Sponsored By

Engel and Elmet are introducing a new low-temperature silicone curing process that speeds processing time for injection molded two-component parts for medical and other applications.  At the heart of the technology is a very innovative mold with integrated UV lamps and transparent plastic inserts.

July 9, 2012

3 Min Read
Unique mold, materials speed LSR two-component molding

Engel and Elmet are introducing a new low-temperature silicone curing process that speeds processing time for injection molded two-component parts for medical and other applications.  At the heart of the technology is a very innovative mold with integrated UV lamps and transparent plastic inserts.

WerkzeugElmetUVVulkanisation2.gif

UV lamps are integrated into Elmet mold shown on an Engel injection molding machine.

"Liquid silicone can now be combined with a wide range of thermoplastics directly in injection molding," said Leopold Praher, sales chief for Elast/LIM at Engel Austria at the world introduction for the process at the Engel Symposium 2012 held last month in St. Valentin, Austria. Components made from Momentive materials were molded on an Engel victory 200/80 LIM (liquid injection molding) machine.

"Enhancements to silicone rubbers in the past two years have opened the door to new applications in multi-component technology for this material class" said Georg Steinbichler, head of research and development technologies at Engel Austria.

Polypropylene opportunity
"In the two-shot molding, we see the combination with low-temperature plastics such as polypropylene as the biggest opportunity," Clemens Trumm, manager of the German Application Development Center at Momentive Performance Materials, told PlasticsToday. "That covers face masks, closures, valves, soft touch....The whole two-component portfolio more or less."

Silicone elastomers used in two-shot applications typically are cured by heat or at room temperature using crosslinking processes such as peroxide cure, hydrosilylation cure, or condensation cure. In the new approach, newly developed materials are cured with UV light with a UV sensitive curing system that is integral to the Elmet mold.

Application of the technology to injection molding is brand new.

In the traditional process, a standard LSR for injection molding can be cured at around 356-392ºF. However, curing temperatures need to be reduced for large parts so that molds can be filled completely and to eliminate trapped air. Examples are insulators, cable joints, cable terminations, or surge arrestors. The new process shown by Elmet and Engel requires a "UV transparent" mold. Examples of materials that can be used in place of steel are quartz glass or acrylic.

In the demonstration at last month's Symposium, polypropylene was overmolded with liquid silicone to produce wine stoppers. The irradiation time for the vulcanization of the silicone components took 20 seconds.

ENGEL_Symposium_2012_Exponat_Flaschenverschluss_2.jpg

A two-component wine stopper was molded in the LSR technology demonstration.

"In the conventional high-temperature process, silicone parts with a similar wall thickness need more than a minute for cross-linking", said Steinbichler. "UV vulcanization not only facilitates new applications, therefore, but also reduces the cycle times and energy consumption associated with silicone processing."

Important for extrusion
The new technology also has significant implications for extruded silicones.There are a few extrusion applications although "this whole technology is very new for the market," Trumm told PlasticsToday.

"The driver for this technology in extrusion is the energy savings, the better profile stability and the low-temp curing that enables production of coextruded/cover of low-temperature-resistant polymers, drugs, or electronics," Trumm said.

The development is important because of the increasing use of silicones due to their unique profile:

  • Temperature resistance above 392ºF,

  • Elasticity at temperatures below -76ºF,

  • Good aging stability and weather resistance, and

  • Bio-inertness.

Trumm feels the big play in the medical market on the extrusion side will be drugs integrated into silicone.

Picture1.gif

In the extrusion process, the UV exposure time for the cure can be as short as 0.5 second, depending on the speed of the line and the UV intensity.

Sign up for the PlasticsToday NewsFeed newsletter.

You May Also Like