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Effect of web tension on load- and moisture-induced waviness
Karlstad University, Faculty of Technology and Science. (Paper Technology)
2005 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 20, no 2, 237-241 p.Article in journal (Refereed) Published
Abstract [en]

Paper is affected by both tension and moisture. When paper is tensed between rollers, shrinkage and expansion are restricted. Waves can then appear on the paper web. These conditions are assumed to be partly responsible for the waviness problem in heatset web offset printing. The printed papers then exhibits a wavy shape, with corrugations aligned in the printing direction. The waves caused by mechanical loading and moisture were evaluated. The change in topography of a paper web under tension was studied during moistening and drying. A 70 g/m2 paper was tested at tension levels between 480 N/m and 1400 N/m. The moisture uptake was 3 – 5 g/m2. The wavelength of the topography decreased with increasing web tension. The tension had no significant effect on the height of the waviness. Four weeks storage of the samples did not yield any significant relaxation of the waviness amplitude.

Place, publisher, year, edition, pages
2005. Vol. 20, no 2, 237-241 p.
Identifiers
URN: urn:nbn:se:kau:diva-6320OAI: oai:DiVA.org:kau-6320DiVA: diva2:347912
Available from: 2010-09-03 Created: 2010-09-03 Last updated: 2010-11-15Bibliographically approved
In thesis
1. Laboratory method for the study of moisture-induced waviness in paper
Open this publication in new window or tab >>Laboratory method for the study of moisture-induced waviness in paper
2004 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Paper that is subjected to moisture undergoes dimensional changes. It expands during moistening and shrinks during drying. When the paper is under tension between rollers, the effects are complex since shrinkage and expansion are restricted in the width direction. Waves can then appear on the paper web. This can be a problem in heatset web offset printing. The problem is known as waviness or fluting. The printed papers exhibit a wavy shape, which is visually disturbing due to light reflections which create glossy streaks. The aim of the work described in this thesis was to develop a method suitable for studying the moisture- and tension-induced waviness. Experiments were carried out on a laboratory scale to study how such waves develop during moistening and drying. The experimental setup was based on a modified tensile tester. A CCD camera and image analysis based on the STFI-OptiTopo technique was used to characterise the waviness. Moistening and drying were achieved by changing the surrounding air humidity. The method was used to study the effect of moisture uptake by the paper, and to evaluate the effect of tension on the waviness. It was found that increasing moisture resulted in a higher waviness amplitude, but that the web tension controlled the wavelength of the waviness. A high tension gave rise to a shorter wavelength. The measured wavelength was compared with a previously suggested model and the predicted wavelength was about twice as high as the measured wavelength.

Abstract [en]

When paper becomes damp it can develop waves which can be a problem with heatset web offset printing. Paper with waves may have glossy streaks after printing. Laboratory experiments studied the effect of moisture uptake by the paper. Readings were taken at a range of air humidities. The effect of tension on the waviness was also measured. The waviness was characterised using a charge coupled device (CCD) camera and the STFI-Packforsk OptiTopo technique to analyse the images. When the humidity was increased the amplitude of the waves increased. A high tension resulted in shorter wavelengths. Results from a previous model were used as a comparison.

Place, publisher, year, edition, pages
Karlstads universitet: Karlstad, 2004. 33 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2004:42
Keyword
method, moisture, paper, paper web, wavelength, waviness
National Category
Paper, Pulp and Fiber Technology
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-6425 (URN)91-85335-11-8 (ISBN)
Presentation
2004-11-05, 10:00 (Swedish)
Supervisors
Available from: 2010-10-04 Created: 2010-09-28 Last updated: 2010-10-04Bibliographically approved

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