Super durable polyester

< br / >'Super durablepolymers < br / > Abstract: This paper discusses the related factors of outdoor degradation of coatings, including heat, moisture and pollutants that play a catalytic role in degradation< br / > preface < br / > light is a part of the earth receiving solar energyThe terrain receiving solar energy is basically constant, but it varies greatly with different regions (latitudes) and climate types (relative humidity), and also changes with seasons< br / > due to the continuous improvement of outdoor durability of coatings, it is particularly important to get the answer in a short time by accelerated test, but it is required that there should be a good correlation between the test results and long-term natural exposure< br / > generally, we discuss the emission spectrum of light source, filtering of different wavelengths and Simulation of test cycle in order to obtain the best correlation of test resultsThe purpose of this paper is to explore other important factors, such as the influence of temperature and the dependence of coating color< br / > the coating properties (QUALICOAT and AAAM) of super durable polyester were discussedIn order to obtain the weathering test results quickly, various accelerated tests were carried out and compared with Florida exposure results< br / > it is proposed to replace the factors related to natural exposure test with correction factorsCorrection factor refers to the comparison value between the super durability system with the same formula and the conventional coating systemIt is worth noting that UV-A test is simple and cheapThis simple method has two advantages: < br / >< br / >< br / > this means that the correction factor is a valuable parameter for the immature modified system, or it can give a prediction value for the outdoor durability of the modified system under specific conditions< br / > organic coating has dual functions, which can protect the substrate from corrosion or erosion and has decorative effectIn most cases, people use appropriate chemical pretreatment methods to achieve the purpose of anti-corrosionThe aesthetic appeal of certain luster and color is more attractive than the essence of the substrate < br / > due to the influence of atmosphere, the durability of the coating is limited, and then the decorative property is lost Maintenance or repainting will increase the additional cost In addition, people are inert, and they are unwilling to restore the beauty of the coating through repeated repainting, which is why people are constantly improving the outdoor durability of the coating There are two ways to improve the durability of paint: using stabilizer and polyester with long life < br / > in terms of powder coating, TGIC curing polyester system was developed 25 years ago, which is suitable for finishing coat 10 years ago, super durable polyester was put on the market, and the outdoor exposure test of its weatherability was mostly carried out in Florida, so as to get the test results quickly According to the results of outdoor exposure test, the probability life of super durable polyester is 4 times that of conventional polyester < br / > in order to better understand the outdoor application performance of super durable polyester and improve it, people first proposed to analyze the degradation mechanism of coating Next, we will discuss the aging test method and its correlation with natural exposure, explain the super durable polyester and compare it with other polymers < br / > degradation mechanism < br / > as mentioned above, durability refers to the retention of luster and color of the coating in outdoor exposure test, while the anticorrosion of the coating is not described here, because it is mainly affected by the pretreatment of metal substrate < br / > the film degrades under the action of light, heat, moisture and other environmental factors Sunlight will induce photolysis of chemical bonds, while active oxygen will promote photooxidation The joint action of moisture and heat causes the hydrolysis of chemical bonds, while the catalysis of pollutants, such as acid rain, accelerates the hydrolysis < br / > sunlight < br / > the sun was born 4.6 billion years ago, 150 million kilometers away from the earth The energy it radiates comes from the thermonuclear fission of hydrogen atoms In the past 10 years, from satellite observation, the solar radiation has not changed much, which is composed of 9% ultraviolet light, 45% visible light and 46% infrared light Sunspot activity may affect solar radiation, but because the sunspot area is less than 1% of the total surface area of the sun, we can think that the total energy of solar radiation is basically constant < br / > the earth's orbit is not a perfect circle, and its eccentricity is 3.5% in a year around the sun In addition, the interaction between planets will also change the earth's orbit, but this change will take millions of years < br / > the intercepted energy on the earth's surface is only a small part of the huge energy radiated by the sun In other words, the solar radiation energy received by the earth in 10 years is only equal to the energy released by the burning of all available minerals on the earth, or equivalent to one million times of the global power generation in the same period < br / > the earth's axis has a 23.5 ° inclination, which means that the solar radiation energy received in different latitudes must be different In the narrow band (340nm), there is the following relationship: < br / > the radiation energy 340nm = 0.118 × latitude + 7.63 < br / > according to the exposure test of unstable polycarbonate in different latitudes, the above relationship is confirmed, If the outdoor service life is 20 days at 10 ° n, the time to reach the same degradation level at 70 ° n will be extended to 140 days < br / > that is to say, the radiant energy of the sun is basically constant, while the radiant energy received on the earth's surface mainly varies with latitude The change of solar incidence angle and season is also an important factor affecting solar radiation The change of solar incidence angle and season includes the change of substrate temperature and the percentage of ultraviolet radiation received by the earth's surface < br / > the energy received by the earth < br / > during the journey of solar radiation to the earth's surface, space particles only scatter the solar radiation < br / > Rayleigh scattering < br / > according to Rayleigh scattering and Mie scattering (the method of measuring the transmitted and reflected light of sunlight), particles with particle size less than the radiation wavelength can be distinguished from particles close to the radiation wavelength, such as clouds, raindrops and dust Part of solar radiation (mainly UV and visible light) is sent back to space by reflection, but the reflection rate of infrared (IR) radiation is not high, which means that most of UV light is scattered, while a large number of IR radiation is absorbed, which changes the solar spectrum Fortunately for humans, only a very small amount of visible light is absorbed < br / > the composition of the atmosphere affects the solar radiation flux received on the earth's surface Clouds will condense into rain and absorb solar radiation Clouds will also scatter or absorb solar radiation received on the earth's surface For the two regions with little difference in latitude and climate, the solar radiation absorbed is also different, as shown in Table 1 > < br / > 6055 < br / > < br / > 7865 < br / > UV (MJ / m2) < br / > < br / > 306< In this paper, the author analyzes the characteristics of, However, due to the small number of particles in the clouds and air in Arizona, the solar radiation energy received is nearly 30% more than that in Florida, but the UV radiation is less than 20% less than that in Florida < br / > another important factor affecting the absorption of sunlight is the relative humidity In Arizona, water spray is used to simulate the climate of Florida rainforest, but due to the low relative humidity, the water will evaporate quickly, and the test panel will dry quickly after the water spray stops Florida, however, will not have this situation After a long time of rain, the test panel is still wet < br / > see Figure 1 for the seasonal variation of the solar radiation received by the two-phase exposure in Florida and Arizona < br / > Fig 1 seasonal variation of solar radiation received by solar farms in Arizona and Florida < br / > due to the absorption and scattering of energy, some solar radiation cannot reach the earth's surface This situation varies with latitude, that is, the climate varies from year to year at the same exposure site (Table 2) < br / > Table 2 climate change in Florida sun farms < br / > years < br / > < br / > radiation (TUV), / > 0.94 < br / > < br / > 17.0 < br / > < br / > 0.97 < br / > 1992 < br / > < br / > 265 < br / > < br / > 0.84 < br / > < br / > 1993 < br / > < br / > 315 < br / > < br / > 1.00 < br />< br / > 17.5 < br / > The coating is a dark grey TGIC coating formulation (ral7021) with crylcoat342 as the base material < br / > it can be seen from table 2 that the solar radiation energy received on the earth's surface is consistent with the time required to achieve the same degradation < br / > fortunately, for coatings with long service life, such as super durable polyester, if the exposure time is very long, the solar radiation and climate change tend to be consistent < br / > contaminants < br / > the stability of some chemical bonds may be affected by moisture and heat, such as hydrolysis of ester chains The catalyst (mainly acid compounds) can accelerate this reaction, and its activity depends on the pollution source, exposure location and pollutant life < br / > nitrogen and sulfur derivatives are strong acids, which are effective catalysts; carbon dioxide has a greenhouse effect, which makes the temperature rise and many chemical reactions accelerate, but its influence is often exaggerated If the concentration of CO2 in the atmosphere doubles, the global temperature will rise by 2.5 ° K In addition, particles in water and air also absorb solar radiation < br / > the sources of pollutants are different Some of them are short-lived and limited to local areas The pollution caused by these pollutants is very limited Table 3 summarizes the characteristics of some pollutants < br / > Table 3 characteristics of some pollutants < br / > pollutants < br / > < br / > Natural (%, source) < br / > < br / > human (%, source) < br / > < br / > life span < br / > < br / > change < br / > N2O < br / > < br / > 63, forest and ocean < br / > < br / > 37, combustion and agriculture < br / > < br / > 150A < br / > < br / > + 0.3% P.A < br / > NOx < br / > < br / > 45 soil and biology < br / > < br / > 55, Automobile, (thunder) electro-optic < br / > < br / > several days (local) < br / > < br / > Sox < br / > < br / > 55, biology, sea water, volcano < br / > < br / > 45, coal, industry < br / > < br / > 2D (local) < br / > < br / > CO < br / > < br / > 54, methane < br / > < br / > 46, Forest and fuel < br / > < br / > 2-3 months (local) < br / > < br / > + 1% P.A < br / > CO2 < br / > < br / > carbonate < br / > < br / > forest and fuel < br / > < br / > 250A < br / > < br / > + 4% P.A < br / > chlorine < br / > < br / > 0 < br / > < br / > 100, Fluorocarbon compounds < br / > < br / > 65 ～ 20A < br / > < br / > water scatters and absorbs solar radiation < br / > particles: sea salt accounts for 65% < br / > particles: dust accounts for 35% < br / > from table 3, it can be seen that SO2 pollutants have strong regional characteristics As long as the humidity is high enough, only two days later, SO2 will be converted into acid, limiting the pollution source to the original place The situation of nitrogen peroxide is the same as that of SO2 < br / > aging test < br / > in terms of aging test, the first thing people consider is to accelerate the natural aging effect, and the way to take is to directly expose to the sun at a small angle in the low latitude area first In order to get the results as soon as possible, we can put the sample at a low latitude with very low solar radiation