JPH06265854A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide the bright reflection type color liquid crystal element by laminating combined films formed by dispersing liquid crystals contg. dichromatic dyestuff into porous high-polymer films by each of threshold electric fields of electrooptical characteristics and functions of color development. CONSTITUTION:The porous high-polymer films 1 to 3 varying in the sizes of fine pores are formed into a three-layered structure by dispersing nematic liquid crystals 4 to 6 varying in threshold voltage in the respective films 1 to 3 and forming combined films 10 to 12 if the combined films are constituted by lamination. The dichromatic 7 to 9 varying in color development are incorporated into the respective nematic liquid crystals 4 to 6. The combined films 10 to 12 laminated in three layers are clamped by transparent substrates 15, 16 formed with ITO electrodes 13, 14 and a light scattering layer 17 is arranged on the rear surface of the one substrate. Any porous high-polymer films 1 to 3 are usable as the porous high-polymer films, insofar as these films are relatively uniform in the fine pores and are adjustable in size.

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 element which constitutes a display body.

[0002]

2. Description of the Related Art In recent years, a liquid crystal display device in which a liquid crystal and a polymer are dispersed has attracted attention as a bright liquid crystal display device which does not use a polarizing plate. The operating principle of this liquid crystal display element utilizes the difference in the refractive index between the liquid crystal and the polymer. When the electric field is applied, the liquid crystal and the polymer show a transmissive state. If they differ, the scattering state is shown (Japanese Patent Publication No. 58-501631).
Such). In addition, a liquid crystal display device of the opposite mode, which transmits light when no electric field is applied and scatters when an electric field is applied, has also been developed (M
ol. Cryst. Liq. Cryst. , 1991,
vol. 198, pp. 357-370. For these modes, a method of improving visibility by mixing a dye has also been proposed.

[0003]

However, there is no disclosure of a technique which can obtain a plurality of display colors with a simple structure while exhibiting sufficient brightness by the method described above.
Therefore, an object of the present invention is to provide a method for colorizing a liquid crystal display device of a system of switching scattering-transmission.

[0004]

In order to achieve the above object, the liquid crystal display device of the present invention has the following constitution.

(1) A nematic liquid crystal containing a dichroic dye, a composite film formed by dispersing the nematic liquid crystal in a porous polymer film, a coloring of the dichroic dye and a threshold electric field. It is characterized by comprising a composite film formed by laminating a plurality of different composite films, and a substrate which covers both front and back surfaces of the laminated composite film and at least one of which has a transparent electrode layer.

(2) A light scattering layer is arranged on the back surface of the substrate.

(3) A light absorbing layer is arranged on the back surface of the substrate, and a mirror surface layer is arranged on the back surface of the light absorbing layer.

[0008]

【Example】

(Embodiment 1) FIG. 1 shows an embodiment of the present invention.
A structure in which three layers of composite films are laminated will be shown. Porous polymer films 1, 2 and 3 having different fine pore sizes, and nematic liquid crystals 4 and 5 having different threshold voltages in the films.
6 are dispersed to form composite films 10, 11, 12 and 3
It has a layered structure. In these nematic liquid crystals,
It contains dichroic dyes 7, 8 and 9 having different colors.
The composite film laminated in three layers is sandwiched by the transparent substrates 15 and 16 on which the ITO electrodes 13 and 14 are formed, and the light scattering layer 17 is arranged on the back surface of one substrate.

FIG. 2 shows the optical response to the electric field strength when the composite films 10, 11 and 12 are sandwiched between transparent electrodes each having an ITO electrode formed thereon. When the electric field E = 0, the liquid crystal molecules and the dichroic dye randomly exist due to the wall surface of the fine pores. Therefore, a display color is obtained by adding light scattering to the absorption color of the dichroic dye. In this example, in order to make the coloring effect of the dye in each composite film efficient, a liquid crystal having a small refractive index anisotropy was selected to suppress light scattering, particularly backscattering. On the other hand, when an electric field sufficiently higher than the threshold electric field strength is applied, the liquid crystal molecules and the dichroic dye are oriented in the direction of the electric field, and the absorption and light scattering of the dye are eliminated and the device becomes transparent. The threshold electric field strength is adjusted by the size of the micropores and the nematic liquid crystal that disperses them. As shown in FIG. 2, the difference in the threshold electric field strength between the laminated composite films satisfies the conditions of E2 <E3 and E4 <E5, and the liquid crystal display has a large color difference of display colors and high visibility. It becomes an element. In this example, by increasing the size of the micropores, a composite film having a low threshold electric field strength characteristic was obtained, and by decreasing the size of the micropores, a composite film having a high threshold electric field strength characteristic was obtained. A film was obtained. Furthermore, the driving margin and visibility were improved by changing the threshold electric field strength of the liquid crystal to be dispersed. The electro-optical characteristics can be adjusted also by the thickness of the porous polymer film.

The operating principle of the liquid crystal display device of this embodiment will be described below. The liquid crystal display element of the present embodiment mixes three colors of dichroic dyes in the electric field E <E1. For example, when yellow, magenta, and cyan are used, black display is performed.
When E = E2, the liquid crystal molecules 4 of the composite film 10 and the dichroic dye 7 are oriented in the direction of the electric field, so that a display color obtained by adding the dichroic dyes 8 and 9 is obtained. Furthermore, E = E4
In the case, since the liquid crystal molecules of the composite films 10 and 11 and the dichroic dye are oriented in the electric field direction, the display color of the dichroic dye 9 is obtained. In the case of E> E6, the liquid crystal molecules of each composite film and the dichroic dye are aligned in the direction of the electric field, so that the light scattering layer 17 arranged on the back surface of the transparent substrate 16 displays white.

The liquid crystal display device of the present invention can use liquid crystal having a large anisotropy of refractive index. In this case, since backscattering in the composite film becomes large, the display color of the dichroic dye 7 becomes E = E when the electric field E <E1.
2 is the display color of the dichroic dye 8 and E = E4 is the display color of the dichroic dye 9. When E> E6, the light scattering layer 17 is displayed in white.

The porous polymer membrane used in the present invention is applicable if the fine pores are relatively uniform and the size can be adjusted. In this embodiment, polymethacrylate (PMM
Porous polymer films 1, 2 and 3 were prepared in A), and the size of the micropores was about 3.0 μm, about 1.5 μm, and about 0.5 μm, respectively. The film thickness of the porous polymer was 10 μm. Further, the nematic liquid crystals 4, 5 and 6 to be dispersed are RDP-2 manufactured by Roddick Corporation respectively.
0517 (refractive index anisotropy Δn = 0.13), RDP-0
0239 (Δn = 0.13), RDP-20215 (Δ
n = 0.083) was used to impregnate the porous polymer film in a vacuum atmosphere. The dichroic dye was previously dissolved in the nematic liquid crystal. In the present embodiment, the nematic liquid crystals 4, 5 and 6 each have SI553 (magenta, 1.5 wt%) M361 (yellow, manufactured by Mitsui Toatsu Dye Co., Ltd.).
2.0 wt%) and M483 (blue, 1.0 wt%) were used (however, the dye concentration represents the weight% with respect to the liquid crystal). The composite film thus obtained was laminated on the glass substrate 15 on which the ITO electrode was formed, and laminated on the polycarbonate film 16 on which the ITO electrode was formed. Further, the light scattering layer 17 was arranged on the back surface of the glass substrate 15. When an electric field was applied to the liquid crystal display element of the present example obtained in this way, when the electric field was off, black, green when the electric field E = E2, blue when the electric field E = E4, and electric field E = E respectively.
At 6, a white display was obtained. (Embodiment 2) FIG. 3 shows the structure of a liquid crystal display element according to Embodiment 2 of the present invention. In this example, in the structure of the liquid crystal display element in Example 1, instead of the light scattering layer, a light absorbing layer 37 showing red color and an aluminum mirror layer 38 on the back surface thereof.
Was placed. Other configurations and materials are the same as those in the first embodiment.

When an electric field was applied to the liquid crystal display element of the present example obtained in this way, in the electric field shown in FIG. 2, black when the electric field was off, green when the electric field E = E2,
Blue was obtained when the electric field E = E4, and red was obtained when the electric field E = E6. Further, by disposing the mirror surface layer on the back surface of the light absorption layer, the optical path length is increased, and a clear display color is obtained.
Further, in the structure of the second embodiment, when the pixels are miniaturized and the color mixing effect is utilized, a full-color reflective liquid crystal display element is possible.

[0014]

As described above, according to the present invention, a composite film in which a liquid crystal containing a dichroic dye is dispersed in a porous polymer film is used to produce a threshold electric field of electro-optical characteristics and color development. By stacking layers according to function, it is possible to provide a bright reflective color liquid crystal display device. Further, in the configuration of the present invention, it is not necessary to drive a plurality of liquid crystal display elements in parallel, so that it is possible to switch the color display by a simple driving method. Furthermore, full-color display is also possible due to the miniaturization of display pixels and the effect of color mixing.

[Brief description of drawings]

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

FIG. 2 is a diagram showing electro-optical characteristics of a composite film used in the present invention.

FIG. 3 is a sectional view of a liquid crystal display element according to a second embodiment of the present invention.

[Explanation of symbols]

 1. Porous polymer membrane 2. Porous polymer film 3. Porous polymer membrane 4. Nematic liquid crystal 5. Nematic liquid crystal 6. Nematic liquid crystal 7.2 dichroic dye 8.2 dichroic dye 9.2 dichroic dye 10. Laminated first composite film 11. Second laminated composite film 12. Laminated third composite film 13. ITO electrode 14. ITO electrode 15. Transparent substrate 16. Transparent substrate 17. Light scattering layer 21. 22. Electro-optical properties of the laminated first composite film Electro-optical characteristics of laminated second composite film 23. Electro-optical properties of laminated third composite film 31. Porous polymer film 32. Porous polymer film 33. Porous polymer film 34. Nematic liquid crystal 35. Nematic liquid crystal 36. Nematic liquid crystal 37.2 chromatic dye 38.2 chromatic dye 39.2 chromatic dye 40. Laminated first composite film 41. Second laminated composite film 42. Laminated third composite film 43. ITO electrode 44. ITO electrode 45. Transparent substrate 46. Transparent substrate 47. Light absorbing layer 48. Mirror layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hidehito Iizaka 3-3-5 Yamato, Suwa City, Nagano Seiko Epson Corporation

Claims (3)

[Claims] 1. A nematic liquid crystal containing a dichroic dye, a composite film formed by dispersing the nematic liquid crystal in a porous polymer film, and a dichroic dye having different coloring and threshold electric fields. A liquid crystal display comprising: a composite film formed by stacking a plurality of the composite films; and a substrate having front and back surfaces of the stacked composite films and at least one of which has a transparent electrode layer. element. 2. A liquid crystal display device according to claim 1, wherein a light scattering layer is arranged on the back surface of the substrate. 3. A light absorbing layer on the back surface of the substrate, and a mirror surface layer on the back surface of the light absorbing layer.
The liquid crystal display element described.