Weather resistance refers to the durability of a powder coating film when exposed to outdoor atmospheric conditions.
Almost all traffic guardrails are used outdoors. The atmospheric environment including sunlight, oxygen and ozone, hot and cold temperature changes, water and relative humidity, as well as microorganisms and insects will all affect the service life of the coating.
Traffic guardrails generally need to be used outdoors for more than 10 years without obvious discoloration, cracks and cracks, and maintain the integrity and decorativeness of the coating film. Therefore, the weather resistance requirements of powder coatings are very important.
The main factor affecting weather resistance is sunlight. In sunlight, only the light energy with wavelengths of 250 to 1400 nm radiates to the earth's surface. Among them, the wavelength of 780 to 1400 nm is infrared, accounting for 42% to 60% of the total solar radiation. It mainly radiates heat energy to objects; the wavelength of 380 to 780 nm is visible light. , accounting for 39% to 53% of the total solar radiation, mainly affects objects through thermal energy and chemical reactions; ultraviolet light with a wavelength of 250~400nm mainly affects objects through chemical reactions.
Tests have shown that the most destructive effect on polymer resins is ultraviolet rays with a wavelength of 290 to 400 nm, especially ultraviolet rays with a wavelength of about 300 nm, which is the main factor leading to the deterioration of polyolefin resins.
Temperature has an impact on weather resistance. For every 10°C increase in temperature, the photochemical reaction rate will double.
In addition to causing hydrolysis reaction and water absorption deformation of the coating film, rainwater also has erosion and damage effects. Water can wash away dirt and aging products on the guardrail surface, but it reduces the protective effect and accelerates the aging trend.
Improving the weather resistance of powder coatings means studying the factors that cause coating film deterioration and finding countermeasures to solve the problems. In recent years, my country's powder coatings have done a lot of fruitful work in raw material selection, additive preparation, mixing, extrusion and crushing, which has significantly improved the weather resistance of powder coatings.
However, it should be pointed out that the current quality of powder production in my country is uneven, with large differences. A few manufacturers purely pursue profits, add recycled materials, fill with cheap additives, lack inspection methods, and have low product quality. The powder will change color and crack within a short time after coating. , and a good powder-coated traffic guardrail can indeed reach more than 10a for outdoor use.
The weather resistance test often uses artificial accelerated aging test and natural climate exposure test. The artificial aging test simulates atmospheric conditions and then compares it with the sample. It can only calculate the equivalent outdoor aging time. The results of the natural exposure test are more realistic, but take a longer time.
