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

Abstract

Provided are a method for producing a methacrylic resin, a methacrylic resin, a resin composition, and a resin film. The method 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, and in the polymerization step, the polymerization temperature until 90% or more of the methacrylic resin is generated is set to be lower than 100 DEG C, and the polymerization temperature is set to be lower than 100 DEG C until 90% or more of the methacrylic resin is generated. The polymerization initiator has a 10-hour half-life temperature of 45 DEG C or more, the amount of the chain transfer agent used is 0.15 mol% or more with respect to 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, and the weight-average molecular weight (Mw) of the methacrylic resin obtained by gel permeation chromatography (GPC) is 90,000 or more.

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 due to their excellent transparency, weather resistance, processability, etc. In particular, resin films obtained by molding methacrylic resins are also used for optical applications such as display devices due to their excellent optical properties. The methacrylic resins are produced by, for example, polymerizing monomer components containing methyl methacrylate as a main component in the presence of a polymerization initiator and a chain transfer agent (see, for example, Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2019 / 088025 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] However, the present inventors have found through studies that the heat resistance or thermal stability of the obtained methacrylic resin decreases depending on conditions such as the type of polymerization initiator used in synthesizing the methacrylic resin.

[0008] The present invention aims to provide a method for producing a methacrylic resin having excellent heat resistance and thermal stability, 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 using the resin film.

[0009] Solutions for solving problems

[0010] Specific means for solving the above-mentioned problems include the following embodiments.

[0011] <1> A method for producing a methacrylic resin, comprising: 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,

[0012] In the polymerization step, the polymerization temperature until 90% or more of the obtained methacrylic resin is generated is set to be lower than 100° C.

[0013] The 10-hour half-life temperature of the polymerization initiator is 45° C. or higher,

[0014] The amount of the chain transfer agent used is 0.15 mol% or more relative to the total amount of the monomer components.

[0015] 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,

[0016] The weight average molecular weight (Mw) of the obtained methacrylic resin measured by gel permeation chromatography (GPC) was 90,000 or more.

[0017] <2> according to <1> In the method for producing a methacrylic resin, the melting point of the polymerization initiator is lower than 100°C.

[0018] <3> according to <1> or <2> The method for producing a methacrylic resin comprises the step of performing aqueous polymerization in the polymerization step.

[0019] <4> according to <1> ~ <3> The method for producing a methacrylic resin according to any one of the preceding claims, wherein the polymerization initiator comprises at least one selected from the group consisting of an azo polymerization initiator and a peroxide polymerization initiator.

[0020] <5> according to <4> In the method for producing a methacrylic resin, the azo polymerization initiator is a nitrile azo polymerization initiator.

[0021] <6> according to <1> ~ <4> The method for producing a methacrylic resin according to any one of the preceding claims, wherein in the polymerization step, the monomer components are polymerized in the presence of the polymerization initiator, the chain transfer agent, and a reducing agent.

[0022] <7> A methacrylic resin, wherein the ratio of structural units derived from methyl methacrylate is 98% by mass or more,

[0023] The weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) is 90,000 or more,

[0024] The syndiotacticity expressed as triad is 55% or more,

[0025] The ratio of the bonded sulfur atoms to the structural units derived from methyl methacrylate exceeds 0 mol%,

[0026] The ratio of the terminal double bonds to the structural units derived from methyl methacrylate is less than 0.008 mol %.

[0027] <8> according to <7> The methacrylic resin has a thermal weight loss rate of less than 2.9% when exposed to 280° C. for 15 minutes in a nitrogen atmosphere.

[0028] <9> according to <7> or <8> The methacrylic resin has a ratio (Mw / Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) measured by gel permeation chromatography (GPC) of 1.6 to 2.5.

[0029] <10> according to <7> ~ <9> The methacrylic resin described in any one of the preceding claims has a glass transition temperature of 120° C. or higher.

[0030] <11> according to <7> ~ <10> The methacrylic resin according to any one of the preceding claims, wherein the syndiotacticity expressed by triads is 70% or less.

[0031] <12> A resin composition comprising <7> ~ <11> The methacrylic resin described above.

[0032] <13> A resin film comprising <7> ~ <11> The methacrylic resin described above.

[0033] <14> according to <13> The resin film is an optical film.

[0034] <15> according to <13> or <14> The resin film has a haze of less than 2.0%.

[0035] <16> according to <13> ~ <15> The resin film described above has an internal haze of 1.5% or less.

[0036] <17> according to <13> ~ <16> The resin film according to any one of the preceding claims, wherein the resin film is a polarizer protective film.

[0037] <18> A polarizing plate is a polarizing plate <13> ~ <17> The resin films described above are stacked.

[0038] <19> A display device comprising <18> The polarizing plate.

[0039] Effects of the Invention

[0040] According to the present invention, there are provided a method for producing a methacrylic resin having excellent heat resistance and thermal stability, 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 using the resin film. DETAILED DESCRIPTION

[0041] Hereinafter, specific embodiments of the present invention will be described in detail. The symbol "to" indicating a numerical range is used to include the lower limit and upper limit of the range unless otherwise specified. In addition, the physical property values ​​of components such as polymerization initiators and methacrylic resins all mean values ​​under 1 atmosphere unless otherwise specified.

[0042] <Method for producing methacrylic resin>

[0043] 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.

[0044] In the polymerization step, the polymerization temperature until 90% or more of the methacrylic resin is produced is set to be lower than 100° C. from the viewpoint of controlling the syndiotacticity of the methacrylic resin obtained and productivity. Here, “until 90% or more of the methacrylic resin obtained is produced” means that when the polymerization reaction is carried out to a conversion rate of 100%, it means “until the conversion rate reaches at least 90%”, for example, when the polymerization reaction is terminated at a conversion rate of 50%, it means “until the conversion rate reaches at least 45%”. The polymerization temperature until 90% or more of the methacrylic resin obtained is preferably 20° C. or more and lower than 100° C., more preferably 30 to 95° C., further preferably 50 to 90° C., and particularly preferably 60 to 85° C. The polymerization temperature may be raised to 100° C. or higher after 90% or more of the methacrylic resin obtained is produced for the purpose of reducing residual monomer components, deactivating residual polymerization initiators, and the like.

[0045] The weight average molecular weight (Mw) of the methacrylic resin obtained by the manufacturing method described in this embodiment is 90,000 or more, preferably 100,000 or more. If the weight average molecular weight (Mw) of the methacrylic resin is 90,000 or more, there is a tendency that the mechanical properties of the obtained molded body are 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 further preferably 150,000 or less.

[0046] In addition, the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the methacrylic resin described in this embodiment, that is, the dispersion (Mw / Mn), is preferably 1.6 to 2.5, and more preferably 1.7 to 2.2. When the dispersion (Mw / Mn) of the methacrylic resin is 1.6 or more, the fluidity of the methacrylic resin tends to be improved and molding is easy, and when the dispersion (Mw / Mn) of the methacrylic resin is 2.5 or less, the mechanical properties such as impact resistance, toughness, and bending resistance of the obtained molded body tend to be improved.

[0047] The weight average molecular weight (Mw) and number average molecular weight (Mn) in this specification are values ​​calculated in terms of standard polystyrene measured by gel permeation chromatography (GPC), and are measured by the method described in Examples below.

[0048] It should be noted that the weight average molecular weight (Mw) and number average molecular weight (Mn) of the methacrylic resin can be controlled by adjusting the type and amount of the polymerization initiator and chain transfer agent used in synthesizing the methacrylic resin.

[0049] As a method for producing the methacrylic resin, a conventionally known polymerization method can be used, for example, a free radical polymerization method such as a continuous bulk polymerization method, a solution polymerization method, an emulsion polymerization method, an emulsifier-free (soap-free) emulsion polymerization method, and a suspension polymerization method can be used. Among them, from the viewpoints of the degree of freedom in structural design of the methacrylic resin, the simplicity of polymerization, and productivity, a production method that performs aqueous polymerization is preferred, and a suspension polymerization method and an emulsion polymerization method are more preferred, and a suspension polymerization method is still more preferred.

[0050] It should be noted that when the methacrylic resin described in the present embodiment is manufactured by water-based polymerization, it is also advantageous from the viewpoint of impurities in the resin. For example, in anionic solution polymerization, an organometallic compound is used as a polymerization initiator, so the metal ions derived from the organometallic compound will remain in the resin for about 100 mass ppm. On the other hand, in water-based polymerization, an organometallic compound is not used as a polymerization initiator, so the total of the residual metal ions in the resin can be made to be less than 100 mass ppm. In the case of carrying out water-based polymerization, the Al content in the preferred resin is less than 1 mass ppm and the Li content is less than 1 mass ppm. In addition, in water-based polymerization, it is not necessary to remove the process of residual metal ions, so the economy is excellent. And then, in water-based polymerization, organic solvents such as aliphatic hydrocarbons and alicyclic hydrocarbons used in anionic solution polymerization are not used, so it is also excellent in terms of environment.

[0051] [Suspension polymerization method]

[0052] In the suspension polymerization method, the methacrylic resin is synthesized in an aqueous suspension mixed with water, monomer components, dispersants, polymerization initiators, chain transfer agents, and optional other additives. The order in which the components are mixed is not particularly limited. For example, the components can be mixed simultaneously to prepare an aqueous suspension. Alternatively, after mixing water, a polymerization initiator, and optional other additives to prepare an aqueous solution, the monomer components and the chain transfer agent are added, and then the dispersant is 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.

[0053] As the monomer component, a component having a methyl methacrylate content of 98% by mass or more, preferably 99% by mass or more, and more preferably 100% by mass is used.

[0054] 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 norbornyl 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 norbornyl methacrylate; aromatic vinyl compounds such as styrene and α-methylstyrene; acrylamide; methacrylamide; acrylonitrile; methacrylonitrile, and the like.

[0055] As dispersants, there can be listed, for example, poorly water-soluble inorganic salts such as tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, kaolin, etc.; water-soluble polymers such as polyvinyl alcohol, methylcellulose, polyacrylamide, polyvinyl pyrrolidone, etc. When using poorly water-soluble inorganic salts as dispersants, it is effective to use anionic surfactants such as sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate in combination. These dispersants can be added during the polymerization process as needed.

[0056] As the polymerization initiator, a substance having a 10-hour half-life temperature of 45° C. or higher is used. By using such a polymerization initiator, there is a tendency for the thermal stability of the methacrylic resin 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.

[0057] It should be noted that the 10-hour half-life temperature of the polymerization initiator can be measured by, for example, placing a benzene solution or toluene solution containing 0.05 to 0.10 mol / L of the polymerization initiator into a glass tube, sealing the tube after nitrogen substitution, and thermally decomposing the tube in a thermostatic bath at a predetermined temperature. When a commercially available polymerization initiator is used, the 10-hour half-life temperature described in the manufacturer's product manual or the like can be used.

[0058] In order to carry out polymerization by aqueous polymerization, the melting point of the polymerization initiator is preferably lower than 100°C.

[0059] 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%.

[0060] The hydrogen abstraction ability of the polymerization initiator can be measured, for example, by a radical trapping method using an α-methylstyrene dimer (ie, an α-methylstyrene dimer trapping method).

[0061] Specific examples of the polymerization initiator include azo polymerization initiators such as 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), and 2,2'-azobis(isobutyric acid)dimethyl ester; and peroxide polymerization initiators such as lauroyl peroxide, tert-hexyl peroxy-2-ethylhexanoate, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, tert-butyl peroxy pivalate, tert-hexyl peroxy pivalate, tert-butyl peroxy neodecanoate, 1,1-bis(tert-hexylperoxy)cyclohexane, and 3,5,5-trimethylhexanoyl peroxide. These polymerization initiators may be used alone or in combination of two or more.

[0062] Among these polymerization initiators, from the viewpoint of hydrogen abstraction ability, an azo polymerization initiator is preferred, and a nitrile azo polymerization initiator is more preferred.

[0063] It should be noted that, as a polymerization initiator, a redox initiator capable of generating free radicals at a relatively low temperature of about room temperature to about 40°C can be used. As a redox initiator, for example, a combination of the above-mentioned organic peroxide polymerization initiator and a reducing agent (tertiary amine, cycloalkane salt, thiol, etc.) can be cited. By making a combination of redox initiators, polymerization can be efficiently carried out at a temperature lower than the 10-hour half-life temperature of the above-mentioned polymerization initiator.

[0064] The amount of the polymerization initiator is preferably 0.10 mass part or less, more preferably 0.05 mass part or less, and further preferably 0.04 mass part or less relative to 100 mass parts of the total amount of the monomer components. The lower limit of the amount of the polymerization initiator is not particularly limited, but from the viewpoint of polymerization speed, it is preferably 0.001 mass part or more relative to 100 mass parts of the total amount of the monomer components.

[0065] Examples of the chain transfer agent include primary alkyl mercaptan chain transfer agents such as n-butyl mercaptan, n-octyl mercaptan, n-hexadecyl mercaptan, n-dodecyl mercaptan, and n-tetradecyl mercaptan; secondary alkyl mercaptan chain transfer agents such as sec-butyl mercaptan and sec-dodecyl mercaptan; tertiary alkyl mercaptan chain transfer agents such as tert-dodecyl mercaptan and tert-tetradecyl mercaptan; thioglycolates such as 2-ethylhexyl thioglycolate, ethylene glycol dimercaptoacetate, trimethylolpropane tris(thioglycolate), and pentaerythritol tetra(thioglycolate); thiophenol, tetraethylthiuram disulfide, pentanephenylethane, acrolein, methacrolein, allyl alcohol, carbon tetrachloride, vinyl bromide, styrene oligomers (α-methylstyrene dimer, etc.), terpinolene, etc. These chain transfer agents may be used alone or in combination of two or more.

[0066] Among these chain transfer agents, from the viewpoints of handling properties, stability, thermal stability of the resulting methacrylic resin, etc., alkylthiol chain transfer agents and thioglycolates are preferred. As the alkylthiol chain transfer agent, n-octyl mercaptan is more preferred, and as the thioglycolate, 2-ethylhexyl thioglycolate is more preferred.

[0067] The amount of the chain transfer agent used is 0.15 mol% or more relative to the total amount of the monomer components. The upper limit of the amount of the chain transfer agent used is not particularly limited, but is preferably 0.45 mol% or less relative to the total amount of the monomer components.

[0068] By setting the chain transfer agent to the above amount, a methacrylic resin containing a structure derived from the chain transfer agent can be obtained. The structure derived from the chain transfer agent refers to: when using, for example, an alkyl mercaptan chain transfer agent or thioglycolate, a structure generated by a reaction between a propagating radical and hydrogen of the alkyl mercaptan chain transfer agent or thioglycolate (in other words, a saturated bond terminal structure); a resin structure generated by a reaction between a thiol radical generated by hydrogen being taken away from the alkyl mercaptan chain transfer agent or thioglycolate and a monomer (in other words, a sulfur-containing resin structure), etc.

[0069] In order to reduce the proportion of terminal double bonds of the obtained methacrylic resin and improve thermal stability, 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. The ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is preferably 7.0 or more, more preferably 8.0 or more, and further 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, and is preferably 50 or less, for example.

[0070] It should be noted that in order to initiate polymerization with a small amount of polymerization initiator, the polymerization reaction is preferably carried out by reducing the amount of dissolved oxygen. The amount of dissolved oxygen in the polymerization raw material is preferably less than 10ppm, more preferably less than 5ppm, further preferably less than 4ppm, and particularly preferably less than 2ppm. By making the amount of dissolved oxygen in this range, there is a tendency that the polymerization reaction is carried out smoothly and the coloring of the molded body of the methacrylic resin is suppressed. As a method for removing dissolved oxygen in the polymerization raw material, for example, inert gases such as nitrogen are continuously conveyed to the reaction vessel before, during and after the temperature is raised to the specified polymerization temperature. In order to remove dissolved oxygen from the raw materials added during the polymerization, it is preferred that inert gases are also separately introduced into these raw materials.

[0071] In order to smoothly carry out the polymerization reaction, when the monomer mixture contains a polymerization inhibitor, it is preferred to remove the polymerization inhibitor in advance by distillation, alkali extraction or using an adsorbent such as alumina, silica gel, molecular sieve, activated carbon, ion exchange resin, zeolite, acid clay, etc.

[0072] In order to remove the dispersant, the suspension containing the methacrylic resin obtained by suspension polymerization may be subjected to a cleaning operation such as acid cleaning, water cleaning, or alkaline cleaning. The number of times these cleaning operations are performed can be selected to be the optimal number considering the work efficiency and the removal efficiency of the dispersant, and may be once or multiple times.

[0073] 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 removing water by suction on a porous belt or a filtration membrane, and the like.

[0074] The methacrylic resin in a water-containing state obtained by the above dehydration can be dried and recovered by a conventionally known method. Examples of drying methods include hot air drying in which hot air is sent into the tank by a hot air blower, a blast heater, etc.; vacuum drying in which the system is depressurized and then heated as needed; drum drying in which the obtained methacrylic resin is rotated in a container to disperse water; and spin drying in which the methacrylic resin is dried using centrifugal force. These drying methods may be implemented alone or in combination of two or more.

[0075] [Emulsion polymerization method]

[0076] In the emulsion polymerization method, the methacrylic resin is synthesized in an emulsion in which water, a monomer component, an emulsifier, a polymerization initiator, a chain transfer agent, and optionally other additives are mixed.

[0077] As the monomer component, a component having a methyl methacrylate content of 98% by mass or more, preferably 99% by mass or more, and more preferably 100% by mass is used.

[0078] Examples of emulsifiers include anionic surfactants such as alkyl sulfonates, alkylbenzene sulfonates, dialkyl sulfosuccinates, α-olefin sulfonates, naphthalene sulfonate-formaldehyde condensates, alkylnaphthalene sulfonates, N-methyl-N-acyltaurates, phosphate ester salts (polyoxyethylene alkyl ether phosphates, etc.); nonionic surfactants, etc. In addition, examples of the above-mentioned 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. It should be noted that the emulsifier used in the emulsion polymerization may remain in the final methacrylic resin.

[0079] When the pH of the emulsion deviates from neutrality and becomes acidic or alkaline, an appropriate pH adjuster may be used to prevent hydrolysis of methyl methacrylate as a monomer or a structural unit derived from methyl methacrylate in a methacrylic resin obtained by polymerization. Examples of the pH adjuster include boric acid-potassium chloride-potassium hydroxide, potassium dihydrogen phosphate-sodium hydrogen phosphate, boric acid-potassium chloride-potassium carbonate, citric acid-potassium hydrogen citrate, potassium dihydrogen phosphate-boric acid, and sodium dihydrogen phosphate-citric acid.

[0080] Examples of the polymerization initiator and the chain transfer agent include the same ones as those used in the above-mentioned suspension polymerization method.

[0081] It should be noted that, as in the case of suspension polymerization, a redox initiator can be used as a polymerization initiator. As a redox initiator that can be used in emulsion polymerization, for example, a combination of an organic peroxide polymerization initiator and a reducing agent (ferrous sulfate, sulfite, etc.) and an activator (sodium formaldehyde sulfoxylate, glucose) can be cited.

[0082] In order to reduce the proportion of terminal double bonds of the obtained methacrylic resin and improve thermal stability, 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. The ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is preferably 7.0 or more, more preferably 8.0 or more, and further 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, and is preferably 50 or less, for example.

[0083] The methacrylic resin in solid or powdered form can be obtained by subjecting the latex of the methacrylic resin obtained by emulsion polymerization to heat drying or spray drying, or by subjecting it to a known method (adding a water-soluble electrolyte such as a salt or an acid to solidify it, and then separating the resin component from the aqueous phase after heat treatment to dry it, etc.). The above-mentioned salt is not particularly limited, and is preferably a divalent salt. Specifically, calcium salts such as calcium chloride and calcium acetate; magnesium salts such as magnesium chloride and magnesium sulfate, etc. can be listed. Among these salts, magnesium salts such as magnesium chloride and magnesium sulfate are preferred. During solidification, commonly added additives such as antioxidants and ultraviolet absorbers can be added.

[0084] Before the coagulation operation, the latex is preferably filtered using a filter, a mesh, etc. to remove fine polymerized scales in advance. This can reduce fish eyes, foreign matter, etc. caused by fine polymerized scales when the methacrylic resin is molded.

[0085] In this embodiment, the methacrylic resin obtained by aqueous polymerization may be in the form of a powder, a granule, or a powder and granule containing both powder and granule. Regarding the primary particles constituting the powder, granule, and powder and granule, suspension polymerization is suitable when producing primary particles with an average particle size of about 10 to 1,000 μm, and emulsion polymerization is suitable when producing primary particles with an average particle size of about 50 to 500 nm. The powder, granule, and powder and granule may contain an aggregate of the above primary particles, that is, an aggregate.

[0086] After the polymerization is completed, volatile components such as residual monomers, residual oligomers, and chain transfer agents in the methacrylic resin can be removed as needed. The removal method is not particularly limited, and heating devolatilization is preferred. As a devolatilization method, for example, a treatment based on an extruder with vents can be cited. The vents of the extruder are preferably vacuum vents or open vents, and the screw of the extruder is preferably a twin-shaft screw. Compared with a uniaxial screw, a twin-shaft screw has a large shear energy applied to the resin and a large degree of surface renewal, so it can be devolatilized efficiently. The barrel heating temperature of the extruder is preferably 150 to 270°C, more preferably 160 to 260°C, and further preferably 180 to 250°C. By setting the barrel heating temperature to below 270°C, the thermal decomposition of the methacrylic resin can be suppressed.

[0087] <Methacrylic resin>

[0088] In the methacrylic resin described in the present embodiment, the proportion of the structural unit derived from methyl methacrylate is 98% by mass or more, and the proportion of the structural unit derived from the monomer other than methyl methacrylate is 2% by mass or less. In the methacrylic resin described in the present embodiment, the proportion of the structural unit derived from methyl methacrylate is preferably 99% by mass or more, and more preferably 100% by mass (i.e., homopolymer of methyl methacrylate). It should be noted that the structural unit derived from methyl methacrylate is represented by the following formula.

[0089]

[0090] 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 norbornyl 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 norbornyl methacrylate; aromatic vinyl compounds such as styrene and α-methylstyrene; acrylamide; methacrylamide; acrylonitrile; methacrylonitrile, and the like.

[0091] The weight average molecular weight (Mw) of the methacrylic resin described in the present embodiment is 90,000 or more, preferably 100,000 or more. If the weight average molecular weight (Mw) of the methacrylic resin is 90,000 or more, there is a tendency that the mechanical properties of the obtained molded body are 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 further preferably 150,000 or less.

[0092] In addition, the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the methacrylic resin described in this embodiment, that is, the dispersion (Mw / Mn), is preferably 1.6 to 2.5, and more preferably 1.7 to 2.2. When the dispersion (Mw / Mn) of the methacrylic resin is 1.6 or more, the fluidity of the methacrylic resin tends to be improved and molding is easy, and when the dispersion (Mw / Mn) of the methacrylic resin is 2.5 or less, the mechanical properties such as impact resistance, toughness, and bending resistance of the obtained molded body tend to be improved.

[0093] The syndiotacticity (rr) of the methacrylic resin described in this embodiment, expressed by a triad, is 55% or more, preferably 56% or more, and more preferably 57% or more. If the syndiotacticity (rr) expressed by a triad is 55% or more, there is a tendency that the glass transition temperature (Tg) of the methacrylic resin becomes higher and the heat resistance is improved. In addition, if the syndiotacticity (rr) is 55% or more, there is a tendency that the solvent resistance of the resulting molded body is improved. The upper limit of the syndiotacticity (rr) is not particularly limited, and from the viewpoint of the molding temperature, and the toughness and secondary processability of the molded body, it is preferably 70% or less, more preferably 67% or less, further preferably 65% ​​or less, and particularly preferably 63% or less.

[0094] Syndiotacticity (rr) is the ratio of two chains (diads) of a chain of three consecutive structural units (triads) that are both racemic (rr). It should be noted that in the chains (diads) of structural units in polymer molecules, the same stereo configuration is called meso, and the opposite is called racemo, which are expressed as m and r, respectively.

[0095] The syndiotacticity (rr) can be calculated as described in the Examples below: The syndiotacticity (rr) is measured in deuterated chloroform at 22°C and 16 accumulation times. 1 H-NMR spectrum, from which the area (X) of the region of 0.60 to 0.95 ppm and the area (Y) of the region of 0.60 to 1.25 ppm when tetramethylsilane (TMS) was set to 0 ppm were measured, and calculated using the formula: (X / Y)×100.

[0096] In addition, the glass transition temperature (Tg) of the methacrylic resin described in this embodiment is preferably 120° C. or higher, more preferably 121° C. or higher, and further preferably 122° C. or higher. The upper limit of the glass transition temperature (Tg) is not particularly limited, but is preferably 135° C. or lower, and may be 130° C. or lower, from the viewpoint of the molding temperature and the secondary processability of the molded body.

[0097] The glass transition temperature (Tg) in this specification is a midpoint glass transition temperature obtained from a DSC curve, and is measured by the method described in Examples below.

[0098] It should be noted that the syndiotacticity (rr) and 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 preferred for increasing the syndiotacticity (rr) of the methacrylic resin and increasing the glass transition temperature (Tg). In addition, the glass transition temperature (Tg) can also be controlled by adjusting the molecular weight of the methacrylic resin.

[0099] In addition, the ratio of the bonded sulfur atoms in the methacrylic resin according to the present embodiment relative to the structural unit derived from methyl methacrylate exceeds 0 mol%, preferably 0.10 mol% or more, more preferably 0.11 mol% or more, and further preferably 0.12 mol% or more. When the ratio of the bonded sulfur atoms is within the above range, the thermal stability of the methacrylic resin tends to be improved. The upper limit of the ratio of the bonded sulfur atoms is not particularly limited, but is preferably 0.25 mol% or less, and more preferably 0.22 mol% or less.

[0100] The ratio of the bonded sulfur atom to the structural unit derived from methyl methacrylate is calculated by the method described in Examples below.

[0101] In addition, the ratio of the terminal double bonds in the methacrylic resin according to the present embodiment to the structural units derived from methyl methacrylate is less than 0.008 mol%, preferably less than 0.007 mol%, more preferably less than 0.006 mol%, and further preferably less than 0.005 mol%. When the ratio of the terminal double bonds is within the above range, the thermal stability of the methacrylic resin tends to be improved.

[0102] The methacrylic resin described in this embodiment can be manufactured by a free radical polymerization method as shown in the above-mentioned manufacturing method. The methacrylic resin manufactured by the free radical polymerization method contains terminal double bonds generated by a disproportionation termination reaction in polymerization, a hydrogen abstraction reaction of a monomer based on a polymerization initiator, etc. The terminal double bonds affect the thermal stability of the resin, so it is preferred that the proportion is small. The proportion of the terminal double bonds is controlled by the method described below. If it can be reduced to a range of 0.001 mol% or more and less than 0.008 mol%, there is a tendency that the thermal stability of the methacrylic resin is greatly improved.

[0103] The ratio of the terminal double bond to the structural unit derived from methyl methacrylate can be calculated as described in the Examples below: The ratio of the terminal double bond to the structural unit derived from methyl methacrylate can be calculated as follows ... 1 H-NMR spectrum, from which the total area (X) of the peaks derived from the terminal double bonds of the methacrylic resin (5.47 to 5.51 ppm and 6.21 ppm) and the area (Y) of the peak derived from the α-methyl group of the methacrylic resin (0.5 to 1.25 ppm) were measured, and calculated using the formula: [(3×X) / (2×Y)]×100.

[0104] It should be noted that the proportion of terminal double bonds in the methacrylic resin can be controlled by adjusting the amounts of the polymerization initiator and 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, increasing the amount of the chain transfer agent, lowering the polymerization temperature, and extending the polymerization time are preferred for reducing the proportion of terminal double bonds.

[0105] As described above, the methacrylic resin according to the present embodiment has excellent thermal stability. The thermal weight loss rate of the methacrylic resin according to the present embodiment when exposed to a nitrogen atmosphere at 280° C. for 15 minutes is preferably less than 2.9%, and more preferably less than 2.0%. The thermal weight loss rate is measured by the method described in the examples described below.

[0106] In addition, the methacrylic resin described in this embodiment preferably has a small thermal weight loss rate caused by other than residual methyl methacrylate when heat-treated under the following conditions: 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 then maintaining at 270°C for 2.5 minutes. If the thermal weight loss rate caused by other than residual methyl methacrylate is large, there is a tendency that the resin strands are easy to foam and difficult to pelletize during extrusion molding. The thermal weight loss rate caused by other than residual methyl methacrylate is preferably less than 2.0%. The thermal weight loss rate caused by other than residual methyl methacrylate is measured by the method described in the examples described later.

[0107] The methacrylic resin described in the present embodiment is not only excellent in heat resistance and thermal stability, but also can be expected to be suitable for reuse, i.e. recycling, after being discarded. As a recycling method for methacrylic resin, for example, chemical recycling (a method of recovering decomposition oil in the form of decomposition products by thermal decomposition and reusing it as a chemical raw material or fuel) is known. In general, in order to improve the heat resistance and thermal stability of methacrylic resin, an operation of introducing a cyclic structure into the molecular structure of methacrylic resin or copolymerizing a monomer having a rigid structure is performed. However, these structures will become impurities for chemical recycling, so they are not preferred. In this regard, it can be predicted that the proportion of structural units derived from methyl methacrylate in the methacrylic resin described in the present embodiment is high, and the yield of monomers recovered in the form of decomposition oil is high, and it can be expected to show good chemical recyclability.

[0108] <Resin composition>

[0109] The resin composition according to this embodiment contains the methacrylic resin according to the above-mentioned embodiment.

[0110] From the viewpoint of further improving the light resistance of the obtained molded body, the resin composition described in the present embodiment preferably contains an ultraviolet absorber. As the ultraviolet absorber, there is no particular limitation, and ultraviolet absorbers that have been blended into various resins can be used. As the ultraviolet absorber, for example, benzotriazole compounds, triazine compounds, oxalylanilide compounds, cyanoacrylate compounds, salicylate compounds, benzophenone compounds, etc. can be listed. Among these, from the viewpoint of the light resistance of the resin composition, triazine compounds are preferably used.

[0111] 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-triazine-2-yl]-5-(octyloxy)phenol, 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[(hexyl)oxy]phenol, 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol, and 2,4,6-tris(2-hydroxy-4-alkoxy-3-methylphenyl)-1,3,5-triazine. 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.

[0112] Among these triazine compounds, 2-(4,6-diphenyl-1,3,5-triazine-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-triazine-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol can be obtained as ADEKASTAB LA-46 (manufactured by ADEKA Corporation). 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine can be obtained as ADEKASTAB LA-F70 (manufactured by ADEKA Corporation). These ultraviolet absorbers may be used alone or in combination of two or more.

[0113] When the resin composition described in the present embodiment contains an ultraviolet absorber, the amount used varies depending on the type of ultraviolet absorber, the conditions of use, etc., and is preferably 0.1 to 5 parts by mass, and more preferably 0.2 to 3 parts by mass relative to 100 parts by mass of methacrylic resin. If the amount of the ultraviolet absorber is 0.1 parts by mass or more, the ultraviolet absorption effect can be improved. In addition, if the amount of the ultraviolet absorber is 5 parts by mass or less, the coloring of the obtained molded body can be suppressed, and the deterioration of transparency caused by the increase in the haze of the molded body can be suppressed.

[0114] In addition, from the viewpoint of further improving the thermal stability and mechanical properties of the obtained molded article, the resin composition according to the present embodiment preferably contains multilayered polymer particles. The multilayered polymer particles are not particularly limited, and known particles can be used as appropriate.

[0115] When the resin composition described in this embodiment contains multilayer structure polymer particles, the blending ratio of the methacrylic resin and the multilayer structure polymer particles varies depending on the use of the molded body, etc., and the blending amount of the methacrylic resin is preferably 30 to 98 parts by mass, and the blending amount of the multilayer structure polymer particles is preferably 2 to 70 parts by mass, relative to 100 parts by mass of the total blending amount of the two components.

[0116] The resin composition described in this embodiment may also contain known additives such as light stabilizers, heat stabilizers, matting agents, light diffusers, colorants, dyes, pigments, antistatic agents, heat ray reflective materials, lubricants, plasticizers, stabilizers, flame retardants, mold release agents, polymer processing aids, fillers, etc.; resins other than methacrylic resins. As resins other than methacrylic resins, for example, styrene resins such as acrylonitrile styrene resins and styrene maleic anhydride resins; polycarbonate resins; polyvinyl acetal resins; acylated cellulose resins; fluorine resins such as polyvinylidene fluoride and polyfluoroalkyl (meth)acrylate resins; silicone resins; polyolefin resins; polyethylene terephthalate resins; polybutylene terephthalate resins, etc.

[0117] In addition, in order to adjust the oriented birefringence of the molded body, the resin composition described in this embodiment may contain inorganic fine particles with birefringence described in Japanese Patent No. 3648201, Japanese Patent No. 4336586, etc., and low molecular weight compounds with birefringence and a molecular weight of 5,000 or less (preferably 1,000 or less) described in Japanese Patent No. 3696649.

[0118] The form of the resin composition according to the present embodiment is not particularly limited, and may be a powder, may be a granular form, may be a powder or granular form including both a powder and a granular form, or may be a pellet form.

[0119] <Molding>

[0120] The methacrylic resin described in this embodiment or the resin composition described in this embodiment can be made into a molded body by a known molding method. As molding methods, for example, melt molding methods such as T-die method (lamination method, co-extrusion method, etc.), inflation method (co-extrusion method, etc.), compression molding method, blow molding method, calendaring molding method, vacuum molding method, injection molding method (insert method, two-color method, pressurization method, Core Back method, sandwich method, etc.); solution casting method, etc.

[0121] <Resin film>

[0122] The resin film described in the present embodiment includes the methacrylic resin described in the above-mentioned present embodiment. The resin film described in the present embodiment is manufactured by, for example, a melt extrusion method using the resin composition described in the above-mentioned present embodiment. When the resin film is manufactured by the melt extrusion method, first, after pre-drying the resin composition described in the present embodiment, it is supplied to an extruder for heating and melting, and supplied to a T-die. Then, the resin composition supplied to the T-die is extruded in the form of a sheet-like molten resin, and cooled and solidified using a cooling roller, thereby obtaining a resin film.

[0123] The thickness of the resin film described in this embodiment is, for example, preferably 500 μm or less, more preferably 300 μm or less, and further preferably 200 μm or less. In addition, the thickness of the resin film described in this embodiment is, for example, preferably 10 μm or more, more preferably 30 μm or more, further preferably 50 μm or more, and particularly preferably 60 μm or more. If the thickness of the resin film is within the above range, there is an advantage that the resin film is not easily deformed when vacuum forming is performed using the resin film, and it is not easy to break in the deep drawing portion. Furthermore, there is also an advantage that the optical properties are uniform and a resin film with good transparency can be manufactured.

[0124] The total light transmittance of the resin film according to this embodiment is preferably 85% or more, more preferably 88% or more, and further preferably 90% or more. If the total light transmittance is within the above range, the transparency is high and thus the film can be applied to optical applications requiring light transmittance.

[0125] The glass transition temperature of the resin film according to the present embodiment is preferably 110° C. or higher, more preferably 115° C. or higher, and further preferably 120° C. or higher. When the glass transition temperature is within the above range, the heat resistance of the resin film becomes sufficient.

[0126] The haze of the resin film described in this embodiment is preferably 2.0% or less, more preferably 1.5% or less, further preferably 1.3% or less, and particularly preferably 1.0% or less. In addition, the internal haze of the resin film is preferably 1.5% or less, more preferably 1.0% or less, further preferably 0.5% or less, and particularly preferably 0.4% or less. If the haze and internal haze are within the above ranges, the transparency is high, so it can be used for optical applications requiring light transmittance. It should be noted that the haze includes the haze inside the film and the haze on the surface (outside) of the film, which are expressed as internal haze and external haze, respectively.

[0127] The YI (Yellow Index) of the resin film according to the present embodiment is preferably 1.2 or less, more preferably 1.0 or less. When the YI is within the above range, the transparency is high and thus the film can be applied to optical applications requiring light transmittance.

[0128] The resin film of this embodiment preferably has a moisture permeability of 200 g / m at 40° C. and a relative humidity of 90%. 2 24h or less, more preferably 100g / m 2 Less than 24 hours.

[0129] From the viewpoint of further improving light resistance, the resin film of this embodiment preferably contains an ultraviolet absorber. The purpose of the ultraviolet absorber is to improve light resistance by absorbing ultraviolet rays with a wavelength of 400 nm or less. The transmittance of the resin film of this embodiment at a wavelength of 380 nm is preferably 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%.

[0130] The resin film described in the present embodiment can be suitably used as an optical film such as a polarizer protective film. When the resin film described in the present embodiment is used as a polarizer protective film, it is preferred that the optical anisotropy is small. It is particularly preferred that not only the optical anisotropy of the in-plane direction (length direction, width direction) of the resin film is small, but also the optical anisotropy of the thickness direction is small. In other words, it is preferred that the absolute values ​​of the in-plane phase difference and the thickness direction phase difference are small. For example, when the measurement wavelength is set to 590nm, the absolute value of the in-plane phase difference is preferably less than 20nm, more preferably less than 15nm. In addition, the absolute value of the thickness direction phase difference is preferably less than 50nm, more preferably less than 20nm, and further preferably less than 15nm.

[0131] Phase difference is an index value calculated based on birefringence. The in-plane phase difference (Re) and the thickness direction phase difference (Rth) can be calculated using the following formulas. In an ideal resin film that is completely optically isotropic in three dimensions, the in-plane phase difference Re and the thickness direction phase difference Rth are both 0.

[0132] Re=(nx-ny)×d

[0133] Rth=〔(nx+ny) / 2-nz〕×d

[0134] In the above formula, nx, ny and nz represent the refractive index of each axial direction when the in-plane extension direction (orientation direction of the polymer chain) is set as the X axis, the direction perpendicular to the X axis is set as the Y axis, and the thickness direction of the resin film is set as the Z axis. In addition, d represents the thickness of the resin film, and nx-ny represents the orientation birefringence. It should be noted that the MD direction of the film is set as the X axis, and in the case of a stretched film, the stretching direction is set as the X axis.

[0135] The orientation birefringence value of the resin film according to this embodiment is preferably -5.0×10 -4 ~5.0×10 -4 , more preferably -4.0×10 -4 ~4.0×10 -4 , more preferably -3.8×10 -4 ~3.8×10 -4When the orientation birefringence is within the above range, birefringence does not occur during molding, and there is a tendency that stable optical characteristics can be obtained.

[0136] (Stretch)

[0137] The resin film according to this embodiment may be further stretched. By stretching the resin film, the mechanical strength of the resin film and the film thickness accuracy can be improved.

[0138] When the resin film according to the present embodiment is stretched, the resin composition according to the present embodiment is temporarily formed into a resin film in an unstretched state, and then uniaxially stretched or biaxially stretched. Thus, a stretched film (uniaxially stretched film or biaxially stretched film) can be manufactured.

[0139] The stretch 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. Depending on the stretching temperature, the stretch ratio is usually preferably selected in the range of 1.1 to 5 times, more preferably in the range of 1.3 to 4 times, and further preferably in the range of 1.5 to 3 times. If the stretch ratio is within the above range, there is a tendency to significantly improve the mechanical properties of the film, such as elongation, tear propagation strength, and rubbing fatigue resistance.

[0140] (use)

[0141] The resin film described in this embodiment can be used for various purposes such as transportation equipment, solar cell components, civil engineering and construction components, daily necessities, electrical and electronic equipment, optical components, medical supplies, etc. In particular, the resin film described in this embodiment has excellent heat resistance and optical properties, and can therefore be used for optical purposes. As optical uses, for example, front panels (cover windows) of various display devices, diffusers, polarizer protective films, polarizer protective films, phase difference films, light diffusion films, optical isotropic films, etc. can be listed.

[0142] Among these, the resin film described in the present embodiment can be suitably used as a polarizer protective film or a front panel (cover window) of a display device. When the resin film described in the present embodiment is used as a front panel (cover window) of various display devices, a functional coating layer such as a primer layer and a hard coat layer can be formed on at least one main surface of the resin film as required. In addition, when the resin film described in the present embodiment is used as a polarizer protective film, the resin film described in the present embodiment is laminated to a polarizer to form a polarizing plate. The polarizer is not particularly limited, and any existing known polarizer can be used. The polarizing plate can be used in display devices such as liquid crystal display devices and organic EL display devices.

[0143] Example

[0144] Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0145] The measuring methods of various physical properties described in Examples and Comparative Examples are as follows.

[0146] (1) Syndiotacticity expressed in triads (rr)

[0147] The methacrylic acid resin was measured using a nuclear magnetic resonance apparatus (AVANCE III 400 MHz, manufactured by Bruker) in a deuterated chloroform solution at 22°C and 16 accumulation times. 1 H-NMR spectrum. Based on the spectrum, the area (X) of the region of 0.60 to 0.95 ppm and the area (Y) of the region of 0.60 to 1.25 ppm when tetramethylsilane (TMS) is set to 0 ppm are measured, and then the syndiotacticity (rr) expressed by triads is calculated using the formula: (X / Y)×100.

[0148] (2) Weight average molecular weight (Mw), and the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn)

[0149] The weight average molecular weight (Mw), number average molecular weight (Mn), and the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the methacrylic resin and the resin composition (pellets) were calculated by a standard polystyrene conversion method using gel permeation chromatography (GPC). Specifically, the analysis was performed using a sample solution prepared by dissolving 4 mg of the methacrylic resin or the resin composition (pellets) in 2 mL of chloroform using the following apparatus and conditions.

[0150] Measuring device: HLC-8220GPC (manufactured by Tosoh Corporation)

[0151] Detector: RI detector

[0152] Guard column: KF-G 4A (manufactured by RESONAC)

[0153] Analytical columns: KF-806M and KF-806L manufactured by RESONAC were connected in series.

[0154] Eluent: Chloroform

[0155] Eluent flow rate: 1mL / min

[0156] Measurement temperature: 40℃

[0157] Standard material for standard curve: polystyrene

[0158] (3) Ratio of terminal double bonds

[0159] As a preliminary treatment, a methacrylic resin was dissolved in dichloromethane, and the solution was dropped into methanol to precipitate and purify the resin. The precipitated resin was recovered by suction filtration and dried for analysis. 20 mg of the dried methacrylic resin was dissolved in 0.6 to 0.7 mL of deuterated chloroform to prepare a solution, and a nuclear magnetic resonance apparatus (made by Bruker, AVANCE NEO 700 MHz) was used for analysis. 1 H-NMR measurement. The measurement temperature was set to 20°C, the number of accumulations was set to 8,192 times, and the Excitation Sculpting (ES) method, which is one of the solvent elimination methods, was used to eliminate the peak of the methoxy group derived from the methacrylic resin (3.60 ppm, the value when the chemical shift of the peak of the solvent was set to 7.26 ppm). 1 The total area (X) of the peaks (5.47 to 5.51 ppm and 6.21 ppm) derived from the terminal double bond 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 were measured by H-NMR spectrum, and then the ratio of the terminal double bond of the methacrylic resin was calculated using the formula: [(3×X) / (2×Y)]×100.

[0160] (4) Glass transition temperature (Tg)

[0161] The glass transition temperature of the methacrylic resin is measured by the following method. As a prior treatment, a thermogravimetric analyzer (manufactured by Hitachi High-Technologies Corporation, STA7200) is used for heat treatment for the purpose of removing the residual monomers and decomposition products of the polymerization initiator in the methacrylic resin. Specifically, the heat treatment is carried out under the following conditions: under a nitrogen gas flow of 200 mL / min, the temperature is increased from 40°C to 270°C at a heating rate of 10°C / min, and maintained at 270°C for 2.5 minutes. The glass transition temperature (Tg) of the methacrylic resin after the heat treatment is measured using a differential scanning calorimeter (DSC; manufactured by Hitachi High-Technologies Corporation, DSC7000X). First, DSC measurement was performed under the following conditions: the first temperature increase was performed at a heating rate of 10°C / min from 40°C to 160°C at a nitrogen flow rate of 40 mL / min, and after cooling to 40°C, the second temperature increase was performed at a heating rate of 10°C / min from 40°C to 160°C. And, the midpoint glass transition temperature (the intersection temperature of a straight line having an equal distance in the vertical axis direction from both a straight line obtained by extending the baseline before the inflection point toward the high temperature side and a straight line obtained by extending the baseline after the inflection point toward the low temperature side and a curve of the step-shaped change portion of the glass transition) was read from the DSC curve measured during the second temperature increase.

[0162] (5) Retention thermal stability and mass reduction rate in heat treatment before measuring retention thermal stability

[0163] The retention thermal stability of the methacrylic resin was evaluated using a thermogravimetric analyzer (manufactured by Hitachi High-Technologies Corporation, STA7200). First, in order to remove the residual monomers and decomposition products of the polymerization initiator in the methacrylic resin, a heat treatment was performed under the following conditions: the temperature was raised from 40°C to 270°C at a heating rate of 10°C / min under a nitrogen gas flow of 200 mL / min, and the temperature was maintained at 270°C for 2.5 minutes. Here, the mass at 40°C is defined as X (40℃) , the mass at the end of the heat treatment at 270°C is defined as X (270℃) , find the formula:〔(X (40℃) -X (270℃) ) / X (40℃) 〕×100. Determine the value obtained by subtracting the amount of residual methyl methacrylate in the methacrylic resin calculated by the method described below from this value (mass reduction rate during heat treatment). After the above-mentioned heat treatment at 270°C, cool to 40°C. Next, record the mass change under the following conditions: increase the temperature from 40°C to 280°C at a heating rate of 10°C / min, and maintain at 280°C for 30 minutes. The mass when the sample temperature reaches 280°C is set to X (0分), the mass when kept at 280℃ for 15 minutes is defined as X (15分) , according to the formula: (0分) -X (15分) ) / X (0分) The retention thermal stability was evaluated by calculating the mass reduction rate by 〕×100.

[0164] The retention thermal stability of the resin composition (pellets) was evaluated using the same apparatus as described above. The mass change was recorded under the following conditions: the temperature was raised from 40°C to 190°C at a rate of 10°C / min under a nitrogen gas flow of 200 mL / min, and then cooled to 40°C. Then, the temperature was raised from 40°C to 280°C at a rate of 10°C / min, and maintained at 280°C for 30 minutes. The mass of the sample when the temperature reached 280°C was set as X. (0分) , the mass when kept at 280℃ for 15 minutes is defined as X (15分) , according to the formula: 〔(X (0分) -X (15分) ) / X (0分) The retention thermal stability was evaluated by calculating the mass reduction rate by 〕×100.

[0165] (Quantitative determination method of residual methyl methacrylate in methacrylic resin)

[0166] The amount of residual methyl methacrylate in the methacrylic resin was determined by the following method. A gas chromatograph (manufactured by Agilent Technologies, 7890B) was used, and 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 the 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 the following conditions: the temperature was increased from 35°C to 210°C at a heating rate of 30°C / min, then from 210°C to 260°C at a heating rate of 10°C / min, and then from 260°C to 320°C at a heating rate of 20°C / min, and maintained for 3 minutes. Chlorobenzene was used as the internal standard substance, and a calibration curve was prepared by the internal standard method to calculate the residual amount of methyl methacrylate in the methacrylic resin.

[0167] (6) Ratio of bonded sulfur atoms

[0168] The ratio of bonded sulfur atoms of methacrylic resin is obtained by the following operation. As a preliminary treatment, methacrylic resin is dissolved in dichloromethane, and the solution is added dropwise to methanol to precipitate and purify the resin. The precipitated resin is recovered and dried by suction filtration for analysis. An appropriate amount of dried methacrylic resin is accurately weighed and fixed to volume, and set in an automatic sample combustion device (Nittoseiko Analytech, AQF-2100), decomposed at high temperature, and the generated gas is absorbed by ultrapure water containing aqueous hydrogen peroxide and hydrazine hydrate. Using the resulting liquid (decomposed gas aqueous solution), sulfate ions are quantified using an ion chromatograph (Thermo Fisher Scientific, Integrion RFIC, columns: AG18-4μm, AS18-4μm). Next, the mass Wp (mass %) of sulfur atoms per unit mass of the dried methacrylic resin is calculated. Furthermore, the ratio Sp (mol %) of bonded sulfur atoms is calculated using the following formula.

[0169] Sp=Wp×(100 / 32)

[0170] (7) Foaming

[0171] The methacrylic resin was extruded using a 15 mm diameter intermeshing co-rotating twin-screw extruder (manufactured by TECHNOVEL, KZW15TWIN-45MG, L / D=45). In addition, the resin extruded in the form of strands from the die head disposed at the exit of the extruder was observed to evaluate the presence or absence of foaming. Specifically, the strands were foamed, difficult to cut using a granulator, and the resin composition in pellet form could not be obtained as "bad", and the strands were not observed to be foamed, and after cooling in a water tank, they could be pelletized using a granulator, and the resin composition could be obtained as "good".

[0172] (8) Haze measurement

[0173] The haze of the stretched resin film was measured using a haze meter (Suga Test Instruments, HZ-V3) in accordance with JIS K7136. In addition, the two sides of the resin film were sandwiched with glycerin and glass in sequence and the same measurement was performed, and the value obtained was set as the internal haze. The obtained result was converted into a value equivalent to a film thickness of 40 μm.

[0174] (9) Total light transmittance

[0175] The total light transmittance of the stretched resin film was measured using a haze meter (HZ-V3 manufactured by Suga Test Instruments) in accordance with JIS K7361-1.

[0176] (10)YI

[0177] The YI of the stretched resin film was measured using a spectrocolorimeter (manufactured by Suga Test Instruments, SC-P) in accordance with JIS K7373. The obtained result was converted into a value equivalent to a film thickness of 40 μm.

[0178] (11) Moisture permeability

[0179] According to JIS Z0208, the water vapor permeability of the stretched resin film was measured under the conditions of 40° C. and a relative humidity of 90%.

[0180] <Example 1>

[0181] Into a 2-liter glass reactor equipped with a three-way backward blade type stirrer, 170 parts by mass of deionized water, 0.10 parts by mass of disodium hydrogen phosphate as a suspension aid, and 0.031 parts by mass of 2,2'-azobis(2-methylbutyronitrile) (V-59, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., hydrogen abstraction ability: 1%) as a polymerization initiator were placed. The aqueous solution in the reactor was stirred at 550 rpm, and nitrogen (oxygen concentration of 0.2 ppm) was passed to replace 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. Next, 0.375 parts by mass of a water-soluble polymer METOLOSE 90SH-100 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.) was added as a dispersant to the reactor. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 79°C to start polymerization. After the monomers were reacted 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 this temperature for 1 hour to terminate the polymerization. The obtained resin was washed with deionized water in an amount 5 times the amount of monomers charged, and dried to obtain a bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 1.

[0182] The obtained methacrylic resin was extruded at a resin temperature of 256°C using an intermeshing co-rotating twin-screw extruder (manufactured by TECHNOVEL, KZW15TWIN-45MG, L / D=45) with a diameter of 15 mm. The resin extruded in the form of strands from the die head provided at the outlet of the extruder was cooled in a water tank and pelletized using a pelletizer to obtain a resin composition. The physical properties of the obtained resin composition (pellets) are shown in Table 1.

[0183] The obtained resin composition was dried at 90° C. for 4 hours and then extruded at a resin temperature of 244° C. using an intermeshing co-rotating twin-screw extruder (manufactured by TECHNOVEL, KZW15TWIN-45MG, L / D=45) equipped with a T-die with a diameter of 15 mm at the extruder outlet. The sheet-like molten resin extruded from the T-die was cooled by a cooling roll to obtain a resin film with a width of 150 mm and a thickness of 160 μm.

[0184] A small piece of 100 mm × 100 mm was cut from the obtained resin film in a manner that both sides were parallel to the extrusion direction. The small piece was installed in a pantograph biaxial stretching device and was simultaneously biaxially stretched at 135°C in a manner that the stretching speed in each direction was 100 mm / min. Thereafter, it was taken out at room temperature and quenched to obtain a resin film with a thickness of 41 μm. The physical properties of the resin film are shown in Table 1.

[0185] <Example 2>

[0186] Into a 2-liter glass reactor equipped with a three-way backward blade type stirrer, 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 placed. The aqueous solution in the reactor was stirred at 550 rpm, and nitrogen (oxygen concentration was 0.2 ppm) was introduced to replace 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. Next, 0.375 parts by mass of a water-soluble polymer METOLOSE 90SH-100 (manufactured by Shin-Etsu Chemical Co., Ltd., hydroxypropyl methylcellulose) as a dispersant was added to the reactor. After stirring for 30 minutes, the liquid temperature in the reactor was raised to 72°C to start polymerization. After the monomer was reacted at 72°C for 7.2 hours, the liquid in the reactor was heated to 81°C and reacted for 40 minutes, and then the liquid in the reactor was heated to 95°C. The reaction solution was stirred at this temperature for 1 hour to terminate the polymerization. The obtained resin was washed with deionized water in an amount 8 times the amount of monomer charged, and dried to obtain a bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 1.

[0187] The obtained methacrylic resin was pelletized under the same conditions as in Example 1 except that the resin temperature of the obtained methacrylic resin was 252° C., thereby obtaining a resin composition.

[0188] <Comparative Example 1>

[0189] Into a 2-liter glass reactor equipped with a three-way backward blade type stirrer, 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) (V-65, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., hydrogen abstraction ability: 1%) as a polymerization initiator were placed. The aqueous solution in the reactor was stirred at 550 rpm, and nitrogen (oxygen concentration of 0.2 ppm) was passed to replace 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. Next, 0.375 parts by mass of a water-soluble polymer METOLOSE 60SH-50 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.) was added as a dispersant to the reactor. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 52°C to start polymerization. After the monomer was reacted 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 this temperature for 1 hour to terminate the polymerization. The obtained resin was washed with deionized water in an amount twice the amount of the monomer feed, and dried to obtain a beaded methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 1.

[0190] The obtained methacrylic resin was pelletized and formed into a film under the same conditions as in Example 1. Furthermore, the resin film was simultaneously biaxially stretched under the same conditions as in Example 1 to obtain a resin film having a thickness of 41 μm. The physical properties of the resin film are shown in Table 1.

[0191] <Comparative Example 2>

[0192] Into a 2-liter glass reactor equipped with a three-way backward blade type stirrer, 170 parts by mass of deionized water, 0.10 parts by mass of disodium hydrogen phosphate as a suspension aid, and 0.340 parts by mass of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were placed. The aqueous solution in the reactor was stirred at 550 rpm, and nitrogen (oxygen concentration of 0.2 ppm) was passed to replace 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. Next, 0.375 parts by mass of a water-soluble polymer METOLOSE 60SH-50 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.) 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 start polymerization. After the monomer was reacted 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 this temperature for 1 hour to terminate the polymerization. The obtained resin was washed with deionized water in an amount twice the amount of the monomer feed, and dried to obtain a beaded methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 1.

[0193] Extrusion was performed under the same conditions as in Example 1 except that the resin temperature of the obtained methacrylic resin was 258° C. However, the resin strands extruded from the die were foamed and difficult to cut with a pelletizer, and a pelletized resin composition could not be obtained.

[0194] <Comparative Example 3>

[0195] 170 parts by mass of deionized water, 0.10 parts by mass of disodium hydrogen phosphate as a suspension aid, and 2.280 parts by mass of di-sec-butyl peroxydicarbonate (Luperox 225M50 manufactured by Arkema Yoshitomi Co., Ltd.) as a polymerization initiator were added to a 2-liter glass reactor equipped with a three-way backward blade mixer. The aqueous solution in the reactor was stirred at 550 rpm, and nitrogen (oxygen concentration was 0.2 ppm) was introduced to replace the air in the reactor, and 100 parts by mass of methyl methacrylate (MMA) was added to the reactor. Next, 0.375 parts by mass of water-soluble polymer METOLOSE 90SH-100 (Shin-Etsu Chemical Co., Ltd., hydroxypropyl methylcellulose) as a dispersant was added to the reactor. Thereafter, after stirring for 30 minutes, the liquid temperature in the reactor was raised to 70°C to start polymerization. However, 4 minutes after the temperature was raised to 70°C, the droplets containing the monomers merged into one, and the polymerization in the suspended state above this level could not be continued. The bulk of the methacrylic resin produced by the merging of the droplets was collected, washed with deionized water, and then dried. Table 1 shows the physical properties of the obtained methacrylic resin.

[0196] <Comparative Example 4>

[0197] 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) (V-70, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were added to a 2-liter glass reactor equipped with a three-way backward blade stirrer. The aqueous solution in the reactor was stirred at 550 rpm, and nitrogen (oxygen concentration was 0.2 ppm) was introduced to replace the air in the reactor, and then 100 parts by mass of methyl methacrylate (MMA) was added to the reactor. Next, 0.375 parts by mass of water-soluble polymer METOLOSE 90SH-100 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.) as a dispersant was added to the reactor. After that, after stirring for 30 minutes, the liquid temperature in the reactor was raised to 32°C to start polymerization. After the monomers were reacted 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 this temperature for 1 hour to terminate the polymerization. The obtained resin was washed with deionized water in an amount 5 times the amount of monomers charged, and dried to obtain a bead-like methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 1.

[0198] The obtained methacrylic resin was extruded under the same conditions as in Example 1 except that the resin temperature was set to 249° C. However, the resin strands extruded from the die were foamed, and the resin was not melted sufficiently, so small pieces formed by the aggregation of bead-like methacrylic resin adhered to the strands. Therefore, it was difficult to cut with a pelletizer, and a pellet-like resin composition could not be obtained.

[0199] [Table 1]

[0200]

[0201] As shown in Table 1, in Examples 1 and 2, which used a polymerization initiator having a 10-hour half-life temperature of 45°C or higher and set the molar ratio of the chain transfer agent to the polymerization initiator to 7.0 or higher, a methacrylic resin having a small proportion of terminal double bonds, a small mass reduction rate when kept at 280°C for 15 minutes, and excellent retention thermal stability was obtained. In addition, the methacrylic resins obtained in Examples 1 and 2 had high syndiotacticity, and as a result, a high glass transition temperature.

[0202] In contrast, in Comparative Example 1, in which a polymerization initiator having a 10-hour half-life temperature of 45°C or higher was used but the molar ratio of the chain transfer agent to the polymerization initiator was set to 2.0, the ratio of the terminal double bonds contained in the obtained methacrylic resin was higher than that in Examples 1 and 2, and the retention thermal stability of the methacrylic resin was poor. In addition, 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 chain transfer agent to the polymerization initiator was set to 2.0, the ratio of the terminal double bonds contained in the obtained methacrylic resin was higher than that in Examples 1 and 2, and the retention thermal stability of the methacrylic resin was poor. Furthermore, in Comparative Example 2, during extrusion molding of the methacrylic resin, the resin strands foamed, and a pelletized resin composition could not be obtained.

[0203] In Comparative Examples 3 and 4, which used a polymerization initiator having a 10-hour half-life temperature of less than 45° C. and did not use a chain transfer agent, the ratio of terminal double bonds contained in the obtained methacrylic resin was higher than that in Examples 1 and 2, and the retention thermal stability of the methacrylic resin was poor. Furthermore, in Comparative Example 4, during extrusion molding of the methacrylic resin, the resin strands foamed, and a pelletized resin composition could not be obtained.

Claims

1. A method for producing a methacrylic resin, comprising: 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 obtained methacrylic resin is generated is set to be lower than 100° C. The 10-hour half-life temperature of the polymerization initiator is above 45°C, The amount of the chain transfer agent used is 0.15 mol% or more relative to 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, The weight average molecular weight (Mw) of the obtained methacrylic resin measured by gel permeation chromatography (GPC) was 90,000 or more.

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

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

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

5. The method for producing a methacrylic resin according to claim 4, wherein The azo polymerization initiator is a nitrile azo polymerization initiator.

6. The method for producing a methacrylic resin according to claim 1 or 2, wherein: In the polymerization step, the monomer components are polymerized in the presence of the polymerization initiator, the chain transfer agent, and a reducing agent.

7. A methacrylic resin, wherein The proportion of structural units derived from methyl methacrylate is 98% by mass or more, The weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) is 90,000 or more, The syndiotacticity expressed as triad is 55% or more, The ratio of the bonded sulfur atoms to the structural units derived from methyl methacrylate exceeds 0 mol%, The ratio of the terminal double bonds to the structural units derived from methyl methacrylate is less than 0.008 mol %.

8. The methacrylic resin according to claim 7, which has a thermal weight loss rate of less than 2.9% when exposed to 280°C for 15 minutes in a nitrogen atmosphere.

9. The methacrylic resin according to claim 7 or 8, 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. 10 . The methacrylic resin according to claim 7 , which has a glass transition temperature of 120° C. or higher.

11. The methacrylic resin according to claim 7 or 8, wherein The syndiotacticity expressed by triads is 70% or less. 12 . A resin composition comprising the methacrylic resin according to claim 7 . 13 . A resin film comprising the methacrylic resin according to claim 7 or 8 .

14. The resin film according to claim 13, wherein The resin film is an optical film.

15. The resin film according to claim 13, which has a haze of 2.0% or less.

16. The resin film according to claim 13, which has an internal haze of 1.5% or less.

17. The resin film according to claim 13, wherein The resin film is a polarizer protective film.

18. A polarizing plate comprising a polarizer and the resin film according to claim 13 laminated together. 19 . A display device comprising the polarizing plate according to claim 18 .

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