Pigments are solid, insoluble powders that provide color to various materials, including paints, coatings, and inks. They are commercially available in a wide range of colors and chemistries. While the pigment options seem endless, they all have something in common: they must be properly dispersed for optimal performance and appearance.
What is Pigment Dispersion?
Pigment dispersion is the process of suspending insoluble pigments in a liquid medium, typically water or organic solvent, so they can be used to create products such as inks, paints, and coatings. Traditionally, pigment dispersion is comprised of three main steps: wetting, deagglomeration, and stabilization. These three steps are outlined in further detail below.
Pigment Wetting
When solid pigments are first added to the liquid medium, they are typically agglomerated together, with air entrapped on and within the pigment agglomeration. For proper wetting to occur, the air entrapped in the pigment needs to be replaced with the liquid medium. Using an additive called a wetting agent reduces surface tension and enables the liquid to achieve complete wetting of the pigment more easily.
Deagglomeration
Once complete wetting of the pigment particles is achieved, the large agglomerations of pigment must be broken up to reduce the particle size. This is commonly achieved through mechanical shear via a grinding mill. Reducing the surface tension in the liquid medium by a pigment wetting agent allows for faster deagglomeration and a more homogeneous particle size in the dispersion.
Stabilization
The deagglomerated pigment particles must then be stabilized to prevent reagglomeration. In this step, pigment dispersion additives are added that adsorb onto the pigment particles and keep them separated. Stabilizing pigments in suspension can be achieved by either electrostatic or steric means.
Electrostatic Dispersants
Electrostatic dispersant additives carry an ionic charge. They interact with the surface of the pigment particles to produce like-charged surfaces, which are typically cationic. These like charges on the surface of the pigment particles repel each other and keep the pigment from reagglomerating. Changing pH or adding ionic material can destabilize particles suspended with electrostatic dispersants.
Steric Dispersants
Steric dispersant additives are molecules with an anchoring head group attracted to the pigment particles and tails attracted to the liquid phase of the dispersion. The head groups adsorb onto the surface of the pigments, and the tails orient themselves outward from the surface. The protruding tails repel each other and keep the pigment particles separated and suspended. Steric stabilization is incredibly stable at high salt concentrations and over a wide pH range.
Why are Pigment Wetting Agents & Dispersants Important?
In many cases, the pigment is the most expensive ingredient in an ink, paint, or coating formulation because of its cost and the high concentration it is used. Optimizing the wetting and dispersion of pigments ensures optimal appearance and physical properties in the formulation while using the least amount of pigment possible. Selecting the right wetting agent and dispersion additive for coating, ink, and paint formulations is critical for producing high-quality products with minimized production costs. .
Surfactants as Wetting Agents and Dispersants
Surfactants, or surface-active agents, are additives that reduce surface tension at the interface between two substances. In the case of wetting and dispersing pigments, reducing the surface tension between the solid pigment particles and the liquid carrier allows for faster and more efficient wetting and deagglomeration. Additionally, surfactants can adsorb onto the surface of pigment particles and provide steric stabilization of the dispersion. Commercially, many types of nonionic surfactants and anionic surfactants are used today as wetting agents and dispersants in inks, paints, and coatings. These surfactants are compared below based on performance characteristics.
Surfactant Type
Reduction of Surface Tension
Foam Tendency
Addition Rate (%)
Alcohol Ethoxylate
Moderate
Moderate
1-3
Sulfosuccinate
Good
High
1-3=
Fluorosurfactants
Excellent
Low
0.01-0.05
Polyether Siloxane
Moderate
Moderate
1-3
Acetylene Diol
Good
Low
0.1-1
Selecting the appropriate surfactant for pigment wetting and dispersion should be based on the liquid carrier (aqueous or organic solvent), the pigment, and the end use application. While there is no one-size-fits-all solution, fluorosurfactants provide the highest level of surface reduction at the lowest addition rate, are anti-foaming, and can provide greater cost savings over traditional nonionic and anionic surfactants.
Capstone™ - Fluorosurfactant Wetting Agents
Capstone™ fluorinated surfactants are powerful pigment wetting agents suited for waterborne and solventborne paints, coatings, and inks. Capstone™ surfactants can be added at a much lower rate than traditional surfactants (typically 0.01%–0.05%) and often reduce or eliminate the need for other additives like defoamers. For example, in many cases for waterborne coatings, the requirement for other pigment wetting agents may be reduced by 30%–100% and defoamer additives may be reduced by 50%–100%. Eliminating such wetting agents and defoamer additives typically results in net cost savings.
Commercially Available Capstone™ Grades
The Capstone™ grades listed below are designed to provide optimal pigment wetting for inks, paints, and coatings while eliminating the need for other wetting agents and defoamers. All grades listed below can be used for waterborne systems, but Capstone™ FS-3100 may be used for both waterborne and solventborne systems.
ChemPoint is a technical resource and distributor for coating, paint, and ink resins and additives. Click below to speak with one of our product specialists to find the Capstone™ grade that is right for your application.
