WO2008027204A1

WO2008027204A1 - Extrudable gas generant

Info

Publication number: WO2008027204A1
Application number: PCT/US2007/018202
Authority: WO
Inventors: Ivan V. Mendenhall; Robert D. Taylor
Original assignee: Autoliv Asp, Inc.
Priority date: 2006-08-28
Filing date: 2007-08-16
Publication date: 2008-03-06
Also published as: EP2061736A4; EP2061736A1; US20090008001A1; US20060289096A1; CN101528642A; JP2010502544A

Abstract

Extrudable gas generant compositions which, upon combustion, produce or result in an improved effluent and related methods for generating inflation gas for use in an inflatable restraint system are provided. Such extrudable gas generant compositions include a non-azide, organic, nitrogen-containing fuel, at least one copper-containing compound, a perchlorate additive and a polymeric binder material. The at least one copper-containing compound may be selected from basic copper nitrate, cupric oxide, a copper diammine- ammonium-nitrate mixture wherein the ammonium nitrate is present in the mixture in a range of about 3 to about 90 weight percent, and/or a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate. The perchlorate additive is present in an. amount effective to result in a gaseous effluent, when the gas generant composition is combusted, having a reduced content of at least one species selected from carbon monoxide, ammonia, nitrogen dioxide and nitric oxide, as compared to a same gas generant free from the perchlorate additive. The polymeric binder material is effective to render the gas generant composition extrudable.

Description

EXTRUDABLE GAS GENERANT

BACKGROUND OF THE INVENTION

This invention relates generally to materials for use in gas generation such as for forming an inflation gas such as for inflating inflatable devices such as airbag cushions included in automobile inflatable restraint systems and, more particularly, to extrudable, perchlorate-containing gas generant compositions which produce or result in gaseous effluents having reduced levels of various undesirable constituents and which are conducive or easily adaptable to manufacture or production by extrusion processing.

It is generally well known to protect a vehicle occupant using a cushion or bag, e.g., an "airbag cushion," that is inflated or expanded with a gas when a vehicle experiences sudden deceleration, such as in the event of a collision. Such airbag restraint systems normally include: one or more airbag cushions, housed in an uninflated and folded condition to minimize space requirements; one or more crash sensors mounted on or to the frame or body of the vehicle to detect sudden deceleration of the vehicle; an activation system electronically actuated by the crash sensors; and an inflator device that produces or supplies a gas to inflate the airbag cushion. Tn the event of a sudden deceleration of the vehicle, the crash sensors actuate the activation system which in turn actuates the inflator device which begins to inflate the airbag cushion in a matter of milliseconds.

Many types of inflator devices have been disclosed in the art for inflating one or more inflatable restraint system airbag cushions. Inflator devices which form or produce inflation gas via the combustion of a gas generating pyrotechnic material, e.g., a "gas generant," are well known. For example, inflator devices that use the high temperature combustion products, including additional gas products, generated by the burning of the gas generant to supplement stored and pressurized gas to inflate one or more airbag cushions are known, hi other known inflator devices, the combustion products generated by burning the gas generant may be the sole or substantially sole source for the inflation gas used to inflate the airbag cushion. Typically, such inflator devices include a filter to remove dust or particulate matter formed during the combustion of a gas generant composition from the inflation gas to limit or prevent occupant exposure to undesirable and/or toxic combustion byproducts.

In view of an increased focus on passenger safety and injury prevention, many automotive vehicles typically include several inflatable restraint systems, each including one or more inflator devices. For example, a vehicle may include a driver airbag, a passenger airbag, one or more seat. belt pretensioners, one or more knee bolsters, and/or one or more inflatable belts, each with an associated inflator device, to protect the driver and passengers from frontal crashes. The vehicle may also include one or more head/thorax cushions, thorax cushions, and/or curtains, each with at least one associated inflator device, to protect the driver and passengers from side impact crashes. Generally, the gaseous effluent or inflation gas produced by all of the inflator devices within a particular vehicle, when taken as whole, are required to satisfy strict content limitations in order to meet current industry safety guidelines. Thus, it is desired that the gas generant compositions used in such inflator devices produce aslittle as possible of undesirable effluents such as hydrogen chloride, carbon monoxide, nitrogen dioxide and nitric oxide.

A number of gas generant compositions are known that include perchlorate additives such as, for example, ammonium perchlorate and/or alkali metal perchlorates as an oxidizer. Such perchlorate additives are typically employed in gas generant compositions as a source of oxygen which promotes efficient combustion of the gas generant composition, e.g., complete conversion of carbon to carbon dioxide, hydrogen to water, and nitrogen to nitrogen gas. Perchlorate additives, however, commonly also produce hydrogen chloride as a gaseous byproduct of combustion which, in too large a concentration, may be toxic and/or corrosive. Hydrogen chloride can be removed from the combustion gas stream by including an alkali or alkaline earth metal salt in the gas generant composition. Such alkali or alkaline earth metal salts react with the hydrogen chloride to produce less or nontoxic alkali or alkaline earth metal chlorides such as, for sample, sodium or potassium chloride. Such alkali or alkaline earth metal chlorides, however, undesirably form as fine particulate matter or dust which can escape the inflator device. Additionally, the inclusion of perchlorate additives, however, typically increases the combustion temperature of a pyrotechnic gas generant composition often resulting in increased levels of undesirable and potentially toxic effluent gases such as ammonia and carbon monoxide.

One technique of controlling the composition of gaseous effluent generated via combustion of the gas generant composition involves manipulation of the equivalence ratio such as, for example, by varyingthe concentration of oxidizer in the gas generant composition.

While the manipulation of the equivalence ratio of gas generant materials is a technique commonly used to adjust the effluent levels of gas generant materials, such manipulation is prone to performance sometimes referred to as the equivalence ratio "teeter- totter." That is, as the equivalence ratio is lowered, under-oxidized species, such as carbon monoxide (CO) and ammonia (NH₃), increase and over-oxidized species, such as nitric oxide (NO) and nitrogen dioxide (NO₂), decrease. The reverse is true when the equivalence ratio is increased. In view of the above, there is a need and a demand for gas generant compositions which produce or result in desirably low levels of undesirable effluents such as carbon monoxide, ammonia, nitrogen dioxide and nitric oxide and fine particulate matter.

Generally, such gas generant compositions are produced using a spray dry process. In such spray drying processes, the gas generant compositions are typically prepared as a slurry of particulate materials in a carrier fluid such as, for. example, water or alcohol. The slurried compositions are then sprayed as a fine mist such that the carrier fluid is simultaneously dried and a powder material is recovered. Thepowdermaterial is subsequently consolidated using high speed presses into gas generant bodies such as, for example, in the form of pellets, tablets, wafers and the like. Those skilled in the art will appreciate and understand, however, that such two step processing, e.g., spray drying followed by consolidation, results in increased production time and expense due to the use of multiple processing steps and/or systems to form the final gas generant product. Thus, it is desired that the gas generant compositions used in such inflator devices can be produced in an economical and/or efficient manner. One such process for more efficiently preparing solid gas generant bodies for use in an associate inflator device includes, for example, an extrusion process. Such extrusion processes are typically processes wherein a viscous or paste-like gas generant composition may be compounded and extruded into a desired shape. Individual gas generant bodies may be formed such as by cutting or otherwise portioning the gas generant composition as it is extruded. Such individual gas generant bodies may be cut into various desirable sizes such as, for example, in a size that permits multiple bodies to be placed within a combustion chamber of an inflator device or, alternatively, in a size that permits the placement of a single monolithic grain within the combustion chamber. Thus, as those skilled in the art would appreciate, such extrusion processes can desirably be employed to reduce production costs such as by eliminating separate formation and consolidation steps and reducing equipment costs. In addition to the above-identified desirable properties and characteristics, gas generant materials for use in automotive inflatable restraint applications must be sufficiently reactive such that upon the proper initiation of the reaction thereof, the resulting gas producing or generating reaction occurs sufficiently rapidly such that an associated inflatable air bag cushion is properly inflated so as to provide desired impact protection to an associate vehicle occupant.

Gas generant compositions which can be employed in extrusion processes commonly include a binder material that holds the components of the composition together and imparts rigidity and/or strength the extruded grain. Unfortunately, such binder materials can undesirably lower the burn rate of the gas generant composition which can have a deleterious effect on the rate at which inflation gas is produced and/or the quantity of inflation gas produced to inflate an associated airbag cushion.

In view of the above, there is an additional need and a demand for pyrotechnic gas generant compositions that can be extruded to form multiple individual gas generant bodies or a single monolithic grain having a burning rate that, when employed in an airbag inflator device, rapidly, reliably and/or effectively produces a desired quantity of gaseous effluent to inflate an associate airbag cushion.

SUMMARY OF THE INVENTION

A general object of the invention is to provide an improved gas generant composition.

A more specific objective of the invention is to overcome one or more of the problems described above.

The general object of the invention can be attained, at least in part, through an extrudable gas generant composition including a non-azide, organic, nitrogen-containing fuel, at least one copper-containing compound, a perchlorate additive and a polymeric binder effective to render the gas generant composition extrudable. The at least one copper-containing compound is selected from basic copper nitrate, cupric oxide, a copper diammine dinitrate-arnrnoniurn nitrate mixture wherein ammonium nitrate is present in the mixture in a range of about 3 to about 90 weight percent, copper diammine bitetrazole, a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate, or combinations thereof. The perchlorate additive includes at least one perchlorate material selected from alkali metal perchlorates and ammonium perchlorate. The perchlorate additive is present in a relative amount effective to result in a gaseous effluent, when the gas generant composition is combusted, having a reduced content of at least one species selected from carbon monoxide, ammonia, nitrogen dioxide and nitric oxide, as compared to a same gas generant composition which is free of the perchlorate additive. The prior art generally fails to provide gas generant compositions that facilitate or otherwise permit the inclusion of one or more perchlorate additives while simultaneously inhibiting the formation or otherwise reducing the amounts or levels of undesirable effluents such as carbon monoxide, ammonia, nitrogen dioxide and nitric oxide. The prior art further generally fails to provide gas generant compositions containing one or more perchlorate additives that maybe extruded to form multiple individual gas generant bodies or a monolithic grain having a burn rate effective to reliably and rapidly produce a gaseous effluent to inflate an associated airbag cushion.

The invention further comprehends an extrudable gas generant composition comprising: a non-azide, organic, nitrogen-containing fuel present in a relative amount of 5 to 60 composition weight percent; a copper-containing compound selected from the group consisting of basic copper nitrate, cupric oxide, copper diammine dinitrate-ammonium nitrate mixture wherein ammonium nitrate is present in the mixture in a range of about 3 to about 90 weight percent, copper diammine bitetrazole, a copper-nitrate complex resulting from reaction of

5-aminotetrazole with basic copper nitrate, and combinations thereof, the at least one copper- containing compound present in a relative amount of 10 to 80 composition weight percent; a perchlorate additive comprising at least one perchlorate material selected from the group consisting of alkali metal perchlorates and ammonium perchlorate, the perchlorate additive, present in a relative amount of 1 to about 10 composition weight, effective to result in a gaseous effluent, when the gas generant composition is combusted, having a reduced content of at least one species selected from the group consisting of carbon monoxide, ammonia, nitrogen dioxide and nitric oxide, as compared to a same gas generant composition free of the perchlorate additive; and a polymeric binder material present in a relative amount of 1 to 20 composition weight percent and effective to render the gas generant composition extrudable, the polymeric binder material selected from the group consistingof cellulosicmaterials, natural gums,polyacrylates, polyacrylamides, polyurethanes, polybutadienes, polystyrenes, polyvinyl alcohols, polyvinyl acetates, silicones and combinations of two or more thereof.

The invention still further comprehends an extrudable gas generant composition comprising: 5 to 60 composition weight percent guanidine nitrate;

10 to 80 composition weight percent of a copper-containing compound selected from the group consisting of basic copper nitrate, cupric oxide, copper diammine dinitrate-ammonium nitrate mixture wherein ammonium nitrate is present in the mixture in a range of about 3 to about 90 weight percent, copper diammine bitetrazole, a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper , nitrate, and combinations thereof;

1 to 10 composition weight percent of a perchlorate additive including at least one perchlorate material selected from the group consisting of alkali metal perchlorates and ammonium perchlorate; and 1 to 20 composition weight percent of a polymeric binder material selected from the group consisting of cellulosic materials, natural gums, polyacrylates, polyacrylamides, polyurethanes, polybutadienes, polystyrenes, polyvinyl alcohols, polyvinyl acetates, silicones and combinations of two or more thereof.

In addition, corresponding or associated methods for generating an inflation gas for inflating an airbag cushion of an inflatable restraint system of a motor vehicle are provided.

Such methods typically involve igniting the particular extrudable gas generant composition to produce a quantity of inflation gas, and then inflating the airbag cushion with the inflation gas.

As used herein, the term "equivalence ratio" is understood to refer to the ratio of the number of moles of oxygen in a gas generant composition or formulation to the number of moles needed to convert hydrogen to water, carbon to carbon dioxide, and any metal to a thermodynamically predicted metal oxide. Thus, a gas generant composition having an equivalence ratio greater than 1.0 is over-oxidized, a gas generant composition having an equivalence ratio less than 1.0 is under-oxidized, and a gas generant composition having an equivalence ratio equal to 1.0 is perfectly oxidized. As used herein, the expression "substantially free of, in reference to possible gaseous effluent constituents such as hydrogen chloride, carbon monoxide, ammonia, nitrogen dioxide and nitric oxide, similarly refers to a gaseous effluent or inflation gas that includes such constituent in an amount that is equal to or less than an amount of such constituent permitted by or allowed under current industry standards (USCAR specifications). For example, if a vehicle includes a single inflatable airbag cushion with a single inflator including a gas generant composition, the gaseous effluent or inflation gas produced by the combustion of the gas generant composition is substantially free of hydrogen chloride if it includes about

5 parts per million hydrogen chloride or less when the inflator is discharged into a 100 ft³ tank; is substantially free of carbon monoxide if it includes about 461 parts per million carbon monoxide or less when the inflator is discharged into a 100 ft³ tank; is substantially free of ammonia if it includes about 35 parts per million ammonia or less when the inflator is discharged into a 100 ft³ tank; is substantially free of nitrogen dioxide if it includes about 5 parts per million nitrogen dioxide or less when the inflator is discharged into a 100 ft³ tank; and is substantially free of nitric oxide if it includes about 75 parts per million nitric oxide or less when the inflator is discharged into a 100 ft³ tank.

Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended cl aims and drawing.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a simplified schematic, partially broken away, view illustrating the deployment of an airbag cushion from an airbag module assembly within a vehicle interior, in accordance with one embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an improved gas generant composition. More specifically, it has been discovered that a gas generant effluent product can be dramatically improved (e.g., the resulting effluent has a significantly reduced content of undesirable materials such as one or more of carbon monoxide, ammonia, nitrogen dioxide and nitric oxide) via the inclusion, in the gas generant composition, of one or more perchlorate additives.

Further, it has been found that such gas generant compositions may be rendered extrudable without an undesirable decrease in burn rate through the inclusion of a polymeric binder material and at least one copper-containing compound.

As discussed above, perchlorate additives are particularly effective oxidizers for gas generant compositions used in the inflation of automobile inflatable restraint systems.

However, the use of such perchlorate additives typically results in the formation undesirable byproducts such as hydrogen chloride or fine particulate matter such as sodium chloride when an alkali or alkaline earth metal scavenger compound is also used. In accordance with the present invention, it has been found that utilizing a copper-containing compound in an extrudable gas generant composition results in an improved gaseous effluent or inflation gas.

■ In particular, it has generally been found that a filterable copper chloride byproduct is produced that results in a gaseous effluent or inflation gas that has a reduced content of particular undesirable effluent species. Additionally, it has advantageously been found that a filterable copper chloride byproduct is produced that results in a reduction in the level of particulate that exits the inflator device.

Moreover, it has unexpectedly been found that including a perchlorate additive and at least one copper-containing cQmpound in an extrudable gas generant composition does not result in an undesirable increase in the level of carbon monoxide in the gaseous effluent or inflation gas produced upon combustion of such a gas generant composition. Such a finding is unexpected in that generally it has been found that including perchlorate additives in a gas generant composition typically results in an increased temperature of combustion which in turn results in the production of increased levels of carbon monoxide in the gaseous effluent or inflation gas. Additionally, it has unexpectedly been found that a decrease in carbon monoxide content from expected levels occurs without a countervailing increase in the levels of undesirable oxides of nitrogen such as nitric oxide (NO) or nitrogen dioxide (NO₂) which is the usual case. Further, it has been unexpectedly found that the principal chlorine-containing species found in the gaseous effluent or inflation gas produced by the combustion of an extrudable gas generant composition including a perchlorate additive and a copper-containing compound is copper (II) chloride (CuCl₂) with little or no hydrogen chloride detected. Such a finding is unexpected in that standard thermodynamic prediction computer programs such as the Naval Weapons Center Propellant Evaluation Program (PEP) generally predict the principal chlorine species in the gaseous effluent or inflation gas produced by the combustion of such an extrudable gas generant composition to be cuprous chloride (CuCl) and a trimer of cuprous chloride (Cu₃Cl₃) with some hydrogen chloride.

Also, as discussed above, the inclusion of a polymeric binder material in an amount effective to render a gas generant composition extrudable can normally have a deleterious effect upon the burn rate of the extrudable gas generant composition. However, in addition to providing extrudable gas generants that produce improved gaseous effluents upon combustion, it has also been found that the burn rates of extrudable gas generant compositions in accordance with the invention can also be improved. Such improved burn rates may be obtained as a result of catalyzing the decomposition of the perchlorate additive without adversely affecting the quality of the gaseous effluent. Advantageously, there are a wide variety of materials that may be used to enhance the burn rate of extrudable pyrotechnic or gas generant compositions that contain perchlorate additives.

In view of the above, the present invention is directed to an extrudable gas generant composition including at least one non-azide, organic nitrogen-containing fuel, at least one copper-containing compound, a perchlorate additive, and a polymeric binder material effective to render the gas generant composition extrudable. The perchlorate additive is present in an amount effective to result in a gaseous effluent, when the gas generant composition is combusted, having a reduced content of at least one species selected from the groups consisting of carbon monoxide, ammonia, nitrogen dioxide and nitric oxide, as compared to a same gas generant composition free of the perchlorate additive. In practice, the extrudable gas generant composition can include about 5 to about 60 composition weight percent of at least one non-azide, organic nitrogen-containing fuel, about 10 to about 80 composition weight percent of at least one copper-containing compound, about 1 to about 20 composition weight percent of a perchlorate additive, and about 1 to about 20 composition weight percent of a polymeric binder material. Useful non-azide, organic, nitrogen-containing fuels for use in the extrudable gas generant composition include: amine nitrates, nitramines, heterocyclic nitro compounds, tetrazole compounds, and combinations thereof. While various non-azide, organic, nitrogen- containing fuels may be used in the extrudable gas generant composition, in accordance with certain preferred embodiments, the non-azide, organic, nitrogen-containing fuel may advantageously be guanidine nitrate. Generally, guanidine nitrate may be desirable due to its good thermal stability, low cost and high gas yield when combusted.

The extrudable gas generant composition can include about 5 to about 60 composition weight percent of at least one non-azide, organic, nitrogen-containing fuel. In accordance with certain embodiments, the extrudable gas generant composition can include about 5 to about 30 composition weight percent of at least one non-azide, organic, nitrogen- containing fuel. In accordance with certain other embodiments, the extrudable gas generant composition can include about 5 to about 20 composition weight percent of at least one non- • azide, organic nitrogen-containing fuel.

In accordance with one embodiment, the gas generant composition may include about 5 to about 60 composition weight percent guanidine nitrate. In a further embodiment, the gas generant composition may include about 5 about 30 composition weight percent guanidine nitrate. In a still further embodiment, the gas generant composition may include about 5 to about 20 composition weight percent guanidine nitrate.

The extrudable gas generant composition also includes at least one copper- containing compound. While various copper-containing compounds may be used in the extrudable gas generant composition, suitably the copper-containing compound is selected from copper-nitrate complexes (such as a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate), basic copper nitrate, cupric oxide, copper dinitrate-ammonium nitrate mixture wherein ammonium nitrate is present in the mixture in a range of about 3 to about 90 weight percent, copper diammine bitetrazole, and combinations thereof.

In accordance with certain embodiments, the extrudable gas generant composition can include about 10 to about 80 composition weight percent of at least one copper-containing compound.

One suitable copper-containing compound for use in the practice of this invention includes a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate. In particular, the copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate is believed to be a copper, hydroxy nitrate lH-tetrazol-5-amine complex.

In accordance with one embodiment, the extrudable gas generant composition may include about 10 to about 60 composition weight percent of a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate. In accordance with another embodiment, the extrudable gas generant composition may include about 20 to about 60 composition weight percent of a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate. In a further embodiment, the gas generant composition can include about 30 to about 60 composition weight percent of a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate. In accordance with other embodiments, the extrudable gas generant composition may include a combination of basic copper nitrate and a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate. In^" particular, the copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate is believed to be a copper, hydroxy nitrate lH-tetrazol-5-amine complex.

In accordance with one embodiment, the gas generant composition can include about 10 to about 80 composition weight percent of such combination of basic copper nitrate and the copper-nitrate complex. In accordance with another embodiment, the extrudable gas generant composition may include about 30 to about 80 composition weight percent of such combination of basic copper nitrate and the copper-nitrate complex. In a further embodiment, the extrudable gas generant composition may include about 50 to about 80 composition weight

< percent of such combination of basic copper nitrate and the copper-nitrate complex.

In practice, the combination of basic copper nitrate and the copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate includes about 20 to about 80 weight percent basic copper nitrate based on the total weight of the combination and about 20 to about 80 weight percent of the copper-nitrate complex based on total weight of the combination. In accordance with one embodiment the combination of basic copper nitrate and the copper-nitrate complex includes about 20 to about 40 weight percent basic copper nitrate based on the total weight of the combination and about 60 to about 80 weight percent of the copper-nitrate complex based on total weight of the combination.

The extrudable gas generant compositions further include a perchlorate additive present in an amount effective to result in a gaseous effluent, when the gas generant composition is combusted, having a reduced content of at least one species selected from carbon monoxide, ammonia, nitrogen dioxide and nitric oxide, as compared to a same gas generant composition free of the perchlorate additive. The perchlorate additive includes at least one perchlorate material selected from alkali metal perchlorates and ammonium perchlorate. In practice, the gas generant composition can include about 1 to about 10 composition weight perchlorate additive.

In accordance with certain embodiments the perchlorate additive includes at least one alkali metal perchlorate such as, for example, perchlorates of lithium, sodium, potassium, rubidium and cesium. In practice, sodium perchlorate and potassium perchlorate are believed to be particularly desirable alkali metal perchlorates for use in the practice of the

π invention based on performance and cost with the use of potassium perchlorate being particularly preferred, at least in part as a result of the lower hygroscopicity associated therewith.

In accordance with other embodiments, the perchlorate additive is ammonium perchlorate. In practice, the gas generant composition can include about 1 to about 10 composition weight percent ammonium perchlorate.

In practice, it may be desirable and/or advantageous to manipulate the heterogeneity of the extrudable gas generant composition. It is theorized that the larger the particle size of the perchlorate additive incorporated into an extrudable gas generant composition of the invention, the higher the degree of heterogeneity resulting therefrom.

Consequently, a greater effect on effluent toxicity is realized as a result of the inclusion of the sized perchlorate additive particles in a particular extrudable gas generant composition. It is further theorized that the effectiveness of the perchlorate additive in reducing the generation of undesirable species in the gaseous effluent, produced when the extrudable gas generant composition is combusted, is reduced as the resulting perchlorate-containing gas generant composition becomes more homogeneous. For example, the use of perchlorate particles having a mean particle size of less than 100 microns results in an extrudable gas generant composition having reduced heterogeneity and reduced effectiveness to inhibit the generation of undesirable species in the gaseous effluent. More specifically, it has been found that the inclusion, in an extrudable gas generant composition, of perchlorate additives having a mean particle size in excess of 100 microns and, in accordance with certain embodiments, a mean particle size of at least about 200 microns can dramatically improve the effluent resulting from the combustion of an extrudable gas generant composition which includes such sized perchlorate additive particles, as compared to the effluent resulting from the combustion of the same gas generant composition but without the so sized perchlorate additive particles. In accordance with at least certain other embodiments of the invention, it has been found advantageous that perchlorate additive particles included in extrudable gas generant compositions have a mean particle size in the range of about 350 to about 450 microns. The extrudable gas generant composition further includes a polymeric binder material effective to render the gas generant composition extrudable. In practice, the extrudable gas generant composition includes about 1 to about 20 composition weight percent polymeric binder material. Tn accordance with certain embodiments the extrudable gas generant composition can include about 3 to about 10 composition weight percent polymeric binder material. In accordance with certain further embodiments, the extrudable gas generant composition includes about 3 to about 6 composition weight percent polymeric binder material.

Suitable polymeric binder materials for use in the extrudable gas generant composition include, but are not limited to, cellulosic materials, natural gums, polyacrylates, polyacrylamides, polyurethanes, polybutadienes, polystyrenes, polyvinyl alcohols, polyvinyl acetates, silicones and combinations of two or more thereof. In accordance with certain embodiments, the polymeric binder material may be a cellulosic material selected from ethyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose and combinations of two or more thereof. In accordance with certain other embodiments, the polymeric binder material maybe a natural gum selected from guar, xanthan, arabic and combination of two or more thereof.

In accordance with one embodiment, the gas generant composition includes guar gum such as in a relative amount of about 1 to about 20 composition weight percent. In accordance with certain embodiments the extrudable gas generant composition can include about 3 to about 10 composition weight percent guar gum. In accordance with certain further embodiments, the extrudable gas generant composition includes about 3 to about 6 composition weight percent guar gum. If desired, an extrudable gas generant composition in accordance with the invention may advantageously contain at least one metal oxide burn rate enhancing and slag formation additive. Such metal oxide additives may be added to enhance the burn rate of the extrudable gas generant composition or may be added to assist in the removal of undesirable combustion byproducts by forming filterable particulate material or slag. In practice, the extrudable gas generant compositions of the present invention may include up to about 10 composition weight percent of at least one such metal oxide additive. Suitable metal oxide additives include, but are not limited to, silicon dioxide, aluminum oxide, zinc oxide, and combinations thereof. In accordance with certain embodiments, the extrudable gas generant compositions include about 1 to about 5 composition weight percent of at least one such metal oxide additive. Extrudable gas generant compositions in accordance with certain other embodiments desirably contain about 1.5 to about 5 composition weight percent of aluminum oxide metal oxide burn rate enhancing and slag formation additive and up to about 1 composition weight percent of silicon dioxide metal oxide burn rate enhancing and slag formation additive.

In certain embodiments, the extrudabl e gas generant composition may desirably include at least one compound effective to enhance the combustion of theperchlorate additive. In practice, the extrudable gas generant compositions of the present invention may include up to about 10 composition weight percent of at least one such combustion enhancer. Suitable perchlorate additive combustion enhancers include, but are not limited to, iron oxide, copper chromite, ferricyanide/ferrocyanide pigments, and combinations thereof.

In certain embodiments, the extrudable gas generant advantageously includes at least one ferricyanide/ferrocyanidepigment. Such ferricyanide/ferrocyanide pigments, also referred to as "Iron Blue Pigments" are to be understood to generally refer to that class, family or variety of pigment materials based on microcrystalline Fe(II)Fe(III) cyano complexes. According to results obtained by X-ray and infrared spectroscopy, the basic general chemical formula for the Iron Blue Pigments is believed to be: Me(I)Fe(II)Fe(III)(CNVH₂O. (1)

In this formula, Me(I) stands for potassium, sodium or ammonium, with the alkali ion being believed to play a decisive role in the color properties of Iron Blue. Iron Blue Pigments, also sometimes referred to as "iron ferricyanides," have been produced or sold under a variety of different names related to either the place where the compound was made or to represent particular optical properties. Examples of such different names include: "Berlin Blue",

"Bronze Blue", "Chinese Blue", "Milori Blue", "Non-bronze Blue", "Paris Blue", "Prussian Blue", "Toning Blue" and "Turnbull's Blue", for example.

Those skilled in the art and guided by the teachings herein provided will appreciate that, as identified above, a wide variety of specific or particular Iron Blue Pigment iron ferricyanide materials are available. MANOX-Blue 4050 Iron Blue Pigment iron ferricyanide produced or sold by Degussa Corp. is a currently preferred Iron Blue Pigment material for use in the practice of the invention.

Additional additives such as processing aids and/or lubricants may also be included in the extrudable gas generant composition to improve processability of the composition. Generally, such additives may be included in the extrudable gas generant composition in relatively minor concentrations such as no more than about 5 composition weight percent. In view of the above, an extrudable gas generant composition in accordance with certain embodiments may include: at least one non-azide, organic, nitrogen-containing fuel present in a relative amount of 5 to 60 composition weight percent; at least one copper-containing compound selected from basic copper nitrate, cupric oxide, a copper diammine dinitrate-ammonium nitrate mixture wherein ammonium nitrate is present in the mixture in a range of about 3 to 90 weight percent, copper diammine bitetrazole, a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate, and combinations thereof, the at least one copper-containing compound present in a relative amount of 10 to 80 composition weight percent; a perchlorate additive including at least one perchlorate material selected from alkali metal perchlorates and ammonium perchlorate, the perchlorate additive present in a relative amount of 1 to 10 composition weight percent and effective to result in a gaseous effluent, when the gas generant composition is combusted, having a reduced content of at least one species selected from carbon monoxide, ammonia, nitrogen dioxide and nitric oxide, as compared to a same gas generant composition free of the perchlorate additive; and a polymeric binder material present in a relative amount of 1 to 20 composition weight percent and effective to render the gas generant composition extrudable, the polymeric binder material selected from cellulosic materials, natural gums, polyacrylates, polyacrylamides, polyurethanes, polybutadienes, polystyrenes, polyvinyl alcohols, polyvinyl acetates, silicones and combinations of two or more thereof.

Further, in view of the above, an extrudable gas generant composition in accordance with certain other embodiments may include 5 to 60 composition weight percent guanidine nitrate, 10 to 80 composition weight percent of a combination of basic copper nitrate and a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate, 1 to 10 composition weight percent ammonium perchlorate, and 1 to 20 composition weight percent guar gum. The ammonium perchlorate is effective to result in a gaseous effluent, when the gas generant composition is combusted, having a reduced content of at least one species selected from carbon monoxide, ammonia, nitrogen dioxide and nitric oxide, as compared to a same gas generant composition free of ammonium perchlorate.

Still further, in view of the above, an extrudable gas generant composition in accordance with certain other embodiments may include 5 to 60 composition weight percent guanidine nitrate, 10 to 60 composition weight percent of a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate, 1 to 10 composition weight percent ammonium perchlorate, and 1 to 20 composition weight percent guar gum.

The invention further comprehends methods for inflating an airbag cushion of an inflatable restraint system of a motor vehicle including the steps of igniting an extruded gas generant composition to produce a quantity of inflation gas and then inflating the airbag cushion with the inflation gas. As will be appreciated, the inflation gas has a reduced content of at least one species selected from carbon monoxide, ammonia, nitrogen dioxide and nitric oxide. As will be appreciated, extrudable gas generant compositions in accordance with the invention can be incorporated, utilized or practiced in conjunction, with a variety of different structures, assemblies and systems. As representative, the drawing illustrates a vehicle 10 having an interior 12 wherein an inflatable vehicle occupant safety restraint system, generally designated by the reference numeral 14, is positioned. As will be appreci ated, certain standard elements not necessary for an understanding of the invention may have been omitted or removed from the drawing for purposes of facilitating illustration and comprehension.

The vehicle occupant safety restraint system 14 includes an open-mouthed reaction canister 16 which forms a housing for an inflatable vehicle occupant restraint 20, e.g., an inflatable airbag cushion, and an apparatus, generally designated by the reference numeral 22, for generating or supplying inflation gas for the inflation of an associated occupant restraint. As identified above, such a gas generating device is commonly referred to as an "inflator."

The inflator 22 contains a quantity of a gas generant composition in accordance with the invention and such as described above. The inflator 22 also includes an ignitor, such as known in the art, for initiating combustion of the gas generant composition in ignition communication with the gas generant composition. As will be appreciated, the specific construction of the inflator device does not form a limitation on the broader practice of the invention and such inflator devices can be variously constructed such as is also known in the art. In practice, the airbag cushion 20 upon deployment desirably provides for the protection of a vehicle occupant 24 by restraining movement of the occupant in a direction toward the front of the vehicle, i.e., in the direction toward the right as viewed in the drawing. ^J The present invention is described in further detail in connection with the following examples which illustrate or simulate various aspects involved in the practice of the invention. It is to be understood that all changes that come within the spirit of the invention are desired to be protected and thus the invention is not to be construed as limited by these examples.

EXAMPLES Comparative Examples 1-4 and Example 1

Five gas generant compositions, Example 1 (EX 1) and Comparative Examples 1-4 (CEl - CE4), as shown in TABLE 1, below, were prepared. All compound values are given in terms of "composition weight percent."

TABLE 1

Compound (wt %) CEl CE2 CE3 CE4 EX l

Guanidine nitrate 50.38 27.49 49.37 26.94 23.65

Basic copper nitrate 46.62 14.35 45.69 14.06 14.87

5-ATN/bCN Complex 55.16 54.06 48.78

Ammonium perchlorate 7.00

Guar gum 2.00 2.00 3.00

Aluminum oxide 3.00 3.00 2.94 2.94 2.70

Total: 100.00 100.00 100.00 100.00 100.00

Burn Rate @ 3000 psi 0.82 2.11 0.33 1.32 2.30 where,

5-ATN/bCN = a copper-nitrate complex resulting from reaction of

5-aminotetrazole with basic copper nitrate; and Burn Rate @ 3000 psi = inches per second. More specifically, for Comparative Examples 1 and 2, the guanidine nitrate, the copper-containing compounds and the aluminum oxide were slurry mixed and then spray dri ed to form a powder precursor. The resulting powder precursor was then appropriately tableted using common tableting processing.

Comparative Example 3, Comparative Example 4, and Example 1 were prepared by slurry mixing the guanidine nitrate, the copper-containing compounds and the aluminum oxide. The resulting slurry was spray dried to form a powder precursor. The powder precursor was dry blended with the guar gum and, for Example 1, the ammonium perchlorate. The diy blend mixture was wetted with water, dried and granulated. The resulting granulated mixture was then appropriately tableted using common tableting processing.

The burn rate data, as shown in TABLE 1 above, was obtained by first pressing samples of the respective gas generant compositions into the shape or form of a 0.5 inch diameter cylinder. Typically, enough composition was used to result in a cylinder length of 0.5 inch. The cylinders were then each coated on all surfaces except the top surface with a krylon ignition inhibitor to help ensure a linear burn in the test apparatus. In each case, the so- coated cylinders were placed in a 1 -liter closed vessel or test chamber capable of being pressurized to several thousand psi with nitrogen and equipped with a pressure transducer for accurate measurement of test chamber pressure. A small sample of igniter powder was placed on top of the cylinder and a nichrome wire was passed through the igniter powder and connected to electrodes mounted in the lid of the test chamber. The test chamber was then pressurized to the desired pressure and the sample ignited by passing a current through the nichrome wire. Pressure versus time data was collected as each of the respective samples were burned. Since combustion of each of the samples generated gas, an increase in test chamber pressure signaled the start of combustion and a "leveling off' of pressure signaled the end of combustion. The time required for combustion was equal to t₂-t,, where t₂ is the time at the end of combustion and t, is the time at the start of combustion. The sample weight was divided by combustion time to determine the burning rate in grams per second. Burning rates were typically measured at four pressures; 900, 1350, 2000 and 3000 psi, respectively (6205, 9308, 13790 and 20,684 kPa, respectively). The log of the burn rate versus the log of average pressure was then plotted. From this line the burn rate at any pressure can be calculated using the following burn rate equation: r_b = K(P)ⁿ where: ij, = burn rate (linear) K = constant P = pressure n = pressure constant. Discussion of Results

As can be seen in TABLE 1 , the inclusion of a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate (5-ATN/bCN) has a significant impact on the burn rate of the gas generant composition. For example, when 5-ATN/bCN is added to the gas generant of Comparative Example 1 to produce the gas generant composition of Comparative Example 2, the burn rate increased from 0.82 inches/second to 2.11 inches/second (about 2.08 cm/second to 5.36 cm/second). Similarly, when 5-ATN/bCN was added to the extrudable gas generant composition of Comparative Example 3 to produce the extrudable gas generant composition of Comparative Example 4, the burn rate increased from_t 0.33 inches/second to 1.32 inches/second (about 0.84 cm/second to about 3.35 cm/second).

However, as can be seen in TABLE 1, the inclusion of guar gum has a deleterious impact on the burn rate of the gas generant composition. For example, when guar gum was added to the gas generant composition of Comparative Example 1 to produce the extrudable gas generant composition of Comparative Example 3, the burn rate declined from 0.82 inches/second to 0.33 inches/second (about 2.08 cm/second to about 0.84 cm/second).

Similarly, when guar gum was added to the gas generant composition of Comparative Example 2 to produce the extrudable gas generant composition of Comparative Example 4, the burn rate declined form 2.11 inches/second to 1.32 inches/second (about 5.36 cm/second to about 3.35 cm/second). In contrast, the extrudable gas generant composition in accordance with the invention (e.g., Example 1) was found to have a burn rate of 2.30 inches/second (about 5.84 cm/second). It is theorized that the inclusion of the ammonium perchlorate additive results in a gaseous effluent having a reduced content of undesirable components while inclusion of the 5-ATN/bCN offsets the decrease in burning rate due to the presence of the polymeric binder material. Thus, an extrudable gas generant composition such as that of Example 1 has both an improved effluent profile and an improved burn rate over extrudable and non-extrudable gas generant compositions which are free of ammonium perchlorate such as, for example, those gas generant compositions described in Comparative Examples 1-4.

The invention illustratively disclosed herein suitably may be practiced in the absence of any element, part, step, component, or ingredient which is not specifically disclosed herein. While in the foregoing detailed description this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.

Claims

What is claimed is:

1. An extrudable gas generant composition comprising: at least one non-azide, organic, nitrogen-containing fuel; at least one copper-containing compound selected from the group consisting of basic copper nitrate, cupric oxide, a copper diammine dinitrate- ammonium nitrate mixture wherein ammonium nitrate is present in the mixture in a range of about 3 to about 90 weight percent, copper diammine bitetrazole, a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate, and combinations thereof; a perchlorate additive comprising at least one perchlorate material selected from the group consisting of alkali metal perchlorates and ammonium perchlorate, the perchlorate additive present in a relative amount effective to result in a gaseous effluent, when the gas generant composition is combusted, having a reduced content of at least one species selected from the group consisting of carbon monoxide, ammonia, nitrogen dioxide and nitric oxide, as compared to a same gas generant composition free of the perchlorate additive; and a polymeric binder material effective to render the gas generant composition extrudable.

2. The extrudable gas generant composition of claim 1 wherein the polymeric binder material is selected from the group of cellulosic materials, natural gums, polyacrylates, polyacrylamides, polyurethanes, polybutadienes, polystyrenes, polyvinyl alcohols, polyvinyl acetates, silicones and combinations of two or more thereof.

3. The extrudable gas generant composition of claim 2 wherein the polymeric binder material is a cellulosic material selected from the group consisting of ethyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose and combinations of two or more thereof.

4. The extrudable gas generant composition of claim 2 wherein the polymeric binder material is a natural gum selected from the group consisting of guar, xanthan, arabic and combinations of two or more thereof.

5. The extrudable gas generant composition of claim 1 wherein the polymeric binder material is present in a relative amount of 1 to 20 composition weight percent.

6. The extrudable gas generant composition of claim 1 wherein the at least one non-azide, organic, nitrogen-containing fuel comprises guanidine nitrate.

7. The extendable gas generant composition of claim 1 wherein the at least one non-azide, organic, nitrogen-containing fuel is present in a relative amount of 5 to 60 composition weight percent.

8. The extrudable gas generant composition of claim 1 wherein the at least one copper-containing compound is present in a relative amount of 10 to 80 composition weight percent.

9. The extrudable gas generant composition of claim 1 wherein the perchlorate additive is present in a relative amount of 1 to 10 composition weight percent.

10. The extrudable gas generant composition of claim 1 wherein the perchlorate additive is selected from the group consisting of ammonium perchlorate, potassium perchlorate, sodium perchlorate and combinations thereof.

11. An extrudable gas generant composition comprising: at least one non-azide, organic, nitrogen-containing fuel present in a relative amount of 5 to 60 composition weight percent; at least one copper-containing compound selected from the group consisting of basic copper nitrate, cupric oxide, copper diammine dinitrate-ammonium nitrate mixture wherein ammonium nitrate is present in the mixture in a range of about 3 to about 90 weight percent, copper diammine bitetrazole, a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate, and combinations thereof, the at least one copper-containing compound present in a relative amount of 10 to 80 composition weight percent; a perchlorate additive comprising at least one perchlorate material selected from the group consisting of alkali metal perchlorates and ammonium perchlorate, the perchlorate additive, present in a rel ative amount of 1 to 10 composition weight percent, effective to result in a gaseous effluent, when the gas generant composition is combusted, having a reduced content of at least one species selected from the group consisting of carbon monoxide, ammonia, nitrogen dioxide and nitric oxide, as compared to a same gas generant composition free of the perchlorate additive; and a polymeric binder material present in a relative amount of 1 to 20 composition weight percent and effective to render the gas generant composition extrudable, the polymeric binder material selected from the group of cellulosic materials, natural gums, polyacrylates, polyacrylamides, polyurethanes, polybutadienes, polystyrenes, polyvinyl alcohols, polyvinyl acetates, silicones and combinations of two or more thereof.

12. The extrudable gas generant composition of claim 11 wherein the polymericbinder material is a natural gum selected from the group consisting of guar, xanthan, arabic and combinations of two or more thereof.

13. The extrudable gas generant composition of claim 11 wherein the polymeric binder material is guar gum.

14. The extrudable gas generant composition of claim 11 wherein the at least one non-azide, organic, nitrogen-containing fuel comprises guanidine nitrate.

15. The extrudable gas generant composition of claim 11 wherein the perchlorate additive comprises ammonium perchlorate

16. The extrudable gas generant composition of claim 11 wherein the perchlorate additive has a particle size of at least about 200 microns.

17. The extrudable gas generant composition of claim 11 wherein the copper-containing compound is a copper-nitrate complex resulting from reaction of 5- aminotetrazole with basic copper nitrate.

18. The extrudable gas generant composition of claim 11 wherein the copper-containing compound is a combination of basic copper nitrate and a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate.

19. The extrudable gas generant of claim 11 additionally comprising a metal oxide burn rate enhancing and slag formation additive selected from the group consisting of silicon dioxide, aluminum oxide, zinc oxide, and combinations thereof.

20. The extrudable gas generant composition of claim 11 additionally comprising a combustion enhancer selected from the group consisting of iron oxide, copper chromite, Iron Blue pigments, and combinations thereof.

21. An extrudable gas generant composition comprising: 5 to 60 composition weight percent guanidine nitrate;

10 to 80 composition weight percent of a combination of at least one copper-containing compound selected from the group consisting ofbasic copper nitrate, cupric oxide, a copper diammine dinitrate-ammonium nitrate mixture wherein the ammonium nitrate is present in the mixture in a range of about 3 to about 90 weight percent, copper diammine bitetrazole, a copper-nitrate complex resulting from reaction of 5-aminotetrazole with basic copper nitrate, and combinations thereof;

1 to 10 composition weight percent of a perchlorate additive comprising at least one perchlorate material selected from the group consisting of alkali metal perchlorates and ammonium perchlorate; and

1 to 20 composition weight percent of polymeric binder material effective to render the gas generant composition extrudable, wherein the polymeric binder material is selected from the group consisting of cellulosic materials, natural gums, polyacrylates, polyacrylamides, polyurethanes, polybutadienes, polystyrenes, polyvinyl alcohols, polyvinyl acetates, silicones and ςombinations of two or more thereof.