Compositions – Light transmission modifying compositions – Producing polarized light
Reexamination Certificate
2001-01-05
2003-02-11
Dawson, Robert (Department: 1712)
Compositions
Light transmission modifying compositions
Producing polarized light
C252S582000, C252S583000, C359S296000
Reexamination Certificate
active
06517746
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polyhalide particles of improved stability for use in light valves and in set suspensions and to a method of making such particles.
BACKGROUND
1. The Light Valve
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 called 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 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.
Light valves have been proposed for many purposes including, e.g., alpha-numeric displays, television displays, windows, sunroofs, sunvisors, mirrors, eyeglasses and the like to control the amount of light passing there through. 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 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 is thus a film having droplets of a liquid suspension of particles distributed in the film.
A type of light valve film made by phase separation from a homogeneous solution is disclosed in U.S. Pat. No. 5,409,734. Light valve films made by cross-linking emulsions are disclosed in U.S. Patent Nos. 5,463,491 and 5,463,492 assigned to the assignee of the present invention. All of those patents and other patents and articles cited herein are incorporated herein by reference.
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. In these set suspensions, however, the particles are immovable. See e.g., U.S. Pat. Nos. 2,178,996 and 2,041,138.
2. Liquid Light Valve Suspension
A. Liquid Suspending Media and Stabilizers
The liquid light valve suspension for use with the particles obtained from the method of the present invention may be any liquid light valve suspension known in the art and may be formulated according to known techniques. The term “liquid light valve suspension” as used herein means a “liquid suspending medium” in which a plurality of small particles is 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 of 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 are useful herein, such as but 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.
B. Particles
As is known, inorganic and organic particles may be used in a light valve suspension. However, the present invention relates to an improved method of preparing particles that are polyhalides (sometimes referred to in the prior art as perhalides) of alkaloid acid salts and the like. The polyhalide particles of the present invention may be light-polarizing, such as halogen-containing light-polarizing materials, e.g., polyhalides of alkaloid acid salts. (The term “alkaloid” is used herein to mean an organic nitrogenous base, as defined in Hackh's Chemical Dictionary, Fourth Edition, McGraw-Hill Book Company, New York, 1969). As is known, if a polyhalide of an alkaloid acid salt is prepared, the alkaloid moiety may be a quinine alkaloid, as defined in Hackh's Chemical Dictionary, supra. U.S. Pat. Nos. 2,178,996 and 2,289,712 refer in detail to the use of polyhalides of quinine alkaloid acid salts. The particles may be light-absorbing or light-reflecting.
Also, the particles of the present invention may be a hydrogenated polyhalide of a quinine alkaloid acid salt, such as dihydrocinchonidine sulfate polyiodide, as described in U.S. Pat. No. 4,131,334.
More recently, improved polyhalide particles having advantageous features 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 halide, alkali metal halide or alkaline earth metal halide. These “polyhalide particles” can be advantageously prepared by the method of the present invention.
Prior art polyhalide particles are also discussed in detail 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 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.I4.6H
2
O in The Merck Index, 10th Ed. (Merck & Co., Inc., Rahway, N.J.). In polyiodide compounds, the iodine anion is thought to form chains and the compounds are strong light polarizers. See U.S. Pat. No. 4
Fanning Barry
Saxe Robert L.
Slovak Steven M.
Thompson Jean
Thompson Robert I.
Cooper & Dunham L.L.P.
Dawson Robert
Research Frontiers Incorporated
Robertson Jeffrey B.
Thompson Jean
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