A Study of the Abrasion of Squeegees Used in Screen Printing and Its Effect on Performance with Application in Printed Electronics

This article presents a novel method for accelerated wear of squeegees used in screen printing and describes the development of mechanical tests which allow more in-depth measurement of squeegee properties. In this study, squeegees were abraded on the screen press so that they could be used for subsequent print tests to evaluate the effect of wear on the printed product. Squeegee wear was found to vary between different squeegee types and caused increases in ink transfer and wider printed features. In production this will lead to greater ink consumption, cost per unit and a likelihood of product failure. This also has consequences for the production of functional layers, etc., used in the construction of printed electronics. While more wear generally gave greater increases in ink deposition, the effect of wear differed, depending on the squeegee. There was a correlation between the angle of the squeegee wear and ink film thickness from a worn squeegee. An ability to resist flexing gave a high wear angle and presented a sharper edge at the squeegee/screen interface thus mitigating the effect of wear. There was also a good correlation between resistance to flexing and ink film thickness for unworn squeegees, which was more effective than a comparison based on Shore A hardness. Squeegee indentation at different force levels gave more information than a standard Shore A hardness test and the apparatus used was able to reliably measure reductions in surface hardness due to solvent absorption. Increases in ink deposition gave lower resistance in printed silver lines; however, the correlation between the amount of ink deposited and the resistance, remained the same for all levels of wear, suggesting that the wear regime designed for this study did not induce detrimental print defects such as line breakages

Removal of NOx and CO from a burner system

This paper presents the development of an emissions-controlling technique for oil burners aimed especially to reduce oxides of nitrogen (NOx). Another emission of interest is carbon monoxide (CO). In this research, a liquid fuel burner is used. In the first part, five different radial air swirler blade angles, 30°, 40°, 45°, 50°, and 60°, respectively, have been investigated using a combustor with 163 mm inside diameter and 280 mm length. Tests were conducted using kerosene as fuel. Fuel was injected at the back plate of the swirler outlet. The swirler blade angles and equivalence ratios were varied. A NOx reduction of more than 28% and CO emissions reduction of more than 40% were achieved for blade angle of 60° compared to the 30° blade angle. The second part of this paper presents the insertion of an orifice plate at the exit plane of the air swirler outlet. Three different orifice plate diameters of 35, 40, and 45 mm were used with a 45° radial air swirler vane angle. The fuel flow rates and orifice plate’s sizes were varied. NOx reduction of more than 30% and CO emissions reduction of more than 25% were obtained using the 25 mm diameter orifice plate compared to the test configuration without the orifice plate. The last part of this paper presents tests conducted using the air-staging method. An industrial oil burner system was investigated using the air staging method in order to reduce emission, especially NOx. Emissions reduction of 30% and 16.7% were obtained for NOx and CO emissions, respectively, when using air staging compared to the non-air-staging tests

Studies on the 3D printing of nanocellulose structures

Nanocellulose has a variety of advantages, which make the material most suitable for use in biomedical devices such as wound dressings. The material is strong, can be used for producing transparent films, can keep a moist environment and form elastic gels with bio-responsive characteristics. In this study we explore the application of nanocellulose as a bioink for use in a bioprinting process. Two different nanocelluloses were used, prepared with TEMPO mediated oxidation and a combination of carboxymethylation and periodate oxidation. The combination of carboxymethylation and periodate oxidation produced a homogeneous material with short nanofibrils. The small dimensions of the nanofibrils reduced the viscosity of the nanocellulose thus yielding a material with good rheological properties for use as a bioink. We also demonstrated that both nanocelluloses inhibited bacterial growth, which is an interesting property of these novel materials

Effect of impression pressure and anilox specification on solid and halftone density

Controlling the transfer of ink to the substrate is a key requirement of the flexographicprinting process. Its ability to transfer ink from the image carrier to the substrate at low pressuresenables the process to be used for the production of printed matter using pressure-sensitivematerials. These can range from substrates where high pressures can damage surface structure(e.g. corrugated board), to specialist inks, which can be damaged by the high shearing actionassociated with other volume print processes. This paper evaluates the effect of pressure changeson print quality for different anilox specifications and line rulings on the plate.Data collected from an experimental print trial were used to quantify the effects of aniloxroll specifications, dot pitch, and plate-to-substrate engagement on the reproduction of both acontinuous ink film and the formation of discrete halftone dots.The ink-carrying volume of the cells of the anilox roll was shown to have the greatest influenceon solid density (a parameter used as an indirect measure of ink film thickness) and halftonedot formation; however, the geometrical characteristics of the cells were also shown to havean effect. An initial increase in the pressure within the printing nip resulted in a significantrise in both solid density and tone gain (growth of the halftone dots) due to improved inktransfer from the plate to the substrate. Subsequent increases in pressure produced little furtherincrease of solid density, indicating ink transfer had reached a plateau. The rate of increase ofhalftone density was found to be reduced as pressure increased, which was attributed to the inkapproaching its maximum capability for spreading on the substrate