Brookfield Engineering

Interior Latex Flat Paint

Laboratory Viscometer Application Data Sheet

Paints, Inks, Coatings

USE: indoor ceilings and walls making their appearance more attractive.

Test Equipment:

  • Spring Torque Range: CAP 2000+L (High Torque Low Temperature)
  • Spindle: Cone-01
  • Speed, rpm: 50, 150, 300, 450, 600, 750 and 900 rpm.
  • Temperature: 25°C

For our viscosity testing we used a CAP 2000+L viscometer with Capcalc v3.0 software for automated instrument control and data acquisition. We mixed the paint at 2330 rpm for 15 minutes prior to testing. We used Cone-01 to achieve on-scale results. We recommend (for Cone-01) using 67 µL of fluid, to receive proper cone coverage. After applying this amount of fluid you should see a very small amount of fluid around the circumference of the cone. We used a fresh portion of sample for each trial. Three trials for each brand were done to ensure repeatability. We equilibrated the sample and cone for two minutes prior to testing. The cone and plate were cleaned before every testing. We recommend using the solvent trap to help prevent evaporation. Representative data from the analyses are shown in Figures 1, 2, and 3 below:

Figure 1: Interior Latex Flat Paint Brands A and B, at 25°C.

Figure 1 demonstrates that the viscosity of the paints decreased as the speed increased. This is known as "shear- thinning" or pseudoplastic behavior. Brand A had significantly higher viscosities than Brand B at all shear rates tested. The data were repeatable.

Figure 2: Brand A Interior Latex Flat Paint, at 25°C.

Figure 3: Brand B Interior Latex Flat Paint, at 25°C.

Figure 2 and 3 show the paints fitted to a Power Law model. The power law model is = kDn, where is Shear Stress, D is Shear Rate, k is the Consistency Index and n is the Flow Index. Brand A has a Confidence of Fit of 98.1% and Brand B has a Confidence of Fit of 97.5%. Confidence of Fit is a measurement of how well the raw data fits the curve of the model, 100% being a perfect fit. Brand A's Flow Index of 0.466 is higher than Brand B's Flow Index of 0.333. A higher Flow Index suggests that Brand A may be less "shear-thinning" than Brand B. Brand B's Consistency Index of 40033 cP is larger than Brand A's Consistency Index of 20583 cP. A larger Consistency Index suggests that at very low shear rates the viscosity of Brand B may be higher than the viscosity of Brand A.