Polarizer protective film, polarizing plate, and display device

Abstract

The present invention provides a polarizer protective film containing a methacrylic resin with excellent thermal stability, as well as a polarizer plate and display device using the polarizer protective film. [Solution] The polarizer protective film according to the present invention is a polarizer protective film containing a methacrylic resin, wherein the proportion of structural units derived from methyl methacrylate is 98% by mass or more, the triple-represented syndiotacticity is 55% or more, it contains terminal structures represented by formula (1) derived from a polymerization initiator, and the proportion of terminal double bonds to structural units derived from methyl methacrylate is less than 0.020 mol%. 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. However, R 1 , R 2 , and R 3 At least one of them represents an ester group or an amide group. TIFF2026062785000007.tif34134

Description

[Technical Field]

[0001] The present invention relates to a polarizer protective film, a polarizing plate, and a display device. [Background technology]

[0002] Methacrylic resin is widely used in various fields due to its excellent transparency, weather resistance, and processability. In particular, resin films obtained by molding methacrylic resin are 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 mainly composed of methyl methacrylate in the presence of a polymerization initiator and a chain transfer agent (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2019 / 088025 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, the inventors' investigations revealed that depending on conditions such as the type of polymerization initiator used during the synthesis of methacrylic resin, the thermal stability of the resulting methacrylic resin can decrease.

[0005] The present invention aims to provide a polarizer protective film containing a methacrylic resin with excellent thermal stability, as well as a polarizer plate and a display device using the polarizer protective film. [Means for solving the problem]

[0006] The following embodiments are specific means for solving the above problems. <1> The proportion of the structural unit derived from methyl methacrylate is 98% by mass or more, the syndiotacticity of the triad display is 55% or more, it contains a terminal structure represented by the following formula (1) derived from a polymerization initiator, a methacrylic resin in which the proportion of the terminal double bond with respect to the structural unit derived from methyl methacrylate is less than 0.020 mol%. [Chemical formula] (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. However, at least one of R 1 , R 2 , and R 3 represents an ester group or an amide group. Two of R 1 , R 2 , and R 3 may be bonded to each other to form an alicyclic structure. * indicates a bond with a structural unit derived from a monomer.) <2> The methacrylic resin according to <1>, wherein the thermal weight loss rate when exposed to 280 °C for 15 minutes in a nitrogen gas atmosphere is less than 2.5%. <3> The methacrylic resin according to <1> or <2>, wherein the terminal structure represented by the formula (1) is a terminal structure derived from at least one selected from 2,2'-azobis(isobutyric acid)dimethyl and 1,1'-azobis(cyclohexanecarboxylic acid methyl). <4> The methacrylic resin according to any one of <1> to <3>, wherein the weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) is 50,000 to 200,000. <5> The methacrylic resin according to any one of <1> to <4>, wherein the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by gel permeation chromatography (GPC) is 1.6 to 2.5.

[0007] <6> A polymerization step is included, in which a monomer mixture having a methyl methacrylate content of 98% by mass or more is polymerized at 100°C or lower until a polymerization conversion rate reaches 90% or more in the presence of a non-nitrile azo polymerization initiator and a chain transfer agent. 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 mol amount of the chain transfer agent to the total mol amount of the non-nitrile azo polymerization initiator is 2.0 or more. <7> The method for producing a methacrylic resin according to <6>, wherein aqueous polymerization is carried out in the polymerization step. <8> The method for producing a methacrylic resin according to <6> or <7>, wherein the non-nitrile azo polymerization initiator contains at least one selected from 2,2'-azobis(isobutyric acid)dimethyl and 1,1'-azobis(cyclohexanecarboxylic acid methyl). <9> A resin composition containing the methacrylic resin according to any one of <1> to <5>. <10> The resin composition according to <9>, which contains an ultraviolet absorber. <11> A resin film containing the methacrylic resin according to any one of <1> to <5>. <12> The resin film according to <11>, which contains an ultraviolet absorber. <13> The resin film according to <11> or <12>, wherein the resin film is a polarizer protection film. <14> A polarizing plate formed by laminating a polarizer and the resin film according to any one of <11> to <13>. <15> A display device including the polarizing plate according to <14>.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a polarizer protective film containing a methacrylic resin with excellent thermal stability, as well as a polarizer plate and a display device using the polarizer protective film. [Modes for carrying out the invention]

[0009] The following describes in detail specific embodiments to which the present invention is applied. Unless otherwise specified, the symbol "~" which represents a numerical range is intended to include the lower and upper limits of that range.

[0010] <Methacrylic resin> The methacrylic resin according to this embodiment has a proportion of structural units derived from methyl methacrylate of 98% by mass or more, and a proportion of structural units derived from monomers other than methyl methacrylate of 2% by mass or less. Preferably, the methacrylic resin according to this embodiment has a proportion of structural units derived from methyl methacrylate of 99% by mass or more, and more preferably 100% by mass (i.e., it is 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; methacrylonitrile; and others.

[0013] The methacrylic resin according to this embodiment has a triple-representation syndiotacticity (rr) of 55% or more, preferably 56% or more, and more preferably 57% or more. When the triple-representation syndiotacticity (rr) is 55% or more, the glass transition temperature (Tg) of the methacrylic resin tends to increase, and the heat resistance tends to improve. There is no particular upper limit to the syndiotacticity (rr), but from the viewpoint of molding temperature and the toughness and secondary processability of the molded article, it is preferably 67% or less, more preferably 65% ​​or less, and even more preferably 63% or less.

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

[0015] Syndiotacticity (rr) was determined in deuterated chloroform at 22°C and with 16 cumulative cycles, as described in the examples below. 1By measuring the 1H-NMR spectrum, the area (X) of the region between 0.60 and 0.95 ppm (with tetramethylsilane (TMS) set to 0 ppm) and the area (Y) of the region between 0.60 and 1.25 ppm can be measured from the spectrum, and the result 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. The upper limit of the glass transition temperature (Tg) is not particularly limited, but from the viewpoint of molding processing temperature and secondary processability of the molded article, it is preferably 135°C or lower, and may also be 130°C or lower.

[0017] In this specification, the glass transition temperature (Tg) is the midpoint glass transition temperature determined from the DSC curve, and is measured by the method described in the examples below.

[0018] Furthermore, the syndiotacticity (rr) and glass transition temperature (Tg) of methacrylic resin can be controlled by adjusting the polymerization temperature during synthesis. 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] Furthermore, the methacrylic resin according to this embodiment includes an end structure represented by the following formula (1) derived from the 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. However, R 1 , R 2 , and R 3At least one of them represents an ester group or an amide group. 1 , R 2 , and R 3 Two of these may be bonded together to form an alicyclic structure. (* indicates a bond with a structural unit derived from a monomer.)

[0021] Examples of alkyl groups include linear or branched alkyl groups having 1 to 6 carbon atoms. Substituents that alkyl groups may have include hydroxyl groups, carboxyl groups, alkoxy groups, halogen atoms, and the like.

[0022] Examples of ester groups include -COOR 4 The group represented by R is an example. 4 This represents an alkyl group having 1 to 6 carbon atoms, and may have substituents such as a hydroxyl group, a carboxyl group, an alkoxy group, or a halogen atom.

[0023] Examples of amide groups include -C(O)NR 5 The group represented by R is an example. 5 This represents an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group, or an alkenyl group having 2 to 6 carbon atoms, and may have substituents such as a hydroxyl group, a carboxyl group, an alkoxy group, or a halogen atom.

[0024] The terminal structure represented by formula (1) above can be introduced into the molecule of methacrylic resin by using a non-nitrile azo polymerization initiator represented by formula (2) below when synthesizing methacrylic resin. 1 , R 2 , and R 3 This is equivalent to formula (1) above. Using such a non-nitrile azo polymerization initiator tends to improve the thermal stability of the resulting methacrylic resin compared to using polymerization initiators other than non-nitrile azo polymerization initiators (for example, nitrile azo polymerization initiators). Furthermore, non-nitrile azo polymerization initiators are preferable because they tend to have lower toxicity in the initiator itself and its decomposition products compared to nitrile azo polymerization initiators.

[0025] [ka]

[0026] Examples of non-nitrile azo polymerization initiators represented by formula (2) above include 2,2'-azobis(isobutyrate)dimethyl, 1,1'-azobis(cyclohexanecarboxylate methyl), 2,2'-azobis[N-(2-propenyl)-2-methylpropionamide], 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis(N-cyclohexyl-2-methylpropionamide), 2,2'-azobis{2-methyl-N-[2-(1-hydroxyethyl)]propionamide}, and 2,2'-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propionamide}. Among these, at least one selected from 2,2'-azobis(isobutyrate)dimethyl and 1,1'-azobis(cyclohexanecarboxylate methyl) is preferred from the viewpoint of half-life temperature, cost, etc.

[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%. When the ratio of terminal double bonds is within the above range, the thermal stability of the methacrylic resin tends to improve.

[0028] The methacrylic resin according to this embodiment can be produced by radical polymerization, as described in the production method below. Methacrylic resin produced by radical polymerization contains terminal double bonds generated by disproportionation termination reactions during polymerization, hydrogen abstraction reactions of monomers by polymerization initiators, etc. Since terminal double bonds affect the thermal stability of the resin, it is preferable to have a small proportion of them. The proportion of terminal double bonds can be controlled by the method described below, and if it 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 improve significantly.

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

[0030] The proportion of terminal double bonds in methacrylic resin can be controlled by adjusting the amount of polymerization initiator and chain transfer agent used, the polymerization temperature, and the polymerization time during the synthesis of the methacrylic resin. For example, reducing the amount of polymerization initiator, increasing the amount of chain transfer agent, lowering the polymerization temperature, and lengthening the polymerization time are preferable for reducing the proportion of terminal double bonds.

[0031] As described above, the methacrylic resin according to this embodiment exhibits excellent thermal stability. The methacrylic resin according to this embodiment preferably has a thermal weight loss rate of less than 2.5% when exposed to 280°C for 15 minutes in a nitrogen gas atmosphere, and more preferably less than 2.3%. This thermal weight loss rate 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 improve, and when the weight-average molecular weight (Mw) of the methacrylic resin is 200,000 or less, the moldability tends to improve.

[0033] Furthermore, the methacrylic resin according to this embodiment preferably has a dispersion degree (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 dispersion degree (Mw / Mn) of the methacrylic resin is 1.6 or higher, the fluidity of the methacrylic resin tends to improve, making it easier to mold, and when the dispersion degree (Mw / Mn) of the methacrylic resin is 2.5 or lower, the mechanical properties such as impact resistance, toughness, and bending resistance of the resulting molded article tend to improve.

[0034] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) used herein are values ​​on a standard polystyrene basis, measured by gel permeation chromatography (GPC), and are measured by the method described in the examples below.

[0035] Furthermore, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of methacrylic resin can be controlled by adjusting the type and amount of polymerization initiator and chain transfer agent used during the synthesis of the methacrylic resin.

[0036] The methacrylic resin according to this embodiment is expected to have excellent thermal stability and be suitable for reuse after disposal, i.e., recycling. As a method of recycling methacrylic resin, for example, chemical recycling (a method of recovering decomposition oil as a decomposition product by thermal decomposition and reusing it as a chemical raw material or fuel) is known. In general, in order to improve the heat resistance and thermal stability of methacrylic resin, a cyclic structure is introduced into the molecular structure of the methacrylic resin or monomers having a rigid structure are copolymerized. However, these structures become impurities in chemical recycling and are undesirable. In this respect, the methacrylic resin according to this embodiment has a large proportion of structural units derived from methyl methacrylate, and it is expected that the monomer recovered as decomposition oil will have a high yield, and is expected to exhibit good chemical recyclability.

[0037] <Methacrylic resin manufacturing method> The method for producing methacrylic resin according to this embodiment includes a polymerization step in which a monomer mixture having a methyl methacrylate content of 98% by mass or more is polymerized at 100°C or below in the presence of a non-nitrile azo polymerization initiator (hereinafter also simply referred to as "polymerization initiator") and a chain transfer agent until the polymerization conversion rate reaches 90% or more. Conventional known polymerization methods can be used as the method for producing methacrylic resin, and for example, radical polymerization methods such as continuous bulk polymerization, solution polymerization, emulsion polymerization, soap-free emulsion polymerization, and suspension polymerization can be used. Among these, from the viewpoint of the degree of freedom in structural design of the methacrylic resin, the simplicity of polymerization, and productivity, a method of production using aqueous polymerization is preferred, suspension polymerization and emulsion polymerization are more preferred, and suspension polymerization is even more preferred.

[0038] Furthermore, when the methacrylic resin according to this embodiment is produced by aqueous polymerization, it is also advantageous in terms of impurities in the resin. For example, in the anionic solution polymerization method, an organometallic compound is used as a polymerization initiator, so metal ions derived from the organometallic compound remain in the resin at a concentration of several hundred ppm by mass. On the other hand, in aqueous polymerization, an organometallic compound is not used as a polymerization initiator, so the total amount of residual metal ions in the resin can be kept below 100 ppm by mass. When aqueous polymerization is performed, it is preferable that the Al content in the resin is 1 ppm by mass or less, and the Li content is 1 ppm by mass or less. In addition, aqueous polymerization is economically superior because it does not require a step to remove residual metal ions. Furthermore, aqueous polymerization is environmentally friendly because it does not use organic solvents such as aliphatic hydrocarbons and alicyclic hydrocarbons used in methods such as anionic solution polymerization.

[0039] [Suspension polymerization] In the suspension polymerization method, 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 mixing each component simultaneously. Alternatively, an aqueous solution may be prepared by mixing water, a polymerization initiator, and optionally other additives, followed by the addition of the monomer mixture and chain transfer agent, and then the addition of the dispersant to prepare the aqueous suspension. 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] As the monomer mixture, one is used in which the methyl methacrylate content is 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, methylcellulose, polyacrylamide, and polyvinylpyrrolidone. When using poorly water-soluble inorganic salts as dispersants, it is effective to use anionic surfactants such as sodium α-olefin sulfonate and sodium dodecylbenzenesulfonate in combination. These dispersants may be added during polymerization as needed.

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

[0043] Generally, polymerization initiators used in radical polymerization include azo polymerization initiators and peroxide polymerization initiators. Free radicals generated from polymerization initiators are known to undergo hydrogen abstraction reactions in addition to addition reactions to monomers, if a substance that readily donates hydrogen is present. In this respect, azo polymerization initiators only generate alkyl radicals, and therefore have lower hydrogen abstraction ability compared to peroxide polymerization initiators. If the hydrogen abstraction ability of the polymerization initiator is high, for example, when methyl methacrylate is used as the monomer, hydrogen is abstracted from the α-methyl group of methyl methacrylate or the methyl group of the ester by the free radicals generated from the polymerization initiator, and polymerization proceeds from the newly generated radicals on the α-methyl group or the methyl group of the ester, resulting in the formation of a polymer in which double bonds derived from the monomer structure remain at the ends. Therefore, when a polymerization initiator with high hydrogen abstraction ability is used, the thermal stability of the resulting methacrylic resin tends to be insufficient. Thus, to obtain a methacrylic resin with high thermal stability, azo polymerization initiators are preferable to peroxide polymerization initiators.

[0044] The hydrogen abstraction ability of polymerization initiators can be measured, for example, by radical trapping using α-methylstyrene dimer (i.e., α-methylstyrene dimer trapping).

[0045] The amount of polymerization initiator used is preferably 0.1 parts by mass or less, more preferably 0.05 parts by mass or less, and even more preferably 0.04 parts by mass or less, per 100 parts by mass of the total amount of monomer mixture. There is no particular lower limit to the amount of polymerization initiator used, but from the viewpoint of polymerization rate, it is preferably 0.001 parts by mass or more, per 100 parts by mass of the total amount of 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, trimethylolpropanetris (thioglycolate), and pentaerythritol tetrakiss (thioglycolate); thiophenol, tetraethyl thiuram 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 individually or in combination of two or more.

[0047] Among these chain transfer agents, alkyl mercaptan-based chain transfer agents and thioglycolic acid esters are preferred from the viewpoint of handling, stability, and the thermal stability of the resulting methacrylic resin. Among alkyl mercaptan-based chain transfer agents, n-octyl mercaptan is more preferred, and among thioglycolic acid esters, 2-ethylhexyl thioglycolate is more preferred.

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

[0049] By using the above-mentioned amount of chain transfer agent, a methacrylic resin containing structures derived from the chain transfer agent can be obtained. Structures derived from the chain transfer agent include, for example, structures generated by the reaction between a growing radical and hydrogen of an alkyl mercaptan chain transfer agent or thioglycolic acid ester (i.e., saturated bond-end structures) when an alkyl mercaptan chain transfer agent or thioglycolic acid ester is used, or resin structures generated by the reaction of sulfur radicals, which are produced when hydrogen is abstracted from an alkyl mercaptan chain transfer agent or thioglycolic acid ester, with monomers (i.e., sulfur-containing resin structures). In the methacrylic resin according to this embodiment, the amount of sulfur contained in the resin, i.e., bound 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 bound sulfur atoms is the amount relative to the monomer-derived structural units in the methacrylic resin.

[0050] To reduce the proportion of terminal double bonds in the resulting methacrylic resin and improve its thermal stability, the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is set to 2.0 or higher. Preferably, the ratio is 4.0 or higher, more preferably 8.0 or higher, and even more preferably 10 or higher. There is no particular upper limit to the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator, but for example, it is preferably 50 or less.

[0051] The polymerization temperature when synthesizing methacrylic resin is set to 100°C or lower, preferably 20-100°C, more preferably 30-98°C, even more preferably 50-96°C, and particularly preferably 60-95°C, from the viewpoint of controlling the syndiotacticity of the resulting methacrylic resin and productivity. After completing the main reaction in the first polymerization step, a post-polymerization step may be carried out by raising the temperature higher than that of the first step in order to reduce the amount of residual monomer.

[0052] Furthermore, since polymerization is initiated with a small amount of polymerization initiator, it is preferable to carry out the polymerization reaction with a low amount of dissolved oxygen. 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 amount of dissolved oxygen within this range, the polymerization reaction proceeds smoothly, and discoloration of the molded methacrylic resin 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 is supplied to the reaction vessel before, during, and after raising the temperature to a predetermined polymerization temperature. In order to remove dissolved oxygen from the raw materials added during polymerization, it is preferable to separately pass an inert gas through these raw materials as well.

[0053] Furthermore, in order to ensure that the polymerization reaction proceeds smoothly, if the monomer mixture contains a polymerization inhibitor, it is preferable to remove the polymerization inhibitor by distillation, alkaline 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 methacrylic resin obtained by suspension polymerization may be washed using methods such as acid washing, water washing, or alkaline washing to remove the dispersant. The number of times these washing operations are performed should be selected to be optimal considering the work efficiency and the efficiency of dispersant removal, and may be performed once or multiple times.

[0055] Conventional dehydration methods can be used to separate methacrylic resin from a suspension containing methacrylic resin. Examples of dehydration methods include using a centrifuge, or removing water by suction on a porous belt or filter membrane.

[0056] The hydrated methacrylic resin obtained after the above dehydration process can be dried and recovered by conventionally known methods. Examples of drying methods include hot air drying, in which hot air is blown into a tank from a hot air fan, blow heater, etc.; vacuum drying, in which the system is depressurized and heated as needed; barrel drying, in which the moisture is removed by rotating the obtained methacrylic resin in a container; and spin drying, in which centrifugal force is used for drying. These drying methods may be carried out individually or in combination of two or more.

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

[0058] As the monomer mixture, one is used in which the methyl methacrylate content is 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, alkylbenzene sulfonates, dialkyl sulfosuccinates, α-olefin sulfonates, naphthalene sulfonate-formaldehyde condensates, alkylnaphthalene sulfonates, N-methyl-N-acyl taurate salts, and phosphate ester salts (such as polyoxyethylene alkyl ether phosphates); and nonionic surfactants. Examples of salts include lithium salts, sodium salts, potassium salts, calcium salts, and magnesium salts. These emulsifiers may be used individually or in combination of two or more. Note that emulsifiers 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, an appropriate pH adjuster can be used to prevent hydrolysis of the monomer methyl methacrylate or the 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 dihydrogen phosphate-citric acid.

[0061] Examples of polymerization initiators and chain transfer agents include those similar to those used in the suspension polymerization method described above.

[0062] To reduce the proportion of terminal double bonds in the resulting methacrylic resin and improve its thermal stability, the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is set to 2.0 or higher. Preferably, the ratio is 4.0 or higher, more preferably 8.0 or higher, and even more preferably 10 or higher. There is no particular upper limit to the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator, but for example, it is preferably 50 or less.

[0063] Solid or powdered methacrylic resin can be obtained by subjecting the latex of methacrylic resin obtained by emulsion polymerization to heat drying or spray drying, or by subjecting it to known methods such as adding a water-soluble electrolyte such as a salt or acid to solidify it, then performing heat treatment and separating the resin component from the aqueous phase and drying it. The salts mentioned above are not particularly limited, but divalent salts are preferred, specifically calcium salts such as calcium chloride and calcium acetate; magnesium salts such as magnesium chloride and magnesium sulfate; and among these salts, magnesium salts such as magnesium chloride and magnesium sulfate are preferred. During solidification, commonly added additives such as antioxidants and ultraviolet absorbers may be added.

[0064] Prior to the above solidification operation, it is preferable to filter the latex using a filter, mesh, etc., to remove fine polymerization scale. This reduces fish eyes and foreign matter caused by fine polymerization scale when the methacrylic resin is molded into an article.

[0065] In this embodiment, the methacrylic resin obtained by aqueous polymerization may be in the form of a powder, granules, or a powder-granule mixture containing both powder and granules. For the powder, granules, and primary particles constituting the powder-granule mixture, suspension polymerization is preferred when producing primary particles with an average particle diameter of about 10 to 1,000 μm, and emulsion polymerization is preferred when producing primary particles with an average particle diameter of about 50 to 500 nm. The powder, granules, and powder-granule mixture may contain aggregates which are aggregates of the above primary particles.

[0066] After polymerization is complete, volatile components such as residual monomers, residual oligomers, and chain transfer agents in the methacrylic resin may be removed as needed. The removal method is not particularly limited, but heat defloration is preferred. As a defloration method, for example, treatment with an extruder equipped with a vent can be used. The extruder vent is preferably a vacuum vent or an open vent, and the extruder screw is preferably a twin-screw. A twin-screw imparts greater shear energy to the resin and a greater degree of surface renewal compared to a single-screw, thus enabling efficient defloration. The cylinder heating temperature of the extruder is preferably 150 to 270°C, more preferably 160 to 260°C, and even more preferably 180 to 250°C. By setting the cylinder heating temperature to 270°C or lower, thermal decomposition of the methacrylic resin can be suppressed.

[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 this 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 various ultraviolet absorbers that have been conventionally incorporated into 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-triazine-2-yl]-5-(octyloxy)phenol, 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[(hexyl)oxy]phenol, 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol, and 2,4,6-tris(2-hydroxy-4-alkoxy-3-methylphenyl)-1,3,5-triazine. The alkoxy group 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-triazine-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol and 2,4,6-tris(2-hydroxy-4-alkoxy-3-methylphenyl)-1,3,5-triazine are preferred. 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol 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 UV absorbers may be used individually or in combination of two or more types.

[0071] When the resin composition according to this embodiment contains an ultraviolet absorber, the amount used is not uniform depending on the type of ultraviolet absorber, the usage conditions, etc., but it 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 methacrylic resin. If the amount of ultraviolet absorber used is 0.1 parts by mass or more, the ultraviolet absorption effect can be improved. Furthermore, if the amount of ultraviolet absorber used is 5 parts by mass or less, discoloration 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 this embodiment preferably contains multilayer polymer particles from the viewpoint of further improving the thermal stability and mechanical properties of the resulting molded article. The multilayer polymer particles are not particularly limited, and known ones can be used as appropriate.

[0073] When the resin composition according to this embodiment contains multilayer polymer particles, the blending ratio of methacrylic resin and multilayer polymer particles will vary depending on the intended use of the molded article, but it is preferable that the amount of methacrylic resin is 30 to 98 parts by mass and the amount of multilayer polymer particles is 2 to 70 parts by mass per 100 parts by mass of the total amount of both components.

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

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

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

[0077] <Molded body> The methacrylic resin or resin composition according to this embodiment can be molded into a molded article by known molding methods. Examples of molding methods include melt molding methods such as the T-die method (laminate method, co-extrusion method, etc.), inflation method (co-extrusion method, etc.), compression molding, blow molding, calendering, vacuum molding, and injection molding (insert method, two-color method, press method, core-back method, sandwich method, etc.); and solution casting.

[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 manufactured, for example, by a melt extrusion method using the resin composition according to this embodiment described above. When manufacturing the resin film by melt extrusion, first, the resin composition according to this embodiment is pre-dried, then supplied to an extruder to be heated and melted, and then supplied to a T-die. Next, the resin composition supplied to the T-die is extruded as a sheet of molten resin, and the resin film is obtained by cooling and solidifying it using a cooling roll or the like.

[0079] The thickness of the resin film according to this embodiment is preferably, for example, 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. Furthermore, the thickness of the resin film according to this embodiment is preferably, for example, 10 μm or more, more preferably 30 μm or more, even more preferably 50 μm or more, and particularly preferably 60 μm or more. When the thickness of the resin film is within the above range, there is an advantage that it is less likely to deform when vacuum forming is performed using the resin film, and that breakage in the deep-drawn section is less likely to occur. In addition, there is an advantage that a resin film with uniform optical properties and good transparency can be manufactured.

[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 therefore it can be suitably used in optical applications where light transmission is required.

[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 heat resistance of the resin film will be sufficient.

[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. If the haze and internal haze are within the above ranges, the transparency is high, making it suitable for optical applications where light transmittance is required. Note that the haze consists of internal haze and external haze on the film surface, and these are referred to as internal haze and external haze, respectively.

[0083] The Yellow Index (YI) of the resin film according to this embodiment is preferably 1.2 or less, and more preferably 1.0 or less. When the YI is within the above range, the transparency is high, making it suitable for use in optical applications where light transmittance is required.

[0084] The resin film according to this embodiment preferably contains an ultraviolet absorber from the viewpoint of further improving light resistance. The purpose of the ultraviolet absorber is 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 the optical anisotropy is small not only in the in-plane direction (length direction and width direction) of the resin film, but also in the thickness direction. That is, it is preferable that both the absolute values ​​of the in-plane phase difference and the thickness direction phase difference are small. For example, when the measurement wavelength is 590 nm, the absolute value of the in-plane phase difference is preferably 20 nm or less, and more preferably 15 nm or less. Furthermore, the absolute value of the thickness direction phase difference is preferably 50 nm or less, more preferably 20 nm or less, and even more preferably 15 nm or less.

[0086] Phase difference is an index value calculated based on birefringence. The in-plane phase difference (Re) and the thickness-direction phase difference (Rth) can be calculated using the following formulas. In an ideal resin film that is perfectly optically isotropic in three dimensions, both the in-plane phase difference Re and the thickness-direction phase difference 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 indices in the respective axial directions, where the in-plane stretching direction (orientation direction of polymer chains) is the X-axis, the direction perpendicular to the X-axis is the Y-axis, and the thickness direction of the resin film is the Z-axis. Also, d represents the thickness of the resin film, and nx-ny represents the orientation birefringence. Note that the MD direction of the film is considered the X-axis, but in the case of a stretched film, the stretching direction is considered 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 More preferably -3.8 × 10 -4 ~3.8×10 -4Therefore, if the orientation birefringence is within the above range, it tends to be possible to obtain stable optical properties without birefringence occurring during the molding process.

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

[0090] When stretching the resin film according to this embodiment, an unstretched resin film is first formed from the resin composition according to this embodiment, and then uniaxial stretching or biaxial stretching is performed. This makes it possible to manufacture a stretched film (uniaxially oriented film or biaxially oriented film).

[0091] The stretching ratio of the stretched film is not particularly limited and is determined appropriately according to the mechanical strength, surface properties, thickness accuracy, etc. of the stretched film to be manufactured. Although it also depends on the stretching temperature, the stretching ratio is generally preferably selected in the range of 1.1 to 5 times, more preferably in the range of 1.3 to 4 times, and even more preferably in the range of 1.5 to 3 times. If the stretching ratio is within the above range, the mechanical properties of the film, such as elongation, tear propagation strength, and kneading fatigue resistance, tend to be significantly improved.

[0092] (Application) The resin film according to this embodiment can be used in a variety of applications, including transportation equipment, solar cell components, civil engineering and construction components, daily necessities, electrical and electronic equipment, optical components, and medical supplies. In particular, the resin film according to this embodiment is suitable for optical applications due to its excellent heat resistance and optical properties. Examples of optical applications include front panels (cover windows) of various display devices, diffusers, polarizer protective films, polarizer plate protective films, phase difference films, light diffusion films, and optical isotropic films.

[0093] Among these, the resin film according to this embodiment can be suitably used as a polarizer protective film or as a front panel (cover window) for a display device. When the resin film according to this embodiment is used as a front panel (cover window) for 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 needed. When the resin film according to this embodiment is used as a polarizer protective film, the resin film according to this embodiment is bonded to a polarizer to form a polarizing plate. The polarizer is not particularly limited, and any conventionally known polarizer can be used. This polarizing plate is used, for example, in display devices such as liquid crystal display devices and organic EL display devices. [Examples]

[0094] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples. The methods for measuring the 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 determined from the ratio of the weight of the methacrylic resin obtained after washing and drying to the weight of the monomer used. For the weight of the methacrylic resin obtained after washing and drying, the value obtained by subtracting the weight of the residual monomer in the methacrylic resin, as determined by the analysis described below, was used. In Comparative Examples 2 and 3, the weight of the methacrylic resin obtained by precipitation and purification after polymerization was used as is. (Analysis conditions) A gas chromatograph (Agilent Technologies, 7890B) was used, and a DB-1 column (Agilent Technologies, 0.8 μm film thickness × 0.20 mm inner diameter × 30 m length) was used as the analytical column. The analysis was performed under the conditions of an inlet temperature of 150°C and a detector temperature of 320°C. The column temperature was set by heating 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 finally from 260°C to 320°C at a heating rate of 20°C / min, and held for 3 minutes. A calibration curve was created using the internal standard method with chlorobenzene as the internal standard substance, and after calculating the remaining amount of monomers in the methacrylic resin, the polymerization conversion rate was calculated.

[0096] (2) Syndiotacticity (rr) with triple display Methacrylic resin 1 The 1H-NMR spectrum was measured using a nuclear magnetic resonance spectrometer (Bruker AVANCE III 400MHz) in a deuterated chloroform solution at 22°C with 16 integration cycles. From the spectrum, the area (X) of the region between 0.60 and 0.95 ppm and the area (Y) of the region between 0.60 and 1.25 ppm were measured, with tetramethylsilane (TMS) set to 0 ppm. Subsequently, the triple-represented syndiotacticity (rr) 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 methacrylic resin were calculated using a standard polystyrene equivalent method with gel permeation chromatography (GPC). Specifically, a sample solution prepared by dissolving 20 mg of methacrylic resin in 10 mL of tetrahydrofuran was used for analysis under the following apparatus and conditions. Measuring instrument: HLC-8220GPC (Tosoh) Detector: RI detector Solvent: tetrahydrofuran Guard column: TSKgel guardcolumn 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 1-5 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 and dried before being subjected to analysis. For Comparative Examples 2 and 3, the reaction solution after polymerization was added dropwise to methanol to precipitate and purify, and the resin obtained after drying was subjected to analysis as is. A solution was prepared by dissolving 20 mg of the dried methacrylic resin in 0.6-0.7 mL of deuterated chloroform, and the solution was analyzed using a nuclear magnetic resonance spectrometer (Bruker, AVANCE NEO 700 MHz). 1 1H-NMR measurements were performed at a measurement temperature of 20°C, with 8,192 cumulative measurements. The measurement was carried out while eliminating the peak derived from the methoxy group of the methacrylic resin (3.60 ppm, value when the chemical shift of the solvent peak was set to 7.26 ppm) using the Excitation Sculpting (ES) method, a type of solvent elimination method. 1 From the 1H-NMR spectrum, the sum of the areas (X) of peaks originating from the terminal double bonds of the methacrylic resin (5.47-5.53 ppm and 6.21 ppm) and the area (Y) of peaks originating from the α-methyl groups of the methacrylic resin (0.5-1.25 ppm) were measured. Then, the proportion of terminal double bonds in the methacrylic resin was calculated using the formula: [(3 × X) / (2 × Y)] × 100.

[0099] (5) Glass transition temperature (Tg) The glass transition temperature of 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 polymerization initiators. Specifically, the heat treatment was performed under conditions of heating from 40°C to 270°C at a heating rate of 10°C / min under a nitrogen gas flow of 200 mL / min, and holding at 270°C for 2.0 to 2.5 minutes. The glass transition temperature (Tg) of the methacrylic resin after heat treatment was measured using a differential scanning calorimetry analyzer (DSC; DSC7000X, Hitachi High-Tech Science Corporation). First, under a nitrogen flow rate of 40 mL / min, the temperature was increased from 40°C to 160°C at a heating rate of 10°C / min. After cooling to 40°C, a second heating was performed from 40°C to 160°C at a heating rate of 10°C / min. DSC measurements were then taken under these conditions. The midpoint glass transition temperature (the temperature at which the curve representing the stepwise change of the glass transition intersects with a line equidistant in the vertical axis from both the line obtained by extrapolating the baseline before the inflection point to the higher temperature side and the line obtained by extrapolating the baseline after the inflection point to the lower temperature side) was read from the DSC curve measured during the second heating.

[0100] (6) Retention thermal stability The thermal stability of methacrylic resin was evaluated using a thermogravimetric analyzer (Hitachi High-Tech Science Corporation, STA7200). First, to remove residual monomers and decomposition products of polymerization initiators in the methacrylic resin, it was heat-treated under conditions of heating from 40°C to 270°C at a heating rate of 10°C / min under a nitrogen stream of 200 mL / min, and holding at 270°C for 2.0 to 2.5 minutes. Next, after cooling to 40°C, the temperature was raised from 40°C to 280°C at a heating rate of 10°C / min, and the mass change was recorded under conditions of holding at 280°C for 30 minutes. The mass when the sample temperature reached 280°C was X0, and the mass after holding at 280°C for 15 minutes was X0. 15 Let the formula be: [(X0-X 15 The heat retention stability was evaluated from the mass loss rate calculated using the formula ) / X0 × 100.

[0101] (7) Bonded sulfur atomic weight The amount of bound sulfur atoms in methacrylic resin was determined as follows. As a pretreatment, 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 and dried for analysis. An appropriate amount of dried methacrylic resin was accurately weighed and brought to a fixed volume, then placed in an automatic sample combustion device (Nitto Seikou Airanatech Co., Ltd., AQF-2100) and decomposed at high temperature. The generated gas was absorbed with hydrogen peroxide solution and ultrapure water containing hydrated hydrazine. The obtained liquid (aqueous solution of decomposition gas) was used to quantify sulfate ions using an ion chromatograph (Thermo Fisher Scientific Co., Ltd., Integrion RFIC, columns: AG18-4μm, AS18-4μm). Next, the mass Wp (mass%) of sulfur atoms per unit mass of the dried methacrylic resin was calculated. Furthermore, the amount of bound 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 glycerin and then glass sandwiched between both sides of the resin film, and the resulting value was defined as the internal haze. The obtained results were then converted to the equivalent of a 40 μm film thickness.

[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 a UV-Vis 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 K7373. The obtained results were converted to the equivalent of a 40 μm film thickness.

[0106] <Example 1> In a 2-liter glass reactor equipped with a three-way swept-back vane stirrer, 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 dimethyl 2,2'-azobis(isobutyrate) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., V-601) as a polymerization initiator were charged. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was passed through to replace the air in the reactor. Then, monomer solutions 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 were added to the reactor. Subsequently, 0.375 parts by mass of 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 81°C to start polymerization. The monomers were reacted at 81°C for 4.5 hours, after which the temperature of the mixture in the reactor was raised to 95°C. The reaction mixture was stirred at the same temperature for 1 hour to complete the polymerization. The average temperature of the entire polymerization process from the time the temperature was raised to 81°C until the end of polymerization was 84°C. The obtained resin was washed with 3.9 times the amount of deionized water and dried to obtain bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 1.

[0107] <Example 2> In a 2-liter glass reactor equipped with a three-way swept-back vane stirrer, 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 dimethyl 2,2'-azobis(isobutyrate) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., V-601) as a polymerization initiator were charged. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was passed through to replace the air in the reactor. Then, monomer solutions containing 100 parts by mass of methyl methacrylate (MMA) and 0.220 parts by mass of n-octyl mercaptan (n-OM) as a chain transfer agent were added to the reactor. Subsequently, 0.375 parts by mass of 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 78°C to start polymerization. The monomers were reacted at 78°C for 6.5 hours, after which the temperature of the mixture in the reactor was raised to 93°C. The reaction mixture was stirred at the same temperature for 1 hour to complete the polymerization. The average temperature of the entire polymerization process from the time the temperature was raised to 78°C until the end of polymerization was 80°C. The obtained resin was washed with 2.9 times the amount of deionized water and dried to obtain bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 1.

[0108] <Example 3> In a 4-liter glass reactor equipped with an H-type agitator, 150 parts by mass of deionized water, 0.140 parts by mass of tricalcium phosphate (a dispersant), 0.0075 parts by mass of sodium α-olefin sulfonate, and 0.30 parts by mass of sodium chloride were charged. 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, monomer solutions containing 100 parts by mass of methyl methacrylate (MMA), 0.289 parts by mass of n-octyl mercaptan (n-OM) (a chain transfer agent), and 0.037 parts by mass of dimethyl 2,2'-azobis(isobutyrate) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., V-601) (a polymerization initiator) were added to the reactor. Subsequently, the temperature of the solution in the reactor was raised to 80°C and polymerization was started. 0.10 parts by mass of tricalcium phosphate was added to the reaction mixture 1 hour and 40 minutes after the start of polymerization. Subsequently, the temperature of the liquid in the reactor was gradually increased until it reached 87°C 4 hours after the start of polymerization. At that point, 0.22 parts by mass of tricalcium phosphate was added to the reaction mixture. After another 10 minutes, 0.037 parts by mass of 2,2'-azobis(isobutyrate)dimethyl was added to the reaction mixture. Next, the temperature of the liquid in the reactor was increased to 95°C, and polymerization was terminated when stirring was continued at 95°C for 1 hour and 30 minutes. The average temperature of the entire polymerization from the time the temperature was raised to 80°C until the end of polymerization was 87°C. Acid washing was performed using 1 N hydrochloric acid in a weight ratio of 0.1 times the amount of the charged monomer, followed by washing with water and drying to obtain bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 1.

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

[0110] The obtained resin composition was dried at 90°C for 4 hours, and then extruded at a resin temperature of 240°C using a 15 mm diameter coaxial twin-screw extruder (Technovel Co., Ltd., 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 with a width of 130 mm and a thickness of 160 μm.

[0111] From the obtained resin film, small pieces measuring 100 mm x 100 mm were cut so that two sides were parallel to the extrusion direction. These pieces were set in a pantograph-type biaxial stretching apparatus and simultaneously biaxially stretched at 137°C, twice in the direction parallel to the extrusion direction and twice in the direction perpendicular to it. The stretching speed in each direction was set to 100 mm / min. After that, the pieces were removed at room temperature and rapidly cooled 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> To 100 parts by mass of the methacrylic resin obtained in Example 3, 0.7 parts by mass of an ultraviolet absorber (ADEKA Corporation, ADEKA Stub LA-F70) was mixed and kneaded and extruded at 255°C using a 15 mm diameter interlocking type co-rotating twin-screw extruder (Technovel Corporation, KZW15TWIN-45MG, L / D=45). The resin that came out as strands from the die at the extruder outlet was cooled in a water bath and then pelletized in a pelletizer to obtain the resin composition.

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

[0114] <Example 5> In a glass sample bottle, 150 parts by mass of deionized water, 0.400 parts by mass of tricalcium phosphate (a dispersant), 0.0075 parts by mass of sodium α-olefin sulfonate, and 0.30 parts by mass of sodium chloride were charged. While the aqueous solution in the sample bottle was being stirred with a stirring bar, monomer solutions containing 100 parts by mass of methyl methacrylate (MMA), 0.093 parts by mass of 2,2'-azobis(isobutyrate)dimethyl (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., V-601) (a polymerization initiator), and 0.289 parts by mass of n-octyl mercaptan (n-OM) (a chain transfer agent) were added. The suspension in the sample bottle was transferred to a 120 mL metal pressure vessel equipped with a semicircular stirrer, and the air in the reaction vessel was replaced by passing nitrogen gas (oxygen concentration 0.2 ppm) through it while stirring at 150 rpm. Subsequently, the liquid temperature in the reaction vessel was raised to 97°C to initiate polymerization, which was completed after 5 hours and 20 minutes. The average temperature throughout the polymerization, from the time the temperature was raised to 97°C until the end of polymerization, was 97°C. After cooling the liquid in the reaction vessel, it was drained and acid washing was performed using 1N hydrochloric acid in an amount equal to 0.5 times the weight of the charged monomer. After washing with water and drying, bead-shaped methacrylic resin was obtained. The physical properties of the obtained methacrylic resin are shown in Table 1.

[0115] <Comparative Example 1> In a 2-liter glass reactor equipped with a three-way swept-back vane stirrer, 170 parts by mass of deionized water, 0.10 parts by mass of disodium hydrogen phosphate as a suspension aid, and 0.040 parts by mass of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., V-65) as a polymerization initiator were charged. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was passed through to replace the air in the reactor. Then, monomer solutions 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 were added to the reactor. Subsequently, 0.375 parts by mass of 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 70°C to begin polymerization. The monomers were reacted at 70°C for 6 hours, after which the temperature of the liquid in the reactor was raised to 95°C. The reaction mixture was stirred at the same temperature for 1 hour to complete polymerization. The average temperature for the entire polymerization process, from raising the temperature to 70°C until completion, was 74°C. The obtained resin was washed with 7.0 times the amount of deionized water and dried to obtain bead-shaped methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 1.

[0116] <Comparative Example 2> In a 120 mL metal pressure vessel equipped with a U-shaped stirrer, 1800 parts by mass of o-dichlorobenzene, the polymerization solvent, was added. Further, monomer solutions containing 100 parts by mass of methyl methacrylate (MMA), 0.037 parts by mass of 2,2'-azobis(isobutyrate)dimethyl (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., V-601), the polymerization initiator, and 0.289 parts by mass of n-octyl mercaptan (n-OM), the chain transfer agent, were added. After replacing the air in the reaction vessel by passing nitrogen gas (oxygen concentration 50 ppm) through it, polymerization was started by raising the liquid temperature in the reaction vessel to approximately 140°C while stirring. Polymerization was terminated when the monomers were reacted at approximately 140°C for a further 6 hours. The average temperature for the entire polymerization process from raising the temperature to approximately 140°C until the end of polymerization was 142°C. After cooling the liquid in the reaction vessel, it was drained, and the reaction solution was added dropwise to methanol to precipitate the resin. The precipitated resin was recovered by filtration and then dried to obtain methacrylic resin. The physical properties of the obtained methacrylic resin are shown in Table 1.

[0117] <Comparative Example 3> In a 2-liter glass reactor equipped with a three-way swept-back vane stirrer, 339 parts by mass of methanol, the polymerization solvent, was added, followed by 100 parts by mass of methyl methacrylate (MMA) and a monomer solution containing 2.46 parts by mass of 2,2'-azobis(isobutyrate)dimethyl (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., V-601), 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 reaction vessel to replace the air inside the vessel. Polymerization was then started by raising the temperature of the solution in the reaction vessel to 60°C while stirring. Polymerization was terminated when the monomers were reacted at 60°C for a further 3 hours. At that point, the resulting resin precipitated at the bottom of the reaction vessel. The average temperature for the entire polymerization process, from raising the temperature 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 vessel was dissolved in 400 parts by mass of chloroform, and the chloroform solution was added dropwise to 2500 parts by mass of methanol to reprecipitate the resin. The reprecipitated resin was recovered by filtration and then dried to obtain 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 2,2'-azobis(isobutyrate)dimethyl, a non-nitrile azo polymerization initiator, showed a smaller weight loss rate and higher heat retention stability when held at 280°C for 15 minutes compared to Comparative Example 1, which used 2,2'-azobis(2,4-dimethylvaleronitrile), a nitrile azo polymerization initiator, at the same usage ratio (mol%). Similarly, Example 2, which used the same usage ratio (mol%) of 2,2'-azobis(isobutyrate)dimethyl, a non-nitrile azo polymerization initiator, as Example 1, but with a lower usage ratio (mol%) of n-octyl mercaptan (n-OM), a chain transfer agent, also showed a smaller weight loss rate and higher heat retention stability when held at 280°C for 15 minutes compared to Comparative Example 1, which used 2,2'-azobis(2,4-dimethylvaleronitrile), a nitrile azo polymerization initiator. Furthermore, in Example 3, which used a higher proportion (mol%) of 2,2'-azobis(isobutyrate)dimethyl, a non-nitrile azo polymerization initiator, and a lower proportion (mol%) of n-octyl mercaptan (n-OM), a chain transfer agent, compared to Example 1, the weight loss rate after holding at 280°C for 15 minutes was smaller and the heat retention stability was higher compared to Comparative Example 1, which used 2,2'-azobis(2,4-dimethylvaleronitrile), a nitrile azo polymerization initiator. In addition, when comparing Example 3 and Example 4, the light transmittance at a wavelength of 380 nm was lower in Example 4, which had an added UV absorber, than in Example 3. Furthermore, in Example 5, which used a higher proportion (mol%) of 2,2'-azobis(isobutyrate)dimethyl, a non-nitrile azo polymerization initiator, than in Example 3, and had a higher average polymerization temperature than in Example 3, the weight loss rate when held at 280°C for 15 minutes was smaller and the heat retention stability was higher compared to Comparative Example 1, which used 2,2'-azobis(2,4-dimethylvaleronitrile), a nitrile azo polymerization initiator.

[0120] Furthermore, Comparative Example 2, which was polymerized under conditions where the average polymerization temperature exceeded 100°C, showed a larger weight loss rate after holding at 280°C for 15 minutes and inferior heat retention stability compared to Examples 1 and 2, despite using 2,2'-azobis(isobutyrate)dimethyl, a non-nitrile azo polymerization initiator, at the same usage ratio (mol%) as in Examples 1 and 2. In addition, Comparative Example 3, in which the resin was polymerized without using a chain transfer agent, had a higher proportion of terminal double bonds and a larger weight loss rate after holding at 280°C for 15 minutes compared to Examples 1-5, resulting in inferior heat retention stability.

Claims

1. A polarizer protective film containing methacrylic resin, The methacrylic resin is The proportion of structural units derived from methyl methacrylate is 98% by mass or more. The syndiotacticity of the triple display is 55% or higher. It contains an end structure represented by the following formula (1) derived from a polymerization initiator, The proportion of terminal double bonds to structural units derived from methyl methacrylate is less than 0.020 mol%, A polarizer protective film having a thermogravimetric loss rate of less than 2.5% when exposed to 280°C for 15 minutes in a nitrogen gas atmosphere. 【Chemistry 1】 (wherein, R １ , R ２ , and R ３ each independently represents an alkyl group, a substituted alkyl group, an ester group, or an amide group. However, at least one of R １ , R ２ , and R ３ represents an ester group or an amide group. Two of R １ , R ２ , and R ３ may be bonded to each other to form an alicyclic structure. * indicates a bond to a structural unit derived from a monomer.)

2. The polarizer protective film according to claim 1, wherein the terminal structure represented by formula (1) is derived from at least one selected from 2,2'-azobis(isobutyrate)dimethyl and 1,1'-azobis(cyclohexanecarboxylate)methyl.

3. The polarizer protective film according to claim 1, wherein the methacrylic resin has a weight-average molecular weight (Mw) of 50,000 to 200,000 as measured by gel permeation chromatography (GPC).

4. The polarizer protective film according to claim 1, wherein the methacrylic resin has a ratio (Mw / Mn) of 1.6 to 2.5 of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) measured by gel permeation chromatography (GPC).

5. A polarizer protective film according to claim 1, comprising an ultraviolet absorber.

6. A polarizing plate comprising a polarizer and a polarizer protective film according to any one of claims 1 to 5, laminated together.

7. A display device comprising the polarizing plate described in claim 6.

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