JP2003114330A - Optical compensation sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device reduced in tint change caused by viewing angles. SOLUTION: The optical compensation sheet has a cellulose acetate film having 59.0 to 61.5% acetylation degree and an optical anisotropic layer made of a liquid crystal compound applied on the cellulose acetate film. The optical compensation sheet having the A value of the cellulose acetate film defined by formula (1): A=Re(420)/Re(550) ranging from 1.0 to 2.0 is used for a liquid crystal display device. In the formula (1), Re(420) represents the retardation of the film for the light at 420 nm wavelength and Re(550) represents the retardation of the film for the light at 550 nm wavelength.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical compensation sheet using a cellulose acetate film.

[0002]

2. Description of the Related Art A liquid crystal display device comprises a polarizing plate and a liquid crystal cell. In the TN mode TFT liquid crystal display device which is currently mainstream, an optical compensation film is inserted between a polarizing plate and a liquid crystal cell as described in JP-A-8-50206 to realize a liquid crystal display device with high display quality. ing. However, this method has a problem that the liquid crystal display device itself becomes thick. Japanese Patent Application Laid-Open No. 1-68940 uses an elliptical polarizing plate having a retardation film on one surface of a polarizing film and a protective film on the other surface to increase the front contrast without making the liquid crystal display device thick. There is a statement that it is possible. However, it has been found that the retardation film of the present invention is apt to cause a retardation due to strain such as heat and has a problem in durability.

To solve the problem of phase difference caused by distortion, Japanese Patent Laid-Open No. 7-191217 and European Patent 0911
In the specification of 656A2, an optical compensation film in which an optically anisotropic layer made of a discotic compound is coated on a transparent support is directly used as a protective film of a polarizing plate without increasing the thickness of the liquid crystal display device. Solved the problem of durability. With these conventional techniques, a liquid crystal display device having high contrast and sufficiently satisfying durability can be realized. However, when it is used for a large-sized panel, especially for a television, there is a problem in that the tint changes greatly depending on the viewing angle, so that multiple people cannot see the same image at the same time.

[0004]

According to the research conducted by the present inventor, the cause of the change in tint depending on the viewing angle is found in JP-A-7-1912.
It was found that the birefringence of the transparent support, particularly cellulose triacetate film, described in JP-A-17 and EP0911656A2 depends on the wavelength. Cellulose triacetate film is disclosed in
As described in JP-A-218724, the longer the measurement wavelength, the larger the birefringence. On the other hand, the birefringence of the liquid crystal compound used in the commercially available liquid crystal cell becomes smaller as the measurement wavelength becomes larger. When viewed with 550 nm light, which has high visibility, the contrast change depending on the viewing angle is highly compensated,
There is a slight shift in optical compensation at short wavelengths and long wavelengths, resulting in a change in tint. Particularly in the case of an optical compensation sheet having an optically anisotropic layer made of a liquid crystal compound on a cellulose triacetate film, when the ratio of the short wavelength retardation / long wavelength retardation of the optical anisotropic layer is larger than that in the liquid crystal cell. In addition, this color change is large.

An object of the present invention is to provide an optical compensatory sheet comprising a cellulose acetate film coated with a liquid crystal compound, which is capable of highly compensating for a tint change depending on the viewing angle of a liquid crystal cell.
An object of the present invention is to provide a liquid crystal display device which is arranged on one side of a polarizing film and has a high display quality without causing any problems with a thickness below the conventional one. Still another object of the present invention is to add an optical compensation function to a polarizing plate without increasing the number of components of the polarizing plate. As a result of the research conducted by the present inventor, the problem that the tint change occurs when a transparent support has a cellulose acetate film having an A value defined by the following formula (1) in the range of 1.0 to 2.0. It turned out to be a solution.

[0006]

The objects of the present invention have been achieved by the following optical compensation sheets (1) to (6). (1) An optical compensation sheet having a cellulose acetate film having a degree of acetylation in the range of 59.0 to 61.5% and an optically anisotropic layer made of a liquid crystalline compound coated on the cellulose acetate film. A defined by the following formula (1) of the cellulose acetate film:
Optical compensatory sheet characterized by a value in the range of 1.0 to 2.0: A value = Re (420) / Re (550) [wherein Re (420) is for light with a wavelength of 420 nm. Retardation value of film; Re (55
0) is the retardation value of the film for light having a wavelength of 550 nm]. (2) The Re retardation value of the cellulose acetate film is in the range of 0 to 200 nm, and R
The optical retardation sheet according to (1), which has a th retardation value in the range of 70 to 400 nm.

(3) Cellulose acetate film
Cellulose acetate, and cellulose acetate 1
The optical compensation sheet as described in (1), which contains 0.01 to 20 parts by mass of an aromatic compound having at least two aromatic rings with respect to 00 parts by mass. (4) The maximum wavelength of the molar extinction coefficient of the aromatic compound is 15
It is characterized by being in the range of 0 to 400 nm (3)
The optical compensation sheet according to item 1. (5) The optical compensation sheet according to (1), wherein the thickness of the cellulose acetate film is in the range of 10 to 70 μm. (6) The optical compensation sheet as described in any one of (1) to (5), wherein the liquid crystal compound is a discotic compound.

[0008]

The present inventor has succeeded in optically compensating for a tint change due to the viewing angle of a liquid crystal cell without causing side effects, and has found a manufacturing method which can be mass-produced at low cost. A polarizing plate using the optical compensation sheet of the present invention as a protective film is TN
It can be advantageously used for a (Twisted Nematic) type liquid crystal display device.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION [Film retardation]
The Re retardation value of the film is defined by the following formula. Retardation value (Re) = (nx−ny) × d where nx is the in-plane retardation index of the retardation plate (maximum in-plane index of refraction); ny is the retardation Is the refractive index in the direction normal to the slow axis in the plane of the plate; and d is
It is the thickness (nm) of the retardation film.

The A value of the film is defined by the following equation (1). A value = Re (420) / Re (550) [wherein, Re (420) is the retardation value of the film with respect to light having a wavelength of 420 nm; Re (55)
0) is the retardation value of the film for light with a wavelength of 550 nm. The A value is preferably 1.0 to 1.5, and more preferably 1.02 to 1.3 in order to minimize the change in tint depending on the viewing angle.
Since the change in tint is determined by matching with the A value of the liquid crystal used in the cell, it is preferable to adjust the A value appropriately according to the liquid crystal cell.

The Rth retardation value of the film is defined by the following formula (II). (II) Rth = {(nx + ny) / 2-nz} × d In the formula (II), nx is the refractive index in the slow axis direction (direction in which the refractive index is maximum) in the film plane; ny is ,
Fast axis direction in the film plane (direction in which the refractive index is minimum)
Is the refractive index of the film; nz is the refractive index in the thickness direction of the film; and d is the film thickness in nm.

In the present invention, the Re retardation value of the cellulose acetate film is adjusted to 0 to 200 nm, and the Rth retardation value is adjusted to 70 to 400 nm. When two optically anisotropic cellulose acetate films are used in a liquid crystal display device, the Rth of the film is
The retardation value is preferably 70 to 250 nm. When one optically anisotropic cellulose acetate film is used for the liquid crystal display device, the Rth of the film is
The retardation value is preferably 150 to 400 nm. The birefringence (Δn: nx-ny) of the cellulose acetate film is 0.00 to 0.00.
It is preferably 2. The birefringence of the cellulose acetate film in the thickness direction {(nx + ny) / 2-
nz} is preferably 0.001 to 0.04.

[Cellulose Acetate] In the present invention, cellulose acetate having an acetylation degree of 59.0 to 61.5% is used. The degree of acetylation means the amount of bound acetic acid per unit mass of cellulose. Acetification degree is AST
M: According to the measurement and calculation of the degree of acetylation in D-817-91 (testing method for cellulose acetate, etc.). The viscosity average degree of polymerization (DP) of cellulose acetate is 25
It is preferably 0 or more, more preferably 290 or more. The cellulose acetate used in the present invention preferably has a narrow molecular weight distribution of Mw / Mn (Mw is a mass 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.

Generally, the second and third positions of cellulose acetate
The hydroxyl groups at the 6- and 6-positions are not evenly distributed in 1/3 of the total substitution degree, and the substitution degree of the 6-position hydroxyl group tends to be small. In the present invention, cellulose acetate 6
The degree of substitution of the hydroxyl groups at positions 2 and 3 is preferably the same, and more preferably increased. As a specific ratio, the substitution degree at the 6th position is the total substitution degree (2nd position,
It is preferably 32% or more, more preferably 33% or more, and most preferably 34% or more with respect to the total of the substitution degrees at the 3rd and 6th positions. As a specific numerical value, the 6-position substitution degree of cellulose acetate is
It is preferably 0.88 or more. The substitution degree at each position can be measured by NMR. Cellulose acetate as described above can be obtained by the method described in JP-A No. 11-5851, paragraphs [0043] to [0044] [Examples].
[Synthesis example 1], paragraph numbers [0048] to [0049]
[Synthesis example 2], paragraph numbers [0051] to [0052]
It can be obtained by the method of [Synthesis example 3].

[Retardation Raising Agent] The retardation and wavelength dispersion of the cellulose acetate film can be adjusted by using the same compound. For example, a retardation increasing agent can be used to control chromatic dispersion. Specifically, the retardation and the wavelength dispersion can be controlled by using an aromatic compound having at least two aromatic rings as an additive. 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. In order to adjust the wavelength dispersion in the visible region, it is preferable that the absorption maximum wavelength of the aromatic compound is as long as possible. However, when the wavelength is too long, the aromatic compound colors the film. The absorption maximum wavelength of the aromatic compound is preferably 150 to 400 nm, and 180 to 370 n
More preferably m, 200 to 350 nm
Is most preferable. The wavelength dispersion is preferably adjusted by adjusting the addition amount of the aromatic compound. The aromatic compound is preferably used in the range of 0.1 to 15 parts by mass, more preferably 1.0 to 10 parts by mass with respect to 100 parts by mass of cellulose acetate. You may use together two or more types of aromatic compounds.

The aromatic ring of the aromatic compound contains an aromatic heterocycle 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, a 6-membered ring or a 7-membered ring, more preferably a 5-membered ring or a 6-membered ring. The aromatic heterocycle generally has the largest number of double bonds. As the hetero atom, a nitrogen atom, an oxygen atom and a sulfur atom are preferable, and a nitrogen atom is particularly preferable. Examples of the aromatic hetero ring are a furan ring, a thiophene ring, a pyrrole ring, an oxazole ring, an isoxazole ring, a thiazole ring, an isothiazole ring, an imidazole ring, a pyrazole ring, a furazan ring, a triazole ring, a pyran ring and a pyridine ring. , A pyridazine ring, a pyrimidine ring, a pyrazine ring and a 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, A benzene ring and a 1,3,5-triazine ring are more preferable. 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 2
It is preferably from 20 to 20, more preferably from 2 to 12, even more preferably from 2 to 8, and most preferably from 2 to 6. The bonding relationship between two aromatic rings is (b) when forming a condensed ring (a).
It can be classified into a case where it is directly connected by a single bond and a case where it is connected through a linking group (c) (because it is an aromatic ring, a spiro bond cannot be formed). The connection relation may be any of (a) to (c).

Examples of the condensed ring of (a) (condensed ring of two or more aromatic rings) include indene ring, naphthalene 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,
A phenanthridine ring, a xanthene ring, a phenazine ring, a phenothiazine ring, a phenoxathiine ring, a phenoxazine ring and a thianthrene ring are included. A naphthalene ring, an azulene ring, an indole ring, a benzoxazole ring, a benzothiazole ring, a benzimidazole ring, a benzotriazole ring and a quinoline ring are preferable. The single bond (b) is preferably a bond between carbon atoms of two aromatic rings. Connect two aromatic rings with two or more single bonds,
An aliphatic ring or a non-aromatic heterocycle may be formed between the two aromatic rings.

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

The aromatic ring and the linking group may have a substituent. Examples of the substituent include a halogen atom (F, C
1, 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 sulfonamide group, aliphatic substituted amino group, aliphatic substituted carbamoyl group, aliphatic substituted sulfamoyl group, aliphatic substituted ureido group and non-aromatic An aromatic heterocyclic group is included.

The number of carbon atoms in the alkyl group is preferably 1-8. A chain alkyl group is preferable to a cyclic alkyl group, and a straight chain 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 straight chain 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 straight chain 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 number of carbon atoms of the aliphatic acyl group is 1 to 1
It is preferably 0. Examples of the aliphatic acyl group include acetyl, propanoyl and butanoyl. The number of carbon atoms of the aliphatic acyloxy group is preferably 1-10. Examples of the aliphatic acyloxy group include acetoxy. The number of carbon atoms of the alkoxy group is preferably 1-8. The alkoxy group may further have a substituent (eg, an alkoxy group). Examples of alkoxy groups (including substituted alkoxy groups) include methoxy, ethoxy, butoxy and methoxyethoxy. The alkoxycarbonyl group preferably has 2 to 10 carbon atoms. Examples of the alkoxycarbonyl group include methoxycarbonyl and ethoxycarbonyl. The alkoxycarbonylamino group preferably has 2 to 10 carbon atoms. Examples of the alkoxycarbonylamino group include methoxycarbonylamino and ethoxycarbonylamino.

The number of carbon atoms in the alkylthio group is 1 to 1.
It is preferably 2. Examples of the alkylthio group include methylthio, ethylthio and octylthio.
The alkylsulfonyl group preferably has 1 to 8 carbon atoms. Examples of alkylsulfonyl groups include methanesulfonyl and ethanesulfonyl. The number of carbon atoms in the aliphatic amide group is preferably 1-10. Examples of the aliphatic amide group include acetamide. The aliphatic sulfonamide group preferably has 1 to 8 carbon atoms. Examples of the aliphatic sulfonamide group include methanesulfonamide, butanesulfonamide and n-octanesulfonamide. The aliphatic substituted amino group preferably has 1 to 10 carbon atoms. Examples of the aliphatic substituted amino group include dimethylamino, diethylamino and 2-carboxyethylamino. The number of carbon atoms of the aliphatic-substituted carbamoyl group is preferably 2-10. Examples of the aliphatic substituted carbamoyl group include methylcarbamoyl and diethylcarbamoyl. The number of carbon atoms of the aliphatic-substituted sulfamoyl group is preferably 1-8. Examples of the aliphatic substituted sulfamoyl group include methylsulfamoyl and diethylsulfamoyl. The aliphatic substituted ureido group preferably has 2 to 10 carbon atoms. Examples of the aliphatic substituted ureido group include methylureido. Examples of the non-aromatic heterocyclic group include piperidino and morpholino. The molecular weight of the retardation increasing agent is preferably 300 to 800. For the retardation increasing agent, see JP-A-200
0-11104, 2000-275434, 2000-284124, 2001-13323, and WO 00/65384.

[Production of Cellulose Acetate Film]
It is preferable to produce the cellulose acetate film by the solvent casting method. In the solvent cast method, a film is manufactured using a solution (dope) in which cellulose acetate is dissolved in an organic solvent. The organic solvent is
It contains a solvent selected from ether having 3 to 12 carbon atoms, ketone having 3 to 12 carbon atoms, ester having 3 to 12 carbon atoms, and halogenated hydrocarbon having 1 to 6 carbon atoms. preferable. The ether, ketone and ester may have a cyclic structure. Functional groups of ethers, ketones and esters (ie -O
A compound having two or more of any one of —, —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 kinds of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group.

Examples of ethers 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 ester having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate. Examples of organic solvents having two or more types of functional groups,
Includes 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol. The number of carbon atoms in the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of hydrogen atoms of the halogenated hydrocarbon substituted with halogen is preferably 25 to 75 mol%, and 3
It is more preferably 0 to 70 mol%, further preferably 35 to 65 mol%, and 40 to 60
Most preferably, it is mol%. Methylene chloride is a typical halogenated hydrocarbon. You may mix and use 2 or more types of organic solvents.

The cellulose acetate solution can be prepared by a general method. The general method means treatment at a temperature of 0 ° C. or higher (normal temperature or high temperature). The solution can be prepared by using the dope preparation method and apparatus in the usual solvent casting method. In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly methylene chloride) as the organic solvent. The amount of cellulose acetate is adjusted so that the obtained solution contains 10 to 40% by mass. The amount of cellulose acetate is more preferably 10 to 30% by mass. The organic solvent (main solvent) may contain any of the additives described below. The solution can be prepared by stirring cellulose acetate and an organic solvent at room temperature (0 to 40 ° C.). The highly concentrated solution may be stirred under pressure and heat. Specifically, the cellulose acetate and the organic solvent are placed in a pressure vessel and sealed, and the mixture is stirred under pressure while being heated to a temperature not lower than the boiling point of the solvent at room temperature and not boiling the solvent. The heating temperature is usually 40 ° C. or higher, preferably 60 to 200 ° C., and more preferably 80 to 110 ° C.

The respective components may be roughly mixed in advance and then placed in a container. Moreover, you may throw in in a container one by one. The container must be configured to allow stirring. The container can be pressurized by injecting an inert gas such as nitrogen gas. Alternatively, the increase in vapor pressure of the solvent due to heating may be used.
Alternatively, after sealing the container, each component may be added 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. It is also possible to heat the entire container 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 use this to stir. The stirring blade is preferably long enough to reach 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 wall of the container. 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 cooled and then taken out from the container, or after taking out, it is cooled using a heat exchanger or the like.

The solution can be prepared by the cooling dissolution method. In the cooling dissolution method, cellulose acetate can be dissolved even in an organic solvent which is difficult to dissolve by a usual dissolution method. Even if the solvent is a solvent that can dissolve cellulose acetate by an ordinary dissolution method, the cooling dissolution method has an effect of rapidly obtaining a uniform solution. 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 this mixture in an amount of 10 to 40% by mass. The amount of cellulose acetate is more preferably 10 to 30% by mass. Furthermore, any additives described below may be added to the mixture.

Next, the mixture is heated 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, 12
Most preferably, it is at least ° C / min. The higher the cooling rate, the more preferable, but 10000 ° C./sec is the theoretical upper limit, 1000 ° C./sec is the technical upper limit, and 1
00 ° C./sec is a practical upper limit. The cooling rate is
It 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.

Further, this is 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C.,
When heated to the most preferably 0 to 50 ° C., the cellulose acetate dissolves in the organic solvent. The temperature may be raised by leaving it at room temperature or by heating it in a warm bath. The heating rate is preferably 4 ° C / min or more, and 8 ° C / min.
It is more preferably at least minutes, and most preferably at 12 ° C./minute or more. The higher the heating rate, the more preferable, but 10000 ° C./sec is the theoretical upper limit,
0 ° C./sec is the technical upper limit and 100 ° C./sec 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 to the final heating temperature. . 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 judged only by visually observing the appearance of the solution.

In the cooling dissolution method, it is desirable to use a closed container in order to avoid mixing of water due to dew condensation during cooling. In the cooling and heating operation, pressure is applied during cooling,
If the pressure is reduced during heating, the dissolution time can be shortened. In order to carry out the pressurization and depressurization, it is desirable to use a pressure resistant container. A 20% by mass solution of cellulose acetate (acetylation degree: 60.9%, viscosity average degree of polymerization: 299) dissolved in methyl acetate by a cooling dissolution method was 3% by differential scanning calorimetry (DSC).
A quasi-phase transition point between a sol state and a gel state exists near 3 ° C., and at this temperature or lower, a uniform gel state is obtained. Therefore,
This solution must be kept at a temperature not lower than the pseudo phase transition temperature, preferably about 10 ° C. plus the gel phase transition temperature. However, this pseudo-phase transition temperature differs depending on the degree of acetylation of cellulose acetate, the viscosity average degree of polymerization, the solution concentration and the organic solvent used.

A cellulose acetate film is produced from the prepared cellulose acetate solution (dope) by the solvent casting method. The dope is cast on a drum or band and the solvent is evaporated to form a film. The dope before casting is preferably adjusted in concentration so that the solid content is 18 to 35%. The surface of the drum or band is preferably mirror-finished. Regarding the casting and drying methods in the solvent casting method, US Pat.
No. 03, No. 2492078, No. 2492977, No. 2492978, No. 2607704, No. 27390.
No. 69, No. 2739070, British Patent 640731.
Nos. 736,892 and JP-B-45-455
4, JP-A-49-5614, JP-A-60-176834.
Nos. 60-203430 and 62-115035. The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or lower.
After casting, it is preferable to apply air for 2 seconds or more to dry. It is also possible to strip the obtained film from the drum or band and further dry it with hot 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, the time from casting to stripping can be shortened. 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.

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

When casting a plurality of cellulose acylate liquids of two or more layers, it is possible to cast a plurality of cellulose acylate solutions, and a plurality of castings are provided at intervals in the traveling direction of the support. A film may be produced by casting a solution containing cellulose acylate from the mouth and laminating the solutions, for example, JP-A-61-158414, JP-A-1-122419, and JP-A-11-19828.
The method described in each publication of No. 5 can be applied. Further, it may be formed into a film by casting a cellulose acylate solution from two casting ports.
0-27562, JP-A-61-94724, JP-A-61-942245, JP-A-61-104813,
JP-A-61-158413 and JP-A-6-134
It can be carried out by the method described in each publication of No. 933. Further, a cellulose acylate film described in JP-A-56-162617, in which the flow of a high-viscosity cellulose acylate solution is wrapped with a low-viscosity cellulose acylate solution, and the high- and low-viscosity cellulose acylate solutions are simultaneously extruded. A casting method may be used.

Alternatively, by using two casting ports, the film formed on the support by the first casting port is peeled off, and the second casting is carried out on the side in contact with the surface of the support. , A film may be prepared, for example, Japanese Patent Publication No.
This is the method described in Japanese Patent Publication No. 4-20235. The cellulose acylate solutions to be cast may be the same solution or different cellulose acylate solutions and are not particularly limited. In order to impart a function to a plurality of cellulose acylate layers, a cellulose acylate solution corresponding to the function may be extruded from each casting port. Further, the cellulose acylate solution of the present invention can be simultaneously cast with other functional layers (for example, an adhesive layer, a dye layer, an antistatic layer, an antihalation layer, a UV absorbing layer, a polarizing layer, etc.).

In the conventional monolayer solution, it is necessary to extrude a high-concentration and high-viscosity cellulose acylate solution in order to obtain a required film thickness, and in this case, the stability of the cellulose acylate solution is poor. As a result, solid matters are generated, which leads to problems such as defective spots and poor flatness. As a solution to this problem, by casting a plurality of cellulose acylate solutions through a casting port, it is possible to simultaneously extrude a highly viscous solution onto a support, thereby improving the flatness and producing an excellent planar film. Not only can you
By using a concentrated cellulose acylate solution, it is possible to reduce the drying load and increase the film production speed.

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

A deterioration inhibitor (eg, antioxidant, peroxide decomposer, radical inhibitor, metal deactivator, acid scavenger, amine) may be added to the cellulose acetate film. For the deterioration preventing agent, see JP-A-3-19920.
No. 1, No. 5-1907073, No. 5-194789
Nos. 5,271,471 and 6,107,854. The addition amount of the deterioration inhibitor 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. If the addition amount is less than 0.01% by mass, the effect of the deterioration inhibitor is hardly recognized. Addition amount is 1% by mass
If it exceeds the range, bleed-out (bleeding) of the deterioration preventive agent on the film surface may be observed. Butylated hydroxytoluene (BHT) and tribenzylamine (TBA) can be mentioned as examples of particularly preferable deterioration preventing agents.

[Biaxial Stretching] The cellulose acetate film of the present invention is preferably stretched in order to reduce virtual strain. Since the virtual strain in the stretching direction can be reduced by stretching, biaxial stretching is more preferable in order to reduce the strain in all in-plane directions. Biaxial stretching includes a simultaneous biaxial stretching method and a sequential biaxial stretching method,
From the viewpoint of continuous production, the sequential biaxial stretching method is preferable, after casting the dope, peeling from the band or drum,
After stretching in the width direction (longitudinal method), the longitudinal direction (width direction)
Is stretched. The method of stretching in the width direction is described in, for example, JP-A-62-115035, JP-A-4-152125,
It is described in each gazette of the above-mentioned 4-284221, 4-298310, and 11-48271.
The film is stretched at room temperature or under heating.
The heating temperature is preferably below the glass transition temperature of the film. The film can be stretched during the treatment during drying, and is particularly effective when the solvent remains. In the case of stretching in the longitudinal direction, for example, the film is stretched by adjusting the speed of the film transport roller so that the film winding speed is faster than the film stripping speed. In the case of stretching in the width direction, the film can also be stretched by conveying while holding the width of the film with a tenter and gradually widening the width of the tenter. After the film is dried, it may be stretched using a stretching machine (preferably uniaxial stretching using a long stretching machine). The stretch ratio of the film (the ratio of the increase due to the stretching to the original length) is 5 to
50% is preferable, more preferably 10 to 40%,
Most preferably, it is 15 to 35%.

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

[Hygroscopic Expansion Coefficient] A method for measuring the hygroscopic expansion coefficient is shown below. A sample with a width of 5 mm and a length of 20 mm was cut out from the produced film, and one end was fixed to 25
It was hung in an atmosphere of 20 ° C. and 20% RH. A weight of 0.5 g was hung on the other end and left for a certain period of time. Next, with the temperature kept constant, the humidity was set to 80% RH and the amount of deformation of the length was measured. The measurement was performed on 10 samples of the same sample, and the average value was adopted. It has been found that the dimensional change of the film due to moisture absorption can be achieved by reducing the free volume in the polymer film. The free volume is largely influenced by the amount of residual solvent during film formation, and the smaller the amount of residual solvent, the smaller the dimensional change. General techniques for reducing residual solvent include:
It is necessary to dry at high temperature for a long time, but if it is too long, the productivity naturally lowers.
It is preferably from 01% by mass to 1% by mass, and 0.0
2 mass% to 0.07 mass% is more preferable, and 0.03 mass% to 0.05 mass% is the most preferable.
By controlling the residual solvent amount, a polarizing plate having an optical compensation ability can be manufactured at low cost and with high productivity. Further, as a method for reducing the dimensional change due to the moisture absorption, it is preferable to add a compound having hydrophobicity. The material having hydrophobicity is not particularly limited as long as it has a hydrophobic group such as an alkyl group or a phenyl group in the molecule, but the material corresponding to the plasticizers and deterioration inhibitors described below is particularly preferable. Used. The addition amount is preferably 0.01 to 10% by mass of the solution (dope) to be adjusted,
0.1 to 5 mass% is more preferable, and 1 to 3 mass%
Is most preferred.

[Surface Treatment of Cellulose Acetate Film] The cellulose acetate film is preferably surface-treated. Specific methods include corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment and ultraviolet irradiation treatment. In addition, JP-A-7-
Providing an undercoat layer as described in Japanese Patent No. 333433 is also preferably used. From the viewpoint of maintaining the flatness of the film, the temperature of the cellulose acetate film in these treatments is preferably Tg or lower, specifically 150 ° C. or lower. When using the optical compensation sheet as a transparent protective film of a polarizing plate, from the viewpoint of adhesiveness with the polarizing film,
It is particularly preferable to carry out acid treatment or alkali treatment, that is, saponification treatment of cellulose acetate. The surface energy of the film after surface treatment is
It is preferably 55 mN / m or more, and 60 mN / m
More preferably, it is 75 mN / m or less.

The alkali saponification treatment will be specifically described below as an example. The saponification treatment is preferably performed in a cycle in which the film surface is immersed in an alkaline 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 ion in alkaline solution is
0.1N to 3.0N is preferred, 0.5N
To 2.0 N is more preferable. The temperature of the alkaline solution is preferably room temperature to 90 ° C., 4
It is more preferably 0 to 70 ° C. From the viewpoint of productivity, it is preferable to apply an alkali solution, and after the saponification treatment, remove the alkali from the film surface by washing with water. From the viewpoint of wettability, IPA, n-butanol, alcohols such as methanol and ethanol are preferable as the coating solvent, and water, propylene glycol, ethylene glycol and the like are preferably added as an alkali dissolution aid.

The surface energy of a solid can be determined by the contact angle method, the heat of wetting method, and the adsorption method as described in "Basic Wetting and Application of Wetting" (published by Realize Co., December 12, 1989). In the case of the cellulose acetate film of the present invention, it is preferable to use the contact angle method. Specifically, two kinds of solutions having known surface energies are dropped onto a cellulose acetate film, and at the intersection between the surface of the droplet and the film surface, the angle between the tangent line drawn to the droplet and the film surface is used. The surface energy of the film can be calculated by defining the angle containing the drop as the contact angle.

[Liquid Crystalline Compound] The liquid crystal compound used in the present invention may be a rod-shaped liquid crystal or a discotic liquid crystal, and they are a high-molecular liquid crystal or a low-molecular liquid crystal, and further, a low-molecular liquid crystal is cross-linked to form a liquid crystal compound. Including those that no longer show. As the rod-shaped liquid crystal, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes,
Cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolans and alkenylcyclohexylbenzonitriles are preferably used. The rod-shaped liquid crystallinity also includes a metal complex. Further, a liquid crystal polymer containing rod-shaped liquid crystalline molecules in the repeating unit can also be used as the rod-shaped liquid crystal.
In other words, the rod-shaped liquid crystal may be combined with a (liquid crystal) polymer. Regarding the rod-shaped liquid crystal, Quarterly Chemical Review No. 2
Volume 2 Liquid Crystal Chemistry (1994) Chapter 4 edited by The Chemical Society of Japan,
Chapters 7 and 11, Liquid Crystal Device Handbook Chapter 3 of the 142nd Committee, Japan Society for the Promotion of Science, and JP-A-200
There is a description in 0-304932.

The discotic liquid crystal is most preferable as the liquid crystal compound. Examples of discotic liquid crystals include C.I. Report of Destrade et al., Mol. Cr
yst. 71, page 111 (1981), benzene derivatives, C.I. Report of Destrade et al., Mol. Cryst. Volume 122, p. 141 (198
5 years), Physics lett, A, 78, 82
The truxene derivatives described on page (1990),
B. Kohne et al., Angew. Chem.
96, 70 (1984), and cyclohexane derivatives described in J. M. Lehn et al., J. C
hem. Commun. , P. 1794 (1985),
J. Research report by Zhang et al. Am. Chem. S
oc. 116, pp. 2655 (1994), such as azacrown type and phenylacetylene type macrocycles. The discotic liquid crystal is generally a structure in which these are the mother nuclei of the molecular center, and a linear alkyl group, an alkoxy group, a substituted benzoyloxy group or the like is radially substituted as the linear chain,
Shows liquid crystallinity. However, the molecule itself has negative uniaxiality,
The present invention is not limited to the above description as long as it can impart a certain orientation. Further, in the present invention, the term “formed from a discotic compound” does not necessarily mean that the final product is the compound, and for example, the low molecular weight discotic liquid crystal has a group that reacts with heat, light or the like. Therefore, those which are polymerized or crosslinked by reaction with heat, light, etc., and have a high molecular weight to lose liquid crystallinity are also included. A preferred example of the discotic liquid crystal is described in JP-A-8-50206.

The optically anisotropic layer is a layer having a negative birefringence composed of a compound having a discotic structural unit, and the surface of the discotic structural unit is inclined with respect to the transparent support surface, and the discotic The angle formed by the surface of the structural unit and the surface of the transparent support preferably changes in the depth direction of the optically anisotropic layer.

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

The optical anisotropic layer is generally prepared by applying a solution of a discotic compound and another compound dissolved in a solvent onto the alignment film, drying it, and then heating it to a discotic nematic phase forming temperature, and then aligning it (in the discotic state). It is obtained by cooling while maintaining the tick nematic phase). Alternatively, the optically anisotropic layer is formed by applying a solution of a discotic compound and another compound (further, for example, a polymerizable monomer or a photopolymerization initiator) dissolved in a solvent onto the alignment film, drying and then applying the discotic nematic phase. It is obtained by heating to the formation temperature, polymerizing (by irradiation with UV light, etc.), and further cooling. The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystalline compound used in the present invention is preferably 70 to 300 ° C, and particularly preferably 70 to 170 ° C.

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

The above-mentioned plasticizer, surfactant and polymerizable monomer have compatibility with the discotic compound,
Any compound can be used as long as it can change the tilt angle of the liquid crystal discotic compound or does not hinder the alignment. Of these, polymerizable monomers (eg, compounds having a vinyl group, a vinyloxy group, an acryloyl group and a methacryloyl group) are preferable.
The above compound is generally used in an amount of 1 to 50% by mass (preferably 5 to 30% by mass) based on the discotic compound. Further, examples of preferable polymerizable monomers include polyfunctional acrylates. The number of functional groups is 3
It is preferably functional or higher, and more preferably tetrafunctional or higher. Most preferred are hexafunctional monomers. Preferred examples of the hexafunctional monomer include dipentaerythritol hexaacrylate. It is also possible to mix and use these polyfunctional monomers having different numbers of functional groups.

As the polymer, any polymer can be used as long as it is compatible with the discotic compound and can change the tilt angle of the liquid crystalline discotic compound. Cellulose ester can be mentioned as an example of a polymer. Preferred examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, hydroxypropyl cellulose and cellulose acetate butyrate. The polymer is generally 0.1 to 10% by mass (preferably 0.1 to 8% by mass, particularly 0.1 to 5% by mass) relative to the discotic compound so as not to hinder the alignment of the liquid crystalline discotic compound. ) Amount used.

The optical compensation sheet comprises a cellulose acetate film, an alignment film provided thereon, and an optically anisotropic layer made of a discotic liquid crystal formed on the alignment film. The alignment film is formed by rubbing the surface of the crosslinked polymer.

[Alignment Film] The alignment film is preferably a layer composed of two crosslinked polymers. It is possible to use any polymer which is crosslinkable with a crosslinking agent, even if at least one polymer is itself crosslinkable. The alignment film is a polymer having a functional group or a polymer having a functional group introduced,
Formed by reacting between polymers by heat, pH change, or the like; or, by using a crosslinking agent which is a compound having high reaction activity, introducing a linking group derived from the crosslinking agent between the polymers to crosslink between the polymers. Can be formed.

Such cross-linking is usually carried out by applying a coating solution containing the above-mentioned polymer or a mixture of the polymer and the cross-linking agent on a transparent support and then heating the solution, but at the stage of the final product. Since it suffices to ensure the durability, the treatment for crosslinking may be carried out at any stage after the alignment film is applied on the transparent support until the final optical compensation sheet is obtained. Considering the orientation of the compound having a discotic structure (optically anisotropic layer) formed on the orientation film, it is also preferable that the compound having the discotic structure is oriented and then sufficiently crosslinked. That is, on the transparent support,
When a coating solution containing a polymer and a cross-linking agent capable of crosslinking the polymer is applied, it is dried by heating (generally, crosslinking is carried out, but when the heating temperature is low, it was heated to the discotic nematic phase formation temperature. (Cross-linking sometimes progresses further), rubbing treatment is performed to form an alignment film,
Then, a coating solution containing a compound having a disc-shaped structural unit is applied onto the alignment film, heated to a discotic nematic phase formation temperature or higher, and then cooled to form an optically anisotropic layer.

As the polymer used for the alignment film, either a polymer which itself is crosslinkable or a polymer which is crosslinked by a crosslinking agent can be used. Of course, some polymers are capable of both. Examples of the above polymer include polymethylmethacrylate, acrylic acid / methacrylic acid copolymer, styrene / maleinimide copolymer, polyvinyl alcohol and modified polyvinyl alcohol, poly (N-methylolacrylamide), styrene / vinyltoluene copolymer. Polymers such as chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, ethylene / vinyl acetate copolymer, carboxymethyl cellulose, polyethylene, polypropylene and polycarbonate. Examples thereof include compounds such as silane coupling agents. Examples of preferable polymers are water-soluble polymers such as poly (N-methylol acrylamide), carboxymethyl cellulose, gelatin, polyvinyl alcohol and modified polyvinyl alcohol, and further gelatin, polyvinyl alcohol and modified polyvinyl alcohol are preferable, and especially polyvinyl alcohol is preferable. Bill alcohol and modified polyvinyl alcohol can be mentioned.

Among the above polymers, polyvinyl alcohol or modified polyvinyl alcohol is preferable, and it is most preferable to use two kinds of polyvinyl alcohol or modified polyvinyl alcohol having different degrees of polymerization in combination. The polyvinyl alcohol has, for example, a saponification degree of 70 to 100%, and generally has a saponification degree of 80 to 100%.
More preferably, the saponification degree is 85 to 95%. The degree of polymerization is preferably in the range of 100 to 3000.
As the modified polyvinyl alcohol, one modified by copolymerization (as the modifying group, for example, COONa, Si (OX))
₃ , N (CH ₃ ) ₃ · Cl, C ₉ H ₁₉ COO, SO ₃ ,
Na, C ₁₂ H _25, etc. introduced thereinto, those modified by chain transfer (as modifying groups such as COONa, SH,
C ₁₂ H ₂₅ etc. introduced, modified by block polymerization (as a modifying group, for example, COOH, CO
NH ₂ , COOR, C ₆ H _{5 and the} like are introduced) and modified polyvinyl alcohol. Among these, unmodified or modified polyvinyl alcohol having a saponification degree of 80 to 100%, and more preferably unmodified or alkylthio-modified polyvinyl alcohol having a saponification degree of 85 to 95%. The method for synthesizing these modified polymers, the visible absorption spectrum measurement, and the method for determining the introduction rate y are
The details are described in JP-A-8-338913.

The following may be mentioned as specific examples of the cross-linking agent used together with the above-mentioned polymers such as polyvinyl alcohol. These include the above water-soluble polymers, particularly polyvinyl alcohol and modified polyvinyl alcohol (the above-mentioned specific modified products). Is also included). For example, activating aldehydes (eg, formaldehyde, glyoxal and glutaraldehyde), N-methylol compounds (eg, dimethylolurea and methyloldimethylhydantoin), dioxane derivatives (eg, 2,3-dihydroxydioxane), and carboxyl groups. Compounds that act by (eg, carbenium, 2-naphthalene sulfonate, 1,1-bispyrrolidino-1-
Chloropyridinium and 1-morpholinocarbonyl-3
-(Sulfonatoaminomethyl)), an active vinyl compound (eg 1,3,5-triacroyl-hexahydro-s)
-Triazine, bis (vinyl sulfone) methane and N,
N′-methylenebis- [β- (vinylsulfonyl) propionamide]), active halogen compound (eg, 2,4-
Dichloro-6-hydroxy-S-triazine), isoxazoles, dialdehyde starch, and the like. These can be used alone or in combination. In view of productivity, it is preferable to use aldehydes having high reaction activity, especially glutaraldehyde.

The cross-linking agent is not particularly limited, and the addition amount tends to improve as the addition amount increases with respect to the moisture resistance. However, since the alignment ability as an alignment film decreases when 50% by mass or more is added to the polymer,
0.1 to 20 mass% is preferable, and 0.5 to 15 mass% is particularly preferable. The alignment film of the present invention contains some cross-linking agent that has not reacted even after the completion of the cross-linking reaction, but the amount of the cross-linking agent is preferably 1.0% by mass or less in the alignment film. It is particularly preferably 0.5% by mass or less. If the cross-linking agent is contained in the alignment film in an amount exceeding 1.0 mass, sufficient durability cannot be obtained. That is,
When used in a liquid crystal display device, reticulation may occur when it is used for a long period of time or left in a high temperature and high humidity atmosphere for a long period of time.

The alignment film is basically formed by coating on a transparent support containing the above-mentioned polymer and a cross-linking agent, which is a material for forming an alignment film, followed by heat drying (cross-linking) and rubbing treatment. As described above, the crosslinking reaction may be carried out at any time after coating on the transparent support. When using a water-soluble polymer such as the polyvinyl alcohol as an alignment film forming material, the coating liquid is preferably a mixed solvent of an organic solvent such as methanol and a water having an antifoaming action, and the ratio is mass. Water by ratio:
Methanol is generally 0: 100 to 99: 1,
It is preferably 0: 100 to 91: 9. Thereby, the generation of bubbles is suppressed, and the defects on the alignment film and, further, on the surface of the optically anisotropic layer are significantly reduced. Examples of the coating method include a spin coating method, a dip coating method, a curtain coating method, an extrusion coating method, a bar coating method and an E-type coating method. The E-type coating method is particularly preferable. The film thickness is 0.
It is preferably 1 to 10 μm. Heat drying at 20 ℃ to 11 ℃
It can be carried out at 0 ° C. In order to form sufficient cross-linking, the temperature is preferably 60 ° C to 100 ° C, particularly 80 ° C to 10 ° C.
0 ° C is preferred. The drying time can be 1 minute to 36 hours. It is preferably 5 minutes to 30 minutes. p
H is also preferably set to an optimum value for the cross-linking agent used, and when glutaraldehyde is used, the pH is 4.
5 to 5.5, especially 5 is preferable.

The alignment film is provided on the transparent support or on the undercoat layer. The alignment film can be obtained by crosslinking the polymer layer as described above and then rubbing the surface. The alignment film functions so as to define the alignment direction of the liquid crystal discotic compound provided thereon.

For the rubbing treatment, a treatment method widely adopted as a liquid crystal alignment treatment process for LCD can be used. That is, a method of obtaining orientation by rubbing the surface of the orientation film in a certain direction with paper, gauze, felt, rubber, nylon, polyester fiber or the like can be used. Generally, it is carried out by rubbing several times with a cloth or the like in which fibers having uniform length and thickness are evenly flocked.

[Polarizing plate] A polarizing plate is a polarizing film or both.
It consists of two transparent protective films arranged on the side. One side protection
Using the above cellulose acetate film as the film
You can The other protective film is a normal cellulose acetate.
Cate film may be used. Iodine on the polarizing film
-Based polarizing film, dye-based polarizing film using dichroic dye, and polyene
There is a polarizing film. Iodine type polarizing film and dye type polarizing film
Is generally manufactured using a polyvinyl alcohol film.
Build. Slow axis and polarization of cellulose acetate film
The membrane is arranged so as to be substantially parallel to the transmission axis of the membrane.
The moisture permeability of the protective film is important for the productivity of polarizing plates
I understood it. Water-based adhesive for polarizing film and protective film
The adhesive solvent is a protective film.
It is dried by diffusing in the glass. Protective film
The higher the moisture permeability, the faster the drying, and the more productive
Improves, but if it gets too high, the operating environment of the liquid crystal display device
Depending on the boundary (under high humidity), water enters the polarizing film and is polarized.
Noh is reduced. The moisture permeability of the optical compensation sheet is
Thickness of the film (and polymerizable liquid crystal compound), free volume,
It is determined by hydrophilicity / hydrophobicity, etc. Polarizing film protection film
When used as, the moisture permeability is 100 to 1000g / m
²-Preferably 24 hrs, 300 to 70
0 g / m²-It is more preferable that it is 24 hrs. light
The thickness of the film for film compensation depends on the lip flow rate and the
Adjustable by in-speed or stretching / compression
You can The moisture permeability differs depending on the main material used
It is possible to adjust the thickness to a preferable range.
It The free volume of the optical compensation film is
It can be adjusted by temperature and time. In this case
Also, since the moisture permeability differs depending on the main material used, it is a free body
It is possible to set a preferable range by adjusting the product. light
The hydrophilicity / hydrophobicity of the compensation film can be adjusted by additives.
You can Add hydrophilic additive in the free volume
By doing so, the moisture permeability becomes high, and conversely, a hydrophobic additive is added.
Therefore, the moisture permeability can be lowered. The above moisture permeability is independent
A polarizing plate with optical compensation ability can be obtained by controlling it vertically.
It becomes possible to manufacture at low cost with high productivity.

[Liquid Crystal Display Device] The above optical compensation sheet,
Alternatively, a polarizing plate using the above optical compensation sheet is advantageously used in a liquid crystal display device. TN, MVA, and OC
The B-mode liquid crystal display device includes a liquid crystal cell and two polarizing plates arranged on both sides of the liquid crystal cell. The liquid crystal cell carries liquid crystal between two electrode substrates. One optical compensation sheet is arranged between the liquid crystal cell and one of the polarizing plates, or two optical compensation sheets are arranged between the liquid crystal cell and both of the polarizing plates. In the case of an OCB mode liquid crystal display device, the optical compensation sheet of the present invention comprises a discotic compound on a polymer film,
Alternatively, it may have an optically anisotropic layer containing a rod-shaped liquid crystal compound. The optically anisotropic layer is formed by orienting a discotic compound (or a rod-shaped liquid crystal compound) and fixing the orientation state. Discotic compounds generally have a large birefringence. In addition, the discotic compound has various orientation forms. Therefore, by using the discotic compound, it is possible to produce an optical compensation sheet having optical properties that cannot be obtained by a conventional stretched birefringent film. Regarding the optical compensation sheet using a discotic compound, JP-A-6-214116, US Pat. No. 5,583,679,
No. 5646703, West German Patent Publication 3911620A1.
There is a description in each specification of the issue.

In the polarizing plate, the above polymer film is used as a transparent protective film arranged between the liquid crystal cell and the polarizing film. One of the polarizing plates (between the liquid crystal cell and the polarizing film)
The above polymer film is used only for the transparent protective film, or the above polymer film is used for the two transparent protective films (between the liquid crystal cell and the polarizing film) of both polarizing plates.
The liquid crystal cell is preferably in VA mode, OCB mode, or TN mode. In a VA mode liquid crystal cell, rod-shaped liquid crystal molecules are aligned substantially vertically when no voltage is applied. The VA-mode liquid crystal cell includes (1) a VA-mode liquid crystal cell in a narrow sense in which rod-shaped liquid crystal molecules are aligned substantially vertically when no voltage is applied, and are aligned substantially horizontally when a voltage is applied (Japanese Patent Laid-Open No. HEI 2-200,600). 176625 gazette), and (2) a liquid crystal cell (SID9) in which the VA mode is multi-domain (MVA mode) for widening the viewing angle.
7. Digest of tech. Papers 28 (199)
7) 845), (3) A liquid crystal cell of a mode (n-ASM mode) in which rod-like liquid crystal molecules are substantially vertically aligned when no voltage is applied and twisted in multi-domain alignment when a voltage is applied (preliminary report of the Japan Liquid Crystal Conference). Vol 58-59 (1998)
Description) and (4) SURVAIVAL mode liquid crystal cell (announced at LCD International 98). In the OCB mode liquid crystal cell, rod-shaped liquid crystal molecules are substantially opposite to each other (symmetrically) in the upper and lower parts of the liquid crystal cell.
A liquid crystal display device using a bend alignment mode liquid crystal cell for alignment, which is disclosed in US Pat. Nos. 4,583,825 and 5,410.
No. 422 is disclosed in each specification. Since the rod-shaped liquid crystalline molecules are symmetrically aligned in the upper part and the lower part 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 (Optic
ally 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-shaped liquid crystal molecules are substantially horizontally aligned when no voltage is applied, and further twisted and aligned at 60 to 120 °. The TN mode liquid crystal cell is most often used as a color TFT liquid crystal display device, and is described in many documents.

[0066]

EXAMPLES [Example 1] The following composition was put into a mixing tank and stirred with heating to dissolve each component,
A cellulose acetate solution was prepared.

[0067] ────────────────────────────────────   Cellulose acetate solution composition ────────────────────────────────────   100 parts by mass of cellulose acetate having a degree of acetylation of 60.9%   Triphenyl phosphate (plasticizer) 7.8 parts by mass   Biphenyl diphenyl phosphate (plasticizer) 3.9 parts by mass   Methylene chloride (first solvent) 300 parts by mass   Methanol (second solvent) 54 parts by mass   1-butanol (3rd solvent) 11 parts by mass ────────────────────────────────────

In another mixing tank, a retardation increasing agent (maximum absorption wavelength:
(275 nm), 25 parts by mass, 80 parts by mass of methylene chloride and 20 parts by mass of methanol were added and stirred with heating to prepare a retardation increasing agent solution. 25 parts by mass of the retardation increasing agent solution was mixed with 474 parts by mass of the cellulose acetate solution and sufficiently stirred to prepare a dope. The addition amount of the retardation increasing agent was 5.5 parts by mass with respect to 100 parts by mass of cellulose acetate.

[0069]

[Chemical 1]

The obtained dope was cast using a band casting machine. After the film surface temperature on the band reached 40 ° C, it was dried for 1 minute, peeled off, and then dried with 140 ° C dry air.
A cellulose acetate film (thickness: 50 μm) having a residual solvent amount of 0.3% by mass was produced. The optical characteristics of the produced cellulose acetate film (CAF-01) were measured. The results are shown in Table 1. The optical characteristics are ellipsometer (M-150, JASCO Corporation).
Re retardation value and Rth retardation value at a wavelength of 550 nm, and further Re
The wavelength dispersion of the retardation value was measured.

The produced cellulose acetate film was treated with 1.5N potassium hydroxide / (water / IPA / PG = 14).
/ 86/15 vol%) is applied at 5 cc / m ² for about 10
After holding at 60 ° C. for 2 seconds, potassium hydroxide remaining on the film surface was washed with water and dried. The surface energy of this cellulose acetate film was 63 mN / m as determined by the contact angle method. Onto this cellulose acetate film, a coating solution having the following composition was applied at 28 ml / m ² with a # 16 wire bar coater. It was dried with hot air of 60 ° C. for 60 seconds and further with hot air of 90 ° C. for 150 seconds.
Then, the formed film was rubbed in a direction parallel to the longitudinal direction of the cellulose acetate film.

[0072] ────────────────────────────────────   Alignment film coating liquid composition ────────────────────────────────────   The following modified polyvinyl alcohol 10 parts by mass   Water 371 parts by mass   119 parts by mass of methanol   Glutaraldehyde (crosslinking agent) 0.5 parts by mass ────────────────────────────────────

[0073]

[Chemical 2]

(Formation of Optically Anisotropic Layer) The following discotic (discotic liquid crystalline) compound 41.01 was formed on the alignment film.
g, ethylene oxide modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.)
4.06 g, cellulose acetate butyrate (CAB
551-0.2, Eastman Chemical Co., Ltd.) 0.90
g, cellulose acetate butyrate (CAB531-
0.23 g, a photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy) 1.
A coating liquid prepared by dissolving 35 g and 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 wire bar of # 3.6. This was heated in a constant temperature zone of 130 ° C. for 2 minutes to orient the discotic compound. Next, in an atmosphere of 60 ° C, 1
UV irradiation was carried out for 1 minute using a 20 W / cm high pressure mercury lamp to polymerize the discotic compound. Then, it stood to cool to room temperature.
In this way, an optically anisotropic layer was formed, and an optical compensation sheet (KH-01) was produced. The Re retardation value of the optically anisotropic layer measured at a wavelength of 550 nm was 43 nm. The angle (tilt angle) between the disk surface and the first transparent support surface was 42 ° on average.

[0075]

[Chemical 3]

Example 2 The dope obtained in Example 1 was cast using a band casting machine. After the film surface temperature on the band reached 40 ° C, the film was dried for 1 minute, peeled off, stretched in the transverse uniaxial direction by 30% using a tenter in an atmosphere at 130 ° C, and dried with 140 ° C dry air. , A cellulose acetate film having a residual solvent amount of 0.3% by mass (thickness:
110 μm) was produced. The optical characteristics of the produced cellulose acetate film (CAF-02) were measured. The results are shown in Table 1. The optical characteristics were measured using an ellipsometer (M-150, manufactured by JASCO Corporation).
The Re retardation value and the Rth retardation value at a wavelength of 550 nm, and further the wavelength dispersion of the Re retardation value were measured. The prepared cellulose acetate film was treated with 2.0 N potassium hydroxide / IPA 5
After applying cc / m ² and holding for about 10 seconds (room temperature),
The potassium hydroxide remaining on the surface of the film was washed with water and dried. The surface energy of this cellulose acetate film was 63 mN / m as determined by the contact angle method. 28 ml of a coating solution having the following composition on the cellulose acetate film with a # 16 wire bar coater.
/ M ^{2 was} applied. 60 seconds with hot air at 60 ℃, then 90 ℃
It was dried with warm air for 150 seconds. Next, the formed film was rubbed in the direction of 45 ° with respect to the longitudinal direction of the cellulose acetate film.

[0077] ────────────────────────────────────   Alignment film coating liquid composition ────────────────────────────────────   Modified polyvinyl alcohol used in Example 1 10 parts by mass   Water 371 parts by mass   119 parts by mass of methanol   Glutaraldehyde (crosslinking agent) 0.5 parts by mass ────────────────────────────────────

(Formation of Optically Anisotropic Layer) On the alignment film, 41.01 g of the discotic (discotic liquid crystal) compound used in Example 1, ethylene oxide-modified trimethylolpropane triacrylate (V # 360, Osaka Organic Chemical Co., Ltd. 4.06 g, photopolymerization initiator (Irgacure 907, Ciba Geigy) 1.35 g, sensitizer (Kayakyu DETX, Nippon Kayaku Co., Ltd.) 0.45 g
Was applied to 102 g of methyl ethyl ketone to apply it with a wire bar of # 3.0. This is 130
The discotic compound was oriented by heating for 2 minutes in a constant temperature zone of ° C. Next, UV irradiation was carried out for 1 minute using a 120 W / cm high pressure mercury lamp in an atmosphere of 60 ° C. to polymerize the discotic compound. Then, it stood to cool to room temperature. In this way, an optically anisotropic layer was formed, and an optical compensation sheet (KH-02) was produced. R of the optically anisotropic layer measured at a wavelength of 550 nm
The e retardation value was 31 nm. The angle (tilt angle) between the disk surface and the surface of the first transparent support was 35 ° on average.

Example 3 The following composition was put into a mixing tank and stirred while heating to dissolve each component, thereby preparing a cellulose acetate solution.

[0080] ────────────────────────────────────   Cellulose acetate solution composition ────────────────────────────────────   100 parts by mass of cellulose acetate having a degree of acetylation of 60.9%   Triphenyl phosphate (plasticizer) 7.8 parts by mass   Biphenyl diphenyl phosphate (plasticizer) 3.9 parts by mass   Methylene chloride (first solvent) 300 parts by mass   Methanol (second solvent) 54 parts by mass   1-butanol (3rd solvent) 11 parts by mass ────────────────────────────────────

To another mixing tank, 14 parts by mass of the following wavelength dispersion controlling agent, 80 parts by mass of methylene chloride and 20 parts by mass of methanol were charged and stirred with heating to prepare a wavelength dispersion controlling agent solution. 25 parts by mass of the wavelength dispersion controlling agent solution was mixed with 474 parts by mass of the cellulose acetate solution and sufficiently stirred to prepare a dope. The addition amount of the retardation increasing agent is 10% by weight of cellulose acetate.
It was 3.0 parts by mass with respect to 0 parts by mass.

[0082]

[Chemical 4]

The obtained dope was cast using a band casting machine. After the film surface temperature on the band reached 40 ° C, it was dried for 1 minute, peeled off, and then dried with 140 ° C dry air.
A cellulose acetate film (thickness: 100 μm) having a residual solvent amount of 0.3% by mass was produced. The optical characteristics of the produced cellulose acetate film (CAF-03) were measured. The results are shown in Table 1. Furthermore, the produced cellulose acetate film (CAF-03)
Was immersed in a 1.5 N potassium hydroxide solution (40 ° C.) for 5 minutes, neutralized with sulfuric acid, washed with pure water, and dried. When the surface energy of this cellulose acetate film (CAF-03) was determined by the contact angle method, it was 68 mN.
Was / m.

(Preparation of Alignment Film and Optically Anisotropic Layer) In the same manner as in Example 1, an alignment film and an optically anisotropic layer were coated on this cellulose acetate film, and an optical compensation sheet (KH-03 was prepared. ) Was produced. The Re retardation value of the optically anisotropic layer measured at a wavelength of 550 nm is 45 nm.
Met. The angle (tilt angle) between the disk surface and the surface of the first transparent support was 43 ° on average.

[Comparative Example 1] A cellulose acetate solution (CAF) having a residual solvent content of 0.5% by mass and a thickness of 160 μm (CAF) was used as it was (without adding a retardation increasing agent).
-H1) was prepared. The results of the optical properties are shown in FIG.
Shown in the table.

FIG. 1 shows Example 1 (film CAF-0.
1), Example 2 (film CAF-02), Example 3
(Film CAF-03) and Comparative Example 1 (Film C)
It is a graph which shows the wavelength dispersion of the film produced in AF-H1). Film CAF-02 and Film CA
The result was exactly the same as that of F-03.

[0087]

[Table 1]                                 Table 1 ──────────────────────────────────── Film retardation increasing agent Re Rth A value ──────────────────────────────────── CAF-01 5.5 parts by mass 8 nm 80 nm 1.413 CAF-02 5.5 parts by mass 40 nm 185 nm 1.044 CAF-03 3.0 parts by mass 6 nm 82 nm 1.044 Without CAF-H1 4nm 78nm -0.505 ────────────────────────────────────

Example 4 Iodine was adsorbed to a stretched polyvinyl alcohol film to prepare a polarizing film, and KH-01 prepared in Example 1 was used as a polarizing film with CAF-01 as a polarizing film using a polyvinyl alcohol adhesive. It was attached to one side of the polarizing film so that it would be the side. 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.
The absorption axis of the polarizing film and the slow axis of KH-01 were arranged in parallel. In this way, a polarizing plate was produced.

Example 5 Iodine was adsorbed on a stretched polyvinyl alcohol film to prepare a polarizing film, and KH-02 prepared in Example 2 was used as CAF-02 for the polarizing film by using a polyvinyl alcohol adhesive. It was attached to one side so that its slow axis was parallel to the transmission axis of the polarizing film. Commercially available cellulose triacetate film (Fujitac TD80UF, Fuji Photo Film Co., Ltd.)
Saponification treatment was performed and the product was attached to the opposite side of the polarizing film using a polyvinyl alcohol adhesive. In this way, a polarizing plate was produced.

Example 6 Iodine was adsorbed on a stretched polyvinyl alcohol film to prepare a polarizing film, and KH-03 prepared in Example 2 was used as CAF-03 for the polarizing film by using a polyvinyl alcohol adhesive. It was attached to one side so that its slow axis was parallel to the absorption axis of the polarizing film. Commercially available cellulose triacetate film (Fujitac TD80UF, Fuji Photo Film Co., Ltd.)
Saponification treatment was performed and the product was attached to the opposite side of the polarizing film using a polyvinyl alcohol adhesive. In this way, a polarizing plate was produced.

COMPARATIVE EXAMPLE 2 Iodine was adsorbed to a stretched polyvinyl alcohol film to prepare a polarizing film, and KH-H1 prepared in Example 2 was replaced with CAF-H1 by using a polyvinyl alcohol adhesive. It was attached to one side so that its slow axis was parallel to the absorption axis of the polarizing film. Commercially available cellulose triacetate film (Fujitac TD80UF, Fuji Photo Film Co., Ltd.)
Saponification treatment was performed and the product was attached to the opposite side of the polarizing film using a polyvinyl alcohol adhesive. In this way, a polarizing plate was produced.

[Example 7] A pair of polarizing plates provided in a liquid crystal display device (6E-A3, manufactured by Sharp Corporation) using a TN type liquid crystal cell was peeled off, and the polarized light produced in Example 4 was used instead. One plate was attached to each of the viewer side and the backlight side via an adhesive so that KH-01 was on the liquid crystal cell side. The transmission axis of the polarizing plate on the observer side and the transmission axis of the polarizing plate on the backlight side were arranged so as to be in the O mode. For the manufactured liquid crystal display device, a measuring instrument (E
Using Z-Contrast 160D, manufactured by ELDIM), the viewing angle was measured in 8 steps from black display (L1) to white display (L8). The results are shown in Table 2.

[Example 8] A pair of polarizing plates provided in a liquid crystal display device (6E-A3, manufactured by Sharp Corporation) using a TN type liquid crystal cell was peeled off, and the polarized light produced in Example 6 was used instead. One plate was attached to each of the viewer side and the backlight side via an adhesive so that KH-03 was on the liquid crystal cell side. The transmission axis of the polarizing plate on the observer side and the transmission axis of the polarizing plate on the backlight side were arranged so as to be in the O mode. For the manufactured liquid crystal display device, a measuring instrument (E
Using Z-Contrast 160D, manufactured by ELDIM), the viewing angle was measured in 8 steps from black display (L1) to white display (L8). The results are shown in Table 2.

[Comparative Example 3] A pair of polarizing plates provided in a liquid crystal display device (6E-A3, manufactured by Sharp Corporation) using a TN type liquid crystal cell was peeled off, and the polarized light produced in Comparative Example 2 was used instead. One plate was attached to each of the viewer side and the backlight side via an adhesive so that KH-H1 was on the liquid crystal cell side. The transmission axis of the polarizing plate on the observer side and the transmission axis of the polarizing plate on the backlight side were arranged so as to be in the O mode. For the manufactured liquid crystal display device, a measuring instrument (E
Using Z-Contrast 160D, manufactured by ELDIM), the viewing angle was measured in 8 steps from black display (L1) to white display (L8). The results are shown in Table 2.

[0095]

[Table 2]                                 Table 2 ────────────────────────────────────   LCD viewing angle                     Contrast ratio ≧ 10 Range without gradation inversion Display device Upper and lower left and right ──────────────────────────────────── Example 7 70 ° 45 ° 160 ° Example 8 75 ° 45 ° 160 ° Comparative Example 3 15 ° 25 ° 37 ° ──────────────────────────────────── (Note) Gray-scale inversion on the black side: Inversion between L1 and L2

[0096]

[Table 3]                                 Table 3 ────────────────────────────────────   Liquid crystal color change                           Range where Δuv ≦ 0.02 Display device Upper and lower left and right ──────────────────────────────────── Example 7 80 ° 80 ° 120 ° Example 8 80 ° 80 ° 100 ° Comparative Example 3 45 ° 80 ° 80 ° ──────────────────────────────────── (Note) Δuv uses the color difference by CIE1976u, v chroma as an index.

Example 9 (Fabrication of Bend Alignment Liquid Crystal Cell) A glass substrate with an ITO electrode was provided with a polyimide film as an alignment film, and the alignment film was rubbed. The two glass substrates obtained were opposed to each other in such a manner that the rubbing directions were parallel to each other, and the cell gap was set to 6 μm. Δn is 0.13 in the cell gap
96 liquid crystal compounds (ZLI1132, manufactured by Merck Ltd.) were injected to prepare a bend alignment liquid crystal cell. Two elliptically polarizing plates prepared in Example 5 were attached so as to sandwich the prepared bend alignment cell. The elliptically polarizing plate was arranged so that the optically anisotropic layer faced 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. The normally white mode of white display 2V and black display 5V was adopted. Using the transmittance ratio (white display / black display) as the contrast ratio, measuring equipment (EZ-Contrast160D, ELD
IM product), using black display (L1) to white display (L1)
The viewing angle was measured in 8 steps up to 8). The results are shown in Table 4.

[0098]

[Table 4]                                 Table 4 ────────────────────────────────────   Liquid crystal viewing angle (range where contrast ratio is 10 or more and there is no gradation reversal on the black side) Display device Upper and lower left and right ──────────────────────────────────── Example 8 80 ° 80 ° 80 ° ──────────────────────────────────── (Note) Gray-scale inversion on the black side: Inversion between L1 and L2

[Brief description of drawings]

FIG. 1 is an example 1, an example 2, an example 3, and a comparative example 1.
3 is a graph showing the wavelength dispersion of the film produced in 1.

[Explanation of symbols] CAF-01 Film prepared in Example 1 CAF-02 Film prepared in Example 2 CAF-03 Film prepared in Example 3 CAF-H1 Film produced in Comparative Example 1

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H049 BA06 BA25 BA27 BA42 BB03                       BB20 BB33 BB43 BB51 BB62                       BC02 BC03 BC09 BC14 BC22                 2H091 FA08X FA08Z FA11X FA11Z                       FB02 FC09 GA13 HA07 KA02                       LA20                 4F006 AA02 AB62 BA14 CA05 DA04                       EA02

Claims (6)

[Claims] 1. Optical compensation having a cellulose acetate film having an acetylation degree of 59.0 to 61.5% and an optically anisotropic layer made of a liquid crystalline compound coated on the cellulose acetate film. In the sheet, the optical compensation sheet is characterized in that the A value of the cellulose acetate film defined by the following formula (1) is in the range of 1.0 to 2.0: A value = Re (420) / Re (550) [In the formula, Re (420) is the retardation value of the film with respect to the light of wavelength 420nm; Re (55)
0) is the retardation value of the film for light having a wavelength of 550 nm]. 2. Re of cellulose acetate film
The retardation value is in the range of 0 to 200 nm,
The optical compensation sheet according to claim 1, wherein the Rth retardation value is in the range of 70 to 400 nm. 3. A cellulose acetate film comprising cellulose acetate and cellulose acetate 100.
The optical compensatory sheet according to claim 1, wherein an aromatic compound having at least two aromatic rings is contained in an amount of 0.01 to 20 parts by mass with respect to parts by mass. 4. The optical compensatory sheet according to claim 3, wherein the maximum wavelength of the molar extinction coefficient of the aromatic compound is in the range of 150 to 400 nm. 5. The optical compensation sheet according to claim 1, wherein the thickness of the cellulose acetate film is in the range of 10 to 70 μm. 6. The optical compensation sheet according to claim 1, wherein the liquid crystal compound is a discotic compound.