Explosive and thermic compositions or charges – Processes of making
Reexamination Certificate
2000-01-27
2001-11-13
Carone, Michael J. (Department: 3641)
Explosive and thermic compositions or charges
Processes of making
C149S108600, C149S019400, C149S061000
Reexamination Certificate
active
06315847
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for the preparation of high density igniter granules, and in particular to the substantially water-free preparation of high density igniter granules, which igniter granules are especially suitable for use in waterless extrusion applications.
2. Description of Related Art
Among the various applications in which thermoplastic elastomer-coated igniters extruded from granules may be employed are, by way of example, air bag assemblies, pyrotechnic ordinances, flares, thrust decoys, and solid propellant rocket motors. Especially suited for these applications are igniter compositions comprising boron/potassium nitrate (B/KNO
3
) as the fuel/oxidizer ingredients. When ignited, the igniters initiate combustion of the larger specified gas generant composition.
Processes for preparing igniter granules are disclosed in U.S. Pat. Nos. 4,405,534 to Deisenroth and 5,565,651 to Kim, the disclosures of which are incorporated herein by reference to the extent that these disclosures are compatible with this invention. The Deisenroth patent discloses a process in which a crystalline water-insoluble explosive is incorporated into a fully reacted aqueous polyurethane dispersion that is substantially free of organic solvent to form a uniform mixture. The mixture is then coagulated to form granules, which are dried. The process disclosed in the Kim patent differs from that of Deisenroth, yet similarly involves the use of an aqueous solution.
The presence of water in the above-discussed processes imparts the processes with several drawbacks. In particular, water-sensitive materials that are soluble in water, such as B/KNO
3
, cannot be effectively granulated by these water-intensive processes. Additionally, other water-sensitive materials, such as magnesium compounds, may produce volatile and explosive by-products when exposed to water.
A water-free process for preparing igniter granules is disclosed in U.S. Pat. No. 4,979,999 to Briere, the disclosure of which is incorporated herein by reference to the extent that it is compatible with this invention. According to the process disclosed in Briere, a binder is first dissolved in a solvent to form a binder solution. Ignitable magnesium particles are then added to the binder solution, and thereafter a non-solvent is introduced into the solution. However, the addition of ignitable particles to the binder solution before introducing the non-solvent to the ignitable particles causes a paste to form. Drawbacks associated with paste include the need to subject the paste to additional processing steps and equipment, such as an oven heater and a mesh sieve. Moreover, the igniter granules produced by this conventional technique typically are characterized by poorly distributed coatings, irregular shapes and a wide distribution of granule sizes, typically between approximately 0.1 mm to 1 mm. The lack of uniformity in granule coating, configuration, and dimension makes the igniter granules more sensitive to impact, friction, and electrical static discharge (ESD).
Thus, it would be a significant advancement in the art to provide a substantially water-free method for making uniformly coated extrudable igniter granules of substantially uniform shape and size without the need for either oven drying to evaporate water or complicated distillation processes to distill organic solvents.
SUMMARY OF THE INVENTION
It is, therefore, an object of this invention to provide a process which achieves the above-discussed advancement in the art for producing igniter granules of uniform configuration, coating, and dimension and suitable for subsequent waterless extrusion.
In accordance with the principles of this invention, this and other objects are attained by the provision of a process comprising dispersing at least fuel and oxidizer particles (also referred to herein as particulates or ignitable particles), at least one of which is water-sensitive and can be a powder, into a first liquid comprising at least one first non-solvent to form a slurry that is substantially water-free. As referred to herein, non-solvent means that the particles are dispersible, yet substantially insoluble, therein. Separately, a binder solution is prepared by dissolving at least one binder, preferably a thermoplastic elastomer, into at least one solvent. Next, at least a portion of the binder solution in a substantially water-free state and at least a portion of the slurry are mixed, for example by stirring, to coat the particles with the binder so that the particles are immobilized, thereby forming coated igniter granules. A surfactant comprising at least one second non-solvent, which may be the same as or different from the first non-solvent, is then added to the coated igniter granules to harden and reduce agglomeration of the granules. Finally, the coated igniter granules are filtered and dried, preferably at room temperature of from 20° C. to 25° C. The resulting coated igniter granules are substantially uniform in distribution of thermoplastic coating, size, and shape.
Preferably, the method of this invention does not utilize water, so that one or more of the igniter components may be water sensitive, e.g., soluble in water, or moisture sensitive. It is understood, however, that the inventive process can be carried out in a substantially water-free state, meaning that the amount of water introduced during the process is below the solubility limit (i.e., the point at which the particles begin to appreciably dissolve into the water) of the fuel and oxidizer particles dispersed in the non-solvent.
These and other objects, features, and advantages of the present invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the present invention.
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John Wiley & Sons, “Encyclopedia Of Polymer Science And Engineering”, vol. 6, Emulsion Polymerization to Fibers, Manufacture, pp. 570-631.
Kirk-Othmer, Encyclopedia of Chemical Technology, Fourth Edition, vol. 20, Power Generation To Recycling, Glass, pp. 680-697.
Doll Daniel W.
Lee Kenneth E.
Lund Gary K.
Baker Aileen J.
Carone Michael J.
Cordant Technologies Inc.
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