0. Foreword
Synthetic resin emulsion exterior wall paint [1-2] is based on synthetic resin emulsion as base material, adding pigments, fillers and various additives configuration of water-based paint. Because of its low energy consumption, low pollution to the environment, and no fire hazards, it has attracted more and more attention and has been widely used in the decoration and protection of exterior walls. In addition, the exterior wall latex paint is rich in color, convenient in construction, convenient in maintenance, light in weight, and safe and reliable. Therefore, it is gradually replacing the tile to become the dominant material for exterior wall cladding in China. However, the serious lack of stain resistance has become an important issue for the promotion and application of external wall coatings in China. How to determine whether the stain resistance of the exterior paint is qualified or not, and to prevent substandard products from being applied to the exterior wall, the detection method is particularly important. At present, the standard adopted by countries for the detection of stain resistance is GB/T9780-2005 “Test Method for Stain Resistance of Architectural Paint Coatingsâ€. After many years of practice, it has been found that the method itself has a large test error and poor repeatability. Therefore, any influencing factors cannot be ignored in the inspection process, and the control of each link must be strengthened. This article has conducted a tentative discussion on various factors that affect the detection of stain resistance.
1. The principle and method of stain resistance test
The ash was used as a source of contamination, and it was made into a suspension, which was attached to a coating test panel by brushing. With the specified pressure and amount of water, uniform flushing is performed within a certain period of time. The stain resistance of the coated test panel is evaluated by measuring the change in the emission coefficient before and after the test.
2. Influencing factors that should be noted during the stain resistance test
2.1 Test source
The standard specifies the source of pollution for the test: fineness 0.045mm square hole sieve, sieve residue 5.0%±2.0%, loss on ignition 12%±2%, density 2.70±0.20g/cm3, specific surface area 440±20m2 /kg, reflection coefficient 37% ± 3%. It is difficult to meet all of the requirements for such a formulated ash mix. If the specifications are not uniform, the accuracy of the test results cannot be guaranteed at all. Therefore, it should be purchased in a unified way. Due to the fact that the pollution is light and light, the dispersibility after adding water is unsatisfactory, in which the black material easily floats on the surface of the water. Before each brushing, it should be fully stirred. After mixing, it should be brushed.
2.2 Brushing of Pollution Sources
According to the standard, the brushing quality of each test panel is 0.7±1g, too much or too little will affect the test results. With different soft brush, the size of the brushing force has a great influence on the test results. The width and length of the brush, the weight and frequency of the force applied are greater than 0.7g. If the width of the brush is different, some of the sources of the brush are one, some are two, and there are overlaps between the two. These factors will affect the number of sources of pollution. Stay on the test panel and check whether the source of contamination on the test panel is even. Excessive brushing often results in damage to the coating and affects the test results.
2.3 Water temperature
Since the standard does not stipulate the test environment temperature and the flushing water temperature, the results of water flushing at different temperatures are not the same, and the test results for the same type of paint in summer and winter are often quite different. Articles [3] studied the effect of temperature on stain resistance. For the same coating film, the reflection coefficient of the coating film at 23°C decreases more than 15°C, which can exceed 5 percentage points.
2.4 coating test plate
If the coated test plate has low density, high porosity and high water absorption, it will instantly absorb excess water in the coating when the coating is applied, resulting in unsatisfactory film formation of the coating. At the same time, there will be more needles on the surface of the test plate after completion. Holes are more likely to be contaminated during stain resistance tests. Since asbestos-cement-cement slabs are treated with soaking water to remove alkali, they will be deformed during this process. This will cause uneven thickness during the coating process. This unevenness has a great influence on reflectivity.
2.5 Scrape process
The standard does not specify the strength, speed, and amount of paint applied, but in practice these factors will affect the coating and the final result. Different squeegeeing forces will result in different pressures when the bar coater contacts the test plate, resulting in different coating film thicknesses and different reflectance test results after the same type of paint is applied. The speed of the squeegee speed will also affect the thickness of the coating film. Generally speaking, the film thickness obtained by the faster speed is thinner. Too little paint may cause incomplete film coating, and may cause thinner coating film at the end of the draw.
2.6 Reflectance Tester
The reflectance tester should meet the requirements of 4.3 in GB/T9270-1988 and should be regularly calibrated. Before use, if there is not enough time for warm-up, data drift will be more serious. When working continuously, the measuring head should be placed on the blackboard during the test gap to prevent the photoelectric fatigue of the selenium photocell.
2.7 Washing device
The flushing device should be strictly in accordance with the provisions of the standard, because the tank volume, the height of the tank, the internal diameter of the water pipe, the angle of the sample rack, etc., will directly affect the pressure of the water contacted by the sample, causing deviation of the test results.
2.8 Washing process
When flushing with water, the speed of the test plate has a certain influence on the flushing result. Moving the test plate around with a faster frequency and at a slower frequency will result in different results. Moving the test plate with a slower frequency, the fly ash on the local surface of the test plate will be flushed more, and even the phenomenon that the surface of the test plate after scouring is contaminated is inconsistent. Regarding the amount of flushing, the flushing process requires uniform flushing, but there are no regulations in the standard.
3. in conclusion
Such a large number of factors have resulted in the dispersion of the test results of stain resistance. It is difficult to control the integration of such many factors. Therefore, it is necessary to pay attention to the control of each link in the ordinary detection process.
Synthetic resin emulsion exterior wall paint [1-2] is based on synthetic resin emulsion as base material, adding pigments, fillers and various additives configuration of water-based paint. Because of its low energy consumption, low pollution to the environment, and no fire hazards, it has attracted more and more attention and has been widely used in the decoration and protection of exterior walls. In addition, the exterior wall latex paint is rich in color, convenient in construction, convenient in maintenance, light in weight, and safe and reliable. Therefore, it is gradually replacing the tile to become the dominant material for exterior wall cladding in China. However, the serious lack of stain resistance has become an important issue for the promotion and application of external wall coatings in China. How to determine whether the stain resistance of the exterior paint is qualified or not, and to prevent substandard products from being applied to the exterior wall, the detection method is particularly important. At present, the standard adopted by countries for the detection of stain resistance is GB/T9780-2005 “Test Method for Stain Resistance of Architectural Paint Coatingsâ€. After many years of practice, it has been found that the method itself has a large test error and poor repeatability. Therefore, any influencing factors cannot be ignored in the inspection process, and the control of each link must be strengthened. This article has conducted a tentative discussion on various factors that affect the detection of stain resistance.
1. The principle and method of stain resistance test
The ash was used as a source of contamination, and it was made into a suspension, which was attached to a coating test panel by brushing. With the specified pressure and amount of water, uniform flushing is performed within a certain period of time. The stain resistance of the coated test panel is evaluated by measuring the change in the emission coefficient before and after the test.
2. Influencing factors that should be noted during the stain resistance test
2.1 Test source
The standard specifies the source of pollution for the test: fineness 0.045mm square hole sieve, sieve residue 5.0%±2.0%, loss on ignition 12%±2%, density 2.70±0.20g/cm3, specific surface area 440±20m2 /kg, reflection coefficient 37% ± 3%. It is difficult to meet all of the requirements for such a formulated ash mix. If the specifications are not uniform, the accuracy of the test results cannot be guaranteed at all. Therefore, it should be purchased in a unified way. Due to the fact that the pollution is light and light, the dispersibility after adding water is unsatisfactory, in which the black material easily floats on the surface of the water. Before each brushing, it should be fully stirred. After mixing, it should be brushed.
2.2 Brushing of Pollution Sources
According to the standard, the brushing quality of each test panel is 0.7±1g, too much or too little will affect the test results. With different soft brush, the size of the brushing force has a great influence on the test results. The width and length of the brush, the weight and frequency of the force applied are greater than 0.7g. If the width of the brush is different, some of the sources of the brush are one, some are two, and there are overlaps between the two. These factors will affect the number of sources of pollution. Stay on the test panel and check whether the source of contamination on the test panel is even. Excessive brushing often results in damage to the coating and affects the test results.
2.3 Water temperature
Since the standard does not stipulate the test environment temperature and the flushing water temperature, the results of water flushing at different temperatures are not the same, and the test results for the same type of paint in summer and winter are often quite different. Articles [3] studied the effect of temperature on stain resistance. For the same coating film, the reflection coefficient of the coating film at 23°C decreases more than 15°C, which can exceed 5 percentage points.
2.4 coating test plate
If the coated test plate has low density, high porosity and high water absorption, it will instantly absorb excess water in the coating when the coating is applied, resulting in unsatisfactory film formation of the coating. At the same time, there will be more needles on the surface of the test plate after completion. Holes are more likely to be contaminated during stain resistance tests. Since asbestos-cement-cement slabs are treated with soaking water to remove alkali, they will be deformed during this process. This will cause uneven thickness during the coating process. This unevenness has a great influence on reflectivity.
2.5 Scrape process
The standard does not specify the strength, speed, and amount of paint applied, but in practice these factors will affect the coating and the final result. Different squeegeeing forces will result in different pressures when the bar coater contacts the test plate, resulting in different coating film thicknesses and different reflectance test results after the same type of paint is applied. The speed of the squeegee speed will also affect the thickness of the coating film. Generally speaking, the film thickness obtained by the faster speed is thinner. Too little paint may cause incomplete film coating, and may cause thinner coating film at the end of the draw.
2.6 Reflectance Tester
The reflectance tester should meet the requirements of 4.3 in GB/T9270-1988 and should be regularly calibrated. Before use, if there is not enough time for warm-up, data drift will be more serious. When working continuously, the measuring head should be placed on the blackboard during the test gap to prevent the photoelectric fatigue of the selenium photocell.
2.7 Washing device
The flushing device should be strictly in accordance with the provisions of the standard, because the tank volume, the height of the tank, the internal diameter of the water pipe, the angle of the sample rack, etc., will directly affect the pressure of the water contacted by the sample, causing deviation of the test results.
2.8 Washing process
When flushing with water, the speed of the test plate has a certain influence on the flushing result. Moving the test plate around with a faster frequency and at a slower frequency will result in different results. Moving the test plate with a slower frequency, the fly ash on the local surface of the test plate will be flushed more, and even the phenomenon that the surface of the test plate after scouring is contaminated is inconsistent. Regarding the amount of flushing, the flushing process requires uniform flushing, but there are no regulations in the standard.
3. in conclusion
Such a large number of factors have resulted in the dispersion of the test results of stain resistance. It is difficult to control the integration of such many factors. Therefore, it is necessary to pay attention to the control of each link in the ordinary detection process.
Guangzhou Jointair Co., Ltd. , https://www.jointair.cn