Interpretation of common problems during UV aging test

Climate and sunlight are the main causes of damage to coatings, plastics, inks and other polymer materials. Such damages include loss of gloss, fading, yellowing, cracking, peeling, embrittlement, strength reduction, and delamination. Even indoor light and sunlight transmitted through glass windows will age some materials, such as causing pigments and dyes to fade or change color. Because solar radiation has the dual effects of thermal radiation and photochemical effects, high-temperature tests cannot replace light aging tests, and pure ultraviolet and infrared radiation cannot replace solar radiation tests. Therefore, the UV aging test for products is very necessary. At present, the UV aging test for products is mainly through the artificial accelerated UV aging test, which is our common UV ultraviolet aging test. This article focuses on introducing you to the UV ultraviolet aging test. The flow of the experiment. UV ultraviolet aging test principle: UV aging belongs to sunlight aging. UV is the abbreviation of Ultraviolet (ultraviolet). It is usually used to evaluate the aging speed of products under ultraviolet rays. Sunlight aging is the main aging damage to outdoor materials. For indoor materials, they are also subject to a certain degree of aging due to sunlight or ultraviolet rays in artificial light sources (such as ultraviolet lamps, ultraviolet bands in fluorescent lamps, etc.). Solar radiation is mainly concentrated in the visible light part (400nm～760nm), and there are few parts of infrared light (>760nm) with wavelength greater than visible light and ultraviolet light (<400nm) less than visible light. Among the total radiant energy, more than 99% have wavelengths between 150nm and 4000nm, and they are mainly distributed in the visible region and the red and ultraviolet regions. The visible region accounts for about 50% of the total solar radiation energy, and the infrared region accounts for about 43%. Solar radiation energy in the ultraviolet region is very small, accounting for only about 7% of the total. Ultraviolet light is a general term for radiation with wavelengths from 10nm to 400nm in the electromagnetic spectrum, which cannot cause people's vision. Ultraviolet light is divided into A ray, B ray and C ray (abbreviated as UVA, UVB and UVC), and the wavelength ranges are 400-315nm, 315-280nm, and 280-190nm respectively. According to the introduction of ASTM G154, UV (ultraviolet) cannot simulate full-spectrum sunlight. Its principle is that for durable materials exposed outdoors, the short-wavelength wavelength of ultraviolet light of 300~400nm is the main cause of aging damage. In the short-wave region of ultraviolet rays, that is, from 365nm to the lowest wavelength of sunlight, UV fluorescent lamps can simulate sunlight well. UV aging test stage: UV aging test can set three aging modes: light, condensation and spray. Illumination stage: Simulate the length of daylight in the natural environment (usually between 0.35W/m2~1.35W/m2, and the solar intensity at noon in summer is about 0.55W/m2) and test temperature (50℃~85℃) , In order to simulate the various use environments of the product and meet the testing requirements of different regions and industries. Condensation stage: Simulate the phenomenon of fogging on the surface of the sample at night, turn off the fluorescent UV lamp (dark state) in the condensation stage, only control the test temperature (40~60℃), and the humidity of the sample surface is 95~100%RH. Spraying stage: It simulates the process of rain by continuously spraying water on the surface of the sample. Because the artificial ultraviolet accelerated aging test conditions are much harsher than the natural environment, the aging damage that can only occur in the natural environment for several years can be simulated and reproduced within a few days or weeks. Material aging: Material aging includes fading (organic dyes are denatured in the natural environment), strength reduction (polymer material fracture), cracking (polymer fracture and stress action), chalking (polymer fracture and reorganization), coating shedding ( The hydrogen bond between the paint and the base layer is broken) and so on. In addition, according to the different spectral distributions, fluorescent ultraviolet lamps can be divided into UVA and UVB lamps. Among them, UVA lamps emit light energy below 300nm less than 2% of the total output light energy, and UVB lamps emit light below 300nm. The light energy is greater than 10% of the total output light energy. There are three commonly used UV aging lamps: UVA-340: The main purpose is to simulate the short and medium wavelength range in the ultraviolet part of the sun, and it is generally used for the light aging test of outdoor products. UVA-351: The main purpose is to simulate the short and medium wavelength range in the ultraviolet part of the sunlight filtered by the window glass. It is generally used for indoor products. UVB-313: They emit a considerable amount of radiation below 300nm, and 300nm is the nominal cutoff wavelength of solar radiation. This will cause some aging phenomena that do not occur outdoors. It is not recommended to use this lamp to simulate sunlight. This kind of test is mainly used to accelerate the durability test of materials, as a qualitative comparison of two or more materials. Other: Some other common UV test standards such as ISO4892.3, GB16422.3, also have a more detailed introduction to UV test. However, which standard is most suitable depends on product requirements and customer requirements. For the specific test requirements in the standard, you can refer to the relevant standard, but the standard also clearly states that the test conditions are for reference only and are not mandatory. More about: UV weathering tester

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