Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
1999-09-03
2001-07-31
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S029000, C528S031000, C252S582000, C252S585000, C359S665000, C359S649000, C348S844000
Reexamination Certificate
active
06268458
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to projection televisions and, in particular, to coupler fluids for use in optically coupling a projection lens system of such a television to a cathode ray tube (CRT).
BACKGROUND OF THE INVENTION
Projection televisions are widely used in both the consumer (home entertainment) and commercial (presentation) markets. Instead of employing direct viewing of an image formed by electron beam impingement on the phosphors of a cathode ray tube, such televisions use a projection lens system to form an enlarged image of the face of one or more CRT tubes on a viewing screen.
For color systems, one three-color CRT and one projection lens system can be used or, more commonly, three CRTs and three projection lens systems are used, with each CRT/projection lens system combination producing an individual color image, e.g., red, green, and blue images, which are superimposed at the viewing screen to form a full color image. The projection television can be of the front or rear projection type depending on whether the viewer and the CRT/projection lens system(s) are on the same or opposite sides of the viewing screen.
A typical projection lens system contains at least three lens elements, at least some of which are typically composed of plastic materials, such as, acrylic or polyolefin. Plastic lens elements are desired both from a weight and cost perspective, especially when a particular lens element needs to have an aspherical surface to provide aberration correction. The projection lens system can be either air coupled or liquid coupled to the faceplate of the CRT. As the names imply, in an air coupled system, the interface between the CRT and the lens system, or more particularly, the last lens element of the lens system, is air, while in a liquid coupled system, it is a coupling fluid (coupling liquid).
The present invention is concerned with liquid coupled systems and, in particular, with providing improved coupling fluids for use in such systems. The requirements for an ideal coupling fluid are numerous. Among other things, the fluid should minimize reflection loss at the interface between the fluid and the CRT, should cool the CRT, and should generally improve the veiling glare of the system.
To date, ethylene glycol, mixtures of ethylene glycol and glycerol, and mixtures of ethylene glycol and water have been employed extensively as coupling fluids in projection TVs. The preferred fluid in recent years has been ethylene glycol/glycerol mixtures due to the relatively low volatility of the constituent components. As a result, the loss of coupling fluid through the last lens element of the projection lens system has been minimized. Also, the refractive index of an ethylene glycol/glycerol mixture is higher than pure ethylene glycol or a mixture of ethylene glycol and water. In addition, ethylene glycol/glycerol mixtures exhibit reasonable environmental friendliness, the ability to operate near 90° C., low cost, good compatibility with molded optics, good thermal conductivity, and good optical clarity.
A preferred composition for coupling fluids of this type has been 80% ethylene glycol and 20% glycerol. Further addition of glycerol would cause the projected image to squirm, due to natural convection associated with thermal gradients in a viscous fluid.
Mixtures of ethylene glycol/glycerol, however, do have some properties which limit their usefulness. For example, the inherent electrical conductivity of this mixture is a problem. If an accidental spill occurs and the fluid gets onto a printed circuit board, the board has to be discarded to avoid electrical malfunction and even possible fire caused by the relatively high electrical conductivity of the fluid. Even more basically from an optics point of view, the refractive index of the mixture is lower than desired. Accordingly, couplers employing this mixture still suffer from relatively high levels of reflection at the CRT/coupler fluid interface. These reflections, in turn, lower the overall contrast of the projected image, making projection televisions less acceptable to some users in comparison to direct view televisions.
DESCRIPTION OF THE PRIOR ART
Discussions of liquid coupled projection televisions can be found in a variety of issued U.S. patents, including: Tucker, U.S. Pat. No. 4,151,554; Hodges, U.S. Pat. No. 4,163,990; Bauer, U.S. Pat. No. 4,511,927; Fukuda, U.S. Pat. No. 4,620,773; Watanabe et al., U.S. Pat. No. 4,646,143; Roberts, U.S. Pat. No. 4,710,820; and Altman, U.S. Pat. No. 4,764,806.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of this invention to provide coupling fluids for projection televisions that possess some and preferably all of the following properties:
(1) The fluid is optically clear.
(2) The fluid will remain optically clear through repeated temperature cycles in the presence of the ambient moisture of room air.
(3) The fluid has a high refractive index, preferably in the range of 1.52 to 1.53, to match the index of refraction of the glasses used to form the faceplates of CRTs.
(4) The fluid is compatible with molded thermoplastic lens elements so that an element can endure multiple temperature cycles in the presence of the fluid without substantial loss of its optical properties.
(5) The fluid is compatible with lens housing materials, such as, glass-filled polycarbonate, glass-filled nylon, polyphenylene sulfide, and other filled or unfilled high performance engineering thermoplastics.
(6) The fluid is environmentally friendly, e.g., it exhibits low volatility, low odor, and low toxicity.
(7) The fluid has a moderate viscosity, e.g., a viscosity of less than about 10,000 centipoise at room temperature.
(8) The fluid has adequate thermal conductivity to help dissipate heat generated by the CRT.
(9) The fluid has a relatively low electrical conductivity and, preferably, is a non-conductor.
To achieve these properties, the invention provides a coupling fluid which either comprises a siloxane polymer having methyl, phenyl, and hydrophilic side groups or comprises a mixture of a siloxane polymer having methyl and phenyl side groups with a siloxane polymer having methyl and hydrophilic side groups. As used herein, a side group can also be a terminal group when the group occurs at the end of a polymer chain. Siloxane polymers having such organic pendant groups attached to their silicon atoms as side groups are also known as “silicones”.
The fundamental aspects of the invention are thus: (1) at least one polymer having a siloxane backbone, i.e., at least one polymer having a —Si—O—Si—O—Si— backbone, and (2) methyl, phenyl, and hydrophilic groups attached to the silicon atoms of the backbone.
Moderate viscosity and low volatility are achieved by adjusting the degree of polymerization (or chain length) of the component or components of the coupling fluid, including the degree of polymerization of the hydrophilic side groups when polymeric materials, such as polyethylene glycol, are used for such groups (see below). Typically, average molecular weights above several hundred daltons offer both desirable viscosity/volatility combinations and chemical inertness so that the coupling fluid does not attack the lens materials by, for example, causing them to craze.
A high index of refraction is obtained by aromatic substitution of side groups, thus phenyl-substituted siloxanes. Generally, phenylmethyl siloxanes form a key ingredient or starting material for the formulation or downstream chemical modification to derive the final fluid.
Moisture compatibility is afforded by hydrophilic substitution as side/terminal groups. In particular, selected locations are modified by the introduction of polar groups. This must be done with care, however, as too much substitution deteriorates compatibility with the plastic lenses. Also, the level of hydrophilic substitution must be chosen so that the amount of water absorbed by the coupling fluid at elevated temperatures is not so high as to result in the creation of haze in the fluid when the fluid is cooled to room
Soane David S.
Soane Zoya M.
Corning Precision Lens
Klee Maurice M.
Michaelsen Alfred L.
Moore Margaret G.
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