Offset printing technology makes use of a simple yet elegant technology which has made it immensely popular through the course of time. The fundamental idea behind it is the fact that oil and water essentially have different surface tension values making them immiscible substances. Offset inks have been designed keeping this fact in consideration and hence they are all oil based inks. But the advancement of machine manufacturing techniques and increased productivity has raised many more challenges for the ink designer. These inks need to possess several qualities making it usable at high speed press environments.
Conventional sheetfed offset inks dry using oxidative polymerization of the ink film on the substrate surface. In presence of atmospheric oxygen, a chemical reaction occurs which leads to an oxygen induced free radicle polymerization of the unsaturated vegetable oils present within the ink. In order to accelerate these processes usually a transition metal based drier1 is added during the formulation of the ink. But care has to be taken because if the percentage of drier is high then “skin” formation will occur on the ink while in the ink duct and on the ink metering rollers. To avoid adverse conditions as mentioned, ink designers typically use substituted phenol based compounds known as anti-oxidants2 which decelerates the rate of oxidative-polymerization reaction. This work presents a study towards achieving an optimum mixture dosage of drier and anti-oxidant in order to stabilize the ink while press run and also help in the drying process for the ink film on the substrate. Keeping most of the ingredients unchanged, the ratio of drier to anti-oxidant was altered using multiple drier and anti-oxidant combination, and the best suited ratio and combination was selected for designing the final ink which is suitable for being used in high speed printing presses.
The experimental data were plotted and the results were analysed. It was important to extract a pivotal co-relation between the ratio of drier to anti-oxidant and the drying time of the ink film on substrate, so that an optimum ratio for the two can be found. The results presented conclusively shows that there exists a strong co-relation between the drying time and ratio of drier-anti-oxidant. For multiple combinations of driers and anti-oxidants at different dosage levels, it was observed that “Ratio 4” was most suitable as it provided quicker drying times in most combinations except for “Drier 1 & Anti-Oxidant 1” combination, where “Ratio 5” was the optimum level for dosage. The work done clearly confirms that other parameters remaining constant, the drier/anti-oxidant ratio clearly affects the ink-film drying times of an offset ink and the optimum dosage of drier/anti-oxidant which will provide good drying capabilities to the ink given a fixed drier/anti-oxidant combination. Further analysis may also include the probable causes which lead to variations in drying time for an ink-film depending upon which drier/anti-oxidant family combination is used.