JP2007263993A - Optical molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical molding having low photo-elastic birefringence, favorable transparency/hue/strength and showing negative orientation birefringence when it is stretched and oriented. <P>SOLUTION: The optical molding is obtained by molding a resin composition containing the following copolymer (A) and showing a melt mass flow rate (MFR) of 0.1 to 3 g/10 minutes measured at 200°C under 49 N load based on JIS K7210. The copolymer (A) is a styrene-(meth)acrylate copolymer having styrene monomer units of 70 to 10 mass% and (meth)acrylate monomer units of 30 to 90 mass% in the ratio of structural monomers. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an optical molded body.

In recent years, thin liquid crystal display elements, electroluminescence elements, and the like, which replace CRT-type television monitors, have been developed, and optical components based on transparent resin materials are frequently used in terms of lightness, productivity, and cost.

Although methacrylic resins are widely used in this field, methacrylic resins have good optical properties such as transparency and low birefringence, but problems such as being unable to be wound into a roll due to low strength for film applications. was there. On the other hand, a film of triacetyl cellulose (hereinafter referred to as “TAC”) has been widely used for optical film applications. However, since a TAC film is produced by a solution casting method, production cost is high, and the appearance of an inexpensive optical film is desired. ing.
Recently, there has been a demand for an optical film having low photoelastic birefringence that does not generate birefringence due to external stress.
In addition, only films with positive orientation birefringence made of polycarbonate or amorphous cyclic polyolefin have been used for retardation films, but by using both films with positive and negative orientation birefringence. In order to simplify the process and improve productivity, the appearance of an optical film exhibiting negative orientation birefringence is awaited. On the other hand, as an optical film showing negative orientation birefringence, for example, the following are known, but have not yet been put into practical use due to problems of hue and cost.
JP 2004-315788 A

An object of the present invention is to provide an optical molded article having low photoelastic birefringence, good transparency, hue and strength, and exhibiting negative orientation birefringence when stretched and oriented.

That is, the present invention
(1) A resin composition containing the following copolymer (A), which has a melt mass flow rate (MFR) of 0.1 to 3 g / 10 min measured at a temperature of 200 ° C. and a load of 49 N based on JIS K7210. A molded article for optics, which is obtained by molding a resin composition. Copolymer (A): Styrene- (meth) acrylic acid ester copolymer, in which the ratio of constituting monomers is 70 to 10% by mass of a styrene monomer unit, (meth) acrylic acid ester The copolymer which is 30-90 mass% of monomer units.
(2) The optical composition according to (1), wherein the resin composition comprises 99.9 to 90 parts by mass of the copolymer (A) and 0.1 to 10 parts by mass of a butadiene copolymer. Molded body.
(3) The optical system as described in (1) or (2), wherein the butadiene-based copolymer is composed of one or more selected from the following butadiene-based copolymers (B) and (C). Molded body.
Copolymer (B): Styrene-butadiene block copolymer, the ratio of the monomer units constituting the styrene monomer units is 50 to 20% by mass, and the butadiene monomer units are 50 to 80% by mass. % Copolymer. However, the absolute value of the refractive index difference between the copolymer (A) and the copolymer (B) is 0.005 or less.
Copolymer (C): a copolymer obtained by polymerizing a styrene monomer and a (meth) acrylic acid ester monomer in the presence of a butadiene rubber, and constituting monomer units The copolymer resin whose ratio is 35-55 mass% of styrene monomer units, 5-15 mass% of butadiene monomer units, and 60-30 mass% of (meth) acrylic acid ester monomer units. However, the absolute value of the refractive index difference between the copolymer (A) and the copolymer (C) is 0.005 or less.
(4) The resin composition is selected from a hindered phenol compound, a lactone compound, a phosphorus compound, and a sulfur compound with respect to a total of 100 parts by mass of the copolymers (A) to (C). The optical molded body according to any one of (1) to (3), which contains 0.01 to 2 parts by mass of a heat-resistant stabilizer of one or more species.
(5) The optical molded body according to any one of (1) to (4), wherein the optical molded body is an optical film substrate.
(6) The optical molded body according to (5), wherein the optical film substrate has a photoelastic constant of −2 × 10 ⁻¹² to 2 × 10 ⁻¹² / Pa.
(7) The optical molded body according to (5) or (6), which is an optical film using the substrate for optical film.
(8) The optical molded body according to (7), wherein the optical film is a retardation film or an antireflection film.
(9) The optical molded body according to (7) or (8), wherein the optical film is a film subjected to a stretching treatment.
It is.

Since the optical molded body of the present invention has good transparency, hue, strength, and low photoelastic birefringence, a retardation film, a polarizing film protective film, a viewing angle improving film, a polarizing film, an antireflection film, etc. It is suitable and useful as a base film for optical films. When oriented, it exhibits negative orientation birefringence and is particularly useful for retardation films.

The copolymer (A) is a styrene- (meth) acrylic acid ester copolymer, and is mainly composed of styrene monomer units and (meth) acrylic acid ester monomer units. The butadiene-based copolymer is a copolymer containing a butadiene-based monomer unit, and is preferably a copolymer (B) or a copolymer (C). The copolymer (B) is a styrene-butadiene block copolymer and is mainly composed of a styrene monomer unit and a butadiene monomer unit. The copolymer (C) is a copolymer resin obtained by polymerizing a styrene monomer and a (meth) acrylic acid ester monomer in the presence of a butadiene rubber. It is mainly composed of units, butadiene monomer units, and (meth) acrylic acid ester monomer units.

Examples of the styrene monomer unit include units such as styrene, α-methylstyrene, p-methylstyrene, o-methylstyrene, m-methylstyrene, ethylstyrene, and pt-butylstyrene. Styrene is preferred. These styrenic monomer units may be used alone or in combination of two or more.

As the (meth) acrylic acid ester monomer unit, methacrylic acid ester such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-methylhexyl acrylate, Although units such as 2-ethylhexyl acrylate and acrylate esters such as decyl acrylate can be exemplified, methyl methacrylate is preferred. These (meth) acrylate monomer units may be used alone or in combination of two or more.

Examples of butadiene monomer units include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3- Although units such as hexadiene can be mentioned, 1,3-butadiene is preferred. These butadiene monomer units may be used alone or in combination of two or more.

Further, if necessary, a vinyl monomer unit copolymerizable with these monomers, for example, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, N-phenylmaleimide, N-cyclohexylmaleimide, or a copolymer ( It may be included as long as it is less than 10 parts by mass with respect to 100 parts by mass of each copolymer of A), copolymer (B), or copolymer (C).

The copolymer (A) is a copolymer obtained by polymerizing a styrene monomer and a (meth) acrylic acid ester monomer. The polymerization method is not particularly limited, but radical copolymerization using an organic peroxide is preferable, and the production process of the copolymer (A) is preferably a bulk continuous polymerization process using a small amount of solvent. A method obtained by a suspension polymerization or emulsion polymerization process may not provide sufficient transparency.
Examples of the organic peroxide added during polymerization include t-butyl peroxybenzoate, t-butyl peroxy-2-ethylhexanoate, 1,1-bis (t-butylperoxy) -3,3,5- Trimethylcyclohexane, 1,1-bis (t-butylperoxy) -cyclohexane, 2,2-bis (4,4-di-butylperoxycyclohexyl) propane, t-butylperoxyisopropyl monocarbonate, di-t- Known materials such as butyl peroxide, dicumyl peroxide, ethyl-3,3-di- (t-butylperoxy) butyrate can be used. The addition amount of the organic peroxide is preferably 0.001 to 5 parts by mass with respect to 100 parts by mass in total of the styrene monomer and the (meth) acrylic acid ester monomer.
Solvents include aliphatic hydrocarbons such as butane, pentane, hexane, isopentane, heptane, octane and isooctane, alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane and ethylcyclohexane, or benzene and toluene. Aromatic hydrocarbons such as ethylbenzene and xylene can be used, and the addition amount of the solvent is 5 to 20 parts by mass with respect to 100 parts by mass in total of the styrene monomer and the (meth) acrylic acid ester monomer. preferable.
Further, a known molecular weight modifier such as 4-methyl-2,4-diphenylpentene-1, t-dodecyl mercaptan, n-dodecyl mercaptan may be added during the polymerization.
The polymerization temperature is preferably 80 to 170 ° C, more preferably 100 to 160 ° C.

The ratio of the monomer unit which comprises a copolymer (A) is 70-10 mass% of styrene-type monomer units, and 30-90 mass% of (meth) acrylic acid ester-type monomer units. Preferably 60-20% by mass of styrene monomer units, 40-80% by mass of (meth) acrylic acid ester monomer units, more preferably 58-42% by mass of styrene monomer units, (meth) acrylic. It is 42-58 mass% of acid ester type monomer units.
When the ratio of the monomer unit constituting the copolymer (A) exceeds 70% by mass of the styrene monomer unit and is less than 10% by mass of the (meth) acrylate monomer unit, the photoelasticity This is not preferable because the absolute value of birefringence increases. If the styrene monomer unit is less than 10% by mass and the (meth) acrylate monomer unit is more than 90% by mass, the absolute value of photoelastic birefringence increases and the absolute value of orientation birefringence decreases. Therefore, it is not preferable.

The copolymer (B) is a block copolymer obtained by polymerizing a styrene monomer and a butadiene monomer. The method of polymerization is not particularly limited, but anionic polymerization using an organolithium compound is preferable, and a solution polymerization process using a solvent is preferable as a production process of the copolymer (B).
An organic lithium compound is a compound in which one or more lithium atoms are bonded in the molecule, such as ethyl lithium, n-propyl lithium, isopropyl lithium, n-butyl lithium, sec-butyl lithium, and tert-butyl lithium. A monofunctional organolithium compound or a polyfunctional organolithium compound can be used. The addition amount of the organic lithium compound is preferably 0.001 to 5 parts by mass with respect to 100 parts by mass in total of the styrene monomer and the butadiene monomer.
Solvents include aliphatic hydrocarbons such as butane, pentane, hexane, isopentane, heptane, octane and isooctane, alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane and ethylcyclohexane, or benzene and toluene. Aromatic hydrocarbons such as ethylbenzene and xylene can be used, but the amount of the solvent added is preferably 50 to 200 parts by mass with respect to 100 parts by mass in total of the styrene monomer and the butadiene monomer.
Further, a known randomizing agent such as tetrahydrofuran (THF) may be added during the polymerization.
The polymerization temperature is preferably 40 to 120 ° C, more preferably 50 to 100 ° C.

The copolymer (B) is a block copolymer having a polymer block composed of at least one styrene monomer and a polymer block mainly composed of at least a butadiene monomer. Here, the polymer block mainly composed of a butadiene monomer is a polymer block having a butadiene monomer content of 50% by mass or more, preferably 70% by mass or more. The styrene monomer copolymerized in the polymer block mainly composed of a butadiene monomer may be uniformly distributed in the polymer block or may be distributed in a tapered shape.

The ratio of the monomer units constituting the copolymer (B) is preferably 50 to 20% by mass of styrene monomer units, 50 to 80% by mass of butadiene monomer units, and more preferably styrene monomer units. It is a monomer unit 48-32 mass%, and a butadiene-type monomer unit 52-68 mass%.
When the ratio of the monomer unit constituting the copolymer (B) exceeds 50% by mass of the styrene monomer unit and less than 50% by mass of the butadiene monomer unit, the absolute value of photoelastic birefringence May increase, which may be undesirable. On the other hand, if the styrene monomer unit is less than 20% by mass and the butadiene monomer unit exceeds 80% by mass, the transparency may be lowered, which may not be preferable.

The copolymer (C) is a copolymer resin obtained by polymerizing a styrene monomer and a (meth) acrylic acid ester monomer in the presence of a butadiene rubber. As a method for producing such a ternary resin, a method in which butadiene rubber is continuously bulk polymerized in a state where butadiene rubber is dissolved in a styrene monomer and a (meth) acrylate monomer (hereinafter referred to as continuous bulk). Polymerization method), bulk polymerization with butadiene rubber dissolved in styrene monomer and (meth) acrylate monomer, and suspension polymerization when rubber particles are formed by phase inversion ( There are several methods such as bulk suspension polymerization method) and emulsion graft polymerization method (hereinafter referred to as emulsion polymerization method) while polymerizing styrene monomer and (meth) acrylate monomer on butadiene rubber latex. Although known, a continuous bulk polymerization method is preferred. The bulk suspension polymerization method and emulsion polymerization method do not provide sufficient transparency, and the resulting copolymer resin tends to become turbid, especially when used for a light guide plate with a long optical path, etc. is there.
In the continuous bulk polymerization method, during polymerization, a solvent such as ethylbenzene or toluene is preferably 25 parts by mass or less, more preferably 100 parts by mass or less, based on a total of 100 parts by mass of the styrene monomer and the (meth) acrylate monomer. 5 to 20 parts by mass can be used. The use of a solvent may lower the viscosity during polymerization, improve the polymerization controllability, and may stabilize the physical properties of the resulting copolymer resin.
The polymerization temperature is preferably 80 to 170 ° C, more preferably 100 to 160 ° C.
At the time of polymerization, t-butylperoxybenzoate, t-butylperoxy-2-ethylhexanoate, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1- Bis (t-butylperoxy) -cyclohexane, 2,2-bis (4,4-di-butylperoxycyclohexyl) propane, t-butylperoxyisopropyl monocarbonate, di-t-butyl peroxide, dicumylper It is preferable to add a known polymerization initiator such as oxide, ethyl-3,3-di- (t-butylperoxy) butyrate, and two or more kinds having different half-life temperatures are used from the viewpoint of impact resistance. Further preferred.
The addition amount of the polymerization initiator is preferably 0.005 to 5 parts by mass, more preferably 0.01 to 1 part by mass with respect to 100 parts by mass in total of the styrene monomer and the (meth) acrylic acid ester monomer. Part. If it is outside this range, the balance between transparency and impact resistance may be poor.
Further, a known molecular weight modifier such as 4-methyl-2,4-diphenylpentene-1, t-dodecyl mercaptan, n-dodecyl mercaptan may be added during the polymerization.

The ratio of the monomer units constituting the copolymer (C) is preferably 35 to 55% by mass of a styrene monomer unit, 5 to 15% by mass of a butadiene monomer unit, and a (meth) acrylic acid ester type. 60 to 30% by mass of monomer units, more preferably 38 to 53% by mass of styrene monomer units, 5 to 15% by mass of butadiene monomer units, 57 to 57% of (meth) acrylate monomer units 32% by mass.
The proportion of monomer units constituting the copolymer (C) is less than 35% by mass of styrene monomer units, less than 5% by mass of butadiene monomer units, and (meth) acrylic acid ester monomer units. If it exceeds 60% by mass, the strength is low and the absolute value of photoelastic birefringence increases, which may not be preferable. Further, when the styrene monomer unit exceeds 55% by mass, the butadiene monomer unit exceeds 15% by mass, and the (meth) acrylic acid ester monomer unit is less than 60% by mass, the photoelastic birefringence is reduced. Since the absolute value increases, it may not be preferable.

The resin composition containing the copolymer (A) has a melt mass flow rate (MFR) measured at a temperature of 200 ° C. and a load of 49 N based on JIS K7210, 0.1 to 3 g / 10 minutes, preferably 0.1 to 0.1 g. The amount is 2.5 g / 10 minutes, more preferably 0.2 to 2 g / 10 minutes.
If the MFR exceeds 3 g / 10 min, the strength is lowered and the orientation birefringence may be reduced, which is not preferable. On the other hand, if the MFR is less than 0.1 g / 10 min, film formation becomes difficult, which is not preferable.
The measurement of MFR was performed using a Toyo Seiki Seisakusho melt indexer (F-F01).

The weight average molecular weight (hereinafter referred to as Mw) of the copolymer (A) is not particularly limited, but is 70,000 to 200,000, and more preferably 100,000 to 170,000. The Mw of the copolymer (B) is not particularly limited, but is 70,000 to 250,000, and more preferably 90,000 to 200,000. The Mw of the copolymer resin (C) is not particularly limited, but is 70,000 to 200,000, and more preferably 100,000 to 170,000. In addition, Mw of this invention is Mw of polystyrene conversion measured by GPC, and measured on the measurement conditions of the following description.
Device name: SYSTEM-21 Shodex (manufactured by Showa Denko)
Column: 3 series PL gel MIXED-B Temperature: 40 ° C
Detection: Differential refractive index Solvent: Tetrahydrofuran Concentration: 2% by mass
Calibration curve: produced using standard polystyrene (PS) (manufactured by PL), and the weight average molecular weight was expressed in terms of polystyrene.

The absolute value of the difference in refractive index between the copolymer (A) and the copolymer (B) is preferably 0.005 or less, and more preferably 0.004 or less. The absolute value of the difference in refractive index between the copolymer (A) and the copolymer (C) is preferably 0.005 or less, and more preferably 0.004 or less.
The absolute value of the refractive index difference between the copolymer (A) and the copolymer (B), and the absolute value of the refractive index difference between the copolymer (A) and the copolymer (C) exceed 0.005. In some cases, the transparency is lowered.

The rubber particle diameter in the copolymer (C) is not particularly limited, but is preferably in the range of 0.1 to 1.0 μm, and more preferably 0.1 to 0.5 μm. The rubber particle diameter is obtained from the following formula [Equation 1] by measuring the particle diameter Di (equivalent circle diameter) of about 3000 rubber particles in the photograph from an ultra-thin section transmission electron micrograph of the resin. The average particle diameter is determined.

The toluene insoluble content of the copolymer (C) is not particularly limited, but is preferably in the range of 8 to 30% by mass, more preferably 12 to 25% by mass. The toluene insoluble matter is measured as follows.
A sample of 0.35 g was precisely weighed (a) and dissolved in 35 ml of toluene at a temperature of 25 ° C. for 24 hours, and then the lysate was transferred to a centrifuge tube having a mass (b) measured in advance and having a maximum centrifugal radius. Using a 10.7 cm angle rotor, centrifuge at 14,000 rpm for 40 minutes at a temperature of 10 ° C. or less, remove the non-precipitate by decantation, and dry for 24 hours in a vacuum dryer at a temperature of 70 ° C. The mass (d) is measured, and the toluene insoluble matter is calculated by the following formula [Equation 2].

The swelling index of the copolymer (C) is preferably from 8 to 20, and more preferably from 9 to 17. The swelling index is measured as follows. A sample of 0.35 g was precisely weighed (a) and dissolved in 35 ml of toluene at a temperature of 25 ° C. for 24 hours, and then the lysate was transferred to a centrifuge tube having a mass (b) measured in advance and having a maximum centrifugal radius. Using a 10.7 cm angle rotor, the mixture is centrifuged at 14,000 rpm for 40 minutes at a temperature of 10 ° C. or less, and after removing non-precipitates by decantation, the mass (c) of the centrifuge tube before drying is measured. It is dried in a vacuum dryer at a temperature of 70 ° C. for 24 hours, the mass (d) of the centrifuge tube after drying is measured, and the swelling index is calculated by the following equation [Equation 3].

It may be preferable that the optical molded body contains a heat-resistant stabilizer.
The heat stabilizer is not particularly limited as long as it has the effect, and examples thereof include heat stabilizers such as hindered phenol compounds, lactone compounds, phosphorus compounds, and sulfur compounds. . These may be used alone or in combination of two or more. The blending amount is preferably 0.01 to 2 parts by weight, more preferably 0.01 to 100 parts by weight in total of the copolymer (A), the copolymer (B), and the copolymer (C). -1 part by mass.

It may be preferable that the molded article for optics contains a light-resistant stabilizer.
Although a light-resistant stabilizer will not be specifically limited if it has the effect, For example, a hindered amine type compound and a benzotriazole type compound are mentioned. These may be used alone or in combination of two or more. The blending amount is preferably 0.01 to 2 parts by mass, more preferably 0.01 to 100 parts by mass in total of the copolymer (A), the copolymer (B), and the copolymer (C). -1 part by mass.

Optical moldings may contain other additives such as lubricants, plasticizers, colorants, antistatic agents, mineral oils, etc., but there is a possibility that transparency may be hindered, and the addition amount is small or It is preferable not to add.

The blending of the copolymer (A), the copolymer (B) and the copolymer (C), and the blending of the heat-resistant stabilizer and the light-resistant stabilizer are not particularly limited, and a known method can be adopted. Further, the granulation method is not particularly limited, and a known method can be adopted. For example, copolymer, heat stabilizer, light stabilizer and additives to be used as needed are mixed uniformly in advance with a tumbler or Henschel mixer, and supplied to a single screw extruder or twin screw extruder. There are a melt-kneading method, a heat-resistant stabilizer, a light-resistant stabilizer, and an additive to be used as necessary at the stage of bulk continuous polymerization or after devolatilization, and a method of granulating after adding and mixing.

As the optical molded body, for example, a known molded body such as an injection molded body, a sheet, or a film can be adopted. However, it is preferably a film having a thickness of 10 to 300 μm and is preferably used as a substrate for an optical film. A known method can be adopted as a method for forming an optical molded body, but it is preferable to obtain a film by melt extrusion using a film extruder.
The photoelastic constant of the optical film substrate is preferably −2 × 10 ⁻¹² to 2 × 10 ⁻¹² / Pa, more preferably −0.9 × 10 ^{−12 to} 0.9 × 10 ⁻¹² / Pa, It is. If the photoelastic constant is not in the range of −2 × 10 ⁻¹² to 2 × 10 ⁻¹² / Pa, birefringence occurs due to external stress, which is not preferable.
The substrate for an optical film can be used for a known optical film such as a retardation film, a polarizing film protective film, a viewing angle improving film, a polarizing film and an antireflection film.
If the substrate for optical film is oriented by being laterally stretched, negative orientation birefringence is generated, which may be more preferable.

Hereinafter, although detailed content is demonstrated using an Example, this invention is not limited to a following example.

[Experiment A-1]
A complete mixing type reactor having a capacity of about 20 liters equipped with a stirrer, a tower type plug flow type reactor having a capacity of about 40 liters, and a devolatilization tank equipped with a preheater were connected in series. Dissolved in a mixed solution composed of 52 parts by mass of styrene, 48 parts by mass of methyl methacrylate (hereinafter referred to as MMA), and 12 parts by mass of ethylbenzene, and further 1,1-bis (t-butylperoxy) -cyclohexane (manufactured by NOF Corporation) Perhexa C) 0.03 parts by mass, octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (IRGANOX 1076, manufactured by Ciba Specialty Chemicals) is mixed with 0.1 part by mass It was set as the solution. This raw material solution was introduced into a fully mixed reactor controlled at a temperature of 130 ° C. at 6 kg per hour. The reaction solution was continuously withdrawn from the first complete mixing reactor, and 1.0 g / h of n-dodecyl mercaptan (Tiocalcol 20 manufactured by Kao Co., Ltd.) was added to the reaction solution, and the temperature was controlled at 130 ° C. Introduced into the vessel. In addition, the stirring number of the complete mixing type reactor was 180 rpm. Next, the reaction liquid was continuously withdrawn from the complete mixing type reactor and introduced into a column type plug flow type reactor adjusted so as to have a gradient of 130 ° C. to 150 ° C. in the flow direction. While this reaction solution was heated with a preheater, it was introduced into a devolatilization tank controlled at a temperature of 240 ° C. and a pressure of 1.0 kPa to remove volatile components such as unreacted monomers. This resin liquid was extracted with a gear pump, and extruded into a strand shape to obtain a pellet-shaped copolymer A-1. Mw = 170,000.

[Experimental example A-2]
A copolymer A-2 was obtained in the same manner as in Experimental Example A-1, except that 41 parts by mass of styrene and 59 parts by mass of MMA were used. Mw = 160,000.

[Experimental example A-3]
A copolymer A-3 was obtained in the same manner as in Experimental Example A-1, except that 60 parts by mass of styrene and 40 parts by mass of MMA were used. Mw = 180,000.

[Experimental example A-4]
A copolymer A-4 was obtained in the same manner as in Experimental Example A-1, except that 0 part by mass of styrene and 100 parts by mass of MMA were used. Mw = 150,000.

[Experimental example A-5]
A copolymer A-5 was obtained in the same manner as in Experimental Example A-1, except that 75 parts by mass of styrene and 25 parts by mass of MMA were used. Mw = 190,000.

[Experiment A-6]
A copolymer A-6 was obtained in the same manner as in Experimental Example A-1, except that octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate was not added. Mw = 170,000.

[Experimental example A-7]
A copolymer A-7 was obtained in the same manner as in Experimental Example A-1, except that n-dodecyl mercaptan (thiocalcol 20 manufactured by Kao Corporation) was changed to 2.5 g per hour. Mw = 150,000.

[Experiment A-8]
A copolymer A-8 was obtained in the same manner as in Experimental Example A-1, except that n-dodecyl mercaptan (thiocalcol 20 manufactured by Kao Corporation) was changed to 4.0 g per hour. Mw = 130,000.

[Experiment B-1]
A polymerization vessel having an internal volume of 200 liters was charged with 65 liters of cyclohexane, 5.0 g of tetrahydrofuran (randomizing agent) and 3.2 kg of styrene and stirred at 30 ° C. with 120 ml of n-butyllithium (10% cyclohexane solution). ) (Initiator) was added, the temperature was raised, and polymerization was carried out at 80 ° C. for 40 minutes. Next, 4.8 kg of styrene and 12 kg of butadiene were added and polymerized at 80 ° C. for 40 minutes. Thereafter, excess methanol was added to the polymerization solution to stop the polymerization, and the solvent was removed and dried to obtain a copolymer B-1. Mw = 110,000.

[Experiment B-2]
Copolymer B-2 was prepared in the same manner as in Experimental Example B-1, except that 3.2 kg of the initial styrene was changed to 2.4 kg, 4.8 kg of the added styrene was changed to 3.6 kg, and 12 kg of butadiene was changed to 14 kg. Obtained. Mw = 110,000.

[Experiment B-3]
Copolymer B- was prepared in the same manner as in Experimental Example B-1, except that 3.2 kg of the initial styrene was changed to 4.2 kg, 4.8 kg of the added styrene was changed to 6.2 kg, and butadiene 12 kg was changed to 9.6 kg. 2 was obtained. Mw = 110,000.

[Experimental example C-1]
A first fully mixed reactor having a volume of about 5 liters equipped with a stirrer, a second fully mixed reactor having a volume of about 15 liters equipped with a stirrer, a column type plug flow reactor having a volume of about 40 liters, preheating A devolatilizing tank equipped with a vessel was connected in series. 12.5 parts by mass of styrene-butadiene rubber (ASAPRENE 670A manufactured by Asahi Kasei Chemicals Corporation) is dissolved in a mixed solution composed of 52 parts by mass of styrene, 48 parts by mass of methyl methacrylate (hereinafter referred to as MMA), and 12 parts by mass of ethylbenzene. 1,1-bis (t-butylperoxy) -cyclohexane (Perhexa C, manufactured by NOF Corporation), octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate ( 0.2 parts by mass of IRGANOX 1076) manufactured by Ciba Specialty Chemicals was mixed to obtain a raw material solution. This raw material solution was introduced into a first complete mixing reactor controlled at a temperature of 108 ° C. at 6 kg / hour. The reaction solution was continuously withdrawn from the first complete mixing reactor, and 2.5 g of n-dodecyl mercaptan (Kio Co., thiocalcol 20) was added to the reaction solution every hour, and then the temperature was controlled at 130 ° C. It was introduced into the type reactor. The second complete mixing reactor was stirred at 180 rpm. Next, the reaction solution was continuously withdrawn from the second complete mixing reactor, 2.5 g / h of n-dodecyl mercaptan was added to the reaction solution at a rate of 0.5 g / h, and then the temperature was changed from 130 ° C. to 150 ° C. in the flow direction. It was introduced into a column type plug flow reactor adjusted so as to have a gradient of ° C. While this reaction solution was heated with a preheater, it was introduced into a devolatilization tank controlled at a temperature of 240 ° C. and a pressure of 1.0 kPa to remove volatile components such as unreacted monomers. The resin liquid was extracted with a gear pump, and extruded into a strand shape to obtain a pellet-shaped copolymer C-1. Mw = 150,000.

[Experimental example C-2]
A copolymer C-2 was obtained in the same manner as in Experimental Example C-1, except that Toughden 2000A manufactured by Asahi Kasei Chemicals Corporation was used as the styrene-butadiene rubber, and 40 parts by mass of styrene and 60 parts by mass of MMA were used. Mw = 150,000.

[Examples and Comparative Examples]
The copolymer (A), copolymer (B), and copolymer (C) produced in the experimental example were mixed at a ratio (mass%) shown in Tables 1 to 3 using a Henschel mixer. Using a shaft extruder (TEM-35B manufactured by Toshiba Machine Co., Ltd.), the mixture was melt-kneaded at a cylinder temperature of 230 ° C. and pelletized to obtain a resin composition. In Example 15, bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate as a hindered amine-based compound with respect to a total of 100 parts by mass of the copolymer (A) and the copolymer (B). And 0.1 parts by mass of 2- (2H-benzotriazol-2-yl) -4,6-di-t-pentylphenol as a benzotriazole-based compound were added to a Henschel mixer to obtain a resin composition. . The MFR of the resin composition was measured.
The resin composition was extruded on a roll by extruding a 150 μm thick film at a cylinder temperature of 230 ° C. and a die temperature of 230 ° C. using a film extruder equipped with a T die.
The obtained film was uniaxially stretched 1.8 times at 100 ° C. using a tenter transverse stretching machine to obtain an optical film. The measurement results of the obtained optical film are shown in Tables 1 to 3.

The evaluation was based on the following method.
(1) Transparency Based on ASTM D1003, the haze (unit:%) of the stretched film was measured using a haze meter (NDH-1001DP type manufactured by Nippon Denshoku Industries Co., Ltd.). 1% or less was accepted.
(2) The b value (unit: none) of the stretched film was measured using a hue color difference meter (Σ-80 manufactured by Nippon Denshoku Industries Co., Ltd.). 1 or less was accepted.
(3) The retardation (hereinafter, “Re”, unit: nm) of the stretched film was measured using a birefringence phase difference measuring apparatus (KOBRA-WR manufactured by Oji Scientific Co., Ltd.). 400 to 600 nm, which is preferable for STN retardation films, was regarded as acceptable. Moreover, by observing with a phase-contrast microscope, it confirmed that the sign of orientation birefringence was negative in all the samples in an Example and a comparative example.
(4) An evaluation sample was obtained by stacking the films before photoelastic birefringence stretching and press molding at 230 ° C. using a 20 mm diameter cylindrical mold. The birefringence value when stress was applied to this evaluation sample was measured using a birefringence measuring apparatus ABR-10A manufactured by Uniopt, and the photoelastic constant (unit: / Pa) was calculated. The occurrence of birefringence due to external stress was reduced, and −2 × 10 ⁻¹² to 2 × 10 ⁻¹² / Pa suitable for an antireflection film was regarded as acceptable.
(5) In film roll-up at the time of film film extrusion, the film cutting status is 1 point (wound without cutting), 2 points (wound by changing the conditions), 3 points (not wound) Rated by stage. Two points or less were accepted.

The examples according to the present application had good transparency, hue and strength, and low photoelastic birefringence. It is suitable and useful as a base film for optical films such as retardation films, polarizing film protective films, viewing angle improving films, polarizing films and antireflection films. Furthermore, the examples according to the present application showed negative orientation birefringence when oriented. From this result, in the retardation film application, the process having the negative orientation birefringence of the present application and the film having the positive orientation birefringence such as polycarbonate or amorphous cyclic polyolefin can be used to simplify the process. It was found to be effective for improving the productivity and productivity.

Claims (9)

A resin composition containing the following copolymer (A), a resin composition having a melt mass flow rate (MFR) of 0.1 to 3 g / 10 minutes measured at a temperature of 200 ° C. and a load of 49 N based on JIS K7210 An optical molded body characterized by being molded.
Copolymer (A): Styrene- (meth) acrylic acid ester copolymer, in which the ratio of constituting monomers is 70 to 10% by mass of a styrene monomer unit, (meth) acrylic acid ester The copolymer which is 30-90 mass% of monomer units. 2. The optical molded body according to claim 1, wherein the resin composition comprises 99.9 to 90 parts by mass of the copolymer (A) and 0.1 to 10 parts by mass of a butadiene copolymer. . 3. The optical molded body according to claim 1, wherein the butadiene-based copolymer comprises at least one selected from the following butadiene-based copolymers (B) and (C). 4.
Copolymer (B): Styrene-butadiene block copolymer, the ratio of the monomer units constituting the styrene monomer units is 50 to 20% by mass, and the butadiene monomer units are 50 to 80% by mass. % Copolymer. However, the absolute value of the refractive index difference between the copolymer (A) and the copolymer (B) is 0.005 or less.
Copolymer (C): a copolymer obtained by polymerizing a styrene monomer and a (meth) acrylic acid ester monomer in the presence of a butadiene rubber, and constituting monomer units The copolymer resin whose ratio is 35-55 mass% of styrene monomer units, 5-15 mass% of butadiene monomer units, and 60-30 mass% of (meth) acrylic acid ester monomer units. However, the absolute value of the refractive index difference between the copolymer (A) and the copolymer (C) is 0.005 or less. The resin composition is at least one selected from a hindered phenol compound, a lactone compound, a phosphorus compound, and a sulfur compound with respect to a total of 100 parts by mass of the copolymers (A) to (C). The optical molded body according to any one of claims 1 to 3, comprising 0.01 to 2 parts by mass of a heat-resistant stabilizer. The optical molded body according to claim 1, wherein the optical molded body is a substrate for an optical film. The optical molded body according to claim 5, wherein the optical film substrate has a photoelastic constant of −2 × 10 ⁻¹² to 2 × 10 ⁻¹² / Pa. It is an optical film using the said base material for optical films, The optical molded object of Claim 5 or Claim 6 characterized by the above-mentioned. The optical molded body according to claim 7, wherein the optical film is a retardation film or an antireflection film. The optical molded body according to claim 7 or 8, wherein the optical film is a film subjected to a stretching treatment.