Imperial Chemical Industries Limited

Ici Canada, Inc.

Ici Plc

Steven J Graham

Graeme Allan Leiper

Sek Kwan Chan

Ian John Kirby

Moira Logan

Charles A Bishop

The pyrotechnic ignition device of this invention comprises a hollow tubular coiled charge of pyrotechnic sheet material defining an ignition initiation position, the internal diameter of the charge decreasing and the wall thickness increasing over at least a portion of the charge extending from the initiation position in the direction of burning. This configuration enhances the reliability of ignition and the rate of flame development. Preferably the adjacent plies of the coiled charge are spaced apart. The preferred coiled charge also has a portion downstream from the initiation position in the direction of burning which decreases in external diameter and wall thickness in a direction extending away from the initiation position, the configuration of this portion being effective to enhance the speed and violence of burning of a main gas-generating propellant charge ignited by the coiled charge. In the preferred device a pyrotechnic sheet comprising a substrate of oxidizing polymeric film coated with an oxidizable metal, for example magnesium, is coiled around a cruciate axial former so that the end edges define helices. Conveniently the coiled charge may be formed by winding the sheet into a right cylindrical tubular coil and pushing out the coil axially from the centre in the direction of burning.

Pyrotechnic ignition device

The invention provides pyrotechnic sheet material comprising a substrate of porous, vapour-permeable oxidizing polymeric film, for example a halogenopolymeric film, having a layer of oxidizable material for example magnesium, on at least part of its surface, the substrate and the oxidizable material being conjointly capable of reacting together on ignition. Advantageously at least part of the oxidizing material is accommodated within the polymer pores. The pyrotechnic sheet material burns faster than material comprising solid polymeric film.

Pyrotechnic sheet material

The invention provides pyrotechnic sheet material comprising a substrate of oxidizing polymeric film, for example a film of halogenopolymer, having a layer of oxidizable material, for example magnesium on at least part of its surface. The substrate and the oxidizable material are capable of reacting together exothermically on ignition. The oxidizable material is covered with an overlying protective barrier layer of passivating material comprising a passive metal or an oxide of a passive metal. The barrier layer is effective to extend the storage life of the pyrotechnic sheet material by providing a dense non-porous oxide layer which prevents oxidization of the oxidizable material until ignition of the pyrotechnic sheet material occurs.

Pyrotechnic sheet material having an outer protective barrier layer of a

A hybrid inflator for a gas bag safety restraint system for use in a motorized vehicle comprises a compressed supply of stored gas heated by means of a gasless pyrotechnic material in sheet form. The sheeted pyrotechnic material may advantageously be located within the compressed gas storage vessel in a thin container or in direct contact with the gas. The invention also includes a heating element for a hybrid inflator. The preferred pyrotechnic material comprises a substrate of an oxidizing polymeric material for example, polytetrafluoroethylene (PTFE), coated with an oxidizable material, for example magnesium, which is capable of reacting exothermally with the oxidizing polymeric material. The pyrotechnic sheet produces solid products in very fine particle form which gives improved energy transfer to the stored gas. The invention facilities simple, cheaper constructions of hybrid inflators.

Hybrid inflator

A vehicle occupant safety restraint gas generator is provided in which the ignition system for the propellant comprises a pyrotechnic layer (22), e.g. a reactive film, preferably comprising a substrate of oxidizing polymeric film such as polytetrafluoro-ethylene (PTFE) having at least a portion of its surface covered with a layer of oxidizable material, for example magnesium, which may be vapour-deposited on the surface. The propellant is preferably a propellant train (12, 14, 16, 18) which comprises a plurality of adjacent propellant grains such as toroidal discs which surround the pyrotechnic layer or are completeley encased thereby. The gas generator is simpler and more economical to manufacture, and has improved safety during use.

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Fairlie, United Kingdom

Steven J Graham