In this thesis the Walker and Fetsko ink transfer equation was used as an analytic tool to determine how the physical properties of the transfer surface change from printing on unprinted paper to overprinting on another wet ink film. The equation has three parameters, b, k, and f, which indicate what is happening in the nip of the press during the moment of impression. Parameter b represents the maximum absorptive capacity of the paper, parameter k is highly reflective of printing smoothness, and parameter f represents the fraction of free ink film which splits to the paper surface. The I.G.T. Printability Tester was used to simulate the wet-on-wet trapping which occurs on a lithographic press. Heatset inks and uncoated paper were used to conduct the testing. Application of the equation to the experimental data showed that the surface in wet-on-wet trapping is less absorbent, smoother, and increases the fraction of free ink film which splits to the paper in comparison to the surface of the unprinted paper. The first two observations are explained simply by considering that in wet-on-wet trapping the paper porosity and the low spots on the paper surface are filled by the first-down ink film. The third observation regarding parameter f is explained by considering a model in which the ink film cavities expand and the ink film ruptures more readily in areas of high vehicle concentration and low viscosity. In printing to the unprinted paper the vehicle drains more quickly into the paper than the pigment particles due to its lower viscosity and lower molecular weight. Thus there is a higher concentration of vehicle nearer the paper surface, causing the split to occur here. On the other hand, the surface in wet-on-wet trapping at the moment the second ink film is transferred is not very absorbent. Therefore, the vehicle does not drain that quickly into the surface, causing the viscosity of the ink film to be the same throughout, which tends to create a fifty percent split.
Print Media (BS)
Department, Program, or Center
Printing Industry Center (CIAS)
Powell, Sam, "An analysis of wet-on-wet trapping using the Walker and Fetsko ink transfer equation" (1987). Thesis. Rochester Institute of Technology. Accessed from
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