Classifications

• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06D—MEANS FOR GENERATING SMOKE OR MIST; GAS-ATTACK COMPOSITIONS; GENERATION OF GAS FOR BLASTING OR PROPULSION (CHEMICAL PART)
  • C06D5/00—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets
  • C06D5/06—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets by reaction of two or more solids
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B45/00—Compositions or products which are defined by structure or arrangement of component of product

Definitions

• the present Invention is directed to gas generant compositions for inflating automotive airbags and other devices in which rapid production of high volumes of gas is required. More particularly, the invention is directed a gas generant charge which is a heterogeneous mixture of two types of gas generant compositions.
• the gas generant compositions of the heterogeneous mixture complement each other, producing combustion products which are both low in undesirable gases and low in particulate matter.
• azole compounds including tetrazole and triazole compounds.
• Tetrazole compounds include 5-amino tetrazole (AT), tetrazole, bitetrazole and metal salts of these compounds.
• Triazole compounds include 1,2,4-triazole-5-one, 3-nitro 1,2,4-triazole-5-one and metal salts of these compounds.
• Gas generant systems include, in addition to the fuel component, an oxidizer.
• Proposed oxidizers for use in conjunction with azole fuels include alkali and alkaline earth metal salts of nitrates, chlorates and perchlorates.
• spherical prills In order to properly feed the tablet press, one needs well formed spherical prills. Without prills, plugging or bridging in the feed system is a common occurrence. Without prills, it is difficult to achieve uniform, high speed filling of the tablet press. These prills will not form in the spray drying step without at least a portion of the generant being water soluble. Typical slurries contain up to 35% water and it is preferred that at least 15% of the solid ingredients need to be soluble in the slurry.
• a problem encountered with gas generant compositions which utilize tetrazoles or triazoles as fuel is the production of undesirable gases, such as CO, NO x , NH 3 , and HCN.
• U.S. Patent No. 5,467,715 to Robert Taylor et al describes a gas generant composition which uses as fuel, in addition to a tetrazole or triazole, a water-soluble fuel, such as guanidine nitrate, and as the oxidizer, a transition metal oxide, plus, preferably, an additional oxidizer, such as strontium nitrate.
• This composition is aqueous-processable, and also minimizes levels of undesirable combustion gases. Nevertheless, the automotive industry is becoming increasingly sensitive to undesirable combustion gases and is imposing increasingly stricter standards. Thus, there is a continuing need to provide gas generant formulations producing further reduced levels of undesirable gases.
• the gas generant composition described in above-referenced U.S. Patent No. 5,476,715 are auto-ignitable, auto-igniting, e.g., in the event of a vehicle fire, at a temperature substantially below temperatures where ignitor housings, particularly aluminum ignitor housings, weaken.
• U.S. Patent No. 3,785,149 issued 15 January 1974 to Timmerman, the teachings of which are incorporated herein by reference, describes gas generant compositions which produce combustion gases which are substantially entirely carbon dioxide and water.
• the gas generant compositions of U.S. Patent No. 3,785,149 use as the fuel an organic compound which contains only the elements carbon, hydrogen and oxygen, the organic compound being a compound containing carboxylic acid groups or carboxylic acid salt groups and therefore being high in oxygen content.
• the oxidizer is an alkali metal, preferably sodium or potassium, chlorate or perchlorate.
• One problem with this type of fuel is that it produces high levels of particulate material which appear as smoke in the interior of a vehicle when the airbag deploys.
• gas generant compositions may produce different types of undesirable effluents, either gases or particulates. Often, it is difficult to reduce one or more specific undesirable effluent below a predetermined standard.
• Formulating a gas generant composition for any particular application requires balancing of a number of pyrotechnic parameters, such as burn rate, combustion temperature, gas volume per weight of generant composition, etc. In addition, production of undesirable effluents, including both gases and particulates, must be considered.
• a heterogeneous mixture between a first separately compounded gas generant composition and at least a second separately compounded gas generant composition, whereby the pyrotechnic and gas effluent profiles of the heterogeneous gas generant composition resembles a weighted average of the gas generant compositions.
• a gas generant charge which provides low levels of undesirable gases and low levels of particulate matter upon combustion is a heterogeneous mixture of two gas generant compositions, the mixture comprising between about 80 and about 95 wt% of a first gas generant composition 1) and between about 5 and about 20 wt% of a second gas generant composition 2).
• the first gas generant composition 1) comprises between about 20 and about 40 wt% of fuel A) and between about 60 and about 80 wt% of oxidizer B).
• a triazole or tetrazole A 1 between about 15 and about 50 wt% of the fuel is a watersoluble fuel A 2 ) such as guanidine nitrate, ethylene diamine dinitrate or similar compounds.
• a watersoluble fuel A 2 such as guanidine nitrate, ethylene diamine dinitrate or similar compounds.
• At least about 20 wt% of the oxidizer B) up to 100%, preferably at least about 50 wt%, comprises a transition metal oxide B 1 ); balance of the oxidizer B 2 ) alkali and/or alkaline earth metal nitrates, chlorates or perchlorates.
• transition metal oxides as a major oxidizer component results in lower combustion temperatures, resulting in lower production of toxic oxides.
• the second gas generant composition 2) comprises between about 30 and about 65 wt% of a fuel C) which is an organic compound containing only the elements carbon, hydrogen, and oxygen, the oxygen content being between about 35 and about 65 wt% of the organic compound, and between about 35 and about 70 wt% of an oxidizer D) which is an alkali metal chlorate or perchlorate.
• a fuel C which is an organic compound containing only the elements carbon, hydrogen, and oxygen
• the oxygen content being between about 35 and about 65 wt% of the organic compound
• an oxidizer D which is an alkali metal chlorate or perchlorate.
• each gas generant composition and its components are calculated relative to the active ingredients, i.e., the total of fuel and oxidizer components.
• the weight percentages of other ingredients, such as coolants, fillers, pressing aids, etc. are calculated relative to the total active ingredients of each gas generant composition, the total of oxidizer plus fuel being 100%.
• the major fuel component A 1 ) of the first gas generant composition 1) may be selected from any of the tetrazole and triazole compounds listed above and mixtures thereof; from an availability and cost standpoint, 5-aminotetrazole (AT) is presently the azole compound of choice.
• the purpose of the fuel is to produce carbon dioxide, water and nitrogen gases when burned with an appropriate oxidizer or oxidizer combination. The gases so produced are used to inflate an automobile gas bag or other such device.
• AT is combusted to produce carbon dioxide, water and nitrogen according to the following equation: 2CH 3 N 5 + 7/2O 2 ⁇ 2CO 2 + 3H 2 O + 5N 2 .
• a minor portion of the first 1) fuel i.e., between about 15 and about 50 wt% of the fuel, is a water soluble fuel A 2 ).
• water-soluble oxidizers such as strontium nitrate also facilitate water-processing, over-reliance on such water-soluble oxidizers tend to produce undesirably high combustion temperatures.
• Specific desirable characteristics of water-soluble fuels are:
• any transition metal oxide will serve as an oxidizer B 1 ).
• Particularly suitable transition metal oxides include ferric oxide and cupric oxide.
• the preferred transition metal oxide is cupric oxide which, upon combustion of the gas generant, produces copper metal as a slag component.
• the purpose of the oxidizer is to provide the oxygen necessary to oxidize the fuel; for example, CuO oxidizes AT according to the following equation: 4CH 3 N 5 + 14CuO ⁇ 14Cu + 4CO 2 + 6H 2 O + 10N 2 .
• the transition metal oxide B 1 may comprise the sole oxidizer in the first fuel or it may be used in conjunction with other oxidizers B 2 ) including alkali and alkaline earth metal nitrates, chlorates and perchlorates and mixtures of such oxidizers. Of these, nitrates (alkali and/or alkaline earth metal salts) are preferred, and strontium nitrate is currently most preferred. Nitrate oxidizers increase gas output slightly. Alkali metal nitrates are particularly useful as ignition promoting additives.
• the first gas generant composition 1) may optionally contain a catalyst up to about 3 wt%, typically between about 1 and about 2 wt%. Boron hydrides and iron ferricyanide are such combustion catalysts. Certain transition metal oxides, such as copper chromate, chromium oxide and manganese oxide, in addition to the oxidizer function, further act to catalyze combustion.
• coolants may also optionally be included in the first gas generant composition at up to about 10 wt%, typically between about 1 and about 5 wt%.
• Suitable coolants include graphite, alumina, silica, metal carbonate salts, transition metals and mixtures thereof.
• the coolants may be in particulate form, although if available, fiber form is preferred, e.g., graphite, alumina and alumina/silica fibers.
• Suitable fuels C) for the second gas generant composition 2) include, but are not limited to oxalic acid, malonic acid, succinic acid, tartaric acid, mucic acid, citric acid, salts thereof and mixtures thereof.
• a currently preferred fuel is tartaric acid.
• Fuel compounds containing carboxylic acids are reactive with transition metal oxides; thus, the components of the first gas generant composition and second gas generant composition cannot be compounded together. Accordingly, the gas generant charges of the present invention must be heterogeneous.
• the oxidizer D) for the second gas generant composition 2) is an alkali metal chlorate or perchlorate, particularly sodium chlorate, potassium chlorate, sodium perchlorate and potassium perchlorate.
• slag formers As with the first gas generant composition, other ingredients known in the art, such as slag formers, processing aids, and/or burn rate catalysts may be optional or desirable in the second gas generant composition.
• the first and second gas generant compositions are mutually beneficial when provided in a gas generant charge.
• the second gas generant composition reduces undesirable gases produced by the first gas generant composition.
• the first gas generant composition minimizes particulate matter produced by the second gas generant composition.
• a heterogeneous charge may be provided in several manners. Powders of the two composition may be separately pressed into tablets or wafers and loaded into the inflator as two separate tablets or wafers.
• a "two headed" tablet can be manufactured of the two gas generant compositions by partial compaction of powders of one of the compositions, addition of powder of the second composition and final compaction for loading into the inflator as tablet or wafers.
• the currently preferred method is to dry blend powders of the two composition and press the dry-blended mixture into tablets or wafers.
• the gas generant composition powders have particle sizes between about 25 and about 250 microns.
• the gas generant composition It is generally desirable to pelletize the gas generant composition. If so, up to about 1 wt%, typically 0.2-0.5 wt% of a pressing aid or binder may be employed. If the two generants are separately pelletized or tableted, binders or pressing aids will be added to each gas generant composition. If powders of the two generant compositions are pelletized or tableted together, the binder or pressing aid will be added to a mixture of powders of the two gas generant compositions.
• alkali metal nitrate in the presence of molybdenum disulfide results in the formation of alkali metal sulfate, rather than toxic sulfur species. Accordingly, if molybdenum disulfide is used, alkali metal nitrate is used as a portion of the oxidizer in an amount sufficient to convert substantially all of the sulfur component of the molybdenum disulfide to alkali metal sulfate. This amount is at least the stoichiometric equivalent of the molybdenum disulfide, but is typically several times the stoichiometric equivalent. On a weight basis, an alkali metal nitrate is typically used at between about 3 and about 5 times the weight of molybdenum disulfide used.
• a first gas generant composition is formulated as follows: 69.55 wt% cupric oxide, 19.45 wt% 5-aminotetrazole, 6 wt% guanidine nitrate, and 5 wt% strontium nitrate.
• a second gas generant composition is formulated with 59.08 wt% potassium perchlorate and 40.92 wt% tartaric acid. Each of these compositions was manufactured by charging a vessel with water sufficient to yield a 30 wt% slurry, adding the solid ingredients, and mixing with a high shear mixture. Each slurry was poured into a tray and dried in an oven at 85-105°C until the material was dry enough to be pressed through a 6 mesh screen. Drying was then completed.
• Comparative Example 1 was the first gas generant composition alone. Comparative Example 2 is the second gas generant composition alone.
• Example 3 was a mixture 88 wt% of tablets of the first gas generant composition and 12 wt% of the second gas generant composition.
• Example 4 was tablets of a dryblended mixture of the first and second gas generant compositions in the same weight percentages as Example 3.
• Inflator tests using a 55 gram load exhausted into a 100 cubic foot tank are shown in the table below. Gas levels are given in parts per million by volume (ppm); particulate matter is expressed in grams. Comparative Example 1 Comparative Example 2** Example 3 Example 4 NO x 60-100 N/A 30-40 10-20 Ammonia 200-200 N/A 1-5 1-5 HCN 5-10 N/A 1-5 1-5 Particulate ⁇ 0.5 >2.0 ⁇ 0.5 ⁇ 0.5 I.C.* good poor to unacceptable fair fair *Inflator compatibility **In Comparative Example 2, only 25 grams of generant is used because higher loads result in excessively high pressures; particulate levels are calculated relative to a 55 gram charge.
• the invention applies generally to heterogeneous mixing of a first and a at least a second gas generant compositions.
• the pyrotechnic and effluent characteristics including gas effluent and particulate effluent, tends to be a weighted average of the heterogeneously mixed gas generant compositions.
• the invention has been exemplified with respect to heterogenous mixtures of two gas generant compositions, heterogeneous mixing should apply as well to mixtures of three or more gas generant compositions.
• the invention provides for relative predictability of pyrotechnic and effluent profiles when using two or more gas generant compositions. As airbag applications become more specific, e.g., driver-side, passenger-side, side-impact, and with specifics for particular vehicles, there is a need to be able to customize pyrotechnic and gas effluent profiles.
• the invention provides the ability to so customize pyrotechnic and effluent characteristics with substantial predictability and confidence.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Crystallography & Structural Chemistry (AREA)
• Air Bags (AREA)

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Citations (10)

• 1996
  • 1996-10-03 DE DE69609793T patent/DE69609793T2/de not_active Expired - Fee Related
  • 1996-10-03 EP EP96307233A patent/EP0767155B1/fr not_active Expired - Lifetime
  • 1996-10-04 JP JP8264480A patent/JPH09118582A/ja active Pending

Patent Citations (10)

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