WO1998054114A1

WO1998054114A1 - Gas-generative composition comprising aminoguanidine nitrate, potassium perchlorate and/or potassium nitrate and polyvinyl alcohol

Info

Publication number: WO1998054114A1
Application number: PCT/US1998/009376
Authority: WO
Inventors: James D. Martin; Brian Wheatley; Steve Scheffee; Robert Lynch; Merlin Larimer
Original assignee: Atlantic Research Corporation
Priority date: 1997-05-28
Filing date: 1998-05-15
Publication date: 1998-12-03

Abstract

The invention concerns a thermally stable gas-generative composition for inflating devices, such as airbags, said composition comprising about 30 to about 70 % by weight aminoguanidine nitrate, an oxidizing effective amount of potassium perchlorate and an effective amount as a binder of up to about 15 % by weight of polyvinyl alcohol, the oxidizer to fuel ratio being about 0.92 to about 0.98. As an alternative oxidizer or a co-oxidizer, potassium nitrate may be employed and low levels of guanidine nitrate may be utilized as an adjunct to aminoguanidine nitrate. The invention also involves the use of the composition to inflate an occupant restraint device and a gas generator for inflating an inflatable device containing said gas-generative composition.

Description

GAS GENERATIVE COMPOSITION COMPRISING A INOGUANIDINE NITRATE, POTASSIUM PERCHLORATE AND/OR POTASSIUM NITRATE

AND POLYVINYL ALCOHOL

Field of Invention

This invention involves a composition for producing a low particulate, non-flammable, odorless, non-toxic and colorless gas for inflating emergency inflatable devices, such as a passenger restraint device in an automobile. The composition comprises aminoguanidine nitrate (AGN) with highly oxygenated inorganic perchlorates and/or inorganic nitrates. Examples of such compositions include AGN/KP (potassium perchlorate) , AGN/KN (potassium nitrate) , or mixtures thereof, to which PVA (polyvinyl alcohol) is added as a binder. Low levels of guanidine nitrate (GN) can be used as an adjunct to AGN. The composition finds particular use in generating gas to inflate an air bag in an occupant restraint device in an automobile.

Prior Art

The public increasingly expects that vehicles will be provided with airbags to protect and to ensure the safety of the occupants therein. However, although new compositions may be formulated to generate suitable gases in a high volume, there are important factors that must be considered in determining whether any particular composition is acceptable for commercial use. While it is self-evident that the gas produced by a potential gas- generative composition must provide a high volume of gas, which is non-toxic and non-flammable, there are other properties that are equally important, but not as apparent. Thus, the temperature of the gas generated must be sufficiently low for it to be readily tolerated by the occupants of any vehicle in which it is employed. Moreover, since any gas with a smoke-like appearance may cause an occupant of the vehicle to suspect the possibility of a fire, compositions containing components that produce visible particulates must be avoided, because of psychological reasons, as well as possible physiological effects.

Moreover, of increasing concern is the long term stability of the gas-generative compositions, which must withstand different temperature conditions that may be encountered over long periods of time after the air bag system is installed in a vehicle. In addition to the foregoing, there are ecological and environmental hazards that may be created by failing to consider the possible consequences of permitting the gas-generative compositions to remain in vehicles that are no longer operable and must be scrapped. The failure to meet the standards imposed by industry, the public, government and common sense eliminates many compositions from being considered for vehicle restraint devices. On the other hand, it is difficult, if not impossible, to predetermine which compositions will function in a satisfactory manner, without the noted drawbacks, to accomplish the desired objectives set forth above in the absence of actual comprehensive testing of a particular formulation. Many patents disclose lists of oxidizers that include the alkali and alkaline earth perchlorates and nitrates, as well as lists of materials that may be employed to serve as a fuel to be oxidized and thereby generate a gas. In general, the literature, including the patented literature, seldom focuses on specific combinations of oxidizers, fuels and binders in disclosed proportions that would be particularly effective, economical and safe .

On the other hand, U.S. Patent No. 4,948,439 refers to a mixture of ammonium perchlorate and sodium nitrate in a 1 to 1 mole ratio as an especially useful oxidizer

"compound". Various salts, including ammonium, alkali metal and alkaline earth metal nitrates and perchlorates are among the oxidizers described. Ammonium perchlorate, the patentee cautions, although a good oxidizer, is not useful by itself because it produces hydrogen chloride or other toxic products if not balanced by the presence of a metal such as sodium or potassium. The foregoing limits the use of chlorine-containing oxidizers to the sodium and potassium salts, unless a sufficiently reactive metal compound that is not itself harmful or productive of toxic end products, is included in the composition.

In recent U.S. Patent No. 5,482,579, the patentee refers to a prior art composition comprising an oxidizer agent, a binder, cellulose acetate and a carbon- containing combustion controller. The composition is said to contain 78% to 92% by weight of a chlorate or perchlorate of an alkali metal or alkaline earth metal as the oxidizing agent, 7.9% to 17.2% by weight of a cellulose acetate and 0.1% to 0.8% by weight of a carbon- containing combustion controller.

At column 4, beginning at line 20, of the above- identified patent, the patentee describes the use of a nitrogen-containing non-metallic compound to control the combustion temperature as one selected from the group consisting of guanidine compounds, oximes, amides, tetrazole derivatives, aromatic nitro compounds and ammonium nitrate. The use of guanidine nitrate is specifically highlighted. In the Tables, the weight percent of potassium perchlorate varies from approximately 45% to about 82%. The utility for said composition, as well as that for the compositions of the former patent, is the same as that of the composition herein, i.e., for generating a gas to inflate a crash bag. The inflation of an emergency device or a restraint device is not the only purpose for producing gas. U.S. Patent No. 3,909,324 describes the provision of a novel pyrotechnic composition for disseminating smoke dyes, pesticides, agents for chemical warfare and the like. Among the components of the compositions in said patent are aminoguanidium nitrate or a condensation product thereof, as a fuel, and inorganic oxidizers which are readily combustible at atmospheric pressure. In claim 1 of the patent, a pyrotechnic disseminating formulation is described wherein about 8% to about 40% by weight aminoguanidium nitrates or condensation products thereof are combined with 8% to about 30% by weight of an alkali metal or ammonium chlorate or perchlorate as oxidizer, with the balance being an effective amount of a chemical warfare agent, an incapacitating agent, a smoke dye or a plant growth regulant to be disbursed.

In U.S. patent No. 4,543,136, a water-in-oil emulsion explosive composition is the described subject matter. Said composition includes an inorganic oxidizer salt which may be one of various nitrates, chlorates or perchlorates, including alkali metal or alkaline earth metal perchlorates. The inorganic oxidizer salts are used alone or in the admixture of at least two members . The oxidizer salt is generally present in 5% to 90%, preferably 40% to 85% and is employed in the form of an aqueous solution. At column 5, beginning at line 17, the patentee discusses sensitizers effective for improving the detonation liability and low temperature detonability of the resulting water-in-oil explosive. Among the various substances is guanidine nitrate. The compounding amount of the sensitizer is said to be 0% to 40%, preferably 0.5% to 30%.

Recently issued U.S. Patent No. 5,538,567, at column 2, discloses a gas-generative propellant mix consisting of from about 55% to about 75% by weight guanidine nitrate; from about 25% to about 45% by weight of an oxidizer selected from potassium and ammonium perchlorates; from about 0.5% to about 5.0%^' by weight of a flow enhancer, and up to about 5% by weight of a binder. As suitable flow enhancers, graphite and carbon black are mentioned. The only binder taught is calcium resinate .

Aside from the specific composition, the particle size of each component in the patented composition is indicated as being important. Thus, the average recommended particle size of GN is said to be between 75 and 350 microns; of the oxidizer, about 50 to about 200 microns; and of the flow enhancer, about 7 to about 70 microns . None of the known prior art is believed to disclose or suggest the present invention.

Background of the Invention

The present invention has as one of its objects the provision of a composition for generating a particulate- free, non-toxic, non-flammable, odorless and colorless gas for use in various environments, primarily for the inflation of inflatable emergency devices, such as an air bag in an automotive vehicle. Of course, the composition of this invention may also be employed to inflate such items as an inflatable raft or a passenger escape chute of an airplane.

The unique advantage of employing the formulations of the instant invention resides in the cycling and/or the ballistics of the composition. Whereas many prior art composition grains consisting essentially of a fuel, e.g., GN, and an oxidizer, e.g., KP, do not maintain their size during 200 cycles at -40 to +107°C (225°F) and

17 days at 107°C, the instant formulations, containing a significant amount of AGN, together with an oxidizing effective amount of potassium perchlorate and/or potassium nitrate (KN) and polyvinyl alcohol (PVA) with a low level up to about 25% by weight guanidine nitrate, exhibit no significant change in diameter or in strength during said tests. Likewise, in contrast to compositions described in the prior art, the formulations of the present invention, consisting essentially of AGN, KP and

PVA, exhibit materially higher burning rates, in ips

(inches per second), at 2000 and 4000 psi.

The gas generated by the compositions of the instant invention may be utilized by positioning the composition in an enclosed pressure chamber having at least one exit port. A composition in the form of a powder charge or pressed into propellant grains of a suitable shape, is located within said compression chamber. The described composition comprises a propellant containing amino- guanidine nitrate, optionally a minor amount of guanidine nitrate, mixed with potassium chlorate and/or potassium nitrate, as oxidizers and a polyvinyl alcohol binder.

The AGN is combined with the inorganic perchlorates and/or inorganic nitrates. To compositions such as AGN/KP, AGN/KN or mixtures thereof, PVA is added as a binder. Low levels of GN can be used as an adjunct to

AGN. The PVA and AGN (also GN if it is present) are formed into a solid solution via an aqueous solution which is subsequently vacuum dried to eliminate all water. The combination of AGN and PVA in a solid solution takes advantage of the miscibility of AGN and

PVA and provides surprising synergism since stability during required cycling (200 cycles from -40 to +107°C) and aging (17 days at 107°C) is superior to that obtained with simple mixtures of AGN/PVA or GN/PVA powders. Summary of the Invention

The gas-generative composition of the instant invention comprises a) about 30 to about 70% by weight aminoguanidine nitrate, b) an oxidizing effective amount of potassium perchlorate and/or potassium nitrate, c) a low level up to about 25% by weight guanidine nitrate and an effective binder amount up to about 15% by weight polyvinyl alcohol .

The invention also includes the method of generating a gas by employing the propellant of the present invention, optionally with suitable other gas generators, or the production of non-toxic, non-flammable, odor- free gas . The method is carried out in a conventional air bag inflator .

Brief Description of the Figures

Figure 1 is a conventional passenger-side inflator that may be used in practicing the method of the instant invention.

Figure 2 is a conventional driver-side inflator that may be used in practicing the method of the present invention.

Detailed Description of the Invention

Figure 1 depicts a conventional passenger-side ^• inflator for an automobile. In practice, the initiator (1) ignites in response to a sensor (not shown) that senses rapid deceleration indicative of a collision. The initiator gives off hot gases that ignite the ignition charge (2) which causes the main generant charge (8) to combust, generating the inflation gas mixture (3) . When the pressure in said gas mixture increases to a certain point, the seal disk (6) ruptures, permitting the gas mixture to exit the manifold (4) through the outlet ports

(5) and inflate an air bag. The generant container (9) holds the main generant charge (8) . All the charges in the inflation gas mixture are enclosed in the pressure tank (7) .

Figure 2 is a drawing of a pyrotechnic generator in which the instant invention may be employed. Since no part of the inflator is reserved for storage capacity, the device is smaller than its counterpart hybrid inflator. In this figure, there is an initiator (11) that will combust in response to a signal from a sensor (not shown) , that generates said signal as a result of a change in conditions, e.g., a sudden deceleration of a vehicle (indicative of a crash) , in which the inflator is installed. The initiator (11) gives off hot gases that ignite the main generant charge (16) , which combusts, generating an inflation gas mixture. Said mixture exits the manifold (14) through the exit ports (15) . To insure that the gas generating propellant (16) will be ignited well below its autoignition temperature (T_ig) and well below that temperature where the materials of construction of the hardware begin to weaken, an autoignition propellant (AIP) (13) having a suitably low T is used to ignite the ignition charge (12) , which then ignites the propellant (16) .

Additional objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description wherein only the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications of various obvious respects, all without departing from the invention.

Accordingly, the drawing and description are to be regarded as illustrative in nature and not as restrictive . The present invention involves a composition for generating a non-toxic, low particulate, non-flammable, odorless and colorless gas, which may be used to inflate automotive air bags and similar inflatable devices or to provide a carrier gas for chemical fire suppressants in fire extinguishment systems. It is a further object to provide a composition with improved cycling stability and ballistic properties. The instant invention involves compositions with improved thermal cycling stability over the range of -40 to +107°C and having 1) an increased burning rate; 2) a decreased pressure exponent; and/or 3) a decreased ignition delay.

Examples

Test pellets for airbag applications sustain thermal and tensile shock during igniter functioning. For balistic performance to remain unaffected, pellets must be sufficiently strong to stay intact during gas generative functioning. Pellets must retain this capacity even after aging (17 days exposure to 107°C) and cycling (200 cycles -40 to +107°C) . Conservative limits for dimensional stability and final pellet strength after cycling/aging have been adopted. These limits are less than 3% dimensional change and pellet strength greater than 4000 psi at ambient test conditions. The 4000 psi limit at 25°C allows a margin of error for functioning units under hot conditions where pellet strengths often begin to decrease. The less than 3% dimension change requirement would allow a typical pellet with a diameter of 0.522 inches to increase up to a diameter of 0.538 inches.

In addition to the foregoing, it must be pointed out that the oxidizer to fuel ratio determines the concentration of KP/KN and AGN/GN, and is held between

0.92 and 0.98 to maintain non-toxic exhaust products which could include carbon monoxide, nitrogen oxides, or partially combusted hydrocarbon fragments. The use of

AGN provides significant increases in burning rate over

KP/GN mixtures alone. The mixture is used as either a pressed charge or as a granular powder. Opacifiers, such as carbon black or graphite, are incorporated to aid the ignition properties and provide smoother burning properties of the pressed charges. PVA concentrations up to 15% (1-5% preferred) may be used. AGN contents of 30 to 70% (33 to 56% preferred) likewise may be employed. Low levels of GN, up to 25%, may be added as a co- oxidizer to AGN. These results are depicted in the following Table :

Comparison of Example 1 with Example 104A and Example 104B illustrates the higher burning rate obtained with AGN. Likewise, comparison of Example No. 2 with Example No. 104A and Example No. 104B shows the superior dimensional stability (no change) and higher pellet crush strength obtained with AGN/PVA solid solutions.

Only the preferred embodiment of the invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.

Claims

1. A thermally stable gas -generative composition for inflating an inflatable emergency device comprising a) about 30 to about 70% by wt . aminoguanidine nitrate

(AGN) , b) an oxidizing effective amount of potassium perchlorate (KP) and/or potassium nitrate (KN) , c) a low level up to about 25% by wt . of guanidine nitrate (GN) and d) an effective binder amount up to about 15% by wt . polyvinyl alcohol (PVA) , the oxidizer to fuel ratio being about 0.92 to about 0.98.

2. The thermally stable gas -generative composition according to claim 1 comprising a) about 33 to about 56% by wt . AGN, b) about 40 to about 60% by wt . KP or about 50 to about 60% by wt . KN, c) 0 to about 20% by wt . GN and d) about 1 to about 10% by wt . PVA.

3. The thermally stable gas -generative composition according to claim 1 comprising a) about 56% by wt . AGN, b) about 41% by wt . KP c) 0% GN and d) about 3% by wt . PVA.

4. The thermally stable gas-generative composition according to claim 1 comprising a) about 62% by wt . AGN, b) about 37% by wt . KP, c) 0% GN and d) about 1% by wt . PVA.

5. The thermally stable gas -generative composition according to claim 1 comprising: a) about 33% by wt . AGN, b) about 57% by wt . KP, c) 0% GN and d) about 10% by wt . PVA.

6. The thermally stable gas-generative composition according to claim 1 comprising a) about 36% by wt . AGN, b) about 41% by wt . KP, c) about 20% by wt . GN, and d) about 3% by wt . PVA.

7. The thermally stable gas-generative composition according to claim 1 exhibiting improved ballistic properties comprising an increased burning rate and/or decreased pressure exponent or ignition delay.

8. The thermally stable gas-generative composition according to claim 1 also including a minor amount of an opacifier effective to provide smoother burning properties .

9. The thermally stable gas-generative composition according to claim 1 which is compacted into pressed structurally stable grains of a suitable shape, said grains exhibiting high strength during and after a test at 17 days at 107┬░C and reveal only up to a small acceptable change in diameter during 200 thermal cycles (-40/+107┬░C) .

10. The gas generative composition according to claim 1 which is in the form of a dry powder.

11. A method for inflating an inflatable restraint device for the occupant of a vehicle with a low particulate, non- oxic, non-flammable, odorless and colorless gas comprising the following steps: 1) providing an enclosed pressure chamber having exit ports;

2) placing within said pressure chamber a gas- generative composition which is fast burning, said gas- generative composition comprising: a) about 30 to about 70% by wt . AGN; b) an oxidizing effective amount of KP and/or KN; c) 0 to about 20% by wt. GN and d) an effective binder amount up to about 15% by wt . of an organic binder; and

3) providing means for igniting said gas- generative composition upon detection by a sensor of the pressure chamber being subjected to a sudden deceleration characteristic of a crash, whereby said gas is substantially instantly generated and conducted through the exit ports of said pressure chamber to an inflatable restraint device.

12. The method according to claim 11 wherein the gas -generative composition consists essentially of: a) about 33 to about 56% by wt . AGN, b) about 40 to about 60% by wt . KP or about 50 to about 60% by wt . KN, c) 0 to about 20% by wt . GN and d) about 1 to about 10% by wt . PVA.

13. The method according to claim 11 wherein the gas-generative composition consists essentially of: a) about 56% by wt . AGN, b) about 41% by wt . KP, c) 0% GN, and d) about 3% by wt . PVA.

14. The method according to claim 11 wherein the gas-generative composition consists essentially of: a) about 62% by wt . AGN, b) about 37% by wt . KP, c) 0% GN, and d) about 1% by wt . PVA.

15. The method according to claim 11 wherein the gas-generative composition consists essentially of: a) about 33% by wt . AGN, b) about 57% by wt . KP, c) 0% GN, and d) about 10% by wt . PVA.

16. The method according to claim 11 wherein the gas-generative composition consists essentially of: a) about 36% by wt . AGN, b) about 41% by wt . KP, c ) about 20% by wt . GN, and d) about 3% by wt . PVA.

17. The method according to claim 11 wherein the gas -generative composition includes an effective amount of an opacifier to provide smoother burning properties.

18. The method according to claim 11 wherein the gas -generative composition is in the form of a dry powder .

19. The method according to claim 11 wherein the gas -generative composition is compacted into pressed structurally stable grains of a suitable shape, said grains exhibiting high strength during and after a test at 17 days at 107┬░C and revealing only a small acceptable change in diameter during 200 thermal cycles (-40/107┬░C) .

20. In a gas generator for inflating an inflatable emergency device, said generator containing a gas- generative composition, the improvement wherein the gas- generative composition consists essentially of: a) about 30 to about 70% by wt . AGN, b) an oxidizing effective amount of KP and/or KN, c) a low amt up to about 25% by wt . GN, and d) an effective binder amount up to about

15% by wt . of PVA, the oxidizer to fuel ratio being about 0.92 to about 0.98.