Physical Properties of LWC Papers and Gravure Ink Mileage Renmei Xu a , Alexandra Pekarovicova a , Paul D. Fleming a , and Valery Bliznyuk b a Center for Ink and Printability Department of Paper Engineering, Chemical Engineering and Imaging b Department of Materials Science and Engineering College of Engineering and Applied Science Western Michigan University Kalamazoo, MI 49008 ABSTRACT Paper properties, such as roughness, air permeability, pore size and their relationships to the ink mileage were studied. Ink mileage was measured using commercial toluene based gravure coated inks marked with trace metal carboxylates, which can be detected after printing by means of Inductively Coupled Argon Plasma (ICAP/ICP) Atomic Emission Spectroscopy (AES). Magenta ink was doped one metal carboxylate, while cyan and black inks were doped with another metal carboxylate. The amount of ink transferred was calculated from the ICP analysis of both wet ink and printed samples. Commercial LWC coated papers for rotogravure were used as testing substrates. Paper surface properties studied were air permeability (Parker Print-Surf (PPS) porosity), mercury intrusion porosimetry, and surface roughness, measured by PPS, Emveco stylus profilometer and Atomic Force Microscopy (AFM). It was found that compressed cells transferred more ink than elongated and normal cells. Paper porosity, permeability and pore size have more profound effects than surface roughness on amount of ink transferred to paper. However, the correlations between surface properties and ink transfer are not as clear as expected. Possible reasons could be the interaction between surface roughness and pore properties, or other unknown factors such as coating formulation and structure. .INTRODUCTION It is always a goal for printers to achieve desired print quality with little consumption of printing inks. Ink requirement is defined as the quantity of ink needed per unit paper surface area to attain a specific level of relative print density. Ink mileage 1 expressed as the number of square meters covered by a kilogram of ink is conceptually the opposite of ink requirement. 2 Variation in the ink film thickness affects ink density. Uneven contact between the ink layer and the paper surface is a reason for variation of ink film thickness, 3 and thus ink optical density, also known as print mottle. In rotogravure printing, ink spreading and penetration happen within a fraction of second. The ink behavior on the surface of paper has been found to depend mainly on roughness and permeability. 1,4 Therefore, it is very important to understand how these properties affect the ink mileage. Ink estimating charts have been used for many years to make the calculation of ink consumption. 5 These charts are based on the approximate number of thousand square inches that can be printed with a pound of a particular type of ink on a particular type of paper. In offset printing, the amount of ink transferred to paper is determined by weighing the amount of ink in ink pan before and after printing. The corresponding print