Tadeja Muck

Characterization of pigments in coating formulations for high-end ink-jet papers

Abstract The effect of the two inorganic pigments widely used for coating of high-end ink-jet papers—amorphous silica and precipitated calcium carbonate (PCC)—and poly(vinyl alcohol) binder on ink-jet paper and print quality was studied. Multivariate analysis of results revealed that the type and the proportion of the pigments significantly influences several paper and print characteristics as determined by wicking, mottling, striking through, ink absorption and electrical surface resistance. Water absorption characteristics of paper are not related to ink-jet print quality but rather to the hydrophobicity/hydrophilicity of base paper sheet. The effect of the coat weight on the printed paper performance is considerable only in cases where 100% silica or silica–PCC combinations were applied. In coatings with 100% PCC, this effect is much smaller in comparison to that of the pigment itself.

THE INFLUENCE OF INK CONCENTRATION AND LAYER THICKNESS ON YELLOW COLOUR REPRODUCTION IN LIQUID ELECTROPHOTOGRAPHY TONER

Original scientific paper In liquid toner electrophotography, colour gamut is often diminished in the yellow region leading to problems with photo quality prints. It is known that the concentration of pigment particles in the printing ink and its thickness when applied on a paper substrate decisively influence final print quality. Variation of these two parameters for the yellow process ink was performed by modifying the printing process of the electrophotographic printer HP Indigo S1000. Printed colour patches of ECI test chart were analysed colorimetrically and using image analysis approach. Two-way analysis of variance was implemented to statistically assess the obtained results. Both studied responses – colour gamut volume and area coverage of halftone dots – were found to be primarily influenced by the yellow ink layer thickness and much less by the ink concentration. Increase from one to two ink layers had a significantly stronger effect on each of the two responses when compared to an additional increase from two to three layers.

Multi-color 2D Datamatrix codes with poorly readable colors

Datamatrix code is a type of 2D codes that can encode much more data on the same or smaller area than the linear barcodes. This makes 2D codes usable for marking even very small items. 2D codes can be decoded by the readers in retails but also with the mobile phones equipped with camera and appropriate software. 2D codes can be depicted in different materials or printed on different printing substrates. The application of the codes is broad, from magazines and newspapers to posters and packaging. Successful reading of 2D codes is possible if the code is printed in appropriate contrast between the printing ink and substrate, like black ink printed on white matt paper. Problems can occur if the code is printed in colors. The readability of 2D Datamatrix codes printed in cyan, magenta, yellow and black was studied. Yellow is proved to be poorly readable. In addition, the bi-colored and multi-colored 2D Datamatrix codes were studied. When four colors are used in creation of the 2D Datamatrix code, poorly readable elements, yellow codewords, may cause the reading failure. 2D Datamatix codes are capable to ensure good readability even if they contain a defined number of poorly readable codewords due to the Reed – Solomon error-correction system. The aim of the study was to determine the position of yellow printed, poorly readable, codewords in multi-colored 2D Datamatrix code, where the code still remains readable.

Evaluation of the Quality of Ink-Jet Printed Paper by Planar Chromatography

Paper chromatography and thin-layer chromatography (TLC) are two efficient analytical methods that can be used to characterize interactions between the ink (dye) and the paper surface in ink-jet printing. Both methods enable determination of ink adhesion rate as a function of fiber composition, pigment type, amount of binder, and dye fixation agent, etc. Paper chromatography was used to investigate the influence of fiber type and dye fixative on ink adhesion rate (comparison of RF values) and the waterfastness of printing on uncoated papers. The results suggested that Canon printing ink is more suitable for use on papers containing predominantly bleached, wood-free, i.e. chemical, fibers whereas the HP ink proved more appropriate for papers made from mechanical pulp. Addition of as little as 1% (w/w) dye fixative significantly improved print waterfastness. TLC was especially useful for optimization of coating color recipes for papers intended for photo-quality prints. The best color results were achieved with coatings based on a 1:1 combination of precipitated calcium carbonate and silica.