1. Introduction

Resin-free pigment dispersion has emerged as a critical colorant technology in modern industrial coatings, addressing the compatibility limitations of traditional resin-based color pastes. Unlike conventional color pastes that rely on film-forming resin carriers to stabilize pigment particles, resin-free dispersions employ hyperdispersants — molecules with anchoring groups and solvated chains — to maintain pigment stability without introducing additional resin components. This fundamental design difference enables resin-free color pastes to achieve broad compatibility across multiple binder systems while maintaining high pigment loading and low viscosity.

Dongguan DENSON Functional Materials Co., Ltd. (DENSON) has developed the RFNC series of resin-free pigment dispersions, specifically engineered for multi-sector surface coating applications including electric vehicles, motorcycles, automotive interior and exterior components, small home appliances, and 3C electronics. This article examines the technical principles, application cases, and key selection parameters of RFNC resin-free color pastes, providing engineering guidance for coating manufacturers and end users. For more technical resources, visit the DENSON literature section.

Figure 1. RFNC series resin-free pigment dispersions, full color spectrum, factory background.

2. Technical Features and Mechanism

A resin-free pigment dispersion is a high-concentration pigment dispersion that contains no film-forming resin carrier, relying solely on hyperdispersant anchoring groups and solvated chain segments for colloidal stability. The RFNC series exhibits five core technical characteristics:

1. Resin-free carrier design: High pigment content (50-75%), low system viscosity, low addition levels (3-10%), and minimal interference with binder curing reactions.

2. Broad compatibility: Excellent compatibility with CAB (cellulose acetate butyrate), vacuum metallizing resins, hydroxyl acrylic resins, polyester-modified hydroxyl acrylics, thermoplastic acrylics, thermosetting resins, and epoxy resins — seven or more major binder classes.

3. Wide application coverage: Suitable for electric vehicle body panels, battery enclosures, charging port covers, motorcycle fuel tanks and fairings, automotive interior/exterior trim, small appliance housings, and 3C electronic enclosures.

4. Performance advantages: High tinting strength, high transparency, migration resistance, excellent solvent resistance, and no negative impact on coating adhesion, hardness, flexibility, or impact resistance across solvent-borne 2K PU, one-pack acrylic, thermosetting acrylic, epoxy, and UV-curable systems.

5. High color-matching efficiency: The absence of resin carriers means no carrier conflict when mixing different color pastes, enabling complex multi-color formulations and rapid color adjustment.

The dispersion mechanism is based on combined steric stabilization and electrostatic stabilization. Hyperdispersant anchoring groups — including polyamines, polyacids, and aromatic-containing structures — adsorb onto pigment surfaces through ionic bonds, hydrogen bonding, van der Waals forces, and π-π stacking. The solvated chain segments (polyester, polyether, or polyacrylate) extend into the dispersion medium, providing steric hindrance that prevents particle agglomeration. Research published in the Journal of Applied Polymer Science (2025, DOI: 10.1002/app.56144) demonstrated that PEGylated partially hydrolyzed poly(N-vinyl amide) dispersants achieve optimal carbon black dispersion stability at 60-75% anchoring group coverage, with zeta potential absolute values exceeding 30 mV.

3. Application Case 1: Electric Vehicle Plastic Component Coatings

Substrate and coating system: PP/EPDM-T20 plastic bumpers and fenders, two-component polyurethane (2K PU) coatings with hydroxyl acrylic resin binder and HDI trimer curing agent.

Application process: After pretreatment (degreasing → plasma treatment → PP primer), the color coat is applied via rotary bell electrostatic spraying at 15-20 μm film thickness, followed by 5 minutes flash-off and 30 minutes baking at 80°C, then clear coat application.

Key results with RFNC:

• RFNC black (carbon black) and dark gray pastes added at 4-8% by binder weight

• Excellent compatibility with hydroxyl acrylic resin, fineness ≤10 μm, no flocculation or coarsening

• No NCO consumption due to resin-free formulation; coating crosslink density remains normal, adhesion grade 0 (GB/T 9286-1998)

• Low viscosity characteristics improve atomization uniformity in rotary bell spraying, DOI (distinctness of image) values exceeding 80

• Batch color difference ΔE reduced from 0.8 to 0.4, rework rate decreased from 3.2% to 1.1%, color paste consumption reduced by 18%

Figure 2. Automated robotic spray application of automotive components, RFNC pastes demonstrate stable performance in automated coating lines.

4. Application Case 2: 3C Electronic UV-Curable Coatings

Substrate and coating system: Aluminum alloy laptop housings (anodized or bead-blasted), UV-curable coatings based on urethane acrylate oligomers with TPGDA/HDDA reactive diluents and photoinitiators 184/1173.

Application process: Degreasing → passivation → UV primer (10-15 μm) → partial cure (300 mJ/cm²) → UV color coat (15-20 μm) → full cure (600-800 mJ/cm²) → UV clear coat (10-15 μm) → full cure.

Key results with RFNC:

• RFNC blue (phthalocyanine blue 15:3) paste at 4-6% addition

• Excellent compatibility with UV monomers and oligomers, no flocculation or precipitation, fineness ≤5 μm

• No interference with UV curing rate; pencil hardness H-2H achieved

• Coating gloss (60°) ≥95%, DOI ≥88, no particles or orange peel

• Artificial sweat resistance: 48 hours exposure with no discoloration or delamination

• Color paste cost reduced by approximately 25% compared to imported alternatives

5. Application Case 3: Motorcycle Fuel Tank and Plastic Part Coatings

Substrate and coating system: Phosphated cold-rolled steel fuel tanks with 2K PU coatings; ABS side fairings and PP front fenders with 2K PU coatings.

Application process: Steel tanks: phosphating → e-coat primer → surfacer → 2K PU color coat (20-25 μm) → 140°C bake 20 min. Plastic parts: plasma treatment → PP primer → 2K PU color coat → 80°C bake 30 min.

Key results with RFNC:

• Motorcycle fuel tanks require gasoline resistance; RFNC pigments achieve solvent resistance grade ≥4, with no color bleeding or softening after 72 hours immersion in 93# gasoline

• RFNC high-transparency organic pigments (quinacridone red, phthalocyanine blue) deliver vivid colors without disrupting aluminum flake orientation in metallic finishes

• Same RFNC paste usable across both steel tank 2K PU and plastic part 2K PU systems, reducing color paste inventory SKUs

Figure 3. Automated robotic spray application of plastic housings, RFNC pastes provide uniform atomization and stable color in automated coating lines.

6. Key Selection Parameters and Usage Recommendations

Usage recommendations: (1) Mix at low speed (≤3 m/s peripheral speed) for 3-5 minutes before use; high-speed dispersion (>5 m/s) may cause hyperdispersant desorption. (2) Pre-mix color paste with a small portion of binder before adding to the main paint for faster dispersion. (3) Multi-color mixing requires no carrier compatibility concerns — pastes can be directly blended by ratio. (4) Store at 5-35°C, protected from freezing and prolonged high-temperature exposure. (5) For 3C electronic and high-appearance coatings, filter through 100-200 mesh before use. For more product information, visit DENSON official website.

7. Conclusion

The DENSON RFNC series of resin-free pigment dispersions, based on hyperdispersant anchoring and solvated chain stabilization, delivers high pigment loading, low viscosity, broad binder compatibility, and zero curing interference across electric vehicle, motorcycle, automotive, small appliance, and 3C electronic surface coating systems, representing a technically superior and cost-effective alternative to traditional resin-based color pastes.

8. FAQ

Q1: What is the fundamental difference between resin-free and traditional color pastes?
A: Resin-free color pastes contain no film-forming resin carrier, relying solely on hyperdispersants for pigment stabilization. This eliminates carrier conflict and enables compatibility with virtually any binder system, whereas traditional pastes are limited to binder systems compatible with their carrier resin.

Q2: Will RFNC pastes affect the curing of two-component polyurethane coatings?
A: No. RFNC pastes contain no reactive hydroxyl groups or other curable functional groups. The hyperdispersant chains are inert and do not consume NCO curing agent, so coating crosslink density and mechanical properties remain unaffected.

Q3: Can different RFNC colors be directly mixed for color matching?
A: Yes. Since all RFNC pastes share the same resin-free dispersion medium, there is no carrier conflict when mixing different colors. This makes RFNC particularly suitable for complex multi-color formulations and rapid color adjustment.

Q4: What is the shelf life and proper storage condition for RFNC pastes?
A: The shelf life is 12 months in original sealed packaging. Store at 5-35°C in a dry, ventilated area away from direct sunlight, heat sources, and open flame. Freezing temperatures below 0°C may cause hyperdispersant chain contraction and pigment agglomeration.

Q5: Are RFNC pastes suitable for UV-curable coating systems?
A: Yes. RFNC pastes are compatible with UV monomers (TPGDA, HDDA, TMPTA) and oligomers (urethane acrylate, epoxy acrylate). They do not absorb UV energy or interfere with photoinitiator activity. For dark colors (black, deep blue), keep addition levels below 8% and increase cure energy by 20-30% to ensure through-cure.