Compositions – Oxidative bleachant – oxidant containing – or generative – Contains inorganic nitrogen containing compound
Reexamination Certificate
1999-11-09
2002-01-01
Anthony, Joseph D. (Department: 1714)
Compositions
Oxidative bleachant, oxidant containing, or generative
Contains inorganic nitrogen containing compound
C149S019100, C149S019500, C149S019910, C149S062000, C149S070000, C149S072000, C149S108200
Reexamination Certificate
active
06334961
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to gas generant compositions, especially gas generant compositions employed in the inflation of vehicle occupant passive restraint systems.
BACKGROUND AND SUMMARY OF THE INVENTION
Various inflators for inflating vehicle occupant passive restraint systems (known colloquially in the art as “air bags”) are known. Among the various types of inflators is one that utilizes a quantity of stored compressed gas which is selectively released to inflate the air bag. A related type of inflator generates a gas source from a combustible gas-generating material which, upon ignition, provides a quantity of gas sufficient to inflate the air bag. In still another type (known as a hybrid inflator), the air bag inflating gas is provided by the combination of a stored compressed gas and the combustion products of the gas generating material.
Inflators which depend entirely or partially on the generation of gases by virtue of combustion of combustible materials have several disadvantages. For example, the burning of the propellant and the initiator materials in such inflators results in the production or undesired particulate matter. Thus, using inflators that are particulate-containing or which generate particulates upon combustion as part of a passive restraint system in a vehicle might result in undesirable particulates being released into the occupant zone of the vehicles and thereby inhaled by the occupants. In particular, asthmatic reactions may be caused by inhalation of particulate matter, creating a health risk for the occupants. For this reason, automobile manufacturers limit the quantity and type of particulates released by the inflator system. Insoluble particulates are preferred over soluble particulates, as the latter are believed to cause greater reaction.
Particulates may arise from any energetic component, including gas generants and ignition systems, as well as through secondary combustion of inert inflator components. Reduction in the contribution of particulates from one or more of these components will generate a beneficial reduction in particulates for the whole inflator assembly.
One prior inflator is disclosed in commonly owned U.S. Pat. No. 5,589,141 to Sides et al (the entire content of which is expressly incorporated hereinto by reference). In the Sides et al '141 patent, the composition of the inflator comprises conducting ignition in the presence of an ammonium nitrate oxidizer and using a suitable propellant, e.g., aminoguanidine nitrate or a nitramine, such as cyclotrimethylenenitramine (RDX) and/or cyclotetramethylenetetranitramine (HMX), and in the presence of argon and a molecular oxygen-containing gas. The ratio of the oxygen-containing gas to argon is variably selected so as to provide only non-toxic reaction products in the exhaust gas.
Theory predicts that a successful ignition material for an inflator will give off hot particles or gases that will subsequently condense onto the cooler surface of the material being ignited and thereby transfer heat and produce “hot spots” which, in turn, lead to ignition. However, high levels of condensed species in the exhaust products of air bag inflators is undesirable due to respiratory effects on the automobile occupants s noted previously. Therefore a balanced ignition material is essential which contains minimal, but effective, levels of hot particles of condensed species. Furthermore, condensed species are preferred to be insoluble in water as these are considered to have less impact on occupants with respiratory ailments, such as asthma.
Broadly, the present invention is embodied in solid gas generant and ignition compositions which produce low particulates of the slightly-soluble or insoluble type when combusted. More specifically the present invention is embodied in solid gas generants and/or ignition compositions comprised of a nitramine, at least one oxidizer selected from the nitrate salts of strontium, copper, or cerium and/or complex nitrate salts of copper or cerium, in admixture with or without potassium perchlorate, and a binder. The gas generant and/or ignition compositions are usefully employed in inflatable passive vehicle occupant restraint systems (e.g., air bag systems). In contrast to many other igniter-booster formulations, these compositions burn readily at low temperature and pressure, and effectively ignite AN-based gas generants which are notoriously difficult to rapidly ignite under cold/low pressure conditions.
These and other aspects and advantages will become more clear from the following detailed description of the preferred exemplary embodiments thereof.
DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS
The gas generant and igniter compositions of this invention necessarily include a nitramine fuel which contributes clean, particulate-free gas, and high flame temperatures to the composition. The preferred nitramines are those that contain a high percentage of oxygen. As will be discussed below, they enable the composition to be formulated with low amounts of the preferred oxidizers, the importance of which will be described in more detail below. The preferred nitramines burn readily at atmospheric pressures, an important attribute for ignition systems in inflator applications. Most preferably, the nitramine that is employed in the present invention is cyclotrimethylenetrinitramine (RDX) and/or cyclotetramethylenetetranitramine (HMX), but could also include CL-20, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW). The nitramine is employed in amounts between about 45 to about 90 wt. % and more preferably between about 45 to about 60 wt. % based on the total composition weight. The particle size of the nitramine affects the ballistic properties and compressive strength of pressed charges in the present invention. Fluid-energy-mill (FEM) ground nitramine produced higher compressive strength but did not burn as rapidly as coarser (i.e., Class I) particle sizes. In the present invention, the particle size of the selected nitramines will be tailored to meet the specific ballistic requirements of individual inflator designs.
The most preferred nitramine is HMX. In the present invention HMX was found to produce stronger pressed charges than RDX (tested under compression to the first stress-relief crack formed), and was found to have better stability under thermal cycling conditions (200 cycles over the temperature range of −40 to +107 C.). Further, in the present invention, HMX was found to provide lower pressure exponents over the pressure range of 1000 to 4000 psi which lead to more stable burning rates at high pressures in compressed charges (i.e, pellets or tablets). Typical properties are shown in Table B. This is an important attribute since ballistic reproducibility is linked closely to low pressure exponents and stable burning properties. RDX is less pure than HMX, is commercially easier to produce, and is obtained at lower cost, so the present invention may require use of RDX in part or in total to keep the cost of the invention low.
The gas generant and ignitor compositions of this invention will also necessarily include an oxidizer selected from at least one of the nitrate salts of strontium, copper, and/or cerium, or the complex nitrate salts of cerium and/or copper. These oxidizers, alone or in combination are the primary source of condensed species in the combustion process. These condensed species are typically one or more of the group which includes the parent metal, its oxides, hydroxides, and/or carbonates, all of which are of the desired form which is either slightly soluble or insoluble in water. Further, these oxidizers produce condensed particulates which plate-out or adhere readily to internal surfaces of the combustion chamber. This is an important attribute of the invention, as the particulates from these oxidizers tend to remain in the combustion chamber rather than exiting into the external environment of the inflator (i.e, automobile interior). For igniter application
Lundstrom Norman H.
Lynch Robert D.
Martin James D.
Scheffee R. Stephen
Wheatley Brian K.
Anthony Joseph D.
Atlantic Research Corporation
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