An Ef;cient Approach to Dispersing Pigments
concentrate suppliers would be a 6
Hegman or above. Samples C and D
both had grinds over 7 on the Hegman
scale. Sample C had a higher viscosity
but good grind after one hour; this indicates that the dispersant loading was
not optimized. Further work will continue to create an optimized formulation with this dispersant. For Sample D,
there was a very low viscosity and high
grind, indicating that this was a suitable
dispersant loading for this formulation.
Color acceptance and color strength research will also be done to con;rm the
performance of the additives.
Violet-Titanium Dioxide Results
Viscosity parameters for the violet
samples were the same as previously
mentioned for the yellow iron oxide formulations (Figure 8). Initial viscosity was
very low for the blank and Sample D.
Sample A had a very high viscosity at a
low shear rate but, as the shear rate increased, the viscosity lowered. Samples B
and C both had shear thinning curves.
Samples were tested for particle size
using a Beckman Coulter LS 13-320
Laser Diffraction Particle Size Analyzer
(Figure 9). The blank, Sample B, and
Sample C showed the lowest median
particle size after one hour of grinding.
However, the results are still too high for
an organic pigment. (Note: There is also
titanium dioxide in this formulation. It
is possible that this could be skewing
the particle size measurements.) These
formulations likely require more energy
to break up the remaining agglomerates
and aggregates. Additional measurements will be taken over longer grind
time periods to see if this will lower the
particle size.
Pigment dispersions were evaluated
for color acceptance and color strength
using a commercial grade architectural
paint at 4% by volume (Figures 10-11).
Drawdowns were made on Leneta 3B
cards at 3 mils wet and allowed to air dry
before color measurements were taken
using an X-Rite 962 spectrophotometer.
The blank has a high color strength
but also a very high ∆E. This indicates
that while the blank may look stable, af-
ter the pigment is disrupted, it falls out
of stabilization. Sample A and Sample D
both had lower color strengths and higher
∆E values. This would be unacceptable
to paint manufacturers because not only
Figure 8. Initial viscosities of violet-titanium dioxide formulations.
Figure 9. Median particle size of violet-titanium dioxide formulations.
Figure 10. Color strength values for violet-titanium dioxide formulations.
