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Studying the impact of non-uniform absorption on print mottle of coated boards with barrier patterns
Innventia AB, Stockholm.
Innventia AB, Stockholm.
Innventia AB, Stockholm.
Innventia AB, Stockholm.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Absorption and surface roughness of a substrate are believed to impact flexographic print mottle. However, their respective contributions are not that well recognized as they always co-exist. In addition to average absorption rate, absorption uniformity is of higher importance and even more difficult to separate from surface roughness. Therefore we propose a method to independently study the effects of absorption non-uniformity on print quality. This is achieved by introducing artificial absorption non-uniformity with well-controlled barrier patterns. The barrier patterns are added onto coated boards by means of flexographic printing with appropriate chemicals. These patterns modify not only surface chemistry but also pore structure by closing the surface pores.

This article provides proof of the concept, which has successfully been applied to seven coated liquid boards. For the first time, this technique enables one to create a property-matrix, absorption non-uniformity vs. e.g. surface roughness. From this matrix the impact from either of the properties on print mottle can be studied independently. Experimental investigations showed that the level of absorption non-uniformity in a coated board had clear impact on print mottle. In most cases the relationship appeared to be linear, though the degree of impact differed from one board to another. This suggests that the print was more sensitive to uneven absorbency on some samples. This may be contributed to relative importance of other properties including the original non-uniformity of the board surface. When absorption non-uniformity is at a constant and low level, the effects of surface roughness becomes more pronounced.

Keyword [en]
Liquid absorption, absorption non-uniformity, print mottle, flexography, coated packaging board
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-34909OAI: oai:DiVA.org:kau-34909DiVA: diva2:780799
Available from: 2015-01-15 Created: 2015-01-15 Last updated: 2015-02-12Bibliographically approved
In thesis
1. Absorption non-uniformity characterisation and its impact on flexographic ink distribution of coated packaging boards
Open this publication in new window or tab >>Absorption non-uniformity characterisation and its impact on flexographic ink distribution of coated packaging boards
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

There are high demands on flexographic print quality to be sufficiently high and consistent in order to create a competitive packaging. At the same time the production efficiency need to be high. Printers thus need to achieve the same quality every time and quickly start-up new printing jobs. To accomplish this, one needs to gain a thorough understanding of how the liquid packaging board interacts with the ink and impacts the print quality.

This thesis focuses on water-based ink absorption of liquid packaging boards and particularly on a) how uniformity of ink absorption can be measured and b) to what extent the absorption characteristics contribute to print mottle in flexographic printing.

The work encompasses two parts. First, an absorption non-uniformity test method has been developed using a staining technique. This method is unique as it measures how unevenly an aqueous solution is absorbed, in a short time period and without impact from surface roughness. Moreover, the contributions from white-top mottle and absorption non-uniformity can be quantified simultaneously from one single measurement.

Second, a method to independently study the effects of absorption non-uniformity on print quality has been established. This is achieved by introducing artificial absorption non-uniformities with well-controlled barrier patterns. A barrier pattern may modify local pore structure and/or surface energy, hence lead to lateral absorption variations. By these means, it is possible to produce a substrate property-matrix; encompassing absorption non-uniformity and for example surface roughness. It was demonstrated that non-uniform absorption indeed has a negative impact on print quality, both on smoother and rougher boards. Low absorption made print density decrease and uneven absorption caused print mottle. This was the case when other properties of the samples were kept within a narrow range; otherwise surface roughness appeared to determine print mottle ranking.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2015. 70 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2015:7
Keyword
Liquid absorption, Absorption non-uniformity, Characterisation, Measurement technique, Print Mottle, Flexography, Coated packaging boards
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-34910 (URN)978-91-7063-618-9 (ISBN)
Presentation
2015-03-05, Nyqvistsalen, Karlstads universitet, Karlstad, 10:00 (English)
Opponent
Supervisors
Available from: 2015-02-12 Created: 2015-01-15 Last updated: 2015-02-12Bibliographically approved

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