Abstract:
The present invention relates to a method for preparing an in situ cured  ster explosive by mixing explosive crystals with a prepolymer solution comprising a carboxyl (or hydroxyl)-terminated hydrophobic polyester and epoxidized linseed oil with chromium octanoate as a catalyst. The explosive mixture is pressed into desired size and cured at 60° C. to 70° C. for about 96 hours. The resulting in situ cured explosive has desirable safety and physical properties.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention provides for a method for making pressed explosives which are less hazardous and more desirable than those presently used. 
     2. Description of the Prior Art 
     Some previous pressed explosives use wax as a binder and are difficult to manufacture. The resulting pellets tend to fracture when handled, and a high percentage of these are rejected for being out of specification. 
     Other pressed explosives use fluoroelastomers (Viton) or tetrafluoroethylenes (Teflon) as binders. Viton and Teflon are expensive and the resulting explosives tend to detonate when subjected to cook-off tests. 
     There is a need for a safer explosive, that employs a tough inexpensive binder, and which does not readily detonate. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention relates to a method for preparing an in situ cured booster explosive by coating an explosive filler with a prepolymer binder that is rubbery and pliable and desensitizes the explosive by binding together the particles of explosive filler to form a tough composite explosive. The coated explosive is pressed into pellets or billets and cured at 60°-70° C. for about 96 hours. 
     OBJECTS OF THE PRESENT INVENTION 
     One object of the present invention is to make a pressed explosive safer than those made in the previous art. 
     Another object is to make a pressed explosive that does not fracture when handled. 
     Still another object is to make an explosive from low cost materials which are readily available. 
     And finally, an object is to produce an explosive having high quality, and excellent reliability, and superior physical properties. 
     These objects and other features of the present invention are illustrated in the following detailed description, and are not found in the previous art. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A method for preparing an in situ cured booster explosive is described by the following example: 
     About 90 percentage (%) to about 97 percentage (%) by weight of 1,3,5-trinitro-1,3,5-triazocyclohexane explosive filler crystals also known as cyclotrimethylenetrinitramine or RDX (Class A, Type II) are coated with liquid prepolymer binder composed of about 2.30% to about 7.66% by weight of carboxyl-terminated poly-1,6-hexanediol dimerate (2000 molecular weight and with about 0.70% to about 2.34% by weight of epoxidized vegetable oil such as Epoxol 9-5, also known as epoxidized linseed oil, and adding about 0.3% by weight of chromium octanoate as a cure catalyst. 
     The coating technique for large scale preparations comprises adding 0.3 liters of n-hexane to each kilogram of the RDX and binder composition and then slowly mixing for about a half hour. The excess n-hexane is removed by applying a vacuum during the mixing process. 
     The resulting mixture is a powder ready for pressing into either pellets (0.5 inches diameter by 1 inch height) or into larger billets (3 inches diameter by 5 inches height). The pressing is accomplished at room temperature (about 70° F.) under 25,000 pounds per square inch (psi) for about 60 seconds. 
     Alternatively, different qualities of the explosive may be obtained by varying the amounts of binder and explosive. Explosives other than RDX can be used, as well as other carboxyl-terminated or hydroxyl-terminated hydrophobic polyesters as binders. If a hydroxyl-terminated polymer binder is used, it is cured with dimeryl dissocyanate. Possible binders are listed in Table I. 
     TABLE I 
     Possible Binders 
     hydroxyl or carboxyl terminated prepolymers yielding a rubbery pliable coating: 
     polybutadiene 
     polyether 
     TABLE I 
     polypropylene gycol 
     polyethylene glycol (plasticized) polyesters 
     (4-20) aliphatic or cycloaliphatic dicarboxylic acids esterified with diols or triols typically 1,6-hexanediol or polyethylene gycols 
     dimer acid plus diols and triols 
     neopentyl glycol 
     1,6-hexanediol 
     α,ω-dihydroxyalkanes 
     Table II lists the comparative physical properties of in situ cured booster explosives. The example previously cited has excellent qualities for use in ordnance. Polymer formation and consequent toughening occurs during curing, preventing cracking of the coating, and samples scanned under an electron microscope reveal homogeneous coating. 
     Furthermore the tests show that the example cited is superior in resistance to abrasion, friction, and impact and is equivalent in electrostatic and thermal stability when compared to conventional explosives such as CH-6. 
     
                                           TABLE II__________________________________________________________________________COMPARATIVE PROPERTIES OF BOOSTER EXPLOSIVES    A-1-a A-2-a               D-1 A-4 CH-6 PBXN6__________________________________________________________________________NominalCompositionWeight % 95/5  95/5 95/5                   97/3                       98.5/1.5                            95/5RDX/BinderImpactSensitivity    26    25   23  23  21   2150% pt. cm2.5 Kg Wt.FrictionSensitivity    794   589  692 486 479  74150% pt(lbs) ABL sliding friction test Allegheny Ballistic Lab.Electrostatic (Spark)Sensitivity    10/10NF          10/10NF               10/10NF 10/10NF                            10/10NF0.25 JoulesVacuum ThermalStability100° C.    0.06  0.11 0.24                   0.07                       0.08 0.05ml/gm/48 hrs. Vol. of Gas measured as ml of/gas/gm/48 hrs.Abrasiontest     1.1   2.3  3.5 14.2                       23.5 2.3Weight loss %PressedDensity  1.65  1.64 1.66                   1.685                       1.702                            1.758gm/cc__________________________________________________________________________ *NF, no fire A-1-a: RDX/poly 1,6hexanediol dimerate cured with Epoxol 9-5 (95/5) A-2-a: RDX/carboxyl terminated polybutadiene cured with Epoxol 9-5 (95/5) D-1: RDX/R45HT cured with dimeryl diisocyanate, retarded with noctyl salicylate (95/5) A-4: RDX desensitized with wax CH-6: RDX desensitized with wax PBXN6: RDX desensitized with Viton 
    
     It is a relatively safe explosive, in view of the following considerations: 
     The uniform and adherant polymeric binder coating of this explosive is able to remove heat more efficiently (by endothermic dissociation and vaporization) from a decomposing particle of explosive filler than are waxes which melt and flow away from the filler surface. Fluorocarbon polymers are not efficient in this regard since they decompose at temperatures well above the decomposition of RDX and common explosive fillers. 
     Partial curing of the molding powder prior to pressing and final curing can further improve the quality and adhesiveness of the binder on the RDX crystals, which further decreases the explosive&#39;s sensitivity. 
     Furthermore, solvents other than n-hexane can be used as a coating media. 
     TABLE III 
     Equivalent Ratios 
     The preferred equivalent ratio of epoxy to carboxyl terminated resin is 1.5. However, it can be varied from 1.1 to 1.8. 
     At the ratio of 1.5 the weight % of Epoxol 9-5 is 23.45 and carboxyl resin is 76.55. 
     At the ratio of 1.1 weight % Epoxol is 17.19 and Carboxyl resin is 82.81%. 
     TABLE III (Continued) 
     At the ratio of 1.8 the weight % Epoxol is 28.14 and the carboxyl resin is 71.86. 
     These wide ranges of composition can be attained because of the high functionality of the Epoxol 9-5 (f&gt;4). 
     
         ______________________________________       Weight %E/C           Epoxy   Carboxyl______________________________________1.1           17.19   82.811.5           23.45   76.551.8           28.14   71.88______________________________________ 
    
     The advantages and new features of the present invention are apparent from the preceding description. 
     It is made from low cost materials that are readily available, and provides for a safer explosive with superior physical quantities. 
     The foregoing illustrates to one skilled in the art, the methods for preparing the present invention, and its properties. However, this invention is not limited by its description but only by the claims.