An inflatable vehicle occupant protection device, such as an air bag, is inflated by gas provided by an inflator. The inflator contains a body of ignitable gas generating material. The inflator further includes an igniter. The igniter is actuated so as to ignite the body of gas generating material when the vehicle experiences a collision for which inflation of the air bag is desired. As the body of gas generating material burns, it generates a volume of inflation gas. The inflation gas is directed into the vehicle air bag to inflate the air bag. When the air bag is inflated, it expands into the vehicle occupant compartment and helps to protect the vehicle occupant.
A convenient way of making gas generating material is by extrusion. Gas generating material which is extruded can be configured into a variety of shapes, including rods, channels, and other structural shapes suitable for use in various types of inflators.
It is desirable that gas generating material for inflating an inflatable vehicle occupant protection device produces, upon combustion, an inflation gas which is substantially smoke-free and substantially free of toxic materials. Gas generating material which is extruded includes an oxidizer and a cross-linked elastomeric polymer. Since conventional cross-linked elastomeric polymers used in extrusion processing have a low oxygen content, either an oxidizer containing a high amount of oxygen or a high oxidizer content is required in the gas generating material. Alternatively, gaseous oxygen may be used in the inflator to convert the carbon in the gas generating material fully to carbon dioxide during combustion.
Several energetic elastomeric polymers have a high oxygen content capable of converting the carbon in the gas generating composition to carbon dioxide during combustion. However these energetic elastomeric polymers fail to meet other gas generating material requirements including mechanical integrity over a wide temperature range, chemical stability and safety.
U.S. Pat. No. 5,540,794 discloses an energetic binder useful for making thermoplastic elastomer low vulnerability ammunition propellants and energetic compositions which comprise at least one energetic thermoplastic elastomer binder, at least one plasticizer, and nitrocellulose.