1. Introduction

PUE (polyether polyol-based) color pastes have enabled a new generation of high-efficiency, low-VOC polyurethane (PU) processing technologies. As automotive, footwear, and furniture manufacturers demand shorter demold times, consistent color quality, and zero solvent emissions, PUE pastes have become an enabling material for process innovation. This article presents three industrial case studies demonstrating how DENSON PUE pastes are deployed in cold-cure high-resilience (HR) seat foam, reaction injection molding (RIM) self-skin components, and microcellular elastomer shoe soles. Each case includes process parameters, measured results, and practical lessons.

2. Technical Features and Mechanism

PUE color paste is a pigment concentrate dispersed in polyether polyol carrier, designed to be metered directly into the PU polyol stream before reaction with isocyanate. The carrier participates in NCO curing, eliminating solvent residues and color migration. Key attributes: pigment loading 15–40%, fineness ≤5 μm for high-gloss applications and ≤15 μm for general foam, viscosity 2000–8000 mPa·s, and heat stability up to 120°C. All three cases below use DENSON PUE series products meeting HG/T 4762-2014 and GB/T 5211.15-2014 requirements.

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

A Tier-1 automotive seat supplier in southern China converted a production line from conventional hot-cure foam to cold-cure HR foam using DENSON PUE blue and black pastes. The line uses a high-pressure metering machine with PUE paste dosed at 0.3–0.8% into the polyol B component (blend of polyether triol and polymer polyol POP). Isocyanate is MDI prepolymer at NCO index 102. Mold temperature 55–60°C, demold time 5–6 min.

Results: foam density 42–48 kg/m³, 25% ILD 220–280 N, sag factor ≥2.4, resilience ≥55%. Color uniformity ΔE≤0.8 across 12 cavities per mold (measured by spectrophotometer D65, 10° observer per GB/T 11186.2). After 22 h compression set at 70°C, compression set ≤6%, no color transfer to PVC cover fabric. Compared with the previous solvent-borne paste, VDA 270 bag VOC dropped from 4.2 mg/m³ to 0.6 mg/m³, meeting OEM cabin air quality requirements.

4. Application Case Study 2: RIM Self-Skin Steering Wheel

An automotive steering wheel manufacturer switched to RIM self-skin technology using DENSON PUE black and two-tone gray pastes. The RIM process uses a heated mold at 80–90°C; the PUE paste (carbon black FW200, 20% loading in polyether diol, fineness 8 μm) is dosed at 1.2–1.8% into the NCO-reactive mixture. Injection pressure 120–150 bar, shot time 0.8–1.2 s, post-cure 30 min at 110°C.

Results: self-skin layer 0.8–1.2 mm, Shore A 85–90, gel content ≥95%, MEK double-rub resistance 60 cycles. Skin gloss 8–12 GU at 60° (soft-touch finish). QUV 1000 h accelerated aging (GB/T 16422.3) showed ΔE≤1.5, no cracking or chalking. The PUE carrier eliminated the skin blooming previously observed with solvent-borne pastes after 6 months of cabin use.

5. Application Case Study 3: Microcellular PU Shoe Sole

A midsole producer adopted the one-shot microcellular PU process using DENSON PUE red, navy, and white pastes. The pastes are based on polyester polyol carrier (for shoe soles, PUE polyester variant), fineness 5 μm, pigment loading 20–30%. They are dosed into the polyol stream at 1.5–3.0% depending on color, reacted with TDI-based prepolymer, and injected into aluminum molds at 45°C.

Results: sole density 0.35 g/cm³, Shore C 55, DIN abrasion ≤80 mm³, rebound resilience 45%. Color difference between left and right shoe ≤ΔE 0.5. Flexing resistance: 100,000 cycles per GB/T 3903.2 without cracking or color loss. No blooming after 168 h at 70°C. Compared with dry color masterbatch, the PUE paste reduced speck defects by 90% and cut color changeover time from 45 min to 15 min.

6. Key Selection Parameters and Usage Recommendations

| Parameter | HR Foam | RIM Self-Skin | Microcellular Sole |

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

| Recommended paste type | PUE-polyether | PUE-polyether | PUE-polyester |

| Fineness | ≤15 μm | ≤8 μm | ≤5 μm |

| Typical dosage | 0.3–1.0% | 1.0–2.0% | 1.5–3.0% |

| Carrier polyol MW | 3000–5000 | 1000–2000 | 2000 |

| Viscosity (25°C) | 3000–6000 mPa·s | 4000–8000 mPa·s | 2000–5000 mPa·s |

Recommendations: (1) Always pre-blend paste with polyol for 15–20 min before metering; (2) Use positive-displacement metering pumps, not gear pumps, to avoid pigment shear degradation; (3) Verify catalyst compatibility—phthalocyanine and carbon black pastes may require +0.1 phr catalyst; (4) For multi-color production, flush lines with clean polyol for 5 min between colors. See DENSON's PU color product range at https://www.denson168.com/ for matching specific systems.

7. Conclusion

The three case studies demonstrate that PUE polyol carrier color pastes enable reliable coloration across cold-cure HR foam, RIM self-skin, and microcellular PU sole processes, with consistent color, low VOC, and no blooming. The choice of polyether vs polyester carrier and fineness specification is critical to matching the target process. Dongguan DENSON Functional Materials Co., Ltd. supplies tailored PUE pastes for each PU process route, supported by on-site application engineering.

8. FAQ

Q1: Can PUE color pastes be used for both polyether and polyester PU systems?

A1: Yes, but the carrier must match the system. PUE-polyether pastes are designed for polyether-based PU (foam, RIM), while PUE-polyester pastes are formulated for polyester-based PU (shoe soles, elastomers). Using a mismatched carrier risks poor compatibility and blooming. DENSON offers both series.

Q2: What causes color specks in PU foam after adding PUE paste?

A2: Specks usually result from insufficient dispersion, pigment re-agglomeration, or metering contamination. Check: paste fineness ≤15 μm, pre-blend time ≥15 min, and clean metering lines. If specks persist, request a higher-fineness grade (≤10 μm) and verify no dried paste residue in the pump.

Q3: How does PUE paste dosage affect PU foam physical properties?

A3: At normal dosage (0.3–1.0%), impact on density, resilience, and compression set is ≤5%. Excessive dosage (>2%) can disrupt cell structure, increase density, and reduce resilience. Always run dose-response trials; keep dark colors below 1.5% and use white paste as a base for light colors.

Q4: How should PUE pastes be stored?

A4: Store sealed at 5–35°C, away from direct sunlight. Shelf life is 12 months from manufacture. Before use, stir or roll drums for 15–20 min. Do not freeze; if freezing occurs, warm to 25°C and re-mix until uniform. Keep containers closed to prevent moisture pickup, which reacts with isocyanate and causes foam defects.