JP2015197483A - Retardation film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a retardation film which is single-layered and yet offers not only sufficient heat resistance and mechanical properties but also a sufficiently low photoelastic coefficient and superior inverse-wavelength dispersibility.SOLUTION: A retardation film of the present invention contains a copolymer containing 10-55 mass% of a prescribed methacrylic monomer unit (A), 40-85 mass% of a prescribed maleimide monomer unit (B), and 5-29 mass% of a prescribed aromatic vinyl monomer unit (C), and retardation values Re(450) and Re(550) measured at wavelengths of 450 nm and 550 nm, respectively, satisfy the following relational expression: Re(450)/Re(550)<0.9.

Description

  The present invention relates to a retardation film.

  A retardation film such as a half-wave plate or a quarter-wave plate is used in many applications such as an antireflection film in an organic EL display or a liquid crystal display device (see, for example, Patent Document 1). Although the absolute value of the birefringence of the conventional retardation film monotonously decreases with respect to the wavelength, the retardation film having excellent display characteristics has a wavelength dispersion property that the absolute value of the retardation increases as the wavelength of light increases. Desired. In this specification, according to the name commonly used by those skilled in the art, this property is based on the fact that it is opposite to the wavelength dispersion exhibited by a general optical member made of a polymer. "

  As a current phase difference film, for example, a phase difference film that exhibits reverse wavelength dispersion by laminating a birefringent film having a large phase difference and a birefringent film having a small phase difference is disclosed (for example, , See Patent Document 2).

  Further, for example, Patent Document 3 discloses a retardation film that exhibits a reverse wavelength dispersion in a single layer using a special polycarbonate alignment film. This achieves reverse wavelength dispersion by copolymerizing a polymer having positive refractive index anisotropy and a polymer having negative refractive index anisotropy.

JP 2007-273275 A JP-A-5-27118 Japanese Patent No. 3325560

  However, in order to achieve a necessary retardation characteristic in a wide wavelength region using a laminated film, it is necessary to laminate two or more polymer films while strictly adjusting them. In addition, in a retardation film using a special polymer, it is difficult to uniformly exhibit retardation characteristics in a wide wavelength band. In addition, when a polycarbonate alignment film is used, there is a problem that a photoelastic coefficient is high and birefringence due to stress is large, and light leakage occurs when used as a retardation film.

  The present invention has been made in view of the above-described problems of the prior art, and not only has sufficient heat resistance and mechanical properties even in a single layer, but also has a sufficiently low photoelastic coefficient, An object is to provide a retardation film having excellent reverse wavelength dispersion.

  As a result of intensive studies to solve the above problems, the present inventors include a methacrylic monomer unit, a maleimide monomer unit, and an aromatic vinyl monomer unit at a specific ratio. By using a copolymer, it discovered that the optical film which shows favorable reverse wavelength dispersion was obtained, and came to complete this invention.

（式中、Ｒ₁はメチル基を示す。Ｒ₂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、または下記Ａ群から選ばれる少なくとも１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：ハロゲン基、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、Ｒ₃は、炭素数６〜１４のアルキル基、炭素数６〜１４の環状アルキル基、炭素数６〜１４のアリール基、または下記Ｂ群から選ばれる少なくとも１種の置換基を有する炭素数６〜１４のアリール基を示し、Ｒ₄及びＲ₅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：ハロゲン基、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６〜１４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Ｒ₆及びＲ₇は、それぞれ同一でも、異なっていてもよく、水素原子、ハロゲン原子、水酸基、アルコキシ基、ニトロ基又は直線状若しくは分岐状の炭素数が１〜６のアルキル基を示す。ｎは、０〜５の整数を示す。）
［２］
前記マレイミド系単量体（Ｂ）が、Ｎ−シクロヘキシルマレイミド及び／又はＮ−フェニルマレイミドを含む、［１］に記載の位相差フィルム。
［３］
前記芳香族ビニル系単量体単位（Ｃ）が、イソプロペニルベンゼン及び／又はスチレンを含む、［１］に記載の位相差フィルム。
［４］
光弾性係数の絶対値が５５×１０^-12Ｐａ^-1以下である、［１］〜［３］のいずれかに記載の位相差フィルム。 That is, the present invention is as follows.
[1]
10-55 mass% of methacrylic monomer units (A) represented by the following formula (1), 40-85 mass% of maleimide monomer units (B) represented by the following formula (2), An aromatic vinyl monomer unit represented by the following formula (3) (C) 5 to 29% by mass, and a copolymer containing:
A retardation film in which retardation values Re (450) and Re (550) measured at wavelengths of 450 nm and 550 nm satisfy the following relational expression.
Re (450) / Re (550) <0.9

(In the formula, R ₁ represents a methyl group. R ₂ 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, or An aryl group having 6 to 14 carbon atoms and having at least one substituent selected from Group A is shown.
Group A: a halogen group, 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 formula, R ₃ represents an alkyl group having 6 to 14 carbon atoms, a cyclic alkyl group having 6 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or at least one substituent selected from the following group B: And an aryl group having 6 to 14 carbon atoms, and R ₄ and R ₅ 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 B: a halogen group, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, an alkyl group having 6 to 14 carbon atoms, and an arylalkyl group having 7 to 14 carbon atoms. )

(Wherein R ₆ and R ₇ may be the same or different and each represents a hydrogen atom, a halogen atom, a hydroxyl group, an alkoxy group, a nitro group, or a linear or branched alkyl group having 1 to 6 carbon atoms. N represents an integer of 0 to 5)
[2]
The retardation film according to [1], wherein the maleimide monomer (B) includes N-cyclohexylmaleimide and / or N-phenylmaleimide.
[3]
The retardation film according to [1], wherein the aromatic vinyl monomer unit (C) contains isopropenylbenzene and / or styrene.
[4]
The retardation film according to any one of [1] to [3], wherein the absolute value of the photoelastic coefficient is 55 × 10 ⁻¹² Pa ⁻¹ or less.

  According to the present invention, there is provided a retardation film that not only has sufficient heat resistance and mechanical properties even in a single layer, but also has a sufficiently low photoelastic coefficient and also has excellent reverse wavelength dispersion. can do.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be appropriately modified and implemented within the scope of the gist. In the present specification, “monomer unit” or “unit” refers to a unit constituting a copolymer corresponding to a predetermined monomer.

The retardation film of the present embodiment includes 10 to 55% by mass of a unit (A) derived from a methacrylic monomer represented by the following formula (1) and a maleimide monomer represented by the following formula (2). Co-weight containing 40 to 85% by mass of the unit (B) derived from the body and 5 to 29% by mass of the unit (C) derived from the aromatic vinyl monomer represented by the following formula (3) Retardation values Re (450) and Re (550) measured at wavelengths of 450 nm and 550 nm satisfy the following relational expression.
Re (450) / Re (550) <0.9

（式中、Ｒ₁はメチル基を示す。Ｒ₂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、または下記Ａ群から選ばれる少なくとも１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：ハロゲン基、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。）

(In the formula, R ₁ represents a methyl group. R ₂ 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, or An aryl group having 6 to 14 carbon atoms and having at least one substituent selected from Group A is shown.
Group A: a halogen group, 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. )

（式中、Ｒ₃は、炭素数６〜１４のアルキル基、炭素数６〜１４の環状アルキル基、炭素数６〜１４のアリール基、または下記Ｂ群から選ばれる少なくとも１種の置換基を有する炭素数６〜１４のアリール基を示し、Ｒ₄及びＲ₅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：ハロゲン基、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６〜１４のアルキル基及び炭素数７〜１４のアリールアルキル基。）

(In the formula, R ₃ represents an alkyl group having 6 to 14 carbon atoms, a cyclic alkyl group having 6 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or at least one substituent selected from the following group B: And an aryl group having 6 to 14 carbon atoms, and R ₄ and R ₅ 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 B: a halogen group, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, an alkyl group having 6 to 14 carbon atoms, and an arylalkyl group having 7 to 14 carbon atoms. )

（式中Ｒ₆及びＲ₇は、それぞれ同一でも、異なっていてもよく、水素原子、ハロゲン原子、水酸基、アルコキシ基、ニトロ基又は直線状若しくは分岐状の炭素数が１〜６のアルキル基を示す。ｎは、０〜５の整数を示す。）

(Wherein R ₆ and R ₇ may be the same or different and each represents a hydrogen atom, a halogen atom, a hydroxyl group, an alkoxy group, a nitro group, or a linear or branched alkyl group having 1 to 6 carbon atoms. N represents an integer of 0 to 5)

  Since the retardation film of the present embodiment is configured as described above, it not only has sufficient heat resistance and mechanical properties even if it is a single layer, but also has a sufficiently low photoelastic coefficient and is further excellent. It can also have reverse wavelength dispersion. That is, the retardation film of the present embodiment is a single layer film that exhibits reverse wavelength dispersion, can provide a retardation film with high heat resistance, and can be used as an antireflection film for organic EL displays and the like. More specifically, the retardation film of the present embodiment is configured to include three components of a methacrylic monomer unit, a maleimide monomer unit, and an aromatic vinyl monomer unit at a specific ratio. Therefore, even if it is a single layer, it can be suitably used as a polymer stretched oriented film, has a tendency that the retardation increases as the measurement wavelength becomes longer, and can exhibit high retardation characteristics in a wide wavelength region. it can. In addition, the other monomer unit which can be copolymerized can also be copolymerized in the range which can achieve the effect of this embodiment.

<Other vinyl monomers copolymerizable with methacrylic acid ester monomers>
As another vinyl monomer copolymerizable with the methacrylic acid ester monomer mentioned above, an acrylic acid ester monomer represented by the following general formula (4) is exemplified.

（一般式（４）中、Ｒ₈は水素原子を示し、Ｒ₉は炭素数が１〜１８のアルキル基を示す。）

(In the general formula (4), R ₈ represents a hydrogen atom, and R ₉ represents an alkyl group having 1 to 18 carbon atoms.)

  Examples of the acrylate monomer represented by the general formula (4) include, but are not limited to, methyl acrylate, ethyl acrylate, n-propyl acrylate, and n-butyl acrylate. , Sec-butyl acrylate, 2-ethylhexyl acrylate, and the like. In particular, methyl acrylate, ethyl acrylate, and n-butyl acrylate are preferable, and methyl acrylate is more easily available and more preferable.

  Further, the vinyl monomer other than the acrylic acid ester monomer of the general formula (4), which can be copolymerized with the methacrylic acid ester monomer, is not limited to the following examples. Examples thereof include α, β-unsaturated acids such as acrylic acid and methacrylic acid, unsaturated group-containing divalent carboxylic acids such as maleic acid, fumaric acid, itaconic acid, cinnamic acid, and alkyl esters thereof.

  Each monomer unit (also referred to as a monomer component) is described in detail below.

<Methacrylic acid ester monomer unit (A)>
The copolymer in the present embodiment includes a methacrylic acid ester monomer unit (A) represented by the above formula (1) (hereinafter may be referred to as component (A) or (A)).

In said formula (1), R < ₁ > shows a methyl group. R ₂ 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, or at least one substituent selected from the following group A. And an aryl group having 6 to 14 carbon atoms.
Group A: a halogen group, 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.

  Specific examples of the methacrylic acid ester monomer represented by the above formula (1) are not particularly limited, but include butyl methacrylate, ethyl methacrylate, methyl methacrylate, propyl methacrylate, isopropyl methacrylate, methacrylic acid. Examples include cyclohexyl, phenyl methacrylate, methacrylic acid (2-ethylhexyl), methacrylic acid (t-butylcyclohexyl), benzyl methacrylate, methacrylic acid (2,2,2-trifluoroethyl) and the like. In view of the above, ethyl methacrylate is preferable. The said methacrylic acid ester monomer unit may be used individually by 1 type, and may use 2 or more types together.

  From the viewpoint of optical properties and mechanical strength, the methacrylic acid ester monomer unit is contained in the copolymer for retardation film of this embodiment in an amount of 10 to 55% by mass, preferably 11 to 50% by mass, and more preferably. Is contained in an amount of 12 to 40% by mass.

<Maleimide monomer unit (B)>
The copolymer in the present embodiment includes a maleimide monomer unit (B) represented by the above formula (2) (hereinafter, may be referred to as (B) component or (B)).

R ₃ in the above formula (2) is at least one selected from an alkyl group having 6 to 14 carbon atoms, a cyclic alkyl group having 6 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or the following group B: It represents one selected from the group consisting of a C6-C14 aryl group having a substituent.
Group B: a halogen group, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, an alkyl group having 6 to 14 carbon atoms, and an arylalkyl group having 7 to 14 carbon atoms. )

  Specific examples of the maleimide monomer unit (B) are not particularly limited, but maleimide, N-methylmaleimide, N-ethylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N- (o -Chlorophenyl) maleimide, N- (m-chlorophenyl) maleimide, N- (p-chlorophenyl) maleimide and the like. Preferable examples include N-cyclohexylmaleimide, N-phenylmaleimide, N- (o-chlorophenyl) maleimide, N- (m-chlorophenyl) maleimide, N- (p-chlorophenyl) maleimide, and availability and heat resistance. From the viewpoint of imparting, N-cyclohexylmaleimide and N-phenylmaleimide are more preferable, and N-phenylmaleimide is more preferable. That is, in this embodiment, it is particularly preferable that the maleimide monomer (B) contains N-cyclohexylmaleimide and / or N-phenylmaleimide. The maleimide monomer units (B) described above may be used alone or in combination of two or more.

  The maleimide monomer unit (B) is contained in the copolymer for a retardation film in an amount of 40 to 85% by mass, preferably 45 to 80% by mass, from the viewpoint of imparting good retardation and heat resistance. Preferably 50 to 75 mass% is contained.

<Aromatic vinyl monomer unit (C)>
The copolymer in the present embodiment includes an aromatic vinyl monomer unit (C) represented by the above formula (1) (hereinafter may be referred to as (C) component or (C)). .

In the general formula (3), R ₆ and R ₇ may be the same or different and each has a hydrogen atom, a halogen atom, a hydroxyl group, an alkoxy group, a nitro group, or a linear or branched carbon number of 1 to 6 represents an alkyl group. n shows the integer of 0-5. In addition, (C) component in this embodiment can also be called monomer unit with negative refractive index anisotropy.

  The aromatic vinyl monomer unit (C) is contained in an amount of 5 to 29% by mass, preferably 10 to 25% by mass, and more preferably 10 to 20% by mass from the viewpoint of good retardation characteristics and surface hardness. Yes.

  Specific examples of the aromatic vinyl monomer are not particularly limited, but styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, 2,5 -Dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, p-ethylstyrene, p-tert-butylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, 1,1-diphenylethylene, isopropenylbenzene (α-methylstyrene), isopropenyltoluene, isopropenylethylbenzene, isopropenylpropylbenzene, isopropenylbutylbenzene, isopropenylpentylbenzene, isopropenylhexylbenzene, isopropenyloctylbenzene, etc. And the like. These can be appropriately selected according to the properties required for the copolymer in the present embodiment. Among these, styrene and isopropenylbenzene are preferable, and styrene is more preferable from the viewpoints of imparting fluidity and reducing unreacted monomers by improving the polymerization conversion rate. That is, in this embodiment, it is particularly preferable that the aromatic vinyl monomer unit (C) contains isopropenylbenzene and / or styrene. The above aromatic vinyl monomers (C) may be used alone or in combination of two or more.

[Reverse chromatic dispersion characteristics of phase difference]
The retardation in the present specification refers to a retardation value in retardation measurement, and is based on a difference in the traveling speed of light in a direction perpendicular to the film orientation direction when light is transmitted through the film. The phase difference. In general, the absolute value of the phase difference decreases as the wavelength of light increases. This is called forward wavelength dispersion. The half-wave plate and the quarter-wave plate are required to have reverse wavelength dispersion in which the absolute value of the phase difference increases as the wavelength increases.

  Specifically, the reverse wavelength dispersion in the retardation film of the present embodiment can be evaluated as follows. That is, the retardation values Re (450) and Re (550) measured at wavelengths of 450 nm and 550 nm satisfy the relational expression “Re (450) / Re (550) <0.95”. Preferably, “1.1 <Re (800) / Re (550) <1.7” is satisfied by using a retardation value measured at a wavelength of 800 nm, and more preferably “Re (450) / Re (550) <0”. .9 ”, more preferably“ 1.1 <Re (800) / Re (550) <1.6 ”. In addition, the said retardation value can be calculated | required by the method as described in the Example mentioned later.

[Photoelastic coefficient]
The absolute value of the photoelastic coefficient of the retardation film of the present embodiment is preferably 55 × 10 ⁻¹² Pa ⁻¹ or less, more preferably 45 × 10 ⁻¹² Pa ⁻¹ or less, and further preferably 35 ×. 10 ⁻¹² Pa ⁻¹ or less. When the absolute value is 55 × 10 ⁻¹² Pa ⁻¹ or less, birefringence due to stress can be sufficiently reduced, and light leakage when used as a retardation film tends to be more effectively prevented. In addition, the said photoelastic coefficient can be calculated | required by the method as described in the Example mentioned later.

[Molecular weight of copolymer]
It is preferable that the copolymer for retardation films of this embodiment has a weight average molecular weight of 60,000 to 400,000. A copolymer having a weight average molecular weight within this range tends to be excellent in mechanical strength, solvent resistance and fluidity. From the same viewpoint, it is preferably 60,000 to 350,000, and more preferably 70,000 to 300,000.

  The molecular weight distribution (weight average molecular weight / number average molecular weight: Mw / Mn) is preferably 1.5 or more and 5 or less in consideration of the balance between fluidity, mechanical strength, and solvent resistance. More preferably, it is 1.7 or more and 4.5 or less, More preferably, it is 1.8 or more and 4.0.

  The weight average molecular weight, number average molecular weight, and peak molecular weight of the retardation film copolymer of the present embodiment can be measured by gel permeation chromatography (GPC).

[Method for producing copolymer]
Hereinafter, although the manufacturing method of the copolymer in this embodiment is demonstrated, it is not limited to the method shown below.

  The copolymer uses a methacrylic acid ester monomer (A), a maleimide monomer (B), and an aromatic vinyl monomer (C), and is not limited to the following, for example, a bulk polymerization method, It can be produced by a solution polymerization method, suspension polymerization method, precipitation polymerization method, emulsion polymerization method or the like. A bulk polymerization method, a solution polymerization method, and a suspension polymerization method are preferably used.

  In the production of the methacrylic resin of this embodiment, the polymerization temperature is 40 ° C to 90 ° C, preferably 50 ° C to 80 ° C. When the polymerization temperature is 90 ° C. or higher, it is difficult to obtain a resin having a single composition, which is not preferable.

  In various polymerization methods for producing the copolymer in the present embodiment, that is, in the polymerization step in the bulk polymerization method, the solution polymerization method, the suspension polymerization method, etc., the polymerization is started for the purpose of adjusting the polymerization degree of the polymer to be produced. An agent may be used.

  As a polymerization initiator, when performing radical polymerization, it is not limited to the following. For example, di-t-butyl peroxide, lauroyl peroxide, stearyl peroxide, benzoyl peroxide, t-butylperoxyneodecanate, t -Butylperoxypivalate, dilauroyl peroxide, dicumyl peroxide, t-butylperoxy-2-ethylhexanoate, 1,1-bis (t-butylperoxy) -3,3,5-trimethyl Organic peroxides such as cyclohexane and 1,1-bis (t-butylperoxy) cyclohexane, azobisisobutyronitrile, azobisisovaleronitrile, 1,1-azobis (1-cyclohexanecarbonitrile), 2 , 2'-Azobis-4-methoxy-2,4-azobisisobutyro Tolyl, 2,2'-azobis-2,4-dimethylvaleronitrile, mention may be made of conventional radical polymerization initiator azo such as 2,2'-azobis-2-methylbutyronitrile. These may be used alone or in combination of two or more.

  These polymerization initiators are generally used in the range of 0 to 1 part by mass with respect to 100 parts by mass of the total amount of all monomers used, taking into consideration the polymerization temperature and the half-life of the initiator. Can be selected as appropriate.

  In the production process of the copolymer in the present embodiment, the molecular weight of the polymer to be produced can be controlled within a range that does not impair the purpose of the present embodiment. Examples of the control method include, but are not limited to, chain transfer agents such as alkyl mercaptans, dimethylacetamide, dimethylformaldehyde, and triethylamine, and iniferters such as dithiocarbamates, triphenylmethylazobenzene, and tetraphenylethane derivatives. The molecular weight can be controlled by using it, and the molecular weight can be adjusted by adjusting the addition amount thereof. These can be appropriately added according to the required molecular weight, but generally used in the range of 0.001 to 3 parts by mass with respect to 100 parts by mass of the total amount of all monomers used.

  Other molecular weight control methods are not limited to the following, but include, for example, a method for changing the polymerization method, a method for adjusting the amount of the polymerization initiator, a method for changing the polymerization temperature, and forcibly stopping the reaction during the polymerization. Methods and the like.

  As these molecular weight control methods, only one type of method may be used alone, or two or more types may be used in combination.

  The glass transition temperature of the copolymer in the present embodiment can be arbitrarily controlled by the resin composition, but is preferably 130 ° C. or higher, more preferably 140 ° C. or higher, from the viewpoint of industrial applicability. In addition, the said glass transition temperature can be calculated | required by the method as described in the Example mentioned later.

  The retardation film of this embodiment can be produced by stretching an unoriented film in which polymer chains are not substantially oriented. The stretching method is not particularly limited, and may be uniaxial stretching of either longitudinal or lateral stretching, or may be any of width-free uniaxial stretching and fixed width uniaxial stretching. Biaxial stretching may be either sequential biaxial or simultaneous biaxial stretching. More specifically, although not limited to the following, for example, industrially, uniaxial stretching method by roll stretching or tenter stretching, sequential secondary stretching method by combination of roll stretching and tenter stretching, simultaneous biaxial stretching method by tenter stretching A stretched film can be produced by a biaxial stretching method using tubular stretching.

  The stretching ratio is preferably 0.1% or more and 300% or less, more preferably 1% or more and 200% or less, and still more preferably 2% or more and 150% or less, at least in any one of them. When the stretching ratio is designed in the above range, a stretched molded body (film) more preferable in terms of birefringence and strength tends to be obtained.

The draw ratio can be determined from the following relational expression by shrinking the obtained film at a temperature 20 ° C. or more higher than the glass transition temperature. The glass transition temperature can be determined by a DSC method or a viscoelastic method.
Stretch ratio (%) = [(length before shrinkage / length after shrinkage) −1] × 100

[Other additives]
You may add another additive to the copolymer in this embodiment. Examples of the additives include, but are not limited to, antioxidants such as hindered phenolic antioxidants and / or phosphorus antioxidants, and preferably hindered phenolic antioxidants. .

  Although it does not specifically limit as a hindered phenolic antioxidant, As a specific example, pentaerythritol tetrakis (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate), thiodiethylene-bis (3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate), octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, N, N′-hexane -1,6-diylbis (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionamide), diethyl ((3,5-bis (1,1-dimethylethyl) -4-hydroxyphenyl) Methyl) phosphate, 3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-t-butyl-a, a ′, a ″-(mesitylene-2,4 6-triyl) tri-p-cresol, ethylenebis (oxyethylene) bis (3- (5-t-butyl-4-hydroxy-m-tolyl) propionate), hexamethylene-bis (3- (3,5- Di-t-butyl-4-hydroxyphenyl) propionate), 1,3,5-tris (3,5-di-t-butyl-4-hydroxybenzyl) -1,3,5-triazine-2,4 6 (1H, 3H, 5H) -trione, 1,3,5-tris ((4-tert-butyl-3-hydroxy-2,6-xylyl) methyl) -1,3,5-triazine-2,4 , 6 (1H, 3H, 5H) -trione, 2,6-di-t-butyl-4- (4,6-bis (octylthio) -1,3,5-triazin-2-ylamino) phenol, 3, 9-bis (2- (3- (3-t- Chill-4-hydroxy-5-methylphenyl) propionyloxy) -1,1-dimethylethyl) -2,4,8,10-spiro (5,5) undecane. These may be used alone or in combination of two or more.

  Moreover, you may use a commercially available phenolic antioxidant as a hindered phenolic antioxidant, Although it does not specifically limit as such a commercially available phenolic antioxidant, As a specific example, Irganox 1010 (Irganox 1010: pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], manufactured by Ciba Specialty Chemicals), Irganox 1076 (Irganox 1076: octadecyl-3- ( 3,5-di-t-butyl-4-hydroxyphenyl) propionate (manufactured by Ciba Specialty Chemicals), Irganox 1330 (3,3 ′, 3 ″, 5,5 ′, 5 ″) -Hexa-t-butyl-a, a ', a' '-( Sicilene-2,4,6-triyl) tri-p-cresol, manufactured by Ciba Specialty Chemicals), Irganox 3114: 1,3,5-tris (3,5-di-t-butyl- 4-hydroxybenzyl) -1,3,5-triazine-2,4,6 (1H, 3H, 5H) -trione, manufactured by Ciba Specialty Chemicals), Irganox 3125 (Irganox 3125, Ciba Specialty) Chemicals), Sumilizer BHT (Sumilizer BHT, manufactured by Sumitomo Chemical), Cyanox 1790 (Cyanox 1790, manufactured by Cytec), Sumilizer GA-80 (Sumizer GA-80, manufactured by Sumitomo Chemical), Sumilizer GS (Sumilizer GS, Sumitomo Chemical) , Bitami E (manufactured by Eisai), and the like. Among these, it is particularly preferable to use Irganox 1010, Irganox 1076, Sumilizer GS, or the like. These may be used alone or in combination of two or more.

  Further, the phosphorus-based antioxidant is not particularly limited, but specific examples include tris (2,4-di-t-butylphenyl) phosphite, bis (2,4-bis (1,1-dimethylethyl). ) -6-methylphenyl) ethyl ester phosphorous acid, tetrakis (2,4-di-t-butylphenyl) (1,1-biphenyl) -4,4′-diylbisphosphonite, bis (2,4 -Di-t-butylphenyl) pentaerythritol diphosphite, bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, bis (2,4-dicumylphenyl) pentaerythritol- Diphosphite, tetrakis (2,4-t-butylphenyl) (1,1-biphenyl) -4,4′-diylbisphosphonite, di-t-butyl-m Cresyl - phosphonite, and the like. These may be used alone or in combination of two or more.

  Furthermore, a commercially available phosphorus antioxidant may be used as the phosphorus antioxidant, and such a commercially available phosphorus antioxidant is not particularly limited, but specific examples thereof include Irgafos 168 (Irgafos 168). : Tris (2,4-di-t-butylphenyl) phosphite, manufactured by Ciba Specialty Chemicals), Irgafos 12 (Irgafos 12: Tris [2-[[2,4,8,10-tetra-t- Butyldibenzo [d, f] [1,3,2] dioxaphosphin-6-yl] oxy] ethyl] amine, manufactured by Ciba Specialty Chemicals, Irgafos 38 (Irgafos 38: Bis (2,4 -Bis (1,1-dimethylethyl) -6-methylphenyl) ethyl ester phosphorous acid, Ciba Specialty Ke Kalz), ADK STAB 329K (ADK STAB 329K, manufactured by Asahi Denka), ADK STAB PEP36 (ADK STAB PEP36, manufactured by Asahi Denka), ADK STAB PEP-8 (ADK STAB PEP-8, manufactured by Asahi Denka), Sandstab P-EPQ (Clariant) Manufactured), Weston 618 (manufactured by Weston 618, manufactured by GE), Weston 619G (manufactured by Weston 619G, manufactured by GE), Ultranox 626 (manufactured by Ultranox 626, manufactured by GE), Sumilizer GP (manufactured by Sumitizer GP, manufactured by Sumitomo Chemical), and the like. These may be used alone or in combination of two or more.

(UV absorber)
The copolymer in the present embodiment may contain an ultraviolet absorber. In particular, when used for optical applications, it preferably has an ultraviolet absorption effect. For example, when used as a retardation film around a liquid crystal display, it can be said that it is particularly preferable to impart an ultraviolet absorption effect.

  Although it does not specifically limit as an ultraviolet absorber, As a specific example, a benzotriazole type compound, a benzotriazine type compound, a benzoate type compound, a benzophenone type compound, an oxybenzophenone type compound, a phenol type compound, an oxazole type compound, a malonic acid ester Compounds, cyanoacrylate compounds, lactone compounds, salicylic acid ester compounds, benzoxazinone compounds, and the like. Among these, benzotriazole compounds and benzotriazine compounds are preferable. These may be used alone or in combination of two or more.

Since the ultraviolet absorber tends to be excellent in moldability, the vapor pressure (P) at 20 ° C. is preferably 1.0 × 10 ⁻⁴ Pa or less, more preferably 1.0 × 10 ⁻⁶ Pa. Or less, more preferably 1.0 × 10 ⁻⁸ Pa or less. In the present specification, “excellent in molding processability” indicates, for example, that the low molecular compound adheres little to the roll during film formation. For example, when a low molecular compound adheres to a roll, the low molecular compound can adhere to the surface of the optical material molded body via the roll. It can be said that it is preferable from a viewpoint of making the external appearance and optical characteristics better. Here, the “low molecular compound” in the present specification refers to, for example, a thermal decomposition product or a volatile matter derived from an ultraviolet absorber.

  Since the ultraviolet absorbent tends to be excellent in moldability, the melting point (Tm) is preferably 80 ° C. or higher, more preferably 130 ° C. or higher, and further preferably 160 ° C. or higher.

  Since the ultraviolet absorbent tends to be excellent in moldability, the weight reduction rate of the ultraviolet absorbent when heated at a rate of 20 ° C./min from 23 ° C. to 260 ° C. is preferably 50% or less, More preferably, it is 15% or less, More preferably, it is 2% or less.

  The retardation film of the present embodiment preferably has a spectral transmittance at 380 nm measured with a spectrophotometer of 5% or less and a spectral transmittance at 400 nm of 65% or more. The lower the spectral transmittance at 380 nm in the ultraviolet region, the lower the deterioration of the polarizer and the liquid crystal element, and the higher the 400 nm spectral transmittance in the visible region, the better the color reproducibility. it can.

  The copolymer in the present embodiment can be mixed with other polymers as long as the effects of the present embodiment are not impaired. Such a polymer is not particularly limited, and specifically, polyolefin resin such as polyethylene and polypropylene, polyamide resin, polyphenylene sulfide resin, polyether ether ketone resin, polyester resin, polysulfone resin, polyphenylene oxide resin, polyimide Examples thereof include thermoplastic resins such as resins, polyetherimide resins, and polyacetals; thermosetting resins such as phenol resins, melamine resins, silicone resins, and epoxy resins.

  Moreover, arbitrary additives can be further mix | blended with the copolymer in this embodiment according to various objectives. The kind of said additive will not be specifically limited if it is generally used for the mixing | blending of resin. Specifically, rubbery polymers; rubber particles having a multilayer structure such as butadiene-based ABS rubber, acrylic, polyolefin-based, silicone-based, and fluorine rubber; inorganic fillers such as silicon dioxide; pigments such as iron oxide; stearin Lubricants such as acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, ethylene bisstearamide; mold release agent; paraffinic process oil, naphthenic process oil, aromatic process oil, paraffin, organic polysiloxane Softeners and plasticizers such as mineral oil, flame retardants, antistatic agents, reinforcing agents such as organic fibers, glass fibers, carbon fibers, and metal whiskers; colorants; other additives or a mixture thereof.

  Hereinafter, although this embodiment is described based on an Example and a comparative example, this embodiment is not limited to the following examples. Each component used in Examples and Comparative Examples is as follows.

[Molecular weight measurement of copolymer]
The weight average molecular weight and molecular weight distribution of the copolymer obtained in each example were measured with the following apparatus and conditions.
Measuring apparatus: Tosoh Corporation gel permeation chromatography (HLC-8320GPC) was used.
Column: One TSK guard column SuperH-H, two TSK gel Super HM-Ms, and one TSK gel Super H 2500 were connected in series in this order. That is, this column was configured so that the high molecular weight component eluted earlier and the low molecular weight component eluted later.
Detector: RI (differential refraction) detector was used.
Detection sensitivity: 3.0 mV / min.
Column temperature: 40 ° C.
Sample: A 20 mL tetrahydrofuran solution of 0.02 g methacrylic resin was used.
Injection volume: 10 μL.
Developing solvent: tetrahydrofuran, flow rate; 0.6 mL / min.
Internal standard: 2,6-di-t-butyl-4-methylphenol (BHT) was added at 0.1 g / L.
Standard sample for calibration curve: The following 10 polymethyl methacrylates (manufactured by Polymer Laboratories; PMMA Calibration Kit M-M-10) having different molecular weights and known monodisperse weight peak molecular weights were used.

Weight peak molecular weight (Mp)
Standard sample 1 1,916,000
Standard sample 2 625,500
Standard sample 3 298,900
Standard sample 4 138,600
Standard sample 5 60,150
Standard sample 6 27,600
Standard sample 7 10,290
Standard sample 85,000
Standard sample 9 2,810
Standard document 10 850

  Under the above conditions, the RI detection intensity with respect to the elution time of the methacrylic resin was measured. The weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the methacrylic resin were determined based on the area area in the GPC elution curve and a calibration curve of a seventh-order approximation.

[Measurement of glass transition temperature of copolymer]
The glass transition temperature (Tg) of the copolymer of each example obtained by polymerization was determined using a differential scanning calorimeter (Diamond DSC, manufactured by PerkinElmer Japan Co., Ltd.) and α-alumina as a reference in a nitrogen gas atmosphere. Based on JIS-K-7121, the sample was calculated by a midpoint method from a DSC curve obtained by heating about 10 mg of a sample from room temperature to 250 ° C. at a rate of temperature increase of 20 ° C./min.

[Molding of press film]
The retardation film obtained in each example was preheated at 260 ° C. under atmospheric pressure for 25 minutes using a vacuum compression molding machine (SFV-30 type, manufactured by Shindo Metal Industries Co., Ltd.), and then under vacuum (about 10 kPa). ), And compressed at 260 ° C. and about 10 MPa for 5 minutes to form a press film.

[Molding of stretched film]
The retardation film obtained in each example was uniaxially stretched at a stretching temperature (Tg + 20) ° C. and a stretching speed of 500 mm / min using an Instron 5t tensile tester to prepare a stretched film. The draw ratio was drawn at 100%.

[Inverse wavelength dispersion measurement of phase difference]
Using a phase difference measuring device (KOBRA-WR, manufactured by Oji Scientific Instruments), the retardation of the stretched film at 23 ° C. was measured in the wavelength range of 400 nm to 800 nm. Here, a value defined by the following equation was adopted as the in-plane retardation (Re).
Re = (nx−ny) × d
(Where nx, ny: in-plane main refractive index, d: thickness)

  The obtained retardation was evaluated in terms of a film thickness of 100 μm. By obtaining Re (450 nm) / Re (550 nm), the reverse wavelength dispersion of the phase difference was evaluated.

[Photoelastic coefficient]
A birefringence measuring apparatus described in Polymer Engineering and Science 1999, 39, 2349-2357 was used. Specifically, the stretched film pulling device (manufactured by Imoto Seisakusho) is placed in the laser beam path, and the birefringence is applied using a RETS-100 manufactured by Otsuka Electronics Co., Ltd. while applying stretching stress at 23 ° C. It measured about the range of wavelength 400nm -800nm by the rotation analyzer method. 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 stretching stress σR, the slope of the straight line was obtained by least square approximation, and the photoelastic coefficient (CR) was calculated. For the calculation, data with an extensional stress between 2.5 MPa ≦ σR ≦ 10 MPa was used.
CR = | Δn | / σR
| Δn | = | nx−ny |
(CR: photoelastic coefficient, σR: stretching stress, | Δn |: absolute value of birefringence, nx: refractive index in the stretching direction, ny: refractive index perpendicular to the stretching direction)

[Measurement of bending strength (evaluation of toughness)]
Various press films obtained by the above press molding were bent 180 ° and tested for bending strength. The following ○ to × were used as judgment criteria.
○: It was not cracked by bending 180 ° twice or more.
(Triangle | delta): It was not cracked by 180 degree | times bending once. It broke by bending twice or more.
X: Cracked by one 180 ° bending.

[Surface pencil hardness]
The measurement was performed according to JIS-K5600 standard for various press films obtained by the above press molding, and used as an index of surface pencil hardness.

[Example 1]
The copolymer contained in the retardation film of Example 1 was produced by a bulk polymerization method. That is, 6 g of ethyl methacrylate (simply indicated as “MMA” in Table 1), 10 g of N-phenylmaleimide (simply indicated as “PMI” in Table 1) and styrene (simply indicated as “St in Table 1) in a test tube. 4 g) was added, 0.02 g of lauroyl peroxide as an initiator and 0.02 g of n-octyl mercaptan as a chain transfer agent were added, and the mixture was allowed to stand at 60 ° C. for about 3 hours for polymerization. The polymerized sample was dissolved in 50 ml tetrahydrofuran, and reprecipitation operation was performed in 2 L methanol. This process was repeated twice to remove residual monomer.

  The resulting resin was press-molded to obtain an unstretched film of about 200 μm. And an unstretched film was cut out so that a width | variety might be set to 50 mm, and it was uniaxially stretched using a tensile tester (between chucks: 50 mm, chuck movement temperature: 500 mm / min), and obtained the uniaxially stretched film. The above evaluation was performed on this oriented film. The evaluation results are shown in Table 1.

[Examples 2-6, Comparative Examples 1-4]
In the composition described in Table 1, a film was prepared in the same manner as in Example 1, and the above evaluation was performed. The results are shown in Table 1. In Examples 5 and 6, N-cyclohexylmaleimide (simply referred to as “CyMI” in Table 1) was used as the B component in the formulation shown in Table 1.

  About Examples 1-6, it had sufficient heat resistance and the phase difference showed the reverse wavelength dispersion which was excellent. Moreover, the balance of a photoelastic coefficient, heat resistance, and surface hardness was also favorable. In Comparative Examples 1 to 4, the phase difference exhibited forward wavelength dispersion, and the balance of heat resistance, photoelastic coefficient, and surface hardness was not preferable.

  The retardation film of the present invention has industrial applicability as a half-wave plate or a quarter-wave plate used as an antireflection film in an organic EL display or the like.

Claims (4)

10-55 mass% of methacrylic monomer units (A) represented by the following formula (1), 40-85 mass% of maleimide monomer units (B) represented by the following formula (2), An aromatic vinyl monomer unit represented by the following formula (3) (C) 5 to 29% by mass, and a copolymer containing:
A retardation film in which retardation values Re (450) and Re (550) measured at wavelengths of 450 nm and 550 nm satisfy the following relational expression.
Re (450) / Re (550) <0.9

(In the formula, R ₁ represents a methyl group. R ₂ 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, or An aryl group having 6 to 14 carbon atoms and having at least one substituent selected from Group A is shown.
Group A: a halogen group, 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 formula, R ₃ represents an alkyl group having 6 to 14 carbon atoms, a cyclic alkyl group having 6 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or at least one substituent selected from the following group B: And an aryl group having 6 to 14 carbon atoms, and R ₄ and R ₅ 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 B: a halogen group, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, an alkyl group having 6 to 14 carbon atoms, and an arylalkyl group having 7 to 14 carbon atoms. )

(Wherein R ₆ and R ₇ may be the same or different and each represents a hydrogen atom, a halogen atom, a hydroxyl group, an alkoxy group, a nitro group, or a linear or branched alkyl group having 1 to 6 carbon atoms. N represents an integer of 0 to 5)   The retardation film according to claim 1, wherein the maleimide monomer (B) contains N-cyclohexylmaleimide and / or N-phenylmaleimide.   The retardation film according to claim 1, wherein the aromatic vinyl monomer unit (C) contains isopropenylbenzene and / or styrene. The retardation film as described in any one of Claims 1-3 whose absolute value of a photoelastic coefficient is 55 * 10 <^-12> Pa < ^{-1 >} or less.