JP2008268929A - Resin composition for optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin composition for optical element which has small absolute value of a photoelastic coefficient, has high birefringence and applies retardation of large absolute value to a molding. <P>SOLUTION: The resin composition for optical element comprises an acrylic type resin (A) and a styrene type resin (B), wherein the styrene type resin (B) is a styrene-methacrylic acid copolymer (B-1) and the content of methacrylic acid in the styrene-methacrylic acid copolymer (B-1) is more than 8 mass% and is 50 mass% or less. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a resin composition for an optical element, which is mainly used for producing an optical element such as a polarizing plate protective film or a retardation film.

  In recent years, with the expansion of the display market, there has been an increasing demand for clearer images, and as an optical material to be used, not only has transparency, but also higher optical properties have been imparted. There is a need for materials. One such optical characteristic is birefringence. In general, a polymer has birefringence because the refractive index differs between the molecular main chain direction and the direction perpendicular thereto. Depending on the application, it is required to strictly control this birefringence. For example, as a typical protective film used for a polarizing plate of a liquid crystal, there is a film made of triacetyl cellulose. On the other hand, by using this birefringence, it is possible to change linearly polarized light into circularly polarized light (1/4 wavelength plate, etc.) or compensate for the birefringence of liquid crystal (optical compensation film such as retardation film). It becomes. Polycarbonate is well known as such a birefringent optical material.

  In recent years, liquid crystal displays have been increased in size, and accordingly, it has been necessary to increase the size of polymer optical elements such as retardation films. However, when the optical element is increased in size, the bias of external force is generated. Therefore, when the optical element is made of a material that easily changes birefringence due to an external force such as polycarbonate, birefringence distribution occurs and the contrast becomes non-uniform. There is. The ease of occurrence of birefringence change due to external force is expressed by a photoelastic coefficient. However, since the above-mentioned polycarbonate has a large photoelastic coefficient, a birefringent optical material having a small photoelastic coefficient instead of these is eagerly desired.

  As a resin composition containing an acrylic resin and a styrene resin, a blend itself of an acrylic resin and a styrene-methacrylic acid copolymer is known (Patent Document 1). However, this blend is not used for optical materials.

  Furthermore, recently, there is a demand for controlling not only the in-plane retardation of the retardation film but also the retardation in the thickness direction in order to obtain a higher image quality of the liquid crystal screen. And in the case of the phase difference film for horizontal electric field (IPS) mode liquid crystal displays which attracted attention in recent years, it is preferable that the thickness direction retardation is a negative value. However, a film made of triacetyl cellulose or polycarbonate, which is a general optical film, or a retardation film disclosed in Patent Document 2 has a positive retardation value in the thickness direction. Therefore, in addition to a small absolute value of the photoelastic coefficient, an optical film having a negative retardation in the thickness direction is demanded.

JP-A-56-98251 JP 2004-212971 A

  In view of the above circumstances, the problem to be solved by the present invention is for an optical element having a small absolute value of photoelastic coefficient, high birefringence, and capable of imparting a retardation having a large absolute value to a molded product. It is to provide a resin composition.

  As a result of intensive studies on the above problems, the present inventors have found that in the resin composition for an optical element containing the styrene resin (A) and the acrylic resin (B), styrene as the acrylic resin (B). By using the methacrylic acid copolymer (B-1) and further adjusting the content of methacrylic acid in the styrene-methacrylic acid copolymer (B-1) to a specific range, the above problems can be solved. The present invention was completed.

  ADVANTAGE OF THE INVENTION According to this invention, the absolute value of a photoelastic coefficient is small, and the resin composition for optical elements which has high birefringence can be provided. Since the resin composition for optical elements of the present invention has high birefringence, it is possible to impart in-plane and thickness direction retardations having a large absolute value to a molded product obtained by molding the resin composition. It is. In addition, since the molded product obtained by molding the resin composition for optical elements of the present invention has excellent optical properties, liquid crystal displays, plasma displays, organic EL displays, field emission displays, rear projection televisions, etc. It can be suitably used as an optical element such as a polarizing plate protective film and a retardation film used in the display.

  Hereinafter, although this invention is demonstrated in detail with desirable embodiment, this invention is not limited to these aspects.

  The resin composition for an optical element of the present invention is a resin composition containing an acrylic resin (A) and a styrene resin (B), and the styrene resin (B) is a styrene-methacrylic acid copolymer ( B-1), and the content of methacrylic acid in the styrene-methacrylic acid copolymer (B-1) is more than 8% by mass and 50% by mass or less.

Acrylic resin (A)
In the present invention, the acrylic resin (A) refers to a polymer containing acrylic acid, methacrylic acid or a derivative thereof as a monomer component. Specific examples of the acrylic resin (A) in the present invention include, for example, methacrylic acid alkyl esters such as cyclohexyl methacrylate, t-butyl cyclohexyl methacrylate, and methyl methacrylate; methyl acrylate, ethyl acrylate, butyl acrylate, What polymerized 1 or more types of monomers chosen from acrylic acid alkylesters, such as isopropyl acrylate and acrylic acid 2-ethylhexyl, is mentioned.

  Among these, a polymer containing methyl methacrylate as a monomer component is particularly preferable because of high compatibility with a styrene-methacrylic acid copolymer (B-1) described later.

  The polymer containing methyl methacrylate as a monomer component may be a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate and another monomer. Monomers copolymerizable with methyl methacrylate include alkyl methacrylates other than methyl methacrylate; alkyl acrylates; styrene, o-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, Aromatic vinyl compounds such as nuclear alkyl-substituted styrene such as ethylstyrene and p-tert-butylstyrene, and α-alkyl-substituted styrene such as α-methylstyrene and α-methyl-p-methylstyrene; acrylonitrile, methacrylonitrile, etc. Examples thereof include vinyl cyanides; maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide; unsaturated carboxylic acid anhydrides such as maleic anhydride; unsaturated carboxylic acids such as acrylic acid, methacrylic acid and maleic acid. These monomers can be used alone or in combination of two or more.

  Among these monomers copolymerizable with methyl methacrylate, acrylic acid alkyl esters, in particular, have reduced thermal decomposition resistance of acrylic resins obtained by copolymerizing them, and fluidity during molding processing. This is preferable because it tends to be high. Here, the heat-resistant decomposability means the ease of decomposing acrylic resins at high temperatures.

  The amount of alkyl acrylates used when methyl acrylate is copolymerized with methyl methacrylate is 0.1% by mass or more based on the entire monomer mixture from the viewpoint of thermal decomposition resistance. Is preferable, and it is preferable that it is 15 mass% or less from a heat resistant viewpoint. It is more preferably 0.2% by mass or more and 14% by mass or less, and further preferably 1% by mass or more and 12% by mass or less.

  Among the alkyl acrylates, methyl acrylate and ethyl acrylate are preferable because only a small amount of methyl methacrylate is copolymerized to obtain a remarkable improvement effect on the fluidity during the molding process.

  The weight average molecular weight of the acrylic resin (A) is preferably 50,000 or more, more preferably 70,000 or more, from the viewpoint of the strength of the resin composition molded body, and from the viewpoint of molding processability and fluidity of the resin composition. Therefore, it is preferably 200,000 or less, more preferably 150,000 or less. In addition, the weight average molecular weight here means the average value when the acrylic resin (A) is a mixture of two or more of the following.

  The acrylic resin (A) may be a mixture of two or more styrene resins having different compositions and molecular weights.

  In the present invention, as the acrylic resin (A), isotactic polymethacrylic acid ester and syndiotactic polymethacrylic acid ester can be used simultaneously.

  As the acrylic resin (A), a commercially available product can be used as it is, and it can also be produced from a commercially available product by a known method. As a method for producing the acrylic resin (A), generally used polymerization methods such as cast polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, and anionic polymerization can be used. Among them, bulk polymerization and solution polymerization without using a suspending agent or an emulsifier are preferable because it is possible to reduce the mixing of minute foreign matters that are inconvenient for optical applications.

  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 used in radical polymerization can be used. For example, azo compounds such as azobisisobutylnitrile, benzoyl peroxide, lauroyl peroxide, t-butylperoxy An organic peroxide such as -2-ethylhexanoate can be used.

  In particular, when polymerization is carried out at a high temperature of 90 ° C. or higher, solution polymerization is generally used. Therefore, a peroxide, azobis, which has a 10-hour half-life temperature of 80 ° C. or higher and is soluble in the organic solvent used. Initiators and the like are preferred. Specifically, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-di-t-butylperoxy-3,3,3-trimethylcyclohexane, cyclohexane per Examples thereof include oxide, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, 1,1-azobis (1-cyclohexanecarbonitrile), 2- (carbamoylazo) isobutyronitrile and the like. These initiators are preferably used in the range of 0.005 to 5% by mass with respect to 100% by mass of the whole monomer, for example.

  As the molecular weight regulator used as necessary in the polymerization reaction, any one generally used in radical polymerization can be used. For example, mercaptan compounds such as butyl mercaptan, octyl mercaptan, dodecyl mercaptan, 2-ethylhexyl thioglycolate, etc. Particularly preferred. These molecular weight regulators are added in a concentration range such that the molecular weight of the acrylic resin (A) is controlled within the above preferred range.

  Although it does not specifically limit as a manufacturing method of acrylic resin (A), For example, the method etc. which are described in Japanese Patent Publication No.63-1964 etc. can be used.

The photoelastic coefficient of the acrylic resin (A) when not stretched is preferably −60 × 10 ⁻¹² Pa ⁻¹ or more, more preferably −30 × 10 ⁻¹² Pa ⁻¹ or more, and further preferably −6 × 10. ^-12 Pa ^-1 or more. It is preferable that the photoelastic coefficient of the acrylic resin (A) is within the above range because the absolute value of the photoelastic coefficient of the resin composition for an optical element of the present invention tends to be small.

The “photoelastic coefficient” in the present invention is a coefficient representing the ease with which birefringence changes due to external force, and is described in various documents (for example, Chemical Review, No. 39, 1998 (Academic Publishing Center) Issuance)), a coefficient defined by the following formula.
CR [Pa-1] = Δn / σR Δn = nx−ny
(In the formula, CR: photoelastic coefficient, σR: stretching stress [Pa], Δn: birefringence when stress is applied, nx: refractive index in a direction parallel to the stretching direction, ny: refractive index in a direction perpendicular to the stretching direction. )

  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 optical properties are excellent.

Styrene resin (B)
In the present invention, a styrene-methacrylic acid copolymer (B-1) is used for the styrene resin (B). By using the styrene-methacrylic acid copolymer (B-1) as the styrene-based resin (B), excellent heat resistance and transparency can be imparted to the obtained molded article for optical elements.

  In the present invention, it is important that the content of methacrylic acid in the styrene-methacrylic acid copolymer (B-1) exceeds 8% by mass and is 50% by mass or less. It is more preferable that the amount is not more than mass%. When the content of methacrylic acid exceeds 8% by mass, high birefringence can be imparted to the resin composition for optical elements, and when it is 50% by mass or less, the resin composition for optical elements has excellent transparency. It becomes possible to grant.

  The weight average molecular weight of the styrene-methacrylic acid copolymer (B-1) is preferably 50,000 or more, more preferably 100,000 or more, and preferably 80 from the viewpoint of moldability and fluidity of the resin composition. 10,000 or less, more preferably 500,000 or less. In addition, the weight average molecular weight here means the average value, when the styrene-methacrylic acid copolymer (B-1) is a mixture of two or more of the following.

  As the styrene-methacrylic acid copolymer (B-1), two or more kinds of copolymers having different composition ratios, molecular weights and the like in a range where the content of methacrylic acid exceeds 8 mass% and is 50 mass% or less. It can also be used together.

  The styrene-methacrylic acid copolymer (B-1) may be hydrogenated with an unsaturated double bond of the benzene ring. The hydrogenation rate at that time can be measured by a nuclear magnetic resonance apparatus (NMR).

  As the styrene-methacrylic acid copolymer (B-1), a commercially available product can be used as it is, or it can be produced from a commercially available product by a known method. It does not specifically limit as a manufacturing method of a styrene-methacrylic acid copolymer (B-1), A well-known anion, lump, suspension, emulsion, or solution polymerization method is employable. Among them, bulk polymerization and solution polymerization methods that do not use a suspending agent or an emulsifier are preferable because it is possible to reduce the mixing of minute foreign substances that are inconvenient for optical applications.

The photoelastic coefficient when the styrene-methacrylic acid copolymer (B-1) is unstretched is preferably 60 × 10 ⁻¹² Pa ⁻¹ or less, more preferably 30 × 10 ⁻¹² Pa ⁻¹ or less. More preferably, it is 6 × 10 ⁻¹² Pa ⁻¹ or less. It is preferable that the photoelastic coefficient of the styrene-methacrylic acid copolymer (B-1) is within the above range because the photoelastic coefficient of the resin composition for an optical element of the present invention tends to be small.

Resin Composition The mass ratio ((A) / (B)) of the acrylic resin (A) and the styrene resin (B) in the resin composition of the present invention is preferably from the viewpoint of moisture permeability and optical properties. It is 20 / 80-60 / 40, More preferably, it is 30 / 70-50 / 50.

  When the mass ratio ((A) / (B)) of the acrylic resin (A) and the styrene resin (B) is increased, the resin composition of the present invention tends to increase the water absorption rate of the molded product. Moreover, when mass ratio ((A) / (B)) is made small, the water absorption rate of a molded object tends to become small. Therefore, by adjusting the mass ratio of resin ((A) / (B)), a molded article having a desired water absorption rate can be easily produced.

  Moreover, in this invention, polymers other than acrylic resin (A) and styrene resin (B) can be mixed in the resin composition in the range which does not impair the effect of this invention. Examples of such polymers include polyolefin resins such as polyethylene and polypropylene; polyamide resins; polyphenylene sulfide resins; polyether ether ketone resins; thermoplastic resins such as polyester, polysulfone, polyphenylene oxide, polyimide, polyetherimide, and polyacetal; Examples thereof include thermosetting resins such as phenol resins, melamine resins, silicone resins, and epoxy resins, and one or more of these can be mixed. It is preferable that the ratio of the other polymer to mix is 20 mass parts or less with respect to 100 mass parts of resin compositions.

  Furthermore, arbitrary additives can be mix | blended in a resin composition according to various objectives within the range which does not impair the effect of this invention. The additive that can be blended is not particularly limited as long as it is generally used for blending resins and rubber-like polymers.

  Examples of such additives include inorganic fillers such as silicon dioxide; pigments such as iron oxide; lubricants such as stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, and ethylene bisstearamide; Mold release agents: Softeners and plasticizers such as paraffinic process oil, naphthenic process oil, aromatic process oil, paraffin, organic polysiloxane and mineral oil; hindered phenolic antioxidants; phenolic compounds with acrylate groups Antioxidants; Antioxidants such as phosphorus heat stabilizers; Hindered amine light stabilizers; Flame retardants; Antistatic agents; Reinforcing agents such as organic fibers, glass fibers, carbon fibers, metal whiskers; Colorants; Benzotriazoles Compounds, benzotriazine compounds, benzoate compounds, benzofe Emissions-based compounds, phenol compounds, oxazole compounds, malonic acid ester compounds, ultraviolet absorbers such as lactone compounds; Other additives or mixtures thereof. The addition amount of these additives is preferably 0.01 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the resin composition.

  Among the above-mentioned various additives, in particular, UV absorbers such as benzotriazole compounds, benzotriazine compounds, benzoate compounds, benzophenone compounds, phenol compounds, oxazole compounds, malonic acid ester compounds, lactone compounds, etc. The resin composition to which this is added is preferable because it has the effect of reducing the absolute value of the photoelastic coefficient. Among these, benzotriazole compounds and benzotriazine compounds are more preferable. These may be used alone or in combination of two or more.

The additive is preferable because the resin composition obtained has excellent moldability when the vapor pressure (P) at 20 ° C. is 1.0 × 10 ⁻⁴ Pa or less. A more preferable range of the vapor pressure (P) is 1.0 × 10 ⁻⁶ Pa or less, and a more preferable range is 1.0 × 10 ⁻⁸ Pa or less. Here, being excellent in moldability means that, for example, the adhesion of the additive to the roll is small during film formation. If the additive adheres to the roll, for example, it adheres to the surface of the molded body and deteriorates the appearance and optical characteristics, which may be undesirable as an optical material.

  Moreover, an additive is preferable when the melting point (Tm) is 80 ° C. or higher because the resulting resin composition is excellent in moldability. A more preferable range of the melting point (Tm) is 130 ° C. or higher, and a more preferable range is 160 ° C. or higher.

  Furthermore, the additive is preferable because the resin composition obtained has excellent molding processability when the weight reduction rate when the temperature is increased from 23 ° C. to 260 ° C. at a rate of 20 ° C./min is 50% or less. A more preferable range of the weight reduction rate is 15% or less, and a further preferable range is 2% or less.

  It does not restrict | limit especially as a manufacturing method of the resin composition of this invention, A well-known method can be used. For example, using a melt kneader such as a single screw extruder, twin screw extruder, Banbury mixer, Brabender, various kneaders, etc., adding a resin component, if necessary, adding a hydrolysis resistance inhibitor and the above other components to melt It can be produced by kneading.

Optical Element Molded Body The method for producing the optical element molded body of the present invention is not particularly limited. For example, the resin composition is formed by injection molding, sheet molding, blow molding, injection blow molding, inflation molding, or extrusion molding. Further, it can be produced by molding by a known method such as foam molding, and a secondary processing molding method such as compressed air molding or vacuum molding can also be used.

  When the optical element molded body of the present invention is a film or a sheet, for example, an unstretched film can be extruded using an extruder or the like equipped with a T die, a circular die, or the like. When obtaining a molded body by extrusion molding, the acrylic resin (A) and the styrene resin (B) may be melt-kneaded in advance, but can also be molded through melt-kneading at the time of extrusion molding. It is also possible to obtain an unstretched film or sheet by cast molding using a good solvent common to the acrylic resin (A) and the styrene resin (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, a uniaxial stretching method by roll stretching or tenter stretching, a sequential biaxial stretching method by a combination of roll stretching and tenter stretching, a simultaneous biaxial stretching method by tenter stretching, a biaxial stretching method by tubular stretching, etc. A stretched film can be produced.

  The draw ratio is preferably 0.1% or more and 300% or less, more preferably 1% or more and 200% or less, and further preferably 2% or more and 100% or less in at least one direction. By designing the draw ratio in the above range, a stretched product that is preferable in terms of birefringence, retardation, and strength tends to be obtained.

Here, the draw ratio can be determined from the following relational expression by shrinking the obtained stretched film or sheet 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, a film means a film having a thickness of 300 μm or less, and a sheet means a film having a thickness exceeding 300 μm. In the present invention, the thickness of the film is preferably 1 μm or more, more preferably 5 μm or more, and the thickness of the sheet is preferably 10 mm or less, more preferably 5 mm or less.

In the molded article for an optical element of the present invention, the absolute value of the photoelastic coefficient is 0 to 5 × 10 ⁻¹² / Pa, preferably 0 to 4 × 10 ⁻¹² / Pa, and more preferably 0 to 3 × 10 ⁻¹² / Pa. Pa. If the photoelastic coefficient is within the above range, the change in birefringence due to external force is small, so that when it is used in a large liquid crystal display device or the like, the contrast and the uniformity of the screen are excellent. The photoelastic coefficient can be adjusted to a desired range by adjusting the mass ratio and composition ratio of the resin components, or by adding the above additives.

In the molded article for an optical element of the present invention, in the resin composition containing the acrylic resin (A) and the styrene resin (B), a styrene-methacrylic acid copolymer (B-1) is used as the styrene resin (B). ), And further, the molded product obtained by molding by making the content of methacrylic acid in the styrene-methacrylic acid copolymer (B-1) more than 8% by mass and 50% by mass or less. In-plane retardation (Re) and thickness direction retardation (Rth) having a large absolute value can be provided. Here, the in-plane retardation (Re) and the thickness direction retardation (Rth) are defined by the following equations.
Re = (nx−ny) × d
Rth = ((nx + ny) / 2) −nz) × d
(Wherein, nx: main refractive index in the x direction when x is the direction in which the refractive index is maximum in the surface of the molded body, ny: y direction when y is the direction perpendicular to the x direction in the surface of the molded body) Nz: main refractive index in the thickness direction of the molded body, d: thickness (nm) of the molded body.)

  When the molded article for an optical element of the present invention is used as a quarter wavelength plate, the in-plane retardation (Re) is preferably 100 nm or more and 190 nm or less, more preferably 120 nm or more and 160 nm or less, and further preferably 130 nm or more. 150 nm or less.

  Moreover, when using the molded object for optical elements of this invention as a 1/2 wavelength plate, it is preferable that the absolute value of the in-plane retardation (Re) is 240-320 nm, More preferably, it is 260-300 nm, More preferably, it is 270 or more and 290 nm or less. The value of Re can be adjusted by the stretching ratio in the MD and TD directions, the film thickness, and the mass ratio of the acrylic resin (A) and the styrene resin (B).

  The thickness direction retardation (Rth) in the molded article for an optical element of the present invention is preferably −20 nm or less, more preferably −60 nm or less, and further preferably −90 nm or less. The value of Rth can be adjusted by the draw ratio in the MD and TD directions, the film thickness, and the mass ratio of the acrylic resin (A) and the styrene resin (B).

  The molded article for an optical element of the present invention has an in-plane and thickness direction retardation with a small absolute value of the photoelastic coefficient and a large absolute value. Therefore, the liquid crystal display, plasma display, organic EL display, field emission It can be suitably used as an optical element such as a polarizing plate protective film and a retardation film used in displays such as displays and rear projection televisions.

  The molded article for an optical element of the present invention may be appropriately subjected to surface functionalization treatment such as antireflection treatment, transparent conductive treatment, electromagnetic wave shielding treatment, gas barrier treatment and the like.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the examples described below. In the following, “%” means “% by weight”.
[Measuring method]
The measuring method of the physical property etc. in this specification is as follows.
(1) Measurement of birefringence and photoelastic coefficient The birefringence measuring apparatus 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 0.3% / min (between chucks: 30 mm, chuck moving speed: 0.1 mm / min), and the test piece width was 7 mm. Plotting birefringence (Δn) as y-axis and stretching stress (σR) as x-axis, the photoelastic coefficient (CR) was calculated from the relationship by finding the slope of the straight line in the linear region by least square approximation.
(2) In-plane retardation (Re) and thickness direction retardation (Rth)
(Measurement of in-plane retardation (Re))
The thickness d (nm) of the film was measured using a thickness gauge. This value is input to a birefringence measuring apparatus RETS-100 manufactured by Otsuka Electronics Co., Ltd., a sample is placed so that the measurement surface is perpendicular to the measurement light, and in-plane retardation (Re ) Was measured and calculated.
(Measurement of thickness direction retardation (Rth))
The average refractive index n of the optical film was measured at 23 ° C. using a Metricon laser refractometer Model 2010. And average refractive index n and film thickness d (nm) were inputted into Otsuka Electronics Co., Ltd. birefringence measuring apparatus RETS-100, and thickness direction retardation (Rth) was measured and calculated at 23 degreeC.
(3) Measurement of molecular weight (i) Acrylic resin (A)
Tosoh Corporation Gel Permeation Chromatography (HLC-8120 + 8020) column, Tosoh Corporation TSK Super HH-M (2) and Super H2500 (1) are arranged in series, and a differential refraction detector is used as a detector. Using. 0.02 g of acrylic resin as a measurement sample was dissolved in 20 cc of a THF solvent, and the elution time and strength were measured at an injection amount of 10 mL and a development flow rate of 0.3 mL / min. The weight average molecular weight of the acrylic resin of the measurement sample was determined using a calibration curve using a monodisperse methacrylic resin having a known weight average molecular weight manufactured by GL Science Co., Ltd. as a standard sample.
(Ii) Styrenic resin (B)
GPC (measuring device: GPC-8020 manufactured by Tosoh Corporation), detection: differential refraction detector (RI), column: Shodex K-805, manufactured by Showa Denko 801), solvent is chloroform, measurement temperature is 40 ° C, The weight average molecular weight was calculated in terms of commercial standard polystyrene.
(4) Measurement of haze The haze value of the film was measured according to ASTM D1003.
(5) Measurement of glass transition temperature (Tg) In DSC-7 type (manufactured by Perkin Elmer Co., Ltd.), when measuring temperature rise from room temperature to 200 ° C., raw film sample weight 8 at a rate of temperature rise of 20 ° C./min. 0.0 to 10 mg of Tg was measured.
(6) Measurement of methacrylic acid content in styrene-methacrylic acid copolymer A styrene-methacrylic acid copolymer serving as a sample is dissolved in deuterated chloroform, and 1H-NMR (JNM ECA-500) manufactured by JEOL Ltd. is used. NMR measurement was performed at a frequency of 500 MHz and at room temperature. From the measurement results, the molar ratio of the styrene unit and the methacrylic acid unit in the sample was determined from the area ratio of the proton peak of the benzene ring in the styrene unit (around 7 ppm) and the proton peak of the alkyl group in the methacrylic acid unit (around 1 to 3 ppm). The ratio was determined. The methacrylic acid content in the styrene-methacrylic acid copolymer was determined from the obtained molar ratio and the mass ratio of each monomer unit (styrene unit: methacrylic acid unit = 104: 86).

[Preparation of raw materials]
(1) Acrylic resin (A)
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. 0.0294 parts by weight of cyclohexane and 0.115 parts by weight of n-octyl mercaptan were added and mixed 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 volatile matter was removed under a certain condition, and the volatile matter was continuously transferred to an extruder in a molten state to obtain a methyl methacrylate / methyl acrylate copolymer pellet as an acrylic resin (A). 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. and a load of 3.8 kg measured in accordance with ASTM-D1238 was 1.0 g / Minutes. The photoelastic coefficient at 23 ° C. (unstretched) was −4.4 × 10 ⁻¹² / Pa.

(2) Styrenic resin (B)
(I) Styrene-methacrylic acid copolymer (B-1-1)
Continuous solution polymerization was carried out using all the equipment made of stainless steel. 74.4% by mass of styrene, 5.6% by mass of methacrylic acid, and 20% by mass of ethylbenzene were used as a preparation liquid, and 1,1-tert-butylperoxy-3,3,5-trimethylcyclohexane was used as a polymerization initiator. This prepared solution was added at 1 L / hr. The mixture was continuously fed to a fully mixed polymerization reactor equipped with a stirrer having an internal volume of 2 L at a speed of
A polymerization liquid 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.
The obtained styrene-methacrylic acid copolymer (B-1-1) was colorless and transparent. As a result of compositional analysis by NMR measurement, the styrene content was 90.5% by mass, the methacrylic acid content was 9.5% by mass, and the weight average molecular weight. Was 220,000. The photoelastic coefficient (unstretched) at 23 ° C. was 4.5 × 10 ⁻¹² / Pa.
(Ii) Styrene-methacrylic acid copolymer (B-1-2)
Polymerization was carried out in the same manner as (B-1-1) except that the charged amount was changed to 70.4% by mass of styrene and 9.6% by mass of methacrylic acid.
The obtained styrene-methacrylic acid copolymer (B-1-2) was colorless and transparent. As a result of composition analysis by NMR measurement, the styrene content was 85% by mass, the methacrylic acid content was 15% by mass, and the weight average molecular weight was 350,000. Met. Met. Further, the photoelastic coefficient at 23 ° C. (unstretched) was 4.0 × 10 ⁻¹² Pa ⁻¹ and the intrinsic birefringence was negative.
(Iii) Styrene-methacrylic acid copolymer (B-1-3)
As a comparative example, polymerization was carried out in the same manner as (B-1-1) except that the charged amount was changed to 75.2% by mass of styrene and 4.8% by mass of methacrylic acid.
The obtained styrene-methacrylic acid copolymer (B-1-3) was colorless and transparent. As a result of composition analysis by NMR measurement, the styrene content was 92% by mass, the methacrylic acid content was 8% by mass, and the weight average molecular weight was 190,000. Met. Met. The photoelastic coefficient (unstretched) at 23 ° C. was 4.8 × 10 ⁻¹² / Pa, and the intrinsic birefringence was negative.

[Examples 1 to 10, Comparative Examples 1 to 4]
Using the resin composition with the compounding ratio shown in Table 1, using a Technobel T-die mounting extruder (KZW15TW-25MG-NH type / width 150 mmT die mounting / lip thickness 0.5 mm), screw rotation speed, extrusion An unstretched film was obtained by adjusting the resin temperature in the cylinder of the machine and the temperature of the T die to the conditions shown in Table 1 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.
Then, the unstretched film was cut out to have a width of 50 mm, and uniaxial stretching (between chucks: 50 mm, chuck moving speed: 500 mm / min) was performed using the tensile tester under the conditions shown in Table 1, Example 1 -7, 9 and the uniaxially stretched film of Comparative Examples 1-4 were obtained.
Further, the uniaxially stretched film was cut out so as to have a width of 50 mm, and uniaxial stretching (between chucks: 50 mm, chuck moving speed: 500 mm / min) was performed using a tensile tester under the conditions shown in Table 1, Example 8. Ten biaxially stretched films were obtained.

  Table 1 shows the composition of each stretched film, extrusion molding conditions, stretching conditions, film thickness, glass transition temperature, in-plane retardation (Re), thickness direction retardation (Rth), photoelastic coefficient, and haze.

As is clear from the results shown in Table 1, the resin compositions for optical elements 1 to 10 of the present invention have a small absolute value of the photoelastic coefficient and a high birefringence. It was possible to give an in-plane retardation and a thickness direction retardation having a large absolute value to a molded body obtained by molding the composition.
On the other hand, the optical element resin compositions of Comparative Examples 1 to 4 had almost the same absolute value of the photoelastic coefficient as the examples, but were inferior in birefringence compared to the resin compositions of the examples. For this reason, a retardation having a large absolute value could not be imparted to a molded product obtained by molding.

  The resin composition for an optical element of the present invention is a waveguide in the fields of a display front plate, a display substrate, a touch panel, a transparent substrate used for a solar cell, and other optical communication systems, an optical switching system, an optical measurement system, etc. It can be used as an optical material for manufacturing various optical elements such as lenses, optical fibers, optical fiber coating materials, LED lenses, and lens covers. In particular, since the molded article of the resin composition for an optical element of the present invention can provide a retardation having a large absolute value, it can serve both as a protective film and as a retardation film. It can be suitably used as a polarizing plate protective film.

Claims (5)

A resin composition for optical elements comprising an acrylic resin (A) and a styrene resin (B),
The styrene resin (B) is a styrene-methacrylic acid copolymer (B-1),
The resin composition for optical elements whose content of methacrylic acid in the said styrene-methacrylic acid copolymer (B-1) exceeds 8 mass% and is 50 mass% or less.   The resin composition for an optical element according to claim 1, wherein the content of methacrylic acid in the styrene-methacrylic acid copolymer (B-1) is 9% by mass or more and 20% by mass or less.   A molded article for an optical element obtained by molding the resin composition for an optical element according to claim 1 or 2.   A polarizing plate protective film comprising the molded article for an optical element according to claim 3.   A retardation film comprising the molded article for an optical element according to claim 3.