JP2001228328A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type liquid crystal display device having high reflectance in which display with good contrast can be obtained. SOLUTION: The reflection type liquid crystal display device has a liquid crystal cell produced by inserting a layer of a liquid crystal material into a pair of transparent substrate having electrodes, a polarizing plate, a reflection plate and an optical anisotropic material having a twist structure, and a driving voltage selected from two or more voltages is applied on the layer of the liquid crystal material.)In this device, the polarizing plate is disposed in the side of one face of the liquid crystal material layer, the reflection plate is disposed in the side of the other face of the liquid crystal material layer, and the optical anisotropic material is disposed between the polarizing plate and the reflection plate. When the ratio of refractive index anisotropy Δn at the wavelength λ=450 nm to that at λ=590 nm is defined as a birefringent wavelength dispersion α=Δn(450)/Δn(590), the birefringent wavelength dispersion α1 of the liquid crystal material layer and the birefringent wavelength dispersion α2 of the optical anisotropic material ranges from 1.01 to 1.35 and from 1.11 to 1.40, respectively.

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 having an optical anisotropic body and a polarizing plate and having good contrast.

[0002]

2. Description of the Related Art In recent years, due to the remarkable improvement of display performance due to the progress of liquid crystal display technology, the application of liquid crystal display devices from calculators to word processors and personal computer displays has been expanding. further,
There is a growing expectation for a market expansion as a display for portable information terminal equipment, which makes full use of the thin and light weight features of liquid crystal display devices. For portable applications, since it is usually driven by a battery, it is important to reduce power consumption. Therefore, as a liquid crystal display device for portable use, a reflection type liquid crystal display device which does not need to use a backlight which consumes a large amount of power and which can be reduced in power consumption, thinned, and reduced in weight is particularly attracting attention. I have. Conventionally, as a liquid crystal display device, a TN (twisted nematic) type and a STN (super twisted nematic) type are mainly used. The STN type liquid crystal display device generally has a structure in which a liquid crystal cell is sandwiched between a pair of polarizing plates. In the case of a reflective liquid crystal display device,
Usually, it has a configuration in which a reflection plate is further arranged outside the reflection plate. In the STN mode liquid crystal display device, the twist angle of the liquid crystal molecules in the liquid crystal cell is set to 90 ° or more, and the setting angle of the transmission axis of the polarizing plate with respect to the elliptically polarized light generated by the birefringence effect of the liquid crystal cell is optimized. Therefore, a sudden change in molecular alignment due to the application of a voltage can be reflected in a change in birefringence of the liquid crystal, and an electro-optical characteristic exhibiting a sudden optical change above a threshold can be realized.

In an STN type liquid crystal display device, yellow-green or dark blue may occur as a background color of display due to birefringence of liquid crystal. In order to improve the coloring phenomenon, a liquid crystal cell for optical compensation or a retardation plate formed of a polymer such as polycarbonate or a twisted retardation film is superimposed on the STN liquid crystal cell for display. Thus, a liquid crystal display device configured to perform color compensation and perform a display similar to a black and white display is used as a so-called paper white type liquid crystal display device. However, in the STN mode liquid crystal display device, the transmittance of the polarizing plate is about 9 even when linearly polarized light is incident parallel to the polarization axis.
0%, and there is a problem that sufficient brightness cannot be obtained with the conventional configuration using two polarizing plates.
In particular, in the case of a reflection type liquid crystal display device, a backlight is not used, and since the incident light passes through the polarizing plate a total of four times before being emitted, attenuation of the light amount becomes a problem.
As a conventional technique for solving this problem, Japanese Patent Laid-Open Publication No.
There is a technique described in Japanese Patent Application Laid-Open No. 9519 or JP-A-6-11711. These include a configuration in which a polarizing plate, a retardation plate, a liquid crystal cell, and a reflecting plate are laminated in this order, that is, from a reflective liquid crystal display device using a commonly used STN type liquid crystal cell to a polarizing plate on the reflecting plate side. Is disclosed. By adopting such a configuration, the number of times that the incident light passes through the polarizing plate before the light is emitted becomes twice, so that it is expected that a high luminance is inevitably obtained and a white display with high reflectance can be performed. . However, when forming a reflective liquid crystal display device having such a configuration,
Due to the low degree of structural freedom that one polarizing plate also serves as polarized light before and after reflection, it is difficult to configure each layer such as a retardation plate to provide a good high-contrast display. .

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reflection type liquid crystal display device having a high reflectance and a display with good contrast.

[0005]

According to the first aspect of the present invention,
A liquid crystal cell in which a layer of a liquid crystal substance is inserted into a pair of transparent substrates provided with electrodes, a polarizing plate, a reflecting plate, and an optically anisotropic body having a twisted structure, and a voltage value of two or more values is selected, In a reflection type liquid crystal display device in which a driving voltage is applied to a liquid crystal material layer, the polarizing plate is disposed on one surface side of the liquid crystal material layer, and the reflection plate is disposed on the other surface side of the liquid crystal material layer. And the optically anisotropic member is disposed between the polarizing plate and the reflecting plate, and the wavelength λ = 450 nm and λ =
If the ratio of the refractive index anisotropy [Delta] n in 590nm was defined as the birefringence wavelength dispersion α α = Δn (450) / Δn (590), the birefringence wavelength dispersion alpha ₁ of the liquid crystal material layer and the optical anisotropic body The present invention relates to a reflective liquid crystal display device, characterized in that the birefringence wavelength dispersion α ₂ is in the range of α ₁ = 1.01 to 1.35 α ₂ = 1.11 to 1.40.

According to a second aspect of the present invention, in the liquid crystal material layer, the twist angle θ ₁ of the liquid crystal material molecules from the polarizing plate side to the reflecting plate side is in a range of + 200 ° to + 270 °, Angle θ from the polarizing plate side to the reflecting plate side of the slow axis of
₂ is in the range of −155 ° to −220 °, and the liquid crystal material layer has a refractive index anisotropy Δn at a wavelength λ = 550 nm.
The product (△ n ₁ · d ₁ ) of ₁ and thickness d ₁ is 700 nm to 100
0 nm, and the wavelength λ of the optically anisotropic body is 550.
The product of the refractive index anisotropy Δn ₂ in nm and the thickness d ₂ of the optically anisotropic body (Δn ₂ · d ₂ ) is 550 nm to 850 nm.
2. The reflection type liquid crystal display device according to claim 1, wherein: The invention according to claim 3 relates to the reflection type liquid crystal display device according to claim 1 or 2, wherein the optically anisotropic body is made of a liquid crystal film. The invention according to claim 4 relates to the reflective liquid crystal display device according to claim 1, further comprising at least one light diffusion layer between the polarizing plate and the reflection plate.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The reflection type liquid crystal display device of the present invention comprises:
It includes a liquid crystal cell, a polarizing plate, a reflecting plate, and an optically anisotropic body. The liquid crystal cell has a pair of transparent substrates having electrodes and a layer of a liquid crystal material inserted between the transparent substrates. As the transparent substrate, a substrate that aligns the liquid crystal material in a specific alignment direction can be used. Specifically, either a transparent substrate having the property of aligning the liquid crystal substance itself or a transparent substrate provided with an alignment film or the like having the property of aligning the liquid crystal substance can be used. By holding two transparent substrates having such a specific alignment direction such that the alignment directions are in a twisted relationship, and forming a layer of a liquid crystal material between the transparent substrates, a layer of the liquid crystal material is formed. , Can give a specific twist angle. In addition, the electrode of the liquid crystal cell can be usually provided on the surface of the transparent substrate that is in contact with the layer of the liquid crystal substance. When a transparent substrate having an alignment film is used, the electrode is provided between the transparent substrate and the alignment film. be able to. As the liquid crystal substance, various substances usually used for STN type liquid crystal display devices can be used.

The refractive index anisotropy Δn of the liquid crystal material used in the liquid crystal cell generally depends on the wavelength λ (nm), and the characteristic generally has a negative tendency with respect to the wavelength λ. Wavelength λ = 450 nm and λ = 590 nm of liquid crystal material
(Hereinafter referred to as “Δn ₁ (45
0) ”and“ Δn ₁ (590) ”. ) Is defined as birefringence wavelength dispersion α ₁ , α ₁ = Δn ₁ (450) / Δn ₁ (590). α ₁ is the same if the liquid crystal materials are exactly the same, but may be the same even if different liquid crystal materials are used. In the reflective liquid crystal display device of the present invention, a driving voltage is applied to the layer of the liquid crystal material by selecting two or more voltage values. The two or more voltage values are not particularly limited as long as they are effective voltage values for performing liquid crystal display, and may be voltage values before and after a sharp change in reflectance occurs. Thereby, the layer of the liquid crystal material can function as an active optical layer that provides a bright achromatic color and a dark achromatic color.

The polarizing plate is arranged on one side of the liquid crystal material layer. In general, it is usually arranged on one of the front surface or the back surface of the liquid crystal cell, in other words, it is arranged on the surface of the transparent substrate which is not the liquid crystal material layer interface side of one transparent substrate. A polarizing plate can be disposed between the liquid crystal material layer, that is, in the liquid crystal cell. When a polarizing plate is provided on the front surface or the back surface of the liquid crystal cell, the polarizing plate may be provided via an optically anisotropic body or the like. The polarizing plate used in the present invention is not particularly limited, and various general polarizing plates 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. Is sandwiched between
It can be used as a polarizing plate with high transmittance.

The reflecting plate is usually installed on the surface of the liquid crystal cell opposite to the side where the above-mentioned polarizing plate is installed. In other words, when the polarizing plate is arranged on the front side of the liquid crystal cell, the reflecting plate is arranged on the back side of the liquid crystal cell. When the polarizing plate is arranged on the back side of the liquid crystal cell, the reflecting plate is reflected on the front side. A plate is placed.
This reflector can be installed in a liquid crystal cell, similarly to the above-mentioned polarizing plate, but in this case, the transparent substrate adjacent to the reflecting plate is a transparent substrate facing the transparent substrate adjacent to the polarizing plate. is there. When the reflection plate is provided in the liquid crystal cell, the reflection plate can also function as an electrode of the liquid crystal cell. An aluminum foil, a silver foil, or the like can be used for the reflector, and an aluminum layer or a silver layer can be vacuum-deposited on a transparent glass substrate by a vacuum deposition method to form a reflector.

The optically anisotropic body means an optically anisotropic body having a structure in which the optically anisotropic axis is twisted from one surface to the other surface. Therefore, the optically anisotropic material referred to here has the same characteristics as those obtained by laminating a plurality of optically anisotropic layers so that each optically anisotropic axis is continuously twisted. , Like a normal TN liquid crystal cell or the like. As the optically anisotropic body of the present invention, a twist-aligned liquid crystal cell itself, a liquid crystal film, or a laminate of a retardation film can be used. Among them, a liquid crystal film is preferable. As a twisted liquid crystal cell that can be used for an optically anisotropic body, a liquid crystal material layer inserted between two transparent substrates is oriented in a specific direction and twisted in the same manner as the above-described driving liquid crystal cell. An example is a liquid crystal cell having a corner. The liquid crystal film used for the optically anisotropic body means a film having a structure in which a layer having an optically anisotropic axis is continuously twisted in one film. This liquid crystal film can be generally obtained by forming a liquid crystalline material having a twist characteristic into a film. As a liquid crystalline substance having a twisting characteristic, for example, regardless of the shape of liquid crystal molecules such as a rod-like or not, whether low-molecular or high-molecular,
Any liquid crystal compound or liquid crystal composition that can exhibit optically positive uniaxiality 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.

As units for inducing twist, optically active 2-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 2-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-mentioned diols may be either R-form or S-form, or may be a mixture of R-form and S-form. The liquid crystal film referred to in the present invention does not matter whether the film itself exhibits liquid crystallinity. The liquid crystal film referred to in the present invention can be usually obtained by fixing the alignment state formed by the liquid crystalline substance in the liquid crystal state as described above, for example, by a method such as photocrosslinking, thermal crosslinking, or cooling. Another example that can be used as the optically anisotropic material of the present invention is a retardation film. A retardation film is generally formed by precisely uniaxially stretching a transparent plastic film typified by polycarbonate or polymethacrylate.A plurality of films are formed. It can be created by laminating so that

The optical anisotropic body of the present invention has a temperature compensation effect in which the product (Δn ₂ · d ₂ ) of the refractive index anisotropy Δn ₂ and the thickness d ₂ of the optical anisotropic body changes with temperature. It is preferable to have. Even if the ambient temperature changes, the color development does not change,
This is because it is possible to provide a reflection type liquid crystal display element capable of excellent monochrome display. In this case, the temperature change of Δn ₂ · d ₂ is caused by the product of the refractive index anisotropy Δn ₁ of the liquid crystal material layer in the liquid crystal cell used for driving and the thickness d ₁ (Δn ₁ · d _2). It is desirable that the change due to the temperature of d ₁ ) is substantially equal to d ₁ ). Further, the optically anisotropic material used in the present invention preferably has a different optical anisotropy dispersion depending on the wavelength. Wavelength λ of optical anisotropic body = 45
The ratio of the refractive index anisotropy at 0 nm and λ = 590 nm (hereinafter referred to as “Δn ₂ (450)” and “Δn ₂ (590)”) is the birefringence wavelength dispersion α ₂ , α ₂ = Δn ₂ (450) / Δn ₂ (590). alpha ₂ but is identical if the liquid crystal material is identical, is that the same be a different liquid crystal material. The optical anisotropic body of the present invention is disposed between a polarizing plate disposed on one side of the driving liquid crystal cell and a reflector disposed on the other side. Usually, it is disposed between the polarizing plate and the liquid crystal cell or between the liquid crystal cell and the reflecting plate, but it is particularly preferable to provide between the polarizing plate and the liquid crystal cell.

In the reflection type liquid crystal display device of the present invention, a light diffusion layer can be further provided between the polarizing plate and the reflecting plate. The reflection type liquid crystal display element having a natural viewing angle with a small viewing angle dependence can be suppressed by providing a light diffusion layer, particularly when the reflection plate is a specular reflection type, so that characteristic deterioration due to liquid crystal alignment disorder can be suppressed. Can be obtained. The light diffusion layer as referred to herein means a layer having a property of diffusing incident light isotropically or anisotropically, and its material is not limited. As the light diffusion layer, a plastic sheet showing light diffusion properties,
It may be formed from a plastic film, a plastic substrate, a substrate other than plastic, and the like.A self-supporting sheet or film in which particles having a refractive index different from that of the matrix are dispersed in an adhesive matrix. It may be a thing. The sheet, film, substrate and the like may have self-supporting properties or may not have self-supporting properties. When the film does not have self-supporting properties, it is only necessary that the film is held on a film or a transparent substrate having self-supporting properties by some means so that the light diffusing property is not impaired as a whole.
Further, on the optically anisotropic body, a compound or a composition capable of forming a light diffusion layer is applied by means such as melt coating or solution application, and if necessary, an electric field, a magnetic field, and some treatment such as polarized light irradiation is performed. Alternatively, a light diffusion layer may be formed. However, it is necessary to perform the melt coating or the solution coating so that the film strength of the optically anisotropic body does not decrease.

The light-diffusing layer having an adhesive property includes an acrylic adhesive, a rubber adhesive, a silicone adhesive, an ethylene-vinyl acetate copolymer adhesive, a urethane adhesive, a vinyl ether adhesive, and a polyvinyl alcohol adhesive. Adhesives, polyacrylamide-based adhesives and a matrix composed of such a mixed adhesive, for example, an average particle size of 0.5 to
Organic fine particles such as polystyrene fine particles and polymethacrylic acid fine particles of 5 μm, silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide,
Examples thereof include dispersions of appropriate particles such as inorganic fine particles such as antimony oxide, hollow fine particles containing gas, and microcapsules containing liquid. Among them, acrylic pressure-sensitive adhesives are preferable 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 group, ethyl group, n-propyl group, isopropyl group, n-butyl group, t-butyl group, isobutyl group, amyl group, isoamyl group, hexyl group, heptyl group, cyclohexyl group, 2-ethylhexyl group, octyl Group, isooctyl group, nonyl group, isononyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, linear or branched having 1 to 18 carbon atoms such as octadecyl group An adhesive based on an acrylic polymer using one or two or more acrylic acid alkyl esters composed of an ester of acrylic acid or methacrylic acid having an alkyl group is exemplified.

The light-diffusing layer having an adhesive property includes, for example, a petroleum-based resin as long as the effects of the present invention are not impaired.
Tackifiers such as rosin resin, terpene resin, synthetic petroleum resin, phenolic resin, xylene resin, alicyclic petroleum resin, coumarone indene resin, styrene resin, dicyclopentadiene resin and the like, phthalate Acid esters,
Softening agents such as phosphate esters, paraffin chloride, polybutene, polyisobutylene or other various fillers,
Appropriate additives such as an antioxidant and a crosslinking agent 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. Specifically, polyimide, polyamide imide, polyamide, polyether imide, polyether ether ketone, polyether ketone, polyketone sulfide, polyether sulfone, polysulfone, polyphenylene sulfide, polyphenylene oxide, polyethylene terephthalate, polybutylene terephthalate, polyethylene na Phthalate, polyacetal, polycarbonate, polyarylate, acrylic resin, polyvinyl alcohol, polystyrene, polyurethane, polyethylene, polypropylene, cellulosic plastics, epoxy resin, phenolic resin, etc., the inorganic fine particles, organic fine particles, and gas as exemplified above. Plastic film substrate in which encapsulated hollow microparticles and liquid-encapsulated microcapsules are dispersed Etc. can be mentioned. Although the thickness of the light diffusion layer is not particularly limited, it is usually 10 μm or more and 500 μm or more.
μm or less. The total light transmittance of the light diffusion layer is 50
% Or more, and particularly preferably 70% or more. Further, the diffusion transmittance of the light diffusion layer is usually 5 to 99%, preferably 50 to 99%.
In the reflection type liquid crystal display device of the present invention, light enters through a polarizing plate, passes through an optically anisotropic body and a liquid crystal material layer,
Further, the light is reflected by the reflecting plate, passes through the optically anisotropic body and the liquid crystal material layer in the opposite direction, and further passes through the polarizing plate to be emitted.

In the reflection type liquid crystal display device of the present invention, the twist angle θ ₁ of the liquid crystal material molecules from the polarizing plate side to the reflecting plate side in the liquid crystal material layer in the liquid crystal cell is + 200 ° to +270.
° range. When the torsion angle is less than + 200 °, a change in liquid crystal state when time-division driving is performed at a high duty ratio that requires a steep change in transmittance is small. Also, +2
If it exceeds 70 °, hysteresis tends to occur.
In the present specification, the + direction and the − direction of the angle mean the rotation direction of the relative angle, and if the counterclockwise direction from the polarizing plate toward the reflecting plate is +, the clockwise direction is When the clockwise direction is set to +, the counterclockwise direction is set to-. However, the case where both are set to + is included in the scope of the present invention, and equivalent effects can be obtained. In the reflective liquid crystal display device of the present invention, the product of the refractive index anisotropy Δn ₁ of the liquid crystal material layer in the liquid crystal cell and the thickness d ₁ (Δn ₁ ···
d ₁ ) is in the range of 700 nm to 1000 nm. 7
If it is less than 00 nm, the change in the state of the liquid crystal when a voltage is applied is small, and if it exceeds 1000 nm, the viewing angle characteristics and the responsiveness deteriorate. In the reflection type liquid crystal display device of the present invention, the twist angle θ ₂ of the slow axis of the optically anisotropic body from the polarizing plate side to the reflecting plate side is in the range of −155 ° to −220 °.
The product of the refractive index anisotropy Δn ₂ of the optically anisotropic body and the thickness d ₂ of the optically anisotropic body (Δn ₂ · d ₂ ) is 550 nm to 8
The range is 50 nm. As described above, θ ₂ and θ ₁ are each set to a value in a specific range, and Δn ₁ · d ₁ and Δn ₂ ·
By setting d ₂ to a value in a specific range, a good contrast can be realized.

In the reflection type liquid crystal display device of the present invention, θ ₁ ,
In addition to restricting θ ₂ , Δn ₁ · d ₁ and Δn ₂ · d ₂ to specific ranges, wavelengths λ = 450 nm and λ = 590 nm
Is the ratio of the refractive index anisotropy Δn at
When defined as Δn (450) / Δn (590), the birefringent wavelength dispersion α _{1 of the} liquid crystal material layer and the birefringent wavelength dispersion α ₂ of the optically anisotropic body are α ₁ = 1.01 to 1.35. By setting α ₂ = 1.11 to 1.40, it is possible to provide an achromatic and high-contrast reflective monochrome display device. In the reflection type liquid crystal display device of the present invention, θ ₁ , θ ₂ , Δn ₁ · d ₁ , Δn ₂ · d ₂ , α ₁ ,
In addition to regulating the alpha ₂ in a specific range, from the angle theta ₃ and the absorption axis of the polarizing plate to the slow axis on the plane of the polarizing plate side of the optically anisotropic medium from the absorption axis of the polarizing plate of the liquid crystal material layer It is preferable to adjust the angle θ ₄ with respect to the alignment direction on the surface on the side of the polarizing plate as follows, since less coloring and good contrast can be realized. θ ₃ = 0 to + 40 ° or +90 to + 130 ° θ ₄ = 0 to + 40 ° or +90 to + 130 ° In particular, the angle θ ₄ is when the optically anisotropic substance is disposed between the polarizing plate and the liquid crystal material layer. Is more preferably in the range of +90 to + 130 °, and even more preferably in the range of 0 to + 40 ° when the optically anisotropic body is disposed between the liquid crystal material layer and the reflector.

The relationship between the above angles will be specifically described with reference to FIG. 1. In FIG. 1, 1 is a polarizing plate, 2 is an optically anisotropic body, and 3A is a liquid crystal material layer (a transparent substrate having electrodes). Are not shown), 4 is a reflector (layer), and 6 is external light. The orientation direction 31 on the surface of the liquid crystal material 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 θ ₁ . Slow axis direction 21 on the surface of the optically anisotropic body 2 on the side of the polarizing plate 1
And the direction 22 of the slow axis on the surface on the side of the reflection plate 4,
The angle θ ₂ is formed. The absorption axis 11 of the polarizing plate 1
And the direction 21 of the slow axis on the surface of the optical anisotropic body 2 on the side of the polarizing plate 1 forms an angle θ _3, and the absorption axis 11 of the polarizing plate 1
And the orientation direction 31 on the surface of the liquid crystal material layer 3A on the side of the polarizing plate 1 forms an angle θ ₄ . FIG. 2 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. In FIGS. 1 and 2, θ _{1 to} θ ₄ are all rotated counterclockwise from the polarizing plate toward the reflecting plate, that is, relatively rotated in the same direction, for convenience of explanation. in the liquid crystal display element, the direction of rotation of the theta ₁ is always the theta ₂ opposite directions. The reflection type liquid crystal display element of the present invention includes a liquid crystal cell, a polarizing plate, a reflection plate, and the optically anisotropic body as essential components, and further includes a light diffusion layer as necessary. In addition, other components may be provided. Specifically, for example, by further providing a color filter, a color reflection type liquid crystal display element capable of multicolor or full-color display with high color purity can be obtained.

[0020]

The reflection type liquid crystal display device of the present invention has a polarizing plate only on one surface side of a liquid crystal material layer (liquid crystal layer) and has a specific liquid crystal cell and an optically anisotropic body. It is possible to realize a display with high efficiency and good contrast, and to obtain a much higher display quality as compared with a conventional reflection type liquid crystal display device.

[0021]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In this example, an experiment was performed by creating an apparatus in which the counterclockwise direction was + and the clockwise direction was-from the polarizing plate side to the reflecting plate side. However,
When the clockwise direction from the polarizing plate side to the reflecting plate side is +, and the counterclockwise direction is-, the same result can be obtained by performing the same experiment.

Example 1 An STN reflective liquid crystal display device schematically shown in FIG. 3 was prepared. As shown in FIG. 3, the liquid crystal cell 3 includes a pair of opposing transparent substrates 3 </ b> C, electrodes 3 </ b> B provided on inner surfaces thereof, and an alignment film printed and formed thereon and subjected to an alignment process. 3E. 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 transparent substrate, thereby forming a liquid crystal layer 3A. Alignment film 3 using ZLI-5049 as a liquid crystal material
The liquid crystal layer 3A was aligned in a predetermined direction by adjusting the alignment treatment direction of E, and twisted to θ ₁ = + 250 °. Further, the product Δn ₁ · d ₁ of the refractive index anisotropy Δn ₁ of the liquid crystal material in the liquid crystal cell 3 at a wavelength of 550 nm and the thickness d ₁ of the liquid crystal layer 3A was approximately 790 nm. Birefringence wavelength dispersion of ZLI-5049 α ₁ (α ₁ = Δn ₁ (450) / Δn ₁ (5
90)) was 1.21.

The polarizing plate 1 is arranged on the display surface side (upper side in the figure) of the liquid crystal cell 3, while the back side (lower side in the figure) of the liquid crystal cell 3 is arranged.
The reflection plate 4 was arranged at the bottom. An optically anisotropic body 2 is disposed between the polarizing plate 1 and the liquid crystal cell 3, and a light diffusion sheet IDS-21 manufactured by Dai Nippon Printing Co., Ltd. is provided between the optically anisotropic body 2 and the liquid crystal cell as a light diffusion layer 5. (Total light transmittance 91.1%, haze 5
1.6) was arranged. The optical product △ n ₂ · d ₂ of the refractive index anisotropy △ n ₂ and thickness d ₂ at a wavelength of 550nm of the anisotropic body 2 is approximately 650 nm, and theta ₂ = -190 °, the birefringence wavelength dispersion alpha ₂ ( α ₂ = Δn ₂ (450) / Δn ₂ (590)) was set to 1.24. Further, the angle θ ₃ = + ₃ 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.
The angle θ ₄ = + 100 ° from the absorption axis of the polarizing plate 1 to the alignment direction on the surface of the liquid crystal layer 3A on the polarizing plate side was set to 15 °. To this liquid crystal display device, a driving voltage was applied from a driving circuit (not shown) to the transparent electrode 3B, and the relationship with the reflectance was obtained. FIG. 4 shows the results. FIG. 5 is a diagram illustrating spectral characteristics when the electric field is on and when the electric field is off. Further, the contrast when driven at 1/100 duty and the optimum bias and the luminous reflectance (Y value) when the electric field was turned on were determined. Table 1 shows the results. From the results shown in FIG. 4, it can be seen that in this liquid crystal display device, the reflectance sharply changes from around the driving voltage of 2.1 V. In addition, it can be seen from the results of FIG. 5 that this liquid crystal display device achieves good black-and-white display.

Example 2 ZLI-5049 (α ₁ = 1.21) was used as the liquid crystal material, Δn ₁ · d ₁ was set to approximately 790 nm, and the optical anisotropic material was α ₂ = 1.21. And △ n ₂ · d ₂ is approximately 6
50 nm, θ ₁ = + 250 °, θ ₂ = −190 °, θ
A liquid crystal display device was prepared in the same manner as in Example 1 except that ₃ = + 15 ° and θ ₄ = + 100 °, and the relationship between the drive voltage and the reflectance, the spectral characteristics when the electric field was on and when the electric field was off, and 1 / 1
The contrast at the time of driving with 00 duty and the optimum bias and the reflectance (Y value) at the time of light were obtained. The results are shown in FIG. It can be seen from the results in FIG. 6 that good black-and-white display has been achieved.

Comparative Example ZLI-5049 (α ₁ = 1.21) was used as a liquid crystal material, Δn ₁ · d ₁ was set to approximately 790 nm, and an optically anisotropic material having α ₂ = 1.10 was used. And △ n ₂ · d ₂ is approximately 6
50 nm, θ ₁ = + 250 °, θ ₂ = −190 °, θ
A liquid crystal display device was prepared in the same manner as in Example 1 except that ₃ = + 15 ° and θ ₄ = + 100 °, and the relationship between the drive voltage and the reflectance, the spectral characteristics when the electric field was on and when the electric field was off, and 1 / 1
The contrast at the time of driving with 00 duty and the optimum bias and the reflectance (Y value) at the time of light were obtained. The results are shown in FIG. It can be seen from the results of FIG. 7 that good black-and-white display has not been achieved.

[0026]

[Table 1]

By 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 significantly improved contrast as compared with the device of the comparative example. You can see that. From the above results, it was confirmed that the reflection type liquid crystal display device of the present invention had significantly higher display quality than the device of the comparative example.

Example 3 A reflection type color liquid crystal display device including a color filter 7 as schematically shown in FIG. 8 was prepared. 8, components common to those of the apparatus shown in FIG. 2 are denoted by the same reference numerals. As shown in FIG. 8, between the transparent substrate 3C on the display surface side of the liquid crystal cell 3 and the transparent electrode 3B, a color filter 7 including pixels of three colors of red, green and blue was inserted. By providing the color filter layer with such a configuration, a favorable multi-color or full-color display could be performed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the position and angle relationship of each component in a liquid crystal display device of the present invention.

FIG. 2 is a plan view illustrating an angle relationship among an absorption axis of a polarizing plate, an alignment direction of a liquid crystal material layer, and a slow axis direction of an optically anisotropic body in the liquid crystal display device of the present invention.

FIG. 3 is an elevational sectional view schematically showing the device of Example 1.

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 the device of Example 1 when an electric field is turned on and when an electric field is turned off.

FIG. 6 is a diagram showing the device of Example 2 when the electric field is on and when the electric field is off.

FIG. 7 is a diagram showing a device of a comparative example when an electric field is on and when an electric field is off.

FIG. 8 is an elevational sectional view schematically showing the device of Example 3.

[Explanation of symbols]

Reference Signs List 1 polarizing plate 2 optical anisotropic body 3A liquid crystal layer 3B electrode 3C transparent substrate 3D sealant 3E alignment film 4 reflective layer (plate) 5 light diffusion layer 6 external light 7 color filter 11 absorption axis of polarizing plate 21 optical anisotropic body Slow axis on the surface on the polarizing plate side 22 Slow axis on the surface on the reflecting plate side of the optically anisotropic material 31 Orientation direction of molecules of the liquid crystal material on the surface on the polarizing plate side of the layer of the liquid crystal material 32 Orientation of liquid crystal molecules on the reflector side of the layer

Continuation of the front page (72) Inventor Takehiro Toyooka 8 Chidori-cho, Naka-ku, Yokohama-shi, Kanagawa Prefecture Nishiishi Mitsui Co., Ltd. Central Research Laboratory F-term (reference) 2H049 BA02 BA06 BA42 BB03 BB44 BB46 BB51 BB63 BC22 2H091 FA02Y FA08X FA11X FA32X FB02 HA10 KA02 KA03 LA16 LA17

Claims (4)

[Claims] 1. A liquid crystal cell in which a layer of a liquid crystal substance is inserted into a pair of transparent substrates having electrodes, a polarizing plate, a reflecting plate, and an optically anisotropic body having a twisted structure, and a voltage value of two or more values. Is selected, and a driving voltage is applied to the liquid crystal material layer, wherein the polarizing plate is disposed on one surface side of the liquid crystal material layer, and the reflection plate is the liquid crystal material layer. The optical anisotropic body is disposed between the polarizing plate and the reflecting plate, and the ratio of the refractive index anisotropy Δn at wavelengths λ = 450 nm and λ = 590 nm is determined by the birefringence wavelength dispersion α α = Δn (450) / Δn (590), the birefringent wavelength dispersion α _{1 of the} liquid crystal material layer and the birefringent wavelength dispersion α ₂ of the optically anisotropic body are α ₁ = 1.01. 35 α ₂ = 1.11 to 1.40 Liquid crystal display device. 2. The liquid crystal substance layer has a twist angle θ ₁ of liquid crystal substance molecules from the polarizing plate side to the reflecting plate side of + 200 ° to + 200 °.
+ 270 °, and the twist angle θ ₂ of the slow axis of the optically anisotropic body from the polarizing plate side to the reflecting plate side is −155 ° −−
220 °, and the product of the refractive index anisotropy Δn ₁ and the thickness d _{1 at} the wavelength λ = 550 nm of the liquid crystal material layer (Δn ₁ · d ₁ ) is 700 nm.
And the wavelength λ of the optically anisotropic body.
= Product of the refractive index anisotropy Δn _{2 at} 550 nm and the thickness d ₂ of the optically anisotropic body (Δn ₂ · d ₂ ) is from 550 nm to 8
2. The reflective liquid crystal display device according to claim 1, wherein the range is 50 nm. 3. The reflective liquid crystal display device according to claim 1, wherein the optically anisotropic member is made of a liquid crystal film. 4. The apparatus according to claim 1, further comprising at least one polarizing plate and a reflecting plate.
4. The reflective liquid crystal display device according to claim 1, further comprising a light diffusion layer.