PurposeThe purpose of this paper is to carry out a comprehensive experimental investigation into the role of screen and conductive carbon material formulation on line conductivity and printing capability in the screen printing process, to provide design knowledge and further understanding of the screen printing for printed carbon.Design/methodology/approachA full factorial experiment was carried out where six carbon materials were printed through ten screens to a polyester substrate under a set of standard conditions.FindingsMaterial characterization showed that viscosity and the corresponding viscous and elastic material modulli increased with solids content and that the elastic properties at low shear are significant. The solids carbon content materials were unable to produce the minimum printable line features possible with the low carbon materials. Increasing the solids contents reduced the final cured line resistance, reduced the printed line width, increased the film thickness, increased the cross sectional area and reduced the material resistivity. Material resistivities were around 700 to 950 μΩcm were obtained in the printed lines.Research limitations/implicationsLower material resistivities were obtained with higher solids materials and it is postulated that the increased visco‐elastic nature of the solids content materials, play a role in determining the microscopic structure of the cured film through alignment of the carbon graphite platelets.Practical implicationsA dataset which allows material, screen and print characteristics has been created allowing process optimization and formulation development to be accelerated.Originality/valueThe work provides insight into the role of material properties and process settings on the electrical and physical characteristics of printed carbon.

Abstract:A comprehensive experimental investigation has been carried out into the role of film thickness variation and silver material formulation on printing capability in the screen printing process. A full factorial experiment was carried out where two formulations of silver materials were printed through a range of screens to a polyester substrate under a set of standard conditions. The materials represented a novel low silver content (45%-49%) polymer material and traditional high silver content (65%-69%) paste. The resultant prints were characterised topologically and electrically. The study shows that more cost effective use of the silver in the ink was obtained with the low silver polymer materials, but that the electrical performance was more strongly affected by the mesh being used (and hence film thickness). Thus, while optimum silver use could be obtained using materials with a lower silver content, this came with the consequence of reduced process robustness.

Controlling the transfer of ink to the substrate is a key requirement of the flexographic printing process. Its ability to transfer ink from the image carrier to the substrate at low pressures enables the process to be used for the production of printed matter using pressure-sensitive materials. 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 action associated with other volume print processes. This paper evaluates the effect of pressure changes on 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 anilox roll specifications, dot pitch, and plate-to-substrate engagement on the reproduction of both a continuous 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 influence on solid density (a parameter used as an indirect measure of ink film thickness) and halftone dot formation; however, the geometrical characteristics of the cells were also shown to have an effect. An initial increase in the pressure within the printing nip resulted in a significant rise in both solid density and tone gain (growth of the halftone dots) due to improved ink transfer from the plate to the substrate. Subsequent increases in pressure produced little further increase of solid density, indicating ink transfer had reached a plateau. The rate of increase of halftone density was found to be reduced as pressure increased, which was attributed to the ink approaching its maximum capability for spreading on the substrate.

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, OPEN ACCESSCoatings 2014, 4 357 suggesting that the wear regime designed for this study did not induce detrimental print defects such as line breakages.