Modeling the Viscosity of Silicone Rubber During High-Speed Infrared CuringPart of:
For the treatment or diagnose of neural diseases like deafness or epilepsy, silicone-rubber-based implants are available in several standard sizes. Although these implants fit to idealized anatomies, they do not perfectly fit to the individual anatomy of each patient. To overcome this, we developed a layer by layer 3D printing process for typically used viscous “medical grade” silicone rubber materials. To cure the printed silicone rubber an infrared high-speed-curing system (1) is used, which heats up the printed silicone rubber instantly and thereby cures the initially viscous silicone rubber material before it spreads out during the curing process. To optimize the fabrication accuracy and resolution of this system, a time-temperature profile for the curing process should be evaluated, where the spreading of the silicone rubber material is minimal. Therefore, further knowledge about the rheological behavior of the silicone rubber is mandatory. As the spreading dynamics of polymeric liquids depends in general on the viscosity of the polymeric liquid (2), a rheology model was developed which correlates the infrared heat-related temperature profile of the printed silicone rubber with its curing-related viscosity rise and its temperature related viscosity fall. Two typical silicone rubbers (Silpuran 2430, Wacker Chemie AG and Sylgard 184, Dow Corning GmbH) were characterized with a vulcameter at different isothermal temperatures (20°C - 60°C). Their isothermal behavior was correlated via an empirical viscosity expression by using a two-stage Arrhenius equation. To cope with a realistic nonisothermal curing process, a time-temperature integral for the degree of cure was introduced into the isothermal model. Good correlations between the nonisothermal model and the vulcameter measurements at different heat rates (5 K/min - 60 K/min) were observed, giving the ability to optimize the time-temperature profile of the curing system to the rheological behavior of the silicone rubber.