Study On Preparation, Characterization And Pressure-Sensitive Properties Of Silica-Sol/Polyacrylate Composite Latexes

Water-based polyacrylic latexes have been widely used as pressure-sensitive adhesives (PSAs). They can be easily tailored to control the polymer conditions, and equally important, they have a competitive cost. Furthermore acrylic PSAs, by virtue of their saturated backbone, have superior environmental stability and greater resistance to oxidation when compared with rubber-based PSAs. They have super adhesive ability for all kinds of materials. But the acrylic pressure-sensitive adhesives have bad integrate adhesive properties. In recent years, great efforts have been dedicated to supply further integrate adhesive ability by the addition of the inorganic materials. The silica/polyacrylate core-shell latexes are prepared through semi-continuous emulsion polymerization using nano-silica as core and acrylate polymer as shell. But this method is relatively complex, and the latex may be not stable. The silica-sol/polyacrylate core-shell composite latexes are prepared using non-modified silica-sol and acrylate monomers.In this paper, the composite latexes of silica-sol/polyacrylate were prepared via semi-continuous emulsion polymerization. The influence of diameter of silica-sol, the content of silica-sol, the monomer content in the shell layer and the MMA content in the shell layer on the emulsion polymerization and adhesive properties were studied. The morphology of the core-shell latex particles was determined by transmission electron microscopy (TEM), and the diameter and its distribution of latex were measured by dynamic light scattering (DLS). The results showed that the instantaneous and overall conversion were all high. Comparison of theoretically calculated particle diameters with those measured experimentally showed that the particles had grown without significant secondary nucleation occurring. The molecular movement of PSAs was characterized by DMA, and calculated the entanglement molecular weight (Me) according to the empirical equations. The gel contents were measured according to the swagging method at room temperature to interpret the relationship between the properties and internal structurs. With a small addition of the silica-sol to the core layer in composite latexes, the shear resistance increased greatly, and loop tack and peel force kept relative high level. ForP(BA-co-AA-co-MMA) shell copolymer, the shear resistance was improved further, while the loop tack decresed, and the peel force passed through a maximum value.