Roll-up Phenomenon in Woodfree Heavy Grammage Papers

Abstract

The intention of this thesis is to present and evaluate the phenomenon of roll-up formation, which is a problem experienced especially on the woodfree uncoated paper grades with high grammage. Roll-ups, which are known by various names amongst papermakers, tend to form at the printing houses during paper handling processes. The theoretical part of the thesis is concentrated on the application of traditional wear theories and on the scanning of essential paper properties and characteristics that affect the phenomenon. In the light of the theories presented, the development of a suitable wear test method is discussed. In the experimental part of the thesis, a self-designed pin-on-disc wear method is developed, and its suitability to the purpose is evaluated from the viewpoint of its practicality and reproducibility of the results. Finally, altogether 10 paper samples are tested with the new test set-up, and the test results are reflected to the results gained by various traditional laboratory tests. Results indicate, that the pin-on-disc test can be applied to the measurement of roll-up resistance. The main paper property to be in correlation to roll-up resistance is dry abrasion resistance. Top side surface roughness and internal bond strength present also weak correlation to roll-up resistance. Moreover, roll-ups are more usually formed to the top side of paper and roll-up resistance decreases when papers are slid in fibre cross-direction. In addition, pea starch in surface sizing increases roll-up resistance in comparison to corn starch.