Effects of coating composition and folding direction on the fold cracking of coated paper

The effect of latex binder, pigment and folding direction on the fold cracking of coated paper was investigated. Image analysis technique was used to analyze crack area of coated papers in MD and CD, and the tensile strength and strain property of the coating layers were evaluated. CD folding gave larger crack areas than MD folding due to the anisotropy of fiber orientation. Use of a styrene/acrylate latex increased the strain of coating layers, which was attributed the low level of cross linking between the polymer chains. Clay gave significantly larger % elongations for coating layers than GCC. However, clay coating gave a larger fold crack area than GCC coating especially in the case of CD folding of a high grammage coated paper. The tensile strain of clay coated paper appeared to provide the delay in the time of crack initiation until the strain concentrated on the clay coating surface gave a rupture of both coating layer and base paper.