Chitosan for Dye Fixation of Highly Lightfast Gelatine Coatings

Abstract

Fixation of the ink is one of the important factors determining the quality of inkjet media for photo glossy applications as well as for mat inkjet paper. In our previous paper, presented at the NIP 19, we have shown that depending on the IEP (number of acidic and basic groups) of gelatine and the pH of the coating formulation, some dye fixation can be achieved by gelatine itself. To further improve dye fixation quaternary amines, like poly-DADMACs, are very often used. Unfortunately, besides affecting the image quality, these compounds reduce the lightfastness of the prints. GELITA has now tested various chitosan types as dye fixing agents. We tested the compatibility of these compounds to different gelatine types. These mixtures show substantial differences in viscosity. Some low viscosity formulations, which are suitable for coating, have been identified. Coatings on polyethylene base paper have been prepared with these gelatine/chitosan mixtures. The coatings show excellent dye fixation and give good image qualities and dry time. We tested the lightfastness of these papers and compared them to gelatine coated papers containing other dye fixing agents. Here we found a much better stabilization of the dyes by the gelatine/chitosan formulations. Therefore chitosan as an additive for gelatine coatings improves dye fixation of the coating and keeps the lightfastness of the image at the high level observed for pure gelatine coatings. A patent application about these findings has been recently filed.