JP2011058002A - Cellulose-lower fatty acid ester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To raise the Rth, retardation value of a cellulose-lower fatty acid ester film. <P>SOLUTION: A compound having at least two aromatic rings and a molecular structure which does not stereochemically hinder steric conformation of the two aromatic rings is used as a retardation-raising agent for the cellulose-lower fatty acid ester film. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a retardation increasing agent for a lower fatty acid ester film of cellulose, an optical compensation sheet using the same, and a liquid crystal display device.

Lower fatty acid ester films of cellulose, especially cellulose acetate films, are used in various photographic materials and optical materials because of their toughness and flame retardancy. The cellulose ester film is a typical support for photographic light-sensitive materials. Cellulose ester films are also used in liquid crystal display devices. The cellulose ester film is characterized by high optical isotropy (low retardation value) compared to other polymer films. Therefore, it is common to use a cellulose ester film for a protective film or a color filter of a liquid crystal display device that requires optical isotropy, for example, a polarizing element.
On the contrary, an optical compensation sheet (phase difference film) which is an element of another liquid crystal display device is required to have 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 the optical compensation sheet made of a synthetic polymer film, an optical compensation sheet in which an optically anisotropic layer containing a discotic liquid crystalline molecule is provided on a transparent support has also been proposed (see, for example, Patent Documents 1 to 4). ). 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 the transparent support is required to have high optical isotropy (low retardation value), a cellulose ester film is usually used.

Conventional optical compensation sheets using discotic liquid crystalline molecules are mainly designed to optically compensate TN (Twisted Nematic) mode liquid crystal cells for TFTs. Even if such an optical compensation sheet is used for a liquid crystal cell in a VA (Vertically Aligned) mode, an OCB (Optically Compensatory Bend) mode, or a HAN (Hybrid Aligned Nematic) mode, there arises a problem that the optical compensation sheet cannot be handled (cannot be optically compensated).
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 crystalline molecules, the VA mode, OCB mode or HAN mode is used. It can be considered 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 functions as a support (physical properties and affinity with a coating layer). Therefore, a laminate in which a cellulose ester film having excellent function as a support (however, a low retardation value) and a synthetic polymer film having a high retardation value are bonded together is used as an optically anisotropic support. It is considered desirable.
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) When a retardation value is required, it is a general principle to use a cellulose ester film.

JP-A-3-9325 Japanese Patent Laid-Open No. 6-148429 JP-A-8-50206 JP-A-9-26572

The present inventor overturned the conventional general principle and examined the use of a cellulose ester film for applications requiring optical anisotropy (high retardation value). The cellulose ester film has an excellent function as a support as compared with a synthetic polymer film. If a cellulose ester film having a high optical anisotropy (having a high retardation value) is obtained, the cellulose ester film can be used also in the application of an optical compensation sheet requiring optical anisotropy.
However, in the prior art, a cellulose ester film having a low retardation value is 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 raising the retardation value has hardly been studied.
Therefore, the present inventor has studied and investigated a compound (retardation increasing agent) having a function of increasing the retardation of cellulose lower fatty acid ester film.
An object of the present invention is to provide a retardation increasing agent for a lower fatty acid ester film of cellulose.
Another object of the present invention is to provide an optical compensation sheet using a cellulose lower fatty acid ester film having a high retardation value.
Furthermore, an 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.

The object of the present invention is achieved by the following (1) cellulose retardation increasing agent for lower fatty acid ester films, the following (2) to (5) optical compensation sheets, and the following (6) to (8) liquid crystal display devices. It was done.
(1) A retardation increasing agent for a lower fatty acid ester film of cellulose, which comprises a compound having a molecular structure that has at least two aromatic rings and does not sterically hinder the conformation of the two aromatic rings.

(2) 0.3 to 20 weight percent of a compound having a molecular structure that has at least two aromatic rings and does not sterically hinder the conformation of the two aromatic rings with respect to 100 weight parts of the lower fatty acid ester of cellulose. An optical compensation sheet comprising a lower fatty acid ester film of cellulose having a retardation value (Rth ⁵⁵⁰ ) in the thickness direction at a wavelength of 550 nm of 70 to 400 nm.
(3) 0.3 to 20 weight percent of a compound having a molecular structure that has at least two aromatic rings and does not sterically hinder the conformation of the two aromatic rings with respect to 100 weight parts of the lower fatty acid ester of cellulose. An optically anisotropic layer containing a discotic liquid crystalline molecule on a lower fatty acid ester film of cellulose having a retardation value (Rth ⁵⁵⁰ ) in the thickness direction at a wavelength of 550 nm of 70 to 400 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 optical compensation sheet according to (2) or (3), wherein the lower fatty acid ester film of cellulose has a thickness of 40 to 120 μm.

(6) A liquid crystal cell having a liquid crystal supported between two electrode substrates, two polarizing elements disposed on both sides thereof, and at least one optical compensation between the liquid crystal cell and the polarizing element A liquid crystal display device comprising a sheet, 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 does not sterically hinder the conformation of the two aromatic rings. A liquid crystal display device comprising a lower fatty acid ester film of cellulose containing 0.3 to 20 parts by weight of a compound having a molecular structure and having a retardation value (Rth ⁵⁵⁰ ) in the thickness direction at a wavelength of 550 nm of 70 to 400 nm .
(7) The liquid crystal display device according to (6), wherein an optically anisotropic layer containing a discotic liquid crystalline molecule 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 (6), wherein the liquid crystal cell is a VA mode, OCB mode or HAN mode liquid crystal cell.

According to the research of the present inventors, a compound having a molecular structure having at least two aromatic rings and not sterically hindering the conformation of the two aromatic rings is capable of increasing the retardation of the lower fatty acid ester film of cellulose. It was found to have Examples of ultraviolet absorbers and plasticizers for the lower fatty acid ester film of cellulose include the aromatic compounds as described above. However, these compounds are used in amounts that satisfy the functions of UV absorbers and plasticizers (in a range that does not significantly increase the retardation of the film) and are used to increase 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 for an optical compensation sheet in a liquid crystal display device. Further, in an optical compensation sheet in which an optically anisotropic layer containing discotic liquid crystalline molecules is provided on a support, a cellulose ester film having a high retardation value can be used as the support.
An optical compensation sheet comprising a cellulose ester film having a high retardation value as a support and an optically anisotropic layer containing a discotic liquid crystalline molecule provided thereon is a VA (Vertically Aligned) type, OCB (Optically Compensatory Bend). ) Type or HAN (Hybrid Aligned Nematic) type liquid crystal display devices.

It is a cross-sectional schematic diagram of a general liquid crystal display device. It is sectional drawing which shows typically the orientation of the liquid crystalline compound in the liquid crystal cell of VA mode at the time of no voltage application. It is sectional drawing which shows typically the orientation of the liquid crystalline compound in the liquid crystal cell of VA mode at the time of voltage application. It is a schematic diagram of a refractive index ellipsoid obtained by viewing a VA mode liquid crystal cell in which polarizing elements are arranged in crossed Nicols from the normal direction of the cell substrate. It 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. It is a cross-sectional schematic diagram which shows the combination of the liquid crystal cell of VA mode, and two optical compensation sheets. It is a cross-sectional schematic diagram which shows the combination of the liquid crystal cell of VA mode, and one optical compensation sheet. It is a cross-sectional schematic diagram of the optical compensation sheet used for a VA type liquid crystal display device. It is a cross-sectional schematic diagram of a typical VA type liquid crystal display device. It is sectional drawing which shows typically the orientation of the liquid crystalline compound in the liquid crystal cell of OCB mode. It is sectional drawing which shows typically the orientation of the liquid crystalline compound in the liquid crystal cell of HAN mode. It is a cross-sectional schematic diagram which shows the combination of the liquid crystal cell of OCB mode and the optically anisotropic layer of two optical compensation sheets. It is a cross-sectional schematic diagram which shows the combination of the liquid crystal cell of HAN mode and the optically anisotropic layer of one optical compensation sheet. It is a cross-sectional schematic diagram of a typical OCB type liquid crystal display device. It is a cross-sectional schematic diagram of a typical HAN type liquid crystal display device.

[Retardation raising agent]
In the present invention, a compound having a molecular structure having at least two aromatic rings and not sterically hindering the conformation of the two aromatic rings is used as a retardation increasing agent for a lower fatty acid ester film of cellulose.
In this specification, “a retardation increasing agent for lower fatty acid ester film of cellulose” means a letter of lower fatty acid ester film of cellulose when used in an amount that does not cause a problem due to a large amount of addition such as bleed out. This means a compound having a function of increasing the retardation (specifically, the retardation value in the thickness direction at a wavelength of 550 nm = Rth ⁵⁵⁰ ) to 2 times or more (usually 2 to 10 times) that in the case of no addition. . The amount in a range where the retardation sufficiently increases and does not cause a problem due to addition of a large amount is generally 0.3 to 20 parts by weight with respect to 100 parts by weight of the lower fatty acid ester of cellulose. The retardation value in the thickness direction of a lower fatty acid ester film of cellulose obtained by using a retardation increasing agent at a wavelength of 550 nm is generally 70 to 400 nm.

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

The number of aromatic rings contained in the retardation increasing agent is preferably 2 to 20, more preferably 2 to 12, still more preferably 2 to 8, and most preferably 2 to 6. preferable. In the case of having three or more aromatic rings, the conformation of at least two aromatic rings should not be sterically hindered.
The bonding relationship between two aromatic rings can be classified into (a) when a condensed ring is formed, (b) when directly linked by a single bond, and (c) when linked via a linking group (for aromatic rings). , Spiro bonds cannot be formed). From the viewpoint of the retardation increasing function, any of (a) to (c) may be used. However, in the case of (b) or (c), it is necessary not to sterically hinder the conformation of the two aromatic rings.

Examples of the condensed ring (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, a naphthacene ring, Pyrene ring, indole ring, isoindole ring, benzofuran ring, benzothiophene ring, indolizine ring, benzoxazole ring, benzothiazole ring, benzimidazole ring, benzotriazole ring, purine ring, indazole ring, chromene ring, quinoline ring, isoquinoline Ring, quinolidine ring, quinazoline ring, cinnoline ring, quinoxaline ring, phthalazine ring, pteridine ring, carbazole ring, acridine ring, phenanthridine ring, xanthene ring, phenazine ring, phenothiazine ring, phenoxathiin ring, phenoxazine ring and thiant It includes emissions ring. Naphthalene ring, azulene ring, indole ring, benzoxazole ring, benzothiazole ring, benzimidazole ring, benzotriazole ring and quinoline ring are preferred.
The single bond (b) is preferably a bond between carbon atoms of two aromatic rings. Two aromatic rings may be bonded with two or more single bonds to form an aliphatic ring or a non-aromatic heterocyclic ring between the two aromatic rings.

The linking group in (c) is also preferably bonded to carbon atoms of two aromatic rings. The linking group is preferably an alkylene group, an alkenylene group, an alkynylene group, —CO—, —O—, —NH—, —S—, or a combination thereof. Examples of linking groups composed of combinations are shown below. In addition, the relationship between the left and right in the following examples of 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, the substituent is required not to sterically hinder the conformation of the two aromatic rings. In steric hindrance, the type and position of substituents are problematic. As the type of the substituent, a sterically bulky substituent (for example, a tertiary alkyl group) tends 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 halogen atom (F, Cl, Br, I), hydroxyl, carboxyl, cyano, amino, nitro, sulfo, carbamoyl, sulfamoyl, ureido, alkyl group, alkenyl group, alkynyl group, aliphatic acyl group , Aliphatic acyloxy group, alkoxy group, alkoxycarbonyl group, alkoxycarbonylamino group, alkylthio group, alkylsulfonyl group, aliphatic amide group, aliphatic sulfonamido group, aliphatic substituted amino group, aliphatic substituted carbamoyl group, aliphatic Substituted sulfamoyl groups, aliphatic substituted ureido groups and non-aromatic heterocyclic groups are included.

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

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

The alkylthio group preferably has 1 to 12 carbon atoms. Examples of the alkylthio group include methylthio, ethylthio and octylthio.
The alkylsulfonyl group preferably has 1 to 8 carbon atoms. Examples of the alkylsulfonyl group include methanesulfonyl and ethanesulfonyl.
The aliphatic amide group preferably has 1 to 10 carbon atoms. Examples of the aliphatic amide group include acetamide.
The aliphatic sulfonamide group preferably has 1 to 8 carbon atoms. Examples of the aliphatic sulfonamido group include methanesulfonamido, butanesulfonamido and n-octanesulfonamido.
The number of carbon atoms of the aliphatic substituted amino group is preferably 1 to 10. Examples of the aliphatic substituted amino group include dimethylamino, diethylamino and 2-carboxyethylamino.
The aliphatic substituted carbamoyl group preferably has 2 to 10 carbon atoms. Examples of the aliphatic substituted carbamoyl group include methylcarbamoyl and diethylcarbamoyl.
The aliphatic substituted sulfamoyl group preferably has 1 to 8 carbon atoms. Examples of the aliphatic substituted sulfamoyl group include methylsulfamoyl and diethylsulfamoyl.
The number of carbon atoms in the aliphatic substituted ureido group is preferably 2 to 10. Examples of the aliphatic substituted ureido group include methylureido.
Examples of non-aromatic heterocyclic groups include piperidino and morpholino.

The molecular weight of the retardation increasing agent is preferably 300 to 800. 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 / DTA100, manufactured by Seiko Electronics Industry Co., Ltd.).
Specific examples of the retardation increasing agent are shown below. In each specific example, the aromaticity of the aromatic ring is indicated by a circle.

[Lower fatty acid ester of cellulose]
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 the physical properties of the film, the average degree of acetylation is more preferably 58.0% or more and less than 62.5%. However, when a cellulose acetate having an average acetylation degree of 55.0% or more and less than 58.0% (preferably 57.0% or more and less than 58.0%) is used, a film having a very high retardation value is produced. be able to.
The degree of acetylation means the amount of bound acetic acid per unit weight of cellulose. The degree of acetylation follows the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like).
The viscosity average polymerization degree (DP) of the cellulose ester is preferably 250 or more, and more preferably 290 or more.
The cellulose ester used in the present invention preferably has a narrow molecular weight distribution of Mw / Mn (Mw is a weight average molecular weight, Mn is a number average molecular weight) by gel permeation chromatography. The specific value of Mw / Mn is preferably 1.0 to 1.7, more preferably 1.3 to 1.65, and most preferably 1.4 to 1.6. preferable.

[Film retardation value]
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 perpendicular to the film film surface, the measurement result of the in-plane retardation with respect to the slow axis, and the incident direction is inclined with respect to the vertical direction with respect to the film film surface. Obtained by extrapolation from the measured results. The measurement can be performed using an ellipsometer (for example, M-150: manufactured by JASCO Corporation).
The retardation value (Rth) in the thickness direction and the in-plane retardation value (Re) are calculated according to the following formulas (1) and (2), respectively.
Formula (1)
Retardation value in the thickness direction (Rth) = {(nx + ny) / 2−nz} × d
Formula (2)
In-plane retardation value (Re) = (nx−ny) × d
Where nx is the refractive index in the x direction in the film plane, ny is the refractive index in the y direction in the film plane, nz is the refractive index in the direction perpendicular to the film plane, and d is the film's refractive index. Thickness (nm).
In the present invention, the retardation value (Rth ⁵⁵⁰ ) in the thickness direction at a wavelength of 550 nm of the film is adjusted to 70 to 400 nm. The retardation value in the thickness direction is preferably 100 to 400 nm, more preferably 150 to 400 nm, still more preferably 200 to 400 nm, still more preferably 200 to 300 nm, and even more preferably 200 to 400 nm. Most preferably, it is 250 nm.

The absolute value of the slope (a) of the Rth distribution with the retardation value (Rth ⁵⁵⁰ ) in the thickness direction at a wavelength of 550 nm as the reference value (= 1) is preferably less than 0.0012. The slope (a) of the Rth distribution is the retardation value in the thickness direction (Rth ⁴⁰⁰ ) at a wavelength of ⁴⁰⁰ nm, 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). ) Is calculated according to the following formula (3).
Formula (3)
Rth distribution slope (a) = | Rth ⁷⁰⁰ −Rth ⁴⁰⁰ | / 300Rth ⁵⁵⁰
Therefore, Rth ⁴⁰⁰ , Rth ⁵⁵⁰ and Rth ⁷⁰⁰ preferably satisfy the following formula (11).
Formula (11)
| Rth ⁷⁰⁰ −Rth ⁴⁰⁰ | / 300Rth ⁵⁵⁰ <0.0012
Rth ⁴⁰⁰ , Rth ⁵⁵⁰ and Rth ⁷⁰⁰ more preferably satisfy the following formula (13).
Formula (13)
−0.0012 <(Rth ⁷⁰⁰ −Rth ⁴⁰⁰ ) / 300Rth ⁵⁵⁰ <0.0006

Furthermore, the absolute value of the slope (b) of the Re distribution with the in-plane retardation value (Re ⁵⁵⁰ ) at a wavelength of 550 nm as the reference value (= 1) is preferably less than 0.002. The slope (b) of the Re distribution has three values: an in-plane retardation value at a wavelength of 400 nm (Re ⁴⁰⁰ ), an in-plane retardation value at a wavelength of 550 nm (Re ⁵⁵⁰ ), and an in-plane retardation value at a wavelength of 700 nm (Re ⁷⁰⁰ ). It calculates from the measurement data of a point according to following formula (4).
Formula (4)
Re distribution slope (b) = | Re ⁷⁰⁰ −Re ⁴⁰⁰ | / 300Re ⁵⁵⁰
Therefore, Re ⁴⁰⁰ , Re ⁵⁵⁰ and Re ⁷⁰⁰ preferably satisfy the following formula (12).
Formula (12)
| Re ⁷⁰⁰ −Re ⁴⁰⁰ | / 300Re ⁵⁵⁰ <0.002
Re ⁴⁰⁰ , Re ⁵⁵⁰ and Re ⁷⁰⁰ more preferably satisfy the following formula (14).
Formula (14)
−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 cast method. In the solvent cast method, a film is produced using a solution (dope) in which cellulose ester is dissolved in an organic solvent.
The organic solvent is a solvent selected from ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and halogenated hydrocarbons having 1 to 6 carbon atoms. It is preferable to contain.
The ether, ketone and ester may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, —O—, —CO— and —COO—) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group.

Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole.
Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone.
Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate.
Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol.
The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogen atoms in the halogenated hydrocarbon substituted with halogen is preferably 25 to 75 mol%, more preferably 30 to 70 mol%, and 35 to 65 mol%.
More preferably, it is 40 to 60 mol%. Methylene chloride is a typical halogenated hydrocarbon.

Two or more organic solvents may be mixed and used.
Particularly preferred organic solvents are mixed solvents of three different types of 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 halogenated hydrocarbon having 1 to 6 carbon atoms is selected, the second solvent is selected from linear monohydric alcohol having 1 to 5 carbon atoms, and the third solvent has a boiling point of 30 to 170. It is selected from alcohols having a temperature of C and hydrocarbons having a boiling point of 30 to 170C.
The ether, ketone, ester and halogenated hydrocarbon as 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 end of the hydrocarbon straight chain (primary alcohol) or may be bonded to the middle (secondary alcohol). Specifically, the second solvent 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 alcohol having a boiling point of 30 to 170 ° C. and hydrocarbon having a boiling point of 30 to 170 ° C.
The alcohol is preferably monovalent. The hydrocarbon portion of the alcohol may be linear, branched or cyclic. The hydrocarbon moiety is preferably a saturated aliphatic hydrocarbon. The hydroxyl group of the alcohol may be any of primary to tertiary.
Examples of alcohols include methanol (boiling point: 64.65 ° C.), ethanol (78.325 ° C.), 1-propanol (97.15 ° C.), 2-propanol (82.4 ° C.), 1-butanol (117. 9 ° C), 2-butanol (99.5 ° C), t-butanol (82.45 ° C), 1-pentanol (137.5 ° C), 2-methyl-2-butanol (101.9 ° C) and cyclo Hexanol (161 ° C.) is included.

As for the alcohol, it overlaps with the definition of the second solvent, but any alcohol different 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 included in the definition of the second solvent (methanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol) , 2-pentanol or 3-pentanol) may be used as the third solvent.
The hydrocarbon may be linear, branched or cyclic. Either aromatic hydrocarbons or aliphatic hydrocarbons can be used. The aliphatic hydrocarbon may be saturated or unsaturated.
Examples of hydrocarbons include cyclohexane (boiling point: 80.7 ° C), hexane (69 ° C), benzene (80.1 ° C), toluene (110.6 ° C) and xylene (138.4-144.4 ° C). Is included.

The three kinds of mixed solvents preferably contain 50 to 95% by weight of the first solvent, more preferably 60 to 92% by weight, still more preferably 65 to 90% by weight, and 70 to 88%. Most preferably, it is contained by weight. The second solvent is preferably contained in an amount of 1 to 30% by weight, more preferably 2 to 27% by weight, further 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, further preferably 3 to 24% by weight, and more preferably 4 to 22% by weight. Most preferred.
Furthermore, another organic solvent may be used in combination to form a mixed solvent of four or more types. In the case of using four or more kinds of mixed solvents, the fourth and subsequent solvents are also 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-dioxolane, tetrahydrofuran, anisole, Phenetol) or nitromethane may be used in combination.

[Preparation of solution (general method)]
In the present invention, the 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 (room temperature or high temperature). The solution can be prepared using a dope preparation method and apparatus in a normal solvent cast method. In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly methylene chloride) as the organic solvent.
The amount of the cellulose ester is adjusted so as to be contained in the obtained solution by 10 to 40% by weight. The amount of cellulose ester is more preferably 10 to 30% by weight. Arbitrary additives described later may be added to the organic solvent (main solvent).
The solution can be prepared by stirring the cellulose ester and the organic solvent at room temperature (0 to 40 ° C.). High concentration solutions may be stirred under pressure and heating conditions. Specifically, the cellulose ester and the organic solvent are placed in a pressure vessel and sealed, and stirred while heating to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 40 ° C. or higher, preferably 60 to 200 ° C., more preferably 80 to 110 ° C.

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

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

The mixture is then cooled to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to -20 ° C, most preferably -50 to -30 ° C). The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). When cooled in this manner, the mixture of cellulose ester and organic solvent solidifies.
The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The faster the cooling rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at the start of cooling and the final cooling temperature by the time from the start of cooling until the final cooling temperature is reached.

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

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

[Production of film]
From the prepared cellulose ester solution (dope), a cellulose ester film is produced by a solvent cast method.
The dope is cast on a drum or band, and the solvent is evaporated to form a film. It is preferable to adjust the concentration of the dope before casting so that the solid content is 18 to 35%. The surface of the drum or band is preferably finished in a mirror state. As for casting and drying methods in the solvent casting method, U.S. Pat. No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-1115035.
The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less.
After casting, it is preferable to dry it by applying air for 2 seconds or more. The obtained film can be peeled off from the drum or band, and further dried by high-temperature air whose temperature is successively changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the drum or band during casting. 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 additives]
A plasticizer can be added to the cellulose ester film in order to improve mechanical properties or increase the drying rate. As the plasticizer, phosphoric acid ester or carboxylic acid ester is used. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCP). Representative examples of the carboxylic acid ester include phthalic acid esters and citric acid esters. Examples of phthalic acid esters include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethylhexyl phthalate (DEHP). Examples of citrate esters include triethyl O-acetylcitrate (OACTE) and tributyl O-acetylcitrate (OACTB). Examples of other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic acid esters. Phthalate plasticizers (DMP, DEP, DBP, DOP, DPP, DEHP) are preferably used. DEP and DPP are particularly preferred.
The addition amount of the plasticizer is preferably 0.1 to 25% by weight, more preferably 1 to 20% by weight, and most preferably 3 to 15% by weight of the amount of the cellulose ester.

Degradation inhibitors (eg, antioxidants, peroxide decomposers, radical inhibitors, metal deactivators, acid scavengers, amines) and UV inhibitors may be added to the cellulose ester film. The deterioration preventing agents are described in JP-A-3-199201, JP-A-51907073, JP-A-5-194789, JP-A-5-271471, and JP-A-6-107854. The addition amount of the deterioration preventing agent is preferably 0.01 to 1% by weight of the solution (dope) to be prepared, and more preferably 0.01 to 0.2% by weight. When the addition amount is less than 0.01% by weight, the effect of the deterioration preventing agent is hardly recognized. When the added amount exceeds 1% by weight, bleed-out (bleeding) of the deterioration preventing agent to the film surface may be observed. As a particularly preferred example of the deterioration preventing agent, butylated hydroxytoluene (BHT) can be mentioned. The ultraviolet ray preventing agent is described in JP-A-7-11056.
The cellulose acetate having an average degree of acetylation of 55.0 to 58.0% is more stable than the cellulose triacetate having an average degree of acetylation of 58.0% or more, and the produced film. There is a disadvantage that the physical properties are inferior. However, this drawback can be substantially eliminated by using the above-described deterioration preventing agent, particularly an antioxidant such as butylated hydroxytoluene (BHT).

[Configuration of general liquid crystal display device]
The cellulose ester film can be used in various applications. The cellulose ester film of the present invention is particularly effective when used as an optical compensation sheet for liquid crystal display devices. Since the cellulose ester film of the present invention is characterized by a high retardation value in the thickness direction, the film itself can be used as an optical compensation sheet.
The liquid crystal display device includes a liquid crystal cell having a liquid crystal supported 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. An optical compensation sheet is arranged.
A configuration of a general liquid crystal display device will be described with reference to FIG.

FIG. 1 is a schematic cross-sectional view of a general liquid crystal display device.
The liquid crystal layer (7) is provided between the resin substrates (5a, 5b). Transparent electrode layers (6a, 6b) are provided on the liquid crystal side of the resin substrates (5a, 5b). The above liquid crystal layer, resin substrate and transparent electrodes (5 to 7) constitute a liquid crystal cell.
Optical compensation sheets (4a, 4b) are bonded to the top and bottom of the liquid crystal cell. The cellulose ester film of the present invention can be used as this optical compensation sheet (4a, 4b). The optical compensation sheet (4a, 4b) also has a function of protecting the side of the polarizing film (3a, 3b) where the protective film (2a, 2b) is not provided.
Polarizing elements (2a, 2b, 3a, 3b) are provided above and below the optical compensation sheets (4a, 4b). 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 the polarizing element on one side. The surface treated film (1) is provided on the side viewed by a person 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 sealing liquid crystal in a space formed by sandwiching a spacer between two substrates. The transparent electrode layer is formed on the 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 adhesion of the transparent electrode layer). These layers are usually provided on the 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 the color of the liquid crystal screen. The cellulose ester film itself of the present invention 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 and a film exhibiting a birefringence opposite to that (a positive / negative relationship) may be used as an optical compensation sheet. The range of the thickness of the optical compensation sheet is the same as the preferable thickness of the above-described film of the present invention.

Examples of the polarizing film of the polarizing element include an iodine polarizing film, a dye polarizing film using a dichroic dye, and a polyene polarizing film. Any polarizing film is generally produced using a polyvinyl alcohol film.
The protective film of the polarizing plate preferably has a thickness of 25 to 350 μm, more preferably 50 to 200 μm.
A surface treatment film may be provided as in the liquid crystal display device shown in FIG. The functions of the surface treatment film include hard coat, anti-fogging treatment, anti-glare treatment and antireflection treatment.

  As described above, there has also been proposed an optical compensation sheet in which an optically anisotropic layer containing a liquid crystal (particularly a discotic liquid crystalline molecule) is provided on a support (Japanese Patent Application Laid-Open Nos. 3-9325 and 6-148429). Nos. 8-50206 and 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 crystalline molecules having negative uniaxiality and tilting orientation. The angle formed by the disc surface of the discotic liquid crystal molecule and the support surface is preferably changed (hybrid alignment) in the depth direction of the optically anisotropic layer. The optical axis of the discotic liquid crystalline molecule exists in the normal direction of the disk surface. The discotic liquid crystalline molecule has birefringence in which the refractive index in the disc surface direction is larger than the refractive index in the optical axis direction.
The optically anisotropic layer is preferably formed by aligning the discotic liquid crystalline molecules with an alignment film described later and fixing the discotic liquid crystalline molecules in the aligned state. The discotic liquid crystalline molecules are preferably fixed by a polymerization reaction.
In the optically anisotropic layer, there is no direction in which the retardation value becomes 0. In other words, the minimum retardation value of the optically anisotropic layer is a value exceeding 0.

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

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

  In the formula (I), the divalent linking group (L) is selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, —CO—, —NH—, —O—, —S—, and combinations thereof. A divalent linking group is preferred. The divalent linking group (L) is a combination of at least two divalent groups selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, —CO—, —NH—, —O—, and —S—. More preferably, it is a group. 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 number of carbon atoms in the arylene group is preferably 6 to 10. The alkylene group, alkenylene group and arylene group may have a substituent (eg, alkyl group, halogen atom, cyano, alkoxy group, 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 bonded to the polymerizable group (P). 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-O-CO-
L19: -O-CO-AR-O-AL-O-AL-O-AL-O-CO-
L20: -S-AL-
L21: -S-AL-O-
L22: -S-AL-O-CO-
L23: -S-AL-S-AL-
L24: -S-AR-AL-

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

The polymerizable group (P) is preferably an unsaturated polymerizable group (P1, P2, P3, P7, P8, P14, P15, P16) or an epoxy group (P6), and is an unsaturated polymerizable group. Is more preferable, and an ethylenically unsaturated polymerizable group (P1, P7, P8, P14, P15, P16) is most preferable.
In the formula (I), n is an integer of 4 to 12. A specific number is determined according to the type of discotic core (D). In addition, although the combination of several L and P may differ, it is preferable that it is the same.
Two or more kinds of discotic liquid crystalline molecules (for example, a molecule having an asymmetric carbon atom in a divalent linking group and a molecule not having it) may be used in combination.

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

The coating liquid can be applied by a known method (eg, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method).
The aligned discotic liquid crystalline molecules are fixed while maintaining the alignment 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. A photopolymerization reaction is preferred.
Examples of the photopolymerization initiator include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ether (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatic acyloin. Compound (described in US Pat. No. 2,722,512), polynuclear quinone compound (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (US Pat. No. 3,549,367) Acridine and phenazine compounds (JP-A-60-105667, U.S. Pat. No. 4,239,850) and oxadiazole compounds (U.S. Pat. No. 4,212,970).

The amount of the photopolymerization initiator used is preferably 0.01 to 20% by weight, more preferably 0.5 to 5% by weight, based on the solid content of the coating solution.
Light irradiation for polymerization of discotic liquid crystalline molecules is preferably performed using ultraviolet rays.
The irradiation energy is preferably 20 mJ / cm ^{2 to} 50 J / cm ² , and more preferably 100 to 800 mJ / cm ² . In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions.
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 crystalline molecules of the optically anisotropic layer.
The alignment film is an organic compound (eg, ω-tricosanoic acid) formed by rubbing treatment of an organic compound (preferably polymer), oblique deposition of an inorganic compound, formation of a layer having a microgroove, or Langmuir-Blodgett method (LB film). , Dioctadecylmethylammonium chloride, methyl stearylate). Furthermore, an alignment film in which an alignment function is generated by application of an electric field, application of a magnetic field or light irradiation is also known.
The alignment film is preferably formed by polymer rubbing treatment. Polyvinyl alcohol is a preferred polymer. Particularly preferred is a modified polyvinyl alcohol to which a hydrophobic group is bonded. Since the hydrophobic group has an affinity for the discotic liquid crystalline molecules of the optically anisotropic layer, the discotic liquid crystalline molecules can be uniformly aligned by introducing the hydrophobic group into polyvinyl alcohol. The hydrophobic group is bonded to the main chain terminal or side chain of polyvinyl alcohol.
The hydrophobic group is preferably an aliphatic group having 6 or more carbon atoms (preferably an alkyl group or an alkenyl group) or an aromatic group.

When a hydrophobic group is bonded to the main chain terminal of polyvinyl alcohol, it is preferable to introduce a linking group between the hydrophobic group and the main chain terminal. Examples of the linking group include —S—, —C (CN) R ¹ —, —NR ² —, —CS—, and combinations thereof. R ¹ and R ² are each a hydrogen atom or an alkyl group having 1 to 6 carbon atoms (preferably an alkyl group having 1 to 6 carbon atoms).
When a hydrophobic group is introduced into the side chain of polyvinyl alcohol, a part of the acetyl group (—CO—CH ₃ ) of the vinyl acetate unit of polyvinyl alcohol is substituted with an acyl group (—CO—R) having 7 or more carbon atoms. ³ ). R ³ is an aliphatic group or aromatic group having 6 or more carbon atoms.
Commercially available modified polyvinyl alcohol (eg, MP103, MP203, R1130, manufactured by Kuraray Co., Ltd.) may be used.
The saponification degree of the (modified) polyvinyl alcohol used for the alignment film is preferably 80% or more. The degree of polymerization of (modified) polyvinyl alcohol is preferably 200 or more.
The rubbing process is performed by rubbing the surface of the alignment film several times in a certain direction with paper or cloth. It is preferable to use a cloth in which fibers having uniform length and thickness are uniformly planted.
In addition, after aligning the discotic liquid crystalline molecules using the alignment film, the optically anisotropic layer is formed by fixing the discotic liquid crystalline molecules in the aligned state, and only the optically anisotropic layer is formed. It may be transferred onto a support. The discotic liquid crystalline molecules fixed in the alignment state can maintain the alignment state even without the 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]
The cellulose ester film of the present invention is particularly advantageously used as a support for an optical compensation sheet of a VA liquid crystal display device having a VA mode liquid crystal cell.
A VA liquid crystal display device will be described with reference to FIGS.
FIG. 2 is a cross-sectional view schematically showing the orientation of the liquid crystal compound in the VA mode liquid crystal cell when no voltage is applied.
As shown in FIG. 2, the 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). The liquid crystalline compound (12) used in the 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 crystal compound (12) are vertically aligned as shown in FIG. When a pair of polarizing elements (not shown) are arranged in crossed Nicols on both sides of the upper and lower substrates (11, 13), no retardation occurs in the normal direction (14) of the substrate surface. As a result, light cannot be transmitted in the normal direction (14) of the substrate surface, resulting in black display.
If the line of sight is shifted in the direction (15) inclined from the normal direction (14) of the substrate, retardation is generated and light is transmitted, resulting in a decrease in contrast. This oblique retardation can be compensated by the optical anisotropy of the optical compensation sheet. Details will be described later (explained with reference to FIG. 5).
In FIG. 2, all of the liquid crystalline compound (12) is perfectly aligned in the vertical direction, but in actuality, it is slightly inclined (pretilt) in a certain direction. This is because all the liquid crystalline compounds are tilted in a certain direction (pretilt direction) when a voltage is applied (described in FIG. 3 below).

FIG. 3 is a cross-sectional view schematically showing the orientation of the liquid crystal compound in the VA mode liquid crystal cell when a voltage is applied.
Each of the upper substrate (21) and the lower substrate (23) has an electrode layer (not shown), and a voltage can be applied to the liquid crystalline 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 the horizontal alignment state, but the liquid crystal molecules in the vicinity of the alignment film are not in the horizontal alignment state and are tilted in the pretilt direction. When the line of sight is shifted from the normal direction (24) of the substrate surface to the inclined direction (25), the change in retardation angle is small, whereas when the line of sight is moved in another direction (26), the change in angle of retardation. Is big. Therefore, if the pretilt direction of the liquid crystal compound (the same direction as 26) is the downward direction of the image, the horizontal viewing angle is symmetric and wide, the downward viewing angle is wide, but the upward viewing angle is narrow. Viewing angle characteristics. In order to improve this viewing angle characteristic, it is necessary to compensate for retardation caused by tilted liquid crystal molecules that are not horizontally aligned when a voltage is applied.
The optical compensation sheet has a function of compensating for the retardation and improving visual characteristics (removing asymmetry in the visual direction of the transmittance when a voltage is applied).

FIG. 4 is a schematic diagram of a refractive index ellipse obtained by viewing a VA mode liquid crystal cell in which polarizing elements are arranged in crossed Nicols from the normal direction of the cell substrate. 4A shows a refractive index ellipse when no voltage is applied, and FIG. 4B shows a refractive index ellipse when a voltage is applied.
In the crossed Nicol arrangement, the transmission axes (31a, 31b) of the polarization element on the incident side and the transmission axes (32a, 32b) of the polarization element on the output side are arranged vertically.
When no voltage is applied, the liquid crystal molecules in the cell are aligned perpendicular to the cell substrate surface. Therefore, 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 aligned 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 an ellipse. In this case, since the retardation of the liquid crystal cell has a non-zero value, 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 liquid crystal cell substrate surface.

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

FIG. 6 is a schematic cross-sectional view showing a combination of a VA mode liquid crystal cell and two optical compensation sheets.
As shown in FIG. 6, the two optical compensation sheets (53, 54) can be combined with the VA mode liquid crystal cell (50) in any of the four types of variations (a) to (d). .
In the variations of (a) and (c), the optically anisotropic layer (51) side including the discotic liquid crystalline molecules of the optical compensation sheet (53, 54) is stretched over the VA mode liquid crystal cell (50). Use together. In the variation (a), an orientation film is provided on the transparent support (52) side of the optically anisotropic layer (51) to align the discotic liquid crystalline 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 the discotic liquid crystalline molecules.
In the variations (b) and (d), the transparent support (52) side of the optical compensation sheet (53, 54) is attached to the VA mode liquid crystal cell (50). In the variation (b), an alignment film is provided on the transparent support (52) side of the optically anisotropic layer (51) to align the discotic liquid crystalline molecules. In the variation (d), an alignment film is provided outside the optically anisotropic layer (51) to align the discotic liquid crystalline molecules.

FIG. 7 is a schematic cross-sectional view showing a combination of a VA mode liquid crystal cell and one optical compensation sheet.
As shown in FIG. 7, the single optical compensation sheet (63) can be combined with the VA mode liquid crystal cell (60) in any of the four types of variations (e) to (h).
In the variations of (e) and (g), the side of the optically anisotropic layer (61) containing the discotic liquid crystalline molecules of the optical compensation sheet (63) is bonded to the VA mode liquid crystal cell (60). use. In the variation of (e), an alignment film is provided on the transparent support (62) side of the optically anisotropic layer (61) to align the discotic liquid crystalline molecules. In the variation (g), an orientation film is provided on the VA mode liquid crystal cell (60) side of the optically anisotropic layer (61) to align the discotic liquid crystalline molecules.
In the variations of (f) and (h), the transparent support (62) side of the optical compensation sheet (63) is attached to the 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 the discotic liquid crystalline molecules. In the variation (h), an alignment film is provided outside the optically anisotropic layer (61) to align the discotic liquid crystalline molecules.

FIG. 8 is a schematic cross-sectional view of an optical compensation 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 structure corresponds to the optical compensation sheet shown in FIGS. 6A and 6B or FIGS. 7E and 7F. The alignment film (72) is given an alignment function by rubbing in a certain direction (75).
The discotic liquid crystalline molecules (73a, 73b, 73c) contained in the optically anisotropic layer (73) are planar molecules. The discotic liquid crystal molecules (73a, 73b, 73c) have only one plane, that is, a disc surface (Pa, Pb, Pc). The disk surfaces (Pa, Pb, Pc) are inclined from the surfaces (71a, 71b, 71c) parallel to the surface of the support (71). The angles between the disk surfaces (Pa, Pb, Pc) and the surfaces (71a, 71b, 71c) parallel to the support surface are inclination angles (θa, θb, θc). As the distance from the alignment film (72) increases along the normal (74) of the support, the tilt angle also increases (θa <θb <θc).
The inclination angles (θa, θb, θc) are preferably changed in the range of 0 to 60 °. The minimum value of the tilt angle is preferably in the range of 0 to 55 °, more preferably in the range of 5 to 40 °. The maximum value of the inclination 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 more preferably in the range of 10 to 40 °.
When the tilt angle is changed as shown in FIG. 8, the viewing angle expansion function of the optical compensation sheet is significantly improved. Further, the optical compensation sheet with the tilt angle changed has a function of preventing the reversal of the display image, the gradation change, or the occurrence of coloring.

FIG. 9 is a schematic cross-sectional view of a typical VA liquid crystal display device.
The liquid crystal display device illustrated 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 liquid crystal cells disposed between the liquid crystal cell and the polarizing element. It consists of an optical compensation sheet (OC1, OC2) and a backlight (BL). Only one of the optical compensation sheets (OC1, OC2) may be disposed.
The arrows (R1, R2) of the optical compensation sheet (OC1, OC2) are the rubbing directions (corresponding to the arrow 75 in FIG. 8) of the alignment film provided on the optical compensation sheet. In the liquid crystal display device shown in FIG. 9, the optically anisotropic layer of the optical compensation sheet (OC1, OC2) is disposed 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 disposed on the polarizing element (A, B) side, the rubbing directions (R1, R2) of the alignment film are opposite to those in FIG.
The arrows (RP1, RP2) of the liquid crystal cell (VAC) indicate the rubbing direction of the alignment film provided on the liquid crystal cell substrate.
The arrows (PA, PB) of the polarizing elements (A, B) are the polarization transmission axes of the polarizing elements, respectively.

It is preferable that the rubbing direction (R1, R2) of the alignment film provided on the optical compensation sheet and the rubbing direction (RP1, RP2) of the alignment film provided on the liquid crystal cell substrate are substantially parallel or antiparallel, respectively. The polarization transmission axes (PA, PB) of the polarizing element are preferably arranged so as to be substantially orthogonal or parallel. Substantially orthogonal, parallel or anti-parallel means that the angular deviation is less than 20 ° (preferably less than 15 °, more preferably less than 10 °, most preferably less than 5 °).
The angle between the rubbing direction (RP1, RP2) of the alignment film provided on the liquid crystal cell substrate and the transmission axis (PA, PB) of the polarization of the polarizing element is preferably 10 to 80 °, and 20 to 70, respectively. More preferably, the angle is 35 ° to 55 °.

In the optical compensation sheet used for the VA liquid crystal display device, it is preferable that the direction in which the absolute value of retardation is minimum does not exist in the plane of the optical compensation sheet or in the normal direction.
The optical properties of the optical compensation 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.
Optical properties include (1) optically anisotropic layer, (2) support and (3) in-plane retardation (Re), thickness direction retardation (Rth) and (3) optical compensation sheet as a whole. The angle (β) between the direction in which the absolute value of 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 entire optical compensation sheet, nx, ny, and nz in the above-described definitions mean in-plane main refractive indexes that satisfy nx ≧ ny ≧ nz.

When two optical compensation sheets are used in the 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 preferably 0 ≦ | Re ³¹ | ≦ 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 ||) may be 5 nm or less, and the optically anisotropic layer and the support may be arranged so that the slow axis in each plane is substantially vertical. preferable.
When one optical compensation sheet is used in the VA liquid crystal display device, the in-plane retardation of the optical compensation sheet is preferably in the range of −10 nm to 10 nm. Therefore, the absolute value of the in-plane retardation (R ³² ) of one optical compensation sheet is preferably 0 ≦ | Re ³² | ≦ 10.
In order 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 (|| Re ¹ | − | Re ² ||) may be 10 nm or less, and the optically anisotropic layer and the support may be arranged so that the slow axis in each plane is substantially vertical. preferable.

Regarding the optical compensation sheet used in the VA liquid crystal display device, preferred ranges of the optical properties of (1) the optically anisotropic layer, (2) the support, and (3) the entire optical compensation 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 compensation sheet.
The meanings of Re ³¹ and Re ³² are as described above. The preferred range of retardation (Rth ² ) in the thickness direction of the support is as defined as the optical properties of the cellulose ester film described above. When two or more supports are provided, the in-plane retardation (Re ² ) of the entire support corresponds to the total value of the in-plane retardation of each support.

─────────────────────────────────────
Preferred range More preferred range Most preferred range ─────────────────────────────────────
0 <| Re ¹ | ≦ 200 5 ≦ | Re ¹ | ≦ 150 10 ≦ | Re ¹ | ≦ 100
0 ≦ | Re ² | ≦ 200 5 ≦ | Re ² | ≦ 150 10 ≦ | Re ² | ≦ 100
0 ≦ | Re ³¹ | ≦ 4.5 0 ≦ | Re ³¹ | ≦ 4 0 ≦ | Re ³¹ | ≦ 3.5
0 ≦ | Re ³² | ≦ 9 0 ≦ | Re ³² | ≦ 8 0 ≦ | 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 | ≦ 400
─────────────────────────────────────
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 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 the liquid crystal compound in the OCB mode liquid crystal cell. FIG. 10 shows a black display state, corresponding to a voltage application in the normally white mode or no voltage application 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 crystalline compound (12) is small in the vicinity of the lower substrate (13) and the liquid crystalline compound (12) in the vicinity of the upper substrate (11) in the light traveling direction (16a). The birefringence of is large. With respect to this direction (16a), the birefringence of the liquid crystalline compound (12) is large in the vicinity of the lower substrate (13) in the direction (16b) that is symmetric about the normal line of the substrate, and the upper substrate (11) The birefringence of the liquid crystal compound (12) in the vicinity 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 cross-sectional view schematically showing the orientation of the liquid crystal compound in the HAN mode liquid crystal cell. FIG. 11 shows a black display state, which corresponds to a voltage application in the normally white mode or no voltage application in the normally black mode.
As shown in FIG. 11, 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 an OCB mode (transmission type) liquid crystal cell is applied to a reflection type liquid crystal cell. In the HAN mode liquid crystal cell, the birefringence of the liquid crystalline compound (22) in the vicinity of the upper substrate (21) is large with respect to the incident light (27). The birefringence of the liquid crystalline compound (22) is small near the lower substrate (23). On the other hand, regarding the emitted light (28), the birefringence of the liquid crystalline compound (22) is large near the lower substrate (23), and the birefringence of the liquid crystalline compound (22) near the upper substrate (21) is small. Thus, the HAN 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 the OCB mode or HAN mode liquid crystal cell, if the viewing angle is increased, the transmittance of light from the black display portion is remarkably increased and the contrast is lowered. The optical compensation sheet is used to prevent a decrease in contrast upon incidence of light in an oblique direction, to improve viewing angle characteristics, and to further improve the front contrast.
When the liquid crystal cell has positive uniaxiality in black display, as described with reference to FIG. 5, optical compensation is performed using a negative uniaxial optical compensation sheet.

FIG. 12 is a schematic cross-sectional view showing a combination of an OCB mode liquid crystal cell and an optically anisotropic layer of two optical compensation sheets.
As shown in FIG. 12, the two optical compensation sheets are preferably used in combination so that the optically anisotropic layers (51, 52) sandwich the OCB mode liquid crystal cell (50). The discotic liquid crystalline molecules of the optically anisotropic layer (51, 52) have an alignment state corresponding to (optically compensated for) the alignment state of the liquid crystal molecules of the OCB mode liquid crystal cell (50).

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.
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 corresponding to (optically compensated for) the alignment state of the liquid crystal molecules of the HAN mode liquid crystal cell (60).

As shown in FIGS. 12 and 13, the alignment state of the OCB mode and HAN mode liquid crystal cells can be optically compensated by an optical anisotropic layer containing discotic liquid crystal molecules. However, the optically anisotropic layer alone is insufficient to correct the retardation of the liquid crystal cell and the retardation generated in the optically anisotropic layer itself. Therefore, as described above, the retardation is corrected by using the support as optical anisotropy.
The combination of the optically anisotropic layer and the optically anisotropic support, that is, the basic configuration (cross-sectional schematic diagram) of the optical compensation sheet is the optical compensation sheet used in the VA liquid crystal display device described in FIG. It is the same.

FIG. 14 is a schematic cross-sectional view of a typical OCB type liquid crystal display device.
The liquid crystal display device shown in FIG. 14 includes an OCB mode liquid crystal cell (OCBC), a pair of polarizing elements (A, B) provided on both sides of the liquid crystal cell, and a pair of liquid crystal cells disposed between the liquid crystal cell and the polarizing element. It consists of an optical compensation sheet (OC1, OC2) and a backlight (BL). Only one of the optical compensation sheets (OC1, OC2) may be disposed.
The arrows (R1, R2) of the optical compensation sheet (OC1, OC2) indicate 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. 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 disposed on the polarizing element (A, B) side, the rubbing directions (R1, R2) of the alignment film are opposite to those in FIG.
The arrows (RP1, RP2) of the liquid crystal cell (OCBC) are the rubbing directions of the alignment film provided on the liquid crystal cell substrate.
The arrows (PA, PB) of the polarizing elements (A, B) are the polarization transmission axes of the polarizing elements, respectively.

The rubbing direction (R1, R2) of the alignment film provided on the optical compensation sheet and the rubbing direction (RP1, RP2) of the alignment film provided on the liquid crystal cell substrate are preferably substantially parallel or antiparallel. The polarization transmission axes (PA, PB) of the polarizing element are preferably arranged so as to be substantially orthogonal or parallel. Substantially orthogonal, parallel or anti-parallel means that the angular deviation is less than 20 ° (preferably less than 15 °, more preferably less than 10 °, most preferably less than 5 °).
The angle between the rubbing direction (RP1, RP2) of the alignment film provided on the liquid crystal cell substrate and the transmission axis (PA, PB) of the polarization of the polarizing element is preferably 10 to 80 °, and 20 to 70, respectively. More preferably, the angle is 35 ° to 55 °.

FIG. 15 is a schematic cross-sectional view of a typical HAN type liquid crystal display device.
A liquid crystal display device shown in FIG. 15 includes a HAN mode liquid crystal cell (HANC), a polarizing element (A) provided on the display surface side of the liquid crystal cell, and an optical compensation sheet (A) disposed between the liquid crystal cell and the polarizing element ( OC) and a reflector (RB).
The arrow (R) of the optical compensation sheet (OC) is the rubbing direction of the alignment film provided on the optical compensation sheet.
The arrow (RP) of the liquid crystal cell (HANC) is 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.
It is preferable that 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 substantially parallel or antiparallel, respectively. Substantially parallel or anti-parallel means that the angular deviation is less than 20 ° (preferably less than 15 °, more preferably less than 10 °, most preferably less than 5 °).
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, it is 35 to 55 °.

In the optical compensation sheet used for the OCB type liquid crystal display device or the HAN type liquid crystal display device, it is preferable that the direction in which the absolute value of retardation is minimum does not exist in the plane of the optical compensation sheet or in the normal direction.
The optical properties of the optical compensation sheet used in the OCB type liquid crystal display device or the HAN type liquid crystal display device are also the optical properties of the optical anisotropic layer, the optical properties of the support, and the optical anisotropic layer and the support. Is determined by the arrangement of Details of their optical properties are described below.
The optical properties include in-plane retardation (Re) and retardation in the thickness direction (Rth) for each of (1) optically anisotropic layer, (2) support and (3) the entire optical compensation sheet. is important. In the OCB type liquid crystal display device or HAN type liquid crystal display device, (4) the relative relationship with the optical properties (in-plane retardation and retardation in the thickness direction) of the liquid crystal cell 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 entire optical compensation sheet, nx, ny, and nz in the above-described definitions mean in-plane main refractive indexes that satisfy nx ≧ ny ≧ nz.

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

The preferred ranges of the optical properties of the (1) optically anisotropic layer, (2) support and (3) optical compensation 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 compensation sheet. The preferred range of retardation (Rth ² ) in the thickness direction of the support is as defined as the optical properties of the cellulose ester film described above. When two or more supports are provided, the in-plane retardation (Re ² ) of the entire support corresponds to the total value of the in-plane retardation of each support. Further, the in-plane retardation (Re ³ ) of the optical compensation sheet is adjusted in relation to the above-mentioned 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 | ≦ 200 5 ≦ | Re ² | ≦ 150 10 ≦ | Re ² | ≦ 100
0 ≦ | Re ³ | ≦ 4.5 0 ≦ | Re ³ | ≦ 4 0 ≦ | Re ³ | ≦ 3.5
─────────────────────────────────────
50 ≦ | Rth ¹ | ≦ 1000 50 ≦ | Rth ¹ | ≦ 800 100 ≦ | Rth ¹ | ≦ 50050 ≦ | Rth ³ | ≦ 1000 60 ≦ | Rth ³ | ≦ 500 100 ≦ | Rth ³ | ≦ 400 ──────────────────────────────────

[Example 1]
At room temperature, 45 parts by weight of cellulose acetate having an average degree of acetylation of 60.9%, 0.90 part by weight of the retardation increasing agent (5), 232.72 parts by weight of methylene chloride, 42.57 parts by weight of methanol and n-butanol 8 A solution (dope) was prepared by mixing 50 parts by weight.
The obtained solution (dope) was cast using a band casting machine having an effective length of 6 m so that the dry film thickness was 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. 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), the retardation increasing agent (6), (7), (31), (36), (37), (38), (44), (50) and (81) A film was produced and evaluated in the same manner as in Example 1 except that the same amount was used. The results are shown in Table 1.

[Comparative Examples 2 to 5]
A film was produced in the same manner as in Example 1 except that the same amounts of the following comparative compounds (x1), (x2), (x3) and (x4) were used instead of the retardation increasing agent (5). ,evaluated. The results are shown in Table 1.

Table 1 ─────────────────────────────────────
Film Retardation raising agent Retardation value (Rth ⁵⁵⁰ )
─────────────────────────────────────
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, cellulose acetate having an average degree of acetylation of 60.9% 45 parts by weight, retardation increasing agent (3) 0.90 part by weight, triphenyl phosphate (plasticizer) 2.75 parts by weight, biphenyl diphenyl phosphate 2 A solution (dope) was prepared by mixing 20 parts by weight, 232.72 parts by weight of methylene chloride, 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 was 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 film surface was observed and the presence or absence of bleed-out was evaluated. 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]
A film was produced and evaluated in the same manner as in Example 1 except that the same amount of each of the retardation increasing agents (8), (31) and (75) was used in place of the retardation increasing agent (3). The results are shown in Table 2.

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]
A film was produced and evaluated in the same manner as in Examples 11 to 14 except that the amount of the retardation increasing agent used was changed from 0.90 parts by weight to 0.20 parts by weight. The results are shown in Table 3.

Table 3 ─────────────────────────────────────
Film Retardation Raising Agent Rth ⁵⁵⁰ Bleed Out ─────────────────────────────────────
Comparative Example 6 None 50 nm None Example 15 (3) 240 nm None Example 16 (8) 240 nm Slightly Example 17 (31) 300 nm Yes Example 18 (75) 200 nm None ────────── ────────────────────────────

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

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

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

(Formation of alignment film)
On the support, a coating solution having the following composition was applied at 25 ml / m ² with a slide coater. Drying was performed with warm air of 60 ° C. for 60 seconds, and further with warm air of 90 ° C. for 150 seconds.
Next, the formed film was rubbed in a direction parallel to the slow axis direction of the support.

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

(Formation of optically anisotropic layer)
On the alignment film, 1.8 g of the following discotic liquid crystalline compound, 0.2 g of ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.), cellulose acetate butyrate (CAB551-0. 2, Eastman Chemical Co., Ltd.) 0.04 g, photopolymerization initiator (Irgacure 907, Ciba Geigy Co., Ltd.) 0.06 g, sensitizer (Kayacure DETX, Nippon Kayaku Co., Ltd.) 0.02 g, A coating solution dissolved in .43 g of methyl ethyl ketone was applied with a # 2.5 wire bar. This was attached to a metal frame and heated in a thermostatic chamber at 130 ° C. for 2 minutes to align the discotic liquid crystalline compound. Next, UV irradiation was performed for 1 minute using a 120 W / cm high-pressure mercury lamp at 130 ° C. to crosslink the discotic liquid crystalline compound. Then, it stood to cool to room temperature. Thus, an optical compensation sheet (1) was produced.

(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 zero.
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 is minimum and the normal line of the sheet was 28 °. The in-plane retardation was 15 nm (Re ¹ = 15), and the thickness direction retardation was 35 nm (Rth ¹ = 35).
The optical compensation sheet (1) was cut vertically along the rubbing direction using a microtome to obtain a very thin vertical piece (sample). Samples were left in an OsO ₄ atmosphere for 48 hours to stain. The stained sample was observed with a transmission electron microscope (TEM) to obtain a micrograph thereof. In the stained sample, the acryloyl group of the discotic liquid crystalline compound was stained and recognized as a photographic image.
As a result of examining this photograph, it was confirmed that the discotic structural unit of the discotic liquid crystalline compound was tilted from the surface of the support. Furthermore, the inclination angle continuously increased as the distance from the support surface increased.

(Creation 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 then rubbed to form a vertical alignment film. The rubbing treatment was performed so that the two glass substrates were in opposite directions. Two glass substrates were faced to each other so that the cell gap (d) was 5.5 μm. A liquid crystal compound (Δn: 0.05) mainly composed of ester and ethane was injected into the cell gap to produce a VA mode liquid crystal cell. The product of Δn and d was 275 nm.

(Creation of VA liquid crystal display device)
In the VA mode liquid crystal cell, two optical compensation sheets (1) were disposed so as to sandwich the cell, and the optically anisotropic layer of the optical compensation sheet and the glass substrate of the liquid crystal cell faced 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.
A voltage was applied to the VA 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 transmittance ratio (white display / black display) was the contrast ratio. The contrast ratio from the top and bottom and the left and right was measured with an instrument (EZ-Contrast 160D, manufactured by ELDIM). As a result, a favorable result was obtained in which the front contrast ratio was 300 and the viewing angle (the viewing angle at which a contrast ratio of 10 was obtained) was 70 degrees in all directions.

[Example 21]
(Support for optical compensation sheet)
The cellulose acetate film prepared in Example 11 was used as a support for the optical compensation sheet.

(Formation of alignment film)
On the support, a coating solution having the following composition was applied at 25 ml / m ² with a slide coater. Dried at 60 ° C. for 2 minutes.
Next, rubbing treatment was performed on the formed film in a direction parallel to the direction of the main refractive index in the plane of the support. The rubbing conditions were a rubbing roll diameter of 150 mm, a conveyance speed of 10 m / min, a lapping angle of 6 °, and a rubbing roll rotational speed of 1200 rpm.

─────────────────────────────────────
Alignment film coating solution composition ──────────────────────────────────────
10% by weight aqueous solution of modified polyvinyl alcohol used in Example 20
24g
73g of water
Methanol 23g
0.2 g of 50% by weight aqueous solution of glutaraldehyde (crosslinking agent)
─────────────────────────────────────

(Formation of optically anisotropic layer)
On the alignment film, 1.8 g of the discotic liquid crystalline compound used in Example 20, 0.2 g of ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.), cellulose acetate butyrate ( CAB551-0.2, manufactured by Eastman Chemical Co., Ltd.) 0.04 g, cellulose acetate butyrate (CAB531-1.0, manufactured by Eastman Chemical Co.) 0.01 g, photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy Co.) A coating solution prepared by dissolving 0.06 g and 0.02 g of a sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) in 3.4 g of methyl ethyl ketone was applied with a # 6 wire bar. This was affixed to a metal frame and heated in a constant temperature bath at 140 ° C. for 3 minutes to align the discotic liquid crystalline compound. Next, UV irradiation was performed for 1 minute using a 120 W / cm high-pressure mercury lamp at 140 ° C. to crosslink the discotic liquid crystalline compound. Then, it stood 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 zero. When the retardation value was fitted by simulation, a hybrid alignment 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 compensation sheet (2) was cut vertically along the rubbing direction using a microtome to obtain a very thin vertical piece (sample). Samples were left in an OsO ₄ atmosphere for 48 hours to stain. The stained sample was observed with a transmission electron microscope (TEM) to obtain a micrograph thereof. In the stained sample, the acryloyl group of the discotic liquid crystalline compound was stained and recognized as a photographic image.
As a result of examining this photograph, it was confirmed that the discotic structural unit of the discotic liquid crystalline compound was tilted from the surface of the support. Furthermore, the inclination angle continuously increased as the distance from the support surface increased.

(Creation 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 were in opposite directions. Two glass substrates were opposed to each other so that the cell gap (d) was 8 μm. A liquid crystal compound (ZLI1132, manufactured by Merck & Co., Inc.) having Δn of 0.1396 was injected into the cell gap to produce an OCB mode liquid crystal cell. The product of Δn and d was 1117 nm, and the in-plane retardation was 92 nm (Re ⁴ = 92).

(Creation of OCB type liquid crystal display device)
In the OCB mode liquid crystal cell, two optical compensation sheets (2) were disposed so as to sandwich the cell, and the optically anisotropic layer of the optical compensation sheet and the glass substrate of the liquid crystal cell faced 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.
A voltage was applied to the OCB mode liquid crystal cell with a 55 Hz rectangular wave. The NW mode of white display 2V and black display 6V was used, and the transmittance ratio (white display / black display) was set as the contrast ratio. The contrast ratio from the top, bottom, left and right was measured with a meter (LCD-5000, manufactured by Otsuka Electronics Co., Ltd.). As a result, good results were obtained in which the upper viewing angle (the viewing angle at which a contrast ratio of 10 was obtained) was 80 degrees or more, the lower viewing angle was 58 degrees, and the left and right viewing angles were both 66 degrees. .

[Example 22]
(Creation of HAN 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. Another glass substrate with an ITO electrode was prepared, and silicon oxide was deposited to form an alignment film. Two glass substrates were opposed to each other so that the cell gap (d) was 4 μm. A liquid crystal compound having a Δn of 0.1396 (ZLI1132, manufactured by Merck & Co., Inc.) was injected into the cell gap to prepare a HAN mode liquid crystal cell. The product of Δn and d was 558 nm, and the in-plane retardation was 46 nm (Re ⁴ = 46).

(Creation 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. 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 were arranged to be antiparallel. A polarizing element was placed on the optical compensation sheet so 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 disposed on the opposite side of the HAN mode liquid crystal cell.
A light source was placed in a direction inclined 20 ° from the normal direction of the display surface of the created HAN type liquid crystal display device, and light was irradiated. A voltage was applied to the HAN mode liquid crystal cell with a 55 Hz rectangular wave. The NW mode of white display 2V and black display 6V was used, and the transmittance ratio (white display / black display) was set as the contrast ratio. The contrast ratio from the top and bottom and the left and right was measured with a meter (bm-7, manufactured by TOPCON). As a result, a favorable result was obtained that the upper viewing angle (the viewing angle at which a contrast ratio of 10 was obtained) was 44 degrees, the lower viewing angle was 26 degrees, and the left and right viewing angles were both 39 degrees.

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, 22 Liquid crystalline compound 13, 23 Lower substrate 14, 24 of liquid crystal cell Normal direction of substrate 15, 25, 26 Direction inclined from normal of substrate 16a, 16b Direction of light travel 27 Incident light 28 Emitted light 31a, 31b Incident Transmission axis 32a, 32b of the polarizing element on the side The transmission axis 33a of the polarizing element on the output side 33a The refractive index ellipse of the VA mode liquid crystal cell when no voltage is applied 33b The refractive index ellipse of the VA mode liquid crystal cell when the voltage is applied 34 VA mode Orthographic projection of the optical axis of liquid crystal molecules in the liquid crystal cell onto the surface of the liquid crystal cell substrate 41 Index ellipsoid of 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 the 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 plane parallel to liquid crystal cell substrate 44z Refractive index in thickness direction of liquid crystal cell 50, 60 Liquid crystal cell 51, 61, 73 Optical anisotropic layer 52, 62, 71 Support 53, 54, 63, OC1, OC2, OC Optical compensation sheet 72 Alignment films 73a, 73b, 73c Discotic liquid crystalline molecules Pa, Pb, Pc Disc surfaces of discotic liquid crystalline molecules 71a, 71b, 71c Surfaces parallel to the surface of the support θa, θb , Θc Tilt angle 74 Normal to 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

Claims (1)

  A retardation increasing agent for a lower fatty acid ester film of cellulose comprising a compound having a molecular structure which has at least two aromatic rings and does not sterically hinder the conformation of the two aromatic rings.

Images