Explosive and thermic compositions or charges – Structure or arrangement of component or product – Solid particles dispersed in solid solution or matrix
Reexamination Certificate
2003-03-20
2004-02-10
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
C149S019100, C280S741000, C523S180000
Reexamination Certificate
active
06689236
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to a binder matrix for a gas generant composition such as those used for the inflation of inflatable devices like airbag cushions included in inflatable restraint systems for automobile passengers. In particular, the invention relates to a binder matrix, including a non-energetic binder material and a non-energetic plasticizer, that has a softening temperature above at least about 125° C.
It is well know to protect a vehicle occupant using a cushion or bag, e.g., an “airbag cushion” that is inflated or expanded with a gas when a vehicle experiences sudden deceleration, such as in the event of a collision. Such airbag restraint systems normally include: one or more airbag cushions, housed in an uninflated and folded condition to minimize space requirements; one or more crash sensors mounted on or to the frame or body of the vehicle to detect sudden deceleration of the vehicle; an activation system electronically triggered by the crash sensors; and an inflator device that produces or supplies a gas to inflate the airbag cushion. In the event of a sudden deceleration of the vehicle, the crash sensors trigger the activation system which in turn triggers the inflator device which begins to inflate the airbag cushion in a matter of milliseconds.
Many types of inflator devices have been disclosed in the art for inflating one or more inflatable restraint system airbag cushions. Inflator devices which form or produce inflation gas via the combustion of a gas generating material, e.g., a “gas generant”, are well known. One such inflator device, generally known as a hybrid gas generator, uses the high temperature combustion products, including additional gas products, generated by the burning of the gas generant to supplement stored and pressurized gas to inflate one or more airbag cushions are known. Often the stored and pressurized gas includes an oxidizing gas to assist in converting the reaction products generated by the combustion of the gas generant to less hazardous compounds such as carbon dioxide, water and nitrogen gases.
One type of gas generant that may be used in such hybrid gas generators is a low vulnerability ammunition propellant, also known as a LOVA-type gas generant. Originally developed as a safer propellant for military ammunition, LOVA-type gas generants have found use in inflator devices for airbag cushions because of their high burning rates and fast ignition reaction times. Such LOVA-type gas generant compositions, typically in the form of extrudlets or pellets, generally include a binder material, a plasticizer and high explosive such as, for example, cyclotrimethylenetrinitramine (RDX). The binder material, as well as the plasticizer, may be an energetic or non-energetic material. For example, U.S. Pat. No. 6,170,868 to Butt et al., herein incorporated by reference, discloses a LOVA-type gas generant composition including a nitramine explosive such as RDX, a non-energetic binder material such as a cellulose derivative, and either an energetic plasticizer or acetyl triethyl citrate non-energetic plasticizer.
Unfortunately, for some gas generant compositions such as certain LOVA-type gas generant compositions, particularly those including cellulose acetate butyrate as a binder material, the binder softening temperature is very near the required aging temperatures for gas generants used in automotive inflator devices. Additionally, the binder softening temperature can be further reduced by the addition of the plasticizer. The lower softening temperature of the binder material can cause the surface of the gas generant extrudlets or pellets to soften and become tacky which can cause the extrudlets or pellets to stick together resulting in a change in the ballistic response of the of the inflator device, sometimes by as much as 30 to 40 percent, due to the change in the surface area of the gas generant. This sticking phenomena is most evident after exposure to temperature cycling, aging and thermal shock environments such as those that an inflator device may be exposed to during an automobile's lifetime. Thus, the performance of such an inflator device becomes a function of the environment that each automobile would experience and, thus, less predictable. In some extreme cases where an automobile may be exposed to a relatively severe environment, the inflator devices may fail to protect an occupant in the event of a collision.
The sticking phenomena may be alleviated by blending or coating the extrudlets or pellets of the gas generant with a powdered additive, such as graphite, silica, or hydrophobic fumed silica so that the extrudlets or pellets do not physically touch during the application of thermal stimuli such as temperature fluctuations. However, this type of treatment increases the number of operations needed to manufacture the gas generant composition and hence increases the costs of manufacture.
Thus there is a need and a demand for a binder matrix that has a higher softening temperature. In particular, there is a need or a demand for a gas generant composition in pellet-form that has a reduced propensity to soften and stick together. There is a further need and a demand for a gas generant composition that is cost effective to prepare.
SUMMARY OF THE INVENTION
A general object of the invention is to provide an improved binder matrix for use in a gas generant composition.
A particular object of the invention is to provide a binder matrix having a higher softening temperature.
A more specific objective of the invention is to overcome one or more of the problems described above.
The general object of the invention can be attained, at least in part, through providing a binder matrix having a softening temperature above at least about 125° C. that includes a non-energetic binder material and a non-energetic plasticizer, wherein the non-energetic plasticizer is dimethyl malonate.
The prior art has generally failed to provide a binder matrix that is as effective as desired in satisfying one or more of the above-identified performance criteria. Furthermore, the prior art has generally failed to address the sticking phenomena that may occur in gas generant compositions such as LOVA-type gas generant compositions that include non-energetic binder materials having relatively low softening temperatures, particularly, cellulose acetate butyrate, and a plasticizer that further lowers the softening temperature of the binder material. Additionally, the prior art has generally failed to identify dimethyl malonate as a particularly compatible non-energetic plasticizer that may be used in combination with a non-energetic binder material to alleviate one or more of the above-identified performance inhibiting phenomena.
The invention further comprehends a gas generant composition including a binder matrix having a softening temperature above at least about 125° C., a fuel and a stabilizer. The binder matrix includes about 8 to about 15 composition weight percent of a non-energetic binder material such as cellulose acetate and about 5 to about 12 composition weight percent dimethyl malonate plasticizer. The gas generant composition further includes about 70 to about 85 composition weight percent of a fuel such as a nitramine fuel and about 0.2 to about 0.5 composition weight percent of a stabilizer such as N-methyl-p-nitroaniline.
The invention still further comprehends a method for inflating an airbag cushion of an inflatable restraint system of a motor vehicle. The method includes igniting a gas generant composition to produce a quantity of inflation gas and inflating the airbag cushion with the inflation gas. The gas generant composition includes a fuel, a stabilizer, and a binder matrix having a softening temperature above at least about 125° C. The binder matrix includes a non-energetic binder material and dimethyl malonate plasticizer.
Reference herein to a “binder” or a “binder material” is to be understood to refers to a material or substance that creates uniform consistency, solidification, or cohesion
Hess Gregory B.
Smith Gary L.
Taylor Robert D.
Autoliv ASP Inc.
Brown Sally J.
Erickson James D.
Miller Edward A.
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