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Evolutions in food packaging printing

You are here: Conferences & Events * 2008 Valencia * Abstracts * 2. Printing and printing materials

2. Printing and printing materials

2.16. Considerations for thermally engineered coated printing papers: focus on electrophotography

Philip Gerstner(1), Patrick A. C. Gane(2)

(1) Helsinki University of Technology
Faculty of Chemistry and Materials Science, Department of Forest Products Technology
Vuorimiehentie 1A, P.O. Box 6300, 02150 Espoo, Finland
E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

(2) Gane is also Head of Research and Development
Omya Development AG, CH-4665 Oftringen, Switzerland

For the printing of coated papers, the coating layer fulfils a specific role as the image receiving interface. Its physical properties are vital for quality and efficiency of the printing process. This work takes the thermal properties of the coating layer into consideration as heat is applied to its surface, and illustrates its role in respect to toner adhesion as a print quality parameter in the electrophotography process. Pigment tablets are used to provide experimental values of thermal diffusivity and conductivity. Three types of coating pigments are studied: ground calcium carbonate, both very fine and coarse grades (vfGCC, cGCC), a very porous and bulky modified calcium carbonate (MCC) and talc. Temperature gradients within the coating and base sheet substrate, and fusing nip conditions, are studied adopting finite element simulation. Toner adhesion is measured by a tape test on laboratory coated paper samples. The simulation of the fusing nip clearly shows advantages of having a thermally insulating MCC coated substrate, in that the local, surface concentrated, temperature gradients are beneficial for the fusing process and the base paper is shielded, thus minimizing heat losses. Because of the strong influence of surface roughness on the printed sheets, and the high fusing temperature/degree provided by commercially applicable printers, no direct relation between the toner adhesion measurements and the thermal conductivity of the coating layer could be seen. However, it is recognized that a smooth and even printing surface, in combination with an insulating coating structure, could be used to lower the specific energy required to fuse toner, provided the surface structure continuity/packing density is sufficient.

Keywords: Electrophotography, thermal properties, toner adhesion, surface roughness, printability

2.17. Highly accurate material characterization of paper for the simulation of printing processes

Thomas Kaulitz, Edgar Dörsam

Technische Universität Darmstadt, Institute for Printing Science and Technology
Magdalenenstraße 2, 64289 Darmstadt, Germany
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Precise and reproducible measurements from characterization of material are the basis of a good simulation of the printing process. Paper has not yet been properly analyzed in engineering terms in this regard. It is known that paper displays an orthotropic material behavior in the three primary directions MD, CD and ZD. The existing measurement data found in the literature cannot be designated as confirmed. Only the uniaxial tensile tests in the MD and CD direction are completed.

Moreover, there is unclarity of the relationship between tensile and compressive loads in the material.

This article is limited to the characterization of paper in the MD direction. It shows that the material behavior of paper is not identical under a tensile and compressive load. Measurement techniques and a classification system are proposed for generating reproducible and highly precise measurement results. The need for such investigations is illustrated by a practical example: The determination of the conveying speed of a roll with a paper web looped around.

Keywords: Experimental, force-deformation behavior MD, paper
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