Classifications

• • 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
  • C06B33/06—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 oxygen-halogen salt
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B29/00—Compositions containing an inorganic oxygen-halogen salt, e.g. chlorate, perchlorate
  • C06B29/02—Compositions containing an inorganic oxygen-halogen salt, e.g. chlorate, perchlorate of an alkali metal
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06C—DETONATING OR PRIMING DEVICES; FUSES; CHEMICAL LIGHTERS; PYROPHORIC COMPOSITIONS
  • C06C9/00—Chemical contact igniters; Chemical lighters

Definitions

• compositions Self-initiating compositions, electrical initiators using such compositions and gas generators comprising such initiators
• the present invention relates to a self-initiating pyrotechnic composition, intended, generally but not exclusively, to be implemented in bulk or in the form of a compressed layer in the electric initiator of a gas generator and to initiate the combustion of a composition generating gas exposed to a temperature significantly higher than its normal temperature of use.
• the invention relates more particularly to the field of automotive safety.
• Safety airbags for the safety of motor vehicle passengers deploy under the action of the gas generated by the combustion of a pyrotechnic composition, called a gas-generating composition, contained in a gas generator comprising a casing of resistant metal to corrosion.
• a gas-generating composition contained in a gas generator comprising a casing of resistant metal to corrosion.
• the choice of the metal constituting the envelope is generally dictated by the requirements of minimizing the weight of the vehicle in order to improve its performance in terms of fuel consumption. Because of its low density, aluminum is often chosen.
• the inflation gas released by the exothermic decomposition reaction is typically nitrogen. Examples of inflation devices are described in US patents US 4923212, US 4907819 and US 4865635. When the gas generators are intended for automotive safety, they must remain stable at high temperatures for long periods of time.
• the decomposition rate of the gas-generating composition must be controlled for the bag to deploy quickly but not too violently. This control is primarily ensured by a good design of the gas generating composition and the architecture of the generator.
• the combustion of the gas-generating composition is generally triggered by an electrical initiator contained in the gas generator, said initiator comprising an envelope, a resistive element and at least one charge composed of a pyrotechnic substance or a mixture of pyrotechnic substances.
• electrical initiator is meant a device whose function is to convert an input energy of an electrical nature into an output energy of a pyrotechnic nature, much higher than the input energy.
• This electrical initiator is typically connected via electrical wires to at least one collision detection device.
• Most initiators operate by heat exchange between the resistive element and the load in contact with the resistive element.
• the pyrotechnic substances constituting the charge may be pyrotechnic compositions operating by reaction between several constituents. These are generally mixtures of oxidants and reducing agents, and in particular mixtures of oxidants and inorganic reducers to which a more powerful explosive is optionally added or, on the contrary, a phlegmatizer, a binder or any other additive intended to obtain specific properties or to facilitate the implementation of the composition.
• Electrical initiators generally comprise a second pyrotechnic composition, called the main charge, as energetic as the charge in contact with the resistive element, but reacting less violently, in particular for initiating gas-generating compositions.
• the main loads used in electrical initiators intended for automobile safety and in particular in airbags are described in US Pat. Nos. 5847310 and 5672843. Gas generators are designed to withstand all the temperatures that may be encountered. be reached in an automobile under normal use (-40 0 C, 9O 0 C).
• self-initiation temperature is meant, in the present invention, the temperature at which a substance or a mixture of substances undergoes an exothermic decomposition reaction. This decomposition can be assimilated to a combustion, but it can lead to a blast or even a detonation. Temperature Thus, self-initiation of said substance or mixture of substances can generally be assimilated to its self-ignition temperature. Under high initial temperatures, the rate of combustion of the gas generating compositions tends to become excessive.
• the pressure generated is then such that the envelope of the gas generator, usually made of aluminum, can lose its mechanical integrity and explode with projections of metallic bodies that are dangerous for people in the vicinity. This explosion is even more likely when the critical temperature of mechanical strength of the metal constituting the envelope is reached at the time of firing.
• This problem can not be solved properly by choosing a gas-generating composition having a self-initiation temperature, i.e. voluntarily reduced self-ignition, without further precaution. Indeed, such compositions operate too quickly when their autoignition temperatures are reached (global inflammation of the entire charge).
• self-initiating composition is meant a substance or a mixture of substances contained in the gas generator whose self-initiation temperature is lower than the self-ignition temperature of the gas generating composition employed.
• the role of the self-initiating composition is therefore to decompose exothermically, so that the evolution of heat triggers the combustion of the gas generating composition in a controlled manner, before its autoignition temperature is reached. and before the temperature at which the gas generator envelope loses its structural integrity is reached.
• the heat evolution must be sufficient to provide the activation energy required to ignite the gas generating composition.
• the self-initiating composition may be one of the compositions constituting the normal pyrotechnic chain in the initiator, in particular the main charge or an additional charge, or it may be a charge external to the initiator, in particular an initiating reinforcement charge.
• power boosting charge which is generally placed between the initiator and the gas generating composition.
• additional load is meant a load which is neither the primary load nor the secondary (main) load, and whose role is to initiate the main load.
• initiation reinforcement charge is meant a charge serving as a complement to the main charge for the initiation of the gas generating composition, which therefore acts as a "booster".
• the initiator reinforcing fillers comprise most of the time a mixture of boron and potassium nitrate.
• the autoinitizer composition may also be placed out of the normal pyrotechnic chain near the gas generating composition, in a place where the temperature rises rapidly, or even be mixed into pellets (without an envelope) or a capsule.
• the gas-generating composition the pellets of the self-initiating composition and those of the gas-generating composition are distinct. This latter solution is generally accepted for its lack of interference with the normal operation of the device.
• the first gas generator compositions for large-scale safety air bags have been made of sodium azide mixed with oxidants and additives.
• the decomposition reaction of such compositions generates nitrogen.
• the temperature of self-initiation of the self-initiator composition is less than 230 0 C, a temperature of the order of 200 0 C fully satisfactory, most often.
• the self-initiating compositions generally consist of an energetic compound decomposing under a suitable temperature, such as nitrocellulose, or a mixture of oxidants and organic or inorganic reducing agents.
• a suitable temperature such as nitrocellulose, or a mixture of oxidants and organic or inorganic reducing agents.
• the inorganic reducers are chosen from the powders of metals and metalloids, the reducing agents organic are typically sugars or carbohydrates.
• the inorganic oxidants are selected from nitrates, chlorates, perchlorates, peroxides and low electropositive metal oxides.
• the first self-initiating compositions such as those described in US Pat. No. 4,561,675, were made based on nitrocellulose and propellant powders.
• Various additives have been added to the nitrocellulose powders to fulfill this self-initiation function.
• the self-initiating compositions based on nitrocellulose have the disadvantage of being unstable at storage under high temperatures, the corresponding gas generators giving poor results in the stability test at 107 ° C. for 408 hours.
• nitrocellulose tends to decompose over time, so that the amount of energy released upon initiation decreases over time and may become insufficient to properly initiate combustion of the gas generating composition.
• Self-initiating compositions incorporating mixtures of potassium or sodium chlorate and organic compounds, most commonly a carbohydrate such as lactose, have been found to be more stable. Such compositions have been widely described, in particular by Scheffee in international application WO 94/14637 and US Pat. No. 5,542,888, and Nagahashi, which claims in US Pat. No. 5,847,310 to the production of an electrical initiator containing a self-adhesive composition. initiator based on carbohydrates and chlorates. However, the sodium chlorate / carbohydrate mixtures are not stable enough to meet the environmental test at 107 0 C for 408 hours when compressed and confined in initiators. The actual usable autoinitiation compositions claimed by the patents cited above all have high self-initiation temperatures, greater than 180 0 C; in practice, greater than 190 ° C., most often.
• the gas generating compositions based on sodium azide are poor in the volume of gas released per unit mass or volume of composition, generate abundant slag that must be filtered.
• the use of sodium azide is unsatisfactory because of its toxicity.
• Sodium azide-free gas generating compositions have been described more recently.
• the sodium azide is replaced by organic compounds rich in nitrogen and low in carbon, such as 5-aminotetrazole, 1-nitroguanidine, diguanidinium 5,5-azotetrazolate or triaminoguanidinium nitrate.
• the combustions of these gas-generating compositions become unstable if one of their constituents is in the liquid state at the self-initiation temperature of said compositions, which can lead to excessive operational pressures.
• Some conventional constituents have sufficiently low melting temperatures to be melted at the self-initiation temperature of the composition, for example 5-aminotetrazole, which melts at 202-204 ° C. and 1-nitroguanidine, which melts at 226 ° C. -228 0 C. the combustion of the corresponding gas-generating compositions are unstable at temperatures in the range 200-250 0 C.
• compositions based on iron oxide or ferrocene and at least one compound selected from oxalates, persulfates, permanganates, nitrates, nitrides, perborates, bismuthates, formates, sulfamates, bramates and peroxides.
• These compositions may also comprise a reducing agent, preferably titanium powder, and an explosive used as a fuel, such as guanidinium nitrate, 1-nitroguanidine, 5-aminotetrazole nitrate or 3-nitro-1, 2,4-triazol-5-one (NTO).
• a reducing agent preferably titanium powder
• an explosive used as a fuel such as guanidinium nitrate, 1-nitroguanidine, 5-aminotetrazole nitrate or 3-nitro-1, 2,4-triazol-5-one (NTO).
• the self-initiating compositions described in US Pat. these documents consist of a mixture of a metal powder, mainly molybdenum, and an oxidizing composition resulting from a mixture, possibly by co-melting, of at least two oxidants, the first being generally the nitrate of silver or ammonium nitrate and the second is usually potassium nitrate or guanidinium nitrate.
• Metal oxides which exert a catalytic effect by lowering the self-initiation temperature, may optionally be added. It is furthermore possible to mix with these self-initiating compositions a power-enhancing composition (booster), composed of an energetic oxidizer (perchlorate or nitrate) and boron or a metal (Mg, Ti or Zr).
• the self-initiating composition ignites, initiates the combustion of the power-increasing composition, which initiates the combustion of the gas-generating composition.
• Such self-initiating compositions have many disadvantages. Their implementation, which involves in particular the mixing of two oxidants by melting and then solidification, is complex. The use of silver nitrate is undesirable because it harms the stability of the compositions at 107 ° C. for 408 hours. In addition, silver nitrate is soluble in water, unstable in light, expensive and toxic. It is also preferable not to use ammonium nitrate which can become very unstable in the presence of other compounds and which, because of the ammonium ion, can cause instability of other constituents. In particular, the compositions described in US Pat. No. 622,117 are too unstable to be used in compressed form and under confinement, as is the case in electrical initiators.
• compositions which are perfectly stable at 107 ° C. for 408 hours (or at least at 90 ° C. for 1000 hours), in bulk or in compressed form, in the open air or contained in a holster. or in an initiator and preferably in a hermetic initiator with compressed pyrotechnic layers.
• non-hygroscopic self-initiating compositions preferably stable to light and moisture, which do not generate toxic substances or contain toxic compounds such as those based on lead, mercury, barium, cadmium arsenic, beryllium, chromium, cobalt or nickel, which have a flowability facilitating their implementation and whose manufacturing process is simple, are also needs that manufacturers seek to meet.
• autoinitiation compositions having a self-initiation temperature below 130 0 C can not be used in gas generators because a safety temperature of no initiation of 130 0 C is generally required by the Car manufacturers. It has been previously stated that self-initiating compositions having a self-initiation temperature greater than 180 ° C. are of less practical interest today.
• compositions having self-initiation temperatures below 180 ° C. are thereby reinforced.
• a composition responding to need must have a self-initiation temperature ranging from 130 0 C to 180 0 C, and have a set of satisfactory characteristics.
• the composition must not be initiated under a temperature below 130 ° C., in the system where it is used, even after an environmental test, which pushes back the minimum temperature of the range of self-initiation temperatures allowed. Beyond 150 ° C. Thus, the useful range becomes very narrow: 150-180 ° C., at a heating rate of less than or equal to 14 ° C./minute.
• the object of the present invention is to provide a self-initiating composition satisfying the aforementioned criteria and overcoming the disadvantages of the self-initiating compositions of the prior art.
• the present invention also relates to an electrical initiator comprising an envelope, a resistive element and at least one charge, using the self-initiating composition according to the invention as a charge.
• the present invention also relates to a gas generator comprising such an electric initiator and a gas generating composition, and finally a gas generator comprising an electric initiator, a gas generating composition and at least one initiating reinforcement charge, using the self-initiating composition according to the invention as initiating reinforcement filler.
• a self-initiating composition comprising a main formulation comprising:
• main formulation further comprises:
• component (b) 0 to 60% by weight of at least one metal or metal hydride selected from zirconium, titanium, TiH 2 , ZrH 2 , aluminum, silicon and iron, preferably 0 to 40%, better 10 to 35%, (c) 0 to 50% by weight of at least one transition metal oxide, preferably 0 to 35%, more preferably 0.5 to 35%, the mass percentages being based on the weight of the main formulation and the mass percentages of component (a) and component (c) can not be simultaneously zero.
• metal or metal hydride selected from zirconium, titanium, TiH 2 , ZrH 2 , aluminum, silicon and iron, preferably 0 to 40%, better 10 to 35%
• transition metal oxide preferably 0 to 35%, more preferably 0.5 to 35%
• compositions having self-initiation temperatures low enough to protect gas generators of explosive reactions, it is however necessary that the self-initiation temperature remains greater than 130 ° C., even if slow heating ("Slow Heat Test").
• the autoinitatoire compositions according to the invention are characterized by quantities of constituents assuring them a self-initiation temperature ranging from 130 to 220 ° C., preferably ranging from 150 to 180 ° C., and a stability at a temperature of 107 ° C. C for 408 hours or at a temperature of 90 ° C. for 1000 hours in all the configurations in which they are used.
• a composition is said to be stable at a given temperature for a given time when a stay in an enclosure at said temperature during said time does not cause any degradation detrimental to the operation of the self-initiating composition itself or the other components of the generator. gas or initiator. Stability is observed for a composition in bulk or compressed, in the open air or contained in a case or in an initiator, said initiator being able to be a hermetic initiator with compressed pyrotechnic layers.
• a self-initiating composition must not, for example, be initiated unexpectedly during an environmental test.
• compositions comprising a main formulation comprising, in appropriate amounts, at least one oxidant, at least one energetic organic compound, optionally one or more reducing compounds of a metal nature. , metalloid or metal hydride and optionally a transition metal oxide.
• the self-initiating composition according to the invention comprises 20 to 80% by weight of at least one alkali metal chlorate, used as an oxidant.
• Alkali metal chlorates suitable for the present invention are selected from potassium chlorate, sodium chlorate and mixtures thereof.
• Sodium chlorate does not produce much lower temperatures than potassium chlorate but is more hygroscopic and adversely affects the flow of the composition and its stability.
• the preferred alkali metal chlorate is therefore potassium chlorate.
• Silver nitrate, an oxidant widely used in the self-initiating compositions of the prior art can certainly lower their self-initiation temperatures, but its use is not desirable for the reasons stated above.
• self-initiating compositions of comparable self-initiation temperatures using silver nitrate rather than potassium chlorate as the oxidant are less stable in environmental tests.
• the principle of the use of a mixture of oxidants by co-fusion, as described in certain compositions of the prior art, or even a eutectic mixture of oxidants, with the aim of lowering the temperature of self-initiation, is not necessary with the self-initiating compositions according to the invention.
• the self-initiating composition according to the invention also comprises 5 to 50% by weight of at least one energetic organic compound.
• the term "energetic organic compound” is intended to mean an organic compound whose decomposition is exothermic. The inventors have discovered that the use of such compounds makes it possible to lower the self-initiation temperature of a self-initiating composition to a suitable value. It is preferable that the organic character of this energetic organic compound is not too pronounced in order to cause the least possible harm to the stability of said composition at 107 ° C. for 408 hours. Guanidinium nitrate is the preferred energetic organic compound for the invention.
• guanidinium nitrate it is preferably used as a single energetic organic compound, however, it may also be used in admixture with or replaced by other energetic organic compounds, in particular by aliphatic or heterocyclic compounds having amino, amide, imide or imine and their salts, especially the ⁇ -substituted derivatives of guanidinium nitrate. Just like guanidinium nitrate, these other organic compounds energy are used as fuel.
• the self-initiating composition according to the invention comprises, according to another embodiment, at least one energetic organic compound chosen from guanidinium nitrate, aminoguanidinium nitrate, nitroguanidinium nitrate, methylguanidinium nitrate, diaminoguanidinium nitrate (DAGN), triaminoguanidinium nitrate (TAGN), azodicarbonamide, 5-aminotetrazole, 5-aminotetrazole nitrate, triaminoguanidinium 5-aminotetrazolate, bistetrazole, bistetrazole amine, 5,5 ' diguanidinium azotetrazolate (GZT), guanylurea dinitramide (GUDN), guanidine dinitramide (GDN), 3-nitro-1,2,4-triazol-5-one (NTO), RDX (hexahydro-1, 3 5-trinitro-1,3,5-triazine or hexogen) and HMX
• Some of these compounds have disadvantages such as a too low melting temperature (below 150 ° C. for example) or can generate eutectic mixtures having a low melting temperature (the initiation becomes probable when the temperature exceeds said temperature fusion).
• Azodicarbonamide and 5-aminotetrazole for example, do not have these disadvantages and can be used without particular risk, but are of less interest than guanidinium nitrate to obtain adequate self-initiation temperatures.
• guanidinium nitrate to obtain adequate self-initiation temperatures.
• Highly energetic compounds such as HMX, RDX or NTO, which are high-potency explosives, can be introduced into the self-initiating compositions according to the invention, preferably up to 20% by weight, more preferably up to 20% by weight. at 15% by weight, relative to the mass of the main formulation.
• the preferred energetic organic compounds are guanidinium nitrate, aminoguanidinium nitrate, diaminoguanidinium nitrate (DAGN), triaminoguanidinium nitrate (TAGN), nitroguanidinium nitrate, methylguanidinium nitrate, 5-aminotetrazole, nitrate of 5-aminotetrazole, triaminoguanidinium 5-aminotetrazolate, bistetrazole, amine bistetrazole, 5,5'- diguanidinium azotetrazolate (GZT) and 3-nitro-1,2,4-triazol-5-one (NTO).
• DAGN diaminoguanidinium nitrate
• TAGN triaminoguanidinium nitrate
• nitroguanidinium nitrate methylguanidinium nitrate
• 5-aminotetrazole nitrate of 5-aminotetrazole
• the oxidizing / organic energetic compound mixture described above may be accompanied by one or more reducing compounds of a metal, metalloid or metal hydride nature.
• the reducing agents suitable for the present invention may be transition metals, preferably iron, manganese, cobalt, copper, titanium or zirconium, metals, preferably aluminum, metalloids, preferably boron and silicon, transition metal hydrides, preferably titanium hydrides such as TiH 2 and TiH n (n ⁇ 2) subhydrides, TiH 2 titanium dihydride being the preferred titanium hydride, zirconium dihydride ZrH 2 , or mixtures of all these reducers.
• reducing agents are preferably used in the form of fine powders, that is to say with a particle size ranging from 0.1 to 100 ⁇ m, better still ranging from 1 to 50 ⁇ m.
• Some of these reducing agents act as a catalyst for decomposition of chlorates and energetic organic compounds such as energetic organic nitrates, in particular guanidinium nitrate. This catalytic activity results in a lowering of the self-initiation temperature of a self-initiating composition incorporating such reducing agents.
• the term "catalytic activity” and "catalyst” means a catalytic activity and a catalyst involved in the field of the decomposition of chlorates and nitrates, in particular organic nitrates.
• the preferred reducer or mixture of preferred reducers can reconcile the achievement of a self-initiation temperature low enough for its functionality but compatible with the stability requirements of car manufacturers.
• the inventors have found that metals, metalloids and metal hydrides, with comparable particle size, could be classified in the following manner as to their effectiveness in lowering the self-initiation temperature of a self-initiating potassium chlorate composition.
• guanidinium nitrate / metal, metalloid or metal hydride Mo, Cr, W, V> B, Mn, Co, Cu> Ti, TiH 2 , Fe, Si, Zr, ZrH 2 , Ni, Al (1)
• the Group VIB metals can lead to excessive degradation during the stability test at 107 ° C. for 408 hours.
• vanadium and Group VIB metals Chromium, nickel and silver are toxic, so do not use them. Boron, manganese, cobalt and copper have a more moderate catalytic activity than vanadium and metals of group VIB, and change more significantly the potential and the rate of combustion of self-initiating compositions than zirconium, titanium , zirconium and titanium hydrides, iron, silicon and aluminum.
• a reducing agent fulfilling a decomposition catalyst function for chlorates and nitrates for example boron, manganese, cobalt, copper or their mixtures can partially or totally replace the reducing agents chosen from zirconium, titanium, zirconium hydrides and titanium, iron, silicon, aluminum and mixtures thereof in the autoinitiation compositions of the invention.
• the reaction vivacity and the self-initiation temperature of said compositions can thus be regulated by their mass content of boron, manganese, cobalt, copper or mixtures thereof.
• the autoinitiation composition according to the invention contains (a) 0 to 60% by weight of at least one metal or metalloid selected from boron, manganese, cobalt and copper, (b) 0 to 60% by weight of at least one metal or metal hydride chosen from zirconium, titanium, iron, aluminum, silicon, TiH 2 and ZrH 2 , and (c) 0 to 50% by weight of at least one transition metal oxide, the mass percentages of component (a) and component (c) not being simultaneously zero.
• the transition metal oxides are used in the present invention as catalysts for the decomposition of alkali metal chlorates or energetic organic compounds such as energetic organic nitrates, particularly guanidinium nitrate. They allow in particular to lower the self-initiation temperature of a self-initiating composition metal, metalloid or metal hydride / alkali chlorate / organic nitrate energetic in a suitable range.
• the transition metals and their oxides actually have catalytic properties used for many chemical reactions, particularly in the field of pyrotechnics for oxygen-generating compositions.
• Zhang Yunchang's work highlights probable mechanisms: "Catalytic effects of metal oxides on the thermal decomposition of sodium chlorate", Zhang, Y., Kshirsagar, G., Ellison, JE, Cannon JC Thermochimica Acta 1993, 228 and publications later.
• Some of the metals used in the present invention may be covered by a surface layer of oxide. It is possible, although not proven, that this oxide layer contributes to the catalytic activity of said metals.
• metal oxides or metalloid oxides usable as catalysts in the present invention there may be mentioned MOO 3 , CuO, V 2 O 5 , CrO 3 , Cr 2 O 3 , MnO 2 , Co 3 O 4 , Cu 2 O, Nb 2 O 5 and Ag 2 O, or mixtures thereof.
• the inventors have found that the oxides of metals or metalloids, with comparable particle size, could be classified in the following manner as to their effectiveness concerning the lowering of the self-initiation temperature of a self-initiating chlorate potassium composition.
• guanidinium nitrate / metal, metalloid or metal hydride
• the self-initiation temperature of a self-initiating composition can be lowered by the addition of a metal oxide of a more active metal as a catalyst according to equation (1) than the metal reducing agent, metalloid or metal hydride used.
• a metal oxide of a more active metal as a catalyst according to equation (1) than the metal reducing agent, metalloid or metal hydride used.
• a boron / alkali chlorate / guanidinium nitrate composition will have its self-initiation temperature lowered by the addition of molybdenum oxide.
• the transition metal oxides which are particularly suitable for the present invention are preferably chosen from among MOO 3 , CuO and mixtures thereof.
• active metal oxides MOO 3 and CuO
• a metal or active metal in the form of a metal powder, such as B, Mn, Co , Cu or mixtures thereof.
• active metal oxides is essential to obtain a self-initiation temperature satisfying the aforementioned objectives in the case of compositions containing only weakly active metals or metalloids such as zirconium, titanium, TiH 2 , ZrH 2 , iron, aluminum or silicon.
• compositions having a self-initiation temperature in line with the set objectives may be obtained even if they contain no metal, metalloid or metal hydride reductant, provided they contain an appropriate amount of minus an active transition metal oxide.
• such compositions are low in energy and low light and are preferably not used as main charges.
• transition metal oxides in the form of extremely fine powders so as to benefit from a large active surface area at a low mass proportion.
• they are used in the form of nanoscale powders, an expression by which is meant, in the present invention, a powder having a particle size ranging from 1 to 100 nm, preferably from 3 to 30 nm.
• the self-initiating compositions according to the invention may comprise a number of additives, examples of which are given below and in no way limit the present invention.
• the self-initiating compositions according to the invention comprise a binder, and generally contain 1 to 10% by weight of this binder, preferably 2 to 10% by weight of this binder, better still 2 to 8%, this percentage being expressed in relation to the mass of the formulation principal and not with respect to the total mass of the composition.
• the binder is hydrophobic.
• the preferred binder is a fluoroelastomer binder such as Viton ® .
• a fluorinated elastomeric binder such as Viton ® improves the stability of the self-initiator composition without raising its many self-initiation temperature.
• binders Like other binders, it reduces the sensitivity to friction, shock and static electricity of the composition and provides a particle size distribution facilitating the implementation of the powders.
• the coating with this energetic and hydrophobic binder also gives excellent resistance to moisture. Its global role is largely beneficial.
• Ultra-fine silica is understood to mean, in the present invention, an extremely fine silica powder having a specific surface area ranging from 100 to 200 m 2 ⁇ g ⁇ 1. The ultra-fine silica facilitates the implementation of the autoinitiation compositions according to the invention.
• compositions according to the invention making it possible to fulfill the objectives set are given below.
• One of the self-initiating compositions according to the invention comprises: a main formulation comprising:
• ultra fine silica 0 to 1% of ultra fine silica, or else: a main formulation comprising: 2 to 25% boron, better 2 to 15%,
• potassium chlorate 25 to 80% of potassium chlorate, more preferably 25 to 70%, and further comprises:
• ultra-fine silica 0 to 1% of ultra-fine silica, or else: a main formulation comprising: 20 to 60% of zirconium, titanium, TiH 2 , ZrH 2 , iron, silicon, aluminum or their mixtures, better still 20 to 50%,
• transition metal oxides such as MoO 3 or CuO, better still 0.5 to 35%, and furthermore comprises:
• compositions of the invention differ widely from the compositions cited in the prior patents and in particular those of patents US 5959242, US 5739460, US 6101947 and US 6221187 by the absence of silver nitrate, molybdenum or ammonium nitrate, by the implementation of a simpler process without premixing of the oxidants by co-melting then crystallization and by the use of a fluoroelastomer binder.
• the self-initiation temperature of the self-initiating compositions according to the invention decreases when the compression ratio of said compositions increases, variations of several tens of degrees can be observed.
• the self-initiation temperature decreases when the compactness increases, even beyond a compression ratio of the order of 2000 bars, or even 3000 bars, which also ensure excellent mechanical strength. It may be advantageous to adjust the self-initiation temperature by varying the compression ratio of the autoinitizer composition.
• the self-initiation temperature of the autoinitiation compositions according to the invention decreases when the confinement of said compositions increases, that is to say when they are trapped by walls. However, their stability also decreases as containment increases. It is possible to explain these phenomena by an action of auto-catalytic type of decomposition products increased by imprisonment. It is therefore necessary to adjust the formulation of the self-initiating composition according to the implementation.
• the importance of the compression ratio and containment parameters varies according to the compositions.
• the self-initiating compositions according to the invention are prepared according to the usual processes for the production of ZPP (zirconium, potassium perchlorate) and THPP (titanium hydride, potassium perchlorate) compositions, which are well known to those skilled in the art, and do not do not require the development of a new process, which is interesting in terms of investment. In all cases, a mixture of dry constituents should be avoided for reasons of safety.
• the dry mixing method does not make it possible to introduce a binder into the self-initiating composition. It is preferable to mix oxidants, energetic organic compounds and reducing agents by dispersion in a solvent in which they are insoluble, but in which the binder is soluble, if a binder is used.
• the oldest method is to prepare the mixture oxidants / energetic organic compounds / reducing agents / solvent in the form of a paste, then partially evaporating the solvent in order to granulate the composition by forcing it on a grid having an adequate mesh size.
• the granulated composition is optionally sieved to obtain a more precise particle size distribution.
• This method makes it possible to obtain self-initiating compositions according to the invention that are entirely functional, but it is not optimal because the granulation and sieving operations thus carried out present a risk of ignition.
• the second method and the third method are reserved for self-initiating compositions comprising a binder.
• the so-called "Shock Gel” process which is more recent, consists of gelling the binder by addition of an anti-solvent in the oxidant / energetic organic compounds / reducing agent / binder / solvent suspension with stirring.
• the particles of oxidants, energetic organic compounds and reductants encapsulated by the binder form grains having a relatively homogeneous distribution of constituents, which can be sieved under antisolvent and then dried.
• This second method is of great interest in terms of handling safety.
• the binder is a fluorinated elastomer such as Viton ®, acetone or methyl ethyl ketone are effective solvents, and aliphatic hydrocarbons such as heptane are suitable anti-solvents.
• a third method is to charge the device or initiator with the mixture oxidants / organic compounds energetic / reducing agents / binder / solvent in the form of paste, then to dry the whole.
• This method has no advantage over the "Shock Gel” process as regards the implementation of the self-initiating compositions according to the invention, but it makes it possible to obtain the same functional results.
• Ultra-fine silica if it is used, is generally introduced into the self-initiating composition according to the invention after drying of said composition.
• the self-initiating compositions of the invention may be implemented in an initiator, preferably an electrical initiator. Their compression ratios are then preferably between 50 and 500 bar.
• the self-initiating compositions of the invention can also be used in uncompressed form, in bulk in electrical initiators or compartmentalized in preferably metal cases. Their potential applications, however, are not limited to a self-initiation function inside an initiator.
• the self-initiating compositions of the invention may be used compressed in the form of pellets without a container. Compression rates of 500 to 3000 bar are then well suited.
• the self-initiating compositions of the invention can be implemented compressed in preferably metal cases, for example in aluminum caps optionally closed by a flap. Compression rates ranging from 200 to 2000 bar are then well adapted.
• the self-initiating compositions of the invention may also be used in uncompressed form outside the initiators, in which case they are compartmentalized in preferably metal cases.
• the present invention further relates to an electrical initiator comprising an envelope, a resistive element and at least one load, characterized in that it uses the self-initiating composition according to the invention as a charge.
• the self-initiating composition according to the invention can be used therein as a main filler or as an additional filler.
• the self-initiating compositions of the invention can thus replace the compositions constituting the main charges of the initiators, which are very often compositions boron / potassium nitrate, THPP (titanium hydride / potassium perchlorate), TPP (titanium / perchlorate of potassium) or ZPP (zirconium / potassium perchlorate).
• the autoinitatoire compositions of the invention are placed between the composition in contact with the resistive element and the main charge or, preferably at the bottom of the holster after the main charge in the functional order.
• the electric initiator according to the invention is a hermetic electric initiator compressed pyrotechnic layers and type GTMS (Glass to Metal Seal) or PTMS ® (Plastic To Metal Seal).
• compressed pyrotechnic layer initiator is meant an initiator whose charge in contact with the resistive element, at least, is under the form of a compressed layer.
• An electric initiator of the GTMS type is a compressed pyrotechnic layer initiator in which the current-carrying pins pass through a base of glass or ceramic and metal, providing electrical isolation and hermeticity. Examples of description of such initiators well known in the art, can be found in US Patent 5099762, WO 02/46687 and US 5639986.
• An electric type initiator PTMS ® differs from an initiator simply type JSWG in that the pins pass through a plastic material instead of a glass-to-metal assembly. Examples of description of such initiators, well known to those skilled in the art, can be found in international application WO 03/058154 and French patent FR 2698687.
• the self-initiating compositions of the invention may be used in a gas generator or any other pyrotechnic device.
• they are intended to be used in airbags, whatever the function they fulfill.
• Having a self-initiation temperature ranging preferably from 150 to 180 ° C., they are suitable for use in gas generators using gas-generating compositions based in particular on 5-aminotetrazole, 1-nitroguanidine, 5,5 ' diguanidinium azotetrazolate or triaminoguanidinium nitrate, but also based on sodium azide, the gas generating compositions based on this compound having much higher decomposition temperatures (generally greater than 35O 0 C).
• the self-initiating compositions of the invention are generally placed in thermally exposed areas of the gas generator or electric initiator, in compressed or bulk form. They can be used as initiator reinforcing (booster) charges outside the initiator, and are then generally placed between the initiator and the gas generating composition. They may also be mixed with the gas generating compositions (or placed nearby), in compressed form (pellets, capsule), provided that they do not affect or non-significantly affect the properties of said gas-generating compositions.
• the pellets or capsules of the self-initiating composition and those of the gas-generating composition are distinct.
• the first method according to the invention for initiating the combustion of a gas-generating composition comprises the following three steps:
• pellets of self-initiating composition by compression, in the matrix of a pelletizer, adding one or more pellets of said autoinitiation composition to the pellets of the gas-generating composition.
• the inflammation of a pellet of self-initiating composition when its temperature reaches its self-initiation temperature, initiates the pellets of the gas generating composition that surround it, the firing propagating to the whole of the charge of the gas generator.
• the pellets of self-initiating composition may be placed in a cell of the wall of the gas generator (communicating with the gas generating composition) and not mixed with the pellets of the gas generating composition.
• the second method according to the invention for initiating the combustion of a gas-generating composition comprises the following three steps:
• the third method according to the invention for initiating the combustion of a gas-generating composition comprises the following three steps:
• composition Self-initiating composition having a self-initiation temperature lower than that of the gas-generating composition (or the pyrotechnic composition) to be initiated, loading in bulk or by compression, the composition Self-initiator in an electric initiator, as an additional load or as a main load,
• the self-initiating composition reaches its self-initiation temperature, the released energy initiates the entire charge of the initiator, which in turn initiates the initiation reinforcement charge (booster), which initiates the gas generating composition as in normal operation.
• initiation reinforcement charge boost
• the fourth method according to the invention for initiating the combustion of a gas-generating composition comprises the following two steps:
• the self-initiating composition in a gas generator comprising an electrical initiator, as an initiating reinforcement charge, by placing it between the electric initiator and the gas generating composition.
• the temperature of the self-initiating composition reaches its self-initiation temperature, the released energy initiates the gas generating composition as during normal operation.
• the thermal initiation properties of the autoinitiation compositions described in the present application have been characterized by measuring their self-initiation temperature according to different methods. Any self-initiation temperature value is accompanied by the rate at which the temperature was elevated in its determination, expressed as 0 C / minute. This accuracy is desirable since the value of the self-initiation temperature varies depending on the conditions under which it is measured, particularly with the rate of temperature rise. Temperatures t1 to t4 are self-initiation temperatures of self-initiating compositions roughly determined during "oven tests" (the uncertainty on these measurements is of the order of 20 ° C.). An "oven test” consists of introducing a composition sample (20 to 50 mg) into an isothermal oven.
• t2 self-initiation temperature of a self-initiating composition introduced into an oven after being compressed under 200 bar using a pelletizer, expressed in 0 C.
• t3 self-initiation temperature of a self-initiating composition introduced into an oven after having been compressed under 1000 bar by means of a pelletizer, expressed in 0 C.
• t4 temperature self-initiation of a self-initiator composition introduced into a furnace after being compressed under 1000 bar by means of a pelletizer then stayed 15 hours in an oven at 14O 0 C, expressed as 0 vs.
• Temperatures T1 to T7 can be considered as self-initiation temperatures of self-initiating compositions. They are determined by DSC (Differential Scanning Calorimetry), during a "test
• This test consists in introducing a sample of composition (1 to
• T1 determined on a bulk self-initiating composition, with a temperature rise of 10 0 C / minute, expressed in O C.
• T2 determined on a bulk self-initiating composition, with a temperature rise of 50 0 C / minute, expressed in 0 C.
• T3 determined on a self-initiating bulk composition, with a temperature rise of 50 0 C / minute, after the crucible has been kept for 15 hours in an oven at 140 0 C, expressed in 0 C.
• ⁇ T 32 T3 - T2.
• T4 determined on a self-initiating composition compressed at 200 bars by means of a pelletizer, with a temperature rise of 50 ° C./min, expressed in 0 C.
• T5 determined on a self-initiating composition compressed at 1000 bar by means of a pelletizer, with a temperature rise of 10 0 C / minute, expressed in 0 C.
• T6 determined on a self-initiating composition compressed at 1000 bar using a pelletizer, with a temperature rise of 50 ° C./min, expressed in 0 C.
• T7 determined on a self-initiating composition compressed at 1000 bar by means of a pelletizer, with a temperature rise of 50 ° C./minute, after the crucible has been kept for 15 hours in an oven at 140 ° C., expressed in 0 C.
• the "Bonfire Test” and the “Slow Heat Test” only apply to complete gas generators.
• the "Bonfire Test” involves a rapid temperature rise (of the order of 50 0 C / minute) and makes it possible to verify the absence of explosion of the gas generator during a fire.
• the "Slow Heat Test” is a “Bonfire Test” with a slower rise in temperature ( ⁇ 14 0 C / minute). This test is much more severe because of the progressive heating of the gas generators. Both of these tests are described in SAE / USCAR-24, USCAR Inflator Technical Requirements and Validation.
• Temperatures T'1 to T'5 are temperatures of self-initiation of self-initiating compositions having undergone a "Slow Heat Test" type test after introduction into a device. These tests are conducted as follows: the device containing the self-initiating composition (50 to 60 mg) is placed in a bomb equipped with a temperature sensor and the bomb placed in a chamber regulated temperature. The bomb is subjected to a temperature rise of the order of 5 to 10 0 C / minute and the temperature inside thereof during the operation of the device is noted (T'1 to T'5) .
• T'1 determined on a device composed of 60 mg of autoinitiation composition compressed under 1000 bar and confined in an aluminum case, the lips of the holster having been folded down on an aluminum flap resting on the composition.
• An artifice of this type can be introduced into a gas generator to provide a self-initiation function.
• T'2 determined on a device composed of 60 mg of autoinitiation composition compressed under 1000 bar and confined in an aluminum case, the lips of the case having been folded on an aluminum flap resting on the composition. The device has previously stayed 48 hours in an oven at 120 0 C.
• T'3 determined on a device composed of 60 mg of autoinitiation composition compressed under 1000 bar and confined in an aluminum case, the lips of the case having been folded on an aluminum flap resting on the composition. The device has previously stayed 48 hours in an oven at 140 0 C.
• T'4 determined on 50 mg of self-initiating composition compressed at 200 bar and confined in an electric initiator of GTMS type completely hermetic, without free volume.
• An initiator of this type can be introduced into a gas generator to provide a self-initiation function.
• T'5 determined on 50 mg of self-initiating composition compressed at 200 bar and confined in an electric initiator of GTMS type completely hermetic, without free volume. The initiator has previously stayed 48 hours in an oven at 120 ° C. The notation "NF” means that the GTMS device or initiator did not operate during a "Slow Heat Test” test described above.
• E c energy of combustion of the self-initiating composition, measured by means of a calorimeter, expressed in cal.g "1.
• Tests 13, 14, 16, 21 and 52-54 highlight the interest of combining reducing agents having a catalytic activity, such as manganese, to metals such as zirconium
• the combustion of the self-initiating composition resulting from this combination releases a much greater amount of energy than when the manganese cobalt, copper or their mixtures are used as the only reducing agent Zirconium can be substituted or combined with Ti, TiH 2 , ZrH 2 , Fe or Al to produce similar effects.
• the term “Fire” signifies that the self-initiating composition has functioned unexpectedly at 120 ° C. or below 140 ° C., during the environmental test (stability test at a given temperature for a given time) prior to the test in question. .
• the presence of this mention highlights some of the so-called “unstable” compositions within the meaning of the invention. Gas generators and their constituents must withstand, without any functional degradation, these accelerated aging tests.
• the storage test at 107 ° C. for 408 hours, which is particularly restrictive, is reserved only for qualifications of self-initiated compositions already developed.
• the test 120 0 C / 48 hours practiced on a device is roughly equivalent to several hundred hours under 107 0 C and can predict with a high probability the behavior of the self-initiating composition contained in a device to the test d environment 107 0 C / 408 hours.
• a lack of inadvertent operation of the device during the test 140 0 C / 48 hours is very satisfactory.
• obtaining a value of the self-initiation temperature T'3 slightly modified with respect to T'1 proves a high stability of the autoinitiation composition, well beyond the test 107 0 C / 408 hours.
• Table 1 shows 54 tests corresponding to 54 self-initiating compositions, divided into 8 groups A, B, C, D, E, F, G and H. They were prepared by varying the nature of the reducing mixture, the mixture of organic compounds, the oxidizing mixture, metal oxides and additives in order to study the impact of the nature of the constituents on various properties of said compositions, in particular their self-initiation temperature and their stability.
• Group A comprises compositions having a temperature T'1 of less than 125 ° C., that is to say compositions having a self-initiation temperature which is too low in compressed form and under confinement to be of practical interest. These compositions contain molybdenum or MOO 3 combined with boron. These compositions have not satisfied at least one stability test with the exception of the composition N 0 6 containing 0.5% of silica.
• Group B comprises compositions containing boron which have a temperature T'1 of between 125 and 130 ° C., which is still too low for use under a high compression ratio (1000 bar), but which have satisfied the tests of stability to which they have been subjected, and which have self-initiation temperatures T'4 of the order of 150-160 0 C hermetic electrical initiators (GTMS) under a compression ratio of 200 bar. These temperatures are little modified after environmental test (T'5).
• Such compositions are of major interest for providing the self-initiation function as electrical initiators.
• Group C comprises compositions containing boron or tungsten and a high content (40%) of guanidinium nitrate, leading to temperatures T'1 of the order of 135-150 ° C. and a clear lack of stability (T3 ) in the 140 ° C./15 hours test under reduced confinement and with a low mass (1 to 2 mg, in bulk). These results show the influence of guanidinium nitrate content on stability.
• Group D includes compositions having temperatures
• compositions containing manganese, cobalt or copper which have temperatures T'1 of between 150 and 180 ° C., even after an environmental test (T'2) of 120 ° C./48 hours (tests 12, 13 , 14, 16, 50, 51) are particularly advantageous for providing a self-initiation function in the form of pellets or in capsules intended to be inserted into the gas generators (compression ratio: 1000 bars).
• Compositions which contain about 30% zirconium with only about 10% manganese, cobalt or copper are particularly advantageous by their high energy of combustion.
• the other compositions of group D (tests 17 to 23) are of less interest because of higher self-initiation temperatures. However, tests 53 and 54 associated with tests 50 to 52 show the possibility of setting the self-initiation temperature to high values in order to favor stability.
• compositions of groups E, F, G and H were sorted in order of increasing temperature T1.
• Group E comprises the compositions which have a T1 temperature (bulk) of between 170 and 196 ° C. These compositions are strongly degraded during environmental tests 140 ° C./15 hours in a crucible as revealed by the DSC tests: ⁇ T 32 e [40; 178] 0 C.
• This group includes compositions containing vanadium, chromium, tungsten associated with CuO or titanium hydride associated with OOM 3, molybdenum compositions / silver nitrate / guanidinium nitrate, and that potassium chlorate / lactose compositions optionally comprising boron. These compositions are too unstable for use in compressed form and under confinement (tests 29-31).
• Group F which includes the comparative test N 0 35 carried out without a metal, metalloid or metal hydride and without a metal oxide reducing agent, groups together compositions having a temperature T1 of between 197 and 240 ° C. and which withstand the test of environment 140 0 C / 15 hours in crucible as revealed by DSC tests: ⁇ T 32 e [-6; 15] 0 C.
• This group includes compositions containing aluminum, iron, nickel, zirconium, but also compositions azodicarbonamide / potassium chlorate optionally comprising boron and a composition 5- aminotetrazole / chlorate potassium. 5-aminotetrazole and azodicarbonamide can replace guanidinium nitrate as an energetic organic compound (tests 33, 36, 38) in the self-initiating compositions according to the invention.
• Group G comprises zirconium / silver nitrate / guanidinium nitrate compositions having T1 temperatures included between 300 and 350 0 C, which excludes any application in the field of self-initiation.
• Group H essentially comprises zirconium / potassium perchlorate (ZPP) compositions, which are not within the scope of the present invention and which are used in Table 1 for comparison purposes.
• ZPP type compositions zirconium, potassium perchlorate, test 49
• THPP titanium hydride, potassium perchlorate
• TPP titanium, potassium perchlorate
• the ZPP, THPP or TPP compositions have self-initiation temperatures greater than 380 ° C. and therefore can not satisfy the objective set.
• compositions of Zr / KCIO 3 / guanidinium nitrate (tests 19, 22, 40) and Zr / NaClO 3 / guanidinium nitrate (test 15) have T1 self-initiation temperatures of the order of 200 - 220 0 C.
• the Table 2 contains the tests of Table 1 corresponding to reducing compositions / potassium chlorate / guanidinium nitrate and optionally metal oxide, silica or without binder (including the comparative test N 0 35), which allow directly highlight the influence of the reducing agent and the metal oxide on the self-initiation temperatures T1 to T3 and T'1.
• the tests were sorted by increasing order of T1 temperatures, which are more accurate measurements than T2 or t1.
• the activity of MoO 3 is revealed by the comparison of tests 4 and 10. This oxide has an important activity in the presence of titanium hydride (test 28) which is still manifested in the presence of boron (test 4).
• This table makes it possible to classify the reducing agents in three groups with regard to their catalytic activity: too active (Mo, Cr, W, V), useful (B, Mn, Co, Cu) and inactive or little active (Al, Si, TiH 2 , Ti, Fe, Zr, Ni).
• compositions having self-initiation temperatures ranging from 130 to 220 ° C., better still from 150 to 200 ° C. and even better ranging from 150 to 180 ° C., have been developed by a adequate choice of constituents and their proportions.
• Certain Group D compositions containing manganese, copper or cobalt have self-initiation temperatures of the order of 150 ° to 180 ° C., a satisfactory stability, are not ignited during prolonged storage (48 hours) at 120 ° C. and operate without a large difference in autoignition temperature after this environmental test.
• compositions zirconium / manganese, cobalt or copper / potassium chlorate / guanidinium nitrate / Viton ® / silica are particularly interesting for applications under high compression ratio, zirconium to obtain a higher combustion energy and greater reaction rate.
• the "GTMS" electrical initiator tests (T'4, T'5) show that certain compositions (group B) containing boron, potassium chlorate and guanidinium nitrate have self-initiation temperatures ranging from at 167 0 C with satisfactory stability.
• the self-initiation temperature for a given temperature rise rate, can be adjusted, preferably from 130 to 220 ° C., better still from 150 to 200 ° C. and even more preferably from 150 to 200 ° C. 180 0 C, by varying the proportions of the constituents, in particular within the compositions of groups B, D and F of Table 1, as well as the compression ratios of these compositions.
• the compositions in these groups do not necessarily correspond to optimal formulations, but formulations adapted to artifices meeting the objectives set can easily be developed by those skilled in the art from the constituents in these groups, by routine experimentation.
• the specific surfaces of the various constituents employed are presented in Table 3. They are expressed in m 2 .g -1 and were determined according to the BET method. correlation between the activity of a reductant (comparison with temperature T1) and its specific surface area In particular, molybdenum has one of the weakest specific surfaces while it has the strongest influence on the temperature On the other hand, the high activity of boron may be due in part to its high specific surface area.

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