The fineness of the paint refers to the uniformity of the pigment contained in the paint dispersed in the paint, expressed in µm. The fineness of the paint directly affects the gloss, water permeability and storage stability of the paint film. The fineness of the coating is small, which can make the coating smooth and even, and play a beautifying effect on the appearance and decorative performance. Due to different varieties, the required fineness of the primer and topcoat is different. The fineness of the topcoat is generally required to be 20~40µm, and the fineness of the automobile, electrical appliances, and decorative topcoat is 10~20µm. The fineness can be thicker, generally 40~80µm. Some high-end cars and electrical appliances even require a fineness of ≤10µm.
The fineness is measured according to the national standard GB1724-89 (79), using a scraper Fineness Meter. It is constructed as a polished flat plate made of tool alloy steel. There is a groove on the board, and there are scale marks on the edge of the groove, which are divided into several specifications such as 0~50µm, 0~100µm, and 0~150µm. It is also equipped with a scraper, both edges are polished.
The technique of using this method is:
(1) Select Fineness Meters with different measuring ranges according to different coating types, and use a rough test with a large range first;
(2) On the top of the test plate, drop about 1~2g of paint sample, not too much or too little;
(3) Hold the scraper with both hands, make the scraper touch the surface of the polished plate vertically, and pull it from the deep part of the groove to the shallow part at an appropriate speed (generally takes 3 seconds), so that the sample is filled with the groove and flat No residual paint is left on;
(4) Read quickly in the sun (should not exceed 5 seconds), so that the line of sight is 15~30° from the surface of the ditch, and the reading shall be taken at the place where more than three particles are evenly exposed, and the reading method example is shown in the figure below);
(5) After use, the Fineness Meter needs to be carefully washed with a soft finger Busch reef solvent and dried.
The empirical method for determining the fineness is to measure whether the particles contained in a small amount of paint are uniform every day.
Products with unqualified fineness are mostly caused by improper grinding of pigments, entry of external impurities, and coarsening of pigments. It can be returned to the factory and then filtered, ground, or downgraded for use.
