JP5074010B2 - Excellent resin composition for optical material and molded article - Google Patents

Description

The present invention relates to a resin composition suitable for use as a material for manufacturing an optical element, that is, an optical material.
In particular, the present invention relates to a resin composition for optical materials having excellent optical properties and a molded body comprising the resin composition.

Recently, for example, with the expansion of the display market, there has been an increasing demand for clearer images, and there is a demand for optical materials with higher optical properties rather than simple transparent materials.
In general, a polymer has birefringence because the refractive index differs between the molecular main chain direction and the perpendicular direction. Depending on the application, it is required to strictly control this birefringence. In the case of a protective film used for a polarizing plate of a liquid crystal, a polymer material having a smaller birefringence even if the total light transmittance is the same. A molded body is required, and triacetyl cellulose is used as a typical material. On the other hand, a retardation film such as a quarter-wave plate having a function of changing light polarized by a polarizing plate into circularly polarized light is given a function by intentionally generating birefringence in a polymer material molded body. Polycarbonate and the like are listed as typical materials.
In recent years, as the size of liquid crystal displays has increased and the moldings of polymer optical materials necessary for them have increased in size, the birefringence changes due to external forces, i.e. the photoelastic coefficient, have been reduced in order to reduce the distribution of birefringence caused by the bias of external forces. There is a need for materials with small absolute values. As a material having a small absolute value of the photoelastic coefficient, methyl methacrylate homopolymer (PMMA) and amorphous polyolefin (APO) are known (for example, see Non-Patent Document 1). However, even with these materials, there is a demand for materials that still have a large change in birefringence due to an external force and a small change in birefringence due to an external force.
Chemical Review, No. 39, 1998 (published by Academic Publishing Center)

  An object of this invention is to provide the resin composition for optical materials with a small absolute value of a photoelastic coefficient.

As a result of intensive studies, the inventors of the present invention have a specific low molecular weight compound in a thermoplastic resin composition having a photoelastic coefficient of −4.5 × 10 ⁻¹² / Pa or more and less than 0 × 10 ⁻¹² / Pa. As a result, it was found that the photoelastic coefficient of the resin composition can be increased by adding, and as a result, the absolute value of the photoelastic coefficient can be reduced, thereby completing the present invention.
That is, the present invention is as follows.
More than the photoelastic coefficient of the thermoplastic resin composition (A) having a photoelastic coefficient of −4.5 × 10 ⁻¹² / Pa or more and less than 0 × 10 ⁻¹² / Pa, and the thermoplastic resin composition (A). A resin composition for an optical material comprising a low molecular compound (B) having a tendency to increase a photoelastic coefficient.

  ADVANTAGE OF THE INVENTION According to this invention, the resin composition for optical materials with a small absolute value of a photoelastic coefficient can be provided.

The present invention will be specifically described below.
The photoelastic coefficient when the thermoplastic resin composition (A) in the present invention is unstretched is −4.5 × 10 ⁻¹² / Pa or more and 0 × 10 ⁻¹² / Pa, preferably −3.7 × 10. ⁻¹² / Pa or more and less than 0 × 10 ⁻¹² / Pa, more preferably −3.0 × 10 ⁻¹² / Pa or more and less than 0 × 10 ⁻¹² / Pa, particularly preferably −2.0 × 10 ^−12. / Pa or more and less than 0 × 10 ⁻¹² / Pa.
The photoelastic coefficient is described in various documents (see, for example, Non-Patent Document 1) and is defined by the following equation.
C _R [/ Pa] = Δn / σ _R Δn = nx−ny
(In the formula, C _{R is a} photoelastic coefficient, σ _{R is an} extension stress [Pa], Δn is a birefringence when stress is applied, nx is a refractive index in a direction parallel to the extension direction, and ny is a direction perpendicular to the extension direction. Refractive index)
The closer the value of the photoelastic coefficient is to zero, the smaller the change in birefringence due to external force, which means that the change in birefringence designed for each application is small.

The low molecular compound (B) in the present invention is a compound that increases the photoelastic coefficient of the thermoplastic resin composition (A). The molecular weight is preferably a compound having a molecular weight of 5000 or less, more preferably 1000 or less. Examples of the low molecular compound (B) in the present invention include benzotriazole compounds, benzotriazine compounds, benzoate compounds, benzophenone compounds, phenol compounds, oxazole compounds, malonic acid ester compounds, lactone compounds, and the like. Preferred are benzotriazole compounds and benzotriazine compounds. These may be used alone or in combination of two or more.
The general formulas (1) and (2) of the benzotriazole compound, which is a low molecular compound (B) preferably used in the present invention, and the general formula (3) of the benzotriazine compound are shown below.

[In General Formula (1), X ₁ represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms or an alkoxy group, and R _{1 to} R ₄ are each a hydrogen atom or a substituted or unsubstituted carbon atom having 1 to 20 carbon atoms. Represents a substituted alkyl group. In the general formula (2), X ₂ and X ₃ are each a hydrogen atom and a halogen atom, R ₅ and R ₆ are each a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, and R ₇ is a carbon number 1 Represents an alkylene group of ~ 4. In the general formula (3), R ₈ represents an alkyl group having 1 to 20 carbon atoms or an alkoxy group, and R ₉ and R ₁₀ each represents a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms. ]

The low molecular weight compound (B) is excellent in molding processability when the vapor pressure (P) at 20 ° C. is 1.0 × 10 ⁻⁴ Pa or less. A more preferable range is a vapor pressure (P) of 1.0 × 10 ⁻⁶ Pa or less, and a particularly preferable range is a vapor pressure (P) of 1.0 × 10 ⁻⁸ Pa or less. “Excellent molding processability” means, for example, that there is little adhesion of a low molecular compound to a roll during film molding. If it adheres to the roll, for example, it adheres to the surface of the molded body and deteriorates the appearance and optical properties, so that it is not preferable as an optical material.
The low molecular compound (B) is preferable because it has excellent molding processability when the melting point (Tm) is 80 ° C. or higher. A more preferable range is a melting point (Tm) of 130 ° C. or higher, and a particularly preferable range is a melting point (Tm) of 160 ° C. or higher.

The low molecular compound (B) is excellent in molding processability when the weight reduction rate of the low molecular compound (B) is 50% or less when the temperature is increased from 23 ° C. to 260 ° C. at a rate of 20 ° C./min. . A more preferable range is a weight reduction rate of 15% or less, and a particularly preferable range is a weight reduction rate of 2% or less.
In the present invention, the amount of the low molecular compound (B) is such that the amount of the low molecular compound (B) is from 1 part by weight to 10 parts by weight with respect to 100 parts by weight of the thermoplastic resin composition (A). preferable. If it is 0.1 parts by weight or more, the absolute value of the photoelastic coefficient is decreased, and if it is 10 parts by weight or less, molding processability is improved.

Further, the resin composition for an optical material of the present invention comprises a thermoplastic resin composition (A) having a photoelastic coefficient of −4.5 × 10 ⁻¹² / Pa or more and less than −3 × 10 ⁻¹² / Pa and a low molecular compound. In the case of (B), the amount of the low molecular compound (B) is preferably 1 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the thermoplastic resin composition (A), and preferably 2 parts by weight or more and 9 parts by weight or less. The amount is more preferably not more than parts by weight, particularly preferably not less than 2.5 parts by weight and not more than 8 parts by weight. If it is 1 part by weight or more, the absolute value of the photoelastic coefficient is small, and if it is 10 parts by weight or less, molding processability is improved.
Moreover, the resin composition for optical materials of the present invention comprises a thermoplastic resin composition (A) and a low molecular compound (B) having a photoelastic coefficient of −3 × 10 ⁻¹² / Pa or more and less than 0 × 10 ⁻¹² / Pa. The amount of the low molecular compound (B) is preferably 0.1 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the thermoplastic resin composition (A). The amount is more preferably 3 parts by weight or less, and particularly preferably 0.5 part by weight or more and 2 parts by weight or less. When the amount is 0.1 parts by weight or more, the absolute value of the photoelastic coefficient is decreased, and when the amount is 5 parts by weight or less, molding processability is improved.

The amount of the low molecular weight compound can be quantified by gas chromatography (GC) or the like after extraction from the resin using a nuclear magnetic resonance apparatus (NMR) or a good solvent.
The photoelastic coefficient of the resin composition for an optical material of the present invention comprising the thermoplastic resin composition (A) and the low molecular compound (B) when unstretched is preferably −3 × 10 ⁻¹² / Pa or more + 3 × 10. ⁻¹² / Pa or less, more preferably −2 × 10 ⁻¹² / Pa to + 2 × 10 ⁻¹² / Pa, particularly preferably −1 × 10 ⁻¹² / Pa to + 1 × 10 ⁻¹² / Pa. By being in this range, it can be suitably used for optical applications such as a polarizing plate protective film and a retardation film.

  The molded article for optical material of the present invention preferably has a spectral transmittance at 380 nm of 5% or less and a spectral transmittance at 400 nm of 65% or more. The lower the spectral transmittance at 380 nm in the ultraviolet region, the lower the deterioration of the polarizer and the liquid crystal element, and the higher the 400 nm spectral transmittance in the visible region, the better the color reproducibility. Therefore, it can be preferably used as an optical film.

In the present invention, the thermoplastic resin composition (A) is any thermoplastic resin composition as long as the photoelastic coefficient when unstretched is −4.5 × 10 ⁻¹² / Pa or more and less than 0 × 10 ⁻¹² / Pa. However, the resin composition which consists of acrylic resin (A-1) and styrene resin (A-2) is mentioned suitably.
In the present invention, the acrylic resin (A-1) is methacrylic acid ester such as cyclohexyl methacrylate, t-butyl cyclohexyl methacrylate, methyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, isopropyl acrylate. One or more monomers selected from acrylic acid esters such as 2-ethylhexyl acrylate and the like are polymerized. Of these, a homopolymer of methyl methacrylate or a copolymer with other monomers is preferable. Examples of monomers copolymerizable with methyl methacrylate include other alkyl methallylic esters, alkyl acrylates, styrene and o-methyl styrene, p-methyl styrene, 2,4-dimethyl styrene, ethyl styrene, aromatic vinyl compounds such as nuclear alkyl-substituted styrene such as p-tert-butylstyrene, α-alkyl-substituted styrene such as α-methylstyrene and α-methyl-p-methylstyrene, vinyl cyanide such as acrylonitrile and methacrylonitrile , Maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide, unsaturated carboxylic acid anhydrides such as maleic anhydride, and unsaturated acids such as acrylic acid, methacrylic acid and maleic acid.

  Among these monomers that can be copolymerized with methyl methacrylate, alkyl acrylates are particularly excellent in heat decomposability, and methacrylic resins obtained by copolymerizing alkyl acrylates are not suitable for molding. High fluidity is preferable. The amount of alkyl acrylates used when methyl acrylate is copolymerized with methyl methacrylate is preferably 0.1% by weight or more from the viewpoint of thermal decomposition resistance, and 15% from the viewpoint of heat resistance. % Or less is preferable. The content is more preferably 0.2% by weight or more and 14% by weight or less, and particularly preferably 1% by weight or more and 12% by weight or less. Among these alkyl acrylates, especially methyl acrylate and ethyl acrylate are remarkably most preferable even when they are copolymerized with a small amount of methyl methacrylate. The said monomer which can be copolymerized with methyl methacrylate can also be used 1 type or in combination of 2 or more types.

  The acrylic resin (A-1) preferably has a weight average molecular weight of 50,000 to 200,000. The weight average molecular weight is desirably 50,000 or more from the viewpoint of the strength of the molded product, and desirably 200,000 or less from the viewpoint of molding processability and fluidity. A more desirable range is 70,000 to 150,000. In the present invention, isotactic polymethacrylate and syndiotactic polymethacrylate can be used simultaneously. As a method for producing an acrylic resin, for example, generally used polymerization methods such as cast polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, and anionic polymerization can be used. It is preferable to avoid mixing of foreign substances as much as possible. From this viewpoint, bulk polymerization or solution polymerization without using a suspending agent or an emulsifier is desirable. When solution polymerization is performed, a solution prepared by dissolving a mixture of monomers in an aromatic hydrocarbon solvent such as toluene or ethylbenzene can be used. In the case of polymerization by bulk polymerization, the polymerization can be started by irradiation with free radicals generated by heating or ionizing radiation as is usually done.

  As the initiator used in the polymerization reaction, any initiator generally used in radical polymerization can be used. For example, an azo compound such as azobisisobutylnitrile, benzoyl peroxide, lauroyl peroxide, t-butylperoxy When an organic peroxide such as 2-ethylhexanoate is used and the polymerization is carried out particularly at a high temperature of 90 ° C. or higher, solution polymerization is common, so the 10-hour half-life temperature is 80 Peroxides and azobis initiators that are soluble in the organic solvent to be used are preferable, and specifically, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, cyclohexane par. Oxide, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, 1,1-azobis (1-cyclohex Down-carbonitrile), and 2- (carbamoylazo) isobutyronitrile. These initiators are used in the range of 0.005 to 5 wt%. As the molecular weight regulator used as necessary in the polymerization reaction, any one used in general radical polymerization is used. For example, mercaptan compounds such as butyl mercaptan, octyl mercaptan, dodecyl mercaptan, 2-ethylhexyl thioglycolate are particularly preferable. It is mentioned as preferable. These molecular weight regulators are added in a concentration range such that the degree of polymerization is controlled within the above range. As a method for producing the acrylic resin (A-1), a method described in JP-B-63-1964 can be used. As the acrylic resin (A-1), two or more types having different molecular weights, compositions, and the like can be used at the same time.

  In the present invention, the styrene resin (A-2) is a polymer composed of at least a styrene monomer component. Here, the styrene monomer means a monomer having a styrene skeleton in the structure thereof, in addition to styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, And vinyl aromatic compound monomers such as ethyl styrene, nuclear alkyl-substituted styrene such as p-tert-butyl styrene, and α-alkyl-substituted styrene such as α-methyl styrene and α-methyl-p-methyl styrene. A typical one is styrene.

  The styrene resin (A-2) includes those obtained by copolymerizing a styrene monomer component with another monomer component. Examples of the copolymerizable monomer include alkyl methacrylates such as methyl methacrylate, cyclohexyl methacrylate, methylphenyl methacrylate, and isopropyl methacrylate, and alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate. Saturated carboxylic acid alkyl ester monomers, methacrylic acid, acrylic acid, itaconic acid, maleic acid, fumaric acid, cinnamic acid and other unsaturated carboxylic acid monomers, maleic anhydride, itaconic acid, ethyl maleic acid, methyl itaconic acid , Unsaturated dicarboxylic acid anhydride monomers such as chloromaleic acid, unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile, 1,3-butadiene, 2-methyl Conjugated dienes such as -1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene and the like may be copolymerized. Is possible.

As the styrene resin (A-2) that can be suitably used in the present invention, in particular, a styrene-acrylonitrile copolymer (A-2-1), a styrene-methacrylic acid copolymer (A-2-2), A styrene-maleic anhydride copolymer (A-2-3) is mentioned. These are preferable because they have characteristics required for optical materials such as heat resistance and transparency.
Further, styrene-acrylonitrile copolymer (A-2-1), styrene-methacrylic acid copolymer (A-2-2), and styrene-maleic anhydride copolymer (A-2-3) are acrylic. Since the compatibility with the resin (A-1) is high, the transparency is high, and it is also preferable because a molded body that does not cause phase separation during use and does not deteriorate in transparency can be obtained. From such a viewpoint, it is particularly preferable when a polymer containing methyl methacrylate as a monomer component is used as the acrylic resin (A-1).

  In the case of the styrene-acrylonitrile copolymer (A-2-1), the acrylonitrile content in the copolymer is preferably 1 to 40% by mass. A more preferable range is 1 to 30% by mass, and an especially preferable range is 1 to 25%. When the content of acrylonitrile in the copolymer is 1 to 40% by mass, it is preferable because of excellent transparency.

  In the case of a styrene-methacrylic acid copolymer (A-2-2), the methacrylic acid content in the copolymer is preferably 0.1 to 50% by mass. A more preferable range is 0.1 to 40% by mass, and a further preferable range is 0.1 to 30% by mass. If the methacrylic acid content in the copolymer is 0.1% by mass or more, the heat resistance is excellent, and if it is in the range of 50% by mass or less, the transparency is excellent, which is preferable.

  In the case of the styrene-maleic anhydride copolymer (A-2-3), the maleic anhydride content in the copolymer is preferably 0.1 to 50% by mass. A more preferable range is 0.1 to 40% by mass, and a further preferable range is 0.1 to 30% by mass. If the maleic anhydride content in the copolymer is 0.1% by mass or more, the heat resistance is excellent, and if it is in the range of 50% by mass or less, the transparency is excellent, which is preferable.

  Different types of styrene-based resin (A-2) such as composition and molecular weight can be used in combination. These can be obtained by known anion, block, suspension, emulsion or solution polymerization methods. In the styrene resin, the unsaturated double bond of the benzene ring of the conjugated diene or styrene monomer may be hydrogenated. The hydrogenation rate can be measured by a nuclear magnetic resonance apparatus (NMR). In the present invention, the styrene resin refers to a resin component containing more than 50% by weight of a styrene monomer.

  In the present invention, the range of the ratio (parts by weight) of the styrene resin (A-2) in the thermoplastic resin composition (A) comprising the acrylic resin (A-1) and the styrene resin (A-2) is light. From the viewpoint of the elastic modulus, it is preferably from 0.1 parts by weight to 60 parts by weight, more preferably from 0.2 parts by weight to less than 40 parts by weight, and from 0.3 parts by weight to 30 parts by weight. Particularly preferred. In the present invention, the thermoplastic resin composition (A) is mixed with a polymer other than the acrylic resin (A-1) and the styrene resin (A-2) within a range that does not impair the object of the present invention. Can do. Polymers that can be mixed include polyolefins such as polyethylene and polypropylene, polyamides, polyphenylene sulfide resins, polyether ether ketone resins, polyesters, polysulfones, polyphenylene oxides, polyimides, polyether imides, polyacetals and other thermoplastic resins, and At least one or more of thermosetting resins such as a phenol resin, a melamine resin, a silicone resin, and an epoxy resin can be further added.

  Furthermore, arbitrary additives can be mix | blended according to various objectives within the range which does not impair the effect of this invention remarkably. The type of additive is not particularly limited as long as it is generally used for blending resins and rubber-like polymers. Inorganic fillers such as silicon dioxide, pigments such as iron oxide, lubricants such as stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, ethylene bisstearamide, mold release agents, paraffinic process oil, naphthene Process oils, aromatic process oils, softeners and plasticizers such as paraffin, organic polysiloxane and mineral oil, hindered phenol antioxidants, phosphorus heat stabilizers and other antioxidants, UV absorbers, hindered amines Examples thereof include system light stabilizers, flame retardants, antistatic agents, organic fibers, glass fibers, carbon fibers, metal whiskers and other reinforcing agents, colorants, other additives, and mixtures thereof.

The method for producing the molded article for optical material in the present invention is not particularly limited, and a known method can be used. For example, resin compositions are manufactured using melt kneaders such as single screw extruders, twin screw extruders, Banbury mixers, brabenders, various kneaders, and then injection molding, sheet molding, blow molding, injection blow molding, inflation It can be formed by a known method such as molding, extrusion molding, foam molding or the like, and a secondary processing molding method such as pressure forming or vacuum forming can also be used.
When the molded article for an optical material according to the present invention is a film or a sheet, for example, an unstretched film can be extruded by using an extruder equipped with a T die, a circular die, or the like. When a molded product is obtained by extrusion molding, if a material in which a thermoplastic resin (A) component and a low molecular compound (B) component are melted and kneaded in advance can be used, molding is performed through melt kneading at the time of extrusion molding. You can also. It is also possible to obtain an unstretched film or sheet by cast molding using a good solvent common to the components (A) and (B), for example, a solvent such as chloroform.

Further, if necessary, the unstretched film or sheet can be stretched uniaxially in the machine flow direction (MD) and uniaxially stretched in the direction (TD) perpendicular to the mechanical flow direction. For example, industrially, by uniaxial stretching method by roll stretching or tenter stretching, sequential biaxial stretching method by combination of roll stretching and tenter stretching, simultaneous biaxial stretching method by tenter stretching, biaxial stretching method by tubular stretching, etc. A stretched film can be produced. The final draw ratio can be determined from the heat shrinkage rate of the obtained molded body. The stretching ratio is preferably 0.1% or more and 300% or less in at least one direction, more preferably 1% or more and 200% or less, and particularly preferably 2% or more and 100% or less. By designing in this range, a stretched molded article preferable in terms of birefringence and strength can be obtained. The draw ratio can be determined from the following relational expression by shrinking the obtained stretched film at a temperature 20 ° C. or higher than the glass transition temperature. The glass transition temperature can be determined by a DSC method or a viscoelastic method.
Stretch ratio (%) = [(length before shrinkage / length after shrinkage) −1] * 100

  In the present invention, the difference between a film and a sheet is only the thickness, the film means a thickness of 300 μm or less, and the sheet exceeds 300 μm. In the present invention, the film is desirably 1 μm or more, more desirably 5 μm or more, and the sheet is desirably 10 mm or less, more desirably 5 mm or less. The molded product of the present invention is a light guide plate, a diffusion plate, a polarizing plate protective film, a quarter-wave plate, used as an optical material for displays such as liquid crystal displays, plasma displays, organic EL displays, field emission displays, rear projection televisions, A half-wave plate, a viewing angle control film, a retardation film such as a liquid crystal optical compensation film, a display front plate, a display substrate, a lens, a touch panel, etc., and a transparent substrate used in solar cells can be suitably used. . In addition, in the fields of optical communication systems, optical switching systems, and optical measurement systems, they can also be used for waveguides, lenses, optical fibers, optical fiber coating materials, LED lenses, lens covers, and the like. The optical material by the molded body of the present invention can be subjected to surface functionalization treatment such as antireflection treatment, transparent conductive treatment, electromagnetic wave shielding treatment, gas barrier treatment and the like.

EXAMPLES Next, although an Example is given and demonstrated in detail, this invention is not restrict | limited to these examples.
First, the evaluation method will be described.
<Evaluation method>
(1) Measurement of birefringence and photoelastic coefficient A birefringence measuring device described in detail in Macromolecules 2004, 37, 1062-1066 was used. A film tensioning device was placed in the laser beam path, and birefringence was measured while applying a tensile stress at 23 ° C. The strain rate during stretching was 20% / min (chuck interval: 30 mm, chuck moving speed: 6 mm / min), and the test piece width was 7 mm. Plotting birefringence (Δn) as the y-axis and stretching stress (σ _R ) as the x-axis, the photoelastic coefficient (C _R ) was calculated by obtaining the slope of the straight line in the linear region by least square approximation. The smaller the absolute value of the slope is, the closer the photoelastic coefficient is to 0, indicating a preferable optical characteristic.
(2) Measurement of spectral transmittance A spectral spectrum was measured using U-3310 manufactured by Hitachi, Ltd., and a transmittance at 380 nm was obtained.

(3) Molding processability Molding processability is determined when the resin extruded from the T-die during film molding solidifies on the roll.
◎ when there is almost no adhesion to the roll,
○ when there is little adhesion to the roll,
A case where the adhesion to the roll was recognized to some extent and the process control of the molding conditions required special attention was marked with Δ.
(4) Weight reduction rate Using Thermo Plus TG8120 manufactured by Rigaku Corporation, the weight reduction rate of the low molecular weight compound when the temperature was increased from 23 ° C to 260 ° C at a rate of 20 ° C / min was determined.

  <Raw materials used>

1. Acrylic resin (A-1)
1,1-di-t-butylperoxy-3,3,3-trimethyl was added to a monomer mixture consisting of 89.2 parts by weight of methyl methacrylate, 5.8 parts by weight of methyl acrylate, and 5 parts by weight of xylene. Add 0.0294 parts by weight of cyclohexane and 0.115 parts by weight of n-octyl mercaptan and mix uniformly. This solution is continuously supplied to a closed pressure-resistant reactor having an internal volume of 10 liters, polymerized with stirring at an average temperature of 130 ° C. and an average residence time of 2 hours, and then continuously sent to a reservoir connected to the reactor. The acrylic resin (A-1) used in the following examples was removed from the volatile component under certain conditions and transferred to the extruder continuously in a molten state (methyl methacrylate / methyl acrylate). Copolymer pellets were obtained. The resulting copolymer had a methyl acrylate content of 6.0%, a weight average molecular weight of 145,000, and a melt flow value measured at 230 ° C. of 3.8 kg measured in accordance with ASTM-D1238 was 1.0 g / min. Met. Moreover, the photoelastic coefficient (unstretched) was −5.2 × 10 ⁻¹² / Pa, and the intrinsic birefringence was negative.

2. Styrene resin (A-2)
(2-1) Styrene-acrylonitrile copolymer (A-2-1)
A monomer mixture composed of 72% by mass of styrene, 13% by mass of acrylonitrile, and 15% by mass of ethylbenzene was continuously fed into a complete mixing reactor equipped with a stirrer, and a polymerization reaction was performed at 150 ° C. and a residence time of 2 hours.
The obtained polymerization solution was continuously supplied to an extruder, and unreacted monomers and a solvent were collected by the extruder to obtain pellets of a styrene-acrylonitrile copolymer (A-2-1).
The obtained styrene-acrylonitrile copolymer (A-2-1) was colorless and transparent, and as a result of compositional analysis by neutralization titration, the styrene content was 80% by mass, the acrylonitrile content was 20% by mass, and conformed to ASTM-D1238. The melt flow rate value at 220 ° C. and 10 kg load was 13 g / 10 min. The photoelastic coefficient (unstretched) was 5.0 × 10 ⁻¹² / Pa, and the intrinsic birefringence was negative.

(2-2) Styrene-methacrylic acid copolymer (A-2-2)
Continuous solution polymerization was carried out using all the equipment made of stainless steel. 75.2% by mass of styrene, 4.8% by mass of methacrylic acid, and 20% by mass of ethylbenzene are used as a preparation liquid, and 1,1-tert-butylperoxy-3,3,5-trimethylcyclohexane is used as a polymerization initiator. This prepared solution was added at 1 L / hr. The mixture was continuously fed at a rate of 1 to a completely mixed polymerization reactor with an internal volume of 2 L and equipped with a stirrer, and polymerization was carried out at 136 ° C.
A polymerization solution containing 49% of solid content is continuously taken out, first preheated to 230 ° C., kept at 230 ° C., and supplied to a devolatilizer depressurized to 20 torr. It discharged continuously from the gear pump at the lower part of the volatilizer to obtain a styrene / methacrylic acid copolymer (A-2-2).
The obtained styrene-methacrylic acid copolymer (A-2-2) was colorless and transparent, and as a result of compositional analysis by neutralization titration, the styrene content was 92 mass% and the methacrylic acid content was 8 mass%. The melt flow rate value measured at 230 ° C. under a load of 3.8 kg measured in accordance with ASTM-D1238 was 5.2 g / 10 minutes. The photoelastic coefficient (unstretched) was 4.8 × 10 ⁻¹² / Pa, and the intrinsic birefringence was negative.

(2-3) Styrene-maleic anhydride copolymer (A-2-3)
Continuous solution polymerization was carried out using all the equipment made of stainless steel. A total of 100 parts by mass was prepared at a ratio of 91.7 parts by mass of styrene and 8.3 parts by mass of maleic anhydride. (However, the two are not mixed.) 5 parts by mass of methyl alcohol and 0.03 parts by mass of 1,1-tert-butylperoxy-3,3,5-trimethylcyclohexane as a polymerization initiator are mixed with styrene. It was set as the preparation liquid. 0.95 kg / hr. Was continuously supplied to a jacketed complete mixing polymerization machine having an internal volume of 4 L.
On the other hand, maleic anhydride heated to 70 ° C. was used as the second preparation liquid at 0.10 kg / hr. Was fed to the same polymerization machine at a speed of When the polymerization conversion rate became 54%, the polymerization solution was continuously removed from the polymerization machine, first preheated to 230 ° C., kept at 230 ° C., and supplied to a devolatilizer reduced to 20 torr, with an average retention of 0 After 3 hours, it was continuously discharged from the lower gear pump of the devolatilizer to obtain a styrene-maleic anhydride copolymer (A-2-3).
The obtained styrene-maleic anhydride copolymer (A-2-3) was colorless and transparent, and as a result of compositional analysis by neutralization titration, the styrene content was 85% by mass and the maleic anhydride unit was 15% by mass. The melt flow rate value measured at 230 ° C. under a load of 2.16 kg measured according to ASTM-D1238 was 2.0 g / 10 min. The photoelastic coefficient (unstretched) was 4.1 × 10 ⁻¹² / Pa, and the intrinsic birefringence was negative.

3. Low molecular weight compound (B)
(3-1) ADK STAB LA-31 (B-1)
Adekastab LA-31 manufactured by Asahi Denka Co., Ltd., which is a benzotriazole compound (vapor pressure (P) at 20 ° C .: less than 1.0 × 10 ⁻⁴ Pa, melting point (Tm): 195 ° C., weight reduction rate: 0 0.03%) was used.
(3-2) Tinuvin P (B-2)
TinuvinP (a vapor pressure (P) at 20 ° C .: 1.5 × 10 ⁻⁴ Pa, melting point (Tm): 128 ° C., weight loss rate: 34%) manufactured by Ciba Specialty Chemicals Co., Ltd., a benzotriazole-based compound ) Was used.

[Examples 1 to 15 and Comparative Examples 1 to 10]
Using the copolymers (A-1) and (A-2) and the low molecular weight compound (B), a resin composition for optical materials was prepared with the compositions shown in Tables 1 to 3, and this was made into a plastic engineering laboratory T Table 1 shows the screw rotation speed, resin temperature in the cylinder of the extruder, and the temperature of the T die using a die mounting extruder (BT-30-C-36-L type / width 400 mmT die mounting / lip thickness 0.8 mm). The unstretched film of Examples 1, 8, and 11 and Comparative Examples 1-10 was obtained by adjusting to the conditions shown in -3 and performing extrusion molding. The flow (extrusion direction) of the film was defined as the MD direction, and the direction perpendicular to the MD direction was defined as the TD direction.
Moreover, the longitudinal (MD direction) uniaxial stretching of the unstretched film obtained by the composition and the molding conditions shown in Tables 1 to 3 was performed using a roll-type longitudinal stretching machine manufactured by Ichikin Kogyo Co., and Examples 4, 5, and 9 were used. 10, 14, and 15 uniaxially stretched films were obtained. In addition, in order to set it as the target setting draw ratio 50%, the rotational speed of two rolls (low speed side roll / high speed side roll) was changed and it extended | stretched between rolls.
Furthermore, the longitudinally uniaxially stretched film obtained by extending | stretching the unstretched film obtained by the composition and the molding conditions shown in Tables 1-3 longitudinally similarly to Example 4, 5, 9, 10, 14, 15. Lateral (TD direction) stretching was performed using a tenter stretching machine manufactured by Ichikin Kogyo Co., Ltd. In addition, in order to obtain a target set stretching ratio of 100%, stretching was performed at a flow rate of 5 m / min while changing the distance between the tenter chucks.
Tables 1, 2 and 3 show the composition of the resin composition for optical materials, the blending amount of the low molecular compound (B), the draw ratio, the moldability, the film thickness, the photoelastic coefficient, and the spectral transmittance.

As Examples 1 to 14 and Comparative Examples 1 to 10 show, the resin compositions containing the thermoplastic resin composition composed of the acrylic resin (A-1) and the styrene resin (A-2) are all light. Although the absolute value of the elastic modulus is small, among these, a low molecular weight compound (B) is added to the thermoplastic resin composition (A) having a photoelastic coefficient of −4.5 × 10 ⁻¹² / Pa or more and less than 0 × 10 ⁻¹² / Pa. ) Was able to realize a smaller photoelastic coefficient.
In addition, by blending the low molecular weight compound (B), a low spectral transmittance at 380 nm, which is important as an optical material characteristic, can be realized.

  On the other hand, as the comparison between Comparative Example 9 and Comparative Example 10 shows, when the low molecular weight possible substance (B) is blended with the thermoplastic resin composition having a positive photoelastic coefficient, the absolute value of the photoelastic coefficient is It was further undesirably large.

However, in Examples 3, 5, 7, 10, 13 and 15 using (B-2) having a vapor pressure (P) of 1.5 × 10 ⁻⁴ Pa at 20 ° C. as the low molecular compound (B). However, some adhesion of the low molecular weight compound (B) to the roll was recognized during the molding process, and process management related to roll adhesion prevention measures was necessary.
On the other hand, Examples 1, 2, 4, 6, 8 using (B-1) having a vapor pressure (P) at 20 ° C. of less than 1.0 × 10 ⁻⁴ Pa as the low molecular compound (B). , 9, 11, 12 and 14, there was no adhesion of the low molecular compound (B) to the roll during the molding process, and good molding processability was exhibited.

Since the molded body using the resin composition for optical materials of the present invention has a small absolute value of photoelastic coefficient and high transparency, liquid crystal displays, plasma displays, organic EL displays, field emission displays, rear projection televisions, etc. It is suitable for an optical film used for a display.
In particular, the resin composition for an optical material of the present invention is an optical element that requires high birefringence and low photoelastic coefficient, such as a liquid crystal display, a plasma display, an organic EL display, a field emission display, a rear projection television, and the like. It can use suitably as an optical material for manufacturing the polarizing plate protective film and retardation film which are used for a display.

Claims (12)

One or more styrene resins (A) selected from the group consisting of an acrylic resin (A-1), a styrene-acrylonitrile copolymer, a styrene-methacrylic acid copolymer, and a styrene-maleic anhydride copolymer. -2), and has a photoelastic coefficient of −4.5 × 10 ⁻¹² / Pa or more and −1.8 × 10 ⁻¹² / Pa or less, and a thermoplastic resin composition ( A low molecular compound (B) having a tendency to increase the photoelastic coefficient more than the photoelastic coefficient of A),
Amounts der than 5 parts by weight or more 0.1 part by weight of the thermoplastic resin composition (A) a low molecular weight compound with respect to 100 parts by weight of (B) is,
An optical molded body comprising a resin composition for an optical material, wherein the absolute value of the photoelastic coefficient is smaller than the absolute value of the photoelastic coefficient of the thermoplastic resin composition (A) . 2. The optical molded body according to claim 1, wherein the absolute value of the photoelastic coefficient is 3 × 10 ⁻¹² / Pa or less. The photoelastic coefficient of the thermoplastic resin composition (A) is −4.5 × 10 ^-12 / Pa or more -3 × 10 ^-12 It is less than / Pa, The optical molded object of Claim 1 or 2 characterized by the above-mentioned. The low molecular weight compound (B) is selected from the group consisting of benzotriazole compounds, benzotriazine compounds, benzoate compounds, benzophenone compounds, phenol compounds, oxazole compounds, malonate compounds, and lactone compounds. The optical molded body according to any one of claims 1 to 3 , wherein the optical molded body is at least one low-molecular compound. The optically molded product according to any one of claims 1 to 4, wherein the low-molecular compound (B) is a benzotriazole compound and / or a benzotriazine compound. The molecular weight of the low molecular compound (B), the optical molded article according to 5 any one of claims 1, characterized in that 5000 or less. The optical molded body according to any one of claims 1 to 6, wherein the vapor pressure (P) of the low molecular compound (B) at 20 ° C is 1.0 x 10 ^-4 Pa or less. Melting point of the low molecular compound (B) (Tm) is, the optical molded article according to 7 any one of claims 1, characterized in that at 80 ° C. or higher. Low molecular compounds when heated at a rate of 20 ° C. / min from 23 ° C. to 260 ° C. The weight loss percentage (B) is, in 8 any one of claims 1, characterized in that 50% or less The optical molded body described. The optical film or optical sheet which consists of an optical molded object of any one of Claim 1 to 9 . A polarizing plate protective film comprising the optical film or the optical sheet according to claim 10 . A retardation film comprising the optical film or the optical sheet according to claim 10 .