Resin composition and method for producing the same

Abstract

This invention provides a resin composition comprising a methacrylic acid resin having a syndiotactic regularity of 55% or more and a weight-average molecular weight (Mw) of 500,000 or more as determined by gel permeation chromatography (GPC), and acrylic crosslinked particles. Furthermore, a method for manufacturing the resin composition, a casting solution for manufacturing a membrane containing the resin composition, a resin membrane containing the resin composition, and a polarizing plate and a display device utilizing the resin membrane are provided.

Description

Technical Field

[0001] This invention relates to resin compositions and methods for manufacturing the same. Background Technology

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

[0003] Known methods for manufacturing resin films include melt extrusion using a T-die and solution casting, where a casting solution in which resin is dissolved in a solvent is cast onto a support surface and the solvent evaporates to form a film. Solution casting, in particular, has the advantages of minimizing the physical stress applied to the resin film during casting, thus reducing the likelihood of polymer orientation and resulting in isotropic resin films with high strength and optical properties. Furthermore, solution casting also offers the advantage of achieving extremely high thickness accuracy in the obtained resin film.

[0004] When manufacturing resin films using solution casting, high molecular weight methacrylic resins are typically used. Using high molecular weight methacrylic resins not only makes them suitable for solution casting, but also results in resin films with improved mechanical properties.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2019 / 167471 Summary of the Invention

[0008] However, the inventors have discovered through research that there is room for improvement in the heat resistance and mechanical properties of resin films using this high molecular weight methacrylic resin.

[0009] The objective of this invention is to provide a resin composition containing methacrylic resin capable of producing molded articles that maintain transparency while exhibiting excellent heat resistance and mechanical properties, and a method thereof.

[0010] The specific means used to solve the above problems include the following implementation methods.

[0011] <1> A resin composition comprising:

[0012] Methacrylic acid resins having a syndiotactic regularity of ≥55% in their triunit groups and a weight-average molecular weight (Mw) of ≥500,000 as determined by gel permeation chromatography (GPC); and

[0013] Acrylic cross-linked particles.

[0014] <2> According to the resin composition described in <1>, the mass ratio of the methacrylic resin to the acrylic crosslinked particles is 99.9:0.1 to 65:35.

[0015] <3> According to the resin composition described in <1> or <2>, the proportion of structural units derived from methyl methacrylate in the methacrylic resin is 99.5% by mass or more.

[0016] <4> The resin composition according to <1> or <2>, wherein the weight-average molecular weight (Mw) to number-average molecular weight (Mn) ratio (Mw / Mn) of the above-mentioned methacrylic resin is 1.6 to 2.8.

[0017] <5> The resin composition according to any one of <1> to <4>, wherein the proportion of the terminal double bond of the methacrylic resin to the structural unit from methyl methacrylate is less than 0.02 mol%.

[0018] <6> The resin composition according to any one of <1> to <5>, wherein the methacrylic resin comprises an end structure represented by the following formula (1) from the polymerization initiator.

[0019]

[0020] (where R) 1 R 2 and R 3 Each can independently represent an alkyl group, a substituted alkyl group, an ester group, or an amide group. Among them, R... 1 R 2 and R 3 At least one of them represents an ester group or an amide group. R 1 R 2 and R 3 Two of them can bond to each other to form an alicyclic structure. * indicates a bonding site with a structural unit from the monomer.

[0021] <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.

[0022] <8> A casting solution for film manufacturing based on solution casting, comprising the resin composition and solvent described in any one of <1> to <7>.

[0023] The solvents mentioned above include a first solvent with a hydrogen bond term δH of 1 to 12 in the Hansen solubility parameter and a second solvent with a hydrogen bond term δH of 14 to 24.

[0024] <9> A resin film comprising any one of the resin compositions described in <1> to <7>.

[0025] <10> The resin film according to <9> has a glass transition temperature of 120°C or higher.

[0026] <11> The resin film according to <9> or <10>, wherein the number of flexural cycles in the MIT bending resistance test is more than 2500.

[0027] <12> The resin film according to any one of <9> to <11>, wherein the internal haze is 0.4% or less.

[0028] <13> The resin film according to any one of <9> to <12>, wherein the b* value is 0.3 or less.

[0029] <14> A method for manufacturing a resin composition, which is the method for manufacturing the resin composition described in any one of <1> to <7>, wherein the method includes a method for manufacturing a methacrylic resin, said method for manufacturing a methacrylic resin comprising a polymerization step of polymerizing a monomer mixture containing methyl methacrylate at a content of 99.5% by mass or more in the presence of a polymerization initiator and a chain transfer agent.

[0030] In the above polymerization process, the polymerization temperature is less than 100°C until more than 90% of the obtained methacrylic acid resin is produced.

[0031] The amount of the chain transfer agent used is less than 0.03 mol% relative to the total amount of the monomer mixture.

[0032] 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.

[0033] <15> The method for manufacturing the resin composition according to <14>, wherein, in the method for manufacturing the methacrylic resin, the polymerization initiator is a non-nitrile azo polymerization initiator.

[0034] <16> The method for manufacturing the resin composition according to <14> or <15>, wherein, in the method for manufacturing the methacrylic resin, aqueous polymerization is carried out in the polymerization step.

[0035] <17> The resin film according to any one of <9> to <13>, wherein the resin film is an optical film.

[0036] <18> The resin film according to any one of <9> to <13>, wherein the resin film is a polarizer protective film.

[0037] <19> A polarizing plate is formed by laminating a polarizer and a resin film as described in any one of <9> to <13>.

[0038] <20> A display device comprising the polarizing plate described in <19>.

[0039] According to the present invention, a resin composition capable of producing a molded article with excellent heat resistance and mechanical properties while maintaining transparency, a method for manufacturing the same, and a resin film comprising the resin composition can be provided. Detailed Implementation

[0040] The following is a detailed description of specific embodiments of the application of this invention. Unless otherwise specified, the symbol “~” representing a numerical range is used to mean that it includes both the lower and upper limits of the range.

[0041] <Methacrylic Resin>

[0042] The syndiotactic regularity (rr) of the terunit group of the methacrylic resin in this embodiment is 55% or more, more preferably 56% or more, and even more preferably 57% or more. If the syndiotactic regularity (rr) of the terunit group is 55% or more, the glass transition temperature (Tg) of the methacrylic resin tends to increase, and its heat resistance improves. There is no particular upper limit to the syndiotactic regularity (rr), but from the viewpoint of molding processing temperature, as well as the toughness and secondary processability of the molded article, it is preferably 67% or less, more preferably 65% ​​or less, and even more preferably 63% or less.

[0043] Synthetic regularity (rr) is the proportion of chains of three consecutive structural units (triads) where two chains (diads) have racemic configurations (rr). It should be noted that in polymer molecules, chains of structural units (diads) with identical stereoconfigurations are called meso, and those with opposite stereoconfigurations are called racemo, denoted as m and r respectively.

[0044] As described in the examples below, the synthetic stereoregularity (rr) can be calculated as follows: measured in deuterated chloroform at 22°C for a cumulative total of 16 times. 1 The H-NMR spectrum was used to measure 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. The result was calculated using the formula: (X / Y) × 100.

[0045] Furthermore, the glass transition temperature (Tg) of the methacrylic resin in this embodiment is preferably 120°C or higher, more preferably 122°C or higher, and even more preferably 124°C or higher. There is no particular limitation on the upper limit of the glass transition temperature (Tg), but from the viewpoint of molding processing temperature and the secondary processability of the molded article, it is preferably 135°C or lower, and can be 130°C or lower.

[0046] The glass transition temperature (Tg) in this specification is the midpoint glass transition temperature obtained from the DSC curve and determined by the method described in the examples below.

[0047] It should be noted that the syntactic regularity (rr) and glass transition temperature (Tg) of methacrylic acid resin can be controlled by adjusting the polymerization temperature during the synthesis of the methacrylic acid resin. For example, lowering the polymerization temperature is preferred for increasing the syntactic regularity (rr) and glass transition temperature (Tg) of the methacrylic acid resin. Additionally, the glass transition temperature (Tg) can also be controlled by adjusting the molecular weight of the methacrylic acid resin.

[0048] In this embodiment, the weight-average molecular weight (Mw) of the methacrylic resin is 500,000 or more. If the weight-average molecular weight (Mw) of the methacrylic resin is 500,000 or more, there is a tendency to improve the mechanical properties of the resulting molded article; for example, a resin film with excellent flexural strength 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. There is no particular upper limit to the weight-average molecular weight (Mw), but from the viewpoint of moldability, it is preferably 4 million or less, more preferably 3.5 million or less, even more preferably 3 million or less, even more preferably 2 million or less, and particularly preferably 1.5 million or less.

[0049] Furthermore, in this embodiment, the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) of the methacrylic resin, i.e., the dispersibility (Mw / Mn), is preferably 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. If the dispersibility (Mw / Mn) of the methacrylic resin is 1.6 or higher, the methacrylic resin tends to have improved flowability and easier molding; if the dispersibility (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 flexural strength, tend to be improved.

[0050] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) in this specification are values ​​converted from standard polystyrene by gel permeation chromatography (GPC), determined by the methods described in the examples below.

[0051] It should be noted that the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of methacrylic resin can be controlled by adjusting the type and amount of polymerization initiator and chain transfer agent used during the synthesis of methacrylic resin.

[0052] In this embodiment, the methacrylic resin preferably contains 99.5% by mass or more of structural units derived from methyl methacrylate, and 0.5% by mass or less of structural units derived from monomers other than methyl methacrylate. By ensuring that the proportion of structural units derived from methyl methacrylate is 99.5% by mass or more, the resin film formed from the resin composition of this embodiment, described later, can have good transparency. Furthermore, since the content of methyl methacrylate is high, there are fewer impurities, which is also preferable from a recycling viewpoint. It should be noted that the structural units derived from methyl methacrylate are represented by the following formula.

[0053]

[0054] Other monomers besides methyl methacrylate include, for example, alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; aryl acrylates such as phenyl acrylate; cyclohexyl acrylates such as cyclohexyl acrylate and norbornyl acrylate; alkyl methacrylates other than methyl methacrylate such as ethyl methacrylate, propyl methacrylate, and butyl methacrylate; aryl methacrylates such as phenyl methacrylate; cyclohexyl methacrylates such as cyclohexyl methacrylate and norbornyl methacrylate; aromatic vinyl compounds such as styrene and α-methylstyrene; acrylamide; methacrylamide; acrylonitrile; and methacrylonitrile.

[0055] Furthermore, the 5% weight loss temperature of the methacrylic resin in this embodiment is preferably 300°C or higher, thereby exhibiting excellent thermal stability.

[0056] Generally, when manufacturing resins with high molecular weights, methods are adopted to reduce the amount of chain transfer agent and / or polymerization initiator used. However, for example, when a thiol compound is used as a chain transfer agent, the proportion of growth free radicals that stop due to hydrogen abstraction from the chain transfer agent decreases, and relatively speaking, polymers with double-bond ends are easily generated in large quantities through disproportionation termination reactions between growth free radicals. It is known that terminal double bonds undergo thermal decomposition at temperatures lower than the main chain of methacrylic acid resin (e.g., T. Kashiwagi, et al., Macromolecules, 1986, 19, pp. 2160-2168, etc.), which is a cause of deterioration in the thermal stability of the resin. In this regard, the methacrylic acid resin of this embodiment reduces the proportion of terminal double bonds by adjusting the ratio of chain transfer agent dosage to polymerization initiator dosage to an appropriate range during manufacturing. As a result, the methacrylic acid resin of this embodiment, despite having a high molecular weight (Mw) of 500,000 or more, can still achieve a 5% weight loss temperature of 300°C or higher.

[0057] The 5% weight loss temperature in this specification is the temperature obtained from the thermogravimetric curve and determined by the method described in the examples below.

[0058] In the methacrylic resin of this embodiment, from the viewpoint of setting the 5% weight loss temperature to 300°C or higher, the proportion 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%.

[0059] The methacrylic resin of this embodiment, as shown in the manufacturing method described later, can be manufactured by free radical polymerization. The methacrylic resin manufactured by free radical polymerization contains terminal double bonds formed through disproportionation termination reactions during polymerization, hydrogen abstraction reactions of monomers using polymerization initiators, etc. As mentioned above, terminal double bonds affect the thermal stability of the resin, therefore their proportion is preferably low. The proportion of terminal double bonds is controlled by the method described later; if it can be reduced to less than 0.015 mol%, there is a tendency for a significant increase in the thermal stability of the methacrylic resin. It should be noted that the lower limit of the proportion of terminal double bonds is preferably 0 mol%, but can be 0.0005 mol%.

[0060] The ratio of terminal double bonds to structural units derived from methyl methacrylate, as described in the examples described later, can be calculated as follows: in deuterated chloroform, measured at 20°C for a cumulative total of 8192 cycles. 1The total area (X) of the peaks (5.47–5.52 ppm and 6.21 ppm) of the terminal double bond from the methacrylic resin and the area (Y) of the peaks (0.5–1.25 ppm) of the α-methyl group from the methacrylic resin were measured based on the 1H-NMR spectrum, and the result was calculated using the formula: [(3×X) / (2×Y)]×100.

[0061] It should be noted that the proportion of terminal double bonds in methacrylic resin can be controlled by adjusting the amount of polymerization initiator and chain transfer agent used, the polymerization temperature, and the polymerization time during the synthesis of methacrylic resin. For example, reducing the amount of polymerization initiator, increasing the amount of chain transfer agent, lowering the polymerization temperature, and extending the polymerization time are preferred for reducing the proportion of terminal double bonds.

[0062] In addition, the methacrylic resin of this embodiment preferably contains the end structure represented by the following formula (1) from the polymerization initiator.

[0063]

[0064] (where R) 1 R 2 and R 3 Each can independently represent an alkyl group, a substituted alkyl group, an ester group, or an amide group. Among them, R... 1 R 2 and R 3 At least one of them represents an ester group or an amide group. R 1 R 2 and R 3 Two of them can bond to each other to form an alicyclic structure. * indicates a bonding site with a structural unit from the monomer.

[0065] Examples of alkyl groups include straight-chain or split-chain alkyl groups having 1 to 6 carbon atoms. Substituents that alkyl groups may contain include hydroxyl, carboxyl, alkoxy, and halogen atoms.

[0066] As an ester group, for example, -COOR 4 The group represented. R 4 Alkyl groups, representing 1 to 6 carbon atoms, may have substituents such as hydroxyl, carboxyl, alkoxy, and halogen atoms.

[0067] Examples of amide groups include -C(O)NR. 5 The group represented. R 5 It represents an alkyl, cycloalkyl, or alkenyl group having 1 to 6 carbon atoms, and may have substituents such as hydroxyl, carboxyl, alkoxy, or halogen atoms.

[0068] The terminal structure represented by formula (1) above can be introduced into the molecule of methacrylic resin by using the non-nitrile azo polymerization initiator represented by formula (2) below during the synthesis of methacrylic resin. R in the formula... 1 R 2 and R 3 This has the same meaning as formula (1) above. By using this non-nitrile azo polymerization initiator, compared with the case of using polymerization initiators other than non-nitrile azo polymerization initiators (e.g., nitrile azo polymerization initiators), the thermal stability of the obtained methacrylic resin tends to be improved. In addition, non-nitrile azo polymerization initiators tend to have lower toxicity of the initiator itself and decomposition products compared with nitrile azo polymerization initiators, which is also preferred.

[0069]

[0070] Examples of non-nitrile azo polymerization initiators represented by formula (2) above include 2,2'-azobis(isobutyrate) dimethyl ester, 1,1'-azobis(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}, and 2,2'-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propionamide}. From the viewpoints of half-life temperature and cost, at least one of 2,2'-azobis(isobutyrate) dimethyl ester and 1,1'-azobis(cyclohexanecarboxylate) methyl ester is preferred.

[0071] The residual rate of the chain transfer agent in the methacrylic resin of this embodiment is preferably 0.005% by mass or less, more preferably substantially 0% by mass (i.e., less than the detection limit). The residual rate of the chain transfer agent is determined by the method described in the examples below.

[0072] The methacrylic resin of this embodiment not only exhibits excellent heat resistance and thermal stability, but also shows promise for reuse after disposal, i.e., recycling. As a recycling method for methacrylic resin, chemical recycling is known, for example (a method of recovering decomposed oil in the form of decomposition products through thermal decomposition and reusing it as a chemical feedstock or fuel). Generally, to improve the heat resistance and thermal stability of methacrylic resin, cyclic structures are introduced into the molecular structure of the methacrylic resin, or monomers with rigid structures are copolymerized. However, these structures become impurities for chemical recycling and are therefore undesirable. In this regard, it can be predicted that the methacrylic resin of this embodiment has a high proportion of structural units derived from methyl methacrylate and a high yield of monomers recovered in the form of decomposed oil, thus exhibiting good chemical recyclability.

[0073] <Methacrylic Resin Manufacturing Method>

[0074] The method for manufacturing methacrylic resin according to this embodiment includes a polymerization step in which a monomer mixture containing methyl methacrylate at a mass percentage of 99.5% or more is polymerized in the presence of a polymerization initiator and a chain transfer agent. In this polymerization step, the polymerization temperature is less than 100°C until at least 90% of the obtained methacrylic resin is produced. Here, "until at least 90% of the obtained methacrylic resin is produced" means "at least 90% conversion rate" when the polymerization reaction is carried out to 100% conversion rate, and "at least 45% conversion rate" when the polymerization reaction ends at 50% conversion rate. After at least 90% of the obtained methacrylic resin is produced, the polymerization temperature can be increased to 100°C or higher for purposes such as reducing residual monomer content and deactivating residual polymerization initiator. Conventionally known polymerization methods can be used as the method for manufacturing methacrylic resin, such as continuous bulk polymerization, solution polymerization, emulsion polymerization, emulsion-free (soap-free) emulsion polymerization, suspension polymerization, and other free radical polymerization methods. From the perspectives of the freedom of structural design, ease of polymerization, and productivity of methacrylic resin, the manufacturing method of aqueous polymerization is preferred, suspension polymerization and emulsion polymerization are more preferred, and suspension polymerization is further preferred.

[0075] [Suspension polymerization method]

[0076] In suspension polymerization, methacrylic acid resin is synthesized in an aqueous suspension containing water, a monomer mixture, a dispersant, a polymerization initiator, a chain transfer agent, and optional other additives. The order in which the components are mixed is not particularly limited. For example, the components can be mixed simultaneously to prepare the aqueous suspension. Alternatively, the monomer mixture and chain transfer agent can be added after preparing an aqueous solution by mixing water, the polymerization initiator, and optional other additives, followed by the addition of the dispersant to prepare the aqueous suspension. The mass ratio of the resulting methacrylic acid resin to water (methacrylic acid resin / water) is preferably 1.0 / 0.6 to 1.0 / 3.0.

[0077] As a monomer mixture, the preferred content of methyl methacrylate is 99.5% by mass or more.

[0078] 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, methylcellulose, polyacrylamide, and polyvinylpyrrolidone. When using poorly water-soluble inorganic salts as dispersants, combining them with anionic surfactants such as sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate is effective. These dispersants can be added as needed during the polymerization process.

[0079] As polymerization initiators, known polymerization initiators such as azo polymerization initiators and peroxide polymerization initiators can be used. Among known polymerization initiators, azo polymerization initiators are preferred from the viewpoint of improving the thermal stability of the obtained methacrylic resin.

[0080] It is known that free radicals generated by polymerization initiators, in addition to undergoing addition reactions to monomers, can also undergo hydrogen abstraction reactions in the presence of substances that readily donate hydrogen. In this respect, since azo polymerization initiators only generate alkyl radicals, their hydrogen abstraction ability is lower than that of peroxide polymerization initiators. Here, if the polymerization initiator has a high hydrogen abstraction ability, then, for example, when using methyl methacrylate as a monomer, the free radicals generated by the polymerization initiator abstract hydrogen from the α-methyl group of methyl methacrylate and the methyl group of the ester, and polymerization is carried out by the free radicals on the newly generated α-methyl group and the methyl group of the ester. As a result, polymers with double bonds remaining at the ends from the monomer structure are easily formed. Therefore, when using polymerization initiators with high hydrogen abstraction ability, there is a tendency for the obtained methacrylic resin to have insufficient thermal stability. Therefore, to obtain methacrylic resins with high thermal stability, azo polymerization initiators are more suitable than peroxide polymerization initiators.

[0081] The hydrogen abstraction ability of polymerization initiators can be determined, for example, by using the free radical capture method of α-methylstyrene dimer (i.e., α-methylstyrene dimer capture method).

[0082] Furthermore, the inventors conducted studies using various polymerization initiators and found that, compared with methacrylic resins synthesized using polymerization initiators other than non-nitrile azo polymerization initiators (e.g., nitrile azo polymerization initiators), the end structures introduced into the molecule of methacrylic resins synthesized using non-nitrile azo polymerization initiators are thermally stable. Therefore, among azo polymerization initiators, non-nitrile azo polymerization initiators are more preferred. As non-nitrile azo polymerization initiators, examples include the substances represented by the above formula (2), and from the viewpoints of half-life temperature, cost, etc., at least one of 2,2'-azobis(isobutyric acid) dimethyl ester and 1,1'-azobis(cyclohexanecarboxylate) methyl ester is preferred.

[0083] The amount of 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 monomer mixture. There is no particular limitation on the lower limit of the amount of polymerization initiator used, but from the viewpoint of polymerization rate, it is preferably 0.001 parts by mass or more relative to 100 parts by mass of the monomer mixture.

[0084] Examples of chain transfer agents include primary alkyl thiols such as n-butylthiol, n-octylthiol, n-hexadecylthiol, n-dodecylthiol, and n-tetradecylthiol; secondary alkyl thiols such as sec-butylthiol and sec-dodecylthiol; tertiary alkyl thiols such as tertiary dodecylthiol and tertiary tetradecylthiol; thioglycolic acid esters such as 2-ethylhexyl mercaptoacetate, ethylene glycol dimercaptoacetate, trimethylolpropane tris(thioglycolic acid ester), and pentaerythritol tetra(thioglycolic acid ester); thiophenol, tetraethylthiuram disulfide, pentanephenylethane, acrolein, methacrolein, allyl alcohol, carbon tetrachloride, vinyl bromide, styrene oligomers (such as α-methylstyrene dimers), and terpenoid oils. These chain transfer agents can be used alone or in combination of two or more.

[0085] Among these chain transfer agents, from the viewpoints of processability, stability, and thermal stability of the resulting methacrylic resin, alkyl thiol chain transfer agents and mercaptoacetic acid esters are preferred. As alkyl thiol chain transfer agents, n-octyl thiol is more preferred, and as mercaptoacetic acid esters, 2-ethylhexyl mercaptoacetate is more preferred.

[0086] The amount of chain transfer agent used relative to the total amount of the monomer mixture is 0.03 mol% or less, more preferably 0.025 mol% or less. There is no particular limitation on the lower limit of the amount of chain transfer agent used, but it is preferably 0.0015 mol% or more relative to the total amount of the monomer mixture.

[0087] To obtain a methacrylic resin with 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 preferably 3.0 or less, more preferably 2.6 or less, and even more preferably 2.0 or less. There is no particular limitation on the lower limit of the ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator, but for example, it is preferably 0.1 or more.

[0088] From the viewpoint of controlling the isotactic regularity of the obtained methacrylic resin and improving productivity, the polymerization temperature for synthesizing methacrylic resin is less than 100°C, preferably 20°C or higher and less than 100°C, more preferably 30–95°C, further preferably 50–90°C, and particularly preferably 60–85°C. After the main reaction is completed in the first stage of polymerization, in order to reduce residual monomers, the temperature can be increased to a higher temperature than that of the first stage to carry out subsequent polymerization.

[0089] It should be noted that, in order to initiate polymerization with a small amount of polymerization initiator, the polymerization reaction is preferably carried out with a low dissolved oxygen content. The dissolved oxygen content in the polymerization feedstock is preferably 10 ppm or less, more preferably 5 ppm or less, further preferably 4 ppm or less, and particularly preferably 2 ppm or less. By keeping the dissolved oxygen content within this range, the polymerization reaction tends to proceed smoothly, and the coloring of the molded methacrylic resin is also suppressed. As a method for removing dissolved oxygen from the polymerization feedstock, examples include continuously introducing inert gases such as nitrogen into the reaction vessel before, during, and after heating to the predetermined polymerization temperature. To remove dissolved oxygen from the feedstock added during the polymerization process, it is preferable to also introduce inert gases into these feedstocks.

[0090] In addition, in order to facilitate the polymerization reaction, if the monomer mixture contains polymerization inhibitors, it is preferable to remove the polymerization inhibitors in advance by distillation, alkaline extraction, or by using adsorbents such as alumina, silica gel, molecular sieves, activated carbon, ion exchange resins, zeolite, and acid clay.

[0091] To remove the dispersant, the suspension containing methacrylic resin obtained through suspension polymerization can be subjected to cleaning operations such as acid washing, water washing, and alkali washing. The number of these cleaning operations can be selected optimally by considering both operational efficiency and dispersant removal efficiency; it can be performed once or multiple times.

[0092] As a method for separating methacrylic resin from a suspension containing methacrylic resin, conventionally known dehydration methods can be employed. Examples of dehydration methods include using a centrifuge, or removing water by suction from a porous belt or filter membrane.

[0093] The aqueous methacrylic resin obtained after the above dehydration process can be dried and recovered using conventionally known methods. Examples of drying methods include hot air drying, which involves supplying hot air into the tank from a hot air blower or blower heater; vacuum drying, which involves heating the system as needed while reducing pressure; drum drying, which disperses moisture by rotating the obtained methacrylic resin in a container; and rotary drying, which utilizes centrifugal force. These drying methods can be implemented individually or in combination of two or more.

[0094] [Emulsion polymerization]

[0095] In emulsion polymerization, methacrylic resins are synthesized in an emulsion containing water, a monomer mixture, an emulsifier, a polymerization initiator, a chain transfer agent, and optional other additives.

[0096] As a monomer mixture, it is preferable to use a monomer mixture containing methyl methacrylate at a content of 99.5% by mass or more, and more preferably a monomer mixture containing 100% by mass.

[0097] Examples of emulsifiers include anionic surfactants such as alkyl sulfonates, alkylbenzene sulfonates, dialkyl sulfosuccinates, α-olefin sulfonates, naphthalene sulfonate-formaldehyde condensates, alkyl naphthalene sulfonates, N-methyl-N-acyl taurate, and phosphate salts (such as polyoxyethylene alkyl ether phosphates); and nonionic surfactants. Additionally, examples of the aforementioned salts include lithium salts, sodium salts, potassium salts, calcium salts, and magnesium salts. These emulsifiers can be used individually or in combination of two or more. It should be noted that the emulsifiers used in emulsion polymerization may remain in the final methacrylic resin.

[0098] When the pH of the emulsion deviates from neutral and becomes acidic or alkaline, a suitable pH adjuster can be used to prevent the hydrolysis of the structural units derived from methyl methacrylate in the monomer methyl methacrylate and the methacrylic resin obtained through 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.

[0099] As polymerization initiators and chain transfer agents, the same substances as those used in the suspension polymerization method described above can be cited. Polymerization initiators can be combined with redox systems as needed.

[0100] To obtain a methacrylic resin with high weight-average molecular weight (Mw) and a low 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 3.0 or less. Preferably, the ratio is 2.6 or less, more preferably 2.0 or less. There is no particular limitation on the lower limit of the ratio, but for example, it is preferably 0.1 or more.

[0101] The latex of methacrylic resin obtained by emulsion polymerization is subjected to heat drying or spray drying, or to a known method, thereby obtaining solid or powdered methacrylic resin. The known method involves adding water-soluble electrolytes such as salts or acids to coagulate the resin, further performing heat treatment, and then separating the resin components from the aqueous phase for drying. There are no particular limitations on the salts used, but divalent salts are preferred. Specifically, examples include calcium salts such as calcium chloride and calcium acetate, and magnesium salts such as magnesium chloride and magnesium sulfate. Among these salts, magnesium salts such as magnesium chloride and magnesium sulfate are preferred. Anti-aging agents, ultraviolet absorbers, and other commonly added additives can be added during coagulation.

[0102] Before the aforementioned coagulation process, it is preferable to filter the latex using a filter or mesh to remove fine polymer oxide scale. This reduces fisheyes and foreign matter caused by fine polymer oxide scale when molding the methacrylic resin.

[0103] In this embodiment, the methacrylic resin obtained by aqueous polymerization can be in the form of powder, granules, or a mixture of both powder and granules. Regarding the primary particles constituting the powder, granules, and powder-granules, suspension polymerization is suitable when producing primary particles with an average particle size of approximately 10 to 1000 μm, while emulsion polymerization is suitable when producing primary particles with an average particle size of approximately 50 to 500 nm. The powder, granules, and powder-granules can also contain aggregates of the aforementioned primary particles.

[0104] After polymerization, the methacrylic resin can be purified as needed. Purification methods include, for example, dissolving the methacrylic resin in a solvent and adding it dropwise to a poor solvent to precipitate it; or heating the methacrylic resin to evaporate impurities. These methods can be selected appropriately depending on the application and can be combined.

[0105] <Acrylic cross-linked particles>

[0106] By using a resin composition containing acrylic crosslinked particles, it is possible to obtain a resin film with excellent transparency and color tone, and thus excellent mechanical strength such as bending resistance.

[0107] There are no particular limitations on the acrylic crosslinked particles; a wide range of rigid or soft crosslinked particles can be used, and they can be single-layered or multi-layered. As rigid crosslinked particles, raw materials can include methyl methacrylate and other methacrylates, as well as polyfunctional monomers having two or more non-conjugated double bonds, but as described later, they can also be in the form of core-shell polymers. Core-shell elastomers having a core layer composed of a rubbery polymer with excellent thermal stability and a shell layer composed of a glassy polymer are particularly preferred.

[0108] Acrylic crosslinked particles can be formed, for example, from graft copolymers known as multilayer polymers or so-called core-shell polymers. Multilayer polymers are polymers with polymer layers (shells) obtained by polymerizing a mixture of monomers in the presence of polymer particles (core layers).

[0109] In acrylic crosslinked particles, the average particle size of the core layer is preferably 125–400 nm. If the average particle size of the core layer is 125 nm or more, the manufactured resin film exhibits excellent strength. Furthermore, if it is 400 nm or less, the manufactured resin film exhibits excellent transparency, appearance, and optical properties. The average particle size of the core layer is more preferably 130–380 nm, and particularly preferably 200–260 nm. The average particle size of the core layer of the acrylic crosslinked particles in this invention is calculated by measuring light scattering at a wavelength of 546 nm using a spectrophotometer in the polymer latex state of the core layer before the shell layer is polymerized.

[0110] The acrylic crosslinked particles are preferably those that swell easily when dissolved and dispersed in the solvent used in the casting solution. The degree of swelling can be determined by the method described in International Publication No. WO2018 / 212227.

[0111] The gel fraction of the acrylic crosslinked particles is preferably 90% or less. Gel fraction refers to the mass ratio of the insoluble component of the acrylic crosslinked particles to the total amount of acrylic crosslinked particles. If the gel fraction of the acrylic crosslinked particles is 90% or less, then the acrylic crosslinked particles contain a considerable amount of soluble component in methyl ethyl ketone (MEK), and due to this soluble component, the primary particles of the acrylic crosslinked particles are easily dispersed in the casting solution. A gel fraction is more preferably 87% or less, further preferably 85% or less, even more preferably 83% or less, and particularly preferably 80% or less. There is no particular limitation on the lower limit of the gel fraction, but if it is too low, the mechanical properties of the resin film, such as flexural strength, cracking during slitting, and cracking during punching, may decrease. Therefore, it is preferably 65% ​​or more, more preferably 68% or more, further preferably 70% or more, and most preferably 73% or more. The gel fraction can be determined by the method described later.

[0112] In a preferred embodiment, the core layer of the acrylic crosslinked particles comprises a hard polymer (I) and a soft polymer (II). The hard polymer (I) comprises, as a constituent unit, 40-100% by mass of methacrylate units (a-1), 60-0% by mass of other monomer units (a-2) having double bonds that can copolymerize with it, and 0.01-10 parts by mass of multifunctional monomer units relative to a total of 100 parts by mass of (a-1) and (a-2). The soft polymer (II) comprises, as a constituent unit, 60-100% by mass of acrylate units (b-1), 0-40% by mass of other monomer units (b-2) having double bonds that can copolymerize with it, and 0.01-10 parts by mass of multifunctional monomer units relative to a total of 100 parts by mass of (a-1) and (a-2). And 0.1 to 5 parts by mass of multifunctional monomer units relative to a total of 100 parts by mass of (b-1) and (b-2) above; soft polymer (II) is bonded to hard polymer (I), and the shell contains hard polymer (III), which, as a constituent unit, contains 60 to 100% by mass of methacrylate unit (c-1), 40 to 0% by mass of other monomer units (c-2) having double bonds that can copolymerize therewith, and 0 to 10 parts by mass of multifunctional monomer units relative to a total of 100 parts by mass of (c-1) and (c-2) above; hard polymer (III) is grafted to hard polymer (I) and / or soft polymer (II).

[0113] As a preferred embodiment, the acrylic crosslinked particles can be obtained by the method described in International Publication No. WO2018 / 212227. The polymer layer formed by polymerization stages (I) to (II) corresponds to the core layer, and the polymer layer formed after polymerization stage (III) corresponds to the shell layer.

[0114] (I) Aggregation Phase

[0115] (I) In the polymerization stage, it is preferable to polymerize a monomer mixture (a) consisting of 40 to 100% by mass of methacrylate (a-1) and 60 to 0% by mass of other monomers (a-2) having double bonds that can copolymerize therewith, and 0.01 to 10 parts by mass of a multifunctional monomer relative to a total of 100 parts by mass of (a-1) and (a-2) and 0.1 to 4.0 parts by mass of a chain transfer agent to obtain a rigid polymer (I).

[0116] As other monomers having copolymerizable double bonds (hereinafter also referred to as "copolymerizable monomers"), alkyl acrylates and / or aromatic vinyl monomers with alkyl groups having 1 to 12 carbon atoms are preferred.

[0117] The monomer mixture (a) described above preferably consists of 40-100% by mass of methacrylate, 0-35% by mass of acrylate, 0-10% by mass of aromatic vinyl monomers, and 0-15% by mass of other monomers having copolymerizable double bonds. Particularly preferred is a mixture of 51-96.8% by mass of methacrylate, 3.1-29% by mass of acrylate, 0.1-10% by mass of aromatic vinyl monomers, and 0-10% by mass of other monomers having copolymerizable double bonds. Within this range, zipper depolymerization under high-temperature conditions can be suppressed, thereby improving thermal stability, and the resulting acrylic crosslinked particles can be incorporated into methacrylic resin without impairing the optical properties of the methacrylic resin, such as transparency and hue.

[0118] Examples of the aforementioned methacrylates include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, isobornyl methacrylate, phenyl methacrylate, and benzyl methacrylate. Among these, alkyl methacrylates with 1 to 4 carbon atoms in the alkyl group are preferred, such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, and tert-butyl methacrylate. These can be used alone or in combination of two or more, with methyl methacrylate being particularly preferred.

[0119] The other monomers having copolymerizable double bonds are preferably selected from at least one of acrylates, aromatic vinyl monomers, and copolymerizable monomers other than (meth)acrylates and aromatic vinyl monomers, more preferably one or more of alkyl acrylates with 1 to 12 carbon atoms, aromatic vinyl monomers, and copolymerizable monomers other than (meth)acrylates and aromatic vinyl monomers. As the other monomers having copolymerizable double bonds, alkyl acrylates and / or aromatic vinyl monomers with 1 to 12 carbon atoms are preferred.

[0120] Compared to the total of 100 parts by mass in (a-1) and (a-2) above, the amount of the multifunctional monomer used in the polymerization stage (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. If the amount of multifunctional monomer used is 0.01 parts by mass or more, the transparency of the resulting film is improved; if it is 10 parts by mass or less, the film can be endowed with excellent mechanical properties.

[0121] As a multifunctional monomer, any substance known as a crosslinking agent or crosslinking monomer can be used. As a crosslinking monomer, it is further preferred to use allyl methacrylate alone or in combination with other multifunctional monomers.

[0122] (I) In the polymerization stage, it is preferable to polymerize the above monomer mixture (a) and the above multifunctional monomer mixture in the presence of a chain transfer agent to obtain a rigid polymer (I).

[0123] Relative to the total mass of (a-1) and (a-2) above, the amount of chain transfer agent used in the polymerization stage (I) is preferably 0.1 to 4.0 parts by mass. 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 has the effect of increasing the free polymer with low molecular weight, the more chain transfer agent used, the lower the degree of crosslinking of the core layer, the easier the core layer absorbs the solvent, the higher the swelling degree of the acrylic crosslinked particles, the easier the primary particles of the acrylic crosslinked particles are to disperse, and the less likely the casting solution will become turbid. On the other hand, if the chain transfer agent is used in excess, sometimes it is not possible to obtain sufficient mechanical properties of the resin film, such as flexural strength, cracking during cutting, and cracking during punching. However, if the chain transfer agent is used within the above range, the casting solution is less likely to become turbid, and acrylic crosslinked particles that can impart excellent mechanical properties to the resin film can be obtained.

[0124] There are no particular limitations on the chain transfer agent used in the (I) polymerization stage; any chain transfer agent known in the art may be used. Chain transfer agents may be used alone or in combination of two or more.

[0125] If the chain transfer agent contains sulfur, the thermal stability of the acrylic crosslinked particles is improved. Therefore, alkyl thiol chain transfer agents and thiophenol are preferred, and alkyl thiol chain transfer agents are more preferred. Among them, n-octyl thiol and n-dodecyl thiol are preferred, and n-octyl thiol is particularly preferred.

[0126] The rigid polymer (I) obtained in the polymerization stage (I) of the acrylic crosslinked particles preferably has an alkyl thio group derived from an alkyl thiol chain transfer agent, more preferably has a primary alkyl thio group and / or a secondary alkyl thiol chain transfer agent. An alkyl thio group refers to the structure represented by the chemical formula RS- (R being alkyl), and primary alkyl thio group and / or secondary alkyl thio group refers to the aforementioned R being a primary alkyl group and / or a secondary alkyl group.

[0127] (II) Aggregation Stage

[0128] (II) In the polymerization stage, a monomer mixture (b) consisting of 60 to 100% by mass of acrylate (b-1) and 0 to 40% by mass of other monomers (b-2) having double bonds that can copolymerize therewith, and 0.1 to 5 parts by mass of a multifunctional monomer relative to a total of 100 parts by mass of (b-1) and (b-2) and 0 to 2.0 parts by mass of a chain transfer agent are preferably polymerized to obtain a soft polymer (II).

[0129] As other monomers having copolymerizable double bonds as described above, preferably at least one is selected from methacrylates and other monomers having copolymerizable double bonds.

[0130] As acrylates, alkyl acrylates with 1 to 12 carbon atoms in the alkyl group are preferred, such as ethyl acrylate, n-butyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate. These acrylates can be used alone or in combination of two or more. As alkyl acrylates, n-butyl acrylate is preferred, and combinations of n-butyl acrylate and ethyl acrylate, or n-butyl acrylate and 2-ethylhexyl acrylate are also preferred. In particular, in the acrylates used in the (II) polymerization stage, the content of n-butyl acrylate is preferably 50 to 100% by mass, and particularly preferably 80 to 100% by mass.

[0131] For the methacrylates, other monomers having copolymerizable double bonds, polyfunctional monomers, and chain transfer agents used in the polymerization stage (II), the same substances as those described in the polymerization stage (I) above can be cited. In the polymerization stage (II), chain transfer agents may or may not be used, but it is preferred not to use them.

[0132] (III) Aggregation Phase

[0133] (III) In the polymerization stage, it is preferable to polymerize a monomer mixture (c) consisting of 60 to 100% by mass of methacrylate (c-1) and 40 to 0% by mass of other monomers (c-2) having double bonds that can copolymerize therewith, and 0 to 10 parts by mass of a multifunctional monomer relative to a total of 100 parts by mass of (c-1) and (c-2) and 0 to 6 parts by mass of a chain transfer agent to obtain a rigid polymer (III).

[0134] To lower the glass transition temperature of the rigid polymer (III) formed through polymerization stage (III), the monomer mixture (c) preferably contains acrylate. The amount of acrylate 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.

[0135] The acrylic crosslinked particles preferably have a structure in which a rigid polymer (III) is grafted onto a rigid polymer (I) and / or a flexible polymer (II). This grafting can be complete, or it can be a portion of the rigid polymer (III) grafted onto the rigid polymer (I) and / or the flexible polymer (II), with the remainder existing as a polymer component (free polymer) ungrafted onto either the rigid polymer (I) or the flexible polymer (II). This ungrafted polymer component also constitutes part of the acrylic crosslinked particles.

[0136] (III) The methacrylates, other monomers having copolymerizable double bonds, multifunctional monomers, and chain transfer agents used in the polymerization stage may be the same substances described in the polymerization stage (I). (III) In the polymerization stage, multifunctional monomers and / or chain transfer agents may be used or not, preferably not.

[0137] (IV) Convergence Phase

[0138] Acrylic crosslinked particles may include polymerization stages other than those described in (I) to (III) above.

[0139] (IV) In the polymerization stage, a monomer mixture (d) consisting of 40 to 100% by mass of methacrylate (d-1), 0 to 60% by mass of acrylate (d-2), and 0 to 5% by mass of other monomers (d-3) having copolymerizable double bonds, and 0 to 10 parts by mass of a multifunctional monomer relative to a total of 100 parts by mass of the above (d-1), (d-2), and (d-3), and 0 to 6 parts by mass of a chain transfer agent are preferably polymerized to obtain a rigid polymer (IV).

[0140] In order to lower the glass transition temperature of the rigid polymer (IV) formed through the (IV) polymerization stage, the amount of acrylate (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.

[0141] (IV) The methacrylates, acrylates, other monomers having copolymerizable double bonds, polyfunctional monomers, and chain transfer agents used in the polymerization stage can be the same substances described in (I) to (III) above. (IV) Polyfunctional monomers and / or chain transfer agents may be used in the polymerization stage, or they may not be used, but preferably not.

[0142] In the preferred embodiment described above, the acrylic crosslinked particles may have a structure in which a rigid polymer (IV) is grafted onto a rigid polymer (I) and / or a soft polymer (II) and / or a rigid polymer (III). This grafting may involve all of the rigid polymer (IV) being grafted onto the rigid polymer (I) and / or the soft polymer (II) and / or the rigid polymer (III), or it may involve a portion of the rigid polymer (IV) being grafted onto the rigid polymer (I) and / or the soft polymer (II) and / or the rigid polymer (III), with the remaining portion existing as a polymer component not grafted onto any of the rigid polymer (I), soft polymer (II), and rigid polymer (III). This ungrafted polymer component also constitutes part of the acrylic crosslinked particles.

[0143] Acrylic crosslinked particles can be manufactured using known emulsifiers and through conventional emulsion polymerization.

[0144] From the viewpoint of improving the thermal stability of the resin film, the polymerization initiator used in the polymerization of acrylic crosslinking particles is preferably a polymerization initiator with a 10-hour half-life temperature of 100°C or lower. There is no particular limitation on the polymerization initiator as long as it has a 10-hour half-life temperature of 100°C or lower, but the 10-hour half-life temperature of the polymerization initiator is preferably 100°C or lower, more preferably 80°C or lower, and particularly preferably 75°C or lower. Furthermore, persulfates are preferred, such as potassium persulfate, sodium persulfate, and ammonium persulfate. Potassium persulfate is particularly preferred.

[0145] The polymerization initiator is preferably used during polymerization in stage (I), and more preferably during polymerization in stage using a chain transfer agent. Furthermore, it is particularly preferred to use the above-mentioned polymerization initiator during all polymerization stages of the acrylic crosslinked particles.

[0146] 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 monomer mixture constituting the acrylic crosslinked particles. When acrylic crosslinked particles are obtained through polymerization stages (I) to (III), and the monomer mixture in each polymerization stage (I) to (III) is set to 100 parts by mass, the amount of polymerization initiator used is preferably 0.01 to 1.85 parts by mass in polymerization stage (I), 0.01 to 0.6 parts by mass in polymerization stage (II), and 0.01 to 0.90 parts by mass in polymerization stage (III). Furthermore, relative to the total amount of polymerization initiator used, the amount of polymerization initiator used in polymerization stage (I) is preferably more than 1% by mass and less than 29% by mass.

[0147] The core layer of acrylic crosslinked particles refers to the crosslinked polymer structure obtained by polymerization up to stage (II) (i.e., the outermost layer of the core layer is a soft polymer formed by stage (II)), and the shell layer refers to the hard polymer obtained by polymerization after stage (II).

[0148] The acrylic cross-linked particle latex obtained in this way can be spray-dried or by known methods to obtain solid or powdered acrylic cross-linked particles. The aforementioned known methods involve coagulation by adding water-soluble electrolytes such as salts or acids, followed by heat treatment, separation of resin components from the aqueous phase, appropriate washing, and drying.

[0149] Here, "soft" refers to a polymer with a glass transition temperature of less than 10°C. From the viewpoint of improving impact resistance and other properties such as crack resistance, the glass transition temperature of soft polymers is preferably less than 0°C, and more preferably less than -20°C. Conversely, "hard" refers to a polymer with a glass transition temperature of 10°C or higher.

[0150] The rigid polymer constituting the shell layer of the acrylic crosslinked particles (or, when the shell layer is multilayered, the layer with the highest glass transition temperature among the multilayers) preferably has a glass transition temperature of 10°C to 92°C. By setting the glass transition temperature of this rigid polymer to below 92°C, the bonding force between the polymer molecular chains in the shell layer weakens, the aggregation force between the primary particles of the acrylic crosslinked particles decreases, the primary particles of the acrylic crosslinked particles are easily dispersed, and turbidity of the casting solution is less likely to occur.

[0151] The glass transition temperatures of “soft” and “hard” polymers are given by the following values: values ​​recorded in the Polymer Handbook (J. Brandrup, Interscience 1989) and calculated using Fox’s formula (e.g., 105°C for polymethyl methacrylate and -54°C for polybutyl acrylate).

[0152] In a preferred embodiment, polymer (I) obtained in polymerization stage (I) is a rigid polymer, polymer (II) obtained in polymerization stage (II) is a flexible polymer, and polymer (III) obtained in polymerization stage (III) is a rigid polymer. Additionally, polymer (IV) obtained in polymerization stage (IV) is a rigid polymer. Acrylic crosslinked particles with this configuration exhibit a well-balanced combination of appearance, transparency, durability, gloss, processability, and thermal stability when mixed with various methacrylic resins. Therefore, a film with excellent thermal stability, durability, gloss, and processability can be provided without compromising the excellent color, appearance, and transparency characteristic of the mixed methacrylic resin.

[0153] <Resin Composition>

[0154] The resin composition of this embodiment contains the methacrylic resin and acrylic crosslinked particles described in this embodiment.

[0155] In the resin composition of this embodiment, the mixing ratio of methacrylic resin to acrylic crosslinked particles varies depending on the intended use of the molded article, etc. The preferred mass ratio of methacrylic resin to acrylic crosslinked particles is 99.9:0.1 to 65:1, more preferably 35, or 99:1 to 65:35. When the acrylic crosslinked particles are core-shell type particles, the preferred mass ratio of methacrylic resin to acrylic crosslinked particles is 95:5 to 65:35, and more preferably 90:10 to 60:40.

[0156] If the amount of methacrylic resin in the formulation is 65 parts by mass or more relative to the total amount of methacrylic resin and acrylic crosslinked particles (100 parts by mass), the properties of methacrylic resin can be fully utilized. If it is less than 95 parts by mass, the mechanical strength of methacrylic resin can be significantly improved.

[0157] 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 radiation reflective materials, lubricants, plasticizers, stabilizers, flame retardants, release agents, polymer processing aids, antioxidants, and fillers, as well as resins other than methacrylic acid resins. Examples of resins other than methacrylic acid resins include, for example, styrene-based resins such as acrylonitrile-styrene resin and styrene-maleic anhydride resin; polycarbonate resins; polyvinyl alcohol acetal resins; acylated cellulose resins; fluorinated resins such as polyvinylidene fluoride and polyfluoroalkyl (meth)acrylate resins; silicone resins; polyolefin resins; polyethylene terephthalate resins; and polybutylene terephthalate resins.

[0158] In addition, in order to adjust the orientation birefringence of the molded article, the resin composition of this embodiment may contain inorganic microparticles with birefringence as described in Japanese Patent No. 3648201, Japanese Patent No. 4336586, etc., and low molecular weight compounds with birefringence and a molecular weight of 5000 or less (preferably 1000 or less) as described in Japanese Patent No. 3696649.

[0159] The form of the resin composition in this embodiment is not particularly limited; it can be a powder, a granule, a powder-granule mixture that includes both powder and granules, or it can be granular.

[0160] Casting solution

[0161] The casting solution used to manufacture resin films by solution casting contains the resin composition and solvent described in this embodiment. The solvent preferably includes a first solvent with a hydrogen bonding term δH of 1 to 12 and a second solvent with a hydrogen bonding term δH of 14 to 24 in the Hansen solubility parameters. Similar to the resin composition described in this embodiment, the casting solution of this embodiment may further contain other components such as multilayer polymer particles. The methacrylic resin, multilayer polymer particles, and other components are dissolved or dispersed in the solvent.

[0162] As a first solvent with a hydrogen bond term δH of 1 to 12, solvents described in International Publication No. WO2018 / 212227 may be used, for example. One of these first solvents may be used alone, or two or more may be used in combination. Among these first solvents, from the viewpoint of excellent solubility and rapid evaporation of methacrylic resin, methyl ethyl ketone (5.1), chloroform (5.7), and dichloromethane (7.1) are preferred, with dichloromethane being more preferred. It should be noted that the numbers in parentheses indicate the value of the hydrogen bond term δH.

[0163] Examples of second solvents with a hydrogen bond term 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). It should be noted that the numbers in parentheses indicate the value of the hydrogen bond term δH. These second solvents can be used individually or in combination of two or more. Among these second solvents, methanol and ethanol are preferred, and ethanol is more preferred.

[0164] The proportion of the first solvent contained in the solvent is preferably 55-95% by mass, more preferably 60-95% by mass, and even more preferably 70-95% by mass.

[0165] The content of methacrylic resin in the casting solution is not particularly limited, and can be appropriately determined by considering factors such as the solubility of methacrylic resin in the solvent used and the implementation conditions of the solution casting method. The preferred content of methacrylic resin is 5-50% by mass, more preferably 10-45% by mass, and even more preferably 15-40% by mass.

[0166] The viscosity of the casting solution can be adjusted by regulating the content of methacrylic resin and other components. From the perspectives of coatability and filtration accuracy, the optimal viscosity of the casting solution is 1000 Poise (=100 Pa). s) or less, more preferably 500 Poise (=50 Pa) s) or less, more preferably 300 Poise (=30 Pa) s) below. It should be noted that the viscosity of the casting solution was determined by the method described in the examples described later.

[0167] The casting solution is used to manufacture resin films via solution casting. In manufacturing a resin film via solution casting, firstly, the casting solution of this embodiment is cast onto the surface of a support, and then coated into a uniform film using a coating applicator to form a coating. Alternatively, a pressure die can be used to cast the casting solution onto the support. Next, the formed coating is heated on the support to evaporate the solvent and form a resin film. The conditions for solvent evaporation can be appropriately determined based on the boiling point of the solvent used. Then, the formed resin film is peeled off from the surface of the support. It should be noted that the obtained resin film can be appropriately used in drying processes, heating processes, stretching processes, etc.

[0168] <Resin Film>

[0169] The resin film of this embodiment comprises the resin composition of this embodiment described above. The resin film of this embodiment is manufactured, for example, by solution casting using the casting solution of this embodiment described above.

[0170] The thickness of the resin film in this embodiment is 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 in this embodiment is 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, it has the advantage of being less prone to deformation and breakage during deep drawing when using this resin film for vacuum forming. Furthermore, it also has the advantage of being able to manufacture resin films with uniform optical properties and good transparency.

[0171] The total light transmittance of the resin film in this 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, thus making it suitable for optical applications requiring high light transmittance.

[0172] The glass transition temperature of the resin film in 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 heat resistance of the resin film is sufficient.

[0173] Furthermore, the 5% weight loss temperature of the resin film in this embodiment is preferably 300°C or higher, more preferably 305°C or higher. This results in excellent thermal stability.

[0174] The haze of the resin film in 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. Furthermore, 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. If the haze and internal haze are within the above ranges, the transparency is high, thus making it suitable for optical applications requiring high light transmittance. It should be noted that the haze consists of the haze inside the film and the haze on the film surface (outside), referred to as internal haze and external haze, respectively.

[0175] The b* value of the resin film in this embodiment is preferably 0.3 or less, more preferably 0.25 or less, and even more preferably 0.20 or less.

[0176] The yellowness index (YI) of the resin film in this embodiment is preferably 1.2 or less, more preferably 1.0 or less, and even more preferably 0.5 or less. If the YI is within the above range, the transparency is high, and therefore it is suitable for optical applications requiring high light transmittance.

[0177] The resin film of this embodiment preferably has excellent mechanical properties, such as high flexural strength. Known methods for evaluating flexural strength include the MIT flexural strength test and the flip-top flexural strength test. For example, the resin film of this embodiment preferably undergoes 2500 or more bends in the MIT flexural strength test, more preferably 3000 or more. If the number of bends until breakage is within the above range, the flexural strength of the resin film is sufficient. It should be noted that the number of bends in the MIT flexural strength test is determined by the method described in the examples described later.

[0178] The resin film of this embodiment is suitable for use as an optical film such as a polarizer protective film. When the resin film of this embodiment is used as a polarizer protective film, low optical anisotropy is preferable. Particularly preferable is low optical anisotropy not only in the in-plane direction (length direction and width direction) of the resin film, but also in the thickness direction. That is, it is preferable that the absolute values ​​of both the in-plane phase difference and the thickness direction phase difference are small. For example, when the measurement wavelength is 590 nm, the absolute value of the in-plane phase difference is preferably 20 nm or less, more preferably 15 nm or less. In addition, the absolute value of the thickness direction phase difference is preferably 50 nm or less, more preferably 20 nm or less, and even more preferably 15 nm or less.

[0179] Phase difference is an index value calculated based on birefringence. The in-plane phase difference (Re) and the thickness-direction phase difference (Rth) can be calculated using the following formulas. In an ideal resin film that is optically isotropic in three dimensions, both the in-plane phase difference Re and the thickness-direction phase difference Rth are 0.

[0180] Re = (nx - ny) × d

[0181] Rth=〔(nx+ny) / 2-nz〕×d

[0182] In the above formula, nx, ny, and nz represent the refractive indices along each axis when the in-plane stretching direction (the orientation direction of the polymer chains) is set as the X-axis, the direction perpendicular to the X-axis is set as the Y-axis, and the thickness direction of the resin film is set as the Z-axis. Additionally, d represents the thickness of the resin film, and nx-ny represents orientation birefringence. It should be noted that the MD direction of the film is set as the X-axis, but in the case of a stretched film, the stretching direction is set as the X-axis.

[0183] In this embodiment, the preferred orientation birefringence value of the resin film is -5.0 × 10⁻⁶. －4 ~5.0×10 －4 More preferably -4.0×10 －4 ~4.0×10 －4 Further preferred value is -3.8 × 10⁻⁶. －4 ~3.8×10 －4 If the oriented birefringence is within the above range, there is a tendency to obtain stable optical properties without producing birefringence during molding and processing.

[0184] (Stretching)

[0185] The resin film of this embodiment can be further stretched. By stretching the resin film, the mechanical strength and thickness accuracy of the resin film can be improved.

[0186] When stretching the resin film of this embodiment, the resin film is temporarily formed into an unstretched state by the casting solution of this embodiment, and then uniaxial or biaxial stretching is performed. Alternatively, during the forming of the resin film, a stretching operation can be appropriately applied along with the film-forming and solvent degassing processes. This allows the manufacture of stretched films (uniaxial or biaxial stretched films). Stretching during film forming and stretching after film forming can be appropriately combined.

[0187] There are no particular limitations on the stretch ratio of the stretched film, and it can be appropriately determined based on the mechanical strength, surface properties, thickness accuracy, etc. of the stretched film being manufactured. It also depends on the stretching temperature; the stretch ratio is generally preferably selected in the range of 1.1 to 5 times, more preferably in the range of 1.3 to 4 times, and even more preferably in the range of 1.5 to 3 times. If the stretch ratio is within the above range, there is a tendency to significantly improve the film's elongation, tear propagation strength, and resistance to tumbling fatigue, among other mechanical properties.

[0188] (use)

[0189] The resin film of this embodiment can be used in various applications such as transportation equipment, solar cell components, civil engineering components, daily necessities, electrical and electronic equipment, optical components, and medical supplies. In particular, the resin film of this embodiment has excellent heat resistance and optical properties, making it suitable for optical applications. Examples of optical applications include front panels (covering windows) of various display devices, diffuser plates, polarizer protective films, polarizing plate protective films, retardation films, light diffusion films, and isotropic optical films.

[0190] Among these, the resin film of this embodiment can be suitable for use as a polarizer protective film or a front panel (covering window) of a display device. When using the resin film of this embodiment as a front panel (covering window) of various display devices, a functional coating layer such as a primer layer or a hard coating layer can be formed on at least one main surface of the resin film as needed. Furthermore, when using the resin film of this embodiment as a polarizer protective film, the resin film of this embodiment is bonded to a polarizer to form a polarizing plate. There are no particular limitations on the polarizer; any conventionally known polarizer can be used. This polarizing plate is used, for example, in display devices such as liquid crystal display devices and organic EL display devices.

[0191] Example

[0192] The present invention will now be described in more detail with reference to embodiments and comparative examples, but the present invention is not limited to the embodiments described below. It should be noted that the methods for measuring various physical properties described in the embodiments and comparative examples are as follows.

[0193] (1) Aggregation conversion rate (conversion rate)

[0194] The polymerization conversion rate was determined by gravimetric method, based on the ratio of the weight of the remaining solids after drying to the weight of the added monomers. The weight of the solids was determined by drying the resin beads in an oven heated to 150°C for 30 minutes.

[0195] Conversion rate (%) = (weight of solid components / weight of monomers added) × 100

[0196] (2) Average particle size of acrylic crosslinked particles

[0197] The average particle size was determined in the latex state. As the measuring apparatus, a Hitachi High-Technologies Corporation U-5100 ratio beam spectrophotometer was used, and the particle size was determined by light scattering at a wavelength of 546 nm.

[0198] (3) Gel fraction of acrylic crosslinked particles

[0199] 1 g of acrylic crosslinked particles were dissolved in 40 mL of methyl ethyl ketone (MEK), and then centrifuged to separate the MEK-insoluble polymer component (gel polymer) and the MEK-soluble component. The obtained gel polymer was dried at 60 °C and 5 torr for 10 hours, and the dried gel polymer was recovered. The MEK-soluble component was added to 200 mL of methanol and reprecipitated, thereby separating the methanol-soluble component and the methanol-insoluble component (free polymer). The free polymer and the methanol-soluble component were dried under the same conditions as above, and the dried free polymer and the dried methanol-soluble component were recovered separately. The gel fraction (%) was calculated using the following formula based on the weight of the dried gel polymer, the weight of the dried free polymer, and the weight of the dried methanol-soluble component.

[0200] (Gel fraction) = (Weight of dried gel polymer) / (Weight of dried gel polymer + Weight of dried free polymer + Weight of dried methanol-soluble components) × 100

[0201] (4) The isostructural regularity (rr) of the three-unit group representation

[0202] The properties of methacrylic resin were determined using a nuclear magnetic resonance (NMR) apparatus (Bruker, AVANCE III 400 MHz) in deuterated chloroform solution at 22°C for a cumulative 16 times. 1 H-NMR spectrum. Based on 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. Then, the syndiotactic regularity (rr) represented by the ternary unit group is calculated by the formula: (X / Y)×100.

[0203] (5) Average molecular weight and molecular weight distribution

[0204] 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 serves as an indicator of molecular weight distribution, of methacrylic resin were calculated using the standard polystyrene conversion method of gel permeation chromatography (GPC). Specifically, the analysis was performed using a sample solution prepared by dissolving 40 mg of methacrylic resin in 2 mL of chloroform, under the following apparatus and conditions.

[0205] Measurement equipment: HLC-8220GPC (Tosoh)

[0206] Detector: RI detector

[0207] Eluent: Chloroform

[0208] Protective pillar: KF-G 4A (manufactured by Resonac Corporation)

[0209] Analysis columns: Resonac Corporation KF-806M and KF-806L connected in series.

[0210] Measurement temperature: 40℃

[0211] Eluent flow rate: 1 mL / min

[0212] Standard reference material: Standard polystyrene (Tosoh)

[0213] (6) Terminal double bond amount

[0214] As a pretreatment, methacrylic acid resin was dissolved in dichloromethane, and the solution was added dropwise to methanol to precipitate and purify the resin. The precipitated resin was recovered by filtration and dried for analysis. A solution was prepared by dissolving 20 mg of the dried methacrylic acid resin in 0.6–0.7 mL of deuterated chloroform, and analyzed using a nuclear magnetic resonance (NMR) apparatus (Bruker, AVANCE NEO 700 MHz). 1 ¹H-NMR determination was performed at 20°C, with a cumulative count of 8192. Excitation sculpting (ES), a solvent elimination method, was used to eliminate the methoxy group peak from the methacrylic acid resin (3.60 ppm, the value when the chemical shift of the solvent peak was set to 7.26 ppm). The determination was then performed simultaneously. 1 The total area (X) of the peaks (5.47–5.53 ppm and 6.21 ppm) of the terminal double bonds from the methacrylic resin and the area (Y) of the peaks (0.5–1.25 ppm) of the α-methyl group from the methacrylic resin were measured by ¹H-NMR spectroscopy. Then, the proportion of terminal double bonds in the methacrylic resin was calculated by the formula: 〔(3×X) / (2×Y)〕×100.

[0215] (7) Residual rate of chain transfer agent

[0216] The residual rate of chain transfer agent in methacrylic resin was quantified using a gas chromatograph (Agilent Technologies, 7890B). A DB-1 column (Agilent Technologies, 0.8 μm film thickness × 0.20 mm inner diameter × 30 m length) was used as the analytical column, with an injection port temperature of 150 °C and a detector temperature of 320 °C. The column temperature was set as follows: increasing from 35 °C to 210 °C at a rate of 30 °C / min, then increasing from 210 °C to 260 °C at a rate of 10 °C / min, and further increasing from 260 °C to 320 °C at a rate of 20 °C / min, holding for 3 minutes. A standard curve was constructed using dichloromethane as the analytical solvent and chlorobenzene as the internal standard, and the residual rate of chain transfer agent in the methacrylic resin was calculated.

[0217] (8) Viscosity of casting solution

[0218] Methacrylic acid resin was dissolved in a mixed solvent consisting of 93% by mass dichloromethane and 7% by mass ethanol to prepare casting solutions with a solids 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 viscosity of the casting solution was measured using a Type B viscometer (Made by Toki Kogyo Co., Ltd., BMII). The temperature of the test sample was adjusted to 23°C, and the reading was taken at 30 rpm (12 rpm for Examples 1 and 3) using a No. 2 rotor.

[0219] (9) Glass transition temperature (Tg)

[0220] The glass transition temperature of the resin film was determined using the following method. As a pretreatment, to remove residual monomers and decomposition products of the polymerization initiator from the methacrylic resin, heat treatment was performed using a thermogravimetric analysis apparatus (Hitachi High-Tech Science Company, STA7200). Specifically, under a nitrogen flow rate of 200 mL / min, the temperature was increased from 40 °C to 190 °C at a rate of 10 °C / min, and held at 190 °C for 2.0–2.5 minutes. The glass transition temperature (Tg) of the heat-treated methacrylic resin was determined using a differential scanning calorimeter (DSC; Hitachi High-Tech Science Company, DSC7000X). First, a first heating was performed at a nitrogen flow rate of 40 mL / min, increasing the temperature from 40 °C to 160 °C at a rate of 10 °C / min. After cooling to 40 °C, a second heating was performed at a rate of 10 °C / min, increasing the temperature from 40 °C to 160 °C. DSC measurements were then performed under the aforementioned conditions. Then, based on the DSC curve measured during the second heating, the midpoint glass transition temperature (the temperature at which the curve of the staged change portion of the glass transition intersects the curve of the line that is equidistant from the line extending outward towards the high-temperature side from the baseline before the inflection point and the line extending outward towards the low-temperature side from the baseline after the inflection point) is read.

[0221] (10) 5% weight loss temperature (Td5)

[0222] The 5% weight loss temperature (Td5) of the resin film and acrylic crosslinked particle powder was determined using a thermogravimetric analysis apparatus (Hitachi High-Tech Science Company, STA7200). First, a first heating was performed at a rate of 10°C / min from 40°C to 190°C under a nitrogen flow of 200 mL / min. The sample was then cooled to 40°C, followed by a second heating at a rate of 10°C / min from 40°C to 500°C. The 5% weight loss temperature (Td5) was defined as the temperature at which the weight of the sample, calculated from the thermogravimetric (TG) curve determined during the second heating, was reduced to 95% of the initial weight at the start of the second heating.

[0223] (11) Retention thermal stability

[0224] The retention thermal stability of the resin film was evaluated using a thermogravimetric analysis (Hitachi High-Tech Science Company, STA7200). First, the film was heat-treated by heating from 40°C to 190°C at a rate of 10°C / min under a nitrogen flow of 200 mL / min, and holding at 190°C for 2.0–2.5 minutes. Next, the film was cooled to 40°C, then heated from 40°C to 280°C at a rate of 10°C / min, and held at 280°C for 30 minutes. The mass change was recorded under these conditions. The mass at which the sample temperature reached 280°C was designated as X0, and the mass at which it was held at 280°C for 15 minutes was designated as X... 15 According to the formula: [(X0-X] 15 The mass reduction rate calculated by ( ) / X0]×100 is used to evaluate the thermal stability of the residence.

[0225] (12) Total light transmittance

[0226] The total light transmittance of the stretched resin film was determined using a haze meter (Suga Test Instruments, HZ-V3) according to JIS K7361-1.

[0227] (13) Internal haze

[0228] The internal haze of the stretched resin film was measured using a haze meter (Suga Test Instruments, HZ-V3) according to JIS K7136. The film was clamped between glycerol and glass on both sides sequentially, and the haze was measured. The results were converted to a value equivalent to a film thickness of 40 μm.

[0229] (14) Yellowness (YI)

[0230] The yellowness (YI) of the stretched resin film was measured using a spectrophotometer (Suga Test Instruments, SC-P) according to JIS K7373. The results were then converted to a value equivalent to a film thickness of 40 μm.

[0231] (15) b* value

[0232] The b* value of the stretched resin film was determined using a spectrophotometer (Suga Test Instruments, SC-P) according to JIS Z8781-4.

[0233] (16) MIT bending resistance test

[0234] The stretched resin film was cut into strips 15 mm wide and used as test pieces. These test pieces were placed on a Toyo Seiki Co., Ltd. MIT Flexibility Fatigue Testing Machine (Type D) with creases perpendicular to the stretching direction. Tests were conducted under the following conditions: a test load of 1.96 N, a speed of 175 cycles / minute, a bending radius R of 0.38 mm, and a bending angle of 135° to the left and right. The number of reciprocating bends at which the test piece broke was determined. Five measurements were performed, and the arithmetic mean was taken as the MIT reciprocating bend count.

[0235] <Manufacturing of Methacrylic Resin (Resin A)>

[0236] 150 parts by mass of deionized water, 0.40 parts by mass of tricalcium phosphate as a dispersant, 0.0075 parts by mass of sodium α-olefin sulfonate, and 0.30 parts by mass of sodium chloride were added to a 5-liter glass reactor equipped with an H-type impeller stirrer. Under a nitrogen atmosphere, while stirring at 250 rpm, 100 parts by mass of methyl methacrylate (MMA), 0.02 parts by mass of n-octylthiol (n-OM) as a chain transfer agent, and 0.012 parts by mass of dimethyl 2,2'-azobis(isobutyrate) (manufactured by Fujifilm and Kazumitsu Chemical Co., Ltd., V-601) as a 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 tricalcium phosphate was added to the reaction solution. At 4 hours and 35 minutes after the start of polymerization, an exothermic peak accompanied by a gelation effect was observed. The temperature was raised to 95°C after 5 hours and 30 minutes from the start of polymerization. The conversion rate was 94% after 5 hours and 30 minutes. Three hours after reaching 95°C, the reactor was cooled to room temperature to end the polymerization. The conversion rate at the end of polymerization was 99%.

[0237] The methacrylic acid bead dispersion obtained by the above polymerization was acid-washed and water-washed using 1 equivalent of hydrochloric acid in a mass ratio of 0.1 to the amount of monomer added, thereby removing the dispersant and the like. It was then further dehydrated and dried to obtain bead-shaped methacrylic acid (resin A).

[0238] <Manufacturing of Acrylic Crosslinked Particles (1)>

[0239] Add 175 parts by weight of deionized water, 0.01 parts by weight of polyoxyethylene lauryl ether phosphoric acid, 0.5 parts by weight of boric acid, and 0.05 parts by weight of sodium carbonate to an 8L polymerization unit equipped with a mixer.

[0240] After fully purging the polymer with nitrogen to a temperature of 80°C, 26% of (I) shown in Table 1 was added to the polymer. Then, 0.06 parts by mass of sodium formaldehyde sulfoxylate, 0.006 parts by mass of sodium ethylenediaminetetraacetate-2-, 0.001 parts by mass of ferrous sulfate, and 0.02 parts by mass of tert-butyl hydroperoxide were added. After 15 minutes, 0.03 parts by mass of tert-butyl hydroperoxide were added, and polymerization continued for another 15 minutes. Next, 0.01 parts by mass of sodium hydroxide and 0.09 parts by mass of polyoxyethylene lauryl ether phosphoric acid were added in a 2% aqueous solution, and the remaining 74% of (I) was continuously added over 60 minutes. After 30 minutes of addition, 0.07 parts by mass of tert-butyl hydroperoxide were added, and polymerization continued for another 30 minutes to obtain the polymer of (I).

[0241] Then, 0.03 parts by mass of sodium hydroxide and 0.08 parts by mass of potassium persulfate were added in a 2% aqueous solution, followed by continuous addition of (II) as shown in Table 1 over a period of 150 minutes. After the addition was completed, 0.02 parts by mass of potassium persulfate were added in a 2% aqueous solution, and polymerization continued for 120 minutes to obtain polymer (II). The average particle size was 225 nm.

[0242] Then, 0.02 parts by weight of potassium persulfate were added to a 2% aqueous solution, and (III-1) as shown in Table 1 was added continuously over a period of 45 minutes, followed by polymerization for another 30 minutes.

[0243] Then, (III-2) as shown in Table 1 was added continuously over a period of 25 minutes, and polymerization continued for another 60 minutes to obtain the latex of acrylic crosslinked particles (1). The obtained latex was precipitated 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℃, and the gel fraction was 93.7%.

[0244] <Manufacturing of Acrylic Crosslinked Particles (2)>

[0245] Add 180 parts by weight of deionized water, 0.003 parts by weight of polyoxyethylene lauryl ether phosphoric acid, 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 to an 8L polymerization apparatus equipped with a mixer.

[0246] After fully purging the polymer with nitrogen to a temperature of 80°C, 0.03 parts by mass of potassium persulfate were added in a 2% aqueous solution. Then, (I) as shown in Table 1 was continuously added over a period of 81 minutes. Polymerization was continued for another 60 minutes to obtain polymer (I).

[0247] Then, 0.03 parts by mass of sodium hydroxide and 0.08 parts by mass of potassium persulfate were added to a 2% aqueous solution, followed by continuous addition of (II) as shown in Table 1 over a period of 150 minutes. After the addition was completed, 0.02 parts by mass of pure potassium persulfate were added to a 2% aqueous solution, and polymerization was continued for 120 minutes to obtain polymer (II). The average particle size was 224 nm.

[0248] Then, 0.02 parts by mass of potassium persulfate were added to a 2% aqueous solution, and the mixture was continuously added over 70 minutes as shown in Table 1 (III). Polymerization continued for another 60 minutes to obtain a latex of acrylic crosslinked particles (2). The obtained latex was precipitated with magnesium chloride, coagulated, washed with water, and dried to obtain a white powder of acrylic crosslinked particles (2). The Td5 of the acrylic crosslinked particles (2) was 338℃, and the gel fraction was 79.0%.

[0249] Table 1

[0250]

[0251] <Example 1>

[0252] Add 93% by mass of dichloromethane to a solenoid container, and while stirring with a magnetic stirrer, gradually add 10 parts by mass of acrylic crosslinked particle powder (1). Disperse the resulting acrylic crosslinked particle dispersion using a homogenizer (IKA, ULTRA-TURRAX T25) at 8000 rpm for 10 minutes. Then, add 7% by mass of ethanol to the dispersion. Next, while stirring, gradually add 90 parts by mass of methacrylic resin (resin A) until completely dissolved to prepare a resin casting solution with a solid content of 12%.

[0253] The above casting solution was cast onto a glass substrate and coated into a uniform film using a coating applicator. The gaps were adjusted so that the dried thickness was approximately 80 μm. After coating, the film was dried in an oven at 40°C for 1 hour, and then the resulting resin film was peeled off the glass substrate. The side attached to the glass substrate was designated as side B, and the other side 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 the resin film. The resulting resin film was then subjected to a fixed-width uniaxial stretch at 145°C. The stretching ratio was 2 times, resulting in a stretched resin film (stretched film). Table 2 shows the various physical properties.

[0254] <Example 2>

[0255] Instead of 10 parts by mass of acrylic crosslinking particles (1) and 90 parts by mass of methacrylic resin (resin A) in Example 1, 20 parts by mass of acrylic crosslinking particles (1) and 80 parts by mass of methacrylic resin (resin A) were used, and resin films and stretch films were obtained by the same method as in Example 1. Table 2 shows the physical properties.

[0256] <Example 3>

[0257] Instead of 10 parts by weight of acrylic crosslinking particles (1) and 90 parts by weight of methacrylic resin (resin A) in Example 1, 20 parts by weight of acrylic crosslinking particles (2) and 80 parts by weight of methacrylic resin (resin A) were used. Otherwise, resin films and stretch films were obtained by the same method as in Example 1. Table 2 shows the physical properties.

[0258] <Comparative Example 1>

[0259] Add 93% by mass of dichloromethane and 7% by mass of ethanol to a spiral container. While stirring with a magnetic stirrer, gradually add 100 parts by mass of methacrylic resin (resin A) until completely dissolved to prepare a resin casting solution with a solid component concentration of 12%.

[0260] The above casting solution was cast onto a glass substrate and coated into a uniform film using a coating applicator. The gaps were adjusted so that the dried thickness was approximately 80 μm. After coating, the film was dried in an oven at 40°C for 1 hour, and then the resulting resin film was peeled off 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 the resin film. The resulting resin film was then subjected to a fixed-width uniaxial stretch at 145°C. The stretching ratio was 2 times, resulting in a stretched resin film (stretched film). Table 2 shows the physical properties. Compared to Examples 1-3, MIT exhibits fewer reciprocating bends and lower bending resistance.

[0261] <Comparative Example 2>

[0262] Instead of the methacrylic resin (resin A) in Comparative Example 1, methacrylic resin (resin B) (manufactured by KURARAY CO., LTD., PARAPET HR-F) was used. Otherwise, the resin film and the stretched film were obtained using the same method as in Comparative Example 1. Table 2 shows the various physical properties. Compared to Examples 1-3, the glass transition temperature is lower and the heat resistance is insufficient; the number of MIT reciprocating bends is very low, and the bending resistance is very low.

[0263] <Comparative Example 3>

[0264] Instead of 10 parts by weight of acrylic crosslinked particles (1) and 90 parts by weight of methacrylic resin (resin A) in Example 1, 20 parts by weight of acrylic crosslinked particles (1) and 80 parts by weight of methacrylic resin (resin B) were used. Otherwise, resin films and stretched films were obtained using the same method as in Example 1. Table 2 shows the physical properties. Compared to Examples 1-3, the glass transition temperature is lower and the heat resistance is insufficient; the number of MIT reciprocating bends is lower and the bending resistance is lower; and the total light transmittance is less than 90%, resulting in lower transparency.

[0265] <Comparative Example 4>

[0266] Instead of 10 parts by weight of acrylic crosslinking particles (1) and 90 parts by weight of methacrylic resin (resin A) in Example 1, 20 parts by weight of acrylic crosslinking particles (1) and 80 parts by weight of methacrylic resin (resin C) (manufactured by KURARAY CO.,LTD., PARAPET HR-S) were used. Otherwise, resin films and stretched films were obtained by the same method as in Example 1. Table 2 shows the physical properties. Compared with Examples 1-3, the glass transition temperature is lower and the heat resistance is insufficient; the total light transmittance is less than 91% and the transparency is low.

[0267] Table 2

[0268]

Claims

1. A resin composition comprising: Methacrylic acid resins having a syndiotactic regularity of ≥55% in their tripartite representations and a weight-average molecular weight (Mw) of ≥500,000 as determined by gel permeation chromatography (GPC); and Acrylic cross-linked 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. The resin composition according to claim 1 or 2, wherein, The proportion of structural units derived from methyl methacrylate in the methacrylic resin is 99.5% by mass or more.

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

8.

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

6. The resin composition according to claim 1 or 2, wherein, The methacrylic resin comprises a terminal structure derived from the polymerization initiator represented by the following formula (1). In the formula, R 1 R 2 and R 3 Each can independently represent an alkyl group, a substituted alkyl group, an ester group, or an amide group, wherein R 1 R 2 and R 3 At least one of them represents an ester group or an amide group, R 1 R 2 and R 3 The two can bond to each other to form an alicyclic structure, and * indicates the bonding site with the structural unit from the monomer.

7. The resin composition according to claim 1 or 2, 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 casting solution for film manufacturing based on solution casting, comprising the resin composition and solvent according to claim 1 or 2. The solvent comprises a first solvent with a hydrogen bond term δH of 1 to 12 in the Hansen solubility parameter and a second solvent with a hydrogen bond term δH of 14 to 24.

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

10. The resin film according to claim 9, wherein the glass transition temperature is 120°C or higher.

11. The resin film according to claim 9, wherein the number of bends in the MIT bending resistance test is more than 2500.

12. The resin film according to claim 9, wherein the internal haze is 0.4% or less.

13. The resin film according to claim 9, wherein the b* value is 0.3 or less.

14. A method for manufacturing a resin composition, which is the method for manufacturing the resin composition according to claim 1 or 2, comprising a method for manufacturing a methacrylic resin, said methacrylic resin manufacturing method comprising a polymerization step of polymerizing a monomer mixture containing methyl methacrylate at a content of 99.5% by mass or more in the presence of a polymerization initiator and a chain transfer agent. In the polymerization process, the polymerization temperature is less than 100°C until more than 90% of the resulting methacrylic resin is produced. The amount of the chain transfer agent used relative to the total amount of the monomer mixture is less than 0.03 mol%. 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 manufacturing the resin composition according to claim 14, wherein, In the method for manufacturing the methacrylic resin, the polymerization initiator is a non-nitrile azo polymerization initiator.

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

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

18. The resin film according to claim 9, wherein, The resin film is a protective film for the polarizer.

19. A polarizing plate is formed by laminating a polarizer and the resin film of claim 9.

20. A display device comprising the polarizing plate of claim 19.

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