Tomislav Cigula

The characterization of microcapsules printed by screen printing and coating technology

The graphic industry is one of the first that began to utilize microcapsules, which are nowadays used in various fields of applications such as: medicine, pharmacy, agriculture, construction industry, chemical industry, food industry, biotechnology, cosmetic industry, photography, electronics, textile and printing industry (Boh et al., 1999; Arshady & Boh, 2003; Boh, 2007; Poncelet & Boh, 2008). Microcapsules are tiny spheres that usually consist of two parts: the core and the shell (Gosh, 2000). Microencapsulation enables the core material to reach the “target” areas without getting affected by the surroundings, while the microcapsule microscopic size enables the consumption of the very small active agent quantity (Gosh, 2000; Dubey et al., 2009; McShane & Ritter, 2010; Microtek Laboratories Inc., 2015). One of the simplest and the most frequently used encapsulation method in the graphic industry is “in situ” polymerization, which provides high active agent loadings and smoothly shaped microcapsules with good mechanical properties (Kuković & Knez, 1998; Gosh, 2000; Nelson, 2001; Starešinič, Šumiga & Boh, 2011; Ocepek et al., 2012). Microcapsules used in printing applications can be activated by the use of different mechanisms, which are mainly based on external pressure, abrasion and heat or light activation (Gosh, 2000; Nelson, 2001; Boh & Šumiga, 2008; Sensor Products Inc., 2015). Rastko Milošević1, Nemanja Kašiković1, Tomislav Cigula2, Urška Stanković Elesini3 and Raša Urbas3

Surface quality of the Ni-TiO2 Composite coatings produced by electroplating

Composite nickel coatings on a brass substrate were produced from suspensions consisted of a conventional nickel sulphate bath and fine TiO2 particles (dp < 0.35 μm). Characterization of coatings surface was performed by using optical and SEM micrographs, by EDS analysis and by determining the surface roughness parameters. Metallographic analysis has also been done in order to get an insight about particles distribution throughout the thickness of the coating layer. Presence of TiO2 particles in electrodeposited metal affected the surface morphology. Particles were embedded as smaller or bigger agglomerates within the coatings, as well as the individual particles. Metallographic analysis showed uniform distribution of particles and their agglomerates within the coating. Surface roughness parameters of the composites have had up to 35 times higher values than the ones of the pure nickel coatings. Roughness maxima appeared at the concentration of particles between 10 and 20 g dm-3. Then it drops down and remains constant for concentrations > 40 gdm-3. SEM micrographs showed irregularities like single-nodule, or beads of nodules on the surface. Relationship between surface roughness and current density has not been noted.

Formation of the Printing Elements in the Photopolymer Material Used in Flexography

Starting point of this paper is photopolymer printing plate used for flexographic printing. It is used for transfer of the printing ink onto the printing surface during the reproduction process. Photopolymer printing plate consists of several layers: polyester basis, photo sensitive polymer material and LAMS - Laser Ablation Mask. In the platemaking process the photosensitive material, which will form a printing plate, has to be several time exposed to different radiation in order to obtain a functional printability performance. LAMS layer has a role of masking in the exposure process. Upon pre-exposure, LAMS layer has to be removed by laser ablation only at the surfaces where photopolymer printing plate needs to be exposed. After ablation the exposures to UV lights follows and the plate will be finished with chemical removal of the unexposed parts of the polymer. Functionality of the finished printing plate has to be characterised and monitored in every procedure step because the formed image element on the printing plate has a major influence on the quality of the finished printed product. In this paper observing of the changes in the polymer material which is caused by exposure through LAMS layer will be performed. The aim is to measure the surface openings on the LAMS mask and to measure surface coverage (image elements) on the polymer material formed by exposure through the LAMS. Measuring will be made by image analysis software based on microscopic images of the control fields of differing halftone values. It is assumed that there will be a correlation between the LAMS openings and formed image elements on the printing plates. Preliminary results indicate that certain differences in image elements can be detected and are probably the consequence of the different amount of irradiated surface of the polymer material. Since the polymer material which forms the printing plate should be stable in the graphic reproduction process, results of the paper will explain the influence of UV exposures on polymerisation process and on the functional printability performance of the plates.

Influence of the Print Run on Silver Halide Printing Plates

The most common printing technique today is lithography. The difference between printing and nonprinting areas on a printing plate is accomplished by opposite physical and chemical properties of those areas (MacPhee, 1998). The printing areas are made of photoactive layer that attracts oil and chemical substances with oil solvent – printing inks. The nonprinting areas are made of aluminium-oxide which attracts water based substances – the fountain solution. There are many of various types of photoactive layer which are used for production of offset printing plates, among others is silver halide layer. The usage of the silver halide technology in the graphic reproduction is not a novelty. The filmmaking phase is based on the usage of the silver halide as the photographically active ingredient, for instance, AgBr (silver bromide). The new, digital plate making technology (Computer to Plate, CtP) eliminates the filmmaking phase and therefore enables control of the printing plate’s exposure made by computer. CtP technology eliminates the filmmaking phase, but it also results with the reduction of needed material quantities and required time for the production (Limburg, 1994 ; Seydel, 1996). In this paper the basis of the graphic reproduction by using the silver halide digital printing plates was described. The changes of the AgX copying layer and the surface of the aluminium base in the printing process have been observed. The surface characteristics were determined by measuring the relevant surface roughness parameters. In addition, measurements of coverage values on the prints, detailed at smaller print run, were conducted. Results showed that surface changes on the printing plate are changing during printing process and that these changes influence transfer of the printing ink on the printing substrate. These measurements proved to be of great interest in the graphic reproduction as they enable us to determine consistency of the printing plates during the printing process, to predict the endurance as well as to define the print run which will result with optimal quality prints.