Pressure Sensitive Tape Recap:
- An adhesive tape that is tacky at room temperature.
- Requires no more than finger or hand pressure to adhere.
- Activationby water, solvent or heat are not necessary to exert a strong adhesive force toward diverse materials such as paper, glass, wood, plastic or metals.
A Pressure Sensitive Adhesive Tape relies ona balance between adhesion, cohesion, and tack.
Adhesion: the attraction between an adhesive and substrate
Adhesion, the most important parameter in any application, is defined as the attraction between an adhesive and substrate. The adhesion of a product is determined by various factors, including the adhesive mass, substrate, pressure, time, and conditions.
- Usually increases during the first few days
- Measured by "peel adhesion" in N/cm
- Must not be confused with tack
Substrate - simply the surface being applied to.
Consider, for a minute, an unwaxed car when washed. The water, when applied, will spread out on the car, and create puddles. In this case the unwaxed car is displaying high surface energy. But on a waxed car, what is the difference? The water instead beads up, because it is displaying low surface energy. The same is true with pressure sensitive tape. Pressure sensitive adhesives bond well withhigh surface energy materials (as with the unwaxed car) but not so much with low surface energy materials (the waxed car).
- High Surface Tension/Energy POLAR (>36 dyn) - includes substrates such as steel, glass, aluminum, copper, zinc, polycarbonate, PVC, PET, and PMMA. These substrates are easier to bond.
- Low Surface Tension/Energy NON-POLAR (<36 dyn) - includes substrates such as rubber, PE, PP, powder coating, silicone, and teflon. These substrates are critical to bond.
Cohesion: the inner strength or bond of the adhesive.
Cohesion is defined as the force of attraction between molecules of the same substance, or the ability of the adhesive to resist splitting when submitted to stress. Cohesion is measured by its resistance to forces parallel to the surface.
- High cohesion goes together with higher temperature resistance, lower tack, and higher holding power.
- Measured via:"dynamic shear resistance" (at speed of 50mm/min) in N/mm and"static shear resistance" (at 70C) in minutes
Tack: the wetting at first contact to the substrate
Tack is the property that allows the PSA to adhere to a surface with very light pressure and a minimum contact time.
- Effective under minimum pressure and minimum contact time
- Tack depends on type of adhesive mass and coating weight
- High tack supports adhesion to rough surfaces
- Measured via: "loop test": yes/no or the "rolling ball test" in mm