Benefiting the environment with digital flexographic ink applications
Principle problems encountered during the pre-printing processes of paper are largely attributed to the toner adhesion properties. With this in mind, the various partners within the project measured toner transfer to paper and toner adhesion. They then compared their results, and established mutually accepted and improved methods for reliable implementation procedures for the future. Besides the toner adhesion properties, the print quality had to be characterised and this resulted in three methods being developed. One concerns the visual examination of the whole test chart with its classification according to merit. Another visual examination method concerns the microscopic view of the target showing toner squatter. The third method measures the line smoothness and edge sharpness by image analysis. Paper properties also had to be analysed, as had the simulation of the hot roll fusing stations with independent and reproducible fusing parameters. The influence that these parameters had on toner quality was observed, whilst comparisons between two toners printed on the same machine indicated low viscosity toner improved toner adhesion to paper. It transpired that toner transfer is governed by electrostatic charging of the paper surface, and that toner adhesion is governed by the surface energy of the paper. This in turn led to the qualitative and quantitative characterisation of toner adhesion properties and was benchmarked against the EN 12283: 1996, "Paper - Copy papers - Determination of toner adhesion" standard. The measurements, repeatability and the precision of flexographic ink applications have shown to demonstrate exemplary results as opposed to those obtained with the EN 12283 standard. With water-based inks being more eco-friendly than traditional offset inks for pre-printing applications, not only will printed-paper quality increase, but the environment will also benefit.