Gas generant igniter coating materials and methods

Abstract

Gas generant grains, such as tablets, granules or particulates, are coated with a dispersion of oxidizer particulates, metal fuel particulates, a fluoropolymer binder with which at least a portion of the metal fuel is reactive, and a solvent for the fluoropolymer.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention is generally directed to gas generants and materials for igniting the same and, more particularly, to gas generants coated with ignition material. Even more particularly, the invention is directed to coating small grains of gas generant with ignition material such that good adhesion is obtained between the ignition material and the gas generant without a substantial decrease in performance by the gas generant.

[0002] It is well known to protect a vehicle occupant using a cushion or bag, e.g., an “airbag cushion,” that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins to be inflated, in a matter of no more than a few milliseconds, with gas produced or supplied by a device commonly referred to as an “inflator.”

[0003] Many types of inflator devices have been disclosed in the art for use in the inflating of one or more inflatable restraint system airbag cushions. Many prior art inflator devices include solid form gas generant materials which are burned to produce or form gas used in the inflation of an associated airbag cushion.

[0004] Gas generant compositions commonly utilized in the inflation of automotive inflatable restraint airbag cushions have previously most typically employed or been based on sodium azide. Such sodium azide-based compositions, upon initiation, normally produce or form nitrogen gas. While the use of sodium azide and certain other azide-based gas generant materials meets current industry specifications, guidelines and standards, such use may involve or raise potential concerns such as involving the safe and effective handling, supply and disposal of such gas generant materials.

[0005] Such inflator devices tend to involve rather complex ignition processes. For example, it is relatively common to employ an electrically initiated squib to ignite a separate charge of an igniter composition. The products of such ignition are then used to ignite a gas generant material, also contained within the inflator device. In practice, the ignition process employed in many various prior inflator devices requires a separate igniter charge because the squib generally does not itself supply sufficient hot gas, condensed phase particles or other ignition products to sufficiently heat the gas generant material to result in the reaction of the gas generant and desired gas generation.

[0006] While ignition of the gas generant may ultimately be achieved through the use of such an igniter charge, such an ignition process may be undesirably complicated and may tend to undesirably complicate the manufacture, production and design of the associated inflator device as well. For example, such use necessitates that an igniter composition be manufactured or made and then subsequently handled such as through manufacture of a container to hold or store the igniter composition for subsequent incorporation into the inflator device design as a part of an igniter assembly.

[0007] As will be appreciated, space is often at a premium in modem vehicle designs. Consequently, it is generally desired that the space requirements for various vehicular components, including inflatable vehicle occupant restraint systems, be reduced or minimized to as great an extent as possible. The incorporation of an igniter assembly such as described above and associated support structure(s), may require a larger than desired volume of space within an associated inflator device. In particular, such volume of space could alternatively potentially be utilized to store or contain gas generant material and thereby permit the volume of space required by the inflator device to be reduced.

[0008] In addition, the incorporation and use of an ignition assembly and process, such as described above, can detrimentally impact either or both the weight and cost of the corresponding apparatus hardware.

[0009] Thus, there is a need and a demand for alternative airbag inflator device ignition schemes and, in particular, there is a need and a demand for avoiding the requirement or inclusion of separate igniter composition charges and associated hardware. Various patents, including U.S. Pat. Nos. 4,698,107; 4,806,180; and 5,034,070, disclose processing wherein an ignition coating is applied, such as in the form of a liquid or a water slurry, to azide-based gas generant formulations. Such processing typically necessitates first the formation of the azide-based gas generant, including the proper forming and drying of gas generant grains in selected shapes, followed by the coating of the grain with a wet slurry of the ignition material, such as by immersion of the grain in a slurry of the coating material, and then final drying.

[0010] In such dip coat processing, generally either individual gas generant tablets or wafers are coated as they pass through a coating slurry on a conveyer belt, or the gas generant tablets or wafers are put in bulk containers and submerged in the slurried coating material. These types of process are typically relatively slow and may lead to problems such as coated tablets/wafers sticking to themselves, associated equipment, such as conveyer belts, or both.

[0011] In addition, dependent on the shape of the gas generant tablet or wafer there may also be problems in obtaining application of a uniform coating. For example, if the gas generant has a relatively flat form, the slurry coating may tend to pool and may therefore dry to form a coating of variable thicknesses.

[0012] Also, dip coating equipment (e.g., dip baskets and conveyer belts) may easily be contaminated with igniter material, leading to potential or increased safety concerns.

[0013] Thus, there is a need and demand for alternatives to azide-based pyrotechnics and related gas generants as well as for alternative improved ignition enhanced gas generating materials such as used in the inflation of inflatable devices such as an inflatable vehicle occupant restraint airbag cushions and related methods of processing such as may permit or facilitate the placement of an ignition composition onto a gas generant having a selected form. In particular, there is a need and a demand for ignition enhanced gas generating materials such as may further desirably avoid the requirement or inclusion of a separate or distinct igniter composition charge.

[0014] At least partially in response to such need and demand, U.S. Pat. No. 6,077,372 issued to Mendenhall et al. discloses an ignition enhanced gas generant formulation and method of making the same utilizing a solvent effective to partially solubilize at least one component of each of a selected ignition composition and, upon application to the gas generant, at least one component of an associated gas generant.

[0015] While such ignition enhanced gas generants and methods may be effective in overcoming or minimizing various of the shortfalls of prior ignition assemblies and processes, further particular improvements have been sought and desired. For example, it is generally desired that a coating of ignition material strongly adhere to a gas generant such that the ignition material does not readily or easily separate from the gas generant either during handling or when subjected to normal vibration such as may be experienced by an inflator during its lifetime in an automotive vehicle.

[0016] In this regards it is noted that many driver and side impact inflator devices utilize or contain gas generants in the form of small pellets or tablets, e.g., cylindrical pellets such as 6.35 mm in diameter and 2.0 mm in height. Typically, such small pellets or tablets weigh only between about 0.10 and 0.25 grams. Further, the uniform ignition coating of such small gas generant tablets or pellets generally requires a separate “off-line” process whereby the gas generant tablets or pellets are first coated with an ignition material, dried and, subsequently, loaded into an inflator. As will be appreciated, such coated materials may undergo significantly rigorous handling during such processing.

[0017] In view of the above, there is a need and a demand for improved igniter materials such as for coating gas generant formulations, particularly gas generants in the form of small pellets or grains. Further, there is a need and a demand for improved igniter material-coated gas generant that are self-igniting, and to methods of producing ignition material-coated gas generant formulations

SUMMARY OF THE INVENTION

[0018] A general object of the invention is to provide an improved grain of gas generant formulation, such as containing or including a coating of ignition material, such as in the form of a film or layer. In particular, the invention is directed to providing such a coated grain with improved adhesion between the ignition material layer and the gas generant with desirably, at most, a minimal decrease in performance.

[0019] A more specific objective of the invention is to overcome one or more of the problems described above.

[0020] The general object of the invention can be attained, at least in part, by an ignition material that includes finely divided particulates of metal fuel, finely divided oxidizer particulates, and a fluoropolymer binder. In accordance with a preferred embodiment of the invention, the metal fuel is desirably reactive with the binder, e..g., reactive with fluorine moieties of a fluoropolymer. Further, the finely divided particulates of metal fuel and the finely divided oxidizer particulates are desirably substantially uniformly distributed within the binder.

[0021] Further, an ignition material in accordance with certain preferred embodiments consists essentially of finely divided particulates of metal fuel, finely divided oxidizer particulates, and a fluoropolymer binder, such as identified above, and may additionally contain up to about 10 wt. % of a desensitizing additive.

[0022] The general object of the invention is obtained, at least in part, by an ignition material comprising oxidizer particulates, fuel particulates comprising metal fuel, and fluorocarbon binder reactive with the metal fuel, and fluorocarbon binder reactive with the metal fuel at a level of between 1 wt. % and 5 wt. % of the ignition material.

[0023] The general object of the invention is achieved, at least in part, by a method of coating a gas generant grain that provides an adherent ignition material film thereon. In the method, a fluoropolymer is dissolved in a solvent to form a solution. Fuel particulates and oxidizer particulates are dispersed in the solution to form a dispersion, and the dispersion is used to coat grains of gas generant material.

[0024] As used herein, bodies of gas generant material, including large bodies, particles, tablets or granules, are referred to generically as “grains”.

[0025] The terms “film” and “layer” are generally synonymous when used to define a coating of ignition material on a gas generant grain.

[0026] The term “dispersion” is used herein to define a mixture of liquid and solid particulates and includes what may be considered to be a slurry.

[0027] “Small grains” are bodies of gas generant material that in uncoated form, weigh between about 0.01 and about 3.0 grams.

[0028] The term “self-igniting” generally refers to a material that when exposed to the energy put out by a typical automotive squib (e.g., a squib that contains 60-200 mg of zirconium potassium perchlorate) combusts rapidly enough and with the generation of sufficient heat to simultaneously ignite an associated supply of gas generant grains to result in deployment of an associated airbag cushion, as measured by tank pressure, typically within 6 milliseconds.

[0029] References to a material as an “elastomer,” “elastomeric” or the like generally refer to a material that can deform when subjected to an external stress and which material generally returns to its original shape when the stress is removed.

[0030] Percentages are by weight, unless otherwise noted.

[0031] Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention provides improved ignition materials that may be coated directly on gas generant grains, whereby gas generators (inflators) do not require a separate ignition assembly. These ignition materials include a uniformly distributed mixture of oxidizer particulates, fuel particulates, including metal fuel, and fluoropolymer elastomer. The provided ignition material preferably contains the gfluoropolymer at levels of between 1 wt. % and 5 wt. %, whereby decreased performance of gas generant material grains occasioned by the use of a binder is minimized. The present invention further provides a coating method in which a fluoropolymer binder is dissolved in a suitable solvent to form a solution, particulates of oxidizer and metal fuel are dispersed in the solution to form a dispersion or slurry, and the dispersion or slurry is coated, such in the form of a film or layer, onto gas generant grains.

[0033] It is proposed to incorporate a soluble polymeric material in an ignition material dispersion that, upon application to a gas generant formulation substrate and drying to remove solvent, forms a film that imparts a cohesiveness to the ignition material and an adhesive physical bond to the gas generant formulation substrate. In general, the degree of adhesion of the ignition material film to the gas generant formulation is proportional to the level of polymeric material in the slurry. It has been found, however, that the addition of the polymeric material to the formulation decreases performance of the ignition material/gas generant formulation system as is manifest by a delay in ignition; which delay in ignition is roughly proportional to the amount of polymeric additive. Accordingly, a polymer additive and additive level are desirably selected that achieve an acceptable balance of an increase in adhesion with any decrease in performance.

[0034] Herein it is proposed to utilize a polymeric binder that reacts with other components of the ignition system, whereby adequate adhesion with the gas generant material can be achieved, while any decrease in igniter performance is avoided or minimized. Accordingly, it is proposed that a fluorocarbon polymer be used as the binder and that at least a significant proportion of the fuel component of the ignition system be a metal, mixture of metals, or alloys of metals that react with the fluorocarbon polymer, particularly the fluorine component thereof, such as to form the metal(s) fluoride(s).

[0035] Fluoropolymers, such as the fluoropolymer elastomers sold as Viton®, are known to react with magnesium and other metals, as described in U.S. Pat. Nos. 5,253,584,4,846,368 and 4,817,828. Other fluoropolymer-reactive metals, in addition to magnesium and useful in the practice of the invention include, but are not limited to, aluminum, boron, beryllium, calcium, strontium, barium, sodium, lithium, titanium and zirconium. Mixtures and alloys of fluoropolymer-reactive metals are likewise useful in accordance with the invention.

[0036] Preferred fluorocarbon-reactive metals for use within the present invention are magnesium, aluminum and mixtures or alloys thereof. In accordance with certain preferred embodiments of the invention, minor amounts of boron may also be used in combination with other metals, e.g., magnesium and/or aluminum. In particular, such incorporation of boron may advantageously provide a desirably more rapid initiation of the ignition mixture at ambient pressure. Preferably, the fluoropolymer-reactive metal is a mixture or alloy of magnesium, aluminum and, optionally, boron. Preferred such mixtures or alloys of metals comprise between about 20 and about 50 wt. % magnesium and between about 50 and about 80 wt. % aluminum, and 0 to 20 wt. % boron, which weight percentages are based on total weight of metal fuel. If boron is included as part of the metal fuel, it is typically incorporated at a level of at least 1 wt. % of total metal fuel, with the relative amount of boron typically balanced against the material cost thereof. The metal fuel component is generally preferably used as finely divided particulates in the coating slurry, the mean particulate diameter of the metal fuel particulates typically being between about 1 and about 10 microns.

[0037] The ignition material further comprises or includes an oxidizer. Suitable oxidizers include nitrates of strontium and alkali metals, and combinations thereof. Preferably, the amount of oxidizer relative to the amount of fuel equals or approximates, i.e., within about 20 mole percent, the stoichiometric equivalent of the fuel. Generally, the ignition material comprises between about 55 and about 75 wt. % oxidizer, between about 10 and about 40 wt. % metal fuel, and between about 1 and about 5 wt. % fluoropolymer based on the total weight of ignition material. Like the metal fuel, the oxidizer materials are used as finely divided particulates. The oxidizer particulates have mean particulate diameters between about 1 and about 20 microns in diameter.

[0038] In addition, ignition materials in accordance with the invention may advantageously contain or include one or more desensitizer additives such as to desirably desensitize the material to the effect of one or more stimuli such as friction, impact and electrostatic discharge, for example. Suitable such additive materials for use in the practice of the invention include, bentonite clay, silicon dioxide, aluminum oxide, zirconium oxide, titanium oxide and mixtures thereof, for example, with bentonite clay being found to be particularly effective in this regard. In general, such additives can desirably be included in the ignition materials of the invention in an amount corresponding up to about 10 wt. % of the total weight of the ignition material.

[0039] The fluoropolymer is added to promote cohesion of the ignition material layer and adhesion of this layer to the gas generant material. The fluoropolymer further provides fluorine such as can desirably exothermically react with the metal fuel and thereby minimizes the decrease in performance commonly exhibited by ignition material when a polymer binder is used. Increased or improved cohesion and adhesion are generally exhibited when the fluoropolymer is elastomeric, i.e., exhibits rubbery characteristics throughout the ambient temperature range to which the gas generants will commonly be subjected, e.g., −40° C. to 50° C. Examples of elastomeric fluoropolymers useful in accordance with the invention are sold as Viton® A, which is a copolymer of vinylidene fluoride and hexafluoropropene, and Viton®B, which is a copolymer of vinylidene fluoride hexafluoropropene and tetrafluoroethene. In practice, these polymers can or will react exothermically with Mg and Al, for example, to form MgF2 and AlF3, respectively. The fluoropolymers also react with the other metal fuels set forth above to form the corresponding metal fluorides.

[0040] As detailed below, such an ignition material can desirably be applied, as a dispersion (including slurry), to a particular or desired gas generant substrate. To form the dispersion, a solvent is employed to dissolve the fluoropolymer binder. The solvent is used in an amount at least sufficient to dissolve the fluoropolymer. Beyond that, additional solvent may be used to increase the flow-ability and spray-ability of the dispersion, although the inclusion or use of too much solvent is generally to be avoided because excessive solvent levels can undesirably lead to increased or excessive drying times. Preferred solvents are esters and ketones, such as acetone, ethyl acetate, butyl acetate and amyl acetate. Ketones are particularly preferred solvents for use in the practice of the invention as such solvents generally provide or result in high evaporation rates that translate into quick drying times of the dispersion after coating.

[0041] To coat a gas generant material substrate, the dispersion of ignition material is coated onto the substrate and solvent is removed to dry the ignition material such as to form or result in a layer being formed upon the substrate. From the standpoint of obtaining uniformity of coating, spray coating of the gas generant material tablets, granules, or particulates is generally preferred, although other coating methods, such as dip coating may be employed. Spray coating of the gas generant grains may take place in a fluidized bed of the grains so as to ensure generally uniform coating thickness of the ignition material on all surfaces of the gas generant grains. The ignition material is generally applied as a (dried) film in an amount sufficient to ensure rapid and uniform ignition at all surfaces of the gas generant substrate. Typically, the ignition material is applied to a (dry) average film thickness of between about 250 and about 1000 microns. Although the oxidizer and fuel particulates are generally uniformly distributed within the binder, the heterogeneous nature of the ignition material results in coatings that cannot be precisely of uniform thickness. In the ignition material-coated gas generant grain, the ignition material is used at between about 1 and about 10 wt. % based on the weight of the gas generant grain as 100%.

[0042] The gas generant material of which the grains are formed may be any such formulation known in the art, including sodium (or other alkali metal) azide gas generant formulations, as well as non-azide gas generant formulations formed of mixtures of organic and/or inorganic fuel plus oxidizers. The ignition materials and method of coating are applicable to coating gas generant formulation grains of any size or dimension. The invention is particularly useful for coating small pellets, granules or particles, which are herein referred to collectively as “grains”. The invention is most advantageously used for coating small grains, e.g., bodies of gas generant material that in uncoated form, weigh between about 0.01 and about 3.0 grams. In inflators using such small grains, a number of such grains are held together within a container. When such a collection of grains is subjected to the vibrations associated with automotive operation, there is a tendency for the ignition material to separate from the gas generant grains; thus the particular need for improved adhesion and cohesion of the ignition material film.

[0043] It has previously been proposed to coat large, shaped grains with combustion-enhancing compositions that contain fluoropolymers, oxidizers, and metal fuel particles. Examples of such coating compositions as used on large gas generant grains are found, for example, in U.S. Pat. Nos. 4,817,828 and 4,846,368. The combustion-enhancing compositions in these patents contain additional materials and large amounts of fluoropolymer binders, i.e., at least 10 wt. %. The combustion-enhancing compositions described in U.S. Pat. Nos. 4,817,828 and 4,846,368 do not appear to be self-igniting within the meaning of the present invention, as a self-contained igniter assembly is required in a central bore of stacked gas generant material grains. In any case, the large amount of fluoropolymer binder used, e.g., 10 to 15 wt. %, would detract from the performance of this material as the sole ignition material.

[0044] In contrast, the ignition material-coated gas generant grains of the present invention are self-igniting, obviating the need for a separate, self-contained igniter assembly.

[0045] 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 limited by these examples.

EXAMPLES

[0046] This example compared the adhesion (retention) advantage and performance disadvantage of three polymeric binders: silicone resin, hydroxypropyl cellulose (HPC), and Viton® B, a copolymer of vinylidene fluoride hexafluoropropene and tetrafluoroethene.

[0047] In each case, the ignition material was a composition of 50/50 aluminum/magnesium alloy, strontium nitrate and the specified polymeric additive, where the level or relative amount the polymeric binder was an optimized compromise between the adhesion advantage and performance disadvantage for the particular polymer. More particularly, the polymeric additives were employed in the following respective relative amounts: silicone resin 2 wt. %, HPC 2 wt. %, and Viton® B 3.5 wt. %, where the weight percentages are relative to the total amount of ignition material.

[0048] The testing was performed by slurrying each ignition material formulation in an equal weight of ethanol and spraying onto ¼ inch (0.56 cm) diameter, 0.060 inch (0.15 cm) thick gas generant tablets containing basic copper nitrate, guanidine nitrate and aluminum oxide, such as described in U.S. Pat. No. 6,143,102 to Mendenhall et al. and whose disclosure is hereby incorporated by reference in its entirety. Coated tablets of each formulation in an amount weighing 80 grams were vibrated on a 25 mesh screen for 5 minutes. Weight was recorded before and after vibration and loss of ignition material was calculated. TABLE 1, below, reports the results in terms of percentage retention.

[0049] Heavyweight hardware testing was performed by sequentially loading a 32 gram sample of each of the respective coated gas generants into an inflator simulator and firing the loaded inflator simulator into an open room. In each case the pressure in the combustion chamber was measured vs. time and the period of time until a first indication of pressure in the pressure vs. time curve is the delay reported in TABLE 1, below. 1 TABLE 1 Vibration test Delay POLYMERIC ADDITIVE retention (%) (milliseconds) Silicone Resin 22.8 0.5 HPC 96.20 5.0 Viton ® B 83.37 2.0

[0050] The data shows that ignition material retention is greatly improved with the HPC (2 wt. %), but a very significant (5.0 milliseconds) delay is observed. 3.5 wt. % Viton® B was required to achieve a retention of 81.37%, but even at this higher binder concentration, only a 2.0 millisecond delay is observed. Viton® B readily reacts with the magnesium and aluminum of the magnesium aluminum alloy in the formulation and produces great quantities of heat, contributing to the energy of the igniter combustion as compared to the sluggish reaction of the strontium nitrate oxidizer with hydroxypropyl cellulose. In summation, incorporation of the fluoropolymer into the ignition material increases adhesion with minimal impact on igniter performance.

[0051] Thus, the invention provides a gas generant composition coated with ignition material such that, in an inflator, a separate ignition assembly is not needed. The adhesion and cohesion of the ignition material as a film on a gas generant grain ensures that the film will adequately bind to the gas generant grain throughout the life of an automotive vehicle. The exothermic reaction of the fluorocarbon binder with the fuel, and the use of the fluorocarbon binder in minimal amounts, ensures that decrease in performance due to the inclusion and use of a binder is minimized.

[0052] The invention illustratively disclosed herein suitably may be practiced in the absence of any element, part, step, component, or ingredient that is not specifically disclosed herein.

[0053] 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

1. An ignition material comprising:

finely divided particulates of metal fuel, the metal fuel being reactive with fluorine moieties of a fluoropolymer,

finely divided oxidizer particulates, and

a fluoropolymer binder in which the finely divided particulates of metal fuel and the finely divided oxidizer particulates are substantially uniformly distributed.

2. The ignition material of claim 1 comprising the oxidizer particulates at between about 55 and about 75 wt. %, the metal particulates at between about 10 and about 40 wt. %, and the fluoropolymer binder at between about 1 and about 5 wt. %, said weight percentages being based on total weight of ignition material.

3. The ignition material of claim 1 wherein the metal fuel is selected from the group consisting of magnesium, aluminum, boron, beryllium, calcium, strontium, barium, sodium lithium, titanium and zirconium, mixtures of these metals and alloys of these metals.

4. The ignition material of claim 1 comprising magnesium.

5. The ignition material of claim 1 comprising aluminum.

6. The ignition material of claim 1 comprising boron.

7. The ignition material of claim 1 comprising a mixture or alloy of magnesium and aluminum.

8. The ignition material of claim 7 further comprising boron.

9. The material of claim 1 wherein the metal fuel comprises between about 20 and about 50 wt. % magnesium and between about 50 and about 80 wt. % aluminum, said weight percentages of magnesium and aluminum being based on total weight of magnesium and aluminum, and 0 to 20 wt. % boron, said weight percentage of being based on total weight of ignition material.

10. The ignition material of claim 9 containing at least 1 wt. % boron, said weight percentage of being based on total weight of ignition material.

11. The ignition material of claim 1 additionally comprising up to about 10 wt. % of a desensitizing additive, said weight percentage being based on total weight of ignition material.

12. The ignition material of claim 11 wherein the ignition material includes the desensitizing agent bentonite clay.

13. The ignition material of claim 1 in a form suitable for coating a substrate further comprising a solvent for said fluoropolymer binder in an amount sufficient to dissolve said fluoropolymer binder.

14. A method of providing an ignition material-coated gas generant substrate comprising providing a gas generant substrate and coating the gas generant substrate with the ignition material of claim 13.

15. The method of claim 14 wherein the ignition material is coated on the gas generant substrate by spray coating.

16. An ignition material-coated gas generant formulation comprising a gas generant having a coating of the ignition material of claim 1.

17. The ignition material-coated gas generant formulation of claim 16, wherein the substrate is a gas generant grain having a maximum weight of about 3.0 grams and the ignition material-coated gas generant formulation is capable of self-ignition.

18. An ignition material useful for coating a gas generant material substrate, the ignition material comprising oxidizer particulates, fuel particulates comprising metal fuel, and a fluoropolymer reactive with the metal fuel, the fluoropolymer being present at a level of between about 1 and about 5 wt. % of the ignition material.

19. The ignition material of claim 18 wherein the oxidizer particulates are present at a level of between about 55 and about 75 wt. % of ignition material and the metal particulates are present at between about 10 and about 40 wt. % of ignition material.

20. The ignition material of claim 19 additionally comprising up to about 10 wt. % of a desensitizing additive, said weight percentage being based on total weight of ignition material.

21. An ignition material-coated gas generant comprising a gas generant material substrate having a coating of the ignition material of claim 18.

22. The ignition material-coated gas generant of claim 21, wherein the gas generant material substrate is a gas generant grain having a maximum weight of about 3.0 grams and wherein the ignition material-coated gas generant is capable of self-ignition.

23. A method of coating a gas generant material to provide an adherent ignition material film thereon; the method comprising,

dissolving a fluoropolymer in a solvent to form a fluoropolymer solution,

dispersing particulates of oxidizer and fuel in the fluoropolymer solution to form a dispersion, and

coating a gas generant substrate with the dispersion.

24. The method of claim 23 wherein the fluoropolymer comprises between about 1 and about 5 wt. % of the dispersion, exclusive of the solvent.

25. The method of claim 23 wherein the dispersion is coated onto the gas generant substrate by spray coating.

26. The method of claim 23 wherein the dispersion is coated onto the gas generant substrate by spray coating in a fluidized bed.

27. The method according to claim 23 wherein the gas generant substrate is a gas generant grain having a maximum weight of about 3.0 grams, the coated gas generant substrate is capable of self-ignition.