Prepainted Steel Sheets

Brief introduction

Prepainted steel sheet is coated with the organic layer, which provides higher anti-corrosion property and a longer lifespan than that of galvanized steel sheets.

The base metals for the prepainted steel sheet consist of cold-rolled, HDG electro-galvanized and hot-dip alu-zinc coated. The finish coats of prepainted steel sheets can be classified into groups as follows: polyester, silicon modified polyesters, polyvinylidene fluoride, high-durability polyester, etc.

The production process has evolved from one-coating-and-one-baking to double-coating-and-double-baking and even three-coating-and-three-baking.

The color of the prepainted steel sheet has a very wide selection, like orange, cream-colored, dark sky blue, sea blue, bright red, brick red, ivory white, porcelain blue, etc.

The prepainted steel sheets can also be classified into groups by their surface textures, namely regular prepainted sheets, embossed sheets, and printed sheets.

The prepainted steel sheets are mainly provided for various commercial purposes covering architectural construction, electrical household appliances, transportation, etc.

History of prepainted steel sheet

The production of prepainted steel sheet originated in the United States in the mid-1930s. In the beginning, the technology was only adopted in producing a prepainted steel strip. Till 1995, the first batch of coating equipment for broad strip steel was invented and produced in the United States in 1955. In the 1960s, the production of the prepainted steel sheet made rapid development in the United States, Europe, and Japan. Besides, prepainted steel products were also developed greatly all over the world.

By the end of the 1980s, the production of the prepainted steel sheet in China had been almost blank. Until the 1980s, Wusteel and Baosteel established the double-coating-double-baking production lines of prepainted steel sheets in succession. With increasingly promotion and application of Baosteel’s prepainted steel sheets at home, more and more people make themselves acquainted with the production of steel sheets. Thus, at the turning point of the 20th century the 21st century, a lot of production lines of prepainted steel sheets emerged like bamboo shoots after a spring rain and there was also a great demand for such products. With partial regional results tallied, the consumption of prepainted steel sheets at home had already amounted to 3.2 million tons or so in 2004.

Coating Structure

1 Type of coating structure
2/1: Coat the top surface of the steel sheet twice, coat the lower
surface once, and bake the sheet twice.
2/2: Coat the top/lower surface twice and bake twice.
2 Usage of different coating structures
2/1: The anti-corrosion property and scratch-resistance of the single-layer backside coating is poor, however, its adhesive property is good. The prepainted steel sheet of this kind is mainly used for sandwich panel;
2/2: The anti-corrosion property, scratch resistance and processing property of the backside coating of prepainted steel sheet is better, so it is widely used for roll forming. But its adhesive property is poor, so it is not used for sandwich-panel.

Introduction of Usage


The prepainted steel sheet for construction is an attractive substitute for wood and other materials, owing to its advantages, including fast color, good durability performance, chalking resistance, etc. It minimizes the maintenance cost. At the same time, various colors, surface structures, and coatings provide such products with great flexibility and option. In China, more than 90% of color coated sheets are applied in construction, and the prepainted steel sheets are also widely used in such fields. The prepainted steel sheets satisfy the large-scale halls’ rigorous requirements in construction in material color, shape, quality, property, etc. They have been recognized by many landmark buildings in China, covering hall centers, sports halls, aviation knobs, cultural facilities, etc. After 15 years’ continuous research and improvement, Baosteel has been not only widely used but also been commonly recognized in auto, non-ferrous metal, power industry, coal mining, light industry, medicine, foodstuff, etc. Baosteel’s construction steel has already substituted traditional building materials with its safety, durability esthetic quality and environmental-friendly property, for always building up a comfortable, harmonious and cozy living environment, from schools and residences to commercial buildings, and from villas to top-grade commercial apartments.

Household appliances

The prepainted steel sheet for household appliances often takes electro-galvanized, hot-dip zinc-coated and cold rolled steel sheets as its base metal, which is widely applied in manufacturing refrigerators, large-scale air-conditioning systems, refrigerating cabinet, bread maker, furniture, etc. The distribution of electrical household appliances is started from their good appearances. Sino Metal Roof (SMR) promises to guarantee the quality of its prepainted steel products. Its products can be applied to refrigerators, refrigerating cabinets, washers, air conditioning, and other household appliances.  Sino Metal Roof (SMR) production lines of prepainted steel products are equipped with first-grade equipment of production control, check, and inspection, at the same time; its products also take the leading potion among fellow ones with Sino Metal Roof (SMR) abundant experience in the production of prepainted steel sheets. With excellent packing and convenient logistic systems, Sino Metal Roof (SMR) guarantees to deliver its customers the products with zero defects. Batches of prepainted steel products with good luster and high quality that have already delivered to all the providers of electrical household appliances offer them a powerful competitive force in quality.

Introduction of Base Metals

The base metals for the prepainted steel sheet consist of cold-rolled, HDG electro-galvanized and hot-dip alu-zinc-coated steel sheet.

Cold-rolled base metal

The prepainted steel sheet processed with cold-rolled base metal features in its smooth and beautiful appearance and the machinability of cold-rolled steel sheet, however, in case of any tiny scratch on the top coating may expose the cold-rolled base metal in the air and the exposed base metal may rust soon. Thus, the products of this kind can only be used as temporary
isolation measures and indoor materials with low requirements.

Hot-dip zinc-coated base metal

The prepainted steel sheet with hot-dip zinc-coated base metal as its base metal not only has the protective function of zinc coating but also has an isolation and protection function with its organic layer that prevents it from rusting and prolongs its service span longer, than that of hop-dip zinc steel sheet.The zinc content of hop-dip zinc base metal is generally 180 per
1 square meter (both sides), while that of the hot-dip zinc base metal for construction outdoors is 275 square meters per 1 square meter.

Hop-dip alu-zinc base metal

The hop-dip alu-zinc base metal adopts the hot-dip zinc-aluminum coated steel sheet (55%AI-Zn) as its prepainted base metal. The corrosive resistance of the hot-dip alu-zinc coated steel sheet is twice to 5 times as much as that of the hot-dip zinc-coated base metal. It can satisfy the processing requirements of rolling, coiling and other processes alike.
Its color won’t change while continuously or intermittently working
with an ambient temperature up to 316C. Neither serious oxygenation nor oxide scale might appear while continuously or intermittently working with an ambient temperature up to 490C. Its heat and the light reflected are respectively twice as much as those of hot-dip zinc steel sheet, and its reflectivity is more than 0.75, exceeding 0.65(required by the EPA Energy Star Standard), which is an ideal construction material of saving

Electro-galvanized base metal

The prepainted electro-galvanized steel sheet adopts an electro-galvanized
base metal coated and baked with an organic coating. Owing to the thin zinc-coated layer of the electro-galvanized base metal, the zinc content of the prepainted steel sheet of electro-galvanized base metal is usually 20/20g/m2, and the products of this kind are not suitable for building walls
or roofs outdoors. However, it has an esthetic appearance and excellent machinability, which makes it suitable for electrical household appliances, acoustic devices, steel household appliances, interior decoration, etc.

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