Color pigments are critical components in the composition of paints, coatings and inks providing designed aesthetic qualities. Both organic and inorganic color pigments can achieve these properties depending on the desired effect.
Careful selection of pigments is essential in achieving optimal performance.
What Factors Influence Pigment Stability?
Understanding the various pigment types, properties and chemical families can help the formulator determine the most effective pigment chemistry and manufacturing process for the best final coating. Choosing the correct pigment for your desired application is the first step in achieving a stable system during the formulation process.
Other factors that influence pigment stability include:
- Purity: To ensure pigments have minimal impurities, the manufacturer should test for tint strength, pH, conductivity, oil absorption and viscosity.
- Wetting: In this process, it is essential to employ an additive that can lessen the water’s surface tension, penetrate pigment pores and wet the pigments for dispersal.
- Dispersion: Dispersed pigments have a strong tendency to return to their initial agglomerated state and create the effect of pigment flooding and pigment floating. Due to this tendency, proper selection of the wetting additive and a dispersing agent for pigments is crucial in obtaining a stable formula.
- Controlled flocculation: This mechanism focuses on the protection of substrates, mainly in high-build film systems. It can yield pseudoelasticity, thixotropy and anti-sagging effects.
- Deflocculation: This mechanism focuses on optical appearance, primarily on topcoats and pigment concentrates. The stabilization effects that deflocculation produce are high gloss, low haze, low viscosity and an enhanced flow. Deflocculation is important because it will show the original nature of the pigments.
Achieving Pigment Dispersion Stability
The keys to achieving a stable coating with optimal performance and value are proper pigment selection, additive selection and the appropriate means to achieve complete dispersion. Dispersion agents maintain the dispersion properties over time and prevent the re-agglomeration of pigment particles. If pigment dispersion is not stable, flocculation results.
The chemical structure of the dispersion additive will determine the stabilization mechanism of the pigment particles — electrostatic, steric or electro-steric repulsion. Here are three examples of additives that can help achieve dispersion stability:
- Dispersion additives: For adequate pigment stabilization, the dispersing agent must be able to adsorb onto the surface of the pigment. Therefore, the additive must have anchor groups with a high affinity for the pigment surface.
- Thixotropes & Suspension Agents: Using an appropriate thixotrope and suspension agent helps build sufficient viscosity and a network structure that suspends pigments and can prevent hard settling.
- Deflocculation agents: Using a deflocculation agent reduces viscosity or prevents flocculation.
Tests like viscosity measurements and tint strength, or hue evaluations can determine the success of sufficient dispersion.
Request a Quote From Active Minerals International Today
Active Minerals International (AMI) supplies a full line of products that help achieve pigment stability when used as directed, including:
- Min-U-Gel® 400 attapulgite thixotropic thickener and suspension agent is effective in controlling rheology and suspension and preventing hardpack settling.
- Acti-Gel® 208 purified magnesium aluminosilicate provides the same benefits as Min-U-Gel 400 but also allows an increase in solids without raising viscosity and greatly improves flowability of pigment dispersions.
- Our Acti-Min® kaolin products provide performance benefits in sheen and gloss control, anti-settling, enamel holdout and sanding properties.