JP2000111914A - Retardation raising agent for low fatty acid cellulose ester film, optical compensation sheet and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liq. crystal display device using cellulose ester film, which has excellent property as supporter, for an optical compensation sheet by composing of a compd. having a molecular structure, which contains at least two aromatic rings and has no steric hindrance in the two aromatic rings. SOLUTION: A retardation-raising agent comprising a compd. having a molecular structure, which contains at least two aromatic rings and has no steric hindrance in conformations of the two aromatic rings, is used for a low fatty acid cellulose ester film. In this case, a liq. crystal layer 7 is arranged between resin substrates 5a, 5b. Transparent electrode layers 6a, 6b are arranged on a liq. crystal side of the resin substrates 5a, 5b. These liq. crystal layer 7 and resin substrates 5-7 constitute the liq. crystal cell. Optical compensation sheets 4a, 4b are adhered on upper and lower surfaces of this liq. crystal cell. And the cellulose ester film can be used as this optical compensation sheets 4a, 4b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retardation enhancer for lower fatty acid ester films of cellulose, and to an optical compensation sheet and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art Cellulose lower fatty acid ester films, particularly cellulose acetate films, are used in various photographic materials and optical materials because of their toughness and flame retardancy. Cellulose ester films are typical supports for photographic light-sensitive materials. Cellulose ester films are also used in liquid crystal display devices. Cellulose ester film has higher optical isotropy (lower retardation value) than other polymer films
There is a feature. Therefore, a cellulose ester film is generally used for a liquid crystal display device that requires optical isotropy, for example, a protective film or a color filter of a polarizing element. Conversely, an optical compensation sheet (retardation film), which is an element of another liquid crystal display device, requires a high retardation value. Therefore, it is common to use a synthetic polymer film having a high retardation value, such as a polycarbonate film or a polysulfone film, as the optical compensation sheet. In addition to an optical compensation sheet made of a synthetic polymer film, an optical compensation sheet in which an optically anisotropic layer containing discotic liquid crystal molecules is provided on a transparent support has been proposed (JP-A-3-93).
No. 25, No. 6-148429, No. 8-50206,
No. 9-26572). The high retardation value required for the optical compensation sheet is achieved by an optically anisotropic layer containing discotic liquid crystalline molecules. On the other hand, since a transparent support is required to have high optical isotropy (low retardation value), cellulose ester films are commonly used.

A conventional optical compensation sheet using discotic liquid crystal molecules is mainly composed of a TN (Twisted Nematic) for a TFT.
matic) mode is designed to optically compensate the liquid crystal cell. Such an optical compensation sheet is provided by VA (Vertic
ally aligned mode, OCB (Optically Compensato)
ry Bend) mode or HAN (Hybrid Aligned Nem)
A problem that cannot be dealt with (optical compensation cannot be achieved) even when used in a liquid crystal cell of the (atic) mode. Therefore, the support of the optical compensation sheet is also made optically anisotropic, and in cooperation with the optical anisotropy of the optically anisotropic layer containing discotic liquid crystal molecules, the VA mode, OCB mode or HAN mode is used. It is conceivable to correspond to the liquid crystal cell (optical compensation). A synthetic polymer film having a high retardation value, such as a polycarbonate film or a polysulfone film, can be used as an optically anisotropic support.
However, such a synthetic polymer film has poor function as a support (physical properties and affinity with a coating layer).
Therefore, it has a good function as a support (however,
It is considered that a laminate obtained by laminating a cellulose ester film having a low retardation value and a synthetic polymer film having a high retardation value is preferably used as an optically anisotropic support. As described above, in the technical field of optical materials such as optical compensation sheets, when optical anisotropy (high retardation value) is required, a synthetic polymer film is used, and optical isotropy (low retardation value) is used. When a retardation value is required, it is a general principle to use a cellulose ester film.

[0004]

SUMMARY OF THE INVENTION The inventor of the present invention has sought to use conventional cellulose ester films for applications requiring optical anisotropy (high retardation value). investigated. Cellulose ester films are more excellent in function as a support than synthetic polymer films. If a cellulose ester film having a high optical anisotropy (having a high retardation value) can be obtained, the cellulose ester film can be used also in an optical compensatory sheet requiring optical anisotropy. However, in the prior art, a cellulose ester film having a low retardation value was considered to be an excellent cellulose ester film.
Therefore, even though the means for lowering the retardation value of the cellulose ester film has been studied in detail, the means for increasing the retardation value has hardly been studied.

Accordingly, the present inventors have studied and investigated a compound having a function of increasing the retardation of a lower fatty acid ester film of cellulose (a retardation increasing agent). An object of the present invention is to provide a retardation increasing agent for cellulose lower fatty acid ester films. The object of the present invention is
Another object of the present invention is to provide an optical compensation sheet using a lower fatty acid ester film of cellulose having a high retardation value. Still another object of the present invention is to provide a liquid crystal display device using a cellulose ester film having excellent properties as a support as an optical compensation sheet.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a retardation enhancer for a lower fatty acid ester film of cellulose of the following (1), an optical compensation sheet of the following (2) to (5) and the following (6) to (5). This was achieved by the liquid crystal display device of (8). (1) A retardation enhancer for cellulose lower fatty acid ester films comprising a compound having at least two aromatic rings and having a molecular structure that does not hinder the conformation of the two aromatic rings.

(2) Lower fatty acid ester of cellulose 1
Has at least two aromatic rings with respect to 00 parts by weight,
0.3 to 20 parts by weight of a compound having a molecular structure that does not sterically hinder the conformation of two aromatic rings, and has a wavelength of 550
The retardation value in the thickness direction at nm (Rth
⁵⁵⁰ ) an optical compensatory sheet comprising a lower fatty acid ester film of cellulose having a thickness of 70 to 400 nm. (3) 0.3 to 20 parts by weight of a compound having at least two aromatic rings and having a molecular structure that does not hinder the conformation of the two aromatic rings with respect to 100 parts by weight of the lower fatty acid ester of cellulose. And an optically anisotropic layer containing discotic liquid crystal molecules is provided on a lower fatty acid ester film of cellulose having a thickness direction retardation value (Rth ⁵⁵⁰ ) of 70 to 400 nm at a wavelength of 550 nm. Compensation sheet. (4) The optical compensation sheet according to (2) or (3), wherein the lower fatty acid ester of cellulose is cellulose acetate. (5) The lower fatty acid ester film of cellulose is 4
The optical compensation sheet according to (2) or (3), having a thickness of 0 to 120 μm.

(6) A liquid crystal cell holding a liquid crystal between two electrode substrates, two polarizing elements disposed on both sides thereof, and at least one polarizing element between the liquid crystal cell and the polarizing element. A liquid crystal display device in which the optical compensation sheet is disposed, wherein the optical compensation sheet has at least two aromatic rings with respect to 100 parts by weight of the lower fatty acid ester of cellulose, and has a conformation of two aromatic rings. 0.3 to 20 parts by weight of a compound having a molecular structure that does not cause steric hindrance;
The retardation value in the thickness direction at 50 nm (Rth
⁵⁵⁰ ) comprising a cellulose lower fatty acid ester film having a film thickness of 70 to 400 nm. (7) The liquid crystal display device according to claim 6, wherein an optically anisotropic layer containing discotic liquid crystal molecules is provided on the liquid crystal cell side of the lower fatty acid ester film of cellulose. (8) When the liquid crystal cell is in VA mode, OCB mode or H mode
7. The liquid crystal display device according to claim 6, wherein the liquid crystal display device is an AN mode liquid crystal cell.

[0009]

According to the study of the present inventors, a compound having at least two aromatic rings and having a molecular structure which does not hinder the conformation of the two aromatic rings is a letter of a lower fatty acid ester film of cellulose. It was found that it had a function to raise the dating. Examples of the ultraviolet absorber and the plasticizer of the lower fatty acid ester film of cellulose include the aromatic compounds described above. However, these compounds are used in an amount that satisfies the function as an ultraviolet absorber or a plasticizer (an amount that does not significantly increase the retardation of the film), and is used for the purpose of increasing the retardation of the film. I never did. When 0.3 to 20 parts by weight of the aromatic compound is added to 100 parts by weight of the lower fatty acid ester of cellulose, the retardation value (Rth ⁵⁵⁰ ) in the thickness direction at a wavelength of 550 nm is 70 to 400 nm. A lower fatty acid ester film is obtained. The cellulose ester film having such a high retardation value can be used as it is as an optical compensation sheet in a liquid crystal display. In an optical compensatory sheet in which an optically anisotropic layer containing discotic liquid crystal molecules is provided on a support, a cellulose ester film having a high retardation value can be used as the support. An optically compensatory sheet comprising a support made of a cellulose ester film having a high retardation value and an optically anisotropic layer containing discotic liquid crystal molecules provided thereon has a VA (Vertically Aligned).
It can be particularly advantageously used for a liquid crystal display device of a liquid crystal display type, an OCB (Optically Compensatory Bend) type or a HAN (Hybrid Aligned Nematic) type.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION [Retardation increasing agent] In the present invention, a compound having a molecular structure having at least two aromatic rings and having no steric hindrance to the conformation of the two aromatic rings is used as a lower cellulose ester. Used as a retardation enhancer for fatty acid ester films. In this specification,
"The retardation increasing agent for cellulose lower fatty acid ester film" refers to the retardation of cellulose lower fatty acid ester film (specifically, when used in an amount that does not cause a problem due to addition of a large amount such as bleed-out). Is the retardation value in the thickness direction at a wavelength of 550 nm = Rth ⁵⁵⁰ ).
It means a compound having a function of increasing by a factor of 2 or more (usually 2 to 10 times). The amount within a range where the retardation is sufficiently increased and no problem is caused by the addition of a large amount is generally 0.3 to 20 parts by weight based on 100 parts by weight of the lower fatty acid ester of cellulose. The retardation value in the thickness direction at a wavelength of 550 nm of a lower fatty acid ester film of cellulose obtained by using a retardation increasing agent is generally 70 to 400 nm.

The compound having at least two aromatic rings has a π-bonding plane of 7 or more carbon atoms. Unless the configuration of the two aromatic rings is sterically hindered, the two aromatic rings form the same plane. According to the study of the present inventors, it is important to form the same plane with a plurality of aromatic rings in order to increase the retardation of a cellulose ester film. In the present specification, the “aromatic ring” includes an aromatic hetero ring in addition to an aromatic hydrocarbon ring. An aromatic hydrocarbon ring is a 6-membered ring (ie,
Benzene ring). Aromatic heterocycles are generally unsaturated heterocycles. The aromatic hetero ring is preferably a 5-, 6-, or 7-membered ring, more preferably a 5- or 6-membered ring.
Aromatic heterocycles generally have the most double bonds.
As the hetero atom, a nitrogen atom, an oxygen atom and a sulfur atom are preferable, and a nitrogen atom is particularly preferable. Examples of the aromatic hetero ring include a furan ring, a thiophene ring, a pyrrole ring,
Oxazole ring, isoxazole ring, thiazole ring,
Isothiazole ring, imidazole ring, pyrazole ring, furazane ring, triazole ring, pyran ring, pyridine ring, pyridazine ring, pyrimidine ring, pyrazine ring and 1,3,
Includes a 5-triazine ring. As the aromatic ring, a benzene ring, a furan ring, a thiophene ring, a pyrrole ring, an oxazole ring, a thiazole ring, an imidazole ring, a triazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring and a 1,3,5-triazine ring are preferable.

The number of aromatic rings contained in the retardation increasing agent is preferably 2 to 20, and preferably 2 to 12
Is more preferably, 2 to 8 is more preferable, and 2 to 6 is most preferable. When the compound has three or more aromatic rings, the configuration of at least two aromatic rings need not be sterically hindered. The bonding relationship between two aromatic rings can be classified into (a) a case where a condensed ring is formed, (b) a case where they are directly connected by a single bond, and (c) a case where they are bonded via a linking group. , A spiro bond cannot be formed). In terms of the retardation increase function,
Any of (a) to (c) may be used. However, in the case of (b) or (c), it is necessary that the conformation of the two aromatic rings is not sterically hindered.

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 biphenylene 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,
A quinolidine ring, a quinazoline ring, a cinnoline ring, a quinoxaline ring, a phthalazine ring, a pteridine ring, a carbazole ring, an acridine ring, a phenanthridine ring, a xanthene ring, a phenazine ring, a phenothiazine ring, a phenoxatiin ring, a phenoxazine ring and a thianthrene ring; included. Preferred are a naphthalene ring, an azulene ring, an indole ring, a benzoxazole ring, a benzothiazole ring, a benzimidazole ring, a benzotriazole ring and a quinoline ring. The single bond in (b) is preferably a bond between carbon atoms of two aromatic rings. Two aromatic rings may be linked by two or more single bonds to form an aliphatic ring or a non-aromatic heterocyclic ring between the two aromatic rings.

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

The aromatic ring and the linking group may have a substituent. However, it is necessary that the substituent does not hinder the conformation of the two aromatic rings. For steric hindrance, the type and position of the substituents become a problem. As the type of the substituent, a sterically bulky substituent (for example, a tertiary alkyl group) is likely to cause steric hindrance. As the position of the substituent, steric hindrance is likely to occur when a position adjacent to the bond of the aromatic ring (ortho position in the case of a benzene ring) is substituted. Examples of the substituent include a halogen atom (F, Cl, B
r, 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 Groups, aliphatic substituted sulfamoyl groups, aliphatic substituted ureido groups and non-aromatic heterocyclic groups.

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

The 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 aliphatic acyloxy group preferably has 1 to 10 carbon atoms. Examples of the aliphatic acyloxy group include acetoxy. The alkoxy group preferably has 1 to 8 carbon atoms. The alkoxy group may further have a substituent (eg, an alkoxy group). Examples of alkoxy groups (including substituted alkoxy groups) include methoxy, ethoxy, butoxy and methoxyethoxy. The alkoxycarbonyl group preferably has 2 to 10 carbon atoms. Examples of 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 of 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 the alkylsulfonyl group include methanesulfonyl and ethanesulfonyl. The aliphatic amide group preferably has 1 to 10 carbon atoms. Examples of the aliphatic amide group include acetamide. The aliphatic sulfonamide group preferably has 1 to 8 carbon atoms. Examples of the aliphatic sulfonamide group include methanesulfonamide, butanesulfonamide and n-octanesulfonamide. The aliphatic substituted amino group preferably has 1 to 10 carbon atoms. Examples of the aliphatic substituted amino group include dimethylamino, diethylamino and 2-carboxyethylamino. The 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 aliphatic substituted ureido group preferably has 2 to 10 carbon atoms. Examples of the aliphatic substituted ureido group include methyl ureide. Examples of the non-aromatic heterocyclic group include piperidino and morpholino.

The molecular weight of the retardation enhancer is 30
It is preferably from 0 to 800. The boiling point of the retardation increasing agent is preferably 260 ° C. or higher.
The boiling point can be measured using a commercially available measuring device (for example, TG / DTA10).
0, manufactured by Seiko Denshi Kogyo KK).
Hereinafter, specific examples of the retardation increasing agent are shown. In each of the specific examples, the aromaticity of the aromatic ring is indicated by a circle.

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[Lower Fatty Acid Ester of Cellulose] The lower fatty acid means a fatty acid having 6 or less carbon atoms.
The number of carbon atoms is preferably 2 (cellulose acetate), 3 (cellulose propionate) or 4 (cellulose butyrate). Cellulose acetate is particularly preferred. Mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate may be used. The average acetylation degree (acetylation degree) of cellulose acetate is preferably 55.0% or more and less than 62.5%. From the viewpoint of physical properties of the film, the average acetylation degree is more preferably 58.0% or more and less than 62.5%. However, the average degree of acetylation is from 55.0% to less than 58.0% (preferably from 57.0% to 58.0%).
%), A film having an extremely high retardation value can be produced. The degree of acetylation means the amount of bound acetic acid per unit weight of cellulose. The degree of acetylation is determined according to ASTM: D-817-
According to the measurement and calculation of the degree of acetylation in 91 (test method for cellulose acetate and the like). The viscosity average degree of polymerization (DP) of the cellulose ester is preferably 250 or more, more preferably 290 or more. In addition, the cellulose ester used in the present invention has a Mw / Mn (M
(w is a weight average molecular weight, and Mn is a number average molecular weight). Specifically, the value of Mw / Mn is preferably 1.0 to 1.7, and 1.3.
It is more preferably from 1.65 to 1.65, and most preferably from 1.4 to 1.6.

[Retardation Value of Film] The retardation value in the thickness direction of the cellulose ester film is a value obtained by multiplying the birefringence in the thickness direction by the thickness of the film. Specifically, the incident direction of the measurement light is set to the direction perpendicular to the film surface, and the in-plane retardation measurement result with respect to the slow axis, and the incident direction is inclined with respect to the direction perpendicular to the film surface. Extrapolated from the measured results. The measurement was performed using an ellipsometer (eg, M-15
0: manufactured by JASCO Corporation). The thickness direction retardation value (Rth) and the in-plane retardation value (Re) are calculated according to the following equations (1) and (2), respectively. Formula (1) Retardation value (Rth) in the thickness direction = ｛(nx + n
y) / 2-nz｝ × d Equation (2) In-plane retardation value (Re) = (nx−ny) × d where nx is a refractive index in the x direction in the film plane,
ny is the refractive index in the y direction in the plane of the film, nz is the refractive index in the direction perpendicular to the film plane, and d is the thickness (nm) of the film. In the present invention, the retardation value in the thickness direction at a wavelength of 550nm of the film a (Rth ^550), adjusted to 70 to 400 nm. The retardation value in the thickness direction is preferably from 100 to 400 nm, more preferably from 150 to 400 nm, further preferably from 200 to 400 nm, even more preferably from 200 to 300 nm, and from 200 to 400 nm. Most preferably, it is 250 nm.

It is preferable that the absolute value of the gradient (a) of the distribution of Rth with respect to the retardation value (Rth ⁵⁵⁰ ) in the thickness direction at a wavelength of 550 nm as a reference value (= 1) is less than 0.0012. The slope (a) of the distribution of Rth is
From the measured data of three points of the retardation value in the thickness direction at a wavelength of 400 nm (Rth ⁴⁰⁰ ), the retardation value in the thickness direction at a wavelength of 550 nm (Rth ⁵⁵⁰ ), and the retardation value in the thickness direction at a wavelength of 700 nm (Rth ⁷⁰⁰ ), It is calculated according to equation (3). Equation (3) Rth distribution slope (a) = | Rth ⁷⁰⁰ −Rth ⁴⁰⁰ | / 3
00Rth ⁵⁵⁰ Thus, Rth ^400, Rth ⁵⁵⁰ and Rth ⁷⁰⁰ preferably satisfies the following formula (11). Equation (11) | Rth ⁷⁰⁰ -Rth ⁴⁰⁰ | / 300 Rth ⁵⁵⁰ <0.001
2 Rth ⁴⁰⁰ , Rth ⁵⁵⁰ and Rth ⁷⁰⁰ are represented by the following formula (13)
Is more preferably satisfied. Formula (13) -0.0012 <(Rth ⁷⁰⁰ -Rth ⁴⁰⁰ ) / 300Rth
⁵⁵⁰ <0.0006

Further, an in-plane retardation value (Re ⁵⁵⁰ ) at a wavelength of 550 nm is defined as a reference value (= 1).
The absolute value of the gradient (b) of the distribution of e is preferably less than 0.002. The slope (b) of the distribution of Re is wavelength 4
In-plane retardation value (Re at 00 nm)
⁴⁰⁰ ), an in-plane retardation value (Re ⁵⁵⁰ ) at a wavelength of ⁵⁵⁰ nm and an in-plane retardation value (Re ⁷⁰⁰ ) at a wavelength of 700 nm.
It is calculated according to the following equation (4). Equation (4): slope of distribution of Re (b) = | Re ⁷⁰⁰ −Re ⁴⁰⁰ | / 3
00Re ⁵⁵⁰ Therefore, Re ^400, Re ⁵⁵⁰ and Re ^700, it is preferable to satisfy the following equation (12). Formula (12) | Re ⁷⁰⁰ -Re ⁴⁰⁰ | / 300Re ⁵⁵⁰ <0.002 Re ⁴⁰⁰ , Re ⁵⁵⁰ and Re ⁷⁰⁰ are represented by the following formula (13)
Is more preferably satisfied. Formula (13) -0.002 <(Rth ⁷⁰⁰ -Rth ⁴⁰⁰ ) / 300Rth
⁵⁵⁰ <0.001

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

Examples of the ethers having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolan, tetrahydrofuran, anisole and phenetole. Examples of the ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone. Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate. Examples of the organic solvent having two or more types of functional groups include
Includes 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol. The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogen atoms substituted by halogen atoms in halogenated hydrocarbons is preferably 25 to 75 mol%, and preferably 3 to 75 mol%.
The content is more preferably 0 to 70 mol%, still more preferably 35 to 65 mol%, and 40 to 60 mol%.
Most preferably, it is mol%. Methylene chloride is a typical halogenated hydrocarbon.

[0092] Two or more kinds of organic solvents may be used as a mixture. Particularly preferred organic solvents are mixed solvents of three different solvents, wherein the first solvent is an ether having 3 to 12 carbon atoms, a ketone having 3 to 12 carbon atoms, an ester having 3 to 12 carbon atoms and The second solvent is selected from a linear monohydric alcohol having 1 to 5 carbon atoms, and the third solvent is selected from a halogenated hydrocarbon having 1 to 6 carbon atoms and a third solvent having a boiling point of 30 to 170. ° C and hydrocarbons having a boiling point of 30 to 170 ° C.
The ether, ketone, ester and halogenated hydrocarbon of the first solvent are as described above. The second solvent is selected from linear monohydric alcohols having 1 to 5 carbon atoms. The hydroxyl group of the alcohol may be bonded to the terminal of the hydrocarbon straight chain (primary alcohol) or may be bonded in the middle (secondary alcohol). The second solvent is
Specifically, it is selected from methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol and 3-pentanol. The number of carbon atoms of the linear monohydric alcohol is preferably 1 to 4, more preferably 1 to 3, and most preferably 1 or 2. Ethanol is particularly preferably used.

The third solvent is selected from alcohols having a boiling point of 30 to 170 ° C. and hydrocarbons having a boiling point of 30 to 170 ° C. Preferably, the alcohol is monovalent.
The hydrocarbon portion of the alcohol may be linear, branched, or cyclic. The hydrocarbon portion is
Preferably, it is a saturated aliphatic hydrocarbon. The hydroxyl group of the alcohol may be any of primary to tertiary.
Examples of alcohol include methanol (boiling point: 64.65
C), ethanol (78.325C), 1-propanol (97.15C), 2-propanol (82.4).
C), 1-butanol (117.9C), 2-butanol (99.5C), t-butanol (82.45C),
1-pentanol (137.5 ° C), 2-methyl-2-
Butanol (101.9 ° C) and cyclohexanol (161 ° C).

Although the definition of the alcohol is the same as the definition of the second solvent, any alcohol of a different kind from the alcohol used as the second solvent can be used as the third solvent. For example, when ethanol is used as the second solvent, other alcohols (methanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol) included in the definition of the second solvent are used. , 2-pentanol or 3-pentanol)
May be used as the third solvent. The hydrocarbon may be linear, branched, or cyclic. Both aromatic hydrocarbons and aliphatic hydrocarbons can be used. Aliphatic hydrocarbons may be saturated or unsaturated. Is more preferable. Examples of hydrocarbons include cyclohexane (boiling point: 80.7 ° C.),
Hexane (69 ° C), benzene (80.1 ° C), toluene (110.6 ° C) and xylene (138.4-14)
4.4 ° C).

The first solvent is preferably contained in the mixed solvent of 50 to 95% by weight, more preferably 60 to 92% by weight, and more preferably 65 to 90% by weight.
More preferably, the content is most preferably 70 to 88% by weight. The second solvent is preferably contained in an amount of 1 to 30% by weight, more preferably 2 to 27% by weight, even more preferably 3 to 24% by weight, and more preferably 4 to 22% by weight. Most preferred. The third solvent is preferably contained in an amount of 1 to 30% by weight, more preferably 2 to 27% by weight, even more preferably 3 to 24% by weight, and more preferably 4 to 22% by weight. Most preferred.
Further, another organic solvent may be used in combination to form a mixed solvent of four or more kinds. When four or more kinds of mixed solvents are used, the fourth and subsequent solvents are preferably selected from the three kinds of solvents described above. As a solvent other than the above-mentioned three kinds of solvents, ethers having 3 to 12 carbon atoms (eg, diisopropyl ether, dimethoxyethane, diethoxyethane,
1,4-dioxane, 1,3-dioxolan, tetrahydrofuran, anisole, phenetole) or nitromethane may be used in combination.

[Preparation of Solution (General Method)] In the present invention, a solution can be prepared by a general method without employing the cooling dissolution method. The general method means that the treatment is performed at a temperature of 0 ° C. or higher (normal temperature or high temperature). The solution can be prepared using a dope preparation method and apparatus in a usual solvent casting method. In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly, methylene chloride) as the organic solvent. The amount of the cellulose ester is adjusted so that the obtained solution contains 10 to 40% by weight. More preferably, the amount of cellulose ester is from 10 to 30% by weight. In the organic solvent (main solvent), any additives described below may be added. The solution can be prepared by stirring the cellulose ester and the organic solvent at room temperature (0 to 40 ° C.). The highly concentrated solution may be stirred under pressure and heating conditions. Specifically, the cellulose ester and the organic solvent are put in a pressurized container, sealed, and stirred while being heated under pressure to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 40 ° C. or higher, preferably 60 to 200 ° C., and more preferably 80 to 1 ° C.
10 ° C.

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

[Preparation of Solution (Cooling Dissolution Method)] A solution can also be prepared by a cooling dissolution method. In the cooling dissolution method, the cellulose ester can be dissolved in an organic solvent (an organic solvent other than a halogenated hydrocarbon) which is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent (for example, halogenated hydrocarbon) which can dissolve the cellulose ester by the usual dissolution method, the cooling dissolution method has an effect that a uniform solution can be obtained quickly. In the cooling dissolution method, first, a cellulose ester is gradually added to an organic solvent at room temperature while stirring. It is preferable to adjust the amount of the cellulose ester so that the mixture contains 10 to 40% by weight of the mixture. More preferably, the amount of cellulose ester is from 10 to 30% by weight. Further, an optional additive described below may be added to the mixture.

Next, the mixture is cooled to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to -10 ° C).
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.). Upon such cooling, the mixture of the cellulose ester and the organic solvent solidifies. The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and 12 ° C./min.
/ Min or more is most preferable. A higher cooling rate is preferred, but 10,000 ° C./sec is a theoretical upper limit, 1000 ° C./sec is a technical upper limit, and
0 ° C./sec is a practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at which the cooling is started and the final cooling temperature by the time from when the cooling is started to when the temperature reaches the final cooling temperature.

Further, the temperature is raised to 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C.,
When heated to the temperature of 0 to 50 ° C., the cellulose ester dissolves in the organic solvent. The temperature may be raised only by leaving it at room temperature or may be heated 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 heating rate is preferably as high as possible, but the theoretical upper limit is 10,000 ° C./sec.
C / sec is a technical upper limit, and 100 C / sec is a practical upper limit. Note that the heating rate is a value obtained by dividing the difference between the temperature at which heating is started and the final heating temperature by the time from when the heating is started until the final heating temperature is reached. . As described above, a uniform solution is obtained. In addition,
If the dissolution is insufficient, the operation of cooling and heating may be repeated. Whether or not the dissolution is sufficient can be determined only by visually observing the appearance of the solution.

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

[Production of Film] A cellulose ester film is produced from the prepared cellulose ester solution (dope) by a solvent casting method. The dope is
Cast on a drum or band and evaporate the solvent to form a film. The concentration of the dope before casting is preferably adjusted so that the solid content is 18 to 35%.
It is preferable that the surface of the drum or the band is finished in a mirror state. Regarding the casting and drying methods in the solvent casting method, US Pat. No. 2,336,310,
No. 2367603, No. 2492078, No. 2492
977, 2492978, 2607704,
Nos. 2739069 and 2739070, British Patent 6
Nos. 40731 and 736892, Japanese Patent Publication No. Sho 4
Nos. 5-4554 and 49-5614, JP-A-60-1
No. 76834, No. 60-203430, No. 62-11
There is a description in each publication of No. 5035. The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less. It is preferable to dry the film by blowing it for 2 seconds or more. The obtained film can be peeled off from the drum or band, and further dried with high-temperature air whose temperature is gradually changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in JP-B-5-17844. According to this method, the time from casting to stripping can be reduced. In order to carry out this method, it is necessary that the dope gels at the surface temperature of the drum or band during casting. The solution (dope) prepared according to the present invention satisfies this condition. The thickness of the film to be produced is preferably 40 to 120 μm, more preferably 70 to 100 μm.

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

The cellulose ester film may be added with a deterioration inhibitor (eg, an antioxidant, a peroxide decomposer, a radical inhibitor, a metal deactivator, an acid scavenger, an amine) or an ultraviolet inhibitor. Good. Regarding the deterioration inhibitor, see JP-A-Hei 3
-199201, 5-1907073, 5-1
No. 94789, No. 5-271471, No. 6-1078
No. 54 describes each of them. The addition amount of the deterioration inhibitor
It is preferably 0.01 to 1% by weight, more preferably 0.01 to 0.2% by weight of the solution (dope) to be prepared. If the amount is less than 0.01% by weight, the effect of the deterioration inhibitor is hardly recognized. If the amount exceeds 1% by weight, bleeding out (bleeding out) of the deterioration inhibitor on the film surface may be observed.
A particularly preferred example of the deterioration inhibitor is butylated hydroxytoluene (BHT). The UV inhibitors are described in JP-A-7-11056. Note that cellulose acetate having an average acetylation degree of 55.0 to 58.0% has an average acetylation degree of 58.0%.
As compared with the above-mentioned cellulose triacetate, there is a defect that the stability of the prepared solution and the physical properties of the produced film are inferior. However, this disadvantage can be substantially eliminated by using an antioxidant such as the above-mentioned deterioration inhibitor, particularly butylated hydroxytoluene (BHT).

[Configuration of General Liquid Crystal Display Device] The cellulose ester film can be used for various purposes. The cellulose ester film of the present invention is particularly effective when used as an optical compensation sheet for a liquid crystal display.
Since the cellulose ester film of the present invention is characterized by having a high retardation value in the thickness direction, the film itself can be used as an optical compensation sheet. A liquid crystal display device has a liquid crystal cell holding liquid crystal between two electrode substrates, two polarizing elements disposed on both sides thereof, and at least one sheet between the liquid crystal cell and the polarizing element. It has a configuration in which an optical compensation sheet is arranged. The configuration of a general liquid crystal display device will be described with reference to FIG.

FIG. 1 is a schematic sectional view of a general liquid crystal display device. The liquid crystal layer (7) is provided between the resin substrates (5a, 5b). A transparent electrode layer (6a, 6b) is provided on the liquid crystal side of the resin substrate (5a, 5b). The above liquid crystal layer,
The resin substrate and the transparent electrodes (5 to 7) constitute a liquid crystal cell. Optical compensation sheets (4a, 4b) above and below the liquid crystal cell
Is glued. The cellulose ester film of the present invention can be used as the optical compensation sheet (4a, 4b). In addition, the optical compensation sheet (4a, 4b)
Also has a function of protecting the side of the polarizing film (3a, 3b) on which the protective film (2a, 2b) is not provided. Above and below the optical compensation sheets (4a and 4b), polarizing elements (2a,
2b, 3a, 3b) are provided. The polarizing element includes a protective film (2a, 2b) and a polarizing film (3a, 3b). In the liquid crystal display device shown in FIG. 1, a surface treatment film (1) is further provided on one side of the polarizing element. The surface treatment film (1) is provided on the side where a person views from the outside.
The backlight of the liquid crystal display device is provided on the opposite side (2b side). Hereinafter, the liquid crystal cell, the optical compensation sheet, and the polarizing element will be further described.

The liquid crystal layer of the liquid crystal cell is usually formed by enclosing liquid crystal in a space formed by sandwiching a spacer between two substrates. The transparent electrode layer is formed on a substrate as a transparent film containing a conductive substance. The liquid crystal cell may further be provided with a gas barrier layer, a hard coat layer or an undercoat layer (used for bonding the transparent electrode layer). These layers are usually provided on a substrate. The substrate of the liquid crystal cell generally has a thickness of 80 to 500 μm.

The optical compensation sheet is a birefringent film for removing coloring of the liquid crystal screen. The cellulose ester film of the present invention itself can be used as an optical compensation sheet. Further, in order to improve the viewing angle of the liquid crystal display device, the cellulose ester film of the present invention,
A film exhibiting the opposite birefringence (positive / negative relationship) may be used as an optical compensatory sheet. The thickness range of the optical compensation sheet is the same as the preferred thickness of the film of the present invention described above.

As the polarizing film of the polarizing element, an iodine-based polarizing film,
There are a dye-based polarizing film using a dichroic dye and a polyene-based polarizing film. All polarizing films are generally manufactured using a polyvinyl alcohol-based film. The protective film of the polarizing plate is 25
It preferably has a thickness of from 350 to 350 μm, more preferably from 50 to 200 μm. As in the liquid crystal display device shown in FIG. 1, a surface treatment film may be provided. The functions of the surface treatment film include a hard coat, an anti-fog treatment, an anti-glare treatment and an anti-reflection treatment.

As described above, an optical compensatory sheet in which an optically anisotropic layer containing a liquid crystal (particularly discotic liquid crystalline molecules) is provided on a support has been proposed (Japanese Patent Laid-Open No. 3-9).
No. 325, No. 6-148429, No. 8-50206
No. 9-26572). The cellulose ester film of the present invention can also be used as a support for such an optical compensation sheet.

[Optically Anisotropic Layer Containing Discotic Liquid Crystalline Molecules] The optically anisotropic layer is preferably a layer containing discotic liquid crystal molecules having negative uniaxiality and being obliquely aligned. It is preferable that the angle between the discotic surface of the discotic liquid crystalline molecules and the support surface changes in the depth direction of the optically anisotropic layer (hybrid alignment). The optical axis of the discotic liquid crystal molecule exists in the direction normal to the disk surface. Discotic liquid crystal molecules have a 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 aligning the discotic liquid crystal molecules by an alignment film described later and fixing the discotic liquid crystal molecules in the aligned state. The discotic liquid crystal molecules are preferably fixed by a polymerization reaction. The optically anisotropic layer has no direction in which the retardation value becomes zero. In other words, the minimum value of the retardation of the optically anisotropic layer is a value exceeding 0.

Discotic liquid crystalline molecules are described in various literatures (C. Destrade et al., Mol. Crysr. Liq. Cryst., V
ol. 71, page 111 (1981); edited by The Chemical Society of Japan, quarterly chemistry review, No. 22, Liquid Crystal Chemistry, Chapter 5, Chapter 10, Section 2
(1994); B. Kohne et al., Angew. Chem. Soc. Chem. C
omm., page 1794 (1985); J. Zhang et al., J. Am. Che
m. Soc., vol. 116, page 2655 (1994)). Regarding the polymerization of discotic liquid crystalline molecules,
It is described in JP-A-8-27284. In order to fix the discotic liquid crystal molecules by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystal molecules. However, when a polymerizable group is directly connected to the disc-shaped core, it becomes difficult to maintain an oriented state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable group. Therefore, the discotic liquid crystalline molecule having a polymerizable group is preferably a compound represented by the following formula (I).

(I) D (-LP) _{n wherein} D is a discotic core; L is a divalent linking group; P is a polymerizable group; and n is 4 to 12 Is an integer. An example of the discotic core (D) of the formula (I) 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).

[0114]

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[0115]

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[0116]

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[0117]

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[0118]

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[0119]

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[0120]

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In the formula (I), the divalent linking group (L)
Is an alkylene group, alkenylene group, arylene group,-
It is preferably a divalent linking group selected from the group consisting of CO-, -NH-, -O-, -S- and a combination thereof. The divalent linking group (L) includes an alkylene group, an alkenylene group, an arylene group, -CO-, -NH-,-
More preferably, the group is a group obtained by combining at least two divalent groups selected from the group consisting of O- and -S-. The divalent linking group (L) is most preferably a group obtained by combining at least two divalent groups selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, -CO- and -O-. The alkylene group preferably has 1 to 12 carbon atoms. The alkenylene group preferably has 2 to 12 carbon atoms. The arylene group preferably has 6 to 10 carbon atoms. The alkylene group, alkenylene group and arylene group may have a substituent (eg, an alkyl group, a halogen atom, a cyano, an alkoxy group, an acyloxy group).

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 a polymerizable group (P).
To join. AL represents an alkylene group or an alkenylene group, and AR represents an arylene 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-OC
O-L19: -O-CO-AR-O-AL-O-AL-OA
L-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) in the formula (I) is determined according to the type of the polymerization reaction. Examples of the polymerizable group (P) are shown below.

[0125]

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[0126]

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[0127]

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[0128]

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[0129]

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[0130]

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The polymerizable group (P) is an unsaturated polymerizable group (P
1, P2, P3, P7, P8, P14, P15, P1
6) or an epoxy group (P6),
More preferably, it is an unsaturated polymerizable group, and an ethylenically unsaturated polymerizable group (P1, P7, P8, P14, P1
5, P16). In the formula (I), n is an integer of 4 to 12. The specific numbers are
It is determined according to the type of discotic core (D). The combination of a plurality of L and P may be different, but is preferably the same. Two or more discotic liquid crystalline molecules (for example, a molecule having an asymmetric carbon atom in a divalent linking group and a molecule having no asymmetric carbon atom) may be used together.

The optically anisotropic layer is formed by applying a coating liquid containing discotic liquid crystal molecules, the following polymerizable initiator and other additives on the alignment film. As a solvent used for preparing the coating solution, an organic solvent is preferably used. Examples of the organic solvent include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethylsulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, ,
Chloroform, dichloromethane), ester (eg, methyl acetate, butyl acetate), ketone (eg, acetone, methyl ethyl ketone), ether (eg, tetrahydrofuran,
1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination.

The coating solution can be applied by a known method (eg, extrusion coating, direct gravure coating, reverse gravure coating, die coating). The aligned discotic liquid crystalline molecules are fixed while maintaining the aligned state. The immobilization is preferably performed by a polymerization reaction of the polymerizable group (P) introduced into the discotic liquid crystalline molecule. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. Photopolymerization reactions are preferred. Examples of the photopolymerization initiator include α-carbonyl compounds (described in U.S. Pat. Nos. 2,367,661 and 2,367,670) and acyloin ethers (U.S. Pat.
828), α-hydrocarbon-substituted aromatic acyloin compounds (described in US Pat. No. 2,722,512),
Polynuclear quinone compounds (U.S. Pat.
51758), a combination of a triarylimidazole dimer and p-aminophenyl ketone (described in US Pat. No. 3,549,367), an acridine and phenazine compound (Japanese Unexamined Patent Publication No. Sho 60-105667).
No. 4,239,850) and oxadiazole compounds (described in US Pat. No. 4,221,970).

The photopolymerization initiator is preferably used in an amount of 0.01 to 20% by weight of the solid content of the coating solution.
More preferably, it is 5 to 5% by weight. Light irradiation for the polymerization of discotic liquid crystalline molecules preferably uses ultraviolet light. The irradiation energy is 20 mJ /
cm ^{2 to} 50 J / cm ² , preferably 10
More preferably, it is 0 to 800 mJ / cm ² . Light irradiation may be performed under heating conditions to promote the photopolymerization reaction. The thickness of the optically anisotropic layer is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm, and most preferably 1 to 5 μm.

[Alignment Film] The alignment film has a function of defining the alignment direction of the discotic liquid crystal molecules in the optically anisotropic layer. The alignment film is an organic compound (preferably a polymer)
Rubbing treatment, oblique deposition of inorganic compounds, formation of a layer having microgrooves, or organic compounds by Langmuir-Blodgett method (LB film) (eg, ω-tricosanoic acid, dioctadecylmethylammonium chloride, methyl stearylate) Can be provided by means such as accumulation of Further, an alignment film in which an alignment function is generated by application of an electric field, a magnetic field, or light irradiation is also known. The alignment film is preferably formed by rubbing a polymer. Polyvinyl alcohol is a preferred polymer. Modified polyvinyl alcohol to which a hydrophobic group is bonded is particularly preferred. Since the hydrophobic group has an affinity for the discotic liquid crystalline molecules of the optically anisotropic layer,
By introducing a hydrophobic group into polyvinyl alcohol, discotic liquid crystal molecules can be uniformly aligned. 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 terminal of the main chain of polyvinyl alcohol, it is preferable to introduce a linking group between the hydrophobic group and the terminal of the main chain. Examples of linking groups include -S
—, —C (CN) R ¹ —, —NR ² —, —CS— and combinations thereof. The above R ¹ and R ²
Is 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 replaced with an acyl group (—CO—R) having 7 or more carbon atoms. ³ ). R ³ is an aliphatic group or an aromatic group having 6 or more carbon atoms. A commercially available modified polyvinyl alcohol (eg, MP103, MP203, R1130, manufactured by Kuraray Co., Ltd.) may be used. The saponification degree of (modified) polyvinyl alcohol used for the alignment film is preferably 80% or more. (Modified) The polymerization degree of polyvinyl alcohol is preferably 200 or more. The rubbing treatment is performed by rubbing the surface of the alignment film several times with paper or cloth in a certain direction. It is preferable to use a cloth in which fibers having uniform length and thickness are uniformly planted. In addition, after aligning the discotic liquid crystal molecules using the alignment film, the discotic liquid crystal molecules are fixed in the aligned state to form an optically anisotropic layer, and only the optically anisotropic layer is formed. It may be transferred onto a support. Discotic liquid crystalline molecules fixed in an aligned state can maintain the aligned state without an alignment film. Therefore, in the optical compensation sheet, the alignment film is not an essential element (although it is essential in the production of the optical compensation sheet containing discotic liquid crystalline molecules).

[VA-Type Liquid Crystal Display Device] The cellulose ester film of the present invention is particularly advantageously used as a support for an optical compensation sheet of a VA-type liquid crystal display device having a VA-mode liquid crystal cell. The VA liquid crystal display device will be described with reference to FIGS. FIG. 2 is a cross-sectional view schematically showing the orientation of a liquid crystal compound in a VA mode liquid crystal cell when no voltage is applied. As shown in FIG. 2, the liquid crystal cell
It has a structure in which a liquid crystal compound (12) is sealed between an upper substrate (11) and a lower substrate (13). The liquid crystal compound (12) used for a VA mode liquid crystal cell generally has a negative dielectric anisotropy. When the applied voltage of the VA mode liquid crystal cell is 0 (when no voltage is applied), the molecules of the liquid crystalline compound (12) are vertically aligned as shown in FIG. A pair of polarizing elements (not shown) are provided on both sides of the upper and lower substrates (11, 13).
Are arranged in crossed Nicols, the normal direction (1
No retardation occurs in 4). As a result, light cannot be transmitted in the normal direction (14) of the substrate surface, and black display is performed. When the line of sight is shifted from the normal direction (14) of the substrate to the direction (15) inclined, light is transmitted due to the occurrence of retardation, and the contrast is reduced. This oblique retardation can be compensated by the optical anisotropy of the optical compensation sheet. Details will be described later (with reference to FIG. 5). In FIG. 2, all of the liquid crystal compound (12) is completely oriented in the vertical direction, but is actually slightly tilted (pretilted) in a certain direction. This is because all the liquid crystal compounds are tilted in a fixed direction (pretilt direction) when a voltage is applied (described with reference to FIG. 3 below).

FIG. 3 is a sectional view schematically showing the orientation of a liquid crystal compound in a VA mode liquid crystal cell when a voltage is applied. The upper substrate (21) and the lower substrate (23) each have an electrode layer (not shown), and can apply a voltage to the liquid crystal compound (22). As shown in FIG. 3, when a voltage is applied, the molecules of the liquid crystal compound at the center of the liquid crystal cell are horizontally aligned. As a result, retardation occurs in the normal direction (24) of the substrate surface, and light is transmitted. As described above, the liquid crystal molecules in the central portion of the liquid crystal cell are in a horizontal alignment state, but the liquid crystal molecules in the vicinity of the alignment film are not in the horizontal alignment state but are inclinedly aligned in the pretilt direction. Moving the line of sight in the direction (25) inclined from the normal direction (24) of the substrate surface causes a small change in retardation angle, whereas moving the line of sight in another direction (26) changes the angle of retardation. Is big. Accordingly, when the pretilt direction of the liquid crystalline compound is the downward direction of the image (the same direction as 26), the viewing angle in the left-right direction is symmetric and wide, and the viewing angle in the downward direction is wide, but the viewing angle in the upward direction is narrow and vertically asymmetric. Viewing angle characteristics. In order to improve the viewing angle characteristics, it is necessary to compensate for the retardation caused by the liquid crystal molecules that are not horizontally aligned but tilted when a voltage is applied. The optical compensatory sheet has a function of compensating for the above-mentioned retardation and improving visual characteristics (removing asymmetry in the visual direction of transmittance when a voltage is applied).

FIG. 4 is a schematic view of a refractive index ellipse obtained from a VA mode liquid crystal cell in which polarizing elements are arranged in a crossed Nicols when viewed from the normal direction of the cell substrate. FIG. 4 (a)
Is a refractive index ellipse when no voltage is applied, and (b) is a refractive index ellipse when voltage is applied. In the crossed Nicols arrangement, the transmission axis (31a, 31b) of the polarization element on the incident side and the transmission axis (32a, 32b) of the polarization element on the emission side are arranged perpendicularly. When no voltage is applied, the liquid crystal molecules in the cell are oriented perpendicular to the cell substrate surface. Accordingly, the refractive index ellipse (33a) obtained from the normal direction of the cell substrate is circular. In this case, since the retardation of the liquid crystal cell is 0, no light is transmitted. On the other hand, when a voltage is applied, the liquid crystal molecules in the cell are oriented substantially horizontally with respect to the cell substrate surface. Therefore, the refractive index ellipse (33b) obtained from the normal direction of the cell substrate is elliptical. In this case, since the retardation of the liquid crystal cell has a value other than 0, light is transmitted. FIG. 4B also shows an orthogonal projection (34) of the optical axis of the liquid crystal molecules in the cell onto the surface of the liquid crystal cell substrate.

FIG. 5 is a schematic diagram showing the refractive index ellipse of a positive uniaxial liquid crystal cell and the refractive index ellipse of a negative uniaxial optical compensation sheet. When positive uniaxial optical anisotropy occurs in the liquid crystal cell (43), the refractive index (44x, 44y) in the plane parallel to the liquid crystal cell substrate and the refractive index (44x) in the thickness direction of the liquid crystal cell. The refractive index ellipse (44) formed by the above has a rugby ball standing shape as shown in FIG. When the liquid crystal cell having such a rugby ball-shaped (not spherical) refractive index ellipse is viewed from an oblique direction (15 in FIG. 2) as described with reference to FIG. 2, retardation occurs. This retardation is canceled by the negative uniaxial optical compensation sheet (42), and light leakage can be suppressed. Optical compensation sheet having negative uniaxiality (42)
Then, the main refractive index in the plane of the optical compensation sheet (41x, 41x)
y) and the main refractive index (41z) in the thickness direction of the optical compensation sheet
(41) of the refractive index of the optical compensation sheet formed by
Has an unpan shape as shown in FIG. So 4
The sum of 1x and 44x, the sum of 41y and 44y, and the sum of 41z and 44z have almost the same value. As a result, retardation generated in the liquid crystal cell is canceled. The optical compensation sheet of the present invention has a function of preventing light leakage at oblique incidence when no voltage is applied as described above, in addition to the function of improving the visual characteristics described above.

FIG. 6 is a schematic sectional view showing a combination of a VA mode liquid crystal cell and two optical compensation sheets.
As shown in FIG. 6, two optical compensation sheets (53, 5
4) is any of the four variations (a) to (d) and can be combined with the VA mode liquid crystal cell (50). In the variations (a) and (c), the side of the optically anisotropic layer (51) containing discotic liquid crystal molecules of the optical compensation sheet (53, 54) is
It is used by being attached to an A-mode liquid crystal cell (50).
In the variation of (a), the optically anisotropic layer (51)
An alignment film is provided on the transparent support (52) side to align discotic liquid crystal molecules. In the variation (c), an alignment film is provided on the VA-mode liquid crystal cell (50) side of the optically anisotropic layer (51) to align discotic liquid crystal molecules. In the variations (b) and (d), the side of the transparent support (52) of the optical compensation sheet (53, 54) is connected to the VA mode liquid crystal cell (5).
0) to use. In the variation (b), an alignment film is provided on the transparent support (52) side of the optically anisotropic layer (51) to align discotic liquid crystal molecules. In the variation (d), an alignment film is provided outside the optically anisotropic layer (51) to align the discotic liquid crystal molecules.

FIG. 7 is a schematic sectional view showing a combination of a VA mode liquid crystal cell and one optical compensation sheet.
As shown in FIG. 7, one optical compensation sheet (63)
Any of the four variations (e) to (h) can be combined with the VA mode liquid crystal cell (60). In variations of (e) and (g),
The optical compensatory sheet (63) is used by bonding the optically anisotropic layer (61) containing discotic liquid crystalline molecules to a VA mode liquid crystal cell (60). In the variation (e), an alignment film is provided on the transparent support (62) side of the optically anisotropic layer (61) to align discotic liquid crystal molecules. In the variation of (g),
VA mode liquid crystal cell (6) of optically anisotropic layer (61)
An alignment film is provided on the 0) side to align the discotic liquid crystalline molecules. In the variations (f) and (h), the transparent support (62) of the optical compensation sheet (63) is used.
Side is attached to a VA mode liquid crystal cell (60). In the variation (f), an alignment film is provided on the transparent support (62) side of the optically anisotropic layer (61) to align discotic liquid crystal molecules. In the variation (h), an alignment film is provided outside the optically anisotropic layer (61) to align discotic liquid crystal molecules.

FIG. 8 is a schematic sectional view of an optical compensatory sheet used in a VA liquid crystal display device. The optical compensation sheet shown in FIG. 8 has a layer structure in the order of a support (71), an alignment film (72), and an optically anisotropic layer (73). This layer configuration is
This corresponds to the optical compensation sheet of FIGS. 6A and 6B or FIGS. 7E and 7F. The alignment film (72) is provided with an alignment function by rubbing in a certain direction (75). The discotic liquid crystal molecules (73a, 73b, 73c) contained in the optically anisotropic layer (73) are planar molecules. Discotic liquid crystal molecules (73a, 7
3b and 73c) have only one plane in the molecule, that is, a disk surface (Pa, Pb, Pc). Disk surface (Pa,
Pb, Pc) is a plane (71) parallel to the plane of the support (71).
a, 71b, 71c). Disk surface (P
a, Pb, Pc) and the planes (71a, 71) parallel to the support surface.
b, 71c) are the inclination angles (θa, θb, θ
c). As the distance from the alignment film (62) increases along the normal line (74) of the support, the inclination angle also increases (θa <θb <θc). Tilt angle (θa, θb, θc)
Preferably changes within a range of 0 to 60 °. The minimum value of the tilt angle is preferably in the range of 0 to 55 °, and more preferably in the range of 5 to 40 °. The maximum value of the tilt angle is preferably in the range of 5 to 60 °, and more preferably in the range of 20 to 60 °. The difference between the minimum value and the maximum value of the inclination angle is preferably in the range of 5 to 55 °, and preferably 10 to 40 °
More preferably, it is within the range. When the inclination angle is changed as shown in FIG. 8, the viewing angle expanding function of the optical compensation sheet is significantly improved. Further, the optical compensation sheet having the changed inclination angle has a function of preventing inversion, gradation change, or coloring of the displayed image.

FIG. 9 is a schematic cross-sectional view of a typical VA liquid crystal display device. The liquid crystal display device shown in FIG. 9 includes a VA mode liquid crystal cell (VAC), a pair of polarizing elements (A, B) provided on both sides of the liquid crystal cell, and a pair of polarizing elements disposed between the liquid crystal cell and the polarizing element. Optical compensation sheet (OC1, OC2)
And a backlight (BL). Only one of the optical compensation sheets (OC1, OC2) may be arranged. Arrows (R1, R2) of optical compensation sheets (OC1, OC2)
Is the rubbing direction of the alignment film provided on the optical compensation sheet (corresponding to arrow 75 in FIG. 8). In the liquid crystal display device shown in FIG. 9, the optically anisotropic layers of the optical compensation sheets (OC1, OC2) are arranged on the liquid crystal cell side. The optically anisotropic layer of the optical compensation sheet (OC1, OC2) may be disposed on the polarizing element (A, B) side. When the optically anisotropic layer is arranged on the polarizing element (A, B) side, the rubbing directions (R1, R2) of the alignment film are opposite to those in FIG. Arrows (RP1, RP2) of the liquid crystal cell (VAC) indicate the rubbing direction of the alignment film provided on the liquid crystal cell substrate. Arrows (PA, PB) of the polarizing elements (A, B) are transmission axes of polarized light of the polarizing elements, respectively.

The rubbing directions (R1, R2) of the alignment film provided on the optical compensation sheet and the rubbing directions (RP1, RP2) of the alignment film provided on the liquid crystal cell substrate are substantially parallel or antiparallel, respectively. Is preferred. It is preferable that the transmission axes (PA, PB) of the polarized light of the polarizing element are arranged to be substantially orthogonal or parallel. Substantially orthogonal,
Parallel or anti-parallel means that the angle shift is 20 °
Less than (preferably less than 15 °, more preferably less than 10 °
, Most preferably less than 5 °). Rubbing direction (RP) of alignment film provided on liquid crystal cell substrate
1, RP2) and the transmission axis (PA, P
The angle with B) is preferably from 10 to 80 °, more preferably from 20 to 70 °, and most preferably from 35 to 55 °.

In the optical compensatory sheet used for the VA liquid crystal display device, it is preferable that the direction in which the absolute value of the retardation is minimum does not exist in the plane of the optical compensatory sheet nor in the normal direction. The optical properties of the optical compensatory sheet used in the VA liquid crystal display device are determined by the optical properties of the optically anisotropic layer, the optical properties of the support, and the arrangement of the optically anisotropic layer and the support. . Details of their optical properties are described below. Regarding the optical properties, (1) the optically anisotropic layer, (2) the support, and (3) the entire optical compensation sheet, the in-plane retardation (Re), the retardation in the thickness direction (Rth) and The angle (β) between the direction in which the absolute value of the retardation is minimum and the normal line of the sheet is important. The in-plane retardation and the retardation in the thickness direction are the same as the definition of the cellulose ester film described above. However, in the optically anisotropic layer and the optical compensation sheet as a whole, n
x, ny, and nz mean in-plane principal refractive indices satisfying nx ≧ ny ≧ nz.

When two optical compensation sheets are used in a VA liquid crystal display device, the in-plane retardation of the optical compensation sheet is preferably in the range of -5 nm to 5 nm. Therefore, the absolute value of the in-plane retardation (Re ³¹ ) of each of the two optical compensation sheets is 0 ≦ | Re ³¹
It is preferable that | ≦ 5. In order to adjust Re ³¹ to the above range, the difference between the absolute value of the in-plane retardation (Re ¹ ) of the optically anisotropic layer and the absolute value of the in-plane retardation (Re ² ) of the support (|| Re ¹ | − | Re ² |
|) Is set to 5 nm or less, and the optically anisotropic layer and the support are preferably arranged such that the in-plane slow axes are substantially perpendicular to each other. When one optical compensatory sheet is used for a VA liquid crystal display device, the in-plane retardation of the optical compensatory sheet is set to -10 nm to 10 nm.
Is preferably within the range. Therefore, the absolute value of the in-plane retardation (R ³² ) of one optical compensation sheet is
It is preferable that 0 ≦ | Re ³² | ≦ 10. To adjust Re ³² to the above range, the difference between the absolute value of the in-plane retardation (Re ¹ ) of the optically anisotropic layer and the absolute value of the in-plane retardation (Re ² ) of the support. (|| R
e ¹ | − | Re ² ||) is set to 10 nm or less, and the optically anisotropic layer and the support are arranged so that the slow axes in their planes are substantially perpendicular to each other. preferable.

Regarding the optical compensatory sheet used for the VA type liquid crystal display device, the preferable ranges of the optical properties of (1) the optically anisotropic layer, (2) the support and (3) the entire optical compensatory sheet are summarized below. Show. The unit of Re and Rth is n
m. The superscript number 1 means the value of the optically anisotropic layer, the superscript number 2 means the value of the support, and the superscript number 3 means the value of the optical compensatory sheet. The meanings of Re ³¹ and Re ³² are as described above. The preferred range of the retardation (Rth ² ) in the thickness direction of the support is as defined above as the optical properties of the cellulose ester film. When two or more supports are provided, the in-plane retardation (Re ² ) of the entire support corresponds to the sum of the in-plane retardations of the respective supports.

────────────────────────────────────Preferable range Further preferred range Most preferred range─── ───────────────────────────────── 0 <| Re ¹ | ≦ 200 5 ≦ | Re ¹ | ≦ 150 10 ≦ | Re ¹ | ≦ 100 0 ≦ | Re ² | ≦ 2005 5 ≦ | Re ² | ≦ 150 10 ≦ | Re ² | ≦ 100 0 ≦ | Re ³¹ | ≦ 4.50 ≦ | Re ³¹ | ≦ 40 ≦ | Re ³¹ | ≦ 3.5 0 ≦ | Re ³² | ≦ 90 ≦≦ Re ³² | ≦ 80 ≦ | Re ³² | ≦ 7 ───────────────────10 ≦ | Rth ¹ | ≦ 400 20 ≦ | Rth ¹ | ≦ 300 30 ≦ | Rth ¹ | ≦ 200 10 ≦ | Rth ³ | ≦ 600 60 ≦ | Rth ³ | ≦ 500 100 ≦ | Rth ³ | ≦ 4 00 ──────────────────────────────────── 0 ° <β ¹ ≦ 60 ° 0 ° <β ¹ ≦ 50 ° 0 ° <β ¹ ≦ 40 ° 0 ° ≦ β ² ≦ 10 ° 0 ° ≦ β ² ≦ 5 ° 0 ° ≦ β ² ≦ 3 ° 0 ° <β ³ ≦ 50 ° 0 ° <β ³ ≦ 45 ° 0 ° <β ³ ≤ 40 ° ────────────────────────────────────

[OCB Type Liquid Crystal Display Device and HAN Type Liquid Crystal Display Device] The cellulose ester film of the present invention comprises:
It is also advantageously used as a support for an optical compensation sheet of an OCB type liquid crystal display device having an OCB mode liquid crystal cell or a HAN type liquid crystal display device having a HAN mode liquid crystal cell. The OCB type liquid crystal display device and the HAN type liquid crystal display device will be described with reference to FIGS. FIG. 10 is a cross-sectional view schematically showing the orientation of a liquid crystal compound in an OCB mode liquid crystal cell. FIG. 10 shows a state of black display, which corresponds to a case where a voltage is applied in the normally white mode or a case where no voltage is applied in the normally black mode. As shown in FIG. 10, the OCB mode liquid crystal cell has a structure in which a liquid crystal compound (12) is sealed between an upper substrate (11) and a lower substrate (13). In the OCB mode liquid crystal cell, the birefringence of the liquid crystal compound (12) is small near the lower substrate (13) and the liquid crystal compound (12) near the upper substrate (11) in a certain light traveling direction (16a). Has large birefringence. In the direction (16b) that is symmetrical with respect to this direction (16a) about the normal line of the substrate, the liquid crystal compound (12) has a large birefringence near the lower substrate (13) and the upper substrate (11). In the vicinity of the liquid crystal compound (1
2) The birefringence is small. As described above, the OCB mode liquid crystal cell has an optical self-compensation function because the retardation is symmetric about the normal line of the substrate. Therefore, the OCB mode liquid crystal cell has a wide viewing angle in principle.

FIG. 11 is a sectional view schematically showing the orientation of a liquid crystal compound in a HAN mode liquid crystal cell. FIG.
Is a state of black display, which corresponds to a voltage application in the normally white mode or a voltage non-application in the normally black mode. As shown in FIG.
The HAN mode liquid crystal cell also has a structure in which a liquid crystal compound (22) is sealed between an upper substrate (21) and a lower substrate (23). The HAN mode is a liquid crystal cell in which the concept of the OCB mode (transmission type) liquid crystal cell is applied to a reflection type liquid crystal cell. In the HAN mode liquid crystal cell, the incident light (27)
With respect to the liquid crystal compound (2) near the upper substrate (21).
2) Large birefringence. The birefringence of the liquid crystal compound (22) is small near the lower substrate (23). On the other hand, outgoing light (28)
As for the liquid crystal compound (2) near the lower substrate (23),
The birefringence of 2) is large, and the birefringence of the liquid crystal compound (22) near the upper substrate (21) is small. Thus, HAN
The mode liquid crystal cell has an optical self-compensation function because the retardation of incident light and reflected light is symmetric. Therefore, the HAN mode liquid crystal cell also has a wide viewing angle in principle.

Even in a liquid crystal cell of OCB mode or HAN mode, when the viewing angle is increased, the transmittance of light from the black display part is significantly increased, and the contrast is reduced. The optical compensatory sheet is used to prevent a decrease in contrast when light is incident in an oblique direction, improve viewing angle characteristics, and further improve frontal contrast. When the liquid crystal cell has positive uniaxiality in black display, optical compensation is performed using a negative uniaxial optical compensation sheet as described with reference to FIG.

FIG. 12 is a schematic sectional view showing a combination of an OCB mode liquid crystal cell and optically anisotropic layers of two optical compensation sheets. As shown in FIG. 12, the two optical compensation sheets have optically anisotropic layers (51, 52) of OCB.
It is preferable to combine and use the liquid crystal cells (50) in the mode. Optically anisotropic layer (51, 52)
Have an alignment state (optically compensated) corresponding to the alignment state of the liquid crystal molecules of the OCB mode liquid crystal cell (50).

FIG. 13 is a schematic sectional view showing a combination of a HAN mode liquid crystal cell and an optically anisotropic layer of one optical compensation sheet. As shown in FIG. 13, one optical compensation sheet is preferably used in combination so that the optically anisotropic layer (61) is on the display surface side of the HAN mode liquid crystal cell (60). The discotic liquid crystal molecules of the optically anisotropic layer (61) have an alignment state (optically compensated) corresponding to the alignment state of the liquid crystal molecules of the HAN mode liquid crystal cell (60).

As shown in FIGS. 12 and 13, OCB
Mode and HAN mode liquid crystal cell alignment can be optically compensated by an optically anisotropic layer containing discotic liquid crystal molecules. However, with the optically anisotropic layer alone, the correction of the retardation of the liquid crystal cell and the correction of the retardation generated in the optically anisotropic layer itself are insufficient. Therefore, as described above, the retardation is corrected by setting the support to optical anisotropy. The combination of the optically anisotropic layer and the optically anisotropic support, that is, the basic configuration (cross-sectional schematic view) of the optical compensatory sheet is the optical compensatory sheet used for the VA liquid crystal display device described with reference to FIG. Is the same as

FIG. 14 is a schematic sectional view of a typical OCB type liquid crystal display device. The liquid crystal display device shown in FIG.
CB mode liquid crystal cell (OCBC), a pair of polarizing elements (A, B) provided on both sides of the liquid crystal cell, a pair of optical compensation sheets (OC) disposed between the liquid crystal cell and the polarizing element.
1, OC2) and a backlight (BL). Only one of the optical compensation sheets (OC1, OC2) may be arranged. Arrows (R) of the optical compensation sheets (OC1, OC2)
1, R2) is the rubbing direction of the alignment film provided on the optical compensation sheet. In the liquid crystal display device shown in FIG. 14, the optically anisotropic layers of the optical compensation sheets (OC1, OC2) are arranged on the liquid crystal cell side. Optical compensation sheet (OC1, OC
The optically anisotropic layer 2) may be arranged on the polarizing element (A, B) side. When the optically anisotropic layer is disposed on the polarizing element (A, B) side, the rubbing direction of the alignment film (R1, R2)
Is in the opposite direction to FIG. Liquid crystal cell (OCBC)
Arrows (RP1, RP2) indicate the rubbing direction of the alignment film provided on the liquid crystal cell substrate. Arrows (PA, PB) of the polarizing elements (A, B) are transmission axes of polarized light of the polarizing elements, respectively.

The rubbing directions (R1, R2) of the alignment film provided on the optical compensation sheet and the rubbing directions (RP1, RP2) of the alignment film provided on the liquid crystal cell substrate are substantially parallel or antiparallel, respectively. Is preferred. It is preferable that the transmission axes (PA, PB) of the polarized light of the polarizing element are arranged to be substantially orthogonal or parallel. Substantially orthogonal,
Parallel or anti-parallel means that the angle shift is 20 °
Less than (preferably less than 15 °, more preferably less than 10 °
, Most preferably less than 5 °). Rubbing direction (RP) of alignment film provided on liquid crystal cell substrate
1, RP2) and the transmission axis (PA, P
The angle with B) is preferably from 10 to 80 °, more preferably from 20 to 70 °, and most preferably from 35 to 55 °.

FIG. 15 is a schematic sectional view of a typical HAN type liquid crystal display device. The liquid crystal display device shown in FIG.
From an AN mode liquid crystal cell (HANC), a polarizing element (A) provided on the display surface side of the liquid crystal cell, an optical compensation sheet (OC) and a reflector (RB) disposed between the liquid crystal cell and the polarizing element. Become. The arrow (R) of the optical compensation sheet (OC) indicates the rubbing direction of the alignment film provided on the optical compensation sheet. The arrow (RP) of the liquid crystal cell (HANC) indicates the rubbing direction of the alignment film provided on the liquid crystal cell substrate. An arrow (PA) of the polarizing element (A) is a transmission axis of polarized light of the polarizing element. The rubbing direction (R) of the alignment film provided on the optical compensation sheet and the rubbing direction (RP) of the alignment film provided on the liquid crystal cell substrate are preferably substantially parallel or antiparallel, respectively. Substantially parallel or antiparallel means that the angle shift is less than 20 ° (preferably less than 15 °, more preferably less than 10 °, most preferably 5 °).
Less). The angle between the rubbing direction (RP) of the alignment film provided on the liquid crystal cell substrate and the polarization transmission axis (PA) of the polarizing element is preferably 10 to 80 °, and more preferably 20 to 70 °. Preferably
Most preferably, it is 35 to 55 °.

In the optical compensatory sheet used for the OCB type liquid crystal display device or the HAN type liquid crystal display device, the direction in which the absolute value of the retardation is minimum does not exist in the plane of the optical compensatory sheet nor in the normal direction. preferable. The optical properties of the optical compensatory sheet used in the OCB type liquid crystal display device or the HAN type liquid crystal display device also include the optical properties of the optically anisotropic layer, the optical properties of the support, and the optically anisotropic layer and the support. Is determined by the arrangement. Details of their optical properties are described below. As for the optical properties, the in-plane retardation (R) of each of (1) the optically anisotropic layer, (2) the support, and (3) the entire optical compensatory sheet.
e) and the retardation (Rth) in the thickness direction are important. In the OCB type liquid crystal display device or the HAN type liquid crystal display device, (4) the optical properties of the liquid crystal cell (in-plane retardation and retardation in the thickness direction)
The relative relationship with is also important. The in-plane retardation and the retardation in the thickness direction are the same as the definition of the cellulose ester film described above. However, in the optically anisotropic layer and the optical compensation sheet as a whole, nx, ny, and nz in the above-described definitions mean an in-plane principal refractive index satisfying nx ≧ ny ≧ nz.

In the embodiment using two optical compensation sheets,
The relationship between the in-plane retardation of the optical compensation sheet and (Re ³⁾ and the in-plane retardation of the liquid crystal cell (Re ^4),
It is preferable to adjust so as to satisfy the following expression. Re ⁴ −20 ≦ | Re ³ | × 2 ≦ Re ⁴ +20 In the embodiment in which one optical compensation sheet is used, the in-plane retardation (Re ³ ) of the optical compensation sheet and the in-plane retardation (Re ⁴ ) of the liquid crystal cell are used. Is preferably adjusted so as to satisfy the following expression. Re ⁴ −20 ≦ | Re ³ | ≦ Re ⁴ +20

The preferred ranges of the optical properties of (1) the optically anisotropic layer, (2) the support and (3) the optical compensatory sheet are summarized below. The unit of Re and Rth is nm. The superscript number 1 means the value of the optically anisotropic layer, the superscript number 2 means the value of the support, and the superscript number 3 means the value of the optical compensatory sheet. The preferred range of the retardation (Rth ² ) in the thickness direction of the support is as defined above as the optical properties of the cellulose ester film. When two or more supports are provided, the in-plane retardation (Re ² ) of the entire support corresponds to the sum of the in-plane retardations of the respective supports. Further, the in-plane retardation (Re ³ ) of the optical compensation sheet is adjusted in relation to the above-described in-plane retardation (Re ⁴ ) of the liquid crystal cell.

──────────────────────────────────── Preferred range More preferred range Most preferred range ─── ───────────────────────────────── 0 <| Re ¹ | ≦ 200 5 ≦ | Re ¹ | ≦ 150 10 ≦ | Re ¹ | ≦ 100 0 ≦ | Re ² | ≦ 2005 5 ≦ | Re ² | ≦ 150 10 ≦ | Re ² | ≦ 100 0 ≦ | Re ³ | ≦ 4.50 ≦ | Re ³ | ≦ 40 ≦ | Re ³ | ≦ 3.5────────────────────────────────────50 ≦ | Rth ¹ ≤ 1000 50 ≤ | Rth ¹ | ≤ 800 100 ≤ | Rth ¹ | ≤ 500 50 ≤ | Rth ³ | ≤ 1000 60 ≤ | Rth ³ | ≤ 500 100 ≤ | Rth ³ | ≤ 400 ─────── ─────────────────────── ─────

[0163]

[Example 1] At room temperature, average acetylation degree 6
45 parts by weight of 0.9% cellulose acetate, 0.90 parts by weight of the retardation increasing agent (5), 232.72 parts by weight of methylene chloride, 42.57 parts by weight of methanol and 8.50 parts by weight of n-butanol were mixed. To prepare a solution (dope). The obtained solution (dope) was cast using a band casting machine having an effective length of 6 m so that the dry film thickness became 100 μm, and dried. For the produced cellulose acetate film, an ellipsometer (M-1) was used.
50, by using JASCO the Corp.), the retardation value in the thickness direction at a wavelength of 550nm (the Rth ⁵⁵⁰⁾ was measured. The results are shown in Table 1.

Comparative Example 1 A film was produced and evaluated in the same manner as in Example 1 except that the retardation increasing agent (5) was not added. The results are shown in Table 1.

[Examples 2 to 10] Instead of the retardation increasing agent (5), a retardation increasing agent (6),
(7), (31), (36), (37), (38),
A film was produced and evaluated in the same manner as in Example 1 except that the same amounts of (44), (50) and (81) were used. The results are shown in Table 1.

[Comparative Examples 2 to 5] In place of the retardation increasing agent (5), the following comparative compounds (x1) and (x
2) A film was produced and evaluated in the same manner as in Example 1, except that (x3) and (x4) were used in the same amounts. The results are shown in Table 1.

[0167]

Embedded image

[0168]

Embedded image

[0169]

[Table 1] Table 1 ──────────────────────────────────── Film Retardation enhancer Retardation Value (Rth ⁵⁵⁰ ) 比較 Comparative Example 1 None 20 nm Example 1 ( 5) 181 nm Example 2 (6) 200 nm Example 3 (7) 222 nm Example 4 (31) 99 nm Example 5 (36) 158 nm Example 6 (37) 158 nm Example 7 (38) 166 nm Example 8 (44 71 nm Example 9 (50) 75 nm Example 10 (81) 80 nm Comparative Example 2 (x1) 30 nm Comparative Example 3 (x2) 30 nm Comparative Example 4 (x3) 30 nm Comparative Example 5 (x4) 30 nm ─────────────────── ──────────

Example 11 At room temperature, 45 parts by weight of cellulose acetate having an average acetylation degree of 60.9%, 0.90 part by weight of a retardation increasing agent (3), and 2.75 of triphenyl phosphate (plasticizer) Parts by weight, 2.20 parts by weight of biphenyldiphenyl phosphate, 232.7 methylene chloride
A solution (dope) was prepared by mixing 2 parts by weight, 42.57 parts by weight of methanol and 8.50 parts by weight of n-butanol. The obtained solution (dope) was cast using a band casting machine having an effective length of 6 m so that the dry film thickness became 100 μm, and dried. For cellulose acetate film produced, ellipsometer using (M-0.99, manufactured by JASCO Corporation), the retardation value in the thickness direction at a wavelength of 550nm and (Rth ⁵⁵⁰⁾ was measured. Furthermore, the presence or absence of bleed-out was evaluated by observing the film surface. The results are shown in Table 2.

Comparative Example 6 A film was produced and evaluated in the same manner as in Example 1 except that the retardation increasing agent (3) was not added. The results are shown in Table 2.

[Examples 12 to 14] Instead of the retardation increasing agent (3), a retardation increasing agent (8),
Except that (31) and (75) were used in the same amounts,
A film was manufactured and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0173]

Table 2 ──────────────────────────────────── Film Retardation Raising Agent Rth ⁵⁵⁰ Bleed-out ──────────────────────────────────── Comparative Example 6 None 50 nm None Example 11 (3) 120 nm None Example 12 (8) 120 nm None Example 13 (31) 180 nm None Example 14 (75) 120 nm None ──────────────────────── ────────────

Examples 15 to 18 Films were produced and evaluated in the same manner as in Examples 11 to 14, except that the amount of the retardation increasing agent was changed from 0.90 part by weight to 0.20 part by weight. did. The results are shown in Table 3.

[0175]

[Table 3] Table III Film Retardation Raising Agent Rth ⁵⁵⁰ Bleed-out 比較 Comparative Example 6 None 50 nm None Example 15 (3) Example 16 (8) 240 nm Slightly available Example 17 (31) 300 nm Available Example 18 (75) 200 nm None ２４０ ──────────────

[Example 19] (Preparation of liquid crystal cell) A polyimide film was provided as an alignment film on a glass substrate provided with electrodes (ITO), and rubbing treatment was performed. The two glass substrates thus obtained were faced to face each other, the cell gap was set to 10 μm, and a liquid crystal (ZLI1132, manufactured by Merck) was injected to form an OCB mode liquid crystal cell.

(Preparation of Liquid Crystal Display) Two cellulose acetate films prepared in Example 11 were arranged as optical compensation sheets so as to sandwich a liquid crystal cell. A polarizing element was arranged outside the outside so as to sandwich the whole. When a voltage of 55 Hz square wave was applied to the created liquid crystal display device,
A clear image without coloring was obtained.

[Example 20] (Support of optical compensation sheet) The cellulose acetate film prepared in Example 11 was used as a support of the optical compensation sheet.

(Formation of Alignment Film) A coating solution having the following composition was applied on a support with a slide coater at 25 ml / m ² . 60 seconds with 60 ° C hot air, and 15 seconds with 90 ° C hot air
Dry for 0 seconds. Next, a rubbing treatment was performed on the formed film in a direction parallel to the slow axis direction of the support.

<< Composition of Alignment Film Coating Solution >>変 性 The following modified polyvinyl alcohol 10 parts by weight Water 371 parts by weight Methanol 119 parts by weight Glutaraldehyde (crosslinked Agent) 0.5 parts by weight ────────────────────────────────────

[0181]

Embedded image

(Formation of Optically Anisotropic Layer) 1.8 g of the following discotic liquid crystalline compound and ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.) were placed on the alignment film. 0.2 g, cellulose acetate butyrate (CAB551-0.
2, Eastman Chemical Co., Ltd.) 0.04 g, photopolymerization initiator (Irgacure 907, Ciba Geigy Co., Ltd.)
A coating solution prepared by dissolving 0.62 g of a sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) in 8.43 g of methyl ethyl ketone was applied using a # 2.5 wire bar. This was attached to a metal frame and heated in a thermostat at 130 ° C. for 2 minutes to align the discotic liquid crystalline compound. Next, UV irradiation was performed at 130 ° C. for 1 minute using a 120 W / cm high-pressure mercury lamp to crosslink the discotic liquid crystalline compound. Then, it was left to cool to room temperature. Thus, an optical compensation sheet (1) was produced.

[0183]

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(Evaluation of Optical Compensation Sheet) The thickness of the optically anisotropic layer was about 1.0 μm. When the retardation value of only the optically anisotropic layer was measured along the rubbing axis, there was no direction in which the retardation was 0. The average inclination angle of the optical axis of the optically anisotropic layer, that is, the angle (β ¹ ) between the direction in which the retardation was minimized and the normal line of the sheet was 28 °. The in-plane retardation was 15 nm (Re ¹ = 15), and the retardation in the thickness direction was 35 nm (Rth ¹ = 35). The optical compensatory sheet (1) was cut vertically using a microtome along the rubbing direction to obtain an extremely thin vertical fragment (sample). The samples were left in the OsO ₄ atmosphere for 48 hours to stain. The stained sample was observed with a transmission electron microscope (TEM), and a micrograph was obtained. In the stained sample, the acryloyl group of the discotic liquid crystalline compound was stained and observed as a photograph image. As a result of examining this photograph, it was confirmed that the discotic structural units of the discotic liquid crystalline compound were inclined from the surface of the support. Furthermore, the tilt angle continuously increased as the distance from the support surface increased.

(Preparation of VA Mode Liquid Crystal Cell) 1% by weight of octadecyldimethylammonium chloride (coupling agent) was added to a 3% by weight aqueous solution of polyvinyl alcohol. This was spin-coated on a glass substrate with an ITO electrode, heat-treated at 160 ° C., and rubbed to form a vertical alignment film. The rubbing treatment was performed so that the two glass substrates face in opposite directions.
Two glass substrates faced each other so that the cell gap (d) became 5.5 μm. In the cell gap, a liquid crystalline compound (Δn: 0.
05) was injected to form a VA mode liquid crystal cell. Δn
And d was 275 nm.

(Preparation of VA Type Liquid Crystal Display Device) In a VA mode liquid crystal cell, two optical compensatory sheets (1) were sandwiched between the optical compensatory sheets (1). Were arranged to face each other. The rubbing direction of the alignment film of the VA mode liquid crystal cell and the rubbing direction of the alignment film of the optical compensation sheet were arranged to be antiparallel. Polarizing elements were arranged in crossed Nicols on both sides of these. VA
A voltage was applied to the mode liquid crystal cell with a 55 Hz rectangular wave. The NB mode of black display 2V and white display 6V was used, and the ratio of transmittance (white display / black display) was defined as the contrast ratio. The contrast ratio from the top, bottom, left and right can be measured using an instrument (EZ-Contra
st160D, manufactured by ELDIM). as a result,
A favorable result was obtained in which the front contrast ratio was 300, and the viewing angle (viewing angle at which a contrast ratio of 10 was obtained) was 70 degrees in both the upper, lower, left and right directions.

Example 21 (Support of Optical Compensation Sheet) The cellulose acetate film prepared in Example 11 was used as a support of the optical compensation sheet.

(Formation of Alignment Film) A coating solution having the following composition was applied on a support with a slide coater at 25 ml / m ² . Dry at 60 ° C. for 2 minutes. Next, rubbing treatment was performed on the formed film in a direction parallel to the direction in which the main refractive index was large in the plane of the support. The rubbing conditions were as follows: the rubbing roll diameter was 150 mm, the transport speed was 10 m / min, the lapping angle was 6 °, and the rubbing roll rotation speed was 1200 rpm.

<< Composition of Alignment Film Coating Solution >> １０ 10% by weight aqueous solution of the modified polyvinyl alcohol used in Example 20 24 g Water 73 g Methanol 23 g Glutar 0.2 g of 50% by weight aqueous solution of aldehyde (crosslinking agent)

(Formation of Optically Anisotropic Layer) On the alignment film, the discotic liquid crystal compound 1.8 used in Example 20 was used.
g, ethylene oxide modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.)
0.2 g, cellulose acetate butyrate (CAB5
51-0.2, manufactured by Eastman Chemical Company) 0.04
g, cellulose acetate butyrate (CAB531-
1.0, manufactured by Eastman Chemical Co., Ltd.) 0.01 g, photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy)
A coating solution prepared by dissolving 0.06 g of a sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) in 3.4 g of methyl ethyl ketone was applied using a # 6 wire bar. This was affixed to a metal frame and heated in a thermostat at 140 ° C. for 3 minutes to align the discotic liquid crystalline compound. Next, UV irradiation was performed at 140 ° C. for 1 minute using a 120 W / cm high-pressure mercury lamp to crosslink the discotic liquid crystal compound. Then, it was left to cool to room temperature. Thus, an optical compensation sheet (2) was produced.

(Evaluation of Optical Compensation Sheet) The thickness of the optically anisotropic layer was 2.0 μm. When the retardation value of only the optically anisotropic layer was measured along the rubbing axis, there was no direction in which the retardation was 0. When the retardation value was fitted by simulation, a hybrid orientation state in which the negative uniaxiality continuously changed from 4 ° to 68 ° in the thickness direction could be confirmed. The in-plane retardation of the optically anisotropic layer was 43 nm (Re ¹ = 43), and the retardation in the thickness direction was 135 nm (Rth ¹ = 135). The optical compensatory sheet (2) was cut vertically using a microtome along the rubbing direction to obtain an extremely thin vertical fragment (sample). The samples were left in the OsO ₄ atmosphere for 48 hours to stain. The stained sample was observed with a transmission electron microscope (TEM), and a micrograph was obtained.
In the stained sample, the acryloyl group of the discotic liquid crystalline compound was stained and observed as a photograph image. As a result of examining this photograph, it was confirmed that the discotic structural units of the discotic liquid crystalline compound were inclined from the surface of the support. Furthermore, the tilt angle continuously increased as the distance from the support surface increased.

(Preparation of OCB Mode Liquid Crystal Cell) A polyimide film was provided as an alignment film on a glass substrate with an ITO electrode, and a rubbing treatment was performed. The rubbing treatment was performed so that the two glass substrates face in opposite directions. Two glass substrates faced each other so that the cell gap (d) became 8 μm. In the cell gap, Δn is 0.139
The liquid crystal compound No. 6 (ZLI1132, manufactured by Merck) was injected to prepare an OCB mode liquid crystal cell. The product of Δn and d is 1117 nm, and the in-plane retardation is 92 nm
(Re ⁴ = 92).

(Preparation of OCB Type Liquid Crystal Display Device) In an OCB mode liquid crystal cell, two optical compensatory sheets (2) were sandwiched between the optical compensatory sheets (2), the optically anisotropic layer of the optical compensatory sheet and the glass substrate of the liquid crystal cell. Were arranged to face each other. The rubbing direction of the alignment film of the OCB mode liquid crystal cell and the rubbing direction of the alignment film of the optical compensation sheet were arranged to be antiparallel. Polarizing elements were arranged in crossed Nicols on both sides of these. A voltage was applied to the OCB mode liquid crystal cell with a 55 Hz rectangular wave. The NW mode of 2 V for white display and 6 V for black display was used, and the ratio of transmittance (white display / black display) was defined as the contrast ratio. The contrast ratio from the top, bottom, left and right
CD-5000, manufactured by Otsuka Electronics Co., Ltd.). As a result, favorable results were obtained in which the upper viewing angle (viewing angle at which a contrast ratio of 10 was obtained) was 80 degrees or more, the lower viewing angle was 58 degrees, and both the left and right viewing angles were 66 degrees. .

[Example 22] (Preparation of HAN mode liquid crystal cell) A polyimide film was provided as an alignment film on a glass substrate with an ITO electrode, and rubbing treatment was performed. Another glass substrate with an ITO electrode was prepared, and silicon oxide was deposited to form an alignment film. Two glass substrates faced each other so that the cell gap (d) became 4 μm. In the cell gap, Δn is 0.13
96 liquid crystal compounds (ZLI1132, manufactured by Merck) were injected to prepare HAN mode liquid crystal cells. The product of Δn and d is 558 nm, and the in-plane retardation is 46 nm
(Re ⁴ = 46).

(Preparation of HAN Type Liquid Crystal Display Device) One optical compensation sheet (2) prepared in Example 21 was placed on the display surface side of the HAN mode liquid crystal cell so that the optically anisotropic layer was on the cell side. Placed. The rubbing direction of the alignment film of the HAN mode liquid crystal cell and the rubbing direction of the alignment film of the optical compensation sheet are:
They were arranged to be antiparallel. The polarizing element was arranged on the optical compensation sheet such that the angle between the transmission axis of the polarizing element and the rubbing direction of the liquid crystal cell was 45 °. A diffusion plate was disposed on the polarizing element. A mirror (reflector) was arranged on the opposite side of the HAN mode liquid crystal cell. The light source was placed in a direction inclined by 20 ° from the normal direction of the display surface of the prepared HAN type liquid crystal display device, and irradiated with light. A voltage was applied to the HAN mode liquid crystal cell with a 55 Hz rectangular wave. White display 2
V, black display 6V NW mode, and the transmittance ratio (white display / black display) was taken as the contrast ratio. The contrast ratio from the top, bottom, left and right was measured with a meter (bm-7, manufactured by TOPCON). As a result, favorable results were obtained in which the upper viewing angle (viewing angle at which a contrast ratio of 10 was obtained) was 44 degrees, the lower viewing angle was 26 degrees, and both the left and right viewing angles were 39 degrees.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a general liquid crystal display device.

FIG. 2 is a cross-sectional view schematically showing the orientation of a liquid crystalline compound in a VA mode liquid crystal cell when no voltage is applied.

FIG. 3 is a cross-sectional view schematically showing the orientation of a liquid crystal compound in a VA mode liquid crystal cell when a voltage is applied.

FIG. 4 is a schematic diagram of a refractive index ellipsoid obtained when a VA mode liquid crystal cell in which polarizing elements are arranged in crossed Nicols is viewed from the normal direction of the cell substrate.

FIG. 5 is a schematic diagram showing a refractive index ellipse of a positive uniaxial liquid crystal cell and a refractive index ellipse of a negative uniaxial optical compensation sheet.

FIG. 6 is a schematic cross-sectional view showing a combination of a VA mode liquid crystal cell and two optical compensation sheets.

FIG. 7 is a schematic cross-sectional view showing a combination of a VA mode liquid crystal cell and one optical compensation sheet.

FIG. 8 is a schematic cross-sectional view of an optical compensation sheet used for a VA liquid crystal display device.

FIG. 9 is a schematic cross-sectional view of a typical VA liquid crystal display device.

FIG. 10 is a cross-sectional view schematically showing the orientation of a liquid crystal compound in an OCB mode liquid crystal cell.

FIG. 11 is a cross-sectional view schematically showing the orientation of a liquid crystal compound in a HAN mode liquid crystal cell.

FIG. 12 is a schematic sectional view showing a combination of an OCB mode liquid crystal cell and optically anisotropic layers of two optical compensation sheets.

FIG. 13 is a schematic cross-sectional view showing a combination of a HAN mode liquid crystal cell and an optically anisotropic layer of one optical compensation sheet.

FIG. 14 is a schematic sectional view of a representative OCB type liquid crystal display device.

FIG. 15 is a schematic sectional view of a typical HAN type liquid crystal display device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Surface treatment film 2a, 2b Protective film of polarizing element 3a, 3b Polarizing film 4a, 4b Optical compensation sheet 5a, 5b Resin substrate of liquid crystal cell 6a, 6b Transparent electrode layer 7 Liquid crystal layer 11, 21 Upper substrate of liquid crystal cell 12, Reference Signs List 22 liquid crystal compound 13, 23 lower substrate of liquid crystal cell 14, 24 normal direction of substrate 15, 25, 26 direction tilted from substrate normal 16a, 16b light traveling direction 27 incident light 28 emitted light 31a, 31b incident Transmission axes 32a, 32b of the polarizing elements on the output side Transmission axes 33a of the polarization elements on the emission side 33a Refractive index ellipse of VA mode liquid crystal cell when no voltage is applied 33b Refractive index ellipse of VA mode liquid crystal cell when voltage is applied 34 VA mode Projection of the optical axis of the liquid crystal molecules in the liquid crystal cell on the liquid crystal cell substrate surface 41 Refractive index ellipsoid of the negative uniaxial optical compensation sheet 41x, 41y In the optical compensation sheet In-plane main refractive index 41z Main refractive index in the thickness direction of optical compensation sheet 42 Negative uniaxial optical compensation sheet 43 Positive uniaxial liquid crystal cell 44 Refractive index ellipsoid 44x of positive uniaxial liquid crystal cell 44y Refractive index in a plane parallel to the liquid crystal cell substrate 44z Refractive index in the thickness direction of the liquid crystal cell 50, 60 Liquid crystal cell 51, 61, 73 Optically anisotropic layer 52, 62, 71 Support 53, 54, 63 OC1, OC2, OC Optical compensation sheet 72 Alignment film 73a, 73b, 73c Discotic liquid crystalline molecules Pa, Pb, Pc Disc surfaces 71a, 71b, 71c of discotic liquid crystalline molecules Surfaces parallel to the surface of support θa, θb , Θc Tilt angle 74 Normal line of support 75, R1, R2, R Rubbing direction of alignment film of optical compensation sheet VAC VA mode liquid crystal cell OCBC OCB mode liquid Cell HANC HAN-mode liquid crystal cell A of, B polarizing element BL backlight RP1, RP2, RP transmission axis RB reflector polarization transmission axis PB polarizing element B of polarization of the rubbing direction PA polarizing element A of the alignment layer of the liquid crystal cell

Continued on the front page (72) Inventor Kaji Yabuki 210 Nakanakanuma, Minamiashigara-shi, Kanagawa Prefecture Fuji Photo Film Co., Ltd. F-term (reference) 2H049 BA02 BA06 BA42 BB03 BB49 BC04 BC05 BC22 2H091 FA08X FA08Z FA11X FA11Z FB02 FB12 HA09 HA18 AKAA4F07 AC02 AC06 AC07 AC10 AC12 AC19 AF31 AF35 AH12 BC01 4J002 AB011 AB021 EA046 EA066 EE036 EH126 EH146 EJ066 EL096 EL106 EL136 EP016 ET006 EU046 EU076 EU136 EU176 EU186 EU236 EV306 EV316 FD206 GP00

Claims (8)

[Claims] 1. A retardation increasing agent for cellulose lower fatty acid ester film comprising a compound having at least two aromatic rings and having a molecular structure that does not hinder the conformation of the two aromatic rings. 2. A lower fatty acid ester 100 of cellulose.
0.3 to 20 parts by weight of a compound having at least two aromatic rings and having a molecular structure that does not hinder the conformation of the two aromatic rings with respect to parts by weight, and a wavelength of 550 nm
Optical compensation sheet retardation value in the thickness direction (Rth ⁵⁵⁰⁾ consists of cellulose lower fatty acid ester film is 70 to 400nm in. 3. A lower fatty acid ester of cellulose 100.
0.3 to 20 parts by weight of a compound having at least two aromatic rings and having a molecular structure that does not hinder the conformation of the two aromatic rings with respect to parts by weight, and a wavelength of 550 nm
An optical compensatory sheet comprising an optically anisotropic layer containing discotic liquid crystal molecules provided on a cellulose lower fatty acid ester film having a thickness direction retardation value (Rth ⁵⁵⁰ ) of 70 to 400 nm in the above. 4. The optical compensation sheet according to claim 2, wherein the lower fatty acid ester of cellulose is cellulose acetate. 5. The optical compensatory sheet according to claim 2, wherein the lower fatty acid ester film of cellulose has a thickness of 40 to 120 μm. 6. A liquid crystal cell carrying a liquid crystal between two electrode substrates, two polarizing elements arranged on both sides thereof, and at least one sheet between the liquid crystal cell and the polarizing element. A liquid crystal display device provided with an optical compensation sheet, wherein the optical compensation sheet has at least two aromatic rings with respect to 100 parts by weight of a lower fatty acid ester of cellulose, and has a three-dimensional conformation of two aromatic rings. wherein 0.3 to 20 parts by weight of a compound having a molecular structure that does not fault, the thickness direction retardation at a wavelength of 550 nm (Rth ⁵⁵⁰⁾ 7
A liquid crystal display device comprising a cellulose lower fatty acid ester film having a thickness of 0 to 400 nm. 7. The liquid crystal display device according to claim 6, wherein an optically anisotropic layer containing discotic liquid crystal molecules is provided on the liquid crystal cell side of the lower fatty acid ester film of cellulose. 8. The liquid crystal display device according to claim 6, wherein the liquid crystal cell is a VA mode, OCB mode, or HAN mode liquid crystal cell.