Method for obtaining firing pastes in an acoustic resonance mixer

Abstract

The present invention relates to a method for obtaining a firing paste which comprises mixing the different ingredients constituting said paste in an acoustic resonance mixer. The invention also relates to a method for obtaining an ignition charge which comprises the deposit of the firing paste obtained according to the above method on a combustible support, and the drying of the combustible support.

Description

[0001] PROCESS FOR OBTAINING LIGHTER PASTES IN AN ACOUSTIC RESONANCE MIXER

[0002] Field of invention.

[0003] The field of the invention is that of ignition charges for propellant shell charges. More specifically, the invention relates to a method for obtaining an ignition paste with a cellulose binder. The ignition paste is intended to be deposited on a combustible structure and then dried to form an ignition charge with performances equivalent to those of the prior art obtained by conventional methods.

[0004] State of the art

[0005] The performance, reliability and reproducibility of ignition charges are essential for the operation of barreled weapons. However, their energy does not contribute significantly to the energy performance of the propellant charge. Those skilled in the art have therefore favored the optimization of propellant charges while avoiding modification of functional and standardized ignition compounds. The architectures of these ignition charges have, however, been more frequently studied to ensure a more uniform ignition of the propellant charge. The field of ignition compounds constituting the ignition charges is therefore conventional and not very inclined to novelty. The same applies to the processes for obtaining these ignition compounds.

[0006] The composition of the ignition powder traditionally used is black powder (NP) consisting of a mixture of potassium nitrate (saltpeter), charcoal and sulfur.

[0007] The black powder used is preferably of mass composition:

[0008] -potassium nitrate (P): ~ 75%

[0009] - charcoal (C): ~ 15%

[0010] - sulfur (S): ~ 10%.

[0011] The 3 ingredients of black powder are subject to standardized MIL military specifications well known to those skilled in the art.

[0012] Black powder is obtained by intimately mixing the 3 constituents, and comes in the form of hard, shiny grains. These grains are obtained by mechanical processes (crushing, roller grinding, granulation, etc.). Military black powder complies with the military standard MIL-P-223C. It is classified in risk division 1.1 explosive according to the UN GHS classification (UN Globally Harmonized System of Classification and Labeling of Chemicals), and therefore requires strict handling precautions.

[0013] There are also other ignition powder compositions, including: Boron / KNO3, generally in a ratio of 70 / 30 (% by mass), a metal (e.g. iron, aluminum, zinc) / perchlorate type oxidant (e.g. potassium perchlorate) or fluoropolymer type (e.g. PTFE such as products in the (Teflon™) range or a fluoroelastomer such as products in the Viton™ range) (see Table 1 below). These ignition powders are, like black powder, classified in hazard division 1.1.

[0014] Table 1

[0015] The ignition charges (tablets and / or block(s)) described in the prior art consist of an ignition powder, generally black powder, agglomerated, possibly with a cellulose binder. In the latter case, the ignition charge is obtained by mixing the constituents of the ignition powder with a collodion (solvent(s) + binder), followed by evaporation of the solvent(s) from the collodion. The ignition charge usually called "Bénite" is black powder agglomerated with a nitrocellulose binder. US Patent 3182595 describes the production of Bénite strands by mechanically mixing the ingredients of the black powder with the collodion followed by an extrusion and drying step. Another process consists of mechanically mixing the black powder with the collodion and then packaging it tightly in a cartridge so as to have a paste which can be deposited in patterns on a combustible support to obtain an ignition charge.It is this latter process that is currently used for the supply of ignition paste for the production of patterned ignition charges based on black powder with a nitrocellulose binder. The reference values ​​indicated in Table 16 are obtained with ignition pastes obtained according to this process. Although the collodion loaded with ignition powder is classified in hazard division 1.4 within the meaning of the UN GHS classification (UN Globally Harmonized System of Classification and Labeling of Chemicals), the prior art processes have the major drawback of simultaneously handling the ingredients of the black powder or the black powder itself in hazard division 1.1 for their introduction into the collodion. The manufacture by mechanical action of the paste is likely to generate friction points causing untimely ignition of the ignition powder or the ingredients brought into contact.This is especially true since the latter, whose distribution in the mechanical mixer is not controlled, can be in direct contact without having yet been wetted by the collodion. The manufacture of ignition pastes using conventional processes therefore requires suitable and restrictive installations in terms of pyrotechnic risk.

[0016] The person skilled in the art is therefore looking for an efficient method for obtaining a lighting paste to be deposited, not requiring the presence or handling of an explosive product of risk division 1.1, avoiding dry stresses on the powder or its ingredients in contact, and with performances approaching those of conventional pastes. The manufacture of lighting paste would then be possible in manufacturing installations in risk division 1.3 only relating to the risk of live or deflagrating combustion.

[0017] On another level, patent application WO 2009 / 091430 discloses a method for loading a container with an energetic mixture which comprises a step of mixing the various constituents of the mixture, for example by acoustic resonance. Patent application US 2017 / 0152196 describes a method for obtaining ignition compositions containing a metal reducing agent, an oxidant and a binder. The method comprises mixing the various constituents of the composition and then granulating the resulting mixture. Mixers of the Simpson Mix-Muller or VibroAcoustic™ Mixers type are mentioned as being suitable for mixing. However, the examples in this patent application do not contain any indication of the type of mixer used. Summary of the invention

[0018] In the remainder of the document, the term "reducing charge" refers to the reducing ingredient(s) of an ignition powder and the term "oxidizing charge" refers to the oxidizing ingredient(s) of an ignition powder. When several ingredients are present in a reducing or oxidizing charge, they may have been partially or completely premixed.

[0019] According to one aspect, the present invention relates to a method for obtaining an ignition paste comprising the ingredients of an ignition powder, namely a reducing filler, an oxidizing filler, and a cellulose collodion. The method comprises a step of premixing, in an acoustic resonance mixer, the reducing filler and / or the oxidizing filler with collodion.

[0020] In one embodiment, the oxidizing charge and the reducing charge are mixed separately and simultaneously with collodion in an acoustic resonance mixer, the two premixes obtained are then mixed together in the same mixer.

[0021] In one embodiment, the reducing charge and collodion are mixed first (in the mixer), then the oxidizing charge is added and everything is mixed (still in the mixer).

[0022] In one embodiment, the oxidizing charge and collodion are mixed first (in the mixer), then the reducing charge is added and everything is mixed (still in the mixer).

[0023] In one embodiment, a premix of reducing charge and collodion, and a premix of oxidizing charge and collodion are separately prepared in an acoustic resonance mixer, and then these two premixes are mixed in an acoustic resonance mixer.

[0024] The resulting ignition paste is intended to be deposited on a combustible support and dried by evaporation of the collodion solvent(s) to obtain a dry ignition charge. The combustible support coated with the ignition charge constitutes an ignition charge.

[0025] According to one aspect, the invention relates to a method of obtaining an ignition charge, which comprises depositing the ignition paste obtained as indicated above on a combustible support, and drying the combustible support.

[0026] Brief description of the figures

[0027] Figure 1 shows a lighting paste obtained according to the method of the invention. Figure 2 shows a lighting paste obtained according to the method of the invention.

[0028] Figure 3 shows a lighting paste obtained according to the method of the invention.

[0029] Figure 4 shows an image obtained by scanning electron microscopy of an ignition paste obtained according to the method of the invention.

[0030] Description of the invention

[0031] According to one aspect, the present invention relates to a method for obtaining an ignition paste containing the ingredients of an ignition powder, namely a reducing filler, an oxidizing filler, and a cellulose collodion, based on cellulose ether or cellulose ester. The method comprises a step of premixing, in an acoustic resonance mixer, the reducing filler and / or the oxidizing filler with collodion.

[0032] In one embodiment, the reducing (or oxidizing) charge, collodion, and the oxidizing (or reducing) charge are introduced into an acoustic resonance mixer in superimposed layers, the collodion thus constituting an interlayer between the oxidizing charge and the reducing charge within the acoustic resonance mixer. In a first phase, a low acoustic intensity mixing of the superposition of layers is carried out. “Low intensity” means an intensity which ensures premixing of each charge with collodion, by phlegmatization by film-forming wetting of each of the charges with collodion. This low intensity mixing results in a layer of reducing charge premixed with the collodion, a residual intercalary layer of collodion, and a layer of oxidizing charge premixed with the collodion. The two charges are therefore not likely to be in direct dry contact.This embodiment therefore makes it possible to avoid handling the pre-constituted ignition powder and the safety constraints relating to risk division class 1.1. Advantageously, the low-intensity mixing is carried out in stages of increasing acceleration, over a range of values ​​from approximately 10g to approximately 50g. As indicated above, at the end of this first phase, there is therefore present within the acoustic resonance mixer a layer consisting of the reducing charge premixed with (“phlegmatized by”) the collodion, a residual intercalary layer of collodion, and a layer consisting of the oxidizing charge premixed with (“phlegmatized by”) the collodion. In a second phase, preferably at higher acoustic intensity, the whole is intimately mixed to obtain the ignition paste.As indicated above, the mixing is advantageously carried out in steps of increasing acceleration, over a range of values ​​from approximately 50g to approximately 100g. In one embodiment, the oxidizing charge of the ignition paste or the reducing charge of the ignition paste is premixed with collodion, in an acoustic resonance mixer. This produces a premix of one of the two charges with the collodion. The complementary charge (to that mixed with the collodion, i.e. the reducing charge or the oxidizing charge) of the ignition paste is then added to the acoustic resonance mixer to obtain the ignition paste. Advantageously, each of the two steps above is advantageously carried out in steps of increasing acceleration, over a range of values ​​from approximately 10g to approximately 100g.This embodiment ensures an optimum level of safety since a charge of the ignition powder ingredients is already phlegmatized by the collodion before its introduction into the mixer in the presence of the complementary reducing or oxidizing charge. The two charges are therefore not likely to be in direct dry contact. This embodiment also has the advantage of never putting the oxidizing and reducing charges in direct dry contact.

[0033] In one embodiment, the reducing and oxidizing charges of the ignition powder are each mixed separately with collodion, in an acoustic resonance mixer. Two separate products are thus obtained, consisting on the one hand of the premixture of the oxidizing charge with collodion and on the other hand of the premixture of the reducing charge with collodion. These two premixtures are then mixed in an acoustic resonance mixer to obtain the ignition paste. Advantageously, the quantity of collodion used in a mixture with the reducing charge is substantially equal to the quantity of collodion used in a mixture with the oxidizing charge. By "substantially equal" is meant a proportion (by mass) of collodion ranging from approximately 40 / 60 (i.e. 40% for the reducing charge and 60% for the oxidizing charge) to approximately 60 / 40 (i.e. 40% for the oxidizing charge and 60% for the reducing charge).Advantageously, each of the three steps above is advantageously carried out in stages of increasing acceleration, over a range of values ​​from approximately 10g to approximately 100g. In all embodiments, the final acoustic resonance mixing can be carried out in the cartridge (so-called “Mix in case” process) used for depositing the paste on the combustible structure, for example a tubular structure of the type described in patent application WO 2021 / 144539, thus avoiding a step of transferring the paste from the mixer container into the deposition cartridge. The cellulose collodion used in the context of the invention is based on cellulose ester, typically of the cellulose ester + solvent type, or based on cellulose ether, typically of the cellulose ether + solvent type.In one embodiment, the cellulose base of the collodion consists of a cellulose ester or a cellulose ether (for approximately 70% to approximately 90% by mass) and generally additionally contains, conventionally, at least one plasticizer (approximately 1% to approximately 20% by mass, preferably approximately 10% by mass) and at least one stabilizer of the cellulose base (approximately 0.5% to approximately 5% by mass). It also generally contains at least one additive (>0% to approximately 1% by mass), for example chosen from anti-adhesion agents, anti-glare agents, antioxidants. It is likely to contain a residual quantity of solvent(s), in particular phlegmatization solvent(s) or (and) solvent(s) for dissolving the cellulose base used during its manufacture.

[0034] Advantageously, the cellulose ether used as the major component of the cellulose base is ethylcellulose, for example the ethylcellulose described in patent application FR 3 064 639.

[0035] Advantageously, the cellulose ester used as the major component of the cellulose base is chosen from cellulose nitrate, cellulose acetate or nitrocellulose, the latter being preferred. The mass nitrogen content of the nitrocellulose is suitably 10.5% to 13.5% of grade E7 to E12 (degree of polymerization of nitrocellulose according to ISO 14446), preferably grade Eli nitrocellulose with a mass nitrogen content of 11.8% to 12.3%, advantageously equal to 12%.

[0036] The plasticizer used to prepare the collodion may include a ketone (such as camphor), a vinyl ether (such as LUTA™50-50 marketed by East Harbour Group), a polyurethane (such as NEPPLAST™ 2001 marketed by Hagedorn-NC), an adipate (such as dioctyl adipate) or a citrate (such as triethyl 2-acetyl citrate).

[0037] The stabilizer used to prepare the collodion may be, in particular, a compound whose chemical formula includes aromatic nuclei (opportunely two aromatic nuclei), capable of fixing nitrogen oxides from the decomposition of nitric esters (presently nitrocellulose). Examples of stabilizers include 2-nitrodiphenylamine (2NDPA), 1,3-diethyl-1,3-diphenyl urea (centrality I), 1,3-dimethyl-1,3-diphenyl urea (centrality II), and 1-methyl-3-ethyl-1,3-diphenyl urea (centrality III). The optional additive used to prepare the collodion may be chosen, in particular, from anti-adhesive agents, such as silicone-type anti-adhesive agents, anti-glare agents, antioxidants, colorants, surfactants, anti-agglomeration agents and hydrophobic agents.

[0038] The solvent may be a double solvent of the acetone / butyl acetate (AB) type at 50% / 50% by mass or a double solvent of the ethyl lactate type for 35% to 60% by mass and butyl acetate for 40% to 65% by mass for a total of 100%.

[0039] The viscosity of the collodion, fixed by the nitrocellulose base / solvent(s) ratio, for its implementation by the process of the invention is advantageously between 2 and 4 Pa.s, measured at 20°C using a Brookfield viscometer. In this viscosity range, the process of the invention can be implemented at room temperature, therefore without heating, so as to lead to a film-forming coating of the pre-constituted powder or the reducing and oxidizing charges after mixing to obtain the ignition paste.

[0040] Collodion is advantageously formulated to result in a dry extract (after evaporation of the solvent) of 10% to 40%, by mass.

[0041] Table 2 below shows a collodion formulation at 14% dry extract by mass.

[0042] Table 2

[0043] *Cellulosic base of the Nitrofilm™ product marketed by the company Eurenco

[0044] The ignition paste formed from the collodion charged with the premixed ignition powder or with the reducing and oxidizing charges of the ignition powder comprises about 50% to about 70% by mass of reducing and oxidizing charges, and the balance to 100% (i.e., about 30% to about 50% by mass) of collodion.

[0045] The oxidizing and reducing charges consist of ingredients conventionally used to prepare an ignition powder, for example black powder or the other ignition powders listed in Table 1. As a general rule, the mass ratios of the oxidizing and reducing ingredients included in the reducing and oxidizing charges are equivalent to those of an ignition powder. These mass ratios can nevertheless be modified if necessary to adjust the performance of the ignition paste obtained according to the invention.

[0046] Table 3 below gives an example of ignition paste in collodion composition from Table 2, loaded with ignition powder, pre-constituted or not.

[0047] Table 3

[0048] After deposition and drying (evaporation of the solvent) of the ignition paste, the ignition charge (dry) adheres to the surface of the combustible structure and comprises approximately 88% to approximately 92% by mass of ignition powder, approximately 7% to approximately 10% by mass of cellulose ester, the remainder to 100% being provided by at least one compound chosen from a plasticizer, an additive and a residual solvent.

[0049] The ignition pastes according to the invention are classified in hazard division 1.3 within the meaning of the UN GHS classification (UN Globally Harmonized System of Classification and Labeling of Chemicals). The danger zones to be taken into account for handling the charged collodion are therefore reduced, which facilitates the operations of depositing the collodion on the combustible structure. In addition, the pastes according to the invention have a self-ignition temperature by progressive heating (TACP) greater than 400°C, TACP which is therefore not controlled by that (~180°C) of the nitrocellulose contained in the charge.

[0050] Ignition pastes obtained according to the invention were produced in an acoustic resonance mixer in batches of 400 g. These pastes have the viscosity suitable for direct deposition in the form of patterns by extrusion using a syringe plunger or a single-screw. Ignition pastes obtained according to the invention were deposited in a helical pattern inside a cellulose felt tube (of the type described in patent application WO 2021 / 144539) having a mass of approximately 20 g. After evaporation of the solvent from the loaded collodion, each felt tube contains an ignition charge having a mass of approximately 11.5 g. Visually (appearance of combustion residues), the deposition results are equivalent to those obtained with a conventional ignition paste.The combustion tests carried out in a manometric enclosure of these tubes loaded with the ignition pastes of the invention lead to characteristic combustion values ​​reproducible between the samples and in accordance with the reference values ​​obtained according to the prior art with black powder in grains mechanically mixed with collodion with the mass percentages of table 3 (see table 16 at the end of the description).

[0051] The method of the invention is more efficient in terms of speed, quality and safety of mixing than those of the prior art for obtaining ignition pastes with a cellulose binder. Certain embodiments also provide gains in terms of safety by avoiding the handling of pre-constituted powder of risk division 1.1. The method of the invention also makes it possible to avoid direct dry contact of the oxidizing and reducing charges of the ignition powder. It also optionally allows the mixing of the ingredients directly in a cartridge which, after closure, is ready for use for depositing ignition patterns.

[0052] According to another aspect, the invention relates to a method for obtaining an ignition charge, which comprises preparing an ignition paste according to the method defined above, depositing the ignition paste thus prepared on a combustible support, and drying the combustible support.

[0053] The invention is illustrated by the following examples, given for information purposes only. In these examples, the acoustic resonance mixer used is a Resodyn LabRam mixer with a maximum acceleration of 100 g at 60 Hz.

[0054] Example 1 (reference)

[0055] A mixture of the Benite B type (as presented in patent application WO 2021 / 144538) was prepared with the ingredients given in Table 4.

[0056] Table 4

[0057] * black powder according to Mil-P 223 specifications.

[0058] ** equivalent to that of table 2.

[0059] The pot of an acoustic resonance mixer was filled in three layers: 50% of the total mass of collodion (82 g) / 100% of the mass of PN7 (236 g) / 50% of the total mass of collodion (82 g). An acoustic mixing cycle with an acceleration setpoint of 35 g for 60 s was applied to the contents of the mixer to obtain a homogeneous mixture. A homogeneous ignition paste with a conformal appearance was obtained (Figure 1). Its viscosity of 85,000 mPa.s (Brookfield RV5 at 5 rpm - measurement temperature 21°C) ensures its flowability for deposition on a combustible structure.

[0060] The combustion results of this ignition paste deposited and dried on a combustible felt are reported in Table 16 at the end of the description.

[0061] Example 2

[0062] A lighting paste similar to the Bénite type was prepared from black powder. The basic ingredients of the lighting paste are those contained in standard black powder: potassium nitrate (P), sulfur (S), charcoal (C), and collodion is that of Table 2.

[0063] The ingredients P, S and C are chosen according to MIL military standards well known to those skilled in the art.

[0064] The hazard divisions within the meaning of the UN GHS (UN Globally Harmonized System of Classification and Labelling of Chemicals) classification of these ingredients given in Table 5 are outside Class 1 and therefore do not generate a pyrotechnic risk.

[0065] Table 5

[0066] The mass percentages of the ingredients used in the ignition paste are presented in Table 6. Table 6

[0067] * equivalent to table 2.

[0068] The mixture of ingredients according to the mass percentages given in table 6 leads, after deposition and evaporation of the solvent, to a dry ignition charge whose composition is given in table 7.

[0069] Table 7

[0070] This example uses the ingredients and proportions in Table 6 to obtain a final mass of ignition paste of 400 g.

[0071] A premix of the reducing charge C+S was first made. Since sulfur tends to appear in the form of agglomerates, the mixture was made in an acoustic resonance mixer, in stages of increasing acceleration up to 70 g for a period of 4 minutes in order to break these agglomerates. After mixing, a homogeneous gray powder was obtained.

[0072] The following were then placed in a pot for acoustic resonance mixing, in this order and in superimposed layers: the homogeneous gray powder, the collodion and then the KNO3, previously roughly broken down manually. A progressive acoustic mixing intensity ramp leading to increasing acceleration levels from 11 to 80 g was applied to obtain the ignition paste over a period of 6 minutes. Table 8 gives the mixing cycle levels. A temperature rise of less than 14°C was observed during the mixing cycle.

[0073] The low acceleration at the start of mixing ensures, on the one hand, a premixing of the homogeneous gray powder (reducing charge) with collodion, and on the other hand a premixing of the oxidizing charge with collodion. These premixes ensure film-forming wetting (coating) by the collodion of the reducing and oxidizing charges before a progressively more vigorous overall mixing. This avoids the dry contact of the reducing charge and the oxidizing charge, which could lead to a pyrotechnic event.

[0074] Table 8

[0075] After mixing, a homogeneous and conforming lighting paste was obtained. Its viscosity of 100,000 mPa.s (Brookfield RV5 at 5 rpm - measuring temperature 21°C) ensures its flowability for deposition on a combustible structure.

[0076] The combustion results of this ignition paste deposited and dried on a combustible felt are reported in Table 16 at the end of the description.

[0077] Example 3

[0078] As in Example 2, a lighting paste approaching the blessed type based on black powder was prepared, using the ingredients and proportions in Table 6 to obtain a final mass of lighting paste of 400 g.

[0079] A C+S mixture and a P+collodion premix were previously made before combining them to create a mixture to obtain the ignition paste.

[0080] Thus, charcoal (C) and sulfur (S) were premixed in the pot of an acoustic resonance mixer under the same conditions as those described in Example 2, to give a homogeneous gray powder. Separately, potassium nitrate (P), previously roughly broken down manually, and collodion were mixed in the pot of another acoustic resonance mixer. This gives a premix of the oxidizing charge with the collodion. This premix was carried out with a progressive intensity ramp leading to increasing accelerations up to 70 g for a duration of 3 minutes as indicated in Table 9. A slight temperature rise of approximately 4°C was observed at the end of the mixing cycle. A white paste was obtained, consisting of potassium nitrate grains coated with collodion which has the film-forming property.This allows the mixture to be phlegmatized which will be produced when this white paste is placed in the presence of the reducing charge (C+S).

[0081] Table 9

[0082] Finally, the homogeneous gray powder C+S and the white paste (P+collodion) were placed in the pot of an acoustic resonance mixer. The acoustic mixing was carried out with 3 intensity levels leading to successive accelerations of ~23 g, ~41 g and ~57 g for a duration of 3 minutes as indicated in Table 10. A slight temperature rise of approximately 8°C was observed at the end of the mixing cycle.

[0083] Table 10

[0084] After mixing, a homogeneous and conformal appearance ignition paste was obtained. Its viscosity of 70,000 mPa.s (Brookfield RV5 at 5 rpm - measuring temperature 21°C) ensures its flowability for deposition on a combustible structure (Figure 2). The combustion results of this ignition paste deposited and dried on a combustible felt are reported in Table 16 at the end of the description.

[0085] Example 4

[0086] A lighter paste was prepared containing boron (B), potassium nitrate (P) and the collodion of Table 2. This lighter paste, when dried, approximates the polyester-bound BKNO3 lighter powder conforming to MIL-P-46994B containing 70.7% ± 2.0% P, 23.7% ± 2.0% B and 5.6% ± 2.0% polyester binder.

[0087] B and P are chosen according to this MIL standard with the exception of the particle size of P which can be less than 100 pm instead of the maximum 15 pm indicated in the MIL-P-46994B standard; this particle size of P makes it possible to obtain a paste with better homogeneity and flowability.

[0088] The collodion used is that of table 2. The mass percentages of the ingredients used in the ignition paste are presented in table 11.

[0089] Table 11

[0090] * equivalent to table 2.

[0091] The mixture of ingredients according to the mass percentages given in table 11 leads, after deposition and evaporation of the solvent, to a dry ignition charge whose composition is given in table 12.

[0092] Table 12 This example uses the ingredients and proportions in Table 11 to obtain a final mass of ignition paste of 400g.

[0093] Boron, collodion and then KNO3, previously roughly disintegrated manually, were arranged in this order in superimposed layers in a pot for acoustic resonance mixing. A progressive acoustic mixing intensity ramp leading to increasing acceleration steps from 6 to approximately 61 g was applied to obtain the ignition paste over a period of 15 minutes. A temperature rise of less than 14°C was observed during the mixing cycle.

[0094] The low acceleration at the start of mixing ensures premixing of the boron (reducing charge) with the collodion and premixing of the KNO3 (oxidizing charge) with the collodion. These premixes ensure film-forming wetting (coating) by the collodion of the reducing and oxidizing charges before progressively more vigorous overall mixing. This avoids the dry contact of the reducing charge and the oxidizing charge, which could lead to a pyrotechnic event.

[0095] The resulting paste has a gutter combustion velocity of 91 mm / s and a TACP greater than 400°C. Friction sensitivity is negligible and impact sensitivity remains within the permitted values ​​for granular explosive materials. These preliminary safety results are therefore favorable and will certainly lead to the paste being used (handling, transport) in risk division 1.3.

[0096] The same type of test was carried out with a paste containing 60% fillers (45% KNO3, 15% Boron) and 40% collodion to evaluate the influence of the mass content of nitrocellulose in the paste on the TACP. Even at this higher nitrocellulose content, the TACP of the paste remains higher than 400°C. After mixing according to a cycle identical to the previous one, a homogeneous ignition paste with a conformal appearance was obtained. Its viscosity of approximately 100,000 mPa.s (Brookfield RV5 at 5 rpm - measurement temperature 21°C) ensures its flowability for deposition on a combustible structure (Figure 3). Figure 4 shows an image obtained by scanning electron microscopy of the ignition charge after drying of this paste. We observe a very good homogeneity of the distribution of boron (black grains) and KNO3 (whitish grains) charges in cohesion with the nitrocellulose binder (not visible on the image).

[0097] Example 5

[0098] A lighting paste was prepared containing magnesium (Mg), polytetrafluoroethylene (PTFE), commercially known under the brand name Teflon™ PTFE 7A X from Chemours, and the collodion of Table 2. The magnesium powder has a purity greater than 97% and a particle size less than 0.21 mm, the PTFE grains have a particle size less than 0.42 mm. The preparation process for this lighting paste is similar to that of Examples 2 and 4: the magnesium, the collodion and then the PTFE were arranged in this order in superimposed layers in a pot for acoustic resonance mixing. A progressive ramp of acoustic mixing intensity leading to stages of increasing acceleration, similar to those mentioned in Table 8, was applied to obtain the lighting paste over a period of approximately 4 minutes. A temperature rise of less than 14 °C was observed during the mixing cycle.

[0099] The low acceleration at the start of mixing ensures premixing of the magnesium (reducing charge) with the collodion and premixing of the PTFE (oxidizing charge) with the collodion. These premixes ensure film-forming wetting (coating) by the collodion of the reducing and oxidizing charges before progressively more vigorous overall mixing. This avoids the dry contact of the reducing charge and the oxidizing charge, which could lead to a pyrotechnic event.

[0100] This ignition paste, once dried, is similar to the MTV ignition powder with Viton™ B binder (hexafluoroisoprene-vinylidene fluoride copolymer) marketed by Chemours, containing 58% Mg, 38% Teflon™ PTFE 7A X and 4% Viton™ B.

[0101] The collodion used is that of table 2. The mass percentages of the ingredients used in the ignition paste are presented in table 13.

[0102] Table 13

[0103] * equivalent to table 2. The mixture of ingredients according to the mass percentages given in table 13 leads, after deposition and evaporation of the solvent, to a dry ignition charge whose composition is given in table 14.

[0104] Table 14

[0105] The process of the invention according to its various embodiments, beyond the compositions of Examples 2 to 5, can be implemented to obtain any pyrotechnic paste containing an oxidizing charge, a reducing charge and a collodion based on cellulose ether or cellulose ester. Table 15 below lists, without being exhaustive, pairs of oxidizing charge and reducing charge that can be used. The composition of the paste can also contain, depending on the desired properties, mixtures of oxidizing charges and reducing charges chosen from different pairs, for example the pair C / KNO3 or C+S / KNO3 and the pair sodium benzoate / KCIO4. Table 15 Table 16

[0106] * obtained according to the prior art with black powder grains mechanically mixed with collodion with the mass percentages in table 3.

Claims

Demands 1. A process for obtaining an ignition paste containing as ingredients a reducing charge, an oxidizing charge and a collodion based on cellulosic ether or cellulosic ester, said process comprising a premixing step, in an acoustic resonance mixer, of the reducing charge and / or the oxidizing charge with collodion.

2. A process according to claim 1, comprising: a) premixing, in an acoustic resonance mixer, one of the reducing and oxidizing charges with collodion; b) mixing, in an acoustic resonance mixer, the product obtained in step a) with the other of the reducing and oxidizing charges.

3. A method according to claim 2, wherein each of the steps a) and b) is carried out in increments of increasing acceleration.

4. A process according to claim 1, comprising: a) premixing, in an acoustic resonance mixer, the reducing charge with collodion; b) premixing, in an acoustic resonance mixer, the oxidizing charge with collodion; c) mixing, in an acoustic resonance mixer, the product obtained in step a) with the product obtained in step b).

5. A method according to claim 4, wherein substantially equal quantities of collodion are used in step a) and in step b).

6. A method according to claim 1, wherein: a) the reducing agent, collodion, and oxidizing agent are introduced in superimposed layers into an acoustic resonance mixer, such that the collodion forms an intercalated layer between the reducing agent and the oxidizing agent; b) an acoustic intensity is applied to the superimposed layers, in increments of increasing acceleration, such that a layer consisting of a reducing charge premixed with collodion, an intercalated residual layer of collodion, and an oxidizing charge layer premixed with collodion; c) the premixes obtained in step b) are subjected to an acoustic intensity greater than that used in step b), by increasing acceleration steps.

7. Method according to claim 6, wherein in step b) increasing acceleration steps are implemented over a range of values ​​from about 10g to about 50g.

8. A method according to any one of the preceding claims, wherein the ignition paste comprises, by mass, 50% to 70% reducing and oxidizing fillers, and 30% to 50% collodion.

9. A process according to any one of claims 1 to 8, wherein the collodion is based on cellulosic ester.

10. Process according to claim 9, wherein the collodion comprises, by mass: 70% to 90% of a cellulosic ester, preferably nitrocellulose; 1% to 20% of at least one plasticizer; 0.5% to 5% of at least one stabilizer of the cellulosic ester; >0% to 1% of at least one additive.

11. A process according to any one of claims 1 to 8, wherein the collodion is based on cellulosic ether.

12. A process according to claim 11, wherein the collodion comprises, by mass: 70% to 90% of a cellulosic ether, preferably ethylcellulose; 1% to 20% of at least one plasticizer; 0.5% to 5% of at least one stabilizer of the cellulosic ether; >0% to 1% of at least one additive.

13. A method for obtaining an ignition charge, comprising the preparation of an ignition paste according to the method defined in any one of claims 1 at 12, the application of the ignition paste thus prepared onto a combustible support, and the drying of the combustible support.

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