Knowledge for Prepainted Steel

1、Brief Introduction for Prepainted Steel


(1) Prepainted Steel Coil/Sheet is coated with organic layer, which provides higher anti-corrosion property and a longer lifespan than that of galvanized steel coil/sheet.

(2) The base metals for Prepainted Steel Coil/Sheet consist of cold rolled steel coil/sheet, HDG steel coil/sheet, electro-galvanized steel coil/sheet and hot-dip alu-zinc coated steel coil/sheet. The finish coats of Prepainted Steel Coil/Sheet can be classified into groups as follows: polyester, silicon modified polyesters, polyvinylidene fluoride, high-durability polyester, etc.

(3) The production process of Prepainted Steel Coil/Sheet has evolved from one-coating-and-one-baking to double-coating-and-double-baking, and even three-coating-and-three-baking.

(4) The color of the Prepainted Steel Coil/Sheet has a very wide selection, like orange, cream-colored, dark sky blue, sea blue, bright red, brick red, ivory white, porcelain blue, etc.

(5) The Prepainted Steel Coil/Sheet can also be classified into groups by their surface textures, namely regular prepainted coil/sheet, embossed coil/sheet and printed coil/ sheet.

(6) The Prepainted Steel Coil/Sheet are mainly provided for various commercial purposes covering architectural construction, electrical household appliances, transportation, etc.

2、Development History for Prepainted Steel

(1) The production of Prepainted Steel Coil/Sheet originated in the United States in the mid 1930s. At the beginning, the technology was only adopted in producing 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 Prepainted Steel Coil/Sheet made a rapid development in the United States, Europe and Japan. Besides, the Prepainted Steel Coil/Sheet were also developed greatly all over the world.

(2) By the end of the 1980s, the production of Prepainted Steel Coil/Sheet in China had been almost blank. Until the 1980s, Wusteel and Baosteel established the double-coating-double-baking production lines of Prepainted Steel Coil/Sheet in succession. With increasingly promotion and application of Prepainted Steel Coil/Sheet at home, more and more people make themselves acquainted with the production of Prepainted Steel Coil/Sheet. Thus, at the turning point of the 20th century the 21st century, a lot of production lines of Prepainted Steel Coil/Sheet emerged like bamboo shoots after a spring rain and there was also a great demand for such products. 


3、Diagram of Main Production Process of Prepainted Steel



4、Detailed Process of Prepainted Steel 





5、Coating Structure of Prepainted Steel

(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.
2/1M: Coat and bake twice for both top surface and undersurface (The thickness of bottom side coating is smaller than that of the product type 2/2).
2/2: Coat the top/lower surface twice and bake twice.

(2) Usage of Different Coating Structure

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 of this kind is mainly used for sandwich panel;
2/1M: Back coating has good corrosion resistance, scratch resistance and molding performance, besides it has good adhesion and is applicable for single layer panel and sandwich sheet.
2/2: The anti-corrosion property, scratch resistance and processing property of the backside coating of prepainted steel is better, so it is widely used for roll forming, but its adhesive property is poor, so it is not used for sandwich panel.

6、Category & Coding of Prepainted Steel

applicationsconstruction external useJW
construction internal useJN
steel windowsGC
household applianceJD
surface finishnormal coatedTC
types of top coatingPEPE
silicon modified polyesterSMP
high-durability polyesterHDP
polyvinylindene fluoridePVDF
base metalelectro-galvanized base metalZE
hot dip zinc coated base metalZ
hot dip Al-Zn steel sheetAZ

coating surface structure of substrate

small spangleX
zero spangleM

pretreatment types of substrate surface

normal chemical pretreatmentC
chrome free chemical pretreatmentC5
coating typetop side two coatings, bottom side one coatings2/1
top side two coatings, bottom side two coating2/2
top side two coatings, bottom side two coating
(Note: the thickness of bottom side coating is smaller than that of the type 2/2)
2/1 M

7、Introduction of Usage of Prepainted Steel

(1) Construction


The Prepainted Steel Coil/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 Prepainted Steel Coil/Sheet with great flexibility and option. In China, more than 90% Prepainted Steel Coil/Sheet are applied in construction.

(2) Household Appliance


The Prepainted Steel Coil/Sheet for household appliances often takes electro-galvanized, hot-dip zinc-coated and cold rolled steel sheet 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 of Prepainted Steel Coil/Sheet is started from their good appearances.

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