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Slot die stripe coating of low viscous fluids

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Abstract

Slot die coating is applied to deposit thin and homogenous films in roll-to-roll and sheet-to-sheet applications. The critical step in operation is to choose suitable process parameters within the process window. In this work, we investigate an upper limit for stripe coatings. This maximum film thickness is characterized by stripe merging which needs to be avoided in a stable process. It is shown that the upper limit reduces the process window for stripe coatings to a major extent. As a result, stripe coatings at large coating gaps and low viscosities are only possible for relatively thick films. Explaining the upper limit, a theory of balancing the side pressure in the gap region in the cross-web direction has been developed.

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Abbreviations

CF:

Correction factor

ETOH:

Ethanol

h :

Height (z-axis) (µm)

l :

Length (x-axis) (mm)

n :

Power law exponent

p :

Pressure (mbar)

PAA:

Polyacrylamide

q:

Specific volume flow (m2/min)

t :

Time (s)

u :

Speed (m/min)

w :

Width (y-axis) (mm)

x :

x-axis in web direction

y :

y-axis in cross-web direction

\(\dot{\gamma }\) :

Shear rate (1/s)

\(\eta\) :

Newtonian viscosity (Pa s)

\(\theta\) :

Static contact angle (°)

\(\vartheta\) :

Dynamic contact angle (°)

\(\kappa\) :

Consistency factor (Pa sε)

\(\sigma\) :

Surface tension (mN/m)

approx.:

Approximated

Bead:

Bead

Ca:

Capillary number

Cap:

Capillary

crit:

Critical

D:

Downstream

G:

Gap

Fluid:

Fluid

max:

Maximum

min:

Minimum

s:

Slot

Side:

Side

solid:

Solid

spacer:

Spacer

spread:

Spread

U:

Upstream

Vac:

Vacuum

w:

Web

wet:

Wet

1:

Position 1

2:

Position 2

3:

Position 3

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Acknowledgments

The authors acknowledge financial support via the projects KOBALT and POESIE of the German Federal Ministry of Education and Research (Contract Nos. 13N0883 and 13N13692) and Philips Technologie GmbH Innovative Technologies, Aachen. We would like to thank all involved mechanics, assistants, and students for contributing to this work as well as TSE Troller AG, Murgenthal, Switzerland, for technical support.

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Authors and Affiliations

  1. Institute of Thermal Process Engineering, Thin Film Technology, Karlsruhe Institute of Technology, Karlsruhe, Germany

    Sebastian M. Raupp, Marcel Schmitt, Anna-Lena Walz, Ralf Diehm, Philip Scharfer & Wilhelm Schabel

  2. Chemistry and Biotechnology, University of Applied Sciences, FH Aachen, Jülich, Germany

    Helga Hummel

  3. InnovationLab, Heidelberg, Germany

    Sebastian M. Raupp, Ralf Diehm & Philip Scharfer

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  1. Sebastian M. Raupp
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Correspondence to Sebastian M. Raupp.

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Raupp, S.M., Schmitt, M., Walz, AL. et al. Slot die stripe coating of low viscous fluids. J Coat Technol Res 15, 899–911 (2018). https://doi.org/10.1007/s11998-017-0039-y

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