Overview
Color paint fineness plate, also known as scraper fineness meter, is an instrument used to determine the degree of dispersion of pigments, fillers and other particles in color paint, varnish and other similar products. The working principle is to place the specimen on a grooved plate with a depth gradient and scrape it at a uniform speed with a scraper to form a wet film from thick to thin. Observe the position of the particles and correspond to the trench depth scale to determine the fineness of the sample. Fineness is an important index to evaluate the quality, storage stability and appearance of the final coating film of the coating grinding process, and its measurement results directly affect the application performance of the product.
Preparation before operation
The operating environment should be clean, dry and vibration-free, the temperature should be controlled at 23±2°C, and the relative humidity should be 50%±5%. Ensure that the measuring surface of the fineness plate and scraper is clean and wear-free and free of residual specimens. Before use, you can wipe it with a soft cotton cloth dipped in a suitable solvent, and check whether the blade of the scraper is straight and there are no gaps. The sample to be tested should be thoroughly stirred and filtered or diluted according to the product standard if necessary to ensure that the sample is representative and the viscosity is suitable.
Procedure:
Drop an appropriate amount of stirred specimen on the deeper end of the groove of the fineness plate so that it is full and slightly redundant. Hold the scraper in both hands so that it is perpendicular to the surface of the plate, and pull the scraper from the deep to the shallow part of the groove at a uniform speed (about 1-2 seconds), so that the specimen is laid flat in the trench to form a flat wet film. The scraping action should be consistent and smooth, ensuring that the scraper remains perpendicular and in full contact with the slab surface throughout the process. After scraping, within 5 seconds, under the specified lighting conditions (usually uniformly diffused natural light or artificial light source, observed at an angle of 20°-30° from the surface of the plate), the location of particle aggregation in the wet film should be observed.
Method of interpreting results
When observing, the line of sight should be basically perpendicular to the trench plane. The interpretation point of the fineness value is usually the starting position of continuous or discontinuous particle stripes, and the groove depth scale value corresponding to this position is the fineness of the specimen. If the particles are evenly distributed and there are no obvious strials, it is interpreted as the position where the individual particles are clearly visible. Three parallel assays are usually performed, and the instrument is cleaned before each assay. If the three readings are consistent within the accuracy range of the instrument, the value is taken as the final result; If there is a discrepancy, find the cause and re-measure. The results are expressed in microns (μm) and indicate the fineness plate range used (e.g., 0-25 μm, 0-50 μm, 0-100 μm, etc.). The fineness value (D) can be regarded as a characteristic parameter of the size distribution of the particle group, and its significance can be approximated as the critical size of the larger particles in the sample.
Notes:
It should be interpreted immediately after scraping to avoid solvent volatilization affecting observation. Fineness plates in different ranges are suitable for samples with different fineness ranges, and improper selection can lead to inaccurate results or damage to the instrument. During operation, the impact or jump of the scraper with the plate should be avoided. Immediately after use, the fineness plate and scraper should be thoroughly washed with a suitable solvent, dried with a clean soft cloth, and stored in a dry and non-corrosive environment. Regularly check the instrument's groove depth using a standard calibration plate or gauge block to ensure measurement accuracy. If there are visible scratches or wear on the working surface, stop using it.
FAQs
| phenomenon | Possible causes |
| Poor repeatability of readings | the sample is not uniformly dispersed; uneven scraping speed; Environmental conditions fluctuate. |
| Scratches appear on the wet film | the blade edge of the scraper is damaged; The surface of the plate has hard particles. |
| The stripe borders are blurred | poor lighting conditions; improper observation angle; The sample solvent volatilizes too quickly. |
| The reading is always biased at one end of the range | Improper selection of range; The sample viscosity is too high or too low. |
Cited Literature
GB/T 1724-2019 Colored paints, varnishes and printing inks - Determination of grinding fineness
ASTM D1210-21 Standard Test Method for Fineness of Dispersion of Pigment- Vehicle Systems by Hegman-Type Gage
ISO 1524:2020 Paints, varnishes and printing inks — Determination of fineness of grind