Impact of ink/paper interactions on printability of aqueous publication gravure inks - Part IV. Ink transfer and spreading on paper

Spreading of two inks of different surface tension on LWC paper was evaluated by a dynamic contact angle technique. Effect of paper roughness on ink spreading and the relevance of "free" spreading to the real "on press" situation were briefly discussed. It was found that no "free" spreading of the ink should take place on the press even at maximum ink transfer. Additional "free" spreading of the ink due to ink sagging when the web travels from the nip to the dryer is possible only in the direction opposite to the direction of printing. Based on the analysis of dot gain a mechanistic picture of ink transfer was proposed. Both, capillary flow of the ink in the grooves, formed between the paper and land area of the printing cylinder, and mechanical squeezing of the ink between the printing cylinder and impression roller are responsible for significant dot gain in gravure printing.