Explosive and thermic compositions or charges – Structure or arrangement of component or product – Solid particles dispersed in solid solution or matrix
Reexamination Certificate
1990-01-25
2004-12-21
Miller, Edward A. (Department: 3641)
Explosive and thermic compositions or charges
Structure or arrangement of component or product
Solid particles dispersed in solid solution or matrix
C149S019900
Reexamination Certificate
active
06833037
ABSTRACT:
The present invention relates to polymer bonded energetic materials.
Polymer bonded energetic materials comprising an energetic filler material, usually in the form of a solid crystalline powder, formed into a consolidated mass having suitable mechanical properties and insensitivity by a polymeric binder are well known and are used in a variety of military and civilian applications. Such materials in various compositions are used for example as high explosives for use in demolition, welding, detonating, cutting charges and munition fillings, as propellants for guns and rockets, as gas generators and as pyrotechnics.
Binders used in polymer bonded energetic materials need to be (amongst other things) compatible with the other ingredients of the material and suitably processed together with the other ingredients into the appropriate shapes required in the various applications.
Polymeric binders may be classified generally into chemically cured materials and thermoplastic materials. Chemically cured materials, eg. thermosetting resins, rely on the chemical reaction between different components to provide the desired polymeric structure.
The reacting components are normally brought together during manufacture of the end product material, eg. when the material is shaped, eg. cast, moulded or extruded. The cure time can be lengthy, and hence costly, and it can be difficult to control the chemical reaction involved.
Thermoplastic binders allow energetic materials containing them to be processed at elevated temperatures, usually outside the in-service envelope of the end product, but cool to give dimensionally stable sheet, bars, cylinders and other shapes. Shaping of the end product relies on purely physical changes taking place in the binder of the material. Reject materials may be re-cycled by re-heating. This may not normally be achieved with materials based on chemically cured binders.
The use of thermoplastic binders in known energetic materials has shown disadvantages in each case.
For example, a known material described in UK Patent No.1,082,641 herein called “Composition A” comprising RDX (1,3,5-cyclotrimethylene-2,4,6-trinitramine) as energetic filler and a mixture of polyisobutylene, di-(2-ethylhexyl)sebacate and polytetrafluoroethylene as thermoplastic binder is used as a conventional service material in a number of military applications as a plastic bonded high explosive but this material suffers from the problems (a) that it is difficult to shape under pressure, eg by extrusion, (b) when rolled into sheets it has anisotropic properties, and (c) when deformed it has little elastic memory to regain its original shape.
It is known to produce polymer bonded energetic materials such as solid explosives and propellants using an ethylene-vinyl acetate (EVA) copolymer as a thermoplastic binder. UK Patent Specification No.1,554,636 describes for use in explosive compositions EVA copolymers which are mixed with a plasticiser in order to reduce the temperatures at which the binder may be processed.
We have discovered however that EVA copolymers modified in the manner described in UKP 1,554,636 are not ideal in a number of respects, particularly as regards their mechanical properties, for use in polymer bonded energetic materials such as explosives.
It is the purpose of the present invention to provide a novel thermoplastic polymer bonded energetic material in which the polymer binder is specially selected to overcome the problems shown in the prior art by known thermoplastic polymer bonded energetic materials.
According to the present invention a thermoplastic polymer bonded energetic material comprises a composition which comprises:
Component A: an energetic filler material; and
Component B: a polymeric binder for the energetic filler material;
wherein the ratio of the weight of Component A present to the weight of Component B present in the composition is in the inclusive range from 1:10 to 199:1 and wherein Component B comprises an intimate mixture of Ingredients 1 and 2 as follows:
Ingredient 1: a copolymer of ethylene and vinyl acetate;
Ingredient 2: a copolymer of butadiene and acrylonitrile; the ratio of the weight of Ingredient 1 present to the weight of Ingredient 2 present in Component B being in the inclusive range from 1:10 to 10:1.
Ingredients 1 and 2 will be referred to herein as “EVA” and “BN” respectively. The terms “EVIA” and “BN” will herein be understood to include compounds in which other units are optionally copolymerised with the ethylene and vinyl acetate units on the one hand and the butadiene and acrylonitrile units on the other hand. These terms will also be understood to include coplymers containing optional substituents, eg. halides or methyl groupings, in the ethylene, vinyl acetate, butadiene and acrylonitrile units.
Preferably, the softening point of Component B is greater than 60° C. desirably greater than 80° C.
Preferably, the BN per se (prior to introduction to the other components) is in the form of a liquid having a viscosity greater than 50 cst when measured at a temperature of 20° C. and a molecular weight in the range 200 to 20,000, desirably in the inclusive range 2000 to 5000. Such a compound may be modified in the course of processing to form a product.
The material according to the present invention may, for example, be in the form of a consolidated rubbery mass, the energetic filler Component A preferably being a particulate, eg. powdered, solid, being embedded in the binder Component B.
The polymer bonded energetic materials according to the present invention give mechanical properties superior to those of the prior art materials described in UKP 1,554,636. The plasticisers employed in the polymer bonded explosive compositions described in UKP 1,554,636 are generally non-viscous mobile liquids of viscosity less than 50 cst, typically 10 cst at 20° C. which can exude from the compositions containing them during temperature cycling in storage or use. This causes the composition to become brittle with age. Furthermore, the said plasticisers do not give satisfactory adhesion to the explosive material and this can result in useless crumbly material at some plasticiser concentrations.
In contrast, the BN polymers employed in the compositions according to the present invention to plasticise the EVA do not substantially migrate during storage or use and give good adhesion to the energetic filler material as well as to the EVA and this provides compositions having improved physical, mechanical and ageing properties.
The materials according to the present invention can show improvements over the materials of UKP 1,082,641 in that they have properties which are substantially isotropic and may be formed more easily into desired shapes, such as by rolling, pressing, moulding, extruding or casting, which can retain their elastic memory and repair their shape when deformed.
In Component B of the materials according to the present invention, optional additives may be included in the mixture together, with EVA and BN. Examples of such additives include plasticisers and antioxidants. Examples of suitable optional additives are given hereinafter.
Preferably, the optional additives will comprise in total not more than 20 percent by weight, normally less than 10 percent by weight, of Component B.
Component B may comprise from 25 to 85, preferably 50 to 75 percent, by weight EVA and from 20 to 60, preferably 25 to 50, percent weight BN.
The EVA present in Component B may have a vinyl acetate content of from 25 percent to 75 percent, desirably from 33 to 60 percent inclusive, especially 40 to 45 percent inclusive. This polymer may be provided in the form of a mixture of different EVA compounds having different vinyl acetate contents.
An EVA copolymer containing 45 percent by weight vinyl acetate has been shown to provide a particularly satisfactory example.
The BN present in Component B may have a bound acrylonitrile content in the inclusive range 5 to 50 percent by weight, desirably in the inclusive range 10 to 30 percent by weight. The BN polymer contained
Hallam Deirdre
Holes Pauline J.
Hollands Ronald E.
BAE Systems PLC
Miller Edward A.
Nixon & Vanderhye P.C.
LandOfFree
Polymer bonded energetic materials does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polymer bonded energetic materials, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polymer bonded energetic materials will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3274186