1. Introduction

Automotive coatings represent one of the most technically demanding segments of the industrial coatings industry, with OEM (Original Equipment Manufacturer) and refinish coatings requiring exceptional dispersion stability, weatherability, and compatibility across complex binder systems. Automotive interior and exterior coatings typically employ hydroxyl-functional acrylic resins, polyester-modified hydroxyl acrylics, CAB (Cellulose Acetate Butyrate), and vacuum metallizing silver resins as primary binders. The colorant used in these systems must maintain dispersion stability without interfering with the NCO/OH curing reaction or compromising film mechanical properties.

DENSON's NA Series solvent-borne nano pigment pastes are specifically engineered for automotive interior and exterior coatings. Featuring nano-scale dispersion (D50 < 100nm for colors, < 80nm for black), high-performance weather-resistant pigments, and a dispersant system optimized for CAB and hydroxyl acrylic compatibility, the NA Series delivers consistent color quality and film performance across a wide range of automotive coating applications. This article provides a technical overview of the NA Series, covering dispersion mechanism, application cases, and selection parameters based on established engineering standards and peer-reviewed research.

For additional technical resources, visit the DENSON Literature Center.

Figure 1: Automotive paint shop with bell-type electrostatic spraying robots. The NA Series is optimized for high-shear bell spraying processes.

2. Technical Features and Mechanism

Nano pigment paste is defined as a high-concentration pigment dispersion in which primary pigment particles are controlled below 100nm and stabilized by a hyperdispersant anchor-solvation协同 mechanism in a solvent-borne carrier system. The NA Series offers five key technical advantages:

(1) No negative impact on film properties. When added at typical dosage levels (3-8% by binder weight), the NA Series does not adversely affect adhesion, hardness, flexibility, impact resistance, or gloss. This is achieved through a carrier resin designed for compatibility with automotive binders and a dosage level that does not significantly alter the system's crosslink density.

(2) Excellent compatibility with CAB and metallizing silver resins. In automotive coating systems containing CAB (Cellulose Acetate Butyrate) and vacuum metallizing silver/leafing aluminum resins, the NA Series maintains dispersion stability without flocculation or coarsening, and does not interfere with aluminum pigment orientation or mirror effect. CAB, with its unique butyryl/acetyl substitution pattern, has a solubility parameter (SP value) of approximately 19-20 (MPa)^0.5, which often causes compatibility issues with conventional pigment paste carriers. The NA Series addresses this by tuning the dispersant solvation chain polarity and SP value to approximately 18.5-19.5, achieving excellent matching with CAB systems.

(3) Superior weatherability with minimal color shift. Using high-performance weather-resistant pigments (quinacridones, DPP reds, phthalocyanine blue/green, high-color carbon black, etc.) combined with nano-scale dispersion, the NA Series achieves low color change (ΔE) under QUV/xenon arc aging and natural exposure, without gloss loss or chalking. QUV 1000h aging results show ΔE < 2.5 for colors and < 2.0 for black.

(4) Excellent solvent resistance with no bleed or migration. The pigments used in the NA Series have solvent resistance ratings of grade 4 or higher (GB/T 5211.9), ensuring no color bleed, migration, or contamination of adjacent coatings in multi-layer systems, recoating, tape adhesion tests, or high-temperature service conditions.

(5) Exceptional compatibility with hydroxyl acrylic and polyester-modified hydroxyl acrylic resins. In automotive coating systems based on hydroxyl acrylic resins and polyester-modified hydroxyl acrylic resins, the NA Series maintains dispersion stability without flocculation, does not interfere with the NCO/OH curing reaction, and does not compromise film crosslink density or mechanical properties.

2.1 Hyperdispersant Anchor-Solvation Stabilization Mechanism

The dispersion stability of nano pigments in solvent-borne media follows the combined principles of DLVO theory and steric stabilization. Hyperdispersant molecules consist of two functional segments: anchor groups that firmly adsorb onto the pigment surface through ionic bonds, hydrogen bonds, van der Waals forces, or π-π stacking, and solvated chains that extend into the dispersion medium to form a 5-20nm thick solvation layer. When two pigment particles approach each other, overlap of the solvation layers generates entropic and osmotic repulsive forces that prevent agglomeration.

Research published in the Journal of Applied Polymer Science (2025, DOI: 10.1002/app.56144) on PEGylated partially hydrolyzed poly(N-vinyl amide) as a carbon black dispersant confirmed that anchor group coverage of 60-75% of the pigment specific surface area yields maximum zeta potential absolute value (> 30mV) and minimum sedimentation rate. The NA Series dispersant design is based on this principle, selecting anchor groups matched to the surface characteristics (acidic/basic/neutral) of different pigments.

2.2 Effect of Nano Dispersion on Weatherability

Pigment particle size is a critical factor influencing coating weatherability. When pigment particle size is reduced from micron-scale (1-5μm) to nano-scale (< 100nm), the specific surface area increases from approximately 10-20 m²/g to 50-100 m²/g. This has two effects: first, nano-pigments significantly improve UV scattering and absorption efficiency, providing more effective shielding of the resin matrix from UV degradation; second, nano-particles have high surface energy, and if dispersion is unstable, they readily agglomerate into larger particles, which can actually accelerate film chalking.

ACS Applied Polymer Materials (2026, 8(6), 4573-4586, DOI: 10.1021/acsapm.6c00349) reported a soft-core/hard-shell gradient copolymer encapsulation strategy for pigments, which improves dispersion stability while forming a "UV buffer layer" on the pigment surface, reducing QUV 1000h color change ΔE from 3.2 to 1.5. The NA Series employs a similar nano dispersion process, using bead mills to control pigment D50 below 100nm (black below 80nm), combined with high-performance weather-resistant pigments to achieve QUV 1000h ΔE < 2.5.

Figure 2: NA Series blue nano pigment paste with D50 < 100nm, offering high tinting strength and transparency.

3. Application Case 1: 2K PU Automotive Topcoat for Bumpers

An automotive parts supplier producing bumper topcoats for a joint-venture SUV used a two-component polyurethane system based on hydroxyl acrylic resin (OH value ~80 mgKOH/g) and HDI trimer curing agent (NCO content ~23%). The original imported colorant caused flocculation-related particle defects during bell electrostatic spraying.

After switching to DENSON NA Series pigment paste, the formulation was as follows:

Application parameters: bell electrostatic spraying, 60kV output voltage, 200mL/min flow rate, curing at 80°C for 30min. Film properties: 60° gloss 92%, crosshatch adhesion grade 0 (GB/T 9286), pencil hardness 2H, impact resistance 50 kg·cm (GB/T 1732), QUV 1000h ΔE = 1.8.

4. Application Case 2: CAB-Based Automotive Metallic Topcoat

An automotive coatings manufacturer producing metallic topcoats for passenger car bodies used a blend of CAB (butyryl content 37%) and hydroxyl acrylic resin, with non-leafing aluminum paste (particle size 15μm) as the metallic pigment. The original colorant showed flocculation and coarsening in the CAB system, resulting in poor aluminum orientation and mottling.

The NA Series solution involved: reducing CAB dosage from 8% to 5% (minimizing competition with the paste carrier), controlling colorant dosage at 4-6%, and ensuring the dispersant solvation chain SP value matched CAB. After application, the metallic effect was uniform with well-oriented aluminum flakes, mirror reflectance improved by approximately 15%, and no mottling was observed.

Figure 3: Automotive bell electrostatic spraying booth. The NA Series is compatible with high-shear bell spraying processes.

5. Application Case 3: Automotive Interior Plastic Parts Coating

Automotive interior plastic parts (instrument panels, door panels, center consoles) are typically made of PP/ABS or PC/ABS substrates, with coating systems based on thermoplastic acrylic or modified polyurethane. Key requirements for colorants in these systems include: migration resistance, no bleed, good adhesion to plastic substrates, and low VOC.

The NA Series at 3-5% dosage in these systems achieves: migration resistance grade 5 (no bleed at 80°C for 72h against white PVC, per internal test method), crosshatch adhesion grade 0, and VOC content ≤ 450g/L, complying with GB/T 38597-2025 low-VOC requirements.

6. Key Selection Parameters and Usage Recommendations

Usage recommendations: (1) Stir gently at low speed (300rpm for 3min) before use to avoid high-shear dispersant desorption; (2) When mixing with CAB systems, pre-blend the colorant with CAB solution before adding to the base binder; (3) For color matching, add colorant gradually from low concentration to avoid over-dosage flocculation; (4) Store at 5-35°C, avoid high temperatures that may cause pigment agglomeration; (5) Shelf life is 12 months unopened; use within 3 months after opening.

7. Conclusion

DENSON NA Series solvent-borne nano pigment pastes, through hyperdispersant anchor-solvation协同 stabilization, nano-scale dispersion (D50 < 100nm), and carrier design matched to CAB and hydroxyl acrylic systems, deliver exceptional dispersion stability, weatherability (QUV 1000h ΔE < 2.5), and compatibility in automotive interior and exterior coatings, without compromising film mechanical properties. The NA Series is a reliable coloring solution for automotive coatings. For product details, visit Dongguan DENSON Functional Materials Co., Ltd..

8. FAQ

Q1: How is the nano particle size of NA Series pigment pastes controlled?

A: The NA Series uses horizontal bead mills with 0.3-0.5mm zirconium oxide beads through multiple grinding passes to control pigment D50 below 100nm (black below 80nm). Particle size is monitored online by laser diffraction to ensure batch-to-batch consistency.

Q2: Why does the NA Series not flocculate in CAB systems?

A: The key is that the dispersant solvation chain solubility parameter (SP value ~18.5-19.5) is close to that of CAB (SP value ~19-20), and the carrier resin is a low-molecular-weight hydroxyl acrylic with good miscibility with CAB, avoiding flocculation caused by solubility parameter mismatch.

Q3: Does the NA Series affect the curing reaction of two-component polyurethane?

A: No. The NA Series does not contain organic amines, organotins, or other substances that catalyze or inhibit the NCO/OH reaction. The hydroxyl content of the carrier resin is designed so that it does not significantly alter the system's NCO/OH ratio, with gel time variation ≤ 5%.

Q4: How is the weatherability of the NA Series measured?

A: Weatherability testing follows GB/T 1865 "Color and varnish - Artificial weathering and exposure to artificial radiation (filtered xenon arc radiation)", using a QUV aging chamber (UVA-340 lamps, irradiance 0.89W/m² at 340nm), with a cycle of 60°C light for 4h + 50°C condensation for 4h. After 1000h, ΔE is measured with a spectrophotometer.

Q5: Can the NA Series be used in waterborne automotive coatings?

A: The NA Series is a solvent-borne nano pigment paste primarily designed for solvent-borne automotive coating systems. DENSON also offers the GT Series waterborne pigment pastes for waterborne automotive coatings. Direct addition of solvent-borne paste to waterborne systems may cause emulsion breaking and flocculation, so the GT Series is recommended for waterborne applications.