How to Choose a Dispersant for Pigment Pastes?
Choosing a suitable dispersant for a pigment paste requires comprehensive consideration of its composition,
application scenario, and performance requirements. The following are systematic selection steps and key factors:
1. Determine the Chemical Properties of the Pigment Paste
Pigment Type:
Organic pigments (e.g., Phthalocyanine Blue, Azo Red): Typically require polymeric dispersants (e.g., polyurethane, acrylates)
to stabilize particles through steric hindrance.
Inorganic pigments (e.g., Titanium Dioxide, Carbon Black): Anionic dispersants (e.g., phosphate esters, sulfonates) can be
used, relying on charge repulsion for stable dispersion.
Solvent/Media:
Aqueous systems: Select water-soluble dispersants (e.g., polycarboxylates, nonionic surfactants).
Oil-based systems: Use oil-soluble dispersants (e.g., fatty acid derivatives, polymeric dispersants).
UV-curing systems: Require dispersants compatible with photoinitiators (e.g., modified polyethers).
2. Mechanism of Action of Dispersants
Charge-stabilized (ionic) dispersants: Suitable for aqueous systems, preventing flocculation through electrostatic
repulsion (e.g., sodium dodecylbenzenesulfonate).
Stereohedral (nonionic) dispersants: Form a protective layer on particle surfaces through long-chain molecular
adsorption (e.g., RK-4033, RK-4016C).
Synergistic dispersants: Combine charge and steric hindrance (e.g., RK-4017E), suitable for high-concentration
pigment pastes.
3. Key Performance Indicators
Compatibility: Dispersants must be compatible with resins/solvents (e.g., aqueous acrylic resins combined
with polyether dispersants).
HLB value: Hydrophilic-lipophilic balance values must match the system (HLB > 10 for aqueous systems,
HLB < 10 for oily systems).
Molecular weight:
Low molecular weight (< 1000): Suitable for inorganic pigments.
High molecular weight (> 5000): Suitable for organic pigments, providing stronger steric hindrance.
Dosage: Generally 10-30% of pigment mass, requires experimental optimization.
4. Application Scenarios
High-gloss coatings: Require a low-foaming dispersant (e.g., RK-4012).
High-shear systems (e.g., inkjet inks): Use a shear-resistant dispersant (e.g., RK-4044).
Weather resistance requirements: Avoid dispersants containing easily hydrolyzable groups (e.g., esters).
5. Experimental Verification Methods
Dispersion effect test:
Fineness test (scraper fineness meter): ≤10μm is optimal.
Sedimentation test: Observe stratification after standing for 24 hours.
Stability assessment:
Viscosity change (Stormer viscometer): Viscosity increase after storage <10%.
Heat storage test: No coarsening or flocculation after 7 days at 50℃.
6. Commonly Recommended Products
Pigment Type | Recommended Dispersant
Organic Pigments: RK-4033 (solvent-based), RK-4010 (water-based)
Carbon Black: RK-4035 (solvent-based), RK-4017E (water-based)
Titanium Dioxide: RK-4013 (solvent-based), RK-4008DE (water-based)
Phthalocyanine Blue: RK-4045 (UV system), RK-4017EA (water-based)
7. Precautions
Avoid excessive addition: May lead to increased viscosity or affect film performance.
Compound Testing: Synergistic effects with wetting agents, leveling agents, and other additives need to
be verified.
Environmental Requirements: Choose dispersants that are APEO-free and low in VOCs (such as RK-4036).
Through the above steps, dispersants can be selectively screened, and the selection can be optimized based
on experimental data. In practical applications, it is recommended to cooperate with suppliers to obtain samples
for parallel testing.
