Pre-painted Steel (PPGI / PPGL) for Roll Forming

1. Definition

Pre-painted steel (also called color-coated or prepainted coil) is metallic-coated steel that receives a factory-applied multi-layer organic coating system on a continuous coil coating line before the strip is roll-formed or fabricated. Unlike post-painting after forming, coil coating cures the film under controlled oven conditions with uniform thickness and adhesion.

Two trade names dominate building-product RFQs:

• PPGI — Pre-Painted Galvanized (Iron/Steel): zinc-coated substrate + paint
• PPGL — Pre-Painted Galvalume: 55% Al–Zn (approx.) alloy-coated substrate + paint

2. PPGI vs PPGL

Choose by exposure class and project specification—not by color chip alone. The paint system and metallic coat mass both matter.

3. Layer Stack

Industry guides describe a typical functional stack:

Film thicknesses above are orientation from supplier/technical guides, not a universal ZTRFM guarantee—order the micrometers your project requires.

4. Coil Coating Process

On a continuous coil coating line (CCL), the strip typically follows:

1. Uncoil metallic-coated feedstock
2. Clean / degrease (alkaline, brushes)
3. Chemical pretreatment / conversion coat
4. Roll-coat primer; bake
5. Roll-coat topcoat (and backcoat as designed); bake / cure
6. Cool, inspect, oil if specified, recoil

Uniform roller coating and controlled oven curing are why pre-paint is preferred over field painting for long building panels.

5. Paint Systems (PE / SMP / HDP / PVDF)

• PE (polyester) — common, economical, general building use
• SMP (silicone-modified polyester) — improved weatherability vs basic PE in many catalogs
• HDP (high-durability polyester) — mid/high durability positioning in supplier lines
• PVDF (fluoropolymer) — high-end exterior durability / color retention when specified

Match paint chemistry to UV load, coastal chloride, industrial pollutants, and warranty language. Do not assume PE equals PVDF life.

6. Metallic Coating Designations

Buyers see both metric and imperial tags:

• Zinc (PPGI substrate): Z100, Z180, Z275 (g/m² total both sides, typical notation) or G60 / G90 style imperial tags
• Al–Zn (PPGL substrate): AZ50, AZ70, AZ150, etc.

Higher metallic mass generally helps substrate life, especially where paint is thin or cut edges are exposed. Confirm whether the number is total both sides and which standard defines it.

7. Substrate Mechanicals

Formability and structural capacity come from the base metal grade (e.g. forming grades such as DX51D / SGCC-type designations, or structural S250GD / S350GD-type yield classes in EN systems). Guides for roofing often discuss yield bands and T-bend / reverse-impact checks for coating integrity under bend—order mechanicals and coating tests that match your flower severity.

Read yield, tensile, and elongation on the material certificate the same way you would for bare coil; then add coating mass and paint system data.

8. Standards Context

Pre-painted coil packages are often discussed alongside families such as ASTM A755 (prepainted metallic-coated sheet), metallic coating specs (e.g. A653 / A792 contexts), EN 10169, and regional JIS coil-coating references (e.g. JIS G3312 mentioned in trade guides). Name the edition your project requires on the PO.

9. Roll Forming Practice

• Use polished / protected rolls; polyurethane sleeves or nylon guides on visible faces where plants adopt them for scuff control
• Respect larger inside radii than bare steel when cosmetics matter—paint can microcrack before the substrate splits
• Control entry guiding to avoid edge rub
• Choose lubricants compatible with the paint system (or run dry if the coating supplier allows)
• Minimize stop marks and coil breaks on high-gloss topcoats

A flower proven on bare GI does not automatically prove a glossy PVDF coil will leave the line unmarked.

10. Coating Defects in Forming

11. RFQ Checklist

1. PPGI or PPGL (metallic system)
2. Base metal grade / thickness (BMT)
3. Metallic coating mass (Z / AZ / G)
4. Paint chemistry + topcoat/primer micrometers
5. Color / gloss / texture (RAL or supplier code)
6. Mechanicals + coating formability tests required
7. Standards and certificate type

12. Storage and Handling

• Keep coils dry; trapped moisture under wrap causes white rust / staining under paint at edges
• Avoid dragging painted faces across floors or unfinished tables
• Rotate stock—do not assume infinite outdoor storage life under tarps

13. Boundaries

• PPGI/PPGL ≠ post-painted after fabrication.
• Paint color ≠ corrosion warranty by itself.
• This page does not publish price or lead-time claims.
• Dedicated galvanized / galvalume substrate pages may exist elsewhere in the wiki—this entry focuses on the pre-paint system.

14. Buyer / Engineer FAQ

Is PPGI always cheaper than PPGL?

Trade guides often position PPGI as more cost-effective for general use and PPGL for harsher climates, but commercial terms vary. Specify performance first.

Can I roll-form PVDF the same as PE?

Often with more care on marking and bend radius. Prove on the actual topcoat; do not assume identical shop practice.

What is T-bend?

A coating flexibility check expressing bend severity relative to thickness (e.g. 1T / 2T language in supplier and ASTM A755-related discussions). Use it as a coating integrity gate for your radii.

Does zinc mass replace paint?

No. Metallic coat and organic film are a system. Cut edges still need design awareness.

Why did paint crack but steel did not split?

Organic film ductility / adhesion limit was exceeded first. Increase radius, warm the coil, or change paint system.

Bare CRC vs PPGI for roofing?

Roofing/cladding almost always wants metallic + paint (or at least metallic). Bare CRC is usually substrate before coating.

How should certificates look?

Expect substrate mechanicals plus coating mass / paint system data on the same or companion documents. See MTC page.

15. Typical Applications

• Roofing and wall cladding panels
• Flashings, gutters, downpipes
• Garage doors, appliances (selected systems)
• Ceiling grid and visible trim (lighter coats)

16. Plant Communication Notes

Write cosmetic acceptance separately from structural crack criteria. A hairline paint crack on a visible rib can fail customer QA even when the panel still carries load.

When changing from matte PE to high-gloss PVDF mid-program, schedule a proving run and roll-clean checklist before promising delivery dates.

Attach coil ID, paint system code, and bend photos to every coating complaint—color memory alone is not evidence.

• Keep felt/wipe stations clean on entry guides
• Log ambient temperature on cold-morning starts
• Segregate soft topcoat jobs from abrasive tooling campaigns

1. Confirm PPGI vs PPGL on the traveler
2. Confirm topcoat chemistry matches the PO
3. Confirm r/t vs supplier T-bend guidance
4. Confirm packaging for painted faces

Do not invent a universal “safe bend radius for all PPGI.” Paint chemistry, film build, ambient temperature, and substrate yield all move the cosmetic limit.

For export packs, document which face is the show side and which is backcoat-facing so installers do not mount panels reversed.

Additional Engineering Notes (1)

Keep purchasing, process engineering, and quality aligned on definitions. Write measurable acceptance criteria into travelers and RFQs so operators are not guessing from adjectives.

When a defect appears after a coil change, pull the mill certificate, lubrication log, and last setup sheet before cutting new rolls. Most surprises are heat, friction, or alignment—not mysterious machine failure.

• Record units consistently across drawings and emails.
• Attach heat numbers to scrap photos.
• Separate cosmetic criteria from structural crack criteria on coated coil.
• Re-prove after grade, coating, or lubricant brand changes.
• Archive CAE inputs with roll drawing revisions when simulation was used.

1. State the decision this page supports.
2. List the three fields to check on the certificate or setup sheet.
3. List shop symptoms that should reopen this topic.
4. Name the next encyclopedia page to read.
5. File the lesson after the CAPA closes.

Training reminder: Boundaries sections exist to prevent over-application of one metric to every failure mode on the line.

Operations reminder: rising motor load at constant thickness can be higher yield or drier friction—verify both before forcing roll gaps.

Design reminder: inside radius, thickness, and grade belong on the same note block so formability constraints travel with geometry.