1.What is the UV resistance of galvanized coils and color-coated steel sheets?
Galvanized coil: Poor UV resistance. Zinc will oxidize under the action of ultraviolet rays from sunlight, oxygen and moisture to form "white rust" (basic zinc carbonate), making the surface gray and porous and losing its metallic luster.
Color coated steel plate is strong. Anti-ultraviolet agent and weather-resistant resin are added to the color coating, which can effectively resist the degradation of ultraviolet rays and maintain color and gloss for a long time.
2.What is the difference in appearance between galvanized coil and color-coated steel plate?
Galvanized coils lose their luster quickly and noticeably in a short period of time, becoming dull and showing white or gray corrosion products, which have a poor appearance.
Color-coated steel plates age slowly and steadily. High-quality color-coated steel plates can be guaranteed to last 5-10 years or even longer without noticeable fading, loss of gloss, or powdering.
3.Why is galvanized coil not "sun-resistant"?
What we commonly refer to as "exposure" is actually a comprehensive aging process, primarily involving the following:
Ultraviolet radiation: breaks down chemical bonds, causing material degradation.
Moisture (rain, dew): contributes to electrochemical corrosion.
Temperature fluctuations: cause thermal expansion and contraction, potentially leading to microcracks in the coating.
When galvanized coils are exposed directly, the zinc on the surface reacts with oxygen, carbon dioxide, and water in the air to form basic zinc carbonate (also known as "white rust"). This process is greatly accelerated in exposure to sunlight and rain. Although UV rays do not directly react with zinc, they accelerate these chemical processes. As a result, galvanized coils left outdoors quickly become dull and rough, losing their aesthetic appeal.
4.Why is color steel plate "sun-resistant"?
Color-coated steel sheets are made from galvanized steel coils. After surface pretreatment (cleaning and phosphating), they are coated with multiple layers of organic coatings (primer and topcoat), which are then baked and cured. This color coating serves the following functions:
Barrier effect: It completely isolates the zinc layer and steel base from the external environment.
UV resistance: The topcoat formula is specifically designed for weather resistance. The resin (such as PVDF) and stabilizers in it effectively absorb or reflect UV rays, protecting it and the underlying material from degradation.
Color and gloss retention: High-quality coatings maintain their vibrant color and surface gloss over time.
5.What are the scenarios when galvanized coils should be selected?
Internal structural components not directly exposed to the outdoors.
Substrates for other materials, such as color-coated panels and film-faced panels.
Temporary structures and warehouse enclosures where appearance is not a priority.
Workpieces requiring subsequent painting or other coating treatments.