How to do material aging test: UV aging

1. What is UV aging?

 Ultraviolet aging detection uses fluorescent ultraviolet lamps as the light source, and conducts accelerated weather resistance tests on materials by simulating the ultraviolet radiation and condensation in natural sunlight to obtain the results of the weather resistance of the materials. UV aging detection is widely applicable to Non-metallic materials and organic materials (such as paint, paint, rubber, plastic and their products) have been tested for the degree and condition of aging of related products and materials under changes in climate conditions such as sunlight, humidity, temperature, and condensation.

2. Why do aging test?

 When the product is left in the atmosphere for a period of time, different problems will occur, such as changes in appearance, including cracks, spots, chalking, or color changes, and even a decline in performance. The possible reason is the loss of molecules in the resin. The chemical bonds in the molecular structure have changed, mainly due to sunlight, industrial exhaust gas, bacteria, etc. The aging performance of the product directly affects the use time of the product, so the aging test is of great significance! Atmospheric natural aging test is to put the plastic sample on the exposure rack, directly under the natural climatic environment, withstand the sun The synergistic effects of light, heat, atmospheric humidity, oxygen and ozone, industrial pollution and other factors are used to measure the performance changes before and after the test to evaluate the weather resistance of the material. The selection of the test site in the aging test can represent a certain The most severe area of the first type of climate, or close to the actual application area of the material, the test site should be open and flat, and there is no influence around Obstacles to test results. The test frame should face the equator and make an angle of 45° with the ground. When the main performance indicators of the sample have fallen to the lowest allowable value in actual use or below a certain critical retention rate, the test party ends. In most cases it is a sample The test is terminated when the main performance index drops to 50% of the initial value. Since the natural aging process is a very slow process, and there are great differences in different geographical environments, this brings difficulties to the evaluation of the aging resistance of the product. People try to evaluate the aging performance of plastics in a short period of time. This is the accelerated aging test. The accelerated aging test can use human light sources that simulate fluorescent lamps, including carbon arc lamps, xenon arc lamps, and fluorescent ultraviolet lamps. These artificial light sources will produce much stronger light than natural sunlight on the ground. When using these artificial light sources, condensers are often used to simulate the combined effects of rain and dew to perform aging tests on products.

3. How to choose aging conditions?

 As we know, the three major elements of material aging are light, heat and water. Therefore, the selection of UV aging detection conditions is also considered from these three aspects.

The choice of light: the choice of UV lamps, according to different product usage and testing purposes, according to the light source and purpose of different UV lamps to choose. Such as exterior wall paint can be considered as UVB-313 lamp. Thermal selection: Blackboard temperature (BPT) is used to characterize the aging box. Because the maximum temperature of the exposed sample surface mainly depends on the radiation intensity of the light source, the absorption of radiant heat, the heat conduction of the sample itself, and the heat transfer between the sample and the air or the sample holder. The blackboard temperature is the surface temperature of the dark sample with good thermal conductivity, which is used to characterize the temperature condition of the aging box. Water selection: the choice of condensation and spray conditions. The exposure time of outdoor materials and moisture can be as long as 12 hours a day. Research results show that the main cause of this outdoor humidity is dew, not rain. The testing machine simulates the influence of outdoor moisture by condensing the liquid water originally condensed on the surface of the sample. Generally, each condensation cycle lasts at least 4 hours. For some applications, water spray can better simulate the environmental conditions of the final use. Because water spray is to simulate mechanical erosion caused by temperature changes and rain erosion. For example, studies have shown that for the coating layer of wood, including paint and colorants, the scouring action of rain water can affect the surface of the material The coating layer with anti-degradation effect is washed away, so that the material itself is directly exposed to the destructive influence of UV and moisture; if this process repeat many times, the material will be degraded. The influence of this moisture can’t be achieved by the way of condensation.

4. The light source selection of fluorescent ultraviolet lamp

UV-A: 315 ~ 400nm The main area that causes the aging of polymer materials-UVA-340 UV-B: 280 ~ 315nm including the shortest ultraviolet light that can reach the earth's ground-UVB-313 Can be filtered out by window glass-UVA-351 UV-C: 100 ~ 280nm only exists in space outside the atmosphere UV aging simulates two types of light sources: UV-A and UV-B. The shorter the wavelength, the higher the energy contained, and the more likely it is to break the chemical bonds of molecules.

5. The purpose of QUV lamps

UVA-340: Comparative test of different formulations, recommended for testing most plastics, textiles, coatings, pigments and UV stabilizers UVB-313: Best for QC and R&D, it is recommended to test for durable materials (such as roofing materials, some exterior coatings, etc.)

UVA-351: Used to simulate UV light passing through window glass, recommended for testing some automotive interior parts, textiles, inks, etc.