On the Mechanisms of Wet and Dry Strength of Paper Coatings: Part 1 - Experimental Studies, 2012 PaperCon Conference

Please Note: This document will be available in PDF format in the "My Electronic Documents" link on the home page once your order has been completed. Please make sure you have the latest version of Acrobat Reader. Click on the Acrobat Reader icon to check for the latest version, it’s FREE. To print a hardcopy of a PDF file correctly you must have a postscript printer. If you are not sure if your printer is a postscript printer please refer to your owner’s manual.

Purchase of electronic (downloadable) documents made at www.tappi.org by credit cards, followed by instant download CANNOT be cancelled. We do not offer refunds on electronic download documents.

A large experimental study aimed at a better fundamental understanding of the dry and wet strength of coating layers has been carried out, using in-plane tensile properties and water absorption kinetics of unsupported coating films. Experiments over a broad range of pigment volume concentrations (latex levels) were designed to investigate the impact of the pigment type, the coating structure, the pigment-latex adhesion and the polymer film cohesive strength. Results obtained with the unsupported pigmented films showed good correlation with the lab print tested dry and wet strength measurements of coated paper. Experiments comparing the ratio of the pigmented film strength to the strength of the polymer film in the dry and wet state showed that the adhesion between the latex and the pigment is weakened in presence of water. The results suggest that the coating failure mode in the dry state is more cohesive but that adhesive failure dominates in the presence of water. Higher levels of carboxylic acid in the latex were beneficial for dry strength, but reduced wet strength in high PVC films. Further experiments showed that the dispersant can introduce a water sensitive layer between the pigment and the binder resulting in a reduction of wet strength.