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
  • C06B35/00—Compositions containing a metal azide

Definitions

• the present invention relates to the field of automobile safety. More precisely, the invention relates to a new pyrotechnic composition generating non-toxic cold gases and its manufacturing process.
• the composition according to the invention can in particular be used in pyrotechnic generators intended to inflate, in the event of an accident, protective cushions for occupants of a motor vehicle.
• a group of pyrotechnic compositions satisfying these requirements is made up of compositions comprising an alkali or alkaline earth azide such as sodium azide and a mineral oxidant such as an alkali or alkaline earth nitrate, an alkali or alkaline earth perchlorate, a metal oxide, a metal sulfide or even sulfur.
• Such compositions are for example described in US patents 4,369,079, 4,092,190, 4,243,443 or 4,203,787.
• compositions have the drawback of requiring, in the generator, an effective filtration chamber because they give off during combustion many hot solid particles which are entrained with the combustion gases but which must absolutely not enter the bag. inflatable so as not to introduce hot spots. Furthermore, some of these particles, consisting of sodium oxide, are extremely corrosive.
• the basic constituents, azide, oxidant and possibly silica are used in powder form.
• the mixture is agglomerated by simple compression, generally in the form of pellets which are stored in the combustion chamber. These pellets do not have good mechanical cohesion and tend to deteriorate over time under the effect of vibrations transmitted by the motor vehicle. This mechanical alteration leads to an alteration of the combustion law of the composition.
• sodium azide is a body sensitive to humidity and the generator containing this type of composition must be well protected against humidity.
• the object of the present invention is to provide pyrotechnic compositions generating non-toxic cold gases based on azide which have good mechanical strength, good protection of the azide against humidity and a reduction in the solid particles emitted during combustion.
• the invention therefore relates to a solid pyrotechnic composition generating non-toxic gases comprising at least one alkali or alkaline earth azide, a mineral oxidant chosen from the group consisting of alkali or alkaline earth nitrates, alkaline or alkaline earth perchlorates, metal oxides, metal sulfides and sulfur, characterized in that it contains an inorganic binder which is the product of an inorganic polycondensation reaction of mixtures based on alkali silico-aluminates and whose weight content relative to the total weight of said composition is between 5% and 40%.
• said mineral binder is the product of polymerization of a silico-aluminate of formula (Si2O5, Al2O2) and of silica S i O2 in the presence of aqueous soda and / and aqueous potassium hydroxide.
• the invention also relates to a process for manufacturing the compositions according to the invention characterized in that, after mixing and shaping of the various constituents of the composition, the polymerization of the said binder is firstly carried out by heating the said constituents in a sealed closed enclosure and in that, in a second step, the composition is dried.
• compositions according to the invention find a preferred application in pyrotechnic generators of non-toxic cold gases intended to inflate in the event of an accident, airbags for occupants of a motor vehicle.
• the invention relates to a solid pyrotechnic composition generating non-toxic cold gases comprising at least one alkali or alkaline earth azide and a mineral oxidant.
• azide sodium azide will advantageously be used.
• mineral oxidant it is possible to use most of the mineral oxidants traditionally used in gas-generating compositions containing an azide and in particular alkali or alkaline earth nitrates, alkali or alkaline earth perchlorates, metal oxides, metal sulfides, sulfur.
• mineral oxidant which can be used in the context of the present invention, potassium nitrate, calcium nitrate, potassium perchlorate, iron oxides, manganese dioxide, nickel oxide, molybdenum alone or in admixture with sulfur.
• the mineral oxidants preferred in the context of the present invention are alkali or alkaline earth nitrates and in particular potassium nitrate.
• a composition according to the invention contains a mineral binder.
• the mineral binders which can be used in the context of the present invention are the product of an inorganic polycondensation reaction of mixtures based on alkaline silico-aluminates. These mineral polymers are obtained by polymerization of a mixture of silicon and aluminum oxides in the presence of aqueous soda and / or aqueous potassium hydroxide. They are, for example, described, with their methods of obtaining, in French patents 2,464,227, 2,489,290 and 2,489,291 or their American correspondents 4,349,386 and 4,472,199.
• the polymers preferred in the context of the present invention are obtained by polymerization of a silico-aluminate of formula (Si2O5, Al2O2) and colloidal silica S i O2 in the presence of aqueous sodium hydroxide and / or aqueous potassium hydroxide.
• a silico-aluminate of formula (Si2O5, Al2O2) and colloidal silica S i O2 in the presence of aqueous sodium hydroxide and / or aqueous potassium hydroxide.
• poly (sialate-siloxo) of sodium and / or potassium and correspond to the formula following global: in which : M represents a sodium or potassium atom, S i represents a silicon atom, Al represents an aluminum atom, O represents an oxygen atom, n represents an integer.
• the silico-aluminate oxide (S i 2O5, Al2O2) which is different from the ordinary silico-aluminate (2SiO2, Al2O3) is for example described in French patent 2,621,260 or in its American correspondent 4,859,367.
• compositions according to the invention may contain between 5% and 40% by weight of mineral binder relative to the total weight of the composition, and preferably between 10% and 30% by weight. Thanks to the presence of the mineral binder which, after polymerization, is a real cement, the compositions according to the invention exhibit remarkable mechanical resistance, in particular when they are in the form of pellets. It has also been observed by the applicant that, despite the presence of the mineral binder, the compositions according to the invention have a combustion rate which is entirely compatible with the standards imposed in terms of motor vehicle safety and which is even sometimes higher. at the burning rate of traditional equivalent compositions without binder.
• the binder being entirely mineral, it does not generate any toxic gas during the combustion of the composition according to the invention and, after combustion, the compositions according to the invention have a mass of pulverulent residues much lower than the equivalent traditional compositions without binder because the polymerized binder does not disintegrate and functions, during combustion, as a first internal filter.
• the compositions according to the invention therefore require in a pyrotechnic gas generator for airbag fewer filters and reduce the weight of the generator.
• the presence of the polymerized mineral binder provides partial protection of the azide against humidity.
• compositions according to the invention are therefore very suitable for constituting the loading of a pyrotechnic generator of non-toxic cold gases intended to inflate a safety bag for occupants of a motor vehicle.
• the compositions according to the invention make it possible in particular to constitute in this case fillings in the form of pellets which have an excellent capacity for preservation over time.
• the invention also relates to a process for manufacturing the compositions according to the invention.
• This process consists, after having mixed the various constituents of the composition and having put them in the form of use of the composition, pellets, blocks or other forms, to ensure firstly the polymerization of said binder and secondly separate the drying of the composition.
• the constituents of the solid compositions according to the invention are of two kinds: on the one hand the traditional constituents such as azide and mineral oxidants which are pulverulent solids and on the other hand the mineral binder which, before polymerization, is in the form liquid and most often is marketed in the form of two separate solutions.
• the preferred binders of the invention are generally marketed in the form of an aqueous solution of silico-aluminate and of an aqueous solution of colloidal silica in soda and / or potash, the pH of which is generally close to 14.
• the pulverulent constituents will be mixed in a solid mixer while the mineral binder is prepared not polymerized by mixing its constituent solutions.
• the unpolymerized binder thus prepared does not react at room temperature and can be stored in the liquid state.
• the unpolymerized mineral binder and the mixture of pulverulent solids are then introduced into a kneader and all the constituents of the composition are mixed by rotating the kneader.
• the kneader will generally be cooled to avoid any heating of the constituents of the composition and any start of polymerization of the mineral binder.
• the mixture of the constituents of the composition is put into the form desired for the final composition: generally pellets, blocks or granules. At this stage it is necessary to distinguish different types of mixtures according to the content of the mixture in non-polymerized liquid binder.
• the mixtures in which the weight of unpolymerized binder is less than or equal to 15% of the total weight of the constituents of the composition have the consistency of a very slightly wet flour. These mixtures can be shaped by pelletizing, even if they have a slight tendency to form lumps. They can also be shaped by compression in a mold to form a block.
• Mixtures in which the weight of non-polymerized binder is greater than 25% of the total weight of the constituents of the composition have the consistency of a flowable paste. They lend themselves well to the technique of extrusion-injection to form granules.
• the preferred surfactants of the applicant are phosphorus-containing organo titanates.
• the mineral binder is first polymerized by heating the constituents.
• the polymerization rate increases with the heating temperature, but, taking into account the particular nature of the other constituents of the composition, the latter cannot be raised too much.
• the Applicant has found that heating for 24 hours at 60 ° C. ensures complete polymerization without risk.
• the polymerization reaction involves the participation of water molecules, it is important not to lose water by evaporation during polymerization. The applicant therefore recommends carrying out the polymerization in a sealed closed enclosure. It has been experimentally observed that water does not degrade the azide during this polymerization phase due to the strongly basic pH of the medium, and this despite the heating operation which accompanies the polymerization.
• the composition is subsequently dried by removing excess water.
• This drying is advantageously carried out by heating in a ventilated enclosure, at ordinary pressure or at reduced pressure.
• a simple solution consists in maintaining the composition in the polymerization enclosure, the doors of which are opened, and in maintaining the heating at 60 ° C. for a new period of 24 hours.
• compositions according to the invention are then available ready for use.
• composition cylinders were placed in a closed desiccator with 100% relative humidity in a ventilated oven at 60 ° C for 4 hours. We then measured their tensile strength which is almost zero.
• the surfactant used was a phosphorus organo-titanate marketed by the company KENRICH Pperichemicals under the name "LICA 12".
• the powdered azide / nitrate mixture was prepared in a "Turbula" type solid mixer.
• the preparation time was one hour.
• the mixture of constituents thus obtained was put into the form of cylinders by compression.
• the actual polymerization was carried out in a closed enclosure heated to 60 ° C. for 24 hours.
• the drying was carried out in a ventilated oven, heated to 60 ° C, for 24 hours.
• the breaking strength of these cylinders was more than 147N and their elasticity of 4.1%.
• the binder was obtained by mixing 13.4 parts by weight of solution B with 16.6 parts by weight of solution A.
• the surfactant was the same as that used in set 2.
• the binder was obtained by mixing 10.4 parts by weight of solution B with 19.6 parts by weight of solution A.
• the binder was obtained by mixing 10.4 parts by weight of solution B with 19.6 parts by weight of solution A.
• the surfactant was the same as that used in Example 2.

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

Applications Claiming Priority (2)

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Cited By (4)

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Citations (6)

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• 1990
  • 1990-06-27 FR FR9008096A patent/FR2663924B1/fr not_active Expired - Fee Related
• 1991
  • 1991-06-18 JP JP3145148A patent/JPH0725634B2/ja not_active Expired - Lifetime
  • 1991-06-25 EP EP91401701A patent/EP0467731B1/de not_active Expired - Lifetime
  • 1991-06-25 DE DE69105846T patent/DE69105846D1/de not_active Expired - Lifetime
  • 1991-06-25 US US07/720,628 patent/US5236526A/en not_active Expired - Fee Related

Patent Citations (6)

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