EP0079273B1 - Self-fragmenting fireworks - Google Patents

Description

The invention relates to an illuminating pyrotechnic device, intended to emit a light flux from multiple mobile point sources, in particular during fireworks shows, this pyrotechnic device consisting of an envelope which contains a solid pyrotechnic composition made from at least one polymerized binder, an oxidant and a combustible metal.

Pyrotechnic devices comprising an incombustible or scarcely combustible external envelope are in common use, and for example the Bengal lights are very often constituted by a thick cardboard tube in which is poured and solidified the illuminating pyrotechnic composition which adheres completely to this envelope .

Illuminating pyrotechnic compositions with polymerized binder are known, and for example French patent 2 248 252 relates to such compositions which have a high luminous efficacy and which use a binder which can be either a polybutadiene carboxylic or a silicone, such compositions being intended to be shaped into cylinders, in order to constitute signaling torches or lighting devices which have a long operating life since these compositions burn in parallel layers, as a propellant would do, and the combustion rate is low, generally less than 2 millimeters per second. More particularly, such illuminating compositions using a binder of the phenoplast type are also known from patent FR 2 471 959, which describes in particular a block burning in parallel layers with a diameter of 45 millimeters in which the mineral oxidant has a particle size less than 100 micrometers and which comprises a metallic fuel, the patent GB 1 202390 also describing compositions with a polymerized binder of the phenoplast type comprising an oxidant and a combustible metal.

The object of the present invention is to produce pyrotechnic devices, the composition of which bursts into a multitude of incandescent fragments after ignition, the different fragments continuing to burn and to emit sparks with a bright glow which marks their aerial trajectories, l 'assembly constituting an immense star or an immense scintillating sheaf, and, the invention is characterized in that on the one hand this block comprises incipient fractures within this composition, caused by rapid cooling after polymerization which creates tensions internal, and on the other hand the pyrotechnic composition only partially adheres to the envelope, so that this composition bursts after the ignition of the device.

These characteristics allow the fragmentation of the pyrotechnic composition, the firing taking place not only on the free surface of the composition, but also in the zones of non-adhesion to the envelope, which has the effect of creating zones local lateral overpressures which favor the bursting of the initial block of composition into a multitude of fragments. According to the usual embodiment, the envelope is cylindrical and has an internal diameter greater than 20 millimeters for the most effective compositions, with easy comminution, and greater than 30 millimeters for the compositions with current comminution.

More particularly, the phenoplast binder is an alkaline phenolic resin which polymerizes at a temperature above 140 ° C. In fact, it has been observed during the tests that the resins which catalyze in an acid medium and the phenol-formaldehyde-resorcinol resins make it only difficult to obtain self-dispersible compositions, and require a much greater heat treatment which is difficult to reproduce. During these tests, it was also discovered that below a polymerization temperature of 140 ° C., the self-dispersing effect considerably diminishes, all the more so since the phenolic resin is very alkaline and is very condensed, the condensation being in direct relation with the length of the molecular chain of the prepolymer and therefore with the initial viscosity of this prepolymer.

Advantageously, the unpolymerized phenoplast binder has a concentration of less than 60% and constitutes from 25 to 45% of the total weight of the pyrotechnic composition. The concentration is the percentage of solid products relative to the solvent, this solvent possibly being in particular water, alcohol or formaldehyde, and a concentration rate of less than 60% makes it possible to obtain a polymerization shrinkage sufficient for producing detachments between the polymerized composition and the envelope which partially surrounds this composition, which facilitates the subsequent bursting of the block of polymerized composition. The tests carried out made it possible to note that the proportions of phenoplast binder in the composition had a direct influence on the fragmentation of the polymerized block at the time of ignition and, it was observed on the one hand that below 25% of binder most of the compositions prepared no longer burst, even when the concentration was less than 50% and the cooling rate was increased, and on the other hand, that above 45% of binder, the swelling during the polymerization was such that deep slits could appear in the composition, which weakens its mechanical strength and affects the possibilities of transport or storage.

More particularly, the phenoplast binder is combined with an oxidant chosen from the group of perchlorates of alkaline character, and more particularly with potassium perchlorate, introduced in proportions of between 40% and 60% of the total weight of the composition. The particle size of the oxidant is one of the essential parameters which allows the adjustment of the burst effect, and preferably the particle size is less than 100 micrometers and even less than 70 micrometers when the cooling of the composition is not fast enough or when blocks with a diameter less than 50 millimeters want to be obtained.

More particularly, the phenoplast binder is combined with a combustible metal which constitutes from 10% to 30% of the total weight of the pyrotechnic composition, and the combustible metal can be passivated aluminum such as oxidized or surface chromated aluminum.

Advantageously, the pyrotechnic composition is polymerized in place in the outer envelope, but it is then desirable for the binder to be an alkaline phenolic resin, the polymerization temperature of which is greater than 140 ° C., and this outer envelope is conveniently constituted by a cylindrical tube. provided with a bottom. According to another embodiment of the invention, cylindrical blocks of polymerized composition can be added in external envelopes, but it is then advantageous that on the one hand a clearance of at least a few tenths of a millimeter is provided, and that on the other hand, a discontinuous bonding is carried out between this block and this envelope so as to provide zones of lateral inflammation, the zones of non-adhesion having to be all the more important on the surface the smaller the dimension of the block. .

According to an essential characteristic of the invention, after the polymerization time of the binder, carried out in an oven, the device is immediately placed in the open air, the various devices being sufficiently distant from each other so that the thermal interactions are negligible . The internal tensions and the incipient fractures, constituted by microcracks which determine a three-dimensional network of cracks, can be increased either by choosing an alkaline phenolic resin which polymerizes at higher temperature, or by carrying out a more rapid cooling after polymerization, for example , by placing the fireworks in a stream of air at room temperature, or by placing the fireworks in cells formed in metal plates which are partially immersed in a coolant.

The advantages obtained thanks to this invention essentially lie in the distribution of the light source within a very large volume. Such a distribution can be used in particular in the context of a firework show to constitute "very large flashovers which are similar to light fountains since each fragment of the initial block emits multiple stars, which remain lit for a few seconds or a few fractions of seconds, and which mark the wake of these fragments. This distribution of the light source in a very large volume can also be useful for intense short-term illumination, generally less than 5 seconds, which attenuates the shadows cast, and, applications can be envisaged either for the lighting of monuments, or sites as part of a "sound and light show using articles, or for the temporary lighting of a" battlefield ".

In what follows, the invention is explained in more detail with the aid of some exemplary embodiments belonging to the preferred field.

• 25 à 45% de résine phénolique légèrement alcaline et faiblement condensée durcissant à une température supérieure à 160 °C,
• 40 à 60 % de perchlorate de potassium,
• 10 à 30% d'aluminium oxydé,

et les proportions relatives de ces constituants étant définies par les relations :

The best bursting and self-dispersing properties have been obtained with compositions of the type: phenolic resin, alkaline perchlorate and combustible metal, when a slightly alkaline phenolic resin is used, which solidifies above 140 ° C, and that on the other hand the solidified composition is brought quickly to room temperature. The work carried out made it possible to select the other most appropriate constituents and to determine their respective proportions, and the best results in terms of the distribution and intensity of the light source were obtained by using potassium perchlorate and the passivated aluminum, the weight limits being as follows:

• 25 to 45% of slightly alkaline and weakly condensed phenolic resin hardening at a temperature above 160 ° C,
• 40 to 60% potassium perchlorate,
• 10 to 30% oxidized aluminum,

and the relative proportions of these constituents being defined by the relationships:

With regard to the manufacture of the fireworks according to the present invention, it should be noted that the non-polymerized composition is in the form of a more or less thick pourable liquid, or of an injectable soft paste, which offers great manufacturing safety since the fluid composition is hardly flammable and no significant evacuation of solvent is to be expected. In addition, in the preferred area defined above, all of the compositions are pourable and, for the most part, require only cooling in the open air after polymerization in an oven, the use of forced air or refrigeration tanks. may nevertheless be necessary for compositions close to the limits of the preferential range.

This preferred area of the invention therefore excludes the phenoplast binders which catalyze in an acid medium, because these binders lead to a very reduced and not instantaneous dispersion, the device then tending to behave more like an illuminating fountain with irregular frontal combustion than like a self-dispersing block; more the use of an acidic catalytic system requires the use of rigorously passivated aluminum in order to avoid attack by the acid, and the evolution of hydrogen which accentuates the swelling at the time of the polymerization harms a homogeneous and reproducible polymerization. The phenolic resin sold by the French company CDF-CHIMIE under the reference 1221 constitutes an example of binder with which it is very difficult to carry out the invention in a satisfactory manner.

The preferred field of the invention also excludes very alkaline and very condensed phenolic resins which are self-hardening at 120 ^D C because such resins, for example that marketed by the company HOECHST under the reference PHENODUR PW 799, cause significant swelling of the paste into during polymerization, but the device obtained fragments only partially and irregularly, in particular when rapid cooling is only carried out in the open air.

In the preferred field of the invention, one of the resins allowing the best results to be obtained is the resin sold by the company HOECHST under the reference PHENODUR PW 759. It is a resin which uses water as solvent, this which is particularly advantageous in terms of safety, which is self-hardening in one hour at 170 ° C., which is slightly alkaline, which has a concentration of 50%, and which is weakly condensed. It should however be noted that the raw aluminum is slightly attacked by this resin and that it is therefore preferable to use passivated aluminum to obtain a more spectacular light effect. The nature, the rate and the quality of the combustible metal to be used are essentially determined by the light effects sought by a person skilled in the art, and, for example, by choosing as a base a rate of 13% of thinly oxidized fine aluminum. , combined with potassium perchlorate with a particle size of 40 μm and with HOECHST resin reference PW 759, the various examples below illustrate the possibilities of implementation:

The tests were carried out by pouring these compositions, given as examples, into 1.5 mm thick cardboard tubes, provided with an insert also made of cardboard, the internal diameter of which is 34 millimeters and the height of 50 millimeters. , the composition weight being 45 grams per tube, which corresponds to an initial filling substantially equal to three quarters of the internal volume of the tubes. After polymerization in an oven at a temperature of 170 ° C for one hour, the fireworks are extracted from the oven and suddenly pass from 170 ° C to 18 ° C in a ventilated room, these fireworks being spaced apart from each other by about 25 centimeters and being arranged on the same plane.

This rapid cooling which follows the swelling of the resin during the polymerization creates stresses in the block which contracts, and this effect triggers two reactions: on the one hand the block of composition peels off partially from the walls of a few tenths of a millimeter avoiding the blocking of the block by the cardboard tube, and on the other hand the composition block cracks randomly, thus creating a sort of three-dimensional network which will promote separation into fragments at the time of ignition. The swelling during the polymerization is very important since it can reach a quarter of the initial volume, while the contraction by cooling is much weaker, however it is the cooling phase which is essential to obtain the bursting of the block and it is these cooling conditions which must be adapted to optimize the desired effect, the initial bursting regime more or less close to an internal explosion being caused by the very large initial combustion surface offered by the internal slots and the detached areas of the carton, which ensure the initial pressurization and determine the bursting of the composition block. This bursting phenomenon also depends on the particle size of the oxidant and the smallest dimension of the block, the bursting being favored by a fine particle size, less than 70 micrometers, and by the increase in the smallest dimension, if possible beyond 25 millimeters.

The ignition of the test devices was carried out with a simple drill bit in contact with the free surface of the cylindrical block of composition, but any other means of ignition commonly used by the fireworks can be used, in particular a relay charge , a primer, or a pyrotechnic delay.

The ignitions of the devices of examples n ^Ds 2, 3 and 4 determine real instantaneous explosions which project in a radius of 40 meters small incandescent and very bright fragments. The number of fragments and the directions of projections are random, but there are compensation effects between the thousands of ejected fragments, and the overall effects are very well reproducible. Each incandescent fragment is accompanied by a trail of stars which remain lit for a few seconds, and the combustion of the largest fragments can reach 5 seconds.

The manufacturing of the device n ° 1 leads to an excessive swelling during the polymerization which leads to poorer mechanical properties, as for the devices in Example 5, cooling in the open air is no longer suitable, because the block burns with strong projections of incandescent elements, which causes an effect appreciable aesthetics, but the artifice does not burst significantly and repetitively.

• 33 % de résine PW 759,
• 42 % de perchlorate de potassium (40 µ),
• 25 % d'aluminium oxydé,

donne entière satisfaction et éclate instantanément lors de la mise à feu lorsque les blocs présentant un diamètre de 30 millimètres ou de 50 millimètres mais, par contre, il a été observé qu'un bloc d'un diamètre de 12 millimètres ne pouvait pas éclater, malgré les différents essais effectués en abaissant la granulométrie du perchlorate, en adoptant une enveloppe résistante, ou en trempant les blocs à la sortie de l'étuve de polymérisation. Le taux de résine peut être abaissé jusqu'à 25 %, mais toutefois en dessous d'un taux de 30 % la viscosité commence a être importante pour conserver un procédé de remplissage des enveloppes tubulaires externes par coulée, et un procédé d'injection est alors souhaitable, bien que la présence de bulles au sein de la composition ou entre la composition et l'enveloppe ne constitue pas un inconvénient majeur.The use of a higher rate of combustible metal is possible while remaining in the preferred field of the invention, and compositions with 25% of passivated aluminum have been produced. A composition such as:

• 33% PW 759 resin,
• 42% potassium perchlorate (40 µ),
• 25% oxidized aluminum,

gives complete satisfaction and bursts immediately upon firing when the blocks having a diameter of 30 millimeters or 50 millimeters but, on the other hand, it has been observed that a block with a diameter of 12 millimeters could not burst, despite the various tests carried out by lowering the particle size of the perchlorate, by adopting a resistant envelope, or by soaking the blocks at the outlet of the polymerization oven. The rate of resin can be lowered up to 25%, but however below a rate of 30% the viscosity starts to be important to preserve a process of filling of the external tubular casings by casting, and an injection process is then desirable, although the presence of bubbles within the composition or between the composition and the envelope does not constitute a major drawback.

The pyrotechnic lighting device according to the invention can be surrounded by a resistant tube which transforms the multidirectional burst into a directed jet whose incandescent fragments and generators of lasting sparks are projected at great distance.

Claims (16)

1. Illuminating pyrotechnic device consisting of an envelope containing a block of pyrotechnic composition, the smallest dimension of which is greater than 15 millimetres, the said block being produced from at least one polymerised binder of the phenoplast type, an oxydising agent of particle size less than 150 micrometres and a combustible metal, characterised in that, on the one hand, this block possesses rupture starting points within the said composition, these being created by rapid cooling after polymerisation so as to create internal stresses, and that, on the other hand, the pyrotechnic composition only adheres partially to the envelope, so that the composition bursts after the device has been lit.

2. Pyrotechnic device according to Claim 1, characterised in that the envelope is cylindrical and has an internal diameter greater than 20 millimetres.

3. Pyrotechnic device according to Claim 1, characterised in that the phenoplast binder is a phenolic resin.

4. Pyrotechnic device according to Claim 3, characterised in that the phenolic resin polymerises at a temperature above 140 °C.

5. Pyrotechnic device according to Claim 3 or 4, characterised in that the phenolic resin is an alkaline resin.

6. Pyrotechnic device according to one of Claims 1 or 3, characterised in that the unpolymerised phenoplast binder has a concentration of less than 60 %.

7. Pyrotechnic device according to one of Claims 1 or 3, characterised in that the phenoplast binder constitutes from 25 to 45 % of the total weight of the unpolymerised pyrotechnic composition.

8. Pyrotechnic device according to one of Claims 1, 3 or 7, characterised in that the phenoplast binder is combined with an oxidising agent chosen from the group of the alkaline perchlorates.

9. Pyrotechnic device according to one of Claims 1 or 8, characterised in that the oxidising agent has a particle size of less than 100 micrometres.

10. Pyrotechnic device according to one of Claims 8 or 9, characterised in that the alkaline perchlorate is potassium perchlorate introduced in proportions of between 40 and 60 % of the total weight of the composition.

11. Pyrotechnic device according to one of Claims 9 or 10, characterised in that the potassium perchlorate has a particle size of less than 70 micrometres.

12. Pyrotechnic device according to one of Claims 1, 3 or 7, characterised in that the phenoplast binder is combined with a combustible metal which constitutes from 10 to 30 % of the total weight of the pyrotechnic composition.

13. Pyrotechnic device according to one of Claims 1 or 12, characterised in that the combustible metal consists of passivated aluminium.

14. Pyrotechnic device according to one of Claims 1, 4 or 5, characterised in that the pyrotechnic composition is polymerised in situ in the outer envelope.

15. Pyrotechnic device according to one of Claims 1, 2 or 14, characterised in that the envelope consists of a cylindrical tube provided with a bottom.

16. Pyrotechnic device according to one of Claims 1 or 14, characterised in that after the period of polymerisation of the binder, carried out in an oven, the device is immediately exposed to the atmosphere.