There are three main factors to consider when attempting to fully understand adhesion power: tensile strength, shear resistance, and peel adhesion. Peel adhesion is defined as the force needed to “peel” an adhesive tape from any given surface, whether flexible, smooth, or rigid. This “peel” force is always and only measured across the width of the taped substrate, making it the more difficult separating force to resist. It is important to understand the peel adhesion factor, as it can serve as a guide for choosing the right tape for the application.
Peel adhesion is a very important consideration for both kinds of adhesive applications, temporary and permanent. For a temporary application, the peel adhesion needs to maintain an optimal balance between maintaining proper adhesion and allowing ease of removal. Most masking tapes are excellent examples of tapes that offer adequate peel adhesion during the application, and can also be removed cleanly from the substrate after usage. For temporary application, it is always important to be aware that the peel adhesion force builds up over time. Appropriate lab testing may be required to determine whether or not a specific tape is suited for the desired application.
For permanent bonding applications, maximizing resistance to peel force should be the target. In most cases, the tape products of choice are double-sided tapes. For permanent bonding applications, the following parameters can be evaluated by peel adhesion tests to determine which application conditions might adversely affect adhesion:
- Adhesion level to the component parts; for example metal, plastic, fabric, or smooth versus rough surfaces.
- Application temperatures and environmental conditions; for example test at 80°C, test at room temperature after 168 hours' humidity exposure.
- Strength development; for example test after one minute; test after 72 hours; test after 14 days.
In all cases, peel adhesion is one of three separating forces that aids in determining whether or not a tape will work in the specific application. Whether the application is temporary or permanent, optimal peel adhesion values can only be achieved if the substrates are clean, free of dust or grease, and have sufficient pressure or dwell time.