WO2005077862A2

WO2005077862A2 - Gas-generating pyrotechnical compositions and pyrotechnical compounds for automotive safety

Info

Publication number: WO2005077862A2
Application number: PCT/FR2005/000282
Authority: WO
Inventors: Georges Chounet; Eric Giraud; Bernard Thibieroz
Original assignee: Snpe Materiaux Energetiques
Priority date: 2004-02-10
Filing date: 2005-02-09
Publication date: 2005-08-25
Also published as: US20070181236A1; JP4575395B2; CN100390110C; EP1713745A2; CN1918086A; FR2866022A1; JP2007523823A; WO2005077862A3; FR2866022B1

Abstract

The invention relates to a gas-generating pyrotechnical composition and pyrotechnical compounds which can be obtained from said composition. The compound comprises copper nitrate, guanidine nitrate, a specific additional reducing charge and/or a specific additional oxidizing charge, in addition to a specific binder.

Description

The present invention relates to the pyrotechnic generation of gas, in particular for inflating protective cushions used in systems for protecting the occupants of a motor vehicle. The invention relates more particularly to pyrotechnic compositions generating, at temperatures acceptable for motor vehicle safety, clean, so-called "cold" gases, rich in nitrogen and non-toxic, as well as pyrotechnic compounds capable of being obtained from such compositions. For different pyrotechnic needs and in particular to ensure correct inflation of the protective cushions, the pyrotechnic gas generators must supply in extremely short times, of the order of thirty milliseconds, clean gases, that is to say free of particles. solids capable of constituting hot spots which can damage the wall of the cushion, and non-toxic, that is to say low contents of nitrogen oxides, carbon oxides and chlorinated products. US Patent 5,608,183 discloses gas-generating pyrotechnic compositions comprising a reducing charge constituted by guanidine nitrate (NG) and an oxidizing charge constituted by basic copper nitrate (BCN) in predetermined proportions. These compositions are very advantageous because they burn at low temperatures below 2000 K, which allows them to be used in gas generators for protective cushion, and because they allow to obtain during their combustion high gas yields . However, as described for example in US Pat. No. 6,143,102, these compositions have low combustion rates, in particular due to the presence of guanidine nitrate in the composition (see also column 3 of US Pat. No. 6,550,808). In addition, it has been noted that these compositions are difficult to ignite and that they have very low combustion temperatures, which greatly penalizes their swelling power (the swelling power is defined by the product of the gaseous efficiency of combustion by its combustion temperature). In an automotive safety use to inflate a protective cushion, it is necessary that the combustion temperature of the composition remains low and if possible lower than 2200 K. In fact, at temperatures lower than 2200 K, it is still possible to use protective cushions whose wall internal is uncoated. Financially, this can prove decisive in a market as competitive as the automobile market. However, a too low combustion temperature penalizes the inflation power of the composition too strongly. It is moreover known from patent applications EP 1 279 655 and 1 130 008, methods for manufacturing gas-generating compounds. The lists given of products which may be suitable as constituents of these compounds, such as reducing charge, oxidizing charge and additives, are long. It is described, in general, the production of monolithic mono-perforated compounds of small diameter. The object of the invention is therefore to propose an extrudable pyrotechnic composition (generally suitable for preparing monolithic mono- or multi-perforated compounds) capable of generating clean, non-toxic gases, at low temperatures, below 2300 K, allowing its use to inflate an uncoated protective cushion, which lights up easily and has a satisfactory inflation power. This object is achieved by a gas-generating pyrotechnic composition comprising an oxidizing charge constituted by basic copper nitrate (BCN), a reducing charge constituted by guanidine nitrate (NG), as well as a binder, characterized in that it also includes:

+ an additional reducing charge chosen from the group formed by hexogen (RDX), octogen (H MX), pentrite (PETN), triaminoguanidine nitrate (TAGN), nitroguanidine, 3-nitro-1, 2,4-triazol-5-one (ONTA) and mono- and bi-tetrazoles; and / or, advantageously and,

+ an additional oxidizing charge which forms, with guanidine nitrate (NG), a solid solution by substitution; and in that the water-soluble binder is based on a mixture of at least one high molecular weight carboxymethylcellulose and at least one low molecular weight carboxymethylcellulose, in a mass ratio between 95/5 and 60/40. According to the invention, the basic copper nitrate (hereinafter BCN), of formula Cu (Nθ ₃ ) ₂ , 3Cu (OH) ₂ , is chosen as oxidant because it has the advantage of being perfectly stable and, associated with a reducing agent, to burn, forming easily filterable copper residues. In addition, the BCN is insoluble in water which is advantageous when the composition uses a water-soluble binder allowing it to be manufactured by extrusion. BCN also has a satisfactory gas yield, higher than that of compounds such as copper oxide, and a relatively high oxygen balance (called OB for "Oxygen Balance") of + 30%. According to an advantageous embodiment of the invention, basic copper nitrate (BCN) is at a mass fraction of between 40 and 60% (very advantageously between 50 and 60%) of the total mass of the composition. According to the invention, the reducing charge chosen is guanidine nitrate (NG). Guanidine nitrate (NG) is an organic compound rich in nitrogen, stable and inexpensive. Indeed, guanidine nitrate (NG) has very good aging resistance measured by the 400 hour test at 107 ° C. In addition, the presence of guanidine nitrate (NG) in the composition improves the gas yield of the composition. Guanidine nitrate (NG) exhibits an enthalpy of negative formation which also has the effect of lowering the combustion temperature of the composition. According to an advantageous embodiment of the invention, guanidine nitrate (NG) is at a mass fraction of between 20 and 55% (very advantageously between 20 and 40%) of the total mass of the composition. The presence of the additional reducing charge in the composition of the invention makes it possible in particular to improve the gas yield and to facilitate the ignition of said composition, therefore to make it more reliable, and to be able to overcome the use of an ignition relay. Ignition relays are expensive products, the use of a composition according to the invention therefore makes it possible to reduce the cost of the gas generator. According to a preferred embodiment, the additional reducing charge chosen is hexogen (RDX) or octogen (HMX). Said additional reducing charge, when it is present, is generally present at a mass fraction of less than 15% relative to the total mass of the composition. The presence of the specific additional oxidizing charge in the composition of the invention makes it possible in particular:

- improve the gas yield;

- to facilitate the ignition of said composition, and - also to improve the rate of combustion of said composition. It also facilitates the implementation of the process for obtaining said composition and the compounds, from said composition. The additional oxidizing charge, which may be involved, is therefore not any oxidizing charge. It is selected to form with guanidine nitrate (NG) a solid solution by substitution. This type of solid solution by substitution (eutectic) is per se known to those skilled in the art. The chemicals in question (in this case, guanidine nitrate, on the one hand and the second oxidant, on the other hand) must have: a close molecular size, the same type of crystal lattice, and the same valence ( or degree of oxidation). The inventors have, quite surprisingly, highlighted the great interest of this type of solution, within the framework of the invention. The impact on the rate of combustion is considerable. Among the many known oxidants, already used in pyrotechnics, therefore suitable, within the compositions of the invention, only those which form with guanidine nitrate a solid solution by substitution. Particularly suitable are ammonium perchlorate, potassium perchlorate, ammonium nitrate, sodium nitrate and potassium nitrate. Particularly suitable are ammonium perchlorate and potassium perchlorate. The intervention of ammonium perchlorate is particularly recommended. We return below to these particular oxidants. In general, said additional oxidizing charge, when it is present, is at a mass fraction of less than 15%, advantageously less than 10%, of the total mass of the composition. Ammonium perchlorate is a very strong oxidant and has a very good gas yield. Its strongly oxidizing nature makes it possible in particular to increase the proportion of reducing charge and therefore guanidine nitrate (NG) in the composition, the latter also having a very good gas yield. The presence of ammonium perchlorate in the composition makes it possible, like the additional reducing charge, to facilitate ignition of the composition. In motor vehicle safety, almost all of the pyrotechnic composition must have burned, under a pressure of the order of 20 MPa, in 30 to 40 milliseconds for use in a passenger or driver airbag or in 10 milliseconds for use in a side airbag. These combustion times constitute an imperative to be observed in a composition intended for automobile safety. When present, ammonium perchlorate plays the role of "booster" in the composition. In addition, when the pyrotechnic product obtained burns in parallel layers, the combustion speed V _c complies with the following law: V _c = a * p ⁿ in which a is a constant and n is the pressure exponent. The combustion of a pyrotechnic compound is above all a chemical reaction, it is therefore dependent on the temperature. However, the use of ammonium perchlorate makes it possible to lower the pressure exponent, which makes the composition less dependent on the pressure and therefore less dependent on the temperature. According to the invention, the pressure exponent is particularly low, well below 0.7, which makes it possible to be able to operate the pyrotechnic compound at temperatures between -35 ° C and 85 ° C. The composition according to the invention can therefore be used in a motor vehicle. Even if ammonium perchlorate or potassium perchlorate is a strong oxidant and has interesting properties in combustion, its use in a composition leads to obtaining high combustion temperatures and to the generation of combustion gases comprising a rate fairly high hydrogen chloride. To avoid these drawbacks, it is strongly recommended to use these oxidants, at low levels, generally less than 10%, preferably less than 10% (by mass of the composition). These maximum values of 15%, 10%, have moreover been indicated, in general, with reference to the intervention of any suitable additional oxidant. The composition of the invention is moreover capable of containing a transition metal oxide to catalyze the decomposition of the additional oxidant. This transition metal oxide can in particular be an iron, copper or manganese oxide, generally present at a level of less than 5% by weight. It has been indicated that the compositions of the invention contain an additional reducing charge, as described above and / or an additional oxidizing charge, as described above.

Advantageously, they contain such an additional reducing charge and such an additional oxidizing charge. They are therefore advantageously of the type which contain:

- basic copper nitrate (BCN) and an additional oxidizing charge; and

- guanidine nitrate (NG) and an additional reducing charge. These specific oxidant (s) and reducer (s) are typically involved in a specific water-soluble binder. Said specific water-soluble binder is interesting:

- in that it is water-soluble (Certain patent applications, such as patent application No. FR 2 772 370 describe the use of a crosslinked reducing binder based on silicone resin or based on epoxy resin. The binder is present in this composition at a rate advantageously between 6% and 10% of the total weight of the composition.To be able to be obtained by extrusion with a twin-screw extruder, a composition must include a binder rate of the order of, for example, 4 or 5% of the total mass of the composition and requires the use of a solvent for the binder The binders used in this composition of the prior art require the use of organic or halogenated solvents. halogens such as, for example, trichlorethylene is regulated, which greatly complicates the manufacture of such a composition and increases its manufacturing cost. Similarly, the use of organic solvents such as that, for example, ketone type solvents (acetone, methyl ethyl ketone, etc.) leads to the implementation of complex solutions to control the emissions of volatile organic compounds (VOCs). The water-soluble binder of the compositions of the invention avoids having to use such organic or halogenated solvents, during the granulation or extrusion stages involved in the pyrotechnic compounds)

- based on a mixture of at least one high molecular weight carboxymethylcellulose and at least one low molecular weight carboxymethylcellulose in a mass ratio between 95/5 and 60/40; i.e. in that it contains long fibers and short fibers, in the ratio indicated above. The concepts of high and low molecular weights are specified below. These are obviously average molecular weights. By high molecular weight is meant, in the present application and the appended claims, an average molecular weight greater than 250,000 g / mol, advantageously greater than or equal to 700,000 g / mol. By low molecular weight is meant, in the present application and the appended claims, an average molecular weight of less than 100,000 g / mol, generally much less than 90,000 g / mol. Those skilled in the art will not be surprised at all by such definitions. Carboxymethylcellulose is effective in that it has:

- good resistance to aging, in particular measured during an aging test carried out for 400 hours at 107 ° C; and

- an interesting oxygen balance. It is known that in the field of automotive safety, the compositions must have a balanced oxygen balance (called OB for “Oxygen Balance”). By definition, a composition is said to be balanced in oxygen when the composition contains enough oxygen so that after reaction, the various compounds of the composition are found in the form of CO ₂ , H ₂ O and N ₂ . The oxygen balance of the binder should be as small as possible. Carboxymethylcellulose has a much higher oxygen balance than the oxygen balance of elastomeric binders. Carboxymethylcellulose, a mixture of short fibers and long fibers, as defined above, is particularly effective in reference to granulation, compression and extrusion operations and is therefore perfectly suited for packaging the composition in the form of pellets, discs or monolithic blocks, mono- or even multi-perforated. The mixture of short fibers and long fibers makes it possible to obtain:

- in solution, in a minimum of water, a pumpable and continuously dosable gel, accepting a high rate of solid loads, and

- an extruded product, which does not deform under the action of its own weight. The specific water-soluble binder, as specified above, is generally present, within the compositions of the invention, at a mass fraction of between 2 and 15% of the total mass of the composition. Beyond 15%, its influence is likely to be damaging on the oxygen balance of the composition. The specificity of the binder of the compositions of the invention made it possible to obtain, by continuous extrusion, using a continuous twin-screw extruder, compounds, under a geometry described in the profession as a block (or grain ) monolithic with mono- or multi-perforations, with an outside diameter varying from a few millimeters to about twenty millimeters. The number of perforations can vary from 1 to 19, for perforations from 0.5 to 1.5 mm in diameter. The composition of the invention may also comprise additives and in particular additives playing the role of combustion catalysts or agents for trapping the solid particles emitted during combustion. Said agents make it possible to trap solid particles emitted during combustion so as to create residues of a size large enough to be able to be filtered. Additives well known in the field of compositions for automotive safety such as alumina or silica can be added to the composition according to the invention. According to a second object, the present invention relates to compounds capable of being obtained from the pyrotechnic compositions described above. According to a first variant, pyrotechnic compounds having a composition as described above are produced and shaped by a process of pelletizing or of compression of discs. According to a second variant, pyrotechnic compounds having a composition as described above are produced and shaped by an extrusion process. According to the invention, pyrotechnic compounds having a composition according to the invention can be produced at a high rate by compression of discs or by pelleting. Before the pelletizing operation, a step of preparing the powder must be carried out. This step cannot be reduced to a simple dry mixing of the various constituents. In fact, in order to be able to carry out the pelletizing operation, it is necessary to obtain a powder which flows well. This preparation step is a granulation operation consisting of starting from the various materials entering into the composition of the composition according to the invention and present in pulverulent form to make grains with a higher particle size of the order of a few hundred microns. Once this powder has been obtained, the pelletizing operation can be carried out. These pelletizing or compression processes are per se known to those skilled in the art. According to the invention, pyrotechnic compounds having a composition according to the invention can also be obtained by extrusion. Extrusion is made possible, even optimized, by the presence of the carboxymethylcellulose added with water. In the event that ammonium or potassium perchlorate is involved, care should be taken to incorporate a small amount of water so as to avoid the solubilization of said perchlorate. The process for obtaining pyrotechnic compounds by extrusion advantageously comprises a step of continuous supply of a kneading and extrusion apparatus, such as for example a twin-screw extruder, on the one hand with the charge (s) ( s) oxidizing (s) (BCN and optionally the additional oxidizing charge) and on the other hand with the reducing charge (s) (NG and possibly the additional reducing charge) premixed with the binder used (the specific binder used). After mixing, using the extruder, a profiled rod is extruded which is hardened in an oven and then cut to the desired length, for example to form aggregates. Cutting can also be carried out, in certain cases where the geometric requirements are lower, before hardening in an oven. The monolithic compounds obtained can be mono- or multi-perforated. The specificity of the binder (mixture of short fibers and long fibers) makes it possible to obtain such multi-perforated compounds.

Table 1 presented below shows some examples of formulation of compositions according to the invention. The percentages given are percentages by mass.

C *: Constituents Ex. **: Examples

In this table, the following abbreviations have been used: CMC-Na = Sodium carboxymethylcellulose (quantity expressed in percent). The binder used is a mixture of CMC-Na with a high average molecular weight: Mw ≈ 700,000 g / mol (BLANOSE ^® from AQUALON HERCULES - grade 7H -) and CMC-Na with a low average molecular weight: Mw “90,000 g / mol (BLANOSE ^® from AQUALON HERCULES - grade 12UL -). The mixtures in question are generally 85/15 mixtures (mass ratio: CMC-Na high molecular weight / CMC-Na low molecular weight).

BCN = Basic Copper Nitrate (quantity expressed in percent) NG = Guanidine Nitrate (quantity expressed in percent) RDX = Hexogenic (quantity expressed in percent) HMX = Octogen (Quantity expressed in percent) ONTA = 3-nitro-l, 2 , 4-triazol-5-one (quantity expressed in percent)

OM = Metallic Oxide (quantity expressed in percent) as SiO ₂ or AI ₂ O used in particular as a ballistic catalyst and / or particle trapping agent. For compositions according to Table 1 above, the theoretical results presented in Table 2 below are obtained.

Table 2

BO = Oxygen Balance (indicated in percent)

Yld. = Gas yield (indicated in moles per kg of composition burned)

Te = Combustion temperature (in K)

It appears from table 2 above, that with adjustment in equivalent Oxygen Balance (BO), the new formulations proposed allow a gain in terms of gas yield and / or in combustion temperature, which results in a volume of larger gas obtained for the same mass of propellant. Similarly, as these examples show, it is also possible to adjust the BO of these compositions to adapt it to the needs of each application. The good performance of these compositions is confirmed by the results in manometric chambers (Table 4 below).

Table 3 below presents the results obtained for a shot in a 60-liter, 30-gram tank of a composition according to different examples in Table 1.

Table 3

Talllδ = time to reach the pressure of 18 MPa in the generator chamber used for the tests.

Tt0.9 = delay separating the ignition time from the moment at which the tank pressure is equal to 90% of the maximum pressure in the tank.

For shots in a manometric enclosure, the results presented in Table 4 below are obtained: Table 4

Vc = Burning speed

In the reference example above, the composition is ignited with 140 mg of TiPP powder (powder based on titanium hydride and potassium perchlorate) as well as with 450 mg of relay charge. On the other hand, for the compositions of Examples 2, 10 and 11, ignition is carried out with only 140 mg of TiPP powder. This shows that the presence of ammonium perchlorate or RDX in the compositions makes it possible to greatly improve the ignition and to get rid of the ignition relay.

Claims

1. Pyrotechnic gas-generating composition comprising an oxidizing charge constituted by basic copper nitrate (BCN), a reducing charge constituted by guanidine nitrate (NG), as well as a binder, characterized in that it also comprises: + an additional reducing charge chosen from the group formed by hexogen (RDX), octogen (HMX), pentrite (PETN), triaminoguanidine nitrate (TAGN), nitroguanidine, 3-nitro-1,2 , 4-triazol-5-one (ONTA) and mono- and bi-tetrazoles; and / or, advantageously and

+ an additional oxidizing charge which forms with guanidine nitrate (NG) a solid solution by substitution; and in that the water-soluble binder is based on a mixture of at least one high molecular weight carboxymethylcellulose and at least one low molecular weight carboxymethylcellulose in a mass ratio between 95/5 and 60/40 .

2. Composition according to claim 1, characterized in that the basic copper nitrate (BCN) is at a mass fraction of between 50 and 60% of the total mass of the composition.

3. Composition according to claim 1 or 2, characterized in that the guanidine nitrate (NG) is at a mass fraction of between 20 and 40% of the total mass of the composition.

4. Composition according to any one of claims 1 to 3, characterized in that the additional reducing charge present is hexogen or octogen.

5. Composition according to any one of claims 1 to 6, characterized in that the additional reducing charge is present at a mass fraction of less than 15% relative to the total mass of the composition.

6. Composition according to any one of claims 1 to 5, characterized in that the additional oxidizing charge present is chosen from the group formed by ammonium perchlorate, potassium perchlorate, ammonium nitrate, nitrate of sodium and potassium nitrate.

7. Composition according to any one of claims 1 to 6, characterized in that the additional oxidizing charge present is chosen from the group formed by ammonium perchlorate and potassium perchlorate; in that said additional oxidizing charge advantageously consists of ammonium perchlorate.

8. Composition according to any one of claims 1 to 7, characterized in that the additional oxidizing charge is present at a mass fraction of less than 15% of the total mass of the composition.

9. Composition according to any one of claims 1 to 8, characterized in that the binder is present at a mass fraction of between 2 and 15% of the total mass of the composition.

10. Pyrotechnic compounds, capable of being obtained from a composition according to any one of claims 1 to 9.

11. Pyrotechnic compounds according to claim 10, manufactured and shaped by a pelletizing or disc compression process.

12. Pyrotechnic compounds according to claim 10, manufactured and shaped by an extrusion process.

13. Pyrotechnic compounds according to one of claims 10 or 12, of monolithic, mono- or multi-perforated type.