INNOVATION | LIQUID SILICONE RUBBER


Right: Elkem demonstrated production of parts in its new LSR Select system at the Medical Design & Manufactur- ing (MD&M) West exhibition in Anaheim, CA,USA in February


tures as low as 80°C and possibly even lower, which can expand the range of applications and substrates in injection overmoulding. Some thermoplastics cannot be used with traditional LSRs, since they cannot withstand the curing temperature. LSR Select materials are said to offer the same distinctive advantages of easy processing and release as the company’s more conventional two-part LSR products. Elkem says LSR Select “offers easy start up and shutdown, with no kit matching or off-ratio purging needed, resulting in a more efficient process with less waste.” Elkem has cooperated with dosing equipment


producer Elmet, which now offers an optional hardware/software package for processing LSR Select on its existing Top 5000 P dosing systems. Elmet Sales Director Mark Ostermann says several companies are already using the equipment in the USA, and more in Europe are likely to start up soon. The cooperation between Elkem and Elmet is


non-exclusive, but Ostermann says that for the moment, Elmet is the only company offering a dosing system designed specifically for LSR Select. Elkem says it is working with several other dosing equipment suppliers to enable LSR Select readiness. Another major LSR producer,Wacker, has been tackling the issue of post-cure. Articles made from conventional silicone rubber often do not meet legal requirements unless they have been post- cured in a heat treatment process, it says, but novel grades it introduced a couple of years ago eliminate


this laborious process step for many applications. Post-cure, which needs to be performed on


articles made from conventional liquid silicone rubber for use in the baby-care, food-contact and medical sectors for example, removes volatile or extractable residues from the elastomer. It involves putting parts in a well-ventilated oven at up to 200°C for several hours. The procedure is costly, time consuming and work-intensive, says Wacker. Whereas injection moulding and packaging of


the articles are fully automated steps with short cycle times, post-curing is still largely a manual process: filling and emptying of the post-curing oven is usually done by hand. Wacker found a way to do without this process


With Elkem’s LSR Select, processors can blend base polymers to obtain the specific hardness they require. The Control component enables adjustment of cure kinetics


Typical Properties Appearance


Specific Gravity


Durometer Hardness, Shore A Tensile strength, N/mm2


ASTM TP 038 TP 013 D2240 D412


step. With Elastosil LR 5040 series grades, it says, articles show very good mechanical properties and comply with the regulatory standards relating to volatiles for sensitive applications (see also Injection World April 2018). The products are currently available in hardness levels between 30 and 70 Shore A, including a 45-Shore-A version suitable for numerous applications in the baby-care sector. Wacker says the new liquid silicones’ claim of being especially pure is also underlined by their optical appearance: they are translucent and have a delicate blue shimmer. Furthermore, the tenden- cy to yellow, which occurs with some post-cured LSR articles during storage, has been reduced to a minimum. The LRS 5040 LSR grades show good tear


LSR Select 20 LSR Select 35 LSR Select 50 Clear 1.09 21


Clear 1.10 34


8.9 8.1


Clear 1.11 50


8.5


LSR Select 70 Clear 1.13 69


7.8


Typical properties of Elkem’s LSR Select grades incorporating 1% Control, press cured for five minutes at 177°C. The single-component base polymers are available in 20, 35, 50 and 70 Shore A hardnesses, and can be blended to achieve a custom formulation


34 INJECTION WORLD | April 2019 www.injectionworld.com


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