Abstract
Abstract Functional model inks were formulated and printed using flexography in order to assess the influence of ink extensional elasticity and print velocity on the morphological and electrical properties of printed layers. Increased extensional elasticity and higher print velocity resulted in the printing of more isotropic prints, both morphologically and electronically. Furthermore, a correlation between the prints’ morphological and electrical anisotropy strongly suggests that print uniformity has a considerable influence on functionality and that ink rheology may be used to control such characteristics.
Highlights
Flexography is a roll-to-roll printing process that is well-established in the packaging industry and capable of high speed, patterned deposition of fluids of a range of viscosities [1]
Solutions of polyvinyl alcohol (PVA) of molecular weight 20–30×103 g/mol and degree of hydrolysis 88% (Acros Organics) in deionised water were mixed with a water-based Orgacon PEDOT:PSS solution by Agfa before the addition of aqueous E122 azorubine dye (FastColors LLP) to highlight printed patterns and polyacrylamide (PAM) of molecular weight 5–6 x 106 g/mol (Acros Organics) in deionised water to provide extensional elasticity
All inks show mild shear thinning properties with η decreasing from approximately 0.1 Pa⋅s to about 0.03 Pa⋅s over three orders of shear rate. This is qualitatively typical of aqueous PEDOT:PSS solutions [40]
Summary
Flexography is a roll-to-roll printing process that is well-established in the packaging industry and capable of high speed, patterned deposition of fluids of a range of viscosities [1]. Competition between viscous and surface tension forces typically leads to the formation of fingers with a characteristic wavelength which decreases with the dimensionless capillary number Ca = v/ (where v is printing velocity and η and σ are fluid shear viscosity and surface tension, respectively) [7,12] This parameter does not consider viscoelastic fluid properties which are often displayed in functional printing inks (that typically contain significant amounts of polymer binder and solid particles of various shapes and sizes). It was reported that features induced by instabilities in flexography became significantly smaller with increased ink elasticity This effect can be linked to filamentation [21] a phenomenon characteristic of the extensional flows that are often observed in roller processes [17,22]. The influence of ink extensional properties and printing velocity on the uniformity and subsequent functionality of prints was isolated and examined
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