JP2001100031A - Optical compensation sheet, elliptically polarizing plate and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately optically compensate a TN liquid crystal cell. SOLUTION: The optical compensation sheet has a transparent support and an optical anisotropic layer formed from discotic liquid crystal molecules aligned at 5 to 85 average tilt angle in which the tilt angle of the discotic liquid crystal molecules changes with the distance of the discotic liquid crystal molecules from the face o the transparent support. In this sheet, a polymer film having optically positive uniaxial or optically biaxial property and having the direction of the maximum refractive index substantially parallel to the transparent support face is used for the transparent support. The transparent support is disposed in such a manner that the direction of the maximum refractive index of the transparent support is substantially parallel or perpendicular to the average direction of lines obtained by projecting the normal lines of the disc faces of the discotic liquid crystal molecules onto the transparent support side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical compensation sheet, an elliptically polarizing plate, and a liquid crystal display.

[0002]

2. Description of the Related Art A TN (Twisted Nematic) type liquid crystal display device includes a TFT (Thin Film Transistor) and an MIM (Meta
l is the most widely used liquid crystal display device in combination with an active element such as an Insulator Metal. TN
The liquid crystal display device includes a TN liquid crystal cell and two polarizing elements. The liquid crystal cell is composed of rod-like liquid crystal molecules, two substrates for enclosing the same, and an electrode layer for applying a voltage to the rod-like liquid crystal molecules. In a TN type liquid crystal cell, 90
An alignment film for aligning rod-like liquid crystalline molecules with a twist angle of ゜ is provided on two substrates. In order to improve the viewing angle of a TN liquid crystal display device, an optical compensation sheet (retardation plate) is generally provided between a liquid crystal cell and a polarizing element. The laminate of the polarizing element (polarizing film) and the optical compensation sheet functions as an elliptically polarizing plate. As the optical compensation sheet, a stretched birefringent film has been conventionally used.

It has been proposed to use an optical compensatory sheet having an optically anisotropic layer containing discotic liquid crystalline molecules on a transparent support instead of an optical compensatory sheet comprising a stretched birefringent film. The optically anisotropic layer is formed by aligning discotic liquid crystal molecules and fixing the alignment state. Discotic liquid crystalline molecules are
Generally, it has a large birefringence. The use of discotic liquid crystal molecules makes it possible to produce an optical compensatory sheet having optical properties that cannot be obtained with a conventional stretched birefringent film. An optical compensation sheet for a TN type liquid crystal cell using discotic liquid crystal molecules is disclosed in JP-A-6-214116, US Pat.
3679 and 5646703, German Patent 3911
No. 620A1. In an optical compensation sheet for a TN type liquid crystal cell, discotic liquid crystal molecules are oriented at an average tilt angle of 5 to 85 degrees in the optically anisotropic layer, and the tilt angle of the discotic liquid crystal molecules is further adjusted to the discotic liquid crystal property. It is changed according to the distance between the molecule and the transparent support surface.

[0004]

By using discotic liquid crystal molecules in place of the conventional stretched birefringent film, it has become possible to optically compensate the TN type liquid crystal cell more accurately than before. . However, according to the research of the present inventors, it is very difficult to completely optically compensate a TN-type liquid crystal cell without any problem even if discotic liquid crystal molecules are used. When the present inventor studied a conventional optical compensatory sheet, light leakage was observed from the oblique direction of the polarizing plate, and the viewing angle was not sufficiently enlarged (to the extent theoretically expected). An object of the present invention is to provide an optical compensatory sheet capable of accurately and optically compensating a liquid crystal cell.

[0005]

The object of the present invention has been attained by the following optical compensation sheets (1) to (4), an elliptically polarizing plate (5) and a liquid crystal display device (6). (1) A transparent support and an optically anisotropic layer formed from discotic liquid crystal molecules oriented at an average tilt angle of 5 to 85 degrees, wherein the tilt angle of the discotic liquid crystal molecules is discotic liquid crystal. An optical compensatory sheet that changes with the distance between the hydrophilic molecule and the surface of the transparent support, wherein the transparent support has optically positive uniaxial or optical biaxiality, and has a direction of the maximum refractive index. Consists of a polymer film substantially parallel to the transparent support surface, and the direction of the maximum refractive index of the transparent support is obtained by projecting the normal of the discotic liquid crystal molecule disc surface onto the transparent support surface. An optical compensatory sheet, wherein the optical compensatory sheet is disposed so as to be substantially parallel or orthogonal to the average direction.

(2) The optical compensation sheet according to (1), wherein the transparent support comprises a polycarbonate film. (3) The optical compensation sheet according to (1), wherein the transparent support comprises a uniaxially or biaxially stretched polycarbonate film. (4) The transparent support is composed of a laminate of a polycarbonate film and a cellulose ester film, the polycarbonate film has optically positive uniaxial or optical biaxiality, and the direction of the maximum refractive index is different from that of the transparent support surface. It is substantially parallel, and the direction of the maximum refractive index is substantially parallel or perpendicular to the average direction of the line obtained by projecting the normal of the discotic liquid crystal molecule onto the transparent support surface. The optical compensation sheet according to (1), which is arranged as follows. (5) An optically anisotropic layer formed of discotic liquid crystal molecules oriented at an average tilt angle of 5 to 85 degrees, a transparent support, a polarizing film, and a transparent protective film are laminated in this order. An elliptically polarizing plate, wherein the transparent support comprises a polymer film having optically positive uniaxial or optical biaxiality and having a direction of maximum refractive index substantially parallel to the transparent support surface. And, the direction of the maximum refractive index of the transparent support is substantially parallel or orthogonal to the average direction of the line obtained by projecting the normal of the discotic liquid crystal molecule onto the transparent support surface. An elliptically polarizing plate, which is disposed.

(6) A liquid crystal display device comprising a TN type liquid crystal cell and two polarizing plates disposed on both sides thereof.
An optically anisotropic layer, a transparent support, a polarizing film, and a transparent protective film formed of a discotic liquid crystalline molecule in which at least one of the polarizing plates is oriented at an average tilt angle of 5 to 85 degrees is a liquid crystal. An elliptically polarizing plate laminated in this order from the cell side, wherein the transparent support has optically positive uniaxial or optical biaxiality, and the direction of the maximum refractive index is substantially the same as the transparent support surface. It is made of a polymer film that is parallel, and the direction of the maximum refractive index of the transparent support is substantially parallel to the average direction of the line obtained by projecting the normal of the discotic liquid crystal molecule disc surface onto the transparent support surface. Alternatively, the liquid crystal display device is arranged so as to be orthogonal to the liquid crystal display device. The average tilt angle of the discotic liquid crystal molecules means the average angle between the disc surface of the discotic liquid crystal molecules and the plane of the transparent support. Substantially parallel or orthogonal means that the angle difference from strict parallel or orthogonal is less than ± 20 °. The angle difference is preferably less than ± 16 °, more preferably less than ± 12 °, even more preferably less than ± 8 °, and most preferably less than ± 4 °.

[0008]

As a result of the study by the present inventors, a specific optical anisotropy was introduced into the transparent support, and in cooperation with the discotic liquid crystal molecules contained in the optically anisotropic layer, a TN type liquid crystal cell was obtained. It has been found that, by optically compensating, the viewing angle of the liquid crystal display device can be sufficiently enlarged (to the extent theoretically expected). Specifically, a polymer film having optically positive uniaxiality or optical biaxiality and having a direction of the maximum refractive index substantially parallel to the transparent support surface is used as the transparent support. Furthermore, the transparent support is transparent so that the direction of the maximum refractive index is substantially parallel or perpendicular to the average direction of the line obtained by projecting the normal of the discotic liquid crystal molecules onto the transparent support surface. The support and the optically anisotropic layer are arranged. The optical anisotropy of the discotic liquid crystal molecules and the optical anisotropy of the transparent support cooperate, and to the extent that conventional optical anisotropy of the discotic liquid crystal molecules alone is not possible, It is possible to accurately correspond (optically compensate) to the optical properties of the cell. By using such an optical compensatory sheet, light leakage from the oblique direction of the polarizing plate is prevented, and the viewing angle of the TN type liquid crystal display device can be sufficiently (more than conventionally) increased.

[0009]

FIG. 1 is a schematic diagram showing a basic structure of a TN type liquid crystal display device. The TN type liquid crystal display device shown in FIG. 1 includes, in order from the backlight (BL) side, a transparent protective film (1a), a polarizing film (2a), a transparent support (3a),
Optically anisotropic layer (4a), lower substrate of liquid crystal cell (5a), rod-like liquid crystal molecules (6), upper substrate of liquid crystal cell (5b), optically anisotropic layer (4b), transparent support (3b) , Polarizing film (2
b) and a transparent protective film (1b). Lower substrate of liquid crystal cell, rod-like liquid crystal molecules and upper substrate of liquid crystal cell (5a
To 5b) constitute a TN type liquid crystal cell. The transparent support and the optically anisotropic layers (3a to 4a and 4b to 3b) constitute an optical compensation sheet. Transparent protective film, polarizing film, transparent support and optically anisotropic layer (1a-4a and 4b-1b)
Constitutes an elliptically polarizing plate.

FIG. 2 is a schematic diagram showing another basic configuration of the TN type liquid crystal display device. The TN type liquid crystal display device shown in FIG. 2 includes a transparent protective film (1a), a polarizing film (2a), a transparent support (3a), an optically anisotropic layer (4a), Cell lower substrate (5a), rod-like liquid crystalline molecules (6), liquid crystal cell upper substrate (5b), transparent protective film (1b), polarizing film (2b), and transparent protective film (1
c). The lower substrate of the liquid crystal cell, the rod-like liquid crystal molecules, and the upper substrate (5a-5b) of the liquid crystal cell constitute a TN type liquid crystal cell. Transparent support and optically anisotropic layer (3a-4
a) constitutes the optical compensation sheet. The transparent protective film, the polarizing film, the transparent support and the optically anisotropic layers (1a to 4a) constitute an elliptically polarizing plate.

FIG. 3 is a schematic diagram showing still another basic configuration of the TN type liquid crystal display device. The TN type liquid crystal display device shown in FIG. 3 includes, in order from the backlight (BL) side, a transparent protective film (1a), a polarizing film (2a), and a transparent protective film (1).
b), lower substrate of liquid crystal cell (5a), rod-like liquid crystalline molecules (6), upper substrate of liquid crystal cell (5b), optically anisotropic layer (4
b), a transparent support (3b), a polarizing film (2b), and a transparent protective film (1c). The lower substrate of the liquid crystal cell, the rod-like liquid crystalline molecules and the upper substrate (5a-5b) of the liquid crystal cell are TN.
A liquid crystal cell. The transparent support and the optically anisotropic layers (4b to 3b) constitute an optical compensation sheet. Transparent protective film, polarizing film, transparent support and optically anisotropic layer (4b-1
c) constitutes an elliptically polarizing plate.

[Transparent Support] In the present invention, an optically anisotropic polymer film is used as the transparent support of the optical compensation sheet. In-plane retardation (Re) of transparent support
Is preferably at least 20 nm, more preferably at least 30 nm. Further, the retardation (Rth) in the thickness direction is preferably at least 10 nm, more preferably at least 15 nm. The in-plane retardation (Re) and the retardation in the thickness direction (Rth) are respectively defined by the following equations. Re = (nx−ny) × d Rth = [{(nx + ny) / 2} −nz] × d where nx and ny are in-plane refractive indices of the transparent support, and nz is the thickness of the transparent support. Is the refractive index in the direction, and d is the thickness of the transparent support.

The polymer forming the transparent support includes:
A cellulose ester (eg, cellulose acetate) or a synthetic polymer (eg, polycarbonate, polysulfone, polyethersulfone, polyacrylate, polymethacrylate, norbornene resin) is generally used. In the present invention, it is preferable to use a cellulose ester film or a polycarbonate film, and it is particularly preferable to use a polycarbonate film. Note that the cellulose ester film is generally known as a polymer film having high optical isotropy (low retardation). However, European Patent 091165
The use of (1) the use of a retardation increasing agent, (2) the reduction of the acetylation degree of cellulose acetate, or (3) the production of a film by a cooling dissolution method described in JP-A-656-A2 describes a high retardation (optical). An (anisotropic) cellulose ester film can be obtained.

The transparent support may be a laminate of two polymer films. As two polymer films,
A combination of a polycarbonate film and a cellulose ester film is preferred. When two polymer films are combined, it is only necessary that at least one has the optical properties defined by the present invention. In the combination of a polycarbonate film and a cellulose ester film, it is preferable that the polycarbonate film has the optical properties defined by the present invention. If one polymer film (eg, a polycarbonate film) has the optical properties defined by the present invention, the other (eg, a cellulose ester film) may be optically isotropic. In a combination of a polycarbonate film and a cellulose ester film, it is preferable that the cellulose ester film is disposed on the optically anisotropic layer (or alignment film) side. The polymer film is preferably formed by a solvent casting method. The formed polymer film generally obtains optical anisotropy by stretching. That is, to obtain a polymer film having an optically positive uniaxial property or an optical biaxial property and having a direction of the maximum refractive index substantially parallel to the transparent support surface by a uniaxial stretching treatment or a biaxial stretching treatment. Can be.

The uniaxial stretching is preferably carried out in the longitudinal direction (casting direction) or in the transverse direction (direction perpendicular to the casting direction), more preferably in the transverse direction. The stretching ratio is preferably from 0.2 to 20%, more preferably from 0.5 to 10%, most preferably from 1 to 5%. The biaxial stretching is preferably performed in the longitudinal direction (casting direction) and the transverse direction (width direction) of the film. The stretching ratio in the machine direction is preferably from 0.1 to 10%, more preferably from 0.2 to 5%, and most preferably from 0.5 to 2%. The stretching ratio in the horizontal direction is preferably from 0.2 to 20%, more preferably from 0.5 to 10%, and most preferably from 1 to 5%. The direction of the maximum refractive index of the transparent support is arranged so as to be substantially parallel or perpendicular to the average direction of the line obtained by projecting the normal of the discotic liquid crystal molecule onto the transparent support surface. . In the manufacturing process, the rubbing direction of the alignment film described below and the stretching direction of the polymer film may be arranged so as to be substantially parallel or orthogonal. The thickness of the transparent support is preferably from 20 to 500 μm, more preferably from 50 to 200 μm. To improve the adhesion between the transparent support and the layer provided thereon (adhesive layer, alignment film or optically anisotropic layer), the transparent support is subjected to a surface treatment (eg, glow discharge treatment, corona discharge treatment, ultraviolet light ( UV) treatment, flame treatment). An adhesive layer (undercoat layer) may be provided on the transparent support.

[Alignment Film] The alignment film is formed by rubbing an organic compound (preferably a polymer), obliquely depositing an inorganic compound, forming a layer having microgrooves, or by using a Langmuir-Blodgett method (LB film). (Eg, ω-tricosanoic acid, dioctadecylmethylammonium chloride, methyl stearylate). In addition, the application of an electric field,
There is also known an alignment film in which an alignment function is generated by applying a magnetic field or irradiating light. An alignment film formed by rubbing a polymer is particularly preferable. The rubbing treatment is performed by rubbing the surface of the polymer layer several times with paper or cloth in a certain direction. As the polymer constituting the alignment film, it is preferable to use a polymer that does not reduce the surface energy of the alignment film (a normal polymer for an alignment film). The thickness of the alignment film is preferably 0.01 to 5 μm,
More preferably, the thickness is 0.05 to 1 μm. The optically anisotropic layer may be transferred onto a transparent support after the discotic liquid crystalline molecules of the optically anisotropic layer are aligned using an alignment film. Discotic liquid crystalline molecules fixed in an aligned state can maintain the aligned state without an alignment film.

[Optical Anisotropic Layer] The optically anisotropic layer is formed from discotic liquid crystalline molecules. In the optically anisotropic layer, discotic liquid crystal molecules are aligned at an average tilt angle of 5 to 95 degrees. The average inclination angle is preferably 5 to 45 degrees. Further, the tilt angle of the discotic liquid crystal molecules changes with the distance between the discotic liquid crystal molecules and the surface of the transparent support. Discotic liquid crystalline molecules are described in various literatures (C. Destrade et al., Mol. Cry
sr. Liq. Cryst., vol. 71, page 111 (1981); 22, Liquid Crystal Chemistry, 5th
Chapter 10, Chapter 2, 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 (19
94)). It is preferable that the discotic liquid crystal molecules fix the alignment state by a polymerization reaction. The polymerization of discotic liquid crystal molecules is described in JP-A-8-27284. In order to fix the discotic liquid crystal molecules by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystal molecules. However, when a polymerizable group is directly connected to the disc-shaped core, it becomes difficult to maintain an oriented state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable group. Therefore, the discotic liquid crystal molecule is preferably a compound represented by the following formula (I).

(I) D (-LQ) _{n wherein} D is a discotic core; L is a divalent linking group; Q is a polymerizable group; and n is 4 to 12 Is an integer. An example of the discotic core (D) of the above formula is shown below. In each of the following examples, LQ (or QL) means a combination of a divalent linking group (L) and a polymerizable group (Q).

[0019]

Embedded image

[0020]

Embedded image

[0021]

Embedded image

[0022]

Embedded image

[0023]

Embedded image

[0024]

Embedded image

[0025]

Embedded image

In the above formula, the divalent linking group (L) is
Alkylene group, alkenylene group, arylene group, -CO
It is preferably a divalent linking group selected from the group consisting of-, -NH-, -O-, -S- and a combination thereof. The divalent linking group (L) is an alkylene group, an alkenylene group, an arylene group, -CO-, -NH-, -O-
And a group obtained by combining at least two divalent groups selected from the group consisting of and -S-.
The divalent linking group (L) is most preferably a group obtained by combining at least two divalent groups selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, -CO- and -O-. The alkylene group preferably has 1 to 12 carbon atoms. The alkenylene group preferably has 2 to 12 carbon atoms. The arylene group preferably has 6 to 10 carbon atoms. The alkylene group, alkenylene group and arylene group may have a substituent (eg, an alkyl group, a halogen atom, a cyano, an alkoxy group, an acyloxy group). Examples of the divalent linking group (L) are shown below. The left side is bonded to the discotic core (D), and the right side is bonded to the polymerizable group (Q). 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-AL-AR-O-AL-O-CO- L17: -O-CO-AR-O-AL-CO- L18: -O -CO-AR-O-AL-O-CO-L19: -O-CO-AR-O-AL-O-AL-OC
O-L20: -O-CO-AR-O-AL-O-AL-OA
L-O-CO-L21: -S-AL-L22: -S-AL-O-L23: -S-AL-O-CO-L24: -S-AL-S-AL-L25: -S-AR -AL-

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

[0030]

Embedded image

The polymerizable group (Q) is an unsaturated polymerizable group (Q1
To Q7), an epoxy group (Q8) or an aziridinyl group (Q9), more preferably an unsaturated polymerizable group, and more preferably an ethylenically unsaturated polymerizable group (Q
1 to Q6) are most preferred. In the formula (I), n is an integer of 4 to 12. Specific numbers are determined according to the type of discotic core (D).
The combination of a plurality of L and Q may be different, but is preferably the same.

Two or more discotic liquid crystal molecules may be used in combination. For example, the polymerizable discotic liquid crystal molecules and the non-polymerizable discotic liquid crystal molecules described above can be used in combination. The non-polymerizable discotic liquid crystal molecule is preferably a compound in which the polymerizable group (P) of the polymerizable discotic liquid crystal molecule is changed to a hydrogen atom or an alkyl group. That is, the non-polymerizable discotic liquid crystalline molecule is preferably a compound represented by the following formula (II). (II) D (-LR) _{n wherein} D is a discotic core; L is a divalent linking group; R is a hydrogen atom or an alkyl group;
Is an integer of 4 to 12. An example of the discotic core (D) of formula (II) is that LP (or PL) is replaced by LR (or R
Except for changing to L), it is the same as the example of the polymerizable discotic liquid crystal molecule described above. Further, a divalent linking group (L)
Is the same as the example of the polymerizable discotic liquid crystal molecule described above. The alkyl group represented by R has 1 to 4 carbon atoms.
It is preferably 0, more preferably 1 to 30. A chain alkyl group is more preferable than a cyclic alkyl group, and a straight-chain alkyl group is more preferable than a branched chain alkyl group. R is particularly preferably a hydrogen atom or a linear alkyl group having 1 to 30 carbon atoms.

The optically anisotropic layer is formed of a discotic liquid crystal molecule or the following polymerizable initiator and optional additives (eg,
Plasticizer, monomer, surfactant, cellulose ester,
It is formed by applying a discotic liquid crystal composition (coating liquid) containing a 1,3,5-triazine compound, a chiral agent) on the alignment film. As the solvent used for preparing the discotic liquid crystal composition, an organic solvent is preferably used. Examples of the organic solvent include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethylsulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, , Chloroform, dichloromethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone), and ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination. The discotic liquid crystal composition can be applied by a known method (eg, a wire bar coating method, an extrusion coating method, a direct gravure coating method, a reverse gravure coating method, a die coating method).

The discotic liquid crystal molecules are preferably oriented substantially uniformly, and more preferably are fixed in a state where they are substantially uniformly oriented. Most preferably, it is fixed. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. Photopolymerization reactions are preferred. Examples of photopolymerization initiators include α
-Carbonyl compounds (U.S. Pat.
369670), acyloin ethers (described in US Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (described in US Pat. No. 272251)
No. 2), polynuclear quinone compounds (US Pat. No. 304)
Nos. 6127 and 2951758), a combination of a triarylimidazole dimer and p-aminophenyl ketone (described in US Pat. No. 3,549,367), an acridine and phenazine compound (JP-A-60-105667, U.S. Pat. No. 4,239,850) and oxadiazole compounds (U.S. Pat. No. 4,221,970). The amount of the photopolymerization initiator used is preferably 0.01 to 20% by weight, more preferably 0.5 to 5% by weight of the solid content of the coating solution. Light irradiation for the polymerization of discotic liquid crystalline molecules preferably uses ultraviolet light.
The irradiation energy is 20 mJ / cm ^{2 to} 50 J / cm
² , preferably 100 to 800 mJ / cm
More preferably, it is ² . Light irradiation may be performed under heating conditions to promote the photopolymerization reaction. The thickness of the optically anisotropic layer is independently preferably from 0.1 to 20 μm, more preferably from 0.5 to 15 μm, and most preferably from 1 to 10 μm.

[Polarizing Film] As the polarizing film, an iodine-based polarizing film,
There are a dye-based polarizing film using a dichroic dye and a polyene-based polarizing film. The iodine-based polarizing film and the dye-based polarizing film are generally manufactured using a polyvinyl alcohol-based film. The transmission axis (polarization axis) of the polarizing film corresponds to a direction perpendicular to the stretching direction of the film.

[Transparent protective film] As the transparent protective film, an optically isotropic polymer film is used. That the protective film is transparent means that the light transmittance is 80% or more. Specifically, the optical isotropy means that the in-plane retardation (Re) is preferably 10 nm or less,
More preferably, it is 5 nm or less. Further, the retardation (Rth) in the thickness direction is preferably at most 40 nm, more preferably at most 20 nm. The definition of the in-plane retardation (Re) and the retardation in the thickness direction (Rth) are as described above for the transparent support. As the transparent protective film, a cellulose ester film, preferably a triacetyl cellulose film, is generally used. The cellulose ester film is preferably formed by a solvent casting method. The thickness of the transparent protective film is 20 to 500 μ
m, more preferably 50 to 200 μm.

[Liquid Crystal Display Device] The present invention can be applied to liquid crystal cells of various display modes. However, in the present invention, TN
This is particularly effective in a (Twisted Nematic) mode liquid crystal display device.

[0038]

[Example 1] (Preparation of first transparent support) 2,2'-bis (4-hydroxyphenyl) propane polycarbonate resin (viscosity average molecular weight: 28000) was dissolved in dichloromethane,
An 18% by weight solution was obtained. This solution was degassed under vacuum to obtain a dope. The dope was cast on a band, dried at 50 ° C. for 10 minutes, peeled off, and further dried at 100 ° C. for 10 minutes. The obtained polycarbonate film having a thickness of 60 μm was thermally relaxed at 190 ° C. for 1 hour. Add one more film
The film was stretched 1.8% in the longitudinal uniaxial direction at 70 ° C. Thus, a first transparent support made of a stretched polycarbonate film was produced. The in-plane retardation (Re) was measured at a wavelength of 546 nm from the normal direction of the film.
nm, and showed optically positive uniaxiality. The surface of the first transparent support was subjected to a corona discharge treatment.

(Preparation of Second Transparent Support) At room temperature,
45 parts by weight of cellulose acetate having an average acetylation degree of 60.9%, 1.35 parts by weight of the following retardation increasing agent, 232.72 parts by weight of methylene chloride, methanol 42.
A solution (dope) was prepared by mixing 57 parts by weight and 8.5 parts by weight of n-butanol.

[0040]

Embedded image

The obtained dope was dried while stretching it by 1% in the casting direction and 1% in the width direction using a band casting machine having an effective length of 6 m to obtain a second transparent support having a thickness of 100 μm. . When the obtained second transparent support was measured using an ellipsometer, the in-plane retardation (Re) in the casting direction was 5 nm and the retardation (Rth) in the thickness direction was 80 nm. On the second transparent support,
A 0.1 μm thick gelatin subbing layer was provided.

(Formation of alignment film) On the undercoat layer, the following terminal acrylate-modified polyvinyl alcohol was applied,
After drying with hot air at 80 ° C., a rubbing treatment was performed to form an alignment film. The rubbing direction of the alignment film was parallel to the casting direction of the transparent support.

[0043]

Embedded image

(Formation of Optically Anisotropic Layer) 1.8 g of the following discotic liquid crystal compound (1) and ethylene oxide-modified trimethylolpropane triacrylate (V #
360, 0.2 g of Osaka Organic Chemical Co., Ltd., 0.04 g of cellulose acetate butyrate (CAB551-0.2, manufactured by Eastman Chemical Company), photopolymerization initiator (Irgacure 907, Nippon Ciba Geigy Co., Ltd.) 0.06
g and 0.02 g of a photosensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) were dissolved in 3.43 g of methyl ethyl ketone to prepare a coating solution.

[0045]

Embedded image

The coating solution was applied on the alignment film with a # 4 wire bar. This was adhered to a metal frame and fixed, and heated in a thermostat at 120 ° C. for 3 minutes to align discotic liquid crystal molecules. While maintaining the temperature of 120 ° C., ultraviolet rays were irradiated for 1 minute using a high-pressure mercury lamp of 120 W / cm to polymerize the vinyl group of the discotic liquid crystal molecules and fix the alignment state. Then, it cooled to room temperature. The thickness of the formed optically anisotropic layer is 2.0 μm.
m. The average tilt angle of the discotic liquid crystalline molecules was determined by measuring the angle dependence of the retardation with an ellipsometer, and was found to be 38 degrees. The retardation (Rth) in the thickness direction of the optically anisotropic layer was 70 nm.

(Preparation of Optical Compensation Sheet) The first transparent support was attached to the back side of the second transparent support on which the optically anisotropic layer was formed, using an acrylic adhesive. The slow axis (direction of the maximum refractive index) of the first transparent support and the rubbing direction of the alignment film were arranged in parallel. Thus, an optical compensation sheet was produced.

(Preparation of Elliptical Polarizing Plate) Iodine was adsorbed on a stretched polyvinyl alcohol film to prepare a polarizing film. One surface of the polarizing film and the transparent support surface of the produced optical compensation sheet were adhered using a polyvinyl alcohol-based adhesive. The slow axis (direction of the maximum refractive index) of the first transparent support and the transmission axis of the polarizing film were arranged so as to be parallel. On a surface opposite to the polarizing film, a saponification treatment was performed using a 100 μm-thick triacetyl cellulose film (Fujitac, manufactured by Fuji Photo Film Co., Ltd.) as a transparent protective film, and then a polyvinyl alcohol-based adhesive was used. Pasted. Thus, an elliptically polarizing plate was produced.

(Production of Liquid Crystal Display) A polyimide alignment film was provided on a glass substrate provided with an ITO transparent electrode, and a rubbing treatment was performed. Two substrates were stacked via a 4.5 μm spacer so that the alignment films faced each other.
The two substrates were arranged such that the rubbing directions of the alignment films were orthogonal. In the gap between the substrates, rod-like liquid crystalline molecules (ZLI-4
792, manufactured by Merck & Co., Inc.) to form a rod-shaped liquid crystal layer. On both sides of the TN liquid crystal cell produced as described above, two elliptically polarizing plates produced were adhered so that the optically anisotropic layer faced the substrate, thereby producing a liquid crystal display device. The rubbing direction of the alignment film and the rubbing direction of the alignment film of the liquid crystal cell adjacent thereto were arranged to be antiparallel. A rectangular wave voltage of 55 Hz is applied to the liquid crystal cell of the liquid crystal display device,
The viewing angle at which a contrast ratio of 10 was obtained in the upper, lower, left, and right directions was measured using the transmittance of white display and black display at 2 V for white display and 5 V for black display as the contrast ratio. The measurement result is
It is shown in the table.

Example 2 In the preparation of the optical compensatory sheet of Example 1, except that the slow axis (direction of the maximum refractive index) of the first transparent support and the rubbing direction of the alignment film were perpendicular to each other. Are the same as those in Example 1;
An elliptically polarizing plate and a liquid crystal display were produced and evaluated. The results are shown in Table 1.

Example 3 A 2,2′-bis (4-hydroxyphenyl) propane polycarbonate resin (viscosity average molecular weight: 28,000) was dissolved in dichloromethane.
An 18% by weight solution was obtained. This solution was degassed under vacuum to obtain a dope. The dope was cast on a band, dried at 50 ° C. for 10 minutes, peeled off, and further dried at 100 ° C. for 10 minutes. The obtained polycarbonate film having a thickness of 60 μm was thermally relaxed at 190 ° C. for 1 hour. Add one more film
1. Stretch 1.0% in the machine direction at 70 ° C.
The film was stretched by 0%. Thus, a first transparent support made of a stretched polycarbonate film was produced. Wavelength 54
The in-plane retardation (Re) measured at 6 nm from the normal direction of the film was 50 nm. Further, the retardation (Rth) in the thickness direction was 90 nm, indicating optical biaxiality. The surface of the first transparent support was subjected to a corona discharge treatment. An optical compensatory sheet, an elliptically polarizing plate and a liquid crystal display were produced and evaluated in the same manner as in Example 1 except that the first transparent support produced as described above was used. The results are shown in Table 1.

Example 4 (Preparation of a transparent support) At room temperature, the average acetylation degree was 60.
45 parts by weight of 9% cellulose acetate, 1.35 parts by weight of the retardation increasing agent used in Example 1, 232.72 parts by weight of methylene chloride, 42.57 parts by weight of methanol and 8.5 parts by weight of n-butanol Thus, a solution (dope) was prepared. The obtained dope is treated with an effective length of 6 m.
1% in the casting direction and 1% in the width direction using a band casting machine
The film was dried while being stretched by 5% to obtain a transparent support having a thickness of 100 μm. When the obtained transparent support was measured using an ellipsometer, the in-plane retardation (R
e) was 45 nm, and the retardation (Rth) in the thickness direction was 80 nm. Then, the refractive index in the width direction was larger than that in the stretching direction, indicating optical biaxiality. A gelatin subbing layer having a thickness of 0.1 μm was provided on the transparent support.

(Formation of Alignment Film) The terminal acrylate-modified polyvinyl alcohol used in Example 1 was applied onto the undercoat layer, dried with warm air at 80 ° C., and then rubbed to form an alignment film. The rubbing direction of the alignment film was perpendicular to the casting direction (slow axis) of the transparent support.

(Formation of Optically Anisotropic Layer) 1.8 g of the discotic liquid crystal compound (1) used in Example 1 and ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.) ) 0.2 g,
Cellulose acetate butyrate (CAB551-0.
2, 0.04 g of Eastman Chemical Co., Ltd., photopolymerization initiator (Irgacure 907, Nippon Ciba Geigy Co., Ltd.)
Co., Ltd.) and a photosensitizer (Kayacure DET)
X, manufactured by Nippon Kayaku Co., Ltd.) was dissolved in 3.43 g of methyl ethyl ketone to prepare a coating solution. The coating solution was applied on the alignment film using a # 3 wire bar. This was adhered to a metal frame and fixed, and heated in a thermostat at 120 ° C. for 3 minutes to align discotic liquid crystal molecules. While maintaining the temperature of 120 ° C.,
Ultraviolet rays were irradiated for 1 minute using a high-pressure mercury lamp of W / cm to polymerize the vinyl groups of the discotic liquid crystal molecules and fix the alignment state. Then, it cooled to room temperature.
The thickness of the formed optically anisotropic layer was 1.5 μm.
The average tilt angle of the discotic liquid crystalline molecules was determined by measuring the angle dependence of the retardation with an ellipsometer, and was found to be 36 degrees. The retardation (Rth) in the thickness direction of the optically anisotropic layer is:
70 nm. Thus, an optical compensation sheet was produced. The optical compensation sheet was immersed in an aqueous alkaline solution and subjected to a saponification treatment.

(Preparation of Elliptically Polarizing Plate) Iodine was adsorbed to a stretched polyvinyl alcohol film to prepare a polarizing film. One surface of the polarizing film and the transparent support surface of the produced optical compensation sheet were adhered using a polyvinyl alcohol-based adhesive. The rubbing direction of the alignment film and the absorption axis of the polarizing film were arranged so as to be parallel. A 100 μm-thick triacetyl cellulose film (Fujitac, manufactured by Fuji Photo Film Co., Ltd.) was adhered to the opposite surface of the polarizing film as a transparent protective film using a polyvinyl alcohol-based adhesive. Thus, an elliptically polarizing plate was produced.

(Fabrication of Liquid Crystal Display) Two elliptically polarizing plates were fabricated on both sides of the TN liquid crystal cell fabricated in Example 1.
The liquid crystal display was manufactured by attaching the optically anisotropic layer so as to face the substrate. The rubbing direction of the alignment film and the rubbing direction of the alignment film of the liquid crystal cell adjacent thereto were arranged to be antiparallel. 5 in the liquid crystal cell of the liquid crystal display
Applying 5 Hz rectangular wave voltage, white display 2V, black display 5V
The viewing angle at which a contrast ratio of 10 was obtained in the upper, lower, left, and right directions was measured using the transmittance of white display and black display as a contrast ratio. The measurement results are shown in Table 1.

[Comparative Example 1] (Preparation of liquid crystal display device) A commercially available polarizing plate (HLC2-5618HC, a liquid crystal display device) was provided on both sides of the TN liquid crystal cell prepared in Example 1.
(Manufactured by Sanritz Co., Ltd.), and a liquid crystal display device was manufactured. The absorption axis direction of the polarizing film and the rubbing direction of the alignment film of the liquid crystal cell adjacent to the polarizing film were arranged in parallel. A rectangular wave voltage of 55 Hz is applied to the liquid crystal cell of the liquid crystal display device, and the transmittance between white display and black display at 2 V white display and 5 V black display is defined as a contrast ratio, and a viewing angle at which a contrast ratio of 10 can be obtained in up, down, left and right directions. Was measured. The measurement results are shown in Table 1.

[0058]

[Table 1] Table 1 光学 Optical compensation sheet Vertical viewing angle Left and right Viewing angle ──────────────────────────────────── Example 1 130 ° 150 ° Example 2 125 ° 155 ゜ Example 3 120 ゜ 150 ゜ Example 4 120 ゜ 140 ゜ Comparative Example 1 (none) 40 ゜ 90 ゜────────────

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a basic configuration of a TN type liquid crystal display device.

FIG. 2 is a schematic diagram showing another basic configuration of a TN type liquid crystal display device.

FIG. 3 is a schematic diagram showing still another basic configuration of the TN type liquid crystal display device.

[Explanation of symbols]

 BL backlight 1a, 1b, 1c Transparent protective film 2a, 2b Polarizing film 3a, 3b Transparent support 4a, 4b Optically anisotropic layer 5a Liquid crystal cell lower substrate 5b Liquid crystal cell upper substrate 6 Rod-like liquid crystal molecules

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13363 G02F 1/13363 F-term (Reference) 2H049 BA04 BA06 BA42 BB03 BB23 BB33 BB44 BB46 BB49 BC04 BC09 BC22 2H088 EA47 HA03 JA05 KA07 MA07 MA20 2H091 FA08X FA08Z FA11X FA11Z FB02 FC23 FC25 FD06 GA13 GA16 GA17 HA07 KA02 LA19 4F100 AG00 AJ06B AK01A AK21 AK25C AK45A AL06 AR00A AR00C BA02 BA03 J07 EBA37B10 EG

Claims (6)

[Claims] 1. An optically anisotropic layer formed from discotic liquid crystal molecules oriented at an average tilt angle of 5 to 85 degrees, wherein the tilt angle of the discotic liquid crystal molecules is discotic. An optical compensatory sheet that changes with the distance between the tick liquid crystalline molecules and the transparent support surface, wherein the transparent support has an optically positive uniaxial or optical biaxial property and has a maximum refractive index. The direction of the maximum refractive index of the transparent support is obtained by projecting the normal of the discotic liquid crystal molecule disc surface onto the transparent support surface. An optical compensatory sheet, which is arranged so as to be substantially parallel or orthogonal to the average direction of the lines. 2. The optical compensation sheet according to claim 1, wherein the transparent support is made of a polycarbonate film. 3. The optical compensation sheet according to claim 1, wherein the transparent support is made of a uniaxially or biaxially stretched polycarbonate film. 4. A transparent support comprising a laminate of a polycarbonate film and a cellulose ester film, wherein the polycarbonate film has an optically positive uniaxial or optical biaxial property and the direction of the maximum refractive index is transparent. It is substantially parallel to the body surface, and the direction of the maximum refractive index is substantially parallel or orthogonal to the average direction of the line obtained by projecting the normal of the discotic liquid crystal molecule onto the transparent support surface. The optical compensatory sheet according to claim 1, wherein the optical compensatory sheet is arranged such that 5. An optically anisotropic layer formed from discotic liquid crystalline molecules oriented at an average tilt angle of 5 to 85 degrees, a transparent support, a polarizing film, and a transparent protective film are laminated in this order. Wherein the transparent support is optically positive uniaxial or optical biaxial, and the direction of the maximum refractive index is substantially parallel to the transparent support surface. And the direction of the maximum refractive index of the transparent support is substantially parallel or orthogonal to the average direction of the line obtained by projecting the normal of the discotic liquid crystal molecule onto the transparent support surface. An elliptically polarizing plate characterized by being arranged as follows. 6. A liquid crystal display device comprising a TN type liquid crystal cell and two polarizing plates disposed on both sides thereof, wherein at least one of the polarizing plates is oriented at an average tilt angle of 5 to 85 degrees. An optically anisotropic layer formed from discotic liquid crystalline molecules, a transparent support, a polarizing film, and a transparent protective film are elliptically polarizing plates laminated in this order from the liquid crystal cell side, and the transparent support is A polymer film having optically positive uniaxiality or optical biaxiality and having a maximum refractive index direction substantially parallel to the transparent support surface, and a transparent support having a maximum refractive index direction A liquid crystal display device, wherein the liquid crystal display device is disposed so as to be substantially parallel or orthogonal to an average direction of a line obtained by projecting a normal of a discotic liquid crystal molecule onto a transparent support surface.