Impact of non-uniform water absorption on water-interference print mottle in offset printing

Abstract

<jats:title>Abstract</jats:title> <jats:p>Print mottle is a serious and yet common print defect in offset printing. An imbalance between the feed of fountain solution and the ability of the paper substrate to absorb and transport this water away from the surface can cause moisture/water interference problems. In the study presented here, we have investigated the uniformity of aqueous absorption and coating structure of pilot-coated papers with different types and dosages of dispersants and linked this to print mottle and uncovered areas (UCA). In earlier studies, the print quality of these papers indicated that a moderate addition of excess dispersant caused ink refusal, ink-lift-off (ink-surface adhesion failure) and water-interference mottle when printing at elevated fountain feed. In the present study, we have shown that a majority of the samples with uneven water/moisture absorption and an uneven burn-out reflectance tended to have more severe printing problems related to surface-moisture/water.An aqueous staining technique was used to characterise the absorption non-uniformities. This method has been developed previously with focus on absorption of flexographic water-based inks but can clearly give relevant information also for offset printing, when it comes to moisture/water interference mottle.</jats:p>

Towards Expanding the Use of Paper Made from Recycled and Non-Woody Plants: Enhancing the Print Quality through the Application of Nano-Modified Offset Inks

“…The results are also influenced by the paper composition, fiber type, and surface roughness. The importance of the water absorptiveness and print stability in offset printing has already been investigated in [59][60][61]. In those studies, the influence of different types of papers with standardized and non-standardized water absorptiveness values on the requirements of the printing process, on the stability of the paper sheets during storage, and on the print quality were analyzed in detail.…”

Back-trap mottle: A review of mechanisms and possible solutions

“…Back-trap mottle is the most common type of print mottle and is typically the result of non-uniform ink absorbency across the surface of printed paper, which leads to uneven immobilization of the ink, non-uniform tack buildup, and splitting of the ink (Kim-Habermehl et al 1998;Xiang et al 1999Xiang et al , 2000Engström 2016;Thorman et al 2018). This results in a non-uniform ink transfer from the contact print image on the paper surface to the following printing blanket of the next printing units, which causes further uneven contact with the following paper surface throughout the subsequent printing units (Thorman et al 2018). Several research groups have reported the relationship between back-trap mottle and non-uniform surface porosity (i.e., the distribution of pores and clustering of closed areas) in paper (Kim-Habermehl et al 1998;Xiang et al 2000;Chinga and Helle 2003;Shen et al 2005;Preston et al 2008).…”

“…Water-interference mottle results from the imbalance between the amount of fountain solution or dampening solution applied to the paper surface and the ability of the paper to absorb this (Plowman 1994;Lie and Kolseth 2007;Preston et al 2008;Thorman et al 2018). Water-interference mottle can occur when only a single printing unit is used and with any ink formulation.…”

Indirect Ink Transfer for Offset Printing, Taking Into Account the Roughness of the Offset Printing Plate Surface

“…The uniformity of water absorption and the structure of the coating on pilot-coated paper with different types and dosages of dispersants have been studied [11]. It was found that most of the samples with uneven water-moisture absorption and uneven reflectance to burn-in tended to have more severe printing problems related to surface moisture/water.…”