Explosive and thermic compositions or charges – Containing inorganic nitrogen-oxygen salt
Reexamination Certificate
2000-11-17
2003-08-05
Carone, Michael J. (Department: 3641)
Explosive and thermic compositions or charges
Containing inorganic nitrogen-oxygen salt
C149S046000
Reexamination Certificate
active
06602365
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to gas generation such as involved in the inflation of automotive inflatable restraint airbag cushions and, more particularly, to gas generant materials which contain metal complexes of guanylurea nitrate.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an “airbag cushion,” that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Such systems typically also include one or more crash sensors mounted on or to the frame or body of the vehicle to detect sudden decelerations of the vehicle and to electronically trigger activation of the system. Upon system actuation, the cushion begins to be inflated in a matter of no more than a few milliseconds with gas produced or supplied by a device commonly referred to as an “inflator.”
Gas generant compositions commonly utilized in the inflation of automotive inflatable restraint airbag cushions have previously most typically employed or been based on sodium azide. Such sodium azide-based compositions, upon initiation, normally produce or form nitrogen gas. While the use of sodium azide and certain other azide-based gas generant materials meets current industry specifications, guidelines and standards, such use may involve or raise potential concerns such as involving the safe and effective handling, supply and disposal of such gas generant materials.
In view thereof, significant efforts have been directed to minimizing or avoiding the use of sodium azide in automotive airbag inflators. Through such efforts, various combinations of non-azide fuels and oxidizers have been proposed for use in gas generant compositions. These non-azide fuels are generally desirably less toxic to make and use, as compared to sodium azide, and may therefore be easier to dispose of and thus, at least in part, found more acceptable by the general public. Further, non-azide fuels composed of carbon, hydrogen, nitrogen and oxygen atoms typically yield all gaseous products upon combustion. As will be appreciated by those skilled in the art, fuels with high nitrogen and hydrogen contents and a low carbon content are generally attractive for use in such inflatable restraint applications due to their relatively high gas outputs (such as measured in terms of moles of gas produced per 100 grams of gas generant material).
In addition to low toxicity and high gas outputs, fuel components for use in gas generant materials desirably are relatively inexpensive, thermally stable (i.e., desirably decompose only at temperatures greater than about 160° C.), and have a low affinity for moisture.
Oxidizers known in the art and commonly employed in such gas generant compositions are metal oxides or salts of oxygen-bearing anions (e.g., nitrates, perchlorates, etc.). During combustion, the metallic component of such oxidizers, however, typically ends up as a solid. Thus, the amount of oxidizer included in such gas generant materials can significantly effect the amount of gas produced upon combustion of the gas generant material. In view thereof, efforts have been directed to reducing or minimizing the amount of oxidizer required in such gas generant formulations. One approach used with at least some success in reducing or minimizing the required amount of oxidizer involves the incorporation of oxygen in greater relative amounts in the fuel component of the gas generant composition. Thus, desirable fuels for use in such gas generant compositions may preferably include a relatively high content of oxygen.
An additional complication results from the fact that at least certain transition metal-containing compounds or materials, such as commonly employed transition metal-containing oxidizers, may undesirably react with other composition materials to form metallic derivatives of a highly explosive nature and such as are unsuited for various general uses such as in an automotive inflatable restraint system or a gas generating device used in such a safety system. Thus, when including transition metal-containing compounds or materials in such formulations care is required to ensure that the formulation does not also include a material which may undesirably react therewith to form such explosive metallic derivatives.
U.S. Pat. No. 6,024,812 discloses propellant formulations which include nitroaminoguanidine as a main component, a secondary fuel or explosive ingredient such as dicyandiamidine nitrate (also known as “guanylurea nitrate”) and an oxidizing agent. This patent discloses that oxidizing agents useful in the propellant formulation thereof include nitrates of alkali and alkaline earth elements, perchlorates of alkali and alkaline earth elements, ammonium nitrate, ammonium perchlorate or mixtures of these compounds.
Those skilled in the art will appreciate that nitroaminoguanidine exists in a form which has acid characteristics and can form metallic derivatives of a highly explosive nature. Thus, compounds or materials which contain a transition metal are incompatible with nitroaminoguanidine in known automotive inflatable restraint system gas generation applications.
In addition to the above-identified desirable properties and characteristics, gas generant materials for use in automotive inflatable restraint applications must be sufficiently reactive such that upon the proper initiation of the reaction thereof, the resulting gas producing or generating reaction occurs sufficiently rapidly such that a corresponding inflatable airbag cushion is properly inflated such as to provide impact protection to an associated vehicle occupant. In general, the burn rate for a gas generant composition can be represented by the equation (1), below:
Rb=Bp
n
(1)
where,
Rb
=
burn
rate
(
linear
)
B
=
constant
P
=
pressure
n
=
pressure
exponent
,
where
the
pressure
exponent
is
the
slope
of
the
plot
of
the
log
of
pressure
along
the
x
-
axis
versus
the
log
of
the
burn
rate
along
the
y
-
axis
Guanidine nitrate (CH
6
N
4
O
3
) is a non-azide fuel with many of the above-identified desirable fuel properties or characteristics. For example, guanidine nitrate is commercially available, relatively low cost, non-toxic, provides excellent gas output due to a high content of nitrogen, hydrogen and oxygen and a low carbon content and has sufficient thermal stability to permit spray dry processing. As a result, guanidine nitrate has found wide use in the automotive airbag industry.
Unfortunately, guanidine nitrate suffers from a lower than may be desired bum rate. Further, guanidine nitrate may, when combined with certain other common gas generant formulation components, undesirably form eutectic mixtures. The lower melting points associated with such eutectic mixtures may in turn exacerbate concerns regarding the aging characteristics or properties of the gas generant formulation.
Thus, there remains a need and a demand for an azide-free gas generant material which may more effectively overcome one or more of the problems or shortcomings described above. In particular, there is a need and a demand for gas generant materials which, while effective in overcoming one or more of the problems or shortcomings identified above, also provides or results in a desirably rapid burn rate as required or desired for particular applications, while
Autoliv ASP Inc.
Brown Sally J.
Carone Michael J.
Erickson James D.
Felton Aileen B.
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