JP2009162996A - Retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film excelling in phase difference exhibiting efficiency, having a small photoelastic coefficient and low in wavelength dispersion represented by Re(480)/Re(550). <P>SOLUTION: The retardation film is obtained by stretching a polymeric film including a copolymer having certain repetition units and other specific units including a maleimide skeleton having an aromatic ring, wherein the content ratio of the maleimide skeleton having the aromatic ring is 2-30 mol% to the total of all the repetition units of the copolymer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a retardation film.

Conventionally, in a liquid crystal display device, a retardation film is used to compensate for the birefringence of a liquid crystal cell. As a typical retardation film, a stretched film of polycarbonate resin having a large retardation is known (Patent Documents 1 and 2). However, the stretched film of the polycarbonate resin has a drawback that the photoelastic coefficient is large and phase difference unevenness is likely to occur. On the other hand, polymethyl methacrylate is known as a material having a small photoelastic coefficient (Non-patent Document 3). However, even when polymethyl methacrylate is stretched, a desired phase difference cannot be obtained.
JP-A-63-189804 JP-A-1-201608 Chemical Review, No. 39, 1998, published by Academic Publishing Center

  The present invention has been made in order to solve the above-described conventional problems, and the object thereof is excellent in phase difference expression efficiency, a small photoelastic coefficient, and further represented by Re (480) / Re (550). An object of the present invention is to provide a retardation film having a small wavelength dispersion.

ここで、Ｒ_１は、メチル基、エチル基、ｎ−プロピル基またはｉ−プロピル基を表す。

ここで、Ｒ_１は上記一般式（Ｉ）のＲ_１と同様であり、Ｒ_２およびＲ_３は、それぞれ独立に、炭素数１〜４の直鎖状若しくは分鎖状のアルキル基を表し、Ｒ_４は、水素原子を表し、Ｒ_５は、水素原子または炭素数１〜４の直鎖状若しくは分鎖状のアルキル基を表し、Ｒ_３、Ｒ_４およびＲ_５から選ばれる隣り合う２つの基がベンゼン環を形成することによって、ナフチル環を形成してもよく、該ナフチル環は置換基として、炭素数１〜４の直鎖状若しくは分鎖状のアルキル基を有してもよい。 The retardation film of the present invention has a repeating unit represented by the following general formula (I) and a repeating unit represented by the following general formula (II) containing a maleimide skeleton having an aromatic ring, It is obtained by stretching a polymer film containing a copolymer having a maleimide skeleton content of 2-30 mol% with respect to the total of all repeating units of the copolymer.

Here, R ₁ represents a methyl group, an ethyl group, an n-propyl group, or an i-propyl group.

Wherein, R ₁ is the same as R ₁ in formula (I), R ₂ and R ₃ each independently represents a linear or branched alkyl group having 1 to 4 carbon atoms, R ₄ represents a hydrogen atom, R ₅ represents a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, and two adjacent groups selected from R ₃ , R ₄ and R ₅ When the group forms a benzene ring, a naphthyl ring may be formed, and the naphthyl ring may have a linear or branched alkyl group having 1 to 4 carbon atoms as a substituent.

ここで、Ｒ_１、Ｒ_６およびＲ_７は、それぞれ独立に、メチル基、エチル基、ｎ−プロピル基またはｉ−プロピル基を表す。 In a preferred embodiment, the copolymer further has a repeating unit represented by the following general formula (III), and the content ratio of the repeating unit represented by the following general formula (III) is It is more than 0 mol% and 30 mol% or less with respect to the total of the repeating unit represented by (I) and the repeating unit represented by the following general formula (III).

Here, R ₁ , R ₆ and R ₇ each independently represents a methyl group, an ethyl group, an n-propyl group or an i-propyl group.

  In a preferred embodiment, the retardation film has a refractive index profile of nx> ny ≧ nz.

In a preferred embodiment, the retardation film has a photoelastic coefficient of 40 × 10 ⁻¹² m ² / N or less.

  In a preferred embodiment, the retardation film has an in-plane retardation (Re (550)) of 60 nm or more at a wavelength of 550 nm.

  In a preferred embodiment, the retardation film has an in-plane retardation (Re (480)) at a wavelength of 480 nm and an in-plane retardation (Re (550)) at a wavelength of 550 nm, Re (480) / Re (550). <1.01 is satisfied.

  In a preferred embodiment, the retardation film has a thickness of 20 μm to 110 μm.

  According to another aspect of the present invention, a polarizing plate is provided. The polarizing plate of this invention contains the said retardation film as a polarizer protective film.

  According to the present invention, a film is formed using a copolymer having a maleic anhydride-alkyl vinyl ether repeating unit and a repeating unit of an imidized maleic anhydride-alkyl vinyl ether repeating unit having an aromatic ring. It is possible to provide a retardation film that is excellent in expression and has a small photoelastic coefficient and wavelength dispersion.

(Definition of terms and symbols)
Definitions of terms and symbols used herein are as follows:
(1) “nx” is the refractive index in the direction in which the in-plane refractive index is maximum (ie, the slow axis direction), and “ny” is the direction perpendicular to the slow axis in the plane (ie, fast phase). (Nz direction), and “nz” is the refractive index in the thickness direction. For example, “ny = nz” includes not only the case where ny and nz are exactly equal, but also the case where ny and nz are substantially equal. In this specification, “substantially equal” is intended to include the case where ny and nz are different within a range that does not practically affect the optical properties of the film.
(2) In-plane retardation Re (λ)
The in-plane retardation Re (λ) refers to an in-plane retardation value at 23 ° C. and a wavelength λ nm. Re is obtained by Re = (nx−ny) × d, where d (nm) is the thickness of the film.
(3) Thickness direction retardation Rth (λ)
The thickness direction retardation Rth (λ) refers to the thickness direction retardation value at 23 ° C. and the wavelength λ nm. Rth is determined by Rth = (nx−nz) × d, where d (nm) is the thickness of the film.
(4) Nz coefficient The Nz coefficient is obtained by Nz = Rth / Re.

ここで、Ｒ_１は、メチル基、エチル基、ｎ−プロピル基またはｉ−プロピル基であり、好ましくはメチル基である。

ここで、Ｒ_１は上記一般式（Ｉ）のＲ_１と同様である。Ｒ_２およびＲ_３は、それぞれ独立に、炭素数１〜４の直鎖状若しくは分鎖状のアルキル基であり、好ましくはメチル基またはエチル基である。Ｒ_２およびＲ_３が上記置換基を有することで、立体障害による反発力により、上記一般式（ＩＩ）で表される繰り返し単位を後述の好適な立体配置とすることができる。Ｒ_４は、水素原子を表す。Ｒ_５は、水素原子または炭素数１〜４の直鎖状若しくは分鎖状のアルキル基であり、好ましくはメチル基、エチル基または水素原子である。さらに好ましくはＲ_３、Ｒ_４およびＲ_５から選ばれる隣り合う２つの基がベンゼン環を形成することによって、ナフチル環を形成する。該ナフチル環は置換基として、炭素数１〜４の直鎖状若しくは分鎖状のアルキル基を有してもよい。なお、芳香環が３以上になると、可視光領域にまで吸収端波長が伸び、共重合体の着色が生じるため、好ましくない。 A. Retardation Film Material The retardation film of the present invention is a copolymer having a repeating unit represented by the following general formula (I) and a repeating unit represented by the following general formula (II) containing a maleimide skeleton having an aromatic ring. It is obtained by stretching a polymer film containing a coalescence.

Here, R ₁ is a methyl group, an ethyl group, an n-propyl group or an i-propyl group, preferably a methyl group.

Wherein, _{R 1} is the same as _{R 1} in formula (I). R ₂ and R ₃ are each independently a linear or branched alkyl group having 1 to 4 carbon atoms, preferably a methyl group or an ethyl group. When R ₂ and R ₃ have the above substituent, the repeating unit represented by the general formula (II) can be in a suitable configuration described later due to repulsive force due to steric hindrance. R ₄ represents a hydrogen atom. R ₅ is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, preferably a methyl group, an ethyl group or a hydrogen atom. More preferably, two adjacent groups selected from R ₃ , R ₄ and R ₅ form a benzene ring to form a naphthyl ring. The naphthyl ring may have a linear or branched alkyl group having 1 to 4 carbon atoms as a substituent. When the aromatic ring is 3 or more, the absorption edge wavelength extends to the visible light region and the copolymer is colored, which is not preferable.

  The aromatic ring is preferably arranged orthogonal to the main chain of the copolymer. In the present specification, the orthogonal arrangement means an arrangement in which the plane of the aromatic ring is substantially orthogonal to the main chain direction of the copolymer. If it is set as the said orthogonal arrangement | positioning, the retardation film which has the characteristic excellent in both retardation development and wavelength dispersion can be obtained. More specifically, when an aromatic ring is introduced into the copolymer, an effect that the wavelength dispersion of the obtained retardation film can be reduced can be obtained, while the problem that the retardation is reduced is the above orthogonal arrangement. Thus, a larger retardation development property can be obtained, so that a retardation film with a small wavelength dispersion can be obtained while ensuring a sufficient retardation development property.

  The content ratio of the maleimide skeleton having an aromatic ring is preferably 2 to 30 mol%, more preferably 3 to 20 mol%, based on the total of all repeating units of the copolymer. If a copolymer in such a range is used, a retardation film having excellent retardation development and small wavelength dispersion can be obtained.

ここで、Ｒ_１およびＲ_２は、上記一般式（ＩＩ)のＲ_１およびＲ_２と同様である。Ｒ_８は、水素原子または炭素数１〜４の直鎖状若しくは分鎖状のアルキル基であり、好ましくはメチル基またはエチル基である。Ｒ_２およびＲ_８をこのような置換基とすることで、芳香環が共重合体の主鎖に対して上記直交配置をとることができる。 The copolymer having a repeating unit represented by the general formula (II) preferably has a repeating unit represented by the following general formula (IV). If a copolymer having such a repeating unit is used, the effect of reducing the wavelength dispersion can be maximized. Therefore, the wavelength dispersion is small even with a small amount of maleimide skeleton having an aromatic ring, and the aromatic ring has an aromatic ring. Since the amount of the maleimide skeleton is small, a retardation film having excellent retardation can be obtained.

Wherein, _{R 1} and _{R 2} are the same as _{R 1} and _{R 2} in the general formula (II). R ₈ is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, preferably a methyl group or an ethyl group. By using R ₂ and R ₈ as such substituents, the aromatic ring can take the above-described orthogonal configuration with respect to the main chain of the copolymer.

  The content ratio of the repeating unit represented by the general formula (IV) is preferably 80 to 100 mol%, more preferably 90 to 100 mol%, more preferably 95 in the repeating unit represented by the general formula (II). ˜100 mol%, most preferably 100 mol%.

ここで、Ｒ_１は上記化学式（Ｉ）のＲ_１と同様である。Ｒ_６およびＲ_７は、それぞれ独立に、メチル基、エチル基、ｎ−プロピル基またはｉ−プロピル基であり、好ましくはメチル基またはエチル基である。好ましくは、上記一般式（ＩＩ）のＲ_６およびＲ_７は同一であり、好ましくは共にメチル基またはエチル基である。 In the copolymer, the maleic anhydride moiety of the repeating unit represented by the general formula (I) may be ring-opened. That is, the copolymer may have a repeating unit represented by the general formula (I), a repeating unit represented by the general formula (II), and a repeating unit represented by the following general formula (III). . By using such a polymer film containing a copolymer, in addition to the properties of excellent retardation development, small photoelastic coefficient and small wavelength dispersion, a retardation film having excellent moisture resistance is obtained. be able to.

Wherein, _{R 1} is the same as _{R 1} of Formula (I). R ₆ and R ₇ are each independently a methyl group, an ethyl group, an n-propyl group or an i-propyl group, preferably a methyl group or an ethyl group. Preferably, R ₆ and R _{7 in} the general formula (II) are the same, and preferably both are a methyl group or an ethyl group.

  The content ratio of the repeating unit represented by the general formula (III) is 0 mol with respect to the total amount of the repeating unit represented by the general formula (I) and the repeating unit represented by the general formula (III). % To 30 mol% or less, preferably more than 0 mol% to 25 mol% or less, more preferably more than 0 mol% to 20 mol% or less. When the copolymer is a copolymer containing more than 30 mol% of the repeating unit represented by the general formula (III), the glass transition temperature of the obtained retardation film is 100 ° C. or less, which may be inferior in heat resistance.

  The copolymer having a repeating unit represented by the general formula (I) can be produced by any appropriate method. Examples of the production method include solution polymerization of maleic anhydride and alkyl vinyl ether. A commercial product may be used as the copolymer having the repeating unit represented by the general formula (I). Specific examples of commercially available products include “GANTRETZ AN-149” manufactured by International Specialty Products, which is a maleic anhydride-methyl vinyl ether copolymer.

  The copolymer having the repeating unit represented by the general formula (I) and the repeating unit represented by the general formula (II) can be produced by any appropriate method. Examples of the production method include a method in which a copolymer having a repeating unit represented by the above general formula (I) is reacted with an aromatic compound having an amino group in the presence of an acid catalyst. The aromatic compound having an amino group preferably has a linear or branched alkyl group having 1 to 4 carbon atoms at least in the ortho position, and more preferably has a methyl group or an ethyl group in at least the ortho position. . When the alkyl group is a substituent having 5 or more carbon atoms, the reactivity when introducing the aromatic compound having the amino group into the copolymer having the repeating unit represented by the general formula (I) is poor, It is not preferable. In addition, also when the said copolymer has a repeating unit represented by the said general formula (IV), it can be manufactured by this manufacturing method.

  The copolymer further having the repeating unit represented by the general formula (III) can be produced by ring-opening (esterification) the maleic acid site of the repeating unit represented by the general formula (I). . Specifically, after the copolymer having the repeating unit represented by the general formula (I) is dissolved in an organic solvent, an alkyl alcohol is added and refluxed at 60 to 65 ° C. Specific examples of the alkyl alcohol include methanol, ethanol, 1-propanol, and 2-propanol. By adjusting the addition amount of the alkyl alcohol, the degree of ring opening of the maleic acid moiety of the copolymer having the repeating unit represented by the general formula (I), that is, the repeating represented by the general formula (I) The content ratio of the unit and the repeating unit represented by the general formula (III) can be controlled. The amount of the alkyl alcohol added is preferably 30 mol% or less, more preferably 25 mol% or less, and most preferably based on the maleic anhydride moiety of the copolymer having a repeating unit represented by the general formula (I). Is 20 mol% or less. When the addition amount is in such a range, a retardation film can be obtained which is easy to produce a retardation, excellent in heat resistance, small in retardation change due to heat, and excellent in moisture resistance.

  The polymer film can be produced by any suitable forming method. Specific examples include compression molding method, transfer molding method, injection molding method, extrusion molding method, blow molding method, powder molding method, FRP molding method, casting method and the like. The copolymer is preferably formed into a sheet by a casting method. This is because the smoothness of the resulting film can be improved and good optical uniformity can be obtained.

  The thickness of the polymer film is preferably 40 μm to 170 μm, more preferably 60 μm to 130 μm, and more preferably 70 μm to 120 μm.

B. Method for producing retardation film The retardation film of the present invention can be produced by stretching the polymer film. Specific examples include lateral uniaxial stretching, free end uniaxial stretching, fixed end biaxial stretching, fixed end uniaxial stretching, and sequential biaxial stretching. Preferably, it is free end uniaxial stretching. In addition, when uniaxial stretching is performed in the present invention, the slow axis direction of the obtained retardation film is the same as the stretching direction.

  The temperature at which the polymer film is stretched (stretching temperature) is preferably 100 ° C to 230 ° C, more preferably 110 ° C to 210 ° C, and still more preferably 115 ° C to 190 ° C. If the stretching temperature is lower than 100 ° C, the polymer film may be broken. If the stretching temperature exceeds 230 ° C, the polymer film may start to melt.

  The magnification (drawing ratio) for stretching the polymer film is preferably 1.5 times or more and 5 times or less, and more preferably 1.5 times or more and 3 times or less. If it is less than 1.5 times, the retardation development property may be deteriorated, and if it exceeds 5 times, the polymer film may be broken.

  The speed at which the polymer film is stretched (stretching speed) is preferably 3 to 9 mm / sec, and more preferably 5 to 7 mm / sec.

C. Properties of Retardation Film The retardation film of the present invention has a refractive index distribution of nx> ny ≧ nz. That is, the retardation film has a refractive index distribution of nx> ny = nz in one embodiment, and a refractive index distribution of nx>ny> nz in another embodiment.

  When the refractive index distribution of the retardation film of the present invention satisfies nx> ny = nz, the Nz coefficient of the retardation film is more than 0.9 and less than 1.1. When the refractive index distribution satisfies nx> ny> nz, the Nz coefficient of the retardation film is preferably 1.1 to 3.0, more preferably 1.1 to 2.0, and particularly preferably. Is 1.1 to 1.7, most preferably 1.1 to 1.5.

  When the refractive index distribution of the retardation film of the present invention satisfies nx> ny = nz, Re (550) of the retardation film is preferably 60 nm or more, more preferably 60 to 200 nm, and further preferably 70. It is -160 nm, Most preferably, it is 90-140 nm. The Rth (550) of the retardation film is substantially equal to Re (550).

  When the refractive index distribution of the retardation film of the present invention satisfies nx> ny> nz, Re (550) of the retardation film is preferably 60 nm or more, more preferably 60 to 200 nm, and further preferably 70. It is -160 nm, Most preferably, it is 90-140 nm.

  When the refractive index distribution of the retardation film of the present invention satisfies nx> ny> nz, Rth (550) of the retardation film is preferably 60 nm or more, more preferably 75 to 250 nm, and further preferably 90. It is -200 nm, Most preferably, it is 110-175 nm.

  Any appropriate thickness can be adopted as the thickness of the retardation film of the present invention as long as the effects of the present invention are exhibited. Typically, the thickness can vary depending on the desired phase difference. Specifically, the thickness is preferably 20 μm to 110 μm, more preferably 30 μm to 90 μm, and particularly preferably 50 μm to 70 μm. Since the retardation film of the present invention is excellent in retardation development property, a desired retardation can be obtained even when such a thin retardation film is used, and it is suitable for a liquid crystal display device that is desired to be thin. It can be a phase difference film.

  The wavelength dispersion Re (480) / Re (550) of the retardation film of the present invention is Re (480) / Re (550) <1.01, preferably 0.8 ≦ Re (480) / Re (550). ) <1.01. The chromatic dispersion Re (550) / Re (650) is Re (550) / Re (650) <1.011, and preferably 0.8 ≦ Re (550) / Re (650) <1.011. It is. By using the retardation film in such a range, a liquid crystal display device excellent in color display can be provided.

The absolute value C (550) (m ² / N) of the photoelastic coefficient of the retardation film of the present invention is preferably 40 × 10 ⁻¹² m ² / N or less, more preferably 30 × 10 ⁻¹² m ^2. / N or less, and most preferably 2 × 10 ^{−12 to} 20 × 10 ⁻¹² m ² / N. By using the retardation film in such a range, an image display device free from display unevenness due to the heat of the backlight can be obtained.

  The glass transition temperature of the retardation film of the present invention is preferably 120 ° C to 200 ° C, more preferably 130 ° C to 180 ° C, and more preferably 135 ° C to 160 ° C. The retardation film of the present invention thus has a high glass transition temperature, excellent heat resistance, and can withstand use in a high temperature environment.

D. Polarizing plate The polarizing plate of the present invention comprises the retardation film of the present invention as a polarizer protective film. Preferably, the polarizing plate includes a polarizer formed from a polyvinyl alcohol-based resin and the retardation film of the present invention, and the polarizer is bonded to the retardation film via an adhesive layer.

  Any suitable polarizer may be used as long as it converts natural light or polarized light into linearly polarized light. The polarizer is preferably a stretched film mainly composed of a polyvinyl alcohol resin containing iodine or a dichroic dye. The thickness of the polarizer is usually 5 μm to 50 μm.

  Any appropriate adhesive layer can be selected as long as it joins the surfaces of adjacent members and integrates them with practically sufficient adhesive force and adhesion time. Examples of the material for forming the adhesive layer include an adhesive, a pressure-sensitive adhesive, and an anchor coating agent. The adhesive layer may have a multilayer structure in which an anchor coat agent layer is formed on the surface of the adherend, and an adhesive layer or a pressure-sensitive adhesive layer is formed on the anchor coat agent layer. It may be a thin layer (also called a hairline). The adhesive layer disposed on one side of the polarizer and the adhesive layer disposed on the other side may be the same or different.

  The angle at which the polarizer and the retardation film are attached to the polarizing plate can be appropriately set according to the purpose. For example, when the polarizing plate is used as a circular polarizing plate, the angle formed by the absorption axis direction of the polarizer and the slow axis direction of the retardation film is preferably 25 ° to 65 °, Preferably it is 35 degrees-55 degrees. The in-plane retardation of the retardation film when used as a circularly polarizing plate is preferably about 1/4 of the wavelength of visible light. When used as a viewing angle widening film, in the polarizing plate, the angle formed by the absorption axis direction of the polarizer and the slow axis direction of the retardation film is substantially parallel or substantially orthogonal. In this specification, “substantially parallel” includes an angle formed by the absorption axis direction of the polarizer and the slow axis direction of the retardation film in a range of 0 ° ± 10 °, preferably 0 ° ± 5 °. “Substantially orthogonal” means that the angle between the absorption axis direction of the polarizer and the slow axis direction of the retardation film includes a range of 90 ° ± 10 °, preferably 90 ° ± 5 °. .

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. Evaluation was performed as follows.

(1) Phase difference values (Re, Rth):
Refractive indexes nx, ny and nz of the retardation film are measured by an automatic birefringence measuring device (manufactured by Oji Scientific Instruments Co., Ltd., automatic birefringence meter KOBRA-WPR), and in-plane retardation Re and thickness direction retardation Rth are measured. Calculated. The measurement temperature was 23 ° C. and the measurement wavelength was 550 nm. The wavelength dispersion characteristics were measured at 480, 550 and 650 nm.
(2) Measuring method of absolute value (C (550)) of photoelastic coefficient:
Using a spectroscopic ellipsometer [product name “M-220” manufactured by JASCO Corporation], the sample (size 2 cm × 10 cm) is sandwiched at both ends and stress (5 to 15 N) is applied to the phase difference in the center of the sample. The value (23 ° C./wavelength 590 nm) was measured and calculated from the slope of the function of stress and retardation value.
(3) Glass transition temperature:
Using a differential scanning calorimeter [product name “DSC-6200” manufactured by Seiko Instrument Co., Ltd.], it was determined by a method according to JIS K 7121 (1987) (measurement method of plastic transition temperature). Specifically, a 3 mg powder sample was heated twice (heating rate: 10 ° C./min) in a nitrogen atmosphere (gas flow rate: 80 ml / min) and measured twice, and the second data was adopted. The calorimeter corrected the temperature using a standard material (indium).

Reference Example 1 Preparation of Maleic Anhydride-Methyl Vinyl Ether Copolymer As raw materials, 37.6 g maleic anhydride, 24 g methyl vinyl ether, 0.96 g lauryl peroxide and 560 g benzene were prepared. 37.6 g of maleic anhydride and 496 g of benzene were placed in a 1 L reactor equipped with a stirrer, a reflux condenser and an internal temperature adjusting device to prepare a benzene solution of maleic anhydride. Thereafter, the internal temperature was raised to 80 ° C., and while maintaining the temperature at 80 ° C., 0.8 g of methyl vinyl ether was continuously fed from the bottom of the reactor over 10 minutes with stirring to obtain maleic anhydride and methyl vinyl ether. A homogeneous benzene solution was prepared. Subsequently, a polymerization initiator solution in which 0.96 g of lauryl peroxide was dissolved in 64 g of benzene was continuously added over 5 hours from the other supply port of the reaction can while supplying the above methyl vinyl ether in the same manner and speed. Supplied. After the supply of methyl vinyl ether and the polymerization initiator solution was completed, the mixture was left for another 1 hour while maintaining the state, and then cooled to complete the reaction. The reaction solution was desolvated using a centrifuge and a drier to obtain 30.8 g of a white powder.

[Reference Example 2]: Preparation of Imidized Maleic Anhydride-Methyl Vinyl Ether Copolymer A 15 wt% cyclopentanone solution of 60 g of maleic anhydride-methyl vinyl ether copolymer obtained in Reference Example 1 was prepared. 1-Amino-2-methyl-naphthalene (2 g) was added and stirred at 70 ° C. for 1.5 hours. Subsequently, 1.2 g of p-toluenesulfonic acid hydrate and 7 g of N-methylpyrrolidone were added, and water formed together with cyclopentanone evaporated while heating and stirring at 145 ° C. was distilled off. After stirring with heating at 145 ° C. for 4 hours, the reaction was terminated, cooled to room temperature, and purified by reprecipitation with methanol. The precipitate was collected by filtration and dried to obtain 55 g of an extremely thin brownish resin solid (a).

[Reference Example 3]
A 15 wt% cyclopentanone solution of 60 g of maleic anhydride-methyl vinyl ether copolymer obtained in Reference Example 1 was prepared, and 3.5 g of 1-amino-2-methyl-naphthalene was added thereto, Stir for 1.5 hours. Subsequently, 2.1 g of p-toluenesulfonic acid hydrate and 12.3 g of N-methylpyrrolidone were added, and water formed together with cyclopentanone evaporated while heating and stirring at 145 ° C. was distilled off. After stirring with heating at 145 ° C. for 4 hours, the reaction was terminated, cooled to room temperature, and purified by reprecipitation with methanol. The precipitate was collected by filtration and dried to obtain 54 g of an extremely thin brownish resin solid (b).

[Reference Example 4]
A 15 wt% cyclopentanone solution of 60 g of maleic anhydride-methyl vinyl ether copolymer obtained in Reference Example 1 was prepared, 0.5 g of 1-amino-2-methyl-naphthalene was added thereto, Stir for 1.5 hours. Subsequently, 0.6 g of p-toluenesulfonic acid hydrate and 3.5 g of N-methylpyrrolidone were added, and water formed together with cyclopentanone evaporated while heating and stirring at 145 ° C. was distilled off. After stirring with heating at 145 ° C. for 4 hours, the reaction was terminated, cooled to room temperature, and purified by reprecipitation with methanol. The precipitate was collected by filtration and dried to obtain 51 g of an extremely thin brownish resin solid (c).

  An acetone solution containing 10% by weight of the resin solid (a) obtained in Reference Example 2 was prepared and supplied onto a glass plate by a casting method, followed by natural drying for 0.5 hours. Thereafter, the obtained film was peeled off from the glass plate and dried by a hot oven at 70 ° C. until the acetone concentration became 3% or less to obtain a polymer film. The thickness of the obtained polymer film was 85 μm. The obtained polymer film was cut into strips having a width of 80 mm and a length of 120 mm, and the free end was uniaxially stretched twice at a stretching temperature of 140 ° C. and a tensile speed of 6 mm / sec in the length direction using a stretching device, A retardation film A was obtained. The properties of the retardation film A are shown in Table 1.

  A retardation film B was produced under the same conditions and method as in Example 1 except that the resin solid was obtained as the resin solid (b) obtained in Reference Example 3. The properties of the retardation film B are shown in Table 1.

[Comparative Example 1]
A retardation film C was produced under the same conditions and method as in Example 1 except that the resin solid was obtained as the resin solid (c) obtained in Reference Example 4. The properties of the retardation film C are shown in Table 1.

  As is clear from the results shown in Table 1, it is confirmed that the retardation film of the present invention has excellent retardation development and small wavelength dispersion represented by Re (480) / Re (550). It was done. Moreover, since the absolute value (C (550)) of the photoelastic coefficient of the said polymer film is small, the obtained retardation film has small retardation unevenness. Furthermore, it was confirmed that the retardation film of the present invention functions as a so-called positive A plate that satisfies the relationship represented by nx> ny = nz.

  The retardation film of the present invention can be suitably used for various image display devices (liquid crystal display devices, organic EL display devices, PDPs, etc.). More specifically, it can be used as a λ / 4 plate, a λ / 2 plate, a viewing angle widening film, an antireflection film for a flat panel display, and a polarizer protective film of a liquid crystal display device.

Claims (8)

The repeating unit represented by the following general formula (I) and the repeating unit represented by the following general formula (II) including the maleimide skeleton having an aromatic ring, and the content ratio of the maleimide skeleton having the aromatic ring are the same. Retardation film obtained by stretching a polymer film containing a copolymer, which is 2 to 30 mol% based on the total of all repeating units of the polymer

Here, R ₁ represents a methyl group, an ethyl group, an n-propyl group or an i-propyl group,

Wherein, R ₁ is the same as R ₁ in formula (I), R ₂ and R ₃ each independently represents a linear or branched alkyl group having 1 to 4 carbon atoms, R ₄ represents a hydrogen atom, R ₅ represents a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, and two adjacent groups selected from R ₃ , R ₄ and R ₅ When the group forms a benzene ring, a naphthyl ring may be formed, and the naphthyl ring may have a linear or branched alkyl group having 1 to 4 carbon atoms as a substituent. The copolymer further has a repeating unit represented by the following general formula (III), and a content ratio of the repeating unit represented by the following general formula (III) is represented by the general formula (I). The retardation film according to claim 1, wherein the content is greater than 0 mol% and 30 mol% or less with respect to the total of the repeating units represented by formula (III) below.

Here, R ₁ , R ₆ and R ₇ each independently represents a methyl group, an ethyl group, an n-propyl group or an i-propyl group.   The retardation film according to claim 1, wherein the refractive index distribution is nx> ny ≧ nz. The retardation film in any one of Claim 1 to 3 whose photoelastic coefficient is 40 * 10 < ^-12 > m < ² > / N or less.   The retardation film in any one of Claim 1 to 4 whose in-plane phase difference (Re (550)) in wavelength 550nm is 60 nm or more.   The in-plane retardation at a wavelength of 480 nm (Re (480)) and the in-plane retardation at a wavelength of 550 nm (Re (550)) satisfy a relationship of Re (480) / Re (550) <1.01. The retardation film according to any one of 1 to 5.   The retardation film according to claim 1, wherein the thickness is 20 μm to 110 μm. A polarizing plate comprising the retardation film according to claim 1 as a polarizer protective film.