Explosive and thermic compositions or charges – Structure or arrangement of component or product – Coated component
Reexamination Certificate
1999-04-14
2001-10-16
Jordan, Charles T. (Department: 3641)
Explosive and thermic compositions or charges
Structure or arrangement of component or product
Coated component
C149S046000, C149S061000
Reexamination Certificate
active
06302978
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a coated oxidizer and a fuel composition. Specifically, the present invention relates to an oxidizer coated with inorganic particles, and a fuel composition comprising the coated oxidizer and a fuel. The present invention also relates to a method for reducing the mechanical energy sensitivity of an oxidizer, which comprises coating the oxidizer with inorganic particles.
BACKGROUND ART
Combustible oxidizers are usually used as exothermic materials in smoking agents. The combustible oxidizers may also be used in pyrotechnics or as gas generators for automotive air bags.
As a conventional combustible oxidizer, potassium chlorate, potassium nitrate and the like have been mainly used. However, these combustible oxidizers are often highly sensitive to mechanical energy, i.e., energy generated by friction or shock. In particular, potassium chlorate has a high risk of exploding when handled, and hence, Japan Explosive Industry Association regulates its use.
Up to now, there has been no effective method developed for reducing the mechanical energy sensitivity of these combustible oxidizers. When such combustible oxidizers were used, there was no alternative but to handle them carefully.
Exothermic materials used in smoking agents have a risk of detonative reaction during their preparation or transport, since a combustible oxidizer and a fuel are mixed therein and are directly in contact with each other, which then can be easily ignited by mechanical energy such as friction or shock.
On the other hand, gas generators composed mainly of sodium azide are used in automotive air bags. However, with these, there are problems of the disposal of wastes containing sodium residue and the generation of toxic gas. Various efforts have been made to solve these problems; for example, a combination of tetrazoles with an oxidizer or a combination of azodicarbonamide (ADCA) with an oxidizer has been extensively studied as alternative materials to sodium azide.
Japanese patent laid-open publication Hei 3-242392 (1991) teaches a method for desensitizing an oxidizer highly sensitive to friction by forming a matrix with a polymer such as poly glycols. However, most of potential polymers for this invention have softening points of 100° C. or less, and thus they are difficult to handle at an elevated temperature since their lower softening points lead to blocking in a dryer when oxidizers in a matrix are dried. Such polymer-matrix oxidizers have another problem in that they are less ignitable. This is because oxidizers dispersed in the polymer matrix cannot come in direct contact with fuel.
It is also kmown that some oxidizers such as potassium chlorate are unstable under acidic conditions, but no action has been taken to improve the stability of these oxidizers.
An object of the present invention is to provide an oxidizer less sensitive to mechanical energy and a method for reducing its mechanical energy sensitivity in order to make the handling easy and safe.
Another object of the present invention is to solve the problems of the above conventional oxidizers such as poor stability to heat or acids, and to solve the problems of the above conventional polymer-matrix oxidizers such as difficulties of handling them at an elevated temperature as well as poor ignitability.
A further object of the present invention is to provide a combustible composition having a low risk of, for example, detonative reaction.
A still further object of the present invention is to provide a gas generator for use in an air bag having a proper maximum pressure. Such air bag can then be produced at low cost.
DISCLOSURE OF THE INVENTION
We have made every effort to reduce the mechanical energy sensitivity of an oxidizer while improving its handling at an elevated temperature, its stability to heat or acids and its ignitability. As a result, we have found that an oxidizer with desired properties could be attained by coating the oxidizer with inorganic particles. Thus, the present invention has been achieved.
Accordingly, the present invention provides an oxidizer coated with inorganic particles. The present invention also provides a method for reducing the mechanical energy sensitivity of an oxidizer, which comprises coating the oxidizer with inorganic particles. The present invention further provides a combustible composition comprising the oxidizer coated with inorganic particles and a fuel. The present invention further provides a gas generator comprising the oxidizer coated with inorganic particles and a fuel.
The coated oxidizer of the present invention is less sensitive to mechanical energy as a result of coating with inorganic particles. In the present invention, it is advantageous to use oxidizers highly sensitive to mechanical energy, i.e., those which may cause a rapid and accelerated oxidation such as an explosive reaction initiated by a slight energy generated by friction or shock. For example, the oxidizers highly sensitive to mechanical energy may have a ⅙ explosion point of 21.6 kgf or less, preferably 19.2 kgf or less, more preferably 16.0 kgf or less, as measured in BAM friction sensitivity test. Such oxidizers include, but are not limited to, potassium chlorate, potassium bromate, potassium iodate, potassium perchlorate, sodium chlorate, ammonium nitrate and potassium nitrate. The oxidizers may be used alone or in combination. The oxidizer may have a particle diameter, for example, between 0.01 and 5 mm, preferably between 0.1 and 3 mm.
Inorganic materials used in the present invention may be inactive. The term “inactive” used here means non-reactive with the oxidizer to be coated. Such inorganic materials include, but are not limited to, talc, calcium silicate, clay, bentonite and carprex, out of which, talc and calcium silicate are preferred. The inorganic materials may be used alone or in combination. Particles of the inorganic materials may have a particle diameter, for example, between 0.5 and 50 &mgr;m, preferably between 2 and 20 &mgr;m.
The coated oxidizers of the present invention can be used as combustible oxidizers such as exothermic materials for smoking agents, oxidizers for pyrotechnics, and oxidizer components of gas generators for automotive air bags.
An air bag having a proper maximum pressure can be produced at low cost when the technique of the present invention is applied to the preparation of a gas generator for the air bag.
The present invention also encompasses a combustible composition comprising the oxidizer coated with inorganic particles and a fuel.
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Baker Aileen J.
Chugai Seiyaku Kabushiki Kaisha
Jordan Charles T.
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