JP2009126911A - Copolymer and retardation film using the copolymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film which shows a negative intrinsic birefringence value and ensures large wavelength dispersion of in-plane retardation, and a copolymer from which such a retardation film is obtained. <P>SOLUTION: The copolymer includes a specific acrylate-based repeating unit, a specific vinyl-based repeating unit and a specific acrylonitrile-based repeating unit, wherein the content ratio of the acrylate-based repeating unit is 1-30 mol% relative to the total amount of repeating units constituting the copolymer, the content ratio of the acrylonitrile-based repeating unit is 10-35 mol% relative to the total amount of the repeating units constituting the copolymer, and the total content ratio of the acrylate-based repeating unit, the vinyl-based repeating unit and the acrylonitrile-based repeating unit is ≥70 mol% relative to the total amount of the repeating units constituting the copolymer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a copolymer and a retardation film using the copolymer.

  As a retardation plate showing a predetermined phase difference for all light in the visible light region, an in-plane intrinsic birefringence value positive optical anisotropic layer and an intrinsic birefringence value negative optical anisotropic layer, A laminated phase difference plate is known that is laminated so that the optical axes thereof are parallel to each other. However, there are relatively few known optical materials having a negative intrinsic birefringence value, and there is a problem that the room for material selection is narrow when the laminated retardation plate is manufactured.

The laminated retardation plate is often produced in order to realize a so-called reverse wavelength dispersion characteristic in which the phase difference on the short wavelength side is small and the phase difference on the long wavelength side is large. Therefore, an optically anisotropic layer having a positive intrinsic birefringence value is required to have a small wavelength dispersion of in-plane retardation in the visible light region, while an optically anisotropic layer having a negative intrinsic birefringence value is What has the same wavelength dispersion is required. Thus, an optical material having a large wavelength dispersion in the visible light region and a negative intrinsic birefringence value is required.
JP 2002-156525 A JP 2006-208604 A

  The present invention has been made to solve the above-described conventional problems, and its purpose is to provide a retardation film exhibiting a negative intrinsic birefringence value and having a large in-plane retardation wavelength dispersion, and such a retardation film. It is in providing the copolymer from which a film is obtained.

ここで、Ｒ_１は、水素原子またはメチル基であり、Ｒ_２は、−Ｏ−ＣＨ_２−ＣＨ_２−Ｏ−または酸素原子である。

ここで、Ｒ_３は、水素原子またはメチル基である。 The copolymer of the present invention comprises an acrylate repeating unit represented by the following general formula (I), a vinyl repeating unit represented by the following general formula (II), and an acrylonitrile repeating unit represented by the following general formula (III). A copolymer containing units, wherein the content of the acrylate repeating unit represented by the general formula (I) is 1 to 30 mol% based on the total amount of the repeating units constituting the copolymer, The content of the acrylonitrile-based repeating unit represented by the formula (III) is 10 to 35 mol% based on the total amount of the repeating units constituting the copolymer, and the general formulas (I), (II) and (III) The total content of the repeating units represented by is 70 mol% or more based on the total amount of the repeating units constituting the copolymer.

Here, R ₁ is a hydrogen atom or a methyl group, and R ₂ is —O—CH ₂ —CH ₂ —O— or an oxygen atom.

Here, R ₃ is a hydrogen atom or a methyl group.

  According to another aspect of the present invention, a retardation film is provided. The retardation film of the present invention is obtained by stretching a polymer film containing the copolymer.

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

  In a preferred embodiment, the retardation film has an in-plane retardation at a wavelength of 480 nm (Re (480)) and an in-plane retardation at a wavelength of 550 nm (Re (550)) of 1.045 <Re (480) / Satisfies the relationship of Re (550).

  In a preferred embodiment, the retardation film exhibits an optical characteristic having a negative intrinsic birefringence value.

  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 negative intrinsic birefringence value is exhibited by stretching a polymer film containing a copolymer containing the repeating units represented by the general formulas (I) to (III) at a predetermined ratio, A retardation film having a large in-plane retardation wavelength dispersion can be obtained.

(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, “nx = nz” includes not only the case where nx and nz are exactly equal, but also the case where nx and nz are substantially equal. In the present specification, “substantially equal” is intended to encompass the case where nx and nz are different within a range that does not have a practical effect on 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、水素原子またはメチル基である。Ｒ_２は、−Ｏ−ＣＨ_２−ＣＨ_２−Ｏ−または酸素原子である。

ここで、Ｒ_３は、水素原子またはメチル基である。 A. Synthesis of Copolymer The copolymer of the present invention comprises an acrylate repeating unit represented by the following general formula (I), a vinyl repeating unit represented by the following general formula (II), and the following general formula (III). Contains the acrylonitrile-based repeating unit represented.

Here, R ₁ is a hydrogen atom or a methyl group. R ₂ is —O—CH ₂ —CH ₂ —O— or an oxygen atom.

Here, R ₃ is a hydrogen atom or a methyl group.

  The content ratio of the acrylate-based repeating unit represented by the general formula (I) is 1 to 30 mol%, preferably 5 to 20 mol%, more preferably, based on the total amount of the repeating units constituting the copolymer. 10 to 15 mol%. If it is such a content rate, the retardation film using the obtained copolymer will be excellent in heat resistance.

  The content ratio of the acrylonitrile-based repeating unit represented by the general formula (III) is 10 to 35 mol%, preferably 15 to 30 mol%, more preferably, based on the total amount of the repeating units constituting the copolymer. It is 20-30 mol%. If it is such a content rate, the retardation film using the obtained copolymer will show an optical characteristic with a negative intrinsic birefringence value as will be described later, and a large wavelength dispersion characteristic. Therefore, when the retardation film and an optical material having a positive intrinsic birefringence value are combined, a laminated retardation plate exhibiting excellent reverse wavelength dispersion characteristics can be obtained. The inverse wavelength dispersion characteristic is a characteristic in which the phase difference on the short wavelength side is small and the phase difference on the long wavelength side is large.

  The contents of the acrylate repeating unit represented by the general formula (I), the vinyl repeating unit represented by the general formula (II), and the acrylonitrile repeating unit represented by the general formula (III) are as follows. The total is 70 mol% or more, preferably 75% or more, and more preferably 80 mol% or more based on the total amount of the repeating units constituting the copolymer.

  The copolymer may further be polymerized by containing other appropriate monomers depending on the purpose. Examples of other monomers include (meth) acrylate monomers and N-vinylcarbazole. Specific examples of the (meth) acrylate monomer include alkyl (meth) acrylates such as methyl (meth) acrylate, and ethylene oxide adducts of methyl (meth) acrylate (for example, trade name “M- 230G "), polypropylene glycol di (meth) acrylate (for example, trade name" FA-P270A "manufactured by Hitachi Chemical Co., Ltd.). When the polymerization is carried out including alkyl (meth) acrylate, the polymerizability can be improved, and a polymer film having a large molecular weight can be obtained. When polymerization is carried out including N-vinylcarbazole, a retardation film having a large wavelength dispersion can be obtained. When polymerization is carried out including an ethylene oxide adduct of methyl (meth) acrylate, a retardation film having excellent flexibility can be obtained. When polymerized by including polypropylene glycol di (meth) acrylate, a retardation film having excellent film strength can be obtained.

  The copolymer can be produced by any appropriate method. As a production method, for example, a polymer obtained by solution polymerization of a monomer represented by the above general formula (I), a monomer represented by the above general formula (III) and a vinyl acetate monomer is obtained. The method of saponifying is mentioned. According to this method, the copolymer having the repeating unit represented by the general formula (II) obtained by saponifying the vinyl acetate repeating unit can be obtained. In addition, the vinyl acetate repeating unit may remain after the saponification reaction. The residual amount of the vinyl acetate repeating unit is preferably 10 mol% or less, more preferably 5 mol% or less, based on the total amount of the copolymer.

B. Method for producing retardation film The retardation film of the present invention is produced by stretching a polymer film containing the above-mentioned copolymer.

  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 compression molding method.

  The polymer film may further contain any appropriate additive. Examples of the additive include an antioxidant, a plasticizer, a heat stabilizer, a light stabilizer, a lubricant, an antioxidant, an ultraviolet absorber, a flame retardant, a colorant, an antistatic agent, a compatibilizing agent, a crosslinking agent, And thickeners. The content of the additive is preferably 0 to 10 mol% with respect to the copolymer.

  Any appropriate stretching method can be adopted as a method of stretching the polymer film. Specific examples of the stretching method 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.

  The temperature at which the polymer film is stretched (stretching temperature) is preferably 80 to 200 ° C, more preferably 90 to 160 ° C, and still more preferably 100 to 140 ° C. If the stretching temperature is lower than 80 ° C, the polymer film may be broken. If the stretching temperature exceeds 200 ° C, the polymer film may start to melt.

  The magnification (drawing ratio) for stretching the polymer film is preferably 1.5 to 5 times, more preferably 1.5 to 3 times. 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 1 to 7 mm / sec, and more preferably 3 to 5 mm / sec.

C. Properties of Retardation Film The retardation film of the present invention has a refractive index distribution of nx = nz> ny. Further, the retardation film preferably exhibits optical characteristics having a negative intrinsic birefringence value. The “intrinsic birefringence value” is a birefringence value (that is, a birefringence value under an ideal alignment condition) when the bond chain (main chain) is fully extended and oriented to an ideal state. “Optical characteristics having a negative intrinsic birefringence value” means that when a polymer film is stretched in one direction, the direction in which the in-plane refractive index increases (the slow axis direction) is substantially the same as the stretching direction. An orthogonal one. Therefore, when the polymer film is uniaxially stretched in the present invention, the slow axis direction of the obtained retardation film is substantially orthogonal to the stretch direction.

  Re (550) of the retardation film is preferably 60 nm or more, more preferably 60 to 200 nm, still more preferably 70 to 160 nm, and particularly preferably 90 to 160 nm.

  The retardation film may have a retardation Rth (590) in the thickness direction when nx and nz are not strictly equal. In this case, Rth (590) is preferably −10 to 10 nm, more preferably −8 to 4 nm, still more preferably −5 to 2 nm, and most preferably −2 to 1 nm.

  The Nz coefficient of the retardation film is preferably −0.2 to 0.2, more preferably −0.1 to 0.1, and particularly preferably −0.06 to 0.05.

  Any appropriate thickness can be adopted as the thickness of the retardation film 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 10 to 200 μm, more preferably 50 to 100 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 is 1.045 <Re (480) / Re (550), and preferably 1.045 <Re (480) / Re (550) ≦. 1.15, more preferably 1.06 <Re (480) / Re (550) ≦ 1.15. The chromatic dispersion Re (550) / Re (650) is preferably 1.045 <Re (550) / Re (650), and more preferably 1.045 <Re (550) / Re (650) ≦ 1.15, more preferably 1.06 <Re (550) / Re (650) ≦ 1.15. By using a retardation film in such a range, when a laminated phase difference plate is produced by combining the retardation film and an optical material having a positive intrinsic birefringence value, a laminated position with excellent reverse wavelength dispersion characteristics is obtained. A phase difference plate can be obtained.

The absolute value C (550) (m ² / N) of the photoelastic coefficient of the retardation film is preferably 30 × 10 ⁻¹² m ² / N or less, and more preferably 20 × 10 ⁻¹² m ² / N. Or less, most preferably −10 × 10 ⁻¹² to 10 × 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 is 80 to 180 ° C, preferably 100 to 160 ° C, and more preferably 110 to 140 ° 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).

Synthesis of copolymer 1
In a 1 L separable flask equipped with a reflux condenser and a stirrer, 65.5 g (11.5 mol%) of dicyclopentanyl methacrylate (manufactured by Hitachi Chemical Co., Ltd., trade name “FA-513M”), 99.5 g of vinyl acetate monomer (45 mol%), N-vinylcarbazole 24.7 g, methyl methacrylate 17.8 g, methyl methacrylate EO adduct (trade name “M-230G” manufactured by Shin-Nakamura Chemical Co., Ltd.) 33.5 g, 2,2′-azobis ( 2.17 g of a 5% toluene solution of 2,4-dimethylvaleronitrile) (trade name “V-65” manufactured by Wako, Inc.) and 32.25 g of t-butanol were added, and the temperature was raised to 90 ° C. while stirring. . Subsequently, 57.8% toluene of methyl methacrylate 17.8 g, acrylonitrile 32.1 g (23.5 mol%), and 2,2′-azobis (2,4-dimethylvaleronitrile) were added to the reaction solution from separate dropping nozzles. The dropwise addition of 7.5 g of solution, 11 g of toluene and 20.9 g of t-butanol was started simultaneously. The dropping was continuously performed, and the dropping speed was kept constant. Each dropping time was 60 minutes for methyl methacrylate and acrylonitrile, 240 minutes for 2,2′-azobis (2,4-dimethylvaleronitrile), t-butanol and toluene. After completion of the dropwise addition of 2,2′-azobis (2,4-dimethylvaleronitrile), the mixture was aged at 110 ° C. for 90 minutes to complete the polymerization. After completion of the polymerization, the polymerization reaction solution was cooled, 49.3 g of a 1.5% methanol solution of sodium hydroxide separately prepared was added dropwise over 10 minutes, and the mixture was stirred at 40 ° C. for 1 hour for saponification. The saponification solution was reprecipitated with a large amount of methanol, and the precipitate was collected by filtration. The filtered product was dried under reduced pressure to obtain 140 g of a pale yellow solid copolymer (a).

Synthesis of copolymer 2
A 1 L separable flask equipped with a reflux condenser and a stirrer was charged with 112 g (15 mol%) of dicyclopentanyl methacrylate, 117 g (40 mol%) of vinyl acetate monomer, 25.5 g of methyl methacrylate, 2,2′-azobis (2, 4.47 g of a 5% toluene solution of 4-dimethylvaleronitrile) and 37.17 g of t-butanol were added, and the temperature was raised to 90 ° C. while stirring. Subsequently, 5.9 g of a 5% toluene solution of 25.5 g of methyl methacrylate, 54 g of acrylonitrile (30 mol%), and 2,2′-azobis (2,4-dimethylvaleronitrile) were added to the reaction solution from separate dropping nozzles. Then, dropwise addition of 11 g of toluene and 20.1 g of t-butanol was started simultaneously. The dropping was continuously performed, and the dropping speed was kept constant. Each dropping time was 60 minutes for methyl methacrylate and acrylonitrile, 240 minutes for 2,2′-azobis (2,4-dimethylvaleronitrile), t-butanol and toluene. After completion of the dropwise addition of 2,2′-azobis (2,4-dimethylvaleronitrile), the mixture was aged at 110 ° C. for 90 minutes to complete the polymerization. After completion of the polymerization, the polymerization reaction solution was cooled, 52.2 g of a 1.5% methanol solution of sodium hydroxide prepared separately was added dropwise over 10 minutes, and the mixture was stirred at 40 ° C. for 1 hour for saponification. The saponification solution was reprecipitated with a large amount of methanol, and the precipitate was collected by filtration. The filtered product was dried under reduced pressure to obtain 165 g of a light yellow solid copolymer (b).

Copolymer synthesis 3
In a 1 L separable flask equipped with a reflux condenser and a stirrer, 73 g (11 mol%) of dicyclopentanyl methacrylate, 143.3 g (55 mol%) of vinyl acetate monomer, 6.0 g of N-vinylcarbazole, 13.6 g of methyl methacrylate. 16 g of a methyl methacrylate EO adduct similar to that used in Example 1, 9.06 g of a 2% toluene solution of 2,2′-azobis (2,4-dimethylvaleronitrile), and 27.3 g of t-butanol were added. The temperature was raised to 90 ° C. with stirring. Subsequently, 13.6 g of methyl methacrylate, 37.6 g of acrylonitrile (23.5 mol%), and 5% toluene of 2,2′-azobis (2,4-dimethylvaleronitrile) were added to the reaction solution from separate dropping nozzles. The dropwise addition of 6.0 g of the solution, 10 g of toluene and 14.7 g of t-butanol was started simultaneously. The dropping was continuously performed, and the dropping speed was kept constant. Each dropping time was 60 minutes for methyl methacrylate and acrylonitrile, 240 minutes for 2,2′-azobis (2,4-dimethylvaleronitrile), t-butanol and toluene. After completion of the dropwise addition of 2,2′-azobis (2,4-dimethylvaleronitrile), the mixture was aged at 110 ° C. for 90 minutes to complete the polymerization. After completion of the polymerization, the polymerization reaction liquid was cooled, and 71.03 g of a 1.5% methanol solution of sodium hydroxide separately prepared was added dropwise over 10 minutes, followed by stirring at 40 ° C. for 1 hour to perform saponification. The saponification solution was reprecipitated with a large amount of methanol, and the precipitate was collected by filtration. The filtered product was dried under reduced pressure to obtain 166 g of a light yellow solid copolymer (c).

Synthesis of copolymer 4
In a 1 L separable flask equipped with a reflux condenser and a stirrer, 114.5 g (15 mol%) of dicyclopentanyl methacrylate, 177.5 g (59.5 mol%) of vinyl acetate monomer, 6.5 g of N-vinylcarbazole, methyl 15.6 g of methacrylate, 10.6 g of methyl methacrylate EO adduct similar to that used in Example 1, polypropylene glycol # 700 diacrylate (manufactured by Hitachi Chemical Co., Ltd., trade name “FA-P270A”) 3.0 g, 2, 9.52 g of a 5% toluene solution of 2′-azobis (2,4-dimethylvaleronitrile) and 42 g of t-butanol were added, and the temperature was raised to 90 ° C. while stirring. Subsequently, 15.6 g of methyl methacrylate, 27.8 g of acrylonitrile (15 mol%), 3.0 g of polypropylene glycol # 700 diacrylate, 2,2′-azobis (2,4- Addition of 7.8 g of a 5% toluene solution of dimethylvaleronitrile), 10 g of toluene, and 14 g of t-butanol was started simultaneously. The dropping was continuously performed, and the dropping speed was kept constant. Each dropping time was 60 minutes for methyl methacrylate, acrylonitrile and polypropylene glycol # 700 diacrylate, 240 minutes for 2,2′-azobis (2,4-dimethylvaleronitrile), t-butanol and toluene. After completion of the dropwise addition of 2,2′-azobis (2,4-dimethylvaleronitrile), the mixture was aged at 110 ° C. for 90 minutes to complete the polymerization. After completion of the polymerization, the polymerization reaction solution was cooled, and 87.9 g of a separately prepared 1.5% methanol solution of sodium hydroxide was added dropwise over 10 minutes, followed by stirring at 40 ° C. for 1 hour for saponification. The saponification solution was reprecipitated with a large amount of methanol, and the precipitate was collected by filtration. The filtered product was dried under reduced pressure to obtain 218 g of a pale yellow solid copolymer (d).

  The copolymer (a) obtained in Example 1 was sandwiched with a polyimide film (trade name “Kapton V”, manufactured by Toray DuPont), and 220 ° C. using a small heat transfer press (manufactured by Toyo Seiki). And hot pressing at 35 MPa. After the pressing, the film was rapidly cooled to room temperature, and then the copolymer pressed with the polyimide film was peeled off to obtain a polymer film formed into a film by pressing. Table 1 shows the film thickness of the obtained polymer film. Next, the obtained polymer film was cut into strips having a width of 80 mm and a length of 120 mm, and uniaxially stretched twice at a stretching speed of 4 mm / sec under a temperature condition of 120 ° C. with a stretching apparatus to obtain a retardation film. Obtained. The properties of the obtained retardation film are shown in Table 1.

  A retardation film was produced under the same conditions and method as in Example 5 except that the draw ratio was 2.5. The properties of the obtained retardation film are shown in Table 1.

  A retardation film was produced under the same conditions and method as in Example 5 except that the draw ratio was set to 3. The properties of the obtained retardation film are shown in Table 1.

  A retardation film was produced under the same conditions and method as in Example 5 except that the copolymer (b) obtained in Example 2 was used and the draw ratio was changed to 2.3 times. The properties of the obtained retardation film are shown in Table 1.

  A retardation film was produced under the same conditions and method as in Example 8 except that the draw ratio was 2.5. The properties of the obtained retardation film are shown in Table 1.

  A retardation film was produced under the same conditions and method as in Example 8, except that the draw ratio was 2.8. The properties of the obtained retardation film are shown in Table 1.

A retardation film was produced under the same conditions and method as in Example 5 except that the copolymer (c) obtained in Example 3 was used and the draw ratio was 1.5 times. The properties of the obtained retardation film are shown in Table 1. The results of ¹ H-NMR measurement of the obtained retardation film are shown in FIG. The ¹ H-NMR spectrum was measured using a deuterated chloroform solution with TMS as an internal standard.

  A retardation film was produced under the same conditions and method as in Example 11 except that the draw ratio was set to 2. The properties of the obtained retardation film are shown in Table 1.

  A retardation film was produced under the same conditions and method as in Example 5 except that the copolymer (d) obtained in Example 4 was used and the draw ratio was changed to 1.8 times. The properties of the obtained retardation film are shown in Table 1.

  A retardation film was produced under the same conditions and method as in Example 13 except that the draw ratio was 2.1 times. The properties of the obtained retardation film are shown in Table 1.

[Comparative Example 1]
Copolymer synthesis 5
In a 1 L separable flask equipped with a reflux condenser and a stirrer, 110 g (15 mol%) of dicyclopentanyl methacrylate, 86 g (30 mol%) of vinyl acetate monomer, 20 g of methyl methacrylate, 2,2,2′-azobis (2,4- A 5% toluene solution of 5% dimethylvaleronitrile) and 36.2 g of t-butanol were added, and the temperature was raised to 90 ° C. while stirring. Subsequently, 30 g of methyl methacrylate, 70.9 g (40 mol%) of acrylonitrile, and 8.0 g of 5% toluene solution of 2,2′-azobis (2,4-dimethylvaleronitrile) were added to the reaction solution from separate dropping nozzles. The dropwise addition of 17.8 g of toluene and 17.8 g of t-butanol was started simultaneously. The dropping was continuously performed, and the dropping speed was kept constant. Each dropping time was 60 minutes for methyl methacrylate and acrylonitrile, 240 minutes for 2,2′-azobis (2,4-dimethylvaleronitrile), t-butanol and toluene. After completion of the dropwise addition of 2,2′-azobis (2,4-dimethylvaleronitrile), the mixture was aged at 110 ° C. for 90 minutes to complete the polymerization. After completion of the polymerization, the polymerization reaction solution was cooled, and separately prepared 25.57 g of a 1.5% methanol solution of sodium hydroxide was added dropwise over 10 minutes, followed by stirring at 40 ° C. for 1 hour to saponify. The saponification solution was reprecipitated with a large amount of methanol, and the precipitate was collected by filtration. The filtered product was dried under reduced pressure to obtain 144 g of a light yellow solid copolymer (e).

[Comparative Example 2]
A retardation film was produced under the same conditions and method as in Example 5 except that the copolymer (e) obtained in Comparative Example 1 was used and the draw ratio was 2.1 times. The properties of the obtained retardation film are shown in Table 1.

[Comparative Example 3]
A retardation film was produced under the same conditions and method as in Comparative Example 2 except that the draw ratio was 2.4 times. The properties of the obtained retardation film are shown in Table 1.

[Comparative Example 4]
A retardation film was produced under the same conditions and method as in Example 5 except that polystyrene was used and the draw ratio was 1.5 times. The properties of the obtained retardation film are shown in Table 1.

[Comparative Example 5]
A retardation film was produced under the same conditions and method as in Comparative Example 4 except that the draw ratio was set to 2. The properties of the obtained retardation film are shown in Table 1.

  As is apparent from the results shown in Table 1, it was confirmed that the retardation film of the present invention is an excellent retardation film having excellent retardation development and large wavelength dispersion. Furthermore, it was confirmed that the retardation film of the present invention functions as a so-called negative A plate that satisfies the relationship represented by nx = nz> ny.

  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.

Is ^{the 1 H-NMR} measurement results of the retardation film obtained in Example 7 of the present invention.

Claims (6)

A copolymer comprising an acrylate repeating unit represented by the following general formula (I), a vinyl repeating unit represented by the following general formula (II), and an acrylonitrile repeating unit represented by the following general formula (III) ,
The content ratio of the acrylate repeating unit represented by the general formula (I) is 1 to 30 mol% with respect to the total amount of the repeating units constituting the copolymer,
The content ratio of the acrylonitrile-based repeating unit represented by the general formula (III) is 10 to 35 mol% with respect to the total amount of the repeating units constituting the copolymer,
The copolymer whose total content rate of the repeating unit represented by this general formula (I), (II) and (III) is 70 mol% or more with respect to the whole quantity of the repeating unit which comprises this copolymer.

Here, R ₁ is a hydrogen atom or a methyl group, and R ₂ is —O—CH ₂ —CH ₂ —O— or an oxygen atom.

Here, R ₃ is a hydrogen atom or a methyl group.   A retardation film obtained by stretching a polymer film containing the copolymer according to claim 1.   The retardation film according to claim 2, wherein the refractive index distribution is nx = nz> ny.   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 1.045 <Re (480) / Re (550). The retardation film according to 2 or 3.   The retardation film according to claim 2, wherein the intrinsic birefringence value exhibits a negative optical characteristic.   A polarizing plate comprising the retardation film according to claim 2 as a polarizer protective film.

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