JP5919611B2 - Retardation plate with low photoelastic coefficient - Google Patents

Description

  The present invention relates to a retardation plate having a low photoelastic coefficient.

  Examples of the transparent optical material include methacrylic resin represented by methyl methacrylate homopolymer (PMMA), polystyrene (PS), styrene / methyl methacrylate copolymer (MS), polycarbonate (PC) and the like.

  In recent years, with the progress of flat panel displays such as liquid crystal displays, plasma displays, organic EL displays, infrared sensors, optical waveguides, etc., the optical materials used have not only excellent transparency but also high heat resistance. In addition, it is required that the required birefringence is expressed and that no birefringence distribution occurs in the optical material.

  For example, in the case of a polarizing plate protective film used for a liquid crystal polarizing plate, an optical material having a smaller birefringence (= phase difference) is required even if the total light transmittance is the same. In the case of a quarter-wave plate having a function of changing the linearly polarized light into circularly polarized light, an optical material that can express a birefringence (= phase difference) of a necessary size is necessary.

  In addition, with the increase in size of flat panel displays, the molded body made of a required optical material is also increased in size, and therefore, birefringence distribution is generated due to the bias of external force, and the contrast tends to decrease. In order to reduce the birefringence distribution, an optical material having a small change in birefringence due to an external force, that is, a small absolute value of the photoelastic coefficient is required (Non-Patent Documents 1 and 2).

  For example, Patent Documents 1 to 3 disclose peripheral techniques for controlling the birefringence of an optical material.

  Patent Document 1 includes 70 to 85% by weight of methyl methacrylate monomer units and 15 to 30% by weight of one or more N-substituted maleimide monomer units. An optical element made of a copolymer of 0.002 to +0.002 is disclosed. However, the copolymer tends to hardly exhibit a sufficient retardation.

  On the other hand, in Non-Patent Document 3, the birefringence of the molded body as optical uniformity is not only the magnitude of the intrinsic birefringence of the resin used, but also manifests as a result of molding processes such as injection molding and extrusion molding. The birefringence is included. Specifically, when a lens, an optical disk, or the like is obtained by injection molding, the intrinsic birefringence (orientation) birefringence is reflected: 1) minimize the intrinsic birefringence, and 2) select processing conditions. However, the birefringence distribution (= optical inhomogeneity) is generally present in the molded body since the birefringence due to stress strain (photoelasticity) remains in the vicinity of the gate. There is. That is, in order to improve the optical uniformity, it is necessary to separately develop a method for minimizing the photoelastic coefficient.

  Patent Document 2 includes a copolymer resin comprising 89 to 40% by weight of methyl methacrylate units, 10 to 30% by weight of aromatic vinyl compound units, and 1 to 50% by weight of maleimide and / or N-substituted maleimide units. A retardation plate is disclosed. However, the phase difference plate still tends to have a large photoelastic coefficient.

  Patent Document 3 is composed of 45 to 85% by mass of (meth) acrylic acid ester units, 10 to 40% by mass of aromatic vinyl compound units, and 5 to 20% by mass of aromatic maleimide units. An optical stretched film obtained by stretching a copolymer having a group maleimide unit content is disclosed. The stretched film expresses a large negative phase difference and has excellent thermal decomposition characteristics, but has a large photoelastic coefficient and insufficient light resistance.

  On the other hand, as a peripheral technique for controlling the photoelastic coefficient of an optical material, Patent Document 4 discloses an optical element material that adjusts the photoelastic coefficient to zero by combining a monomer having a positive sign and a negative monomer. It is disclosed. However, the optical element material cannot exhibit a sufficient phase difference and has insufficient heat resistance.

  Patent Document 5 discloses a co-polymerization consisting of 98 to 50% by weight of methacrylic acid ester units, 1 to 20% by weight of arylmaleimide units, 1 to 30% by weight of alkylmaleimide units and 0 to 15% by weight of other monomer units. A composition comprising a coalescence and a rubber-modified thermoplastic resin is disclosed. However, a molded body formed from the composition tends to have a large photoelastic coefficient.

  As a retardation film having a low photoelastic coefficient, for example, Patent Document 6 discloses a quaternary copolymer consisting of methyl methacrylate, styrene, maleic anhydride, and benzyl methacrylate (MMA / St / MAH / BzMA = 50). / 20/29/1 wt%) is disclosed. However, the quaternary copolymer tends to have insufficient light resistance and long-term stability of the absolute value of retardation.

Japanese Patent Application Laid-Open No. 06-242301 Japanese Patent No. 2886893 JP 2011-38053 A Japanese Patent Laid-Open No. 04-76013 Japanese Patent No. 4424636 International Publication No. 2010/013557

Chemical Review, 1988, No. 39 (Academic Publishing Center) Monthly display, April 2005 issue Molding, 2009, Vol. 21, No. 7, p. 426

  As described above, it is difficult to provide a retardation plate having both a low photoelastic coefficient and a necessary phase difference, and having heat resistance and light resistance, using a conventional optical material.

  Accordingly, an object of the present invention is to provide a retardation plate having a low photoelastic coefficient and further having excellent heat resistance and light resistance, and a polarizing plate and an image display device including the same.

  The present invention is suitable as a retardation plate because a film and sheet made of a specific thermoplastic resin have a low photoelastic coefficient and retardation, and have excellent heat resistance and light resistance. It was made to find out.

［式中、Ｒ^１は、水素原子、炭素数１〜１２のアルキル基、炭素数５〜１２のシクロアルキル基、炭素数７〜１４のアリールアルキル基、炭素数６〜１４のアリール基、又は、下記Ａ群より選ばれる少なくとも一種の置換基を有する炭素数６〜１４のアリール基、を示す。
Ａ群：ハロゲン原子、ヒドロキシル基、ニトロ基、炭素数１〜１２のアルコキシ基及び炭素数１〜１２のアルキル基。］

［式中、Ｒ^２は、炭素数７〜１４のアリールアルキル基、炭素数６〜１４のアリール基、又は、下記Ｂ群より選ばれる少なくとも一種の置換基を有する炭素数６〜１４のアリール基、を示し、Ｒ^３及びＲ^４はそれぞれ独立に、水素原子、炭素数１〜１２のアルキル基又は炭素数６〜１４のアリール基を示す。
Ｂ群：ハロゲン原子、ヒドロキシル基、ニトロ基、炭素数１〜１２のアルコキシ基、炭素数１〜１２のアルキル基及び炭素数７〜１４のアリールアルキル基。］

［式中、Ｒ^５は、水素原子、炭素数３〜１２のシクロアルキル基、炭素数１〜１２のアルキル基、又は、下記Ｃ群より選ばれる少なくとも一種の置換基を有する炭素数１〜１２のアルキル基、を示し、Ｒ^６及びＲ^７はそれぞれ独立に、水素原子、炭素数１〜１２のアルキル基又は炭素数６〜１４のアリール基を示す。
Ｃ群：ハロゲン原子、ヒドロキシル基、ニトロ基及び炭素数１〜１２のアルコキシ基。］
［２］熱可塑性樹脂は、フィルム成形した場合の面内方向の位相差（Ｒｅ）の絶対値が、１００μｍ厚み換算で３０ｎｍを超え、３００ｎｍ以下である［１］に記載の位相差板。
［３］熱可塑性樹脂のガラス転移温度が１２０℃以上である、［１］又は［２］に記載の位相差板。
［４］熱可塑性樹脂は、フィルム成形した場合の全光線透過率が８５％以上である、［１］〜［３］のいずれか１つに記載の位相差板。
［５］熱可塑性樹脂を押出成形したシート又はフィルムを、少なくとも１軸方向に延伸し、その延伸倍率が０．１〜３００％である、［１］〜［４］のいずれか１つに記載の位相差板。
［６］熱可塑性樹脂を溶液キャスト成形したシート又はフィルムを、少なくとも１軸方向に延伸し、その延伸倍率が０．１〜３００％である、［１］〜［４］のいずれか１つに記載の位相差板。
［７］Ｒ^１が、メチル基又はベンジル基であり、Ｒ^２が、フェニル基又はＢ群より選ばれる少なくとも一種の置換基を有するフェニル基であり、Ｒ^５が、シクロヘキシル基である、［１］〜［６］のいずれか１つに記載の位相差板。
［８］［１］〜［７］のいずれか１つに記載の位相差板を備える、偏光板。
［９］［１］〜［７］のいずれか１つに記載の位相差板を備える、画像表示装置。 That is, the present invention relates to the following.
[1] Heat having a first structural unit represented by the following formula (1), a second structural unit represented by the following formula (2), and a third structural unit represented by the following formula (3) The thermoplastic resin is formed from a plastic resin, and the total amount of the thermoplastic resin is 50 to 90% by mass of the first structural unit, 0.1 to 15% by mass of the second structural unit, and 0.1 to 49.%. A phase difference plate having 9% by mass of a third structural unit and having an absolute value of a photoelastic coefficient of the thermoplastic resin of 2.5 × 10 ⁻¹² Pa ⁻¹ or less.

[Wherein, R ¹ represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an arylalkyl group having 7 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or And an aryl group having 6 to 14 carbon atoms and having at least one substituent selected from the following group A.
Group A: a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, and an alkyl group having 1 to 12 carbon atoms. ]

[Wherein, R ² represents an arylalkyl group having 7 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or an aryl group having 6 to 14 carbon atoms having at least one substituent selected from the following group B: R ³ and R ⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms.
Group B: a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, an alkyl group having 1 to 12 carbon atoms, and an arylalkyl group having 7 to 14 carbon atoms. ]

[Wherein, R ⁵ represents a hydrogen atom, a cycloalkyl group having 3 to 12 carbon atoms, an alkyl group having 1 to 12 carbon atoms, or at least one substituent having at least one substituent selected from the following group C. R ⁶ and R ⁷ each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms.
Group C: a halogen atom, a hydroxyl group, a nitro group, and an alkoxy group having 1 to 12 carbon atoms. ]
[2] The phase difference plate according to [1], wherein the thermoplastic resin has an in-plane retardation (Re) absolute value of more than 30 nm and not more than 300 nm in terms of 100 μm thickness when the film is formed.
[3] The retardation plate according to [1] or [2], wherein the thermoplastic resin has a glass transition temperature of 120 ° C. or higher.
[4] The retardation plate according to any one of [1] to [3], wherein the thermoplastic resin has a total light transmittance of 85% or more when film-formed.
[5] The sheet or film obtained by extruding the thermoplastic resin is stretched in at least one axial direction, and the stretch ratio is 0.1 to 300%, according to any one of [1] to [4] Phase difference plate.
[6] In any one of [1] to [4], a sheet or film obtained by solution cast molding of a thermoplastic resin is stretched in at least a uniaxial direction, and the stretch ratio is 0.1 to 300%. The retardation plate described.
[7] R ¹ is a methyl group or a benzyl group, R ² is a phenyl group or a phenyl group having at least one substituent selected from group B, and R ⁵ is a cyclohexyl group. ] The phase difference plate as described in any one of [6].
[8] A polarizing plate comprising the retardation plate according to any one of [1] to [7].
[9] An image display device comprising the phase difference plate according to any one of [1] to [7].

  According to the present invention, a retardation plate having a low photoelastic coefficient and further excellent heat resistance and light resistance can be provided. The polarizing plate provided with the retardation plate of the present invention can be suitably used for an image display device, for example. In addition, the image display device including the retardation plate of the present invention is excellent in image display characteristics such as a change in color tone when viewed from an oblique direction.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

[Thermoplastic resin]
The retardation plate of this embodiment is formed from a thermoplastic resin having a first structural unit, a second structural unit, and a third structural unit. Hereinafter, each structural unit constituting the thermoplastic resin will be described.

(First structural unit)
The first structural unit is a structural unit represented by the following formula (1).

式中、Ｒ^１は、水素原子、炭素数１〜１２のアルキル基、炭素数５〜１２のシクロアルキル基、炭素数７〜１４のアリールアルキル基、炭素数６〜１４のアリール基、又は、下記Ａ群より選ばれる少なくとも一種の置換基を有する炭素数６〜１４のアリール基、を示す。ここで、Ａ群は、ハロゲン原子、ヒドロキシル基、ニトロ基、炭素数１〜１２のアルコキシ基及び炭素数１〜１２のアルキル基からなる群である。

In the formula, R ¹ is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an arylalkyl group having 7 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or The C6-C14 aryl group which has at least 1 type of substituent chosen from the following A group is shown. Here, group A is a group consisting of a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, and an alkyl group having 1 to 12 carbon atoms.

  In the present specification, the alkyl group may be linear or branched. Further, the alkyl group in the arylalkyl group and the alkyl group in the alkoxy group may be linear or branched.

Examples of the alkyl group having 1 to 12 carbon atoms in R ^1, preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms. The alkyl group having 1 to 12 carbon atoms in ^{R 1,} a methyl group, an ethyl group, n- propyl group, an isopropyl group, n- butyl group, an isobutyl group, t- butyl, 2-ethylhexyl, nonyl , Decanyl group, lauryl group, etc. Among these, in terms of further improving the transparency and weather resistance of the thermoplastic resin, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, An isobutyl group, a t-butyl group, and a 2-ethylhexyl group are preferable, and a methyl group is more preferable.

Examples of the cycloalkyl group having 5 to 12 carbon atoms in R ¹ include a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a tricyclodecyl group, a bicyclooctyl group, a tricyclododecyl group, an isobornyl group, and an adamantyl group. And tetracyclododecyl group. Among these, a cyclopentyl group, a cyclohexyl group, a cyclooctyl group, a tricyclodecyl group, a bicyclooctyl group, a tricyclododecyl group, and an isobornyl group are preferable.

Examples of the arylalkyl group having 7 to 14 carbon atoms in R ¹ include benzyl group, 1-phenylethyl group, 2-phenylethyl group, 3-phenylpropyl group, 6-phenylhexyl group, and 8-phenyloctyl group. Among these, benzyl group, 1-phenylethyl group, 2-phenylethyl group, and 3-phenylpropyl group are preferable.

The aryl group having 6 to 14 carbon atoms in R ^1, a phenyl group, a naphthyl group, anthracenyl group and the like, among these, phenyl groups are preferred.

R ¹ may be an aryl group having 6 to 14 carbon atoms having a substituent, wherein the substituent is a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, or 1 carbon atom. A group selected from the group consisting of ˜12 alkyl groups (Group A).

In R ¹ , the aryl group having 6 to 14 carbon atoms having a substituent is preferably a phenyl group having a substituent. Examples of the aryl group having 6 to 14 carbon atoms having a substituent include 2,4,6-tribromophenyl group, 2-chlorophenyl group, 4-chlorophenyl group, 2-bromophenyl group, 4-bromophenyl group, 2-methylphenyl group, 4-methylphenyl group, 2-ethylphenyl group, 4-ethylphenyl group, 2-methoxyphenyl group, 4-methoxyphenyl group, 2-nitrophenyl group, 4-nitrophenyl group, 2, Examples include 4,6-trimethylphenyl group. Among these, 2,4,6-tribromophenyl group is preferable in terms of imparting flame retardancy.

  The content of the first structural unit is 50 to 50 based on the total amount of the thermoplastic resin because it is necessary to be contained in an amount superior to other structural units in order to maintain the excellent transparency and light resistance of the methacrylic resin. It is 90 mass%, Preferably it is 60-90 mass%, More preferably, it is 70-90 mass%. When the content of the first structural unit is within this range, the obtained thermoplastic resin is excellent in transparency and light resistance, and a preferable heat resistance improving effect is easily obtained.

Regarding optical characteristics (in-plane retardation (Re)) described later, in order for the thermoplastic resin according to the present embodiment to have a negative retardation, the content ratio (X _wt ) of the first structural unit is It is preferably 80 to 90% by mass based on the total amount of the thermoplastic resin. On the other hand, in order for the thermoplastic resin according to the present embodiment to have a positive phase difference, the content ratio (X _wt ) of the first structural unit is 50 to 80% by mass based on the total amount of the thermoplastic resin. preferable.

In order that the absolute value of the in-plane retardation (Re) of the thermoplastic resin according to the present embodiment exceeds 30 nm, the content ratio (X _wt ) of the first structural unit is based on the total amount of the thermoplastic resin. It is preferable that it is less than 65 mass%, More preferably, it is less than 60 mass%. However, the phase difference here is a value obtained by converting a value measured for a film obtained by molding a thermoplastic resin into a film thickness of 100 μm.

  When a methacrylic acid ester monomer having an aromatic group, for example, benzyl methacrylate, 2,4,6-tribromophenyl methacrylate or the like is used in combination with a methyl methacrylate monomer, its content is From the viewpoint of the optical properties such as the properties and birefringence, 0.1 to 10% by mass is preferable based on the total amount of the thermoplastic resin. More preferably, it is 0.1-8 mass%, More preferably, it is 0.1-6 mass%. When it is within this range, the obtained thermoplastic resin can obtain an effect of improving optical properties such as birefringence without a large decrease in heat resistance.

  The resin may contain only one kind of the first structural unit, or may contain two or more kinds of the first structural unit.

For example, the thermoplastic resin may have a structural unit in which R ¹ is an alkyl group and a structural unit in which R ¹ is an arylalkyl group or an aryl group. At this time, the content of the latter structural unit is preferably 0.1 to 10% by mass, more preferably 0.1 to 8% by mass based on the total amount of the thermoplastic resin, and 0.1 to 6%. More preferably, it is mass%. According to the thermoplastic resin in this range, an effect of improving optical characteristics such as birefringence can be obtained without a large decrease in heat resistance.

  The first structural unit is formed from, for example, a first monomer selected from methacrylic acid monomers and methacrylic acid esters. The first monomer can be represented by the following formula (1-a).

式中、Ｒ^１は式（１）におけるＲ^１と同義である。

Wherein, ^{R 1} has the same meaning as ^{R 1} in Formula (1).

  Examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate; methacrylic acid. Cyclopentyl, cyclohexyl methacrylate, cyclooctyl methacrylate, tricyclodecyl methacrylate, fine cyclooctyl methacrylate, tricyclododecyl methacrylate, isobornyl methacrylate, phenyl methacrylate, benzyl methacrylate, 1-phenylethyl methacrylate, methacrylic acid Examples include 2-phenoxyethyl, 3-phenylpropyl methacrylate, 2,4,6-tribromophenyl methacrylate, and the like. These first monomers may be used alone or in combination of two or more. Of the methacrylic acid esters, methyl methacrylate is preferred because the thermoplastic resin obtained has excellent transparency and weather resistance. 2,4,6-Tribromophenyl methacrylate is preferred in terms of imparting flame retardancy.

(Second structural unit)
The second structural unit is a structural unit represented by the following formula (2).

式中、Ｒ^２は、炭素数７〜１４のアリールアルキル基、炭素数６〜１４のアリール基、又は、下記Ｂ群より選ばれる少なくとも一種の置換基を有する炭素数６〜１４のアリール基、を示し、Ｒ^３及びＲ^４はそれぞれ独立に、水素原子、炭素数１〜１２のアルキル基又は炭素数６〜１４のアリール基を示す。Ｂ群は、ハロゲン原子、ヒドロキシル基、ニトロ基、炭素数１〜１２のアルコキシ基、炭素数１〜１２のアルキル基及び炭素数７〜１４のアリールアルキル基からなる群である。

In the formula, R ² is an arylalkyl group having 7 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or an aryl group having 6 to 14 carbon atoms having at least one substituent selected from the following group B; R ³ and R ⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms. Group B is a group consisting of a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, an alkyl group having 1 to 12 carbon atoms, and an arylalkyl group having 7 to 14 carbon atoms.

Examples of the arylalkyl group having 7 to 14 carbon atoms in R ² include benzyl group, 1-phenylethyl group, 2-phenylethyl group, 3-phenylpropyl group, 6-phenylhexyl group, and 8-phenyloctyl group. Of these, a benzyl group is preferred in that optical properties such as heat resistance and low birefringence are further improved.

Examples of the aryl group having 6 to 14 carbon atoms in R ² include a phenyl group, a naphthyl group, and an anthracenyl group, and among these, optical characteristics such as heat resistance and low birefringence are further improved. In the formula, a phenyl group is preferred.

R ² may be an aryl group having 6 to 14 carbon atoms having a substituent, wherein the substituent is a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, or 1 carbon atom. A group selected from the group consisting of ˜12 alkyl groups and arylalkyl groups having 7 to 14 carbon atoms (Group B).

  Examples of the halogen atom as a substituent include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

  As a C1-C12 alkoxy group as a substituent, a C1-C10 alkoxy group is preferable and a C1-C8 alkoxy group is more preferable. Moreover, as a C1-C12 alkoxy group as a substituent, a methoxy group, an ethoxy group, n-propyloxy group, isopropyloxy group, n-butyloxy group, isobutyloxy group, t-butyloxy group, 2-ethylhexyl An oxy group, 1-decyloxy group, 1-dodecyloxy group, etc. are mentioned.

Examples of the alkyl group having 1 to 12 carbon atoms and the arylalkyl group having 7 to 14 carbon atoms as the substituent are exemplified as the alkyl group having 1 to 12 carbon atoms and the arylalkyl group having 7 to 14 carbon atoms in R ¹ . Groups are exemplified as well.

In R ² , the aryl group having 6 to 14 carbon atoms having a substituent is preferably a phenyl group having a substituent or a naphthyl group having a substituent. Examples of the aryl group having 6 to 14 carbon atoms having a substituent include 2,4,6-tribromophenyl group, 2-chlorophenyl group, 4-chlorophenyl group, 2-bromophenyl group, 4-bromophenyl group, 2-methylphenyl group, 4-methylphenyl group, 2-ethylphenyl group, 4-ethylphenyl group, 2-methoxyphenyl group, 4-methoxyphenyl group, 2-nitrophenyl group, 4-nitrophenyl group, 2, Examples include 4,6-trimethylphenyl group. Among these, 2,4,6-tribromophenyl group is preferable in that flame retardancy is imparted.

Examples of the alkyl group having 1 to 12 carbon atoms in R ³ and ^{R 4,} preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms. Moreover, as a C1-C12 alkyl group in R < ³ > and R < ⁴ >, a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group , Nonyl group, decanyl group, lauryl group, etc. Among these, in terms of further improving the transparency and weather resistance of the thermoplastic resin, methyl group, ethyl group, n-propyl group, isopropyl group, n- A butyl group, an isobutyl group, a t-butyl group, and a 2-ethylhexyl group are preferable, and a methyl group is more preferable.

Examples of the aryl group having 6 to 14 carbon atoms in R ³ and R ⁴ include a phenyl group, a naphthyl group, and an anthracenyl group, and among these, optical characteristics such as heat resistance and low birefringence are further improved. In this respect, a phenyl group is preferred.

R ³ and R ⁴ are preferably a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and more preferably a hydrogen atom.

  The content of the second structural unit is from 0.1 to 15% by mass, preferably from 0.1 to 13% by mass, more preferably from the viewpoint of heat resistance and optical properties, based on the total amount of the thermoplastic resin. Is 0.1 to 10% by mass, more preferably 1 to 10% by mass.

  The thermoplastic resin may contain only one kind of the second structural unit, or may contain two or more kinds of the second structural unit.

  The second structural unit is formed from, for example, a second monomer selected from N-substituted maleimide compounds represented by the following formula (2-a).

^Wherein, R 2, ^{R 3} and ^{R 4} have the same meaning as ^R 2, ^{R 3} and ^{R 4} in each formula (2).

  As the second monomer, N-phenylmaleimide, N-benzylmaleimide, N- (2-chlorophenyl) maleimide, N- (4-chlorophenyl) maleimide, N- (4-bromophenyl) maleimide, N- ( 2-methylphenyl) maleimide, N- (2-ethylphenyl) maleimide, N- (2-methoxyphenyl) maleimide, N- (2-nitrophenyl) maleimide, N- (2,4,6-trimethylphenyl) maleimide N- (4-benzylphenyl) maleimide, N- (2,4,6-tribromophenyl) maleimide, N-naphthylmaleimide, N-anthracenylmaleimide, 3-methyl-1-phenyl-1H-pyrrole 2,5-dione, 3,4-dimethyl-1-phenyl-1H-pyrrole-2,5-dione, 1,3-diph Sulfonyl -1H- pyrrole-2,5-dione, 1,3,4-triphenyl -1H- pyrrole-2,5-dione, and the like. These second monomers may be used alone or in combination of two or more. Of these second monomers, N-phenylmaleimide and N-benzylmaleimide are preferable because they are excellent in heat resistance of the thermoplastic resin and excellent in optical properties such as birefringence. Furthermore, N- (2,4,6-tribromophenyl) maleimide is preferable because flame retardancy can be imparted.

(Third structural unit)
The third structural unit is a structural unit represented by the following formula (3).

式中、Ｒ^５は、水素原子、炭素数３〜１２のシクロアルキル基、炭素数１〜１２のアルキル基、又は、下記Ｃ群より選ばれる少なくとも一種の置換基を有する炭素数１〜１２のアルキル基、を示し、Ｒ^６及びＲ^７はそれぞれ独立に、水素原子、炭素数１〜１２のアルキル基又は炭素数６〜１４のアリール基を示す。Ｃ群は、ハロゲン原子、ヒドロキシル基、ニトロ基及び炭素数１〜１２のアルコキシ基からなる群である。

In the formula, R ⁵ is a hydrogen atom, a C 3-12 cycloalkyl group, a C 1-12 alkyl group, or a C 1-12 having at least one substituent selected from the following group C. An alkyl group, and R ⁶ and R ⁷ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms. Group C is a group consisting of a halogen atom, a hydroxyl group, a nitro group, and an alkoxy group having 1 to 12 carbon atoms.

Examples of the cycloalkyl group having 3 to 12 carbon atoms in R ⁵ include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a tricyclodecyl group, a bicyclooctyl group, a tricyclododecyl group, Examples include an isobornyl group, an adamantyl group, a tetracyclododecyl group, and among these, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group are preferable, and the weather resistance of the thermoplastic resin In addition, a cyclohexyl group is more preferable from the viewpoint of further improving optical properties such as transparency and imparting low water absorption to the thermoplastic resin.

The alkyl group having 1 to 12 carbon atoms in ^{R 5,} preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms. The alkyl group having 1 to 12 carbon atoms in ^{R 5,} a methyl group, an ethyl group, n- propyl group, an isopropyl group, n- butyl group, an isobutyl group, t- butyl group, n- pentyl group, n- Examples include hexyl group, n-octyl group, n-dodecyl group, n-octadecyl group, 2-ethylhexyl group, 1-decyl group, 1-dodecyl group, etc. Among them, weather resistance and transparency of thermoplastic resin The methyl group, ethyl group, and isopropyl group are preferable because the optical properties such as the above are further improved.

R ⁵ may be a C 1-12 alkyl group having a substituent, wherein the substituent is a group consisting of a halogen atom, a hydroxyl group, a nitro group and a C 1-12 alkoxy group ( Group C).

  Examples of the halogen atom as a substituent include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

  As a C1-C12 alkoxy group as a substituent, a C1-C10 alkoxy group is preferable and a C1-C8 alkoxy group is more preferable. Moreover, as a C1-C12 alkoxy group as a substituent, a methoxy group, an ethoxy group, n-propyloxy group, isopropyloxy group, n-butyloxy group, isobutyloxy group, t-butyloxy group, 2-ethylhexyl An oxy group, 1-decyloxy group, 1-dodecyloxy group, etc. are mentioned.

In R ⁵ , examples of the alkyl group having 1 to 12 carbon atoms having a substituent include a dichloromethyl group, a trichloromethyl group, a trifluoroethyl group, and a hydroxyethyl group, and among these, a trifluoroethyl group is preferable. It is.

Examples of the alkyl group having 1 to 12 carbon atoms in R ⁶ and ^{R 7,} preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms. The alkyl group having 1 to 12 carbon atoms in ^{R 6} and ^{R 7,} methyl group, ethyl group, n- propyl group, an isopropyl group, n- butyl group, an isobutyl group, t- butyl group, a 2-ethylhexyl group , Nonyl group, decanyl group, lauryl group, etc. Among these, in terms of further improving the transparency and weather resistance of the thermoplastic resin, methyl group, ethyl group, n-propyl group, isopropyl group, n- A butyl group, an isobutyl group, a t-butyl group, and a 2-ethylhexyl group are preferable, and a methyl group is more preferable.

Examples of the aryl group having 6 to 14 carbon atoms in R ⁶ and R ⁷ include a phenyl group, a naphthyl group, and an anthracenyl group, and among these, optical characteristics such as heat resistance and low birefringence are further improved. In this respect, a phenyl group is preferred.

R ⁶ and R ⁷ are preferably a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and more preferably a hydrogen atom.

  The content of the third structural unit is 0.1 to 49.9% by mass on the basis of the total amount of the thermoplastic resin from the viewpoint of optical properties such as light resistance and transparency, preferably 0.1 to 47 mass%, More preferably, it is 2.5-47 mass%.

  The thermoplastic resin may contain only one type of third structural unit, or may contain two or more types of third structural unit.

  The third structural unit is formed of, for example, a third monomer selected from N-substituted maleimide compounds represented by the following formula (3-a).

^Wherein, R 5, ^{R 6} and ^{R 7} have the same meanings as ^R 5, ^{R 6} and ^{R 7} in each formula (3).

  Examples of the third monomer include N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, N-isopropylmaleimide, Nn-butylmaleimide, N-isobutylmaleimide, and Ns-butyl. Maleimide, Nt-butylmaleimide, Nn-pentylmaleimide, Nn-hexylmaleimide, Nn-heptylmaleimide, Nn-octylmaleimide, N-laurylmaleimide, N-stearylmaleimide, N-cyclo Propylmaleimide, N-cyclobutylmaleimide, N-cyclopentylmaleimide, N-cyclohexylmaleimide, N-cycloheptylmaleimide, N-cyclooctylmaleimide, 1-cyclohexyl-3-methyl-1-phenyl-1H-pyrrole-2,5 -Dione, 1-cyclohex 3,4-dimethyl-1-phenyl-1H-pyrrole-2,5-dione, 1-cyclohexyl-3-phenyl-1H-pyrrole-2,5-dione, 1-cyclohexyl-3,4-diphenyl- 1H-pyrrole-2,5-dione and the like can be mentioned. These third monomers may be used alone or in combination of two or more. N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, and N-cyclohexylmaleimide are preferred because the resulting thermoplastic resin is excellent in light resistance and optical properties such as low birefringence. N-cyclohexylmaleimide is particularly preferred because it can provide low water absorption.

  In the thermoplastic resin, the total content of the second structural unit and the third structural unit is preferably 10 to 50% by mass based on the total amount of the thermoplastic resin. More preferably, it is 10-45 mass%, More preferably, it is 10-40 mass%. When it is within this range, the obtained thermoplastic resin has sufficient heat resistance and light resistance, and further has a favorable improvement effect for controlling optical properties. In addition, when the content of the second structural unit and the content of the third structural unit exceeds 50% by mass, the reactivity of the monomer component is reduced during the polymerization reaction, and the monomer that remains unreacted The amount increases, and the physical properties of the thermoplastic resin may deteriorate.

  In the thermoplastic resin, the total content of the first structural unit, the second structural unit, and the third structural unit may be 80% by mass or more based on the total amount of the thermoplastic resin. As a result, the thermoplastic resin exhibits better optical properties.

  As described above, the thermoplastic resin according to the present invention contains the second structural unit and the third structural unit as essential components. As its effect, a thermoplastic resin having excellent heat resistance and light resistance and excellent transparency may be obtained, but the essential effect is a significant value of optical properties (birefringence and photoelastic coefficient) described later. It is possible to highly control (positive / negative / zero). That is, a thermoplastic resin containing only one of the second structural unit and the third structural unit can provide not only those having insufficient heat resistance and light resistance, but also has insufficient control of optical properties. Depart from the scope of the present invention.

(Fourth structural unit)
The thermoplastic resin may further contain a structural unit other than the above. For example, the thermoplastic resin further has a structural unit derived from another monomer that can be copolymerized with the first, second, and third monomers as long as the object of the invention is not impaired. May be. Hereinafter, a structural unit other than the first, second, and third structural units in the thermoplastic resin is referred to as a fourth structural unit.

  Other monomers that can be copolymerized include aromatic vinyl; unsaturated nitrile; cyclohexyl group, benzyl group, or acrylic acid ester having an alkyl group having 1 to 18 carbon atoms; olefin; diene; vinyl ether; vinyl ester; Examples thereof include vinyl chloride; allyl ester or methallyl ester of saturated fatty acid monocarboxylic acid such as allyl propionate; polyvalent (meth) acrylate; polyvalent arylate; glycidyl compound; unsaturated carboxylic acid. The other monomer may be one or a combination of two or more selected from these groups.

  Examples of the aromatic vinyl include styrene, α-methylstyrene, divinylbenzene, and the like. Examples of the unsaturated nitrile include acrylonitrile, methacrylonitrile, ethacrylonitrile, phenylacrylonitrile and the like. Examples of the acrylic ester include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, tert-butyl acrylate, amyl acrylate, isoamyl acrylate, and acrylic acid. Examples include octyl, 2-ethylhexyl acrylate, decyl acrylate, lauryl acrylate, cyclohexyl acrylate, and benzyl acrylate.

  Examples of the olefin include ethylene, propylene, isobutylene, diisobutylene and the like. Examples of the diene include butadiene and isoprene. Examples of the vinyl ether include methyl vinyl ether and butyl vinyl ether. Examples of the vinyl ester include vinyl acetate and vinyl propionate. Examples of the vinyl fluoride include vinylidene fluoride.

  Examples of the polyvalent (meth) acrylate include ethylene glycol (meth) acrylate, diethylene glycol (meth) acrylate, trimethylolpropane tri (meth) acrylate, hexanediol di (meth) acrylate, pentaerythritol tetra (meth) acrylate, and dipenta Erythritol hexa (meth) acrylate, di (meth) acrylate of bisphenol A ethylene oxide or propylene oxide adduct, di (meth) acrylate of halogenated bisphenol A ethylene oxide or propylene oxide adduct, isocyanurate ethylene oxide or propylene Examples thereof include di- or tri (meth) acrylates of oxide adducts.

  Examples of the polyvalent arylate monomer include diallyl phthalate and triallyl isocyanurate. Examples of the glycidyl compound monomer include glycidyl (meth) acrylate and allyl glycidyl ether. Examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and half-esterified products or anhydrides thereof.

  When the thermoplastic resin contains the structural unit represented by the formula (4), the content ratio is preferably 0.1 to 20% by mass, more preferably 0.1 to 15%, based on the total amount of the thermoplastic resin. % By mass, more preferably 0.1 to 10% by mass. From the viewpoint of light resistance, the content of the structural unit represented by the formula (4) is preferably less than 10% by mass, and more preferably less than 7% by mass.

  The content of the fourth structural unit in the thermoplastic resin is preferably 0 to 15% by mass, more preferably 0 to 13% by mass, and more preferably 0 to 10% by mass based on the total amount of the thermoplastic resin. % Is more preferable. When the content is more than 15% by mass, the heat resistance of the resulting thermoplastic resin is lowered, the light resistance is insufficient, the photoelastic coefficient is increased, and the preferred range of the present invention is deviated.

  The thermoplastic resin may have only one kind of the fourth structural unit, or may have two or more kinds.

    An example of the fourth structural unit is a structural unit represented by the following formula (4).

In the formula, R ⁸ and R ⁹ may be the same or different, and each represents a hydrogen atom, a halogen atom, a hydroxyl group, a nitro group, a linear or branched alkoxy group having 1 to 12 carbon atoms, and It is one selected from the group consisting of chain-like or branched alkyl groups having 1 to 12 carbon atoms. a represents an integer of 1 to 3.

Examples of the alkyl group having 1 to 12 carbon atoms in R ^8, preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms. Examples of the alkyl group having 1 to 12 carbon atoms in R ⁹ include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, 1- A decyl group, 1-dodecyl group, etc. are mentioned, Among these, a methyl group is suitable.

Examples of the halogen atom for R ⁹ include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

The alkyl group having 1 to 12 carbon atoms in ^{R 9,} preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms. Examples of the alkyl group having 1 to 12 carbon atoms in R ⁹ include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, 1- Decyl group, 1-dodecyl group, etc. Among these, in terms of further improving the transparency and weather resistance of the thermoplastic resin, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group , Isobutyl group, t-butyl group and 2-ethylhexyl group are preferable, and methyl group is more preferable.

Further, the alkoxy group having 1 to 12 carbon atoms in ^{R 9,} preferably an alkoxy group having 1 to 10 carbon atoms, more preferably an alkoxy group having 1 to 8 carbon atoms. Moreover, as a C1-C12 alkoxy group as a substituent, a methoxy group, an ethoxy group, n-propyloxy group, isopropyloxy group, n-butyloxy group, isobutyloxy group, t-butyloxy group, 2-ethylhexyl Examples thereof include an oxy group, a 1-decyloxy group, and a 1-dodecyloxy group, and among these, a methoxy group is preferable.

  The structural unit represented by the formula (4) can be formed from, for example, a monomer represented by the following formula (4-a).

式中、Ｒ^８、Ｒ^９及びａはそれぞれ式（４）におけるＲ^８、Ｒ^９及びａと同義である。

^Wherein, R 8, ^{R 9} and a have the same meanings as ^R 8, ^{R 9} and a in each formula (4).

  Examples of the fourth monomer include styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, and 2-methyl-4-chlorostyrene. 2,4,6-trimethylstyrene, α-methylstyrene, cis-β-methylstyrene, trans-β-methylstyrene, 4-methyl-α-methylstyrene, 4-fluoro-α-methylstyrene, 4-chloro -Α-methylstyrene, 4-bromo-α-methylstyrene, 4-t-butylstyrene, 2-fluorostyrene, 3-fluorostyrene, 4-fluorostyrene, 2,4-difluorostyrene, 2-chlorostyrene, 3 -Chlorostyrene, 4-chlorostyrene, 2,4-dichlorostyrene, 2,6-dichlorostyrene, 2-bromostyrene , 3-bromostyrene, 4-bromostyrene, 2,4-dibromostyrene, α-bromostyrene, β-bromostyrene, 2-hydroxystyrene, 4-hydroxystyrene, and the like. Even when used alone, two or more may be used in combination. Of these monomers, styrene and α-methylstyrene are preferable because copolymerization with the first monomer, the second monomer, and the third monomer is easy. When the fourth structural unit is contained, the hygroscopicity of the thermoplastic resin is further improved.

  When the thermoplastic resin contains styrene as the fourth structural unit, the content ratio of the first structural unit is preferably 68 to 90% by mass. More preferably, it is 70-90 mass%, More preferably, it is 75-90 mass%. When it exists in this range, the preferable improvement effect with which the absolute value of a photoelastic coefficient becomes small tends to be acquired.

In the thermoplastic resin, the content of the second total amount of content C ₄ of the fourth structural unit represented by the content C ₂ and wherein the structural units _{(4) (C 2 + C} 4) and the third structural unit The molar ratio (C ₂ + C ₄ ) / C ₃ of the amount C ₃ is preferably 2.8 or more and 15 or less, and more preferably 2.8 or more and 10 or less. When the molar ratio (C ₂ + C ₄ ) / C ₃ is in this range, the thermoplastic resin exhibits better optical properties.

  The total of the monomers remaining in the thermoplastic resin (constituting the structural unit of the copolymer) is preferably 0.5% by mass or less, more preferably 0.4% by mass with respect to 100% by mass of the copolymer. % Or less, more preferably 0.3% by mass or less. When the total amount of residual monomers exceeds 0.5% by mass, there is a problem that a molded product that is not suitable for practical use can be obtained, such as being colored when heated during molding processing or the heat resistance and light resistance of the molded product are reduced. is there.

  The halogen atom content in the thermoplastic resin is preferably less than 0.47% by mass, more preferably 0.45% by mass or less, based on the total amount of the thermoplastic resin. When the thermoplastic resin contains less than 0.47% by mass of halogen atoms, even when the thermoplastic resin is handled at a high temperature during melt molding or the like, it is difficult for halogen-based gas to be generated, and corrosion of equipment caused by the halogen-based gas. And the work environment is prevented from deteriorating. In addition, when discarding the thermoplastic resin (or its molded body, etc.), there is an advantage that it is difficult to generate a halogen-based gas having a relatively large environmental load.

  It is preferable that the weight average molecular weight (Mw) of the conversion of a polymethylmethacrylate by the GPC measuring method of a thermoplastic resin is 3000-1 million. If the Mw of the thermoplastic resin is 3000 or more, the required strength as a polymer can be expressed, and if it is 1000000 or less, a molded body can be formed by press molding. The Mw of the thermoplastic resin is more preferably 50,000 to 800,000, still more preferably 50,000 to 500,000, particularly preferably 100,000 to 500,000.

  Moreover, it is preferable that the molecular weight distribution (Mw / Mn) by the GPC measuring method of a thermoplastic resin is 1-10. The thermoplastic resin composition can be polymerized by a living radical polymerization method, and the molecular weight distribution can be adjusted as necessary. From the viewpoint of adjusting to a resin viscosity suitable for molding, the molecular weight distribution of the thermoplastic resin is more preferably 1.1 to 7.0, still more preferably 1.2 to 5.0, and particularly preferably 1.5 to 4.0.

  The glass transition temperature (Tg) of the thermoplastic resin is preferably 120 ° C. or higher. When Tg is 120 ° C. or higher, the film has necessary and sufficient heat resistance as a recent liquid crystal display film molded body. The Tg of the thermoplastic resin is preferably 130 ° C. or higher, more preferably 135 ° C. or higher. On the other hand, the upper limit of Tg is preferably 180 ° C.

(Optical characteristics of thermoplastic resin)
(I) Absolute value of the photoelastic coefficient C The absolute value of the photoelastic coefficient C of the thermoplastic resin is 2.5 × 10 ⁻¹² Pa ⁻¹ or less and 2.0 × 10 ⁻¹² Pa ⁻¹ or less. It is preferably 1.5 × 10 ⁻¹² Pa ⁻¹ or less, more preferably 1.0 × 10 ⁻¹² Pa ⁻¹ or less.

Here, the photoelastic coefficient is described in various documents (see, for example, Chemical Review, No. 39, 1998 (published by the Academic Publishing Center)), and is defined by the following formulas (ia) and (ib). It is what is done. As the value of photoelastic coefficient C _R is close to zero, it can be seen that change in birefringence due to an external force is small.

C _R = | Δn | / σ _R (i-1)
| Δn | = nx−ny (i−2)
Wherein, C _R photoelastic coefficient, sigma _R is tensile stress, | [Delta] n | is the absolute value of the birefringence, nx is the refractive index of stretching direction, ny is the refractive index of stretching direction perpendicular to the direction in the plane, the Each is shown.

  The photoelastic coefficient C of the thermoplastic resin is sufficiently small as compared with existing resins (for example, PMMA, PC, triacetyl cellulose resin, cyclic olefin resin, etc.). Therefore, since it does not cause birefringence due to external force (photoelasticity), it is difficult to undergo birefringence change. In addition, since birefringence caused by residual stress at the time of molding (photoelasticity) hardly occurs, the birefringence distribution in the molded body is also small.

(Ii) Total light transmittance The thermoplastic resin preferably has a total light transmittance of 85% or more when formed into a film, more preferably 88% or more, and even more preferably 90% or more. . Here, the total light transmittance is a value obtained by converting to a thickness of 100 μm. When the total light transmittance is less than 85%, the transparency is lowered, and it may not be used for applications requiring high transparency.

[Method for producing thermoplastic resin]
The resin can be obtained, for example, by the following polymerization step. Moreover, it can refine | purify by the following devolatilization process.
(Polymerization process)
The thermoplastic resin of this embodiment can be obtained by polymerizing a monomer group including a first monomer, a second monomer, and a third monomer.

  In the polymerization reaction of the thermoplastic resin according to the present embodiment, combining the monomers that are close to each other and / or the monomer having a high copolymerization property, the resin composition ratio of the obtained thermoplastic resin, This is desirable because it can be easily controlled based on the raw material composition ratio charged into the reaction solution. On the other hand, when monomers having significantly different reactivity are combined, a) a monomer having low reactivity does not sufficiently react and remains as an unreacted monomer, b) a resin composition of the resulting thermoplastic resin Problems such as difficulty in predicting the ratio can occur. In particular, if unreacted monomers remain, there are problems such as deterioration of the properties of the thermoplastic resin, such as transparency and light resistance.

  As a polymerization method of the thermoplastic resin according to the present invention, for example, generally used polymerization methods such as cast polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, living radical polymerization, and anionic polymerization can be used. . In order to use a thermoplastic resin as an optical material, it is preferable to avoid the introduction of minute foreign substances as much as possible. From this viewpoint, it is desirable to use cast polymerization or solution polymerization without using a suspending agent or an emulsifier.

  Moreover, as a polymerization form, any of a batch polymerization method and a continuous polymerization method can be used, for example. The batch polymerization method is desirable from the viewpoint of simple polymerization operation, and the continuous polymerization method is desirably used from the viewpoint of obtaining a polymer having a more uniform composition.

  The temperature and polymerization time at the time of the polymerization reaction can be appropriately adjusted according to the type and ratio of the monomer used, for example, the polymerization temperature is 0 to 150 ° C., the polymerization time is 0.5 to 24 hours, Preferably, the polymerization temperature is 80 to 150 ° C. and the polymerization time is 1 to 12 hours.

  In the radical polymerization reaction, a polymerization initiator may be added as necessary. As the polymerization initiator, any initiator generally used in radical polymerization can be used. For example, cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide Organic peroxides such as oxide, t-butylperoxyisopropyl carbonate, t-amylperoxy-2-ethylhexanoate; 2,2′-azobis (isobutyronitrile), 1,1′-azobis (cyclohexane Carbonitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), azo compounds such as dimethyl-2,2′-azobisisobutyrate, and the like. These polymerization initiators may be used alone or in combination of two or more.

  The amount of the polymerization initiator used may be appropriately set according to the combination of the monomers and reaction conditions, and is not particularly limited, but is preferably used in the range of 0.005 to 5% by mass.

  As the molecular weight regulator used as necessary in the polymerization reaction, any one used in general radical polymerization is used. It is mentioned as preferable. These molecular weight regulators are added in a concentration range such that the degree of polymerization is controlled within the aforementioned range.

  When a solvent is used during the polymerization reaction, examples of the polymerization solvent include aromatic hydrocarbon solvents such as toluene, xylene, and ethylbenzene; ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone; ether solvents such as tetrahydrofuran; Can be mentioned. These solvents may be used alone or in combination of two or more. When the boiling point of the solvent to be used is too high, the residual volatile content of the finally obtained thermoplastic resin increases. Therefore, a solvent having a boiling point of 50 to 200 ° C. is preferable.

  Moreover, you may add an organophosphorus compound and an organic acid as needed at the time of a polymerization reaction. When these compounds coexist, the side reaction may be suppressed and / or coloring during molding of a thermoplastic resin obtained by reducing the amount of unreacted N-substituted maleimide may be reduced. is there.

  Examples of the organic phosphorus compound include alkyl (aryl) phosphonous acid and diesters or monoesters thereof; dialkyl (aryl) phosphinic acid and esters thereof; alkyl (aryl) phosphonic acids and diesters or monoesters thereof; alkyl Phosphinic acid and esters thereof; phosphorous acid diester, phosphorous acid monoester, phosphorous acid triester; phosphoric acid diester, phosphoric acid monoester, phosphoric acid triester and the like. These organophosphorus compounds may be used alone or in combination of two or more. The amount of the organophosphorus compound used is preferably 0.001 to 5.0 mass% with respect to the total amount of monomers.

  On the other hand, as the organic acid, for example, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, stearic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, cyclohexanecarboxylic acid, Examples thereof include phthalic acid, isophthalic acid, terephthalic acid and the like, and acid anhydrides thereof. These organic acids may be used alone or in combination of two or more. The amount of the organic acid used is preferably 0.001 to 1.0% by mass with respect to the total amount of monomers.

  When carrying out the polymerization reaction, the polymer concentration is preferably 10 to 95% by mass, and 75% by mass or less in order to make the viscosity of the reaction solution appropriate from the viewpoint of heat removal during the polymerization. More preferred is 60% by mass or less. If it is 10 mass% or more, adjustment of molecular weight and molecular weight distribution is easy. If it is 95 mass% or less, a high molecular weight polymer can be obtained.

  On the other hand, a polymerization solvent can be appropriately added from the viewpoint of appropriately maintaining the viscosity of the obtained polymerization reaction solution. By appropriately maintaining the viscosity of the reaction solution, heat removal can be controlled and generation of microgel in the reaction solution can be suppressed. In particular, in the latter half of the polymerization reaction in which the viscosity rises, it is more preferable to control the addition of a polymerization solvent so that it becomes 50% by mass or less.

  The form in which the polymerization solvent is appropriately added to the polymerization reaction solution is not particularly limited, and for example, the polymerization solvent may be added continuously or the polymerization solvent may be added intermittently. By controlling the concentration of the thermoplastic resin produced in the polymerization reaction solution in this way, the temperature uniformity inside the reactor can be improved and the gelation of the reaction solution can be more sufficiently suppressed. The polymerization solvent to be added may be, for example, the same type of solvent used during the initial charging of the polymerization reaction or a different type of solvent, but the solvent used during the initial charging of the polymerization reaction. It is preferable to use the same type of solvent. Moreover, the polymerization solvent to be added may be only one kind of single solvent or two or more kinds of mixed solvents.

  When the thermoplastic resin is polymerized by the suspension polymerization method, it is carried out in an aqueous medium, and a suspending agent and, if necessary, a suspending aid are added. Examples of the suspending agent include water-soluble polymers such as polyvinyl alcohol, methylcellulose, and polyacrylamide, and inorganic substances such as calcium phosphate and magnesium pyrophosphate. The water-soluble polymer is preferably used in an amount of 0.03 to 1% by mass based on the total amount of monomers, and the inorganic substance is used in an amount of 0.05 to 0.5% by mass based on the total amount of monomers. Is preferred. As the suspension aid, there are anionic surfactants such as sodium dodecylbenzenesulfonate. When an inorganic substance is used as the suspension agent, it is preferable to use a suspension aid. The suspension aid is preferably used in an amount of 0.001 to 0.02% by mass with respect to 100% by mass of the monomer.

(Devolatilization process)
The devolatilization step means a step of removing a volatile component such as a polymerization solvent, a residual monomer, and moisture under reduced pressure heating conditions as necessary. If this removal treatment is insufficient, residual volatile components in the obtained thermoplastic resin increase, and coloring due to alteration during molding, or molding defects such as bubbles or silver streaks may occur. The residual volatile content is preferably 0.5% by mass or less, more preferably 0.4% by mass or less, and still more preferably 0.3% by mass or less with respect to 100% by mass of the thermoplastic resin. The amount of residual volatile matter corresponds to the total amount of residual monomer, polymerization solvent, and side reaction product that did not react during the polymerization reaction described above.

  As an apparatus used for a devolatilization process, the devolatilizer which consists of a heat exchanger and a devolatilization tank; Extruder with a vent; What arranged the devolatilizer and the extruder in series etc. are mentioned, for example. When using an extruder with a vent, one or a plurality of vents may be used, but it is preferable to have a plurality of vents.

  The temperature in the devolatilization step is preferably 150 to 350 ° C, more preferably 170 to 330 ° C, and still more preferably 200 to 300 ° C. If this temperature is less than 150 ° C., the residual volatile matter may increase. On the other hand, when the temperature exceeds 350 ° C., the obtained thermoplastic resin may be colored or decomposed.

  The pressure in the devolatilization step is preferably 931 to 1.33 hPa (700 to 1 mmHg), more preferably 800 to 13.3 hPa (600 to 10 mmHg), and still more preferably 667 to 20.0 hPa (500 to 15 mmHg). When this pressure exceeds 931 hPa (700 mmHg), volatile matter may remain easily. Conversely, if the pressure is less than 1.33 hPa (1 mmHg), industrial implementation may be difficult.

  The treatment time is appropriately selected depending on the amount of residual volatile matter, but a shorter time is more preferable in order to suppress coloring and decomposition of the obtained thermoplastic resin.

  When the monomer reaction conversion rate during the polymerization reaction is low, a large amount of unreacted monomer remains in the polymerization solution. In that case, in order to reduce the residual volatile content of the thermoplastic resin obtained, the treatment is performed at a high treatment temperature for a long time, but there is a problem that coloring and decomposition are likely to occur. When processing a polymerization reaction solution containing a large amount of unreacted monomer, the monomer in question is, for example, an aromatic hydrocarbon solvent, a hydrocarbon solvent, or an alcohol solvent in the polymerization solution. After the addition, homogenizer (emulsification dispersion) treatment is performed, and the unreacted monomer can be separated from the polymerization reaction solution by pretreatment such as liquid-liquid extraction or solid-liquid extraction. When the polymerization reaction liquid after monomer separation by pretreatment is subjected to the devolatilization step described above, the total amount of monomers remaining in 100% by mass of the obtained thermoplastic resin can be suppressed to 0.5% by mass or less. it can.

  The smaller the number of foreign substances contained in the thermoplastic resin, the better when used for optics. As a method for reducing the number of foreign matters, in the polymerization reaction step, the devolatilization step, and the molding step, the thermoplastic resin solution or melt is used, for example, with a leaf disk polymer filter having a filtration accuracy of 1.5 to 15 μm. The method of filtering etc. are mentioned.

[Thermoplastic resin composition]
The thermoplastic resin composition contains the thermoplastic resin and is excellent in transparency, heat resistance, and low birefringence. Moreover, the molded object formed by shape | molding a thermoplastic resin composition has favorable mechanical characteristics, and is excellent in handleability.

  The thermoplastic resin composition may contain various additives as long as the effects of the present invention are not significantly impaired. The type of additive is not particularly limited as long as it is generally used for blending resins and rubber-like polymers.

  Examples of additives include inorganic fillers; pigments such as iron oxides; lubricants and mold release agents such as stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, and ethylene bisstearamide; paraffinic processes Softeners and plasticizers such as oils, naphthenic process oils, aromatic process oils, paraffins, organic polysiloxanes and mineral oils; hindered phenolic antioxidants, antioxidants such as phosphorus thermal stabilizers, hindered amines Examples thereof include light stabilizers, benzotriazole-based ultraviolet absorbers, flame retardants, antistatic agents; reinforcing agents such as organic fibers, glass fibers, carbon fibers, and metal whiskers; colorants; other additives; The content of the additive is preferably 0 to 5% by mass, more preferably 0 to 2% by mass, and still more preferably 0 to 1% by mass.

  The thermoplastic resin composition is within a range that does not impair the object of the present invention. For example, polyolefin resin such as polyethylene and polypropylene; polystyrene, styrene / acrylonitrile copolymer, styrene / maleic anhydride copolymer, styrene / methacrylic acid. Styrenic resins such as copolymers; Polymethacrylate resins; Polyamides; Polyphenylene sulfide resins; Polyether ether ketone resins; Polyester ether resins; Polysulfones; Polyphenylene oxides; Polyimides; Polyether imides; Polyacetals; Norbornene-based resin; thermoplastic resin such as cellulose resin such as triacetyl cellulose; and phenol resin; melamine resin; silicone resin; thermosetting resin such as epoxy resin; It can be contained.

[Phase difference plate]
The thermoplastic resin according to the present invention is formed into, for example, an extrusion-molded body such as a sheet, film, strand or pipe, an injection-molded body such as a disk, cube or plate, and a press-molded body. Can do. The retardation plate according to the present embodiment is a molded body formed by molding a thermoplastic resin into, for example, a sheet or film shape. As the processing method, extrusion molding, solution cast molding, or the like can be used.

  Specifically, in extrusion molding, a sheet or film can be formed from molten resin using an extruder or the like equipped with a T die, a circular die, or the like. At this time, it is possible to obtain a molded body obtained by melt-kneading various additives and thermoplastic resins other than the acrylic thermoplastic resin together with the acrylic thermoplastic resin. In solution cast molding, for example, a resin can be dissolved in a solvent such as chloroform or methylene dichloride to form a polymer solution, and then cast, dried and solidified to form a sheet or film.

  The stretching of the sheet or film can be carried out continuously by extrusion molding and cast molding. For example, an unstretched film or sheet is longitudinally uniaxially stretched in the mechanical flow direction, transversely uniaxially stretched in a direction perpendicular to the mechanical flow direction, or a sequential biaxial stretching method of roll stretching and tenter stretching, A biaxially stretched film can be obtained by stretching by an axial stretching method, a biaxial stretching method by tubular stretching, or the like.

  The strength of the molded body can be improved by stretching. The draw ratio is preferably 0.1 to 300% in at least one direction, more preferably 0.2 to 290%, and still more preferably 0.3 to 280%. By stretching in this range, a molded article having excellent optical properties such as strength, transparency and birefringence can be obtained.

  Heat treatment (annealing) or the like can be performed on the stretched molded body for the purpose of stabilizing the mechanical properties and optical properties. The conditions for the heat treatment may be appropriately selected similarly to the conditions for the heat treatment performed on a conventionally known sheet or film, and are not particularly limited.

  Furthermore, when a film-like or sheet-like molded product is used as a retardation plate, as a required birefringence, an in-plane direction retardation (Re) is required depending on a requirement of a liquid crystal mode to be applied, and an absolute value thereof is It is preferably designed in the range of 30 to 300 nm. (Here, the phase difference is a value obtained by converting a value measured as a film into a thickness of 100 μm.) For example, when a quarter wavelength plate is assumed, a necessary phase difference ( The absolute value of Re) is preferably 100 to 180 nm, more preferably 120 to 160 nm, and still more preferably 130 to 150 nm. When a half-wave plate is assumed, the absolute value of the necessary phase difference (Re) is preferably 240 to 320 nm, more preferably 260 to 300 nm, and still more preferably 270 to 290 nm.

  The retardation plate according to the present invention has a retardation (Re) as birefringence of (i) composition control of the thermoplastic resin of the present invention, or (ii) polymer chain orientation control by stretching after molding. Furthermore, it is controlled by any method of the combination of (i) and (ii).

  In general, stretching is not limited to birefringence control, but may be performed for the purpose of increasing the mechanical strength of the film. Regardless of whether birefringence is imparted or mechanical strength is imparted, a material whose birefringence changes greatly by a slight stretching has a problem in that it is difficult to control the required phase difference.

  The thickness of the sheet or film formed as described above is preferably 1 to 10,000 μm, more preferably 1 to 5000 μm, and still more preferably 1 to 3000 μm.

  The glass transition temperature (Tg) of the retardation plate of the present embodiment is preferably 120 ° C. or higher, more preferably 130 ° C. or higher, and still more preferably 135 ° C. or higher. When the glass transition temperature is less than 120 ° C., the glass transition temperature may not be used for applications requiring high heat resistance such as poor dimensional stability under the use environment temperature.

  The total light transmittance of the retardation plate of the present embodiment is preferably 85% or more, more preferably 88% or more, and still more preferably 90% or more. When the total light transmittance is less than 85%, the transparency is lowered, and it may not be used for applications requiring high transparency.

  Regarding the light resistance of the retardation plate of the present embodiment, the rate of change (ΔYI) of the yellow index (YI) is preferably less than 1, more preferably less than 0.9, and still more preferably 0.8. Is less than. When ΔYI exceeds 1, it may not be used for applications requiring transparency.

  The phase difference plate of the present invention is characterized by having a low photoelastic coefficient and easily controlling the phase difference by stretching compared to a phase difference plate made of an acrylic thermoplastic resin that has existed conventionally. .

  The retardation plate of this embodiment, for example, a sheet or a film, can be subjected to surface functionalization treatment such as antireflection treatment, transparent conductive treatment, electromagnetic wave shielding treatment, gas barrier treatment, and the like. The retardation plate of the present embodiment is mainly used for applications requiring birefringence, for example, a retardation film (specifically, a viewing angle control film used in various liquid crystal modes such as TN, VA, IPS, OCB, etc.) Liquid crystal optical compensation film), retardation plates such as quarter-wave plates and half-wave plates, and the like.

[Polarizer]
The polarizing plate of this embodiment can be produced by a general method. The retardation film of the present invention is preferably bonded to at least one surface of the polarizing plate. That is, it is preferable that the back side of the retardation film of the present invention is bonded to at least one surface of a polarizing film produced by dipping and stretching in an iodine solution via a primer solution. As the primer solution, an aqueous adhesive such as an aqueous solution of polyvinyl alcohol or an aqueous solution of polyvinyl alcohol or polyurethane resin, or a solvent adhesive such as an epoxy curing agent or an external line curable adhesive is used. As long as the film can be adhered, any known one may be used.

  The retardation film may be used on the other surface, or another polarizing plate protective film may be used. Another polarizing plate protective film is preferably provided with a surface treatment layer such as a hard coat layer, an antiglare hard coat layer, an antireflection layer, an antistatic layer, or an antifouling layer.

  A polarizing film, which is a main component of a polarizing plate, is an element that allows only light of a polarization plane in a certain direction to pass through. A typical polarizing film currently known is a polyvinyl alcohol polarizing film, a polyvinyl alcohol film. There are dyed iodine and dyed dichroic dye. As the polarizing film, a polyvinyl alcohol aqueous solution is formed and dyed by uniaxial stretching, or uniaxially stretched after dyeing, and preferably subjected to a durability treatment with a boron compound. On the surface of the substantially polarizing film, the retardation film of the present invention and one surface of another polarizing plate protective film are bonded together to form a polarizing plate.

[Image display device]
The structure of the image display device of the present embodiment is not particularly limited as long as the retardation plate of the present embodiment is incorporated. The image display device of this embodiment is, for example, a liquid crystal display device, and various liquid crystal display devices with excellent visibility can be manufactured by incorporating the polarizing plate according to the present invention into the display device. For example, a mode in which the polarizing plate of the present embodiment is used at least on either the viewing side or the backlight side is preferable.

  As the liquid crystal mode of the liquid crystal display device, for example, in-plane switching (IPS) mode, fringe field switching (FFS) mode, vertical alignment (VA) mode, twisted nematic (TN) mode, super twisted nematic (STN) mode, Examples include optically compensated bend (OCB) mode.

Hereinafter, the contents of the present invention will be described more specifically with reference to Examples , Reference Examples and Comparative Examples. In addition, this invention is not limited to the following Example.

The measuring method of each measured value used for this invention is as follows.
<a> Analysis of thermoplastic resin (1) Structural unit

^{From 1} H-NMR and ¹³ C-NMR measurements, (i) the first structural unit, (ii) the second structural unit, (iii) the third structural unit, and (iv) the fourth structural unit are identified. The abundance was calculated.
Measuring instrument: DPX-400 manufactured by Blue Car Co., Ltd.
Measurement solvent: CDCl ₃ or d ⁶ -DMSO
Measurement temperature: 40 ° C

(2) Glass transition temperature The glass transition temperature (Tg) is JIS-K-7121 using a differential scanning calorimeter (Diamond DSC, manufactured by PerkinElmer Japan Co., Ltd.) under a nitrogen gas atmosphere and α-alumina as a reference. Based on the DSC curve obtained by heating about 10 mg of the sample from room temperature to 200 ° C. at a rate of temperature increase of 10 ° C./min, it was calculated by the midpoint method.

(3) Molecular weight The weight average molecular weight and the number average molecular weight were determined by gel permeation chromatograph (HLC-8220 manufactured by Tosoh Corporation), the solvent was tetrahydrofuran, at a set temperature of 40 ° C., and converted into a commercial standard PMMA.

(4) Light resistance The light resistance was measured by using a spectrocolor meter after exposure for about 150 hours in an environment of 63 ° C. and 60% humidity using an i-super UV tester (SUV-W151 manufactured by Iwasaki Electric Co., Ltd .; metal halide lamp). The yellow index (YI) was measured by Nippon Denshoku Industries Co., Ltd. SD-5000), and the rate of change (ΔYI) was evaluated.

<B> Optical Characteristic Evaluation (1) Production of Optical Film Sample (1-a) Press Film Molding Using a vacuum compression molding machine (SFV-30 model, manufactured by Kondo Metal Industry Co., Ltd.) under atmospheric pressure, 260 After preheating at 25 ° C. for 25 minutes, the film was compressed under vacuum (about 10 kPa) at 260 ° C. and about 10 MPa for 5 minutes to form a press film.

(1-b) Molding of stretched film A stretched film was molded by uniaxial free stretching at a stretching temperature (Tg + 20) ° C. and a stretching speed (500 mm / min) using an Instron 5t tensile tester. The draw ratio was drawn at 100%, 200%, and 300%.

(2) Measurement of birefringence Measurement was performed by a rotating analyzer method using RETS-100 manufactured by Otsuka Electronics. The value of birefringence is a value of light having a wavelength of 550 nm. Birefringence (Δn) was calculated by the following formula. The obtained value was converted to a film thickness of 100 μm to obtain a measured value.
Δn = nx−ny
(Δn: birefringence, nx: refractive index in the stretching direction, ny: refractive index perpendicular to the stretching direction)
The absolute value (| Δn |) of birefringence (Δn) was determined as follows.
| Δn | = | nx−ny |

(3) Phase difference measurement <In-plane phase difference>
Using a RETS-100 manufactured by Otsuka Electronics Co., Ltd., measurement was performed for a wavelength range of 400 to 800 nm by a rotary analyzer method. The obtained value was converted to a film thickness of 100 μm to obtain a measured value.
The absolute value of birefringence (| Δn |) and the phase difference (Re) have the following relationship.
Re = | Δn | × d
(| Δn |: absolute value of birefringence, Re: phase difference, d: thickness of sample)

The absolute value (| Δn |) of birefringence is a value shown below.
| Δn | = | nx−ny |
(Nx: refractive index in the stretching direction, ny: refractive index perpendicular to the stretching direction in the plane)

<Thickness direction retardation>
Using a phase difference measuring device (KOBRA-21ADH) manufactured by Oji Scientific Instruments, the phase difference at a wavelength of 589 nm was measured, and the obtained value was converted to a film thickness of 100 μm to obtain a measured value.

The absolute value of birefringence (| Δn |) and the phase difference (Rth) have the following relationship.
Rth = | Δn | × d
(| Δn |: absolute value of birefringence, Rth: phase difference, d: thickness of sample)

The absolute value (| Δn |) of birefringence is a value shown below.
| Δn | = | (nx + ny) / 2−nz |
(Nx: refractive index in the stretching direction, ny: refractive index in the plane perpendicular to the stretching direction, nz: refractive index in the thickness direction out of the plane perpendicular to the stretching direction)
(In an ideal film that is completely isotropic in the three-dimensional direction, both in-plane retardation (Re) and thickness direction retardation (Rth) are zero.)

(4) Measurement of photoelastic coefficient A birefringence measuring apparatus described in detail in Polymer Engineering and Science 1999, 39, 2349-2357 was used. A film tensioning device (manufactured by Imoto Seisakusho) was placed in the laser beam path, and the birefringence was measured by the rotating analyzer method using RETS-100 manufactured by Otsuka Electronics Co., Ltd. while applying a tensile stress at 23 ° C. Measurements were made in the 400-800 nm range. The strain rate during stretching was 50% / min (between chucks: 50 mm, chuck moving speed: 5 mm / min), and the test piece width was 6 mm. From the relationship between the absolute value of birefringence (| Δn |) and the extensional stress (σ _R ), the slope of the straight line was obtained by least square approximation, and the photoelastic coefficient (C _R ) was calculated. For the calculation, data with a tensile stress between 2.5 MPa ≦ σ _R ≦ 10 MPa was used.
C _R = | Δn | / σ _R
| Δn | = | nx−ny |
(C _R : photoelastic coefficient, σ _R : stretching stress, | Δn |: absolute value of birefringence, nx: refractive index in the stretching direction, ny: vertical refractive index in the stretching direction)

[Synthesis of thermoplastic resin]
<Methyl methacrylate / N-phenylmaleimide / N-cyclohexylmaleimide polymer>
[Example 1]
Methyl methacrylate (MMA), N-phenylmaleimide (PheMI), and N-cyclohexylmaleimide (CyMI) were weighed in a glass container having a volume of 100 ml at a charging ratio shown in Table 3 so that the total amount was 50 g, and then stirred. While mixing, dissolved. Next, the solution was replaced with nitrogen gas to prepare a raw material solution.

  Next, 0.015 g of dilauroyl peroxide and 0.05 g of n-octyl mercaptan were added to the raw material solution and completely dissolved. Again, the inside of the glass container was brought into a nitrogen atmosphere with nitrogen gas, and then sealed.

  The glass container was reacted in an oil bath set at 68 ° C. for 20 hours, then the oil bath temperature was changed to 120 ° C., and further reacted for 10 hours to complete the polymerization reaction.

  After collecting the polymer mass from the glass container, it was dissolved in 200 g of tetrahydrofuran, and the resulting tetrahydrofuran solution was added dropwise to 1000 ml of methanol as a poor solvent to separate and collect the precipitated polymer. It was dried at 130 ° C. for 2 hours under vacuum to obtain the desired thermoplastic resin.

[ Reference Examples 2 and 3]
Except having changed the raw material preparation ratio of a thermoplastic resin into the composition ratio shown in Table 1, operation similar to Example 1 was performed and the thermoplastic resin was obtained.

Using the thermoplastic resins obtained in Example 1 and Reference Examples 2 and 3, after forming a press film according to the above-mentioned method (1-a), 100% stretched film according to the above-mentioned method (1-b) The optical characteristics as a phase difference plate were evaluated. The results are shown in Table 1.

  In the evaluation of the low photoelastic coefficient, the absolute value of the photoelastic coefficient is 2.5 or less (◯), and the absolute value of the photoelastic coefficient exceeds 2.5 (×). In addition, the evaluation of the phase difference was made such that the absolute value of the phase difference exceeded 30 nm (◯), and the absolute value of the phase difference was 30 nm or less (×). Furthermore, the evaluation of light resistance was set to be inferior to PMMA (O: less than ΔYI <1) and obviously yellow (×: 1 <ΔYI).

The retardation plates produced in Example 1 and Reference Examples 2 and 3 both had high heat resistance and good light resistance, as well as a low photoelastic coefficient and a sufficient phase difference.

[Comparative Example 1]
In a glass container having a volume of 100 m, methyl methacrylate was weighed at a charging ratio shown in Table 3 so that the total amount was 50 g, and then mixed and dissolved while stirring. Next, the solution was replaced with nitrogen gas to prepare a raw material solution.

  Next, 0.015 g of dilauroyl peroxide and 0.05 g of n-octyl mercaptan were added to the raw material solution and completely dissolved. Again, the inside of the glass container was brought into a nitrogen atmosphere with nitrogen gas, and then sealed.

  The glass container was reacted in an oil bath set at 68 ° C. for 20 hours, then the oil bath temperature was changed to 120 ° C., and the reaction was further continued for 10 hours to complete the polymerization reaction.

  After collecting the polymer mass from the glass container, it was dissolved in 200 g of tetrahydrofuran, and the resulting tetrahydrofuran solution was added dropwise to 1000 ml of methanol as a poor solvent to separate and collect the precipitated polymer. It was dried at 130 ° C. for 2 hours under vacuum to obtain a thermoplastic resin.

[Comparative Examples 2 to 10]
A thermoplastic resin was obtained in the same manner as in Comparative Example 1 except that the raw material charge ratio of the thermoplastic resin was changed to the composition ratio shown in Table 2.

  Using the thermoplastic resins obtained in Comparative Examples 1 to 10, press film molding was performed according to the above-described method (1-a), and then a 100% stretched film was prepared according to the above-described method (1-b). The optical properties as a plate were evaluated. The results are shown in Table 2.

  The retardation plate produced in Comparative Example 1 has a large photoelastic coefficient, and the retardation plates produced in Comparative Examples 2 to 7 have insufficient light resistance even when the photoelastic coefficient is large or the photoelastic coefficient is small. there were. On the other hand, the retardation plate produced in Comparative Example 8 has a large photoelastic coefficient, and the retardation plates produced in Comparative Examples 9 and 10 have insufficient light resistance.

<Methyl methacrylate / N-phenylmaleimide / N-cyclohexylmaleimide / styrene polymer>
[Example 4]
Methyl methacrylate, N-phenylmaleimide, N-cyclohexylmaleimide, and styrene were weighed in a charging ratio shown in Table 3 so as to be 50 g in a total amount in a glass container having a volume of 100 ml, and then mixed and dissolved while stirring. Next, the solution was replaced with nitrogen gas to prepare a raw material solution.

  Next, 0.015 g of dilauroyl peroxide and 0.05 g of n-octyl mercaptan were added to the raw material solution and completely dissolved. Again, the inside of the glass container was brought into a nitrogen atmosphere with nitrogen gas, and then sealed. The glass container was reacted in an oil bath set at 68 ° C. for 20 hours, then the oil bath temperature was changed to 120 ° C., and further reacted for 10 hours to complete the polymerization reaction.

  After collecting the polymer mass from the glass container, it was dissolved in 200 g of tetrahydrofuran, and the resulting tetrahydrofuran solution was added dropwise to 1000 ml of methanol as a poor solvent to separate and collect the precipitated polymer. The target thermoplastic resin (Example 4) was obtained by drying at 130 ° C. for 2 hours under vacuum.

[Examples 5 and 6 and Reference Example 7]
Except having changed the raw material preparation ratio of a thermoplastic resin into the composition ratio shown in Table 3, operation similar to Example 4 was performed and the thermoplastic resin was obtained.

[Comparative Examples 11 and 12]
Except having changed the raw material preparation ratio of a thermoplastic resin into the composition ratio shown in Table 1, operation similar to Example 4 was performed and the thermoplastic resin was obtained.

Using the thermoplastic resins obtained in Examples 4 to 6, Reference Example 7, and Comparative Examples 11 and 12, press film molding was performed according to the above-described method (1-a), and then according to the above-described method (1-b). A 100% stretched film was produced, and the optical properties as a retardation plate were evaluated. The results are shown in Table 3.

The retardation plates produced in Examples 4 to 6 and Reference Example 7 all had high heat resistance and good light resistance, as well as a low photoelastic coefficient and a sufficient phase difference. On the other hand, the retardation plate produced in Comparative Examples 11 and 12 had a large photoelastic coefficient.

[ Reference Example 8, Example 9 ]
The retardation film produced from the thermoplastic resin obtained in Reference Example 2 and Example 5 was processed into a uniaxial free 200% stretched film and a uniaxial free 300% stretched film in accordance with the above-described method, and the draw ratio and its film optics. The change of characteristics was evaluated. The results are shown in Table 4.

  The retardation plate of the present invention can be designed to have an arbitrary retardation (positive and negative), a retardation plate such as a quarter wavelength plate or a half wavelength plate, a retardation film as an optical compensation film, or the like. It is suitable for use.

  The retardation plate of the present invention has a low photoelastic coefficient and a significant retardation, and has good heat resistance and light resistance. Therefore, the retardation plate mainly uses birefringence, for example, a retardation film ( Specifically, liquid crystal optical compensation films such as viewing angle control films used in various liquid crystal modes such as TN, VA, IPS, OCB), retardation plates such as ¼ wavelength plates, ½ wavelength plates, etc. It can be used suitably.

Claims (7)

50-90 mass% of the first structural unit represented by the following formula (1), 0.1-15 mass% of the second structural unit represented by the following formula (2), 0.1-49. A thermoplastic resin having 9% by mass of the third structural unit represented by the following formula (3) and 0 to 10% by mass of the fourth structural unit represented by the following formula (4) on the basis of the total amount. Formed from
The total content of the second structural unit and the fourth structural unit with respect to the content of the third structural unit is 2.8 to 15 in terms of molar ratio,
A retardation plate having an absolute value of a photoelastic coefficient of the thermoplastic resin of 2.5 × 10 ⁻¹² Pa ⁻¹ or less.

[Wherein, R ¹ represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an arylalkyl group having 7 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or And an aryl group having 6 to 14 carbon atoms and having at least one substituent selected from the following group A.
Group A: a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, and an alkyl group having 1 to 12 carbon atoms. ]

[Wherein, R ² represents an arylalkyl group having 7 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or an aryl group having 6 to 14 carbon atoms having at least one substituent selected from the following group B: R ³ and R ⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms.
Group B: a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, an alkyl group having 1 to 12 carbon atoms, and an arylalkyl group having 7 to 14 carbon atoms. ]

[Wherein, R ⁵ represents a hydrogen atom, a cycloalkyl group having 3 to 12 carbon atoms, an alkyl group having 1 to 12 carbon atoms, or at least one substituent having at least one substituent selected from the following group C. R ⁶ and R ⁷ each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms.
Group C: a halogen atom, a hydroxyl group, a nitro group, and an alkoxy group having 1 to 12 carbon atoms. ]

[Wherein R ⁸ and R ⁹ may be the same or different, and each represents a hydrogen atom, a halogen atom, a hydroxyl group, a nitro group, a linear or branched alkoxy group having 1 to 12 carbon atoms, and One selected from the group consisting of linear or branched alkyl groups having 1 to 12 carbon atoms is shown, and a represents an integer of 1 to 3. ]   2. The retardation plate according to claim 1, wherein the thermoplastic resin has an in-plane retardation (Re) absolute value of more than 30 nm and not more than 300 nm in terms of 100 μm thickness when formed into a film.   The phase difference plate of Claim 1 or 2 whose glass transition temperature of the said thermoplastic resin is 120 degreeC or more.   The retardation plate according to any one of claims 1 to 3, wherein the thermoplastic resin has a total light transmittance of 85% or more when formed into a film. R ¹ is a methyl group or a benzyl group,
R ² is a phenyl group or a phenyl group having at least one substituent selected from the group B;
Wherein R ⁵ is a cyclohexyl group, a retardation plate according to any one of claims 1-4. A polarizing plate provided with the phase difference plate of any one of Claims 1-5 . An image display apparatus provided with the phase difference plate of any one of Claims 1-5 .