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How self-lubricating silicones improve the design of needle-less valves

Healthcare 17.03.2021

Silicones are widely used as a key raw material for making needle free valves safe and cost effective. Generally, these valves are produced with a silicone component in conjunction with a plastic housing.

Throughout the last several years Elkem has worked with our customer base to improve their designs and solve challenges related to self- healing of silicones. While Silicones are a great choice due to their biocompatibility, chemical inertness, environmental stability, and high performing physical properties, there can be some limitations appearing in the design of valves containing pre-slit septums.

To overcome this Elkem Silicones worked in conjunction with our customer base to develop a range of self-lubricating liquid silicone rubber (LSR). This product line brings the same high physical properties as standard medical grade LSRs with the addition of a self-bleeding lubricant, acting as a barrier against the slit healing phenomenon. In addition, self-lubricating LSRs have a lower coefficient of friction, increasing the mechanical performance of the silicone valve in the plastic housing. This product line can also be considered for manufacturing O-rings and seals requiring a low coefficient of friction.

Benefits of self-lubricating LSRs

Drag against plastics

Silicones by nature tend to be grabby or tacky at the surface, and it becomes more pronounced as the durometer of silicone rubber decreases.  This can have a detrimental effect to the performance of the valve as it increases the force required for the silicone portion of the valve to slide up against the plastic housing.  By helping our customers change from a standard LSR to a self-lubricating LSR, this greatly reduces the coefficient of friction and allows for a more uniform force to move the valve.  In most cases the same tooling for a component made from a standard LSR can still be used with the self-lubricating LSR.

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Slit re-healing   

When silicone valves are produced, they are slit afterwards either robotically or manually to allow a controlled path for the fluids to pass through. When silicones are molded the cure, process is not 100% complete.   Over time, and after undergoing a sterilization process, a crosslinking of both sides of the slit can occur, which results in the complete or partial closing of the slit. This phenomenon is referred to as “slit healing” or “self-healing” and can pose a safety and efficiency issue for the functionality of the valve.

 In some cases, a drop of Fluoro-silicone oil is used to prevent the healing process and allow the valve to function normally, although that can be an expensive secondary step.  By introducing self-lubricating LSRs to this application the tendency for the slit to heal post-production is greatly reduced and so is the need for secondary processing.   This means less scrap and less cost in post processing procedures.

Bowl feeding in automation 

In development of this line, and in partnership with various customers, we found another unexpected benefit of self-lubricating LSRs.  Many times, the silicone valves are just a portion of an assembly.  Often, when the final product is being assembled it typically employs the use of automated bowl feeders. Standard silicones can have a tendency to stick together in such environment and either slow down manufacturing or contribute to scrapped parts.  By the introduction of a self-lubricating LSR into this process the parts will feed far easier and consistently, allowing for less down time in an automated assembly.