Materials: LSR Grades Offer Low-Temperature Curing, Primerless Adhesion to Copolyester

Curing at a lower temperature makes it feasible to overmold the materials onto heat-sensitive substrates, including copolyesters.

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Two new Dow Corning QP1-33X0 liquid silicone rubber (LSR) grades and new Dow Corning QP1-5040 self-adhesive LSR grades were launched by Dow Medical Solutions, a business unit of the DowDuPont Specialty Products Division. Each is a low-temperature cure (LTC) technology.

At the MD&M West 2018 show in Anaheim, Dow Corning officials said the company has been collaborating with Eastman Chemical, manufacturer of the popular Tritan copolyester to tailor the LSR and develop a data set for combining the materials. Company representatives said that the collaboration with Eastman goes beyond product design to processing parameters, including proper molding, drying, and handling to determine how those factors can impact adhesion.

In addition to allowing overmolding with heat-sensitive substrates, Dow Corning said QP1-33X0 LSR allows fast injection speeds under low injection pressures. Those lower pressures and temperatures are growing more important as LSRs are increasingly used to encapsulate sensitive electronics in wearable devices.

In addition, Dow Corning representatives said they have seen improved thick section cure rates during testing with a faster overall cure reaction. At this time, the company is working on biocompatibility testing but it has already received positive cytotoxicity results. In terms of hardness, there is currently a 40 durometer grade, with a 30 durometer and others in the works.