Primer plays a vital role in the paint system. It is the first layer of the coating system and is mainly used to enhance the adhesion of the topcoat, improve the uniformity of the coating, increase the fullness of the coating and provide resistance Alkaline and anti-corrosion features. Additionally, primer ensures the performance of the entire paint system.
Electrochemical properties of zinc powder:
Zinc powder is an important electrochemical anti-corrosion pigment. It is lighter than iron, has excellent ductility, and can be alloyed with iron. Importantly, zinc powder has high electrochemical activity, and its standard electrode potential is -0.76V, which is more active than iron's potential (-0.44V). Because of this potential difference, the zinc powder will corrode first as it acts as the anode in the coating, while the base steel acts as the cathode and is therefore protected.
The mechanism of action of zinc-rich primer:
In zinc-rich primers, when the coating is corroded, the zinc powder acts as the anode and is corroded first, while the base steel becomes the cathode and is therefore protected. Zinc generates oxides during the corrosion process, and these oxides seal the coating to a certain extent and enhance the protection of the substrate. In addition, the zinc powder in the coating is gradually consumed, but very slowly. This results in a reduction in the potential difference between the coating and the substrate, so that when the coating is damaged, the newly exposed metallic zinc will rapidly increase the potential difference, resulting in a strong cathodic protection effect. Therefore, even if the coating is damaged, the rust in the zinc-rich coating will not spread to the surroundings.
Classification and zinc content of zinc-rich primers:
Zinc-rich primers are generally divided into two types: inorganic zinc-rich primers and organic zinc-rich primers.
Inorganic zinc-rich primer uses silicate as the binder, and the zinc powder content is not less than 74%.
Organic zinc-rich primer uses epoxy resin as a binder, with a zinc powder content of not less than 77%.
Organic zinc-rich primers are less conductive and therefore contain higher amounts of zinc. In some single-coat long-lasting anti-corrosion inorganic zinc-rich primers, the zinc powder content can reach 75% in water-soluble primers, and even more than 82% in solvent-based primers.
Characteristics of epoxy zinc-rich primer:
Epoxy zinc-rich primer uses zinc powder as filler, solid epoxy resin as base material, polyamide resin or amine adduct as curing agent, and an appropriate amount of mixed solvent. The content of zinc powder in this primer is usually over 85% to ensure a continuous, tight coating that is in close contact with the metal. Since zinc has a lower potential than steel, when the coating is corroded, the zinc in the coating acts as an anode and is corroded first, while the base steel acts as a cathode and is therefore protected. The oxidation products of zinc play a sealing role in the coating and enhance the protection of the coating film on the substrate.
Epoxy zinc-rich primer has the following properties:
Dry quickly
Recoat intervals are relatively short
Impact resistant
Heat resistance up to 120°C
Good wear resistance
Strong adhesion and good adhesion to the next coating
Application scope:
Epoxy zinc-rich primer is suitable for use in many fields, including but not limited to chemical equipment, petroleum equipment, electric power equipment, railways, bridges, pipelines, automobiles, tractors, cranes, boilers, machine tools, steel structure workshops, hydraulic equipment, etc. Manufacturing and repair. It performs particularly well in acidic and saline environments.
The preparation method includes mixing epoxy resin, zinc powder and curing agent in an appropriate mixed solvent. During the construction process, the curing agent needs to be mixed according to a certain mass ratio to achieve curing. Due to its high zinc content, epoxy zinc-rich primers do not cause damage and peeling during the welding process and are therefore suitable for shop pre-priming. A 20μm epoxy zinc-rich primer coating provides corrosion protection for over 6 months.
Conclusion:
Epoxy zinc-rich primers are not only guardians of steel structures, they also play a key role in multiple industrial sectors. Its electrochemical anti-corrosion mechanism and high zinc content make it a reliable coating option that can extend the service life of equipment and structures, reduce maintenance costs, and improve safety performance. In the future, environmental protection and sustainability will continue to drive innovation in the field of anti-corrosion coatings to ensure that various equipment and infrastructure can resist the threat of corrosion and erosion in the long term.
