● Color-coated steel sheets, formally known as pre-painted galvanized steel coils, are composite building materials manufactured by applying one or multiple layers of organic coatings onto cold-rolled, hot-dip galvanized, or aluminum-zinc alloy coated steel substrates through a continuous roller coating process. The production involves precise pre-treatment stages, including degreasing, phosphating, and chromate conversion, followed by high-temperature curing. This technology seamlessly integrates the substrate's anti-corrosion properties with the coating's decorative function, making it an essential material for modern industrial buildings, commercial facilities, and residential structures. Its core value lies in unifying functionality and aesthetics through material science and process innovation. Structurally, color-coated sheets form a composite system of "substrate-chemical conversion layer-primer-topcoat". The substrate provides structural strength and basic corrosion resistance (zinc coating weight: 20-275/㎡ optional), the conversion layer enhances coating adhesion, the primer offers additional barrier protection, while the topcoat determines final color and weather resistance. Topcoat materials can be selected according to application environments: cost-effective Polyester (PE) for general construction; Siliconized Polyester (SMP) with enhanced durability for moderately polluted areas; PVDF coatings maintaining color stability for over 25 years in harsh environments due to exceptional UV resistance. The development of functional coatings, including nano-self-cleaning, antibacterial, and thermal insulation varieties, has further expanded product applications.
The substrate is the "skeleton" of the pre-painted sheet, providing strength and basic corrosion resistance.
Substrate Type
Galvanized Steel (GI): Cost-effective, widely used.
Galvalume Steel (GL): Most common in construction, 2-4x corrosion resistance of GI, good heat resistance.
Aluminium-Zinc-Magnesium Steel (AZM): New generation product with top-tier corrosion resistance, especially cut-edge protection.
Substrate Thickness
Conventional Range: 0.15mm ~ 1.5mm
Common for roofing: 0.5mm ~ 0.8mm
Common for wall cladding: 0.4mm ~ 0.7mm
Coating Weight (Coating Mass)
Unit: g/m² (Total both sides)
Galvanized (GI): Z120 (60/60), Z150 (75/75), Z180 (90/90), Z200 (100/100)
Galvalume (GL): AZ100 (50/50), AZ120 (60/60), AZ150 (75/75) - AZ150 is the gold standard for building applications.
Aluminium-Zinc-Magnesium (AZM): AZM100, AZM120, AZM150, AZM180
The coating is the "garment" of the steel, determining its appearance, durability, and color retention.
Coating System
Primer: Typically 5-7µm, main functions are adhesion and corrosion resistance.
Topcoat: Determines color, gloss, and weatherability.
Topcoat Resin Type - Core Selection
Polyester (PE): Cost-effective, good flexibility, suitable for interiors or mild environments. General weatherability.
High Durability Polyester (HDP): Most common for building walls. 2-3x weatherability of PE, excellent cost-performance.
Silicone Modified Polyester (SMP): Better weatherability and durability than PE, but less flexible. Suitable for roofing.
Polyvinylidene Fluoride (PVDF): Top-tier weatherability. Used for landmarks or highly corrosive environments, guarantees 20-25 years against severe chalking/fading.
Coating Thickness
Unit: µm, usually refers to the exposure side thickness.
Conventional Requirement: ≥ 20µm
High Standard Requirement: ≥ 25µm (Topcoat thickness recommended ≥ 18-20µm)
Color & Surface Finish
Color: Standard color charts or custom. Light colors have better weatherability.
Gloss:
Low Gloss: 10° - 30° - Most popular in architecture, good weatherability, hides imperfections.
Medium Gloss: 40° - 60°
High Gloss: ≥ 70°
Coating Texture: Smooth, Fine Texture, Orange Peel, Embossed.
Weathering Resistance
QUV Accelerated Weathering Test:
PE: ≥ 400 hours
HDP: ≥ 600 - 800 hours
PVDF: ≥ 1500 - 2000 hours
No blistering/cracking/peeling after test, minimal change in ΔE, and gloss.
Mechanical Properties
Pencil Hardness: ≥ F (Typically H)
T-Bend: 3T (Typical value, indicates formability)
Reverse Impact: ≥ 9J (Ensures coating resistance to impact)
Chemical Resistance
Passes acid, alkali, and solvent resistance tests to ensure resistance to atmospheric pollution and rain erosion.
Adhesion
Cross-Cut Test: Grade 0 or 1 (Best)
| Category | Parameter | Recommended Specification | Notes |
| Substrate | Type | Galvalume (GL) AZ150 or Al-Zr-Mg AZM150 | Best corrosion resistance |
| Substrate | Thickness | 0.5mm (Roof), 0.6mm (Wall) | Based on load calculation |
| Substrate | Coating Weight | AZ150 (75/75) or AZM150 (75/75) | Standard choice |
| Coating | Topcoat Resin | HDP (General) / PVDF (Premium) | HDP is the best cost-performance choice |
| Coating | Coating Thickness | ≥ 25μm (Exposure Side) | Guarantee of durability |
| Coating | Gloss | 20° - 40° (Matte) | Aesthetic and weather durable |
| Coating | Color | Light colors (White, Beige, Light Grey) | Best weatherability |
| Performance | Weatherability (QUV) | ≥ 600 hours (HDP) | - |
| Performance | T-Bend | ≤ 3T | - |
| Performance | Adhesion | Class 0 | - |
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