The influence factors of the stain resistance test of the coating on the exterior wall of the building are discussed briefly

0 Foreword
synthetic resin emulsion exterior coating is a synthetic resin emulsion as the base material, adding pigments, fillers and a variety of additives configured as a water-based coating. Because of its low energy consumption, low pollution to the environment, no fire danger and so on, more and more people pay attention to, is widely used in the decoration and protection of the exterior wall. In addition, the outer wall latex paint rich in color, easy construction, easy maintenance, self-weight light, safe and reliable, so is gradually replacing the surface brick to become my foreign wall finish material leading . However, the serious lack of resistance to contamination has become an important problem in the promotion and application of wall coatings abroad. How to judge whether the stain resistance of the exterior paint is qualified, put an end to unqualified products applied to the external wall, its detection method is particularly important.
The current standard for stain-resistant testing countries is G B/T 9780-2005 "Building coating stain resistance test method", after many years of practice, found that the test error of the method itself is large, poor repeatability. Therefore, in the detection process for any factors can not be ignored, need to strengthen the control of all links. In this paper, a try-action discussion is made on various factors affecting stain resistance detection.principles and methods of the 1 stain resistance test
using the preparation of ash as the source of contamination, making it into a suspension solution, and attaching it to the coating test plate by brushing. With the prescribed water pressure, water quantity, in a certain period of time for even flushing, by measuring the change in the emission coefficient before and after the test to assess the resistance of the coating plate.2 Factors to be noted in the process of soil resistance testing
2.1 Pollution sources for testing
The standard has clear provisions for the pollution sources used in the test: fine 0.045 m square hole sieve, screen balance 5.0% ±2.0 12% ±2%, density (2.70±0.20) g/c m3, compared to surface area (440±20) m2/k g, reflection coefficient of 37% ±3%. Such a preparation of ash if they mix, it is difficult to meet all its requirements, if the specifications are not uniform, the accuracy of the test results can not be guaranteed, so should be to the standard home unit unified purchase. Because the pollution comes from a very light weight, water after dispersion is not ideal, where the black matter is easy to float on the surface of the water, each brush should be fully stirred, to be mixed evenly and then painted.
2.2 Brushing of the source of contamination
The brush quality of each test plate is (0.7±1) g according to the standard requirements, and too much or too little will affect the test results. With different soft brushes, the strength of the brush, have a great impact on the test results. Brush width and hair length, force weight and number of times than 0.7 g impact is greater, brush width is different, brush pollution source is one, some are two, two there is overlap, these factors will affect how many pollution sources remain on the test board, left on the test board pollution source is uniform. The result of excessive brushing often damages the coating film and affects the detection effect.
2.3 Water temperature
Because the standard does not specify the ambient temperature of the test and the temperature of the flushing water, the results of water flushing at different temperatures are different, summer and winter on the same variety of paint test results are often very different. The effect of temperature on stain resistance is studied in some articles. For the same coating film, the reflection coefficient drop rate of the coating film at 23 degrees C is higher than 15 degrees C, which can be more than 5 percentage points.
2.4 coating test plate
coating test plate if the density is low, the porosity rate is large, the water absorption rate is high, when scraping the coating will instantly absorb excess moisture in the coating, resulting in the coating film is not ideal, while the finished test plate surface will have more pinholes, in the soil resistance test is more susceptible to contamination. Because asbestos cement slab pre-treatment to soak water de-alkali, so in the process will produce deformation, so that in the scraping process will cause thick and uneven, this unevenness on the reflectivity has a great impact.
2.5 Scraping Process
does not specify scraping strength, speed and paint usage, but in practice these factors have an impact on the coating and the final result. Different scraping efforts will result in different pressures when the wire rod coater is in contact with the test plate, resulting in different coating thicknesses and different reflectivity test results after scraping of the same coating. The speed of scraping can also affect the thickness of the coating film, in general, the faster resulting coating thickness is thinner. The amount of paint is too low, which may cause the coating film to be incomplete, especially if the coating end of the coating is thinner.
2.6 reflectivity meter
reflectivity meter should comply with G B/T 9270-1988 4.3, and should be calibrated regularly. Before use, if there is not enough time to warm up, the data drift will be more serious. When working continuously, the measuring head should be placed on the blackboard during the test clearance to prevent photoelectrelation of selenium-optical batteries.
2.7 Flushing device
Flushing device should be strictly in accordance with the provisions of the standard, because the water tank volume, tank height, water pipe diameter, the angle of the model frame, etc. will directly affect the water flow pressure of the model contact, resulting in deviation from the test results.
2.8 Flushing process
the speed of the plate has an effect on the flushing results when flushed with water. The results will be different when the test plate is moved around at a faster frequency and at a slower frequency. With a slower frequency to move the test board, the test plate on the local surface of the powder ash will be washed away more, and even will appear after washing the test board surface contamination of the situation is very inconsistent. With regard to the amount of flushing, the flushing process requires uniform flushing, but is not specified in the standard.3 Conclusion
So many factors cause the test results of stain resistance to be more scattered, it is difficult to control the unity of so many factors, so in the usual testing process must pay attention to the control of each link.