March 2013

Nils Enlund






Flexographic printing of PEDOT:PSS on coated papers for printed functionality

Dimitar Valtakari1, Roger Bollström1, Mikko Tuominen2, Hannu Teisala2, Mikko Aromaa3,
Martti Toivakka
1, Jurkka Kuusipalo2, Jyrki M. Mäkelä3, Jun Uozumi4, Jarkko J. Saarinen 1, 5
1 Laboratory of Paper Coating and Converting, Center for Functional Materials, Åbo Akademi University
2 Paper Converting and Packaging Technology, Department of Energy and Process Engineering, Tampere University of Technology
3 Aerosol Physics Laboratory, Department of Physics, Tampere University of Technology
4 Faculty of Engineering, Hokkai-Gakuen University
5 Faculty of Engineering, Hokkai-Gakuen University


Large area printed conductive surfaces are expected to have an impact on printed functionality ranging from electronics to photonics such as printed solar cells. We report here a study on formation of such conductive surfaces by flexographic printing using a PEDOT:PSS conductive ink on various coated papers. Printability of multilayer coated paper and TiO2 nanoparticle coated paperboard generated by the liquid flame spray process are compared to plastic film typically used in printed functionality applications. The wettability of TiO2 nanoparticle coating can be altered between superhydrophobic and superhydrophilic states by ultraviolet light. It is observed that superhydrophobicity of paperboard induced by TiO2 nanoparticles results in poorer ink setting with the water-based PEDOT:PSS yielding lower conductivities. Therefore, we observe conductivity only after several successive prints. A solvent-based silver ink was used for comparison. It is believed that renewable natural fibre based substrates, such as coated paper meeting criteria for sustainable development will find more applications in the future.

Keywords: nanoparticle, printing, flexography, wettability, sustainable development

JPMTR 015 | 1210 Research paper
UDC 655.326.1:676:22

Received: 2012-06-13
Accepted: 2013-02-08

A multi colour separation system for graphic images

Eifion Jewell, Timothy C. Claypole and David C. Bould
Welsh Centre for Printing and Coating University of Wales Swansea Singleton Park, Swansea SA2 8PP Wales, UK


This paper reports on the development of a unique six colour separation system for the rendition of multi coloured images which has the elimination of practical printing issues at its focus. An algorithm is described which can be used for six colour separation of complex photographic images in order to maximise image gamut. Using a custom set of six co- lours a Yule Nielsen modified Neugebauer equation is used to produce a colour model to predict colour mixing using 64 Neugebauer primaries. Over 60 % of the model predictions were within a ΔE of 5. Some larger errors could be associated with the optical brighteners in the paper substrate. This model was considered sufficiently accurate for the basis of a co- lour separation model. To reduce computational effort at the separation stage a large pure lookup table was created to store the results of the colour model. This table creation is computationally heavy at the table creation stage, but fast for the user at the separation stage. The one-to-many mapping from XYZ to six colourants was dealt with by enabling a uni- que rule based system based on practical printing requirements and a smoothing function. The rule based system is based on practical printing issues which limits problems that could be experienced on press. The system was developed with maximum flexibility such that it can be adapted for an increased number of base colourants and alternate printing rules.

Keywords: colour separation, multi colour printing, Neugebauer

JPMTR 016 | 1216 Research paper
UDC 535.64:681.6

Received: 2012-11-04
Accepted: 2013-02-01

The effects of laser-engraving settings on etch depth of polymer clichés and pad printing quality

Renmei Xu, Susan C. Londt and James C. Flowers
University of Wuppertal Printing and Media Technologies Wuppertal, Germany
Ball State University Department of Technology Muncie, IN 47306, USA


Laser has been used in many fields since its invention several decades ago. It can easily cut polymers. In this study, laser was applied in pad printing to engrave polymer clichés. It eliminated film and chemicals required in the conventional photographic method involving exposure with film positives followed by development. It also ensured direct image output and eliminated the myriad variables and time-consuming steps in the photographic method which affected consistent quality. A CO2 laser cutter/engraver from Universal Laser Systems was used to engrave the image areas on polymer clichés. The laser system has a power of 150 Watts and the laser beam has a spot diameter of 0.001 inch, which ensures fine detail reproduction. Image resolutions are determined by pulses per inch (ppi) in the x-axis and dots per inch (dpi) in the y-axis. The highest available resolution was used, which was 1 000 ppi by 1 000 dpi. Laser power and engraving speed determine the depth of the ink wells, so these two engraving parameters were varied to obtain optimum results. It was found that 100 % speed (70 inch/second) with 11 % power (17.5 Watts) created an optimum etch depth. A line art as well as images with large open areas that were screened with different settings were laser-engraved on clichés and printed on a pad printer Model Sealcup 60 from Trans Tech. The engraved sidewalls appeared to be straight and pooling of ink did not occur in the printing process, thus producing high print quality of line art. Images with large open areas that were screened at a maximum angle of 45° with the doctoring direction and a high screen frequency of 200 lpi had the best print quality and highest print density. Differences between dot shapes were only observed when the screen frequency was low.

Keywords: laser engraving, polymer cliché, etch depth, pad printing, quality

JPMTR 016 | 1215 Research paper
UDC 762.655.224.3

Received: 2012-09-07
Accepted: 2013-03-13

Minimizing the print quality limitations imposed by ISO screen angle choice when eliminating secondary Moiré in monochrome halftone screen printing

Ramesh Dendge
Government Institute of Printing Technology Dr D. N. Road, Sir J. J. School of Arts Campus Mumbai, India


Screen printing offers high ink deposition on a variety of substrates. This is a major advantage of this printing technology compared to offset, flexography and gravure. Due to developments in mesh manufacturing technology, we can now comfortably print halftone, with some losses in highlight and shadow areas, at a resolution of 100 LPI (lines per inch) and above. This has helped screen printing to improve the quality of monochrome continuous tone and full color graphic reproduction. The screen mesh parameters such as mesh count, thread diameter, and weaving method affect smoothness and uniformity of the reproduced halftone image. This may be addressed by using different combinations of dot shape and screen angle in the positive image used. ISO 12647:5 recommends screen angles for process color printing, but in the case of single color halftone printing the screen printer is required to use only one screen angle. This research contribution is aimed at identifying the optimum screen angle for monochrome halftone printing that results in minimum light interference, i.e., minimizing secondary Moiré fringes as a function of mesh weave, using trials involving two mesh counts, four screen angles and two screen ruling frequencies.

Keywords: screen angle, screen ruling, dot area, mesh count, thread diameter

JPMTR 012 | 1209 Professional communication
UDC 655.332+655.3.023

Received: 2012-05-27
Accepted: 2012-10-20