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Casson equation and rheological determination
The Casson equation is an important rheological calculation formula, ethylene acrylic acid copolymer dispersion as shown in the following formula:
(19-4) where the shear rate is the viscosity of D, dPa·s;
Respect ~ the viscosity of co shear rate, dPa·s;
ro—yield value, 0.1Pa;
D-Shear rate, sl;
7 is an index, usually n=0.5, then the above formula is simplified to:
√mb=√r+√to/√D(19-5) Brookfield Rotary Viscometer tests the viscosity at low shear rate, and the shear rate is in the range of 0.1~100s’. The viscosity at the shear rate co can be obtained from the viscosity at the low shear rate. Specifically, the reciprocal of the square root of the shear rate is plotted against the square root of the Brookfield viscosity. The square of the intercept is the viscosity at a shear rate of one~, slope The square of is the yield value to. Because latex paint has the property of shear thinning, there is a nonlinear relationship between viscosity and shear rate, n. And r are always derived from the low shear rate viscosity.
Chengqinghe et al. 16 measured the yield value of the thickener when used alone. The yield values of the associative polyurethane thickener SN612NC, the associative alkali swelling thickener SN636 and the hydroxyethyl cellulose thickener HEC were 0.2 respectively. Pa, 1.0Pa and 1.5Pa.
Thickener types and thickening characteristics
The rheological requirements of latex paint are met by the use of thickeners. There are many kinds of thickeners, and have their own thickening characteristics, which will be introduced below.
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