General knowledge of coating: Discussion on test method of coating weatherability

Core tip: 0 Introduction Outdoor weather resistance is one of the most important performance indexes of coating, especially for external coating It refers to the performance that the coating can resist various changes of the external environment when exposed to the sun, such as the loss of light, discoloration, pulverization, adhesion, strength and corrosion of the coating Outdoor mechanical products, such as automobiles, airplanes, trains, bridges, and recently developed wind power energy equipment, all put forward higher and higher requirements for the protection of coatings, especially for outdoor weather resistance How to evaluate the weatherability of coating has been a long-term research in coating industry Paint knowledge how about Akzo Nobel Powder Coating Recommended introduction: powder coating is a kind of coating with different form from general coating, which is in powder form It is a new type of coating, because of its own advantages and more and more known by people Let's introduce Akzo Nobel Powder coating Akzo Nobel Powder coating is a cost-effective coating solution, which can be applied to different kinds of products After the treatment of static electricity and fire baking, a tough and durable coating surface will be formed, with the least impact on the environment Since the introduction of this technology, powder coating has been able to continue to maintain the Outdoor weather resistance is one of the most important performance indexes of coatings, especially for external coatings It refers to the performance that the coating can withstand various changes of the external environment when exposed to the sun, such as the loss of light, color, pulverization, adhesion, strength, and corrosion of the coating Outdoor mechanical products, such as automobiles, airplanes, trains, bridges, and recently developed wind power energy equipment, all put forward higher and higher requirements for the protection of coatings, especially for outdoor weather resistance How to evaluate the weatherability of coating has been a long-term research topic in the coating industry The process of coating damage is mainly the oxidation degradation caused by light and the degradation of water in the environment of sunlight, water and air High humidity environment will promote the oxidative degradation of light and water degradation; at high temperature, the oxidative degradation of light and the degradation of water will be enhanced; in acid environment, acid rain will promote the degradation of water In the atmosphere, nitrogen, carbides and ozone will degrade the polymer in the coating The change of atmospheric temperature and humidity will cause the coating or substrate to expand and contract, which will cause the coating to crack The speed of these processes depends on the composition of the coating, the treatment of the substrate and the region where it is located, as well as the seasonal changes 1 Evaluation and test methods of coating weatherability evaluation and test methods of coating weatherability are divided into outdoor exposure test and laboratory artificial climate accelerated aging test 1.1 outdoor natural exposure test outdoor exposure test is a relatively reliable method, but it takes a long time (generally 2-3 a exposure) In order to shorten the exposure time, we usually choose the subtropical climate environment with high temperature, high humidity and high sunlight For example, South Florida in the United States, Hainan in China is the ideal place for coating exposure Generally, outdoor exposure test takes a long time, which is not suitable for predicting the actual performance or as the choice of research projects 1.2 accelerated aging test method of artificial climate the accelerated aging test method of artificial climate in China was proposed by the Ministry of mechanical and electronic industry, and approved by the State Bureau of technical supervision as the national standard GB / T 14522-1993 from June 10, 1993, mainly for plastic, coating and rubber materials for mechanical industrial products The implementation of the standard of artificial climate accelerated aging test provides a certain basis for the evaluation, selection and production of coating varieties However, due to the use of artificial light source, whether standard ultraviolet condensation test or artificial climate test, the test results still have a certain gap with the outdoor exposure test results, based on some cases, the opposite results will be obtained Too much dependence on the results of accelerated aging test of artificial climate can sometimes mislead the choice of good coating varieties, and even cause unnecessary economic losses The results of artificial climate accelerated aging test of some coating products are ideal, but in practical use, the coating will be damaged in a short time 2 there are many problems in accelerated weathering test of artificial weathering Many instruments are used as artificial weathering tests for coatings They are tested under UV light sources with different wavelengths and subjected to cyclic tests of water spray (or high humidity) Although it is currently widely used as a test method, its results are often quite different from the results of outdoor exposure test, or even have the opposite results Typical examples: for example, in order to further improve the durability of the coating, HALS was added to evaluate the coating through the accelerated aging test of artificial climate Due to the unsatisfactory results, the application of the coating was almost abandoned, but its outdoor exposure test results were good, which attracted the attention of researchers, so it continued to improve and develop Another typical example is that polyester polyurethane coating is evaluated by artificial climate accelerated test, and the conclusion is that no common instrument is applicable, because all artificial light sources will cause the loss of o-or m-phthalate groups in polyester polyurethane coating, which has not been found in outdoor exposure test (such as 45 ° south of Florida, USA) It is generally considered that the weather resistance of polyester polyurethane coating with phthalate group in artificial climate accelerated aging test is worse than that of acrylic polyurethane coating The loss of o-or m-phthalate groups caused by the accelerated aging test of artificial climate is due to the strong and unnatural radiation of short wave light (< 290nm) from artificial light source The author has spent several years comparing the artificial climate accelerated aging test and outdoor exposure test (Xi'an area) of polyester polyurethane coating and acrylic polyurethane coating used in automobile and industrial products with higher requirements at home and abroad The results also fully confirm the above views Some polyester polyurethane coatings can only pass the accelerated test of artificial climate for about 300 hours, even worse if ultraviolet absorbers are added to the coatings; acrylic polyurethane coatings can generally pass the accelerated aging test of artificial climate for 600-1000 hours or longer, while the same coating varieties can be exposed to the sun for 1-3 a in the outdoor It is found that the test results of most coating products are basically opposite to the accelerated test of artificial climate (see Table 1) Results of outdoor exposure test for several polyester polyurethane coatings and acrylic polyurethane coatings note: (1) coating sample: b-015 is imported hydroxy acrylic resin, NV (nonvolatile content) is 70%, hydroxyl value is about 150; b-2960 is domestic hydroxy acrylic resin, NV is 60%, hydroxyl value is 100; c-015 is domestic hydroxy polyester resin, NV is 70%, hydroxyl value is 150; c-028 It is a domestic hydroxyl polyester resin with Nv of 60% and hydroxyl value of about 100 (2) Exposure location: the top of the factory building in Xi'an western suburb industrial park faces 45 ° south (3) Plate making: iron red polyurethane primer, white polyester polyurethane coating or acrylic polyurethane coating Home of coatings is specialized in coatings, diatom mud, paint coating, coating technology, fire retardant coating news and coating, diatom mud, paint coating, coating technology, fire retardant coating decoration knowledge and decoration renderings,