Smokeless propellant is conventionally manufactured by dehydrating and granulating wet nitrocellulose, which is then mixed with a solvent or solvent mixtures such as alcohol, acetone, or isopropyl acetate to obtain a dough-like, at least partially gelatinized mixture, which can be further admixed with nitroglycerine to obtain double base propellant. The nitrocellulose/solvent mixture is then conventionally pressed or densified, extruded, cut, dried and screened, as desired, to obtain raw grain propellant. Art-recognized techniques for carrying out the production of smokeless propellant are described in further detail, for instance, in U.S. Pat. Nos. 3,346,675, 2,027,114 and 2,885,736.
Unfinished small grain smokeless propellant has a tendency to fire too rapidly, and initially produce too high a barrel pressure. For this reason, such propellant grains are routinely coated with one or more deterrent compositions such as powdered Vinsol.RTM. pine-stump resin*.sup.1, dinitrotoluene, dialkyl and diaryl phthalates, and the like, to slow down the initial firing rate and to maintain a Time/Pressure relation more suitable for ballistic purposes. FNT *.sup.1 A product of Hercules Incorporated.
Antistatic agents such as powdered graphite are also routinely applied to smokeless propellants as an overcoat to avoid charge accumulation and sparking.
Most deterrent coatings, unfortunately, also have an adverse effect on the ignition properties of smokeless propellants. This on-going problem can sometimes be minimized by admixing both treated (i.e. deterrent- and graphite-coated) and untreated (graphite-coated) propellant grains in precise predetermined ratios, which vary with each batch. Such mixtures are difficult to obtain and maintain until firing, in the absence of ideal mixing and storage conditions.
It is an object of the present invention to improve the ignition properties of deterrent-coated smokeless propellants and to maintain satisfactory burn rates and pressures for ballistics purposes without using complicated mixing and storing procedures.