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Journal of Coatings Technology and Research

, Volume 12, Issue 5, pp 877–887 | Cite as

Analytical determination of process windows for bilayer slot die coating

  • Marcel Schmitt
  • Sebastian Raupp
  • Dennis Wagner
  • Philip Scharfer
  • Wilhelm Schabel
Article

Abstract

Slot die coating is a film casting process with a highly diverse variety of everyday applications. As a pre-metered process it not only guarantees excellent film uniformity, but is also suitable for simultaneously applied multilayer coatings. Characteristic singularities like the behavior of the liquid–liquid interface and the impact of the additional mid-lip on film uniformity were already investigated before. However, the effect of an altered gap pressure regime on commonly used coating windows has not yet been discussed. In this work, we therefore extended available single-layer coating windows for Newtonian and power-law liquids to the bilayer case. Here, the emphasis was laid on the air entrainment limit. Subsequently, the theoretical results were compared to experimental data. It was found that the onset of air entrainment strongly depends on the top to bottom film thickness ratio for bilayer coatings. A critical film thickness ratio which delivers similar coating limits as those for single-layer coatings was derived and confirmed by experimentally gained results.

Keywords

Multilayer Bilayer slot die coating Process window Non-newtonian flow Lithium-ion batteries 

Nomenclature

Letters

h

Height (z-axis) (µm)

l

Length (x-axis) (mm)

p

Pressure (mbar)

u

Speed (m/min)

Greek letters

\(\dot{\gamma }\)

Shear rate (1/s)

\(\varepsilon\)

Power law exponent

\(\kappa\)

Consistency factor (Pa s n )

\(\eta\)

Newtonian viscosity (Pa s)

Indices

crit

Critical

D

Downstream

G

Gap

M

Mid-lip

U

Upstream

W

Web

Notes

Acknowledgments

Part of this work has been supported in the frame of the project Competence E (KIT) by the German Federal Ministry of Economics and Technology on the basis of a decision by the German Bundestag (Funding Nr. 03ET6016). The authors would like to thank all involved mechanics, assistants and the students Robert Schneider, Susanne Unger, Caroline Schober and Michael Wittek for their supporting work and building of the experimental set-up. We specially thank Valentin Wenzel and Steffen Schmelzle (KIT-MVM-VM) for mixing support, Boris Bitsch (KIT-MVM-AM) for rheological measurements, Kevin Stella and Matthias Loeble (KIT-COMPETENCE E) and Anke Scherf (KIT-IAM-WK-PM) for REM measurements. We also want to thank our cooperation partners TSE Troller AG, Switzerland for the technical support.

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Copyright information

© American Coatings Association 2015

Authors and Affiliations

  • Marcel Schmitt
    • 1
  • Sebastian Raupp
    • 1
  • Dennis Wagner
    • 1
  • Philip Scharfer
    • 1
  • Wilhelm Schabel
    • 1
  1. 1.Institute of Thermal Process Engineering, Thin Film TechnologyKarlsruhe Institute of TechnologyKarlsruheGermany

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