Views: 340 Author: Site Editor Publish Time: 2020-05-19 Origin: Site
Climate and sunlight exposure are the main causes of damage to paints, plastics, inks, and other polymer materials. Such damage includes loss of gloss, discoloration, yellowing, cracking, peeling, embrittlement, reduced strength, and delamination. Even indoor light and sunlight transmitted through glass windows will cause some materials to age, such as causing fading or discoloration of pigments and dyes. Because solar radiation has the dual effects of thermal radiation and photochemical effects, high temperature tests cannot replace light aging tests, nor can pure UV radiation and infrared radiation replace solar radiation tests.
UV aging belongs to sunlight irradiation aging. UV stands for Ultraviolet (Ultraviolet). It is usually used to evaluate the speed of product aging under ultraviolet rays. Sunlight irradiation aging is the main aging damage suffered by materials used outdoors. For indoor materials, it is also A certain degree of aging due to sunlight irradiation or aging caused by ultraviolet rays in artificial light sources (such as ultraviolet lamps, ultraviolet bands in fluorescent lamps, etc.).
Solar radiation is mainly concentrated in the visible part (400nm ~ 760nm), and the infrared part with a wavelength greater than visible light (> 760nm) and less than visible light (<400nm) are few. Of the total radiant energy, the wavelength between 150nm and 4000nm accounts for more than 99%, and 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 energy in the ultraviolet region is very small, accounting for only about 7% of the total.
Ultraviolet light is a general term for radiation in the electromagnetic spectrum with a wavelength from 10nm to 400nm, and cannot cause people's vision. Ultraviolet light is divided into A ray, B ray and C ray (abbreviated as UVA, UVB and UVC), the wavelength range is 400-315nm, 315-280nm, 280-190nm.
According to the introduction of ASTM G154, UV (ultraviolet) cannot simulate full spectrum sunlight. Its principle is that for long-lasting materials exposed outdoors, the short-wavelength wavelength of 300 to 400 nm of ultraviolet rays is the most important 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 can set three aging modes: light, condensation and spray.
Illumination phase: Simulate the length of daylight in the natural environment (usually between 0.35W / m2 ~ 1.35W / m2, the summer noon's solar intensity is about 0.55W / m2) and the test temperature (50 ℃ ~ 85 ℃) , In order to simulate various use environments of products to meet the test requirements of different regions and industries.
Condensation phase: Simulate the phenomenon of fogging on the surface of the sample at night. During the condensation phase, turn off the fluorescent UV lamp (dark state), only control the test temperature (40 ~ 60 ℃), and the sample surface humidity is 95 ~ 100% RH.
Spraying stage: Simulate the raining process by continuously spraying water on the sample surface. Since 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 days or weeks.
Material aging includes fading (denaturation of organic dyes in the natural environment), strength reduction (polymer breakage), cracking (polymer breakage and stress), powdering (polymer breakage and reorganization), coating shedding (paint and base Hydrogen bond breaks) and so on.
In addition, according to the different spectral distribution, fluorescent ultraviolet lamps can be divided into UVA and UVB lamps, where the UVA lamp emits light energy below 300nm is less than 2% of the total output light energy, and the UVB lamp emits light The light energy is greater than 10% of the total output light energy.
UVA-340: The main purpose is to simulate the medium and short wavelength range in the ultraviolet part of sunlight, and 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, generally used in indoor products.
UVB-313: They emit considerable radiation below 300nm, and 300nm is the nominal cut-off wavelength of solar radiation. This will cause some aging that does not happen outdoors. It is not recommended to use this lamp to simulate sunlight. This test is widely used to accelerate the durability test of materials as a qualitative comparison of two or more materials.
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