APPROACHES FOR CHARACTERIZING INTERACTIONS IN PAPER COATING SUSPENSIONS

The interactions of clay particles with latices were characterized by determining the maximum packing volume fractions in aqueous suspensions and in dry coatings applied on an impervious substrate using a conventional latex binder and a latex containing functional groups designed to create interactions with clay. In addition, the changes in both gloss and reflectance over black during the drying stage of the coating suspensions were monitored and two critical solids volume concentrations were established that were then correlated with the volume fractions of the maximum packing determined above. Analysis of the flow curves confirmed that the addition of latex leads to the formation of bulkier structures when the latex interacts with clay. However, upon centrifugation all the suspensions, independent of their composition, gave similar packing behavior. In the dry coatings the addition of latex that interacts with clay resulted in enhanced void fraction, light scattering, and oil absorption rate, and lower gloss. The effect of the interacting latex on the properties of both the aqueous suspensions and the dry coatings tended to disappear at high latex content. A comparison of the values of concentration of maximum packing showed that the bulky structures formed in the wet suspensions collapse upon drying, the extent of collapse increasing with latex content. These results indicate that the information obtained from measurements made on the coating suspension cannot always be used to predict the properties of the dry coatings. © 1992.