JP4999977B2 - Liquid crystal display - Google Patents

Description

The present invention relates to a liquid crystal display device.

A polarizing plate is usually manufactured by laminating a film mainly composed of cellulose triacetate as a protective film on both sides of a polarizing film in which iodine or a dichroic dye is oriented and adsorbed on polyvinyl alcohol. Cellulose triacetate has characteristics such as toughness, flame retardancy, and high optical isotropy (low retardation value), and is widely used as the protective film for polarizing plates described above.
The liquid crystal display device is composed of a polarizing plate and a liquid crystal cell. At present, in the TN mode TFT liquid crystal display device which is the mainstream of the liquid crystal display device, as described in Patent Document 1, by inserting an optical compensation sheet (phase difference film) between the polarizing plate and the liquid crystal cell, A liquid crystal display device with high display quality has been realized. However, this method has a problem that the liquid crystal display device itself becomes thick.

In Patent Document 2, a polarizing plate (ellipsoidal polarizing plate) having an optical compensation sheet on one side of the 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 description that can be done. However, it has been found that the optical compensation sheet of the present invention is likely to cause a phase difference due to distortion caused by heat or the like and has a problem in durability.
With respect to the problem of phase difference generation due to distortion, in Patent Documents 3 and 4, an optical compensation sheet in which an optically anisotropic layer made of a discotic compound is coated on a transparent support is used directly as a protective film for a polarizing plate. The above-mentioned durability problem was solved without increasing the thickness of the liquid crystal display device.

JP-A-8-50206 JP-A-1-68940 Japanese Patent Laid-Open No. 7-191217 European Patent 0911656A2

Although the display quality of the liquid crystal display device has been improved by using the above optical compensation sheet, the distortion applied to the optical compensation sheet tends to increase with the recent increase in the size of the liquid crystal panel and the increase in brightness. , it is becoming impossible to ignore this distorted body.
The purpose of the present invention, no problems with the same thickness as conventional even without causing a high display quality, and a high luminance, is to provide a large liquid crystal display device of the panel size.

  By adjusting the elastic modulus of the material used for the optical compensation sheet (details will be described later), the temperature of the material due to the heat generated around the material is improved by adjusting the elastic modulus of the material used for the optical compensation sheet. It has been found that a characteristic that the optical characteristic is stable can be imparted to a change.

Accordingly, the present invention provides a liquid crystal display device comprising a TN mode liquid crystal cell and two polarizing plates disposed on both sides thereof, wherein at least one polarizing plate is an optical compensation sheet on at least one surface of the polarizing film. Are arranged such that the optical compensation sheet of the polarizing plate is on the liquid crystal cell side, and the optical compensation sheet is composed of a cycloolefin polymer film (hereinafter sometimes referred to as a polymer film). In both the film and the optical compensation sheet, the Re retardation value defined by the following formula (I) is in the range of 20 to 50 nm, and the Rth retardation value defined by the following formula (II) is 70 to 400 nm. in the range, and especially at least one direction in the range near the modulus 4000 to 10000MPa Turkey In the liquid crystal display device with.
(I) Re = (nx−ny) × d
(II) Rth = {(nx + ny) / 2−nz} × d
In the formula, 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, and nz is the refractive index in the thickness direction of the film, D is the thickness of the film.

In the polarizing plate, the slow axis and the transmission axis of the polarizing optical compensation sheet, it is preferably arranged to be substantially parallel.

In the present specification, “substantially vertical”, “substantially parallel”, or “substantially 45 °” means within a range of less than ± 5 ° from a strict angle. This range is preferably less than ± 4 °, more preferably less than ± 3 °, and most preferably less than ± 2 °. In the present specification, the “slow axis” is the direction in which the refractive index is maximum, the “fast axis” is the direction in which the refractive index is minimum, and “
The transmission axis means the direction in which the transmittance is maximum.

The optical compensation sheet of the present invention is characterized in that its elastic modulus is in the range of 4000 to 10,000 MPa.
In the present invention, by adjusting the elastic modulus of the optical compensation sheet, while maintaining the excellent optical characteristics of the conventionally used optical compensation sheet, further, the expression of birefringence due to heat (in the liquid crystal display device, It is possible to add characteristics with less light leakage in the black display state.
Accordingly, by using the optical compensation sheet of the present invention or a polarizing plate using the same for a liquid crystal display device, a liquid crystal display device having a high display quality and a large panel size can be produced while maintaining the conventional thickness. Can do.
The above optical compensatory sheet, a liquid crystal display equipment of TN (Twisted Nematic) type, it can be used particularly advantageously.

[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, and ny is the fast axis direction (refractive index in the film plane). Is the refractive index in the direction in which the minimum is, and d is the thickness of the film with the unit of nm. In the formula (II), nz is a refractive index in the thickness direction of the film.
In the present invention, the Re retardation value of the polymer film is 20 to 50 nm at a wavelength of 633 nm, and the Rth retardation value is adjusted to 70 to 400 nm.

[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. The polymer film is preferably one that does not easily exhibit birefringence due to external force. Examples of the polymer film, trade name Arton (manufactured by JSR (Ltd.)) and product names ZEONEX (manufactured by Nippon Zeon Co., Ltd.), and the norbornene-based polymer over such.

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).

These polymer films preferably contain an ultraviolet absorber or the like. In addition, in order to improve the adhesion between the polymer film and the layer (adhesive layer, alignment film, or optically anisotropic layer) provided on the polymer film, surface treatment (eg, glow discharge treatment, corona discharge treatment) is performed on the polymer film. , Ultraviolet treatment, flame treatment). In addition, an adhesive layer (undercoat layer) may be provided on the polymer film as described in JP-A-7-333433. The thickness of the adhesive layer is preferably 0.1 to 2.0 μ, more preferably 0.2 μ to 1.0 μ.

[Elastic modulus control]
A polarizing plate used in a liquid crystal display device is punched out to an appropriate angle and size, and is bonded to a panel via an adhesive. When heat is applied to the panel, the optical compensation sheet tends to shrink (or expand), but because the deformation is suppressed by the adhesive, birefringence occurs as if it is stretched (or compressed). However, light leakage occurs in the black display state. When external force is applied, the phenomenon that causes optical anisotropy (birefringence) according to the stress generated inside is called photoelasticity. The larger the photoelastic coefficient of the material, the larger the optical anisotropy, Therefore, light leakage increases.

That is, it can be seen that light leakage due to this photoelasticity should be reduced in order to manufacture a liquid crystal display device having a large panel size with excellent display quality. Therefore, it is understood that the stress generated in the optical compensation sheet due to the heat generated by the liquid crystal display device or the heat in the use environment may be reduced, or a material having a small photoelastic coefficient may be used for the optical compensation sheet. In order to reduce the stress generated in the optical compensation sheet, a material having a small linear expansion coefficient may be used for the optical compensation sheet.
However, the optical compensation sheet requires not only the thermal characteristics of the material but also the optical characteristics. Therefore, eliminating distortion due to heat by selecting a material may sacrifice optical characteristics, and none of the above methods is a preferable solution.

  The inventors' diligent research has revealed that the photoelastic coefficient of a material can be reduced by adjusting the elastic modulus of the same material. In other words, by adjusting the elastic modulus of the material used for the optical compensation sheet, the material has excellent optical characteristics, and further exhibits birefringence due to heat (in a liquid crystal display device, light leakage in a black display state). ) Has been found to be added.

In the polarizing plate in which the optical compensation sheet and the polarizing film are integrated, the elastic modulus in at least one direction in the plane of the optical compensation sheet is preferably 4000 to 10,000 MPa, and more preferably 5000 to 10,000.
The elastic modulus of the optical compensation sheet can be controlled by stretching the polymer film (and the polymerizable liquid crystal compound).
The thickness of the polymer film is preferably 40 to 200 μm, and more preferably 70 to 150 μm.
The draw ratio is preferably 5 to 100%, more preferably 10 to 90%, and most preferably 20 to 70%. The polymer film is preferably stretched so that the slow axis in the plane of the polymer film and the transmission axis of the polarizing plate are parallel to each other by roll-to-roll. It is preferable to be stretched in the transverse direction. A tenter method is preferably used as the method of stretching in the transverse direction.

The film temperature during stretching is preferably Tg (glass transition temperature) ± 30 degrees of the polymer film, more preferably Tg ± 25 degrees, and most preferably Tg ± 20 degrees. The heating method is roughly classified into a roll heating method and a hot air heating method, and the former is known from Japanese Examined Patent Publication No. 39-29214. On the other hand, it is preferable to control the temperature distribution in the width direction by heating with hot air to make the physical property values (elastic modulus, optical characteristics, etc.) in the film width direction uniform. For this reason, it is preferable to use a two-dimensional nozzle for hot air heating.
In the case of lateral stretching by the tenter method, in order to prevent the bowing phenomenon, it is preferable to use a stretching method in which after the transverse stretching, once cooled to Tg or less, the stretching stress is released and heat treatment is performed again. The details of these stretching techniques are described in “Plastic Film Stretching Technology and Evaluation” (published by Information Technology Association 1992.10.16).
The elastic modulus was obtained by calculation from a stress-strain curve at room temperature and normal humidity by attaching a strip having a width of 50 mm, a thickness of 100 μm, and a length of 100 mm to a tensile tester.

[Retardation control]
In order to adjust the retardation of the polymer film, a method of applying an external force such as stretching is generally used. Further, as described in European Patent 0911656A2, the retardation of an aromatic compound having at least two aromatic rings can be adjusted in the polymer film using 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. 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 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 3 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 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, a 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 thianthrene ring Be 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 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 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.

[Manufacture of polymer film]
The polymer film is preferably produced by a solvent cast 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 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 a solvent.
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 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 more preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogenated hydrocarbon hydrogen atoms 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. A typical example of the halogenated hydrocarbon is methylene chloride.
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 by 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. Further, the entire container can 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 a 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 the 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. is there.
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).

In the cellulose acetate film, the retardation can be further adjusted by a stretching treatment. The draw ratio is preferably 3 to 100%.
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 the polarizing plate is produced by bonding the optical compensation sheet and the polarizing film, it is preferable to perform a surface treatment from the viewpoint of the adhesiveness between the polymer film used for the optical compensation sheet and the polarizing film. Examples of the surface treatment include saponification treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment. Saponification treatment includes acid saponification treatment and alkali saponification treatment. Plasma treatment includes corona discharge treatment and glow discharge treatment. In order to maintain the flatness of the film, in these surface treatments, the temperature of the polymer film is preferably set to a glass transition temperature (Tg) or lower.

Hereinafter, the example which performs an alkali saponification process is demonstrated concretely.
The alkali saponification treatment is preferably carried out in a cycle in which the polymer film is immersed in an alkali solution, neutralized with an acidic solution, washed with water and dried. Examples of the alkaline solution include potassium hydroxide solution and sodium hydroxide solution. The specified concentration of hydroxide ions in the alkaline solution is preferably 0.1N to 3.0N, more preferably 0.5N to 2.0N. The temperature of the alkaline solution is preferably in the range of 0 to 90 ° C, more preferably 40 to 70 ° C.

Next, another optical compensation sheet of the present invention formed by laminating a polymer film and an optically anisotropic layer containing a liquid crystal compound will be described.
By providing an optically anisotropic layer containing a liquid crystalline compound on the optical compensation sheet of the present invention comprising only a polymer film obtained as described above, it has optical properties that cannot be obtained with a stretched birefringent film. Another optical compensation sheet of the present invention can be produced. An optical compensation sheet having an optically anisotropic layer can be produced by coating an alignment film on the polymer film to form an optically anisotropic layer containing a liquid crystalline compound.
Further, an adhesion layer (undercoat layer) may be provided between the polymer film and the alignment film. The adhesive layer is described in JP-A-7-333433. The thickness of the adhesion layer is preferably 0.1 to 2 μm, and more preferably 0.2 to 1 μm.

[Alignment film]
The alignment film has a function of defining the alignment direction of the liquid crystalline compound of the optically anisotropic layer.
The alignment film is an organic compound (eg, ω-tricosanoic acid) formed by rubbing treatment of an organic compound (preferably polymer), oblique deposition of an inorganic compound, formation of a layer having a microgroove, or Langmuir-Blodgett method (LB film). , Dioctadecylmethylammonium chloride, methyl stearylate). Furthermore, an alignment film in which an alignment function is generated by application of an electric field, application of a magnetic field, or light irradiation is also known.

The alignment film is preferably formed by polymer rubbing treatment. Polyvinyl alcohol is a preferred polymer. Particularly preferred is a modified polyvinyl alcohol to which a hydrophobic group is bonded. Since the hydrophobic group has an affinity with the liquid crystalline compound of the optically anisotropic layer, the liquid crystalline compound can be uniformly aligned by introducing the hydrophobic group into polyvinyl alcohol. The hydrophobic group is bonded to the main chain terminal or side chain of polyvinyl alcohol.
The hydrophobic group is preferably an aliphatic group having 6 or more carbon atoms (preferably an alkyl group or an alkenyl group) or an aromatic group.
When a hydrophobic group is bonded to the main chain terminal of polyvinyl alcohol, it is preferable to introduce a linking group between the hydrophobic group and the main chain terminal. Examples of linking groups include -S-, -C (CN) R ^{1
-, - NR 2 -, -} CS- and a combination thereof. R ¹ and R ² are each a hydrogen atom or an alkyl group having 1 to 6 carbon atoms (preferably an alkyl group having 1 to 6 carbon atoms).

When a hydrophobic group is introduced into the side chain of polyvinyl alcohol, a part of the acetyl group (—CO—CH ₃ ) of the vinyl acetate unit of polyvinyl alcohol is substituted with an acyl group (—CO—R) having 7 or more carbon atoms. ³ ). R ³ is an aliphatic group or aromatic group having 6 or more carbon atoms.
Commercially available modified polyvinyl alcohol (eg, MP103, MP203, R1130, manufactured by Kuraray Co., Ltd.) may be used.
The saponification degree of the (modified) polyvinyl alcohol used for the alignment film is preferably 80% or more. The degree of polymerization of (modified) polyvinyl alcohol is preferably 200 or more.
The rubbing process is performed by rubbing the surface of the alignment film several times in a certain direction with paper or cloth. It is preferable to use a cloth in which fibers having uniform length and thickness are uniformly planted.

The alignment film is essential in the production of the optically anisotropic layer in which the liquid crystalline compound is aligned, but is not essential in the optical compensation film. Therefore, if the liquid crystalline compound of the optically anisotropic layer is aligned and then the aligned liquid crystalline compound is fixed, only the optically anisotropic layer is transferred to another transparent support to form an optical compensation film. Is also possible.
When the alignment film is provided between the transparent support and the optically anisotropic layer, it is preferable to further provide an undercoat layer (adhesive layer) between the transparent support and the alignment film.

[Optically anisotropic layer]
The liquid crystalline compound contained in the optically anisotropic layer includes a rod-like liquid crystalline compound or a discotic liquid crystalline compound. The rod-like liquid crystalline compound is formed by orienting rod-like liquid crystalline molecules and fixing the alignment state. The discotic liquid crystalline compound is formed by orienting discotic liquid crystalline molecules and fixing the alignment state.
Examples of rod-like liquid crystalline molecules include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines. , Phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used.
The birefringence of the rod-like liquid crystal molecule is preferably 0.001 to 0.7. The rod-like liquid crystalline molecule preferably has a polymerizable group in order to fix its alignment state. The example of a polymeric group is the same as the example of the polymeric group of the disk shaped compound mentioned later.
The rod-like liquid crystal molecules preferably have a molecular structure that is substantially symmetric with respect to the minor axis direction. For that purpose, it is preferable to have a polymerizable group at both ends of the rod-like molecular structure.

The optically anisotropic layer is preferably a layer containing a discotic compound having negative uniaxiality and tilting orientation. In the discotic compound, as shown in FIG. 2, the angle formed by the disc surface of the discotic compound and the transparent support surface changes in the depth direction of the optically anisotropic layer (hybrid orientation). It is preferable. The optical axis of the discotic compound exists in the normal direction of the disc surface. The discotic compound has birefringence in which the refractive index in the disc surface direction is larger than the refractive index in the optical axis direction.
The optically anisotropic layer is preferably formed by orienting a discotic compound with an orientation film described later and fixing the discotic compound in the oriented state. The discotic compound is preferably fixed by a polymerization reaction.
In the optically anisotropic layer, there is no direction in which the retardation value becomes 0. In other words, the minimum retardation value of the optically anisotropic layer is a value exceeding 0.

Discotic compounds are described in various documents (C. Destrade et al., Mol. Crysr. Liq. Cryst., Vol. 71, page 111 (1981); edited by the Chemical Society of Japan, Quarterly Chemical Review, No. 22, Chemistry, Chapter 5, Chapter 10 Section 2 (1994); B. Kohne et al., Angew. Chem. Soc. Chem. Comm., Page 1794 (1985); J. Zhang et al., J. Am Chem. Soc., Vol. 116, page 2655 (1994)). The polymerization of the discotic compound is described in JP-A-8-27284.
In order to fix the discotic compound by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic compound. However, when the polymerizable group is directly connected to the disc-shaped core, it becomes difficult to maintain the orientation state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable group. Therefore, the discotic compound having a polymerizable group is preferably a compound represented by the following formula (III).

(III) D (-LP) _n
Where D is a discotic core; L is a divalent linking group, P is a polymerizable group, and n is an integer from 4 to 12.
An example of the disk-shaped core (D) is shown below. In each of the following examples, LP (or PL) means a combination of a divalent linking group (L) and a polymerizable group (P).

  In the formula (III), the divalent linking group (L) is selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, —CO—, —NH—, —O—, —S—, and combinations thereof. A divalent linking group is preferred. The divalent linking group (L) is a divalent combination of at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, -CO-, -NH-, -O-, and -S-. More preferably, it is a linking group. The divalent linking group (L) is most preferably a divalent linking group in which at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, -CO- and -O- are combined. . The alkylene group preferably has 1 to 12 carbon atoms. The alkenylene group preferably has 2 to 12 carbon atoms. The number of carbon atoms in the arylene group is preferably 6 to 10.

Examples of the divalent linking group (L) are shown below. The left side is bonded to the discotic core (D), and the right side is bonded to the polymerizable group (P). AL represents an alkylene group or an alkenylene group, and AR represents an arylene group. The alkylene group, alkenylene group and arylene group may have a substituent (eg, an alkyl group).
L1: -AL-CO-O-AL-
L2: -AL-CO-O-AL-O-
L3: -AL-CO-O-AL-O-AL-
L4: -AL-CO-O-AL-O-CO-
L5: -CO-AR-O-AL-
L6: -CO-AR-O-AL-O-
L7: -CO-AR-O-AL-O-CO-
L8: -CO-NH-AL-
L9: -NH-AL-O-
L10: -NH-AL-O-CO-

L11: -O-AL-
L12: -O-AL-O-
L13: -O-AL-O-CO-
L14: -O-AL-O-CO-NH-AL-
L15: -O-AL-S-AL-
L16: -O-CO-AR-O-AL-CO-
L17: -O-CO-AR-O-AL-O-CO-
L18: -O-CO-AR-O-AL-O-AL-O-CO-
L19: -O-CO-AR-O-AL-O-AL-O-AL-O-CO-
L20: -S-AL-
L21: -S-AL-O-
L22: -S-AL-O-CO-
L23: -S-AL-S-AL-
L24: -S-AR-AL-

  The polymerizable group (P) of the formula (III) is determined according to the type of polymerization reaction. Examples of the polymerizable group (P) are shown below.

The polymerizable group (P) is preferably an unsaturated polymerizable group (P1, P2, P3, P7, P8, P15, P16, P17) or an epoxy group (P6, P18). More preferably, it is most preferably an ethylenically unsaturated polymerizable group (P1, P7, P8, P15, P16, P17).
In the formula (III), n is an integer of 4 to 12. A specific number is determined according to the type of the disk-shaped core (D). In addition, although the combination of several L and P may differ, it is preferable that it is the same.
The optically anisotropic layer can be formed by applying a discotic compound and, if necessary, a coating liquid containing a polymerizable initiator and optional components on the alignment film.

The oriented discotic compound is fixed while maintaining the orientation state. The immobilization is preferably performed by a polymerization reaction. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. A photopolymerization reaction is preferred.
Examples of the photopolymerization initiator include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ether (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatic acyloin. Compound (described in US Pat. No. 2,722,512), polynuclear quinone compound (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (US Pat. No. 3,549,367) Acridine and phenazine compounds (JP-A-60-105667, U.S. Pat. No. 4,239,850) and oxadiazole compounds (U.S. Pat. No. 4,212,970).

The amount of the photopolymerization initiator used is preferably 0.01 to 20% by mass, more preferably 0.5 to 5% by mass, based on the solid content of the coating solution.
The light irradiation for the polymerization of the discotic compound preferably uses ultraviolet rays.
The irradiation energy is preferably 20 to 5000 mJ / cm ^2, and more preferably in the range of 100 to 800 mJ / cm ^2. In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions.
A protective layer may be provided on the optically anisotropic layer.

[Polarizer]
In general, a polarizing plate used for a liquid crystal display device includes a polarizing film and two transparent protective films disposed on both sides thereof. 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.
And, by making one protective film of the polarizing plate an optical compensation sheet made of the above polymer film, or an optical compensation sheet formed by laminating a polymer film and an optically anisotropic layer containing a liquid crystalline compound, The polarizing plate of this invention can be produced. Moreover, you may laminate | stack a normal cellulose acetate film as the other protective film of a polarizing film. Thus, the polarizing plate of the present invention can be obtained by laminating the optical compensation sheet and the polarizing film (with an adhesive) having an elastic modulus in the range of 4000 to 10,000 MPa.
In the polarizing plate of the present invention, the relationship between the slow axis of the polymer film and the transmission axis of the polarizing film varies depending on the type of liquid crystal display device to be applied. When the polarizing plate of the present invention is used in a TN, MVA, and OCB mode liquid crystal display device, the slow axis of the polymer film and the transmission axis of the polarizing film are arranged substantially in parallel to form a reflective liquid crystal When used in a display device, it is preferable to arrange the slow axis of the polymer film and the transmission axis of the polarizing film so as to be substantially 45 degrees.

[Liquid Crystal Display]
The optical compensation sheet of the present invention or the polarizing plate using the same is advantageously used for a transmissive liquid crystal display device or a reflective liquid crystal display device.
Examples of the transmissive liquid crystal display device include TN, MVA, and OCB mode liquid crystal display device liquid crystals. These liquid crystal display devices are composed of a cell and two polarizing plates arranged on both sides thereof. The liquid crystal cell carries a liquid crystal between two electrode substrates. In the case of an OCB mode liquid crystal display device, the optical compensation sheet of the present invention preferably has an optically anisotropic layer containing a discotic compound or a rod-shaped liquid crystal compound on a polymer film. 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.

When the optical compensation sheet of the present invention is used in a liquid crystal display device, one optical compensation sheet is disposed between the liquid crystal cell and one polarizing plate, or between the liquid crystal cell and both polarizing plates. Arrange two. In this way, the optical compensation sheet of the present invention is inserted between the normal polarizing plate and the liquid crystal cell, so that the liquid crystal cell is optically compensated in the same manner as in the past, and further light leakage in black display is reduced. be able to.
When the polarizing plate of the present invention is used in a liquid crystal display device, at least one of the two polarizing plates of the liquid crystal display device may be the polarizing plate of the present invention. By using the polarizing plate of the present invention, excellent viewing angle characteristics can be obtained, and distortion of the optical compensation sheet due to heat can be reduced, so that it can sufficiently cope with an increase in the size of the liquid crystal panel.

  In a VA mode liquid crystal cell, rod-like liquid crystalline 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) (2) Liquid crystal cell (SID97, Digest of tech. Papers (Preliminary Proceed) 28 (1997) 845 in which the VA mode is converted into a multi-domain (MVA mode) for widening the viewing angle ), (3) A liquid crystal cell 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 (Preliminary collections 58-59 of the Japan Liquid Crystal Society) (1998)) and (4) SURVAVAL mode liquid crystal cells (announced at LCD 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 crystalline molecules are aligned in a substantially opposite direction (symmetrically) between the upper part and the lower part of the liquid crystal cell. It is disclosed in the specifications of Japanese Patent Nos. 45882525 and 5410422. 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 of high response speed.

In a TN mode liquid crystal cell, 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.

Examples 1, 3, 4, 6, and 8 to 10 are reference examples.
[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) 300 parts by weight Methanol (No. 1) 2 solvents) 54 parts by mass 1-butanol (third solvent) 11 parts by mass ───────────────────────────────── ───

In 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 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 was horizontally stretched at a stretch ratio of 33% using a tenter under the conditions of 130 ° C. to produce a cellulose acetate film (thickness: 80 μm).
About the produced cellulose acetate film (optical compensation sheet), 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.
Furthermore, the elastic modulus in the stretching direction of the produced cellulose acetate film was measured and found to be 5700 MPa.

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

────────────────────────────────────
Cycloolefin solution composition ────────────────────────────────────
ZEONOR (manufactured by ZEON) 100 parts by mass Cyclohexane (first solvent) 400 parts by mass ────────────────────────────── ──────

In another mixing tank, 25 parts by mass of the following retardation increasing agent and 75 parts by mass of cyclohexane were added and stirred while heating to prepare a retardation increasing agent solution.
A dope was prepared by mixing 25 parts by mass of the retardation increasing agent solution with 475 parts by mass of the cycloolefin solution and stirring sufficiently. The addition amount of the retardation increasing agent was 5 parts by mass with respect to 95 parts by mass of the cycloolefin.

The obtained dope was cast using a band casting machine. A film having a residual solvent amount of 15% by mass was horizontally stretched at a stretch ratio of 45% using a tenter under the conditions of 150 ° C. to produce a cycloolefin film (thickness: 30 μm).
About the produced cycloolefin film (optical compensation sheet), the Re retardation value and Rth retardation value in wavelength 550nm were measured using the ellipsometer (M-150, JASCO Corporation make). The results are shown in Table 1.
Furthermore, the elastic modulus in the stretching direction of the produced cycloolefin film was measured and found to be 4200 MPa.

[Example 3]
The addition amount of the retardation increasing agent is 3 with respect to 100 parts by mass of cellulose acetate.
. The cellulose acetate film (optical compensation sheet) produced in the same manner as in Example 1 except that the amount was adjusted to 0 parts by mass and the draw ratio was changed to 20%. An ellipsometer (M-150, JASCO Corporation) The Re retardation value and the Rth retardation value at a wavelength of 550 nm were measured. The results are shown in Table 1.
On this cellulose acetate film, a coating solution having the following composition was applied at 28 ml / m ² with a # 16 wire bar coater. The alignment film was formed by drying with warm air of 60 ° C. for 60 seconds and further with warm air of 90 ° C. for 150 seconds.
Next, the formed film was rubbed in the direction of 45 ° with the slow axis of cellulose acetate film (measured at a wavelength of 632.8 nm).

────────────────────────────────────
Alignment film coating solution composition ────────────────────────────────────
Modified polyvinyl alcohol 10 parts by weight Water 371 parts by weight Methanol 119 parts by weight Glutaraldehyde (crosslinking agent) 0.5 parts by weight ─────────────────────── ─────────────

(Formation of optically anisotropic layer)
On the alignment film, 41.01 g of the following discotic (liquid crystalline) 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, manufactured by Eastman Chemical Co., Ltd.) 0.90 g, cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemical Co., Ltd.) 0.23 g, photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy Co.) 1.35 g, A coating solution prepared by dissolving 0.45 g of a sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) in 102 g of methyl ethyl ketone was applied with a # 3 wire bar. This was affixed to a metal frame and heated in a thermostatic chamber at 130 ° C. for 2 minutes to orient the discotic compound. Next, using a 120 W / cm high-pressure mercury lamp at 130 ° C., UV irradiation was performed for 1 minute to polymerize the discotic compound. Then, it stood to cool to room temperature. In this way, an optically anisotropic sheet was prepared by forming an optically anisotropic layer.
The Re retardation value of the optically anisotropic layer measured at a wavelength of 546 nm was 38 nm. The angle (tilt angle) between the disk surface and the transparent support (cellulose acetate film) surface was 40 ° on average. The results are shown in Table 1.
Furthermore, the elastic modulus of the produced optical compensation sheet was measured in the stretching direction of the cellulose acetate film and found to be 4600 MPa.

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

────────────────────────────────────
Polycarbonate solution composition ────────────────────────────────────
Carbonate (made by Teijin) 100 parts by weight Methylene chloride (first solvent) 400 parts by weight ──────────────────────────────── ────

The obtained dope was cast using a band casting machine to produce a polycarbonate film (thickness: 50 μm). About the produced polycarbonate film (optical compensation sheet), the Re retardation value and Rth retardation value in wavelength 550nm were measured using the ellipsometer (M-150, JASCO Corporation make). The results are shown in Table 1.
Furthermore, the elastic modulus in the stretching direction of the produced polycarbonate film was measured and found to be 2500 MPa.

Table 1 ────────────────────────────────────
Film retardation increasing agent draw ratio Re Rth
────────────────────────────────────
Example 1 3.5 parts by mass 33% 40 nm 130 nm
Example 2 5.0 parts by mass 45% 50 nm 240 nm
Example 3 3.0 parts by mass 20% 20 nm 110 nm
Comparative Example 1 None Unstretched 30 nm 40 nm
────────────────────────────────────

[Example 4]
A polarizing film is prepared by adsorbing iodine to a stretched polyvinyl alcohol film, and using the polyvinyl alcohol adhesive, the cellulose triacetate film prepared in Example 1 is placed on one side of the polarizing film and the other is a commercially available cellulose triacetate. The film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) was saponified and pasted, and then dried at 80 ° C. for 10 minutes.
The transmission axis of the polarizing film and the slow axis of the cellulose acetate film prepared in Example 1 were arranged in parallel. The transmission axis of the polarizing film and the slow axis of the commercially available cellulose triacetate film were arranged in parallel.
In this way, a polarizing plate was produced.

[Example 5]
A polarizing plate was produced in the same manner as in Example 4 except that the cycloolefin film produced in Example 2 was used.

[Comparative Example 2]
A polarizing film is prepared by adsorbing iodine to a stretched polyvinyl alcohol film, and using the polyvinyl alcohol adhesive, the polycarbonate film prepared in Comparative Example 1 is placed on one side of the polarizing film, and the other is a commercially available polycarbonate film ( After affixing Teijin Ltd.), the film was dried at 80 ° C. for 30 minutes. However, the polarizing ability was lowered, and the function as a polarizing plate was not sufficiently performed.

[Example 6]
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 4 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, the viewing angle was measured in eight steps from black display (L1) to white display (L8) using the measuring machine (EZ Contrast 160D, ELDIM). The results are shown in Table 2.

[Example 7]
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. Was attached to the observer side through an adhesive so that the cellulose acetate film produced in Example 2 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, the viewing angle was measured in eight steps from black display (L1) to white display (L8) using the measuring machine (EZ Contrast 160D, ELDIM). The results are shown in Table 2.

[Comparative Example 3]
About a liquid crystal display device (VL-1530S, manufactured by Fujitsu Limited) using a vertical alignment type liquid crystal cell, from a black display (L1) to a white display (L8) using a measuring device (EZ Contrast 160D, manufactured by ELDIM) The viewing angle was measured in 8 stages. The results are shown in Table 2.

Table 2 ────────────────────────────────────
Liquid crystal viewing angle (contrast ratio of 10 or more and no black-side gradation inversion)
Display device Transmission axis direction 45 ° from transmission axis ─────────────────────────────────────
Example 6> 80 °> 80 °
Example 7> 80 °> 80 °
Comparative Example 3> 80 ° 44 °
────────────────────────────────────
(Ii) Black-side gradation inversion: inversion between L1 and L2

[Example 8]
A polarizing film is prepared by adsorbing iodine to a stretched polyvinyl alcohol film. Using the polyvinyl alcohol-based adhesive, the cellulose triacetate film prepared in Example 3 is placed on one side of the polarizing plate, and the other is a commercially available cellulose triacetate. The film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) was saponified and pasted, and then dried at 80 ° C. for 10 minutes.
The transmission axis of the polarizing plate and the slow axis of the cellulose acetate film prepared in Example 3 were arranged in parallel. Furthermore, the transmission axis of the polarizing plate and the slow axis of the discotic layer of the optical compensation sheet prepared in Example 3 were arranged to be substantially 45 degrees. The transmission axis of the polarizing plate and the slow axis of the commercially available cellulose triacetate film were arranged so as to be parallel. Thus, an elliptically polarizing plate was produced.

[Example 9]
(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 rubbed. The obtained two glass substrates were faced to each other so that the rubbing directions were parallel to each other, and the cell gap was set to 6 μm. A bend-aligned liquid crystal cell was prepared by injecting a liquid crystal compound (ZLI1132, manufactured by Merck & Co., Inc.) having a Δn of 0.1396 into the cell gap.
Two elliptical polarizing plates prepared in Example 8 were attached so as to sandwich the manufactured 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 and the rubbing direction of the optically anisotropic layer facing it were antiparallel.
A rectangular wave voltage of 55 Hz was applied to the liquid crystal cell. A normally white mode of 2V white display and 5V black display was set. Using the measuring device (EZ Contrast 160D, manufactured by ELDIM) as the contrast ratio, the viewing angle can be adjusted in 8 steps from black display (L1) to white display (L8). It was measured. The results are shown in Table 3.

Table 3 ────────────────────────────────────
Liquid crystal viewing angle (contrast ratio of 10 or more and no black-side gradation inversion)
Display device Up / Down Left / Right ────────────────────────────────────
Example 9 80 ° 80 ° 80 °
────────────────────────────────────
(Ii) Black-side gradation inversion: inversion between L1 and L2

[Example 10]
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 4 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 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, the viewing angle was measured in eight steps from black display (L1) to white display (L8) using the measuring machine (EZ Contrast 160D, ELDIM). The results are shown in Table 4.

[Comparative Example 4]
About liquid crystal display device (6E-A3, manufactured by Sharp Corporation) using TN type liquid crystal cell, from black display (L1) to white display (L8) using measuring machine (EZ Contrast 160D, manufactured by ELDIM) The viewing angle was measured in 8 stages. The results are shown in Table 4.

Table 4 ────────────────────────────────────
Liquid crystal viewing angle (contrast ratio of 10 or more and no black-side gradation inversion)
Display device Up / Down Left / Right ────────────────────────────────────
Example 10 18 ° 23 ° 77 °
Comparative Example 4 15 ° 25 ° 37 °
────────────────────────────────────
(Ii) Black-side gradation inversion: inversion between L1 and L2

Claims (7)

A liquid crystal display device comprising a TN mode liquid crystal cell and two polarizing plates arranged on both sides thereof, wherein at least one polarizing plate has an optical compensation sheet bonded to at least one surface of the polarizing film. The optical compensation sheet of the polarizing plate is disposed on the liquid crystal cell side, and the optical compensation sheet is composed of a cycloolefin polymer film. Both the cycloolefin polymer film and the optical compensation sheet are defined by the following formula (I): The Re retardation value is in the range of 20 to 50 nm, the Rth retardation value defined by the following formula (II) is in the range of 70 to 400 nm, and the elastic modulus in at least one direction is 4000 to 10,000 MPa. a liquid crystal display device comprising a range near Turkey:
(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 liquid crystal display device according to claim 1, wherein the cycloolefin polymer is a norbornene polymer. 2. The liquid crystal display device according to claim 1, wherein the cycloolefin polymer film comprises a stretched cycloolefin polymer film having an elastic modulus in the stretch direction of 4000 to 10,000 MPa. 4. The liquid crystal display device according to claim 3, wherein a stretching ratio in the stretching direction of the cycloolefin polymer film is 20 to 70%. 5. The liquid crystal display device according to claim 4, wherein a stretching ratio in the stretching direction of the cycloolefin polymer film is 45 to 70%. The liquid crystal display device according to claim 1, wherein the transmission axis of the polarizing film and the slow axis of the optical compensation sheet bonded thereto are arranged substantially in parallel . 2. The liquid crystal display device according to claim 1, wherein the Rth retardation value defined by the formula (II) is in the range of 70 to 240 nm .