Low-temperature silicone vulcanization process

Enhancement in the silicone vulcanisation process has given rise to new opportunities. This was unveiled by a new multicomponent technology that paves the way for silicone vulcanisation at low temperatures at the ENGEL Symposium 2012 in St. Valentin where ENGEL demonstrated this new process producing wine bottle stoppers. The new process presents multiple benefits to various applications and has been seen as a major step forward in improving the vulcanisation process for silicone.

“Enhancements to silicone rubbers in the past two years have opened the door to new applications in multi-component technology for this material class,” reveals Professor Georg Steinbichler, head of research and development technologies at ENGEL AUSTRIA. Whereas conventional silicone rubbers require high temperatures for cross-linking, the new types vulcanise with exposure to light in the ultraviolet wavelength range at room temperature. This enables silicones to be combined with a wide range of thermoplastics via two-component and multi-component injection moulding. Even temperature-sensitive materials such as polypropylene can now be processed with silicone in a single step.

Cavity inserts in the injection mould that are permeable to light are the prerequisite for UV vulcanisation. For this application, ENGEL partner firm Elmet from Oftering in Austria utilises translucent plastic inserts for UV light and integrates UV lamps into the mould for irradiation.

Reduced cycle time and energy consumption

At the Symposium, ENGEL demonstrated the UV vulcanization process by producing wine bottle stoppers on an ENGEL victory 200/80 LIM injection moulding machine using an Elmet mould.

In the process, polypropylenes are overmoulded with liquid silicone from Momentive Performance Materials. The irradiation time for the vulcanisation of the silicone components is around 20 seconds. “In the conventional high-temperature process, silicone parts with a similar wall thickness need more than a minute for crosslinking”, said Mr. Steinbichler. “UV vulcanisation not only facilitates new applications, therefore, but also reduces the cycle times and energy consumption associated with silicone processing.”

Silicone elastomers used in two-shot applications are usually cured by heat or at room temperature using crosslinking processes such as peroxide cure, hydrosilylation cure, or condensation cure. The new processed allows for new advanced materials to be cNike