WO2011135262A1

WO2011135262A1 - Gas-generating pyrotechnic compound and production process

Info

Publication number: WO2011135262A1
Application number: PCT/FR2011/050964
Authority: WO
Inventors: Frédéric MARLIN; Stéphane BESOMBES
Original assignee: Sme
Priority date: 2010-04-29
Filing date: 2011-04-28
Publication date: 2011-11-03
Also published as: FR2959508B1; FR2959508A1; EP2563746A1

Abstract

The present invention relates to gas-generating pyrotechnic compounds and also to a process for obtaining same. Said compounds may be obtained continuously by extrusion and have a composition which contains, in a crosslinked oxygen-containing hydrocarbon binder, an oxidizing charge: - said oxidizing charge comprising a main oxidizing charge constituted of at least one inorganic perchlorate (main oxidizing charge which represents from 64 to 93.5% by weight of the total weight of the composition) and, for at most 10% by weight (of the total weight of the composition), a complementary oxidizing charge constituted of at least one nitrate chosen from alkali and alkaline-earth metal nitrates; - said crosslinked oxygen-containing hydrocarbon binder having been obtained by crosslinking an elastomer in the presence of at least one crosslinking agent and at least one oxygen-containing hydrocarbon plasticizer of said elastomer; said elastomer, preferably chosen from polyesters and polyacrylates, having a molecular weight greater than 200 000 and said at least one oxygen-containing hydrocarbon plasticizer being chosen from plasticizers for which the molecular weight is greater than 350 g/mol and the oxygen balance is greater than or equal to ‑280% and less than or equal to ‑235%, and mixtures thereof; and, - said composition does not contain a nitrogen-containing organic compound.

Description

Pyrotechnic gas generating compound; process of obtaining

The present invention relates to pyrotechnic compounds gas generators and a method for obtaining them. Said pyrotechnic compounds present:

a high inflating power (the intrinsic inflation power of a formulation is given by the product of the gaseous molar yield of said formulation (in mol / kg) by the temperature T (in K) .This product is equivalent to the product of the pressure times the volume and therefore reflects the ability of a formulation to generate a quantity of gas);

a high inflating surface flow rate (the inflation surface flow rate is estimated by the product pxnx T x Vc, where p is the density of the material (in g / cm ³ ), n the molar gas yield of the combustion (in mole / g), T the combustion temperature (in K) and Vc the combustion rate in cm / s Thus, the inflation surface flow rate parameter is expressed in mol.K / cm ² .s); and

- Good resistance to long-term aging at high temperature. They meet the stringent tests imposed by car manufacturers (aging of 3000 h at 110 ° C).

Moreover, the combustion of said pyrotechnic compounds generates few condensed particles.

The present invention is in the technical field of pyrotechnic generation of gas. It is particularly applicable in vehicle occupant protection systems, protection by means of damping cushions (so-called "airbags"), which are inflated by the combustion gases of pyrotechnic compounds.

• The technical field of airbags inflated by gas generators including pyrotechnic compounds based on pyrotechnic compositions has known for the last twenty years a very important boom. This field is now mature and the majority of systems produced and sold rely on formulations with strong similarities. The pyrotechnic compositions used in these systems are so-called "cold" compositions whose combustion temperature is generally between 1800 and 2200 K. The use of this type of composition has the following advantages:

the low temperature makes it possible to limit the thickness of the bag;

- the gaseous effluents are generally of good quality vis-à-vis the acceptable toxicity standards in force in the field (USCAR).

These compositions, on the other hand, have drawbacks that can penalize certain applications:

- The gas yield is generally low. The necessary mass of product is therefore important;

the temperature being relatively low and the gas yield low, the inflation power is limited;

- combustion emitting solid residues, filters are necessary to reduce the emission of particles. These filters further reduce the inflation power due to the thermal losses they induce. The filters further induce an increase in the volume and cost of the generator;

- The "cold" compositions have, in almost all cases, low combustion rates. This cumulative point at low inflation power induces low inflation surface flow rates. These low inflation surface flow rates are compensated for by the use of thin pellets and small diameters which induce a strong initial surface of pyrotechnic product and a low loading density.

In general, the high initial "cold" product surface at low combustion speed induces, in addition to the aforementioned drawbacks, the following difficulties:

- the combustion of the product starts slowly and a strong ignition charge is necessary;

- Small pellets, necessary to obtain the flow over the duration of the combustion, induce a high flow at the start and therefore a high pressure rise at the beginning of combustion in the bag. This is damaging for said bag in the first milliseconds, when it is folded and said bag is therefore strongly subjected to positioning constraints in the deployment phase;

the combustion of pellets with a decreasing surface evolution induces a decrease in the flow rate as the combustion progresses while the functional need is on the contrary a constant or increasing flow over time.

The inflation power of a composition being associated with the gaseous molar yield and temperature, the compositions having a high inflation power have a high combustion temperature and a low level of particles produced during combustion. The low level of particles is necessary to have the maximum amount of gas emitted and so as to avoid aggression on the bags. Tests in airbag modules have indeed shown that the damage of the bags by the combustion products is exacerbated by the presence of particles in case of use of "hot" compositions.

For all of the above reasons, a composition with a high inflating power, a high inflating surface flow rate and no particles has many advantages with respect to the operation and miniaturization of airbag system gas generators. This miniaturization is required for reasons of cost, weight and integration inside the vehicles.

Compounds obtained from extrudable, solvent-free, high-inflation compositions have already been employed in airbag systems. Such double base compositions containing nitrocellulose and nitroglycerin have been used in the 1990s as monolithic blocks. Details of dual base propellant formulations and compounds can be found in the Davenas 'Solid Propellant Technology' publication, Masson 1989 edition, and an example of use of these compounds can be found in patent application FR 2 853 872. The formulations have a high gaseous yield, a relatively high combustion temperature and a low particle level, tests conducted in airbag modules with these compounds have shown that the operation can be good in relatively thin uncoated bag (~ 470 The aggression on the bag is acceptable despite the high temperature due to the low level of particles produced and because of the operation induced by the monolithic block which limits aggression on the bag at the beginning of deployment. However, they are no longer used on new equipment because they do not have sufficient resistance (resistance) to aging at high temperature, such as as required by the builders automobiles. In addition to the problem of aging in temperature, these compounds have an oxygen balance shifted to negative values (oxygen deficiency) which induces a carbon monoxide level well above the maximum standards in force for the application in question. The oxygen balance is the mass percentage of oxygen released (positive value) or absorbed (negative value) during the combustion reaction of a constituent. By way of example, a CH ₂ group, the basic element of aliphatic polymers, has an oxygen balance of 343%. Indeed, it takes three oxygen atoms whose molar mass is 48 g to balance the combustion of 14 g / mole of CH ₂ .

To overcome these difficulties, compositions based on silicone binder were then proposed. Compositions based on binder "RTV" ("room temperature vulcanizable") and potassium perchlorate have been described in patent applications FR 2 190 776 and FR 2 213 254. Patent application FR 2 728 562 describes a version improved of these products, manufacturable by a process of kneading and continuous extrusion. In the latter document, the silicone binder is combined with a mixture of ammonium perchlorate and sodium nitrate; said sodium nitrate serving as a chlorine sensor. The compositions according to these documents exhibit an acceptable gas yield, a high combustion temperature and a high rate of combustion. The inflating surface flow rate is therefore relatively high. In addition, compared to compositions based on nitrocellulose and nitroglycerine, these compositions have the advantage of being very stable in temperature and can be adjusted to "oxygen balance" (balance oxygen) to meet the standards of toxicity of gaseous effluents. However, these compositions have the disadvantage of emitting a high level of particles (approximately 37% by weight of the total mass emitted during combustion), in particular sodium chloride and silica, which requires the use of a bag having a high thickness and a protective coating of the inner face of said bag.

The patent application EP 1 216 977 describes a solvent-free extrudable composition essentially comprising a two-component oxygenated hydrocarbon binder (an elastomer (a rubber) and a plasticizer), a nitrogen-containing organic compound (nitrogen generator) and oxidizing charges. Said oxidizing charges consist of ammonium perchlorate and a chlorine sensor. Said chlorine sensor, as its name indicates, is present to capture the chlorine gas emitted during the combustion of ammonium perchlorate. It intervenes, for this purpose, high content (about 15 to 20% by weight in the composition). It consists advantageously of sodium nitrate and sodium chloride (solid) is then formed. This composition has an inflation power and a surface flow of the same order of magnitude as the silicone bases, due to a slightly lower combustion rate and a lower particle rate. Despite said low level of particles and the presence of the nitrogenous organic compound, the gas yield, and therefore the inflation power, is limited by the presence of the chlorine sensor (which thus induces the formation of a solid salt). The overall content of solid combustion residues of these compositions is about 14%. The burning rates of these compositions, from about 20 to 40 mm / s at a combustion pressure of 20 MPa, remain insufficient for the intended application. In addition, the high pressure exponent of these compositions, from about 0.63 over the pressure range 15 MPa to 35 MPa, makes it difficult to adjust the ballistic operation of said gas generator compositions. The combustion of these compositions at low pressure (P <10 MPa) is also not satisfactory and can lead to extinctions. Finally, these compositions do not exhibit, with reference to the severe tests mentioned above, long-term aging behavior at a satisfactory high temperature.

In an attempt to overcome the disadvantages of the compositions described in patent application EP 1 216 977, the Applicant has, in the past, proposed, in the patent application WO 2008/145935, compositions containing, in a binder, an oxidizing charge which comprises at least one inorganic perchlorate and which does not include a chlorine sensor. These compositions may contain a nitrogenous organic compound, such as guanidine nitrate (NG). These compositions, free of chlorine sensor, therefore have the disadvantage of emitting hydrogen chloride (the level of hydrogen chloride emitted is about 0.2 g / g), which, at the end of combustion, condenses with the water formed during said combustion. Said condensed hydrogen chloride can then be captured by the bag. In order to limit the diffusion of said chloride Hydrogen in the passenger compartment of the vehicle, the bag can conveniently be coated with chlorine sensors. The absence of the oxidizing charge represented by the chlorine sensor is, within these compositions, compensated by the presence, in the composition of the binder, of a highly oxygenated hydrocarbon plasticizer having an oxygen balance greater than or equal to 230%. These compositions have a high swelling power, a low particle level, a high rate of combustion, from about 40 to 50 mm / s at 20 MPa, a low pressure exponent, about 0.5 over the pressure range 15 to 15 MPa. 35 MPa and good operation at low pressure. These compositions, however, require the use of highly oxygenated hydrocarbon plasticizers, of the diester type, more particularly of diester type plasticizers with ether functions. Most of these plasticizers are manufactured by trans-esterification from precursor compounds, which consist for the most part of a mixture of compounds of various molecular masses, so that the plasticizer itself consists of a mixture of compounds of various molecular masses in which are present compounds of more or less low molecular weight. The use of such plasticisers then require, for the applications under consideration, a purification step in order to eliminate these compounds of low molecular weight (detrimental to the thermal stability of the final product). In some cases, the addition of stabilizing additives (antioxidant type) is also required to inhibit the degradation mechanisms to which plasticizers containing ether functions may be subject. These steps significantly increase the cost of the plasticizer, which is undesirable. Furthermore, the compositions according to said application WO 2008/145935 do not show, either, with reference to the severe tests mentioned above, a good long-term aging behavior at high temperature.

In a context where it is now accepted that the compositions can be free of chlorine sensor, the skilled person is always looking for compositions with high combustion temperature, generating little particles (in order to increase the inflation capacity and the inflating surface flow rate, so as to reduce the volumes, masses and costs of gas generators for airbag system) and toxic effluents (by a balance value in oxygen close to 0), having a high combustion rate and good low-pressure combustion, a moderate pressure exponent, a satisfactory long-term aging behavior at high temperature, with reference to the severe tests mentioned above, these compositions being capable of advantageously be shaped by extrusion without solvent, which allows the realization of monolithic form facilitating loading, improving the loading density of the generator.

Starting from the teaching of the applications EP i 216 977 and WO 2008/145935, the inventors wished to propose improved pyrotechnic gas generating compounds. In particular, they have set themselves the goal;

to conserve the gas yield and the combustion properties of the compounds of application WO 2008/145935;

- to limit the rate of particles emitted (solid combustion residues); to improve the resistance to long-term aging at high temperature;

while substituting for the highly oxygenated hydrocarbon plasticizers (diester type with ether functions) compounds of the patent application

WO 2008/145935, less oxygenated hydrocarbon plasticizers, free of ether function (see the oxygen balance values indicated below), such as those of the application EP 1 216 977, easier to implement.

The fixed improvement objective has been achieved. The inventors currently propose high-performance pyrotechnic compounds, with reference to the specification above, pyrotechnic compounds that perform better than the compounds of applications EP 1 216 977 and

WO 2008/145935 and that it is possible to obtain more easily than the compounds of the application WO 2008/145935.

The pyrotechnic compounds of the invention (solid compounds) have a composition of the type of that of the compounds according to the application

EP 1 216 977, in that it contains:

an oxidizing charge comprising a main oxidizing charge consisting of at least one inorganic perchlorate (advantageously ammonium perchlorate) and a complementary oxidizing charge consisting of at least one nitrate chosen from alkaline and alkaline-earth nitrates (advantageously nitrate); sodium and / or nitrate potassium and / or strontium nitrate, most preferably sodium nitrate);

in a crosslinked oxygenated hydrocarbon binder obtained by crosslinking an elastomer (of the gum type according to EP 1 216 977) in the presence of at least one crosslinking agent and at least one oxygenated hydrocarbon plasticizer of said elastomer. The plasticizer (s) is (are) obviously perfectly miscible (s) in the elastomer, so as not to exude temperature and thus lower the glass transition temperature of said elastomer.

Characteristically, within the composition of said compounds of the invention:

said main oxidizing charge represents from 64 to 93.5%, advantageously from 72 to 82% by weight;

said complementary oxidizing charge does not represent more than 10% by mass;

no nitrogenous organic compound is found; and

said elastomer, preferably chosen from polyesters and polyacrylates, has a molecular weight greater than 200,000 and said at least one oxygenated hydrogenated plasticizer is chosen from plasticizers, whose molecular mass is greater than 350 g / mol (its tension Steam remains sufficiently low at 120 ° C (to limit or even avoid any problem of evaporation, migration ...)) and the oxygen balance equal to or greater than -280% and less than or equal to -235% , and their mixtures.

The pyrotechnic compounds of the invention differ from the compounds according to the application EP 1 216 977 in that their composition contains a reduced level of alkaline and / or alkaline earth nitrate and does not contain any nitrogenous organic compound. Moreover, the nature of the plasticisers present is specified.

The pyrotechnic compounds of the invention differ from the compounds according to the application WO 2008/145935 in that their composition contains a complementary oxidizing charge consisting of at least one nitrate chosen from alkaline and alkaline earth nitrates and does not contain a very high plasticizer. oxygen.

The pyrotechnic gas-generating compounds of the invention therefore contain, in their composition, from 64 to 93.5%, preferably from 72 to 82% by weight (% by weight relative to the total weight of said compounds) of at least one inorganic perchlorate.

The pyrotechnic gas-generating compounds of the invention thus contain, in their composition, only a low level of complementary oxidant (s) (not more than 10% by weight), a low level of at least one nitrate selected from alkaline nitrates and alkaline earth nitrates. The function of the said additional oxidizing agent (s) is to allow the equilibrium of the oxygen balance of the composition which does not contain a highly oxygenated plasticizer. Said at least one additional oxidant (nitrate) introduced into the composition of the compounds of the invention also incidentally plays the role of a chlorine sensor and makes it possible to reduce, even at a low level, the amount of chlorine gas produced by the combustion.

The at least one nitrate chosen from alkaline nitrates and alkaline earth nitrates (advantageously from alkaline nitrates) is generally chosen from sodium, potassium and strontium nitrates and their mixtures. It consists advantageously of sodium nitrate and / or potassium nitrate, very advantageously sodium nitrate.

The additional oxidizing charge (= said at least one nitrate selected from alkali and alkaline earth nitrates) represents at most 10% by weight of the total mass of the compound. It advantageously represents from 0.5 to 10%, very advantageously from 3 to 7% by weight of said total mass of the compound.

Surprisingly, the objective of improvement fixed (see above) - to propose compounds with particular ballistic properties (see more particularly their pressure exponent) and an interesting gas yield, likely to be obtained by a method of good technical feasibility - has been achieved by introducing, at low level, the additional oxidizing charge specified above in the composition of the compounds of the invention. In a context where it was now accepted that the presence of a chlorine sensor is not required, the presence of a low level of a complementary oxidizing charge type chlorine sensor and the beneficial effects of said presence were in no way obvious. The pyrotechnic gas-generating compounds of the invention do not contain, in their composition, nitrogenous organic compound (nitrogenous organic compound present in the compositions of the application EP 1 216 977 and in those exemplified of the application WO 2008/145935, such as guanidine nitrate). This is particularly advantageous with reference to their thermal stability. Said compounds of the invention in fact support aging of 3000 hours at 110 ° C. The inventors have in fact shown the detrimental influence of guanidine nitrate on the thermal stability of the pyrotechnic compounds of the invention. This harmful influence was not expected. Thus, it is known that pelletized compositions based on guanidine nitrate (NG) combined with basic copper nitrate (BCN) or in combination with basic copper nitrate (BCN) and with potassium perchlorate exhibit a certain behavior. at aging in temperature quite satisfactory.

The crosslinked oxygenated hydrocarbon binder of the compounds of the invention therefore associates with a particular elastomer at least one specific plasticizer. It is not a highly oxygenated plasticizer in the sense of the application WO 2008/145935 (it is a plasticizer which has an oxygen balance between -280% and -235%: see above) . Surprisingly, within the compounds of the invention, the presence of a highly oxygenated binder has not proved indispensable and its absence has on the other hand proved positive on the resistance to long-term aging at high temperature.

Thus, surprisingly, the compounds of the invention, the composition of which does not contain any nitrogenous organic compound, does not contain a highly oxygenated plasticizer (-280% <OB <-235%) and only closes a low additional oxidizing agent (s)), have proved to be very efficient.

Said at least one oxygenated hydrocarbon plasticizer, having the required molecular weight and oxygen balance, is advantageously chosen from the family of aliphatic diesters (adipates, sebacates, azelates, etc.), aromatic diesters (phthalates, etc.) and aromatic triesters (trimellitates, etc.), esters containing only ester-type oxygen functions in their formula (esters without ether function). Said at least one oxygenated plasticizer is very advantageously chosen from;

dioctyl adipate (DOA) or di- (2-ethylhexyl) adipate (DEHA): molecular weight 370 g / mol, OB = -264%,

diisononyl adipate (DINA): molecular weight 398 g / mol,

OB = -269%

diisodecyl adipate (DIDA): molecular weight 426 g / mol, OB = -274%,

dioctyl sebacate (DOS): molecular mass 426 g / mol, OB = -274%,

dioctyl azelate (DOZ); molecular weight 412 g / mol, OB = -272%,

diisodecyl phthalate (DIDP): molecular weight 446 g / mol, OB = -269%,

dipropylheptyl phthalate (DPHP): molecular weight 446 g / mol, OB = -269%,

tri-n-hexyl trimellitate: molecular weight 462 g / mol, OB = -239%,

trioctyl trimellitate (TOTM): molecular weight 546 g / mol, OB = -255%,

tri- (heptyl, nonyl) trimellitate: molecular weight (average) 547 g / mol, OB = -255% (average value),

trimellitate of tri- (octyl, decyl): molecular mass (average) 588 g / mol, OB = -261% (average value),

mixtures of said esters with each other.

The nature of the second main component (plasticizer) of the crosslinked oxygenated hydrocarbon binder (binder = crosslinked elastomer + plasticizer) of the pyrotechnic compounds of the invention has above all been specifically specified. It is proposed hereinafter to give, in no way limiting, details on each of the constituents of said compounds and their respective amount of intervention.

The main oxidizing charge consists of at least one inorganic perchlorate. It represents from 64 to 93.5% by weight of the total mass of the compound, advantageously from 72 to 82% by weight of said total mass. It is the main constituent of the compounds of the invention.

Said main oxidizing charge advantageously comprises ammonium perchlorate. Said main oxidizing charge is very advantageously ammonium perchlorate. Said ammonium perchlorate is advantageously used in several granulometries so as to improve its incorporation and its distribution in the elastomer and to reduce the toxicity of the gaseous effluents during combustion.

The additional oxidizing charge has been described above.

The crosslinked oxygenated hydrocarbon binder generally represents from 6 to 20% by weight of the total mass of the compound. It advantageously represents from 8 to 16% by weight of the total mass. It comprises the crosslinked elastomer and said at least one oxygenated plasticizer. The elastomer in question is a high molecular weight elastomer: Mw> 200,000 g / mol. It is preferably chosen from the family of polyesters and polyacrylates. The polyacrylates may have reactive functionality of the chlorine / carboxyl, chlorine, hydroxyl or epoxy type. The polyesters may have hydroxyl-type reactive terminations. They advantageously have such hydroxyl-type reactive terminations. The elastomer present in the composition of the compounds of the invention has been crosslinked via its reactive functional groups by at least one crosslinking agent (= crosslinking agent). Suitable crosslinking agents are known to those skilled in the art. Thus, such a crosslinking agent, for the crosslinking of a polyester-type elastomer, advantageously consists of a diisocyanate or a triisocyanate.

In general: said at least one elastomer and said at least one crosslinking agent represent from 3 to 10% by weight, advantageously from 4 to 9% by weight, of the total mass of the compounds of the invention; and / or, advantageously and,

said at least one plasticizer represents from 3 to 10% by weight, advantageously from 4 to 8% by weight, of the total mass of said compounds.

In addition to the two components described above; the oxidizing charge

(main + additional) and the crosslinked oxygenated hydrocarbon binder (elastomer + at least one crosslinking agent + at least one oxygenated plasticizer), the compounds of the invention may comprise, in their composition, the following additional constituents;

at least one ballistic catalyst (which makes it possible, among other things, to improve the rate of combustion). The skilled person knows that such Ballistic catalyst consists of a transition metal oxide, with high specific surface area (which accelerates the decomposition of the oxidizing charge). A te! at least one ballistic catalyst is advantageously selected from copper oxide, iron oxide, manganese oxide, zinc oxide and cobalt oxide. Generally, such at least one ballistic catalyst is between 0 and 5%, advantageously between 2 and 4%, by weight within the compounds of the invention; and or

at least one wetting agent chosen from organosilanes and titanates. Such at least one wetting agent is advantageously chosen from vinyltris- (2-methoxyethoxy) silane, vinyltriethoxysilane, tris- (3-trimethoxysilylpropyl) isocyanurate, γ-methacryloxypropyltriethoxysilane, diethoxydiacetoxysilane, diacetoxydiethoxysilane and dibutoxyethoxymethylsilane. Such at least one wetting agent makes it possible to reduce the viscoelasticity and the residual porosity of the compound. Generally, such at least one wetting agent intervenes between 0 and 4%, advantageously between 0.2 and 3%, by weight within the compounds of the invention.

In view of the above, it has been understood that the mass composition of the compounds of the invention is generally:

64 to 93.5%, advantageously 72 to 82%, of a main oxidizing charge;

- 0.5 to 10%, advantageously 3 to 7%, of at least one nitrate selected from alkali and alkaline earth nitrates (additional oxidizing charge);

6 to 20%, advantageously 8 to 16%, of at least one crosslinked oxygenated hydrocarbon binder;

0 to 5%, advantageously 2 to 4%, of at least one ballistic catalyst; and

0 to 4%, advantageously 0.2 to 3%, of at least one wetting agent.

The constituents (main and additional oxidizing charges + crosslinked oxygenated hydrocarbon binder + any constituents chosen from those identified above) of the composition of the compounds of the invention, listed above, represent at least 95% by weight of said compounds, generally at least 98% (or 100%) by mass of the said compounds. The complement, if any, is generally composed of additives, such as auxiliaries (aids) manufacturing.

The compounds of the invention, of which the method of production is specified below, can be of different types. These are usually monolithic compounds that can be full, mono- or multi-perforated.

Said compounds are particularly effective. Their composition is high-yield gas (about 34 mol / kg) with combustion temperatures around 2950 K (it is indeed so-called "hot" compositions). Their burning rate is fast, about 55 mm / s at a pressure of 20 MPa. Because of their composition, they generate few solid particles (at a rate of less than or equal to 6%). Their composition is also likely, according to advantageous variants, to have an oxygen balance value between -1% and -3%, ie they do not generate toxic gas and they are quite suitable for a application in the field of airbags. The inflating surface flow rates of the compositions of the compounds of the invention are very interesting. They are about 975 mol.K / cm ² .s. Their resistance to aging at high temperature is very satisfactory.

The compounds of the invention generally have the disadvantage of emitting hydrogen chloride, the low rate of chlorine sensor introduced into the compound does not allow to trap all of the chlorine formed by combustion. At the end of combustion, said hydrogen chloride condenses with the water formed by the combustion and can be captured by the bag. The level of hydrogen chloride emitted by the compounds according to the invention is approximately 0.2 g / g. In order to limit the diffusion of hydrogen chloride into the passenger compartment of the vehicle, the bag can be coated with chlorine sensors. In addition, the composition being hot, in comparison with so-called "cold" compositions, the vents can be reduced so as to compensate for the deflation of the bag by cooling the gases, (taking into account the nature of the composition of the gases which contain 50 % of condensable (H ₂ 0) when the temperature decreases) so as to increase the capture rate by condensation of acidified water in the bag. After operation, the bag naturally deflates due to the drop in temperature and condensation of condensables. The process for obtaining the compounds of the invention is advantageously a method by analogy, as described in application WO 2008/145935. It is very advantageously a process carried out continuously, without solvent, in a twin-screw mixer-extruder.

More generally, said method comprises:

- implemented continuously, the solvent-free mixture of the oxidizing charges (main and complementary), the elastomer, the at least one crosslinking agent and the at least one plasticizer, optionally also at least one ballistic catalyst and / or at least one wetting agent and the extrusion of the dough resulting from said mixture;

- The heat treatment of said extruded paste to ensure the crosslinking of said elastomer.

As indicated above, said mixtures and extrusions are advantageously used in a twin screw mixer-extruder.

Said method advantageously comprises cutting the extruded paste in loadings and heat treatment of said loadings (crosslinked loadings = compounds of the invention).

In no way limiting, we can specify below an alternative embodiment of the method of the invention.

The twin-screw mixer-extruder includes a mixing and mixing chamber, a compression chamber and an extrusion head. The solid and liquid components are introduced into the mixing and kneading compartment by two different feed openings, a solids feed opening and a liquid feed opening, and then transported and kneaded. The homogeneous paste thus formed is degassed in the compression compartment, then extruded with the aid of an extrusion head in the form of rods, and finally, the rods thus formed are cut into loadings using an apparatus. cutting, then these charges are made to crosslink at a temperature generally between 100 ° C and 150 ° C.

The charges thus formed find their preferential application as a pyrotechnic charge in gas generators intended to inflate a protective cushion for occupants of a motor vehicle. Indeed, the burning rate of these loadings, as well as the rate of solid residues produced and the rate of carbon monoxide and nitrogen oxides produced are particularly suitable (see above).

It is now proposed to illustrate, in a non-limiting manner, the presently claimed invention.

FIG. 1 shows pressure curves, over time, pressure detected during combustion (after prior conditioning of the generator at 20 ° C.) of a sample of 14.5 g of compound according to (Example 1 of) the invention in a generator provided with a nozzle. The size of the nozzle

diameter of 8 mm for curve I

9 mm diameter for curve II

diameter of 9.5 mm for curve III

diameter of 10 mm for curve IV, and

diameter of 10.5 mm for curve V

allows to control the combustion pressure of the sample. These curves show that the combustion is stable at high pressure as at low pressure (see in particular curve V for pressures between 2 and 4 MPa).

The compositions of pyrotechnic compounds have been evaluated by means of thermodynamic calculations and physical measurements.

These compositions and compounds correspond to compositions and compounds of the prior art (compositions A and B hereinafter) or to a composition and a compound of the invention.

Composition A (prior art):

This composition, with binder, contains:

- 59% by weight of ammonium perchlorate,

- 21% by weight of sodium nitrate,

5% by weight of guanidine nitrate, and

- 15% by weight of acrylic elastomer, crosslinking agent and plasticizer (dioctyl adipate).

This composition is a composition according to patent application EP 1 216 977. It is extruded and crosslinked to generate compounds (block type). The oxygen balance of this composition is -2%. Its theoretical density is 1.7 g / cm ³ .

Its combustion temperature is about 2800 K at 20 MPa and its molar yield is 31.5 mol / kg at 1000 K and 1 bar.

The level of particles emitted is 16%.

Its pressure exponent is 0.63 between 15 MPa and 35 MPa.

The burning rate of the compounds (extruded) is 38 mm / sec at 20 MPa (see Table 1 below).

Composition B (prior art); It contains:

- 79.9% by mass of ammonium perchlorate,

6.2% by weight of acrylic elastomer + crosslinking agent,

6.4% by weight of DBEEEG (dibutoxyethoxyethoxyethyl glutarate: highly oxygenated plasticizer),

1% by weight of vinyltris- (2-methoxyethoxy) -silane,

- 5.5% by weight of guanidine nitrate, and

1% by weight of ferric oxide.

This composition is a composition according to patent application WO 2008/145935. It is extruded and crosslinked to generate compounds (block type). The oxygen balance of this composition is -2.3%. Its theoretical density is 1.73 g / cm ³ .

Its combustion temperature is about 3000 K at 20 MPa and its molar yield is 36.1 mol / kg at 1000 K and 1 bar.

The particle content is less than 2%.

Its pressure exponent is 0.5 between 15 MPa and 35 MPa.

Depending on the particle size of the charges used, the burning rate of the compounds (extruded) is between 40 and 50 mm / s at 20 MPa (see Table 1 below). Composition 1 of a compound of the invention;

The composition comprises:

- 79.7% by weight of ammonium perchlorate,

- 5.2% by weight of sodium nitrate,

7.6% by weight of acrylic elastomer + crosslinking agent,

4.8% by weight of plasticizer (dioctyl adipate)

0.6% by weight of vinyltris- (2-methoxyethoxy) silane,

2.1% by weight of ferric oxide.

This composition is extruded and crosslinked to generate compounds (block type).

The oxygen balance of this composition is -1%. Its theoretical density is 1.78 g / cm ³ .

Its combustion temperature is about 2960 K at 20 MPa and its molar yield is 34.3 mol / kg at 1000 K and 1 bar.

The particle ratio is about 5%.

Its pressure exponent is 0.5 between 15 MPa and 35 MPa.

Depending on the particle size of the charges used, the burning rate of the compounds (extruded) is between 50 and 60 mm / s at 20 MPa (see Table 1 below).

The performances of compositions A, B and 1 and those of the corresponding compounds are given in Table 1 below.

Most of the values shown in Table 1 are calculated values. Burning rates, pressure exponents, and porosities were measured on the compounds obtained from the compositions. The resistance to aging at high temperature of the compounds of the invention (having the composition 1) has moreover been tested. After aging for 3000 hours at 110 ° C., the mass loss of said compounds and their ballistic performance were measured. Said mass loss remains very limited (- 0.04%). Ballistic performance is unchanged. In support of this assertion, ballistic enclosure characterizations have shown that: the combustion rate Vc at 20 MPa of the compounds of the invention does not vary by more than 2% after aging, and

the pressure exponent on the pressure range between 15 MPa and 35 MPa of said compounds is about 0.44 after aging for about 0.50 before aging.

Table 1

The results of Table 1 above indicate that the volume of the composition of the compound of the invention is greater than that of the composition of EP 1 216 977 and close to that of the composition according to WO 2008/145935.

The composition of the compound of the invention has a balance in oxygen (-1%) better balanced than that of the compositions of the prior art, which is conducive to avoid the generation of toxic gases, such as carbon monoxide.

In addition, the higher rate of combustion of the compounds of the invention compared with those of the compounds of the prior art results in a higher inflation surface flow rate. With respect to the extruded blocks of composition A, the characteristic dimension of the object to be burned can be doubled to ensure an equivalent operating time. The extruded block made from the compositions of the invention can therefore be very compact and allow the development of small generators containing a low pyrotechnic mass.

The compounds of the invention have a low pressure exponent between 15 MPa and 35 MPa, equivalent to that of the composition B of the prior art.

Although the residue level obtained with the composition of the invention is (logically) higher than that obtained with the composition B of the prior art (without a chlorine sensor), it remains within acceptable values. Thus, gas generators employing the compounds of the invention may be, to some extent, devoid of particulate filters. In doing so, the thermal losses of the gases are reduced.

It should also be noted that the shaping of these compositions in the form of a monolithic block with a very high combustion rate makes it possible to achieve a low flow rate ignition, and this because of the small initial combustion surface of the block. The monolithic geometry of the loading also allows the design of shapes to deliver a progressive or constant flow.

A conductive gas generator containing a compound according to the invention 14 g emits 2.8 g of hydrogen chloride. In the unlikely absence of capture, the hydrogen chloride level is of the order of 700 ppm in a cabin of 2.8 m ³ .

Claims

A pyrotechnic gas generating compound, the composition of which contains, in a crosslinked oxygenated hydrocarbon binder, an oxidizing charge:

said oxidizing charge comprising a main oxidizing charge consisting of at least one inorganic perchlorate and a complementary oxidizing charge consisting of at least one nitrate chosen from alkali and alkaline earth nitrates;

- said crosslinked oxygenated hydrocarbon binder, having been obtained by crosslinking an elastomer in the presence of at least one crosslinking agent and at least one oxygenated hydrocarbon plasticizer of said elastomer;

characterized in that

said main oxidizing charge represents from 64 to 93.5%, advantageously from 72 to 82%, by weight of said composition;

said complementary oxidizing charge does not represent more than 10% by weight of said composition;

said composition does not contain any nitrogenous organic compound; and

said elastomer, preferably chosen from polyesters and polyacrylates, has a molecular weight greater than 200 000 and said at least one oxygenated hydrocarbon plasticizer is chosen from plasticizers, whose molecular mass is greater than 350 g / mol and the balance of oxygen equal to or greater than -280% and less than or equal to -235%, and mixtures thereof.

2. Compound according to claim 1, characterized in that said at least one oxygenated hydrocarbon plasticizer is chosen from aliphatic diesters, aromatic diesters, aromatic triesters and mixtures thereof; said diesters and triesters containing in their formula only oxygen functions of ester type.

3. Compound according to claim 1 or 2, characterized in that said at least one oxygenated plasticizer is chosen from:

dioctyl adipate,

di- (2-ethylhexyl) adipate

- diisononyl adipate,

- diisodecyl adipate,

- dioctyl sebacate, - dioctyl azelate,

- diisodecyl phthalate,

dipropylheptyl phthalate,

tri-n-hexyl trimellitate,

trioctyl trimellitate,

tri- (heptyl, nonyl) trimellitate,

tri-trimellitate (octyl, decyl), and

- their mixtures.

4. Compound according to any one of claims 1 to 3, characterized in that said main oxidizing charge consists of ammonium perchlorate.

5. Compound according to any one of claims 1 to 4, characterized in that said complementary oxidizing charge, which advantageously consists of sodium nitrate, represents 0.5 to 10%, advantageously 3 to 7%, by weight of the total mass of said compound.

6. Compound according to any one of claims 1 to 5, characterized in that said crosslinked oxygenated hydrocarbon binder represents 6 to 20%, preferably 8 to 16% by weight of the total mass of said compound.

7. Compound according to any one of claims 1 to 6, characterized in that said at least one elastomer and said at least one crosslinking agent represent from 3 to 10%, advantageously from 4 to 9% by weight of the total mass said compound; and / or, advantageously, and said at least one plasticizer represents from 3 to 10%, advantageously from 4 to 8% by weight of the total mass of said compound.

8. Compound according to any one of claims 1 to 7, characterized in that its composition also contains at least one ballistic catalyst, preferably selected from copper oxide, iron oxide, manganese oxide, zinc oxide and cobalt oxide.

9. Compound according to any one of claims 1 to 8, characterized in that its composition also contains at least one wetting agent selected from organosilanes and titanates, advantageously chosen from vinyltris- (2-methoxyethoxy) silane, vinyltriethoxysilane, tris- (3-trimethoxysilylpropyl) isocyanurate, γ-methacryloxypropyltriethoxysilane, diethoxydiacetoxysilane, diacetoxydiethoxysilane and dibutoxyethoxymethylsilane.

10. Compound according to any one of claims 1 to 9, characterized in that its composition comprises, expressed in percentages by weight:

From 64 to 93.5%, advantageously 72 to 82%, of a main oxidizing charge;

0.5 to 10%, advantageously 3 to 7%, of at least one nitrate chosen from alkali and alkaline earth nitrates;

0 to 5%, advantageously 2 to 4%, of at least one ballistic catalyst; and

0 to 4%, advantageously 0.2 to 3%, of at least one wetting agent.

11. Compound according to any one of claims 1 to 10, of monolithic type, solid, mono- or multi-perforated.

12. Process for obtaining a compound according to any one of claims 1 to 11, characterized in that it comprises:

- implemented continuously, the solvent-free mixture of said main and complementary oxidizing charges, said elastomer, said at least one crosslinking agent and said at least one plasticizer, optionally also said at least one ballistic catalyst and / or said at least one agent wetting and extruding the paste resulting from said mixture;

heat treatment of said extruded paste to ensure crosslinking of said elastomer.

13. Process according to claim 12, characterized in that said mixing and extrusion are carried out in a twin-screw extruder mixer.

14. The method of claim 12 or 13, characterized in that it comprises the cutting of the extruded paste in loadings and the heat treatment of said loadings.