JP5282310B2 - Optical film, polarizing plate using the same, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film having a low photoelastic coefficient, excellent laminating property with a polarizer, and superior developing property of retardation; and to provide a polarizing plate and a liquid crystal display device having high durability. <P>SOLUTION: The optical film contains a polymer (A) having a repeating unit expressed by general formula (I). In formula (I), R<SB>1</SB>, R<SB>2</SB>, R<SB>3</SB>and R<SB>4</SB>may be the same or different from one another, each representing a hydrogen atom or a 1-12C alkyl group which may have a substituent. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an optical film, a polarizing plate using the optical film, and a liquid crystal display device.

  In recent years, the rise of liquid crystal display devices (liquid crystal displays), plasma displays, and organic EL displays has been remarkable as thin displays replacing CRT displays. These new generation displays are equipped with many optical films, but due to their thinness, demands for improving the performance of various functions of these optical films are becoming stricter year by year. Therefore, the appearance of an optical film with improved performance is awaited.

  On the other hand, the development of thinner and lighter notebook computers, larger screens, and higher definition is progressing. Along with this, there has been an increasing demand for thinner, wider and higher quality optical films for liquid crystal display devices.

  Various resins are used as optical films for liquid crystal display devices, but resin films such as cellulose esters, polycarbonates, and cyclic olefins are known for optical use, and are mainly used for optical compensation films for liquid crystal display devices. It has been. Among them, an optical film having a cellulose ester (hereinafter also referred to as a cellulose ester film) is widely used because of its excellent bonding property to polyvinyl alcohol used for a polarizer.

  However, the cellulose ester film has a disadvantage that it has a large photoelastic coefficient and is likely to cause uneven retardation. A cyclic olefin resin film is known as an optical film having a small photoelastic coefficient, but its bonding property with polyvinyl alcohol as a polarizer is insufficient. Therefore, development of an optical film having a small photoelastic coefficient and excellent bonding property with polyvinyl alcohol as a polarizer has been demanded.

  For example, Patent Document 1 proposes a method in which a low molecular organic compound having a specific structure is added to reduce the photoelastic coefficient of a cellulose ester film. However, this patent is aimed at obtaining an optical film having a small retardation, and a method for obtaining a film having a small photoelastic coefficient and a large retardation is not disclosed.

  Patent Document 2 discloses a polymer having a 5-membered lactone ring. However, this patent relates to a photographic element containing silver halide as a constituent component, and is not described as an optical film application. In addition, there has been no example of using a polymer having a 5-membered lactone ring for optical applications.

JP 2006-293255 A Japanese Patent Laid-Open No. 57-179841

  This invention is made | formed in view of the said problem, and the 1st objective of this invention is to provide the optical film with a small photoelastic coefficient and excellent in pasting property with a polarizer. A second object is to provide an optical film excellent in retardation development in addition to the above object. Furthermore, it is providing the polarizing plate and liquid crystal display device with favorable durability using this optical film.

The above object of the present invention can be achieved by the following configuration.
1. An optical film comprising a polymer (A) having a repeating unit represented by the following general formula (I).

(In the formula, R ₁ , R ₂ , R ₃ and R ₄ are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms which may have a substituent.)
2. An optical film comprising a polymer (A) having a repeating unit represented by the general formula (I) and a cellulose ester (B).
3. 3. The optical film as described in 1 or 2 above, wherein the polymer (A) is represented by the following general formula (II).

(Wherein R ₁ , R ₃ , R ₄ and R ₅ may be the same or different and each represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms which may have a substituent.)
4). 4. The optical film as described in any one of 1 to 3 above, wherein the cellulose ester (B) is cellulose acetate propionate and simultaneously satisfies the substitution degrees of the following formulas (1) and (2): .

Formula (1) 2.0 <= X + Y <= 2.8
Formula (2) 0.5 <= Y <= 1.5
(In the formula, X represents the degree of substitution of the acetyl group. Y represents the degree of substitution of the propionyl group.)
5. The polymer (A) and the cellulose ester (B) are contained in a mass ratio of (A) :( B) = 20: 80 to 50:50. The optical film as described.
The retardation Ro represented by the following formula (I) is 20 to 100 nm and the Rth represented by the following formula (II) is 70 with respect to light having a wavelength of 590 nm in an environment of 6.23 ° C. and 55% RH. The optical film as described in any one of 1 to 5 above, which has a thickness of ˜300 nm.

Formula (I) Ro = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
(However, nx represents the refractive index in the direction x in which the refractive index is maximum in the in-plane direction of the optical film, and ny represents the refractive index in the direction y orthogonal to the direction x in the in-plane direction of the optical film. , Nz represents the refractive index in the thickness direction z of the optical film, and d (nm) represents the thickness of the optical film.)
7). 7. The optical film as described in any one of 1 to 6 above, which has a photoelastic coefficient of −5 × 10 ⁻¹² Pa ⁻¹ or more and 10 × 10 ⁻¹² Pa ⁻¹ or less.
8). A polarizing plate comprising the optical film according to any one of 1 to 7 on at least one surface of a polarizer.
9. 9. A liquid crystal display device comprising the polarizing plate according to 8 on at least one surface of a liquid crystal cell.

  ADVANTAGE OF THE INVENTION According to this invention, a photoelastic coefficient is small and can provide the optical film excellent in pasting property with a polarizer. Furthermore, in addition to the above effects, an optical film having excellent retardation can be provided. In addition, a polarizing plate and a liquid crystal display device having good durability can be provided using the optical film.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail, but the present invention is not limited thereto.

  As a result of intensive studies to solve the above problems, the present inventors have not clarified the detailed reason, but an optical film containing a lactone polymer having a repeating unit represented by the general formula (I) is an optical film. It has been found that the elastic modulus is small and the bonding property with the polarizer is excellent. Further, the present inventors have found that the lactone polymer is well compatible with the cellulose ester, an optical film having excellent retardation, a low photoelastic coefficient, and excellent adhesion to a polarizer can be obtained. Furthermore, it is found that a polarizing plate and a liquid crystal display device having good durability can be obtained by using the obtained optical film, and it is as soon as the present invention has been achieved.

  Hereinafter, the present invention will be described in detail.

(Optical film)
In the present invention, the “optical film” is a functional film used for various display devices such as a liquid crystal display, a plasma display, and an organic EL display, and more specifically, a polarizing plate protective film and a retardation film for a liquid crystal display device. , An antireflection film, a brightness enhancement film, a hard coat film, an antiglare film, an antistatic film, an optical compensation film for expanding the viewing angle, and the like.

(Polymer (A) having a repeating unit represented by formula (I))
The optical film in the present invention contains a polymer (A) having a repeating unit represented by the general formula (I).

In the general formula (I), R ₁ , R ₂ , R ₃ and R ₄ may be the same or different and each may have a hydrogen atom or a substituent and may have 1 to 12 carbon atoms. Represents.

Specific examples of the alkyl group represented by R ₁ , R ₂ , R ₃ and R ₄ in the general formula (I) include a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, and an n-butyl group. Group, iso-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, iso-pentyl group, 2-ethyl-hexyl group, n-octyl group, n-decyl group, trifluoromethyl group, etc. Can be mentioned.

In the general formula (I), the alkyl group represented by R ₁ , R ₂ , R ₃ and R ₄ may have a substituent, and examples of the substituent include a halogen atom (for example, a fluorine atom, Chlorine atom, bromine atom, etc.), alkyl group (eg, methyl group, ethyl group, propyl group, butyl group, pentyl group, iso-pentyl group, 2-ethyl-hexyl group, octyl group, decyl group, etc.), cycloalkyl Group (for example, cyclohexyl group, cycloheptyl group, etc.), aryl group (for example, phenyl group, naphthyl group, etc.), heterocyclic group (for example, pyridine group, furan group, thiophene group), alkoxy group (for example, methoxy group, Ethoxy group, propoxy group, etc.), aryloxy group (eg, phenoxy group), alkylcarbonyloxy group (eg, acetyloxy group), al Ruthio group (for example, methylthio group, trifluoromethylthio group, etc.), carboxyl group, alkylcarbonylamino group (for example, acetylamino group, etc.), ureido group (for example, methylaminocarbonylamino group, etc.), alkylsulfonyl group (for example, Methanesulfonyl group, trifluoromethanesulfonyl group, etc.), carbamoyl group (for example, carbamoyl group, N, N-dimethylcarbamoyl group, N-morpholinocarbonyl group, etc.), sulfamoyl group (sulfamoyl group, N, N-dimethylsulfamoyl group) , Morpholino sulfamoyl group, etc.), trifluoromethyl group, hydroxy group, nitro group, cyano group, alkylsulfonamide group (eg methanesulfonamide group, butanesulfonamide group etc.), alkylamino group (eg amino group, N N-dimethylamino group, N, N-diethylamino group, etc.), sulfo group, phosphono group, sulfite group, sulfino group, alkylsulfonylaminocarbonyl group (for example, methanesulfonylaminocarbonyl group, ethanesulfonylaminocarbonyl group, etc.), Alkylcarbonylaminosulfonyl group (for example, acetamidosulfonyl group, methoxyacetamidosulfonyl group, etc.), alkylaminocarbonyl group (for example, acetamidocarbonyl group, methoxyacetamidocarbonyl group, etc.), alkylsulfinylaminocarbonyl group (for example, methanesulfinylaminocarbonyl group) Ethanesulfinylaminocarbonyl group, etc.). Moreover, when there are two or more substituents, they may be the same or different.

In the general formula (I), the alkyl group having 1 to 12 carbon atoms which may have a hydrogen atom or a substituent represented by R ₁ is a carbon atom which may have a hydrogen atom or a substituent. An alkyl group having 1 to 8 carbon atoms is preferable, a hydrogen atom or an optionally substituted carbon atom having 1 to 5 carbon atoms is more preferable, and a hydrogen atom or a methyl group is particularly preferable.

In the general formula (I), the hydrogen atom represented by R ₂ , R ₃ and R ₄ or the alkyl group having 1 to 12 carbon atoms which may have a substituent includes a hydrogen atom or a substituent. An optionally substituted alkyl group having 1 to 8 carbon atoms is preferred, a hydrogen atom or an optionally substituted alkyl group having 1 to 5 carbon atoms is more preferred, a hydrogen atom or a methyl group is further preferred, and a hydrogen atom Is particularly preferred.

  The content ratio of the repeating structure represented by the general formula (I) in the polymer (A) is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, still more preferably 15 to 80% by mass, Most preferably, it is 20-70 mass%.

  The polymer (A) is preferably one represented by the general formula (II).

In the general formula (II), R ₁ , R ₃ , R ₄ and R ₅ may be the same or different and each may have a hydrogen atom or a substituent and may have 1 to 12 carbon atoms. Represents.

In the general formula (II), the alkyl groups represented by R ₁ , R ₃ , R ₄ and R ₅ are specifically represented by R ₁ , R ₂ , R ₃ and R ₄ in the general formula (I). The group similar to the alkyl group represented can be mentioned.

In the general formula (II), the alkyl group having 1 to 12 carbon atoms which may have a hydrogen atom or a substituent represented by R ₁ may be a carbon atom which may have a hydrogen atom or a substituent. An alkyl group having 1 to 8 carbon atoms is preferable, a hydrogen atom or an optionally substituted carbon atom having 1 to 5 carbon atoms is more preferable, and a hydrogen atom or a methyl group is particularly preferable.

In the general formula (II), the hydrogen atom represented by R ₃ and R ₄ or the optionally substituted alkyl group having 1 to 12 carbon atoms has a hydrogen atom or a substituent. May be an alkyl group having 1 to 8 carbon atoms, more preferably a hydrogen atom or an optionally substituted carbon atom having 1 to 5 carbon atoms, still more preferably a hydrogen atom or a methyl group, and particularly preferably a hydrogen atom. .

In the general formula (II), the hydrogen atom represented by R ₅ or the alkyl group having 1 to 12 carbon atoms which may have a substituent is a carbon atom which may have a hydrogen atom or a substituent. An alkyl group having 1 to 8 carbon atoms is preferable, an alkyl group having 1 to 5 carbon atoms which may have a hydrogen atom or a substituent is more preferable, and an alkyl having 1 to 3 carbon atoms which may have a substituent A group is further preferred, and a methyl group is particularly preferred.

  The polymer (A) may have a structure derived from at least one arbitrary monomer in addition to the repeating unit represented by the general formula (I). The optional monomer is not particularly limited as long as it can be synthesized, but (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, N, N-dimethylacrylamide, vinyl acetate, N-vinylpyrrolidone, methyl vinyl ether, ethyl vinyl ether, isobutyl vinyl ether, styrene, α-methyl styrene, maleic acid, maleic anhydride, dimethyl maleate, diethyl maleate, dimethyl fumarate, And monomers such as dimethyl fumarate, allyl acetate, 2-methyl-2-propenyl acetate, 3-buten-2-yl acetate, allyl alcohol, β-methallyl alcohol, 1-buten-3-ol, and acrylonitrile.

  If the weight average molecular weight of the polymer (A) is too high, the solubility in a solvent is deteriorated. On the other hand, if the weight average molecular weight is too low, the coating property is deteriorated, so that it is preferably 1,000 to 5,000,000. More preferably, it is 5,000-1,000,000, Most preferably, it is 10,000-100,000. The weight average molecular weight was calculated by measurement using gel permeation chromatography (GPC) under the following measurement conditions.

Solvent: Tetrahydrofuran Column: TSKgel SuperHM-M (manufactured by Tosoh Corporation)
Column temperature: 40 ° C
Sample concentration: 0.1% by mass
Apparatus: HLC-8220 (manufactured by Tosoh Corporation)
Flow rate: 0.6ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000 to 500 samples are used. Thirteen samples are used at approximately equal intervals.

  Although the preferable specific example of the said polymer (A) is described below, this invention is not limited by these.

  The polymer (A) can be synthesized by any appropriate method. Synthetic methods include, for example, copolymerization of maleic acid or fumaric acid anhydride or ester derivatives with allyl alcohol or methallyl alcohol or acetic acid ester of these alcohols, and then esterification. It can be obtained by intramolecular lactonization using a catalyst. As another synthesis method, for example, it can be obtained by copolymerizing the above-mentioned arbitrary monomer copolymerizable with γ-crotonolactone.

  Although the specific synthesis method of the said polymer (A) is described below, the synthesis method of the polymer (A) of this invention is not limited to these.

(Synthesis Example 1, Synthesis of Exemplary Compound 1)
A 4-head Kolben with a capacity of 300 ml equipped with a stirrer, a thermometer, a cooling pipe, and a nitrogen gas introduction pipe was charged with 72.1 g (1.0 mol) of β-methallyl alcohol and 144.1 g (1.0 mol) of dimethyl fumarate. In addition, the mixture was refluxed at 120 ° C. for 1 hour under a nitrogen stream and deaerated. After allowing the reaction solvent to cool to room temperature, 1.65 g of 2,2′-azobisisobutyronitrile was added, and the reaction solution was heated to 80 ° C. and stirred for 5 hours. The mixture was allowed to cool to room temperature, and 200 g of tetrahydrofuran was added and dissolved. The reaction solution was poured into 1,000 ml of toluene and reprecipitated. The precipitated solid was filtered, washed with toluene, and then dried at 100 ° C. and 133 Pa for 5 hours to obtain 120.3 g of a white solid copolymer. The weight average molecular weight of the obtained copolymer was 30,000.

  Subsequently, 100 g of β-methallyl alcohol allyl-dimethyl fumarate copolymer obtained above and 200 g of methyl isobutyl ketone, phenylphosphonic acid were added to a 500 ml three-headed Kolben equipped with a stirrer, a thermometer and a condenser. 1.0g was added and it stirred at 100 degreeC under nitrogen stream for 6 hours. After cooling to room temperature, the reaction solution was poured into 1,000 ml of methanol and reprecipitated. The precipitated solid was filtered, washed with methanol, and then dried at 50 ° C. and 133 Pa for 5 hours to obtain 84.3 g of a white solid polymer (Exemplary Compound 1).

(Synthesis Example 2, Synthesis of Exemplary Compound 2)
100 g of 1,2-dichloroethane was added to a 4-head Kolben having a capacity of 300 ml equipped with a stirrer, a thermometer, a cooling pipe, and a nitrogen gas introduction pipe, and the mixture was refluxed at 84 ° C. for 1 hour in a nitrogen stream and deaerated. After allowing the reaction solvent to cool to room temperature, 23.2 g (0.2 mol) of allyl acetate, 19.6 g (0.2 mol) of maleic anhydride and 0.33 g of 2,2′-azobisisobutyronitrile were added. The reaction solution was heated to 80 ° C. and stirred for 5 hours. The mixture was allowed to cool to room temperature, and the precipitated solid was filtered and washed with 1,2-dichloroethane. The solid was dried at 50 ° C. and 133 Pa for 5 hours to obtain 36.4 g of a white solid allyl acetate-maleic anhydride copolymer. The weight average molecular weight of the obtained copolymer was 34,000.

  Subsequently, 30.0 Kolben having a capacity of 500 ml equipped with a stirrer, a thermometer, and a cooling tube was added to 30.0 g of the allyl acetate-maleic anhydride copolymer obtained above, 245 ml of n-butanol, 48 ml of water, concentrated sulfuric acid. 10.5 ml was added and stirred at 95 ° C. for 24 hours. The reaction solution was allowed to cool to room temperature and left overnight. As a white solid precipitated, the supernatant was removed by decantation. The remaining solid was dissolved in 180 ml of acetone, poured into 1.5 L of water and reprecipitated. The precipitated solid was filtered, washed with water, and then dried at 50 ° C. and 133 Pa for 5 hours to obtain 18.1 g of a white solid polymer (Exemplary Compound 2).

(Cellulose ester)
The optical film in the present invention preferably contains a cellulose ester in addition to the polymer (A) in order to enhance the retardation.

  The cellulose ester used in the present invention is not particularly limited, but the ester group is preferably a linear or branched carboxylic acid ester having about 2 to 22 carbon atoms, and these carboxylic acids may form a ring. It may be an aromatic carboxylic acid ester. In addition, these carboxylic acids may have a substituent. The cellulose ester is particularly preferably a lower fatty acid ester having 6 or less carbon atoms.

  As a preferred cellulose ester, specifically, in addition to cellulose acetate, a propionate group or a butyrate group is bonded in addition to an acetyl group such as cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate. Mention may be made of mixed fatty acid esters of cellulose. Of these, cellulose acetate propionate is particularly preferred.

  It is preferable that the cellulose acetate propionate used in the present invention satisfies the substitution degrees of the following formulas (1) and (2) at the same time.

Formula (1) 2.0 <= X + Y <= 2.8
Formula (2) 0.5 <= Y <= 1.5
(In the formula, X represents the degree of substitution of the acetyl group. Y represents the degree of substitution of the propionyl group.)
The measuring method of the substitution degree of these acyl groups can be measured according to ASTM-D817-96.

  A smaller total acyl group substitution degree tends to increase the phase difference, but the dimensional change, haze, and water absorption tend to deteriorate. When the total acyl group substitution degree is too large, it becomes difficult to develop a phase difference.

  Further, in order to obtain optical characteristics that meet the purpose, resins having different degrees of substitution may be mixed and used. The mixing ratio is preferably 10:90 to 90:10 (mass ratio).

  The number average molecular weight of the cellulose ester used in the present invention is preferably in the range of 60,000 to 300,000 because the mechanical strength of the resulting film is strong. Furthermore, the thing of 70000-200000 is used preferably.

  The weight average molecular weight Mw and the number average molecular weight Mn of the cellulose ester can be measured using gel permeation chromatography (GPC).

  An example of measurement conditions is as follows, but is not limited to this, and an equivalent measurement method can be used.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three products manufactured by Showa Denko KK)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) Mw = 100000 to 500 calibration curves with 13 samples are used. Thirteen samples are used at approximately equal intervals.

  The cellulose used as a raw material for the cellulose ester used in the present invention is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

  Cellulose esters such as cellulose acetate and cellulose acetate propionate used in the present invention can be produced by known methods. Specifically, it can be synthesized with reference to the method described in JP-A-10-45804.

  In the optical film, the content of the cellulose ester is preferably such that the mass ratio of the polymer (A) and the cellulose ester (B) is (A) :( B) = 5: 95 to 95: 5, A) :( B) = 10: 90 to 70:30 is more preferable, and (A) :( B) = 20: 80 to 50:50 is particularly preferable.

  In addition to the polymer (A) and the cellulose ester, the optical film may contain at least one of a sugar ester compound, a plasticizer, an ultraviolet absorber, an antioxidant, and fine particles described below.

(Sugar ester compound)
Examples of the polyester resin added to the polymer (A) and the cellulose ester include sugar ester compounds.

  Examples of the sugar ester compound include ester compounds in which at least one pyranose structure or furanose structure is 1 to 12 and all or part of the OH groups in the structure are esterified.

  The proportion of esterification is preferably 70% or more of the OH groups present in the pyranose structure or furanose structure.

  Examples of the sugar as a raw material for synthesizing the sugar ester compound include the following, but the present invention is not limited thereto.

  Glucose, galactose, mannose, fructose, xylose or arabinose, lactose, sucrose, nystose, 1F-fructosyl nystose, stachyose, maltitol, lactitol, lactulose, cellobiose, maltose, cellotriose, maltotriose, raffinose or kestose .

  In addition, gentiobiose, gentiotriose, gentiotetraose, xylotriose, galactosyl sucrose, and the like are also included.

  Among these compounds, compounds having both a pyranose structure and a furanose structure are particularly preferable.

  Examples include sucrose, kestose, nystose, 1F-fructosyl nystose, stachyose, and more preferably sucrose.

  The monocarboxylic acid used for esterifying all or part of the OH groups in the pyranose structure or furanose structure is not particularly limited, and is a known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic A group monocarboxylic acid or the like can be used. The carboxylic acid used may be one type or a mixture of two or more types.

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid , Saturated fatty acids such as tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid, Examples include unsaturated fatty acids such as undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid and octenoic acid.

  Examples of preferable alicyclic monocarboxylic acids include acetic acid, cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, and derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include aromatic monocarboxylic acids having an alkyl group or alkoxy group introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, cinnamic acid, benzylic acid, biphenylcarboxylic acid, and naphthalene. Examples thereof include aromatic monocarboxylic acids having two or more benzene rings such as carboxylic acid and tetralin carboxylic acid, or derivatives thereof. More specifically, xylyl acid, hemelic acid, mesitylene acid, prenylic acid, γ-isoduric acid, jurylic acid, mesitic acid, α-isoduric acid, cumic acid, α-toluic acid, hydroatropic acid, atropic acid, hydrocinnamic acid, salicylic acid, o-anisic acid, m-anisic acid, p-anisic acid , Creosote acid, o-homosalicylic acid, m-homosalicylic acid, p-homosalicylic acid, o-pyroca Succinic acid, β-resorcylic acid, vanillic acid, isovanillic acid, veratromic acid, o-veratrumic acid, gallic acid, asaronic acid, mandelic acid, homoanisic acid, homovanillic acid, homoveratrumic acid, o-homoveratrumic acid, phthalonic acid, p- Although coumaric acid can be mentioned, benzoic acid is particularly preferable.

  An oligosaccharide ester compound can be used as a compound having 1 to 12 of at least one of pyranose structural units or furanose structural units.

  An oligosaccharide is produced by allowing an enzyme such as amylase to act on starch, sucrose, etc., and examples of the oligosaccharide include maltooligosaccharide, isomaltooligosaccharide, fructooligosaccharide, galactooligosaccharide, and xylo-oligosaccharide. .

  Examples of sugar ester compounds are listed below, but the present invention is not limited thereto.

  Monopet SB: manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Monopet SOA: manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

  As addition amount of these sugar ester compounds, it is preferable to contain 0.5-30 mass% with respect to the total mass of the said polymer (A) and a cellulose ester, It is preferable to contain especially 5-20 mass%. .

(Plasticizer)
The optical film can contain a plasticizer. The plasticizer is not particularly limited, but is preferably a polycarboxylic acid ester plasticizer, a glycolate plasticizer, a phthalate ester plasticizer, a fatty acid ester plasticizer, a polyhydric alcohol ester plasticizer, or a polyester. It is selected from plasticizers, acrylic plasticizers and the like. Of these, when two or more plasticizers are used, at least one plasticizer is preferably a polyhydric alcohol ester plasticizer.

  The polyhydric alcohol ester plasticizer is a plasticizer comprising an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule. Preferably it is a 2-20 valent aliphatic polyhydric alcohol ester.

  The polyhydric alcohol preferably used in the present invention is represented by the following general formula (a).

General formula (a) Ra- (OH) _n
(However, Ra represents an n-valent organic group, n represents a positive integer of 2 or more, and an OH group represents an alcoholic and / or phenolic hydroxyl group.)
Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these. Adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3- Butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol, 3-methylpentane- Examples include 1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol and the like. In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for polyhydric alcohol ester, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

  Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with the cellulose ester is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanoic acid, undecylic acid, lauric acid, tridecylic acid, Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which 1 to 3 alkoxy groups such as alkyl group, methoxy group or ethoxy group are introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, biphenylcarboxylic acid, Examples thereof include aromatic monocarboxylic acids having two or more benzene rings such as naphthalenecarboxylic acid and tetralincarboxylic acid, or derivatives thereof. Benzoic acid is particularly preferable.

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose ester.

  The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

  The glycolate plasticizer is not particularly limited, but alkylphthalylalkyl glycolates can be preferably used. Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl Glycolate, ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl phthalyl ethyl glycolate, propyl phthalyl butyl glycol Butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl glycolate, octyl phthalyl methyl glycolate, octyl phthalate Ethyl glycolate, and the like.

  Examples of the phthalate ester plasticizer include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, and dicyclohexyl terephthalate.

  Examples of the citrate plasticizer include acetyl trimethyl citrate, acetyl triethyl citrate, and acetyl tributyl citrate.

  Examples of fatty acid ester plasticizers include butyl oleate, methylacetyl ricinoleate, and dibutyl sebacate.

  Examples of the phosphate ester plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate and the like.

  The polyvalent carboxylic acid ester compound is composed of an ester of divalent or higher, preferably divalent to 20 valent polyvalent carboxylic acid and alcohol. The aliphatic polyvalent carboxylic acid is preferably 2 to 20 valent, and in the case of an aromatic polyvalent carboxylic acid or an alicyclic polyvalent carboxylic acid, it is preferably 3 to 20 valent.

  The polyvalent carboxylic acid is represented by the following general formula (b).

Formula (b) Rb (COOH) _m (OH) _n
(Where Rb is an (m + n) -valent organic group, m is a positive integer of 2 or more and 6 or less, n is an integer of 0 or more and 4 or less, a COOH group is a carboxyl group, and an OH group is an alcoholic or phenolic hydroxyl group. Represents.)
Examples of preferred polyvalent carboxylic acids include the following, but the present invention is not limited to these. Trivalent or higher aromatic polyvalent carboxylic acids such as trimellitic acid, trimesic acid, pyromellitic acid or derivatives thereof, succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid, fumaric acid, maleic acid, tetrahydrophthal An aliphatic polyvalent carboxylic acid such as an acid, an oxypolyvalent carboxylic acid such as tartaric acid, tartronic acid, malic acid and citric acid can be preferably used. In particular, it is preferable to use an oxypolycarboxylic acid from the viewpoint of improving retention.

  There is no restriction | limiting in particular as alcohol used for the said polyhydric carboxylic acid ester compound, Well-known alcohol and phenols can be used. For example, an aliphatic saturated alcohol or aliphatic unsaturated alcohol having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10. In addition, alicyclic alcohols such as cyclopentanol and cyclohexanol or derivatives thereof, aromatic alcohols such as benzyl alcohol and cinnamyl alcohol, or derivatives thereof can also be preferably used.

  When an oxypolycarboxylic acid is used as the polycarboxylic acid, the alcoholic or phenolic hydroxyl group of the oxypolycarboxylic acid may be esterified with a monocarboxylic acid. Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10.

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, tridecylic acid, Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more rings such as biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralincarboxylic acid. And aromatic monocarboxylic acids possessed by them, or derivatives thereof.

  Of these monocarboxylic acids, acetic acid, propionic acid, and benzoic acid are particularly preferable.

  The molecular weight of the polyvalent carboxylic acid ester compound is not particularly limited, but is preferably in the range of 300 to 1000, and more preferably in the range of 350 to 750. The larger one is preferable in terms of improvement in retention, and the smaller one is preferable in terms of moisture permeability and compatibility with cellulose ester.

  The alcohol used for the polyvalent carboxylic acid ester may be one kind or a mixture of two or more kinds.

  The acid value of the polyvalent carboxylic acid ester compound is preferably 1 mgKOH / g or less, and more preferably 0.2 mgKOH / g or less. Setting the acid value in the above range is preferable because the environmental fluctuation of the retardation is also suppressed.

(Acid value)
The acid value means the number of milligrams of potassium hydroxide necessary for neutralizing the acid (carboxyl group present in the sample) contained in 1 g of the sample. The acid value is measured according to JIS K0070.

  Examples of particularly preferred polyvalent carboxylic acid ester compounds are shown below, but the present invention is not limited thereto. For example, triethyl citrate, tributyl citrate, acetyl triethyl citrate (ATEC), acetyl tributyl citrate (ATBC), benzoyl tributyl citrate, acetyl triphenyl citrate, acetyl tribenzyl citrate, dibutyl tartrate, diacetyl dibutyl tartrate, Examples include tributyl trimellitic acid and tetrabutyl pyromellitic acid.

  The polyester plasticizer is not particularly limited, and a polyester plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be used. Although it does not specifically limit as a polyester plasticizer, For example, the aromatic terminal ester plasticizer represented by the following general formula (c) can be used.

Formula (c) B-COO-((G-O-) _m -CO-A-COO-) _n G-O-CO-B
(In the formula, B represents a benzene ring and may have another substituent. G represents an alkylene group having 2 to 12 carbon atoms, an arylene group having 6 to 12 carbon atoms, or an oxyalkylene having 4 to 12 carbon atoms. Group A represents an alkylene group having 2 to 10 carbon atoms or an arylene group having 4 to 10 carbon atoms, and m and n represent a repeating unit.)
The compound of the general formula (c) is a benzene monocarboxylic acid group represented by BCOOH, an alkylene glycol group, an oxyalkylene glycol group or an aryl glycol group represented by HO— (GO—) ₁ H, HOCO-A It is synthesized from an alkylenedicarboxylic acid group or aryldicarboxylic acid group represented by —COO—H, and can be obtained by the same reaction as a normal polyester plasticizer.

  Examples of the benzene monocarboxylic acid component of the raw material of the polyester plasticizer include, for example, benzoic acid, para-tert-butyl benzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethyl benzoic acid, ethyl benzoic acid, normal propyl benzoic acid, There are aminobenzoic acid, acetoxybenzoic acid and the like, and these can be used as one kind or a mixture of two or more kinds, respectively.

  Examples of the alkylene glycol component of the polyester plasticizer include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,2-propane. Diol, 2-methyl 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2,2-diethyl- 1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane), 3-methyl-1,5-pentane Diol 1,6-hexanediol, 2,2,4-trimethyl 1,3-pentanediol, 2-ethyl 1,3-he There are sun diol, 2-methyl 1,8-octane diol, 1,9-nonane diol, 1,10-decane diol, 1,12-octadecane diol, etc., and these glycols are one kind or a mixture of two or more kinds. Used as. In particular, an alkylene glycol having 2 to 12 carbon atoms is particularly preferable because of excellent compatibility with a cellulose ester.

  Examples of the oxyalkylene glycol component having 4 to 12 carbon atoms as the raw material for the aromatic terminal ester include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. One kind or a mixture of two or more kinds can be used.

  Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms as the raw material for the aromatic terminal ester include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. These are used as one kind or a mixture of two or more kinds, respectively. Examples of the arylene dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, and the like.

  The polyester plasticizer has a number average molecular weight of preferably 300 to 1500, more preferably 400 to 1000. The acid value is 0.5 mgKOH / g or less, the hydroxyl value is 25 mgKOH / g or less, more preferably the acid value is 0.3 mgKOH / g or less, and the hydroxyl value is 15 mgKOH / g or less.

(Acrylic polymer)
The optical film can also contain a (meth) acrylic polymer as a plasticizer.

  The (meth) acrylic polymer is preferably a polymer Y having a weight average molecular weight of 500 or more and 3000 or less obtained by polymerizing an ethylenically unsaturated monomer Ya having no aromatic ring.

  As the (meth) acrylic polymer, at least an ethylenically unsaturated monomer Xa having no aromatic ring and a hydroxyl group in the molecule and an ethylenically unsaturated monomer Xb having no aromatic ring in the molecule and having a hydroxyl group are used. The polymer X having a weight average molecular weight of 3000 to 30000 obtained by polymerization and the polymer Y having a weight average molecular weight of 500 to 3000 obtained by polymerizing an ethylenically unsaturated monomer Ya having no aromatic ring More preferably, it is a mixture.

  More preferably, the polymer X is represented by the following general formula (X), and the polymer Y is represented by the following general formula (Y).

Formula (X)
_{- [CH 2 -C (Rc)} (CO 2 Rd) -] m - [CH 2 -C (Re) (CO 2 Rf-OH) -] n - [Xc] p -
General formula (Y)
_{Ry- [CH 2 -C (Rg)} (CO 2 Rh-OH) -] k - [Yb] q -
(In the formula, Rc, Re and Rg represent H or CH _3. Rd represents an alkyl group having 1 to 12 carbon atoms or a cycloalkyl group. Rf and Rh represent —CH ₂ —, —C ₂ H ₄ —. Or -C ₃ H _6- , Ry represents OH, H or an alkyl group having 3 or less carbon atoms, Xc represents a monomer unit that can be polymerized to Xa and Xb, and Yb can be copolymerized to Ya Represents a monomer unit, m, n, k, p and q represent molar composition ratios, provided that m ≠ 0, n ≠ 0, and k ≠ 0.
As addition amount of these plasticizers, it is preferable to contain 0.5-30 mass% with respect to the total mass of the said polymer (A) and a cellulose ester, and it is preferable to contain 5-20 mass% especially.

(UV absorber)
The optical film can also contain an ultraviolet absorber. The ultraviolet absorber is intended to improve durability by absorbing ultraviolet rays of 400 nm or less, and in particular, the transmittance at a wavelength of 370 nm is preferably 10% or less, more preferably 5% or less, and further Preferably it is 2% or less.

  The ultraviolet absorber is not particularly limited, and examples thereof include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders, and the like. It is done.

  For example, 5-chloro-2- (3,5-di-sec-butyl-2-hydroxyphenyl) -2H-benzotriazole, (2-2H-benzotriazol-2-yl) -6- (linear and side Chain dodecyl) -4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, etc., and tinuvin 109, tinuvin 171, tinuvin 234, tinuvin 326, tinuvin 327, tinuvin 328, There are tinuvins such as tinuvin 928, all of which are commercially available from Ciba Japan and can be preferably used.

  The UV absorbers preferably used in the present invention are benzotriazole UV absorbers, benzophenone UV absorbers, and triazine UV absorbers, particularly preferably benzotriazole UV absorbers and benzophenone UV absorbers. .

  In addition, a discotic compound such as a compound having a 1,3,5-triazine ring is also preferably used as the ultraviolet absorber.

  The optical film preferably contains two or more ultraviolet absorbers. As the UV absorber, a polymer UV absorber can also be preferably used, and in particular, a polymer type UV absorber described in JP-A-6-148430 is preferably used.

  The method of adding the UV absorber can be added to the dope after dissolving the UV absorber in an alcohol such as methanol, ethanol or butanol, an organic solvent such as methylene chloride, methyl acetate, acetone or dioxolane or a mixed solvent thereof. Or you may add directly in dope composition.

  For an inorganic powder that does not dissolve in an organic solvent, a dissolver or a sand mill is used in the organic solvent and cellulose ester to disperse and then added to the dope.

  The amount of the UV absorber used is not uniform depending on the type of UV absorber, the operating conditions, etc., but when the dry film thickness of the polarizing plate protective film is 30 to 200 μm, it is 0.5 with respect to the polarizing plate protective film. -10 mass% is preferable, and 0.6-4 mass% is still more preferable.

(Antioxidant)
Antioxidants are also referred to as deterioration inhibitors. When a liquid crystal image display device or the like is placed in a high humidity and high temperature state, the optical film may be deteriorated.

  The antioxidant has a role of delaying or preventing the optical film from being decomposed by, for example, the residual solvent amount of halogen in the optical film or phosphoric acid of the phosphoric acid plasticizer. It is preferable to contain.

  As such an antioxidant, a hindered phenol compound is preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octa Sil-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like.

  In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di- A phosphorus processing stabilizer such as t-butylphenyl) phosphite may be used in combination.

  The addition amount of these compounds is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to the total mass of the polymer (A) and the cellulose ester.

(Fine particles)
The optical film preferably contains fine particles.

  Examples of the fine particles include inorganic compounds such as silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, and aluminum silicate. Mention may be made of magnesium silicate and calcium phosphate. Further, fine particles of an organic compound can also be preferably used. Examples of organic compounds include polytetrafluoroethylene, cellulose acetate, polystyrene, polymethyl methacrylate, polypropyl methacrylate, polymethyl acrylate, polyethylene carbonate, acrylic styrene resin, silicone resin, polycarbonate resin, benzoguanamine resin, melamine resin Also, pulverized and classified products of organic polymer compounds such as polyolefin-based powders, polyester-based resins, polyamide-based resins, polyimide-based resins, polyfluorinated ethylene-based resins, and starches. Alternatively, a polymer compound synthesized by a suspension polymerization method, a polymer compound made spherical by a spray dry method or a dispersion method, or an inorganic compound can be used.

  Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable.

  The average primary particle diameter of the fine particles is preferably 5 to 400 nm, and more preferably 10 to 300 nm.

  These may be mainly contained as secondary aggregates having a particle size of 0.05 to 0.3 μm, and may be contained as primary particles without being aggregated if the particles have an average particle size of 100 to 400 nm. preferable.

  The content of these fine particles in the polarizing plate protective film is preferably 0.01 to 1% by mass, particularly preferably 0.05 to 0.5% by mass. In the case of a polarizing plate protective film having a multilayer structure by the co-casting method, it is preferable to contain fine particles of this addition amount on the surface.

  Silicon dioxide fine particles are commercially available, for example, under the trade names Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (above Nippon Aerosil Co., Ltd.). it can.

  Zirconium oxide fine particles are commercially available, for example, under the trade names Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.), and can be used.

  Examples of the polymer include silicone resin, fluororesin and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120, and 240 (manufactured by Toshiba Silicone Co., Ltd.) It is marketed by name and can be used.

  Among these, Aerosil 200V and Aerosil R972V are particularly preferably used because they have a large effect of reducing the friction coefficient while keeping the turbidity of the polarizing plate protective film low. In the said polarizing plate protective film, it is preferable that the dynamic friction coefficients of at least one surface are 0.2-1.0.

  Various additives may be batch-added to a dope that is a resin-containing solution before film formation, or an additive solution may be separately prepared and added in-line. In particular, it is preferable to add a part or all of the fine particles in-line in order to reduce the load on the filter medium.

  When the additive solution is added in-line, it is preferable to dissolve a small amount of resin in order to improve mixing with the dope. A preferable amount of the resin is 1 to 10 parts by mass, and more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.

  In order to perform in-line addition and mixing in the present invention, for example, an in-line mixer such as a static mixer (manufactured by Toray Engineering), SWJ (Toray static type in-tube mixer Hi-Mixer) or the like is preferably used.

(Production method)
Next, a method for producing the optical film will be described.

  The optical film can be preferably used regardless of whether it is a film produced by a solution casting method or a film produced by a melt casting method.

  The optical film is produced by dissolving a resin and additives in a solvent to prepare a dope, casting a dope onto an endless metal support that moves indefinitely, and drying the cast dope as a web. It is performed by a step, a step of peeling from a metal support, a step of stretching or maintaining the width, a step of further drying, and a step of winding up the finished film.

  The process for preparing the dope will be described. It is preferable that the concentration of the resin in the dope is higher because the drying load after casting on the metal support can be reduced. However, if the concentration of the resin is too high, the load during filtration increases and the filtration accuracy deteriorates. As a density | concentration which makes these compatible, 10-35 mass% is preferable, More preferably, it is 15-25 mass%.

  The solvent used in the dope may be used alone or in combination of two or more. However, it is preferable to use a mixture of a good solvent and a poor solvent of the resin in terms of production efficiency, and there are many good solvents. Is preferable from the viewpoint of the solubility of the resin. The preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass for the good solvent and 2 to 30% by mass for the poor solvent. With a good solvent and a poor solvent, what melt | dissolves the resin to be used independently is defined as a good solvent, and a solvent that swells or does not dissolve alone is defined as a poor solvent. For example, when cellulose ester is used as the resin, the good solvent and the poor solvent vary depending on the average acetylation degree (acetyl group substitution degree). For example, when acetone is used as the solvent, cellulose acetate ester (acetyl group substitution degree 2 .4), cellulose acetate propionate is a good solvent, and cellulose acetate (acetyl group substitution degree 2.8) is a poor solvent.

  The good solvent is not particularly limited, and examples thereof include organic halogen compounds such as methylene chloride, dioxolanes, acetone, methyl acetate, and methyl acetoacetate. Particularly preferred is methylene chloride or methyl acetate.

  Moreover, although the said poor solvent is not specifically limited, For example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone etc. are used preferably. Moreover, it is preferable that 0.01-2 mass% of water contains in dope. Moreover, the solvent used for melt | dissolution of resin collect | recovers the solvent removed from the film by drying at the film-forming process, and uses this again. The recovery solvent may contain a small amount of additives added to the resin, such as plasticizers, UV absorbers, polymers, monomer components, etc., but even if these are included, they should be reused preferably Can be purified and reused if necessary.

  As a method for dissolving the resin when preparing the dope described above, a general method can be used. When heating and pressurization are combined, it is possible to heat above the boiling point at normal pressure. It is preferable to stir and dissolve while heating at a temperature that is equal to or higher than the boiling point of the solvent at normal pressure and that the solvent does not boil under pressure, in order to prevent the generation of massive undissolved materials called gels and mamaco. Moreover, after mixing resin with a poor solvent and making it wet or swell, the method of adding a good solvent and melt | dissolving is also used preferably.

  The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or a method of developing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  The heating temperature with the addition of the solvent is preferably higher from the viewpoint of the solubility of the resin, but if the heating temperature is too high, the required pressure increases and the productivity deteriorates. A preferable heating temperature is 45 to 120 ° C, more preferably 60 to 110 ° C, and still more preferably 70 ° C to 105 ° C. The pressure is adjusted so that the solvent does not boil at the set temperature.

  Alternatively, a cooling dissolution method is also preferably used. For example, cellulose ester or the like can be dissolved in a solvent such as methyl acetate.

  Next, the solution in which the resin is dissolved is filtered using a suitable filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like, but there is a problem that the filter medium is likely to be clogged if the absolute filtration accuracy is too small. For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium with 0.001 to 0.008 mm is more preferable, and a filter medium with 0.003 to 0.006 mm is still more preferable.

  There are no particular restrictions on the material of the filter medium, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel do not drop off fibers. preferable. It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material resin by filtration.

Bright spot foreign matter means that when two polarizing plates are placed in a crossed Nicol state, an optical film or the like is placed between them, light is applied from one polarizing plate side, and observation is performed from the other polarizing plate side. It is a point (foreign matter) where light from the opposite side appears to leak, and the number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less. More preferably, it is 100 pieces / cm < ² > or less, More preferably, it is 50 pieces / m < ² > or less, More preferably, it is 0-10 pieces / cm < ² > or less. Further, it is preferable that the number of bright spots of 0.01 mm or less is small.

  The dope can be filtered by a normal method, but the method of filtering while heating at a temperature not lower than the boiling point of the solvent at normal pressure and in a range where the solvent does not boil under pressure is the filtration pressure before and after filtration. The expression of the difference (referred to as differential pressure) is small and preferable. A preferred temperature is 45 to 120 ° C, more preferably 45 to 70 ° C, and still more preferably 45 to 55 ° C.

  A smaller filtration pressure is preferred. The filtration pressure is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and further preferably 1.0 MPa or less.

  Here, the dope casting will be described.

  The metal support in the casting (casting) step preferably has a mirror-finished surface. As the metal support, a stainless steel belt or a drum whose surface is plated with a casting is preferably used. The cast width can be 1 to 4 m. The surface temperature of the metal support in the casting step is −50 ° C. to a temperature lower than the boiling point of the solvent, and a higher temperature is preferable because the web can be dried faster. May deteriorate. A preferable support body temperature is 0-40 degreeC, and 5-30 degreeC is still more preferable. Alternatively, it is also a preferable method that the web is gelled by cooling and peeled from the drum in a state containing a large amount of residual solvent. The method for controlling the temperature of the metal support is not particularly limited, and there are a method of blowing hot air or cold air, and a method of contacting hot water with the back side of the metal support. It is preferable to use warm water because heat transfer is performed efficiently, so that the time until the temperature of the metal support becomes constant is short. When warm air is used, wind at a temperature higher than the target temperature may be used.

  In order for the optical film to exhibit good flatness, the residual solvent amount when peeling the web from the metal support is preferably 10 to 150% by mass, more preferably 20 to 40% by mass or 60 to 130% by mass. Yes, particularly preferably 20 to 30% by mass or 70 to 120% by mass.

  In the present invention, the amount of residual solvent is defined by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
M is the mass of a sample collected during or after the production of the web or film, and N is the mass after heating M at 115 ° C. for 1 hour.

  Further, in the optical film drying step, the web is peeled off from the metal support and further dried, and the residual solvent amount is preferably 1% by mass or less, more preferably 0.1% by mass or less, particularly Preferably it is 0-0.01 mass% or less.

  In the film drying step, generally, a roll drying method (a method in which webs are alternately passed through a plurality of rolls arranged above and below) and a method in which the web is dried while being conveyed by a tenter method are employed.

  In order to produce the optical film, it is particularly preferable to perform stretching in the width direction (lateral direction) by a tenter method in which both ends of the web are held with clips or the like. Peeling is preferably performed at a peeling tension of 300 N / m or less.

  The means for drying the web is not particularly limited, and can be generally performed with hot air, infrared rays, a heating roll, microwave, or the like, but is preferably performed with hot air from the viewpoint of simplicity.

  The drying temperature in the web drying step is preferably increased stepwise from 40 to 200 ° C.

  Although the film thickness of an optical film is not specifically limited, 10-200 micrometers is used. In particular, the film thickness is particularly preferably 10 to 100 μm. More preferably, it is 20-60 micrometers.

  The optical film having a width of 1 to 4 m is used. In particular, those having a width of 1.4 to 4 m are preferably used, and particularly preferably 1.6 to 3 m. If it exceeds 4 m, conveyance becomes difficult.

(Stretching operation, refractive index control)
In the step of producing the optical film, it is preferable to perform refractive index control, that is, retardation control by a stretching operation.

  For example, biaxial stretching or uniaxial stretching can be performed sequentially or simultaneously with respect to the longitudinal direction (film forming direction) of the film and the direction orthogonal to the longitudinal direction of the film, that is, the width direction. Simultaneous biaxial stretching includes stretching in one direction and contracting the other tension by relaxing.

  It is preferable that the draw ratios in the biaxial directions perpendicular to each other are finally in the range of 0.8 to 1.5 times in the casting direction and 1.1 to 2.5 times in the width direction. It is preferable to carry out in the range of 0.9 to 1.0 times in the direction and 1.2 to 2.0 times in the width direction.

  The stretching temperature is preferably 120 ° C to 200 ° C, more preferably 140 ° C to 180 ° C.

  The residual solvent in the film at the time of stretching is preferably 20 to 0%, more preferably 15 to 0%.

  There is no particular limitation on the method of stretching the web. For example, a method in which a difference in peripheral speed is applied to a plurality of rolls, and the roll peripheral speed difference is used to stretch in the longitudinal direction between the rolls. And a method of stretching in the vertical direction, a method of stretching in the horizontal direction and stretching in the horizontal direction, a method of stretching in the vertical and horizontal directions and stretching in both the vertical and horizontal directions, and the like. Of course, these methods may be used in combination. In the case of the so-called tenter method, driving the clip portion by the linear drive method is preferable because smooth stretching can be performed and the risk of breakage and the like can be reduced.

  It is preferable to perform the width maintenance or the transverse stretching in the film forming process by a tenter, and it may be a pin tenter or a clip tenter. In addition, you may extend | stretch sequentially, even if a conveyance direction and the width direction are extended | stretched simultaneously.

(Optical compensation film)
Since liquid crystal displays use anisotropic liquid crystal materials and polarizing plates, there is a viewing angle problem that even if a good display is obtained when viewed from the front, the display performance is degraded when viewed from an oblique direction. In order to improve performance, a viewing angle compensator is necessary. The average refractive index distribution is larger in the cell thickness direction and smaller in the in-plane direction. Therefore, a compensation plate that can cancel this anisotropy and has a so-called negative uniaxial structure in which the refractive index in the film thickness direction is smaller than the in-plane direction is effective. The film can also be used as an optical compensation film having such a function.

  When the optical film is used in the VA mode (mode using a vertically aligned liquid crystal), a mode in which a total of two sheets are used on each side of the cell (two-sheet type) and one of the upper and lower sides of the cell It may be used for any of the forms (single-sheet type) used only in

  The optical film has a retardation Ro of 23 ° C. and 55% RH represented by the following formula, a wavelength of 590 nm and a wavelength of 20 to 100 nm, an Rth of 23 ° C. and 55% RH, and a wavelength of 590 nm. It is preferable that it is 70-300 nm.

Formula (I) Ro = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
(However, nx represents the refractive index in the direction x in which the refractive index is maximum in the in-plane direction of the optical film, and ny represents the refractive index in the direction y orthogonal to the direction x in the in-plane direction of the optical film. , Nz represents the refractive index in the thickness direction z of the optical film, and d (nm) represents the thickness of the optical film.)
These retardation values can be measured using an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments).

  When the slow axis or the fast axis of the optical film is present in the film plane and the angle formed by the fast axis and the film forming direction is θ1, θ1 is preferably −1 ° or more and + 1 ° or less, − More preferably, it is 0.5 ° or more and + 0.5 ° or less. This θ1 can be defined as an orientation angle, and θ1 can be measured using an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments). Each of θ1 satisfying the above relationship can contribute to obtaining high luminance in a display image, suppressing or preventing light leakage, and contributing to obtaining faithful color reproduction in a color liquid crystal display device.

(Photoelasticity)
The photoelastic coefficient of the optical film is preferably −5 × 10 ⁻¹² Pa ⁻¹ or more and 10 × 10 ⁻¹² Pa ⁻¹ or less, more preferably 0 or more and 8 × 10 ⁻¹² Pa ⁻¹ or less. preferable.

  The photoelastic coefficient can be measured using a retardation measuring device (KOBUURA 31PR, manufactured by Oji Scientific Instruments).

(Physical properties)
The moisture permeability of the optical film is preferably 10 to 1200 g / m ² · 24 h at 40 ° C. and 90% RH. The moisture permeability can be measured according to the method described in JIS Z 0208.

  The optical film preferably has a breaking elongation of 10 to 80%.

  The optical film has a visible light transmittance of preferably 90% or more, and more preferably 93% or more.

  The haze of the optical film is preferably less than 1%, particularly preferably 0 to 0.1%.

  Further, a retardation value over a wider range can be obtained by further applying a liquid crystal layer or a resin layer to the optical film, or by further stretching it.

(Polarizer)
The optical film can be used for a polarizing plate having a polarizing plate protective film and the liquid crystal display device using the polarizing plate. The optical film is preferably a film that also functions as a polarizing plate protective film. In this case, it is not necessary to prepare an optical film having a phase difference separately from the polarizing plate protective film. Thinning the manufacturing process can be simplified.

  In the liquid crystal display device, it is preferable that the polarizing plate is bonded to both surfaces of the liquid crystal cell via an adhesive layer.

  The polarizing plate can be produced by a general method. The side of the optical film to be bonded to the polarizer is subjected to alkali saponification treatment, and bonded to at least one surface of the polarizer (prepared by immersing and stretching in an iodine solution) using a completely saponified polyvinyl alcohol aqueous solution. Is preferred. Another polarizing plate protective film can be bonded to the other surface. When the optical film is a liquid crystal display device, the optical film is preferably provided on the liquid crystal cell side of the polarizer, and a conventional polarizing plate protective film can be used as the film outside the polarizer.

  For example, as a conventional polarizing plate protective film, a commercially available cellulose ester film (for example, Konica Minoltak KC8UX, KC5UX, KC8UCR3, KC8UCR4, KC8UCR5, KC8UY, KC6UY, KC4UY, KC4UE, KC8UE, KC8HY-X, KC8UXW-RHA-C, KC8UXW-RHA-NC, KC4UXW-RHA-NC, manufactured by Konica Minolta Opto Co., Ltd.) are preferably used.

  In addition to the antiglare layer or the clear hard coat layer, the polarizing plate protective film used on the surface side of the display device preferably has an antireflection layer, an antistatic layer, an antifouling layer, and a backcoat layer.

  A polarizer, which is a main component of a polarizing plate, is an element that allows only light of a plane of polarization in a certain direction to pass. A typical polarizer currently known is a polyvinyl alcohol-based polarizing film, which is polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

  For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound. The film thickness of the polarizer is preferably 5 to 30 μm, particularly preferably 10 to 20 μm.

(Liquid crystal display device)
By using a polarizing plate using the optical film for a liquid crystal display device, the liquid crystal display device having various visibility can be manufactured.

  The optical film and the polarizing plate can be used for liquid crystal display devices of various drive systems such as STN, TN, OCB, HAN, VA (MVA, PVA), IPS, OCB.

  In particular, it is preferably used for a VA (MVA, PVA) type liquid crystal display device.

  In particular, even in a large-screen liquid crystal display device with a 30-inch screen or more, it is possible to obtain a liquid crystal display device with excellent visibility such as front contrast by reducing coloring during black display due to light leakage.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited to a following example, unless the summary is exceeded.

Example 1
<Preparation of optical film 101>
<Fine particle dispersion 1>
Aerosil R972V (silica fine particles; primary particle size 16 nm; manufactured by Nippon Aerosil Co., Ltd.) 11 parts by weight Ethanol 89 parts by weight The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin.

<Fine particle addition liquid 1>
With the following composition, the fine particle dispersion 1 was slowly added to a dissolution tank containing methylene chloride while sufficiently stirring. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution 1.

Methylene chloride 99 parts by mass Fine particle dispersion 1 5 parts by mass (Preparation of main dope solution)
A main dope solution having the following composition was prepared. First, methylene chloride and ethanol were added to the pressure dissolution tank. Exemplified compound 1 and fine particle additive solution 1 were added to a pressurized dissolution tank containing a solvent while stirring. This is completely dissolved with heating and stirring. This was designated as Azumi Filter Paper No. The main dope solution was prepared by filtration using 244.

<Composition of main dope solution>
Methylene chloride 340 parts by mass Ethanol 64 parts by mass Exemplified compound 1 100 parts by mass Particulate additive solution 1 1 part by mass The above was put into a sealed container and dissolved while stirring to prepare a dope solution. Next, using an endless belt casting apparatus, the dope solution was uniformly cast on a stainless steel belt support at a temperature of 33 ° C. and a width of 1500 mm. The temperature of the stainless steel belt was controlled at 30 ° C.

  On the stainless steel belt support, the solvent was evaporated until the residual solvent amount in the cast (cast) film was 75%, and then peeled off from the stainless steel belt support with a peeling tension of 130 N / m.

  The peeled optical film was stretched 20% in the width direction using a tenter while applying heat at 140 ° C. The residual solvent at the start of stretching was 15%.

  Next, drying was terminated while the drying zone was conveyed by a number of rolls. The drying temperature was 130 ° C. and the transport tension was 100 N / m.

  As described above, an optical film 101 having a dry film thickness of 40 μm was obtained.

<Preparation of optical films 102-105>
Optical films 102 to 105 were prepared in the same manner as in the production of the optical film 101 except that the type of the polymer (A) or the type of comparative resin in place of the polymer (A) was changed as shown in Table 1.

  The materials used are shown below.

Comparative resin 1 (cellulose ester example): cellulose acetate propionate having an acetyl substitution degree of 1.6, a propionyl substitution degree of 0.9, and a total acyl group substitution degree of 2.5 (denoted as CAP1 in the table)
Comparative resin 2 (example of cyclic olefin resin): ARTON-G7810 (manufactured by JSR) (described as ARTON in the table)
Comparative resin 3 (acrylic resin example): polymethyl methacrylate BR85 (manufactured by Mitsubishi Rayon Co., Ltd.) (described as BR85 in the table)
<Evaluation of optical film>
Each optical film sample produced as described above was evaluated as described below. The results are shown in Table 1.

(Measurement of photoelastic coefficient)
The both ends in the width direction of the obtained optical film sample are held, and the retardation (Ro) in the film surface is measured while applying a load, and this is divided by the thickness (d) of the film to obtain Δn (= Ro / d ) Δn was determined while changing the load, the load-Δn curve was measured, and the slope was taken as the photoelastic coefficient. The retardation (Ro) in the film plane was measured at a wavelength of 589 nm in an environment of 23 ° C. and 55% RH using a retardation measuring device (KOBUURA 31PR, manufactured by Oji Scientific Instruments).

<Preparation of polarizing plates 101-105>
A polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times).

  This was immersed in an aqueous solution consisting of 0.075 parts by mass of iodine, 5 parts by mass of potassium iodide, and 100 parts by mass of water, and then from 6 parts by mass of potassium iodide, 7.5 parts by mass of boric acid, and 100 parts by mass of water. It was immersed in an aqueous solution at 68 ° C. This was washed with water and dried to obtain a polarizer.

  Next, the front side of the polarizer and the optical films 101 to 105 are bonded according to the following steps 1 to 5, and Konica Minolta Tack KC4UY (cellulose ester film manufactured by Konica Minolta Opto Co., Ltd.) is bonded to the back side of the polarizing plate. Was made.

  Step 1: The optical films 101 to 105 are immersed in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried to obtain an optical film having a saponified side to be bonded to a polarizer. It was.

  Process 2: The said polarizer was immersed in the polyvinyl alcohol adhesive tank of 2 mass% of solid content for 1-2 seconds.

  Step 3: Excess adhesive adhered to the polarizer in Step 2 was gently wiped off, and this was placed on the optical film treated in Step 1.

Step 4: the optical film 101 to 105 were laminated in the step 3 and the surface of the polarizer side of the polarizer superimposed Konica Minolta TAC KC4UY optical film, a pressure 20-30 N / cm ^2, bonding at about 2m / min conveyor speed did.

  Step 5: A sample obtained by bonding the polarizer prepared in Step 4 with the optical films 101 to 105 and Konica Minoltac KC4UY in a drier at 80 ° C. is dried for 2 minutes, and the corresponding polarizing plates 101 to 105 are manufactured. did.

[Evaluation of polarizing plate]
Next, the adhesiveness between the optical film and the polarizer was evaluated as follows.

(Adhesiveness)
The polarizing plate obtained in the above manner was treated at 80 ° C. and 90% RH for 1200 hours, and the bonding state between the cellulose ester film and the polarizer was observed and ranked according to the following criteria.

A: No peeling B: Peeling is slightly observed C: Peeling is recognized D: Peeling is recognized in a very wide range Here, it was judged that A and B were practically satisfactory levels.

  Table 1 shows the evaluation results of the photoelastic coefficient and adhesiveness obtained as described above.

  As is clear from Table 1, the optical films 101 and 102 of the present invention have a smaller photoelastic coefficient than the comparative optical films 103 to 105 and are excellent in adhesiveness with polyvinyl alcohol as a polarizer. It turns out that it is a film.

(Example 2)
<Preparation of optical film 201>
<Fine particle dispersion 1>
Aerosil R972V (silica fine particles; primary particle size 16 nm; manufactured by Nippon Aerosil Co., Ltd.) 11 parts by weight Ethanol 89 parts by weight The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin.

<Fine particle addition liquid 1>
With the following composition, the fine particle dispersion 1 was slowly added to a dissolution tank containing methylene chloride while sufficiently stirring. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution 1.

Methylene chloride 99 parts by mass Fine particle dispersion 1 5 parts by mass (Preparation of main dope solution)
A main dope solution having the following composition was prepared. First, methylene chloride and ethanol were added to the pressure dissolution tank. Cellulose ester 1, exemplified compound 1 and fine particle additive solution 1 were charged into a pressure dissolution tank containing a solvent while stirring. This is completely dissolved with heating and stirring. This was designated as Azumi Filter Paper No. The main dope solution was prepared by filtration using 244.

<Composition of main dope solution>
Methylene chloride 340 parts by mass Ethanol 64 parts by mass Cellulose ester 1 (cellulose acetate propionate having an acetyl substitution degree of 1.6, a propionyl substitution degree of 0.9, and a total acyl group substitution degree of 2.5 (denoted as CAP1 in the table))
60 parts by mass Exemplified Compound 1 40 parts by mass Fine Particle Additive Solution 1 1 part by mass The above was put into a sealed container and dissolved while stirring to prepare a dope solution. Next, using an endless belt casting apparatus, the dope solution was uniformly cast on a stainless steel belt support at a temperature of 33 ° C. and a width of 1500 mm. The temperature of the stainless steel belt was controlled at 30 ° C.

  On the stainless steel belt support, the solvent was evaporated until the residual solvent amount in the cast (cast) film was 75%, and then peeled off from the stainless steel belt support with a peeling tension of 130 N / m.

  The peeled optical film was stretched 20% in the width direction using a tenter while applying heat at 140 ° C. The residual solvent at the start of stretching was 15%.

  Next, drying was terminated while the drying zone was conveyed by a number of rolls. The drying temperature was 130 ° C. and the transport tension was 100 N / m.

  As described above, an optical film 201 having a dry film thickness of 40 μm was obtained.

<Preparation of optical films 202-211>
In preparation of the optical film 201, it is the same except having changed the kind of cellulose ester, the kind of the said polymer (A) instead of the exemplary compound 1, and the mass part of the cellulose ester and the said polymer (A) as shown in Table 2. Optical films 202 to 209 were produced. The optical film 210 was prepared in the same manner as the optical film 201 except that 10 parts by mass of the comparative compound 1 was used instead of the exemplified compound 1 and 90 parts by mass of the cellulose ester 4 was used instead of the cellulose ester 1. When 40 parts by mass of comparative compound 1 and 60 parts by mass of cellulose ester 4 were used, comparative compound 1 was precipitated and a transparent optical film was not obtained. The optical film 211 was produced in the same manner as in the production of the optical film 201 except that 100 parts by mass of the comparative resin 1 was used instead of the exemplified compound 1 and the cellulose ester.

  The materials used are shown below.

Cellulose ester 2: Cellulose acetate propionate having an acetyl substitution degree of 1.1, a propionyl substitution degree of 1.1 and a total acyl group substitution degree of 2.2 (denoted as CAP2 in the table)
Cellulose ester 3: Cellulose diacetate having an acetyl substitution degree of 2.4 (denoted as DAC in the table)
Cellulose ester 4: Cellulose acetate with an acetyl substitution degree of 2.92 (denoted as TAC in the table)
Comparative resin 1 (example of cyclic olefin resin): ARTON-G7810 (manufactured by JSR)
Moreover, the structure of the comparative compound 1 is as follows.

<Evaluation of optical film>
Each optical film sample produced as described above was evaluated as described below. The results are shown in Table 2.

(Measurement of retardation)
The retardation value of the center part of the width direction of the obtained optical film sample was measured. For measurement, an automatic birefringence meter KOBURA 21ADH (manufactured by Oji Scientific Instruments Co., Ltd.) was used to measure three-dimensional birefringence at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH. Was obtained by substituting into the following equation.

In-plane retardation Ro = (nx−ny) × d
Thickness direction retardation Rth = ((nx + ny) / 2−nz) × d
In the formula, d is the thickness (nm) of the film, the refractive index nx (the maximum refractive index in the plane of the film, also referred to as the refractive index in the slow axis direction), ny (the direction perpendicular to the slow axis in the film plane). ) (Refractive index of the film in the thickness direction).

(Measurement of photoelastic coefficient)
The both ends in the width direction of the obtained optical film sample are held, and the retardation (Ro) in the film surface is measured while applying a load, and this is divided by the thickness (d) of the film to obtain Δn (= Ro / d ) Δn was determined while changing the load, the load-Δn curve was measured, and the slope was taken as the photoelastic coefficient. The retardation (Ro) in the film plane was measured at a wavelength of 589 nm in an environment of 23 ° C. and 55% RH using a retardation measuring device (KOBUURA 31PR, manufactured by Oji Scientific Instruments).

  Table 2 shows the in-plane retardation Ro, the thickness direction retardation Rth, and the photoelastic coefficient obtained as described above.

  As is apparent from Table 2, the optical films 201 to 208 of the present invention are practically excellent optical films having excellent retardation and low photoelastic coefficient compared to the comparative optical films 209 to 211. I understand that there is.

(Example 3)
<Preparation of polarizing plate>
A polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times).

  This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a polarizer.

  Next, the front side of the polarizer and the optical films 201 to 211 are bonded according to the following steps 1 to 5, and Konica Minolta Tack KC4UY (cellulose ester film manufactured by Konica Minolta Opto Co., Ltd.) is bonded to the back side of the polarizing plate. Was made.

  Step 1: The optical films 201 to 211 are immersed in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried to obtain an optical film having a saponified side to be bonded to a polarizer. It was.

  Process 2: The said polarizer was immersed in the polyvinyl alcohol adhesive tank of 2 mass% of solid content for 1-2 seconds.

  Step 3: Excess adhesive adhered to the polarizer in Step 2 was gently wiped off, and this was placed on the optical film treated in Step 1.

Step 4: The optical films 201 to 211 laminated in Step 3 and the Konica Minoltack KC4UY optical film are stacked on the surface of the polarizer on the polarizer side, and bonded at a pressure of 20 to 30 N / cm ² and a conveyance speed of about 2 m / min. did.

  Step 5: A sample obtained by bonding the polarizer prepared in Step 4 with the optical film 201-211 and Konica Minoltack KC4UY in a drier at 80 ° C. is dried for 2 minutes to produce the corresponding polarizing plates 201-211. did.

[Evaluation of polarizing plate]
Next, the adhesiveness between the optical film and the polarizer and the durability (light resistance and heat and humidity resistance) of the polarizing plate were evaluated as follows.

(Adhesiveness)
The polarizing plate obtained in the above manner was treated at 80 ° C. and 90% RH for 1200 hours, and the bonding state between the cellulose ester film and the polarizer was observed and ranked according to the following criteria.

A: No peeling B: Peeling is slightly observed C: Peeling is recognized D: Peeling is recognized in a very wide range Here, it was judged that A and B were practically satisfactory levels.

(Evaluation of light resistance)
The parallel transmittance (H0) and the direct transmittance (H90) of the undegraded sample were measured, and the degree of polarization was calculated according to the following equation. After that, each polarizing plate was subjected to forced deterioration treatment for 500 hours under the condition that there was no UV cut filter, and again, parallel transmittance (H0 ′) and direct transmittance (H90 ′) after forced deterioration treatment. Was measured, polarization degrees P0 and P500 were calculated according to the following formula, and the degree of polarization degree change was determined by the following formula.

(Calculation of polarization degree P0, P500)
Polarization degree P0 = [(H0−H90) / (H0 + H90)] 1/2 × 100
Polarization degree P500 = [(H0′−H90 ′) / (H0 ′ + H90 ′)] 1/2 × 100
Polarization degree change = P0−P500
P0: Polarization degree before forced deterioration treatment P500: Polarization degree after 500 hours of forced deterioration treatment The degree of polarization change obtained as described above was determined according to the following criteria, and light resistance was evaluated. The results are shown in Table 3.

A: Polarization degree change amount is less than 2% B: Polarization degree change amount is 2% or more and less than 10% C: Polarization degree change amount is 10% or more and less than 25% D: Polarization degree change amount is 25% or more , B was judged to be a level with no practical problems.

(Heat resistant)
Vertical or horizontal center line portion when two 500 mm × 500 mm polarizing plate samples obtained as described above are subjected to a heat and humidity treatment (conditions: left at 100 ° C. for 90 hours at 90 ° C.) and brought into an orthogonal state. The length of the white-out portion of the larger edge was measured, and the ratio to the side length (500 mm) was calculated, and the following determination was made according to the ratio. Edge blanking can be determined visually by the fact that the edge portion of the polarizing plate that does not transmit light in an orthogonal state passes light. In the state of the polarizing plate, the display of the edge portion becomes invisible. The results are shown in Table 3.

A: Edge whiteness is less than 5% (a level that is not a problem as a polarizing plate)
B: White outline of edge is 5% or more and less than 10% (a level at which there is no problem as a polarizing plate)
C: White edge of edge is 10% or more and less than 20% (a level that can be managed as a polarizing plate)
D: Edge blank is 20% or more (a problematic level as a polarizing plate)
Here, it was determined that A and B were at a level having no practical problem.

  As is clear from Table 3, the optical films 201 to 208 of the present invention are superior in adhesiveness to the polarizer as compared with the comparative optical films 210 and 211, and the obtained polarizing plates 201 to 208 of the present invention are It can be seen that it is a practically excellent polarizing plate having good durability as compared with the comparative optical films 209 to 211.

Example 4
<Production of liquid crystal display device>
A liquid crystal panel for viewing angle measurement was produced as follows, and the characteristics as a liquid crystal display device were evaluated.

  The polarizing plates on both sides of the 40-inch display KLV-40J3000 made in advance were peeled off, and the prepared polarizing plates 201 to 211 were bonded to both surfaces of the glass surface of the liquid crystal cell, respectively.

  At that time, the direction of bonding of the polarizing plate is such that the surface of the optical film of the present invention is on the liquid crystal cell side, and the absorption axis of the polarizing plate bonded in advance and the polarizing plates 201 to 211. The absorption axis was directed in the same direction, and the corresponding liquid crystal display devices 201 to 211 were respectively produced.

(Characteristic evaluation as a liquid crystal display device)
The liquid crystal display device produced as described above was evaluated as described below. The results are shown in Table 4.

(Front contrast unevenness)
The measurement was performed after the backlight of each liquid crystal display device was lit continuously for one week in an environment of 23 ° C. and 55% RH. For measurement, EZ-Contrast 160D manufactured by ELDIM was used to measure the luminance from the normal direction of the display screen of white display and black display with a liquid crystal display device, and the ratio was defined as the front contrast.

Front contrast = Brightness of white display measured from the normal direction of the display device / Brightness of black display measured from the normal direction of the display device Measure the front contrast of any 5 points on the liquid crystal display device, and use the following criteria evaluated.

A: Front contrast is 0 to less than 5% variation and unevenness is small B: Front contrast is less than 5 to 10% variation and slightly uneven C: Front contrast is 10% or more variation, Unevenness is large Here, A and B were judged to be at a level where there is no practical problem.

(Viewing angle degradation)
The viewing angle of the liquid crystal display device was measured using EZ-Contrast 160D manufactured by ELDIM in an environment of 23 ° C. and 55% RH. Subsequently, the viewing angle of the produced liquid crystal display device was measured in an environment of 23 ° C., 20% RH, and further 23 ° C., 80% RH, and evaluated according to the following criteria. Finally, viewing angle measurement was performed again in an environment of 23 ° C. and 55% RH, and it was confirmed that the change during the measurement was a reversible fluctuation. These measurements were performed after the liquid crystal display device was placed in the environment for 5 hours.

A: No viewing angle variation is observed B: Viewing angle variation is slightly recognized C: Viewing angle variation is observed Here, A and B were determined to be at a level that is not problematic in practice.

  As is apparent from Table 4, the liquid crystal display devices 201 to 208 using the polarizing plates 201 to 208 of the present invention have a front contrast unevenness compared to the liquid crystal display devices 209 to 211 using the comparative polarizing plates 209 to 211. It can be seen that the liquid crystal display device is extremely stable and excellent in durability with no viewing angle variation even under conditions where the humidity varies.

Claims (9)

An optical film comprising a polymer (A) having a repeating unit represented by the following general formula (I).

(In the formula, R ₁ , R ₂ , R ₃ and R ₄ are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms which may have a substituent.)   An optical film comprising a polymer (A) having a repeating unit represented by the general formula (I) and a cellulose ester (B). The optical film according to claim 1 or 2, wherein the polymer (A) is represented by the following general formula (II).

(Wherein R ₁ , R ₃ , R ₄ and R ₅ may be the same or different and each represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms which may have a substituent.) The said cellulose ester (B) is a cellulose acetate propionate, and satisfy | fills the substitution degree of following formula (1) and (2) simultaneously, The any one of Claims 1-3 characterized by the above-mentioned. Optical film.
Formula (1) 2.0 <= X + Y <= 2.8
Formula (2) 0.5 <= Y <= 1.5
(In the formula, X represents the degree of substitution of the acetyl group. Y represents the degree of substitution of the propionyl group.)   The polymer (A) and the cellulose ester (B) are contained at a mass ratio of (A) :( B) = 20: 80 to 50:50. 2. An optical film according to item 1. Retardation Ro represented by the following formula (I) is 20 to 100 nm and Rth represented by the following formula (II) is 70 to 300 nm with respect to light having a wavelength of 590 nm in an environment of 23 ° C. and 55% RH. The optical film according to claim 1, wherein the optical film is a film.
Formula (I) Ro = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
(However, nx represents the refractive index in the direction x in which the refractive index is maximum in the in-plane direction of the optical film, and ny represents the refractive index in the direction y orthogonal to the direction x in the in-plane direction of the optical film. , Nz represents the refractive index in the thickness direction z of the optical film, and d (nm) represents the thickness of the optical film.) The optical film according to any one of claims 1 to 6, wherein the photoelastic coefficient is -5 × ¹⁰ -12 ^{Pa -1} or ¹⁰ × 10 -12 ^{Pa -1} or less.   A polarizing plate comprising the optical film according to claim 1 on at least one surface of a polarizer.   A liquid crystal display device comprising the polarizing plate according to claim 8 on at least one surface of a liquid crystal cell.