1. Introduction

PUE (Polyether polyol-based) color pastes are pigment dispersions manufactured using polyether polyol as the carrier resin, specifically engineered for in-situ coloring of polyurethane (PU) systems. Unlike conventional solvent-borne color pastes, PUE pastes use the same polyol chemistry that forms the soft segment of PU, ensuring chemical compatibility without introducing foreign solvents or incompatible resins. As PU processing evolves toward low-VOC, high-efficiency molding technologies—including cold-cure high-resilience foam, reaction injection molding (RIM), and cast elastomer processes—PUE color pastes have become the standard coloring solution. The global PU color paste market reached approximately RMB 2.8 billion in 2025, with PUE-type pastes accounting for over 45% of volume, particularly in automotive seating, footwear, and furniture foam sectors.

2. Technical Features and Mechanism

PUE color paste is defined as a pigment concentrate in which organic or inorganic pigments are dispersed in polyether polyol (typically propylene oxide-based diols or triols with molecular weight 1000–3000) through bead milling to a fineness of ≤15 μm. The coloration mechanism relies on uniform pigment dispersion within the PU matrix: when pigment particle size approaches or falls below visible light wavelengths (400–700 nm), Rayleigh and Mie scattering produce high tinting strength and transparency; particles larger than 15 μm cause gloss loss and settling.

Carrier compatibility is the defining technical feature. Since the polyether polyol carrier shares the same chemical structure as PU soft segments, it participates directly in the NCO curing reaction without interface migration or blooming. Key performance specifications include: fineness ≤15 μm (GB/T 6753.1 grind gauge), pigment loading 15–40%, viscosity 2000–8000 mPa·s at 25°C, fineness stability (no re-agglomeration after 72 h at 50°C), and compatibility with MDI/TDI prepolymers (no flocculation or separation after 24 h). Reference standards: HG/T 4762-2014 (PU color pastes), GB/T 5211.15-2014 (pigment fineness determination). DENSON PUE series pastes are engineered around these specifications with tight batch-to-batch control.

3. Application Case Study 1: Cold-Cure HR Seat Foam

An automotive seat manufacturer integrated DENSON PUE blue paste into their high-resilience cold-cure foam production line. The paste used phthalocyanine blue BGS (C.I. 74160) at 25% pigment loading in a polyether triol carrier (EO-capped, Mw=5000), fineness 10 μm. It was dosed at 0.3–0.8% via a metering pump into the polyol B component, blended with POP polymer polyol, triethylenediamine catalyst, and water, then reacted with MDI at NCO index 102. Mold temperature 60°C, demold time 6 min.

Results: foam density 45 kg/m³, ILD 280N, color uniformity ΔE≤0.8 (GB/T 11186.2). After 22 h compression set at 80°C, no color migration to fabric surface. Compared with solvent-borne paste, VOC emission (VDA 270) dropped from 3.5 mg/m³ to 0.8 mg/m³, and foam resilience remained ≥55%.

4. Application Case Study 2: RIM Self-Skin Instrument Panel

An automotive interior parts producer manufactured TPU/PU self-skin instrument panel skins using DENSON PUE black paste. Pigment was carbon black FW200 (C.I. 77266) at 20% loading in polyether diol carrier (Mw=2000), fineness 8 μm. The paste was added at 1.5% before RIM injection, reacted with NCO prepolymer in a heated mold at 85°C, with 30 min post-cure.

Results: skin thickness 0.8–1.2 mm, Shore A hardness 85, MEK double-rub resistance 50 cycles without breakthrough. QUV 500 h aging showed ΔE≤2.0 (GB/T 1865). No surface blooming or whitening after long-term use, because the PUE carrier participates fully in the skin-core interlayer without exuding.

5. Application Case Study 3: Cast PU Elastomer Roller

A CPU polyurethane roller manufacturer used DENSON PUE red paste for colored printing rollers. Pigment was permanent red F5RK (C.I. 12485) at 30% loading in polycaprolactone diol carrier (Mw=2000), fineness 5 μm. The paste was added to the NCO prepolymer before casting, vacuum-degassed, and poured.

Results: roller Shore A hardness 90, tensile strength 40 MPa, Akron abrasion 0.06 cm³/1.61 km. No color specks under D65 illumination. After 1 million meters of continuous printing, no pigment transfer to paper. The PUE carrier gave a more uniform molecular weight distribution, increasing elongation at break by 8% compared with solvent-borne paste.

6. Key Selection Parameters and Usage Recommendations

| Parameter | Specification | Measurement Standard |

|---|---|---|

| Fineness | ≤5 μm (elastomer); ≤15 μm (foam) | GB/T 6753.1 |

| Pigment content | 15–40% | Gravimetric |

| Viscosity (25°C) | 2000–8000 mPa·s | GB/T 2794 |

| NCO compatibility | No gelation/settling 24 h | Lab test |

| Heat migration | ΔE≤3.0 after 168 h at 80°C | GB/T 1766 |

Usage recommendations: (1) Stir paste for 15 min before use; (2) Use automatic metering pumps for consistent dosing; (3) Conduct compatibility trials with catalysts and blowing agents; (4) Adjust dosage 0.1–0.3 phr to compensate for catalytic interference from pigments like phthalocyanine blue or carbon black. More technical details on DENSON PU color pastes are available at https://www.denson168.com/.

7. Conclusion

PUE polyether polyol carrier color pastes solve the compatibility and migration issues of conventional solvent-borne pastes through a "carrier-as-raw-material" design, becoming the standard coloring solution for cold-cure foam, RIM self-skin, and CPU casting processes. As electric vehicle interiors and biodegradable PU materials grow, low-VOC and bio-based PUE pastes represent the next technology direction. Dongguan DENSON Functional Materials Co., Ltd. provides a full range of PUE color paste solutions from general foam to high-performance elastomers.

8. FAQ

Q1: What is the difference between PUE color paste and solvent-borne color paste?

A1: PUE paste uses polyether polyol as carrier, chemically compatible with PU raw materials and participating in the curing reaction, with zero solvent VOC and no migration. Solvent-borne paste uses organic solvents that can leave residues causing odor, VOC exceedance, and blooming. PUE paste costs slightly more but has largely replaced solvent-borne pastes in automotive and furniture applications.

Q2: What is the typical dosage of PUE color paste?

A2: It depends on pigment type and target shade. Dark colors (black, deep blue) in general foam use 0.3–1.0%; light colors require 1–3% with white paste; transparent elastomers and colorful footwear use 1–3%. Always run small-scale trials to determine the optimal dosage, as excessive addition affects PU curing and mechanical properties.

Q3: Does PUE color paste affect PU cure speed?

A3: Properly formulated PUE paste has minimal impact (gel time change ≤5%). However, some pigments (phthalocyanine blue, carbon black) are weakly acidic or adsorb catalysts and may delay curing. Compatibility testing with the PU system is recommended, adjusting catalyst by 0.1–0.3 phr to compensate.

Q4: How to determine if a PUE paste is compatible with my PU system?

A4: A simple test: add the paste at actual dosage to the polyol component, stir, and observe for 24 h. If no separation, flocculation, or sedimentation occurs, and it foams/cures normally with MDI, it is compatible. More rigorous tests include color stability (ΔE≤1.0 after 72 h at 50°C) and mechanical property comparison (tensile strength change ≤10%).