Details:
Summary:
It is known that one of the many factors promoting the formation of piling is the presence of calcium ions. Besides calcium carbonate filler, one of the potential sources of these detrimental ions is the Lithol Rubin molecule present in the magenta ink. Our objective was to determine the effect of chemical conditions on the potential contamination of the blanket and the wetting solution system by calcium ions present in the magenta pigment. We have used an ion selective electrode to measure the release or uptake of calcium by Lithol Rubin at different pH values and at different ionic strengths. The objective being to try and recreate the same conditions present in a web offset press. We have used a conductometric titration protocol to determine the amount of both carboxylic and sulfonic acid groups present in the Lithol Rubin sample. We have also characterized impurities that could interfere with the ion selective electrode using ICP-OES and the potential presence of free calcium ions. Results indicated that as the pH was lowered, the amount of free calcium in Lithol Rubin solutions was rising. The effect of the ionic strength was more complicated: release or uptake of calcium have been observed depending on reaction time. Based on these results, we have concluded that high ionic strength and low pH conditions could promote the dissociation of the Lithol Rubincalcium complex and the formation of deposits on blankets and in the wetting solution system.