1.What is the main reason for fading due to high temperature?
Thermal degradation of resin: Organic resins (polyester, silicon-modified polyester, fluorocarbon, etc.) in the coating will undergo chemical reactions such as molecular chain breakage and oxidation under continuous high temperatures, causing the coating to become powdery, glossy, and brittle. This degradation will accelerate the exposure and shedding of pigments, which will manifest as fading.
Insufficient thermal stability of pigments: Some organic pigments or low-quality inorganic pigments are chemically unstable at high temperatures and are prone to decomposition or discoloration (e.g. some red and orange pigments tend to darken or turn brown). High temperatures can significantly accelerate this change.
Thermal oxidation: Under high temperature conditions, oxygen is more likely to react with the resin and pigment in the coating (thermal oxidation), causing aging and discoloration of the material.
Synergistic effect with UV rays (most common): High temperatures greatly accelerate the photochemical reaction caused by UV rays! This is the main reason for fading in high temperature outdoor environments (such as roofs in summer): High temperatures make resin molecules more active and more easily damaged by UV rays. High temperatures promote the consumption and failure of UV absorbers/stabilizers. Dark coatings absorb more heat, and the surface temperature can reach 70°C~80°C or even higher (much higher than the air temperature), forming an extreme aging environment of "high temperature + strong UV rays".
2.How do different finish types perform at high temperatures?
PVDF (fluorocarbon coating): Best high temperature resistance: Fluorocarbon bonds have extremely high bond energy and excellent thermal stability, and the long-term use temperature can reach 120°C.
Performance: In a pure high temperature (no strong UV) environment, PVDF itself will hardly fade due to thermal degradation. In the "high temperature + strong UV" outdoor environment, its excellent weather resistance can resist fading and chalking to the greatest extent, and its color retention is far superior to other coatings.
SMP (silicon modified polyester): Design advantage is heat resistance: By introducing silicone, the heat resistance of the coating is significantly improved (temperature resistance can reach 100°C~120°C) and heat deformation resistance.
Performance: In pure high temperature environment (such as kitchen equipment, chimney packaging), the heat discoloration resistance is worse than standard polyester. However, in the outdoor "high temperature + strong UV" environment, its UV resistance is not as good as HDP or PVDF, and the fading risk caused by comprehensive weather resistance is higher than HDP/PVDF.
HDP (High Durability Polyester): Improved Weathering Resistance: UV resistance and weathering resistance have been greatly improved by optimizing the resin and adding high-efficiency additives (UV absorbers, light stabilizers).
Performance: Heat resistance is better than standard polyester but lower than SMP/PVDF. In high-temperature outdoor environments, its excellent UV resistance is the key to preventing fading. Its overall performance is better than SMP and close to PVDF (especially in terms of anti-powdering and color retention).
PE (standard polyester): The weakest heat resistance: When exposed to an environment above 80°C for a long time, the risk of thermal degradation increases significantly.
Performance: In a high temperature environment (especially when superimposed with ultraviolet rays), the resin is prone to powdering and degradation, and the pigment is easily exposed and falls off, fading and losing gloss the fastest. Dark and bright colors are particularly sensitive.
3.What are the key factors affecting fading?
Topcoat resin type, pigment quality and type, temperature level and duration, whether UV is superimposed, coating thickness, substrate temperature
4.How do these influencing factors affect high temperature fading?
Topcoat resin type: PVDF > SMP ≈ HDP > PE (PVDF has the best heat resistance and comprehensive weather resistance; SMP has good pure heat resistance but is not as good as HDP in comprehensive weather resistance; PE is the worst).
Pigment quality and type: Inorganic pigments with good heat resistance (such as titanium dioxide and iron oxide series) are far superior to organic pigments. Dark/bright organic pigments are more likely to change color at high temperatures.
Temperature level and duration: The higher the temperature (especially >80°C) and the longer the exposure time, the more fading risk increases sharply.
Whether to superimpose ultraviolet rays: High temperature + ultraviolet rays are the most stringent combination for outdoor fading, and the synergistic destructive effect is extremely strong.
Coating thickness: A thicker topcoat layer provides a better physical barrier to delay the penetration of heat and ultraviolet rays.
Substrate temperature: Dark coatings and poorly ventilated environments will greatly increase the actual surface temperature of the color board (30°C+ higher than the air temperature), exacerbating deterioration.
5.How to prevent or reduce high temperature fading?
Choose the right coating: PVDF is the first choice: used in high temperature or strong UV environments (such as metal roofs, tropical/highland areas, industrial plants).
HDP is the second choice: a cost-effective choice with excellent weather resistance, suitable for most high-temperature outdoor scenes.
Use SMP with caution: only use it in situations where heat resistance is the main concern and UV rays are weak (such as high-temperature equipment that is not exposed to direct sunlight).
Avoid PE: not recommended for continuous high temperature or harsh outdoor environments.
Choose stable pigments: Require suppliers to use highly weather-resistant and heat-resistant pigments (especially sensitive colors such as red, yellow, and orange). Light colors (white, light gray) are usually more stable.
Pay attention to surface temperature control: Strengthen ventilation and heat dissipation design to avoid local overheating (such as roof ridges and poorly ventilated areas). Consider using light-colored or highly reflective coatings to reduce heat absorption (such as cool roof coatings).