Summary

Press blankets are sometimes called the soul of the offset printing process. Their influence on print quality can be realized when comparing the printing results from di-litho presses with those from offset presses. The transfer of the image from the plate to the paper surface via a rubber blanket is not only protecting the plate against wear, but first of all is providing the smoothness and flexibility to the transferred image for a better penetration and fixation to the paper substrate. To optimize this effect it is necessary to know the relevant blanket parameters. That’s why NATS and IFRA have started a research project in cooperation with the Swedish Graphic Arts Research Laboratory (GFL) in Stockholm, Sweden, on this matter. The results have shown that surface hardness and compressibility are the parameters which have the greatest influence on print quality, with harder and less compressible blankets leading to the optimum. The surface structure has the highest effect on print contrast, measured with a 70% screen area, but also influences the ink and water feed level. To a certain extent laboratory tests can be used to predict the behaviour of blankets in production presses as far as print quality is concerned. We hope that the explanations given with this report will serve our members in their decision making process when relevant printing problems occur and a new press blanket type has to be chosen.