Explosive and thermic compositions or charges – Containing inorganic oxygen-halogen salt – Ammonium perchlorate
Reexamination Certificate
2000-05-09
2003-03-18
Cardone, Michael J. (Department: 3641)
Explosive and thermic compositions or charges
Containing inorganic oxygen-halogen salt
Ammonium perchlorate
C149S045000
Reexamination Certificate
active
06533878
ABSTRACT:
The present invention relates to the technical field of the pyrotechnic generation of gases that can be used especially in systems for protecting the occupants of a motor vehicle by means of bags which are inflated by the combustion gases of a pyrotechnic charge. More specifically, the invention relates to pyrotechnic compositions generating, at temperatures acceptable for motor-vehicle safety, clean gases, called “cold” gases, which are rich in nitrogen and are non-toxic.
For various pyrotechnic requirements and especially for ensuring that airbags are inflated correctly, the pyrotechnic gas generators must deliver, in extremely short times, of the order of thirty milliseconds, gases which are clean, that is to say contain no solid particles liable to form hot spots that can damage the wall of the bag, and are non-toxic, that is to say have low contents of nitrogen oxides, of carbon oxides and of chlorinated products.
Various families of pyrotechnic compositions have been developed for this purpose.
A first family relates to compositions based on an alkaline or alkaline-earth azide in the presence of a mineral oxidizing agent such as potassium nitrate or a metal oxide. These compositions, which may where appropriate include a binder, have major drawbacks. Firstly, when they burn they produce a great deal of dust which has to be filtered by relatively large filtration systems, thereby increasing both the weight and the cost of the generator. Secondly, azides are very toxic products which in addition have the possibility of forming lead azides or azides of other heavy metals, which are primary explosives. These compositions are therefore difficult to store satisfactorily for several years in a motor vehicle.
A second family relates to compositions based on nitrocellulose and on nitroglycerin. These compositions, also known by the name of “double-base powders”, are very advantageous since they burn very quickly and produce no dust. However, they have the drawback of not being completely stable over time, which phenomenon, over the years, impairs the effectiveness of these compositions in a motor vehicle.
A third family relates to compositions called “composites”, basically consisting of an organic binder and of an oxidizing mineral filler, especially such as a mineral perchlorate. These compositions are very advantageous since they have a good burn rate and excellent ageing stability.
Compositions have thus been proposed, in patent FR-A-2,137,619 or in its corresponding patent U.S. Pat. No. 3,723,205, in which the binder is a polyvinyl chloride and the oxidizing filler is an ammonium perchlorate in the presence of sodium nitrate as an internal chlorine scavenger. Nevertheless, the use of a chlorinated binder in the presence of energy-generating fillers is a tricky operation, especially from the standpoint of safety and from the non-toxicity of the gases generated.
Composite compositions have also been proposed which consist of a silicone binder that can be crosslinked at room temperature, also known by the name “RTV” (Room Temperature Vulcanizable) binder, and of potassium perchlorate, the potassium atom acting as an internal chlorine scavenger. Such compositions are, for example, described in patents FR-A-2,190,776 and FR-B-2,213,254 or their corresponding United States patents U.S. Pat. No. 3,986,908 and U.S. Pat. No. 3,964,256. However, these compositions have the drawback of generating very oxygen-rich gases which are not desirable for manufacturers in the motor-vehicle industry.
Composite compositions have therefore been proposed which consist of a silicone binder and of a mixture of ammonium perchlorate and sodium nitrate. Such compositions, which are described for example in French patent FR-A-2,728,562 or in its corresponding United States patent U.S. Pat. No. 5,610,444, do indeed generate clean, nitrogen-rich and non-toxic gases but they have the drawback of burning at very high temperatures.
Compositions have also been proposed which are based on ammonium perchlorate and sodium nitrate that are mixed with nitrogen compounds such as azides or metal nitrides. However, these compositions which are described for example in United States patent U.S. Pat. No. 3,814,694, have the drawbacks mentioned above with regard to compositions containing azides.
Finally, compositions have also been proposed which consist of a mixture of ammonium perchlorate and sodium nitrate, this mixture being combined with a nitrogen compound of triazole or of tetrazole. Such compositions, which are described for example in United States patent U.S. Pat. No. 4,909,549, do indeed generate clean, nitrogen-rich gases but these gases are relatively toxic and have to be diluted with air in order to be able to be used for motor-vehicle safety.
Those skilled in the art are thus still seeking pyrotechnic compositions which ignite easily, exhibit sustained combustion and generate, at temperatures acceptable for motor-vehicle safety, clean, nitrogen-rich, non-toxic clean gases. The object of the present invention is specifically to propose such compositions.
The invention therefore relates to a pyrotechnic gas-generating composition comprising especially a crosslinked reducing binder, additives and a main oxidizing filler comprising at least a mixture of ammonium perchlorate and of a chlorine scavenger chosen from the group consisting of sodium nitrate, lithium carbonate and potassium carbonate, the ammonium perchlorate/chlorine scavenger weight ratio being less than 5.0, characterized in that the weight content of the said binder represents at most 10% of the total weight of the composition, in that the weight content of the said main oxidizing filler is between 50% and 75% of the total weight of the composition and in that the said additives contain at least one copper compound chosen from the group consisting of cupric oxide CuO and of basic copper nitrate Cu(NO
3
)
2
.3Cu(OH)
2
and contain at least one organic nitrogen compound chosen from the group consisting of nitroguanidine, guanidine nitrate, oxamide, dicyandiamide of formula C
2
H
4
N
4
, and metal cyanamides.
According to a first preferred embodiment of the invention, the said binder is chosen from the group consisting of crosslinkable binders based on a silicone resin, of crosslinkable resins based on an epoxy resin and of polyacrylic rubbers having reactive terminal groups such as, especially, epoxy or hydroxyl terminal groups. The weight content of the said binder will advantageously be between 6% and 10% of the total weight of the composition and the weight content of the said main oxidizing filler will then advantageously be between 70% and 75% of the total weight of the composition. Also advantageously, the ammonium perchlorate/chlorine scavenger weight ratio will be less than 4.0 and preferably less than 1.5.
A preferred chlorine scavenger is sodium nitrate and, in this case, according to a second preferred embodiment of the invention, the said main oxidizing filler will consist of coprecipitated ammonium perchlorate and sodium nitrate particles. Such particles are obtained, for example, by atomizing a solution of ammonium perchlorate and sodium nitrate and by evaporating the water contained in the droplets thus obtained. This atomization and this evaporation may be carried out using the apparatuses normally used to obtain coprecipitated salt granules. When the main oxidizing filler contains, alongside the sodium nitrate, other chlorine scavengers, it is also possible to make the latter participate in the coprecipitation.
The coprecipitated ammonium perchlorate and sodium nitrate particles generally have a particle size of between 10 &mgr;m and 50 &mgr;m.
According to a fourth preferred embodiment of the invention, the ammonium perchlorate/chlorine scavenger weight ratio is approximately 0.95.
According to a fifth preferred embodiment of the invention, the metal cyanamides will be chosen from sodium, zinc and copper cyanamides. Zinc cyanamide, of formula ZnCN
2
, is particularly preferred.
According to a sixth preferred embodiment of the in
Bucknam and Archer
Cardone Michael J.
Felton Aileen B.
Societe Nationale des Poudres et Explosifs
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