June 2020

A letter from the Editor
Gorazd Golob

Editor-in-chief

The present issue of the Journal comes at a time, despite different wishes and some predictions, marked by a pandemic. Fortunately, the authors, reviewers, and editors have been persistent, and this time we are publishing four papers. The first two are classified as original scientific papers, as they are distinguished from the others by a strong theoretical basis and an original approach. The first paper discusses the mechanical behavior and loads of paper, what is interesting especially for experts who are researching the manipulation of several sheets of paper at the same time, and practical applicability of the study could be seen mainly in the field of bookbinding, which is rarely considered in research. The second paper is devoted to the investigation of printing pad geometry, mainly the use of various methods for simulation and optimal determination of the shape of the key element in this widespread technique of indirect gravure printing. The third article is a research paper and was chosen for publication despite some concerns due to the results of the experiment, based on which the authors conclude that the tested printed surface does not affect sound absorption, but this claim opens up some new challenges for future research. The fourth, final paper is a case study. This is a result of unique, very extensive research, which would not be possible without strong industrial partner’s support, access to the specially made cardboard with known characteristics, and a printing press in the otherwise not very widespread gravure cardboard printing technique equipped with appropriate measuring equipment. The challenges are mainly in conducting a similar study in a lab environment, where full reproducibility of the experiment can also be ensured. In the Topicalities the Editor Markéta Držková (marketa.drzkova@jpmtr.org) is bringing news from Drupa, a new alliance of US printers, reports from European Intergraf and recent printing-related research projects from MIT and EU-funded Horizon 2020. In the Bookshelf, you can find an overview of books from the fields covering management, typography, intellectual property, history, new materials, and technologies beyond traditional printing. Three doctoral theses are also presented in the Bookshelf. Chun-Ho Lin defended his thesis on perovskite synthesis, fabrication and characterization at the King Abdullah University in Thuwal, Kingdom of Saudi Arabia. At the TU Chemnitz, Germany, Chadha Bali defended her dissertation on the study of coffee-ring-effect used as self-assembly mechanism in inkjet printing of organic printed electronic elements. Stephan Behnke defended his thesis at the Technical University of Darmstadt, Germany. His research was oriented towards the optimization of the printing and manufacturing process of metal packaging. In the Events section, a number of conferences, workshops, seminars, and other events are presented, however, many of them are postponed or adopted to the current situation with online sessions, access to tutorials, and some of them are even moved to new locations. Also some other changes can still occur. The call for papers is open constantly and we received two or three manuscripts every month this year. In the preliminary assessment of suitability for publication, we follow the Journal’s policy according to which only papers that are of high quality, interesting, showing interesting research results or open new dilemmas and questions are suitable for review, editing, and publication. I am pleased that, despite the relatively high standards for the acceptance and publication of submitted manuscripts, we are receiving more and more quality papers appropriate to fulfil our mission. Join us and submit the results of your research and scientific work for publication in the Journal. We will appreciate publishing them, of course after a successful review, audit, and editing process.

Ljubljana, June 2020

An empirical model for describing the mechanical behavior of paper and paper stacks in the perpendicular to the in-plane direction

Jian Chen1, Dieter Spiehl2, Edgar Dörsam2, Arash Hakimi Tehrani2 and Simon Weißenseel2

E-mails: chenjian.tud@hotmail.com; spiehl@idd.tu-darmstadt.de; doersam@idd.tu-darmstadt.de; arash.hakimi.t@gmail.com; simon.weissenseel@alcon.com

1 School of Mechanical Engineering, Yangzhou University, Huayang Weststr. 196, 225127 Yangzhou, China

2 Institute of Printing Science and Technology,
Darmstadt University of Technology,
Magdalenenstr. 2, 64289 Darmstadt, Germany

Abstract

The mechanical behavior of paper materials under compression in the out-of-plane direction is highly nonlinear. If the influence of the surface topography is not taken into account, the stress–strain curve of paper materials in the loading process is a typical example of materials with J-shaped compressive curves. When compression is released, the stress–strain curve in the unloading process is also nonlinear. The main purpose of this paper is to establish a suitable mathematical model and actualize the description of the compression curve for paper and paper stacks. The loading and unloading nonlinearities of paper stress–strain relations can be approximated by using different equations. In this paper, the loading curve of paper is calculated by using the sextic polynomial equation and the unloading curve is described by using the modified exponential function. All the used coefficients for determining the functions are expressed as the functions of the stress at the start point of unloading. The compressive behavior of paper under some given forces are also calculated by using the identified equation and verified by means of the experimental data. For multiple sheets, it is assumed that when the force is the same, the deformation of the paper stack is directly proportional to the number of sheets. Based on this assumption, the force–deformation relation of the paper stack is derived. The comparative analysis of the experimental results demonstrates the effectiveness of the description model.

Keywords: out-of-plane direction, loading and unloading stages, stress–strain relationship, force–deformation curve, paper and paper stacks

JPMTR 132 | 1910 Original scientific paper
DOI 10.14622/JPMTR-1910
UDC 676.2:538.3|53.07

Received: 2019-10-28
Accepted: 2020-05-28

Investigation of printing pad geometry by using FEM simulation

Ahmad Al Aboud, Edgar Dörsam and Dieter Spiehl

E-mails: aboud@idd.tu-darmstadt.de; doersam@idd.tu-darmstadt.de; spiehl@idd.tu-darmstadt.de

Technische Universität Darmstadt,
Institute of Printing Science and Technology, Magdalenenstr. 2, 64289 Darmstadt, Germany

Abstract

Pad printing is an indirect gravure printing for printing on objects with complicated geometries or rough surfaces. Although pad printing is a proven and widely used printing process, there are few scientific studies on the shape and hardness of printing pads and their influence on printing quality. The shape and hardness of printing pads are therefore still determined today by experience. Even in the age of digitalization, the manufacturing of printing pads is still a manual process. So far, no modern tools are known to support this manufacturing process. In this paper, using simulations with commercially available finite element method (FEM) software (Abaqus) or open source software (Salome-Meca) as possible development tools for silicone rubber printing pads is investigated. The FEM simulation of this hyperelastic material requires various input parameters such as material model, special material parameters as well as mesh types and sizes. This paper shows how these parameters are determined, which material tests are necessary and how sensitive the simulation result is to these input parameters. Based on the comparison with experimental data, the results show that silicone rubber printing pads with small deformations can be simulated very well with both the commercial FEM software Abaqus and the free open source FEM software Salome-Meca. Mooney–Rivlin or the polynomial material equations are used. Finally, a workflow is shown with which the geometry of a printing pad can be evaluated and optimized.

Keywords: pad printing, pad geometry, silicone rubber, hyperelastic material, mesh

JPMTR 133 | 1913 Original scientific paper
DOI 10.14622/JPMTR-1913
UDC 655.1:517.9+004.92

Received: 2019-12-11
Accepted: 2020-05-31

Impact of printing surfaces with UV-curable inks on sound absorption

Vlado Kitanovski1, Jonny Nersveen2, Anton Strand3 and Marius Pedersen1

E-mails: vlado.kitanovski@ntnu.no; jonny.nersveen@ntnu.no; anton.strand@canon.no; marius.pedersen@ntnu.no

1 Department of Computer Science,
Norwegian University of Science and Technology, Building A, Teknologiveien 22, 2815 Gjøvik, Norway

2 Department of Manufacturing and Civil Engineering,
Norwegian University of Science and Technology, Building B, Teknologiveien 22, 2815 Gjøvik, Norway

3 Canon Norway AS, P.O. Box 33, Holmlia N-1201, Oslo, Norway

Abstract

The recent UV-curable inks, used in modern inkjet printing systems, bring several advantages and therefore a potential to expand to new applications, including décor printing. In this work, we investigate the impact of printing with UV-curable inks on sound absorption. The sound absorption curves of three different sound-absorbing decorative wall plates are calculated from the reverberation times measured in a reverberation room. The comparison between the sound absorption from unprinted and printed decorative plates showed that printing with UV-curable inks has no significant impact on the sound absorbing characteristics of materials.

Keywords: sound-absorbing plate, reverberation time measurement, décor printing, UV-curable inkjet printing

JPMTR 134 | 2003 Research paper
DOI 10.14622/JPMTR-2003
UDC 667.5:534.2

Received: 2020-03-26
Accepted: 2020-06-24

Influence of paperboard production on web movement and register quality in printing process

Tobias Enk1, Peter Urban1, Michael Dattner2, Hannes Vomhoff 3 and Axel Heise4

E-mails: toenk@uni-wuppertal.de; purban@uni-wuppertal.de; michael.dattner@beuth-hochschule.de; hannes.vomhoff@holmen.com;
axel.heise@gundlach.de

1 University of Wuppertal, School of Electrical, Information and Media Engineering, Rainer-Gruenter-Straße 21, D-42119 Wuppertal

2 Beuth University of Applied Sciences Berlin, School of Information Technology and Media,
Luxemburger Straße 10, D-13353 Berlin

3 Holmen AB, Strandvägen 1, SE-114 84 Stockholm

4 Gundlach Verpackung GmbH, Hellweg 21-25, D-33813 Oerlinghausen

Abstract

Register quality is often influenced by challenging web runnability. For fiber-based materials like paperboard it can be originated in the boardmaking process and tried to be compensated by web guiding and register control systems in printing process. Within an interdisciplinary research cooperation with different participants along the value chain of paperboard packaging production, the influence of different paperboard production conditions and register control strategies on web movement and register quality in a production scale gravure printing machine was performed in this study. Based on different boardmaking conditions, 13 different paperboard qualities were produced and each printed with 3 different register control strategies. The resulting register quality in cross direction (CD) and machine direction (MD) were measured as well as web movement, web tension and web moisture with several sensors along the printing machine. To assign the root causes of paperboard-induced web movement to boardmaking conditions, mechanical properties like tensile stiffness index in MD and CD and tensile stiffness orientation of the paperboard material have been measured and compared with data on web movement in the printing press. Further, web edge data were analyzed in frequency domain, to assign characteristic frequency components to their different mechanical root causes in boardmaking and printing process. It was found that CD position on tambour is the most influential board side parameter on lateral web movement and register quality. The lateral web shift differs significantly for middle and edge reels. Main reason for misregister in this study was attributed to board side slow lateral web movements with increasing amplitudes along the printing press. A register control strategy with an increasing gain per printing unit was most effective to improve register quality for this runnability behavior.

Keywords: board production conditions, register control strategies, web runnability, lateral web movement, misregister

JPMTR 135 | 2009 Research paper
DOI 10.14622/JPMTR-2009
UDC 676.22-023.881-021.465

Received: 2020-05-04
Accepted: 2020-06-16