JP2002302561A - Method for producing optically compensating film and polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optically compensating film, capable of optically compensating a liquid crystal cell by coating a liquid crystalline compound on a cellulose acetate film, and further to provide a method for producing a polarizing plate capable of improving light leakage and striped unevenness, and capable of providing a large liquid crystal display device having high display quality and high brightness by arranging the optically compensating film on one surface of a polarizing film. SOLUTION: The optically compensating film is produced by subjecting a cellulose acetate film having a protecting layer formed on one surface to a saponification treatment to carry out the saponification treatment only of one surface on which the protecting layer is not formed, forming an oriented layer on the surface subjected to the saponification treatment, and coating an optically anisotropic layer comprising a liquid crystalline compound on the oriented layer to produce an optically compensating film. The polarizing plate is produced by peeling the protective layer of the optically compensating film, subjecting the peeled surface of the cellulose acetate to the saponification treatment, and laminating the surface subjected to the saponification treatment on one surface of the polarizing film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical compensation film widely used for a liquid crystal display or the like and a method for producing a polarizing plate with an optical compensation film.

[0002]

2. Description of the Related Art A liquid crystal display device comprises a polarizing plate and a liquid crystal cell. In a TN mode TFT liquid crystal display device which is currently mainstream, an optical compensation film is inserted between a polarizing plate and a liquid crystal cell as described in JP-A-8-50206, and a liquid crystal display device with high display quality is realized. ing. However, this method has a problem that the liquid crystal display device itself becomes thicker.

Japanese Patent Application Laid-Open No. 1-68940 discloses that an elliptically polarizing plate having a retardation plate on one side of a polarizing film and a protective film on the other side is used to increase the front contrast without increasing the thickness of the liquid crystal display device. There is a statement that it can be raised. However, it has been found that the retardation film of the present invention easily causes a retardation due to distortion such as heat and has a problem in durability. To solve the problem of phase difference due to distortion, JP-A-7-191217 and EP0911656A2 disclose an optical compensation film in which an optically anisotropic layer made of a discotic compound is coated on a transparent support. By directly using the film as a protective film for a polarizing plate, the above-mentioned problem relating to durability was solved without increasing the thickness of the liquid crystal display device.

However, when a polarizing plate using the optical compensation film as a protective film was mounted on a high-luminance large panel of 17 inches or more, it was found that light leakage due to the above-described thermal distortion was not completely eliminated. Further, it has been found that streak-like unevenness newly appears as the luminance increases.

[0005] The inventor's earnest research has revealed that this light leakage is the following two causes. One is that the expansion or shrinkage of the polymer film due to the change in wet heat conditions is suppressed as a whole, and the optical characteristics of the optical compensation sheet are changed. A temperature distribution occurs in the sheet surface, and the thermal strain causes similar optical characteristics. In particular, it has been found that a polymer having a hydroxyl group such as cellulose ester has a large effect on the environment. That is, in order to eliminate the light leakage, the change in the optical characteristics of the optical compensation sheet may be reduced, and the temperature distribution applied to the optical compensation sheet may be reduced. Further studies by the present inventors have revealed that this change in optical properties is determined by the product of the photoelastic coefficient, thickness, virtual distortion due to environment, and elastic modulus of the optical compensation sheet. Therefore, light leakage is significantly reduced by lowering the photoelastic coefficient, reducing the thickness, reducing distortion due to the environment, and reducing the elastic modulus of the optical compensatory sheet. Next, regarding the temperature distribution,
It is reduced by increasing the thermal conductivity of the optical compensation sheet, and light leakage is also reduced.

[0006]

However, even if such light leakage is reduced, there is no effect on the streak-like unevenness, and a solution has been required. The inventor has
Through diligent research, it has been found that streak-like unevenness is caused by deterioration of the flatness of the cellulose acetate film. As a result of further research, it was found that the planarity of the cellulose acetate film was degraded by the solvent-based undercoat layer provided for providing adhesion between the cellulose acetate film and the optically anisotropic layer or the alignment film. That is, in order not to deteriorate the planarity of the cellulose acetate film, it is sufficient that the cellulose acetate film is not provided with an undercoat layer, and that the adhesiveness with the optically anisotropic layer or the alignment film can be imparted. By performing saponification treatment on the cellulose acetate film surface, the adhesion was successfully imparted without impairing the flatness. However, when the saponification treatment is performed on both surfaces, the saponified surface comes into contact with the saponified surface and blocking occurs. When the saponified surface without an alignment film and the alignment film (especially aqueous) come into contact, blocking also occurs. In addition, a problem such as a change in alignment ability occurs.

An object of the present invention is to provide a method for producing an optical compensation film capable of optically compensating a liquid crystal cell by coating a liquid crystal compound on a cellulose acetate film, and disposing the optical compensation film on one side of a polarizing film. Accordingly, it is an object of the present invention to provide a method for manufacturing a polarizing plate capable of providing a large-sized, high-brightness liquid crystal display device having high display quality.
In particular, an object of the present invention is to improve light leakage and uneven stripes,
An object of the present invention is to provide a method for producing a polarizing plate using the above-described chemical compensation film, which does not cause blocking.

[0008]

According to the present invention, a method for producing an optical compensation film and a polarizing plate having the following constitutions is provided, and the above object of the present invention is achieved. 1. By providing a protective layer on one side of the cellulose acetate film and performing saponification treatment, only one side without the protective layer is saponified, and an orientation layer is provided on the saponified film surface, and an orientation layer is provided. A method for producing an optical compensation film, comprising coating an optically anisotropic layer comprising a liquid crystal compound thereon. 2. The thickness of the cellulose acetate film is 10 to 70
2. The method for producing an optical compensation film as described in 1 above, wherein the thickness is μm. 3. The polarizing plate, wherein the protective layer of the optical compensation film according to 1 or 2 above is peeled off, the peeled cellulose acetate surface is saponified, and the saponified surface is bonded to at least one side of the polarizing film. Production method.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The inventor of the present invention has proposed that the thickness is less than the conventional thickness.
The present inventors have succeeded in optically compensating a liquid crystal cell without side effects and have found a manufacturing method that can be mass-produced at lower cost. To prevent the occurrence of streak-like unevenness, by saponifying the cellulose acetate film surface on which the optically anisotropic layer is applied,
It is preferable to provide adhesion. In order to be saponified again when the polarizing plate is formed, it is preferable to saponify only the surface on the side of the optically anisotropic layer. It is preferably used. In order to prevent the frame-shaped transmittance from increasing, the thickness of the cellulose acetate film is preferably from 10 to 70 μm, more preferably from 20 to 60 μm, and most preferably from 30 to 50 μm. The photoelastic coefficient of the cellulose acetate film is preferably 1.0 × 10 ⁻⁶ cm ² / Kg or less. The elastic modulus is preferably 3000 MPa or less, more preferably 2500 MPa or less. In order to reduce the virtual strain, the plane orientation of the polymer molecule is increased by biaxial stretching, or the coefficient of hygroscopic expansion is 30 × 10 ⁻⁵ /
cm ² /% RH or less, preferably 15 × 10 ⁻⁵
/ cm ² /% RH or less, and most preferably 10 × 10 ⁻⁵ / cm ² /% RH or less. Here, the coefficient of hygroscopic expansion is indicated by the amount of change in the length of the sample when the relative humidity is changed at a constant temperature. Further, the thermal conductivity of the cellulose acetate film of the present invention is 1 W / m ·
It is preferably at least K. The optical compensatory sheet and the polarizing plate using the optical compensatory sheet as a protective film are TN (Twisted Nematic) type, MVA (Multi-domai).
n-Vertical-Aligned) type, OCB (Optical-Compensate)
d-Birefringence) type liquid crystal display device. Hereinafter, the method of the present invention will be described in more detail.

[Cellulose Acetate] In the present invention, it is preferable to use cellulose acetate having an acetylation degree of 59.0 to 61.5%. The degree of acetylation means the amount of bound acetic acid per unit weight of cellulose. The degree of acetylation is
According to the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like). The viscosity average degree of polymerization (DP) of the cellulose ester is
It is preferably at least 250, more preferably at least 290. Further, the cellulose acetate used in the present invention preferably has a narrow molecular weight distribution represented by Mw / Mn (Mw is a weight average molecular weight, Mn is a number average molecular weight) determined by gel permeation chromatography. Specific values of Mw / Mn are 1.0-1.
7, more preferably 1.3 to 1.65, and most preferably 1.4 to 1.6.

[Retardation Raising Agent] The retardation of the cellulose acetate film can be adjusted as required. The Re retardation value and Rth retardation value of the film are defined by the following formulas (I) and (II), respectively. Formula (I): Re = (nx−ny) × d Formula (II): Rth = {(nx + ny) / 2−nz} × d In the above formulas (I) and (II), nx represents the in-plane of the film. This is the refractive index in the slow axis direction (the direction in which the refractive index is maximized). ny is the refractive index in the fast axis direction (the direction in which the refractive index is minimum) in the film plane. nz is the refractive index in the thickness direction of the film. d is the thickness of the film (n
m).

In the present invention, it is preferable that the cellulose acetate film has a Re retardation value of 0 to 70 nm and an Rth retardation value of 70 to 400 nm. When two optically anisotropic cellulose acetate films are used in a liquid crystal display device, the Rth retardation value of the films is preferably from 70 to 250 nm. When one optically anisotropic cellulose acetate film is used for a liquid crystal display device, the Rth retardation value of the film is preferably 150 to 400 nm. The birefringence (Δn: nx−ny) of the cellulose acetate film is 0.00 to 0.5.
002 is preferable. Further, the birefringence in the thickness direction of the cellulose acetate film ｛(nx + ny) /
2-nz} is preferably 0.001 to 0.04.

In order to adjust the retardation, a known compound for adjusting the retardation may be used, and an aromatic compound having at least two aromatic rings is preferably used as a retardation increasing agent. Such an aromatic compound is preferably used in the range of 0.01 to 20 parts by mass with respect to 100 parts by mass of cellulose acetate. The aromatic compound is more preferably used in the range of 0.05 to 15 parts by mass, and even more preferably in the range of 0.1 to 10 parts by mass, based on 100 parts by mass of the cellulose acetate. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic hetero ring in addition to the aromatic hydrocarbon ring.

An aromatic hydrocarbon ring is a six-membered ring (ie,
Benzene ring). Aromatic heterocycles are generally unsaturated heterocycles. The aromatic hetero ring is preferably a 5-, 6- or 7-membered ring, more preferably a 5- or 6-membered ring.
Aromatic heterocycles generally have the most double bonds.
As the hetero atom, a nitrogen atom, an oxygen atom and a sulfur atom are preferable, and a nitrogen atom is particularly preferable. Examples of the aromatic hetero ring include a furan ring, a thiophene ring, a pyrrole ring,
Oxazole ring, isoxazole ring, thiazole ring,
Isothiazole ring, imidazole ring, pyrazole ring, furazane ring, triazole ring, pyran ring, pyridine ring, pyridazine ring, pyrimidine ring, pyrazine ring and 1,3,
Includes a 5-triazine ring. Preferred aromatic rings include a benzene ring, a furan ring, a thiophene ring, a pyrrole ring, an oxazole ring, a thiazole ring, an imidazole ring,
Examples thereof include a triazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring and a 1,3,5-triazine ring, and a benzene ring and a 1,3,5-triazine ring are more preferred. It is particularly preferred that the aromatic compound has at least one 1,3,5-triazine ring.

The number of aromatic rings in the aromatic compound is 2
-20, more preferably 2-12, even more preferably 2-8,
Most preferably, it is 6. The bonding relationship between two aromatic rings can be classified into (a) a case where a condensed ring is formed, (b) a case where they are directly connected by a single bond, and (c) a case where they are bonded via a linking group. , A spiro bond cannot be formed). The connection relationship may be any of (a) to (c).

Examples of the condensed ring of (a) (condensed ring of two or more aromatic rings) include an indene ring, a naphthalene ring, an azulene ring, a fluorene ring, a phenanthrene ring, an anthracene ring, an acenaphthylene ring, a naphthacene ring, Pyrene ring, indole ring, isoindole ring, benzofuran ring, benzothiophene ring, indolizine ring, benzoxazole ring, benzothiazole ring, benzimidazole ring, benzotriazole ring, purine ring, indazole ring, chromene ring, quinoline ring, isoquinoline Ring, quinolidine ring, quinazoline ring, cinnoline ring, quinoxaline ring, phthalazine ring, pteridine ring, carbazole ring, acridine ring,
It includes a phenanthridine ring, a xanthene ring, a phenazine ring, a phenothiazine ring, a phenoxatiin ring, a phenoxazine ring and a thianthrene ring. Preferred are a naphthalene ring, an azulene ring, an indole ring, a benzoxazole ring, a benzothiazole ring, a benzimidazole ring, a benzotriazole ring and a quinoline ring. The single bond in (b) is preferably a bond between carbon atoms of two aromatic rings. Two aromatic rings may be linked by two or more single bonds to form an aliphatic ring between the two aromatic rings. Further, two aromatic rings are bonded by a single bond of (b), and each aromatic ring is further bonded by a connecting group of (c), and an aliphatic ring or a non-aromatic ring is provided between the two aromatic rings. May form a heterocyclic ring.

The connecting group (c) is also preferably bonded to carbon atoms of two aromatic rings. The linking group is an alkylene group, alkenylene group, alkynylene group, -CO-, -O
-, -NH-, -S- or a combination thereof is preferred. Examples of the linking group consisting of a combination are shown below. Note that the left and right relationships in the following examples of the linking group may be reversed. c1: -CO-O-c2: -CO-NH-c3: -alkylene-O-c4: -NH-CO-NH-c5: -NH-CO-O-c6: -O-CO-O-c7: -O-alkylene-O-c8: -CO-alkenylene-c9: -CO-alkenylene-NH-c10: -CO-alkenylene-O-c11: -alkylene-CO-O-alkylene-O-CO
-Alkylene-c12: -O-alkylene-CO-O-alkylene-O-
CO-alkylene-O-c13: -O-CO-alkylene-CO-O-c14: -NH-CO-alkenylene- c15: -O-CO-alkenylene-

The aromatic ring and the linking group may have a substituent. Examples of the substituent include a halogen atom (F, C
l, Br, I), hydroxyl, carboxyl, cyano, amino, nitro, sulfo, carbamoyl, sulfamoyl, ureido, alkyl, alkenyl, alkynyl, aliphatic acyl, aliphatic acyloxy, alkoxy, alkoxycarbonyl , Alkoxycarbonylamino group, alkylthio group, alkylsulfonyl group, aliphatic amide group, aliphatic sulfonamide group, aliphatic substituted amino group, aliphatic substituted carbamoyl group, aliphatic substituted sulfamoyl group, aliphatic substituted ureido group and non-aromatic Group heterocyclic groups.

The alkyl group preferably has 1 to 8 carbon atoms. A chain alkyl group is preferable to a cyclic alkyl group, and a linear alkyl group is particularly preferable. The alkyl group may further have a substituent (eg, hydroxy, carboxy, alkoxy group, alkyl-substituted amino group). Examples of alkyl groups (including substituted alkyl groups) include methyl, ethyl, n-butyl, n-hexyl, 2-
Includes hydroxyethyl, 4-carboxybutyl, 2-methoxyethyl and 2-diethylaminoethyl.
The alkenyl group preferably has 2 to 8 carbon atoms. A chain alkenyl group is preferable to a cyclic alkenyl group, and a linear alkenyl group is particularly preferable. The alkenyl group may further have a substituent. Examples of the alkenyl group include vinyl, allyl and 1-hexenyl. The alkynyl group preferably has 2 to 8 carbon atoms. A chain alkynyl group is preferable to a cyclic alkynyl group, and a linear alkynyl group is particularly preferable. The alkynyl group may further have a substituent. Examples of the alkynyl group include ethynyl, 1-butynyl and 1-hexynyl.

The aliphatic acyl group has 1 to 10 carbon atoms.
It is preferable that Examples of the aliphatic acyl group include acetyl, propanoyl and butanoyl. The aliphatic acyloxy group preferably has 1 to 10 carbon atoms. Examples of the aliphatic acyloxy group include acetoxy. The alkoxy group preferably has 1 to 8 carbon atoms. The alkoxy group may further have a substituent (eg, an alkoxy group). Examples of alkoxy groups (including substituted alkoxy groups) include methoxy, ethoxy, butoxy and methoxyethoxy.
The alkoxycarbonyl group preferably has 2 to 10 carbon atoms. Examples of alkoxycarbonyl groups include:
Includes methoxycarbonyl and ethoxycarbonyl. The number of carbon atoms of the alkoxycarbonylamino group is 2
It is preferably from 10 to 10. Examples of the alkoxycarbonylamino group include methoxycarbonylamino and ethoxycarbonylamino.

The number of carbon atoms of the alkylthio group is 1 to 12
It is preferable that Examples of the alkylthio group include methylthio, ethylthio and octylthio. The alkylsulfonyl group preferably has 1 to 8 carbon atoms. Examples of the alkylsulfonyl group include methanesulfonyl and ethanesulfonyl. The aliphatic amide group preferably has 1 to 10 carbon atoms. Examples of the aliphatic amide group include acetamide. The aliphatic sulfonamide group preferably has 1 to 8 carbon atoms. Examples of the aliphatic sulfonamide group include methanesulfonamide, butanesulfonamide and n-octanesulfonamide. The aliphatic substituted amino group preferably has 1 to 10 carbon atoms. Examples of the aliphatic substituted amino group include dimethylamino, diethylamino and 2-carboxyethylamino. The number of carbon atoms of the aliphatic substituted carbamoyl group is 2 to
It is preferably 10. Examples of the aliphatic substituted carbamoyl group include methylcarbamoyl and diethylcarbamoyl. The aliphatic substituted sulfamoyl group preferably has 1 to 8 carbon atoms. Examples of the aliphatic substituted sulfamoyl group include methylsulfamoyl and diethylsulfamoyl. The aliphatic substituted ureido group preferably has 2 to 10 carbon atoms. Examples of the aliphatic substituted ureido group include methyl ureide. Examples of the non-aromatic heterocyclic group include piperidino and morpholino.

The molecular weight of the retardation enhancer is 30
It is preferably from 0 to 800. Specific examples of the retardation increasing agent include JP-A-2000-111914 and JP-A-2000-275434, PCT / JP
And the compounds described in WO 00/02619.

[Production of Cellulose Acetate Film]
The cellulose acetate film of the present invention is preferably produced by a solvent casting method. In the solvent casting method, a film is produced using a solution (dope) in which cellulose acetate is dissolved in an organic solvent. The organic solvent is a solvent selected from ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and halogenated hydrocarbons having 1 to 6 carbon atoms. It is preferable to include Ethers, ketones and esters may have a cyclic structure. Functional groups of ether, ketone and ester (i.e., -O
-, -CO-, and -COO-) can also be used as the organic solvent.
The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any one of the functional groups.

Examples of the ethers having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolan, tetrahydrofuran, anisole and phenetole. Examples of the ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone. 3 to 12 carbon atoms
Examples of the esters of include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate.
Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol. The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The ratio of halogen atoms substituted by halogen atoms in halogenated hydrocarbons is preferably 25 to 75 mol%, and 30 to 7 mol%.
0 mol% is more preferable, and 35 to 65 mol%
Is more preferable, and most preferably 40 to 60 mol%. Methylene chloride is a typical halogenated hydrocarbon. Two or more organic solvents may be used as a mixture.

The cellulose acetate solution can be prepared by a general method. The general method means that the treatment is performed at a temperature of 0 ° C. or higher (normal temperature or high temperature). The solution can be prepared using a dope preparation method and apparatus in a usual solvent casting method. In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly, methylene chloride) as the organic solvent. The amount of cellulose acetate is adjusted so that the resulting solution contains 10 to 40% by mass. More preferably, the amount of cellulose acetate is 10 to 30% by mass. In the organic solvent (main solvent), any additives described below may be added. Solution at room temperature (0-
(40 ° C.) to stir the cellulose acetate and the organic solvent. Highly concentrated solutions
Stirring may be performed under pressure and heating conditions. In particular,
The cellulose acetate and the organic solvent are put in a pressurized container and sealed, and the mixture is stirred while being heated under pressure to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 40 ° C. or higher, preferably 60 to
The temperature is 200 ° C, more preferably 80 to 110 ° C.

The components may be roughly mixed in advance and then placed in a container. Moreover, you may put in a container sequentially. The container must be configured to be able to stir. The container can be pressurized by injecting an inert gas such as nitrogen gas. Further, an increase in the vapor pressure of the solvent due to heating may be used.
Alternatively, each component may be added under pressure after the container is sealed. When heating, it is preferable to heat from outside the container. For example, a jacket-type heating device can be used. Alternatively, a plate heater may be provided outside the container, and the entire container may be heated by circulating the liquid through piping. It is preferable to provide a stirring blade inside the container and stir using the stirring blade. The stirring blade is preferably long enough to reach near the wall of the container. It is preferable to provide a scraping blade at the end of the stirring blade in order to renew the liquid film on the container wall. Instruments such as a pressure gauge and a thermometer may be installed in the container. Dissolve each component in the solvent in the container.
The prepared dope is taken out of the vessel after cooling, or is taken out and then cooled using a heat exchanger or the like.

The solution can be prepared by the cooling dissolution method. In the cooling dissolution method, cellulose acetate can be dissolved even in an organic solvent that is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent which can dissolve cellulose acetate by an ordinary dissolution method, the cooling dissolution method has an effect that a uniform solution can be obtained quickly. In the cooling dissolution method, first, cellulose acetate is gradually added to an organic solvent at room temperature while stirring. It is preferable to adjust the amount of cellulose acetate so that the mixture contains 10 to 40% by mass. More preferably, the amount of cellulose acetate is 10 to 30% by mass. Further, an optional additive described below may be added to the mixture.

Next, the mixture is heated at -100 to -10 ° C, preferably at -80 to -10 ° C, more preferably at -50 to-
Cool to 20C, most preferably -50 to -30C.
Cooling is performed, for example, in a dry ice / methanol bath (−75
° C) or a cooled diethylene glycol solution (-30 to-
20 ° C.). Upon such cooling, the mixture of cellulose acetate and the organic solvent solidifies. The cooling rate is preferably 4 ° C / min or more, more preferably 8 ° C / min or more, and most preferably 12 ° C / min or more. The cooling rate is preferably as high as possible, but the theoretical upper limit is 10,000 ° C./sec.
C / sec is a technical upper limit, and 100 C / sec is a practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at which the cooling is started and the final cooling temperature by the time from when the cooling is started to when the temperature reaches the final cooling temperature.

When the mixture is heated to 0 to 200 ° C., preferably 0 to 150 ° C., more preferably 0 to 120 ° C., and most preferably 0 to 50 ° C., the cellulose acetate dissolves in the organic solvent. The temperature may be raised only at room temperature or may be heated in a warm bath. The heating rate is
It is preferably at least 4 ° C./min, more preferably at least 8 ° C./min, most preferably at least 12 ° C./min. The heating rate is preferably as fast as possible,
000 ° C./sec is the theoretical upper limit, 1000 ° C./sec is the technical upper limit, and 100 ° C./sec is the practical upper limit. Note that the heating rate is a value obtained by dividing the difference between the temperature at which heating is started and the final heating temperature by the time from when the heating is started until the final heating temperature is reached. . As described above, a uniform solution is obtained. If the dissolution is insufficient, the operation of cooling and heating may be repeated. Whether or not the dissolution is sufficient can be determined only by visually observing the appearance of the solution.

In the cooling dissolution method, it is desirable to use a closed container in order to avoid water contamination due to condensation during cooling. Also, in the cooling and heating operation, pressurization during cooling,
By reducing the pressure during the heating, the dissolution time can be shortened. In order to perform pressurization and decompression, it is desirable to use a pressure-resistant container. According to differential scanning calorimetry (DSC), a 20% by mass solution of cellulose acetate (degree of acetylation: 60.9%, viscosity average polymerization degree: 299) dissolved in methyl acetate by a cooling dissolution method was 3%.
A pseudo phase transition point between the sol state and the gel state exists near 3 ° C., and below this temperature, the gel state becomes uniform. Therefore,
This solution must be maintained at a temperature equal to or higher than the pseudo phase transition temperature, preferably at a temperature of about 10 ° C. plus the gel phase transition temperature. However, the pseudo phase transition temperature varies depending on the acetylation degree of cellulose acetate, the viscosity average polymerization degree, the solution concentration, and the organic solvent used.

From the prepared cellulose acetate solution (dope), a cellulose acetate film is produced by a solvent casting method. The dope is cast on a drum or band and the solvent is evaporated to form a film. It is preferable to adjust the concentration of the dope before casting so that the solid content is 18 to 35% by mass. It is preferable that the surface of the drum or the band is finished in a mirror state. The casting and drying methods in the solvent casting method are described in U.S. Pat.
No. 603, No. 2492078, No. 2492977,
No. 2492978, No. 2607704, No. 2739
Nos. 069 and 2739070, British Patent 640731
Nos. 736892 and JP-B-45-455.
No. 4, No. 49-5614, JP-A-60-176834.
And JP-A-60-203430 and JP-A-62-115035. The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less.
After casting, it is preferable to dry by blowing on air for 2 seconds or more. The obtained film can be peeled off from the drum or band, and further dried with hot air having a temperature gradually changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in JP-B-5-17844. According to this method, the time from casting to stripping can be reduced. In order to carry out this method, it is necessary that the dope gels at the surface temperature of the drum or band during casting.

Using the prepared cellulose acetate solution (dope), a film can be formed by casting two or more layers. In this case, it is preferable to produce a cellulose acetate film by a solvent casting method. The dope is cast on a drum or band and the solvent is evaporated to form a film. The concentration of the dope before casting is preferably adjusted so that the solid content is 10 to 40%. It is preferable that the surface of the drum or the band is finished in a mirror state.

When casting a plurality of cellulose acetate solutions of two or more layers, a plurality of cellulose acetate solutions can be cast, and a plurality of cellulose acetate solutions can be cast from a plurality of casting ports provided at intervals in the traveling direction of the support. A film may be produced while casting and laminating a solution containing cellulose acetate, for example, JP-A-61-158414, JP-A-1-122419, JP-A-11-198285,
And the like. Alternatively, a film may be formed by casting a cellulose acetate solution from two casting ports.
562, JP-A-61-94724 and JP-A-61-9
No. 47245, Japanese Unexamined Patent Application Publication No.
It can be carried out by the method described in 1-158413 and JP-A-6-134933. Also, JP-A-56-16261
The cellulose acetate film casting method of wrapping a flow of the high-viscosity cellulose acetate solution described in No. 7 with a low-viscosity cellulose acetate solution and simultaneously extruding the high- and low-viscosity cellulose acetate solution may be used.

Alternatively, by using two casting ports, the film formed on the support is peeled off by the first casting port, and the second casting is performed on the side in contact with the support surface. A film may be prepared. For example, Japanese Patent Publication No. Sho 44-2
No. 0235. The cellulose acetate solution to be cast may be the same solution or different cellulose acetate solutions, and is not particularly limited.
In order to give a function to a plurality of cellulose acetate layers, a cellulose acetate solution according to the function may be extruded from each casting port. Further, in the present invention, the cellulose acetate solution can be simultaneously cast with other functional layers (for example, an adhesive layer, a dye layer, an antistatic layer, an antihalation layer, a UV absorbing layer, a polarizing layer, and the like). .

In the conventional monolayer liquid, it is necessary to extrude a high-concentration and high-viscosity cellulose acetate solution in order to obtain a necessary film thickness. In many cases, a problem occurred due to the occurrence of an object, a bump failure, or poor flatness. As a solution to this, by casting a plurality of cellulose acetate solutions from a casting port, it is possible to simultaneously extrude a high-viscosity solution onto a support, thereby improving flatness and producing an excellent planar film. Not only,
By using a concentrated cellulose acetate solution, a reduction in the drying load can be achieved, and the production speed of the film can be increased.

A plasticizer can be added to the cellulose acetate film in order to improve mechanical properties or to increase a drying speed. As a plasticizer,
Phosphate or carboxylate esters are used. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCC).
P) is included. Representative carboxylic esters are phthalic esters and citric esters. Examples of phthalate esters include dimethyl phthalate (DM
P), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethylhexyl phthalate (DEHP). Examples of citrate esters include O-acetyl triethyl citrate (OACT
E) and tributyl O-acetylcitrate (OACT
B) is included. Examples of other carboxylic esters include butyl oleate, methylacetyl ricinoleate,
It includes dibutyl sebacate and various trimellitate esters. Phthalate ester plasticizers (DMP, DE
P, DBP, DOP, DPP, DEHP) are preferably used. DEP and DPP are particularly preferred. The amount of the plasticizer added is preferably 0.1 to 25% by mass of the amount of the cellulose ester, more preferably 1 to 20% by mass, and most preferably 3 to 15% by mass.

The cellulose acetate film may contain a deterioration inhibitor (eg, an antioxidant, a peroxide decomposer, a radical inhibitor, a metal deactivator, an acid scavenger, and an amine). Regarding the deterioration inhibitor, see JP-A-3-19920.
No. 1, 5-1907073, 5-194789
And JP-A-5-271471 and JP-A-6-107854. The amount of the deterioration inhibitor to be added is preferably 0.01 to 1% by mass, more preferably 0.01 to 0.2% by mass of the solution (dope) to be prepared. When the addition amount is less than 0.01% by mass, the effect of the deterioration inhibitor is hardly recognized. If the addition amount exceeds 1% by mass, bleed-out (bleeding out) of the deterioration inhibitor on the film surface may be observed. Particularly preferred examples of the deterioration inhibitor include butylated hydroxytoluene (BHT) and tribenzylamine (TBA). The cellulose acetate film may contain polyester-urethane. Such polyester-urethanes are described in JP-A-5-19703.

[High Thermal Conductive Particles] Various high thermal conductive particles are used to improve the thermal conductivity of the cellulose acetate film. High thermal conductive particles include aluminum nitride, silicon nitride, boron nitride, magnesium nitride,
Examples thereof include silicon carbide, aluminum oxide, silicon oxide, zinc oxide, magnesium oxide, carbon, diamond, and metal. It is desirable to use transparent particles so as not to impair the transparency of the film. The amount of the high thermal conductive particles in the cellulose acetate film is
It is preferable to fill in the range of 5 to 50 parts by mass with respect to 100 parts by mass of cellulose acetate. If the compounding amount is less than 5 parts by mass, the improvement in heat conduction is poor, and filling more than 50 parts by mass is difficult in terms of productivity and makes the cellulose acetate film brittle. The average particle size of the high thermal conductive particles is 0.05 to 80 μm, preferably 0.1 to 1 μm.
0 μm is preferred. Spherical particles or needle-like particles may be used.

[Biaxial stretching] The cellulose acetate film of the present invention is preferably stretched in order to reduce virtual distortion. By stretching, virtual strain in the stretching direction can be reduced, and therefore, biaxial stretching is more preferable to reduce strain in all directions in the plane. In biaxial stretching, there are simultaneous biaxial stretching method and sequential biaxial stretching method,
From the viewpoint of continuous production, a sequential biaxial stretching method is preferable, after casting the dope, peeling off from a band or a drum,
After stretching in the width direction (longitudinal method), the longitudinal direction (width direction)
Stretched. Methods for stretching in the width direction include, for example, JP-A-62-115035, JP-A-4-152125,
4-284221, 4-298310, 11
-48271. The stretching of the film is performed at normal temperature or under heating conditions. The heating temperature is preferably equal to or lower than the glass transition temperature of the film. The film can be stretched by a treatment during drying, and is particularly effective when a solvent remains. In the case of stretching in the longitudinal direction, for example, the film is stretched by adjusting the speed of a film transport roller so that the film winding speed is higher than the film peeling speed. In the case of stretching in the width direction, the film can also be stretched by transporting the film while holding it with a tenter and gradually increasing the width of the tenter. After drying the film, the film can be stretched using a stretching machine (preferably, uniaxial stretching using a long stretching machine). The stretching ratio of the film (ratio of increase by stretching to the original length) is preferably 5 to 50%, more preferably 10 to 40%, and most preferably 1 to 50%.
5 to 35%.

The steps from casting to post-drying may be performed in an air atmosphere or in an atmosphere of an inert gas such as nitrogen gas. The winding machine related to the production of the cellulose acetate film of the present invention may be a commonly used winding method such as a constant tension method, a constant torque method, a taper tension method, and a program tension control method with a constant internal stress. Can be wound up.

[Protective Layer] In the present invention, the protective layer provided on one surface of the triacetyl cellulose film may be peelable or substantially non-peelable. Here, "substantially non-peelable" means that the triacetyl cellulose film and / or the protective layer cannot be peeled without destruction.

When the peelable protective layer is coated with a film-forming resin that dissolves in a solution that does not swell the triacetyl cellulose film and then dried, or when a curable resin solution is applied and cured, an adhesive film having an adhesive layer is used. May be provided by any method, such as laminating a triacetyl cellulose film and an incompatible resin by co-extrusion. It must be a layer to be obtained.

Examples of the material of the protective layer that can be used in the present invention include polyethylene, polypropylene,
Polyvinyl chloride, polyester, polymethylpentene,
Examples include polyphenylene sulfide and fluoro resin.

When an adhesive film is used, it may be peeled off immediately after the saponification treatment, or
It may be peeled off after it has been completed as a final form (adhesive coated product, reflective plate bonded product, etc.). As the adhesive film, any film can be used as long as the surface of the triacetyl cellulose film is resistant to alkali to the extent that it is not affected by the saponification treatment and can be peeled off after the saponification treatment. However, when high heat is required in the process after saponification, it is necessary to have the required heat resistance unless it is peeled off before heat treatment. As an adhesive,
Rubber-based, acrylic-based, and silicone-based adhesives can be used.

Using various acetylcellulose films obtained as described above, only one side of which is saponified, an alignment layer is provided on the saponified side, and rubbing treatment is performed if necessary. An optically anisotropic layer made of a compound is provided. When bonding the protective layer to the polarizing film, the protective layer is peeled off and then bonded to the polarizing film by a known method. At that time, it is preferable from the viewpoint of adhesiveness that the peeled cellulose acetate surface is saponified and then the polarizing film is bonded. In particular,
The saponification treatment of the acetylcellulose film is performed to the extent necessary for lamination with the polarizing film (time for immersion in alkali, temperature of alkali solution, same concentration). Thereafter, a polarizing film is bonded to the treated surface of the triacetyl cellulose film by a known method to obtain a polarizing plate.

[Saponification Treatment] From the viewpoint of maintaining the flatness of the film, the temperature of the cellulose acetate film in these treatments is preferably set to Tg or lower, specifically 150 ° C. or lower. It is particularly preferable to carry out an acid treatment or an alkali treatment, that is, a saponification treatment for cellulose acetate. The surface energy is preferably 55 mN / m or more, and 60 mN / m or more and 75 mN / m.
m is more preferable. Hereinafter, an alkali saponification treatment will be described as an example. After the film surface is immersed in an alkaline solution, it is preferably neutralized with an acidic solution, washed with water and dried. Examples of the alkaline solution include a potassium hydroxide solution and a sodium hydroxide solution, and the specified concentration of hydroxide ion is 0.1N to 3.0N.
It is preferably 0N, more preferably 0.5N to 2.0N. Alkaline solution temperature is from room temperature to 9
The range of 0 ° C is preferable, and 40 ° C to 70 ° C is more preferable. Surface energy of solids
(Published by Realize Inc., 1989.12.10), it can be determined by a contact angle method, a wet heat method, and an adsorption method. In the case of the cellulose acetate film of the present invention, it is preferable to use the contact angle method. Specifically, two types of solutions whose surface energies are known are dropped on a cellulose acetate film. The angle containing the drop is defined as the contact angle, and the surface energy of the film can be calculated by calculation.

[Liquid Crystal Compound] The liquid crystal compound used in the present invention may be a rod-shaped liquid crystal or a discotic liquid crystal. Includes those that no longer have the property. Preferable examples of the rod-shaped liquid crystal are disclosed in
No. 00-304932, paragraphs 0016 to 0033 can be referred to, and specific examples thereof include (N1) to (N47). The most preferred liquid crystalline compound used in the present invention is a discotic liquid crystal.

Examples of the discotic liquid crystal of the present invention include C.I. Destrade et al., Mol. Cr
yst. 71, p. 111 (1981); Destrade et al., Mol. Cryst. 122, 141 pages (198
5 years), Physics lett, A, Vol. 78, 82
Truxene derivatives described on page (1990),
B. Research report by Kohne et al., Angew. Chem.
Vol. 96, p. 70 (1984) and cyclohexane derivatives described in J. Am. M. Lehn et al., J. Am. C
hem. Commun. , P. 1794 (1985),
J. Research report by Zhang et al. Am. Chem. S
oc. 116, p. 2655 (1994). The discotic liquid crystal has a structure in which these are generally used as a core of a molecular center, and a linear alkyl group, an alkoxy group, a substituted benzoyloxy group, or the like is radially substituted as the linear chain.
Shows liquid crystal properties. However, the molecule itself has negative uniaxiality,
It is not limited to the above description as long as it can give a certain orientation. In the present invention, the term "formed from a discotic compound" does not mean that the final product is required to be the compound. For example, the low-molecular discotic liquid crystal has a group that reacts with heat, light, or the like. As a result, those which are polymerized or cross-linked by reaction with heat, light, or the like to have a high molecular weight and lose liquid crystallinity are also included. Preferred examples of the discotic liquid crystal are described in JP-A-8-50206.

The optically anisotropic layer of the present invention is a layer having a negative birefringence made of a compound having a discotic structural unit, and the surface of the discotic structural unit is inclined with respect to the transparent support surface, and It is preferable that the angle between the surface of the discotic structural unit and the surface of the transparent support changes in the depth direction of the optically anisotropic layer.

The angle (tilt angle) of the surface of the discotic structure unit generally increases or decreases in the depth direction of the optically anisotropic layer and as the distance from the bottom surface of the optically anisotropic layer increases. Preferably, the angle of inclination increases with increasing distance. Further, as the change of the inclination angle, a continuous increase, a continuous decrease, an intermittent increase, an intermittent decrease, a change including the continuous increase and the continuous decrease, and an intermittent change including the increase and the decrease may be cited. it can. The intermittent change includes a region where the inclination angle does not change in the thickness direction. It is preferable that the inclination angle increases or decreases as a whole, even if it includes a region that does not change. Further, the inclination angle is preferably increased as a whole, and is particularly preferably changed continuously.

In general, the optically anisotropic layer is formed by applying a solution in which a discotic compound and another compound are dissolved in a solvent onto an orientation film, drying the solution, and then heating the solution to a discotic nematic phase formation temperature. It is obtained by cooling while maintaining the discotic nematic phase). Alternatively, the optically anisotropic layer is formed by applying a solution in which a discotic compound and another compound (for example, a polymerizable monomer and a photopolymerization initiator) are dissolved in a solvent onto an alignment film, drying, and then discotic nematic It is obtained by heating to a phase formation temperature, polymerizing (by irradiation with UV light or the like), and further cooling. The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystalline compound used in the present invention is 70 to 70.
300 ° C is preferable, and 70 to 170 ° C is particularly preferable.

For example, the tilt angle of the discotic unit on the support side can be generally adjusted by selecting a discotic compound or a material of an alignment film, or by selecting a rubbing treatment method. In addition, for the tilt angle of the discotic unit on the surface side (air side), a discotic compound or another compound (eg, a plasticizer, a surfactant, a polymerizable monomer and a polymer) to be used together with the discotic compound is generally selected. Can be adjusted. Further, the degree of change of the inclination angle can be adjusted by the above selection.

The plasticizer, surfactant and polymerizable monomer are compatible with the discotic compound.
Any compound can be used as long as it can change the tilt angle of the liquid crystalline discotic compound or does not hinder the alignment. Among these, a polymerizable monomer (eg, a compound having a vinyl group, a vinyloxy group, an acryloyl group, and a methacryloyl group) is preferable.
The above compounds are generally used in an amount of 1 to 50% by mass (preferably 5 to 30% by mass) based on the discotic compound.

As the polymer, any polymer can be used as long as it has compatibility with the discotic compound and can change the tilt angle of the liquid crystalline discotic compound. Examples of the polymer include a cellulose ester. Preferred examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, hydroxypropylcellulose and cellulose acetate butyrate. The polymer is generally 0.1 to 10% by mass (preferably 0.1 to 8% by mass, particularly 0.1 to 5% by mass) based on the discotic compound so as not to hinder the alignment of the liquid crystalline discotic compound. ). The thickness of the optically anisotropic layer is 0.1 to 20 (in the case where a plurality of optically anisotropic layers are provided, each independently).
μm, more preferably 0.5 to 15 μm, and most preferably 1 to 10 μm.

The optical compensation sheet of the present invention is an optical compensation sheet comprising a cellulose acetate film, an alignment film (alignment layer) provided thereon, and a discotic liquid crystal formed on the alignment film (alignment layer). A rubbed film composed of a polymer in which the alignment film is crosslinked is preferable. Here, the orientation film is synonymous with the orientation layer.

[Alignment Film] The alignment film used in the present invention is preferably composed of two kinds of crosslinked polymers. Any polymer cross-linked by a cross-linking agent can be used, even if the at least one polymer is a cross-linkable polymer itself. The alignment film is formed by reacting a polymer having a functional group or a polymer obtained by introducing a functional group into the polymer by light, heat, a change in pH, or the like; It can be formed by introducing a bonding group derived from a cross-linking agent between polymers by using an agent and cross-linking between the polymers.

Such crosslinking is usually carried out by applying a coating solution containing the above-mentioned polymer or a mixture of the polymer and the crosslinking agent on a transparent support, followed by heating or the like. As long as durability can be ensured, crosslinking treatment may be performed at any stage after coating the alignment film on the transparent support until obtaining the final optical compensation sheet. Considering the orientation of the compound having a disc-shaped structure (optically anisotropic layer) formed on the alignment film, it is also preferable to perform sufficient crosslinking after the compound having the disc-shaped structure is oriented. That is, on a transparent support,
When a coating solution containing a polymer and a cross-linking agent capable of cross-linking the polymer is applied, it is heated and dried (generally, cross-linking is performed. Rubbing treatment is performed to form an alignment film,
Next, a coating solution containing a compound having a disc-shaped structural unit is applied on the alignment film, heated to a temperature higher than a discotic nematic phase formation temperature, and then cooled to form an optically anisotropic layer.

The polymer used for the alignment film of the present invention is:
Either a polymer crosslinkable by itself or a polymer crosslinked by a crosslinking agent can be used. Of course, some polymers are both possible. Examples of the polymer include polymethyl methacrylate, acrylic acid / methacrylic acid copolymer, styrene / maleimide copolymer, polyvinyl alcohol and modified polyvinyl alcohol, poly (N-methylol acrylamide), styrene / vinyl toluene copolymer , Chlorosulfonated polyethylene,
Nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, ethylene / vinyl acetate copolymer, carboxymethyl cellulose, polymers such as polyethylene, polypropylene and polycarbonate, and silane coupling agents Compounds can be mentioned. Examples of preferred polymers are water-soluble polymers such as poly (N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinyl alcohol and modified polyvinyl alcohol, and further preferred are gelatin, polyvinyl alcohol and modified polyvinyl alcohol. Bill alcohol and modified polyvinyl alcohol can be mentioned.

Among the above polymers, polyvinyl alcohol
Or modified polyvinyl alcohol is preferred,
Different polyvinyl alcohol or modified polyvinyl alcohol
It is most preferable to use two kinds of tools in combination. Polyvinyl
As the alcohol, for example, one having a saponification degree of 70 to 100%
And generally has a degree of saponification of 80 to 100%,
More preferably, it has a saponification degree of 85 to 95%. polymerization
The degree is preferably in the range of 100 to 3000. Strange
Copolymerizable polyvinyl alcohol
(As modifying groups, for example, COONa, Si (O
X)_Three, N (CH_Three)_Three・ Cl, C₉H₁₉COO, SO_Three,
NaC₁₂H_{twenty five}Are denatured by chain transfer.
(For example, COONa, SH, C
₁₂H_{twenty five}Etc.), modification by block polymerization
(Modifying groups such as COOH, CON
H_Two, COOR, C₆H _FiveEtc. are introduced)
And modified alcohols. these
In unmodified to modified polyvinyl having a saponification degree of 80 to 100%
Alcohol, more preferably a saponification degree of 85 to 95%
Of unmodified or alkylthio-modified polyvinyl alcohol
It is.

As the modified polyvinyl alcohol, in particular,
The following general formula (1):

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(Where R ¹ represents an unsubstituted alkyl group or an acryloyl group, a methacryloyl group or an alkyl group substituted with an epoxy group, W represents a halogen atom, an alkyl group or an alkoxy group, X represents an active ester, Represents the group of atoms necessary to form an acid anhydride and an acid halide, p represents 0 or 1, and n represents an integer of 0 to 4) with a polyvinyl alcohol Are preferred. The reactant (specific modified polyvinyl alcohol) further has the following general formula (2):

[0063]

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(Where X ¹ represents an atom group necessary for forming an active ester, an acid anhydride and an acid halide, and m represents an integer of 2 to 24) and polyvinyl. Reactants with alcohols are preferred.

The polyvinyl alcohol used for reacting with the compounds represented by the general formulas (1) and (2) includes the unmodified polyvinyl alcohol and the copolymer-modified polyvinyl alcohol, ie, chain transfer. And modified products of polyvinyl alcohol such as those modified by block polymerization. Preferred examples of the specific modified polyvinyl alcohol include the following compounds. These are described in detail in the specification of Japanese Patent Application No. 7-20583.

Methods for synthesizing these polymers, measuring the visible absorption spectrum, and determining the introduction ratio y are described in Japanese Patent Application Laid-Open No.
There is a detailed description in JP-A-338913.

Specific examples of the cross-linking agent used together with the above-mentioned polymer such as polyvinyl alcohol include the following. These are water-soluble polymers, especially polyvinyl alcohol and modified polyvinyl alcohol (the above-mentioned specific modified product). Is also preferable. Specific examples of the crosslinking agent include, for example, aldehydes (eg, formaldehyde, glyoxal and glutaraldehyde), N-methylol compounds (eg, dimethylol urea and methylol dimethylhydantoin), dioxane derivatives (eg, 2,3-dihydroxy dioxane), carboxyl Compounds that act by activating groups (eg, carbenium, 2-naphthalenesulfonate, 1,1-bispyrrolidino-1-chloropyridinium and 1-morpholinocarbonyl-3- (sulfonatoaminomethyl)),
Active vinyl compounds (eg, 1,3,5-triacloyl-
Hexahydro-s-triazine, bis (vinylsulfone) methane and N, N'-methylenebis- [β- (vinylsulfonyl) propionamide]), active halogen compounds (eg, 2,4-dichloro-6-hydroxy-S-) Triazine), isoxazoles, dialdehyde starch and the like. These can be used alone or in combination. In consideration of productivity, the use of aldehydes having high reaction activity, particularly glutaraldehyde, is preferred.

The cross-linking agent is not particularly limited, and the addition amount of the cross-linking agent tends to be improved when it is added in terms of moisture resistance. However, since the alignment ability as an alignment film is reduced when it is added in excess of 50% by mass with respect to the polymer, the content is preferably 0.1 to 20% by mass, particularly preferably 0.5 to 15% by mass.
% By mass is preferred. The alignment film used in the present invention contains a certain amount of the unreacted crosslinking agent even after the crosslinking reaction is completed, but the amount of the crosslinking agent is 1.0% in the alignment film.
It is preferably at most 0.5% by mass, particularly preferably at most 0.5% by mass. If the cross-linking agent is contained in the alignment film in an amount exceeding 1.0 mass, sufficient durability cannot be obtained. That is, when used in a liquid crystal display device, long-term use,
Or, if left for a long time in an atmosphere of high temperature and high humidity,
Reticulation may occur.

The alignment film used in the present invention is subjected to a rubbing treatment by applying a coating solution containing the above-mentioned polymer as a material for forming an alignment film and a cross-linking agent onto a transparent support, followed by heating and drying, and simultaneously cross-linking. Can be formed. The cross-linking reaction can be carried out at any time after coating on the transparent support. When using a water-soluble polymer such as the polyvinyl alcohol as the alignment film forming material, the coating liquid is preferably a mixed solvent of an organic solvent such as methanol having a defoaming effect and water,
The ratio of water: methanol is 0: 100-9 by mass ratio.
9: 1 is common and preferably 0: 100 to 91: 9. Thereby, generation of bubbles is suppressed, and defects on the alignment film and further on the surface of the optically anisotropic layer are significantly reduced. The coating method includes spin coating, dip coating, curtain coating, extrusion coating, bar coating, and E coating.
A mold coating method can be used. In particular, the E-type coating method is preferable. The thickness is preferably from 0.1 to 10 μm. Heating and drying can be performed at 20 ° C to 110 ° C. In order to form sufficient crosslinking, the temperature is preferably from 60 ° C to 100 ° C, particularly preferably from 80 ° C to 100 ° C. Drying time is 1
This can be done in minutes to 36 hours. Preferably, it is 5 minutes to 30 minutes. The pH is also preferably set to an optimum value for the cross-linking agent to be used. When glutaraldehyde is used, the pH is preferably 4.5 to 5.5, particularly preferably 5.

The alignment film is provided on a transparent support. The orientation film can be obtained by subjecting the surface to rubbing after crosslinking the polymer layer as described above. The alignment film functions to define the alignment direction of the liquid crystalline discotic compound provided thereon.

For the rubbing treatment, a treatment method widely used as a liquid crystal alignment treatment step for LCD can be used. That is, a method of rubbing the surface of the alignment film in a certain direction using paper, gauze, felt, rubber, nylon, polyester fiber or the like to obtain the alignment can be used. Generally, rubbing is performed about several times using a cloth or the like in which fibers having a uniform length and thickness are planted on average.

[Polarizing Plate] The polarizing plate comprises a polarizing film and two transparent protective films disposed on both sides thereof. As one protective film, the above-mentioned cellulose acetate film can be used. As the other protective film, a normal cellulose acetate film may be used. Further, it is preferable that an antireflection layer is provided on the surface of the cellulose acetate film. The polarizing film includes an iodine-based polarizing film, a dye-based polarizing film using a dichroic dye, and a polyene-based polarizing film. The iodine-based polarizing film and the dye-based polarizing film are generally manufactured using a polyvinyl alcohol-based film. It is preferable that the slow axis of the cellulose acetate film and the transmission axis of the polarizing film are arranged substantially in parallel.

The moisture permeability of the protective film is important for the productivity of the polarizing plate. The polarizing film and the protective film are bonded together with an aqueous adhesive, and the adhesive solvent is dried by diffusing in the protective film. The higher the moisture permeability of the protective film, the faster the drying and the higher the productivity. , The polarization ability is reduced. The moisture permeability of the optical compensation sheet is determined by the thickness, free volume, hydrophilicity / hydrophobicity and the like of the polymer film and the polymerizable liquid crystal compound. When used as a protective film for a polarizing plate, the moisture permeability is 100 to 1000 g / m ² · 2.
4 hrs, preferably 300 to 700 g / m
It is more preferably ² · 24hrs. In the case of film formation, the thickness of the optical compensation film can be adjusted by the lip flow rate and the line speed, or by stretching and compression. Since the moisture permeability differs depending on the main material to be used, it is possible to adjust the thickness to a preferred range. The free volume of the optical compensation film can be adjusted by the drying temperature and time in the case of film formation. Also in this case, since the moisture permeability differs depending on the main material used, it is possible to adjust the free volume to a preferable range. The hydrophilicity / hydrophobicity of the optical compensation film can be adjusted by an additive. By adding a hydrophilic additive to the above-mentioned free volume, the moisture permeability increases, and conversely, by adding a hydrophobic additive, the moisture permeability can be reduced. By independently controlling the moisture permeability, a polarizing plate having optical compensation ability can be manufactured at low cost and with high productivity.

[Liquid crystal display device] The optical compensation sheet comprising the above-mentioned cellulose acetate film or the polarizing plate using the above-mentioned cellulose acetate film is advantageously used for a liquid crystal display device, especially for a transmission type liquid crystal display device.
The transmission type liquid crystal display device includes a liquid crystal cell and two polarizing plates disposed on both sides of the liquid crystal cell. A liquid crystal cell carries a liquid crystal between two electrode substrates. One optical compensation sheet is provided between the liquid crystal cell and one of the polarizing plates, or two optical compensation sheets are provided between the liquid crystal cell and both of the polarizing plates. T
In an N-mode liquid crystal cell, rod-like liquid crystalline molecules are substantially horizontally aligned when no voltage is applied, and further twist-aligned at 60 to 120 °. The TN mode liquid crystal cell has a color TF
It is most frequently used as a T liquid crystal display device, and is described in many documents. In a VA mode liquid crystal cell, rod-like liquid crystalline molecules are substantially vertically aligned when no voltage is applied.

The VA mode liquid crystal cell includes (1) a VA mode liquid crystal cell in a narrow sense in which rod-like liquid crystal molecules are aligned substantially vertically when no voltage is applied and substantially horizontally when voltage is applied. Japanese Unexamined Patent Publication No. Hei 2-176625),
(2) A liquid crystal cell (SID97, Dige) in which the VA mode is multi-domain (in the MVA mode) to enlarge the viewing angle
st of tech. Papers 28 (1997) 845
Description), (3) a liquid crystal cell (n-ASM mode) in which rod-like liquid crystal molecules are substantially vertically aligned when no voltage is applied, and twisted multi-domain alignment when voltage is applied (Preliminary Collection 58- 59 (1998)) and (4) SURVAIVAL mode liquid crystal cell (LC
D International 98).

The OCB mode liquid crystal cell is a liquid crystal display device using a bend alignment mode liquid crystal cell in which rod-like liquid crystal molecules are substantially (symmetrically) aligned in upper and lower directions of the liquid crystal cell. And disclosed in U.S. Pat. Nos. 4,583,825 and 5,410,422. Since the rod-like liquid crystal molecules are symmetrically aligned at the upper and lower portions of the liquid crystal cell, the bend alignment mode liquid crystal cell has a self-optical compensation function. Therefore, this liquid crystal mode is OCB
(Optically Compensatory Bend) Also called liquid crystal mode. The bend alignment mode liquid crystal display device has an advantage that the response speed is high. In a TN mode liquid crystal cell, rod-like liquid crystal molecules are substantially horizontally aligned when no voltage is applied, and further twisted at 60 to 120 °.

[0077]

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to the examples and is not interpreted.

Example 1 The following composition was placed in a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acetate solution.

(Composition of Cellulose Acetate Solution) 100 parts by mass of cellulose acetate having a degree of acetylation of 60.9% Triphenyl phosphate (plasticizer) 7.8 parts by mass Biphenyl diphenyl phosphate (plasticizer) 3.9 parts by mass Methylene chloride (No. 1 solvent) 300 parts by weight Methanol (second solvent) 54 parts by weight 1-butanol (third solvent) 11 parts by weight

Into another mixing tank, 16 parts by mass of the following retardation increasing agent, 80 parts by mass of methylene chloride and 20 parts by mass of methanol were added, and the mixture was stirred while heating to prepare a retardation increasing solution.
25 parts by mass of the prepared retardation increasing solution was mixed with 474 parts by mass of the cellulose acetate solution, and the mixture was sufficiently stirred to prepare a dope. The addition amount of the retardation increasing agent is based on 100 parts by mass of cellulose acetate.
It was 3.5 parts by mass.

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The obtained dope was cast using a band casting machine. After the film surface temperature on the band became 40 ° C., it was dried for 1 minute and peeled off.
A cellulose acetate film (thickness: 50 μm) having a residual solvent amount of 0.3% by mass was produced. The optical properties of the produced cellulose acetate film (CAF-01) were measured. The results are shown in Table 1. The optical characteristics were measured using an ellipsometer (M-150, JASCO Corporation)
Re) and Rth retardation values at a wavelength of 550 nm were measured.

One side of the produced cellulose acetate film was applied to a film manufactured by Sanei Kaken (SAT-106TS).
And a 2.0 N potassium hydroxide solution (25
℃) for 2 minutes, neutralized with sulfuric acid, washed with pure water,
Dried. When the surface energy of the non-laminated cellulose acetate film was determined by a contact angle method, it was 63 mN / m. On this unlaminated cellulose acetate film, a coating solution having the following composition was applied for 28 m using a # 16 wire bar coater.
1 / m ^{2 was} applied. 60 seconds with warm air at 60 ° C, 90 seconds
The film was dried with warm air of 150 ° C. for 150 seconds to form a film. Next, a rubbing treatment was performed on the formed film in a direction parallel to the longitudinal direction of the cellulose acetate film to obtain a cellulose acetate film with an alignment film.

(Composition of Alignment Layer Coating Solution) The following modified polyvinyl alcohol 10 parts by mass Water 371 parts by mass Methanol 119 parts by mass Glutaraldehyde (crosslinking agent) 0.5 part by mass

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(Formation of Optically Anisotropic Layer) On the alignment film, 41.01 g of the following discotic (liquid crystalline) compound, ethylene oxide modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.) ) 4.06 g, cellulose acetate butyrate (CAB551-0.
2, 0.90 g of Eastman Chemical Co., Ltd., 0.23 g of cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemical Co.), 1.35 g of photopolymerization initiator (Irgacure 907, Ciba Geigy), sensitization (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) 0.4
A coating solution in which 5 g was dissolved in 102 g of methyl ethyl ketone was applied using a # 3.6 wire bar. This is 13
The mixture was heated in a constant temperature zone of 0 ° C. for 2 minutes to orient the discotic compound. Next, UV irradiation was performed for 1 minute using a 120 W / cm high pressure mercury lamp in an atmosphere of 60 ° C. to polymerize the discotic compound. Then, it was left to cool to room temperature. In this way,
Forming an optically anisotropic layer, an optical compensation sheet (KH-01)
Was prepared. The Re retardation value of the optically anisotropic layer measured at a wavelength of 546 nm was 43 nm. The angle (tilt angle) between the disk surface and the first transparent support surface was 42 ° on average.

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Example 2 The following composition was charged into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acetate solution.

(Cellulose Acetate Solution Composition) 100 parts by mass of cellulose acetate having an acetylation degree of 60.9% triphenyl phosphate (plasticizer) 7.8 parts by mass biphenyl diphenyl phosphate (plasticizer) 3.9 parts by mass methylene chloride 1 solvent) 300 parts by weight Methanol (second solvent) 54 parts by weight 1-butanol (third solvent) 11 parts by weight

A separate mixing tank was charged with 16 parts by mass of the above-mentioned retardation increasing agent, 80 parts by mass of methylene chloride and 20 parts by mass of methanol, and stirred with heating to prepare a retardation increasing agent solution.
25 parts by mass of a retardation increasing solution was mixed with 474 parts by mass of the cellulose acetate solution, and the mixture was sufficiently stirred to prepare a dope. The addition amount of the retardation enhancer
The amount was 5.5 parts by mass based on 100 parts by mass of cellulose acetate.

The obtained dope was cast using a band casting machine. A film having a residual solvent content of 15% by mass
Under a condition of 0 ° C., the film was horizontally stretched at a stretch ratio of 25% using a tenter to obtain a cellulose acetate film (CAF-0).
2) was manufactured. For the prepared CAF-02, the Re retardation value and the Rth retardation value at a wavelength of 550 nm were measured using an ellipsometer (M-150, manufactured by JASCO Corporation). The results are shown in Table 1.

[0092]

[Table 1]

Further, 100 points of the film thickness of 1 square meter (1 m × 1 m) of the produced CAF-02 were measured using a digital film thickness meter (K-402B manufactured by Anritsu). The average value is 102.0 μm and the standard deviation is 1.5
μm. Example 1 was obtained for the obtained CAF-02.
After laminating with a film manufactured by Sanei Kaken as in
A saponification treatment was performed to provide an alignment film. Next, a rubbing treatment was performed in the direction of 45 ° with respect to the slow axis (measured at a wavelength of 632.8 nm) of the cellulose acetate film to obtain a cellulose acetate film with an alignment film.

(Formation of Optically Anisotropic Layer) On this alignment film,
41.01 g of the discotic (liquid crystal) compound, 4.06 g of ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.),
Cellulose acetate butyrate (CAB551-0.
2, 0.90 g of Eastman Chemical Co., Ltd., 0.23 g of cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemical Co.), 1.35 g of photopolymerization initiator (Irgacure 907, Ciba Geigy), sensitization (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) 0.4
A coating solution of 5 g dissolved in 102 g of methyl ethyl ketone was applied with a # 3 wire bar. This was attached to a metal frame and heated in a thermostat at 130 ° C. for 2 minutes to orient the discotic compound. Next, at 130 ° C., 120 W /
UV irradiation was performed for 1 minute using a cm high-pressure mercury lamp to polymerize the discotic compound. Then, it was left to cool to room temperature. Thus, the optical compensation sheet with an optically anisotropic layer (KH-0)
2) was formed. This KH-02 has a wavelength of 546n.
The Re retardation value of the optically anisotropic layer measured by m was 38 nm. The angle (tilt angle) between the disk surface and the first transparent support surface was 40 ° on average.

Comparative Example 1 An optical compensation film (KH-H1) was prepared in the same manner as in Example 1 except that the following undercoating was performed instead of the alkali saponification treatment.

(Preparation of Undercoat Layer) A coating solution having the following composition was applied to the above cellulose acetate film (CAF-01) for 2 minutes.
8 cc / m ^{2 was} applied and dried to provide a 0.1 μm gelatin layer. Gelatin 0.542 parts by weight Formaldehyde 0.136 parts by weight Salicylic acid 0.160 parts by weight Acetone 39.1 parts by weight Methanol 15.8 parts by weight Methylene chloride 40.6 parts by weight Water 1.2 parts by weight

Further, 7 cc of a coating solution having the following composition
/ M ^{2 and} dried. The following anionic copolymer (x: y: z = 50/25/25) 0.079 part by mass Monoethyl citrate 1.01 part by mass Acetone 20 parts by mass Methanol 87.7 parts by mass Water 4.05 parts by mass

[0098]

Embedded image

Further, a coating solution having the following composition was applied to the layer on the side opposite to that described above at 25 cc / m ^{2 and} dried to form a back layer. Cellulose diacetate (degree of acetylation: 55%) 0.656 parts by mass Silica-based matting agent (average particle size: 1μ) 0.065 parts by mass Acetone 67.9 parts by mass Methanol 10.4 parts by mass

[Embodiment 3] KH-0 prepared in Embodiment 1
After peeling off the film manufactured by Sunei Kaken No. 1, alkali saponification treatment (immersion in 2.0 N NaOH at 55 ° C. for 2 minutes) (KH-01S). Iodine is adsorbed on the stretched polyvinyl alcohol film to form a polarizing film, and the above-described KH-01 is formed using a polyvinyl alcohol-based adhesive.
S was attached to one side of the polarizing film so that CAF-01 was on the polarizing film side. Commercially available cellulose triacetate film (Fujitac TD80UF, Fuji Photo Film Co., Ltd.)
Was subjected to a saponification treatment, and attached to the opposite side of the polarizing film using a polyvinyl alcohol-based adhesive. The transmission axis of the polarizing film and the slow axis of KH-01S were arranged in parallel. Thus, a polarizing plate was produced.

Embodiment 4 Embodiment 3 is different from Embodiment 3 in Embodiment 1.
KH-01 prepared in Example 2 was replaced with KH-02 prepared in Example 2.
A polarizing plate was produced in the same manner as in Example 3, except that CAF-02 was on the polarizing film side and the slow axis was attached to one side such that the slow axis was at 45 ° to the transmission axis of the polarizing film. .

Comparative Example 2 A polarizing film was prepared by adsorbing iodine on a stretched polyvinyl alcohol film, and KH-H1 prepared in Comparative Example 1 was prepared using a polyvinyl alcohol-based adhesive in the same manner as in Example 3. CAF-01 is on the polarizing film side, and its slow axis is
It was stuck on one side so as to be 5 °. A commercially available cellulose triacetate film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) was subjected to a saponification treatment, and affixed to the opposite side of the polarizing film using a polyvinyl alcohol-based adhesive. Thus, a polarizing plate was produced.

Example 5 A pair of polarizing plates provided in a liquid crystal display device (6E-A3, manufactured by Sharp Corporation) using a TN type liquid crystal cell was peeled off, and the polarized light produced in Example 3 was used instead. The plates were adhered one by one to the observer side and the backlight side via an adhesive so that KH-01 was on the liquid crystal cell side. The transmission axis of the polarizing plate on the observer side and the transmission axis of the polarizing plate on the backlight side were arranged so as to be in the O mode. About the manufactured liquid crystal display device, a measuring device (E
Using a Z-Contrast 160D (manufactured by ELDIM), the viewing angle was measured in eight steps from black display (L1) to white display (L8). At the same time, it was also evaluated. The results are shown in Table 2.

[0104]

[Table 2]

The black-side gradation inversion is an inversion between L1 and L2. Regarding the light leakage when the backlight is turned on, mount the backlight on a 20-inch sharp TV in the same manner as in Example 5, turn on the backlight continuously for 5 hours at room temperature and normal humidity, and then change the entire black display state to a dark room. It was evaluated visually.

Example 6 (Preparation of Bend Alignment Liquid Crystal Cell) A polyimide film was provided as an alignment film on a glass substrate with an ITO electrode, and the alignment film was subjected to a rubbing treatment. The two glass substrates thus obtained were placed so that the rubbing directions were parallel to each other, and the cell gap was set to 6 μm. Δn is 0.13 in the cell gap
96 liquid crystal compounds (ZLI1132, manufactured by Merck Ltd.) were injected to prepare bend alignment liquid crystal cells.

Two elliptically polarizing plates produced in Example 4 were attached so as to sandwich the produced bend alignment cell. The optically anisotropic layer of the elliptically polarizing plate was arranged so as to face the cell substrate, and the rubbing direction of the liquid crystal cell was antiparallel to the rubbing direction of the optically anisotropic layer facing the cell substrate. 55H for liquid crystal cell
A rectangular wave voltage of z was applied. A normally white mode of 2 V for white display and 5 V for black display was set. The ratio of transmittance (white display / black display) is defined as the contrast ratio, and is measured using a measuring instrument (EZ-Co.
The viewing angle was measured in eight stages from black display (L1) to white display (L8) using an Ntrast 160D (manufactured by ELDIM). Table 3 shows the results.

[0108]

[Table 3]

The gray scale inversion on the black side is an inversion between L1 and L2.

Comparative Example 3 A pair of polarizing plates provided in a liquid crystal display device (6E-A3, manufactured by Sharp Corporation) using a TN type liquid crystal cell was peeled off, and the polarized light produced in Comparative Example 2 was used instead. The plates were adhered one by one to the observer side and the backlight side via an adhesive so that KH-H1 was on the liquid crystal cell side. The transmission axis of the polarizing plate on the observer side and the transmission axis of the polarizing plate on the backlight side were arranged so as to be in the O mode.

[Evaluation of streak-like unevenness] The panels prepared in Examples 5 and 6 and Comparative Example 3 were displayed in black, and streak-like unevenness was visually observed from above. Table 4 summarizes the results.

[0112]

[Table 4]

From the above results, it is clear that the liquid crystal display device provided with the polarizing plate of the present invention has been improved with respect to light leakage and streak-like unevenness.

[0114]

According to the present invention, an optical compensation film capable of optically compensating a liquid crystal cell is produced by coating a liquid crystal compound on a cellulose acetate film,
By arranging this optical compensation film on one side of the polarizing film, a polarizing plate capable of providing a large-sized, high-brightness liquid crystal display device with high display quality is manufactured. In particular, the polarizing plate manufactured using the optical compensation film can suppress the occurrence of light leakage and streak-like unevenness of the liquid crystal display device.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13363 G02F 1/13363 // C08L 1:12 C08L 1:12 F term (Reference) 2H049 BA06 BA25 BB03 BB23 BB30 BB49 BB51 BB54 BC02 BC03 BC09 BC22 2H091 FA08X FA08Z FA11X FA11Z FC25 FD06 LA12 LA16 4F006 AA02 AB03 AB63 BA00 CA05 DA04 4F071 AA09B AA78B AF35B AG09 AH16 CA01 CB02 CB01 A01B03A55B

Claims (3)

[Claims] 1. A cellulose acetate film provided with a protective layer on one side and subjected to a saponification treatment so that only one side without the protective layer is saponified, and an orientation layer is formed on the saponified film surface. Wherein an optically anisotropic layer comprising a liquid crystal compound is provided on the alignment layer. 2. The method according to claim 1, wherein the thickness of the cellulose acetate film is 10 to 70 μm. 3. A method comprising peeling off the protective layer of the optical compensation film according to claim 1 or 2, saponifying the peeled cellulose acetate surface, and laminating the saponified surface to at least one surface of the polarizing film. Characteristic method for producing a polarizing plate.