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Water-based Flexographic Printing on Polymer-coated Board
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
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: urn:nbn:se:kth:diva-603ISBN: 91-7178-252-4 (print)OAI: oai:DiVA.org:kth-603DiVA: diva2:14589
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
List of papers
1. Rheology and surface tension of water-based flexographic inks and implications for wetting of PE-coated board
Open this publication in new window or tab >>Rheology and surface tension of water-based flexographic inks and implications for wetting of PE-coated board
2005 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 4, 399-409 p.Article in journal (Refereed) Published
Abstract [en]

This study systematically characterises a matrix of water-based flexographic inks with respect to their rheology, surface tension and wetting of liquid packaging board, to provide a basis for interpretation and prediction of their printing performance. For all pigment and acrylate polymer vehicles and mixing proportions the inks were shown to be shear thinning and thixotropic, with plastic viscosity, yield stress and storage and loss moduli increasing strongly with content of solution polymer (at comparable solids contents). The solution polymer decreases the static surface tension of the inks, but generally leads to an increase in their equilibrium drop contact angle oil the polyethylene- (PE-) coated board due to increase in the ink-board interfacial energy. The solution polymer also decreases the drop spreading rate, and a simple model is tested to express the spreading dynamics in terms of equilibrium contact angle and a rate parameter given by the effective ratio of surface tension to viscosity.

Keyword
flexography, water-based ink, polyethylene, corona treatment, rheology, surface tension, wetting
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-9042 (URN)000235258200005 ()
Note
QC 20100916Available from: 2006-01-27 Created: 2006-01-27 Last updated: 2017-12-14Bibliographically approved
2. Influence of formulation and properties of water-based flexographic inks on printing performance for PE-coated board
Open this publication in new window or tab >>Influence of formulation and properties of water-based flexographic inks on printing performance for PE-coated board
2005 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 4, 410-417 p.Article in journal (Refereed) Published
Abstract [en]

In this study the flexographic printing of lowdensity polyethylene- (LDPE-) coated liquid packaging board is analysed for a range of water-based inks, varying in type of pigment and acrylate-polymer vehicle and pigment/vehicle mixing proportions. One vehicle is solely based on emulsion polymer, another contains solution polymer, and the third is a 50150 blend of these two. Vehicle type and relative amount are shown to have a strong and systematic bearing on the absolute amount of ink transferred and its corresponding print density, gloss, and uniformity. For both ink colours (cyan and black), transferred amount increases with pigment content and is highest for the 50150 intermediate vehicle. Print density and homogeneity are generally highest for the vehicle containing highest content of solution polymer, at least with the lower anilox volumes, and this vehicle also gives highest print gloss. The wet amount of ink transferred is shown to be well correlated to its surface tension and viscosity.

Keyword
flexography, water-based ink, polyethylene, rheology, surface tension, print quality
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-9043 (URN)000235258200006 ()
Note
QC 20100916Available from: 2006-01-27 Created: 2006-01-27 Last updated: 2017-12-14Bibliographically approved
3. Correlations between properties of water-based flexographic inks and their print uniformity on PE-coated board
Open this publication in new window or tab >>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.

Keyword
flexography, water-based ink, polyethylene, print quality, mottling, packaging board
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-9044 (URN)000241531500016 ()
Note
Uppdaterad från submitted till published: 20100916 QC 20100916Available from: 2006-01-27 Created: 2006-01-27 Last updated: 2017-12-14Bibliographically approved
4. Effect of corona treatment of PE-coated board on water-based flexographic print resistance
Open this publication in new window or tab >>Effect of corona treatment of PE-coated board on water-based flexographic print resistance
2006 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 2, 202-210 p.Article in journal (Refereed) Published
Abstract [en]

The effect of corona treatment of Polyethylene-(PE-) coated liquid packaging board on its surface chemistry was quantified using surface energy determination by drop spreading and dyne-liquids, x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The increase in total surface energy, due to its polar component, with increasing corona dosage, and its decrease on aging and washing, was strongly correlated to surface oxidation fraction from XPS. A fine structure of nano-mounds formed by oxidised material was revealed by AFM, with size and substrate coverage increasing with corona dosage, but no longer visible after washing. Resistance properties of water-based flexographic prints on these treated PE substrates were tested, with only wet rub resistance exhibiting a significant dependence on corona dosage. This property first increased at lower dosages before decreasing at higher levels, presumably due to worsened water resistance from soluble oxidised material dissolved in the ink film.

Keyword
flexography, water-based ink, polyethylene, corona discharge treatment, print quality, print resistance, LMWOM, AFM, XPS
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-9045 (URN)000238726200006 ()
Note
QC 20100916Available from: 2006-01-27 Created: 2006-01-27 Last updated: 2017-12-14Bibliographically approved
5. Print quality and resistance for water-based flexography on polymer-coated boards: Dependence on ink formulation and substrate pretreatment
Open this publication in new window or tab >>Print quality and resistance for water-based flexography on polymer-coated boards: Dependence on ink formulation and substrate pretreatment
2006 (English)In: Progress in organic coatings, ISSN 0300-9440, E-ISSN 1873-331X, Vol. 57, no 3, 183-194 p.Article in journal (Refereed) Published
Abstract [en]

The performance of water-based acrylic flexographic inks laboratory printed on three different polymer-coated boards, namely coated with LDPE, OPP and PP, have been analysed and interpreted. The print quality and resistance properties obtained were related to varying ink formulation, in particular choice of emulsion polymer and presence of silicone additive in the vehicle, as well as varying levels of corona pretreatment. Print mottle and adhesion were worst on PP, while wet (water) rub and scratch resistance were worst on OPP and PE, respectively. However, these properties could be greatly influenced by the ink formulation, more so than corona level. In general addition of silicone improved scratch resistance, due to reduction in polar energy component of the print surface, but at the expense of worsened wet rub resistance. The emulsion polymer giving best resistance performance was generally found to give poorest optical properties, presumably due to more limited resolubility on press.

Keyword
water-based ink, polyethylene, polypropylene, corona discharge treatment, print quality, print resistance
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-9046 (URN)10.1016/j.porgcoat.2006.08.003 (DOI)000242746800002 ()
Note
QC 20100916, Uppdaterad från submitted till published: 20100916Available from: 2006-01-27 Created: 2006-01-27 Last updated: 2017-12-14Bibliographically approved

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