The influence of pigment modulus on failure resistance of paper barrier coatings

Pigments are often used in water borne barrier coatings but tend to make the coatings prone to failure. The pigment properties effects on this issue is lacking in literature. In this work, coatings that used pigments with different moduli but with similar size and aspect ratio were characterized in terms of water vapor resistance before and after folding. Coatings with talc had better water vapor resistance than coatings with similar sized kaolin. Talc also limited the degradation of barrier properties when folded. Coatings with metalized poly(ethylene terephthalate) (PET) flakes had better failure resistance than coatings with similarly sized rigid mica. Both results are likely caused by the ability of the low modulus pigment to deform and allow for strain to occur in the pigment as well as the latex phase. Styrene-butadiene (SB) and natural rubber (NR) latex coatings had a better failure resistance than styrene-acrylate (SA) latex, which is likely due to their low glass transition temperatures and high strain-to-failure values. However, coatings with high amounts of SB or NR latex may lead to blocking issues in production. Adding kaolin into SA and SB latex mixtures resulted in improved water vapor barrier property and failure resistance.