Methacrylic resin and method for producing same, resin composition, dope, and resin film

Abstract

Provided are: a methacrylic resin having a proportion of structural units derived from methyl methacrylate of 98 mass% or higher, a weight-average molecular weight (Mw) measured by gel permeation chromatography (GPC) of 400,000 or greater, a ratio (Mw / Mn) of weight-average molecular weight (Mw) to number-average molecular weight (Mn) of 1.6-2.8, a triad syndiotacticity of 55% or greater, a 5% weight loss temperature of 300°C or higher, and a residual level of chain transfer agent of 0.005 mass% or lower; and a method for producing the methacrylic resin. Also provided are a resin composition and a dope containing the methacrylic resin, a resin film containing the methacrylic resin, and a polarizing plate and a display device in which the resin film is used.

Description

Methacrylic resin and its manufacturing method, resin composition, dope, and resin film

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

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

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

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

[0005] International Publication No. 2019 / 167471

[0006] However, the inventors have conducted research and found that there is room for improvement in the heat resistance and thermal stability of such high molecular weight methacrylic resins.

[0007] The present invention aims to provide a methacrylic resin that is excellent in heat resistance and thermal stability and that can be used to produce molded articles with excellent mechanical properties, a method for producing the same, a resin composition and dope containing the methacrylic resin, a resin film containing the methacrylic resin, and a polarizing plate and a display device that use the resin film.

[0008] Specific means for solving the above problems include the following embodiments. <1> A methacrylic resin having a proportion of structural units derived from methyl methacrylate of 98% by mass or more, a weight average molecular weight (Mw) of 400,000 or more as measured by gel permeation chromatography (GPC) and a ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of 1.6 to 2.8, a triad syndiotacticity of 55% or more, a 5% weight loss temperature of 300°C or more, and a residual rate of a chain transfer agent of 0.005% by mass or less. <2> The methacrylic resin according to <1>, which contains a terminal structure represented by the following formula (1) derived from a polymerization initiator: (In the formula, R １ , R ２ , and R ３ each independently represents an alkyl group, a substituted alkyl group, an ester group, or an amide group. １ , R ２ , and R ３ At least one of R represents an ester group or an amide group. １ , R ２ , and R ３ two of which may be bonded to each other to form an alicyclic structure. * indicates a bond to a structural unit derived from a monomer.) <3> The methacrylic resin according to <1> or <2>, in which the ratio of terminal double bonds to the structural units derived from methyl methacrylate is less than 0.015 mol%. <4> The methacrylic resin according to any one of <1> to <3>, in which the glass transition temperature is 120°C or higher.

[0009] <5> A method for producing a methacrylic resin, comprising: a polymerization step of polymerizing a monomer mixture containing 98% or more by mass of methyl methacrylate in the presence of a polymerization initiator and a chain transfer agent at less than 100°C until a polymerization conversion rate of 90% or more and a residual rate of the chain transfer agent is 0.005% by mass or less, wherein the amount of the chain transfer agent used is 0.03 mol% or less with respect to the total amount of the monomer mixture, and the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiators is 1.6 or less. <6> The method for producing a methacrylic resin according to <5>, wherein the polymerization initiator is a non-nitrile azo polymerization initiator. <7> The method for producing a methacrylic resin according to <5> or <6>, wherein aqueous polymerization is performed in the polymerization step. <8> A resin composition comprising the methacrylic resin according to any one of <1> to <4>, and optionally multilayered structure polymer particles. <9> A dope for producing a film by a solution casting method, comprising the methacrylic resin according to any one of <1> to <4> and a solvent, wherein the solvent comprises a first solvent having a hydrogen bond parameter δH of 1 to 12 in the Hansen solubility parameters, and a second solvent having the hydrogen bond parameter δH of 14 to 24. <10> A resin film comprising the methacrylic resin according to any one of <1> to <4>. <11> The resin film according to <10>, which can be bent 6,000 times or more until breakage occurs in a clamshell bending test. <12> The resin film according to <10> or <11>, which contains multilayer structure polymer particles. <13> The resin film according to any one of <10> to <12>, which is a polarizer protective film. <14> A polarizing plate obtained by laminating a polarizer and the resin film according to any one of <10> to <13>. <15> A display device comprising the polarizing plate according to <14>.

[0010] According to the present invention, it is possible to provide a methacrylic resin that can be used to produce molded articles having excellent heat resistance and thermal stability and excellent mechanical properties, a method for producing the same, a resin composition and dope containing the methacrylic resin, a resin film containing the methacrylic resin, and a polarizing plate and a display device using the resin film.

[0011] Specific embodiments of the present invention will be described in detail below. The symbol "to" indicating a range of values ​​is used to mean that the range includes both the lower and upper limits, unless otherwise specified.

[0012] <Methacrylic Resin> The methacrylic resin according to this embodiment has a ratio of structural units derived from methyl methacrylate of 98% by mass or more, and a ratio 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 ratio 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 units derived from methyl methacrylate are represented by the following formula:

[0013]

[0014] Examples of monomers other than methyl methacrylate include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; aryl acrylates such as phenyl acrylate; cycloalkyl acrylates such as cyclohexyl acrylate and norbornenyl acrylate; alkyl methacrylates other than methyl methacrylate such as ethyl methacrylate, propyl methacrylate, and butyl methacrylate; aryl methacrylates such as phenyl methacrylate; cycloalkyl methacrylates such as cyclohexyl methacrylate and norbornenyl methacrylate; aromatic vinyl compounds such as styrene and α-methylstyrene; acrylamide; methacrylamide; acrylonitrile; and methacrylonitrile.

[0015] The methacrylic resin according to this embodiment has a weight-average molecular weight (Mw) of 400,000 or more. When the weight-average molecular weight (Mw) of the methacrylic resin is 400,000 or more, the mechanical properties of the resulting molded body tend to be improved, and for example, a resin film with excellent bending resistance can be obtained. The weight-average molecular weight (Mw) of the methacrylic resin is preferably 600,000 or more, more preferably 700,000 or more, and even more preferably 800,000 or more. The upper limit of the weight-average molecular weight (Mw) is not particularly limited, but from the viewpoint of moldability, it is preferably 2.5 million or less, more preferably 2 million or less, even more preferably 1.5 million or less, and particularly preferably 1.2 million or less.

[0016] Furthermore, the methacrylic resin according to this embodiment has a polydispersity (Mw / Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), of 1.6 to 2.8, preferably 1.7 to 2.5, more preferably 1.7 to 2.4, and even more preferably 1.7 to 2.3. When the polydispersity (Mw / Mn) of the methacrylic resin is 1.6 or more, the fluidity of the methacrylic resin tends to be improved and it tends to be easier to mold, and when the polydispersity (Mw / Mn) of the methacrylic resin is 2.8 or less, the mechanical properties of the resulting molded article, such as impact resistance, toughness, and flex resistance, tend to be improved.

[0017] The weight average molecular weight (Mw) and number average molecular weight (Mn) in this specification are values ​​measured by gel permeation chromatography (GPC) in terms of standard polystyrene, and are measured by the method described in the examples below.

[0018] The weight average molecular weight (Mw) and number average molecular weight (Mn) of the methacrylic resin can be controlled by adjusting the types and amounts of the polymerization initiator and chain transfer agent used when synthesizing the methacrylic resin.

[0019] Furthermore, the methacrylic resin according to this embodiment has a syndiotacticity (rr) of 55% or more, preferably 56% or more, and more preferably 57% or more. When the syndiotacticity (rr) of 55% or more, the glass transition temperature (Tg) of the methacrylic resin increases, and the heat resistance tends to improve. The upper limit of the syndiotacticity (rr) is not particularly limited, but from the viewpoint of the molding temperature and the toughness and secondary processability of the molded body, it is preferably 67% or less, more preferably 65% ​​or less, and even more preferably 63% or less.

[0020] Syndiotacticity (rr) is the proportion of two chains (diads) in a chain of three consecutive structural units (triad) that are both racemo (rr). Chains (diads) of structural units in a polymer molecule that have the same configuration are called meso, and those with the opposite configuration are called racemo, and are represented by m and r, respectively.

[0021] As described in the Examples below, syndiotacticity (rr) was measured in deuterated chloroform at 22°C and 16 cycles. １ A H-NMR spectrum is measured, and from the spectrum, the area (X) of the region from 0.60 to 0.95 ppm and the area (Y) of the region from 0.60 to 1.25 ppm when tetramethylsilane (TMS) is set to 0 ppm are measured, and the chromaticity can be calculated using the formula: (X / Y) × 100.

[0022] The methacrylic resin according to this embodiment preferably has a glass transition temperature (Tg) of 120° C. or higher, more preferably 122° C. or higher, and even more preferably 124° C. or higher. The upper limit of the glass transition temperature (Tg) is not particularly limited, but from the viewpoint of the molding temperature and secondary processability of the molded article, it is preferably 135° C. or lower, and may be 130° C. or lower.

[0023] The glass transition temperature (Tg) in this specification is the midpoint glass transition temperature determined from a DSC curve, and is measured by the method described in the examples below.

[0024] 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 preferable for increasing the syndiotacticity (rr) of the methacrylic resin and increasing the glass transition temperature (Tg). The glass transition temperature (Tg) can also be controlled by adjusting the molecular weight of the methacrylic resin.

[0025] Furthermore, the methacrylic resin according to this embodiment has a 5% weight loss temperature of 300° C. or higher and has excellent thermal stability.

[0026] Generally, when producing a resin with a high molecular weight, a method is adopted in which the amount of chain transfer agent and / or polymerization initiator used is reduced. However, for example, when a thiol compound is used as a chain transfer agent, the proportion of propagating radicals terminated by hydrogen abstraction reactions from the chain transfer agent is reduced, and relatively more polymers with terminal double bonds are likely to be produced by disproportionation termination reactions between propagating radicals. Terminal double bonds are known to thermally decompose at a lower temperature than the main chain of the methacrylic resin (e.g., T. Kashiwagi, et al., Macromolecules, 1986, 19, pp. 2160-2168, etc.), which can cause the thermal stability of the resin to deteriorate. In this regard, in the methacrylic resin according to this embodiment, the proportion of terminal double bonds is reduced by adjusting the ratio of the amount of chain transfer agent to the amount of polymerization initiator during production to an appropriate range. As a result, in the methacrylic resin according to this embodiment, despite having a high molecular weight of 400,000 or more in weight average molecular weight (Mw), it is possible to make the 5% weight loss temperature 300°C or higher.

[0027] The 5% weight loss temperature in this specification is a temperature determined from a thermogravimetric curve, and is measured by the method described in the examples below.

[0028] In the methacrylic resin according to the present embodiment, from the viewpoint of setting the 5% weight loss temperature to 300°C or higher, the ratio of terminal double bonds to structural units derived from methyl methacrylate is preferably less than 0.015 mol%, more preferably less than 0.010 mol%, and even more preferably less than 0.006 mol%.

[0029] The methacrylic resin according to this embodiment can be produced by radical polymerization, as shown in the production method described below. The methacrylic resin produced by radical polymerization contains terminal double bonds generated by disproportionation termination reactions during polymerization, hydrogen abstraction reactions of monomers by a polymerization initiator, and the like. As described above, terminal double bonds affect the thermal stability of the resin, so a low proportion of terminal double bonds is preferable. The proportion of terminal double bonds is controlled by the method described below, and if it can be reduced to less than 0.015 mol%, the thermal stability of the methacrylic resin tends to be significantly improved. The lower limit of the proportion of terminal double bonds is preferably 0 mol%, but may be 0.001 mol%.

[0030] The ratio of terminal double bonds to structural units derived from methyl methacrylate was determined by the following procedure, as described in the Examples below, under the conditions of 8,192 cycles of accumulation in deuterated chloroform at 20°C. １ A H-NMR spectrum is measured, and from the spectrum, the sum (X) of the areas of the peaks (5.47 to 5.52 ppm and 6.21 ppm) derived from the terminal double bonds of the methacrylic resin and the area (Y) of the peaks (0.5 to 1.25 ppm) derived from the α-methyl groups of the methacrylic resin are measured, and the % methyl group can be calculated using the formula: [(3 × X) / (2 × Y)] × 100.

[0031] The proportion of terminal double bonds in the methacrylic resin can be controlled by adjusting the amounts of polymerization initiator and chain transfer agent used when synthesizing the methacrylic resin, the polymerization temperature, the polymerization time, etc. For example, it is preferable to reduce the amount of polymerization initiator used, increase the amount of chain transfer agent used, lower the polymerization temperature, and extend the polymerization time in order to reduce the proportion of terminal double bonds.

[0032] Furthermore, the methacrylic resin according to this embodiment preferably contains a terminal structure represented by the following formula (1) derived from a polymerization initiator.

[0033] (In the formula, R １ , R ２ , and R ３ each independently represents an alkyl group, a substituted alkyl group, an ester group, or an amide group. １ , R ２ , and R ３ At least one of R represents an ester group or an amide group. １ , R ２ , and R ３ Two of these may be bonded to each other to form an alicyclic structure. * indicates a bond to a structural unit derived from a monomer.)

[0034] Examples of the alkyl group include linear or branched alkyl groups having 1 to 6 carbon atoms. Examples of the substituent that the alkyl group may have include a hydroxy group, a carboxy group, an alkoxy group, and a halogen atom.

[0035] Examples of the ester group include -COOR ４ Examples of the group include a group represented by R ４ represents an alkyl group having 1 to 6 carbon atoms, which may have a substituent such as a hydroxy group, a carboxy group, an alkoxy group, or a halogen atom.

[0036] Examples of the amide group include —C(O)NR ５ Examples of the group include a group represented by R ５ represents an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group, or an alkenyl group having 2 to 6 carbon atoms, which may have a substituent such as a hydroxy group, a carboxy group, an alkoxy group, or a halogen atom.

[0037] The terminal structure represented by the above formula (1) can be introduced into the molecule of the methacrylic resin by using a non-nitrile azo polymerization initiator represented by the following formula (2) when synthesizing the methacrylic resin. １ , R ２ , and R ３is synonymous with the above formula (1). Use of such a non-nitrile azo polymerization initiator tends to improve the thermal stability of the resulting methacrylic resin compared to the use of a polymerization initiator other than a non-nitrile azo polymerization initiator (for example, a nitrile azo polymerization initiator). In addition, non-nitrile azo polymerization initiators are also preferred in that the toxicity of the initiator itself and decomposition products tends to be lower compared to nitrile azo polymerization initiators.

[0038]

[0039] Examples of the non-nitrile azo polymerization initiator represented by the formula (2) include 2,2'-azobis(dimethyl isobutyrate), 1,1'-azobis(methyl cyclohexanecarboxylate), 2,2'-azobis[N-(2-propenyl)-2-methylpropionamide], 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis(N-cyclohexyl-2-methylpropionamide), 2,2'-azobis{2-methyl-N-[2-(1-hydroxyethyl)]propionamide}, 2,2'-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propionamide}, etc. Among these, from the viewpoints of half-life temperature, cost, etc., at least one selected from 2,2'-azobis(dimethyl isobutyrate) and 1,1'-azobis(methyl cyclohexanecarboxylate) is preferred.

[0040] The methacrylic resin according to this embodiment is characterized in that the residual rate of the chain transfer agent is 0.005% by mass or less, and the proportion of the chain transfer agent remaining in the resin is low. The lower limit of the residual rate of the chain transfer agent is not particularly limited, and it is preferably substantially 0% by mass (i.e., below the detection limit). The residual rate of the chain transfer agent is measured by the method described in the Examples below.

[0041] The methacrylic resin according to this embodiment not only has excellent heat resistance and thermal stability, but is also expected to be suitable for reuse after disposal, i.e., recycling. Known recycling methods for methacrylic resin include chemical recycling (a method in which cracked oil is recovered as a cracked product by thermal decomposition and reused as a chemical raw material or fuel). Generally, to improve the heat resistance and thermal stability of methacrylic resin, a cyclic structure is introduced into the molecular structure of the methacrylic resin or a monomer having a rigid structure is copolymerized. However, these structures become impurities in chemical recycling and are undesirable. In this regard, the methacrylic resin according to this embodiment has a high proportion of structural units derived from methyl methacrylate, and the monomer recovered as cracked oil is expected to have a high yield, and is therefore expected to exhibit good chemical recyclability.

[0042] <Method for Producing Methacrylic Resin> The method for producing a methacrylic resin according to this embodiment includes a polymerization step of polymerizing a monomer mixture containing 98% or more by mass of methyl methacrylate in the presence of a polymerization initiator and a chain transfer agent at less than 100°C until the polymerization conversion rate reaches 90% or more and the residual rate of the chain transfer agent reaches 0.005% by mass or less. Conventional polymerization methods can be used to produce the methacrylic resin, including radical polymerization methods such as continuous bulk polymerization, solution polymerization, emulsion polymerization, emulsifier-free (soap-free) emulsion polymerization, and suspension polymerization. Among these, from the viewpoints of the degree of freedom in structural design of the methacrylic resin, ease of polymerization, productivity, and the like, a production method involving aqueous polymerization is preferred, with suspension polymerization and emulsion polymerization being more preferred, and suspension polymerization being even more preferred.

[0043] [Suspension Polymerization Method] In the suspension polymerization method, a methacrylic resin is synthesized in an aqueous suspension containing a mixture of water, a monomer mixture, a dispersant, a polymerization initiator, a chain transfer agent, and optionally other additives. The order in which the components are mixed is not particularly limited. For example, the aqueous suspension may be prepared by simultaneously mixing the components. Alternatively, an aqueous suspension may be prepared by mixing water, a polymerization initiator, and optionally other additives to prepare an aqueous solution, followed by adding the monomer mixture and the chain transfer agent, and then adding the dispersant. The mass ratio of the resulting methacrylic resin to water (methacrylic resin / water) is preferably 1.0 / 0.6 to 1.0 / 3.0.

[0044] The monomer mixture used has a methyl methacrylate content of 98% by mass or more, preferably 99% by mass or more, and more preferably 100% by mass.

[0045] Examples of dispersants include poorly water-soluble inorganic salts such as tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, and kaolin; and water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, and polyvinylpyrrolidone. When a poorly water-soluble inorganic salt is used as a dispersant, it is effective to use it in combination with an anionic surfactant such as sodium α-olefin sulfonate or sodium dodecylbenzene sulfonate. These dispersants may be added during the polymerization as needed.

[0046] As the polymerization initiator, known polymerization initiators such as azo polymerization initiators, peroxide polymerization initiators, etc. can be used. Among known polymerization initiators, azo polymerization initiators are preferred from the viewpoint of improving the thermal stability of the resulting methacrylic resin.

[0047] It is known that free radicals generated from polymerization initiators can not only undergo addition reactions with monomers, but also hydrogen abstraction reactions in the presence of substances that readily donate hydrogen. In this regard, azo polymerization initiators only generate alkyl radicals, and therefore have lower hydrogen abstraction capacity than peroxide polymerization initiators. Here, if the polymerization initiator has high hydrogen abstraction capacity, for example, when methyl methacrylate is used as the monomer, free radicals generated from the polymerization initiator abstract hydrogen from the α-methyl group of methyl methacrylate or the methyl group of the ester, and polymerization proceeds from the newly generated radicals on the α-methyl group or the methyl group of the ester, resulting in the production of a polymer with a terminal double bond derived from the monomer structure. Therefore, when a polymerization initiator with high hydrogen abstraction capacity is used, the resulting methacrylic resin tends to have insufficient thermal stability. Therefore, to obtain a methacrylic resin with high thermal stability, azo polymerization initiators are more suitable than peroxide polymerization initiators.

[0048] The hydrogen abstraction ability of the polymerization initiator can be measured, for example, by a radical trapping method using α-methylstyrene dimer (ie, α-methylstyrene dimer trapping method).

[0049] Furthermore, as a result of investigations conducted by the present inventors using various polymerization initiators, they found that methacrylic resins synthesized using non-nitrile azo polymerization initiators have terminal structures introduced into the molecules that are more thermally stable than methacrylic resins synthesized using polymerization initiators other than non-nitrile azo polymerization initiators (e.g., nitrile azo polymerization initiators). For this reason, among azo polymerization initiators, non-nitrile azo polymerization initiators are more preferred. Examples of non-nitrile azo polymerization initiators include those represented by the above formula (2). From the standpoints of half-life temperature, cost, and the like, at least one selected from 2,2'-azobis(isobutyrate)dimethyl and 1,1'-azobis(cyclohexanemethyl carboxylate) is preferred.

[0050] The amount of the polymerization initiator used is preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, and even more preferably 0.1 parts by mass or less, relative to 100 parts by mass of the total amount of the monomer mixture. There is no particular lower limit to the amount of the polymerization initiator used, but from the viewpoint of the polymerization rate, it is preferably 0.001 parts by mass or more, relative to 100 parts by mass of the total amount of the monomer mixture.

[0051] Examples of the chain transfer agent include primary alkyl mercaptan chain transfer agents such as n-butyl mercaptan, n-octyl mercaptan, n-hexadecyl mercaptan, n-dodecyl mercaptan, and n-tetradecyl mercaptan; secondary alkyl mercaptan chain transfer agents such as s-butyl mercaptan and s-dodecyl mercaptan; tertiary alkyl mercaptan chain transfer agents such as t-dodecyl mercaptan and t-tetradecyl mercaptan; thioglycolic acid esters such as 2-ethylhexyl thioglycolate, ethylene glycol dithioglycolate, trimethylolpropane tris(thioglycolate), and pentaerythritol tetrakis(thioglycolate); thiophenol, tetraethylthiuram disulfide, pentanephenylethane, acrolein, methacrolein, allyl alcohol, carbon tetrachloride, ethylene bromide, styrene oligomers (such as α-methylstyrene dimer), and terpinolene. These chain transfer agents may be used alone or in combination of two or more.

[0052] Among these chain transfer agents, alkyl mercaptan chain transfer agents and thioglycolic acid esters are preferred from the viewpoints of ease of handling, stability, and the thermal stability of the resulting methacrylic resin, and n-octyl mercaptan is more preferred as the alkyl mercaptan chain transfer agent, and 2-ethylhexyl thioglycolate is more preferred as the thioglycolic acid ester.

[0053] The amount of the chain transfer agent used is 0.03 mol % or less, preferably 0.025 mol % or less, based on the total amount of the monomer mixture. There is no particular lower limit to the amount of the chain transfer agent used, but it is preferably 0.005 mol % or more, based on the total amount of the monomer mixture.

[0054] In order to obtain a methacrylic resin having a high weight-average molecular weight (Mw) and a low proportion of terminal double bonds, the ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator is set to 1.6 or less. The ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator is preferably 1.5 or less, more preferably 1.0 or less. There is no particular lower limit to the ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator, but it is preferably, for example, 0.3 or more.

[0055] The polymerization temperature during synthesis of the methacrylic resin is set to less than 100° C., preferably 20° C. or higher but less than 100° C., more preferably 30 to 98° C., even more preferably 50 to 96° C., and particularly preferably 60 to 95° C., from the viewpoints of controlling the syndiotacticity of the resulting methacrylic resin and productivity. After the main reaction is completed in the first-stage polymerization, post-polymerization may be carried out at a temperature higher than that of the first stage in order to reduce the residual monomer.

[0056] In addition, since polymerization can be initiated with a small amount of polymerization initiator, it is preferable to carry out the polymerization reaction with a low dissolved oxygen content. The amount of dissolved oxygen in the polymerization raw materials is preferably 10 ppm or less, more preferably 5 ppm or less, even more preferably 4 ppm or less, and particularly preferably 2 ppm or less. By setting the dissolved oxygen content within this range, the polymerization reaction proceeds smoothly and coloration of the methacrylic resin molded body tends to be suppressed. As a method for removing dissolved oxygen from the polymerization raw materials, for example, an inert gas such as nitrogen gas can be fed into the reaction vessel before, during, and after heating to a predetermined polymerization temperature. In order to remove dissolved oxygen from raw materials added during polymerization, it is preferable to separately ventilate these raw materials with an inert gas.

[0057] In order to ensure smooth progress of the polymerization reaction, when a polymerization inhibitor is contained in the monomer mixture, it is preferable to remove the polymerization inhibitor by distillation or alkali extraction, or by using an adsorbent such as alumina, silica gel, molecular sieve, activated carbon, ion exchange resin, zeolite, or acid clay.

[0058] The suspension containing the methacrylic resin obtained by suspension polymerization may be subjected to a washing operation such as acid washing, water washing, alkali washing, etc. in order to remove the dispersant. The number of times these washing operations are performed may be selected optimally in consideration of the working efficiency and the efficiency of removing the dispersant, and may be performed once or multiple times.

[0059] As a method for separating the methacrylic resin from the suspension containing the methacrylic resin, a conventionally known dehydration method can be used, such as a method using a centrifuge or a method of removing water by suction on a porous belt or a filter membrane.

[0060] The hydrous methacrylic resin obtained through the dehydration can be dried and recovered by a conventionally known method. Examples of drying methods include hot air drying, which involves blowing hot air into a tank from a hot air blower, blow heater, etc.; vacuum drying, which involves reducing the pressure in the system and then heating it as needed; barrel drying, which involves rotating the obtained methacrylic resin in a container to remove moisture; and spin drying, which involves drying using centrifugal force. These drying methods may be used alone or in combination of two or more.

[0061] [Emulsion Polymerization Method] In the emulsion polymerization method, a methacrylic resin is synthesized in an emulsion obtained by mixing water, a monomer mixture, an emulsifier, a polymerization initiator, a chain transfer agent, and optionally other additives.

[0062] The monomer mixture used has a methyl methacrylate content of 98% by mass or more, preferably 99% by mass or more, and more preferably 100% by mass.

[0063] Examples of emulsifiers include anionic surfactants such as alkyl sulfonates, alkyl benzene sulfonates, dialkyl sulfosuccinates, α-olefin sulfonates, naphthalene sulfonate-formaldehyde condensates, alkyl naphthalene sulfonates, N-methyl-N-acyltaurine salts, and phosphate ester salts (such as polyoxyethylene alkyl ether phosphates); nonionic surfactants; and the like. Examples of the above salts include lithium salts, sodium salts, potassium salts, calcium salts, and magnesium salts. These emulsifiers may be used alone or in combination of two or more. The emulsifier used in emulsion polymerization may remain in the final methacrylic resin.

[0064] When the pH of the emulsion deviates from neutral and becomes acidic or basic, a suitable pH adjuster can be used to prevent hydrolysis of the monomer methyl methacrylate or structural units derived from methyl methacrylate in the methacrylic resin obtained by polymerization. Examples of pH adjusters that can be used include boric acid-potassium chloride-potassium hydroxide, potassium dihydrogen phosphate-sodium hydrogen phosphate, boric acid-potassium chloride-potassium carbonate, citric acid-potassium hydrogen citrate, potassium dihydrogen phosphate-boric acid, and sodium dihydrogen phosphate-citric acid.

[0065] The polymerization initiator and chain transfer agent may be the same as those used in the suspension polymerization method. The polymerization initiator may be a redox initiator, if necessary.

[0066] In order to obtain a methacrylic resin having a high weight-average molecular weight (Mw) and a low proportion of terminal double bonds, the ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator is set to 1.6 or less. The ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator is preferably 1.5 or less, more preferably 1.0 or less. There is no particular lower limit to the ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator, but it is preferably, for example, 0.3 or more.

[0067] A solid or powdery methacrylic resin can be obtained by subjecting the methacrylic resin latex obtained by emulsion polymerization to heat drying or spray drying, or by coagulating the latex by adding a water-soluble electrolyte such as a salt or an acid, followed by heat treatment, separating the resin component from the aqueous phase, and drying the resulting mixture, or by other known methods. The salt is not particularly limited, but divalent salts are preferred. Specific examples include calcium salts such as calcium chloride and calcium acetate; magnesium salts such as magnesium chloride and magnesium sulfate; and the like. Among these salts, magnesium salts such as magnesium chloride and magnesium sulfate are preferred. During coagulation, commonly added additives such as antioxidants and ultraviolet absorbers may be added.

[0068] Before the coagulation operation, it is preferable to filter the latex with a filter, a mesh, etc. to remove fine polymerization scales. This can reduce fish eyes, foreign matter, etc. caused by the fine polymerization scales when the methacrylic resin is molded into a molded article.

[0069] In this embodiment, the methacrylic resin obtained by aqueous polymerization may be in the form of a powder, granules, or a granular powder containing both powder and granules. Regarding the primary particles constituting the powder, granules, and granular powder, suspension polymerization is suitable for producing primary particles having an average particle size of about 10 to 1000 μm, while emulsion polymerization is suitable for producing primary particles having an average particle size of about 50 to 500 nm. The powder, granules, and granular powder may contain aggregates, which are aggregates of the primary particles.

[0070] After the polymerization is completed, the methacrylic resin may be purified as necessary. Examples of purification methods include dissolving the methacrylic resin in a solvent and dropping the solution into a poor solvent to cause precipitation; heating the methacrylic resin to volatilize and remove impurities; and the like. These methods may be appropriately selected depending on the application, and may be combined with each other.

[0071] <Resin Composition> The resin composition according to this embodiment contains the methacrylic resin according to this embodiment described above.

[0072] The resin composition according to the present embodiment preferably contains multilayered polymer particles from the viewpoint of further improving the thermal stability and mechanical properties of the resulting molded article. The multilayered polymer particles are not particularly limited, and known particles can be used as appropriate.

[0073] When the resin composition according to the present embodiment contains multilayered polymer particles, the blending ratio of the methacrylic resin and the multilayered polymer particles varies depending on the application of the molded article, etc., but it is preferable that the blending amount of the methacrylic resin is 30 to 98 parts by mass and the blending amount of the multilayered polymer particles is 2 to 70 parts by mass per 100 parts by mass of the total blending amount of both components.

[0074] The resin composition according to the present embodiment may further contain known additives such as light stabilizers, ultraviolet absorbers, heat stabilizers, matting agents, light diffusing agents, colorants, dyes, pigments, antistatic agents, heat ray reflecting materials, lubricants, plasticizers, stabilizers, flame retardants, mold release agents, polymer processing aids, and fillers, as well as resins other than methacrylic resins. Examples of resins other than methacrylic resins include styrene-based resins such as acrylonitrile-styrene resins and styrene-maleic anhydride resins; polycarbonate resins; polyvinyl acetal resins; cellulose acylate resins; fluorine-based resins such as polyvinylidene fluoride and polyfluorinated alkyl (meth)acrylate resins; silicone-based resins; polyolefin-based resins; polyethylene terephthalate resins; and polybutylene terephthalate resins.

[0075] Furthermore, in order to adjust the orientation birefringence of the molded article, the resin composition according to this embodiment may contain inorganic fine particles having birefringence as described in Japanese Patent No. 3648201, Japanese Patent No. 4336586, etc., or a low molecular weight compound having birefringence and a molecular weight of 5,000 or less (preferably 1,000 or less) as described in Japanese Patent No. 3696649.

[0076] The form of the resin composition according to this embodiment is not particularly limited, and may be a powder, granules, a powder-granular material containing both powder and granules, or pellet-shaped.

[0077] <Dope> The dope according to this embodiment contains the methacrylic resin according to this embodiment and a solvent, and is used to produce a resin film by a solution casting method. The solvent includes a first solvent having a hydrogen bond parameter δH of 1 to 12 in the Hansen solubility parameters, and a second solvent having a hydrogen bond parameter δH of 14 to 24. The dope according to this embodiment may further contain other components such as multilayer structure polymer particles, similar to the resin composition according to this embodiment described above. Each component, such as the methacrylic resin and the multilayer structure polymer particles, is dissolved or dispersed in the solvent.

[0078] Examples of first solvents having a hydrogen bond parameter δH of 1 to 12 include 1,4-dioxane (9.0), 2-phenylethanol (11.2), acetone (7.0), acetonitrile (6.1), chloroform (5.7), dibasic acid ester (8.4), diacetone alcohol (10.8), N,N-dimethylformamide (11.3), dimethyl sulfoxide (10.2), ethyl acetate (7.2), γ-butyrolactone (7.4), methyl ethyl ketone (5.1), methyl isobutyl ketone (4.1), methylene chloride (7.1), n-butyl acetate (6.3), N-methyl-2-pyrrolidone (7.2), propylene carbonate (4.1), 1,1,2,2-tetrachloroethane (5.3), tetrahydrofuran (8.0), and toluene (2.0). The numbers in parentheses indicate the values ​​of the hydrogen bond parameters δH. These first solvents may be used alone or in combination of two or more. Among these first solvents, methyl ethyl ketone, chloroform, and methylene chloride are preferred, and methylene chloride is more preferred, because they have excellent solubility for the methacrylic resin and a fast evaporation rate.

[0079] Examples of second solvents having a hydrogen bond parameter δH of 14 to 24 include methanol (22.3), ethanol (19.4), isopropanol (16.4), butanol (15.8), and ethylene glycol monoethyl ether (14.3). The numbers in parentheses indicate the value of the hydrogen bond parameter δH. These second solvents may be used alone or in combination of two or more. Among these second solvents, methanol and ethanol are preferred, and ethanol is more preferred.

[0080] The proportion of the first solvent contained in the solvent is preferably 55 to 95% by mass, more preferably 60 to 95% by mass, and even more preferably 70 to 95% by mass.

[0081] The content of the methacrylic resin in the dope according to the present embodiment is not particularly limited and is appropriately determined in consideration of the solubility of the methacrylic resin in the solvent used, the conditions for carrying out the solution casting method, etc. The content of the methacrylic resin is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 15 to 40% by mass.

[0082] The viscosity of the dope according to this embodiment can be adjusted appropriately by adjusting the content of the methacrylic resin and other components in the dope. From the viewpoint of coatability, filtration accuracy, etc., the viscosity of the dope is preferably 1,000 Poise (= 100 Pa s) or less, more preferably 500 Poise (= 50 Pa s) or less, and even more preferably 300 Poise (= 30 Pa s) or less. The viscosity of the dope is measured by the method described in the examples below.

[0083] The dope according to this embodiment is used to produce a resin film by a solution casting method. When producing a resin film by the solution casting method, the dope according to this embodiment is first cast onto the surface of a support and coated with an applicator to form a uniform film to form a dope film. Alternatively, the dope may be cast onto the support using a pressure die. Next, the formed dope film is heated on the support to evaporate the solvent and form a resin film. The conditions for evaporating the solvent can be determined appropriately depending on the boiling point of the solvent used. The formed resin film is then peeled off from the surface of the support. The obtained resin film may be subjected to a drying process, a heating process, a stretching process, or the like, as appropriate.

[0084] <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 solution casting method using the dope according to this embodiment described above.

[0085] The thickness of the resin film according to this embodiment is, for example, preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. Furthermore, the thickness of the resin film according to this embodiment is, for example, preferably 10 μm or more, more preferably 30 μm or more, even more preferably 50 μm or more, and particularly preferably 60 μm or more. If the thickness of the resin film is within the above range, there is an advantage that the resin film is less likely to deform when vacuum forming is performed using the resin film, and breakage is less likely to occur at the deep drawing portion. Furthermore, there is also an advantage that a resin film with uniform optical properties and good transparency can be produced.

[0086] The total light transmittance of the resin film according to the present embodiment is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. If the total light transmittance is within the above range, the transparency is high, and the film can be suitably used for optical applications that require light transmittance.

[0087] The glass transition temperature of the resin film according to this embodiment is preferably 110° C. or higher, more preferably 115° C. or higher, even more preferably 120° C. or higher, and particularly preferably 124° C. or higher. If the glass transition temperature is in the above range, the resin film will have sufficient heat resistance.

[0088] The haze of the resin film according to this embodiment is preferably 2.0% or less, more preferably 1.5% or less, even more preferably 1.3% or less, and particularly preferably 1.0% or less. The internal haze of the resin film is preferably 1.5% or less, more preferably 1.0% or less, even more preferably 0.5% or less, and particularly preferably 0.4% or less. When the haze and internal haze are within the above ranges, the film has high transparency and can be suitably used for optical applications requiring light transmittance. The haze consists of the haze inside the film and the haze on the film surface (external), which are referred to as internal haze and external haze, respectively.

[0089] The resin film according to the present embodiment preferably has a YI (Yellow Index) of 1.2 or less, more preferably 1.0 or less. When the YI is in the above range, the film has high transparency and can be suitably used for optical applications that require light transmittance.

[0090] The resin film according to the present embodiment preferably has excellent mechanical properties, for example, high bending resistance. The MIT bending resistance test and the clamshell bending test are known methods for evaluating bending resistance. For example, the resin film according to the present embodiment preferably has a bending count of 6,000 or more, more preferably 10,000 or more, until breakage in the clamshell bending test. If the bending count until breakage is within the above range, the bending resistance of the resin film is sufficient. The bending count until breakage in the clamshell bending test is measured by the method described in the Examples below.

[0091] The resin film according to this embodiment can be suitably used as an optical film such as a polarizer protective film. When the resin film according to this embodiment is used as a polarizer protective film, it is preferable that the optical anisotropy is small. In particular, it is preferable that not only the optical anisotropy in the in-plane direction (length direction, width direction) of the resin film but also the optical anisotropy in the thickness direction is small. In other words, it is preferable that the absolute values ​​of both the in-plane retardation and the thickness direction retardation are small. For example, when the measurement wavelength is 590 nm, the absolute value of the in-plane retardation is preferably 20 nm or less, more preferably 15 nm or less. Furthermore, the absolute value of the thickness direction retardation is preferably 50 nm or less, more preferably 20 nm or less, and even more preferably 15 nm or less.

[0092] The retardation is an index value calculated based on birefringence. The in-plane retardation (Re) and thickness direction retardation (Rth) can be calculated by the following formulas. In an ideal resin film that is completely optically isotropic in three-dimensional directions, the in-plane retardation Re and thickness direction retardation Rth are both 0.

[0093] Re = (nx - ny) x d Rth = [(nx + ny) / 2 - nz] x d In the above formulas, nx, ny, and nz represent the refractive index in the respective axial directions, where the in-plane stretching direction (polymer chain orientation direction) is the X axis, the direction perpendicular to the X axis is the Y axis, and the thickness direction of the resin film is the Z axis. Also, d represents the thickness of the resin film, and nx - ny represents the orientation birefringence. The MD direction of the film is the X axis, but in the case of a stretched film, the stretching direction is the X axis.

[0094] The resin film according to this embodiment preferably has an orientation birefringence value of −5.0×10 －４ ~5.0 x 10 －４ , more preferably −4.0×10 －４ ~4.0 x 10 －４ , and more preferably −3.8×10 －４ ~3.8 x 10 －４ If the orientation birefringence is within the above range, birefringence does not occur during molding and stable optical properties tend to be obtained.

[0095] (Stretching) The resin film according to this embodiment may be further stretched. Stretching the resin film can improve the mechanical strength and thickness accuracy of the resin film.

[0096] When stretching the resin film according to the present embodiment, an unstretched resin film is first formed from the dope according to the present embodiment, and then uniaxially or biaxially stretched. Alternatively, during the formation of the resin film, a stretching operation is appropriately performed as the film formation and solvent degassing processes progress. This allows the production of a stretched film (uniaxially or biaxially stretched film). Stretching during film formation and stretching after film formation may be appropriately combined.

[0097] The stretching ratio of the stretched film is not particularly limited and is determined appropriately depending on the mechanical strength, surface properties, thickness accuracy, etc. of the stretched film to be produced. Although it also depends on the stretching temperature, the stretching ratio is generally preferably selected from the range of 1.1 to 5, more preferably from 1.3 to 4, and even more preferably from 1.5 to 3. If the stretching ratio is within the above range, the mechanical properties of the film, such as elongation, tear propagation strength, and flexural fatigue resistance, tend to be significantly improved.

[0098] (Applications) The resin film according to this embodiment can be used for various applications such as transportation equipment, solar cell components, civil engineering and construction components, daily necessities, electrical and electronic devices, optical components, and medical supplies. In particular, the resin film according to this embodiment has excellent heat resistance and optical properties, and therefore can be suitably used for optical applications. Examples of optical applications include front panels (cover windows) for various display devices, diffusion plates, polarizer protective films, polarizing plate protective films, retardation films, light diffusion films, and optically isotropic films.

[0099] Among these, the resin film according to the present embodiment can be suitably used as a polarizer protective film or a front panel (cover window) of a display device. When the resin film according to the present embodiment is used as a front panel (cover window) of various display devices, a functional coating layer such as a primer layer or a hard coat layer may be formed on at least one main surface of the resin film, as necessary. Furthermore, when the resin film according to the present embodiment is used as a polarizer protective film, the resin film according to the present embodiment is bonded to a polarizer to form a polarizing plate. The polarizer is not particularly limited, and any conventionally known polarizer can be used. This polarizing plate is used in display devices such as liquid crystal display devices and organic EL display devices.

[0100] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The methods for measuring various physical properties described in the examples and comparative examples are as follows.

[0101] (1) Polymerization Conversion Rate The polymerization conversion rate of the methacrylic resin was calculated from the ratio of the weight of the methacrylic resin obtained by washing with water and drying to the weight of the monomer used. The weight of the methacrylic resin obtained by washing with water and drying was calculated by subtracting the weight of the remaining monomer in the methacrylic resin, which was calculated by the following analysis. (Analysis Conditions for Examples 1 and 2) Using a nuclear magnetic resonance spectrometer (AVANCEIII 400 MHz, manufactured by Bruker), the polymerization conversion rate of the methacrylic resin was measured in a deuterated chloroform solution at 22°C and with 16 accumulations. １ The H-NMR spectrum was measured. From the spectrum, the area (Y) of the peak (3.60 ppm) derived from the methoxy group when tetramethylsilane (TMS) was set to 0 ppm, and the sum (X) of the areas of the peaks of the residual monomer (6.11 ppm and 5.56 ppm when the monomer is methyl methacrylate) were calculated. The proportion of the residual monomer was calculated from the formula: [(3 × X) / (2 × Y)] × 100, and then this value was used to calculate the ratio of the residual monomer to the peak area (Y) of the peak area (3.60 ppm) derived from tetramethylsilane (TMS) when the monomer is methyl methacrylate. １ The residual monomer ratio calculated by H-NMR and the residual monomer amount determined by gas chromatographic analysis were substituted into a correlation equation. The polymerization conversion rate was calculated using the remaining amount of monomer in the resulting methacrylic resin. (Analysis Conditions for Example 3, Comparative Example 2, and Comparative Example 3) A gas chromatograph (Agilent Technologies, 7890B) was used, and a DB-1 analytical column (Agilent Technologies, 0.8 μm film thickness × 0.20 mm inner diameter × 30 m length) was used. Analysis was performed under conditions of an inlet temperature of 150°C and a detector temperature of 320°C. The column temperature was set as follows: the temperature was increased from 35°C to 210°C at a rate of 30°C / min, then increased from 210°C to 260°C at a rate of 10°C / min, and then increased from 260°C to 320°C at a rate of 20°C / min, and maintained at this temperature for 3 minutes. A calibration curve was prepared by the internal standard method using chlorobenzene as an internal standard substance, and the amount of the remaining monomer in the methacrylic resin was calculated, and then the polymerization conversion rate was calculated.

[0102] (2) Residual Rate of Chain Transfer Agent The residual rate of chain transfer agent in the methacrylic resin was quantified using a gas chromatograph (Agilent Technologies, 7890B). A DB-1 analytical column (Agilent Technologies, 0.8 μm film thickness × 0.20 mm inner diameter × 30 m length) was used, with the inlet temperature set to 150°C and the detector temperature set to 320°C. The column temperature was raised from 35°C to 210°C at a heating rate of 30°C / min, then from 210°C to 260°C at a heating rate of 10°C / min, and further raised from 260°C to 320°C at a heating rate of 20°C / min, and held for 3 minutes. A calibration curve was prepared by the internal standard method using dichloromethane as the measurement solvent and chlorobenzene as the internal standard, and the residual rate of chain transfer agent in the methacrylic resin was calculated.

[0103] (3) Triad syndiotacticity (rr) of methacrylic resin １ The H-NMR spectrum was measured using a nuclear magnetic resonance spectrometer (AVANCEIII 400 MHz, manufactured by Bruker) in a deuterated chloroform solution at 22°C with 16 accumulations. From the spectrum, the area (X) of the region from 0.60 to 0.95 ppm and the area (Y) of the region from 0.60 to 1.25 ppm, when tetramethylsilane (TMS) was set to 0 ppm, were measured, and the syndiotacticity (rr) expressed in triad form was then calculated using the formula: (X / Y) × 100.

[0104] (4) Weight-average molecular weight (Mw), and 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 ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) of the methacrylic resin were calculated by a standard polystyrene conversion method using gel permeation chromatography (GPC). Specifically, analysis was carried out using a sample solution prepared by dissolving 20 mg of methacrylic resin in 10 mL of tetrahydrofuran, with the following equipment and conditions. Measurement equipment: HLC-8220GPC (Tosoh) Detector: RI detector Solvent: Tetrahydrofuran Guard column: TSKgel guard column SuperHZ-H (Tosoh) Analytical column: TSKgel SuperHZM-H x 2 (Tosoh) Measurement temperature: 40 ° C. Standard material: Standard polystyrene (Tosoh)

[0105] (5) Proportion of Terminal Double Bonds Approximately 20 mg of methacrylic resin was dissolved in 0.6 to 0.7 mL of deuterated chloroform to prepare a solution, and the proportion of terminal double bonds was measured using a nuclear magnetic resonance apparatus (AVANCE NEO 700 MHz, manufactured by Bruker). １ H-NMR was measured. The measurement temperature was 20°C, the number of accumulations was 8,192, and the measurement was performed while eliminating the peak derived from the methoxy group of the methacrylic resin (3.60 ppm, the value when the chemical shift of the solvent peak was set to 7.26 ppm) using the Excitation Sculpting (ES) method, which is a type of solvent elimination method. １ From the H-NMR spectrum, the total area (X) of the peaks (5.47 to 5.52 ppm and 6.21 ppm) derived from the terminal double bonds of the methacrylic resin and the area (Y) of the peaks (0.5 to 1.25 ppm) derived from the α-methyl groups of the methacrylic resin were measured, and then the proportion of the terminal double bonds of the methacrylic resin was calculated using the formula: [(3 × X) / (2 × Y)] × 100.

[0106] (6) Glass transition temperature (Tg) The glass transition temperature (Tg) of the methacrylic resin and the resin film before stretching was measured using a differential scanning calorimeter (DSC; Hitachi High-Tech Science Corporation, DSC7000X). First, under a nitrogen flow rate of 40 mL / min, the first temperature increase was performed from 40 ° C. to 160 ° C. at a heating rate of 10 ° C. / min, and then cooled to 40 ° C., and then the second temperature increase was performed at a heating rate of 10 ° C. / min from 40 ° C. to 160 ° C. The DSC measurement was performed under these conditions. Then, from the DSC curve measured during the second temperature increase, the midpoint glass transition temperature (the line extrapolated from the baseline before the inflection point to the high temperature side, and the line extrapolated from the baseline after the inflection point to the low temperature side) was read. The temperature at the point where the line equidistant in the vertical direction from both the line and the curve of the stepwise change in the glass transition intersect.

[0107] (7) 5% Weight Loss Temperature (Td5) The 5% weight loss temperature (Td5) of the methacrylic resin was measured using a thermogravimetric analyzer (Hitachi High-Tech Science Corporation, STA7200). Under a nitrogen flow of 200 mL / min, the first temperature increase was performed from 40 ° C. to 190 ° C. at a heating rate of 10 ° C. / min to remove moisture absorbed by the methacrylic resin, and then cooled to 40 ° C., and then heated a second time from 40 ° C. to 500 ° C. at a heating rate of 10 ° C. / min. The temperature at which the weight of the sample decreased to 95%, as determined from the thermogravimetric (TG) curve measured during the second heating, was taken as the 5% weight loss temperature (Td5).

[0108] (8) Dope Viscosity A methacrylic resin was dissolved in a mixed solvent consisting of 93% by mass of methylene chloride and 7% by mass of ethanol to prepare dopes with solid content (SC) of 10% by mass (Examples 1 and 2), 12% by mass (Example 3), or 25% by mass (Comparative Examples 1 and 2). The dope viscosity was measured using a Brookfield viscometer (BMII, manufactured by Toki Sangyo Co., Ltd.). The temperature of the measurement sample was adjusted to 23°C, and the reading was read at 30 rpm (12 rpm for Examples 1 and 3) using a No. 2 rotor.

[0109] (9) Haze Measurement The haze of the stretched resin film was measured using a haze meter (HZ-V3, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K7136. The same measurement was also carried out by sandwiching both sides of the resin film between glycerin and then glass, and the resulting value was taken as the internal haze. The obtained result was converted into a film thickness equivalent to 40 μm.

[0110] (10) Total Light Transmittance The total light transmittance of the stretched resin film was measured using a haze meter (HZ-V3, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K7361-1.

[0111] (11) YI The YI of the stretched resin film was measured using a spectrophotometer (SC-P, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K 7373. The obtained results were converted into a film thickness equivalent to 40 μm.

[0112] (12) Clamshell Bending Test The bending resistance of the stretched methacrylic resin film was evaluated using a clamshell-type desktop durability tester (DMLHP-CS, manufactured by Yuasa System Co., Ltd.). The conditions were set at 23°C, 55% relative humidity, a radius of curvature of 0.35 mm, and a test speed of 30 r / min (30 times / min). The film was cut into strips measuring 2 cm wide and 5 cm long and used as test pieces. The test was performed by setting the strips so that they were creased perpendicular to the stretching direction. The test was continued until the test piece broke. The test was performed three times for each sample, and the bending resistance was evaluated from the number of times until breakage.

[0113] Example 1 A 2-liter glass reactor equipped with a three-way swept-blade stirrer was charged with 170 parts by mass of deionized water, 0.10 parts by mass of disodium hydrogen phosphate as a suspension aid, and 0.037 parts by mass of 2,2'-azobis(isobutyrate)dimethyl (V-601, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was passed through to replace the air inside the reactor. Then, a monomer solution containing 100 parts by mass of methyl methacrylate (MMA) and 0.017 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 Metolose 60SH-50 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.), a water-soluble polymer, as a dispersant, was added to the reactor. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 77°C to initiate polymerization. The monomers were reacted at 77°C for 4 hours, and then the temperature of the liquid in the reactor was raised to 95°C. The reaction liquid was stirred at the same temperature for 1 hour to terminate the polymerization. The resulting resin was washed with deionized water in an amount 4.6 times the amount of resin and dried to obtain bead-like particles. The particles were dissolved in methylene chloride to a concentration of 10% by mass, and the solution was added dropwise to methanol in an amount 5 times the amount of the methylene chloride solution to precipitate the resin. The precipitated resin was collected by suction filtration and dried to obtain a methacrylic resin after precipitation purification.

[0114] A mixed solvent consisting of 93% by mass of methylene chloride and 7% by mass of ethanol was placed in a screw tube container, and the dried methacrylic resin was then added thereto. The solution was stirred until the methacrylic resin was completely dissolved to prepare a dope with a solid content (SC) of 10% by mass.

[0115] The dope prepared above was cast onto a PET film substrate (Cosmoshine A4100, manufactured by Toyobo Co., Ltd.) and coated with an applicator to form a uniform film. The clearance was adjusted so that the thickness after drying would be approximately 60 μm. After coating, the dope film was dried in an oven at 40°C for 1 hour, and then the resulting resin film was peeled off from the PET film substrate. The resin film was then fixed to a stainless steel frame and dried in an oven at 140°C for 2 hours to remove residual solvent, thereby obtaining a resin film. Furthermore, the resulting resin film was subjected to width-fixed uniaxial stretching at 135°C. The stretching ratio was 1.5 times and the stretching speed was 100 mm / min. The average thickness of the resin film after stretching was 43 μm.

[0116] The physical properties of the methacrylic resin, the dope, and the resin film in Example 1 are shown in Table 1.

[0117] Example 2 The same procedure as in Example 1 was carried out, except that the amount of n-octyl mercaptan (n-OM) used was changed to 0.036 parts by mass, and the amount of deionized water used for washing the obtained resin was changed to 4.3 times the amount of the resin. The average thickness of the obtained stretched resin film was 41 μm. The physical properties of the methacrylic resin, dope, and resin film in Example 2 are shown in Table 1.

[0118] Example 3 A 4-liter glass reactor equipped with an H-shaped impeller stirrer was charged with 150 parts by mass of deionized water, 0.400 parts by mass of tribasic calcium phosphate as a dispersant, 0.0075 parts by mass of sodium α-olefin sulfonate, and 0.30 parts by mass of sodium chloride. While stirring the aqueous solution in the reactor at 250 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was passed through to replace the air in the reactor. Then, a monomer solution containing 100 parts by mass of methyl methacrylate (MMA), 0.017 parts by mass of n-octyl mercaptan (n-OM) as a chain transfer agent, and 0.037 parts by mass of 2,2'-azobis(isobutyrate)dimethyl (V-601, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was added to the reactor. The temperature of the solution in the reactor was then raised to 80°C to initiate polymerization. After 45 minutes from the start of polymerization, an additional 0.10 parts by mass of tricalcium phosphate was added to the reaction solution. Two hours after the start of polymerization, the temperature of the solution in the reactor was raised to 95°C, and stirring was continued at 95°C for 1 hour, at which point the polymerization was terminated. Acid washing was performed twice using 1N hydrochloric acid in an amount 0.1 times by weight relative to the amount of charged monomer, followed by water washing and drying to obtain bead-shaped resin particles. The particles were dissolved in methylene chloride to a concentration of 7% by mass, and the resulting methylene chloride solution was filtered through a pressure filter equipped with a 5 μm filter. The filtrate containing the resin was then dried in an oven at 70°C for 12 hours and at 140°C for 2 hours. The dried resin was immersed in methanol in an amount 2.5 times by weight relative to the resin and allowed to stand at room temperature for 12 hours and at 50°C for 5 hours. The resin was recovered by suction filtration and then dried in an oven at 70°C for 12 hours and at 140°C for 5 hours. Furthermore, the resin was vacuum dried at 140°C for 2 hours to obtain a purified methacrylic resin.

[0119] A mixed solvent consisting of 93% by mass of methylene chloride and 7% by mass of ethanol was placed in a screw tube container, and the dried methacrylic resin was then added thereto. The solution was stirred until the methacrylic resin was completely dissolved to prepare a dope with a solid content (SC) of 12% by mass.

[0120] The dope prepared above was cast onto a PET film substrate (Cosmoshine A4100, manufactured by Toyobo Co., Ltd.) and coated with an applicator to form a uniform film. The clearance was adjusted so that the thickness after drying would be approximately 60 μm. After coating, the dope film was dried in an oven at 40°C for 1 hour, and then the resulting resin film was peeled off from the PET film substrate. The resin film was then fixed to a stainless steel frame and dried in an oven at 140°C for 2 hours to remove residual solvent, thereby obtaining a resin film. Furthermore, the resulting resin film was subjected to width-fixed uniaxial stretching at 132°C. The stretching ratio was 1.5 times and the stretching speed was 100 mm / min. The average thickness of the resin film after stretching was 41 μm.

[0121] The physical properties of the methacrylic resin, the dope, and the resin film in Example 3 are shown in Table 1.

[0122] Comparative Example 1 Parapet HR-S (manufactured by Kuraray Co., Ltd., a copolymer of methyl methacrylate (MMA) and methyl acrylate (MA), MMA / MA = 98.9 / 1.1 (mass ratio)) was used as the methacrylic resin, and precipitation purification from a methylene chloride solution of the methacrylic resin into methanol was not performed. However, precipitation purification was performed only when preparing a sample for quantifying terminal double bonds. Using this methacrylic resin, the same operation as in Example 1 was performed, except that the solid content concentration (SC) of the dope was changed to 25 mass % and the stretching temperature of the resin film was changed to 125°C. The average film thickness of the obtained stretched resin film was 36 μm. The physical properties of the methacrylic resin, dope, and resin film in Comparative Example 1 are shown in Table 1.

[0123] Comparative Example 2 A 2-liter glass reactor equipped with a three-way swept-blade stirrer was charged with 170 parts by mass of deionized water, 0.10 parts by mass of disodium hydrogen phosphate as a suspension aid, and 0.037 parts by mass of 2,2'-azobis(isobutyrate)dimethyl (V-601, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was passed through to replace the air inside the reactor. Then, a monomer solution containing 100 parts by mass of methyl methacrylate (MMA) and 0.270 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 Metolose 60SH-50 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.), a water-soluble polymer, as a dispersant, was added to the reactor. 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 liquid in the reactor was heated to 94°C. The reaction liquid was stirred at the same temperature for 1 hour to terminate the polymerization. The resulting resin was washed with deionized water in an amount 3.4 times the amount of resin and dried to obtain bead-like particles. The particles were dissolved in methylene chloride to a concentration of 10% by mass, and the solution was added dropwise to methanol in an amount 5 times the amount of the methylene chloride solution to precipitate the resin. The precipitated resin was collected by suction filtration and dried to obtain a methacrylic resin after precipitation purification.

[0124] A mixed solvent consisting of 93% by mass of methylene chloride and 7% by mass of ethanol was placed in a screw tube container, and the dried methacrylic resin was then added thereto. The solution was stirred until the methacrylic resin was completely dissolved to prepare a dope with a solid content (SC) of 25% by mass.

[0125] The dope prepared above was cast onto a PET film substrate (Cosmoshine A4100, manufactured by Toyobo Co., Ltd.) and coated with an applicator to form a uniform film. The clearance was adjusted so that the thickness after drying would be approximately 40 μm. After coating, the dope film was dried in an oven at 40°C for 1 hour, and then the resulting resin film was peeled off from the PET film substrate. The resin film was then fixed to a stainless steel frame and dried in an oven at 140°C for 2 hours to remove residual solvent, yielding a resin film. Furthermore, the resulting resin film was subjected to width-fixed uniaxial stretching at 132°C. The stretching ratio was 1.5 times and the stretching speed was 100 mm / min. The average thickness of the stretched resin film was 38 μm.

[0126] The physical properties of the methacrylic resin, the dope, and the resin film in Comparative Example 2 are shown in Table 1.

[0127] Comparative Example 3 A 0.5-liter glass reactor equipped with an H-shaped impeller stirrer was charged with 170 parts by mass of deionized water, 0.10 parts by mass of disodium hydrogen phosphate as a suspension aid, and 1.00 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. While stirring the aqueous solution in the reactor at 380 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was passed 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 Metrose 60SH-50 (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 30°C to initiate polymerization. After reacting the monomers at 30°C for 3 hours, the liquid in the reactor was heated to 50°C for 1 hour, then heated to 70°C for 30 minutes, and then heated to 95°C for 1 hour and stirred to complete the polymerization. The resulting resin was washed with deionized water in an amount 7 times the amount of resin and dried to obtain bead-like particles. The particles were dissolved in methylene chloride to a concentration of 10% by mass, and the solution was added dropwise to methanol in an amount 5 times the amount of the methylene chloride solution to precipitate the resin. The precipitated resin was collected by suction filtration and dried to obtain a methacrylic resin after precipitation purification. The physical properties of the methacrylic resin in Comparative Example 3 are shown in Table 1.

[0128]

[0129] As shown in Table 1, in Examples 1 to 3, methacrylic resins with high syndiotacticity and, as a result, high glass transition temperatures (Tg) were obtained, and resin films containing such methacrylic resins were also obtained. Furthermore, in Examples 1 to 3, the resin films exhibited excellent flex resistance due to the high weight-average molecular weight (Mw) of the methacrylic resin. Specifically, the stretched resin film of Example 1 did not break even after being bent more than 20,000 times, the stretched resin film of Example 2 did not break until the number of bends reached 11,000 to 13,000 times, and the stretched resin film of Example 3 did not break even after being bent more than 20,000 times. Furthermore, in Examples 1 to 3, the 5% weight loss temperature (Td5) of the methacrylic resin exceeded 300°C. That is, Examples 1 to 3 were excellent in heat resistance (glass transition temperature (Tg)), thermal stability (5% weight loss temperature (Td5)), and the mechanical properties (flex resistance) of the molded articles.

[0130] On the other hand, in Comparative Example 1, although the 5% weight loss temperature (Td5) of the methacrylic resin was high, the syndiotacticity was low, and as a result, the glass transition temperature (Tg) of the methacrylic resin and the resin film was lower than those of Examples 1 to 3. In addition, in Comparative Example 1, the weight average molecular weight (Mw) of the methacrylic resin was small, and therefore the mechanical properties of the resin film were inferior to those of Examples 1 to 3. Specifically, the resin film after stretching in Comparative Example 1 could only be bent 3,000 to 4,500 times before breaking.

[0131] In Comparative Example 2, the syndiotacticity was high, resulting in a methacrylic resin and resin film with a high glass transition temperature (Tg), and the 5% weight loss temperature (Td5) of the methacrylic resin was also high. However, because the weight average molecular weight (Mw) of the methacrylic resin was small, the mechanical properties of the resin film were inferior to those of Examples 1 to 3. Specifically, the resin film after stretching in Comparative Example 2 could only be bent 1,000 to 2,000 times before breaking.

[0132] In Comparative Example 3, a methacrylic resin having a high syndiotacticity and a high glass transition temperature (Tg) was obtained. However, because the proportion of terminal double bonds in the methacrylic resin was high, the 5% weight loss temperature (Td5) was below 300°C, and the thermal stability was low.

Claims

1. 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 400,000 or more, and the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 1.6 to 2.8; The syndiotacticity of the triad is 55-67%; The 5% weight loss temperature is 300° C. or higher, A methacrylic resin having a residual rate of a chain transfer agent of 0.005% by mass or less.

2. The methacrylic resin according to claim 1, comprising a terminal structure represented by the following formula (1) derived from a polymerization initiator. 【Chemistry 1】 (In the formula, R １ , R ２ , and R ３ each independently represents an alkyl group, a substituted alkyl group, an ester group, or an amide group. １ , R ２ , and R ３ At least one of R represents an ester group or an amide group. １ , R ２ , and R ３ Two of the above may be bonded to each other to form an alicyclic structure. * indicates a bond to a structural unit derived from a monomer.)

3. The methacrylic resin according to claim 1, wherein the ratio of terminal double bonds to structural units derived from methyl methacrylate is less than 0.015 mol%.

4. The methacrylic resin according to claim 1, having a glass transition temperature of 120°C or higher.

5. 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 400,000 or more, and the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 1.6 to 2.8; The syndiotacticity of the triad is 55% or more, The glass transition temperature is 120 to 135°C. The 5% weight loss temperature is 300° C. or higher, A methacrylic resin having a residual rate of a chain transfer agent of 0.005% by mass or less.

6. Resin beads comprising a methacrylic resin described in any one of claims 1 to 5.

7. The method includes a polymerization step of polymerizing a monomer mixture having a methyl methacrylate content of 98% by mass or more in the presence of a polymerization initiator and a chain transfer agent at less than 100° C. until a polymerization conversion rate reaches 90% or more and a residual rate of the chain transfer agent reaches 0.005% by mass or less, the amount of the chain transfer agent used is 0.03 mol % or less based on the total amount of the monomer mixture; 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 1.6 or less.

8. The method for producing a methacrylic resin according to claim 7, wherein the polymerization initiator is a non-nitrile azo polymerization initiator.

9. The method for producing a methacrylic resin according to claim 7 or 8, wherein aqueous polymerization is performed in the polymerization step.

10. A resin composition comprising the methacrylic resin according to any one of claims 1 to 5 and optionally multilayer structure polymer particles.

11. The methacrylic resin according to any one of claims 1 to 5 and a solvent are contained, The dope for film production by a solution casting method includes a first solvent having a hydrogen bond parameter δH of 1 to 12 in the Hansen solubility parameters, and a second solvent having a hydrogen bond parameter δH of 14 to 24.

12. A resin film comprising the methacrylic resin according to any one of claims 1 to 5.

13. The resin film according to claim 12, which can be bent 6,000 times or more until it breaks in a clamshell bending test.

14. The resin film according to claim 12, comprising multilayered polymer particles.

15. A resin film as described in claim 12, having a haze of 2.0% or less.

16. A resin film as described in claim 12, having an internal haze of 1.5% or less.

17. The resin film described in claim 12, wherein the resin film is a stretched film.

18. The resin film described in claim 12, wherein the resin film is a biaxially oriented film.

19. The resin film described in claim 12, wherein the resin film is an optical film.

20. The resin film according to claim 12 , which is a polarizer protective film.

21. A polarizing plate comprising a polarizer and the resin film according to claim 12 laminated together.

22. A display device comprising the polarizer of claim 21.

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