EP1866265B1 - Electrical initiators using self-initiating compositions and gas generators comprising said initiators - Google Patents

Description

The present invention relates to a self-initiating pyrotechnic composition implemented in bulk or in the form of a compressed layer in the electric initiator of a gas generator and for initiating 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. 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 gas generators are intended for automotive safety, they must remain stable at high temperatures for long periods of time. Perfect preservation of the characteristics of the generator during an environmental test conducted under 107 ° C for 408 hours has been a classic requirement for automotive safety since the early 1990s. The rate of decomposition 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. By 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 particular 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. Main charges used in electrical initiators for automotive safety and in particular in airbags are described in US patents US 5847310 and US 5672843 . Gas generators are designed to withstand all the temperatures that can be reached in an automobile under normal use (-40 ° C, 90 ° C).

However, in the case of a fire, the temperature of the gas generator will grow until a composition or a substance in the pyrotechnic chain reaches its self-initiation temperature. By 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 self-initiation of said substance or said mixture of substances can therefore, in general, be assimilated to its autoignition 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 correctly by choosing a composition generating a gas having a self-initiation temperature, that is to say self-ignition voluntarily reduced, without any other precaution. Indeed, such compositions operate too quickly when their autoignition temperatures are reached (global inflammation of the entire charge).

The problem can be solved by using a self-initiating composition, as explained in the publication of P. Moussier "Controlled ignition of gas generating compositions: Electrical initiators including an autoignition function", International Pyrotechnics Automotive Safety Symposium, pp 215-226, 22-23 November 2005 .

By 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. By "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. By "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 self-initiating composition can also be placed out of the normal pyrotechnic chain near the gas generating composition, at a place where the temperature rises rapidly, or even be mixed into pellets (without an envelope) or a capsule with 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 airbags implemented on a large scale were made of sodium azide mixed with oxidants and additives. The decomposition reaction of such compositions generates nitrogen. To ensure the absence of explosion of aluminum gas generators containing compositions generating gas-based sodium azide, it is generally necessary that the self-initiation temperature of the self-initiating composition is less than 230 ° C, a temperature of the order of 200 ° 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. 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 the US patent US 4561675 , were made based on nitrocellulose and propellant powders. Various additives have been added to the nitrocellulose powders to fulfill this self-initiation function. However, self-initiating compositions based on nitrocellulose have the drawback 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. In addition, 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 the international application WO 94/14637 and the US patent US 5542688 , and Nagahashi, who claims in the US patent US 5847310 the production of an electrical initiator containing a self-initiating composition based on carbohydrates and chlorates. However, sodium chlorate / carbohydrate mixtures are not stable enough to meet the environmental test at 107 ° C for 408 hours when compressed and confined in initiators. The actual usable self-initiating compositions claimed by the aforementioned patents all have high self-initiation temperatures above 180 ° C; in practice, greater than 190 ° C, most often.

In addition, 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. Unfortunately, it is common for the self-initiation temperatures of these gas generating compositions to be slightly higher than the melting temperature of some of their constituents. However, 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 components 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 ° C. The combustion of the corresponding gas generating compositions becomes unstable at temperatures of the order of 200-250 ° C. In order to avoid the explosion of aluminum gas generators containing such gas generating compositions free of metal azide, the manufacturers have sought to find self-initiating compositions having a self-initiation temperature of less than 180 ° It should be noted that the use of ammonium nitrate in the gas generating compositions, although it has already been described, is undesirable because of its too low melting temperature (160 ° C.). The US patent US 5084118 , which discloses one of the first examples of composition generating gas free of sodium azide, claims a self-initiating composition based on 2,4-dinitrophenylhydrazine and chlorates, but this composition is too sensitive to shocks to be put implemented. The US patent US 6177028 describes a self-initiating composition based on nitrogenous organic compounds, potassium nitrate, metal powders, metal oxides (MoO ₃ ) and various additives. The complex formulation is difficult to implement.

The US patent US 6453816 describes self-initiating compositions based on iron oxide or ferrocene and at least one compound selected from oxalates, persulfates, permanganates, nitrates, nitrides, perborates, bismuthates, formates, sulfamates, bromates 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).

Knowlton, in US patents US 5959242 , US 5739460 , US 6101947 , US 6221187 , US 6749702 and his article " Low temperature autoignition materials ", Proceedings of the International Pyrotechnics Seminar 2000, 27, 107-117 , describes self-initiating compositions whose purpose is to trigger the combustion of a pyrotechnic main charge in a gas generator or pyrotechnic device, when it is exposed to a flame or a high temperature environment. The US patent US 6605167 relies on the compositions claimed in the US patents US 5959242 , US 5739460 and US 6101947 for obtaining self-initiation temperatures of between 80 and 250 ° C. The self-initiating compositions described in these documents consist of a mixture of a metal powder, mainly molybdenum, and an oxidizing composition resulting from a mixture, optionally by co-fusion, of at least two oxidants, the the first being generally silver nitrate or ammonium nitrate and the second being generally 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). In case of exposure to a flame or at high temperature, 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 severely affects the stability of the compositions under 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 the US patent US 6221187 are too unstable to be used in compressed form and under confinement, as is the case in electrical initiators.

There is therefore a need for self-initiating compositions which are perfectly stable at 107 ° C. for 408 hours (or at least 90 ° C. for 1000 hours), in bulk or in compressed form, in the open air or in a holster. or in an initiator and preferably in a hermetic initiator with compressed pyrotechnic layers.

The implementation of 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. In addition, self-initiating compositions having a self-initiation temperature below 130 ° C can not be used in gas generators because a non-initiation safety temperature of 130 ° C is generally required. by car manufacturers. It has been previously stated that self-initiating compositions having a self-initiation temperature above 180 ° C are of lesser practical interest today. Today, manufacturers of gas generators tend to implement gas generating compositions increasingly efficient but whose combustion becomes unstable at lower and lower temperatures, below 200 ° C. The need for compositions having self-initiation temperatures below 180 ° C is thereby reinforced. A composition responding to need must have a self-initiation temperature ranging from 130 ° C to 180 ° C, and have a satisfactory set of characteristics. The composition should not be initiated at a temperature below 130 ° C, in the system where it is used, even after environmental testing, which pushes the minimum temperature of the range of self-initiation temperatures allowed to- beyond 150 ° C. Thus, the useful range becomes very narrow: 150-180 ° C, under a heating rate of less than or equal to 14 ° C / minute.

The aim of the present invention is to provide a self-initiating composition satisfying the abovementioned criteria and overcoming the drawbacks of the self-initiating compositions of the prior art, which is used in an electrical initiator comprising an envelope, a resistive element and a less a charge. This self-initiating composition is used according to the invention as a filler. 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, where the Self-initiating composition is used according to the invention as an initiating reinforcement filler.

• 20 à 80 % en masse d'au moins un chlorate de métal alcalin, de préférence 25 à 70 %, mieux 25 à 50 %,
• 5 à 50 % en masse d'au moins un composé organique énergétique, tel que défini dans la revendication 1, de préférence 10 à 40 %, et caractérisée en ce que la formulation principale comprend en outre :
  1. (a) 0 à 60 % en masse d'au moins un métal ou métalloïde choisi parmi le bore, le manganèse, le cobalt et le cuivre, de préférence 0 à 40 %, mieux 5 à 20 %,
  2. (b) 0 à 60 % en masse d'au moins un métal ou hydrure métallique choisi parmi le zirconium, le titane, TiH₂, ZrH₂, l'aluminium, le silicium et le fer, de préférence 0 à 40 %, mieux 10 à 35 %,
  3. (c) 0 à 50 % en masse d'au moins un oxyde de métal de transition, de préférence 0 à 35 %, mieux 0,5 à 35 %,

les pourcentages massiques étant exprimés par rapport à la masse de la formulation principale et les pourcentages massiques de composant (a) et de composant (c) ne pouvant pas être simultanément nuls.The above aims are achieved, and this is one of the objects of the present invention, by the implementation of a self-initiating composition, comprising a main formulation comprising:

• 20 to 80% by weight of at least one alkali metal chlorate, preferably 25 to 70%, more preferably 25 to 50%,
• 5 to 50% by weight of at least one energetic organic compound, as defined in claim 1, preferably 10 to 40%, and characterized in that the main formulation further comprises:
  1. (a) 0 to 60% by weight of at least one metal or metalloid selected from boron, manganese, cobalt and copper, preferably 0 to 40%, more preferably 5 to 20%,
  2. (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%,
  3. (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 expressed relative to the mass of the main formulation and the mass percentages of component (a) and component (c) can not be simultaneously zero.

If it is desirable to have compositions having self-initiation temperatures low enough to protect gas generators from explosive reactions, it is necessary, however, that the self-initiation temperature remains higher than 130 ° C. even when slow heating ("Slow Heat Test"). The self-initiating 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 stability at a temperature of 107 ° C for 408 hours or at a temperature of 90 ° C for 1000 hours in all configurations where they are used. A composition is said to be stable at a given temperature for a given time when a residence in an enclosure at said temperature during said time does not cause any detrimental degradation to the operation of the self-initiating composition itself or to 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. Thus, to be stable, a self-initiating composition must not, for example, be initiated unexpectedly during an environmental test.

The aims described above are achieved according to the invention by producing a composition 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 used 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. In particular, 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 used according to the invention.

The self-initiating composition used according to the invention also comprises 5 to 50% by weight of at least one energetic organic compound. For the purposes of the present invention, 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 so as 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. 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 amine, amide, imide or imine and their salts, especially N- substituted derivatives of guanidinium nitrate. Just like guanidinium nitrate, these other organic compounds energy are used as fuel. Thus, the self-initiating composition used 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 (1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane or octogen). 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. Those skilled in the art will ensure that the choice of the energetic organic compound or compounds makes it possible to obtain the desired stability properties. 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 energetic organic compounds used according to the invention are guanidinium nitrate, aminoguanidinium nitrate, diaminoguanidinium nitrate (DAGN), triaminoguanidinium nitrate (TAGN), nitroguanidinium nitrate, methylguanidinium nitrate, 5- aminotetrazole, 5-aminotetrazole nitrate, triaminoguanidinium 5-aminotetrazolate, bistetrazole, bistetrazole amine, 5,5'-azotetrazolate diguanidinium (GZT) and 3-nitro-1,2,4-triazol-5-one (NTO).

In order to constitute a self-initiating composition, 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. They are preferably used in the form of fine powders, that is to say with a particle size ranging from 0.1 to 100 μm, better still ranging from 1 to 50 μm. Some of these reducing agents, in addition to their role of reactive vis-à-vis oxygen, 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. For the purposes of the present invention, 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)

Titanium, TiH ₂ and iron exert only a weak catalytic effect or no catalytic effect in the decomposition of chlorates and nitrates, whereas nickel, aluminum, zirconium, ZrH ₂ and silicon n 'exert none. Vanadium and metals in Group 6 of the Periodic Table, or VIB according to convention, chromium, molybdenum and tungsten, have too high catalytic activities. They can give self-initiating compositions containing them self-initiation temperatures too low to meet safety requirements (less than 130 ° C under confinement). On the other hand, Group VIB metals can lead to excessive degradation in the stability test at 107 ° C for 408 hours. It is therefore preferable not to use 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 self-initiating 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 self-initiating 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. Yunchang Zhang's work highlights likely 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 subsequent publications. 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. As metal oxides or metalloid oxides useful as catalysts in the present invention, mention may be made of 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:

MoO ₃ >CuO> Fe ₂ O ₃ , ZnO> SiO ₂ (2)

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. For example, 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 MoO ₃ , CuO and mixtures thereof. In practice, it is not necessary to incorporate active metal oxides (MoO ₃ and CuO) with the self-initiating compositions of the invention containing a metal or active metal in the form of a metal powder, such as B, Mn, Co , Cu or mixtures thereof. The addition of active metal oxides, on the other hand, 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. In addition, self-initiating 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. However, such compositions are low in energy and low light and are preferably not used as main charges.

It is advantageous to use 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. Preferably, 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.

In addition to the main formulation, the self-initiating compositions used according to the invention may comprise a number of additives, examples of which are given below and in no way limit the present invention.

Generally, the self-initiating compositions used 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. Preferably, the binder is hydrophobic. The preferred binder is a fluoroelastomer binder such as Viton®. A fluorinated elastomer binder such as Viton® improves the stability of the self-initiating composition without greatly increasing its self-initiation temperature. 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.

It is also possible to include a mass quantity up to 1%, preferably from 0.2 to 1% (this percentage being expressed relative to the mass of the main formulation and not to the total mass of the composition), an ultra fine silica called "silica fume", in the self-initiating compositions according to the invention. Ultra fine silica is understood to mean, in the present invention, an extremely fine silica powder having a specific surface ranging from 100 to 200 m ² .g ^-1 . The ultra fine silica facilitates the implementation of the self-initiating compositions according to the invention (better grain flow) and improves their stability when used in bulk or in compressed form. It is possible that this increased stability results from a simple physical effect of reagent separation. Whatever the mechanism, silica plays a role of stabilizer. It is also possible to use talc, graphite or boron nitride to facilitate the implementation of the composition. The overall content of these additives remains less than 1% by weight (this percentage being expressed relative to the weight of the main formulation and not with respect to the total mass of the composition).

• une formulation principale comprenant :
  • 5 à 60 % de manganèse, cobalt, cuivre ou leurs mélanges, de préférence 5 à 40 %, mieux 5 à 20 %,
  • 0 à 60 % de zirconium, titane, TiH₂, ZrH₂, fer, silicium, aluminium ou leurs mélanges, de préférence 0 à 40 %, mieux 10 à 35 %,
  • 5 à 50 % de nitrate de guanidinium, mieux 10 à 40 %,
  • 25 à 70 % de chlorate de potassium, mieux 25 à 50 %,
• et comporte en outre :
  • 2 à 8 % d'un liant élastomère fluoré comme le Viton®,
  • 0 à 1 % de silice ultra fine,
  ou bien :
  • une formulation principale comprenant :
    • 2 à 25 % de bore, mieux 2 à 15 %,
    • 0 à 60 % de zirconium, titane, TiH₂, ZrH₂, fer, silicium, aluminium ou leurs mélanges, mieux 0 à 40 %,
    • 5 à 50 % de nitrate de guanidinium, mieux 10 à 40 %,
    • 25 à 80 % de chlorate de potassium, mieux 25 à 70 %,
  • et comporte en outre :
    • 2 à 8 % d'un liant élastomère fluoré comme le Viton®,
    • 0 à 1 % de silice ultra fine,
  ou bien :
  • une formulation principale comprenant :
    • 20 à 60 % de zirconium, titane, TiH₂, ZrH₂, fer, silicium, aluminium ou leurs mélanges, mieux 20 à 50 %,
    • 5 à 50 % de nitrate de guanidinium, mieux 10 à 40 %,
    • 25 à 70 % de chlorate de potassium, mieux 25 à 50 %,
    • 0,5 à 50 % d'oxydes de métaux de transition tels MoO₃ ou CuO, mieux 0,5 à 35 %,
  • et comporte en outre :
    • 2 à 8 % d'un liant élastomère fluoré comme le Viton®,
    • 0 à 1 % de silice ultra fine,

les pourcentages étant exprimés par rapport à la masse de la formulation principale.Nonlimiting examples of compositions according to the invention making it possible to fulfill the objectives set are given below. One of the self-initiating compositions used according to the invention comprises:

• a main formulation comprising:
  • 5 to 60% of manganese, cobalt, copper or mixtures thereof, preferably 5 to 40%, better still 5 to 20%,
  • 0 to 60% of zirconium, titanium, TiH _2, ZrH _2, iron, silicon, aluminum or mixtures thereof, preferably 0 to 40%, better 10 to 35%,
  • 5 to 50% of guanidinium nitrate, better 10 to 40%,
  • 25 to 70% of potassium chlorate, more preferably 25 to 50%,
• and further comprises:
  • 2 to 8% of a fluoroelastomer binder such as Viton®,
  • 0 to 1% ultra-fine silica,
  or :
  • a main formulation comprising:
    • 2 to 25% boron, better 2 to 15%,
    • 0 to 60% of zirconium, titanium, TiH ₂ , ZrH ₂ , iron, silicon, aluminum or mixtures thereof, better 0 to 40%,
    • 5 to 50% of guanidinium nitrate, better 10 to 40%,
    • 25 to 80% potassium chlorate, more preferably 25 to 70%,
  • and further comprises:
    • 2 to 8% of a fluoroelastomer binder such as Viton®,
    • 0 to 1% ultra-fine silica,
  or :
  • a main formulation comprising:
    • 20 to 60% of zirconium, titanium, TiH ₂ , ZrH ₂ , iron, silicon, aluminum or mixtures thereof, better 20 to 50%,
    • 5 to 50% of guanidinium nitrate, better 10 to 40%,
    • 25 to 70% of potassium chlorate, more preferably 25 to 50%,
    • 0.5 to 50% of transition metal oxides such as MoO ₃ or CuO, better 0.5 to 35%,
  • and further comprises:
    • 2 to 8% of a fluoroelastomer binder such as Viton®,
    • 0 to 1% ultra-fine silica,

the percentages being expressed relative to the mass of the main formulation.

Thus, the self-initiating compositions of the invention differ widely from the compositions cited in the prior patents and in particular those of the 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 inventors have furthermore discovered that the self-initiation temperature of the self-initiating compositions used 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 self-initiating composition. The self-initiation temperature of the self-initiating compositions used 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. In addition, the importance of the compression ratio and containment parameters varies according to the compositions.

The self-initiating compositions used according to the invention are prepared according to the usual processes for the production of the compositions ZPP (zirconium, potassium perchlorate) and THPP (titanium hydride, potassium perchlorate), which are well known to those skilled in the art, and 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. In addition, 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. We will give three examples of processes. 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 process makes it possible to obtain self-initiating compositions used according to the invention which 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 anti-solvent and then dried. This second method is of great interest in terms of handling safety. When the binder is a fluoroelastomer such as Viton®, acetone or methyl ethyl ketone are effective solvents, and aliphatic hydrocarbons such as heptane are suitable anti-solvents. Licences US 3876477 and US 4012244 describe the principle of this second method. 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. The ultra-fine silica, if it is used, is generally introduced into the self-initiating composition used according to the invention after drying of said composition.

The self-initiating compositions of the invention are used 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. According to a second embodiment, the self-initiating compositions of the invention can be used compressed in the form of pellets without a container. Compression rates of 500 to 3000 bar are then well suited. According to a third embodiment, the self-initiating compositions of the invention can be used 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 thus 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 of the invention as a charge. The self-initiating composition can be used as the main charge or as an additional charge. 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). When used as additional charges inside an initiator, the self-initiating compositions of the invention are placed between the composition in contact with the resistive element and the main charge or, preferably on the bottom of the case after the main charge in the functional order. Preferably, the electrical initiator according to the invention is a hermetic electric initiator with compressed pyrotechnic layers and of GTMS (Glass To Metal Seal) or PTMS® (Plastic To Metal Seal) type. By "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 to those skilled in the art, can be found in the patents US 5099762 , WO 02/46687 and US 5639986 . An PTMS® electric initiator differs from a GTMS type initiator simply 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 the international application WO 03/058154 and the French patent FR 2698687 .

The self-initiating compositions of the invention may be used in a gas generator or any other pyrotechnic device. In particular, 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 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 higher than 350 ° 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.

Several nonlimiting methods for initiating the combustion of a gas-generating composition (or a pyrotechnic composition) contained in a gas generator or a pyrotechnic device when said gas generator or pyrotechnic device is exposed to an elevated temperature are now be described.

• préparer une composition auto-initiatrice utilisée selon l'invention, ayant une température d'auto-initiation inférieure à celle de la composition génératrice de gaz (ou de la composition pyrotechnique) devant être initiée,
• fabriquer des pastilles de composition auto-initiatrice, par compression, dans la matrice d'une pastilleuse,
• ajouter une ou plusieurs pastilles de ladite composition auto-initiatrice aux pastilles de la composition génératrice de gaz. L'inflammation d'une pastille de composition auto-initiatrice, lorsque sa température atteint sa température d'auto-initiation, initie les pastilles de la composition génératrice de gaz qui l'environnent, la mise à feu se propageant à l'ensemble de la charge du générateur de gaz. De manière alternative, les pastilles de composition auto-initiatrice peuvent être placées dans une alvéole de la paroi du générateur de gaz (communiquant avec la composition génératrice de gaz) et non pas mélangées aux pastilles de la composition génératrice de gaz.

The first method according to the invention for initiating the combustion of a gas-generating composition comprises the following three steps:

• preparing a self-initiating composition used according to the invention, having a self-initiation temperature lower than that of the gas-generating composition (or the pyrotechnic composition) to be initiated,
• manufacture pellets of self-initiating composition, by compression, in the matrix of a pelletizer,
• adding one or more pellets of said self-initiating 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. Alternatively, 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.

• préparer une composition auto-initiatrice utilisée selon l'invention, ayant une température d'auto-initiation inférieure à celle de la composition génératrice de gaz (ou de la composition pyrotechnique) devant être initiée,
• charger par compression la composition auto-initiatrice dans des étuis métalliques puis obturer, éventuellement au moyen de paillets métalliques sur lesquels les parois des étuis sont rabattues par sertissage,
• placer ces étuis chargés de composition auto-initiatrice dans une alvéole de la paroi du générateur de gaz (communiquant avec la composition génératrice de gaz), de manière à ce que l'énergie dégagée par la composition auto-initiatrice contenue dans l'étui, lorsque sa température atteint sa température d'auto-initiation, initie les pastilles de la composition génératrice de gaz qui l'environnent, la mise à feu se propageant à l'ensemble de la charge du générateur de gaz.

The second method according to the invention for initiating the combustion of a gas-generating composition comprises the following three steps:

• preparing a self-initiating composition used according to the invention, having a self-initiation temperature lower than that of the gas-generating composition (or the pyrotechnic composition) to be initiated,
• compressing the self-initiating composition in metal holsters and then sealing, possibly by means of metal flakes on which the walls of the holsters are folded down by crimping,
• placing these loaded cases of self-initiating composition in a cell of the wall of the gas generator (communicating with the gas-generating composition), so that the energy released by the self-initiating composition contained in the case, when its temperature reaches its self-initiation temperature, initiates the pellets of the gas generating composition that surround it, the firing propagating to the entire load of the gas generator.

• préparer une composition auto-initiatrice utilisée selon l'invention, ayant une température d'auto-initiation inférieure à celle de la composition génératrice de gaz (ou de la composition pyrotechnique) devant être initiée,
• charger en vrac ou par compression, la composition auto-initiatrice dans un initiateur électrique, en tant que charge additionnelle ou en tant que charge principale,
• placer l'initiateur électrique dans le logement du générateur de gaz prévu à cet effet. Lorsque la température de la composition auto-initiatrice atteint sa température d'auto-initiation, l'énergie dégagée initie l'ensemble de la charge de l'initiateur, qui initie à son tour la charge de renfort d'initiation (booster), qui initie la composition génératrice de gaz comme lors d'un fonctionnement normal.

The third method according to the invention for initiating the combustion of a gas-generating composition comprises the following three steps:

• preparing a self-initiating composition used according to the invention, having a self-initiation temperature lower than that of the gas-generating composition (or the pyrotechnic composition) to be initiated,
• load in bulk or compression, the self-initiator composition in an electric initiator, as an additional charge or as a main charge,
• place the electric initiator in the housing of the gas generator provided for this purpose. When the temperature of 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.

• préparer une composition auto-initiatrice utilisée selon l'invention, ayant une température d'auto-initiation inférieure à celle de la composition génératrice de gaz (ou de la composition pyrotechnique) devant être initiée,
• charger en vrac ou par compression, la composition auto-initiatrice dans un générateur de gaz comprenant un initiateur électrique, en tant que charge de renfort d'initiation, en la plaçant entre l'initiateur électrique et la composition génératrice de gaz. Lorsque la température de la composition auto-initiatrice atteint sa température d'auto-initiation, l'énergie dégagée initie la composition génératrice de gaz comme lors d'un fonctionnement normal.

The fourth method according to the invention for initiating the combustion of a gas-generating composition comprises the following two steps:

• preparing a self-initiating composition used according to the invention, having a self-initiation temperature lower than that of the gas-generating composition (or the pyrotechnic composition) to be initiated,
• loading in bulk or compression, the self-initiating composition in a gas generator comprising an electrical initiator, as an initiating reinforcement charge, placing it between the electric initiator and the gas generating composition. When 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 following examples illustrate the present invention without limitation. The percentages of the various constituents are all expressed relative to the mass of the main formulation.

Examples Determination of self-initiation temperatures:

The thermal initiation properties of the self-initiating 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 in ° 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.

• t1: température d'auto-initiation d'une composition auto-initiatrice introduite en vrac dans un four, exprimée en °C.
• t2 : température d'auto-initiation d'une composition auto-initiatrice introduite dans un four après avoir été comprimée sous 200 bars au moyen d'une pastilleuse, exprimée en °C.
• t3 : température d'auto-initiation d'une composition auto-initiatrice introduite dans un four après avoir été comprimée sous 1000 bars au moyen d'une pastilleuse, exprimée en °C.
• t4 : température d'auto-initiation d'une composition auto-initiatrice introduite dans un four après avoir été comprimée sous 1000 bars au moyen d'une pastilleuse puis séjourné 15 heures dans une étuve à 140°C, exprimée en °C.

The 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. If it did not start spontaneously after 5 minutes, the sample is replaced with a new sample after the oven temperature has been raised by 20 ° C. The operation is repeated until its self-initiation is observed. The tests for determining the self-initiation temperature "in the oven", in the open air show a strong influence of the compression ratio of the composition. These tests are fairly representative of pellets of compositions for self-initiation, introduced among the pellets of gas generating compositions, or in another suitable location of the gas generator.

• t1: self-initiation temperature of a self-initiating composition introduced in bulk in a furnace, expressed in ° C.
• t2: self-initiation temperature of a self-initiating composition introduced into an oven after having been compressed at 200 bars by means of a pelletizer, expressed in ° C.
• t3: self-initiation temperature of a self-initiating composition introduced into an oven after having been compressed at 1000 bar by means of a pelletizer, expressed in ° C.
• t4: self-initiation temperature of a self-initiating composition introduced into an oven after having been compressed at 1000 bar by means of a pelletizer and then kept for 15 hours in an oven at 140 ° C., expressed in ° C.

• T1 : déterminée sur une composition auto-initiatrice en vrac, avec une élévation de température de 10 °C / minute, exprimée en °C.
• T2 : déterminée sur une composition auto-initiatrice en vrac, avec une élévation de température de 50 °C / minute, exprimée en °C.
• T3 : déterminée sur une composition auto-initiatrice en vrac, avec une élévation de température de 50 °C / minute, après que le creuset ait séjourné 15 heures dans une étuve à 140 °C, exprimée en °C. $${\mathrm{\Delta T}}_{\mathrm{32}}=\mathrm{T}\mathrm{3}-\mathrm{T}\mathrm{2.}$$
  
• T4 : déterminée sur une composition auto-initiatrice comprimée sous 200 bars au moyen d'une pastilleuse, avec une élévation de température de 50 °C / minute, exprimée en °C.
• T5 : déterminée sur une composition auto-initiatrice comprimée sous 1000 bars au moyen d'une pastilleuse, avec une élévation de température de 10 °C / minute, exprimée en °C.
• T6 : déterminée sur une composition auto-initiatrice comprimée sous 1000 bars au moyen d'une pastilleuse, avec une élévation de température de 50 °C / minute, exprimée en °C.
• T7 : déterminée sur une composition auto-initiatrice comprimée sous 1000 bars au moyen d'une pastilleuse, avec une élévation de température de 50 °C / minute, après que le creuset ait séjourné 15 heures dans une étuve à 140 °C, exprimée en °C.

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 "DSC test". This test involves introducing a sample composition (1 to 2 mg) in a stainless steel crucible closed hermetically but containing a relatively large volume of air. A certain confinement is thus ensured, although it is very inferior to that of most artifices. The temperature of the peak of the first exotherm, significant of a firing on a larger amount of composition, is noted (T1 to T7).

• T1: determined on a self-initiating composition in bulk, with a temperature rise of 10 ° C / min, expressed in ° C.
• T2: determined on a bulk self-initiating composition, with a temperature rise of 50 ° C / minute, expressed in ° C.
• T3: determined on a self-initiating composition in bulk, 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 ° C. $${\mathrm{DT}}_{\mathrm{32}}=\mathrm{T}\mathrm{3}-\mathrm{T}\mathrm{2.}$$
  
• T4: determined on a self-initiating composition compressed at 200 bars by means of a pelletizer, with a temperature rise of 50 ° C / minute, expressed in ° C.
• T5: determined on a self-initiating composition compressed at 1000 bar by means of a pelletizer, with a temperature rise of 10 ° C / minute, expressed in ° C.
• T6: determined on a self-initiating composition compressed at 1000 bar by means of a pelletizer, with a temperature rise of 50 ° C / minute, expressed in ° 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 ° C.

Monitoring the behavior of self-initiating compositions in sealed crucibles by DSC makes it possible to determine their self-initiation temperatures much more precisely than during "oven tests". The measurements carried out on compacted compositions at 1000 bar are particularly representative of the self-initiation temperatures that would be observed during a "Bonfire Test" with a temperature rise of 50 ° C./minute (T6), and a "Slow Heat Test" with a temperature rise of 10 ° C / minute (T5), the second temperatures being lower than the first of about 20 ° C. The results are fairly representative of self-initiation temperatures of pellets of self-initiating compositions placed without strong confinement in a gas generator.

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 ° 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 ° 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.

• T'1 : déterminée sur un artifice composé de 60 mg de composition auto-initiatrice comprimée sous 1000 bars et confinée dans un étui en aluminium, les lèvres de l'étui ayant été rabattues sur un paillet en aluminium en appui sur la composition. Un artifice de ce type peut être introduit dans un générateur de gaz afin d'y assurer une fonction d'auto-initiation.
• T'2 : déterminée sur un artifice composé de 60 mg de composition auto-initiatrice comprimée sous 1000 bars et confinée dans un étui en aluminium, les lèvres de l'étui ayant été rabattues sur un paillet en aluminium en appui sur la composition. L'artifice a au préalable séjourné 48 heures dans une étuve à 120 °C.
• T'3 : déterminée sur un artifice composé de 60 mg de composition auto-initiatrice comprimée sous 1000 bars et confinée dans un étui en aluminium, les lèvres de l'étui ayant été rabattues sur un paillet en aluminium en appui sur la composition. L'artifice a au préalable séjourné 48 heures dans une étuve à 140 °C.
• T'4 : déterminée sur 50 mg de composition auto-initiatrice comprimée sous 200 bars et confinée dans un initiateur électrique de type GTMS tout à fait hermétique, sans volume libre. Un initiateur de ce type peut être introduit dans un générateur de gaz afin d'y assurer une fonction d'auto-initiation.
• T'5 : déterminée sur 50 mg de composition auto-initiatrice comprimée sous 200 bars et confinée dans un initiateur électrique de type GTMS tout à fait hermétique, sans volume libre. L'initiateur a au préalable séjourné 48 heures dans une étuve à 120 °C.

La mention "NF" signifie que l'artifice ou l'initiateur GTMS n'a pas fonctionné durant une épreuve de type « Slow Heat Test » décrite ci-dessus.Temperatures T'1 to T'5 (expressed in ° C) 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 ° 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 self-initiating composition compressed under 1000 bar and confined in an aluminum case, the lips of the case 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 self-initiating 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 ° C.
• T'3: determined on a device composed of 60 mg of self-initiating 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. The device has previously stayed 48 hours in an oven at 140 ° 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.

The results of measurements carried out on compositions compressed at 1000 bar and confined in cases with aluminum walls (T'1 to T'3) are very close to what would occur with the same devices introduced into gas generators during a "Slow Heat Test".

Determination of the energy of combustion:

E _c : combustion energy of the self-initiating composition, measured by means of a calorimeter, expressed in cal.g ^-1 (cal.g ^-1 = 4.186 g J ^-1 ). Tests 13, 14, 16, 21 and 52-54 demonstrate the advantage of combining reducing agents having a catalytic activity, such as manganese, with 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 mixtures thereof are used as the only reducing agents. Zirconium can be substituted or combined with Ti, TiH ₂ , ZrH ₂ , Fe or Al to produce similar effects.

Stability tests :

The word "Fire" means that the self-initiating composition has functioned unexpectedly under 120 ° C or 140 ° C, during the environmental test (stability test under 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 under 107 ° C for 408 hours, particularly restrictive, is reserved only for qualifications of self-initiated compositions already developed. For the sake of saving time, shorter tests under higher temperatures were used during the development phases: 120 ° C or 140 ° C / 48 hours for self-initiating compositions arranged in fireworks, 140 ° C / 15 hours for auto compositions -initiators little confined, to cause possible degradation of said compositions. Obtaining similar self-initiation temperature values before and after these environmental tests proves a high stability of the self-initiating composition under consideration. For the DSC tests, a self-initiation temperature difference of more than 30 ° C between the two values is unsatisfactory and reflects a reduction of the reaction energy. For Slow Heat Test, a deviation greater than 10 ° C in one direction or the other is an index of stability failure. The 120 ° C / 48 hours test performed on a device is roughly equivalent to several hundred hours under 107 ° C and makes it possible to predict with a high probability the behavior of the self-initiating composition contained in a fireproof device. environment 107 ° C / 408 hours. A lack of inadvertent operation of the device during the test 140 ° C / 48 hours is very satisfactory. Thus, obtaining a value of the self-initiation temperature T'3 slightly modified with respect to T'1 proves a high stability of the self-initiating composition, well beyond the 107 ° C test. / 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.

The groups A, B, C and D were sorted in ascending order of the temperature T'1, measured during a test of the "Slow Heat Test" type, a severe test that has the advantage of involving a mass of relatively large composition (60 mg), a high compression ratio (1000 bar) and a confinement ensured by a holster with aluminum walls.

Group A comprises compositions having a temperature T'1 of less than 125 ° C, i.e. compositions having a self-initiation temperature 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 composition No. 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 bars), 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 ° 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 comprises compositions having temperatures T'1 of between 150 and 220 ° C which have satisfied different stability tests. Compositions containing manganese, cobalt or copper which have temperatures T'1 of between 150 and 180 ° C including 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 (tests 13, 14, 52, 54) 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.

The compositions of groups E, F, G and H were sorted in order of increasing temperature T1.

Group E comprises compositions which have a T1 temperature (bulk) of between 170 and 196 ° C. These compositions are strongly degraded during environmental tests at 140 ° C./15 hours in a crucible as revealed by the DSC tests: ΔT ₃₂ ∈ [40; 178] ° C. This group includes compositions containing vanadium, chromium, CuO-associated tungsten or MoO ₃ -massed titanium hydride, molybdenum / silver nitrate / guanidinium nitrate compositions, and chlorate compositions. potassium / lactose optionally comprising boron. These compositions are too unstable for use in compressed form and under confinement (tests 29-31).

Group F, which includes comparative test No. 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 are resistant to the test of environment 140 ° C / 15 hours in a crucible as revealed by the DSC tests: ΔT ₃₂ ∈ [-6; 15] ° C. This group comprises compositions containing aluminum, iron, nickel, zirconium, but also compositions azodicarbonamide / potassium chlorate optionally comprising boron, and a 5-aminotetrazole / potassium chlorate composition. 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 ° 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) or TPP (titanium, potassium perchlorate), well known to those skilled in the art, are widely used in the electric initiators with compressed pyrotechnic layers for initiating gas generators for airbags (references). But ZPP, THPP, or TPP compositions have self-initiation temperatures above 380 ° C and therefore can not meet the set target. Copper oxide and especially molybdenum oxide lower their self-initiation temperatures (tests 47, 48). A high proportion of molybdenum powder (20%) makes it possible to lower the self-initiation temperature from 513 ° C. to 424 ° C. (tests 46 and 49). The replacement of potassium perchlorate with sodium chlorate reduces the autoignition temperature from 507 ° C (test 48) to 330 ° C (test 44). The addition to the composition of test 49 (ZPP) guanidinium nitrate also achieves a self-initiation temperature of the order of 330 ° C (test 45). The effect of replacing potassium perchlorate in a ZPP composition with an alkali metal chlorate combined with the addition of guanidinium nitrate was not predictable. Both actions have a cooperative effect. Thus, the compositions of Zr / KClO ₃ / guanidinium nitrate (tests 19, 22, 40) and Zr / NaClO ₃ guanidinium nitrate (test 15) have self-initiation temperatures T1 of the order of 200.degree. 220 ° C. The combustion energy expressed in cal.g ^-1 in Table 1 is obtained in Jg ^-1 by multiplying the value in cal.g ^-1 by 4.1868. Table 2 groups together the tests of Table 1 corresponding to reducing agent / potassium chlorate / guanidinium nitrate and optionally metal oxide, without binder or silica (including Comparative Test No. 35), which make it possible to 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).

Thus, new self-initiating compositions having self-initiation temperatures ranging from 130 to 220 ° C, more preferably from 150 to 200 ° C and more preferably 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 150-180 ° C, satisfactory stability, are not ignited during prolonged storage (48 hours) at 120 ° C and operate without much difference in autoignition temperature after this environmental test. The 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 ° C with satisfactory stability.

In general, the self-initiation temperature, for a given temperature rise rate, may be adjusted, preferably from 130 to 220 ° C, more preferably from 150 to 200 ° C and more preferably from 150 to 200 ° C. 180 ° 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.

Specific surfaces :

Tableau 3 Constituant Fe Mn W Mo Ti Si Ni Co TiH₂ Cu Cr Zr V Al B MoO₃ CuO Surface spécifique 0,11 0,19 0,28 0,35 0,39 0,5 0,53 0,58 0,79 0,9 1,12 1,2 1,83 10,5 22 35 43 The specific surfaces of the various constituents employed (reducing agents and metal oxides) are presented in Table 3. They are expressed in m ² · g ^-1 and were determined according to the BET method. This table reveals that there is no correlation between the activity of a reducer (comparison at the temperature T1) and its specific surface. In particular, molybdenum has one of the weakest specific surfaces while it has the strongest influence on the self-initiation temperature of the compositions. In contrast, the high activity of boron may be due in part to its high specific surface area.

<b> Table 3 </ b> Component Fe mn W MB Ti Yes Or Co TiH ₂ Cu Cr Zr V al B MoO ₃ CuO Specific surface 0.11 0.19 0.28 0.35 0.39 0.5 0.53 0.58 0.79 0.9 1.12 1.2 1.83 10.5 22 35 43

Claims (23)

1. Electrical initiator containing an envelope, a resistive element and at least one charge, characterized in that it uses a self-initiating composition as charge, said self-initiating composition comprising a main formulation which contains:

   - 20 to 80 mass % of at least one alkali metal chlorate,

   - 5 to 50 mass % of at least one energetic organic compound,

   and characterized in that the energetic organic compound is selected from guanidine nitrate, aminoguanidine nitrate, diaminoguanidine nitrate (DAGN), triaminoguanidine nitrate (TAGN), nitroguanidine nitrate, methylguanidine nitrate, 5-aminotetrazole, 5-aminotetrazole nitrate, triaminoguanidinium 5-aminotetrazolate, bis tetrazole, bis tetrazole amine, 5,5' bis(guanidinium)azotetrazolate (GZT) and 3-nitro-1,2,4-triazol-5-one (NTO),
   and in that the main formulation also contains:

   (a) 0 to 60 mass % of at least one metal or metalloid selected from boron, manganese, cobalt and copper,

   (b) 0 to 60 mass % of at least one metal or metal hydride selected from zirconium, titanium, TiH₂, ZrH₂, aluminium, silicon and iron,

   (c) 0 to 50 mass % of at least one transition metal oxide,

   the mass percentages being expressed in relation to the main formulation mass and the mass percentages of component (a) and component (c) which cannot simultaneously be equal to zeros.
2. Electrical initiator according to claim 1, characterized in that the main formulation contains a single energetic organic compound, guanidine nitrate.
3. Electrical initiator according to any one of claims 1 and 2, characterized in that said transition metal oxides are selected from MoO₃ and CuO.
4. Electrical initiator according to claim 3, characterized in that said transition metal oxides are in the form of powder with a particle size ranging from 1 to 100 nm, preferably from 3 to 30 nm.
5. Electrical initiator according to any one of the above claims, characterized in that said alkali metal chlorates are selected from potassium chlorate and sodium chlorate.
6. Electrical initiator according to any one of the above claims, characterized in that said self-initiating composition comprises a binder.
7. Electrical initiator according to claim 6, characterized in that said self-initiating composition contains 1 to 10 mass % of a binder, this percentage being expressed in relation to the main formulation mass.
8. Electrical initiator according to either of claims 6 and 7, characterized in that the binder is a fluorinated elastomer such as Viton®.
9. Electrical initiator according to any one of the above claims, characterized in that said self-initiating composition contains a mass quantity ranging up to 1%, preferably from 0.2 to 1% of ultrafine silica, this percentage being expressed in relation to the main formulation mass.
10. Electrical initiator according to any one of the above claims, characterized in that said self-initiating composition comprises a main formulation containing:

    - 25 to 70 mass % of at least one alkali metal chlorate,

    - 10 to 40 mass % of at least one of said energetic organic compounds,

    (a) 0 to 40 mass % of at least one metal or metalloid selected from boron, manganese, cobalt and copper,

    (b) 0 to 40 mass % of at least one metal or metal hydride selected from zirconium, titanium, TiH₂, ZrH₂, aluminium, silicon and iron,

    (c) 0 to 35 mass % of at least one transition metal oxide,

    the mass percentages being expressed in relation to the main formulation mass.
11. Electrical initiator according to any one of claims 1 to 9, characterized in that said self-initiating composition comprises a main formulation containing:

    - 5 to 60% of manganese, cobalt, copper or mixtures thereof, preferably 5 to 40%, better 5 to 20%,

    - 0 to 60% of zirconium, titanium, TiH₂, ZrH₂, iron, silicon, aluminium or mixtures thereof, preferably 0 to 40%, better 10 to 35%,

    - 5 to 50% of guanidine nitrate, better 10 to 40%,

    - 25 to 70% of potassium chlorate, better 25 to 50%, and characterized in that said main formulation also contains:

    - 2 to 8% of a fluorinated elastomer binder such as Viton®,

    - 0 to 1% of ultrafine silica,

    the percentages being expressed in relation to the main formulation mass.
12. Electrical initiator according to any one of claims 1 to 9, characterized in that said self-initiating composition comprises a main formulation containing:

    - 2 to 25% of boron, better 2 to 15%,

    - 0 to 60% of zirconium, titanium, TiH₂, ZrH₂, iron, silicon, aluminium or mixtures thereof, better 0 to 40%,

    - 5 to 50% of guanidine nitrate, better 10 to 40%,

    - 25 to 80% of potassium chlorate, better 25 to 70%, and characterized in that said main formulation also contains:

    - 2 to 8% of a fluorinated elastomer binder such as Viton®,

    - 0 to 1% of ultrafine silica,

    the percentages being expressed in relation to the main formulation mass.
13. Electrical initiator according to any one of claims 1 to 9, characterized in that said self-initiating composition comprises a main formulation which contains:

    - 20 to 60% of zirconium, titanium, TiH₂, ZrH₂, iron, silicon, aluminium or mixtures thereof, better 20 to 50%,

    - 5 to 50% of guanidine nitrate, better 10 to 40%,

    - 25 to 70% of potassium chlorate, better 25 to 50%,

    - 0.5 to 50% of transition metal oxides such as MoO₃ or CuO, better 0.5 to 35%, and characterized in that said main formulation also contains:

    - 2 to 8% of a fluorinated elastomer binder such as Viton®,

    - 0 to 1% of ultrafine silica,

    the percentages being expressed in relation to the main formulation mass.
14. Electrical initiator according to any one of the above claims, characterized in that said self-initiating composition is in compressed form, with a compression rate ranging from 50 to 500 bars.
15. Electrical initiator according to any one of claims 1 to 13, characterized in that said self-initiating composition is in the form of pellets without packaging with a compression rate ranging from 500 to 3000 bars or in preferably metal cases with a compression rate ranging from 200 to 2000 bars.
16. Electrical initiator according to any one of the above claims, characterized in that said self-initiating composition is stable at a temperature of 107°C during 408 hours or 90°C during 1000 hours.
17. Electrical initiator according to any one of the above claims, characterized in that said self-initiating composition has a self-initiation temperature ranging from 130 to 220°C, preferably ranging from 150 to 180°C.
18. Electrical initiator according to any one of the above claims, characterized in that the self-initiating composition is used as primary charge.
19. Electrical initiator according to any one of the above claims, characterized in that the self-initiating composition is used as additional charge.
20. Electrical initiator according to any one of the above claims, characterized in that it constitutes a hermetic electrical initiator with compressed pyrotechnic layers.
21. Gas generator containing a gas generating composition, characterized in that it also contains an electrical initiator according to any one of claims 1 to 20.
22. Gas generator containing an electrical initiator, a gas generating composition and at least one booster charge, characterized in that it uses an electrical initiator according to any one of claims 1 to 20 and in that said self-initiating composition is used as booster charge.
23. Gas generator containing an electrical initiator, a gas generating composition and at least one booster charge, characterized in that it uses an electrical initiator according to any one of claims 1 to 13 and in that said initiator uses said self-initiating composition in non-compressed form, loose in said electrical initiator or compartmentalized in preferably metal cases and in that said self-initiating composition is used as booster charge.