Investigation into the distribution of ink components on printed coated paper: Part 1: optical and roughness considerations

Changes in the composition of an offset lithographic ink film have been studied as a function of the substrate porosity. Using optical and topographical characterisation techniques, evidence is presented that the surface composition of the ink film varies with the rate of ink vehicle removal. In the case of microporous substrates there is fast removal of ink oils which leads to concentration of organic pigment, consequent depletion of resin binder and hence less glossy ink films. The resulting surface is therefore optically rough. In contrast, substrates that give slower removal of the ink vehicle generate a high gloss due to comparatively optically smooth ink film which has a lower pigment concentration at the surface. In Part II further evidence in support of this mechanism is presented using surface analytical spectroscopic techniques.