The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Using Slit Rheometry in Characterising Coating Colour Flow in the Blade Coating Process

Natalia Egorova

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Forest Products Technology for public examination and debate in Auditorium 216 at Helsinki University of Technology (Otakaari 4, Espoo, Finland) on the 19th of May, 2006, at 12 noon.

Overview in PDF format (ISBN 951-22-8051-5)   [614 KB]
Dissertation is also available in print (ISBN 951-22-8050-7)

Abstract

The aim of the present work was to evaluate the suitability of SLIT rheometry for characterising the coating colour flow in paper coating. The detailed aims were to determine the mechanisms governing the flow through the SLIT; to find out what kind of information on the coating colour flow that can be obtained with the SLIT; and to evaluate the ability of the SLIT to predict the relationship between coat weight and blade pressure.

For this purpose, flows of Newtonian model fluids and coating colours were studied both with conventional capillary and SLIT geometries attached to a high-shear rheometer. Correlations with laboratory coating data were determined for both geometries.

It was found that the flow through the SLIT does not attain a fully developed velocity profile and is unstable along the whole length of the SLIT. The instability caused by entrance effects is present at the exit from the SLIT as residual entrance pressure.

The SLIT geometry was found to be more sensitive to differences in coating colour formulations and also able to differentiate between coating colours displaying similar flow behaviour in conventional capillary measurements.

In a laboratory trial, the differences in coating formulations reflected by the SLIT measurements were found to be in good correlation with the blade position required to achieve the target weights. Coating colours demonstrating greater flow resistance in SLIT measurements required a smaller blade distance to achieve the required coat weight.

This thesis consists of an overview and of the following 5 publications:

  1. Mäkinen, M., Egorova, N., Happonen, J., Lehtinen, E., Laine, J. E., Using slit viscometers to predict coating performance on high speed Coaters, Paper Technology 42 (9): 30-34 (2001).
  2. Egorova, N., Laine, J. E., Paulapuro, H., On capillary and SLIT die rheometry (Part I), Nordic Pulp and Paper Research Journal 18 (4): 441-445 (2003).
  3. Egorova, N., Laine, J. E., Paulapuro, H., On capillary and SLIT die rheometry (Part II), Nordic Pulp and Paper Research Journal 19 (2): 208-212 (2004).
  4. Egorova, N., Laine, J. E., Paulapuro, H., Influence of coating colour composition on the SLIT flow, Paperi ja Puu, accepted for publication.
  5. Egorova, N., Laine, J. E., Paulapuro, H., Geometry of the SLIT and its effect on the correlation with the coating process, Nordic Pulp and Paper Research Journal 21 (1): 99-104 (2006).

Keywords: paper coating, high shear rate, capillary rheometer, slit rheometer

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© 2006 Helsinki University of Technology

Last update 2011-05-26