EP0763511A2

EP0763511A2 - Igniter compositions for non-azide gas generants

Info

Publication number: EP0763511A2
Application number: EP96306440A
Authority: EP
Inventors: Christopher Hock; Michael W. Barnes
Original assignee: Morton International LLC
Current assignee: Morton International LLC
Priority date: 1995-09-15
Filing date: 1996-09-05
Publication date: 1997-03-19
Also published as: EP0763511A3; JPH09118580A

Abstract

In an inflator module for an automotive airbag which contains a gas generant, particularly a non-azide gas generant, an igniter composition is provided for igniting the generant such that the generant produces lower volumes of toxic gaseous combustion products. The igniter composition has a fuel component which is 5 wt% to 100% Mg, TiH₂, Al or Ti, 0 to 95 wt% carbohydrate fuel having an oxygen content of 35 to 65 wt%; and an oxidizer component which is potassium or sodium chlorate or potassium or sodium perchlorate. The igniter composition has an oxygen-to-fuel ratio of at least 1 and preferably at least 1.05.

Description

The present invention is directed to compositions for igniting gas generants for use in automotive airbag applications in conjunction with non-azide gas generants, particularly gas generant compositions containing both nitrogen and oxygen atoms and/or both nitrogen and hydrogen atoms and/or both nitrogen and carbon atoms.
Most present-day automotive airbag inflators use a gas generant based on sodium azide. This material has the advantage of producing, upon combustion, pure non-toxic nitrogen as a gaseous combustion product. However, sodium azide as a raw material is toxic, presenting disposal problems.
Accordingly, there has been a desire to replace sodium azide with less toxic gas generant compositions. A number of such gas generant compositions have been described, for example, in U.S. Patents Nos. 3,468,730, 5,084,118, and 5,035,757, the teachings of each of which are incorporated herein by reference. The combustion of most non-azide gas generant compositions, which contain the elements C, H, O, and N, produce generally non-toxic gases (N₂, H₂O, and/or CO₂); however, they also tend to produce undesirable gas by-products, such as NH₃, NO_x, CO, and HCN, each of which may be harmful in the range of 25 to 1000 ppm. When an airbag is deployed, it must rapidly inflate, e.g., in the range of between 30 and 100 milliseconds, and then rapidly deflate. During deflation, the gases are vented into the passenger compartment of a vehicle, and undesirable by-product gases may present a hazard to the occupants of the vehicle. This is one of the major impediments in the commercialization of non-azide pyrotechnic inflators.
A typical automotive airbag system consists of an airbag and a pyrotechnic inflator module in which the gases are produced which inflate the airbag. Inflators, are described, for example, in U.S. Patents Nos. 4,943,086, 5,221,109, 5,241,910, the teachings of each of which are incorporated herein by reference. In a typical airbag inflator deployment system, a remote sensor senses the force of a collision. The sensor is electrically connected to a squib in the inflator, and electrically generated heat in the squib ignites a small charge of pyrotechnic material in the squib. The pyrotechnic charge, in turn, produces heat that sets off a larger charge of igniter composition. The heat from the igniter composition then sets off a much larger charge of gas generant composition that produces substantial volumes of gases for inflating the airbag. It is also understood that there are variations of this typical system to which the present invention is applicable; for example, hybrid inflators which inflate airbags with a combination of pyrotechnic- generated gases and compressed gases, such as that described in U.S. Patent No. 5,290,060, the teachings of which are incorporated herein by reference.
A very common igniter material is B/KNO₃, in which boron is the fuel and potassium nitrate the oxidizer. This composition is a standard ignitor composition in the inflator industry. This ignitor is generally proportioned to be fuel rich (that is oxygen-poor). Fuel-rich mixtures tend to have high burn temperatures, a feature desirable in igniting a gas generant composition. Furthermore, a fuel (boron)-rich ignitor composition ejects hot particles of boron or boron oxide which hasten combustion of the gas generant composition through direct thermal contact with the gas generant composition to be ignited.
In accordance with the present invention there is provided an igniter composition for a non-azide gas generant composition in which the gas generant composition contains any combination of C, H, O and/or N atoms which results in a reduction of undesired gas by-products produced by combustion of the gas generant composition. The igniter composition has a fuel component of which between about 5 and 100 wt% is a fuel selected from Mg, Ti, Al, TiH₂, and mixtures thereof, and up to about 95 wt% of which comprises a combustible carbohydrate fuel, that is, a fuel which contains only the elements carbon, hydrogen and oxygen. Between about 35 and about 65 wt% of the carbohydrate fuel, if used, is oxygen content. The igniter composition further comprises an oxidizer component which does not contain nitrogen, particularly an oxidizer selected from the group consisting of KClO₃, NaClO₃, KClO₄, NaClO₄, and mixtures thereof.
The igniter composition in accordance with the present invention is designed to burn with a sufficiently high temperature to ignite the gas generant composition. Although, the igniter composition, like the gas generant composition, produces gases upon combustion, this is not its primary purpose; hence, igniter compositions are not necessarily selected to maximize their gas output. The igniter composition is used at a very low mass ratio relative to the gas generant. A typical automotive driver side airbag inflator may contain about 2 grams of igniter composition and about 60 to 100 grams of gas generant composition. Passenger- side airbags and side airbags may have different amounts of gas generant material, but likewise contain a greater amount of gas generant material relative to igniter material.
While the igniter composition is used at a very low level compared to the gas generant composition, it is surprisingly found that the selection of igniter composition can have a significant effect on the levels of undesirable gas by-products, especially NO₄, NH₃, CO and/or HCN produced upon combustion of a non-azide gas generant composition. Non-azide gas generant compositions to which the invention is directed are those which contain the combinations of N plus O and/or N plus H, giving rise to NO_x (especially NO and NO₂) and NH₃ combustion products. Such gas generant compositions commonly also contain carbon atoms, further giving rise to CO and HCN combustion products.
The igniter composition contains oxidizer component in an amount sufficient so as to be at least stoichiometrically balanced with the fuel, i.e., have an oxygen-to-fuel ratio (O/F) of at least 1, and preferably is oxygen-rich, having an O/F stoichiometric ratio of at least about 1.05. The igniter composition must have an O/F ratio consistent with providing sufficient energy to ignite the gas generant composition. The igniter composition must be least stoichiometrically balanced. That is, there must be sufficient oxidizer to oxidize the metal or metal-containing fuel to the appropriate metal oxide and any carbohydrate fuel to CO₂ and H₂O. When the amount of oxidizer is just sufficient to do this, the oxidizer-to-fuel ratio (O/F) is defined as equal to 1.0. If there is a 5% excess of oxidizer the O/F ratio is 1.05 and so forth. Preferred compositions have O/F greater than 1.05. This is in contrast to conventional B/KNO₃ igniter composition which is fuel rich (oxygen deficient).
While a high O/F ratio tends to lower the combustion temperature of the igniter compositions, the combustion temperatures of the igniter compositions of the present invention are sufficiently high to ignite most non-azide gas generant compositions. For any combination of any particular gas generant composition with any particular igniter composition, the upper limit of O/F ratio is the point where the igniter composition no longer combusts hot enough to ignite the gas generant composition. Generally, igniter compositions in accordance with the invention will have O/F limits no higher than about 1.3 (i.e. 30 molar% over-oxidized).
Why an oxygen-balanced or oxygen-rich igniter composition should have a significant effect on the levels of toxic gases produced by the gas generant material is not fully understood and applicants are not bound by theory. However, it is found that by using oxygen-balanced or oxygen-rich igniter compositions in accordance with the present invention, gas pressure in the inflator rises much more rapidly than when oxygen-poor igniter materials are used. Experience has shown that low-pressure combustion favors higher production of certain toxic gases, such as NO_x, CO, HCN, and NH₃ and that high-pressure combustion produces less of such gases. It may also be that, in preferred oxygen-rich igniter compositions, the slight amount of additional oxygen serves to favor oxidation of the undesired gases, such as CO to CO₂ or NH₃ to N₂ and H₂O.
The fuel component may be entirely a metal or a metal hydride selected from the group consisting of Mg, Ti, Al, TiH₂, and mixtures thereof. Of these, Ti is least preferred due to associated health risks. Mg and TiH₂ are currently preferred. While other metal hydrides, such as aluminum hydrides, might work as igniter fuels, they are generally considered to be too moisture-sensitive for automotive airbag inflators. TiH₂, however, is found to have good moisture stability. Metals and metal hydrides have the important function in igniter compositions as producing metal oxide particulates, such as aluminum oxide or titanium oxide. Such particulates contribute to a rapid initial pressure by heating the gas generant composition by direct conduction.
The fuel component may also include an organic C, H, O compound (carbohydrate) fuel having a relatively high oxygen content, i.e., between about 35 and about 65 wt%. The oxygen component is preferably high so as to require a relatively low corresponding amount of oxygen in the igniter mixture. If used, the carbohydrate fuel is generally used at a level of at least about 20 wt% of the fuel component, more typically at a level of at least about 50 wt% of the fuel component, and most typically at a level of at least about 60 wt% of the fuel component, up to about 95% of the fuel component. The carbohydrate fuel, if used, is included to produce high volumes of gas and therefore contribute to an initial high gas pressure within the inflator module, high pressure being believed to reduce levels of toxic gases. Some suitable carbohydrate fuels include, but are not limited to tartaric acid, succinic acid, malonic acid, lactose and mixtures thereof.
The oxidizer component is a non-nitrogen-containing oxidizer. Preferred oxidizers are chlorates and perchlorates, such as potassium chlorate, sodium chlorate, potassium perchlorate, sodium perchlorate, or mixtures thereof.
The invention will now be described in greater detail by way of specific examples.

Example 1

A gas generant composition formed of 5-aminotetrazole, cupric oxide, strontium nitrate and guanidine nitrate, of the type described in U.S. Patent No. 5,431,103, the teaching of which are incorporated herein by reference, were ignited with (as a control) a B/KNO₃ igniter composition having an O/F ratio of 0.54. The identical composition was ignited using titanium hydride/potassium perchlorate (TiH₂/KClO₄) igniter compositions with varying O/F ratios. Results are shown in the table below:

Composition O/F NO_x (ppm) NH₃ (ppm) CO (ppm) HCN (ppm)

B/KNO₃ 88 282 198 10

TiH₂/KClO₄ 0.85 71 183 264 11

TiH₂/KClO₄ 1.30 70 164 274 8

TiH₂/KClO₄ 1.45 71 142 193 5

Claims

An igniter composition comprising
A) a fuel component, between 5 wt% and 100 wt% of said fuel component being selected from Mg, TiH₂, Al, Ti, and mixtures thereof, and up to 95 wt% of said fuel component comprising an organic fuel which contains only the elements carbon, hydrogen, and oxygen, said organic fuel having an oxygen content of between 35 and 65 wt%, and

B) an oxidizer component which contains no nitrogen,
said igniter composition having an oxygen-to-fuel ratio of at least 1:1.
A composition according to Claim 1 wherein said oxygen-to-fuel ratio is at least 1.05:1.
A composition according to Claim 1 or Claim 2 wherein said fuel component comprises TiH₂.
A composition according to Claim 1 or Claim 2 wherein said fuel component comprises Mg.
A composition according to Claim 1 or Claim 2 wherein said fuel component comprises Ti.
A composition according to Claim 1 or Claim 2 wherein said fuel component comprises Al.
A composition according to any preceding claim wherein said oxidizer is selected from KClO₄, NaClO₄, NaClO₃, and KClO₃ and mixtures thereof.
A composition according to Claim 7 wherein said oxidizer component comprises KClO₄.
A composition according to Claim 7 wherein said oxidizer component comprises NaClO₄.
A composition according to Claim 7 wherein said oxidizer component comprises KClO₃.
A composition according to Claim 7 wherein said oxidizer component comprises NaClO₃.
A composition according to any preceding claim wherein said organic fuel is present at between 20 and 95 wt% of said fuel component.
A composition according to Claim 12 wherein said organic fuel is present at between 50 and 95 wt% of said fuel component.
A composition according to Claim 13 wherein said organic fuel is present at between 60 and 95 wt% of said fuel component.
A composition according to any preceding claim wherein said organic fuel is selected from tartaric acid, succinic acid, malonic acid, lactose, and mixtures thereof.
An automotive airbag inflator module containing a generant combustible for producing gases to inflate an airbag and an igniter composition according to any preceding claim for initiating combustion of said generant.