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Jan/Feb 2025
WACKER Develops Self-Adhesive Liquid Silicone Rubber
By Daniel Hawk, Polymer and Elastomer Processing Engineer, Wacker Chemical Corporation
hen we look at the many uses for liq- uid silicone rubber, one that comes up many times is the combination of silicone rubber with a harder plastic sub- strate into a single part. The possibilities for these combinations are fascinating to think about.
W
Most standard silicone offerings cannot naturally bond to the surface of thermo- plastics as some chemistries and additives interfere with the bonding mechanisms. One long-time need from the industry is for LSR to strongly bond to polycarbonate plas- tics for many applications.
No Pretreatment
These self-adhesive liquid silicone rubber grades cure extremely fast and establish a firm bond with the thermo- plastic polycarbonate without the need to pretreat its surface. This liquid silicone that not only overcomes the traditional issues with LSR bonding to Polycarbonate but also paves the way for innovative Silicone and PC hybrid products. WACKER’s ELASTOSIL® LR 3078, with durometer offerings from 20-70, is designed to be as user-friendly as any conventional molding grade of liquid silicone in an injec-
tion molding process. These materials can be injection molded with the same characteris-
between the PC and the LSR, all in the same tool in the molding machine.
New tool conditioning should be con- sidered before applying any of the self- adhesive silicone to the tooling. Wacker recommends using ELASTOSIL Aux Mould Release Agent 32 to support the start-up phase when using LR 3078 in new tooling. Without a release agent, the self- adhesive LSR will want to stick quite strongly to the tool surface.
Beginning to mold with ELASTOSIL LR 3078 material starts more with the polycarbonate side of the equation. Establishing the PC side of the tool first and getting that part of the process nailed down will make it easier to find the opti- mal time and temperatures for the sili- cone.
Tensile Testing
Respiratory mask made of ELASTOSIL LR 3078.
tics and typical machine settings as the com- pany’s standard grade LSRs. The recom- mended molding technique, the 2K process, ensures the highest levels of bonding
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When looking at how materials bond to each other, we typically measure the force needed to pull one side away from the other. The lab equipment required to calculate this force is a tensile tester with the appropri- ate load cell and sample holding fixture to col- lect this force data. Data is typically reported
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