| Abstract | Za visokokvalitetni višebojni otisak na elektrofotografskom tiskarskom stroju treba pripremiti
i podlogu na koju se otiskuje. Da bi se tekuće elektrofotografsko bojilo optimalno vezalo na
podlogu, treba oplemenjivanjem postići optimalnu površinsku napetost. To se postiže korona
tretmanom ili premazivanjem tekućinom za oplemenjivanje. U okviru disertacije provest će
se istraživanje i redefiniranje utjecaja snage korone i debljine nanosa tekućine za
oplemenjivanje na kvalitetu višebojne reprodukcije. U tiskarskom procesu to podrazumijeva
utvrđivanje razlika u volumenu obojenja, strukturi karakterističnih tiskovnih elemenata,
amplitudno moduliranom rastriranju i povećanju broja višebojnih separacija. Na osnovi
rezultata odredit će se optimalne višetonske vrijednosti reproduciranih tonova (Lab i prirast
RTV-a) kojima će se ostvariti bolja kvaliteta digitalnih otisaka i redefinirati trenutni
industrijski standard za digitalni tisak.
Rezultati pokazuju da, u odnosu na idealni PSD otisak, minimalne devijacije primarnih boja
iznose: ∆EC(1g/m2_0W) = 1,49; ∆EM(0g/m2_450W) = 2,21; ∆EY(0,5g/m2_0W) = 1,85; ∆EK(0g/m2_0W) =
2,79. Korona tretman neće značajno utjecati na kolornu promjenu procesnih boja (∆EY =
0,01; ∆EK = 0,55). Pri tom otisci nastali pretiskivanjem ostvaruju značajnije kolorne
promjene, ali još uvijek ispod vizualne granice (∆Emax. = 0,88). Nanosom same tekućine za
regulaciju površinske napetosti (prajmer) ostvarene devijacije primarnih boja ostaju niske
(∆EC = 0,02; ∆EK = 0,61), pri čemu i sekundarne boje ostaju gotovo nepromijenjene (∆Emax. =
0,29). |
| Abstract (english) | Today, for the needs of modern packaging, digital printing technology has been increasingly
used, with the main representatives of Electro photography and Inkjet. Their share in the total
value in the graphics industry is 20 %. High-quality multicolor printing in
electrophotographic printing requires an additional preparation of the printing substrate to
which special colors are printed. In order for the liquid electrophotographic ink to be
optimally adhered to the substrate, it is necessary to achieve the ideal substrate surface
tension with additional enrichment. To ensure the desired bonding of the ink to the printing
substrate, the corona treatment and coating with the liquid for regulating the surface tension
are applied. The corona treatment generates surface modification that is manifested in micro
roughness resulting in better ink binding. In the case of printing substrates whose surface is
uneven, preparatory coating should be applied to improve the surface layer properties.
Within the scope of thesis, the research and redefining of the influence of the corona power
and the thickness of the applied of surface tension regulation fluids on the quality of
multicolor reproduction has been carried out. The HP Indigo WS 6800 electrophotographic
printing machine equipped with a Vetaphone corona unit and a 5-cylinder Michelman primer
unit, was used in the experiment. As a printing substrate is used a certified art paper Condat
90 g / m2 intended for the realization of high-quality prints.
The methods used to detect changes in prints are nondestructive and are based on colorimetry
and spectrophotometry These methods allow to determine the differences in the color gamut,
the structure of the characteristic screening elements, the amplitude-modulated screening and
the increase in the number of multicolored separations, in the printing process itself. Based on
the obtained results, the optimal color tones values (Lab and dot gain) with which the higher
quality of digital prints is achieved have been determined, leading to the redefinition of the
current industry standard for digital printing.
Three basic hypotheses have been put in the dissertation. The first hypothesis selectively
examines the variation effect of corona power on multi-color reproduction of the HP Indigo
printing machine, while the second hypothesis examines the thickness influence of applied
fluid for regulation of surface tension on the required print quality. The third hypothesis is
most comprehensive and gives a general analysis of the defined sample experiment and
correlates them to the existing standard for the graphics industry (ISO 12647-8).The results show that in comparison to the ideal PSD imprint, minimal deviations of the
primary colors are: ∆EC(1g/m2_0W) = 1,49; ∆EM(0g/m2_450W) = 2,21; ∆EY(0,5g/m2_0W) = 1,85;
∆EK(0g/m2_0W) = 2,79. Corona treatment will not significantly effect on colour changes of
process colors (∆EY = 0,01; ∆EK = 0,55). In the case of these imprints created by overprint,
significant color changes are achieved, but still below the visual boundary (∆Emax. = 0,88). By
applying the same surface tension regulation fluid (primer), the resulting primary color
deviations remain low (∆EC = 0,02; ∆EK = 0,61), with the secondary colors remaining almost
unchanged (∆Emax. = 0,29).
The obtained results visually do not show any significant color change for the glossy coated
substrate. However, bringing them in correlation with other printing parameters
(photoreceptor illumination, photoreceptor developing, toner fixation ...) can contribute to the
stability of electro photographic press with liquid toner (ElectroInk), which ensures
reproduction consistency in areas with different tonal coverage. The type of pigment in
ElectroInk dyes and the treatment of printing substrate have different impacts on the
realization of the required color results and the resulting tone changes. Cyan ElectroInk color
will be the most stable (the slightest color change), while the black ElectroInk color will be
significantly more unstable (color changes are visible to the human eye). |
