Classifications

• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B25/00—Compositions containing a nitrated organic compound
  • C06B25/34—Compositions containing a nitrated organic compound the compound being a nitrated acyclic, alicyclic or heterocyclic amine
• • 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

Definitions

• the present invention relates to solid propellants for gas generators (gas-generating mixtures), wherein said propellants are mainly intended for use in propelling charges for gas generators used in airbags or seat-belt pretentioning devices, wherein the propellant for gas generators has a very good long-term thermal stability.
• An airbag essentially comprises a housing of the gas generator filled with the propelling charges for gas generators, generally in tablet form, and an initial detonator (squib) for detonating the propelling charge for gas generators, and also a gas bag.
• squib initial detonator
• Suitable detonators are disclosed, for example in U.S. Pat. No. 4,931,111.
• the gas bag which is initially folded into a small bag, is filled, after the initial detonation, with the gases produced in the burn-up of the propelling charge for gas generators and reaches its full volume in a time period of about 10-50 ms.
• DE-A-44 35 790 of the present applicant discloses propellants for gas generators on the basis of guanidine compounds on suitable carriers, which essentially exhibit an improved burn-up behaviour and an improved building of the slag.
• the propellant for gas generators disclosed in DE-A-44 35 790 comprises (A) at least one carbonate, hydrogen carbonate or a nitrate of guanidine, aminoguanidine, diaminoguanidine or triaminoguanidine in an amount of about 20-55 percent by weight based on the total amount of the components (A) and (B), (B) at least one alkaline or alkaline earth nitrate or ammonium nitrate as an oxidizing agent in an amount of about 80-45 percent by weight based on the total amount of components (A) and (B), and to moderate burn-up and to improve the formation of slags in an amount of 5-45 percent by weight based on the total amount of the components (A) and (B), (Cl) at least one carrier
• DE-A-19812372 also of the present applicant, discloses propellants for gas generators, comprising:
• At least one fuel selected from the group comprising guanidine nitrate, dicyanamide, ammonium dicyanamide, sodium dicyanamide, copper dicyanamide, tin dicyanamide, calcium dicyanamide, guanidine dicyanamide, ammonium guanidine bicarbonate, ammonium guanidine nitrate, triamino guanidine nitrate, nitroguanidine, dicyan diamide, azodicarbonamide as well as tetrazole, 5-aminotetrazole, 5-nitro-1,2,4-triazole-3-one, salts and mixtures thereof,
• the essentially chemically-inert slag trap with high fusion point in highly dispersed form i.e. these compounds are prepared by way of flame hydrolysis, functions as an internal filter and, thus, substantially prevents the formation and exit of dust type slag portions from the housing of the gas generator.
• a part of the highly dispersed slag traps can serve as a carrier for catalyst metals.
• the object underlying the present invention is to provide propellants for gas generators which comply with the more strict requirements more and more requested by the automobile industry with respect to the stability under heat aging over at least 400 hours at a temperature of 110° C. under conservation of functionality.
• a propellant for gas generators comprising:
• Nitroguanidine is virtually non-toxic, non-hygroscopic, sparely water soluble, thermally stable, burning at low temperature and of low impact sensitivity and friction sensibility.
• the gas yield during burn-up is high, wherein a high portion of nitrogen gas is obtained.
• a nitroguanidine which is particularly preferred according to the present invention is a nitroguanidine containing 0.1 to 0.5% nitroguanidinium hydrogen sulfate and nitroguanidinium nitrate.
• This kind of nitroguanidine stabilized by means of an acid will be referred to in the following as stabilized nitroguanidine.
• the pH value of an aqueous extract (5 g nitroguanidine per 200 ml water; 20° C.) of said stabilized nitroguanidine is in a range of from 3.5 to 4.4.
• Such kind of stabilized nitroguanidine is available as for example NIGU LBD SS from NIGU CHEMIE GmbH, Waldkraiburg, Germany.
• Conventional NIGU has a pH value of from 4.5-7.0 (5 g nitroguanidine per 200 ml water; 20° C.).
• Examples of oxidizing agents, component (B), are alkali metal- or alkaline earth metal nitrates (such as lithium nitrate, sodium nitrate, potassium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate or barium nitrate), alkali metal- or alkaline earth metal chlorates and -perchlorates (such as lithium-, sodium-, potassium-, magnesium-, calcium-, strontium- or barium chlorate and lithium-, sodium-, potassium-, magnesium-, calcium-, strontium- or barium perchlorate), ammonium nitrate, ammonium perchlorate, oxidizing copper compounds (such as Cu(NO 3 ) 2 .3Cu(OH) 2 and Cu 2 (OH) 3 NO 3 , respectively, CuCO 3 and CuO), and mixtures thereof.
• alkali metal- or alkaline earth metal nitrates such as lithium nitrate, sodium nitrate, potassium nitrate, magnesium
• Potassium nitrate, potassium perchlorate, strontium nitrate, ammonium nitrate, ammonium perchlorate and Cu(NO 3 ) 2 .3Cu(OH) 2 (copper(II)trihydroxy nitrate) are preferred.
• mixtures of alkali metal- or alkaline earth metal nitrates with ammonium perchlorate are preferred and mixtures of potassium nitrate or sodium nitrate with ammonium perchlorate are in particular preferred.
• Examples of stabilizers, component (C), are inorganic and organic acids.
• a particularly preferred inorganic acid is boric acid.
• Particularly preferred organic acids are citric acid, tartaric acid, cyanuric acid, terephthalic acid and fumaric acid.
• a further suitable stabilizer is hydrophobic SiO 2 (obtainable for example as Aerosil R812S of Degussa AG, Germany; hydrophobizing agent: hexamethylene disilazane) if stabilized NIGU is used as a fuel.
• Hydrophobic SiO 2 is a material which is not wetted by water, i.e. it swims on the water surface (see below, “Schriften-2 Pigmente”, Nr. 11, pages 55ff).
• Preferably hydrophobic SiO 2 is present in combination with a further stabilizer.
• gaseous reaction products obtained during burn-up of the propellants for gas generators according to the present invention essentially consist of carbon dioxide, nitrogen and water vapour.
• Possible toxic gaseous burn-up products such as CO, NO x and NH 3 are below the required maximum limits.
• Nitroguanidine, component (A), is present in the propellants for gas generators according to the present invention in an amount of about 33 to about 60 percent by weight, preferably of about 40 to about 60 percent by weight and in particular of about 45 to about 55 percent by weight.
• the oxidizing agent, component (B), is present in an amount of about 35 to about 55 percent by weight, preferably of about 38 to about 52 percent by weight and in particular of about 40 to about 48 percent by weight.
• the stabilizer, component (C) is present in an amount of up to about 5 percent by weight, preferably of up to about 3 percent by weight and in particular of up to about 1.6 percent by weight and in particular is present in a range of about 0.5 to about 1.6 percent by weight.
• propellants for gas generators contain further components.
• the propellants for gas generators according to the present invention optionally contain as component (D) at least one burn-up stabilizer and burn-up moderator, respectively, which can also function as a slag former and slag trap, respectively.
• component (D) at least one burn-up stabilizer and burn-up moderator, respectively, which can also function as a slag former and slag trap, respectively.
• Examples include Al 2 O 3 , in particular highly dispersed Al 2 O 3 with a BET surface (according to DIN 66131) of 100+15 m 2 /g (for example obtainable as Aluminiumoxid C from Degussa AG, Germany), Fe 2 O 3 , SiO 2 , iron acetyl acetonate, mixtures thereof as well as mixtures of highly dispersed Al 2 O 3 and SiO 2 , for example a mixture of about 16% highly dispersed Al 2 O 3 and about 84% highly dispersed SiO 2 (for example available as Aerosil COK 84 from Degu
• pyrogenic oxides are prepared by means of high temperature hydrolysis (flame hydrolysis) of the gaseous metal chloride (AlCl 3 ) under the influence of the water obtained in the occuring hydrogen-oxygen reaction under temperature conditions which are characteristic for this kind of reaction (4 AlCl 3 +6H 2 +3 O 2 ⁇ 2 Al 2 O 3 +12 HCl) (see committeeen Research Pigmente, “Highly Dispersed Metal Oxides Obtained According To The Aerosil® Process”, No. 56, 4th edition 1989, Degussa AG).
• the burn-up stabilizers and moderators, respectively, component (D), cause inter alia a linear burn-up behaviour, i.e. an exponential increase of pressure and temperature during the burn-up is prevented.
• Fe 2 O 3 for example can act under particular burn-up conditions as an oxygen supplier.
• these compounds can also be used as slag formers to prevent the formation of powder (dust-type) burn-up products.
• Component (D) is present in the propellants for gas generators in an amount of up to about 7 percent by weight, preferably in an amount up to about 5 percent by weight and in particular in an amount of about 0.4 to about 5 percent by weight.
• Highly dispersed Al 2 O 3 is present in the propellants of the present invention, preferably in an amount up to 5 percent by weight, preferably in an amount of 0.5-3 percent by weight and in particular 2-3 percent by weight. Due to this low amount of Al 2 O 3 a high gas yield can be guaranteed.
• the propellants for gas generators according to the present invention may contain as component (E) at least one binder.
• suitable binders are cellulose compounds, polymers of one or more polymerizable olefinic unsaturated monomers, metal salts of stearic acid being insoluble in water at room temperature and graphite. Graphite is particularly preferred.
• cellulose compounds are cellulose ethers, such as carboxymethylcellulose, methylcelluloseethers, in particular methylhydroxyethylcellulose, a methylhydroxyethylcellulose which can be used satisfactorily is CULMINAL®, MHEC 30000 PR supplied by the company Aqualon.
• Suitable polymers having binding action are polyvinylpyrrolidone, polyvinylacetate, polyvinylalcolhol and polycarbonates.
• the binder, component (E) serves as desensitizing agent and as processing aid in the production of granular material or tablets (pellets) from the propellant for gas generators. It furthermore serves to reduce the hydrophilic nature of the propelling charges for gas generators.
• Component (E) is present in an amount of up to about 5 percent by weight, perferably of up to about 3 percent by weight, more preferably of up to 1 percent by weight and in particular of about 0.2 to about 0.5 percent by weight.
• Preferred propellants for gas generators according to the present invention comprise nitroguanidine, in particular nitroguanidine stabilized according to the present invention as a fuel (component (A)), Cu(NO 3 ) 2 .3Cu(OH) 2 , Sr(NO 3 ) 2 , KNO 3 or a mixture of KNO 3 and NH 4 ClO 4 as an oxidizing agent (component (B)), at least one stabilizer selected from the group consisting of hydrophobic SiO 2 , and boric acid, citric acid, tartaric acid, cyanuric acid, terephthalic acid and fumaric acid, optionally as a mixture with hydrophobic SiO 2 (component C)), highly dispersed Al 2 O 3 , optionally as a mixture with iron(III) oxide as component (D) and graphite as component (E).
• component (A) fuel
• a propellant for gas generators comprising:
• a propellant for gas generators containing stabilized NIGU as a fuel and Sr(NO 3 ) 2 and a mixture of NaNO 3 or KNO 3 with NH 4 ClO 4 , respectively, as oxidizing agent shows a good or excellent long-term stability under heat aging conditions at 110° C. even in the presence of burn-up stabilizers/moderators and slag formers/traps.
• a stabilizer component (C)
• the starting materials (A), (B), (C), optionally (D) and optionally (E) have been mixed and have been milled and predensified, respectively, by means of a ball mill.
• the granulation of the propellant mixture for gas generators has been carried out in a vertical mixer in that about 20 percent of water has been added during stirring and at an elevated temperature of about 40° C. After a short venting and predrying, respectively, the obtained mixed mass has been grinded at room temperature through a grinding machine having a 1 mm sieve. The thus obtained granulate has been dried for about 2 hours at 80° C. in a drying ofen.
• the starting materials (A), (B), (C), optionally (D) and optionally (E) are mixed in a dry state and are then compacted under pressure for example by means of a gear wheel compacting mill. Then the compacted mass is broken up to a granulate and formed into tablets by means of a rotary-pelleting machine.
• the tablets and pellets, respectively, used in the gas generators and prepared in the propellants for gas generators can be prepared according to processes known in the art, for example by extruding, in rotary-pelleting (compression) machines or tabletting machines.
• the size of the pellets and tablets, respectively, depends on the desired burning time in each individual case.
• the propellant for gas generators according to the present invention consists of non-toxic, inexpensive components which can be easily prepared and the processing of which is not problematic.
• the mixtures are readily ignitable. They are fast-burning and ensure high gas yields with a very low proportion of CO, NO x and NH 3 , which proportion is below the admissible upper limit.
• the propellants for gas generators according to the present invention have a very good stability under heat aging conditions of 110° C. for more than 400 hours.
• the mixtures according to the present invention are in particular suitable as gas generating agents in the various airbag systems, as well as extinguishing agents or propellants.
• Granulate prepared according to the wet process as described above.
• GuNO 3 is an abbreviation for guanidinium nitrate and acts as an auxiliary fuel of lower energy.
• NIGU stabilized means nitroguanidine which is stabilized with 0.2% in total of nitroguanidinium hydrogen sulfate and nitroguanidinium nitrate.
• comparison examples 1 to 5 illustrate the conventional stability of propellants for gas generators on the basis of conventional nitroguanidine as a fuel.
• the instability of propellants for gas generators increases with an increasing amount of highly dispersed Al 2 O 3 .
• the propellant for gas generators does not contain Al 2 O 3 and shows a satisfactory long-term stability over an aging period of 400 hours and 1000 hours, respectively.
• such kind of propellant for gas generators is not suitable to be used in practice since the burn-up behaviour is insufficient. Indeed, the burn-up behaviour improves with an increasing amount of Al 2 O 3 , however, the stability of the propellant for gas generators rapidly decreases.
• Comparative example 4 shows a distinct increase of the stability by the addition of hydrophobic SiO 2 .
• the recipe according to comparative example 5 there is only a loss of weight of 0.62% after aging period of 400 hours in comparison to 1.45% for the recipe according to comparative example 5 for a tablet with a diameter of 4 mm and a height of 2 mm.
• Both recipes according to comparative example 4 as well as according to comparative example 5 contain a sufficient amount of 2.6 percent by weight Al 2 O 3 .
• the improvement of the stability is not sufficient in order to fulfill the requirements asked for by the automobile industry.
• Comparative example 7 shows the instability of a propellant for gas generators containing stabilized nitroguanidine in the presence of Cu(NO 3 ) 2 .3Cu(OH) 2 .
• a mixture of oxidizing agents comprising Sr(NO 3 ) 2 and Cu(NO 3 ) 2 .3Cu(OH) 2 .
• Al 2 O 3 being present in the recipe according to comparative example 9 again causes a decrease of the stability.
• the stability of stabilized nitroguanidine in the presence of CuCO 3 and CuO, respectively, has been examined.
• example 1 of the present invention (table II) a very good stabilization is obtained in a propellant for gas generators containing Al 2 O 3 as component (D) by combining stabilized NIGU as a fuel and hydrophic SiO 2 as a stabilizer (see example 1 and comparative examples 4 and 6).
• a further distinct improvement of the stability is obtained in the presence of a further stabilizer selected from the group of inorganic and organic acids (see examples 2 to 4).
• a very good stability is also obtained for propellants for gas generators containing conventional NIGU as a fuel and Al 2 O 3 as component (D) if stabilizers are used selected from the group consisting of inorganic and organic acids (see examples 5 to 10).
• KNO 3 has been used as an oxidizing agent (component (B)) in combination with highly dispersed Al 2 O 3 and iron(III) oxide as component (D).
• the recipe according to example 12 contains KClO 4 as oxidizing agent (component (B)) and Aerosil COK 84 as component (D). Also in this case a very good stability is obtained for the granulate.
• examples 13 to 15 show that a stable propellant for gas generators can be obtained even in the presence of Al 2 O 3 (see example 14) without the addition of a stabilizer if a mixture of KNO 3 and NH 4 ClO 4 is used as an oxidizing agent in combination with stabilized NIGU as a fuel.
• a comparison with comparative example 5 demonstrates that such a good stability cannot be obtained with conventional nitroguanidine as a fuel and KNO 3 as oxidizing agent in the presence of Al 2 O 3 .
• example 15 shows the good stability of propellants for gas generators which contain besides nitroguanidine as a fuel also guanidinium nitrate (GuNO 3 ) as an auxiliary fuel with lower energy.
• examples 18 to 20 Sr(NO 3 ) 2 has been used as an oxidizing agent. These examples show an excellent stability of stabilized nitroguanidine in the presence of Sr(NO 3 ) 2 and Al 2 O 3 . The addition of boric acid as a stabilizer even more improves the stability.
• Examples 21 and 22 prove the stabilizing effect of boric acid in compositions containing Sr(NO 3 ) 2 and Cu(NO 3 ) 2 .3Cu(OH) 2 as oxidizing agent (see comparative exampies 8 and 9).

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Air Bags (AREA)
• Feeding, Discharge, Calcimining, Fusing, And Gas-Generation Devices (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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• 2000
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