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

Abstract The processing of optical liquid silicone rubber (LSR) formulations is associated with significant quality issues and high rejection rates. Often, the quality issues can be attributed to deviations in LSR dosing. To address these issues, specific mixing ratios of components A and B that deviate from the standard 1:1 ratio were intentionally created. These mixtures were characterized via differential scanning calorimetry, rheometer, and Fourier‐transform infrared spectroscopy. The mixtures were then processed via injection molding and mechanical properties such as shrinkage, density, hardness, and tensile properties were determined and analyzed. The results show that deviating mixing ratios for optical LSR have a significant influence on processing in terms of shifts in cross‐linking temperature and exothermic energy released, viscosity, and cavity pressure, as well as on the final component properties in terms of varying shrinkage, density, hardness, tensile strength, and elongation at break. This study shows that even small deviations have a major influence and should therefore be avoided. The requirements for the accuracy of the dosing system with regard to the mixing ratio must therefore be very high. In practice, such deviations in the mixing ratios are most likely to be detected in geometry via shrinkage, hardness, or tensile properties. Highlights More component A leads to faster but less dense cross‐linking Component B can be characterized by Fourier‐transform infrared spectroscopy via Si–H bending band at 905 cm −1 . More component B leads to higher shrinkage, density, hardness, and strength. Deviations in the mixing ratio must be avoided as they lead to drastic changes. A general shift of the mixing ratio in favor of component B is less dramatic.