In 1958, Preucil suggested an equation to calculate ink trap based on measurements of a printed sheet with a densitometer. Preucil's equation was based on the additivity rule and the proportional rule. However, these rules do not hold in all cases. Several alternative equations have been suggested. This study intends to examine the effectiveness of three ink trap equations using densitometry by means of comparing the calculated values to those measured by the gravimetric method. An attempt is also made to estimate the value of maximum printable density, Dm, in Hamilton's equation. The theoretical basis of each equation is briefly introduced. The causes attributing to the failure of additivity and proportionality are discussed as well. Also reviewed are several methods for measuring ink trap, such as colorimetric, spectrophotometric, and magnetic methods, and factors involved in the efficiency of ink trapping. In the experiment, two newsprint and one coated paper were printed with cyan, magenta, and yellow ink in a simulated wet-on-wet condition on the IGT printability tester. Each ink had a specific tack. The second-down inks were transferred on the first ink layers with low, medium, and high thickness. The percent ink trapping on printed strips were then calculated by both the densitometric methods and the gravimetric method. The factors causing poor trapping and back-trap in the experiment are discussed. Preucil's equation was found to correspond better with gravimetric trap values than Brunner's equation. However, both under estimated ink trap in the majority of the tested conditions. As the ink trap measured gravimetrically increased, the discrepancy of ink trap calculated by Preucil's equation increased. This applied to Brunner's equation as well, but not obviously to Hamilton's equation. Hamilton's equation proved to reduce the differences between gravimetric ink trap and densitometric ink trap significantly. A Dm value of 1.59 for newsprint A, 1.99 for newsprint B, and 2.5 for coated paper resulted in the greatest accuracy over the conditions tested. When the Dm value approaches infinity, Hamilton's equation becomes the equivalent of Preucil's equation. The experiment suggests that a range of Dm values between 1.5 and 2.5 was suitable for the tested conditions. For future research, a larger selection of various types of papers and inks are needed to specify a Dm value for general conditions. It might also be useful to specify a theoretical maximum printable density for general conditions, with which the maximum printable density of a given paper can be compared. Thus, the reproduction quality of the paper can be predicted before the printing is conducted. Since the effects of back-trap and ink contamination influence the accuracy of Hamilton's equation in this experiment, studies for compensating this inaccuracy are suggested.
Library of Congress Subject Headings
Printing ink--Testing; Color printing--Technique--Analysis; Densitometry
Department, Program, or Center
School of Print Media (CIAS)
Hsu, Jui-lin, "A study of ink trapping comparing gravimetric and densitometric methods of measurement" (1989). Thesis. Rochester Institute of Technology. Accessed from
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