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 Autoignition compositionsUSPTO Application #: 20070044675Title: Autoignition compositions Abstract: An autoignition composition 14 is provided to manage the safe combustion of a primary gas generant composition 12. The autoignition composition 14 contains carboxylic acid and potassium chlorate. A method of managing the safe combustion of the primary gas generant composition 12 is also provided. (end of abstract) Agent: L.c. Begin & Associates, PLLC - Milford, MI, US Inventors: Sean P. Burns, Graylon K. Williams USPTO Applicaton #: 20070044675 - Class: 102530000 (USPTO) Related Patent Categories: Ammunition And Explosives, Jacketed Or Cartridge Gas Generator The Patent Description & Claims data below is from USPTO Patent Application 20070044675. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATION(S) [0001] The present application claims the benefit of U.S. Provisional Application Ser. No. 60/606,322 filed on Aug. 31, 2004. BACKGROUND OF THE PRESENT INVENTION [0002] The present invention relates to vehicle occupant protection systems or gas generant systems in general. Various compositions employed in such systems include gas generant compositions, autoignition compositions, and booster compositions. Autoignition compositions, for example, are employed to auto-ignite at relatively lower temperatures than the main gas generant of the system in the event of a fire in the vehicle. Sequentially, the autoignition composition ignites to provide the impetus necessary to begin combustion of the main gas generant composition thereby preventing potentially harmful explosions. Certain pyrotechnic compositions are not necessarily suitable for autoignition compositions given that they tend to melt prior to their respective autoignition temperature thereby increasing the exposed composition surface area subject to combustion once the reaction begins. The result may therefore be a violent combustion reaction rather than a controlled combustion reaction. By controlling the effective combustion surface area of the autoignition composition once combustion begins, due to a fire around an associated vehicle for example, safer and more predictable management of the sequence of combustion reactions in a vehicle occupant protection system may be achieved. [0003] Furthermore, pyrotechnic compositions such as autoignition compositions must also pass a thermal aging test at 107.degree. C. for 400 hours to satisfy certain U.S. car safety requirements. At the same time, the post-aging autoignition temperature of the composition must not substantially deviate from the base-line or pre-aging autoignition temperature of the composition. SUMMARY OF THE PRESENT INVENTION [0004] The above-referenced concerns are resolved by the implementation of autoignition compositions within various gas generating systems, whereby the compositions are tailored to mitigate melting and a resultant increase in available combustion surface area, prior to ignition of the autoignition composition. An autoignition composition of the present invention includes a fuel formed from a racemic mixture of a carboxylic acid, or equimolar amounts of two optically active enantiomers of a given carboxylic acid. Accordingly, a first enantiomer may be characterized as a dextro-enantiomer indicating the optical activity of the enantiomer, and, a second enantiomer may be characterized as a levo-enantiomer indicating an optical activity exactly opposite of the first enantiomer. DL-tartaric acid is one example of a carboxylic acid of the present invention, whereby the fuel contains equimolar amounts of D-tartaric acid and L-tartaric acid. [0005] A second component of the autoignition composition includes potassium chlorate as an oxidizer. The fuel and the oxidizer are mixed in respective amounts that are determined based on the design criteria of a given application. BRIEF DESCRIPTION OF THE DRAWINGS [0006] FIG. 1 is an exemplary airbag inflator containing an autoignition composition formed in accordance with the present invention. [0007] FIG. 2 is a schematic representation of an exemplary gas generating system or vehicle occupant restraint system incorporating the inflator of FIG. 1 and an autoignition composition in accordance with the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) [0008] Autoignition compositions for vehicle occupant protection systems, for example, and more specifically, for airbag inflators, contain a mixture of potassium chlorate (KC), and a carboxylic acid. Carboxylic acid is selected from of DL-tartaric acid, succinic acid, glutamic acid, adipic acid, and mucic acid. [0009] The choice of carboxylic acid is based on the desired autoignition temperature and degree of stability during thermal aging. For most automotive airbag inflator applications, it is desirable to have a composition that will survive aging for 400 h at 107.degree. C. and will autoignite at a temperature of less than 200.degree. C., or relatively close to 200.degree. C. EXAMPLES [0010] TABLE-US-00001 Literature Amount Baseline Post-Aging Example Name MP ( C.) with KC Autoignition Autoignition 1 L-Tartaric Acid 168-170 43% 154 Ignited During Aging 2 D-Tartaric Acid 168-170 43% 154 Ignited During Aging 3 DL-Tartaric Acid 206 43% 185 188 4 Meso-Tartaric Acid 140 43% 146 Ignited During Aging 5 L-Tartaric Acid, >250 48% >250 >250 Mono-K Salt 6 DL-Malic Acid 131-133 35% >250 >250 7 Succinic Acid 188-190 30% 210 210 8 Diglycolic Acid 142-145 36% 155 213 9 Malonic Acid 135-137 39% >250 >250 10 Trans-Glutaconic 137-139 26% 188 211 Acid 11 D-Glutamic Acid 200-202 26% 235 230 12 Adipic Acid 152-154 22% 237 248 13 Mucic Acid 215 37% 223 221 14 2,2-Bis(hydroxymethyl) 189-191 23% >250 >250 propionic acid 15 Citric Acid 152-154 36% >250 >250 16 Phenylmalonic Acid 153 20% >250 >250 17 D-Quinic Acid 168 25% >250 >250 Examples 1-17 [0011] Stoichiometric mixtures of each of the acids with potassium chlorate (KC) were made by grinding the raw materials separately in a vibratory grinder, and then blending by hand in a mortar and pestle. The autoignition test consisted of an aluminum fixture placed on a laboratory hot plate. The fixture was machined to accommodate a 0.3-0.5 g sample of autoignition material and a thermocouple probe. The tip of the probe was positioned directly below the autoignition composition, between the sample and the hotplate surface. The thermocouple was connected to a digital readout display and the hot plate was turned on to a heating rate of 30-50.degree. C. per minute. The autoignition temperature was recorded as the temperature at which the sample combusted vigorously. Each sample was tested for thermal stability by placing about 15 g in a sealed glass vial and placing in a chamber at 107.degree. C. for 400 hours. The hot plate autoignition was tested again after aging was complete. Examples 18-19 [0012] Compositions were made containing DL-tartaric acid and KC in different ratios. This illustrates that the autoignition temperature does not substantially change if the composition is fuel-rich or oxidizer-rich. TABLE-US-00002 Auto- DL-Tartaric KC Oxygen Balance ignition Example Acid (wt. %) (wt. %) (wt. % O2) (C.) 18 30 70 +11.4 184 19 55 45 -11.7 183 3 (for comparison) 43 57 -0- 185 [0013] For comparison purposes, some of the compositions were tested on a TGA (thermogravimetric analyzer) with a smaller sample size and at a slower heating of 10.degree. per minute. The results are as follows. This illustrates that the relative autoignition temperature does not substantially change with the sample size and heating rate. TABLE-US-00003 Composition From Hot Plate AI (0.3-0.5 TGA AI (20-50 Example g at 30-50 C./min) mg at 10 C./min) 1 154 142 3 185 171 13 223 200 11 235 213 12 237 222 [0014] Is should be noted that the stereochemistry of the carboxylic acids described herein is relevant to this invention. For example, Tartaric Acid has three stereoisomers as follows. [0015] L-Tartaric Acid. Also known as L-(+)-Tartaric Acid or (2R,3R)-(+)-tartaric Acid. [0016] D-Tartaric Acid. Also known as D-(-)-Tartaric Acid or (2S,3S)-(-)-Tartaric Acid. [0017] Meso-Tartaric Acid. This is an achiral molecule describing the (2R,3S) and (2S,3R) configurations. [0018] L-Tartaric Acid and D-Tartaric Acid are enantiomers, meaning that they rotate the plane of polarized light an equal amount but in an opposite direction. DL-Tartaric Acid is a racemic mixture of L-Tartaric Acid and D-Tartaric Acid, meaning that it is an equimolar mixture of the enantiomers. As indicated in examples 1 and 2, L-Tartaric Acid and D-Tartaric Acid have the same melting point and function in the same way when mixed with KC. Meso-Tartaric Acid has different physical properties than both D-Tartaric and L-Tartaric Acid; it forms a hydrate and has a lower melting point, for example. When combined with KC, the autoignition temperature is lower, but it still ignites when aged at 107.degree. C. As described in example 3, DL-Tartaric Acid has a higher melting point than either the D-tartaric Acid or L-Tartaric Acid alone, autoignites at a relatively higher temperature, and is stable when aged at 107.degree. C. It is believed, although not confirmed, that the mixture of the two isomers is more stable because of hydrogen bonding. It will be appreciated that this concept may be applied to other carboxylic acids with more than one stereoisomer. [0019] Carboxylic acid may be defined as given by Hawley, or as generally known by one of ordinary skill in the art. Hawley describes a carboxylic acid as any of a broad array of organic acids that primarily include alkyl (hydrocarbon) groups (CH.sub.2, CH.sub.3), usually in a straight chain (aliphatic), terminating in a carboxyl group (COOH). Exceptions to this structure are formic acid (HCOOH) and oxalic acid (HOOCCOOH). The number of carbon atoms ranges from one (formic) to 26 (cerotic), the carbon of the terminal group being counted as part of the chain. Carboxylic acids include the large and important class of fatty acids and may be either saturated or unsaturated. A few contain halogen atoms (chloracetic). There are also some natural aromatic carboxylic acids (b enzoic, salicylic) as well as alicyclic types (abietic, chaulmoogric). Continue reading... Full patent description for Autoignition compositions Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Autoignition compositions 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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