Process for obtaining ignition pastes in an acoustic resonance mixer

Abstract

A process for obtaining an ignition paste which includes mixing the various ingredients constituting the paste in an acoustic resonance mixer. Also, a process for obtaining an ignition charge, which includes depositing the ignition paste, obtained according to the above process, on a combustible support, and drying the combustible support.

Description

FIELD OF INVENTION

[0001] The field of the invention is that of ignition charges for shell propellant charges. More specifically, the invention concerns a process for obtaining an ignition past of the cellulose-binder type. 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 processes.STATE OF THE ART

[0002] The performance, reliability and reproducibility of ignition charges are essential for the operation of tube weapons. However, their energy does not contribute significantly to the energy performance of the propellant charge. The person skilled in the art has therefore favored optimizing propellant charges while avoiding modifying standardized functional ignition compounds. The architectures of these ignition charges have, on the other hand, been more frequently studied to ensure more uniform ignition of the propellant charge. The field of ignition compounds making up ignition charges is therefore conventional and not very prone to novelty. The same applies to the processes for obtaining these ignition compounds.

[0003] The composition of the ignition powder traditionally used is black powder (BP), a mixture of potassium nitrate (saltpetre), charcoal and sulphur.

[0004] The black powder used is preferably of weight composition:

[0005] potassium nitrate (P):~75%

[0006] charcoal (C):~15%

[0007] sulphur(S):~10%.

[0008] The 3 black powder ingredients are covered by standardized MIL military specifications that are well known to those skilled in the art.

[0009] 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, rolling, granulation, etc.). Military black powder complies with military standard MIL-P-223C. It is classified as risk division 1.1 explosive under the UN GHS classification (UN Globally Harmonised System of Classification and Labelling of Chemicals), and therefore requires stringent handling precautions.

[0010] There are also other ignition powder compositions, in particular of the type: Boron / KNO3, in a ratio generally of 70 / 30 (% by weight), a metal (e.g. iron, aluminum, zinc) / perchlorate oxidant (e.g. potassium perchlorate) or fluoropolymer oxidant (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 risk division 1.1.TABLE 1Ignition powder constituentsChemical formulaeBoron / potassium nitrateB / KNO3Aluminum / potassium perchlorateAl / KClO4Magnesium / Teflon ™Mg / PTFEZirconium / barium chromateZr / BaCrO4Aluminum / copper oxideAl / CuOMagnesium / sodium nitrate / potassium nitrateMg / NaNO3 / KNO3Zirconium / lead chromateZr / PbCrO4Zirconium-nickel / potassium perchlorate-barium nitrateZrNi / KClO4 Ba(NO3)2Caesium decahydroborate / potassium nitrateCS2B10H10 / KNO3

[0011] The ignition charges (tablets and / or block(s)) described in the prior art consist of an ignition powder, generally black powder, agglomerated, optionally 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 collodion solvent(s). The ignition charge usually referred to as “Bénite” is black powder agglomerated with a nitrocellulose binder. U.S. Pat. No. 3,182,595 describes a process of obtaining Benite strands by mechanically mixing the black powder ingredients with the collodion, followed by an extrusion and drying step. Another process consists of mechanically mixing the black powder with the collodion and then sealingly packaging it in a cartridge so as to obtain a paste that can be deposited in a pattern on a combustible support to obtain an ignition charge. This is the process currently used to supply ignition paste for the production of patterned ignition charges based on black powder with a nitrocellulose binder. The reference values shown in Table 16 are obtained with ignition pastes obtained using this process. Although collodion charged with ignition powder is classified in risk division 1.4 within the meaning of the UN GHS classification (UN Globally Harmonised System of Classification and Labelling of Chemicals), the processes of the prior art have the major disadvantage of simultaneously handling the ingredients of the black powder or the black powder itself in risk 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 together. This is all the more the case as the latter, whose distribution in the mechanical mixer is not controlled, may be in direct contact without yet having been wetted by the collodion. The manufacture of ignition pastes using conventional processes therefore requires adapted and restrictive installations in terms of pyrotechnical risk.

[0012] The person skilled in the art is therefore looking for an efficient process for obtaining an ignition 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 brought together, and with performances approaching those of conventional pastes. The manufacture of ignition pastes could then be envisaged for manufacturing installations in risk division 1.3 relating solely to the risk of live or deflagrating combustion.

[0013] On another level, WO 2009 / 091430 describes a process for charging a container with an energetic mixture which comprises a step of mixing the various constituents of the mixture, for example by acoustic resonance. US patent application 2017 / 0152196 describes a process for obtaining ignition compositions containing a metallic reductant, an oxidant and a binder. The process comprises mixing the various constituents of the composition and then granulating the mixture obtained. Mixers of the Simpson Mix-Muller or VibroAcoustic™ Mixers type are mentioned as likely to be used for mixing. However, the examples in this patent application do not contain any indication of the type of mixer used.SUMMARY OF THE INVENTION

[0014] In the remainder of this document, the reducing ingredient(s) of an ignition powder is referred to as a “reducing charge” and the oxidizing ingredient(s) of an ignition powder is referred to as an “oxidizing charge”. When several ingredients are present in a reducing or oxidizing charge, they may have been partially or totally premixed.

[0015] According to one aspect, the present invention relates to a process for obtaining an ignition paste containing the ingredients of an ignition powder, namely a reducing charge, an oxidizing charge and a cellulose collodion. The process comprises a step of premixing, in an acoustic resonance mixer, the reducing charge and / or the oxidizing charge with a collodion.

[0016] In one embodiment, the oxidizing charge and the reducing charge are mixed separately and simultaneously with collodion in an acoustic resonance mixer, and the two premixes obtained are then mixed together in the same mixer.

[0017] In one embodiment, the reducing charge and collodion are first mixed (in the mixer), then the oxidizing charge is added and the whole is mixed (still in the mixer).

[0018] In one embodiment, the oxidizing charge and collodion are first mixed (in the mixer), then the reducing charge is added and the whole is mixed (still in the mixer).

[0019] In one embodiment, a premix of reducing charge and collodion and a premix of oxidizing charge and collodion are prepared separately in an acoustic resonance mixer, and these two premixes are then mixed in an acoustic resonance mixer.

[0020] The ignition paste obtained 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. According to one aspect, the invention relates to a process for obtaining an ignition charge, which comprises depositing the ignition paste obtained as indicated above on a combustible support, and drying the combustible support.BRIEF DESCRIPTION OF THE FIGURES

[0021] FIG. 1 shows an ignition paste obtained according to the process of the invention.

[0022] FIG. 2 shows an ignition paste obtained according to the process of the invention.

[0023] FIG. 3 shows an ignition paste obtained according to the process of the invention.

[0024] FIG. 4 shows an image obtained by scanning electron microscopy of an ignition paste obtained according to the process of the invention.DESCRIPTION OF THE INVENTION

[0025] According to one aspect, the present invention relates to a process for obtaining an ignition paste containing the ingredients of an ignition powder, namely a reducing charge, an oxidizing charge, and a cellulose collodion, based on cellulose ether or cellulose ester. The process comprises a step of premixing, in an acoustic resonance mixer, the reducing charge and / or the oxidizing charge with collodion.

[0026] 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 forming an intermediate layer between the oxidizing charge and the reducing charge within the acoustic resonance mixer. In the first phase, the superimposed layers are mixed at low acoustic intensity. By “low intensity” is meant an intensity which ensures premixing of each charge with collodion, by phlegmatisation through film-forming wetting of each of the charges by collodion. The result of this low-intensity mixing is a layer of reducing charge premixed with the collodion, a residual layer of collodion in between, 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 eliminates the need to handle the pre-constituted ignition powder and the safety constraints associated with risk division class 1.1. Advantageously, low-intensity mixing is carried out in increments of increasing acceleration, over a range of values from approximately 10 g to approximately 50 g. As indicated above, at the end of this first phase, a layer consisting of the reducing charge premixed with (“phlegmatised by”) the collodion, a residual collodion interlayer, and a layer consisting of the oxidizing charge premixed with (“phlegmatised by”) the collodion are therefore present within the acoustic resonance mixer. In a second phase, preferably at higher acoustic intensity, the whole is intimately mixed to obtain the ignition paste. As indicated above, mixing is advantageously carried out in increments of increasing acceleration, over a range of values from about 50 g to about 100 g.

[0027] 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 above two steps is carried out in increments of increasing acceleration, over a range of values from approximately 10 g to approximately 100 g. This embodiment ensures an optimum level of safety since one of the charges of the ignition powder ingredients is already phlegmatised by the collodion before being introduced 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 bringing the oxidizing and reducing charges into direct dry contact.

[0028] In one embodiment, the reducing and oxidizing charges of the ignition powder are each mixed separately with collodion in an acoustic resonance mixer. Two distinct products are thus obtained, consisting on the one hand of the premix of the oxidizing charge with collodion and on the other hand of the premix of the reducing charge with collodion. These two premixes are then mixed in an acoustic resonance mixer to obtain the ignition paste. Advantageously, the quantity of collodion used in mixing with the reducing charge is substantially equal to the quantity of collodion used in mixing with the oxidizing charge. By “substantially equal” is meant a proportion (by weight) 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 above three steps is carried out in increments of increasing acceleration, over a range of values from about 10 g to about 100 g. In all embodiments, the final mixing by acoustic resonance can be carried out in the cartridge (so-called “Mix in case” process) used for depositing the paste on the combustible structure, a tubular structure for example 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.

[0029] The cellulose collodion used in the invention is based on a cellulose ester, typically of the cellulose ester+solvent type, or on a 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 about 70% to about 90% by weight) and generally additionally contains, conventionally, at least one plasticizer (about 1% to about 20% by weight, preferably about 10% by weight) and at least one stabilizer of the cellulose base (about 0.5% to about 5% by weight). It also generally contains at least one additive (>0% to approximately 1% by weight), for example chosen from anti-adhesion agents, anti-glare agents and antioxidants. It can contain a residual quantity of solvent(s), in particular phlegmatisation solvent(s) or (and) solvent(s) for dissolving the cellulose base used during its manufacture.

[0030] Advantageously, the cellulose ether used as the majority component of the cellulose base is ethyl cellulose, for example the ethyl cellulose described in patent application FR 3 064 639.

[0031] Advantageously, the cellulose ester used as the majority component of the cellulose base is chosen from cellulose nitrate, cellulose acetate or nitrocellulose, the latter being preferred. The nitrogen content by weight of the nitrocellulose is appropriately 10.5% to 13.5% of grade E7 to E12 (degree of polymerisation of nitrocellulose according to standard ISO 14446), preferably grade E11 nitrocellulose with a nitrogen content by weight of 11.8% to 12.3%, advantageously equal to 12%.

[0032] The plasticizer used to prepare the collodion can be, in particular, 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).

[0033] The stabilizer used to prepare the collodion can be, in particular, a compound whose chemical formula includes aromatic rings (appropriately two aromatic rings), capable of fixing the nitrogen oxides from the decomposition of nitric esters (currently nitrocellulose). Examples of stabilizers include 2-nitrodiphenylamine (2NDPA), 1,3-diethyl-1,3-diphenyl urea (centralite I), 1,3-dimethyl-1,3-diphenyl urea (centralite II) and 1-methyl-3-ethyl-1,3-diphenyl urea (centralite III).

[0034] The optional additive used to prepare the collodion can be chosen in particular from anti-adhesion agents, such as silicone-type anti-adhesion agents, anti-glare agents, antioxidants, dyes, surfactants, anti-caking agents and hydrophobic agents.

[0035] The solvent can be a double solvent of the acetone / butyl acetate (AB) type at 50% / 50% by weight or a double solvent of the ethyl lactate type for 35% to 60% by weight and butyl acetate for 40% to 65% by weight for a total of 100%.

[0036] The viscosity of the collodion, set by the nitrocellulose base / solvent(s) ratio, for use in 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 carried out at room temperature, and therefore without heating, so as to produce a film-forming coating of the preconstituted powder or of the reducing and oxidizing charges after mixing to obtain the ignition paste.

[0037] The collodion is advantageously formulated to give a dry extract (after evaporation of the solvent) of 10% to 40% by weight.

[0038] Table 2 below shows a collodion formulation at 14% solids by weight.TABLE 2CollodionComposition (% by weight)Cellulose base*Nitrocellulose8414Plasticizer10Stabilizer3.5Other (additive(s),2.5water, solvent, etc.)Total100AB43Acetone43Total100*Cellulose base of Nitrofilm ™ marketed by Eurenco

[0039] 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 weight of reducing and oxidizing charges, and the remainder to 100% (i.e. about 30% to about 50% by weight) of collodion.

[0040] The oxidizing and reducing charges are made up 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 weight ratios of oxidizing and reducing ingredients in the reducing and oxidizing charges are equivalent to those of an ignition powder. These weight ratios can nevertheless be modified if necessary to adjust the performance of the ignition paste obtained according to the invention.

[0041] Table 3 below gives an example of an ignition paste with the collodion composition of table 2, charged with an ignition powder, whether pre-constituted or not.TABLE 3Composition Raw materials(% by weight)Ignition powder (pre-mixed or not)56Collodion44Total100

[0042] After deposition and drying (evaporation of the solvent) of the ignition paste, the (dry) ignition charge adheres to the surface of the combustible structure and comprises approximately 88% to approximately 92% by weight of ignition powder, approximately 7% to approximately 10% by weight of cellulose ester, the remainder to 100% being provided by at least one compound chosen from a plasticizer, an additive and a residual solvent.

[0043] Ignition pastes according to the invention are classified in risk division 1.3 within the meaning of the UN GHS classification (UN Globally Harmonised System of Classification and Labelling of Chemicals). The danger zones to be taken into account when handling the loaded collodion are therefore reduced, which makes it easier to deposit the collodion on the combustible structure. In addition, the pastes according to the invention have a auto-ignition temperature by gradual heating (ATGH) of over 400° C., an ATGH which is therefore not controlled by that (~180° C.) of the nitrocellulose contained in the charge. Ignition pastes obtained according to the invention were produced in an acoustic resonance mixer in 400 g batches. These pastes have a 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 weight of approximately 20 g. After evaporation of the charged collodion solvent, each felt tube contains an ignition charge having a weight of approximately 11.5 g. From a visual point of view (appearance of the combustion residue), the deposition results are equivalent to those obtained with a conventional ignition paste. The combustion tests carried out in a manometric chamber on these tubes loaded with the ignition pastes of the invention produced characteristic combustion values which were reproducible between the samples and conformed to the reference values obtained in the prior art with granular black powder mechanically mixed with collodion in the weight percentages shown in table 3 (see table 16 at the end of the description).

[0044] The process of the invention is more efficient in terms of mixing speed, quality and safety than those of the prior art for obtaining ignition pastes of the cellulose-binder type. In addition, certain embodiments provide gains in terms of safety by avoiding the handling of preconstituted powder of risk division 1.1. The process of the invention also makes it possible to avoid direct dry contact between the oxidizing and reducing charges of the ignition powder. It also allows the ingredients to be optionally mixed directly in a cartridge which, once sealed, is ready to use for depositing ignition patterns.

[0045] According to another aspect, the invention relates to a process for obtaining an ignition charge, which comprises preparing an ignition paste according to the process defined above, depositing the ignition paste thus prepared on a combustible support, and drying the combustible support.

[0046] The invention is illustrated by the following examples, which are given by way of illustration. In these examples, the acoustic resonance mixer used is a Resodyn LabRam mixer with a maximum acceleration of 100 g at 60 Hz.Example 1 (Reference)

[0047] A mixture was prepared of the type Bénite B (as presented in patent application WO 2021 / 144538) with the ingredients given in Table 4.TABLE 4Weight Composition Raw materials(g)(% by weight)Black powder PN 7*23659Collodion**16441Total400100* Black powder according to Mil-P 223 specifications.**equivalent to that shown in Table 2.

[0048] The pot of an acoustic resonance mixer was filled in three layers: 50% of the total weight of collodion (82 g) / 100% of the weight of PN7 (236 g) / 50% of the total weight of collodion (82 g). An acoustic mixing cycle with an acceleration set at 35 g for 60 s was applied to the contents of the mixer to obtain a homogeneous mixture. A homogeneous ignition paste was obtained (FIG. 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.

[0049] The combustion results of this ignition paste deposited and dried on a combustible felt are given in Table 16 at the end of the description.Example 2

[0050] An ignition paste was prepared, similar to the Bénite type based on black powder.

[0051] The basic ingredients of the ignition paste are those contained in standard black powder:

[0052] Potassium nitrate (P),

[0053] Sulphur(S),

[0054] Charcoal (C) and,

[0055] the collodion is that shown in Table 2.

[0056] The ingredients P, S and C are selected in accordance with MIL military standards, well known to the skilled person.

[0057] The UN GHS (UN Globally Harmonised System of Classification and Labelling of Chemicals) risk divisions of these ingredients given in table 5 are outside class 1 and therefore do not generate a pyrotechnic risk.TABLE 5IngredientsRisk division (according to UN standard)Collodion  3 (flammable liquid)P5.1 (solid oxidizer)C4.2 (materials subject to spontaneous combustion)S4.1 (flammable solid).

[0058] The percentages by weight of the ingredients used in the ignition paste are shown in Table 6.TABLE 6Weight IngredientspercentagesChargesPotassium nitrate44.4%Sulphur 6.2%Charcoal 9.4%Total charge  60%CollodionDry cellulose base* 6.4%Solvent AB16.8%Solvent Acetone16.8%Total collodion  40%*equivalent to table 2.

[0059] Mixing the ingredients according to the weight percentages given in Table 6 led, after deposition and evaporation of the solvent, to a dry ignition charge whose composition is given in Table 7.TABLE 7Weight percentagein the dryignitionConstituentschargeP66.9%S 9.4%C14.1%Cellulose binder 9.6%Total 100%

[0060] This example uses the ingredients and proportions shown in Table 6 to obtain a final ignition paste weight of 400 g.

[0061] A premix of the reducing charge C+S was first carried out. As sulphur tends to be in the form of agglomerates, the mixture was mixed in an acoustic resonance mixer, in increments of increasing acceleration up to 70 g for a period of 4 minutes, in order to break up the agglomerates. After mixing, a homogeneous grey powder was obtained.

[0062] The homogeneous grey powder, the collodion and then KNO3, which had been coarsely de-coated by hand, were then placed in layers in this order in an acoustic resonance mixing pot. A progressive ramp of acoustic mixing intensity leading to increasing acceleration increments from 11 to 80 g was applied to obtain the ignition paste over a period of 6 minutes. Table 8 shows the increments of the mixing cycle. A temperature increase of less than 14° C. was observed during the mixing cycle.

[0063] The low acceleration at the start of mixing ensures that the homogeneous grey powder (reducing charge) is premixed with collodion, and that the oxidizing charge is premixed with collodion. These premixes ensure film-forming wetting (coating) of the reducing and oxidizing charges by the collodion before progressively more vigorous overall mixing. This prevents the reducing charge and oxidizing charge from coming into dry contact with each other, which could lead to a pyrotechnic incident.TABLE 8Mixing cycleDurationIntensityAcceleration(s)(%)(g)30301130502760704060806460907312010080

[0064] After mixing, a homogeneous ignition paste with a consistent appearance was obtained. Its viscosity of 100,000 mPa·s (Brookfield RV5 at 5 rpm-measurement temperature 21° C.) ensures that it can be poured onto a combustible structure.

[0065] 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.Example 3

[0066] As in Example 2, an ignition paste approaching the Bénite type based on black powder was prepared, using the ingredients and proportions in Table 6 to obtain a final weight of ignition paste of 400 g.

[0067] A C+S mixture and a P+collodion premix were made beforehand, before combining them to obtain a mixture for the ignition paste.

[0068] Charcoal (C) and sulphur(S) were thus premixed in the pot of an acoustic resonance mixer under the same conditions as those described in Example 2, to give a homogeneous grey powder. Separately, potassium nitrate (P), which had previously been coarsely broken down by hand, and the collodion were mixed in the pot of another acoustic resonance mixer. A premix of the oxidizing charge with the collodion was thus obtained. This premixing was carried out with a progressive intensity ramp leading to increasing accelerations up to 70 g for a duration of 3 minutes as shown in Table 9. A slight temperature increase of about 4° C. was observed at the end of the mixing cycle. A white paste was obtained, consisting of grains of potassium nitrate coated with collodion, which has a film-forming property. This makes it possible to phlegmatise the mixture that will be produced when this white paste is placed in the presence of the reducing charge (C+S).TABLE 9Mixing cycleDurationIntensityAcceleration(s)(%)(g)605048306057307063308069909074

[0069] Finally, the homogeneous grey C+S powder and the white paste (P+collodion) were brought together in the pot of an acoustic resonance mixer. Acoustic mixing was carried out with 3 intensity increments leading to successive accelerations of ~23 g, ~41 g and ~57 g for a duration of 3 minutes as shown in Table 10. A small temperature increase of about 8° C. was observed at the end of the mixing cycle.TABLE 10Mixing cycleDuration Intensity Acceleration(s)(%)(g)603023605041607057

[0070] After mixing, a homogeneous ignition paste with a consistent appearance was obtained. Its viscosity of 70,000 mPa·s (Brookfield RV5 at 5 rpm-measurement temperature 21° C.) ensures that it can be poured onto a combustible structure (FIG. 2).

[0071] 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.Example 4

[0072] An ignition paste containing boron (B), potassium nitrate (P) and the collodion shown in Table 2 was prepared. Once dried, this ignition paste is similar to BKNO3 ignition powder with a polyester binder conforming to MIL-P-46994B containing 70.7%±2.0% P, 23.7%±2.0% B and 5.6%±2.0% polyester binder.

[0073] The B and P are selected in accordance with this MIL standard, with the exception of the particle size of the P, which may be less than 100 μm instead of the maximum 15 μm indicated in MIL-P-46994B; this particle size of the P makes it possible to obtain a paste with better homogeneity and flowability.

[0074] The collodion used is that shown in Table 2. The weight percentages of the ingredients used in the ignition paste are shown in Table 11.TABLE 11Weight IngredientspercentagesChargesPotassium nitrate52.4%Boron17.6%Total charge  70%CollodionDry cellulose base* 4.8%Solvent AB12.6%Solvent Acetone12.6%Total collodion  30%*equivalent to table 2.

[0075] Mixing the ingredients according to the weight percentages given in Table 11 led, after deposition and evaporation of the solvent, to a dry ignition charge whose composition is given in Table 12.TABLE 12Weight percentagein the dryignitionConstituentscharge.Potassium nitrate70.1%Boron23.5%Cellulose binder 6.4%Total 100%

[0076] This example uses the ingredients and proportions shown in Table 11 to obtain a final ignition paste mass of 400 g.

[0077] Boron, collodion and then KNO3, which had previously been coarsely broken down by hand, were arranged in this order in superimposed layers in a pot for mixing by acoustic resonance. A progressive ramp of acoustic mixing intensity leading to increasing acceleration increments from 6 to about 61 g was applied to obtain the ignition paste over a period of 15 minutes. A temperature increase of less than 14° C. was observed during the mixing cycle.

[0078] The low acceleration at the start of mixing ensures premixing of the boron (reducing charge) with the collodion and premixing of KNO3 (oxidizing charge) with the collodion. These premixes ensure film-forming wetting (coating) of the reducing and oxidizing charges by the collodion before progressively more vigorous overall mixing. This prevents the reducing charge and oxidizing charge from coming into dry contact with each other, which could lead to a pyrotechnic incident.

[0079] The paste obtained has a gutter combustion speed of 91 mm / s and an ATGH in excess of 400° C. Sensitivity to friction is negligible and sensitivity to impact remains within the values accepted for granular explosive materials. These preliminary safety results are therefore favourable and will undoubtedly lead to the paste being used (handled and transported) in risk division 1.3.

[0080] The same type of test was carried out with a paste containing 60% charges (45% KNO3, 15% boron) and 40% collodion to assess the influence of the nitrocellulose weight ratio in the paste on the ATGH. Even with this higher nitrocellulose content, the ATGH of the paste remains above 400° C. After mixing in a cycle identical to the previous one, a homogeneous ignition paste was obtained with a consistent appearance. Its viscosity of about 100,000 mPa·s (Brookfield RV5 at 5 rpm-measurement temperature 21° C.) ensures that it can be poured onto a combustible structure (FIG. 3). FIG. 4 shows an image obtained by scanning electron microscopy of the ignition charge after drying of this paste. A very good homogeneity of the distribution of the boron (black grains) and KNO3 (whitish grains) charges in cohesion with the nitrocellulose binder (not visible in the image) was observed.Example 5

[0081] An ignition paste was prepared containing magnesium (Mg), polytetrafluoroethylene (PTFE), commercially known as Teflon™ PTFE 7A X from the company Chemours, and the collodion of Table 2. The magnesium powder has a purity greater than 97% and a particle size of less than 0.21 mm, the PTFE grains have a particle size of less than 0.42 mm. The process for preparing this ignition paste is similar to that of examples 2 and 4: the magnesium, collodion and then PTFE were arranged in this order in superimposed layers in a pot for mixing by acoustic resonance. A progressive ramp of acoustic mixing intensity leading to increments of increasing acceleration, similar to those mentioned in Table 8, was applied to obtain the ignition paste over a period of about 4 minutes. A temperature increase of less than 14° C. was observed during the mixing cycle.

[0082] 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) of the reducing and oxidizing charges by the collodion before progressively more vigorous overall mixing. This prevents the reducing charge and oxidizing charge from coming into dry contact with each other, which could lead to a pyrotechnic incident.

[0083] Once dried, this ignition paste is similar to the MTV ignition powder with binder Viton™ B (hexafluoroisoprene-vinylidene fluoride copolymer) marketed by the company Chemours containing 58% Mg, 38% Teflon™ PTFE 7A X and 4% Viton™ B.

[0084] The collodion used is that shown in Table 2. The weight percentages of the ingredients used in the ignition paste are shown in Table 13.TABLE 13Weight IngredientspercentagesChargesPTFE23.3%Magnesium35.6%Total charge  59%CollodionDry cellulose base* 6.6%Solvent AB17.2%Solvent Acetone17.2%Total collodion  41%*equivalent to table 2.

[0085] Mixing the ingredients according to the weight percentages given in Table 13 led, after deposition and evaporation of the solvent, to a dry ignition charge, the composition of which is given in Table 14.TABLE 14Weight percentagein the dryignitionConstituentscharge.PTFE35.6%Magnesium54.4%Cellulose binder  10%Total 100%

[0086] The process of the invention in its various embodiments, in addition to the compositions of Examples 2 to 5, can be used to obtain any pyrotechnic paste containing an oxidizing charge, a reducing charge and a cellulose ether- or cellulose ester-based collodion. Table 15 below lists, by no means exhaustively, oxidizing charge and reducing charge pairs which can be used. Depending on the properties required, the paste composition can also contain mixtures of oxidizing and reducing charges chosen from different pairs, for example the C / KNO3 or C+S / KNO3 pair and the sodium benzoate / KClO4 pair.TABLE 15Reducing charge / oxidizing charge pairChemical formulaAluminum / potassium perchlorateAl / KClO4Zirconium / barium chromateZr / BaCrO4Aluminum / copper oxideAl / CuOMagnesium / sodium nitrate-potassium nitrateMg / NaNO3 / KNO3Zirconium / lead chromateZr / PbCrO4Zirconium-nickel / potassium perchlorate-barium nitrateZrNi / KClO4-Ba(NO3)2Caesium decahydroborate / potassium nitrateCS2B10H10 / KNO3Sodium benzoate / potassium perchlorateC7H5NaO2 / KClO4TABLE 16Weightof theMeanMeanWeightignitionMax.derivativevelocity ofType of ignitionof thechargePressuredP / dtStrengthdetonationchargeSampletube (g)(g)(MPa)(MPa / ms)(MJ / kg)A0 (1 / s)Reference values (*)~19.5~11.761.390.43153.3Ignition charge ofRIC119.8911.4260.768.040.430132.40example 2RIC220.1211.561.277.430.429121.22RIC320.3611.5862.127.450.429119.91Ignition charge ofRIC420.2311.7262.018.210.429132.49example 3RIC520.0811.6961.277.680.427125.33RIC620.411.5762.438.800.431140.94(*) obtained in the prior art with black granular powder mechanically mixed with collodion in the weight percentages shown in Table 3.

Examples

example 1 (

Example 1 (Reference)

[0047]A mixture was prepared of the type Bénite B (as presented in patent application WO 2021 / 144538) with the ingredients given in Table 4.

TABLE 4Weight Composition Raw materials(g)(% by weight)Black powder PN 7*23659Collodion**16441Total400100* Black powder according to Mil-P 223 specifications.**equivalent to that shown in Table 2.

[0048]The pot of an acoustic resonance mixer was filled in three layers: 50% of the total weight of collodion (82 g) / 100% of the weight of PN7 (236 g) / 50% of the total weight of collodion (82 g). An acoustic mixing cycle with an acceleration set at 35 g for 60 s was applied to the contents of the mixer to obtain a homogeneous mixture. A homogeneous ignition paste was obtained (FIG. 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.

[0049]The combustion results of this ignition paste deposited and dried on a combustible felt are ...

example 2

[0050]An ignition paste was prepared, similar to the Bénite type based on black powder.

[0051]The basic ingredients of the ignition paste are those contained in standard black powder:[0052]Potassium nitrate (P),[0053]Sulphur(S),[0054]Charcoal (C) and,[0055]the collodion is that shown in Table 2.

[0056]The ingredients P, S and C are selected in accordance with MIL military standards, well known to the skilled person.

[0057]The UN GHS (UN Globally Harmonised System of Classification and Labelling of Chemicals) risk divisions of these ingredients given in table 5 are outside class 1 and therefore do not generate a pyrotechnic risk.

TABLE 5IngredientsRisk division (according to UN standard)Collodion  3 (flammable liquid)P5.1 (solid oxidizer)C4.2 (materials subject to spontaneous combustion)S4.1 (flammable solid).

[0058]The percentages by weight of the ingredients used in the ignition paste are shown in Table 6.

TABLE 6Weight IngredientspercentagesChargesPotassium nitrate44.4%Sulphur 6.2%Charc...

example 3

[0066]As in Example 2, an ignition paste approaching the Bénite type based on black powder was prepared, using the ingredients and proportions in Table 6 to obtain a final weight of ignition paste of 400 g.

[0067]A C+S mixture and a P+collodion premix were made beforehand, before combining them to obtain a mixture for the ignition paste.

[0068]Charcoal (C) and sulphur(S) were thus premixed in the pot of an acoustic resonance mixer under the same conditions as those described in Example 2, to give a homogeneous grey powder. Separately, potassium nitrate (P), which had previously been coarsely broken down by hand, and the collodion were mixed in the pot of another acoustic resonance mixer. A premix of the oxidizing charge with the collodion was thus obtained. This premixing was carried out with a progressive intensity ramp leading to increasing accelerations up to 70 g for a duration of 3 minutes as shown in Table 9. A slight temperature increase of about 4° C. was observed at the end o...

FIELD OF INVENTION

[0001] The field of the invention is that of ignition charges for shell propellant charges. More specifically, the invention concerns a process for obtaining an ignition past of the cellulose-binder type. 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 processes.STATE OF THE ART

[0002] The performance, reliability and reproducibility of ignition charges are essential for the operation of tube weapons. However, their energy does not contribute significantly to the energy performance of the propellant charge. The person skilled in the art has therefore favored optimizing propellant charges while avoiding modifying standardized functional ignition compounds. The architectures of these ignition charges have, on the other hand, been more frequently studied to ensure more uniform ignition of the propellant charge. The field of ignition compounds making up ignition charges is therefore conventional and not very prone to novelty. The same applies to the processes for obtaining these ignition compounds.

[0003] The composition of the ignition powder traditionally used is black powder (BP), a mixture of potassium nitrate (saltpetre), charcoal and sulphur.

[0004] The black powder used is preferably of weight composition:

[0005] potassium nitrate (P):~75%

[0006] charcoal (C):~15%

[0007] sulphur(S):~10%.

[0008] The 3 black powder ingredients are covered by standardized MIL military specifications that are well known to those skilled in the art.

[0009] 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, rolling, granulation, etc.). Military black powder complies with military standard MIL-P-223C. It is classified as risk division 1.1 explosive under the UN GHS classification (UN Globally Harmonised System of Classification and Labelling of Chemicals), and therefore requires stringent handling precautions.

[0010] There are also other ignition powder compositions, in particular of the type: Boron / KNO3, in a ratio generally of 70 / 30 (% by weight), a metal (e.g. iron, aluminum, zinc) / perchlorate oxidant (e.g. potassium perchlorate) or fluoropolymer oxidant (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 risk division 1.1.TABLE 1Ignition powder constituentsChemical formulaeBoron / potassium nitrateB / KNO3Aluminum / potassium perchlorateAl / KClO4Magnesium / Teflon ™Mg / PTFEZirconium / barium chromateZr / BaCrO4Aluminum / copper oxideAl / CuOMagnesium / sodium nitrate / potassium nitrateMg / NaNO3 / KNO3Zirconium / lead chromateZr / PbCrO4Zirconium-nickel / potassium perchlorate-barium nitrateZrNi / KClO4 Ba(NO3)2Caesium decahydroborate / potassium nitrateCS2B10H10 / KNO3

[0011] The ignition charges (tablets and / or block(s)) described in the prior art consist of an ignition powder, generally black powder, agglomerated, optionally 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 collodion solvent(s). The ignition charge usually referred to as “Bénite” is black powder agglomerated with a nitrocellulose binder. U.S. Pat. No. 3,182,595 describes a process of obtaining Benite strands by mechanically mixing the black powder ingredients with the collodion, followed by an extrusion and drying step. Another process consists of mechanically mixing the black powder with the collodion and then sealingly packaging it in a cartridge so as to obtain a paste that can be deposited in a pattern on a combustible support to obtain an ignition charge. This is the process currently used to supply ignition paste for the production of patterned ignition charges based on black powder with a nitrocellulose binder. The reference values shown in Table 16 are obtained with ignition pastes obtained using this process. Although collodion charged with ignition powder is classified in risk division 1.4 within the meaning of the UN GHS classification (UN Globally Harmonised System of Classification and Labelling of Chemicals), the processes of the prior art have the major disadvantage of simultaneously handling the ingredients of the black powder or the black powder itself in risk 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 together. This is all the more the case as the latter, whose distribution in the mechanical mixer is not controlled, may be in direct contact without yet having been wetted by the collodion. The manufacture of ignition pastes using conventional processes therefore requires adapted and restrictive installations in terms of pyrotechnical risk.

[0012] The person skilled in the art is therefore looking for an efficient process for obtaining an ignition 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 brought together, and with performances approaching those of conventional pastes. The manufacture of ignition pastes could then be envisaged for manufacturing installations in risk division 1.3 relating solely to the risk of live or deflagrating combustion.

[0013] On another level, WO 2009 / 091430 describes a process for charging a container with an energetic mixture which comprises a step of mixing the various constituents of the mixture, for example by acoustic resonance. US patent application 2017 / 0152196 describes a process for obtaining ignition compositions containing a metallic reductant, an oxidant and a binder. The process comprises mixing the various constituents of the composition and then granulating the mixture obtained. Mixers of the Simpson Mix-Muller or VibroAcoustic™ Mixers type are mentioned as likely to be used for mixing. However, the examples in this patent application do not contain any indication of the type of mixer used.SUMMARY OF THE INVENTION

[0014] In the remainder of this document, the reducing ingredient(s) of an ignition powder is referred to as a “reducing charge” and the oxidizing ingredient(s) of an ignition powder is referred to as an “oxidizing charge”. When several ingredients are present in a reducing or oxidizing charge, they may have been partially or totally premixed.

[0015] According to one aspect, the present invention relates to a process for obtaining an ignition paste containing the ingredients of an ignition powder, namely a reducing charge, an oxidizing charge and a cellulose collodion. The process comprises a step of premixing, in an acoustic resonance mixer, the reducing charge and / or the oxidizing charge with a collodion.

[0016] In one embodiment, the oxidizing charge and the reducing charge are mixed separately and simultaneously with collodion in an acoustic resonance mixer, and the two premixes obtained are then mixed together in the same mixer.

[0017] In one embodiment, the reducing charge and collodion are first mixed (in the mixer), then the oxidizing charge is added and the whole is mixed (still in the mixer).

[0018] In one embodiment, the oxidizing charge and collodion are first mixed (in the mixer), then the reducing charge is added and the whole is mixed (still in the mixer).

[0019] In one embodiment, a premix of reducing charge and collodion and a premix of oxidizing charge and collodion are prepared separately in an acoustic resonance mixer, and these two premixes are then mixed in an acoustic resonance mixer.

[0020] The ignition paste obtained 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. According to one aspect, the invention relates to a process for obtaining an ignition charge, which comprises depositing the ignition paste obtained as indicated above on a combustible support, and drying the combustible support.BRIEF DESCRIPTION OF THE FIGURES

[0021] FIG. 1 shows an ignition paste obtained according to the process of the invention.

[0022] FIG. 2 shows an ignition paste obtained according to the process of the invention.

[0023] FIG. 3 shows an ignition paste obtained according to the process of the invention.

[0024] FIG. 4 shows an image obtained by scanning electron microscopy of an ignition paste obtained according to the process of the invention.DESCRIPTION OF THE INVENTION

[0025] According to one aspect, the present invention relates to a process for obtaining an ignition paste containing the ingredients of an ignition powder, namely a reducing charge, an oxidizing charge, and a cellulose collodion, based on cellulose ether or cellulose ester. The process comprises a step of premixing, in an acoustic resonance mixer, the reducing charge and / or the oxidizing charge with collodion.

[0026] 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 forming an intermediate layer between the oxidizing charge and the reducing charge within the acoustic resonance mixer. In the first phase, the superimposed layers are mixed at low acoustic intensity. By “low intensity” is meant an intensity which ensures premixing of each charge with collodion, by phlegmatisation through film-forming wetting of each of the charges by collodion. The result of this low-intensity mixing is a layer of reducing charge premixed with the collodion, a residual layer of collodion in between, 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 eliminates the need to handle the pre-constituted ignition powder and the safety constraints associated with risk division class 1.1. Advantageously, low-intensity mixing is carried out in increments of increasing acceleration, over a range of values from approximately 10 g to approximately 50 g. As indicated above, at the end of this first phase, a layer consisting of the reducing charge premixed with (“phlegmatised by”) the collodion, a residual collodion interlayer, and a layer consisting of the oxidizing charge premixed with (“phlegmatised by”) the collodion are therefore present within the acoustic resonance mixer. In a second phase, preferably at higher acoustic intensity, the whole is intimately mixed to obtain the ignition paste. As indicated above, mixing is advantageously carried out in increments of increasing acceleration, over a range of values from about 50 g to about 100 g.

[0027] 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 above two steps is carried out in increments of increasing acceleration, over a range of values from approximately 10 g to approximately 100 g. This embodiment ensures an optimum level of safety since one of the charges of the ignition powder ingredients is already phlegmatised by the collodion before being introduced 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 bringing the oxidizing and reducing charges into direct dry contact.

[0028] In one embodiment, the reducing and oxidizing charges of the ignition powder are each mixed separately with collodion in an acoustic resonance mixer. Two distinct products are thus obtained, consisting on the one hand of the premix of the oxidizing charge with collodion and on the other hand of the premix of the reducing charge with collodion. These two premixes are then mixed in an acoustic resonance mixer to obtain the ignition paste. Advantageously, the quantity of collodion used in mixing with the reducing charge is substantially equal to the quantity of collodion used in mixing with the oxidizing charge. By “substantially equal” is meant a proportion (by weight) 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 above three steps is carried out in increments of increasing acceleration, over a range of values from about 10 g to about 100 g. In all embodiments, the final mixing by acoustic resonance can be carried out in the cartridge (so-called “Mix in case” process) used for depositing the paste on the combustible structure, a tubular structure for example 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.

[0029] The cellulose collodion used in the invention is based on a cellulose ester, typically of the cellulose ester+solvent type, or on a 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 about 70% to about 90% by weight) and generally additionally contains, conventionally, at least one plasticizer (about 1% to about 20% by weight, preferably about 10% by weight) and at least one stabilizer of the cellulose base (about 0.5% to about 5% by weight). It also generally contains at least one additive (>0% to approximately 1% by weight), for example chosen from anti-adhesion agents, anti-glare agents and antioxidants. It can contain a residual quantity of solvent(s), in particular phlegmatisation solvent(s) or (and) solvent(s) for dissolving the cellulose base used during its manufacture.

[0030] Advantageously, the cellulose ether used as the majority component of the cellulose base is ethyl cellulose, for example the ethyl cellulose described in patent application FR 3 064 639.

[0031] Advantageously, the cellulose ester used as the majority component of the cellulose base is chosen from cellulose nitrate, cellulose acetate or nitrocellulose, the latter being preferred. The nitrogen content by weight of the nitrocellulose is appropriately 10.5% to 13.5% of grade E7 to E12 (degree of polymerisation of nitrocellulose according to standard ISO 14446), preferably grade E11 nitrocellulose with a nitrogen content by weight of 11.8% to 12.3%, advantageously equal to 12%.

[0032] The plasticizer used to prepare the collodion can be, in particular, 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).

[0033] The stabilizer used to prepare the collodion can be, in particular, a compound whose chemical formula includes aromatic rings (appropriately two aromatic rings), capable of fixing the nitrogen oxides from the decomposition of nitric esters (currently nitrocellulose). Examples of stabilizers include 2-nitrodiphenylamine (2NDPA), 1,3-diethyl-1,3-diphenyl urea (centralite I), 1,3-dimethyl-1,3-diphenyl urea (centralite II) and 1-methyl-3-ethyl-1,3-diphenyl urea (centralite III).

[0034] The optional additive used to prepare the collodion can be chosen in particular from anti-adhesion agents, such as silicone-type anti-adhesion agents, anti-glare agents, antioxidants, dyes, surfactants, anti-caking agents and hydrophobic agents.

[0035] The solvent can be a double solvent of the acetone / butyl acetate (AB) type at 50% / 50% by weight or a double solvent of the ethyl lactate type for 35% to 60% by weight and butyl acetate for 40% to 65% by weight for a total of 100%.

[0036] The viscosity of the collodion, set by the nitrocellulose base / solvent(s) ratio, for use in 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 carried out at room temperature, and therefore without heating, so as to produce a film-forming coating of the preconstituted powder or of the reducing and oxidizing charges after mixing to obtain the ignition paste.

[0037] The collodion is advantageously formulated to give a dry extract (after evaporation of the solvent) of 10% to 40% by weight.

[0038] Table 2 below shows a collodion formulation at 14% solids by weight.TABLE 2CollodionComposition (% by weight)Cellulose base*Nitrocellulose8414Plasticizer10Stabilizer3.5Other (additive(s),2.5water, solvent, etc.)Total100AB43Acetone43Total100*Cellulose base of Nitrofilm ™ marketed by Eurenco

[0039] 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 weight of reducing and oxidizing charges, and the remainder to 100% (i.e. about 30% to about 50% by weight) of collodion.

[0040] The oxidizing and reducing charges are made up 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 weight ratios of oxidizing and reducing ingredients in the reducing and oxidizing charges are equivalent to those of an ignition powder. These weight ratios can nevertheless be modified if necessary to adjust the performance of the ignition paste obtained according to the invention.

[0041] Table 3 below gives an example of an ignition paste with the collodion composition of table 2, charged with an ignition powder, whether pre-constituted or not.TABLE 3Composition Raw materials(% by weight)Ignition powder (pre-mixed or not)56Collodion44Total100

[0042] After deposition and drying (evaporation of the solvent) of the ignition paste, the (dry) ignition charge adheres to the surface of the combustible structure and comprises approximately 88% to approximately 92% by weight of ignition powder, approximately 7% to approximately 10% by weight of cellulose ester, the remainder to 100% being provided by at least one compound chosen from a plasticizer, an additive and a residual solvent.

[0043] Ignition pastes according to the invention are classified in risk division 1.3 within the meaning of the UN GHS classification (UN Globally Harmonised System of Classification and Labelling of Chemicals). The danger zones to be taken into account when handling the loaded collodion are therefore reduced, which makes it easier to deposit the collodion on the combustible structure. In addition, the pastes according to the invention have a auto-ignition temperature by gradual heating (ATGH) of over 400° C., an ATGH which is therefore not controlled by that (~180° C.) of the nitrocellulose contained in the charge. Ignition pastes obtained according to the invention were produced in an acoustic resonance mixer in 400 g batches. These pastes have a 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 weight of approximately 20 g. After evaporation of the charged collodion solvent, each felt tube contains an ignition charge having a weight of approximately 11.5 g. From a visual point of view (appearance of the combustion residue), the deposition results are equivalent to those obtained with a conventional ignition paste. The combustion tests carried out in a manometric chamber on these tubes loaded with the ignition pastes of the invention produced characteristic combustion values which were reproducible between the samples and conformed to the reference values obtained in the prior art with granular black powder mechanically mixed with collodion in the weight percentages shown in table 3 (see table 16 at the end of the description).

[0044] The process of the invention is more efficient in terms of mixing speed, quality and safety than those of the prior art for obtaining ignition pastes of the cellulose-binder type. In addition, certain embodiments provide gains in terms of safety by avoiding the handling of preconstituted powder of risk division 1.1. The process of the invention also makes it possible to avoid direct dry contact between the oxidizing and reducing charges of the ignition powder. It also allows the ingredients to be optionally mixed directly in a cartridge which, once sealed, is ready to use for depositing ignition patterns.

[0045] According to another aspect, the invention relates to a process for obtaining an ignition charge, which comprises preparing an ignition paste according to the process defined above, depositing the ignition paste thus prepared on a combustible support, and drying the combustible support.

[0046] The invention is illustrated by the following examples, which are given by way of illustration. In these examples, the acoustic resonance mixer used is a Resodyn LabRam mixer with a maximum acceleration of 100 g at 60 Hz.Example 1 (Reference)

[0047] A mixture was prepared of the type Bénite B (as presented in patent application WO 2021 / 144538) with the ingredients given in Table 4.TABLE 4Weight Composition Raw materials(g)(% by weight)Black powder PN 7*23659Collodion**16441Total400100* Black powder according to Mil-P 223 specifications.**equivalent to that shown in Table 2.

[0048] The pot of an acoustic resonance mixer was filled in three layers: 50% of the total weight of collodion (82 g) / 100% of the weight of PN7 (236 g) / 50% of the total weight of collodion (82 g). An acoustic mixing cycle with an acceleration set at 35 g for 60 s was applied to the contents of the mixer to obtain a homogeneous mixture. A homogeneous ignition paste was obtained (FIG. 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.

[0049] The combustion results of this ignition paste deposited and dried on a combustible felt are given in Table 16 at the end of the description.Example 2

[0050] An ignition paste was prepared, similar to the Bénite type based on black powder.

[0051] The basic ingredients of the ignition paste are those contained in standard black powder:

[0052] Potassium nitrate (P),

[0053] Sulphur(S),

[0054] Charcoal (C) and,

[0055] the collodion is that shown in Table 2.

[0056] The ingredients P, S and C are selected in accordance with MIL military standards, well known to the skilled person.

[0057] The UN GHS (UN Globally Harmonised System of Classification and Labelling of Chemicals) risk divisions of these ingredients given in table 5 are outside class 1 and therefore do not generate a pyrotechnic risk.TABLE 5IngredientsRisk division (according to UN standard)Collodion  3 (flammable liquid)P5.1 (solid oxidizer)C4.2 (materials subject to spontaneous combustion)S4.1 (flammable solid).

[0058] The percentages by weight of the ingredients used in the ignition paste are shown in Table 6.TABLE 6Weight IngredientspercentagesChargesPotassium nitrate44.4%Sulphur 6.2%Charcoal 9.4%Total charge  60%CollodionDry cellulose base* 6.4%Solvent AB16.8%Solvent Acetone16.8%Total collodion  40%*equivalent to table 2.

[0059] Mixing the ingredients according to the weight percentages given in Table 6 led, after deposition and evaporation of the solvent, to a dry ignition charge whose composition is given in Table 7.TABLE 7Weight percentagein the dryignitionConstituentschargeP66.9%S 9.4%C14.1%Cellulose binder 9.6%Total 100%

[0060] This example uses the ingredients and proportions shown in Table 6 to obtain a final ignition paste weight of 400 g.

[0061] A premix of the reducing charge C+S was first carried out. As sulphur tends to be in the form of agglomerates, the mixture was mixed in an acoustic resonance mixer, in increments of increasing acceleration up to 70 g for a period of 4 minutes, in order to break up the agglomerates. After mixing, a homogeneous grey powder was obtained.

[0062] The homogeneous grey powder, the collodion and then KNO3, which had been coarsely de-coated by hand, were then placed in layers in this order in an acoustic resonance mixing pot. A progressive ramp of acoustic mixing intensity leading to increasing acceleration increments from 11 to 80 g was applied to obtain the ignition paste over a period of 6 minutes. Table 8 shows the increments of the mixing cycle. A temperature increase of less than 14° C. was observed during the mixing cycle.

[0063] The low acceleration at the start of mixing ensures that the homogeneous grey powder (reducing charge) is premixed with collodion, and that the oxidizing charge is premixed with collodion. These premixes ensure film-forming wetting (coating) of the reducing and oxidizing charges by the collodion before progressively more vigorous overall mixing. This prevents the reducing charge and oxidizing charge from coming into dry contact with each other, which could lead to a pyrotechnic incident.TABLE 8Mixing cycleDurationIntensityAcceleration(s)(%)(g)30301130502760704060806460907312010080

[0064] After mixing, a homogeneous ignition paste with a consistent appearance was obtained. Its viscosity of 100,000 mPa·s (Brookfield RV5 at 5 rpm-measurement temperature 21° C.) ensures that it can be poured onto a combustible structure.

[0065] 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.Example 3

[0066] As in Example 2, an ignition paste approaching the Bénite type based on black powder was prepared, using the ingredients and proportions in Table 6 to obtain a final weight of ignition paste of 400 g.

[0067] A C+S mixture and a P+collodion premix were made beforehand, before combining them to obtain a mixture for the ignition paste.

[0068] Charcoal (C) and sulphur(S) were thus premixed in the pot of an acoustic resonance mixer under the same conditions as those described in Example 2, to give a homogeneous grey powder. Separately, potassium nitrate (P), which had previously been coarsely broken down by hand, and the collodion were mixed in the pot of another acoustic resonance mixer. A premix of the oxidizing charge with the collodion was thus obtained. This premixing was carried out with a progressive intensity ramp leading to increasing accelerations up to 70 g for a duration of 3 minutes as shown in Table 9. A slight temperature increase of about 4° C. was observed at the end of the mixing cycle. A white paste was obtained, consisting of grains of potassium nitrate coated with collodion, which has a film-forming property. This makes it possible to phlegmatise the mixture that will be produced when this white paste is placed in the presence of the reducing charge (C+S).TABLE 9Mixing cycleDurationIntensityAcceleration(s)(%)(g)605048306057307063308069909074

[0069] Finally, the homogeneous grey C+S powder and the white paste (P+collodion) were brought together in the pot of an acoustic resonance mixer. Acoustic mixing was carried out with 3 intensity increments leading to successive accelerations of ~23 g, ~41 g and ~57 g for a duration of 3 minutes as shown in Table 10. A small temperature increase of about 8° C. was observed at the end of the mixing cycle.TABLE 10Mixing cycleDuration Intensity Acceleration(s)(%)(g)603023605041607057

[0070] After mixing, a homogeneous ignition paste with a consistent appearance was obtained. Its viscosity of 70,000 mPa·s (Brookfield RV5 at 5 rpm-measurement temperature 21° C.) ensures that it can be poured onto a combustible structure (FIG. 2).

[0071] 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.Example 4

[0072] An ignition paste containing boron (B), potassium nitrate (P) and the collodion shown in Table 2 was prepared. Once dried, this ignition paste is similar to BKNO3 ignition powder with a polyester binder conforming to MIL-P-46994B containing 70.7%±2.0% P, 23.7%±2.0% B and 5.6%±2.0% polyester binder.

[0073] The B and P are selected in accordance with this MIL standard, with the exception of the particle size of the P, which may be less than 100 μm instead of the maximum 15 μm indicated in MIL-P-46994B; this particle size of the P makes it possible to obtain a paste with better homogeneity and flowability.

[0074] The collodion used is that shown in Table 2. The weight percentages of the ingredients used in the ignition paste are shown in Table 11.TABLE 11Weight IngredientspercentagesChargesPotassium nitrate52.4%Boron17.6%Total charge  70%CollodionDry cellulose base* 4.8%Solvent AB12.6%Solvent Acetone12.6%Total collodion  30%*equivalent to table 2.

[0075] Mixing the ingredients according to the weight percentages given in Table 11 led, after deposition and evaporation of the solvent, to a dry ignition charge whose composition is given in Table 12.TABLE 12Weight percentagein the dryignitionConstituentscharge.Potassium nitrate70.1%Boron23.5%Cellulose binder 6.4%Total 100%

[0076] This example uses the ingredients and proportions shown in Table 11 to obtain a final ignition paste mass of 400 g.

[0077] Boron, collodion and then KNO3, which had previously been coarsely broken down by hand, were arranged in this order in superimposed layers in a pot for mixing by acoustic resonance. A progressive ramp of acoustic mixing intensity leading to increasing acceleration increments from 6 to about 61 g was applied to obtain the ignition paste over a period of 15 minutes. A temperature increase of less than 14° C. was observed during the mixing cycle.

[0078] The low acceleration at the start of mixing ensures premixing of the boron (reducing charge) with the collodion and premixing of KNO3 (oxidizing charge) with the collodion. These premixes ensure film-forming wetting (coating) of the reducing and oxidizing charges by the collodion before progressively more vigorous overall mixing. This prevents the reducing charge and oxidizing charge from coming into dry contact with each other, which could lead to a pyrotechnic incident.

[0079] The paste obtained has a gutter combustion speed of 91 mm / s and an ATGH in excess of 400° C. Sensitivity to friction is negligible and sensitivity to impact remains within the values accepted for granular explosive materials. These preliminary safety results are therefore favourable and will undoubtedly lead to the paste being used (handled and transported) in risk division 1.3.

[0080] The same type of test was carried out with a paste containing 60% charges (45% KNO3, 15% boron) and 40% collodion to assess the influence of the nitrocellulose weight ratio in the paste on the ATGH. Even with this higher nitrocellulose content, the ATGH of the paste remains above 400° C. After mixing in a cycle identical to the previous one, a homogeneous ignition paste was obtained with a consistent appearance. Its viscosity of about 100,000 mPa·s (Brookfield RV5 at 5 rpm-measurement temperature 21° C.) ensures that it can be poured onto a combustible structure (FIG. 3). FIG. 4 shows an image obtained by scanning electron microscopy of the ignition charge after drying of this paste. A very good homogeneity of the distribution of the boron (black grains) and KNO3 (whitish grains) charges in cohesion with the nitrocellulose binder (not visible in the image) was observed.Example 5

[0081] An ignition paste was prepared containing magnesium (Mg), polytetrafluoroethylene (PTFE), commercially known as Teflon™ PTFE 7A X from the company Chemours, and the collodion of Table 2. The magnesium powder has a purity greater than 97% and a particle size of less than 0.21 mm, the PTFE grains have a particle size of less than 0.42 mm. The process for preparing this ignition paste is similar to that of examples 2 and 4: the magnesium, collodion and then PTFE were arranged in this order in superimposed layers in a pot for mixing by acoustic resonance. A progressive ramp of acoustic mixing intensity leading to increments of increasing acceleration, similar to those mentioned in Table 8, was applied to obtain the ignition paste over a period of about 4 minutes. A temperature increase of less than 14° C. was observed during the mixing cycle.

[0082] 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) of the reducing and oxidizing charges by the collodion before progressively more vigorous overall mixing. This prevents the reducing charge and oxidizing charge from coming into dry contact with each other, which could lead to a pyrotechnic incident.

[0083] Once dried, this ignition paste is similar to the MTV ignition powder with binder Viton™ B (hexafluoroisoprene-vinylidene fluoride copolymer) marketed by the company Chemours containing 58% Mg, 38% Teflon™ PTFE 7A X and 4% Viton™ B.

[0084] The collodion used is that shown in Table 2. The weight percentages of the ingredients used in the ignition paste are shown in Table 13.TABLE 13Weight IngredientspercentagesChargesPTFE23.3%Magnesium35.6%Total charge  59%CollodionDry cellulose base* 6.6%Solvent AB17.2%Solvent Acetone17.2%Total collodion  41%*equivalent to table 2.

[0085] Mixing the ingredients according to the weight percentages given in Table 13 led, after deposition and evaporation of the solvent, to a dry ignition charge, the composition of which is given in Table 14.TABLE 14Weight percentagein the dryignitionConstituentscharge.PTFE35.6%Magnesium54.4%Cellulose binder  10%Total 100%

[0086] The process of the invention in its various embodiments, in addition to the compositions of Examples 2 to 5, can be used to obtain any pyrotechnic paste containing an oxidizing charge, a reducing charge and a cellulose ether- or cellulose ester-based collodion. Table 15 below lists, by no means exhaustively, oxidizing charge and reducing charge pairs which can be used. Depending on the properties required, the paste composition can also contain mixtures of oxidizing and reducing charges chosen from different pairs, for example the C / KNO3 or C+S / KNO3 pair and the sodium benzoate / KClO4 pair.TABLE 15Reducing charge / oxidizing charge pairChemical formulaAluminum / potassium perchlorateAl / KClO4Zirconium / barium chromateZr / BaCrO4Aluminum / copper oxideAl / CuOMagnesium / sodium nitrate-potassium nitrateMg / NaNO3 / KNO3Zirconium / lead chromateZr / PbCrO4Zirconium-nickel / potassium perchlorate-barium nitrateZrNi / KClO4-Ba(NO3)2Caesium decahydroborate / potassium nitrateCS2B10H10 / KNO3Sodium benzoate / potassium perchlorateC7H5NaO2 / KClO4TABLE 16Weightof theMeanMeanWeightignitionMax.derivativevelocity ofType of ignitionof thechargePressuredP / dtStrengthdetonationchargeSampletube (g)(g)(MPa)(MPa / ms)(MJ / kg)A0 (1 / s)Reference values (*)~19.5~11.761.390.43153.3Ignition charge ofRIC119.8911.4260.768.040.430132.40example 2RIC220.1211.561.277.430.429121.22RIC320.3611.5862.127.450.429119.91Ignition charge ofRIC420.2311.7262.018.210.429132.49example 3RIC520.0811.6961.277.680.427125.33RIC620.411.5762.438.800.431140.94(*) obtained in the prior art with black granular powder mechanically mixed with collodion in the weight percentages shown in Table 3.

Examples

example 1 (

Example 1 (Reference)

[0047]A mixture was prepared of the type Bénite B (as presented in patent application WO 2021 / 144538) with the ingredients given in Table 4.

TABLE 4Weight Composition Raw materials(g)(% by weight)Black powder PN 7*23659Collodion**16441Total400100* Black powder according to Mil-P 223 specifications.**equivalent to that shown in Table 2.

[0048]The pot of an acoustic resonance mixer was filled in three layers: 50% of the total weight of collodion (82 g) / 100% of the weight of PN7 (236 g) / 50% of the total weight of collodion (82 g). An acoustic mixing cycle with an acceleration set at 35 g for 60 s was applied to the contents of the mixer to obtain a homogeneous mixture. A homogeneous ignition paste was obtained (FIG. 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.

[0049]The combustion results of this ignition paste deposited and dried on a combustible felt are ...

example 2

[0050]An ignition paste was prepared, similar to the Bénite type based on black powder.

[0051]The basic ingredients of the ignition paste are those contained in standard black powder:[0052]Potassium nitrate (P),[0053]Sulphur(S),[0054]Charcoal (C) and,[0055]the collodion is that shown in Table 2.

[0056]The ingredients P, S and C are selected in accordance with MIL military standards, well known to the skilled person.

[0057]The UN GHS (UN Globally Harmonised System of Classification and Labelling of Chemicals) risk divisions of these ingredients given in table 5 are outside class 1 and therefore do not generate a pyrotechnic risk.

TABLE 5IngredientsRisk division (according to UN standard)Collodion  3 (flammable liquid)P5.1 (solid oxidizer)C4.2 (materials subject to spontaneous combustion)S4.1 (flammable solid).

[0058]The percentages by weight of the ingredients used in the ignition paste are shown in Table 6.

TABLE 6Weight IngredientspercentagesChargesPotassium nitrate44.4%Sulphur 6.2%Charc...

example 3

[0066]As in Example 2, an ignition paste approaching the Bénite type based on black powder was prepared, using the ingredients and proportions in Table 6 to obtain a final weight of ignition paste of 400 g.

[0067]A C+S mixture and a P+collodion premix were made beforehand, before combining them to obtain a mixture for the ignition paste.

[0068]Charcoal (C) and sulphur(S) were thus premixed in the pot of an acoustic resonance mixer under the same conditions as those described in Example 2, to give a homogeneous grey powder. Separately, potassium nitrate (P), which had previously been coarsely broken down by hand, and the collodion were mixed in the pot of another acoustic resonance mixer. A premix of the oxidizing charge with the collodion was thus obtained. This premixing was carried out with a progressive intensity ramp leading to increasing accelerations up to 70 g for a duration of 3 minutes as shown in Table 9. A slight temperature increase of about 4° C. was observed at the end o...

Claims

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

2. The process of claim 1, which comprises: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. The process of claim 2, comprising incrementing an increased acceleration in each of steps a) and b).

4. The process of claim 1, which comprises:a) premixing the reducing charge with collodion in an acoustic resonance mixer;b) premixing the oxidizing charge with collodion in an acoustic resonance mixer;c) mixing, in an acoustic resonance mixer, the product obtained in step a) with the product obtained in step b).

5. The process of claim 4, wherein substantially equal amounts of collodion are used in step a) and step b).

6. The process of claim 1, comprising:a) introducing the reducing charge, the collodion and the oxidizing charge in superimposed layers into an acoustic resonance mixer, whereby the collodion forms an intermediate layer between the reducing charge and the oxidizing charge;b) applying an acoustic intensity to the superimposed layers, in increments of increasing acceleration, whereby a layer of reducing charge premixed with the collodion, a residual layer of collodion inbetween, and a layer of oxidizing charge premixed with the collodion are formed in the mixer;c) applying an acoustic intensity greater than that used in step b) to the premixes obtained in step b), in increments of increasing acceleration.

7. The process of claim 6, comprising implementing in step b) increments of increasing acceleration over a range of values from about 10 g to about 50 g.

8. The process of claim 1, in which the ignition paste comprises about 50% to about 70% by weight of reducing and oxidizing charges, and about 30% to about 50% by weight of collodion.

9. The process of claim 1, in which the collodion is a cellulose ester-based collodion.

10. The process of claim 9, in which the collodion comprises, by weight:about 70% to about 90% of a cellulose ester;about 1% to about 20% of at least one plasticizer;about 0.5% to about 5% of at least one cellulose ester stabilizer;>0% to about 1% of at least one additive.

11. The process of claim 1, in which the collodion is a cellulose ether-based collodion.

12. The process of claim 11, in which the collodion comprises, by weight:about 70% to about 90% of a cellulose ether;about 1% to about 20% of at least one plasticizer;about 0.5% to about 5% of at least one cellulose ether stabilizer;>0% to about 1% of at least one additive.

13. A process of obtaining an ignition charge, which comprises preparing an ignition paste according to the process defined in claim 1, depositing the ignition paste thus prepared on a combustible support, and drying the combustible support.

14. The process of claim 10, in which the cellulose ester is nitrocellulose.

15. The process of claim 12, in which the cellulose ether is ethyl cellulose.

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