LOW PERMEABILITY AIRBAG CUSHIONS HAVING FILM COATINGS OF EXTREMELY LOW THICKNESS

Abstract: Coated inflatable fabrics (26), more particularly airbags to which very low add-on amounts of coating have been applied, are provided which exhibit extremely low air permeabilities. The fabrics are primarily for use in automotive restraint cushions which require low permeability characteristics (such as side curtain airbags). The fabric utilizes an inexpensive, very thin coating to provide such necessary low permeability levels. Thus, the inventive coated airbag possesses a coating of at most 2.5 ounces per square yard, most preferably about 0.8 ounces per square yard, and exhibits a leak-down time of at least 7 seconds. All coatings, in particular elastomeric, nonsilicon coatings, and coated airbags, meeting these criteria are intended to reside within the scope of this invention.

Description: Description LOW PERMEABILITY AIRBAG CUSHIONS HAVING FILM COATINGS OF EXTREMELY LOW THICKNESS Technical Field This invention relates generally to coated inflatable fabrics and more particularly concerns airbag cushions to which very low add-on amounts of 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 coating to provide such necessarily low permeability levels. Thus, the inventive coated inflatable airbag comprises a film laminated on at least a portion of the target fabric surface wherein the film possesses a tensile strength of at least 2,000 and an elongation at break of at least 180%. The film provides a low permeability airbag cushion exhibiting a leak-down time of at least 5 seconds wherein the film is present on the surface in an amount of at most 2.5 ounces per square yard of the fabric. Background 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 weaving 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 nitrogen 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. Patent 4,921,735; U.S. Patent 4,977,016; and U.S. Patent 5,073,418 (all incorporated herein by reference). Silicone coatings typically utilize either solvent based or complex two component reaction systems. Dry coating weights for silicone have been in the range of about 3 to 4 ounces per square yard or greater 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, silicone exhibits very low tensile strength and elongation at break characteristics which do not withstand high pressure inflation easily without the utilization of very thick coatings. The use of certain polyurethanes as coatings as disclosed in U.S. Patent 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, fails 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 either 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. Patent 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 with 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. 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 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 accomplish this, these side curtains are generally coated with very large amounts of sealing materials on both the front and back sides. Since most side curtain airbag fabrics comprise woven blanks that are either sewn, sealed, or integrally woven together, discrete areas of potentially high leakage of gas are prevalent, particularly at and around the seams. It has been accepted as a requirement that heavy coatings were necessary to provide the low permeability (and thus high leak-down time) necessary for side curtain airbags. Without such heavy coatings, such airbags would most likely deflate too quickly and thus would not function properly during a rollover collision. As will be well understood by one of ordinary skill in this art, such heavy coatings add great cost to the overall manufacture of the target side curtain airbags. There is thus a great need to manufacture low permeability side curtain airbags with less expensive (preferably lower coating add-on weight) coatings without losing the aging, humidity, and permeability characteristics necessary for proper functioning upon deployment. To date, there has been little accomplished, if anything at all, alleviating the need for such thick and heavy airbag coatings from side curtain airbags. Furthermore, there is a current drive to store such low permeability side curtain airbags within cylindrically shaped modules. Since these airbags are generally stored within the rooflines of automobiles, and the area available is quite limited, there is always a great need to restrict the packing volume of such restraint cushions to their absolute minimum. However, the previously practiced low permeability side curtain airbags have proven to be very cumbersome to store in such cylindrically shaped containers at the target automobile's roofline. The actual time and energy required to roll such heavily coated low permeability articles as well as the packing volume itself, has been very difficult to reduce. Furthermore, with such heavy coatings utilized, the problems of blocking (i.e., adhering together of the different coated portions of the cushion) are amplified when such articles are so closely packed together. The chances of delayed unrolling during inflation are raised when the potential for blocking is present. Thus, a very closely packed, low packing volume, low blocking side curtain low permeability airbag is highly desirable. Unfortunately, the prior art has again not accorded such an advancement to the airbag industry. Disclosure of Invention In light of the background above, it can be readily seen that there exists a need for a low permeability, side curtain airbag that utilizes lower, and thus less expensive, amounts of coating, and therefore exhibits a substantially reduced packing volume over the standard low permeability type side curtain airbags. Such a coated low permeability airbag must provide a necessarily high leak-down time upon inflation and after long-term storage. Such a novel airbag and a novel coating formulation provides marked improvements over the more expensive, much higher add-on airbag coatings (and resultant airbag articles) utilized in the past. It is therefore an object of this invention to provide a coated airbag, wherein the coating is present in a very low add-on weight, possessing extremely high leak- down time characteristics after inflation and thus complementary low permeability characteristics. Another object of the invention is to provide an inexpensive side curtain airbag cushion. A further object of this invention is to provide an highly effective airbag coating formulation which may be applied in very low add-on amounts to obtain extremely low permeability airbag structures after inflation. An additional object of this invention is to provide an airbag coating formulation which not only provides beneficial and long-term low permeability, but also exhibits excellent long-term storage stability (through heat aging and humidity aging testing). Yet another object of the invention is to provide a low permeability side curtain airbag possessing a very low rolled packing volume and non-blocking characteristics for effective long-term storage within the roofline of an automobile. Accordingly, this invention is directed to an airbag cushion comprising a coated fabric, wherein said fabric is laminated with a film, wherein said film is present in an amount of at most 2.5 ounces per square yard of the fabric; and wherein said airbag cushion, after long-term storage, exhibits a characteristic leak-down time of at least 5 seconds. Also, this invention concerns an airbag cushion comprising a coated fabric, wherein said fabric is coated with a laminate film; wherein said laminate film possesses a tensile strength of at least 2,000 and an elongation of at least 180%; and wherein said airbag cushion, after long-term storage, exhibits a characteristic leak- down time of at least 5 seconds. The term "characteristic leak-down time" is intended to encompass the measurement of time required for the entire amount of inflation gas introduced within an already-inflated (to a peak initial pressure which "opens" up the areas of weak sealing) and deflated airbag cushion upon subsequent re-inflation at a constant pressure at 10 psi. It is well known and well understood within the airbag art, and particularly concerning side curtain (low permeability) airbag cushions, that retention of inflation gas for long periods of time is of utmost importance during a collision. Side curtain airbags are designed to inflate as quickly as driver- and passenger-side bags, but they must deflate very slowly to protect the occupants during roll over and side impact. Thus, it is imperative that the bag exhibit a very low leakage rate after the bag experiences peak pressure during the instantaneous, quick inflation. Hence, the coating on the bag must be strong enough to withstand the shock and stresses when the bag is inflated so quickly. Thus, a high characteristic leak-down time measurement is paramount in order to retain the maximum amount of beneficial cushioning gas within the inflated airbag. Airbag leakage after inflation (and after peak pressure is reached) is therefore closely related to actual pressure retention characteristics. The pressure retention characteristics (hereinafter referred to as "leak- down time") of already-inflated and deflated side curtain airbags can be described by a characteristic leak-down time t, wherein: Bag volume(ft 3 ) t (second) = X3600 Volumetric leakage rate(SCFH*) at 10 Psi *SCFH: standard cubic feet per hour. It is understood that the 10 psi constant is not a limitation to the invention; but merely the constant pressure at which the leak-down time measurements are made. Thus, even if the pressure is above or below this amount during actual inflation or after initial pressurizing of the airbag, the only limitation is that if one of ordinary skill in the art were to measure the bag volume and divide that by the volumetric leakage rate time (measured by the amount leaking out of the target airbag during steady state inflation at 10 psi), the resultant measurement in time would be at least 5 seconds. Preferably, this time is greater than about 9 seconds; more preferably, greater than about 15 seconds; and most preferably, greater than about 20 seconds. Alternatively, and in a manner of measurement with uninflated side curtain airbags, the term "leak-down time" may be measured as the amount of time required for at half of the introduced inflation gas to escape from the target airbag after initial peak pressure is reached. Thus, this measurement begins the instant after peak initial pressure is reached upon inflation (such as, traditionally, about 30 psi) with a standard inflation module which continues to pump gas into the target airbag during and after peak initial pressure is reached. It is well understood that the pressure of gas forced into the airbag after peak initial pressure is reached will not remain stable (it decreases during the subsequent introduction of inflation gas), and that the target airbag will inevitably permit escape of a certain amount of inflation gas during that time. The primary focus of such side curtain airbags (as noted above) is to remain inflated for as long as possible in order to provide sufficient cushioning protection to vehicle occupants during rollover accidents. The greater amount of gas retained, the better cushioning effects are provided the passengers. Thus, the longer the airbag retains a large amount of inflation gas, and consequently the greater the characteristic leak- down time, the better cushioning results are achieved. At the very least, the inventive airbag must retain at least half of its inflated gas volume 5 seconds subsequent to reaching peak initial pressure. Preferably, this time is 9 seconds, more preferably 15 seconds, and most preferably 20 seconds. Likewise, the term, "after long-term storage" encompasses either the actual storage of an inventive airbag cushion within an inflator assembly (module) within an automobile, and/or in a storage facility awaiting installation. Such a measurement is generally accepted, and is well understood and appreciated by the ordinarily skilled artisan, to be made through comparable analysis after representative heat and humidity aging tests. These tests generally involve 107° C oven aging for 16 days, followed by 83° C and 95% relative humidity aging for 16 days and are universally accepted as proper estimations of the conditions of long-term storage for airbag cushions. Thus, this term encompasses such measurement tests. The inventive airbag fabrics must exhibit proper characteristic leak-down times after undergoing such rigorous pseudo- storage testing. The inventive coating, here a film, must possess a tensile strength of at least 2,000 psi and an elongation to break of greater than about 180%. Preferably, the tensile strength is at least 3,000 psi, more preferably, 6,000, and most preferably at least about 8,000 (the high end is basically the highest one can produce which can still adhere to a fabric surface). The preferred elongation to break is more than about 200%, more preferably more than about 300%, and most preferably more than about 600%. These characteristics of the film translate to a coating that is both very strong (and thus will withstand enormous pressures both at inflation and during the time after inflation and will not easily break) and can stretch to compensate for such large inflation, etc., pressures. The film itself is produced prior to actual contact with the target airbag cushion, or fabric, surface. In order to apply such a film, a lamination procedure must be performed through the simultaneous exposure of heat and pressure over the film while in contact with the target surface. The laminate may be applied over any portion of the target structure, although preferably it coats the entire cushion or fabric. Also, more than one laminated film may be present on the target cushion as one type of film (possessing certain tensile strength and elongation characteristics) may be preferably applied to certain discrete areas of the target cushion while a different film with different characteristics may be selected at other locations (such as at the seams). The only requirement is that the final product exhibit the aforementioned high leak-down properties. This film appears to act by "cementing" the contacted individual yarns in place and possibly preventing leakage through open areas between woven yarns and/or stitches. During inflation, then, the coating prevents leakage through the interstitial spaces between the yarns and aids in preventing yarn shifting (which may create larger spaces for possible gas escape). The utilization of such high tensile strength and high elongation at break components permits the consequent utilization, surprisingly, of extremely low add-on weight amounts of such films. Normally, the required coatings (which are not films, but actual coating formulations applied to the surface which then may form non- laminated films) on side curtain airbags are very high, at least 3.5 ounces per square yard (with the standard actually much higher than that, at about 4.0). The inventive airbag cushions require merely about 2.7 ounces per square yard of the desired film coating (preferably less, such as about 2.5, more preferably about 2.2, still more preferably, less than 2.2) ounces per square yard of this inventive coating to effectuate the desired high leak-down (low permeability). Furthermore, the past coatings were required to exhibit excellent heat and humidity aging stability. Unexpectedly, even at such low add-on amounts, and particularly with historically questionable coating materials (polyurethanes, for example), the inventive coatings, and consequently, the inventive coated airbag cushions, exhibit excellent heat aging and humidity aging characteristics. Thus, the coating compositions and coated airbags are clearly improvements within this specific airbag art. Of particular interest as the desired films are polyurethanes, although any film which possesses the same desired tensile strength and elongation characteristics noted above may function within this inventive low permeability airbag cushion. Copolymers of polyurethanes, polyamides, and the like, maybe utilized, as merely one type of example. Also, such films may or may not be cross-linked on the airbag surface. Preferably, the film is a polyurethane and most preferably is a polycarbonate polyurethane or a polyurethane film based on polytetramethylene glycol diol (available from Deerfield Urethane, Inc., Ivyland, PA, under the tradename Dureflex™ PT9400). This specific film exhibits a tensile strength of 8,000 psi and an elongation at break of about 600%. Such a film may be added in an amount of as low as 2.2 ounces per square yard on the desired cushion and still provide the requisite high leak-down time characteristics. Of course, any other film meeting the characteristics as noted above is encompassed within this invention; however, the add¬ on weights of other available films may be greater than this preferred one, depending on the actual tensile strength and elongation properties available. However, the upper limit of 2.5 ounces per square yard should not be exceeded to meet this invention. The desired films may be added in multiple layers if desired as long the required thickness for the overall coating is not exceeded. Alternatively, the multiple layer film/coating system may also be utilized as long as at least one film possessing the desired tensile strength and elongation at break is utilized and the requisite low permeability is exhibited. Other possible components present within or on these films are thickeners, antioxidants, flame retardants, coalescent agents, adhesion promoters, and colorants. In accordance with the potentially preferred practices of the present invention, a primer adhesive coating is first applied to the target cushion surface. Upon drying of this first layer, the desired film is then laminated through heat and pressure to the selected areas of the target surface for a sufficient time to effectuate lamination. Preferably, the preferred film (or films) will not include any silicone, due to the extremely low tensile strength (typically below about 1,500 psi) characteristics exhibited by such materials. However, in order to provide effective aging and non- blocking benefits, such components may be applied to the film as a topcoat as long as the add-on weight of the entire film and topcoat does not exceed 2.5 ounces per square yard. Additionally, elastomers comprising polyester or polyether segments or other similar components, are undesirable, particularly at very low add-on weights (i.e., 0.8- 1.2 oz/yd 2 ) due to stability problems in heat and humidity aging (polyesters easily hydrolyze in humidity and polyethers easily oxidize in heat); however, such elastomers may be utilized in topcoat formulations as long, again, as the 2.5 ounces per square yard is not exceeded. Among the other additives particularly preferred within or on the film (or films) are heat stabilizers, flame retardants, primer adhesives, and materials for protective topcoats. A potentially preferred thickener is marketed under the trade designation NATROSOL™ 250 HHXR by the Aqualon division of Hercules Corporation which is believed to have a place of business at Wilmington, Delaware. In order to meet Federal Motor Vehicle Safety Standard 302 flame retardant requirements for the automotive industry, a flame retardant is also preferably added to the compounded mix. One potentially preferred flame retardant is AMSPERSE F/R 51 marketed by Amspec Chemical Corporation which is believed to have a place of business at Gloucester City New Jersey. As noted above, primer adhesives may be utilized to facilitate adhesion between the surface of the target fabric and the film itself. Thus, although it is preferable for the film to be the sole component of the entire coating in contact with the fabric surface, it is possible to utilize adhesion promoters, such as isocyanates, epoxies, functional silanes, and other such resins with adhesive properties, without deleteriously effecting the ability of the film to provide the desired low permeability for the target airbag cushion. A topcoat component, as with potential silicones, as noted above, may also be utilized to effectuate proper non- blocking characteristics to the target airbag cushion. Such a topcoat may perform various functions, including, but not limited to, improving aging of the film (such as with silicone) or providing blocking resistance due to the adhesive nature of the coating materials (most noticeably with the preferred polyurethane polycarbonates). Airbag fabrics must pass certain tests in order to be utilized within restraint systems. One such test is called a blocking test which indicates the force required to separate two portions of coated fabric from one another after prolonged storage in contact with each other (such as an airbag is stored). Laboratory analysis for blocking entails pressing together coated sides of two 2 inch by 2 inch swatches of airbag fabric at 5 psi at 100°C for 7 days. If the force required to pull the two swatches apart after this time is greater than 50 grams, or the time required to separate the fabrics utilizing a 50 gram weight suspended from the bottom fabric layer is greater than 10 seconds, the coating fails the blocking test. Clearly, the lower the required separating shear force, the more favorable the coating. For improved blocking resistance (and thus the reduced chance of improper adhesion between the packed fabric portions), topcoat components may be utilized, such as talc, silica, silicate clays, and starch powders, as long as the add-on weight of the entire elastomer composition (including the topcoat) does not exceed 2.5 ounces per square yard (and preferably exists at a much lower level, about 1.5, for instance). Two other tests which the specific coated airbag cushion must pass are the oven (heat) aging and humidity aging tests. Such tests also simulate the storage of an airbag fabric over a long period of time upon exposure at high temperatures and at relatively high humidities. These tests are actually used to analyze alterations of various different fabric properties after such a prolonged storage in a hot ventilated oven (>100°C) (with or without humid conditions) for 2 or more weeks. For the purposes of this invention, this test was used basically to analyze the air permeability of the coated side curtain airbag by measuring the characteristic leak-down time (as discussed above, in detail). The initially produced and stored inventive airbag cushion should exhibit a characteristic leak-down time of greater than about 5 seconds (upon re-inflation at 10 psi gas pressure after the bag had previously been inflated to a peak pressure above about 15 psi and allowed to fully deflate) under such harsh storage conditions. Since polyurethanes, the preferred elastomers in this invention, may be deleteriously affected by high heat and humidity (though not as deleteriously as certain polyester and polyether-containing elastomers), it may be prudent to add certain components within a topcoat layer and/or within the elastomer itself. Antioxidants, antidegradants, and metal deactivators may be utilized for this purpose. Examples include, and are not intended to be limited to, Irganox® 1010 and Irganox® 565, both available from CIBA Specialty Chemicals. This topcoat may also provide additional protection against aging and thus may include topcoat aging improvement materials, such as, and not limited to, polyamides, NBR rubbers, EPDM rubbers, and the like, as long as the elastomer composition (including the topcoat) does not exceed the 2.5 ounces per square yard (preferably much less than that, about 1.5 at the most) of the add-on weight to the target fabric. The substrate to which the thin film coatings are applied to form the airbag base fabric in accordance with the present invention is preferably a woven fabric formed from yarns comprising synthetic fibers, such as polyamides or polyesters. Such yarn preferably has a linear density of about 105 denier to about 840 denier, more preferably from about 210 to about 630 denier. Such yarns are preferably formed from multiple filaments wherein the filaments have linear densities of about 7 denier per filaments or less, more preferably about 6 dpf or less, and most preferably about 4 dpf or less. In the more preferred embodiment such substrate fabric will be formed from fibers of nylon, and most preferred is nylon 6,6. It has been found that such polyamide materials exhibit particularly good adhesion and maintenance of resistance to hydrolysis when used in combination with the coating according to the present invention. Such substrate fabrics are preferably woven using fluid jet weaving machines as disclosed in U.S. Patents 5,503,197 and 5,421,378 to Bower et al. (incorporated herein by reference). Such woven fabric will be hereinafter referred to as an airbag base fabric. As noted above, the inventive airbag must exhibit extremely low permeability and thus must be what is termed a "side curtain" airbag. As noted previously and extensively, such side curtain airbags (a.k.a., cushions) must retain a large amount of inflation gas during a collision in order to accord proper long-duration cushioning protection to passengers during rollover accidents. Any standard side curtain airbag may be utilized in combination with the low add-on coating to provide a product which exhibits the desired leak-down times as noted above. Most side curtain airbags are produced through labor-intensive sewing or stitching (or other manner) together two separate woven fabric blanks to form an inflatable structure. Furthermore, as is well understood by the ordinarily skilled artisan, such sewing, etc., is performed in strategic locations to form seams (connection points between fabric layers) which in turn produce discrete open areas into which inflation gasses may flow during inflation. Such open areas thus produce pillowed structures within the final inflated airbag cushion to provide more surface area during a collision, as well as provide strength to the bag itself in order to withstand the very high initial inflation pressures (and thus not explode during such an inflation event). Other side curtain airbag cushions exist which are of the one-piece woven variety. Basically, some inflatable airbags are produced through the simultaneous weaving of two separate layers of fabric which are joined together at certain strategic locations (again, to form the desired pillowed structures). Such cushions thus present seams of connection between the two layers. It is the presence of so many seams (in both multiple-piece and one-piece woven bags) which create the aforementioned problems of gas loss during and after inflation. The possibility of yarn shifting, particularly where the yarns shift in and at many different ways and amounts, thus creates the quick deflation of the bag through quick escaping of inflation gasses. Thus, the base airbag fabrics do not provide much help in reducing permeability (and correlated leak-down times, particularly at relatively high pressures). It is this seam problem which has primarily created the need for the utilization of very thick, and thus expensive, coatings to provide necessarily low permeability in the past. Recently, a move has been made away from both the multiple-piece side curtain airbags (which require great amounts of labor-intensive sewing to attached woven fabric blanks) and the traditionally produced one-piece woven cushions, to more specific one-piece woven fabrics which exhibit substantially reduced floats between woven yarns to substantially reduce the unbalanced shifting of yarns upon inflation, such as in Ser. No. 09/406,264, to Sollars, Jr., the specification of which is completely incorporated herein. These one-piece woven bags are generally produced on dobby or jacquard fluid-jet looms, preferably the utilized one-piece airbag is made from a jacquard weaving process. With such an improvement, the possibility of high leakage at seams is substantially reduced. These airbags provide balanced weave constructions at and around attachment points between two layers of fabrics such that the ability of the yarns to become displaced upon inflation at high pressures is reduced as compared with the standard one-piece woven airbags. Unfortunately, such inventive one-piece woven bags are still problematic in that the weave intersections may be displaced upon high pressure inflation such that leakage will still most likely occur at too high a rate for proper functioning. As a result, there is still a need to coat such one-piece woven structures with materials which reduce and/or eliminate such an effect. However, such one-piece woven structures permit extremely low add-on amounts of elastomeric coatings for low permeability effects. In fact, these inventive airbags function extremely well with low add-on coatings below 1.5 and as low as about 0.8 ounces per square yard. Furthermore, although it is not preferred in this invention, it has been found that the inventive coating composition provides similar low permeability benefits to standard one-piece woven airbags, particularly with the inventive low add-on amounts of high tensile strength, high elongation, non-silicone coatings; however, the amount of coating required to permit high leak-down times is much higher than for the aforementioned Sollars, Jr. inventive one-piece woven structure. Thus, add-on amounts of as much as 1.5 and even up to about 2.7 ounces per square yard may be necessary to effectuate the proper low level of air permeability for these other one- piece woven airbags. Even with such higher add-on coatings, the inventive coatings themselves clearly provide a marked improvement over the standard, commercial, prior art silicone, etc., coatings (which must be present in amounts of at least 3.0 ounces per square yard). Additionally, it has also been found that the inventive film coating compositions, at the inventive add-on amounts, etc., provide the same types of benefits with the aforementioned sewn, stitched, etc., side curtain airbags. Although such structures are highly undesirable due to the high potential for leakage at these attachment seams, it has been found that the inventive coating provides a substantial reduction in permeability (to acceptable leak-down time levels, in fact) with correlative lower add-on amounts than with standard siliconeand neoprene rubber coating formulations. Such add-on amounts will approach the 2.7 ounces per square yard limit, but lower amounts have proven effective (2.2 ounces per square yard, for example) depending on the utilization of a sufficiently high tensile strength and sufficiently stretchable elastomeric component within the film coating composition directly in contact with the target fabric surface. Again, with the ability to reduce the amount of coating materials (which are generally always quite expensive), while simultaneously providing a substantial reduction in permeability to the target airbag structure, as well as high resistance to humidity and extremely effective aging stability, the inventive coating composition, and the inventive coated airbag itself is clearly a vast improvement over the prior airbag coating art. Of particular importance within this invention, is the ability to pack the coated airbag cushions within cylindrical storage containers at the roof line of a target automobile in as small a volume as possible. In a rolled configuration (in order to best fit within the cylindrical container itself, and thus in order to best inflate upon a collision event downward to accord the passengers sufficient protection), the inventive airbag may be constricted to a cylindrical shape having a diameter of at most 23 millimeters. In such an instance, with a 2 meter long cylindrical roofline storage container, the necessary volume of such a container would equal about 830 cm 3 . (with the volume calculated as 2[Pi]radius ) Standard rolled packing diameters are at least 25 millimeters for commercially available side curtain airbag cushions (due to the thickness of the required coating to provide low permeability characteristics). Thus, the required cylindrical container volume would be at least 980 cm . Preferably, the rolled diameter of the inventive airbag cushion during storage is at most 20 millimeters (giving a packed volume of about 628 cm 3 ) which is clearly well below the standard packing volume. In relation, then, to the depth of the airbag cushion upon inflation (i.e., the length the airbag extends from the roofline down to its lowest point along the side of the target automobile, such as at the windows), the quotient of the inventive airbag cushion's depth (which is standard at approximately 17 inches or 431.8 millimeters) to its rolled packed diameter should be at least about 18.8. Preferably this quotient should be about 21.6 (20 millimeter diameter), and, at its maximum, should be about 24 (with a minimum diameter of about 18 millimeters). Of course, this range of quotients does not require the depth to be at a standard of 17 inches, and is primarily a function of coating thickness, and thus add-on weight. While the invention will be described and disclosed in connection with certain preferred embodiments and practices, it is in no way intended to limit the invention to those specific embodiments, rather it is intended to cover equivalent structures structural equivalents and all alternative embodiments and modifications as may be defined by the scope of the appended claims and equivalence thereto. Detailed Description of the Preferred Embodiment of the Invention Surprisingly, it has been discovered that any film with a tensile strength of at least 2,000 psi and an elongation at break of at least 180% coated onto and over both sides of a side curtain airbag fabric surface at a weight of at most 2.7 ounces per square yard, and preferably below about 2.5, more about 2.2, and most preferably less than about 2.2 ounces per square yard, provides a coated airbag cushion which exhibits extremely low and extended permeability upon and after inflation. This unexpectedly beneficial type and amount of film coating thus provides an airbag cushion which will easily inflate after prolonged storage and will remain inflated for a sufficient amount of time to ensure an optimum level of safety within a restraint system. Furthermore, it goes without saying that the less film coating composition required, the less expensive the final product. Additionally, a lower required amount of film coating composition will translate into a decrease in the packing volume of the airbag fabric within an airbag device. This benefit thus improves the packability for the airbag fabric. The preferred airbag cushion of this invention was produced in accordance with the following Example: EXAMPLE First, an adhesive primer formulation was produced having the composition: Component Parts by weight Desmoderm® 43195 (Bayer Corporation, polyurethane resin) 25 grams Dimethylformamide (Aldrich, solvent) 75 grams Desmodur® CB-75N (Bayer, polyisocyanate adhesion promoter) 4 grams This primer coating was applied to both sides of a 2.5 liter size Jacquard woven nylon airbag (of 440 denier fibers), made in accordance with the Figures and preferred embodiments within United States Patent Application Ser. No. 09/406,264, to Sollars, Jr., previously incorporated by reference. The primer coating was dried at about 160°C for about 2 minutes to obtain a dry coating weight of about 0.25 ounces per square yard on each side. Subsequently, a 2 mil thick polyurethane film (Dureflex™ PT9400) was then laminated on both sides of the primer coated airbag utilizing a hotpress providing about 80 psi pressure at about 188°C with a residence tim eof about 1 minute. The total polyurethane film add-on weight on each side of the airbag was about 2.2 ounces per square yard. The airbag was then rapidly inflated to 30 psi air pressure. More than 28 seconds elapsed before the air pressure leaked down to 8 psi. The leakage rate was thus measured at 10 psi to be about 4 SCFH. The characteristic leak-down time was an astounding amount, greater than 80 seconds. Description of the Drawings FIG. 1 depicts the side, inside view of a vehicle prior to deployment of the inventive side curtain airbag. FIG. 2 depicts the side, inside view of a vehicle after deployment of the inventive side curtain airbag. Detailed Description of the Drawings As depicted in FIG. 1, an interior of a vehicle 10 prior to inflation of a side curtain airbag (not illustrated) is shown. The vehicle 10 includes a front seat 12 and a back seat 14, a front side window 16 and a back-side window 18, a roofline 20, within which is stored a cylindrically shaped container 22 comprising the inventive side curtain airbag (not illustrated). Also present within the roofline 20 is an inflator assembly 24 which ignites and forces gas into the side curtain airbag (26 of FIG. 2) upon a collision event. FIG. 2 shows the inflated side curtain airbag 26. As noted above, the airbag 26 is coated with at most 2.5 ounces per square of a coating formulation (not illustrated), preferably polyurethane polycarbonate. The inventive airbag 26 will remain sufficiently inflated for at least 5 seconds, and preferably more, as high as at least 20 seconds, most preferably. There are, of course, many alternative embodiments and modifications of the present invention which are intended to be included within the spirit and scope of the following claims.

Claims: CLAIMS WHAT IS CLAIMED IS: 1. An airbag cushion comprising a coated fabric, wherein said fabric is coated with a laminate film in an amount of at most 2.7 ounces per square yard of the fabric; and wherein said airbag cushion exhibits a characteristic leak-down time after inflation of at least 5 seconds. 2. The airbag cushion of Claim 1 wherein said film is silicone free. 3. The airbag cushion of Claim 1 wherein said film composition comprises polyurethane. 4. The airbag cushion of Claim 1 wherein said coated fabric is woven from polyamide yams. 5. The airbag cushion of Claim 4 wherein said polyamide yarns are formed from nylon 6,6 fiber. 6. The airbag cushion of Claim 4, wherein said polyamide yams are multifilament yams characterized by a linear density of about 210-630 denier. 7. The airbag cushion of Claim 6, wherein wherein said multifilament yams are characterized by a filament linear density of about 7 denier per filament or less. 8. The airbag cushion of Claim 1 wherein said film is present on said airbag fabric surface in an amount of at most 2.5 ounces per square yard. 9. The airbag cushion of Claim 8 wherein said film is present on said airbag fabric in an amount of at most 2.2 ounces per square yard. 10. An airbag cushion comprising a coated fabric, wherein said fabric is coated with a laminate film; wherein said film possesses a tensile strength of at least 2,000 and an elongation at break of at least 180%; and wherein said airbag cushion exhibits a leak-down time after inflation of at least 5 seconds. 11. The airbag cushion of Claim 9 wherein said film comprises polyurethane. 12. The airbag cushion of Claim 10 wherein said coated fabric is woven from polyamide yams. 13. The airbag cushion of Claim 11 wherein said polyamide yams are formed from nylon 6,6 fiber. 14. The airbag cushion of Claim 12, wherein said polyamide yams are multifilament yams characterized by a linear density of about 210-630 denier. 15. The airbag cushion of Claim 13, wherein said multifilament yams are characterized by a filament linear density of about 7 denier per filament or less. 16. The airbag cushion of Claim 10 wherein said film is present on said airbag fabric surface in an amount of at most 2.5 ounces per square yard. 17. The airbag cushion of Claim 16 wherein said film is present coated on said airbag fabric surface in an amount of at most 2.2 ounces per square yard.

Inventors: LI SHULONG, LI, SHULONG
Applicants: MILLIKEN & CO, MILLIKEN & COMPANY
Application year: 2000
Main classification: B60R21
IPC codes: B32B27, B60R21, D06N3