Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-10-23
2001-09-18
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S086000
Reexamination Certificate
active
06292243
ABSTRACT:
TECHNICAL FIELD
This invention relates to a liquid crystal panel and electronic equipment that uses such a liquid crystal panel.
BACKGROUND ART
In addition to various kinds of timepieces used as wristwatches, such as an analog timepiece displaying time by hands and a digital timepiece displaying time on a liquid crystal device, there has recently been developed a two-layer display type of timepiece in which a liquid crystal panel is superimposed on the surface of an analog timepiece, as disclosed in, for example, Japanese Patent Publication No. 59-32755. With such a two-layer display type of timepiece, a digital time display can be superimposed on top of an analog time display, to make it visible.
In the prior art, the display of a liquid crystal panel is often of a color that has a low brightness, such as black, which means that the display of the liquid crystal panel cannot be clearly seen if the analog dial plate is not of a color that has a high level of brightness, such as white. This limits the design of such a dial plate.
That is why a display element having a polymer dispersed liquid crystal layer has been developed, as disclosed in International Publication No. WO94/23331. This liquid crystal layer has the property of being transparent when no electrical field is applied thereto, but it diffuses or scatters light when an electrical field is applied. Therefore, a light-scattering region to which an electrical field has been applied appears to be white or gray, making it possible to display characters or the like. Since the color of this display portion is white or gray, that in itself is novel, and it means that the dial plate can be given a color of a low level of brightness, such as black, blue, or red, and thus the dial plate can be freely designed.
In this case, light is scattered both forward and backward with respect to the direction in which the light is incident, within a region of the polymer dispersed liquid crystal layer to which the electrical current is applied. When a transmissive type of liquid crystal panel has been fabricated by using this polymer dispersed liquid crystal layer, light that is scattered forward in the direction in which light is incident (hereinafter called “forward-scattered light”) strikes the eyes of the observer, so this forward-scattered light can be used to provide a liquid crystal display that is white or gray.
A wristwatch or the like is required to be compact, lightweight, and energy-thrifty, so it is often inevitable that a reflective liquid crystal panel is used therefor. In such a case, light that is scattered backward with respect to the light-incident direction (hereinafter called “backward-scattered light”) strikes the eyes of the observer. On the other hand, forward-scattered light is directed along the direction in which light is incident, so it does not strike the eyes of the observer.
Research performed by the present inventors has shown that, when a reflective liquid crystal panel has been constructed by using a polymer dispersed liquid crystal layer, there is insufficient backward-scattered light, so that it is not possible to provide a suitable liquid crystal display in white or gray if the forward-scattered light is not reflected. They have determined that this is particularly obvious when the quantity of backward-scattered light is greater than the quantity of forward-scattered light.
In this two-layer display type of timepiece, a member capable of reflecting the forward-scattered light is simply the dial plate, which is disposed forward of the liquid crystal panel in the direction in which light is incident. However, if this dial plate has a low level of brightness, insufficient light is reflected from the dial plate, and thus the display on the liquid crystal layer can not be seen. To counter this, there is no option but to make the dial plate a reflective surface, but this has the effect of further limiting the design of the dial plate.
When a structure is used that causes the forward-scattered light to be reflected outside of the liquid crystal panel, the forward-scattered light diffuses within the space between the liquid crystal panel and the dial plate, generating a loss of light reflected off the dial plate and returning towards the front side.
Furthermore, if forward-scattered light is reflected at a location far from the liquid crystal layer that generates the backward-scattered light, and if the line of sight of the viewer is at an angle to the perpendicular of the liquid crystal panel, there is a danger that a duplicated display will be caused by the pattern formed by backward scattering and the pattern formed by forward scattering.
Such problems are not limited to a two-layer display type of timepiece; they form a common subject of technical concern in the design of other types of electronic equipment in which a background display portion is provided behind a liquid crystal layer.
DISCLOSURE OF THE INVENTION
This invention was devised in the light of the above described problems and has as an objective thereof the provision of a liquid crystal panel which makes it possible to expand the design limits of electronic equipment and which also makes the display thereof clearly visible.
A further objective of this invention is to provide a two-layer display type of electronic equipment which makes it possible to expand the design limits and which also makes the display thereof clearly visible.
A yet further objective of this invention is to provide electronic equipment which can reduce the occurrence of duplicated displays.
In order to solve the above described technical problems, there is provided a liquid crystal panel in accordance with a first aspect of this invention, comprising:
a first substrate which is disposed on a side on which external light is incident and on which is formed at least one first electrode;
a second substrate which is disposed facing the first substrate and on which at least one second electrode is formed;
a liquid crystal layer which is inserted between opposing surfaces of the first and second substrates and which is set to one of a light-transmitting state and a light-scattering state, based on a voltage applied between the at least one first electrode and the at least one second electrode; and
at least one transparent layer disposed forward of the liquid crystal layer in the light-incident direction;
wherein the at least one transparent layer is formed of a material having a refractive index that differs from the refractive index of an optically transmissive medium in contact with the transparent layer.
With this aspect of the invention, the liquid crystal layer in a region in which a voltage equal to or more than the threshold voltage of the liquid crystal is applied by the at least one first electrode and the at least one second electrode (hereinafter called “voltage application region”) is set to a light-scattering state. Of this light, the light that is scattered forward with respect to the light-incident direction is incident on the transparent layer. This transparent layer has a refractive index that differs from that of the optically transmissive medium in contact therewith. Thus, part of the forward-scattered light passes through the transparent layer, but, since there is a discontinuity in refractive index at the interface between the transparent layer and the optically transmissive medium, another part thereof is reflected by that interface. Therefore, both backward-scattered light and forward-scattered light generated in the voltage application region of the liquid crystal layer strike the eyes of the observer, increasing the degree of light-scattering. This makes it possible to display a liquid crystal display pattern which is of a color having a high level of brightness, such as white or gray, and which also has increased illuminance.
In a region in which no voltage is applied, or in which a voltage that is less than the threshold voltage of the liquid crystal is applied, (hereinafter called “voltage non-application region”), the liquid crystal layer is in a lig
Kanamori Kiminori
Makiba Hidenori
Miyazaki Takashi
Okuhara Kenichi
Shingu Hiroshi
Chowdhury Tarifur R.
Harness & Dickey & Pierce P.L.C.
Seiko Epson Corporation
Sikes William L.
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