The test methods of paint weather resistance and light resistance at home and abroad are discussed briefly

Exposure of coatings, plastics and other organic materials to natural climatic conditions and light radiation can occur over time as a result of loss of light, fading, yellowing, peeling, cracking, loss of stretch strength and shedding of the entire layer. Even indoor light or sunlight through the window glass can cause damage to substances such as pigments or dyes.
for outdoor use of coatings, such as exterior coatings and automotive coatings, weather and light resistance is the most important testing project
China
. While everyone agrees that the weather and light resistance of coatings is important, they have different opinions about what is the best testing method for them. At home and abroad, there are many ways to evaluate paint weather resistance and light resistance. The methods of artificial accelerated climate aging test, such as natural climate aging test, xenon arc lamp exposure, or carbon arc lamp exposure, ultraviolet light exposure, etc. are commonly used. This article explores how to choose the right test method.1 Natural Climate Aging Test The
Climate Aging Test Method is widely used at home and abroad. The main reason is that the results of natural climate aging experiments are more realistic, the cost is low and the operation is simple and convenient. Although we can conduct natural climate aging tests anywhere, the internationally recognized test site is Florida in the United States because of its abundant sunlight.
the shortcomings of natural climate aging tests are that they take a long time to test, and testers may not have so many years to wait for the results of a product. In addition, even in Florida, the climate cannot be exactly the same year after year, so the reappearance of the test results is not ideal.2 Xenon Arc Radiation Test
Xenon Arc Radiation Test is considered to be the most effective simulation of the full solar spectrum because it produces ultraviolet, visible and infrared light. Because of this, it is considered to be the most widely used method at home and abroad. GB/T 1865 - 1997 (equivalent to ISO 113411: 1994) describes this approach in detail. However, this method also has its limitations, that is, the stability of the xenon arc light source and the complexity of the experimental system. Xenon arc light sources must be filtered to reduce unenrexpected radiation. A variety of filter glass types are available to achieve different irradiance distributions.
glass to be selected depends on the type of material being tested and its end use. Changing the filter glass can change the type of short wavelength of ultraviolet light passing through, thereby changing the speed and type of material damage. There are three types of filtering commonly used: daylight, window glass, and extended ultraviolet light types (methods 1 and 2 mentioned in national standard GB/T 1865-1997 correspond to the first two types).
typical xenon arc radiation is equipped with an irradiance control system. Irradiance control systems are important in xenon arc radiation testing, because the spectral stability of xenon arc light sources is less visible than that of fluorescent UV light. A foreign study examined the difference between a new xenon arc lamp and an old xenon arc lamp with 1,000 h used. It was found that the spectral energy distribution not only changed significantly in the long wavelength range of the light source with the extended use time of the lamp, but also changed significantly in the short wavelength range. This change is caused by the aging of the xenon arc lamp, which is its own internal characteristics.
can also take a variety of remedial measures against such changes. For example, increase the frequency of changing lamps to mitigate the effects of light aging. Or you can use a sensor to control irradiance. Despite the changes in spectral energy distribution caused by lamp aging, xenon arc lamps are still a reliable and reflective light source for weather and sun exposure tests. Most xenon arc radiation tests use water spray and/or temperature automatic control systems when simulating wetting conditions (the "surface water spray" proposed by national standard GB/T 1865-1997).
limitation of the water spray method is that when relatively low-temperature water is sprayed on a relatively high-temperature test plate, the test plate cools down, which slows down the process of material destruction. In xenon arc radiation tests, high purity water is required to prevent sediment from forming on the test plate surface. As a result, the operating costs are higher.
3 Ultraviolet light exposure test
UV lamp irradiation aging test using fluorescent UV lamp to simulate the destructive effect of sunlight on durable materials. This is different from the aforementioned xenon arc lamps, where fluorescent UV lamps are electrically similar to normal lighting cold-light fluorescent lamps, but produce more ultraviolet light than visible or infrared light. For different exposure applications, there are different types of lamps with different spectra to choose from. The U VA-340 lamp simulates sunlight well in the main short wavelength UV spectral range. The spectral energy distribution (SPD) of the U VA -340 lamp is very similar to the spectral map from the solar spectrum of 360 nm.
U V-B lamps are also commonly used for accelerated artificial climate aging test lamps. It destroys materials faster than UV-A lamps, but its shorter wavelength energy output than 360 nm can cause many materials to deviate from actual test results.
irradiance (light intensity) control is necessary to obtain accurate and reproducible results. Most UV aging test devices are equipped with irradiance control systems. These precise irradiance control systems allow the user to select irradiance measurements when conducting experiments. Through the feedback control system, irradiance can be continuously and automatically monitored and precisely controlled. The control system automatically compensates for insufficient illumination due to lamp aging or other causes by adjusting the power of the lamp. Fluorescent UV lamps make irradiance control simple because of their inward spectral stability. All lamp sources weaken over time. But fluorescent lamps, unlike other types of lamps, do not vary in spectral energy distribution over time. This feature improves the reproducity of the test results and is therefore a major advantage. Tests have shown that there is no significant difference in the output power of a lamp that uses 2 h and a lamp that uses 5,600 h in an aging test system equipped with irradiance control, and that the irradiance control maintains a constant light intensity.
, their distribution of spectral energy has not changed, which is very different from xenon arc lamps. One of the main advantages of using purple lamp aging test is that it can simulate the damage to materials in a more realistic outdoor humid environment. When the material is placed outdoors, it is estimated that at least 12 h is frequently subjected to moisture every day. Because most of this damp action takes the form of condensation, a special condensation principle is used to imitate outdoor humidity in accelerating artificial climate aging tests.
in such a condensation cycle, heat the sink at the bottom of the test box to produce steam. The hot steam keeps the environment of the test case 100% relative humidity at high temperatures. When designing a test case, make the test plate actually form the side wall of the test case. The back of the test plate is exposed to indoor air at room temperature. The cooling of the indoor air reduced the temperature of the test plate surface by several degrees compared to the steam temperature. These temperature differences allow water to continuously drop to the surface under test during the condensation cycle. The resulting condensate is a stable, pure distilled water. This water can improve the reproducity of the experimental results, eliminate water sediment pollution and simplify the installation and operation of test equipment. Because the material is generally subjected to moisture outdoors for a long time, a typical circulating condensation system has a minimum test time of 4 h.
the condensation process is carried out under warm conditions ( 50 degrees C ) , which greatly speeds up the damage to the material caused by moisture . Condensation cycles over long periods of time and under heating conditions are more effective than other methods such as water spraying, impregnation and other high humidity environments in reproducing the phenomenon of wet environmental damage materials.4 Conclusion
Although the national standard stipulates and the current domestic anti-aging test method is xenon arc radiation, but in foreign radon arc radiation and ultraviolet aging test are widely used test methods. The two methods are based on completely different principles. The xenon light exposure test box mimics the entire solar spectrum, including ultraviolet, visible and infrared light, with the aim of simulating sunlight.
ultraviolet aging test is not an attempt to mimic the sun's rays, but merely to mimic the destructive effects of the sun's rays. It is based on the principle that long-term exposure to durable materials outdoors, by short-wave ultraviolet light caused by the greatest damage caused by aging. In addition, even in the natural climate for aging testing, there is an accelerated method, is to install the test model in a model frame that can rotate as the sun rises and lands, so that the model most of the time to maintain the state of direct sunlight, in order to obtain accelerated test results.
the 1980s, parallel tests with carbon arc lamps or direct ultraviolet lamps could also shorten the test cycle. Which test method is the best? There is no simple answer. Which method to choose depends on the material to be tested, the final application of the material, the pattern of material damage and financial resources of concern.