JPH06265850A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To greatly improve a black level so that a sufficiently high contrast is obtd. by forming a liquid crystal having a chiral property as a light control layer, making only the circularly polarized light incident on this light control layer and reflecting this light thereby making dark display. CONSTITUTION:This liquid crystal display device is constructed by providing one outer side of a liquid crystal panel 19 having two sheets of transparent glass substrates 15 which are provided with transparent electrodes 16 of ITO respectively on the inner side and a liquid crystal material 18 which is dispersed into a high-polymer matrix 17 and has the chiral property, with a reflection mirror 11, a back light 12, a linear polarizing plate 13 and a quarter-wave plate 14. The light emitted from this back light 12 is first polarized to linearly polarized light by this linear polarizing plate 13 and is polarized to the light circularly polarized in one way by this quarter-wave plate 14. The light is not emitted at all from the entire surface of the display panel in this state and is dark-displayed. The turbid state of a light scattering state is made as bright display, by which the sufficiently high contrast is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having a novel display system.

[0002]

2. Description of the Related Art Conventionally, liquid crystal display devices of TN type and STN type using nematic liquid crystals have been put into practical use. Also, a liquid crystal device using a ferroelectric liquid crystal has been proposed. These elements have a problem that the viewing angle is narrow when a linear polarizer has to be used as crossed Nicols or parallel Nicols when used as an element.

In recent years, there has been an increasing demand for a large-sized panel, but in the above-mentioned liquid crystal display device, it is easy to use a large-sized liquid crystal display panel due to the problem that the substrate intervals must be made uniform with high precision. It has a problem that it cannot be manufactured.

On the other hand, a method of encapsulating a liquid crystal and dispersing liquid crystal droplets in a polymer is known as a method of providing a liquid crystal display device which has a wide viewing angle and can be relatively easily enlarged. Japanese Patent Publication No. 58-501631, USP
4435047). In the liquid crystal display device disclosed in the above specification, liquid crystal molecules encapsulated in polyvinyl alcohol and having a positive dielectric anisotropy are aligned in the electric field direction in the presence of an electric field, and the refractive index n _{0 of the} liquid crystal and the polymer when the refractive index n _p is equal indicates transparency, the electric field is removed, the liquid crystal array returns to a random sequence, the refractive index of the liquid crystal droplets is deviated from the n _o, the liquid crystal droplets scatter light at the boundary surface, The thin layer becomes cloudy. In addition to the above-mentioned techniques, there are some known techniques for forming a thin film of a polymer in which the encapsulated liquid crystal is encapsulated, for example, JP-A-61-502.
No. 18 discloses a liquid crystal dispersed in an epoxy resin, and JP-A-2-83534 discloses a liquid crystal dispersed in a urethane acrylate resin. However, in such a polymer-dispersed liquid crystal display device, the scattering state of light is used as a dark display and the transmission state is used as a bright display.
The dark display merely sees white turbidity in a light-scattering state. Therefore, since transparency is bright and white turbidity is dark, there is a problem that a sufficient contrast between light and dark cannot be obtained.

Further, a color liquid crystal display using a dispersion type liquid crystal prepared by dispersing a cholesteric liquid crystal having a negative dielectric anisotropy in a polymer matrix is disclosed in Japanese Patent Laid-Open No. 3-300.
It is disclosed in Japanese Patent Publication No. 209425. In this liquid crystal display device, transmitted light is colored and color-displayed by selectively reflecting light having a wavelength determined by the spiral pitch of cholesteric liquid crystal. Also in this method, since a wide viewing angle can be obtained because a polarizer such as crossed Nicols is not used, this liquid crystal display device also has a light scattering state, that is, white turbidity as a dark display. Similar to the above, there was a problem that the black level of dark display could not be sufficiently obtained and the contrast of light and dark could not be sufficiently obtained.

[0006]

In the conventional dispersion type liquid crystal display device, the viewing angle can be relatively widened and the size can be expected to be large. However, the white turbidity of the light scattering state is displayed darkly and the light transmission state is transmitted. However, it was very difficult to obtain a sufficient black level for dark display, and it was not possible to obtain a sufficiently high contrast. SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal display device having a sufficiently high contrast so as to solve the above-mentioned problems and to cope with a direct-view type.

[0007]

In order to achieve the above object, a liquid crystal display device according to the present invention comprises a first substrate, a second substrate arranged to face the first substrate, and the first substrate. A dimming layer containing a chiral liquid crystal material sandwiched between a substrate and a second substrate, circularly polarized light incident means for making only circularly polarized light circularly polarized in one direction into the dimming layer, and the liquid crystal material Is provided with a control means for controlling the state of reflecting the circularly polarized light and the state of scattering or transmitting the circularly polarized light.

That is, according to the present invention, when the helical axis of a liquid crystal material having chirality is parallel to the incident axis of circularly polarized light, and at the same time, the spiral winding direction and the circularly polarized light rotating direction are the same, The liquid crystal display device is configured so that this state is a dark display by using the property of selectively reflecting. The chiral liquid crystal material (the liquid crystal material in which liquid crystal molecules are spirally wound around an axis) has a circular shape in at least the same direction when the spiral axis is substantially parallel to the incident axis of incident light. Any material that selectively reflects polarized light may be used, and not only a single liquid crystal material exhibiting a cholesteric phase, but also a mixture of liquid crystal materials exhibiting a plurality of cholesteric phases, or a smectic liquid crystal material thereof,
Alternatively, it may be a mixture with a nematic liquid crystal material.

Further, as an incident means for injecting only the circularly polarized light polarized in one direction, there is a means for firstly linearly polarizing natural light and then circularly polarizing it with a quarter wavelength plate or the like. As a linearly polarized light, a polarizer such as a polaroid plate, a Nicol prism, a Glan-Taylor prism, or a Glan-Thompson prism, as a circularly polarized light, a plastic sheet phase plate, a phase difference plate made of a crystal exhibiting birefringence, a crystal phase difference plate, Calcite retarder, mica retarder, Fresnel-Rom prism, phase compensator, Babinet compensator,
A Soleil compensator, a retardation plate using liquid crystal, or the like may be used.

As a means for controlling the light control layer, when a chiral liquid crystal material having negative dielectric anisotropy is used, a spiral axis of the liquid crystal material is changed by applying a voltage. The circularly polarized light is controlled so as to be substantially parallel to and circularly polarized with the circularly polarized light, and the circularly polarized light is selectively reflected. On the other hand, there is a method of randomly aligning the liquid crystal material without applying a voltage and scattering the circularly polarized light incident on the light control layer. In this case, when the circularly polarized light incident on the light control layer from the backlight is reflected, no light is emitted from the entire surface of the display panel.Therefore, this is a dark display, and the white turbid state in which light is scattered is referred to as a bright display. By doing so, it becomes possible to obtain a sufficiently high contrast.

The present invention is not limited to the dispersion type liquid crystal panel, and there is also a method of utilizing the phase transition effect by subjecting the dimming layer to, for example, horizontal alignment treatment and making the cholesteric liquid crystal into a planar or Granduian structure. In this case, a bright display is made by applying a voltage to cause the planar or Granduan structure to be nematically arranged and transmitting light. On the other hand, when no voltage is applied, the cholesteric liquid crystal is in the state of the planar or Granjuan texture, and thus the incident circular knitting light is reflected to provide a dark display. However, in this case, the dielectric anisotropy is positive (p
Type) cholesteric liquid crystal must be used.

The angle formed by the helical axis of the liquid crystal material with respect to the incident axis of the circularly polarized light is preferably parallel in order to obtain the best contrast, but the angle is such that 40% or more of the circularly polarized light amount is reflected. Even if it is tilted, the contrast is remarkably improved as compared with the conventional dispersion type liquid crystal display device.

The relationship between the spiral pitch and the circularly polarized light of the chiral liquid crystal of the present invention is as follows: n _o P <λ <n _e P (λ: wavelength of light in vacuum, P: helix pitch, n _o : normal light refractive index , N _e : refractive index of extraordinary light), the effect is sufficiently exhibited. A chiral liquid crystal selectively reflects circularly polarized light in the same direction as the spiral's palmarity. When the electric vector when viewed in a face-to-face direction is rotated counterclockwise and left-handed circularly polarized light) is completely reflected, and the black level in dark display can be earned.

[0014]

[Function] A liquid crystal material having a chiral property is used as a light control layer, and only the circularly polarized light is incident on this light control layer to reflect the light, thereby producing a dark display, thereby significantly improving the black level and corresponding to the direct view type. As much as possible, it becomes possible to obtain a sufficiently high contrast.

[0015]

The present invention will be described below with reference to the illustrated embodiments. 1 is a schematic view of a liquid crystal display device according to a first embodiment of the present invention. The liquid crystal panel 19 has two transparent glass substrates 15 each having an ITO transparent electrode 16 inside and a liquid crystal material 18 dispersed in a polymer matrix 17 and having a chiral property. The structure is such that the reflecting mirror 11, the backlight 12, the linear polarizing plate 13, and the quarter-wave plate 14 are provided in this order from the side away from. One or both of the glass substrates 15 have wirings arranged in a matrix and switching elements such as TFTs, so that matrix display is possible.

The liquid crystal panel 19 is constructed in particular except that the liquid crystal material 18 dispersed in the polymer matrix 17 has a chiral liquid crystal material, for example, a chiral nematic liquid crystal phase having a negative dielectric anisotropy. There is no limitation, and the liquid crystal is dispersed in a supporting medium made of a photocurable resin such as an acrylic resin as in the conventional one. Depending on the liquid crystal material used, it is necessary to control the temperature within a certain range in order to achieve the chiral nematic liquid crystal state, and heating and cooling means and temperature control means are required.

In the liquid crystal display device having the above structure, the light emitted from the backlight 12, which is a light source, is first reflected by the linear polarizing plate 1.
After being linearly polarized by 3, the 1/4 wave plate 1
4 results in circularly polarized light polarized in one direction. At this portion, only the circularly polarized light is incident on the liquid crystal panel 19.

In order to obtain circularly polarized light, the polarization axis and 1
It is necessary to set the crystal axis of the / 4 wave plate 14 to ± 45 °, but here, the chiral nematic liquid crystal 18 which is set so as to be left-handed circularly polarized light and is dispersed is left-handed.

In the liquid crystal display device configured as described above,
When a voltage is applied between the electrodes 16, the dispersed chiral nematic liquid crystal 18 has a negative dielectric anisotropy, so that the spiral axis is perpendicular to the substrate surface and is substantially parallel to the incident axis of left circularly polarized light. . In this case, the left-handed circularly polarized light is reflected, cannot pass through the liquid crystal panel 19, and shows a dark display. On the other hand, when no voltage is applied, the liquid crystal material 18 is randomly oriented, and thus the circularly polarized light that is incident light is scattered,
Due to this scattered light, a bright display is shown.

Next, a method of manufacturing the liquid crystal display device of the first embodiment will be described. First, butyl acrylate 11% by weight, acrylic oligomer M-1200 (manufactured by Toagosei Kagaku)
15 μm in a solution consisting of 1.0% by weight, Darocur 1116 (manufactured by Merck) as a photo-curing initiator, 64% by weight of liquid crystal ZLI-2806 (manufactured by Merck) and 16% by weight of S811 (manufactured by Merck). Add spacers and disperse well. The mixture was applied onto a glass substrate with ITO, and the glass substrate with ITO was overlaid and exposed for 2 minutes by an ultraviolet irradiation device to produce a dispersion type liquid crystal display panel 19.

The contrast of the liquid crystal display device thus prepared was calculated to be 1:45, which is remarkably higher than that of the conventional one in which transmitted light is displayed brightly and scattered light is displayed darkly, which is 1: 5. Improved.

Next, a second embodiment of the present invention will be shown. Although the present invention improves the contrast of a direct-viewing type liquid crystal display device, the present invention can be applied to a projection type liquid crystal display device. In this embodiment, the liquid crystal display device produced according to the first embodiment is applied to a projection type.

The liquid crystal display panel 19 manufactured similarly to the first embodiment is projected and displayed by the projection optical system as shown in FIG. In the figure, 21 is a mercury arc lamp, 22 is a lens, 23 is a UV filter, 24 is an IR filter, 13 is a linear polarizing plate, 14 is a 1/4 polarizing plate, 19 is a liquid crystal panel prepared in the first embodiment, and 25 Schlieren stop,
26 is a screen. When the contrast of such a projection type liquid crystal display device was measured, a good value of 1:78 was obtained.

Next, a third embodiment of the present invention will be shown. In this example, the structure was the same as that of the first example, and the liquid crystal panel was manufactured by changing the method as described below. First, 15% by weight of iso-dodecyl-acrylate, 10% by weight of long-chain aliphatic diacrylate C-2000 (manufactured by SATOMER), and Darocur 1 as a photocuring initiator.
116 (manufactured by Merck) 1.0%, liquid crystal ZLI-280
A 6 μm (manufactured by Merck) 60% by weight and a solution of S811 (manufactured by Merck) at 14% by weight were added with a 15 μm spacer and well dispersed. The mixture is coated on a glass substrate with ITO, the glass substrate with ITO is overlaid,
The dispersion type liquid crystal display panel 19 was manufactured by exposing for 90 seconds with an ultraviolet irradiation device.

The liquid crystal display panel 19 thus prepared was used as a dispersion type liquid crystal display device as shown in FIG. 1, and the contrast was calculated to be a good value of 1:40. Next, a fourth embodiment of the present invention will be shown. In this embodiment, the liquid crystal panel 19 produced in the third embodiment is of a projection type as shown in FIG.

When the contrast of the liquid crystal display device produced in this example was calculated, a favorable value of 1:55 was obtained. Next, a fifth embodiment of the present invention will be shown. In this example, the structure was the same as that of the first example, and the liquid crystal panel was manufactured by changing the method as described below.

First, pentyl glycol / polypropylene glycol modified diacrylate C-9003 (SAT
21% by weight of OMER Co., 0.8% of Darocur 1173 (manufactured by Merck) as a photo-curing initiator, liquid crystal ZL
64% by weight of I-2806 (Merck), S811
A 15 μm spacer is added to a 16% by weight solution (manufactured by Merck & Co.) to disperse well. The mixture is ITO
The glass substrate with ITO was coated on the glass substrate, the glass substrate with ITO was superposed on the glass substrate, and the dispersion type liquid crystal display panel 19 was produced by exposing the glass substrate with an ultraviolet ray for 90 seconds.

The liquid crystal display panel thus prepared was used as a direct-viewing type liquid crystal display device as shown in FIG. 1, and the contrast was calculated. As a result, a favorable value of 1:36 was obtained.
Next, a sixth embodiment of the present invention will be shown. In this embodiment, the liquid crystal panel produced in the fifth embodiment is of a projection type as shown in FIG. When the contrast of the liquid crystal display device produced in this example was calculated, a good value of 1:51 was obtained.

[0029]

As described above, according to the present invention, the contrast of the liquid crystal display device can be made sufficiently high, and the dispersion type liquid crystal, which has been conventionally difficult, can be directly visualized.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a dispersion type liquid crystal display device of the present invention.

FIG. 2 is a schematic view of a projection type liquid crystal display device of the present invention.

[Explanation of symbols]

 11 Reflector 12 Backlight 13 Linear Polarizer 14 Quarter Wave Plate 15 Glass Substrate 16 Electrode 17 Polymer Matrix 18 Liquid Crystal Material with Chirality 19 Liquid Crystal Panel 21 Mercury Arc Lamp 22 Lens 23 UV Filter 24 IR Filter 25 Schlieren Stop 26 screen

Claims (1)

[Claims] 1. A liquid crystal material having a chiral property, which is sandwiched between a first substrate, a second substrate opposed to the first substrate, and the first substrate and the second substrate. A light layer, a circularly polarized light incident means for making only circularly polarized light circularly polarized in one direction into the light control layer, a state in which the liquid crystal material reflects the circularly polarized light and a state in which the circularly polarized light is scattered or transmitted. And a control means for controlling the liquid crystal display device.