The sagging performance of the coating is an important index for determining the thick build (thick film) coating. Due to the inappropriate flow of paint on the vertical surface to be coated, the uneven streaks and flow marks of the paint film are the sag phenomenon, which is reflected in the construction. The anti-sag performance is the maximum wet film thickness that the paint can make at one time .
The national standard GB9264-88 stipulates the method for measuring the relative sagging performance of colored paints. The instrument used is composed of three multi-groove scrapers (the test ranges are 50~275µm, 250~475µm, 450~675µm) and a base. Each scraper can scrape the color paint to be tested into 10 parallel wet films of different thicknesses, the width of each wet film is 6mm, the distance between the strips is 1.5mm, and the thickness The difference is 25µm. (See Figure 3_7_2, Figure 3_7_3).
There are the following steps and precautions during the test.
(1) Put the glass plate on the appropriate position of the base.
(2) Place the scraper on the top of the test panel with the scale facing the operator.
(3) Pour a sufficient amount of well-stirred sample evenly on the opening in front of the scraper applicator. Note that the two-component coating should be stirred evenly and have a certain potency and service life. The single-component coating should not allow the solvent to volatilize excessively .
(4) Hold the west end of the scraper applicator with the west hand, make it scrape smoothly and continuously from top to bottom, and keep it straight without ups and downs, and complete this operation within 2 to 3 seconds.
(5) Immediately place the test panel after scraping the coating film vertically, and pay attention to make the strip film horizontal and keep "thin at the top and thick at the bottom" when placing it, that is, place the strip film with a small scale on the top of the test panel. When observing the reading, check the sagging situation. If the film of this thickness does not flow into the film of the next thickness, that is, when the dividing line is clear, the thickness of this film is the humidity thickness without sagging, in µm. Due to the reason of scraping, the area within 20mm at the west end of the coating film is not counted, and the dividing line in the middle section of the film is observed.
The measurement of anti-sag performance can judge the dry film thickness and coating dosage of a film-forming coating. Generally, the anti-sagging performance of thick-film coatings should be above 400µm wet film, which can ensure the dry film thickness required for anti-corrosion. For some special types of one-time film-forming coatings, its wet film can reach 1200µm in one spray or one-step coating, and its anti-sag test result is above 1200µm, and the scraper for judging the anti-sag performance above 600µm needs to be customized from the manufacturer.
