WO2001049637A1 - Method of producing gas-operated vehicle safety devices and the pyrotechnic gas-generating substances produced using the method - Google Patents

Method of producing gas-operated vehicle safety devices and the pyrotechnic gas-generating substances produced using the method Download PDF

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Publication number
WO2001049637A1
WO2001049637A1 PCT/SE2001/000001 SE0100001W WO0149637A1 WO 2001049637 A1 WO2001049637 A1 WO 2001049637A1 SE 0100001 W SE0100001 W SE 0100001W WO 0149637 A1 WO0149637 A1 WO 0149637A1
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Prior art keywords
gas
ofthe
generating
oxygen
generating substance
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PCT/SE2001/000001
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French (fr)
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Per Sjöberg
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Nexplo Bofors Ab
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    • CCHEMISTRY; METALLURGY
    • C06EXPLOSIVES; MATCHES
    • C06DMEANS FOR GENERATING SMOKE OR MIST; GAS-ATTACK COMPOSITIONS; GENERATION OF GAS FOR BLASTING OR PROPULSION (CHEMICAL PART)
    • C06D5/00Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets
    • C06D5/06Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets by reaction of two or more solids
    • CCHEMISTRY; METALLURGY
    • C06EXPLOSIVES; MATCHES
    • C06BEXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
    • C06B25/00Compositions containing a nitrated organic compound
    • CCHEMISTRY; METALLURGY
    • C06EXPLOSIVES; MATCHES
    • C06BEXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
    • C06B25/00Compositions containing a nitrated organic compound
    • C06B25/34Compositions containing a nitrated organic compound the compound being a nitrated acyclic, alicyclic or heterocyclic amine

Definitions

  • the pyrotechnic gas-generating substance in an airbag device is intended to quickly fill the cloth bag with gas so that it provides a shock absorbent protection between the passenger and the interior ofthe vehicle.
  • the function and safety ofthe airbag and the surrounding environment set a number of requirements for the pyrotechnic gas-generating substance and the gas that is generated. The same requirements are set for the pyrotechnic gas-generating substances in other gas-operated vehicle safety devices such as belt tensioners, inflatable neck protectors etc.
  • the gas generated in all such vehicle safety applications shall not therefore contain hot solid particles which could burn through the main system components, the gas filled cloth bags and injure passengers or place the entire function ofthe safety device at risk.
  • the most common pyrotechnic gas-generating substances used at present in the form of different sodium azide compositions do not entirely fulfil these requirements and for this reason extra reinforced cloth bags are used in combination with these gas-generating substances in order to stop solid particles formed at the combustion of sodium azide.
  • extra reinforced cloth bags are used in combination with these gas-generating substances in order to stop solid particles formed at the combustion of sodium azide.
  • the necessity of this extra reinforcement results in each such vehicle safety device having a greater weight and volume than would otherwise be required by the intended function.
  • the toxic gases which primarily could be relevant in this context are nitrous compounds, NO x and carbon monoxide as these are formed by the combustion of gas-generating substances. If chlorine is included in the gas-generating substance, hydrochloric acid is also formed.
  • a gas-generating pyrotechnic substance in a gas- operated vehicle safety device it is also required of a gas-generating pyrotechnic substance in a gas- operated vehicle safety device that this substance shall have a high degree of efficiency which means that it shall give a large amount of gas per weight or volume unit gas-generating substance.
  • sodium azide compositions these do not have a specially high degree of efficiency insofar as gas is generated by only approximately 40% ofthe solid substance. This low degree of efficiency has the result that when sodium azide is used as the gas-generating substance, it is difficult to fulfil the vehicle manufacturers' requirements of low weight and small volume for the vehicle components in question.
  • Nitro-cellulose is one example of a substance that does not fulfil this requirement but which would otherwise be conceivable, and which is at present used for this purpose despite giving the vehicle safety device in question a limited service life.
  • the pyrotechnic gas-generating substance used in the vehicle safety products must fulfil several requirements concerning own burning characteristics.
  • the ideal pyrotechnic gas-generating substance used for this purpose shall have a high rate of combustion which is not influenced by pressure and/or temperature.
  • sodium azide compositions are ideal substances but as already stated these substances have several disadvantages.
  • nitramine-based propellant compositions such as RDX which for example is used in compounds with cellulose acetyl butyrate.
  • RDX nitramine-based propellant
  • One disadvantage ofthe nitramine based propellant is however that its combustion rate is very pressure dependent. In a pressure which is too low, burning ceases completely while in a too high pressure it changes to an explosion. It has been possible to counteract these disadvantages as is demonstrated in USA patent 5695216, by constructing powerful enclosures for the gas generating substance and fitting these enclosures with pressure reliefs, but although this functions well it means that the construction is burdened with extra parts and higher costs.
  • guanidine dinitramide which is easily produced from guanidine and ammonium dinitramide and is described in the Swedish patent application 9804611-3.
  • Guanidine dinitramide can be used for this purpose either in pure form or together with other gas forming or oxygen producing substances such as guanyl urea dinitramide with the help of which the combustion and gas forming rates ofthe pyrotechnic substance can be adjusted to individual requirements.
  • guanidine dinitramide and compounds in which it is the main component are those substances themselves contain both oxidisers and fuel. It is therefore in principle a mono-propellant that does not require any additions or access to the oxygen in the air for its own combustion.
  • guanidine dinitramide' s combustion rate and thereby the gas generation rate ofthe substance can be adjusted by the inclusion of other gas-generating or oxygen producing substances such as guanyl urea dinitramide.
  • gas-generating pyrotechnic substance salt compounds consisting of at least one fuel selected from a group including such dinitromethane-based salts whose main characteristic is that they include a nitrogen-rich powerful base with a Pka for the protonised base >9 and at least one oxygen generator selected from a group including oxygen-rich salts based on one ofthe metals Li, Na, K, Mg; Ca or Sr and whose oxygen-rich component consists of one ofthe substituents NO , NO 2 , CIO 3 , CIO 4 or dinitromethane.
  • the fuel component base substituent should preferably be guanidine, guanyl urea or ammonium.
  • guanidine dinitromethane which has the following chemical formula:
  • guanidine dinitramide and guanyl urea dinitramide can then be added in the quantities required to the substances which are gas-generating at combustion in order to obtain the desired combustion rate.
  • An example of a gas-generating substance with a suitable combustion rate for certain gas operated vehicle safety devices is one containing approximately 70% by weight guanidine dinitromethane as fuel and approximately 30% by weight potassium dinitromethane as oxygen generator.
  • the metal salt and dinitromethane based gas-generating substances cause such a small degree of smoke formation that an activated airbag device does not risk being mistaken for a fire in the vehicle as has been the case with earlier types of airbag device for example those containing azides as gas-generating substances.
  • All ofthe gas-generating substances proposed are pressed to tablets with good structural strength at least if they have a small quantity of binder which should then preferably not exceed 10% by weight.
  • the substances in question have the advantage that when they have served as potential gas-generating substances in vehicle safety devices, which hopefully have not been used in active operation, they can be easily recycled by means of recrystallisation and used as gas-generating substances in other or similar products.
  • Sodium azide which is used extensively in vehicle safety devices today is therefore in practice always used in the form of a composition in which FE 2 O 3 and silicate are included and at present there is no plan for the recycling of sodium azide.
  • Sodium azide is furthermore extremely toxic and for this reason one can see no possibility other than destruction as soon as possible after the vehicle safety device in which it is included has completed its service life.
  • the present invention therefore makes available a gas-generating product which is adapted to the purpose and has a high combustion rate and low pressure dependence which together mean that it is possible to make cheaper airbag devices and that these do not need to withstand great overpressure and that they can be loaded with larger propellant tablets than has been possible previously as the products in accordance with the invention will never require extreme combustion areas.

Abstract

The present invention refers to a method of manufacturing a new general type of pyrotechnic gas-generating substance for gas operated vehicle safety devices such as airbags, belt tensioners, and also to the gas-generating substances produced in accordance with this method. The main characteristic of the gas-generating substances in accordance with the invention is that they consist of a salt composition consisting of at least one fuel selected from a group containing such dinitromethane based salts whose base substituent is selected from guanidine, guanyl urea or ammonium and at least one oxygen generating substance selected from a group consisting of the metals Li, Na, K, Mg, Ca and Sr based oxygen-rich salts whose oxygen component consists of one of the substituents NO3, NO2, CIO3, CIO4 or dinitromethane.

Description

Case 3821
Method of producing gas-operated vehicle safety devices and the pyrotechnic gas- generating substances produced using the method
The pyrotechnic gas-generating substance in an airbag device is intended to quickly fill the cloth bag with gas so that it provides a shock absorbent protection between the passenger and the interior ofthe vehicle. The function and safety ofthe airbag and the surrounding environment set a number of requirements for the pyrotechnic gas-generating substance and the gas that is generated. The same requirements are set for the pyrotechnic gas-generating substances in other gas-operated vehicle safety devices such as belt tensioners, inflatable neck protectors etc.
The gas generated in all such vehicle safety applications shall not therefore contain hot solid particles which could burn through the main system components, the gas filled cloth bags and injure passengers or place the entire function ofthe safety device at risk. The most common pyrotechnic gas-generating substances used at present in the form of different sodium azide compositions, do not entirely fulfil these requirements and for this reason extra reinforced cloth bags are used in combination with these gas-generating substances in order to stop solid particles formed at the combustion of sodium azide. The necessity of this extra reinforcement results in each such vehicle safety device having a greater weight and volume than would otherwise be required by the intended function.
The environmental requirements for the pyrotechnic gas-generating substances used for this purpose stipulate that these substances shall not create gas compounds which contain toxic gases in quantities that are injurious to the health. The toxic gases which primarily could be relevant in this context are nitrous compounds, NOx and carbon monoxide as these are formed by the combustion of gas-generating substances. If chlorine is included in the gas-generating substance, hydrochloric acid is also formed.
Furthermore, it is also required of a gas-generating pyrotechnic substance in a gas- operated vehicle safety device that this substance shall have a high degree of efficiency which means that it shall give a large amount of gas per weight or volume unit gas-generating substance. As regards sodium azide compositions, these do not have a specially high degree of efficiency insofar as gas is generated by only approximately 40% ofthe solid substance. This low degree of efficiency has the result that when sodium azide is used as the gas-generating substance, it is difficult to fulfil the vehicle manufacturers' requirements of low weight and small volume for the vehicle components in question.
Another requirement for these pyrotechnic gas-generating substances is that all shall be thermally stable and not be affected by the very high temperatures which can prevail in a vehicle panel in hot climates. Nitro-cellulose is one example of a substance that does not fulfil this requirement but which would otherwise be conceivable, and which is at present used for this purpose despite giving the vehicle safety device in question a limited service life.
Besides the requirements stated above, to ensure satisfactory function the pyrotechnic gas-generating substance used in the vehicle safety products must fulfil several requirements concerning own burning characteristics. The ideal pyrotechnic gas-generating substance used for this purpose shall have a high rate of combustion which is not influenced by pressure and/or temperature. In this respect, sodium azide compositions are ideal substances but as already stated these substances have several disadvantages.
Another group of substances which are gas-generating during combustion and have been tested in vehicle safety parts are nitramine-based propellant compositions such as RDX which for example is used in compounds with cellulose acetyl butyrate. One disadvantage ofthe nitramine based propellant is however that its combustion rate is very pressure dependent. In a pressure which is too low, burning ceases completely while in a too high pressure it changes to an explosion. It has been possible to counteract these disadvantages as is demonstrated in USA patent 5695216, by constructing powerful enclosures for the gas generating substance and fitting these enclosures with pressure reliefs, but although this functions well it means that the construction is burdened with extra parts and higher costs. Another specific type of pyrotechnic gas-generating substance which is well adapted to airbag devices is the compound guanidine dinitramide which is easily produced from guanidine and ammonium dinitramide and is described in the Swedish patent application 9804611-3.
Guanidine dinitramide can be used for this purpose either in pure form or together with other gas forming or oxygen producing substances such as guanyl urea dinitramide with the help of which the combustion and gas forming rates ofthe pyrotechnic substance can be adjusted to individual requirements.
An important advantage of guanidine dinitramide and compounds in which it is the main component is that these substances themselves contain both oxidisers and fuel. It is therefore in principle a mono-propellant that does not require any additions or access to the oxygen in the air for its own combustion.
As already referred to above it is stated in the Swedish patent application that guanidine dinitramide' s combustion rate and thereby the gas generation rate ofthe substance can be adjusted by the inclusion of other gas-generating or oxygen producing substances such as guanyl urea dinitramide.
An original idea which in time led to the present invention was that if guanidine dinitramide and guanyl urea dinitramide are good gas-generating substances for vehicle safety devices, the corresponding dinitromethanes should also have the same characteristic. It was not however so simple as these dinitromethanes do not function as complete mono-propellants.
Our efforts to find better gas-generating substances for vehicle safety devices resulted however in the present invention in accordance with which we use as the gas-generating pyrotechnic substance salt compounds consisting of at least one fuel selected from a group including such dinitromethane-based salts whose main characteristic is that they include a nitrogen-rich powerful base with a Pka for the protonised base >9 and at least one oxygen generator selected from a group including oxygen-rich salts based on one ofthe metals Li, Na, K, Mg; Ca or Sr and whose oxygen-rich component consists of one ofthe substituents NO , NO2, CIO3, CIO4 or dinitromethane.
As regards the fuel component base substituent we have found that it should preferably be guanidine, guanyl urea or ammonium.
An example of a suitable fuel component in accordance with the invention is therefore guanidine dinitromethane which has the following chemical formula:
Figure imgf000005_0001
Figure imgf000005_0002
These components should then be combined in such quantities that provide an oxygen balanced final product with the desired combustion characteristics. The previously known substances for this purpose, guanidine dinitramide and guanyl urea dinitramide, can then be added in the quantities required to the substances which are gas-generating at combustion in order to obtain the desired combustion rate.
An example of a gas-generating substance with a suitable combustion rate for certain gas operated vehicle safety devices is one containing approximately 70% by weight guanidine dinitromethane as fuel and approximately 30% by weight potassium dinitromethane as oxygen generator.
As is the case with guanidine dinitramide and guanyl urea dinitramide compounds proposed previously, the metal salt and dinitromethane based gas-generating substances cause such a small degree of smoke formation that an activated airbag device does not risk being mistaken for a fire in the vehicle as has been the case with earlier types of airbag device for example those containing azides as gas-generating substances. All ofthe gas-generating substances proposed are pressed to tablets with good structural strength at least if they have a small quantity of binder which should then preferably not exceed 10% by weight.
In accordance with the present invention, the substances in question have the advantage that when they have served as potential gas-generating substances in vehicle safety devices, which hopefully have not been used in active operation, they can be easily recycled by means of recrystallisation and used as gas-generating substances in other or similar products.
Although at present in all manufacture of chemical substances it is required for environmental reasons to consider how these new products can be recovered and reused, none ofthe gas-generating substances used at present in vehicle safety devices can be easily recovered when they have served out their service life but not been put into active use. As vehicle safety devices are by nature products which preferably are not put into practical operation one can expect that the number of unused gas- generating substances which must be taken care of when the vehicles are scrapped will increase at the same rate as such safety devices are installed in the range of new vehicles.
Sodium azide which is used extensively in vehicle safety devices today is therefore in practice always used in the form of a composition in which FE2 O3 and silicate are included and at present there is no plan for the recycling of sodium azide. Sodium azide is furthermore extremely toxic and for this reason one can see no possibility other than destruction as soon as possible after the vehicle safety device in which it is included has completed its service life. Nor is not possible to re-use nitro-cellulose as the substance is unstable and is consequently degraded with the passage of time. The only practical method of destruction is to remove the nitro-cellulose from the scrapped products and incinerate it as in the case of sodium azide.
The substances now suggested are however unified and stable and are also easy to recrystallize. Should degradation have taken place to any extent these products can still be re-used following recrystallization. In recrystallization, all the possible degradable products are washed away and the recrystallized product is completely comparable with newly manufactured products. This capability to recover and re-use gas-generating products in scrapped vehicle safety devices of this type is of course a great environmental advantage compared with the azides and nitro-cellulose propellants normally used at present which also must be destroyed by incineration while the previously mentioned nitramine propellant can be recovered by recrystallization.
The invention in its different parts has been defined in the following patent claims and a principle diagram which shows the combustion/pressure graph for the product in accordance with the invention compared with sodium azide compositions used at present, and a general sodium propellant is shown in the enclosed figure.
From these plots it can be seen that the products in accordance with the invention generally have the same low pressure dependence for combustion rate as the sodium compositions used at present and that both these product groups differ on this point from most other propellants. (Nitro-cellulose has combustion plots that are almost the same as those for nitramine propellants). The figures also show that the products in accordance with the invention have a combustion rate which is greater than the sodium azide compositions in present use.
The present invention therefore makes available a gas-generating product which is adapted to the purpose and has a high combustion rate and low pressure dependence which together mean that it is possible to make cheaper airbag devices and that these do not need to withstand great overpressure and that they can be loaded with larger propellant tablets than has been possible previously as the products in accordance with the invention will never require extreme combustion areas.

Claims

PATENT CLAIMS
1. Method of manufacturing gas-operated vehicle safety devices such as airbags, belt tensioners, inflatable neck cushions and equivalent, in which the chemicals used in the gas-generating substance in the event the device is not subjected to active use and following the removal ofthe original installation at the time ofthe end of its normal use, can be recovered, w h e r e i n the gas-generating pyrotechnic substance used consists of salt compositions consisting of at least one'fuel selected from a group containing such dinitromethane based salts whose main characteristic is that they include a nitrogen rich powerful base with a Pka for the protonised base >9 and at least one oxygen generating substance selected from a group consisting ofthe metals Li, Na, K, Mg, Ca and Sr based oxygen rich salts whose oxygen component consists of one ofthe substituents NO3, NO2, CIO3, CIO or dinitromethane.
2. Method in accordance with Claim l w h e r e i n guanidine, guanyl urea or ammonium is selected as the fuel component base substituent.
3. Pyrotechnic gas-generating substance for gas operated vehicle safety devices such as airbags, belt tensioners etc manufactured in accordance with either Claim 1 or 2 w h e r e i n the substance consists of salt composition consisting of at least one fuel selected from a group containing such dinitromethane based salts whose main characteristic is that they include a nitrogen rich powerful base with a Pka for the protonised base >9 and at least one oxygen generating substance selected from a group consisting ofthe metals Li, Na, K, Mg, Ca and Sr based oxygen rich salts whose oxygen component consists of one ofthe substituents NO3, NO2, CIO3, CIO4 or dinitromethane.
4. Pyrotechnic gas-generating substance w h e r e i n the base substituent ofthe fuel component consists of guanidine, guanyl urea or ammonium.
5. Pyrotechnic gas-generating substance in accordance with Claim 4 w h e r e i π it includes several ofthe different fuel and oxygen generating substances stated in Claims 1-4 and which together form the gas generating substance.
6. Pyrotechnic gas-generating substance in accordance with Claims 1-5 w h e r e i n at least one ofthe compounds guanide dimtramide or guanyl urea dinitramide is included as well as one out of each group ofthe fuels and oxygen generating substances defined in Claims 1-5.
PCT/SE2001/000001 2000-01-03 2001-01-02 Method of producing gas-operated vehicle safety devices and the pyrotechnic gas-generating substances produced using the method WO2001049637A1 (en)

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SE0000005-9 2000-01-03
SE0000005A SE515717C2 (en) 2000-01-03 2000-01-03 Methods of producing gas-powered car safety details and pyrotechnic gas generators produced accordingly

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2738150A3 (en) * 2012-11-28 2017-08-09 Diehl Defence GmbH & Co. KG Use of a dinitromethane salt

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998055428A1 (en) * 1997-05-21 1998-12-10 Försvarets Forskningsanstalt New chemical compound, explosive containing the compound and use of the compound in gas generators

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998055428A1 (en) * 1997-05-21 1998-12-10 Försvarets Forskningsanstalt New chemical compound, explosive containing the compound and use of the compound in gas generators

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2738150A3 (en) * 2012-11-28 2017-08-09 Diehl Defence GmbH & Co. KG Use of a dinitromethane salt
AU2013257394B2 (en) * 2012-11-28 2017-09-28 Diehl Defence Gmbh & Co. Kg Use of dinitromethane salt

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SE0000005D0 (en) 2000-01-03
SE0000005L (en) 2001-07-04

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