Short notice given only substantially as follows: To make airbags more recyclable, a Japanese company has proposed making them from polyamide (PA) fabric with an elastomeric PA coating. In European Patent 2 042 649 (see also, US Patent 2009/087601 ), Toyoda Gosei Co Ltd says that the coating must provide sufficient air tightness so that the bag remains inflated long enough to protect the vehicle's occupants, but not be so stiff that it can't be folded into a small space or weigh too much. The company's invention consists of a woven fabric of PA as the base cloth with a polyamide (PA) elastomer coating on at least one side. The coating polymer has a melting point of 135-200 deg C, which is 80-120 deg C lower than that of the fibres of the base cloth. To apply the coating, particles of 0.05-5.00 micron are dispersed in water and applied to the base fabric. The coating is then heated to a temperature of 5-30 deg C higher than its melting point for between 0.5 and 5 min. For the fibre, PA 6.6 is preferred because it has a relatively high melting point (250-260 deg C) and a larger heat capacity (and so resistance to the heat generated when the airbag is deployed). Among the polyamide, PA 6.6 also has a better balance of properties such as abrasion resistance. Typically, a multiply wound yarn of 200-700 dtex is used. Normally the cloth is a plain weave, but twill and sateen are also used. In any case, the preferred cover factor of the cloth should be 1800-2000. The cover factor helps to determine the right balance between the conflicting requirements of air tightness, on the one hand, and sufficient flexibility and low weight, on the other. The PA elastomer is selected to match the fibre polymer. For instance, if the fibre is PA 6.6 then a block copolymer, thermoplastic elastomer (TPE) is the preferred choice. This coating should have a number of characteristics, the patent adds. Firstly, its melting point should be 135-200 deg C, ideally 155-165 deg C. It is desirable that the difference in the melting points of the fibre and the elastomer are 85-105 deg C. If the elastomer's melting point is too high, it is difficult to ensure enough flexibility in the coated airbag textile. The coating elastomer should also have tensile elongation of 200% or more. Lower than this and the flexibility is compromised, leading to possible cracking of the coating and loss of air tightness. Similarly, if the bending elastic modulus is too high, then the film is not flexible enough: the upper limit is 200 MPa. Too high a balanced water absorption rate induces the coating to absorb moisture and peel. The inventor recommends that the balanced water absorption rate should be lower than that of the PA 6.6 fibre in order to improve the adhesiveness of the coating. Suitable materials that meet these criteria include polyether block polyamide (PEBA), crystalline-reduced types; polymer alloys; and PA with plasticizers added to soften it.
Airbags made for recycling
Advances in Textiles Technology ; Jul ; 7-8
2009
2 Seiten
Aufsatz (Zeitschrift)
Englisch
Umweltfreundliches Recycling von Airbags.
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