| Pressure Sensitive Adhesives (PSAs) based on low T g acrylics are widely used in tape and label applications due to their optical clarity, UV and oxidative stability and migration resistance. Aqueous tackifier dispersion could be added into acrylic emulsion to increase peel and loop tack of the film. Adding high Tg rosin ester tackifier into poly(2 ethyl hexyl acrylate-stat-vinyl acetate-stat-dioctyl maleate-stat-acrylic acid) emulsion resulted in film with shear holding power 4 times lower than that of the neat emulsion film because the inability of the linear polymer to entangle with the microgels as a result of tackification.; Model emulsion based on poly(2 ethyl hexyl acrylate-stat-acrylic acid) and poly(n-butyl acrylate-stat-acrylic acid) were synthesized to study the effect of molecular parameters on adhesive performance. It was found that by having low level of isobutoxymethylacrylamide (IBMA) in the copolymer enabled interlinking of the microgels by the linear polymer in the film when heated provided that the weight average molecular weight (Mw) of the linear polymer was at least 2 times the entanglement molecular weight (Me) and the molecular weight between crosslinks (Mc) of the microgel was greater than Me. This would result in significantly higher shear in acrylic emulsion film compared to that without any interlinkages.; High gel containing acrylic lattices were blended with gel free acrylic-stat-IBMA latex at various weight ratios. It was found that the emulsion blend film could show higher peel, loop tack and shear compared to those of the acrylic solution film provided that the above conditions were met. The reactivity of the microgels toward IBMA could be enhanced by increasing surface acidity of the latex particles by either adding Amoniurn Persulfate late in the emulsion polymerization or using higher level of acrylic acid. |
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