Adidas and BASF develop use of TPU in performance trainers

By Liz White, UT staffHerzogenaurach, Germany-In a joint development programme over four years, sportswear manufacturer Adidas AG and BASF AG have come up with a trainer sole that uses structural elements made of BASF's thermoplastic polyurethane. And the logical outcome of these developments may be the "foamless trainer," indicated Klaus Knörr, senior manager for technical materials with the Adidas Innovation Team at Herzogenaurach, near Nuremberg, south Germany. Work on these TPU 'spring' elements began in 2001, and such soles are in the process of replacing ones largely composed of microcellular EVA foam, in order to "optimise energy absorption, support the foot and accelerate the motion," according to Martin Vallo, sales and technical service manager for footwear with BASF's polyurethane unit, Elastogran. BASF was promoting this development in a press meeting at Adidas' Herzogenaurach event hall, 13 April: it is one example of what the German chemicals giant sees as a successful approach to adding value in various performance products by joint development in partnership with customers, indicated John Feldmann, BASF board member responsible for polyurethanes. The A3 sole developed in 2001 was the first shoe to start using the tri-dimensional damping system, in which Adidas wanted to dampen heel impact when the foot first hits the ground, transfer the energy of impact forward along the sole to the forefoot, and feed it into the toe area to give more spring lift off to the next step. The TPU elements are used to transfer the movement energy towards the toe, said Klaus Knörr, senior manager for technical materials with the Adidas Innovation Team at Herzogenaurach. Volle and Frank Dassler, Adidas' general counsel, pointed out that in initial tests of various material types, over 1000 km, EVA was shown to lose 40 percent of its cushioning, PU some 20 percent, but TPU only 5 percent. Adidas wanted a sole design which would deaden impact as the heel comes down, but then, "return as much energy as possible to the athlete, like a catapult, it must be very elastic," Knorr explained. Trapped air in foam materials may be the cause of difficulties in getting foam behaviour which meets the demands, he added. Adidas and Elastogran spent some time developing the complex tooling needed for making the sole with TPU spring elements in one piece. Finite element analysis proved invaluable in the next step of optimising the design details to prevent stress cracking of the elements, and also in optimisation for improved flow and geometry, Knörr pointed out. The next development stages will include a foamless forefoot, lighter TPU elements, and a different heel structure, Knörr added. The latest Ultraride model is down to "some 15 percent foam content," Vallo pointed out. Vallo also pointed to further developments with the design, for the Megaride trainer, in which the tooling has been simplified by moulding some of the larger TPU flex elements individually and assembling them during production. This will also allow elements of different Shore A hardness of say 80 and 60, to be combined, he explained, for better performance for athletes in, say, basketball. In the photo, the red trainer-the Megaride-now has some individual heel flex elements, while the earlier blue and white Ultraride below has the highly complex one-piece TPU moulding of structural elements connected by TPU sheet."