JP2013109285A - Optical film and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film excellent in optical isotropy, mechanical strength and dimensional stability at a high temperature, and a method for manufacturing the same.SOLUTION: The optical film contains, as a main component, an acrylic thermoplastic resin having 50 to 95 mass% of a first structural unit formed of a first monomer selected from a methacrylic acid monomer and methacrylic acid esters, 0.1 to 20 mass% of a second structural unit formed of a second monomer selected from specified N-substituted maleimide compounds, and 0.1 to 49.9 mass% of a third structural unit formed of a third monomer different from the second monomer and selected from specified N-substituted maleimide compounds. In the film, an absolute value of thermal shrinkage is 1.5% or less both in an MD direction and in a TD direction when the film is heated at 120°C for 30 minutes, a folding endurance frequency is 5 times or more both in the MD direction and in the TD direction, an absolute value of a phase difference in an in-plane direction is 20 nm or less, and an absolute value of a phase difference in a thickness direction is 20 nm or less.

Description

  The present invention relates to an optical film and a method for producing the same.

  The amount of optical films used for display devices including liquid crystal displays is increasing year by year, and at the same time, higher functionality is required. Conventionally, polarizing plates are arranged on both sides of a glass substrate on the surface of a liquid crystal panel of a liquid crystal display device, and this polarizing plate is usually a stretched polyvinyl alcohol (PVA) film to which an iodine compound is added. It is used. Moreover, in order to improve the reliability of a protective function, methods, such as sticking the protective film which consists of a triacetyl cellulose, are applied to both surfaces of a PVA film.

  However, since the performance of triacetyl cellulose changes depending on humidity and temperature, there is a possibility that the function of the polarizing plate may be lowered. Further, the protective film made of triacetyl cellulose has a relatively small birefringence (Nx−Ny) in the film plane, but a relatively large absolute value of birefringence ((Nx + Ny) / 2−Nz) in the thickness direction. . Therefore, there is a problem that a phase difference is generated with respect to incident light from an oblique direction, which affects the viewing angle characteristics of the liquid crystal display.

  In view of the problem of the protective film made of triacetyl cellulose described above, a protective film made of an acrylic resin such as polymethyl methacrylate, which is a resin material excellent in optical properties, has been proposed. However, acrylic resin is brittle and easy to break, and sheets with a thickness of 1 mm or more are relatively easy to form, but thin films with a thickness of about 0.2 mm or less are brittle and have a sufficient practical strength for protecting a polarizer. It is difficult to form into a film.

  In view of such a problem, various technical proposals related to a polarizing plate (polarizer) protective film have been conventionally made. For example, Patent Documents 1 and 2 below disclose techniques for improving optical characteristics and strength by adding a styrene elastomer, a soft acrylic resin, and the like to an acrylic resin, respectively. In Patent Document 3 below, as a method for improving the mechanical strength such as bending strength while maintaining the transparency of the acrylic resin film, cold stretching is performed at a temperature not lower than the glass transition temperature Tg of the resin and not higher than Tg + 40 ° C. A stretching method is disclosed. Patent Document 4 listed below discloses a technique that achieves both mechanical strength and heat shrinkability at 80 ° C. by biaxially stretching an acrylic resin at a specific stretching ratio. Further, Patent Document 5 below discloses a technique for improving mechanical strength while maintaining optical isotropy by producing an acrylic resin film by an inflation method.

JP 2006-284881 A JP 2006-284882 A JP-A-2-43023 JP 2008-216586 A JP 2010-100801 A

  However, the optical film is desired to be excellent in dimensional stability in a high temperature environment in addition to the characteristics of optical isotropy and mechanical strength in the film plane and in the thickness direction. For example, when it is heated to a high temperature of 100 ° C. or higher in a manufacturing process of a product using an optical film as a member, curling caused by a difference in thermal shrinkage with other functional layers laminated by coating or pasting It is required to prevent.

  An object of this invention is to provide the optical film which is excellent in optical isotropy, mechanical strength, and the dimensional stability in a high temperature environment, and its manufacturing method.

  As a result of intensive research in order to solve the above-mentioned problems, the present inventor has obtained an optical isotropy by melt-thermoforming an acrylic thermoplastic resin containing repeating units derived from three specific types of monomers. It has been found that an optical film having excellent properties, mechanical strength, and dimensional stability under a high temperature environment can be obtained, and the present invention has been made based on this finding.

［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。］
ＪＩＳ Ｋ−７１３３に従って測定される１２０℃で３０分間加熱した時の熱収縮率の絶対値が、ＭＤ方向及びＴＤ方向のいずれも１．５％以下であり、ＪＩＳ Ｐ−８１１５に従って測定される耐折回数がＭＤ方向及びＴＤ方向のいずれも５回以上であり、下記式（ａ）で表される面内方向の位相差（Ｒｅ）の絶対値が２０ｎｍ以下、かつ、下記式（ｂ）で表される厚さ方向の位相差（Ｒｔｈ）の絶対値が２０ｎｍ以下である、光学フィルム。
Ｒｅ＝（Ｎｘ−Ｎｙ）×ｄ （ａ）
Ｒｔｈ＝〔（Ｎｘ＋Ｎｙ）／２−Ｎｚ〕×ｄ （ｂ）
［式中、ＮｘはＸ軸方向の屈折率を、ＮｙはＹ軸方向の屈折率を、ＮｚはＺ軸方向の屈折率をそれぞれ示し、ｄは厚さを示す。］
［２］第三の構造単位の含有量に対する第二の構造単位の含有量のモル比が、０より大きく１５以下である、［１］に記載の光学フィルム。
［３］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］又は［２］のに記載の光学フィルム。
［４］前記アクリル系熱可塑性樹脂のガラス転移温度Ｔｇが１２５℃以上である、［１］〜［３］のいずれかに記載の光学フィルム。
［５］［１］〜［４］のいずれかに記載の光学フィルムの製造方法であって、アクリル系熱可塑性樹脂を含む原料樹脂からシートを形成する工程と、該シートを、ＭＤ方向及びＴＤ方向に、それぞれの延伸倍率が３０〜４００％となる範囲で二軸延伸する工程と、を有する光学フィルムの製造方法。
［６］［１］〜［４］のいずれかに記載の光学フィルムよりなる偏光板保護フィルム。
［７］［１］〜［４］のいずれかに記載の光学フィルムよりなる透明プラスチック基板。 That is, the present invention relates to the following.
[1] An optical film containing an acrylic thermoplastic resin, and the acrylic thermoplastic resin is based on the total amount of the first structural unit represented by the following formula (1): 50 to 95% by mass; It has 0.1-20 mass% of 2nd structural units represented by Formula (2), and 0.1-49.9 mass% of 3rd structural units represented by following formula (3). ,

[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 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. ]
The absolute value of the heat shrinkage rate when heated at 120 ° C. for 30 minutes measured according to JIS K-7133 is 1.5% or less in both the MD direction and the TD direction, and the resistance value measured according to JIS P-8115. The number of folding is 5 or more in both the MD direction and the TD direction, the absolute value of the phase difference (Re) in the in-plane direction represented by the following formula (a) is 20 nm or less, and the following formula (b) The optical film whose absolute value of the retardation (Rth) of the thickness direction represented is 20 nm or less.
Re = (Nx−Ny) × d (a)
Rth = [(Nx + Ny) / 2−Nz] × d (b)
[In the formula, Nx represents the refractive index in the X-axis direction, Ny represents the refractive index in the Y-axis direction, Nz represents the refractive index in the Z-axis direction, and d represents the thickness. ]
[2] The optical film according to [1], wherein the molar ratio of the content of the second structural unit to the content of the third structural unit is greater than 0 and 15 or less.
[3] 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. ] Or the optical film as described in [2].
[4] The optical film according to any one of [1] to [3], wherein a glass transition temperature Tg of the acrylic thermoplastic resin is 125 ° C. or higher.
[5] A method for producing an optical film according to any one of [1] to [4], wherein the sheet is formed from a raw material resin including an acrylic thermoplastic resin, and the sheet is formed in the MD direction and TD. And a step of biaxially stretching in the direction in which the respective stretching ratios are 30 to 400%.
[6] A polarizing plate protective film comprising the optical film according to any one of [1] to [4].
[7] A transparent plastic substrate comprising the optical film according to any one of [1] to [4].

  According to the present invention, it is possible to provide an optical film excellent in optical isotropy, mechanical strength, and dimensional stability under a high temperature environment, and a method for producing the same.

  A preferred embodiment of the present invention will be described below. However, the present invention is not limited to the following embodiments.

[Acrylic thermoplastic resin]
The optical film of this embodiment contains an acrylic thermoplastic resin. The acrylic thermoplastic resin has a first structural unit, a second structural unit, and a third structural unit. Hereinafter, each structural unit 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 acrylic 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.

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 95% by mass, preferably 60 to 92% by mass, more preferably 70 to 90% by mass, based on the total amount of the acrylic thermoplastic resin. When the content of the first structural unit is 50% by mass or more, high total light transmittance and environmental resistance are exhibited.

  The acrylic thermoplastic 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 acrylic 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 acrylic thermoplastic resin. More preferably, it is -6 mass%. According to the acrylic 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 and benzyl methacrylate are preferred because the acrylic thermoplastic resin obtained has excellent transparency and weather resistance.

(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 terms of further improving optical properties such as heat resistance and low birefringence.

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 acrylic thermoplastic resin, methyl group, ethyl group, n-propyl group, isopropyl group, An 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 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 0.1 to 49.9% by mass, preferably 0.1 to 35% by mass, more preferably 0.1% by mass based on the total amount of the acrylic thermoplastic resin. ˜20 mass%. When the content of the second structural unit is within this range, the transparency of the acrylic thermoplastic resin is maintained, and the heat resistance is improved without yellowing and without impairing the environmental resistance.

  The acrylic thermoplastic resin may contain only one second structural unit, or may contain two or more second structural units.

  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. Of these second monomers, N-phenylmaleimide and N-benzylmaleimide are preferred because the acrylic thermoplastic resin has excellent heat resistance and optical properties such as birefringence. These second monomers may be used alone or in combination of two or more.

(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, Isobornyl group, adamantyl group, tetracyclododecyl group, etc., among them, cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group are preferred, and acrylic thermoplastic resin A cyclohexyl group is more preferable in terms of further improving optical properties such as weather resistance and transparency and imparting low water absorption to the acrylic 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- Hexyl group, n-octyl group, n-dodecyl group, n-octadecyl group, 2-ethylhexyl group, 1-decyl group, 1-dodecyl group, and the like. Among these, weather resistance of acrylic thermoplastic resin and A methyl group, an ethyl group, and an isopropyl group are preferable because optical properties such as transparency 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 acrylic thermoplastic resin, methyl group, ethyl group, n-propyl group, isopropyl group, An 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 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, preferably 0.1 to 35% by mass, and more preferably 0.1 to 35% by mass based on the total amount of the acrylic thermoplastic resin. 30% by mass. If content of a 3rd structural unit is this range, transparency will be maintained and low hygroscopicity will be exhibited.

  The acrylic thermoplastic resin may contain only one third structural unit, or may contain two or more third structural units.

  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 preferable because of the excellent weather resistance of the acrylic thermoplastic resin, and low hygroscopicity that is recently required for optical materials is excellent. N-cyclohexylmaleimide is particularly preferred.

  In the acrylic thermoplastic resin, the total content of the second structural unit and the third structural unit is preferably 5 to 50% by mass based on the total amount of the acrylic thermoplastic resin. More preferably, it is 5-40 mass%, More preferably, it is 10-35 mass%, More preferably, it is 10-30 mass%, Most preferably, it is 15-30 mass%. When it is within this range, the acrylic thermoplastic resin has a more sufficient heat resistance improvement effect, and more preferable improvement effects in terms of weather resistance, low water absorption, and 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 acrylic thermoplastic resin may decrease.

In the acrylic thermoplastic resin, the molar ratio C ₂ / C ₃ of the content C ₂ of the _second structural unit and the content C ₃ of the third structural unit is desirably greater than 0 and 15 or less. From the viewpoint of optical characteristics (low birefringence, low photoelastic coefficient) described later, the molar ratio C ₂ / C ₃ is more preferably 10 or less. When the molar ratio C ₂ / C ₃ is in this range, the acrylic thermoplastic resin of the present embodiment exhibits much better optical characteristics.

  In the acrylic 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 acrylic thermoplastic resin. . As a result, the acrylic thermoplastic resin exhibits better optical characteristics.

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

  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.

  The content of the fourth structural unit in the acrylic thermoplastic resin is preferably 0.1 to 20% by mass, and preferably 0.1 to 15% by mass, based on the total amount of the acrylic thermoplastic resin. Is more preferable, and it is still more preferable that it is 0.1-10 mass%. When the content is in the above range, the hygroscopicity of the acrylic thermoplastic resin is further improved. From the viewpoint of weather resistance, the content is preferably less than 10% by mass, and more preferably less than 7% by mass.

  The acrylic 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 represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and R ⁹ represents a halogen atom, a hydroxyl group, a nitro group, an alkyl group having 1 to 12 carbon atoms or an alkoxy group 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 and the like. Among these, in terms of further improving the transparency and weather resistance of the acrylic 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.

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 Down, 3-bromostyrene, 4-bromostyrene, 2,4-dibromostyrene, alpha-bromostyrene, beta-bromostyrene, 2-hydroxystyrene, 4-hydroxystyrene, and the like. From the point that it is excellent in copolymerizability with the first monomer, the second monomer and the third monomer constituting the acrylic thermoplastic resin, and the optical properties can be adjusted with a small amount of use. Styrene and α-methylstyrene are particularly preferred. These fourth monomers may be used alone or in combination of two or more.

  The acrylic thermoplastic resin according to the present embodiment may be composed of one kind of copolymer, or one or more kinds of the first structural unit, the second structural unit, and the third structural unit. It may be a blend of two or more copolymers having structural units. For example, the acrylic thermoplastic resin may be a resin composed of one kind of copolymer having a first structural unit, a second structural unit, and a third structural unit. Alternatively, the acrylic thermoplastic resin may be a blend composed of two or more types of copolymers having a first structural unit, a second structural unit, and / or a third structural unit. Alternatively, it may be a blend composed of a polymer having the first structural unit, a polymer having the second structural unit, and a polymer having the third structural unit. From the viewpoint of transparency and uniformity, the acrylic thermoplastic resin is a copolymer having the first structural unit, the second structural unit, and the third structural unit, or the first structural unit, It is preferably a blend composed of two or more kinds of copolymers having the second structural unit and / or the third structural unit. The first structural unit, the second structural unit, and the first structural unit A copolymer having three structural units is particularly preferred.

  The content of halogen atoms in the acrylic thermoplastic resin is preferably less than 0.47% by mass and more preferably 0.45% by mass or less based on the total amount of the acrylic thermoplastic resin. Because acrylic thermoplastic resin contains less than 0.47% by mass of halogen atoms, it is difficult to generate halogen gas even when acrylic thermoplastic resin is handled at high temperatures during melt molding, etc. Corrosion of equipment to be used and work environment deterioration are prevented. In addition, when the acrylic thermoplastic resin (or a molded product thereof) is discarded, 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 polymethylmethacrylate conversion by the GPC measuring method of an acrylic thermoplastic resin is 3000-1 million. If Mw is 3000 or more, an optical film having a required strength can be obtained by molding. Moreover, if Mw is 1000000 or less, necessary and sufficient heat fluidity can be obtained at the time of various melt molding. Mw is more preferably 30,000 to 800,000, still more preferably 60000 to 600,000. Particularly preferably, it is 100,000 to 400,000.

  It is preferable that the molecular weight distribution (Mw / Mn) in terms of polymethyl methacrylate by GPC measurement method of the acrylic thermoplastic resin is 1-10. The acrylic thermoplastic resin can be polymerized by a living radical polymerization method, and the molecular weight distribution can be adjusted as necessary. From the viewpoint of adjusting the resin viscosity suitable for molding processing, the molecular weight distribution (Mw / Mn) is more preferably 1.1 to 7.0, further preferably 1.2 to 5.0, It can also be set to 1.5 to 4.0.

<Physical characteristics of acrylic thermoplastic resin>
(Photoelastic coefficient)
The absolute value of the photoelastic coefficient of the film or sheet-like molded product obtained by molding the acrylic thermoplastic resin is preferably 3.0 × 10 ⁻¹² Pa ⁻¹ or less, and 2.0 × 10 ⁻ more preferably ¹² Pa ^-1 or less, further preferably 1.0 × ¹⁰ -12 ^{Pa -1} or less.

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 formula. 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
| Δn | = nx−ny
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 extension direction perpendicular to the refractive index, respectively.

  The photoelastic coefficient of the acrylic thermoplastic resin is sufficiently smaller than that of existing resins (for example, PMMA, PC, triacetyl cellulose resin, cyclic olefin resin, etc.). Accordingly, birefringence due to external force (photoelasticity) does not occur, so that it is difficult to undergo birefringence change. In addition, birefringence distribution in the molded body is small because birefringence (photoelasticity) due to residual stress at the time of molding hardly occurs.

(Birefringence change rate | K |)
Obtained from the slope of the least squares approximate linear relationship (A) between the birefringence (Δn (S)) expressed when the film obtained by molding an acrylic thermoplastic resin is uniaxially stretched and the draw ratio (S) The absolute value of the birefringence change rate K to be satisfied preferably satisfies the following formula (B).
Δn (S) = K × S + C (A)
| K | ≦ 0.30 × 10 ⁻⁵ (B)
In the formula, C is a constant and indicates a birefringence value when not stretched. Birefringence is a value obtained by converting a value measured as a film into a thickness of 100 μm.

The birefringence change rate | K | is more preferably | K | ≦ 0.15 × 10 ⁻⁵ , and further preferably | K | ≦ 0.10 × 10 ⁻⁵ . As the birefringence change rate | K | is smaller, birefringence due to stretching becomes less likely to occur.

Here, the value of K was determined by measuring the glass transition temperature (Tg) by DSC measurement of the acrylic thermoplastic resin, and performing uniaxial stretching at a stretching temperature of (Tg + 20) ° C. and a stretching speed of 500 mm / min. Is the time value. In general, it is known that the increase in birefringence decreases when the stretching speed is decreased. The value of K is, for example, the value of birefringence (Δn (S)) expressed by a uniaxially stretched film obtained by stretching the stretching ratio (S) as 100%, 200% or 300%, These values can be calculated by plotting against the draw ratio and approximating the least squares method. The draw ratio (S) is a value represented by the following equation, where L _{0 is} the distance between chucks before stretching and L ₁ is the distance between chucks after stretching.

  An acrylic thermoplastic resin film or sheet may be stretched for the purpose of increasing mechanical strength. In the above relational expression, the value of the birefringence change rate | K | represents the magnitude of the change in birefringence (Δn (S)) with respect to the draw ratio (S), and the larger | K | It means that the larger the amount of change and the smaller | K |, the smaller the amount of change in birefringence with respect to stretching.

  The acrylic thermoplastic resin has a sufficiently small birefringence change rate | K | as compared with existing resins (for example, PMMA, PC, triacetyl cellulose resin, cyclic olefin resin, etc.). Therefore, the existing resin has a characteristic that birefringence increases due to the stretch orientation during the stretching process, whereas the birefringence hardly increases even if the stretching process is performed.

(Glass-transition temperature)
The acrylic thermoplastic resin preferably has a glass transition temperature (Tg) of 125 ° C. or higher. If the acrylic thermoplastic resin has a Tg of 125 ° C. or higher, the necessary and sufficient heat resistance can be obtained more easily as a recent lens molded body and a film molded body optical film for a liquid crystal display. From the viewpoint of dimensional stability under the use environment temperature, the Tg of the acrylic thermoplastic resin is more preferably 130 ° C. or higher, and further preferably 135 ° C. or higher. On the other hand, the upper limit of the Tg of the acrylic thermoplastic resin is preferably 180 ° C. or lower.

Acrylic thermoplastic resin has a sufficiently small photoelastic coefficient (C _R ) (approximately zero), and when formed into an optical film, it is in-plane as an optical film regardless of whether or not it is stretched. It is characterized by the small absolute value of the phase difference between the direction and the thickness direction (approximately zero). Thereby, it is possible to realize optically complete isotropy that cannot be achieved by conventionally known resins. Furthermore, the acrylic thermoplastic resin of the present embodiment can simultaneously achieve high heat resistance.

[Acrylic thermoplastic resin composition]
The acrylic thermoplastic resin according to the present embodiment can be used as an acrylic thermoplastic resin composition by mixing with an additive or a resin other than the acrylic thermoplastic resin as long as the object of the present invention is not impaired. . That is, it is desirable that the acrylic thermoplastic resin composition has the same heat resistance and optical characteristics as the acrylic thermoplastic resin.

  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 or mold release agents such as stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, and ethylene bisstearamide; paraffinic processes Softeners or plasticizers such as oils, naphthenic process oils, aromatic process oils, paraffins, organic polysiloxanes and mineral oils; antioxidants such as hindered phenolic antioxidants and phosphorus heat stabilizers; hindered amines Examples include light stabilizers; benzotriazole-based UV absorbers; flame retardants; antistatic agents; reinforcing agents such as organic fibers, glass fibers, carbon fibers, and metal whiskers; colorants; and mixtures thereof. 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, based on the total amount of the acrylic thermoplastic resin composition.

  Examples of resins other than acrylic thermoplastic resins include polyolefin resins such as polyethylene and polypropylene, styrene such as polystyrene, styrene / acrylonitrile copolymers, styrene / maleic anhydride copolymers, and styrene / methacrylic acid copolymers. Resin, cellulose resin such as triacetyl cellulose, polymethacrylate resin, polyamide resin, polyphenylene sulfide resin, polyether ether ketone resin, polyester resin, polysulfone resin, polyphenylene oxide resin, polyimide resin, polyetherimide resin, Thermoplastic resins such as polyacetal resins, cyclic olefin resins, and norbornene resins; and phenol resins, melamine resins, silicone resins, and epoxy resins And the like. These resins can be used alone or in combination of two or more.

  The optical film formed by molding the acrylic thermoplastic resin or acrylic thermoplastic resin composition of the present embodiment is suitable mainly for applications that do not require birefringence, such as a polarizing plate protective film.

[Production method of optical film]
The optical film according to the embodiment includes a step of forming a sheet from the raw material resin including the acrylic thermoplastic resin described above, and the sheet in a range in which the respective stretching ratios in the MD direction and the TD direction are 30 to 400%. And an axial film stretching step. Here, MD direction means the mechanical flow direction at the time of producing a film, and is also called a film longitudinal direction. The TD direction means a direction orthogonal to the mechanical flow direction and is also referred to as a film width direction.

  The optical film of this embodiment can be manufactured by, for example, tenter method sequential biaxial stretching, tenter method simultaneous biaxial stretching, and inflation method stretching.

  The optical film production method by the tenter method sequential biaxial stretching is a single-screw or twin-screw extruder supplied with the raw material resin mainly composed of the above-mentioned acrylic thermoplastic resin, melt-kneaded, and extruded from a T-die. The sheet is guided onto a cast roll and solidified. Next, the extruded sheet is introduced into a roll-type longitudinal stretching machine and stretched in the mechanical flow direction (MD direction), and then the longitudinally stretched sheet is introduced into a tenter-type lateral stretching machine, and the direction perpendicular to the mechanical flow direction ( (TD direction). The tenter sequential biaxial stretching has the advantage that the stretching ratio can be easily controlled, and a film having a balanced orientation in the MD and TD directions can be obtained.

  The stretching temperature for stretching the acrylic thermoplastic resin is preferably Tg + 5 ° C. to Tg + 50 ° C., more preferably Tg + 10 ° C. to Tg + 45 ° C., and still more preferably Tg + 15 ° C. to Tg + 40 ° C.

  The draw ratios in the MD direction and the TD direction are both in the range of 30% to 400%, preferably in the range of 50% to 350%, and more preferably in the range of 100% to 300%. When both the MD and TD stretch ratios are less than 30%, the bending strength tends to be insufficient, and when it exceeds 400%, the film is frequently continuously broken and broken during the film production process. Tends to be unable to be produced.

In the method for producing an optical film of the present embodiment, a method of obtaining a target film by co-extrusion with a multilayer die using a target film and a non-adhesive resin, and then removing the non-adhesive resin layer. Can be used. This manufacturing method is preferable from the viewpoints of the following (a) to (c).
(A) The film-forming stability can be improved by the heat insulating effect by the non-adhesive resin layer and the effect of improving the film strength.
(B) It has an effect of preventing dust, airborne substances such as dust, additives, and other foreign matters from adhering to the film during film formation.
(C) The film surface has an effect of preventing damage to the film surface during handling after film formation and preventing foreign matter such as dust from adhering.

  The method of co-extrusion using a non-adhesive resin only on one side of the acrylic thermoplastic resin can also achieve the effects (a) to (c) above, but both sides of the acrylic thermoplastic resin are non-adhesive. The method of sandwiching with resin and co-extrusion is more effective.

  Non-adhesive resin co-extruded with a multilayer die has good compatibility when the solubility parameter value is close to that of the resin that makes up the film, and tends to mix when blended. Then, the resin layers that come into contact tend to adhere easily. Therefore, when a non-adhesive resin is selected, it is preferable to select a resin having a large difference in solubility parameter values with different polarities.

  Further, if the temperature and viscosity of the two kinds of resins that are in contact with each other at the time of coextrusion are greatly different from each other, there is a tendency that an interlayer is disturbed at the interface between the resins that are in contact with each other and a film with good transparency cannot be obtained. Therefore, when selecting a non-adhesive resin for the acrylic thermoplastic resin that is the main component of the film, the acrylic thermoplastic resin is used at a temperature close to the temperature of the acrylic thermoplastic resin in the die. It is preferable to select a resin having a viscosity close to the viscosity.

  As the non-adhesive resin, a wide variety of thermoplastic resins can be used as long as the above-described conditions are satisfied. Preferably, polyolefin resins, styrene resins, nylon resins, or fluorine-containing resins are used. Polyolefin resins are preferable, and polypropylene resins are particularly preferable.

[Characteristics of optical film]
(Film thickness)
The thickness of the optical film of the present embodiment is preferably in the range of 5 μm to 200 μm. If the thickness is 5 μm or more, a practically sufficient strength can be ensured and it is difficult to break easily during handling. In addition, when the thickness of the optical film is 200 μm or less, the above-described retardation (Re, Rth) and bending strength are well balanced.

  When used as a polarizer protective film, the thickness of the optical film is preferably 5 μm to 100 μm, more preferably 10 μm to 80 μm, and even more preferably 10 μm to 60 μm. When used as a transparent plastic substrate, the thickness of the optical film is preferably 20 μm to 180 μm, more preferably 20 μm to 160 μm, and even more preferably 30 μm to 160 μm.

(In-plane direction phase difference)
In the optical film of the present embodiment, the absolute value of the in-plane retardation (Re) represented by the following formula (a) is 20 nm or less.
Re = (Nx−Ny) × d (a)
In formula (a), Nx represents the refractive index in the X-axis direction of the film, and Ny represents the refractive index in the X-axis direction of the film. The X-axis is an axial direction showing the maximum refractive index in the plane of the film, and the Y-axis is an axial direction perpendicular to the X-axis in the plane of the film. d represents the thickness of the film.

  The absolute value of Re is more preferably 10 nm or less, and further preferably 5 nm or less. When the absolute value of Re is larger than 20 nm, the phase difference with respect to light incident perpendicularly to the film surface increases, and it tends to be difficult to obtain good optical characteristics.

  In general, the absolute value of Re is an index representing the magnitude of birefringence. The birefringence of the acrylic thermoplastic resin is sufficiently small compared to the birefringence when using an existing resin (for example, PMMA, PC, triacetyl cellulose resin, cyclic olefin resin, etc.). Suitable for applications requiring zero birefringence.

(Thickness direction phase difference)
In the optical film of the present embodiment, the absolute value of the retardation (Rth) in the thickness direction represented by the following formula (b) is 20 nm or less.
Rth = [(Nx + Ny) / 2−Nz] × d (b)
In formula (b), Nx represents the refractive index in the X-axis direction, Ny represents the refractive index in the Y-axis direction, and Nz represents the refractive index in the Z-axis direction. The X axis is an axial direction showing the maximum refractive index in the plane of the film, the Y axis is an axial direction perpendicular to the X axis in the plane of the film, and the Z axis is the X axis, Y The thickness direction is perpendicular to the axis. d represents the thickness of the film.

  The absolute value of Rth is more preferably 10 nm or less, and further preferably 5 nm or less. When Rth is greater than 20 nm, the phase difference increases with respect to incident light from the oblique direction of the film, and the viewing angle characteristics of the liquid crystal display tend to be adversely affected.

  Acrylic thermoplastic resin is characterized in that the absolute value of Rth is very small when used as an optical film, compared to the case where an existing resin (for example, PMMA, PC, triacetyl cellulose resin, cyclic olefin resin, etc.) is used. Have

(Folding strength)
The folding strength of the film can be evaluated by a folding test in which the film is bent under a predetermined condition. In the optical film of the present embodiment, the folding endurance measured according to JIS P-8115 is 5 times or more in both the MD direction and the TD direction of the film. The folding strength is more preferably 10 times or more in both the MD direction and the TD direction, and further preferably 30 times or more. When the bending strength in either the MD direction or the TD direction is less than 5 times, the handleability tends to be inferior.

  In order to increase the bending strength, it is possible to optimize the draw ratio in the MD direction and the TD direction.

(Heat shrinkage)
In the optical film of the present embodiment, the absolute value of the heat shrinkage rate when heated at 120 ° C. for 30 minutes measured according to JIS K-7133 is 1.5% or less in both the MD direction and the TD direction. The heat shrinkage rate of the film is more preferably 1.0% or less, and further preferably 0.5% or less. If the absolute value of the thermal shrinkage of the film exceeds 1.5%, after applying various functional layers such as hard coat on the acrylic thermoplastic resin film in the subsequent process, or after the acrylic thermoplastic resin film and others After pasting the film, there is a possibility of curling due to the difference in thermal shrinkage of each layer when heated to 120 ° C.

[Mode of use of film]
The optical film of the present embodiment may have a single-layer film configuration containing the above-described acrylic thermoplastic resin or acrylic thermoplastic resin composition, but in addition to the above acrylic thermoplastic on a predetermined base material or functional layer. You may use as a multilayer structure which laminated | stacked the layer containing resin. For example, a film containing an acrylic thermoplastic resin on the base material of glass, a polyolefin resin, and a resin excellent in gas barrier properties (ethylene vinyl alcohol copolymer resin, vinylidene chloride resin, polycarbonate resin, polyester resin, etc.) It can be laminated via. Moreover, raw material resin containing an acrylic-type thermoplastic resin and the resin which forms the said base material can be practically used as a laminated structure by performing multilayer coextrusion molding.

[Usage]
The optical film of this embodiment can be used as a film for display devices such as a liquid crystal display (LCD) and a plasma display (PDP). Furthermore, as a polarizer protective film, in addition to the case where the film is used alone, the film can be used as a film that serves as a support for a film used by laminating predetermined functional films such as a viewing angle widening film and a conductive film. .

  In optical film applications, specifically, a polarizer protective film for protecting a polarizing film used in a liquid crystal display, a support for a viewing angle widening film used by being attached to a polarizing plate, and coating a predetermined liquid crystal or the like. It is a support for an anti-glare (anti-glare) film that is used by sticking to the outermost surface of a polarizing plate in order to realize a display screen that suppresses glare and is easy to see, and is used by coating a predetermined anti-glare layer. Also used as a film, a film support for anti-reflection film and coated with a predetermined low-reflection layer, etc., a film support for conductive film and used by depositing a conductive layer such as ITO it can.

  When used as a polarizer protective film, an easy adhesion treatment for improving adhesion may be performed on a surface in contact with a predetermined polarizer. Examples of the easy adhesion treatment include various surface treatments such as corona treatment, plasma treatment, low-pressure UV treatment, saponification treatment, and predetermined treatment for forming an anchor layer. As the easy adhesion treatment, corona treatment and anchor layer formation treatment are particularly preferable. In addition, the optical film in the present embodiment may be attached to both surfaces of a predetermined polarizer, for example, attached to only one surface, and another protective film, for example, a cellulose resin film, to the other surface, Various physical properties such as moisture permeability, durability, and strength can be appropriately controlled.

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

[Preparation of acrylic thermoplastic resin]
(Preparation Example 1: Methyl methacrylate / N-phenylmaleimide / N-cyclohexylmaleimide copolymer)
A SUS polymerization reactor (capacity 0.5 L) equipped with a stirrer, temperature sensor, cooling pipe, nitrogen gas introduction nozzle, raw material solution introduction nozzle, initiator solution introduction nozzle and polymerization solution discharge nozzle was used. The pressure of the SUS polymerization reactor was slightly pressurized, and the reaction temperature was controlled at 130 ° C. with an oil bath.

  After mixing 576 g of methyl methacrylate (MMA), 61 g of N-phenylmaleimide (N-PheMI), 83 g of N-cyclohexylmaleimide (N-CyMI) and 480 g of methyl isobutyl ketone, a raw material solution was prepared by replacing with nitrogen gas. . Further, 8.63 g of Perhexa C (manufactured by NOF Corporation; concentration 75 wt%) was dissolved in 91.37 g of methyl isobutyl ketone, and then substituted with nitrogen gas to prepare an initiator solution.

  The raw material solution was introduced from the raw material solution introduction nozzle at 8.25 mL / min using a pump. The initiator solution was introduced from the initiator solution introduction nozzle at 0.08 mL / min using a pump. After 30 minutes, the polymer solution was discharged from the polymerization solution discharge nozzle at a constant flow rate of 500 mL / hr using a pump.

  The polymer solution was collected separately in the initial flow tank for 1.5 hours after discharge. The polymer solution was collected for 2.5 hours after 1.5 hours from the start of discharge. The obtained polymer solution and methanol as an extraction solvent were simultaneously supplied to a homogenizer and subjected to emulsion dispersion extraction. The separated and precipitated polymer was collected and dried under vacuum at 130 ° C. for 2 hours to obtain the desired acrylic thermoplastic resin.

(Preparation Example 2: Methyl methacrylate / N-phenylmaleimide / N-cyclohexylmaleimide / styrene copolymer)
A glass polymerization reactor (capacity 1.0 L) equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen gas introduction nozzle, a raw material solution introduction nozzle, and an initiator solution introduction nozzle was used. The pressure of the glass polymerization reactor was controlled at a slight pressure, and the reaction temperature was controlled at 100 ° C. with an oil bath.

  After mixing 140 g of methyl methacrylate (MMA), 14 g of N-phenylmaleimide (N-PheMI), 34 g of N-cyclohexylmaleimide (N-CyMI), 12 g of styrene (St) and 200 g of methyl isobutyl ketone, the gas was replaced with nitrogen gas. A raw material solution was prepared. Moreover, after dissolving 0.32 g of perhexa C (manufactured by NOF Corporation; concentration 75 wt%) in 1.00 g of methyl isobutyl ketone, the solution was replaced with nitrogen gas to prepare an initiator solution.

  The raw material solution was introduced from the raw material solution introduction nozzle into the glass reactor by pressure feeding. The initiator solution was introduced from the initiator solution introduction nozzle with a syringe to start the polymerization reaction. After 3 hours from the start of the reaction, the reaction was terminated, and the polymer solution was recovered. The obtained polymer solution and methanol as a poor solvent were simultaneously supplied to a homogenizer, and emulsified, dispersed and extracted. The separated and precipitated polymer was collected and dried under vacuum at 130 ° C. for 2 hours to obtain the desired acrylic thermoplastic resin.

(Preparation Example 3: Methyl methacrylate polymer)
In Preparation Example 1, an acrylic thermoplastic resin was obtained in the same manner as in Preparation Example 1, except that only 960 g of methyl methacrylate and 240 g of methyl isobutyl ketone were used.

(Preparation Example 4: Methyl methacrylate / styrene / maleic anhydride copolymer)
The target acrylic thermoplastic resin was obtained by a known method (for example, the method described in Japanese Patent Publication No. 63-1964) using methyl methacrylate, styrene and maleic anhydride as monomers.

(Composition analysis of acrylic thermoplastic resin)
Acrylic thermoplastic resin obtained by polymerization is dissolved in CDCl ₃ and measured by ¹ H-NMR and ¹³ C-NMR (measurement temperature: 40 ° C.) using trade name “DPX-400” manufactured by Bruker Co., Ltd. The amount of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit was identified, and the composition was confirmed from the ratio.

(Measurement of weight average molecular weight of acrylic thermoplastic resin)
The weight average molecular weight (Mw) and number average molecular weight (Mn) of the acrylic thermoplastic resin obtained by polymerization are developed using a gel permeation chromatograph (trade name “HLC-8220” manufactured by Tosoh Corporation). It calculated | required by solvent standard tetrahydrofuran conversion with commercially available standard PMMA at the preset temperature of 40 degreeC.

[Examples 1 to 4]
As the acrylic thermoplastic resin, methyl methacrylate / N-phenylmaleimide / N-cyclohexylmaleimide copolymer or methyl methacrylate / N-phenylmaleimide / N-cyclohexylmaleimide / styrene copolymer shown in Table 1 below is used. An optical film was produced.

  Specifically, the acrylic thermoplastic resin that had been previously dried was supplied to a single screw extruder, melted and kneaded, and the sheet-shaped molten resin was extruded from a T-die. Next, the sheet obtained by melt extrusion was introduced onto a cast roll and solidified, and then introduced into a roll-type longitudinal stretching machine, and stretched in the mechanical flow direction (MD direction). The obtained longitudinally stretched sheet was introduced into a tenter-type lateral stretcher and stretched in a direction (TD direction) perpendicular to the mechanical flow direction, and then both ends of the film were slit and a film having a thickness of 40 μm was wound up.

  Control the roll temperature, roll speed ratio, temperature in the tenter transverse stretcher, and the tenter rail width of the roll longitudinal stretcher so that the stretching temperature and stretch ratio in the MD and TD directions are as shown in Table 1 below. did.

[Comparative Examples 1-4]
As an acrylic thermoplastic resin, Examples and Examples were used except that methyl methacrylate / N-phenylmaleimide / N-cyclohexylmaleimide copolymer, methyl methacrylate polymer or methyl methacrylate / styrene / maleic anhydride copolymer was used. Similarly, an optical film was produced.

  However, the roll temperature of the roll type longitudinal stretching machine, the roll speed ratio, the temperature in the tenter type lateral stretching machine, and the tenter rail width so that the stretching temperature in each of the MD direction and TD direction and the stretching ratio are as shown in Table 1 below. Controlled.

(Glass-transition temperature)
Based on JIS-K7121, the glass transition temperature Tg of the acrylic thermoplastic resin was measured. First, 4 points (4 locations) of about 10 mg each were cut out from a sample that was conditioned in a standard state (23 ° C., 65% RH) (left at 23 ° C. for 1 week). Next, using a differential scanning calorimeter (thermal flow rate type DSC) manufactured by Perkin-Elmer: DSC-7 type (trade name), a nitrogen gas flow rate of 25 mL / min at room temperature (10 ° C./min) 23 ° C) to 200 ° C (primary temperature rise), held at 200 ° C for 5 minutes to completely melt, then cooled down to 40 ° C at 10 ° C / min and held at 40 ° C for 5 minutes Furthermore, among the DSC curves drawn during the second temperature increase (secondary temperature increase) under the above temperature increase condition, the vertical direction is from the step-like change partial curve at the time of the secondary temperature increase and each baseline extension line. The crossing point (midpoint glass transition temperature) with a straight line equidistant to each other was measured as Tg (unit: ° C). An arithmetic average of four points per sample (rounded off after the decimal point) was calculated and used as a measured value.

  In addition, the heat resistance of the optical film shape | molded becomes high, so that the glass transition temperature of resin used for an optical film is high. Therefore, the heat resistance of the optical film using this acrylic thermoplastic resin can be indirectly evaluated by measuring the glass transition temperature of the acrylic thermoplastic resin.

(Measurement of photoelastic coefficient)
A birefringence measuring apparatus described in detail in Polymer Engineering and Science 1999, 39, 2349-2357 was used. A film made of an acrylic thermoplastic resin (thickness: about 150 μm, width: 6 mm) that has been cured for 24 hours or more in a constant temperature and humidity chamber adjusted to 23 ° C. and a humidity of 60%, and similarly installed in the constant temperature and humidity chamber A film was placed on a tensioning apparatus (manufactured by Imoto Seisakusho Co., Ltd.) so that the distance between chucks was 50 mm. Next, the birefringence measuring apparatus (trade name “RETS-100”, manufactured by Otsuka Electronics Co., Ltd.) described later is set so that the laser beam path is at the center of the film, and the strain rate is 50% / min (between chucks: 50 mm, chuck moving speed The birefringence was measured while applying an extensional stress at 5 mm / min). 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 an extensional stress between 2.5 MPa ≦ σR ≦ 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)

(Calculation of birefringence change rate | K |)
A film (thickness: about 300 μm, width: 40 mm) obtained by molding the acrylic thermoplastic resin composition is stretched at a stretching temperature (Tg + 20) ° C. and a stretching speed (500 mm / min) using an Instron 10t tensile tester. Uniaxial free stretching was performed to form a stretched optical isotropic support plate. The draw ratio was drawn at 100%, 200%, and 300%. Subsequently, the birefringence of the obtained stretched film was measured by the above-described method, and the birefringence (Δn (S)) expressed when uniaxially stretched was determined. Least square method approximate linear relational expression (A) obtained by plotting the obtained birefringence (Δn (S)) value of the obtained stretched optical isotropic support plate against the stretch ratio (S) The value of the birefringence change rate K obtained from the slope of was obtained. It means that the smaller the absolute value of K, the smaller the birefringence (Δn (S)) and its change.
Δn (S) = K × S + C (C is a constant: birefringence value when unstretched) (A)
Here, the birefringence is a value obtained by converting a measured value to a thickness of 100 μm.

The draw ratio (S) is a value represented by the following formula, where L _{0 is} the distance between chucks before stretching and L ₁ is the distance between chucks after stretching.

(Film thickness)
The thickness of the film was measured using a micrometer according to JIS-K-7130.

<Evaluation of optical isotropy>
In-plane phase difference (Re) and thickness direction phase difference (Rth) were measured using a trade name “KOBRA-21ADH” which is an automatic birefringence meter manufactured by Oji Scientific Instruments.

The optical isotropy was evaluated as follows using absolute values of Re and Rth.
A: The absolute values of both Re and Rth are 5 nm or less.
B: The absolute value of either Re or Rth is higher than 5 nm and not higher than 20 nm.
C: The absolute value of either Re or Rth is higher than 20 nm.

<Evaluation of bending strength>
The folding strength of the film was measured in accordance with JIS P-8115 by applying a load of 9.8 N to a film test piece having a width of 15 mm and performing a bending test in the MD direction and the TD direction of the film. .

The folding strength of the film was evaluated as follows.
A: The number of folding strengths in the MD and TD directions is 30 times or more.
B: The number of folding strengths in any of the MD and TD directions is 1 or more and less than 30 times.
C: The number of folding strengths in the MD and TD directions is zero.

<Evaluation of dimensional stability>
Based on JIS K-7133, the thermal contraction rate of MD direction and TD direction when it heated at 120 degreeC for 30 minute (s) was measured.

The dimensional stability was evaluated as follows using the absolute value of the thermal shrinkage rate of the film.
A: Absolute value of thermal shrinkage in MD and TD directions is 0.5% or less.
B: Absolute value of thermal shrinkage in MD and TD directions is higher than 0.5% and not higher than 1.5%.
C: Absolute value of thermal shrinkage in MD and TD directions is higher than 1.5%.

<Evaluation of overall evaluation of film>
The overall evaluation of the film was evaluated as follows by combining optical isotropy, bending strength, and dimensional stability.
A: A film whose optical isotropy, bending strength, and dimensional stability evaluation results are all A.
B: A film containing B in any of the optical isotropy, bending strength, and dimensional stability evaluation results.
C: A film containing C in any of the optical isotropy, bending strength, and dimensional stability evaluation results.

  Table 1 below shows the results of the thickness, optical physical properties (Re and Rth), folding resistance (times), thermal shrinkage rate, and comprehensive evaluation of the optical films prepared in Examples and Comparative Examples.

  As shown in Table 1, all of the optical films produced in Examples 1 to 4 had practically sufficient optical isotropy and bending strength and good dimensional stability.

  The optical film of the present invention is a film used for optical applications used inside a liquid crystal display (LCD) or the like, specifically, a polarizer protective film, a support for a viewing angle widening film, anti-glare (anti-glare). It can utilize as a support body for films, a support body for antireflection films, and a support body for transparent conductive films.

Claims (7)

An optical film containing an acrylic thermoplastic resin,
The acrylic thermoplastic resin is, based on the total amount, 50 to 95% by mass of the first structural unit represented by the following formula (1) and the second structural unit represented by the following formula (2): 1 to 20% by mass, and a third structural unit represented by the following formula (3) 0.1 to 49.9% by mass,

[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 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. ]
The absolute value of the heat shrinkage rate when heated at 120 ° C. for 30 minutes measured according to JIS K-7133 is 1.5% or less in both the MD direction and the TD direction,
The folding endurance measured according to JIS P-8115 is 5 times or more in both the MD direction and the TD direction,
The absolute value of the in-plane direction retardation (Re) represented by the following formula (a) is 20 nm or less, and the absolute value of the thickness direction retardation (Rth) represented by the following formula (b) is 20 nm. An optical film that is:
Re = (Nx−Ny) × d (a)
Rth = [(Nx + Ny) / 2−Nz] × d (b)
[In the formula, Nx represents the refractive index in the X-axis direction, Ny represents the refractive index in the Y-axis direction, Nz represents the refractive index in the Z-axis direction, and d represents the thickness. ]   2. The optical film according to claim 1, wherein a molar ratio of the content of the second structural unit to the content of the third structural unit is greater than 0 and 15 or less. 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;
The optical film according to claim 1, wherein R ⁵ is a cyclohexyl group.   The optical film as described in any one of Claims 1-3 whose glass transition temperature Tg of the said acrylic thermoplastic resin is 125 degreeC or more. It is a manufacturing method of the optical film as described in any one of Claims 1-4,
Forming a sheet from a raw material resin containing the acrylic thermoplastic resin;
Biaxially stretching the sheet in the MD direction and the TD direction in a range where the respective stretching ratios are 30 to 400%;
The manufacturing method of the optical film which has.   The polarizing plate protective film which consists of an optical film as described in any one of Claims 1-4.   The transparent plastic substrate which consists of an optical film as described in any one of Claims 1-4.