PITCH DEPOSITION IN NEWSPRINT MILLS USING CERTAIN KAOLIN PIGMENTS

A sharp increase in press section pitch deposition sometimes accompani es the use of calcined kaolin pigments to enhance the opacity and brig htness in some newsprint-related papers. This article reviews research reported in three previous papers that has led to the discovery of a new mechanism for pitch deposition. The cause of deposition appears to be tetrasodium pyrophosphate, a dispersant widely used for stabilizin g kaolin slurries. It can liberate aluminum from the kaolin pigment in to the aqueous phase of the slurry and raise the pH to values above 6. Under these conditions, sticky aluminum soaps can form through the re action of aluminum with the soap anions of fatty and resin acids prese nt in paper machine white water. Avoiding this type of pitch depositio n problem should be possible with other dispersants.