The bond between these two polymers is typically mechanical, with engineered geometries to aid in the physical interlocking of the two materials. Premold surface preparations can be explored with your resin suppliers to possibly promote a more covalent surface between the two materials. However, this step will add to the assembly time and can be time-sensitive, based on the particular pretreatment method chosen.

Injection pressure, shrink, the glass transition temperature of the polycarbonate, and the need to concentrate the shutoff areas around the area to be overmolded must be considered in the design of the part and tool. The overmolded polymer creates dynamic pressure on the base part and can be difficult to eject after overmolding if you don’t consider proper relief on the part and tool. The polycarbonate will insulate your second shot, so cooling will be inhibited and cycle times will increase. The processing temperature and shrink delta of the second polymer will determine how far the polymer can be pushed and will drive the design of the mechanical bond geometry.

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