JP2007003679A - Retardation plate, polarizer, and liquid crystal display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation plate excellent in durability of a polarization degree and prevention of light leakage, and to provide a polarizer using the retardation plate, and a liquid crystal display apparatus using the polarizer. <P>SOLUTION: The retardation plate essentially comprises cellulose ester and is characterized in that the total acyl group substitution degree of the cellulose ester ranges from 2.4 to 2.8, the retardation plate contains the following compounds (1) and (2) in total by 5 to 25 mass%, and the content (a) (mass%) of the component (1) and the content (b) (mass%) of the component (2) satisfy a= b/4 to 4b. The compounds are (1) a polyester compound which increases the elastic modulus of the cellulose ester by 5 to 20% when the compound is added by 10 mass% to the cellulose ester, and (2) an aromatic polyvalent carboxylic acid ester compound having a valency of 3 or more which decreases the elastic modulus of the cellulose ester by 5 to 20% when the compound is added by 10 mass% to the cellulose ester. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  In recent years, a liquid crystal display device has been widely used as a display device for displaying information. However, the liquid crystal display device has a problem that a viewing angle is narrow. In order to solve this problem, for example, a method using an optical compensation film (retardation plate) has been proposed (see, for example, Patent Documents 1 and 2).

  Moreover, the polarizing plate used for a liquid crystal display device generally has a configuration in which both surfaces of a polarizer are sandwiched between polarizing plate protective films.

  In recent years, it has become possible to reduce the number of members used for a polarizing plate by using a retardation plate as a polarizing plate protective film.

  In general, a cellulose ester resin is used as a polarizing plate protective film. Various methods have been proposed for imparting the function of a retardation plate to the polarizing plate protective film.

  For example, a method of coating an optically anisotropic layer made of a discotic compound on a cellulose ester film, a method of stretching a cellulose ester resin by adding a retardation increasing agent, and a suitable degree of substitution of total acyl groups in the cellulose ester resin. The method of extending | stretching a film, setting it, etc. is raised (for example, refer patent documents 3-6).

On the other hand, the retardation plate not only has a function of optically compensating the liquid crystal cell, but also needs to have excellent durability due to changes in the usage environment. When a polarizing plate used as a film is mounted, particularly in a large panel of 17 inches or more, light leakage presumed to be caused by thermal distortion may occur, and durability due to changes in the usage environment is not sufficient.

  As a method for improving light leakage due to thermal strain, a method of reducing the thickness of a retardation plate is known (see, for example, Patent Documents 7 and 8).

  However, since the retardation is proportional to the film thickness, if the film thickness is reduced, the retardation required for the retardation plate is increased, so the amount of addition of the retardation increasing agent is increased, and the total acyl substitution degree of the cellulose ester is further reduced. It is necessary to take measures such as

When the amount of addition of the retardation increasing agent is increased, bleed out, dimensional change, etc. occur due to deterioration of retention. In addition, if the total acyl substitution degree of cellulose ester is lowered, the hygroscopicity is deteriorated, so that the polarization degree of the polarizing plate is deteriorated at high temperature and high humidity, and the light modulus is sufficiently improved because the elastic modulus is increased. There wasn't. As described above, it is difficult to improve the light leakage without degrading the degree of polarization with the conventional retardation plate.
JP-A-6-75116 JP-A-6-174920 Japanese Patent Laid-Open No. 7-191217 JP 2000-1111914 A JP 2002-62430 A JP 2002-71957 A JP 2002-71948 A JP 2002-169023 A

  An object of the present invention is to provide a retardation plate having excellent polarization degree durability and light leakage prevention properties, a polarizing plate using the retardation plate, and a liquid crystal display device using the polarizing plate.

(Claim 1)
A phase difference plate comprising cellulose ester as a main component, wherein the cellulose ester has a total acyl group substitution degree of 2.4 to 2.8, and the phase difference plate comprises the following compounds (1) and (2): When the total content is 5 to 25% by mass, the content of the following (1) is a (% by mass) and the content of the following (2) is b (% by mass), a = b / 4 to 4b A retardation plate characterized by being.
[(1) A polyester compound in which the elastic modulus of the cellulose ester is increased by 5 to 20% when 10% by mass is added to the cellulose ester.
(2) A trivalent or higher aromatic polyvalent carboxylic acid ester compound in which the elastic modulus of the cellulose ester is reduced by 5 to 20% when 10% by mass is added to the cellulose ester. ]
(Claim 2)
The retardation plate according to claim 1, wherein the polyester compound has a plurality of ester bonds obtained from an aromatic dicarboxylic acid and alkylene glycol or oxyalkylene glycol.

(Claim 3)
The retardation plate according to claim 1, wherein the trivalent or higher aromatic polyvalent carboxylic acid ester compound is trimesic acid ester, trimellitic acid ester or pyromellitic acid ester.

(Claim 4)
The retardation film according to claim 1, wherein the retardation film contains 2 to 10% by mass of a polyhydric alcohol ester compound.

(Claim 5)
The retardation plate according to any one of claims 1 to 4, wherein the polyhydric alcohol ester compound is an ester compound obtained from trimethylolpropane or pentaerythritol and an aromatic carboxylic acid.

(Claim 6)
The cellulose ester is cellulose acetate propionate or cellulose acetate butyrate, the total acyl group substitution degree is 2.4 to 2.8, and the substitution degree of propionyl group or butyryl group is 0.5 to 1.5. The retardation film according to claim 1, wherein the retardation film is a retardation plate.

(Claim 7)
The thickness of the retardation plate is 30 to 60 μm, and the retardation (Ro) in the in-plane direction defined by the following formula (I) is 30 to 100 nm, in the thickness direction defined by the following formula (II). Retardation (Rt) is 100-300 nm, The phase difference plate of any one of Claims 1-6 characterized by the above-mentioned.
(I) Ro = (nx−ny) × d
(II) Rt = {(nx + ny) / 2−nz} × d
[Where nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, nz is the refractive index in the thickness direction of the film, and d is It is the thickness of the film]
(Claim 8)
A polarizing plate using the retardation plate according to claim 1.

(Claim 9)
The polarizing plate according to claim 8, wherein a polyethylene-polyvinyl alcohol copolymer film having a thickness of 10 to 20 μm is used as the polarizer.

(Claim 10)
A liquid crystal display device using the polarizing plate according to claim 8.

  According to the above configuration of the present invention, a retardation plate having excellent polarization degree durability and light leakage prevention properties, a polarizing plate using the retardation plate, and a liquid crystal display device using the polarizing plate can be provided.

  The present invention is a retardation plate mainly composed of cellulose ester, wherein the cellulose ester has a total acyl group substitution degree of 2.4 to 2.8, and the retardation plate is represented by the following (1) and (2 ) In a total of 5 to 25% by mass, the content of the following (1) is a (% by mass), and the content of the following (2) is b (% by mass), a = b / 4 ~ 4b.

  In the present invention, a retardation plate having excellent polarization degree durability and excellent light leakage prevention properties, a polarizing plate using the retardation plate, and this polarizing plate, in particular, by combining the compounds (1) and (2) above. The liquid crystal display device used can be provided.

((1) Polyester compound in which the elastic modulus of cellulose ester increases by 5 to 20% when added to cellulose ester by 10% by mass (hereinafter also referred to as compound (1)))
The elastic modulus according to the present invention refers to an elastic modulus measured according to the method described in JIS K7127. The shape of the test piece at this time is a No. 1 type test piece, and the test speed is 100 mm / min.

  Compound (1) is a polyester compound, and is a compound in which the elastic modulus of the cellulose ester increases by 5 to 20% when the polyester compound is added to the cellulose ester by 10% by mass.

  Here, when the elastic modulus is increased by 5 to 20%, the cellulose ester in which 10% by mass of the compound (1) is added to the cellulose ester with respect to the elastic modulus of the cellulose ester film composed of the cellulose ester to which no additive is added. It means that the elastic modulus of the cellulose ester film made of is 5 to 20% higher.

  The polyester compound according to the present invention refers to a compound containing 4 or more ester bonds in the main chain of the molecule (which means a molecular chain having the most ester bonds among the molecular chains linked via ester bonds).

  As the compound (1) according to the present invention, a polyester compound having an aromatic ring or a cycloalkyl ring in the molecule is preferably used.

  Among these, a compound having an aromatic ring at both ends of the main chain is preferable, and a compound having an aromatic ring in the main chain other than both ends is preferably used.

  Further, a compound having a plurality of ester bonds obtained from an aromatic dicarboxylic acid and alkylene glycol or oxyalkylene glycol is preferable, and in addition, a compound having an aromatic ring at both ends of the main chain is preferable.

  Preferred examples of the compound (1) include compounds represented by the following general formula (1).

General formula (1) B- (GA) n-GB
(In the formula, B represents a benzene monocarboxylic acid residue, G represents an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms. Represents a group, A represents an alkylene dicarboxylic acid residue having 2 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
Examples of the benzene monocarboxylic acid include benzoic acid, para-tert-butyl benzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethyl benzoic acid, ethyl benzoic acid, normal propyl benzoic acid, aminobenzoic acid, acetoxybenzoic acid and the like. These may be used alone or in a mixture of two or more.

  Examples of the alkylene glycol having 2 to 12 carbon atoms include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, and 2-methyl-1,3-propane. Diol, 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-pentanediol 1,6-hexanediol, 2, 2,4-trimethyl 1,3-pentanediol, 2-ethyl 1,3-hexanediol, 2-methyl 1,8-octanedio Le, 1,9-nonanediol, 1,10-decanediol, 1,12 has octadecanediol etc., these glycols may be used alone or in a mixture of two or more.

  Examples of the oxyalkylene glycol having 4 to 12 carbon atoms include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. These glycols are used as one kind or a mixture of two or more kinds. I can do it.

  Examples of the aryl glycol having 6 to 12 carbon atoms include 1,3 dihydroxybenzene and 1,4 dihydroxymethylbenzene.

  Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and the like. Used as a mixture of two or more.

  Examples of the arylene dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, isophthalic acid, terephthalic acid, 1,5 naphthalene dicarboxylic acid, and 1,4 naphthalene dicarboxylic acid.

  As a number average molecular weight of a compound (1), 400-2000 are preferable and the range of 500-1500 is more preferable.

  Specific examples of the compound represented by the general formula (1) are listed below.

((2) A trivalent or higher aromatic polyvalent carboxylic acid ester compound (hereinafter sometimes simply referred to as compound (2)) in which the elastic modulus of the cellulose ester film is reduced by 5 to 20% when 10% by mass is added to the cellulose ester. ))
The compound (2) is a trivalent or higher aromatic polyvalent carboxylic acid ester compound, and is a compound in which the elastic modulus of the cellulose ester is reduced by 5 to 20% when added by 10% by mass to the cellulose ester.

  Here, when the elastic modulus is reduced by 5 to 20%, the cellulose ester in which 10% by mass of the compound (2) is added to the cellulose ester with respect to the elastic modulus of the cellulose ester film composed of the cellulose ester to which no additive is added. It means that the elastic modulus of the cellulose ester film made of is 5 to 20% lower.

  The trivalent or higher aromatic polyvalent carboxylic acid ester compound according to the present invention is a compound having an ester bond obtained by a reaction between a trivalent or higher aromatic polyvalent carboxylic acid and an alcohol.

  As the trivalent or higher aromatic carboxylic acid, trimesic acid, trimellitic acid or pyromellitic acid is preferably used. That is, as the compound (2), trimesic acid ester, trimellitic acid ester or pyromellitic acid ester is preferable.

  Moreover, as alcohol, C1-C8 alcohol is used preferably, for example, each alcohol, such as methyl, ethyl, propyl, butyl, hexyl, cyclohexyl, is mentioned.

  Examples of the compound (2) include tributyl trimesate, trihexyl trimesate, tri-2-ethyl-hexyl trimesate, tricyclohexyl trimesate, tributyl trimellitic acid, trihexyl trimellitic acid, tri-2-ethyl-hexyl trimellitic acid. , Trimellitic acid tricyclohexyl, pyromellitic acid tetrabutyl, pyromellitic acid tetrahexyl, pyromellitic acid tetra2-ethyl-hexyl, pyromellitic acid tetracyclohexyl, and the like.

(Contents of Compound (1) and Compound (2))
In the present invention, the total amount of the compound (1) and the compound (2) is 5 to 25% by mass from the viewpoint of polarization degree durability and light leakage prevention property, and the content of the compound (1) is a (mass). %), Where the content of the compound (2) is b (mass%), it is necessary that a = b / 4 to 4b.

  When the total content of the compound (1) and the compound (2) is less than 5%, the sufficient effect of the present invention cannot be obtained. Is not enough.

  The ratio of the content of the compound (1) and the compound (2) is a = b / 4 to 4b, more preferably a = b / 3 to 3b.

  In the present invention, the effects of the present invention can be obtained by combining the compound (1) and the compound (2). This effect is estimated as follows.

  In the cellulose ester film, there is a space in which molecules called free volume can move relatively freely. When the free volume is large, moisture absorption and movement of the molecular chain of the cellulose ester occur easily, so that the moisture permeability and dimensional change deteriorate. The free volume is filled with the compound (1) and the compound (2), and the effect of the present invention is expressed by the interaction between the molecular chain of cellulose and each of the compound (1) and the compound (2). Guessed.

(Plasticizer)
Although the compounds (1) and (2) according to the present invention also have a function as a plasticizer, other plasticizers may be added to the retardation plate of the present invention as necessary.

  The plasticizer that can be used is not particularly limited, for example, polyhydric alcohol ester plasticizer, glycolate plasticizer, phosphate ester plasticizer, phthalate ester plasticizer, and the like, A polyhydric alcohol ester plasticizer is preferably used.

  The polyhydric alcohol ester plasticizer is a polyhydric alcohol ester compound, for example, an ester compound of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and has an aromatic ring or a cycloalkyl ring in the molecule. The polyhydric alcohol ester having is preferably used.

  The polyhydric alcohol used for the polyhydric alcohol ester compound is represented by the following general formula (2).

Formula (2) R ^1- (OH) n
In the formula, R ¹ represents an n-valent organic group, n represents a positive integer of 2 or more, and the OH group represents an alcoholic or phenolic hydroxyl group.

  Examples of preferable polyhydric alcohols include the following. 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, pentaerythritol, dipentaerythritol and the like. Of these, trimethylolpropane and pentaerythritol are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for the ester compound of a polyhydric alcohol, 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 preferable in terms of improving moisture permeability and retention. Examples of preferred monocarboxylic acids include the following.

  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.

  The use of acetic acid is preferred because the compatibility with the cellulose ester is increased, and it is also preferred 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-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, Examples thereof include unsaturated fatty acids such as oleic acid, sorbic acid, linoleic acid, linolenic acid and arachidonic acid.

  Examples of preferable alicyclic monocarboxylic acids include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, and 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 benzene rings such as biphenyl carboxylic acid, naphthalene carboxylic acid, and tetralin carboxylic acid. Aromatic monocarboxylic acids possessed by them, or derivatives thereof. In particular, benzoic acid is preferably used.

  The molecular weight of the ester compound of the polyhydric alcohol is not particularly limited, but is preferably in the range of 300 to 1500, and more preferably in the range of 350 to 750.

  A higher molecular weight is preferable because it is less likely to volatilize, but if the molecular weight is too large, the compatibility with the cellulose ester is degraded. The carboxylic acid used for the ester compound of the polyhydric alcohol 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. Specific examples of the ester compound of polyhydric alcohol are given below.

  In this invention, in addition to the compound (1) and compound (2) which concern on this invention, it is preferable to contain a polyhydric alcohol type plasticizer in 2 to 10% of range. As content in this case, it is preferable that it is 10 mass%-60 mass% with respect to the total amount of the said compound (1) and compound (2), and also it is 10 mass%-40 mass%. Is preferred.

  As glycolate plasticizers, ethyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, and phosphate ester plasticizers are triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl. For phthalate plasticizers such as phosphate, trioctyl phosphate, tributyl phosphate, etc., diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, butyl benzyl phthalate, di-2-ethylhexyl phthalate, etc. can be used . In addition, citrate plasticizers such as acetyltributyl citrate, epoxidized oil plasticizers, and the like can also be used.

  These plasticizers can be added as long as the effects of the present invention are not impaired. The addition amount of the plasticizer is preferably 5 to 25% by mass in total of the compound (1), the compound (2) and other plasticizers from the viewpoint of polarization degree durability.

(Cellulose ester)
The cellulose ester used in the present invention is a cellulose ester having a total acyl substitution degree of 2.4 to 2.8.

  The cellulose ester is preferably a lower fatty acid ester of cellulose. The lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms. For example, cellulose acetate, cellulose propionate, cellulose butyrate and the like, and JP-A Nos. 10-45804 and 08-231761 Further, mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate as described in US Pat. No. 2,319,052 can be used.

  Among the above descriptions, the lower fatty acid esters of cellulose that are particularly preferably used are cellulose diacetate, cellulose triacetate, and cellulose acetate propionate.

  The most preferable lower fatty acid ester of cellulose has an acyl group having 2 to 4 carbon atoms as a substituent, and when the substitution degree of acetyl group is X and the substitution degree of propionyl group or butyryl group is Y, the following formula ( It is a cellulose ester containing the cellulose ester which satisfy | fills 1) and (2) simultaneously.

Formula (1) 2.4 <= X + Y <= 2.8
Formula (2) 0.5 <= Y <= 1.5
The portion that is not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by known methods.

  The cellulose ester satisfying the above (1) and (2) is excellent in polarization degree durability and light leakage prevention while exhibiting a phase difference. Further, from the viewpoint of heat resistance, the propionyl group is more advantageous than the butyryl group. The degree of propionyl substitution is more preferably 0.8 ≦ Y ≦ 1.3. The cellulose ester used in the present invention has a weight average molecular weight (Mw) / number average molecular weight (Mn) value of 1.4 to 3. It is preferably 0, and more preferably in the range of 1.4 to 2.2.

  This range of Mw / Mn is preferable from the viewpoint of retardation development and white turbidity prevention when the cellulose ester film is stretched. This is presumably because the smaller the Mw / Mn value, the smaller the molecular weight distribution, so that the polymer molecules are easily oriented and a uniform film with few voids is likely to be formed. However, if the value of Mw / Mn is too small, an increase in production cost or a decrease in molecular weight is likely to occur, so it is practical to set the value to 1.4 or more.

  The average molecular weight and molecular weight distribution of the cellulose ester can be measured by a known method using high performance liquid chromatography. Using these, the number average molecular weight and the weight average molecular weight can be calculated, and the ratio (Mw / Mn) can be calculated.

  The molecular weight of the cellulose ester is preferably 60000-200000 in terms of number average molecular weight (Mn), more preferably 70000-170000. If the molecular weight of the cellulose ester is large, the rate of change of the retardation value due to humidity becomes small. However, if the molecular weight is too high, the viscosity of the cellulose ester solution becomes too high and the productivity may decrease.

  The measurement conditions of the number average molecular weight and the weight average molecular weight using high performance liquid chromatography are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
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 Corp.) Mw = 100000 to 500 samples are used. It is preferable to obtain 13 samples at approximately equal intervals.

  As the cellulose ester, cellulose ester synthesized using cotton linter, wood pulp, kenaf or the like as a raw material can be used alone or in combination. In particular, it is preferable to use a cellulose ester synthesized from a cotton linter (hereinafter sometimes simply referred to as linter) alone or in combination.

(Phase difference)
The retardation plate of the present invention has a film thickness of 20 to 85 μm, an in-plane retardation (R _O ) defined by the following formula (I) of 30 to 200 nm, and is defined by the following formula (II). The retardation in the thickness direction (R _t ) is preferably 100 to 400 nm.

The retardation R ₀ in the in-plane direction and the retardation R _{t in} the film thickness direction can be measured using an automatic birefringence meter. Using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments), the birefringence measurement at 590 nm of the cellulose ester film is performed in an environment of 23 ° C. and 55% RH, and the refractive indexes nx and ny , Nz, and R0 and Rt are calculated according to the following formulas (I) and (II).
(I) R ₀ = (nx−ny) × d
(II) R _t = {(nx + ny) / 2−nz} × d
(Where nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, nz is the refractive index in the thickness direction of the film, and d is (The thickness of the film (nm).)
In the present invention, the retardation R ₀ in the in-plane direction of the cellulose ester film is preferably 30 to 200 nm, and more preferably 30 to 100 nm.

The thickness direction retardation R _t is preferably 100 to 400 nm, and more preferably 100 to 300 nm. In particular, R _t / R ₀ is preferably 1.5 to 6.0.

  The film thickness of the cellulose ester film is preferably 20 to 85 μm and more preferably 30 to 60 μm from the viewpoints of polarization degree durability, retardation development and light leakage prevention.

The retardation plate of the present invention has a film thickness of 30 to 60 μm and an in-plane retardation (R _O ) defined by the above formula (I) of 30 to 100 nm, defined by the above formula (II). preferably the thickness direction retardation (R _t) is 100~300nm being, in addition, it is preferable R _t / R ₀ is 1.5 to 6.0.

  Furthermore, in the retardation film of the present invention, the degree of polarization p determined according to the following formula is preferably 0.9990 or more, more preferably 0.9999 or more, and further preferably 0.99995 or more. Preferably, 0.99999 or more is particularly preferable.

p = 1−sin ² (2θ1) · sin ² (πR0 / λ)
(In the formula, λ represents a measurement wavelength (nm) and is 590. θ1 (radian) was obtained from θ0 (°).)
(Other additives)
In the retardation plate according to the present invention, additives such as an ultraviolet absorber, a dye, a matting agent, and a deterioration preventing agent may be added to the cellulose ester as necessary.

  From the viewpoint of preventing deterioration of the liquid crystal, an ultraviolet absorber that is excellent in the ability to absorb ultraviolet light having a wavelength of 370 nm or less and that absorbs less visible light having a wavelength of 400 nm or more is preferably used from the viewpoint of good liquid crystal display properties.

  In particular, the ultraviolet absorber preferably has a transmittance of 10% or less at a wavelength of 370 nm, more preferably 5% or less, and still more preferably 2% or less.

  As the ultraviolet absorber added to the retardation plate according to the present invention, an ultraviolet absorber having two or more aromatic rings in the molecule is particularly preferably used.

  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, and inorganic powders. . The UV absorber preferably used in the present invention is preferably a benzotriazole-based UV absorber or a benzophenone-based UV absorber that has high transparency and is excellent in the effect of preventing the deterioration of the polarizing plate and the liquid crystal element, and has less unnecessary coloring. Benzotriazole ultraviolet absorbers are particularly preferred. As specific examples of the ultraviolet absorber used in the present invention, for example, TINUVIN109, TINUVIN171, TINUVIN326, TINUVIN327, and TINUVIN328 manufactured by Ciba Specialty Chemicals can be preferably used, but the present invention is limited to these. It is not a thing. 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. An ultraviolet absorber may be used independently and 2 or more types of mixtures may be sufficient as it.

  The ultraviolet absorber may be added to the dope after dissolving the ultraviolet absorber in an organic solvent such as alcohol, methylene chloride, dioxolane, or directly into the 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 compound, use conditions, etc., but when the dry film thickness of the cellulose ester film is 30 to 200 μm, 0.5 to 4.0 mass relative to the cellulose ester film. % Is preferable, and 0.6 g to 3.5% by mass is more preferable.

  If necessary, fine particles such as silicon oxide may be added to the retardation plate according to the present invention as a matting agent. The fine particles as the matting agent are preferably surface-treated with an organic material because the haze of the film can be reduced.

  Preferred organic materials for the surface treatment include halosilanes, alkoxysilanes, silazanes, siloxanes, and the like.

  In the present invention, from the viewpoint of the effect of the matting agent and transparency, the average primary particle diameter is preferably 5 to 50 nm, and more preferably 7 to 20 nm.

  The fine particles of silicon oxide are not particularly limited, and examples thereof include Aerosil 200, 200V, 300, R972, R972V, R972CF, R974, R202, R805, R812, OX50, and TT600 manufactured by Aerosil Co., preferably AEROSIL 200. 200V, R972, R972V, R974, R202, R805, R812 and the like.

  The retardation plate according to the present invention may be added with a deterioration inhibitor (an antioxidant, a peroxide decomposer, a radical inhibitor, a metal deactivator, an acid scavenger, an amine, etc.) as necessary. good.

  The addition of the deterioration inhibitor has an effect of suppressing the deterioration of the polarization degree. The deterioration preventing agents are described in JP-A-3-199201, JP-A-5-1907073, JP-A-5-194789, JP-A-5-271471, and JP-A-6-107854.

  The addition amount of the deterioration inhibitor is preferably 0.01 to 1% by mass of the solution to be adjusted, and more preferably 0.01 to 0.2% by mass.

  Various additives may be batch-added to a dope solution in which a cellulose ester is dissolved, or an additive solution may be separately prepared and added in-line.

  When the additive solution is added in-line, it is preferable to dissolve a small amount of cellulose ester in order to improve mixing with the dope.

  The amount of the cellulose ester is preferably 1 to 10 parts by mass, more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.

  In the present invention, for example, a static mixer (manufactured by Toray Engineering Co., Ltd.) can be used for in-line addition and mixing of a dope solution in which cellulose ester is dissolved in a solvent and a solution in which various additives and a small amount of cellulose ester are dissolved. ), An in-line mixer such as SWJ (Toray static type in-tube mixer Hi-Mixer) is preferably used. When using an in-line mixer, it is preferable to concentrate and dissolve under high pressure, and the type of the pressurized container is not particularly limited, as long as it can withstand a predetermined pressure and can be heated and stirred under pressure. In addition to the pressure vessel, other instruments such as a pressure gauge and a thermometer are appropriately disposed.

<Production method of retardation plate>
Next, a method for producing a retardation plate according to the present invention will be described.

  The production of the phase difference plate includes the steps of preparing a dope by dissolving additives such as cellulose ester and plasticizer in a solvent, the step of casting the dope on a belt-shaped or drum-shaped metal support, the cast dope By the step of drying as a web (retardation plate), the step of peeling from the metal support, the step of stretching, the step of further drying, the step of further heat-treating the obtained film (retardation plate), and the step of winding after cooling Done.

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

  The solvent used for 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 cellulose ester in terms of production efficiency, and there are many good solvents. This is preferable from the viewpoint of the solubility of the cellulose ester. 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 dissolve | melts the cellulose ester to be used independently is defined as a good solvent, and what poorly swells or does not melt | dissolve is defined as a poor solvent. Therefore, depending on the acyl group substitution degree of the cellulose ester, the good solvent and the poor solvent change. For example, when acetone is used as the solvent, the cellulose ester acetate ester (acetyl group substitution degree 2.4) and cellulose acetate propionate are good. As a solvent, cellulose acetate (acetyl group substitution degree 2.8) is a poor solvent.

  The good solvent that can be used in the present invention 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 a poor solvent is not specifically limited, For example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone etc. are used preferably.

  A general method can be used as a method of dissolving the cellulose ester when preparing the dope described above. When heating and pressurization are combined, it can be heated 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 mamacos. Moreover, after mixing a cellulose ester with a poor solvent and making it wet or swell, the method of adding a good solvent and melt | dissolving is also used preferably. A cooling dissolution method is also preferably used.

  The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or a method of increasing 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 cellulose ester, 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.

  Next, this cellulose ester solution 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. However, if the absolute filtration accuracy is too small, there is a problem that the filter medium is likely to be clogged. 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 cellulose ester by filtration.

A bright spot foreign substance is when two polarizing plates are placed in a crossed Nicol state, a cellulose ester film is placed between them, light is applied from the side of one polarizing plate, and observed from the side of the other polarizing plate. 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 100 / cm ² or less, more preferably 50 or / m ² or less, more preferably 0 to 10 / 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 an ordinary 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 increase in 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, and a stainless steel belt or a drum whose surface is plated with a casting is preferably used as the metal support. The cast width can be 1 to 4 m. The surface temperature of the metal support in the casting step is set to −50 ° C. to a temperature at which the solvent boils and does not foam.

  A higher temperature is preferable because the web can be dried faster, but if the temperature is too high, the web may foam or the flatness may deteriorate.

  The preferable support temperature is appropriately determined at 0 to 100 ° C, and more preferably 5 to 30 ° C. 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.

  In the case of using warm air, in consideration of a decrease in the temperature of the web due to the latent heat of vaporization of the solvent, there is a case where air having a temperature higher than the target temperature is used while preventing foaming. In particular, it is preferable to perform drying efficiently by changing the temperature of the support and the temperature of the drying air during the period from casting to peeling.

  In order for the cellulose ester film (retardation plate) 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 It is 60-130 mass%, Most preferably, it is 20-30 mass% or 70-120 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.

  In the film drying process, generally, a roll drying method (a method in which a plurality of rolls arranged on the upper and lower sides are alternately passed through and dried) or a tenter method is used while drying the web.

  When peeling from the casting support, the film can be stretched in the longitudinal direction by the peeling tension and the subsequent conveying tension. For example, it is preferable to peel at a peeling tension of 210 N / m or more, and particularly preferably 220 to 300 N / m.

  An example of a stretching process (also referred to as a tenter process) for producing the retardation film according to the present invention will be described.

  In order to obtain the effect of the present invention, it is particularly preferable to carry out the web peeled from the metal support while being dried, and further to stretch in the width direction by a tenter method in which both ends of the web are gripped by pins or clips. A predetermined phase difference can be given. The preferred draw ratio is preferably 1.05 to 2 times, and preferably 1.15 to 1.6 times.

  The stretching operation may be performed in multiple stages. Moreover, you may extend | stretch only to the width direction and it is also preferable to implement biaxial stretching to a casting direction and a width direction. Also, when biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be performed stepwise.

  In this case, stepwise means that, for example, stretching in different stretching directions can be sequentially performed, stretching in the same direction is divided into multiple stages, and stretching in different directions is added to any one of the stages. Is also possible. In the case of simultaneous biaxial stretching, the film may be contracted in the longitudinal direction, or may be contracted so as to be 0.8 times to 0.99 times, preferably 0.9 times to 0.99 times.

  Preferably, the area is preferably 1.12 times to 1.44 times and more preferably 1.15 times to 1.32 times due to transverse stretching and longitudinal stretching or shrinkage. This can be determined by the draw ratio in the longitudinal direction × the draw ratio in the transverse direction.

  In addition, the stretching direction is usually used in the sense of directly applying a stretching stress when performing a stretching operation. It may be used to mean the larger one (that is, the direction that usually becomes the slow axis).

  FIG. 2 is a schematic diagram illustrating an example of a stretching process.

  In FIG. 2, in step A, the web transported from a web transport step (not shown) is gripped by gripping means, and in the next step B, the web is stretched in the width direction (film In the process C, stretching is completed, the film is conveyed while being gripped, and this grip is released.

  When the web is stretched in the width direction, it is well known that the optical slow axis distribution (hereinafter, orientation angle distribution) deteriorates in the width direction of the web. Since the widthwise stretching is performed with the Rt and Ro values at a constant ratio and the orientation angle distribution in a good state, there is a preferable web temperature relative relationship in the A, B, and C steps. When the web temperatures at the end points of Steps A, B, and C are Ta ° C., Tb ° C., and Tc ° C., respectively, it is preferable that Ta ≦ Tb−10. Moreover, it is preferable that Tc ≦ Tb. More preferably, Ta ≦ Tb−10 and Tc ≦ Tb.

  In order to improve the orientation angle distribution, the web heating rate in the B process is preferably in the range of 0.5 to 10 ° C./second.

  The stretching time in step B is preferably a short time. However, the minimum required stretching time range is defined from the viewpoint of web uniformity. Specifically, the range is preferably 1 to 10 seconds, and more preferably 4 to 10 seconds.

  Moreover, the temperature of B process is 40-180 degreeC, Preferably it is 100-160 degreeC. It is also preferable to provide a neutral zone between different temperature zones so that the zones do not interfere with each other.

In the tenter process, the heat transfer coefficient may be constant or changed. The heat transfer coefficient preferably has a heat transfer coefficient in the range of 41.9 to 419 × 10 ³ J / m ² hr. More preferably, in the range of ^{41.9~209.5 × 10 3 J / m 2} hr, and most preferably a range of ^{41.9~126 × 10 3 J / m 2} hr.

  The stretching speed in the width direction in step B may be constant or may be changed.

  The stretching speed is preferably 50 to 500% / min, more preferably 100 to 400% / min, and most preferably 200 to 300% / min.

  In the tenter process, it is preferable that the temperature distribution in the width direction of the atmosphere is small from the viewpoint of improving the uniformity of the web. The temperature distribution in the width direction in the tenter process is preferably within ± 5 ° C, and within ± 2 ° C Is more preferable, and within ± 1 ° C. is most preferable. By reducing the temperature distribution, it can be expected that the temperature distribution at the width of the web is also reduced.

  In Step C, it is preferable to relax in the width direction. Specifically, it is preferable to adjust the web width so that the final web width after stretching in the previous step is in the range of 95 to 99.5%.

  After the treatment in the tenter process, it is preferable to further provide a post-drying process (hereinafter referred to as process D1). It is preferable to carry out at 50-160 degreeC. More preferably, it is the range of 80-140 degreeC, Most preferably, it is the range of 110-130 degreeC.

  Moreover, in the drying process of the cellulose ester film, the web is peeled off from the metal support, further dried, and the residual solvent amount is dried to 0.5% by mass or less.

  In step D1, it is preferable that the atmospheric temperature distribution in the width direction of the web is small from the viewpoint of improving the uniformity of the web. Within ± 5 ° C is preferable, within ± 2 ° C is more preferable, and within ± 1 ° C is most preferable.

  Although the web conveyance tension | tensile_strength in process D1 is influenced by the physical property of dope, the temperature at the time of peeling, 120-200 N / m is preferable and 140-200 N / m is still more preferable. 140 to 160 N / m is most preferable.

  It is preferable to provide a tension cut roll for the purpose of preventing the web from stretching in the transport direction in step D1.

  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 in terms of simplicity.

  The drying temperature in the web drying step is preferably increased stepwise from 30 to 160 ° C.

  After the predetermined heat treatment, it is preferable to provide a slitter and cut off the end portion before winding to obtain a good winding shape. Furthermore, it is preferable to knurling both ends of the width.

  The knurling process can be formed by pressing a heated embossing roll. Fine embossing is formed on the embossing roll. By pressing this embossing roll, unevenness can be formed on the web and the end can be made bulky.

  The height of the knurling at the both lateral ends of the web (retardation plate) is preferably 4 to 20 μm and the width is 5 to 20 mm.

  In the present invention, the knurling process is preferably provided after the drying in the web film-forming step and before winding.

  A retardation plate having a multilayer structure by a co-casting method can also be preferably used. Even when the retardation film has a multilayer structure, it has a layer containing a plasticizer, which may be a core layer, a skin layer, or both.

  The center line average roughness (Ra) of the surface of the retardation film according to the present invention is preferably 0.001 to 1 μm.

<Polarizer>
The polarizing plate of the present invention will be described.

  The polarizing plate can be produced by a general method. After the retardation plate of the present invention (hereinafter also referred to as a retardation film) is subjected to alkali saponification treatment, it is preferably bonded to at least one surface of the polarizer using a completely saponified polyvinyl alcohol aqueous solution. With respect to the retardation film of the present invention, a commercially available cellulose ester film is preferably used for the polarizing plate protective film used on the other surface. For example, as a commercially available cellulose ester film, KC8UX2M, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5 (above, manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used. By using it in combination with an antireflection film, a polarizing plate having excellent visibility and a stable viewing angle expansion effect can be obtained.

  As the polarizer, a stretched and dyed polyvinyl alcohol film is preferably used. In particular, ethylene-modified polyvinyl alcohol having an ethylene unit content of 1 to 4 mol%, a polymerization degree of 2000 to 4000, and a saponification degree of 99.0 to 99.99 mol% is preferably used. Among them, an ethylene-modified polyvinyl alcohol film having a hot water cutting temperature of 66 to 73 ° C. is preferably used. The difference in hot water cutting temperature between two points 5 cm away in the TD direction of the film is more preferably 1 ° C. or less in order to reduce color spots, and two points separated 1 cm in the TD direction of the film. In order to reduce color spots, it is more preferable that the difference in hot water cutting temperature between them is 0.5 ° C. or less.

  A polarizer using this ethylene-modified polyvinyl alcohol film is excellent in polarization performance and durability, and has few color spots, and is particularly preferably used for a large-sized liquid crystal display device.

  As the ethylene-modified polyvinyl alcohol (ethylene-modified PVA) used in the present invention, an ethylene-vinyl ester polymer obtained by copolymerizing ethylene and a vinyl ester monomer is saponified to convert the vinyl ester unit into a vinyl alcohol unit. Can be used. Examples of the vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valelate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, and the like. Of these, vinyl acetate is preferably used.

  The ethylene unit content (ethylene copolymerization amount) in the ethylene-modified PVA is 1 to 4 mol%, preferably 1.5 to 3 mol%, more preferably 2 to 3 mol%. When the content of the ethylene unit is within this range, the polarization performance and durability performance are improved, and color spots are reduced, which is preferable.

  Furthermore, the following monomers can also be copolymerized with ethylene-modified polyvinyl alcohol. When copolymerizing with a vinyl ester monomer, the preferred range is 15 mol% or less, more preferably 5 mol% or less. Examples of monomers copolymerizable with such vinyl ester monomers include olefins having 3 to 30 carbon atoms such as propylene, 1-butene and isobutene; acrylic acid and salts thereof; methyl acrylate, ethyl acrylate, Acrylic acid esters such as n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, etc. Methacrylic acid and salts thereof; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-methacrylic acid 2- Ethylhexyl, dodecyl methacrylate, methacrylate Methacrylic acid esters such as octadecyl acid; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salt, acrylamidopropyldimethylamine and its salt, N- Acrylamide derivatives such as methylolacrylamide and its derivatives; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts, N-methylolmethacrylamide and its Methacrylamide derivatives such as derivatives; N-vinyl such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone Mido; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; acrylonitrile, methacrylonitrile, etc. Nitriles; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts or esters; itaconic acid and its salts or its Esters; Vinylsilyl compounds such as vinyltrimethoxysilane; N-vinylamines such as isopropenyl acetate, N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone Mention may be made of mids.

  The degree of polymerization of the ethylene-modified PVA constituting the polarizer is 2000 to 4000 from the viewpoint of polarization performance and durability, preferably 2200 to 3500, and particularly preferably 2500 to 3000. When the degree of polymerization is less than 2000, the polarizing performance and durability performance of the polarizer are lowered, which is not preferable. Moreover, it is preferable that the polymerization degree is 4000 or less because color spots of the polarizer hardly occur.

  The degree of polymerization of ethylene-modified PVA is the weight average degree of polymerization determined from GPC measurement. This weight average degree of polymerization is a value obtained by performing GPC measurement at 40 ° C. using hexafluoroisopropanol (HFIP) in which 20 mmol / liter sodium trifluoroacetate is added to the mobile phase using monodispersed PMMA as a standard. is there.

  The saponification degree of the ethylene-modified PVA constituting the polarizer is 99.0 to 99.99 mol%, more preferably 99.9 to 99.99 mol%, from the viewpoint of the polarization performance and durability of the polarizer. Particularly preferred is .95 to 99.99 mol%.

  Although it does not specifically limit as a method to manufacture an ethylene modified PVA film, The casting film forming method and the melt extrusion film forming method are preferable from a viewpoint of obtaining a favorable ethylene modified PVA film. The obtained ethylene-modified PVA film is subjected to drying and heat treatment as necessary.

  Examples of the solvent for dissolving the ethylene-modified PVA used in producing the ethylene-modified PVA film include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, and triethylene. Glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, glycerin, water and the like can be mentioned, and one or more of these can be used. Among these, dimethyl sulfoxide, water, or a mixed solvent of glycerin and water is preferably used.

  The ratio of ethylene-modified PVA in the ethylene-modified PVA solution or water-containing ethylene-modified PVA used in producing the ethylene-modified PVA film varies depending on the degree of polymerization of ethylene-modified PVA, but is preferably 20 to 70% by mass. 25-60 mass% is more preferable, 30-55 mass% is further more preferable, and 35-50 mass% is the most preferable. If the proportion of ethylene-modified PVA exceeds 70% by mass, the viscosity of ethylene-modified PVA containing ethylene-modified PVA solution or water becomes too high, making filtration and defoaming difficult when preparing a stock solution of the film. It is difficult to obtain a film without any defects. On the other hand, when the proportion of the ethylene-modified PVA is lower than 20% by mass, the viscosity of the ethylene-modified PVA solution or the ethylene-modified PVA containing water becomes too low, and it becomes difficult to produce a PVA film having a target thickness. Further, this ethylene-modified PVA solution or ethylene-modified PVA containing water may contain a plasticizer, a surfactant, a dichroic dye, or the like as necessary.

  When producing an ethylene-modified PVA film, it is preferable to add a polyhydric alcohol as a plasticizer. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, etc., and one or more of these are used. can do. Among these, diglycerin, ethylene glycol, and glycerin are preferably used because of the effect of improving stretchability.

  As addition amount of a polyhydric alcohol, 1-30 mass parts is preferable with respect to 100 mass parts of ethylene modified PVA, 3-25 mass parts is more preferable, 5-20 mass parts is the most preferable. When the amount is less than 1 part by mass, the dyeability and stretchability may be lowered. When the amount is more than 30 parts by mass, the ethylene-modified PVA film becomes too flexible and the handleability may be lowered.

  The ethylene-modified PVA film used for the production of the polarizer preferably has a thickness of 10 to 120 μm, and more preferably 20 to 100 μm. If the thickness is less than 10 μm, the film strength is too low to perform uniform stretching, and color spots of the polarizer are likely to occur. When the thickness exceeds 100 μm, when a polarizer is produced by uniaxially stretching an ethylene-modified PVA film, a thickness change easily occurs due to neck-in at the end, and color spots of the polarizer are easily emphasized, which is not preferable.

  In order to produce a polarizer from the ethylene-modified PVA film of the present invention, for example, the ethylene-modified PVA film may be dyed, uniaxially stretched, fixed, and dried, and further heat treated as necessary. There is no restriction | limiting in particular in the order of operation of a uniaxial stretching and a fixing process. Moreover, you may perform uniaxial stretching twice or more.

  Dyeing can be performed before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. As a dye used for dyeing, iodine-potassium iodide, a dichroic dye, or the like can be used in one kind or a mixture of two or more kinds. Ordinary dyeing is generally performed by immersing the PVA film in a solution containing the above-mentioned dye, but the processing conditions and processing method are particularly limited, such as mixing with the PVA film to form a film. is not.

  For uniaxial stretching, wet stretching or dry heat stretching can be used, using warm water such as an aqueous boric acid solution (in a solution containing the dye or in a fixing treatment bath described later) or an ethylene-modified PVA film after water absorption. Can be done in air. The stretching temperature is not particularly limited, and is preferably 30 to 90 ° C. when the ethylene-modified PVA film is stretched (wet stretching) in warm water, and 50 to 180 ° C. is preferable when it is dry-heat stretched.

Further, the stretching ratio of uniaxial stretching (the total stretching ratio in the case of multi-stage uniaxial stretching) is preferably 4 times or more, and most preferably 5 times or more from the viewpoint of the polarization performance of the polarizer. The upper limit of the stretching ratio is not particularly limited, but it is preferably 8 times or less because uniform stretching is easily obtained. 2-50 micrometers is preferable and, as for the thickness of the film (polarizer) after extending | stretching, 10-20 micrometers is more preferable.
Fixing treatment is often performed for the purpose of strengthening the adsorption of the dye to the ethylene-modified PVA film.

Usually, boric acid and / or boron compounds are added to the treatment bath used for the fixing treatment. Moreover, you may add an iodine compound in a processing bath as needed.
It is preferable to perform the drying process of the obtained polarizer at 30-150 degreeC, and it is more preferable to carry out at 50-150 degreeC.

  Since the polarizing film is stretched in a uniaxial direction (usually the longitudinal direction), when the polarizing plate is placed in a high-temperature and high-humidity environment, the stretching direction (usually the longitudinal direction) shrinks, and the direction perpendicular to the stretching (usually the width direction) ) Will grow. As the thickness of the polarizing plate protective film becomes thinner, the expansion / contraction ratio of the polarizing plate increases, and in particular, the amount of contraction in the stretching direction of the polarizing film increases. Normally, the stretching direction of the polarizing film is bonded to the casting direction (MD direction) of the polarizing plate protective film. Therefore, when making the polarizing plate protective film thin, it is particularly important to suppress the stretching rate in the casting direction. It is. Since the retardation film of the present invention is excellent in dimensional stability, it is suitably used as such a polarizing plate protective film.

  That is, even in the durability test under the conditions of 60 ° C. and 90% RH, the wavy unevenness does not increase, and good visibility can be provided without changing the viewing angle characteristics after the durability test.

  The polarizing plate can be constituted by further bonding a protective film on one surface of the polarizing plate and a separate film on the other surface. The protective film and the separate film are used for the purpose of protecting the polarizing plate at the time of shipping the polarizing plate and at the time of product inspection. In this case, the protect film is bonded for the purpose of protecting the surface of the polarizing plate, and is used on the side opposite to the surface where the polarizing plate is bonded to the liquid crystal plate. Moreover, a separate film is used in order to cover the contact bonding layer bonded to a liquid crystal board, and is used for the surface side which bonds a polarizing plate to a liquid crystal cell.

  By using this polarizing plate, a liquid crystal display device with high display performance can be provided. In particular, in a liquid crystal display device using a direct type backlight, it is possible to obtain a liquid crystal display device in which environmental fluctuation is small and light leakage at the periphery of the screen is reduced.

(Display device)
By incorporating the polarizing plate of the present invention into a display device, the display device of the present invention having various visibility can be manufactured. The retardation plate of the present invention can be used for liquid crystal display devices of various drive systems such as STN, TN, OCB, HAN, VA (MVA, PVA), and IPS, but in particular, VA (MVA, PVA) type liquid crystal display devices. Can be preferably applied.

  In particular, even in the case of a large-screen liquid crystal display device having a 30-inch screen or more, it is possible to obtain a liquid crystal display device in which environmental fluctuation is small and light leakage due to thermal distortion at the periphery of the screen is reduced.

  In addition, the backlight used in the liquid crystal display device using the polarizing plate of the present invention may be a sidelight type, a direct type, or a combination of these. Preferably there is.

  A particularly preferred direct type backlight is an LED backlight for a color liquid crystal display device having a red (R) LED, a green (G) LED, and a blue (B) LED, for example, the peak of the red (R) LED. Preferably, the wavelength is 610 nm or more, the peak wavelength of the green (G) LED is in the range of 530 ± 10 nm, and the peak wavelength of the blue (B) LED is 480 nm or less.

  Examples of types of green (G) LEDs having a peak wavelength within the above range include DG1112H (manufactured by Stanley Electric Co., Ltd.), UG1112H (manufactured by Stanley Electric Co., Ltd.), and E1L51-3G (manufactured by Toyoda Gosei Co., Ltd.). E1L49-3G (manufactured by Toyoda Gosei Co., Ltd.), NSPG500S (manufactured by Nichia Chemical Co., Ltd.), and the like. As a kind of LED used as a red (R) LED, for example, FR1112H (manufactured by Stanley Electric Co., Ltd.), FR5366X (manufactured by Stanley Electric Co., Ltd.), NSTM515AS (R) (manufactured by Nichia Corporation), Examples thereof include GL3ZR2D1COS (manufactured by Sharp Corporation), GM1JJ35200AE (manufactured by Sharp Corporation), and the like. As types of LEDs used as blue (B) LEDs, DB1112H (manufactured by Stanley Electric Co., Ltd.), DB5306X (manufactured by Stanley Electric Co., Ltd.), E1L51-3B (manufactured by Toyoda Gosei Co., Ltd.), E1L4E-SB1A (manufactured by Stanley Electric Co., Ltd.) Toyoda Gosei Co., Ltd.), NSPB630S (Nichia Chemical Co., Ltd.), NSPB310A (Nichia Chemical Co., Ltd.), and the like.

  The above-described three color LEDs can be combined to form a backlight, and a white LED can also be used.

  In addition, as a direct type backlight (or direct type), a direct type backlight described in JP-A No. 2001-281656, a direct type backlight using a point light source such as an LED described in JP-A No. 2001-305535, Examples include a direct backlight described in JP-A-2002-311412, but are not limited thereto.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

<Preparation of dope solution>
The following materials were sequentially put into a sealed container, the temperature in the container was raised from 20 ° C. to 80 ° C., and the mixture was stirred for 3 hours while maintaining the temperature at 80 ° C. to completely dissolve the cellulose ester. . Then, stirring was stopped and the liquid temperature was lowered to 43 ° C. The dope was filtered using a filter paper (Azumi filter paper No. 244, manufactured by Azumi Filter Paper Co., Ltd.) to obtain a dope.

(Preparation of dope solution A)
Methylene chloride 300 parts by weight Ethanol 40 parts by weight Cellulose ester (cellulose acetate propionate; acetyl group substitution degree 1.6, propionyl group substitution degree 1.0) 100 parts by weight Compound (1) (Polyester compound (elastic modulus increasing agent below) 1)) 5 parts by mass Compound (2) (aromatic polyvalent carboxylic acid ester compound (tributyl trimellitic acid)) 5 parts by mass Tinuvin 109 (manufactured by Ciba Specialty Chemicals) 1.2 parts by mass Tinuvin 171 (Ciba Specialty) Chemicals Co., Ltd.) 0.5 parts by mass Silicon oxide fine particles (Aerosil R972V (Nippon Aerosil Co., Ltd.))
0.1 part by mass The dope solution A prepared as described above is cast on a support at 30 ° C. made of a stainless steel endless belt through a casting die kept at 30 ° C., and a web is formed. After drying on the body and drying on the support until the residual solvent amount of the web reached 80% by mass, the web was peeled from the support with a peeling roll.

  Next, the web is dried with a drying air at 70 ° C. in a transport drying process using a plurality of rolls arranged on the top and bottom, and then the web and the both ends of the web are gripped with a tenter, and then a temperature and a draw ratio so that a predetermined phase difference is obtained. And stretched 1.3 times in the width direction at 130 ° C.

  After stretching with a tenter, the web was dried with a drying air at 105 ° C. in a conveying and drying process using a plurality of rolls arranged vertically, and dried to a residual solvent amount of 0.3% by mass to obtain a film. A retardation film 101 having an in-plane retardation Ro = 50 nm, a thickness direction retardation Rt = 140 nm, and a film thickness of 40 μm was measured under the conditions of 23 ° C. and 55% RH.

  Table 1 shows the compound (1) (polyester compound), compound (2) (aromatic polyvalent carboxylic acid ester compound) to be used, the types and addition amounts of other plasticizers, the total acyl group substitution degree of the cellulose ester, and the propionyl substitution degree. The film 102 to 164 with Ro = 50 nm, Rt = 140 nm, and 40 μm film thickness (corresponding to the polarizing plates 102 to 164 in Tables 1 and 2) in the same manner as the retardation film 101. To display). In the film 142, when the total acyl group substitution degree was 3.0, the above retardation could not be expressed.

Abbreviations of the compound (1) and other compounds used as plasticizers are as follows. The values in parentheses represent the rate of increase in elastic modulus (%) when 10% by mass is added to the polyester.
Elastic modulus increasing agent 1: Sealing polyester ends of phthalic acid and 1,2-propylene glycol with benzoic acid Molecular weight 800 (11%)
Elastic modulus increase 2: Polyester end of terephthalic acid and ethylene glycol is sealed with benzoic acid. Molecular weight 700 (9%)
Elasticity increasing agent 3: Sealing polyester ends of phthalic acid and 1,2-propylene glycol with benzoic acid Molecular weight 400 (6%)
Elasticity increasing agent 4: Sealing polyester ends of phthalic acid and 1,2-propylene glycol with benzoic acid Molecular weight 500 (9%)
Elastic modulus increasing agent 5: Polyester ends of phthalic acid and 1,2-propylene glycol are sealed with benzoic acid. Molecular weight 1500 (11%)
Elastic modulus increasing agent 6: Polyester ends of phthalic acid and 1,2-propylene glycol are sealed with benzoic acid. Molecular weight 2000 (9%)
Polyester 1: Adipic acid and 1,2-propylene glycol polyester ends sealed with propionic acid Molecular weight 800 (2%)
Polyester 2: Polyester ends of adipic acid and ethylene glycol are sealed with acetic acid. Molecular weight 800 (23%)
Polyhydric alcohol ester 1: Trimethylolpropane tribenzoate Polyhydric alcohol ester 2: Pentaerythritol tetrabenzoate The elastic modulus of the obtained retardation film was measured.

<Elastic modulus>
The sample was conditioned for 24 hours in an environment of 23 ° C. and 55% RH, and the elastic modulus was measured according to the method described in JIS K 7127. Tensilon RTC-1225A manufactured by Orientec Co., Ltd. was used as the tensile tester, the shape of the test piece was a No. 1 type test piece, and the test speed was 100 mm / min. The elastic modulus was calculated with an elastic modulus analysis start point of 2 (MPa) and an elastic modulus analysis end point of 60 (MPa).

<Production of polarizing plate>
The obtained retardation film was used as a polarizing plate protective film on one side, and KC4UY (Konica Minolta Opto's cellulose triacetate film) was used as a polarizing plate on the opposite side to prepare a 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 polarizing film.

Production of Polarizer 100 parts by mass of polyvinyl alcohol having a saponification degree of 99.92 mol% and a polymerization degree of 3000 were impregnated with 10 parts by mass of glycerin and 200 parts by mass of water, melt-kneaded, defoamed, and then from the T-die. It was melt-extruded into a metal roll and dried to obtain a polyvinyl alcohol film having a thickness of 90 μm.

  The thus obtained polyvinyl alcohol film was continuously treated in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying, and heat treatment to prepare a polarizer. That is, the polyvinyl alcohol film is pre-swelled by immersing it in water at 30 ° C. for 60 seconds, and 2% in a 35 ° C. aqueous solution having a boric acid concentration of 40 g / liter, an iodine concentration of 0.4 g / liter, and a potassium iodide concentration of 60 g / liter. Soaked for a minute. Subsequently, it was uniaxially stretched 6 times in an aqueous solution at 55 ° C. with a boric acid concentration of 4%, and in an aqueous solution at 30 ° C. with a potassium iodide concentration of 60 g / liter, a boric acid concentration of 40 g / liter, and a zinc chloride concentration of 10 g / liter. For 5 minutes, and fixed. Thereafter, the polyvinyl alcohol film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes to prepare a polarizer 1.

  A polarizer 2 was prepared in the same manner as described above except that ethylene-modified polyvinyl alcohol having an ethylene unit content of 2.1 mol%, a saponification degree of 99.92 mol%, and a polymerization degree of 3000 was used instead of polyvinyl alcohol. did.

  The transmittance of the obtained polarizer 1 and polarizer 2 was 43%, and the degree of polarization was 99.9%.

  Next, according to the following steps 1 to 4, the long polarizer 1 and the respective retardation films 101 to 164 and KC4UY (Konica Minolta Opto's cellulose triacetate film) are continuously bonded to the opposite surface side. Polarizing plates 101 to 164 were prepared, respectively.

  Step 1: Soaked in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried to obtain a saponified cellulose ester film on the side to be bonded to the polarizer.

  Step 2: The polarizing film was coated with a polyvinyl alcohol adhesive having a solid content of 2% by mass and placed on the cellulose ester film treated in Step 1.

Step 3: pressure 20-30 N / cm ² the laminated film in the step 2, the conveyance speed was pasted at approximately 2m / min.

  Process 4: The sample bonded together in 80 degreeC drying machine was dried for 5 minutes, and the polarizing plate was produced.

  Further, a polarizing plate 165 was prepared in the same manner as described above except that the polarizer 2 was used instead of the polarizer 1 (101 is used for the retardation film).

<Change in polarization degree>
The transmittance of the produced polarizing plate was measured using a haze meter (NDH2000, manufactured by Nippon Denshoku Co., Ltd.). At this time, in order to cancel the influence of the polarization of light at the time of measurement, the polarizing plate is measured twice with the reference and tilted by 90 °, and the average value is calculated. The initial transmittance is usually 50%. The polarizing plate was subjected to a durability test for 2000 hours under the conditions of 60 ° C. and 90% RH, and the transmittance after the durability test was measured in the same manner as described above. The change in transmittance before and after the durability test was calculated according to the following formula to determine the change in polarization degree, which was used as an index for durability of polarization degree.

Polarization degree change = (transmittance after durability test) − (transmittance before durability test)
The change in the degree of polarization is preferably as small as possible, but is preferably 10% or less, but if it is 20% or less, there is no practical problem.

<Production of liquid crystal display device>
A liquid crystal panel was produced using the produced polarizing plate as follows, and the characteristics as a liquid crystal display device were evaluated.

  The polarizing plates on both sides of the 15-inch display VL-150SD manufactured by Fujitsu were previously peeled off, and the above-prepared polarizing plates 101 to 165 were each pasted on the glass surface of a liquid crystal cell (VA type). 101-165 were made.

  At that time, the direction of bonding of the polarizing plate is such that the surface on which the retardation film of the present invention is bonded is the liquid crystal cell side, and the same direction as the polarizing plate previously bonded. The liquid crystal display devices 101 to 165 were each manufactured so that the absorption axis of the liquid crystal display devices faced.

<Corner spots>
The manufactured liquid crystal display device was subjected to a 1000 hour durability test in a constant temperature bath of 60 ° C. (no humidity control) or 60 ° C. and 90% RH, and then the backlight was lit continuously for 5 hours in an environment of 23 ° C. and 55% RH. The whole black display state was visually observed in a dark room to observe corner spots. Corner spots are more likely to occur at 60 ° C. and 90% RH than at 60 ° C. (no humidity control). The results were ranked according to the following criteria and used as indicators of light leakage prevention. Although it is preferable that it is above the level, there is no practical problem if it is above the Δ level. A: Corner spots are not observed even when the durability test is performed at 60 ° C. and 90% RH.
○: Corner spots are not observed under the condition of 60 ° C. (no humidity control), but slight occurrence is observed under the condition of 60 ° C. and 90% RH.
(Triangle | delta): A corner spot is slightly observed on the conditions of 60 degreeC (no humidity control).
X: Corner spots are clearly observed under conditions of 60 ° C. (no humidity control).

  The results are shown in Tables 1 and 2. From Tables 1 and 2, it can be seen that the retardation plate (retardation film) of the present invention is excellent in polarization degree durability and excellent in light leakage prevention properties.

It is a figure explaining the extending | stretching angle in an extending | stretching process at the time of manufacturing the phase difference plate of this invention. It is the schematic which shows an example of an extending process at the time of manufacturing the phase difference plate of this invention.

Claims (10)

A phase difference plate comprising cellulose ester as a main component, wherein the cellulose ester has a total acyl group substitution degree of 2.4 to 2.8, and the phase difference plate comprises the following compounds (1) and (2): When the total content is 5 to 25% by mass, the content of the following (1) is a (% by mass) and the content of the following (2) is b (% by mass), a = b / 4 to 4b A retardation plate characterized by being.
[(1) A polyester compound in which the elastic modulus of the cellulose ester is increased by 5 to 20% when 10% by mass is added to the cellulose ester.
(2) A trivalent or higher aromatic polyvalent carboxylic acid ester compound in which the elastic modulus of the cellulose ester is reduced by 5 to 20% when 10% by mass is added to the cellulose ester. ] The retardation plate according to claim 1, wherein the polyester compound has a plurality of ester bonds obtained from an aromatic dicarboxylic acid and alkylene glycol or oxyalkylene glycol. The retardation plate according to claim 1, wherein the trivalent or higher aromatic polyvalent carboxylic acid ester compound is trimesic acid ester, trimellitic acid ester or pyromellitic acid ester. The retardation film according to claim 1, wherein the retardation film contains 2 to 10% by mass of a polyhydric alcohol ester compound. The retardation plate according to any one of claims 1 to 4, wherein the polyhydric alcohol ester compound is an ester compound obtained from trimethylolpropane or pentaerythritol and an aromatic carboxylic acid. The cellulose ester is cellulose acetate propionate or cellulose acetate butyrate, the total acyl group substitution degree is 2.4 to 2.8, and the substitution degree of propionyl group or butyryl group is 0.5 to 1.5. The retardation film according to claim 1, wherein the retardation film is a retardation plate. The thickness of the retardation plate is 30 to 60 μm, and the retardation (Ro) in the in-plane direction defined by the following formula (I) is 30 to 100 nm, in the thickness direction defined by the following formula (II). Retardation (Rt) is 100-300 nm, The phase difference plate of any one of Claims 1-6 characterized by the above-mentioned.
(I) Ro = (nx−ny) × d
(II) Rt = {(nx + ny) / 2−nz} × d
[Where nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, nz is the refractive index in the thickness direction of the film, and d is It is the thickness of the film] A polarizing plate using the retardation plate according to claim 1. The polarizing plate according to claim 8, wherein a polyethylene-polyvinyl alcohol copolymer film having a thickness of 10 to 20 μm is used as the polarizer. A liquid crystal display device using the polarizing plate according to claim 8.

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