With the development of industry, many towns are in the environment of industrial atmosphere, the air contains a lot of industrial waste gas and acid mist and other chemical gases, especially in the equipment, components, pipes, buildings, etc. used in chemical plants and their adjacent areas. , the hazards are more serious, so the coatings used in these areas must not only have a certain weather resistance, but also need to have a higher ability to resist the corrosion of chemical gases. In addition to the on-site hanging piece or on-site coating for assessment, in order to quickly obtain test results, S02 or NH3 is generally used in the laboratory to conduct corrosion tests on the paint film for chemical gas resistance. This is also an item of the corrosion resistance test of the coating film.
The test can be carried out in an airtight box, and S02 can be supplied from gas cylinders or gas generating equipment, and equipped with suitable adjustment and measuring devices. When the test coating does not exceed 40µm, it is generally recommended to use 0.2LS02. Since the dry SO2 is not very corrosive, the test needs to be carried out under a certain temperature and humidity.
In addition, the S0 2 injected into each test cycle is the same volume, so the total area of the test panel in the box is an important condition, because the rate and degree of absorption of S0 2 by different types of paint films are different, so the test conditions will be affected by the box. Influence of the type of internal test plate.
In order to make the test closer to the actual situation, the S0 2 (or NH 3 ) test is also combined with the artificial accelerated aging test to simulate the outdoor environmental conditions of the chemical plant, so that the test results are more consistent with the actual application.
Generally, the temperature suitable for mold growth is 15-35°C, and the most suitable temperature is 25-35°C. When the temperature is lower than 0°C and higher than 40°C, the mold will not actually grow. The relative humidity suitable for mold growth is above 80%. When it exceeds 95%, the growth is the most vigorous. When it is lower than 75%, the mold does not grow, but it does not die. Therefore, the most suitable climatic conditions for mold growth are temperature 30°C and relative humidity. 95%~100%.
The destructive effect of mold on paint is firstly that the growth of mold on the paint film causes spots and blisters on the surface of the paint film; at the same time, due to the organic acids produced by the mold during the metabolism process, it can cause the dissolution of the pigment on the surface of the paint film and the deterioration of the paint base. Hydrolyzes, thereby penetrating the underlying layer, causing damage to the paint film and loss of its protective effect. Therefore, it is necessary to carry out anti-mildew test for the coating varieties used in southern my country and exported to humid tropical areas.
The strains to be selected in the test vary with the climatic conditions in different regions and seasons; the strains used in the mold test method standards of various countries and regions are also different. According to the specific conditions and test requirements of our country, the following strains are considered to be representative, and the alternatives are: Aspergillus niger, Aspergillus flavus, Aspergillus terreus, Aspergillus pylorus, Aspergillus sarsaueri, Aspergillus versicolor, Aspergillus terrestris, Penicillium chrysogenum, Chaetomium globosa, Trichoderma, Paecilomyces wanshii, Cladosporium cereus, etc.
In addition to the necessary temperature and humidity, various molds need to supply certain carbon sources, nitrogen sources and other trace elements in the growth process. In the laboratory, we can prepare various media to meet the nutrients needed for mold cultivation. The culture medium is divided into two types: the culture medium that is all prepared with chemicals of a certain purity is called a synthetic medium, such as Cai's medium, carbon-free medium, etc.; if the medium containing natural substances is called a natural medium, Such as potato medium, wort medium, etc.
Anti-mildew test methods generally include hanging method and petri dish method, and local method can also be used for the paint film surface of large finished products. The suspension method requires a special mold Test Chamber. The effective space where the samples are suspended in the chamber should be kept at a constant temperature of 28~30°C, and the relative humidity should be kept in the range of 95%~100%. A large amount of condensation is not allowed on the surface of the samples. The petri dish method can use a general oven or a low-temperature oven to keep the temperature at 28-30°C, and the relative humidity is maintained by the culture medium in the petri dish, which does not need to be controlled.
Judging from the actual test results, the growth rate of mold by the suspension method is slow, it takes a long time, and it is not easy to observe. The stipulated 28 days has a tendency to be extended, but it is suitable for the mildew test of parts or complete machines. The Petri dish method has a fast growth rate of mold and is easy to check. The regulation is 21 days. In fact, 14 days can basically be graded, but the test needs to be made into small pieces of 15mmx40mm. Severe, mildew grade is generally 2~3 grades faster than the hanging method.
高瑾 米琪 - 《《防腐蚀涂料与涂装》》