Long-term outdoor sunlight exposure, high temperature and humidity are the main causes of coating cracking, loss of gloss, fading, yellowing and chalking. The weather resistance of the coating is related to the spectral sensitivity of the coating components. For outdoor paints, UV rays are the main cause of paint aging. The UV accelerated aging test can simulate the damage of the UV part of sunlight to the coating, and reproduce the damage that occurs outdoors for months or even years in days or weeks.
UV test chambers can help to select new materials and evaluate the impact of material formulations on durability, to achieve the purpose of verifying the performance of coatings. The necessary UV accelerated aging test ensures the long-term weather resistance of the coating to avoid losses caused by weather resistance during use. Ultraviolet rays in sunlight are the main cause of photodegradation and photoaging of photo products, so the selection of new products and new materials must be tested for weather resistance of products.
Ultraviolet aging test is a type of test method to evaluate the resistance of new products to ultraviolet light, which is usually tested in a laboratory by an accelerated ultraviolet aging test chamber. Products and materials that need to be tested for UV resistance mainly include: non-metallic materials, organic materials (such as coatings, paints, dyes, fabrics, printing and packaging, adhesives, cosmetics, metals, electronics, electroplating, rubber, plastics and other materials products, etc.).
How to test the weather resistance of paint coatings ? The weather resistance test and evaluation of paint coatings must have sufficient basis, not fabricated out of thin air. At present, two methods are generally promoted internationally: natural exposure and artificial accelerated aging test, and it is emphasized that the two test methods should be combined and comprehensively considered to draw more reliable conclusions. Natural exposure is based on the exposure of Florida, USA. The state is located at the southern end of the United States and is surrounded by the sea.
The sun is abundant and strong throughout the year. The moisture and salt in the air are very high. Compared with other places on the earth, except for a small part of In addition to extreme weather phenomena, the natural conditions here can be regarded as a very harsh environment for coatings. Insert the prepared standard sample of paint and coating into the exposure frame, facing south at an angle of 5° or 45°, regularly test the gloss and color change, and record it. The general test period is in years, and the coating gloss and color change curve can be drawn at the end of the test.
Natural exposure is accurate and intuitive, and the data is credible, but the test period is too long to quickly guide scientific research and production. Therefore, most of the relevant tests are completed by artificial accelerated aging. The artificial accelerated aging test simulates natural conditions, such as controlling a certain temperature, humidity and rainfall cycle, and selecting different wavelengths of light to simulate sunlight. The test period is short and usually only takes 200 to 1000 hours, and a conclusion can be drawn quickly. There are many light sources used in the artificial accelerated aging test, and the common ones are: xenon arc sunlight, fluorescent ultraviolet rays, and carbon arc lamps.
|●||The xenon lamp aging test can be used for the selection of new materials, the improvement of existing materials or the evaluation of changes in the durability of material compositions; it can provide corresponding simulated test environments and accelerated tests for scientific research, product development and quality control.||Xenon Lamp Aging Test|
|●||The xenon lamp aging test is a test that simulates the full sunlight spectrum. The xenon lamp aging test is currently the best test for simulating artificial climate reliability testing. It can simulate a natural artificial climate test in a short time. It can better simulate changes in products exposed to sunlight in different environments.|
|●||The spectral energy distribution of the xenon lamp aging test in the ultraviolet region and the visible region is similar to that of sunlight. The radiation emitted by the xenon lamp is filtered by a filter to filter out shorter ultraviolet light waves with wavelengths below 290 nm and infrared light waves with wavelengths above 1200 nm. The spectrum reaching the surface of the specimen is close to that of sunlight.|
|●||Coatings, plastics and other organic materials will lose their gloss, fade, yellow, peel, crack, lose tensile strength and peel off over time when exposed to natural weather conditions and light radiation. Even indoor light or sunlight shining through window panes can cause damage to substances such as pigments or dyes.|
These two methods can test the durability of paint coatings. The xenon arc radiation is mild, which is more suitable for pigments, plastics, etc., and the test period is longer. Fluorescent UV lamps have good acceleration and are suitable for rapid inspection, and have a wide range of UV wavelength selection, which can adapt to a variety of inspection requirements. There are also accelerated natural exposure tests, such as the EMKAQUA test (in Arizona, USA), which use special mirrors to intensify sunlight, combined with periodic spraying and temperature control. It has been observed that this method correlates well with Florida exposure while aging 5-6 times faster.
Statistics show that cars placed outdoors will be wet for a long time every day. Dew formed by moisture is a major factor in outdoor humidity, and dew is more harmful to car paint coatings than rain because it adheres to the paint coating for a longer time, causing more severe moisture absorption.With the development of the automobile industry, there are more and more electronic control components, navigation, entertainment, wireless multimedia electronic components, etc. The system of the car is becoming more and more complex, and the importance of the reliability of electronic components is also highlighted, which directly determines the driving safety of the vehicle and the reliability of the product.
At present, there are two main test methods for weather resistance and aging resistance of interior and exterior parts, namely artificial accelerated aging test and natural climate exposure aging test. Most Chinese auto companies focus on controlling the aging performance of parts and components, supplemented by the evaluation of vehicle outdoor exposure. Combining the two can achieve the purpose of shortening the material development cycle and reducing quality risks. The test and evaluation of the aging performance of the parts are mainly carried out through the artificial accelerated aging test in the laboratory. The main problem is that the correlation research between artificial accelerated aging test and natural climate exposure aging test is not deep enough.
Nowadays, the light sources used in artificial accelerated aging test equipment mainly include carbon arc lamps, ammonia arc lamps and fluorescent ultraviolet lamps, among which nitrogen arc lamps and fluorescent ultraviolet lamps are the most widely used. According to the different working conditions of interior and exterior parts, the test standard has two test conditions: interior and exterior. Different organizations and institutions have developed relevant standards, such as ISO, SAE, ASTM, GB, etc. Some auto companies have established corporate standards through years of research and accumulation, such as GM, VW, FORD, etc.
|●||The ultraviolet spectrum and visible spectrum of nitrogen arc lamp are very close to the solar spectrum, which is the closest to the solar spectrum among the existing artificial light sources, and the simulation is relatively good.||Nitrogen Arc Lamp|
|●||According to the cooling method of the lamp, the nitrogen lamp aging tester is divided into two types: water-cooled and air-cooled, and the operating cost is high (the cost of the lamp as a consumable is high).|
|●||Different models (such as B-313 nm, A-340 nm) have different peaks of UV spectrum of fluorescent UV lamps.||Fluorescent UV Lamps|
|●||The UV spectrum of UVB 313 nm (270-360 nm) may accelerate the aging of some polymer materials more than the carbon arc lamp or ammonia arc lamp is large, and the ultraviolet spectrum (312~400 nm) of UVA 340 nm is consistent with the sunlight spectrum.|
|●||Fluorescent UV lamps do not simulate the solar spectrum as well as ammonia arc lamps, but have lower operating costs.|
Why do UV testing ? What lights are there for UV testing ? What is the wavelength of UV aging tester ? The UV aging test is a process of simulating the various factors involved in the actual use conditions of the product to carry out the corresponding conditions to strengthen the experiment. The UV aging test experiment is mainly aimed at plastic materials. The common aging mainly includes light aging, damp heat aging , hot air aging. Some outdoor products are exposed to sunlight for a long time, so the yellowing resistance test and aging resistance test of the product are very important.
To understand the service life of the product outdoors, it is necessary to carry out a UV aging test simulation test, that is, a UV test. Since the intensity of the UV test in the laboratory is greater than that of the outdoor light, the UV aging test can save the staff’s time. The test time can get the service life of the product outdoors in a short time.
Which products need to be UV tested ? UV test is very important, UV aging test is mainly used to test plastics, lamps, paint inks, resins, printing and packaging, aluminum profiles, automobile and motorcycle industries, cosmetics, etc. UV testing to reproduce damage from sunlight, rain and dew. The device conducts the test by exposing the material to be tested to a controlled alternating cycle of sunlight and moisture while raising the temperature. UV test chamber uses UV fluorescent lamps to simulate sunlight, and can also simulate moisture effects by condensation or spray.
|●||The chemical bonds of polymer materials have different sensitivities to different wavelengths of sunlight in sunlight, and generally correspond to a threshold. The short-band ultraviolet rays of sunlight are the main reasons for the aging of physical properties of most polymers, such as CN (carbon-nitrogen) bonds. The threshold of action is 393 nm. However, long-wavelength UV light and even visible light can also damage certain dyes and pigments, causing discoloration and fading.||Lighting||Weathering Test Principle|
|●||The higher the temperature, the faster the chemical reaction speed. The aging reaction is a photochemical reaction. The temperature does not affect the photoinduced reaction speed in the photochemical reaction, but affects the subsequent chemical reaction speed. Therefore, the effect of temperature on material aging is often nonlinear.||Temperature|
|●||Water will directly participate in the material aging reaction. Relative humidity, dew and rain are the main forms of water in nature. Studies have shown that outdoor materials will be in a wet state for a long time every day (up to 8 to 12 hours per day on average). And dew is the main cause of outdoor humidity. Dew is more harmful than rain because it sticks to the material longer and creates more severe wet erosion.||Humidity|
Plastics have good chemical properties, mechanical properties, electrical properties and dimensional stability. But its biggest disadvantage is that it is not resistant to aging, and the aging mechanism is also very complicated. At present, the change of mechanical properties caused by aging is generally analyzed through experiments, such as the change of mechanical properties through artificial accelerated aging.
Plastic aging is a process in which the performance of plastic products changes from good to bad. Due to the wide variety of plastics, the use environment and use conditions are very different, so the aging phenomenon and characteristics are also different. At present, some phenomena of plastic aging can be summarized into the following four changes.
|●||Sticky, hardened, brittle, deformed, discolored, lost gloss, blistered, cracked and even chalked up.||Appearance Changes|
|●||There are mainly changes in properties such as dissolution, swelling, rheology, cold resistance, heat resistance, air permeability and water permeability. The main manifestation of swelling is the change in size.||Changes in Physical Properties|
|●||There are mainly changes in tensile strength, bending strength, impact strength, hardness and elasticity, elongation, stress relaxation and other properties.||Changes in Mechanical Properties|
|●||Such as surface resistance, volume resistance, insulation resistance, dielectric constant, electrical breakdown performance and other performance changes.||Changes in Electrical Properties|
In terms of accelerated aging test, except for a few Japanese companies that still use carbon arc lamps, the main test methods are ultraviolet light and xenon lamps. However, the xenon arc accelerated aging test chamber cannot simulate all aging parameters, and there are some test variables that are prone to cause erroneous test results, resulting in erroneous conclusions. However, the results of outdoor exposure can be used as a reference to check the authenticity of the accelerated aging test, which will make the accelerated aging test more practical.
The temperature and humidity treatment test simulates the temperature and humidity experienced by the transportation unit during transportation, and considers the resistance of the transportation unit to temperature and temperature. Temperature and humidity have a greater impact on corrugated and plastic packaging, but not so much on wood packaging and metal packaging. Corrugated packaging is sensitive to humidity. Humidity will affect the water content of corrugated paper, which in turn will affect the strength of corrugated packaging. High temperature will greatly reduce the strength of corrugated paper, resulting in collapse and rupture of corrugated packaging.
During storage or transportation, if the corrugated packaging at the bottom is not strong enough to cause collapse, the entire stack will collapse or the top load will be directly pressed to the contents, causing pressure damage to the contents. For some shipping or transportation or storage in hot and humid areas, it is still necessary to do temperature and humidity treatment tests during simulated transportation tests.
|●||How to evaluate the anti-aging performance and life of plastics ? The natural aging test is to test the sample under natural conditions, and analyze the change of its performance before and after to evaluate the weather resistance of the material. The natural conditions include natural atmospheric conditions, natural storage conditions, and seawater exposure conditions. This method has a longer test period and is suitable for specific exposure test sites.||Natural Aging Test|
|●||The artificial aging test is to expose the material to the specified environmental conditions, simulating the natural conditions of light, heat, oxygen, humidity, rain, etc., by testing the irradiance or radiation on the surface of the sample and the change in the performance of the sample. Evaluate the weatherability of materials.||Artificial Aging Test|
|●||The performance before and after aging can be compared with the following: appearance change, mechanical property change, molecular weight and distribution change, electrical property change, size change, volume change, mass change, etc. In the actual analysis process, one or more physical properties can be selected for evaluation according to the key impact performance of the product.||Comparison of Physical Properties Before and After Aging|
Wood packaging will also cause wood decay and strength reduction in a long-term temperature and humidity environment. Wood packaging has a certain service life. In terms of the impact of this single item in simulated transportation, the defect may not be exposed, but it may be damaged after experiencing the combined effects of subsequent shock, compression and vibration. The packaging simulation transportation test is a sequential comprehensive simulation, which needs to be carried out comprehensively to achieve the purpose of verification.