In the actual application process, the paint is often directly contacted with humid air or water. With the expansion and water permeability of the paint film, various damage phenomena such as blistering, discoloration, peeling, and decreased adhesion will occur, which directly affect the paint. Therefore, some coating products need to be tested for water resistance. The water resistance of the paint film is related to factors such as the polar groups contained in the resin, the water-soluble salt in the pigment, and various additives in the coating film, and is also affected by the surface treatment of the coated object and the drying conditions of the coating film, etc. factors.
At present, the commonly used water resistance determination methods generally include the following: normal temperature water immersion method; boiling water method; accelerated water resistance method.
(1) Normal temperature water immersion method
The normal temperature water immersion method is a commonly used method, which is suitable for most varieties such as alkyd and amino paints. The national standard GB/T1733-93 stipulates that 2/3 of the area of the painted sample should be placed in the steaming water at a temperature of 23°C ± 2°C, and taken out after the soaking time specified in the product standard is reached, and visually evaluate whether there is foaming or loss. Light, discoloration and other phenomena can also be used to measure the loss of light and the degree of adhesion of the paint film. This method is simple and easy to implement, but the water quality used has a great influence on the water resistance of the paint film.
(two) soaking water method
The method of immersion in boiling water is suitable for the coating film that is often in contact with the utensils containing hot water, hot soup, etc. to draw objects. When measuring, immerse 2/3 of the area of the painted sample in boiling steaming water, take it out after reaching the time specified in the product standard, and visually inspect damage phenomena such as blistering, rust, loss of gloss, and discoloration. In this method, the boiling water should always be kept in a boiling state. In order to maintain the same liquid level during the test, it is also necessary to supplement it with boiling water.
(3) Accelerated water resistance method
Although the room temperature water immersion method is simple and easy, it takes a long time to test some coatings, which affects the turnover of products. In order to shorten the cycle and speed up the test process, GB/T5209-85 "Determination of Water Resistance of Paints and Varnishes - Immersion Method" stipulates that the flowing water method at 40 °C ± 1 °C is used to specify the water quality. Use a Circulating Chiller or pass in dry, oil-free compressed air to keep the water flowing, and the conductivity of the water should not be greater than 2µs/m.
Through the test, it can be found that the white amino paint reaches the same level of damage when compared with the immersion method at 25 °C ± 1 °C in flowing water at 40 °C ± 1 °C, and the acceleration rate is 6 to 9 times. The test that takes 3 days can now be shortened to the same day and the results can be obtained, which greatly improves the test efficiency.
