Coatings World - April 2017

An Efficient Approach to Dispersing Pigments
April 2017 www.coatingsworld.com Coatings World | 43

used as anchors for certain pigment types.

Dispersants with aromatic rings have an affinity for surfaces of organic pigments. They adsorb onto the surface by van der Waals forces. Dispersants with hydroxyl, carbonyl, or carboxyl groups have a high affinity for the surface of inorganic pigments. These adsorb onto the surface by hydrogen bonding or induced dipole interactions. Amine groups have high affinity for carbon black surfaces. Without nitrogen, there is not much suit-ability for carbon black.

Experimental Design

For this study, two of the most difficult
pigments were chosen to prepare pigment
concentrates: yellow iron oxide and or-
ganic violet (Tables 1-2). Four 100%-ac-
tive additives were chosen to be tested,
ranging from 10% to 30% additive solids
on pigment.

•Additive A: low-molecular-weight
alkoxylate
•Additive B: medium-weight poly-
ether with aromatic groups
•Additive C: medium-weight poly-
ether phosphate with acid groups
•Additive D: high-molecular-weight
polymer with hyper-branched polyester
chains with aromatic and acid groups
All samples were made in 8-ounce
glass jars with 100 g of material to work
with. Glass beads of size 2.4-2.9 mm
were added as grinding media in a 1:1
ratio. The formulations were processed
on a Skandex shaker for one hour. After
dispersing was completed, samples were
cooled to room temperature and filtered
through a mesh cone filter.

Yellow Iron Oxide Formulations

The yellow iron oxide formulations consist of 55% pigment loading, with 10% additive solid on pigment (ASOP). Because of increasing environmental demands, an exempt solvent (Oxsol 100) was chosen for this study.

Pigment Violet Formulations

Price is a big driving factor in the pigment concentrate market. Because organic pigments are normally more expensive, titanium dioxide was coupled in this formulation to reduce price. The pigment loading for violet was 6% and titanium dioxide was 30%, with 30% additive solid on pigment.

Yellow Iron Oxide Results

Viscosity was measured on a Haake Rheostress 1 Rheometer equipped with PP35 Ti L03 089 plate and tested under a 0.20 mm gap at room temperature (Figure 6). Initial viscosity studies showed that the blank and Sample A had very shear thickening behavior, meaning their viscosities rose along with the shear rate. This is not ideal for pigment concentrates because it could clog the dosing machine when tinting white base paints. Sample B had a shear thinning viscosity until 1000/s, where there was a rise in viscosity. This indicates that there was not enough dispersant to wet out the remaining pigment. Samples C and D had shear thinning curves, with viscosity being the lowest overall for Sample D. This is attractive to pigment concentrate suppliers because a low viscosity means more pigment loading is possible. Viscosity will also be tested after a storage period at elevated temperatures to confirm the performance of the additives.