Guidelines for Selecting Dispersants in Coating Systems
Core logic: First distinguish the system (water-based/oil-based) and pigment type (inorganic pigment/organic pigment/charcoal black), then match the dispersant anchoring group and solvation chain while considering subsequent indicators such as anti-floating color, anti-settling, gloss, water resistance, and storage stability
I. Oil-based/solvent-based coating systems
With weak effects from hydrophilic and hydrophobic forces, the primary stabilization mechanism relies on steric hindrance, making polymeric super-dispersants the mainstream
1. Organic pigments, high-pigment carbon black
Preferred polyurethane and polyacrylate block super-dispersants
The anchoring group matches the surface of organic pigments (aromatic groups, amide groups), while the solvation chain ensures compatibility with resin/solvent, addressing issues such as pigment paste flocculation, poor gloss, and uneven color development, making it suitable for high-end solvent-based industrial paints and plastic coatings
Recommended models: RK-4035AC, RK-4029, RK-4054EF
2. Inorganic pigments (titanium dioxide, fillers)
Optional: Polyester based super dispersant, phosphate ester dispersant
Phosphates: Excellent anchoring and viscosity reduction for titanium dioxide, suitable for ordinary solvent paints; Disadvantages: Some may affect drying and weather resistance
Recommended models: RK-4012, RK-4013A, RK-4013C
Polyester polymer super dispersant: more versatile, weather resistant and stable, suitable for topcoats and weather resistant systems
Recommended models: RK-4029, RK-4061C0
Attention: Traditional fatty acid dispersants are only suitable for low requirement primers and are prone to yellowing, affecting weather resistance
II、 Water based coating system
Water based media have high polarity, and dispersants are mainly ionic and polycarboxylic acids. They rely on charge repulsion and steric hindrance to stabilize pigments
1. Organic pigments, carbon black (colorants, colored topcoats)
Preferred polymer block copolymer (non-ionic/anionic polymer dispersant), recommended models: RK-4017EA, RK-4059, RK-4054EF
Features: Long solvation chain, mainly steric hindrance, wetting the surface of organic pigments, effectively preventing floating color, flower formation, flocculation, enhancing coloring power and luster; Suitable for water-based industrial paint, water-based color paste, water-based automotive paint
⚠️ Small molecule wetting and dispersing agents should be used with caution, as they are prone to foaming, migration, and affect water resistance
2. Inorganic pigments (titanium dioxide, iron oxide, talc powder, calcium carbonate, nano inorganic powder)
Preferred polycarboxylate anionic dispersants, recommended models: RK-4047, RK-4017F0
Advantages: Strong anchoring, strong charge repulsion, good viscosity reduction effect, anti settling, high cost-effectiveness; Suitable for ordinary interior wall paint and primer
Limitations: There is a risk to high water resistance and high gloss systems, and some varieties are prone to affecting water resistance
Addendum: Nano inorganic powders (nano zirconia, silicon powder) are preferred for high molecular weight polycarboxylate ammonium salts, and short chain small molecule dispersants are prone to flocculation. Recommended model: RK-4008DH
III、 Key selection criteria
1. Compatibility: The solvent chain of the dispersant must match the matrix resin and solvent. Poor compatibility can result in loss of gloss and shrinkage of pores
2. Special performance selection
-To prevent settlement: high molecular weight dispersant (in combination with rheological agents)
-To achieve high coloring power and high gloss: narrow molecular weight distribution polymer hyperdispersants
-High requirements for water resistance and weather resistance: avoid small molecule ionic dispersants
-Multi pigment composite system (inorganic+organic co grinding): Prioritize broad-spectrum polymer dispersants to avoid floating colors
3. Process matching: Sand grinding and color slurry integrated grinding, dispersant should be added first during the grinding stage, and should not be added later
4. Addition amount: Based on the surface area of the pigment (not the total mass of the formula), excessive amount will affect water resistance, adhesion, and recoating properties; Insufficient will cause flocculation and sedimentation
IV、 Common pitfalls to avoid
-Direct use of oil-based hyperdispersants in aqueous systems: incompatible, directly flocculates
-Organic pigments using small molecule polycarboxylates: exhibiting chromatic aberration and easily floating color
-Blind use of ordinary dispersant for nano powder: the specific surface area of the powder is large, the dispersant adsorption is insufficient, and the short-term thickening
-Poor compatibility of dispersants and other additives (defoamers, leveling agents) can induce shrinkage and bubbles
V、 Simplified selection shorthand
Water based inorganic pigments → polycarboxylates; Water based organic/carbon black → polymer block copolymer
Oil based inorganic pigment → phosphate ester/polyester super dispersant; Oil organic/carbon black → polyurethane/acrylic acid super dispersant
