Pressure sensitive adhesive debonding

Pressure-sensitive adhesives form physical bonds with other materials upon brief contact and with light pressure. Examples include self-stick stamps, packaging tape, double-sided tapes, paper labels, and the ubiquitous Post-iE notes. Bond formation results from the polymeric material being able to flow under light pressure, thereby establishing good contact area with the substrate. The debonding step involves deformation of the polymeric material under stress (see Section 12.8.3), followed by separation from the substrate. The adhesives most often involve triblock copolymers such as poly(styrene-h/ock-isoprene-h/ock-styrene) or poly(styrene-Wodc-butadiene-h/ock-styrene), SBR elastomers, natural rubber, or acrylic copolymers (92). 

Most adhesive tapes are composed of a flexible backing (paper, plastic, cloth, metal foil, etc.) to which a pressure-sensitive adhesive has been applied to one side (both sides for double-sided tapes). Pressure-sensitive adhesives typically consist of a rubbery material with a modifying tactifier that may be applied to the tape by a solvent system, hot melt, or by other means. One would expect such materials to be sensitive to the mode of stress (tensile versus shear) in the region where debonding occurs. Furthermore, since tacky rubbers of the type used in pressure-sensitive adhesive are viscoelastic, one would anticipate material properties to be time- and rate-dependent. Are these expectations consistent with the observations from your simple peel test ... 

Rheological properties and interfacial properties interact in both the bonding and the debonding processes for adhesives including pressure-sensitive adhesives. In this section, we will examine some of the important requirements on both the interfacial properties and the adhesive rheology and how they are coupled. 

An effective pressure-sensitive adhesive must provide resistance to debonding from the substrate. However, in many PSA applications, (masking tape, for example) it is desired that the adhesive be removable with some moderate force. Unlike structural adhesives, stronger is not always better. It is also generally desirable that the PSA separate from the substrate and not fail cohesively within the bulk of the adhesive. In tape applications, it is undesirable for the PSA to separate from the backing, leaving adhesive residue on the substrate. 

The particular category of Pressure-Sensitive Adhesives (PSA s) where the polymer exhibit visco-elastic properties able to develop adhesion during the bonding step as well as cohesion to resist to the debonding. No physical or chemical transformation of the adhesive is required to form the bonded joint. 

Abstract The basic concepts, formulations, and test methods of pressure-sensitive adhesives are presented. The importance of interfacial interactions, viscous loss, and extensibility are stressed. The common rheological tests are described and the equivalence of deformation rate and test temperature is emphasized. The much longer time scale for bond formation versus the rate of deformation upon debonding in peel or tack is exploited by the formulator to optimize properties. The formulation principles and common ingredients for preparing acrylic- and rubber-based adhesives are described, and the performance capabilities of these two types of pressure-sensitive adhesives are contrasted. 

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