Problems such as floating color, blooming, and uneven coloring in coatings or inks are usually caused by uneven
pigment dispersion, poor system compatibility, or surface tension imbalance. The following are systematic solutions:
1. Problem Analysis **Phenomenon and Main Causes:** Floating Color: Large differences in pigment density/particle size
lead to stratification (e.g., carbon black floats when mixed with titanium dioxide). Blooming Color: Uneven solvent evaporation
rate or surface tension gradient induces Bénard cells, forming irregular patterns. Floating Color: Poor pigment compatibility
with resin leads to localized aggregation and uneven surface color (common in metallic paints).
2. Solutions and Measures
(1) Optimize Formulation Design
Adjust pigment density matching:
Add density modifiers (e.g., fumed silica) to reduce density differences.
Pre-grind high-density pigments (e.g., iron oxide) to a finer particle size (D50 < 1 μm).
Control solvent evaporation rate:
Mix fast-drying and slow-drying solvents (e.g., xylene + DBE) to smooth the evaporation gradient.
Adding high-boiling-point solvents (such as propylene glycol methyl ether acetate, PMA) delays surface drying.
Enhancing compatibility:
Using adhesion promoters (such as RK-5263) for organic pigments improves their bonding with the resin.
Metallic pigments (aluminum powder) require orientation aids (such as RK-6028).
(2) Improving the dispersion process
Dispersant selection:
Floating pigment: Use synergistic dispersants (such as RK-4029, which combines charge and steric stabilization).
Floating pigment: Use foam-controlling dispersants (such as RK-4045) to reduce surface disturbance.
Grinding fineness control:
Ensure pigment fineness ≤15μm (using a scraper fineness gauge); if necessary, use a sand mill for multiple cycles.
Optimizing the addition sequence:
Add dispersant + some solvent first, then slowly add pigment (to avoid excessively high local concentrations).
(3) Adjusting Construction Conditions
Environmental Control:
Temperature 20-30℃, humidity <70%, avoid rapid surface drying causing eddies.
Construction Parameters:
Adjust spray viscosity to 25-30s (Ford Cup 4), spray gun pressure 0.3-0.5MPa.
Avoid excessive stirring during brushing.
(4) Adding Functional Additives Problem Type Recommended Additive Mechanism of Action RK-4004
(Anti-floating dispersant): Improves the wetting and solubility of the system, promoting uniform pigment distribution.
Anti-floating color blooming additive (RK-8035): Eliminates surface tension gradient, suppressing Bénard eddies.
Floating wax-based orienting agents help metallic pigments align parallelly, reducing random reflections.
3. Emergency Treatment Methods
Floating on the coated surface:
Lightly spray the surface with thinner (≤10%) to re-level.
Cover with a thin layer of transparent resin (such as acrylic varnish) to cover the defect.
Pigment Floating:
Add 0.1-0.5% thixotropic agent (e.g., bentonite) to thicken and prevent sedimentation.
Stir at low speed (<500 rpm) for 30 minutes before testing.
4. Preventive Measures
Storage Management:
Stir pigments for ≥15 minutes before use. Store metallic pigments in a sealed, light-protected container.
Quality Control:
Test the oil absorption (GB/T 5211.15) and resin acid value of each batch to ensure compatibility.
Process Validation:
Add a fluorescent tracer in a small-scale test and observe the dispersion uniformity under a UV lamp.
5. Case Reference
Case 1: Floating of a Water-Based Wood Coating
Cause: Significant difference between phthalocyanine blue (density 1.6) and titanium dioxide (density 4.2).
Solution: Add 2% HR-4017E dispersant + 0.3% fumed SiO₂, reducing the fineness from 25μm to 8μm.
Case 2: Surface inclusions in automotive metallic paint
Cause: Disordered aluminum powder arrangement.
Solution: Switch to wax paste, adjust spray viscosity to 22s (Ford cup #4).
The above methods can systematically solve the problem. If the problem persists, it is recommended to contact the
additive supplier (such as Hongrui or Ruikun) for formulation diagnosis.
