Fineness is used to measure the size and uniformity of dispersion of particles such as pigments and extender pigments in the paint, expressed in microns (μm). The back paint and top coat of coil coatings have high requirements on the fineness, which is generally controlled at 15-25 μm, while the fineness of the primer can be coarser, 20-40 μm. Generally speaking, coatings with small fineness can make the coating smooth and uniform, have a coalification effect on appearance and decoration, and have good mechanical properties.
The measurement of fineness mainly adopts a scraper Fineness Meter with a range of 0-50 μm, and the inspection method and standard equivalent adopt the national standard GB1724-89 coating fineness measurement method. The structure of the scraper fineness gauge is a polished flat plate made of tool alloy steel. There is a groove on the board (there are also 2 grooves), and there are scale marks on the edge of the groove, generally divided into several specifications such as 0-50μm/0-100μm/0-150μm, and equipped with a scraper with a hardness lower than that of the scraper .
When measuring the fineness of paint, pay special attention to the following aspects:
1. Choose Fineness Meters with different measuring ranges according to different coatings;
2. Drop about 1-2g of paint sample on the top of the side plate;
3. Hold the scraper in balance with both hands, make the scraper contact with the surface of the scraper vertically, and scrape it off at an appropriate speed to ensure that the sample is filled with the groove and no residue is left on the scraper.
4. Take the reading quickly under the light, keep the line of sight and the surface of the groove at an angle of 15-30° when reading, and take the reading where more than three particles are evenly exposed.
5. In order to ensure the test accuracy of the paint fineness index, it is recommended to take the average value of multiple measurements.
