Characterization of silver nanoparticle inks toward stable roll-to-roll gravure printing

The rheological properties of silver inks are analyzed, and the printing results are presented based on the inks and roll-to-roll printing speed. The shear viscosity, shear modulus, and extensional viscosity of the inks are measured using rotational and extensional rheometers. The inks exhibit the shear thinning power law fluids because the concentration of dispersed nanoparticles in the solvent is sufficiently low, which minimizes elasticity. After the inks are printed on a flexible substrate through gravure printing, the optical images, surface profiles, and electric resistances of the printed pattern are obtained. The width and height of the printed pattern change depending on the ink viscosity, whereas the printing speed does not significantly affect the widening. The drag-out tail is reduced at high ink viscosities and fast printing speeds, thereby improving the printed pattern quality in the roll-to-roll process. Based on the results obtained, we suggest ink and printing conditions that result in high printing quality for complicated printings, such as overlay printing registration accuracy, which imposes pattern widening and drag-out tails in printed patterns.

Studies on Mitigation of Printing Cost, Volatile Organic Compounds Emission and Sustainability in Printing Industries by Using Water-based Inks

Organic solvents have been frequently and excessively used in the printing process for a long time. The use of organic solvents in solvent-based ink is responsible for fire hazards, volatile organic compounds emission, and high manufacturing cost during printing. The present study aimed at replacing solvent based ink with water-based ink for reducing the volatile organic compounds emissions and carbon footprints in gravure printing without affecting overall printing quality. The PET film was printed with a water-based ink laser engraved cylinder having reduced cell depth and it resulted in the transfer of a low volume of inks on printing substrate. The cost of printing one kg of polyester film with water-based ink was reduced by US$ 1.95 compared to solvent-based ink. The volatile organic compounds emissions for water-based ink were measured at 2478 ppm against 3373 ppm for solvent-based ink. The water-based ink reduced the carbon footprint by 3.04 kg, which was equivalent to CO2 during printing of one kg polyester film used for making flexible pouches compared to solvent-based ink. The outcome of this study may be the benchmark to authorities for green manufacturing systems in gravure printing applications for the betterment of the environment and humanity.

Low-Temperature Growth of ZnO Nanowires from Gravure-Printed ZnO Nanoparticle Seed Layers for Flexible Piezoelectric Devices

Zinc oxide (ZnO) nanowires (NWs) are excellent candidates for the fabrication of energy harvesters, mechanical sensors, and piezotronic and piezophototronic devices. In order to integrate ZnO NWs into flexible devices, low-temperature fabrication methods are required that do not damage the plastic substrate. To date, the deposition of patterned ceramic thin films on flexible substrates is a difficult task to perform under vacuum-free conditions. Printing methods to deposit functional thin films offer many advantages, such as a low cost, low temperature, high throughput, and patterning at the same stage of deposition. Among printing techniques, gravure-based techniques are among the most attractive due to their ability to produce high quality results at high speeds and perform deposition over a large area. In this paper, we explore gravure printing as a cost-effective high-quality method to deposit thin ZnO seed layers on flexible polymer substrates. For the first time, we show that by following a chemical bath deposition (CBD) process, ZnO nanowires may be grown over gravure-printed ZnO nanoparticle seed layers. Piezo-response force microscopy (PFM) reveals the presence of a homogeneous distribution of Zn-polar domains in the NWs, and, by use of the data, the piezoelectric coefficient is estimated to be close to 4 pm/V. The overall results demonstrate that gravure printing is an appropriate method to deposit seed layers at a low temperature and to undertake the direct fabrication of flexible piezoelectric transducers that are based on ZnO nanowires. This work opens the possibility of manufacturing completely vacuum-free solution-based flexible piezoelectric devices.

BANKNOTES OF UKRAINE WITH MANUFACTURER’S DEFECTS AND PECULIARITIES OF ITS FORENSIC RESEARCH

The article briefly describes the history of the emergence and development of paper money in Ukraine, special attention is paid to the period of independence of our state. In less than 30 years, the National Bank of Ukraine has issued four generations of banknotes. As of January 01, 2021, there were about 3 billion banknotes in circulation. Among the circulated banknotes, there are also those that differ slightly from the banknotes presented by the National Bank of Ukraine (NBU). Based on the Resolution of the Board of the National Bank of Ukraine dated 03.12.2018 No. 134 (as amended) “Rules for determining payment characteristics and exchange of banknotes, exchange and circulating coins of the national currency of Ukraine”, the concepts of “banknotes with manufacturer defects” and “banknote defects” are disclosed. The article describes the technological process of making paper money. At the first stage, sheets of special paper are made in the banknote paper factory. Further, these sheets are sent to the NBU Banknote Factory, where all the images are applied on the sheets and cutting is carried out. The authors propose to systematize the types of defects in accordance with the stage of the technological process of manufacturing banknotes, at which these defects could arise. It is also proposed to distinguish four such stages: in the process of manufacturing banknote paper; at the stage of applying images on the front and back sides of sheets using forms of offset and gravure printing; when applying serial numbers; when cutting sheets into separate banknotes. The list of possible types of defects that may arise at one stage or another of the production process is given quite fully, some of them are illustrated for clarity, and variants of defects that are found in banknotes of different generations are analyzed. Based on the study of the problem, the authors propose an algorithm for researching such banknotes, offer options for intermediate and final expert conclusions.