Electrostatic spray, Faraday-cage corners, oven cure cycles. The finish that runs every fabrication shop, and why edge coverage is where most jobs fail.
The powder charges positive, the part grounds. Powder wraps edges and recesses a wet gun can't see directly. That's why panel backs come out coated.
In tight internal corners the electric field cancels. Powder bounces off. Shops manual-spray those zones first, then the rest in the booth on auto.
The polymer cross-links during the cure. Cut time or temperature and the coating stays soft, chips, and yellows in the sun. Datalog the oven on every batch.
Pull powder thicker than 100 µm and it cracks at corners as it cures. Two thinner coats beat one heavy. Edge film thickness is the real failure mode.
Common resin systems and where each one belongs in the spec.
| Resin | Thickness · UV life | Typical use |
|---|---|---|
| Epoxy | 60-80 μm · 1-2 yr UV | Indoor only, chemical resistance |
| Polyester (TGIC / HAA) | 60-80 μm · 10+ yr UV | Outdoor standard |
| Epoxy-polyester hybrid | 60-80 μm · 3-5 yr UV | Indoor + light outdoor |
| Super-durable polyester | 60-80 μm · 20+ yr UV | Coastal, façades |
| Fluoropolymer (FEVE) | 60-80 μm · 30+ yr UV | Critical façades, signage |
| Texture / structure | 80-120 μm | Anti-glare, anti-scratch |
| Zinc-rich primer + topcoat | 40 + 70 μm | Corrosion class C5 |
Powder is not paint. Different chemistry, different rules.
Get this one decision wrong and your façade chalks white in 18 months. Epoxy is harder and more chemical-resistant, but UV destroys it. Polyester (TGIC or TGIC-free) holds gloss 10+ years outdoors.
Metal temperature must hit 180-200°C for 10-15 minutes. Under-cured powder is soft, scratches on a fingernail, and pulls off in flakes. Most field failures are under-cure, not surface prep.
Sharp internal angles repel the electrostatic charge. The powder hits the flat panel and refuses to coat the corner. Tribo guns or pre-heated parts help; the only sure fix is a second pass with the gun aimed into the corner.
Below 50 μm you see substrate. Above 120 μm you get orange-peel texture and cure problems. Spec 60-80 μm DFT and verify with a coating gauge at QC.
Reds, yellows and dark blues fade fastest. Whites, light greys and metallic silvers hold longest. For 20-year exterior fade resistance, demand a super-durable polyester with QUV-A 1000-hour data on the spec sheet.
Polyester, super-durable, hybrid and texture powders sprayed in a controlled-humidity booth, cured to spec metal temperature with conveyor profiling on every batch.
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