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Gas generant

Gas generant description/claims

This application is a continuation-in-part of co-pending U.S. application Ser. No. 11/542,302 and claims the benefit thereof.

The present invention relates generally to gas generating systems, and to gas generant compositions employed in gas generator devices for automotive restraint systems, for example.

The present invention relates to gas generant compositions that upon combustion produce a relatively small amount of solids and a relatively abundant amount of gas. It is an ongoing challenge to reduce the amount of solids and increase the amount of gas thereby decreasing the filtration requirements for an inflator. As a result, the filter may be either reduced in size or eliminated altogether thereby reducing the weight and/or size of the inflator.

An equally important challenge is to manufacture gas generants that exhibit relatively low sensitivity with regard to impact, friction, or electrostatic discharge stimuli.

Yet another challenge with gas generant compositions that produce relatively small amounts of solids, sometimes known as “smokeless” compositions, is that not all non-metallic constituents contribute to stable ballistic performance when subjected to environmental conditioning. In fact, one fuel that is favored because of its propensity to produce all or mostly gas is bis-1(2)H-tetrazol-5-yl)-amine (BTA-1NH3) and derivatives thereof. When combined with other gas generant constituents such as an oxidizer, and formed into a gas generant composition, this fuel contributes to greater amounts of gas upon combustion of the composition.

Furthermore, some gas generants, such as those formed by the combination of the monoammonium salt of bis-(1(2)H-tetrazol-5-yl)-amine (BTA-1NH3) with ammonium nitrate or phase stabilized ammonium nitrate (PSAN) exhibit many favorable qualities, such as high gas production, and therefore are useful in automotive passenger restraints. BTA-1NH3 is a high energy, high-nitrogen fuel that exhibits excellent stability and very favorable levels of hygroscopicity and sensitivity. The properties of ammonium nitrate and potassium nitrate when co-precipitated include minimal or no sensitivity when subjected to impact, friction, and electrostatic discharge stimuli. One concern with PSAN-containing propellants is that they exhibit less-than desirable behavior with regard to ballistic properties, particularly with respect to thermal shock conditioning when ballistically tested at elevated temperatures.

It is also required that airbag inflators be subjected to environmental conditioning, such as high temperature heat aging, thermal aging, thermal cycling, thermal shock, humidity cycling, and so forth. It is therefore desirable to have a gas generant and inflator system that performs the same regardless of conditioning. The present invention provides a solution to many of these possibilities.

Many gas generants are moisture-sensitive due to the inherent hygroscopicity of many common components including oxidizers such as nitrate salts, naturally occurring hydrates of fuels such as 5-aminotetrazole, bis-(1(2)H-tetrazol-5-yl)-amine, carboxymethyl cellulose and its salts, clays, and others. It is therefore imperative that these types of gas generants are kept dry for repeatable performance.

Moisture or volatile contaminants can be introduced to gas generating systems in many ways. A few examples include: improperly processed gas generants that contain excess moisture; moisture introduced to the system via humidity during assembly; moisture introduced to the system during environmental conditioning such as high humidity cycling or salt spray; moisture introduced to the system via decomposition of materials within the system such as auto-ignition materials, seals, gaskets, greases, and other gas generator constituents. The use of certain additives, preferably zeolites such as molecular sieves, calcium sulfate (Drierite™), or calcium oxide can minimize, and in some cases eliminate any problems that may occur in these situations.

Accordingly, it would be an improvement in the art to provide compositions that contain BTA-1NH3 that contribute to a “smokeless” gas generant composition, or one that when combusted produces 90% or more of gas as a product, while yet passing thermal cycling standards.

The above-referenced concerns are resolved by gas generators containing gas generating compositions including a fuel such as BTA-1NH3 and an oxidizer such as phase stabilized ammonium nitrate. The gas generator contains a separate additive or contaminant scavenger such as molecular sieves. The separate additive is an adsorbent or absorbent contained within the gas generator to facilitate scavenging of any moisture or volatiles as it evolves or occurs within the propellant bed. It has been found that the addition of adsorbents or absorbents such as molecular sieves has resulted in compositions that are now able to withstand typical thermal cycling/thermal shock tests.

The use of certain additives, preferably zeolites such as molecular sieves, calcium sulfate (Drierite™), or calcium oxide can minimize, and in some cases eliminate contaminants occurring within the inflator over time. In particular, molecular sieves function to better retain moisture and other contaminants in the presence of relatively high temperatures such as 107 degrees Celsius, thereby ensuring predictable performance of associated inflators. Stated another way, molecular sieves retain moisture/contaminants at elevated temperatures at least as high as 107 degrees Celsius thereby facilitating consistent performance predictability of inflators incorporating one or more types of these additives.

Accordingly, the present invention includes a gas generator containing a gas generating composition and a scavenging additive that is provided within the gas generator in heterogenous relationship with the gas generating composition, and in vapor/gaseous communication therewith.

In further accordance with the present invention, a gas generator and a vehicle occupant protection system incorporating the gas generant composition and scavenging additive are also included.

• Provisional Patent
• Utility Patent

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