Effect of Viscosity on Halftone Reproduction in Rotogravure Printing


Document ID: 
G.R.Davies, S.M.Hamblyn, T.C.Claypole and D.T.Gethin


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Photo, Member: 
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Rotogravure printing is still arguably the best reproductive method for high speed printing of quality publications, with the ability to print discrete dots of ink varying in size and volume creating the illusion of constant tone. The size and shape of the printed dots is dependant on a number of factors such as substrate, cylinder manufacture, cell shape and size and ink viscosity. Some print plants see viscosity as a suitable and applicable method for control of colour on the print by adding solvent to reduce the pigment concentration per unit volume; hence reducing the saturation. In addition some companies use higher solvent concentrations to increase the drying speed of certain types of solvent-based inks by speeding up the rate of evaporation. As part of a series of investigations into the consequence of changing process parameters the effects of viscosity changes in a solvent based ink printed on to a porous paper substrate were investigated. The result of viscosity reductions on the halftone dot reproduction was established by the use of spectrophotometric and image processing methods. As the viscosity was lowered the pigment concentration fell resulting in a reduction in the print density of the solid. However for the halftones reductions in ink density were to some extent offset by an increased flow of ink across the substrate, the result of which would be to lower the print contrast and image sharpness on the final print.

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