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)
  • C06D3/00—Generation of smoke or mist (chemical part)
• • 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
  • C06B33/12—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 two or more oxygen-yielding compounds
  • C06B33/14—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 two or more oxygen-yielding compounds at least one being an inorganic nitrogen-oxygen salt
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B23/00—Compositions characterised by non-explosive or non-thermic constituents
  • C06B23/007—Ballistic modifiers, burning rate catalysts, burning rate depressing agents, e.g. for gas generating
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B23/00—Compositions characterised by non-explosive or non-thermic constituents
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B31/00—Compositions containing an inorganic nitrogen-oxygen salt
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B45/00—Compositions or products which are defined by structure or arrangement of component of product
• • 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 pyrotechnic compounds (or pyrotechnic objects) which generate gas simultaneously having a moderate combustion temperature (less than 2200 K) and a high combustion speed (equal to or greater than 20 mm / s at 20 MPa) and generating combustion residues in agglomerated form, thus easily filterable residues.
• Said gas-generating pyrotechnic compounds are particularly suitable for use in systems for protecting the occupants of motor vehicles, more especially for inflating front shock absorbing cushions (called “airbags”) (see below).
• Front airbags differ from side airbags essentially in the time required for deployment and installation of the airbag. Typically, this time is higher for a front airbag (of the order of 40-50 ms, against 10-20 ms for a side airbag).
• pyrotechnic composition for obtaining gas-generating pyrotechnic compounds particularly suitable for use in systems for protecting the occupants of motor vehicles, have already been proposed to date.
• the pyrotechnic compounds which seem to offer the best compromise, in terms of combustion temperature, gas yield, toxicity of combustion gases and pyrotechnic safety of implementation, contain, in their composition, as main ingredients of guanidine nitrate (NG) as a reducing filler and basic copper nitrate (BCN) as an oxidizing filler.
• NG guanidine nitrate
• BCN basic copper nitrate
• the use of the NG / BCN couple makes it possible to obtain a low combustion temperature, typically of the order of 1800 K.
• the patent US 5,608,183 describes compounds of this type obtained by a wet manufacturing process. These compounds, however, remain difficult to ignite and intrinsically exhibit a combustion rate at best equal to 20 mm / s at 20 MPa.
• additives based on a transition metal oxide, playing the role of ballistic catalyst.
• Such additives are well known to those skilled in the art, in that they are traditionally used in the field of propellants (as a ballistic catalyst) to increase the combustion speed, both at low, medium and high. pressure.
• a ballistic catalyst is thus described, consisting of an oxide chosen from Al 2 O 3 , TiO 2 , ZnO, MgO and ZrO 2 , at a mass rate of 0.5% up to 5% .
• metal oxides and hydroxides playing the role of ballistic catalyst (qualified as combustion adjustment agent) are also mentioned, such as Cr 2 O 3 , MnO 2 , Fe 2 O 3 , Fe 3 O 4 , CuO, Cu 2 O, CoO, V 2 O 5 , WO 3 , ZnO, NiO, Cu (OH) 2 . They can be incorporated up to 10% by mass.
• the pyrotechnic compounds formulated from basic copper nitrate (BCN) have the major drawback of generating, during combustion, a high rate of solid residues which are difficult to filter.
• This low filterability results from the fact that the copper residues, in liquid form at the combustion temperature in the gas generator, inherently have poor agglomeration and can easily be entrained with the flow of combustion gases to solidify at the outlet of said generator. .
• the resulting hot solid particles are then liable to damage the wall of the airbag. Due to the high level of BCN in the pyrotechnic compounds described above, it is therefore necessary to equip the gas generator with a substantial filter system in order to guarantee satisfactory capture of the copper particles, to the detriment of the sizing. , the weight and therefore the cost of the gas generator.
• patent US 6,143,102 and patent applications EP 1 342 705 and EP 1,568,673 also describe the use of an agglomerating agent, such as SiO 2 , Si 3 N 4 , SiC or clay, in addition to a ballistic catalyst additive, at a mass rate which may also range from 0.5% to 5% or even 10%.
• an agglomerating agent such as SiO 2 , Si 3 N 4 , SiC or clay
• the first additive playing the role of ballistic catalyst
• the second additive ensuring the agglomeration of copper residues
• the first additive can represent up to 10%, or even 15%, by mass of the composition of the compound, which contributes to a detrimental decrease in the gas yield value of said composition.
• Patent applications EP 0 949 225 and EP 1 006 096 thus describe compositions which contain, as main ingredients, a reducing charge consisting of or containing a guanidine derivative and an oxidizing charge containing BCN and a metal oxide, associated with a chlorate, perchlorate and / or nitrate.
• the metal oxide introduced at a high mass rate (20 to 70%, or even 80%, by mass of the total mass of oxidizing charge), acts as an oxidizing charge in its own right. It helps to regulate the overall oxygen balance of the composition.
• Said metal oxide generally consists of CuO but other oxides such as Cr 2 O 3 and MnO 2 are mentioned.
• compositions of pyrotechnic gas-generating compounds incorporating, as main ingredients, NG and BCN and containing two types of additives: a combustion catalyst (consisting of a metal oxide) and an agglomerating agent (such as SiO 2 , nitride or silicon carbide). It also describes compositions containing NG and BCN as well as a high level of metal oxide, as a substitution oxidizing charge (partial, or even total) for said BCN.
• compositions which can incorporate a strontium derivative such as SrO, SrCO 3 , Sr (OH) 2 or SrTiO 3 , are described in the patent application. JP 2009 137 821 .
• These compositions contain a reducing agent, an oxidizing agent, a binder, a phosphorus-containing agent for reducing the combustion temperature and a strontium derivative whose role is to limit the production of phosphorus oxide during combustion.
• Additives of the type of those mentioned above can also be present in these compositions.
• These compositions are not of the type of those of the invention.
• the teaching of this document in no way suggests the bi-function of SrTiO 3 within the compositions of the compounds of the invention (see below).
• NG guanidine nitrate
• BCN basic copper nitrate
• the inventors wished to propose improved pyrotechnic compounds (improved pyrotechnic objects), particularly suitable for use in front airbags. More precisely, the inventors wished to propose pyrotechnic compounds in the composition of which the presence of a single (type of) bi-functional additive (at a low rate, ie with a limited impact on the gas yield) makes it possible to jointly satisfy the technical problem of the agglomeration of combustion residues and that of obtaining a high combustion speed (in this case at least as high as that of the compounds of the prior art described in the patent US 6,143,102 ).
• the solid pyrotechnic gas-generating compounds (objects) of the invention are of the conventional NG / BCN-based type and their composition typically contains at least one inorganic titanate the melting point of which is greater than 2100 K. Said at less one inorganic titanate acts as an agglomeration agent for solid combustion residues and as a ballistic catalyst.
• Said at least one titanate is a refractory compound, the melting point of which (greater than 2100 K) is significantly higher than the combustion temperatures of the NG / BCN bases in which it is present. Thus, it retains its physical state as a pulverulent solid (it obviously occurs in this form) at the combustion temperature, a characteristic necessary to obtain an effect of agglomeration of the liquid copper residues.
• said at least one titanate is a refractory compound, the melting point of which is significantly higher than the combustion temperatures of the NG / BCN bases in which it is present, it is specified what follows.
• the combustion temperature of any NG / BCN base is in fact always less than 1950 K.
• an NG (53.7% by mass) / BCN base (46.3 % by mass) exhibiting an oxygen balance value of -3.3%, has a combustion temperature of 1940 K at 20 MPa and 1941 K at 50 MPa.
• the maximum combustion temperature of an NG / BCN base is obtained for a ratio of 53.5% by mass of NG and 46.5% by mass of BCN, exhibiting an oxygen balance value of -3.2% , its value is 1942 K at 20 MPa, 1943 K at 50 MPa. This further confirms the fact that the combustion temperature is only likely to vary by a few degrees Kelvin with the operating pressure of the gas generator, and always remains below 1950 K, whatever the operating pressure of the gas generator. gas. Thus the required value, greater than 2100 K, for the melting point of said at least one titanate (original bi-functional additive of the compositions of the compounds of the invention) is always significantly higher (by at least 150 K) than the maximum combustion value of an NG / BCN base.
• the at least one inorganic titanate, the melting point of which is greater than 2100 K, present in the composition of the compounds of the invention, is advantageously chosen from metal titanates, alkaline earth titanates and their mixtures. It very advantageously consists of a metal titanate or an alkaline earth titanate.
• the composition of the compounds of the invention contains strontium titanate (SrTiO 3 ) and / or calcium titanate (CaTiO 3 ) and / or aluminum titanate (Al 2 TiO 5 ).
• the at least one bifunctional additive of the invention is between 1 and 5% (limits included) by mass, advantageously between 2 and 4% by mass (limits included), within the composition (by weight) of the compounds of the invention.
• composition of the compounds of the invention is generally free of binder (preferred variant). Indeed, the rheo-plastic behavior of guanidine nitrate a priori makes the presence of any binder superfluous, in particular for obtaining, by dry process, formed pyrotechnic objects, granules, pellets and compressed monolith blocks. (see below). However, the presence of such a binder cannot be completely excluded.
• the compounds of the invention incorporating a binder can in particular exist in the form of monolithic blocks obtained by extrusion, optionally in the wet process.
• the ingredients of the three types above can quite represent 100% by mass of the total mass of the compounds of the invention.
• the possible presence of at least one other additive, chosen, for example, from processing aids (calcium stearate, graphite, silica in particular), is expressly provided for, at a rate of less than 0.5% by mass.
• Such at least one other additive does not consist of a binder.
• the ingredients of the three types above (guanidine nitrate, basic copper nitrate, bi-functional additive (s)) therefore generally represent more than 99.5% by mass of the composition of the pyrotechnic compound which is free from binder.
• strontium titanate (SrTiO 3 ), calcium titanate (CaTiO 3 ), and aluminum titanate (Al 2 TiO 5 ) therefore have a refractory character (their temperature melting temperature is, respectively, 2353 K, 2248 K and 2133 K, ie significantly higher than the combustion temperature of the NG / BCN base, which is always lower than 1950 K (see above)).
• these additives retain their physical state as a pulverulent solid (they obviously occur in this form) at the combustion temperature of the composition, a characteristic necessary to obtain an agglomeration effect of the liquid copper residues.
• said at least one bifunctional additive is in a fine pulverulent form (of micrometric dimension, advantageously of nanometric dimension): with a median diameter of less than 5 ⁇ m, advantageously of less than 1 ⁇ m. It advantageously has a specific surface area greater than 1 m 2 / g (advantageously greater than 5 m 2 / g or more).
• Guanidine nitrate is preferred as a reducing agent, among others for reasons of pyrotechnic safety and for its rheoplastic behavior, suitable for the implementation of the compacting and pelletizing phases of a dry process (see below ), ensuring good densification of the starting powder pyrotechnic composition while limiting the compressive force to be applied.
• the manufacture of compounds of the invention by a dry process can comprise up to four main steps (see below), which have in particular been described in the patent application. WO 2006/134311 .
• the at least one additive (bifunctional, chosen from inorganic titanates whose melting point is greater than 2100 K) is advantageously involved with the other constituent ingredients, NG + BCN mainly, or even exclusively (at the start of the manufacturing process) or is added, more downstream, in the manufacturing process of the compounds of the invention.
• the pyrotechnic compounds of the invention can also be obtained by a wet process.
• said method comprises the extrusion of a paste containing the constituents of the compound.
• said method includes a step of dissolving all or some main constituents in aqueous solution comprising a solubilization of at least one of the main constituents (reducing agent) and then obtaining a powder by spray drying, the addition to the powder obtained of the constituent (s) which have not been added in solution, then shaping the powder in the form of objects by the usual dry process.
• the preferential process for obtaining the pyrotechnic compounds of the invention includes a dry compacting stage of a mixture of powdered constituent ingredients of said compounds (except, optionally, said at least one additive which can be added later). Dry compaction is generally carried out, in a manner known per se , in a roller compactor, at a compaction pressure of between 10 8 and 6.10 8 Pa. It can be carried out according to different variants (with a characteristic step "simple" compaction followed by at least one complementary step or with a characteristic compacting step coupled with a shaping step).
• the pyrotechnic compounds of the invention can also be obtained in the dry process by simple pelletizing of the powder obtained by mixing their constituents.
• the constituent ingredients of the compounds of the invention advantageously have a fine particle size, less than or equal to 20 ⁇ m.
• Said particle size (value of the median diameter) is generally between 1 and 20 ⁇ m.
• the compounds described in the present invention express their full potential if they are obtained by a dry process from powders having a median diameter of between 5 to 15 ⁇ m for guanidine nitrate, between 2 to 7 ⁇ m for nitrate. basic copper and between 0.5 to 5 ⁇ m for the at least one bi-functional additive.
• the present invention relates to a pulverulent composition (mixture of powders), precursor of a compound of the invention, the composition of which therefore corresponds to that of a compound of the invention (see above).
• the present invention relates to gas generators containing a pyrotechnic solid charge which generates gas; said charge containing at least one pyrotechnic compound of the invention.
• Said generators, loaded in particular with pellets of the invention, are perfectly suitable for airbags, in particular front airbags (see above).
• Table 1 shows three examples (Ex.1, Ex.2 and Ex.3) of the composition of compounds of the present invention, as well as the performances of said compounds compared to those of a compound of the art previous (Ref. 1) according to US 6,143,102 (said compounds of the invention and of the prior art were produced by a dry process).
• the compounds were evaluated by means of thermodynamic calculations or from physical measurements carried out on granules or pellets made from the compositions via the process of mixing powders - compacting - granulation - and optionally dry pelletizing.
• the reference compound 1 (Ref. 1) of the prior art contains guanidine nitrate, basic copper nitrate as well as an aluminum oxide (Al 2 O 3 ) as a ballistic catalyst and silica ( SiO 2 ) as an agglomerating additive (“slaggant” additive).
• the compounds of Examples 1 to 3 contain in their composition, in addition to the two components guanidine nitrate and basic copper nitrate of reference 1, a single bifunctional additive as described in the present invention.
• the levels of the constituents were adjusted in order to keep an oxygen balance value close to -3.3%, so as to be able to directly compare the performance of these compounds.
• Examples 1 and 2 of Table 1 show that the addition, at a moderate rate (mass content of 4%), of an additive, strontium titanate (SrTiO 3 ) or calcium titanate (CaTiO 3 ), in a composition of the type of that of reference compound 1, leads to the production of agglomerated combustion residues (in the form of a skeleton of the pyrotechnic block) and, to a combustion rate value over the pressure range 10 MPa - 20 MPa greater than a pressure exponent value lower than an inflation surface flow rate higher than those of the reference compound 1 of the prior art.
• a moderate rate mass content of 4%
• an additive strontium titanate
• CaTiO 3 calcium titanate
• Example 3 of Table 1 show that the addition, at a reduced rate (mass content of 2.7%) of calcium titanate (CaTiO 3 ) compared to Example 2 (mass content of 4% ), improves the performances (increase of the combustion speed value over the range 10-20 MPa, of the gas yield value and ultimately of the inflation surface flow value) compared to those of the compound according to the example 2, while making it possible to maintain a quality of agglomeration of combustion residues satisfying the functional need.
• Table 1 ⁇ /u> Examples Ref. 1 Ex. 1 Ex. 2 Ex.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Inorganic Chemistry (AREA)
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• Botany (AREA)
• Pest Control & Pesticides (AREA)
• Plant Pathology (AREA)
• Air Bags (AREA)
• Feeding, Discharge, Calcimining, Fusing, And Gas-Generation Devices (AREA)

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