EP1448497A2

EP1448497A2 - Gas-generant formulations containing guanidine dinitramide and inflatable devices employing the same

Info

Publication number: EP1448497A2
Application number: EP02784228A
Authority: EP
Inventors: Norman H. Lundstrom; Robert S. Scheffee; Robert D. Lynch; Jamie B. Neidert
Original assignee: ARC Automotive Inc
Current assignee: ARC Automotive Inc
Priority date: 2001-10-31
Filing date: 2002-10-24
Publication date: 2004-08-25
Also published as: WO2003037859A2; AU2002348016A1; WO2003037859A3; JP2006502067A

Abstract

Gas generant formulations containing guanidine dinitramide (GDN) generate substantially entirely 100% water-insoluble particulates when combusted. In preferred forms, the gas-generant formulations comprise GDN as a fuel component and an alkaline earth metal nitrate salt as an oxidizer component. Most preferably, the alkaline earth metal nitrate salt is selected from nitrate salts of magnesium, calcium and strontium. Low toxicity high purity strontium nitrate with a low barium content is especially preferred.

Description

GAS-GENERANT FORMULATIONS CONTAINING GUANIDINE DINITRAMIDE AND INFLATABLE DEVICES EMPLOYING THE SAME

FIELD OF THE INVENTION

The present invention relates generally to gas-generant formulations for use in devices such as protective passive restraints or air bags used in motor vehicles, escape slide chutes, life rafts, and the like.

BACKGROUND AND SUMMARY OF THE INVENTION

Various inflators for inflating vehicle occupant passive restraint systems (known colloquially in the art as "air bags") are known. Among the various types of inflators is one that utilizes a quantity of stored compressed gas which is selectively released to inflate the air bag. A related type of inflator generates a gas source from a combustible gas- generating material which, upon ignition, provides a quantity of gas sufficient to inflate the air bag. In still another type (known as a hybrid inflator), the inflating air bag gas is provided by the combination of a stored compressed gas and the combustion products of the gas generating material.

Inflators which depend entirely or partially on the generation of gases by virtue of combustion of combustible materials have several disadvantages. For example, the burning of the propellant and the initiator materials in such inflators can result in the production of undesired particulate matter. Thus, using inflators with gas generant compositions which generate certain types of solid particuiates upon combustion as part of a passive restraint system in a vehicle could result in such undesirable particuiates being released into the occupant zone of the vehicle and thereby inhaled by the occupants. In particular, asthmatic reactions could possibly be caused by inhalation of soluble paniculate matter, creating a health risk for the occupants. Water insoluble particuiates are preferred over soluble particuiates, as the latter are believed to potentially cause a greater asthmatic reaction.

Particuiates may arise from the energetic component, including gas generants and ignition systems, as well as through secondary combustion of inert inflator components. Reduction in the contribution of particuiates from one or more of these components will generate a beneficial reduction in particuiates for the whole inflator assembly.

Gas generant formulations containing guanidine dinitramide (GDN) generally are known from U.S. Patent No. 6,004,410 to Blomquist (the entire content of which is expressly incorporated hereinto by reference, and hereinafter referenced as "the Blomquist '410 patent"). In this regard, the Blomquist '410 patent discloses gas generant compositions wherein the fuel component is a dinitramide salt having the formula X⁺[N(N0₂)2Jn^" and wherein n is equal to one or more, and X⁺ is a cationic derivative of an organic compound having one or more tetravalent nitrogen atoms. A fuel component is guanidine dinitramide (GDN), while a preferred oxidizer is ammonium nitrate (AN). Unfortunately, when AN is used as an oxidizer, a phase stabilizer, generally a potassium salt, must be added. When the gas generant is combusted, highly alkaline water soluble potassium oxide is formed which readily forms potassium hydroxide which is highly caustic and poisonous. Also with respect to the GDN/AN combination, the Blomquist '410 patent notes that a burn rate exponent of about 2 or less is desirable for vehicle gas generant compositions. Improvements to GDN-containing formulations and gas generants in general are, however, still needed. For example, it would be highly desirable if GDN-containing formulations could be provided which exhibit decreased toxicity, improved ballistics and relatively low amounts of substantially water-insoluble combustion products. It is towards providing such improved GDN-containing formulations that the present invention is directed.

Broadly, the present invention relates to gas generant formulations containing guanidine dinitramide (GDN) which, upon combustion with alkaline earth metal nitrate salts, generate substantially water-insoluble particuiates. Most preferably, the alkaline earth metal nitrate salt is selected from nitrate salts of magnesium, calcium and strontium. Low toxicity, high purity strontium nitrate with a low barium content is especially preferred.

Of course, when burned in a constant pressure gas generating device, a burning rate exponent less than unity is required.

These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.

DETAILED DESCRIPTION OF THE INVENTION

The formulations of the present invention necessarily will include guanidine dinitramide (GDN) as a fuel component. In this regard, the amount of the fuel component in the gas generant compositions of the present invention is that amount sufficient to achieve sustained combustion and an oxygen balance with the oxidizer such that essentially

100% of the combustion gases include carbon dioxide, nitrogen and water. Preferably, the fuel component will be present in the formulations of the present invention in an amount between about 40 wt.% to about 90 wt.%. Unless noted to the contrary all weight percentages herein are expressed on the basis of the total formulation weight.

An auxiliary fuel component in addition to the primary GDN fuel component may also be employed in amounts sufficient to tailor the physical and ballistic properties, e.g., to increase strength and to decrease the burning rate pressure exponent. The compositions of this invention may also include an auxiliary-fuel, such as 5-aminotetrazole (5ATZ), nitroguanidine (NQ) (including high bulk density NQ, HBNQ), amino guanidine nitrate (AGN), guanidine nitrate (GN) and diammonium bitetrazole (DABT); and a coolant such as lithium carbonate (LC). The auxiliary fuel and/or coolant, if present, will most preferably be employed in the formulations in an amount up to about 60 wt.%, and more preferably between about 2 wt.% to about 20 wt.%.

The formulations of the present invention will also necessarily include an oxidizer component, especially an alkaline earth metal nitrate oxidizer. In this regard, the preferred alkaline earth metal nitrates include nitrate salts of magnesium, calcium and strontium. Most preferred is low toxicity high purity strontium nitrate (Sr(NO₃)₂) with a low barium content.

The oxidizer will be present in the formulations of the present invention in amounts between about 10 wt % to about 60 wt %, and most preferably between about 25 wt % to about 45 wt. %.

A standard grade of strontium nitrate for Grade B used in tracer compositions is not desirable for use in this invention because the maximum barium allowed is up to 1.5 wt.%. Thus, for the purpose of the present invention, a "low barium content" in the low toxicity high purity strontium nitrate should not exceed about 0.05 wt.%. Typical barium content in the strontium nitrate will be between about 0.01 to about 0.03 wt.%. Most preferably, strontium nitrate according to Mil Spec Mil-S- 20322B Grade A or comparable is employed in the practice of the present invention.

The compositions of this invention may be used in the form of powders, granules, extruded, or compression-molded pellets or other formed configurations, and the like. The compositions are most preferably used in the form of a solid compression-molded mixture of the above components. It is important that the form of the invention have sufficient strength to withstand forces due to initiator shock or long term thermal aging and/or thermal cycling without loss of physical integrity. In this regard, the compositions will therefore in their compressed or extruded configuration most preferably include a highly oxygenated polymeric binder in an amount sufficient to bind the components into a more durable, stronger solid form (e.g., pellet).

Highly oxygenated binders may also be employed so as to achieve the low levels of solid combustion products required by new automotive specifications. Great emphasis is placed on airborne or suspended solids which may initiate asthmatic reactions, particularly in the water-soluble forms. Higher oxygen contents in the binder affect the quantity of solid ash produced by decreasing the amount of metal nitrate oxidizer required to maintain the necessary oxidizerfuel ratio (O:F). O:F ratio is defined as the ratio of the amount of oxygen present in the composition to the amount of oxygen required to fully burn all carbon and hydrogen to CO₂ and H₂O, respectively, and all other elements to their corresponding steady state oxidized form. Balanced O:F ratios of substantially about 1.0 (e.g., 1.0 ± 0J) are needed to maintain non-toxic levels of CO and NO_x in the combustion products. In the preferred embodiments of the present invention, the oxidizer is the only major source of solid ash so that by minimizing oxidizer contents, the amount of solid ash is held to a minimum. For instance, the oxidizer strontium nitrate in the present invention yields strontium oxide, strontium hydroxide, and/or strontium carbonate solid ash. The ash is substantially insoluble (that is, at most minimally soluble) in water. As the oxygen content of the binder is increased, the amount of oxidizer is reduced and thus the amount of solid ash is reduced. Most preferably, the substantially water-insoluble ash that is generated on combustion by the formulations of the present inventions will be less than about 15% and preferably less than about 10.0 wt.%.

The binder will typically be present in an amount based upon the total composition weight, of between 1 and 15 percent, and preferably between about 3 and 7 percent. The preferred binders are generally highly oxygenated and include cellulose acetate, cellulose acetate butyrate, methyl cellulose, polymethylmethacrylate (PMMA with about 32 wt. % oxygen), polyvinyl alcohols (PVA with about 36 wt. % oxygen), and/or polyalkylene carbonates. Examples of polyalkylene carbonates that may be employed in this invention are those that are commercially available from PAC Polymers, Inc. as polypropylene carbonate) copolymer (e.g., QPAC-40 containing about 47 wt. % oxygen) and poly(ethylene carbonate) copolymer (e.g., QPAC-25 containing about 54 wt. % oxygen).

The compositions of this invention may also include an ignition accelerator/augmentor in the form of a graphite powder. The preferred graphite powder has an average particle size of about 40 microns. One particularly preferred graphite powder is Microfyne Graphite commercially available from Joseph Dixon Crucible Company of Jersey City, New Jersey. When used, the graphite accelerator/augmentor is present in the compositions of this invention in an amount between about 0.1 wt.% to about 2.0 wt.%, and more preferably between about 0.25 wt.% to about 0.5 wt.%.

Virtually any additive conventionally employed in gas generant compositions, such as binders, coatings, stabilizers, processing aids, ballistic additives, burn rate catalysts, coolants, slag formers, co-oxidizers, multiple fuels and the like may be employed in the compositions of this invention. Thus, the compositions of this invention may be uncatalyzed (i.e., the composition is void of a combustion catalyst), or may be catalyzed. That is, the composition may include a combustion catalyzing effective amount of a combustion catalyst.

The present invention will be further understood by reference to the following non-limiting Examples.

Examples

The formulations as identified in Table 1 below were theoretically evaluated for various performance characteristics. More specifically, theoretical performance characteristics were calculated for formulations containing strontium nitrate (Sr(N0₃)2) as an oxidizer component with guanidine dinitramide (GDN) as a fuel component in accordance with the present invention (identified as formulation "F1 "). For comparison, the use of strontium nitrate with other fuel components, namely, either ureaguanyl dinitramide (UGDN) (identified as comparative formulation "CF1 ") or cyclotrimethylenetrinitramine (RDX) (identified as comparative formulation "CF2") were also evaluated. The oxygen ratio (OR) for each formulation was unity. Table 1

As can be seen from the data of Table 1 above, the formulation in accordance with the present invention yields a substantially lower amount of water-insoluble ash. Theoretically, all of the strontium exists as SrO(c), which is substantially insoluble, as the combustion products are expanded to atmospheric pressure. As the combustion products are further cooled to ambient temperature, SrO (c) is converted to SrCO₃(c), which is also substantially insoluble.

A A A A A A A A A A A AA A AA A AA A AAA A

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A gas generant formulation comprising guanidine dinitramide as a fuel component, and an alkaline earth metal nitrate as an oxidizer component, and having an oxidation ratio of 1.0 ± 0.1.

2. The gas generant formulation of claim 1 , wherein the oxidizer component is at least one alkaline earth metal nitrate selected from the group consisting of magnesium nitrate, calcium nitrate and strontium nitrate.

3. The gas generant formulation of claim 1 , wherein the oxidizer component is a nitrate salt of strontium.

4. The gas generant formulation of any one of claims 1-3, wherein the fuel component is present in an amount between about 40 to about 90 wt.%, based on the total formulation weight.

5. The gas generant formulation as in claim 4, wherein the oxidizer component is present in an amount between about 10 to about 60 wt.%, based on the total formulation weight .

6. The gas generant formulation as in claim 5, wherein the oxidizer component is present in an amount between about 10 wt.% to about 45 wt.%.

7. The gas generant formulation as in claim 6, which comprises a binder.

8. The gas generant formulation of claim 7, wherein the binder is at least one selected from the group consisting of cellulose acetate, cellulose acetate butyrate, methyl cellulose, polymethylmethacrylates, polyvinyl alcohols, and polyalkylene carbonates.

9. The gas generant formulation of claim 1 , in the form of a loose, granular powder.

10. The gas generant formulation of claim 1 , in the form of a pressed or extruded shaped structure.

11. The gas generant formulation of claim 1 , wherein the oxidizer is strontium nitrate with a low barium content.

12. The gas generant formulation of claim 11 , wherein the strontium nitrate has a barium content of less than about 0.05 wt.%.

13. An inflatable device which comprises a gas generant composition as in any one of claims 1-3 and 11-12.

14. An inflatable device which comprises a gas generant composition as in claim 4.

15. An inflatable device which comprises a gas generant composition as in claim 5.

16. An inflatable device which comprises a gas generant composition as in claim 6.

17. An inflatable device which comprises a gas generant composition as in claim 7.

18. An inflatable device which comprises a gas generant composition as in claim 8.

19. An inflatable device which comprises a gas generant composition as in claim 9.

20. An inflatable device which comprises a gas generant composition as in claim 10.