EP0079273A1 - Self-fragmenting fireworks - Google Patents

Abstract

Pyrotechnic device intended to emit a luminous flux from multiple mobile point sources, in particular during fireworks shows. The lighting pyrotechnic device is constituted by an envelope containing a block of pyrotechnic composition produced from at least one polymerized binder, an oxidant and a combustible metal. In order to obtain the bursting of the composition into a multitude of incandescent fragments during the ignition of the device, the pyrotechnic composition is produced from a binder of the phenoplast type and from an oxidant whose particle size is less than 150 micrometers, and the block, the smallest dimension of which is greater than 15 millimeters, has undergone rapid cooling which creates internal tensions and incipient fractures within this composition.

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 being constituted by 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 hardly 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.

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 the pyrotechnic composition is carried out starting from a binder of the phenoplast type and an oxidizing agent whose particle size is lower at 150 micrometers, and on the other hand the smallest dimension of the block is greater than 15 millimeters, this block having undergone rapid cooling after polymerization, which creates internal tensions and incipient fractures within this composition.

According to an embodiment which facilitates the fragmentation of the pyrotechnic composition, this composition only partially adheres to the envelope, so that the ignition takes place not only on the free surface of the composition, but also in areas of non-adhesion to the envelope, which has the effect of creating local areas of lateral overpressure 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-Formol-Resorcin resins do not allow it is difficult to obtain self-dispersing 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 diminishes considerably, 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 bursting effect, and preferably the particle size is less than 100 micrometers and even less than 70 micrometers when the composition is not cooled enough. fast or when blocks with a diameter less than 50 millimeters want to be obtained.

More particularly the phenoplast binder is combined with a metal fuel which constitutes from 10 _% to 30% of the total weight of the pyrotechnic composition, and the combustible metal can be passive 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 greater 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. , by placing the fireworks in a stream of air at room temperature, or by placing the fireworks in cells provided in metal plates which are partially immersed in a coolant.

The advantages obtained thanks to this invention lie essentially in the distribution of the light source within a very large volume. Such a distribution can be used in particular in as part of a fireworks show to constitute very large "conflagrations" 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 thus 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 fireworks, 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 using on the one hand a slightly alkaline phenolic resin which solidification takes place 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 passive 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% of potassium perchlorate,
• - 10 to 30% of 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 field of the invention therefore excludes the phenoplast binders which catalyze in an acid medium, since 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; in addition, the use of an acidic catalytic system requires the use of strictly passive aluminum in order to avoid attack by the acid, and the evolution of hydrogen which accentuates the swelling at the time of 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 a binder with which it is very difficult to carry out the invention satisfactorily.

The preferred field of the invention also excludes very alkaline and highly condensed phenolic resins which are self-hardening at 120 ° 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 enabling the best results to be obtained is the commercial resin. read by the company HOECHST under the reference PHENODUR PW 759. It is a resin which uses water as solvent, 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 passive 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 ¿"m and with HOECHST resin reference PW 759, the different examples below illustrate the possibilities of implementation:

Les essais ont été réalisés en coulant ces compositions données en exemple dans des tubes de carton de 1,5 mm d'épaisseur, munis d'un fond rapporté également en carton, dont le diamètre intérieur est de 34 millimètres et la hauteur de 50 millimètres, le poids de composition étant de 45 grammes par tube, ce qui correspond à un remplissage initial sensiblement égal aux trois quarts du volume interne des tubes. Après polymérisation en étuve à une température de 170°C pendant une heure, les artifices sont extraits de l'étuve et passent brutalement de 170°C à 18°C dans un local aéré, ces artifices étant espacés les uns des autres d'environ 25 centimètres et étant disposés sur un même plan.

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 on 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 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 fragments ejected, and the overall effects are very well reproduc tibles. 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 manufacture of the device No. 1 leads to excessive swelling during the polymerization, which leads to poorer mechanical properties, as for the devices of Example No. 5, cooling in the open air is no longer suitable. , because the block burns with strong projections of incandescent elements, which results in an appreciable aesthetic effect, but the device does not burst significantly and repetitively.

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 passive aluminum have been produced.

• 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.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 (17)

1- Illuminating pyrotechnic device constituted by an envelope containing a block of pyrotechnic composition produced from at least one polymerized binder, an oxidant and a combustible metal, characterized in that, on the one hand, the pyrotechnic composition is produced from '' a binder of the phenoplast type, and an oxidant whose particle size is less than 150 micrometers, and on the other hand the smallest dimension of the block is greater than 15 millimeters, this block having undergone rapid cooling after polymerization which creates internal tensions and incipient fractures within this composition, so that this composition bursts after the ignition of the device. 2- pyrotechnic device according to claim 1, characterized in that the pyrotechnic composition only partially adheres to the envelope. 3- pyrotechnic device according to one of claims 1 or 2 characterized in that the envelope is cylindrical and has an internal diameter greater than 20 millimeters. 4- pyrotechnic device according to claim 1, characterized in that the phenoplast binder is a phenolic resin. 5- pyrotechnic device according to claim 4, characterized in that the phenolic resin polymerizes at a temperature above 140 ° C. 6- Pyrotechnic device according to claim 4 or 5, characterized in that the phenolic resin is an alkaline resin. 7- Pyrotechnic device according to one of claims 1 or 4, characterized in that the unpolymerized phenolic binder has a concentration of less than 60%. 8- Pyrotechnic device according to one of claims 1 or 4, characterized in that the phenoplast binder constitutes from 25 to 45 _% of the total weight of the non-polymerized pyrotechnic composition. 9- Pyrotechnic device according to one of claims 1, 4 or 8, characterized in that the phenoplast binder is combined with an oxidant chosen from the group of perchlorates of alkaline character. 10- Pyrotechnic device according to one of claims 1 or 9 characterized in that the oxidant has a particle size less than 100 micrometers. 11- Pyrotechnic device according to one of claims 9 or 10, characterized in that the perchlorate alkaline character.is potassium perchlorate introduced in proportions of between 40 and 60% of the total weight of the composition. 12- Pyrotechnic device according to one of claims 10 or 11, characterized in that the potassium perchlorate has a particle size less than 70 micrometers. 13- Pyrotechnic device according to one of claims 1, 4 or 8, characterized 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. 14- Pyrotechnic device according to one of claims 1 or 13, characterized in that the combustible metal consists of passive aluminum. 15- Pyrotechnic device according to one of claims 2, 5 or 6, characterized in that the pyrotechnic composition is polymerized in place in the outer casing. 16- Pyrotechnic device according to one of claims 1, 2, 3 or 15, characterized in that the envelope is constituted by a cylindrical tube provided with a bottom. 17- Pyrotechnic device according to one of claims 1 or 15, characterized in that after the polymerization time of the binder, carried out in an oven, the device is immediately placed in the open air.