EP0930284B1 - Ablative solid material for hybrid gas generator - Google Patents

Abstract

Solid ablatable materials composed principally of an organic binder, at least one reductive organic filler and additives, where: (i) the reductive organic filler is 3,5-diaminotriazole, dimethyl bitetrazole, tetraformaltrisazine, melamine or 5-aminotetrazole; (ii) the binder content is 4-80 wt.% total product weight; and (iii) the enthalpy of formation DELTA Hf of the material is at least 1250 kJ/kg.

Description

The present invention relates to the field of compositions which may constitute loads for modular thrusters and for generators gas pyrotechnics intended to inflate cushions protection, in particular those for the occupants of a motor vehicle. More specifically the invention relates to solid materials which can constitute ablatable loads in hybrid generators with solid loading. It is said of a load that it is ablatable when it cannot burn and generate by combustion of gaseous molecules with only a contribution oxidizer exterior.

To inflate protective cushions occupants of a motor vehicle it has been largely proposed to use pyrotechnic gas generators for which all of the gases used to inflate the protective cushion comes from the combustion of a pyrotechnic charge. Two large families of pyrotechnic compositions are generally used to constitute these loads. A first family relates to compositions based on mineral azides and especially sodium azide. These compositions have the disadvantage of providing, by combustion, large amounts of hot solid residue which must be filtered to prevent them from entering the airbag. A second family concerns propellant powders which can be based on nitrocellulose and nitroglycerin or based on oxidizing compound coated with a reducing organic binder. These propellant powders provide little, if any at all, solid residues but present the major drawback of having very high combustion temperatures.

In order to provide solutions to the problems of solid residue and temperature these gases from combustion generators have also been proposed so-called "hybrid" gases containing both a charge solid pyrotechnics and a pressurized gas reserve in which the gases from the combustion of the solid charge dilutes when contained gases in this reserve are inert, or even end up burn when the gases in this reserve are oxidants. In the latter case, advantageously used solid fuel loads under oxygen such as described for example in European patent applications EP-A-0 768 218 or EP-A-0 779 260. These generators hybrids already reduce very significant the content of the gases generated in residues solid and also allow to lower slightly their temperature.

In order to further lower the gas temperature coming out of the hybrid generators we then proposed hybrid generators containing as a component pyrotechnics a simple pyrotechnic initiator, and also containing a reserve of oxidizing gas under pressure which is usually oxygen and a solid loading made up not of a material fuel under oxygen but with an ablatable material. Such solid-load hybrid generators ablatable and not combustible are for example described in patent application PCT / FR 97/01260 or also in American patents US-A-5,509,981 and US-A-5,619,011. The constituents of ablatable materials which are described in these patents and which is based on highly nitrogenous compounds and organic polymers, make it possible to obtain ablatable materials supplying at a moderate temperature gases free from solid residue, but these gases sometimes contain too high nitrogen oxides and carbon monoxide carbon which are toxic gases and moreover the ablation speed of the materials thus obtained is not always sufficient with regard to the requirements of motor vehicle manufacturers.

The skilled person therefore still needs power have easily ablatable solid materials and usable in gas generators intended for inflate protective cushions for occupants of a motor vehicle, i.e. of materials solids with velocity and temperature of ablation meeting the standards of the manufacturers of motor vehicles and thus supplying gases essentially constituted by nitrogen and by carbon dioxide and practically free of residue solids, nitrogen oxides and carbon monoxide. Of such easily ablatable materials can also be used to constitute loads of modular thrusters and in particular downstream loading "bichambre" thrusters including the upstream chamber includes a self-fueling charge generating a gas oxidant, the variation of the combustion pressure in this upstream chamber for modulating the thrust of these thrusters.

The object of the present invention is specifically to offer materials that meet on all points to these needs.

i) les charges réductrices organiques sont choisies dans le groupe constitué par le diamino-3,5 triazole, le diméthyl bitétrazole, la tétraformaltrisazine, la mélamine et le 5-amino tétrazole,

ii) la teneur pondérale du liant par rapport au poids total du matériau est comprise entre 4% et 80%,

iii) l'enthalpie de formation ΔHf du dit matériau est au moins égale à 1250 kJ/kg,

iv) les additifs ne comportent pas de groupe oxydant.

The invention therefore relates to a composite ablatable solid material intended to react with an oxidizing gas, said material consisting mainly of an organic binder, at least one organic reducing filler and optionally by additives, characterized in that:

i) the organic reducing charges are chosen from the group consisting of diamino-3,5 triazole, dimethyl bitetrazole, tetraformaltrisazine, melamine and 5-amino tetrazole,

ii) the weight content of the binder relative to the total weight of the material is between 4% and 80%,

iii) the enthalpy of formation ΔHf of said material is at least equal to 1250 kJ / kg,

iv) the additives do not contain an oxidizing group.

It was thus discovered that to meet the above criteria, the ablatable solid material must be essentially reducing and must present imperatively a formation enthalpy ΔHf clearly positive, at least equal to 1250kJ / kg.

To do this, the usable loads are nitrogen reducing organic charges having a enthalpy of positive formation.

When the organic binder used is a binder having a negative formation enthalpy or weakly positive, as is particularly the case for thermoplastic hydrocarbon polymers and for polymers based on a crosslinked epoxy resin by a polyamine, the weight content of binder by relative to the total weight of the material will advantageously between 4% and 10%, preferably between 6% and 8%. In this case the material will be put in the form of blocks extruded using a solvent for the phase extrusion, either in the form of pellets by solvent-free granulation and compression.

When the organic binder used is a binder having a strongly positive enthalpy of formation as for example the case for polyazides with alcohol functionality crosslinked with a polyisocyanate, we can use this binder at a weight content between 4% and 80% of the total weight of the material and preferably between 20% and 60%. Load organic reducing agent will then preferably be chosen from the group consisting of dimethyl bitetrazole and by tetraformaltrisazine which react little or no with isocyanate groups. With this second group of binders the material will be generally put in the form of extruded blocks, the extrusion doing without solvent before completion of the crosslinking. Other shaping techniques remain however possible and in particular the granulation followed by compression when the rate of binder is relatively weak.

Initiated by a pyrotechnic initiator in the presence of an oxidizing gas like air or oxygen, materials according to the invention quickly ablate at temperatures often below 1600 ° K. Gases as well products mainly consist of nitrogen and by carbon dioxide they are free from solid residues and contain only traces nitrogen oxides and carbon monoxide.

The materials according to the invention find their preferred application in gas generators ablatable solid-loading hybrids for inflate protective cushions for occupants of a motor vehicle.

a detailed description is given below of preferred embodiment of the invention.

The ablatable materials according to the invention are so composite solid materials that contain basically an organic binder and a filler organic so as not to produce by ablation of solid residues. They may optionally contain small amounts of additives, these additives do not with no oxidizing groups so that the material remains completely ablatable and does not become combustible part.

So that this material has a speed ablation compatible with safety requirements automobile it was discovered that he must present a enthalpy of formation ΔHf very positive, at least equal at 1250kJ / kg.

To this end the organic charge is a charge organic reducing nitrogen with enthalpy of formation positive.

Table 1 below gives the names, formulas, structures and enthalpies of ΔHf formation of the different fillers that can be used in the context of the invention.

Given the training enthalpies, it is observe that if dimethyl bitetrazole, the tetraformaltrisazine and 5-amonotetrazole can be used as single fillers, against diamino-3,5 tetrazole and melamine cannot be used as add-on fillers mixed with at least one of the three previous charges.

These charges are held by an organic binder of which the weight content is between 4% and 80% of the total weight of the composition. It should be noted that, in the context of the present invention, the polymers highly oxygenated such as polyesters and polycarbonates cannot be used as binders and that, on the other hand, a polymer cannot, by itself, be an ablatable material, but must contain a or more of the above reducing organic fillers at least about 25% of its own weight.

In practice we will distinguish two main families of binders usable in the context of the invention.

The first family includes enthalpy binders negative or very weakly positive, in practice less than 200 kJ / kg. This family includes in particular polymers based on epoxy resin crosslinked by a polyamine and polymers thermoplastic hydrocarbons.

When an ablatable material according to the invention is made from a binder belonging to this first family, it is only or essentially the reducing organic charge which brings the enthalpy of positive material formation. The latter will contain therefore little binder, in practice from 4 to 10% by weight, preferably from 6 to 8% by weight relative to the total weight of the material.

The second family includes enthalpy binders of highly positive training, in practice at less close to 800kJ / kg. This family includes especially alcohol-functional polyazides crosslinked with a polyisocyanate.

When an ablatable material according to the invention is made from a binder belonging to this second family, it is both the binder and the reducing organic charge which provide the enthalpy of positive formation of the material. The latter can therefore contain a lot of binder, in practice from 4 to 80% by weight, preferably between 20 and 60%, relative to the total weight of said material. But it is once again emphasized that, even in this case, the binder cannot, by itself, constitute all of the ablatable material, in particular for questions of ablation speed. With this type of binder, the organic reducing charges which do not contain an amino-NH _{2 group} reactive with respect to the isocyanate -NCO groups, that is to say dimethyl bitetrazole and tetraformaltrisazine, will be preferred.
The following examples illustrate, without limitation, certain possibilities for implementing the invention.

Example 1 to 3

hollow extruded cylindrical blocks were made at from the following three compositions:

Example 1:

• binder: epoxide crosslinked with a polyamine: 6% in weight
• filler: 5-aminotetrazole: 94% by weight.

Example 2

• binder: glycidyl polyazide with OH functions crosslinked with a polyisocyanate: 55% in weight.
• filler: dimethyl bitetrazole: 45% by weight.

Example 3

• binder: glycidyl polyazide with OH functions crosslinked with a polyisocyanate: 55% in weight.
• filler: 5-amino tetrazole: 45% by weight.

ω =

rapport pondéral air/solide ablatable.

Ta =

température d'ablation en °C.

Rdt global =

rendement gazeux en litres/gramme du chargement global du générateur hybride (air et solide ablatable).

Rdt abl. =

rendement gazeux en litres par gramme du seul chargement solide ablatable du générateur hybride.

% rés. =

pourcentage pondéral de résidus solides dans les gaz.

COppm =

teneur gazeuse en monoxyde de carbone exprimée en ppm dans un volume de 2,5m³, à partir d'un coussin de 60 litres gonflé par les gaz provenant du générateur.

NOxppm =

teneur gazeuse en oxydes d'azote exprimée en ppm dans un volume de 2,5m³ à partir d'un coussin de 60 litres gonflé par les gaz provenant du générateur.

Exemple 1 ω 12,35 7,14 5,38 4,29 Ta 830 1260 1549 1803 Rdt global 3,16 4,42 5,26 6,01 Rdt abl. 42 35,4 33,5 31,7 % rés. 0 0 0 0 COppm 0 0 0 0 NOxppm 1 9 18 25 Exemple 2 ω 12,35 7,14 5,38 4,29 Ta 1267 1900 2276 2214 Rdt global 4,37 6,16 7,25 7,30 Rdt abl. 58 50,5 46,2 38,6 % rés. 0 0 0 0 COppm 0 0 83 376 NOxppm 10 32 13 0 Exemple 3 ω 12,37 7,16 5,37 4,296 Ta 1074 1620 1981 2258 Rdt global 3,83 5,33 6,42 7,25 Rdt abl. 28,8 65,3 40,9 38,4 % rés. 0 0 0 0 COppm 0 0 3 45 NOxppm 6,7 34 47 50 For reasons of simplicity of the tests to be carried out, the blocks thus obtained were used to constitute the ablatable load of hybrid generators whose oxidizing gas was air and intended to inflate 60-liter cushions. Tables 2 to 4 which follow summarize the loading conditions of the generators and the firing results. In these tables the following abbreviations have been used:

ω =

air / solid weight ratio ablatable.

Ta =

ablation temperature in ° C.

Global yield =

gas yield in liters / gram of the overall load of the hybrid generator (air and ablatable solid).

YT abl. =

gas yield in liters per gram of the single ablatable solid charge of the hybrid generator.

% res. =

weight percentage of solid residues in gases.

COppm =

gaseous carbon monoxide content expressed in ppm in a volume of 2.5m ³ , from a 60 liter cushion inflated by the gases coming from the generator.

NOxppm =

gas content of nitrogen oxides expressed in ppm in a volume of 2.5m ³ from a 60 liter cushion inflated by gases from the generator.

Example 1 ω 12.35 7.14 5.38 4.29 Your 830 1260 1549 1803 Global yield 3.16 4.42 5.26 6.01 YT abl. 42 35.4 33.5 31.7 % res. 0 0 0 0 COppm 0 0 0 0 NOxppm 1 9 18 25 Example 2 ω 12.35 7.14 5.38 4.29 Your 1267 1900 2276 2214 Global yield 4.37 6.16 7.25 7.30 YT abl. 58 50.5 46.2 38.6 % res. 0 0 0 0 COppm 0 0 83 376 NOxppm 10 32 13 0 Example 3 ω 12.37 7.16 5.37 4,296 Your 1074 1620 nineteen eighty one 2258 Global yield 3.83 5.33 6.42 7.25 YT abl. 28.8 65.3 40.9 38.4 % res. 0 0 0 0 COppm 0 0 3 45 NOxppm 6.7 34 47 50

These examples show that ablatable materials according to the invention allow well when they are used in hybrid generators containing gases oxidants, to supply at moderate temperatures gases clean, free of solid residues, and non-toxic, especially when the oxidant gas / solid weight ratio ablatable is high enough.

Claims (7)

1. Composite ablatable solid material for pyrotechnic gas generators for inflating airbags for protecting the occupants of a motor vehicle, consisting mainly of an organic binder, at least one organic reductive filler, and additives, characterized in that:

   i) the organic reductive fillers are chosen from the group consisting of 3,5-diaminotriazole, dimethylbitetrazole, tetraformaltrisazine, melamine and 5-aminotetrazole,

   ii) the weight content of the binder relative to the total weight of the material is between 4% and 80%,

   iii) the enthalpy of formation ΔHf of the said material is at least equal to 1250 kJ/kg,

   iv) the said additives do not comprise oxidizing groups.
2. Material according to Claim 1, characterized in that the binder is chosen from the group consisting of thermoplastic hydrocarbon-based polymers and polymers based on epoxy resin crosslinked with a polyamine, and in that the weight content of the binder relative to the total weight of the material is between 4% and 10%.
3. Material according to Claim 2, characterized in that the weight content of the binder relative to the total weight of the material is between 6% and 8%.
4. Material according to Claim 1, characterized in that the binder is chosen from the group consisting of polyazides containing alcohol functionality, crosslinked with a polyisocyanate.
5. Material according to Claim 4, characterized in that the weight content of the binder relative to the total weight of the material is between 20% and 60%.
6. Material according to Claim 5, characterized in that the said organic reductive filler is chosen from the group consisting of dimethylbitetrazole and tetraformaltrisazine.
7. Use of a composite ablatable solid material according to any one of Claims 1 to 6, for the preparation of an ablatable solid charge for a hybrid gas generator containing an oxidizing gas, for inflating airbags for protecting the occupants of a motor vehicle.