Characterization of Tack Strength Based on Cavity-Growth Criterion.

Area of Science:

• Materials Science
• Adhesion Science
• Polymer Science

Background:

• Tack, a measure of adhesive force in pressure-sensitive adhesives (PSAs), is typically measured using probe tack tests.
• Accurate tack measurement is challenging with thin PSAs due to uneven contact from cylindrical probes.
• Spherical probes offer better reproducibility, but contact area effects on tack performance require consideration.

Purpose of the Study:

• To investigate the influence of contact area and PSA thickness on tack measurements.
• To determine the relationship between adhesive stress, strain, and contact parameters.
• To establish a reliable method for evaluating the maximum adhesive stress in PSAs.

Main Methods:

• Tack measurements were performed on PSAs of varying thicknesses and contact areas using a spherical probe.
• Video microscopy was employed to observe cavity growth at the PSA-probe interface.
• Theoretical estimations were developed, incorporating the effect of confining thin layers.

Main Results:

• Larger contact areas on thinner PSAs resulted in higher adhesive stress and greater strain.
• Maximum adhesive stress was independent of contact pressure but correlated with the contact radius to PSA thickness ratio.
• Cavity growth at the interface consistently coincided with the point of maximum adhesive stress.

Conclusions:

• A criterion based on cavity growth effectively evaluates maximum adhesive stress in PSAs.
• Experimental results align with theoretical estimations that account for thin-layer confinement.
• The study defines "ultimate tack strength" as a material property independent of PSA thickness and contact area.