Method for producing methacrylic resin

Abstract

The present invention provides: a methacrylic resin which comprises structural units derived from methyl methacrylate at a ratio of 98% by mass or more, has a triad syndiotacticity of 55% or more, and contains a terminal structure that is derived from a polymerization initiator and is represented by formula (1), wherein the ratio of terminal double bonds to the structural units derived from methyl methacrylate is less than 0.020 mol%; and a method for producing this methacrylic resin. In formula (1), each of R1, R2 and R3 independently represents an alkyl group, a substituted alkyl group, an ester group or an amide group, provided that at least one of R1, R2 and R3 represents an ester group or an amide group. The present invention also provides: a resin composition which contains this methacrylic resin; a resin film which contains this methacrylic resin; and a polarizing plate and a display device, each of which uses this resin film.

Description

[Technical Field]

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

[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. This methacrylic resin is produced, for example, by polymerizing a monomer mixture 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). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 088025 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the inventors have found through their investigations that the thermal stability of the resulting methacrylic resin may be reduced depending on the conditions, such as the type of polymerization initiator used during synthesis of the methacrylic resin.

[0005] An object of the present invention is to provide a methacrylic resin having excellent thermal stability and a method for producing the same, 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. [Means for solving the problem]

[0006] Specific means for solving the above problems include the following embodiments. <1> The proportion of structural units derived from methyl methacrylate is 98% by mass or more, The syndiotacticity of the triplet display is 55% or more, It contains a terminal structure represented by the following formula (1) derived from a polymerization initiator, A methacrylic resin in which the ratio of terminal double bonds to structural units derived from methyl methacrylate is less than 0.020 mol %. [ka] (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. <2> The thermal weight loss rate when exposed to 280°C for 15 minutes in a nitrogen gas atmosphere is less than 2.5%. <1> The methacrylic resin according to claim 1. <3> The terminal structure represented by the formula (1) is a terminal structure derived from at least one selected from dimethyl 2,2'-azobis(isobutyrate) and methyl 1,1'-azobis(cyclohexanecarboxylate). <1> or <2> The methacrylic resin according to claim 1. <4> The weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) is 50,000 to 200,000. <1> ~ <3> The methacrylic resin according to any one of the above. <5> 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. <1> ~ <4> The methacrylic resin according to any one of the above.

[0007] <6> 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 non-nitrile azo polymerization initiator and a chain transfer agent at 100°C or less until a polymerization conversion rate reaches 90% or more, the amount of the chain transfer agent used is 0.10 mol % or more based on the total amount of the monomer mixture; A method for producing a methacrylic resin, wherein the ratio of the total molar amount of the chain transfer agent to the total molar amount of the non-nitrile azo polymerization initiator is 2.0 or more. <7> In the polymerization step, aqueous polymerization is performed. <6> A method for producing the methacrylic resin described in <8> the non-nitrile azo polymerization initiator comprises at least one selected from dimethyl 2,2'-azobis(isobutyrate) and methyl 1,1'-azobis(cyclohexanecarboxylate); <6> or <7> A method for producing the methacrylic resin described in <9> <1> ~ <5> A resin composition comprising the methacrylic resin according to any one of claims 1 to 4. <10> Contains ultraviolet absorbers, <9> The resin composition according to claim 1. <11> <1> ~ <5> A resin film comprising the methacrylic resin according to any one of claims 1 to 10. <12> Contains ultraviolet absorbers, <11> The resin film according to claim 1. <13> The resin film is a polarizer protective film. <11> or <12> The resin film according to claim 1. <14> A polarizer; <11> ~ <13> 10. A polarizing plate obtained by laminating the resin film according to any one of claims 1 to 9. <15> <14> A display device comprising the polarizing plate according to claim 1. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a methacrylic resin having excellent thermal stability and a method for producing the same, 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 OF THE INVENTION

[0009] Specific embodiments of the present invention will be described in detail below. The symbol "to" used to represent a range of values ​​is intended to include both the lower and upper limits of the range, unless otherwise specified.

[0010] <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:

[0011] [ka]

[0012] 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.

[0013] The methacrylic resin according to this embodiment has a syndiotacticity (rr) expressed as a triad of 55% or more, preferably 56% or more, and more preferably 57% or more. When the syndiotacticity (rr) expressed as a triad of 55% or more, the glass transition temperature (Tg) of the methacrylic resin tends to be high and the heat resistance tends to be improved. There is no particular upper limit for the syndiotacticity (rr), but from the viewpoints of the molding temperature and the toughness and secondary processability of the molded body, it is preferably 67% or less, more preferably 65% ​​or less, and even more preferably 63% or less.

[0014] Syndiotacticity (rr) is the proportion of two diads in a triad of three consecutive structural units that are both racemo (rr). Diads in polymer molecules with the same configuration are called meso, and those with the opposite configuration are called racemo, and are abbreviated as m and r, respectively.

[0015] As described in the Examples below, syndiotacticity (rr) was measured in deuterated chloroform at 22°C and 16 cycles. 1The H-NMR spectrum is measured, and 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 are measured from the spectrum when tetramethylsilane (TMS) is set to 0 ppm, and the amount of fluorine can be calculated using the formula: (X / Y) × 100.

[0016] Furthermore, the methacrylic resin according to this embodiment preferably has a glass transition temperature (Tg) of 120° C. or higher, more preferably 121° C. or higher, and even more preferably 122° C. or higher. There is no particular upper limit to the glass transition temperature (Tg), but from the viewpoints 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.

[0017] 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.

[0018] The syndiotacticity (rr) and glass transition temperature (Tg) of the methacrylic resin can be controlled by adjusting the polymerization temperature during synthesis of the methacrylic resin. For example, lowering the polymerization temperature is preferable for increasing the syndiotacticity (rr) and glass transition temperature (Tg) of the methacrylic resin. The glass transition temperature (Tg) can also be controlled by adjusting the molecular weight of the methacrylic resin.

[0019] The methacrylic resin according to this embodiment also contains a terminal structure represented by the following formula (1) derived from a polymerization initiator.

[0020] [ka] (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 3At 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.

[0021] 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.

[0022] Examples of the ester group include -COOR 4 Examples of such groups include groups 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.

[0023] The amide group includes, for example, —C(O)NR 5 Examples of such groups include groups 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.

[0024] The terminal structure represented by the above formula (1) can be introduced into the molecule of the methacrylic resin by using a non-nitrile azo polymerization initiator represented by the following formula (2) when synthesizing the methacrylic resin. 1 , R 2 , and R 3 is synonymous with the above formula (1). Use of such a non-nitrile azo polymerization initiator tends to improve the thermal stability of the resulting methacrylic resin compared to the use of a polymerization initiator other than a non-nitrile azo polymerization initiator (for example, a nitrile azo polymerization initiator). In addition, non-nitrile azo polymerization initiators are also preferred in that the toxicity of the initiator itself and decomposition products tends to be lower compared to nitrile azo polymerization initiators.

[0025] [ka]

[0026] Examples of non-nitrile azo polymerization initiators represented by the above formula (2) include dimethyl 2,2'-azobis(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 dimethyl 2,2'-azobis(isobutyrate) and 1,1'-azobis(methyl cyclohexanecarboxylate) is preferred.

[0027] Furthermore, in the methacrylic resin according to this embodiment, the ratio of terminal double bonds to structural units derived from methyl methacrylate is less than 0.020 mol%, preferably less than 0.015 mol%, more preferably less than 0.010 mol%, and even more preferably less than 0.006 mol%. If the ratio of terminal double bonds is within the above range, the thermal stability of the methacrylic resin tends to be improved.

[0028] The methacrylic resin according to this embodiment can be produced by radical polymerization, as shown in the production method described below. The methacrylic resin produced by radical polymerization contains terminal double bonds generated by disproportionation termination reactions during polymerization, hydrogen abstraction reactions of monomers by a polymerization initiator, and the like. Because terminal double bonds affect the thermal stability of the resin, a low proportion of terminal double bonds is preferable. The proportion of terminal double bonds can be controlled by the method described below. If the proportion can be reduced to a range of 0.001 mol% or more and less than 0.020 mol%, the thermal stability of the methacrylic resin tends to be significantly improved.

[0029] The ratio of terminal double bonds to structural units derived from methyl methacrylate was determined by the following conditions: in deuterated chloroform, 20°C, and 8,192 cycles. 1 The H-NMR spectrum is measured, and from the spectrum, the sum (X) of the areas of the peaks (5.47 to 5.53 ppm and 6.21 ppm) derived from the terminal double bonds of the methacrylic resin and the area (Y) of the peaks (0.5 to 1.25 ppm) derived from the α-methyl groups of the methacrylic resin are measured, and the chromaticity can be calculated using the formula: [(3 × X) / (2 × Y)] × 100.

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

[0031] As described above, the methacrylic resin according to this embodiment has excellent thermal stability. The methacrylic resin according to this embodiment preferably exhibits a thermal weight loss of less than 2.5%, more preferably less than 2.3%, when exposed to 280°C in a nitrogen gas atmosphere for 15 minutes. This thermal weight loss is measured by the method described in the Examples below.

[0032] The methacrylic resin according to this embodiment preferably has a weight-average molecular weight (Mw) of 50,000 to 200,000, and more preferably 90,000 to 150,000. When the weight-average molecular weight (Mw) of the methacrylic resin is 50,000 or more, the mechanical properties of the resulting molded article tend to be improved, and when the weight-average molecular weight (Mw) of the methacrylic resin is 200,000 or less, the moldability tends to be improved.

[0033] Furthermore, the methacrylic resin according to this embodiment preferably 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 2.5, and more preferably 1.7 to 2.2. When the polydispersity (Mw / Mn) of the methacrylic resin is 1.6 or more, the flowability 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 2.5 or less, the mechanical properties of the resulting molded article, such as impact resistance, toughness, and flex resistance, tend to be improved.

[0034] 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.

[0035] 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.

[0036] The methacrylic resin according to this embodiment not only has excellent thermal stability, but is also expected to be suitable for reuse after disposal, i.e., recycling. Known methods for recycling methacrylic resin include chemical recycling (a method in which cracked oil is recovered as a cracked product by thermal decomposition and reused as a chemical raw material or fuel). Generally, to improve the heat resistance and thermal stability of methacrylic resin, a cyclic structure is introduced into the molecular structure of the methacrylic resin or a monomer having a rigid structure is copolymerized. However, these structures become impurities in chemical recycling and are undesirable. In this regard, the methacrylic resin according to this embodiment has a high proportion of structural units derived from methyl methacrylate, and the yield of monomers recovered as cracked oil is expected to be high, and the resin is expected to exhibit good chemical recyclability.

[0037] <Methacrylic resin manufacturing method> 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 non-nitrile azo polymerization initiator (hereinafter also referred to simply as "polymerization initiator") and a chain transfer agent at 100°C or less until a polymerization conversion rate reaches 90% or more. Conventional polymerization methods can be used to produce methacrylic resins, 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 flexibility in structural design of the methacrylic resin, ease of polymerization, productivity, and the like, aqueous polymerization production methods are preferred, suspension polymerization and emulsion polymerization are more preferred, and suspension polymerization is even more preferred.

[0038] In addition, producing the methacrylic resin according to this embodiment by aqueous polymerization is advantageous in terms of impurities in the resin. For example, anionic solution polymerization uses an organometallic compound as a polymerization initiator, and metal ions derived from the organometallic compound remain in the resin at approximately several hundred ppm by mass. On the other hand, aqueous polymerization does not use an organometallic compound as a polymerization initiator, and therefore the total amount of residual metal ions in the resin can be reduced to 100 ppm by mass or less. When performing aqueous polymerization, the Al content in the resin is preferably 1 ppm by mass or less, and the Li content is preferably 1 ppm by mass or less. Furthermore, aqueous polymerization does not require a process for removing residual metal ions, making it economically advantageous. Furthermore, aqueous polymerization does not use organic solvents such as aliphatic hydrocarbons and alicyclic hydrocarbons, which are used in anionic solution polymerization, making it environmentally advantageous.

[0039] [Suspension polymerization method] In the suspension polymerization method, a methacrylic resin is synthesized in an aqueous suspension prepared by mixing 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.

[0040] 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.

[0041] 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 using poorly water-soluble inorganic salts as dispersants, it is effective to use them 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.

[0042] Examples of non-nitrile polymerization initiators include non-nitrile azo polymerization initiators represented by the above formula (2). Among the non-nitrile azo polymerization initiators represented by the above formula (2), at least one selected from dimethyl 2,2'-azobis(isobutyrate) and methyl 1,1'-azobis(cyclohexanecarboxylate) is preferred from the viewpoints of half-life temperature, cost, etc.

[0043] Polymerization initiators commonly used in radical polymerization methods include azo polymerization initiators and peroxide polymerization initiators. 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. If the polymerization initiator has high hydrogen abstraction capacity, for example, when methyl methacrylate is used as the monomer, the free radicals generated by 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. As a result, polymers with terminal double bonds derived from the monomer structure are likely to be produced. Therefore, when a polymerization initiator with high hydrogen abstraction capacity is used, the resulting methacrylic resin tends to have insufficient thermal stability. Therefore, azo polymerization initiators are more suitable than peroxide polymerization initiators for obtaining methacrylic resins with high thermal stability.

[0044] The hydrogen abstraction ability of the polymerization initiator can be measured, for example, by a radical trapping method using α-methylstyrene dimer (that is, α-methylstyrene dimer trapping method).

[0045] The amount of the polymerization initiator used is preferably 0.1 part by mass or less, more preferably 0.05 part by mass or less, and even more preferably 0.04 part 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 part by mass or more, relative to 100 parts by mass of the total amount of the monomer mixture.

[0046] Examples of chain transfer agents 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.

[0047] 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.

[0048] The amount of the chain transfer agent used is 0.10 mol % or more, preferably 0.15 mol % or more, based on the total amount of the monomer mixture. There is no upper limit to the amount of the chain transfer agent used, but it is preferably 0.45 mol % or less, based on the total amount of the monomer mixture.

[0049] By using the chain transfer agent in the above-mentioned amount, a methacrylic resin containing a structure derived from the chain transfer agent can be obtained. Examples of the structure derived from the chain transfer agent include, for example, a structure (i.e., a saturated bond terminal structure) generated by the reaction of a propagating radical with hydrogen from the alkyl mercaptan chain transfer agent or thioglycolic acid ester when an alkyl mercaptan chain transfer agent or thioglycolic acid ester is used, and a resin structure (i.e., a sulfur-containing resin structure) generated by the reaction of a sulfur radical generated by hydrogen abstraction from the alkyl mercaptan chain transfer agent or thioglycolic acid ester with a monomer. In the methacrylic resin according to this embodiment, the amount of sulfur contained in the resin, i.e., the amount of bonded sulfur atoms, is preferably 0.05 mol% or more, and more preferably 0.10 mol% or more, from the viewpoint of the thermal stability of the resin. Here, the amount of bonded sulfur atoms is the amount relative to the structural units derived from the monomer in the methacrylic resin.

[0050] In order to reduce the proportion of terminal double bonds in the resulting methacrylic resin and improve thermal stability, the ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator is set to 2.0 or more. The ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator is preferably 4.0 or more, more preferably 8.0 or more, and even more preferably 10 or more. There is no particular upper 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, 50 or less.

[0051] The polymerization temperature during synthesis of the methacrylic resin is set to 100° C. or lower, preferably 20 to 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.

[0052] In order to initiate polymerization 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 keeping the dissolved oxygen content within this range, the polymerization reaction proceeds smoothly and coloration of the methacrylic resin molded body tends to be suppressed. A method for removing dissolved oxygen from the polymerization raw materials includes, for example, feeding an inert gas such as nitrogen gas into the reaction vessel before, during, and after heating to a predetermined polymerization temperature. To remove dissolved oxygen from raw materials added during polymerization, it is preferable to separately pass an inert gas through these raw materials.

[0053] 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.

[0054] 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 dispersant removal efficiency, and may be one or more times.

[0055] A conventionally known dehydration method can be used to separate the methacrylic resin from the suspension containing the methacrylic resin, such as a method using a centrifuge or a method of removing water by suction on a porous belt or a filter membrane.

[0056] The hydrous methacrylic resin obtained through the dehydration process can be dried and recovered by a conventional method. Examples of drying methods include hot air drying, which involves blowing hot air into a tank from a hot air blower, blow heater, or the like; vacuum drying, which involves reducing the pressure in the system and then heating it as needed; barrel drying, which involves rotating the resulting 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.

[0057] [Emulsion polymerization method] In the emulsion polymerization method, a methacrylic resin is synthesized in an emulsion containing water, a monomer mixture, an emulsifier, a polymerization initiator, a chain transfer agent, and optionally other additives.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Examples of the polymerization initiator and chain transfer agent include the same polymerization initiator and chain transfer agent as those used in the suspension polymerization method described above.

[0062] In order to reduce the proportion of terminal double bonds in the resulting methacrylic resin and improve thermal stability, the ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator is set to 2.0 or more. The ratio of the total molar amount of chain transfer agent to the total molar amount of polymerization initiator is preferably 4.0 or more, more preferably 8.0 or more, and even more preferably 10 or more. There is no particular upper 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, 50 or less.

[0063] 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 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. Commonly added additives such as antioxidants and UV absorbers may be added during coagulation.

[0064] 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.

[0065] In this embodiment, the methacrylic resin obtained by aqueous polymerization may be in the form of a powder, granules, or a powder-granular mixture containing both powder and granules. Regarding the primary particles constituting the powder, granules, and powder-granular mixture, suspension polymerization is suitable for producing primary particles having an average particle size of about 10 to 1,000 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 powder-granular mixture may contain aggregates, which are aggregates of the primary particles.

[0066] After the polymerization is completed, volatile components such as residual monomers, residual oligomers, and chain transfer agents in the methacrylic resin may be removed as needed. While the removal method is not particularly limited, thermal devolatilization is preferred. Examples of devolatilization methods include treatment using an extruder equipped with a vent. The extruder vent is preferably a vacuum vent or an open vent, and the extruder screw is preferably a twin-screw. Twin-screws impart greater shear energy to the resin than single-screws, resulting in a greater degree of surface renewal, allowing for more efficient devolatilization. The cylinder heating temperature of the extruder is preferably 150 to 270°C, more preferably 160 to 260°C, and even more preferably 180 to 250°C. Setting the cylinder heating temperature to 270°C or less can suppress thermal decomposition of the methacrylic resin.

[0067] <Resin composition> The resin composition according to this embodiment contains the methacrylic resin according to this embodiment described above.

[0068] The resin composition according to the present embodiment preferably contains an ultraviolet absorber from the viewpoint of further improving the light resistance of the resulting molded article. The ultraviolet absorber is not particularly limited, and ultraviolet absorbers that have conventionally been incorporated into various resins can be used. Examples of ultraviolet absorbers include benzotriazole compounds, triazine compounds, oxalic acid anilide compounds, cyanoacrylate compounds, salicylate compounds, and benzophenone compounds. Among these, triazine compounds are preferred from the viewpoint of the light resistance of the resin composition.

[0069] Examples of triazine compounds include 2,4-diphenyl-6-(2-hydroxyphenyl-4-hexyloxyphenyl)-1,3,5-triazine, 2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-(octyloxy)phenol, 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]phenol, 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol, and 2,4,6-tris(2-hydroxy-4-alkoxy-3-methylphenyl)-1,3,5-triazine. The alkoxy group contained in 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.

[0070] Among these triazine compounds, 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol and 2,4,6-tris(2-hydroxy-4-alkoxy-3-methylphenyl)-1,3,5-triazine are preferred. 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol is available as Adeka STAB LA-46 (manufactured by ADEKA Corporation). 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine is available as Adeka STAB LA-F70 (manufactured by ADEKA Corporation). These ultraviolet absorbers may be used alone or in combination of two or more.

[0071] When the resin composition according to the present embodiment contains an ultraviolet absorber, the amount used varies depending on the type of ultraviolet absorber, the conditions of use, etc., but is preferably 0.1 to 5 parts by mass, and more preferably 0.2 to 3 parts by mass, per 100 parts by mass of the methacrylic resin. When the amount of ultraviolet absorber used is 0.1 part by mass or more, the ultraviolet absorption effect can be improved. Furthermore, when the amount of ultraviolet absorber used is 5 parts by mass or less, coloration of the resulting molded article can be suppressed, and deterioration of transparency due to an increase in haze of the molded article can be suppressed.

[0072] Furthermore, the resin composition according to the present embodiment preferably contains multilayer structure polymer particles from the viewpoint of further improving the thermal stability and mechanical properties of the resulting molded article. The multilayer structure 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, 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, heat stabilizers, matting agents, light diffusing agents, colorants, dyes, pigments, antistatic agents, heat reflective 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] <Molded body> The methacrylic resin according to the present embodiment or the resin composition according to the present embodiment can be molded into a molded article by a known molding method, such as a melt molding method such as a T-die method (lamination method, co-extrusion method, etc.), an inflation method (co-extrusion method, etc.), a compression molding method, a blow molding method, a calendar molding method, a vacuum molding method, or an injection molding method (insert method, two-color method, press method, core-back method, sandwich method, etc.); a solution casting method; or the like.

[0078] <Resin film> The resin film according to this embodiment contains the methacrylic resin according to this embodiment described above. The resin film according to this embodiment is produced, for example, by a melt extrusion method using the resin composition according to this embodiment described above. When producing a resin film by the melt extrusion method, the resin composition according to this embodiment is first pre-dried, then fed to an extruder, heated and melted, and fed to a T-die. Next, the resin composition fed to the T-die is extruded as a sheet-shaped molten resin, and cooled and solidified using a cooling roll or the like to obtain a resin film.

[0079] 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. 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. When 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-drawn portion. Another advantage is that a resin film with uniform optical properties and good transparency can be produced.

[0080] The total light transmittance of the resin film according to this embodiment is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. If the total light transmittance is within the above range, the transparency is high, and the film can be suitably used for optical applications that require light transmittance.

[0081] The glass transition temperature of the resin film according to this embodiment is preferably 110° C. or higher, more preferably 115° C. or higher, and even more preferably 120° C. or higher. If the glass transition temperature is within the above range, the resin film will have sufficient heat resistance.

[0082] 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 transparency. The haze consists of the haze inside the film and the haze on the film surface (external), and these are referred to as internal haze and external haze, respectively.

[0083] The resin film according to this embodiment preferably has a YI (Yellow Index) of 1.2 or less, more preferably 1.0 or less. If the YI is within the above range, the film has high transparency and can be suitably used for optical applications that require light transmittance.

[0084] The resin film according to this embodiment preferably contains an ultraviolet absorber from the viewpoint of further improving light resistance. The ultraviolet absorber aims to improve light resistance by absorbing ultraviolet light with a wavelength of 400 nm or less. The resin film according to this embodiment preferably has a transmittance at a wavelength of 380 nm in the range of 2 to 30%, more preferably in the range of 4 to 20%, and even more preferably in the range of 5 to 10%.

[0085] 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 directions (length direction and 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.

[0086] The retardation is an index value calculated based on birefringence. The in-plane retardation (Re) and thickness direction retardation (Rth) can be calculated using the following formulas. In an ideal resin film that is completely optically isotropic in three-dimensional directions, both the in-plane retardation Re and thickness direction retardation Rth are 0.

[0087] Re=(nx-ny)×d Rth = [(nx + ny) / 2 - nz] × d In the above formula, 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.

[0088] The resin film according to this embodiment preferably has an orientation birefringence value of −5.0×10 -4 ~5.0×10 -4 , more preferably -4.0 × 10 -4 ~4.0×10 -4 , and more preferably −3.8×10 -4 ~3.8×10 -4If the orientation birefringence is within the above range, birefringence does not occur during molding and stable optical properties tend to be obtained.

[0089] (Stretching) The resin film according to this embodiment may be further stretched. By stretching the resin film, it is possible to improve the mechanical strength of the resin film and improve the film thickness accuracy.

[0090] When stretching the resin film according to the present embodiment, an unstretched resin film is first formed from the resin composition according to the present embodiment, and then uniaxially or biaxially stretched, thereby producing a stretched film (uniaxially or biaxially stretched film).

[0091] 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 the range of 1.3 to 4, and even more preferably from the range of 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.

[0092] (Application) The resin film according to this embodiment can be used in various applications such as transportation equipment, solar cell components, civil engineering and construction components, daily necessities, electrical and electronic devices, optical components, and medical supplies. In particular, the resin film according to this embodiment has excellent heat resistance and optical properties, and is therefore suitable 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.

[0093] 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, if necessary. When the resin film according to the present embodiment is used as a polarizer protective film, the resin film according to the present embodiment is bonded to a polarizer to form a polarizing plate. The polarizer is not particularly limited, and any conventionally known polarizer can be used. This polarizing plate is used in display devices such as liquid crystal display devices and organic EL display devices. [Example]

[0094] 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.

[0095] (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 determined by the following analysis. The weight of the methacrylic resin in Comparative Examples 2 and 3 was calculated by the weight of the methacrylic resin obtained by precipitation purification after polymerization. (Analysis conditions) Analysis was performed using a gas chromatograph (Agilent Technologies, 7890B) with a DB-1 analytical column (Agilent Technologies, 0.8 μm film thickness, 0.20 mm internal diameter, 30 m length) at an inlet temperature of 150°C and a detector temperature of 320°C. The column temperature was increased from 35°C to 210°C at a rate of 30°C / min, then from 210°C to 260°C at a rate of 10°C / min, and then from 260°C to 320°C at a rate of 20°C / min, where it was held for 3 minutes. A calibration curve was prepared using chlorobenzene as an internal standard, and the amount of residual monomer in the methacrylic resin was calculated. The polymerization conversion was then calculated.

[0096] (2) Syndiotacticity (rr) Methacrylic resin 1 The H-NMR spectrum was measured using a nuclear magnetic resonance spectrometer (Bruker, AVANCEIII 400MHz) 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 were measured when tetramethylsilane (TMS) was set to 0 ppm, and then the syndiotacticity (rr) in triad notation was calculated using the formula: (X / Y) × 100.

[0097] (3) Weight average molecular weight (Mw) and the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) The weight-average molecular weight (Mw), number-average molecular weight (Mn), and the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) of the methacrylic resin were calculated by the standard polystyrene conversion method using gel permeation chromatography (GPC). Specifically, analysis was performed using a sample solution prepared by dissolving 20 mg of methacrylic resin in 10 mL of tetrahydrofuran with the following equipment and conditions. Measuring 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℃ Standard material: Standard polystyrene (Tosoh)

[0098] (4) Percentage of terminal double bonds For Examples 1 to 5 and Comparative Example 1, as a pretreatment, the methacrylic resin was dissolved in methylene chloride, and the solution was added dropwise to methanol to precipitate and purify the resin. The precipitated resin was collected by suction filtration, dried, and then subjected to analysis. For Comparative Examples 2 and 3, the reaction solution after polymerization was added dropwise to methanol to precipitate and purify the resin, and the resin obtained after drying was subjected to analysis as it was. A solution of 20 mg of the dried methacrylic resin was prepared in 0.6 to 0.7 mL of deuterated chloroform, and the resin was analyzed 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 5.53 ppm and 6.21 ppm) derived from the terminal double bonds of the methacrylic resin and the area (Y) of the peaks (0.5 to 1.25 ppm) derived from the α-methyl groups of the methacrylic resin were measured, and then the proportion of the terminal double bonds of the methacrylic resin was calculated using the formula: [(3 × X) / (2 × Y)] × 100.

[0099] (5) Glass transition temperature (Tg) The glass transition temperature of the methacrylic resin was measured using the following method. As a pretreatment, the methacrylic resin was heat-treated using a thermogravimetric analyzer (STA7200, Hitachi High-Tech Science Corporation) to remove residual monomers and decomposition products of the polymerization initiator. Specifically, the heat treatment was performed under conditions of a 200 mL / min nitrogen flow, heating from 40°C to 270°C at a rate of 10°C / min, and holding at 270°C for 2.0 to 2.5 minutes. The glass transition temperature (Tg) of the heat-treated methacrylic resin was measured using a differential scanning calorimeter (DSC; DSC7000X, Hitachi High-Tech Science Corporation). 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 the sample was cooled to 40 ° C., followed by a second temperature increase at a heating rate of 10 ° C. / min from 40 ° C. to 160 ° C. DSC measurements were performed under these conditions. Then, from the DSC curve measured during the second temperature increase, the midpoint glass transition temperature (the temperature at the point where the curve of the stepwise change in the glass transition intersects with a line equidistant in the vertical direction from both a line extrapolated from the baseline before the inflection point to the higher temperature side and a line extrapolated from the baseline after the inflection point to the lower temperature side) was read.

[0100] (6) Retention thermal stability The retention thermal stability of the methacrylic resin was evaluated using a thermogravimetric analyzer (STA7200, Hitachi High-Tech Science Corporation). First, to remove residual monomers and decomposition products of the polymerization initiator in the methacrylic resin, the sample was heat-treated under conditions of a 200 mL / min nitrogen flow, where the temperature was increased from 40°C to 270°C at a rate of 10°C / min and held at 270°C for 2.0 to 2.5 minutes. Next, after cooling to 40°C, the sample was heated from 40°C to 280°C at a rate of 10°C / min and held at 280°C for 30 minutes, and the mass change was recorded. The mass when the sample temperature reached 280°C was X0, and the mass after holding at 280°C for 15 minutes was X. 15 The formula is: (X0-X 15 The retention thermal stability was evaluated from the mass loss rate calculated by [( ...

[0101] (7) Bonded sulfur atomic weight The amount of bonded sulfur atoms in the methacrylic resin was determined as follows. As a pretreatment, the methacrylic resin was dissolved in methylene chloride, and the solution was added dropwise to methanol to precipitate and purify the resin. The precipitated resin was collected by suction filtration, dried, and then subjected to analysis. An appropriate amount of the dried methacrylic resin was precisely weighed to a constant volume, placed in an automatic sample combustion apparatus (Nitto Seiko Air Analytec Co., Ltd., AQF-2100), and decomposed at high temperature. The generated gas was absorbed with ultrapure water containing hydrogen peroxide and hydrazine hydrate. The resulting liquid (aqueous decomposition gas solution) was used to quantify sulfate ions using an ion chromatograph (Thermo Fisher Scientific, Integrion RFIC, columns: AG18-4 μm, AS18-4 μm). Next, the mass of sulfur atoms per mass of the dried methacrylic resin, Wp (mass%), was calculated. Furthermore, the amount of bonded sulfur atoms, Sp (mol%), was calculated using the following formula: Sp=Wp×(100 / 32)

[0102] (8) 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 performed with both sides of the resin film sandwiched 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.

[0103] (9) 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.

[0104] (10) Light transmittance at a wavelength of 380 nm The light transmittance of the stretched resin film at a wavelength of 380 nm was measured using an ultraviolet-visible spectrophotometer (V-560, manufactured by JASCO Corporation).

[0105] (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.

[0106] 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 (a suspension aid), and 0.037 parts by mass of 2,2'-azobis(isobutyrate)dimethyl (V-601, Fujifilm Wako Pure Chemical Industries, Ltd.). While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was passed through to purge the air inside the reactor. Then, a monomer solution containing 100 parts by mass of methyl methacrylate (MMA) and 0.322 parts by mass of n-octyl mercaptan (n-OM), a chain transfer agent, was added to the reactor. Next, 0.375 parts by mass of the water-soluble polymer Metolose 60SH-50 (hydroxypropyl methylcellulose, Shin-Etsu Chemical Co., Ltd.), used as a dispersant, was added to the reactor. After stirring for 30 minutes, the temperature of the solution in the reactor was raised to 81°C to initiate polymerization. After reacting the monomers at 81°C for 4.5 hours, 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 complete the polymerization. The average temperature throughout the polymerization, from the time the temperature was raised to 81°C until the end of the polymerization, was 84°C. The resulting resin was washed with deionized water in an amount 3.9 times the resin volume and then dried to obtain beads of methacrylic resin. The physical properties of the resulting methacrylic resin are shown in Table 1.

[0107] <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 (a suspension aid), and 0.037 parts by mass of 2,2'-azobis(isobutyrate)dimethyl (V-601, Fujifilm Wako Pure Chemical Industries, Ltd.). While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was passed through the reactor to purge the air inside. Then, a monomer solution containing 100 parts by mass of methyl methacrylate (MMA) and 0.220 parts by mass of n-octyl mercaptan (n-OM), a chain transfer agent, was added to the reactor. Next, 0.375 parts by mass of the water-soluble polymer Metolose 60SH-50 (hydroxypropyl methylcellulose, Shin-Etsu Chemical Co., Ltd.), used as a dispersant, was added to the reactor. After stirring for 30 minutes, the temperature of the solution in the reactor was raised to 78°C to initiate polymerization. After reacting the monomers at 78°C for 6.5 hours, the temperature of the liquid in the reactor was raised to 93°C. The reaction liquid was stirred at the same temperature for 1 hour to complete the polymerization. The average temperature throughout the polymerization, from the time the temperature was raised to 78°C until the end of the polymerization, was 80°C. The resulting resin was washed with deionized water in an amount 2.9 times the resin volume and then dried to obtain beads of methacrylic resin. The physical properties of the resulting methacrylic resin are shown in Table 1.

[0108] Example 3 A 4-liter glass reactor equipped with an H-shaped impeller stirrer was charged with 150 parts by weight of deionized water, 0.140 parts by weight of tribasic calcium phosphate (dispersant), 0.0075 parts by weight of sodium α-olefin sulfonate, and 0.30 parts by weight 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 purge the air inside the reactor. Then, a monomer solution containing 100 parts by weight of methyl methacrylate (MMA), 0.289 parts by weight of n-octyl mercaptan (n-OM) as a chain transfer agent, and 0.037 parts by weight of dimethyl 2,2'-azobis(isobutyrate) (V-601, 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. One hour and 40 minutes after the start of polymerization, an additional 0.10 parts by mass of tricalcium phosphate was added to the reaction solution. The temperature of the solution in the reactor was then gradually increased until it reached 87°C four hours after the start of polymerization. At that point, 0.22 parts by mass of tricalcium phosphate was added to the reaction solution. After another 10 minutes, 0.037 parts by mass of dimethyl 2,2'-azobis(isobutyrate) was added to the reaction solution. The temperature of the solution in the reactor was then increased to 95°C, and stirring was continued at 95°C for 1 hour and 30 minutes, at which point the polymerization was terminated. The average temperature throughout the polymerization, from the time the temperature was increased to 80°C until the end of polymerization, was 87°C. Acid washing was performed using 0.1 times the weight of 1N hydrochloric acid relative to the amount of charged monomer, followed by water washing and drying, yielding beads of methacrylic resin. The physical properties of the resulting methacrylic resin are shown in Table 1.

[0109] The obtained methacrylic resin was extruded at a resin temperature of 255°C using a 15 mm diameter intermeshing co-rotating twin-screw extruder (manufactured by Technovel Corporation, KZW15TWIN-45MG, L / D = 45). The resin that came out as strands from a die provided at the extruder outlet was cooled in a water tank and then pelletized in a pelletizer to obtain a resin composition.

[0110] The resulting resin composition was dried at 90°C for 4 hours and then extruded at a resin temperature of 240°C using a 15mm diameter intermeshing co-rotating twin-screw extruder (Technovel Corporation, KZW15TWIN-45MG, L / D=45) equipped with a T-die at the extruder outlet. The sheet-like molten resin extruded from the T-die was cooled with a cooling roll to obtain a resin film 130mm wide and 160µm thick.

[0111] A 100 mm x 100 mm piece was cut from the resulting resin film so that two sides were parallel to the extrusion direction. The piece was placed in a pantograph-type biaxial stretching device and simultaneously biaxially stretched at 137°C by 2 times in the direction parallel to the extrusion direction and 2 times in the direction perpendicular to the extrusion direction. The stretching speed in each direction was 100 mm / min. The piece was then removed from the extrusion film and quenched at room temperature to obtain a resin film with a thickness of 39 μm. The physical properties of the resin film are shown in Table 1.

[0112] Example 4 100 parts by mass of the methacrylic resin obtained in Example 3 was mixed with 0.7 parts by mass of an ultraviolet absorber (ADEKA STAB LA-F70, manufactured by ADEKA CORPORATION), and the mixture was kneaded and extruded at 255°C using a 15 mm diameter intermeshing co-rotating twin-screw extruder (TECHNOBEL CORPORATION, KZW15TWIN-45MG, L / D=45). The resin that emerged as strands from a die installed at the extruder outlet was cooled in a water tank and then pelletized using a pelletizer to obtain a resin composition.

[0113] Using the obtained resin composition, a resin film having a width of 130 mm and a thickness of 160 μm was obtained in the same manner as in Example 3. This resin film was then simultaneously biaxially stretched in the same manner as in Example 3 to obtain a resin film having a thickness of 39 μm. The physical properties of the resin film are shown in Table 1.

[0114] <Example 5> A glass sample bottle was charged with 150 parts by weight of deionized water, 0.400 parts by weight of tribasic calcium phosphate (dispersant), 0.0075 parts by weight of sodium α-olefin sulfonate, and 0.30 parts by weight of sodium chloride. While stirring the aqueous solution in the sample bottle with a stirrer, a monomer solution containing 100 parts by weight of methyl methacrylate (MMA), 0.093 parts by weight of dimethyl 2,2'-azobis(isobutyrate) (Fujifilm Wako Pure Chemical Industries, Ltd., V-601) (polymerization initiator), and 0.289 parts by weight of n-octyl mercaptan (n-OM) (chain transfer agent) was added. The suspension in the sample bottle was transferred to a 120 mL metal pressure vessel equipped with a semicircular stirrer. The air in the vessel was then purged by passing nitrogen gas (oxygen concentration 0.2 ppm) through the vessel while stirring at 150 rpm. The liquid temperature in the reactor was then raised to 97°C to initiate polymerization, and the polymerization was terminated after 5 hours and 20 minutes of reaction. The average temperature throughout the polymerization, from when the temperature was raised to 97°C until the end of polymerization, was 97°C. The liquid in the reactor was cooled and then discharged. Acid washing was performed using 1N hydrochloric acid in an amount 0.5 times the weight of the charged monomer, followed by water washing and drying to obtain beads of methacrylic resin. The physical properties of the resulting methacrylic resin are shown in Table 1.

[0115] <Comparative 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 (suspension aid), and 0.040 parts by mass of 2,2'-azobis(2,4-dimethylvaleronitrile) (V-65, Fujifilm Wako Pure Chemical Industries, Ltd.). While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was introduced to purge the air from the reactor. Then, a monomer 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 the water-soluble polymer Metolose 60SH-50 (hydroxypropyl methylcellulose, Shin-Etsu Chemical Co., Ltd.) as a dispersant was added to the reactor. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 70°C to initiate polymerization. After reacting the monomers at 70°C for 6 hours, the liquid in the reactor was heated to 95°C. The reaction liquid was stirred at the same temperature for 1 hour to terminate the polymerization. The average temperature throughout the polymerization, from the time the temperature was raised to 70°C until the end of polymerization, was 74°C. The resulting resin was washed with deionized water in an amount 7.0 times the resin volume and then dried to obtain beads of methacrylic resin. The physical properties of the resulting methacrylic resin are shown in Table 1.

[0116] <Comparative Example 2> A 120 mL metal pressure vessel equipped with a U-shaped stirrer was charged with 1,800 parts by mass of o-dichlorobenzene as the polymerization solvent, followed by a monomer solution containing 100 parts by mass of methyl methacrylate (MMA), 0.037 parts by mass of 2,2'-azobis(isobutyrate)dimethyl (V-601, Fujifilm Wako Pure Chemical Industries, Ltd.) as the polymerization initiator, and 0.289 parts by mass of n-octyl mercaptan (n-OM) as the chain transfer agent. Nitrogen gas (oxygen concentration 50 ppm) was passed through the reaction vessel to displace the air inside the vessel, and the temperature of the solution in the reaction vessel was raised to approximately 140 °C while stirring to initiate polymerization. The monomer was allowed to react at approximately 140 °C for an additional 6 hours, at which point the polymerization was deemed complete. The average temperature throughout the polymerization, from the time the temperature rose to approximately 140 °C until the end of polymerization, was 142 °C. The solution in the reaction vessel was cooled and then discarded, and the reaction solution was added dropwise to methanol to precipitate the resin. The precipitated resin was collected by filtration and then dried to obtain a methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 1.

[0117] <Comparative Example 3> A 2-liter glass reactor equipped with a three-way, swept-back blade stirrer was charged with 339 parts by mass of methanol as the polymerization solvent, followed by a monomer solution containing 100 parts by mass of methyl methacrylate (MMA) and 2.46 parts by mass of 2,2'-azobis(isobutyrate)dimethyl (V-601, Fujifilm Wako Pure Chemical Industries, Ltd.) as the polymerization initiator. While stirring the aqueous solution in the reactor at 220 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was passed through the reactor to displace the air inside the reactor. The temperature of the solution in the reactor was then raised to 60°C while stirring to initiate polymerization. The monomer was allowed to react at 60°C for an additional 3 hours, at which point the polymerization was deemed complete. The resulting resin precipitated at the bottom of the reactor. The average temperature throughout the polymerization, from the time the temperature was raised to 60°C until the end of polymerization, was 60°C. After cooling the liquid in the reaction vessel, the resin precipitated at the bottom of the reaction vessel was dissolved in 400 parts by weight of chloroform, and the chloroform solution was added dropwise to 2,500 parts by weight of methanol to reprecipitate the resin. The reprecipitated resin was collected by filtration and then dried to obtain a methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 1.

[0118] [Table 1]

[0119] As shown in Table 1, Example 1, which used the non-nitrile azo polymerization initiator dimethyl 2,2'-azobis(isobutyrate), had a smaller weight loss rate and higher retention heat stability when maintained at 280°C for 15 minutes than Comparative Example 1, which used the nitrile azo polymerization initiator 2,2'-azobis(2,4-dimethylvaleronitrile) at the same usage ratio (mol%). Example 2, which used the non-nitrile azo polymerization initiator dimethyl 2,2'-azobis(isobutyrate) at the same usage ratio (mol%) as Example 1 but used a lower usage ratio (mol%) of the chain transfer agent n-octyl mercaptan (n-OM), also had a smaller weight loss rate and higher retention heat stability when maintained at 280°C for 15 minutes than Comparative Example 1, which used the nitrile azo polymerization initiator 2,2'-azobis(2,4-dimethylvaleronitrile). Furthermore, Example 3, in which the proportion (mol%) of the non-nitrile azo polymerization initiator, 2,2'-azobis(isobutyrate)dimethyl was used higher than in Example 1 and the proportion (mol%) of the chain transfer agent, n-octyl mercaptan (n-OM), was lower than in Example 1, also showed a smaller weight loss rate when maintained at 280°C for 15 minutes and higher residence heat stability than Comparative Example 1, in which the nitrile azo polymerization initiator, 2,2'-azobis(2,4-dimethylvaleronitrile), was used. In addition, when Example 3 and Example 4 were compared, Example 4, in which an ultraviolet absorber was added, showed a smaller light transmittance at a wavelength of 380 nm than Example 3. Furthermore, in Example 5, in which the usage ratio (mol%) of the non-nitrile azo polymerization initiator, 2,2'-azobis(isobutyrate)dimethyl, was higher than in Example 3 and the average polymerization temperature was higher than in Example 3, the weight loss rate when maintained at 280°C for 15 minutes was smaller and the retention thermal stability was higher than in Comparative Example 1, in which the nitrile azo polymerization initiator, 2,2'-azobis(2,4-dimethylvaleronitrile), was used.

[0120] In Comparative Example 2, polymerization was performed under conditions where the average polymerization temperature exceeded 100°C. Although the non-nitrile azo polymerization initiator, 2,2'-azobis(isobutyrate)dimethyl, was used in the same proportion (mol%) as in Examples 1 and 2, the weight loss rate when maintained at 280°C for 15 minutes was larger and the residence heat stability was poorer than in Examples 1 and 2. In Comparative Example 3, in which the resin was polymerized without using a chain transfer agent, the proportion of terminal double bonds was higher and the weight loss rate when maintained at 280°C for 15 minutes was also larger and the residence heat stability was poorer than in Examples 1 to 5.

Claims

1. 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 non-nitrile azo polymerization initiator and a chain transfer agent at 100°C or less until a polymerization conversion rate reaches 90% or more, the amount of the chain transfer agent used is 0.10 mol % or more based on the total amount of the monomer mixture; A method for producing a methacrylic resin, wherein the ratio of the total molar amount of the chain transfer agent to the total molar amount of the non-nitrile azo polymerization initiator is 2.0 or more.

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

3. The non-nitrile azo polymerization initiator comprises at least one selected from 2,2'-azobis(isobutyric acid) dimethyl and 1,1'-azobis(cyclohexane carboxylate) methyl. The method for producing a methacrylic resin according to claim 1 or 2.

Images