The Effect of Ink Jet Paper Roughness on Print Gloss

©2005, IS&T—The Society for Imaging Science and Technology pigment particle size distribution, particle shape, binder type, film shrinkage, drying conditions, coating holdout, and coating weight.6 Research groups studying the roughness and its effect on gloss have agreed upon the fact that common roughness numbers are insufficient to predict gloss.9 It sometimes occurs that the rougher surfaces have higher gloss. Among the classical roughness measuring methods, the Parker Print-Surf (PPS) method has been widely used in the paper and printing industries because of the possibility of measuring roughness at different pressures, 500–1000– 2000 kPa, to mimic the conditions at a printing nip. The PPS tester uses a contact air leak principle, measuring airflow between substrate in a 51 μm wide ring. It recalculates the airflow into a mean gap between the surface and the flat circular land pressed against it.10 The measurement obtained from all air leak instruments is called macroroughness. One key disadvantage is that these instruments lack the sensitivity to measure on a scale small enough to be relevant to printing. For example, a halftone dot can range from 20 to 60 μm in diameter, whereas various air leak measurements can span widths ranging from 51 to 13,500 μm.11 Therefore, the need for measuring microroughness is growing. Surface characterization using atomic force microscopy (AFM) is now possible.12–14 AFM was invented by Binnig, and introduced in 1985 by Binnig, Quate, and Gerber,15 as an offshoot from the scanning tunneling microscope (STM).16 Since then, AFM has rapidly developed into a powerful and invaluable surface analysis technique on both microand nanoscale. The sample surface is scanned with a sharp tip mounted on a cantilever. The small deflections of the cantilever are measured using a focused laser beam, which is reflected off the cantilever to a photodiode detector. The x, y, z piezoelectric scanner located under the sample provides the precise movement of the sample. The variation in voltage signals from the Introduction The worldwide importance of electronic print processes is constantly increasing. Multi-color ink jet technology is growing, especially for the home and office markets.1 A large and growing consumer market for ink jet has developed in packaging, publication, and specialty areas. The quality of ink jet printing is influenced by the printers in use, as well as by the physico-chemical properties of printing ink and print substrate. To mention a few, these interactions are influenced by interfacial charges, wetability, and adsorption phenomena. An ink jet recording sheet comprises a support such as paper, at least one ink receiving layer on the support, and a gloss providing layer formed on the ink receiving layer. The ink receiving layer consists essentially of a pigment and a binder.2–6 The gloss providing layer consists of a pigment and a synthetic polymer formed from a latex or water soluble polymer as a binder.2–7 Roughness, or smoothness, of paper is a very important property for print quality. Surface roughness is usually divided into microscale and macroscale components.8,9 Although there is not total agreement on the boundary between those two, we define the macroscale component as consisting of features larger than 10 μm which are usually due to poor fiber dispersion, ionic destabilization or flocculation, roughness of base paper, or insufficient coating or calendering. The microscale component consists of features considerably smaller than 10 μm, due to The Effect of Ink Jet Paper Roughness on Print Gloss