Coating processes – Solid particles or fibers applied
Reexamination Certificate
2001-04-06
2002-10-01
Beck, Shrive P. (Department: 1762)
Coating processes
Solid particles or fibers applied
C427S372200, C427S385500, C427S387000, C280S728100
Reexamination Certificate
active
06458412
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to novel airbag coating compositions and systems comprising pre-expanded or non-expandable microspheres that provide effective insulation for the target airbag fabric during exothermic inflation. The inventive airbag fabrics are either pre-calendered prior to application of this composition or are coated through a floating knife method with such heat-expandable microsphere-containing compositions. The coated airbag fabrics and cushions may then be heated to evaporate the solvent within the coating composition. The resultant fabric thus exhibits the presence of the microsphere constituents of the coating compositions both within the interstices between the individual yarns of the fabric and over the raised yarns of the fabric. Such a coating system thus provides an extremely high degree of protection from heat exposure that permits structural integrity of the target airbag cushion airbag and provides protection from such high inflation temperatures to a vehicle passenger cushion during such a highly exothermic inflation event. The method of forming such specific airbag coating systems on airbag fabrics is also encompassed within this invention.
BACKGROUND OF THE INVENTION
Airbags for motor vehicles are well known and have been used for a substantial period of time. These devices are installed on the driver and passenger side of automobiles, as well as on the sides of both the front and rear compartments of vehicles (i.e., side airbags) and, in the event of a collision, are rapidly inflated with gas to act as an energy absorbing barrier between the driver or passenger and the steering wheel, dashboard, windows, or interior sides of the automobile. Such airbags (a.k.a., airbag cushions) must meet several important criteria. Included in this list are the ability to inflate quickly (within 0.1 seconds) after a collision event, the ability to rapidly deflate at a uniform rate (such as for front-seat airbags to provide a relatively soft cushion), the ability to retain inflation pressure for a relatively long duration (such as for at least 7 seconds for side airbags during rollover collisions), the ability to retain seam integrity over the target airbag fabric or cushion during and after an inflation event, and, possibly of greatest importance, the ability to withstand extremely high inflation pressures and temperatures during and after a collision event. This last issue concerns the utilized fabric's structural integrity and thus its performance within an airbag cushion during a collision. Sodium azide has been the prominent inflation chemical utilized within standard airbag cushions for many years. In essence, upon collision, the inflation canister ignites the sodium azide (which is, in its pure form, highly toxic to humans) creating a small explosion forcing the released gas into the area of lowest pressure. In such an instance, the uninflated airbag cushion provides the escape route for such gas during the explosion. Thus, the airbag cushion inflates providing the protection for the driver or passenger as noted above. This entire inflation step occurs in about 0.1 seconds from the time of the collision event. In order to produce such a rapid inflation, the explosion produces a tremendous amount of heat within the inflation assembly, which also includes within the airbag cushion itself. Thus, the utilized airbag fabric must be able to withstand such large temperature variations and such exposure to heat without losing its ability to protect the driver or passengers.
There has been a recent movement away from sodium azide (due to its high toxicity, among other reasons) as the explosion ignition chemical utilized within airbag inflation assemblies. Although such a chemical may prove quite damaging to humans, it has, in the past, also provided a method of quick inflation for airbag cushions that required relatively low inflation temperatures (about 1200° F.). New ignition chemicals, such as nitrocellulose-based compounds, have proven safer from a toxicity standpoint and less expensive to utilize, but these also produce extremely exothermic reactions. The use of nitrocellulose inflators (which do not need to be filtered as do the sodium azide-containing types) represents an improvement from a cost perspective over the sodium azide technology, but these unfortunately also produce even greater temperatures during deployment (about 2000° F.).
In view of this movement away from sodium azide, modifications of airbag fabrics and cushions are now necessary to protect the structural integrity of such fabrics and cushions during such an extremely high-temperature inflation event. Some thought has been given to utilizing higher denier yarns (i.e., 515, 630, and greater) to provide greater heat capacities for the target fabrics. However, such higher denier materials also create greater packed volumes for such target airbag cushions and increase the costs of manufacture for such airbag fabrics and cushions as to offset the savings provided through the use of a new inflation assembly. Thus, in order to benefit from the cost reductions associated with utilizing nitrocellulose inflator assemblies, there is a desire to utilize lower denier yarns (i.e., up to about 420 denier) with modified coatings to provide the necessary heat resistance. Such coatings must also provide the same performance standards as noted above for different airbag cushions (i.e., quick inflation, long-duration inflation, etc.). To date, there has been no discussion of altering prior well-known airbag fabric coating compositions to compensate for this potential change from low-temperature sodium azide-containing inflation assemblies to those comprising chemicals which produce much higher temperature (about 2000° F.) explosions and inflations.
In the past, coatings have been applied to fabrics intended for use in automotive airbags, both to resist the unwanted permeation of air through the fabric and to protect the fabric from detriment by the hot gases used to inflate the bags. Polychloroprene was the polymer of choice in the early development of such a product; however, the desire to decrease the folded size of the completed airbag, and the tendency of polychloroprene to degrade upon exposure to heat and release the components of hydrochloric acid (thereby potentially degrading the fabric component as well as releasing hazardous chemicals), has led to the acceptance of other coating compounds. Such compounds include silicone (polydimethylsiloxane, as merely one example), polyurethane, other rubber compositions, and the like. Such compositions have been well known as providing the desired permeability characteristics for such target airbag fabrics and cushions as well as temperature protection from the heat generated by sodium azide inflation explosions. However, and again, as noted above, there has been no teaching nor fair suggestion of any improvements in temperature protection for higher temperature, less expensive, and less toxic to humans, inflation chemicals within airbag inflation assemblies.
DESCRIPTION OF THE INVENTION
Although silicones and neoprene have been the predominant coatings utilized in the airbag industry traditionally, as noted above, it has been determined that these coatings exhibit certain shortcomings when exposed to the high temperatures associated with the unfiltered, non-sodium azide inflation assemblies. For example, since a complete coating (over the raised yarns of such airbag fabrics and within the interstices between such yarns) is necessary to effectuate the proper high temperature protection during an inflation event, large amounts of (expensive) silicones would be required. Also, low amounts of silicone elastomers do not provide the same heat resistance as thicker compounds. Thus, a composition of low amounts (cost-effective) of silicones which completely coats the desired airbag fabric is necessary. Unfortunately, the prior art has not accorded the industry such a coating system. Neoprene degrades very easily and thus does not exhibit suffic
Child Andrew D.
Kozlowski Derek S.
Beck Shrive P.
Blanton Rebecca A.
Milliken & Company
Moyer Terry T.
Parks William S.
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