FR2779426A1 - SOLID GAS-GENERATING PYROTECHNICAL CHARGES BASED ON WATER-CONTAINING COMPOSITIONS - Google Patents

Abstract

The invention concerns the field of gas-generating solid pyrotechnic compositions consisting of a binding agent with gelling effect, such as polyvinyl alcohol, impregnated with a water and hydroxylammonium nitrate solution in the presence, optionally, of oxidants such as ammonium nitrate or nitramines, stabilising and thickening agents. The invention also concerns the continuous manufacture of pyrotechnic loads (13) by forming said compositions in an extruder (1). The resulting loads are useful in pyrotechnic extinguishers and in gas generators designed for safety in motor vehicles.

Description

I The present invention relates to the field of compositions

  pyrotechnics generating cold gases, non-toxic and free of solid residues. More precisely, the invention relates to the field of composite pyrotechnic compositions with an amorphous structure comprising one or more oxidants and an organic binder in the gel state. The compositions according to the invention are very suitable for constituting fillings intended to inflate protective cushions or to ensure the functioning of a

pyrotechnic fire extinguisher.

  For many applications such as automobile safety or fire fighting, pyrotechnic compositions are sought which generate cold gases, non-toxic and free of solid residues. The term "cold" gases means gases which are

  products at a temperature below about 1800 C.

  Furthermore, those skilled in the art wish, in these fields of applications, to be able to have available compositions which can be manufactured and shaped.

by continuous processes.

  To obtain cold gases and free of solid residues, those skilled in the art have sought to develop liquid propellants constituted by aqueous solutions of compounds such as hydroxylammonium nitrate, triethanolammonium nitrate, aminotetrazole nitrate, nitrate aminotriazole, the

  urea nitrate, biuret nitrate, etc.

  Such liquid propellants are for example

  described in US Patents 5,060,973 and US 5,684,269.

  However, these liquid propellants require suitable gas generators, the structure of which is

  complex and which are of a high cost price.

  In the field of solid loadings, the skilled person has sought to develop for this purpose composite compositions constituted by a binder such as polyvinyl alcohol and by solid eutectics based on ammonium nitrate and guanidine nitrates or aminoguanidine in the presence of potassium nitrate or perchlorate. These compositions, which are for example described in PCT application WO 97/46502, however have the double drawback of not being suitable for continuous use since they are shaped by compression and, moreover, of

  provide still relatively hot gases.

  Finally, in the field of solid propulsion, solid loads consisting of a winding of polyvinyl alcohol sheets impregnated with a liquid eutectic based on the abovementioned nitrates have been proposed, for example by US Pat. No. 5,386,777, said loads containing in addition to aluminum as a reducing agent. Like the previously mentioned technique, this solution provides excessively hot gases and is not suitable for use in

continued.

  There is therefore an unmet need for solid pyrotechnic compositions which supply by combustion "cold" gases, non-toxic and free of solid residues and which can be manufactured and put

continuously shaped.

  The object of the present invention is precisely to

meet this need.

  The invention therefore relates to solid pyrotechnic compositions producing by combustion gases free of solid residues and constituted by at least one organic binder with gelling effect and by at least one main oxidizing system in the liquid phase absorbed by said binder, said compositions being characterized in that: i) the said organic binder with gelling effect is

  chosen from the group consisting of poly- alcohol

  vinyl, hydroxyethylcellulose, and xantham gum. ii) the said main oxidizing system in the liquid phase consists of a mixture of water and nitrate

hydroxylammonium (HAN).

  Polyvinyl alcohol is the preferred binder because it improves the chemical stability of the compositions according to

the invention.

  The solid compositions according to the invention thus have an amorphous structure in which the binder is in the form of a solid gel impregnated with the aqueous hydroxylammonium phase. By combustion, these compositions release the water included in the gel in the form of water vapor which contributes to lowering very

  appreciably the temperature of the combustion gases.

  Advantageously, the water content by weight of the compositions according to the invention will be between 5 and%. The invention thus makes it possible to have compositions which contain water contents much higher than the moisture contents of the compositions.

previously known.

  Advantageously also, the weight of the hydroxylammonium nitrate represents at least 50% of the total weight of the composition, the content of the latter in hydroxylammonium nitrate being preferably between 60% and 70%. One of the advantages of the present invention resides in the fact that at the indicated contents the water / hydroxylammonium nitrate mixtures remain liquid as long as the temperature of the latter does not drop

  below zero degrees Celsius.

  According to a first preferred variant, the compositions according to the invention also contain secondary oxidants which are advantageously chosen from the group consisting of ammonium nitrate, hexogen (RDX) and octogen (HMX). These secondary oxidants make it possible to increase the number of gaseous molecules produced by the combustion of a given volume of composition without the temperature of the combustion gases increasing too much thanks to the water contained.

in the composition.

  According to a second preferred variant, when the compositions are intended to constitute pyrotechnic charges for gas generators which have to inflate protective cushions for the occupants of a motor vehicle, the use of ammonium nitrate will be avoided or in any case the weight content of the ammonium nitrate composition will be limited to

a few percent.

  For this application, the compositions will most often contain stabilizing additives which will be chosen from bipyridine,

  ammonium hydrogen phosphate and ammonium acetate.

  The weight content of these stabilizers in the composition will be close to 2%. Bipyridine and ammonium hydrogen phosphate are preferred stabilizers.

  Advantageously also, for applications intended for motor vehicle safety, the compositions will contain thickening additives which will be chosen from the group consisting of water-soluble isocyanates, melamine-formaldehyde resins and borax

  which is a sodium tetraborate of formula: Na2B407, 10H20.

  The invention also relates to a process for the continuous production of solid pyrotechnic charges with an amorphous structure, the composition of which corresponds to the compositions described above and which is characterized in that: i) a mixing and extrusion apparatus is continuously supplied on the one hand with a liquid phase containing at least water and hydroxylammonium nitrate and on the other hand with solid granules comprising at least one binder with gelling effect, ii) after kneading, a profiled rod is extruded which is hardened in an oven and cut to the desired length,

  for example in the form of tubes or crowns.

  Advantageously, the kneading apparatus and

  extrusion is a twin screw extruder.

  According to a preferred embodiment of the process according to the invention, the binder with gelling effect is polyvinyl alcohol and the twin-screw extruder is heated to a temperature of between 500 ° C. and 60 ° C., the temperature inside the oven. being close to 80 C. In a particularly preferred manner all the constituents other than the binder and which are soluble in water will be mixed with the liquid phase containing the water and the hydroxylammonium nitrate before introduction of this

last in the twin screw extruder.

  The pyrotechnic charges thus obtained can in particular be used either in pyrotechnic extinguishers to constitute the source of engine gas in these extinguishers, or in pyrotechnic gas generators intended to inflate protective cushions for the occupants of a motor vehicle.

  A detailed description is given below of

  preferred embodiment of the invention with reference to FIG. i which represents the diagram of an installation of

  continuous manufacturing of loads according to the invention.

  The installation represented in FIG. I basically comprises a twin-screw extruder 1 extended by an extrusion head 2, a conveyor belt 3 passing inside an oven 4 and a cutting system 5. At the start of the extruder are provided two

feeding devices.

  The first device consists of a pipe 6 connected via a tap 7 to a tank 8 provided with a

agitator 9.

  Downstream in the operating direction of the extruder 1 is a second feeding device constituted by a hopper 10 and a belt

carrier 11.

  The tank 8 contains a liquid mixture A consisting of water, hydroxylammonium nitrate and, where appropriate, the constituents other than the binder and soluble in water such as ammonium nitrate. The reactive constituents with respect to water are not

  incorporated into this aqueous liquid phase.

  The conveyor belt 11 feeds the hopper 10 with a mixture of granules B comprising granules of binder and, if necessary, granules of additives which are not soluble in water and in particular granules of oxidants.

  not soluble in water such as hexogen or octogen.

  The extruder 1 is temperature controlled to present an internal temperature of between 50 ° C. and

   C when the binder is polyvinyl alcohol.

  The liquid phase A and the granules B are mixed in the extruder 1 to form, by gelation of the binder, a composite paste with an amorphous structure which is extruded through the extrusion head 2 in the form of a profiled rod 12. This rod may be a simple cylindrical strand, possibly provided with internal channels, to give, after cutting, loose grains or be a rod of larger dimensions, with, if necessary, a worked external profile, to give

  after cutting solid or annular blocks.

  This rod 12 is led via the conveyor belt 3 through a heated oven to cause hardening of the gelled binder. When the binder is polyvinyl alcohol, the temperature of the oven will be close to 80 ° C. and the residence time of the

  rod in the oven will be a few minutes.

  On leaving the oven, the rod 12 is cut using the cutting system 5 into elementary loads 13 which are stored in a container 14. Examples 1 and 2 Loads in the form of cylindrical crowns were thus produced. These loads had the following compositions: Example 1 Example 2 water 8 15% polyvinyl alcohol 20% 15% hydroxylammonium nitrate 68.5% 66.5% ammonium nitrate 3.5% 3.5%

Claims (15)

Claims   1. Pyrotechnic composition producing by combustion of gases free of solid residues and constituted by at least one organic binder with gelling effect and by at least one main oxidizing system in liquid phase absorbed by said binder, characterized in that: i) said organic binder with gelling effect is chosen from the group consisting of polyvinyl alcohol, hydroxyethylcellulose and xanthan gum, ii) the said main oxidizing system in liquid phase consists of a mixture of water and hydroxylammonium nitrate. 2. Composition according to claim 1 characterized in that the water content by weight of said composition is between 5% and 20%.   3. Composition according to claim 2 characterized in that the weight of said hydroxylammonium nitrate represents at least 50% of the total weight of the composition.   4. Composition according to claim 3 characterized in that the weight content of hydroxylammonium nitrate   of said composition is between 60% and 70%.   5. Composition according to claim 1 characterized in   what it contains secondary oxidants.   6. Composition according to claim 5 characterized in that the said secondary oxidants are chosen from the group consisting of ammonium nitrate, hexogen and octogen.   7. Composition according to claim 1 characterized in that it contains stabilizing additives. 8. Composition according to Claim 7, characterized in that the said stabilizing additives are chosen from   the group consisting of bipyridine, hydrogen   ammonium phosphate and ammonium acetate.   9. Composition according to claims 8 characterized in   that the stabilizing additive is selected from the group consisting of bipyridine and hydrogen phosphate ammonium.   10. Composition according to claim 1 characterized in   that it contains thickening additives.   11. Composition according to claim 10 characterized in that the said thickening additives are chosen from the group consisting of isocyanates,   melamine-formaldehyde resins and borax.   12. Method for manufacturing solid pyrotechnic charges with an amorphous structure, the composition of which   corresponds to any one of claims 1 to 11   characterized in that: i) a mixing and extrusion apparatus (1) is fed continuously with a liquid phase (A) containing at least water and hydroxylammonium nitrate and other share with solid granules (B) comprising at least one binder with gelling effect, ii) after kneading, a profiled rod (12) is extruded which is hardened in an oven (4) and cut to the desired length. 13. The method of claim 12 characterized in that the kneading and extruding apparatus is a twin screw extruder.   14. The method of claim 13 characterized in that the binder with gelling effect is polyvinyl alcohol and in that the twin-screw extruder is heated to a temperature between 50 C and 60 C, the temperature at inside of the oven being close to C. 15. The method of claim 14 characterized in that all the constituents other than the binder and soluble in water are mixed with the liquid phase containing water and hydroxyl ammonium nitrate before   introduction of the latter into the bis- extruder screw.