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Why Steel Is Painted?

Painting is a protective layer of base metal, which is also a cost-effective method to keep metal from rusting and corrosion. It can prolong the service life of the base metal. On the other hand, the steel will look great if it is painted with colorful coatings. That’s why color-coated steel can be found in many applications, particularly in roofing and wall systems.

Painted Steel in Building

Painted Steel in Building

Why is Coating Necessary?

Corrosion begins from the exposed surface and damages the material layer by layer.  A layer of coating will be more protective. It can keep the base metal from corrosion, chemical damage, and UV light to prolong its service life. At the same time, it can make the metal surface smooth and good-looking. That’s why the coating process is necessary.

For example,  color coated steel (PPGI and PPGL) consists of zinc coating or Al-Zn coating, prime coating, and finish coating. Commonly, both two sides are coated. Compared to the top coating, the coating for the back side is called back coating. Let’s review the function of each layer of paint.

Color Coated Steel Structure

Color Coated Steel Structure

Primer Paint

The primer paint aims to increase the adhesion between the substrate and finish coating. It is not as durable as finish coating. But it can still provide an extra protective layer for steel sheets. Commonly, PE (polyethylene) is often used as primer paint due to its great adhesion.

Finish Paint

The finish painting refers to the top coating, which can make the surface beautiful and durable. In general, it has the advantages of good gloss, rich colors, beautiful surface, stain resistance, friction resistance, and other properties. For example, HDP and PVDF are great options.

Back Paint

The back paint is also able to improve the adhesion and corrosion resistance of steel. While considering that the back side will not be exposed, the back coating is thinner than the top coating. Besides, if the steel sheet is used for sandwich panels, the back side is suggested to be painted once.

Coil Coating Process

Coil Coating Process

Types of Paints

The commonly-used paints are PE, SMP, PVDF, HDP. Below is a short introduction to the paint.

PE (polyethylene)

It has good comprehensive performance and its good weather ability meets the basic requirements of exterior building. It is usually applied to the range of industrial buildings, commercial buildings such as roofs, and external walls.

SMP (Silicone Modified Polyester)

It has ultra-weathering pigments to ensure the permanent brightness of the color. Moreover, the SMP paint provides a special silicone structure to enhance the hardness of coating which can not only increase wear resistance and metal scratching but also withstand the deep processing of stamping.

PVDF (polyvinylidene fluoride)

The PVDF paint has more than 70% of the polyvinylidene fluoride content, It gives the coating good weather resistance, acid and alkali, and environmental pollution performance. The PVDF paint uses advanced inorganic ceramic pigments to block the UV and maintain a gloss color for coating.

HDP (High durability polyester)

HDP has more colors than PVDF. Due to this paint’s special polyester structure and good hydrolysis resistance, HDP also has excellent chemical resistance and durability.

You can choose the paints according to the intended uses, service environment, your budget, the surroundings, etc.

Conclusion

The coating is effective to prolong the service life of base metal. At the same time, it makes steel products diverse. That’s why color coated steel is widely used in many areas. Wanzhi Steel adopts coil coating process, which can apply paints smoothly and evenly. Also, we have different colors and patterns to choose from. You can select one according to the RAL Color or send us a sample. More than that, there are different paintings and paint brands, such as Nippon, Akzo Nobel, etc., to meet different needs. Welcome to talk to us for details!

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