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

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A laboratory offset press has been developed over the last five years at PAPRO for testing print quality on newsprint, as at present, there is no good way for the mills to test this issue. In this project a comparison has been made between a laboratory offset press and a commercial press to see if the laboratory offset 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 image analysis techniques. All together eighteen samples were tested which is enough to give comparable results. The print quality showed a high variation, the values from the laboratory offset press and the commercial press were not following the same trends. At present time the laboratory offset press need some further development before it can be used as a reliable test method for halftone prints. Even so some conclusions were made. The newsprint that has been used came from Norske Skog Tasman Mill (Kawerau), since the other aim of this project was to do a repeatability study of their three existing paper machines to distinguish possible differences in the production. The paper samples were taken from each paper machine on six different dates to give a representative result. This also gave the opportunity to compare the machines between themselves. Comparison between the machines shows that the wire side gives a better and more even result than the topside on the prints from the laboratory offset press. According to the result from the commercial press the wire side shows a higher degree of variability. Samples from paper machine 2 and 3 were less ...