Method for preparing a smoke agent

An improved method for preparing a "plasticized" red phosphorous smoke ag through the steps comprising mixing particulate red phosphorous with a non-swollen, commercial latex polymer "plasticizer." In the preferred embodiment the latex polymer plasticizer is a butyl rubber.

DESCRIPTION OF THE INVENTION 
This invention relates to an improved method for preparing a "plasticized" 
i.e., coated red phosphorous smoke agent for filling munitions. 
The invention further relates to an improved method for preparing a latex 
"plasticized" red phosphorous composition. 
The invention still further relates to an improved method for preparing a 
plasticized red phosphorous smoke agent without the use of hazardous 
strong organic solvents for pre-swelling the polymer plasticizer. 
The prior art method for "plasticizing" both red and white phosphorous has 
been essentially the method disclosed in the U.S. Pat. Nos. 2,574,466 and 
2,658,874 to J. P. Clay et al. wherein red phosphorous is plasticized by 
mixing the phosphorous with various natural or synthetic polymers, e.g., 
rubber, isobutylmethacrylate polymers or other organic polymers which 
thicken or gel flammable organic liquids when added thereto in minor 
proportions. The polymers are pre-swollen in strong organic solvents such 
as gasoline, toluene or benzene before being added to the phosphorous to 
effect the desired incorporation. The organic solvents used in the prior 
methods are extremely hazardous, both in toxicity and high flammability. 
Thus, only low energy processes can be used with the organic solvent 
swelled polymer. A further disadvantage of the prior art methods of using 
polymers swelled by organic solvents is that it takes several days for the 
polymers to swell to the degree necessary for mixing with the red 
phosphorous. 
It has also been proposed in the art that particulate amorphous red 
phosphorous be protected from oxidation in moist air by coating the red 
phosphorous with an elastomer, as in the process disclosed in British 
Patent Application No. 30134/73 of June 25 1973 by P. J. R. Bryant et al. 
In the above process, a suitable elastomer such as styrene/butadiene 
copolymers or butyl rubber is applied to the surface of the particulate 
stabilizied red phosphorous by conventional coating techniques such as 
heating the elastomer to make it fluid or dissolving the elastomer in an 
organic solvent such as a halogenated hydrocarbon and then mixing the 
"fluid" elastomer with the red phosphorous. The resulting coated red 
phosphorous is then extruded and then dried. The process thus suffers from 
the same disadvantages as the other prior art process in that it requires 
either hazardous organic solvents to swell the elastomer or special 
preheating and requires substantially prolonged processing time. 
The process of the present invention uses commercially manufactured and 
ready to use latexes as the plasticizer component of "plasticized" red 
phosphorous, without the need for prior swelling of the "plasticizer" with 
hazardous organic solvents, preheating, or through use of specialized 
processing equipment as in the prior art processes. As a result of this 
invention, "plasticized" i.e., coated red phosphorous can be produced by 
safer, more rapid and flexible techniques, utilizing a wide variety of 
higher energy equipment. 
The present invention further allows for coating unstabilized red 
phosphorous, as well as the stabilized red phosphorous used exclusively in 
the prior art processes. 
SUMMARY OF THE INVENTION 
An improved method for preparing a "plasticized" i.e., coated red 
phosphorous smoke agent for use in a munition wherein particulate red 
phosphorous is coated by mixing the red phosphorous with a polymer 
plasticizer, the improvement consisting essentially of using a 
non-swollen, commercial latex polymer as the "plasticizer" for coating the 
red phosphorous wherein the step of swelling the polymer plasticizer in a 
strong organic solvent is eliminated. 
The principal object of this invention is to provide an improved method for 
preparing a "plasticized" red phosphorous smoke agent by mixing 
particulate red phosphorous with a non-swollen, commercially manufactured 
latex polymer as the "plasticizer" i.e., coating component. 
A further object of this invention is to provide an improved method for 
preparing a plasticized red phosphorous smoke agent through use of a 
commercially available latex plasticizer which can be mixed with red 
phosphorous without pre-swelling. 
A still further object of this invention is to provide a more rapid, yet 
safe, and flexible method for plasticizing red phosphorous without the 
need for hazardous strong organic solvents which are toxic and highly 
flammable. 
These and other objects of this invention will become apparent from the 
following detailed description of the invention. 
In accordance with this invention, a red phosphorous smoke agent is 
prepared through the process of mixing red phosphorous with a natural or 
synthetic latex which is ready to use in its commercially manufactured 
form. The red phosphorous and latex polymer may be mixed in any manner 
conventionally known in the art. No special low energy equipment is 
necessary for proper mixing. 
The red phosphorous smoke agent manufacturing process of this invention 
involves mixing 32 to 92 percent red phosphorous with 68 to 8 percent 
synthetic or natural latex (containing about 63 percent polymer) and up to 
one percent of a conventional curative/antioxidant. The curative is used 
to reduce the rate of oxidation of the red phosphorous smoke agent and may 
be any suitable curative/antioxidant of the type used in latex 
formulations, such as PbO.sub.2 (50% dispersion) and GMF.TM. (50% 
dispersion of P-Quinone Dioxime). The curative may be incorporated into 
the latex solution prior to mixing with the red phosphorous. The mixture 
thus contains 32 to 76 percent red phosphorous, 5 to 11 percent polymer, 7 
to 70 percent water and up to one percent curatives. The mixture is then 
dried by conventional means, such as air drying or oven drying at 
90.degree. to 100.degree. C., to give a mixture containing 75 to 95 
percent red phosphorous, 25 to 5 percent polymer plasticizer, and up to 
one percent curatives. When the mixture is dried to approximately 9.25 
percent moisture, it can be extruded through a high energy pellet mill. 
The pellets are then cured by complete drying either in air overnight or 
in an oven at 90.degree. to 100.degree. C. for approximately two hours. 
Curing significantly reduces the sensitivity of the final product to water 
by essentially cross-linking the polymer coating with the red phosphorous 
to prevent moisture adsorption by the phosphorous and thus avoid 
phosphorous degradation to phosphoric acid. 
Alternatively, the moisture content of the mixture can be adjusted by 
selection of the initial water content of the starting components to give 
the proper moisture content of the mixture for pelleting, i.e., 
approximately 9.25% for high energy pelleting mills, and thereby eliminate 
the need for drying before pelleting.

EXAMPLE 
Approximately 9080 gm of red phosphorous was initially mixed with a 
solution of 567 ml distilled water and 44 ml of concentrated NH.sub.4 OH 
(containing 58% NH.sub.4 OH) in a Hobart blender to give a mixture with a 
pH of approximately 8.4. The resulting mixture was then mixed with a 
solution of 765 ml of butyl latex (63% butyl rubber - Exxon 100 butyl 
latex.TM.), 38.2 ml of PbO2 (50% dispersion), 19.1 ml of P-quinone dioxime 
(50% dispersion-GMF.TM.) and 1.46 ml concentrated NH.sub.4 OH. The final 
resulting mixture contained 9.25% moisture. This mixture was then 
pelletized in a California mill to give a "plasticized" i.e., coated red 
phosphorous pellet which when oven dried for 2 hours at 90.degree. C., 
contained 95% red phosphorous and 5% butyl rubber polymer. The product 
pellet had a density of 1.65 gm/cm.sup.3, which gave similarly ignition 
and burning results to that obtained by prior art processes. 
The density of the final pelleted red phosphorous can be varied to obtain 
the desired burning characteristics, with burning rate increasing with 
density since the time of burning varies with the surface area of the 
phosphorous. 
The latex used should be slightly basic, i.e., pH 7-10 with a pH of 8-9 
being preferred for optimum curing of the red phosphorous pellet product. 
When the pH is over 10, there are problems encountered in the curing step. 
The pH should be adjusted by addition of a base, such as NH.sub.4 OH, to 
give a pH below 10 when curing is to be used. 
The particular latex used in the present invention can be selected from any 
of the commercially manufactured latex compositions which have been 
commonly used in the paint industry for the last thirty years, e.g., 
styrene/butadiene rubber copolymers. 
The curatives/antioxidants can also be selected from any conventional 
stabilizers used in latex formulation for reducing the rate of oxidation 
by air or degradation due to the presence of metallic impurities, 
especially copper. 
The mixing operation can be carried out in a wide variety of ways utilizing 
apparatus conventionally used for mixing latex formulations. The actual 
time of mixing is relatively rapid but is not critical in itself and can 
be varied to achieve the desired consistency. Mixing apparatus such as 
food mixing machines with dough hook mixing blades can be used, but high 
energy equipment also has utility. 
Similarly, the extrusion can be carried out through high energy pellet 
mills, mincing type machines, and any other conventional venture orifice 
means or extrusion means commonly used in the art. 
The essential feature of this invention is that red phosphorous is 
plasticized for use in a conventional munition by the rapid and efficient 
one step process of mixing red phosphorous with a commercial latex which 
has not been pretreated or pre-swollen with strong organic solvent such as 
gasoline, benzene, tolene or the like. Thus the present invention 
eliminates the hazardous and time-consuming prior art step of pre-swelling 
natural or synthetic polymers of the "plasticizer" component without 
effecting the overall munition performance. 
Applicant having disclosed this invention, obvious modification will be 
apparent to one skilled in the related chemical and smoke munition art. 
Applicant therefore wishes to be limited only by the scope of the appended 
claims.