MXPA00001630A - Polyurethane/polyacrylate dispersion coating for airbag fabrics - Google Patents

Abstract

This invention relates to novel airbag coating compositions comprising a mix of polyurethane and polyacrylate constituents which provides a highly effective low permeability treatment on a target fabric surface. This inventive composition also provides a low-cost alternative to other standard airbag coatings and exhibits excellent aging stability as well. An airbag fabric coated with this inventive composition is also contemplated within this invention.

Description

COATING WITH A POLYURETHANE / POLYACRATE DISPERSION R TO FABRICS FOR AIR BAGS TECHNICAL FIELD This invention relates to novel air bag coating compositions, which consist of a mixture of polyurethane and polyacrylate constituents that offer a highly efficient low permeability treatment on a target fabric surface. This composition of the invention also offers a low cost alternative to other coatings for normal air bags and presents excellent aging stability as well. An air bag fabric coated with this composition of the inventiveness is also contemplated within this invention.

Background Art Air bags for motor vehicles are known and have been used for a considerable time. These devices are installed on the driver's and passenger's side of automobiles and, in the event of a collision, are quickly inflated with gas to act as a barrier between the driver or passenger and the automobile's steering wheel or dashboard. Coatings have been applied to fabrics proposed for use in automobile air bags, to resist unwanted permeation of air through the fabric and, to a lesser extent, to protect the fabric from deterioration by the hot gases used for 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 complete air bag, and the tendency of polychloroprene to degrade, with exposure to heat, to release the acid components hydrochloric (potentially degrading the fabric component by this means as well as releasing hazardous chemicals), has given rise to the almost universal acceptance of silicone (polydimethylsiloxane or similar materials) as a more suitable coating. With the demand for the most compact folded size possible, polymer coating levels have dropped from about 2.5 ounces per square yard of the fabric to levels that reach 0.5 ounces per square yard. New developments in air bags, particularly the newer designs being placed on the sides of the passenger compartment, have introduced the requirement that the bags maintain the pressure more time in use. This, and the evolution of the lower levels of coating of the silicone polymer have begun to highlight the effect that, when a seam is put under tension, a coating of naturally lubricating silica gel can allow the yarns of which this built the fabric. This displacement can lead to leakage of the inflator gas through the new pores formed of the displaced yarns, or, in drastic cases, can cause the seam to fail. Since the airbag must maintain its integrity during a crash event, to sufficiently protect the driver or passenger, there is a great need to provide coatings that offer effective permeability characteristics and sufficient restriction to the displacement of the threads so that the bag air work properly, if and when necessary. Therefore, there is a need for a cost effective coating that offers low permeability, resistance to yarn displacement and resistance to aging during extended storage periods.

Description of the invention Polyurethanes generally have very good flexibility and tensile strength over a wide range of temperatures. These properties make them good candidates as a material for air bag coverings. However, after intensive thermal oxidation and exposure to moisture during aging, polyurethane coatings (especially with relatively low coating weights) can undergo significant changes in their physical properties. Polyacrylates have very good aging properties alone; however, these polymers can not seal a textile substrate particularly along the seams at the high air pressure (10-30 Psi) as well as the polyurethanes. It has now been observed that a mixture of polyurethane and a polyacrylate offers a strong, highly effective coating material with at the same time excellent aging properties. An air bag covered with such a mixture also has very low air permeability at high air pressure before and after curing. This synergistic effect is surprising considering the operation of these two components alone in the same fabric. In addition, it has been found that other benefits are in accordance with the user of such coating composition on the air bags and fabrics for air bags. These benefits include, and are not proposed to be limited to the following:. (1) lower costs for the complete composition compared to a polyurethane only since the polyacrylates are significantly less expensive and do not reduce the overall strength of the coating composition in its introduction in relatively high proportions; and (2) improvements in flexibility since a similar amount of the polyurethane-containing coating will only produce a relatively stiff fabric. The polyurethane / polyacrylate dispersions, as already noted, retain approximately the same degree of air permeability and strength as polyurethane alone and at the same time also offer a fabric that is less rigid than the polyurethane coating itself. In general, the polyurethane constituent can be selected from any well-known polyurethane composition that adheres well to fabrics and that exhibits a tensile strength greater than 2,000 psi (preferably greater than 4,000 psi) on the surface of the fabric and that is compatible with polyacrylates to effect a stable, adequate dispersion of the two components. Such a polyurethane composition, and a potentially preferred polyurethane is available from Stahl USA, Peabody Massachusetts, under the trademark Ru 40-350 (40% solids). The polyacrylate can be selected from any of the polymers that have some degree of compatibility with the surface of the objective fabric and also be compatible with the polyurethane as already noted. The selected polyacrylate must also be self-crosslinkable or at least crosslinkable with the addition of a suitable crosslinking agent (such as melamine formaldehyde or any other standard polyacrylate crosslinking agent). Such a self-crosslinking polyacrylate, and thus a potentially preferred polyacrylate, is available to Rohm & Hass, with the brand Rhoplex7 E-358 (60% solids). The ratio of polyurethane to polyacrylate should be in an amount from about 0.1: 1 to about 10: 1; preferably from about 1: 1 to about 8: 1; more preferably from about 2: 1 to about 5: 1; and more preferably at about 2.5: 1. The substrate through which the crosslinked elastomeric resin coatings are applied to form the base fabric for the air bag according to the present invention is preferably a flat woven fabric formed of yarns containing polyamide or polyester fibers. Such yarns preferably have a linear density of about 100 denier to about 630 denier. The yarns are thus preferably formed from multiple filaments, wherein the filaments have linear densities from about 6 denier per filament or less and more preferably about 4 denier per filament or less. Substrate fabrics are thus preferably woven using jacquard looms or possibly by the use of fluid jet weaving machines as described in U.S. Patent Nos. 5,503,197 and 5,421,378 to Bo er et al. (incorporated herein by reference). The substrate fabric with coating applied onwards will be mentioned as a base fabric for air bag. Other possible components present within the crosslinked elastomeric resin coating composition are thickeners, antioxidants, flame retardants, coalescing agents, adhesion promoters and dyes. In theory, and with no intention of sticking to it, the polyurethane and polyacrylate constituents of the composition of the inventive airbag coating can, to some extent, for a single film or polymerized or crosslinked coating through the interaction of Free formaldehyde on polyacrylate with free carboxyl in polyurethane [sic]. In addition, another non-limiting theory has been developed that these polymers actually form a network with a relatively uniform distribution of the constituents through the coating. However, it is very likely, and again without the attempt to stick to such a theory, it seems that the two constituents may not actually join or copolymerize or crosslink each other and in this way there may be small "patches" of polyurethane surrounded by polyacrylate areas only (or vice versa) on the surface of the target fabric. In any case, the inventive airbag coating offers unexpected and beneficial aging resistance and stability properties at an extremely low cost. In accordance with the potentially preferred practices of the present invention, a microdispersion in water of the two components is formed by mixing the polyurethane and polyacrylate in a mixing vessel with a thickener and a flame retardant to produce a dispersion with a viscosity of about 8,000 centipoise. or older. Any well-known thickener for polyurethanes and / or polyacrylates can be used in this invention. A potentially preferred thickener is marketed under the trade designation NATROSOLJ 250 HHXR from Aqualon, a division of Hercules Corporation which is believed to have its business address in Wilmington, Delaware. Also, to comply with the requirements of the flame retardant in accordance with the Federal Motor Vehicle Safety 302 standard for the automotive industry, a flame retardant is also preferably added to the composite mixture. Any well-known flame retardant for airbags can be used (including aluminum trihydrate, simply as an example). A potentially preferred flame retardant is DE-83R, 70% Dispersion marketed by Great Lakes Chemical. Once the composition is complete, the dispersion is preferably covered through the substrate fabric and dried and cured to form a thin coating. The scraped coating in this sense includes, and is not limited to, knife coating methods, in particular a discontinuous table knife, floating knife, and knife on foam cushion, to name a few different methods. The final dry weight of the coating is preferably from about 0.6 to about 1.0 ounce per square yard or less and more preferably 0.8 ounce per square yard or less. The resulting base fabric is substantially impermeable to air when measured in accordance with ASTM Test D737, "Air Permeability of Textile Genera", standards at about 10 to about 30 psi. As already noted, the substrate web is preferably a woven nylon material. In the most preferred embodiment such a substrate web will be formed of 6.6 nylon fibers woven in a jacquard loom. It has been found that polyamide materials thus exhibit particularly good adhesion and maintain resistance to hydrolysis when used in combination with the coating according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS In order to further describe the present invention, the following non-limiting examples are set forth. The polyurethane / polyacrylate dispersion (coating composition) described above and discussed in more detail below is the most preferred embodiment of the invention These examples are provided only for purposes of illustrating some preferred embodiments of the invention and should not be considered. as limiting the scope of the invention in no sense.

Example 1 Synergistic mixture of polyurethane and polyacrylate Component Quantity Ru 40-350 (40% solids) 150 grams Rhoplex E-358 (60% solids) 60 grams DE-83R, 70% Dispersion 30 grams Natrosol 250 HHXR 1.6 grams Example 2 (comparative) Only polyurethane Component Quantity Ru 40-350 (40% solids) 200 grams DE-83R, 70% Dispersion 10 grams Natrosol 250 HHXR 1.6 grams Example 1 Single polyacrylate Component Quantity Ru 40-350 (40% solids) 100 grams Water 50 grams DE-83R, 70% Dispersion 25 grams Natrosol 250 HHXR 1.8 grams These formulations were then applied as coatings on identical samples of air bag fabric, nylon 6.6 woven in two layers of Jacquard containing numerous woven seams between the layers. Each mixture was covered on the airbag fabric using a knife coater on foam cushion and dried at 350E F [sic] for 3 minutes. Both sides of the fabric were covered in the same way at a coating weight of approximately 0.8 oz / yd5 [sic] per side. The air leak was then measured at 9 Psi of air pressure before and after curing. The results are established in the following table.

TABLE Fugue (SCFH) * Example # Before curing After curing ** 1 15 35 2 12.5 > 70 3 > 70 > 70 * SCFH - standard cubic foot per hour. ** Condition of the curing: curing in oven at 150EC [sic] for 42 hours.

Of course, there are multiple alternative embodiments and modifications of the present invention that are proposed to be included within the spirit and scope of the following claims.

Claims (6)

1. An air bag fabric covered with a dispersion composition containing at least one polyurethane and at least polyacrylate.

2. The air bag fabric of claim 1, wherein the ratio of polyurethane to polyacrylate in the dispersion is from about 0.1: 1 to about 10: 1.

3. The air bag fabric of claim 2, wherein the ratio of polyurethane to polyacrylate in the dispersion is from about 1: 1 to about 8: 1.

4. The air bag fabric of claim 3, wherein the ratio of polyurethane to polyacrylate in the dispersion is from about 2: 1 to about 5: 1.

5. The air bag fabric of claim 4, wherein the ratio of polyurethane to polyacrylate in the dispersion is from about 2.5: 1.

6. The air bag fabric of claim 1, wherein the dispersion further comprises at least one thickener and at least one flame retardant.