Dow offers LSR moulders fast-cure technologies

Düsseldorf, Germany — Medical moulders need liquid silicone rubber materials that cure quickly and at lower temperatures. Dow Performance Silicones, a global business unit of DowDuPont Inc. featured the novel, innovative elastomers at two recent presentations.

Stéphane Cornelis, responsible for medical application engineering and technical service at Dow Performance Silicones in Seneffe, Belgium, spoke 14 Nov about development and benchmark evaluation of the new QP1-33XX series medical quality LSR.

The material, launched at the Compamed trade fair in Düsseldorf, cures well below 140° C, which enables moulders to use thermally sensitive additives and to do two-component moulding of LSR with thermoplastics with lower heat resistance than glass-fiber-reinforced nylon or polybutylene terephthlate, which are the plastics most frequently used for LSR/thermoplastic moulding.

Biocompatible LSR

In a separate Dow Performance Silicones presentation at the 15 Nov Compamed suppliers forum, Pennadam Sivanand, EMEA manager in Seneffe medical technology development, application engineering and technical service, talked about another new low-temperature and fast-cure Dow material, the QP1-5040 self-adhesive (SA) Shore A40 hardness medical-grade LSR.

Sivanand illustrated the material’s low-temperature cure by showing the same 100° C cure profile chart for QP1-3350 as Cornelis had done the previous day — the one with up to 133 seconds faster cure than competitors’ LSR grades.

Disinfection requirements

Sivanand said medical industry OEMs seek biocompatible elastomer solutions that withstand disinfection requirements and can be moulded with fast cycle times. He said attractiveness of the new SA LSR is due to ability to eliminate mechanical interlocking and primers, with the higher efficiency and faster moulding cycle time resulting in cost reduction.

Dow chose to investigate QP1-5040 bond strength in two-component moulding with Tritan copolyester from Capelle aan den Ijssel, Netherlands-based Eastman Chemical BV, a thermoplastic resin similar in cost to medical-grade polycarbonate, yet free of bisphenol A and with higher stress cracking resistance to aggressive chemicals. Sivanand also talked about Tritan’s high clarity and UV resistance.

The SA technology behind QP1-5040 is based on use of “well-known system D adhesion promoters” acting as coupling agents to establish bonded interfaces through “diffuse interphase interpenetrating networks,” Sivanand said.

LSR/copolyester adhesive pull-off tests on compression moulded plaques with co-polyesters with 66 psi (0.46 MPa) heat distortion temperatures (HDT) of 95°C, 100°C and 110°C showed pull-off force rising from 154 N/25 mm for one of two 95°C HDT grades to 183 N/25 mm for the 110°C HDT copolyester.

Cohesive failure, meaning extent of damage to the substrate with which the LSR was bonded, was understandably 0% for stainless steel, with large differences between PC grades (below 1% and 65%), yet highest at 95% with copolyester.

Applications

Target applications for the new SA-LSR/Tritan material combinations include respiratory care masks (as an alternative to more expensive transparent nylon and similar-cost PC substrates). Potential is also seen in medical components, devices, enclosures, wearable monitors and various moulded-on gaskets and seals.

Aside from the presentations by Cornelis and Sivanand in the Compamed suppliers forum, Dow Medical global strategic marketing director Gary Lord held a short material science choices presentation in the Medica medical industry fair. Dow exhibited at both of the parallel shows.

Lord talked about how Dow contributes with its silicone materials to the “growing phenomenon of the internet of medical things.”