, aqueous polymerization is carried out in the polymerization step.

17. The resin film according to claim 9, which is an optical film.

18. The resin film according to claim 9, which is a polarizer protective film.

19. A polarizing plate comprising a polarizer and the resin film according to claim 9 laminated together.

20. A display device comprising the polarizing plate according to claim 19.

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