Classifications

• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B21/00—Apparatus or methods for working-up explosives, e.g. forming, cutting, drying
  • C06B21/0033—Shaping the mixture
  • C06B21/0066—Shaping the mixture by granulation, e.g. flaking
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B21/00—Apparatus or methods for working-up explosives, e.g. forming, cutting, drying
  • C06B21/0033—Shaping the mixture
  • C06B21/0041—Shaping the mixture by compression
• • 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

Definitions

• the present invention relates to the pyrotechnic generation of gas, in particular for inflating cushions used in occupant protection systems of a motor vehicle.
• the present invention more specifically relates to so-called cold pyrotechnic compositions rapidly generating at acceptable temperatures for automotive safety (qualified low temperatures, that is to say less than 2200 K) clean and non-toxic gases.
• the present invention also relates to a process for obtaining such pyrotechnic compositions.
• the pyrotechnic compositions used in the gas generators must provide the quantity of gas required for the introduction of the airbag in an extremely short time, typically between 10 and 40 milliseconds.
• the gases generated must be clean, that is to say free of solid particles (which may constitute hot spots that may damage the wall of said cushion) and non-toxic, that is to say, low in content. carbon monoxide, nitrogen oxides and chlorinated products.
• compositions that appear to offer the best compromise in terms of gas temperature, gas yield, emitted particle content and toxicity contain, as main ingredients, guanidine nitrate (NG) and basic copper nitrate ( BCN).
• NG guanidine nitrate
• BCN basic copper nitrate
• the material passing between them is compacted in the form of a flat plate.
• Such an operation generates on the mixture a high compression and shear rate which improves the intimacy between the constituents.
• the compacted product from the compactor is then broken and forced through a rasp to generate pellets.
• Such granules generally prove to be easier to handle than the powders of departure.
• a single device generally provides compacting and granulation successively.
• the present invention thus relates to pyrotechnic gas generating compositions which combine two characteristics.
• a second oxidizing charge in the form of at least one alkali metal perchlorate said charges representing at least 95% by weight (generally at least 98% by mass) of the charges present;
• the pyrotechnic compositions of the invention containing a specific reducing charge (in the form of at least one nitrogen-containing organic compound) and a specific oxidizing charge (in the form of at least one basic metal nitrate), contain a limited quantity of a second specific oxidizing charge (in the form of at least one alkali metal perchlorate) and are obtained from a process which includes a step of dry-roller compaction of the powder mixture including said reducing and specific oxidants.
• Dry roll compacting is carried out, in a known manner, in a roller compactor, generally at a compacting pressure of 10 8 to 6.10 8 Pa.
• the method for obtaining the pyrotechnic compositions of the invention which typically includes a dry roll compacting step is further described in the present text. It can be implemented according to different variants (with a "simple" roller compacting characteristic step followed by at least one complementary step, with a roller compacting step coupled to a shaping step). and the pyrotechnic compositions of the invention therefore exist in different forms. In fact :
• pellets After dry roller compacting followed by granulation and then pelletization (dry compression), pellets are obtained;
• the granules according to the invention generally have a particle size (a median diameter) of between 200 and 800 ⁇ m
• the pellets according to the invention generally have a thickness of between 1 and 3 mm; and that within the extruded monolithic blocks, the granules are found in a dry binder (gel).
• part of the first object of the invention is in particular:
• the at least one nitrogenous organic compound constituting the reducing charge can be chosen in particular from guanidine nitrate, nitroguanidine, guanyl urea dinitramide and mixtures thereof. It consists advantageously of guanidine nitrate (NG).
• the at least one basic metal nitrate constituting the (first) oxidizing charge can be chosen in particular from nitrate basic copper, basic zinc nitrate, basic bismuth nitrate and their mixtures. It consists advantageously of the basic nitrate of copper (BCN).
• the at least one alkali metal perchlorate may in particular be chosen from potassium perchlorate, sodium perchlorate and mixtures thereof. It consists advantageously of potassium perchlorate (KCIO 4 ).
• the main constitutive ingredients of the compositions of the invention are therefore: guanidine nitrate (NG)
• said at least one nitrogen-containing organic compound present in a proportion of 45 to 65% by weight
• the pyrotechnic compositions of the invention contain;
• NG guanidine nitrate
• BCN basic copper nitrate
• KCIO 4 potassium perchlorate
• the pyrotechnic compositions of the invention in the form of formed articles, granules and pellets, consist essentially of (at least 95% by weight, generally at least 98% by weight) or even exclusively (at 100% by weight), the principal constitutive ingredients (charges) identified above: said at least one compound nitrogenous organic compound, said at least one basic metal nitrate and said at least one alkali metal perchlorate. Said ingredients can in fact alone constitute 100% the charges of said pyrotechnic compositions (this is generally the case), or even constitute 100% said pyrotechnic compositions.
• compositions of the invention of other charges in minimum quantities can not be ruled out (in any event, the charges identified above represent at least 95% by mass, generally at least 98% by weight of the charges present) and / or that of at least one additive (auxiliary type of manufacture).
• compositions of the invention in the form of extruded monolithic blocks, contain the main constituent ingredients (fillers) identified above (plus possibly other fillers in minimum amounts) in a dry gel.
• This gel extrudable per se or mixed with a solvent, is used upstream to allow extrusion. It has intervened in an effective amount (to allow extrusion) but limited so as not to significantly affect the performance of the compositions of the invention.
• extruded monolithic blocks of the invention generally do not contain more than 10% by weight of such a dry gel. They contain advantageously from 4 to 6% by weight. Within them, the synergy of the invention develops with the same intensity.
• the presence of at least one additive is also not excluded from this context.
• the main constituent ingredients (fillers) and the dry gel generally represent at least 95% by weight, very generally at least 98% by weight (or even 100% by weight) of said compositions.
• Said gel is generally chosen from cellulosic gels, gels obtained from acrylic elastomers, ethylene-vinyl-acetate copolymers with a high acetate content (containing more than 60% by weight of acetate units), polyester polymers, and their mixtures.
• Said gel advantageously consists of a sodium carboxymethylcellulose gel.
• the present invention relates to the process for obtaining pyrotechnic compositions as described above; a process which typically includes dry compacting of powders.
• the method comprises:
• the dry mixture of powders (of fillers) consisting of at least 95% by weight of a pulverulent reducing filler in the form of at least one nitrogenous organic compound, a pulverulent oxidizing filler in the form of at least one basic nitrate of metal and less than 30% by weight of a second powdery oxidizing charge in the form of at least one alkali metal perchlorate; and dry-roller compacting the resulting powder mixture.
• the constitutive ingredients of the desired pyrotechnic compositions occur in the form of powders.
• said powders have a fine particle size, less than or equal to 40 microns. Said particle size (value of the median diameter) is generally between 3 and 40 microns.
• the dry powder mixing and dry roll compacting steps of the resulting mixture are carried out in a conventional manner. With regard to dry roller compaction, it has been seen that it is implemented by passing the mixture of powders between two rolls, the pressure exerted then generally being between 10 8 and 6.10 8 Pa. a "simple" compaction with two cylinders having unmachined external surfaces or compaction coupled to a shaping with cylinders, the outer surface of at least one of which is machined to have cavities.
• the process of the invention can be limited to these two successive stages of mixing and compacting with dry rollers, in the following context: that of the direct obtaining of formed objects, in the assumption of the implementation of a roller compacting coupled to a shaping (the outer surface of at least one of the compacting rolls having cells).
• the method of the invention in addition to said two dry (“simple") dry roll mixing and compaction steps, may include: a) a dry granulation step (the compacted powder mixture is mechanically forced by a wet rotor; through a rasp exercising the sieve function whose mesh generally ranges from 500 microns to 3 mm). Roller compaction and granulation can be implemented in a single device or in two independent devices.
• the pyrotechnic compositions obtained are then in the form of granules (see above); b) a dry granulation step (see above) followed by pelletizing (dry compression during which the granules undergo a pressure generally between 4.10 8 and 10 9 Pa.
• the pyrotechnic compositions obtained are then in the form of pellets (see above); c) a dry granulation step (see above) followed by mixing the granules obtained with an extrudable binder and extruding said mixture.
• the pyrotechnic compositions finally obtained are in the form of extruded monolithic blocks loaded with granules.
• Variants of the process of the invention which include steps b) and c) above are particularly preferred.
• the method of the invention includes the steps of compacting rollers ("simple") and dry granulation of the mixture of starting powders.
• the powders (raw materials) used have a fine grain size: a median diameter of approximately 20 ⁇ m for KCIO 4 , 4.5 ⁇ m for BCN, 10 ⁇ m for NG.
• Table I presented below shows examples of formulation as well as the thermodynamic and ballistic performances of pellets (about 2 mm thick) obtained by pelletizing (carried out at 5.10 8 Pa) of previously uncompressed compacted powder mixtures. .
• Example 4 which offers the best compromise between combustion rate, gas yield and combustion temperature, was conditioned, for example 5, by implementing a roller compacting process (pressure between the rolls of 4.10 8 Pa) and granulation (forcing the compacted material by a rotor through a rasp equivalent to a sieve having a mesh of about 1 mm) dry process, upstream of the pelletizing.
• the granules obtained at the end of the roller compacting and granulation stage had a median particle size of approximately 500 ⁇ m. They were pelletized (easily, to the extent that there is no more flow problem) under the same conditions as the powders of Examples 1 to 4 (pressure of 5.10 8 Pa).
• Table II presented below shows the contribution of the roller compacting process to the ballistic performance of the composition.
• Example 4 of the method of compacting rollers and dry granulation induces an increase in the combustion rate to 20 MPa of the order of 20%. This increased speed is attributed to a better intimacy of the ingredients after passing through the compactor.
• the roller compacting phase induces on the mixture compressive and shear stresses which improves the quality of the mixture. Tests conducted with various pressures on the compactor confirmed this point. To a certain extent, the ballistics of the formulation is therefore adjustable by the pressure applied to the rollers during the compaction phase.
• roller compacting and granulation phase generates fines (small particle size) called ironings that can be reintroduced into the system.
• This reintroduction further generates an increase in the burning rate, which can reach 40 mm / s at 20 MPa, in the case of the composition of Example 5 with 20% ironing.
• Pyrotechnic compositions having the formulation specified in Table III below, were prepared by extrusion using 4% by weight of sodium carboxymethylcellulose as binder. The same process of kneading and continuous extrusion is implemented.
• Example 6 the powders are directly introduced (with the binder) into the device.
• Example 7 said powders were previously compacted and granulated under the conditions specified above for Example 5 and the resulting granules are introduced (with the binder) into the device.
• the intervention of the binder is certainly detrimental to the performance, in terms of rate of combustion, of the composition (of Example 7 compared to that similar to Example 5).
• the implementation of the roller compacting on the dry powders leads to significantly improve said combustion rate.
• the gain obtained is of the same order of magnitude, namely about 20%.

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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)

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Citations (3)

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• 2005
  • 2005-10-13 FR FR0510437A patent/FR2892117B1/fr not_active Expired - Lifetime
• 2006
  • 2006-10-12 WO PCT/FR2006/051026 patent/WO2007042735A2/fr not_active Ceased
  • 2006-10-12 JP JP2008535078A patent/JP5273609B2/ja active Active
  • 2006-10-12 EP EP06820288A patent/EP1934158A2/de not_active Withdrawn
  • 2006-10-12 CN CN201210352802XA patent/CN102816038A/zh active Pending
  • 2006-10-12 CN CN200680043374.5A patent/CN101312930B/zh not_active Expired - Fee Related
  • 2006-10-12 US US12/083,317 patent/US20090308509A1/en not_active Abandoned

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