The purity of the coating is high, so the corrosion resistance of the coating with the same thickness is better than that of the hot-dip galvanizing product. According to the test, the red rust resistance time of one micron coating is 12 hours for electro
galvanizing and less than 10 hours for hot galvanizing. However, it is very difficult to obtain thick electroplated zinc coating (high power consumption, high cost, and technical difficulty). As a color coated substrate, electroplated zinc is also mainly
used in household appliances, steel furniture, doors and windows, etc.
The formulation of coil coating usually contains several components, and the raw materials generally used are:
Pigment coloring pigment, antirust pigment, physical pigment;
Resin: polyester, high weather resistant polyester, silicon modified polyester, epoxy, poly, PVC, etc;
Solvents: aromatics, esters, ethers, etc;
dispersant, agent, surfactant, etc;
Others: catalyst, organic or inorganic filling agent, functional assistant (conductive material, agent, etc.).
The main component of the coating is resin, which is used as the base material in the coating
formulation. According to different coatings, coatings can be divided into three categories: primer, finish and back pain
Primer: the primer can be divided into polyester primer, polyurethane primer, epoxy primer, etc. according to the different
needs of users, different primers can be selected. Commonly used is epoxy primer and polyurethane primer, with zinc chrome yellow, strontium chrome yellow and other antirust pigment processing and manufacturing.
Topcoat: generally, polyester resin,
high weather resistant polyester resin, silicone modified polyester resin, resin, polyvinylidene resin and polyurethane are used. The heat curing cross-linking curing system uses methyl ether resin or closed resin, and pigments with high temperature and
weather resistance are selected.
Back paint: at present, it is divided into 2 / 1, 2 / 2 and 2 / 1m systems in China. The back of 2 / 1 system can be painted with one primer or only one coat of back paint, which is mainly used for sandwich panel,
and the coating is required to have good bonding and foaming performance. 2 / 2 system adopts two coating system of primer and back paint, which generally does not require foaming performance and is used as single board. 2 / 1m system is generally applied
with 3 μ m primer and 6 μ m back paint, which can replace 2 / 1, and the back can be foamed.
PVDF fluorocarbon coating
PVDF fluorine-containing resin coating (≥ 70%) started in 1960s. After more than 60 years of practical use, it has been
proved that the weather resistance is very excellent, which is different in the current coil coating, and fluorine polymer also has very high chemical properties.
PVDF resin has UV resistance, but it can't block UV by itself. It needs to use pigments
in the coating to block UV, so that the primer won't be eroded by UV. Therefore, the pigments used must have excellent weather resistance and chemical resistance, and can withstand 20-30 years of outdoor exposure. Most of the organic pigments will degrade
or fade under the action of sunlight and atmosphere, while the inorganic high-temperature calcined metal oxide pigments have relatively better chemical properties and are suitable for long-term protection.
In recent years, fluorine-containing resins
copolymerized with trifluorochlor and ester monomers have become popular in China, which are widely used in exterior walls and metal plates of buildings. Because the content of ester monomers and fluorine which are easy to hydrolyze is lower than PVDF,
there is a certain gap between their weatherability and PVDF
HDP high weather resistant polyester coatin present, the common polyester coating is mainly used for building color board. After 8-10 years of use, the coating will gradually lose
light, protection and decoration. In the synthesis of high weather resistant polyester (HDP) resin, the monomer with cyclohexane structure is used to achieve the balance of flexibility, weather resistance and cost of the resin. The polyol and polyacid
without group are used to absorb the UV light of the resin to achieve the high weather resistance of the coating. UV absorbers and HALS were added to the coating formulation.
P silicone modified polyester
The silicone modified polyester coil
coating is modified by cold splicing of silicone resin and tight ester resin, which can guarantee outdoor weatherability for 10 years. The effective way is to directly modify the polyester resin with silicone monomer, further improve the weather resistance
of the silicone modified polyester resin, so that the coating can reach the outdoor weather resistance for 20 years, and become a hot spot. In the modification of polyester resin, the commonly used organosilicon intermediate, when the content of organosilicon
reaches 30% of the resin proportion, and the metal oxide pigment calcined at high temperature is used, the coating section can reach the requirements of 25 years' weather resistance, next to the fluororesin coating.