Two-component injection moulding of thermoplastics with thermoset rubbers: Process development

Abstract

Two-component injection moulding is a manufacturing process for combining polymers with different properties in a single injection moulding process. The process is typically used to combine thermoplastics with another thermoplastic or with a thermoplastic elastomer to create colour differences or hard and soft areas respectively. The present study aims at the development of a two-component injection moulding process for the combination of a thermoset rubber and a thermoplastic. Currently products that consist of those two materials (e.g. wheels, syringes and other products with gaskets) are made by assembling separate components. Implementing the two-component injection moulding technique for these products will result in better interphase properties, savings on rubber and avoiding costs related to the assembly process. A technological challenge is posed by the fact that injection moulding of rubbers and thermoplastics is fundamentally different. The injection moulding of a rubber requires a heated mould (140°C-180°C) whereas thermoplastics need a relatively cold mould (20°C-100°C) for the polymer to solidify. In this study a versatile two-component mould is proposed in which the mould cavities for the rubber and the thermoplastic are thermally separated and equipped with facilities to control the temperature of both cavities individually. The design of the mould also makes it possible to vary the sequence of injection. In this way it is possible to test several processes variations. Preliminary test results will be presented for specific rubber-thermoplastic combinations.