Classifications

• • 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
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B33/00—Compositions containing particulate metal, alloy, boron, silicon, selenium or tellurium with at least one oxygen supplying material which is either a metal oxide or a salt, organic or inorganic, capable of yielding a metal oxide
  • C06B33/04—Compositions containing particulate metal, alloy, boron, silicon, selenium or tellurium with at least one oxygen supplying material which is either a metal oxide or a salt, organic or inorganic, capable of yielding a metal oxide the material being an inorganic nitrogen-oxygen salt

Definitions

• the present invention relates to the field of automotive safety. More specifically the invention relates to new pyrotechnic compositions clean and non-toxic gas generators, essentially consisting of nitrogen and water, and intended to inflate protective cushions for occupants of a motor vehicle.
• compositions based on sodium azide like, for example, those described in the patent US-A-4,929,290.
• the compositions based sodium azide have many disadvantages.
• sodium azide which can lead to explosives primary, by combination with metals to form for example lead azide, these compositions must be subject to precautions when manufacturing and disposal of waste.
• compositions as a propellant for rocket and missile engines are known and described in numerous patents such as, for example, the US-A-3,725,516 which describes propellants for rocket engines constituted by a fluorinated binder, a salt oxidant such as ammonium nitrate or perchlorate potassium and a metal in powder form.
• propellants are not usable in gas generators intended for the automotive safety for at least two reasons. Of a apart from that they contain a very high level of binder, often between 10 and 35%, and therefore produce large quantities of gas by combustion very toxic like carbon monoxide, and other apart they use metallic compounds which generate large amounts of solid residue.
• compositions based on ammonium nitrate and / or potassium perchlorate in combination with tetrazole derivatives and compounds metallic like boron oxide, vanadium oxide or silicates Such compositions which are, for example, described in US-A-5,035,757 give many non-toxic nitrogen-rich gases but still produce many solid residues which make it necessary to have a important filtration.
• compositions expressly excluding the presence of metallic compounds and comprising essentially an oxygenated thermoplastic binder, a energy plasticizer such as polyazide glycidyl and a compound oxidizing charge for at least 85% of its weight by ammonium nitrate.
• the composition contains at least 8% by weight of binder not to mention the energy plasticizer and the skilled person is, at least for some applications, again faced with the problem of gas toxicity.
• the object of the present invention is precisely to propose a family of compositions that meets this need.
• compositions according to the invention are presented therefore as over-oxygenated compositions containing very little binder. Under these conditions these compositions can admit small amounts of boron or which give them the speed of combustion required by automotive safety without production excessive carbon monoxide.
• Another benefit of the invention lies in the fact that the selection of two particular metals, boron and aluminum, avoid the formation of heavy particles capable of build hot spots in the airbag. Indeed, under the combustion conditions of the automotive safety it has been found that these two metals form residue as particles extremely fine, non-toxic solids that do not not require the presence of a filtration system sophisticated in the generator, unlike metals like magnesium, beryllium or zirconium which are commonly used in self propulsion but which absolutely not suitable in the context of this invention.
• the use of boron as a metal is preferred in the scope of the invention.
• the binder rate will advantageously be between 3 and 6% of the total weight of the composition.
• the binder will used without energy plasticizer and will preferably chosen from the group consisting of polymers and copolymers with epoxy units, with units ether, ester motifs, amide motifs or by polyacrylates. Polyepoxy binders are suitable particularly good at implementing the invention.
• the oxidizing charge also includes perchlorate potassium, the content of which is not more than 30% of the total weight of the composition. This content will often between 20% and 30% of the total weight of the composition.
• the oxidizing charge also includes a nitrogen compound chosen from the group consisting of perchlorate ammonium, triaminoguanidine nitrate, hexogen, octogen or hexanitrohexaazaisowurtzitane again known by the acronym "HNIW”.
• a nitrogen compound chosen from the group consisting of perchlorate ammonium, triaminoguanidine nitrate, hexogen, octogen or hexanitrohexaazaisowurtzitane again known by the acronym "HNIW”.
• HNIW hexogen, octogen or hexanitrohexaazaisowurtzitane again known by the acronym "HNIW”.
• HNIW hexogen, octogen or hexanitrohexaazaisowurtzitane again known by the acronym "HNIW”.
• the content of the composition in such a nitrogen compound is at most equal to 15% of its total weight.
• ammonium nitrate will be an ammonium nitrate stabilized by nitrate of potassium in the presence of an organic dye comprising an arylsulfonate group as described for example in French patent application 96.00778 or in the European patent application 97 400 149.7.
• an organic dye comprising an arylsulfonate group as described for example in French patent application 96.00778 or in the European patent application 97 400 149.7.
• the use of this type of ammonium nitrate allows better stability of the mechanical and pyrotechnic properties of material during thermal cycles.
• We will use advantageously a stabilized ammonium nitrate containing 96.5% by weight of ammonium nitrate, 3% of potassium nitrate and 0.5% amaranth.
• the said binder is a flexible binder which has a tensile elongation at 20 ° C equal to or greater than 15% and a coefficient of expansion at least equal to 2x10 -5 % per degree Celsius in the temperature range between -40 ° C and + 110 ° C.
• the binder will advantageously be chosen from the group consisting of polyepoxy binders and polyacrylic binders.
• compositions according to the invention find their preferred use as loads for pyrotechnic gas generators intended for safety automotive, in particular gas generators intended for inflate protective cushions for occupants of a motor vehicle.
• the oxygenated binder is then added in the state liquid, not completely polymerized.
• a thermosetting binder it will be liquid resin mixed with its hardener.
• the hardener will be advantageously a polyamine which is not very reactive so as to have a "pot life" for the binder of about 24 hours.
• compositions according to the invention being to contain only very little binder compared to usual compositions for propellants or low powders "LOVA" type vulnerability, a difficulty not negligible formulation of compositions according to the invention consists in successfully permeating the whole solid constituents, and in particular nitrate ammonium, with this small amount of liquid binder.
• the liquid binder will advantageously be introduced into the mixer in diluted form in a solvent very volatile and inert towards constituents of the composition.
• a polyepoxy binder advantageously use trichloroethane as a diluent.
• the mixer is then started and left on turn, open tank, for about an hour. In these conditions we can permeate all of the solid constituents by the binder and all of the diluent was removed by evaporation during the mixing operation.
• composition which appears at this stage under the appearance of a slightly wet powder is brought to the desired shape by compression. In general it is put in the form of pellets.
• the polymerization of the binder takes place at temperature ambient and after 24 hours, in the case of a binder polyepoxy, the pyrotechnic charges thus obtained have good mechanical strength allowing their use in gas generators intended for the automotive safety.
• compositions according to the invention contain a low level of binder which is not sufficient for fill all the gaps between the nitrate grains ammonium. Therefore putting into the form of pellets by compression leads to objects having a natural porosity corresponding to an increase in the area available for combustion, which is very favorable in terms of the rate of combustion of the composition.
• the gas-generating material must retain all of its properties over time, in particular after a succession of thermal cycles.
• so-called "flexible" oxygenated binders having a tensile elongation at 20 ° C equal to or greater than 15% and a coefficient of expansion, in the temperature range between -40 ° C and +110 ° c, at least equal to 2x10 -5 % per ° C.
• acrylic binders based on methyl acrylate or methacrylate containing a difunctional reactive diluent with long chain (of C 8 and C 15 ) as well as a metallic organic salt as catalyst.
• This last family of binders is particularly interesting because of its anaerobic characteristics that allow it to polymerize at 20 ° C in the absence of oxygen.
• compositions according to the invention were manufactured which have been tested in pyrotechnic operation.
• compositions corresponding to Examples 9 and 10 relate to the use of ammonium nitrate stabilized by 3% by weight of potassium nitrate and 0.5% by weight amaranth as described above. These compositions have have been pelletized and subjected to a standard aging cycle between -35 ° C and + 105 ° C. After this cycle, the pastilles have kept all their mechanical and pyrotechnic properties of operation in a gas generator.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Combustion & Propulsion (AREA)
• Inorganic Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Air Bags (AREA)

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Citations (7)

• 1996
  • 1996-06-28 FR FR9608050A patent/FR2750422B1/fr not_active Expired - Fee Related
• 1997
  • 1997-06-26 DE DE1997605090 patent/DE69705090T2/de not_active Expired - Fee Related
  • 1997-06-26 EP EP19970401483 patent/EP0816307B1/de not_active Expired - Lifetime
  • 1997-06-30 JP JP9173729A patent/JP2927757B2/ja not_active Expired - Fee Related

Patent Citations (8)

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