JP2009279787A - Optical film excellent in appearance quality - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film which has few defects in appearance and a small absolute value of a photoelastic coefficient, can develop excellent display quality when incorporated, for example, into a liquid crystal display etc., and is excellent in optical characteristics. <P>SOLUTION: The optical film is produced by melt-extruding a raw material composition containing a thermoplastic resin composition (A) containing an acrylic resin (A-1) and a styrene resin (A-2) and a polymer carbon radial scavenger (B). The contents of respective components in the raw material composition are as follows: 20-80 pts.mass of (A-1), 80-20 pts.mass of (A-2), and 0.05-0.5 pts.mass of (B). The raw material composition is melt-extruded by using a single-screw extruder equipped with a T die to keep the temperature of the molten resin from the raw material inlet of the extruder to the outlet of the T die below the glass transition temperature of the raw material composition plus 150°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical film having excellent optical properties, which is formed by a melt extrusion method, has few appearance defects, and can exhibit excellent display quality when incorporated in a liquid crystal display device or the like.

In recent years, with the expansion of the display market, there is an increasing demand for clearer images. Therefore, there is a demand for an optical material imparted with higher optical properties, not just a transparent material.
One of such advanced optical characteristics 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, in the case of a protective film used for a polarizing plate of a liquid crystal, a polymer material molded body having a smaller birefringence is required even if the total light transmittance is the same. A typical example is a film made of triacetylcellulose. 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.
Recently, liquid crystal displays have become larger, and accordingly, larger polymer optical elements such as retardation films are required. However, when the optical element is increased in size, the bias of the external force is generated. Therefore, when the optical element is made of a material that easily changes birefringence due to the external force, a distribution of birefringence occurs and the contrast becomes non-uniform. .
The ease of occurrence of birefringence change due to external force is expressed by a photoelastic coefficient. However, since the above-described polycarbonate has a large photoelastic coefficient, a birefringent optical material having a small photoelastic coefficient instead of these is strongly desired. As materials having a small absolute value of photoelastic coefficient, homopolymers of methyl methacrylate (PMMA) and amorphous polyolefin (APO) are known (see Non-Patent Document 1). These materials have absolute photoelastic coefficients. The value is not satisfactory.

In response to such a request, the present inventors have first made a heat containing an acrylic resin and a styrene resin as a material having a small absolute value of the photoelastic coefficient and excellent in other optical characteristics such as transparency. A plastic resin composition has been found (Patent Document 1). In addition to being optically transparent, the optical film formed using this resin composition is further required to have little coloration or discoloration, few appearance defects such as dot or streak. .
However, when a resin or resin composition is formed into a film by melt extrusion, the resin or resin composition deteriorates in the extruder, the film is colored or discolored, or an optically transparent film cannot be obtained. There's a problem. Furthermore, appearance defects such as gels caused by cross-linked products, brown or black dots caused by burnt resin, foaming caused by resin decomposition gas, die lines caused by meani, etc. There are problems such as appearance defects such as streak defects. Even when a thermoplastic resin composition containing an acrylic resin and a styrene resin was molded, the excellent optical properties inherent to the thermoplastic resin composition could not be sufficiently exhibited.
As a method for solving problems such as coloring and discoloration of a resin film formed by melt extrusion, a phenolic antioxidant and phosphorus are added to a resin composition comprising an N-phenylmaleimide / isobutene copolymer and a styrene / acrylonitrile copolymer. A method of adding an antioxidant (Patent Document 2), a method of adding an antioxidant to a resin composition comprising a styrene resin and a crystalline thermoplastic resin (Patent Document 3), and a spirobiindane structure in a repeating unit A method of adding a carbon radical scavenger to a polymer to be contained (Patent Document 4) is disclosed.
In addition, the cross-linked gel is generated in the extruder because the polymer radicals generated by the shear stress are recombined. By adding a lubricant or using a low compression ratio screw, the cross-linked gel is generated. Attempts have also been made to suppress the occurrence. In addition, a method (Patent Document 5) is disclosed in which the appearance of a film is improved by crushing and refining the generated gel by melt extrusion film formation at a certain value or higher.

International Publication No. 2007/043356 Pamphlet JP 2006-45368 A JP 2001-131308 A JP 2006-219612 A JP 2003-311813 A Chemical Review, No. 39, 1998 (published by Academic Publishing Center)

However, when the above-mentioned antioxidant is added to the resin or resin composition as in the methods disclosed in the above-mentioned documents 2 and 3, the photoelastic coefficient of the resulting resin film is greatly changed. In order to prepare such that the absolute value of becomes small, a large amount of antioxidant cannot be used. Therefore, the obtained optical film is not always satisfactory as a film having few appearance defects as used in a liquid crystal display device or the like.
In addition, the method described in the above-mentioned document 5 does not fundamentally suppress the generation of the crosslinked gel, and avoids the appearance of appearance defects due to the oozing of the lubricant onto the film surface and the film surface roughness due to the generated fine gel. Therefore, it is not always satisfactory as an optical application.

  In view of the above circumstances, the present invention exhibits excellent display quality when incorporated in a liquid crystal display device or the like that is formed by a melt extrusion method and has few appearance defects and a small absolute value of a photoelastic coefficient. An object of the present invention is to provide an optical film having excellent optical properties.

  According to the research of the present inventor, the main cause of the appearance defect that occurs when melt-forming a thermoplastic resin composition containing an acrylic resin and a styrene resin is localized due to heating and shear stress during melt extrusion. It was found that this is a carbon radical generated in a polymer exposed to overheating, and the generated carbon radical becomes a gel-like substance or decomposition volatile matter, resulting in a film appearance defect.

  Based on the above findings, the present inventors have conducted intensive studies on a method for forming an optical film with few optical defects and a small absolute value of the photoelastic coefficient and excellent optical properties by a melt extrusion method. Each component in the raw material composition comprising a thermoplastic resin composition (A) containing an acrylic resin (A-1) and a styrene resin (A-2), and a polymer carbon radical scavenger (B). The content is adjusted to a specific range, and the raw material composition is adjusted to the temperature of the molten resin from the raw material inlet of the single screw extruder to the T die outlet using a single screw extruder equipped with a T die. The present invention has been completed by finding that an optical film having few defects in appearance and excellent optical properties can be obtained by maintaining the glass transition temperature less than + 150 ° C. and performing melt extrusion without decreasing coloring or transparency. It was.

That is, the present invention is as follows.
[1]
By melt-extruding a raw material composition containing a thermoplastic resin composition (A) containing an acrylic resin (A-1) and a styrene resin (A-2) and a polymer carbon radical scavenger (B) An optical film formed,
The content of each component in the raw material composition is (A-1) 20 to 80 parts by mass, (A-2) 80 to 20 parts by mass, (B) 0.05 to 0.5 parts by mass,
Using the single screw extruder provided with the T die for the raw material composition, the molten resin temperature from the raw material inlet of the single screw extruder to the T die outlet is less than the glass transition temperature of the raw material composition + 150 ° C. An optical film formed by melt extrusion while maintaining the same.
[2]
The optical film according to [1], wherein the single-screw extruder is an extruder provided with a vent part and a polymer filter.
[3]
The optical film as described in [2] above, wherein the filtration accuracy of the polymer filter is less than 20 μm.
[4]
Any of the above [1] to [3], wherein the polymer carbon radical scavenger (B) is contained in an amount of 0.05 parts by mass to 0.5 parts by mass with respect to 100 parts by mass of the thermoplastic resin composition (A). Or an optical film.
[5]
The polymer carbon radical scavenger (B) is a compound represented by the following general formula (1) having an acrylate group and a phenolic hydroxyl group in the molecule, according to any one of the above [1] to [4]. Optical film.

(In general formula (1), R1 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R2 and R3 each independently represents an alkyl group having 1 to 8 carbon atoms.)
[6]
The optical system according to any one of [1] to [5], wherein the styrenic resin (A-2) is a styrene-maleic anhydride copolymer having a maleic anhydride content of 0.1 to 50% by mass. the film.
[7]
The total content of the acrylic resin (A-1) and the styrene resin (A-2) in the thermoplastic resin composition (A) is 80% by mass or more based on the entire thermoplastic resin composition (A). The mass ratio ((A-1) / (A-2)) of the acrylic resin (A-1) and the styrene resin (A-2) in the thermoplastic resin composition (A) is 20 /. The optical film according to any one of [1] to [6], which is 80 to 80/20.
[8]
Any one of [1] to [7] above, wherein the glass transition temperature is 120 ° C. or more and 200 ° C. or less, the film thickness is 20 μm or more and 300 μm or less, and the appearance defect of 100 μm or more is less than 10 pieces / m ^2. Optical film.
[9]
The optical film according to any one of the above [1] to [8], which has a photoelastic coefficient of −4 × 10 ⁻¹² to 4 × 10 ⁻¹² / Pa.
[10]
The optical film according to any one of [1] to [9], wherein the yellowness ΔYI value is 1.5 or less and the haze value is 0.5% or less.
[11]
The polarizing plate protective film which consists of an optical film in any one of said [1]-[10].
[12]
The retardation film which consists of an optical film in any one of said [1]-[10].
[13]
By melt-extruding a raw material composition containing a thermoplastic resin composition (A) containing an acrylic resin (A-1) and a styrene resin (A-2) and a polymer carbon radical scavenger (B) A method for producing an optical film including a step of forming a film,
The content of each component in the raw material composition is (A-1) 20 to 80 parts by mass, (A-2) 80 to 20 parts by mass, (B) 0.05 to 0.5 parts by mass,
Using the single screw extruder provided with the T die for the raw material composition, the molten resin temperature from the raw material inlet of the single screw extruder to the T die outlet is less than the glass transition temperature of the raw material composition + 150 ° C. The manufacturing method of the optical film including the process of forming into a film by maintaining and melt-extruding.
[14]
The method for producing an optical film according to the above [13], wherein the single-screw extruder is an extruder provided with a polymer filter having a filtration accuracy of less than 20 μm.
[15]
[13] or [14], wherein the optical film has a glass transition temperature of 120 ° C. or more and 200 ° C. or less, a film thickness of 20 μm or more and 300 μm or less, and an appearance defect of 100 μm or more is less than 10 pieces / m ^2. ] The manufacturing method of the optical film of description.

  According to the present invention, an optical film having excellent optical properties that can exhibit excellent display quality when incorporated in a liquid crystal display device or the like having few appearance defects and a small absolute value of a photoelastic coefficient. Can be provided.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as the present embodiment) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

  The optical film of the present embodiment includes a thermoplastic resin composition (A) containing an acrylic resin (A-1) and a styrene resin (A-2), and a polymer carbon radical scavenger (B). An optical film formed by melt-extruding a raw material composition, wherein the ratio of each component in the raw material composition is (A-1) 20 to 80 parts by mass, (A-2) 80 to 20 (B) 0.05 to 0.5 parts by mass, and using the single screw extruder provided with a T die, the raw material composition is transferred from the raw material inlet of the single screw extruder to the T die. It is an optical film formed by melt extrusion while maintaining the molten resin temperature up to the outlet below the glass transition temperature of the raw material composition + 150 ° C.

  First, the thermoplastic resin composition (A) will be described. The thermoplastic resin composition (A) includes an acrylic resin (A-1) and a styrene resin (A-2).

  In this Embodiment, acrylic resin (A-1) is a polymer obtained by superposing | polymerizing the monomer containing acrylic acid, methacrylic acid, and these derivatives.

  Specific examples of the acrylic resin (A-1) include, for example, methacrylic acid alkyl esters such as cyclohexyl methacrylate, t-butyl cyclohexyl methacrylate, methyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, and acrylic. Examples thereof include those obtained by polymerizing one or more monomers selected from acrylic acid alkyl esters such as isopropyl acid and 2-ethylhexyl acrylate. The acrylic resin (A-1) also includes copolymers with other monomers copolymerizable with the above compound.

  Among them, since it is excellent in weather resistance and transparency, and further tends to obtain a high molecular weight polymer with a relatively high polymerization reaction rate, a homopolymer of methyl methacrylate, or methyl methacrylate and other monomers And a copolymer are preferred.

  Examples of other monomers copolymerizable with methyl methacrylate include methacrylic acid alkyl esters other than methyl methacrylate; acrylic acid alkyl esters; styrene and o-methyl styrene, p-methyl styrene, 2,4-dimethyl. Nuclear alkyl-substituted styrenes such as styrene, ethyl styrene, and p-tert-butyl styrene; Aromatic vinyl compounds such as α-alkyl-substituted styrene such as α-methyl styrene and α-methyl-p-methyl styrene; acrylonitrile, methacryl Examples include vinyl cyanides such as nitrile; 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. It is done. These can be used alone or in combination of two or more.

  Among these monomers that can be copolymerized with methyl methacrylate, alkyl acrylates are particularly excellent in heat decomposability, and fluidity during molding of copolymers obtained by copolymerizing them. Is preferable because of a tendency to increase.

  As the alkyl acrylates, methyl acrylate and ethyl acrylate are particularly preferred because they tend to provide a significant improvement in fluidity during molding by simply copolymerizing them with a small amount of methyl methacrylate.

  The amount of alkyl acrylates used when methyl acrylate is copolymerized with methyl methacrylate is preferably 0.1% by mass or more from the viewpoint of heat decomposability, and 15% from the viewpoint of heat resistance. % Or less is preferable. 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.

  In addition, as described above, the acrylic resin (A-1) includes those obtained by copolymerizing acrylic acid, methacrylic acid or derivatives thereof, and other monomer components. The content (copolymerization ratio) of the monomer component is preferably less than 50% by mass with respect to the acrylic resin (A-1).

  The weight average molecular weight of the acrylic resin (A-1) is preferably 50,000 to 200,000. The weight average molecular weight is preferably 50,000 or more from the viewpoint of the strength of the molded product, and preferably 200,000 or less from the viewpoint of molding processability and fluidity. A more preferable range of the weight average molecular weight is 70,000 to 150,000. Here, the weight average molecular weight means a value obtained by polystyrene conversion using GPC (manufactured by Tosoh Corporation) and developing solution as chloroform.

  In this Embodiment, 2 or more types from which molecular weight, a composition, etc. differ can be used simultaneously as acrylic resin (A-1). In the present embodiment, isotactic polymethacrylic acid alkyl ester and syndiotactic polymethacrylic acid alkyl ester can be used simultaneously.

  As a method for producing the acrylic resin (A-1), for example, generally used polymerization methods such as cast polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, anion polymerization and the like can be used. For optical applications, it is preferable to avoid the introduction of minute foreign substances as much as possible. From this viewpoint, it is preferable to produce by bulk polymerization or solution polymerization without using a suspending agent or an emulsifier.

  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, azo compounds such as azobisisobutylnitrile, benzoyl peroxide, lauroyl peroxide, t-butyl peroxide. Organic peroxides such as oxy-2-ethylhexanoate can be used.

  In particular, when polymerization is performed at a high temperature of 90 ° C. or higher, solution polymerization is common, so that the peroxide has a 10-hour half-life temperature of 80 ° C. or higher and is soluble in the organic solvent used. Azobis initiators and the like are preferable. Specifically, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, cyclohexane peroxide, 2,5-dimethyl-2,5-di (benzoyl) Peroxy) hexane, 1,1-azobis (1-cyclohexanecarbonitrile), 2- (carbamoylazo) isobutyronitrile and the like.

  These initiators are preferably used in a concentration range of 0.005 to 5% by mass.

  As the molecular weight regulator used as necessary in the polymerization reaction, any of those used in general radical polymerization can be used, for example, butyl mercaptan, octyl mercaptan, dodecyl mercaptan, 2-ethylhexyl thioglycolate. The mercaptan compounds such as are particularly preferred. These molecular weight regulators are added in such a concentration range that the degree of polymerization of the acrylic resin (A-1) is controlled within the above-mentioned preferred range.

  As a manufacturing method of acrylic resin (A-1), the method etc. which are described in Japanese Patent Publication No.63-1964 etc. can be used, for example.

  In the present embodiment, a heat-resistant acrylic resin can be used as the acrylic resin (A-1). The heat-resistant acrylic resin is a polymer containing an aromatic vinyl monomer and a (meth) acrylic monomer as monomer components, and preferably has a copolymerization ratio of the (meth) acrylic monomer. It is a polymer of 50% by mass or more.

  Here, the aromatic vinyl monomer means a monomer in which a vinyl group is bonded to the side chain of the aromatic hydrocarbon, and the (meth) acrylic monomer means acrylic acid or methacrylic acid. Or these derivatives.

  Specific examples of the (meth) acrylic monomer include, for example, methacrylic acid alkyl esters such as cyclohexyl methacrylate, t-butyl cyclohexyl methacrylate, and methyl methacrylate; methyl acrylate, ethyl acrylate, butyl acrylate, acrylic And alkyl acrylates such as isopropyl acid and 2-ethylhexyl acrylate.

  Specific examples of the aromatic vinyl monomer include, for example, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, and the like. Nuclear alkyl-substituted styrene; α-alkyl-substituted styrene such as α-methylstyrene and α-methyl-p-methylstyrene; Among these, styrene is preferred because it tends to provide a high molecular weight polymer having a high polymerization reaction rate and excellent mechanical strength.

  In the present embodiment, as the heat-resistant acrylic resin, a methacrylic acid ester and / or an acrylic acid ester unit, an aromatic vinyl compound unit and a copolymer containing a compound unit represented by the following general formula (4) (hereinafter, Heat-resistant acrylic resin (A-1-1)) is preferable because a uniform random copolymer is easily obtained and tends to be a high-quality stable polymer.

(Wherein X represents O or N—R, O is an oxygen atom, N is a nitrogen atom, R is a hydrogen atom, an alkyl group, an aryl group or a cycloalkyl group.)

  Specific examples of the methacrylic acid ester and / or acrylic acid ester that are the first monomer component of the heat-resistant acrylic resin (A-1-1) include, for example, methyl methacrylate, ethyl methacrylate, propyl methacrylate, Methacrylic acid alkyl esters such as n-butyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, t-butyl cyclohexyl methacrylate; methyl acrylate, ethyl acrylate, butyl acrylate, isopropyl acrylate, 2-ethylhexyl acrylate And acrylic acid alkyl esters. Among the above, methyl methacrylate is preferable.

  Specific examples of the aromatic vinyl compound that is the second monomer component of the heat-resistant acrylic resin (A-1-1) include, for example, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, Examples thereof include nuclear alkyl-substituted styrenes such as 2,4-dimethylstyrene, ethylstyrene, and p-tert-butylstyrene; α-alkyl-substituted styrenes such as α-methylstyrene and α-methyl-p-methylstyrene. Among the above, styrene is preferable.

  Among the units represented by the general formula (4) which is the third monomer component of the heat-resistant acrylic resin (A-1-1), as X being O, maleic anhydride, itaconic acid, Examples thereof include units derived from unsaturated dicarboxylic acid anhydrides which are anhydrides such as ethyl maleic acid, methyl itaconic acid and chloromaleic acid. Among these, maleic anhydride is preferably a unit derived from maleic anhydride because it can be obtained at low cost and is relatively easy to copolymerize with other monomer components. Examples of X being N—R include units derived from maleimide monomers such as N-phenylmaleimide and N-cyclohexylmaleimide.

  The copolymerization ratio of the monomer units constituting the heat-resistant acrylic resin (A-1-1) is such that the methacrylic acid ester and / or the acrylic acid ester unit is 50% by mass or more from the viewpoint of heat resistance and photoelastic coefficient. Preferably, the aromatic vinyl compound unit is 5% by mass or more and 40% by mass or less, and the compound unit represented by the general formula (4) is 5% by mass or more and 20% by mass or less.

  More preferably, the methacrylic acid ester and / or acrylic acid ester unit is 50% by mass to 83% by mass, the aromatic vinyl compound unit is 12% by mass to 40% by mass, and the compound represented by the general formula (4). A unit is 5 mass% or more and 18 mass% or less.

  More preferably, the methacrylic acid ester and / or the acrylic acid ester unit is 50% by mass to 78% by mass, the aromatic vinyl compound unit is 16% by mass to 40% by mass, and the compound represented by the general formula (4). A unit is 6 mass% or more and 15 mass% or less.

  Further, the ratio of the aromatic vinyl compound unit to the copolymerization ratio of the compound unit represented by the general formula (4) (copolymerization ratio of the aromatic vinyl compound monomer unit / the compound represented by the general formula (4)) The unit copolymerization ratio) is preferably 1 to 3 times.

  Particularly preferable heat-resistant acrylic resin (A-1-1) includes methyl methacrylate-maleic anhydride-styrene copolymer (A-1-1-1), and in particular, methacrylic acid in the copolymer. The methyl unit is 50 to 90% by mass, the maleic anhydride unit is 3 to 20% by mass, the styrene unit is 7 to 40% by mass, and the copolymerization ratio of the styrene unit to the copolymerization ratio of the maleic anhydride unit (styrene (Unit / maleic anhydride unit) is preferably 1 to 3 times from the viewpoint of heat resistance and photoelastic coefficient. The proportion of each unit in the copolymer is more preferably 50 to 90% by mass of methyl methacrylate units, 5 to 19% by mass of maleic anhydride units, and 10 to 40% by mass of styrene units in the copolymer. More preferably, the methyl methacrylate unit in the copolymer is 50 to 88% by mass, the maleic anhydride unit is 6 to 15% by mass, and the styrene unit is 16 to 40% by mass.

  As a method for producing a methyl methacrylate-maleic anhydride-styrene copolymer (A-1-1-1), bulk polymerization using a radical initiator is suitable, but solution polymerization and emulsion polymerization are used. Is also possible.

  For polymerization of methyl methacrylate-maleic anhydride-styrene copolymer (A-1-1-1), it is preferable to apply a diacyl peroxide such as lauroyl peroxide.

  As a preferable polymerization method of the methyl methacrylate-maleic anhydride-styrene copolymer (A-1-1-1), for example, the method described in JP-B-63-1964 can be mentioned.

  The melt index (ASTM D1238; I condition) of the methyl methacrylate-maleic anhydride-styrene copolymer (A-1-1-1) is preferably 10 g / 10 min or less from the viewpoint of the strength of the optical film. More preferably, it is 6 g / 10 minutes or less, More preferably, it is 3 g / 10 minutes or less.

  Another preferred example of the heat-resistant acrylic resin is a ternary or higher copolymer containing a methacrylic acid ester and / or an acrylate ester unit, an aromatic vinyl compound unit, and an acid anhydride unit having a 6-membered ring structure. (Hereinafter referred to as heat-resistant acrylic resin (A-1-2)). This heat-resistant acrylic resin (A-1-2) is suitable for an optical material because it has excellent heat resistance and tends to facilitate the retardation design of the resulting molded article.

  Specific examples of methacrylic acid ester and / or acrylic acid ester and aromatic vinyl compound as the second monomer component of the first monomer component of the heat-resistant acrylic resin (A-1-2), and The preferable copolymerization ratio is the same as that of the above-mentioned heat-resistant acrylic resin (A-1-1).

  In addition, the acid anhydride unit having a 6-membered ring structure, which is the third monomer component of the heat-resistant acrylic resin (A-1-2), includes an unsaturated carboxylic acid monomer and, if necessary, an unsaturated carboxylic acid. After polymerization with an acid alkyl ester monomer and other monomer components to form a copolymer, the copolymer is heated in the presence or absence of a suitable catalyst, and subjected to dealcoholization and / or dehydration. It can be formed by carrying out an intramolecular cyclization reaction. In this case, typically, the carboxyl group of the unsaturated carboxylic acid unit of 2 units is dehydrated by heating the copolymer, or the alcohol of the alcohol from the unsaturated carboxylic acid unit and the unsaturated carboxylic acid alkyl ester unit adjacent to each other is dehydrated. By elimination, one unit of an acid anhydride unit having a 6-membered ring structure is formed.

  Examples of the unsaturated carboxylic acid monomer for forming a 6-membered ring acid anhydride unit include methacrylic acid, acrylic acid, itaconic acid, maleic acid, fumaric acid, cinnamic acid, and the like. Examples of the carboxylic acid alkyl ester monomer include methyl methacrylate and methyl acrylate.

  The heat-resistant acrylic resin (A-1-2) is disclosed in JP-B-02-26641, JP-A-2006-266543, JP-A-2006-274069, JP-A-2006-274071, JP-A-2006-283013, JP-A-2006-283013. With reference to the method described in 2005-162835, the composition ratio can be determined, manufactured, and evaluated.

  In the present embodiment, the styrene resin (A-2) refers to a polymer containing at least a styrene monomer as a monomer component.

  Here, the styrene monomer means a monomer having a styrene skeleton in its structure. For example, in addition to styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4- Vinyl aromatic compound monomers such as nuclear alkyl-substituted styrenes such as dimethyl styrene, ethyl styrene and p-tert-butyl styrene; α-alkyl-substituted styrenes such as α-methyl styrene and α-methyl-p-methyl styrene Of these, styrene is preferred.

  The styrene resin (A-2) includes those obtained by copolymerization of a styrene monomer component and another monomer component. Examples of copolymerizable monomers include alkyl methacrylates such as methyl methacrylate, cyclohexyl methacrylate, methylphenyl methacrylate, and isopropyl methacrylate; alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate. Saturated carboxylic acid alkyl ester monomer; unsaturated carboxylic acid monomer such as methacrylic acid, acrylic acid, itaconic acid, maleic acid, fumaric acid, cinnamic acid; 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.

  The content (copolymerization ratio) of such other monomer components is preferably less than 50% by mass with respect to the styrene resin (A-2).

  As the styrene-based resin (A-2), in particular, the styrene-maleic anhydride copolymer has heat resistance and tends to have good properties such as transparency and folding strength of the optical film. Therefore, it is preferable. In particular, when a polymer containing methyl methacrylate as a monomer component is used as the acrylic resin (A-1), it is preferable to use a styrene-maleic anhydride copolymer as the styrene resin (A-2). .

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

  As the styrene resin (A-2), two or more types having different compositions, molecular weights, and the like can be used in combination. Examples of the method for producing the styrene resin (A-2) include known anions, lumps, suspensions, emulsions, and 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 embodiment, the thermoplastic resin composition (A) includes an acrylic resin (A-1) and a styrene resin (A-2), and the acrylic resin (A) in the thermoplastic resin composition (A) ( The photoelastic coefficient of the optical film can be controlled by adjusting the ratio (parts by mass) of A-1) and the styrene resin (A-2) and the mass ratio thereof.

  The ratio of the acrylic resin (A-1) in the thermoplastic resin composition (A) is preferably 20 to 80 parts by mass with respect to 100 parts by mass of the thermoplastic resin composition (A). The proportion of the styrene resin (A-2) is preferably 20 to 80 parts by mass with respect to 100 parts by mass of the thermoplastic resin composition (A).

  Moreover, the sum total of content of acrylic resin (A-1) and styrene resin (A-2) in a thermoplastic resin composition (A) is preferable with respect to the whole thermoplastic resin composition (A). Is 80% by mass or more, more preferably 95% by mass or more.

  Furthermore, the mass ratio ((A-1) / (A-2)) of the acrylic resin (A-1) and the styrene resin (A-2) in the thermoplastic resin composition (A) is an acrylic resin ( Although depending on the kind of A-1) and styrene resin (A-2), it is preferably 20/80 to 80/20, more preferably 30/70 to 70/30.

  Moreover, polymers other than acrylic resin (A-1) and styrene resin (A-2) can also be mixed with a thermoplastic resin composition (A). Examples of polymers that can be mixed include heat such as polyolefin resins such as polyethylene and polypropylene, polyamide resins, polyphenylene sulfide resins, polyether ether ketone resins, polyesters, polysulfones, polyphenylene oxides, polyimides, polyether imides, and polyacetals. Examples thereof include thermoplastic resins and thermosetting resins such as phenol resins, melamine resins, silicone resins, and epoxy resins. The content of these polymers is preferably 20% by mass or less with respect to the thermoplastic resin composition (A) from the viewpoint of the photoelastic coefficient.

  Furthermore, in the thermoplastic resin composition (A) containing the acrylic resin (A-1) and the styrene resin (A-2), the acrylic resin (A-1) and the styrene resin (A-2) are It is preferable that they are compatible. The compatibility can be realized by appropriately selecting the composition of acrylic resin and styrene resin (including copolymer composition), blending ratio, kneading temperature, kneading pressure, cooling temperature, cooling rate, and the like. The miscible is described in detail in “High Performance Polymer Alloy” (edited by the Society of Polymer Science, published by Maruzen Co., Ltd. in 1991). When the acrylic resin (A-1) and the styrene resin (A-2) are compatible, the thermoplastic resin composition (A) containing the acrylic resin (A-1) and the styrene resin (A-2). There exists a tendency for the total light transmittance of the optical film obtained by shape | molding the raw material composition containing this to become favorable.

  Furthermore, arbitrary additives can be mix | blended with a thermoplastic resin composition (A) according to various objectives within the range which does not impair the effect of this invention remarkably. The kind of such additive is not particularly limited as long as it is generally used for compounding a resin or a rubbery polymer. For example, 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 agent; paraffinic process oil , Naphthenic process oil, aromatic process oil, paraffin, organic polysiloxane, mineral oil and other softeners and plasticizers; other antioxidants; UV absorbers; hindered amine light stabilizers; flame retardants; A reinforcing agent such as organic fiber, glass fiber, carbon fiber, and metal whisker; a coloring agent, other additives, or a mixture thereof.

  Examples of ultraviolet absorbers include benzotriazole compounds, triazine compounds, benzoate compounds, benzophenone compounds, oxybenzophenone compounds, phenol compounds, oxazole compounds, malonic acid ester compounds, cyanoacrylate compounds, lactones. Compounds, salicylic acid ester compounds, benzoxazinone compounds, and the like, preferably benzotriazole compounds and benzotriazine compounds. These may be used alone or in combination of two or more.

  The blending amount of the ultraviolet absorber is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 2 parts by mass with respect to 100 parts by mass of the thermoplastic resin composition (A). More preferably, it is 0.1 to 1.5 parts by mass or less.

  Next, the polymer carbon radical scavenger (B) will be described. The polymer carbon radical scavenger (B) contained in the optical film of the present embodiment is an antioxidant that suppresses the generation of foreign matters due to thermal deterioration in the molding process of the thermoplastic resin composition (A), etc. The thermoplastic resin composition (A) is preferably blended in the range of 0.05 parts by mass or more and 0.5 parts by mass or less, and in the range of 0.1 parts by mass or more and 0.3 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin composition (A). It is more preferable to mix | blend with.

  Here, when the blending amount of the polymer carbon radical scavenger (B) is less than 0.05 parts by mass, the thermal stability at the time of melt film formation of the raw material composition becomes poor and the generation of foreign matters cannot be sufficiently suppressed. On the other hand, when the blending amount exceeds 0.5 parts by mass, the polymer carbon radical scavenger itself is deposited as a large amount of volatile matter, causing surface irregularities of the resulting optical film and the appearance quality of the film. May be reduced.

Phenol-based antioxidants generally known as heat stabilizers capture carboxy radicals (COO ⁻ ) generated by adding oxygen in the air to polymer carbon radicals generated in the molten resin. The polymer carbon radical scavenger of the present embodiment can directly capture the polymer carbon radical itself generated by molecular chain scission or hydrogen abstraction reaction during molding. The polymer carbon radical scavenger is preferably a compound having an acrylate group in the molecule, and more preferably a compound having an acrylate group and a phenolic hydroxyl group in the molecule. Polymeric carbon radical scavengers having an acrylate group in the molecule tend to have a more prominent gelling effect, and even when added in a large amount in the thermoplastic resin composition (A), the photoelastic coefficient is increased. Less likely to change.

  As the polymer carbon radical scavenger having an acrylate group in the molecule, for example, a compound represented by the following general formula (1) can be suitably used.

(In general formula (1), R1 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R2 and R3 each independently represents an alkyl group having 1 to 8 carbon atoms.)

  The alkyl group having 1 to 8 carbon atoms represented by R1 in the general formula (1) may have a straight chain, a branched chain, or a ring structure. R2 and R3 are preferably a structure represented by "*-(CH3) 2-R '" containing a quaternary carbon (* represents a site connected to an aromatic ring, and R' represents a carbon number of 1 to 5 represents an alkyl group).

  R2 is more preferably a t-butyl group, a t-amyl group or a t-octyl group. R3 is more preferably a t-butyl group or a t-amyl group.

  As a compound represented by the above general formula (1), commercially available products include Sumilizer GM (general formula (2)), Sumilizer GS (general formula (3)) (both trade names, manufactured by Sumitomo Chemical Co., Ltd.) and the like. Can be mentioned.

  These polymer carbon radical scavengers may be used alone or in combination of two or more.

  In addition to the polymer carbon radical scavenger, other antioxidants may be added to the optical film of the present embodiment as necessary within a range not inhibiting the effects of the present invention. Examples of such other antioxidants include phenolic antioxidants and phosphorus antioxidants, and these antioxidants may be used alone or in combination of two or more. .

  Examples of phenolic antioxidants include pentaerythritol-tetrakis (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate), thiodiethylene-bis (3- (3,5-di-). t-butyl-4-hydroxyphenyl) propionate), octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N′-hexane-1,6-diylbis (3- ( 3,5-di-t-butyl-4-hydroxyphenyl) propionamide), diethyl ((3,5-bis (1,1-dimethylethyl) -4-hydroxyphenyl) methyl) phosphate, 3,3 ′, 3 '', 5,5 ', 5' '-hexa-t-butyl-a, a', a ''-(mesitylene-2,4,6-triyl) tri-p-cresol, Tylene bis (oxyethylene) bis (3- (5-t-butyl-4-hydroxy-m-tolyl) propionate), hexamethylene-bis (3- (3,5-di-t-butyl-4-hydroxyphenyl) Propionate), 1,3,5-tris (3,5-di-t-butyl-4-hydroxybenzyl) -1,3,5-triazine-2,4,6 (1H, 3H, 5H) -trione, 1,3,5-tris ((4-tert-butyl-3-hydroxy-2,6-xylyl) methyl) -1,3,5-triazine-2,4,6 (1H, 3H, 5H) -trione 2,6-di-t-butyl-4- (4,6-bis (octylthio) -1,3,5-triazin-2-ylamino) phenol, 3,9-bis (2- (3- (3 -T-butyl-4-hydroxy-5-methylphen Le) propionyloxy) -1,1-dimethylethyl) -2,4,8,10-spiro (5,5) undecane.

  Commercially available phenolic antioxidants may be used as the phenolic antioxidant, and examples of such commercially available phenolic antioxidants include Irganox 1010 (Irganox 1010: pentaerythritol tetrakis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], manufactured by Ciba Specialty Chemicals), Irganox 1076: Octadecyl-3- (3,5-di-t-butyl- 4-hydroxyphenyl) propionate, manufactured by Ciba Specialty Chemicals), Irganox 1330 (3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-t-butyl-a, a ′) , A ″-(mesitylene-2,4,6-triyl) tri- -Cresol, manufactured by Ciba Specialty Chemicals), Irganox 3114: 1,3,5-tris (3,5-di-t-butyl-4-hydroxybenzyl) -1,3,5-triazine 2,4,6 (1H, 3H, 5H) -trione, manufactured by Ciba Specialty Chemicals), Irganox 3790: 1,3,5-tris ((4-t-butyl-3-hydroxy-2 , 6-Xylyl) methyl) -1,3,5-triazine-2,4,6 (1H, 3H, 5H) -trione, Ciba Specialty Chemicals (now Ciba Japan Co., Ltd.)), Adekastab AO- 80 (ADK STAB AO-80: 3,9-bis (2- (3- (3-tert-butyl-4-hydroxy-5-methylphenyl) (Lopionyloxy) -1,1-dimethylethyl) -2,4,8,10-tetraoxaspiro (5,5) undecane, manufactured by Adeka Corporation), Irganox 3125 (Irganox 3125, manufactured by Ciba Specialty Chemicals), Examples thereof include Sumitizer BHT (Sumilizer BHT, manufactured by Sumitomo Chemical Co., Ltd.), Cyanox 1790 (Cyanox 1790, manufactured by Cytec Co., Ltd.), Smither GA-80 (Sumizer GA-80, manufactured by Sumitomo Chemical Co., Ltd.), Vitamin E (manufactured by Eisai), and the like.

  Examples of phosphorus antioxidants include tris (2,4-di-t-butylphenyl) phosphite, bis (2,4-bis (1,1-dimethylethyl) -6-methylphenyl) ethyl ester Phosphoric acid, tetrakis (2,4-di-t-butylphenyl) (1,1-biphenyl) -4,4′-diylbisphosphonite, bis (2,4-di-t-butylphenyl) pentaerythritol Diphosphite, bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, bis (2,4-dicumylphenyl) pentaerythritol-diphosphite, tetrakis (2,4-t- Butylphenyl) (1,1-biphenyl) -4,4′-diylbisphosphonite, di-t-butyl-m-cresyl-phosphonite, etc. It is.

  A commercially available phosphorus antioxidant may be used as the phosphorus antioxidant. Examples of such commercially available phosphorus antioxidants include Irgafos 168 (Irgafos 168: Tris (2,4-di-oxide). -T-butylphenyl) phosphite, manufactured by Ciba Specialty Chemicals, Irgafos 12 (Irgafos 12: Tris [2-[[2,4,8,10-tetra-t-butyldibenzo [d, f] [1 , 3,2] dioxaphosphine-6-yl] oxy] ethyl] amine, manufactured by Ciba Specialty Chemicals, Irgafos 38 (bis (2,4-bis (1,1-dimethylethyl)) -6-methylphenyl) ethyl ester phosphorous acid (Ciba Specialty Chemicals), ADK STAB 329K ( DK STAB 329K, manufactured by Asahi Denka), ADK STAB PEP36 (ADK STAB PEP36, manufactured by Asahi Denka), ADK STAB PEP-8 (ADK STAB PEP-8, manufactured by Asahi Denka), Sandstab P-EPQ (manufactured by Clariant), Weston 618 (Weston 618, manufactured by GE), Weston 619G (manufactured by Weston 619G, manufactured by GE), Ultranox 626 (manufactured by Ultranox 626, manufactured by GE), Sumilizer GP (Sumilizer GP: 6- [3- (3-tert-butyl-4-hydroxy-5) -Methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenz [d, f] [1.3.2] dioxaphosphine), manufactured by Sumitomo Chemical Co., Ltd.).

  The optical film of the present embodiment includes a thermoplastic resin composition (A) containing the acrylic resin (A-1) and styrene resin (A-2) described above, a polymer carbon radical scavenger (B), Using a single screw extruder equipped with a T die, a raw resin composition containing a specific ratio of the molten resin temperature from the raw material inlet to the T die outlet of the single screw extruder is the glass transition temperature of the raw material composition +150 It can be obtained by maintaining at less than 0 ° C. and melt extrusion.

  The content of each component in the raw material composition is (A-1) 20 to 80 parts by mass, (A-2) 80 to 20 parts by mass, and (B) 0.05 to 0.5 parts by mass, preferably (A-1) 25-60 parts by mass, (A-2) 75-40 parts by mass, (B) 0.05-0.3 parts by mass, more preferably (A-1) 25-50 parts by mass. Parts, (A-2) 75-50 parts by mass, (B) 0.1-0.3 parts by mass.

  When the content of (A-1) is less than 20 parts by mass, the photoelastic coefficient tends to increase, and when it exceeds 80 parts by mass, the glass transition temperature tends to decrease. Further, when the content of (A-2) is less than 20 parts by mass, not only the heat resistance is insufficient, but also a phase difference tends to be hardly exhibited. When the content exceeds 80 parts by mass, the photoelastic coefficient is large. Tend to be. Furthermore, when the content of (B) is less than 0.05 parts by mass, thermal deterioration during melt processing tends to be suppressed, and when it exceeds 0.5 parts by mass, volatile components during melt processing are present. There is a risk that the appearance defects may be deteriorated due to the increase in the number of particles and the adhesion to the film surface.

  In the melt extrusion method for forming the optical film of the present embodiment, since melt extrusion is performed using a single screw extruder equipped with a barrier flight type screw, excessive shear is not applied to the raw material composition, The molten resin temperature can be kept low. Also, by setting the extruder and T die at a low temperature so that the molten resin temperature is less than the glass transition temperature of the raw material composition + 150 ° C., it is difficult to generate carbon radicals. Formation of gels and decomposition products is suppressed, and an optical film with few appearance defects can be obtained.

  When a twin screw extruder is used as the extruder, the shearing force is stronger than that of a single screw extruder, so that the temperature of the molten resin is likely to be high, and deterioration due to shear is likely to occur. Further, since the inside of the extruder cylinder is operated by starvation filling, it tends to cause oxidative deterioration and gelation due to contact between high-temperature molten resin and air, and the appearance defect of the optical film tends to increase.

  Moreover, when the molten resin temperature at the time of melt extrusion is not less than the glass transition temperature of the raw material composition + 150 ° C., coloring due to deterioration of the resin and transparency of the resulting film are likely to be lowered. Therefore, the molten resin temperature during melt extrusion is preferably less than the glass transition temperature of the raw material composition + 150 ° C., more preferably less than the glass transition temperature + 140 ° C., and less than the glass transition temperature + 130 ° C. Is more preferable.

  The single-screw extruder used for the melt extrusion method preferably includes a volatile component removing means, that is, a vent portion, and the number of vent portions may be one or plural. The pressure in the vent portion during melt extrusion is preferably in the range of 930 to 1.33 hPa (700 to 1 mmHg), and more preferably in the range of 800 to 13.3 hPa (600 to 10 mmHg). When the pressure exceeds 930 hPa, the removal of volatile matter generated during melt extrusion becomes insufficient, and the transparency of the resulting film tends to decrease. When it is less than 1.33 hPa, industrial implementation tends to be difficult. It is in.

  Moreover, it is preferable that the single screw extruder used for a melt extrusion method is provided with the polymer filter whose filtration accuracy is less than 20 micrometers. By providing the polymer filter, it is possible to remove gel-like substances and foreign matters generated at the time of melt extrusion with high accuracy, and to obtain an optical film with fewer appearance defects.

  The glass transition temperature of the optical film of the present embodiment is preferably 120 ° C. or higher and 200 ° C. or lower, more preferably 125 ° C. or higher and 150 ° C. or lower. If the glass transition temperature is less than 120 ° C., there is a risk of dimensional change in heat resistance durability evaluation when used as a liquid crystal display device or the like as an optical film. If the glass transition temperature exceeds 200 ° C., the melt extrusion method is used. Since the molten resin temperature becomes too high in film formation, the polymer carbon radical scavenger volatilizes and the resin is likely to be thermally deteriorated.

  Here, there are various measurement methods for the glass transition temperature. In the present embodiment, the glass transition temperature is defined as a temperature obtained by a midpoint method based on ASTM-D-3418 by a differential scanning calorimeter (DSC).

  The thickness of the optical film of the present embodiment is preferably 20 μm or more and 300 μm or less, and more preferably 25 μm or more and 250 μm or less.

The optical film of the present embodiment preferably has an appearance defect of 100 μm or more and less than 10 pieces / m ² . When the appearance defect of 100 μm or more is 10 pieces / m ² or more, the display quality may be lowered when used as an optical film in a liquid crystal display device or the like. In order to satisfy the currently required display quality, the appearance defect is more preferably less than 5 / m ² , and further preferably less than 1 / m ² .

  Here, the number of appearance defects is, for example, a transmission method using a microscope, and is obtained by a method of counting appearance defects having a major axis of 100 μm or more due to the crosslinked gel and calculating by calculating per unit area. Can do.

The optical film of the present embodiment is preferably one photoelastic coefficient during unstretched at 23 ° C. is less than ^{-4 × 10 -12 / Pa~4 × 10} -12 / Pa. If the photoelastic coefficient is within the above range, the change in birefringence due to external force is small, and thus when used in a large liquid crystal display device or the like, it tends to be excellent in contrast and screen uniformity. The value of the photoelastic coefficient is more preferably ^{-3.0 × 10 -12 /Pa~3.0×10 -12 / Pa} , -2.0 × 10 -12 /Pa~2.0×10 More preferably, it is ^-12 / Pa.

Here, the photoelastic coefficient is a coefficient representing the ease with which birefringence changes due to external force, and is defined by the following equation.
CR [/ Pa] = 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 change in birefringence designed for each application is small.

  The yellowness ΔYI value of the optical film of the present embodiment is preferably 1.5 or less. When the ΔYI value exceeds 1.5, the yellowish color becomes strong and the contrast of the display screen may be lowered.

Here, the yellowness degree ΔYI is a yellow coloration degree of the film, that is, a value indicating the coloration, is defined by JIS T7105, and is obtained by the following formula.
Yellowness difference ΔYI = YI−YI0
Here, ΔYI = yellowness difference, YI = yellowness of molded article, and I0 = yellowness of air.

  The haze of the optical film of the present embodiment is preferably 0.5% or less. If the haze exceeds 0.5%, the contrast of the display screen may be lowered. The ΔYI and haze values of the film can be adjusted by the film forming conditions and the blending amount of the polymer carbon radical scavenger (B).

  Here, the haze is a value indicating the transparency of the film and is defined by ASTM D1003.

  The optical film of the present embodiment can be stretched uniaxially in the longitudinal direction in the mechanical flow direction (MD) and laterally uniaxially in the direction perpendicular to the mechanical flow direction (TD) as necessary. In addition, 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. Can do. The final draw ratio can be determined from the heat shrinkage rate of the obtained film. The draw ratio is preferably 1% or more and 300% or less in at least one direction, and more preferably 10% or more and 200% or less. By designing in this range, a retardation film and a polarizing plate protective film that are 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

  Since the optical film of the present embodiment has few appearance defects and has a small absolute value of photoelastic coefficient and excellent optical characteristics, a liquid crystal display, a plasma display, an organic EL display, a field emission display, a rear projection television, etc. Polarizing plate protective films used in flexible displays of the above; retardation films such as quarter-wave plates and half-wave plates; liquid crystal optical compensation films such as viewing angle control films; display front plates; display substrates; It can be used suitably.

  If necessary, the optical film of the present embodiment can be subjected to surface functionalization treatment such as antireflection treatment, transparent conductive treatment, electromagnetic wave shielding treatment, gas barrier treatment and the like.

Hereinafter, the present embodiment will be described in more detail with reference to examples. However, the present embodiment is not limited to the examples described below.
[Measuring method]
The measurement and evaluation methods for physical properties and the like in this specification are as follows.
(1) Measurement of birefringence and photoelastic coefficient A 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 20% / min (chuck interval: 30 mm, chuck moving speed: 6 mm / min), and the test piece width was 7 mm. From the relationship between Δn of birefringence and tensile stress (σR), the slope of the straight line in the linear region was calculated by least square approximation to obtain the photoelastic coefficient (CR).

(2) Measurement of ΔYI Using Suga Test Instruments Co., Ltd. Multi Light Source Spectrometer MSC-5N-GV5 (equipment under JISZ8722-C conditions), in accordance with JIS T7105 (plastic optical property test method), The degree of yellowness ΔY using the formula
I was measured. ΔYI indicates the degree of yellowing of the molded product, and the smaller the value, the smaller the coloring.
Yellowness difference ΔYI = YI−YI0
ΔYI = Yellowness difference YI = Yellowness of molded film YI0 = Yellowness of air

(3) Measurement of haze The haze value of the film was measured according to ASTM D1003.

(4) Evaluation of the number of defects in the appearance of the film Ten samples were obtained by cutting the obtained optical film into 200 mm × 250 mm, and each sample was subjected to a transmission method using a microscope, and the major axis of the gel or foreign matter was 100 μm. The above appearance defects were counted and converted per 1 m ² unit area. Based on the obtained results, the following evaluation criteria were used.
A: The number of appearance defects is less than 3 / m ² .
○: The number of appearance defects is less than 10 / m ² .
X: The number of appearance defects is 10 / m ² or more.
XX: The number of appearance defects is 50 / m ² or more.

(5) Measurement of glass transition temperature About 10 mg of the obtained film was measured using DSC-7 type manufactured by Perkin Elmer Co., Ltd. at a temperature rising rate of 20 ° C./min from 30 ° C. under the condition of nitrogen flow. The glass transition temperature was determined by the midpoint method according to ASTM-D-3418.

(6) Measurement of maleic anhydride content in styrene-maleic anhydride copolymer A styrene-maleic anhydride copolymer as a sample was dissolved in deuterated chloroform, and 1H-NMR (JNM ECA-500) manufactured by JEOL Ltd. NMR measurement was performed at a frequency of 500 MHz and at room temperature. From the measurement results, the area ratio between the proton peak of the benzene ring in the styrene unit (near 7 ppm) and the proton peak of the alkyl group in the maleic anhydride unit (near 1 to 3 ppm), the styrene unit and maleic anhydride unit in the sample The molar ratio of was determined. From the obtained molar ratio and the mass ratio of each monomer unit (styrene unit: maleic anhydride unit = 104: 98), the content of maleic anhydride in the styrene-maleic anhydride copolymer was determined.

[Raw material composition]
(1) Acrylic resin (A-1)
(1-1) Methyl methacrylate-methyl acrylate copolymer (A-1-1)
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. 0.0294 parts by mass of cyclohexane and 0.115 parts by mass of n-octyl mercaptan were added and mixed uniformly. This solution was continuously supplied to a sealed pressure-resistant reactor having an internal volume of 10 L, 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, Volatile components were removed under certain conditions, and the mixture was continuously transferred to an extruder in a molten state to obtain methyl methacrylate-methyl acrylate copolymer (A-1-1) pellets.
The methyl methacrylate-methyl acrylate copolymer thus obtained had a methyl acrylate content of 6.0% by mass measured by NMR, a weight average molecular weight of 145,000, and 230 ° C. measured in accordance with ASTM-D1238. The melt flow value at a load of 3.8 kg was 1.0 g / min. Moreover, the photoelastic coefficient (unstretched) was −5.2 × 10 ⁻¹² / Pa.

(1-2) Methyl methacrylate-methyl acrylate copolymer (A-1-2)
1,1-di-t-butylperoxy-3,3,3 was added to a monomer mixture consisting of 93.2 parts by weight of methyl methacrylate, 2.3 parts by weight of methyl acrylate, and 3.3 parts by weight of xylene. -Trimethylcyclohexane 0.03 part by mass and n-octyl mercaptan 0.12 part by mass were added and mixed uniformly. This solution was continuously supplied to a sealed pressure-resistant reactor having an internal volume of 10 L, 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, Volatiles were removed under certain conditions. Furthermore, it was continuously transferred to an extruder in a molten state to obtain pellets of methyl methacrylate-methyl acrylate copolymer (A-1-2).
The methyl methacrylate-methyl acrylate copolymer obtained had a methyl acrylate content of 2.0% as measured by NMR, a weight average molecular weight of 102,000, 230 ° C. measured in accordance with ASTM-D1238, The melt flow value with a 3.8 kg load was 2.0 g / 10 min. Moreover, the photoelastic coefficient (unstretched) was −4.5 × 10 ⁻¹² / Pa.

(1-3) Methyl methacrylate-maleic anhydride-styrene copolymer (A-1-3)
A methyl methacrylate-maleic anhydride-styrene copolymer was obtained by the method described in Japanese Patent Publication No. 63-1964. The composition of the obtained methyl methacrylate-maleic anhydride-styrene copolymer (A-1-3) measured by NMR was 74% by mass of methyl methacrylate, 10% by mass of maleic anhydride, and 16% by mass of styrene. Yes, the weight average molecular weight was 122,000, and the melt flow value measured at 230 ° C. under a load of 3.8 kg measured according to ASTM-D1238 was 1.6 g / 10 min. Moreover, the photoelastic coefficient (unstretched) was −2.9 × 10 ⁻¹² / Pa.

(2) Styrenic resin (A-2)
(2-1) Styrene-maleic anhydride copolymer (A-2-1)
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, both were 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 were mixed with styrene to prepare a first 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 .3 hours later, continuously discharged from the gear pump at the lower part of the devolatilizer, further transferred to the extruder in a molten state, and the styrene-maleic anhydride copolymer (A-2-1) Pellets were obtained.
The obtained styrene-maleic anhydride copolymer was colorless and transparent, and as a result of NMR compositional analysis, the styrene content was 85 mass% and the maleic anhydride content was 15 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.

(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 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 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.
The obtained styrene-methacrylic acid copolymer (A-2-2) was colorless and transparent, and as a result of compositional analysis by NMR, 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. Moreover, the photoelastic coefficient (unstretched) was 4.8 × 10 ⁻¹² / Pa.

(3) Cycloolefin resin (COP)
For comparison, a cycloolefin resin (Zeonor 1420R manufactured by Nippon Zeon Co., Ltd.) was used.

(4) Polymer carbon radical scavenger (B)
Sumitizer GS (melting point (Tm): ≧ 115 ° C.) manufactured by Sumitomo Chemical Co., Ltd., which is a polymer carbon radical scavenger having an acrylate group and a phenolic hydroxyl group, was used.

(5) Other antioxidants (5-1) Phenolic antioxidants: IRGANOX 1076 (C-1)
IRGANOX 1076 (melting point (Tm): 50-55 ° C.) manufactured by Ciba Specialty Chemicals Co., Ltd., which is a hindered phenol-based antioxidant, was used.

(5-2) Lactone antioxidant (C-2)
HP-136 (melting point (Tm): 99 ° C. and 124 ° C.) manufactured by Ciba Specialty Chemicals Co., Ltd., which is a lactone-based antioxidant, was used.

[Examples 1 to 5, Comparative Examples 1 to 7]
The raw material composition having the blending ratio shown in Table 1 was charged into a single screw extruder with a vent portion having a 50 mmφ, L / D = 32, barrier flight type screw. Examples 1 to 5 were obtained by performing melt kneading while sucking from a vent port at 13 hPa (10 mmHg), passing through a leaf disk filter having a filtration accuracy of 10 μm using a gear pump, and extruding from a T die having a width of 400 mm. The unstretched film of Comparative Examples 1-7 was obtained. By adjusting the screw rotation speed, the cylinder set temperature, and the T die set temperature, extrusion molding was performed so that the molten resin temperature from the raw material inlet to the T die outlet was less than the glass transition temperature of the raw material composition + 150 ° C. The film thickness of the obtained optical film was 130 to 150 μm.
Table 1 shows the film characteristics (glass transition temperature, photoelastic coefficient, ΔYI, haze, number of appearance defects) of each optical film.

The optical components of Examples 1 to 5 in which the content of each component in the raw material composition was adjusted to a specific range, and the molten resin temperature was maintained below the glass transition temperature + 150 ° C. and extruded using a single screw extruder. The film has a small absolute value of the photoelastic coefficient, and it has no yellowing (coloring) or transparency loss despite the heat history during the molding process, and the number of appearance defects is extremely small. there were.
On the other hand, since the optical film of Comparative Example 1 contained too much acrylic resin, the glass transition temperature was low, the heat resistance was inferior, and the absolute value of the photoelastic coefficient was also large. Moreover, since the optical film of Comparative Example 2 uses a cycloolefin resin instead of the styrene resin, the optical film was significantly inferior in transparency.
Moreover, the optical film of Comparative Example 3 was a film having many appearance defects due to roll contamination during extrusion molding because the content of the polymer carbon radical scavenger (B) was too large.
In Comparative Examples 4 and 5 in which other antioxidants were blended instead of the polymer carbon radical scavenger (B), the generation of foreign matters during molding was not sufficiently suppressed, and the number of appearance defects of the obtained film was satisfactory. Was not obtained.
In Comparative Example 6 in which the molten resin temperature during melt extrusion exceeds the glass transition temperature of the raw material composition + 150 ° C., the obtained film foamed and yellowing (coloring) occurred. Furthermore, Comparative Example 7 using a twin-screw extruder as the extruder increased the number of appearance defects and did not sufficiently satisfy the characteristics as an optical film.

The optical film of the present invention includes a light guide plate, a diffusion plate, a polarizing plate protective film, a quarter-wave plate, a half-wave plate used in a display such as a liquid crystal display, a plasma display, an organic EL display, a field emission display, and a rear projection television. It can be used as a retardation film such as a wave plate, a viewing angle control film, a liquid crystal optical compensation film, etc., and in particular, as a polarizing plate protective film or a retardation film that requires high birefringence and low photoelastic coefficient. Has availability.
In particular, the optical film of the present invention is useful for improving the image quality of IPS mode liquid crystal display devices used for various displays such as televisions, personal computers, mobile phones, car navigation systems, medical equipment, and industrial equipment.
Further, the optical film of the present invention is useful because it can reduce internal reflection of a display device such as a reflective liquid crystal display or an organic EL display by being bonded to a polarizing plate to form a circularly polarizing plate.

Claims (15)

By melt-extruding a raw material composition containing a thermoplastic resin composition (A) containing an acrylic resin (A-1) and a styrene resin (A-2) and a polymer carbon radical scavenger (B) An optical film formed,
The content of each component in the raw material composition is (A-1) 20 to 80 parts by mass, (A-2) 80 to 20 parts by mass, (B) 0.05 to 0.5 parts by mass,
Using the single screw extruder provided with the T die for the raw material composition, the molten resin temperature from the raw material inlet of the single screw extruder to the T die outlet is less than the glass transition temperature of the raw material composition + 150 ° C. An optical film formed by melt extrusion while maintaining the same.   The optical film according to claim 1, wherein the single-screw extruder is an extruder provided with a vent part and a polymer filter.   The optical film according to claim 2, wherein the filtration accuracy of the polymer filter is less than 20 μm.   The polymer carbon radical scavenger (B) is contained in an amount of 0.05 to 0.5 parts by mass with respect to 100 parts by mass of the thermoplastic resin composition (A). The optical film as described. The optical polymer according to any one of claims 1 to 4, wherein the polymer carbon radical scavenger (B) is a compound represented by the following general formula (1) having an acrylate group and a phenolic hydroxyl group in the molecule. the film.

(In general formula (1), R1 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R2 and R3 each independently represents an alkyl group having 1 to 8 carbon atoms.)   The optical film according to any one of claims 1 to 5, wherein the styrenic resin (A-2) is a styrene-maleic anhydride copolymer having a maleic anhydride content of 0.1 to 50% by mass. .   The total content of the acrylic resin (A-1) and the styrene resin (A-2) in the thermoplastic resin composition (A) is 80% by mass or more based on the entire thermoplastic resin composition (A). The mass ratio ((A-1) / (A-2)) of the acrylic resin (A-1) and the styrene resin (A-2) in the thermoplastic resin composition (A) is 20 /. The optical film according to any one of claims 1 to 6, which is 80 to 80/20. 8. The glass transition temperature is 120 ° C. or more and 200 ° C. or less, the film thickness is 20 μm or more and 300 μm or less, and the appearance defect of 100 μm or more is less than 10 pieces / m ² . Optical film. Photoelastic coefficient of ^{-4 × 10 -12 ~4 × 10 -12} / Pa, the optical film of any one of claims 1-8.   The optical film according to claim 1, wherein the yellowness ΔYI value is 1.5 or less and the haze value is 0.5% or less.   The polarizing plate protective film which consists of an optical film of any one of Claims 1-10.   The retardation film which consists of an optical film of any one of Claims 1-10. By melt-extruding a raw material composition containing a thermoplastic resin composition (A) containing an acrylic resin (A-1) and a styrene resin (A-2) and a polymer carbon radical scavenger (B) A method for producing an optical film including a step of forming a film,
The content of each component in the raw material composition is (A-1) 20 to 80 parts by mass, (A-2) 80 to 20 parts by mass, (B) 0.05 to 0.5 parts by mass,
Using the single screw extruder provided with the T die for the raw material composition, the molten resin temperature from the raw material inlet of the single screw extruder to the T die outlet is less than the glass transition temperature of the raw material composition + 150 ° C. The manufacturing method of the optical film including the process of forming into a film by maintaining and melt-extruding.   The method for producing an optical film according to claim 13, wherein the single-screw extruder is an extruder provided with a polymer filter having a filtration accuracy of less than 20 μm. The optical film has a glass transition temperature of 120 ° C to 200 ° C, a film thickness of 20 µm to 300 µm, and an appearance defect of 100 µm or more of less than 10 pieces / m ² . Manufacturing method of optical film.