1.How to choose coating materials in high temperature and high humidity environments?
High temperature accelerates the evaporation and penetration of water, while high humidity causes a long-term water film to adhere to the surface of the coating, which is prone to electrochemical corrosion. Resins with strong water resistance and high chemical stability should be given priority, such as:
Fluorocarbon resin (PVDF): It has a stable molecular structure and is extremely resistant to water, moisture and heat, and UV aging. It can still maintain the integrity of the coating in a high humidity environment above 60°C, and is suitable for high temperature and high humidity areas such as coastal areas and Southeast Asia.
High weather-resistant polyester (HDP): It has a higher cost-effectiveness than PVDF, and better moisture and heat resistance than ordinary polyester, which can meet the needs of medium high temperature and high humidity environments (such as the rainy season in the south).
2.How to choose coating materials in low temperature and dry environment?
Low temperature may cause the coating to become brittle. If there is a large temperature difference between day and night, the coating is prone to microcracks due to thermal expansion and contraction, which becomes a channel for the penetration of corrosive media. It is necessary to select resins with excellent low-temperature flexibility, such as:
Polyurethane resin: It still maintains good elasticity at low temperatures, is not easy to become brittle and crack, and is suitable for cold areas below -30℃.
Modified polyester (such as adding toughening agent): Improve the impact resistance of the coating at low temperatures and reduce the risk of cracks.
3.How to enhance the "shielding" and "self-healing" properties of the coating?
Shielding fillers: Add mica powder, glass flakes, talcum powder and other flaky fillers to the coating to form a physical barrier and extend the penetration path of water and oxygen (for example, glass flakes can extend the penetration path by 5-10 times); add nano-silicon dioxide, zinc oxide, etc., and use the high specific surface area of nanoparticles to fill the pores of the coating to further block penetration.
Sacrificial/corrosion-inhibiting ingredients: Add zinc powder (such as epoxy zinc-rich primer) to the primer. When the coating is damaged, the zinc powder will corrode preferentially as a sacrificial anode to protect the substrate; or add corrosion inhibitors such as chromate (molybdate and silicate can be used for chromium-free systems), which will be released and adsorbed on the substrate surface when water penetrates to inhibit electrochemical corrosion.
4.How to optimize the curing process and improve the cross-linking density of the coating?
Insufficient coating curing will result in unreacted groups remaining in the resin, which are easy to absorb moisture and cause swelling, reducing corrosion resistance. Required:
Precisely control the curing temperature and time to ensure that the resin is completely cross-linked and reduce residual solvents or unreacted monomers.
Use the "gradient curing" process: low-temperature pre-curing (removing solvents) → high-temperature cross-linking (promoting resin reaction) → low-temperature cooling (avoiding internal stress in the coating due to sudden cooling) to reduce the risk of cracking of the coating under temperature and humidity changes.
5.How to choose a highly corrosion-resistant substrate?
Galvanized substrate (GI): The zinc layer protects the steel substrate through the "sacrificial anode". The higher the zinc layer thickness (such as above 80g/m²), the longer the protection period in high humidity and high salinity environments (suitable for coastal non-extreme corrosion environments).
Galvanized substrate (GL): The aluminum-zinc alloy layer (55% aluminum, 43.4% zinc, 1.6% silicon) forms a dense oxide film, which is better than galvanized in moisture and heat resistance, and is not easy to oxidize and fail at high temperatures (suitable for high temperature, high humidity + strong ultraviolet environment, such as tropical areas).
Cold-rolled substrate + thick coating: If the environment is dry (such as inland), cold-rolled substrate can be used, but it needs to be matched with thick primer (≥20μm) + weather-resistant topcoat to completely isolate the corrosive medium through the coating.