US 3723205 A
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March 27, 1973 5, SCHEFFEE 3,723,295
GAS GENERATING COMPOSITION WITH POLYVINYL CHLORIDE BINDER Filed May 7, 1971 Q INFLATABLE DEV/CE D INVENTOR 905527 6. SCHEFFEE nited States atent 3,723,205 Patented Mar. 27, 1973 ABSTRACT OF THE DISCLOSURE An inflation system comprising a gas generator and an inflatable device wherein the gas generator contains a gasgenerating composition which produces combustion products free from corrosive, toxic, or inflammable components. The gas-generating composition comprises plasticized polyvinyl chloride fuel binder and a mixture of inorganic oxidizing salt and halogen-free alkali metal salt in a stoichiometry suflicient at the least to transform all car- 'bon, hydrogen, and halogen in the composition to carbon dioxide, water and alkali metal halide.
BACKGROUND OF THE INVENTION Many devices, such as a protective passive restraint or crash bag used in automobiles, escape slide chutes, life rafts, and the like, are normally stored deflated and are inflated with gas at the time of need. Such devices are generally both stored and used in close proximity to human beings and, therefore, must be designed with a high safety factor effective at all times.
Inflation is generally accomplished by means of a gas, such as air, nitrogen, CO helium, and the like stored under pressure and further pressurized and supplemented at the time of use by the addition of high temperature combustion gas products produced by the burning of a gas-generating composition. In some cases the inflation gases are solely produced by the gas-generating compositions.
It is obviously very important that the gas-generating composition be capable of safe and reliable storage without decomposition or ignition at all temperatures likely to be encountered in the vehicle or other storage environment as, for example, up to temperatures as high as about 220 F. It is also important that substantially all of the combustion products generated during use be non-toxic, non-corrosive, and non-inflammable, particularly where the device is used in a closed environment such as an automobile.
Gas-generating compositions employed hitherto have not met all of the above qualifications. Examples of compositions which have been used include black powder and plasticized nitrocellulose (double base) propellant compositions. The double base propellants are unstable at high ambient temperatures. Storage and use is generally restricted to temperatures below 140 F. Both black powder and double base propellant generate toxic and/ or inflammable gases. Double base propellants produce, in addition to carbon dioxide and Water, carbon monoxide and hydrogen, a mixture which is both toxic and inflammable. Black powder produces carbon monoxide in toxic concentrations as well as being relatively inefficient in volume of gas generated. The use of conventional composite propellants has also been suggested. Such pro pellants, however, have reactive components and stoichi ometries which result in toxic, corrosive, or flammable combustion products, which, in addition to carbon monoxide and hydrogen, may include hydrogen chloride, alkali metal oxides or hydroxides, nitrogen oxides, and the like.
For the applications contemplated herein, it is also im portant to have gas-generating compositions which generate large volumes of gas, which can be stored without adverse degradation for periods as long as 5 to 10 years and which can be mass produced at low cost.
The gas-generating compositions employed in the gasgenerator of the inflation system of this invention have important advantages which result in significantly improved inflation systems. These advantages include inter alia:
(l) Storageability at ambient temperatures up to 220 F.
for as long as five to ten years.
(2) High autoignition temperature, very low impact sensitivity, and very low friction sensitivity.
(3) Combustion products free from toxic, corrosive, and
(4) High volumetric gas-generating capability per unit Weight of gas-generating composition.
(5) Capability for safe, reliable, low-cost, mass production.
SUMMARY OF THE INVENTION The invention is an improvement in conventional inflation systems comprising a gas generator and an inflatable device. The inflatable device may be a bag designed to act as a passive restraint to protect an automobile driver or passenger in case of collision, an aircraft escape chute, a life raft, and the like. The gas generator contains a gas-generating composition capable of producing gaseous combustion products which can be used to pressurize and supplement a primary inflation gas source, such as air, nitrogen, carbon dioxide, helium and the like, maintained under pressure in a separate storage chamber or to inflate the inflatable device directly without an additional gas supply.
The improvement comprises gas-generating compositions which consist essentially of plasticized polyvinyl chloride fuel binder containing dispersed therein an inorganic oxidizer selected from the group consisting of ammonium perchlorate, alkali metal chlorate or perchlorate, alkaline earth metal nitrate, and mixtures thereof, hereinafter called primary oxidizer, and halogen-free alkali metal salt reactive with the combined chlorine in the polyvinyl chloride (and ammonium perchlorate if used as primary oxidizer) to form alkali metal chloride. The halogen-free alkali metal salt may also be an oxidizer in Whole or in part. Total oxidizer and halogen-free alkali metal salt are present in amount at least sufficient to oxidize all available carbon to carbon dioxide and all available hydrogen to Water and to convert all available combined chlorine to the alkali metal halide. Oxidizer and/ or alkali metal salt in excess of these stoichiometric requirements may be employed.
The invention also comprises a method for inflating inflatable devices with gaseous combustion products which are non-toxic, non-corrosive, and non-flammable so that the devices can be safely employed in close proximity to human beings, particularly in confined spaces. The method comprises burning the gas-generating composition aforedescribed and injecting the gaseous combustion products into the inflatable device either solely or as a pressurizing supplement to a separate pressurized gas, such as air, nitrogen, carbon dioxide, or helium.
DRAWINGS The figure is a longitudinal sectional view partly in elevation of an inflation system utilizing a gas generator and an inflation device in accordance with this invention.
DETAILED DESCRIPTION As aforedescribed, the improvement in the inflation system resides in loading the gas generator portion of the inflation system with a gas-generating composition comprising a plasticized polyvinyl chloride fuel binder containing dispersed therein an inorganic oxidizer salt selected from the group consisting of ammonium perchlorate, alkali metal chlorate or perchlorate, alkaline earth metal nitrates, and mixtures thereof, and a halogen-free, alkali metal salt, total oxidizer and alkali metal salt being present in amount at least sufficient to oxidize all avalaible carbon and hydrogen in the composition to carbon dioxide and water and to convert all available combined chlorine to the alkali metal halide.
The term polyvinyl chloride as employed herein includes both the homopolymer and a copolymer containing up to about of a copolymerized component, such as vinyl acetate or vinylidene chloride. Preferably the polyvinyl chloride is essentially fully polymerized and employed in the form of plastisol-grade spheroidal particles.
Any organic liquid plasticizer compatible with polyvinyl chloride may be employed. Such plasticizers are wellknown in the art. Preferably, the plasticizer is of the type suitable for fiuid plastisol formation, as, for example, alkyl and alkoxyalkyl adipates, sebacates, and phthalates, e.g. dibutyl and dioctyl sebacate, dibutyl, dioctyl, and dimethoxyethyl phtha ate, dibutyl dioctyl and di(3,5,5trimethylhexyl) adipate; glycol esters of higher fatty acids and the like. The plastisol-forming lasticizers are high boiling solvents for the polyvinyl chloride which form fluid suspensions with the resin particles at ordinary temperatures because of the low solubility at such temperatures and dissolve the resin at elevated temperatures to form a solid gel.
The preferred ratio of polyvinyl chloride to plasticizer is generally from about 2 parts resin to 3 parts plasticizer to about 3 parts resin to about 2 parts lasticizer for desirable physical properties of the cured gasgenerating grains, such as tensile strength and minimum cold flow. In view of the high solids loadings generally required by the inflation system applications, the higher ratios of plasticizer to resin are desirable in order to maintain processability of the mix. For some inflation applications, physical property requirements are less exacting and the ratio of plasticizer to resin may be increased to as much as 2.5 to 1 while maintaining adequate physical properties of the solid gas-generating grain for the application.
The fluid polyvinyl chloride-plasticizer slurries can accommodate up to as much as 90% of added solids if, as is well-known in the art, particle sizes of the added solids are properly selected and distributed, without loss of adequate fluidity to permit casting and curing without application of high pressures.
The polyvinyl chloride-plasticizer slurry loaded with oxidizer and such other solids as may be required is cured simply by heating to the solution temperature of the polyvinyl chloride in the plasticizer, generally about 160 to 175 C. Since the polyvinyl chloride is fully polymerized, no potentially variable cure reaction occurs and the resulting cured gas-generating grains are highly reproducible and reliable. Polyvinyl chloride plastisol gas-generating propellants and process for making them are described in U.S. Pat. 2,966,403.
The loaded polyvinyl chloride-plasticizer plastisol slurries are particularly amenable to curing and casting by extrusion as disclosed in U.S. Pat. 3,155,749. Briefly, the loaded slurry is introduced into an elongated extruder barrel through which it is advanced by a rotating worm screW with simultaneous generation of frictional heat, which together with heat supplied by means of a heating jacket provides the elevated temperature required for the solution cure. The mix is fully cured when it completes its passage through the extruder barrel though it is still in a sufliciently hot, soft state to be shaped by passage through a die after which the shaped extruding column is cooled and cut into grains of the desired length. The extrusion process is continuous and provides rapid, low-cost mass production of the gas-generating grains.
Use of the specified primary inorganic oxidizer salts in combination with the halogen-free alkali metal salts in the amounts required by the specified stoichiometry provides maximized non-toxic, non-corrosive, non-flammable gas production and neutralization of the chlorine component in the polyvinyl chloride binder in the form of a non-toxic alkali metal chloride product. The primary oxidizers, in addition to oxygen, produce per se or by reaction with the halogen-free alkali metal salt additive, only non-toxic, non-corrosive, and non-flammable combustion products. The halogen-free alkali metal salt additive prevents formation of corrosive HCl or chlorine.
The alkali metal, e.g. Na, K, Li, chlorates and perchlorates form non-toxic alkali metal chlorides, with the remainder of the oxidizer salt molecules providing oxygen for combustion of the fuel. Of these, potassium perchlorate is generally preferred. Ammonium perchlorate is highly useful as an oxidizer because it increases gas production in the form of nitrogen and water and reduces the percentage of solid products. It also provides somewhat lower flame temperatures than the corresponding alkali metal salts. The HCl produced by ammonium perchlorate as a decomposition product is corrosive and must be neutralized by transformation into the alkali metal chloride. Thus, sufficient halogen-free alkali metal salt must be incorporated for this purpose as well as for the neutralization of the HCl decomposition product of the polyvinyl chloride resin binder.
The alkaline earth metal nitrate oxidizer salts, such as Ba(NO or Sr(NO decompose to form highly stable non-toxic oxides as combustion products and thus can be safely and efficiently used as oxidizers in gas-generating compositions. Since burning rates obtained with these oxidizers are generally lower than those obtained with the ammonium or alkali metal chlorates, perchlorates, or nitrates, it is generally preferred to employ the alkaline earth metal nitrate oxidizer in admixture with one of the foregoing oxidizers.
The halogen-free alkali metal salts, as aforementioned, may be any compound which reacts with the chlorine in the polyvinyl chloride and in any ammonium perchlorate used as primary oxidizer to form a non-toxic alkali metal salt. The alkali metal moiety can be, for example, Na, K, or Li. Preferably, though not essentially, the alkali metal salt is also an oxidizer, thereby supplementing the gasforming oxidizing action of the primary oxidizer and contributing to the desired carbon dioxide and Water stoichiometry. Preferred halogen-free alkali metal oxidizers are the nitrates, e.g. NaNO and KNO since they have the additional advantage of forming nitrogen gas as a combustion product and of conferring good combustion properties, such as desired burning rate and pressure exponent. Other alkali metal oxidizers include, for example, the alkali metal nitrites.
Alkali metal salts which do not react as oxidizers may also be used. Preferably they contribute non-toxic, gaseous decomposition products which increase total gas production, decrease concentration of solid combustion products and act as coolants. Examples of suitable non-oxidizer salts include, but are not limited to, alkali metal oxalates, e.g. Na C O K O O carbonates and bicarbonates, e.g. K CO Na CO Nat-K10 azides, e.g. KN and the like.
As aforementioned the total amount of oxidizer, in cluding primary oxidizer and halogen-free alkali metal oxidizer, should be at least suflicient to oxidizer all available carbon and hydrogen present in the composition to carbon dioxide and water. Excess primary oxidizer may be employed and is, in fact, advantageous since its endothermic decomposition contributes to gas formation in the form of free oxygen and to reducing flame temperature, thereby functioning as a coolant. The amount of halogen-free alkali salt should be in amount at least suflicient to transform all available halogen to the alkali metal halide. By available halogen is meant halogen not already combined with alkali metal as in the case of an alkali metal chlorate or perchlorate. The halogen-free alkali metal salt should not be included in substantial excess. The total amount of available alkali metal should not exceed available halogen by more than about 10 mol percent. Although stoichiomet'ric proportions of alkali metal and halogen are preferred, in some cases a small excess of alkali metal may be desirable to ensure complete freedom from HCl or C1 formation since these are considerably more toxic than small amounts of alkali metal oxide or hydroxide.
The particular amounts and relative proportions of primary oxidizer and halogen-free alkali metal salt will obviously vary with the particular binder concentration, the particular plasticizer, and the particular primary oxidizer and halogen-free alkali metal salt employed. They can, however, be readily calculated in accordance with well-known procedures by anyone skilled in the art.
In addition to the components aforedescrbed, othzr conventional additives may be incorporated into the gasgenerating compositions. They include, for example, stabilizers for the polyvinyl chloride, burning rate catalysts, coolants and the like.
The plasticized polyvinyl chloride resin binder gasgenerating compositions are very stable and can be stored at temperatures as low as 50 F. and as high as 220 F. without adverse degradation for periods as long as five to ten years. Ignition temperatures are very high and sensitivity to impact, friction and electrostatic charge is very low so that the gas generators containing the compositions can be stored safely in con-fined spaces in close proximity to human beings. Other advantageous properties include high densities thereby reducing chamber size requirements, easy ignition, high burning rates, and inexpensive raw material requirements.
The figure shows schematically, an inflation system utilizing the improvement of this invention. Pressure vessel 1 contains a gas, such as air, under pressure. Gas generator 2 seated within the pressure vessel comprises a combustion chamber 3 equipped with a restricted aperture or nozzle 4 and containing a shaped gas-generating grain 5 of composition as aforedescribed. Electrically actuated squib 6 is employed to ignite the gas-generating grain. The gas generator is sealed with rupturable cap 7. The pressure chamber is provided with outlet means 8 sealed with rupturable disc 9 and connected by conduit 10 to inflatable device 11. Safety valve 12 is designed to preclude development of excessive pressures in the pressure vessel.
In operation, the gas-generating grain is ignited. When adequate pressure has developed within the gas-generator, seal 7 ruptures and the hot high pressure combustion gases generated by the burning grain vent into the pressurized gas, e.g. air, in the pressure chamber. The air pressure is considerably increased both by the heat and added volume of the combustion gases. Seal 9 ruptures and the high pressure mixture of air and combustion gases pour into and inflate the inflatable device. The compressed air acts as a heat sink to reduce the temperature of hot combustion gases to a safe level.
In some applications, the pressure chamber contaning compressed air or other gas can be dispensed with and the inflatable device connected directly to the gas generator. Temperature reduction of the hot combustion gases can be accomplished by adding coolant compounds to the gas-generating compositions and by storing a vaporizable liquid, such as water, in the inflatable device.
The gas-generating compositions described in the following examples were processed into shaped grains by mixing the plastisol grade polyvinyl chloride with the plasticizers, primary oxidizer, halogen-free alkali metal salt, and other additives, such as stabilizers and burning rate catalyst in a conventional mixer. The viscous but still fluid mixtures were then either poured into molds and heated to the fusion temperature of the polyvinyl chloride in the plasticizer or solution-cured by continuous passage through a heat-jacketed worm extruder barrel, after which the extruding column was passed through a shaping die, cooled, and cut to desired lengths.
Burning rate at 500 p.s.i.a., 70 F.: 0.60 in./sec.
Burning rate at 5000 p.s.i.a., 70 F.: 0.60 in./sec.
Burning rate pressure exponent n: 0.67 Safety data:
Autoignition temperature: 680 F. Impact sensitivity (12 tests negative with 6 kg. at
50 cm.): 300 -kg.-cm.
Friction sensitivity (Esso Screw Friction Test (two screwloaded flat plates with propellant and No. carborundum grit between)): 300 in./1b.
Card-gap test (Tetryl pellet placed against propellant and detonatedno propellant detonation in 4 tests): zero cards EXAMPLE 2 Composition: Percent by weight Polyvinyl chloride 5.616 Dioctyl adipate 8.22.7 Stabilizer 0.158 Carbon black 0.039 K010 55.820 Sr(NO 21.053 KNO 9.087
Burning rate at 1000 p.s.i.a., 70 F.: 0.89 in./sec. Burning rate at 4000 p.s.i.a., 70 F.: 2.51 in./sec. Burning rate pressure exponent n: 0.75
EXAMPLE 3 Composition: Percent by weight Polyvinyl chloride 6.318 Dioctyl adipate 9.477 Carbon black 0.048 Stabilizer 0.196 Ammonium perchlorate 42.598 NaNO 39.407 F3203 Burning rate at 3000 p.s.i.a., 70 R: 1.6 in./sec. Burning rate pressure exponent n: 0.63
EXAMPLE 4 Composition: Percent by weight Polyvinyl chloride 4.513 Dibutyl sebacate 6.770 Stabilizer 0.135 Carbon black 0.034 Ammonium perchlorate 29.032 NaNO 27.139 Sr(N-O 31.029 Fe O 1.348
Burning rate at 3000 p.s.i.a., 70 F.: 1.4 in./sec. Burning rate pressure exponent n: 0.70
Although this invention has been" described with reference to illustrative embodiments thereof, it will be apparent to those skilled in the art that the principles of this invention can be embodied in other forms but within the scope of the claims.
1. A non-toxic, non-corrosive, and non-flammable combustible gas-generating composition for use in inflating an inflatable device comprising:
plasticized polyvinyl chloride fuel binder,
inorganic oxidizer salt selected from the group consisting of ammonium perchlorate, alkali metal chlorates and perchlorates, alkaline earth metal nitrates and mixtures thereof,
halogen-free alkali metal salt reactive with available 8. The composition of claim 2 wherein the inorganic halogen to form alkali metal halide, oxidizer salt is ammonium perchlorate.
said composition containing total oxidizer in amount 9. The composition of claim 3 wherein the inorganic at least suflicient to convert all available carbon to oxidizer salt is ammonium perchlorate. carbon dioxide and all available hydrogen to water, 5
said composition containing available combined alkali References Cited metal in amount at least sufiicient to convert all avail- UNITED STATES PATENTS able halogen to alkali metal halide up to a maximum 3,155,749 11/1964 'Rossen et al 14976 X 82 22;: 10 ml Percent excess the avallable 10 3,180,373 4/1965 Hebenstreit 141-4 2. The composition of claim 1 wherein the halogen- 3107186 10/1963 Scurlock et 149-19 2,904,420 9/ 1959 Holker 1496l X free alkali metal salt is an alkali metal nitrate. 3 066 479 12/1962 K h 149 35 X 3. The composition of claim 2 wherein the alkali metal 0c nitrate is sodium nitrate or potassium nitrate 3362859 1/1968 Sutton et a1 149*19 3,373,062 3/1968 Morris 14919 X 4. The composition of claim 1 wherein the inorganic 15 oxidizer salt is potassium perchlorate.
5. The composition of claim 2 wherein the inorganic CARL D QUARFORTH Primar Examiner oxidizer salt is potassium perchlorate. y
3,692,495 9/1972 Schneiter et a1. 280-150 AB 6. The composition of claim 3 wherein the inorganic E. A. MILLER, Assistant Examiner oxidizer salt is potassium perchlorate. 2O
7. The composition of claim 1 wherein the inorganic X- oxidizer salt is ammonium perchlorate. 149 35, 61 76 AB