Inkjet printing is an excellent printing technique and an attractive alternative to conventional technologies for the production of flexible, low-cost microelectronic devices. Among many parameters that have a significant impact on the correctness of the printing process, the most important is ink viscosity. During the printing process, the ink is influenced by different strains and forces, which significantly change the printing results. The authors present a model and calculations referring to the shear rate of ink in an inkjet printer nozzle. Supporting experiments were conducted, proving the model assumptions for two different ink formulations: initial ink and with the addition of a dispersing agent. The most important findings are summarized by the process window regime of parameters, which is much broader for the inks with a dispersing agent. Such inks exhibit preferable viscosity, better print-ability, and higher path quality with lower resistivity. Presented results allow stating that proper, stable graphene inks adjusted for inkjet technique rheology must contain modifiers such as dispersing agents to be effectively printed.

Purpose: This paper aims to present the results of investigations of inkjet-printed electronic circuits fabricated on a flexible substrate (KAPTON foil) using silver nanoparticles ink. Design/methodology/approach: Fully inkjet-printed conductive circuit tracks were printed on a flexible, transparent KAPTON foil, using a commercial 40LT-15 C nanosilver ink as well as a PixDro LP50 inkjet printer with KonicaMinnolta 512 printhead. After cure, electrical properties by resistance measurements and printing quality by optical and SEM microscopic observation of conductive tracks were examined. Afterwards, the tested samples were annealed for 1, 2 and 3 h at 150°C or subjected to cycling bending. Findings: It was found that silver nanoparticles ink could be used for the preparation of electronic circuits using the inkjet printing technique. The obtained patterns had appropriate mapping and good quality. It was also noticed that thermal annealing caused a decrease in resistivity values of the tested lines irrespective of their width. Approximately 34 per cent decrease was achieved in the values of resistivity of all the tested lines after the first hour of thermal annealing. After the second hour, the values of resistivity decreased by another 50 per cent. There were no visible changes in resistivity values after 1,000 cycles of bending. Originality/value: In this paper, the results of thermal annealing and bending tests of inkjet-printed silver nanoparticle conductive tracks on flexible substrate were presented. That is very important information for producing printed circuit boards using ecological, rapid and low-cost inkjet printing techniques, particularly during the production of printed circuit boards on flexible substrates working in different conditions of mechanical and thermal stresses.

Circular Economy (CE) is one of the approaches which are intensively developed and tested in different areas of industry and services. The aim of this solution is to use many kinds of resources in a closed flow and to achieve as a small amount of waste as it is possible. One of the potential areas of using CE is Radio Frequency Identification (RFID). In RFID systems tags are utilized in various forms. This paper addresses investigation of a recycling process of RFID tags. Different attachment methods of these tags were tested and then, a recycling procedure was prepared based on the obtained results in which adhesives are recommended to be used as an attaching material between a tag and an identified object. The mentioned procedure was evaluated with using paper-face RFID tags. It was confirmed applicability of the proposed solution. Moreover, the conducted research revealed that an adhesion force of the adhesive layers in the prepared RFID tags decreased in the most extent during the first recycling cycle. It was found that in order to preserve a high adhesion force of these layers it is suggested to place the tags on a clean surface.

Purpose: – The purpose of this paper is to investigate screen-printed high-frequency (HF) antennas for radio frequency identification (RFID) on-metal transponders in which a magnetic sheet was used as a substrate material.Design/methodology/approach: – A transponder antenna was designed in the form of square coil using a high-frequency electromagnetic software. Then, the antenna was fabricated with screen printing technique on two different magnetic sheets (RFN4 and RFN7) and on polyethylene naphthalate (PEN) foil for comparison. Its printing was carried out with polymer pastes based on silver flakes (PM-406 and SF). Thickness, track width and spacing were examined for the antennas using digital microscope and contact profilometer. Resistance and inductance were also measured, and resonant frequency, quality factor and target values of capacitance to achieve resonant frequency of the tested antenna at 13.56 MHz were calculated. Finally, RFID chips were mounted to the prepared antennas using an isotropic conductive adhesive, and a maximum read distance was measured with a reader installed in a smartphone.Findings: – It was found that an antenna thickness on the magnetic sheets used was higher than on PEN foil. At the same time, surface roughness of the fabricated antennas on these sheets was revealed to be higher as well. Inductance of the measured antennas exhibited good conformity with the antenna design, but higher divergence was noticed in the measured resistance. Its lowest value was achieved when the antenna was printed with the paste PM-406 on PEN foil and the highest one when it was fabricated with the paste SF on the same substrate. This suggests that high attention needs to be paid to a polymer paste selected for antenna printing. The performed tests showed that the magnetic sheet RFN4 seems to be better substrate for on-metal transponders compared to RFN7 due to lower resistance and higher quality factor of the prepared antennas.Research limitations/implications: – Further investigations are required to examine mechanical and thermal durability of the HF antennas printed on the magnetic sheets.Practical implications: – The investigated HF antennas fabricated on magnetic sheets can find application in near field communication (NFC) transponders designed to be placed on metallic surfaces, e.g. on frames of advertising screens.Originality/value: – Influence of used magnetic sheets and polymer pastes on geometry and electrical properties of HF antennas for RFID on-metal transponders was investigated. The presented investigations can be interesting for NFC/RFID designers who are involved in designing systems suitable for metallic surfaces.