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MOLECULAR STRUCTURE, MECHANICAL BEHAVIOUR AND ADHESION PERFORMANCE OF PRESSURE SENSITIVE ADHESIVES

2000 Dahlquist Award Winner

Albrecht Zosel
BASF AG
Ludwigshafen, Germany

The adhesion performance of a pressure sensitive adhesive is determined by three properties: tack, peel strength and shear resistance. The shear resistance which characterizes the behaviour of an adhesive under static, long lasting stresses will not be discussed in this paper. The work presented here is focussed on the tack; but tack and peel strength are similar in several aspects, so that some conclusions from our studies are also valid for the peel strength.

Tack is a dominant property of pressure-sensitive adhesives which is defined as the ability of an adhesive to form a bond of measurable strength to another material under conditions of low contact pressure and short contact time. Tack is, thus, not a fundamental material property but depends on the test methods and the conditions of measurement.

The procedure for measuring tack is a two-stage process of bond formation and bond separation. During bond formation, contact in molecular dimensions between the adhesive and the adherend is established by deformation and flow as well as by wetting. The second step, the bond separation with a certain rate, is connected with deformation and crack propagation in the adhesive joint. Adhesion and tack are accordingly related to surface properties and to the mechanical behaviour. The latter correlation is the topic of this paper.