JP2000235184A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To unnecessitate the redesigning of molecular structure of liquid crystal molecules for an optical compensation sheet by forming an optical anisotropic layer by the polymn. reaction of a mixture of polymerizable discotic liquid crystal molecules and nonpolymerizable liquid crystal molecules. SOLUTION: The optical anisotropic layer is formed by the polymn. reaction of a mixture of polymerizable discotic liquid crystal molecules and nonpolymerizable liquid crystal molecules. The mixing ratio of the polymerizable discotic liquid crystal molecules and nonpolymerizable liquid crystal molecules is controlled so that the change rate of retardation of the liquid crystal cell and the change rate of retardation of the optical compensation sheet satisfy the formula of |ReLC60/ReLC30-ReOC60/ReOC30|<0.1. In the formula, ReLC60 and ReLC30 are the retardation of the liquid crystal cell at 60 deg.C and at 30 deg.C, respectively, and ReOC60 and ReOC30 are the retardation of the optical compensation sheet at 60 deg.C and at 30 deg.C, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display comprising a liquid crystal cell, a polarizing element and an optical compensation sheet, wherein the optical compensation sheet has a transparent support and an optically anisotropic layer.

[0002]

2. Description of the Related Art A liquid crystal display device comprises a liquid crystal cell, a polarizing element, and an optical compensation sheet (retardation plate). In a transmission type liquid crystal display device, two polarizing elements are attached to both sides of a liquid crystal cell, and one or two optical compensation sheets are arranged between the liquid crystal cell and the polarizing element. In a reflection type liquid crystal display device, a reflection plate, a liquid crystal cell, one optical compensation sheet, and one polarization element are arranged in this order. 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 the liquid crystal cell, the alignment state of the rod-like liquid crystal molecules is different. For the transmission type, TN (Twisted Nematic) and IPS (In-Plane Sw) are used.
itching), FLC (Ferroelectric Liquid Crysta)
l), OCB (Optically Compensatory Bend), STN
(Supper Twisted Nematic), VA (Vertically Align)
ed) and reflection type HAN (Hybrid Aligned Nem).
atic).

[0003] Optical compensatory sheets are used in various liquid crystal display devices in order to eliminate coloring of images and to increase the viewing angle. As the optical compensation sheet, a stretched birefringent film has been conventionally used. It has been proposed to use an optical compensation sheet having an optically anisotropic layer containing liquid crystal molecules (particularly discotic liquid crystal molecules) on a transparent support instead of the optical compensation sheet made of a stretched birefringent film. I have. The optically anisotropic layer is formed by aligning liquid crystalline molecules and fixing the alignment state. In general, an alignment state is fixed by a polymerization reaction using liquid crystal molecules having a polymerizable group. Liquid crystalline molecules have a large birefringence. The liquid crystal molecules have various alignment forms. By using liquid crystal molecules, it has become possible to realize optical properties that cannot be obtained with a conventional stretched birefringent film.

[0004] The optical properties of the optical compensatory sheet are determined according to the optical properties of the liquid crystal cell, specifically, the above-mentioned difference in display mode. When liquid crystal molecules, particularly discotic liquid crystal molecules, are used, an optical compensatory sheet having various optical properties corresponding to various display modes of a liquid crystal cell can be manufactured. As optical compensation sheets using discotic liquid crystal molecules, ones corresponding to various display modes have already been proposed. For example, optical compensation sheets for TN mode liquid crystal cells are disclosed in JP-A-6-214116, US Pat. Nos. 5,583,679 and 5,646,703.
And German Patent Publication No. 391620A1. Further, an optical compensation sheet for a liquid crystal cell of IPS mode or FLC mode is disclosed in Japanese Patent Application Laid-Open No. H10-54982.
There is a description in the publication. In addition, OCB mode or HA
An optical compensation sheet for an N-mode liquid crystal cell is disclosed in US Pat.
05253 and International Patent Application WO 96/37804
No. is described in each specification. Furthermore, an optical compensatory sheet for a liquid crystal cell of the STN mode is disclosed in JP-A-9-26572.
There is a description in the publication. An optical compensation sheet for a VA mode liquid crystal cell is described in Japanese Patent No. 2866372.

[0005] Liquid crystal display devices are used in portable devices (for example, mobile personal computers) by utilizing their light weight and thin characteristics. When the portable device is used outdoors, it is necessary to consider a temperature change as a use condition. Further, although the calorific value of the liquid crystal display device is small, when the liquid crystal display device is used as a display of an automobile or a personal computer, the temperature may become high due to the heat generated by an adjacent machine. The rod-like liquid crystal molecules used in the liquid crystal cell also change optical properties with a change in temperature. As described above, the optical properties of the optical compensation sheet are as follows.
It is designed to correspond to the optical properties of the liquid crystal cell. Therefore, when the optical properties of the liquid crystal cell change, the optical compensatory sheet cannot cope with it (optical compensation). Therefore, it was considered that the optical properties of the optical compensation sheet were changed in the same manner as the optical properties of the liquid crystal cell in response to the temperature change.

Japanese Patent Application Laid-Open No. 7-199174 discloses a liquid crystal display device having an optical retardation plate (optical compensation sheet) made of a polymer film having a mesogen group in a side chain. In the invention described in the publication, a temperature change in the optical properties of the optical compensation sheet is made to correspond to a temperature change in the optical properties of the liquid crystal cell by introducing a mesogen group into the side chain of the polymer. Japanese Patent Application Laid-Open No. Hei 9-101517 discloses an STN having an optical retardation plate (optical compensation sheet) in which a side chain type polymer liquid crystal is dispersed in a film of another polymer.
A liquid crystal display device is disclosed. In the invention described in the publication, the temperature change of the optical property of the optical compensation sheet is made to correspond to the temperature change of the optical property of the liquid crystal cell by using the side chain type polymer liquid crystal.

[0007]

Problems to be Solved by the Invention
The inventions described in JP-A Nos. 4 and 9-101517 each redesign the molecular structure of a substance (mainly liquid crystal molecules) used for the optical compensation sheet, thereby improving the optical properties of the optical compensation sheet. The temperature change corresponds to the temperature change of the optical property of the liquid crystal cell. However, as described above, the optical properties of the optical compensation sheet need to be determined according to the difference in the display mode of the liquid crystal cell. Therefore, in order to carry out the invention described in each of the above publications, in addition to the temperature change of the optical properties of the liquid crystal cell, the molecular structure of the liquid crystal molecules used in the optical compensation sheet is adjusted in accordance with the difference in the display mode. Need to redesign. That is, it is necessary to prepare, as the liquid crystal molecules used for the optical compensation sheet, a number of compounds corresponding to the type of the display mode of the liquid crystal cell × the type of the rod-shaped liquid crystal molecules of the liquid crystal cell. An object of the present invention is that the temperature change rate of the retardation of the optical compensation sheet is close to the temperature change rate of the retardation of the liquid crystal cell without having to redesign the molecular structure of the liquid crystal molecules used in the optical compensation sheet. It is to provide a liquid crystal display device.

[0008]

An object of the present invention is to provide a liquid crystal display comprising a liquid crystal cell, a polarizing element and an optical compensation sheet, wherein the optical compensation sheet has a transparent support and an optically anisotropic layer, The optically anisotropic layer is a layer formed by a polymerization reaction of a mixture of a polymerizable discotic liquid crystal molecule and a non-polymerizable liquid crystal molecule, and has a retardation change rate of a liquid crystal cell and a retardation change rate of an optical compensation sheet. Were satisfied by a liquid crystal display device characterized by satisfying the following expression. │Re ^LC 60 / Re ^LC 30-Re ^OC 60 / Re ^OC 30│
<0.1 where Re ^LC 60 is the retardation of the liquid crystal cell at 60 ° C .; Re ^LC 30 is the retardation of the liquid crystal cell at 30 ° C .; Re ^OC 60 is 60 ° C.
Is the retardation of the optical compensatory sheet at 30 ° C .; and Re ^OC 30 is the retardation of the optical compensatory sheet at 30 ° C.

[0009]

As a result of the study of the present inventors, when an optically anisotropic layer is formed by a polymerization reaction of a mixture of a polymerizable discotic liquid crystal molecule and a non-polymerizable liquid crystal molecule, the optical compensation sheet has Properties (specifically, retardation)
However, it was found that, like the liquid crystal cell, it changed according to the temperature. The temperature change rate of the optical properties can be adjusted by adjusting the mixing ratio of the polymerizable discotic liquid crystal molecules and the non-polymerizable liquid crystal molecules. As described above, an optical compensatory sheet having an optically anisotropic layer formed by a polymerization reaction of polymerizable discotic liquid crystal molecules has already been proposed which corresponds to various display modes of a liquid crystal cell. In the production of such known optical compensatory sheets, by mixing non-polymerizable liquid crystal molecules with polymerizable discotic liquid crystal molecules,
An optical compensatory sheet whose optical properties change in response to temperature changes is obtained. Then, by adjusting the mixing ratio between the polymerizable discotic liquid crystal molecules and the non-polymerizable liquid crystal molecules, the temperature change rate of the retardation of the optical compensation sheet is approximated to the temperature change rate of the retardation of the liquid crystal cell. Can be. As a result, in the liquid crystal display device of the present invention, there is no need to redesign the molecular structure of the liquid crystal molecules used for the optical compensation sheet according to the type of display mode of the liquid crystal cell and the type of rod-shaped liquid crystal molecules of the liquid crystal cell. The temperature change rate of the retardation of the optical compensation sheet can be approximated to the temperature change rate of the retardation of the liquid crystal cell.

[0010]

FIG. 1 is a schematic diagram showing the basic structure of a transmission type liquid crystal display device. In the transmission type liquid crystal display device shown in FIG. 1A, the polarizing element (1a), the transparent support (2a) of the optical compensation sheet, and the optical anisotropy of the optical compensation sheet are arranged in this order from the backlight (BL) side. Layer (3a),
Lower substrate of liquid crystal cell (4a), rod-like liquid crystalline molecules (5), upper substrate of liquid crystal cell (4b), optically anisotropic layer of optical compensation sheet (3b), transparent support of optical compensation sheet (2b) ,
And it consists of a polarizing element (1b). In the transmission type liquid crystal display device shown in FIG. 1B, the polarizing element (1a), the transparent support of the optical compensation sheet (2), and the optical anisotropy of the optical compensation sheet are arranged in this order from the backlight (BL) side. It comprises a layer (3), a lower substrate (4a) of a liquid crystal cell, rod-like liquid crystal molecules (5), an upper substrate (4b) of a liquid crystal cell, and a polarizing element (1b). The transmission type liquid crystal display device shown in FIG. 1C has a polarizing element (1a), a lower substrate (4a) of a liquid crystal cell, a rod-shaped liquid crystal molecule (5), and a liquid crystal cell in order from the backlight (BL) side. It comprises an upper substrate (4b), an optically anisotropic layer (3) of an optical compensation sheet, a transparent support (2) of an optical compensation sheet, and a polarizing element (1b). FIG. 2 is a schematic diagram showing a basic configuration of a reflection type liquid crystal display device. The reflection type liquid crystal display device shown in FIG. 2 includes, in order from the reflection plate (RP) side, a lower substrate (4a) of a liquid crystal cell, rod-like liquid crystal molecules (5), an upper substrate (4b) of a liquid crystal cell, and an optical compensation sheet. It comprises an optically anisotropic layer (3), a transparent support of an optical compensation sheet (2), and a polarizing element (1).

[Optical Anisotropic Layer of Optical Compensation Sheet] The optically anisotropic layer is formed by a polymerization reaction of a mixture of a polymerizable discotic liquid crystal molecule and a non-polymerizable liquid crystal molecule. Discotic liquid crystalline molecules are described in various literatures (C. D.
estrade et al., Mol. Crysr. Liq. Cryst., vol. 71,
page 111 (1981); Chemical Society of Japan, Quarterly Review of Chemistry, N
o. 22, Liquid Crystal Chemistry, Chapter 5, Chapter 10, Section 2 (199
4); B. Kohne et al., Angew. Chem. Soc. Chem. Com.
m., 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 introduce a polymerizable group into a discotic liquid crystalline molecule, it is necessary to bond the polymerizable group as a substituent to the discotic core of the discotic liquid crystalline molecule. 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 polymerizable discotic liquid crystal molecule is preferably a compound represented by the following formula (I).

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

[0013]

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[0014]

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[0015]

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[0016]

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[0017]

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[0018]

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[0019]

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[0020]

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[0021]

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

In order to optically compensate for a liquid crystal cell in which rod-like liquid crystal molecules are twisted in the STN mode, it is preferable that the discotic liquid crystal molecules are also twisted. When an asymmetric carbon atom is introduced into the AL (alkylene group or alkenylene group), the discotic liquid crystal molecule can be twisted and aligned in a helical manner. Further, even when a compound (chiral agent) having an asymmetric carbon atom and exhibiting optical activity is added to the optically anisotropic layer, the discotic liquid crystal molecules can be twisted in a helical manner.

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

[0027]

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[0028]

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[0029]

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[0030]

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[0031]

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[0032]

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The polymerizable group (P) is an unsaturated polymerizable group (P
1, P2, P3, P7, P8, P15, P16, P1
7) or an epoxy group (P6, P18), more preferably an unsaturated polymerizable group,
Ethylenically unsaturated polymerizable groups (P1, P7, P8, P1
5, P16, P17). 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 P may be different, but is preferably the same. Two or more polymerizable discotic liquid crystal molecules may be used in combination.

As the non-polymerizable liquid crystal molecules, rod-shaped liquid crystal molecules or discotic liquid crystal molecules are preferable, and discotic liquid crystal molecules are particularly preferable. As the non-polymerizable rod-like liquid crystal molecules, rod-like liquid crystal molecules generally used in liquid crystal cells can be used. Examples of rod-like liquid crystalline molecules include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, and alkoxy-substituted phenyl Includes pyrimidines, phenyldioxane, tolanes and alkenylcyclohexylbenzonitrile.

The non-polymerizable discotic liquid crystalline molecule is
It is preferable that the compound is obtained by changing the polymerizable group (P) of the polymerizable discotic liquid crystal molecule into 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. Two or more non-polymerizable liquid crystal molecules may be used in combination.

Polymerizable Discotic Liquid Crystalline Molecules and Non-Heavy
The mixing ratio with the compatible liquid crystal molecules is 30 ° C to 60 ° C.
The change rate of the retardation of the liquid crystal cell when
A certain Re^LC60 / Re^LC30 and temperature from 30 ° C to 60 ° C
Change of the optical compensation sheet when
Re, the conversion rate^OC60 / Re^OCDifference from 30 is less than 0.1
Adjust so that Check the liquid crystal cell and optical compensation sheet
The retardation is the in-plane letter date defined by the following formula
(Re). Re = (nx−ny) × d where nx and ny are a liquid crystal cell or an optical compensation sheet.
D is the in-plane principal refractive index; and d is the liquid crystal cell or
Is the thickness of the optical compensation sheet. Layer containing liquid crystalline molecules
Is, as a rule, a letter
Is reduced. Therefore, Re^LC60 / Re^LC30 and
Re^OC60 / Re^OC30 is a value in the range of 0 to 1
become. Increasing the mixing ratio of non-polymerizable liquid crystal molecules,
The retardation change rate (Re) of the optical compensation sheet^OC60
/ Re^OC30) decreases, and the mixing ratio of the non-polymerizable liquid crystalline molecules decreases.
Lowers the retardation change of the optical compensation sheet.
Conversion rate (Re^OC60 / Re ^OC30) rises. like this
By adjusting the mixing ratio to^LC60 / Re^LC30 and
Re^OC60 / Re^OCThe difference from 30 can be adjusted to less than 0.1
You. Polymerizable discotic liquid crystal molecules and non-polymerizable liquid crystals
As for the specific mixing ratio with
To adjust the rate of change of the retardation of the
There are no general restrictions. However, one is extremely small
Does not adjust the retardation change rate. Also, heavy
If the proportion of compatible discotic liquid crystalline molecules is small,
It becomes difficult to fix the orientation state in the biologically anisotropic layer
(There is also a means of fixing using a binder polymer
But). Therefore, polymerizable discotic liquid crystals in the mixture
The ratio of the hydrophilic molecule is preferably 1 to 99.9% by weight.
More preferably, it is 2 to 99.8% by weight.
More preferably 5 to 99.5% by weight.
Most preferably, it is 10 to 99% by weight.

The optically anisotropic layer is composed of polymerizable discotic liquid crystal molecules, non-polymerizable liquid crystal molecules, or the following polymerizable initiators and optional additives (eg, plasticizers, monomers, surfactants, It is formed by applying a coating solution containing a cellulose ester, a 1,3,5-triazine compound, a chiral agent) on the alignment film. As a solvent used for preparing the coating solution, an organic solvent is preferably used. Examples of the organic solvent include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethylsulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, , Chloroform, dichloromethane), 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 application of the coating solution can be performed by a known method (eg, an extrusion coating method, a direct gravure coating method, a reverse gravure coating method, a die coating method).

The aligned liquid crystal molecules are fixed while maintaining the alignment state. The immobilization is performed by a polymerization reaction of the polymerizable group (P) introduced into the polymerizable discotic liquid crystal molecule. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. Photopolymerization reactions are preferred. Examples of photopolymerization initiators include α-carbonyl compounds (U.S. Pat. Nos. 2,367,661 and 2,367).
670), acyloin ethers (described in US Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (described in US Pat. No. 2,722,512), and polynuclear quinone compounds (described in US Pat. No. 304612)
Nos. 7 and 2951758), a combination of a triarylimidazole dimer and p-aminophenyl ketone (described in U.S. Pat. No. 3,549,367), an acridine and phenazine compound (Japanese Unexamined Patent Publication No.
-105667, U.S. Pat. No. 4,239,850) and oxadiazole compounds (U.S. Pat.
12970). 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 preferably from 20 mJ / cm ^{2 to} 50 J / cm ² , more preferably from 100 to 800 mJ / cm ² . Light irradiation may be performed under heating conditions to promote the photopolymerization reaction.

The thickness of the optically anisotropic layer is 0.1 to 10
μm, more preferably 0.5 to 5 μm, and most preferably 1 to 5 μm. As described above, the alignment state of liquid crystal molecules in the optically anisotropic layer is determined according to the type of display mode of the liquid crystal cell. Specifically, the alignment state of liquid crystal molecules is determined by the types of liquid crystal molecules, types of alignment films, and additives in the optically anisotropic layer (eg, plasticizer, binder, surfactant).
Controlled by the use of

[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. The type of polymer used for the alignment film is determined according to the type of display mode of the liquid crystal cell. In a display mode in which many of the rod-like liquid crystal molecules in the liquid crystal cell are substantially vertically aligned (eg, VA, OCB, HAN), the liquid crystal molecules in the optically anisotropic layer are substantially horizontally aligned. An alignment film having the function of causing the alignment is used. In a display mode (eg, STN) in which most of the rod-like liquid crystal molecules in the liquid crystal cell are substantially horizontally aligned, the liquid crystal molecules have a function of substantially vertically aligning the liquid crystal molecules in the optically anisotropic layer. An alignment film is used.
In a display mode (eg, TN) in which most of the rod-like liquid crystal molecules in the liquid crystal cell are substantially obliquely aligned, the liquid crystal molecules have a function of substantially obliquely aligning the liquid crystal molecules of the optically anisotropic layer. An alignment film is used. For specific types of polymers, there are descriptions in the literature on optical compensation sheets using discotic liquid crystalline molecules corresponding to the various display modes described above. After aligning the liquid crystal molecules using an alignment film, the liquid crystal molecules are fixed in the alignment state by polymerization to form an optically anisotropic layer, and only the optically anisotropic layer is transparently supported. It may be transferred onto the body. The liquid crystalline molecules fixed in the alignment state can maintain the alignment state without the alignment film. Therefore, in the liquid crystal display device, the alignment film is not an essential element (although it is essential in the manufacturing process).

[Transparent Support of Optical Compensation Sheet] As a transparent support of the optical compensation sheet, an optically isotropic polymer film is generally used. Transparent support means that the light transmittance is 80% or more. The optical isotropy specifically refers to an in-plane retardation (R
e) is preferably 10 nm or less, more preferably 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 in-plane retardation (Re) and the thickness direction retardation (Rth) of the transparent support are defined by the following formulas. 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.

Depending on the type of liquid crystal display mode, an optically anisotropic polymer film may be used as the transparent support. That is, in some cases, the optical anisotropy of the optically anisotropic layer is added to the optical anisotropy of the transparent support to correspond to the optical anisotropy of the liquid crystal cell (optical compensation). When an optically anisotropic transparent support is used for such a purpose, the in-plane retardation (Re) of the transparent support is used.
Is preferably at least 20 nm, more preferably at least 30 nm. Further, the retardation (Rth) in the thickness direction is preferably 80 nm or more, and more preferably 120 nm or more.

The material for forming the transparent support is determined depending on whether it is an optically isotropic support or an optically anisotropic support. In the case of an optically isotropic support, glass or cellulose ester is generally used. In the case of an optically anisotropic support, a synthetic polymer (eg, polycarbonate, polysulfone, polyethersulfone, polyacrylate, polymethacrylate) is generally used. The cellulose ester or synthetic polymer film is preferably formed by a solvent casting method. In the case of an optically anisotropic support, the optical anisotropy is obtained by stretching a synthetic polymer film. The thickness of the transparent support is preferably 20 to 500 μm,
More preferably, it is 0 to 200 μm. In order 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.

[Liquid Crystal Display Device] The present invention can be applied to liquid crystal cells of various display modes. As described above, the optical compensation sheet using discotic liquid crystal molecules is TN
(Twisted Nematic), IPS (In-Plane Switchin)
g), FLC (Ferroelectric Liquid Crystal), OC
B (Optically Compensatory Bend), STN (Supper
Twisted Nematic), VA (Vertically Aligned) and HAN (Hybrid Aligned Nematic) have already been proposed. The present invention is effective for a liquid crystal display device of any display mode. A polarizing element generally includes a polarizing film and a protective film. The polarizing film includes an iodine-based polarizing film, 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 polarization axis of the polarizing film corresponds to a direction perpendicular to the stretching direction of the film. The protective films are provided on both surfaces of the polarizing film. The transparent support of the optical compensation sheet can also function as a protective film on one side of the polarizing film. As other protective films for the polarizing film, it is preferable to use a cellulose ester film having high optical isotropy, especially a triacetyl cellulose film.

[0045]

[Example 1] A glass plate having a thickness of 0.7 mm was used as a transparent support. A coating solution having the following composition was applied on a transparent support using a bar coater. Coating layer,
Dry at 60 ° C. for 2 minutes. The surface of the coating layer was rubbed to form an alignment film. The thickness of the alignment film is 0.5 μm
Met.

配 向 Coating solution for alignment film───────変 性 The following modified polyvinyl alcohol 2 g Glutaraldehyde 0.1 g Water 75 g Methanol 24 g ────── ──────────────────────────────

[0047]

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A coating solution having the following composition was applied on the alignment film using a bar coater, and heated at 130 ° C. for 2 minutes.
The discotic liquid crystalline compounds (1) and (2) were oriented.

塗布 Coating solution for optically anisotropic layer─── ───────────────────────────────── The following discotic liquid crystalline compound (1) 5 parts by weight The following discotic Liquid crystal compound (2) 4 parts by weight The following plasticizer 1 part by weight Cellulose acetate butyrate (CAB551-0.2, manufactured by Eastman Chemical Company) 0.2 part by weight Cellulose acetate butyrate (CAB531-1.0, Eastman Chemical Co.) 0.05 parts by weight Photopolymerization initiator (Irgacure 907, manufactured by Nippon Ciba Geigy Co., Ltd.) 0.3 parts by weight Methyl ethyl ketone 100 parts by weight ────────────── ──────────────────────

[0050]

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[0051]

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[0052]

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At a temperature of 130 ° C., ultraviolet rays were irradiated for 4 seconds to polymerize the vinyl group of the discotic liquid crystal compound (1), thereby fixing the alignment state. An optical compensation sheet was produced. The retardation of the optical compensation sheet was measured in the range of 20 ° C. to 80 ° C. The results are shown in FIG. Re ^OC 60 / R, which is the rate of change in retardation of the optical compensation sheet when the temperature rises from 30 ° C. to 60 ° C.
e ^OC30 was 0.93.

Two commercially available optical compensation sheets and two polarizing elements were attached to a commercially available TN-type liquid crystal cell to produce a liquid crystal display having the structure shown in FIG. The retardation of the liquid crystal cell was measured in the range of 20 ° C. to 80 ° C. The results are shown in FIG. Re ^LC 60 / Re ^LC 30 is a retardation change of the liquid crystal cell when the temperature rises from 30 ° C. to 60 ° C. was 0.90. FIG.
3 is a graph showing the retardation temperature dependence of the optical compensation sheets and liquid crystal cells produced in Examples 1 and 2 and Comparative Example 1. The vertical axis in FIG. 1 is a relative retardation value where the retardation at 30 ° C. is 1. The horizontal axis in FIG. 1 is temperature (° C.). The liquid crystal display was placed in a constant temperature room at 60 ° C., and the viewing angles (up and down and left and right) at which the contrast ratio became 10 or more were examined. Further, a change from the state of the image at 30 ° C. to the state of the image at 60 ° C. was visually confirmed. The results are shown in Table 1.

Example 2 An optical compensatory sheet was prepared in the same manner as in Example 1, except that the composition of the coating solution for the optically anisotropic layer was changed as follows.

<< Coating Solution for Optically Anisotropic Layer >>デ ィ ス 3 parts by weight of discotic liquid crystalline compound (1) used in Example 1 Discotic liquid crystalline compound (2) used in Example 1 6 parts by weight Plasticizer used in Example 1 1 part by weight Cellulose acetate butyrate (CAB551-0.2, manufactured by Eastman Chemical Company) 0.2 parts by weight Part Cellulose acetate butyrate (CAB531-1.0, manufactured by Eastman Chemical Company) 0.05 part by weight Photopolymerization initiator (Irgacure 907, manufactured by Nippon Ciba Geigy Co., Ltd.) 0.3 part by weight ─────────────────── ──────────────

The retardation of the optical compensation sheet was measured at a temperature in the range of 20 ° C. to 80 ° C. The results are shown in FIG.
Re ^OC 60 / Re ^OC which is the rate of change in retardation of the optical compensation sheet when the temperature rises from 30 ° C. to 60 ° C.
30 was 0.89. To a commercially available TN type liquid crystal cell,
A liquid crystal display device having a configuration shown in FIG. 1A was prepared by attaching the two optical compensation sheets and two polarizing elements. The liquid crystal display was placed in a constant temperature room at 60 ° C., and the viewing angles (up and down and left and right) at which the contrast ratio became 10 or more were examined. Further, a change from the state of the image at 30 ° C. to the state of the image at 60 ° C. was visually confirmed. The results are shown in Table 1.

Comparative Example 1 An optical compensatory sheet was prepared in the same manner as in Example 1, except that the composition of the coating solution for the optically anisotropic layer was changed as follows.

塗布 Coating solution for optically anisotropic layer───デ ィ ス 9 parts by weight of the discotic liquid crystal compound (1) used in Example 1 The following monomer 1 part by weight Cellulose acetate butyrate (CAB551-0.2, manufactured by Eastman Chemical Company) 0.2 part by weight Cellulose acetate butyrate (CAB531-1.0, manufactured by Eastman Chemical Company) 0.05 Parts by weight Photopolymerization initiator (Irgacure 907, manufactured by Nippon Ciba Geigy Co., Ltd.) 0.3 parts by weight Methyl ethyl ketone 100 parts by weight ────────────

[0060]

Embedded image

The retardation of the optical compensation sheet was measured at a temperature in the range from 20 ° C. to 80 ° C. The results are shown in FIG.
Re ^OC 60 / Re ^OC which is the rate of change in retardation of the optical compensation sheet when the temperature rises from 30 ° C. to 60 ° C.
30 was 0.99. To a commercially available TN type liquid crystal cell,
A liquid crystal display device having a configuration shown in FIG. 1A was prepared by attaching the two optical compensation sheets and two polarizing elements. The liquid crystal display was placed in a constant temperature room at 60 ° C., and the viewing angles (up and down and left and right) at which the contrast ratio became 10 or more were examined. Further, a change from the state of the image at 30 ° C. to the state of the image at 60 ° C. was visually confirmed. The results are shown in Table 1.

[0062]

[Table 1] Table 1 ──────────────────────────────────── sample number Re ^LC 60 Re ^OC 60 of the viewing angle image state change / Re ^LC 30 / Re ^OC 30 up, down, left and right 30 ℃ → 60 ℃ ──────────────────────────── ──────── Example 1 0.88 0.93 100 122 No change Example 2 0.88 0.89 101 120 No change Comparative example 1 0.88 0.99 95 100 Changed * ────────────────────────────────── (Note) Change *: When heated from 30 ℃ to 60 ℃, Inversion of the image occurred, and a large change in color was observed.

[Brief description of the drawings]

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

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

FIG. 3 is a graph showing the retardation temperature dependence of the optical compensation sheets and liquid crystal cells produced in Examples 1 and 2 and Comparative Example 1.

[Description of Signs] BL backlight RP reflector 1, 1a, 1b Polarizer 2, 2a, 2b Transparent support of optical compensation sheet 3, 3a, 3b Optically anisotropic layer of optical compensation sheet 4a Below liquid crystal cell Substrate 4b Upper substrate of liquid crystal cell 5 Rod-like liquid crystalline molecules

Claims (1)

[Claims] 1. A liquid crystal display device comprising a liquid crystal cell, a polarizing element and an optical compensation sheet, wherein the optical compensation sheet has a transparent support and an optically anisotropic layer, wherein the optically anisotropic layer is a polymerizable disc. A layer formed by a polymerization reaction of a mixture of a tick liquid crystal molecule and a non-polymerizable liquid crystal molecule, wherein the retardation change rate of the liquid crystal cell and the retardation change rate of the optical compensation sheet satisfy the following formula. Liquid crystal display device. │Re ^LC 60 / Re ^LC 30-Re ^OC 60 / Re ^OC 30│
<0.1 where Re ^LC 60 is the retardation of the liquid crystal cell at 60 ° C .; Re ^LC 30 is the retardation of the liquid crystal cell at 30 ° C .; Re ^OC 60 is 60 ° C.
Is the retardation of the optical compensatory sheet at 30 ° C .; and Re ^OC 30 is the retardation of the optical compensatory sheet at 30 ° C.