JP2001142072A - Normally black mode type tn liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a normally black mode TN liquid crystal display device which has wide viewing angle characteristics and little asymmetry in the lateral viewing angles when a medium tone is displayed and which can display an image of high quality. SOLUTION: The device has an optical compensation film and an optically anisotropic film disposed between a driving liquid crystal cell and a polarizing plate in the observation side. The optical compensation film holds twisted nematic alignment and has the twist angle smaller than the twist angle of a nematic liquid crystal layer of the driving liquid crystal cell when no voltage is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a normally black mode type twisted nematic liquid crystal display device having improved display contrast, gradation characteristics and viewing angle characteristics of display colors.

[0002]

2. Description of the Related Art An active drive twisted nematic liquid crystal display device (hereinafter abbreviated as TN-LCD) using a TFT element or an MIM element is thin, light, and light.
In addition to the low power consumption inherent in LCDs and having image quality comparable to a CRT when viewed from the front, it is widely used as a display device for notebook computers, portable televisions, portable information terminals, and the like.

A normally black mode type TN-LCD (hereinafter referred to as NB-TN) in which a black display is made when no voltage is applied and the liquid crystal alignment state in the cell at the time of black display forms a twisted structure.
-Abbreviated as LCD. ) Is compared with a normally white TN-LCD (hereinafter abbreviated as NW-TN-LCD), which displays white when no voltage is applied because the optical anisotropy is averaged. Good angular characteristics. However, NB
-TN-LCD cannot completely block light over the entire visible region because the liquid crystal alignment state in the cell at the time of black display has a twisted structure, and the black display is colored,
Since the display contrast is reduced, the NW-
A problem remains that color compensation, which cannot be a problem in the TN-LCD, must be performed. In order to solve this problem, various color compensation methods have been reported in recent years. For example, a method of setting a cell gap to an optimum value for each pixel (R, G, B) of an LCD panel (multi-gap method:
Hatta et al., SID 1986 Digest, p296), a method for color compensation using multiple stretched films (Sergan et a.
L., Jpn. J. Appl. Phys., 37 (3A), p889), Method of performing color compensation with a liquid crystal cell for compensation (Yoshida et al., Proceedings of the 16th Liquid Crystal Symposium (1990), 2L307, p222) and the like have been proposed.

However, in the multi-gap method,
Fine processing such as providing a step on the substrate for each display pixel over the entire surface of the cell is required, resulting in a decrease in cell yield and an increase in cost. In the method of performing color compensation using a plurality of stretched films, it is necessary to use four or more films in order to secure contrast, and it is possible to obtain stable characteristics due to variations in the film, accuracy during lamination processing, and the like. Have difficulty. Further, in the method of performing color compensation using a compensation liquid crystal cell, there is a problem that the weight and thickness increase because the cells are stacked. Furthermore, the display characteristics change due to the variation between the panels of the compensation liquid crystal cell, and the in-plane unevenness of the compensation liquid crystal cell appears as display unevenness.
A highly accurate and highly uniform compensating liquid crystal cell is required, resulting in a decrease in cell yield and an increase in cost.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a twisted nematic alignment in which the twist angle is smaller than the twist angle of the nematic liquid crystal layer when no voltage is applied to the driving liquid crystal cell. By holding the optical compensation film holding the optically negative anisotropy film and the driving liquid crystal cell between the two polarizing plates, it has a wider viewing angle characteristic, An object of the present invention is to provide a normally black mode type twisted nematic liquid crystal display device which has a small left-right asymmetry during halftone display and can display high-quality images.

[0006]

SUMMARY OF THE INVENTION A normally black mode TN liquid crystal display device according to the present invention comprises a pair of transparent substrates provided with electrodes and a driving liquid crystal layer having a twisted nematic alignment when no voltage is applied. A liquid crystal cell, an optical compensation film holding a twisted nematic alignment, and a film showing optically negative anisotropy are sandwiched between two polarizing plates, and the optical compensation film is twisted. The absolute value of the angle is smaller than the absolute value of the twist angle of the nematic liquid crystal layer when no voltage is applied to the driving liquid crystal cell. In the normally black mode TN liquid crystal display element of the present invention, the product (Δnd) of the refractive index anisotropy Δn and the thickness d of the liquid crystal layer in the driving liquid crystal cell is in the range of 200 nm to 600 nm, The twist angle at the time of twist orientation is in the range of 80 ° to 100 °, and the product (Δn ₁ d ₁ ) of the refractive index anisotropy Δn ₁ and the thickness d ₁ of the optical compensation film is in the range of 150 to 600 nm. The absolute value of the twist angle of the optical compensation film is smaller than the absolute value of the twist angle of the nematic liquid crystal layer when no voltage is applied to the driving liquid crystal cell, and the difference is 15 degrees or more, and the optically negative The product of the birefringence Δn ₂ and the thickness d _{2 in} the film thickness direction of the film exhibiting anisotropy (Δn ₂ d ₂ ) is −20 to −3.
It is preferably in the range of 00 nm.

The present invention also provides an optical compensation film suitable for being incorporated in the above-mentioned normally black mode type TN liquid crystal display element, and one of the optical compensation films is optically positive. It is composed of a liquid crystal film in which a twisted nematic alignment formed by a thin film of uniaxial polymer liquid crystal in a liquid crystal state is glass-fixed by cooling the thin film. Another one of the optical compensation films according to the present invention is an optical compensation film in which a thin film of a photocurable low-molecular liquid crystal exhibiting optically positive uniaxiality is fixed in a liquid crystal state by a light irradiation on the thin film. Liquid crystal film.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The normally black mode type twisted nematic liquid crystal display device of the present invention (hereinafter referred to as NB-TN-LCD)
Abbreviated. 2) has a structure in which a driving liquid crystal cell, an optical compensation film, and a film having optically negative anisotropy are sandwiched between two polarizing plates. The driving liquid crystal cell is
Basically, a configuration is such that a nematic liquid crystal layer that forms a twisted alignment when no voltage is applied is provided between a pair of transparent substrates provided with electrodes. There is no particular limitation on the types of electrodes, transparent substrates, and nematic liquid crystals used in the liquid crystal cell as long as the liquid crystal cell has the basic configuration, and the method of manufacturing the liquid crystal cell is not particularly limited.

The driving method of the driving liquid crystal cell includes a simple matrix method and an active matrix method using an active element as an electrode. The latter method uses a TFT (Thi).
One that uses an nFilm Transistor electrode as an active element and another that uses an MIM (Metal Insulator)
Metal) electrode or TFD (Thin Film)
Although a (Diode) electrode can be subdivided into a device used for an active element, a driving liquid crystal cell of any driving method can be used for the liquid crystal display device of the present invention. However, the driving liquid crystal cell used in the present invention has a product (Δnd value) of the refractive index anisotropy Δn of the nematic liquid crystal layer and the thickness d of the nematic liquid crystal layer of the driving liquid crystal cell, usually 200 to 600 nm.
Preferably, it is in the range of 300 to 500 nm. When the Δnd value is larger than 600 nm, coloring may increase when combined with an optical compensation film described later. Further, when the Δnd value is smaller than 200 nm, there is a possibility that the front luminance and the contrast may be reduced when combined with the optical compensation film.

The twist angle of the nematic liquid crystal layer when no voltage is applied to the driving liquid crystal cell is usually 80 ° to 10 °.
It is desirably in the range of 0 °, preferably 85 ° to 95 °. If the twist angle is out of the above range, the optical rotation effect cannot be sufficiently obtained, and the display characteristics of the NB-TN-LCD may be significantly reduced. The twist direction of the twist angle may be either the left or right direction. In the liquid crystal display element of the present invention, it is preferable that the twist direction of the twist angle of the optical compensation film provided thereon and the twist angle of the nematic liquid crystal layer when no voltage is applied to the driving liquid crystal cell are opposite. . It is desirable that the absolute value of the twist angle of the optical compensation film is smaller than the absolute value of the twist angle of the nematic liquid crystal layer when no voltage is applied to the driving liquid crystal cell. However, when the absolute value of the twist angle of the optical compensation film is too small, the compensation effect of the film is reduced, and the contrast of a displayed image may be reduced. Further, even when the absolute value of the twist angle of the optical compensation film is set smaller than the absolute value of the twist angle of the nematic liquid crystal layer when no voltage is applied to the driving liquid crystal cell, when the difference between the two angles is small,
There is a possibility that a sufficient viewing angle expanding effect and an asymmetry reducing effect may not be obtained.

In view of the above, in order to realize a high contrast of a displayed image and a sufficient viewing angle enlarging effect and an asymmetry reducing effect, the absolute value of the twist angle of the compensation film is usually at least 5 degrees, preferably at least 5 degrees. Is desirably 10 degrees or more. The absolute value of the torsion angle of the compensation film is smaller than the absolute value of the torsion angle of the nematic liquid crystal layer when no voltage is applied to the driving liquid crystal cell, and the difference is usually 15 degrees or more, preferably 20 degrees or more. Desirably. In the optical compensation film of the present invention, the product of the refractive index anisotropy Δn ₁ of the film and the thickness d _{1 of} the film (Δn ₁ d ₁ ) is particularly limited as long as the effects of the present invention are not impaired. Although not necessarily, usually in the range of 200 nm to 700 nm, preferably 300 nm
It is desirably in the range of 〜600 nm. When the value of Δn ₁ d ₁ is smaller than 200 nm, the front luminance and contrast of the LCD may be reduced, and when it is larger than 700 nm, unnecessary coloring may be seen on the LCD.

The optical compensation film of the present invention can be prepared from a thin film of a polymer liquid crystal or a photocurable low-molecular liquid crystal having optically positive uniaxiality as a liquid crystal material. This liquid crystal material must contain a compound containing an optically active group so that twisted nematic alignment can be exhibited. Incidentally, if the high-molecular liquid crystal or the photo-curable low-molecular liquid crystal itself contains an optically active group, it is not necessary to separately add an optically active group-containing compound to the liquid crystal material. Is added to the liquid crystal material. In any case, the amount of the optically active group contained in the liquid crystal material is different depending on the kind of the polymer liquid crystal or the photocurable low-molecular liquid crystal actually used and the degree of the twist angle desired for the optical compensation film. Although it cannot be said, usually 0.01
To 50% by weight, preferably 0.05 to 40% by weight, more preferably 0.1 to 30% by weight, most preferably 0.1 to 30% by weight.
It is in the range of 2 to 20% by weight. If the content is out of the above range, the twist angle of the finally obtained optical compensation film may deviate from the desired range.

The type of the polymer liquid crystal used for the liquid crystal material is not limited as long as the desired twisted nematic alignment can be fixed, and either a main chain type or a side chain type polymer liquid crystal can be used. is there. Specifically, a main-chain type liquid crystal polymer such as polyester, polyamide, polycarbonate, or polyesterimide, or a side-chain type liquid crystal polymer such as polyacrylate, polymethacrylate, polymalonate, or polysiloxane can be used. Above all, it is desirable to employ a liquid crystalline polyester which has good orientation in forming twisted nematic orientation and is relatively easy to synthesize. Preferable examples of the constituent units of the polymer include an aromatic or aliphatic diol unit, an aromatic or aliphatic dicarboxylic acid unit, and an aromatic or aliphatic hydroxycarboxylic acid unit.

As the liquid crystal material, a photocurable low-molecular liquid crystal can also be used. For example, a biphenyl derivative, a phenylbenzoate derivative, a stilbene derivative or the like into which a functional group such as an acryloyl group, a vinyl group or an epoxy group has been introduced can be used. Any of photocurable low-molecular liquid crystals having a skeleton can be used.
These low-molecular liquid crystals may have either lyotropic properties or thermotropic properties, but those exhibiting thermotropic properties are more suitable from the viewpoint of workability, process and the like. In order to improve the heat resistance of the finally obtained optical compensation film, a cross-linking agent such as a bisazide compound or glycidyl methacrylate may be added to the above-mentioned liquid crystal material in a range that does not hinder the development of the twisted nematic phase. . By adding these crosslinking agents,
Liquid crystal molecules can be crosslinked in a state where a twisted nematic phase is developed. Furthermore, to the liquid crystal material, various additives such as a dichroic dye, a dye, a pigment, an antioxidant, an ultraviolet absorber, and a hard coat agent may be appropriately added as long as the effects of the present invention are not impaired. it can.

In the optical compensation film of the present invention, the above-mentioned liquid crystal material is formed into a thin film, and the thin film is subjected to a heat treatment to form a desired twisted nematic alignment.
It can be obtained by fixing the orientation state. In order to obtain a desired twisted nematic alignment, it is preferable to spread a thin film of a liquid crystal material on an alignment substrate having an alignment regulating force, specifically, to apply the liquid crystal material on the alignment substrate. Here, a method in which the upper and lower interfaces of the coating film of the film material are also sandwiched between the alignment substrates and aligned,
Also, a method of sandwiching a coating film of a film material between a non-alignment substrate having no alignment regulating force and one as an alignment substrate may be employed.

As the alignment substrate, it is desirable to use a material having anisotropy so that the director of the liquid crystal molecules at the substrate interface can be regulated, and glass or plastic can be used as the substrate material. If the substrate on which the liquid crystal material is applied cannot control the director of the liquid crystal molecules at all, there is a possibility that a desired twisted nematic alignment cannot be obtained. Illustrative orientation substrates that can be used for producing the optical compensation film include polyimide, polyamideimide, polyamide, polyetherimide, polyetheretherketone, polyetherketone, polyketonesulfide, polyethersulfone, polysulfone, polyphenylenesulfide, and polyphenyleneoxide. Plastic film substrates such as, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyacetal, polycarbonate, polyarylate, polyvinyl alcohol, polypropylene, cellulose-based plastics, acrylic resin, epoxy resin, phenolic resin, etc. A metal substrate made of aluminum, iron, copper, etc. Tsu DOO shape etched alkaline glass, borosilicate glass, may be mentioned glass substrates, such as flint glass.

A rubbing plastic film substrate obtained by subjecting the plastic film substrate to a rubbing treatment, or a plastic thin film subjected to a rubbing treatment, such as the above various substrates provided with a rubbing polyimide film, a rubbing polyvinyl alcohol film, etc .; A substrate provided with an obliquely deposited film can also be used. Among the various alignment substrates described above, the alignment substrates suitable for producing the optical compensation film of the present invention are listed, various substrates having a rubbing polyimide film, a rubbing polyimide substrate, a rubbing polyetheretherketone substrate, and a rubbing polyether. A ketone substrate, a rubbing polyethersulfone substrate, a rubbing polyphenylene sulfide substrate, a rubbing polyethylene terephthalate substrate, a rubbing polyethylene naphthalate substrate, a rubbing polyarylate substrate, and a rubbing cellulose-based plastic substrate can be exemplified.

The application of the liquid crystal material onto the alignment substrate can be performed in a state where the liquid crystal material is melted, but a solution application performed in a state where the liquid crystal material is dissolved in an appropriate solvent is preferable. The solvent for the liquid crystal material is selected according to the type of the liquid crystal material, and is generally selected from hydrocarbons such as toluene, xylene, butylbenzene, tetrahydronaphthalene, and decahydronaphthalene, ethylene glycol dimethyl ether,
Diethylene glycol dimethyl ether, propylene glycol dimethyl ether, ethers such as tetrahydrofuran, ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, butyl acetate, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, ethyl lactate, γ-butyrolactone, etc. Esters, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, etc., amides such as dichloromethane, carbon tetrachloride, tetrachloroethane, chlorobenzene, etc., butyl alcohol, triethylene glycol, diacetone alcohol And alcohols such as hexylene glycol. If necessary, two or more of these solvents can be used as a mixture.

The solution concentration of the liquid crystal material cannot be unconditionally determined because it varies depending on the solubility of the dissolved liquid crystal material, the thickness of the coating film, etc., but is usually 1 to 60% by weight, preferably 3 to 4% by weight.
0% by weight, more preferably 7-30% by weight. A surfactant or the like can be added to the solution of the liquid crystal material to facilitate application. Examples of surfactants that can be added include cationic surfactants such as imidazoline, quaternary ammonium salts, alkylamine oxides and polyamine derivatives, polyoxyethylene-polyoxypropylene condensates, primary and secondary surfactants. Grade alcohol ethoxylate, alkylphenol ethoxylate,
Polyethylene glycol and its esters, sodium lauryl sulfate, ammonium lauryl sulfate, lauryl sulfate amines, alkyl-substituted aromatic sulfonates, alkyl phosphates, anionic surfactants such as aliphatic or aromatic sulfonic acid formalin condensates, Amphoteric surfactants such as laurylamide propyl betaine and betaine laurylaminoacetate; nonionic surfactants such as polyethylene glycol fatty acid esters and polyoxyethylene alkylamine; perfluoroalkyl sulfonates and perfluoroalkyl carboxylate , Perfluoroalkylethylene oxide adduct, perfluoroalkyltrimethylammonium salt, perfluoroalkyl / hydrophilic group-containing oligomer, perfluoroalkyl / lipophilic group-containing oligomer, Such as fluoroalkyl group-containing fluorine surfactant such as urethane can be exemplified.

The amount of the surfactant to be added depends on the type of the surfactant, the solvent, and the orientation substrate to be coated.
10 ppm to 10% by weight of the liquid crystal material,
Preferably 50 ppm to 5%, more preferably 0.0 ppm
It is in the range of 1% to 1%. To apply a liquid crystal material solution,
For example, roll coating, die coating, bar coating, gravure roll coating, spray coating, dip coating, spin coating, and the like can be employed.

The coating film of the solution of the liquid crystal material formed on the alignment substrate is then dried to remove the solvent from the coating film. The degree of solvent removal is not particularly limited, as long as the solvent can be substantially removed and the coating film does not flow or even falls off. Usually, the solvent can be removed by drying at room temperature, drying in a drying oven, or blowing hot or hot air. The coating film from which the solvent has been removed is subjected to a heat treatment at a temperature at which liquid crystal molecules in the coating film exhibit a twisted nematic phase for a predetermined time to complete twisted nematic alignment in the coating film. Normally, the twist angle in twisted nematic alignment can be adjusted by the concentration of the optically active group contained in the liquid crystal material as described above, but depending on the type of liquid crystal material such as a polymer liquid crystal or a photocurable low-molecular liquid crystal. The twist angle in twisted nematic orientation may vary depending on the heat treatment conditions and the like.
When such a liquid crystal material is used, a method of appropriately controlling the heat treatment conditions in order to obtain a desired twist angle can be employed in the present invention. For example, in order to obtain a twisted nematic alignment with a desired twist angle, heat treatment at a relatively low temperature is required, but at a low temperature, the viscosity of the liquid crystal material is high, and it takes a long time to achieve the desired alignment. May require. In such a case, a method is effective in which a heat treatment is once performed at a high temperature to obtain a monodomain orientation, and then gradually cooled stepwise or continuously to a temperature at which a twisted nematic orientation having a desired twist angle is formed. is there.

As described above, in order to obtain the optical compensation film of the present invention, it is necessary to determine heat treatment conditions according to the characteristics of the liquid crystal material used. Usually, the heat treatment temperature is 40 to 300 ° C, preferably 50 to 280 ° C, more preferably 60 to 260 ° C, and most preferably 70 to 25 ° C.
The temperature range is 0 ° C., and the heat treatment time is usually 5
The range of seconds to 2 hours, preferably 10 seconds to 1 hour, and more preferably 20 seconds to 30 minutes is employed, but these are only examples and do not limit the present invention at all. In the heat treatment of the coating film, a magnetic field or an electric field can be used. The twisted nematic alignment formed on the coating film on the alignment substrate by the above heat treatment is fixed by an appropriate method. For example, when the liquid crystal material forming the coating film is a polymer liquid crystal, the coating film in which the twisted nematic alignment is formed by the heat treatment is rapidly cooled in that state to fix the alignment to glass. When the liquid crystal material forming the coating film is a photocurable low-molecular liquid crystal, the coating film forming the twisted nematic alignment is irradiated with light, heat, an electron beam, or the like in that state. Then, the orientation is fixed.

A coating film in which a twisted nematic alignment is formed and fixed on an alignment substrate, that is, a liquid crystal film having a stable twisted nematic alignment is used as an optical compensation film with an alignment substrate. Can be. When the alignment substrate is not optically isotropic or is opaque in the visible light wavelength region, only the liquid crystal film holding the twisted nematic alignment is optically substantially transparent and isotropic. Or a substrate (hereinafter, referred to as a second substrate film), and can be used as an optical compensation film together with the second substrate film. At the time of transfer, for example, a method is generally adopted in which an adhesive is applied to a liquid crystal film on an alignment substrate, a second substrate film is laminated thereon, the adhesive is cured, and the alignment substrate is separated from the liquid crystal film. You.

Examples of the second substrate film include triacetyl cellulose films such as Fujitac (manufactured by Fuji Photo Film Co., Ltd.) and Konikatac (manufactured by Konica Corporation), and TP.
X film (manufactured by Mitsui Chemicals, Inc.), Arton film (manufactured by Nippon Synthetic Rubber Co., Ltd.), ZEONEX film (manufactured by Nippon Zeon), acrylene film (manufactured by Mitsubishi Rayon Co., Ltd.) and the like can be used. Also, the liquid crystal film on the alignment substrate is
It can also be directly transferred to an appropriate glass substrate, for example, a glass substrate used for a driving liquid crystal cell. Further, transfer to a film exhibiting optically negative anisotropy described later is also possible. When a substantially transparent and isotropic film or substrate is used as the alignment substrate, the above-described transfer operation is not necessarily required, but the optical characteristics required for the optical compensation film or the reliability of the film are required. The transfer can be appropriately performed in consideration of the above. However, if the liquid crystal film itself has sufficient self-supporting properties,
The liquid crystal film can be used alone as an optical compensation film by peeling off the alignment substrate.

The film having an optically negative anisotropy used in the present invention has no special requirements other than exhibiting an optically negative anisotropy. Therefore, any film having birefringence (△ n ₂ ) in the film thickness direction, such as a negative uniaxial film, a negative biaxial film, etc., can be used. Specific examples thereof include polyimide, polyamide imide, polyamide, polyether imide, polyether ether ketone, polyether ketone, polyketone sulfide,
Polyethersulfone, polysulfone, polyphenylene sulfide, polyphenylene oxide, polyethylene terephthalate, polybutylene terephthalate,
Disc-like compounds such as plastic films made of polyethylene naphthalate, polyacetal, polycarbonate, polyarylate, polyvinyl alcohol, polypropylene, cellulose, triacetyl cellulose and their partially saponified products, acrylic resins, epoxy resins, phenolic resins, etc., and discotic liquid crystals And the like. The film having an optically negative anisotropy used in the present invention is a product of the birefringence Δn ₂ and the thickness d _{2 in} the film thickness direction, that is, the value of Δn ₂ d ₂ is usually −20 to −20. In the range of -300 nm, preferably -30 to-
It is desirable to be in the range of 250 nm.

In the NB-TN-LCD of the present invention, the above-mentioned optical compensation film and an optically anisotropic film are sandwiched between two polarizing plates together with a driving liquid crystal cell. These two types of films are provided between the viewing-side polarizing plate and the driving liquid crystal cell. The optical compensation film and the film having optically negative anisotropy do not necessarily have to be laminated. When both are not laminated, a film exhibiting optically negative anisotropy may be placed between the driving liquid crystal cell and the viewing-side polarizing plate, or between the driving liquid crystal cell and the light source-side polarizing plate. No problem. However, the optical compensation film is always provided between the driving liquid crystal cell and the viewing-side polarizing plate.

When the optical compensatory film and the film exhibiting optically negative anisotropy are laminated and used, they are disposed between the driving liquid crystal cell and the polarizing plate on the viewing side. It does not matter whether or not faces the viewing side polarizing plate. However, in any case, in the NB-TN-LCD of the present invention, the rubbing direction of the interface of the transparent substrate (viewing side) in contact with the liquid crystal layer of the driving liquid crystal cell,
The angle formed by the slow axis of the liquid crystal molecules on the surface of the optical compensation film (liquid crystal layer) in contact with the driving liquid crystal cell is usually 70 to 11
0 °, preferably 75-105 °, more preferably 8
The optical compensation film is installed so that the angle is in the range of 0 to 100 °, or the angle is usually −20 to 20 °.
゜, preferably -15 to 15 ゜, more preferably -1
It is desirable to provide the optical compensation film so as to be in the range of 0 to 10 °.

The polarizing plate on the viewing side and the polarizing plate on the light source side in the NB-TN-LCD of the present invention are polarizing plates usually used in the field, and are not particularly limited.
For example, a uniaxially stretched polyvinyl alcohol film, a halogen polarizing film in which iodine molecules having a high degree of polarization are arranged in a fixed direction, or a polarizing plate of a type in which a polyvinyl alcohol film or the like directly dyed with a dye is sandwiched between other supporting films. Can be used.

In the NB-TN-LCD according to the present invention, the polarizing plates are disposed above and below the driving liquid crystal cell. Specifically, it can be provided directly on one surface of the liquid crystal cell, or can be provided via another component such as an optical compensation film. The axial arrangement of the polarizing plate is
There is no particular limitation, and any shaft arrangement may be used as long as the effects of the present invention are not impaired.
Although the NB-TN-LCD of the present invention exerts its function simply by stacking two polarizing plates, a driving liquid crystal cell, and an optical compensation film so as to satisfy the above-described arrangement condition, The components may be bonded together with an adhesive or an adhesive if necessary. In addition, N of the present invention
The B-TN-LCD may include other components as necessary in addition to the driving liquid crystal cell, the upper and lower two polarizing plates, and the optical compensation film provided as essential components. Specifically, a retardation film, a light diffusion layer, and the like can be provided to improve the characteristics. Examples of the retardation film generally include polycarbonate and polymethacrylate, and are not particularly limited as long as they exhibit optical anisotropy. The light diffusion layer is not particularly limited as long as it has a property of diffusing incident light isotropically or anisotropically. Furthermore, by having a color filter,
An NB-TN-LCD that can perform multicolor or full-color display with high color purity can be provided.

[0030]

According to the present invention, the twisted nematic alignment is maintained,
An optical compensatory film whose twist angle is smaller than the twist angle of the nematic liquid crystal layer when no voltage is applied to the driving liquid crystal cell is typically used together with a film exhibiting optically negative anisotropy together with the driving liquid crystal. The normally black mode TN liquid crystal display device of the present invention disposed between the cell and the polarizing plate on the viewing side has a wide viewing angle characteristic and a small left-right asymmetry during halftone display, so that a high-quality image is obtained. Enable display.

[0031]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Reference Example 1 (Production of Optical Compensation Film 1) Under a nitrogen atmosphere using 50 mmol of terephthalic acid, 50 mmol of 2,6-naphthalenedicarboxylic acid, 40 mmol of methylhydroquinone diacetate, 62 mmol of catechol diacetate and 60 mg of N-methylimidazole, Polymerization was performed at 270 ° C. for 12 hours. Next, the obtained reaction product was dissolved in tetrachloroethane, and then purified by reprecipitation with methanol.
4.7 g were obtained (Polymer A). This liquid crystalline polyester had a logarithmic viscosity of 0.17, a nematic phase as a liquid crystal phase, an isotropic-liquid crystal phase transition temperature of 250 ° C. or higher, and a glass transition point of 115 ° C. In addition, biphenyl dicarbonyl chloride 90 mmol, terephthaloyl chloride 1
0 mmol, 2R, 3R-dimethoxybutanediol 1
05 mmol was reacted in dichloromethane at room temperature for 20 hours, and the reaction solution was poured into methanol and reprecipitated to obtain 12.3 g of a liquid crystalline polyester (polymer B). Polymer B had a logarithmic viscosity of 0.11, exhibited a chiral smectic phase at room temperature, and had an isotropic transition temperature between 40 and 50 ° C. Further, Tg was considered to be around room temperature, and could not be observed by measurement by DSC.

A solution was prepared by dissolving 9.81 g of the polymer A prepared above and 0.19 g of the polymer B in 40 g of a phenol / tetrachloroethane mixed solvent (6/4 weight ratio). This solution was applied to a polyimide substrate (Kapton, trade name, manufactured by DuPont) rubbed with rayon cloth by a bar coating method, dried, and dried.
After heat treatment at 30 ° C. for 30 minutes, the mixture was cooled and fixed at room temperature to obtain a uniformly oriented liquid crystal film having an average actual film thickness of 2.34 μm on a polyimide substrate (sample A). The actual thickness of the liquid crystal film was measured using a stylus type thickness gauge. Next, on the prism surface of Abbe refractometer (Type-4 manufactured by Atago Co., Ltd.),
When the refractive index of the liquid crystal film was measured by placing the sample A so that the polyimide substrate surface was in contact with the sample, the liquid crystal film was found to have refractive index anisotropy, and the refractive index in the direction perpendicular to the rubbing direction of the polyimide substrate was 1 .55, the refractive index in the parallel direction was 1.75, and the refractive index in the film thickness direction was constant at 1.55. From this, in the liquid crystal film, on the polyimide substrate interface side, rod-like liquid crystal molecules are plane-oriented parallel to the substrate and the rubbing direction,
It was found that no and ne of the liquid crystal were 1.55 and 1.75, respectively.

When the liquid crystal film surface of the sample A was arranged so that the liquid crystal film surface of the sample A was in contact with the prism surface of the refractometer, and the refractive index of the liquid crystal film was measured in the same manner as above, the refractive index was 45 degrees from the rubbing direction of the substrate. Was 1.55 and the refractive index in the -45 degree direction was 1.75, and the refractive index in the film thickness direction was constant at 1.55. From this, the liquid crystal film of Sample A has a liquid crystal molecule that is largely homogeneously aligned at both the substrate interface and the air interface, and at the substrate interface side and the air interface side, rod-like liquid crystal molecules are twisted at approximately −45 degrees at both interfaces. I was able to confirm that I was there. Since Sample A contains an opaque and optically anisotropic polyimide substrate, a UV-curable adhesive (UV-340
0, manufactured by Toagosei Co., Ltd.) to a thickness of about 5 μm, and a white plate glass substrate (thickness: 1.1 mm) manufactured by Corning Co., Ltd. was laminated thereon as a transfer substrate.
The adhesive was cured by V irradiation, and then the polyimide substrate was peeled off to obtain an optical compensation film with a white glass substrate. Δn ₁ d ₁ of this optical compensation film,
When the twist angle (right twist) was measured, Δn ₁ d ₁ = 4
It was confirmed that 30 nm and the twist angle = -45 °.

Reference Example 2 An optical compensation element comprising an optical compensation film / TAC film in the same manner as in Reference Example 1 except that a triacetyl cellulose (TAC) film having Δn ₂ d ₂ of -150 nm was used as a transfer substrate. I got

[0036]Example 1 ZLI-4792 manufactured by Merck as the liquid crystal material of the driving liquid crystal cell
Cell gap 4.8 μm, Δnd = 470 nm,
TN with 90 ° twist angle (left twist) and 2 ° pretilt angle
A cell was prepared. The optical compensation film obtained in Reference Example 1 was placed in the cell.
Film and △ n _Twod_TwoTAC fill with -150 nm
The system was arranged as shown in FIG. 300H for liquid crystal cell
A rectangular wave of z is applied, black display is set to 0V, and white display is set to 6V.
The drive voltage is set so that the transmittance at the front is divided into eight equal parts.
Specified. Liquid crystal using Topcon's color luminance meter BM-5
The viewing angle of the transmittance of the cell is measured, and the gradation of the liquid crystal cell is measured.
The viewing angle dependence of the characteristics was determined. The results are shown in FIG.

Example 2 The optical compensator obtained in Reference Example 2 was used as an optical compensator in FIG.
In the same manner as in Example 1, the viewing angle dependency of the isocontrast curve and the gradation characteristic was determined. Fig. 4 shows the results.
It was shown to.

Comparative Example 1 A TN cell similar to that of Example 1 was prepared except that a TAC film having Δn ₂ d ₂ of −150 nm was not provided, and the TN cell was arranged as shown in FIG. First, the viewing angle dependence of the gradation characteristics was determined. The results are shown in FIG.

Comparative Example 2 A TN cell similar to that of Example 1 was used except that two TAC films having Δn ₂ d ₂ of −200 nm were used instead of the TAC film having Δn ₂ d ₂ of −150 nm. Then, with the arrangement shown in FIG. 7, the viewing angle dependence of the gradation characteristics was obtained in the same manner as in Example 1. The results are shown in FIG.

Each of the TN cells in the above-described embodiment and the comparative example was compared with each other in terms of left-right asymmetry during halftone display. Table 1 shows the results. It can be seen that the TN cell of the example can reduce left-right asymmetry during halftone display without impairing contrast characteristics, as compared with the comparative example.

[0041]

[Table 1] Degree of asymmetry: 10 · ln [Transmittance (-40 °) / Transmittance (+ 40 °)]

[Brief description of the drawings]

FIG. 1 is a layout diagram of a polarizing plate, an optical compensation film, and a film exhibiting optically negative anisotropy in a TN cell of Example 1.

FIG. 2 is a graph showing the relationship between the gradation and the viewing angle of the TN cell according to the first embodiment.

FIG. 3 is a layout diagram of a polarizing plate, an optical compensation film, and a film having optically negative anisotropy in the TN cell of Example 2.

FIG. 4 is a graph showing the relationship between the gradation and the viewing angle of the TN cell of Example 2.

FIG. 5 is a layout view of a polarizing plate, an optical compensation film, and an optically negative anisotropic film in the TN cell of Comparative Example 1.

FIG. 6 is a graph showing the relationship between the gradation and the viewing angle of the TN cell of Comparative Example 1.

FIG. 7 is a layout diagram of a polarizing plate, an optical compensation film, and a film having optically negative anisotropy in the TN cell of Comparative Example 2.

FIG. 8 is a graph showing the relationship between the gradation and the viewing angle of the TN cell of Comparative Example 2.

[Explanation of symbols]

 1, 1 ': polarizing plate 2: driving liquid crystal cell 3, 3': optical compensation film (element) 4, 4 ': film showing optically negative anisotropy

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA06 BA42 BB03 BB42 BB44 BB49 BC04 BC05 BC22 2H089 HA24 HA25 HA30 QA16 RA05 SA04 SA07 TA14 TA15 2H091 FA08X FA08Z FA11X FA11Z FB04 FC08 FC22 FD06 FD08 FD10 HA07

Claims (4)

[Claims] 1. A driving liquid crystal cell having a liquid crystal layer having a twisted nematic alignment between a pair of transparent substrates provided with electrodes when no voltage is applied, an optical compensation film having a twisted nematic alignment, and an optically negative film. In a liquid crystal display device in which a film exhibiting anisotropy is sandwiched between two polarizing plates, the twist angle of the optical compensation film is calculated from the twist angle of the nematic liquid crystal layer when no voltage is applied to the driving liquid crystal cell. A normally black mode type TN liquid crystal display element characterized by being small. 2. The product (Δnd) of the refractive index anisotropy Δn and the thickness d of the liquid crystal layer in the driving liquid crystal cell is 200 nm.
In the range of ～600Nm, located in helix angle is 80 ° to 100 ° range in the twisted orientation, the product of the refractive index anisotropy △ n ₁ and the thickness d ₁ of the optical compensation film (△ n ₁ d ₁ ) Is 1
In the range of 50 to 600 nm, the absolute value of the twist angle of the optical compensation film is smaller than the absolute value of the twist angle of the nematic liquid crystal layer when no voltage is applied to the driving liquid crystal cell,
The difference is 15 degrees or more, and the product of the birefringence △ n ₂ and the thickness d _{2 in the} film thickness direction of the film exhibiting optically negative anisotropy (△
n ₂ d ₂₎ is according to claim 1 normally black mode type, wherein the range of -20 to-300 nm T
N liquid crystal display element. 3. A liquid crystal film obtained by fixing a twisted nematic alignment formed by a thin film of a polymer liquid crystal having optically positive uniaxiality in a liquid crystal state by cooling the thin film, and using the liquid crystal film as the optical compensation film. The normally black mode type TN liquid crystal display device according to claim 1 or 2, wherein: 4. An optical compensation film comprising: a liquid crystal film in which a twisted nematic alignment formed by a photocurable low-molecular liquid crystal thin film exhibiting optically positive uniaxiality in a liquid crystal state is fixed by irradiating the thin film with light. 3. The normally black mode TN liquid crystal display device according to claim 1, wherein the TN liquid crystal display device is used as the optical compensation film.