Investigation of the influence of different Isopropyl Alcohol (IPA) percentages in offset lithography and its impact on print parameters

Abstract

Isopropyl alcohol, or IPA, is extensively used in the fountain solution for offset printing in India. However, printers use varying amounts of alcohol in the fountain solution. This work aims to analyze the influence of different IPA proportions on print quality, providing practical insights for the industry. The research involved the meticulous preparation and testing of three fountain solutions containing 5%, 8%, and 12% IPA samples. The lab tested these solutions to measure their pH, conductivity, surface tension, water pick-up by emulsified ink, wet pick, wet repellence, and dynamic penetration. The lab tests recorded the values, which were later correlated with the results of press trials conducted on a 4-color Mitsubishi press using a specially designed 4-color sheet-fed test form. The press trials were performed using the three samples of fountain solutions, and ink and dampening duct rotations were recorded to note the amount of ink and fountain solution used as the percentage of IPA was increased. This was followed by densitometrical and visual analysis of the print samples to study the effect of changes in IPA proportion on print quality. The primary aspect of printing influenced by IPA was the ink-water balance and, consequently, water-interference mottling. Graphs were plotted for density, dot gain, contrast, and trapping, directly comparing 5%, 8%, and 12% IPA and establishing specific, consistent trends with the increasing IPA proportion. The final print results for the mottling index were checked with the PapEye Mottling Analysis tool. The samples showed a lower water supply and less IPA could prevent water-interference mottling, offering practical solutions for print quality improvement.