Effects of varying mixing ratios of components A and B on optical liquid silicone rubber

The processing of optical liquid siliconerubber (LSR) formulations is associatedwith significant quality issues and high rejection rates. Often, the quality issuescan be attributed to deviations in LSR dosing. To address these issues, specificmixing ratios of components A and B that deviate from the standard 1:1 ratiowere intentionally created. These mixtures were characterized via differentialscanning calorimetry, rheometer, and Fourier-transform infrared spectroscopy.The mixtures were then processed via injection molding and mechanical proper-ties such as shrinkage, density, hardness, and tensile properties were determinedand analyzed. The results show that deviating mixing ratios for optical LSR have asignificant influence on processing in terms of shifts in cross-linking temperatureand exothermic energy released, viscosity, and cavity pressure, as well as on thefinal component properties in terms of varying shrinkage, density, hardness, ten-sile strength, and elongation at break. This study shows that even small deviationshave a major influence and should therefore be avoided. The requirements for theaccuracy of the dosing system with regard to the mixing ratio must therefore bevery high. In practice, such deviationsin the mixing ratios are most likely tobe detected in geometry via shrinkage, hardness, or tensile properties.