Methacrylic copolymer for inverse wavelength dispersion retardation film, composition, film, method for producing film, and laminate

Abstract

The present invention provides a methacrylic copolymer for forming a reverse wavelength dispersive retardation film, the methacrylic copolymer having a glass transition temperature of 120°C or higher and comprising: 40-87 mass% of a methyl methacrylate unit; 6-30 mass% of a structural unit (R) having in the main chain at least one ring structure selected from the group consisting of a lactone ring unit, a glutaric anhydride unit, and an N-substituted or unsubstituted glutarimide unit; and 7-30 mass% of an α-methyl styrene unit, wherein equations (1) and (2) are satisfied. (1): Re(450) / Re(550)=0.30-0.95, (2): Re(650) / Re(550)=1.02-2.00 (In equations (1) and (2), Re(450), Re(550), and Re(650) represent retardation values at wavelengths of 450 nm, 550 nm, and 650 nm, respectively.)

Description

Technical Field

[0001] The present invention relates to a methacrylic copolymer for a retardation film exhibiting reverse wavelength dispersion, a composition, a film, a method for producing the film, and a laminate.

Background Art

[0002] Image display devices such as liquid crystal displays and organic EL displays are diversifying in usage forms and usage environments, and more advanced functions are also required for the optical films constituting the image display devices.

[0003] One of the functions required for these optical films is to have a higher retardation on the longer wavelength side in the visible light region, so-called reverse wavelength dispersion. An optical film having reverse wavelength dispersion can, for example, bring the retardation of the film close to one-fourth of the wavelength (λ) in a wide wavelength range in the visible light region, and thus can be used as a retardation film (λ / 4 plate) for converting linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light. By using it in combination with a polarizing plate, external light reflection in an image display device can be prevented, and the bright contrast and black reproducibility can be improved. Further, it is also expected to be used as a so-called polarizing plate compensation film for reducing color shift due to the viewing angle of the polarizing plate and as a polarizer protection film with retardation.

[0004] As those that exhibit such reverse wavelength dispersion in a single film, films containing cellulose acetate (see, for example, Patent Document 1) and films containing cellulose acetate propionate (see, for example, Patent Document 2) have been reported. However, films made of cellulose-based resins have insufficient moisture and heat resistance, and there has been a problem that the retardation fluctuates and color unevenness occurs at high temperatures or high humidities.

[0005] (Meth)acrylic resins such as polymethyl methacrylate are widely used as materials for constructing various optical members because of their excellent transparency and low optical distortion. In order to use (meth)acrylic resins as materials for optical films such as polarizer protection films and retardation films, studies have been made to improve their heat resistance and mechanical strength. Patent Document 3 discloses a (meth)acrylic resin having a lactone ring structure. Patent Document 4 discloses an acrylic resin having an imide structure. Patent Document 5 discloses a (meth)acrylic resin having a maleimide unit. Although the heat resistance of these resins is improved, they have positive wavelength dispersion and do not have the reverse wavelength dispersion suitable for a retardation film.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a methacrylic copolymer for forming a reverse wavelength dispersion retardation film, a composition, a film, a method for producing a film, and a laminate, which are excellent in heat resistance and exhibit reverse wavelength dispersion.

Means for Solving the Problems

[0008] As a result of intensive studies to achieve the above object, the present inventors have completed the present invention including the following aspects. [1] A methacrylic copolymer having a glass transition temperature of 120 °C or higher, comprising 40 to 87% by mass of methyl methacrylate units, 6 to 30% by mass of a structural unit (R) having at least one ring structure selected from the group consisting of lactone ring units, glutaric anhydride units, and N-substituted or unsubstituted glutarimide units in the main chain, and 7 to 30% by mass of α-methylstyrene units, Re(450) / Re(550) = 0.30 to 0.95 (1) Re(650) / Re(550) = 1.02 to 2.00 (2) (In formula (1) and formula (2), Re(450), Re(550), and Re(650) represent retardation values at wavelengths of 450 nm, 550 nm, and 650 nm, respectively.) A methacrylic copolymer for forming an inverse wavelength dispersion retardation film that satisfies the above conditions. [2] The methacrylic copolymer for forming an inverse wavelength dispersion retardation film according to [1], wherein the structural unit (R) is an N-substituted or unsubstituted glutarimide unit represented by formula (3).

Chemical formula

[0009] According to the present invention, a methacrylic copolymer for forming a reverse wavelength dispersion retardation film, a composition containing the copolymer, a film, and a laminate, which are excellent in heat resistance, exhibit reverse wavelength dispersion, and also exhibit high retardation expressibility, can be obtained. [Brief Description of the Drawings]

[0010]

Figure 1

[0011] (Methacrylic Copolymer) The methacrylic copolymer of the present invention contains a methyl methacrylate unit, an α-methylstyrene unit, and a structural unit (R). The methacrylic copolymer of the present invention further contains a copolymerizable monomer unit, a methacrylic amide unit represented by the following formula (A), and a 2-(hydroxyalkyl) acrylate unit represented by the following formula (B).

[0012]

Chemical formula

[0013] In the methacrylic copolymer of the present invention, the proportion of the methyl methacrylate unit is preferably 40 to 87% by mass, more preferably 50 to 85% by mass, and still more preferably 65 to 80% by mass based on all the structural units. When the proportion of the methyl methacrylate unit is less than this range, the total light transmittance of the obtained methacrylic copolymer deteriorates. When the proportion of the methyl methacrylate unit is more than this range, the heat resistance of the obtained methacrylic copolymer becomes low.

[0014] In the methacrylic copolymer of the present invention, the proportion of the α-methylstyrene unit is preferably 7 to 30% by mass, more preferably 8 to 27% by mass, and still more preferably 11 to 25% by mass based on all the structural units. When the proportion of the α-methylstyrene unit is less than this range, the saturated water absorption rate of the obtained methacrylic copolymer increases. In addition, a methacrylic copolymer in which the proportion of the α-methylstyrene unit exceeds 30% by mass has low polymerizability and reduced productivity.

[0015] The structural unit (R) is a structural unit having at least one ring structure selected from the group consisting of a lactone ring unit, a glutaric anhydride unit, and an N-substituted or unsubstituted glutarimide unit in the main chain. The structural unit may contain, in the main chain, a methacrylamide unit represented by the above formula (A) and / or a 2-(hydroxyalkyl)acrylate ester unit represented by the above formula (B).

[0016] The lactone ring unit is a structural unit containing a >CH-O-C(=O)- group in the ring structure. The structural unit containing a >CH-O-C(=O)- group in the ring structure preferably has 4 to 8, more preferably 5 to 6, and most preferably 6 ring-constituting elements. Examples of the structural unit containing a >CH-O-C(=O)- group in the ring structure include lactone diyl structural units such as a β-propiolactone diyl structural unit, a γ-butyrolactone diyl structural unit, and a δ-valerolactone diyl structural unit. The structural unit containing a >CH-O-C(=O)- group in the ring structure can be obtained, for example, by intramolecular cyclization of a polymer having a hydroxy group and an ester group with respect to the hydroxy group and the ester group. In the formula, ">C" means that there are two bonds to the carbon atom C.

[0017] For example, examples of the δ-valerolactone diyl structural unit include a structural unit represented by the formula (I).

[0018]

Chemical formula

[0019] In the formula (I), R 6 , R 7 and R 8is each independently a hydrogen atom or an organic group having 1 to 20 carbon atoms, preferably a hydrogen atom or an organic group having 1 to 10 carbon atoms, more preferably a hydrogen atom or an organic group having 1 to 5 carbon atoms. Here, the organic group is not particularly limited as long as it has 1 to 20 carbon atoms, and examples thereof include linear or branched alkyl groups, linear or branched aryl groups, -OCOCH3 groups, -CN groups, etc. The organic group may contain heteroatoms such as oxygen atoms. R 6 and R 7 are preferably methyl groups, and R 8 is preferably a hydrogen atom.

[0020] The lactone ring unit can be incorporated into the methacrylic copolymer by methods described in JP-A-2000-230016, JP-A-2001-151814, JP-A-2002-120326, JP-A-2002-254544, JP-A-2005-146084, etc., for example, by intramolecular cyclization of a structural unit derived from 2-(hydroxyalkyl)acrylate and a structural unit derived from methyl (meth)acrylate. JP-A-2000-230016, JP-A-2001-151814, JP-A-2002-120326, JP-A-2002-254544, and JP-A-2005-146084 are hereby incorporated by reference in their entirety into this specification.

[0021] The glutaric anhydride unit is a unit having a 2,6-dioxodihydropyranediyl structure. Examples of the unit having a 2,6-dioxodihydropyranediyl structure include the structural unit represented by formula (II).

[0022]

Chemical formula

[0023] The unit having a 2,6-dioxodihydropyran diyl structure can be incorporated into a methacrylic copolymer by methods described in, for example, JP-A-2007-197703 and JP-A-2010-96919, such as intramolecular cyclization of structural units derived from two adjacent (meth)acrylic acids, intramolecular cyclization of a structural unit derived from (meth)acrylic acid and a structural unit derived from methyl (meth)acrylate. JP-A-2007-197703 and JP-A-2010-96919 are incorporated herein by reference in their entirety.

[0024] The N-substituted or unsubstituted glutarimide unit is a unit having an N-substituted or unsubstituted 2,6-dioxopiperidine diyl structure. Examples of the unit having an N-substituted or unsubstituted 2,6-dioxopiperidine diyl structure include the structural unit represented by formula (3).

[0025] [Chemical formula] In formula (3), R 1 are each independently a hydrogen atom or a methyl group, preferably a methyl group. R 2 is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an organic group having 6 to 15 carbon atoms containing an aromatic ring, preferably a hydrogen atom, a methyl group, an n-butyl group, a cyclohexyl group or a benzyl group, more preferably a methyl group, an n-butyl group, or a cyclohexyl group. The structural unit represented by formula (3) may be produced, for example, by reaction of the corresponding acid anhydride (IIa) with an imidizing agent represented by R 2 -NH2 as shown in Scheme (i), or by an intramolecular cyclization reaction of a copolymer having a partial structure of formula (C). It is preferable to heat in order to convert the structural unit represented by formula (C) to the structural unit represented by formula (3) by an intramolecular cyclization reaction. Scheme (i) [Chemical formula] (wherein R 1 and R 2 are as defined above.)

[0026] The N-substituted or unsubstituted glutarimide unit can be obtained by the methods described in WO2005 / 10838A1, JP-A-2010-254742, JP-A-2008-273140, JP-A-2008-274187, etc. Specifically, ammonia, methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, tert-butylamine, n-hexylamine and other aliphatic hydrocarbon group-containing amines, aniline, toluidine, trichloroaniline and other aromatic hydrocarbon group-containing amines, cyclohexylamine and other alicyclic hydrocarbon group-containing amines, urea, 1,3-dimethylurea, 1,3-diethylurea, 1,3-dipropylurea and other imidizing agents are reacted with a structural unit derived from two adjacent methyl methacrylates or a glutaric anhydride unit. Among these, methylamine is preferred. After reacting a structural unit derived from two adjacent methyl methacrylates or a glutaric anhydride unit with an imidizing agent, it may be reacted with a dialkyl carbonate such as dimethyl carbonate to convert a carboxylic acid such as methacrylic acid into an alkyl methacrylate such as methyl methacrylate. The carboxylic acid can be produced by hydrolysis of a methacrylic acid ester or a glutaric anhydride unit represented by the formula (II), or when a carboxylic acid and an amide are produced by the reaction of a glutaric anhydride unit represented by the formula (II) with an imidizing agent. The reaction with a dialkyl carbonate such as dimethyl carbonate may be carried out in the presence of a tertiary amine such as triethylamine. WO2005 / 10838A1, JP-A-2010-254742, JP-A-2008-273140, and JP-A-2008-274187 are hereby incorporated by reference in their entirety into this specification.)

[0027] In the methacrylic copolymer of the present invention, the proportion of the structural unit (R) is preferably 6 to 30% by mass, more preferably 7.5 to 25% by mass, still more preferably 8 to 25% by mass, based on all the structural units. By changing the ratio of the structural unit (R) to methyl methacrylate, the orientation birefringence of the methacrylic copolymer can be changed. Further, the higher the content of the structural unit (R), the more the heat resistance of the methacrylic copolymer is improved, but the flexibility is decreased, and the compatibility and moldability with other (co)polymers tend to be decreased.

[0028] In one preferred embodiment of the present invention, the methacrylic copolymer of the present invention may contain the methacrylamide unit represented by the above formula (A) and the 2-(hydroxyalkyl)acrylate unit represented by the above formula (B), each preferably in an amount of 0 to 2% by mass, more preferably 0 to 1.5% by mass, still more preferably 0 to 1.0% by mass, and most preferably 0 to 0.5% by mass, based on all the structural units. When the structural units of the formula (A) and / or (B) exceed the above ranges, the saturated water absorption rate of the resulting methacrylic copolymer increases, or a crosslinked product is formed during molding, resulting in foreign matter defects and a decrease in appearance quality.

[0029] The methacrylic copolymer of the present invention may contain a methyl methacrylate unit, an α-methylstyrene unit, and a structural unit (O) other than (R). Examples of the structural unit (O) include units derived from vinyl monomers having only one polymerizable carbon-carbon double bond in one molecule, such as (meth)acrylamide, (meth)acrylonitrile, (meth)acrylic acid, and styrene, the structural unit represented by the formula (A), and the structural unit represented by the formula (B). Among them, styrene is preferred. The proportion of the structural unit (O) is preferably 20% by mass or less, more preferably 1% by mass or more and 20% by mass or less, still more preferably 3% by mass or more and 10% by mass or less, based on all the structural units. The proportions of the methyl methacrylate unit, the α-methylstyrene unit, the structural unit (R), and the structural unit (O) can be measured by 1 H-NMR or the like.

[0030] The methacrylic copolymer of the present invention has a weight average molecular weight (Mw) of preferably 40,000 to 200,000, more preferably 50,000 to 180,000, and even more preferably 55,000 to 160,000. When Mw is 40,000 or more, the strength, toughness, etc. of the molded article of the present invention are improved. When Mw is 200,000 or less, the fluidity of the methacrylic copolymer of the present invention is improved, and the molding processability is improved.

[0031] The weight average molecular weight (Mw) is a value calculated by converting the chromatogram measured by gel permeation chromatography into the molecular weight of standard polystyrene.

[0032] The methacrylic copolymer of the present invention has an acid value of preferably 0.01 to 0.30 mmol / g, more preferably 0.05 to 0.28 mmol / g. The acid value is a value proportional to the content of carboxylic acid units and carboxylic anhydride units in the methacrylic copolymer. The acid value can be calculated, for example, by the method described in JP-A-2005-23272. When the acid value is within the above range, the balance of heat resistance, mechanical properties, and molding processability is excellent.

[0033] The methacrylic copolymer of the present invention has a glass transition temperature of preferably 120°C, more preferably 121°C, and even more preferably 122°C as the lower limit, and is not particularly limited as the upper limit, but is preferably 160°C. The higher the glass transition temperature of the methacrylic copolymer, the less likely the molded article containing the methacrylic copolymer is to be deformed or shrunk by heat, that is, the higher the heat resistance. In this specification, the "glass transition temperature (Tg)" is measured in accordance with JIS K7121. Specifically, the temperature is raised to 230°C once, then cooled to room temperature, and then the DSC curve is measured under the condition of raising the temperature from room temperature to 230°C at 10°C / min. The midpoint obtained from the DSC curve measured during the second heating is determined as the "glass transition temperature (Tg)".

[0034] The methacrylic copolymer of the present invention preferably has a higher birefringence retardation in the longer wavelength side in the visible light region, that is, it preferably exhibits so-called inverse wavelength dispersion. Specifically, when the retardation value at a wavelength λ (nm) is denoted as Re(λ), the ratio of Re(450) to Re(550) (Re(450) / Re(550)) of the methacrylic copolymer satisfies the following formula (1), and the ratio of Re(650) to Re(550) (Re(550) / Re(650)) preferably satisfies the following formula (2). 0.30≦Re(450) / Re(550)≦0.95 (1) 1.02≦Re(650) / Re(550)≦2.00 (2) When the wavelength dispersion of the retardation of the methacrylic copolymer is within the above range, the state of elliptical polarization when linearly polarized light is incident on the methacrylic copolymer can be made homogeneous regardless of the wavelength, so that the optical compensation ability is good.

[0035] The lower limit of the ratio of Re(450) to Re(550) (Re(450) / Re(550)) is preferably 0.30 or more, more preferably 0.60 or more, further preferably 0.75 or more, and even more preferably 0.79 or more. The upper limit of Re(450) / Re(550) is preferably 0.95 or less, more preferably 0.90 or less, further preferably 0.87 or less, and particularly preferably 0.85 or less. The lower limit of the ratio of Re(650) to Re(550) (Re(650) / Re(550)) is preferably 1.02 or more, more preferably 1.05 or more, further preferably 1.10 or more, and even more preferably 1.15 or more. The upper limit of Re(650) / Re(550) is preferably 2.00 or less, more preferably 1.50 or less, further preferably 1.35 or less, and even more preferably 1.25 or less.

[0036] The methacrylic copolymer of the present invention contains a methyl methacrylate unit, a structural unit (R), and an α-methylstyrene unit, thereby exhibiting reverse wavelength dispersibility. The reason for this is speculated as follows. A polymer composed of methyl methacrylate units has a relatively small negative intrinsic birefringence as exemplified in FIG. 1(b), and has a positive wavelength dispersibility in which the absolute value of the birefringence increases as the wavelength of light becomes shorter. Since the structural unit (R) is a structural unit having a ring structure in the main chain, the polymer composed of this unit is considered to have a positive intrinsic birefringence as exemplified in FIG. 1(a) and to have a positive wavelength dispersibility in which the birefringence increases as the wavelength of light becomes shorter. Therefore, a conventional copolymer containing a methyl methacrylate unit and a structural unit (R) has a positive wavelength dispersibility as exemplified in FIG. 1(e). On the other hand, a polymer composed of α-methylstyrene units is considered to have a negative intrinsic birefringence as exemplified in FIG. 1(c), to have a positive wavelength dispersibility, and to have a relatively large inclination. Therefore, it is considered that the methacrylic copolymer of the present invention exhibits reverse wavelength dispersibility as exemplified in FIG. 1(d) as a result of combining these actions.

[0037] Regarding the phase difference and its dispersibility at each wavelength, they can be arbitrarily adjusted by varying the ratios of the methyl methacrylate unit, the α-methylstyrene unit, and the structural unit (R) within the scope of the present invention.

[0038] The methacrylic copolymer of the present invention can be obtained by a method including subjecting a copolymer of methyl methacrylate and α-methylstyrene (hereinafter sometimes referred to as a precursor polymer) to a ring structure forming reaction. That is, the methacrylic copolymer of the present invention includes a step of continuously supplying a reaction raw material comprising a monomer mixture containing methyl methacrylate, α-methylstyrene, and, if desired, a copolymerizable monomer, a radical polymerization initiator, and, if necessary, a chain transfer agent to a tank reactor, a step of bulk polymerizing the monomer mixture in the tank reactor until a polymerization conversion rate of 30 to 60% by mass to obtain a reaction product, A step of removing the monomer mixture in the reaction product, and A step of subjecting the obtained precursor polymer to a ring structure forming reaction can be obtained by a production method including these steps.

[0039] The precursor polymer is polymerized from a reaction raw material containing a monomer mixture, a radical polymerization initiator, and, if necessary, a chain transfer agent. The monomer mixture preferably contains 51 to 90% by mass, more preferably 65 to 85% by mass of methyl methacrylate in the monomer mixture. Also, α-methylstyrene preferably contains 49 to 10% by mass, more preferably 35 to 15% by mass. The copolymerizable monomer contains 0 to 10% by mass, preferably 0 to 5% by mass. The monomer mixture may contain a copolymerizable monomer other than methyl methacrylate and α-methylstyrene. Examples of such copolymerizable monomers include alkyl methacrylate esters other than methyl methacrylate such as ethyl methacrylate and butyl methacrylate; aryl methacrylate esters such as phenyl methacrylate; cycloalkyl methacrylate esters such as cyclohexyl methacrylate and norbornenyl methacrylate; aryl acrylate esters such as phenyl acrylate; cycloalkyl acrylate esters such as cyclohexyl acrylate and norbornenyl acrylate; aromatic vinyl monomers such as styrene; acrylamide; methacrylamide; acrylonitrile; methacrylonitrile; and vinyl monomers having only one polymerizable alkenyl group in one molecule. The content of the copolymerizable monomer other than methyl methacrylate and alkyl acrylate ester in the monomer mixture is preferably 10% by mass or less, more preferably 5% by mass or less.

[0040] The monomer mixture preferably has a b* value of -1 to 2, more preferably -0.5 to 1.5. When the b* value is within this range, it is advantageous for obtaining a molded article with little coloring at high production efficiency when molding the resulting methacrylic copolymer composition. Note that b* is a value measured in accordance with the International Commission on Illumination (CIE) standard (1976) or JIS Z-8722. The monomer mixture removed from the reaction product by the step of removing the monomer mixture in the reaction product can be recovered and used again in the present invention. When the b* of the recovered monomer mixture increases due to heat added during recovery or the like, it is preferable to purify it by an appropriate method so that b* is within the above-mentioned range.

[0041] The polymerization initiator used in the present invention is not particularly limited as long as it generates reactive radicals. For example, t-hexyl peroxyisopropyl monocarbonate, t-hexyl peroxy 2-ethylhexanoate, 1,1,3,3-tetramethylbutyl peroxy 2-ethylhexanoate, t-butyl peroxy pivalate, t-hexyl peroxy pivalate, t-butyl peroxy neodecanoate, t-hexyl peroxy neodecanoate, 1,1,3,3-tetramethylbutyl peroxy neodecanoate, 1,1-bis(t-hexylperoxy)cyclohexane, benzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, lauroyl peroxide, 2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2-methylbutyronitrile), dimethyl 2,2'-azobis(2-methylpropionate) are preferred; furthermore, t-hexyl peroxy 2-ethylhexanoate, 1,1-bis(t-hexylperoxy)cyclohexane, dimethyl 2,2'-azobis(2-methylpropionate) and the like can be mentioned.

[0042] The polymerization initiator used in the present invention preferably has an average initiator concentration (I) of un-cleaved at the polymerization temperature in the tank reactor described later in the range of 5.1×10 -5 ~2.4×10 -4 (mol / L).

[0043] The amount of the polymerization initiator used is adjusted according to the polymerization temperature and added to the monomer mixture so as to obtain the above initiator concentration (I).

[0044] Examples of the chain transfer agent used in the present invention include alkyl mercaptans such as n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, 1,4-butanedithiol, 1,6-hexanedithiol, ethylene glycol bisthiopropionate, butanediol bisthioglycolate, butanediol bisthiopropionate, hexanediol bisthioglycolate, hexanediol bisthiopropionate, trimethylolpropane tris-(β-thiopropionate), pentaerythritol tetrakisthiopropionate; and terpinolene. Among these, monofunctional alkyl mercaptans such as n-octyl mercaptan and n-dodecyl mercaptan are preferred. These chain transfer agents can be used alone or in combination of two or more. The amount of the chain transfer agent used is preferably 0 to 1 part by mass, more preferably 0.01 to 0.8 part by mass, still more preferably 0.02 to 0.6 part by mass, based on 100 parts by mass of the monomer mixture.

[0045] In bulk polymerization, a solvent is not used in principle, but if it is necessary to adjust the viscosity of the reaction solution, etc., the solvent can be included in the monomer mixture. As the solvent, aromatic hydrocarbons such as benzene, toluene, and ethylbenzene are preferred. These solvents can be used alone or in combination of two or more. The amount of such a solvent used is preferably 30 parts by mass or less, more preferably 10 parts by mass or less, based on 100 parts by mass of the monomer mixture.

[0046] The reaction raw material used in the present invention preferably has a dissolved oxygen amount of 10 ppm or less, more preferably 5 ppm or less, still more preferably 4 ppm or less, and most preferably 3 ppm or less. When the dissolved oxygen amount is within such a range, the polymerization reaction proceeds smoothly, and a molded article without silver streaks or coloring is easily obtained.

[0047] The temperature in the tank reactor, i.e., the temperature of the liquid in the reaction tank, is preferably 110 to 140 °C, more preferably 114 to 135 °C. If the temperature is higher than this range, it is difficult to generate high molecular weight polymers containing α-methylstyrene, which causes a decrease in heat resistance.

[0048] In the method for producing the methacrylic copolymer composition of the present invention, the moisture in the reaction liquid in the tank reactor is preferably 1000 ppm or less, more preferably 700 ppm or less, and even more preferably 280 ppm or less. By setting the moisture to 1000 ppm or less, the generation of resin foreign matters of several μm to several tens of μm during the polymerization reaction can be suppressed, and when the obtained methacrylic copolymer composition is formed into a film or sheet by melt molding, the occurrence of defects with an outer diameter of several tens of μm having the resin foreign matters as nuclei can be significantly reduced.

[0049] In the tank reactor, bulk polymerization is preferably carried out until the polymerization conversion rate reaches 30 to 65% by mass, preferably until it reaches 35 to 60% by mass.

[0050] Also, the average residence time (θ) of the reaction raw materials in the tank reactor is preferably 1.5 to 5 hours, more preferably 2 to 4.5 hours, and even more preferably 2.5 to 4 hours. If the average residence time is too short, the required amount of the polymerization initiator increases. Also, with the increase in the amount of the polymerization initiator, it becomes difficult to control the polymerization reaction and the control of the molecular weight tends to be difficult. On the other hand, if the average residence time is too long, it takes time until the reaction reaches a steady state, and the productivity tends to decrease. The average residence time can be adjusted by the capacity of the tank reactor and the supply amount of the reaction raw materials.

[0051] The bulk polymerization is preferably carried out in an inert gas atmosphere such as nitrogen gas.

[0052] The manufacturing method of the present invention includes a step of removing the monomer mixture in the reaction product. Here, the reaction product is not limited to the reaction product obtained by bulk polymerization in a tank reactor, and may be a reaction product obtained in another reactor connected after the tank reactor as needed, that is, an unreacted monomer mixture in the reaction product obtained by bulk polymerization in the tank reactor is further polymerized by another reactor to increase the polymerization conversion rate. Also, in this step, a solvent may be removed simultaneously as needed. The removal method is not particularly limited, but a heat devolatilization method is preferred. Examples of the heat devolatilization method include an equilibrium flash evaporation method and an adiabatic flash evaporation method, and the adiabatic flash evaporation method is preferred. The temperature at which the adiabatic flash evaporation method is carried out is preferably 200 to 280°C, more preferably 220 to 280°C, and even more preferably 220 to 270°C. If the temperature at which the adiabatic flash evaporation method is carried out is less than 200°C, it takes time for devolatilization, resulting in insufficient devolatilization and possibly causing appearance defects such as silver streaks in the molded product. On the other hand, if the temperature at which the adiabatic flash evaporation method is carried out exceeds 280°C, the methacrylic copolymer composition tends to be colored and depolymerization reactions occur due to oxidation, burning, decomposition, etc. The adiabatic flash evaporation method may be carried out in multiple stages. In this case, the reaction product flowing through the heat transfer tube can be heated with the vapor of the flash-evaporated monomer mixture, and the heated reaction product can be supplied into a low-pressure flash tank for flash evaporation. The reaction product can be pressurized by a pump or the like. After removing the monomer mixture, the methacrylic copolymer composition can be made into pellets or powder according to a known method to facilitate handling as a molding material. The content of the monomer mixture in the methacrylic copolymer composition obtained in the present invention is preferably 1% by mass or less, and more preferably 0.5% by mass or less.

[0053] The precursor polymer has a glass transition temperature which is preferably 114 °C or higher, more preferably 115 °C or higher, still more preferably 117 °C or higher as the lower limit, and preferably 150 °C or lower as the upper limit. The glass transition temperature can be changed by adjusting the molecular weight, the amount of α-methylstyrene copolymerized, etc. The higher the glass transition temperature of the precursor polymer, the better the heat resistance. The methacrylic copolymer obtained using a precursor polymer with a high glass transition temperature has high heat resistance even when the amount of the structural unit (R) is small, and thus is less likely to cause deterioration of the saturated water absorption rate, etc.

[0054] The precursor polymer is not particularly limited as long as the total content of the structural units derived from methyl methacrylate is 70 to 93% by mass and the total content of the structural units derived from α-methylstyrene is 3 to 7% by mass. From the viewpoints of polymerizability, transparency, etc., the total content of the structural units derived from methyl methacrylate in the precursor polymer is preferably 73% by mass or more and 93% by mass or less, more preferably 75% by mass or more and 92% by mass or less, and most preferably 80% by mass or more and 92% by mass or less.

[0055] From the viewpoints of heat resistance, polymerizability, water absorption rate, etc., the total content of the structural units derived from α-methylstyrene in the precursor polymer is preferably 7% by mass or more and 27% by mass or less, more preferably 8% by mass or more and 25% by mass or less. If the amount of the structural units derived from α-methylstyrene is less than this range, sufficient heat resistance cannot be obtained, and if it is more than this range, the polymerizability significantly decreases.

[0056] In the chromatogram obtained by gel permeation chromatography, the weight average molecular weight Mw in terms of polystyrene of the precursor polymer is preferably 30,000 or more and 200,000 or less, more preferably 40,000 or more and 180,000 or less, still more preferably 50,000 or more and 160,000 or less. If the weight average molecular weight Mw is smaller than this range, the obtained molded article becomes brittle, and if it is higher than this range, the productivity deteriorates. Mw can be controlled by adjusting the type, amount, addition timing, etc. of the polymerization initiator and chain transfer agent (optional component) used in the production of the precursor polymer.

[0057] The ring structure forming reaction can be carried out, for example, using an extruder. Examples of the extruder include a single-screw extruder, a twin-screw extruder, a multi-screw extruder, etc. From the viewpoint of mixing performance, a twin-screw extruder is preferred. The twin-screw extruder includes a non-intermeshing co-rotating type, an intermeshing co-rotating type, a non-intermeshing counter-rotating type, and an intermeshing counter-rotating type. The intermeshing co-rotating type is preferred because it enables high-speed rotation and can efficiently promote mixing. These extruders may be used alone or connected in series.

[0058] In the ring structure forming reaction using an extruder, for example, a precursor polymer as a raw material is introduced from the raw material inlet of the extruder, the precursor polymer is melted and filled in the cylinder, and then an imidizing agent (optional component) etc. is injected into the extruder using an addition pump, whereby the ring structure forming reaction can proceed in the extruder. When an imidizing agent is used, the structural unit (R) includes an N-substituted or unsubstituted glutarimide unit and may optionally include a lactone ring unit and / or a glutaric anhydride unit. When no imidizing agent is used, the structural unit (R) is composed of a lactone ring unit and / or a glutaric anhydride unit. A preferred imidizing agent is R 2 -NH2 (R 2 is as defined above). The imidizing agent is used in an amount of 1.6 to 12 parts by mass based on 100 parts by mass of the methacrylic copolymer. When the imidizing agent is used in the above range, the by-production of methacrylamide units can be suppressed.

[0059] The resin temperature in the reaction zone of the extruder is preferably in the range of 180 to 280 °C, more preferably in the range of 200 to 280 °C. If the resin temperature in the reaction zone is less than 180 °C, the heat resistance of the methacrylic copolymer tends to decrease due to a decrease in the reaction efficiency of the ring structure formation reaction, by-production of methacrylamide units, etc. If the resin temperature in the reaction zone exceeds 280 °C, the resin decomposition becomes significant and the mechanical strength such as the tensile breaking strength of the molded body and film made of the obtained methacrylic copolymer tends to decrease. The reaction zone in the extruder refers to the region in the cylinder of the extruder from the injection position of the imidizing agent etc. to the resin discharge port (die part).

[0060] By lengthening the reaction time in the reaction zone of the extruder, the ring structure formation reaction can proceed further. The reaction time in the reaction zone of the extruder is preferably longer than 10 seconds, more preferably longer than 30 seconds. With a reaction time of 10 seconds or less, the ring structure formation reaction may hardly proceed.

[0061] The resin pressure in the extruder is preferably in the range of atmospheric pressure to 50 MPa, more preferably in the range of 1 to 30 MPa. At 50 MPa or more, it exceeds the mechanical pressure resistance limit of a normal extruder and a special device is required, which is not preferable in terms of cost.

[0062] It is preferable to use an extruder having a vent hole capable of reducing the pressure below atmospheric pressure. According to such a configuration, unreacted substances, by-products such as methanol, or monomers can be removed, and the breaking strength of the molded body containing the methacrylic copolymer of the present invention tends to improve.

[0063] For the ring structure formation reaction, instead of an extruder, for example, a high-viscosity compatible reaction device such as a horizontal twin-screw reaction device like the Bivolac manufactured by Sumitomo Heavy Industries, Ltd. or a vertical twin-screw stirring tank like a Super Blend can also be suitably used.

[0064] During the ring structure formation reaction, carboxyl groups may be by-produced in the methacrylic copolymer. Such carboxyl groups may be converted into ester groups by an esterifying agent, a catalyst, etc. as necessary. Thereby, foaming of the resin during the production of the optical film can be reduced. Such ester groups vary depending on the esterifying agent and catalyst used, but from the viewpoints of reducing the resin melt viscosity during melt molding, the reactivity of esterification, and the heat resistance of the resin after esterification, it is preferable to contain methyl methacrylate units, and it is more preferable to contain both methyl methacrylate units and ethyl methacrylate units. As the esterifying agent, dimethyl carbonate is preferable from the viewpoints of cost, reactivity, etc.

[0065] The addition amount of the esterifying agent can be set, for example, so that the acid value of the methacrylic copolymer becomes a desired value.

[0066] In addition to the above esterifying agent, a catalyst can also be used in combination. The type of the catalyst is not particularly limited, and examples thereof include amine compounds such as trimethylamine, triethylamine, monomethyldiethylamine, and dimethylmonoethylamine. Among these, triethylamine is preferable from the viewpoints of cost, reactivity, etc.

[0067] Additives generally used in resin compositions may be contained within a range not impairing the object of the present invention. Examples of the additives include fillers, antioxidants, heat deterioration preventives, ultraviolet absorbers, light stabilizers, lubricants, mold release agents, polymer processing aids, antistatic agents, flame retardants, colorants, dyes, pigments, light diffusing agents, organic dyes, matting agents, impact resistance modifiers, phosphors, etc. The total amount of such additives other than fillers is preferably 7% by mass or less, more preferably 5% by mass or less, and still more preferably 4% by mass or less.

[0068] Examples of the filler include calcium carbonate, talc, carbon black, titanium oxide, silica, clay, barium sulfate, magnesium carbonate, etc. The amount of the filler that can be contained in the methacrylic copolymer composition of the present invention is preferably 3% by mass or less, more preferably 1.5% by mass or less.

[0069] The antioxidant is effective in preventing oxidative degradation of the resin by itself in the presence of oxygen. For example, phosphorus-based antioxidants, hindered phenol-based antioxidants, thioether-based antioxidants, etc. can be mentioned. These antioxidants may be used alone or in combination of two or more.

[0070] The heat degradation inhibitor can prevent the thermal degradation of the resin by capturing polymer radicals generated when exposed to high heat in a substantially oxygen-free state. Examples of the heat degradation inhibitor include 2-tert-butyl-6-(3’-tert-butyl-5’-methyl-hydroxybenzyl)-4-methylphenyl acrylate (manufactured by Sumitomo Chemical Co., Ltd.; trade name Sumilizer GM), 2,4-di-tert-amyl-6-(3’,5’-di-tert-amyl-2’-hydroxy-α-methylbenzyl) phenyl acrylate (manufactured by Sumitomo Chemical Co., Ltd.; trade name Sumilizer GS), etc.

[0071] The ultraviolet absorber is a compound having the ability to absorb ultraviolet rays. The ultraviolet absorber is a compound that is mainly said to have a function of converting light energy into heat energy. Examples of the ultraviolet absorber include benzophenones, benzotriazoles, triazines, benzoates, salicylates, cyanoacrylates, oxalic acid anilides, malonic acid esters, formamidines, etc. These may be used alone or in combination of two or more. Among these, benzotriazoles, triazines, or the maximum value ε of the molar extinction coefficient at a wavelength of 380 to 450 nm max is 1200 dm 3 ·mol -1 cm -1The following ultraviolet absorbers are preferred.

[0072] Benzotriazoles are preferred as the ultraviolet absorber used when applying the molded article of the present invention to optical applications because they have a high effect of suppressing deterioration of optical properties such as coloring by ultraviolet rays. Examples of benzotriazoles include 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (manufactured by BASF; trade name TINUVIN 329), 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (manufactured by BASF; trade name TINUVIN 234), 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol] (manufactured by ADEKA; trade name LA-31), 2-(5-octylthio-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol, and the like.

[0073] In addition, the maximum value ε of the molar extinction coefficient at wavelengths of 380 to 450 nm max is 1200 dm 3 ·mol -1 cm -1 The following ultraviolet absorbers can suppress the yellowness of the obtained molded article. Examples of such ultraviolet absorbers include 2-ethyl-2'-ethoxy-oxalanilide (manufactured by Clariant Japan; trade name Sanduvor VSU). Among these ultraviolet absorbers, benzotriazoles are preferably used from the viewpoint of suppressing resin deterioration by ultraviolet rays.

[0074] Also, when it is desired to efficiently absorb short wavelengths of 380 nm or less, triazine-based ultraviolet absorbers are preferably used. Examples of such ultraviolet absorbers include 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine (manufactured by ADEKA Corporation; trade name LA-F70), hydroxy-phenyltriazine-based ultraviolet absorbers which are analogs thereof (manufactured by BASF Corporation; trade names TINUVIN477, TINUVIN460, and TINUVIN479), 2,4-diphenyl-6-(2-hydroxy-4-hexyloxyphenyl)-1,3,5-triazine, and the like.

[0075] Furthermore, when it is desired to particularly effectively absorb light having a wavelength of 380 to 400 nm, it is preferable to use a metal complex having a ligand with a heterocyclic structure disclosed in WO2011 / 089794A1, WO2012 / 124395A1, JP-A-2012-012476, JP-A-2013-023461, JP-A-2013-112790, JP-A-2013-194037, JP-A-2014-62228, JP-A-2014-88542, JP-A-2014-88543, etc. as an ultraviolet absorber.

[0076] Examples of the ligand of the complex ring structure include 2,2'-iminobisbenzothiazole, 2-(2-benzothiazolylamino)benzoxazole, 2-(2-benzothiazolylamino)benzimidazole, (2-benzothiazolyl)(2-benzimidazolyl)methane, bis(2-benzoxazolyl)methane, bis(2-benzothiazolyl)methane, bis[2-(N-substituted)benzimidazolyl]methane, and their derivatives. As the central metal of such a metal complex, copper, nickel, cobalt, and zinc are preferably used. Further, in order to use these metal complexes as an ultraviolet absorber, it is preferable to disperse the metal complex in a medium such as a low molecular compound or a polymer. The addition amount of the metal complex is preferably 0.01 to 5 parts by mass, more preferably 0.1 to 2 parts by mass, based on 100 parts by mass of the molded body of the present invention. Since the metal complex has a large molar extinction coefficient at a wavelength of 380 to 400 nm, the amount added to obtain a sufficient ultraviolet absorption effect can be small. If the addition amount is small, deterioration of the appearance of the molded body due to bleed-out or the like can be suppressed. Further, since the metal complex has high heat resistance, there is little deterioration or decomposition during molding. Furthermore, since the metal complex has high light resistance, the ultraviolet absorption performance can be maintained for a long period of time.

[0077] The maximum value ε of the molar extinction coefficient of the ultraviolet absorber max is measured as follows. Add 10.00 mg of the ultraviolet absorber to 1 L of cyclohexane and dissolve it so that there is no undissolved matter by visual observation. Inject this solution into a quartz glass cell of 1 cm × 1 cm × 3 cm and measure the absorbance at a wavelength of 380 to 450 nm using a spectrophotometer (manufactured by Hitachi, Ltd.; trade name U-3410). From the molecular weight (M UV ) of the ultraviolet absorber and the maximum value (A max ) of the measured absorbance, calculate according to the following formula to obtain the maximum value ε max of the molar extinction coefficient. ε max = [A max / (10 × 10 -3 )] × M UV

[0078] A light stabilizer is a compound that is mainly said to have a function of capturing radicals generated by oxidation by light. Examples of suitable light stabilizers include hindered amines such as compounds having a 2,2,6,6-tetraalkylpiperidine skeleton.

[0079] Examples of lubricants include stearic acid, behenic acid, stearoamidic acid, methylene bisstearamide, triglyceride hydroxystearate, paraffin wax, ketone wax, octyl alcohol, hydrogenated oil, and the like.

[0080] Examples of release agents include higher alcohols such as cetyl alcohol and stearyl alcohol; glycerin higher fatty acid esters such as monoglyceride stearate and diglyceride stearate. In the present invention, it is preferable to use higher alcohols and glycerin fatty acid monoesters in combination as the release agent. When higher alcohols and glycerin fatty acid monoesters are used in combination, the ratio is not particularly limited, but the usage amount of higher alcohols: the usage amount of glycerin fatty acid monoesters is preferably 2.5:1 to 3.5:1, more preferably 2.8:1 to 3.2:1, by mass ratio.

[0081] As the polymer processing aid, polymer particles (non-crosslinked rubber particles) having a particle diameter of 0.05 to 0.5 μm, which can usually be produced by an emulsion polymerization method, are used. The polymer particles may be single-layer particles composed of a polymer having a single composition ratio and a single limiting viscosity, or may be multi-layer particles composed of two or more polymers having different composition ratios or limiting viscosities. Examples of the antistatic agent include alkyl sulfonates such as sodium heptyl sulfonate, sodium octyl sulfonate, sodium nonyl sulfonate, sodium decyl sulfonate, sodium dodecyl sulfonate, sodium cetyl sulfonate, sodium octadecyl sulfonate, sodium diheptyl sulfonate, potassium heptyl sulfonate, potassium octyl sulfonate, potassium nonyl sulfonate, potassium decyl sulfonate, potassium dodecyl sulfonate, potassium cetyl sulfonate, potassium octadecyl sulfonate, potassium diheptyl sulfonate, lithium heptyl sulfonate, lithium octyl sulfonate, lithium nonyl sulfonate, lithium decyl sulfonate, lithium dodecyl sulfonate, lithium cetyl sulfonate, lithium octadecyl sulfonate, and lithium diheptyl sulfonate. Examples of the flame retardant include metal hydrates having hydroxyl groups or water of crystallization such as magnesium hydroxide, aluminum hydroxide, aluminum silicate hydrate, magnesium silicate hydrate, and hydrotalcite; phosphate compounds such as polyphosphate amines and phosphate esters; and silicon compounds. Phosphate ester-based flame retardants such as trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, tricyclohexyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, dimethylethyl phosphate, methyldibutyl phosphate, ethyldipropyl phosphate, and hydroxyphenyldiphenyl phosphate are preferred. Examples of the dyes and pigments include red organic pigments such as para red, fire red, pyrazolone red, thioindigo red, and perylene red; blue organic pigments such as cyanine blue and indanthrene blue; and green organic pigments such as cyanine green and naphthol green. One or more of these can be used.

[0082] As the organic dye, a compound having a function of converting ultraviolet rays into visible light is preferably used. Examples of the light diffusing agent and the matting agent include glass fine particles, polysiloxane-based crosslinked fine particles, crosslinked polymer fine particles, talc, calcium carbonate, barium sulfate, and the like. Examples of the phosphor include fluorescent pigments, fluorescent dyes, fluorescent whitening dyes, fluorescent brighteners, fluorescent bleaching agents, and the like.

[0083] The methacrylic copolymer composition of the present invention is not particularly limited by its production method. For example, it can be produced by melt-kneading the methacrylic copolymer of the present invention, additives such as an ultraviolet absorber, and, if necessary, other polymers. The melt-kneading can be carried out using a melt-kneading apparatus such as a kneader extruder, an extruder, a mixing roll, or a Banbury mixer. The temperature during kneading can be appropriately set according to the softening temperatures of the methacrylic copolymer and other polymers, and can be set, for example, at 150 to 300 °C. Also, the shear rate during kneading can be set, for example, at 10 to 5000 sec -1 to.

[0084] The methacrylic copolymer composition of the present invention can be formed into pellets or the like in order to enhance convenience during storage, transportation, or molding.

[0085] The film of the present invention contains the methacrylic copolymer or the methacrylic copolymer composition of the present invention. The production method of the film of the present invention is not particularly limited. For example, it can be produced by a solution casting method, a melt casting method, an extrusion molding method, an inflation molding method, a blow molding method, or the like. Among these, from the viewpoint of obtaining a film having excellent transparency, improved toughness, excellent handleability, and excellent balance between toughness and surface hardness and rigidity, the extrusion molding method or the solution casting method is preferable. The temperature of the molten resin discharged from the extruder is preferably set at 160 to 270 °C, more preferably 220 to 260 °C.

[0086] Among the extrusion molding methods, the T-die method is preferred from the viewpoint of obtaining a film with good surface smoothness, good mirror gloss, and low haze. In this T-die method, it is preferable to form a film by sandwiching the molten resin discharged from the T-die through an extruder, a gear pump, a polymer filter, and a mixer between two or more mirror rolls or mirror belts. When sandwiching between the mirror rolls or mirror belts, a bank may or may not be formed. The die has an automatic adjustment function for the lip opening, and the air gap is preferably 100 mm or less. The mirror roll or mirror belt is preferably made of metal. As the mirror roll, a metal rigid body roll, a metal elastic body roll, etc. can be used, and it is preferable to use a combination of a gold elastic body roll and a metal rigid body roll. Also, the surface temperatures of both the mirror roll and the mirror belt are preferably 130°C or lower. Further, at least one of the surface temperatures of a pair of mirror rolls or mirror belts is preferably 60°C or higher. When set to such surface temperatures, the molten resin discharged from the extruder can be cooled at a speed faster than natural cooling, and it is easy to manufacture a film with excellent surface smoothness and low haze. The linear pressure between a pair of rolls or belts is preferably 10 N / mm or more, more preferably 30 N / mm or more. The thickness of the unstretched film obtained by extrusion molding is preferably 10 to 300 μm. The haze of the film is preferably 0.7% or less, more preferably 0.5% or less, and even more preferably 0.3% or less at a thickness of 100 μm.

[0087] The solvent used in the solution casting method is not particularly limited, and examples include chlorine-based solvents such as chloroform and methylene chloride; aromatic solvents such as toluene, xylene, benzene, and mixed solvents thereof; alcohol-based solvents such as methanol, ethanol, isopropanol, n-butanol, and 2-butanol; methyl cellosolve, ethyl cellosolve, butyl cellosolve, dimethylformamide, dimethyl sulfoxide, dioxane, cyclohexanone, tetrahydrofuran, acetone, ethyl acetate, diethyl ether; and the like. These solvents may be used alone or in combination of two or more.

[0088] Examples of devices for forming a film by the solution casting method include a drum casting machine, a band casting machine, a spin coater, and the like.

[0089] The unstretched film obtained as described above may be subjected to a stretching treatment. By the stretching treatment, the mechanical strength can be increased, and a film that is difficult to crack can be obtained. The stretching method is not particularly limited, and examples include a uniaxial stretching method, a simultaneous biaxial stretching method, a sequential biaxial stretching method, and a tubular stretching method. From the viewpoint of being able to stretch uniformly and obtaining a film with high strength, the lower limit of the temperature during stretching is a temperature 10°C higher than the glass transition temperature of the methacrylic copolymer or the methacrylic copolymer composition, and the upper limit of the temperature during stretching is a temperature 40°C higher than the glass transition temperature of the methacrylic copolymer or the methacrylic copolymer composition. Stretching is usually performed at 100 to 5000% / min. After stretching, heat fixation is performed to obtain a film with little heat shrinkage. The thickness of the stretched film is preferably 10 to 200 μm.

[0090] When the film of the present invention is used as a retardation film, its retardation can be arbitrarily selected according to the application within the range of 5 nm to 1000 nm. In particular, when the retardation film of the present invention is used as a film for preventing external light reflection or for the purpose of reducing color shift due to the viewing angle of an image display device, that is, as a member of an optical compensation polarizing plate, the retardation at a wavelength of 550 nm is preferably 70 to 155 nm, more preferably 80 to 150 nm, and still more preferably 85 to 145 nm. When used as a film for preventing external light reflection or as a member of an optical compensation polarizing plate, the wavelength dispersibility of the retardation of the film is particularly important, and an inverse wavelength dispersion having a lower retardation as the wavelength becomes shorter is required. Specifically, it is preferable that the ratio of Re(450) to Re(550) (Re(450) / Re(550)) of the retardation film satisfies the following formula (1) and the ratio of Re(650) to Re(550) (Re(550) / Re(650)) satisfies the following formula (2). 0.30 ≦ Re(450) / Re(550) ≦ 0.95 (1) 1.02 ≦ Re(650) / Re(550) ≦ 2.00 (2) When the wavelength dispersibility of the methacrylic copolymer is within the above range, the state of elliptical polarization when linearly polarized light is incident on the methacrylic copolymer can be made homogeneous regardless of the wavelength, so that the optical compensation ability becomes good.

[0091] A functional layer may be provided on the surface of the film which is one form of the molded body of the present invention. Examples of the functional layer include a hard coat layer, an antiglare layer, an antireflection layer, an anti-sticking layer, a diffusion layer, an antiglare layer, an antistatic layer, an antifouling layer, and a lubricious layer such as fine particles.

[0092] Further, in order to improve the adhesion strength with the above functional layer or the adhesion strength in lamination via an adhesive or an adhesive with another film on at least one side of the film of the present invention, it is preferable to provide an undercoat layer.

[0093] For the undercoat layer, as the resin component, for example, polyester resin, acrylic resin, urethane resin, cellulose resin, polyol resin, polycarboxylic acid resin, cellulose derivative resin, polyvinyl butyral resin, etc. and any composite resin thereof are used. These resins and composite resins may be those modified with hydrophilic groups such as hydroxyl group, amino group, isocyanate group, carboxyl group, etc. From the viewpoint of durability, it is preferable to blend a crosslinking agent having a reactive group such as isocyanate group, epoxy group, silanol group, hydrazide group, carbodiimide group, oxazoline group, acetoacetyl group, aziridine group, etc. into these resins. As the solvent, water; alcohols such as propanol, isopropanol, butanol, 3-methyl-3-methoxy-1-butanol; aromatic hydrocarbons such as toluene, xylene; ketones such as methyl ethyl ketone, methyl isobutyl ketone; ethylene glycol esters such as methoxyethanol, ethoxyethanol and other known solvents can be used. Known coating methods such as microgravure and bar coating can be used to form the undercoat layer. When forming the undercoat layer, its drying temperature and time are extremely important, and it is preferably dried at a temperature of usually 80 °C or higher, preferably 85 °C or higher, more preferably 90 °C or higher, and still more preferably 95 °C or higher. Further, in order to complete the crosslinking reaction, heat treatment is preferable.

[0094] By laminating the layer containing the methacrylic copolymer or methacrylic copolymer composition of the present invention and another material (for example, a layer containing another thermoplastic copolymer), a laminate can be obtained. Examples of other materials used for the laminate include steel materials, plastics (for example, thermoplastic resins), wood, glass, etc. The laminate obtained by the present invention can be suitably used for wallpaper; the surface of automotive interior members; the surface of automotive exterior members such as bumpers; the surface of mobile phones; the surface of furniture; the surface of personal computers; the surface of vending machines; the surface of bathroom members such as bathtubs, etc.

[0095] The film, which is one form of the molded article of the present invention, has high transparency and heat resistance, and thus is suitable for optical applications. It is particularly suitable for use as a polarizer protection film, a liquid crystal protection plate, a surface material of a portable information terminal, a display window protection film of a portable information terminal, a light guide film, a transparent conductive film with silver nanowires or carbon nanotubes coated on its surface, and a front panel application of various displays. Since the film of the present invention has high transparency and heat resistance, it can be used as infrared cut films, anti-crime films, anti-scattering films, decorative films, metal decorative films, shrink films, and films for in-mold labels for applications other than optical applications.

[0096] When the film, which is one form of the molded article of the present invention, is used as a polarizer protection film or a retardation film, it may be laminated on only one side of the polarizer film or on both sides. When laminating with the polarizer film, it can be laminated via an adhesive layer or an adhesive layer. As the polarizer film, a stretched film made of a polyvinyl alcohol-based resin and iodine can be used, and its film thickness is preferably 1 to 100 μm.

Examples

[0097] Next, examples are shown to more specifically explain the present invention. Note that the present invention is not limited by the examples.

[0098] Measurements of physical properties and the like were carried out by the following methods.

[0099] (Polymerization conversion rate) It was calculated based on the analysis performed under the following conditions by connecting GL Sciences Inc.'s INERTCAP1 (df = 0.4 μm, 0.25 mm I.D. × 60 m) as a column to a gas chromatograph GC-14A manufactured by Shimadzu Corporation. injection temperature = 250 °C detector temperature = 250 °C Temperature conditions: Hold at 60 °C for 5 minutes → Heat up to 250 °C at 10 °C / min → Hold at 250 °C for 10 minutes

[0100] (Molecular weight distribution Mw / Mn) The weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the resin were determined by the GPC method (gel permeation chromatography). A sample solution was prepared by dissolving 4 mg of the resin to be measured in 5 ml of tetrahydrofuran. The temperature of the column oven was set at 40°C, and 20 μl of the sample solution was injected into the apparatus at an eluent flow rate of 0.35 ml / min to measure the chromatogram. Ten standard polystyrenes with molecular weights in the range of 400 to 5,000,000 were measured by GPC, and a calibration curve showing the relationship between the retention time and the molecular weight was created. Based on this calibration curve, Mw and Mw / Mn of the resin to be measured were determined. Apparatus: GPC apparatus HLC-8320 manufactured by Tosoh Corporation Separation column: TSKguardcolum SuperHZ-H, TSKgel HZM-M, and TSKgel SuperHZ4000 manufactured by Tosoh Corporation were connected in series Eluent: Tetrahydrofuran Eluent flow rate: 0.35 ml / min Column temperature: 40°C Detection method: Differential refractive index (RI)

[0101] (Each unit composition in the copolymer) Inverse gated decoupling method 13 The integral value ratio of the carbonyl carbon of the methyl methacrylate unit, the aromatic carbon at the 1-position of the α-methylstyrene unit, and the aromatic carbon at the 1-position of the styrene unit was determined by C-NMR, and from this, each unit composition in the copolymer precursor polymer was calculated.

[0102] (Glass transition temperature Tg) The methacrylic copolymer obtained in the examples was heated to 250°C once in accordance with JIS K7121 using a differential scanning calorimeter (DSC-50 (product number) manufactured by Shimadzu Corporation), then cooled to room temperature, and thereafter, the DSC curve was measured under the condition of heating from room temperature to 200°C at 10°C / min. The midpoint glass transition temperature obtained from the DSC curve measured during the second heating was defined as the glass transition temperature in the present invention.

[0103] (Imidization rate) 1 Using 1H-NMR (manufactured by Bruker; trade name ULTRA SHIELD 400 PLUS), the 1H-NMR measurement of the copolymer was carried out, and from the area A of the peak derived from the O-CH3 group of methyl methacrylate in the vicinity of 3.5 to 3.8 ppm and the area B of the peak derived from the N-CH3 group of glutarimide in the vicinity of 3.0 to 3.3 ppm, the value obtained by the following formula was defined as the imidization rate (mol%). 1 Using 1H-NMR (manufactured by Bruker; trade name ULTRA SHIELD 400 PLUS), the 1H-NMR measurement of the copolymer was carried out, and from the area A of the peak derived from the O-CH3 group of methyl methacrylate in the vicinity of 3.5 to 3.8 ppm and the area B of the peak derived from the N-CH3 group of glutarimide in the vicinity of 3.0 to 3.3 ppm, the value obtained by the following formula was defined as the imidization rate (mol%). (Imidization rate (mol%)) = [B / (A + B)] × 100 The content (wt%) of the N-methylglutarimide structural unit was calculated from the imidization rate (mol%).

[0104] (Wavelength dispersibility of retardation) The methacrylic copolymer obtained in the examples was press-molded to obtain a 1.0 mm sheet. From the central part of the obtained press-molded sheet, a 20 mm × 40 mm test piece was cut out and placed on an autograph (manufactured by SHIMADZU) with a heating chamber. The grip distance in the autograph was set to 20 mm, and it was held at the glass transition temperature + 10 °C for 3 minutes. Then, it was stretched 100% in one direction at a speed of 3 mm / min (the grip distance became 40 mm). The obtained stretched film was cooled to 23 °C, removed from the autograph, and using an automatic refractometer KOBRA-WR manufactured by Oji Scientific Instruments, the refractive index when light of each wavelength was incident was measured, and the in-plane retardation Re was calculated based on the following formula. Re(λ) = (nx - ny) × d Here, λ is the wavelength (nm) of the measurement light, nx is the refractive index in the direction of the slow axis in the plane, ny is the refractive index in the direction of the fast axis in the plane, and d is the film thickness (nm). The ratio of Re(450) to Re(550) (Re(450) / Re(550)) and the ratio of Re(650) to Re(550) (Re(550) / Re(650)) were calculated to evaluate the wavelength dispersibility of the retardation.

[0105] <Production Example 1> Purified methyl methacrylate (MMA), α-methylstyrene, 2,2’-azobis(2-methylpropionitrile) (AIBN), and n-octyl mercaptan (n-OM) were charged into an autoclave A equipped with a stirrer at the ratios shown in Table 1 and uniformly dissolved to obtain a polymerization raw material. The polymerization raw material was continuously supplied from the autoclave A at 1.5 kg / hr to a tank-type reactor controlled at the polymerization temperature shown in Table 1, and a polymerization reaction was carried out by a bulk polymerization method with the average residence time shown in Table 1. A liquid containing a methacrylic copolymer was continuously discharged from the tank-type reactor. The polymerization conversion rate became the value shown in Table 1. Next, the liquid discharged from the reactor was heated to 230 °C and supplied to a twin-screw extruder controlled at 240 °C. In the twin-screw extruder, volatile components mainly composed of unreacted monomers were separated and removed, and the methacrylic copolymer was extruded into strands. The strands were cut with a pelletizer to obtain copolymer A-a. The weight-average molecular weight Mw, molecular weight distribution Mw / Mn, each unit composition of the copolymer, and glass transition temperature Tg of the obtained copolymer A-a were measured. The results are shown in Table 1. In this production example, since the content of the structural unit derived from MMA is the amount of units other than the α-methylstyrene unit and the styrene unit, the description in Table 1 was omitted.

[0106]

Table 1

[0107] <Production Examples 2 and 3> Copolymers A-b and A-c were obtained in the same manner as in Production Example 1, except that the monomer composition in the polymerization raw material, the amount of the chain transfer agent (n-OM), the amount of the polymerization initiator (AIBN) used, the polymerization temperature, and the average residence time were changed as shown in Table 1.

[0108] <Example 1> A twin-screw extruder (manufactured by TechnoBel; model name KZW20TW-45MG-NH-600) consisting of a conveying section, a melt-kneading section, a devolatilization section, and a discharging section, and set at a screw rotation speed of 120 rpm and a temperature of 250 °C was fed with the copolymer [A-a] shown in Production Example 1 at 2 kg / hr to the conveying section. Monomethylamine was injected at 0.10 kg / hr from the additive supply port of the twin-screw extruder into the melt-kneading section where a kneading block was installed, and the precursor polymer [A-a] and monomethylamine were reacted. A reverse flight was installed on the screw at the end of the reaction zone. In the devolatilization section set at 20 Torr (about 2.7 kPa), by-products and excess monomethylamine were volatilized from the molten resin that had passed through the melt-kneading section and discharged through the vent. The molten resin extruded as a strand from the die provided at the end of the discharging section of the twin-screw extruder was cooled in a water bath and then cut with a pelletizer to obtain a pelletized methacrylic copolymer (A-a-1).

[0109] A twin-screw extruder (manufactured by TechnoBel; model name KZW20TW-45MG-NH-600) consisting of a conveying section, a melt-kneading section, a devolatilization section, and a discharging section, and set at a screw rotation speed of 100 rpm and a temperature of 230 °C was fed with the copolymer (A-a-1) at 1 kg / hr to the conveying section. A liquid consisting of 0.8 part by mass of dimethyl carbonate and 0.2 part by mass of triethylamine was injected at 0.024 kg / hr into the melt-kneading section where a kneading block was installed, and dimethyl carbonate was reacted with the carboxy groups in the methacrylic copolymer (A-a-1). A reverse flight was installed on the screw at the end of the reaction zone. In the devolatilization section set at 20 Torr (about 2.7 kPa), by-products and excess dimethyl carbonate were volatilized from the molten resin that had passed through the melt-kneading section and discharged through the vent. The molten resin extruded as a strand from the die provided at the end of the discharging section of the twin-screw extruder was cooled in a water bath and then cut with a pelletizer to obtain a pelletized methacrylic copolymer (A-a-2).

[0110] A methacrylic copolymer (A-a-2) was supplied at 1 kg / hr to the conveying section of a twin-screw extruder (manufactured by TechnoBel; trade name KZW20TW-45MG-NH-600) consisting of a conveying section, a melt-kneading section, a devolatilization section, and a discharge section, and set at a screw rotation speed of 100 rpm and a temperature of 230°C. In the devolatilization section set at 20 Torr (about 2.7 kPa), volatile components such as unreacted substances were volatilized from the molten resin that had passed through the melt-kneading section and discharged through the vent. The molten resin extruded as a strand from a die provided at the end of the discharge section of the twin-screw extruder was cooled in a water bath and then cut with a pelletizer to obtain pelletized methacrylic copolymer [1]. The methacrylic copolymer [1] had an imidization rate of 8.6 mol%, a glass transition temperature of 130°C, Re(450) / Re(550) of 0.87, and Re(650) / Re(550) of 1.08. The physical properties of the methacrylic copolymer [1] are shown in Table 2.

[0111] <Example 2> In Example 1, a methacrylic copolymer [2] was obtained in the same manner as in Example 1, except that the addition amount of monomethylamine was 0.15 kg / hr, and a liquid consisting of 0.8 parts by mass of dimethyl carbonate and 0.2 parts by mass of triethylamine was injected at 0.036 kg / hr. The physical properties of the methacrylic copolymer [2] are shown in Table 2.

[0112] <Example 3> In Example 1, A-c was used instead of the precursor polymer A-a, and a methacrylic copolymer [3] was obtained in the same manner as in Example 1, except that the addition amount of monomethylamine was 0.23 kg / hr, and a liquid consisting of 0.8 parts by mass of dimethyl carbonate and 0.2 parts by mass of triethylamine was injected at 0.054 kg / hr. The physical properties of the methacrylic copolymer [3] are shown in Table 2.

[0113] <Example 4> 50 parts by mass of the methacrylic copolymer [2] synthesized in Example 2 and 50 parts by mass of the methacrylic resin [A-b] synthesized in Production Example 2 were kneaded with a small melt kneader under the temperature condition of 230 °C to obtain a methacrylic copolymer composition [4]. The physical properties of the methacrylic copolymer composition [4] are shown in Table 3.

[0114] <Comparative Examples 1, 2, and 3> The physical properties were evaluated in the same manner as in Example 1, except that the methacrylic copolymers [A-a] to [A-c] shown in Production Examples 1 to 3 were used instead of the methacrylic copolymer [1]. The results are shown in Table 3.

[0115]

Table 2

[0116]

Table 3

[0117] The methacrylic copolymers obtained in Examples 1 to 3 and the methacrylic copolymer composition obtained in Example 4 have high heat resistance and show reverse wavelength dispersibility, and thus can be suitably used as a resin for a reverse wavelength dispersive retardation film. On the other hand, the methacrylic copolymers obtained in Comparative Examples 1 to 3 are not within the scope of the present invention, do not show reverse wavelength dispersibility, and are inferior to the present invention.

Claims

**Claim 1**: A methacrylic copolymer having a glass transition temperature of 120°C or higher, comprising 40 to 87% by mass of methyl methacrylate units, 6 to 30% by mass of a structural unit (R) having at least one ring structure selected from the group consisting of lactone ring units, glutaric anhydride units, and N-substituted or unsubstituted glutarimide units in the main chain, and 7 to 30% by mass of α-methylstyrene units, Re(450) / Re(550) = 0.30 to 0.95 (1) Re(650) / Re(550) = 1.02 to 2.00 (2) An inverse wavelength dispersion retardation film comprising a methacrylic copolymer for forming an inverse wavelength dispersion retardation film that satisfies (in formulas (1) and (2), Re(450), Re(550), and Re(650) represent retardation values at wavelengths of 450 nm, 550 nm, and 650 nm, respectively). **Claim 2**: The inverse wavelength dispersion retardation film according to claim 1, wherein the structural unit (R) is an N-substituted or unsubstituted glutarimide unit represented by formula (3). 【Chemical 1】 (In formula (3), each R1 is independently a hydrogen atom or a methyl group, and R2 is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an organic group having 6 to 15 carbon atoms containing an aromatic ring.) **Claim 3**: The inverse wavelength dispersion retardation film according to claim 1, comprising a composition further containing another resin in addition to the methacrylic copolymer. **Claim 4**: A method for producing an inverse wavelength dispersion retardation film according to any one of claims 1 to 3, comprising a step of forming the methacrylic copolymer or the composition into a film by a melt molding method. **Claim 5**: A method for producing an inverse wavelength dispersion retardation film according to any one of claims 1 to 3, comprising a step of forming the methacrylic copolymer or the composition into a film by a solution casting method. **Claim 6**: A laminate having at least one layer comprising the inverse wavelength dispersion retardation film according to any one of claims 1 to 3.

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