An Easy, Tried-and-True Method to Ensure Quality in Coatings
October 2017 www.coatingsworld.com Coatings World | 57
Compared to HEC, Min-U-Gel 400 builds a higher initial yield
point and provides more consistent shear stress values when under shear (Figure 3).
Min-U-Gel 400 attapulgite is also useful as a co-thickener
with associative thickeners. These rheology modifiers provide
favorable leveling and gloss and maintain high viscosity under
high shear for reduced spatter. However, they can cause problems with syneresis, pigment settling and floatation, color development and sag resistance. Manufacturers often use Min-U-Gel
400 to overcome these deficiencies at a rate of 3 to 5 lb/100 gal
( 4 to 6 g/L) in semi-gloss paints and 3 to 7 lb/100 gal ( 4 to 8. 5
g/L) in interior flat paints. Min-U-Gel 400 is also used as a co-thickening thixotrope with alkali-swellable and hydrophobical-ly-modified HEC thickeners to remedy sag resistance, pigment
settling and dripping problems. Typical addition levels is 3 to
5 lb/100 gal ( 4 to 6 g/L)., which adds stabilization to reduce
syneresis, pigment settling, pigment settling and flotation while
improving hide, color development and sag resistance.
Uniform Suspensions
High-quality, U.S. gel grade attapulgite products provide long-
term stability to liquid systems. Their particles remain sus-
pended indefinitely given their small size and interaction with
themselves and other pigments. The gel formation can suspend
relatively large or dense pigments or extenders. If any particles
do settle they form a soft sediment that is easily re-suspended.
The amount of attapulgite needed is reduced at higher PVC val-
ues or, in other applications, as solids rise. Mixtures of typical
pigments and extenders may need less than 0.5% by weight for
suspension or soft settle and those with large, denser particles
may need up to 2.0%.
In-Can Stability
U.S. gel grade attapulgite products maintain the quality of the
finished product and reduce pre-application mixing time. Their
stable gel strength prevents the settling of solids and phase separation or syneresis during storage. The gels are unaffected by
pH, temperature fluctuations, soluble ions, microbes or almost
any additive. They also do not swell or increase aged viscosity.
Conclusions
Attapulgite serves as the undercarriage of many high solids mixtures, ensuring product quality throughout their life cycles as
well as providing valuable thixotropic properties. When well
dispersed in a liquid, high-quality U.S. gel grade attapulgite products improve the stability of complex composites by entrapping
liquids and particles when the mixture is at rest. Maintaining this
dispersed state is reflected in improved stability and components
being able to work to a level of optimal performance. In coatings this is demonstrated by reduced syneresis, pigment flooding/
float, and improved freeze-thaw properties. In addition, when
the mixture is in motion its shear-thinning thixotropic thickening properties improve flow and leveling, workability (pumping,
spraying, spreading, feathering, etc.). As attapulgite’s lattice structure quickly reforms it reduces spatter, sag, and overspray and
allows higher film build. As the most economical thickeners in
their class, high-quality U.S. gel grade attapulgite proudcts can
reduce cost by partially or wholly replacing other thickeners. CW
Min-U-Gel is a registered trademark of Active Minerals
International LLC.
References
1. Haden, Jr., W.L. Attapulgite: Properties and Uses, pp.284-
290. Paper presented at The Tenth National Conference on Clays
and Clay Materials, Austin, Texas, October 14 - 18, 1961.
2. International Agency for Research on Cancer (IARC)
Monograph, Volume 68, pg 247, Table 2. Samples labelled
NIOSH A and NIOSH B are from U.S. deposits of Floridin
Company and Engelhard, now operated by Active Minerals
International and BASF, respectively.
3. International Agency for Research on Cancer (IARC)
Monograph, Volume 68, pg 262, section 5. 5.
For nearly two decades, Jeff Carr has been a leader in sales,
marketing and business management for the two largest global
attapulgite producers. He has developed new products and applications worldwide as well as led a turnaround for one producer. He currently serves at Active Minerals International and
can be reached at j.carr@activemninerals.com.
Figure 3: Comparison of shear stress and viscosity at various shear rates for
Min-U-Gel 400 attapulgite and HEC in water. The loading levels of both
materials have been exaggerated to produce comparable rheological values.
In coatings, where the attapulgite network interacts with particulate solids, the
dosage level of Min-U-Gel 400 is similar to HEC.