Autoignition Compositions

Abstract

A nitrogen-free gas generator 10 includes an autoignition composition that contains an alkali metal chlorate such as potassium chlorate as an oxidizer, a carboxylic acid such as DL tartaric acid as a fuel, and a desiccant in operable communication therewith. Gas generating systems 180 such as vehicle occupant protection systems 180, containing the gas generator 10, are also provided.

Description

TECHNICAL FIELD

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

BACKGROUND OF THE INVENTION

The present invention relates to autoignition compositions that upon ignition provide the flame front and pressure front necessary to safely ignite gas generant compositions in combustible communication therewith. As known in the art, gas generators are typically provided with an autoignition composition that in the event of a fire, ignites responsive to a desired threshold temperature. As a result, the gas generant is ignited prior to melting for example, thereby safely igniting the main gas generant composition to inhibit or prevent the likelihood of an explosive event once the gas generant begins to combust.

The use of potassium chlorate within an autoignition composition has been considered given the autoignition properties of this oxidizer. Furthermore, carboxylic acid in combination with potassium chlorate typically provides a desired autoignition temperature of 200 degrees Celsius or less. Nevertheless, these types of compositions sometimes decompose given their hygroscopicity or tendency to absorb moisture. Unsuccessful attempts have been made to inhibit moisture retention or uptake within these compositions without adversely affecting the desired autoignition temperature.

SUMMARY OF THE INVENTION

The above-referenced concerns are resolved by gas generating systems including an autoignition composition containing an alkali metal Chlorate, such as potassium chlorate, a carboxylic acid as a fuel, and a desiccant or moisture retaining material combined with the oxidizer and fuel. Other constituents including extrusion aids, such as flamed silica and/or graphite, may be included in relatively small amounts.

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

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view showing the general structure of an inflator in accordance with the present invention;

FIG. 2 is a schematic representation of an exemplary vehicle occupant restraint system containing a gas generant composition in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present compositions contain an alkali metal chlorate oxidizer such as potassium chlorate at about 25-75%. and more preferably about 40-60%, by weight of the total composition, a carboxylic acid as a fuel at about 25-75%, and more preferably about 30-40%, by weight of the total composition, and a desiccant at about 5-35%, and more preferably about 10-30%, by weight of the total composition. Extrusion aids or processing additives such as graphite or fumed silica may be added in relatively smaller amounts, such as 0.1-2% by weight of the total composition for example. It has been found that the decomposition typically identified in other potassium chlorate/carboxylic acid compositions that are employed as autoignition compositions is mitigated or eliminated by including a desiccant in the autoignition composition.

The present compositions contain a chlorate such as an alkali, alkaline earth, or transitional metal chlorate; a fuel selected from DL-tartaric acid, carboxylic or dicarboxylic acids, or compounds having at least one —COOH— group; a second fuel selected from an azole including tetrazoles, triazoles, and furazans; an oxidizer selected from metal and nonmetal nitrates or other known oxidizers not containing a perchlorate. The carboxylic acid will have a primary hydrogen or PKA less than or equal to 3.

In one embodiment, the total fuel constituent including the carboxylic fuel and the second fuel is provided at about 20-45% by weight of the total composition; the oxidizer constituent is provided at about 30-50% by weight of the total composition; and the potassium chlorate or metal chlorate is provided at about 10-20% by weight of the total composition, wherein the weight percent of the chlorate is separately calculated from that of the oxidizer. The composition may be formed by wet or dry mixing the constituents in a granulated form in a known manner, and then palletizing or otherwise limning the composition for further use. The constituents may be provided by Fisher Chemical, Aldrich Chemical, GFS, and other known suppliers.

Carboxylic acids may be selected from the group including tartaric acid and its isomers, succinic acid, glutamic acid, adipic acid and mucic acid, and mixtures thereof DL-tartaric acid is particularly preferred.

An exemplary formulation is provided that functions as s booster and an autoignition composition. The formulation utilizes 5-aminotetrazole, DL-tartaric acid, strontium nitrate, and potassium chlorate. The propellant formed from these constituents results in an approximate 67% gas yield. The impact sensitivity of this formulation has an HD50 of 11.5 inches.

It will be appreciated that in further accordance with the present invention, gas generators made as known in the art and also vehicle occupant protection systems manufactured as known in the art are also contemplated, As such, autoignition compositions of the present invention are employed in gas generators, seat belt assemblies, and/or vehicle occupant protection systems, all manufactured as known in the art.

Carboxylic acids may be selected from the group including tartaric acid and its isomers, succinic acid, glutamic acid, adipic acid, and mucic acid, and mixtures thereof. DL-tartaric acid is particularly preferred. The present compositions may also include processing additives such as flow agents and lubricants common in the art such as fumed silica and graphite. The desiccant may be any material that will absorb or react with water to remove it from the other components in the autoignition mixture. Exemplary desiccants are activated or hydrated calcium sulfate (DRIERITE®), clay, silica gel, calcium oxide, and zeolites or molecular sieves. Zeolites, as shown in the tables, are particularly effective in assuring an autoignition temperature at or below 200 C, and also in minimizing the mass differential of an autoignition composition before and after heat aging as defined below. All compositional constituents are available from Sigma-Aldrich, or other known suppliers.

The oxidizer generally contains potassium chlorates, but may also contain one or more other alkali metal chlorates.

Accordingly, autoignition compositions of the present invention typically perform at optimum levels, even after standard heat aging of over 400 hours.

It will be appreciated that in further accordance with the present invention, gas generators made as known in the art and also vehicle occupant protection systems manufactured as known in the art are also contemplated, As such, autoignition compositions of the present invention are employed in. gas generators, seat belt assemblies, and/or vehicle occupant protection systems, all manufactured as known in the art.

In yet another aspect of the invention, the present compositions may be employed within a gas generating system. For example, schematically shown in FIG. 2, a vehicle occupant protection system made in a known way contains crash sensors in electrical communication with an airbag inflator in the steering wheel, and also with a seatbelt assembly, The gas generating compositions of the present invention may be employed in both subassemblies within the broader vehicle occupant protection system or gas generating system. More specifically, each gas generator employed in the automotive gas generating system may contain a gas generating composition as described herein.

Extrusion aides may be selected from the group including, talc, graphite, borazine [(BN)₃], boron nitride, fumed silica, and fumed alumina. The extrusion aid preferably constitutes 0-10% and more preferably constitutes 0-5% of the total composition.

The compositions may be dry or wet mixed using methods known in the art. The various constituents are generally provided in particulate form and mixed to form a uniform mixture with the other gas generant constituents.

It should be noted that all percents given herein are weight percents based on the total weight of the gas generant. composition. The chemicals described herein may be supplied by companies such as Aldrich Chemical Company for example.

As shown in FIG. 1, an exemplary nitrogen-free inflator incorporates a dual chamber design to tailor the force of deployment an associated airbag. In general, an inflator containing a primary gas generant 12 and an autoignition composition 14 formed as described herein, may be manufactured as known in the art, U.S. Pat. Nos. 6,422,601, 6,805,377, 6,659,500, 6,749,219, and 6,752,421 exemplify typical airbag inflator designs and are each incorporated herein by reference in their entirety.

Referring now to FIG. 2, the exemplary nitrogen-free inflator 10 described above may also be incorporated into an airbag system 200. Airbag system 200 includes at least one airbag 202 and an inflator 10 containing a gas generant composition 12 in accordance with the present invention, coupled to airbag 202 so as to enable fluid communication with an interior of the airbag. Airbag system 200 may also include (or be in communication with) a crash event sensor 210. Crash event sensor 210 includes a known crash sensor algorithm that signals actuation of airbag system 200 via, for example, activation of airbag inflator 10 in the event of a collision.

Referring again to FIG. 2, a nitrogen-free airbag system 200 may also be incorporated into a broader, more comprehensive nitrogen—free vehicle occupant restraint system 180 including additional elements such as a safety belt assembly 150. FIG. 2 shows a schematic diagram of one exemplary embodiment of such a restraint system. Safety belt assembly 150 includes a safety belt housing 152 and a safety belt 100 extending from housing 152. A safety belt retractor mechanism 154 (for example, a spring-loaded mechanism) may be coupled to an end portion of the belt. In addition, a safety belt pretensioner 156 containing propellant 12 and autoignition 14 may he coupled to belt retractor mechanism 154 to actuate the retractor mechanism in the event of a collision. Typical seat belt retractor mechanisms which may be used in conjunction with the safety belt embodiments of the present invention are described in U.S. Pat. Nos. 5,743,480, 5,553,803, 5667,161, 5,451,008, 4,558,832 and 4,597,546, each incorporated herein by reference. Illustrative examples of typical pretensioners with which the safety belt embodiments of the present invention may be combined are described in U.S. Pat. Nos. 6,505,790 and 6,419,177, incorporated herein by reference.

Safety belt assembly 150 may also include (or be in communication with) a crash event sensor ¹⁵⁶ (for example, an inertia sensor or an accelerometer) including a known crash sensor algorithm that signals actuation of belt pretensioner 156 via, for example, activation of a pyrotechnic igniter (not shown) incorporated into the pretensioner. U.S. Pat. Nos. 6,505,790 and 6,419,177, previously incorporated herein by reference, provide illustrative examples of pretensioners actuated in such a manner.

It should be appreciated that safety belt assembly 150, airbag system 200, and more broadly, vehicle occupant protection system 180 exemplify but do not limit gas generating systems contemplated in accordance with the present invention.

The present description is for illustrative purposes only, and should not be construed to limit the breadth of the present invention in any way. Thus, those skilled in the art will appreciate that various modifications could be made to the presently disclosed embodiments without departing from the scope of the present invention as defined in the appended claims.

Claims

1. A nitrogen-free gas generator comprising: a nitrogen-free auto-ignition composition consisting essentially of an alkali metal chlorate as an oxidizer provided at about 25-75 weight percent, and a carboxylic acid as a fuel provided at about 25-75 weight percent, said percentages stated by weight of the total composition; anda desiccant in operable communication with said nitrogen-free auto-ignition composition,wherein said nitrogen-free auto-ignition composition auto-ignites at a temperature equal to or below 200 C, and, wherein said nitrogen-free auto-ignition composition when heat aged for 648 hours at 107 C does not react with aluminum in a sealed container.

2. The nitrogen-free gas generator of claim 1 wherein said desiccant is mixed into said composition at about 10-35 weight percent of the total composition, said desiccant selected from the group consisting of zeolite, calcium oxide, and silica.

3. The nitrogen-free gas generator of claim 1 wherein said desiccant is in vapor communication with, but physically separated from, said composition, and said desiccant is provided in amounts resulting in a mass differential of about −5.0 to 5.0% of the composition after heat aging at 107 C for 400 hours.

4. The nitrogen-free gas generator of claim I wherein said composition contains an extrusion aid provided at about 0.1-10 weight percent of the total gas generant composition.

5. The nitrogen-free gas generator of claim 4 wherein said extrusion aid is selected from graphite, fumed silica, and mixtures thereof.

6. The nitrogen-free gas generator of claim 1 wherein said alkali metal chlorate is potassium chlorate.

7. The gas nitrogen-free generator of claim 1 wherein said carboxylic acid is selected from tartaric acid and its isomers, succinic acid, glutamic acid, adipic acid, and mucic acid, and mixtures thereof.

8. The nitrogen-free gas generator of claim 1 wherein said carboxylic acid is DL-tartaric acid.

9. A nitrogen-free gas generating system comprising: a gas generator comprising a composition, said composition containing an all metal chlorate as an oxidizer provided at about 25-75 weight percent, and said composition further containing a carboxylic acid as a fuel provided at about 25-75 weight percent, said percentages stated by weight of the total gas generant composition; anda desiccant in operable communication with said composition.

10. The nitrogen-free gas generating system of claim 9 wherein said desiccant is mixed into said composition at about 10-35 weight percent of the total composition.

11. The nitrogen-free gas generating system of claim 9 wherein said desiccant is in vapor communication with, but physically separated from, said composition.

12. The nitrogen-free gas generating system of claim 9 wherein said system is a vehicle occupant protection system.

13. A nitrogen-free gas generator comprising: a nitrogen-free auto-ignition composition containing potassium chlorate as an oxidizer provided at about 25-75 weight percent, and DL-tartaric acid as a fuel provided at about 25-75 weight percent, said percentages stated by weight of the total composition; anda desiccant in operable communication with said composition,wherein said nitrogen-free composition when aged for 646 hours at 107 C does not react with aluminum within a sealed container.

14. The nitrogen-free gas generator of claim 13 wherein said nitrogen-free composition further comprises zeolite.

15. A nitrogen-free gas generator comprising: a nitrogen-free auto-ignition composition consisting of an alkali metal chlorate as an oxidizer provided at about 25-75 weight percent, and one or more carboxylic acids as a fuel provided at about 25-75 weight percent, said percentages stated by weight of the total composition;anda zeolite in vapor communication with said composition.