1. What is "fading" in galvanized color-coated coils?
Simply put, fading refers to the gradual lightening, darkening, and loss of vibrancy of the surface color of the sheet material. You can think of it like a poor-quality garment that fades slowly after repeated washing in sunlight. Professionally, this usually manifests in two phenomena:
Color change: This refers to a change in color, such as fading from a bright red to a dull pink or white.
Loss of gloss: This means a decrease in the coating's gloss, resulting in a dull and lackluster surface, no longer looking new.
Fading is the initial sign of coating aging. Over time, it may further develop into coating chalking, cracking, and ultimately, corrosion of the substrate.
2. How do inherent deficiencies in the coating and pigments themselves lead to fading?
A: The coating is like the "skin" of the color-coated steel sheet; its material directly determines its resistance to aging. This is the core internal reason for fading.
Differences in coating resins: Different resins have vastly different weather resistance. Ordinary polyester coatings (PE) are like "skin easily sunburned," with the weakest UV resistance, making them most prone to decomposition and fading under prolonged outdoor exposure. In contrast, fluorocarbon coatings (PVDF) are like having built-in "powerful sunscreen," with an extremely stable molecular structure that effectively resists UV rays, maintaining long-lasting vibrant colors.
The impact of pigment quality: Just like dyes on clothing, the quality of the pigments is crucial. Inferior pigments or light-sensitive organic pigments (especially certain red and yellow pigments) are prone to chemical changes under light, causing rapid color shift. Inorganic pigments are generally more stable, but can also fade due to poor quality.
3.What operational errors in the production process accelerate fading?
A: If the material is the "innate gene," then the production process is the "acquired cultivation." Any negligence in the production process can create hidden dangers for fading.
Incomplete pretreatment: This is the most basic and most problematic step. If oil and impurities on the substrate surface are not thoroughly cleaned, or if phosphating and passivation treatments are inadequate, the coating will be like "paper stuck on dirty glass," with significantly reduced adhesion. This will cause the coating to develop micro-cracks prematurely under environmental stress, opening the "easy door" for fading and chalking.
Improper curing process: Curing is crucial for the formation of a dense protective layer. If the baking temperature is insufficient or the time is too short, the coating is like an "underbaked cake," with incomplete cross-linking between internal resin molecules, leading to a significant decrease in its weather resistance and chemical stability, and a sharp drop in fading resistance of more than 30%. Conversely, over-baking will also degrade the coating performance and affect color stability.
Poor coating thickness control: When the coating is too thin (e.g., ≤15μm), it's like wearing a thin coat, unable to effectively resist external erosion; while when it's too thick (e.g., >30μm), it may crack due to excessive internal stress. In addition, uneven coating can also cause localized areas to fade prematurely.
4. How does the external environment accelerate fading?
A: Even the best products are susceptible to damage from harsh environments. The external environment is the direct cause of and accelerates fading, primarily acting as a catalyst.
* **Ultraviolet Radiation:** This is the number one culprit for outdoor fading. Ultraviolet rays in sunlight have high energy and continuously damage the molecular chains of the coating resin, leading to polymer degradation-a process known as "photo-oxidative degradation." In areas with strong ultraviolet radiation, this destructive process is greatly accelerated.
* **Chemical Corrosion:** Acidic waste gases emitted from industrial areas (forming acid rain) and salt spray in coastal areas continuously erode the coating surface, causing chemical fading and loss of gloss.
* **Temperature, Humidity, and Temperature Difference:** High temperatures soften the coating, making it more susceptible to the adhesion of corrosive media. Large diurnal temperature variations cause repeated thermal expansion and contraction of the coating, leading to fatigue and the formation of microcracks, providing pathways for moisture and contaminants to penetrate the coating.
5. From selection to use, what suggestions can be made to prevent or delay fading?
A: To delay fading, you can focus on three aspects: material selection, processing, and use and maintenance:
Material Selection: Focus on the "base material"
Choose a high-weather-resistant coating: For outdoor use, if the budget allows, prioritize PVDF fluorocarbon coatings. Although more expensive, it offers the strongest UV resistance and fade resistance, with a warranty period typically exceeding 20 years. If the budget is limited, choose high-durability polyester coatings such as HDP.
Prefer stable color schemes: Choose stable color schemes based on inorganic pigments, such as gray and white. If you must use bright colors like red or yellow, be sure to confirm that the manufacturer uses high-quality lightfast pigments.
Request warranties and reports: Request specific warranty commitments from the supplier and review third-party testing reports such as QUV accelerated aging tests to confirm that its fade resistance meets standards.