INNOVATION | LIQUID SILICONE RUBBER
– where LSR is used in connector seals and other parts – are for higher performance in materials over long operational periods, he said. Momentive has developed many LSRs with a low compression set, but Silopren LSR 3366/50 has particularly good long-term performance as measured in ISO 815 testing for 1,000 h at 175˚C. A two-colour LSR moulding application was shown by Momentive during the K 2016
Above:
Momentive’s Silopren LSR 3366/50 material is used to mould this two-colour egg cup
Right: At Fakuma 2017, Engel moulded bottle ventila- tion valves using Dow Silicones LSR
show. In a manufacturing cell, the company moulded egg cups in its Silopren LSR 2670 material on an Arburg injection moulding machine using a 4+4 cavity mould from LSR specialist Elmet. A close-loop control documented the amount of colour (or additive) in the material, which is particularly relevant to the healthcare segment. Thomas Frese, Manager Technical Marketing at
Below: Wacker has developed Elastosil LR 5040, a low-volatiles LSR that does not need post-curing
Wacker Chemie, said at the LSR Innovations conference that customers are increasingly requesting LSRs with low volatile organic compounds. This is due to: regulatory pressures in food contact, baby care and medical applications; automotive industry standards; and increasing performance requirements, for example in dealing with fogging and contact resistance. Reduction of volatiles can be done in a thermal post-curing step to allow the LSR moulded part to be used in sensitive applications. But Frese said customers want to eliminate this post-curing step. Wacker has therefore developed Elastosil LR
5040, which are low volatile LSR materials that do not need post-curing for many applications in food contact, health and baby care. At the Fakuma 2017 trade fair in October, the production of baby bottle nipples made from Elastosil LR 5040/45 was demonstrated on the stand of metering and mixing technology group Dopag.
Elastosil LR 5040 is formulated in such a way
that, even without post-curing, it already complies with current regulatory requirements that say baby items and food contact materials should contain no more than 0.5% volatile substances (the company has not revealed how the material achieves this). Post-curing remains mandatory, though, in certain situations: to prevent self-healing completely; to prevent consecutive reactions in some special media resistance applications; to reduce risk of deformation of parts during storage at elevated temperatures; and when long-term compression set is need at temperatures above 100˚C. Patrick Beyer at Dow Silicones discussed the company’s low temperature cure (LTC) silicone materials in his presentation at the LSR Innovations conference. “If you are an injection moulder who needs low temperatures, this is the material that can solve some of your issues,” he said. The benefits include fast moulding, bulk activation and cure acceleration using a Dow Silicones additive. At Fakuma 2017, the company supplied Silastic LTC 9400-50 LSR for the moulding of bottle ventilation valves of high wall thickness, with fast curing by introducing the accelera- tion additive at 0.5%. Beyer said the Silastic LTC 9400 materials also have good potential for overmoulding with polymers with low heat deflection tempera-
tures, such as PC. The bottle venting valves were moulded by
Engel during Fakuma on its Victory 860/160 tie-bar-less injection moulding machine. The group said process consistency is ensured by a patented force divider which enables the moving mould mounting platen to follow the mould exactly while clamping force is building up, and ensures that the clamping force is evenly distributed across the platen face. It said: “Both the outer and inner cavities are therefore kept closed with exactly the same force, ensuring consistent compression of the mould and a consistently high product quality. This almost burr-free, zero-waste, rework-free, and fully automatic processing is the key element in the economic manufacturing of high-tech products from liquid silicone.” At AMI’s LSR Innovations conference, Leopold
Praher, Engel’s head of sales for elastomer machines, discussed the group’s iQ optimisation products. He said numerous outside influences can affect the LSR moulding process and part quality. The iQ weight control software is Engel’s solution to ensure that cavities are filled reliably even when there are fluctuations in the raw material. Using the iQ clamp
30 INJECTION WORLD | April 2018
www.injectionworld.com
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