WO2001016645A1

WO2001016645A1 - Normally-black mode tn liquid crystal display

Info

Publication number: WO2001016645A1
Application number: PCT/JP2000/005438
Authority: WO
Inventors: Takehiro Toyooka
Original assignee: Nippon Mitsubishi Oil Corporation
Priority date: 1999-08-31
Filing date: 2000-08-14
Publication date: 2001-03-08

Abstract

A normally-black mode TN liquid crystal display in which a drive liquid crystal cell having a pair of transparent substrates with electrodes and a liquid crystal layer having twisted nematic orientation during voltage nonapplication and provided between the pair of transparent substrates and an optical compensating film holding twisted nematic orientation and interposed between two polarizing plates, characterized in that the absolute value of the angle of twist of the optical compensating film is smaller than that of the angle of twist of the drive liquid crystal cell during voltage nonapplication.

Description

Specification No. Mary black mode type TN liquid crystal display

[Technical field]

The present invention relates to a normally black mode twisted nematic (TN) liquid crystal display device having improved display contrast, gradation characteristics, and viewing angle characteristics of display colors.

[Background technology]

Twisted nematic liquid crystal display elements (hereinafter abbreviated as TN-LCDs) driven by active elements using TFT elements or MIM elements are thin, light, and have low power consumption. In the case of having a picture quality comparable to that of a CRT, 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 abbreviated as NB-TN-LCD), in which black display is performed when no voltage is applied and the liquid crystal alignment state in the cell during the black display forms a twisted structure, is referred to as an NB-TN-LCD. Viewing angle characteristics compared to a normally white TN-LCD (hereinafter abbreviated as NW-TN-LCD), which displays white when no voltage is applied because the anisotropy is averaged. Is good. However, the NB—TN—LCD cannot twist light completely over the entire visible region because the liquid crystal alignment state in the cell during black display is twisted, and the black display is colored. However, since the contrast of the display is reduced, there remains a problem that color compensation must be performed which cannot be a problem with NW-TN-LCD. Various color compensation methods have been recently reported to solve this problem. For example, a method of setting the cell gap to an optimum value for each pixel of each color (R, G, B) of the LCD panel (multi-gap method: Hatta et al. al., SID 1986 Digest, p296), Method of performing color compensation using multiple Yannaka films (Sergan et al., Jpn. J. Appl. Phys., 37 (3A), p889), Liquid crystal cell for compensation (Yoshida et al., Proceedings of the 16th Liquid Crystal Symposium, 1990), 2L307, p222). 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. Also, in the method of performing color compensation using multiple stretched films, it is necessary to use four or more films in order to secure contrast, and stable characteristics are obtained due to film variations, accuracy during laminating, etc. Difficult to obtain. Also, in the method of performing color compensation using a compensating liquid crystal cell, there is a problem that the weight and thickness increase because the cells are stacked. Furthermore, 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. However, this leads to a decrease in cell yield and an increase in cost.

[Disclosure of the Invention]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a wider viewing angle characteristic, has less left-right asymmetry during halftone display, and is capable of displaying a high-quality image in a normally black mode. The present invention provides a type TN liquid crystal display device. That is, the present invention provides a driving liquid crystal cell in which a liquid crystal layer having a twisted nematic alignment is provided between a pair of transparent substrates provided with electrodes when no voltage is applied, and an optical compensation film holding a twisted nematic alignment. A liquid crystal display device sandwiched between two polarizing plates, wherein the absolute value of the twist angle of the optical compensation film is smaller than the absolute value of the twist angle of the driving liquid crystal cell when no voltage is applied. The present invention relates to a normally black mode TN liquid crystal display device. The present invention also provides 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, and an optical compensation film having a twisted nematic alignment. And a film exhibiting optically negative anisotropy sandwiched between two polarizing plates, wherein the absolute value of the twist angle of the optical compensation film is equal to that of the driving liquid cell. The present invention relates to a normally black mode TN liquid crystal display device characterized by being smaller than the absolute value of the twist ^ when no voltage is applied. A normally-black mode TN liquid crystal display element according to the first invention comprises a driving liquid crystal cell having a liquid crystal layer which is twisted and nematic aligned when no voltage is applied between a pair of transparent substrates provided with electrodes. An optical compensatory film holding the nematic alignment is sandwiched between two polarizing plates, and the absolute value of the twist angle of the optical compensatory film is measured when no voltage is applied to the driving liquid crystal cell. It is characterized by being smaller than the absolute value of the torsion angle of.

In the liquid crystal display element of the first invention, the product of the refractive index anisotropy Δη of the liquid crystal layer in the driving liquid crystal cell and the thickness d of the liquid crystal layer, that is, the value of And is 200 nm or more. It is in the range of 60 Onm, the torsion angle of the driving liquid crystal cell when no voltage is applied is in the range of 80 ° to 100 °, and the twisting direction of the optical compensation film is opposite to that of the driving liquid crystal cell. More preferably, the absolute value of the twist angle is smaller than the absolute value of the torsion angle of the driving liquid crystal cell, and the difference is at least 15 degrees. A normally-black mode TN liquid crystal display element according to a second aspect of the present invention includes a driving liquid crystal cell having a liquid crystal layer that is twisted and nematic aligned when no voltage is applied between a pair of transparent substrates provided with electrodes; The optical compensation film has a configuration in which an optical compensation film that maintains a twisted nematic orientation and a film that exhibits optically negative anisotropy are sandwiched between two polarizing plates. Is smaller than the absolute value of the torsion angle of the driving liquid crystal cell when no voltage is applied.

And, in the normally black mode TN liquid crystal display element of the second invention, the product (And) of the refractive index anisotropy Δη of the liquid crystal layer and the thickness d of the liquid crystal layer in the driving liquid crystal cell is: It is in the range of 200 nm to 600 nm, the torsion angle of the driving liquid crystal cell when no voltage is applied is in the range of 80 ° to 100 °, and the refractive index anisotropy An, and the thickness d, of the optical compensation film are The product (ΔΓ ^ d) is in the range of 150 to 600 nm, and the absolute value of the twist angle of the optical compensation film is smaller than the absolute value of the twist angle of the driving liquid product cell when no voltage is applied. Degrees, and the product (Δη ₂ d ₂ ) of ¾ί refraction Δη ₂ and thickness d ₂ in the film thickness direction of a film exhibiting an optically negative anisotropy is in the range of の₂₀ to 1300 nm ffl. Preferably, there is. The optical compensation film suitable for being incorporated in the normally black mode TN liquid crystal display device of the present invention is a twisted film formed of a thin film of a polymer liquid crystal having optically positive uniaxiality in a liquid crystal state. The liquid crystal film is preferably a liquid crystal film in which the nematic alignment is fixed to the glass by cooling the thin film.

As an optical compensation film suitable for being incorporated into the normally-black mode TN liquid crystal display device of the present invention, a thin film of a photocurable low-molecular liquid crystal exhibiting optically positive uniaxiality is formed in a liquid crystal state. It is preferable that the liquid crystal film has a twisted nematic alignment fixed by irradiating the thin film with light. Hereinafter, the present invention will be described in detail.

A normally-black mode TN liquid crystal display device (hereinafter abbreviated as NB-TN-LCD) of the first invention includes a driving liquid crystal cell, two polarizing plates, and an optical compensation film. .

The NB-TN-LCD of the second invention has a structure in which a driving liquid crystal cell, an optical compensation film, and a film exhibiting optically negative anisotropy are sandwiched between two polarizing plates. . The driving liquid crystal cell basically has a configuration in which a nematic liquid crystal layer which 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.

There are two types of driving methods for driving liquid crystal cells: a simple matrix type and an active matrix type that uses active elements as electrodes.The latter type uses TFT (Thin Film Transistor) electrodes as active elements. , MIM (Meta 1 Insul at or Meta 1) electrode or TFD (Thin Film Diode) electrode can be subdivided into active elements. Kawa This liquid crystal cell can also be used for the liquid product display device of the present invention.

However, the liquid cell for driving used in the present invention is obtained by multiplying the refractive index anisotropy Δη of the nematic liquid crystal layer by the thickness d of the nematic liquid layer of the driving liquid cell (And value). It is always desirable to be in the range from 200 to 600 nm, preferably from 300 to 500 nm. If the And value is larger than 600 nm, coloring may increase when combined with an optical compensation film described later. If the And value is smaller than 20 O nm, the front luminance and contrast may be reduced when combined with an 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 in the range of 80 ° to 100 °, preferably in the range of 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 as 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, the twist direction of the twist angle of the optical compensation film installed thereon and the twist angle of the nematic liquid crystal layer when no voltage is applied to the driving liquid crystal cell are opposite to each other. preferable. 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 driving liquid crystal cell when no voltage is applied.

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 there is a possibility that the contrast of a displayed image may be reduced. Even when the absolute value of the torsion angle of the optical compensation film is set smaller than the absolute value of the torsion angle of the driving liquid crystal cell when no voltage is applied, if the difference between the two angles is small, sufficient visual field can be obtained. There is a possibility that the effect of increasing the angle and the effect of reducing the asymmetry cannot be obtained.

For this reason, in order to achieve high contrast of the 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 or more, preferably. Is preferably at least 10 degrees. The absolute value of the twist angle of the compensation film is at most smaller than the absolute value of the twist angle of the driving liquid crystal cell when no voltage is applied, and the difference is usually 15 degrees or more, preferably 20 degrees or more. Is desirable.

In the optical complementary film of the present invention, 秸 (Δη, d,) between the refractive index anisotropy Δη of the film and the thickness d〗 of the film is particularly limited as long as the effects of the present invention are not impaired. It's not something, but usually 200 nrr! In the range of ~ 700 nm, preferably 3 0 0 nn! It is desirably in the range of ~ 600 nm. When the value of Δ η, is smaller than 200 nm, the front brightness and contrast of the LCD may be reduced. When the value is larger than 700 nm, unnecessary coloring may be seen on the LCD. There is. The optical compensatory film of the present invention can be produced from any liquid crystal material giving the above-mentioned values of twist angle and Δη. Among them, a polymer liquid crystal or an optical liquid having optically positive uniaxiality is preferred. It is preferable to use a curable low-molecular liquid crystal as a liquid crystal material and to prepare it from its thin film.

This liquid crystal material must contain a compound having an optically active group so that twisted nematic alignment can be exhibited. Incidentally, if the polymer 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 optically active groups contained in the liquid crystal material varies depending on the type of polymer liquid crystal or photocurable low-molecular liquid crystal actually used and the degree of twist angle desired for the optical compensation film. Although it cannot be said, it is usually 0.01 to 50% by weight, preferably 0.05 to 40% by weight, more preferably 0.1 to 30% by weight, and most preferably 0.1 to 50% by weight based on the liquid crystal material. It is in the range of 2 to 20% by weight. When 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 polymer liquid crystal used for the liquid crystal material is not limited as long as the desired twisted nematic alignment can be fixed, and any type of main-chain or side-chain polymer liquid crystal can be used. It is. Specifically, main-chain liquid crystal polymers such as polyester, polyamide, polycarbonate, and polyesterimide, or side-chain liquid polymers such as polyacrylate, polymethacrylate, polymalonate, and polysiloxane are used. it can. Above all, it is desirable to use a liquid crystalline polyester which has good orientation for forming twisted nematic orientation and is relatively easy to synthesize. The constituent units of the polymer include, for example, aromatic or aliphatic diol units, aromatic or Examples of preferred examples thereof include an aliphatic dicarboxylic acid unit and an aromatic or aliphatic hydroxycarboxylic acid unit. Photo-curable low-molecular liquid crystals can also be used as the liquid crystal material.Examples include a biphenyl derivative, a phenylbenzoate derivative, and a stilbene derivative having a functional group such as an acryloyl group, a vinyl group, or an epoxy group. Any of the above-mentioned photocurable low-molecular liquid crystals can be used. These low-molecular liquid crystals may have either lyotropic orpicotropic properties, but those exhibiting orotropic properties are more preferable 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 bis azide compound and glycidyl methacrylate is added to the liquid crystal material as long as the twisted nematic phase is not hindered. You can also. By adding these cross-linking agents, liquid crystal molecules can be bridged in a state where a twisted nematic phase is developed.

Furthermore, various additives such as dichroic dyes, dyes, pigments, antioxidants, ultraviolet absorbers, and hard coat agents are appropriately added to the liquid crystal material as long as the effects of the present invention are not impaired. Can also. The optical compensation film of the present invention is obtained by forming the above liquid crystal material into a thin film, subjecting the thin film to heat treatment to form a desired twisted nematic alignment, and then fixing the alignment state. Obtainable.

In order to obtain a desired twisted nematic alignment, a thin film of a liquid crystal material is spread on an alignment substrate having an alignment regulating force.Specifically, a liquid crystal material is coated on an alignment substrate. Is preferred. Here, the upper and lower interfaces of the coating film of the film material are sandwiched between the alignment substrates to orient the film, and the coating film of the film material is applied to one of the alignment substrates and the other to a non-alignment substrate having no alignment regulating force. A method of sandwiching and orienting can also be adopted.

As the alignment substrate, it is desirable to use has anisotropic so that it can regulate the director at the substrate interface of the liquid crystal molecules, the substrate material can be used as glass or plastic power ^s. The substrate on which the liquid material is applied can completely control the liquid crystal molecules. If not, there is a possibility that the desired twisted nematic alignment cannot be obtained. Examples of an alignment substrate that can be used for producing the optical compensation film include polyimide, polyamide imide, polyamide, polyether imide, polyether ether ketone, polyether ketone, polyketone sulfide, polyether sulfone, and polys. Lefon, polyphenylene sulfide, polyphenylene oxide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthate, polyacetal, polycarbonate, polyarylate, polyvinyl alcohol, polypropylene, cellulose plastics, acrylic Plastic film substrates such as resin, epoxy resin, phenol resin, etc. and uniaxially stretched plastic film substrates, aluminum, iron, Examples include a metal substrate such as copper, and a glass substrate such as alkali glass, borosilicate glass, and flint glass whose surface is etched into a slit shape.

Also, a rubbing plastic film substrate obtained by subjecting the above plastic film substrate to rubbing treatment, or a plastic thin film subjected to 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 evaporation 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 below: various substrates having a rubbing polyimide film, a rubbing polyimide substrate, a rubbing polyether ether ketone substrate, A rubbing polyester skeleton substrate, a rubbing polyester sulfone substrate, a rubbing polyphenylene sulfate phthalate substrate, a rubbing polyarylate substrate, and a rubbing cellulose-based plastic substrate can be exemplified. The application of the liquid 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 a hydrocarbon-based solvent such as toluene, xylene, butylbenzene, tetrahydronaphthylene, decahydronaphthalene, or the like. Ethers such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, propylene glycol dimethyl ether, and tetrahydrofuran; ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; ethyl acetate, butyl acetate, and ethylene glycol monomethyl ether Ester such as acetate, propylene glycol monomethyl ether acetate, ethyl lactate, and abutyrolactone, amide such as N-methyl_2-pyrrolidone, dimethylformamide, dimethylacetamide, dichloromethanone, Halogenated hydrocarbons such as carbon chloride, tetrachloroethane, and chlorobenzene, butyl alcohol, triethylene glycol, diacetone alcohol, hexylene glycol, etc. It is selected from alcoholic and others. If necessary, two or more of these solvents can be used as an appropriate mixture. The solution concentration of the liquid crystal material varies depending on the solubility of the dissolved liquid crystal material, the thickness of the coating film, and the like, and cannot be unconditionally determined, but is usually 1 to 60% by weight, preferably 3 to 40% by weight. %, More preferably in the range of 7 to 30% by weight. A surfactant or the like can be added to the liquid crystal material solution 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; Or secondary alcohol ethoxylate, alkylphenol ethoxylate, polyethylene glycol and its ester, sodium lauryl sulfate, ammonium lauryl sulfate, lauryl sulfate amines, alkyl-substituted aromatic sulfonate, alkyl phosphate, aliphatic acid Or anionic surfactants such as aromatic sulfonic acid formalin condensates; amphoteric surfactants such as lauryl propyl betaine and lauryl amino sulphate; poly (ethylene glycol) fatty acid esters; Shetyrenal Nonionic surfactants such as luminin, perfluoroalkyl sulfonate, perfluoroalkyl carboxylate, perfluoroalkyl ethylene oxide adduct, perfluoroalkyltrimethylammonium salt, perfluoroalkyl Groups / Hydrophilic group-containing oligomers, perfluoroalkyl 'oleophilic group-containing oligomers, perfluoroalkyl group-containing urethanes and other fluorinated surfactants.

The amount of surfactant added depends on the type of surfactant, the solvent, and the substrate to be coated. Depending on the weight of the liquid crystal material, however, it is usually in the range of 10 ppm to 10%, preferably 50111 to 5%, more preferably 0.01% to 1%.

For the application of the liquid crystal material solution, 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. The coating film of the liquid crystal material solution formed on the alignment substrate is then dried, and the solvent is removed 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 coated film from which the solvent has been removed is subjected to a heat treatment at a temperature at which the liquid crystal molecules in the coated film exhibit a twisted nematic phase for a predetermined time to complete the twisted nematic alignment of the coated film. Usually, 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. Depending on the type, twist angle in the oriented nematic orientation may vary depending on heat treatment conditions and the like. In the case of using such a liquid crystal material, a method of appropriately controlling the heat treatment conditions to obtain a desired twist angle can be adopted 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 low temperatures, the viscosity of the liquid crystal material is high, and to achieve the desired alignment, May take a long time. In such a case, a method of once heat-treating at a high temperature to obtain a mono-domain orientation, and then gradually or continuously cooling to a temperature at which a twisted nematic orientation having a desired twist angle is formed. Is valid. 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 250 ° C. The range of C is adopted, and the time of heat treatment is usually 5 seconds to 2 hours, preferably 10 seconds to 1 hour, and more preferably 20 seconds to 30 minutes. Is merely an example and does not limit the present invention in any way. 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 heat treatment is quenched in that state to change the alignment to glass. Fix it. When the liquid crystal material forming the coating film is a photocurable low molecular weight liquid crystal, the light, heat or heat is applied to the coating film forming the twisted nematic alignment as it is. The orientation is fixed by irradiation with an electron beam or the like. A coating film in which twisted nematic alignment is formed and fixed on an alignment substrate, that is, a liquid crystal film that maintains stable twisted nematic alignment is an optical compensation film with an alignment substrate. Can be used as In addition, 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, It can be transferred to an isotropic film or substrate (hereinafter, referred to as a second substrate film) and used together with the second substrate film as an optical compensation film. When transferring, for example, a method is generally used 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. Adopted.

Examples of the second substrate film include a triacetyl cell opening film such as Fujitac (manufactured by Fuji Photo Film Co., Ltd.) and Tsunacatac (manufactured by Koniki), TPX film (manufactured by Mitsui Chemicals), Arton film (manufactured by Nihon Gosei) Rubber), ZONEX Film (Zeon Corporation), Acryprene Film (Mitsubishi Rayon), etc. can be used. In addition, the liquid crystal film on the alignment substrate can 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 anisotropic 负 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. Suitable transfer can be performed in consideration of such factors. However, if the liquid crystal film itself has an excellent self-supporting property, peel off the substrate for ffi. Then, the liquid crystal film can be used alone as an optical compensation film. There is no special requirement for the film exhibiting optically negative anisotropy used in the present invention, other than exhibiting optically negative anisotropy. Therefore, any film having birefringence (An 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, polyether sulfone, polysulfone, polyphenylene sulfide, and polyphenylene oxide. Polyethylene terephthalate, polyethylene terephthalate, polyethylene naphthate, polyacetal, polycarbonate, polyarylate, polyvinyl alcohol, polypropylene, cellulose, triacetylcellulose and its partially modified products, acrylic resin, epoxy Examples of the film include a plastic film made of a resin, a phenol resin and the like, and a film made of a discotic compound such as a discotic liquid crystal.

The film having optically negative anisotropy used in the present invention has a product of the birefringence Δη _{2 in the} film thickness direction and the thickness d ₂ , that is, the value of An ₂ d ₂ is usually −20 to −30. It is desirable to be in the range of On m, preferably in the range of 30 to -250 nm. In the NB-TN-LCD of the first invention, the optical compensation film is provided between the driving liquid crystal cell and the viewing-side polarizing plate. When installing the optical compensation film, rubbing the slow axis of liquid crystal molecules on the surface of the optical compensation film (liquid crystal layer) where the liquid crystal cell for driving contacts and the rubbing of the viewing side transparent substrate where the liquid crystal layer of the liquid crystal cell for driving contacts. The angle formed by the direction is usually 70 to 110 °, preferably 75 to: L05 °, more preferably 80 to 100 ° or usually 120 to 20 °, preferably 1 to 15 to 15 °, more preferably 1 to 15 °. It is desirable to arrange them so as to be in the range of 10 to 10 °. In the NB_TN-LCD of the second invention, the optical compensation film and the film exhibiting optically negative anisotropy, the force s, and the driving liquid product cell are sandwiched between the two polarizing plates. These two types of films are installed between the viewing side polarizing plate and the driving liquid crystal cell. Optically supplementary if! Films and films with optically negative anisotropy are not necessarily laminated You don't have to. If both are not laminated, a film exhibiting optically negative anisotropy may be placed between the driving liquid crystal cell and the polarizing plate on the viewing side, or between the driving liquid crystal cell and the polarizing plate on the light source side. No problem. However, the optical compensation film is necessarily provided between the driving liquid crystal cell and the viewing-side polarizing plate.

When an optical compensatory film and a film exhibiting optically negative anisotropy are laminated and used, they are installed between the driving liquid crystal cell and the viewing-side polarizing plate. It does not matter whether it faces the side polarizing plate.

However, in any case, in the NB-TN-LCD of the present invention, the rubbing direction of the transparent substrate (viewing side) interface in contact with the liquid crystal layer of the driving liquid crystal cell, and the driving liquid crystal of the optical compensation film (liquid crystal layer) The angle formed by the slow axis of the liquid crystal molecules on the surface in contact with the cell is usually 70 to; L10 °, preferably 75 to: 105 °, more preferably 80 to 100 °. The optical compensation film is installed so that the angle is usually in the range of 120 to 20 °, preferably in the range of 115 to 15 °, and more preferably in the range of 110 to 10 °. It is desirable to provide an optical compensation film so that The viewing-side polarizing plate and the light-source-side polarizing plate in the NB-TN-LCD of the present invention are polarizing plates generally used in the field, and are not particularly limited. For example, a polarizing plate with a uniaxially stretched polyvinyl alcohol film in which iodine molecules with a high degree of polarization are arranged in a fixed direction and a polyvinyl alcohol film dyed with a direct dye, etc., sandwiched between other support films Can be used. In the NB-TN-LCD of the present invention, the polarizing plates are disposed above and below the driving liquid crystal cell, respectively. Specifically, it can be provided directly on one surface of the liquid crystal cell, or provided via another component such as an optical compensation film. Further, the axial arrangement of the polarizing plate is not particularly limited, and may be any arrangement within L and range where the effect of the present invention may not be impaired.

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. However, it is also possible to bond the components with an adhesive or a bonding agent as necessary. Further, the NB-TN-LCD of the present invention includes, as necessary, other components as well as a driving liquid crystal cell, two upper and lower polarizing plates, and an optical compensation film provided as essential components. Is also good. 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. Further, by providing a color filter or the like, an NB-TN-LCD capable of performing multicolor or full-color display with high color purity can be obtained.

[Best Mode for Carrying Out the Invention]

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. Reference Example 1 (Manufacture of optical compensation film 1)

Terephthalic acid 5 Ommo 1, 2, 6-Naphthylene dicarboxylic acid 50 mmo 1, methylhydroquinone diacetate 40 mmo 1, catechol diacetate 62 mmo 1 and N-methylimidazole 6 Omg The polymerization was performed at 270 ° C. for 12 hours under a nitrogen atmosphere. Next, the obtained reaction product was dissolved in tetrachloroethane, followed by purification by reprecipitation with methanol to obtain 14.7 g of a liquid crystalline polyester (polymer A). The logarithmic viscosity of this liquid crystalline polyester was 0.17, the liquid crystal phase had a nematic phase, the isotropic phase-liquid crystal phase transition temperature was 250 ° C or higher, and the glass transition point was 115 ° C. .

In addition, biphenyldicarbonyl chloride 9 Ommo 1 and terefu-yuko chloride 1 Ommo 1, 2 R, 3 R-dimethoxybutanediol 105 The reaction was allowed to proceed for an hour, and the reaction solution was poured into methanol and reprecipitated to obtain 12.3 g of a liquid crystalline polyester (polymer B). The logarithmic viscosity of the polymer B was 0.11, a chiral smectic phase was exhibited at room temperature, and the isotropic transition temperature was 40 to 50 ° C. In addition, T g was thought to be around room temperature and could not be observed by DSC measurement. A solution was prepared by dissolving 0.7 g of 19.3 of polymer A prepared above and polymer; 6 in 80 g of a mixed solvent of phenol / tetrachlorobenzene (6/4 weight ratio). did. This solution was applied on a polyimide substrate (Kapton, manufactured by DuPont) rubbed with rayon cloth by a bar coating method, dried, and heat-treated at 240 ° C for 30 minutes. A liquid crystal film with an average actual film thickness of 2.34 µm was obtained on a polyimide substrate (Sample A). The actual film thickness of the liquid crystal film was measured using a stylus fl gauge. Next, the refractive index of the liquid crystal film was measured by arranging the polyimide substrate surface of sample A in contact with the prism surface of the Abbe refractometer (Type 4 manufactured by Ayago Co.). Anisotropy was observed, and the refractive index (no) in the direction perpendicular to the rubbing direction of the polyimide substrate was 1.55, and the refractive index (ne) in the direction parallel to the rubbing direction was 1.75. Has a constant refractive index of 1.55. From this fact, the liquid crystal film has planar liquid crystal molecules aligned in parallel with the substrate and rubbing direction on the polyimide substrate interface side, and no and ne of the liquid crystal are 1.55 and 1. It turned out to be 75.

The liquid crystal film of Sample A was placed so that the liquid crystal film surface of 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. 55, 1.75 in the vertical direction, and the refractive index in the enormous direction was constant at 1.55. Therefore, in Sample A, the liquid crystal film in the liquid crystal film was largely homogenous aligned at both the substrate interface and the air interface, and the rod-shaped liquid crystal molecules were twisted at almost 90 degrees at both the interface between the substrate interface and the air interface. 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_3400, manufactured by Toagosei Co., Ltd.) After applying a thickness, laminating a transparent substrate (triacetyl cellulose film) thereon, curing the adhesive by UV irradiation of about 60 OmJ, and then peeling off the polyimide substrate, the liquid crystal film becomes transparent. This was transferred onto a substrate to obtain an optical compensation film 1. The polarization of the obtained optical compensation film 1 (film A) was analyzed, and Δη, ο ^ and twist angle (right twist) of this film A were measured. Ar ^ d! ^ ATS nm, twist angle = — 90 °. Reference example 2

Four types of optical compensation films were obtained in the same manner as in Reference Example 1 except that the ratio of polymer A to polymer B and the film thickness were changed (films B to E). Each film's Δη, d! And the torsion angle are shown in Table 1 together with the measured values of Film A. table 1

Example 1

A drive liquid crystal cell with a cell gap of 4.8〃m, And = 470 nm, a twist angle of 90 ° (left-handed twist), and a pretilt angle of 2 ° using Merck's ZLI-4792 as the liquid crystal material of the drive liquid crystal cell. (TN cell) was prepared.

One optical compensation film (film C) obtained in Reference Example 2 was used for the cell, and as shown in FIG. 1, the polarizing plate (1) / optical compensation film (3) / TN cell (2) / A liquid crystal display panel was prepared by arranging a polarizing plate (Γ) in this order.

A 300 Hz rectangular wave 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 on the front surface was equally divided by eight. Using a Hamamatsu Photonics FFP optical system DVS-3000, the omnidirectional transmittance of the liquid crystal cell was measured, and the viewing angle dependence of the isocontrast curve and gradation characteristics of the liquid crystal display panel was determined. The results are shown in Figs.

Figure 2 shows the isocontrast curves of the liquid product display panel (viewing angle 60 degrees: contrast = 100, 30 and 10 from the inside). FIG. 3 is a graph showing the relationship between the gradation (Y) of the liquid crystal display panel and the viewing angle. As is evident from the results, the area showing a contrast of 10 or more was expanded as compared with Comparative Example 1, and the asymmetry of the left and right gradations was reduced. Example 2

A liquid crystal display panel was produced in the same manner as in Example 1 except that the film D produced in Reference Example 2 was used as the optical compensation film, and the viewing angle dependence of the isocontrast curve and gradation characteristics was determined. The results are shown in FIGS.

Figure 4 shows the isocontrast curve of the liquid crystal display panel (viewing angle 60 degrees: contrast from inside = 100, 30, 10).

FIG. 5 is a graph showing the relationship between the gradation of the liquid crystal display panel and the viewing angle.

As is clear from these results, the area showing a contrast of 10 or more was expanded and the asymmetry of the left and right gradations was reduced as compared with Comparative Example 1. Comparative Example 1

A liquid crystal display panel was manufactured in the same manner as in Example 1 except that the compensation film (film A) manufactured in Reference Example 1 was used as the compensation film, and the viewing angle dependence of the isocontrast curve and the gradation characteristics was determined. I asked. The results are shown in FIGS.

Figure 6 shows the isocontrast curve of the liquid crystal display panel (viewing angle 60 degrees: contrast from inside = 100, 30, 10).

FIG. 7 is a graph showing the relationship between the gradation of the liquid crystal display panel and the viewing angle.

In this liquid crystal display panel, the absolute value of the twist angle of the driving liquid crystal cell when no voltage is applied is equal to the absolute value of the twist angle of the film A. Comparative Example 2

A liquid crystal display panel was produced in the same manner as in Example 1 except that the film B produced in Reference Example 2 was used as the optical compensation film, and the viewing angle dependence of the isocontrast curve and gradation characteristics was determined. The results are shown in Fig. 18 and Fig. 9.

Figure 8 shows the isocontrast curve of the liquid crystal display panel (viewing angle 60 degrees: contrast from the inside = 100, 30, 10). FIG. 9 is a graph showing the relationship between the gradation of the liquid crystal display cell and the viewing angle.

Compared with Comparative Example 1, no improvement was observed in the region showing a contrast of 10 or more and the asymmetry of the left and right gradations. Comparative Example 3

A liquid crystal display panel was produced in the same manner as in Example 1 except that the film E produced in Reference Example 2 was used as the optical compensation film, and the viewing angle dependence of the isocontrast curve and gradation characteristics was determined. The results are shown in FIG. 10 and FIG.

Figure 10 shows the isocontrast curve of the liquid crystal display panel (viewing angle 60 °: contrast from inside = 1◦0, 30, 10).

FIG. 11 is a graph showing the relationship between the gradation of the liquid crystal display panel and the viewing angle.

Compared with Comparative Example 1, although the area showing the contrast of 10 or more and the asymmetry of the left and right gradations were improved, the contrast at the front was reduced, and the area showing the contrast of 100 or more disappeared. Reference Example 3 (Production of optical compensation film 2)

A solution was prepared by dissolving 9.81 g of polymer A and 0.19 g of polymer: 8 prepared in Reference Example 1 in 40 g of a mixed solvent of phenol / tetrachlorobenzene (6/4 weight ratio). . This solution was applied to a polyimide substrate (Kapton, trade name, manufactured by Dubon) rubbed with rayon cloth by a vacuum coating method, dried, heat-treated at 240 ° C for 30 minutes, and then cooled to room temperature. A liquid crystal film with an average actual film thickness of 2.34 m was obtained on a polyimide substrate by cooling and fixing (Sample B). The actual film thickness of the liquid crystal film was measured using a stylus type film thickness meter. Next, the refractive index of the liquid crystal film was measured by placing it on the prism surface of an Abbe refractometer (Type-4 manufactured by Ayago) so that the polyimide substrate surface of sample B was in contact with it. The refractive index (no) in the direction perpendicular to the rubbing direction of the polyimide substrate was 1.55, and the refractive index (ne) in the parallel direction was 1.75. The refractive index was constant at 1.55. From this, the liquid crystal film is a rod-shaped liquid crystal on the polyimide substrate interface side with respect to the substrate and the rubbing direction. Molecules are aligned in parallel and plane, and liquid crystal no and ne are found to be 1.55 and 1.75 respectively.

In addition, the liquid crystal film surface of sample B was placed so that the liquid crystal film surface of sample B 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. 55, — 1.75 in the 45-degree direction, and the refractive index in the g-thick direction was constant at 1.55. Therefore, in Sample B, the liquid crystal film in the sample B had a substantially homogeneous alignment of the liquid crystal molecules at both the substrate interface and the air interface, and the rod-like liquid crystal molecules at the interface between the substrate interface and the air interface were almost 1450 degrees at both interfaces. The appearance of twisting was confirmed. Since Sample B contains an opaque and optically anisotropic polyimide substrate, a UV curable adhesive (UV_3400, manufactured by Toagosei Co., Ltd.) Then, a white glass substrate (1.1 mm in thickness) manufactured by Corning Co., Ltd. was laminated thereon as a transfer substrate, and then the adhesive was cured by UV irradiation of about 60 OmJ. By peeling off, an optical compensation film 2 with a white glass substrate was obtained.

Obtained optical compensation film 2

And the torsion angle (right-handed torsion), it was confirmed that Δn ₁ d] = 430 nm and the torsion angle = _45 °. Reference example 4

As the transfer substrate, An is ₂ d ₂ except for using a triacetyl cellulose (T AC) film is Gar 0.99 nm to obtain an optical compensation element composed of an optical compensation film 2 / TAC film in the same manner as in Reference Example 3 . Example 3

A drive liquid crystal cell (TN) with a cell gap of 4.8〃m, And = 470 nm, a twist angle of 90 ° (left-handed twist), and a pretilt angle of 2 ° using Merck's ZLI-4792 as the liquid crystal material of the drive liquid crystal cell. Cell) was prepared.

An optical compensation film 2 obtained in Reference Example 3 in the cell, eight] ₂ 3 ₂ - a T AC film is 150 nm, as shown in FIG. 12, the polarizing plate from the viewing side (1) / optical compensation off A liquid crystal display panel was prepared by arranging the film (3) / TAC film (4) / TN cell (2) / polarizing plate (Γ) in this order.

A rectangular wave of 300 mm 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 on the front surface was equally divided by eight. The viewing angle of the transmittance of the liquid crystal cell was measured using a color luminance meter ΒΜ-5 manufactured by Topcon Corporation, and the viewing angle dependence of the gradation characteristics of the liquid crystal display panel was determined. Figure 13 shows the relationship between the gradation of the liquid crystal display panel and the viewing angle. Example 4

The optical compensator obtained in Reference Example 4 was used as the optical compensator, and as shown in FIG. 14, the polarizing plate (1) / optical compensator (3 ′) / ΤΝcell (2) / polarizer (Γ ), A liquid crystal display panel was prepared, and the viewing angle dependence of the gradation characteristics of the liquid crystal display panel was determined in the same manner as in Example 3. FIG. 15 shows the relationship between the gradation of the liquid crystal display panel and the viewing angle. Comparative Example 4

△ instead of T AC film n ₂ d ₂ is an 0.99 nm,厶] create the same TN cell and 1 ₂ (1 ₂ Example 3 except for using the two TAC films are _200 nm Then, as shown in Fig. 16, from the viewing side, the polarizing plate (1) / optical compensation film (3) / TAC film (4) / TAC film (4 ') / TN cell (2) / polarizing plate (Γ) Next, the viewing angle dependence of the gradation characteristics of the liquid crystal display panel was determined in the same manner as in Example 3. Fig. 17 shows the relationship between the gradation and the liquid crystal display panel. The relationship with the viewing angle is shown for each cell in Examples 3 and 4 and Comparative Example 4. The asymmetry of the left and right sides during halftone display is compared, and the results are shown in Table 2. In comparison, it can be seen that the @cell of the example can reduce left-right asymmetry during halftone display without impairing contrast characteristics. Table 2

(Note) Degree of asymmetry: 10 1n [Transmittance (-40 °) / Transmittance (+ 40 °;)] [Industrial applicability]

The normally black mode TN liquid crystal display element of the present invention has a wide viewing angle characteristic and has small left-right asymmetry during halftone display, so that high-quality image display is possible.

[Brief description of drawings]

FIG. 1 is a layout diagram of the liquid crystal display panel created in the first embodiment.

FIG. 2 is an isocontrast curve of the liquid crystal display panel created in Example 1.

FIG. 3 is a graph showing the relationship between the gradation and the viewing angle of the liquid crystal display panel created in Example 1.

FIG. 4 is an isocontrast curve of the liquid crystal display panel created in Example 2.

FIG. 5 is a graph showing the relationship between the gradation and the viewing angle of the liquid crystal display panel created in Example 2.

FIG. 6 is an isocontrast curve of the liquid crystal display panel prepared in Comparative Example 1.

FIG. 7 is a graph showing the relationship between the gradation and the viewing angle of the liquid crystal display panel created in Comparative Example 1.

FIG. 8 is an isocontrast curve of the liquid crystal display panel created in Comparative Example 2.

FIG. 9 is a graph showing the relationship between the gradation and the viewing angle of the liquid crystal display panel created in Comparative Example 2.

FIG. 10 is an isocontrast curve of the liquid crystal display panel created in Comparative Example 3.

FIG. 11 is a graph showing the relationship between the gradation and the viewing angle of the liquid crystal display panel created in Comparative Example 3.

FIG. 12 is a layout diagram of the liquid crystal display panel created in the third embodiment.

Fig. 13 is a graph showing the relationship between the gradation and the viewing angle of the liquid crystal display panel created in Example 3. It is.

FIG. 14 is a layout diagram of the liquid crystal display panel created in the fourth embodiment.

FIG. 15 is a graph showing the relationship between the gradation and the viewing angle of the liquid crystal display panel created in Example 4.

FIG. 16 is a layout diagram of the liquid crystal display panel created in Comparative Example 4.

FIG. 17 is a graph showing the relationship between the gradation and the viewing angle of the liquid crystal display panel created in Comparative Example 4.

Claims

The scope of the claims

1. A driving liquid crystal cell having a liquid crystal layer having a twisted nematic alignment between a pair of transparent substrates having electrodes when no voltage is applied, and an optical compensation film having a twisted nematic alignment. A liquid crystal display device sandwiched between two polarizing plates, wherein the absolute value of the twist angle of the optical compensation film is smaller than the absolute value of the twist angle of the driving liquid crystal cell when no voltage is applied. Normally black mode type TN liquid crystal display.

2. The product (And) of the refractive index anisotropy 液晶 n of the liquid crystal layer 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, and the voltage of the driving liquid crystal cell when no voltage is applied The twist angle is in the range of 80 ° to 100 °, and the twist direction of the optical compensation film is opposite to the twist direction of the driving liquid crystal cell, and the absolute value of the twist angle is the twist angle of the driving liquid crystal cell. 2. The normally black mode TN liquid crystal display element according to claim 1, wherein the absolute value of the TN liquid crystal display element is smaller than 15 degrees, and the difference is 15 degrees or more.

3. A driving liquid crystal cell having a liquid crystal layer having a twisted nematic alignment between a pair of transparent substrates having electrodes when no voltage is applied, an optical compensation film having a twisted nematic alignment, and an optical compensating film. A liquid crystal display device in which a film showing negative anisotropy is sandwiched between two polarizing plates, and the absolute value of the twist angle of the optical compensation film is the twist of the driving liquid crystal cell when no voltage is applied. A normally black mode TN liquid crystal display device characterized by being smaller than the absolute value of the angle.

4. The product (And) of the refractive index anisotropy Δη of the liquid crystal layer 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, and the driving liquid crystal cell twists when no voltage is applied. angle is in the range of 80 ° ~ 100 °, the product of the refractive index anisotropy an] and the thickness of the optical compensation film (an, d ₃₎ is in the range of 150 to 600 nm, twist of optical science compensation film The absolute value of the angle is smaller than the absolute value of the torsion angle of the driving liquid crystal cell when no voltage is applied, and the difference is 15 degrees or more. The product of the birefringence Δη ₂ and the thickness d ₂ (Z n ₂ d ₂ ) is-20 to-300 4. The normally black mode type T according to claim 3, wherein the wavelength is in the range of nm.

N liquid crystal display element.

5. The use of a twisted nematic alignment formed by a thin film of polymer liquid crystal exhibiting optically positive uniaxiality in the liquid crystal state, and fixing the glass film by cooling the thin film to use as an optical compensation film. 5. The normally black mode TN liquid crystal display device according to claim 1, 2, 3, or 4.

6. Optical compensation of a liquid crystal film in which the twisted nematic alignment formed by a photocurable low-molecular liquid crystal thin film that exhibits optically positive uniaxiality in the liquid crystal state is fixed by irradiating the thin film with light. 5. The normally black mode TN liquid crystal display device according to claim 1, wherein the TN liquid crystal display device is used as a film.