Coating processes – Particles – flakes – or granules coated or encapsulated – Inorganic base
Reexamination Certificate
1999-10-13
2004-11-02
Cleveland, Michael (Department: 1762)
Coating processes
Particles, flakes, or granules coated or encapsulated
Inorganic base
C427S180000, C427S189000, C427S190000, C427S193000, C427S212000, C427S218000, C427S219000, C427S064000, C427S071000
Reexamination Certificate
active
06811813
ABSTRACT:
BACKGROUND OF THE INVENTION
Inorganic particles that are sensitive to atmospheric materials such as moisture can be coated using liquid based or vapor phase methods. For example, binders and mineral or metallic colloids can be dispersed in liquid media and distributed over the surface of the inorganic particles to be coated. However, the coating materials must be insoluble in, and non-reactive with, the solvent used. Vapor phase coating methods, such as using fluidized bed reactors, require high temperatures and lengthy reaction times which generally result in some surface reaction or modification of the particles to be coated. Further, the equipment is complex and expensive.
As an example, long persistence phosphors are known which, after having been struck by light, continue to emit light after the initial light source is extinguished. For example, europium activated alkaline earth metal sulfides, such as SrS:Eu and CaS:Eu, are known that emit in the orange-red portions of the spectrum. Red-emitting phosphors having long persistence are very rare, but they are very useful, particularly for safety equipment such as “EXIT” signs and the like.
However, these phosphors are water sensitive, and thus cannot be exposed to moisture without deleterious effects on their light emission. Thus they must be protected to prevent exposure to moisture.
Coating or encapsulating water sensitive phosphors with moisture insoluble materials has been tried. The coating particles can be mixed with the phosphor particles to be coated in a liquid medium, but both the coating material and the phosphor must be insoluble in, and non-reactive with, the liquid. In the case of phosphors, moisture sensitive phosphors cannot be immersed in solutions including any moisture.
Vapor phase coating has also been tried; for example tetraethoxysilane or tetramethoxysilane can be passed through a fluidized bed including phosphor particles to deposit a silica layer, but this is an expensive process.
Thus it would be desirable to be able to apply a coating of an inorganic material onto inorganic particles to form a protective coating, or a coating that can modify particular surface properties, or impart a particular surface functionality to the inorganic particles.
In particular, a method of applying a water impervious coating onto phosphor particles that are sensitive to moisture without the aid of an aqueous liquid medium, a method that does not change the color or the strength of the phosphor emission, would be highly desirable.
SUMMARY OF THE INVENTION
The present invention is directed to a method of coating inorganic particles with a thin film of an inorganic coating material that does not require any liquid media for its application. Inorganic particles having a particle size of from 1 up to about 100 micrometers can be coated using a sufficient amount of nanometer sized inorganic powders to completely cover the larger inorganic particles.
The coated inorganic particles are then fired at a temperature high enough to soften or melt the nanometer-sized coating particles surrounding the coated inorganic particles, but a temperature insufficient to change the surface properties of the larger inorganic particles to be coated. The present method does not require that any solvent be used.
REFERENCES:
patent: 3617332 (1971-11-01), Lehmann
patent: 3793055 (1974-02-01), Shodai
patent: 4398119 (1983-08-01), Dodds et al.
patent: 4435219 (1984-03-01), Greigger
patent: 4473634 (1984-09-01), Dodds et al.
patent: 4684540 (1987-08-01), Schulze
patent: 4874985 (1989-10-01), Hase et al.
patent: 5051277 (1991-09-01), Sigai et al.
patent: 5080928 (1992-01-01), Klinedienst et al.
patent: 5087523 (1992-02-01), Sigai et al.
patent: 5126166 (1992-06-01), Dutta et al.
patent: 5330791 (1994-07-01), Aihara et al.
patent: 5489449 (1996-02-01), Umeya et al.
patent: 5747100 (1998-05-01), Petersen
patent: 5874135 (1999-02-01), Yoon et al.
patent: 5892476 (1999-04-01), Gindrup et al.
patent: 5908698 (1999-06-01), Budd
Robert H. Perry, ed. Chemical Engineer's Handbook, 1963, p. 19-17.*
Richard J. Lewis, Sr., ed., Condensed Chemical Dictionary, 1993, p. 1076.*
C. Pantano, “Oxynitride Thin Films from the Sol-Gel Process,” Sol-Gel Technology for Thin Films, Fibers, Preforms, Electronics and Specialty Shapes, edited by Lisa C. Klein, Noyes Publications, 1988, (no month).
Burke, Esq. William J.
Cleveland Michael
Sarnoff Corporation
LandOfFree
Method of coating micrometer sized inorganic particles does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of coating micrometer sized inorganic particles, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of coating micrometer sized inorganic particles will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3289754