1.How does temperature affect the rate of chemical aging?
The doubling rule of chemical reaction rates: According to Van der Hoff's empirical rule, for every 10°C increase in temperature, the rate of most chemical reactions increases by approximately 2-4 times.
Impact on coatings: Coating aging is essentially a series of complex chemical reactions, such as the oxidation and degradation (molecular chain breakage) of resin polymers, and the fading and chalking of pigments.
Under sustained high temperatures (e.g., the surface temperature of color steel plates under direct sunlight can reach above 60-80°C), these chemical reactions are accelerated dramatically, leading to premature coating aging:
Loss of gloss and fading: Pigments and resins lose their original properties due to accelerated oxidation.
Chalking: Surface resin decomposes, exposing pigment particles.
Embrynerateing and cracking: Resin molecular chains break, resulting in loss of flexibility.
2.What are the combined effects of temperature and ultraviolet radiation?
Ultraviolet (UV) radiation is the primary agent responsible for breaking the chemical bonds in coatings. High temperatures significantly enhance the damaging effects of UV radiation on polymers.
The intense sunlight of summer brings the strongest UV radiation and the highest temperatures, making summer the peak period for coating aging.
3.What are the combined effects of temperature and humidity?
High temperatures accelerate the penetration and diffusion of water molecules (including water vapor) within the coating.
When water molecules penetrate the coating or reach the interface between the coating and the substrate, the high temperature triggers a hydrolysis reaction, promoting corrosion and causing the coating to blister and peel off.
This damage is particularly severe in hot and humid climates.
4.What are the synergistic effects of temperature and temperature difference cycling?
This is mechanical and physical damage, equally important as the chemical damage mentioned above.
Diurnal and seasonal temperature differences cause repeated thermal expansion and contraction of the color-coated steel sheet. The difference in thermal expansion coefficients between the coating and the metal substrate generates continuous shear stress at the interface.
Over time, this cyclic stress leads to gradual fatigue of the coating, resulting in microcracks and accelerating the intrusion of moisture and corrosive media.
The greater the temperature difference and the higher the frequency (e.g., large diurnal temperature variations in desert regions), the more severe this thermal stress fatigue becomes.
5.What are the effects of critical temperature nodes?
A key physical property parameter of coating resins is their glass transition temperature (Tg).
When the ambient temperature approaches or exceeds the Tg of the coating, the resin transitions from a glassy state to a highly elastic state. Its hardness, adhesion, and stain resistance decrease dramatically, making it soft and vulnerable, thus greatly accelerating the aging process.