What Is PPGI Sheet in Coil?

What Is PPGI?

PPGI stands for pre-painted galvanized iron, also called pre-painted galvanized steel sheet in coil or colour coated steel coil. It is a hot-dip galvanized steel coil that is cleaned, chemically treated and coated on a continuous paint line with a primer and a top coat, then baked and cooled. The result is a finished building and appliance material that the end user can cut, roll-form, punch and assemble directly, without any painting or surface treatment in the workshop.

How PPGI Is Produced

The substrate is a hot-dip galvanized coil with a zinc coating mass typically between 40 and 275 g/m2. On the coil coating line the strip passes through an alkaline cleaning bath and a chemical conversion treatment, then a primer is roller-applied to both sides at about 5–10 µm, followed by a top coat of 10–25 µm on the visible side and a protective back coat. Each coat is cured in a baking oven, and the finished strip is cooled, inspected and recoiled. Because the line runs continuously, the coating thickness is uniform and the colour consistency is far better than field painting.

Key Benefits

Corrosion protection: the zinc layer gives cathodic protection at cut edges, while the organic coating protects the zinc from wear and weathering

Longer service life: properly selected PPGI lasts about 1.5 times longer than bare galvanized strip in the same environment

Factory finish: uniform colour, gloss and film thickness without on-site painting

Formability: the coating system is formulated to survive bending, roll-forming and light stamping

Economy: one processing step replaces several field operations, reducing labour and rework

Standards and Grades

Three standard families dominate the international market:

JIS G 3312: Japanese standard with grades CGCC (general) and CGCH (structural/hard)

EN 10169: European standard covering DX51D and DX52D substrates with specified coating systems

ASTM A755: US standard for pre-painted steel sheet for building applications

Substrate grades follow the corresponding hot-dip standards: DX51D+Z or DX52D+Z per EN 10346, with yield strengths from about 140 MPa up to structural grades around 550 MPa.

Typical Specification Range

Parameter	Typical Range
Thickness	0.12-2.00 mm
Width	600-1250 mm
Zinc coating	40-275 g/m2
Primer (top/back)	5–10 µm
Top coat (top/back)	10–25 µm
Surface finish	smooth, wrinkle, matt, printed, PVC laminated
Coil inner diameter	508 mm or 610 mm
Coil weight	3-5 t per coil, or customised

Colours can be matched to any RAL code or to a customer-supplied sample, with gloss levels specified separately for roof and wall applications.

Coating Types and Selection

The resin family of the top coat determines the durability: polyester (PE) is economical and fine for indoor and general outdoor use; silicone-modified polyester (SMP) improves weather resistance; high-durability polyester (HDP) and polyvinylidene fluoride (PVDF) systems are chosen for coastal, industrial and architectural applications where 15-25 years of colour retention is required. Match the coating type to the environment: a cheap PE film in a salt-laden coastal atmosphere will chalk and crack far earlier than a PVDF system, even though both pass the same initial tests.

Applications

Roofing sheets and wall cladding of industrial and commercial buildings

Roll-formed purlins, gutters and flashing profiles

Home appliance casings, control cabinets and doors

Furniture components and shelving

Transportation parts such as truck bodies and containers

Quality Notes

Inspect PPGI on receipt for film adhesion, colour uniformity and edge damage. Common acceptance tests include the T-bend test for adhesion, pencil hardness, impact resistance, MEK rub for cure, and salt-spray exposure for corrosion performance, usually referenced against the requirements of EN 10169 or ASTM A755. Coils should be stored indoors on stands, protected from condensation, and handled with fabric slings to avoid edge crushing.

Frequently Asked Questions

Q: What is PPGI sheet in coil?
It is a hot-dip galvanized steel coil that has been cleaned, chemically treated and coated on a continuous paint line with a primer and a topcoat, then baked, cooled and recoiled for direct use in roll-forming, punching and assembly.

Q: What is the difference between PPGI and ordinary galvanized coil?
PPGI adds an organic paint system on top of the zinc layer. The zinc protects the steel cathodically at cut edges while the paint protects the zinc and supplies colour and gloss, roughly doubling the decorative life versus bare galvanizing.

Q: Can PPGI be cut, drilled or roll-formed without damaging the coating?
Yes, provided the tooling is sharp and the coating system is formulated for forming. Cut edges lose the paint but keep the zinc, so cathodic protection continues along the exposed edge.

Q: What does a coating mass of 80 g/m2 mean?
It is the total zinc weight on both surfaces of the sheet, about 80 g/m2, which corresponds to roughly 11 um per side. Heavier coatings of 180-275 g/m2 are ordered for aggressive or coastal environments.

Q: Why does the same RAL colour look different between suppliers?
RAL fixes the colour target, but gloss level, film thickness and substrate surface texture all shift the perceived shade. Comparing panels from the same coil and specifying gloss separately avoids most disputes.

Q: Is PPGI sheet in coil suitable for coastal roofing?
Yes, when the correct system is selected: a higher zinc coating weight plus a PVDF or HDP topcoat. Standard polyester systems should be avoided in salt-laden marine atmospheres.