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Prediction of UnCovered Area occurrence in flexography based on topography: A feasibility study
Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
STFI-Packforsk AB, Stockholm, Sweden .
2006 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 21, no 2, 172-179 p.Article in journal (Refereed) Published
Abstract [en]

This investigation concerns the development and prediction of uncovered areas (UCA) in flexographic full-tone prints based purely on substrate topographic information. Four different predictive models based on topography thresholding were proposed and tested using two independent quality judgement criteria. 

Place, publisher, year, edition, pages
2006. Vol. 21, no 2, 172-179 p.
Keyword [en]
Flexography, OptiTopo, Print quality, Printability, Topography
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-2068DOI: 10.3183/NPPRJ-2006-21-02-p172-179OAI: oai:DiVA.org:kau-2068DiVA: diva2:6106
Available from: 2006-11-09 Created: 2006-11-09 Last updated: 2011-11-29Bibliographically approved
In thesis
1. Influence of Substrate Topography on Ink Distribution in Flexography
Open this publication in new window or tab >>Influence of Substrate Topography on Ink Distribution in Flexography
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The printability of paper in flexography is largely dependent on the topographical characteristics of the substrate. Topography imaging instruments make it possible to obtain three-dimensional scans of paper surfaces that can be further used to calculate valuable quality parameters. The primary aim of the work described in this thesis has been to identify and isolate structural properties of the paper surface which significantly influence the ink distribution during printing and limit the subsequently attainable print quality.

OptiTopo is an optical imaging technique which provides precise and fast topographic scans of both printed and unprinted paper surfaces. The potential and limitations of the technique have been evaluated. The optical requirements on the substrate for an accurate and precise topographic scan were determined. Detail-rendering was substantially improved using a custom-designed restoring filter, and a new enhanced spatial resolution range was established. A combination of further algorithm improvements made it possible also to obtain reflectance-factor-calibrated intensity images of scanned printed surfaces.

Serious deficiencies affecting the quality of flexographic prints may appear in the form of local unprinted areas (UCA) in a full-tone print, generally caused by incomplete ink transfer. An algorithm detecting and quantifying local uncovered area was developed, tested and successfully integrated with the OptiTopo instrument. A UCA occurrence frequency distribution, indicating the percentage of the uncovered area at a certain topographical elevation, was calculated for different prints. The topographic characteristics of the uncovered areas clearly indicate that surface depressions are the primary cause of uncovered areas in flexographic printing.

Four different predictive models based on topography thresholding were proposed and tested using two independent quality judgement criteria. These quality indices took into account both the amount and location of the predictions. A deeper understanding of the topographical features governing UCA occurrence was established with a proposed ink bridging effect. The total risk of non-ink-covered areas in flexography printing due to topographical features was estimated.

The overall influence of paper topography on the flexography printability of full-tone areas was studied and its importance for the ink distribution assessed. The impacts of printing plate hardness, printing pressure, anilox cylinder volume and substrate roughness were quantified. Two typical flexography patterns were identified and their origin discussed: sub-millimetre elongated structures and millimetre-scale blotches.

Place, publisher, year, edition, pages
Fakulteten för teknik- och naturvetenskap, 2006
Series
Karlstad University Studies, ISSN 1403-8099 ; 2006:17
Keyword
paperboard, topography, optical measurement, OptiTopo, flexography, flexo, print quality, printability, uncovered area, UCA, image analysis, frequency analysis, surface properties, paper properties, test equipment, measuring instrument
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-446 (URN)91-7063-048-8 (ISBN)
Public defence
2006-06-15, Ericssonsalen, 9C 204, 10:30
Opponent
Supervisors
Available from: 2006-11-09 Created: 2006-11-09

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