US20050161135A1

US20050161135A1 - Auto-igniting pyrotechnic booster composition

Info

Publication number: US20050161135A1
Application number: US11/044,670
Authority: US
Inventors: Graylon Williams; Sean Burns; Paresh Khandhadia
Original assignee: Automotive Systems Laboratory Inc
Current assignee: Automotive Systems Laboratory Inc
Priority date: 2004-01-28
Filing date: 2005-01-27
Publication date: 2005-07-28
Also published as: JP2007523036A; WO2005072401A2; WO2005072401A3; EP1727776A2

Abstract

The present invention generally relates to auto-ignition/booster compositions for inflators of occupant restraint systems, for example. An exemplary auto-ignition composition in accordance with the present invention includes a metal chlorate, an auto-ignition fuel selected from the group including sugars and orgainic acids, and a nitrogen-containing secondary fuel.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 60/539,798 filed on Jan. 28, 2004.

BACKGROUND OF THE INVENTION

Auto-ignition materials in automotive air bag inflators allow the device to safely deploy in the event of a fire. By including an auto-ignition composition the likelihood of a safety hazard resulting from the bursting of an inflator is substantially reduced.
On the other hand, pyrotechnic booster compositions raise the operating pressure of a pressure vessel or inflator prior to ignition of the main or primary gas generant. As a result, ready ignition of the primary gas generant is facilitated along with sustained combustion thereof.
Accordingly, most inflators or gas generators for vehicle occupant protection systems, for example, typically include an auto-ignition composition juxtaposed next to a discrete booster composition. In the event of a fire, the auto-ignition composition ignites to thereby ignite the booster composition which thereby ignites the main gas generant. As such, the fire hazard is substantially mitigated.
An ongoing challenge is to continue simplification of gas generator manufacturing processes thereby resulting in lower overall costs. As such, combining the auto-ignition and booster compositions into one composition would simplify the manufacture and assembly of a gas generator, one employed in a vehicle occupant protection system for example.

SUMMARY

A pyrotechnic formulation including an auto-ignition fuel, an auto-ignition oxidizer, a booster fuel, a booster oxidizer, and an optional fuel/binder such as silicone that self-ignites at a specific design temperature or temperature range. The pyrotechnic also serves as a booster for pyrotechnic gas generators used as automotive gas generators or air bag inflators. Accordingly, the present compositions may function both as an auto-ignition pyrotechnic and as a booster charge pyrotechnic thereby eliminating the need for two separate compositions in the inflator.
Furthermore, the booster composition also propagates ignition of the main gas generation through flame and/or heat propagation. The sequence of events for the auto-ignition of an inflator includes the ignition of the auto-ignition material, which subsequently ignites the booster material, which in turn ignites the main gas generating pyrotechnic. This invention eliminates the need for individual auto-ignition and booster pyrotechnics, and replaces them with one single pyrotechnic component, greatly simplifying the inflator design, and improving inflator performance.
By integrating the auto-ignition and booster compounds into one composition, the single auto-ignition/booster grain can be molded or pressed to fit the desired inflator design. This component would be larger than a single auto-ignition tablet or grain, whereby a greater surface area facilitates increased heat conduction relative to primary gas generant and relative to the auto-ignition function in case of a fire. This single pyrotechnic also enhances the simplicity of the inflator design.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an inflator assembly in accordance with the present invention; and
FIG. 2 is a schematic view of a gas generating system and a vehicle occupant restraint system incorporating the composition of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An auto-ignition component of the present invention includes a fuel, an oxidizer and an optional fuel/binder that self-ignites at a specific temperature. A fuel is preferably selected from sugars such as d-glucose and organic acids such as tartaric acid at about 15-45 weight percent of the composition. Exemplary organic acids include the various enantiomers of tartaric acid, malic acid, succinic acid, diglycolic acid, malonic acid, trans-glutaconic acid, adipic acid, mucic acid, 2,2-Bis(hydroxymethyl) propionic acid, citric acid, phenylmalonic acid, and quinic acid. Exemplary enantiomers of this group include D-tartaric acid, DL-tartaric acid, Meso-tartaric acid, D-glutamic acid, and D-quinic acid. The organic acid should preferably have a melting point ranging from about 125 to about 250° C. and pass a heat aging test at 107° C. for 400 hours. Typically, the material to be heat aged may be sealed in a glass vial and placed in an oven for 400 hours at 107° C. Or, the composition may be included within an inflator, and the inflator may be placed in an oven at 107° C. for 400 hours. Afterwards, the material may be heated, by induction or by heat gun for example, to determine the auto-ignition temperature of the sample. Or, the inflator may be heated at a ramp rate of about 14° C. per minute and evaluated for the safe deployment thereof. The auto-ignition temperature of the fuel is preferably about 110 to 250° C. as determined by differential scanning calorimetry/thermogravimetric analysis (DSC/TGA).
An auto-ignition component oxidizer contains a metal chlorate salt at about 15-80 weight percent of the composition, preferably potassium chlorate. The metal chlorate salt may be selected from the group including alkali, alkaline earth, and transitional metal chlorates, and mixtures thereof.
A preferred composition includes a fuel/binder formed from silicone at 10-35% by weight of the composition. The term “silicone” as used herein will be understood in its generic sense. Hawley describes silicone (organosiloxane) as any of a large group of siloxane polymers based on a structure consisting of alternate silicon and oxygen atoms with various organic radicals attached to the silicon:

Or, silicone can be more generically represented as shown in Formula 2 (but not thereby limited):

Note, “n” in the Formulas indicates a multiple of the polymeric group or portion of the molecule given within the brackets, to include the organic groups attached to the silicon.
Exemplary silicones include those disclosed in U.S. Pat. Nos. 5,589,662, 5,610,444, and 5,700,532, and, in TECHNOLOGY OF POLYMER COMPOUNDS AND ENERGETIC MATERIALS, Fraunhofer-Institut fur Chemische Technologie (ICT), 1990, each reference and document herein incorporated by reference. Silicone may be provided by any known supplier such as Shin-Etsu Silicones of America, Inc. of Akron, Ohio. It will be appreciated that curing and addition of the silicone is done in accordance with manufacturer instructions.
A most preferred composition contains by weight percent of the composition silicone at 20%, potassium chlorate at 20%, tartaric acid at 20%, and potassium perchlorate at 40%. It is also preferred that the particle size of the gas generant constituents be milled or sized to about 25 microns, although particles of other sizes may also be employed. A ball grinder or vibratory mill such as an M18-5 Sweco vibratory mill may be used to mill the constituents.
A booster component of the present invention contains a fuel and an oxidizer. In general, many known gas generant compositions, for use within vehicle occupant protection systems for example, may be employed as the booster component of the present compositions. Known gas generant compositions as described in U.S. Pat. Nos. 5,035,757, 6,210,505, 6,287,400, 6,074,502, 5,872,329, 5,756,929, and 5,531,941, all incorporated by reference, exemplify booster gas generants that function to raise the pressure of an associated pressure vessel in a known manner, thereby propagating combustion of a primary gas generant bed.
The booster component fuel may therefore be selected from the group of fuels including nitrogen-containing fuels, guanidines, aminoguanidines, tetrazoles, triazoles, metal and nonmetal salts of tetrazoles and triazoles, and mixtures thereof. The booster component oxidizer may therefore be selected from metal and nonmetal salts of chlorates, perchlorates, nitrates, nitrites, permanganates, oxides, and mixtures thereof. The metal salts may be selected from alkali, alkaline earth, and transitional metal salts, and mixtures thereof. The booster fuel, including silicone if desired, preferably represents about 0.1-75 weight percent of the booster component. The booster oxidizer represents 0-60 weight percent of the booster component. A preferred booster oxidizer is potassium perchlorate. It should be noted that the auto-ignition oxidizer when properly milled and when provided in relatively larger amounts, may provide a sufficient oxygen balance to provide an oxidizing effect on both the auto-ignition fuel and on the booster fuel. In that case, the booster oxidizer is not necessary. It should also be noted that the weight percents characterized for both the auto-ignition and booster components are relative to the total composition once both of these components are combined.
When formulating the auto-ignition/booster compositions of the present invention, each constituent of each component is first granulated if provided in solid form. As such, the auto-ignition component may be formed by mixing granulated potassium chlorate with a granulated sugar and/or granulated organic acid. A planetary mixer may be employed to provide substantially uniform or substantially homogeneous mixtures of the various granules. It will be appreciated that tailoring of the burn rates or ballistic properties may be accomplished through iteratively determining the desired average granular size for each constituent. Any other constituents known for their utility in auto-ignition/gas generant compositions may also be incorporated into the auto-ignition component in granulated form. As such, ballistic modifiers, coolants, and other useful additives could also be provided in known effective amounts or in known effective weight percents.
The booster component may be formulated in the same way and therefore the fuel and oxidizer may be granulated and then mixed as described above. Again, other constituents known for their utility in auto-ignition/gas generant compositions such as ballistic modifiers and coolants may also be provided in known effective amounts or in known effective weight percents.
Once each component is formulated, the auto-ignition and booster components may be mixed together as dry granulated solids to result in substantially uniform or homogeneous mixtures. It should be appreciated that the constituents of the present compositions may be mixed together in one batch rather than mixing together in two separate auto-ignition and booster batches respectively. The order of addition of each constituent to the ongoing mixture is not critical so long as a substantially uniform mixture results and the appropriate weight percents of all of the constituents are maintained.
Accordingly, the gas generant constituents may be mixed by known methods. Or, in yet another aspect of the invention, the auto-ignition fuel such as tartaric acid or d-glucose may first be coated with silicone and then preferably dry mixed with the other auto-ignition and booster constituents. The silicone may be cured or uncured prior to mixing with other compositional constituents. The resulting homogeneous mixtures are then pressed into tablets or other useful shapes thereby providing intimate contact with the various constituents. By coating the auto-ignition fuel with silicone, an insulating barrier is then integrated within the gas generant composition between the auto-ignition fuel, and the auto-ignition/oxidizer such as potassium chlorate. Once auto-ignition of the auto-ignition fuel and auto-ignition oxidizer (potassium chlorate) begins, then combustion of the booster component, or silicone and potassium perchlorate is initiated. The silicone coating of the auto-ignition fuel inhibits the Mallard or carmelizing reaction of the fuel, glucose for example, whereby more heat is required for auto-ignition of the auto-ignition fuel thereby improving repeatable performance combustion characteristics. The gas generant constituents of the present invention may be supplied by well known suppliers such as Aldrich Chemical Company of Milwaukee, Wis.
In yet another aspect of the invention, if uncured silicone is added to a mixture of the dry granulated constituents of both the auto-ignition and booster components, an extrudable or thixotropic mixture may be produced. The uncured mixture may then be applied to any desired surface within an associated gas generator within a vehicle occupant protection system, for example, thereby simplifying gas generator manufacture. The extruded mixture must, however, be applied to a surface that remains in thermodynamic communication with the temperature outside of the pressure vessel or inflator, and, also fluidly or thermodynamically communicates with the primary gas generant upon auto-ignition of the extruded mixture.
Typical inflator assembly methods require the formation of an auto-ignition repository within the inflator structure. Auto-ignition tablets may then be placed within the repository and sealed or enclosed within the repository with a taped seal. A booster composition may then be placed proximate to the auto-ignition composition thereby facilitating thermodynamic communication between the two compositions upon auto-ignition of the auto-ignition composition.
In contrast, extrudable auto-ignition/booster mixtures containing uncured silicone may be applied directly to a desired surface that interfaces with the primary gas generant, and then cured thereafter in accordance with manufacturer instructions. As such, the surface area of the auto-ignition composition in contact with the desired surface may be increased and/or optimized to provide a more effective interface to increase and/or tailor thermodynamic communication with the primary gas generant chamber. When compared to typical inflator assembly, the present auto-ignition/booster compositions provide an improved method of assembly thereby resulting in ease of assembly and reduced manufacturing costs.
Alternatively, an auto-ignition/booster composition containing cured silicone will exhibit resilient and compressible characteristics, thereby permitting placement of the composition in any effective area within the inflator that will accommodate impingement of the composition. Stated another way, a separate repository for the auto-ignition composition need not be provided so long as an area within the inflator may be employed to provide an interference fit for the compressible auto-ignition/booster charge. All other aspects of inflator manufacture may be accommodated as known in the art.
Compositions formulated in accordance with the present invention must auto-ignite at about 150 degrees Celsius or less, must function as a booster charge, and must inhibit the production of noxious gases. In essence, the compositions of the present invention burn relatively hotter and therefore the gas pressure is increased. Accordingly, less gas is needed to pressurize the combustion chamber. Unlike certain known auto-ignition compositions, preferred compositions of the present invention also survive standard heat aging testing at 107 degrees Celsius for 400 hours.
As shown in FIG. 1, an inflator incorporating any of the compositions described above may be incorporated into a gas generating system 200, as exemplified in FIG. 2. At least a portion of a primary gas generant 19 is juxtaposed next to composition 17, thereby facilitating thermodynamic communication and/or fluid flow between both compositions upon auto-ignition of the composition 17. Gas generating system 200 includes at least one airbag 202 and an airbag inflator 10 coupled to airbag 202 so as to enable fluid communication with an interior of the airbag for inflating the airbag in the event of a collision. Examples of inflators which may be incorporated into gas generating system 200 are described in U.S. Pat. Nos. 6,764,096, 6,659,500, 6,422,601, 6,752,421 and 5,806,888, both incorporated herein by reference. The inflator includes an embodiment of composition 17 as described above for use within the inflator. Gas generating system 200 may also be in communication with a crash event sensor 210 including a known crash sensor algorithm that signals actuation of airbag system 200 via, for example, activation of airbag inflator 15 in the event of a collision.
Referring to FIG. 2, gas generating system 200 may also be incorporated into a broader, more comprehensive 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 in accordance with the present invention extending from housing 152. A safety belt retractor mechanism 154 (for example, a spring-loaded mechanism) may be coupled to an end portion 153 of the belt. In addition, a safety belt pretensioner 156 may be 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, 5,667,161, 5,451,008, 4,558,832, and 4,597,546, 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 system 150 may be in communication with a crash event sensor 158 (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. Again, composition 17 may also be employed within a micro gas generator formed in a known manner within pretensioner 156.
It will be understood that the foregoing description of an embodiment of the present invention is for illustrative purposes only. As such, the features herein disclosed are susceptible to a number of modifications commensurate with the abilities of one of ordinary skill in the art, none of which departs from the scope of the present invention as defined in the appended claims.

Claims

1. A gas generating system comprising a composition, the composition comprising:

a metal chlorate;

a first fuel selected from the group consisting of sugars and organic acids; and

a nitrogen-containing secondary fuel.

2. The gas generating system of claim 1 wherein said composition comprises silicone as a fuel/binder at about 10-30 weight percent of the composition.

3. The gas generating system of claim 1 wherein said nitrogen-containing secondary fuel is selected from the group consisting of selected from the group consisting of guanidines, aminoguanidines, tetrazoles, triazoles, salts of guanidines, salts of aminoguanidines, salts of tetrazoles, salts of triazoles, nitrogen-containing fuels, and mixtures thereof.

4. The gas generating system of claim 1 comprising a secondary oxidizer selected from the group consisting of metal and nonmetal perchlorates, oxides, nitrites, nitrates, permanganates, and chlorates provided at about 0.1-60 weight percent of the total composition.

5. The gas generating system of claim 1 wherein said system is an airbag inflator.

6. The gas generating system of claim 1 wherein said system is a seatbelt pretensioner.

7. The gas generating system of claim 1 wherein said system is a vehicle occupant protection system.

8. The gas generating system of claim 1 wherein said metal chlorate is provided at about 15-45%, said first fuel is provided at about 15-45%, and said secondary fuel is provided at about 0.1-70%, said percentages stated by weight of the total composition.

9. The gas generating system of claim 1 wherein said metal chlorate is selected from the group consisting of alkali, alkaline earth, and transitional metal chlorates.

10. An auto-ignition composition comprising:

a metal chlorate;

a nitrogen-containing secondary fuel.

11. The auto-ignition composition of claim 10 wherein said metal chlorate is provided at about 15-45%, said first fuel is provided at about 15-45%, and said secondary fuel is provided at about 0.1-70%, said percentages stated by weight of the total composition.

12. The auto-ignition composition of claim 10 wherein said composition further comprises silicone as a fuel/binder at about 10-30 weight percent of the composition.

13. The auto-ignition composition of claim 10 wherein said nitrogen-containing secondary fuel is selected from the group consisting of selected from the group consisting of guanidines, aminoguanidines, tetrazoles, triazoles, salts of guanidines, salts of aminoguanidines, salts of tetrazoles, salts of triazoles, nitrogen-containing fuels, and mixtures thereof.

14. The auto-ignition composition of claim 10 further comprising a secondary oxidizer selected from the group consisting of metal and nonmetal perchlorates, oxides, nitrites, nitrates, permanganates, and chlorates, said secondary oxidizer provided at about 0.1-60 weight percent of the total composition.

15. The auto-ignition composition of claim 10 wherein said metal chlorate is selected from the group consisting of alkali, alkaline earth, and transitional metal chlorates.