JPS6019491B2 - reflective display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new reflective display device in which light scattering can be freely controlled using an electric field.

In general, reflection or refraction at the boundary between two transparent materials is determined by the degree of refractive index matching between the two materials.

That is, if the refractive index matching between the two materials is sufficient, no reflection or refraction will occur, and if the matching is insufficient, large reflection or refraction will occur. Furthermore, if the interface between the two substances is a light scattering surface, the reflection and refraction will result in forward and backward light scattering. Inevitably, if the refractive index matching between the two materials is sufficient, no light scattering will occur, and if the matching is insufficient, large light scattering will occur. On the other hand, among so-called electro-optical materials, there are materials whose refractive index can be controlled by an electric field.For example, the alignment direction of liquid crystal materials changes when an electric field is applied, and due to the refractive index anisotropy of liquid crystal materials, Effective refractive index can be controlled by electric field. Alternatively, even if P is a transparent conductive material such as T, the refractive index can be controlled by an electric field. In the present invention, by using an electro-optical material whose refractive index can be controlled by an electric field, and controlling the degree of refractive index alignment with an adjacent transparent material by an electric field,
The display device, which can freely control the degree of light scattering on the light scattering surface formed at the interface between the two materials, is made into a reflective type, and by using a light wave plate, the display device is significantly improved compared to the transmissive type. This achieves a high light utilization rate.

Hereinafter, a detailed explanation will be given based on examples.

FIGS. 1 and 2 show an embodiment of the present invention in which an (n-type) nematic liquid crystal having negative induced anisotropy is used as an electro-optical material.

1 and 2 are transparent support plates, which are made of glass here.

3 and 4 are transparent electrodes, which in this example are ln203 vacuum sprayed films, which are patterned by etching, and 5, 6A, and 6B are orientation treated layers.

In this example, an n-type nematic liquid crystal is used, the initial alignment is vertical alignment, 5 and 6B are vertical alignment treatment layers, and organic silane DMOAP (N-N dimethyl-N-octadecyl-3-aminopropyltrimethane) is used. quinsilyl chloride) solution. In addition, in order to tilt in one direction without causing disclination when an electric field is applied, it is better to have a "quasi-vertical orientation" where the orientation is slightly tilted in one direction rather than a completely straight orientation. This is a treated layer to obtain "orientation," and here it was obliquely deposited from a direction 85 degrees away from the normal to the Si0 support plate. In this example, by the treatments of No. 5, No. 6A, and No. 68, quasi-vertical orientation about 7 to 1 oo away from the normal to the support plate was obtained.

7 is an n-type nematic liquid crystal, here M old BA (para-methoxybenzylidene-para-butylaniline) 5
A mixed liquid crystal of 0% and 50% of EBBA (para-ethoxybenzylidene-parabuteraniline) is used, and the refractive index n of this liquid crystal with respect to ordinary light.

is n. = 1.54 and the refractive index of glass ns; 1.53
On the other hand, the refractive index ne of this liquid crystal for extraordinary rays is ne=.-81. 8 is a wavelength plate, and 9 is a reflection plate.

Reference numeral 10 denotes a light diffusing surface formed on the support plate, and in this example, it was formed by honing.

Next, the operation of this embodiment will be described.

In FIG. 1, there is no electric field, and the mixed liquid crystal of M old BA and EBBA has positive optical anisotropy, and its refractive index ellipsoid is as shown in FIG. In other words, if the liquid crystal is connected directly to the
As shown in FIG. 11, the refractive index for light incident perpendicularly to the liquid crystal layer corresponds to the axial length of the cross section of the refractive index ellipsoid taken along the xy plane in FIG. 3, and from FIG. Against n
. matches. In this example, the refractive index is n because the direction is quasi-vertical. It spreads around the area, but it is roughly n. It is. As mentioned above, n. ns, there is almost no scattering at the interface between the liquid crystal and the support plate, and the light 12 incident from 11 is hardly scattered, passes through, and is reflected by the reflector before coming out.
FIG. 2 shows the state in which an electric field is applied. The liquid crystal 7 is aligned horizontally to the support plates 1 and 2 by applying an electric field. In this case, the refractive index of the liquid crystal layer for one beam of light incident perpendicularly to the liquid crystal layer corresponds to the axial length of the cut plane of the refractive index ellipsoid on the yz plane in FIG.
n for polarized light parallel to the liquid crystal 7. = 1.81 n for polarized light perpendicular to the liquid crystal 7. = 1.54, therefore n. Thank you.
The polarized light 15 perpendicular to the liquid crystal 7 is transmitted, and the polarized light 15 parallel to the liquid crystal 7 is scattered as 13 and 14 due to ns. On the other hand, the transmitted light 5 becomes right-handed circularly polarized light 16 by the chapter wave plate 8, becomes left-handed circularly polarized light 17 by the reflection plate 9, enters the chapter wavelength plate 8 again, and this time becomes polarized light 18 parallel to the liquid crystal 7. Since the refractive index for polarized light 18 is ne and nellns, scattering occurs again on the light scattering surface 10, and the light is scattered like 20 and 19. As described above, according to the present invention, the electric field facilitates
It is possible to control light reflection and light scattering, and because it is a reflective type and uses a wavelength plate, it can utilize all natural light compared to a transmissive type that uses a polarizing plate, and has excellent light utilization with high contrast. It is now possible to display

Next, a further improved embodiment 2 is shown. In FIGS. 1 and 2, when the distance from the liquid crystal layer 7 to the reflection plate 9 is large, light from the surroundings surrounds the thin pattern in the middle, reducing the contrast. In order to prevent this, it is effective to reduce the distance between the liquid crystal layer 7 and the reflecting plate 9.

In Example 2, as shown in FIG. 4, the lower support plate 2 was provided with the function of a wavelength plate, and the reflection plate 9 was directly provided on the lower support plate 2, thereby suppressing the reflection of the light. Here, a 180 mm thick crystal plate cut parallel to the optical axis is used as the lower support plate.
A reflecting mirror 9 is formed by depositing silver on the back surface. Also, Example 2
Here, a (P-type) nematic liquid crystal having positive dielectric anisotropy was used for the initial alignment and horizontal alignment, and a stranded nematic (TN) structure was created in which the alignments on the upper and lower support plates were orthogonal.

The TN structure makes it possible to keep the operating voltage lower than the general parallel structure. In addition, the liquid crystal layer is composed of a dichroic nematic liquid crystal or a nematic liquid crystal mixed with a dichroic dye, so that the scattering effect of the present invention and the so-called guest-host effect (GH effect) due to absorption of the dichroic dye coexist. You may let them. Furthermore, it goes without saying that if a dichroic dye is mixed into the apparatus shown in FIGS. 1 and 2, a colored scattering state will occur when an electric field is applied, resulting in a new display effect. Furthermore, in order to increase the contrast, it is effective to provide light scattering surfaces on both sides of the electro-optic material.

Alternatively, it may be multi-layered.Furthermore, in Example 2, the support plate 2 on the reflection plate side was formed by a wavelength plate, but it may of course be formed by an upper support plate and another wavelength plate, and this upper wavelength plate may be, for example, It has the effect of depolarizing light using sunglasses, etc. As described above, according to the present invention, light reflection and light scattering can be easily controlled by an electric field.

The reflective display device according to the present invention is superior to other reflective liquid crystal display devices in the following points, namely, in the twisted nematic method (TN method), half of the natural light is used by the polarizing plate. However, in the present invention, by using the wavelength plate 8, all natural light can be utilized. 1st,
It is also possible to use a polarizing plate instead of a wavelength plate as shown in Figure 2, and the convenient use of the wavelength plate 8 has a great advantage in terms of light utilization. This is the same scattering type display as the present invention. Dynamic scattering method (D
Since the DS method uses a current effect and the present invention uses a voltage effect, the present invention is superior to the DS method in terms of driving voltage, power consumption, and life.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams of a reflective display device using an n-type nematic liquid crystal and a wavelength plate according to the present invention, and FIG. 3 is a graph of the refractive index curve of an axial optically anisotropic material. FIG. 4 is a cross-sectional view of a reflective display device according to the present invention, using a P-type nematic liquid crystal and having a support plate made of a wavelength plate. 1, 2... Support plate, 3, 4... Electrode, 5,
6...--Alignment treatment, 7---...Liquid crystal, 8---
--Chapter Wavelength plate, 9---Reflector, 10...
・Light scattering surface. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. An electro-optic material that has birefringence in which the refractive index of ordinary rays and extraordinary rays are different and whose optical axis direction can be changed by an electric field, and an electro-optic material that has a refractive index that is approximately equal to the ordinary ray refractive index of the electro-optic material. a transparent substance having a refractive index and in contact with the electro-optic substance at a light scattering surface; a quarter-wave plate placed outside the electro-optic substance and the transparent substance; and a quarter-wave plate placed outside the quarter-wave plate. 1. A reflective display comprising a mirrored reflector and means for applying an electric field to the electro-optic material, the display being made possible by controlling light scattering and light transmission on a light scattering surface using the electric field. Device. 2. An electro-optic material that has birefringence in which the refractive index of ordinary rays and extraordinary rays are different and whose optical axis direction can be changed by an electric field, and a refractive index that is approximately equal to the ordinary ray refractive index of the electro-optic material and 1/
It consists of a transparent material that has the function of a four-wavelength plate and is in contact with the electro-optic material at a light scattering surface, a reflector placed outside the transparent material, and a means for applying an electric field to the electro-optic material. A reflective display device characterized in that display is enabled by controlling light scattering and light transmission on a light scattering surface.