Pressure sensitive adhesives tackification

In the earlier art, there was some consideration that partial incompatibility of the tackifier resin with the rubber was responsible for the appearance of tack, but this no longer is seriously held in light of continuing studies by many investigators. Aubrey [38] has addressed this in his review of the mechanism of tackification and the viscoelastic nature of pressure sensitive adhesives. Chu [39] uses the extent of modulus depression with added tackifier as a measure of compatibility. Thus in a plot of modulus vs. tackifier concentration, the resin that produces the deepest minimum is the most compatible. On this basis, Chu rates the following resins in order of compatibility for natural rubber rosin ester > C-5 resin > a-pinene resin > p-pinene resin > aromatic resin. 

Besides the higher volume pressure sensitive adhesives discussed above, the industry also uses other synthetic elastomers as the base component for PSA formulation. Most of these elastomers require some form of tackification to make the materials tacky. However, a few materials are low enough in Tg and sufficiently compliant to be useful without requiring compounding with tackifiers. 

A review of the traditional use of resins as tackif iers for elastomers in solvent-applied adhesives is presented. Following is a discussion of how this technology is extended to water-based systems. Data is discussed on the use of various backbone polymer latexes, modified with the proper resin emulsions to achieve pressure—sensitive adhesive properties. Recommendations are also given for the proper choice of resin type to achieve optimum properties with each specific class of elastomer. 

---