Elastomer-containing casings for propellants

Abstract: The present invention relates to a process for producing an encased propellant which comprises overwrapping at least one charge of propellant with an elastomeric coating composition to produce the desired encased propellant. The process is suitably effected by molding, casting, dipping, or otherwise applying the coating composition to the charge of propellant. The process and composition of the present invention is expected to be useful in the production of encased tank ammunition, and the like.

Description: This invention relates generally to propellants, and, more specifically, to the use of aromatic polyurethanes as elastomeric coating compositions for propellant casings. Combustible containers for propellant compositions in commercial use at the present time typically are fabricated by a felting process utilizing paper or cardboard materials. An illustrative container material is KRAFT paper employing 13.4 percent nitrogen-containing nitrocellulose, and the paper can be coated, impregnated or dipped to incorporate various optional additives as desired. Among the disadvantages of prior art combustible containers is the tendency to leave a burn residue in the combustion chamber of guns, as well as to be more water permeable during propellant storage than might be desired. Accordingly, new containers which are cleaner burning during use and which provide enhanced water impermeability during propellant storage would be highly desired by the propellant manufacturing community. From GB-A-2 038 346 polyurethane coatings for a propellant charge are known. The coatings produce little or no smoke upon combustion and may be free of cellulosic compounds. The present invention relates to the use of an aromatic polyurethane as an elastomeric coating composition, being free of any cellulosic compound, for propellant casings not leaving burn residues, the casing containing a propellant charge of a high energy material selected from the group consisting of RDX, NTO, TNT, HMX, TAGN, nitroguanidine, nitrocellulose, nitroglycerine, ammonium nitrate, and combinations thereof. The propellant suitable for encasing in a container obtainable according to the present invention is a high energy material such as, for example, RDX, NTO, TNT, HMX, TAGN, nitroguanidine, nitrocellulose, nitroglycerine and ammonium nitrate. Nitrocellulose propellants may be single-base or multi-base, as described for example- in U.S. Patent 4,950,342, and these materials are commercially available as Olin Corporation's Ball Powder®. Energetic plasticizers are suitably employed in the fabrication of the propellant, including, for example, nitroglycerine, diethylene glycol dinitrate, butane triol trinitrate, and the like. The present invention is based upon the discovery that elastomeric compositions can be fabricated to provide a desired degree of toughness to withstand shock and abrasion during handling, as well as to provide desired water impermeability, and also be clean burning during use as a propellant casing. Although not wishing to be limited, the encased propellants obtainable according to the present invention are expected to be useful in the form of tank ammunition, and the like. The casings useful in the present invention can be fabricated to contain the desired elastomeric composition, alone or in combination with other additives such as oxidizers, e.g., potassium nitrate. The elastomeric composition is fabricated using an aromatic polyurethane. In the present invention the casing is suitably fabricated to overwrap the propellant using any of the well-known coating techniques including, for example, casting, reaction injection molding, dipping, spraying, or the like. A single layer or a multi-layer casing is suitably employed as desired. For example, a two-layer casing can be utilized to provide specific characteristics based upon the advantageous properties of each of the layers. As an illustration, a thermoplastic polyethylene overwrap or a spray coating of a butyl rubber can be used to provide an inner-layer moisture barrier to the casing, and this can be used in combination with a thermosetting polyurethane overwrap to provide a tough outer layer to the casing. The casing is usefully fabricated using optional additives, including oxidizers, burn rate modifiers, stabilizers, fillers, and the like, as desired in order to enhance the desired toughness, combustion profile, or other desired characteristics of the casing. The optional additives are generally present in a total amount of less than 50 weight percent based upon the weight of the casing. The casing is free of any cellulosic compound in order to provide a clean burning casing. In the fabrication of the preferred class of polyurethane casings, any desired polyol may be employed as desired. The various classes of suitable polyols are well-known, and these include polyether polyols, polyester polyols, polymer/polyols, hydroxy-terminated polyisocyanate prepolymers, and the like. Any desired aromatic polyisocyanate is also suitably employed in the fabrication of polyurethane casings, such as toluylene diisocyanate ("TDI") or methylene diphenylene diisocyanate ("MDI"). The duration and temperature of the coating process and the amount of the applied deterrent polymer are variable within the given limits depending upon the exact composition of the nitrocellulose propellant composition and the end use to which it is applied. The following examples are intended to illustrate, but in no way limit the scope of, the present invention. EXAMPLE 1 Preparation of a Casing Composition A prepolymer was made by heating a mixture of 2.44 g 1,1'-methylenebis (isocyanatobenzene) (MDI) and 453.1 g POLY -G 20-56 (A -2000 molecular weight polyether diol from Olin Corp.) to 80°C for 3 hours under a nitrogen atmosphere. The free isocyanate was determined to be 8.78% by back titration of a dibutylamine/prepolymer mixture with 0.1 N hydrochloric acid. The prepolymer (151.2 g) was degassed under vacuum with stirring. The system was flushed with nitrogen and butanediol (BDO) (13.82 g) added. The mixture was evacuated and stirred for 10 minutes. The system was flushed with nitrogen and the mixture poured out into a mold and placed in a 110°C oven overnight (16 hours) to form a molded casing. EXAMPLE 2 Fabrication of Another Casing Composition Potassium nitrate (KNO 3 ) was ground to a fine powder using a mortar and pestle. The KNO 3 was dried in an oven at 60°C, The prepolymer of Example 1 (103.5 g) and the dried KNO 3 (37.67 g) were placed into the reactor and degassed under vacuum with stirring. The system was flushed with nitrogen and butanediol (BDO) 9.46 g) was added. The mixture was evacuated and stirred for 10 minutes. The system was flushed with nitrogen and the mixture poured out into a mold and placed in a 110°C oven overnight (16 hours) to form a molded casing.

Claims: The use of an aromatic polyurethane as an elastomeric coating composition, being free of any cellulosic compound, for propellant casings not leaving burn residues, the casing containing a propellant charge of a high energy material selected from the group consisting of RDX, NTO, TNT, HMX, TAGN, nitroguanidine, nitrocellulose, nitroglycerine, ammonium nitrate, and combinations thereof. The use of claim 1, wherein the coating composition contains an additive selected from the group consisting of oxidizers, burn rate modifiers, stabilizers, and fillers. The use of claim 1 or 2, wherein the propellant charge is overwrapped by the coating composition. The use of claim 3, wherein the overwrapping is effected by molding, spray casting, dipping, or a combination thereof.

Inventors: CANTERBERRY JB, MURRAY TERRY A, CANTERBERRY, JB, MURRAY, TERRY A.
Applicants: OLIN CORP, OLIN CORPORATION
Application year: 1991
Main classification: C06B45
IPC codes: F42B5, C06B45