Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which... – Two or more non-extruded coatings or impregnations
Reexamination Certificate
1999-06-17
2001-01-23
Morris, Terrel (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Coated or impregnated woven, knit, or nonwoven fabric which...
Two or more non-extruded coatings or impregnations
C280S728100, C493S243000, C425S027000, C425S035000, C425S043000, C428S035700, C428S036100, C428S036600, C428S036700, C442S081000, C442S082000, C442S157000, C442S167000, C442S168000, C442S169000, C442S170000, C442S171000, C442S172000, C442S173000
Reexamination Certificate
active
06177365
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to novel airbag coating compositions comprising two separate and distinct layers. The first layer (base coat), being in contact with the airbag surface, comprises a non-silicone composition of at least one coating material, provides excellent adhesion, excellent tensile strength, and lower cost than standard silicone materials. The second layer, being a coating for the first layer, provides reinforcement and excellent aging characteristics to prevent degradation of the first layer. Such a second layer (topcoat) is preferably a silicone material. This two-layer system permits excellent strength and aging properties to prevent seam combing at relatively low cost due to the inexpensive basecoat materials and the relatively low amount required for the topcoat. An airbag fabric coated with this inventive two-layer system is also contemplated within this invention.
BACKGROUND OF THE INVENTION
Airbags for motor vehicles are known and have been used for a substantial period of time. These devices are installed on the driver and passenger side of automobiles and, in the event of a collision, arc rapidly inflated with gas, to act as an energy absorbing barrier between the driver or passenger and the steering wheel or dashboard of the automobile.
With the advent of new curtain-type airbags comprising a plurality of pillows formed from stitched areas of the bag article (to protect passengers during roll-over and side impact collision events), there is now a greater emphasis on providing such curtain-type airbags which will retain their inflation pressure for extended period after deployment, and will perform if and when necessary even upon storage of a long duration (years for example). Such pillowed fabrics thus comprise seams which control the shape and size of the inflated cushion. Upon inflation of such specific airbag cushions, pressure may be applied in great force, particularly on the seams, during an inflation in response to a collision event. These stitched areas thus must retain their strength upon inflation, thereby setting forth the requirement that the individual yarns at such seams will not become unraveled (i.e., “combed-out”) easily (which would result in the leakage air at too great a rate to afford sufficient protection), particularly upon inflation of the airbag. With such an expansion in stitching requirements as compared with traditional driver-side and passenger-side airbags, the areas for potential air leakage have also increased dramatically.
In the past, coatings have been applied to fabrics, intended for use in automotive airbags, to resist the unwanted permeation of air through the fabric and, to a lesser extent, 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 this product, but the desire to decrease the folded size of the completed airbag, and the tendency of polychloroprene to degrade, with exposure to heat, to release the components of hydrochloric acid (thereby potentially degrading the fabric component as well as releasing hazardous chemicals), has led to the almost universal acceptance of silicone (polydimethylsiloxane or similar materials) as a more suitable coating. In the quest for the most compact folded size possible, coating levels of polymer have dropped from around 2.5 ounces per square yard of fabric, to levels approaching 0.5 ounces per square yard.
New developments in airbag technology, particularly newer designs being placed in the sides of the passenger compartment (as noted above), have introduced the requirement that the bags hold pressure longer under use. This, and the evolution of the lower coating levels of silicone polymer, have begun to highlight the effect that, when a sewn seam is put under stress, a naturally lubricating silicone coating may allow the yarns from which the fabric is constructed to shift. This shifting can lead to leakage of the inflating gas through the new pores formed from the shifting yarns, or, in drastic cases, cause the seam to fail. Since the airbag must retain its integrity during a collision event, in order to sufficiently protect the driver or passenger, there is a great need to provide coatings which provide both effective permeability characteristics and sufficient restriction of yarn shifting for the airbag to function properly, if and when necessary. In recent years, silicone coatings have been utilized to provide such desired permeability and strength characteristics. However, the relative cost of such coating materials (such as polydimethylsiloxane) is sufficiently high that new, more inexpensive alternatives are being sought. Thus, there exists a need for providing good adhesion and a strong bond between the individual yarns (in order to effectuate long-term rigidity of the fibers to prevent unraveling) at cut edges or at seams while simultaneously providing aging stability and excellent low air permeability characteristics. Such a necessary improvement has not been afforded the airbag industry within the prior art. However, the inventive two-layer coating system does provide the necessary strength, durability, permeability, and reliability to the airbag industry, particularly for large-scale production of heavily stitched curtain-type airbags.
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 which actually make them undesirable as the sole coatings present on target fabrics. For example, silicones are very expensive and act as natural fiber lubricants rather than adhesives. Silicone elastomers are very flexible which permits facilitation of folding of coated airbags for long-term storage in airbag modules. However, compared with other elastomers, silicones possess poor tensile strength and poor tear resistance. As such, these compounds do not provide the best overall strength to prevent unraveling of seam yams, and certainly are not cost-effective selections for this purpose. Neoprene degrades very easily and thus does not exhibit sufficient aging stability. Furthermore, thicker coatings of such rubber compounds are required to reduce the air permeability to an acceptable level which can result in higher costs, although neoprene is not as expensive as the aforementioned silicones. Lastly, neither of these two traditional coating materials permits a single application over the entire airbag fabric in order to provide both air permeability characteristics over the non-stitched (and thus plain fabric) portion with effective adhesion for the individual fibers within the seamed areas.
Thus, an object of the invention has been to provide excellent strength and adhesion to the seam yarns (or yams at cut edges of the target fabric) while simultaneously allowing for durability (aging stability) as well as desirable low air permeability over the plain fabric of the target airbag fabric, all at a relatively low cost. Another object of the invention has been to provide a coating system or composition which is easy to apply to target airbag fabrics as well.
Accordingly, this invention provides a coating system (i.e., composition) for airbag fabrics comprising at least two layers wherein the first layer is in contact with at least a portion of the airbag fabric and is at least one non-silicone coating material and the second layer is a coating for at least a portion of said first layer and is at least one material providing sufficient aging stability for the first layer material selected from the group consisting of at least one non-silicone compound and at least one silicone compound. In particular, the first layer material must possess certain properties critical to properly seal a woven seam at high pressure. Thus, this layer must be comprised of a non-silicone material exhibiting a tensile strength of greater than 600 psi, preferably greater than 800 psi, and most preferably greater t
Milliken & Company
Morris Terrel
Moyer Terry T.
Parks William S.
Singh Arti
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