JPH10260388A - Reflection type liquid crystal display element and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the reflection type liquid crystal display element which makes a multicolor display by low-voltage driving with one pixel and its driving method. SOLUTION: The reflection type liquid crystal element 14 has a couple of substrates 1 and 2 which are arranged opposite each other and have electrodes 3 and 4, and 5 and 6 on their opposite surfaces while at least one of them is transparent, means 11, 12, and 13 which apply voltages between the electrodes 3 and 4, and 5 and 6, and a liquid crystal layer 10 which is sandwiched between the substrates 1 and 2 and has transition from planar structure in the absence of the applied voltages to focal comic structure in the presence of the applied voltage through a transition area including a reversible phase shift area where reflection characteristics vary reversibly with the voltages, and is driven below a voltage area corresponding to the said reversible phase shift area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device and a method for driving the same, and more particularly, to a reflective liquid crystal display device and a method for driving the same.

[0002]

2. Description of the Related Art In recent years, portable information devices such as notebook personal computers, sub-notebook personal computers, portable telephones, PHSs, PDAs, etc. have received a great deal of attention and are becoming popular. These portable information devices are required to have low power consumption, and the display elements mounted thereon are also required to have low power consumption.

Generally, a liquid crystal display element is used as such a display element. Liquid crystal display elements are usually
Consisting of a pair of electrodes opposed to each other at a fixed distance, an alignment film formed on each of the opposing surfaces of the pair of electrodes, and a liquid crystal layer sandwiched between the electrodes with the alignment film interposed therebetween. The display is performed by utilizing the change in the optical characteristics of the liquid crystal layer. That is, by applying an electric field or a magnetic field to the liquid crystal layer of the liquid crystal display element, the orientation or arrangement of the liquid crystal material constituting the liquid crystal layer changes according to the amount of the applied electric field or the magnetic field. By controlling the characteristics and passing the incident light from the light source through the liquid crystal layer whose optical characteristics are controlled, the display is performed by controlling the wavelength component of the output light.

[0004] Such a liquid crystal display element has a twisted nematic (T) structure due to an electro-optical effect of a liquid crystal material in a liquid crystal layer.
N) elements, super twisted nematic (STN) elements, surface stabilized ferroelectric liquid crystal (SSFLC) elements, antiferroelectric liquid crystal (AFLC) elements, and the like.
Depending on the positional relationship between the light source and the display surface, it is classified into a transmission type liquid crystal display element and a reflection type liquid crystal display element described below.

A transmissive liquid crystal display element generally uses a polarizing plate. Light from a light source is transmitted through the polarizing plate, and light components transmitted through the polarizing plate are passed through the liquid crystal layer.
The display is performed on the substrate surface opposite to the light source. However, in such a liquid crystal display device, since a polarizing plate is used, the light use efficiency is as low as about 50% at the maximum. Therefore, these devices are usually provided with a backlight in order to obtain sufficient brightness. However, since the power consumption of the backlight is very high, there is a problem that the power consumption of the entire device is greatly increased. doing.

[0006] As a low power consumption device, the backlight of the above-mentioned transmissive liquid crystal display device is replaced by a light reflection plate.
N-type and STN-type reflective liquid crystal display elements have also been put to practical use. However, even in such an element, the light use efficiency is low because the polarizing plate is used as described above,
The display performance was insufficient.

As a liquid crystal display device that solves these problems, a reflection type liquid crystal display device that does not use a polarizing plate has been proposed. For example, Japanese Patent Publication No. 58-501631, Japanese Patent Publication No. Sho 6
No. 1-502128 and JP-T-63-501512 disclose a method in which a liquid crystal material is dispersed in a polymer material and the scattering state and the transmission state are electrically controlled by using the birefringence of the liquid crystal. , PDLC (Polymer Dispersed Liquid Crysta) that realizes relatively good viewing angle characteristics without using a polarizing plate
l) is disclosed. However, the liquid crystal display devices disclosed in these publications have a problem that the scattering property is low and the driving voltage is relatively high.

In order to improve the scattering, for example, Japanese Patent Application Laid-Open No. Hei 5-273527 discloses that a half mirror is provided behind a display element as viewed from an observer.
No. 50418 and JP-A-4-318518,
Providing irregularities on the electrode surface in contact with the liquid crystal layer, and
JP-A-6-11712 describes that a diffraction grating formed of a material having a refractive index equal to the ordinary light refractive index of a liquid crystal material is provided in contact with a liquid crystal layer. However, with these methods, it is difficult to obtain good contrast and sufficient brightness.

GH Heilmeier, JEGoldmacher et al. (RCA Lab.), For example, Appl. Phys. Lett., 13, 132 (196)
8) proposes a method of electrically controlling the scattering state and the transmission state using a cholesteric liquid crystal material. In this method, the transmission state is such that the liquid crystal layer is formed in a planar (Planar) structure in which the helical axis formed by the alignment of the liquid crystal molecules is substantially perpendicular to the electrode surface, or the helical structure is eliminated and the liquid crystal molecules become It can be obtained by controlling a homeotropic (Homeotropic) structure oriented perpendicular to the electrode surface. The scattering state can be obtained by controlling the liquid crystal layer to a focal conic structure in which the helical axis is oriented at random but relatively parallel to the electrode surface.

Therefore, in this method, the display is controlled by controlling the structure of the liquid crystal between the planar structure and the focal conic structure when no voltage is applied or between the focal conic structure and the homeotropic structure when a holding voltage is applied. Done. However, even in this method, PD
Like the LC, there is a problem that the reflectance is low and the contrast is low because the scattering property in the focal conic structure is low.

As a reflection type liquid crystal display system using a cholesteric liquid crystal material, apart from the scattering / transmission mode described above, for example, Phys. Rev. Lett., 24, 577 (1970), JEAdams, W. et al.
E. Hass and JJ Wyscocki et al. (Xerox) have proposed a selective reflection mode.

The selective reflection means that in a planar structure, a wavelength defined by the product of the pitch length of a helical periodic structure and the average refractive index of a liquid crystal material is a reflection maximum, and a circularly polarized light component in the same rotational direction as the helix is selectively reflected. It is a phenomenon of reflection. In the selective reflection mode, display is performed by adjusting the helical pitch so as to reflect visible light and controlling the state to the selective reflection state in the planar structure and the scattering state in the focal conic structure. D.-K.Yang, L.-C.Chein and JWDo
ane et al. (Kent State Univ.) reported SID 95 DIGEST p.706
(1995) discloses that a wide viewing angle and a multi-color display can be realized by forming a planar structure into a polydomain.

However, a liquid crystal display device using the above-mentioned cholesteric liquid crystal material requires a relatively high driving voltage as in the case of PDLC. FIG. 5 shows a typical voltage-reflection luminance curve of a liquid crystal display device using a cholesteric liquid crystal material driven in the selective reflection mode. In this figure, the horizontal axis represents the AC voltage applied to the display element,
The vertical axis indicates the reflection luminance of the display element. In this figure, region 51 corresponds to the planar structure, region 52 corresponds to the focal conic structure, and region 53 corresponds to the homeotropic structure.

[0014] In this liquid crystal display device, to change the focal conic structure region 52 is a weakly scattering state of planar structure region 51 is a selective reflection state, it may be set to a voltage V V> V _c. However, the change from the focal conic structure region 52 to the planar structure region 51 needs to go through the homeotropic structure region 53. That is, only by the voltage V below V _a, without causing changes in the structure, is because it can become focal conic structure is maintained even region 54. Therefore, in a liquid crystal display element driven in the selective reflection mode, V
There is a problem that a voltage exceeding _e must be applied and a high drive voltage is required.

In a liquid crystal display device using a cholesteric liquid crystal material driven in a selective reflection mode, a display color is selectively reflected by a selective reflection in a planar structure, weakly scattered in a focal conic structure, or homeotropic. There are only two colors, black due to transmission through the structure. SID
95 DIGEST p.169 describes a display element in which multiple pixels with different colors are juxtaposed, but it is difficult to achieve high resolution with this method, and multicolor display with one pixel is realized. It has not been.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to provide a reflection type liquid crystal display device capable of low voltage driving and multi-color display with one pixel, and a method of driving the same.

[0017]

According to the present invention, there is provided a pair of substrates disposed opposite to each other and having electrodes on the opposite surface, at least one of which is transparent, and means for applying a voltage between the electrodes,
A transition region including a reversible transition region sandwiched between the pair of substrates and exhibiting a planar structure when a voltage is not applied, and having a reflection characteristic reversibly changing with a voltage when a voltage equal to or more than a predetermined value is applied by the voltage application unit; And a liquid crystal layer that transitions to a focal conic structure through the above step, and is driven at a voltage lower than the voltage region corresponding to the reversible transition region.

According to the present invention, in the above-mentioned reflection type liquid crystal display device, at least one of the pair of substrates is subjected to a horizontal alignment treatment on a surface in contact with the liquid crystal layer. According to the present invention, in the reflective liquid crystal display device, the liquid crystal layer contains a polymer.

According to the present invention, in the above-mentioned reflection type liquid crystal display device, the reflection type liquid crystal display device is driven by continuously changing an applied voltage in at least a part of the reversible transition region. Further, the present invention provides a liquid crystal layer exhibiting a planar structure when no voltage is applied, the voltage at which the liquid crystal layer starts changing from a planar structure to a transition structure between the planar structure and the focal conic structure by application of a voltage. A reflective liquid crystal display element, wherein a voltage higher than the upper limit of a voltage range in which the liquid crystal layer reversibly changes between the planar structure and the transition structure in accordance with a change in applied voltage is applied. Is provided.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reflection type liquid crystal display device of the present invention will be described below in more detail. A substrate made of a conductive material such as aluminum, nickel, copper, silver, gold, and platinum can be used as one of a pair of substrates used in the reflective liquid crystal display element of the present invention. Also, glass,
An electrode made of such a conductive material may be formed on a surface of an insulating substrate such as plastic and ceramic by a method such as vapor deposition, sputtering, or photolithography.

At least one of the pair of substrates used in the reflection type liquid crystal display element of the present invention needs to be transparent. As a transparent substrate, at least one principal surface of a transparent substrate such as glass, plastic, and ceramic is provided with an IT
One on which a transparent electrode such as O is formed can be given.

In the reflection type liquid crystal display device of the present invention, a light absorbing layer can be provided on a substrate arranged opposite to the substrate on the display surface side. The material used for the light absorbing layer is not particularly limited as long as it absorbs visible light.

The pair of substrates used in the reflection type liquid crystal display element of the present invention is held so that the distance between the electrodes is constant by, for example, inserting a spherical spacer between the substrates. The material constituting the spherical spacer is not particularly limited as long as it is insulating, non-reactive with the liquid crystal material, insoluble in the liquid crystal layer, and uniformly dispersed on the substrate. And polymers such as divinylbenzene and polystyrene, and inorganic oxides such as alumina and silica.

The particle size of the spherical spacer is selected according to the desired thickness of the liquid crystal layer, and usually has an average particle size of 1 μm to 1 μm.
Those having a size of 20 μm are used. Further, in order to make the distance between the electrodes uniform, it is desirable that the distribution width of the particle size is narrow.

Instead of using a spherical spacer, a plurality of columnar bodies may be provided on the surface of the substrate in contact with the liquid crystal layer such that the plane portion is in contact with the substrate surface and their heights are constant. .

The column is usually 1 μm to 20 μm in diameter,
It is formed at a height of 1 μm to 20 μm. This pillar is
It can be formed by a generally used method such as photolithography. Therefore, the columnar body can be formed at a desired position on the surface of the substrate in contact with the liquid crystal layer and at a desired thickness, and the distance between the electrodes can be made constant.

The material used for the columnar body is not particularly limited as long as it is insulative, non-reactive with the liquid crystal material, and insoluble in the liquid crystal layer. It can be formed by using a cured resin or the like.

Examples of the photosensitive resin include photosensitive resins obtained by converting polyimide, polyamide, polyvinyl alcohol, polyacrylamide, cyclized rubber, novolak resin, polyester, polyurethane, acrylic resin, bisphenol resin, gelatin and the like.

In the reflection type liquid crystal display device of the present invention, a nematic liquid crystal compound and a cholesteric liquid crystal compound can be used as the liquid crystal material constituting the liquid crystal layer.
In the reflective liquid crystal element of the present invention, if the liquid crystal layer exhibits a planar structure in a state sandwiched between the substrates, and can reflect light near the visible light region, that is, light having a wavelength near 400 to 760 nm. It must have a helical pitch.

Therefore, when a cholesteric liquid crystal compound is used as the liquid crystal material, it can be used alone or as a mixture of a plurality of cholesteric liquid crystal compounds. However, when a nematic liquid crystal compound is used as the liquid crystal material, the liquid crystal layer can be used. Optical activity needs to be introduced.

That is, when a nematic liquid crystal compound is used, a nematic liquid crystal compound having an optically active site introduced therein is used, a mixture of a nematic liquid crystal compound and a cholesteric liquid crystal compound is used, and a nematic liquid crystal compound and a compound having optical activity are used. It is necessary to use either a mixture with the above, introducing optical activity into the alignment film provided on the substrate surface, and allowing a solid substance such as a polymer having optical activity to be present in the liquid crystal layer. is there.

It is preferable to use a liquid crystal material having a ratio of torsional elastic constant (PN) to dielectric anisotropy of 0.35 or less, since a sufficiently low driving voltage can be obtained.
When a liquid crystal material having a refractive index anisotropy (birefringence) of 0.2 or more is used, an element having a sufficiently high reflectance can be obtained.

In the reflection type liquid crystal display device of the present invention, a compound other than the liquid crystal compound such as a dichroic dye or a compound having optical activity can be contained in the liquid crystal material. When the liquid crystal material is composed of a mixture of a nematic liquid crystal compound and an optically active compound, their optimum mixing ratio is defined by the reciprocal 1 / pc of the product of the helical pitch length p and the weight concentration c of the optically active compound. Helical Twisting Power,
It is determined from the desired selective reflection wavelength. When a dichroic dye is mixed with the liquid crystal material, it is preferable to use a dye that absorbs outside the selective reflection region.

Hereinafter, the reflective liquid crystal display device of the present invention will be described in more detail with reference to the drawings. FIG.
2 shows a cross-sectional view of a reflective liquid crystal display element according to one embodiment of the present invention.

In FIG. 1, transparent substrates 1, which are arranged opposite to each other,
Electrodes 3, 4 and electrodes 5, 6
Is provided. The distance between the electrodes is kept constant between the transparent substrate 1 and the transparent substrate 2 by the spacer 7, and a liquid crystal layer 10 containing liquid crystal materials 8 and 9 is sandwiched between the transparent substrate 1 and the transparent substrate 2. I have. The electrodes 3 and 4 of the transparent substrate 1
The electrodes 5 and 6 of the transparent substrate 2 are connected to the other terminal of the power supply 11 via switches 12 and 13, respectively.
4 are configured.

The present inventors have found that in the reflective liquid crystal display element 14 having the above structure, the liquid crystal material 8 which exhibits a planar structure when no voltage is applied and changes to the focal conic structure when a predetermined voltage is applied is: At the time of the change, as shown by reference numeral 9, the light passes through a transition structure, in which the reflection luminance changes according to the applied voltage value, and the change between the planar structure and the transition structure is a predetermined value. Can be performed reversibly within the voltage range of

FIG. 2 shows a voltage-reflection luminance curve of the reflection type liquid crystal display device of the present invention. In this figure, the horizontal axis indicates the voltage applied to the display element, and the vertical axis indicates the reflection luminance of the display element. The region 21 corresponds to the planar structure, the region 22 corresponds to the focal conic structure, the region 23 corresponds to the homeotropic structure, and the region 24 corresponds to the transition structure.

[0038] As shown in this figure, increasing the voltage applied to the liquid crystal layer, when the voltage reaches V _a, the liquid crystal material starts changing from a planar structure to a transition structure. In this transition structure, the reflection luminance decreases as the applied voltage increases. When the voltage decreases the applied voltage before exceeding V _b, it increases the reflection brightness accordingly, the voltage V _a
, The transition from the transition structure to the planar structure ends. Here, the range of this voltage V _a ~V _b that reversible transition region.

On the other hand, when the applied voltage was further increased beyond the V _b, a change from the transition structure when the voltage reaches V _c to a focal conic structure ends. However, once the changes to the focal conic structure, by increasing the voltage to more than V _e is changed to homeotropic structure, unless further lowering the voltage to V _a, can not be returned to the planar structure.

Further, the applied voltage even when not raised to V _c, when applying a voltage exceeding V _b, in order to return to the planar structure, when changing the focal conic structure as well as very high voltages Must be applied.

[0041] That is, the liquid crystal layer, with respect to change in the applied voltage, between the planar structure and the transition structure only if less than or equal to the maximum value V _b for reversibly changed capable applied voltage to the structure Change occurs reversibly in response to a change in voltage.

[0042] The voltage V _b is in relation of _{V a <V b <V c} , varies depending on the configuration of the device, in general,
_{(9V a + V c) /} 10 ≦ V b ≦ (8V a + 2V c) /
It is in the range of 10.

When a polymer is contained in the liquid crystal layer, the voltage V
_b can be increased. This is because the inclusion of the polymer in the liquid crystal layer further stabilized the planar structure with respect to the focal conic structure.

The range of the voltage V _b to be enhanced by incorporating a polymer in the liquid crystal layer varies depending on the configuration of the device, in _{general, (8V a + 2V c)} / 10 ≦ V b ≦
(3V _a + 7V _c ) / 10.

The polymer in the liquid crystal layer is obtained by introducing a polymerizable compound mixed with a liquid crystal material between the substrates and performing a polymerization reaction. This method is preferable because the manufacturing process can be simplified.

The polymerizable compound may be any of thermoplastic, thermosetting, and photocurable, but is preferably one that forms a transparent three-dimensional network by a polymerization reaction.

When a monomer is used as the polymerizable compound, styrene, acrylic acid, acrylic ester, acrylic amide, and derivatives thereof, and vinyls such as N-vinylpyrrolidone, N-vinylimidazole, and vinyl acetate are used. be able to. In addition, dibasic acids such as diacrylic acid, dimethacrylic acid, and derivatives thereof
Monovalent monomers, trivalent or tetravalent acrylic acids, methacrylic acids, and the like can also be used. In these molecules, the hydrogen at the α-position, the β-position, or both of the vinyl groups may be substituted with a phenyl group, an alkyl group, a halogen group, a cyano group, or the like.

As the polymerizable compound, an optically active monomer can be used. By using a polymer having optical activity formed by such a monomer, the helical force of the liquid crystal material can be controlled.

FIG. 3 shows a sectional view of a liquid crystal display device according to another embodiment of the present invention. The liquid crystal display element 34 shown in FIG.
Has substantially the same configuration as the element shown in FIG. 1 except that the liquid crystal layer 30 includes a polymer 31 having optical activity and the liquid crystal materials 38 and 39 are formed of a nematic liquid crystal compound having no optical activity. Is different. The liquid crystal material 38
Has a planar structure due to the polymer 31 having optical activity.

In the liquid crystal display element 34 having such a configuration,
Due to the increase in the voltage applied to the liquid crystal layer 30, the voltage from the planar structure (the liquid crystal material 38) to the homeotropic structure (the liquid crystal material 3) can be maintained at a relatively low voltage without going through the focal conic structure.
The change to 9) occurs. Therefore, the change between the planar structure and the homeotropic structure occurs reversibly at a relatively low voltage, so that a higher contrast can be obtained.

As the polymerizable monomer having optical activity, cholesteryl cinnamate, cholesteryl acrylate, 4-acryloyl-4 ′-(2- (S) -methylbutoxy) biphenyl, 4-acryloyl-4 ′-(2
-(R) -methylbutoxy) biphenyl, 4-acryloyl-4 '-(2- (R) -methylbutyl) biphenyl, 4-acryloyl-4'-(2- (S) -methylbutyl) biphenyl, 4- (2 -(S) -methylbutoxy) cyclohexylphenyl acrylate, and 4-
(2- (R) -methylbutoxy) cyclohexylphenyl acrylate and the like can be mentioned.

The polymerizable monomers described above can be used alone, or a plurality of types of polymerizable monomers can be used as a mixture. As the polymerizable compound, an oligomer obtained by polymerizing two or more molecules of the above monomer can also be used. These monomers and oligomers are
Each of them can be used alone, or can be used in combination for adjusting reactivity and viscosity.

As the polymerizable compound, it is particularly preferable to use an acrylic monomer or oligomer which is polymerized by irradiation with ultraviolet rays. 4,4'-bisacryloylbiphenyl, 4-acryloylbiphenyl, 4-acryloyl-
4'-cyanobiphenyl, 4-cyclohexylphenyl acrylate, 2-ethylhexyl acrylate, 2-
It is preferable to use hydroxyethyl acrylate or the like. In addition, Kayarad HDDA, Kayarad MAND
A, Kayarad HX-220, Kayarad HX-62
0, Kayarad R-551, Kayarad R-712, Kayarad R-604, Kayarad R-167 (Nippon Kayaku), acrylic ester BZ, acrylic ester H
Commercially available polymerizable compounds such as X and acrylic ester HP (Mitsubishi Rayon Co., Ltd.) can also be used.

Further, among the above polymerizable compounds, those having a mesogen group in the main chain or side chain are preferably used. When such a polymerizable compound is used, the generated polymer interacts with the liquid crystal compound, and the structure of the liquid crystal layer during the generation of the polymer can be stabilized.

The polymer is preferably contained in the liquid crystal layer in an amount of 0.1 to 10% by weight based on the total weight of the liquid crystal layer. When the content exceeds 10% by weight, scattering by a polymer and an increase in driving voltage increase, and when the content is less than 0.1% by weight,
The effect obtained by introducing the polymer cannot be obtained.

The polymerizable compound can be used together with a modifier such as a polymerization initiator, a crosslinking agent, a surfactant, a polymerization accelerator, a chain transfer agent, and a photosensitizer, if necessary. The polymerization initiator is selected depending on the monomer or oligomer to be used. For example, Darocure 1173 and Darocure 1116 available from Merk, Irgacure 184 and Irgacure 6 available from Ciba-Geigy.
51, Kayacure DET marketed by Nippon Kayaku
A polymerization initiator such as EX and Kayacure EPA can be used.

The polymerization initiator is preferably added in the range of 0.01 to 5% by weight based on the polymerizable compound used. If the addition amount is less than 0.01% by weight, the effect of the addition cannot be sufficiently obtained, and if it exceeds 5% by weight, the retention of the liquid crystal will decrease.

In the reflection type liquid crystal display device of the present invention, it is preferable that one of the pair of substrates has a surface in contact with the liquid crystal layer subjected to a horizontal alignment treatment. here,
The horizontal alignment process is a process for aligning a liquid crystal material substantially parallel to a substrate surface and substantially in one direction.
Thus, when horizontal alignment treatment, it is preferable for the maximum value V _b for reversibly changed capable applied voltage that increases between the transition structure and planar structure liquid crystal layer with respect to change in the applied voltage .

This is because the planar structure is more stabilized than the focal conic structure by performing the horizontal alignment processing on the surface of the substrate which is in contact with the liquid crystal layer. The voltage V _b which is enhanced by the horizontal alignment treatment, varies depending on the configuration of the device, in general, (8V _a + 2V _c)
/ 10 ≦ V _b ≦ (3V _a + 7V _c ) / 10.

The horizontal alignment treatment includes a rubbing treatment in which a substrate surface or a thin film covering the substrate surface is rubbed in one direction with a cloth or the like, and a monomolecular film formed on a water surface is copied onto a substrate and laminated. Known methods such as a Langmuir-Blodgett method for forming a thin film, a method in which a substrate is coated with a polymerizable monomer and photopolymerized by polarized light, and an oblique evaporation method of silicon oxide can be used.

As the material of the thin film covering the substrate surface,
A material that is usually used as a horizontal alignment film, such as polyimide, can be used. The voltage applying means used in the liquid crystal display element of the present invention is capable of applying a voltage to the liquid crystal layer, and includes a power supply, wiring for connecting the power supply to the liquid crystal display element, a circuit for controlling the applied voltage, and the like. It consists of.

In the reflection type liquid crystal display device of the present invention,
When the voltage applied to the liquid crystal layer is changed within a voltage range in which the liquid crystal layer can reversibly change between the planar structure and the transition structure, the wavelength of the reflected light changes accordingly.

FIG. 4 is a graph showing the relationship between the wavelength of the reflected light and the reflectance in the transition structure. In this figure, the horizontal axis represents the wavelength, the vertical axis represents the reflectance, and the curves a to c correspond to the data at the measurement points represented by the same reference numerals in the graph of FIG. doing.

As shown in this figure, in the transition structure,
As the applied voltage increases, the wavelength of the reflected light shifts to the shorter wavelength side. Therefore, within the range of the voltage V _a ~V _b,
Various colors can be displayed by changing the value of the applied voltage.

When the applied voltage V _x is changed between _a low voltage region of 0 ≦ V _x ≦ V _{a and} a high voltage region of V _a <V _x ≦ V _b , 0 ≦ V _x ≦ in at least one voltage value of the voltage range of V _b, the liquid crystal layers are in reflected visible light,
Two-color display is possible.

For example, when the selective reflection wavelength in the low voltage region of the reflective liquid crystal display device of the present invention is set in the infrared region, only the infrared light is reflected and the visible light is transmitted, so that the light absorbing layer is provided. If it is, black is displayed. On the other hand, when a voltage in a high voltage region is applied to this element, the selective reflection wavelength shifts to the shorter wavelength side and reflects light such as red. Therefore, a multi-color display of black and red becomes possible.

Similarly, when the selective reflection wavelength in the low voltage region of the reflection type liquid crystal display device of the present invention is set to blue, when the voltage in the high voltage region is applied to this device, the selective reflection wavelength becomes short. It shifts to the wavelength side and reflects only ultraviolet light. Therefore, a multi-color display of black and blue can be performed.

When the selective reflection wavelength in the low voltage region is set to yellow, the wavelength range corresponding to yellow is very narrow, so that the change in color recognized with respect to the change in the selective reflection wavelength is large. Therefore, visibility can be improved by setting the selective reflection wavelength in the low voltage region to yellow.

In the reflection type liquid crystal display device of the present invention, the liquid crystal material may have a focal conic structure instead of a planar structure when the device is manufactured.
In this case, it is necessary to change the liquid crystal material so that the liquid crystal material exhibits a planar structure by applying a voltage having a height necessary for changing to the homeotropic structure to the element in advance and stopping the application of the voltage. is there.

[0070]

Embodiments of the present invention will be described below. (Example 1) A reflection type liquid crystal display device was manufactured by the following method.

First, a glass substrate having an ITO film formed on one main surface was used as a transparent substrate, and a polyimide AL-1 was coated on the surface on which the ITO film was formed by a spin coater.
051 (Nippon Synthetic Rubber Co., Ltd.) was applied to form a 70 nm-thick film.

As described above, a film is formed on two transparent substrates, and an epoxy adhesive is applied to one of the substrates around the surface on which the film is formed, and the other substrate is coated with an epoxy adhesive. A resin spacer having a particle size of 9 μm was sprayed on the surface on which the coating was formed. These two substrates were bonded together such that the respective coatings faced each other, and a black cloth was provided as a light absorbing layer on the surface of the substrate opposite to the substrate on the display surface side.

Next, 61% by weight of a nematic liquid crystal compound E48 (MERCK) and 39% by weight of an optically active substance C
A liquid crystal material mixed with B15 (MERCK) was injected between the bonded substrates in an isotropic state.
Further, this was sealed, and each substrate was electrically connected to a power supply to produce a reflection type liquid crystal display device.

With respect to the reflection type liquid crystal display device manufactured as described above, the change in the reflectance with respect to the AC voltage (rectangular wave, 60 Hz) was measured, and the voltage V _{a at} which the change from the planar structure to the transition state structure was started was calculated. The voltage V _{c at} which the transition from the transition state structure to the focal conic structure starts, and the maximum applied voltage between the planar structure and the transition state structure that can reversibly change the structure with respect to the voltage change. The value _Vb was checked. As a result, V _a = 5 V, V _b = 6 V,
And V _c = 12V.

This element was driven by changing the applied voltage between 0 V and 6 V. At 0 V, the maximum reflection wavelength was 57%.
At 0 V, yellow is displayed, and at 6 V, the maximum reflection wavelength is 5 nm.
A green color of 45 nm was displayed, and the display color changed reversibly with a change in voltage.

When the voltage applied to the device was continuously changed in the voltage range of 0 V to 6 V, the display color reversibly changed in response to the voltage change, and the reflection maximum wavelength of the display color was changed. It continuously changed in the range of 545 nm to 570 nm.

Example 2 A reflection type liquid crystal display device was prepared in the same manner as in Example 1 except that the coating formed on one substrate was subjected to a parallel alignment treatment by a rubbing treatment, and this coating was used as an alignment film. Was prepared.

The device was examined for V _a , V _b , and V _c in the same manner as in Example 1. As _{a result} , V _a = 5.
V, was V _b = 8V, and V _c = 12V. This element was driven by changing the applied voltage between 0 V and 8 V. At 0 V, yellow with a reflection maximum wavelength of 570 nm was displayed, and at 8 V, green with a reflection maximum wavelength of 530 nm was displayed, and the display color was , Reversibly changed with a change in voltage.

When the voltage applied to the device was continuously changed in the voltage range of 0 V to 8 V, the display color changed reversibly in response to the voltage change, and the reflection maximum wavelength of the display color changed. It changed continuously in the range of 530 nm to 570 nm.

(Example 3) In the same manner as in Example 1, a substrate on which two films were formed was adhered so that the respective films faced each other.

Next, 2,4% by weight of the liquid crystal material relative to the liquid crystal material was mixed with a liquid crystal material having the same composition as in Example 1 as a polymerizable compound.
% Darocur 1173 (Merk) was mixed as a polymerization initiator. This mixture was injected in a state of an isotropic phase between the bonded substrates, and this was sealed. further,
The liquid crystal layer is controlled to have a planar structure, and ultraviolet light in a wavelength range close to the absorption maximum wavelength of the polymerizable compound is applied to the liquid crystal layer by 3 mW / cm ^2.
And the polymerizable compound was cured. Further, each substrate was electrically connected to a power supply to produce a reflective liquid crystal display device.

This device was examined for V _a , V _b , and V _c in the same manner as in Example 1. As _{a result} , V _a = 5
V, was V _b = 8V, and V _c = 12V. This element was driven by changing the applied voltage between 0 V and 8 V. At 0 V, yellow with a reflection maximum wavelength of 570 nm was displayed, and at 8 V, green with a reflection maximum wavelength of 530 nm was displayed, and the display color was , Reversibly changed with a change in voltage.

When the applied voltage was continuously changed in the voltage range of 0 V to 8 V, the display color reversibly changed in response to the voltage change, and the maximum reflection wavelength of the display color was changed. It changed continuously in the range of 530 nm to 570 nm.

Table 1 shows the range of applied voltages of the liquid crystal display elements manufactured in Examples 1 to 3 in which the structure can be reversibly changed with respect to the change in voltage, and the display within the voltage range. It shows the reflection maximum wavelength range of the color.

[0085]

[Table 1]

As is clear from Table 1, the device of Example 2 in which the film formed on the substrate was subjected to the parallel alignment treatment, and the device of Example 3 in which the liquid crystal layer contained a polymer were the same as those of Example 1.
The range of the applied voltage capable of reversibly changing the structure is wider than that of the element. In addition, it can be seen that the range of the maximum reflection wavelength of the display color is also widened accordingly.

Example 4 A reflection type liquid crystal display device was produced in the same manner as in Example 3 except that 4-acryloylbiphenyl was used as the polymerizable compound.

The device was examined for V _a , V _b , and V _c in the same manner as in Example 1. As _{a result} , V _a = 5.
V, was V _b = 8V, and V _c = 12V. This element was driven by changing the applied voltage between 0 V and 8 V. At 0 V, yellow with a reflection maximum wavelength of 570 nm was displayed, and at 8 V, green with a reflection maximum wavelength of 530 nm was displayed, and the display color was , Reversibly changed with a change in voltage.

When the applied voltage was continuously changed in the voltage range of 0 V to 8 V, the display color reversibly changed in response to the voltage change, and the maximum reflection wavelength of the display color was changed. It changed continuously in the range of 530 nm to 570 nm.

(Example 5) In the same manner as in Example 1, a substrate on which two films were formed was adhered so that the respective films faced each other.

Next, 61% by weight of a nematic liquid crystal compound E48 (from MERCK) and 39% by weight of an optically active polymerizable compound 4-acryloyl-4 '-(2 (S)-
Methyl butyl) biphenyl, and 0.05% by weight of Darocur 1173 based on the polymerizable compound.
(Merk) was mixed as a polymerization initiator. This mixture was injected between the above-mentioned laminated substrates in an isotropic state, and the mixture was sealed. Further, the liquid crystal layer was controlled to have a planar structure, and ultraviolet rays in a wavelength range near the absorption maximum wavelength of the polymerizable compound were irradiated at a power of 3 mW / cm ² to cure the polymerizable compound. Further, each substrate was electrically connected to a power supply to produce a reflective liquid crystal display device.

The device was examined for V _a , V _b , and V _c in the same manner as in Example 1. As _{a result} , V _a = 5
V, was V _b = 15V and V _c = 15V,. That is, a change from the planar structure to the homeotropic structure occurred without using the focal conic structure.

This element was driven by changing the applied voltage between 0 V and 15 V. At 0 V, yellow with a maximum reflection wavelength of 570 nm was displayed. At 15 V, the reflection maximum wavelength was in the ultraviolet region, so the liquid crystal layer was almost transparent, and black was displayed by the light absorption layer provided on the substrate facing the display side substrate of the element. The display color changed reversibly with a change in voltage.

When the voltage applied to the device was continuously changed in the voltage range of 0 V to 15 V, the display color changed reversibly with respect to the voltage change, and the reflection maximum wavelength of the display color changed. It changed continuously in the range between the ultraviolet region and 570 nm.

(Example 6) Nematic liquid crystal compound E48
(MERCK) and CB15 (MERCK)
) Was used in the same manner as in Example 2, except that they were used in a ratio of 67% by weight and 33% by weight, respectively.

The device was examined for V _a , V _b , and V _c in the same manner as in Example 1. As _{a result} , V _a = 5
V, was V _b = 8V, and V _c = 12V. When this element was driven by changing the applied voltage between 0 V and 8 V, at 0 V, red light having a reflection maximum wavelength of 660 nm was displayed, and at 8 V, orange light having a reflection maximum wavelength of 620 nm was displayed. It changed reversibly with the change of voltage.

When the applied voltage was continuously changed within a voltage range of 0 V to 8 V, the display color changed reversibly with respect to the voltage change, and the reflection maximum wavelength of the display color was 6.
It changed continuously in the range of 20 nm to 660 nm.

Example 7 Nematic Liquid Crystal Compound E48
(MERCK) and CB15 (MERCK)
) Was used in the same manner as in Example 2 except that the ratio was 57% by weight and 43% by weight, respectively.

The device was examined for V _a , V _b , and V _c in the same manner as in Example 1. As _{a result} , V _a = 5
V, was V _b = 8V, and V _c = 12V. This element was driven by changing the applied voltage between 0 V and 8 V. As a result, at 0 V, green with a reflection maximum wavelength of 530 nm was displayed, and at 8 V, bluish green with a reflection maximum wavelength of 490 nm was displayed, and the display color changed reversibly with a change in voltage.

When the voltage applied to the device was continuously changed in a voltage range of 0 V to 8 V, the display color changed reversibly with the change in voltage, and the reflection maximum wavelength of the display color changed. It changed continuously in the range of 490 nm to 530 nm.

Example 8 Nematic Liquid Crystal Compound E48
(MERCK) and CB15 (MERCK)
) Was used at a ratio of 50% by weight to 50% by weight, respectively, to produce a liquid crystal display device in the same manner as in Example 2.

The device was examined for V _a , V _b , and V _c in the same manner as in Example 1. As _{a result} , V _a = 5
V, was V _b = 8V, and V _c = 12V. The device was driven by changing the applied voltage between 0 V and 8 V. At 0 V, a blue color having a reflection maximum wavelength of 450 nm was displayed. At 8 V, the reflection maximum wavelength was 410 nm. However, since the reflectance was low and the liquid crystal layer was almost transparent, no purple color was displayed, and the light absorption layer provided on the substrate facing the substrate on the display side of the element was used. Black color was displayed. The display color is
It changed reversibly with the change of voltage.

When the applied voltage was continuously changed in this element in the voltage range of 0 V to 8 V, the display color reversibly changed in response to the voltage change, and the reflection maximum wavelength of the display color was:
It changed continuously in the range of 410 nm to 450 nm, which is almost black.

(Example 9) Nematic liquid crystal compound E48
(MERCK) and CB15 (MERCK)
) Was used in the same manner as in Example 2 except that the ratio was 73% by weight and 27% by weight, respectively.

The device was examined for V _a , V _b , and V _c in the same manner as in Example 1. As _{a result} , V _a = 5.
V, was V _b = 8V, and V _c = 12V. This element was driven by changing the applied voltage between 0 V and 8 V. As a result, at 0 V, the reflection maximum wavelength was 740 nm. In addition, since this wavelength has low visibility and a part of the selective reflection wavelength region is included in the infrared region, the liquid crystal layer is almost transparent and is provided on the substrate facing the substrate on the display side of the element. Black was displayed by the light absorbing layer. Also, 8
In the case of V, a red color having a reflection maximum wavelength of 700 nm is displayed,
The display color changed reversibly with a change in voltage.

When the applied voltage was continuously changed within a voltage range of 0 V to 8 V, the display color reversibly changed in response to the voltage change, and the reflection maximum wavelength of the display color was:
It changed continuously in the range from 700 nm to 740 nm, which is almost black.

Example 10 As a liquid crystal compound, 60% by weight of a nematic liquid crystal compound ZLI4900-000 was used.
(MERCK) and a liquid crystal display element was produced in the same manner as in Example 2 except that CB15 (MERCK) was used at a ratio of 40% by weight.

The device was examined for V _a , V _b , and V _c in the same manner as in Example 1. As _{a result} , V _a = 4
V, V _b = 6V, and it was V _c = 10V. When this element was driven by changing the applied voltage between 0 V and 6 V, at 0 V, green with a reflection maximum wavelength of 520 nm was displayed, and at 6 V, blue with a reflection maximum wavelength of 480 nm was displayed, and the display color was , Reversibly changed with a change in voltage.

When the applied voltage was continuously changed in this element in the voltage range of 0 V to 6 V, the display color changed reversibly in response to the voltage change, and the reflection maximum wavelength of the display color was 48.
It continuously changed in the range of 0 nm to 520 nm.

(Example 11) Nematic liquid crystal compound E4
8 (MERCK) at a ratio of 72% by weight, and a liquid crystal display device was produced in the same manner as in Example 2, except that 28% by weight of S811 (MERCK) was used as an optically active substance.

The device was examined for V _a , V _b , and V _c in the same manner as in Example 1. As _{a result} , V _a = 5.
V, was V _b = 8V, and V _c = 12V. When this element was driven by changing the applied voltage between 0 V and 8 V, at 0 V, orange with a reflection maximum wavelength of 620 nm was displayed, and at 8 V, yellow with a reflection maximum wavelength of 580 nm was displayed, and the display color was , Reversibly changed with a change in voltage.

When the voltage applied to the device was continuously changed in the voltage range of 0 V to 8 V, the display color changed reversibly with the change in voltage, and the reflection maximum wavelength of the display color changed. It changed continuously in the range of 580 nm to 620 nm.

[0113]

As described above, according to the reflection-type liquid crystal display device and the method of driving the same according to the present invention, the voltage applied to the device changes the planar structure and the transition structure between the planar structure and the focal conic structure. It is controlled within a voltage range in which the structure can be reversibly changed with respect to a change in voltage, so that it is possible to drive at a low voltage,
And multi-color display with one pixel is possible.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a liquid crystal display element according to one embodiment of the present invention.

FIG. 2 is a graph showing a relationship between applied voltage and reflectance of a liquid crystal display element according to one embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a liquid crystal display element according to another embodiment of the present invention.

FIG. 4 is a graph showing a relationship between an applied voltage and a reflection spectrum of the liquid crystal display element according to one embodiment of the present invention.

FIG. 5 is a graph for explaining a conventional driving method of a liquid crystal display element.

[Explanation of symbols]

 Reference numerals 1, 2, transparent substrate 3-6, electrode 7, spacer 8, 9, liquid crystal material 10, liquid crystal layer 11, power supply 12, 13, switch 14, reflection type liquid crystal display element 21-24, region 30, liquid crystal layer 31, etc. Polymer 34: Liquid crystal display element 38, 39: Liquid crystal material 51-54: Region

Claims (5)

[Claims] 1. A pair of substrates disposed opposite to each other and having electrodes on the opposite surface, at least one of which is transparent; a means for applying a voltage between the electrodes; It exhibits a planar structure when no voltage is applied, and transitions to a focal conic structure through a transition region including a reversible transition region in which reflection characteristics change reversibly with voltage by application of a voltage equal to or more than a predetermined value by the voltage application unit. A reflective liquid crystal display device comprising: a liquid crystal layer that is driven under a voltage range corresponding to the reversible transition region. 2. The reflective liquid crystal display device according to claim 1, wherein at least one of the pair of substrates has a horizontal alignment treatment applied to a surface in contact with the liquid crystal layer. 3. The reflective liquid crystal display device according to claim 1, wherein the liquid crystal layer contains a polymer. 4. At least a part of the reversible transition region,
2. The reflective liquid crystal display device according to claim 1, wherein the device is driven by continuously changing an applied voltage. 5. A liquid crystal layer exhibiting a planar structure when a voltage is not applied, wherein a voltage at which the liquid crystal layer starts changing from a planar structure to a transition structure between a planar structure and a focal conic structure by application of a voltage. A reflective liquid crystal display element, wherein the liquid crystal layer applies a voltage that is equal to or lower than an upper limit value of a voltage range in which the liquid crystal layer reversibly changes between the planar structure and the transition structure according to a change in applied voltage. Drive method.