Crosslinkers significantly improve the performance of synthetic pigment binders in coating colours. They increase the water resistance of the paper coating by immobilising the water soluble co-binders. At the same time a positive influence on the printability can be expected by increasing the wet-pick resistance. Alternatively crosslinkers allow a reduction of the pigment binder level which reduces the tendency of blistering, while the water resistance remains unchanged. Typical crosslinkers are amino resins, glyoxal resins and zirconium salts. For special applications epoxy resins are also used. Chelating of the hydroxyl-containing polymers is postulated to be the crosslinking mechanism for the zirconium salts, other crosslinker types react to form covalent bonds. Properties of the different crosslinker types are presented. Taking melamine resin as an example the influence of increased concentrations on whiteness and wet-pick is described. Furthermore it is shown, that most of the crosslinker added is retained in the final paper.
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