The comparison of densitometric measurement with gravimetric measurement of wet-on-wet ink trapping

Densitometric and gravimetric methods are employed to measure the percent of ink trapped in a wet-on-wet transfer. This study seeks to discover the relationship of the two methods and if there is a significant difference between the percent gravimetric and percent apparent trapping. An IGT Printability tester (Model-A2) with two printing discs is used to apply ink onto paper. When using the gravimetric method the amount of ink on the disc and ink transferred onto paper are weighed with an analytical balance. The author then calculates the percent ink trapping. When using the densitometric methods densities are measured by polarizing and non-polarizing reflection densitometers which are used to generate data to determine percent trapping. The author also applies an antilogarithm trapping formula to determine percent trapping. The experimental factors studied here are the three tack levels of both ink layers, which are defined as low, medium, and high; the three different types of paper, which are newsprint, uncoated paper, and coated paper; and the four measurement methods. These methods are gravimetric, apparent, polarizing apparent, and antilogarithm trapping. The study results reveal that there is significant difference between the four measurement methods. The regression analysis establishes the relationship equations between percent gravimetric and apparant trapping. All of the equations are rejected because they lack accuracy in predicting percent gravimetric trapping using percent apparent trapping. Improved equations for percent trapping on newsprint, uncoated paper, and coated paper are presented. These equations estimate the percent gravimetric trapping on the basis of densitometric data but they are complex, and therefore only useful in the laboratory at this time. The author also determines percent gravimetric trapping using densities in terms of the exponential function and establishes prediction equations of percent trapping for each type of experimental paper. Further study will be needed to develop equations useful to the printing industry