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Topographical micro-changes in corrugated board production: effects on flexographic post-print quality
KTH, School of Computer Science and Communication (CSC), Media Technology and Graphic Arts, Media.
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The appearance and design of a package are key properties to attract and to focus the attention of a customer. Print quality contributes to a great degree to achieve these requirements. Most critical perceived in terms of quality are print defects like mottling, gloss and stripiness, which all appear in the printing of corrugated board. Stripiness is especially critical because it is a defect directly caused by the corrugated board construction. A further cause can be generated by the production process of corrugated board. Pre-studies by Odeberg Glasenapp (2004) revealed a difference in surface micro-roughness between the regions on the peak line of the liner and the regions in the valley between two peaks of the corrugation. This knowledge was the basis for the work described in this thesis.

In a first stage, laboratory trials were conducted with sets of coated and uncoated samples of various grammages. The trial was set-up in order to simulate the conditions in the corrugator as closely as possible. In the evaluations, it was found out that the settings were too high. For that reason, the coated samples were influenced to a too high degree and needed to be excluded from further evaluations. With the uncoated samples, on the other hand, a change in micro surface roughness was detectable. The roughness is decreased on the peaks and the gloss appearance was the conclusion. The analysis of the printed samples focused on shifts in colour and print density. It is unclear if both are affected only surface roughness changes and/or by the typical corrugated board effect of washboarding.

A full-scale test was performed in order to confirm the results of the laboratory test. A test series was chosen with coated and uncoated outer liners. Contrary to the lab-test results, the uncoated grades showed no surface roughness changes. Instead, the coated samples were affected to a great extent. The changes in surface roughness and gloss appearance were similar to the lab-test. This confirms that the lab-test samples were exposed to heat, pressure and shear to a too high degree. The print analysis of the full-scale test did not agree with the laboratory test. Gloss lines were visually detectable, but they were difficult to measure. A reason could be that the ink is capable on forming an ink film layer on top of the surface of the paper. This would cover the micro roughness of the matt parts thereby creating an almost homogeneous glossy appearance.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , ix, 55 p.
Series
Trita-CSC-A, ISSN 1653-5723 ; 2007:21
Keyword [en]
corrugated board, liner, double-facer, double-backer, gloss, surface roughness, micro structure, wear, paper metal friction, flexo, ink-jet, print quality
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-4583ISBN: 978-91-7178-824-5 (print)OAI: oai:DiVA.org:kth-4583DiVA: diva2:12983
Presentation
2007-12-14, Sal D41, KTH, Lindstedtsvägen 17, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101116Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2010-11-16Bibliographically approved
List of papers
1. Topographical micro changes of corrugated board liners induced by heat treatment and their effect on flexographic print quality. In Advances in printing and media technology
Open this publication in new window or tab >>Topographical micro changes of corrugated board liners induced by heat treatment and their effect on flexographic print quality. In Advances in printing and media technology
2006 (English)In: ADVANCES IN PRINTING AND MEDIA TECHNOLOGY, VOL XXXIII / [ed] Enlund N, Lovrecek M, Zagreb: ACTA GRAPHICA PUBL , 2006, 279-287 p.Conference paper, Published paper (Refereed)
Abstract [en]

The effect of washboarding occurs very often in the Corrugated board production process. This is a problem since it creates stripy print images in the flexographic post-print, which are more disturbing than colour deviations or smaller print defects. Much effort has been devoted to locating the problem and trying to minimize it. However, no studies have been made of whether changes in the liner surface could cause such stripy images. The worst conditions that a surface, which is supposed to be printed can be exposed to, are friction, heat, pressure and moisture at one and the same time. Exactly these conditions prevail in the double baker of the corrugated board machine. Therefore, this study was set-up trying to simulate the conditions in the double baker in order to gather knowledge of which factor(s) influence and what to what magnitude. The topography of the sample Surfaces was measured and compared with the original, untreated surface. Furthermore, the treated and untreated samples were printed in the IGT-FI laboratory flexo-printer to gather knowledge about how the above factors influence the print quality. The print was finally evaluated with print density measurements.

Place, publisher, year, edition, pages
Zagreb: ACTA GRAPHICA PUBL, 2006
Series
ADVANCES IN PRINTING SCIENCE AND TECHNOLOGY
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-7840 (URN)000267935100026 ()978-953-7292-03-4 (ISBN)
Conference
33rd International Research Conference of Iarigai/International-Association-of-Research-Organization-for-the-Information-Media-and-Graphic-Arts-Industries Leipzig, GERMANY, SEP, 2006
Note
QC 20101115Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2010-12-06Bibliographically approved
2. Topographical micro-changes on corrugated board liners: A comparison between laboratory and full-scale effects
Open this publication in new window or tab >>Topographical micro-changes on corrugated board liners: A comparison between laboratory and full-scale effects
2007 (English)In: Proceedings of the Technical Association of the Graphic Arts, TAGA, 2007, 367-382 p.Conference paper, Published paper (Refereed)
Abstract [en]

Printing on corrugated board is a complex process; many input variables affect the results to a varying extent. Not only the printing process itself has an influence on print quality; the pre-conditions of the substrate affect it as well. The topography of the liner surface is one of many important influence factors. As a first step, laboratory tests concerning the influence of the corrugated board production process on the liner surface topography were carried out (Rehberger et al., 2006). The result was that the movement of the liner on a hot plate, as compared to unmoved sheets, is the major criteria in surface roughness changes on coated and uncoated liners. Pilot trials have been carried out, since laboratory tests cannot be scaled up to real conditions. The first pilot trial with an uncoated liner did not result in any surface topography changes in conjunction with gloss, even though the corrugator was set to extreme temperature, pressure and speed conditions. These settings were adjusted to the pre-heater and double facer of the corrugator. The second pilot trial with coated liners, though, showed a clear impact on the topography of the liner surface. Using STF1-MicroGloss meter, the visually perceivable gloss lines have been analyzed and, as result, the average gloss line values computed. The results showed that production speed has the highest influence. The topographical measurements with AFM, FRT-MicroProf® and CLSM disclosed that these glossy stripes have a much lower nano-scale surface roughness as compared to the raw material. An extreme condition occurs when the corrugator is restarted after a full-stop. One collected sample from the start-up showed longish bubbles across the flute. Not only low-speed causes gloss lines, so do also the standard settings set by the operator for optimum corrugated board quality. Finally, printing trials in flexography and ink-jet were performed to determine the gloss influence of the substrate and whether the gloss lines still appear in the print. The print images were measured with the STFI-MicroGloss. The result for the flexographic printed images is that none of the gloss lines from the substrate appears in the print. The same is valid for the ink-jet printed images. Only the gloss from the print is recognizable. Further trials are necessary to shed light on the interrelation between substrate, gloss and print quality.

Keyword
Gloss, Liner, Roughness, Surface
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-7841 (URN)2-s2.0-52349089510 (Scopus ID)
Conference
59th Annual Technical Conference on Technical Association of the Graphic Arts, TAGA; Pittsburgh, PA; 18 March 2007 through 21 March 2007
Note
QC 20101115Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2010-12-06Bibliographically approved
3. Corrugated board production and its micro-scale impacts on the liner's topography
Open this publication in new window or tab >>Corrugated board production and its micro-scale impacts on the liner's topography
2007 (English)In: In VIIIth Seminar in Graphic Arts. Pardubice, Czech Republic, 2007Conference paper, Published paper (Refereed)
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-7842 (URN)
Note
QC 20101116Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2010-12-06Bibliographically approved

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