The effect of process parameters on product quality of rotogravure printing

This paper describes an experimental investigation into the process parameter effects on product quality in rotogravure printing. A production printing press was instrumented for the measurement of parameters including strategic temperatures, speeds and web tension. Through-the-run analysis was used to evaluate the fluctuation of the press parameters and the product quality. The trials indicated the parameters where process control is important and allowed the elimination of several parameters, including ink drying, from the main experimental programme. The parameters selected for the main experiments were those most often used for control purposes, or those that were varied between print jobs. Orthogonal array experiments were used, as these allow the simultaneous variation of several parameters and the investigation of interactions between parameters. The experiments were performed using a typical commercial print run once the production of saleable copy had been completed. The analysis of the print quality was carried out in the image areas using spectrophotometry. The experiments highlighted the sensitivity of the process to changes in ink viscosity and the non-linearity of the response. Doctor blade setting was also found to be important, whereas blade load and impression pressure had negligible impact. No interactions were found between any of the parameters investigated. For viscosity change, analysis of the printed image confirmed the importance of hydrodynamic mechanisms, but it was not possible to isolate ink dilution. For doctor blade angular setting, hydrodynamic behaviour appears secondary to cell transport and release mechanisms. This latter mechanism requires further investigation in order to establish a clear understanding.