Prepainted steel coil, also known as pre-coated steel coil or color-coated steel coil, is a product made of hot-dip galvanized steel sheet, hot-dip galvalume steel sheet, electro-galvanized steel sheet, etc. that has been coated with one or more layers of organic paint or other protective coatings.
The prepainting process protects the metal substrate from corrosion. It improves its durability and aesthetic appearance and provides a wide range of color choices.
According to the EN-10169-1 standard, an organic coating material is applied to the rolled metal strip to protect it from corrosion. Cleaning and pretreatment of chemicals are applied to one or both sides of the metal surface with a single or multiple coats of paint or powder.
Prepainted steel coils are widely used in various applications, such as:
1.Indoor and outdoor applications in building and construction (roofing, wall cladding, garage doors)
2.Domestic appliances (refrigerators, washing machines, bakeware)
3.Cabinets and office furniture
4.Transport and automotive sectors
5.Lighting fittings
Prepainted steel coils come in a variety of color coatings, surface textures, and gloss levels. The paint coatings have high chemical resistance, flexibility, and non-stick properties.
The coated coils are available in different cuts. Customers may request coils with narrow widths, profiled, deep drawn, and different lengths and shapes. There are a variety of prepainted steel coils as manufacturers continue to develop modern designs and coatings.
The main features and advantages of prepainted steel coil are obvious, and are widely recognized and used in large quantities through these features:
1. Good durability, corrosion resistance and longer service life compared with galvanized steel sheets.
2. Good heat resistance, compared with galvanized steel sheet, it is not so easy to fade under high temperature.
3. Excellent heat reflectivity.
4. Color-coated coils have similar processing performance and spraying performance to galvanized steel sheets.
5. Excellent welding performance.
6. Color-coated rolls have excellent performance-price ratio, durable performance and competitive price.
Prepainted steel coil usually go through the following processing steps:
Step 1: Cleaning the Metal Strip
Cleaning up the oil, dirt, and impurities of the cold-rolled coil involves brushing, an alkaline dip, a water bath, or brushing.
Step 2: Application of Zinc and Alloy
The application of aluminum and zinc depends on the application and customer requirements. Some products consist of 100 percent zinc, while others contain magnesium alloy.
Step 3: Treatment of the Surface
This step is vital to ensuring that the paint and primer bond well with the metal strip. Due to some chemical restrictions, the surface is treated with chemicals, such as alkaline oxidation, depending on the supplier and country of origin.
Step 4: Metal Rinsing and Drying
Rinsing the metal strip helps ensure that it has no chemical residue before applying primer. Drying the metal is a must to ensure that the subsequent layers bond well.
Step 5: Application of Primer
A coating of primer can be on one or both sides of the metal strip. Primer application hastens the adhesion of the finished paint layer.
Step 6: Curing and Cooling the Strip
Curing takes 15 to 16 seconds. This method allows the primer to harden, dry, and reach the desired temperature before applying the next coating.
Step 7: Front and Back Coating
This step is the final painting stage, wherein two-coat paint systems are applied.
Step 8: Drying, Curing, and Cooling
The product undergoes this step to ensure that the steel product is ready for rewinding, rerolling, and shipping to end users.
Step 9: Packaging
Image showing a coil coating line schematic.
The following are some common national standards for Chinese, British, American and Japanese color-coated coils:
Chinese national standard:
GB/T 12754-2019: Color coated steel sheets and strips
British National Standards:
BS EN 10169: Technical delivery conditions for galvanized and galvanized alloy-coated steel sheet and strip by the continuous hot dip method
American National Standard:
ASTM A755/A755M: Standard Specification for Continuously Coated Metallic Coated Steel Sheet and Strip
Japanese national standard:
JIS G 3312: Prepainted galvanized steel sheets and strips
This standard specifies the terms and definitions of color-coated steel sheets and steel strips, the representation methods, classifications and codes of grades, ordering content, dimensions, shapes, weights, technical requirements, test methods, inspection rules, packaging, signs and quality certificates.
Prepainted steel coil is a decorative material widely used in construction, furniture, electrical appliances and other fields, and has a variety of specifications to choose from. The following are some common prepainted coil specifications
1. Thickness The thickness of prepainted steel coil is usually between 0.2mm and 1.5mm
2. Width The width of prepainted steel coil is generally between 600mm and 1250mm
3. Color prepainted steel coil can be painted according to requirements. The common colors are white, gray, red, blue, etc. It can also be customized according to customer requirements.
4. Surface treatment The surface of color-coated coils can be treated in different ways. Common treatment methods include spraying, embossing, and coating. Different surface treatment methods can give prepainted steel coil different textures and effects, increasing their decoration and durability.
5. Material The prepainted steel coil is usually made of cold-rolled steel or galvanized steel, and stainless steel can also be used. Prepainted steel coil of different materials have different properties and uses, and can be selected according to specific needs.
The allowable error of the thickness of the prepainted steel coil is plus or minus 0.02mm.
Standard documents usually give specific technical requirements and allowable error ranges, such as requirements for thickness, width, length, flatness, color difference, coating adhesion, etc. of coils. These requirements will vary according to the use, grade and technical characteristics of the prepainted steel coil.
