The reason why latex paint needs to be tested for stain resistance is that in actual use, the wall is susceptible to contamination by dust, pollutants, etc., especially in poor air quality or polluted environments, these pollutants will adhere to the surface of the coating, affecting its aesthetics and protective properties. Stain pick-up resistance tests can be used to assess the coating's resistance to contaminants over time, thus ensuring that it will maintain its good appearance and protection over time.
In order to ensure that the emulsion paint has good stain resistance in use, relevant test methods are required. Here are three commonly used methods for testing stain resistance:
1. GB/T9780 Test method for stain resistance of architectural coatings
This method uses fly ash as a contaminant, which is applied to a coating sample and then rinsed with a dose of water. Stain resistance is assessed by measuring the change in reflection coefficient before and after contamination. It is calculated as follows:
where X is the percentage of stain resistance; A is the original reflectance coefficient of the coating; B is the reflection coefficient after contamination; C is the reflection coefficient of fly ash. The disadvantage of this method is that changes in the characteristics of fly ash may affect the reproducibility of test results.
2. ASTM D 3719-2000 Quantitative Test Method for Stain Resistance of Coatings
In this method, the test plate is exposed to a 45° angle position for 61 days, and then stain resistance is assessed by measuring the reflection coefficient before and after exposure. It is calculated as follows:
thereintoDdirtis stain resistant;Liis the reflectance coefficient of the coating after exposure,Lais the reflectance coefficient of the coating before exposure. The challenge with this approach is that the consistency of the test environment is difficult to control and does not match the inclination of the actual wall, which can affect the accuracy of the results.
3. Clariant's stain resistance test method
This method uses a formulated suspension of contaminants as a source of contamination, which is evenly poured onto the test plate, and then the reflectivity of the coating is measured. The test results are averaged over multiple measurements to improve accuracy. This method is closer to the contamination of the actual building coating film, as the contaminant suspension can be formulated to simulate the contamination under different environmental conditions.
