Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-07-30
2001-04-03
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S839000, C524S840000, C524S079000, C524S403000, C524S405000, C524S406000, C524S407000, C524S408000, C524S409000, C524S413000, C524S434000, C524S435000, C524S436000, C524S437000, C075S362000
Reexamination Certificate
active
06211285
ABSTRACT:
This invention relates to a polyisocyanate-based polymer containing a metal salt, a process for the preparation of the polymer, and a process for calcining the obtained polymer to provide a powder substance containing the metal, with said powder having an average particle size of less than 1 micrometer.
BACKGROUND OF THE INVENTION
Metal or metal oxide particles of submicron size are a valuable industrial commodity finding use in many applications including for example in the manufacture of industrial catalyst such as might be employed in the chemical industry, in the manufacture of ceramics, of electronic components, and as fillers for, for example, plastics, paints or cosmetics.
A large variety of techniques are available for the manufacture of metal or metal oxide powders having a very fine particle size. Such techniques include solution processes and high temperature gas phase and condensed phase syntheses. For a comprehensive review of the general techniques available reference is made to the recent publication entitled “Chemical Engineering Aspects of Advanced Ceramic Materials” by V. Hlavacek and J. A. Puszynski published in the Journal of Industrial Engineering and Chemical Research, pages 349-377, Volume 35, 1996.
Despite the numerous procedures available a problem in common to a lesser or greater extent with nearly all methods is the difficulty of obtaining consistently fine uniform particles of good purity and strength. Procedures that can provide a greater consistency in this respect invariably have high costs associated with their operation due to the complexity of the equipment required, the use of expensive raw materials, or high energy consumption. It would therefore be desirable to develop a cost effective procedure leading to the production of metal or metal oxide powders having a consistently fine particle size. It would be of particular advantage if such a procedure could be operated using raw materials readily available and could be operated in the substantial absence of highly specialized equipment and costly solvents or chemical processing aids. It would also be an advantage if such a procedure were able to provide for the production of metal powders in a more attractive yield.
A common objective is the production of a metal powder that has a fine particle size and does not exhibit the problem of agglomeration leading to a wide particle size distribution. To optimize this, it is necessary to develop a process which provides a homogeneous and even distribution, precipitation, of the metal-containing substance in the first instance without providing subsequent opportunity for secondary nucleation leading to agglomeration. With this in mind, laboratory studies have been undertaken to evaluate the use of reactive polymer chemistry in providing the desired homogeneous distribution starting from an aqueous metal salt solution. The reactive polymer of choice is polyurethane; the basic polyurethane reactive components comprising polyisocyanate are commercially available at low cost and exhibit compatibility with water. Patent publications which disclose the manufacture of polyurethane polymer containing metal particles or metal salts and the subsequent calcining or pyrolysis of the resulting polymer include U.S. Pat. Nos. 3,510,323; 4,569,821; and 5,338,334; and the published French Patent application 2,609,915. These documents do not meet the particular needs outlined above.
SUMMARY OF THE INVENTION
In a first aspect, this invention relates to a polyisocyanate-based polymer having dispersed therein a metal salt, said polymer being obtained by reacting an organic polyisocyanate with an aqueous composition of a metal salt, characterized in that the polymer comprises the metal salt in an amount of from at least 10 weight percent based on total dry weight of the salt and the polyisocyanate-based polymer.
In a second aspect, this invention relates to a process for preparing a polyisocyanate-based polymer having dispersed therein a metal salt by reacting an organic polyisocyanate with an aqueous composition of a metal salt characterized in that:
i) the amount of metal salt employed is sufficient to provide the resulting polymer with a metal salt content of at least 10 weight percent based on total dry weight of the salt and the polyisocyanate-based polymer; and in that
ii) the polyisocyanate is present in an amount of from at least 10 parts by weight per 100 parts by weight of the aqueous composition with the proviso that when the aqueous composition comprises an additional isocyanate-reactive substance in an amount of more than about 60 weight percent, the amount of polyisocyanate employed does not exceed more than about 70 parts by weight.
In a third aspect, this invention relates to a process for producing a metal-containing powder having an average particle size of less than 1 micrometer, which process comprises calcining a polyisocyanate-based polymer having dispersed therein a metal salt, at a temperature of from about 300° C. to about 1500° C. characterized in that the polymer has a metal salt content at least 10 weight percent based on total dry weight of the salt and the polyisocyanate-based polymer.
In a fourth aspect, this invention relates to a metal-containing powder obtainable by calcination of a polyisocyanate-based polymer having dispersed therein a metal salt characterized in that the powder has an average particle size of less than about 1 micrometer and an average BET surface area of more than 200 m
2
/gram.
In yet a fifth aspect, this invention relates to a composition containing a metal-containing powder obtainable such a calcination process characterized in that the composition comprises a bulk phase having dispersed therein from about 0.1 to about 50 weight percent of the powder based on total weight of the bulk phase and powder.
The present invention provides for a relatively simple and cost-effective route for the manufacture of metal-containing powders of submicron particles size. Such particles find value in the manufacture of ceramic articles, electronics, industrial catalysts and as fillers in plastics, paints or cosmetics including creams and oils. When used as filler, the smaller particle of the filler provide for a minimum reflection of visible light allowing exploitation of filler properties with minimal disturbance to transparency or visible light transmission properties of the substance to be filled. Transmission of electromagnetic radiation of other wavelengths may be blocked by the presence of the filler.
DETAILED DESCRIPTION OF THE INVENTION
Described hereinafter is a polyisocyanate-based polymer having dispersed therein a metal salt; a process for the preparation of such polymer; a process for calcining the obtained polymer to provide a metal-containing powder; and a metal-containing powder having a submicron particle size.
The metal in the “metal-containing” powder may be present as elemental metal, or as an oxide, carbide or alloy thereof. Whether the powder which is obtained will be a metal, a metal alloy, oxide or carbide will depend upon the metal salt(s) present in the polyisocyanate-based polymer and the conditions of pyrolysis or calcining. It is also to be appreciated that the same factors can influence the characteristics of the particles including their size and surface area.
The metal-containing powder obtained according to this invention is characterized in that it has an average particle size of less than 1 micrometer (1000 nanometers), preferably less than about 0.1 micrometer (100 nanometers), and more preferably less than 0.02 micrometer (20 nanometers). By the term average particle size it is understood that less than about 25, preferably less than about 10, and more preferably less than about 5 percent of the metal particles will have a size in excess of the mentioned particle size. By the term “particle size” it is meant the size of the particle in its largest dimension. The powder is further characterized in that it has an average BET surface area of at least 5, preferably at least 25, more preferably at lea
Broos Jacobus A. F.
Grunbauer Henri J. M.
Pickin Kevin
Bagwell Melanie D.
Seidleck James J.
The Dow Chemical Company
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