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Paint, plastic xenon lamp aging test and UV aging test difference

 Paint, plastic xenon lamp aging test and UV aging test difference

Paint, plastic and other organic materials exposed to natural climatic and light radiation after a period of time will be lost, fading, yellowing, peeling, cracking, loss of tensile strength and the whole layer off and so on. Even indoor light or sunlight through the glass window also cause damage to substances such as pigments or dyes. Therefore, for outdoor use of coatings, such as architectural coatings and automotive coatings, weatherability and light resistance is the most important test items.

Although we all agree that the weatherability and light resistance of the coating are important, but what is their best test method is till a dispute question . There are many ways to evaluate the weather resistance and light resistance of coatings at home and abroad. And commonly used in the natural climate aging test, xenon arc lamp irradiation, or carbon arc lamp irradiation, ultraviolet light irradiation and other artificial accelerated climate aging test method. This article will explore how to choose the appropriate test method.

Natural climate aging test
Natural climate aging test method is widely used at home and abroad methods. The main reason is that the natural climate aging test results are more realistic, the required cost is low and the operation is simple and convenient. Although we can carry out natural climate aging tests anywhere, the internationally recognized test site is Florida in the United States because of its sunny conditions.
However, the weakness of the natural climate aging test is that the test takes a long time, and the test personnel may not have been waiting for the test results of a product for so many years. In addition, even in Florida, the climate can not be exactly the same year after year, so the reproducibility of the test results is not ideal.

Xenon arc radiation test

The xenon arc radiation test is considered to be the most able to simulate the whole solar spectrum test, because xenon lamp chamber can produce ultraviolet light, visible light and infrared light. Because of this, at home and abroad is considered the most widely used method. GB / T1865-1997 (equivalent to IS0113411: 1994) describes this method in detail.

But this method also has its limitations, that is, xenon arc light source stability and the resulting complexity of the test system. The xenon arc light source must be filtered to reduce unwanted radiation. There are a variety of filter glass types to choose from for different irradiance distributions. The choice of glass depends on the type of material being tested and its end use. Changing the filter glass can change the type of short wavelength ultraviolet light that is transmitted, thereby changing the speed and type of damage to the material. There are three types of filters that are commonly used: daylight, glazing, and extended UV type (methods 1 and 2 mentioned in GB GB / T1865-1997 correspond to the first two types).

Typical xenon arc radiation is equipped with a irradiance control system. The irradiance control system is important in the xenon arc radiation test because the inherent stability of the xenon arc light source is worse than that of the fluorescent UV light. Someone abroad inspected a new xenon arc lamp and a use of 1000h old xenon arc lamp spectrum difference. It was found that the spectral energy distribution changed significantly not only in the long wavelength range of the light source, but also in the range of short wavelength. This change is caused by the xenon arc lamp aging, is its inherent characteristics.

A variety of remedies may also be taken for this change. Such as increasing the frequency of lamp replacement to reduce the impact of light aging. Or the sensor can be used to control the irradiance. Despite the change in the spectral energy distribution due to lamp aging, the xenon arc lamp remains a reliable and realistic light source that xenon Accelerated Aging Test Chamber is resistant to weathering and resistance to daylighting.

Most of the xenon arc radiation test uses a water spray and / or a temperature automatic control system (GB / T1865-1997 "Surface Water Spray") when simulating wetting conditions. The limitation of the water spray method is that when the relatively low temperature of the water is sprayed onto the relatively high temperature test plate, the test plate will cool down, which will slow down the process of material damage.

In the xenon arc radiation test, it is desirable to use high purity water to prevent the formation of deposits on the surface of the test panel. So the operating costs are higher.

Ultraviolet light irradiation test
UV light irradiation aging test using fluorescent UV light to simulate the destructive effects of sunlight on durable materials. This is different from the previously mentioned xenon arc lamp, fluorescent UV lamp in the electrical principle and ordinary lighting with cold light fluorescent lamp similar, but can generate more ultraviolet light rather than visible light or infrared light.
For different exposure applications, there are different types of lamps with different spectra for selection. The UVA-340 lamp simulates the sunlight well in the main short wavelength UV spectrum. The spectral energy distribution (SPD) of the UVA-340 lamp is very similar to that of the spectrum at 360 nm from the solar spectrum. UV-B lamps are also commonly used to accelerate the artificial weather aging test lamp. It is faster than the UV-A lamp to break the material, but its output at a shorter wavelength than 360nm will cause deviations from the actual test results for many materials.

Irradiance (light intensity) control is necessary to obtain accurate and reproducible results. Most UV-based Ultraviolet light aging test chamber devices are equipped with an irradiance control system. These precise irradiance control systems allow the user to select the irradiance metric when doing the test. Through the feedback control system, the irradiance can be continuously and automatically monitored and accurately controlled. The control system automatically compensates for insufficient illumination due to lamp aging or other causes by adjusting the power of the lamp.

The fluorescent UV light simplifies the irradiance control due to its inherent spectral stability. All the light source will become weak over time. However, unlike other types of lamps, the spectral energy distribution does not change over time. This feature improves the reproducibility of the test results and therefore , it is a major advantage.

Tests have shown that a lamp with a 2h lamp and a lamp with a 5600h lamp has no significant difference in the output power in an aging test system equipped with irradiance control, and the irradiance control device can maintain a constant light intensity. In addition,small UV aging testing machine spectral energy distribution has no change, which is very different with the xenon arc lamp.

One of the main advantages of using the violet lamp aging test is that it can simulate the destruction of the material in a more realistic outdoor wet environment. When the material is placed outdoors, it is reported that at least 12 hours a day is subjected to frequent dampness. Because this humid effect is mostly manifested as a form of condensation, and thus accelerated in the artificial climate aging test using a special condensation principle to imitate the outdoor wet.

During such a condensing cycle, the bottom of the chamber is heated to produce steam. The hot steam keeps the chamber at 100% relative humidity at high temperatures. In the design of the test chamber, the test panels shall be made to constitute the side walls of the test chamber. So that the back of the test plate is exposed to room temperature in the room air. The cooling effect of the indoor air causes the temperature of the surface of the test panel to be reduced by several degrees than the temperature of the steam. This temperature difference allows the water to continuously drop to the surface under test during the condensing cycle.

The resulting condensate is a stable, pure distilled water. This water can improve the reproducibility of experimental results, eliminate water pollution problems and simplify the installation and operation of test equipment.

Because the material in the outdoor damp time is generally very long, so the typical cycle of condensation system at least 4h test time. The condensation process is carried out under heating (50 ° C), which greatly speeds up the wet destruction of the material. The long-term, condensing cycle under heating conditions is more effective in reproducing moisturizing materials than other methods such as water spray, impregnation and other high-humidity environments.

4 Conclusion
Although the national standard and the current domestic anti-aging test method is xenon arc radiation, but in foreign xenon arc radiation and UV aging test are widely used test methods. These two methods are based on completely different principles. The xenon lamp illuminates the chamber to imitate all the solar spectrum, including ultraviolet light, visible light and infrared light, and its purpose is to simulate the sun. The UV aging test does not attempt to imitate the sun, but only to imitate the destruction of the sun effect. It is based on this principle, long

Outdoor exposure of the durability of materials, by the short-wave ultraviolet light caused by the greatest damage to the aging.

In addition, even in the natural climate under the aging test, there is an accelerated way is to be tested in the test plate can be mounted with the sun rise and fall of the shelf, so that most of the model to keep the state of direct sunlight, To obtain accelerated test results. Before the 1980s, carbon arc lamp or direct use of ultraviolet light irradiation, parallel test, but also shorten the test cycle, which test method is the best? No simple answer. The choice of method depends on the material to be tested, the final application of the material, the material being compromised, and the financial and other factors.


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