The influence of binders on coating layer structure and offset printing properties, 23TAPPICon

The mechanism of ink absorption by a coating layer is complex and highly dependent on the pore structure created by the blend of pigments and additives used in the coating process. The latex content, the amount of PVOH, and the size of the pigments can influence the pore structure by changing not only the total pore volume but also influencing the size distribution of these pores, which in turn changes the capillary forces involved in the absorption process that govern the interaction between the ink and paper. A recent development in paper coating formulations has been the introduction of ultra-fine ground calcium carbonates (ufGCCs) in the market, these finer pigments have been used to create faster ink absorption in formulations containing only calcium carbonate. The work here is focused on understanding how different types of pigment blends (GCC+ufGCC and GCC+Kaolin), as well as latex levels and types, influence the pore structure of a coating layer and as a consequence its absorption properties. It was divided into two parts both using a DOE approach to organize the experiments. The first part of the investigation used a fixed amount of SB latex while varying the pigment types and amounts. In the second experiment the pigment blend was fixed and the amount of binders was changed i.e. PVOH, SA, and SB latex. The coating layer characterized by porosimetry results was subjected to two industry standard printing tests, the Nancy Plowman Associates test (NPA) and the Ink Surface Interaction Tester (ISIT) alongside other common tests. The results show how gloss can be improved using ufGCC and that print gloss can be controlled by latex levels that influence the pore size distribution. The ISIT and NPA Test results agree with these findings.

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