Patent Application
20160115090
1. Field of the Invention
The present invention relates to hand held signal pyrotechnic smoke compositions, and more particularly, to such an compositions that are free of the conventional, but toxic yellow smoke agents Vat Yellow 4 (dibenzochrysenedione) and benzanthrone, and still continue to provide the requisite density, burn time, and good color quality.
2. Background Art
Hand held signal (HHS) pyrotechnic smoke compositions are useful for multiple military purposes—including signaling troop locations or distress, during combat or training operations, or to serve as a beacon for target or landing zone marking. One such pyrotechnic smoke formulation is contained within the US Army M194 HHS—which HHS is launched via a rocket to a height of about 725 feet, at which point the signal is ignited. The M194 HHS provides a dense, highly visible yellow smoke as it falls back to earth via parachute—burning for 9 to 18 seconds (ideally about 13 to about 15 seconds), while producing the desired yellow smoke during this period, before burnout at about 500 to 600 feet. Unfortunately, the current M194 HHS yellow smoke formulation contains two toxic anthraquinone dyes, namely Vat Yellow 4 (aka (dibenzochrysenedione) and benzanthrone. Benzanthrone is a known dermal sensitizer, and is reported as causing liver and nervous system damage; plus, it is also known to be highly toxic to aquatic life. Vat Yellow 4, felt to contain small but significant amounts of dibenzochrysene (an extremely potent carcinogen) is classified as a Group 3 material by the International Agency for Research on Cancer (IARC)—because of evidence of its potential carcinogenic impact remains unsubstantiated.
In the current M194 pyrotechnic formulation, the dense yellow smoke is formed by the cost effective reduction-oxidation (redox) reaction of relatively inexpensive potassium chlorate (an oxidizer), with sugar (a fuel, or reducing agent)—which generates significant heat. The heat, in turn, causes the dye molecules, i.e. the VAT Yellow 4 and benzanthrone—to enter the gas phase (via sublimation) and begin to disperse. After dispersion of the dye molecules, contact with the cool ambient air causes them to condense back to the solid phase, helped by the presence of sodium bicarbonate, which functions as an evaporative cooling agent. Lastly, the formulation contains a binder to “glue” it together, i.e. vinyl alcohol acetate resin (VAAR).
As the binder in the current yellow smoke M194 formulation is available only in a solvent media—the manufacturing process requires that this solvent be driven-off prior to the consolidation of the yellow smoke formulation and its packing into a steel canister within the M194 HHS.
An alternative yellow pyrotechnic smoke formulation has been developed for the simulation of the smoke signature related to ground-launched missiles—part of a Battle Effects Simulator (BES) system. These yellow smoke formulations use an alternative yellow smoke agent, quinoline yellow spirit solution, also commonly known as quinoline yellow ss or solvent yellow 33, in combination with potassium chlorate (the oxidizer), sugar (the fuel/reducing agent), magnesium carbonate (a coolant), stearic acid (a lubricant), and VAAR (a binder). However, while these alternative BES yellow smoke formulations are much safer and more environmentally friendly than the M194 yellow smoke formulations—the burn times are far outside that required for the M194 HHS application, i.e about 37.5 seconds (over twice the maximum time allowed for the M194 yellow smoke application of 9 to 18 seconds).
Therefore, there is a need in the art for a replacement M194 HHS yellow smoke composition that continues to utilize the relatively inexpensive potassium chlorate and sugar redox reaction, and contains an alternative yellow smoke agent that is non-toxic and environmentally safe; which composition will burn for the requisite 9 to 18 seconds, while producing the desired dense, highly visible yellow smoke. Further, there is also a need in the art for an all solid ingredient alternative M194 HHS smoke composition that will rot require any solvent to be driven off during its manufacture—thereby simplifying and making the manufacturing process more effective, efficient, and economical.
In order to overcome the above stated problems of the prior art—the present inventive HHS yellow pyrotechnic smoke formulation preferably contains all solid, powder ingredients which are easily combined via a conventional dry-tumble process—the ingredients being: potassium chlorate (KClO3), an oxidizing agent; sugar (sucrose), a fuel (reducing agent); solvent yellow 33 (SY33, otherwise known as quinoline yellow ss, or as D&C Yellow No. 11), the yellow smoke agent; hydromagnesite (Mg5(CO3)4(OH)2.4H2O), a coolant; stearic acid, a lubricant; hydrophobic fumed silica (available from the Cabot Corporation, under the trademark Cab-O-Sil®), an anti-caking agent; and polyvinyl alcohol (PVA), a binder. These ingredients provide an inventive yellow smoke formulation wherein a redox reaction of the potassium chlorate and sugar forms potassium chloride, carbon dioxide, water vapor, and soot/carbon—which reaction is exothermic. This exothermic reaction releases sufficient heat to cause the yellow smoke agent SY33 to sublimate, disperse over a wide area, and then condense into the desired dense, highly visible yellow smoke. Further, and most importantly, the burn time is within the 9 to 18 second desired, required, smoke production time, when the inventive formulation is compressed into a smoke pellet usable in an M194 HHS.
In an alternative embodiment of the present invention, a small quantity of fumed silica (also known as pyrogenic silica or Cab-O-Sil®),) can be substituted for an equal quantity of the fuel, sugar—the silica acting as an anticaking agent—to aid in the flowability of the inventive formulation during its handling, transport, and packing into the desired HHS container.
If desired, the inventive formulation can contain the alternative binders polyvinyl alcohol (PVA) and/or nitrocellulose (NC). The NC alternative embodiment, wherein the nitrocellulose ingredient is contained within solvent media, will require that after the ingredients are added to the mixture, the resulting now wet mixture will have to be dried in a dryer or oven. When the preferred alternative binder polyvinyl alcohol is utilized in the inventive mixture, the resulting dry mix is useful for the subject application as is, i.e. no drying step is required.
Additional features and advantages of the present invention will be set forth in, or are apparent from, the detailed description of preferred embodiments thereof which follows.
The present inventive HHS yellow pyrotechnic smoke composition is preferably a mixture of solid materials, including about 34.5 weight percent of potassium chlorate (KClO3), an oxidizing agent; about 21.5 to about 22.0 weight percent of a sugar (sucrose), a fuel (reducing agent); about 36 to about 37 weight percent of solvent yellow 33 (SY33, also known as quinoline yellow ss, or as D&C Yellow No. 11), the yellow smoke agent; about 5.5 weight percent hydromagnesite (Mg5(CO3)4(OH)2.4H2O), a cooling agent; about 0 to about 1.0 weight percent stearic acid, a lubricant; and about 0 to about 0.5 weight percent hydrophobic fumed silica, an anti-caking agent. To this mixture of solid powdered materials, a binder or combination of binders may be added, where the most preferred binder is about 0 to about 1.0 weight percent polyvinyl alcohol (PVA), also a solid (such that the resulting mixture need only be dry-tumbled to be completed).
As stated above, in an alternative embodiment of the present invention, a smal quantity, about 0.5 wt. %, of fumed silica (also known as pyrogenic silica) can be substituted for an equal quantity of the fuel, sugar—the silica acting as an anticaking agent—to aid in the flowability of the inventive formulation during its handling, transport, and packing into the desired HHS container.
An alternative binder useful in the present invention includes nitrocellulose (NC)—but, this alternative binder is standardly available in a liquid form, i.e. in a solvent media—such that about 10% by weight must be added and then the solvent driven-off in an oven or dryer—whereby the final quantity of the nitrocellulose is at the desired about 0 to about 1.0 weight percent of the total inventive yellow smoke formulation.
The particular yellow smoke agent useful in the present invention is, as stated above, solvent yellow 33—which material is abbreviated as SY33, and also known as quinoline yellow ss, or as D&C Yellow No. 11. As shown in
The specification of the various ingredients in the above detailed inventive formulation preferably meet the criteria and specifications shown in Table 1 below.
In preparing the inventive yellow smoke formulation, the potassium chlorate was initially oven dried overnight at 140 degrees F.—to ensure its dryness. Then, in the case of the inventive formulation embodiments containing only solid ingredients, the potassium chlorate and other ingredients were tumbled end-over-end in conductive plastic containers for 60 min; while, those containing wet NC were blended in a Hobart mixer for 30 min. Dry-tumbled formulations were taken directly to loading operations without further processing, while NC-based formulations were oven-cured overnight at 140° F. prior to loading. Following blending, the dry mixture was hydraulically pressed into kraft cardboard tubes—which is a distinct advantage over formulations of the prior art. Specifically, the current inventive yellow smoke formulation can be consolidated and delivered in the prior art steel canister, or in other canister materials, such as an aluminum, or even cardboard canisters—and still give the requisite smoke density, color, and duration of burn. And, after consolidation and coating with first-fire composition, the pressed pellets are ready for evaluation/testing.
The inventive formulations were tested and proved to meet the requisite smoke density, color, and burn time in biodegradable cardboard tubes (as shown in
The inventive formulations were tested against the current BES yellow smoke formulation, which was considered a baseline, as it is similar in many respects; but, as stated, has a burn time that is totally unacceptable (twice the maximum allowed rate of 18 seconds). The results of the tests are shown in Table 2, and the summarized below:
aAll formulations contain 1 wt. % stearic acid as a lubricant and, except those noted otherwise or those binder-free, 1 wt. % binder (NC or PVA or VAAR - as stated).
bThe fumed silica, e.g. Cab-O-Sil ® available from the Cabot Corporation, can be omitted entirely and the sugar content increased correspondingly to 22 wt. % with no difference in performance.
cThe coolant being: hydromagnesite (Mg5(CO3)4(OH)2•4H2O).
The procedure used in the static ignition tests, whose results are detailed above, involved using the cylindrical smoke pellets, or smoke candles, (produced as detailed above), wherein the pellet were clamped vertically with the top slurry-coated end facing up. The head of an electric match was placed on the top slurried end. After passing an energy of 2 volts through the electric match, the resulting spit of the electric match lights the igniter slurry. The heat from this ignition event then initiates a reduction-oxidation reaction between the fuel (sugar) and the oxidizer (potassium chlorate) in the tested pressed smoke compositions. The burning of the pressed pellet propagated in a core-burning fashion, from top-down and from inside-out (but surprisingly, not bottom-up). The burn times, linear burning rates, and mass consumption rates were measured for all smoke candles tested—and the results presented above.
Although the invention has been described above in relation to preferred embodiments thereof, it will be understood by those skilled in the art that variations and modifications can be effected in these preferred embodiments without departing from the scope and spirit of the invention.
The inventions described herein may be manufactured, used and licensed by, or for, the U.S. Government, for U.S. Government purposes.
