Concentration and conductivity of fountain solutions: a study of the relationship between concentration of materials/electrochemical conductivity of Fountain Solutions and Offset Lithographic Plate Performance

Abstract

The transfer of the image to the substrate in lithographic printing relies very much on the characteristics of the fountain solution. The quality or desensitization potential of the solution has always been determined by measurements of pH ; and by the more recently proposed method of electrochemical conductivity. The purpose of this study was to determine which of these techniques most suitably measured the efficiency of the solution. Since the fountain solutions were always changing during the press run, the response of pH and conductivity to changes in concentration were used as criteria for measuring their suitability. The effect on print quality variables were also used as a criterion. The design of the experiment was such that the concentration/conductivity was artificially changed by addition of sodium chloride and potassium citrate salts as well as gum based concentrate and alcohol. The investigation included the study of the physical and plate performance characteristics of the solutions at different concentrations. Relationships and comparisons were made on the properties of pH, conductivity, density, surface tension, viscosity, print sharpness, resolution, resistance to scum, contrast and the number of fogged patches that printed. Experimental work was conducted under controlled conditions and depended on the assumption that the conductance of the solution will be directly dependent on the concentration (and type) of materials and inversely related to the viscosity of the solutions. The pH was assumed to be independent of concentration and viscosity of the solutions. The results obtained were graphically and statistically analyzed. Equations that will permit the estimation of physical and print qualities were also obtained as a step towards accomplishing the objective of calibrating the fountain solutions . It is concluded that under some conditions conductivity is a more useful measurement technique than pH. The concentration of the components of the solution certainly has effect on print qualities. The significance of the effect is determined by the nature of the materials and the extent of their concentrations. Further results indicated that an organic salt shows more compatibility with the solutions than an inorganic salt. While the results called for modification of the definition of a fountain solution, there was no evidence to reject the experimental model. Although acidic fountain solutions were used, the result on conductivity and pH agreed with previous investigations and conclusions on alkaline fountain solutions