Correlation of ink viscosity and printability in offset lithography process on paperboard used in packaging
In the recent years, the demands for offset inks with better flow ability and viscosity have risen higher with the improvements of printing techniques. To ensure uniformity in printability sheet after sheet it is very important to maintain certain print conditions for that print job as approved by customers and use this data for future reference of printing. The quality of offset printing process depends on many chemical and physical specifications of the materials and components involved in the process. Most important being printing inks and its rheology. In this work, three process color cyan inks have been formulated with varying levels of viscosity with use of certain rheology modifiers. Trials on the printing machine were conducted using a systematic layout of test elements on a fully automatic offset lithography printing machine using a Solid Bleached Sulphite Board (SBS) and the print results were correlated to rheological parameters such as viscosity and thixotropy. The tone value increase (TVI) was measured and was correlated to viscosity and index of thixotropy. Higher viscosity yields lower dot gain and better color reproducibility. A mathematical relation has been established between ink viscosity, dot area and tone value increase. As the demands for packaging increases, the study about the ink rheology and its effect on print performance can help printers and ink manufacturers with better ink formulations to achieve precise print results.
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