A new pair of hard-soft plastic combination for precision manufacturing of two component plastic parts.

摘要

Two component (2k) injection moulding is growing rapidly even in the field of precision micro moulding. Besides combining different material properties in the same product, two component moulding can eliminate many assembly steps in manufacturing process chain. One of the biggest technical challenges associated with 2k moulding is the unavailability of suitable two component material combinations which can meet the diverse requirement from product and process point of view. This paper presents a new pair of commercial polymer materials (BASF Ultramid A3EG10 and Kraiburg TPE Thermolast K TC5PCZ) that fulfils the criteria for two component moulding both from product and process consideration for a wide range of precision micro 2k applications. Ultramid A3EG10 is PA6.6 thermoplastic with 50 % glass fibre reinforcement. Thermolast K TC5PCZ is a thermoplastic elastomer based on hydrated styrene block copolymers (TPE-S). By using this pair of materials, a demonstrator 2k micro part (Socket house for hearing aid) has been fabricated. This kind of socket is used in Receiver-in-the-canal hearing aid system to connect the receiver with hearing aid processors. The problem with the previous design was lack of sealing between the Plug-Socket combination so, corrosive agents like human sweat, oil and dirt could corrode the contact pins inside the Socket house. The new design of the Socket is an improvement of the old design which contains a micro sealing ring. This 2k micro part was moulded by the use of State-of-the-art two component micro moulding machine named Formica Plast from Desma Tec. The tests performed on the demonstrator showed potential for the material pair to be used in high precision two component moulding applications. The adhesion between the two materials, replication quality of the 2k part, sealing and functional properties of the materials proved to be suitable for precision hearing aid applications. Replication quality of the 2k parts was investigated by visual and microscopic investigation. The adhesion of the two plastic materials was characterized by moulding 2k tensile bar test specimens by both sequential and simultaneous injection of two materials and afterwards by using a precision tensile testing machine. To characterize the sealing properties of the sealing ring material, a sealing test device was developed. It could provide hydraulic pressure inside the socket house and precisely detect the pressure developed inside the socket house and finally could detect the leak of the fluid due to the sealing ring leakage. All the test procedures and results presented in this paper can be a valuable source of information for researchers and scientists who work with two component micro injection moulding.