WO2012014571A1

WO2012014571A1 - Cellulose acetate film, method for producing cellulose acetate film, polarizing plate, liquid crystal display device, and method for producing liquid crystal display device

Info

Publication number: WO2012014571A1
Application number: PCT/JP2011/063033
Authority: WO
Inventors: 佐藤　英幸
Original assignee: コニカミノルタオプト株式会社
Priority date: 2010-07-30
Filing date: 2011-06-07
Publication date: 2012-02-02
Also published as: JPWO2012014571A1; JP5821849B2

Abstract

The purpose of the present invention is to provide a cellulose acetate film which has a high retardation value despite being thin, does not exhibit an increase in internal haze and has a little unevenness in phase difference even if being stretched at a high stretching ratio, and does not exhibit an increase in haze even in a hygrothermal environment; a method for producing the cellulose acetate film; a polarizing plate using the same; and a liquid crystal display device using the same. This cellulose acetate film is characterized by comprising at least a polyester compound represented by general formula (I) and having a hydroxy group at both ends and cellulose acetate having a degree of acetyl substitution of 2.0 to 2.6. (In the formula, B represents linear or branched alkylene having 2-6, inclusive, carbon atoms or a cycloalkylene group; A represents an aromatic ring having 6-14, inclusive, carbon atoms; and n represents a natural number of 1 or more.)

Description

Cellulose acetate film, method for producing cellulose acetate film, polarizing plate, liquid crystal display device and method for producing the same

The present invention relates to a cellulose acetate film, a method for producing a cellulose acetate film, a polarizing plate, a liquid crystal display device, and a method for producing the same.

Among cellulose esters, cellulose acetate is known to be applicable to optical films having a wide range of retardation by changing the degree of acetyl group substitution. Generally, triacetyl cellulose having a high degree of acetyl group substitution is suitably used for a protective film for polarizing plates because of its low retardation. However, when used as an optical compensation film in various liquid crystal modes such as VA and TN, the expression of retardation is insufficient, so that it is necessary to add a retardation increasing agent. (For example, refer to Patent Document 1.)
However, there have been problems such as bleeding out of the retardation increasing agent from the film, and dissolution of the retardation increasing agent into the saponification solution during the saponification step during the production of the polarizing plate.

On the other hand, since diacetyl cellulose having a low degree of acetyl group substitution has high retardation, it is expected to be used as an optical compensation film without adding a retardation increasing agent.

However, with the recent diversification of liquid crystal cells, the retardation value required for optical compensation films tends to be higher, and in order to cope with the thinning of liquid crystal panels, the thickness of optical compensation films has been reduced. The need is also increasing. Therefore, when trying to achieve a high retardation with a thin film, it is necessary to perform a drawing process at a higher magnification than before, and even if diacetyl cellulose is used, an increase in haze under wet heat conditions or a letter in the film is required. It has been found that problems such as phase difference unevenness due to localization of the retardation increasing agent occur.

These problems have been extensively studied by adding physical property modifiers such as polyester compounds to cellulose acetate. (See, for example, Patent Documents 2 to 4.) These have lower scattering properties at higher temperatures than conventionally used phosphate ester plasticizers and phthalate ester plasticizers, and film property modifiers. As a feature, it is also excellent.

However, even when these compounds are used together with diacetylcellulose having a low degree of acetyl group substitution, if the film is stretched at a severe magnification of 1.3 times or more for providing a thin film and high retardation, the internal haze increases and the phase difference Problems such as the occurrence of unevenness and an increase in haze in a humid heat environment have occurred, and an immediate solution has been desired.

European Patent No. 91656 JP 2009-235377 A JP 2009-98674 A JP 2010-66348 A

The present inventor has conducted extensive studies on the above-mentioned problems. As a result, the above problems can be solved by using an aromatic dicarboxylic acid, a polyester compound having hydroxyl groups at both ends synthesized from an alkylene diol, and cellulose acetate having a low degree of acetyl group substitution. The inventors have found that the problem can be solved and have reached the present invention.

That is, an object of the present invention is a cellulose acetate film that has a high retardation even though it is a thin film, does not increase internal haze even when stretched at a high magnification, has small phase difference unevenness, and does not increase haze even in a humid heat environment, It is in providing the manufacturing method of an acetate film, a polarizing plate using the same, and a liquid crystal display device.

In addition, because it is a cellulose acetate film containing a polyester compound that is highly compatible with cellulose acetate with a low degree of acetyl group substitution, it is excellent in curling because it has good flatness even if it is stretched at a high magnification. It is an object of the present invention to provide a cellulose acetate film and a polarizing plate which are less likely to wrinkle and are suitable for the “roll-to-panel manufacturing method” in liquid crystal panel production.

The above object of the present invention is achieved by the following configuration.

1. A cellulose acetate film comprising at least a polyester compound represented by the following general formula (I) having a hydroxyl group at both ends and a cellulose acetate having an acetyl group substitution degree of 2.0 to 2.6.

(In the formula, B represents a linear or branched alkylene or cycloalkylene group having 2 to 6 carbon atoms, A represents an aromatic ring having 6 to 14 carbon atoms, and n represents a natural number of 1 or more. To express.)
2. 2. The cellulose acetate film as described in 1 above, wherein in the polyester compound represented by the general formula (I), A is a naphthalene ring or biphenyl ring which may have a substituent. (The substituent represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group, or an alkoxyl group.)
3. 3. The cellulose acetate film as described in 1 or 2 above, wherein the polyester compound has a hydroxyl value of 170 mgKOH / g to 400 mgKOH / g.

4. 4. The cellulose acetate film as described in any one of 1 to 3 above, wherein the polyester compound is contained in an amount of 1% by mass to less than 5% by mass with respect to the cellulose acetate.

5. 5. The cellulose acetate film according to any one of 1 to 4, wherein the cellulose acetate film has a retardation value Ro represented by the following formula of 20 to 100 nm and Rth of 70 to 300 nm.

Formula (i) Ro = (nx−ny) × d
Formula (ii) Rth = {(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).)
6). 6. The cellulose acetate film as described in any one of 1 to 5 above, which contains 5% by mass or more of a sugar ester compound represented by the following general formula (II) as a hydrolysis inhibitor.

(In the formula, G represents a monosaccharide or disaccharide residue, X ¹ represents —O—, R ¹ represents —CO—R ² , and R ² represents an aliphatic or aromatic group. Represents the total number of hydroxyl groups directly bonded to monosaccharide or disaccharide residues, n represents the total number of OR ¹ groups directly bonded to monosaccharide or disaccharide residues, and 3 ≦ m + n ≦ 8 And n ≠ 0.)
7. 7. The method for producing a cellulose acetate film according to any one of 1 to 6, wherein at least both of the polyester compound represented by the following general formula (I) are hydroxyl groups and the acetyl group substitution degree is 2.0 to A dope containing cellulose acetate of 2.6 is cast on a support and peeled off, and then stretched at a magnification of 1.3 to 1.7 times at least in the width direction while drying. A method for producing a cellulose acetate film.

(In the formula, B represents a linear or branched alkylene or cycloalkylene group having 2 to 6 carbon atoms, A represents an aromatic ring having 6 to 14 carbon atoms, and n represents a natural number of 1 or more. To express.)
8). A polarizing plate comprising the cellulose acetate film according to any one of 1 to 6 bonded to at least one surface of a polarizer.

9. 9. A liquid crystal display device, wherein the cellulose acetate film side according to any one of 1 to 6 of the polarizing plate according to 8 is bonded to at least one surface of a liquid crystal cell.

10. In the manufacturing method of the liquid crystal display device which bonds the polarizing plate of said 8 to a liquid crystal panel, after bonding this polarizing plate to a liquid crystal panel by the roll to panel manufacturing method, this liquid crystal panel is cut by laser to desired size A method for manufacturing a liquid crystal display device.

According to the present invention, a cellulose acetate film that has a high retardation value while being a thin film, does not increase internal haze even when stretched at a high magnification, has small phase difference unevenness, and does not increase haze even in a humid heat environment, the cellulose A method for producing an acetate film, a polarizing plate using the same, and a liquid crystal display device can be provided.

In addition, because it is a cellulose acetate film that contains a polyester compound that is highly compatible with cellulose acetate with a low acetyl group substitution degree, it has excellent flatness even when stretched at a high magnification. It is possible to provide a cellulose acetate film and a polarizing plate which are less likely to wrinkle when combined and are suitable for the “roll to panel manufacturing method” in liquid crystal panel production.

It is a conceptual diagram which shows a roll to panel manufacturing method. It is a schematic diagram which shows the state which dripped glycerin on the slide glass. It is a schematic diagram which shows the state which put the sample film on glycerol. It is a schematic diagram which shows the state which dripped glycerin on the sample film. It is a schematic diagram which shows the state which put the cover glass on glycerol.

Hereinafter, modes for carrying out the present invention will be described in detail, but the present invention is not limited to these.

The cellulose acetate film of the present invention comprises at least a polyester compound represented by the above general formula (I) having a hydroxyl group at both ends and a cellulose acetate having an acetyl group substitution degree of 2.0 to 2.6, This structure provides a cellulose acetate film having a high retardation value while having a thin film thickness and having an optical compensation function without haze increase or contrast decrease.

The acetyl group substitution degree of 2.0 to 2.6 means that the acetyl group substitution degree is 2.0 or more and 2.6 or less.

Patent Documents 2 to 4 describe polyesters having terminal hydroxyl groups, but all of them are applied to triacetyl cellulose having a high degree of acetyl group substitution, or intended for low retardation. Thus, it does not suggest the configuration and purpose of the present invention.

Hereinafter, the present invention will be described in detail.

<Cellulose acetate>
The cellulose acetate film of the present invention has high retardation and can be thinned even when it is a retardation film having a high retardation, and the stretch ratio is kept low even when a high retardation is exhibited. From the viewpoint of avoiding failure such as breakage, a film made of cellulose acetate having an acetyl group substitution degree of 2.0 to 2.6 is used.

The method for measuring the degree of acetyl group substitution can be carried out according to ASTM D-817-91, and the preferred degree of acetyl group substitution is 2.2 to 2.45.

When the degree of acetyl group substitution of cellulose acetate is less than 2.0, film surface quality may be deteriorated due to an increase in dope viscosity, and haze may be increased due to an increase in stretching tension. Moreover, when the acetyl group substitution degree is larger than 2.6, it is difficult to obtain a necessary phase difference.

The number average molecular weight (Mn) of the cellulose acetate is preferably strong in the mechanical strength of the film from which the range of 30000-300000 is obtained. Further, those having 50000-200000 are preferably used.

The ratio Mw / Mn of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of cellulose acylate and cellulose acetate is preferably 1.4 to 3.0.

The number average molecular weight (Mn) and weight average molecular weight (Mw) of cellulose acetate were measured using gel permeation chromatography (GPC).

The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 2.6 ° 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 = 1000,000 to 500 13 calibration curves were used. Thirteen samples are used at approximately equal intervals.

The cellulose acetate used in the present invention can be synthesized by a known method.

There are no particular limitations on the cellulose used as the raw material for cellulose acetate, but examples include cotton linters, wood pulp (derived from conifers and hardwoods), and kenaf. Moreover, the cellulose acetate obtained from them can be mixed and used in arbitrary ratios, respectively.

The cellulose acetate according to the present invention can be produced by a known method. Specifically, it can be synthesized with reference to the method described in JP-A-10-45804.

Commercially available products include Daicel L20, L30, L40, L50, and Eastman Chemical's Ca398-3, Ca398-6, Ca398-10, Ca398-30, and Ca394-60S.

<Compound represented by formula (I)>
The polyester compound of the present invention is represented by the following general formula (I).

(In the formula, B represents a linear or branched alkylene or cycloalkylene group having 2 to 6 carbon atoms, A represents an aromatic ring having 6 to 14 carbon atoms, and n represents a natural number of 1 or more. Show.)
The compound represented by the above formula is obtained from a dicarboxylic acid having an aromatic ring (also referred to as aromatic dicarboxylic acid) and a linear or branched alkylene or cycloalkylene diol having 2 to 6 carbon atoms, and both ends are It is characterized by not being sealed with monocarboxylic acid.

Examples of the aromatic dicarboxylic acid having 6 to 16 carbon atoms include phthalic acid, isophthalic acid, terephthalic acid, 1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,3 -Naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,8-naphthalenedicarboxylic acid, 2,2'-biphenyldicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and the like. Among these, 2,6-naphthalenedicarboxylic acid and 4,4'-biphenyldicarboxylic acid are preferable.

Examples of the linear or branched alkylene or cycloalkylene diol having 2 to 6 carbon atoms include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, and 1,3-butane. Diol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexane Examples thereof include diol and 1,4-cyclohexanedimethanol. Of these, ethanediol, 1,2-propanediol, 1,3-propanediol, and 1,3-butanediol are preferable.

Among them, it is preferable for obtaining the effect of the present invention that A is a naphthalene ring or a biphenyl ring which may have a substituent. Here, the substituent is an alkyl group having 1 to 6 carbon atoms, an alkenyl group, or an alkoxyl group.

The hydroxyl value (OH value) of the polyester compound of the present invention is preferably 100 mgKOH / g or more and 500 mgKOH / g or less, more preferably 170 mgKOH / g to 400 mgKOH / g. If the hydroxyl value is larger or smaller than this range, the compatibility with cellulose acetate having a low acetyl substitution degree is lowered.

If it is larger than this range, the hydrophobicity of the polyester compound becomes larger. If it is smaller than this range, the intermolecular interaction (hydrogen bonding, etc.) between the polyester compounds becomes stronger, so that precipitation in the film proceeds. it is conceivable that.

In addition, for measurement of the hydroxyl value, the acetic anhydride method described in Japanese Industrial Standard JIS K1557-1: 2007 can be applied.

The number average molecular weight (Mn) of the polyester compound of the present invention can be calculated from the following formula.

Mn = (number of hydroxyl groups in the molecule) × 56110 / (hydroxyl value)
= 2 × 56110 / (Hydroxyl value)
The polyester compound of the present invention can be obtained by any of the following methods: a hot melt condensation method using a polyesterification reaction or a transesterification reaction between the dicarboxylic acid and a diol, or an interfacial condensation method between an acid chloride of these acids and a glycol. Can also be easily synthesized.

Examples of the polyester compound in the present invention are shown below.

The compound represented by the general formula (I) is preferably added in an amount of 1% by mass to less than 5% by mass with respect to cellulose acetate.

<Compound represented by formula (II)>
The cellulose acetate film of the present invention preferably uses a compound represented by the following general formula (II) as a hydrolysis inhibitor.

(In the formula, G represents a monosaccharide or disaccharide residue, X ¹ represents —O—, R ¹ represents —CO—R ² , and R ² represents an aliphatic or aromatic group. Represents the total number of hydroxyl groups directly bonded to monosaccharide or disaccharide residues, n represents the total number of OR ¹ groups directly bonded to monosaccharide or disaccharide residues, and 3 ≦ m + n ≦ 8 And n ≠ 0.)
The compound having the structure represented by the general formula (II) is difficult to synthesize a single kind of compound in which the number of hydroxyl groups (m) and the number of OR ¹ groups (n) are fixed. It is known that several types of components having different m and n are mixed. Therefore, the performance as a mixture in which the number of hydroxyl groups (m) and the number of OR ¹ groups (n) are changed is important. In the case of the cellulose acetate film of the present invention, the haze characteristics are represented by the general formula (II). In addition, a compound having a structure in which the mixing ratio of the component m = 0 and the component m> 0 is 45:55 to 0: 100 is preferable. More preferably in terms of performance and cost, the mixing ratio of the component m = 0 and the component m> 0 is in the range of 10:90 to 0.1: 99.9.

The above m = 0 component and m> 0 component can be measured by high performance liquid chromatography by a conventional method.

In the above general formula (II), G represents a monosaccharide or disaccharide residue. Specific examples of monosaccharides include allose, altrose, glucose, mannose, gulose, idose, galactose, talose, ribose, arabinose, xylose, lyxose, and the like.

Hereinafter, structural examples of the compound having a monosaccharide residue represented by the general formula (II) are shown, but the present invention is not limited to these specific examples.

Specific examples of the disaccharide include trehalose, sucrose, maltose, cellobiose, gentiobiose, lactose, and isotrehalose.

Hereinafter, structural examples of the compound having a disaccharide residue represented by the general formula (II) are shown, but the present invention is not limited to these specific examples.

In the structure represented by the general formula (II), X ¹ represents a single bond, —O—, R ¹ represents —CO—R ² , and R ² represents an aliphatic or aromatic group. The aliphatic group and the aromatic group may each independently have a substituent.

m represents the number of hydroxyl groups, and n represents the number of OR ¹ groups. It is necessary that 3 ≦ m + n ≦ 8, and preferably 4 ≦ m + n ≦ 8. Further, n ≠ 0. When n is 2 or more, —X ¹ —R ¹ may be the same as or different from each other.

The aliphatic group will be described below. The aliphatic group may be linear, branched or cyclic, and preferably has 1 to 25 carbon atoms, more preferably 1 to 20 carbon atoms, and more preferably 2 to 15 carbon atoms. Particularly preferred. Specific examples of the aliphatic group include, for example, methyl, ethyl, n-propyl, iso-propyl, cyclopropyl, n-butyl, iso-butyl, tert-butyl, amyl, iso-amyl, tert-amyl, n- Examples include hexyl, cyclohexyl, n-heptyl, n-octyl, bicyclooctyl, adamantyl, n-decyl, tert-octyl, dodecyl, hexadecyl, octadecyl, didecyl and the like.

The above aromatic group will be described below. The aromatic group may be an aromatic hydrocarbon group or an aromatic heterocyclic group, and more preferably an aromatic hydrocarbon group. As the aromatic hydrocarbon group, those having 6 to 24 carbon atoms are preferable, and those having 6 to 12 carbon atoms are more preferable. Specific examples of the aromatic hydrocarbon group include benzene, naphthalene, anthracene, biphenyl, terphenyl and the like. As the aromatic hydrocarbon group, benzene, naphthalene, and biphenyl are particularly preferable. As the aromatic heterocyclic group, those containing at least one of an oxygen atom, a nitrogen atom or a sulfur atom are preferable. Specific examples of the heterocyclic ring include, for example, furan, pyrrole, thiophene, imidazole, pyrazole, pyridine, pyrazine, pyridazine, triazole, triazine, indole, indazole, purine, thiazoline, thiadiazole, oxazoline, oxazole, oxadiazole, quinoline, Examples thereof include isoquinoline, phthalazine, naphthyridine, quinoxaline, quinazoline, cinnoline, pteridine, acridine, phenanthroline, phenazine, tetrazole, benzimidazole, benzoxazole, benzthiazole, benzotriazole, tetrazaindene and the like. As the aromatic heterocyclic group, pyridine, triazine, and quinoline are particularly preferable.

Next, preferred examples of the compound represented by the general formula (II) are shown below, but the present invention is not limited to these specific examples.

(Synthesis example: Synthesis of compound represented by general formula (II))

A four-headed colben equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet tube was mixed with 34.2 g (0.1 mol) of sucrose, 180.8 g (0.8 mol) of benzoic anhydride, 379. 7 g (4.8 mol) was charged, the temperature was raised while bubbling nitrogen gas from a nitrogen gas introduction tube with stirring, and an esterification reaction was carried out at 70 ° C. for 5 hours. Next, the inside of the Kolben is depressurized to 4 × 10 ² Pa or less, and after excess pyridine is distilled off at 60 ° C., the inside of the Kolben is depressurized to 1.3 × 10 Pa or less and the temperature is raised to 120 ° C. Most of the acid and benzoic acid formed were distilled off. Then, 1 L of toluene and 300 g of a 0.5% by mass aqueous sodium carbonate solution were added, and the mixture was stirred at 50 ° C. for 30 minutes and then allowed to stand to separate a toluene layer. Finally, 100 g of water is added to the collected toluene layer, and after washing with water at room temperature for 30 minutes, the toluene layer is separated, and toluene is distilled off at 60 ° C. under reduced pressure (4 × 10 ² Pa or less). A mixture of A-1, A-2, A-3, A-4 and A-5 was obtained. Analysis of the resulting mixture by HPLC and LC-MASS revealed that A-1 was 7% by mass, A-2 was 58% by mass, A-3 was 23% by mass, A-4 was 9% by mass, A-5 Was 3% by mass. A part of the resulting mixture was purified by column chromatography using silica gel to obtain 100% pure A-1, A-2, A-3, A-4 and A-5, respectively. .

(Plasticizer)
The cellulose acetate film of the present invention can contain a plasticizer other than the compounds represented by the general formulas (I) and (II) as necessary for obtaining the effects of the present invention.

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 an ester plasticizer. Agent, acrylic plasticizer and the like.

Of these, when two or more plasticizers are used, at least one is preferably a polyhydric alcohol ester plasticizer.

The polyhydric alcohol ester plasticizer is a plasticizer composed of an ester of a divalent or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule. A divalent to 20-valent aliphatic polyhydric alcohol ester is preferred.

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

Formula (a) R ₁₁ — (OH) _n
However, R ₁₁ represents an n-valent organic group, n represents a positive integer of 2 or more, and the 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, and xylitol.

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.

Preferred examples of the monocarboxylic acid include the following, but the present invention is not limited to this.

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. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. The inclusion of acetic acid is preferred because the compatibility with cellulose acetate increases, and it is also preferred to use a mixture of acetic acid and other monocarboxylic acids.

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 preferable alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, and 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 acetate.

The carboxylic acid used in 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 following are specific compounds of polyhydric alcohol esters.

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 a divalent or higher, preferably a divalent to 20valent polyvalent carboxylic acid and an alcohol. The aliphatic polyvalent carboxylic acid is preferably divalent to 20-valent, and in the case of an aromatic polyvalent carboxylic acid or alicyclic polyvalent carboxylic acid, it is preferably trivalent to 20-valent.

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

Formula (b) R ₁₂ (COOH) _m1 (OH) _n1
In the formula, R ₁₂ represents an (m1 + n1) -valent organic group, m1 represents a positive integer of 2 or more, n1 represents an integer of 0 or more, a COOH group represents a carboxyl group, and an OH group represents an alcoholic or phenolic hydroxyl group.

Preferred examples of the polyvalent carboxylic acid 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.

The alcohol used in the polyvalent carboxylic acid ester compound that can be used in the present invention is not particularly limited, and known alcohols 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. More preferably, it has 1 to 20 carbon atoms, and particularly preferably 1 to 10 carbon atoms.

Also, alicyclic alcohols such as cyclopentanol and cyclohexanol or derivatives thereof, aromatic alcohols such as benzyl alcohol and cinnamyl alcohol, or derivatives thereof can be preferably used.

When an oxypolycarboxylic acid is used as the polyvalent carboxylic 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 straight-chain or side-chain fatty acid having 1 to 32 carbon atoms can be preferably used. More preferably, it has 1 to 20 carbon atoms, and particularly preferably 1 to 10 carbon atoms.

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 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. The aromatic monocarboxylic acid which has, or those derivatives can be mentioned. Particularly preferred are acetic acid, propionic acid, and benzoic acid.

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 acetate.

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

The acid value of the polyvalent carboxylic acid ester compound that can be used in the present invention 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 retardation is also suppressed.

The acid value refers to the number of milligrams of potassium hydroxide necessary to neutralize 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.

(UV absorber)
The cellulose acetate film of the present invention can also contain an ultraviolet absorber. The ultraviolet absorber is intended to improve durability by absorbing ultraviolet light having a wavelength of 400 nm or less, and the transmittance at a wavelength of 370 nm is particularly preferably 10% or less, more preferably 5% or less. Preferably it is 2% or less.

Although the ultraviolet absorber used in the present invention is not particularly limited, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders Examples include the body.

For example, 5-chloro-2- (3,5-di-sec-butyl-2-hydroxylphenyl) -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, etc. These are commercially available products made by BASF 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 an ultraviolet absorber.

Also, as the ultraviolet absorber, a polymeric ultraviolet absorber can be preferably used, and in particular, a polymer type ultraviolet 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 inorganic powders that do not dissolve in organic solvents, use a dissolver or sand mill in the organic solvent and cellulose acetate to disperse them before adding them 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, the amount used is 0.5 to the polarizing plate protective film. Is preferably 10 to 10% by mass, and more preferably 0.6 to 4% by mass.

(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 cellulose acetate film may be deteriorated.

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

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-t-butyl-4-hydroxyphenyl) propionate], oct Decyl-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-tert-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 amount of these compounds added is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to the cellulose derivative.

(Acid scavenger)
Since cellulose acetate is accelerated by acid at high temperatures, it preferably contains an acid scavenger when used in the protective film of the present invention.

Any useful acid scavenger can be used without limitation as long as it is a compound that reacts with an acid to inactivate the acid. Among them, the epoxy group described in US Pat. No. 4,137,201 is particularly useful. A compound having is preferred. Epoxy compounds as such acid scavengers are known in the art and are derived by condensation of diglycidyl ethers of various polyglycols, particularly about 8-40 moles of ethylene oxide per mole of polyglycol. Glycol, diglycidyl ether of glycerol, metal epoxy compounds (such as those conventionally used in and together with vinyl chloride polymer compositions), epoxidized ether condensation products, diphenols of bisphenol A Glycidyl ether (ie, 4,4'-dihydroxydiphenyldimethylmethane), epoxidized unsaturated fatty acid ester (especially an ester of alkyl of about 2 to 2 carbon atoms of fatty acids of 2 to 22 carbon atoms such as butyl Epoxy stearate And epoxidized vegetable oils and other unsaturated natural oils (sometimes these are epoxidized natural glycerides, which can be represented and exemplified by compositions of various epoxidized long chain fatty acid triglycerides and the like (eg, epoxidized soybean oil and the like) Or unsaturated fatty acids, which generally contain 12 to 22 carbon atoms). Moreover, EPON 815C can also be preferably used as a commercially available epoxy group-containing epoxide resin compound.

In addition to the above, acid scavengers that can be used include oxetane compounds, oxazoline compounds, alkaline earth metal organic acid salts and acetylacetonate complexes, and paragraphs 68 to 105 of JP-A-5-194788. Is included.

The acid scavenger may be referred to as an acid scavenger, an acid scavenger, an acid catcher, etc., but in the present invention, they can be used without any difference due to their names.

<Fine particles>
The cellulose acetate film of the present invention has, for example, silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate in order to improve handleability. Further, it is preferable to contain inorganic fine particles such as magnesium silicate and calcium phosphate and a matting agent such as a crosslinked polymer. Of these, silicon dioxide is preferable because it can reduce the haze of the film.

The primary average particle diameter of the fine particles is preferably 20 nm or less, more preferably 5 to 16 nm, and particularly preferably 5 to 12 nm.

These fine particles form secondary particles having a particle size of 0.1 to 5 μm and are preferably contained in the cellulose acetate film, and the preferable average particle size is 0.1 to 2 μm, more preferably 0.2 to 0.6 μm. As a result, irregularities having a height of about 0.1 to 1.0 μm are formed on the film surface, thereby providing appropriate slipperiness to the film surface.

The primary average particle diameter of the fine particles used in the present invention is measured by observing the particles with a transmission electron microscope (magnification of 500,000 to 2,000,000 times), observing 100 particles, measuring the particle diameter, and measuring the average. The value was taken as the primary average particle size.

<Method for producing cellulose acetate film>
Next, the manufacturing method of the cellulose acetate film of this invention is demonstrated.

The cellulose acetate film of the present invention 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.

Production of the cellulose acetate film of the present invention by the solution casting method is a step of preparing a dope by dissolving at least a compound represented by the general formula (I), cellulose acetate, and, if necessary, an additive in a solvent. , A step of casting the dope onto an endless metal support that moves indefinitely, a step of drying the cast dope as a web, a step of peeling from the metal support, a step of stretching or maintaining the width, a step of further drying, This is performed by a step of winding the finished film.

The process for preparing the dope will be described. The concentration of cellulose acetate 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 acetate is too high, the load during filtration increases and the filtration accuracy is poor. Become. The concentration that achieves both of these is preferably 10 to 35% by mass, and more preferably 15 to 25% by mass.

It is preferable to add a prescribed amount of the compound represented by the general formula (I) to the dope preparation kettle.

The solvent used in the dope may be used singly 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 acetate in terms of production efficiency, and there are many good solvents. This is preferable from the viewpoint of solubility of cellulose acetate.

A 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 acetate to be used independently is defined as a good solvent, and what does not swell or dissolve independently is defined as a poor solvent.

Therefore, good solvent and poor solvent change depending on the degree of acetyl group substitution of cellulose acetate.

The good solvent 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.

The poor solvent used in the present invention is not particularly limited, but for example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone and the like are preferably used. The dope preferably contains 0.01 to 2% by mass of water.

Further, as the solvent used for dissolving cellulose acetate, the solvent removed from the film by drying in the film forming process is recovered and reused.

The recovery solvent may contain trace amounts of additives added to cellulose acetate, such as plasticizers, UV absorbers, polymers, monomer components, etc., but these are preferably reused even if they are included. Can be purified and reused if necessary.

A general method can be used as a method for dissolving cellulose acetate when preparing the dope described above. 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 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 formation of massive undissolved material called gel or mamako.

Further, a method in which cellulose acetate is mixed with a poor solvent and wetted or swollen, and then a good solvent is added and dissolved is also preferably used.

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 a solvent is preferably higher from the viewpoint of the solubility of cellulose acetate, but if the heating temperature is too high, the required pressure increases and the productivity deteriorates.

The preferred 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, whereby cellulose acetate can be dissolved in a solvent such as methyl acetate.

Next, the cellulose acetate 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, 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 cellulose acetate 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, still more preferably 50 pieces / m ² or less, still more preferably 0 to 10 pieces / cm ² . 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 increase in the difference (referred to as differential pressure) is small and preferable.

The 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 preferable. 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 process is preferably 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 ~ 4m. The surface temperature of the metal support in the casting step is −50 ° C. to less than the boiling point of the solvent, and a higher temperature is preferable because the web drying speed can be increased. May deteriorate.

The preferred support temperature is 0 to 55 ° C, more preferably 25 to 50 ° 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, but 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 cellulose acetate film to exhibit good flatness, the amount of residual solvent 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. Particularly preferred is 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.

Moreover, in the drying step of the cellulose acetate film, 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 preferred is 0 to 0.01% by mass or less.

In the film drying process, 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 cellulose acetate film of the present invention, it is particularly preferable to stretch 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 in terms of simplicity.

It is preferable that the drying temperature in the web drying process is increased stepwise from 40 to 200 ° C.

The film thickness of the cellulose acetate film of the present invention is preferably a thin film, used in the range of 10 to 200 μm, preferably 10 to 100 μm, more preferably 10 to 60 μm, particularly preferably 20 to 60 μm.

The cellulose acetate film of the present invention has a width of 1 to 4 m. Particularly, 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.

The cellulose acetate film of the present invention has a retardation Ro defined by the formula (i) in the in-plane direction from the viewpoint of taking advantage of high retardation development, although the required retardation is different depending on the required optical compensation effect. It is preferably 20 nm or more, more preferably in the range of 20 to 200 nm, still more preferably in the range of 20 to 100 nm, and the retardation Rth in the thickness direction defined by the formula (ii) is 70 nm or more. It is preferable that there is a range of 70 to 300 nm.

Formula (i) Ro = (nx−ny) × d
Formula (ii) Rth = {(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).)
<Measurement of retardation Ro and Rth>
A 35 mm × 35 mm sample was cut out from the obtained film, conditioned at 25 ° C. and 55% RH for 2 hours, and measured with an automatic birefringence meter (KOBRA21DH, Oji Scientific Co., Ltd.) from the vertical direction at 590 nm and the film. It is calculated from the extrapolated value of the retardation value measured in the same manner while tilting the surface.

The method of adjusting the phase difference is not particularly limited, but a method of adjusting by stretching is common.

In order to obtain the target retardations Ro and Rth in the present invention, it is preferable that the cellulose acetate film has the configuration of the present invention, and the refractive index is controlled by controlling the transport tension and stretching.

For example, it is possible to change the retardation by lowering or increasing the tension in the longitudinal direction.

In addition, the retardation can be changed by biaxially or uniaxially stretching sequentially or simultaneously with respect to the longitudinal direction (film forming direction) of the film and the direction orthogonal to the film plane, that is, the width direction. .

The draw ratios in the biaxial directions perpendicular to each other are preferably in the range of 0.8 to 1.5 times in the casting direction and 1.1 to 2.0 times in the width direction, respectively. More preferably, it is performed in the range of 0.8 to 1.1 times in the direction and 1.3 to 1.7 times in the width direction, and particularly preferably in the range of 1.3 to 1.5 times in the width direction. .

The cellulose acetate film of the present invention is easy to stretch and may easily develop retardation, and has high resistance to process failures such as fracture.

The stretching temperature is preferably 120 ° C. to 200 ° C., more preferably 150 ° C. to 200 ° C., more preferably more than 150 ° C. and 190 ° C. or less.

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

Specifically, it is preferable that the residual solvent is stretched by 11% at 155 ° C., or the residual solvent is stretched by 2% at 155 ° C. Alternatively, it is preferable that the residual solvent is stretched at 11% at 160 ° C, or the residual solvent is stretched at less than 1% at 160 ° C.

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, the both ends of the web are fixed with clips and pins, and the interval between the clips and pins is increased in the traveling direction. 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.

Also, 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 carry out the width maintenance or lateral stretching in the film forming step by a tenter, and it may be a pin tenter or a clip tenter.

The slow axis or fast axis of the cellulose acetate film of the present invention is present in the film plane, and θ1 is preferably −1 ° or more and + 1 ° or less, assuming that the angle formed with the film forming direction is θ1. More preferably, it is 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.

<Physical properties of cellulose acetate film>
The moisture permeability of the cellulose acetate film of the present invention is preferably 300 to 1800 g / m ² · 24 h at 40 ° C. and 90% RH, more preferably 400 to 1500 g / m ² · 24 h, and 40 to 1300 g / m ² · 24 h. Particularly preferred. The moisture permeability can be measured according to the method described in JIS Z 0208.

The cellulose acetate film of the present invention has a breaking elongation of preferably 10 to 80%, more preferably 20 to 50%.

The visible light transmittance of the cellulose acetate film of the present invention is preferably 90% or more, and more preferably 93% or more.

The haze of the cellulose acetate film of the present invention is preferably less than 1%, particularly preferably 0 to 0.1%.

<Polarizer>
The cellulose acetate film of the present invention can be used as an optical compensation film (also referred to as a retardation film) in a polarizing plate and a liquid crystal display device using the polarizing plate.

The polarizing plate is a polarizing plate in which the cellulose acetate film of the present invention is bonded to at least one surface of a polarizer. The liquid crystal display device of the present invention is characterized in that the polarizing plate according to the present invention is bonded to at least one liquid crystal cell surface via an adhesive layer.

The polarizing plate can be produced by a general method. The cellulose acetate film of the present invention can be bonded to at least one surface of a polarizer produced by subjecting the polarizer side of the cellulose acetate film to alkali saponification treatment and immersion drawing in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. preferable.

Even if the cellulose acetate film of the present invention is used on the other surface, it is also preferable to bond another optical film.

For example, commercially available cellulose ester films (for example, Konica Minoltack KC8UX, KC5UX, KC8UCR3, KC8UCR4, KC8UCR5, KC8UY, KC4UY, KC4UE, KC8UE, KC8UY-HA, KC8UX-RHA, KC8UX-RHA, KC8UX KC4UXW-RHA-NC, manufactured by Konica Minolta Opto Co., Ltd.) is preferably used.

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

The polarizer is formed by forming a polyvinyl alcohol aqueous solution into a film and dyeing the film by uniaxial stretching or dyeing or uniaxially stretching, and then performing 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.

Further, the ethylene unit content described in JP-A-2003-248123, JP-A-2003-342322, etc. is 1 to 4 mol%, the degree of polymerization is 2000 to 4000, and the degree of saponification is 99.0 to 99.99 mol%. Ethylene-modified polyvinyl alcohol is also preferably used.

Among them, an ethylene-modified polyvinyl alcohol film having a hot water cutting temperature of 66 to 73 ° C. is preferably used.

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

The polarizer obtained as described above is usually used as a polarizing plate with a protective film bonded to both sides or one side. Examples of the adhesive used for pasting include a PVA-based adhesive and a urethane-based adhesive. Among them, a PVA-based adhesive is preferably used.

<Liquid crystal display device>
By using the polarizing plate bonded with the cellulose acetate film of the present invention for a liquid crystal display device, the liquid crystal display device of the present invention excellent in various visibility can be produced.

Since the cellulose acetate film of the present invention has an optical compensation function, the cellulose acetate film side of the polarizing plate of the present invention is bonded to at least one surface of the liquid crystal cell, and STN, TN, OCB, HAN, VA (MVA) , PVA), IPS, OCB, and other driving system liquid crystal display devices are preferably manufactured.

A VA (MVA, PVA) type liquid crystal display device is preferable.

When the cellulose acetate film of the present invention is used, it is possible to obtain a liquid crystal display device having excellent visibility such as uneven coloring and front contrast, even with a large-screen liquid crystal display device having a size of 30 or more. did it.

Recently, in the manufacturing method of liquid crystal display devices, a method in which a long roll-shaped polarizing plate is continuously bonded to a liquid crystal panel and then the liquid crystal panel is manufactured while being cut to a desired size by a laser is employed for production. It is preferable for improving the property and the yield.

The above manufacturing method is referred to as a “roll to panel manufacturing method”. In this manufacturing method, a polarizing plate is fed directly from a roll without being cut into a roll-shaped long polarizing plate in advance to a liquid crystal panel size. After bonding, it is a manufacturing method of cutting into a liquid crystal panel size with a laser cutter or the like (see FIG. 1). In this case, a bonding roll is pressed when the polarizing plate is bonded to the liquid crystal panel. However, since the polarizing plate is a long polarizing plate, an unreasonable force is easily applied at the time of bonding, and unevenness and wrinkles are easily generated on the polarizing plate. However, the long roll-shaped polarizing plate bonded with the cellulose acetate film of the present invention has good flatness, so there is no curl, etc., generation of useless stress is suppressed, and there is no bonding failure, yield improvement. I can expect.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1
<Production of Cellulose Acetate Film 101>
<Fine particle dispersion 1>
Fine particles (Aerosil R972V 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>
The fine particle dispersion 1 was slowly added to the dissolution tank containing methylene chloride with sufficient stirring. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered through 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 A main dope solution having the following composition was prepared. First, methylene chloride and ethanol were added to the pressure dissolution tank. Cellulose acetate (acetyl group substitution degree 2.45, cellulose acetate of Mw 135000 and Mw 180000 mixed at a mass ratio of 6: 4) was added to 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 acetate (Acetyl group substitution degree 2.45, Mw 135000 and Mw 180000 cellulose acetate mixed at a mass ratio of 6: 4) 100 parts by mass A compound represented by the general formula (I): Exemplary compound PES-2
(Hydroxyl value 100 mg KOH / g) 3.5 parts by mass Sugar ester compound represented by the general formula (II) (Exemplary compounds a1 / a2 / a3 / a4 = mixture at a mass ratio of 25/20/22/33) 9 Part 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 amount of residual solvent in the cast (cast) film reached 75%, and then peeled off from the stainless steel belt support with a peeling tension of 130 N / m.

The peeled cellulose acetate film was stretched 1.15 times in the width direction using a tenter while applying heat at 160 ° C. The residual solvent at the start of stretching was 10%.

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.

Thus, a cellulose acetate film 101 having a dry film thickness of 45 μm and a length of 2000 m was obtained.

Similarly, after adjusting the cast film thickness so that the dry film thickness was 45 μm, cellulose acetate films stretched 1.25 times, 1.35 times, and 1.45 times in the width direction were respectively produced. .

In addition, the measurement of the hydroxyl value of the polyester compound represented by the general formula (I) was performed using the acetic anhydride method described in Japanese Industrial Standards JIS K1557-1: 2007.

<Production of cellulose acetate films 102 to 123>
Cellulose acetate films 102 to 123 were produced in the same manner as the cellulose acetate film 101 except that the dope composition and production conditions were changed as shown in Table 1.

Similarly, cellulose acetate films stretched in the width direction at stretch ratios of 1.15 times, 1.25 times, 1.35 times, and 1.45 times were prepared.

In Table 1,
Comparative compound 1: Terminal hydroxyl group polyester compound (Exemplary P-28) described in JP-A-2009-235377, hydroxyl value 220 mgKOH / g,
Comparative compound 2: Terminal hydroxyl group polyester compound described in JP-A-2009-098674 (Example A-12, Example A-12) hydroxyl value 200 mgKOH / g,
Comparative compound 3: Triazine compound of the following structural formula,

PETB: represents pentaerythritol tetrabenzoate.

<Evaluation>
About each obtained sample, the retardation value and dispersion | variation, an internal haze, and the haze of a wet heat durability test were measured in the following ways.

(Measurement of retardation Ro, Rth, and measurement of Ro width unevenness)
A sample 35 mm × 35 mm was cut out from a sample film stretched at 160 ° C. 1.35 times, conditioned at 25 ° C. and 55% RH for 2 hours, and perpendicular at 590 nm with an automatic birefringence meter (KOBRA 21DH, Oji Scientific Co., Ltd.). It was calculated from the value measured from the direction and the extrapolated value of the retardation measured in the same manner while tilting the film surface.

Similarly, 13 samples were collected in the width direction of 1980 mm and measured, and the average value was obtained.

Also, the (maximum value-minimum value) values of 13 samples were evaluated according to the following criteria.

○: Less than 2 nm Δ: 2 nm or more and less than 4 nm ×: 4 nm or more (internal haze)
The cellulose acetate film stretched at 160 ° C. was passed through a drying zone at 130 ° C. for 20 minutes, sampled, and the internal haze value was evaluated by the following method.

The following evaluation scale was used to evaluate the obtained internal haze value.

○: Less than 0.04 Δ: 0.04 or more and less than 0.08 ×: 0.08 or more <Internal haze measuring device>
Haze meter (turbidity meter) (model: NDH 2000, manufactured by Nippon Denshoku Co., Ltd.)
A 5V9W halogen bulb was used as the light source, and a silicon photocell (with a relative visibility filter) was used as the light receiving unit.

The cellulose acetate film of the present invention preferably has a value of less than 0.04 in the haze measurement of the film when a solvent having a refractive index of ± 0.05 is dropped on the film with this apparatus. . The measurement was performed according to JIS K-7136.

Measure internal haze as follows. A description will be given with reference to FIGS.

First, the blank haze 1 of a measuring instrument other than a film is measured.
1. Drip a drop (0.05 ml) of glycerin on a cleaned glass slide. At this time, care is taken so that bubbles do not enter the droplet. Be sure to use glass that has been cleaned with a detergent because it may look dirty even if it looks clean. (See Figure 2)
2. Place the cover glass on top of it. Glycerin spreads without pressing the cover glass.
3. Set on a haze meter and measure blank haze 1.

Next, the haze 2 including the sample is measured by the following procedure.
4). Glycerol is dropped on the slide glass. (0.05ml)
(See Figure 2)
5. A sample film to be measured is placed thereon so that no air bubbles enter.

(See Figure 3)
6). Glycerol is dropped on the sample film. (0.05ml)
(See Figure 4)
7. Place the cover glass on top of it. (See Figure 5)
8). The laminate prepared as described above (from above, cover glass / glycerin / sample film / glycerin / slide glass) is set on a haze meter and haze 2 is measured.
9. (Haze 2) − (Haze 1) = (Internal haze of the cellulose acetate film of the present invention) is calculated.

All the above haze measurements were performed at 23 ° C. and 55% RH.

Moreover, the glass and glycerin used in the above measurement are as follows.

Glass: MICRO SLIDE GLASS S9213 MATUNAMI
Glycerin: Kanto Kagaku Deer Special Grade (Purity> 99.0%) Refractive index 1.47
(Haze of wet heat durability test)
The difference in the value of (total haze after exposure for 1000 hours at 60 ° C. and 90%) to (total haze before exposure) was measured and used as the haze evaluation of the wet heat durability test. The haze was measured using a haze meter (NDH2000 type, manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS K-7136.

○: Difference is less than 0.0 to less than 0.2 Δ: Difference is less than 0.2 to less than 0.5 ×: Difference is more than 0.5 Table 2 shows the evaluation results.

From the above table, the cellulose acetate film of the present invention has no increase in internal haze even when stretched at a high magnification, has sufficient retardation and stable retardation without variation, and is excellent in haze increase in wet heat durability test. It can be seen that this is a cellulose acetate film.

Example 2
<Production of long roll-shaped polarizing plates 101 to 123>
A polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times) to obtain a 2000 m long PVA film.

This was immersed in an aqueous solution consisting 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. consisting 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 polarizer and the cellulose acetate films 101 to 123 stretched 1.35 times according to the following steps 1 to 5 are bonded together with Konica Minolta Tack KC4UY (cellulose ester film manufactured by Konica Minolta Opto Co., Ltd.) on the back side. Thus, long roll-shaped polarizing plates 101 to 123 were produced.

Step 1: Soaked in a 2 mol / L sodium hydroxide solution at 45 ° C. for 45 seconds, then washed with water and dried to obtain cellulose acetate films 101 to 123 saponified on the side to be bonded to the polarizer. Similarly, KC4UY on the back side was also saponified.

Step 2: The polarizer was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.

Step 3: Excess adhesive adhered to the polarizer in Step 2 was lightly wiped off and placed on the cellulose acetate films 101 to 123 treated in Step 1.

Step 4: The cellulose acetate films 101 to 123, the polarizer, and the back side cellulose ester film laminated in Step 3 were bonded at a pressure of 20 to 30 N / cm ² and a conveying speed of about 2 m / min.

Step 5: A sample prepared by bonding the polarizer prepared in Step 4 with the cellulose acetate films 101 to 123 and Konica Minoltack KC4UY in a drier at 80 ° C. is dried for 2 minutes. Corresponding polarizing plates 101 to 123 were prepared.

Next, an adhesive material having the following composition was prepared and coated on the side surfaces of the cellulose acetate films 101 to 123 with a knife type coater, and then irradiated with ultraviolet rays and dried at 90 ° C. for 1 minute to form an adhesive layer. Long roll polarizing plates 101 to 123 were prepared.

(Adhesive layer composition: abbreviated as N1)
Acrylic copolymer: butyl acrylate and acrylic acid in a mass ratio of 95: 5, polymerized according to a conventional method and having a weight average molecular weight of 1,800,000 100 parts by weight Polyfunctional acrylate monomer: Tris (Acrylloyoxyethyl) isocyanurate (trade name “Aronix M-315” manufactured by Toagosei Co., Ltd.)
15 parts by mass Photopolymerization initiator: Irgacure 500 (manufactured by BASF Japan)
1.5 parts by mass Isocyanate-based cross-linking agent: trimethylolpropane-modified tolylene diisocyanate (“Coronate L” manufactured by Nippon Polyurethane Co., Ltd.) 1 part by mass Silane coupling agent: 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Gaku Kogyo Co., Ltd.) "KBM-403") 0.2 parts by mass (protective film, separate film)
Furthermore, a PET-based protective film was bonded onto KC4UY, and a PET-based separate film was bonded onto the adhesive layer, and wound into a roll.

[Production of liquid crystal display panel]
By the “roll-to-panel manufacturing method” shown in FIG. 1, the produced long roll-shaped polarizing plate was drawn out and bonded onto a liquid crystal panel, and cut into a desired size with a laser cutter to produce a liquid crystal display panel.

<Evaluation>
(Applicability to LCD panel processing)
The presence or absence of wrinkles or twists at the time of bonding between the polarizing plate and the liquid crystal panel during the production of the liquid crystal display panel was visually observed.

◎: There is no wrinkle or crease when bonding, and yield is good ○: There is some wrinkle or crease when bonding, but there is no problem in practical yield △: There is wrinkle or twist when bonding, and yield is low ×: Paste As a result of evaluation, wrinkles and twists remarkably occur at the time of bonding, and the yield is very low. As a result of evaluation, the polarizing plate using the cellulose acetate film of the present invention is evaluated as “◎: No yield of wrinkles or warping at the time of bonding” It was found that the polarizing plate was excellent in flatness.

On the other hand, the polarizing plate using the cellulose acetate film of the comparative example was evaluated as x to Δ, and the yield was low.

DESCRIPTION OF SYMBOLS 1 Long roll-shaped polarizing plate 2 Bonding roll 3 Liquid crystal panel

Claims

A cellulose acetate film comprising at least a polyester compound represented by the following general formula (I) having a hydroxyl group at both ends and a cellulose acetate having an acetyl group substitution degree of 2.0 to 2.6.

(In the formula, B represents a linear or branched alkylene or cycloalkylene group having 2 to 6 carbon atoms, A represents an aromatic ring having 6 to 14 carbon atoms, and n represents a natural number of 1 or more. To express.)
The cellulose acetate film according to claim 1, wherein A is a naphthalene ring or a biphenyl ring which may have a substituent in the polyester compound represented by the general formula (I). (The substituent represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group, or an alkoxyl group.)
3. The cellulose acetate film according to claim 1, wherein the polyester compound has a hydroxyl value of 170 mgKOH / g to 400 mgKOH / g.
The cellulose acetate film according to any one of claims 1 to 3, wherein the polyester compound is contained in an amount of 1% by mass to less than 5% by mass with respect to the cellulose acetate.
The cellulose acetate film according to any one of claims 1 to 4, wherein the cellulose acetate film has a retardation value Ro represented by the following formula of 20 to 100 nm and Rth of 70 to 300 nm.
Formula (i) Ro = (nx−ny) × d
Formula (ii) Rth = {(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).)
The cellulose acetate film according to any one of claims 1 to 5, comprising 5% by mass or more of a sugar ester compound represented by the following general formula (II) as a hydrolysis inhibitor.

(In the formula, G represents a monosaccharide or disaccharide residue, X 1 represents —O—, R 1 represents —CO—R 2 , and R 2 represents an aliphatic or aromatic group. Represents the total number of hydroxyl groups directly bonded to monosaccharide or disaccharide residues, n represents the total number of OR 1 groups directly bonded to monosaccharide or disaccharide residues, and 3 ≦ m + n ≦ 8 And n ≠ 0.)
A method for producing a cellulose acetate film according to any one of claims 1 to 6, wherein at least both of the polyesters represented by the following general formula (I) are hydroxyl groups and the degree of acetyl group substitution is 2.0. A dope containing ~ 2.6 cellulose acetate is cast on a support and peeled, and then stretched at a magnification of 1.3 ~ 1.7 times at least in the width direction while drying. A method for producing a cellulose acetate film.

(In the formula, B represents a linear or branched alkylene or cycloalkylene group having 2 to 6 carbon atoms, A represents an aromatic ring having 6 to 14 carbon atoms, and n represents a natural number of 1 or more. To express.)
A polarizing plate comprising the cellulose acetate film according to any one of claims 1 to 6 bonded to at least one surface of a polarizer.
A liquid crystal display device comprising the polarizing plate according to claim 8 and the cellulose acetate film side according to any one of claims 1 to 6 bonded to at least one surface of a liquid crystal cell.
In the manufacturing method of the liquid crystal display device which bonds the polarizing plate of Claim 8 to a liquid crystal panel, after bonding this polarizing plate to a liquid crystal panel by the roll to panel manufacturing method, this liquid crystal panel is made into a desired size with a laser. A method for manufacturing a liquid crystal display device, comprising cutting.