Lars Kilian, Ph.D.
Senior Staff Scientist
Ashland Performance Materials

A New Approach to Measuring PSA Cohesive Strength Using a Texture Analyzer

Current commonly-used techniques to measure cohesive strength in pressure sensitive adhesives, such as Williams Plasticity and Static Shear (PSTC-7) can be time consuming, highly operator dependent and have poor repeatability. Recently, a stress relaxation technique was developed to address some of the issues cited above. The technique uses a Texture Analyzer to measure stress relaxation over a short period of time and then a relative force retention (FR) value can be calculated. This technique gives rapid and reproducible measurements of cohesive strength directly from 1 mil PSAcoated stock. These measurements exhibit a strong correlation to Williams Plasticity and shear tests. As a result, Force Retention may be predictive for key performance attributes, such as PSA converting ability and resistance to adhesive edge-ooze. Force Retention testing is applicable to all forms of coated acrylic PSA, including solvent-based (crosslinked and thermoplastic) emulsion-based, and radiation-cured PSAs. Force Retention allows direct comparisons between the creep resistances of all types of acrylic pressure-sensitive adhesives at the same coating weight. Our current test constraints include a minimum coat weight of 0.7 mil and the need for relatively incompressible facestocks, such as PET and BOPP. The FR technique has already found utility in accelerating product design evaluations by rapidly screening structure-property relationships such as molecular weight and crosslinking sensitivity, additive effects, and process repeatability. This paper will focus on the methodology, benchmarking comparisons and application examples of Force Retention. The most significant advantages of FR relative to shear and Williams Plasticity are increased quality of the measurements and reduced measurement times.