Ink-Water-Paper Interactions in Printing: An Updated Review, 2006 TAPPI Advanced Coating Fundamentals Symposium

Ink setting is now being examined as a function of the type and amount of coating binder and pigment. Our understanding of the substructure of the ink and its influence on ink gloss has improved. There is a growing understanding of the many types of coated print mottle, involving different paper and press properties. The particular problem of backtrap mottle is now believed to be the result of variations in the micropore structure of the coating. In turn, the chief cause of variations in micropore structure may be variations in coating thickness and mass distribution. Binder migration is no longer considered to be a problem of itself. We are beginning to understand small-scale interactions between ink and uncoated paper on the scale of paper surface pores. Inks are now being examined at high speed in the printing nip, including inks containing emulsified fountain solutions. However, we still lack knowledge on how to quantitatively measure and control these problems, and we also lack a full understanding of the key paper factors controlling print quality, and the methods to measure and control them. In coated papers, there has been progress in understanding how ink components interact with coating components. Ongoing developments in advanced instrumental techniques such as confocal microscopy, X-ray tomography, and even synchrotron spectroscopy – combined with advances in image analysis techniques to process the huge amount of information provided – are helping us to understand the paper and coating structural issues involved.