Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-07-19
2001-02-06
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S332700, C525S474000, C524S079000, C524S188000, C524S268000, C524S086000, C524S003000, C427S126400, C427S397000
Reexamination Certificate
active
06184304
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not applicable.
FIELD OF THE INVENTION
This invention is directed to the preparation of a photoluminescent material from a hydrogen silsesquioxane resin.
BACKGROUND OF THE INVENTION
While the heat treatment of a hydrogen silsesquioxane resin has been described in the prior art, in for example, U.S. Pat. No. 4,756,977 (Jul. 12, 1988); U.S. Pat. No. 5,145,723 (Sep. 8, 1992); U.S. Pat. No. 5,370,903 (Dec. 6, 1994); U.S. Pat. No. 5,370,904 (Dec. 6, 1994); U.S. Pat. No. 5,372,842 (Dec. 13, 1994); U.S. Pat. No. 5,380,567 (Jan. 10, 1995); U.S. Pat. No. 5,403,748 (Apr. 4, 1995); and U.S. Pat. No. 5,693,565 (Dec. 2, 1997); as well as in two copending United States patent applications assigned to the same assignee as the present invention, namely U.S. Ser. No. 08/771,627 filed Dec. 20, 1996, and entitled “Method of Producing Low Dielectric Ceramic-Like Materials”; and U.S. Ser. No. 08/798,405 filed Feb. 7, 1997, and entitled “Method of Producing Coatings on Electronic Substrates”; it is believed that no skilled artisan has previously devised a process similar to the method described herein, nor have skilled artisans determined photoluminescence of a material based on a hydrogen silsesquioxane resin in the manner described herein. Furthermore, unlike U.S. Pat. No. 5,635,249 (Jun. 3, 1997), this invention does not require the addition of a phosphor filler to achieve a luminescent effect.
BRIEF SUMMARY OF THE INVENTION
This invention relates to the preparation of a strongly photoluminescent material by the heat treatment of a hydrogen silsesquioxane resin. The method described herein involves the steps of (i) pyrolyzing a hydrogen silsesquioxane (HSQ) resin in powder form in a crucible in oxygen, by rapidly heating the resin to a temperature above approximately 400° C. for several hours, generally for about two hours; or (ii) preparing a gel from a solution of the resin dissolved in a suitable solvent, and then pyrolyzing the resin gel in oxygen by heating it to a temperature above approximately 400° C. for about two hours.
If desired, the method can include an additional step of further pyrolyzing the photoluminescent material produced by methods (i) or (ii) above, by heating the photoluminescent material in a different gas, i.e. other than oxygen, to a temperature above approximately 400° C. for about two hours. Reactive gases such as ammonia and nitrous oxide, or an inert gas such as nitrogen, can be used in this step.
Photoluminescence of resulting materials can be observed in the visible part of the spectrum, predominately the blue region, upon excitation of converted materials with an ultraviolet (UV) light having a wavelength of, for example, 337 nanometer (nm).
As used herein, the term “rapidly heating” is intended to mean that heating is carried out such that the material melts on its exterior surface before the conversion or cure reaction occurs, i.e., ceramification. Typically, heating should be completed within about three minutes.
These and other features of the invention will become apparent from a consideration of the detailed description.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
Not applicable.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, the material employed is a preceramic silicon-containing resin, more particularly, a hydridosiloxane resin containing units of the formula HSi(OH)
x
(OR)
y
O
z/2
. R is independently an organic group or a substituted organic group, which when bonded to silicon through the oxygen atom, forms a hydrolyzable substituent.
Suitable R groups include alkyl groups such as methyl, ethyl, propyl, and butyl; aryl groups such as phenyl; and alkenyl groups such as allyl or vinyl. The value of x is 0-2; y is 0-2; z is 1-3; and the sum of x+y+z is 3.
These resins may be (i) fully condensed hydrogen silsesquioxane resins (HSiO
3/2
)
n
; (ii) resins which are only partially hydrolyzed, i.e., containing some ≡SiOR; and/or (iii) resins which are partially condensed, i.e., containing some ≡SiOH. In addition, the resin may contain less than about 10% of silicon atoms having either no hydrogen atoms or two hydrogen atoms, or oxygen vacancies, as well as ≡Si—Si≡ bonds, which can occur during their formation or handling.
Hydrogen silsesquioxane resins are ladder or cage polymers which generally conform to the structure depicted below.
Typically, n has a value of four or more. By way of illustration, when n is four, a bond arrangement for a silsesquioxane cubical octamer is depicted below.
As the series is extended, i.e., n being five or more, double-stranded polysiloxanes of indefinitely higher molecular weight are formed, which contain regular and repeated crosslinks in their extended structure.
Hydrogen silsesquioxane resins and a method for their preparation are described in U.S. Pat. No. 3,615,272 (Oct. 26, 1971), which is incorporated herein by reference. According to the method in the '272 patent, nearly fully condensed hydrogen silsesquioxane resin containing up to 100-300 parts per million silanol (≡SiOH), can be prepared by hydrolyzing trichlorosilane (HSiCl
3
) in a benzene sulfonic acid hydrate medium, washing with aqueous sulfuric acid, and subsequently washing with distilled water until neutral. The solution is filtered to remove insoluble material, and is then evaporated to dryness, leaving a solid resinous polymer in powder form.
U.S. Pat. No. 5,010,159 (Apr. 23, 1991), which is also incorporated herein by reference, teaches another method of hydrolyzing hydridosilanes that are dissolved in a hydrocarbon solvent with an aryl sulfonic acid hydrate medium to form the resin. A solid resinous polymer in powder form can be recovered by removing the solvent. The solvent can be removed by distilling off the solvent at atmospheric pressure to form a concentrate containing 40-80% of the resin, and removing the remaining solvent under vacuum and mild heat.
Other suitable resins are described in U.S. Pat. No. 4,999,397 (Mar. 12, 1991) including those resins produced by hydrolyzing an alkoxy or acyloxy silane in an acidic alcoholic medium according to Japanese Kokai Patents J59-178749 (Jul. 6, 1990), J60-86017 (May 15, 1985), and J63-107122 (May 12, 1988), all of which are incorporated by reference.
Solutions of the resinous polymer can be formed by simply dissolving or dispersing the preceramic silicon containing resin in a solvent or in a mixture of solvents. Some suitable solvents which can be employed by way of example are aromatic hydrocarbons such as benzene, toluene, and xylene; alkanes such as n-heptane, hexane, octane, and dodecane; ketones such as methyl ethyl ketone and methyl isobutyl ketone (MIBK); linear polydimethylsiloxanes such as hexamethyldisiloxane and octamethyltrisiloxane; cyclic polydimethylsiloxanes such as octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane; esters such as butyl acetate and isoamyl acetate; or ethers such as diethyl ether and hexyl ether.
Generally, enough solvent is used to form the solutions, which typically range from a solids content of 10 to 85 weight percent of the resin. Gels can be prepared from these solutions by adding a small amount of a solvent that contains an OH group, such as methanol, ethanol, or isopropanol. A small quantity of water can also be used. In either case, typically, between 10
−4
to 10
−2
percent by volume of this additive are sufficient to cause gelation of the solution.
The powder form of the resin, and the resin gels referred to hereinafter in the examples, were prepared generally according to these procedures.
REFERENCES:
patent: 5145723 (1992-09-01), Ballaance et al.
patent: 5837364 (1998-11-01), Zank
patent: 0635554A2 (1995-01-01), None
Cesare James L. De
Dow Corning Corporation
Wu David W.
Zalukaeva Tanya
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