ABSTRACT
Tack is a characteristic of amorphous high polymers above the glass transition temperature (Tg) only. In terms of physical properties the Tg represents the temperature range through which the polymer changes from a hard, glassy state into a liquid, rubberlike state. The structure of the low molecular weight resin is very important to its compatibility with elastomers, and consequently to its effect on the viscoelastic properties and performance as pressure-sensitive adhesives (PSAs). The stress-strain behavior of multiphase rubbery polymers can be adequately modeled by the Mooney-Rivlin equation as an elastic network or using the Guth-Gold equation relating the stress level to the hydrodynamic effects of the styrene blocks, considered as a filler. Pressure-sensitive adhesives are very low-Tg polymers in a continuous fluid state with low viscosity. Thus PSA coalescence above the Tg is given at all temperatures. Low viscosity requirements imply low molecular elastomers as raw materials for hot-melt PSAs the toughness of hot-melt PSAs is also low.
