Pigment Selection for Plastics & Masterbatch
A resin-by-resin selection guide covering PE, PP, PVC, ABS, PS, PC, PET, PA, and POM — with processing temperatures, migration risk assessments, and recommended HP pigment grades for every polymer system.
Choosing pigments for plastics and masterbatch starts with one overriding question: can this pigment survive the processing temperature without migration? Unlike coatings, where the pigment sits on a surface protected by a binder film, plastic pigments are dispersed throughout the polymer matrix. Migration — the movement of pigment molecules through the polymer to the surface — is the #1 failure mode in colored plastics. It manifests as blooming (powdery surface deposit), bleeding (color transfer to adjacent materials), or plate-out (build-up on mold surfaces). Selecting the right pigment requires matching heat stability, migration resistance, and chemical compatibility to your specific resin system.
Resin-by-Resin Selection Table
| Resin Type | Processing Temp (°C) | Key Pigment Requirements | Recommended CIs | Migration Risk Notes |
|---|---|---|---|---|
| PE (Polyethylene) | 180–240 | Migration resistance grade 4–5, no warpage induction | PB15:3, PG7, PR254, PY150, PR101, PY83, PV19 | PE is prone to warpage from organic pigments — evaluate shrinkage in thin-wall injection molding. Avoid excessive loading (>1.5%) for nucleating organics. |
| PP (Polypropylene) | 200–260 | Migration resistance grade 4–5, no nucleating effect on PP crystalline structure | PB15:3, PG7, PR254, PY150, PY83, PV19, PR101 | PP’s semi-crystalline structure amplifies warpage from nucleating pigments. Test dimensional stability at full loading. DPP and quinacridones are low-nucleating choices. |
| PVC (Flexible & Rigid) | 160–200 (rigid), 140–180 (flexible) | Acid resistance (HCl evolution during processing), migration resistance with plasticizers | PB15:3, PG7, PR254, PY83, PR101, PY13, PBr101 | PVC releases HCl during thermal processing. Avoid pigments with acid-sensitive functional groups. In flexible PVC, plasticizer extraction of pigment is a major migration pathway — test at full plasticizer loading. |
| ABS | 220–260 | Heat stability, compatibility with styrene-acrylonitrile matrix | PB15:3, PG7, PR254, PY150, PR101, PV19, PY184 | ABS’s butadiene phase can absorb low-MW organic pigments causing color shift over time. Use pigments with MW > 500 g/mol. |
| PS (Polystyrene) / HIPS | 180–240 | Heat stability, no dissolution in styrene monomer residuals | PB15:3, PG7, PR101, PR254, PY150, PV19 | Residual styrene monomer is an excellent solvent — it can dissolve low-MW pigments at processing temperature. Use high-MW pigments exclusively. |
| PC (Polycarbonate) | 280–320 | Heat stability >300°C, no amine or alkaline residues (catalyze PC degradation) | PR254 (HP RED 2135), PB15:3, PG7, PY184, PV19, PR101 | PC is extremely sensitive to alkaline residues. Avoid pigments processed with amine-based dispersants. Only our HP-grade pigments are validated for PC at 300°C+. Pigment-induced PC degradation causes embrittlement and color shift. |
| PET (Polyester) | 260–290 | Heat stability >280°C, no antimony yellowing, no acetaldehyde generation | PB15:3 (PET grade), PG7, PR254, PY184 | PET’s antimony catalyst can cause severe yellowing with certain pigments. Our PET-grade PB15:3 is surface-passivated to resist Sb-catalyzed degradation. Avoid iron oxides in PET — they catalyze polymer degradation. |
| PA (Nylon 6 / 6,6) | 250–300 | Heat stability >300°C, resistance to amine attack, moisture absorption stability | PR254 (HP RED 2135), PB15:3 (nylon grade), PG7, PY184, PR101 | PA’s amine end groups can chemically attack pigments at processing temperature. Only amine-resistant pigment grades are suitable. Moisture absorption in PA6 causes reversible shade shift in some organics. |
| POM (Acetal / Polyoxymethylene) | 180–220 | Acid resistance (formaldehyde release), no catalytic degradation | PB15:3 (acid-resistant grade), PG7, PR101, PBr101 | POM is the most chemically sensitive polymer. Formaldehyde release at processing temperature creates an acidic environment. Only acid-stable inorganic pigments and specially stabilized phthalocyanines are safe. Most organic reds and yellows catalyze POM depolymerization — avoid them entirely. |
Understanding Migration in Plastics
Migration is the single most important failure mode in colored plastics. It occurs when pigment molecules have sufficient thermal energy and molecular mobility to diffuse through the polymer matrix to the surface. The risk factors are:
- Pigment molecular weight — Migration resistance correlates strongly with molecular weight. Pigments with MW < 400 g/mol are high-risk in all polymers. MW > 800 g/mol (DPP, quinacridones, phthalocyanines) are inherently migration-resistant.
- Pigment solubility in polymer — Even trace solubility (ppm level) at processing temperature can cause visible blooming upon cooling. This is why phthalocyanines (near-zero solubility) outperform monoazo pigments (measurable solubility) in demanding applications.
- Polymer glass transition temperature (Tg) — Above Tg, polymer chain mobility increases dramatically, accelerating pigment migration. Amorphous polymers above their Tg (PS at 100°C, PC at 145°C) are particularly susceptible.
- Plasticizer content — Plasticizers act as internal solvents that extract and mobilize pigment molecules. This is the dominant migration pathway in flexible PVC.
⚠ Critical: Warpage in Polyolefins
Certain organic pigments — particularly phthalocyanines and diarylides — can act as heterogeneous nucleating agents in semi-crystalline polyolefins (PE, PP). This alters the crystallization kinetics, causing differential shrinkage and macroscopic warpage. Always evaluate warpage in thin-wall (1–2 mm) injection-molded parts at full pigment loading. Quinacridones (PV19) and DPP pigments (PR254) are low-nucleating choices for dimensionally critical PE/PP parts.
High-Temperature Plastics: The HP Grade Advantage
For engineering plastics processing above 280°C (PC, PA, PET, PPS, PEEK), standard pigment grades fail. Our HP (High Performance) series is specifically engineered for 300°C+ thermal stability:
- HP RED 2135 (PR254 DPP Red) — Validated at 300°C/5 min dwell in PC and PA66 with ΔE < 1.0. Surface-encapsulated to prevent DPP sublimation and amine interaction.
- HP BLUE 153 (PB15:3) — Amine-passivated crystal form for PA and PC. Prevents phthalocyanine-induced polycarbonate degradation through proprietary surface treatment.
- HP YELLOW 184 (PY184 Bismuth Vanadate) — The only yellow pigment validated for PC at 300°C without antimony catalyst interaction or color shift.
Frequently Asked Questions
Q: Which red pigment survives 300°C in polycarbonate?
Only PR254 (DPP Red) in HP-grade variants reliably survives 300°C polycarbonate processing without color shift. Our HP RED 2135 achieves ΔE < 1.0 after 5-minute dwell at 300°C in PC resin, and its amine-free surface treatment prevents PC degradation. Alternative red pigments that fail at 300°C in PC include: PR48:2 (azo, complete decomposition), PR57:1 (azo lake, severe shade drift at 260°C+), PR170 (naphthol AS, decomposes above 280°C), and PR122 (quinacridone, ΔE > 3.0 at 300°C due to crystal phase change). For opaque reds in PC, PR101 (iron oxide red) is heat-stable but causes PC degradation through catalytic oxidation — not recommended.
Q: Why do some pigments cause warpage in HDPE?
HDPE warpage from pigments occurs because certain organic pigments act as heterogeneous nucleating agents during HDPE crystallization. As the melt cools, these pigments provide nucleation sites that accelerate crystallization locally, creating a non-uniform crystalline structure. Since the crystalline phase is denser than the amorphous phase, differential shrinkage across the part produces macroscopic warpage. Phthalocyanines (PB15:3, PG7) are the most common offenders because their planar molecular structure mimics HDPE’s crystalline lattice. Solutions: (1) select low-nucleating pigments — DPP (PR254) and quinacridones (PV19, PR122) minimize nucleation; (2) reduce pigment loading below the critical nucleation threshold (typically <0.5%); (3) use inorganic pigments (PR101, PY42) which do not nucleate PE.
Q: How do I select pigments for food-contact PP?
Food-contact PP pigment selection is governed by three overlapping requirements: migration resistance, regulatory compliance, and thermal stability. First, choose only pigments demonstrated to have zero migration in PP at use temperature — this typically limits the palette to high-MW organics (phthalocyanines PB15:3, PG7) and selected inorganics (PR101, PY42, PBk7 carbon black). Second, verify regulatory compliance for your target market: FDA 21 CFR §178.3297 for USA (colorants for polymers), EU 10/2011 + AP(89)1 for Europe, and GB 9685 for China. Each regulation has a specific positive list — do not assume cross-recognition. Third, ensure the pigment survives PP processing (200–260°C) without decomposition products that could migrate. Our HP FOOD GRADE series includes PB15:3, PG7, PR101, and PY150 all supported by full migration testing documentation compliant with EU 10/2011.
Need Help Selecting the Right Pigment?
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