What PPGL Coil Is
PPGL is the trade abbreviation for prepainted 55 % aluminium-zinc coated steel coil. The strip is first coated on a continuous hot-dip line with an aluminium-zinc alloy and is then painted, on the same line or a second line, with a primer and a top coat. The metallic coating supplies corrosion protection and the paint supplies colour, gloss and weatherability, so the finished coil can go straight to a roll forming line for roofing and wall cladding.
Because both layers are applied to a moving strip, PPGL offers a uniform coating mass and a consistent colour over the whole coil, which is difficult to match with post-painted sheet. The common substrates are DX51D+AZ in the European system and Q195 or the SGLCC family in the Japanese system, and polyester is the standard paint system for general building products.
Coating Metallurgy of 55 % Al-Zn Sheet
The hot-dip coating is an alloy of approximately 55 % aluminium, 43.4 % zinc and 1.6 % silicon. The aluminium-rich phase provides barrier protection and good resistance to oxidation at high temperature, while the zinc-rich phase gives sacrificial protection at cut edges and scratches. The silicon addition controls the growth of a brittle intermetallic layer at the steel-coating interface, and that is what keeps the coating adherent during roll forming and bending.
For the same coating mass, an aluminium-zinc coating resists atmospheric corrosion considerably better than a plain zinc coating in most rural and urban environments, and its light metallic surface also reflects heat. It is not a universal substitute for zinc, because the aluminium-rich phase can be attacked in strongly alkaline or acidic contact conditions, so the service environment still decides the coating mass.
Substrate Grades and Applicable Standards
| Item | Specification |
|---|---|
| Substrate grades | DX51D, DX52D, DX53D, S220GD, S250GD, S280GD, S350GD and S550GD with the +AZ coating designation |
| Japanese grades | SGLCC, SGLCD, SGLC400, SGLC440, SGLC490 |
| Coated steel standard | EN 10346, which replaced EN 10142 and EN 10147; JIS G3321; ASTM A792/A792M |
| Prepainted steel standard | EN 10169; JIS G3322; ASTM A755/A755M |
| Superseded German standard | DIN 17162, withdrawn in favour of the EN 10346 series |
Dimensions, Coating Mass and Paint Build
| Parameter | Range or value |
|---|---|
| Thickness | 0.12-1.5 mm for coil, heavier sheet and plate up to about 6.0 mm by agreement |
| Width | 600-1500 mm, or cut to the required width |
| Coil weight and bore | 3-20 t per coil, coil inner diameter normally 508 mm or 610 mm |
| Coating mass | AZ30 to AZ150, quoted as the total mass on both surfaces, with AZ150 the usual roofing specification |
| Coating thickness | AZ150 corresponds to roughly 20 micrometres per side |
| Paint build | top coat 15-35 micrometres, back coat 5-10 micrometres |
| Paint systems | polyester, high durability polyester, silicone modified polyester, PVDF |
| Surface treatment | passivation, oiling, lacquer sealing, phosphating, untreated |
| Surface structure | normal spangle, minimised spangle, spangle free |
Service Life, Fabrication and Site Handling
A polyester coating on an AZ150 substrate is the economic standard for roofs and walls and gives around a decade of service in moderate environments. High durability polyester, silicone modified polyester and PVDF systems extend the service life well beyond that in the same climate at a higher cost. Coating life depends on the environment as much as on the coating itself, so coastal, industrial and heavily polluted sites justify both a heavier coating mass and a more durable paint system.
PPGL is designed for roll forming, bending and profiling, and the coating is flexible enough for normal roofing profiles when the grade and paint build are matched to the profile depth. Cut edges are the weak point of any coated steel: the zinc-rich phase protects them galvanically over a limited distance, so edge treatment and a compatible fastener system still matter. Colour consistency is controlled through the paint batch, and coils should be stored indoors on dry dunnage so that condensation staining and interleaving corrosion cannot start.
FAQ
Q: What does PPGL stand for?
PPGL stands for prepainted aluminium-zinc coated steel coil. It combines a 55 % aluminium-zinc hot-dip coating with a paint system, typically a primer plus a polyester top coat.
Q: What is the composition of the coating?
The coating is approximately 55 % aluminium, 43.4 % zinc and 1.6 % silicon. The zinc phase gives sacrificial edge protection and the silicon controls the intermetallic layer for coating adhesion.
Q: Which standards apply to PPGL?
The coated substrate is covered by EN 10346, JIS G3321 or ASTM A792/A792M, and the paint system by EN 10169, JIS G3322 or ASTM A755/A755M. EN 10142, EN 10147 and DIN 17162 are older and have been replaced.
Q: What does AZ150 mean?
AZ150 is the total coating mass of 150 g/m2 on both surfaces, which is about 20 micrometres per side. It is the most common specification for roofing and cladding in moderate environments.
Q: How long does the paint last?
A standard polyester system gives roughly ten years in a moderate climate. High durability polyester, silicone modified polyester and PVDF systems last considerably longer, especially when a heavier coating mass such as AZ150 is used.
Q: Can PPGL be welded or must it be mechanically joined?
It is normally joined with self-drilling fasteners, rivets or clips. Welding requires the coating to be stripped locally, which destroys the corrosion protection at the joint, so the joint has to be re-protected afterwards.
