| Autoignition/booster composition -> Monitor Keywords |
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 Autoignition/booster compositionRelated Patent Categories: Explosive And Thermic Compositions Or Charges, Containing Hydrazine Or Hydrazine DerivativeThe Patent Description & Claims data below is from USPTO Patent Application 20070034307. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional Application Ser. No. 60/703,998 filed on Jul. 29, 2005. TECHNICAL FIELD [0002] The present invention relates generally to gas generating systems, and to autoignition compositions employed in gas generator devices for automotive restraint systems, for example. BACKGROUND OF THE INVENTION [0003] The present invention relates to autoignition compositions that upon ignition provide the flame front and pressure front necessary to safely ignite gas generant compositions in combustible communication therewith. As known in the art, gas generators are typically provided with an autoignition composition that in the event of a fire ignites responsive to a desired threshold temperature. As a result, the gas generant is ignited prior to melting for example, thereby safely igniting the main gas generant composition to inhibit or prevent the likelihood of an explosive event once the gas generant begins to combust. [0004] An ongoing challenge is to simplify the manufacture of a gas generator by reducing the constituents required in the production thereof. For example, in many gas generators used in vehicle occupant protection systems, several discrete compositions are provided to serve correspondingly discrete functions. These compositions often include a primary gas generating composition that when combusted is employed to provide sufficient quantities of gaseous products to operate the associated restraint device, such as an airbag or seatbelt pretensioner. A booster composition is utilized to elevate the pressure and heat within the gas generator prior to combustion of the primary gas generant, thereby creating favorable conditions within the inflator for acceptable combustion of the primary gas generant. Of course, still yet another composition is the auto-ignition composition employed to provide safe combustion of the other compositions in the event of a fire. The auto-ignition composition is designed to ignite at temperatures below the melting point of the primary gas generant for example, thereby ensuring the controlled combustion of the primary gas generant, as opposed to an explosive reaction perhaps. [0005] The use of potassium chlorate within an autoignition composition has been considered given the autoignition properties of this oxidizer. Furthermore, carboxylic acid in combination with potassium chlorate typically provides a desired autoignition temperature of 200 degrees Celsius or less. Nevertheless, these types of compositions typically do not provide anything but auto-ignition function when employed in gas generators used in vehicle occupant protection systems, for example. SUMMARY OF THE INVENTION [0006] The above-referenced concerns and others may be resolved by gas generating systems including an autoignition composition containing a first oxidizer selected from metal chlorates, such as potassium chlorate, a carboxylic acid or dicarboxylic acid as a primary fuel, a secondary oxidizer selected from metal and nonmetal nitrates, nitrites, oxides, basic metal nitrates, and other known oxidizers, and a secondary fuel selected from azoles including tetrazoles, triazoles, and furazans, and salts thereof. Other constituents including extrusion aids, such as fumed silica and/or graphite, may be included in relatively small amounts. In further accordance with the present invention, a gas generator and a vehicle occupant protection system incorporating the autoignition system are also included. BRIEF DESCRIPTION OF THE DRAWINGS [0007] FIG. 1 is a cross-sectional side view showing the general structure of an inflator in accordance with the present invention; [0008] FIG. 2 is a schematic representation of an exemplary vehicle occupant restraint system containing a gas generant composition in accordance with the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) [0009] The present compositions contain a first oxidizer selected from alkali, alkaline earth, and transitional metal chlorates, and mixtures thereof, such as potassium chlorate, at about 10-60 weight%; a primary fuel selected from carboxylic acids and dicarboxylic acids, such as DL-tartaric acid, at about 15-45 weight%; a secondary oxidizer selected from metal and nonmetal nitrates, nitrites, oxides, and other known oxidizers at about 30-50%; and a secondary fuel selected from tetrazoles, triazoles, furazans, and salts thereof at about 0-30 weight %, said weight percent calculated with regard to the weight of the total composition. Extrusion aids or processing additives such as graphite or fumed silica may be added in relatively smaller amounts, such as 0.1-2% by weight of the total composition for example. [0010] The present compositions contain a metal chlorate such as potassium chlorate; a primary fuel selected from carboxylic acids and dicarboxylic including DL-tartaric acid, L-tartaric acid, D-tartaric acid, succinic acid, glutamic acid, adipic acid, mucic acid, fumaric acid, oxalic acid, galactaric acid, citric acid, glycolic acid, L-malic acid, and compounds having at least one--COOH--group, and mixtures thereof; a second fuel selected from an azole including tetrazoles, triazoles, furazans, salts thereof, and mixtures thereof; a secondary oxidizer selected from metal and nonmetal nitrates or other known oxidizers not containing a perchlorate. The carboxylic acid or dicarboxylic acid will preferably have a primary hydrogen or PKA less than or equal to 3. Nevertheless, it has been found that with certain fuels/salts, the pKa of the base acid may range up to 5.0 or less. [0011] In one embodiment, the total fuel constituent including he carboxylic fuel and the second fuel is provided at about 20-45% by weight of the total composition; the oxidizer constituent is provided at about 20-50% by weight of the total composition; and the potassium chlorate or metal chlorate is provided at about 10-60% by weight of the total composition wherein the weight percent of the chlorate is separately calculated from that of the oxidizer. The composition may be formed by wet or dry mixing the constituents in a granulated form in a known manner, and then pelletizing or otherwise forming the composition for further use. The constituents may be provided by Fisher Chemical, Aldrich Chemical, GFS, and other known suppliers. [0012] The present invention is exemplified by the following Examples: Comparative Example 1 [0013] A known autoignition composition was prepared by homogeneously mixing dried and granulated D-glucose at about 26.875 wt% and potassium chlorate at about 73.125 wt%, the percents stated by weight of the total composition. The composition autoignited at about 144 C. as measured by DSC analysis. The propellant formed from the constituents resulted in an approximate 55.5% gas yield. The impact sensitivity of this formulation had an HD50 of 2.0 inches as conducted in conformance with the Bruceton Test. Example 2 [0014] An exemplary formulation was provided that functions as a booster, an autoignition, and a gas generant composition. The formulation contains 5-aminotetrazole at about 19.0 wt%, DL-tartaric acid at about 20.0 wt%, strontium nitrate at about 35.0 wt%, and potassium chlorate at about 26.0 wt%. The constituents were previously and separately ground to a relatively small size in a known manner. They were then dry-mixed to form a substantially homogeneous composition. The composition autoignited at about 140 C. as measured by DSC analysis. The propellant formed from the constituents resulted in an approximate 67% gas yield. The impact sensitivity of this formulation had an HD50 of 11.5 inches as conducted in conformance with the Bruceton Test. The composition was aged for about 480 hours at 107C. and still autoignited at about 145.1C. as determined by DSC analysis. Example 3 [0015] An exemplary formulation was provided that functions as a booster, an autoignition, and a gas generant composition. The formulation contains 5-aminotetrazole at about 19.0 wt%, DL-tartaric acid at about 19.0 wt%, strontium nitrate at about 50.0 wt%, and potassium chlorate at about 12.0 wt%. The constituents were granulated and dry-mixed to form a substantially homogeneous composition. The composition autoignited at about 141 C. as measured by DSC analysis. The propellant formed from the constituents resulted in an approximate 68.2% gas yield. The impact sensitivity of this formulation had an HD50 of 8.8 inches as conducted in conformance with the Bruceton Test. As shown in FIG. 3, the composition reflected a relatively strong burn rate across several pressure regimes, and in particular indicated burn rates of over 0.8 inches per second (ips). Again referring to FIG. 3, it can be seen that the composition exhibited a burn rate of about 0.2 ips at about 200 psig, about 0.35 ips at about 550 psig, about 0.5 ips at about 1000 psig, about 0.55 ips at about 1500 psig, about 0.85 ips at about 2000 psig, about 0.9 ips at about 2500 psig, about 0.85 ips at about 3000 psig; and about 1.2 ips at about 3900 psig. It can therefore be seen that a composition in accordance with the present invention exhibits a satisfactory burn rate (typically 0.4 ips or more at about 2500-3000 psig) thereby ensuring satisfactory functionality as a primary gas generant. The composition was aged for about 480 hours at 107C. and still autoignited at about 174.7C. as determined by DSC analysis. Continue reading... Full patent description for Autoignition/booster composition Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Autoignition/booster composition patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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