Patent Application
20080007029
The accompanying drawings which are incorporated in and which constitute a portion of this specification illustrate an exemplary embodiment of the invention which, together with the detailed description set forth below will serve to explain the principles of the invention wherein;
Reference will now be made to the drawings wherein, to the extent practical like elements are denoted by like reference numerals in the various views. Turning to
As shown, the vehicle 10 includes an air bag in the form of an inflatable curtain 20 for use with an inflator 22 to protect the occupant during a prolonged roll-over collision event. In operation, upon inflation the inflatable curtain 20 deploys downwardly from a storage position along the roof rail of the vehicle 10 into the illustrated position to the side of the occupant 14. As the curtain 20 is inflated it undergoes a natural shortening in its length dimension thereby causing it to be held in tension. By maintaining this tension, the curtain 20 forms an effective resilient barrier preventing ejection of the occupant 14. Thus, in order to maintain the desired end-to-end tension in the curtain 20, it is desirable to maintain inflation for the entire duration of the roll-over event.
In practice, the curtain 20 may be formed from two opposing mirror image panels of material such as a woven textile fabric joined along a perimeter seam. Of course, any number of other construction practices may likewise be utilized. By way of example only, the panels may be portions of a single fabric blank that is folded over upon itself and seamed around open edges. As illustrated, additional adjoining seams may be applied at the interior of the curtain 20 so as to define an arrangement of so called zero length tethers 34 to control gas flow and deployment characteristics within the inflatable curtain 20. The perimeter and/or interior seams may have any construction as desired. By way of example only and not limitation, such seams may be sewn seams formed by passing sewing thread in a stitching arrangement between opposing panels. Other seam constructions including adhesive bonding seams, welded seams and the like may also be used if desired. Of course, it is to be understood that the illustrated curtain 20 is exemplary only and that any number of other curtain geometries as may be known to those of skill in the art are likewise applicable to the present invention.
By way of example only, and not limitation, an illustrative sewn seam construction such as may be used is illustrated in
As shown, in the exemplary seam construction a first panel 36 formed from a blank of suitable construction material such as a woven fabric or the like is joined to a second panel 38 formed from a blank of suitable construction material such as a woven fabric or the like along a seam line 40 by suitable stitching threads 42. in the illustrated and potentially preferred arrangement, a relatively light weight coating 43 of an adherent permeability blocking composition as will be described further hereinafter is disposed across portions of the panels 36, 38. As will be appreciated, such coatings provide gas blockage across seamed and non-seamed portions of the formed air bag 20. In this regard, it is contemplated that the coating 43 may cover substantially the entire surface of the air bag 20. Of course, it is also contemplated that selected portions of the air bag 20 may also be uncoated if desired. The composition forming the coating 43 is preferably adapted to migrate substantially into the seam when applied so as to encapsulate at least a portion of the stitching threads 42 within the seam line 40.
In accordance with the present invention the coating 43 is a water dispersible aliphatic polycarbonate polyurethane resin composition. In the past, it has been common to utilize silicone based coatings. However, one deficiency with such silicone coatings is the relatively high coating weight required to provide good gas retention for prolonged periods. Another approach has been to use solvent based systems such as solvent dispersed polyurethanes and the like. By way of example, representative solvent based polyurethane systems are believed to disclosed in one or more of U.S. Pat. Nos. 6,770,578; 6,753,275; 6,734,123; 6,645,565; 6,350,709; 6,740,607; 6,641,686; 6,458,724; 6,455,449; 6,239,046 (all incorporated herein by reference). However, solvent based systems may be difficult to work with due to the emission of volatile organic compounds and the residual VOC in the fabric. Traditional water disperse polyurethanes have generally been considered unsuitable due to an inability to provide a desired combination of low stiffness, yarn lock down and resistance to seam combing while substantially maintaining tensile strength over extended temperature and humidity aging conditions. However, the water dispersed aliphatic polycarbonate polyurethane resin compositions contemplated in accordance with the instant invention have been found to satisfy this combination of required characteristics.
According to the instant invention, the coating 43 is preferably formed from an aqueous dispersion of a polycarbonate polyurethane composition. In this regard, a potentially preferred polycarbonate polyurethane composition is formed by a condensation reaction of a polyisocyanate and a polyol wherein the polyol component contains a polycarbonate polyol to provide a polycarbonate backbone within the urethane prepolymer. It has been found that the polyisocyanate used is preferably an aliphatic isocyanate so as to promote color stability during ageing and resistance to dry and humid aging at high temperatures. By way of example only, and not limitation, one such polycarbonate polyurethane composition is believed to be manufactured by Cytec Company under the trade designation P-925/IW3475. The aqueous dispersion preferably also includes about 5 parts of a thickener such as WT56 for viscosity adjustment and about 1 part of a water based silicone slip agent such as Dow 84 or 61 or 2-1846 or Ludox XSM-30 or Wacker C792A and a cross linker such as Carbodiimide based Rhodocoat XEZ-M 502 from Rhodia, end blocked isocynate or a free isocynate like XE 410 from Cytec or a Melamine formaldehyde crosslinker like DWX 185, Ucecoat 730. In order to provide desired flow blocking characteristics, such dispersions are preferably applied across portions of the air bag 20 at levels of about 10 to about 50 grams per square meter and most preferably at about 50 grams per square meter on a dry weight basis. The coating composition is thereafter cured in a tenter. Alternatively, the coatings may be cured by other known energy sources including without limitation, ultraviolet irradiation, infrared irradiation, electron beam heating and the like.
Films formed from the contemplated coating compositions are generally characterized by reduced tensile strength and elongation relative to traditional solvent based polycarbonate polyurethanes. By way of example only, and not limitation, a comparative analysis of films cast from the aqueous dispersion materials as described above relative to films of similar weights formed from traditional solvent based polycarbonate polyurethanes such as an aromatic polycarbonate polyurethane marketed by the Cytec under the trade designation DTM 586 and an aliphatic polycarbonate polyurethane marketed by the Cytec company under the trade designation FN 995 is set forth in Table 1 below.
In spite of the substantially reduced tensile strength and elongation character, it has nonetheless been found that a coating of water dispersed polycarbonate polyurethane as described above nonetheless provides excellent gas retaining characteristics while retaining substantial stability following thermal and humidity ageing. In this regard, testing indicates that a coating of water dispersed polycarbonate polyurethane as described above may actually provide substantially improved gas retention performance relative to a number of commercial solvent based coating systems.
In order to evaluate pressure retention performance, side curtain air bags were coated with similar dry add-on weights of the aqueous polycarbonate polyurethane composition as described above and several different commercial coating compositions. The comparative compositions were RU 40-528, a polyether polyurethane material marketed by Stahl USA; RU 41-710, a Aromatic Polyether polyurethane material marketed by Stahl USA; Dow YS 3000, a MDI based polyether polyurethane material marketed by Dow Chemical; Dow YM 2000, a aromatic polyether material marketed by Dow Chemical. The coated curtains were then pressurized to a standard pressure of 140 kPa. The gas supply was terminated and pressure within the curtains was then measured at 6 seconds and 12 seconds to determine the level of gas leakage. The results are set forth in Table 2 below.
As will be appreciated, the above data reflect that a side curtain cushion utilizing a coating of water dispersed polycarbonate polyurethane is characterized by substantial pressure retention over prolonged periods despite relatively low tensile strength and elongation as shown in Table 1. Tensile strength of the water based polyurethane in the Table 1 are about 3× to 4× stronger compared to traditional silicone based coating and it is believed that the combination of physical characteristics of the water dispersed polyurethane may aid in avoiding stress concentrations that promote gas leakage at the seams.
While the present invention has been illustrated and described in relation to certain potentially preferred embodiments and practices, it is to be understood that the illustrated and described embodiments and practices are illustrative only and that the present invention is in no event to be limited thereto. Rather, it is fully contemplated that modifications and variations to the present invention will no doubt occur to those of skill in the art upon reading the above description and/or through practice of the invention. Therefore, it is intended that the present invention shall extend to all such modifications and variations as may incorporate the broad aspects of the invention in the full spirit and scope thereof.
By way of example only, and not limitation such variations may include polyurethane hybrids where a combination of different polyurethanes may be incorporated, provided the major component is still based on polycarbonate polyurethane. Likewise, modifications incorporating copolymers are also contemplated. By way of further non-limiting example, it is contemplated that for non-blocking reasons, providing a non-blocking means on top of the coating would still be within the broad aspects of the invention in the full spirit and scope thereof. Such non-blocking means can be achieved by talc or silica or clay type materials. Such non-blocking means can be incorporated onto the polyurethane itself in a substantially monolithic structure or can be a separate layer:
