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Effects on ink setting in flexographic printing: coating polarity and dot gain
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre.
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences. (INTERACT)ORCID iD: 0000-0002-0995-3823
Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Materials Science.
2006 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 5, 569-574 p.Article in journal (Refereed) Published
Abstract [en]

Research has been carried out to study the factors that affect ink setting, with particular focus on the effects of coating polarity and the printing pressure in flexographic printing. Different coating layers were prepared on non-porous polyester films. The coating colours were based on calcium carbonates of different particle sizes, lattices of different polarities and a carboxymethyl cellulose (CMC) thickener. Two latex films were prepared to characterise the surface tension properties through contact angle measurements, which were repeated several times for each latex film and testing fluid. The coating layers were printed in a laboratory printing press under different printing pressures using a water-based flexographic ink. Results showed different print densities for a given amount of ink transferred on the different substrates, with the latex character rather than the pore size of the substrates affecting the print density. Compared with the less polar substrate, the more polar substrate resulted in a higher print density. A non-linear relationship between physical dot enlargement and printing pressure was visualised, resulting from increasing printing form deformation. A mathematical model for printing plate deformation has been proposed that takes into account elastic deformations. It was found that the diameter of the printed halftone dot was larger in the print direction than in the cross print direction. (7 fig, 6 tab, 17 ref)

Place, publisher, year, edition, pages
Sundsval: Mittuniversitetet , 2006. Vol. 21, no 5, 569-574 p.
National Category
Chemical Engineering Chemical Sciences
Research subject
Chemical Engineering; Chemistry
Identifiers
URN: urn:nbn:se:kau:diva-18664ISI: 000243757900004OAI: oai:DiVA.org:kau-18664DiVA: diva2:592301
Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2015-10-13Bibliographically approved
In thesis
1. Some aspects on flexographic ink-paper and paperboard coating interaction
Open this publication in new window or tab >>Some aspects on flexographic ink-paper and paperboard coating interaction
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Flexographic printing is a process that employs a flexible printing form and low viscous ink, often water-based. The flexible printing form is favourable for printing on rough surfaces, but the high surface tension of the ink may cause printability problems.

This work has focused on the interaction between paper/paperboard coating and water-based flexographic ink, aimed at increasing the knowledge about the printing process in form of physical/chemical parameters that are important for ink setting. The effects of printing conditions on print quality, such as printing pressure and temperature, have also been in focus.

The work has shown that fluids of different polarities, i.e. different dipole moments, behave differently when being absorbed by a coating layer. Due to their chemical compatibility to the coating layer, fluids with large dipole moment fill the pore matrix of the coating to a lesser extent but penetrate further into the coating than fluids with small dipole moments. On the other hand, polarity of the coating layer also affects the print. When printing on coatings with different polarities, higher print densities was obtained on the more polar substrates. As a tentative explanation, it is proposed that the ink builds different layer structures during drying depending on the coating polarity.

Print gloss is related to the ink setting which, in turn, is affected by the solvent retaining capacity of the ink. Large water holding capacity allows the ink components to smoothen out before the structure is set, resulting in a higher print gloss. The rheology of inks is affected by temperature; at a higher temperature the viscosity is reduced. The reduction in ink viscosity at higher temperature has been shown to affect the print quality, e.g., print density and dot gain. It is suggested that a thicker layer is immobilised during impression due to the lower viscosity and that it is an explanation of the higher print density at a higher printing temperature.

The influence of impression pressure on dot gain has been experimentally evaluated and mathematically modelled with good agreement. The dot gain is shown to respond non-linearly to the applied printing pressure.

Studies based on pilot coated and printed paperboards is also reported, and it is shown that the print quality, e.g. print density, print gloss and dot gain, is largely dependent on the type of ink chosen and on the coating characteristics. Higher clay content in the coating resulted in increased dot gain and a decreased mottling.

Place, publisher, year, edition, pages
Fakulteten för teknik- och naturvetenskap, 2007
Series
Karlstad University Studies, ISSN 1403-8099 ; 2007:23
Keyword
Flexography; Ink; Coating; Paperboard; Printing
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-1218 (URN)978-91-7063-126-9 (ISBN)
Public defence
2007-11-09, Sjöströmsalen, 1B 309, Karlstad, 09:00
Opponent
Supervisors
Available from: 2007-10-19 Created: 2007-10-19 Last updated: 2015-10-13

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