Interpretation of common problems during UV aging test1

Weather and sunlight exposure are major causes of damage to coatings, plastics, inks, and other polymeric materials, including loss of gloss, discoloration, yellowing, cracking, peeling, embrittlement, loss of strength, and delamination. Even indoor light and sunlight transmitted through glass windows can degrade some materials, such as causing pigments, dyes, etc. to fade or discolor. Since solar radiation has dual effects of thermal radiation and photochemical effects, high temperature test cannot replace light aging test, and pure ultraviolet radiation and infrared radiation cannot replace solar radiation test. Therefore, it is very necessary to test the UV aging test specifically for the product. At present, the UV aging test for the product is mainly tested by the artificial accelerated UV aging test, which is our common UV aging test. This article focuses on introducing you about the UV aging test. test process. UV aging test principle: UV aging belongs to sunlight aging, UV is the abbreviation of Ultraviolet (ultraviolet), and is usually used to evaluate the aging speed of products under ultraviolet light. Sunlight aging is the main aging damage to outdoor materials. For indoor use materials, it will also be subject to a certain degree of aging caused by sunlight irradiation or ultraviolet rays in artificial light sources (such as ultraviolet lamps, ultraviolet bands in fluorescent lamps, etc.). The solar radiation is mainly concentrated in the visible light part (400nm ~ 760nm), and the wavelength of the infrared light is greater than that of the visible light (>760nm) and less than visible light ultraviolet (<400nm) is less. In the total radiant energy, the wavelength between 150nm and 4000nm accounts for more than 99%, and it is mainly distributed in the visible light region and the red and ultraviolet regions. The visible light region accounts for about 50% of the total solar radiation energy, and the infrared region accounts for about 43%. The solar radiation 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 rays, B rays and C rays (referred to as UVA, UVB and UVC), and the wavelength ranges are 400-315nm, 315-280nm and 280-190nm respectively. According to ASTM G154, UV (ultraviolet) cannot simulate the full spectrum of sunlight. Its principle is that for durable materials exposed to the outdoors, the short-wavelength wavelength of ultraviolet rays of 300~400nm is the most important cause of aging damage. In the short wavelength region of ultraviolet light, 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: illumination, condensation and spray. Lighting stage: simulate the length of daytime light in the natural environment (usually between 0.35W/m2~1.35W/m2, and the solar light 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 test requirements of different regions and industries. Condensation stage: Simulate the phenomenon of fog 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. Spray stage: The process of raining is simulated by continuously spraying water on the surface of the sample. Because the artificial UV accelerated aging test conditions are much harsher than the natural environment, the aging damage that can occur in the natural environment for several years can be simulated and reproduced in a few days or weeks. Material aging: Material aging includes fading (the denaturation of organic dyes in the natural environment), strength reduction (fracture of polymer materials), cracking (fracture of macromolecules and stress), chalking (fracture and reorganization of macromolecules), coating peeling ( The hydrogen bond between the coating and the base layer is broken), etc. In addition, according to the difference in spectral distribution, fluorescent UV lamps can be divided into UVA and UVB lamps, in which UVA lamps emit light below 300nm, which is less than 2% of the total output light energy, while UVB lamps emit light below 300nm. The light energy is greater than 10% of the total output light energy. There are three kinds of commonly used UV aging lamps: UVA-340: The main purpose is to simulate the short and medium wavelength range in the ultraviolet part of sunlight, and it is generally used for the photoaging test of outdoor products. UVA-351: The main purpose is to simulate the short and medium wavelength range in the ultraviolet part of sunlight filtered by window glass, which is generally used in indoor products. UVB-313: They emit a considerable amount of radiation below 300nm, which is the nominal cut-off wavelength of solar radiation. This will cause some aging phenomena that do not occur outdoors. It is not recommended to use this light to simulate sunlight. This test is widely used primarily for durability testing of accelerated materials as a qualitative comparison of two or more materials. Others: Other common UV test standards, such as ISO4892.3, GB16422.3, also have a more detailed introduction to UV test. But which standard is the most suitable should be measured according to product requirements and customer requirements. For the specific test requirements in the standard, you can refer to the relevant standards, but the standard also clearly states that the test conditions are for reference only, not mandatory. More about: UV Aging Tester

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