EP0252803B1 - Pyrotechnic compositions for the production of coloured fireworks - Google Patents

Description

The present invention relates to the field of pyrotechnic mixtures or compositions producing colored fireworks.

The prior art can be illustrated by document US-A-3,214,304, which describes compositions intended to be applied as a propellant.

Example 10 of this patent describes a composition containing 2% cobalt acetylacetonate which, in this case, is only used as a catalyst or combustion regulator, but does not produce any coloring effect, if only due to its concentration too low to exercise such a coloring function.

Until now, it has been impossible to perfectly reconcile the two essential parameters of this type of pyrotechnic composition, namely the liveliness of the combustion and the purity of the color.

• 1°) un oxydant choisi parmi les chlorates de potassium et de baryum, le perchlorate de potassium ou le perchlorate d'ammonium ou le mélange de ces deux derniers sels ;
• 2°) un réducteur comme le soufre, des résines naturelles ou synthétiques, utilisées également comme liant ;
• 3°) des composés du cuivre tels que le cuivre en poudre, les oxydes, des sels comme le sulfate ammoniacal, le chlorure, l'oxychlorure, l'acétoarseniate, le sulfure, etc... ;
• 4°) un "promoteur" de couleur, en général un dérivé chloré tel que des chlorures minéraux ou des molécules organiques chlorées ;
• 5°) un liant (gomme ou résine).

The mixtures usually used to lead for example to blue compositions involve:

• 1) an oxidant chosen from potassium and barium chlorates, potassium perchlorate or ammonium perchlorate or the mixture of these last two salts;
• 2) a reducing agent such as sulfur, natural or synthetic resins, also used as a binder;
• 3) copper compounds such as copper powder, oxides, salts such as ammoniacal sulfate, chloride, oxychloride, acetoarsenate, sulfide, etc ...;
• 4) a color "promoter", in general a chlorinated derivative such as mineral chlorides or chlorinated organic molecules;
• 5) a binder (gum or resin).

Such compositions are not entirely satisfactory in practice, because their flame color remains impure and they do not have a sufficient burning rate, which is very important in particular in the production of fireworks stars for bombs and candles or other colored devices.

If, in this type of aforementioned compositions, sulfur, sulphates or sulphides which are liable to present certain dangers in the presence of chlorates are eliminated and perchlorate, obtaining frank colors leads to compositions that are too slow to be used in the manufacture of colored fireworks.

Among the oxidants mentioned taking into account these restrictions, potassium perchlorate, potassium and barium chlorates give very washed-out colors, on the other hand ammonium perchlorate gives a slightly purer color. But for the combustion speed to be sufficient, we have to add potassium perchlorate which strongly denatures the color. This phenomenon is particularly observed in the case of pyrotechnic compositions of blue color, based on copper.

The object of the present invention is precisely to remedy this drawback.

The compositions which are the subject of the present invention have made it possible, by choosing a very specific metal derivative, namely acetylacetonate, to activate the combustion of the mixtures while retaining excellent color purity in the flame.

• un oxydant,
• un réducteur organique de la famille des oses tels que le sorbitol, des polyoxyoléfines telles que le polyéthylène-glycol, ainsi que des résines naturelles ou synthétiques,
• un acétylacétonate métallique dont le métal est choisi parmi le cuivre, le molybdène, le strontium, le baryum, le calcium, le lanthane et le zirconium, ledit acétylacétonate métallique étant présent à une teneur minimale d'environ 3% en poids de la composition totale.

According to the essential characteristic of the invention, the pyrotechnic composition comprises:

• an oxidant,
• an organic reducing agent from the ose family such as sorbitol, polyoxyolefins such as polyethylene glycol, as well as natural or synthetic resins,
• a metallic acetylacetonate, the metal of which is chosen from copper, molybdenum, strontium, barium, calcium, lanthanum and zirconium, said metallic acetylacetonate being present at a minimum content of approximately 3% by weight of the total composition .

Other characteristics and advantages of the subject of the invention will appear on reading the description made below, in particular by relying on a few specific examples given by way of illustration.

The first constituent of the composition of the invention is the oxidant which will advantageously be chosen from chlorates and perchlorates of alkali, alkaline-earth or even ammonium metals. We particularly prefer to use ammonium perchlorate which does not cause any disturbance in the color of the flame.

Most often this oxidant provides chlorine which improves the color of the flame, in particular in pyrotechnic compositions based on copper, strontium or barium. However, in certain particular cases, it may be useful to add to the oxidant - which is involved in the composition at a level of 60 to 90% by weight - a halogen promoter, in particular a chlorine or bromine promoter. The compositions according to the invention may thus contain up to approximately 5% of such a halogen promoter, for example consisting of chlorinated inorganic or organic derivatives.

The second constituent of the composition according to the invention is the reducing agent which will generally be constituted by an organic reducing agent from the family of oses such as sorbitol, polyoxyolefins such as polyethylene glycol, as well as natural or synthetic resins.

When it is desired to give such a pyrotechnic composition a particular material form, one can of course add to it a binder such as a gum or a resin. It should be noted that, in the case where the reducing agent consists of a resin, the latter can simultaneously play the role of reducing agent and binder.

The third essential constituent of the pyrotechnic compositions according to the invention is metallic acetylacetonate which can for example be obtained by reaction of metals, hydroxides or metallic salts, on acetylacetone.

It will be noted that the reducing couple + metallic acetylacetonate is involved in the pyrotechnic compositions of the invention at a level of 10 to 40% by weight. However, a minimum metal acetylacetonate content of approximately 3% by weight will always be maintained.

Among the following three mixtures, the proportions of which are calculated by respecting the stoichiometry of the combustion reactions (quantity of fuel sufficient to transform carbon into CO), copper acetylacetonate gives the highest combustion rate. I II III AMMONIUM PERCHLORATE 77.3 86.4 64.4 COPPER ACETYLACETONATE (AAC). 22.7 SORBITOL 35.6 COPPER STEARATE 13.56 COPPER POWDER 5.8 * * The proportion of copper is the same as in composition I.

Unlike the other coloring agents for blue flame, the AAC, sublimable product, gives a high flame, without leaving residues, which constitutes a determining advantage in the case of torches and lances, where the slag deteriorates the color .

The gases are therefore rich in flame dye.

In addition, the stability of the complex and its very low solubility in water avoid the possible double decomposition of chlorates and perchlorates in the presence of copper salts, which would lead to copper compounds sensitive to shocks or hygroscopic.

2°) Compositions pour flammes Perchlorate d'ammonium 70 % Glucose 25 % Acétylacétonate de cuivre 5 % Two types of compositions are mentioned below by way of illustration, one for stars, the other for flames, decorative launchers, Bengals, etc.

2 °) Compositions for flames Ammonium perchlorate 70% Glucose 25% Copper acetylacetonate 5%

This latter type of composition has, as mentioned above, the advantage of not smoking and of not leaving residues.

Finally, a few examples of the flame color observed with different metallic acetylacetonates will be indicated in the table below. Acetylacetonate metal Flame color Cu Blue Mo Yellow lemon Sr Red Ba Green It Orange-red The White Zr Dazzling white

Of course, the present invention cannot be limited to the particular embodiments described, of which it is perfectly possible to imagine numerous variant embodiments. Thus it is possible to choose, as reducing agent, or even to add to the reducing agent, different metals such as aluminum, magnesium and titanium which further improve the brightness of the flame produced by the pyrotechnic compositions colored according to the 'invention.

Claims (8)

1. A method of manufacturing a pyrotechnic composition for production of coloured fireworks, characterised in that the following are mixed together:

   - an oxidising agent,

   - an organic reducing agent from the ose family, e.g. sorbitol, or polyoxyolefins such as polyethylene glycol, or natural or synthetic resins, and

   - a metal acetyl acetonate in which the metal is chosen from among copper, molybdenum, strontium, barium, calcium, lanthanum and zirconium, the minimum content of the metal acetyl acetonate being about 3% by weight of the total composition.
2. A method according to claim 1, characterised in that the metal in the acetyl acetonate is copper.
3. A method according to claim 1 or 2, characterised in that the oxide is chosen from among chlorates and perchlorates of alkali metals, alkaline earth metals and ammonium.
4. A method according to claim 3, characterised in that the oxidising agent is ammonium perchlorate.
5. A method according to any of claims 1 to 4, characterised in that a halogen promoter is also added, more particularly a chlorine or bromine promoter.
6. A method according to any of claims 1 to 5, characterised in that a composition is prepared having the following formula:

   
7. A method according to claims 5 or 6, characterised in that up to about 5% by weight of a chlorine or bromine promoter are also added.
8. Application of the methods according to any of claims 1 to 7, to signalling lights and fireworks, more particularly stars for smoke bombs, rockets, Bengal lights, pyrotechnic projectors and torches.