Color-coated panels with paint types of PESMPHDP and PVDF were subjected to an accelerated aging resistance test to investigate the effect of photo-aging time on the thickness of the color-coated panels, analyze the degree of influence, and explore the reasons for the impact. It can be seen from the test results that the coating thickness loss of color-coated panels increases with the increase of UV aging time; color-coated panels of different coating types have different degrees of influence. According to the loss of coating thickness of color-coated panels, the order is PE and SMP>HDP>PVDE; In the ultraviolet aging test, the loss of the coating thickness of the color-coated board is also affected by its color.
The coating thickness of color-coated panels is a very important indicator in the inspection of color-coated panels. It directly affects the performance of the color-coated panels, such as processing performance, aging resistance, and corrosion resistance. There are many reports on this problem at home and abroad, but there are few reports on the influence of the aging process of the coating on the thickness of the color-coated plate. In the actual use process of architectural color-coated panels, under the sun and rain, whether the coating thickness changes with time, and what changes will happen to what extent, the discussion on this issue has certain practical significance.
The main causes of coating aging usually refer to solar radiation, ambient temperature and environmental humidity, and the secondary causes are air pollution, acid rain, biological phenomena, wind and sand, etc. There are many types and manifestations of coating aging, mainly the degradation of polymer chains, including photo-degradation, oxidative degradation, and thermal degradation. The main aging method of color-coated panels used in normal temperature environments should be photo-oxidative degradation.
Sunlight can usually be divided into 3 main wavelength ranges: ultraviolet (wavelength 200~400nm), visible light (wavelength 400~720nm) and infrared (720~2500nm). Among them, ultraviolet rays can be subdivided into short-wave UV (200-290nm), medium-wave UVB (290-320nm) and long-wave UVA (320-400nm) according to the length of the wavelength. After the sunlight passes through the outer space and the high-altitude atmosphere, all the ultraviolet light below the 290nm wavelength is almost filtered out, so the ultraviolet rays that reach the ground are actually only medium-wave UVB and long-wave UVA. Medium-wave UVB damages the color-coated board coating more than long-wave UVA.
The accelerated ultraviolet aging test method used in this article is in accordance with the ultraviolet aging test method in GB/T13448-2006 "Color Coated Steel Sheet and Steel Strip Test Method", the specific test conditions are "8h is a cycle: 4h ultraviolet light, blackboard temperature (60±3)℃ 4h condensation, blackboard temperature (50+3)C” wavelength is 310nm, light intensity is 0.63W/(m2·nm). The test conditions include three major factors that affect the aging of architectural color-coated board coatings, namely light, humidity and temperature. The samples used four different types of color-coated boards: ordinary polyester (PE), silicon modified polyester (SMP), high weather resistance polyester (HDP) and polyvinylidene fluoride (PVDF), 3 pieces each, totaling 12 pieces. : The color of the 3 color-coated plates of each type is different. Among the four types of color-coated plates, samples 1, 5, 7, and 11 are blue color-coated plates, and samples 2, 4, 9, and 10 are white ones. Samples 3, 6, and 812 are gray color coated boards. Accelerated aging test is carried out in accordance with the standard. Before the test, use an eddy current meter to test the coating thickness of the color-coated plate: when the accelerated aging time is 200, 400, 600, 1000, 1500, 2000 and 3000h respectively, use the same eddy current meter, and then under the same calibration conditions. Test the coating thickness of the color-coated board respectively. When testing the coating thickness of the color-coated board, the same sample was tested 12 times, and the average value was taken as the test result. The UUV/SPRAY UV aging test box produced by 0-ab in the United States was used: the coating thickness test instrument for the color-coated board was The eddy current meter is produced by the German fisher company.
The loss of coating thickness of 12 samples at different test times is shown in the bar graph. Among them, the loss of coating thickness under a certain UVB test time = coating thickness before the test-coating thickness after the UVB test time.
It can be seen from the test results that the loss of the coating thickness of the color-coated plate increases with the increase of the UV aging time. However, color-coated sheets of different coating types have different degrees of influence. PE and SMP color-coated sheets have a large loss of coating thickness, HDP color-coated sheets have a small loss of coating thickness, and PVDF color-coated sheets have a small loss of coating thickness. The smallest. For PE, SMP, HDP and PVDF blue and white color coated boards, the loss of coating thickness is linearly positively correlated with the accelerated aging time of ultraviolet light. The correlation coefficient:
0.91, the linear correlation is relatively strong, and the slope of the regression equation for the white color-coated board is smaller than that of the blue color-coated board. During the use of color-coated panels, the coating thickness gradually decreases with time, and the protective performance gradually deteriorates. It is recommended that users of color-coated panels choose color-coated panels with appropriate colors and paint types according to their purpose and use environment.
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