Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-08-25
2003-02-18
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S112000, C359S599000
Reexamination Certificate
active
06522374
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to visual displays, and more particularly to liquid crystal displays with increased contrast and gain between the energized liquid crystals and the background by directing more light incident on the display toward the viewer in a specific and controllable manner.
2. Description of the Related Art
Passive liquid crystal display viewing screens are utilized in hundreds of applications for displaying data to one or more viewers. Such displays are commonly found on wrist watches, clocks, gas pump displays, modern telephones, automobile clocks and instrument clusters, and other applications. These displays typically include a generally light colored background which is visible behind the liquid phase of a liquid crystal composition. When the liquid crystal is energized to display a particular set of information, the liquid crystal turns much darker and creates a contrast between the background and the displayed information. However, under some lighting conditions the contrast is difficult or nearly impossible to see when the conditions minimize the contrast because of reflection on the top layer of the display, low light conditions, high ambient light or other such reasons such as a limited view area.
U.S. Pat. No. 5,534,386 issued to Peterson et al. and entitled “Homogenizer Formed Using Coherent Light and A Holographic Diffuser” discloses a homogenizer in a sheet and a method of making the homogenizer. The homogenizer includes a micro-sculpted surface structure replicated in the sheet which homogenizes the light, and controls the direction and shape of its distribution. This patent discloses that the homogenizer may be used in a transmissive application as well as a reflective application. In the transmissive application the homogenizer is placed between a light source and a viewing area whereby the light passing through the homogenizer improves the quality of light according to the micro-sculpted surface structure. In the reflective application, the homogenizer includes a reflective layer deposited on the same surface as the micro-sculpted surface structures and wherein the reflective layer conforms to the surface structure. Light is then projected onto the homogenizer and reflected by a reflective surface of the homogenizer reflective layer. The reflective surface faces outward in such a construction.
One problem with this construction is that the flow characteristics of the reflective material deposited on these microstructures results in a loss of definition of the structures. For example, a 5° light shaping diffusing surface (i.e., one that produces a cone of light having an angular distribution of 5°) formed in the homogenizer material results in a 20° effective angle on the outward facing reflective surface after deposition of the reflective layer on the embossable layer. Another problem with such a surface is that the reflective layer is somewhat dark and results in a grainy image having medium to low resolution quality. An additional problem with such a surface is that it cannot be cleaned with any frequency because the reflective surface of the layer will be damaged or partially removed when cleaned. Cleaning is not an essential requirement for a liquid crystal display structure incorporating the homogenizer. However, the fact that the surface is too metallic results in excess glare as well as too grainy of an image. A loss of definition of the microstructure is an important problem which will significantly decrease the quality of a liquid crystal display utilizing such a homogenizer.
U.S. Pat. No. 5,609,939 issued to Peterson et al. and assigned to the assignee of the present invention discloses a viewing screen either in a reflective mode or a transmissive mode which utilizes the homogenizer of the '386 patent. The same problems described for the '386 patent are also present in the '939 patent. Related U.S. patents include U.S. Pat. No. 5,631,754 entitled “Holographic High Contrast Viewing Screen Embedded in a Liquid Crystal Display,” and U.S. Pat. No. 5,735,988 entitled “Method of Making Liquid Crystal Display.” Related U.S. patent applications include Ser. No. 08/782,962 entitled “Apparatus for LCD Backlighting,” Ser. No. 08/800,872 entitled “Method of Making Replicas and Compositions for Use Therewith,” Ser. No. 09/052,586 entitled “Method of Making Replicas While Preserving Master” and “Method of Making Hard Substrate Diffuser,” filed Aug. 24, 1998. These above patents and pending applications are incorporated herein by reference.
SUMMARY OF THE INVENTION
The present invention is directed to a liquid crystal display having improved viewing characteristics as a result of an improved light shaping diffuser or homogenizer construction incorporated into the display. One object of the present invention is to provide a liquid crystal display which is particularly well suited for use in passive light or poor lighting conditions. An additional object of the present invention is to provide a liquid crystal display which produces a background which is essentially of a white appearance or very light appearance. A further object of the present invention is to provide a liquid crystal display incorporating a homogenizer or diffuser producing a projected image having a satisfactory fine grain. An additional object of the present invention is to provide a liquid crystal display which directs a substantial portion of light incident the display toward a predefined viewing area in a particular shape or distribution. A further object of the present invention is to provide a viewing screen of the reflective type which homogenizes light and controls the direction and shape of distribution of light and which can be easily cleaned without damaging the homogenizer microstructure of the viewing screen. Another object of the present invention is to provide a reflective viewing screen wherein the definition or resolution of a light shaping surface microstructures of the viewing screen is maintained after adding a reflective layer. A still further object of the present invention is to provide a reflective viewing screen including a homogenizer that reduces the metalic appearance of the screen.
To accomplish these and other objects of the present invention, a liquid crystal display has a liquid crystal element with a front viewing surface and a rear surface. The liquid crystal display also has a substrate layer with a front side disposed against the rear surface of the liquid crystal element. The substrate layer also has a back side opposite the front side. A light shaping surface microstructure is carried in the front side of the substrate layer wherein the microstructure controls the directionality in which light propagates and scatters the light into a controlled distribution having the desired shape and smooth brightness variation. A reflective layer is deposited on the back side of the substrate layer and is capable of reflecting light back toward the front viewing surface of the liquid crystal element.
The reflective layer can be a metal layer of material vacuum formed or otherwise deposited on the back side of the substrate layer or can be some other layer of material having desirable light reflecting properties. The reflective layer is capable of reflecting light incident on the liquid crystal display thru the liquid crystal element.
In another embodiment, the microstructure is integral in the back side of the substrate layer and the reflected layer deposited over the microstructure.
A reference horizontal plane and a reference vertical plane are defined relative to the front viewing surface extending generally perpendicular relative to the screen. The viewing surface also has a reference normal axis perpendicular to the front viewing surface where the horizontal and vertical planes intersect. These imaginary planes define a field of view which has a viewing width angle measurable along the horizontal plane and a viewing height angle measurable along the vertical plane. Each v
Laine Jeffrey A.
Savant Gajendra D.
Shie Rick L.
Nilles and Nilles
Physical Optics Corporation
LandOfFree
Passive matrix liquid crystal display does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Passive matrix liquid crystal display, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Passive matrix liquid crystal display will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3176446