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September/October 2011
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Viscosity Measurement

The viscosity of paints, inks and many related liquid materials varies considerably with temperature. In some cases viscosity can decrease by 10 percent with every 1°C increase in temperature. A proposed new ASTM standard will provide insight into the relationship between temperature and viscosity.

WK33642, Test Method for Measurement of Viscosity of Paints, Inks or Related Liquid Materials as a Function of Temperature, is being developed by Subcommittee D01.24 on Physical Properties of Liquid Paints and Paint Materials, part of ASTM International Committee D01 on Paint and Related Coatings, Materials and Applications.

“It is useful to know the extent of variation, but we do not know of any ASTM standard that establishes the viscosity-temperature variation for these materials,” says Clifford Schoff, Ph.D., Schoff Associates, and chairman of D01.24. “The relationship has important implications for viscosity measurements in general and specifically for processes such as hot spray and for sagging and leveling on baking.”

The proposed standard will give instruction on how to prepare a viscosity-temperature table or curve. This will be useful when ambient conditions do not allow the measurement at the exact temperature stated in a specification or regulation.

“In addition, knowledge of the viscosity dependence on temperature for a given material will indicate the degree of temperature control required in order to do accurate and precise viscosity measurements,” says Schoff. “Another practical application would be to compare viscosity-temperature behavior of different formulations to better understand the effect of additives or components.”

Schoff says D01.24 welcomes interested parties to join in the ongoing revision of the WK33642 draft and also to participate in interlaboratory testing to establish the precision of the proposed standard.

In addition to WK33642, the subcommittee is also beginning work on a standard for measuring the yield stress of paints, ink and related liquids. Participants are sought for this activity as well.

CONTACT

Technical Information: Clifford Schoff, Schoff Associates, Allison Park, Pa.

Phone: 412-487-5289

ASTM Staff: Jeffrey Adkins

Phone: 610-832-9738