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Processing characteristics of prepainted steel coils
No matter what kind of final product of the color coating production line is: coated board, embossed board or laminate (laminate) board, in the pretreatment stage of the unit process section, the surface purification treatment should be carried out, that is, degreasing treatment, chemical conversion film treatment and other two important stages.
The role of purification treatment has the following.
(1) improve the compatibility and compatibility between coating and steel substrate.
Surface treatment in addition to degreasing, friction and other cleaning processes, but also including chemical conversion treatment of the surface that is coated chemical liquid.
After chemical transformation, the surface can form a layer film with a certain roughness, and expand the surface area of contact between the coating and the substrate, which is very beneficial to the adhesion of the coating.
(2) activate the substrate surface.
Remove rust oil, dirt and rust stains applied for rust prevention during substrate production. Dirt can be divided into inorganic and organic. Organic dirt is mainly animal grease, vegetable grease and mineral grease, while inorganic dirt is metal oxide, salt, dust and sand.
In addition, there are organic matter and inorganic waste, such as grinding debris, grinding materials and so on.
Animal and vegetable oils can be removed by alkali soap.
Mineral oil can not be alkali soap removal, need to trichloroethylene, gasoline, petroleum solvent emulsifier removal.
Inorganic contaminants can be dissolved by acid or alkali, removed by acid or alkali impregnation, chemical or electrolysis, and removed by mechanical grinding.
Inorganic and organic mixed sewage, removal is more difficult, in addition to the use of chemical methods, also need to use electrolysis, mechanical grinding and other methods combined application of removal, their presence not only affect the appearance of the coating film, seriously affect the adhesion between the coating and the substrate, so that the film into pieces off.
Therefore, the surface is usually treated by friction before coating to improve the cleanliness and activation of the substrate surface.
(3) enhance the adhesion of the coating to the surface of the object.
After removing the anti-rust oil, rust spot and dust attached to the substrate surface, the clean substrate surface can be chemically coated to form a mesh chemical transformation film with Cr6+ and Cr3+ as the basic framework, so as to increase the adhesion between the substrate and the coating, improve the corrosion resistance of the substrate and the durability of the coating.
In order to ensure the chemical conversion treatment, the substrate surface can form a uniform structure, strong adhesion of the chemical conversion film, to avoid coating due to oil, air, water and other bubbles.
(4) ensure and improve the protective performance of the coating.
In normal use conditions, corrosive ions, such as scale and corrosion could penetrate organic coating, reach the surface of the steel base, because the electrode potential is higher than steel is about 0.15 ~ 0.26 V, so as the cathode, anode caused membrane and steel itself become the corrosion, with the continuous development of corrosion, the organic coating will appear until bubbling destruction, peeling off.
In order to improve the corrosion resistance of organic coated steel plate, finish the surface treatment process before the steel plate coating, so that the corrosion resistance of organic coated steel plate greatly improved, prolong the service life of the coating.