Improving the security of conventional and UV luminescent flexographic prints by modification of the printing inks using nanoparticles

The security and protection of printed products against counterfeiting have become more advanced and increasingly used in the field of graphics technology. In this research, conventional process black (PB) and UV luminescent (UVL) inks used in flexography, modified by nanoscale silicon dioxide (SiO2), anatase and rutile titanium dioxide (TiO2), and zinc oxide (ZnO) at different concentrations were used. The purpose of adding nanoparticles to these inks was to protect PB and observed UVL inks from counterfeiting without significantly affecting the optical appearance and colourimetric properties of the printed motives. The results have shown that nanoparticles did not significantly affect the spectral reflectance of UVL inks observed under UV irradiation or the visual effect of UV luminescence. In addition, the nanoparticles had a negligible effect on the optical and colourimetric properties of PB inks, as evidenced by a slight increase in colour lightness after the addition of nanoparticles. Indirect detection of nanoparticles through their interaction with PB and UVL inks was possible through FTIR-ATR spectroscopy, which showed changes in the spectra of PB and UVL inks with nanoparticles compared to nanoparticle-free inks in the fingerprint region. This research opened the possibility of expanding the use of nanoparticles of different types and concentrations for process, spot, luminescent and other special and conventional inks in the field of graphic technology

Improving the security of conventional and UV luminescent flexographic prints by modification of the printing inks using nanoparticles

The security and protection of printed products against counterfeiting have become more advanced and increasingly used in the field of graphics technology. In this research, conventional process black (PB) and UV luminescent (UVL) inks used in flexography, modified by nanoscale silicon dioxide (SiO2), anatase and rutile titanium dioxide (TiO2), and zinc oxide (ZnO) at different concentrations were used. The purpose of adding nanoparticles to these inks was to protect PB and observed UVL inks from counterfeiting without significantly affecting the optical appearance and colourimetric properties of the printed motives. The results have shown that nanoparticles did not significantly affect the spectral reflectance of UVL inks observed under UV irradiation or the visual effect of UV luminescence. In addition, the nanoparticles had a negligible effect on the optical and colourimetric properties of PB inks, as evidenced by a slight increase in colour lightness after the addition of nanoparticles. Indirect detection of nanoparticles through their interaction with PB and UVL inks was possible through FTIR-ATR spectroscopy, which showed changes in the spectra of PB and UVL inks with nanoparticles compared to nanoparticle-free inks in the fingerprint region. This research opened the possibility of expanding the use of nanoparticles of different types and concentrations for process, spot, luminescent and other special and conventional inks in the field of graphic technology

Customization of flexographic printing plates related to uvc-induced changes in the crosslinking degree

In this paper, the swelling properties of photopolymer flexographic printing plates related to the variations of UVC post-treatment have been analysed. The aim of the research was to interconnect the changes in the cross-linking degree of the photopolymer material occurring due to the modified UVC radiation of the printing plate and the changes of its surface free energy crucial in the graphic reproduction process. Changes in the crosslink-ing degree in the photopolymer materials have been analysed by the swelling experiments. Results have proven that the partial dissolution of the photopolymer material caused by the immersion of the printing plates in vari-ous solvents is in the direct relation with the changes of the dispersive surface free energy. UVC post-treatment, used for the crosslinking termination and the definition of the surface properties of printing plates, is therefore directly affecting the resistivity of the printing plate in the solvent environment. By calculating the correlation coefficients for the weight loss of the photopolymer material in solvents and the dispersive surface free energy, the relation between the crosslinking degree and the UVC post-treatment has been established

Impact of Screen Ruling on the Formation of the Printing Elements on the Flexographic Printing Plate

Flexography is a printing technique widely used in the packaging production. The main feature of flexography is the use of a printing plate elastically deformed during the reproduction process. The printing plate is made of an elastic material, rubber or nowadays of mainly different types of photopolymer. The elasticity of the plate enables the printing on a wide range of printing substrates, which is one of its advantages compared to other printing techniques. On the other hand, deformations of the printing plate in the printing process caused by the pressure between the printing plate and the substrate present a major limitation of flexography. Apart from the functional properties of the printing plate in the printing process, the plate making process, including photo polymerization, considerably influences the value of halftones on the printing plate, and consequently on the final product. The aim of this paper is to examine the influence of screen ruling on the formation of printing elements and the adjustment of the printing plate making process in order to achieve optimal quality of the printing plate and, therefore, the final product. The results have shown that the use of different screen rulings is of great significance in the processes of printing plate curve adjustment. It was proven that the use of different screen ruling has a considerable influence upon relief depth and a cross-section of the printing elements (3D analysis), which again have a significant impact on the quality of the final product, but cannot be detected in 2D analysis

Model poboljšanja izrade fleksotiskarskih tiskovnih formi

Thermal development process of photopolymer printing plates is one of the newest technologies in the flexographic reproduction process. It is solely based on mechanical process and thus enables the elimination of the chemical processing and drying phase from the plate making process. Taking into account that chemical processing is one of the critical problems in standardization of the plate making process, thermal development process should ensure greater quality and stability in the plate making process. This paper evaluates the specific conditions in the plate making procedure based on thermal development. Testing of the back and main exposure duration of the photopolymer plates, as well as duration of the thermal development, were the objects of this research. The thickness and hardness, as well as SEM analysis of the printing plates were performed. Characterization of the produced plates was made and new model for improving the production line of the observed flexographic plates was defined.Proces termalne obrade fotopolimernih tiskovnih formi za fleksotisak novost je u grafičkom reprodukcijskom procesu. Proces je baziran na mehaničkoj obradi tiskovnih formi čime se eliminira proces kemijskog razvijanja i sušenja iz postupaka izrade tiskovnih formi. S obzirom da je kemijsko razvijanje jedno od najnestabilnijih procesa u izradi tiskovnih formi te time otežava standardizaciju postupka izrade tiskovnih formi, proces termalne obrade bi trebao unaprijediti kvalitetu i stabilnost promatranog procesa. U ovom radu su praćene sve faze u izradi tiskovnih formi baziranih na termalnoj obradi. Mjerena je debljina i tvrdoća uzoraka, te je provedena i SEM analiza. Karakterizacija uzoraka je provedena, te je predložen model za poboljšanje uvjeta izrade fleksotiskarskih tiskovnih formi

Thermal, surface and mechanical properties of PCL/PLA composites with coconut fibres as an alternative material to photopolymer printing plates

In this paper, methods of thermal, mechanical and surface analyses of biodegradable PCL/PLA composites with the addition of different concentrations of coconut fibres were performed. The aim was to assess the potential of these composite materials for the relief-printing plates as an alternative to classical photopolymer materials. Differential scanning calorimetry, surface free energy calculations and hardness measurements were performed on the samples. Results have shown that most thermal transitions that are characteristic for PLA and PCL do not take place in the area of temperatures applicable in the printing process. Most thermal transitions were not affected by the addition of coconut fibres. Coconut fibres in the composite structure contributed to the increased hardness of the material. Moreover, the hardness range of the prepared PCL/PLA composites was within the range of some classic photopolymer printing plates. By adding coconut fibres in higher concentrations, surface free energy of the materials decreased, which enables a wider application of the material for the production of printing plates. From the obtained results it can be concluded that there is a potential for the use of PCL/PLA biodegradable composite materials in the manufacture of various relief-printing plates for different printing techniques (letterpress, embossing, label printing)

Quality Assurance of Process Free Thermal Plates

In this paper a method for manual processing of process free printing plates is defined which ensures reproducible results. This decoating procedure can help print service providers with certain quality checks (like linearization) that are otherwise more expensive or even not feasible altogether for such plates. This method holds for quality assurance only and is not suitable for the actual production

Surface Modification and Properties of Thin Ink Films with Added TiO2 and ZnO Nanoparticles Applied on Paperboard Substrates

In this study, the surface modification of thin ink films with added nanoparticles was used to improve the functional properties of ink applied on paperboard substrates. The surface modification was performed by additional exposure of the samples to xenon radiation. Anatase TiO2, rutile TiO2 and ZnO were added to the base ink. The effect of surface modification on the surface, structural, and mechanical properties of the printed ink films was determined by FTIR-ATR spectroscopy, calculating the surface free energy and adhesion parameters, performing the rub resistance test of the printed samples, and by measuring the resistance to bending. Color measurements on the ink films were performed in order to observe the optical properties of unmodified and modified samples. The results showed that surface modification significantly improved the adhesion properties of the thin ink films and the mechanical properties of the samples. The results obtained on uncoated and coated paperboard showed that the addition of rutile TiO2 and ZnO nanoparticles had the greatest effect on the rub resistance of the ink films. The results of the color analysis showed that the addition of nanoparticles did not change the optical properties of the modified ink films and that rutile TiO2 and ZnO nanoparticles improved the lightfastness of the applied ink films