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Striping on flexo post-printed corrugated board
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. (FSCN – Fibre Science and Communication Network)
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Striping is the most common print non-uniformity on corrugated board. It is defined as periodic print density and/or print gloss variations parallel to the flutes. Corrugated boards are mainly printed with flexography, making striping a major concern for the flexographic post-printing industry. In spite of its long history, the basic mechanisms of striping have not been fully understood, and no concrete solution has been provided. The objective of this thesis is to obtain an understanding of the fundamental mechanisms behind and a solution to striping. Both experimental and numerical approaches have been taken in thiswork. Nonlinear finite element models have been constructed in both corrugated board and halftone dot scales to determine the pressure distributions in the printing nip. Ink transfer experiments have been performed to determine the print density vs. pressure relations. Parametric studies have been done for the effects of printing system variables and deformations. The results showed that striping is predominantly print density variations caused by pressure variations in the printing nip. The pressure variations are inherent to the corrugated board structure. Washboarding was shown to play a minor part in causing print density variations, but might contribute to gloss striping. A new printing plate design has been proposed to eliminate the pressure variations and hence the print density striping.

Place, publisher, year, edition, pages
Sundsvall: Mittuniversitetet , 2007.
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 26
Keyword [sv]
Kemiteknik
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-111Local ID: 5136ISBN: 978-91-85317-63-9 (print)OAI: oai:DiVA.org:miun-111DiVA: diva2:1920
Presentation
2007-10-25, 102, M, Holmgatan 10, Sundsvall, 10:00 (English)
Opponent
Supervisors
Available from: 2008-02-18 Created: 2008-02-18 Last updated: 2009-06-08Bibliographically approved
List of papers
1. Nip Mechanics of Flexo Post-Printing on Corrugated Board.
Open this publication in new window or tab >>Nip Mechanics of Flexo Post-Printing on Corrugated Board.
2007 (English)In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 41, no 17, 2129-2145 p.Article in journal (Refereed) Published
Abstract [en]

A finite element model of a flexo printing press has been developed and the material and geometrical properties of the sustem has been investigated. The results showed that it is the photopolymer and the top liner that have the biggest impact on the printing pressure variations.

Keyword
Flexo, Striping, Corrugated Board
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-311 (URN)10.1177/0021998307074135 (DOI)000249099200007 ()2-s2.0-34547522828 (Scopus ID)
Available from: 2008-12-11 Created: 2008-12-11 Last updated: 2016-09-26Bibliographically approved
2. Striping of Corrugated Board in Full-tone Flexo Post-Printing
Open this publication in new window or tab >>Striping of Corrugated Board in Full-tone Flexo Post-Printing
2008 (English)In: Appita journal, ISSN 1038-6807, Vol. 61, no 1, 35-40 p.Article in journal (Refereed) Published
Abstract [en]

Striping is a print defect that is often seen in flexo post-printing on corrugated board. It appears as lines parallel to the flutes of the corrugated medium (fluting). These lines are generally thought to be print density and/or print gloss variations. The objective of this Paper is to obtain fundamental understanding of the striping mechanism. Print density and print gloss have been determined as a function of printing pressure. Typical printing pressure variations have also been determined by a non-linear finite element method. A 2D reflectance mapping has been performed for printed corrugated boards. The results showed that striping is dominated by print density variations for uncoated board, and the print density variations are, in turn, caused by the printing pressure variations. The extent to which the pressure variations appear as print density variations depends on the ink transfer characteristics of the liner board.

National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-312 (URN)000252686700007 ()2-s2.0-38349104629 (Scopus ID)5138 (Local ID)5138 (Archive number)5138 (OAI)
Projects
Nip Mechanics and Hydrodynamics of Flexo Post-Printing and Print Quality
Note
VR-ChemistryAvailable from: 2008-12-10 Created: 2008-12-02 Last updated: 2010-03-05Bibliographically approved
3. Print Uniformity of Corrugated Board in Flexo Printing: Effects of Corrugated Board and Halftone Dot Deformations.
Open this publication in new window or tab >>Print Uniformity of Corrugated Board in Flexo Printing: Effects of Corrugated Board and Halftone Dot Deformations.
2008 (English)In: Packaging technology & science, ISSN 0894-3214, Vol. 21, no 7, 385-394 p.Article in journal (Refereed) Published
Abstract [en]

Print non-uniformity problems are a major concern for flexo post-printers. Many of these non-uniformities are suspected to be caused by the corrugated board structure itself. Striping is the most obvious one, but also other print quality problems might be structure-related. This work focuses on how deformations of the board might lead to print non-uniformities, and if the deformation of halftone dots is the mechanism behind striping in halftone flexo post-printing. The problems were analysed by using finite element models to simulate deformed board and halftone dot compression in the printing nip. Distortions of the board due to non-uniform hygro-thermal strains were shown to be a potential cause of print non-uniformities. Striping in halftone prints was found to be caused by differences in dot gain between ridge and valley areas above the flute structure.

Keyword
corrugated board, dot gain, flexo, halftone, striping, warp
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-313 (URN)10.1002/pts.816 (DOI)000260649100002 ()2-s2.0-55649096951 (Scopus ID)5139 (Local ID)5139 (Archive number)5139 (OAI)
Projects
Nip Mechanics and Hydrodynamics of Flexo Post-Printing and Print Quality
Available from: 2008-12-11 Created: 2008-12-11 Last updated: 2010-03-05Bibliographically approved

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