The effect of process parameters on product quality of rotogravure printing

This paper describes an experimental investigation into the process paramet er effects on product quality in rotogravure printing. A production printin g press was instrumented for the measurement of parameters including strate gic temperatures, speeds and web tension. Through-the-run analysis was used to evaluate the fluctuation of the press parameters and the product qualit y. The trials indicated the parameters where process control is important a nd allowed the elimination of several parameters, including ink drying, fro m the main experimental programme. The parameters selected for the main exp eriments were those most often used for control purposes, or those that wer e varied between print jobs. Orthogonal array experiments were used, as the se allow the simultaneous variation of several parameters and the investiga tion of interactions between parameters. The experiments were performed usi ng 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 im age areas using spectrophotometry. The experiments highlighted the sensitiv ity 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 bla de load and impression pressure had negligible impact. No interactions were found between any of the parameters investigated. For viscosity change, an alysis of the printed image confirmed the importance of hydrodynamic mechan isms, but it was not possible to isolate ink dilution. For doctor blade ang ular setting, hydrodynamic behaviour appears secondary to cell transport an d release mechanisms. This latter mechanism requires further investigation in order to establish a clear understanding.