Process Influences on the Materials Interface of an Injection Molded Hard-Soft-Component

Combining a soft thermoplastic elastomer with a hard polymeric material by multi-component injection molding provides a novel and sophisticated alternative for mounting a vulcanized dynamic elastomeric seal part into a rigid housing. Such assembly injection molding is new and challenging, but promises several economic advantages. The main issue within such a development is the assurance of sufficient bond strength between soft and hard component, in order to withstand the service load conditions safely. This paper studies certain process influences on the interface condition between the materials. The strength of the adhesive bond of composite test specimens consisting of a hard outer ring and a soft inner ring with integrated rotary seal lip are evaluated. The injection molded and investigated composite parts consist of glass fiber reinforced polybutylene terephthalate (PBT-GF30) as hard component and a thermoplastic polyurethane (TPU) as soft component. The required force to reach delamination between hard and soft component is monitored and correlated with the surface structure and properties of differently plasma pre-treated hard components. Supposed a material combination and the contact temperature are defined the surface conditions of the hard component play the major role with respect to the adhesion bond strength.