Method for producing methacrylic resin and methacrylic resin, resin composition, and resin film

Abstract

To provide: a method for producing a methacrylic resin having excellent heat resistance and thermal stability and a methacrylic resin; a resin composition containing the methacrylic resin; a resin film containing the methacrylic resin; and a polarizing plate and a display device including the resin film.SOLUTION: A method for producing a methacrylic resin includes a polymerization step of polymerizing a monomer component having a methyl methacrylate content of 98 mass% or more in the presence of a polymerization initiator and a chain transfer agent. In the polymerization step, the polymerization temperature is set to lower than 100°C until 90% or more of the methacrylic resin to be obtained is formed. The polymerization initiator has a 10-hour half-life temperature of 45°C or higher. The amount of the chain transfer agent used is 0.15 mol% or more with respect to the total amount of the monomer component. The ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is 7.0 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a methacrylic resin, a methacrylic resin, a resin composition, and a resin film.

Background Art

[0002] Methacrylic resins are widely used in various fields because of their excellent transparency, weather resistance, processability, etc. In particular, resin films obtained by molding methacrylic resins are also used in optical applications such as display devices because of their excellent optical properties. This methacrylic resin is produced, for example, by polymerizing a monomer component mainly composed of methyl methacrylate in the presence of a polymerization initiator and a chain transfer agent (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, as a result of investigations by the present inventors, it has been found that the heat resistance or thermal stability of the obtained methacrylic resin may decrease depending on conditions such as the type of polymerization initiator used during the synthesis of the methacrylic resin.

[0005] An object of the present invention is to provide a method for producing a methacrylic resin excellent in heat resistance and thermal stability, a methacrylic resin, a resin composition containing the methacrylic resin, a resin film containing the methacrylic resin, a polarizing plate using the resin film, and a display device.

Means for Solving the Problems

[0006] Specific means for solving the above problems include the following embodiments. <1> It includes a polymerization step of polymerizing a monomer component having a methyl methacrylate content of 98% by mass or more in the presence of a polymerization initiator and a chain transfer agent. In the polymerization step, the polymerization temperature until 90% or more of the resulting methacrylic resin is produced is less than 100°C. The 10-hour half-life temperature of the polymerization initiator is 45°C or more. The amount of the chain transfer agent used is 0.15 mol% or more based on the total amount of the monomer component. A method for producing a methacrylic resin, wherein the ratio of the total mol amount of the chain transfer agent to the total mol amount of the polymerization initiator is 7.0 or more. <2> It includes a polymerization step of polymerizing a monomer component having a methyl methacrylate content of 98% by mass or more in the presence of a polymerization initiator and a chain transfer agent. In the polymerization step, the polymerization temperature until 90% or more of the resulting methacrylic resin is produced is less than 100°C. The 10-hour half-life temperature of the polymerization initiator is 45°C or more. The amount of the chain transfer agent used is 0.15 mol% or more based on the total amount of the monomer component. The ratio of the total mol amount of the chain transfer agent to the total mol amount of the polymerization initiator is 5.0 or more. A method for producing a methacrylic resin, wherein the weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) of the resulting methacrylic resin is 80,000 or more. <3> The method for producing a methacrylic resin according to <1> or <2>, wherein the melting point of the polymerization initiator is less than 100°C. <4> The method for producing a methacrylic resin according to any one of <1> to <3>, wherein aqueous polymerization is carried out in the polymerization step. <5> The method for producing a methacrylic resin according to any one of <1> to <4>, wherein the polymerization initiator contains at least one selected from an azo polymerization initiator and a peroxide polymerization initiator. <6> The method for producing a methacrylic resin according to <5>, wherein the azo polymerization initiator is a nitrile-based azo polymerization initiator. <7> In the polymerization step, the monomer component is polymerized in the presence of the polymerization initiator, the chain transfer agent, and the reducing agent. The method for producing a methacrylic resin according to any one of <1> to <6>.

[0007] <8> The proportion of the structural unit derived from methyl methacrylate is 98% by mass or more, The syndiotacticity of the triad display is 55% or more, The proportion of the bonded sulfur atom with respect to the structural unit derived from methyl methacrylate is more than 0 mol%, A methacrylic resin in which the proportion of the terminal double bond with respect to the structural unit derived from methyl methacrylate is less than 0.008 mol%. <9> The methacrylic resin according to <7>, wherein the weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) is 80,000 to 200,000. <10> The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by gel permeation chromatography (GPC) is 1.6 to 2.5. The methacrylic resin according to <8> or <9>. <11> The thermogravimetric reduction rate when exposed to 280 °C for 15 minutes in a nitrogen gas atmosphere is less than 2.9%. The methacrylic resin according to any one of <8> to <10>. <12> The glass transition temperature is 120 °C or higher. The methacrylic resin according to any one of <8> to <11>.

[0008] <13> A resin composition containing the methacrylic resin according to any one of <8> to <12>. <14> The resin composition according to <13>, wherein the content rate of the block copolymer is less than 1% by mass with respect to the total amount of the methacrylic resin. <15> The resin composition according to <13> or <14>, which is in pellet form. <16> A resin film containing the methacrylic resin according to any one of <8> to <12>. <17> The resin film according to <16>, wherein the resin film is an optical film. <18> The resin film according to <16> or <17>, wherein the resin film is a polarizer protection film. <19> A polarizing plate formed by laminating a polarizer and the resin film according to any one of <16> to <18>. <20> A display device including the polarizing plate according to <19>.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a method for producing a methacrylic resin excellent in heat resistance and thermal stability, the methacrylic resin, a resin composition containing the methacrylic resin, a resin film containing the methacrylic resin, and a polarizing plate and a display device using the resin film.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, specific embodiments to which the present invention is applied will be described in detail. The symbol "~" representing a numerical range is used with the intention of including the lower and upper limits of the range unless otherwise specified. In addition, physical property values of components such as a polymerization initiator and a methacrylic resin mean values under 1 atm unless otherwise specified.

[0011] <Method for Producing Methacrylic Resin> The method for producing a methacrylic resin according to the present embodiment includes a polymerization step of polymerizing a monomer component having a methyl methacrylate content of 98% by mass or more in the presence of a polymerization initiator, a chain transfer agent, and a reducing agent as an optional component.

[0012] In the polymerization process, from the viewpoints of controlling the syndiotacticity of the resulting methacrylic resin and productivity, the polymerization temperature until more than 90% of the resulting methacrylic resin is produced is less than 100°C. Here, "until more than 90% of the resulting methacrylic resin is produced" means "at least until the conversion rate reaches 90%" when the polymerization reaction is carried out until the conversion rate is 100%. For example, when the polymerization reaction is terminated at a conversion rate of 50%, it means "at least until the conversion rate reaches 45%". The polymerization temperature until more than 90% of the resulting methacrylic resin is produced is preferably 20°C or higher and less than 100°C, more preferably 30 - 95°C, even more preferably 50 - 90°C, and particularly preferably 60 - 85°C. After more than 90% of the resulting methacrylic resin is produced, the polymerization temperature may be raised to 100°C or higher for the purpose of reducing the residual monomer component and deactivating the residual polymerization initiator, etc.

[0013] The methacrylic resin obtained by the production method according to this embodiment preferably has a weight average molecular weight (Mw) of 80,000 or more, more preferably 90,000 or more, even more preferably 95,000 or more, and particularly preferably 100,000 or more. When the weight average molecular weight (Mw) of the methacrylic resin is 80,000 or more, the mechanical properties of the resulting molded body tend to be improved. The upper limit of the weight average molecular weight (Mw) of the methacrylic resin is not particularly limited, but from the viewpoint of moldability, it is preferably 200,000 or less, more preferably 180,000 or less, and even more preferably 150,000 or less.

[0014] Also, the methacrylic resin according to this embodiment preferably has a dispersity (Mw / Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), of 1.6 - 2.5, and more preferably 1.7 - 2.2. When the dispersity (Mw / Mn) of the methacrylic resin is 1.6 or more, the fluidity of the methacrylic resin tends to be improved and it becomes easier to mold. When the dispersity (Mw / Mn) of the methacrylic resin is 2.5 or less, the mechanical properties such as impact resistance, toughness, and flexural resistance of the resulting molded body tend to be improved.

[0015] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) in this specification are values in terms of standard polystyrene measured by gel permeation chromatography (GPC), and are measured by the method described in the examples below.

[0016] Note that the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the methacrylic resin can be controlled by adjusting the types and amounts used of the polymerization initiator and chain transfer agent when synthesizing the methacrylic resin.

[0017] As the method for producing the methacrylic resin, a conventionally known polymerization method can be adopted. For example, radical polymerization methods such as continuous bulk polymerization method, solution polymerization method, emulsion polymerization method, surfactant-free (soap-free) emulsion polymerization method, and suspension polymerization method can be adopted. Among them, from the viewpoints of the degree of freedom in the structural design of the methacrylic resin, the simplicity of polymerization, productivity, etc., a production method that performs aqueous polymerization is preferable, the suspension polymerization method and the emulsion polymerization method are more preferable, and the suspension polymerization method is even more preferable.

[0018] Note that when the methacrylic resin according to this embodiment is produced by aqueous polymerization, it is also advantageous from the viewpoint of impurities in the resin. For example, in the anionic solution polymerization method, since an organometallic compound is used as the polymerization initiator, metal ions derived from the organometallic compound remain in the resin at about several hundred mass ppm. On the other hand, in aqueous polymerization, since an organometallic compound is not used as the polymerization initiator, the total residual metal ions in the resin can be made 100 mass ppm or less. When performing aqueous polymerization, preferably, the content of Al in the resin is 1 mass ppm or less, and the content of Li is 1 mass ppm or less. Also, in aqueous polymerization, a step for removing residual metal ions is not required, so it is excellent in economic efficiency. Furthermore, in aqueous polymerization, for example, organic solvents such as aliphatic hydrocarbons and alicyclic hydrocarbons used in the anionic solution polymerization method are not used, so it is also excellent in terms of the environment.

[0019] [Suspension Polymerization Method] In the suspension polymerization method, a methacrylic resin is synthesized in an aqueous suspension obtained by mixing water, a monomer component, a dispersant, a polymerization initiator, a chain transfer agent, and optionally other additives. The order of mixing the respective components is not particularly limited. For example, the respective components may be mixed simultaneously to prepare an aqueous suspension. Alternatively, after preparing an aqueous solution by mixing water, a polymerization initiator, and optionally other additives, the monomer component and the chain transfer agent may be added, and subsequently, a dispersant may be added to prepare an aqueous suspension. The mass ratio of the obtained methacrylic resin to water (methacrylic resin / water) is preferably 1.0 / 0.6 to 1.0 / 3.0.

[0020] As the monomer component, those having a methyl methacrylate content of 98% by mass or more, preferably 99% by mass or more, more preferably 100% by mass are used.

[0021] Examples of monomers other than methyl methacrylate include acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate; aryl acrylate esters such as phenyl acrylate; cycloalkyl acrylate esters such as cyclohexyl acrylate, norbornenyl acrylate; alkyl methacrylate esters other than methyl methacrylate such as ethyl methacrylate, propyl methacrylate, butyl methacrylate; aryl methacrylate esters such as phenyl methacrylate; cycloalkyl methacrylate esters such as cyclohexyl methacrylate, norbornenyl methacrylate; aromatic vinyl compounds such as styrene, α-methylstyrene; acrylamide; methacrylamide; acrylonitrile; methacrylonitrile; and the like.

[0022] Examples of the dispersant include poorly water-soluble inorganic salts such as tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, and kaolin; water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, and polyvinyl pyrrolidone; and the like. When using a poorly water-soluble inorganic salt as the dispersant, it is effective to use a surfactant such as sodium α-olefin sulfonate or sodium dodecylbenzene sulfonate in combination. These dispersants may be added during the polymerization process as needed.

[0023] As the polymerization initiator, one with a 10-hour half-life temperature of 45°C or higher is used. By using such a polymerization initiator, the thermal stability of the methacrylic resin tends to be improved. The 10-hour half-life temperature of the polymerization initiator is preferably 45 to 100°C, more preferably 50 to 95°C.

[0024] The 10-hour half-life temperature of the polymerization initiator can be measured, for example, by putting a benzene solution or toluene solution containing 0.05 to 0.10 mol / L of the polymerization initiator into a glass tube, replacing the air with nitrogen, sealing it, and then thermally decomposing it in a constant-temperature bath at a predetermined temperature. When using a commercially available polymerization initiator, the 10-hour half-life temperature described in the manufacturer's catalog or the like can be adopted.

[0025] In addition, in order to advance the polymerization by aqueous polymerization, the melting point of the polymerization initiator is preferably less than 100°C.

[0026] In addition, in order to reduce the proportion of terminal double bonds in the obtained methacrylic resin, the hydrogen abstraction ability of the polymerization initiator is preferably less than 15%, more preferably less than 10%, and even more preferably less than 5%.

[0027] The hydrogen abstraction ability of the polymerization initiator can be measured, for example, by the radical trapping method using α-methylstyrene dimer (that is, the α-methylstyrene dimer trapping method).

[0028] Specific examples of the polymerization initiator include, for example, azo polymerization initiators such as 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(isobutyric acid)dimethyl; peroxide polymerization initiators such as lauroyl peroxide, t-hexyl peroxy-2-ethylhexanoate, 1,1,3,3-tetramethylbutyl peroxy 2-ethylhexanoate, t-butyl peroxy pivalate, t-hexyl peroxy pivalate, t-butyl peroxy neodecanoate, 1,1-bis(t-hexyl peroxy)cyclohexane, 3,5,5-trimethylhexanoyl peroxide; and the like. These polymerization initiators may be used alone or in combination of two or more.

[0029] Among these polymerization initiators, azo polymerization initiators are preferred from the viewpoint of hydrogen abstraction ability, and nitrile-based azo polymerization initiators are more preferred.

[0030] In addition, as the polymerization initiator, a redox initiator capable of generating radicals at a relatively low temperature from room temperature to about 40 °C may be used. Examples of the redox initiator include, for example, a combination of the above-mentioned organic peroxide polymerization initiator and a reducing agent (tertiary amine, naphthenate, thiol, etc.). By using a combination of redox initiators, it is possible to efficiently proceed the polymerization at a temperature lower than the 10-hour half-life temperature of the above-mentioned polymerization initiator.

[0031] The amount of the polymerization initiator used is preferably 0.10 parts by mass or less, more preferably 0.05 parts by mass or less, and even more preferably 0.04 parts by mass or less with respect to 100 parts by mass of the total amount of the monomer components. The lower limit of the amount of the polymerization initiator used is not particularly limited, but from the viewpoint of the polymerization rate, it is preferably 0.001 parts by mass or more with respect to 100 parts by mass of the total amount of the monomer components.

[0032] Examples of the chain transfer agent include primary alkyl mercaptan-based chain transfer agents such as n-butyl mercaptan, n-octyl mercaptan, n-hexadecyl mercaptan, n-dodecyl mercaptan, and n-tetradecyl mercaptan; secondary alkyl mercaptan-based chain transfer agents such as s-butyl mercaptan and s-dodecyl mercaptan; tertiary alkyl mercaptan-based chain transfer agents such as t-dodecyl mercaptan and t-tetradecyl mercaptan; thioglycolic acid esters such as 2-ethylhexyl thioglycolate, ethylene glycol dithioglycolate, trimethylolpropane tris(thioglycolate), and pentaerythritol tetrakis(thioglycolate); thiophenol, tetraethylthiuram disulfide, pentaphenylethane, acrolein, methacrolein, allyl alcohol, carbon tetrachloride, ethylene bromide, styrene oligomers (such as α-methylstyrene dimer), and terpinolene. These chain transfer agents may be used alone or in combination of two or more.

[0033] Among these chain transfer agents, from the viewpoints of handleability, stability, and thermal stability of the resulting methacrylic resin, alkyl mercaptan-based chain transfer agents and thioglycolic acid esters are preferred. As the alkyl mercaptan-based chain transfer agent, n-octyl mercaptan is more preferred, and as the thioglycolic acid ester, 2-ethylhexyl thioglycolate is more preferred.

[0034] The amount of the chain transfer agent used is 0.15 mol% or more based on the total amount of the monomer components. The upper limit of the amount of the chain transfer agent used is not particularly limited, but it is preferably 0.45 mol% or less based on the total amount of the monomer components.

[0035] By using the chain transfer agent in the above-mentioned amount, a methacrylic resin containing a structure derived from the chain transfer agent can be obtained. The structure derived from the chain transfer agent is, for example, when an alkyl mercaptan-based chain transfer agent or a thioglycolic acid ester is used, a structure generated by the reaction of a growing radical with hydrogen of the alkyl mercaptan-based chain transfer agent or the thioglycolic acid ester (that is, a saturated bond terminal structure), or a resin structure generated by the reaction of a sulfur radical generated by the alkyl mercaptan-based chain transfer agent or the thioglycolic acid ester pulling out hydrogen with a monomer (that is, a resin structure containing sulfur), etc.

[0036] In order to reduce the ratio of terminal double bonds of the obtained methacrylic resin and improve the thermal stability, the ratio of the total mol amount of the chain transfer agent to the total mol amount of the polymerization initiator is set to 7.0 or more. However, when the weight average molecular weight (Mw) of the obtained methacrylic resin is 80,000 or more, the ratio of the total mol amount of the chain transfer agent to the total mol amount of the polymerization initiator may be 5.0 or more, may be 6.0 or more, or may be 7.0 or more. The ratio of the total mol amount of the chain transfer agent to the total mol amount of the polymerization initiator is preferably 8.0 or more, and more preferably 9.0 or more. The upper limit of the ratio of the total mol amount of the chain transfer agent to the total mol amount of the polymerization initiator is not particularly limited, but for example, it is preferably 50 or less.

[0037] In addition, in order to start the polymerization with a small amount of polymerization initiator, it is preferable to carry out the polymerization reaction with a low dissolved oxygen amount. The dissolved oxygen amount in the raw materials for polymerization is preferably 10 ppm or less, more preferably 5 ppm or less, still more preferably 4 ppm or less, and particularly preferably 2 ppm or less. By setting the dissolved oxygen amount within such a range, the polymerization reaction proceeds smoothly, and the coloring of the molded body of the methacrylic resin tends to be suppressed. Examples of the method for removing dissolved oxygen in the raw materials for polymerization include continuously feeding an inert gas such as nitrogen gas into the reaction vessel before, during, and after raising the temperature to a predetermined polymerization temperature. In order to remove dissolved oxygen from the raw materials added during the polymerization, it is also preferable to separately aerate an inert gas through those raw materials.

[0038] In addition, in order to allow the polymerization reaction to proceed smoothly, when a polymerization inhibitor is contained in the monomer mixture, it is preferable to remove the polymerization inhibitor by distillation, alkali extraction, or using an adsorbent such as alumina, silica gel, molecular sieve, activated carbon, ion exchange resin, zeolite, acid clay, etc.

[0039] The suspension containing the methacrylic resin obtained by suspension polymerization may be subjected to washing operations such as acid washing, water washing, and alkali washing in order to remove the dispersant. The number of times these washing operations are performed may be selected as an optimal number in consideration of work efficiency and the removal efficiency of the dispersant, and it may be once or multiple times.

[0040] As a method for separating the methacrylic resin from the suspension containing the methacrylic resin, a conventionally known dehydration method can be adopted. Examples of the dehydration method include a method using a centrifuge, a method of suction-removing water on a porous belt or a filtration membrane, etc.

[0041] The water-containing methacrylic resin obtained through the above dehydration can be dried and recovered by a conventionally known method. Examples of the drying method include hot air drying in which hot air is sent into a tank from a hot air blower, a blow heater, etc.; vacuum drying in which the system is depressurized and then heated as necessary; barrel drying in which the obtained methacrylic resin is rotated in a container to remove moisture; spin drying in which drying is performed using centrifugal force; etc. These drying methods may be implemented individually by one type, or may be implemented in combination of two or more types.

[0042] [Emulsion polymerization method] In the emulsion polymerization method, the methacrylic resin is synthesized in an emulsion obtained by mixing water, a monomer component, an emulsifier, a polymerization initiator, a chain transfer agent, and optionally other additives.

[0043] As the monomer component, those having a methyl methacrylate content of 98% by mass or more, preferably 99% by mass or more, more preferably 100% by mass are used.

[0044] Examples of the emulsifier include anionic surfactants such as alkyl sulfonates, alkylbenzene sulfonates, dialkyl sulfosuccinates, α-olefin sulfonates, naphthalene sulfonate-formaldehyde condensates, alkylnaphthalene sulfonates, N-methyl-N-acyl taurine salts, phosphate esters (such as polyoxyethylene alkyl ether phosphates), etc.; nonionic surfactants; and the like. Examples of the above salts include lithium salts, sodium salts, potassium salts, calcium salts, magnesium salts, etc. These emulsifiers may be used alone or in combination of two or more. Note that the emulsifier used in emulsion polymerization may remain in the final methacrylic resin.

[0045] When the pH of the emulsion deviates from neutrality and becomes acidic or basic, an appropriate pH adjuster can be used to prevent hydrolysis of the monomer methyl methacrylate and the structural units derived from methyl methacrylate in the methacrylic resin obtained by polymerization. Examples of the pH adjuster to be used include boric acid - potassium chloride - potassium hydroxide, potassium dihydrogen phosphate - disodium hydrogen phosphate, boric acid - potassium chloride - potassium carbonate, citric acid - potassium hydrogen citrate, potassium dihydrogen phosphate - boric acid, disodium hydrogen phosphate - citric acid, etc.

[0046] Examples of the polymerization initiator and the chain transfer agent include the same ones as those in the suspension polymerization method described above.

[0047] Note that, similar to the case of the suspension polymerization method, a redox initiator may be used as the polymerization initiator. Examples of the redox initiator applicable to the emulsion polymerization method include, for example, a combination of an organic peroxide polymerization initiator, a reducing agent (ferrous sulfate, sulfite, etc.), and an activator (sodium formaldehyde sulfoxylate, glucose).

[0048] In order to reduce the ratio of terminal double bonds in the obtained methacrylic resin and improve its thermal stability, the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is set to 7.0 or more. However, when the weight average molecular weight (Mw) of the obtained methacrylic resin is 80,000 or more, the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator may be 5.0 or more, may be 6.0 or more, or may be 7.0 or more. The ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is preferably 8.0 or more, and more preferably 9.0 or more. The upper limit of the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is not particularly limited, but for example, it is preferably 50 or less.

[0049] The latex of the methacrylic resin obtained by emulsion polymerization is subjected to heat drying or spray drying, or solid or powdery methacrylic resin can be obtained by adding a water-soluble electrolyte such as a salt or an acid to cause coagulation, and then separating the resin component from the aqueous phase after performing heat treatment and drying by a known method such as this. The above-mentioned salt is not particularly limited, but a divalent salt is preferred, and specifically, calcium salts such as calcium chloride and calcium acetate; magnesium salts such as magnesium chloride and magnesium sulfate; and the like can be mentioned. Among these salts, magnesium salts such as magnesium chloride and magnesium sulfate are preferred. Additives generally added such as an anti-aging agent and an ultraviolet absorber may be added during coagulation.

[0050] Before the above-mentioned coagulation operation, it is preferable to filter the latex with a filter, a mesh, etc. to remove fine polymerization scales. Thereby, when the methacrylic resin is made into a molded body, fish eyes, foreign substances, etc. caused by fine polymerization scales can be reduced.

[0051] In this embodiment, the form of the methacrylic resin obtained by aqueous polymerization may be powder, granules, or a powder-granule mixture containing both powder and granules. For the primary particles constituting the powder, granules, and powder-granule mixture, suspension polymerization is suitable when producing primary particles with an average particle diameter of about 10 to 1,000 μm, and emulsion polymerization is suitable when producing primary particles with an average particle diameter of about 50 to 500 nm. The powder, granules, and powder-granule mixture may contain aggregates that are aggregates of the above primary particles.

[0052] After the polymerization is completed, if necessary, volatile components such as residual monomers, residual oligomers, and chain transfer agents in the methacrylic resin may be removed. The removal method is not particularly limited, but heat devolatilization is preferred. Examples of the devolatilization method include treatment with an extruder equipped with a vent. The vent of the extruder is preferably a vacuum vent or an open vent, and the screw of the extruder is preferably a twin-screw. Since the twin-screw provides greater shear energy to the resin and a higher degree of surface renewal compared to a single-screw, devolatilization can be performed efficiently. The cylinder heating temperature of the extruder is preferably 150 to 270°C, more preferably 160 to 260°C, and even more preferably 180 to 250°C. By setting the cylinder heating temperature to 270°C or lower, thermal decomposition of the methacrylic resin can be suppressed.

[0053] <Methacrylic resin> The methacrylic resin according to this embodiment has a proportion of structural units derived from methyl methacrylate of 98% by mass or more and a proportion of structural units derived from monomers other than methyl methacrylate of 2% by mass or less. The methacrylic resin according to this embodiment preferably has a proportion of structural units derived from methyl methacrylate of 99% by mass or more, and more preferably 100% by mass (i.e., a homopolymer of methyl methacrylate). The structural unit derived from methyl methacrylate is represented by the following formula.

[0054] [Chemical formula]

[0055] Examples of monomers other than methyl methacrylate include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; aryl acrylates such as phenyl acrylate; cycloalkyl acrylates such as cyclohexyl acrylate and norbornenyl acrylate; alkyl methacrylates other than methyl methacrylate such as ethyl methacrylate, propyl methacrylate, and butyl methacrylate; aryl methacrylates such as phenyl methacrylate; cycloalkyl methacrylates such as cyclohexyl methacrylate and norbornenyl methacrylate; aromatic vinyl compounds such as styrene and α-methylstyrene; acrylamide; methacrylamide; acrylonitrile; methacrylonitrile; and the like.

[0056] The methacrylic resin according to this embodiment preferably has a weight average molecular weight (Mw) of 80,000 to 200,000, more preferably 90,000 to 180,000, and even more preferably 90,000 to 150,000. When the weight average molecular weight (Mw) of the methacrylic resin is 80,000 or more, the mechanical properties of the resulting molded article tend to improve. When the weight average molecular weight (Mw) of the methacrylic resin is 200,000 or less, the moldability tends to improve.

[0057] In addition, the methacrylic resin according to this embodiment preferably has a dispersity (Mw / Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), of 1.6 to 2.5, more preferably 1.7 to 2.2. When the dispersity (Mw / Mn) of the methacrylic resin is 1.6 or more, the fluidity of the methacrylic resin improves and it tends to be easier to mold. When the dispersity (Mw / Mn) of the methacrylic resin is 2.5 or less, the mechanical properties such as impact resistance, toughness, and flexural resistance of the resulting molded article tend to improve.

[0058] The weight average molecular weight (Mw) and number average molecular weight (Mn) in this specification are values in terms of standard polystyrene measured by gel permeation chromatography (GPC), and are measured by the method described in the examples below.

[0059] Note that the weight average molecular weight (Mw) and number average molecular weight (Mn) of the methacrylic resin can be controlled by adjusting the types and amounts used of the polymerization initiator and chain transfer agent when synthesizing the methacrylic resin.

[0060] The methacrylic resin according to this embodiment has a syndiotacticity (rr) of 55% or more in terms of triad display, preferably 56% or more, and more preferably 57% or more. When the syndiotacticity (rr) in terms of triad display is 55% or more, the glass transition temperature (Tg) of the methacrylic resin tends to be high and the heat resistance tends to improve. Also, when the syndiotacticity (rr) is 55% or more, the solvent resistance of the resulting molded article tends to improve. The upper limit of the syndiotacticity (rr) is not particularly limited, but from the viewpoints of the molding processing temperature and the toughness and secondary processability of the molded article, it is preferably 70% or less, more preferably 67% or less, still more preferably 65% or less, and particularly preferably 63% or less.

[0061] The syndiotacticity (rr) is the ratio in which the two chains (diads) of the chain (triad) of three consecutive structural units are both racemo (rr). In the chain (diad) of the structural unit in the polymer molecule, those with the same configuration are called meso and those with the opposite configuration are called racemo, and are denoted as m and r, respectively.

[0062] The syndiotacticity (rr) is, as described in the examples below, under the conditions of 22 °C and an integration number of 16 times in deuterated chloroform. 1The 1H-NMR spectrum was measured, and from the spectrum, the area (X) of the region from 0.60 to 0.95 ppm and the area (Y) of the region from 0.60 to 1.25 ppm were measured with tetramethylsilane (TMS) set at 0 ppm, and can be calculated by the formula: (X / Y)×100.

[0063] Moreover, the methacrylic resin according to this embodiment preferably has a glass transition temperature (Tg) of 120°C or higher, more preferably 121°C or higher, and even more preferably 122°C or higher. The upper limit of the glass transition temperature (Tg) is not particularly limited, but from the viewpoints of the molding processing temperature and the secondary processability of the molded body, it is preferably 135°C or lower, and may be 130°C or lower.

[0064] The glass transition temperature (Tg) in this specification is the midpoint glass transition temperature determined from the DSC curve and is measured by the method described in the examples below.

[0065] Note that the syndiotacticity (rr) and the glass transition temperature (Tg) of the methacrylic resin can be controlled by adjusting the polymerization temperature when synthesizing the methacrylic resin. For example, lowering the polymerization temperature is preferable for increasing the syndiotacticity (rr) of the methacrylic resin and raising the glass transition temperature (Tg). Also, the glass transition temperature (Tg) can be controlled by adjusting the molecular weight of the methacrylic resin.

[0066] Moreover, the methacrylic resin according to this embodiment has a proportion of bonded sulfur atoms to the structural unit derived from methyl methacrylate exceeding 0 mol%, preferably 0.10 mol% or more, more preferably 0.11 mol% or more, and even more preferably 0.12 mol% or more. If the proportion of bonded sulfur atoms is within the above range, the thermal stability of the methacrylic resin tends to improve. The upper limit of the proportion of bonded sulfur atoms is not particularly limited, but is preferably 0.25 mol% or less, and more preferably 0.22 mol% or less.

[0067] The ratio of the sulfur atoms bonded to the structural units derived from methyl methacrylate is calculated by the method described in the examples below.

[0068] In addition, for the methacrylic resin according to this embodiment, the ratio of the terminal double bonds to the structural units derived from methyl methacrylate is less than 0.008 mol%, preferably 0.007 mol% or less. If the ratio of the terminal double bonds is within the above range, the thermal stability of the methacrylic resin tends to improve.

[0069] As shown in the above-described production method, the methacrylic resin according to this embodiment can be produced by a radical polymerization method. The methacrylic resin produced by the radical polymerization method contains terminal double bonds generated by disproportionation termination reaction during polymerization, hydrogen abstraction reaction of monomers by a polymerization initiator, and the like. Since the terminal double bonds affect the thermal stability of the resin, the ratio thereof is preferably small. If the ratio of the terminal double bonds can be controlled by the method described below and reduced to the range of 0.001 mol% or more and less than 0.008 mol%, the thermal stability of the methacrylic resin tends to be greatly improved.

[0070] As described in the examples below, the ratio of the terminal double bonds to the structural units derived from methyl methacrylate is measured by measuring the 1H-NMR spectrum at 20 °C in deuterated chloroform under the conditions of an integration number of 8,192 times, and from the spectrum, the sum of the areas (X) of the peaks (5.47 to 5.51 ppm and 6.21 ppm) derived from the terminal double bond portion of the methacrylic resin and the area (Y) of the peak (0.5 to 1.25 ppm) derived from the α-methyl group of the methacrylic resin are measured, and can be calculated by the formula: [(3 × X) / (2 × Y)] × 100. 1 H-NMR spectrum is measured, and from the spectrum, the sum of the areas (X) of the peaks (5.47 to 5.51 ppm and 6.21 ppm) derived from the terminal double bond portion of the methacrylic resin and the area (Y) of the peak (0.5 to 1.25 ppm) derived from the α-methyl group of the methacrylic resin are measured, and can be calculated by the formula: [(3 × X) / (2 × Y)] × 100.

[0071] Incidentally, the ratio of the terminal double bonds of the methacrylic resin can be controlled by adjusting the amounts of the polymerization initiator and the chain transfer agent used, the polymerization temperature, the polymerization time, etc. when synthesizing the methacrylic resin. For example, reducing the amount of the polymerization initiator used, increasing the amount of the chain transfer agent used, lowering the polymerization temperature, and increasing the polymerization time are preferable for reducing the ratio of the terminal double bonds.

[0072] As described above, the methacrylic resin according to this embodiment is excellent in thermal stability. The methacrylic resin according to this embodiment preferably has a thermogravimetric reduction rate of less than 2.9%, more preferably less than 2.8% when exposed to 280°C for 15 minutes in a nitrogen gas atmosphere. This thermogravimetric reduction rate is measured by the method described in the examples below.

[0073] Further, the methacrylic resin according to this embodiment preferably has a small thermogravimetric reduction rate caused by factors other than residual methyl methacrylate when heat-treated under the conditions of heating from 40°C to 270°C at a heating rate of 10°C / min under a nitrogen gas flow of 200 mL / min and holding at 270°C for 2.5 minutes. If the thermogravimetric reduction rate caused by factors other than residual methyl methacrylate is large, the resin strands during extrusion molding tend to foam easily, making pelletization difficult. The thermogravimetric reduction rate caused by factors other than residual methyl methacrylate is preferably less than 2.0%. The thermogravimetric reduction rate caused by factors other than residual methyl methacrylate is measured by the method described in the examples below.

[0074] The methacrylic resin according to this embodiment is not only excellent in heat resistance and thermal stability but also expected to be suitable for reuse, i.e., recycling, after disposal. As a method for recycling methacrylic resin, for example, chemical recycling (a method of recovering cracked oil as a decomposition product by thermal decomposition and reusing it as a chemical raw material or fuel) is known. Generally, in order to improve the heat resistance and thermal stability of methacrylic resin, a cyclic structure is introduced into the molecular structure of methacrylic resin, or a monomer having a rigid structure is copolymerized. However, these structures become impurities in performing chemical recycling, which is not preferable. In this regard, the methacrylic resin according to this embodiment has a large proportion of structural units derived from methyl methacrylate, and it is expected that the monomer recovered as cracked oil has a high yield and exhibits good chemical recyclability.

[0075] <Resin composition> The resin composition according to this embodiment contains the methacrylic resin according to the above-described this embodiment.

[0076] From the viewpoint of further improving the light resistance of the obtained molded article, the resin composition according to this embodiment preferably contains an ultraviolet absorber. The ultraviolet absorber is not particularly limited, and ultraviolet absorbers conventionally blended in various resins can be used. Examples of the ultraviolet absorber include benzotriazole compounds, triazine compounds, oxalic acid anilide compounds, cyanoacrylate compounds, salicylate compounds, benzophenone compounds, and the like. Among these, triazine compounds are preferable from the viewpoint of the light resistance of the resin composition.

[0077] Examples of the triazine compound include 2,4-diphenyl-6-(2-hydroxyphenyl-4-hexyloxyphenyl)-1,3,5-triazine, 2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-(octyloxy)phenol, 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]phenol, 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol, 2,4,6-tris(2-hydroxy-4-alkoxy-3-methylphenyl)-1,3,5-triazine, and the like. The alkoxy group of 2,4,6-tris(2-hydroxy-4-alkoxy-3-methylphenyl)-1,3,5-triazine is preferably a linear or branched alkoxy group having 1 to 10 carbon atoms. Specific examples of 2,4,6-tris(2-hydroxy-4-alkoxy-3-methylphenyl)-1,3,5-triazine include 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine, and the like.

[0078] Among these triazine compounds, 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol and 2,4,6-tris(2-hydroxy-4-alkoxy-3-methylphenyl)-1,3,5-triazine are preferred. 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol is available as Adeka Stab LA-46 (manufactured by ADEKA CORPORATION). 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine is available as Adeka Stab LA-F70 (manufactured by ADEKA CORPORATION). These ultraviolet absorbers may be used alone or in combination of two or more.

[0079] When the resin composition according to this embodiment contains an ultraviolet absorber, the amount used is not uniform depending on the type of ultraviolet absorber, usage conditions, etc., but is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 3 parts by mass, based on 100 parts by mass of the methacrylic resin. When the amount of the ultraviolet absorber used is 0.1 part by mass or more, the ultraviolet absorption effect can be improved. Also, when the amount of the ultraviolet absorber used is 5 parts by mass or less, coloring of the resulting molded article can be suppressed, and deterioration of transparency due to an increase in haze of the molded article can be suppressed.

[0080] Further, from the viewpoint of further improving the thermal stability and mechanical properties of the resulting molded article, the resin composition according to this embodiment preferably contains multilayer structured polymer particles. The multilayer structured polymer particles are not particularly limited, and known ones can be appropriately used.

[0081] When the resin composition according to this embodiment contains multilayer structured polymer particles, the blending ratios of the methacrylic resin and the multilayer structured polymer particles vary depending on the use of the molded article, etc., but based on a total of 100 parts by mass of the blending amounts of both components, the blending amount of the methacrylic resin is preferably 30 to 98 parts by mass, and the blending amount of the multilayer structured polymer particles is preferably 2 to 70 parts by mass.

[0082] The resin composition according to this embodiment may further contain known additives such as a light stabilizer, a heat stabilizer, a matting agent, a light diffusing agent, a coloring agent, a dye, a pigment, an antistatic agent, a heat ray reflecting material, a lubricant, a plasticizer, a stabilizer, a flame retardant, a mold release agent, a polymer processing aid, a filler, etc., and a resin other than the methacrylic resin. Examples of the resin other than the methacrylic resin include styrene resins such as acrylonitrile styrene resin and styrene maleic anhydride resin; polycarbonate resin; polyvinyl acetal resin; cellulose acylate resin; fluorine resins such as polyvinylidene fluoride and polyalkyl (meth)acrylate resin; silicone resins; polyolefin resins; polyethylene terephthalate resin; polybutylene terephthalate resin; and the like.

[0083] In addition, in order to adjust the orientation birefringence of the molded article, the resin composition according to the present embodiment may contain inorganic fine particles having birefringence described in Japanese Patent No. 3648201, Japanese Patent No. 4336586, etc., or a low molecular compound having birefringence described in Japanese Patent No. 3696649 and having a molecular weight of 5,000 or less (preferably 1,000 or less).

[0084] On the other hand, in the resin composition according to the present embodiment, the content of the block copolymer is preferably less than 1% by mass, more preferably less than 0.5% by mass, still more preferably less than 0.1% by mass, and particularly preferably 0% by mass (that is, less than the detection limit) with respect to the total amount of the methacrylic resin.

[0085] Examples of the block copolymer include a polymer having 10 to 80% by mass of a methacrylic acid ester polymer block and 90 to 20% by mass of an acrylic acid ester polymer block (hereinafter referred to as "specific block copolymer"). By having a low content of such a specific block polymer, it is possible to keep the production cost of the resin composition low.

[0086] The methacrylic acid ester polymer block of the specific block polymer has a structural unit derived from a methacrylic acid ester as a main structural unit. The proportion of the structural unit derived from the methacrylic acid ester in the methacrylic acid ester polymer block is, for example, 80% by mass or more. The specific block polymer may have only one methacrylic acid ester polymer block or two or more. On the other hand, the acrylic acid ester polymer block of the specific block polymer has a structural unit derived from an acrylic acid ester as a main structural unit. The proportion of the structural unit derived from the acrylic acid ester in the acrylic acid ester polymer block is, for example, 45% by mass or more. The specific block polymer may have only one acrylic acid ester polymer block or two or more.

[0087] The form of the resin composition according to this embodiment is not particularly limited, and it may be in powder form, granular form, a powder and granule mixture containing both powder and granules, or pellet form.

[0088] <Molded article> The methacrylic resin according to this embodiment or the resin composition according to this embodiment can be made into a molded article by a known molding method. Examples of the molding method include melt molding methods such as the T-die method (lamination method, coextrusion method, etc.), inflation method (coextrusion method, etc.), compression molding method, blow molding method, calender molding method, vacuum molding method, injection molding method (insert method, two-color method, press method, core-back method, sandwich method, etc.); solution casting method; and the like.

[0089] <Resin film> The resin film according to this embodiment contains the methacrylic resin according to this embodiment described above. The resin film according to this embodiment is produced, for example, by a melt extrusion method using the resin composition according to this embodiment described above. When producing a resin film by the melt extrusion method, first, the resin composition according to this embodiment is pre-dried, then supplied to an extruder, heated and melted, and supplied to a T-die. Next, the resin composition supplied to the T-die is extruded as a sheet-like molten resin, and cooled and solidified using a cooling roll or the like to obtain a resin film.

[0090] The thickness of the resin film according to this embodiment is preferably, for example, 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. Also, the thickness of the resin film according to this embodiment is preferably, for example, 10 μm or more, more preferably 30 μm or more, even more preferably 50 μm or more, and particularly preferably 60 μm or more. If the thickness of the resin film is within the above range, there is an advantage that when vacuum molding is carried out using the resin film, it is difficult to deform and breakage at the deep drawing part is less likely to occur. Furthermore, there is also an advantage that a resin film with uniform optical properties and good transparency can be produced.

[0091] The total light transmittance of the resin film according to this embodiment is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. If the total light transmittance is within the above range, since the transparency is high, it can be suitably used for optical applications that require light transmittance.

[0092] The glass transition temperature of the resin film according to this embodiment is preferably 110°C or higher, more preferably 115°C or higher, and even more preferably 120°C or higher. If the glass transition temperature is within the above range, the heat resistance of the resin film will be sufficient.

[0093] The haze of the resin film according to this embodiment is preferably 2.0% or less, more preferably 1.5% or less, even more preferably 1.3% or less, and particularly preferably 1.0% or less. Also, 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 the internal haze are within the above ranges, since the transparency is high, it can be suitably used for optical applications that require light transmittance. Note that the haze consists of the haze inside the film and the haze on the film surface (outside), and they are expressed as internal haze and external haze respectively.

[0094] The YI (Yellow Index) of the resin film according to this embodiment is preferably 1.2 or less, more preferably 1.0 or less. If the YI is within the above range, since the transparency is high, it can be suitably used for optical applications that require light transmittance.

[0095] The water vapor permeability of the resin film according to this embodiment at 40°C and a relative humidity of 90% is preferably 200 g / m 2 ·24h or less, more preferably 100 g / m 2 ·24h or less, and even more preferably 80 g / m 2 ·24h or less.

[0096] From the viewpoint of further improving the light resistance, the resin film according to the present embodiment preferably contains an ultraviolet absorber. The ultraviolet absorber is intended to improve the light resistance by absorbing ultraviolet rays having a wavelength of 400 nm or less. The resin film according to the present embodiment preferably has a transmittance at a wavelength of 380 nm in the range of 2 to 30%, more preferably in the range of 4 to 20%, and even more preferably in the range of 5 to 10%.

[0097] The resin film according to the present embodiment can be preferably used as an optical film such as a polarizer protective film. When the resin film according to the present embodiment is used as a polarizer protective film, it is preferable that the optical anisotropy is small. In particular, it is preferable that not only the in-plane direction (length direction, width direction) optical anisotropy of the resin film but also the optical anisotropy in the thickness direction is small. That is, it is preferable that the absolute values of the in-plane retardation and the retardation in the thickness direction are both small. For example, when the measurement wavelength is 590 nm, the absolute value of the in-plane retardation is preferably 20 nm or less, and more preferably 15 nm or less. Also, the absolute value of the retardation in the thickness direction is preferably 50 nm or less, more preferably 20 nm or less, and even more preferably 15 nm or less.

[0098] The retardation is an index value calculated based on birefringence. The in-plane retardation (Re) and the retardation in the thickness direction (Rth) can be calculated by the following formulas, respectively. In an ideal resin film that is completely optically isotropic in the three-dimensional direction, both the in-plane retardation Re and the retardation in the thickness direction Rth are 0.

[0099] Re = (nx - ny) × d Rth = 〔(nx + ny) / 2 - nz〕× d In the above formula, nx, ny, and nz represent the refractive indices in the respective axial directions when the in-plane stretching direction (orientation direction of polymer chains) is the X-axis, the direction perpendicular to the X-axis is the Y-axis, and the thickness direction of the resin film is the Z-axis. Also, d represents the thickness of the resin film, and nx - ny represents the orientation birefringence. Note that the MD direction of the film is taken as the X-axis, and in the case of a stretched film, the stretching direction is taken as the X-axis.

[0100] The resin film according to this embodiment preferably has an orientation birefringence value of -5.0×10 -4 ~5.0×10 -4 More preferably, it is -4.0×10 -4 ~4.0×10 -4 Even more preferably, it is -3.8×10 -4 ~3.8×10 -4 . If the orientation birefringence is within the above range, birefringence during molding processing is less likely to occur, and stable optical properties tend to be obtained.

[0101] (Stretching) The resin film according to this embodiment may be further stretched. By stretching the resin film, the mechanical strength and film thickness accuracy of the resin film can be improved.

[0102] When stretching the resin film according to this embodiment, first, an unstretched resin film is formed from the resin composition according to this embodiment, and then uniaxial stretching or biaxial stretching is performed. Thereby, a stretched film (uniaxially stretched film or biaxially stretched film) can be manufactured.

[0103] The stretching ratio of the stretched film is not particularly limited and is appropriately determined according to the mechanical strength, surface properties, thickness accuracy, etc. of the stretched film to be manufactured. Although it also depends on the stretching temperature, the stretching 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 stretching ratio is within the above range, the mechanical properties such as the elongation rate, tear propagation strength, and fatigue resistance to rubbing of the film tend to be significantly improved.

[0104] (Use) The resin film according to this embodiment can be used for various applications such as transportation equipment, solar cell members, civil engineering and construction members, daily sundries, electric and electronic equipment, optical members, medical supplies, etc. In particular, since the resin film according to this embodiment is excellent in heat resistance and optical properties, it can be suitably used for optical applications. Examples of optical applications include front panels (cover windows) of various display devices, diffusion plates, polarizer protection films, polarizing plate protection films, retardation films, light diffusion films, optically isotropic films, and the like.

[0105] Among these, the resin film according to this embodiment can be suitably used as a polarizer protection film or a front panel (cover window) of a display device. When the resin film according to this embodiment is used as the front panel (cover window) of various display devices, a functional coating film layer such as a primer layer or a hard coat layer may be formed on at least one main surface of the resin film as necessary. Further, when the resin film according to this embodiment is used as a polarizer protection film, the resin film according to this embodiment is bonded to a polarizer to form a polarizing plate. The polarizer is not particularly limited, and any conventionally known polarizer can be used. This polarizing plate is used, for example, in display devices such as liquid crystal display devices and organic EL display devices.

Examples

[0106] Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

[0107] The measurement methods of various physical properties described in the examples and comparative examples are as follows.

[0108] (1) Syndiotacticity (rr) of triad display Of methacrylic resin 1The 1H-NMR spectrum was measured using a nuclear magnetic resonance apparatus (manufactured by Bruker, AVANCE III 400 MHz) in a deuterated chloroform solution at 22 °C with 16 accumulations. From the spectrum, the area (X) in the region of 0.60 to 0.95 ppm and the area (Y) in the region of 0.60 to 1.25 ppm were measured with tetramethylsilane (TMS) set at 0 ppm. Subsequently, the syndiotacticity (rr) in the triad display was calculated using the formula: (X / Y) × 100.

[0109] (2) Weight-average molecular weight (Mw), and the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) The weight-average molecular weight (Mw), number-average molecular weight (Mn), and the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) of the methacrylic resin and resin composition (pellets) were calculated by the standard polystyrene conversion method using gel permeation chromatography (GPC). Specifically, analysis was performed using the following apparatus and conditions with a sample solution prepared by dissolving 4 mg of the methacrylic resin or resin composition (pellets) in 2 mL of chloroform. Measuring instrument: HLC-8220GPC (manufactured by Tosoh Corporation) Detector: RI detector Guard column: KF-G 4A (manufactured by Resonac Co., Ltd.) Analysis column: A series connection of KF-806M and KF-806L manufactured by Resonac Co., Ltd. Eluent: Chloroform Eluent flow rate: 1 mL / min Measurement temperature: 40 °C Standard substance for calibration curve: Polystyrene

[0110] (3) Ratio of terminal double bonds As a pretreatment, the methacrylic resin was dissolved in methylene chloride, and the solution was dropped into methanol to precipitate and purify the resin. The precipitated resin was collected by suction filtration and dried for analysis. A solution was prepared by dissolving 20 mg of the dried methacrylic resin in 0.6 to 0.7 mL of deuterated chloroform, and using a nuclear magnetic resonance apparatus (manufactured by Bruker, AVANCE NEO 700 MHz) 11H-NMR measurement was performed. The measurement temperature was 20 °C, and the number of integrations was 8,192 times. Using the Excitation Sculpting (ES) method, which is a type of solvent elimination method, the measurement was carried out while eliminating the peak derived from the methoxy group of the methacrylic resin (3.60 ppm, the value when the chemical shift of the solvent peak was 7.26 ppm). The obtained 1 From the 1H-NMR spectrum, the total area (X) of the peaks (5.47 - 5.51 ppm and 6.21 ppm) derived from the terminal double bond part of the methacrylic resin and the area (Y) of the peak (0.5 - 1.25 ppm) derived from the α-methyl group of the methacrylic resin were measured. Then, the ratio of the terminal double bond of the methacrylic resin was calculated by the formula: [(3×X) / (2×Y)]×100.

[0111] (4) Glass transition temperature (Tg) The glass transition temperature of the methacrylic resin was measured by the following method. As a pretreatment, heat treatment was performed using a thermogravimetric analyzer (STA7200, manufactured by Hitachi High-Tech Science Corporation) for the purpose of removing residual monomers and decomposition products of the polymerization initiator in the methacrylic resin. Specifically, under a nitrogen flow of 200 mL / min, the temperature was raised from 40 °C to 270 °C at a heating rate of 10 °C / min and held at 270 °C for 2.5 minutes. The glass transition temperature (Tg) of the heat-treated methacrylic resin was measured using a differential scanning calorimeter (DSC; DSC7000X, manufactured by Hitachi High-Tech Science Corporation). First, the first heating was performed from 40 °C to 160 °C at a heating rate of 10 °C / min under a nitrogen flow rate of 40 mL / min, cooled to 40 °C, and then DSC measurement was performed under the condition of the second heating from 40 °C to 160 °C at a heating rate of 10 °C / min. Then, the midpoint glass transition temperature (a straight line equidistant from the vertical axis direction from both the straight line obtained by extrapolating the baseline before the inflection point to the high temperature side and the straight line obtained by extrapolating the baseline after the inflection point to the low temperature side, and the curve of the stepwise change part of the glass transition) was read from the DSC curve measured during the second heating.

[0112] (5) Retention thermal stability and mass loss rate in the heat treatment before measuring the retention thermal stability The retention thermal stability of the methacrylic resin was evaluated using a thermogravimetric analyzer (STA7200, manufactured by Hitachi High-Tech Science Corporation). First, for the purpose of removing residual monomers and decomposition products of the polymerization initiator in the methacrylic resin, the temperature was raised from 40 °C to 270 °C at a heating rate of 10 °C / min under a nitrogen flow of 200 mL / min, and heat treatment was performed under the condition of holding at 270 °C for 2.5 minutes. Here, the mass at 40 °C is X (40℃) , and the mass at the time when the heat treatment at 270 °C was completed is X (270℃) . Using the formula: [(X (40℃) - X (270℃) ) / X (40℃) × 100, the calculated value was obtained. From this value, the value obtained by subtracting the amount of methyl methacrylate remaining in the methacrylic resin calculated by the method described below (mass reduction rate in heat treatment) was determined. After the heat treatment at 270 °C described above, it was cooled to 40 °C. Then, the temperature was raised from 40 °C to 280 °C at a heating rate of 10 °C / min, and the mass change was recorded under the condition of holding at 280 °C for 30 minutes. The mass when the sample temperature reached 280 °C is X (0分) , and the mass when held at 280 °C for 15 minutes is X (15分) . Using the formula: [(X (0分) - X (15分) ) / X (0分) × 100, the retention thermal stability was evaluated from the calculated mass reduction rate.

[0113] The retention thermal stability of the resin composition (pellets) was evaluated using the same apparatus as above. After the first temperature increase from 40 °C to 190 °C at a heating rate of 10 °C / min under a nitrogen flow of 200 mL / min, it was cooled to 40 °C, and then the temperature was raised from 40 °C to 280 °C at a heating rate of 10 °C / min, and the mass change was recorded under the condition of holding at 280 °C for 30 minutes. The mass when the sample temperature reached 280 °C is X (0分) , and the mass when held at 280 °C for 15 minutes is X (15分) . Using the formula: [(X (0分) - X (15分) ) / X (0分) × 100, the retention thermal stability was evaluated from the calculated mass reduction rate.

[0114] (Method for Quantifying Residual Methyl Methacrylate in Methacrylic Resin) The amount of residual methyl methacrylate in the methacrylic resin was determined by the following method. Using a gas chromatograph (manufactured by Agilent Technologies, 7890B), DB-1 (manufactured by Agilent Technologies, film thickness 0.8 μm × inner diameter 0.20 mm × length 30 m) was used as the analytical column, and analysis was performed under the conditions of an injection port temperature of 150°C and a detector temperature of 320°C. The column temperature was set to increase from 35°C to 210°C at a heating rate of 30°C / min, then increase from 210°C to 260°C at a heating rate of 10°C / min, and further increase from 260°C to 320°C at a heating rate of 20°C / min and hold for 3 minutes. Using chlorobenzene as an internal standard substance, a calibration curve was created by the internal standard method, and the residual amount of methyl methacrylate in the methacrylic resin was calculated.

[0115] (6) Ratio of Bonded Sulfur Atoms The ratio of bonded sulfur atoms in the methacrylic resin was determined as follows. As a pretreatment, the methacrylic resin was dissolved in methylene chloride, and the solution was dropped into methanol to precipitate and purify the resin. The precipitated resin was collected by suction filtration and dried for analysis. An appropriate amount of the dried methacrylic resin was precisely weighed and made up to a fixed volume, set in an automatic sample combustion apparatus (Nitto Seiko Air Nalytics Co., Ltd., AQF-2100), decomposed at a high temperature, and the generated gas was absorbed with ultrapure water containing hydrogen peroxide solution and hydrazine monohydrate. Using the obtained solution (decomposed gas aqueous solution), sulfate ions were quantified by an ion chromatograph (Thermo Fisher Scientific Co., Ltd., Integrion RFIC, column: AG18-4μm, AS18-4μm). Next, the mass Wp (mass%) of sulfur atoms per mass of the dried methacrylic resin was calculated. Furthermore, the ratio Sp (mol%) of bonded sulfur atoms was calculated by the following formula. Sp = Wp × (100 / 32)

[0116] (7) Foaming The methacrylic resin was extruded using an intermeshing co-rotating twin-screw extruder with a diameter of 15 mm (manufactured by Technovel Corporation, KZW15TWIN-45MG, L / D = 45). Then, the resin that came out as a strand from the die provided at the exit of the extruder was observed, and the presence or absence of foaming was evaluated. Specifically, when the strand foamed and it became difficult to cut with a pelletizer and a pellet-shaped resin composition could not be obtained, it was rated as "defective", and when no foaming was observed in the strand and it was pelletized with a pelletizer after cooling in a water tank and a resin composition could be obtained, it was rated as "good".

[0117] (8) Haze measurement The haze of the resin film after stretching was measured in accordance with JIS K7136 using a haze meter (manufactured by Suga Test Instruments Co., Ltd., HZ-V3). Also, the value obtained by performing the same measurement with both sides of the resin film sandwiched in the order of glycerin and then glass was defined as the internal haze. The obtained results were converted to the equivalent of a film thickness of 40 μm.

[0118] (9) Total light transmittance The total light transmittance of the resin film after stretching was measured in accordance with JIS K7361-1 using a haze meter (manufactured by Suga Test Instruments Co., Ltd., HZ-V3).

[0119] (10) YI The YI of the resin film after stretching was measured in accordance with JIS K7373 using a spectrophotometer (manufactured by Suga Test Instruments Co., Ltd., SC-P). The obtained results were converted to the equivalent of a film thickness of 40 μm.

[0120] (11) Moisture vapor transmission rate The moisture vapor transmission rate of the resin film after stretching was measured under the conditions of 40 °C and a relative humidity of 90% in accordance with JIS Z0208.

[0121] <Example 1> In a 2-liter glass reactor equipped with a three-blade retreating blade agitator, 170 parts by mass of deionized water, 0.10 part by mass of disodium hydrogen phosphate as a suspension aid, and 0.040 part by mass of 2,2’-azobis(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Corporation, V-65, hydrogen abstraction ability: 1%) as a polymerization initiator were charged. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was bubbled through to replace the air in the reactor. Then, a raw material liquid containing 100 parts by mass of methyl methacrylate (MMA) and 0.322 part by mass of n-octyl mercaptan (n-OM) as a chain transfer agent was added to the reactor. Subsequently, 0.375 part by mass of Methocel 60SH-50 (hydroxypropylmethylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.) as a water-soluble polymer was added to the reactor as a dispersant. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 70 °C to initiate polymerization. After reacting the monomer at 70 °C for 6 hours, the temperature of the liquid in the reactor was raised to 95 °C. The reaction solution was stirred at the same temperature for 1 hour to complete the polymerization. The obtained resin was washed with deionized water in an amount 7 times the charged amount of the monomer, and then dried to obtain bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 2.

[0122] <Example 2> Into a 2-liter glass reactor equipped with a three-blade retreating blade agitator, 170 parts by mass of deionized water, 0.10 part by mass of disodium hydrogen phosphate as a suspension aid, and 0.031 part by mass of 2,2'-azobis(2-methylbutyronitrile) (V-59, hydrogen abstraction ability: 1%, manufactured by Fuji Film Wako Pure Chemical Corporation) as a polymerization initiator were charged. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was bubbled through to replace the air in the reactor. Then, a raw material liquid containing 100 parts by mass of methyl methacrylate (MMA) and 0.322 part by mass of n-octyl mercaptan (n-OM) as a chain transfer agent was added to the reactor. Subsequently, 0.375 part by mass of Methocel 90SH-100 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.) as a water-soluble polymer was added to the reactor as a dispersant. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 79 °C to initiate polymerization. After reacting the monomer at 79 °C for 6 hours, the temperature of the liquid in the reactor was raised to 92 °C. The reaction solution was stirred at the same temperature for 1 hour to complete the polymerization. The resulting resin was washed with deionized water in an amount five times the charged amount of the monomer and dried to obtain bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 2.

[0123] The obtained methacrylic resin was extruded at a resin temperature of 256 °C using a meshing type co-rotating twin-screw extruder with a diameter of 15 mm (KZW15TWIN-45MG, L / D = 45, manufactured by Technovel Corporation). The resin that came out as a strand from the die provided at the exit of the extruder was cooled in a water bath and then pelletized with a pelletizer to obtain a resin composition. The physical properties of the obtained resin composition (pellets) are shown in Table 2.

[0124] The obtained resin composition was dried at 90 °C for 4 hours and then extruded at a resin temperature of 244 °C using a meshing type co-rotating twin-screw extruder with a diameter of 15 mm equipped with a T-die at the exit (KZW15TWIN-45MG, L / D = 45, manufactured by Technovel Corporation). The sheet-like molten resin extruded from the T-die was cooled with a cooling roll to obtain a resin film with a width of 150 mm and a thickness of 160 μm.

[0125] A 100 mm × 100 mm small piece was cut out from the obtained resin film such that two sides were parallel to the extrusion direction. The small piece was set in a pantograph-type biaxial stretching apparatus and simultaneously biaxially stretched at 135 °C by a factor of 2 in the direction parallel to the extrusion direction and by a factor of 2 in the perpendicular direction. The stretching speed in each direction was 100 mm / min. Then, it was taken out at room temperature and rapidly cooled to obtain a resin film with a thickness of 41 μm. The physical properties of the resin film are shown in Table 2.

[0126] <Example 3> Into a 2-liter glass reactor equipped with a three-side retreating blade agitator, 170 parts by mass of deionized water, 0.10 part by mass of disodium hydrogen phosphate as a suspension aid, and 0.037 part by mass of 2,2'-azobis(isobutyric acid) dimethyl (manufactured by Fujifilm Wako Pure Chemical Corporation, V-601, hydrogen abstraction ability: 1%) as a polymerization initiator were charged. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was bubbled through to replace the air in the reactor, and then a raw material solution containing 100 parts by mass of methyl methacrylate (MMA) and 0.322 part by mass of n-octyl mercaptan (n-OM) as a chain transfer agent was added to the reactor. Subsequently, 0.375 part by mass of Metholose 60SH-50 (manufactured by Shin-Etsu Chemical Co., Ltd., hydroxypropyl methylcellulose), a water-soluble polymer, was added to the reactor as a dispersant. Then, after stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 81 °C to initiate polymerization. After reacting the monomer at 81 °C for 4.5 hours, the temperature of the liquid in the reactor was raised to 95 °C. The reaction solution was stirred at the same temperature for 1 hour to terminate the polymerization. The obtained resin was washed with deionized water in an amount 4 times the charged amount of the monomer and dried to obtain bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 2.

[0127] The obtained methacrylic resin was pelletized and formed into a film under the same conditions as in Example 2. Then, this resin film was biaxially stretched simultaneously under the same conditions as in Example 2 to obtain a resin film with a thickness of 41 μm. The physical properties of the resin composition (pellets) and the resin film are shown in Table 2.

[0128] <Example 4> Into a 2-liter glass reactor equipped with a three-blade retreating blade agitator, 170 parts by mass of deionized water, 0.10 part by mass of disodium hydrogen phosphate as a suspension aid, and 0.037 part by mass of 2,2'-azobis(isobutyric acid) dimethyl (manufactured by Fujifilm Wako Pure Chemical Corporation, V-601, hydrogen abstraction ability: 1%) as a polymerization initiator were charged. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was bubbled through to replace the air in the reactor. Then, a monomer solution containing 100 parts by mass of methyl methacrylate (MMA) and 0.220 part by mass of n-octyl mercaptan (n-OM) as a chain transfer agent was added to the reactor. Subsequently, 0.375 part by mass of Methocel 60SH-50 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.) as a water-soluble polymer was added as a dispersant to the reactor. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 78 °C to initiate polymerization. After reacting the monomer at 78 °C for 6.5 hours, the temperature of the liquid in the reactor was raised to 93 °C. The reaction solution was stirred at the same temperature for 1 hour to complete the polymerization. The obtained resin was washed with deionized water in an amount three times the charged amount of the monomer and dried to obtain bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 2.

[0129] The obtained methacrylic resin was pelletized under the same conditions as in Example 2 except that the resin temperature was 252 °C, and then made into a film under the same conditions as in Example 2 except that the resin temperature was 239 °C. Then, the obtained resin film was biaxially stretched simultaneously under the same conditions as in Example 2 to obtain a resin film with a thickness of 41 μm. The physical properties of the resin film are shown in Table 2.

[0130] <Example 5> 170 parts by mass of deionized water, 0.10 parts by mass of disodium hydrogen phosphate as a suspension aid, and 0.064 parts by mass of lauroyl peroxide (manufactured by Toronto Research Chemicals, hydrogen abstraction ability: 1%) as a polymerization initiator were charged into a 2-liter glass reactor equipped with a three-blade retreating blade agitator. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was bubbled through to displace the air in the reactor. Then, a raw material liquid containing 100 parts by mass of methyl methacrylate (MMA) and 0.322 parts by mass of n-octyl mercaptan (n-OM) as a chain transfer agent was added to the reactor. Subsequently, 0.375 parts by mass of Methocel 90SH-100 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.) as a water-soluble polymer was added to the reactor as a dispersant. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 72°C to initiate polymerization. After reacting the monomer at 72°C for 7.2 hours, the temperature of the liquid in the reactor was raised to 81°C and reacted for 40 minutes, and then the temperature of the liquid in the reactor was raised to 95°C. The reaction solution was stirred at the same temperature for 1 hour to complete the polymerization. The obtained resin was washed with 8 times the amount of deionized water based on the charged amount of the monomer and dried to obtain bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 2.

[0131] The obtained methacrylic resin was pelletized under the same conditions as in Example 2 except that the resin temperature was 252°C to obtain a resin composition.

[0132] <Comparative Example 1> 170 parts by mass of deionized water, 0.10 parts by mass of disodium hydrogen phosphate as a suspension aid, and 0.273 parts by mass of 2,2’-azobis(2,4-dimethylvaleronitrile) (manufactured by Fuji Film Wako Pure Chemical Corporation, V-65, hydrogen abstraction ability: 1%) as a polymerization initiator were charged into a 2-liter glass reactor equipped with a three-wing retreating blade agitator. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was bubbled through to displace the air in the reactor. Then, a raw material solution containing 100 parts by mass of methyl methacrylate (MMA) and 0.322 parts by mass of n-octyl mercaptan (n-OM) as a chain transfer agent was added to the reactor. Subsequently, 0.375 parts by mass of Methocel 60SH-50 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.) as a water-soluble polymer was added to the reactor as a dispersant. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 52 °C to initiate polymerization. After reacting the monomer at 52 °C for 4.3 hours, the temperature of the liquid in the reactor was raised to 96 °C. The reaction solution was stirred at the same temperature for 1 hour to terminate the polymerization. The resulting resin was washed with deionized water in an amount twice the amount of the monomer charged and dried to obtain bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 4.

[0133] The obtained methacrylic resin was pelletized and formed into a film under the same conditions as in Example 2. Then, this resin film was simultaneously biaxially stretched under the same conditions as in Example 2 to obtain a resin film with a thickness of 41 μm. The physical properties of the resin film are shown in Table 4.

[0134] <Comparative Example 2> Into a 2-liter glass reactor equipped with a three-blade retreating blade agitator, 170 parts by mass of deionized water, 0.10 part by mass of disodium hydrogen phosphate as a suspension aid, and 0.340 part by mass of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Corporation, V-70) as a polymerization initiator were charged. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was bubbled through to replace the air in the reactor, and then a raw material solution containing 100 parts by mass of methyl methacrylate (MMA) and 0.322 part by mass of n-octyl mercaptan (n-OM) as a chain transfer agent was added to the reactor. Subsequently, 0.375 part by mass of Methocel 60SH-50 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.) as a water-soluble polymer was added to the reactor as a dispersant. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 36 °C to initiate polymerization. After reacting the monomer at 36 °C for 4.6 hours, the temperature of the liquid in the reactor was raised to 94 °C. The reaction solution was stirred at the same temperature for 1 hour to complete the polymerization. The obtained resin was washed with deionized water in an amount twice the charged amount of the monomer and dried to obtain bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 4.

[0135] The obtained methacrylic resin was extruded under the same conditions as in Example 2 except that the resin temperature was 258 °C. However, the strands of the resin coming out of the die foamed, making it difficult to cut with a pelletizer, and a pellet-shaped resin composition could not be obtained.

[0136] <Comparative Example 3> Into a 2-liter glass reactor equipped with a three-blade retreating blade agitator, 170 parts by mass of deionized water, 0.10 part by mass of disodium hydrogen phosphate as a suspension aid, and 2.280 parts by mass of di-sec-butyl peroxydicarbonate (manufactured by Arkema Kishima Co., Ltd., Lupersol 225M50) as a polymerization initiator were charged. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration: 0.2 ppm) was bubbled through to replace the air in the reactor, and then 100 parts by mass of methyl methacrylate (MMA) was added to the reactor. Subsequently, 0.375 part by mass of Methocel 90SH-100 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.) as a water-soluble polymer was added as a dispersant to the reactor. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 70 °C to initiate polymerization. However, 4 minutes after the temperature was raised to 70 °C, the droplets containing the monomer coalesced, and polymerization in the suspension state could not be continued any further. The mass of the methacrylic resin formed by the coalescence of the droplets was collected, washed with deionized water, and then dried. The physical properties of the obtained methacrylic resin are shown in Table 4.

[0137] <Comparative Example 4> 170 parts by mass of deionized water, 0.10 parts by mass of disodium hydrogen phosphate as a suspension aid, and 3.000 parts by mass of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Corporation, V-70) as a polymerization initiator were charged into a 2-liter glass reactor equipped with a three-wing retreating blade agitator. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was bubbled through to replace the air in the reactor, and then 100 parts by mass of methyl methacrylate (MMA) was added to the reactor. Subsequently, 0.375 parts by mass of Methocel 90SH-100 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.), a water-soluble polymer, was added to the reactor as a dispersant. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 32 °C to initiate polymerization. After reacting the monomer at 32 °C for 2.7 hours, the temperature of the liquid in the reactor was raised to 95 °C. The reaction solution was stirred at the same temperature for 1 hour to complete the polymerization. The resulting resin was washed with deionized water in an amount five times the charged amount of the monomer and dried to obtain bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 4.

[0138] The obtained methacrylic resin was extruded under the same conditions as in Example 2 except that the resin temperature was 249 °C. However, the strands of the resin coming out of the die were foamed, and since the melting of the resin was insufficient, bead-shaped methacrylic resin aggregates adhered to the strands in the form of small lumps. For this reason, cutting with a pelletizer was difficult, and a pellet-shaped resin composition could not be obtained.

[0139]

Table 1

[0140]

Table 2

[0141]

Table 3

[0142]

Table 4

[0143] As shown in Table 2 and Table 4, in Examples 1 to 5 in which a polymerization initiator having a 10-hour half-life temperature of 45°C or higher was used and the molar ratio of the chain transfer agent to the polymerization initiator was 7.0 or higher, the ratio of terminal double bonds was small, the mass loss rate when held at 280°C for 15 minutes was small, and a methacrylic resin excellent in retention heat stability was obtained. Further, the methacrylic resins obtained in Examples 1 to 5 had a high syndiotacticity, and as a result, the glass transition temperature was also high.

[0144] On the other hand, in Comparative Example 1 in which a polymerization initiator having a 10-hour half-life temperature of 45°C or higher was used while the molar ratio of the chain transfer agent to the polymerization initiator was 2.0, the ratio of terminal double bonds contained in the obtained methacrylic resin was larger than that in Examples 1 to 5, and the retention heat stability of the methacrylic resin was inferior. Further, in Comparative Example 2 in which a polymerization initiator having a 10-hour half-life temperature of less than 45°C was used and the molar ratio of the amount of the chain transfer agent to the amount of the polymerization initiator was 2.0, the ratio of terminal double bonds contained in the obtained methacrylic resin was larger than that in Examples 1 to 5, and the retention heat stability of the methacrylic resin was inferior. Furthermore, in Comparative Example 2, the resin strands foamed during the extrusion molding of the methacrylic resin, and a pellet-shaped resin composition could not be obtained.

[0145] Further, in Comparative Examples 3 and 4 in which a polymerization initiator having a 10-hour half-life temperature of less than 45°C was used and no chain transfer agent was used, the ratio of terminal double bonds contained in the obtained methacrylic resin was larger than that in Examples 1 to 5, and the retention heat stability of the methacrylic resin was inferior. Furthermore, in Comparative Example 4, the resin strands foamed during the extrusion molding of the methacrylic resin, and a pellet-shaped resin composition could not be obtained.

Claims

1. The method includes a polymerization step of polymerizing a monomer component having a methyl methacrylate content of 98% by mass or more in the presence of a polymerization initiator and a chain transfer agent, In the polymerization step, the polymerization temperature is set to less than 100° C. until 90% or more of the methacrylic resin is produced, The 10-hour half-life temperature of the polymerization initiator is 45° C. or higher, the amount of the chain transfer agent used is 0.15 mol % or more based on the total amount of the monomer components; A method for producing a methacrylic resin, wherein a ratio of a total molar amount of the chain transfer agent to a total molar amount of the polymerization initiator is 7.0 or more.

2. The method includes a polymerization step of polymerizing a monomer component having a methyl methacrylate content of 98% by mass or more in the presence of a polymerization initiator and a chain transfer agent, In the polymerization step, the polymerization temperature is set to less than 100° C. until 90% or more of the methacrylic resin is produced, The 10-hour half-life temperature of the polymerization initiator is 45° C. or higher, the amount of the chain transfer agent used is 0.15 mol % or more based on the total amount of the monomer components; the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is 5.0 or more; A method for producing a methacrylic resin, wherein the weight average molecular weight (Mw) of the obtained methacrylic resin as measured by gel permeation chromatography (GPC) is 80,000 or more.

3. The method for producing a methacrylic resin according to claim 1 or 2, wherein the melting point of the polymerization initiator is less than 100°C.

4. The method for producing a methacrylic resin according to claim 1 or 2, wherein aqueous polymerization is performed in the polymerization step.

5. The method for producing a methacrylic resin according to claim 1 or 2, wherein the polymerization initiator comprises at least one selected from an azo polymerization initiator and a peroxide polymerization initiator.

6. The method for producing a methacrylic resin according to claim 5, wherein the azo polymerization initiator is a nitrile azo polymerization initiator.

7. The method for producing a methacrylic resin according to claim 1 or 2, wherein in the polymerization step, the monomer component is polymerized in the presence of the polymerization initiator, the chain transfer agent, and a reducing agent.

8. The proportion of structural units derived from methyl methacrylate is 98% by mass or more, The syndiotacticity of the triad is 55% or more, The ratio of bonded sulfur atoms to structural units derived from methyl methacrylate is greater than 0 mol%, A methacrylic resin having a ratio of terminal double bonds to structural units derived from methyl methacrylate of less than 0.008 mol %.

9. The methacrylic resin according to claim 8, having a weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) of 80,000 to 200,000.

10. The methacrylic resin according to claim 8 or 9, wherein the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by gel permeation chromatography (GPC) is 1.6 to 2.

5.

11. The methacrylic resin according to claim 8 or 9, which has a thermal weight loss rate of less than 2.9% when exposed to 280°C for 15 minutes in a nitrogen gas atmosphere.

12. The methacrylic resin according to claim 8 or 9, having a glass transition temperature of 120°C or higher.

13. A resin composition comprising the methacrylic resin according to claim 8 or 9.

14. The resin composition according to claim 13, wherein the content of the block copolymer is less than 1 mass% based on the total amount of the methacrylic resin.

15. The resin composition according to claim 13, which is in the form of pellets.

16. A resin film comprising the methacrylic resin according to claim 8 or 9.

17. The resin film according to claim 16 , which is an optical film.

18. The resin film according to claim 16 , which is a polarizer protective film.

19. A polarizing plate comprising a polarizer and the resin film according to claim 16 laminated together.

20. A display device comprising the polarizer according to claim 19.

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