GB2049651A

GB2049651A - Coating Surfaces with Explosive or Pyrotechnic Compositions

Info

Publication number: GB2049651A
Application number: GB8013272A
Authority: GB
Original assignee: BROCK FIREWORKS
Current assignee: BROCK FIREWORKS
Priority date: 1979-04-30
Filing date: 1980-04-23
Publication date: 1980-12-31
Also published as: GB2049651B

Abstract

A process for applying a pyrotechnic or explosive composition to a surface, which comprises: (i) screen printing the composition in the form of a liquid, slurry or paste onto the surface, and (ii) allowing the layer of the composition thus obtained to dry and/or harden. The process according to the invention is particularly suitable for the production of devices such as delay strips, electric igniters, indoor fireworks or thin layers of explosive material.

Description

SPECIFICATION Process for Applying a Pyrotechnic or Explosive Composition to a Surface The present invention relates to the application of pyrotechnic or explosive compositions to a surface, and more particularly relates to the application of such compositions to a surface by means of screen printing techniques.

Screen printing is a very well known process, and is essentially a mesh-stencil printing method in which an ink is squeezed through the open parts of the mesh on to the surface to be printed. The stencil may be prepared by hand, by photographic processes (particularly when fine-detailed patterns are desired), or by a mixture of both. Screens of metal, plastics, silk or other fibres may be used.

It has now been found that screen printing techniques can advantageously be used to apply a pyrotechnic or explosive composition to a surface which may either be inert, for example that of cardboard, or else be active, for example that of a block of live pyrotechnic composition.

Accordingly, the present invention provides a process for applying a pyrotechnic or explosive composition to a surface which comprises:- (i) screen printing said composition in the form of a liquid, slurry or paste onto said surface; and (ii) allowing the layer of said composition thus obtained to dry and/or harden.

The process of the present invention has advantages over prior art methods in that it enables pyrotechnic or explosive compositions to be conveniently applied to a surface in any desired pattern, and large numbers of surfaces may be printed in one operation. The printed layers also have an even and reproducible thickness.

Any pyrotechnic or explosive composition in the form of a liquid, slurry or paste may be used in the process of the present invention, and although the screen printing technique used is conventional, it is preferred to use a coarse mesh since this not only enables a thick layer of composition to be printed, but also allows relatively large solid particles to pass through without becoming clogged.

By using the process of the present invention, a layer of approximately 0.2 mm to 0.4 mm thick is in particular approximately 0.25 mm thick generally produced, but should a thicker layer be required the process of the present invention may be repeated after drying or hardening of the first layer.

Several layers may be applied in this manner, and each layer may, of course, be the same or different. A final layer of inert material may be overprinted for purposes, for example, of waterproofing, or to prevent ignition at the surface.

If desired, flocking may be applied between steps (i) and (ii) of the process of the present invention in order that the wet layer obtained from step (i) may be coated with, for example, other powder, granules or metal filings, before the drying is carried out in step (ii).

The process of the present invention finds particular application in the preparation of delay strips, electric igniters, indoor fireworks and the preparation of thin layers of explosive coatings.

Delay strips may be prepared by applying a strip of delay composition to an inert surface by means of the process of the present invention, and covering a section of the thus obtained layer with an inert layer, for example varnish or an epoxy resin. Layers of priming composition may be subsequently overprinted at each end of the strip using the process of the present invention.

Electric igniters may be prepared by applying a patch of electrically conducting igniter composition using the process of the present invention, to a printed circuit board so as to complete the circuit between two adjacent metallic strips. Alternatively, a non-conductive igniter composition may be applied by the process of the present invention to a section of conductor on a printed circuit board which is designed to become hot on the passing of a current.

Since a strip of printed composition which has been applied by the process of the present invention tends to burn regularly from one end to the other, interesting effects are obtained with complex patterns of strips which may cross over each other, coloured fire compositions applied according to the process of the present invention being used to form the complex patterns. Such strips find particular application in indoor fireworks.

Examples of compositions which may be applied to a surface by the process of the present invention are given below: Parts {I ) Explosive Coating by Weight Silver fulminate 2 Polyvinyl acetate adhesive (50% solids) 1 Water* (2) Red Fire Composition Resorcinol Formaldehyde Resin (70% solid content) 10 Hexamine (hardener) 0.5 Strontium oxalate 5 Potassium perchlorate 30 Solvent (e.g. Cellosolve)* (3) Delay Composition Resorcinol Formaldehyde Resin (70% solids content) 10 Hexamine (hardener) 0.5 Sulphur 2.5 Potassium nitrate 25 Solvent (e.g. Cellosolve)* (4) Priming Composition SR 252 Composition** 20 Gum Arabic 1 Water* (5) Electrically Igniter Composition (not electrically conducting) Resorcinol Formaldehyde Resin (70% solids content) 10 Hexamine (hardener) 0.5 Lead Thiocyanate 15 Potassium Chlorate 35 Solvent (e.g. Ceilosolve)* *Water or solvent is added until a liquid, slurry or paste suitable for the screen process is obtained.

**SR 252 Composition is: Potassium nitrate 40% Silicon 40% Sulphurless meal gunpowder 20% (Percentages by weight).

Claims

1. A process for applying a pyrotechnic or explosive composition to a surface which comprises: (i) screen printing the composition in the form of a liquid, slurry or paste onto the surface; and (ii) allowing the layer of the composition thus obtained to dry and/or harden.

2. A process as claimed in claim 1 in which a coarse mesh screen is used for screen printing.

3. A process as claimed in claim 1 or claim 2, in which the layer produced is from 0.2 mm to 0.4 mm thick.

4. A process as claimed in claim 3 in which the layer produced is approximately 0.25 mm thick.

5. A process as claimed in any of claims 1 to 4 in which more than one layer is applied to the surface.

6. A process as claimed in claim 5 in which each layer contains a different active ingredient.

7. A process as claimed in claim 5 or claim 6, in which the final layer applied is a layer of inert material.

8. A process as claimed in claim 7 in which the final layer is to a waterproofing layer or a layer to prevent ignition at the surface.

9.A process as claimed in any of claims 1 to 8 in which flacking is applied between steps (i) and (ii).

1 0. A process as claimed in claim 1 substantially as herein described with reference to any of the examples.

1 A pyrotechnic or explosive device which has been produced by a process as claimed in any of claims 1 to 10.

12. A device as claimed in claim 11 which is a delay strip, electric igniter, indoor firework or thin layer of an explosive coating.

1 3. A device as claimed in claim 11 substantially as herein described with reference to any of the Examples.