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Help CenterSteel Coil & Strip & Prepainted Steel Coil，S220GD+Z、S250GD+Z、S320GD+Z、S350GD+Z、S420GD+Z、DX51D+AZ、S350GD+AZ、DX51D+ZM、S350GD+ZM
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1. Product Definition & Core Overview
Color coated steel coil, also known as prepainted steel coil (abbreviated PPGI for galvanized substrate, PPGL for galvalume substrate), is a composite steel material manufactured by continuous roller coating production line. Cold rolled base coil is first hot-dip galvanized, galvalume or zinc-aluminum-magnesium coated, then subjected to degreasing, cleaning and chemical conversion pretreatment, followed by one or multi-layer organic paint roller coating and high-temperature baking curing.
It perfectly combines the mechanical strength of steel substrate, anti-rust protection of metal alloy coating and decorative & weather-resistant performance of organic paint. The surface has uniform bright color, complete coating without secondary on-site painting, excellent bending, roll forming and stamping performance. With lightweight, long service life, easy construction and rich color options, it is widely used in building enclosure, household appliances, transportation, advertising and metal decoration industries. Delivery forms include full master coils, slitted narrow strips, cut-to-length color coated sheets, embossed color steel and printed pattern color coils.
2. Executive Standards
2.1 Chinese National Standards
GB/T 12754-2019 Color coated steel sheets and strips (general core standard)
YB/T 4456-2015 Color coated steel sheets and strips for construction
GB/T 2518 Hot-dip galvanized steel sheets and strips
GB/T 14978 Hot-dip galvalume steel sheets and strips
2.2 International Export Standards
EN 10169 Prepainted flat steel products for construction
ASTM A755/A755M Prepainted galvanized steel sheets
JIS G3312 Prepainted hot-dip galvanized steel sheets
ISO 9227 Neutral salt spray test standard for coating performance
3. Product Classification
3.1 Classification by Base Substrate
PPGI Hot-Dip Galvanized Substrate (DX51D+Z)Zinc coating weight: 60–275g/㎡. Balanced cost and anti-corrosion performance, suitable for indoor factories, ordinary warehouse roofs, civil prefab houses and general atmospheric environment.
PPGL Hot-Dip Galvalume Substrate (DX51D+AZ, 55%Al-Zn)Aluminum-zinc alloy coating with superior UV resistance, high-temperature oxidation resistance and salt spray performance. The first choice for outdoor roofs, coastal areas, humid and corrosive industrial zones, service life 1.5–2 times longer than PPGI.
ZM Zinc-Aluminum-Magnesium Substrate (DX51D+ZM)Add magnesium element to alloy layer, excellent cut-edge anti-rust capacity, suitable for high-salt coastal, chemical park, sewage plant and heavy corrosion environments.
Electro-Galvanized Substrate (SECC)Thin uniform zinc layer, ultra-smooth base surface, mainly applied for high-end household appliance shells with strict surface requirements.
3.2 Classification by Organic Top Coating (Core Weather Resistance Grade)
PE Polyester Coating (Conventional Grade)Salt spray ≥500h, QUV aging ≥600h. Cost-effective, rich color matching, widely used for ordinary factory roof and wall panels, indoor decoration. Top coat thickness 18–25μm, back coat 5–10μm.
SMP Silicone Modified Polyester Coating (Medium Weather Resistance)Improved anti-chalking and color retention, salt spray ≥800h, outdoor service life 8–12 years, suitable for medium industrial buildings and suburban projects.
HDP High Durability Polyester Coating (High Weather Resistance)Superior anti-UV and anti-fading, salt spray ≥1000h, QUV ≥2000h, service life over 15 years, ideal for coastal, high-temperature and strong light areas.
PVDF Polyvinylidene Fluoride Coating (Top Architectural Grade)Fluorocarbon high-performance coating, excellent acid, alkali and ultraviolet resistance, salt spray ≥1500h, outdoor lifespan 20–30 years, used for landmark buildings, airport terminals, high-end commercial facades.
3.3 Classification by Surface Appearance & Processing
Solid matte / semi-gloss / high-gloss color coated coil (gloss range 10–80GU)
Embossed texture color coil (anti-scratch, decorative metal grain surface)
Printed pattern color coil (wood grain, stone grain, camouflage, warning stripe patterns)
Slitted narrow color strip, cut-to-length flat color steel sheet
3.4 Classification by Mechanical Strength Grade
Forming grade: DX51D, DX52D – good bending, roll forming for roof/wall panels
Medium strength: S250GD, S300GD – load-bearing enclosure, partition plates
High tensile hard grade: G550, S550GD – high-strength bearing purlins, large-span roof support panels
4. Complete Specification Range
Total thickness (substrate + coating): 0.12mm ~ 1.5mm; mainstream 0.3mm–1.2mm
Width: 600mm ~ 1500mm; standard widths 900/1000/1200/1250mm
Standard inner coil diameter: 508mm; customized 610mm available
Single coil weight: 3–12 tons; small light coils 1–5 tons on request
Zinc/AZ coating weight: Z60–Z275, AZ100–AZ185, ZM120–ZM230
Coating thickness: Top coat 15–25μm, back protective coat 5–20μm
Color system: Full RAL color card, NCS colors, customized special colors
Appearance Quality Standard
Smooth uniform coating surface without missing coating, scratch, bubble, pinhole, peeling and color difference; consistent gloss and tone of whole coil; neat trimming edges with minor burrs; coating has strong adhesion without falling off after T-bend test.
5. Core Coating & Mechanical Performance Index
5.1 Mechanical Properties (DX51D Forming Grade)
Yield strength: 140–300MPa
Tensile strength: 270–500MPa
Elongation after fracture: ≥22%, pass 180° T-bend test without coating crack
High-strength G550 grade yield ≥550MPa for structural load-bearing
5.2 Coating Technical Indicators
Adhesion: Cross-cut test grade 0, no coating shedding
Impact resistance: Reverse impact ≥9J without paint cracking
Salt spray resistance (neutral ASTM B117): PE≥500h, HDP≥1000h, PVDF≥1500h
Aging resistance (QUV xenon lamp): PE≥600h, PVDF≥3000h, slight color fading only
Hardness: Pencil hardness ≥H, scratch resistant in normal construction
6. Complete Production Process Flow
Cold rolled base coil uncoiling → Surface degreasing & alkaline cleaning → Fresh water rinsing → Chromium-free chemical conversion film treatment → Drying preheating → Double-side roller primer coating → Oven baking curing → Top finish coating secondary baking → Back anti-corrosion coating curing → Air cooling → Surface quality online inspection → Film protective lamination (optional) → Recoiling finished color coated coil → Finishing (slitting / cut-to-length) → Full dimension & coating performance recheck → Laser marking grade, spec, heat & batch number → Edge guard & multi-layer bundling → Moisture-proof export packaging & warehousing
Continuous closed baking line ensures uniform coating curing, stable adhesion and consistent color difference of whole coil.
7. Core Product Advantages
Integrated anti-corrosion double protection Metal zinc/aluminum-zinc substrate sacrifices anode anti-rust + organic paint isolation anti-corrosion, dual-layer protection greatly extend outdoor service life.
Rich decorative color & uniform finish Complete RAL color system, matte/high-gloss/pattern optional, consistent batch color, no on-site painting required to save construction cost and labor.
Excellent forming process performance Good ductility for bending, roll forming, corrugating and stamping; coating maintains integrity without cracking after 1T/2T bending, suitable for various metal profiling equipment.
Light weight & high structural efficiency Low self-weight reduces building foundation load, shortens construction period, widely used for large-span steel structure projects.
Weather & chemical resistance graded selection PE/SMP/HDP/PVDF multi coating grades matching inland, suburban, coastal and heavy chemical corrosion zones, flexible cost control.
Diversified deep processing forms Supply full coils, narrow slits and flat sheets to eliminate secondary slitting/cutting for end customers.
8. Main Application Fields
Construction Industry (Largest Application)Steel structure factory roof & wall panels, warehouse, stadium, airport terminal, prefab house, cold storage enclosure, metal gutter, roof purlin.
Household Appliance ManufacturingRefrigerator, washing machine, air conditioner outdoor unit shell, microwave oven cabinet, electrical distribution box shell.
Transportation IndustryTruck carriage panel, container side plate, caravan outer skin, ventilation duct.
Advertising & DecorationOutdoor billboard substrate, metal door panel, metal furniture, guardrail, interior decorative metal plate.
Agriculture & Light IndustryGreenhouse enclosure, poultry farm wall panel, metal storage cabinet, small stamping hardware parts.
9. Construction, Processing & Storage Specifications
Different coating grades must be selected according to service environment: PVDF/HDP mandatory for coastal salt fog areas, PE only for indoor dry environment.
During roll forming and bending, avoid sharp tool scratching coating surface; adopt matched color coated special fasteners to prevent contact corrosion.
Coil storage must be placed in dry closed warehouse; long-term outdoor stacking is forbidden, cover waterproof tarpaulin if temporary outdoor storage required.
After cutting, seal cut edges with anti-rust paint for PPGI ordinary galvanized coils; PPGL galvalume coils have natural cut-edge anti-rust performance with less maintenance.
Avoid long-term direct contact with acid, alkali, chemical solvent to prevent coating corrosion and discoloration.
Lift coils with dedicated C-shaped lifting clamps; prohibit steel wire rope direct friction on coil edges to avoid coating damage.
10. Export Packaging, Inspection Documents & Customization Services
10.1 Standard Seaworthy Export Packaging
Inner layer: Moisture-proof kraft paper + transparent plastic waterproof film; outer layer: galvanized steel protective sheet; coil two sides equipped with plastic anti-collision edge guards. Multiple radial and circumferential steel straps fasten coil tightly to prevent loose winding during sea transportation. Each coil marked with substrate grade, coating type, thickness, width, coil weight, standard, heat number and batch number for full traceability. Small light coils can be packed into wooden frames as customer request.
10.2 Full Set Factory Delivery Certificates
Original complete documents attached with goods: chemical composition report, mechanical property test sheet, coating salt spray & adhesion test report, dimensional inspection record, factory qualification certificate. Third-party inspection SGS, BV, TÜV available to meet domestic engineering acceptance and overseas customs clearance requirements.
10.3 Customization Support
Custom non-standard thickness & width, ultra-narrow slitted strips, arbitrary fixed-length cutting, embossed/printed pattern surface, matte/high-gloss gloss adjustment, special RAL/NCS custom colors, thickened high weather-resistance PVDF coating. Provide full compliance certificates of GB, EN, ASTM, JIS standards for global construction, home appliance and metal processing manufacturers.
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