Effects of Starch on Latex Migration and on Paper Coating Properties

With increasing awareness of environmental protection and the surging cost of petroleum chemicals, eco-friendly polymer starches are being increasingly used as cobinders to partly replace synthetic polymer latex in the production of high quality coated papers. In this work, the influences of starch on latex migration and on properties of model clay coatings were investigated, in order to better understand interactions between starch and latex and their effects on coating structure development. The results showed that surface carbon content determined from XPS measurements decreased significantly with increasing starch content. This unexpected finding of lower surface carbon content for coatings of higher binder content was explained by assuming that water-soluble starch migrated to the surface would move back into the coating pores as an integral part of the aqueous phase, as the air-water interfaces recede from the coating surface into the capillaries during drying. It has also been found that gloss and porosity of the coatings decreased with starch addition, as expected. However, the K and N ink absorbency values increased with increasing binder content, contradicting literature results for coatings of sole binder systems. This finding was attributed to reduced binder migration to the surface, resulting in a more open surface structure, since surface carbon content decreased with increasing starch addition.