JP7702940B2 - METHACRYLIC COPOLYMER FOR REVERSE WAVELENGTH DISPERSION RETARDATION FILM, COMPOSITION, FILM, PROCESS FOR PRODUCING FILM, AND LAMINATE - Google Patents

Description

The present invention relates to a methacrylic copolymer, composition, film, film manufacturing method, and laminate for a retardation film exhibiting reverse wavelength dispersion.

Image display devices such as liquid crystal displays and organic EL displays are being used in increasingly diverse ways and environments, and more advanced functionality is being demanded of the optical films that make up these image display devices.

One of the functions required for these optical films is that they have a higher phase difference in the visible light region toward the longer wavelength side, i.e., they have so-called reverse wavelength dispersion. Optical films with reverse wavelength dispersion can, for example, bring the phase difference of the film closer to one-quarter of the wavelength (λ) in a wide wavelength range of the visible light region, and can be used as a phase difference film (λ/4 plate) to convert linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light. By using them in combination with a polarizing plate, they can prevent external light reflection in image display devices and improve bright contrast and black reproducibility. They are also expected to be used as a so-called polarizing plate compensation film to reduce color shift due to the viewing angle of the polarizing plate, and as a polarizer protection film with phase difference.

As films 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 resins do not have sufficient resistance to moist heat, and there is a problem that the retardation fluctuates under high temperature or high humidity conditions, causing color unevenness.

(Meth)acrylic resins such as polymethyl methacrylate are widely used as materials for various optical components because they have excellent transparency and little optical distortion. In order to use (meth)acrylic resins as materials for optical films such as polarizer protective films and retardation films, studies have been conducted to improve the 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. All of these resins have improved heat resistance, but they have positive wavelength dispersion and do not have the reverse wavelength dispersion suitable for a retardation film.

JP 2000-137116 A JP 2003-315538 A WO2006/112207 A1 WO2005/108438 A1 JP 2013-033237 A

The object of the present invention is to provide a methacrylic copolymer for forming a reverse wavelength dispersion retardation film which has excellent heat resistance and exhibits reverse wavelength dispersion, as well as a composition, film, film manufacturing method, and laminate containing said copolymer.

（式（３）中、Ｒ^１は、それぞれ独立に、水素原子またはメチル基であり、Ｒ^２は、水素原子、炭素数１～１８のアルキル基、炭素数３～１２のシクロアルキル基または芳香環を含む炭素数６～１５の有機基である。）
［３］
［１］または［２］に記載のメタクリル系共重合体と他の樹脂とを含有する組成物。
［４］
［１］または［２］に記載のメタクリル系共重合体または［３］に記載の組成物を含む逆波長分散性位相差フィルム。
［５］
［１］または［２］に記載のメタクリル系共重合体、または［３］に記載の組成物を溶融成形法によりフィルムに成形する工程を含む、逆波長分散性位相差フィルムの製造方法。
［６］
［１］または［２］に記載のメタクリル系共重合体、または［３］に記載の組成物を溶液キャスト法によりフィルムに成形する工程を含む、逆波長分散性位相差フィルムの製造方法。
［７］
［１］または［２］に記載のメタクリル系共重合体または［３］に記載の組成物を含む層を少なくとも１層有する、積層体。 As a result of intensive research by the present inventors in order to achieve the above object, they 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 structural units (R) having at least one ring structure in the main chain selected from the group consisting of lactone ring units, glutaric anhydride units and N-substituted or unsubstituted glutarimide units, and 7 to 30% by mass of α-methylstyrene units,
Re(450)/Re(550)=0.30~0.95 (1)
Re(650)/Re(550)=1.02~2.00 (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 a phase difference film with reverse wavelength dispersion.
[2]
The methacrylic copolymer for forming a reverse wavelength dispersion retardation film according to [1], wherein the structural unit (R) is an N-substituted or unsubstituted glutarimide unit represented by formula (3):

(In formula (3), each R ¹ is independently a hydrogen atom or a methyl group, and each 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 and containing an aromatic ring.)
[3]
A composition containing the methacrylic copolymer according to [1] or [2] and another resin.
[4]
A reverse wavelength dispersion retardation film comprising the methacrylic copolymer according to [1] or [2] or the composition according to [3].
[5]
A method for producing a reverse wavelength dispersion retardation film, comprising a step of forming the methacrylic copolymer according to [1] or [2], or the composition according to [3], into a film by a melt molding method.
[6]
A method for producing a reverse wavelength dispersion retardation film, comprising a step of forming the methacrylic copolymer according to [1] or [2], or the composition according to [3] into a film by a solution casting method.
[7]
A laminate having at least one layer containing the methacrylic copolymer according to [1] or [2] or the composition according to [3].

According to the present invention, it is possible to obtain a methacrylic copolymer for forming a reverse wavelength dispersion retardation film, which has excellent heat resistance, exhibits reverse wavelength dispersion, and exhibits high retardation expression, as well as a composition, film, and laminate containing the copolymer.

FIG. 1 is a graph showing exemplary shapes of wavelength dispersion curves of retardation of (a) a resin having positive birefringence and showing positive wavelength dispersion (e.g., the structural unit (R) of the present application); (b) a resin having relatively small negative birefringence and showing positive wavelength dispersion (e.g., poly(methyl methacrylate)); (c) a resin having relatively large negative birefringence and showing positive wavelength dispersion (e.g., poly(α-methylstyrene)); (d) a resin having positive birefringence and showing reverse wavelength dispersion; and (e) a graph showing exemplary shapes of wavelength dispersion curves of retardation of a conventional copolymer.

(Methacrylic copolymer)
The methacrylic copolymer of the present invention contains methyl methacrylate units, α-methylstyrene units, and a structural unit (R). The methacrylic copolymer of the present invention further contains copolymerizable monomer units, methacrylic acid amide units represented by the following formula (A), and 2-(hydroxyalkyl)acrylic acid ester units represented by the following formula (B):

(式中、Ｒ^３、Ｒ^４は、それぞれ独立に、水素原子、炭素数１～１８のアルキル基、炭素数３～１２のシクロアルキル基または芳香環を含む炭素数６～１５の有機基であり、Ｒ^５は、水素原子または炭素数１～１８のアルキル基である。)を含んでいてもよい。

(In the formula, R ³ and R ⁴ each independently represent 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, and R ⁵ represents a hydrogen atom or an alkyl group having 1 to 18 carbon atoms.)

In the methacrylic copolymer of the present invention, the proportion of methyl methacrylate units relative to the total structural units is preferably 40 to 87% by mass, more preferably 50 to 85% by mass, and even more preferably 65 to 80% by mass. If the proportion of methyl methacrylate units is less than this range, the total light transmittance of the resulting methacrylic copolymer will deteriorate, and if the proportion of methyl methacrylate units is greater than this range, the heat resistance of the resulting methacrylic copolymer will be reduced.

In the methacrylic copolymer of the present invention, the proportion of α-methylstyrene units relative to the total structural units is preferably 7 to 30 mass%, more preferably 8 to 27 mass%, and even more preferably 11 to 25 mass%. If the proportion of α-methylstyrene units is less than this range, the saturated water absorption of the resulting methacrylic copolymer will be high. Furthermore, a methacrylic copolymer with a proportion of α-methylstyrene units exceeding 30 mass% will have low polymerizability and reduced productivity.

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 a methacrylic acid amide unit represented by the above formula (A) and/or a 2-(hydroxyalkyl)acrylic acid ester unit represented by the above formula (B) in the main chain.

A lactone ring unit is a structural unit containing a CH-O-C(=O)- group in the ring structure. The number of ring constituent elements in a structural unit containing a CH-O-C(=O)- group in the ring structure is preferably 4 to 8, more preferably 5 to 6, and most preferably 6. Examples of structural units containing a CH-O-C(=O)- group in the ring structure include lactone diyl structural units such as β-propiolactone diyl structural units, γ-butyrolactone diyl structural units, and δ-valerolactone diyl structural units. A 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 the hydroxy group and the ester group. In addition, ">C" in the formula means that the carbon atom C has two bonds.

For example, an example of a δ-valerolactonediyl structural unit is a structural unit represented by formula (I).

In formula (I), R ⁶ , R ⁷ and R ⁸ are 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 a linear or branched alkyl group, a linear or branched aryl group, a -OCOCH ₃ group, and a -CN group. The organic group may contain a heteroatom such as an oxygen atom. ^{R 6} and R ⁷ are preferably a methyl group, and R ⁸ is preferably a hydrogen atom.

The lactone ring unit can be incorporated into the methacrylic copolymer by the 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 a 2-(hydroxyalkyl)acrylic acid ester 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, JP-A-2005-146084 are incorporated herein by reference in their entirety.

The glutaric anhydride unit is a unit having a 2,6-dioxodihydropyrandiyl structure. An example of a unit having a 2,6-dioxodihydropyrandiyl structure is the structural unit represented by formula (II).

式（II）中、Ｒ^９はそれぞれ独立に水素原子または炭素数１～５のアルキル基であり、メチル基であるのが好ましい。

In formula (II), each R ⁹ independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and is preferably a methyl group.

Units having a 2,6-dioxodihydropyrandiyl structure can be incorporated into a methacrylic copolymer by methods described in JP 2007-197703 A, JP 2010-96919 A, and the like, such as intramolecular cyclization of two adjacent structural units derived from (meth)acrylic acid, or intramolecular cyclization of a structural unit derived from (meth)acrylic acid and a structural unit derived from methyl (meth)acrylate. JP 2007-197703 A and JP 2010-96919 A are incorporated herein by reference in their entirety.

The N-substituted or unsubstituted glutarimide unit is a unit having an N-substituted or unsubstituted 2,6-dioxopiperidinediyl structure.
An example of a unit having an N-substituted or unsubstituted 2,6-dioxopiperidinediyl structure is a structural unit represented by formula (3).

式（３）中、Ｒ^１はそれぞれ独立に水素原子またはメチル基であり、メチル基であるのが好ましい。Ｒ^２は水素原子、炭素数１～１８のアルキル基、炭素数３～１２のシクロアルキル基、または芳香環を含む炭素数６～１５の有機基であり、好ましくは水素原子、メチル基、ｎ－ブチル基、シクロヘキシル基またはベンジル基であり、より好ましくはメチル基、ｎ－ブチル基、またはシクロヘキシル基である。
式（３）で表される構造単位は、例えばスキーム（ｉ）で示されるように対応する酸無水物（IIa）とＲ^２－ＮＨ_２で表されるイミド化剤の反応により生成してもよく、式（Ｃ）の部分構造を有する共重合体の分子内環化反応により生成してもよい。分子内環化反応により式（Ｃ）で表される構造単位を式（３）で表される構造単位に変換するために加熱することが好ましい。
スキーム（ｉ）

(式中、Ｒ^１、Ｒ^２は前記に定義される通りである。)

In formula (3), R ¹ is independently a hydrogen atom or a methyl group, preferably a methyl group, and 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 and 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, as shown in scheme (i), by the reaction of the corresponding acid anhydride (IIa) with an imidizing agent represented by R ² -NH ₂ , or by an intramolecular cyclization reaction of a copolymer having a partial structure of formula (C). It is preferable to heat the copolymer in order to convert the structural unit represented by formula (C) to the structural unit represented by formula (3) by the intramolecular cyclization reaction.
Scheme (i)

(In the formula, R ¹ and R ² are as defined above.)

N-substituted or unsubstituted glutarimide units can be obtained by the methods described in WO2005/10838A1, JP2010-254742A, JP2008-273140A, JP2008-274187A, etc., specifically, by reacting structural units derived from two adjacent methyl methacrylates or glutaric anhydride units with an imidizing agent such as ammonia, methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, tert-butylamine, n-hexylamine, etc., aliphatic hydrocarbon group-containing amines, aromatic hydrocarbon group-containing amines, aniline, toluidine, trichloroaniline, etc., alicyclic hydrocarbon group-containing amines, cyclohexylamine, etc., urea, 1,3-dimethylurea, 1,3-diethylurea, 1,3-dipropylurea, etc. Among these, methylamine is preferred. Two adjacent structural units derived from methyl methacrylate or glutaric anhydride units may be reacted with an imidizing agent, and then a dialkyl carbonate such as dimethyl carbonate may be reacted to convert a carboxylic acid such as methacrylic acid into an alkyl methacrylate ester such as methyl methacrylate. The carboxylic acid may be generated when a carboxylic acid and an amide are generated by hydrolysis of a methacrylic acid ester or a glutaric anhydride unit represented by formula (II) or by reaction of a glutaric anhydride unit represented by formula (II) with an imidizing agent. The reaction with a dialkyl carbonate ester such as dimethyl carbonate may be carried out in the presence of a tertiary amine such as triethylamine. WO2005/10838A1, JP2010-254742A, JP2008-273140A, and JP2008-274187A are incorporated herein by reference in their entirety.

In the methacrylic copolymer of the present invention, the proportion of the structural unit (R) relative to the total structural units is preferably 6 to 30% by mass, more preferably 7.5 to 25% by mass, and even more preferably 8 to 25% by mass. By changing the ratio of the structural unit (R) to methyl methacrylate, the orientation birefringence of the methacrylic copolymer can be changed. Furthermore, the greater the content of the structural unit (R), the more the heat resistance of the methacrylic copolymer improves, but the more the flexibility decreases, and the compatibility with other (co)polymers and moldability tend to decrease.

In one preferred embodiment of the present invention, the methacrylic copolymer of the present invention may contain methacrylamide units represented by the above formula (A) and 2-(hydroxyalkyl)acrylic ester units represented by the above formula (B) in an amount of preferably 0 to 2 mass%, more preferably 0 to 1.5 mass%, even more preferably 0 to 1.0 mass%, and most preferably 0 to 0.5 mass% based on the total structural units. If the structural units of formula (A) and/or (B) exceed the above range, the saturated water absorption of the resulting methacrylic copolymer will be high, or crosslinks will be formed during molding, resulting in foreign matter defects and reduced appearance quality.

The methacrylic copolymer of the present invention may contain a structural unit (O) other than the methyl methacrylate unit, the α-methylstyrene unit, and the (R). Examples of the structural unit (O) include a unit derived from a vinyl monomer having only one polymerizable carbon-carbon double bond in one molecule, such as (meth)acrylamide, (meth)acrylonitrile, (meth)acrylic acid, and styrene, a structural unit represented by formula (A), and a structural unit represented by formula (B), among which 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, and even more preferably 3% by mass or more and 10% by mass or less, based on the total 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.

The methacrylic copolymer of the present invention preferably has a weight average molecular weight (Mw) of 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 molding processability is improved.

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

The methacrylic copolymer of the present invention preferably has an acid value of 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 moldability is excellent.

The methacrylic copolymer of the present invention has a glass transition temperature of preferably 120° C. as a lower limit, more preferably 121° C., and further preferably 122° C. as an upper limit, which is not particularly limited, and is preferably 160° C. The higher the glass transition temperature of the methacrylic copolymer, the less likely a molded article containing the methacrylic copolymer is to deform or shrink due to heat, i.e., 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 once to 230°C, then cooled to room temperature, and then the DSC curve is measured under conditions of raising the temperature from room temperature to 230°C at a rate of 10°C/min. The midpoint determined from the DSC curve measured during the second heating is determined as the "glass transition temperature (Tg)".

The methacrylic copolymer of the present invention preferably has a birefringence retardation that is higher in the visible light region at longer wavelengths, that is, shows the so-called reverse wavelength dispersion.Specifically, when the retardation value at wavelength λ (nm) is expressed as Re (λ), the ratio (Re (450)/Re (550)) of the methacrylic copolymer to the Re (550) preferably satisfies the following formula (1), and the ratio (Re (550)/Re (650)) of the methacrylic copolymer to the Re (550) 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 elliptically polarized light when linearly polarized light is incident on the methacrylic copolymer can be made uniform regardless of wavelength, resulting in good optical compensation ability.

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, even more 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, even more 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, even more 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, even more preferably 1.35 or less, and even more preferably 1.25 or less.

The methacrylic copolymer of the present invention exhibits reverse wavelength dispersion by containing α-methylstyrene units together with methyl methacrylate units and structural unit (R). The reason for this is presumed to be as follows. A polymer consisting of methyl methacrylate units has a relatively small negative intrinsic birefringence, as exemplified in FIG. 1(b), and has positive wavelength dispersion 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, it is considered that a polymer consisting of this unit has a positive intrinsic birefringence, as exemplified in FIG. 1(a), and has positive wavelength dispersion in which the birefringence increases as the wavelength of light becomes shorter. Therefore, conventional copolymers containing methyl methacrylate units and structural unit (R) have positive wavelength dispersion as exemplified in FIG. 1(e). In contrast, a polymer consisting of α-methylstyrene units has a negative intrinsic birefringence and further has positive wavelength dispersion, as exemplified in FIG. 1(c), and is considered to have a relatively large slope. Therefore, it is believed that the methacrylic copolymer of the present invention exhibits the reverse wavelength dispersion as exemplified in FIG. 1(d) as a result of combining these effects.

The phase difference and its dispersibility at each wavelength can be adjusted arbitrarily by varying the ratio of methyl methacrylate units, α-methylstyrene units, and structural units (R) within the range of the present invention.

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 can be produced by the following steps: continuously supplying a reaction raw material containing a monomer mixture containing methyl methacrylate, α-methylstyrene, and optionally a copolymerizable monomer, a radical polymerization initiator, and optionally a chain transfer agent, to a tank reactor;
a step of bulk polymerizing the monomer mixture in a tank reactor to a polymerization conversion rate of 30 to 60 mass% to obtain a reaction product;
It can be obtained by a production method including 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.

The precursor polymer is polymerized from reaction raw materials including a monomer mixture, a radical polymerization initiator, and optionally a chain transfer agent, and the monomer mixture contains methyl methacrylate in an amount of preferably 51 to 90 mass%, more preferably 65 to 85 mass%, in the monomer mixture. Also, the monomer mixture contains α-methylstyrene in an amount of preferably 49 to 10 mass%, more preferably 35 to 15 mass%, and the copolymerizable monomer in an amount of 0 to 10 mass%, preferably 0 to 5 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; and vinyl monomers having only one polymerizable alkenyl group in one molecule. The content of the copolymerizable monomers other than methyl methacrylate and alkyl acrylate esters in the monomer mixture is preferably 10% by mass or less, more preferably 5% by mass or less.

The monomer mixture preferably has b* of -1 to 2, more preferably -0.5 to 1.5. When b* is in this range, it is advantageous for obtaining molded products with little coloring at high production efficiency when the resulting methacrylic copolymer composition is molded. Note that b* is a value measured in accordance with the Commission Internationale de l'Eclairage (CIE) standard (1976) or JIS Z-8722.
The monomer mixture removed from the reaction product in the step of removing the monomer mixture in the reaction product can be recovered and reused in the present invention. If the b* of the recovered monomer mixture becomes high due to heat applied during recovery, it is preferable to purify it by a suitable method to make the b* within the above range.

The polymerization initiator used in the present invention is not particularly limited as long as it generates reactive radicals. For example, t-hexylperoxyisopropyl monocarbonate, t-hexylperoxy2-ethylhexanoate, 1,1,3,3-tetramethylbutylperoxy2-ethylhexanoate, t-butylperoxypivalate, t-hexylperoxypivalate, t-butylperoxyneodecanoate, t-hexylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, 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), and dimethyl 2,2'-azobis(2-methylpropionate) are preferred; Further examples include t-hexylperoxy 2-ethylhexanoate, 1,1-bis(t-hexylperoxy)cyclohexane, and dimethyl 2,2'-azobis(2-methylpropionate).

The polymerization initiator used in the present invention desirably has an average uncleaved initiator concentration (I) in the range of 5.1×10 ⁻⁵ to 2.4×10 ⁻⁴ (mol/L) at the polymerization temperature in a tank reactor described below.

The amount of polymerization initiator used is adjusted to the polymerization temperature and added to the monomer mixture so as to achieve the above initiator concentration (I).

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), and 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 parts by mass, and even more preferably 0.02 to 0.6 parts by mass, based on 100 parts by mass of the monomer mixture.

In principle, no solvent is used in bulk polymerization, but if it is necessary to adjust the viscosity of the reaction liquid, a 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, per 100 parts by mass of the monomer mixture.

The reaction raw materials used in the present invention preferably have a dissolved oxygen content of 10 ppm or less, more preferably 5 ppm or less, even more preferably 4 ppm or less, and most preferably 3 ppm or less. If the dissolved oxygen content is within such a range, the polymerization reaction proceeds smoothly, making it easier to obtain molded products without silver streaks or coloring.

The temperature inside the tank reactor, i.e., the temperature of the liquid inside the reaction tank, is preferably 110 to 140°C, more preferably 114 to 135°C. If the temperature is higher than this range, it becomes difficult to produce high molecular weight compounds containing α-methylstyrene, which can cause a decrease in heat resistance.

In the method for producing a methacrylic copolymer composition of the present invention, the water content 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 keeping the water content at 1000 ppm or less, it is possible to suppress the generation of resin foreign matter of several μm to several tens of μm during the polymerization reaction, and when the obtained methacrylic copolymer composition is formed into a film or sheet by melt molding, it is possible to significantly reduce the occurrence of defects having an outer diameter of several tens of μm that are caused by the resin foreign matter.

In a tank reactor, it is preferable to carry out bulk polymerization until the polymerization conversion rate reaches 30 to 65% by mass, preferably 35 to 60% by mass.

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 amount of polymerization initiator required increases. Furthermore, an increase in the amount of polymerization initiator makes it difficult to control the polymerization reaction and tends to make it difficult to control the molecular weight. On the other hand, if the average residence time is too long, it takes time for the reaction to reach a steady state, and productivity tends to decrease. The average residence time can be adjusted by the capacity of the tank reactor and the amount of reaction raw materials supplied.

Bulk polymerization is preferably carried out in an inert gas atmosphere such as nitrogen gas.

The manufacturing method of the present invention has 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, but may be a reaction product obtained in another reactor connected after the tank reactor as necessary, that is, a reaction product in which the unreacted monomer mixture in the reaction product obtained by bulk polymerization in a tank reactor is further polymerized in another reactor to increase the polymerization conversion rate. In addition, in this step, the solvent is also removed at the same time as necessary. Although there are no particular limitations on the removal method, a thermal devolatilization method is preferred. Examples of the thermal devolatilization method include equilibrium flash evaporation and adiabatic flash evaporation, and adiabatic flash evaporation is preferred. The temperature at which the adiabatic flash evaporation method is performed 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 performed is less than 200°C, it takes a long time to devolatilize, and the devolatilization becomes insufficient, which may cause poor appearance such as silver streaks on the molded product. On the other hand, when the temperature at which the adiabatic flash evaporation method is carried out exceeds 280°C, the methacrylic copolymer composition tends to be colored and depolymerized 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 to 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 particles according to a known method to facilitate ease of handling as a molding material. The content of the monomer mixture in the methacrylic copolymer composition obtained by the present invention is preferably 1% by mass or less, more preferably 0.5% by mass or less.

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

The precursor polymer is not particularly limited as long as the total content of structural units derived from methyl methacrylate is 70 to 93% by mass and the total content of structural units derived from α-methylstyrene is 30 to 7% by mass. From the viewpoints of polymerizability, transparency, etc., the total content of 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.

From the viewpoints of heat resistance, polymerizability, water absorption, etc., the total content of 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 structural units derived from α-methylstyrene are less than this range, sufficient heat resistance cannot be obtained, and if they are more than this range, polymerizability is significantly reduced.

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

The ring structure forming reaction can be carried out, for example, using an extruder. Examples of extruders include single-screw extruders, twin-screw extruders, and multi-screw extruders. From the viewpoint of mixing performance, twin-screw extruders are preferred. Twin-screw extruders include non-intermeshing co-rotating, intermeshing co-rotating, non-intermeshing counter-rotating, and intermeshing counter-rotating. Intermeshing co-rotating extruders are preferred because they are capable of high-speed rotation and can efficiently promote mixing. These extruders may be used alone or connected in series.

In the ring structure forming reaction using an extruder, for example, a precursor polymer as a raw material is charged from a raw material charging section of the extruder, the precursor polymer is melted, and the cylinder is filled, and then an imidizing agent (optional component) or the like is injected into the extruder using an addition pump, so that the ring structure forming reaction can proceed in the extruder. When an imidizing agent is used, the structural unit (R) contains an N-substituted or unsubstituted glutarimide unit, and may contain a lactone ring unit and/or a glutaric anhydride unit as necessary. When an imidizing agent is not used, the structural unit (R) is composed of a lactone ring unit and/or a glutaric anhydride unit. A preferred imidizing agent is represented by R ² -NH ₂ (R ² is as defined above). The imidizing agent is used in an amount of 1.6 to 12 parts by mass per 100 parts by mass of the methacrylic copolymer. When the amount of the imidizing agent used is within the above range, the by-production of methacrylic acid amide units can be suppressed.

The resin temperature in the reaction zone of the extruder is preferably in the range of 180 to 280°C, and 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 and the by-production of methacrylic acid amide units. 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 methacrylic copolymer obtained tends to decrease. The reaction zone in the extruder refers to the region between the injection position of the imidization agent, etc., in the cylinder of the extruder to the resin discharge port (die part).

By increasing the reaction time in the reaction zone of the extruder, the ring structure forming reaction can proceed more efficiently. The reaction time in the reaction zone of the extruder is preferably longer than 10 seconds, and more preferably longer than 30 seconds. If the reaction time is less than 10 seconds, the ring structure forming reaction may not proceed at all.

The resin pressure in the extruder is preferably in the range of atmospheric pressure to 50 MPa, and more preferably in the range of 1 to 30 MPa. Above 50 MPa, it exceeds the mechanical pressure resistance limit of a normal extruder, and special equipment is required, which is not desirable from a cost perspective.

It is preferable to use an extruder having a vent hole that can reduce the pressure to below atmospheric pressure. With such a configuration, unreacted materials, by-products such as methanol, and monomers can be removed, and the breaking strength of the molded article containing the methacrylic copolymer of the present invention tends to be improved.

For the ring structure formation reaction, instead of an extruder, a horizontal twin-screw reactor such as the Bivolac manufactured by Sumitomo Heavy Industries, Ltd., or a vertical twin-screw agitator such as Superblend, which is suitable for high viscosity reaction, can also be used.

During the ring structure forming reaction, a carboxyl group may be by-produced in the methacrylic copolymer. This carboxyl group may be converted to an ester group by an esterifying agent or a catalyst, if necessary. This can reduce foaming of the resin during the production of an optical film. The ester group varies 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 that the ester group contains a methyl methacrylate unit, and more preferably contains both a methyl methacrylate unit and an ethyl methacrylate unit.
As the esterifying agent, dimethyl carbonate is preferred from the viewpoints of cost, reactivity, etc.

The amount of esterification agent added can be set, for example, so that the acid value of the methacrylic copolymer becomes the desired value.

In addition to the above esterification agent, a catalyst can also be used in combination. The type of catalyst is not particularly limited, but examples include amine compounds such as trimethylamine, triethylamine, monomethyldiethylamine, and dimethylmonoethylamine. Among these, triethylamine is preferred from the standpoint of cost, reactivity, and the like.

Additives generally used in resin compositions may be included to the extent that the object of the present invention is not impaired. Examples of additives include fillers, antioxidants, heat deterioration inhibitors, UV absorbers, light stabilizers, lubricants, release agents, polymer processing aids, antistatic agents, flame retardants, colorants, dyes, pigments, light diffusing agents, organic dyes, matting agents, impact resistance modifiers, and fluorescent materials. The total amount of such additives other than fillers is preferably 7% by mass or less, more preferably 5% by mass or less, and even more preferably 4% by mass or less.

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.

Antioxidants are effective in preventing oxidative deterioration of resins in the presence of oxygen by themselves. Examples include phosphorus-based antioxidants, hindered phenol-based antioxidants, and thioether-based antioxidants. These antioxidants may be used alone or in combination of two or more types.

The heat deterioration inhibitor is capable of preventing the thermal deterioration of a resin by capturing polymer radicals that are generated when the resin is exposed to high heat in a substantially oxygen-free state.
Examples of the heat deterioration inhibitor include 2-tert-butyl-6-(3'-tert-butyl-5'-methyl-hydroxybenzyl)-4-methylphenyl acrylate (manufactured by Sumitomo Chemical Co., Ltd.; product 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.; product name: Sumilizer GS), and the like.

An ultraviolet absorber is a compound that has the ability to absorb ultraviolet rays. An ultraviolet absorber is a compound that is said to have the function of converting light energy into heat energy.
Examples of ultraviolet absorbents include benzophenones, benzotriazoles, triazines, benzoates, salicylates, cyanoacrylates, oxalic anilides, malonic acid esters, and formamidines. These may be used alone or in combination of two or more. Among these, benzotriazoles, triazines, or ultraviolet absorbents having a maximum molar absorption coefficient ε _max of 1200 dm ³ mol ^-1 cm ^-1 or less at a wavelength of 380 to 450 nm are preferred.

Benzotriazoles are highly effective in suppressing deterioration of optical properties such as coloring due to ultraviolet rays, and are therefore preferred as ultraviolet absorbers when the molded article of the present invention is applied to optical applications. Preferred benzotriazoles include 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (manufactured by BASF; product name TINUVIN 329), 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (manufactured by BASF; product name TINUVIN 234), 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol] (manufactured by ADEKA; product name LA-31), and 2-(5-octylthio-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol.

Furthermore, an ultraviolet absorber having a maximum molar absorption coefficient ε _max of 1200 ^{dm mol} cm at wavelengths of 380 to 450 nm or ^less can suppress the yellowing of the resulting molded article. Examples of such ultraviolet absorbers include 2-ethyl-2'-ethoxy-oxalanilide (manufactured by Clariant Japan; product name: Sandubor VSU).
Among these ultraviolet absorbents, benzotriazoles are preferably used from the viewpoint of suppressing resin deterioration due to ultraviolet rays.

In addition, when it is desired to efficiently absorb short wavelengths of 380 nm or less, triazine 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; product name LA-F70) and its analogues, hydroxyphenyltriazine ultraviolet absorbers (manufactured by BASF; product names TINUVIN 477, TINUVIN 460, and TINUVIN 479), and 2,4-diphenyl-6-(2-hydroxy-4-hexyloxyphenyl)-1,3,5-triazine.

Furthermore, when it is desired to absorb light with wavelengths of 380 to 400 nm particularly effectively, it is preferable to use a metal complex having a ligand with a heterocyclic structure as disclosed in WO2011/089794A1, WO2012/124395A1, JP2012-012476A, JP2013-023461A, JP2013-112790A, JP2013-194037A, JP2014-62228A, JP2014-88542A, JP2014-88543A, etc. as an ultraviolet absorber.

Examples of the ligand of the heterocyclic 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 derivatives thereof. Copper, nickel, cobalt, and zinc are preferably used as the central metal of such metal complexes. In addition, in order to use these metal complexes as ultraviolet absorbers, it is preferable to disperse the metal complexes in a medium such as a low molecular weight compound or a polymer. The amount of the metal complex added is preferably 0.01 to 5 parts by mass, more preferably 0.1 to 2 parts by mass, relative to 100 parts by mass of the molded product of the present invention. The metal complex has a large molar absorption coefficient at wavelengths of 380 to 400 nm, so that only a small amount needs to be added to obtain a sufficient ultraviolet absorbing effect. If the amount added is small, deterioration of the appearance of the molded product due to bleed-out or the like can be suppressed. In addition, the metal complex has high heat resistance, so there is little deterioration or decomposition during molding processing. Furthermore, the metal complex has high light resistance, so that the ultraviolet absorbing performance can be maintained for a long period of time.

The maximum molar absorption coefficient ε _max of the ultraviolet absorber is measured as follows. 10.00 mg of ultraviolet absorber is added to 1 L of cyclohexane, and dissolved until no undissolved matter is found by visual observation. This solution is poured into a quartz glass cell measuring 1 cm x 1 cm x 3 cm, and the absorbance at wavelengths of 380 to 450 nm is measured using a spectrophotometer (manufactured by Hitachi, Ltd.; product name U-3410). The maximum molar absorption coefficient ε _max is calculated from the molecular weight (M _UV ) of the ultraviolet absorber and the maximum absorbance (A _max ) measured according to the following formula.
ε _max = [A _max /(10×10 ⁻³ )]×M _UV

Light stabilizers are compounds that are said to have the function of capturing radicals generated mainly by oxidation due to light. Suitable light stabilizers include hindered amines such as compounds with a 2,2,6,6-tetraalkylpiperidine skeleton.

Examples of lubricants include stearic acid, behenic acid, stearamide acid, methylene bisstearamide, hydroxystearic acid triglyceride, paraffin wax, ketone wax, octyl alcohol, and hydrogenated oil.

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

As the polymer processing aid, polymer particles (non-crosslinked rubber particles) having a particle size of 0.05 to 0.5 μm, which can be produced by emulsion polymerization, are usually used. The polymer particles may be single-layer particles made of a polymer with a single composition ratio and a single intrinsic viscosity, or may be multi-layer particles made of two or more polymers with different composition ratios or intrinsic viscosities.
Examples of the antistatic agent include alkylsulfonates 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 a hydroxyl group or crystal water, such as magnesium hydroxide, aluminum hydroxide, hydrated aluminum silicate, hydrated magnesium silicate, and hydrotalcite; phosphate compounds, such as polyamine phosphoric acid esters; and silicon compounds. Of these, preferred are 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, methyl dibutyl phosphate, ethyl dipropyl phosphate, and hydroxyphenyl diphenyl phosphate.
Examples of dyes and pigments include red organic pigments such as Para Red, Fire Red, Pyrazolone Red, Thioindium 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 may be used.

As the organic dye, a compound having a function of converting ultraviolet light into visible light is preferably used.
Examples of the light diffusing agent and the matting agent include glass particles, polysiloxane-based crosslinked particles, crosslinked polymer particles, talc, calcium carbonate, and barium sulfate.
Examples of fluorescent materials include fluorescent pigments, fluorescent dyes, fluorescent white dyes, fluorescent brighteners, and fluorescent bleaches.

The methacrylic copolymer composition of the present invention is not particularly limited by its production method, and can be produced, for example, by melt-kneading the methacrylic copolymer of the present invention with additives such as an ultraviolet absorber, and other polymers as necessary. The melt-kneading can be carried out using a melt-kneading device such as a kneader-ruder, an extruder, a mixing roll, or a Banbury mixer. The temperature during kneading can be appropriately set depending on the softening temperature of the methacrylic copolymer and other polymers, and can be set, for example, to 150 to 300°C. The shear rate during kneading can be set, for example, to 10 to 5000 ^sec-1 .

The methacrylic copolymer composition of the present invention can be made into a form such as pellets to enhance convenience in storage, transportation, or molding.

The film of the present invention comprises the methacrylic copolymer or methacrylic copolymer composition of the present invention. The method for producing the film of the present invention is not particularly limited. For example, the film 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, the extrusion molding method or the solution casting method is preferred from the viewpoint of obtaining a film that has excellent transparency, improved toughness, excellent handling properties, and an excellent balance between toughness, surface hardness, and rigidity. The temperature of the molten resin discharged from the extruder is preferably set to 160 to 270°C, more preferably 220 to 260°C.

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 sandwich 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 to form a film. 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 roll, a metal elastic roll, etc. can be used, and it is preferable to use a combination of a metal elastic roll and a metal rigid roll. In addition, the surface temperatures of both the mirror roll or the mirror belt are preferably 130° C. or less. In addition, it is preferable that at least one of the pair of mirror rolls or mirror belts has a surface temperature of 60° C. or more. When the surface temperature is set at such a level, the molten resin discharged from the extruder can be cooled at a rate faster than natural cooling, and a film with excellent surface smoothness and low haze can be easily produced. The linear pressure between the 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.

Solvents used in the solution casting method are not particularly limited, but examples include chlorine-based solvents such as chloroform and methylene chloride; aromatic solvents such as toluene, xylene, benzene, and mixtures 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, etc. These solvents may be used alone or in combination of two or more.

Examples of equipment used to produce films using the solution casting method include drum-type casting machines, band-type casting machines, and spin coaters.

The unstretched film obtained as described above may be subjected to a stretching treatment. The stretching treatment increases the mechanical strength, and a film that is less likely to crack can be obtained. The stretching method is not particularly limited, and examples include uniaxial stretching, simultaneous biaxial stretching, sequential biaxial stretching, and tubular stretching. From the viewpoint of obtaining a film that can be stretched uniformly and has 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 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 methacrylic copolymer composition. Stretching is usually performed at 100 to 5000%/min. After stretching, a film with little thermal shrinkage can be obtained by heat setting. The thickness of the film after stretching is preferably 10 to 200 μm.

When the film of the present invention is used as a retardation film, the retardation can be arbitrarily selected between 5 nm and 1000 nm depending on the application. 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 part 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 even more preferably 85 to 145 nm. When used as a film for preventing external light reflection or as a part of an optical compensation polarizing plate, the wavelength dispersion of the retardation of the film is particularly important, and the shorter the wavelength, the lower the retardation is required to be the reverse wavelength dispersion. Specifically, it is preferable that the ratio of Re(450) to Re(550) of the retardation film (Re(450)/Re(550)) 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 dispersion of the methacrylic copolymer is within the above range, the state of elliptically polarized light when linearly polarized light is incident on the methacrylic copolymer can be made uniform regardless of wavelength, resulting in good optical compensation ability.

A functional layer may be provided on the surface of the film, which is one form of the molded article of the present invention. Examples of the functional layer include a hard coat layer, an anti-glare layer, an anti-reflection layer, an anti-sticking layer, a diffusion layer, an anti-glare layer, an anti-static layer, an anti-fouling layer, and a slippery layer such as fine particles.

It is also preferable to provide an undercoat layer on at least one side of the film of the present invention in order to improve the adhesive strength with the functional layer and to improve the adhesive strength when laminated with other films via an adhesive or pressure-sensitive adhesive.

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

A laminate can be obtained by laminating a layer containing the methacrylic copolymer or methacrylic copolymer composition of the present invention with another material (e.g., a layer containing another thermoplastic copolymer). Examples of other materials used in the laminate include steel, plastic (e.g., thermoplastic resin), wood, glass, etc. The laminate obtained by the present invention can be suitably used for wallpaper; automobile interior component surfaces; automobile exterior component surfaces such as bumpers; mobile phone surfaces; furniture surfaces; personal computer surfaces; vending machine surfaces; bathroom component surfaces such as bathtubs, etc.

The film, which is one form of the molded article of the present invention, is highly transparent and heat resistant, and therefore suitable for optical applications, and is particularly suitable for polarizer protection films, liquid crystal protection plates, surface materials for portable information terminals, display window protection films for portable information terminals, light guiding films, transparent conductive films with silver nanowires or carbon nanotubes applied to the surface, and front panels for various displays. The film of the present invention is highly transparent and heat resistant, and therefore can be used for applications other than optical applications, such as infrared cut films, security films, shatterproof films, decorative films, metal decorative films, shrink films, and films for in-mold labels.

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

The present invention will now be described in more detail with reference to examples. Note that the present invention is not limited to these examples.

Measurements of physical properties were carried out using the following methods.

(Polymerization Conversion Rate)
A gas chromatograph GC-14A manufactured by Shimadzu Corporation was connected to an INERTCAP1 column (df=0.4 μm, 0.25 mm ID×60 m manufactured by GL Sciences Inc.) under the following conditions, and the analysis was performed based on the results.
Injection temperature = 250℃
Detector temperature = 250℃
Temperature conditions: hold at 60°C for 5 minutes → heat to 250°C at 10°C/min → hold at 250°C for 10 minutes

(Molecular weight distribution Mw/Mn)
The weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the resin were determined by GPC (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 to 40°C, and 20 μl of the sample solution was injected into the device at an eluent flow rate of 0.35 ml/min to measure the chromatogram. Ten standard polystyrene points with molecular weights in the range of 400 to 5,000,000 were measured by GPC, and a calibration curve showing the relationship between retention time and molecular weight was created. The Mw and Mw/Mn of the resin to be measured were determined based on this calibration curve.
Apparatus: Tosoh GPC device HLC-8320
Separation column: TSKguard column Super HZ-H, TSKgel HZM-M, and TSKgel Super HZ4000 manufactured by Tosoh Corporation connected in series Eluent: tetrahydrofuran Eluent flow rate: 0.35 ml/min Column temperature: 40° C.
Detection method: Differential refractive index (RI)

(Composition of each unit in the copolymer)
The integral ratios of the carbonyl carbon of the methyl methacrylate unit, the aromatic carbon at position 1 of the α-methylstyrene unit, and the aromatic carbon at position 1 of the styrene unit were determined by inverse gate decoupling ^13C -NMR, and the composition of each unit in the copolymer precursor polymer was calculated based on this.

(Glass transition temperature Tg)
The methacrylic copolymers obtained in the examples were measured for their DSC curves in accordance with JIS K7121 using a differential scanning calorimeter (Shimadzu Corporation, DSC-50 (product number)) by heating them once to 250° C., then cooling them to room temperature, and then heating them from room temperature to 200° C. at a rate of 10° C./min. The midpoint glass transition temperature determined from the DSC curve measured during the second heating was taken as the glass transition temperature in the present invention.

(Imidization rate)
The copolymer was subjected to ¹ H-NMR measurement using a ¹ H-NMR (manufactured by Bruker; product name ULTRA SHIELD 400 PLUS). The imidization rate (mol%) was calculated from the area A of the peak derived from the O-CH ₃ group of methyl methacrylate near 3.5 to 3.8 ppm and the area B of the peak derived from the N-CH ₃ group of glutarimide near 3.0 to 3.3 ppm using the following formula:
(Imidization rate (mol%))=[B/(A+B)]×100
The content (wt %) of N-methylglutarimide structural units was calculated from the imidization rate (mol %).

(Wavelength dispersion of retardation)
The methacrylic copolymer obtained in the examples was press molded to obtain a sheet of 1.0 mm. A test piece of 20 mm x 40 mm was cut out from the center of the obtained press molded sheet, and the test piece was placed in an autograph with a heating chamber (manufactured by Shimadzu Corporation). The grip distance in the autograph was set to 20 mm, and the sample was held at glass transition temperature + 10 ° C for 3 minutes. Thereafter, the sample was stretched 100% in one direction at a speed of 3 mm / min (grip distance became 40 mm). The obtained stretched film was cooled to 23 ° C, removed from the autograph, and the refractive index when light of each wavelength was incident was measured using an automatic birefringence meter KOBRA-WR manufactured by Oji Scientific Instruments, 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 in-plane slow axis direction, ny is the refractive index in the in-plane fast axis direction, and d is the thickness (nm) of the film.
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 dispersion of the retardation.

<Production Example 1>
Purified methyl methacrylate (MMA), α-methylstyrene, 2,2′-azobis(2-methylpropionitrile) (AIBN) and n-octyl mercaptan (n-OM) were charged in the ratios shown in Table 1 into an autoclave A equipped with a stirrer and dissolved uniformly to obtain polymerization raw materials.
The polymerization raw materials were continuously supplied from the autoclave A at 1.5 kg/hr to a tank reactor controlled at the polymerization temperature shown in Table 1, and polymerization reaction was carried out by the bulk polymerization method at the average residence time shown in Table 1, and a liquid containing a methacrylic copolymer was continuously discharged from the tank reactor. The polymerization conversion rate was 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 matters 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 a 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, the content of structural units derived from MMA is the amount of units other than α-methylstyrene units and styrene units, so it is not shown in Table 1.

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

Example 1
The copolymer [Aa] shown in Production Example 1 was fed at 2 kg/hr to the transport section of a twin-screw extruder (manufactured by Technobel Co., Ltd.; product name KZW20TW-45MG-NH-600) consisting of a transport section, a melt-kneading section, a devolatilizing section, and a discharge section, and set at a screw speed of 120 rpm and a temperature of 250° C., and monomethylamine was injected at 0.10 kg/hr from the additive supply port of the twin-screw extruder in the melt-kneading section equipped with a kneading block, to react the precursor polymer [Aa] with monomethylamine. A reverse flight was installed on the screw at the end of the reaction zone.
In the volatilizing 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 a vent.
The molten resin extruded as a strand from a die provided at the end of the discharge part of the twin-screw extruder was cooled in a water tank and then cut with a pelletizer to obtain a pellet-shaped methacrylic copolymer (Aa-1).

Copolymer (Aa-1) was supplied at 1 kg/hr to the transport section of a twin-screw extruder (manufactured by Technobel Co., Ltd.; product name KZW20TW-45MG-NH-600) consisting of a transport section, a melt-kneading section, a devolatilizing section, and a discharge section, and set at a screw speed of 100 rpm and a temperature of 230° C. In the melt-kneading section in which a kneading block was installed, a liquid consisting of 0.8 parts by mass of dimethyl carbonate and 0.2 parts by mass of triethylamine was injected at 0.024 kg/hr, and dimethyl carbonate was reacted with the carboxyl group in the methacrylic copolymer (Aa-1). A reverse flight was installed on the screw at the end of the reaction zone.
In the volatilizing 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 were discharged through a vent.
The molten resin extruded as a strand from a die provided at the end of the discharge part of the twin-screw extruder was cooled in a water tank and then cut with a pelletizer to obtain a pellet-shaped methacrylic copolymer (Aa-2).

The methacrylic copolymer (Aa-2) was supplied at 1 kg/hr to the transport section of a twin-screw extruder (manufactured by Technobel Corporation; product name KZW20TW-45MG-NH-600), which was composed of a transport section, a melt-kneading section, a devolatilizing section, and a discharge section and had a screw rotation speed of 100 rpm and a temperature of 230° C.
In the volatilizing section set at 20 Torr (about 2.7 kPa), volatile matters such as unreacted substances were volatilized from the molten resin that had passed through the melt-kneading section, and discharged through a vent.
The molten resin extruded as a strand from a die at the end of the discharge section of the twin-screw extruder was cooled in a water tank and then cut with a pelletizer to obtain a pellet-shaped 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.

Example 2
A methacrylic copolymer [2] was obtained in the same manner as in Example 1, except that the amount of monomethylamine added was 0.15 kg/hr and a solution 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.

Example 3
A methacrylic copolymer [3] was obtained in the same manner as in Example 1, except that A-c was used instead of the precursor polymer A-a, and the amount of monomethylamine added 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.

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 in a small melt kneader at a temperature of 230° C. to obtain a methacrylic copolymer composition [4]. The physical properties of the methacrylic copolymer composition [4] are shown in Table 3.

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

The methacrylic copolymers obtained in Examples 1 to 3 and the methacrylic copolymer composition obtained in Example 4 have high heat resistance and exhibit reverse wavelength dispersion, and therefore can be suitably used as resins for reverse wavelength dispersion retardation films. On the other hand, the methacrylic copolymers obtained in Comparative Examples 1 to 3 were not within the scope of the present invention, and therefore did not exhibit reverse wavelength dispersion and were inferior to the present invention.

Claims (6)

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 structural units (R) having at least one ring structure in the main chain selected from the group consisting of lactone ring units, glutaric anhydride units and N-substituted or unsubstituted glutarimide units, and 7 to 30% by mass of α-methylstyrene units,
Re(450)/Re(550)=0.30~0.95 (1)
Re(650)/Re(550)=1.02~2.00 (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 reverse wavelength dispersion retardation film comprising a methacrylic copolymer for forming a reverse wavelength dispersion retardation film that satisfies the following formulas: 2. The reverse 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):
(In formula (3), R ¹ are each independently a hydrogen atom or 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 and containing an aromatic ring. 2. The reverse wavelength dispersion retardation film according to claim 1, which is made of a composition further containing another resin in addition to the methacrylic copolymer. The method for producing a reverse 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. The method for producing a reverse wavelength dispersion retardation film according to any one of claims 1 to 3 , comprising forming the methacrylic copolymer or the composition into a film by a solution casting method. A laminate having at least one layer made of the reverse wavelength dispersion retardation film according to any one of claims 1 to 3 .

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