Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which... – Coated or impregnated synthetic organic fiber fabric
Reexamination Certificate
2000-06-16
2003-05-27
Morris, Terrel (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Coated or impregnated woven, knit, or nonwoven fabric which...
Coated or impregnated synthetic organic fiber fabric
C106S002000, C106S018120, C280S728100, C383S003000, C427S387000, C427S389900, C427S412000, C428S036100, C428S034500, C428S034300, C428S034700, C442S076000, C442S169000, C442S158000
Reexamination Certificate
active
06569788
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to coated inflatable fabrics and more particularly concerns airbag cushions to which very low add-on amounts of silicone-based coating have been applied and which exhibit extremely low air permeability. The inventive inflatable fabrics are primarily for use in automotive restraint cushions that require low permeability characteristics (such as side curtain airbags). Traditionally, heavy, and thus expensive, coatings of compounds such as neoprene, silicones, and the like, have been utilized to provide such required low permeability. The inventive fabric utilizes an inexpensive, very thin, substantially uniform silicone coating to provide such necessarily low permeability levels. Thus, the inventive coating comprises at least a single layer comprising a majority of silicone-based material, wherein the total thickness of the single layer is at most about 3.0 ounces per square yard as applied to a target fabric surface. The inventive airbag exhibits a characteristically long leak-down rate as compared to other coated airbags.
BACKGROUND OF THE PRIOR ART
Airbags for motor vehicles are known and have been used for a substantial period of time. A typical construction material for airbags has been a polyester or nylon fabric, coated with an elastomer such as neoprene, or silicone. The fabric used in such bags is typically a woven fabric formed from synthetic yarn by practices that are well known in the art.
The coated material has found acceptance because it acts as an impermeable barrier to the inflation medium. This inflation medium is generally a gas generated from a gas generator or inflator. Such gas is conveyed into the cushion at a relatively warm temperature. The coating obstructs the permeation of the fabric by such hot gas, thereby permitting the cushion to rapidly inflate without undue decompression during a collision event.
Airbags may also be formed from uncoated fabric which has been woven in a manner that creates a product possessing low permeability or from fabric that has undergone treatment such as calendaring to reduce permeability. Fabrics which reduce air permeability by calendaring or other mechanical treatments after weaving are disclosed in U.S. Pat. Nos. 4,921,735; 4,977,016; and 5,073,418 (all incorporated herein by reference).
Traditional silicone coatings have proven ineffective at low add-on coating weights over target airbag fabric surfaces for low permeability characteristics. Typically, such coatings have required extremely thick layers of materials to provide the desired low permeability levels required for long-term rollover protection situations (particularly for side-curtain airbags). In general, past silicone-based coatings have utilized non-solvent- and solvent-based compositions having dry coating weights for such silicones above 3 and approaching lower levels of at least 4 ounces per square yard for both the front and back panels of side curtain airbags. As will be appreciated by one of ordinary skill in this art, high add-on weights substantially increase the cost of the base fabric for the airbag and make packing within small airbag modules very difficult. Furthermore, traditionally utilized silicones exhibit very low tensile strength and elongation at break characteristics that do not withstand high pressure inflation easily without the utilization of very thick coatings. However, silicones provide excellent durability, aging, and processability benefits, which, if provided with extremely low add-on compositions, would translate into highly desirable airbag coatings. Additionally, as noted in greater detail below, the production of integrally woven side curtain airbags has eliminated the possibility of coating on both the front and back sides of individual fabric panels. As such, there is a greater need to accord relatively thin coating layers on solely the outside panels (i.e., front) of such articles. To date, the ability to restrict coatings to low levels of silicone-based materials has been unavailable.
The use of certain polyurethanes as coatings as disclosed in U.S. Pat. No. 5,110,666 to Menzel et al. (herein incorporated by reference) permits low add on weights reported to be in the range of 0.1 to 1 ounces per square yard but the material itself is relatively expensive and is believed to require relatively complex compounding and application procedures due to the nature of the coating materials. Patentees, however, fail to disclose any pertinent elasticity and/or tensile strength characteristics of their particular polyurethane coating materials. Furthermore, there is no discussion pertaining to the importance of the coating ability (and thus correlated low air permeability) at low add-on weights of such polyurethane materials on side curtain airbags only for fabrics which are utilized within driver or passenger side cushions. All airbags must be inflatable extremely quickly; upon sensing a collision, in fact, airbags usually reach peak pressures within 10 to 20 milliseconds. Regular driver side and passenger side air bags are designed to withstand this enormous inflation pressure; however, they also deflate very quickly in order to effectively absorb the energy from the vehicle occupant hitting the bag. Such driver and passenger side cushions (airbags) are thus made from low permeability fabric, but they also deflate quickly at connecting seams (which are not coated to prevent air leakage) or through vent holes. Furthermore, the low add-on coatings taught within Menzel, and within U.S. Pat. No. 5,945,186 to Li et al., would not provide long-term gas retention; they would actually not withstand the prolonged and continuous pressures supplied by activated inflators for more than about 2 seconds, at the most. The low permeability of these airbag fabrics thus aid in providing a small degree of sustained gas retention within driver and passenger airbag cushions to provide the deflating cushioning effects necessary for sufficient collision protection. Such airbag fabrics would not function well as side curtain airbags, since, at the very least, the connecting seams which create the pillowed, cushioned structures within such airbags, as discussed in greater detail below, would not be coated. As these areas provide the greatest degree of leakage during and after inflation, the aforementioned patented low-coating low-permeability airbag fabrics would not be properly utilized within side curtain airbags. Lastly, polyurethanes suffer from aging and durability problems which requires complexities of mixing and application to overcome such difficulties.
As alluded to above, there are three primary types of different airbags, each for different end uses. For example, driver-side airbags are generally mounted within steering columns and exhibit relatively high air permeabilities in order to act more as a cushion for the driver upon impact. Passenger-side airbags also comprise relatively high air permeability fabrics which permit release of gas either therethrough or through vents integrated therein. Both of these types of airbags are designed to protect persons in sudden collisions and generally burst out of packing modules from either a steering column or dashboard (and thus have multiple “sides”). Side curtain airbags, however, have been designed primarily to protect passengers during rollover crashes by retaining its inflation state for a long duration (for example, exhibiting a retention of at least 50% of the initial pressure after 5 seconds subsequent to high pressure inflation) and generally unroll from packing containers stored within the roofline along the side windows of an automobile (and thus have a back and front side only). Side curtain airbags therefore not only provide cushioning effects but also provide protection from broken glass and other debris. As such, it is imperative that side curtain airbags, as noted above, retain large amounts of gas, as well as high gas pressures, to remain inflated throughout the longer time periods of the entire potential rollover situation. To
Hersey Edwin
Hurst Michael D.
Milliken & Company
Morris Terrel
Moyer Terry T.
Parks William S.
Singh Arti
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