REGULARITIES OF INK-WATER BALANCE STABILITY IN OFFSET PRINTING

Ink transfer onto the printed surface is provided by parameters as follows: dampening solution in ink emulsification level, dampening solution parameters as long as its ingredients and their exact dosing, dampening solution transfer features between fountain rollers, blanket and printing plate and printed material surface characteristics, thickness and volume of ink on the printing plate, level of ink setting on the imprint. Deviations in transfer from the optimal parameters cause the negative consequences. On the other hand there are hardly any new approaches in explanations of mutual influence of the technological environment parameters in the printing contact which results in lowering the printing process effectiveness while printing with minimal layers of ink-water emulsion. In this article the mutual influence correlations of the printing contact technological environment characteristics are revealed, allowing operating the minimal layers of ink-water emulsion on high-productive machines while normalizing the color reproduction and imprints’ quality.

Numerical Characterization of the Effect of Coating Solid on Binder Distribution

Binder is the essential component of coating color recipe. The amount and type of latex binder has a significant effect on both the structure and chemical-physical properties of coated paper, which affect critical surface properties, e.g., print gloss, roughness, ink setting rate via liquid absorption, and print mottle The main aim of this study was to investigate the effect of coating solid on the binder distribution in the method of numerical analysis by Laser Scanning Confocal Microscope (LSCM). In this study, Rhodamine B was used to stain the binder and as the probe to characterize z-directional distribution of the binder using LSCM. The results implied that it was reliable and effective method using LSCM to characterize the z-directional distribution of binder and analyze the influence of coating solid on binder distribution in the z-direction. It could be concluded that the coating solid played an important effect on binder distribution in coated paper and low coating solid with more water accelerated binder migration to the interior of base paper, sample with 60% coating solid is good to binder distribution and coating layer forming.

Calendering Effects on Coating Pore Structure and Ink Setting Behavior

Coating layer pore structure significantly affects surface appearance, optical properties, and print-ability performance of multiply coated papers. Generally, fast ink setting can be realized by use of fine pigments, or pigments with steep particle size distribution. Ink-paper interaction of coated papers also changes significantly in calendering. The objective of this study was to better understand the influence of calendering on the pore structure of multilayered coated papers and to highlight the effect of this pore structure change on ink setting behavior. Laboratory calendering trials demonstrated that the pore structure of calendered paper is reduced with increased calendering temperatures. Mercury porosimetry and image analysis of scanning electron microscope images of calendered papers highlighted the gradual reduction of total pore volume, which, in combination with the reduced surface porosity, resulted in slower ink setting. If ink setting speed is to be preserved, calendering at low surface temperatures and a higher number of nip passes is preferred to reach a desired paper gloss level. Results also were compared to common theoretical models for liquid penetration into porous structures. These models can also be used to describe the influence of calendering-induced pore structure changes on ink setting. This work demonstrates optimization of calendering parameters to reach a balance for paper gloss and ink setting. The optimum depends on the machine equipment available and has to be checked separately for each concept of multiply coated paper and calender conditions.

Comparison of Dynamic Print Gloss Measurement Techniques

Well-defined optical properties are essential in determining the quality of printed papers. The mea-surement of optical properties, such as print gloss, as a function of time provides a means of studying ink-setting behavior and paper-ink interactions. This study compares three different methods for measuring dynamic print gloss: a dynamic gloss meter, a diffractive-optical-element-based gloss meter (DOG), and a polarized-light reflec-tometer. Four double-coated papers were printed at varying ink levels. This paper compares and discusses the tech-nical details of the measurement techniques. Dynamic print gloss results are evaluated in the light of current ink-set-ting theories. Each of the methods is highly applicable to ink-setting studies. With low inking level, the paper properties, surface roughness, and absorption are important for gloss development. Printing conditions such as speed, nip geometry, and materials have significant influence. As the amount of ink used in printing is increased, the printing conditions start to influence the gloss dynamics considerably, especially on glossy papers.