Principle
A scraper fineness meter is an instrument used to determine the degree of dispersion of pigments or solid particles in slurry inks, coatings, and other products. It works by scraping to form a wedge-shaped film, which evaluates the fineness of the sample by observing the position of the scale in which the particles appear in the film. The fineness value, usually expressed in micrometers (μm), reflects the size of the largest particles in the sample or the uniformity of the dispersion of the particle population, and is one of the key indicators for controlling product quality.
The standard scraper fineness meter is mainly composed of two parts: the scraper and the scraper. The surface of the scraper has precise wedge-shaped grooves that increase the groove depth from zero to the maximum depth uniformly along the length and is engraved with a corresponding depth scale. The scraper is a double-edged knife to ensure a close fit with the scraper surface. The material of the instrument must have sufficient hardness, wear resistance and corrosion resistance, usually made of stainless steel or tool steel, and the roughness of the working surface must meet the standard requirements to ensure the uniformity of the scraped film and the measurement accuracy.
Procedure:
Before the assay, ensure that the sample is uniform and crusty and performed under standard temperature and humidity conditions. The specific steps are as follows:
1. Clean the scraper and scraper with solvent to ensure that there is no residue on the surface.
2. Take an appropriate amount of sample and place it at the deep end of the wedge-shaped groove of the scraper.
3. Hold the scraper perpendicular to the surface of the scraper and scrape the sample towards the shallow end of the groove at a uniform speed and appropriate pressure to form a film with a continuous decreasing thickness.
4. After scraping, observe the film at a specific angle (usually 15-30 degrees) under a standard light source (such as north-facing natural light or a prescribed artificial light source). The fineness value is read as a scale value where there are obvious particle streaks or a certain number of particle clusters, which represents the size of the larger particles in the sample.
5. The same specimen is measured at least three times in parallel, and the same or close readings are taken as the results.
Influencing factors
The smaller the measured fineness value, the finer the pigment particle dispersion and the higher the fineness of the product. This result directly affects the printing properties of the ink, such as gloss, coloring power, and leveling. The main influencing factors include: the quality of the sample dispersion process, the compatibility of resin and solvent, ambient temperature and humidity, the technique of scraping (speed and pressure), and the conditions of observation and interpretation. To ensure comparable results, standardized operating procedures must be strictly followed.
Relevant standards
The manufacturing and measurement methods of scraper fineness meters are subject to a number of domestic and foreign standards, which provide a unified basis for quality control.
| GB/T 1724 | Coating fineness measurement method |
| GB/T 6753.1 | Determination of fineness of color paint, varnish and printing ink |
| ASTM D1210 | Fineness test method of pigment-paint system |
| ISO 1524 | Determination of fineness of color paint, varnish and printing ink |
Notes:
The instrument should be thoroughly cleaned with a suitable solvent immediately after use to avoid sample curing damage to the working surface. It should be stored to prevent bumps and corrosion. Regularly use standard plates to check scale accuracy. Pay attention to safety during operation to avoid scratching hands with scraper blades. For samples with different viscosity ranges, it may be necessary to adjust the sampling volume and scraping force, and experience can help improve the consistency of interpretation.
References
National Technical Committee for Standardization of Coatings and Pigments. Coating fineness measurement method. China Standard Press.
American Society for Testing and Materials. Standard Test Method for Fineness of Dispersion of Pigment-Vehicle Systems by Hegman-Type Gage.
International Organization for Standardization. Paints, varnishes and printing inks — Determination of fineness of grind.