Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1997-12-24
2001-04-03
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S104000, C349S113000, C349S137000
Reexamination Certificate
active
06211934
ABSTRACT:
I. CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
II. BACKGROUND OF THE INVENTION
The present invention relates generally to the field of display devices, such as liquid crystal displays (“LCDs”), cathode ray tubes (“CRTs”), and similar display devices. More specifically, the present invention relates to methods of and apparatuses for reducing the infrared loading (e.g., solar loading from the sun) on such display devices by using a reflective material to reflect infrared energy.
A “display” is an image output device that provides information to an observer in a visible form. A “liquid crystal display” (“LCD”) is a display device that includes a liquid crystal cell with a light transmission characteristic that can be controlled in parts of the cell by an array of light control units to cause presentation of an image. A “liquid crystal cell” is an enclosure containing a liquid crystal material. An “active-matrix liquid-crystal display” (“AMLCD”) is an LCD in which each light control unit has a nonlinear switching element that causes presentation of an image segment by controlling a light transmission characteristic of an adjacent part of the liquid crystal cell. An LCD can have a plurality of electrically-separated display regions, each display region also being known as a display cell, or when the regions designate a small portion of the display, each display region is known as a “pixel.” Each pixel in a high density display matrix, such as for LCDs, requires its own active (switching element) driver (e.g., a thin film transistor).
In recent years, LCD devices have become more popularly used in avionics and ground vehicle displays because of the low power consumption, high reliability, high ambient readability, and compact packaging of LCDs. Also, personal computers, portable game machines, hand-held devices, wrist watches, gas station pumps, and numerous other devices requiring a visual interface often use LCDs to display data. All of these types of display devices and many others are likely to be exposed to the sun or radiant energy thus creating a thermal rise due to solar exposure thereon (solar loading).
In most display devices that are subject to receiving radiant energy, the following problems are posed. The display device often experiences a temperature rise of the display device due to solar loading or other radiant energy sources. For example, it is possible for a display device to experience solar loading on its surface up to 116 W/ft
2
depending on its application. This solar loading problem is intensified when cooling methods, such as forced cooling air, are unavailable. As a result, the display device can be permanently damaged, such as is the case with polarizers and adhesives associated with LCDs when exposed to temperatures in excess of 100° C. Also, sometimes the liquid crystal material of an LCD device “clears” (exceeds its operating capability due to the temperature of the liquid crystal). When liquid crystal material “clears” it transitions from the nematic phase and becomes anistropic, effectively randomizing the birefringent characteristic of the liquid crystal material, which takes time and temperature changes to return to its operating state.
To date, some attempts have been directed toward remedying the solar loading phenomena and its associated problems. With regard to LCDs, one proposed solution is to increase the limiting temperature of the liquid crystal materials and polarizers. This approach alleviates the problem, but the availability of these materials is limited. Also, this approach is not practical for commercially-available liquid crystal materials due to a significant cost factor. Another proposed solution has been to force cool air over the exterior face of the display device, i.e., the display device surface that is exposed to the viewer. This approach is practical only when cooling air is available, which is not always the case. Yet another workaround has been the use of a cover to protect the display device from temperature increases due to solar loading. Thus, a need exists to reduce the solar loading on display devices that are subjected to a thermally-challenging environment. Accordingly, the present invention discloses a method of and apparatus for reducing the solar loading on display devices.
III. BRIEF SUMMARY OF THE INVENTION
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can only be gained by taking the entire specification, claims, drawings, and abstract as a whole.
The present invention comprises a display device that receives radiant energy from an external radiant energy source such as the sun, the display device comprises a transparent absorptive material that absorbs heat from the energy source and a reflective material or coating placed between the absorptive material and the energy source to reflect a predetermined infrared wavelength range of the radiant energy, thereby reducing the thermal rise due to the external radiant energy.
Another aspect of the present invention comprises a liquid crystal display (“LCD”) device that receives radiant energy from an energy source such as the sun, the LCD device comprises a first transparent plate and second transparent plate, which are spaced apart with respect to each other to form a liquid crystal cell between the plates, which cell is filled with a liquid crystal material; a front polarizer and rear polarizer contain the first and second transparent plates between them; a cover glass is placed over the front polarizer; and a reflective material or coating is placed between the front polarizer of the LCD, which absorbs heat from the sun, and the energy source to reflect a predetermined infrared wavelength range of the radiant energy. The reflective coating can be on either the interior or exterior surface of the cover glass as long as the radiant energy is reflected before reaching the front polarizer and thus the liquid crystal material. An anti-reflective coating is usually added to the cover glass to reduce specular reflectance, in which case the reflective and anti-reflective material properties are reconciled to accomplish each of their respective purposes. The particular radiant energy to be reflected is in the infrared range, i.e., wavelengths greater than the visible spectrum, which is typically above 0.7-&mgr;m.
Also, the present invention comprises a method for reducing solar loading on display devices. The method comprises the steps of selecting a suitable reflective material to reflect a predetermined wavelength range of the radiant energy; and providing the reflective material between the absorptive material of the display device and the external radiant energy source.
The reflective coating material allows visible light energy to be transmitted, while reflecting the infrared light energy to reduce the solar loading on display devices up to 50%. The present invention removes heat (infrared energy) from the sun by reflection rather than absorption, while preserving the integrity of the visible wavelength range to allow for the presentation of information.
The novel features of the present invention will become apparent to those of skill in the art upon examination of the following detailed description of the invention or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only because various changes and modifications within the spirit and scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.
REFERENCES:
patent: 4687298 (1987-08-01), Aoki et al.
patent: 4749261 (1988-06-01), McLaughlin et al.
patent: 4806221 (1989-02-01), Gillery
patent: 5132
Habing Robert D.
Henz James M.
Maner Randy M.
Wood Teddy J.
Abeyta Andrew A.
Chowdhury Tarifur R.
Honeywell Inc.
Sikes William L.
Yeadon Loria B.
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