Summit focuses on laser marking, foam, Industry 4.0

Milan — Laser marking liquid silicone rubber was demonstrated at the Silicone Elastomers Summit, sponsored by Smithers Rapra, in Milan.

The demonstration involved REA Jet FL fiber laser marking equipment from Mühltal, Germany-based REA Elektronik GmbH.

The Merck KgaA laser marketing pigments were dispersed in Alpa-LSR 550201 and 550202 laser marking grades from Tübingen, Germany-based CHT Germany GmbH.

The project, which made luggage tags, was produced by Freiberg, Germany-based LSR and thermoplastics molder Antech Polymertechnik.

CHT's laser marking grades have compression set 12, Shore hardness 50A and viscosity 300 mPas at 10/s. But values differ for elongation to break at respectively 380 percent and 300 percent, and tensile strength at respectively 8.5 N/mm2 and 7.5 N/mm2.

Depending on laser beam intensity, markings range from light gray to black, on opaque colored or transparent LSR parts, including deeply engraved marking where required.

Also at the Silicone Elastomers Summit, Svenja Marl, a researcher at the UNIpace polymer application center at Kassel University in Germany, spoke about physical foaming LSR. Colleagues had shown water as a foaming agent at the 2017 summit.

Marl presented microscope images of foam structures from 2-4 percent water showing nonhomogenous cell distribution. Mold temperature has significant influence on structure: at 140° C, no foam structure close to the skin and central rough pores; completely foamed structure at 180° C, but still central rough pores.

She then moved onto the next development stage, mixing LSR with Expancel 031 DU 40 expandable thermoplastic microspheres from Stockviksverken, Sweden-based Akzo Nobel Pulp and Performance Chemicals AB.

Researchers, meanwhile, also used Unicell MS 140 DS expandable microspheres from Tramaco, Taiwan. As with Expancel microspheres, these spheres consist of a 2µm-thick 15-20 µm diameter shell filled with hydrocarbon. Marl revealed Unicell microspheres consist of an acrylonitrile/methacrylate copolymer, expanding at 120-125° C to a 50 µm sphere with a 0.1 µm thick shell.

UNIpace used 0.5-3 weight percent Unicell microspheres in LSR. Foaming was good at 1 and 2 wt percent, the latter giving higher Shore hardness due to filler network formation. The microspheres had initially reduced hardness with filler content up to 0.5 wt percent.

While 50 percent weight reduction was obtained with Expancel foaming earplug tips in Dow Silastic LTC 9400-50, weight reduction was lower at 30 percent when molding foam discs and spheres in KEG-2003H-40, a Shin-Etsu Silicone LSR grade from. In general, Marl spoke about 35 percent weight reduction being possible with Unicell MS 140 DS.

Read the full story at LSR world.