Summary: 'Flop' (angle-dependent brightness) in metallic basecoats comes from flake orientation: more particles parallel to the surface means brighter face-on, darker at angle. Orientation is set by evaporation rate, viscosity and spray parameters.
Mechanism
As solvent leaves, flakes rotate and align; too long a flash or too-high viscosity locks them disordered, darkening the face and shifting hue.
Key data
- Air pressure, fan width, gun distance/speed jointly set flow-out and orientation.
- Fast/slow diluents change the evaporation curve, directly affecting lightness and hue.
- Base is typically 2-3 wet-on-wet coats to build orientation and coverage.
Parameter effect
| Variable | Trend |
|---|---|
| High pressure / far | Lighter, risks dry spray |
| Low pressure / near | Darker, better flow |
Defects & fixes
- Dark face: poor orientation — lower pressure or slow diluent.
- Clouding/mottling: uneven passes or long flash — standardise technique.
- Light at angle: over-flattening — adjust viscosity/distance.
FAQ
What is flop?
Same surface looks different brightness head-on vs at angle, from metallic/pearl flake orientation.
Why are metallic repairs hard to match?
The original panel's orientation conditions are hard to reproduce; lightness/hue drift with spray parameters.
How to make it lighter?
Improve parallel orientation: right pressure/reduction, control flash, light mist to open.
Ref: effect-pigment orientation and basecoat spray practice (public).
Kexin New Materials (Guangdong) Co., Ltd. · 2026-09-18