Explosive and thermic compositions or charges – Structure or arrangement of component or product – Solid particles dispersed in solid solution or matrix
Reexamination Certificate
1998-06-01
2004-12-28
Felton, Aileen (Department: 3641)
Explosive and thermic compositions or charges
Structure or arrangement of component or product
Solid particles dispersed in solid solution or matrix
C149S019500
Reexamination Certificate
active
06835255
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates generally to energetic compositions or formulations, particularly solid high energy compositions including propellants, explosives, gas generators and the like. More particularly, the invention focuses on improvements for reducing hazards sensitivity and product cost in propellant compositions.
The hazards sensitivity is reduced by substantially reducing the required relative amount of shock sensitive energetic plasticizers, particularly nitrate esters, such as nitroglycerin (NG), by replacing the conventional binder polymer and part of the plasticizer with a binder polymer more easily plasticized.
One important aspect of the invention focuses on the discovery that amounts of relatively high molecular weight polyester prepolymers, particularly polyester polyols, can be combined successfully with surprisingly low levels of energetic plasticizers (particularly nitrate esters) in energetic compositions that are relatively low cost and characterized by comparable or superior mechanical properties. A preferred binder polymer is an isocyanate-cured, high molecular weight polyester diol poly(1,4-butanediol adipate) or poly(tetramethylene adipate) (PTHA). The invention also enables improved formulae in which high cost, relatively sensitive, high energy, energy adjustment compounds, such as cyclic nitramines of fine particle size, including cyclotrimethylene trinitramine (RDX) or cyclotetramethylene tetranitramine (commonly referred to as HMX) can be, if desired, partially or completely replaced by aluminum and ammonium perchlorate (AP) oxidizer and/or other combinations of particulate solids. Such cyclic nitramines of fine particle size are typically used to increase the energetic performance and to improve the mechanical properties of the composition.
II. Related Art
Solid, high energy compositions such as rocket propellants, gas generators, explosives, and the like, generally contain particulate solids in the form of oxidizers, fuels, burning rate modifiers, solid explosives, etc., dispersed in elastomeric binders. The elastomeric binders themselves may contain inert polymer materials, but these compositions may also contain high energy, hazards sensitive plasticizers, such as nitrate esters. These plasticizing materials are known to enhance the mechanical properties as well as the energy output of the overall composition. The typical ratio, by weight of plasticizer to total polymer (including prepolymers, crosslinkers and curatives) in binder materials (commonly known as the Pl:Po ratio) is about 2-4, i.e., 2 to 4 parts of energetic plasticizer to one part of polymer in the binder.
Recently, more stringent requirements imposed for lower hazards sensitivity have led to an increased demand for lower energy, but not entirely inert, binders which have become known as reduced energy or intermediate energy binders. The general approach to developing these binders has been to replace or dilute very high energy plasticizers with lower energy plasticizers while holding the Pl:Po ratio substantially constant at about 2-4.
An alternative approach to this problem which seemed logical was to simply dilute the high energy plasticizers with additional binder polymer material to reduce the overall binder energy as this would provide a more dense polymeric network which, in turn, would be expected to be a great deal tougher and more resistant to physical damage, another critical consideration for reducing hazards sensitivity. It was found, however, that at the resultant lower Pl:Po ratios, the lower fraction of plasticizer was insufficient to properly plasticize the binder polymer and this resulted in unsatisfactory mechanical properties, especially with regard to low elongation. Thus, there has remained a need to solve the problem of fully plasticizing the binder polymer at lower Pl:Po ratios to reduce hazards sensitivity in a manner which preserves good mechanical properties or even enables improvements in mechanical properties.
Crosslinked binders disclosed by Baczuk et al (U.S. Pat. No. 4,386,978) include urethane rubber materials that include certain polyester diols which contain both aliphatic and aromatic ester functions. These are combined with a poly-functional isocyanate having an NCO (isocyanate) functionality of at least 3. Energetic plasticizers are not reduced, however.
Godsey et al (U.S. Pat. No. 5,468,311) discloses a composition having a binder system that includes polyols which may be polyesters or polyethers having a molecular weight from about 400 to about 4,000 and hydroxyl functionalities from about 2.0 to about 2.8. The preferred polyol is polyethylene glycol adipate. The preferred molecular weight range is from about 2,000 to about 3,000. A further patent to Godsey (U.S. Pat. No. 4,298,411) depicts a propellant system that includes a pre-polymer of a hydroxy-terminated polyester and an isocyanate used in very small amounts as a crosslinking agent.
In U.S. Pat. No. 4,775,432 to Kolonko et al, it has further been proposed to use relatively high molecular weight poly(caprolactone) polymers in propellant binders. Those formulae, however, require a ratio of plasticizer to binder that is at least 2.0:1 and preferably at least 2.5:1.
Whereas each of the above references addresses certain previous drawbacks in the art, none predict a low cost, reduced hazards energetic formulation with desired mechanical properties.
Accordingly, it is a primary object of this invention to provide an improved binder system for energetic compositions which maintains excellent mechanical properties, together with reduced hazards sensitivity.
A further object of the invention is to replace an amount of energetic plasticizers in binders for energetic compositions with binder polymers without sacrificing good mechanical properties.
It is another object of this invention to provide an improved binder system for high energy compositions using high molecular weight polyester prepolymers combined with a relatively low level of energetic plasticizer.
Yet another object of this invention is to provide lower cost energetic compositions of reduced hazards sensitivity and desirable mechanical characteristics.
A still further object of this invention is to provide an improved binder system for high energy compositions utilizing isocyanate crosslinked or cured, relatively high molecular weight PTMA pre-polymer as the binder polymer.
Yet still another object of the invention is to provide lower cost energetic materials by replacing part or all of the RDX or HMX fraction with a suitable solid material combination such as AP and aluminum.
Other objects and advantages will become apparent to those skilled in the art upon becoming familiar with the descriptions and accounts contained herein together with the appended claims.
SUMMARY OF THE INVENTION
The present invention overcomes many drawbacks in prior energetic compositions by the provision of improved reduced energy binder compositions for solid, high energy formulations including propellants, explosives, gas generators and related materials, together with formulations using these binders. The binders of the invention are particularly advantageous because they are relatively low cost and exhibit improved hazards properties relative to similar, higher energy binders. In addition, the binders promote excellent mechanical properties which allow additional composition variation leeway which, in turn, can be used to reduce cost and hazards sensitivity still further. The excellent mechanical properties survive in the formulations even without the reinforcement of fine particle size nitramines such as HMX and RDX.
The binders are useful with any commonly used solid energetic species and successfully employ binder polymer materials to replace at least part of the energetic plasticizers thereby reducing the levels of energetic plasticizers, particularly nitrate esters, required in the binder. The binder system of the invention succeeds mechanically at levels of energetic plasticizers that are
Alliant Techsystems Inc.
Felton Aileen
Mersereau C. G.
Nikolai & Mersereau PA
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