EP0808813B1 - Continuous process for the solventless production of pyrotechnical products having a thermosetting binder - Google Patents

Description

The present invention relates to the field of composite pyrotechnic products and in particular composite powders for tube weapons, propellants composites for rocket engines and explosives composites for ammunition loading. More precisely the invention relates to a continuous process for solvent-free manufacturing of such pyrotechnic products comprising a thermosetting binder.

The composite pyrotechnic products constituted by an organic binder and by a pulverulent energy charge which can be a mineral charge such as for example ammonium nitrate, ammonium perchlorate or potassium perchlorate or else an organic charge and in particular a nitramine such as for example hexogen, octogen, nitroguanidine or 2,4,6,8,10,12 hexanitro-2,4,6,8,10,12 hexaazatetracyclo (5.5.OO ^5,9. 0 ^{3, 11} ) dodecane also called hexanitrohexaaza-isowurtzitane are highly sought after by those skilled in the art because of their high chemical stability and their low vulnerability to thermal impacts and aggressions.

In addition, for security and safety reasons reproducibility of manufacturing, the skilled person prefers continuous processes to discontinuous processes.

Binders usable for the manufacture of composite pyrotechnics can be thermoplastic binders or binders thermosetting.

Thermoplastic binders have the advantage of relatively easily lend themselves to implementation continuously due to the fact that they soften by temperature rise. So the patent application French FR-A-2 723 086 describes a manufacturing process continuous and solvent-free of pyrotechnic products composites based on thermoplastic type binders. However, thermoplastic type binders have the disadvantage of leading to products that have a poor temperature resistance due to the very softening of the binder when the temperature. However for certain applications, such as example weapons with a high rate of fire, the man of profession needs pyrotechnic products presenting good temperature resistance.

From this point of view the pyrotechnic products to thermosetting binder offer the advantage of presenting good temperature resistance.

But, due to the very fact that their binder is irreversibly hardens when cross-linked, these products have the disadvantage of not being well lend to continuous processes.

These products are therefore often used in using batch processes. So the patent US-A-4 128 441 describes a manufacturing process discontinuous by "pouring" of propellant blocks. This process is well suited for making large rocket engine loads but not suitable to manufacture industrially in series of small objects.

US-A-4,405,534 describes a process for manufacturing composite explosives by cold compression of granules of explosives coated with a polyurethane film made plastic thanks to the presence of plasticizers. This process, apart from the fact that it is discontinuous, has the disadvantage additional to require the presence of a strong plasticizer content which is not always favorable to the energy plan.

It was proposed by application WO94 / 05607 a semi-continuous solvent manufacturing process for such products, but the need to use a solvent which must then be removed limits the interest of this process.

When the skilled person wants to implement with thermosetting binders a continuous process solvent-free it faces the problem of short "pot life" of these compositions which means that after mixture of the ingredients of the composition, it does have only a very short time to perform the shaping geometry of the product before the crosslinking of the binder does not make any mechanical work of the dough containing the different ingredients.

It has been proposed to extend the "pot life" by delaying final crosslinking for example by fractional addition of the crosslinking agent as described in US-A-4,657,607 or using a double system of binders of which one of the systems is crosslinkable only by a different energy supply than heat as described in the patent application EP-A-0 367 445.

Nevertheless the possibilities of application of these techniques are limited and the skilled person does not have not a general continuous manufacturing process and solvent-free composite pyrotechnic products to thermosetting binder.

The object of the present invention is precisely to propose such a process as well as an installation industrial allowing the implementation of this process.

i) à mélanger les constituants de départ des dits produits de manière à obtenir une pâte composite homogène de viscosité suffisante pour pouvoir conserver des cotes géométriques stables,

ii) à mettre la pâte ainsi obtenue sous forme de produits intermédiaires ayant les cotes géométriques des produits terminés,

iii) à figer la forme et la composition des produits intermédiaires ainsi obtenus par réticulation du liant,

et étant caractérisé en ce que :

iv) ledit liant liquide de départ est d'abord mélangé à une charge épaississante solide sous forme pulvérulente de manière à obtenir un pré-mélange de consistance graisseuse qui est ensuite mélangé aux dites charges énergétiques,

v) les opérations de mélange et de mise en forme sont conduites à une température inférieure à 40°C.

The invention therefore relates to a continuous process for the manufacture without solvent of finished composite pyrotechnic products, the starting constituents of which comprise in particular a liquid binder which is crosslinkable at a temperature above 40 ° C. and at least one solid oxidizing energy charge, said process consisting especially :

i) mixing the starting constituents of said products so as to obtain a homogeneous composite paste of sufficient viscosity to be able to maintain stable geometric dimensions,

ii) putting the dough thus obtained in the form of intermediate products having the geometric dimensions of the finished products,

iii) freezing the form and composition of the intermediate products thus obtained by crosslinking the binder,

and being characterized in that:

iv) said starting liquid binder is first mixed with a solid thickening filler in pulverulent form so as to obtain a pre-mixture of greasy consistency which is then mixed with said energy charges,

v) the mixing and shaping operations are carried out at a temperature below 40 ° C.

Compared to the known methods of the prior art, the major originality of the process according to the invention lies in the fact that with the exception of the final phase during which the structure and composition of intermediate products are fixed by crosslinking, the different operations are carried out at a temperature at which the binder is, chemically, almost non-scalable. So the formulation of the product composition is perfectly reproducible insofar as it is fully carried out in start of the process without requiring any adjustment ulterior. The skilled person is not confronted with any condition of "pot life" and intermediate products whose geometric dimensions are imperfect can be recycled in manufacturing.

Finally, it should be noted that thanks to the use of solid thickening fillers which give the binder non-evolving liquid sufficient mechanical strength, no plasticizer is required for the present process which thus makes it possible to obtain products very high performance pyrotechnics.

We can also say that unlike previous processes which use a binder thermosetting scalable during the process of which seeks to lower viscosity by using a solvent and / or a plasticizer, the process according to the invention uses a liquid thermosetting binder non-evolving during the process of which the apparent viscosity by use of fillers thickeners.

According to a first preferred variant of the invention, said solid thickening filler consists of a porous material whose particle size is between 0.1 and 10 μm (microns) and whose specific surface is between 60 and 500 m ² / g .

Advantageously, this material will also have combustion modifying properties and will be chosen in the group consisting of carbon black, the colloidal silica, alumina, titanium oxide or polynorbornene.

According to this first variant, the weight ratio between said thickening filler and said binder crosslinkable is between 0.05 and 0.25.

According to a second preferred variant of the invention, said solid thickening filler is constituted by a thermoplastic polymer with hydrocarbon units which may contain, in addition to carbon and hydrogen atoms, oxygen and nitrogen atoms and whose molecular mass weight average is between 3x10 ⁵ and 3x10 ⁶ .

A first group of thermoplastic polymers usable as solid thickening filler in the framework of the present invention is thus constituted by styrene / butadiene / styrene, styrene / isoprene / styrene copolymers, styrene / ethylene / butylene / styrene and styrene / ethylene / propylene.

A second group of thermoplastic polymers usable as solid thickening fillers in the framework of the present invention is constituted by the polyurethanes with polyether and polycarbonate patterns and by polyether / polyamide block copolymers.

According to this second variant, the weight ratio between said thickening filler and said binder crosslinkable is between 10:90 and 50:50.

In addition to solid oxidizing energy charges we can also incorporate into the premix, consisting by the liquid binder and said thickening fillers, at least one solid reducing energy charge like, for example, aluminum or boron powder.

Only when the mixing and form of intermediate products are completed and are deemed satisfactory that we do evolve the binder by causing it to crosslink by heating at a temperature above 40 ° C so to obtain finished crosslinked products.

The method according to the invention thus makes it possible to obtain continuously, without time constraints linked to "pot life" issues and no use of solvents or energy-unwanted plasticizers, Composite pyrotechnic products with crosslinked binder. These products find their preferred applications as propellant powders in strands or in sticks for ammunition intended for the weapons with tube, like blocks of propellants for rocket and rocket engines, as explosive charges for ammunition explosives or as pyrotechnic charges for gas generators intended for both military applications than civil applications like automotive safety.

The invention also relates to an installation particularly suitable for the implementation of method according to the invention.

i) un laminoir à cisaillement constitué par deux rouleaux cylindriques de longueur identique portant des rainures hélicoïdales et dont les axes sont parallèles et situés dans un même plan horizontal en étant espacés de manière à laisser subsister une fente entre les deux rouleaux qui tournent en sens contraire l'un de l'autre,

ii) une pompe volumétrique qui amène à l'extrémité, d'entrée de matière du laminoir le pré-mélange constitué par le liant liquide et la charge épaississante,

iii) au moins une trémie doseuse déversant, entre l'extrémité d'entrée de matière et l'extrémité de sortie de matière du laminoir, les charges énergétiques solides sur les rouleaux de ce dernier,

iv) un dispositif de granulation de la pâte homogène ainsi constituée qui est situé à l'extrémité de sortie du laminoir,

v) une extrudeuse dans laquelle sont repris les granulés provenant du dispositif de granulation,

vi) un dispositif de découpage en produits intermédiaires des joncs extrudés sortant de l'extrudeuse,

vii) un tapis roulant qui assure le transport et le passage dans un four thermique des produits intermédiaires ainsi découpés.

This installation is characterized in that it comprises, in the direction of progression of the material:

i) a shear rolling mill consisting of two cylindrical rollers of identical length carrying helical grooves and whose axes are parallel and located in the same horizontal plane being spaced so as to leave a gap between the two rollers which rotate in opposite directions one of the other,

ii) a positive displacement pump which brings the premix consisting of the liquid binder and the thickening charge to the end of the material inlet of the rolling mill

iii) at least one dosing hopper pouring, between the material inlet end and the material outlet end of the rolling mill, the solid energy charges on the rollers of the latter,

iv) a device for granulating the homogeneous dough thus formed which is situated at the outlet end of the rolling mill,

v) an extruder in which the granules from the granulation device are taken up,

vi) a device for cutting into intermediate products the extruded rods leaving the extruder,

vii) a conveyor belt which ensures the transport and the passage through a thermal oven of the intermediate products thus cut.

A detailed description of the preferred implementation of the method according to the invention in referring to Figure 1 which shows, so schematic, the preferred installation presented above. Figure 2 shows, for reasons of clarity, a simplified top view of the rolling mill shear used.

The invention therefore consists in mixing, at temperature ambient the starting constituents of a composition composite pyrotechnic crosslinkable until obtained a homogeneous composite paste with a viscosity sufficient to be able, always at temperature ambient, be in the form of products intermediaries who already have a stable shape and final dimensions of the finished product that we want to get. The form and composition of these intermediate products are then frozen by hot crosslinking so as to obtain the products desired completions.

To do this we start, as shown in figure 1 by manufacturing in an arm mixer multiples 1 a premix 2 consisting mainly by the binder 3 thermosetting in the liquid state and by thickening solid fillers 4.

It is imperative in the context of this invention that the thermosetting binder is liquid to room temperature and that its crosslinking cannot start only at a temperature above 40 ° C so as to be certain that as long as we stay at one ambient temperature below 40 ° C, this binder will remain chemically non-evolving.

In the present description is meant by "binder liquid "all of the liquid reactive constituents which, after crosslinking, will give the crosslinked binder solid.

The crosslinking reaction can be of the type polycondensation reaction, in which case the binders will in particular be of the polyurethane, polyesters or polyamides.

The crosslinking reaction can be of the type polyaddition reaction with opening of unsaturations ethylenic, in which case the binders will in particular be polyalkylenes, polyacrylates or polymethacrylates. In the latter case, the composition must contain crosslinking catalysts, such as for example peroxides.

As already indicated above in the description, said thickening fillers can be made of porous solid materials of small particle size. In this case we will use advantageously as thickening fillers certain additives usually used as modifiers of combustion like carbon black; the process according to the invention in this case offers the advantage of allowing continuously obtaining pyrotechnic compositions already known but which were only accessible by discontinuous processes.

Said thickening fillers can also be made up of thermoplastic polymers high molecular weight solids so as to get a final product whose binder consists of a alloy of thermoplastic polymers and polymers cross-linked. This type of alloy allows obtaining composite products with characteristics particularly high mechanical properties.

The premix 2 thus formed may also contain other additives of the final composition. he should have the consistency of a thick fat of so that it can be transported continuously using a positive displacement pump while adhering, without sinking, on the surface of a cylinder rotating with a speed angular of a few tens of revolutions per minute.

This premix is therefore transported by means of a circulation pump 34, for example a gear, in a reserve 35 provided with a piston cover 36. The premix is then taken up by a pump doser 5 with gear to be driven, in a equipment where the operations of mixing with solid energy charges and setting in the form of the composite paste thus obtained in the form of intermediate products that already have the ratings geometries of finished products. These two operations can be carried out in a single device like for example a twin screw extruder whose head extrusion will be associated with a cutting device. But, preferentially, these two operations will be carried out by two separate devices, one placed following each other.

The premix 2 is transported by the pump 5 in a mixer which can be a traditional mixer as a "BUSS" co-kneader but which, preferably and as shown in Figure 1, is a rolling mill shear 6 consisting of two cylindrical rollers 7 and 8 of identical length and having grooves helical. Axes 9 and 10 of these two cylinders are parallel and located in the same horizontal plane being spaced so as to leave a slot 11 between the two rollers. Axes 9 and 10 are supported by support blocks 12 and 13, block 12 being a block engine driving in rotation the two cylinders 7 and 8 which rotate in opposite directions to each other at different speeds. Such a shear rolling mill is known to those skilled in the art and described in numerous publications, for example in the patent application FR-A-2 723 086 already cited.

The pump 5 thus brings the premix 2 to the roller 7 which turns the fastest, the premix forming on this roll a sheet which coats this latest. The premix is brought to the end 14 material inlet of the rolling mill 6.

At least one dosing hopper 16 pours between the material inlet end 14 and the end of material outlet 15 from rolling mill 6, the loads solid energy 17 on the premix sheet coating the roller 7. These solid energy charges are then intimately mixed with premix 2 thanks to the shearing action of the rolling mill 6 so as to form on roll 7 a sheet of composite dough homogeneous which already has sufficient viscosity to ability to maintain stable geometric dimensions.

Solid energy charges will mainly constituted by the oxidizing charges of the composition which can be mineral fillers such as ammonium perchlorate, potassium perchlorate or ammonium nitrate, or organic fillers and in particular nitramines such as hexogen, octogen, nitroguanidine or hexanitro-hexaazaisowurtzitane.

Besides solid oxidizing charges, there may have solid reducing energy charges like aluminum or boron and even solid additives which would not have been incorporated into premix 2.

In this case the different charges may be brought either in mixture by a single hopper, or separately by a succession of hoppers.

The composite dough sheet thus obtained is recovered in the form of granules 19 by a device for granulation 18 located at the outlet end 15 of the rolling mill 6. Preferably as shown in the Figure 1, the outlet ends of rollers 7 and 8 are not grooved but are smooth.

The granules 19 are then taken up continuously in an extruder 20, for example a twin extruder screw, fitted with an extrusion head 21 to be profiled in rods 23 driven by a conveyor belt 25.

A cutting device 22 cuts the rods profiles 23 leaving the extrusion head 21 in 24 intermediate products already with the ratings final of finished products. The device cutting 22 has a movement controlled by the speed of progression of the mat 25 on which the rods rest 23.

It should be noted that until this operation of cutting, no heating of the composition pyrotechnic did not take place, the extruder 20 being able even be cooled. The binder of the pyrotechnic composition has therefore not changed and the intermediate products 24 may, if they are found to be unsatisfactory, be recycled in the manufacturing circuit.

These intermediate products 24, when they are deemed satisfactory, are then taken up continuously by the conveyor belt 25 which ensures their transport and passage through a thermal oven 26 where their shape geometric and their composition are definitely frozen by crosslinking their binder, at a temperature higher than 40 ° C. With the usual compositions known to those skilled in the art, the crosslinking will be often performed at a temperature close to 120 ° C for about 5 minutes.

The finished products 27 leaving the oven 26 can then be packaged in their packaging 28.

The method according to the invention thus makes it possible to manufacture in continuous series of products composite pyrotechnics with crosslinked binder, and in particular products of small dimensions, without constraint of "pot life", solvent-free and plasticizer-free undesirable.

The following examples illustrate some possibilities of implementing the invention.

PBHT =

liant à base de polybutadiène à terminaisons hydroxyles réticulé par un polyisocyanate.

PAG =

liant à base de polyazoture de glycidyle à terminaisons hydroxyles réticulé par un polyisocyanate

S.B.S. =

copolymère styrène/butadiène/styrènes

S.I.S. =

copolymère styrène/isoprène/styrène

PE-PA =

copolymère bloc polyéther/polyamide 60/40

RDX =

hexogène

PA =

perchlorate d'ammonium

In these examples, the following abbreviations have been used:

PBHT =

binder based on polybutadiene with hydroxyl endings crosslinked by a polyisocyanate.

PAG =

binder based on glycidyl polyazide with hydroxyl endings crosslinked by a polyisocyanate

SBS =

styrene / butadiene / styrene copolymer

SIS =

styrene / isoprene / styrene copolymer

PE-PA =

polyether / polyamide block copolymer 60/40

RDX =

hexogenic

PA =

ammonium perchlorate

All the percentages given in the examples are percentages by mass, the percentages indicated for the binder including any additives used.

Examples 1 to 3

The 7-hole and 19-hole multi-perforated cylindrical powder strands were produced by the continuous process according to the invention from the following three compositions: Composition 1 Composition 2 Composition 3 binder PBHT: 9% PBHT: 10.5% PAG: 13% thickening filler SIS 6% PE-PA: 4.5% PE-PA: 7% oxidizing charge RDX 85% RDX 85% RDX 80% particle size of the oxidizing charge 100 µm 150 µm 80 µm reducing load 0 0 0

For a material temperature of 35 ° C during extrusion, the following geometries have been obtained: 7 holes 19 holes Composition 1 web (mm) 0.34 ± 0.01 1.48 ± 0.01 d (mm) 0.29 ± 0.005 0.40 ± 0.01 Composition 2 web (mm) 0.35 ± 0.01 1.51 ± 0.01 d (mm) 3.30 ± 0.005 0.40 ± 0.005 Composition 3 web (mm) 0.34 ± 0.01 1.49 ± 0.01 d (mm) 0.31 ± 0.005 0.39 ± 0.01 web = thickness to burn
d = hole diameter

Examples 4 to 6

Blocks of central channel cylindrical propellants for small missile engines were manufactured by the continuous process according to the following compositions: Composition 4 Composition 5 Composition 6 binder PBHT: 10% PBHT: 12.2% PBHT: 10.5% thickening filler polynorbornene = 4% carbon black porous alumina (150m ² / g): 1.8% (80m ² / g: 3.5%) oxidizing charge PA: 85% PA / 85% PA: 85% reducing load Al: 1% Al: 1% Al: 1% The die was a cylindrical die with an outside diameter of 30mm and an inside diameter of 14mm.

On 10 meters of propellant extruded continuously for each of the compositions, the dimensional variations obtained after hot cutting and crosslinking are as follows: Example 4 Example 5 Example 6 outer diameter in mm 30.5 ± 0.002 30.0 ± 0.02 29.9 ± 0.02 inside diameter in mm 13.8 ± 0.003 13.9 ± 0.02 14.05 ± 0.02 length in mm 121 ± 0.1 120.5 ± 0.15 120.4 ± 0.1

Example 7

• liant PBHT   =   11%
• charge épaississante = SIS   =   4%
• charge oxydante : RDX (3µm et 90µm) =85%

Strips of composite explosive with a thickness of between 2 and 5 mm were produced by the continuous process according to the invention from the following composition:

• PBHT binder = 11%
• thickening load = SIS = 4%
• oxidizing charge: RDX (3 µ m and 90 µ m) = 85%

10 meters of 90mm wide strip with thicknesses of 2.3 and 5mm were continuously extruded. After crosslinking the binder, the dimensional variation of the bands was: extrusion thickness 2 mm extrusion thickness 3 mm extrusion thickness 5 mm thickness in mm 1.98 ± 0.01 2.95 ± 0.015 4.99 ± 0.02 width in mm 89.5 ± 0.05 90.2 ± 0.06 89.8 ± 0.04

Example 8

• liant PBHT :   15,8%
• charge épaississante = SBS :   9,2%
• charge oxydante : PA (90µm, 15µm, 3µm) :   73%
• charge réductrice : Al =   2%

Blocks of propellants for a pyrotechnic gas generator were manufactured by the continuous process according to the invention from the following composition:

• PBHT binder: 15.8%
• thickening filler = SBS: 9.2%
• oxidizing charge: PA (90 µ m, 15 µ m, 3 µ m): 73%
• reducing load: Al = 2%

• diamètre : 30mm + 0,025mm
• longueur : 90mm + 0,10mm

The blocks were in the form of cylinders full of dimensions:

• diameter: 30mm + 0.025mm
• length: 90mm + 0.10mm

• vitesse de combustion à 13 MPa = 25,3mm/s
• exposant de pression   = 0,35

These blocks were drawn on the test bench and gave the following results:

• combustion speed at 13 MPa = 25.3mm / s
• pressure exponent = 0.35

Claims (11)

1. Continuous process for the solventless manufacture of terminated composite pyrotechnic products of which the starting constituents comprise in particular a liquid binder which can be cross-linked at a temperature above 40°C and at least one solid oxidizing energetic charge, the process consisting in particular of:

   (i) mixing the starting constituents of the said products so as to obtain a homogeneous composite paste with sufficient viscosity to be able to preserve stable geometric dimensions,

   (ii) putting the paste thus obtained into the form of intermediate products having the geometric dimensions of the said terminated products.

   (iii) setting the form and composition of the intermediate products thus obtained by cross-linking the binder,
   characterized in that :

   (iv) the said starting liquid binder is first of all mixed with a solid thickening filler in powdered form so as to obtain a premix with a greasy consistency which is then mixed with the said energetic charges,

   (v) the mixing and forming operations are carried out at a temperature below 40°C.
2. Process according to claim 1, characterized in that the said solid thickening filler consists of a porous material of which the particle size lies between 0.1 and 10µm and of which the specific area lies between 60 and 500 m²/g.
3. Process according to claim 2 characterized in that the said material is chosen from the group consisting of carbon black, colloidal silica, alumina, titanium oxide and polynorbornene.
4. Process according to claim 1, characterized in that the said solid thickening filler consists of a thermoplastic polymer with hydrocarbon units which can carry oxygen and nitrogen atoms of which the mean molecular mass by weight lies between 3×10⁵ and 3×10⁶.
5. Process according to claim 4 characterized in that the said thickening filler is chosen from the group consisting of styrene/butadiene/styrene, styrene/isoprene/styrene, styrene/ethylene/butylene/styrene, styrene/ethylene/propylene copolymers.
6. Process according to claim 4 characterized in that the said thickening filler is chosen from the group consisting of polyurethanes based on polyethers and polycarbonates and of polyether/polyamide block copolymers.
7. Process according to claim 4 characterized in that the weight ratio between the said thickening filler and the said cross-linking binder lies between 10:90 and 50:50.
8. Process according to claim 2 characterized in that the weight ratio between the said thickening filler and the said cross-linking binder lies between 0.05 and 0.25.
9. Process according to claim 1, characterized in that in addition to the said solid oxidizing energetic charges, at least one solid reducing energetic charge is used.
10. Process according to claim 9 characterized in that the said reducing energetic charge consists of powdered aluminium or boron.
11. Installation for implementing the process according to any one of claims 1 to 10, characterized in that it comprises, in the direction of the progression of the material :

    (i) a shearing rolling mill (6) consisting of two grooved cylindrical rollers (7,8) with identical length carrying helical grooves and of which the axes are parallel and situated in the same horizontal plane while being spaced so as to leave a slit (11) between the two rollers which rotate in opposite directions to each other,

    (ii) a volumetric pump (5) which brings the premix (2) consisting of the liquid binder and the thickening filler to the material inlet end (14) of the rolling mill (6),

    (iii) at least one metering hopper (16) discharging, between the material inlet end (14) and the material outlet end of the rolling mill (6), solid energetic charges (17) onto the rollers of the latter,

    (iv) a granulating device (18) for the homogeneous paste thus constituted which is situated on the outlet end (15) of the rolling mill,

    (v) an extruder (20) in which granules coming from the granulating device are taken up,

    (vi) a device (22) for cutting the extruded beads (23) leaving the extruder into intermediate products (24),

    (vii) a conveyer belt (25) which ensures the transport and passage of the intermediate products thus cut into a heating oven (26).

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