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Published on January 1, 2006

Surface Manipulation of Silicone Rubber Materials by SoftPlasma-Polymerisation

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Date Published January 1, 2006
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This Report has been authored by:Thomas Christensen at Nanon A/S

Silicone rubber becomes more and more common in medical, automotive and other industrial applications. The material has excellent mechanical and chemical properties and thermal resistance. However, one of the drawbacks of silicone rubber often is the low surface tension that makes it impossible to coat, print or glue the material. There exist a lot of surface treatment techniques such as flame and corona treatment, atmospheric plasma etching, low pressure plasma treatment or wet chemical etching that can be used to activate polymer surfaces prior to a coating. Wet chemical etching is always connected to great amounts of toxic chemical and waste. Most plasma activation techniques are quite usable for activation of polymer surfaces, but often it is not possible to activate three-dimensional shaped items. Furthermore, the durability of the activation is short, meaning that especially silicone rubber has to be coated a short time after the activation step. Nanon A/S has developed the so-called “Softplasma™” that can be used favorably for modifying surface properties of silicone rubber because of its low energy level. The surface is etched for a short time, and afterwards a thin polymer layer is plasma polymerized on the surface. The properties of the polymer layer are dependent on the functional groups of the initiated monomer that can be chosen from a broad list of compounds. Compared to other plasma types, the Softplasma™ is able to prevent the functional groups of these monomers from decomposing and activates only the sites that are supposed to polymerize. The surface itself will not be decomposed as is often seen in high energy plasma types. Only some bonds of the outer layer molecules will broken and react with monomer fragments which give strong bonds between the silicone rubber surface and the thin plasma coating. Softplasma™ can be used to make e.g. a PU like surface on silicone rubber to coat afterwards with a PU-varnish or in contrary to make a silicone like surface on a hard plastic to mold afterward with LSR.