The screen printing of a power-law fluid

Abstract

We present a two-dimensional large-aspect-ratio model for the off-contact screen printing of a powerlaw fluid. We extend the work of White et al. (J Eng Math 54:49-70, 2005) by explicitly including the fluid/air free surface that is present beneath the screen ahead of the squeegee. In the distinguished parameter limit of greatest interest to industry, the process is quasi-steady on the time-scale of a print and can be analysed in three separate regions using the method of matched asymptotic expansions. This allows us to predict where the fluid transfers through the screen, the point at which it first makes contact with the substrate, and the amount of fluid deposited on the substrate during a print stroke. Finally, we show that using a shear-thinning fluid will decrease the amount of fluid transferred ahead of the squeegee, but increase the amount of fluid deposited on the substrate.

Screen Printing of Highly Loaded Silver Inks on Plastic Substrates Using Silicon Stencils

“…By contrast, the silver ink can be printed through the line openings as narrow as 5 μm, leading to 22 μm wide lines. The observation that the silver ink can pass through narrower openings than the graphene ink originates from the strong shear thinning behavior of the silver ink, as shown in Figure b, because the shear thinning rheology increases the amount of ink deposited on substrates . Moreover, the high viscosity (at low shear rate) and yield stress of the silver ink (∼1 × 10 3 Pa s at a shear rate of 0.1 s –1 ) prevent ink spreading after printing as described above, so that the printed line width is widened only by ink penetration into the gap between the screen and the substrate during printing.…”

“…The observation that the silver ink can pass through narrower openings than the graphene ink originates from the strong shear thinning behavior of the silver ink, as shown in Figure 1b, because the shear thinning rheology increases the amount of ink deposited on substrates. 27 Moreover, the high viscosity (at low shear rate) and yield stress of the silver ink (∼1 × 10 3 Pa s at a shear rate of 0.1 s −1 ) prevent ink spreading after printing as described above, so that the printed line width is widened only by ink penetration into the gap between the screen and the substrate during printing. On the other hand, the low viscosity of the graphene ink (∼13 Pa s at a shear rate of 0.1 s −1 ) brings about both of ink penetration during printing and ink spreading after printing.…”

Boundary conditions for free surface inlet and outlet problems

“…More recently, it has become possible to solve the full two-dimensional coating flow problems numerically (Coyle, Macosko & Scriven 1990;Gaskell et al 1995), but lubrication-based models remain popular because of their simplicity and susceptibility to asymptotic analysis (Carou et al 2009;Taroni et al 2012). Furthermore, many of these flows involve a triple contact line, which can give rise to a number of mathematical and computational issues.…”

Deposition of High Conductivity Low Silver Content Materials by Screen Printing

“…Theoretical studies of the process have made little advancement in the development of reliable screen printing process models. Early models showed some predicted trends which were in agreement with experimental observation but even the most recent developments require significant oversimplification (e.g., material viscoelasticity is ignored) which limit practical use [6,7]. Establishing process/material characteristics and their impact on printed performance therefore is reliant on experimental studies.…”