JP4611428B2 - VA liquid crystal display device - Google Patents

Description

The present invention relates to a VA-type liquid crystal display equipment using the optical compensation sheet composed of only a polymer film.

Cellulose acetate film is used for various photographic materials and optical materials because of its toughness and flame retardancy. Cellulose acetate film is a typical support for photographic light-sensitive materials. Cellulose acetate films are also used in liquid crystal display devices. The cellulose acetate film is characterized by high optical isotropy (low retardation value) as compared with other polymer films. Therefore, it is common to use a cellulose acetate film for an application requiring optical isotropy, for example, a polarizing plate.
In contrast, optical anisotropy (high retardation value) is required for an optical compensation sheet (phase difference film) of a liquid crystal display device. Therefore, it is common to use a synthetic polymer film having a high retardation value such as a polycarbonate film or a polysulfone film as the optical compensation sheet.
As described above, in the technical field of optical materials, when a polymer film requires optical anisotropy (high retardation value), a synthetic polymer film is used and optical isotropy (low retardation value) is used. It was a general rule to use cellulose acetate film when required.
Patent Document 1 discloses a cellulose acetate film having a high retardation value that can be used for applications requiring optical anisotropy, overcoming the conventional general principle.

European Patent 0911656A2

These polymer films could not be said to have sufficient optical anisotropy to optically compensate the liquid crystal cell. That is, the viewing angle characteristics of the liquid crystal display device still have room for improvement.
When using a conventional polymer film to secure optical anisotropy, it is necessary to stretch the polymer film at a high draw ratio or to set a large amount of additive for adjusting the retardation value. In many cases, the transmittance of the polymer film was lowered. If the transmittance is low, the luminance of the liquid crystal display device is lowered, which is not preferable.

An object of the present invention is to provide a VA-type liquid crystal display device which is optically compensated by the port Rimmer film.

The object of the present invention has been achieved by the following VA type liquid crystal display devices (1) to (4) .

(1) consists of two polarizing plates disposed on the liquid crystal cell and both sides of a VA mode, there in VA type liquid crystal display device comprising two transparent protective films which polarizing plates are disposed on the polarizing film and on both sides thereof Te, one of two transparent protective films disposed between the liquid crystal cell and the polarizing film is an optical compensation sheet comprising a cellulose ester film comprising an aromatic compound having at least two aromatic rings, cellulose ester both the film and the optical compensation sheet, in the range of Re retardation value of 20 to 70nm, which is defined by the following formula (I), Rth retardation value defined by the following formula (II) is 70 to 200 nm in the range, and VA-type liquid crystal display device haze, characterized in that 0.2 to 0.6%:
(I) Re = (nx−ny) × d
(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].
(2) The VA according to (1) , wherein the optical compensation sheet is arranged so that an absolute value of an angle formed by an average direction of the slow axis and a transmission axis of an adjacent polarizing film is 3 ° or less. Type liquid crystal display device.

(3) a two polarizing plates disposed on the liquid crystal cell and both sides of a VA mode, there in VA type liquid crystal display device comprising two transparent protective films which polarizing plates are disposed on the polarizing film and on both sides thereof Te, each of two transparent protective films disposed between the liquid crystal cell and the polarizing film is an optical compensation sheet comprising a cellulose ester film comprising an aromatic compound having at least two aromatic rings, cellulose ester both the film and the optical compensation sheet, in the range of Re retardation value of 20 to 70nm, which is defined by the following formula (I), Rth retardation value defined by the following formula (II) is 70 to 200 nm in the range, and VA-type liquid crystal display device haze, characterized in that 0.2 to 0.6%:
(I) Re = (nx−ny) × d
(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].
(4) The absolute value of the angle formed by the average direction of the slow axis of one optical compensation sheet and the transmission axis of the polarizing film adjacent to the optical compensation sheet and the average direction of the slow axis of the other optical compensation sheet are Two optical compensation sheets are arranged so that the sum of the absolute value of the angle formed with the transmission axis of the polarizing film adjacent to the optical compensation sheet is 3 ° or less, and the VA type according to (3) Liquid crystal display device.

The inventor has succeeded in optically compensating a liquid crystal cell only with a polymer film. By adjusting the type and amount of an additive (specifically, an aromatic compound having two aromatic rings) to the polymer film or the production conditions (for example, the film stretching conditions), the Re retardation value is 20 A polymer film having an Rth retardation value of 70 to 200 nm is obtained .
This polymer film has sufficient optical anisotropy to optically compensate the liquid crystal cell. Therefore, an optical compensation sheet consisting of only one polymer film can be obtained.
If a high retardation value is to be realized with a polymer film, the amount of additive is increased, or a large stretch ratio is likely to be required. By adjusting the kind and amount of the additive used in the present invention or the production conditions, an optical compensation sheet consisting only of a polymer film excellent in transparency can be obtained.
The protective film of the polarizing plate is generally made of a cellulose acetate film. Using the above polymer film as one protective film of the polarizing plate, without increasing the number of components of the polarizing plate, it is possible to add an optical compensation function to the polarizing plate.
Moreover, it is preferable to use a cellulose acetate film as the polymer film used in the present invention. If cellulose acetate having an acetylation degree of less than 59.0 is used, the optical anisotropy can be easily achieved, but the durability is lowered. In the present invention, cellulose acetate having an acetylation degree of 59.0 to 61.5% is used, and by achieving the above retardation value by other means (adjustment of the above additives and production conditions), A cellulose acetate film excellent in both optical anisotropy and durability is obtained.
The optical compensation sheet made of only the above polymer film and the polarizing plate using the above polymer film as a protective film can be used particularly advantageously for a VA (Vertically Aligned) type liquid crystal display device.

[Film retardation]
The Re retardation value and Rth retardation value of the film are defined by the following formulas (I) and (II), respectively.
(I) Re = (nx−ny) × d
(II) Rth = {(nx + ny) / 2−nz} × d
In the formulas (I) and (II), nx is the refractive index in the slow axis direction (direction in which the refractive index is maximum) in the film plane.
In formulas (I) and (II), ny is the refractive index in the fast axis direction (the direction in which the refractive index is minimized) in the film plane.
In the formula (II), nz is a refractive index in the thickness direction of the film.
In the formulas (I) and (II), d is the thickness of the film whose unit is nm.

In the present invention, the Re retardation value of the polymer film is adjusted to 20 to 70 nm, and the Rth retardation value is adjusted to 70 to 200 nm.
The birefringence (Δn: nx−ny) of the polymer film is preferably 0.00025 to 0.00088. The birefringence {(nx + ny) / 2−nz} in the thickness direction of the polymer film is preferably 0.00088 to 0.005.

[Haze]
The haze of the optical compensation sheet is calculated according to the following formula.
Haze (H) = diffuse transmittance (D) / total light transmittance (T) × 100 (%)
The haze is 0 . Is less than or equal to 6%. The haze of the polymer film is generally 0.2% or more.
Even if the optical compensation sheet has a high retardation value, if the haze value is large, the transparency of the optical compensation sheet is low, and the display brightness of the liquid crystal display device cannot be sufficiently obtained.
Although details will be described later, in the present invention, a high retardation value required for the optical compensation sheet is realized by adding a retardation increasing agent, stretching treatment of a polymer film, or the like. Furthermore, an optical compensation sheet having a small haze value is obtained by adjusting the degree of polymerization of the polymer material used for the optical compensation sheet, the type and addition amount of the retardation increasing agent, and the stretching treatment conditions of the polymer film. Thereby, an optical compensation sheet having high transparency (small haze value) and high retardation value can be obtained.

[Slow axis angle of film]
The angle of the slow axis in the polymer film plane is defined by the angle between the slow axis and the reference line, with the width direction of the roll film taken as the reference line (0 °). Set clockwise to +.
The absolute value of the average value of the slow axis angles is preferably 3 ° or less, more preferably 2 ° or less, and most preferably 1 ° or less. The direction of the average value of the slow axis angle is defined as the average direction of the slow axis.
The standard deviation of the slow axis angle is preferably 1.5 ° or less, more preferably 0.8 ° or less, and most preferably 0.4 ° or less.

In a transmissive liquid crystal display device using an optical compensation sheet, a “frame-shaped display unevenness” may occur in the periphery of the screen when time passes after energization. This unevenness is caused by an increase in the transmittance at the periphery of the screen, and is particularly noticeable during black display.
In the transmissive liquid crystal display device, heat is generated from the backlight, and a temperature distribution is generated in the liquid crystal cell surface. The change in the optical characteristics (retardation value, slow axis angle) of the optical compensation sheet due to this temperature distribution is the cause of occurrence of “frame-like display unevenness”. The change in the optical characteristics of the optical compensation sheet is caused by elastic deformation of the optical compensation sheet because expansion or contraction of the optical compensation sheet due to temperature rise is suppressed by adhesion to the liquid crystal cell or the polarizing plate.
In order to suppress the “frame-shaped display unevenness” as described above, it is preferable to use a polymer film having high thermal conductivity for the optical compensation sheet. As the polymer having high thermal conductivity, cellulose acetate (0.22 W / m · ° C.), low density polyethylene (0.34 W / m · ° C.), and ABS (0.36 W / m · ° C.) are preferable.

[Polymer film]
As the polymer film used in the present invention, it is preferable to use a polymer film having a light transmittance of 80% or more. Examples of polymers forming the polymer film include cellulose polymers, norbornene polymers such as trade name Arton (manufactured by JSR Corporation) and trade name ZEONEX (manufactured by Nippon Zeon Corporation), polymethyl methacrylate, and low density polyethylene. , And ABS. As the cellulose polymer, cellulose ester is preferable. As the cellulose ester, cellulose acetate is preferable, and examples thereof include diacetyl cellulose and triacetyl cellulose.
Further, the viscosity average polymerization degree (DP) of the polymer film is preferably 250 or more, and more preferably 290 or more. The polymer film preferably has a narrow molecular weight distribution of Mw / Mn (Mw is a weight average molecular weight and Mn is a number average molecular weight) by gel permeation chromatography. The specific value of Mw / Mn is preferably 1.0 to 1.7, more preferably 1.3 to 1.65, and most preferably 1.4 to 1.6. preferable.

As the polymer film of the present invention, a cellulose acetate film having an acetylation degree of 59.0 to 61.5% is preferably used.
The degree of acetylation means the amount of bound acetic acid per unit weight of cellulose. The degree of acetylation follows the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like).
Two or more types of cellulose acetate may be used for improving the mechanical properties and production stability of the film and adjusting the degree of acetylation. It is known that when two or more types of cellulose acetate are used, haze is likely to occur and transparency is likely to deteriorate. When two or more types of cellulose acetate are used to reduce the haze to 2.0% or less as in the present invention, cellulose acetate having the largest average degree of polymerization (P1) and the smallest degree of polymerization (P2) are used. ) Is used in a range satisfying 1 <P1 / P2 <3.

[Retardation raising agent]
In order to adjust the retardation of the polymer film, an aromatic compound having at least two aromatic rings is used as a retardation increasing agent.
When cellulose acetate film is used as the polymer film, the aromatic compound is used in the range of 0.01 to 20 parts by mass with respect to 100 parts by mass of cellulose acetate. If it is more than this, it becomes difficult to dissolve or compatibilize, haze occurs, and transparency deteriorates. The aromatic compound is preferably used in the range of 0.05 to 15 parts by mass, more preferably in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of 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.

The aromatic hydrocarbon ring is particularly preferably a 6-membered ring (that is, a benzene ring).
The aromatic heterocycle is generally an unsaturated heterocycle. The aromatic heterocycle is preferably a 5-membered ring, 6-membered ring or 7-membered ring, more preferably a 5-membered ring 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 aromatic heterocycles include furan ring, thiophene ring, 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 1,3,5-triazine ring.
As the aromatic ring, benzene ring, furan ring, thiophene ring, pyrrole ring, oxazole ring, thiazole ring, imidazole ring, triazole ring, pyridine ring, pyrimidine ring, pyrazine ring and 1,3,5-triazine ring are preferable, More preferred are a benzene ring and a 1,3,5-triazine ring.
It is particularly preferred that the aromatic compound has at least one 1,3,5-triazine ring.

The number of aromatic rings contained in the aromatic compound is preferably 2 to 20, more preferably 2 to 12, still more preferably 2 to 8, and most preferably 2 to 6. .
The bonding relationship between two aromatic rings can be classified into (a) when a condensed ring is formed, (b) when directly linked by a single bond, and (c) when linked via a linking group (for aromatic rings). , Spiro bonds cannot be formed). The connection relationship may be any of (a) to (c).

Examples of the condensed ring (a condensed ring of two or more aromatic rings) include an indene ring, naphthalene ring, triphenylene ring, azulene ring, fluorene ring, phenanthrene ring, anthracene ring, acenaphthylene ring, 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, phenanthridine ring, xanthene ring, phenazine ring, phenothiazine ring, phenoxathiin ring, phenoxazine ring and thiane It includes Ren ring. Naphthalene ring, azulene ring, indole ring, benzoxazole ring, benzothiazole ring, benzimidazole ring, benzotriazole ring and quinoline ring are preferred.
The single bond (b) is preferably a bond between carbon atoms of two aromatic rings. Two aromatic rings may be bonded with two or more single bonds to form an aliphatic ring or a non-aromatic heterocyclic ring between the two aromatic rings.

The linking group in (c) is also preferably bonded to carbon atoms of two aromatic rings. The linking group is preferably an alkylene group, an alkenylene group, an alkynylene group, —CO—, —O—, —NH—, —S—, or a combination thereof. Examples of linking groups composed of combinations are shown below. In addition, the relationship between the left and right in the following examples of linking groups 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 halogen atom (F, Cl, Br, I), hydroxyl, carboxyl, cyano, amino, nitro, sulfo, carbamoyl, sulfamoyl, ureido, alkyl group, alkenyl group, alkynyl group, aliphatic acyl group , Aliphatic acyloxy group, alkoxy group, alkoxycarbonyl group, alkoxycarbonylamino group, alkylthio group, alkylsulfonyl group, aliphatic amide group, aliphatic sulfonamido group, aliphatic substituted amino group, aliphatic substituted carbamoyl group, aliphatic Substituted sulfamoyl groups, aliphatic substituted ureido groups and non-aromatic heterocyclic groups are included.

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-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 alkenyl groups 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 alkynyl groups include ethynyl, 1-butynyl and 1-hexynyl.

The aliphatic acyl group preferably has 1 to 10 carbon atoms. 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 number of carbon atoms of the alkoxy group is preferably 1 to 8. The alkoxy group may further have a substituent (eg, 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 the alkoxycarbonyl group include methoxycarbonyl and ethoxycarbonyl.
The number of carbon atoms of the alkoxycarbonylamino group is preferably 2 to 10. Examples of the alkoxycarbonylamino group include methoxycarbonylamino and ethoxycarbonylamino.

The alkylthio group preferably has 1 to 12 carbon atoms. 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 sulfonamido group include methanesulfonamido, butanesulfonamido and n-octanesulfonamido.
The number of carbon atoms of the aliphatic substituted amino group is preferably 1 to 10. Examples of the aliphatic substituted amino group include dimethylamino, diethylamino and 2-carboxyethylamino.
The aliphatic substituted carbamoyl group preferably has 2 to 10 carbon atoms. 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 number of carbon atoms in the aliphatic substituted ureido group is preferably 2 to 10. Examples of the aliphatic substituted ureido group include methylureido.
Examples of non-aromatic heterocyclic groups include piperidino and morpholino.
The molecular weight of the retardation increasing agent is preferably 300 to 800.
In order to reduce the addition amount as much as possible and suppress the occurrence of haze, a material having a large birefringence index (Δn: nx−ny) is preferable. Specifically, a retardation increasing agent in which many aromatic rings are bonded to a triphenylene ring or a triazine ring is preferably used.

[Manufacture of polymer film]
It is preferable to produce a polymer film by a solvent casting method. In the solvent cast method, a film is produced using a solution (dope) in which a polymer material is dissolved in an organic solvent. It is preferable to add the above-mentioned retardation increasing agent to the dope.
The production of the polymer film of the present invention will be specifically described by taking cellulose acetate as an example.
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 contain.
The ether, ketone and ester may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, —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 functional group.

Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole.
Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone.
Examples of the esters having 3 to 12 carbon atoms 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 proportion of halogen atoms in the halogenated hydrocarbon substituted with halogen is preferably 25 to 75 mol%, more preferably 30 to 70 mol%, and more preferably 35 to 65 mol%. More preferably, it is 40 to 60 mol%, and most preferably. Methylene chloride is a typical halogenated hydrocarbon.
Two or more organic solvents may be mixed and used.

A 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 (room temperature or high temperature). The solution can be prepared using a dope preparation method and apparatus in a normal solvent cast 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 it is contained in an amount of 10 to 40% by mass in the resulting solution. The amount of cellulose acetate is more preferably 10 to 30% by mass. Arbitrary additives described later may be added to the organic solvent (main solvent).
The solution can be prepared by stirring cellulose acetate and an organic solvent at room temperature (0 to 40 ° C.). High concentration solutions may be stirred under pressure and heating conditions. Specifically, cellulose acetate and an organic solvent are placed in a pressure vessel and sealed, and stirred while heating 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 200 ° C., more preferably 80 to 110 ° C.

Each component may be coarsely mixed in advance and then placed in a container. Moreover, you may put into a container sequentially. The container needs to be configured so that it can be stirred. The container can be pressurized by injecting an inert gas such as nitrogen gas. Moreover, you may utilize the raise of the vapor pressure of the solvent by heating. Or after sealing a container, you may add each component under pressure.
When heating, it is preferable to heat from the outside of the container. For example, a jacket type heating device can be used. The entire container can also be heated by providing a plate heater outside the container and piping to circulate the liquid.
It is preferable to provide a stirring blade inside the container and stir using this. The stirring blade preferably has a length that reaches the vicinity of the wall of the container. A scraping blade is preferably provided at the end of the stirring blade in order to renew the liquid film on the vessel wall.
Instruments such as a pressure gauge and a thermometer may be installed in the container. Each component is dissolved in a solvent in the container. The prepared dope is taken out of the container after cooling, or taken out and then cooled using a heat exchanger or the like.

A solution can also be prepared by a cooling dissolution method. In the cooling dissolution method, cellulose acetate can be dissolved in an organic solvent that is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent which can melt | dissolve a cellulose acetate with a normal melt | dissolution method, there exists an effect that a uniform solution can be obtained rapidly according to a cooling melt | dissolution method.
In the cooling dissolution method, first, cellulose acetate is gradually added to an organic solvent with stirring at room temperature.
The amount of cellulose acetate is preferably adjusted so as to be contained in the mixture at 10 to 40% by mass. The amount of cellulose acetate is more preferably 10 to 30% by mass. Furthermore, you may add the arbitrary additive mentioned later in a mixture.

The mixture is then cooled to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to -20 ° C, most preferably -50 to -30 ° C). The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). When cooled in this way, the mixture of cellulose acetate and 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 faster the cooling rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at the start of cooling and the final cooling temperature by the time from the start of cooling until the final cooling temperature is reached.

Furthermore, when this is heated to 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C., most preferably 0 to 50 ° C.), cellulose acetate is dissolved in the organic solvent. The temperature can be raised by simply leaving it at room temperature or in a warm bath.
The heating rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The higher the heating rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The heating rate is a value obtained by dividing the difference between the temperature at the start of heating and the final heating temperature by the time from the start of heating until the final heating temperature is reached. .
A uniform solution is obtained as described above. If the dissolution is insufficient, the cooling and heating operations may be repeated. Whether or not the dissolution is sufficient can be determined by merely observing the appearance of the solution with the naked eye.

In the cooling dissolution method, it is desirable to use a sealed container in order to avoid moisture mixing due to condensation during cooling. In the cooling and heating operation, when the pressure is applied during cooling and the pressure is reduced during heating, the dissolution time can be shortened. In order to perform pressurization and decompression, it is desirable to use a pressure-resistant container.
In addition, according to differential scanning calorimetry (DSC), a 20 mass% solution obtained by dissolving cellulose acetate (acetylation degree: 60.9%, viscosity average polymerization degree: 299) in methyl acetate by a cooling dissolution method was 33. There exists a quasi-phase transition point between a sol state and a gel state in the vicinity of ° C., and a uniform gel state is obtained below this temperature. Therefore, this solution needs to be stored at a temperature equal to or higher than the pseudo phase transition temperature, preferably about the gel phase transition temperature plus about 10 ° C. However, this pseudo phase transition temperature varies depending on the degree of acetylation of cellulose acetate, the degree of viscosity average polymerization, the concentration of the solution, and the organic solvent used.

A cellulose acetate film is produced from the prepared cellulose acetate solution (dope) by a solvent cast method. It is preferable to add the above-mentioned retardation increasing agent to the dope.
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%. The surface of the drum or band is preferably finished in a mirror state. As for casting and drying methods in the solvent casting method, U.S. Pat. No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-1115035.
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 it by applying air for 2 seconds or more. The obtained film can be peeled off from the drum or band, and further dried by high-temperature air whose temperature is successively changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the drum or band during casting.

A plasticizer can be added to the cellulose acetate film in order to improve mechanical properties or increase the drying rate. As the plasticizer, phosphoric acid ester or carboxylic acid ester is used. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCP). Representative examples of the carboxylic acid ester include phthalic acid esters and citric acid esters. Examples of phthalic acid esters include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethyl hexyl phthalate (DEHP). Examples of citrate esters include triethyl O-acetylcitrate (OACTE) and tributyl O-acetylcitrate (OACTB). Examples of other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic acid esters. Phthalate plasticizers (DMP, DEP, DBP, DOP, DPP, DEHP) are preferably used. DEP and DPP are particularly preferred.
The addition amount of the plasticizer is preferably 0.1 to 25% by mass, more preferably 1 to 20% by mass, and most preferably 3 to 15% by mass of the amount of the cellulose ester.

  A degradation inhibitor (eg, antioxidant, peroxide decomposer, radical inhibitor, metal deactivator, acid scavenger, amine) may be added to the cellulose acetate film. The deterioration preventing agents are described in JP-A-3-199201, JP-A-51907073, JP-A-5-194789, JP-A-5-271471, and JP-A-6-107854. The addition amount of the deterioration preventing agent is preferably 0.01 to 1% by mass of the solution (dope) to be prepared, and more preferably 0.01 to 0.2% by mass. When the addition amount is less than 0.01% by mass, the effect of the deterioration preventing agent is hardly recognized. When the added amount exceeds 1% by mass, bleeding-out (bleeding) of the deterioration preventing agent to the film surface may be observed. Examples of particularly preferred deterioration inhibitors include butylated hydroxytoluene (BHT) and tribenzylamine (TBA).

[Polymer film stretching]
The retardation of the polymer film can be further adjusted by a stretching treatment. However, if the draw ratio is too large, crystallization, craze, and voids are generated and whitening is caused and transparency is deteriorated. The polymer film to be stretched may contain a solvent used for the dope solution. The stretching of the polymer film can be performed by a general known method.
When cellulose acetate film is used, the draw ratio is preferably 3 to 100%, more preferably 3 to 70%, and most preferably 3 to 40%. The thickness of the cellulose acetate film is preferably 40 to 140 μm, and more preferably 70 to 120 μm.

[Surface treatment of polymer film]
When using a polymer film as a transparent protective film of a polarizing plate, it is preferable to surface-treat the polymer film.
As the surface treatment, corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment or ultraviolet irradiation treatment is performed. It is particularly preferred to carry out an acid treatment or an alkali treatment, ie a saponification treatment on the polymer film.

[Polarizer]
A polarizing plate consists of a polarizing film and two transparent protective films arrange | positioned at the both sides. As one protective film, the above polymer film can be used. A normal cellulose acetate film may be used for the other protective film.
Examples of the polarizing film include an iodine polarizing film, a dye polarizing film using a dichroic dye, and a polyene polarizing film. The iodine polarizing film and the dye polarizing film are generally manufactured using a polyvinyl alcohol film.
The angle formed by the average direction of the slow axis of the polymer film and the transmission axis of the polarizing film is preferably 3 ° or less, more preferably 2 ° or less, and 1 ° or less. It is most preferable to arrange so that.

[Liquid Crystal Display]
The optical compensation sheet made of the above polymer film or the polarizing plate using the above polymer film is advantageously used for a liquid crystal display device, particularly a transmissive liquid crystal display device.
The transmissive liquid crystal display device includes a liquid crystal cell and two polarizing plates disposed on both sides thereof. The liquid crystal cell carries a liquid crystal between two electrode substrates.
One optical compensation sheet is disposed between the liquid crystal cell and one polarizing plate, or two optical compensation sheets are disposed between the liquid crystal cell and both polarizing plates.
In the polarizing plate, the above polymer film is used as a transparent protective film disposed between the liquid crystal cell and the polarizing film.
Only the transparent protective film (between the liquid crystal cell and the polarizing film) of one polarizing plate uses the above polymer film, or two transparent protective films (between the liquid crystal cell and the polarizing film) of both polarizing plates The above polymer film is used for the membrane.
In the former case, the polymer film is preferably arranged so that the absolute value of the angle formed by the average direction of the slow axis of the polymer film and the transmission axis of the polarizing film adjacent to the polymer film is 3 ° C. or less.
In the latter case, the average direction of the slow axis of one polymer film is the absolute value of the angle between the transmission axis of the polarizing film adjacent to the polymer film and the average direction of the slow axis of the other polymer film is the polymer. The two polymer films are preferably arranged so that the sum of the absolute value of the angle formed by the transmission axis of the polarizing film adjacent to the film is 3 ° C. or less.
The liquid crystal cell is preferably in VA mode, OCB mode or TN mode.

In the case of the OCB mode liquid crystal display device, the optical compensation sheet of the present invention may have an optically anisotropic layer containing a discotic compound or a rod-shaped liquid crystal compound on the polymer film. The optically anisotropic layer is formed by orienting a discotic compound (or rod-like liquid crystal compound) and fixing its orientation state.
A discotic compound generally has a large birefringence. The discotic compound has various orientation forms. Therefore, by using a discotic compound, an optical compensation sheet having optical properties that cannot be obtained by a conventional stretched birefringent film can be produced. Optical compensation sheets using a discotic compound are described in JP-A-6-214116, US Pat. Nos. 5,583,679, 5,646,703 and West German Patent 3,911,620A1.

In a VA mode liquid crystal cell, rod-like liquid crystal molecules are aligned substantially vertically when no voltage is applied. The VA mode liquid crystal cell includes (1) a narrowly defined VA mode liquid crystal cell in which rod-like liquid crystalline molecules are aligned substantially vertically when no voltage is applied, and substantially horizontally when a voltage is applied (Japanese Patent Laid-Open No. Hei 2-). 176625 and Japanese Examined Patent Publication No. 7-69536) (2) A liquid crystal cell in which the VA mode is multi-domained for widening the viewing angle is included. Specifically, MVA (SID97, Digest of tech. Papers (Preliminary Collection) 28 (1997) 845, SID99, Digest of tech. Papers (Preliminary Collection) 30 (1999) 206, and JP-A-11-258605 ) a SURVIVAL (monthly display, Vol. 6, No. 3 (1999) 14 described), PVA (Asia Display98, Proc.of the 18 th Inter.Display res. Conf. ( Proceedings) (1998) 383 described), Para-A (announced at LCD / PDP International '99), DDVA (SID 98, Digest of tech. Papers (Preliminary Collection) 29 (1998) 838), EOC (SID 98, Digest of tech. Papers (Preliminary Collection) 29 ( 1998) 319 described), PSHA (SID98, Digest of tech. Papers ( preprints) 29 (1998) 1081 described), RFFMH (Asia Display98, Proc.of the 18 th Inter.Display res.Co nf. (Preliminary Collection) (1998) 375), HMD (SID98, Digest of tech. Papers (Preliminary Collection) 29 (1998) 702). In addition, (3) a liquid crystal cell (IWD'98, Proc. Of the 5 ^th ) in a mode (n-ASM mode) in which rod-like liquid crystalline molecules are substantially vertically aligned when no voltage is applied and twisted multi-domain alignment is applied when a voltage is applied. Inter. Display Workshop. (Preliminary book) (1998) 143) is also included.

In the TN mode liquid crystal cell, the rod-like liquid crystal molecules are substantially horizontally aligned when no voltage is applied, and are twisted and aligned at 60 to 120 °.
The TN mode liquid crystal cell is most frequently used as a color TFT liquid crystal display device, and is described in many documents.

(Measurement of optical properties)
About the produced optical compensation sheet, Re retardation value and Rth retardation value in wavelength 550nm were measured using the ellipsometer (M-150, JASCO Corporation make). In addition, the off-axis angle was measured with an automatic birefringence meter (KOBRA-21ADH, Oji Scientific Instruments). Each measurement was performed at 10 points in the width direction, and an average value was obtained. The standard deviation was also obtained for the slow axis angle.
(Measure haze)
About the produced polymer film (retardation plate), haze was measured using the haze meter (NDH1001-DP, Nippon Denshoku Industries Co., Ltd. product). As the haze, an average value of measured values at arbitrary five points was adopted.

[Example 1]
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acetate solution.

────────────────────────────────────
Cellulose acetate solution composition ────────────────────────────────────
Cellulose acetate having an acetylation degree of 60.9% 100 parts by weight Triphenyl phosphate (plasticizer) 7.8 parts by weight Biphenyl diphenyl phosphate (plasticizer) 3.9 parts by weight Methylene chloride (first solvent) 336 parts by weight Methanol (No. 2 solvents) 30 parts by mass ─────────────────────────────────────

In another mixing tank, 16 parts by mass of the following retardation increasing agent, 92 parts by mass of methylene chloride and 8 parts by mass of methanol were added and stirred while heating to prepare a retardation increasing agent solution.
A dope was prepared by mixing 474 parts by mass of the cellulose acetate solution with 25 parts by mass of the retardation increasing agent solution and stirring sufficiently. The addition amount of the retardation increasing agent was 3.5 parts by mass with respect to 100 parts by mass of cellulose acetate.

The obtained dope was cast using a band casting machine. A film having a residual solvent amount of 15% by mass is stretched laterally at a stretch ratio of 25% using a tenter under the conditions of 130 ° C., held at 50 ° C. for 30 seconds with the stretched width, and then clipped to remove cellulose. Acetate film TAC-1 (thickness: 80 μm) was produced.
The produced cellulose acetate film (optical compensation sheet) was measured for optical properties and haze. The results are shown in Table 1.

[Example 2]
The dope obtained in Example 1 was cast using a band casting machine. A film having a residual solvent amount of 15% by mass was stretched laterally at a stretch ratio of 25% using a tenter under the conditions of 130 ° C., held at 50 ° C. for 15 seconds with the stretched width, and then clipped to remove cellulose. Acetate film TAC-2 (thickness: 80 μm) was produced.
The produced cellulose acetate film (optical compensation sheet) was measured for optical properties and haze. The results are shown in Table 1.

[Example 3]
A dope was prepared by mixing 474 parts by mass of a cellulose acetate solution with 56 parts by mass of a retardation increasing agent solution (use 7.8 parts by mass of a retardation increasing agent with respect to 100 parts by mass of cellulose acetate), and adjusting the draw ratio. A cellulose acetate film TAC-3 (optical compensation sheet) was prepared and optical characteristics and haze were measured in the same manner as in Example 1 except that the content was changed to 14%. The results are shown in Table 1.

[Example 4]
A cellulose acetate film TAC-4 (optical compensation sheet) was prepared and optical characteristics and haze were measured in the same manner as in Example 2 except that the dope obtained in Example 1 was used and the draw ratio was changed to 40%. . The results are shown in Table 1.

[Comparative Example 1]
The dope obtained in Example 1 was used and cast using a band casting machine. A film having a residual solvent amount of 15% by mass was horizontally stretched at a stretching ratio of 120% using a tenter under the conditions of 170 ° C., held at 130 ° C. for 15 seconds with the stretched width, then the clip was removed and TAC A −5 cellulose acetate film (thickness: 80 μm) was produced.
The produced cellulose acetate film (optical compensation sheet) was measured for optical properties and haze. The results are shown in Table 1.

[Comparative Example 2]
The dope obtained in Example 1 was cast using a band casting machine. A film having a residual solvent amount of 15% by mass was stretched laterally at a stretch ratio of 25% using a tenter under the conditions of 130 ° C., and immediately after stretching, the clip was removed at 130 ° C. to remove cellulose acetate film TAC-6 (thickness). Sa: 80 μm).
The haze was measured about the produced cellulose acetate film (optical compensation sheet). The results are shown in Table 1.

Table 1 ────────────────────────────────────
Film Re Rth slow axis angle standard deviation haze ─────────────────────────────────────
Example 1 40 nm 130 nm 0.5 ° 0.3 ° 0.3
Example 2 39 nm 132 nm 0.3 ° 0.5 ° 0.3
Example 3 50 nm 240 nm 1.0 ° 0.4 ° 0.4
Example 4 51 nm 137 nm 0.4 ° 0.9 ° 0.9
Comparative Example 1 − − 1.0 ° 2.0 ° 8.5
Comparative Example 2 51 nm 149 nm 4.2 ° 2.5 ° 4.0
────────────────────────────────────

[Example 5]
A polarizing film was prepared by adsorbing iodine to a stretched polyvinyl alcohol film. The cellulose acetate film TAC-1 produced in Example 1 was saponified and attached to one side of the polarizing film using a polyvinyl alcohol-based adhesive. The TAC-1 and the polarizing film were pasted so that the longitudinal directions were parallel. The angle formed by the average direction of the slow axes of TAC-1 and the transmission axis of the polarizing film was 0.5 °.
A commercially available cellulose triacetate film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) was saponified and attached to the opposite side of the polarizing film using a polyvinyl alcohol adhesive. In this way, a polarizing plate was produced.

[Example 6]
A polarizing plate was produced in the same manner as in Example 5 except that the cellulose acetate film produced in Example 2 was used. The angle formed by the average direction of the slow axes of TAC-2 and the transmission axis of the polarizing film was 0.3 °.

[Example 7]
A polarizing plate was produced in the same manner as in Example 5 except that the cellulose acetate film produced in Example 3 was used. The angle formed by the average direction of the slow axes of TAC-3 and the transmission axis of the polarizing film was 1.0 °.

[Example 8]
A polarizing plate was produced in the same manner as in Example 5 except that the cellulose acetate film produced in Example 4 was used. The angle formed by the average direction of the slow axes of TAC-4 and the transmission axis of the polarizing film was 0.4 °.

[Comparative Example 3]
A polarizing plate was produced in the same manner as in Example 5 except that the cellulose acetate film produced in Comparative Example 2 was used. The angle formed by the average direction of the slow axes of TAC-5 and the transmission axis of the polarizing film was 3.9 °.

[Example 9]
A pair of polarizing plates and a pair of optical compensation sheets provided in a liquid crystal display device (VL-1530S, manufactured by Fujitsu Limited) using a vertical alignment type liquid crystal cell were peeled off, and the polarizing plate prepared in Example 5 was used instead. Were attached to the observer side and the backlight side one by one through an adhesive so that the cellulose acetate film produced in Example 1 was on the liquid crystal cell side. The crossed Nicols were arranged so that the transmission axis of the polarizing plate on the viewer side was in the vertical direction and the transmission axis of the polarizing plate on the backlight side was in the horizontal direction.
About the produced liquid crystal display device, contrast ratio was measured in 10 places within a panel surface using the measuring machine (EZ-Contrast160D, ELDIM company make). The results are shown in Table 2.

[Example 10]
A pair of polarizing plates and a pair of optical compensation sheets provided in a liquid crystal display device (VL-1530S, manufactured by Fujitsu Limited) using a vertical alignment type liquid crystal cell are peeled off, and a polarizing plate prepared in Example 6 is used instead. Were attached to the observer side and the backlight side one by one through an adhesive so that the cellulose acetate film produced in Example 2 was on the liquid crystal cell side. The crossed Nicols were arranged so that the transmission axis of the polarizing plate on the viewer side was in the vertical direction and the transmission axis of the polarizing plate on the backlight side was in the horizontal direction.
About the produced liquid crystal display device, contrast ratio was measured in 10 places within a panel surface using the measuring machine (EZ-Contrast160D, ELDIM company make). The results are shown in Table 2.

[Example 11]
A pair of polarizing plates and a pair of optical compensation sheets provided in a liquid crystal display device (VL-1530S, manufactured by Fujitsu Limited) using a vertical alignment type liquid crystal cell are peeled off, and the polarizing plate prepared in Example 7 is used instead. Was attached to the observer side through an adhesive so that the cellulose acetate film produced in Example 3 was on the liquid crystal cell side. In addition, a commercially available polarizing plate (HLC2-5618HCS, manufactured by Sanritz Corporation) was attached to the backlight side. The crossed Nicols were arranged so that the transmission axis of the polarizing plate on the viewer side was in the vertical direction and the transmission axis of the polarizing plate on the backlight side was in the horizontal direction.
About the produced liquid crystal display device, contrast ratio was measured in 10 places within a panel surface using the measuring machine (EZ-Contrast160D, ELDIM company make). The results are shown in Table 2.

[Comparative Example 4]
A pair of polarizing plates and a pair of optical compensation sheets provided in a liquid crystal display device (VL-1530S, manufactured by Fujitsu Limited) using a vertical alignment type liquid crystal cell are peeled off, and a polarizing plate prepared in Comparative Example 3 is used instead. Were attached to the observer side and the backlight side one by one through an adhesive so that the cellulose acetate film produced in Comparative Example 2 was on the liquid crystal cell side. The crossed Nicols were arranged so that the transmission axis of the polarizing plate on the viewer side was in the vertical direction and the transmission axis of the polarizing plate on the backlight side was in the horizontal direction.
About the produced liquid crystal display device, contrast ratio was measured in 10 places within a panel surface using the measuring machine (EZ-Contrast160D, ELDIM company make). The results are shown in Table 2.

  The maximum value and the minimum value of the front contrast ratio within the panel surface are shown in Table 2, respectively. In addition, the viewing angle in the left-right direction at the measurement point with the maximum front contrast ratio and the measurement point with the minimum value is also shown. Here, the viewing angle means an angle range having a contrast ratio of 10 or more.

Table 2 ────────────────────────────────────
LCD device front contrast ratio viewing angle / °
Maximum value Minimum value Maximum Minimum ─────────────────────────────────────
Example 9 400 328> 160 150
Example 10 388 291> 160 140
Example 11 384 328> 160 152
Comparative Example 4 412 40> 160 30
────────────────────────────────────

[Example 12]
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 is peeled off, and a polarizing plate produced in Example 5 is produced in Example 1 instead. The obtained cellulose acetate film was attached to the viewer side and the backlight side one by one through an adhesive so that the cellulose acetate film 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 are orthogonal to each other and are arranged in the O mode.
About the produced liquid crystal display device, contrast ratio was measured in 10 places within a panel surface using the measuring machine (EZ-Contrast160D, ELDIM company make). The results are shown in Table 3.

[Example 13]
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 is peeled off, and a polarizing plate produced in Example 6 is produced in Example 2 instead. The obtained cellulose acetate film was attached to the viewer side and the backlight side one by one through an adhesive so that the cellulose acetate film 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 are orthogonal to each other and are arranged in the O mode.
About the produced liquid crystal display device, contrast ratio was measured in 10 places within a panel surface using the measuring machine (EZ-Contrast160D, ELDIM company make). The results are shown in Table 3.

[Comparative 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 is peeled off, and a polarizing plate produced in Comparative Example 3 is produced in Comparative Example 2 instead. The obtained cellulose acetate film was attached to the viewer side and the backlight side one by one through an adhesive so that the cellulose acetate film 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 are orthogonal to each other and are arranged in the O mode.
About the produced liquid crystal display device, contrast ratio was measured in 10 places within a panel surface using the measuring machine (EZ-Contrast160D, ELDIM company make). The results are shown in Table 3.

  The maximum value and the minimum value of the front contrast ratio in the panel surface are shown in Table 3, respectively. In addition, the viewing angle in the left-right direction at the measurement point with the maximum front contrast ratio and the measurement point with the minimum value is also shown. Here, the viewing angle means an angle range having a contrast ratio of 10 or more.

Table 3 ────────────────────────────────────
LCD device front contrast ratio viewing angle / °
Maximum value Minimum value Maximum Minimum ─────────────────────────────────────
Example 12 227 122 160 110
Example 13 214 112 160 100
Comparative Example 5 149 23 140 30
────────────────────────────────────

Claims (4)

A VA mode liquid crystal display device comprising a VA mode liquid crystal cell and two polarizing plates disposed on both sides thereof, wherein the polarizing plate comprises a polarizing film and two transparent protective films disposed on both sides thereof. one of the two sheets of transparent protective film to be disposed between the cell and the polarizing film is an optical compensation sheet ing a cellulose ester film comprising an aromatic compound having at least two aromatic rings, cellulose ester film and In each of the optical compensation sheets, the Re retardation value defined by the following formula (I) is in the range of 20 to 70 nm, and the Rth retardation value defined by the following formula (II) is in the range of 70 to 200 nm. VA type liquid crystal display device characterized by having haze of 0.2 to 0.6% :
(I) Re = (nx−ny) × d
(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].   2. The VA liquid crystal display according to claim 1, wherein the optical compensation sheet is disposed so that an absolute value of an angle formed by an average direction of the slow axis and a transmission axis of an adjacent polarizing film is 3 ° or less. apparatus.   A VA mode liquid crystal display device comprising a VA mode liquid crystal cell and two polarizing plates disposed on both sides thereof, wherein the polarizing plate comprises a polarizing film and two transparent protective films disposed on both sides thereof. Each of the two transparent protective films disposed between the cell and the polarizing film is an optical compensation sheet made of a cellulose ester film containing an aromatic compound having at least two aromatic rings. Each of the compensation sheets has a Re retardation value defined by the following formula (I) in the range of 20 to 70 nm, an Rth retardation value defined by the following formula (II) in the range of 70 to 200 nm, A VA liquid crystal display device having a haze of 0.2 to 0.6%:
(I) Re = (nx−ny) × d
(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].   The absolute value of the angle formed by the average direction of the slow axis of one optical compensation sheet and the transmission axis of the polarizing film adjacent to the optical compensation sheet and the average direction of the slow axis of the other optical compensation sheet are the optical compensation. 4. The VA liquid crystal display device according to claim 3, wherein two optical compensation sheets are arranged so that a sum of an absolute value of an angle formed by a transmission axis of a polarizing film adjacent to the sheet is 3 ° or less. .