Journal of Adhesion Science and Technology, Vol.17, No.5, 703-723, 2003
Various ways to control the bulk properties of pressure sensitive adhesives
The widespread industrial use of pressure sensitive adhesives (PSAs) is based on the advantage that PSAs can maintain sufficient bond strength, as well as, if needed, they can also be cleanly removed. These two essential requirements must be balanced to be a good PSA, and are not obtained without an accurate, control of rheological properties. In this study, a new type of creep test is devised to measure the rheological behavior of thin film PSAs with high precision. Based on this technique, we studied four different methods to control the viscoelastic properties of PSAs. These are (1) control of the amount of crosslinking agent, (2) use of plasticizers, (3) adjustment of PSA film thickness, and, (4) construction of PSA double-layers. It was found that the levels of creep could be controlled over a wide range by adjusting the amount of crosslinking agent. Samples containing plasticizers behaved similarly to the PSAs with less amount of crosslinker (thus more mobile). The increase of film thickness also led to an increase of creep in a similar fashion as noted above. The creep behavior of the double-layer PSAs, composed of two PSA layers with different levels of crosslinking and thickness, followed a reasonable prediction: the total deformation, delta(t), Was always less than the amount predicted by the two-phase model in which the limits are determined by two single layers of soft and hard PSA; however, delta(t) was greater than the level of creep based on the one-phase model in which a complete mixing of crosslinker within the two PSA layers is assumed. In the last part, some characteristic creep behaviors of selected PSAs are discussed based on a linear viscoelastic model.