Azide-free, gas-generating composition

Abstract

The present invention relates to an azide-free gas-generating composition, in particular for use in safety devices for motor vehicles, comprising a fuel in a proportion of 20 to 60% by weight and consisting of one or more components, and an oxidizer mixture in a proportion of 40 to 80% by weight and consisting of at least three components, each in relation to the total composition. In accordance with the invention, the fuel consists of a guanidine compound in a proportion of at least 95% by weight and a further fuel component in a proportion of 0 to less than 5% by weight, each in relation to the fuel, and the oxidizer mixture consists of one or more transition metal oxides in a proportion of 20 to 80% by weight, basic copper nitrate in a proportion of 0 to 50% by weight, metal chlorate, metal perchlorate, ammonium perchlorate or mixtures thereof in a proportion of 1 to 15% by weight and alkali metal nitrate, alkaline earth metal nitrate or mixtures thereof in a proportion of 1 to 15% by weight, each in relation to the oxidizer mixture.

Description

[0001] The present invention relates to an azide-free, gas-generating composition, in particular for use in safety devices for motor vehicles. BACKGROUND OF THE INVENTION [0002] Gas-generating compositions which are used in safety devices for motor vehicles generally consist of a fuel based on sodium azide and an oxidation agent. Owing to the toxicity of sodium azide, however, a search for alternatives to the gas-generating mixtures containing azide was already begun early on. [0003] The U.S. Pat. No. 5,608,183 describes a gas-generating mixture which contains between approximately 30 and 85% by weight of a fuel and between approximately 15 and approximately 70% by weight of an oxidation agent. At least 60% by weight of the fuel consists of the nitrate salt of an acidic polyamine or of a C2-C3-alkyl diamine, such as for example the nitrate salts of urea, guanidine, aminoguanidine, diaminoguanidine, semicarbazide, ethylene diamine, 1,3-propane diamine or 1,2-propane diamine, or mixtu...

AI Technical Summary

Benefits of technology

[0014] Preferably, the Fe2O3 is present in an amount of at least 4% by weight, and more preferably in an amount of at least 9% by weight, in relation to the total composition. By using Fe2O3 and Cuo simultaneously, the amount of toxic gases in the combustion products can be further reduced.

[0017] The compositions according to the invention are distinguished compared with the mixtures known hitherto by an improved combustion behavior and in particular by an extremely low particle output in combination with a high combustion rate. They are therefore particularly suitable for use in driver's airbag systems. The improved combustion behavior of the compositions according to the invention is promoted by the use of at least one organic compound of the group of guanidine compounds as fuel. The use of guanidine nitrate is particularly preferred owing to its favorable oxygen balance of −26.2%.

[0018] Compared with other organic compounds or mixtures thereof with guanidine nitrate, therefore less oxidizer is required to balance out the mixture. Through this step, therefore, a lower particle output is already achieved.

[0020] The proportion of basic copper nitrate in the oxidizer mixture should in any case amount to a maximum of 50% by weight in relation to the oxidizer mixture. In addition to a high burning speed and extremely low carbon monoxide- and NOx emissions, a good readiness of the mixture to ignite and also an excellent retaining capability with regard to the solid combustion residues are achieved. A higher proportion of basic copper nitrate is not desired, because hereby in particular the NOx proportions in the gas would rise unduly.

[0021] A gas-generating mixture which is particularly preferred according to the invention consists of 40 to 55% by weight guanidine nitrate, 0 to 2.9% by weight cyanuric acid, respectively 15 to 30% by weight copper oxide and basic copper nitrate and also respectively 1 to 5% by weight ammonium perchlorate and alkali- or alkaline earth metal nitrate. Owing to the low proportion of cyanuric acid, this composition ensures a sufficient combustion rate for driver's airbag systems. The simultaneous presence of ammonium perchlorate and alkali- or alkaline earth metal nitrate in a molar ratio of approximately 1:1 (alkali) or respectively 2:1 (alkaline earth) has proved to be particularly favorable for a further reduction of the particle output, because through this combination, compared with mixtures of the other oxidizers, to achieve identical oxidation equivalents, the smallest quantities of solid combustion residues are produced. At the same time, the occurrence of HCl as toxic combustion product is prevented. The addition of small quantities of ammonium perchlorate and metal nitrate has, in addition, a favorable influence on the combustion rate.

Problems solved by technology

Owing to the toxicity of sodium azide, however, a search for alternatives to the gas-generating mixtures containing azide was already begun early on.

The gas-generating mixture known from the U.S. Pat. No. 5,608,183 has an insufficient readiness to ignite and also a combustion rate which is too low.

Owing to the high proportion of basic copper nitrate, in addition an increased proportion of toxic gases is to be found in the released gas mixture.

The processing of the mixture in a wet process requires additional drying stages and is therefore cost-intensive.

The use of an additional fuel, such as cyanuric acid for example, in a proportion of more than 5%, however, results in a distinctly reduced combustion rate of the composition.

The composition is therefore unsuitable for use in gas generators for the driver's side, in which owing to the shorter distance between the vehicle occupant and the vehicle components, high combustion rates are preferred.