The effect of cationic-anionic polyelectrolyte multilayer surface treatment on inkjet ink spreading and print quality

摘要

The focus of the work reported in this thesis was to study and to clarify the effect ofpolyelectrolyte multilayer surface treatment on inkjet ink spreading, absorption and printquality. Surface sizing with a size press, film press with a pilot scale coater, and spray coating,have been used to surface treat uncoated wood-free, experimental wood-free and pigmentcoatedsubstrates. The role of the deposited cationic (polydiallydimethylammonium chloride,PDADMAC) and anionic (sodium carboxymethyl cellulose, NaCMC) polyelectrolyte layerswith and without nanosilica, on liquid absorption and spreading was studied in terms of theirinteraction with water-based pigmented and dye-based inkjet inks.Contact angle measurements were made in attempt to explain the ink spreading and wettingbehavior on the substrate. First, it was noticed that multilayer surface treatment decreased thecontact angle of water, giving a hydrophilic character to the surface. The results showed thatthe number of cationic-anionic polyelectrolyte layers or the order of deposition of thepolyelectrolytes had a significant effect on the print quality. This was seen for example as ahigher print density on layers with a cationic polyelectrolyte in the outermost layer. The numberof layers had an influence on the print quality; the print density increased with increasingnumber of layers, although the increase was strongly dependent on ink formulation andchemistry.The use of nanosilica clearly affected the rate of absorption of polar liquids, which also wasseen as a higher density of the black dye-based print. Slightly unexpected, the use of nanosilicaincreased the tendency for lateral spreading of both the pigmented and dye-based inks. It wasshown that the wetting behavior and wicking of the inks on the polyelectrolyte coatings wasstrongly affected by the hydrophobicity of the substrate, as well as by the composition orstructure of the polyelectrolyte layers.Coating only with a cationic polyelectrolyte was not sufficient to improve dye fixation, but it was demonstrated that a cationic-anionic-complex structure led to good water fastness. A threelayeredstructure gave the same water fastness values as a five-layered structure. Interestingly,the water fastness values were strongly dependent not only on the formed cation-anionpolyelectrolyte complexes but also on the tendency of the coating to dissolve during immersionin water. Results showed that by optimizing the chemistry of the layers, the ink-substrateinteraction can be optimized.