Silicone Over-Mold Bonding Trials

Casco Bay Molding has recently undertaken an extensive Plastic and Metal surface treatment analysis.  The goal is to determine which Silicone bonds are most efficient to a given plastic under a specified surface treatment with or without a particular priming agent.

We tested various combinations of Silicones, Surface Treatments and Priming Agents on the overmolding jobs we run in production.  Below please find a layout of the various materials and treatments we worked with:

– Substrates:
Polysulfone: Liquid Silicone Rubber gasket overmolded onto Polysulfone part
Ultem: Low profile LSR gasket over-molded to an Ultem part
Valox: LSR gasket overmold onto Valox-20% part
Nylon 6/6: 384 Silicone spikes overmolded onto a Nylon 6/6-13% glass fill plate
Glass: 16 Well Silicone grid overmoulded onto a Glass Slide
Steel Tube: Silicone instrument handle molded onto a stainless tube
Steel Plate: Silicone 384 grid structure onto a stainless plate

– Surface Treatments Sampled:
Corona Treatment
Plasma Coating
Flame Treatment
Ultra Violet Treatment

– Priming Agents Tested:

– Liquid Silicone Rubbers Tested:

After testing we have settled on an optimum process and combination for the five production jobs that we run most frequently.  We are reluctant to “blog about” or offer a “general” opinion for a given substrate because we find variation in surface finish and/or % of glass on the surface can change performance dramatically, even with an identical substrate.  Casco Bay Molding would be pleased to work together with customers on your over-molding application.

Liz Thornton