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    Home > Coatings News > Paints and Coatings Market > Super durable polyester

    Super durable polyester

    • Last Update: 2020-02-18
    • Source: Internet
    • Author: User
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    Abstract: This paper discusses the related factors of outdoor degradation of coatings, including heat, moisture and pollutants that play a catalytic role in degradation Light is a part of the earth receiving solar energy The 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 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 Generally, we discuss the emission spectrum of light source, filtering of different wavelengths and Simulation of test period to obtain the best correlation of test results The purpose of this paper is to explore other important factors, such as the influence of temperature and the dependence of coating color The coating properties (QUALICOAT and AAAM) of super durable polyester were discussed In order to obtain the weathering test results quickly, various accelerated tests were carried out and compared with Florida exposure results The correction factor is proposed to replace the factors related to natural exposure test Correction factor refers to the comparison value between the super durability system with the same formula and the conventional coating system It is worth noting that UV-A test is simple and cheap This simple method has two advantages: &; the outdoor durability of the coating is 5 times faster than that of Florida natural exposure test • predict the expected effect of using super durable coatings anywhere in the world 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 Organic coatings have dual functions, which can protect the substrate from corrosion or erosion and have decorative effect In most cases, people use appropriate chemical pretreatment method to achieve the purpose of anti-corrosion The aesthetic appeal of certain luster and color is more attractive than the essence of the substrate Due to the influence of the atmosphere, the durability of the coating is limited, and then the decoration 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 In terms of powder coating, TGIC curing polyester system has been developed 25 years ago, which is suitable for topcoat 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 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 As mentioned above, durability refers to the retention of gloss 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 Under the influence of light, heat, moisture and other environmental factors, the film degrades 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 The sun was born 4.6 billion years ago, 150 million kilometers 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 The earth's orbit is not a perfect circle It has an eccentricity of 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 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 The earth's axis has an inclination of 23.5 °, which means that the solar radiation energy received in different latitudes must be different In the narrow band (340nm), there is the following relationship: radiation energy 340nm = 0.118 × latitude + 7.63 According to the exposure test of unstable polycarbonate in different latitudes, the above relationship is confirmed If the outdoor service life of 10 ° n is 20 days, the time to reach the same degradation level in 70 ° n will be extended to 140 days 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 In the course of the solar radiation to the earth's surface, the space particles only scatter the solar radiation Rayleigh scattering according to Rayleigh scattering and Mie scattering (the method of measuring the transmitted and reflected light of sunlight), the particles whose particle size is less than the radiation wavelength can be distinguished from those 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 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 Table 1 Comparison of received solar radiation between Florida and Arizona total energy at 45 ° angle (MJ / m2) 6000 7765 UV (MJ / m2) 294 337 UV (%) 4.9 4.45 ° total energy (MJ / m2) 6055 7865 UV (MJ / m2) 306 362 UV (%) 5.14.6 temperature (℃) atmosphere 24 22 black plate 29 29 29 relative humidity (%) 81 39 Table 1 shows that the latitude difference between Florida and Arizona is not big, and the difference of solar radiation received at the exposure angle of 5 ° and 45 ° is not big, but because there are fewer particles in the cloud 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 Another important factor affecting the absorption of sunlight is 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 See Figure 1 for the seasonal variation of solar radiation received by Florida and Arizona Figure 1 seasonal variation of solar radiation received in Arizona and Florida sun farms due to energy absorption and scattering, part of the solar radiation can not reach the earth's surface This situation varies with latitude, i.e the climate varies year after year in the same exposure site (Table 2) Table 2 relative radiation time of TUV (MJ / m2) in the year of climate change in Florida sun farm 1998 423 1.34 12.5 1.40 1989 480 1.52 12.0 1.46 1991 295 0.94 17.0.97 1992 265 0.84 1993 315 1.00 17.5 1.00 By monitoring the total ultraviolet radiation (TUV) received in Miami, the time required for the gloss of the sample film to decrease by 25% was determined The coating is a dark grey TGIC coating formulation (ral7021) with crylcoat 342 as the base material 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 equivalent degradation 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 The stability of some chemical bonds of pollutants 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 Nitrogen and sulfur derivatives are strong acids, they 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 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 Table 3 life span change of some pollutants in nature (%, source) human (%), N2O 63, forest, ocean 37, combustion, agriculture 150A + 0.3% P.A NOx 45 soil, biological 55, automobile, (thunder) electro-optic days (local) Sox 55, biological, sea water, volcano 45, coal, industry 2D (local) Co 54, methane 46, forest, fuel for 2-3 months (local) + 1% P.A CO2 carbonate forest, fuel 250A + 4% P.A chlorine 0100, CFC 65-20a water scattering and absorption of solar radiation particles: sea salt accounts for 65% of the total particles; dust accounts for 35% of the total particles It can be seen from table 3 that SO2 pollutants are very regional 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 Aging test In terms of aging test, the first consideration is to accelerate the natural aging effect The method adopted is to directly expose the sample to the sun at a small angle in the low latitude area first In order to obtain the results as soon as possible, the sample can be placed in the low latitude area with very low sunlight radiation, and the small angle is directly exposed to the sun If you want to accelerate the test, you can put the sample into the black box to improve the temperature of the sample and simulate it Environmental conditions inside the car body The control of relative humidity and temperature is the most important factor to simulate natural exposure conditions Chemical reactions such as polyester hydrolysis will be affected by the moisture content in the surrounding environment of the sample, and also by the temperature Accelerated weathering test because of the continuous improvement of outdoor durability of coatings, the assessment of coating weathering takes a long time, so accelerated test is very necessary, but two basic requirements must be considered • acceleration factor:
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