Influence of Molecular Structure on The Wetting Behavior during Probe Tack Testfor Crosslinked Polyacrylic Pressure-Sensitive Adhesives

Abstract

Tack properties of crosslinked poly（n-butyl acrylate-acrylic acid）（A）and poly（2-ethylhexyl acrylate-acrylic acid）random copolymers（B）with an acrylic acid content of 5 wt％ and various adhesive thicknesses（about 15～60μm）as pressure-sensitive adhesive（PSA）were investigated and the wetting behavior was discussed. Tack was measured by the probe tack test. From the temperature dependence, tack increased with adhesive thickness. Tack is affected by two factors: the development of interfacial adhesion and the cohesive strength of PSA. It was found that the increase of adhesive thickness improves both these two factors. Further, the interfacial adhesion can be divided into two kinds: the wetting of PSA molecules to adherend surface（the physical wetting）and the interaction between acrylic acid unit in PSA molecules with adherend surface（the chemical interaction）. The increase of adhesive thickness improves only the physical wetting. The physical wetting progresses gradually with contact time and its effect is B＞A, because the molecular mobility at 20℃ is B＞A from ¹H pulse nuclear magnetic resonance analysis. The effect of chemical interaction appears withshort time and its effect is A＞B, because A decreased the interfacial tension of water/toluene interfacemore effectively than B. The bulky 2-ethylhexyl group acts as steric hindrance for the interactionof acrylic acid unit in PSA molecules.