Suspension-polymerized Latex as an Additive for Surface Sizing and Its Effect on Fold Cracking of Coated Paper

As an approach to decrease the fold cracking of coated paper, suspension-polymerized (SP) latexes were developed and tested as a surface sizing additive. Styrene, ethyl acrylate, butyl acrylate, acrylic acid, and itaconic acid were used as monomers for the SP latex, and oxidized starch and polyvinyl alcohol were used as stabilizers. The SP latexes were found to be more stable against the charge neutralization by salt solutions and flocculation by cationic polyacrylamide than conventional styrenebutadiene and styrene-acrylate latexes, and they were highly compatible with the conventional surface sizing solution. The effect of using SP latexes as a surface sizing additive on the mechanical properties of the paper was examined. The SP latexes had greater tensile strength and extensional properties than the emulsion-polymerized latexes, which suggested their potential applicability for reducing the fold cracking of coated paper. A mill trial was performed to test the use of SP latexes as a surface sizing additive, and the results showed that they had a positive effect in reducing the fold cracking of coated paper.