June 2012

Editor-in-Chief Nils Enlund

JPMTR 005 ⎮ 1105 Research paper

UDC 676.226.017:655.344

Received: 2011-06-28

Accepted: 2012-04-16

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Isolating contributions to gloss from surface mechanical and optical roughness, thin layer refractive index and wavelength filtering as a function of illumination, and geometry of incidence

Patrick Gane1,2, Pertti Silfsten3, Carl-Mikael Tåg4, Pertti Pääkkönen3, Jouni Hiltunen5, Kalle Kuivalainen3, Antti Oksman3, Kai-Erik Peiponen3

1 Aalto University, Helsinki, Finland; E-mail: patrick.gane@tkk.fi

2 Omya Development, Oftringen, Switzerland; E-mail: patrick.gane@omya.com

3 University of Eastern Finland, Joensuu, Finland; E-mails: pertti.paakkonen@uef.fi; kalle.kuivalainen@uef.fi

4 Forest Pilot Center Oy, Raisio, Finland

5 University of Eastern Finland, Joensuu, Finland

Abstract

Gloss is a commonly used parameter to express the surface optical and aesthetic quality of materials. In many cases of finished products, the dependence of gloss values derived from commonly used and emerging instrumentation is poorly understood. Examples of such products are surface lacquered furnishings or dye/pigmented laminates as well as printed matter, including printed paper. Paper is a porous medium and exhibits surface roughness related to the fibrous and filler components and the void structure interface with the surface. This roughness is manifest in both its structural profile evaluated by stylus profilometry, and convoluted with the stylus pressure and dimension, as well as in the form of an optical boundary by using laser profilometric techniques. Relating these two different methods of surface roughness characterisation to the gloss, as determined by broad spectrum illumination at two angles of incidence (60° and 75°), it is possible to show that the data fall into two families depending on whether the paper is printed with offset formulated ink or remains either unprinted or treated with ink diluent oil only. This separation of the data illustrates the impact of both refractive index and roughness on the gloss value obtained. The ratio between specular and diffuse reflectance is probed as a function of incidence angle and angle of acceptance, and further reveals the action of transmittance through the applied optically thin layer (ink). By using a diffractive optical element at well-defined wavelength in a method adopting normal incidence (µDOG), it could be shown that the colour filter effect of the thin printed ink film acting in partial transmittance impacted additionally on the represented gloss by partial absorbance of incident intensity in addition to the inclusion of the rougher underlying substrate boundary reflection. The offset ink colour set yellow (Y), magenta (M) and cyan (C), with the corresponding black (K), in that order, progressively reduced the apparent gloss due to the filtering of the incident red laser light, thus forming a series of separate correlations with structural roughness depending on print colour and optical print density. Similarly, when using laser profilometry to determine roughness, the geometry and wavelength used defines the apparent roughness observed. The role of the scale of roughness amplitude was illustrated by exploring the correlations between printed and unprinted surfaces according to whether the roughness was determined by stylus or optical methods. Using combinations of these techniques it is therefore possible to identify independently the impacts of (i) surface structural and optical roughness, (ii) refractive index, and (iii) thin layer optical filtering on measured gloss.

Keywords: gloss, coated paper, offset printing, composite surface quality, surface roughness and optics, thin layer optics, geometry of gloss measurement

JPMTR 006 ⎮ 1109 Technical paper

UDC 327.2:655.332

Received: 2011-07-27

Accepted: 2012-04-16

Bidirectional flexible mouldable electroluminescent lamps fabricated by screen printing

Karin Weigelt1, Eifion H. Jewell2, Chris O. Phillips3, Timothy C. Claypole3, Arved C. Huebler1

1 TU Chemnitz, Chemnitz, Germany; E-mail name.surname@mb.tu-chemnitz.de

2 Baglan Innovation Centre, Swansea, UK; E-mail: e.jewell@swansea.ac.uk

3 WCPC, Swansea, UK; E-mails: c.o.phillips@swansea.ac.uk; t.c.claypole@swansea.ac.uk

Abstract

Flexible thick film electroluminescent devices illuminating into both directions were fabricated using screen printing. The lamps are based on commercially available materials of electroluminescent phosphors and transparent conducting and dielectric inks. The bidirectional illuminating lamps compare favourably to unidirectional illuminating lamps regarding the emission spectra and the luminance. The emission is uniform in both directions and the luminance is in the range of uni-directional lamps. The printed bidirectional lamps offer a means of producing thin flexible illumination which may be advantageous to the lighting designer.

Keywords: flexible lighting, electroluminescence, bidirectional illumination

JPMTR 006 ⎮ 1111 Research paper

UDC 667.52.033.22:655.353

Received: 2011-07-27

Accepted: 2012-04-16

Formulation of water based silver inks adapted for rotogravure printing on ceramic green tapes

Rita Faddoul, Anne Blayo and Nadège Reverdy-Bruas

Laboratory of Pulp and Paper Science and Graphic Arts, Saint-Martin-d’Hères, France; E-mails: rita.faddoul@pagora.grenoble.fr; anne.blayo@pagora.grenoble.fr; nadege.reverdy@pagora.grenoble.fr

Abstract

The aim of this work is to study the printability of silver inks on LTCC (Low Temperature Co-fired Ceramics) flexible tapes by rotogravure printing. Commercial and newly developed LTCC tapes with different surface energies and pore sizes were investigated. Silver inks were prepared and formulated by adding 35 to 55 % silver particles (D50 ~ 2-3 µm) to a mixture of water/ethylene glycol/glycerol. Ink surface tension and viscosity were determined in order to establish their effects on the ink transfer from the cylinder to the substrate. Substrates were printed by rotogravure printing process with the formulated inks. The printing cylinder was engraved in intaglio, with a 45 µm cell depth to allow deposition of high ink thickness. Printed line properties such as thickness, width and roughness, were determined in order to establish the relationship between substrates characteristics, ink properties and printability. High silver contents (50-55 %) and viscosities allowed deposition of thick lines (5.6 µm). Thus, 55 % silver ink was printed on different substrates. An optimum 45 % silver weight allowed printing of narrower (160 µm) and smoother (1.4 µm) lines.

Keywords: water-based ink forumaltion, surface tension, viscocity, ceramic, surface energy, rotogravure printing, topography

JPMTR 008 ⎮ 1204 Original scientific paper

UDC 667:535.6

Received: 2012-03-02

Accepted: 2012-04-16

Colorimetric characterization of thermochromic composites with different molar ratios of components

Ondrej Panák1, Nina Hauptman2, Marta Klanjšek Gunde2, Marie Kaplanová1

1 University of Pardubice, Czech Republic; E-mails: ondrej.panak@upce.cz; marie.kaplanova@upce.cz

2 University of Ljubljana, Slovenia; E-mails: nina.hauptman@mf.uni-lj.si; marta.k.gunde@ki.si

Abstract

The thermochromic composites used for this study were prepared by applying crystal violet lactone as a leuco dye together with bisphenol A of different molar ratios as a developer and 1-octadecanol as a solvent. The colorimetric properties of all composites were measured during heating and cooling within a broad temperature range, which makes it possible to characterize entire colour hysteresis loops. It was demonstrated how these properties depend on the developer and solvent ratios. The investigations concentrated in particular on the total colour contrast between the coloured and the discoloured states, the temperature interval needed for the colour to change, and the width of the hysteresis loop. It was shown that composites with the same colorimetric properties could be prepared by applying a relatively broad range of dye/developer concentration ratios.

Keywords: crystal violet lactone, bisphenol A, colour hysteresis, total colour contrast, thermochromism