Gas generant composition

Details Gas generant composition Gas generant composition

1999-11-23

2001-10-16

Nelson, Peter A. (Department: 3641)

Explosive and thermic compositions or charges

Containing hydrazine or hydrazine derivative

C149S038000, C149S045000, C149S110000, C149S114000

Reexamination Certificate

active

06302979

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a gas generant composition. More specifically, the invention relates to a non-azide type gas generator composition which supplies gas components by burning for the purpose of inflating an air bag system.
RELATED ART
In the event of collision of vehicles like cars at high speed, the driver and passengers might be injured or killed by clashing against internal hard or dangerous parts of the vehicles such as the handle and front glass. In order to prevent such disasters, air bag systems for automobiles have is been developed which inflate quickly by a gas generated from a gas generant.
Requirements for the gas generant of an automobile air bag system are very severe. At first, the bag should inflate in a very short period of time, usually not longer than 40 to 50 milliseconds. Further, The atmosphere within the bag is most suitable when it corresponds to the air composition in the car. These requirements are satisfied by gas generants which have been currently used in common comprising a base gas generant such as alkali metal salts (in particular sodium azide) or alkaline earth metal salts of hydrazoic acid. However, these gas generants are seriously defective in that the main component, sodium azide is toxic and that the by-products alkali components are also toxic. Hence, environmental pollution brought by a large amount of scrap cars and health hazard of the driver and passengers when the gas is generated are concerned.
For the purpose of overcoming these problems, non-azide type gas generants have been under development in place of sodium azide type. For example, JP-A 3-208878 discloses a composition which comprises a main component of oxygen-containing oxidizer such as tetrazole, triazole, or their metal salts combined with ammonium perchlorate or sodium nitrate and an auxiliary component of a metal oxide such as V
2
O
5
, CuO or Fe
2
O
3
. The metal oxide mentioned forms a solid combustion product, which is easily removed by filtration when undesired components are removed by filtration prior to release the formed gas into the bag in an air bag system, and converts CO which is toxic to human bodies generated from the nitrogen-containing organic compound to CO
2
. JP-B 64-6156 and JP-B 64-6157 disclose a gas generant which contains, as the main component, a metal salt of bitetrazole compound that does not contain hydrogen. JP-A-5-213687 further discloses a gas generant having a transition metal complex of aminoarazole as the main component. These non-azide type compounds disclosed in the series of prior art references are characteristic in that the concentration of carbon monoxide released is low since the carbon number in the one molecule is small; however, the amount of nitrogen oxides, toxic to human bodies, increases in all the cases and the performance is not satisfactory in respect of the inflation period of the bag.
It is described in JP-A 6-32689, JP-A 6-32690 and JP-A 8-227884 that a non-azide type gas generant having a nitrogen-containing organic compound such as azodicarbonamide and a certain inorganic oxygen-containing oxidizer as the effective component is free from environmental pollution, satisfactory in respect of the inflation period of the bag, and advantageous in the cost.
In the combustion of an organic compound containing oxygen, it is well-known that carbon monoxide will generate as incomplete combustion product even when an oxidizer is used in an amount exceeding the chemical equivalence that releases the necessary amount of oxygen for burning combustible elements, such as carbon, hydrogen and others, in the organic compound. In view of this fact, the nitrogen compound, such as azodicarbonamide, used as the main agent in the mentioned gas generant is supposed to release a relatively rather large amount of carbon monoxide and nitrogen oxides since many carbon atoms are contained per molecule. For the purpose of avoiding such by-product carbon monoxide, use of a catalyst may be possible which convert carbon monoxide to carbon dioxide. Many components are known for such catalysts as written in a book “Classified Table for Catalysts depending on Reaction, Vol. I” edited by Tarama et al. of Kyoto University and published by Kagaku Kogyo-sha (see pp. 291-292). However, no catalysts are known that are generally reactive enough in a contact period of time of several dozens milliseconds as required for a gas generant for air bag system; V
2
O
5
, CuO, Fe
2
O
3
and other metal oxides are used at present in spite of their low activity. There are rarely known catalysts that decompose nitrogen oxides in the absence of a reductant. In addition, when a gas generant burns, the highest temperature in the inflator exceeds 2,000° C. and the oxygen molecules existing in surplus react with the nitrogen molecules released whereby a large amount of nitrogen oxides called “thermal NOx” is generated. Toxicity of the NOx contained in a large amount in the released gas is said to be a main reason why non-azide type gas generants are not used in practice notwithstanding many studies. It is desirable to convert NOx to N
2
by some means for reducing the NOx. Many references including patents and papers for NOx reduction suggest that a catalyst might reduce NOx, which comes from a fixed source of automobile exhaust gas, to a certain level in the presence of a reductant. However, there are rarely known catalysts that are reactive enough in a contact period of time of several dozens milliseconds, as required for a gas generant for air bag system, without addition of a reductant.
DISCLOSURE OF THE INVENTION
The present invention relates to a gas generant composition which comprises a nitrogen-containing organic compound, an oxygen-containing inorganic oxidizer, and a third component of at least one selected from the following (1) through (4):
(1) manganese dioxide having a specific surface area not less than 50 m
2
/g;
(2) copper oxide having a specific surface area not less than 1 m
2
/g;
(3) a molybdenum compound of at least one selected from the group consisting of molybdenum dioxide, molybdenum trioxide, molybdic acid and ammonium molybdate; and
(4) a mixture of manganese dioxide and at least one metal oxide selected from the group consisting of copper oxides, cobalt oxides, iron oxides and silver oxides.
The third component may be a blend of two or more.
Furthermore, the present invention provides an air bag system that contains the composition mentioned above in the air bag system as the gas generant; that is, a gas generant in an air bag system is improved by the present invention.
Among the preferable compositions, the following compositions are listed: a composition wherein the third component is (1) mentioned above and has a specific surface area from 100 m
2
/g to 300 m
2
/g; a composition wherein (1) in the third component is contained in an amount of 1 through 40 or 1 through 30 percent by weight of the composition; a composition wherein the third component is (2) mentioned above and has a specific surface area from 1.5 m
2
/g to 100 m
2
/g; a composition wherein the third component is (2) having an average particle size not more than 5 microns; a composition wherein the third component is (2) having an average particle size from 0.5 microns to 5 microns; a composition wherein (2) in the third component is contained in an amount of 1 through 40 percent by weight of the composition; a composition wherein (3) mentioned above in the third component is contained in an amount of 1 through 40 or 1 through 30 percent by weight of the composition; a composition wherein the metal oxide is at least one selected from the group consisting of CuO, Cu
2
O, Co
3
O
4
, Fe
2
O
3
and Ag
2
O; a composition wherein the third component is (4) mentioned above and the ratio of manganese dioxide to the metal oxide by weight is 0.2 through 50; a composition wherein (4) in the third component is contained in an amount of 1 through 40 percent by weight of the composition; a composition wherein the nitrogen-containing organic compound is at

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