If it was injection molded liquid silicone rubber (LSR), it was cured via heat, until now. "LSR first launched in the 1970s, and it's always been thermally cured," explained Sharon Shatto, Americas Marketing Manager, Healthcare for Momentive Performance Materials during Plastec West 2013.
Momentive used an Elmet tool with a transparent acrylic cavity and UV LED lights to cure its new UV curable LSR on an Engel e-motion machine. Silicone typically cures at temperatures above 120°C, limiting overmolded thermoplastics to materials like nylon, but the bottle stopper molded on the e-motion 310/110 LIM injection molding machine featured a polypropylene insert.
Shatto said that Momentive introduced a UV curable LSR to the extrusion market two years ago, with curing there made easier by placing UV lighting at the die exit. Getting UV lighting into an injection molding tool required some recent advances in lighting technology as well as a machined PMMA cavity insert.