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

Abstract

To provide: a methacrylic resin that enables production of a molded article having excellent heat resistance, thermal stability, and mechanical properties and a method for producing the same; a resin composition and a dope containing the methacrylic resin; a resin film including the methacrylic resin; and a polarizing plate and a display device including the resin film.SOLUTION: A methacrylic resin has a proportion of structural units derived from methyl methacrylate of 98 mass% or more, a weight-average molecular weight (Mw) of 500,000 or more as measured by gel permeation chromatography (GPC), a syndiotacticity in terms of triad representation of 55% or more, and a proportion of terminal double bonds relative to the structural units derived from methyl methacrylate of less than 0.015 mol%.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

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

[0003] As methods for producing resin films, a melt extrusion method using a T-die, a solution casting method in which a dope obtained by dissolving a resin in a solvent is cast on the surface of a support and then the solvent is evaporated to form a film, etc. are known. Among these, the solution casting method has the advantage that since the physical stress applied to the resin film during film formation is small, molecular orientation hardly occurs, and the strength and optical properties of the obtained resin film become isotropic. Further, according to the solution casting method, there is also an advantage that the thickness accuracy of the obtained resin film becomes extremely high.

[0004] When producing a resin film by the solution casting method, generally, a methacrylic resin having a high molecular weight is used. By using a high molecular weight methacrylic resin, not only is it suitable as a solution casting method, but also the mechanical properties of the obtained resin film become good.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, as a result of investigations by the present inventors, it has been found that such high molecular weight methacrylic resins have room for improvement in terms of heat resistance and thermal stability.

[0007] An object of the present invention is to provide a methacrylic resin capable of producing a molded article excellent in heat resistance, thermal stability, and mechanical properties, a method for producing the same, a resin composition and a dope containing the methacrylic resin, a resin film containing the methacrylic resin, and a polarizing plate and a display device using the resin film.

Means for Solving the Problems

[0008] 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 weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) is 500,000 or more, The syndiotacticity in triad representation is 55% or more, A methacrylic resin in which the proportion of terminal double bonds with respect to the structural units derived from methyl methacrylate is less than 0.015 mol%. <2> The methacrylic resin according to <1>, wherein the syndiotacticity in triad representation is 70% or less. <3> The methacrylic resin according to <1> or <2>, wherein the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 1.6 to 2.8. <4> The methacrylic resin according to any one of <1> to <3>, wherein the 5% weight loss temperature is 300°C or higher. <5> The methacrylic resin according to any one of <1> to <4>, wherein the glass transition temperature is 120°C or higher.

[0009] <6> A polymerization step of polymerizing a monomer component having a methyl methacrylate content of 98% by mass or more in the presence of a polymerization initiator and a chain transfer agent is included. In the polymerization step, the polymerization temperature until 90% or more of the resulting methacrylic resin is formed is less than 100°C. The 10-hour half-life temperature of the polymerization initiator is 45°C or more. The amount of the chain transfer agent used is 0.030 mol% or less based on the total amount of the monomer component. A method for producing a methacrylic resin, wherein the ratio of the total mol amount of the chain transfer agent to the total mol amount of the polymerization initiator is more than 0 and 3.0 or less. <7> The method for producing a methacrylic resin according to claim 6, wherein the melting point of the polymerization initiator is less than 100°C. <8> The method for producing a methacrylic resin according to <6> or <7>, wherein aqueous polymerization is carried out in the polymerization step. <9> The method for producing a methacrylic resin according to any one of <6> to <8>, wherein the polymerization initiator contains at least one selected from an azo polymerization initiator and a peroxide polymerization initiator. <10> The method for producing a methacrylic resin according to <9>, wherein the azo polymerization initiator is a nitrile-based azo polymerization initiator.

[0010] <11> A resin composition containing the methacrylic resin according to any one of <1> to <5>. <12> Contains the methacrylic resin according to any one of <1> to <5> and a solvent. The solvent contains a first solvent having a hydrogen bond term δH of 1 to 12 and a second solvent having a hydrogen bond term δH of 14 to 24 in the Hansen solubility parameter, and is a dope for film production by the solution casting method. <13> A resin film containing the methacrylic resin according to any one of <1> to <5>. <14> The resin film according to <13>, wherein the number of flexures until breakage in the clam shell type flexure test is 6,000 or more. <15> The resin film according to <13> or <14>, wherein the resin film is a polarizer protection film. <16> A polarizing plate formed by laminating a polarizer and the resin film according to any one of <13> to <15>. <17> A display device including the polarizing plate according to <16>.

Advantages of the Invention

[0011] According to the present invention, there can be provided a methacrylic resin and a method for producing the same, which are excellent in heat resistance and thermal stability and also excellent in mechanical properties, a resin composition and a dope containing the methacrylic resin, a resin film containing the methacrylic resin, and a polarizing plate and a display device using the resin film.

Modes for Carrying Out the Invention

[0012] Hereinafter, specific embodiments to which the present invention is applied will be described in detail. The symbol "~" representing a numerical range is used with the intention of including the lower and upper limits of the range unless otherwise specified. In addition, physical property values of components such as a polymerization initiator and a methacrylic resin mean values under 1 atm unless otherwise specified.

[0013] <Methacrylic Resin> The methacrylic resin according to the present embodiment has a proportion of structural units derived from methyl methacrylate of 98% by mass or more and a proportion of structural units derived from monomers other than methyl methacrylate of 2% by mass or less. The methacrylic resin according to the present embodiment preferably has a proportion of structural units derived from methyl methacrylate of 99% by mass or more, and more preferably 100% by mass (that is, a homopolymer of methyl methacrylate). The structural units derived from methyl methacrylate are represented by the following formula.

[0014] [Chem.]

[0015] Examples of monomers other than methyl methacrylate include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; aryl acrylates such as phenyl acrylate; cycloalkyl acrylates such as cyclohexyl acrylate and norbornenyl acrylate; alkyl methacrylates other than methyl methacrylate such as ethyl methacrylate, propyl methacrylate, and butyl methacrylate; aryl methacrylates such as phenyl methacrylate; cycloalkyl methacrylates such as cyclohexyl methacrylate and norbornenyl methacrylate; aromatic vinyl compounds such as styrene and α-methylstyrene; acrylamide; methacrylamide; acrylonitrile; methacrylonitrile; and the like.

[0016] The methacrylic resin according to this embodiment has a weight average molecular weight (Mw) of 500,000 or more. When the weight average molecular weight (Mw) of the methacrylic resin is 500,000 or more, the mechanical properties of the resulting molded article tend to improve. For example, a resin film excellent in flexural resistance can be obtained. The weight average molecular weight (Mw) of the methacrylic resin is preferably 600,000 or more, more preferably 700,000 or more, and even more preferably 800,000 or more. The upper limit of the weight average molecular weight (Mw) is not particularly limited, but from the viewpoint of moldability, it is preferably 4,000,000 or less, more preferably 3,500,000 or less, even more preferably 3,000,000 or less, particularly preferably 2,000,000 or less, and extremely preferably 1,500,000 or less.

[0017] In addition, for the methacrylic resin according to this embodiment, the dispersity (Mw / Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), is preferably from 1.6 to 2.8, more preferably from 1.7 to 2.5, still more preferably from 1.7 to 2.4, and particularly preferably from 1.7 to 2.3. When the dispersity (Mw / Mn) of the methacrylic resin is 1.6 or more, the fluidity of the methacrylic resin tends to improve and it becomes easier to mold. When the dispersity (Mw / Mn) of the methacrylic resin is 2.8 or less, the mechanical properties such as impact resistance, toughness, and flexural resistance of the resulting molded article tend to improve.

[0018] The weight average molecular weight (Mw) and number average molecular weight (Mn) in this specification are values in terms of standard polystyrene measured by gel permeation chromatography (GPC), and are measured by the method described in the examples below.

[0019] Note that the weight average molecular weight (Mw) and number average molecular weight (Mn) of the methacrylic resin can be controlled by adjusting the types and amounts used of the polymerization initiator and chain transfer agent when synthesizing the methacrylic resin.

[0020] In addition, for the methacrylic resin according to this embodiment, the syndiotacticity (rr) in triad representation is 55% or more, preferably 56% or more, and more preferably 57% or more. When the syndiotacticity (rr) in triad representation is 55% or more, the glass transition temperature (Tg) of the methacrylic resin tends to increase and the heat resistance improves. Also, when the syndiotacticity (rr) is 55% or more, the solvent resistance of the resulting molded article improves and the moisture permeability tends to decrease. The upper limit of the syndiotacticity (rr) is not particularly limited, but from the viewpoints of the molding processing temperature, and the toughness and secondary processability of the molded article, it is preferably 70% or less, more preferably 67% or less, still more preferably 65% or less, and particularly preferably 63% or less.

[0021] Syndiotacticity (rr) is the ratio in which the two chains (dyads) of a chain of three consecutive structural units (triad) are both racemo (rr). In the chain of structural units (dyad) in a polymer molecule, those with the same configuration are called meso, and those with the opposite configuration are called racemo, which are denoted as m and r, respectively.

[0022] Syndiotacticity (rr) is, as described in the examples below, under the conditions of deuterated chloroform, 22 °C, and an integration number of 16 times 1 an 1H-NMR spectrum is measured, and from the spectrum, the area (X) of the region from 0.60 to 0.95 ppm and the area (Y) of the region from 0.60 to 1.25 ppm are measured when tetramethylsilane (TMS) is set to 0 ppm, and it can be calculated by the formula: (X / Y) × 100.

[0023] Also, the methacrylic resin according to this embodiment preferably has a glass transition temperature (Tg) of 120 °C or higher, more preferably 122 °C or higher, and even more preferably 124 °C or higher. The upper limit of the glass transition temperature (Tg) is not particularly limited, but from the viewpoints of the molding processing temperature and the secondary processability of the molded body, it is preferably 135 °C or lower, and may be 130 °C or lower.

[0024] The glass transition temperature (Tg) in this specification is the midpoint glass transition temperature determined from the DSC curve and is measured by the method described in the examples below.

[0025] Note that the syndiotacticity (rr) and the glass transition temperature (Tg) of the methacrylic resin can be controlled by adjusting the polymerization temperature when synthesizing the methacrylic resin. For example, lowering the polymerization temperature is preferable for increasing the syndiotacticity (rr) of the methacrylic resin and raising the glass transition temperature (Tg). Also, the glass transition temperature (Tg) can be controlled by adjusting the molecular weight of the methacrylic resin.

[0026] In addition, the methacrylic resin according to the present embodiment has a ratio of terminal double bonds to the structural unit derived from methyl methacrylate of 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 the terminal double bonds is within the above range, the thermal stability of the methacrylic resin tends to improve.

[0027] The methacrylic resin according to the present embodiment can be produced by a radical polymerization method as shown in the production method described later. The methacrylic resin produced by the radical polymerization method contains terminal double bonds generated by disproportionation termination reaction during polymerization, hydrogen abstraction reaction of monomers by a polymerization initiator, etc. As described above, since the terminal double bonds affect the thermal stability of the resin, the ratio thereof is preferably small. If the ratio of the terminal double bonds can be reduced to less than 0.015 mol% by the method described later, the thermal stability of the methacrylic resin tends to be greatly improved. Note that the lower limit of the ratio of the terminal double bonds is preferably 0 mol%, but may be 0.001 mol%.

[0028] The ratio of the terminal double bonds to the structural unit derived from methyl methacrylate is, as described in the examples described later, in deuterated chloroform at 20 °C under the conditions of an integration number of 8,192 times 1 an 1H-NMR spectrum is measured, and from the spectrum, the total area (X) of the peaks (5.47 to 5.52 ppm and 6.21 ppm) derived from the terminal double bond portion of the methacrylic resin and the area (Y) of the peak (0.5 to 1.25 ppm) derived from the α-methyl group of the methacrylic resin are measured, and it can be calculated by the formula: [(3 × X) / (2 × Y)] × 100.

[0029] Note that the ratio of the terminal double bonds of the methacrylic resin can be controlled by adjusting the amounts of the polymerization initiator and the chain transfer agent used, the polymerization temperature, the polymerization time, etc. when synthesizing the methacrylic resin. For example, reducing the amount of the polymerization initiator used, increasing the amount of the chain transfer agent used, lowering the polymerization temperature, and lengthening the polymerization time are preferable for reducing the ratio of the terminal double bonds.

[0030] As described above, the methacrylic resin according to this embodiment is excellent in thermal stability. The methacrylic resin according to this embodiment preferably has a 5% weight loss temperature of 300°C or higher. This 5% weight loss temperature is the temperature obtained from the thermogravimetric curve and is measured by the method described in the examples below. Further, the methacrylic resin according to this embodiment preferably has a thermogravimetric weight loss rate of less than 8.0% when exposed to 280°C for 15 minutes in a nitrogen gas atmosphere, and more preferably less than 5.0%. This thermogravimetric weight loss rate is measured by the method described in the examples below.

[0031] In addition, the methacrylic resin according to this embodiment has a characteristic that foaming hardly occurs in the resin film when a dope containing the methacrylic resin is cast on the surface of a support and heat-dried to produce a resin film.

[0032] In addition, the methacrylic resin according to this embodiment is expected to be suitable for reuse after disposal, that is, recycling. As a recycling method of 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. Generally, in order to improve the heat resistance and thermal stability of methacrylic resin, a cyclic structure is introduced into the molecular structure of methacrylic resin, or a monomer having a rigid structure is copolymerized. However, these structures become impurities in performing chemical recycling, which is not preferable. In this regard, the methacrylic resin according to this embodiment has a large proportion of structural units derived from methyl methacrylate, and it is expected that the monomer recovered as decomposition oil has a high yield, and it is expected to exhibit good chemical recyclability.

[0033] <Manufacturing method of methacrylic resin> The manufacturing method of the methacrylic resin according to this embodiment includes a polymerization step of polymerizing a monomer component having a methyl methacrylate content of 98% by mass or more in the presence of a polymerization initiator and a chain transfer agent.

[0034] In the polymerization process, from the viewpoints of controlling the syndiotacticity of the resulting methacrylic resin and productivity, the polymerization temperature is less than 100°C until more than 90% of the resulting methacrylic resin is produced. Here, "until more than 90% of the resulting methacrylic resin is produced" means "at least until the conversion rate reaches 90%" when the polymerization reaction is carried out to a conversion rate of 100%. For example, when the polymerization reaction is terminated at a conversion rate of 50%, it means "at least until the conversion rate reaches 45%". The polymerization temperature until more than 90% of the resulting methacrylic resin is produced is preferably 20°C or higher and less than 100°C, more preferably 30 to 95°C, even more preferably 50 to 90°C, and particularly preferably 60 to 85°C. After more than 90% of the resulting methacrylic resin is produced, the polymerization temperature may be raised to 100°C or higher for the purpose of reducing the residual monomer component and deactivating the residual polymerization initiator.

[0035] As a method for producing a methacrylic resin, a conventionally known polymerization method can be adopted. For example, a radical polymerization method such as a continuous bulk polymerization method, a solution polymerization method, an emulsion polymerization method, a soap-free emulsion polymerization method, or a suspension polymerization method can be adopted. Among them, from the viewpoints of the degree of freedom in the structural design of the methacrylic resin, the simplicity of polymerization, and productivity, a production method that performs aqueous polymerization is preferred, the suspension polymerization method and the emulsion polymerization method are more preferred, and the suspension polymerization method is even more preferred.

[0036] [Suspension Polymerization Method] In the suspension polymerization method, a methacrylic resin is synthesized in an aqueous suspension obtained by mixing water, a monomer component, a dispersant, a polymerization initiator, a chain transfer agent, and optionally other additives. The order of mixing each component is not particularly limited. For example, each component may be mixed simultaneously to prepare an aqueous suspension. Alternatively, after mixing water, a polymerization initiator, and optionally other additives to prepare an aqueous solution, a monomer component and a chain transfer agent may be added, and then a dispersant may be added to prepare an 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.

[0037] As the monomer component, those having a methyl methacrylate content of 98% by mass or more, preferably 99% by mass or more, more preferably 100% by mass are used.

[0038] Examples of monomers other than methyl methacrylate include acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate; aryl acrylates such as phenyl acrylate; cycloalkyl acrylates such as cyclohexyl acrylate, norbornenyl acrylate; alkyl methacrylates other than methyl methacrylate such as ethyl methacrylate, propyl methacrylate, butyl methacrylate; aryl methacrylates such as phenyl methacrylate; cycloalkyl methacrylates such as cyclohexyl methacrylate, norbornenyl methacrylate; aromatic vinyl compounds such as styrene, α-methylstyrene; acrylamide; methacrylamide; acrylonitrile; methacrylonitrile; and the like.

[0039] Examples of the dispersant include hardly water-soluble inorganic salts such as tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, kaolin; water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, polyvinyl pyrrolidone; and the like. When using a hardly water-soluble inorganic salt as the dispersant, it is effective to use a anionic surfactant such as sodium α-olefin sulfonate, sodium dodecylbenzene sulfonate in combination. These dispersants may be added during the polymerization as necessary.

[0040] As the polymerization initiator, those having a 10-hour half-life temperature of 45°C or higher are used. By using such a polymerization initiator, the thermal stability of the methacrylic resin tends to be improved. The 10-hour half-life temperature of the polymerization initiator is preferably 45 to 120°C, more preferably 50 to 90°C.

[0041] The 10-hour half-life temperature of the polymerization initiator can be measured, for example, by putting a benzene solution or toluene solution containing 0.05 to 0.10 mol / L of the polymerization initiator into a glass tube, purging with nitrogen, sealing it, and then thermally decomposing it in a constant temperature bath at a predetermined temperature. When using a commercially available polymerization initiator, the 10-hour half-life temperature described in the manufacturer's catalog or the like can be adopted.

[0042] In addition, in order to advance the polymerization by aqueous polymerization, the melting point of the polymerization initiator is preferably less than 100 °C.

[0043] Specific examples of the polymerization initiator include, for example, azo polymerization initiators such as 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(isobutyric acid)dimethyl, 2,2'-azobis(2,4,4-trimethylpentane), 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis{2-methyl-N-[2-(1-hydroxyethyl)]propionamide}, 2,2'-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propionamide}; peroxide polymerization initiators such as lauroyl peroxide, t-butyl peroxy-2-ethylhexanoate, t-hexyl peroxy-2-ethylhexanoate; and the like. These polymerization initiators may be used alone or in combination of two or more.

[0044] Among these polymerization initiators, from the viewpoint of improving the thermal stability of the obtained methacrylic resin, azo polymerization initiators are preferred, and nitrile-based azo polymerization initiators are more preferred.

[0045] The amount of the polymerization initiator used is preferably 1.0 part by mass or less, more preferably 0.5 part by mass or less, and even more preferably 0.1 part by mass or less with respect to 100 parts by mass of the total amount of the monomer components. The lower limit of the amount of the polymerization initiator used is not particularly limited, but from the viewpoint of the polymerization rate, it is preferably 0.001 part by mass or more with respect to 100 parts by mass of the total amount of the monomer components.

[0046] Examples of the chain transfer agent include primary alkyl mercaptan - based chain transfer agents such as n - butyl mercaptan, n - octyl mercaptan, n - hexadecyl mercaptan, n - dodecyl mercaptan, n - tetradecyl mercaptan, etc.; secondary alkyl mercaptan - based chain transfer agents such as s - butyl mercaptan, s - dodecyl mercaptan, etc.; tertiary alkyl mercaptan - based chain transfer agents such as t - dodecyl mercaptan, t - tetradecyl mercaptan, etc.; thioglycolic acid esters such as 2 - ethylhexyl thioglycolate, ethylene glycol dithioglycolate, trimethylolpropane tris(thioglycolate), pentaerythritol tetrakis(thioglycolate), etc.; thiophenol, tetraethylthiuram disulfide, pentaphenylethane, acrolein, methacrolein, allyl alcohol, carbon tetrachloride, ethylene bromide, styrene oligomers (such as α - methylstyrene dimer), terpinolene, etc. These chain transfer agents may be used alone or in combination of two or more.

[0047] Among these chain transfer agents, from the viewpoints of handleability, stability, thermal stability of the resulting methacrylic resin, etc., alkyl mercaptan - based chain transfer agents and thioglycolic acid esters are preferred. As the alkyl mercaptan - based chain transfer agent, n - octyl mercaptan is more preferred, and as the thioglycolic acid ester, 2 - ethylhexyl thioglycolate is more preferred.

[0048] The amount of the chain transfer agent used is 0.030 mol% or less, preferably 0.025 mol% or less, based on the total amount of the monomer mixture. The lower limit of the amount of the chain transfer agent used is not particularly limited, but it is preferably 0.0015 mol% or more, and may be 0.005 mol% or more, based on the total amount of the monomer mixture.

[0049] In order to obtain a methacrylic resin having a high weight-average molecular weight (Mw) and a low ratio of terminal double bonds, the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is set to be more than 0 and 3.0 or less. The ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is preferably 1.6 or less, more preferably 1.0 or less. The lower limit of the ratio of the total molar amount of the chain transfer agent to the total molar amount of the polymerization initiator is not particularly limited, but for example, it is preferably 0.1 or more.

[0050] In addition, in order to initiate the polymerization with a small amount of the polymerization initiator, it is preferable to carry out the polymerization reaction with a low dissolved oxygen amount. The dissolved oxygen amount in the raw materials for the polymerization is preferably 10 ppm or less, more preferably 5 ppm or less, still more preferably 4 ppm or less, and particularly preferably 2 ppm or less. By setting the dissolved oxygen amount within such a range, the polymerization reaction proceeds smoothly, and the coloring of the molded body of the methacrylic resin tends to be suppressed. As a method for removing the dissolved oxygen in the raw materials for the polymerization, for example, before raising the temperature to a predetermined polymerization temperature, during the temperature rise, and continuously after the temperature rise, an inert gas such as nitrogen gas is fed into the reaction vessel. In order to remove the dissolved oxygen also from the raw materials added during the polymerization, it is preferable to separately pass an inert gas through those raw materials.

[0051] Further, in order to allow the polymerization reaction to proceed smoothly, when a polymerization inhibitor is contained in the monomer mixture, it is preferable to remove the polymerization inhibitor by distillation, alkali extraction, or using an adsorbent such as alumina, silica gel, molecular sieve, activated carbon, ion exchange resin, zeolite, acid clay, etc.

[0052] The suspension containing the methacrylic resin obtained by suspension polymerization may be subjected to washing operations such as acid washing, water washing, and alkali washing in order to remove the dispersant. The number of times of performing these washing operations may be selected as an optimal number in consideration of the working efficiency and the removal efficiency of the dispersant, and it may be once or a plurality of times.

[0053] As a method for separating methacrylic resin from a suspension containing methacrylic resin, a conventionally known dehydration method can be adopted. Examples of the dehydration method include a method using a centrifuge, a method of suction-removing water on a porous belt or a filtration membrane, and the like.

[0054] The water-containing methacrylic resin obtained through the above dehydration can be dried and recovered by a conventionally known method. Examples of the drying method include hot air drying in which hot air is sent into a tank from a hot air blower, a blow heater, etc.; vacuum drying in which the system is depressurized and then heated as necessary; barrel drying in which the obtained methacrylic resin is rotated in a container to remove moisture; spin drying in which drying is performed using centrifugal force; and the like. These drying methods may be carried out individually or in combination of two or more.

[0055] [Emulsion polymerization method] In the emulsion polymerization method, methacrylic resin is synthesized in an emulsion obtained by mixing water, a monomer mixture, an emulsifier, a polymerization initiator, a chain transfer agent, and optionally other additives.

[0056] As the monomer mixture, those having a methyl methacrylate content of 98% by mass or more, preferably 99% by mass or more, more preferably 100% by mass are used.

[0057] Examples of the emulsifier include anionic surfactants such as alkyl sulfonates, alkylbenzene sulfonates, dialkyl sulfosuccinates, α-olefin sulfonates, naphthalene sulfonate-formaldehyde condensates, alkyl naphthalene sulfonates, N-methyl-N-acyl taurine salts, phosphate esters (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, magnesium salts, and the like. These emulsifiers may be used individually or in combination of two or more. Note that the emulsifier used in the emulsion polymerization may remain in the final methacrylic resin.

[0058] When the pH of the emulsion deviates from neutrality and becomes acidic or basic, an appropriate pH adjuster can be used to prevent hydrolysis of methyl methacrylate, which is a monomer, and structural units derived from methyl methacrylate in the methacrylic resin obtained by polymerization. Examples of the pH adjuster to be used include boric acid - potassium chloride - potassium hydroxide, potassium dihydrogen phosphate - disodium hydrogen phosphate, boric acid - potassium chloride - potassium carbonate, citric acid - potassium hydrogen citrate, potassium dihydrogen phosphate - boric acid, disodium hydrogen phosphate - citric acid, and the like.

[0059] Examples of the polymerization initiator and the chain transfer agent include the same ones as those in the suspension polymerization method described above.

[0060] The amount of the chain transfer agent used is 0.030 mol% or less, preferably 0.025 mol% or less, based on the total amount of the monomer mixture. The lower limit of the amount of the chain transfer agent used is not particularly limited, but it is preferably 0.0015 mol% or more, and may be 0.005 mol% or more, based on the total amount of the monomer mixture.

[0061] In order to obtain a methacrylic resin having a high weight average molecular weight (Mw) and a small proportion of terminal double bonds, the ratio of the total mol amount of the chain transfer agent to the total mol amount of the polymerization initiator is set to be more than 0 and 3.0 or less. The ratio of the total mol amount of the chain transfer agent to the total mol amount of the polymerization initiator is preferably 1.6 or less, more preferably 1.0 or less. The lower limit of the ratio of the total mol amount of the chain transfer agent to the total mol amount of the polymerization initiator is not particularly limited, but it is preferably 0.1 or more, for example.

[0062] The latex of the methacrylic resin obtained by emulsion polymerization is subjected to heat drying or spray drying, or solidified by adding a water-soluble electrolyte such as a salt or an acid, and further heat-treated, and then the resin component is separated from the aqueous phase and dried by a known method such as this, a solid or powdery methacrylic resin can be obtained. The above salt is not particularly limited, but a divalent salt is preferable, and specifically, calcium salts such as calcium chloride and calcium acetate; magnesium salts such as magnesium chloride and magnesium sulfate; and the like can be mentioned. Among these salts, magnesium salts such as magnesium chloride and magnesium sulfate are preferable. Additives generally added such as an antioxidant and an ultraviolet absorber may be added during coagulation.

[0063] Before the above coagulation operation, it is preferable to filter the latex with a filter, a mesh, etc. to remove fine polymerization scales. Thereby, when the methacrylic resin is made into a molded body, fish eyes, foreign matters, etc. caused by fine polymerization scales can be reduced.

[0064] In the present embodiment, the form of the methacrylic resin obtained by aqueous polymerization may be powder, granules, or powder granules containing both powder and granules. Regarding the powder, granules, and primary particles constituting the powder granules, suspension polymerization is suitable when producing primary particles having an average particle diameter of about 10 to 1000 μm, and emulsion polymerization is suitable when producing primary particles having an average particle diameter of about 50 to 500 nm. Aggregates, which are aggregates of the above primary particles, may be contained in the powder, granules, and powder granules.

[0065] After the polymerization is completed, the methacrylic resin may be purified as necessary. Examples of the purification method include a method of dissolving the methacrylic resin in a solvent and dropping it into a poor solvent for precipitation; a method of heating the methacrylic resin to volatilize and remove impurities; and the like. These methods are appropriately selected according to the application, and may be combined with each other.

[0066] <Resin composition> The resin composition according to this embodiment contains the methacrylic resin according to the above-described embodiment.

[0067] From the viewpoint of further improving the thermal stability and mechanical properties of the resulting molded article, the resin composition according to this embodiment preferably contains multilayer structured polymer particles. The multilayer structured polymer particles are not particularly limited, and known ones can be appropriately used.

[0068] When the resin composition according to this embodiment contains multilayer structured polymer particles, the blending ratios of the methacrylic resin and the multilayer structured polymer particles vary depending on the use of the molded article and the like. However, with respect to a total of 100 parts by mass of the blending amounts of both components, the blending amount of the methacrylic resin is preferably 30 to 98 parts by mass, and the blending amount of the multilayer structured polymer particles is preferably 2 to 70 parts by mass.

[0069] The resin composition according to this embodiment may further contain known additives such as a light stabilizer, an ultraviolet absorber, a heat stabilizer, a matting agent, a light diffusing agent, a colorant, a dye, a pigment, an antistatic agent, a heat ray reflecting material, a lubricant, a plasticizer, a stabilizer, a flame retardant, a release agent, a polymer processing aid, a filler, etc., and resins other than the methacrylic resin. Examples of the resins other than the methacrylic resin include styrene resins such as acrylonitrile styrene resin and styrene maleic anhydride resin; polycarbonate resin; polyvinyl acetal resin; cellulose acylate resin; fluorine-based resins such as polyvinylidene fluoride and polyalkyl (meth)acrylate resin; silicone-based resins; polyolefin-based resins; polyethylene terephthalate resin; polybutylene terephthalate resin; and the like.

[0070] Further, 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 described in Japanese Patent No. 3648201, Japanese Patent No. 4336586, etc., and low molecular weight compounds having birefringence described in Japanese Patent No. 3696649 and having a molecular weight of 5,000 or less (preferably 1,000 or less).

[0071] The form of the resin composition according to this embodiment is not particularly limited, and it may be a powder, may be a granule, may be a powder and granule mixture containing both powder and granules, or may be in pellet form.

[0072] <Dope> The dope according to this embodiment contains the methacrylic resin according to the above-described embodiment and a solvent, and is used for producing a resin film by a solution casting method. The solvent includes a first solvent having a hydrogen bonding term δH of 1 to 12 in the Hansen solubility parameter and a second solvent having a hydrogen bonding term δH of 14 to 24. Similar to the resin composition according to the above-described embodiment, the dope according to this embodiment may further contain other components such as multilayer structure polymer particles. Each component such as the methacrylic resin and the multilayer structure polymer particles is dissolved or dispersed in the solvent.

[0073] Examples of the first solvent having a hydrogen bonding term δH of 1 to 12 include 1,4-dioxane (9.0), 2-phenylethanol (11.2), acetone (7.0), acetonitrile (6.1), chloroform (5.7), dibasic acid ester (8.4), diacetone alcohol (10.8), N,N-dimethylformamide (11.3), dimethyl sulfoxide (10.2), ethyl acetate (7.2), γ-butyrolactone (7.4), methyl ethyl ketone (5.1), methyl isobutyl ketone (4.1), methylene chloride (7.1), n-butyl acetate (6.3), N-methyl-2-pyrrolidone (7.2), propylene carbonate (4.1), 1,1,2,2-tetrachloroethane (5.3), tetrahydrofuran (8.0), toluene (2.0), etc. The numbers in parentheses indicate the values of the hydrogen bonding term δH. These first solvents may be used alone or in combination of two or more. Among these first solvents, methyl ethyl ketone, chloroform, and methylene chloride are preferred, and methylene chloride is more preferred because of their excellent solubility in methacrylic resin and fast evaporation rate.

[0074] Examples of the second solvent with a hydrogen bonding term δH of 14 to 24 include methanol (22.3), ethanol (19.4), isopropanol (16.4), butanol (15.8), ethylene glycol monoethyl ether (14.3), and the like. The numbers in parentheses indicate the values of the hydrogen bonding term δH. These second solvents may be used alone or in combination of two or more. Among these second solvents, methanol and ethanol are preferred, and ethanol is more preferred.

[0075] The proportion of the first solvent contained in the solvent is preferably 55 to 95% by mass, more preferably 60 to 95% by mass, and even more preferably 70 to 95% by mass.

[0076] The content of the methacrylic resin in the dope according to this embodiment is not particularly limited and is appropriately determined in consideration of the solubility of the methacrylic resin in the solvent used, the implementation conditions of the solution casting method, and the like. The content of the methacrylic resin is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 15 to 40% by mass.

[0077] The viscosity of the dope according to this embodiment can be appropriately adjusted by adjusting the content of the methacrylic resin and other components in the dope. From the viewpoints of coatability, filtration accuracy, etc., the viscosity of the dope is preferably 1,000 Poise (= 100 Pa·s) or less, more preferably 500 Poise (= 50 Pa·s) or less, and even more preferably 300 Poise (= 30 Pa·s) or less. The viscosity of the dope is measured by the method described in the examples below.

[0078] The dope according to this embodiment is used for manufacturing a resin film by the solution casting method. When manufacturing a resin film by the solution casting method, first, the dope according to this embodiment is cast on the surface of a support and coated into a uniform film shape with an applicator to form a dope film. Alternatively, the dope may be cast on the support using a pressure die. Next, the formed dope film is heated on the support to evaporate the solvent and form a resin film. The conditions for evaporating the solvent can be appropriately determined according to the boiling point of the solvent used. Then, the formed resin film is peeled off from the surface of the support. Note that the obtained resin film may be appropriately subjected to a drying process, a heating process, a stretching process, etc.

[0079] <Resin film> The resin film according to this embodiment contains the methacrylic resin according to the above-described embodiment. The resin film according to this embodiment is manufactured, for example, by the solution casting method using the dope according to the above-described embodiment.

[0080] The thickness of the resin film according to this embodiment is preferably, for example, 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. Also, the thickness of the resin film according to this embodiment is preferably, for example, 10 μm or more, more preferably 30 μm or more, even more preferably 50 μm or more, and particularly preferably 60 μm or more. If the thickness of the resin film is within the above range, there is an advantage that when performing vacuum forming using the resin film, it is difficult to deform and breakage is less likely to occur at the deep drawing part. Furthermore, there is also an advantage that a resin film having uniform optical properties and good transparency can be manufactured.

[0081] 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, due to high transparency, it can be suitably used for optical applications where light transmittance is required.

[0082] The glass transition temperature of the resin film according to this embodiment is preferably 110°C or higher, more preferably 115°C or higher, even more preferably 120°C or higher, and particularly preferably 124°C or higher. If the glass transition temperature is within the above range, the heat resistance of the resin film will be sufficient.

[0083] The haze of the resin film according to this embodiment is preferably 2.0% or less, more preferably 1.5% or less, even more preferably 1.3% or less, and particularly preferably 1.0% or less. Also, the internal haze of the resin film is preferably 1.5% or less, more preferably 1.0% or less, even more preferably 0.5% or less, and particularly preferably 0.4% or less. If the haze and the internal haze are within the above ranges, the transparency is high, so it can be suitably used for optical applications that require light transmittance. Note that the haze consists of the haze inside the film and the haze on the film surface (outside), and are expressed as internal haze and external haze, respectively.

[0084] The YI (Yellow Index) of the resin film according to this embodiment is preferably 1.2 or less, more preferably 1.0 or less. If the YI is within the above range, the transparency is high, so it can be suitably used for optical applications that require light transmittance.

[0085] The resin film according to this embodiment preferably has excellent mechanical properties, for example, high flex resistance. As an evaluation method for flex resistance, the MIT flex resistance test and the clam shell type flex test are known. The resin film according to this embodiment preferably has, for example, 6,000 or more flexing cycles until breakage in the clam shell type flex test, and more preferably 10,000 or more. If the number of flexing cycles until breakage is within the above range, the flex resistance of the resin film will be sufficient. Note that the number of flexing cycles until breakage in the clam shell type flex test is measured by the method described in the examples below.

[0086] The resin film according to this embodiment can be suitably used as an optical film such as a polarizer protection film. When the resin film according to this embodiment is used as a polarizer protection film, it is preferable that the optical anisotropy is small. In particular, it is preferable that not only the in-plane optical anisotropy (length direction, width direction) of the resin film but also the optical anisotropy in the thickness direction is small. That is, it is preferable that both the absolute values of 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. Also, 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.

[0087] Retardation is an index value calculated based on birefringence. The in-plane retardation (Re) and the thickness-direction retardation (Rth) can be calculated by the following formulas, respectively. In an ideal resin film that is completely optically isotropic in the three-dimensional direction, both the in-plane retardation Re and the thickness-direction retardation Rth become 0.

[0088] Re = (nx - ny) × d Rth = 〔(nx + ny) / 2 - nz〕× d In the above formulas, nx, ny, and nz represent the refractive indices in the respective axial directions when the stretching direction in the plane (the orientation direction of the polymer chains) is the X-axis, the direction perpendicular to the X-axis is the Y-axis, and the thickness direction of the resin film is the Z-axis. Also, d represents the thickness of the resin film, and nx - ny represents the orientation birefringence. Note that the MD direction of the film is taken as the X-axis, but in the case of a stretched film, the stretching direction is taken as the X-axis.

[0089] 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 , even more preferably -3.8×10 -4 ~3.8×10 -4If the orientation birefringence is within the above range, birefringence during molding is less likely to occur, and stable optical properties tend to be obtained.

[0090] (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 and film thickness accuracy of the resin film.

[0091] When stretching the resin film according to this embodiment, first, an unstretched resin film is formed from the dope according to this embodiment, and then uniaxial stretching or biaxial stretching is performed. Alternatively, during the formation of the resin film, a stretching operation is appropriately added as the processes of film formation and solvent degassing progress. Thereby, a stretched film (uniaxially stretched film or biaxially stretched film) can be manufactured. The stretching during film formation and the stretching after film formation may be appropriately combined.

[0092] The stretching ratio of the stretched film is not particularly limited and is appropriately determined according to the mechanical strength, surface properties, thickness accuracy, etc. of the stretched film to be manufactured. Although it also depends on the stretching temperature, the stretching ratio is generally preferably selected in the range of 1.1 to 5 times, more preferably in the range of 1.3 to 4 times, and even more preferably in the range of 1.5 to 3 times. If the stretching ratio is within the above range, the mechanical properties such as the elongation rate, tear propagation strength, and resistance to rubbing fatigue of the film tend to be significantly improved.

[0093] (Applications) The resin film according to this embodiment can be used for various applications such as transportation equipment, solar cell members, civil engineering and construction members, daily sundries, electric and electronic equipment, optical members, and medical supplies. In particular, since the resin film according to this embodiment is excellent in heat resistance and optical properties, it can be suitably used for optical applications. Examples of optical applications include front panels (cover windows) of various display devices, diffusion plates, polarizer protection films, polarizing plate protection films, retardation films, light diffusion films, optically isotropic films, and the like.

[0094] Among these, the resin film according to the present embodiment can be suitably used as a polarizer protection film or a front panel (cover window) of a display device. When the resin film according to the present embodiment is used as the front panel (cover window) of various display devices, a functional coating film layer such as a primer layer or a hard coat layer may be formed on at least one main surface of the resin film as necessary. Further, when the resin film according to the present embodiment is used as a polarizer protection 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, for example, in display devices such as liquid crystal display devices and organic EL display devices.

Examples

[0095] Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

[0096] The measurement methods of various physical properties described in the examples and comparative examples are as follows.

[0097] (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 by drying after washing with water to the weight of the monomer used. For the weight of the methacrylic resin obtained by drying after washing with water, the value obtained by subtracting the weight of the residual monomer in the methacrylic resin determined by the following analysis was used.

[0098] (Calculation of the remaining amount of monomer in methacrylic resin) Using a gas chromatograph (manufactured by Agilent Technologies, model 7890B), with a DB-1 column (manufactured by Agilent Technologies, film thickness 0.8 μm × inner diameter 0.20 mm × length 30 m) as the analytical column, analysis was carried out under the conditions of an injection port temperature of 150 °C and a detector temperature of 320 °C. The column temperature was programmed to increase 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 further from 260 °C to 320 °C at a rate of 20 °C / min and held for 3 minutes. Using chlorobenzene as the internal standard substance, a calibration curve was created by the internal standard method, and the residual amount of the monomer in the methacrylic resin was calculated.

[0099] (2) Syndiotacticity (rr) of triad display For methacrylic resin 1 The 1H-NMR spectrum was measured using a nuclear magnetic resonance spectrometer (manufactured by Bruker, AVANCEIII 400 MHz) in a deuterated chloroform solution at 22 °C with 16 accumulations. From the spectrum, the area (X) in the region of 0.60 - 0.95 ppm and the area (Y) in the region of 0.60 - 1.25 ppm were measured with tetramethylsilane (TMS) set at 0 ppm. Then, the syndiotacticity (rr) of the triad display was calculated by the formula: (X / Y) × 100.

[0100] (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, using a sample solution prepared by dissolving 20 mg of methacrylic resin in 20 mL of chloroform, analysis was carried out under the following apparatus and conditions. Measuring instrument: HLC-8220GPC (manufactured by Tosoh Corporation) Detector: RI detector Solvent: Chloroform Guard column: TSKgel guardcolumn SuperHZ-H (manufactured by Tosoh Corporation) Analysis column: TSKgel SuperHZM-H × 2 (manufactured by Tosoh Corporation) Measurement temperature: 40 °C Standard substance: Standard polystyrene (manufactured by Tosoh Corporation)

[0101] (4) Ratio of terminal double bonds A solution was prepared by dissolving approximately 20 mg of methacrylic resin in 0.6 - 0.7 mL of deuterated chloroform, and 1H-NMR measurement was performed using a nuclear magnetic resonance apparatus (manufactured by Bruker, AVANCE NEO 700 MHz). 1 The measurement temperature was 20 °C, the number of integrations was 8,192 times, and 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 7.26 ppm) using the Excitation Sculpting (ES) method, which is a type of solvent suppression method. From the obtained 1H-NMR spectrum, the total area (X) of the peaks (5.47 - 5.52 ppm and 6.21 ppm) derived from the terminal double bond portion of the methacrylic resin and the area (Y) of the peak (0.5 - 1.25 ppm) derived from the α-methyl group of the methacrylic resin were measured, and then the ratio of the terminal double bonds of the methacrylic resin was calculated using the formula: [(3 × X) / (2 × Y)] × 100. 1

[0102] (5) Glass transition temperature (Tg) ​The glass transition temperature (Tg) of the methacrylic resin was measured using a differential scanning calorimeter (DSC; DSC7000X manufactured by Hitachi High-Tech Science Corporation). First, under a nitrogen flow rate of 40 mL / min, the first heating was performed from 40°C to 160°C at a heating rate of 10°C / min. After cooling to 40°C, DSC measurement was carried out under the condition of performing the second heating from 40°C to 160°C at a heating rate of 10°C / min. Then, from the DSC curve measured during the second heating, the midpoint glass transition temperature (the temperature at the point where a straight line equidistant in the vertical axis direction from both a straight line obtained by extrapolating the baseline before the inflection point to the high temperature side and a straight line obtained by extrapolating the baseline after the inflection point to the low temperature side intersects the curve of the stepwise change part of the glass transition) was read.

[0103] (6) 5% weight loss temperature (Td5) The 5% weight loss temperature (Td5) of the methacrylic resin was measured using a thermogravimetric analyzer (STA7200 manufactured by Hitachi High-Tech Science Corporation). By performing the first heating from 40°C to 190°C at a heating rate of 10°C / min under a nitrogen gas flow of 200 mL / min, moisture and the like adsorbed by the methacrylic resin were removed. After cooling to 40°C, the second heating was then performed from 40°C to 500°C at a heating rate of 10°C / min. The temperature at which the weight of the sample decreased to 95% as determined from the thermogravimetric (TG) curve measured during the second heating was defined as the 5% weight loss temperature (Td5).

[0104] (7) Retention thermal stability The retention thermal stability of the methacrylic resin was evaluated using a thermogravimetric analyzer (STA7200 manufactured by Hitachi High-Tech Science Corporation). First, under a nitrogen gas flow of 200 mL / min, the temperature was raised from 40°C to 190°C at a heating rate of 10°C / min and heat-treated under the condition of holding at 190°C for 2.0 to 2.5 minutes. Then, 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 the condition of holding at 280°C for 30 minutes. Let the mass when the sample temperature reaches 280°C be X0, and the mass when held at 280°C for 15 minutes be X 15 and the formula: [(X0 - X 15The retention thermal stability was evaluated from the mass reduction rate calculated by / X0)×100.

[0105] (8) Haze measurement The haze of the resin film after stretching was measured in accordance with JIS K7136 using a haze meter (HZ-V3, manufactured by Suga Test Instruments Co., Ltd.). Also, the value obtained by performing the same measurement with both sides of the resin film sandwiched between glycerin and then glass in that order was defined as the internal haze. The obtained results were converted to the equivalent of a film thickness of 40 μm.

[0106] (9) Total light transmittance The total light transmittance of the resin film after stretching was measured in accordance with JIS K7361-1 using a haze meter (HZ-V3, manufactured by Suga Test Instruments Co., Ltd.).

[0107] (10) YI The YI of the resin film after stretching was measured in accordance with JIS K7373 using a spectrophotometer (SC-P, manufactured by Suga Test Instruments Co., Ltd.). The obtained results were converted to the equivalent of a film thickness of 40 μm.

[0108] (11) Clamshell type bending test The bending resistance of the resin film after stretching was evaluated using a clamshell type desktop durability tester (DMLHP-CS, manufactured by Yuasa System Devices Co., Ltd.). The conditions were set at a curvature radius of 0.35 mm and a test speed of 30 r / min (30 times / min) in an atmosphere of 23°C and a relative humidity of 55%. A test piece cut into a strip shape with a width of 2 cm and a length of 5 cm was used as the test piece, and it was set and tested in the direction where a fold would be made perpendicular to the stretching direction. The test was continued until the test piece broke. The test was performed three times for each sample, and the bending resistance was evaluated from the number of times until breakage.

[0109] (12) Solvent resistance Using isopropyl alcohol (manufactured by FUJIFILM Wako Pure Chemical Corporation) and xylene (manufactured by FUJIFILM Wako Pure Chemical Corporation) as solvents, the solvent resistance of the resin film after stretching was evaluated in accordance with Method 3 (drop method) of JIS K5600-6-1. The judgment criteria are as follows. -Judgment Criteria- A: No change in appearance. B: Slightly whitens. C: Marked whitening or traces of dissolution remain.

[0110] <Example 1> Into a 5-liter glass reactor equipped with an H-type stirring blade agitator, 150 parts by mass of deionized water, 0.400 parts by mass of tricalcium phosphate as 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 bubbled through to replace the air in the reactor. Then, 100 parts by mass of methyl methacrylate (MMA), 0.017 parts by mass of n-octyl mercaptan (n-OM) as a chain transfer agent, and 0.019 parts by mass of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Corporation, V-65) as a polymerization initiator were added to the reactor as a monomer solution. Thereafter, the temperature of the liquid in the reactor was raised to 75 °C to initiate polymerization. After 45 minutes had elapsed since the start of polymerization, an additional 0.10 parts by mass of tricalcium phosphate was added to the reaction solution. After 4 hours had elapsed since the start of polymerization, the temperature of the liquid in the reactor was raised to 95 °C, and polymerization was terminated when stirring was continued at 95 °C for 3 hours. The polymerization conversion rate at 4 hours from the start of polymerization was 92%. Pickling with 1 N hydrochloric acid in an amount 0.1 times the weight ratio based on the amount of charged monomer was carried out once. The obtained resin was washed with deionized water in an amount 7 times the amount of the resin, and the resin was dried to obtain bead-shaped resin particles. These resin particles were dissolved in methylene chloride to a concentration of 10% by mass, and the solution was dropped into 5 times the amount of methanol of the methylene chloride solution to precipitate the resin. The precipitated resin was collected by suction filtration and dried to obtain a methacrylic resin after precipitation purification.

[0111] A mixed solvent consisting of 93% by mass of methylene chloride and 7% by mass of ethanol was placed in a screw tube container, and then the above-mentioned dried methacrylic resin was added. The solution was stirred until the methacrylic resin was completely dissolved to prepare a dope with a solid content concentration (SC) of 12% by mass.

[0112] The dope prepared above was cast onto a PET film substrate (manufactured by Toyobo Co., Ltd., Cosmo Shine A4100) and coated into a uniform film shape with an applicator. At that time, the clearance was adjusted so that the thickness after drying would be about 60 μm. After coating, the dope film was dried in an oven at 40 °C for 1 hour, and then the obtained resin film was peeled off from the PET film substrate. Thereafter, the resin film was fixed to a stainless steel frame and dried in an oven at 140 °C for 2 hours to remove the residual solvent, obtaining a resin film. Further, the obtained resin film was subjected to uniaxial stretching with width fixation at 132 °C. The stretching ratio was 1.5 times and the stretching speed was 100 mm / min. The average film thickness of the stretched resin film was 41 μm.

[0113] The raw materials in Example 1 are shown in Table 1, and the physical properties of the methacrylic resin and the resin film are shown in Table 2.

[0114] <Example 2> The same operations as in Example 1 were carried out except that the type of polymerization initiator was changed to t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, Perbutyl O). The polymerization conversion rate at the 4th hour from the start of polymerization was 90%. The average film thickness of the obtained stretched resin film was 43 μm. The raw materials in Example 2 are shown in Table 1, and the physical properties of the methacrylic resin and the resin film are shown in Table 2.

[0115] <Example 3> The same operations as in Example 1 were carried out except that the type of polymerization initiator was changed to t-hexylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, Perhexyl O). The polymerization conversion rate at the 4th hour from the start of polymerization was 93%. The average film thickness of the obtained stretched resin film was 40 μm. The raw materials in Example 3 are shown in Table 1, and the physical properties of the methacrylic resin and the resin film are shown in Table 2.

[0116] <Example 4> The type of polymerization initiator was changed to t-hexyl peroxy-2-ethylhexanoate (manufactured by NOF Corporation, Perhexy O), and the addition amount of n-octyl mercaptan (n-OM) as a chain transfer agent was changed to 0.0025 parts by mass. Otherwise, the same polymerization operation as in Example 1 was carried out. After the same washing and drying as in Example 1, a methacrylic resin was obtained. The polymerization conversion rate at 4 hours from the start of polymerization was 93%.

[0117] A screw tube container was filled with a mixed solvent consisting of 93% by mass of methylene chloride and 7% by mass of ethanol, and then the above-mentioned dried methacrylic resin was added. The solution was stirred until the methacrylic resin was completely dissolved to prepare a dope with a solid content concentration (SC) of 5% by mass. Using this dope, when a resin film was produced in the same manner as in Example 1, the average film thickness of the obtained stretched resin film was 41 μm. The raw materials in Example 4 are shown in Table 1, and the physical properties of the methacrylic resin and the resin film are shown in Table 2.

[0118] <Comparative Example 1> As the methacrylic resin, Parapet HR-S (a copolymer of methyl methacrylate (MMA) and methyl acrylate (MA) manufactured by Kuraray Co., Ltd., MMA / MA = 98.9 / 1.1 (mass ratio)) was used, and precipitation purification from a methylene chloride solution of the methacrylic resin to methanol was not performed. However, precipitation purification was carried out only when preparing a sample for the quantification of terminal double bonds. Using this methacrylic resin, the same operation as in Example 1 was carried out except that the solid content concentration (SC) of the dope was changed to 25% by mass and the stretching temperature of the resin film was changed to 125°C. The average film thickness of the obtained stretched resin film was 36 μm. The raw materials in Comparative Example 1 are shown in Table 1, and the physical properties of the methacrylic resin and the resin film are shown in Table 2.

[0119] <Comparative Example 2> To a 2-liter glass reactor equipped with a three-blade retreating blade agitator, 170 parts by mass of deionized water, 0.10 part by mass of disodium hydrogen phosphate as a suspension aid, and 0.037 part by mass of 2,2'-azobis(isobutyric acid) dimethyl (V-601, manufactured by Fujifilm Wako Pure Chemical Corporation) as a polymerization initiator were charged. While stirring the aqueous solution in the reactor at 550 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was bubbled through to replace the air in the reactor. Then, a monomer solution containing 100 parts by mass of methyl methacrylate (MMA) and 0.270 part by mass of n-octyl mercaptan (n-OM) as a chain transfer agent was added to the reactor. Subsequently, 0.375 part by mass of Methocel 60SH-50 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.) as a water-soluble polymer was added to the reactor as a dispersant. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 79 °C to initiate polymerization. After reacting the monomer at 79 °C for 6 hours, the temperature of the liquid in the reactor was raised to 94 °C. The reaction solution was stirred at the same temperature for 1 hour to complete the polymerization. The obtained resin was washed with 3.4 times the amount of deionized water based on the resin amount and dried to obtain bead-like particles. These particles were dissolved in methylene chloride to a concentration of 10% by mass, and the solution was dropped into 5 times the amount of methanol of the methylene chloride solution to precipitate the resin. The precipitated resin was collected by suction filtration and dried to obtain a methacrylic resin after precipitation purification.

[0120] A screw tube container was charged with a mixed solvent consisting of 93% by mass of methylene chloride and 7% by mass of ethanol, and then the above-mentioned dried methacrylic resin was added. The solution was stirred until the methacrylic resin was completely dissolved to prepare a dope with a solid content concentration (SC) of 25% by mass.

[0121] The dope prepared above was cast onto a PET film substrate (manufactured by Toyobo Co., Ltd., Cosmo Shine A4100) and coated into a uniform film shape with an applicator. At that time, the clearance was adjusted so that the thickness after drying would be about 60 μm. After coating, the dope film was dried in an oven at 40 °C for 1 hour, and then the obtained resin film was peeled off from the PET film substrate. Then, the resin film was fixed to a stainless steel frame and dried in an oven at 140 °C for 2 hours to remove the residual solvent, obtaining a resin film. Further, the obtained resin film was subjected to width-fixed uniaxial stretching at 132 °C. The stretching ratio was 1.5 times and the stretching speed was 100 mm / min. The average film thickness of the stretched resin film was 38 μm.

[0122] The raw materials in Comparative Example 2 are shown in Table 1, and the physical properties of the methacrylic resin and the resin film are shown in Table 2.

[0123] <Comparative Example 3> Into a 0.5-liter glass reactor equipped with an H-type stirring blade mixer, 170 parts by mass of deionized water, 0.10 part by mass of disodium hydrogen phosphate as a suspension aid, and 1.00 part by mass of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Corporation, V-70) as a polymerization initiator were charged. While stirring the aqueous solution in the reactor at 380 rpm, nitrogen gas (oxygen concentration 0.2 ppm) was bubbled through to replace the air in the reactor, and then 100 parts by mass of methyl methacrylate (MMA) was added to the reactor. Subsequently, 0.375 part by mass of Methocel 60SH-50 (hydroxypropyl methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd.) as a water-soluble polymer was added to the reactor as a dispersant. After stirring for 30 minutes, the temperature of the liquid in the reactor was raised to 30 °C to initiate polymerization. After reacting the monomer at 30 °C for 3 hours, the temperature of the liquid in the reactor was raised to 50 °C for 1 hour, then to 70 °C for 30 minutes, and further to 95 °C for 1 hour with stirring to complete the polymerization. The resulting resin was washed with 7 times the amount of deionized water based on the resin amount and dried to obtain bead-like particles. These particles were dissolved in methylene chloride to a concentration of 10% by mass, and the solution was dropped into 5 times the amount of methanol of the methylene chloride solution to precipitate the resin. The precipitated resin was collected by suction filtration and dried to obtain a methacrylic resin after precipitation purification.

[0124] A screw tube container was filled with a mixed solvent consisting of 93% by mass of methylene chloride and 7% by mass of ethanol, and then the above-mentioned dried methacrylic resin was added. The solution was stirred until the methacrylic resin was completely dissolved to prepare a dope with a solid content concentration (SC) of 12% by mass.

[0125] The dope prepared above was cast onto a PET film substrate (manufactured by Toyobo Co., Ltd., Cosmo Shine A4100) and coated into a uniform film shape using an applicator. At that time, the clearance was adjusted so that the thickness after drying would be approximately 60 μm. After coating, the dope film was dried in an oven at 40 °C for 1 hour, and then the obtained resin film was peeled off from the PET film substrate. Thereafter, the resin film was fixed to a stainless-steel frame and dried in an oven at 140 °C for 2 hours to remove the residual solvent, obtaining a resin film. Further, uniaxial stretching with width fixation was performed on the obtained resin film at 135 °C. The stretching ratio was 1.5 times and the stretching speed was 100 mm / min. The average film thickness of the stretched resin film was 41 μm.

[0126] The raw materials in Comparative Example 3 are shown in Table 1, and the physical properties of the methacrylic resin and the resin film are shown in Table 2.

[0127]

Table 1

[0128]

Table 2

[0129] As shown in Table 1 and Table 2, in Examples 1 to 3, methacrylic resins with high syndiotacticity and, as a result, high glass transition temperatures (Tg) were obtained. Also, in Examples 1 to 3, since the weight average molecular weight (Mw) of the methacrylic resin was large, the resin film exhibited excellent flexural resistance. Specifically, the stretched resin films of Examples 1 to 3 did not break even when the number of flexures exceeded 200,000 times. Further, the methacrylic resins of Examples 1 to 3 showed values where the 5% weight loss temperature (Td5) exceeded 300 °C, and the mass loss rate when held at 250 °C for 15 minutes was small, indicating excellent thermal stability. Furthermore, the resin films after centrifugation in Examples 1 to 3 were also excellent in solvent resistance.

[0130] On the one hand, although the methacrylic resin of Comparative Example 1 was excellent in thermal stability, its glass transition temperature (Tg) was lower than those of Examples 1 to 3, and it was inferior in heat resistance. Also, in Comparative Example 1, since the weight average molecular weight (Mw) of the methacrylic resin was small, the mechanical properties of the resin film were inferior to those of Examples 1 to 3. Specifically, the number of bending times until breakage of the drawn resin film of Comparative Example 1 remained at 3,000 to 4,500 times. Furthermore, the drawn resin film of Comparative Example 1 was inferior in solvent resistance compared to Examples 1 to 3.

[0131] In Comparative Example 2, a methacrylic resin having a high glass transition temperature (Tg) was obtained, and the thermal stability of the methacrylic resin was also high. However, since the weight average molecular weight (Mw) of the methacrylic resin was small, the mechanical properties of the resin film were inferior to those of Examples 1 to 3. Specifically, the number of bending times until breakage of the drawn resin film of Comparative Example 2 remained at 1,000 to 2,000 times. Also, the drawn resin film of Comparative Example 2 was inferior in solvent resistance compared to Examples 1 to 3.

[0132] In Comparative Example 3, a methacrylic resin having a high glass transition temperature (Tg) was obtained. However, since the ratio of the amount of terminal double bonds in the methacrylic resin was large, the thermal stability was low. Also, the drawn resin film of Comparative Example 3 was inferior in solvent resistance compared to Examples 1 to 3.

Claims

1. The proportion of structural units derived from methyl methacrylate is 98% by mass or more, The weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) is 500,000 or more, The syndiotacticity in triad representation is 55% or more, A methacrylic resin in which the proportion of terminal double bonds with respect to the structural units derived from methyl methacrylate is less than 0.015 mol%.

2. The methacrylic resin according to claim 1, wherein the syndiotacticity in triad representation is 70% or less.

3. The methacrylic resin according to claim 1 or 2, wherein the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 1.6 to 2.

8.

4. The methacrylic resin according to claim 1 or 2, wherein the 5% weight loss temperature is 300°C or higher.

5. The methacrylic resin according to claim 1 or 2, wherein the glass transition temperature is 120°C or higher.

6. A polymerization step of polymerizing a monomer component having a methyl methacrylate content of 98% by mass or more in the presence of a polymerization initiator and a chain transfer agent, In the polymerization step, the polymerization temperature until 90% or more of the resulting methacrylic resin is produced is less than 100°C, The 10-hour half-life temperature of the polymerization initiator is 45°C or higher, The amount of the chain transfer agent used is 0.030 mol% or less with respect to the total amount of the monomer component, A method for producing a methacrylic resin, wherein the ratio of the total mol amount of the chain transfer agent to the total mol amount of the polymerization initiator is more than 0 and 3.0 or less.

7. The method for producing a methacrylic resin according to claim 6, wherein the melting point of the polymerization initiator is less than 100°C.

8. The method for producing a methacrylic resin according to claim 6 or 7, wherein aqueous polymerization is carried out in the polymerization step.

9. The method for producing a methacrylic resin according to claim 6 or 7, wherein the polymerization initiator contains at least one selected from an azo polymerization initiator and a peroxide polymerization initiator.

10. The method for producing a methacrylic resin according to claim 9, wherein the azo polymerization initiator is a nitrile-based azo polymerization initiator.

11. A resin composition containing the methacrylic resin according to claim 1 or 2.

12. Containing the methacrylic resin according to claim 1 or 2 and a solvent, The solvent contains a first solvent having a hydrogen bonding term δH of 1 to 12 in the Hansen solubility parameter and a second solvent having a hydrogen bonding term δH of 14 to 24, and is a dope for film production by the solution casting method.

13. A resin film containing the methacrylic resin according to claim 1 or 2.

14. The resin film according to claim 13, wherein the number of bending times until breakage in the clamp shell type bending test is 6,000 times or more.

15. The resin film according to claim 13, wherein the resin film is a polarizer protection film.

16. A polarizing plate formed by laminating a polarizer and the resin film according to claim 13.

17. A display device including the polarizing plate according to claim 16.

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