Print quality study of newsprint : Further development of the laboratoryoffset press at PAPRO

Sammanfattning: A laboratory offset press has been developed over the last five years at PAPRO for testing print qualityon newsprint, as at present, there is no good way for the mills to test this issue. In this project a comparisonhas been made between a laboratory offset press and a commercial press to see if the laboratoryoffset press can be used as a reliable test method or if a further development is needed.To evaluate the method, similar papers have been printed in both presses and compared using imageanalysis techniques. All together eighteen samples were tested which is enough to give comparableresults. The print quality showed a high variation, the values from the laboratory offset press and thecommercial press were not following the same trends. At present time the laboratory offset press needsome further development before it can be used as a reliable test method for halftone prints. Even sosome conclusions were made.The newsprint that has been used came from Norske Skog Tasman Mill (Kawerau), since the otheraim of this project was to do a repeatability study of their three existing paper machines to distinguishpossible differences in the production. The paper samples were taken from each paper machine on sixdifferent dates to give a representative result. This also gave the opportunity to compare the machinesbetween themselves. Comparison between the machines shows that the wire side gives a better andmore even result than the topside on the prints from the laboratory offset press. According to the resultfrom the commercial press the wire side shows a higher degree of variability. Samples from papermachine 2 and 3 were less variable and had the lowest standard deviation of grey level for solid areas.This suggests that newsprints from PM 2 and PM 3 give a more even print quality with a better inkcoverage.