THERMOMECHANICAL PROPERTIES OF THE POLYMER BINDER AFFECTING THE PROCESSABILITY, STRUCTURE AND PROPERTIES OF DRY SURFACE TREATED PAPERS

摘要

The dry surface treatment (DST) method differs significantly from the conventional pigment-coating processes. Thecoating layer is applied to the substrate in the form of dry powdery particles and fixed on the surface with athermomechanical treatment in a heated nip. In DST, the wetting of the base substrate is avoided, coatingapplication is done without contact with the substrate and immediately to the required coat weight without anyintensive coating penetration into the substrate.In this paper we present the possibility to modify and control the structure and properties of the two-component (thecoating system consists of pigments and a latex binder) dry surface treated papers. It was noted that processability inDST, as well as the properties of the coated paper, were significantly affected by the thermomechanical - thetemperature dependent viscoelastic - properties of the latex binder. It appeared beneficial to have a high stiffnesspolymeric binder, particularly in the temperature region above its main (glass) transition, corresponding to a high gelcontent. This choice of binder decreased DST paper sticking to the heated roll during the fixation step of the coatingand improved the surface strength of the final product.It was found that DST papers are in many respects comparable to conventionally wet-coated papers with similaramount and type of coating components. In the case of DST papers, the coating structure appeared however to bemore open, especially with high gel latexes. This could be an important variable when adjusting to different printingmethods, e.g. with or without drying capacity. Furthermore, coating penetration into the base paper was suppressedby employing the DST.