GERMANY-based chemicals supplier Wacker has introduced two new liquid silicone rubbers (LSRs): one for radiation-sterilisable silicone valves used in medical devices and the other for the solar industry, for flexible thin-film modules to be laminated using roll-to-roll processing.
The LSR, available under the name Silpuran 6610/40, serves in the production of biocompatible silicone valves whose slits do not close up or “heal” during radiation sterilisation. The new silicone rubber allows such valves to be made without the use of additional auxiliaries. For instance, silicone valves ensure that infusion systems administer the correct dose of liquid medication. Medical equipment for administering liquid medication frequently employs valves made from silicone elastomers. These offer high dosing accuracy, are biocompatible and can be very readily sterilised on account of their resistance to heat, radiation and chemicals. However, it is not unknown for the slits of such silicone valves to close up (heal) when radiation-sterilised, a common practice in medical technology.
Meanwhile, Elastosil Solar 2200, is an LSR that vulcanises to form a transparent, pourable silicone. The non-corrosive silicone has adhesive properties, which ensure optimum bonding to all substrates typically used in the manufacture of thin-film modules. As a result, it readily bonds to glass and flexible films made from a variety of materials including aluminum, PET, polyethylene naphthalate (PEN) or activated ethylene tetrafluoroethylene copolymer (ETFE) without the need for a primer.
The rubber system has been formulated to provide a long pot life at room temperature, combined with rapid vulcanisation when heat is applied. The reactivity range of this new encapsulant allows module manufacturers to produce flexible modules cost-effectively using continuous roll-to-roll processing techniques, which are more familiar in the textile and paper industry. This type of roll lamination permits application of the silicone encapsulant, feed of the front film and vulcanisation of the LSR to be performed in a single, continuous and automated process. Elastosil Solar 2200 may be applied to the film to be laminated with the aid of a doctor blade or transfer roller.
In its cured state, the silicone elastomer bonds the composite layers into a stable laminate and provides the thin-film modules with an effective moisture barrier. It is electrically insulating, permanently flexible across a temperature range from -50 to +200 °C and virtually chemically inert. Furthermore, the vulcanised silicone is resistant to weathering and UV radiation, so there is no risk of yellowing, and it does not release any corrosive substances.
The polymer is thus ideally suited for laminating all types of flexible thin-film module, including organic solar cells or thin-film cells from compound semiconductors. Thin-film modules can be incorporated into the facade of buildings as attractive architectural elements and can also be used in textiles due to their inherent flexibility.
In addition to hyperpure polysilicone, the starting material for crystalline solar cells, the Munich-based chemical company also produces that are used as potting materials, adhesives and sealants or encapsul-ants in solar cells and modules. (PRA)
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