WO1998018743A1

WO1998018743A1 - Gas-emitting substance

Info

Publication number: WO1998018743A1
Application number: PCT/SE1997/001787
Authority: WO
Inventors: Per Sjöberg; Staffan Calsson
Original assignee: Bofors Explosives Ab
Priority date: 1996-10-31
Filing date: 1997-10-27
Publication date: 1998-05-07
Also published as: SE9603968D0; SE507997C2; SE9603968L

Abstract

The present invention relates to a gas-emitting substance which is suitable for use in gas generators in different types of motor vehicle airbags and which can also be used as a more general pyrotechnic charge. The main feature of the invention is the use of potassium dinitramide (KDN) as an oxidizing agent, combined with a suitable fuel such as boron, zirconium or titanium.

Description

GAS-EMITTING SUBSTANCE

The present invention relates to the use of a novel type of chlorine- free oxidizing agent in motor vehicle safety equipment of the airbag type or safety belt pretensioner type which depends, for its function, on the combustion of a gas-emitting substance. The invention also includes the use of the same gas-emitting substance as a more general pyrotechnic charge.

Principally as regards the driver and the front seat passengers, work on developing motor vehicle safety has very recently taken a long stride forward now that front airbags and side airbags are beginning to be included, as natural standard components, in virtually all new motor vehicles.

Initially, sodium azide and potassium azide and various types of nitrocellulose-based double-base propel- lant powders were used as gas-emitting substances in the gas generators of airbags. However, both these types of product have obvious disadvantages. Thus, the azides are extremely poisonous and the double-base propellant powders only have a lifespan which is so limited that they have to be replaced long before the average motor vehicle has reached the stage of being scrapped.

US Patent 4.931.112 suggests using 5-nitro-l , 2 , 4- triazol-3-one (NTO) as the gas-emitting substance in airbags. However, while NTO undeniably has many advan- tages in this context in that it is combusted rapidly at a relatively low temperature and in that it does not generate any poisonous gases, it is, at least at present, a very expensive product.

Swedish Patent 9202854-7 (laid-open for inspec- tion under number 470480) describes another group of alternative gas-emitting substances which are suitable for airbag assemblies and which are based on the high- energy explosives octogen (HMX) and hexogen (RDX) . These products, whose general composition most closely resembles that of the low-sensitivity so-called LOVA propellant powders, possess the basic properties which are required in this context and additionally display exceedingly good storage stability. US Patent 5.324.075 proposes using a product which is new in the context of airbags and which is in the form of an ammonium dinitramide, hereinafter termed

ADN, having the general formula

.NO^" NH+ Xi ^ ^l N0₂

This compound belongs to a relatively new group of N, N-dinitramide salts which are described in detail in US Patent 5.254.324 (= EP 487 693). The patent in question primarily relates to the general product in the form of a N, N-dinitramide salt of the formula

in which M is either a singly, doubly or triply charged metal cation, in which case x has the value 1, 2 or 3 , or a nitrogen-containing cation which contains 1-8 nitrogen atoms and which has the cationic charge x, where x is an integer. This patent also describes a method for producing compounds of this type. In the general text, and in connection with the examples, it is stated that N,N- dinitramide salts of this type should be particularly suitable for use as rocket propellants, in which role they are said to be able to replace the currently employed perchlorate compounds since they display the property, which is especially good in this context, of not containing any chlorine.

The two US Patents 5.198.204 and 5.415.852 also describe other methods of preparing these N,N- dinitramides .

However, the nitramide ADN, which the previously mentioned US Patent 5.324.075 proposed for use as a gas emitter in airbag gas generators, suffers from the disadvantages that, firstly, it has a melting point which is as low as approx. 92°C and, secondly, precisely like the products octogen, hexogen and double-base propellant powder, which have also been previously mentioned and have been used for the same purpose, it is classed as an explosive substance which is also, in itself, relatively easy to detonate.

As part of our efforts to develop a suitable gas- emitting substance for airbag gas generators which did not principally contain any material which is classed as an explosive substance, we came to focus our attention on attempting to develop a replacement for the potassium nitrate (KN0₃) or, even more preferably, for the potassium perchlorate (KC10₄) , which is a substantially more powerful oxidizing agent. In this connection, the main aim was to attempt to find a suitable oxidizer which did not emit any undesirable and/or poisonous substances, such as chlorine, and which, together with a suitable fuel, for example boron, zirconium, titanium or the like, would give a gas emission which was sufficiently rapid and was acceptable with regard to quantity without the addition of poisonous substances.

We have now found a substance, which meets our demands, in the N, N-dinitramide salt whose general formula is

and in which the metal cation M of the compound is potassium and in which x = 1.

As a chemical compound, this extremely special potassium salt, which is termed KDN in that which follows, must, in a purely general manner, be regarded as being previously known due to the fact that potassium is included in the enumeration of conceivable metal cations in the N, N-dinitramide salt which is described in US Patent 5,254,324. However, there is no intimation in this patent that, of the dinitramide salts which are highlighted in this document, that with potassium as cation should have any special application. Rather, the enumeration of metal cations, which is made in the patent, constitutes a mere enumeration of all cations which are theoretically conceivable in this context. KDN is also mentioned in PCT/SE96/00976 , which describes methods for preparing ADN which are different from those in the previously mentioned US Patents and in which KDN is an intermediate in the preparation of ADN. KDN has been found to be a powerful oxidizing agent which, together with a suitable fuel such as boron and, where appropriate, a binding agent, provides a supplement of gaseous products which is markedly superior to, and more rapid than, that provided by corresponding mixtures which have previously been used and which contain potassium nitrate as the oxidizing agent.

Thus, an extremely simple comparative experiment, which was carried out in a standard bomb which was fitted with a pressure indicator, showed that while a first mixture containing potassium nitrate as the oxidizing agent gave a maximum pressure of approx. 38 bar, the same charge, but containing KDN as the oxidizing agent, gave 58 bar. In both cases, stoichiometric quantities of boron were used as the f el .

Furthermore, KDN is an out-and-out oxidizing agent and not an explosive like the previously mentioned HMX, RDX and ADN. Thus, it cannot be caused to detonate by means, for example, of an impact test. In addition, it has a melting point which is at adequate distance from the current airbag standard of 107°C at 400 hours. The melting point of KDN is approx. 120°C.

In a general manner, KDN, together with a suitable fuel, preferably boron, can also be regarded as providing a good pyrotechnic charge for more general use. Both for use in gas generators for airbag asse b- lies and for use as a more general pyrotechnic charge, a good standard mixture should probably be regarded as containing

18-27% by weight of boron 0- 6% by weight of a combustible binding agent, for example an acrylate, which is compatible with the other products with the remainder being KDN and the usual impurities. A composition which contains a relatively large or relatively small excess of the fuel which is appropriate in each individual case is used when it is desired, for pyrotechnic purposes, to increase the supply of incandescent particles. The invention has been defined in the patent claims which follow.

Claims

PATENT CLAIMS

1. Gas-emitting substance for gas generators for motor vehicle airbags, safety belt tensioners and other active vehicle passenger protection devices whose function is gas-driven, characterized in that it comprises, as oxidizing agent, potassium dinitramide (KDN), which, together with a suitable fuel such as boron, zirconium, titanium or the like, is responsible, when the substance is combusted, for the majority of the combustion gases which are formed during this process.

2. Gas-emitting substance according to Claim 1, characterized in that it comprises 18-27% by weight of boron

0- 6% by weight of a combustible binding agent, with the remainder being KDN + normal contents of impurities .

3. Gas-emitting substance according to Claim 1 or 2 , characterized in that a conventional electric primer is used for its initiation.

4. Pyrotechnic charge, characterized in that it comprises, as oxidizing agent, potassium dinitramide (KDN) , which is combined with fuel in the form of a finely divided metal, such as boron, titanium, zirconium or the like, and, where appropriate, a binding agent.

5. Pyrotechnic charge according to Claim 4, characterized in that it includes 18-27% by weight of a fuel such as boron

0- 6% by weight of a combustible binding agent with the remainder being KDN + normal contents of impurities .

6. Pyrotechnic charge according to Claim 4, charac- terized in that the said fuel is included in a stoichio- metric excess.