Coating Pigments FAQ
Common questions about pigment selection for paints and coatings
Frequently Asked Questions
What is the best pigment for exterior wall paint?
Iron oxides PR101 (red) and PY42 (yellow) deliver the best cost-performance for exterior paints, with lightfastness grade 8 and decades of proven outdoor durability. For premium applications requiring brighter shades, PR254 (DPP red) offers lightfastness 7-8 and PY150 (benzimidazolone yellow) provides lightfastness 7-8, though at significantly higher cost.
How do I prevent pigment settling in water-based coatings?
Settling is caused by pigment particles larger than 0.5µm or insufficient stabilization. Solutions include: using pigments with finer particle size (D50 < 0.3µm), adding rheology modifiers (bentonite clay at 0.2-0.5% or fumed silica at 0.5-1%), optimizing dispersant dosage (calculate C.A.D. — concentration at agglomerate demand), and maintaining pH 8-9 to maximize electrostatic repulsion (zeta potential > ±30mV).
Which pigments are compatible with epoxy coating systems?
Epoxy systems are alkaline (amine-cured), making alkali-sensitive pigments unsuitable. Avoid PR57:1 (Lithol Rubine, alkali resistance grade 2) and PY12 (diarylide yellow, alkali resistance grade 2). Safe choices with alkali resistance grade 5: PB15:3 (phthalocyanine blue), PG7 (phthalocyanine green), PR101 (iron oxide red), PY42 (iron oxide yellow), PR254 (DPP red), PV19 (quinacridone violet), and all inorganic pigments.
What pigment loading rate for solvent-based industrial coatings?
Typical loading by pigment type: TiO2 (PW6) 15-25% by weight for opacity, organic pigments 5-12% (PR254, PB15:3, PG7, PY150 — higher loading increases cost disproportionately), inorganic pigments 15-40% (PR101, PY42 — lower tinting strength requires higher loading), carbon black (PBk7) 1-3% (extremely high tinting strength). Pigment volume concentration (PVC) typically ranges 5-30%, with critical PVC affecting film properties.
Can I use the same pigment for water-based and solvent-based systems?
Yes for most pigments — PR254, PB15:3, PG7, PR101, PY42 work in both systems when properly dispersed. However, water-based systems require: pigments with pH stability 5-9 (check acid/alkali resistance grades), dispersants optimized for aqueous media (anionic or non-ionic), and wetting agents to overcome higher surface tension of water (72 mN/m vs 25-30 mN/m for solvents). Some pigments, particularly PR57:1 (lake pigments), may hydrolyze in water at elevated pH.
Why is my blue coating turning green over time?
This is typically caused by yellowing of the binder (oxidative degradation of alkyd or aromatic urethane resins), not the PB15:3 pigment itself — phthalocyanine blue is extremely stable. The yellowing binder + blue pigment = perceived green shift. Solutions: switch to non-yellowing binders (aliphatic urethane, acrylic), add UV absorbers (benzotriazole at 1-2%) and HALS (hindered amine light stabilizers at 0.5-1%), use rutile TiO2 only (anatase accelerates binder degradation).
What pigments survive coil coating cure at 250°C?
Pigments with heat stability ≥250°C: PR254 (DPP, stable to 300°C), PV19 (quinacridone, 250°C), PR122 (quinacridone, 250°C), PB15:3 (phthalocyanine blue, 300°C), PG7 (phthalocyanine green, 300°C), PY150 (benzimidazolone, 250°C), PR101 (iron oxide, 500°C+), PY42 (iron oxide, 500°C+). Unacceptable: PR57:1 (fades at 180°C), PY12 (degrades at 180°C), PY83 (degrades at 200°C). All azo pigments are excluded above 220°C.
How to match RAL/Pantone colors with pigment blends?
Start with spectrophotometer measurement of the target color (D65/10° observer, specular included). Use color matching software to predict the nearest single-pigment match — blend only when ΔE > 3. Limit blends to 3-4 pigments maximum to avoid metamerism (color match changes under different lighting). For RAL colors, many are achievable with 2-pigment blends: e.g., RAL 3020 (Traffic Red) ≈ PR254 + small PY150; RAL 5015 (Sky Blue) ≈ PB15:3 + TiO2. Always test the blend at multiple light sources (D65, A, F11) to check metamerism index < 1.0.
Which red pigment is best for automotive basecoat?
PR254 (DPP, CI 56110) is the industry standard for red automotive basecoats — it provides heat stability to 300°C (survives clearcoat bake at 140°C with margin), lightfastness grade 7-8 (5+ years Florida exposure), and the transparency needed for effect layers (metallic/pearlescent basecoats). Alternatives: PR264 (DPP variant, slightly yellower shade), PR179 (perylene maroon for deep reds), PR177 (anthraquinone for transparent reds). Avoid PR170 (naphthol) — weather resistance only grade 3-4, unsuitable for automotive.
What’s the difference between pigment paste and pigment powder for coatings?
Pigment paste (colorant dispersion) is pre-dispersed pigment in a liquid carrier at 30-60% pigment concentration — advantages: faster incorporation (5-10 min vs 30-60 min), lower dust exposure, consistent color strength, no pre-dispersion step. Pigment powder: lower cost per kg pigment (no carrier, no dispersion cost), unlimited shelf life (paste may settle over 6-12 months), flexible for custom formulations. Cost tradeoff: paste costs 20-50% more per kg of active pigment but reduces processing time and quality risk.
Quick Reference Table
| Coating Type | Resin System | Key Pigment Requirement | Recommended CIs |
|---|---|---|---|
| Exterior Architectural | Acrylic, Alkyd | Lightfastness 7+ | PR101, PY42, PR254, PB15:3 |
| Industrial | Epoxy, PU | Chemical resistance 4-5 | PB15:3, PG7, PR254, PY150 |
| Automotive | Acrylic-melamine, PU | Weatherfast 4-5, LS 7-8 | PR254, PV19, PB15:3 |
| Powder Coating | Polyester, Epoxy | Heat stability 200°C+ | PR254, PB15:3, PG7, PY150 |
| Wood Coating | NC, PU, Acrylic | Transparency, lightfastness | PR254, PY150, PB15:3 |
| Water-based | Acrylic, PU dispersion | pH stability 5-9 | PR254, PB15:3, PY42, PR101 |
Pro Tip
Always test pigment compatibility in your specific resin system before production. A pigment that works perfectly in acrylic may fail in epoxy due to chemical incompatibility. Request a 200g evaluation sample from our technical team.
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