MX2013002988A - Pyrotechnic gas generator compounds. - Google Patents

Abstract

The main subject of the present invention is a solid pyrotechnic gas generator compound, the composition of which contains, expressed as weight percentages: - from 60 to 70% of guanidine nitrate, - from 26 to 33%, advantageously 26 to 30%, of potassium perchlorate, - from 2.5 to 6% of at least one combustion modifier chosen from transition metal oxides, the precursors of such oxides and mixtures thereof, from 0 to 6% of at least one additive, and does not contain an explosive ingredient. Such a compound is particularly effective for the inflation of side airbags.

Description

i An object of the present invention are the gas-generating pyrotechnic compounds, suitable for use in systems for protecting the occupants of the motor vehicle; more especially for the inflation of air bags and more particularly for the inflation of the side airbags (see below). ' FIELD OF THE INVENTION The technical field in relation to the protection of the occupants of the motor vehicle has experienced a great expansion in the last twenty years. The latest generation of vehicles from now on integrates within the passenger compartment several security systems, of the air bag type, and the operation of which is carried out by the combustion gases of pyrotechnic compounds. Among air-bag-type systems, we mainly distinguish frontal air bags for frontal impacts and side air bags for lateral impacts.

BRIEF DESCRIPTION OF THE INVENTION Side air bag systems differ from bag systems | frontal air, essentially due to the time necessary for the deployment and positioning of the airbag. Typically, this time is shorter for a side air bag (around 10-20 ms, compared to 40-50 ms for front air bag). For a side air bag, the functional requirement i from . inflating the bag for a short time makes it necessary to resort to a pyrotechnic composition that have a combustion rate high enough (typically equal to or greater than 30 mm / s, or even 35 mm / s, at 20 MPa) over the operating pressure range in the combustion chamber of the generator, in order to obtain a sufficient value of the Cup of inflated per unit area (product p x n x Te x Ve). On the other hand, in order to guarantee a satisfactory start-up of the system, the pyrotechnic composition must also have good flammability characteristics. In addition, given the generally conical surface profile of the charges used (granule type), the composition should ideally have a stable combustion rate and high enough at low pressure. In fact, those experts are aware that the specifications of the side airbags are more restrictive than those of the frontal airbags. Of course, any technological advance in the field of side airbags can also be i advantageously available in the field of frontal airbags. : In the present text, the term, "low pressure" is used to define a pressure P such that: 0.1 = P < 10 Pa, the term "medium pressure" is used to define a pressure P such that: 10 MPa = P < 30 MPa and the term "high pressure" is used to define a pressure P such that: P > 30 MPa. 1 In addition, it is usual to compensate for the low combustion rates of the pyrotechnic compounds used in current gas generators for air bags by using charges composed of pellets with very small dimensions. Although it is not profitable due to the low production yield in weight of the I granulation machines and the tooling costs generated, this makes it possible, to some extent, to partially overcome the lack of combustion speed. However, this solution emphasizes two other disadvantages: difficult ignition, which increases due to the high initial surface of the load, which then requires the use of a reinforced lighter or the addition of an additional load that acts as an ignition relay; a strong reduction of the combustion surface due to the small size of the granules that create a long tail of low pressure combustion. This tail! long low pressure combustion is the source! of the emission of most of the toxic species present in the gases used to inflate 1 a bo 1 s a.

Therefore, it should be noted that the desired increase in the combustion rate of the pyrotechnic compound in question, on the The whole range of pressure, including at low pressure, is therefore necessary not only to increase the gas flow rate in order to meet the inflation delay specifications, but also to ensure the flammability of the composition without resort to the use of a relay load and the harmlessness of combustion products.

In addition, there are restrictions with respect to the combustion temperature.

In general, said temperature of I combustion should not be too high! (must at least stay at less than 2400 K, more i preferably less than 2350 K) so that the temperature of the gases in the airbag does not damage the physical integrity of the occupants. A low combustion temperature allows, on the one hand, to limit the thickness of the bag and, on the contrary, to simplify the design! of the gas generator making it possible to reduce the presence of deflectors and filters inside the generator.

The air bag systems on the Teral can include two types of gas generators: Those which are said to be entirely pyrotechnic (the generation of gas being provided exclusively by the combustion of a pyrotechnic charge) and those which are said to be "hybrids" (originating then the gases with i the combustion of a pyrotechnic charge and a volume of neutral gas stored under pressure in a leak-tight tank). For "hybrid" generators, the pyrotechnic charge must not have too low a combustion temperature for the combustion gases to be sufficiently hot to compensate for the drop in temperature, generated by the volume expansion of the precomprimed neutral gas. Ideally, combustion temperatures above 2000 K are required. 1 Thus, those skilled in the art are looking for pyrotechnic compounds that are suitable for use in fully pyrotechnic gas generators or in hybrid generators, especially intended for lateral air bumpers, that is, they have a moderate combustion temperature at the same time.

I of about 2000-2400 K, more preferably 2000-2350 K and a high rate of combustion over the entire operating pressure range (in particular greater than 30 mm / s at 20 MPa, more preferably greater than 35 mm / s at 20 MPa ), including at low pressure.

In addition, pyrotechnic compounds for air bags should also aim to jointly meet the following requirements: the gases generated by the combustion of the pyrotechnic charge (which comprises a compound or n compounds) must be non-toxic, that is to say, have a low content of carbon monoxide, of oxides of i nitrogen and chlorinated compounds; , the production of the gas (that is, the amount of gas generated by combustion) must be high to give rise to a high inflation power; ' the amount of solid particles generated by combustion must remain low, capable of constituting thermal foci that can damage the wall of the airbag; the exponent of the pressure should be as low as possible, in particular to i medium and high pressure (typically below 0. 35 as described in the prior art), I but also at low pressure. An exponent of low pressure in fact makes it possible to very significantly reduce the operating variability between the low temperature end (around -40 ° C) and the high temperature end (around 90 ° C) that are required in the field of use. As a result, operational reproducibility is improved i and the size of the metal structure of the generator can be advantageously reduced; - The pressure of the combustion of cut (its pressure of the limit of combustion) must also be as close as possible to the atmospheric pressure. i It is also highly desirable that the basic ingredients of the compounds are not dangerous from a pyrotechnic point of view. The presence of the ingredient (s) pertaining to the class of explosives,! as neither t roguanidine, hexogen (RDX) or octogen (HMX), it is advantageously avoided. The term "explosive ingredients" means ingredients classified in risk division 1.1 according to standard NF T 70-502 (see also UNO - Recommendations concerning the i transport of dangerous goods, test manuals and criteria, fourth edition i revised, ST / SG / AC.10 / 11 / Rev.4, ISBN 92-1-239083-8ISSN 1014-7179 and STANAG 4488). Guanidine nitrate and potassium perchlorate, taken separately, are not ingredients classified in this risk division. They do not constitute explosive ingredients, in particular in the sense of the invention.

At this time it should be noted that the incorporation of highly energetic explosive ingredients, such as t roguanidine, even at low levels, per se contributes to the combustion temperature increase of the compounds, beyond the cut-off threshold of 2350 K established by the need for technical improvement desired by the inventors. Thus, the compounds according to : described in the U.S. Patent. 6 893 | 517, consist mainly of a mixture of a guanidine derivative (preferably, guanidine nitrate), a nitrogenous compound explosive (preferably neither t roguanidine) and an inorganic oxidizing agent (such as ammonium perchlorate or potassium perchlorate), do not meet the requirements of the specifications of the present invention. These compounds also include in their composition a low level of a ballistic catalyst, which consists of an oxygen-containing compound of a transition metal, advantageously with a high specific surface area, conventionally used in the field of propellants to increase the combustion rate. at high and medium pressure | (this catalyst accelerates the decomposition Be the oxidant load). Gas microgenerators for safety belt tensioning devices as described in the U.S. Patent. 6 893 517 (and in its priority application EP 1 275 629) operate by impulses, which requires a high rate of combustion at medium and high pressure. An exponent of; high pressure at low pressure and no combustion at I atmospheric pressure of the compounds in question does not pose a problem, since the pressure does not fall again, in the context of the use of the compounds, until a low level 'before the end of the pyrotechnic operation. j This application for tensioning devices, of the seatbelt does not need, for the i? I gas generator, requirements as serious as those necessary in the context of the present invention (air bags and more I particularly side airbags), especially a high combustion rate at low pressure, a drop in the cutoff combustion pressure threshold (as close as possible to atmospheric pressure) and a low pressure exponent over the entire combustion range (in particular at low pressure). 1 i Currently, for frontal air bags, pyrotechnic compounds! what I offer a good compromise, in terms of gas temperature, gas production, level of particles emitted and toxicity, contain, I as main ingredients, guanidine nitrate (G) as reductive filler and basic copper nitrate (BCN) as oxidant filler. The Patents of E.U. 5 608 183 and E.U. 6 143 102 describe such compounds. 1 However, these compounds have relatively low combustion rates, i less than or equal to 20 mm / s at 20 MPa and? also a low gas yield. They are also difficult to light.

From the perspective of improving the flammability of compounds of this type, the addition of perchlorate to its composition based on guanidine nitrate (G) and basic copper nitrate (BCN) has been proposed according to the prior art. Thus, patent application EP 1 526 121 describes the addition of a perchlorate (in particular, potassium perchlorate), in a small amount (less than 5% by weight), to improve the ignition of these compounds. However, the incorporation of perchlorate in such a low amount does not: make it possible to sufficiently increase the rate of I combustion of the compound for its satisfactory use in gas generators of side airbags.

The applications WO 2007/042735 and WO 2009/126702 describe compounds having compositions, of the same type, which contain guanidine nitrate (GN), such as the reducing charge, basic copper nitrate (BCN), as the main oxidant charge, and, in addition, a second oxidant charge, which advantageously consists of potassium perchlorate (KG104). These documents associate the good performances of the compounds, in particular a high rate of combustion at high pressure, with the composition, but also with the specific process to produce the compounds (which the process includes as step of compaction by dry roller for WO). 2007/042735 and two successive stages of spray and compression drying for WO 2009/126702).

From the perspective of improving gas production and_ the combustion rate, compounds based on one (or I more) nitrogenous reducing agent (s) combined (s) with a strong oxidizing agent of the perchlorate type have also been proposed according to the prior art. i US Patent Application 2006/0137785 discloses the combination of a reducing agent of the guanidine type (nitroglyphine or guanidine nitrate) and ammonium perchlorate, the latter necessarily being incorporated in a significantly high amount (30% to 6 | 0% in weight) . The incorporation of ammonium perchlorate in such a high amount results in two major drawbacks which are, first, a significant increase in the combustion temperature (above 2800 K) and, secondly, the generation of chloride of hydrogen (which is a toxic and highly corrosive gas), the hydrogen chloride then being present in the gaseous effluents. i To overcome this problem, the patent describes the need to add to the guanidine mixture i + ammonium perchlorate a compound of the iron oxide type metal type to neutralize the hydrochloric acid present in the combustion gases, which translates into 'a decrease in the value of gas production for the compound.

The incorporation of perchlorate I Potassium instead of ammonium perchlorate would have the advantage of resulting in the formation of potassium chloride (KCl) instead of hydrogen chloride (HC1) (but the drawback of reducing gas production). In any case, the incorporation of KC104 in such large amounts (up to 60% by weight) would produce an increase in the combustion temperature which is totally unacceptable in the context of the desired application. ' Logically, those skilled in the art have focused on compounds consisting of a mixture containing guanidine nitrate (GN, alone or in combination with a co-reducing agent) and potassium perchlorate (KCIO4) in intermediate amounts of about 25%. % to I 45% by weight, as described in the patent application WO 95/25709 and the US patents. 5 854 442 and E.U. 5,997,666, making the mixture possible to obtain compounds that partially meet the essential requirements of the field of application of the present invention, namely: - good gas performance; a moderate combustion temperature; i an intrinsic non-toxicity of the particle effluents; Y a rate of combustion at around 20 MPa, which is a slight increase compared to compositions formulated on the basis of guanidine nitrate (GN) and basic copper nitrate (BCN), but which is still insufficient for use in bags of lateral air. I The thermodynamic characteristics and Í ballistics of such a compound (reference compound 1), the composition ("binary") containing only guanidine nitrate (G) and potassium perchlorate (KC104), are given (in Table 1 hereinafter.

Table 1 (1): the given value is a relative pressure. A j zero-cut combustion pressure corresponds to atmospheric pressure. 1 I The reference compound 1 exhibits I Many advantages among the expected of a compound for the generation of gas for an air bag system. The basic ingredients are simple and easily available, economic and safe with respect to the pyrotechnic aspects (not belonging to the i class of explosive compounds) and non-toxic. The thermodynamic performance (gas production, particle content) is good and the combustion temperature is still moderate and therefore acceptable. The particles i emitted by combustion are non-toxic i (essentially KC1).

However, such a compound does not exhibit the expected total yield, particularly for a side air bag application. First, the combustion rate of approximately 26 mm / s to 20 MPa is increased only by 20 to 30% compared to that of a compound based on guanidine nitrate (GN) and basic copper nitrate (BCN) and follows being low with respect to the established specifications. Then, during the tests with this reference formulation, I he knew that, although the total replacement of I basic copper nitrate (BCN) oxidizing agent i with potassium perchlorate (KC104) makes it possible to increase the rate of combustion above 5 MPa and thus improve flammability, in return and highly detrimentally induces an exponent of very high high pressure at low pressure (greater than 0 (.55 in the range of 6 to 10 MPa) and non-combustion at atmospheric pressure (additional tests demonstrated that the cutting operating pressure is around 1.7 MPa, while a composite formulated based on guanidine nitrate (GN) and basic copper nitrate (BCN) advantageously has a non-zero combustion at atmospheric pressure).

From the known results of the mixture of guanidine nitrate > (GN) / potassium perchlorate (KC104), the inventors wish to propose improved pyrotechnic gas generator compounds are convenient, especially for use in bags I of lateral air. They specifically set the goal, maintaining or improving the other characteristics, to significantly improve the following three points: - reduction of the combustion pressure of cutting, decrease in the pressure exponent (< 0.26), advantageously a large decrease (= 0.2), very advantageously a large decrease (= 0.1) of 6 MPa, increase in the combustion rate over the entire range of pressure, in particular at low pressure. , Totally unexpected, it turned out to be the case where the presence, in the composition of the compounds of the invention, of low content of (at least) an oxygen-containing compound of a transition metal (a transition metal oxide or a compound which is a precursor of an oxide as such), advantageously with a high specific surface area (conventionally used as a ballistic catalyst in the field of propellants to increase the rate of combustion at high pressure (by accelerating the decomposition of the oxidant charge)), (also) has important effects on the three desired points of improvement above (ie, an increase in the rate of combustion (also) at low pressures, a decrease in the pressure of the combustion cut and a decrease in the exponent of the pressure on the entire range of pressure).

The compositions of the inventive gas-generating pyrotechnic compounds (which are more particularly convenient for the air bag, in particular side air bag applications) contain: guanidine nitrate, and potassium perchlorate. ! They are characterized because they contain, expressed as percentages by weight, from: 60 to 70% guanidine nitrate, 26 to 33%, advantageously 26 to 30%, of potassium perchlorate, 2. 5 to 6% of at least one I combustion modifier selected from I of transition metal oxides, 1 the precursors of such oxides and mixtures thereof, I 0 to 6% of at least one additive, and do not contain an explosive ingredient.

According to a variant, the compositions of compounds of the invention consist of (exclusively) the aforementioned ingredients (GN + KC104 + at least one combustion modifier + optionally by at least one additive), taken in the content above indicated. : The ingredients of the first three above types (potassium perchlorate, guanidine nitrate and specific combustion modifier) generally represent more than 90% by weight of the total weight (of the composition) of the compounds of the invention, very generally at least 94% by weight or even more than 98% by weight. It is expressly provided for the optional presence of additives, such as manufacturing aids (calcium stearate, silica, for example). The ingredients of the above three types can represent absolutely 100% by weight of the total weight of the compounds of the invention. i Guanidine nitrate, which represents I from 60 to 70% of the total weight, it is also selected for safety and pyrotechnic reasons and for its reoplastic behavior, suitable for carrying out compacting and optional phases of the dry granulation process (see below), I ensuring a good densification of the starting powdery pyrotechnic composition I while the compressive load to be applied is limited at the same time. The manufacture of the compounds by the dry process comprises up to four main stages (see hereafter), which in particular have been described in the patent application WO 2006/134311.

The potassium lorate is present, in the composition of the compounds of the invention, in a moderate intermediate content (from 26 to 33% by weight, advantageously from 26 to 30% by weight), very particularly in relation to the temperature i of combustion, the "flammability" and the speed of combustion at high pressure that are pursued. ! Within the mixtures of GN + KCIO4, the combustion modifiers, selected by the inventors, develop especially advantageous (unexpected) properties j in relation to the three desired improvement points (see above).

The at least one combustion modifier is chosen from transition metal oxides, the precursors of such oxides and mixtures thereof. A precursor of such oxide results in the formation of an oxide (generates such oxide) at the time1 of its I decomposition in the temperature during the combustion of the pyrotechnic compound. Thus, basic copper nitrate (CU (N03) 2 * 3CU (OH) 2) is decomposed into copper oxide (CuO) (see below).

The at least one combustion modifier is present in an amount which is sufficient (> 2.5% by weight) to be effective (with reference to the three improvement points above) and not excessive (< 6% by weight) for I will not damage the gas production. Such a combustion modifier is generally present, but the presence of at least two of these additives is expressly provided within the scope of the present invention.

Preferably, the at least one combustion modifier is selected from zinc oxide (ZnO), iron oxide (Fe203), chromium oxide (Cr203), manganese dioxide (Mn02), copper oxide (CuO), nitrate basic copper (Cu (N03) 2 · 3Cu (OH) 2) and mixtures thereof. Copper oxide and basic copper nitrate, which is a precursor of copper oxide (in the sense that BCN gives rise to the formation of CuO copper oxide in the i moment of their decomposition at temperature), they are particularly effective. Particularly preferably, the compounds of the invention therefore contain; as a modifier of combustion, copper oxide or copper nitrate basic. The use of these combustion modifiers allows to obtain compounds of the invention, which have an exponent value of pressure less than or equal to 0.1 in the pressure range 6-52 MPa.

Preferably, the at least one combustion modifier according to the I invention has a specific surface area of more than 3 m2 / g, advantageously greater than 10 m2 / g and very advantageously greater than 25 m2 / g. 1 It is understood that the function of the at least one specific combustion modifier (selected from transition metal oxides, its precursors and mixtures thereof) within the composition of the compounds of the invention is not only, as in the art above (see in particular the teaching of US Patents 6 893 517 i remembered above), increase the speed of I combustion at high and medium pressure but also, surprisingly, that confer to the pyrotechnic compounds: a stable and self-sufficient combustion at low pressure (or even at a pressure practically equal to atmospheric pressure), j a low combustion rate i pressure that is greater than that of the prior art compositions, j I a low, or even practically zero, pressure exponent at low, medium and high pressure, which is significantly lower than that of the prior art compositions, this being with "good flammability" of the compounds, without generating too many solid particles in combustion and at a combustion temperature of around 2300 K.

Here it may be indicated that the compounds of the invention, whose composition was specified above, have: a combustion temperature of less than 2350 K, a combustion pressure cut (relative, i.e. with reference to atmospheric pressure) less than or equal to 1.5 MPa, advantageously less than 0.2 MPa! and most advantageously equal to 0.1 MPa, j an exponent pressure of less than or equal to 0.25, advantageously less than or equal to 0.2 and most advantageously less than or equal to 0.1, for a pressure of between 6 and 52 MPa, a combustion rate: | + greater than 24 mm / s, advantageously higher low pressure, + greater mm / s, advantageously supe ri or r 35 mm / s half pressure, + greater mm / s, sale suitably higher mm / s high pressure.

The low pressure, or even very low, exponent values of the compounds of the invention should be emphasized here.

The best results mentioned above i (advantageous variants and very advantageous variants) were obtained in particular with copper oxide and basic copper nitrate1 as a combustion modifier. In support of this claim, reference may be made to the examples hereinafter.

In the context of the present invention, an original use (more particularly with reference to the parameters mentioned above) is therefore proposed for the oxides and oxide precursors in question, in the composition of the compounds of the invention (said use being original with respect to the known conventional use of a ballistic catalyst in various compositions).

In addition to the previous components (GN + KC104 + at least one combustion modifier of the specified type), the pyrotechnic compounds of the invention may contain, at a low content by weight (less than or equal to 6%, generally less than 0.1%), at least one additive, in particular at least one additive which facilitates the preparation of the compounds (the formation during the preparation thereof), such as calcium stearate or magnesium stearate, graphite and / or at least one additive for improve the aggregation of the solid products of its combustion, selected from refractory oxides with a softening or melting point, adapted to the composition, such as silica or alumina. This is advantageously simple, generally introduced in good! powdery form (advantageously of micrometre size, very advantageously of nanometric size) having a high specific surface area (advantageously of 10 0 m2 / g or more), or in the form of small diameter silica fibers (1 to 2 microns) and some tens or hundreds of micras (2 0 to 5 0 0 micras) in length. Surprisingly, it turned out to be the case that the presence, in the pyrotechnic compounds of the invention, of silica at contents between 0. 5 and 6% by weight, advantageously between 0. 5 and 3 5% by weight,; It also has a very significant effect of reducing the pressure of the combustion cut. j It is therefore also in favor of the inventors to have demonstrated this effect of silica in compositions of type GN + KCIO4 (see table 3 hereinafter) and therefore in the compositions of the invention (of type ¡GN + KC10-3 + at least one combustion modifier), where the effect comes from over those (encompassing the fall of the cut combustion pressure) of the at least one combustion modifier present. ! The at least one additive intervenes with the constituent ingredients (GN, KC104 j + by 1 at least one combustion modifier of the type mentioned above) (at the beginning of the process of j manufacture) or is added, later downstream, in the process for the manufacture of the compounds of the invention.

It is recalled that the compositions of the compounds of the invention do not contain an explosive ingredient (see standard NF i and the UNO recommendations specified above), this being in particular with reference to the parameters: combustion temperature and pyrotechnic safety. It is pointed out, on the other hand, that the weights of pyrotechnic compounds required for inflation of the airbag, in particular of a side air bag, are greater than those required for the inflation of a safety belt tensioning device according to the US patent 6 893 517 (without being ? inflations of the same type: inflation time greater than 10-20 ms / per pulse).

The pyrotechnic compounds of the invention can be obtained according to a wet process. According to a variant, the process comprises the extrusion of a paste containing the components of the compound. According to another variant, the process includes a step of placing all (or some of the) major components in aqueous solution, which I it comprises the solubilization of at least one of the main components (oxidizing agent or reducing agent), and then the production of a powder by spray drying, the addition to the powder produced of the component that was not placed in solution and then the formation of dust in the form of objects by the usual processes in dry.

The pyrotechnic compounds of the invention can also be obtained by dry process, for example by simple granulation of the powder obtained by the mixture of. it's components.

The preferred process for obtaining the pyrotechnic compounds of the invention includes a step of dry compaction of a mixture of the constitutive ingredients in powder form of the compounds (except for such at least one additive that can be added during the process). The dry compaction is generally carried out, in a manner known per se, in a roller compactor, at a compaction pressure of between 108 and 6x10a Pa. It can be carried out according to various variants (with a characteristic "simple" compaction step followed by at least one additional step, with a characteristic compaction step coupled to a step of i training). Thus, the novel compounds of the invention are capable of existing in various forms (in particular throughout the manufacturing process, resulting in the final compounds): At the end of the dry compaction coupled to the formation (by using at least one compaction roller, the outer surface of which has cavities), they are obtained i plates with raised patterns, which can be broken to obtain directly shaped pyrotechnic objects; at the end of the dry compaction followed by granulation, the granules are obtained; at the end of the dry compaction followed by granulation, then pellets are obtained (dry compression); at the end of the dry compaction followed by granulation and then mixing the granules obtained with an extractable binder and extruding the binder loaded with the granules, blocks are obtained. Extruded monolithics (loaded with granules).

The invention's pyrotechnic compounds are therefore particularly capable of existing in the form of an object; I next type: granules, pellets, monolithic blocks. j I In a manner that is not limiting in any way, it may be indicated here that: Invintenation granules generally have a particle size (median diameter) of between 200 and 1400 μm (and also a bulk density of between 0.8 and 1.2); The inviting pellets are usually between 1 and 3 mm thick.

When the compounds of the invjención are obtained by means of a secol process the constituent ingredients of the compounds of the invention advantageously have a fine particle size of less than or equal to 20 pm. The particle size (value of the median diameter) is generally between 3 and 20 m. The compounds described in the present invention express all their potential if they are obtained by a dry process of powders having an average diameter of between 10 and 20 μt of KC104 and 5 to 15 μm of guanidine nitrate.

According to another of its subjects, the present invention relates to a pulverulent composition. (mixture of powders), that a precursor of a compound of the invention the composition of which therefore I corresponds to that of a compound of the invention (see above).

According to another of its subjects, the present invention relates to gas generators that contain at least one pyrotechnic com pound of the invention. The generators are perfectly suitable for air bags, in particular side airbags (see above).

It is now proposed to illustrate the invention in a non-limiting manner in any way.

Table 2 hereinafter gives examples of compositions of compounds of the present invention and also the performance of the compounds compared to those of the i reference compound 1 of the prior art. The compounds were evaluated by thermodynamic calculations or based on physical measurements carried out on granules or pellets manufactured from the compositions by means of the secol process of the powder mixture - compaction - granulation - and optionally the formation of pellets.

The reference compound 1 of the prior art (see table 1 above) contains guanidine nitrate and potassium perchlorate and does not contain any combustion modifier within the meaning of the invention. The compounds of Examples 1 to 7 contain such a combustion modifier in their composition, in addition to the two components of the reference compound l.j The quantities of the main components were adjusted to preserve an oxygen balance close to -3%, in order to be able to directly compare the performances of the compounds of table 1.

The results of table 2 show, as expected, according to the teaching of the prior art (teaching of the patent of I E.U. 6 893 517 and the propellant field), that the addition of a combustion modifier in the sense of the invention to a composition of the type of reference compound 1 gives, as a result an increase in the combustion rate at high and medium pressure without no significant modification of the combustion temperature.

Surprisingly, the addition also results in a very large drop in the pressure exponent, whose exponent of the pressure is very low over the entire operating pressure range (beyond 6).

MPa) and in the combustion pressure of cut I and in a considerable increase in the rate of combustion at low pressure.

What is the compound that, when added to the composition of 1, provides the most sign improvements (see example 2). The exponent of is practically null in the whole operjativa range, the pressure of operation of cut is practically equal to the atmospheric pressure.

To the extent that a complex metal, such as BCN, decomposes during exothermic combustion reactions, it generates, in situ, CuO with a high specific surface area (which was experimentally verified), therefore CuO can be replaced with BCN as combustion modifier, with results that are equivalent to those of CuO (see example 7). j CuO and BCN make it possible, when they are incorporated in a low quantity (5% examples), to conserve an advantageous gas production value (> 32 g / mol) and to give as a result, in the end, a very good improvement. significant in the inflation rate by unit area value (of more than 40%) compared to the GN / KClo reference composition!) of reference compound 1.

Table 2 Table 2 (Continued) i Hereinafter, Table 3 shows the second surprising effect demonstrated by the inventors, namely, the very significant decrease in the pressure of the combustion cut (measured in granules) when the silica is introduced at a moderate content in the composition of the compounds of the invention. i This same effect, obtained with another refractory metal oxide such as alumina, is not of sufficient size to be of interest to you.

Table 3 I

Claims (13)

REI INDICATIONS

1. A generator pyrotechnic compound i of gas, solid, the composition of | which contains: guanidine nitrate and potassium perchloride; characterized in that its composition, expressed in percentages by weight, contains from: 60 to 70% of guanidine nitrate; 26 to 33%, selling 26 to 30%, of potassium perchloride; 2.5 to 6% of at least one combustion modifier selected from transition metal oxides, the precursors of such oxides and mixtures thereof; 0 to 6% of at least one additive; and does not contain an explosive ingredient. 1

2. The compound according to | claim 1, characterized in that its composition consists of guanidine nitrate, potassium perchloride, at least one combustion modifier and optionally at least one additive.

3. The compound according to i claim 1 or 2, characterized in that its composition is at least 94% in! weight, advantageously at least 98% by weight or even - l - 100% by weight, made up of guanidine nitrate, potassium perchlorate and at least one combustion modifier.

4. The compound according to any of claims 1 to 3, characterized in that the at least one combustion modifier is selected from zinc oxide (ZnO), iron oxide (Fe203), chromium oxide (r203), and dioxide manganese (Mn02), copper oxide (CuO), basic copper nitrate (Cu (NO3) 2 * 3Cu (OH) 2) 'and mixtures thereof.

5. The compound according to any of claims 1 to 4, characterized in that the at least one combustion modifier consists of copper oxide and / or basic copper nitrate. ! 1

6. The compound according to the rei indication 5, characterized in that it has a pressure exponent less than or equal to 0.1; for j a pressure between 6 and 52 MPa. i

7. The compound according to any of claims 1 to 6, characterized in that the at least one combustion modifier has a specific surface area greater than 3 m2 / g, sale of more than 10 m2 / g and very advantageously greater than 25 m2 / g. .

8. The compound according to any of claims 1 to 7, characterized in that its composition contains silica as an additive.

9. The compound according to i claim 8, characterized in that the silica is in powder form having a high specific surface area, advantageously of 100 m2 / g or more, and of size my c rorné t ri co, advantageously of nanometric size, or in the form of silica fibers from 1 to 20 microns in diameter and from 20 to 500 microns in length.

10. The compound according to any of claims 1 to 9, cured because it is obtained by means of a dry process, which comprises a step of compacting a powder mixture containing the constituent ingredients of the compound in powder form. , optionally followed by a granulation step, optionally followed by a pelletizing step.

11. The compound according to any of claims 1 to 10, characterized in that it is in the form of granules, pellets or monolithic blocks.

12. A pulverulent composition, which is a precursor of a compound according to any of the rei indications 1 to 11, the composition of which corresponds to that of a compound according to any of claims 1 to 9.

13. A gas generator, suitable for i an air bag, characterized in that it contains at least one compound according to any of claims 1 to 11. I