How to further improve the anti-corrosion performance of powder coatings

Update:23-11-2019
Summary:

Powder coating and its coating technology is a new tech […]

Powder coating and its coating technology is a new technology and new technology that has been rapidly developed in China for more than ten years. It has the advantages of saving energy and resources, reducing environmental pollution, simple process, easy automation, strong and durable coating, and powder recyclable. Reuse features. But corrosion problems have plagued the coatings industry.

Physical barrier protection is achieved by means of thickening and anti-seepage of the layered filler. The layered fillers widely used in anticorrosive powder coatings are mainly micaceous iron oxide, sericite and glass flakes. Corrosive media tends to migrate and diffuse linearly in coatings containing spherical fillers, which greatly delays the corrosion progress of the coating. It should also be pointed out that the flaky filler may be difficult to maintain the original sheet shape during the powder coating processing and extrusion process, which limits its application in powder coatings.

In principle, metals that are more reactive than the electrochemical properties of the substrate can be used as pigment fillers for anticorrosive coatings. However, at present, the most widely used metal zinc particles, it is reported that the average diameter of the particles of the ring zinc to achieve the best anti-corrosion performance is 2 μm. The anti-corrosion mechanism of metal zinc is that zinc participates in the corrosion reaction to produce insoluble materials such as ZnFe2O4 and basic zinc carbonate. In particular, after replacing the traditional spherical zinc with flaky metallic zinc, the flaky metallic zinc has unique parallel lap joints. The shielding function further improves the anti-corrosion properties of the coating.

Sustained-release type pigments and fillers can be classified into cathode type and anode type according to the type of reaction involved. Cathodic corrosion inhibitors, such as inorganic salts of magnesium and aluminum, inhibit corrosion of the coating by initiating in situ reaction with hydroxide ions in a neutral environment. An anodic corrosion inhibitor, such as a phosphate, silicate or hydroxide, forms an oxidized protective layer on the metal surface. If the reaction slow release type of filler is insufficient, this will result in a poor electrode area, which will accelerate the corrosion progress. At present, the most widely used slow release type pigments and fillers are phosphate-containing pigments such as zinc phosphate and magnesium phosphate. In addition, there is a class of less toxic slow release pigments, which are spinel-type pigments based on metal oxide mixtures.

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