Using slit rheometry in characterising coating colour flow in the blade coating process
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Doctoral thesis (article-based)
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Date
2006-05-19
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Language
en
Pages
45, [30]
Series
Report / Helsinki University of Technology, Laboratory of Paper Technology. Series A, 25
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.Description
Keywords
paper coating, high shear rate, capillary rheometer, slit rheometer
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Parts
- 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).
- 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).
- 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).
- Egorova, N., Laine, J. E., Paulapuro, H., Influence of coating colour composition on the SLIT flow, Paperi ja Puu, accepted for publication.
- 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).