Search Results (10)

The objective of this research was to fine-tune the surface properties of printed ink layers by incorporating TiO₂ and ZnO nanoparticles into conventional flexographic ink. This modification aimed to improve print quality while simultaneously providing protection against counterfeiting. The presence of nanoparticles in the inks was indirectly detected through FTIR-ATR spectroscopy, which revealed changes in the fingerprint region of the ink spectrum when nanoparticles were added. This alteration enhanced the anti-counterfeiting potential of a produced print. The colorimetric measurements indicated that the addition of nanoparticles did not significantly affect the colorimetric properties of the print, since the maximal calculated ΔE_ab value was 2.83. However, the nanoparticles notably improved the ink coverage on printed line elements and allowed for the printing of elements without the characteristic outline associated with flexographic printing. The best results in terms of line definition and coverage were achieved with the addition of 2% rutile TiO₂ and 1% ZnO to the ink: the measured line segment area covered in ink was 28.5% larger than the same area printed using unmodified ink. This improvement in print quality was attributed to the modified surface free energy (SFE) of the inks, which also influenced the adhesion parameters between the printed layer and the printing substrate. The lowest total SFE was calculated for the ink without added nanoparticles (40.31 mJ/m²), and the highest for the ink with the addition of 2% rutile TiO₂ (48.33 mJ/m²). The work of adhesion increased after adding the nanoparticles to the ink, thereby improving the adhesion. The highest work of adhesion (79.36 mJ/m²) was calculated for the ink with 2% rutile TiO₂. Interfacial tension was low and close to zero for all printed ink layers, and the lowest value was achieved for the ink without added nanoparticles (1.47 mJ/m²). The findings of this research demonstrated that fine-tuning the properties of flexographic inks using nanoparticles can yield several benefits in terms of optimizing the quality of and providing counterfeit protection for specific printed motifs. Full article

This work provides a method for the development of conductive water-based printing inks for gravure, flexography and screen-printing incorporating commercial resins that are already used in the printing industry. The development of the respective conductive materials/pigments is based on the simultaneous (in one step) reduction of silver salts and graphene oxide in the presence of 2,5-diaminobenzenesulfonic acid that is used for the first time as the common in-situ reducing agent for these two reactions. The presence of aminophenylsulfonic derivatives is essential for the reduction procedure and in parallel leads to the enrichment of the graphene surface with aminophenylsulfonic groups that provide a high hydrophilicity to the final materials/pigments. Full article

In this work, three types of photopolymer printing plates for packaging printing were subjected to varied UV (ultraviolet radiation) post-treatments, and their surface free energy (SFE) components were calculated. SFE of the photopolymer printing plate is crucial in the process of transferring the ink from the printing plate to the substrate. Calculated polar and dispersive SFE components were used to build and optimize artificial neural networks for the prediction of the surface properties of different photopolymer materials after the performed UVA and UVC post-treatments. In this way, the production of printing plates with tailored SFE components could be automated and optimized. Consequently, products with improved qualitative properties could be printed. Results of the research have shown that the choice of the neural network’s activation function is most significant for the minimization of the mean squared error (MSE), while the number of neurons and hidden layers in neural networks has less influence on MSE. The optimized neural networks applied for common photopolymer materials in this work have the potential to be applied for the automation of the printing plates’ post-treatment process and the production of printing plates with surface properties tailored to specific printing systems. Full article

Flexible plastic substrates are widely used in printed electronics; however, they cause major climate impacts and pose sustainability challenges. In recent years, paper-based electronics has been studied to increase the recyclability and sustainability of printed electronics. The aim of this paper is to analyze the printability and performance of metal conductor layers on different paper-based substrates using both flexography and screen printing and to compare the achieved performance with that of plastic foils. In addition, the re-pulpability potential of the used paper-based substrates is evaluated. As compared to the common polyethylene terephthalate (PET) substrate, the layer conductivity on paper-based substrates was found to be improved with both the printing methods without having a large influence on the detail rendering. This means that a certain surface roughness and porosity is needed for the improved ink transfer and optimum ink behavior on the surface of the substrate. In the case of uncoated paper-based substrates, the conductivity and print quality decreased by preventing the formation of the proper and intimate ink-substrate contact during the ink transfer. Finally, the re-pulpability trials together with layer quality analysis detected very good, coated substrate candidates for paper-based printed electronics competing with or even outperforming the print quality on the reference PET foil. Full article

This paper researches the issues related to the print quality in flexography, especially the influence of the print run and inadequate printing settings on dot deformation. Dot deformation can lead to inconsistencies in print quality, such as a loss of highlight tones or an unpredictable increase in tonal value. This research was conducted on two concrete examples of flexible packaging printed on transparent films. All significant parameters of dot deformation were evaluated, including dot coverage, dot sharpness and the uniformity of the ink density. The increase in the coverage values in the midtones was linear throughout the entire print run, while in the light tones, it was more logarithmic. The overall percentage deviations from the reference value were 6.3% in the midtones and 52.6% in the light area. The increase in dot coverage was due to the wear of the polymer plate, which caused the side shoulders of the dot to become a part of the printing surface. An analysis of the ink density showed a much more homogeneous shape of the dot at the beginning of the print run. The correct ratio of the anilox roller line screen to the line ruling of the printing plate is important in order to ensure a minimum dot size in print. Full article

The work is framed within Printed Electronics, an emerging technology for the manufacture of electronic products. Among the different printing methods, the roll-to-roll flexography technique is used because it allows continuous manufacturing and high productivity at low cost. Nevertheless, the incorporation of the flexography printing technique in the textile field is still very recent due to technical barriers such as the porosity of the surface, the durability and the ability to withstand washing. By using the flexography printing technique and conductive inks, different printings were performed onto woven fabrics. Specifically, the study is focused on investigating the influence of the structure of the woven fabric with different weave construction, interlacing coefficient, yarn number and fabric density on the conductivity of the printing. In the same way, the influence of the weft composition was studied by a comparison of different materials (cotton, polyester, and wool). Optical, SEM, color fastness to wash, color measurement using reflection spectrophotometer and multi-meter analyses concluded that woven fabrics have a lower conductivity due to the ink expansion through the inner part of the textile. Regarding weft composition, cotton performs worse due to the moisture absorption capacity of cellulosic fiber. A solution for improving conductivity on printed electronic textiles would be pre-treatment of the surface substrates by applying different chemical compounds that increase the adhesion of the ink, avoiding its absorption. Full article

This study characterizes and compares the parameters of the quality reproduction of fine elements in flexography on coated and uncoated paper as well as on OPP film (oriented polypropylene). A monochrome test form was created and printed using cyan UV ink. The analysis of results confirms the importance of interaction between the printing substrate and ink; it also indicates identical line and text deformations on the print. Quality reproduction on coated paper is higher in relation to OPP film for all the research parameters. The ink penetrates significantly more and with more irregularity into the pores and throats of the uncoated paper, which results in less homogeneous elements, and in such way that it loses its original shape. In coated paper and OPP film, the ink spreads more on the substrate area which gives it a significantly more homogeneous shape. However, due to the surface spread of the ink, the biggest changes in the size of fine elements are noticeable in the OPP film. The scientific contribution of this paper is based on the comparison of print quality parameters of fine elements, which can contribute to the optimization of the production process and quality of the final graphical product. Full article

Hybrid flexible bioelectronic systems refer to integrated soft biosensing platforms with tremendous clinical impact. In this new paradigm, electrical systems can stretch and deform with the skin while previously hidden physiological signals can be continuously recorded. However, hybrid flexible bioelectronics will not receive wide clinical adoption until these systems can be manufactured at industrial scales cost-effectively. Therefore, new manufacturing approaches must be discovered and studied under the same innovative spirit that led to the adoption of novel materials and soft structures. Recent works have taken mature manufacturing approaches from the graphics industry, such as gravure, flexography, screen, and inkjet printing, and applied them to fully printed bioelectronics. These applications require the cohesive study of many disparate parts. For instance, nanomaterials with optimal properties for each specific application must be dispersed in printable inks with rheology suited to each printing method. This review summarizes recent advances in printing technologies, key nanomaterials, and applications of the manufactured hybrid bioelectronics. We also discuss the existing challenges of the available nanomanufacturing methods and the areas that need immediate technological improvements. Full article

This review provides an outlook on some of the significant research work done on printed and flexible sensors. Printed sensors fabricated on flexible platforms such as paper, plastic and textiles have been implemented for wearable applications in the biomedical, defense, food, and environmental industries. This review discusses the materials, characterization methods, and fabrication methods implemented for the development of the printed and flexible sensors. The applications, challenges faced and future opportunities for the printed and flexible sensors are also presented in this review. Full article

The aim of this research was to analyze the influence of the solvents commonly used in flexography on photopolymer and ethylene propylene diene monomer (EPDM) flexographic printing plates and prints. EPDM plates are recommended when the reproduction process includes a higher amount of the solvents or aggressive solvents. Since additional UV treatment of flexographic printing plates could decrease the interaction between the plate and solvent, photopolymer and EPDM plates were treated with varied UV radiation and exposed to different types of solvents. Effects of the UV treatment and of the solvents on printing plate properties and on prints were analyzed. Results show that EPDM plates are more resistant to solvents in terms of the degree of swelling; however, surface properties of the plates were affected for both plate materials. In addition, the degree of swelling and increased hardness due to UV radiation were crucial for changes of the width of printed lines, and altered surface free energy affected the thickness of deposited ink film for both plate materials. Therefore, depending on the qualitative requirements of specific printed film, the duration of UV treatment can be adjusted for use with specific types of printing plate and solvent. Full article