JPS5922210B2 - lcd display reflector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION It is known that the construction of digital displays using liquid crystals has certain distinct advantages.

One of the most important of these advantages is the low power required to operate liquid crystal displays, making them easier to combine with modern solid-state circuits and extended-life battery-operated devices. . The advantage of low power is obtained by using the liquid crystal to control ambient or artificial light produced by power sources other than the display itself. Therefore, there is no need for a power value such as is required for most displays to produce light. However, in order to control the light rays, especially the ambient light, at the liquid crystal display, a method must be provided to reflect the light rays passing through the liquid crystal display. There are two ways to use liquid crystals to control the light beam.

One such method uses light scattering, commonly known as dynamic scattering, and the other uses light beams that are polarized by liquid crystals that act as light valves. The latter method is disclosed in, for example, Japanese Patent Application Laid-Open No. 1983-1993, which was filed by the present applicant on March 8, 1972 and published on December 13, 1972.
It is described in detail in the specification of No. 4129 (Japanese Patent Application No. 47-23-52). Both liquid crystal displays based on dynamic scattering or polarized light are provided with some type of reflector behind the display so that ambient light or some low-power light source can be used to illuminate the display. Can be used as a low output device.

In a light scattering display, the liquid crystal material, when activated, scatters light forward, reflects off a reflector behind the display back through the liquid crystal material, and scatters the light forward again. This scattering of light rays causes the activated liquid crystal to appear dark or whitish to the viewer. In a polarizing shutter type liquid crystal display, the liquid crystal cell rotates the plane of polarization of the polarized light beam by 90 degrees.

Such a liquid crystal cell is a twisted nematic liquid crystal. Light can be transmitted to the inactive liquid crystal cell when the liquid crystal cell is placed between crossed polarizers. If a reflector is placed behind the liquid crystal cell and polarizer combination to maintain sufficient polarization after reflection by the reflector, the display will appear bright when inactive. However, when this type of liquid crystal cell is activated by applying a potential, the liquid crystal's ability to rotate the plane of polarization is impaired and the liquid crystal cell appears dark because the incident light is blocked by the reflector. However, it will be appreciated that liquid crystal cells can be configured to normally block light until activated. The result is a liquid crystal cell using zero dynamic scattering, which is essentially the same except that when the liquid crystal cell transmits light and is inactive, the image appears white on a dark background. It is known that highly reflective mirrors can be used as reflectors to construct ambient light displays.

In fact, the back electrode of a liquid crystal cell can be a metallized reflective surface. Although this type of arrangement makes a suitable display, it is very difficult to obtain reflections in the display. Moreover, the obtained viewing angle is not large since the angle of scattering the light beam is based on the liquid crystal material that mainly scatters the light beam. Therefore, the disadvantages of metallized reflectors combined with light scattering liquid crystal displays are difficult background reflections and small viewing angles. Polarization methods for constructing liquid crystal displays can also be implemented by the use of metallized reflectors placed after the last polarizer.

In fact, this is an ideal means of constructing displays using polarized light, since the polarization of the light beam is maintained when reflected off the metallized reflector. However, in practice it has been found that when a single metallized reflector is placed behind a polarized light liquid crystal display, the display has a very small viewing angle. There are also nasty background reflections and a physiologically inappropriate glow to the display. Highly reflective white backgrounds have been investigated to reduce the difficulties encountered in mirror reflectors of polarized light liquid crystal displays. This includes highly reflective backgrounds constructed of alumina, ceramic and alumina plates coated with highly reflective paint, white paper, white plastic and the like. This kind of high reflectance all white reflector has improved viewing angle based on scattered reflection and
It has been found that improvements over metal reflectors result in a sufficiently good contrast ratio between liquid crystal displays in the inactive and activated states. However, the contrast ratio is not as large as expected due to reflection. This is because all white highly reflective surfaces depolarize the light that hits them, resulting in a loss of contrast ratio.
According to the invention, the reflection device provides a polarized liquid crystal display with a large viewing angle, good reflection of polarized light, a high contrast ratio, and no undesirable reflections.

In the practice of the invention, an initial transparent plate made of glass, plastic or other similar material is provided with one side so as to provide a scattering surface behind one of the two polarizers of a polarized liquid crystal display. Scrubbed or sandblasted.

The other side of this transparent plate is aluminum with high reflectivity.
Coated with a metal such as nickel or chrome. The combination of a scattering surface on one side of the transparent plate and a metalized reflective coating on the opposite side results in a scattering reflection that scatters light at a very large angle when placed after a polarizing LCD shutter display. It provides a highly efficient scattering reflector and also provides polarization of the reflected light, resulting in a substantial increase in viewing angle and advantages in contrast over conventional liquid crystal displays. Another feature of the invention is the combination of a lamp or light source with a transparent plate having a scattering surface and a reflective surface on opposite sides, so that the liquid crystal display can be viewed without ambient light. In this latter case, the light rays from the lamps are directed through the transparent part of the edge of the plate and reflected on the metallization behind this plate. The above objects and other objects and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, which form a part of this specification.

To explain the drawings, especially FIGS. 1 and 2, the illustrated liquid crystal cell is disclosed in Japanese Patent Application Laid-Open No. 47-41290, which was filed on March 8, 1972 and published on December 13, 1972. (
It is of the polarizing shutter type described in Japanese Patent Laid-Open No. 47-23252).

The liquid crystal cell consists of a pair of transparent plates 10, 12 separated by a suitable gasket 14. Gasket 14 separates transparent plates 10, 12 by a distance equal to approximately 0.0013 mm (0.0005 inch), and gasket 14 forms a gap between transparent plates 10, 12. Within the enclosure is a layer of nematic phase liquid crystal material of positive induced anisotropy. The liquid crystal substances are bis-(45-n-octyloxybenzal)-2-chlorophenylenediamine and p-methylbenzal-p! -n-butylaniline, such as 20% to 80% of the total composition, with the remainder being p-cyanobenzal-p1-n-butylaniline, 3% to 40% of the total composition. %. This material was transferred to the applicant in 1972.
Japanese Patent Application Laid-open No. 18783/1978 (Patent Application No. 1364/1978) was filed on February 9, 1972 and published on September 16, 1972.
No. 9) It is fully explained in the specification. As shown in FIG. 1, opposing surfaces of transparent plates 10 and 12 are patterned with a transparent conductive material such as titanium oxide or indium oxide.

The transparent plate 12 has four patches 16, 18 of transparent conductive material.
, 20, 22 are provided, and another transparent plate 12 is provided with four sets of mutually insulated strips of transparent conductive material, these four sets of strips are designated 24, 26, 28. ,30
is attached. Transparent plates 10 and 12 are gaskets 14
transparent conductive patches 16, 18 when glued on both sides of
, 20, 22 are a series of strips 24, 26, 2 of the transparent plate 10.
Align with 8,30. Each point 32 of the strip set on the transparent plate 10 is aligned with a corresponding point 34 on the transparent plate 12. The operation of the liquid crystal cell will be explained in more detail below, but it will be clear that when all the strips of the strip set 24 are, for example, opaque and the surrounding areas are transparent, the shape of the figure 8'' will result. Similarly, by making selected strips of strip set 24 opaque, any number from 1 to O can be created clearly. The insulated conductive strips are connected to external leads (not shown) through a number of mutually insulated conductive strips of transparent conductive material 36.

At this point, it can be seen from FIG. 2 that the lower end of transparent plate 10 with strip 36 extends below the remaining portion of liquid crystal cell 38 and that a suitable electrical connector is slid onto the lower portion of transparent plate 10 to provide a conductive strip. It will be appreciated that piece 36 can be connected to an external electrical circuit.
Note that strip 36A extends from the bottom to the top of transparent plate 10 and terminates in a horizontal portion 40 directly opposite a corresponding horizontal portion 42 connected to patch 16 of conductive material in transparent plate 12. be done. A conductive epoxy material or the like is provided in the opening 44 of the gasket 14 to connect the horizontal portions 40,42. In such a configuration, one terminal of the power source can be connected to the strip 36a and subsequently to the terminal strip 36 of the liquid crystal material on one side, and selected portions of the remaining strips 36 can be connected to the same power source. , thereby increasing the potential in the electric field across the selected portion of the liquid crystal material based on the energization of the selected portion of the strip 36 (i.e., connected to the other terminal of the power supply). Achieve a slope of In the fabrication of liquid crystal cells, the layer of transparent conductive material that comes into contact with the nematic phase liquid crystal material must be created by directional painting or rubbing with a cotton cloth, for example.

Furthermore, the transparent conductive material on the transparent plate 12 must be rubbed in a direction perpendicular to the rubbing direction of the transparent conductive material on the transparent plate 10. As a result, the above-mentioned Japanese Patent Application Laid-Open No. 47-4129
0 (Japanese Patent Application No. 47-23252) to create a twisted nematic structure of intercalated liquid crystal material as fully explained in the specification. In contact with the transparent plate 10 is a first polarizing plate 46, and on the back side of the transparent plate 12 is a second polarizing plate 48. The polarization planes of the two polarizing plates 46 and 48 are at right angles to each other, and the polarization plane of the polarizing plate 46 is parallel to the rubbing direction of the transparent conductive material on the transparent plate 10.

Also behind the second polarizing plate 48 is a transparent plate 50 made of glass, plastic or other material with a surface 52 rubbed or sandblasted to form a scattering surface;
The opposite side of the transparent plate 50 is coated with a layer of metal such as aluminum, nickel or chrome with high reflective properties. All of the plates shown in FIG. 1 are assembled in a sanderch structure as specifically shown in FIG. In operation of the liquid crystal cell, ambient light impinging on the front surface of the polarizer 46 passes through the polarizer 46 such that the light is polarized in the direction of the rub line of the transparent conductive material of the transparent plate 10.

This polarized light beam is rotated 9' so that it passes through the layer of liquid crystal material between the transparent plates 10, 12, and if no potential is applied between the conductive coatings on the transparent plates 10, 12, this 90 The rotation occurs over the entire area of the layer of liquid crystal material. The plane of polarization of the polarizing plate 48 is located at 9' with respect to the plane of polarization of the polarizing plate 46. Therefore, if no potential is applied between the conductive coatings on the transparent plates 10 and 12, the polarized light will pass through the entire liquid crystal cell, through the scattering surface 52 of the transparent plate 50, and then be reflected at the surface 54 and reflected again. It passes through a polarizing plate 48, a liquid crystal cell, and a polarizing plate 46.
In this situation, the entire display appears white. Now, if a potential of 5 volts or more is applied to the transparent plate 1.
By acting between the conductive films 9 and 20, the liquid crystal cell no longer rotates the plane of polarization in the energized strip section of the transparent plate 10.

Therefore, under such a situation, the polarizing plate 48 blocks light, and the part that crosses the part on which the potential is applied appears dark on the white background. The number 2'' is shown in FIG. 2, which means that a potential of one polarity is applied to conductive strip 36A, thereby applying a potential of one polarity to conductive material patch 16 of transparent plate 12. The strip 56 of the strip set 24 has an electrical potential and
, 58, 60, 62, 64 by applying potentials of opposite polarity to the conductors connected to them. Similarly,
Other digits are made to appear by selectively energizing each strip of each strip set 26-30 while simultaneously energizing the conductive patches 16-22 on the opposite side of the liquid crystal material. be able to. In assembling a liquid crystal cell, transparent conductive films are provided on transparent plates 10 and 12 and rubbed perpendicularly to each other as described above. A gasket 14 is then provided and a drop of liquid crystal material is introduced into the area surrounded by the gasket 14. Transparent plate 10 is then moved into engagement with gasket 14 and adhered, thereby spreading the drop of liquid crystal material into a thin film. Polarizing plates 46, 48
In addition, a transparent plate 5 having a scattering surface 52 and a metallized surface 54
A reflection device consisting of 0 is provided. The complete device is as seen in FIG. 2 and can be placed in a housing 66 as shown in FIG. If the intensity of the ambient light is not sufficient to represent the digits formed when selected portions of the transparent conductive membrane are energized, lamp 68 is activated as shown in FIGS. , 70 can be provided near the edge of the liquid crystal cell 38.

These lamps 68, 70 direct light onto the transparent plate 50, at least a portion of which is reflected off the metallized backing surface 54 and transmitted through the liquid crystal material and polarizer to a bright background. Then, the numbers appear again in the dark. As explained above, the metallized surface 54 provides excellent reflective properties and the transparent V
i. The scattering surface 52 of the reflector scatters the light with an increased scattering angle such that it is reflected through the 1O and passes through the scattering surface 52 again.

Consequently, light that is scattered twice actually increases the viewing angle, but does not result in any polarization loss. Therefore, when looking forward, there is a large difference in the amount of light that passes through the transparent conductive material sections that are activated and unactivated as explained above. A parallel polarizer is used more than a horizontal polarizer in Japanese Patent Application Laid-Open No. 47-41290 (Japanese Patent Application No. 47-23252).
As described in the specification, the active section transmits light that is differentiated against a dark background. In nematic liquid crystal devices, the viewing angle, ie, the angle with respect to the normal at which the displayed information figure can be observed, is based on the direction of the incident light ray, ie, the angle formed by the incident ray and the normal.

Using a scattering reflector allows a viewer looking at the display at an angle to see not only light that is reflected according to the laws of reflection, but also light from other directions. Therefore, the display can be viewed at large angles that cannot be viewed with a specular reflector. Also, the contrast ratio, or brightness, is improved by using a scattering reflector. That is, by using a diffuse reflector, the reflection is virtually independent of the surrounding light conditions and the contrast is practically always the same. Furthermore, the uniform gray light beam of the diffuse reflector is more amenable to the human eye and is preferred from a physiological point of view to specular reflection. Although the invention has been illustrated and described with reference to particular embodiments, it will be readily apparent to those skilled in the art that the shape and arrangement of parts may be changed as necessary without departing from the spirit and scope of the invention. .

[Brief explanation of drawings]

FIG. 1 is an exploded view of the liquid crystal cell of the present invention, and FIG. 2 is an end view of the assembled liquid crystal cell of the present invention, with the rear side of the liquid crystal cell used to illuminate numbers or other images displayed by the liquid crystal cell. FIG. 3 is a perspective view of a liquid crystal display of the invention mounted in a suitable housing. In the figure, 10, 12: transparent plate, 14: gasket, 16,
18, 20, 22, 24, 26, 28, 30: transparent conductive material, 36: transparent conductive material strip, 44: opening, 46, 48:
Polarizing plate, 50: Transparent plate, 56, 58, 60, 62, 64
: Conductive electric strip, 66: Housing, 68, 70: Lamp.

Claims (1)

[Claims] 1 a layer of twisted nematic liquid crystal material provided between first and second transparent parallel plates covered only in selected areas by a film of transparent conductive material; and an inlet on each side of the layer of liquid crystal material; a polarizer extending generally parallel to the plate to form a sandwich structure through which light rays entering from the side can pass to the exit side; a device for establishing a potential difference between the membranes on each plate to form an image; and a reflecting device provided at the exit side of the sandwich structure to reflect light passing through the liquid crystal material back to the entrance side. A liquid crystal display, wherein the reflective device comprises a third transparent plate having a scattering surface on the side facing the sandwich structure and a reflective surface on the other side.