JPH0728054A - Reflection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device which is low in driving voltage, has a sufficient visual field angle, has no parallax and does not generate coloration by clamping a polymer-dispersed liquid crystal layer with a light transparent electrode and a reflection electrode and laminating and arranging a wavelength plate corresponding to 1/4 the wavelength of the light to generate the max. visible sensitivity and a polarizer on the light transmissive electrode side. CONSTITUTION:The polymer-dispersed liquid crystal layer 5 is clamped by the light transmissive electrode 2 formed on a light transmissive substrate 1 and the reflection electrode 4 formed on a substrate 3. The quarter-wavelength plate 6 and the polarizer 7 are successively disposed in a laminated state on the light transmissive substrate 1. Liquid crystals 8 of the polymer-dispersed liquid crystal layer 5 are randomly oriented and the polarization of the transmitted light is eliminated to be in a bright state when a voltage is not applied to the liquid crystals. The liquid crystals 8 are oriented perpendicularly to the electrodes 2, 4 and a double refraction effect is not generated when the voltage is applied thereto. Then, the light entering from the outside and emitted to the outside passes twice the quarter-wavelength plate 6 and is rotated 90 deg. at the plane of polarization and is, therefore, absorbed in the polarizer 7 at the time of emission to be in a dark state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device used in a display device for electronically displaying information, and more particularly to a reflective liquid crystal display device in which driving voltage is lowered.

[0002]

2. Description of the Related Art Conventionally, as a so-called reflection type liquid crystal display device, a TN (Twisted Nematic) type liquid crystal display device or an STN (Super Twisted Nematic) type liquid crystal display device has been well known and well known. It has been put to practical use. By the way, the STN type liquid crystal display device has a drawback that the display is colored, whereas the TN type liquid crystal display device has almost no such coloring phenomenon.
It has a feature that the viewing angle is slightly wider than that of the STN type liquid crystal display device. However, the viewing angle of the TN type liquid crystal display device is still insufficient, and there is a drawback that parallax occurs. As a technique for improving such problems of viewing angle and coloring, a polymer dispersed liquid crystal in which a liquid crystal is dispersed in a polymer matrix (Polymer Dispersed Liquid Crysuta) is used.
l), various ones using so-called PDLC elements have been proposed.

In this PDLC element, the liquid crystal is randomly aligned when no voltage is applied and aligned in the direction of the electric field when a voltage is applied. Particularly, the liquid crystal is randomly aligned when no voltage is applied. Therefore, there is no problem in view angle and coloring. Further, unlike the TN-type liquid crystal display device and the STN-type liquid crystal display device, there is no need for the alignment treatment of the electrode surface, which simplifies the manufacturing process, and therefore has the advantage of providing an inexpensive device. As a display device using such a polymer-dispersed liquid crystal, for example, as shown in Japanese Patent Laid-Open No. 4-212928, a polymer-dispersed liquid crystal is composed of two polarizers so that their polarization axes are orthogonal to each other. It is publicly known that it is sandwiched. In addition, those utilizing the so-called guest-host effect in polymer-dispersed liquid crystals are known (for example, “Semiconductor Industrial Design 86 D
igest (1986) '' P126 (JFFergason, A. Dalisa, S.
Lu, P. Drzaic))).

[0004]

However, in the case of using the above-mentioned two polarizers, there are problems of insufficient viewing angle and coloring in the TN type liquid crystal display device and the STN type liquid crystal display device. However, there is a problem that parallax occurs due to the use of two polarizers. Further, in the case of using the guest-host effect, there is no problem of insufficient viewing angle and coloring, but there is a problem that the driving voltage becomes higher than that of the TN type liquid crystal display device or the STN type liquid crystal display device. . As described above, in the conventional liquid crystal display device, it is impossible to simultaneously satisfy the requirements of having a sufficient viewing angle, causing no coloring, having no parallax, and having a relatively low driving voltage. There was a problem that we had no choice but to sacrifice the demand for.

The present invention has been made in view of the above circumstances, and provides a reflective liquid crystal display device having a low driving voltage, a sufficient viewing angle, no parallax, and no coloring. is there.

[0006]

In a reflective liquid crystal display device according to the present invention, a polymer-dispersed liquid crystal layer in which a liquid crystal is dispersed and contained in a polymer matrix, a transparent electrode, and the transparent electrode. It is sandwiched by a reflective electrode whose opposite surface is formed as a mirror surface and has a maximum visible sensitivity of 1 / wavelength of light.
A quarter wave plate that produces a phase delay corresponding to 4 and a polarizer are sequentially stacked on the transparent electrode side.

[0007]

Function: The liquid crystal in the polymer dispersed liquid crystal layer is randomly aligned when no voltage is applied, and the light transmitted through this is depolarized, and the display state becomes a bright state, while the liquid crystal transmits light when a voltage is applied. Since the birefringence effect does not occur with respect to the vertically incident light because it is oriented perpendicular to the reflective electrode and the reflective electrode, the light that is incident from the outside and is emitted to the outside again is 1/4. Since it passes through the wave plate twice, it causes a phase change of substantially 1/2 wavelength, and as a result of rotating the polarization plane by 90 degrees, it is absorbed by the polarizer at the time of emission and the display state becomes a dark state. is there.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A reflective liquid crystal display device according to the present invention will be described below with reference to FIG. Here, the drawing is a vertical cross-sectional view of one embodiment of the reflective liquid crystal display device according to the present invention. This reflective liquid crystal display device includes a transparent electrode 2 formed on one surface of a transparent substrate 1 and a reflective electrode 4 formed on one surface of a substrate 3, and a polymer dispersed liquid crystal layer 5 is formed. While sandwiching, the ¼ wavelength plate 6 and the polarizer 7 are sequentially laminated on the other surface side of the transparent substrate 1 (the surface opposite to the surface on which the transparent electrode 1 is formed). It will be done.

The translucent substrate 1 is made of a translucent synthetic resin such as polyethylene terephthalate or volaic carbonate, or glass such as borosilicate glass or quartz glass. It is suitable. The light-transmissive electrode 2 is formed by depositing ITO or SnO2 on one surface of the light-transmissive substrate 1 by a sputtering method or a vapor deposition method, and forming it into a desired pattern by a photo-etching method. The film thickness of the translucent electrode 2 is set within a range in which sufficient transmittance is obtained and the electrode has low resistance. Specifically, 50
To 200 nm is preferable. The substrate 3 is to be the base of the reflective electrode 4, and therefore, the reflective electrode 4 needs to be formed sufficiently flat so as not to have the depolarization property. The member forming the substrate 3 may be the same as the translucent substrate 1, but does not necessarily have to be translucent.

The reflective electrode 4 is formed of a metal member having a high reflectance and a low resistance, such as Al or Ag, by a sputtering method or a vapor deposition method. Therefore, it is necessary that the surface is formed as a mirror surface by controlling the film forming temperature, the film forming speed, and the like. Further, the film thickness thereof needs to be set within a range that provides sufficient reflectance and low resistance, and is preferably about 0.5 to 2 μm. The polymer-dispersed liquid crystal layer 5 may be one in which the liquid crystal 8 is dispersed and held in the polymer matrix 9, for example, one in which the liquid crystal forms independent liquid bubbles and is enclosed in microcapsules. , Those in which these liquid bubbles are in communication are used. Alternatively, the polymer matrix may be crosslinked in a gel form, or the pores of the polymer matrix having a large number of fine holes may be filled with liquid crystal.

Epoxy resin or acrylic resin is suitable for the polymer matrix 9. Further, the liquid crystal 8 is usually a TN such as a cyanobiphenyl type or a phenylcyclohexane type.
The liquid crystal used for the mold and STN type is used. The content ratio of the liquid crystal and the polymer in the polymer dispersed liquid crystal layer 5 is preferably set in the range of about 10 to 95% by weight of the liquid crystal. When the content ratio of the liquid crystal is low, the difference between the refractive index of the polymer and the refractive index of the liquid crystal to ordinary light is 0.04 or less, and more preferably 0.02 in order to improve the transparency when a voltage is applied. It is desirable to be within. If the liquid crystal content is sufficiently high, it is not necessary to pay particular attention to such a point. Further, in order to prevent the liquid crystal from becoming a mirror surface and to reduce the operating voltage, it is preferable that the liquid crystal has a high light scattering property. Therefore, the birefringence is 0.15 or more, more preferably 0.2.
The above is desirable.

The polymer dispersed liquid crystal layer 5 may be produced, for example, by emulsifying water-soluble polyvinyl alcohol as a polymer component, spreading it on a substrate and drying it (for example, Japanese Patent Publication No. No. 52843), a method of preliminarily mixing the raw material of the polymer matrix and liquid crystal and thermally polymerizing to cause phase separation (see, for example, Japanese Patent Laid-Open No. 63-501512), or polymerizing with ultraviolet rays. Therefore, any method of causing phase separation (for example, JP-A-1-198725) may be used. As a method for obtaining the polymer-dispersed liquid crystal layer 5 having a constant thickness, in addition to the emulsification method described above, a mixed solution of the polymer matrix raw material and the liquid crystal is prepared and cast and supplied onto the electrode substrate. Then, as in the case of the conventional TN type liquid crystal display device, the periphery of the electrode substrate is sealed with an adhesive, and a mixed solution of the raw material of the polymer matrix and the liquid crystal is injected through the injection port. A method of curing with heat, ultraviolet rays, or the like can be used.

The quarter-wave plate 6 is, for example, a uniaxially stretched film such as polyethylene sulfone, polymethylmethacrylate, polyvinyl alcohol, and polycarbonate, a parallel-aligned liquid crystal cell, and a parallel-aligned high-definition film. It is formed from a molecular liquid crystal film or the like. In the present embodiment, the wavelength at which the luminosity of the present device is maximized is set to 550 nm, so that the quarter wave plate 6 has a retardation of 138.
It is preferably set to nm. The polarizer 7 and the quarter-wave plate 6 are arranged so that the polarization axis and the stretching axis form 45 degrees with each other. In addition, it is desirable that the polarizer 7 and the quarter-wave plate 6 be bonded together with a translucent adhesive in order to suppress interface reflection. Similarly, it is desirable that the quarter-wave plate 6 and the translucent substrate 1 be bonded together with a translucent adhesive.

In the above structure, however, the liquid crystal 8 of the polymer dispersed liquid crystal layer 5 is randomly aligned when no voltage is applied, and the light transmitted through the liquid crystal is depolarized. Therefore, a certain proportion of light is polarized. The child 7 can be passed through, and the display state of this device becomes a so-called bright state. In this bright state, the polymer-dispersed liquid crystal layer 5 is in a cloudy state, so that even if the surface of the reflective electrode 4 that joins with the polymer-dispersed liquid crystal layer 5 is a mirror surface, so-called reflection from the surroundings may occur. Is small, and so-called visibility is hardly reduced.

On the other hand, when a voltage is applied, the liquid crystal 8 is vertically aligned with respect to the electrodes 2 and 4, so that the birefringence effect does not occur with respect to vertically incident light. Therefore, the change in polarization state is 1 /
It is only due to the four-wave plate 6. Light incident from the outside is reflected by the reflection electrode 4 and passes through the quarter-wave plate 6 and the polarizer 7 and then exits to the outside again. 2 quarter wave plate 6
Since the light beam passes through twice, a phase change of substantially 1/2 wavelength is generated. Therefore, since the plane of polarization is rotated by 90 degrees, it is absorbed by the polarizer 7 at the time of emission and the display state of this device becomes a so-called dark state.

[0016]

As described above, according to the present invention,
By configuring so that display can be performed without using the guest-host effect, in which the driving voltage becomes high in the polymer dispersed liquid crystal, the driving voltage is relatively low, and even if one of the electrodes is a reflective electrode, Due to the cloudy state of the polymer-dispersed liquid crystal, so-called surrounding reflection does not occur, there is no parallax, the viewing angle is wide, and sufficient brightness without coloring is achieved. Further, as described above, since the driving voltage is relatively low and the backlight is not required, it has an effect of lower power consumption and excellent visibility as compared with a liquid crystal display device having a backlight.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a first embodiment of an image input / output device according to the present invention.

[Explanation of symbols]

1 ... Translucent substrate, 2 ... Translucent electrode, 3 ... Substrate, 4
... Reflective electrode, 5 ... Polymer dispersed liquid crystal, 6 ... Quarter wave plate, 7 ... Polarizer, 8 ... Liquid crystal, 9 ... Polymer matrix

Claims (1)

[Claims] 1. A polymer-dispersed liquid crystal layer in which liquid crystal is dispersed and contained in a polymer matrix, comprising a translucent electrode and a reflective electrode having a mirror-finished surface facing the translucent electrode. One of the wavelengths of light that causes maximum visibility while sandwiching
A reflection type liquid crystal display device, characterized in that a quarter wave plate which produces a phase delay corresponding to / 4 and a polarizer are sequentially laminated and arranged on the transparent electrode side.