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Correlations between properties of water-based flexographic inks and their print uniformity on PE-coated board
2006 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 3, 403-410 p.Article in journal (Refereed) Published
Abstract [en]

Uniformity of fulltone flexographic prints on PE-coated board was investigated for a large matrix of aqueous inks with varying acrylic-based vehicles and pigment concentrations, and with their applied amounts varied using a wide range of anilox volumes. Print mottle was characterised by coefficient of variation of reflectance, and partitioned into different feature-size classes. For all prints the mottle was caused by the residual pattern of white (poorly-covered) stripes originating from the anilox ruling, and subsequently distorted and redistributed to both finer and coarser length scales during transfer to, and flow on, the print substrate. Accordingly, mottle was largest on the sub-millimetre scales encompassing these stripe features, and generally increased with anilox volume, approximately proportionally so on above-millimetre scales. While greater pigmentation naturally increased both print density and mottle, the vehicle also exerted a strong influence, with mottle decreasing with increased content of soluble (versus emulsion) polymers. The latter was principally due to the associated increase in low-shear viscosity and decreased surface tension, both serving to reduce substrate dewetting. Empirical relations accurately correlating mottle to these two ink properties, and anilox volume and print density, were established.

Place, publisher, year, edition, pages
2006. Vol. 21, no 3, 403-410 p.
Keyword [en]
flexography, water-based ink, polyethylene, print quality, mottling, packaging board
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-9044ISI: 000241531500016OAI: oai:DiVA.org:kth-9044DiVA: diva2:14586
Note
Uppdaterad från submitted till published: 20100916 QC 20100916Available from: 2006-01-27 Created: 2006-01-27 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Water-based Flexographic Printing on Polymer-coated Board
Open this publication in new window or tab >>Water-based Flexographic Printing on Polymer-coated Board
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This doctoral thesis comprises three studies dealing with water-based flexography on polymer-coated boards, which have been presented in the five papers included at the end of the thesis. The first study (covered in three papers) presents results from characterisation of a matrix of water-based inks with respect to their rheology, surface tension, wetting, and fulltone printing performance on PE-coated board. The commercial water-based inks used vary in type of pigment and acrylic vehicle, and in pigment/vehicle mixing proportions. For all mixing proportions, the inks were shear thinning, with viscosity increasing strongly with content of solution (versus emulsion) polymer in the vehicle. Increasing amount of solution polymer also gave the indirect consequence of lower surface tension values. The wet ink amount transferred to the board and the resulting print uniformity responded sensitively to ink formulation and could be correlated to the corresponding changes in these two ink properties. Transferred amount correlated well with ink plastic viscosity and static surface tension, exhibiting a maximum at intermediate values of both. Print mottle decreased with increasing content of solution polymer, principally due to the associated increase in low-shear viscosity and decreased surface tension, both serving to reduce substrate dewetting.

In the second study, the effect of corona discharge treatment of PE-coated board on its surface chemistry and print resistance properties was evaluated. The increase in total surface energy, due to its polar component, with increasing corona level was strongly correlated to surface oxidation fraction from XPS. AFM revealed oxidised material nano-mounds, which increased in size and substrate coverage with corona level. Wet rub resistance (with water) first increased for lower corona dosages before decreasing at higher dosages. This worsened water resistance at higher dosages is presumably due to the oxidised material dissolved and dispersed in the ink film.

The third study presents results from another set of water-based acrylic inks printed on boards coated with PE, OPP and PP. Print quality and resistance properties, though dependent on the polymer type, were strongly influenced by the choice of emulsion polymer and presence of silicone additive in the vehicle, with corona treatment level playing a lesser role. The emulsion polymer giving best resistance performance was generally found to give poorest press performance and visual appearance. Again the trends could be understood in terms of wet ink surface tension (versus substrate surface energy), dictating print uniformity, and dry print surface energy (and swellability), dictating resistance properties.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. vii, 69 p.
Series
Trita-YTK, ISSN 1650-0490 ; 0602
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-603 (URN)91-7178-252-4 (ISBN)
Public defence
2006-02-13, Sal F3, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100916Available from: 2006-01-27 Created: 2006-01-27 Last updated: 2010-09-16Bibliographically approved

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