Water-borne pressure-sensitive adhesives: Effects of acrylic acid and particle structure

Two types of core-shell pressure-sensitive adhesive latexes have been prepa red by semi-continuous emulsion polymerization: (a) soft-soft latexes with a poly(n-butyl acrylate) core and a poly[(n-butyl acrylate)-co-(acrylic aci d)] (PBA/AA) shell; and (b) rigid-soft latexes with a poly[(methyl methacry late)-co-(allyl methacrylate)] (PMMA/ALMA) core and a PBA/AA shell. Three s eries of soft-soft latexes were prepared in which: (i) the acrylic acid lev el in the PBA/AA shell was fixed at 5 mol% and the volume percentage (vol%) of the PBA/AA shell was varied; (ii) the vol% of the PBA/AA shell was vari ed, but with the acrylic acid level in the shell also being varied such tha t the total acrylic acid level was constant at 5 mol%; and (iii) the PBA/AA shell was fixed at 20 wt% of the total polymer and the acrylic acid level was varied from 0 to 49 mol%. In the rigid-soft latexes, the acrylic acid l evel in the PBA/AA shell was fixed at 5 mol% and the vol% of the PBA/AA she ll was varied. The latexes were adjusted to pH 5.5 using aqueous ammonia so lution before being used to form adhesive bonds between Melinex and glass, for measurement of shear resistance, and between Melinex and steel for meas urement of peel adhesion. The pressure-sensitive adhesive properties of the latex coatings are interpreted in terms of the effects of the changes in l atex particle acrylic acid content and particle structure on the interfacia l and bulk properties of the adhesive materials.