Nikolina Milanovic and Brian O. Casey,
Evonik Coating Additives & Specialty Resins, Evonik Corp., Richmond, VA
Abstract
As problems related to pigment dispersions become more frequent and
requirements regarding color reproducibility become increasingly rigorous, new demands for pigment wetting
agents and dispersants are required to
resolve these pigment stabilization issues. Over the past 20 years, advances
in polymeric dispersants have made
significant improvements in the process
of wetting and stabilizing pigments. As
a result, many dispersant technologies
that better stabilize small pigment particles and that better prevent flocculation are emerging in the marketplace.
This paper explains pigment and dispersant interfaces and how harmonizing and optimizing these interactions
will lead to a better pigment dispersion.
Introduction
Until the development of synthetic pigments, pigments of natural origin – materials such as clay, earth colors, and minerals
– were used to color paints. Vegetable oils
with high lecithin content were used to
wet out natural pigments. Since then, technology has progressed immensely.
Dispersing pigments is sometimes
viewed as an art instead of a technical
process. This is mainly due to the multiple steps that occur during the dispersion process. These processes can seem
confusing, but breaking the steps down
into a structured manner makes them
easier to understand and helps find solutions faster.
The following research explains the
science behind dispersing pigments and
fillers, in hope of reaching a better understanding of how to stabilize them more
efficiently. This study discusses different
types of wetting and dispersing additives
that can be used to stabilize two notoriously difficult pigments.
Pigment and Additive
Interactions
Pigments are tiny solid particles that have
the ability to refract light.1 Pigments serve
two main functions: an optical function
providing color, opacity, and gloss; and
a protective function for the surface beneath the coating.
Pigment Structures
Pigments come in three forms: primary
particles, aggregates, and agglomer-
ates. Primary particles are single, small
particles that form during synthesis.2
These are the smallest components in pig-
ments and fillers, and they mostly consist
of cuboid, rod, and spherical-shaped par-
ticles (Figures 1-2). During calcination,
primary particles may form together to
create larger particles through chemical
bonding. These particles are called ag-
gregates, and they are organized lattice
regions connected from face to face of the
primary particle. Alternatively, particles
that form via physical bonds instead of
chemical bonds are called agglomerates.
These particles are connected by edges, re-
sulting in a smaller surface area and more
difficulty in wetting out the pigment.
Organic and Inorganic Pigments
Pigments are widely classified as either
organic or inorganic. Inorganic pigments
are used for coloristic properties as well
as other properties such as anti-static and
An Efficient Approach
to Dispersing Pigments
Figures 1-2. Transmission electron microscope images of iron oxide pigments.
