Coating processes – Electrical product produced – Fluorescent or phosphorescent base coating
Reexamination Certificate
1999-12-28
2001-06-05
Parker, Fred J. (Department: 1762)
Coating processes
Electrical product produced
Fluorescent or phosphorescent base coating
C427S071000, C427S212000, C427S215000
Reexamination Certificate
active
06242043
ABSTRACT:
This invention relates to improving the moisture resistance of inorganic materials that are sensitive to moisture. More particularly, this invention relates to forming a moisture impervious barrier on alkaline earth metal aluminate phosphors.
BACKGROUND OF THE INVENTION
Alkaline earth aluminate phosphors are known and are available commercially. For example, strontium aluminate phosphors activated with europium emit in the green region of the spectrum. These phosphors are long persistence phosphors which are highly desirable. However, their luminescence disappears after exposure of the phosphor to moisture. Hydrolysis of the phosphor begins after only a few minutes of exposure to moisture, as determined by an increase in pH from about 6 to about 11. The solid phosphor powders also begin to coalesce to form aggregates or even a hard block of cement-like material that is no longer useful. Phosphorescence decreases more slowly, but the phosphor emission becomes very dim after a few hours.
This sensitivity to moisture severely limits the utility of the phosphor, which must be kept away from moisture, as by formulating in a nonaqueous medium.
Other inorganic materials are known to be sensitive to moisture, such as calcium aluminate, barium aluminate, strontium sulfide, calcium sulfide, barium silicate, (CaSrBa) thioaluminate, strontium thiosulfate and the like.
Thus an effective method of protecting each of such inorganic material from moisture would be highly desirable.
SUMMARY OF THE INVENTION
I have found that inorganic materials that are reactive with ammonium fluoride and ammonium difluoride can be coated using ammonium fluoride or ammonium difluoride by firing at a temperature of at least 500° C. The resultant coating is moisture impervious and protects the inorganic particles from the adverse effects of exposure to water. In the case of alkaline earth aluminate phosphors in particular, they can be coated with a moisture impervious coating without changing the long persistence or color of the phosphor.
REFERENCES:
patent: 3617332 (1971-11-01), Lehmann
patent: 3791844 (1974-02-01), Tecotzky et al.
patent: 4684539 (1987-08-01), Chenot et al.
International Search Report for PCT/US00/07940, filed Mar. 24, 2000.
Burke William J.
Parker Fred J.
Sarnoff Corporation
LandOfFree
Method of improving moisture resistance for inorganic... 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 improving moisture resistance for inorganic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of improving moisture resistance for inorganic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2443121