Regarding a bonding between conventional PEBA and TPU, it has following difficulties : (a) The PEBA which has less soft segment, i.e. harder PEBA is difficult to bond with TPU directly by Insert molding. (b) Overmolding TPU onto the inserted PEBA can not get a good bonding. Overmolding PEBA onto inserted TPU should be applied for a good bonding. (c) The bonding strength strongly depends on the chemical structure of the soft segment of TPU.
Daicel-Evonik Ltd. had prepared several kinds of PEBAs based on the concept of the bonding by interfacial reactions for the bonding test with TPU and it was confirmed the concept could solve these problems of conventional PEBA. Additionally it was found that PEBA specimen as an insert was not influenced by a storage time before TPU's overmolding, although TPU specimen lost its bonding performance by the time of the storage. This “PEBA insert system” was not available until Daicel-Evonik's new PEBA and PA12. It is expected that these advantages of Daicel-Evonik's new PEBA and PA12 will be able to contribute to new fine design, cost saving and stable mass production.
These new PEBA and PA12 also can bond with rubber based on K&K concept. Rubber + new PEBA + TPU three layer sheet is introduced as one of the examples of new application.