Requirements for Optical Color-Shifting Pigments for Automotive Coatings.

Optical Color-Shifting Pigments for Automotive Coatings is a type of multi-layer sheet-like pigment that undergoes significant color transitions with changes in observation angle / light source angle. The core consists of an alternating stack of high/low refractive index structures (such as TiO₂/SiO₂/TiO₂), and the layer thickness needs to be controlled within a nanometer tolerance to ensure color consistency.

1. Structural type

Media type (DOVP): Full media layer (such as SiO₂ + TiO₂), transparent, suitable for light-colored substrates, with bright colors and good weather resistance.

Metal reflective type: Metal core (Al/Cr/Ag) + media layer, opaque, with higher color saturation.

Particle size: Commonly 10–50 μm; Fine particle size (<15 μm) is delicate, while coarse particle size (25–50 μm) has strong luster.

Thickness: Single sheet approximately 1 μm, suitable for thin coating systems for automobiles.

2. Optical Performance Requirements (Core)

Chromatic Change Effect (Goniochromism)

Multi-angle Color Difference Value: ΔE ≥ 15 (15° → 110°), Significant Two-Color / Multi-Color Transition (such as Green → Purple, Gold → Blue).

Measurement Standards: ASTM E2539 (Interference Type), ASTM E2194 (Metal Type); Measurement Angles: r15as15°, r15as45°, r15as110°.

Color consistency

Batch color difference: ΔE ≤ 2.0; Uniformity of particle size distribution within the same batch: ≥ 99% (ISO 13320).

Luster and clarity

High luster (20° ≥ 90 GU), high vividness (DOI ≥ 85); orientation degree **≥ 95% (ASTM D5767)**, no stripes / frosting.

3. Application and Compatibility Requirements

System Adaptation

General for solvent-based / water-based / powder coatings; for water-based systems, surface modification (such as SiO₂ coating) is required, to prevent hydrogen gas release and flocculation.

Compatible with polyurethane / acrylic / epoxy resins; recommended curing conditions: 120–160℃/20–30 minutes.

Dosage:

Total solids content: 1–5%; 1–2.5% for normal effect, 2.5–5% for high color intensity.

Construction Requirements

Spray viscosity: 18–25 seconds (for 4 cups of coating); Film thickness: Clear coat 30–50 μm + Pigment coat 20–30 μm.

Electrostatic spraying compatibility: Resistance 10⁶–10⁹ Ω·cm, powder deposition rate ≥ 85%.