In the publication, Silicone Release Coatings: A Closer Look at Release Mechanisms, Dr. Glenn V. Gordon et. al. from Dow-Corning explained the release mechanism for release liners in PSA applications.
The factors affecting the release force over adhesives include:
- Direct bonds between release agent and adhesive. The effect should be minimum.
- Interpenetration of release agent and adhesive. The effect is also minimum since the two systems are incompatible.
- van der Waals forces. Yes. But small since release agents generally have low surface energy. The force should be in the order of 10^-2 to 10^-1 N•m^-1, much less than a typical measured release force of 10^0 to 10^2 N•m^-1
- Low coefficient of friction. This is the reason why silicone release agent is better than fluorocarbons, although fluorocarbon has low surface energy as well.
- Surface roughness
- Mechanical dissipation. Mechanical dissipation is the key factor determining the release force and is the reason behind the peel rate dependent release force, as shown in the following figure.
Mechanical dissipation is determined by the adhesive rheology, particularly the Tan(Delta). The above figure correlates the peel rate dependent release force and adhesive’s Tan (delta) in terms of both magnitude and trend. The rheology of release agent, particularly those with high-release additive (HRA), also has certain contribution (rheology data, G’, G”, and Tan are good indicators). Meanwhile other PSA components, e.g. carriers, such as PET, PP, Paper, would play negligible effects.
Peel frequency calculation. The dynamic frequency ω can be related to the rate of delimitation υ, adhesive thickness h subject to deformation in the peel test (same source).
This equation is quite useful. If the adhesive thickness is 15um, peel rate is 5000mm/s; then the dynamic frequency is (3.14*2)/15*5000*1000=2.1*10^6 rad/s.
Source: Dow corning