JP2001042122A - Optical compensation element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease asymmetric properties when a medium tone is displayed to realize high-quality image display by constituting a photosetting type low mol.wt. liquid crystal showing optically positive uniaxial properties of a low mol.wt. liquid crystal film produced by fixing the twisted nematic alignment formed in the liquid crystal state by a photosetting reaction and a film showing optically negative anisotropy. SOLUTION: The element consists of the combination of a low mol.wt. liquid crystal film in which the twisted nematic alignment is stably maintained and a film showing optically negative anisotropy. The low mol.wt. liquid crystal film is prepared from a liquid crystal material essentially consisting of a low mol.wt. liquid crystal showing optically positive uniaxial properties. As for the photosetting type low mol.wt. liquid crystal showing optically positive uniaxial properties, a liquid crystal having biphenyl derivatives, phenylbenzoate derivatives, stilbene derivatives or the like as the basic structure can be used. As for the low mol.wt. liquid crystal, a liquid crystal showing thermotropic properties is preferable from the viewpoint of the film forming process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical compensator capable of improving the display contrast, gradation characteristics and viewing angle characteristics of display colors of a normally black mode type liquid crystal display device, and an optical compensator comprising the same. And a normally black mode type twisted nematic liquid crystal display device.

[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 (NB) mode TN-LC in which black display is performed when no voltage is applied, and the liquid crystal alignment state in the cell during black display forms a twisted structure.
D (hereinafter abbreviated as NB-TN-LCD) is a normally white TN-LCD (hereinafter abbreviated as N) that displays white when no voltage is applied because the optical anisotropy is averaged.
Abbreviated as W-TN-LCD. ), The viewing angle characteristics are better. However, the 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. Since the contrast is reduced, there remains a problem that color compensation, which cannot be a problem in the NW-TN-LCD, must be performed. Various color compensation methods have been recently reported to solve this problem. For example, each color (R,
Method for setting the cell gap to the optimum value for each pixel of G, B) (multi-gap method: Hatta et al., SID 1986 Dige)
st, p296), a method of performing color compensation using a plurality of stretched films (Sergan et al., Jpn. J. Appl. Phys., 37 (3
A), p889), Method of performing color compensation in a compensating liquid crystal cell (Yoshida et al., Proceedings of the 16th Symposium on Liquid Crystals (1990), 2L307, p22)
2) etc. 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, and as a result, the yield of the cell and the cost are increased. Also, in the method of performing color compensation using a plurality of stretched films, it is necessary to use four or more films 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. Further, since the display characteristics change due to the dispersion of the compensating liquid crystal cells between the panels, and the in-plane unevenness of the compensating liquid crystal cells appears as display unevenness, a highly accurate and highly uniform compensating liquid crystal cell is required. This causes a reduction in cell yield and an increase in cost.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is intended to provide a low-molecular liquid crystal film having a twisted nematic alignment and a film having an optically negative anisotropy. Along with providing an optical compensatory element composed of a combination and disposing the element between a driving liquid crystal cell and a polarizing plate, without deteriorating contrast characteristics, reducing left-right asymmetry during halftone display, and Provided is a normally black mode type twisted nematic liquid crystal display device capable of high-quality image display.

[0004]

That is, the first aspect of the present invention is as follows.
Is a low-molecular liquid crystal film in which a twisted nematic alignment formed by a photocurable low-molecular liquid crystal exhibiting optically positive uniaxiality in a liquid crystal state is fixed by a photocuring reaction,
The present invention relates to an optical compensatory element comprising a combination with a film having optically negative anisotropy. The second aspect of the present invention relates to a normally black mode twisted nematic liquid crystal display device provided with a driving liquid crystal cell and the above-described optical compensation element between two polarizing plates. A third aspect of the present invention is that the product (Δnd value) of the refractive index anisotropy Δn of the liquid crystal layer in the driving liquid crystal cell and the thickness d of the liquid crystal layer is 200 nm to 600 nm.
nm, the twist angle of the liquid crystal layer at the time of twist alignment is in the range of 80 ° to 100 °, and the refractive index anisotropy Δn1 of the low molecular liquid crystal film constituting the optical compensator and the thickness of the film. The product with d1 (ｄn1d1 value) is 150-
In the range of 600 nm, and the twist angle of the twisted nematic orientation held by the film is 80 ° to 10 °.
0 ° range, the twist direction of which is opposite to the twist alignment direction of the nematic liquid crystal in the driving liquid crystal cell, and the film thickness of the optically negative anisotropic film constituting the optical compensation element. The product of the birefringence Δn2 in the direction and the thickness d2 of the film (Δn2d2 value) is −20 to −300 n
m, the normally black mode type twisted nematic liquid crystal display device. Here, the refractive index anisotropy Δn1 of the low molecular liquid crystal film means the refractive index anisotropy of the liquid crystal material forming the film.
The thickness of the low-molecular liquid crystal film means a net thickness, and does not include the thickness of the supporting substrate when the film is supported by a supporting substrate or the like.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The optical compensation element of the present invention is a low-molecular liquid crystal film in which twisted nematic alignment is stably held,
It consists of a combination with a film exhibiting optically negative anisotropy. The low-molecular liquid crystal film can be prepared from a liquid crystal material mainly composed of low-molecular liquid crystal exhibiting optically positive uniaxiality. . Examples of the photocurable low-molecular liquid crystal exhibiting optically positive uniaxiality include those having a basic skeleton of a biphenyl derivative, a phenylbenzoate derivative, a stilbene derivative, or the like. Either lyotropic or thermotropic liquid crystal may be used as the low-molecular liquid crystal, but a liquid crystal exhibiting thermotropic property is more preferable in terms of a film forming process. Photocurable low-molecular liquid crystal, which is the main component of the liquid crystal material,
After the desired twisted nematic orientation, to fix the orientation by a photocuring reaction, a photopolymerizable group that can be polymerized and cured by light irradiation, for example, an acrylic group, a methacryl group, a vinyl group, an allyl group, Epoxy group,
It is essential to have a phthalimide group, a cinnamoyl group and the like. If the low-molecular liquid crystal itself does not have photopolymerizability, it is mixed with a photopolymerizable non-liquid crystal substance. Therefore, whether or not the low-molecular liquid crystal has a photopolymerizable group is not particularly limited, and it is sufficient that the entire liquid crystal material forming the film has photocurability.
When a low-molecular liquid crystal having a photopolymerizable group is used as a main component of the liquid crystal material, and when a non-photopolymerizable low-molecular liquid crystal and a non-liquid crystal substance having a photopolymerizable group are mixed as the main components of the liquid crystal material, the liquid crystal material is used. The amount of the photopolymerizable group relative to the entire low-molecular liquid crystal in the photopolymerizable group is usually 0.005 to 0.005
The amount is 20 mmol, preferably 0.01 to 5 mmol, and more preferably 0.1 to 3 mmol. 0.005m
If the amount is less than mol, the photocuring reaction after twisted nematic alignment may not be sufficiently performed, and thus it may not be possible to fix the film. If the amount is more than 20 mmol, the storage stability of the liquid crystal material or the liquid crystal material solution may be poor. It is essential that the above-mentioned liquid crystal material contains a substance having an optically active group in order to induce twisted nematic alignment. The substance having an optically active group may itself exhibit liquid crystallinity, and may not exhibit liquid crystallinity, but may exhibit liquid crystallinity by being added to a low-molecular liquid crystal to form a composition. Materials that can be used can also be used. Therefore, any material can be used as long as it exhibits desired liquid crystallinity without causing phase separation or the like when formed into a film material. The ratio of the number of moles of the optically active group to the total number of moles of the low-molecular liquid crystal as the main component of the liquid crystal material of the substance having the optically active group is usually 0.01 to 40%, preferably 0.1 to 30%.
%, More preferably 0.2 to 20%, most preferably 0.4 to 10%. When the amount is less than 0.01%, sufficient twisting cannot be given to the nematic liquid crystal. When the amount is more than 40%, the property of inducing twisting is so strong that it may be difficult to obtain a desired twisting angle. is there. Further, a photoreaction initiator can be added to the liquid crystal material used in the present invention. The addition amount of the photoreaction initiator is 0.01 to 20% by weight, preferably 0.1 to 10% by weight, more preferably 0.5 to 5% by weight based on the total weight of the low-molecular liquid crystal which is the main component of the liquid crystal material. Add by weight. Specific examples of the photoreaction initiator include various derivatives such as benzyl, benzoin ether, Michler's ketone, anthraquinone, acetophenone, benzophenone, biimidazole, triazine, thioxanthone, and acylphosphine oxide, and diaryliodonium salts, triarylsulfonium salts, and sulfonic acid esters. And the like.
These photoreaction initiators can be used alone or in combination of two or more. In addition to the photoreaction initiator, a sensitizer can be further added as long as the effect of the present invention is not impaired. In the present invention, EB (electron beam) is used without using any of these photoreaction initiators.
Irradiates the desired twisted nematic alignment. Further, in order to improve the heat resistance of the obtained low-molecular liquid crystal film, a cross-linking agent such as a bisazide compound or glycidyl methacrylate in a range that does not hinder the development of a twisted nematic phase in addition to the low-molecular liquid crystal in the liquid crystal material. It can be added as appropriate. Further, various additives such as a dichroic dye, a dye, a pigment, an antioxidant, an ultraviolet absorber, and a hard coat agent can be appropriately added to the liquid crystal material as long as the effects of the present invention are not impaired.

The low-molecular liquid crystal film of the present invention is formed by subjecting a thin film obtained from the above liquid crystal material to heat treatment to form a desired twisted nematic alignment, and then cross-linking the liquid crystal molecules in the thin film. It can be obtained by fixing the orientation. Here, in order to obtain a desired twisted nematic alignment, it is desirable to form a thin film of a liquid crystal material on an alignment substrate at least one of which has an alignment regulating force. As a specific mode, for example, there is a method of forming a coating film of a liquid crystal material on one alignment substrate. A method of obtaining a thin layer of a liquid crystal material between two alignment substrates, or obtaining a thin layer of a liquid crystal material between substrates in which one is an alignment substrate and the other is a non-alignment substrate having no alignment regulating force. Yes, but with little process benefit. It is desirable that the alignment substrate used to obtain the liquid crystal material coating film has anisotropy so that the director at the substrate interface of the liquid crystal molecules can be defined. If it cannot be specified, the desired twisted nematic orientation may not be obtained. Examples of usable orientation substrates include polyimide, polyamide imide, polyamide, polyether imide, polyether ether ketone, polyether ketone, polyketone sulfide, polyether sulfone, polysulfone, polyphenylene sulfide, polyphenylene oxide, polyethylene terephthalate, and polybutylene. Terephthalate, polyethylene naphthalate, polyacetal, polycarbonate, polyarylate, acrylic resin, polyvinyl alcohol,
Plastic substrates such as polypropylene, cellulosic plastics, epoxy resin and phenolic resin, uniaxially stretched films of the above plastics, metal substrates such as aluminum, iron and copper with slit grooves on the surface, and etching the surface into slits Glass substrates such as alkali glass, borosilicate glass, and flint glass. In addition, a rubbing plastic substrate obtained by subjecting the above plastic film substrate to a rubbing treatment, a plastic film subjected to a rubbing treatment, for example, a rubbing polyimide film, various substrates in which a rubbing polyvinyl alcohol film or the like is laminated, and further, oblique vapor deposition of silicon oxide Various substrates provided with a film can also be used as the alignment substrate. Among the above various alignment substrates and various alignment films, optically sufficient transparency and isotropic properties, and after fixing the twisted nematic alignment, it is used as a low-molecular liquid crystal film without peeling off from the alignment substrate. Triacetylcellulose films are particularly desirable because they can be used. The triacetyl cellulose film can be used as an alignment substrate without any surface treatment or the like, and the film subjected to a surface treatment such as saponification treatment, corona discharge treatment, or UV-ozone treatment is used as the alignment substrate. Can also. Further, the triacetyl cellulose film itself has a high orientation ability, and thus does not particularly require an orientation treatment or the like. Further, in order to enhance the orientation ability, for example, a triacetyl cellulose film having a rubbing treatment or the like directly applied to the film surface can be used as the orientation substrate. Further, an alignment film such as polyimide or polyvinyl alcohol may be formed on the triacetyl cellulose film to form an alignment substrate. When the alignment film is formed on a triacetyl cellulose film, the mechanical strength related to the adhesion between the film and the alignment film may be a problem. In such a case, the problem can be solved by means such as providing an easily adhesive layer such as a gelatin layer between the triacetyl cellulose film and the alignment film.

The preparation of a coating film of a liquid crystal material is performed by applying a liquid solution of the liquid crystal material, preferably a solution of the liquid crystal material, to the surface of the alignment substrate. The solvent of the liquid crystal material varies depending on the type of liquid crystal material to be dissolved therein, but is usually a hydrocarbon such as toluene, xylene, butylbenzene, tetrahydronaphthalene, 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 and cyclohexanone, ethyl acetate, butyl acetate, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, ethyl lactate, γ-
Ester such as butyrolactone, amide such as N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, halogenated hydrocarbon such as dichloromethane, carbon tetrachloride, tetrachloroethane, chlorobenzene, butyl alcohol, triethylene glycol, diethylene glycol Alcohols such as acetone alcohol and hexylene glycol can be used. If necessary, two or more of these solvents can be used as a mixture. The concentration of the prepared solution depends on the molecular weight of the solute, such as low-molecular liquid crystal,
Since it depends on the solubility and the thickness of the optical compensation film (low-molecular liquid crystal film) to be produced, it cannot be said unconditionally, but it is usually 1 to 60% by weight, preferably 3 to 40% by weight.
%, More preferably 7 to 30% by weight. A surfactant or the like may be added to the solution of the liquid crystal material in order to facilitate application. Examples of the surfactant include cationic surfactants such as imidazoline, quaternary ammonium salts, alkylamine oxides, and polyamine derivatives; polyoxyethylene-polyoxypropylene condensates; primary and secondary alcohol ethoxy; , Alkylphenol ethoxylate, polyethylene glycol and its esters, sodium lauryl sulfate, ammonium lauryl sulfate, lauryl sulfate amines, alkyl-substituted aromatic sulfonates, alkyl phosphates, condensates of aliphatic or aromatic sulfonic acid formalin, etc. Ionic surfactants, amphoteric surfactants such as laurylamidopropylbetaine, laurylaminoacetate betaine, and nonionic surfactants such as polyethylene glycol fatty acid esters and polyoxyethylene alkylamine Agents, perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl ethylene oxide adducts,
Fluorinated surfactants such as perfluoroalkyltrimethylammonium salt, perfluoroalkyl group-containing hydrophilic group-containing oligomer, perfluoroalkyl group-containing lipophilic group-containing oligomer, and perfluoroalkyl group-containing urethane can be used. The amount of the surfactant to be added depends on the type of the surfactant, the solvent, and the orientation substrate to be applied, but is usually 10 pp in terms of the weight of the liquid crystal material.
m to 10%, preferably 50 ppm to 5%, more preferably 0.01% to 1%. For applying the liquid crystal material solution to the alignment substrate, for example, a roll coating method, a die coating method, a bar coating method, a gravure roll coating method, a spray coating method, a dip coating method, a spin coating method, or the like can be employed. After coating, remove the solvent,
The conditions for removing the solvent are not particularly limited, and it is sufficient that the solvent can be substantially removed and the coating film does not flow or even run off. Usually, the solvent can be removed by drying at room temperature, drying in a drying oven, or blowing hot or hot air.

[0008] The solvent-removed coating film is subjected to necessary heat treatment to complete twisted nematic alignment. As one method of the heat treatment, there is a method of forming a twisted nematic alignment by temporarily bringing the liquid crystal phase into an isotropic liquid state higher than the temperature range exhibiting a liquid crystal phase, and then lowering the temperature to a temperature range exhibiting a liquid crystal phase. . Alternatively, twisted nematic alignment can be formed by appropriately changing the temperature within a temperature range exhibiting a liquid crystal phase. Specifically, within the temperature range exhibiting the same nematic phase, after heat-treating at a high temperature and largely aligning the liquid crystal, a method of lowering the temperature to increase the degree of order of the liquid crystal alignment, or heat-treating at a temperature exhibiting an isotropic phase In the present invention, a method of lowering the temperature later and orienting in a nematic phase can be employed. As described above, in order to obtain the low-molecular liquid crystal film of the present invention, it is necessary to determine the heat treatment conditions according to the characteristics of the film material used, and usually 40 to 220 ° C., preferably 50 to 180 ° C., and more preferably 60 to 180 ° C. ~ 16
In the range of 0 ° C. and the heat treatment time, it is usually 5 seconds to 2 hours, preferably 10 seconds to 40 minutes, more preferably 20 seconds.
The heat treatment conditions are determined in the range of seconds to 20 minutes. In addition, depending on the type of low-molecular liquid crystal that is a main component of the liquid crystal material, without performing the heat treatment as described above, the liquid crystal material solution is lyotropically aligned at a temperature at which the solvent is removed,
A desired twisted nematic alignment can also be formed. In such a case, the photo-curing reaction can be performed in this state, but the above-mentioned heat treatment can be appropriately performed to more completely form the orientation.

In the twisted nematic alignment of the coating film obtained on the alignment substrate as described above, the coating film is then irradiated with light to cause a photocuring reaction to fix the alignment. The wavelength of light used for light irradiation is not particularly limited, and an electron beam,
Ultraviolet rays, visible rays, and infrared rays (heat rays) can be used as needed. Usually, the wavelength is 150 to 500 nm, preferably 250 to 450 nm, more preferably 300 to
Irradiation light of up to 400 nm of ultraviolet light or visible light is used. Its light sources include low-pressure mercury lamps (germicidal lamps, fluorescent chemical lamps, black lights), high-pressure discharge lamps (high-pressure mercury lamps, metal halide lamps), and short arc discharge lamps (ultra-high-pressure mercury lamps, xenon lamps, mercury xenon lamps), etc. Is mentioned. Above all, ultraviolet light and visible light from a metal halide lamp, a xenon lamp, and a high-pressure mercury lamp are the most common and can be suitably used in the present invention. A filter or the like is provided between these light sources and a coating film (object to be irradiated) on which a twisted nematic orientation is formed, and a specific wavelength region is exposed and shielded, so that the wavelength region of the irradiation light source is limited. You can also. The amount of light emitted from the light source as described above is appropriately determined depending on the type of the object to be cured, the amount of the initiator added, and the like, but is usually ^{2 to} 5000 mJ / cm ² , preferably 10 to 3000 mJ / cm ² , and more preferably. Is 10
The range is from 0 to 2000 mJ / cm ² . The temperature at which light is applied cannot be determined unconditionally because it is strongly affected by the liquid crystal phase behavior, fluidity, curability, etc. of the low molecular liquid crystal as the main component of the liquid crystal material forming the film. ~
The temperature is in the range of 200 ° C, preferably 20 to 180 ° C, more preferably 25 to 160 ° C. However, for example, a photocurable low-molecular liquid crystal having a high-order phase such as a smectic phase or a crystal phase in a low-temperature region near room temperature and a nematic phase in a temperature region above the low-temperature liquid crystal is in a state of a nematic phase. If you want to fix by light curing in
In some cases, light irradiation must be performed at a temperature higher than the phase transition point of the nematic phase. Further, after the orientation by the heat treatment, the liquid crystal is cooled by exposing it to the outside air from the heat treatment atmosphere, and the nematic phase may be fixed by supercooling depending on the type and composition ratio of the liquid crystal. In such a case, the liquid crystal phase may be vitrified and the curing rate may be low due to poor fluidity.However, after the supercooled layer is reheated to have fluidity, light irradiation is performed again. The photo-curing reaction can also be performed by such a method. Further, the twisted nematic alignment can be fixed by dividing the light irradiation into several times.For example, once the light irradiation is performed under heating, the light is hardened to a certain extent, and then the light irradiation is further performed after cooling, so that the light reaction can be further improved. A method of improving the reaction rate can be adopted. Furthermore, so-called aging can be performed in which heat treatment is performed after light irradiation to further react unreacted sites. The atmosphere under which light is irradiated cannot be described unconditionally due to various factors such as the curability of the photocurable low-molecular liquid crystal, which is the main component of the film material, the type of photoreaction initiator, the intensity of irradiation light, and the irradiation temperature. For example, when curing is easily inhibited by oxygen in the air, or when the light is oxidized by oxygen in the air to cause a problem such as coloring, irradiation of strong light from an irradiation light source in the air causes ozone. In the case where the generation of gas can occur, the irradiation atmosphere can be nitrogen gas or the like.
As a further alternative, a suitable cover film that does not impair the effects of the present invention, for example, a polyethylene terephthalate film, a polyethylene naphthalate film,
Polyphenylene sulfide film, polyarylate film, polycarbonate film, polyvinyl alcohol film, polyvinyl acetate film, polyethylene film, polypropylene film, polyvinyl chloride film, polyvinylidene chloride film, polyamide film, polyimide film, polyethylene-vinyl acetate coextruded film, etc. Oxygen can be blocked by covering the surface of the film material layer which is to be cured with the above.

The coating film formed on the alignment substrate by the above-mentioned method, that is, a low-molecular liquid crystal film which retains twisted nematic alignment and is fixed by a photo-curing reaction, has the alignment used in the preparation. If the substrate is optically isotropic and transparent in the visible light wavelength region, it can be used as it is as the low-molecular liquid crystal film of the present invention without peeling off from the alignment substrate. However, if the alignment substrate used for forming the thin film is optically anisotropic or opaque in the visible light wavelength range and the coating has self-supporting properties, From the alignment substrate to form a low-molecular liquid crystal film. When the self-supporting property of the coating film is insufficient, the coating film on the alignment substrate is optically isotropic and is transparent on the visible light wavelength region (hereinafter referred to as a second substrate). ), And this can be used as the low-molecular liquid crystal film of the present invention. In the transfer method, an adhesive is applied to the surface of the liquid crystal layer and bonded to a second substrate. After the adhesive is cured, the alignment substrate is separated from the liquid crystal layer, and the liquid crystal layer is transferred to the second substrate. Can be adopted. As the second substrate, for example, Fujitac (manufactured by Fuji Photo Film Co., Ltd.), Konikatac (manufactured by Konica), TPX film (manufactured by Mitsui Chemicals, Inc.), Arton film (manufactured by Nippon Synthetic Rubber Co., Ltd.), ZEONEX film (Japan Glass substrates and the like can be used, as well as acrylonitrile films (manufactured by Mitsubishi Rayon Co., Ltd.) and the like can be suitably used. Alternatively, the above liquid crystal layer can be directly transferred to a glass substrate or the like constituting a driving liquid crystal cell, and further, the above liquid crystal layer is applied to a film exhibiting optically negative anisotropy described later. The layers can also be transferred.

The low molecular liquid crystal film of the present invention obtained as described above has a refractive index anisotropy (strictly speaking, a refractive index anisotropy of a liquid crystal material forming the film) △ n1
And the thickness d1 of the film (△ n1d1 value)
However, as an average value in the film plane, usually 200nm ~
It is in the range of 600 nm, preferably 300 nm to 500 nm. Here, the thickness of the low-molecular liquid crystal film means the net thickness of the low-molecular liquid crystal film, and does not include the thickness of the second substrate when the film is laminated on a second substrate or the like. When the Δn1d1 value is larger than 600 nm, there is a possibility that many unnecessary colorings may be seen when preparing various LCDs. The value of △ n1d1 is 200n
When it is smaller than m, there is a possibility that the brightness and contrast of the front may be reduced when various LCDs are provided. The low-molecular liquid crystal film of the present invention has an absolute value of the twist angle of usually 40 ° to 120 °, preferably 80 ° to 100 °.
It is in the range of ゜. If the twist angle is out of the above range,
There is a possibility that the front contrast may be reduced when preparing for various LCDs. This twist angle can be appropriately set to a desired twist angle by adjusting the content of the optically active group described above. Further, depending on the type of the optically active group, it can be formed in either a twisted nematic orientation of right twist or left twist. Further, the direction of the twist is determined according to the optical compensating element of the present invention described later in NB-TN-.
When the LCD is provided, it is desirable that the direction is opposite to the twist direction of the liquid crystal in the driving liquid crystal cell constituting the LCD.

The film exhibiting optically negative anisotropy, which constitutes the optical compensatory element of the present invention together with the above-mentioned low molecular liquid crystal film, includes a film which literally exhibits optically negative anisotropy. It can be used regardless of the type. For example, any film having birefringence (△ n2) in the film thickness direction, such as a negative uniaxial film or a negative biaxial film, may be used. More specifically, polyimide, polyamide imide, polyamide, polyether imide, polyether ether ketone, polyether ketone, polyketone sulfide, polyether sulfone, polysulfone, polyphenylene sulfide, polyphenylene oxide, polyethylene terephthalate, polybutylene terephthalate, polyethylene From plastic films made of naphthalate, polyacetal, polycarbonate, polyarylate, acrylic resin, polyvinyl alcohol, polypropylene, cellulose, triacetyl cellulose and their partially saponified products, epoxy resins, phenolic resins, etc., and discotic compounds such as discotic liquid crystals Films and the like can be used in the present invention. The film having optically negative anisotropy, which is a component of the present invention, has a birefringence Δn2 in the film thickness direction and a film thickness d.
2 (△ n2d2 value), and this value is not particularly limited as long as it achieves desired characteristics. In the NB-TN-LCD of the present invention,
Usually -20 to -300 nm, preferably -30 to -25
Desirably, the range is 0 nm.

The optical compensatory element of the present invention comprises the low-molecular liquid crystal film described above and a film exhibiting optically negative anisotropy.
By providing D, the viewing angle characteristics of the LCD can be improved. Above all, a normally black mode type twisted nematic liquid crystal display device (hereinafter referred to as NB-TN-LCD) in which the optical compensation element of the present invention is disposed between a driving liquid crystal cell and a polarizing plate is the LC.
It is possible to reduce left-right asymmetry during halftone display and to display high-quality images without impairing the contrast characteristics of D.

The NB-TN-LCD of the present invention comprises an optical compensator comprising the above-mentioned low molecular liquid crystal film and a film having an optically negative anisotropy between two polarizing plates;
And a driving liquid crystal cell. In this case, a low-molecular liquid crystal film is provided between one of the polarizing plates and the driving liquid crystal cell, and a film having optically negative anisotropy is provided between the other polarizing plate and the driving liquid crystal cell. It can also be provided.
Alternatively, the two films may be stacked and provided between one of the two polarizing plates and the driving liquid crystal cell. When the two films are placed one on top of the other, the film located on the side of the driving liquid crystal cell is a film exhibiting optically negative anisotropy even if it is a low-molecular liquid crystal film. Is also good. However, in the NB-TN-LCD of the present invention, the low-molecular liquid crystal film provided on one side of the driving liquid crystal cell and the driving liquid crystal cell satisfy the following arrangement conditions. It is desirable. That is, the rubbing direction at the interface of the driving liquid crystal cell on the side where the low-molecular liquid crystal film is installed (more specifically, the rubbing direction of the glass substrate constituting the cell) and the low-molecular liquid crystal film (liquid crystal layer) are formed. The angle between the slow axis of the liquid crystal molecules and
70-110 °, preferably 75-105 °, more preferably 80-100 °, or -20-2.
0 °, preferably −15 ° to 15 °, more preferably −
It is desirable to arrange the low molecular liquid crystal film so as to be 10 to 10 °. The two polarizing plates used in the present invention are not particularly limited as long as they can be generally used in the field. For example, a uniaxially stretched polyvinyl alcohol film is formed by laminating a halogen polarizing film in which iodine molecules having a high degree of polarization are arranged in a certain direction or a polyvinyl alcohol film directly dyed with a dye between two appropriate protective films. The film can be used as a polarizing plate in the liquid crystal display device of the present invention. Further, in the liquid crystal display device of the present invention, as in the case of a normal TN-LCD, the two polarizing plates can be arranged such that the transmission axes thereof are orthogonal or parallel to each other. When the transmission axes of the two polarizing plates are arranged to be orthogonal to each other, the transmission axis of the polarizing plate and the rubbing direction of the driving liquid crystal cell closer to the polarizing plate are at an angle of orthogonal, parallel, or 45 degrees. It is desirable to arrange them so that Therefore, in the NB-TN-LCD of the present invention, the angle between the transmission axes of the two polarizing plates is usually 70 to 110 °, preferably 75 to 105 °, more preferably 80 to 100 °, The angle between the transmission axis of the polarizing plate and the rubbing direction of the driving liquid crystal cell closer to the polarizing plate is 70 to 1
10 °, preferably 75-105 °, more preferably 80-100 °, or -10-20
゜, preferably −5 to 15 °, more preferably 0 to 1
It is desirable to arrange them so as to be within the range of 0 °. The NB-TN-LCD of the present invention can function by stacking the above-mentioned components as they are so as to satisfy the above-described arrangement conditions. However, the respective layers are bonded with an adhesive or an adhesive as necessary. Can also be used. Further, the NB-TN-LCD of the present invention may be provided with a retardation film, a light diffusion layer, a color filter, and the like, if necessary, in order to further improve its 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. The addition of a color filter enables a multi-color or full-color display with high color purity.

[0015]

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) 151.3 g of 4- (6-acryloyloxyhexyloxy) benzoic acid in tetrahydrofuran solvent
(518 mmol), 2,6-ditert-butyl-4
1.5 g of methylphenol, 70.1 g (543 mmol) of diisopropylethylamine and 62.1 g (543 mmol) of methanesulfonyl chloride were reacted to synthesize methanesulfonic anhydride of carboxylic acid. Then, an esterification reaction was performed with 29.87 g (246 mmol) of methylhydroquinone, and the obtained crude product was recrystallized to give methylhydroquinone bis (4- (6-acryloyloxyoxyhexyloxy) benzoate) ester (compound 146.9 g of 1) was obtained. The purity of the obtained compound 1 was 98.7%. When Compound 1 was observed on a Mettler hot stage under a polarizing microscope, it turned into a crystalline phase at room temperature and a nematic phase at around 85 ° C., and became an isotropic phase at around 115 ° C. upon further heating. Reference Example 2 Using the same method as in Reference Example 1, 2,3-dimethylhydroquinone bis (4- (11-acryloyloxyundecyloxy) benzoic acid) ester (Compound 2) was obtained. GPC purity of compound 2 is 99.3%
Met. (Reference Example 3) Using the same method as in Reference Example 1, 2-chlorohydroquinone bis (-)-(4- (2-ethylhexyl) benzoic acid) ester (Compound 3) was obtained. Compound 3
Had a dextrorotatory power as measured by a polarimeter. (Reference Example 4) 6.5 g of the compound 1 obtained in Reference Example 1,
2.913 g of the compound 2 obtained in Reference Example 2 and 0.641 g of the compound 3 obtained in Reference Example 3 were dissolved in 90 g of methoxypropyl acetate. To this solution were added a fluorine-based surfactant S-383 (manufactured by Asahi Glass Co., Ltd.), 0.3 g of a photoreaction initiator Irgacure 907 (manufactured by Ciba Geigy), and 0.1 g of a sensitizer diethylthioxanthone, and a photocurable low molecular A liquid crystal composition solution was prepared. Polyvinyl alcohol (manufactured by Kuraray Co., Ltd., trade name Kuraray Poval MP-203) was uniformly applied to a thickness of 0.2 μm on a white plate glass (thickness: 1.1 mm) manufactured by Corning, and the dried surface was rubbed with a rayon cloth. . A photocurable low-molecular liquid crystal composition solution was applied to the rubbed surface with a bar coater. After the application, it was placed on a hot plate set at 80 ° C. and dried for 20 minutes. After drying, the formation of the twisted nematic alignment of the liquid crystal layer had already been completed. afterwards,
The film is put into an oven set at 50 ° C., and the atmosphere is replaced with nitrogen until the oxygen concentration becomes 250 ppm or less.
V irradiation was performed. A high-pressure mercury lamp was used as the UV light source, the irradiation intensity was 120 W / cm ² , and the integrated irradiation amount during the irradiation time of 15 seconds was 1,260 mJ. After irradiation, the low-molecular liquid crystal layer was cured, and its surface hardness was about 2H in pencil hardness. The average actual film thickness of the low-molecular liquid crystal layer measured by the thin film interference method was 3.36 μm. The following experiment was performed to measure the refractive index of the liquid crystal layer in the thus obtained laminate (low-molecular liquid crystal layer / polyvinyl alcohol / white plate glass). A high-refractive-index glass substrate having a rubbing polyimide film under the same conditions using a photocurable low-molecular liquid crystal composition from which a low-molecular liquid crystal layer was obtained (refractive index: 1.8
4) A liquid crystal film was prepared by orientation and fixation thereon, and the refractive index was measured using the liquid crystal film. When the glass substrate is placed in contact with the prism surface of the refractometer and the liquid crystal film is arranged so that the substrate interface side is lower than the air interface side, the refractive index in the film surface is anisotropic and perpendicular to the rubbing direction. The in-plane refractive index is 1.53, and the parallel in-plane refractive index is 1.
67, and the refractive index in the film thickness direction was constant at 1.53 regardless of the direction of the sample. From this, it was found that rod-like liquid crystal molecules were planarly aligned on the glass substrate side with respect to the substrate and parallel to the rubbing axis. From this, it was found that no and ne of the low-molecular liquid crystal layer in Sample 1 were 1.53 and 1.67, respectively. When the obtained low-molecular liquid crystal layer was subjected to ellipsometry, Δn1
d1 = 470 nm, and the twist angle was −90 ° (right twist). (Example 1) A UV-curable adhesive (UV-3400, manufactured by Toagosei Co., Ltd.) was applied to the surface of the low-molecular liquid crystal layer of the laminate (low-molecular liquid crystal layer / polyvinyl alcohol / white glass) obtained in Reference Example 4. It was applied to a thickness of 5 μm, and the three types of transparent substrates shown in Table 1 were laminated on each, and about 600 m
The adhesive was cured by UV irradiation of J (transparent substrate / adhesive / low molecular weight liquid crystal layer / polyvinyl alcohol / white plate glass) to obtain three types of compensating elements.

[0016]

[Table 1]

(Example 2) ZLI manufactured by Merck as a liquid crystal material
-4792, cell gap 4.8 μm, Δnd = 470
nm, twist angle 90 ° (left twist), pretilt angle 2
° TN cell was fabricated. The compensation element 2 obtained in Example 1 was arranged in the cell as shown in FIG. A rectangular wave of 300 Hz was applied to the liquid crystal cell, the black display was set to 0 V, the white display was set to 6 V, and the drive voltage was set so that the transmittance at the front was equally divided into eight. Hamamatsu Photonics FFP optical system DV
The transmittance in all directions of the liquid crystal cell was measured using S-3000, and the viewing angle dependence of the gradation characteristics of the liquid crystal cell was obtained. FIG. 2 shows the obtained gradation characteristics of the left and right viewing angles. (Example 3) Evaluation was performed in the same manner as in Example 2 except that the compensating element 3 obtained in Example 1 was used as the compensating element. The results are shown in FIG. (Example 4) As a compensating element, the compensating element 1 obtained in Example 1 and a polyamide film (Δn2d2 = −150 n)
m) and arranged as shown in FIG. 4 and evaluated in the same manner as in Example 2. The results are shown in FIG. Comparative Example 1 Evaluation was performed in the same manner as in Example 2 except that the compensating element 1 obtained in Example 1 was used as a compensating element.
The results are shown in FIG. (Comparative Example 2) As the compensating element, the compensating element 1 obtained in Example 1 and two modified polycarbonate films (Δn2d2
= −400 nm), and they were arranged as shown in FIG. 7 and evaluated in the same manner as in Example 2. The results are shown in FIG. Although the embodiments of the present invention have been described above, it has been found that as shown in Table 2, left and right asymmetry during halftone display can be reduced without deteriorating the contrast characteristics as compared with each comparative example.

[0018]

[Table 2]

[0019]

The optical compensator of the present invention has a twisted nematic alignment fixed by a photopolymerization reaction, and can be expected to be applied to various liquid crystal display devices. Above all, NB-TN-L having the optical compensation element of the present invention between a driving liquid crystal cell and an upper or lower polarizing plate.
The CD can reduce left-right asymmetry during halftone display and can display high-quality images without impairing contrast characteristics.

[Brief description of the drawings]

FIG. 1 shows a layout of components in a second embodiment.

FIG. 2 shows viewing angle (left and right) characteristics of gradation in Example 2.

FIG. 3 shows a viewing angle (left / right) characteristic of gradation in Example 3.

FIG. 4 shows an arrangement diagram of each component in a fourth embodiment.

FIG. 5 shows the viewing angle (left and right) characteristics of gradation in Example 4.

FIG. 6 shows the viewing angle (left and right) characteristics of gradation in Comparative Example 1.

FIG. 7 shows an arrangement diagram of each component in Comparative Example 2.

FIG. 8 shows the viewing angle (left and right) characteristics of gradation in Comparative Example 2.

[Explanation of symbols]

 1,1 ': polarizing plate 2: drive cell 3: compensation film 4,4': film having optically negative anisotropy

Claims (3)

[Claims] 1. A low-molecular liquid crystal film obtained by fixing a twisted nematic alignment formed by a photo-curable low-molecular liquid crystal having optically positive uniaxiality in a liquid crystal state by a photo-curing reaction, and an optically negative An optical compensation element comprising a combination with a film exhibiting anisotropy. 2. A normally black mode twisted nematic liquid crystal display device comprising a driving liquid crystal cell and an optical compensator according to claim 1 provided between two polarizing plates. 3. The product (ΔΔn) of the refractive index anisotropy Δn of the nematic liquid crystal constituting the driving liquid crystal cell and the thickness d of the liquid crystal layer.
nd value) is in the range of 200 nm to 600 nm, the twist angle of the liquid crystal in the twist orientation is in the range of 80 ° to 100 °, and the refractive index anisotropy of the low molecular weight liquid crystal film constituting the optical compensating element is the product of n1 and the thickness d1 of the film (厚 み n1d1 value) is in the range of 150 to 600 nm;
The twist angle of the twisted nematic orientation held by the film is in the range of 80 ° to 100 °, and the twist direction is opposite to the twist orientation direction of the nematic liquid crystal in the driving liquid crystal cell, and is optically negative. The product (Δn2d2 value) of the birefringence Δn2 in the film thickness direction of the film exhibiting anisotropy of the film and the thickness d2 of the film is −20 to −300 nm.
3. The normally black mode type twisted nematic liquid crystal display device according to claim 2, wherein