Color-coated steel sheets: a new choice of modern materials that combines beauty and performance

At the intersection of industrial materials and architectural decoration, color-coated steel, with its innovative "metal base + color coating" form factor, breaks the limitations of traditional metal materials' single texture. While retaining the strength and durability of sheet metal, it also offers a rich array of colors, textures, and surface finishes, opening up new design possibilities for architectural exteriors, appliance housings, transportation infrastructure, and more. It has become a key material bridging functionality and aesthetics, and is widely used in all aspects of modern life.

I. Definition and Structure: Collaborative Design of Metal Base and Coating
Color-coated steel, also known as color-coated steel, refers to a composite sheet made from a base metal such as cold-rolled steel, hot-dip galvanized steel, or galvanized steel. After surface pretreatment (degreasing, phosphating, and passivation), it is coated with one or more layers of organic coatings (such as polyester, fluorocarbon, or silicone-modified polyester), which are then cured by baking. Its core value lies in the "base provides strength, while the coating provides appearance and protection," achieving a synergistic performance that is "1+1 greater than 2."

From a cross-sectional perspective, high-quality color-coated steel sheets feature a meticulously designed layering scheme, with each layer having distinct functions and being tightly integrated. A typical structure (from the inside out) includes the following:

Metal substrate: The "skeleton" of the color-coated steel sheet, determining its mechanical properties (strength, toughness, and smoothness). Common substrate types include:

Cold-rolled substrate: Low cost and smooth surface, but weak corrosion resistance, suitable only for dry indoor environments (such as internal components of home appliances);

Hot-dip galvanized substrate: Galvanized surface, high corrosion resistance, suitable for outdoor environments with moderate corrosion (such as exterior walls of ordinary factories);

Alu-zinc-coated substrate (such as Galvalume): Contains 55% aluminum and 43.5% zinc, offering corrosion resistance 2-3 times that of hot-dip galvanizing. It is also heat-resistant (above 600°C) and suitable for harsh outdoor environments (such as coastal buildings and high-temperature workshops).

Pretreatment layer: The "bonding bridge" between the substrate and the coating, only 1-3μm thick, consists of a phosphate or passivation film. Its function is to remove oil and scale from the substrate surface, enhance the adhesion of the coating to the substrate, and prevent the coating from peeling during later use.
Primer: The "base layer" of the coating system, with a thickness of 5-10μm, is typically made of epoxy resin or polyurethane. The primer adheres tightly to the pre-treatment layer, further enhancing corrosion resistance. It also provides a uniform adhesion base for the topcoat, preventing "pinholes" or "color variations" in the topcoat caused by minor substrate imperfections.
Topcoat: The "appearance and core protection layer" of the pre-coated sheet, with a thickness of 10-25μm. The material is selected based on the intended use (e.g., polyester, fluorocarbon). The topcoat determines the color (customizable to any RAL color), gloss (high gloss, matte, or matte), and special features (such as scratch resistance, self-cleaning, and antibacterial properties) of the pre-coated sheet. It also protects against external damage such as UV rays, rain, and acids and alkalis. Backcoat (optional): Some color-coated steel sheets (such as architectural color-coated steel sheets) are coated with one or two thin layers of paint (3-5μm thick) on the backside of the substrate. This primarily prevents rust on the backside of the substrate and reduces scratches during transportation and installation, without affecting the front appearance.

II. Classification: Targeted Classification by Coating, Substrate, and Application
Color-coated steel sheets are categorized in a variety of ways, with different categories corresponding to different performance requirements and application scenarios. Downstream companies can select the most suitable product based on their needs. (I) Classification by Coating Material: Determining Core Performance and Lifespan
The coating material is the most critical performance indicator of color-coated steel sheets, directly affecting their weather resistance, corrosion resistance, and service life:

Polyester Coated Steel Sheets (PE)
Features: Moderate cost, a wide range of colors (available in matte and gloss finishes), good weather resistance at room temperature (15-20 years indoors, 5-8 years outdoors), but weak high-temperature resistance (long-term operating temperature ≤ 120°C), and average resistance to UV aging.
Disadvantages: Susceptible to fading and chalking (coating peeling) with prolonged outdoor exposure.
Applicable Applications: Interior decoration (such as suspended ceilings, partitions, and furniture panels), appliance housings (such as washing machine and refrigerator sides), and exterior walls of low-rise factories in non-coastal areas. Silicon-Modified Polyester Coated Sheet (SMP)
Features: The addition of silicon to polyester significantly improves weather and high-temperature resistance (long-term operating temperature ≤ 180°C), resulting in an outdoor service life of 10-15 years. It also exhibits superior chalking and fading resistance compared to PE, and boasts high hardness (pencil hardness ≥ 2H) and scratch resistance.
Disadvantages: Cost is 10%-15% higher than PE, and flexibility is slightly lower (prone to cracking when bent).
Applicable Applications: Outdoor buildings (such as multi-story factory exteriors and warehouse roofs), high-temperature environments (such as kitchen ceilings and oven housings), and moderately corrosive environments (such as industrial buildings). Fluorocarbon Coated Color-Coated Sheet (PVDF)
Features: Primarily composed of polyvinylidene fluoride, it offers "ceiling" weather resistance (outdoor service life of 20-30 years), strong resistance to UV rays, acid rain, and seawater corrosion, excellent color stability (fading rate ≤ 5% over 20 years), and a long-term operating temperature of ≤ 240°C.
Disadvantages: High cost (2-3 times that of PE), requiring specialized coatings for application.
Suitable Applications: High-end buildings (such as office building curtain walls and airport terminals), coastal or highly corrosive environments (such as offshore platforms and chemical plant buildings), and iconic buildings (where long-term aesthetic appeal is crucial). Other Specialty Coated Color-Coated Sheets
Self-Cleaning Color-Coated Sheets: Nano-titanium dioxide (TiO₂) is added to the topcoat, which decomposes surface oil and dust through photocatalysis, leaving it clean after rainwater washes away. Suitable for high-rise curtain walls (difficult to clean).
Antibacterial Color-Coated Sheets: Silver ion antimicrobial agents are added to the coating to inhibit Escherichia coli and Staphylococcus aureus. Suitable for clean spaces such as hospitals, food processing plants, and kindergartens.
Insulating Color-Coated Sheets: Ceramic microbeads or infrared-reflective pigments are added to the topcoat to reflect over 70% of solar heat, reducing indoor temperatures by 3-5°C in summer. Suitable for rooftops in southern China.
(II) Classification by Metal Substrate: Suitable for Different Corrosive Environments
Cold-Rolled Base Color-Coated Sheets: Suitable only for dry, non-corrosive indoor environments, such as internal partitions in home appliances and furniture.
Hot-Dip Galvanized Base Color-Coated Sheets: Suitable for outdoor use in dry or mildly corrosive environments (such as in inland factories), offering a high cost-effectiveness.
Alu-Zinc Base Color-Coated Sheets: Suitable for outdoor use in moderately to severely corrosive environments (such as coastal areas and industrial areas), offering the best weather resistance, making them the preferred choice for high-end architecture. (III) Classification by Application: Focusing on Specific Industry Needs
Architectural Color-Coated Sheet: 0.3-1.2mm thick, mostly hot-dip galvanized or galvanized substrates, with SMP or PVDF coatings. Can be processed into corrugated sheet or sandwich panels (filled with rock wool or foam). Used for roofs and exterior walls of factories, warehouses, and gymnasiums.
Home Appliance Color-Coated Sheet: 0.2-0.5mm thick, cold-rolled or thin hot-dip galvanized substrates, with PE or SMP coatings. Surface flatness and flawlessness are required. Used for refrigerator, washing machine, and air conditioner casings.
Transportation Color-Coated Sheet: 0.8-2.0mm thick, high-strength galvanized or galvanized substrates, with impact- and scratch-resistant coatings. Used for container side panels, RV hulls, and subway car interiors.
Decorative Color-Coated Sheet: 0.8-2.0mm thick, high-strength galvanized or galvanized substrates, with impact- and scratch-resistant coatings. Used for container side panels, RV hulls, and subway car interiors. 0.15-0.3mm, the coating can create simulated textures such as wood grain, stone grain, and brushed metal. It is used in interior ceilings, furniture panels, and advertising signs, where a premium aesthetic is key.

III. Core Performance: Aesthetics and Performance

The reason why color-coated steel sheets can replace traditional coatings, tiles, and wood materials lies in their comprehensive advantages in appearance, protection, and processing adaptability, achieving a perfect balance between aesthetics and practicality. (1) Highly Expressive Appearance: Meets Diverse Design Needs
Rich and Stable Colors: Customizable colors (such as RAL and Pantone) are available, ranging from vibrant reds and yellows to subdued grays and blacks, and even metallics (such as gold and silver). High-quality coatings (such as PVDF) resist fading and discoloration over time.
Diverse and Realistic Textures: Through a "roller printing" process, the coating surface can be created with wood grain (such as oak and walnut), stone grain (such as marble and granite), brushed grain (such as brushed stainless steel), and fabric grain. The visual effect is virtually indistinguishable from natural materials, while avoiding the color variations and imperfections inherent in natural materials.
Controllable Gloss: Choose from high gloss (gloss ≥70%, suitable for modern architecture), matte (gloss 30%-50%, suitable for understated interiors), and matte (gloss ≤10%, suitable for hospitals and libraries where glare is avoided) based on design requirements. (II) Excellent Protective Performance: Durable and Easy to Maintain

Strong Weather Resistance: Different coatings offer weather resistance ranging from 5 to 30 years, adapting to a wide range of environments, from dry inland areas to coastal areas with high salt spray. For example, PVDF-coated color-coated panels have been used at the seaside for 20 years without noticeable surface chalking or fading.

Excellent Corrosion Resistance: The "double protection" of the metal substrate (galvanized/galvanized) + coating resists erosion from rain, acid rain, and industrial exhaust, preventing rust. The coating itself is non-absorbent and mildew-resistant, making it more moisture-resistant than wood or ceramic tiles.

Scratch and Impact Resistance: The coating has a high hardness (PE The coating has a pencil hardness of ≥1H, SMP ≥2H, and is resistant to scratches from daily collisions and friction. The metal base is also tough and will not break even with minor impacts (e.g., a dropped appliance housing will not break).

Easy to clean and low maintenance: The surface coating is smooth and grease-resistant, requiring only water or a neutral detergent for daily cleaning. It does not require regular painting like wood or grouting like tiles, resulting in low long-term cost. (III) Stable Mechanical Properties: Both Strength and Toughness Meet Standards
High Strength: Based on a metal substrate, color-coated steel sheets achieve a yield strength of 235MPa-550MPa (e.g., Q235 and Q355 substrates), capable of withstanding the loads of building roofs and the crushing during transportation of household appliances without deformation.
Good Toughness: With an elongation of 15%-30%, they can be bent, rolled, and stamped (e.g., into 90° angles or corrugated sheets), with the coating resisting cracking and peeling.
High Flatness: During the production process, the sheet shape is controlled using a straightening machine and a flattening machine, resulting in a surface flatness error of ≤2mm/m. They can be used directly for decorative purposes without the need for additional polishing or leveling. (IV) Environmental Protection and Economical: Sustainable and Cost-Effective
Environmentally Friendly and Pollution-Free: The coating cures using a high-temperature baking process, resulting in zero volatile organic compound (VOC) emissions. The finished product contains no harmful substances such as formaldehyde and heavy metals, meeting EU E0 and China GB 18584 environmental standards.
Recyclable: The metal substrate (steel, zinc, aluminum) and the organic coating can be separated and recycled. The steel substrate can be re-smelted, while the zinc and aluminum can be reused in galvanizing/galvanizing, aligning with the concept of a circular economy.
Cost-Effective: While the initial purchase cost of color-coated sheet is higher than that of traditional coatings, its lifespan is 3-5 times that of conventional coatings (re-coating is required every 5-8 years), and installation is convenient (it can be directly spliced), resulting in a lower overall lifecycle cost.
IV. Production Process: Precision Processing from Metal Coil to Color-Coated Sheet
The production of color-coated sheet is a continuous, automated production line. The core of the process is precise control from pretreatment to coating to curing. Deviations in any step will affect the quality of the final product. Taking the mainstream "two-coat, two-bake" process (primer + topcoat, each applied once and baked once) as an example, the core processes include:

Substrate Uncoiling and Pretreatment: Laying the foundation for the coating.

Uncoiling, Shearing, and Butt Welding: Unwinding the coiled metal substrate (such as hot-dip galvanized coil), using a shearing machine to neatly cut the joints between the coils, and then using a butt welding machine to connect them into a continuous strip, ensuring uninterrupted production.

Degreasing: The strip enters an alkaline cleaning tank (such as sodium hydroxide solution) to remove surface oil and dust to prevent coating adhesion.

Pickling/Phosphating: Cold-rolled substrates require pickling (to remove oxide scale), while galvanized/galvanized substrates require phosphating (to form a phosphate film). The phosphate film is 1-2μm thick and has a porous structure, which enhances primer adhesion.

Passivation: Some high-end products also include a passivation step (such as chromate passivation and chromium-free passivation) to further enhance corrosion resistance.

Washing and Drying: Residual chemicals are rinsed with clean water, followed by hot air drying (temperature ≥ 100°C). 80-120°C), ensuring the strip surface is dry and clean.
Coating: Precisely control coating thickness and uniformity.
Primer coating: Utilizing the "roller coating method" (the most popular coating method), the strip passes between two rollers, which evenly transfer the primer to the strip surface. The coating thickness is precisely controlled (with an accuracy of ≤ 1μm) by adjusting roller pressure and speed.
Primer curing: The primed strip enters a curing oven where hot air is heated (200-220°C for 30-60 seconds) to crosslink and cure the resin in the primer, forming a dense primer layer.
Topcoat application: The principle is the same as for primer application. Depending on the application, solid-color or patterned coating can be selected. (The patterned rollers have a textured pattern and transfer the pigment to the strip surface.)
Topcoat curing: The topcoat enters a high-temperature curing oven (220-250°C for 40-80 seconds) to fully cure the topcoat and achieve a stable color and texture. Post-Processing and Finishing: Ensuring Quality and Usability
Cooling: The cured steel strip is at a high temperature (100-150°C) and requires cooling to room temperature via water or air cooling to prevent deformation of the coating due to high temperatures.
Surface Treatment (Optional): Some products may undergo lamination (a protective film applied to prevent scratches during transportation) or embossing (to further enhance the texture).
Slitting and Coiling: Based on customer needs, the continuous steel strip is slit into cut-to-length sheets (e.g., 1.2m x 2.4m) or re-coiled into coils for easier transportation and use.
Quality Inspection: Online inspection equipment (e.g., coating thickness gauges, colorimeters, and surface defect detectors) is used to measure coating thickness, color deviation, and surface defects (e.g., pinholes and scratches). Unqualified products are immediately rejected.
V. Applications: "Universal Penetration" from Construction to Home Appliances
The application of color-coated steel sheets has expanded from their initial application on factory rooftops to encompass a wide range of sectors, including construction, home appliances, transportation, and decoration, making them a ubiquitous material in modern industry and life. (1) Construction: A "Beauty" for Outdoor and Indoor Use
Construction is the largest application area for color-coated steel sheets, accounting for over 60%. Key requirements are weather resistance, aesthetics, and ease of installation.

Roofs and exterior walls primarily utilize color-coated steel sheets with an galvanized substrate and SMP/PVDF coating. These sheets can be processed into corrugated panels (such as Type 760 and Type 840) or sandwich panels (filled with rock wool (fireproofing) and polyurethane (insulation)). These panels are used in factories, warehouses, logistics parks, gymnasiums, and other areas. For example, the roof and exterior walls of JD Asia Logistics Park No. 1 are made of blue SMP color-coated steel sheets, which are both aesthetically pleasing and weather-resistant.

Curtain walls and decoration: PVDF-coated steel sheets are primarily used, often in dark colors (such as dark gray or black) or metallic tones. They are used for curtain walls in office buildings, airports, and high-speed rail stations. For example, part of the curtain wall of Shenzhen Bao'an Airport Terminal 3 utilizes silver-gray PVDF color-coated steel sheets, which create a high-end look.

Interior decoration: Cold-rolled base plate + PE-coated color-coated steel sheets are primarily used. Wood or stone grain finishes are available. They are used for ceilings, partitions, and wall decoration. For example, white is often used for ceilings in hospital corridors.

Antibacterial color-coated steel sheets are easy to clean and antibacterial.
(II) Home Appliances: Balancing Performance and Aesthetics in Housings
The home appliance industry requires color-coated steel sheets to have a flawless surface, stable color, and easy processing:

White appliances: Refrigerator housings (mostly silver or gray PE color-coated steel sheets), Washing machine housings (blue or white SMP color-coated steel sheets, moisture-resistant), Air conditioner outdoor unit housings (hot-dip galvanized substrate + SMP color-coated steel sheets, outdoor corrosion-resistant);
Small appliances: Microwave oven housings (black or stainless steel-colored PE color-coated steel sheets), Rice cooker housings (red or white high-gloss PE color-coated steel sheets), Air fryer housings (high-temperature-resistant SMP color-coated steel sheets, long-term discoloration). (III) Transportation: Balancing Durability and Lightweight
Containers: Container side panels and roof panels utilize hot-dip galvanized substrates and PE color-coated steel sheets, primarily in blue and gray. They must be resistant to seawater corrosion and impact during transportation.
RVs and Special Vehicles: RV exteriors utilize lightweight color-coated steel sheets (0.5-0.8mm thick) with wood grain or metallic finishes, ensuring both aesthetics and weather resistance. Subway and high-speed rail interior panels (such as carriage sidewalls) utilize cold-rolled substrates and antibacterial PE color-coated steel sheets, ensuring easy cleaning and environmental friendliness. (IV) Other Sectors: Niche but Targeted Needs
Advertising and Signage: Advertising signs and light box panels utilize thin, color-coated steel sheets (0.15-0.2mm thick), offering vibrant colors, high flatness, and the ability to be directly printed.
Furniture and Home Furnishings: Wardrobe door panels and desk panels utilize wood-grain color-coated steel sheets, offering an alternative to natural wood, preventing deformation and cracking while offering a lower price.
Agriculture and Animal Husbandry: Greenhouse frame coverings and livestock farm fencing utilize a hot-dip galvanized substrate with PE color-coated steel sheets, offering resistance to moisture and pesticide corrosion.