Coating thickness is the most important guarantee condition of corrosion resistance. The larger the coating thickness is, the better the corrosion resistance is. This has been proved by many accelerated tests and exposure tests.
How to choose the type of coating
The main function of the coating is reflected in the visual effect and protection function. The pigment of the coating can be divided into organic pigment and inorganic pigment, the color of organic
pigment is bright; the inorganic pigment is generally light color, but its chemical performance and ultraviolet resistance are better than organic pigment.
The commonly used topcoats for color steel plate are: polyester (PE), silicon modified polyester
(SMP), high durability polyester (HDP), polyvinylidene fluoride (PVDF). Each topcoat is suitable for different situations. We suggest to use HDP or PVDF products when economic conditions permit.
For the selection of primer, epoxy resin should be
selected if adhesion and corrosion resistance are emphasized; polyurethane primer should be selected if flexibility and UV resistance are more concerned.
For the back coating, if the color coated steel plate is used as veneer, select two layers
of structure, that is, one layer of back primer and one layer of back finish. If the color coated steel plate is used as composite or sandwich plate, epoxy resin shall be applied on the back.
Effect of coating thickness on service life
steel plate coating can play a certain role in anti-corrosion, it uses the coating film to isolate the external corrosive substances. However, the film itself is porous from the microscopic point of view, and a small amount of water vapor in the air will
invade the coating, causing the coating to blister and possibly cause the coating to fall off. For the steel plate, the coating (galvanized or aluminized zinc) has a greater impact on the life of the steel plate.
For the sme coating thickness, the
secondary coating is denser than the primary coating, which has better corrosion resistance and longer service life. For the coating thickness, according to the relevant corrosion test results, we recommend that the front coating should be 20 μ m or more,
because sufficient film thickness can prevent corrosion within the validity period (PVDF requires a thicker coating thickness, usually more than 25 μ m due to its longer service life).