JP2001083515A - Reflective liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type liquid crystal display device having a bright white display, an achromatic black-and-white display with a high contrast and a high optical characteristic with little dependence on a viewing angle. SOLUTION: A twisted nematic reflective liquid crystal display device comprising a driving liquid crystal cell, a polarizing plate disposed on one side of the liquid crystal cell, and a reflector disposed on the other side of the liquid crystal cell. , An optically anisotropic element composed of an optically anisotropic film (A) having a twisted nematic alignment structure fixed thereon and a light diffusion layer (B) is provided between a polarizing plate and a reflecting plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device which has bright and high contrast display characteristics.

[0002]

2. Description of the Related Art In recent years, the application of liquid crystal display elements has been expanding from calculators to word processors and personal computer displays due to the remarkable improvement in display performance due to the progress of liquid crystal display technology. Further, expectations for market expansion as displays of portable information terminal equipment, which can make full use of the thin and lightweight features of liquid crystal display elements, are increasing. For portable applications, since it is usually driven by a battery, it is important to reduce power consumption. For this reason, as a liquid crystal display element for portable use, a reflective liquid crystal display element capable of reducing power consumption, thinning, and light weight can be used without using a backlight that consumes large power. I have. The most important performance required for a reflective liquid crystal display device is how to effectively utilize ambient light. At present, a display mode generally used for calculators, electronic organizers, and the like is a TN (twisted nematic) method in which two polarizing plates and a reflecting plate are combined. However, in the method using two such polarizing plates, any one of two orthogonally polarized linearly polarized light components of elliptically polarized light (including circularly polarized light and linearly polarized light) reflected by the reflecting plate is used. Is absorbed by the polarizer disposed between the reflector and the liquid crystal layer. Therefore, there is a loss of light due to the absorption of the polarizing plate, so that a bright display cannot be obtained. As a conventional technique for solving this problem, Japanese Patent Application Laid-Open No. 8-76111
Japanese Patent Laid-Open Publication No. HEI 9-214969 proposes a reflection type liquid crystal display device in which a polarizing plate, a retardation plate, a liquid crystal cell, and a reflection plate are laminated in this order, and a twisted structure having a direction opposite to that of the liquid crystal cell is provided as the retardation plate. By adopting such a configuration, it is possible to remove the polarizing plate on the reflector side from a reflection type liquid crystal display device using a TN type liquid crystal cell which is generally used, so that high brightness is inevitably obtained. Is expected, and white display with high reflectivity can be expected. However, when a reflective liquid crystal display element having such a configuration is formed, it is difficult to display a monochrome achromatic color. In particular, when the black luminance greatly fluctuates due to a change in the light incident direction, control of the light incident direction is performed. However, in the case of the reflective type, which is more difficult than the transmissive type, this has led to the problem that the optical characteristics are greatly impaired as a result.

[0003]

SUMMARY OF THE INVENTION The present invention provides a reflection type liquid crystal display device which is bright in white display, capable of high-contrast achromatic black-and-white display, has little viewing angle dependence, and has good optical characteristics. The purpose is to:

[0004]

That is, a reflection type liquid crystal display device according to the present invention comprises a driving liquid crystal cell comprising a pair of transparent substrates having electrodes and a nematic liquid crystal, and a driving liquid crystal cell disposed on one side of the liquid crystal cell. In a twisted nematic reflective liquid crystal display device comprising at least a polarizing plate and a reflector disposed on the other side of the liquid crystal cell, a liquid crystal exhibiting optically positive uniaxiality between the polarizer and the reflector An optically anisotropic film (A) substantially formed of a conductive polymer, in which the twisted nematic alignment structure formed in a liquid crystal state of the liquid crystalline polymer is fixed, and at least one light diffusion layer (B). Characterized in that an optically anisotropic element composed of

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The reflection type liquid crystal display device of the present invention comprises:
A driving liquid crystal cell, a polarizing plate, a reflecting plate, and an optically anisotropic element are provided. The driving liquid crystal cell has a pair of transparent substrates provided with electrodes and a liquid crystal material inserted between them. As the transparent substrate, a substrate that aligns a liquid crystal substance in a specific alignment direction can be used. Specifically, a transparent substrate in which the substrate itself has a property of orienting a liquid crystal material, and a transparent substrate in which an alignment film or the like having a property of orienting a liquid crystal material is provided on the substrate, although the substrate itself lacks alignment ability. Can be used. In this way, two transparent substrates having alignment ability in a specific direction are held so that the alignment is in a twisted relationship, and a liquid crystal material is inserted between the substrates to form a liquid crystal layer. A specific twist angle can be given. In addition, the electrode of the liquid crystal cell can be usually provided on the surface of the transparent substrate in contact with the liquid crystal layer. When a substrate having an alignment film is used, it can be provided between the substrate and the alignment film. As the liquid crystal substance, various substances usually used for TN type and / or STN type liquid crystal display devices can be used.

The polarizing plate is disposed on one side of the liquid crystal material layer (liquid crystal layer), and is not disposed on both sides of the liquid crystal layer.
Generally, it is customary to arrange the liquid crystal layer outside one of the transparent substrates, but to provide a polarizing plate between one transparent substrate and the liquid crystal layer, that is, inside the liquid crystal cell. Can also. In the case where a polarizing plate is provided outside one of the transparent substrates sandwiching the liquid crystal layer, other components such as an optically anisotropic element may be interposed between the transparent substrate and the polarizing plate. it can. The polarizing plate used in the present invention is not particularly limited, and any general polarizing plate having an absorption axis can be used. However, in order to obtain a reflective liquid crystal display device having a high reflectance, it is preferable to use a polarizing plate having a high transmittance. Specifically, a halogen-polarized film made by arranging iodine molecules having a high degree of polarization in a certain direction on a uniaxially stretched polyvinyl alcohol film (PVA) or a polyvinyl alcohol film directly dyed with a dye is used as another supporting film. Can be used as a polarizing plate having high transmittance.

[0007] The reflector of the present invention is installed on the liquid crystal cell surface opposite to the side where the above-mentioned polarizing plate is installed, and the reflector and the polarizing plate are not arranged on the same surface of the liquid crystal cell. The reflector is generally provided outside the transparent substrate with the liquid crystal layer interposed therebetween, but a reflector may be provided between the liquid crystal layer and the transparent substrate. When the reflector is provided in the liquid crystal cell, the reflector can also function as an electrode of the liquid crystal cell. The reflection plate is preferably of a specular reflection type. An aluminum foil, a silver foil, or the like can be used for the reflection plate, or an aluminum evaporation layer or a silver evaporation layer can be provided on a substrate such as glass by a vacuum evaporation method or the like and used as the reflection plate.

The optically anisotropic element used in the present invention comprises an optically anisotropic film (A) in which a twisted nematic alignment structure is fixed, and at least one light diffusion layer (B). The optically anisotropic film means a film having an optically anisotropic axis and having a structure in which the optically anisotropic axis is twisted from one surface to the other surface. Therefore, the optically anisotropic film has the same characteristics as a multilayer of optically anisotropic layers in which the optically anisotropic axis is continuously twisted. Like a cell, it has a twist angle. The optically anisotropic film used in the present invention has a structure in which a layer having an optically anisotropic axis is continuously twisted in one film, that is,
It is a film in which a twisted nematic alignment structure is fixed. Such an optically anisotropic film can be generally obtained by forming a liquid crystalline substance having a twist characteristic into a film. As a liquid crystalline substance having a twisting characteristic, for example, it shows optically positive uniaxiality irrespective of the shape of liquid crystal molecules such as a rod shape or the like, a low molecule or a polymer. Any of the resulting liquid crystalline compounds or liquid crystalline compositions can be used. Specifically, a polymer liquid crystal having a unit that induces twisting, for example, a main-chain polymer liquid crystal such as polyester, polyamide, polycarbonate, or polyesterimide exhibiting liquid crystallinity, or polyacrylate, polymethacrylate, polymalonate, or polysiloxane And other side-chain polymer liquid crystals. Among them, polyester is preferred from the viewpoint of easiness of synthesis, orientation, and appropriateness such as glass transition point. Optically active 2 is a unit that induces torsion.
-Methyl-1,4-butanediol, 2,4-pentanediol, 1,2-propanediol, 2-chloro-
1,4-butanediol, 2-fluoro-1,4-butanediol, 2-bromo-1,4-butanediol,
A unit derived from -ethyl-1,4-butanediol or 2-propyl-1,4-butanediol or a derivative thereof (for example, a derivative such as a diacetoxy compound) can be used. The above diols are represented by R
It may be any of the R-form and the S-form, or a mixture of the R-form and the S-form. For fixing the twisted nematic alignment structure formed by the liquid crystalline substance, for example, means such as photocrosslinking, thermal crosslinking, or cooling can be used.

The material of the light diffusion layer of the present invention is not particularly limited as long as it has a property of diffusing incident light isotropically or anisotropically. Therefore, this light diffusion layer
It may be a plastic sheet showing light diffusing properties, a plastic film, a plastic substrate, a substrate other than plastic, or the like, and may have a self-supporting property in which particles having a refractive index different from that of the matrix are dispersed in an adhesive matrix. It may be a sheet-like material, a film-like material, or the like. The sheet, film, substrate and the like may have self-supporting properties or may not have self-supporting properties. When it does not have a self-supporting property, it may be held on a film or a substrate having a self-supporting property by some means, and the light diffusion property may not be impaired as a whole. Further, on the optically anisotropic film described above, a compound or composition capable of forming a light diffusion layer is applied by means such as melt coating or solution coating, and if necessary, an electric field, a magnetic field, polarized light irradiation, etc. A treatment may be performed to integrate the light diffusion layer with the optically anisotropic film. However, it is necessary to perform the melt coating or the solution coating so that the film strength of the optically anisotropic film does not decrease. Examples of the light diffusion layer having adhesive properties include an acrylic adhesive, a rubber adhesive, a silicon adhesive, an ethylene-vinyl acetate copolymer adhesive, a urethane adhesive, a vinyl ether adhesive, and a polyvinyl alcohol adhesive. In a matrix composed of a polyacrylamide-based pressure-sensitive adhesive and a mixed pressure-sensitive adhesive thereof, for example, polystyrene-based fine particles having an average particle size of 0.5 to 5 μm,
Organic fine particles such as polymethacrylic acid-based fine particles, inorganic fine particles such as silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide and antimony oxide, hollow fine particles containing gas, and microcapsules containing liquid Can be exemplified. Among them, acrylic pressure-sensitive adhesives are desirable as a matrix because they are excellent in transparency, weather resistance, heat resistance and the like. When the adhesive light diffusing layers are superposed, the individual adhesive light diffusing layers can be of the same type or different types in an appropriate combination. As the acrylic pressure-sensitive adhesive, any of known materials can be used. For example, methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, isobutyl, amyl, isoamyl, hexyl, heptyl, cyclohexyl,
Straight-chain or branched alkyl having 1 to 18 carbon atoms such as ethylhexyl, octyl, isooctyl, nonyl, isononyl, decyl, undecyl, lauryl, tridecyl, tetradecyl, stearyl, octadecyl; Adhesives mainly composed of acrylic polymers using one or two or more acrylic acid alkyl esters composed of an ester of acrylic acid or methacrylic acid having a group are exemplified. In addition, the light diffusion layer having an adhesive property, for example, in a range that does not impair the effects of the present invention, for example,
Adhesion such as petroleum resin, rosin resin, terpene resin, synthetic petroleum resin, phenolic resin, xylene resin, alicyclic petroleum resin, coumarone indene resin, styrene resin, dicyclopentadiene resin, etc. Appropriate additives such as imparting agents, softening agents such as phthalic acid esters, phosphoric acid esters, paraffin chloride, polybutene, and polyisobutylene or other various fillers, antioxidants, and crosslinking agents can be blended. Examples of the light diffusion layer having no tackiness include a plastic sheet, film, and substrate in which particles having a refractive index different from that of the matrix are dispersed in a resin matrix. In particular,
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 naphthalate, polyacetal, polycarbonate , Polyarylate, acrylic resin, polyvinyl alcohol, polystyrene, polyurethane, polyethylene, polypropylene, cellulosic plastics, epoxy resin, phenolic resin and the like, inorganic fine particles as exemplified above,
Examples include organic fine particles, hollow fine particles containing gas, and plastic film substrates in which microcapsules containing liquid are dispersed. The thickness of the light diffusion layer is
Although not particularly limited, it is usually 10 μm or more and 50 μm or more.
0 μm or less. The total light transmittance of the light diffusion layer is 5
It is preferably at least 0%, particularly preferably at least 70%. Furthermore, the diffusion transmittance of the light diffusion layer is
Usually, it is 5 to 99%, preferably 50 to 99%. The optically anisotropic element composed of the optically anisotropic film (A) and the light diffusion layer (B) as described above is disposed between a polarizing plate and a reflecting plate. Specifically, for example, it can be arranged between the polarizing plate and the driving liquid crystal cell or between the driving liquid crystal cell and the reflecting plate. Above all, it is particularly preferable to provide between the polarizing plate and the liquid crystal cell. Either the optically anisotropic film (A) or the light diffusion layer (B) of the optically anisotropic element may be disposed so as to be closer to the polarizing plate or the driving liquid crystal cell. The reflection type liquid crystal display element of the present invention has a driving liquid crystal cell, a polarizing plate, a reflection plate, and an optically anisotropic element as essential components, but other components can be additionally provided. For example, by attaching a color filter to the reflective liquid crystal display device of the present invention, a reflective color liquid crystal display device capable of performing multicolor or full-color display with high color purity can be manufactured.

[0010]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited thereto. In the present embodiment, the counterclockwise direction from the polarizing plate side to the reflecting plate side is +, and the clockwise direction is-.
And an experiment was conducted. However, the same result can be obtained by performing a similar experiment with the clockwise direction + and the counterclockwise direction − from the polarizing plate toward the reflecting plate side. Production example 1 of optically anisotropic film (A) and optically anisotropic element 1 Terephthalic acid 50 mmol, 2,6-naphthalenedicarboxylic acid 50 mmol, methylhydroquinone diacetate 40 mmol, catechol diacetate 62 mmol,
Using 60 mg of N-methylimidazole and a nitrogen atmosphere, polymerization was carried out at 270 ° C. for 12 hours. Next, the obtained reaction product was dissolved in tetrachloroethane, and then purified by reprecipitation with methanol to obtain 14.7 g of a liquid crystalline polyester. This liquid crystalline polyester has a logarithmic viscosity of 0.17, a nematic phase as a liquid crystal phase, an isotropic phase-liquid crystal phase transition temperature of 250 ° C. or more, and a glass transition point of 11 ° C.
5 ° C. (Polymer 1). Biphenyl dicarbonyl chloride 90 mmol, terephthaloyl chloride 10 m
mol, 2R, 3R-dimethoxybutanediol 105
mmol was reacted in dichloromethane at room temperature for 20 hours, and the reaction solution was poured into methanol and reprecipitated to obtain 12.3 g of a liquid crystalline polyester (polymer 2). Polymer 2 has a logarithmic viscosity of 0.11, shows a chiral smectic phase at room temperature, and has an isotropic transition temperature of 4
It was between 0 and 50 ° C. Further, Tg was considered to be around room temperature, and could not be observed by measurement by DSC. A solution was prepared by dissolving 19.9 g of the polymer 1 and 0.08 g of the polymer 2 in 80 g of a phenol / tetrachloroethane mixed solvent (6/4 weight ratio). This solution was applied by a bar coating method on a polyimide film (Kapton, manufactured by DuPont) rubbed with rayon cloth, dried, heat-treated at 210 ° C. for 30 minutes, and then cooled and fixed at room temperature. Thus, a uniformly oriented liquid crystal film having an actual film thickness of 3.85 μm was obtained (Sample 1). The actual film thickness was measured using a stylus type film thickness meter. First, the following experiment was performed to measure the refractive index of the liquid crystal of Sample 1. In measuring the refractive index, an Abbe refractometer (Type manufactured by Atago Co., Ltd.)
-4) was used. When the polyimide substrate is placed in contact with the prism surface of the refractometer and the liquid crystal film is placed so that the substrate interface side is lower than the air interface side, the refractive index in the film surface has anisotropy and is perpendicular to the rubbing direction. The in-plane refractive index was 1.55, the in-plane refractive index was 1.75, and the refractive index in the film thickness direction was constant at 1.55 regardless of the direction of the sample. From this, on the glass substrate side, rod-like liquid crystal molecules are planarly aligned with respect to the substrate and parallel to the rubbing direction, and the no and ne of the liquid crystal are each 1.5.
5, 1.75. Next, when the optical element film is disposed such that the air interface side of the optical element film is in contact with the prism surface of the refractometer, the in-plane refractive index becomes 1.55 in a direction parallel to the rubbing direction and 1.75 in a direction perpendicular to the rubbing direction. The refractive index in the film thickness direction was constant at 1.55 regardless of the direction of the sample. From this, it was confirmed that the polymer molecules were mostly homogeneously aligned at both the substrate interface and the air interface, and that the rod-like liquid crystal molecules were twisted by approximately 90 degrees in the film plane between the substrate interface and the air interface. Sample 1
Is formed on an opaque and optically anisotropic polyimide film and cannot be used for optical compensation as it is. Therefore, a UV curable adhesive (UV-3400, manufactured by Toagosei Co., Ltd.) is provided on the air interface side of Sample 1.
Is applied to a thickness of about 5 μm, and a white plate glass (1.1 mm thick) manufactured by Corning Co. is laminated on the
The adhesive was cured by mJ UV irradiation. Thereafter, the liquid crystal layer was transferred onto a substantially optically isotropic support by peeling the polyimide film from the laminate in which the glass / adhesive / liquid crystal layer / polyimide film were integrated. The polarization analysis of the obtained compensation film (sample 1) was performed to measure Δn2 · d2 and torsion angle θ2 of the film.
A value of -180 was obtained. Next, Dai Nippon Printing Co., Ltd.
Light diffusion sheet IDS-21 (total light transmittance 91.1)
% And a haze of 51.6) were adhered to the liquid crystalline polyester side of the film via a non-carrier adhesive made by Tomagawa Paper. Through the above steps, an optically anisotropic element having an optically anisotropic film formed on a light diffusion sheet via an adhesive and an alignment substrate was prepared. Production example of optically anisotropic film (A) and optically anisotropic element
2- (15) g of 4- (6-acryloyloxyhexyloxy) benzoic acid in tetrahydrofuran solvent purified by distillation.
(518 mmol), 2,6-ditert-butyl-4
-Methylphenol 1.5 g, diisopropylethylamine 70.1 g (543 mmol), and methanesulfonyl chloride 62.1 g (543 mmol) were reacted to synthesize methanesulfonic anhydride of the carboxylic acid, and then methylhydroquinone 29.87 g (246 mmol) ) To give methylhydroquinone bis (4- (6-acryloyloxyohexyloxy) benzoic acid) ester (compound 1) as a crude product. The crude product was recrystallized from ethyl acetate / methanol to give methylhydroquinone bis (4- (6
-Acryloyloxyhexyloxy) benzoic acid ester 146.9 g was obtained as white crystals. G of compound 1
The purity by PC was 98.7%. GPC uses tetrahydrofuran as an elution solvent, and a Tosoh GPC analyzer CCP & 8000 (CP-8) equipped with a packed column for high-speed GPC (TSKgel G-1000HXL).
000, CO-8000, UV-8000). 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. Using a similar technique, 2,3-dimethylhydroquinone bis (4- (11-acryloyloxyundecyloxy) benzoic acid) ester (Compound 2) was obtained. The purity of Compound 2 measured by GPC was 99.3%. Using a similar technique, 2-chlorohydroquinone bis (-)-(4- (2-ethylhexyl) benzoic acid) ester (Compound 3) was obtained. Compound 3 had dextrorotatory power as measured by a polarimeter. Compound 1 thus obtained
6.5 g, compound 2 (2.913 g), and compound 3 (0.1 g).
Weigh out 587 g, methoxypropyl acetate 90 g
Was dissolved. The solution was added with a fluorine-based surfactant S-383.
(Manufactured by Asahi Glass), 0.3 g of a photoreaction initiator Irgacure 907 (manufactured by Ciba Geigy), and 0.1 g of a sensitizer diethylthioxanthone were added. Triacetyl cellulose film with corona-treated surface (Fujitac, UVD-8
0) Polyvinyl alcohol (Kurarepovar MP-203) was evenly applied to a thickness of 0.2 μm on a gelatin layer via a gelatin layer, and the solution was applied by a bar coater to an oriented substrate whose dried surface was rubbed with a rayon cloth. did.
After coating, paste the back of the film on a blue glass substrate,
The integrated glass-film product was placed on a hot plate set at 80 ° C. and dried for 20 minutes. After drying, the nematic alignment of the liquid crystal layer had already been completed. Thereafter, the film is put into an oven set at 50 ° C. in a state in which the film is in close contact with the glass substrate, and the atmosphere is set at an oxygen concentration of 250 pp for 2 to 3 minutes.
m, the mixture was allowed to cool to the oven setting temperature while being replaced with nitrogen, and then UV irradiation was performed at that temperature. A high-pressure mercury lamp was used as the UV light source, and the irradiation intensity was 120 W /
cm2, the total irradiation amount during the irradiation time of 15 seconds is 1260
mJ. The liquid crystal layer after irradiation was cured, and its surface hardness was about 2H in terms of pencil hardness. (Sample 2) The actual film thickness of the sample 2 measured by the thin film interference method was 5.
It was 5 μm. The following experiment was performed to measure the refractive index of the liquid crystal of Sample 2. Using the liquid crystalline composition used to prepare Sample 2, it was aligned and fixed on a high refractive index glass substrate having a rubbing polyimide film (having a refractive index of 1.84) under the same conditions to prepare a liquid crystal film. The refractive index was measured using this. 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 was 1.53, the parallel in-plane refractive index was 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.
Thus, the no and ne of the liquid crystal layer are 1.53, 1.
It turned out to be 67. Ellipsometry was performed on Sample 2 to measure Δn2 · d2 and the torsion angle of this film. The results were 770 nm and θ2 = −18, respectively.
A value of 0 ° was obtained. This optically anisotropic film (Sample 2) and the polarizing plate were placed on a light diffusion pressure-sensitive adhesive layer (total light transmittance of 8).
9.2% and a haze of 88.6) to obtain an optically anisotropic element. Example 1 Using the optically anisotropic element obtained in Production Example 2 of the optically anisotropic element,
An STN-type reflective liquid crystal display device was prepared with the arrangement shown in FIG. As shown in FIG. 1, the liquid crystal cell 3 includes a pair of opposing substrates 3C, electrodes 3B provided on inner surfaces thereof, and an alignment film 3E printed and formed thereon and subjected to an alignment process. And A liquid crystal substance is sealed in a space defined by the alignment film 3E and a sealant 3D formed by printing and forming around the substrate, thereby forming a liquid crystal layer 3A. Using ZLI-2293 as a liquid crystal material, the liquid crystal layer 3A was aligned in a predetermined direction by adjusting the alignment processing direction of the alignment film 3E, and twisted at θ1 = + 250 °. The product Δn1 · d1 of the refractive index anisotropy Δn1 of the liquid crystal material in the liquid crystal cell 3 and the thickness d1 of the liquid crystal layer 3A is approximately 880 nm.
Met. The polarizing plate 1 was disposed on the display surface side (upper side in the figure) of the liquid crystal cell 3, while the reflector 4 was disposed on the back side (lower side in the figure) of the liquid crystal cell 3. The optically anisotropic element 2 was disposed between the polarizing plate 1 and the liquid crystal cell 3. The product Δn2 · d2 of the refractive index anisotropy Δn2 and the thickness d2 of the optical anisotropic element 2 is approximately 770 nm,
θ2 = −180 °. Further, an angle θ3 = + 20 ° from the absorption axis of the polarizing plate 1 to the slow axis on the surface of the optically anisotropic body 2 on the polarizing plate side, and on the surface of the liquid crystal layer 3A on the polarizing plate side from the absorption axis of the polarizing plate 1 To the orientation direction at θ4 = + 11
5 °. Incidentally, the arrangement positions and angles θ1 to θ4 of the respective constituent members in the above-mentioned STN-type reflective liquid crystal display element are described.
2 and 3 are shown in FIG. In FIG. 2, the orientation direction 31 on the surface of the liquid crystal layer 3A on the side of the polarizing plate 1 and the orientation direction 32 on the surface of the side of the reflection plate 4 form an angle θ1. The direction 21 of the slow axis of the optically anisotropic element 2 on the surface on the side of the polarizing plate 1 and the direction 22 of the slow axis on the surface of the side of the reflecting plate 4 form an angle θ2. Further, the absorption axis 11 of the polarizing plate 1 and the direction 21 of the slow axis on the surface of the optical anisotropic element 2 on the polarizing plate 1 side form an angle θ3, and the absorption axis 11 of the polarizing plate 1 and the liquid crystal layer 3A Has an angle θ4 with the orientation direction 31 on the surface on the polarizing plate 1 side. FIG. 3 is a plan view showing the positional relationship when these are superimposed and viewed from the polarizing plate side toward the reflecting plate side using the same symbols. 2 and 3, θ1 to θ4 are:
For the sake of convenience of explanation, all are rotated counterclockwise from the polarizing plate toward the reflecting plate, that is, relatively rotated in the same direction. However, in the reflective liquid crystal display device of the present invention, the rotating direction of θ1 is always opposite to θ2. Direction. A drive voltage was applied to the above-mentioned liquid crystal display element from a drive circuit (not shown) to the transparent electrode 3B, and the relationship with the reflectance was obtained. FIG. 4 shows the results. Further, the contrast when driven at 1/240 duty and the optimum bias and the luminous reflectance (Y value) when the electric field was turned on were obtained. Table 1 shows the results. As can be seen from the results of FIG. 4, in this liquid crystal display element, the driving voltage was 2.1 to 2.2 V.
It can be seen that the reflectance changes sharply in the vicinity. Comparative Example 1 The optically anisotropic film (sample 2) produced in Production Example 2 of the optically anisotropic element and the polarizing plate were interposed via an adhesive layer having no diffusivity (total light transmittance 98%, haze degree 0). To produce a laminate. Instead of the optically anisotropic element used in Example 1, a liquid crystal display element similar to that of Example 1 was prepared except that the above-described laminate was used.
Spectral characteristics when electric field is on and electric field is off, and 1/240
The duty, the contrast at the time of driving with the optimum bias, and the reflectance (Y value) at the time of light were obtained. The results are shown in FIG. 5 and Table 1, respectively. From the results shown in FIG. 5, it can be seen that the reflectance changes slowly around the driving voltage of 2.1 to 2.2 V.

[0011]

[Table 1]

Comparing the measurement results of the contrast and the reflectance (Y value) shown in Table 1, the reflection type liquid crystal display device of the present invention has improved contrast as compared with the device of the comparative example.
In particular, it can be seen that the brightness (reflectance) is remarkably improved and good black and white display can be achieved. From the above results, it was confirmed that the reflective liquid crystal display element of the present invention had a significantly higher display quality by combining the film having the twisted nematic structure and the light diffusion layer. Example 2 A reflective color liquid crystal display device including the color filter 7 schematically shown in FIG. 6 was produced. 6, components common to those of the apparatus shown in FIG. 1 are denoted by the same reference numerals. As shown in FIG. 6, red, green, and blue colors are provided between the substrate 3C on the display surface side of the liquid crystal cell 3 and the transparent electrode 3B.
A color filter 7 including three color pixels was inserted. By providing a color filter layer in such a configuration,
Good multi-color or full-color display could be performed.

[Brief description of the drawings]

FIG. 1 is an elevational sectional view schematically showing a display element obtained in Example 1.

FIG. 2 is a schematic diagram illustrating the position and angle relationship of each component in the reflective liquid crystal display element of the present invention.

FIG. 3 is a plane illustrating an angle relationship between an absorption axis of a polarizing plate, an alignment direction of a layer of a liquid crystal substance, and a slow axis direction of an optically anisotropic element (optically anisotropic film) in the reflective liquid crystal display element of the present invention. FIG.

FIG. 4 is a diagram showing a change in reflectance with respect to a change in drive voltage of the device of Example 1.

FIG. 5 is a diagram showing a change in reflectance with respect to a change in drive voltage of the device of Comparative Example 1.

FIG. 6 is an elevational sectional view schematically showing a device of Example 2.

[Explanation of symbols]

1: polarizing plate 2: optical anisotropic element 3A: liquid crystal layer 4: reflective layer 5: external light 6: color filter 11: absorption axis of polarizing plate 21: polarizing plate side of optical anisotropic element (optically anisotropic film) 22: slow axis on the surface of the optically anisotropic element (optically anisotropic film) on the side of the reflector 31: molecule of the liquid crystal material on the surface of the layer of the liquid crystal material on the side of the polarizing plate Alignment direction 32: Alignment direction of molecules of the liquid crystal material on the surface of the layer of the liquid crystal material on the side of the reflector.

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Claims (7)

[Claims] 1. A driving liquid crystal cell comprising a pair of transparent substrates provided with electrodes and a nematic liquid crystal; a polarizing plate disposed on one side of the liquid crystal cell; and a polarizing plate disposed on the other side of the liquid crystal cell. What is claimed is: 1. A twisted nematic reflective liquid crystal display device comprising at least a reflector, wherein between the polarizer and the reflector, substantially formed from a liquid crystalline polymer having an optically positive uniaxial property, A reflection type having an optically anisotropic element composed of an optically anisotropic film (A) in which a twisted nematic alignment structure in which molecules are formed in a liquid crystal state is fixed, and at least one light diffusion layer (B). Liquid crystal display element. 2. The reflective liquid crystal display device according to claim 1, wherein the light diffusion layer (B) is a light diffusion adhesive layer. 3. The optically anisotropic film (A) forms a twisted nematic alignment in a liquid crystal state of a liquid crystal polymer exhibiting positive uniaxiality, and then cools from that state to fix the glass in a liquid crystal phase state. 3. The reflective liquid crystal display device according to claim 1, wherein the reflective liquid crystal display device is a stiffened film. 4. The optically anisotropic film (A) is a film in which a photocurable liquid crystalline low-molecular compound exhibiting positive uniaxiality is twisted nematically aligned, and after alignment, is fixed by light or thermal crosslinking. Item 3. A reflective liquid crystal display device according to item 1 or 2. 5. An optically anisotropic film substantially formed of a liquid crystalline polymer having optically positive uniaxiality, wherein the twisted nematic alignment structure formed in a liquid crystal state of the liquid crystalline polymer is fixed. An optically anisotropic element for a reflection type liquid crystal display device, comprising: (A) and at least one light diffusion layer (B). 6. The optically anisotropic element for a reflective liquid crystal display device according to claim 5, wherein the light diffusion layer is a light diffusion adhesive layer. 7. An optical laminate comprising an optically anisotropic element for a reflection type liquid crystal display element and a polarizing plate.