Pre-Painted Galvanized (PPGI): How Coil Coating Works
The continuous coil-coating process that bonds polyester, PVDF and SMP paint systems onto galvanized steel.
PPGI is produced on a Continuous Coil Coating Line (CCL) that takes finished GI coils and applies a fully cured, factory-baked paint system in one uninterrupted pass — eliminating site painting and delivering a 20–40 year exterior life depending on coating system.
1. Pre-Treatment
The GI strip is cleaned with hot alkaline solution to remove passivation and dust, rinsed, then a conversion coating (chromate-free titanium/zirconium based) is applied and dried. This is what gives the paint long-term adhesion to the zinc layer.
2. Primer Application
Both sides of the strip are coated with a thin (5–7 µm) epoxy or polyester primer using precision roll coaters. The strip then runs through a gas-fired catenary oven at 220–240 °C peak metal temperature to cure the primer.
3. Top Coat Application
A second pair of roll coaters lays down the top coat — typically a 15–25 µm polyester for general roofing, or 25–35 µm PVDF (Kynar 500) for premium architectural facades. The colour is matched to RAL or custom standards under controlled light booths.
4. Top Oven Curing
The painted strip travels through the top oven, where it reaches a peak metal temperature of 230–250 °C, fully crosslinking the polymer film. The strip is then quenched in water, dried, and recoiled.
5. Quality Control
Every coil is tested for dry film thickness, gloss, T-bend flexibility, MEK rub resistance, pencil hardness and salt-spray performance. Saffron Steel ships PPGI with full coating warranties from the supplying mill.
Pre-Painted Galvanized Coils (PPGI)
Pre-painted galvanized coils in a full RAL color spectrum.
