Process Enhancements Through Rheology for a New Generation of Liquid Silicone Rubber

Silicone elastomers encompass a broad range of synthetic rubber applications and having been in existence for nearly 70 years, fabricators and end-users alike have sought to exploit the range of benefits that silicone provides in a cured rubber form. A somewhat newer lineage of this polymer family, Liquid Silicone Rubber (LSR) has gained increasing popularity for designers and fabricators for a variety of reasons including short cycle times and flexibility in tool design. Dow Corning Corporation has had many innovations in silicone technology throughout these 70 years. Now with the introduction of yet a fourth generation LSR offering (Gen4-LSR) called XIAMETER^®brand RBL-9200 Series the heritage continues.

This Gen4-LSR effectively compliments the most recent advances in molding technology with a focus on rheological behavior to gain cycle time improvement. While similar in many respects to legacy generations of LSR product families, improvements in the manufacturing process (mixing & treating technology) and optimization of the LSR formulation have delivered clear performance improvements versus prior LSR offerings. The rheological benefits gained from this new technology translate to faster processing and better part quality without the typical tradeoffs in mixed scorch safely through a combination of enhanced mixing technology in conjunction with the use of optimized cross-linker/plasticizer and silica packages.

This paper will serve to qualify and quantify these rheological benefits, with a focus on processing, by showing enhancements in production throughput. This is easily visualized with the aid of Computer Aided Engineering (CAE) software. SigmaSoft^®CAE software with analysis performed by Kruse Analysis, Inc. is useful to characterize LSR materials using a “Shot Glass” mold CAD model and the actual rheological data obtained from testing the subject LSR material in an ATD1000 Alpha Technologies Rheometer. As inputs to the CAE software, the data produces an accurate depiction in a dramatic 3D Simulation. Simulation accuracy is assured by use of the following key material property models:

-       Pressure, volume, and temperature relationship as proposed by Schmidt.

-       Rheology model as proposed by Carreau-WLF.

-       Cure reaction model as proposed by Kamal-Sourour.

Thus, the rheological benefits of this Gen4-LSR can clearly and accurately be demonstrated showing the material’s processability characteristics in time-lapse 3D Isometric view. Finally, using process mold-trials of a complex “Shot Glass” cold runner injection mold produced by MR Mold and Engineering Corporation, a relationship of rheological behavior and injection molding process performance is realized.