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:
Wacker
Dow
NuSil
ShinEtzu

– Liquid Silicone Rubbers Tested:
Wacker
Dow
NuSil
ShinEtzu

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