Maša Žveglič, Valerija Demšar, Raša Urbas, Nina Hauptman, Marijan Maček and Marta Klanjšek Gunde

Abstract
We have analysed thicknesses and shapes of narrow lines, which were screen-printed using commercially available silver-based conductive ink. The influence of wet-to-wet overprinted layers and the influence of the used substrate on the topology of the lines were evaluated by profilometer measurements, optical- and scanning electron micrographs. Finally, the specific resistivity of these lines was measured by the help of the four-terminal method, which enables elimination of the effects of contact resistance. The results show that overprinting of layers does not considerable influence on the shape of the lines but gives rise to smaller resistivity. Printed lines with larger resistivity where obtained on the porous substrate with poor adhesion, whereas on the smooth paper smaller resistivity was obtained. Some influence of the curing time was also measured. When using larger curing dose, lines with a somewhat smaller resistivity were obtained.

Keywords: Printed electronics, Electrical resistivity, Printing ink, Screen printing
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Rahela Kulčar, Mojca Friškovec, Nina Knešaurek, Barbara Sušin, Marta Klanjšek Gunde

Abstract
UV-curable leucodye-based thermochromic inks with activation temperature of 31 °C in blue, red and black shades were analysed. The colour of samples does not depend only on their temperature but also on thermal history – they show colour hysteresis. Similar hysteresis loops were obtained for the red and blue samples and narrower for the black sample, as measured by cycling in 14–40–14 °C region. The blue and black samples have approximately closed loops but a small colour difference was obtained even after one cycle for the red one thus the loop remains slightly opened. The colour of all samples also depends on the UV dose applied at curing. This difference was followed over the whole hysteresis loop. The largest values were measured for the red sample where the CIEDE2000 total colour difference rises above 4 and remains well observable all over the temperature region applied for cycling. One of the possible reasons for this effect might be different degree of polymerisation of the polymer matrix achieved by different UV curing.

Keywords: Thermochromic inks, UV curing, Screen printing, Colorimetry, Dynamic colour, Hysteresis
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Erzsébet Novotny, Ildikó Endrédy

Abstract
Surface refining procedures have an increasing significance in satisfying quality and other special demands (uniqueness, appearance) made on printing house products. Besides the effects intended to be achieved (gloss, mechanical protection) surface refining technologies occasionally can go together with other changes of the optical appearance of the prints.

Within surface refining procedures our tests focused on the effect of varnishing on print appearance. The purpose was to determine the extent and direction of colour changes occurring when paper based cards are produced using different print carrier and varnish combinations.

We examined the change of metric chroma as a function of sample lightness, the change of lightness as a function of the chroma of the samples, hue differences as a function of hue angles of the samples. We established that the Sericol type varnish on matt paper samples showed the biggest, and Wessco type varnish on glossy paper samples the smallest change. Based on our test results we propose some improvement of technological processes.

Keywords: Card printing, UV-varnishing, Gloss measurement, Abrasion test, Colour measurement
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