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Rheology testing: an important component of product and process selection: when using coating formulations, papermakers should not 'go with the flow'--proper testing is a key to avoiding problems.

Rheology is the science relating to the flow behavior of mixed systems such as paper coatings. It can offer important insights into how a coating formulation will affect the delicate papermaking process. Before choosing a coating product or process, papermakers should take advantage of any theology testing services that suppliers offer.

At Dow Chemical Co., for example, before applying a latex coating to paper, customers often request thorough testing on one of Dow's two pilot coater facilities. One unit is in Midland, Michigan, USA, and the other is in Horgen, Switzerland. This process helps customers duplicate a wide variety of mill conditions and machines using virtually any paper or paperboard product. The results ensure that a mill is using the correct latex coating, the correct process, and the correct paper products to maximize potential from an initial run.

Even before testing paper coating products and mill processes on pilot coaters, the paper coating materials should undergo extensive laboratory testing. Rheology testing is an important laboratory service a supplier can offer.

Rheology testing is critical because it allows mills and suppliers to assess the potential runnability of a coating system on a paper machine. Poor coating behavior can result in waste and lower productivity. Rheology testing allows the supplier to design a coating that will minimize such problems and predict them on a small scale in the laboratory. By testing these behaviors initially in the laboratory, suppliers ensure they do not waste time testing products on the pilot coater that are obviously incompatible. Instead, technicians can predict which coatings will offer the best results.


To be effective, laboratories should have the latest rheology testing technology available. After recently upgrading to the Paar Physica USD 200 Rheometer, researchers at the Dow laboratories in North America, Asia, and Europe can study the interaction of coating and paper by measuring rheology of the coating directly on the base paper. This can provide insights about coating immobilization and dynamic water retention, which are crucial to coater runnability and final paper coating performance.

Additionally, advanced instruments can help suppliers design tests for coating and latex stability that can help to predict some facets of paper machine runnability. Effective testing equipment and processes can be very useful in helping suppliers and customers design high performance latexes and coating systems.

The process also goes beyond the rheometer. While the machine provides raw data, the researchers in the laboratory provide expertise. "Effective laboratories are a combination of technology and experienced minds," said Femi Kotoye, technical service and development manager for Dow. "One of the greatest tools a supplier can have for rheology testing is a staff of well trained researchers."

About the author: Jamel Attal is product development leader for Dow Emulsion Polymers' Paper Coating Technical Service and Development group. Contact him by phone at +1 989 638-6481 or by email at
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Title Annotation:Practical Solutions
Author:Attal, Jamel
Publication:Solutions - for People, Processes and Paper
Date:Oct 1, 2002
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