Colorant Additives and Formula Optimization: The Selection of Dispersants Determines the Performance Ceiling of Colorants

Colorant Additives and Formula Optimization: The Selection of Dispersants Determines the Performance Ceiling of Colorants

 

The performance of pigment paste not only depends on the quality of the pigment itself but also on the selection and ratio of additives such as dispersants, wetting agents, and leveling agents. As the most critical component in pigment paste formulations, dispersants directly determine the dispersion state of pigment particles, storage stability, and the performance of the final coating. A thorough understanding of the mechanism and selection principles of dispersants is crucial for accurately evaluating the quality of color paste.

 

The mechanism of action of dispersants

 

The Basic Principles of Pigment Dispersion

During the grinding process of pigment powder, pigment particles are mechanically dispersed from an aggregated state into individual particles or small aggregates. However, the newly exposed pigment surface possesses high surface energy, making it highly prone to re-aggregation (restabilization). The role of dispersants is to form a stable adsorption layer on the pigment particle surface, preventing re-aggregation through electrostatic repulsion, steric hindrance, or a combination of both mechanisms.

 

Three Mechanisms for Dispersed Stability

Electrostatic Stabilization Mechanism: Anionic dispersants (such as sodium polyacrylate and AMP-95) adsorb onto pigment surfaces, imparting a negative charge to the pigment particles. Particles with the same charge generate electrostatic repulsion, preventing them from approaching and aggregating. Electrostatic stabilization is effective in low-electrolyte environments (pure water) but fails in high-electrolyte environments (e.g., industrial coatings containing salts) due to ion shielding effects.

 

Steric Stabilization Mechanism: Nonionic dispersants (such as polyethers or polyesters) or polymer dispersants form a thick polymer adsorption layer on the pigment surface. When two pigment particles approach each other, the polymer chains interpenetrate and compress, generating entropic repulsion that prevents particle aggregation. Steric stabilization is unaffected by electrolytes and is suitable for various coating systems.

 

Electrosteric Stabilization: A stabilization method that combines both electrostatic repulsion and steric hindrance mechanisms. Ammonium polyacrylate and carboxylate-based dispersants fall into this category, representing the most widely used type of dispersant. The CORDINAR microcolloid formulation employs the electrosteric stabilization mechanism, demonstrating excellent dispersibility stability across various aqueous systems.

 

Performance Comparison of Different Dispersant Types

Anionic dispersant

Advantages: High dispersion efficiency, strong coloring power, and cost-effective. Disadvantages: Stability decreases in high electrolyte environments; some anionic dispersants may cause foam issues.

Applicable System: Ordinary water-based architectural coatings with low pigment content and low electrolyte.

Representative products: Sodium polyacrylate, sodium polymethacrylate.

Nonionic dispersant

Advantages: Not affected by electrolytes and exhibits good compatibility with various resin systems. Disadvantages: Slightly lower dispersion efficiency compared to anionic types and requires higher usage.

Applicable Systems: Industrial coatings with high electrolyte content, systems containing pigments and fillers.

Representative products: Polyethylene glycol ethers, polyether-modified silicones.

 

High Molecular Weight Dispersant (Block Copolymer Type)

Advantages: High dispersion efficiency, good storage stability, and strong compatibility with various systems. 

Disadvantages: Relatively high cost.

Applicable Systems: High-end water-based coatings, industrial paints, automotive paints, powder coatings, and other systems with extremely high performance requirements.

Representative products: Modified polyacrylate block copolymers, polyester-polyether block copolymers.

 

The Influence of Dispersants on the Performance of Pigment Paste

Impact on fineness

The selection and dosage of dispersants directly affect grinding efficiency and final fineness. Insufficient dispersant: low pigment grinding efficiency, difficulty in achieving ultra-fine fineness, poor fineness stability. Excessive dispersant: may impact other coating properties (such as reduced water resistance) and increase costs.

Impact on chromaticity

The affinity of the dispersant for the pigment determines the wetting degree on the pigment surface, thereby affecting the tinting strength. If the dispersant has too weak an affinity for the pigment: insufficient wetting occurs, resulting in a loss of tinting strength. If the dispersant has too strong an affinity for the pigment: it may form an excessively thick adsorption layer, reducing the effective concentration of the pigment and affecting color saturation.

Impact on Storage Stability

Dispersed pigments with poor stability may experience issues such as pigment flocculation, sedimentation, and floating color during storage. Verification method for storage stability: observe changes in fineness, color difference, and sedimentation after 30 days of storage at 45°C. Premium-grade pigments should show no significant performance changes after 30 days of storage at 45°C.

Impact on Water Resistance and Weather Resistance

Certain dispersants (such as those containing amines) may affect the water resistance of coatings, leading to blistering or peeling of the film. In anti-corrosion and outdoor coatings, dispersant systems with proven water resistance must be selected.

summary

Dispersants are the key factor determining the performance ceiling of pigment paste, and their selection requires a comprehensive consideration of pigment type, application system, performance requirements, and cost constraints. Wonderchem have independent dispersant R&D capabilities can typically provide optimal pigment paste solutions tailored to different application scenarios. Wonderchem drives continuous dispersant formulation optimization through technological innovation, delivering high-performance and consistently stable pigment paste products to customers, now we developed nano grades of pigment & dyes grinding dispersants. If you are interested in it, please get in touch with us.