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Absorption non-uniformity characterisation and its impact on flexographic ink distribution of coated packaging boards
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
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 [en]
Liquid absorption, Absorption non-uniformity, Characterisation, Measurement technique, Print Mottle, Flexography, Coated packaging boards
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-34910ISBN: 978-91-7063-618-9 (print)OAI: oai:DiVA.org:kau-34910DiVA: diva2:781054
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
List of papers
1. Uniformity of liquid absorption by coatings: Technique and impact of coating composition
Open this publication in new window or tab >>Uniformity of liquid absorption by coatings: Technique and impact of coating composition
2012 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, 456-465 p.Article in journal (Refereed) Published
Abstract [en]

The interaction between a liquid and a paper surface is important for a number of paper treatment processes, where absorption is of special significance during printing. Many absorption measurement techniques use a large available volume of liquid to characterise absorption, when compared to the volume of the coating. The uniformity of the absorption is also seldom characterised. We have developed a new technique, which is presented in this article, to study the uniformity of absorption of a small amount of liquid. This technique is based on the short-time absorption (tenth of a second) of a coloured liquid, the blotting of excess liquid and a characterisation of the pattern of the stain. This method made it possible to detect differences among coating layers with different compositions. In many cases, the absorption non-uniformity could be linked to variations in the coating thickness and/or wettability. The thinner and thicker areas of the coating layers were interpreted as having different pore structures. Neither the coating thickness nor the wettability could provide a full explanation, which showed the need to develop a method to characterise absorption uniformity instead of only relying on measuring the total absorption potential.

Keyword
Coated boards, Flexographic printing, Liquid absorption, Test method
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-34906 (URN)10.3183/NPPRJ-2012-27-02-p459-465 (DOI)
Available from: 2015-01-15 Created: 2015-01-15 Last updated: 2017-12-05Bibliographically approved
2. Simultaneous determination of absorption mottle and white-top mottle in the same area on coated boards
Open this publication in new window or tab >>Simultaneous determination of absorption mottle and white-top mottle in the same area on coated boards
2013 (English)In: Proceedings of the 40th International Research Conference of iarigai / [ed] Enlund, N. & Lovreček, M., Darmstadt, Germany: International Association of Research Organizations for the Information, Media and Graphic Arts Industrie (IARIGAI), 2013, 225-232 p.Conference paper, Published paper (Other academic)
Abstract [en]

The proposed measurement technique offers a number of advantages compared to other absorption methods. It enables one to study liquid absorption in a time period that is relevant to printing. Moreover, with this technique one can quantify the contributions of white-top mottle and absorption mottle at the same location and in great detail. This makes this technique a useful tool for quality control of paper board products and for predicting print mottle of flexographic printing. The reproducibility and reliability of the technique were very promising, as suggested by the Round Robin tests.

Place, publisher, year, edition, pages
Darmstadt, Germany: International Association of Research Organizations for the Information, Media and Graphic Arts Industrie (IARIGAI), 2013
Series
Advances in Printing and Media Technology, ISSN 2225-6067 ; Vol. XL
Keyword
absorption non-uniformity, absorption mottle, white-top mottle, liquid absorption, flexography
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-34908 (URN)978-3-9812704-4-0 (ISBN)
Conference
40th International Research Conference of iarigai, Chemnitz, Germany, September 2013
Available from: 2015-01-15 Created: 2015-01-15 Last updated: 2015-02-12Bibliographically approved
3. Studying the impact of non-uniform absorption on print mottle of coated boards with barrier patterns
Open this publication in new window or tab >>Studying the impact of non-uniform absorption on print mottle of coated boards with barrier patterns
(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
Liquid absorption, absorption non-uniformity, print mottle, flexography, coated packaging board
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-34909 (URN)
Available from: 2015-01-15 Created: 2015-01-15 Last updated: 2015-02-12Bibliographically approved

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