Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-06-07
2003-03-04
Mack, Ricky (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
Reexamination Certificate
active
06529312
ABSTRACT:
FIELD OF INVENTION
The present invention relates to particles of improved stability comprising anisometrically shaped carbon and/or graphite particles for use in light valves and in light valve suspensions.
BACKGROUND
Light valves have been known for over sixty years for modulation of light. As used herein, a light valve may be described as a cell formed of two walls that are spaced apart by a small distance, at least one wall being transparent, the walls having electrodes thereon usually in the form of transparent conductive coatings. The cell contains a light-modulating element, which may be either a liquid suspension of particles or a plastic film in which droplets of a liquid suspension of particles are distributed and encapsulated.
The liquid suspension (sometimes herein referred to as “a liquid light valve suspension”) comprises small particles suspended in a liquid suspending medium. In the absence of an applied electrical field, the particles in the liquid suspension exhibit random Brownian movement, and hence a beam of light passing into the cell is reflected, transmitted or absorbed, depending upon the cell structure, the nature and concentration of the particles and the energy content of the light. The light valve is thus relatively dark in the OFF state. However, when an electric field is applied through the liquid light valve suspension in the light valve, the particles become aligned and for many suspensions most of the light can pass through the cell. The light valve is thus relatively transparent in the ON state.
Use of light valves have been proposed for numerous applications including e.g., alpha-numeric displays, television displays, windows, sunroofs, sunvisors, mirrors, eyeglasses and the like to control the amount of light passing therethrough. Light valves of the type described herein are also known as “suspended particle devices” or SPDs”.
For many applications, it is preferable for the activatable material, i.e. the light modulating element, to be a plastic film rather than a liquid suspension. For example, in a light valve used as a variable light transmission window, a plastic film, in which droplets of liquid suspension are distributed, is preferable to a liquid suspension alone because hydrostatic pressure effects e.g., bulging associated with a high column of liquid suspension can be avoided through use of a film, and the risk of possible leakage can also be avoided. Another advantage of using a plastic film is that, in a plastic film, the particles are generally present only within very small droplets and, hence, do not noticeably agglomerate when the film is repeatedly activated with a voltage.
A “light valve film” as used herein refers to a film having droplets of a liquid suspension of particles distributed in the film.
U.S. Pat. No. 5,409,734 exemplifies a type of light valve film that is made by phase separation from a homogeneous solution. Light valve films made by cross-linking emulsions are also known. See U.S. Pat. Nos. 5,463,491 and 5,463,492 both of which are assigned to the assignee of the present invention. All of the above patents including any other patents and references cited therein or elsewhere herein are incorporated into this application by reference thereto.
For use in set suspensions such as light-polarizing sheets, sometimes called “sheet polarizers”, which can be cut up and formed into polarized sunglass lenses or used as filters, light-polarizing particles can be dispersed or distributed throughout a sheet of suitable film-forming material, such as cellulose acetate or polyvinyl alcohol or the like. Methods of making set suspensions for use in sheet polarizers are well known in the prior art. It is important to note, however, that the light polarizing particles mentioned above are immovable, i.e., fixed. See e.g., U.S. Pat. Nos. 2,178,996 and 2,041,138.
The Liquid Light Valve Suspension
1. Liquid Suspending Media and Stabilizers.
A liquid light valve suspension may be any liquid light valve suspension known in the art and may be formulated according to techniques known to one skilled in the art. The term “liquid light valve suspension” as used herein means a “liquid suspending medium” in which a plurality of small particles are dispersed. The “liquid suspending medium” comprises one or more non-aqueous, electrically resistive liquids in which there is preferably dissolved at least one type of polymeric stabilizer which acts to reduce the tendency of the particles to agglomerate and to keep them dispersed and in suspension.
The liquid light valve suspension useful in the present invention may include any of the liquid suspending media previously proposed for use in light valves for suspending the particles. Liquid suspending media known in the art which are useful herein, include but are not limited to the liquid suspending media disclosed in U.S. Pat. Nos. 4,247,175 and 4,407,565. In general one or both of the liquid suspending medium or the polymeric stabilizer dissolved therein is chosen so as to maintain the suspended particles in gravitational equilibrium.
The polymeric stabilizer when employed, can be a single type of solid polymer that bonds to the surface of the particles but also dissolves in the non-aqueous liquid or liquids of the liquid suspending medium. Alternatively, there may be two or more solid polymeric stabilizers serving as a polymeric stabilizer system. For example, the particles can be coated with a first type of solid polymeric stabilizer such as nitrocellulose which, in effect, provides a plain surface coating for the particles and one or more additional types of solid polymeric stabilizer that bond to or associate with the first type of solid polymeric stabilizer and also dissolve in the liquid suspending medium to provide dispersion and steric protection for the particles. Also, liquid polymeric stabilizers may be used to advantage, especially in SPD light valve films, as described in U.S. Pat. No. 5,463,492.
2. Particles.
Inorganic and organic particles may be used in a light valve suspension, and such particles may be either light-absorbing or light-reflecting.
Conventional SPD light valves have generally employed polyhalide particles of colloidal size, that is the particles generally have a largest dimension averaging about 1 micron or less. Preferably, most polyhalide particles have their largest dimension less than one-half of the wavelength of blue light i.e., 2000 Angstroms or less to keep light scatter extremely low.
A detailed review of prior art polyhalide particles can be found in “The Optical Properties and Structure of Polyiodides” by D. A. Godina and G. P. Faerman published in The Journal of General Chemistry, U.S.S.R. Vol. 20, pp. 1005-1016, (1950).
Herapathite, for example, is defined as a quinine bisulfate polyiodide, and its formula is given under the heading “quinine iodosulfate” as 4C
20
H
24
N
2
O
2
.3H
2
SO
4
.2HI.I
4
.6H
2
O in The Merck Index, 10
th
Ed. (Merck & Co., Inc., Rahway, N.J.). In polyiodide compounds, the iodide anion is thought to form chains and the compounds are strong light polarizers. See U.S. Pat. No. 4,877,313 and Teitelbaun et al. JACS 100 (1978), pp. 3215-3217. The term “polyhalide” is used herein to mean a compound such as a polyiodide, but wherein at least some of the iodide anion may be replaced by another halide anion. More recently, improved polyhalide particles for use in light Valves have been proposed in U.S. Pat. Nos. 4,877,313, 5,002,701, 5,093,041 and 5,516,463. These “polyhalide particles” are formed by reacting organic compounds, usually containing nitrogen, with elemental iodine and a hydrohalide acid or an ammonium or alkali metal halide or alkaline earth metal halide. Such organic compounds are referred to herein as a “Precursor.”
However, for the particles to be commercially useful, it is necessary that the particles used in a liquid light valve suspension, whether or not incorporated into a film, have great chemical and environmental stability. To obtain particles of great environmental stability, in turn, it may be desirable to use
Cooper & Dunham LLP
Mack Ricky
Research Frontiers Incorporated
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