Silicone release products can help eliminate the need for costly platinum catalyst on process rollers while improving processing and line speeds. However, care must be taken to avoid buildup on process rollers when using these materials because this buildup can lead to processing problems. Dow Corning, maker Syl-Off silicone release products, offers a guide and troubleshooting tips about causes, effects, and solutions to process roller buildup.
According to the guide, inadequate cure is a primary cause of roller buildup. Symptoms of inadequate cure include smear or rub-off of the silicone layer or the transfer of uncured silicone to the adhesive surface. Causes of inadequate cure are using an oven temperature that is too low, a dwell time in the oven that is too short, substrate inhibition, improper mixing and contamination of the silicone. Potential solutions for these conditions include:
- Oven Temperature Too Low or Dwell Time Too Short. The right amount of heat and oven dwell time are required to evaporate inhibitors from release coatings to drive cure.
- Substrate Inhibition. This is caused by poisons in the substrate that deactivate the catalyst. Increasing either catalyst or crosslinker levels may alleviate this problem.
- Improper Mixing. This happens when there is not enough catalyst or crosslinker to drive the cure to completion. Add catalyst or crosslinker.
- Contamination of the Catalyst. Some additives used in the manufacture of films and clay- and poly-coated krafts as well as the pre-coat found on most glassines and super-calendered krafts can adversely affect cure by inhibiting or, in some cases, “poisoning” the performance of the platinum-based catalyst. Furthermore, when using offset roller systems to apply platinum-catalyzed coatings, care should be taken with the choice of rubber used for the coated rubber rolls. Materials used to vulcanize the rubber may also inhibit the cure of the silicone coating by influencing the performance of the platinum catalyst.