Hot Melts Hold Fast

To achieve optimal performance of the release coating, cross-linking of the free-radical curing silicones requires inerting with nitrogen to reduce the oxygen level below a 50 ppm threshold. UV units used for curing these silicones are designed for a stable window of operation between 10 and 30 ppm oxygen. Above 50 ppm, an automatic control circuit would increase the nitrogen feed and eventually halt production to avoid rejects.

In one trial, residual oxygen content was pushed to a remarkable 240 ppm (Graph 3). Even at this high level, the silicones did not suffer in subsequent adhesion tests (per FINAT #11). The silicone surface on this liner contains excess oxygen by-products, formed due to poor nitrogen inerting. One-day release data show a noticeable increase in release (stronger adhesion) with adhesives 7, 8, and 9. Adhesives that contain aromatic tackifiers, based on C9 or rosin ester, show an increased release level, and worse, poor release stability. This points to a chemical reaction of these components with oxygen by-products at the silicone layer.