Overview
Ink fineness plate inspection is a classic method used to assess the degree of dispersion of pigment particles in binding materials. The detection intuitively reflects the grinding process quality and dispersion stability of the ink by observing the aggregation of pigment particles on a specific scraping plate. Fineness values are usually expressed in microns, and smaller values indicate more uniform pigment dispersion and tend to have better printability, gloss, and color saturation. This method is widely used in ink manufacturing and quality control due to its ease of operation and intuitive results.
Detection principle
The core principle of inspection is the use of a scraper with precision wedge-shaped grooves. An appropriate amount of ink sample is placed at the deeper end of the groove and scraped along the length of the groove with a squeegee at a constant speed and pressure. Since the groove depth decreases linearly to zero in the direction of scraping, the pigment particles dispersed in the ink spread with the scratch. When the groove depth is less than the pigment aggregate size, the aggregate is "plowed out" by the edge of the scraper, forming visible streaks or particle spots along the scrape path. Observe the scale position where these stripes begin to appear densely, and the groove depth value corresponding to this position is the fineness of the ink.
The main testing instrument is the fineness plate, usually made of single or double stainless steel plates, and its wedge groove processing accuracy must meet relevant standards. Auxiliary tools include scrapers, ink mixers, and illuminated observation devices. The fineness value D can be calculated by the geometric relationship of groove depth, if the scraping length is L, the total groove depth is H, and the distance between the point of the streak and the starting point is l, then the approximate is:
D ≈ H × (l / L)
Operation process
First, make sure that the fineness plate and scraper are clean and free of wear. Take an appropriate amount of uniform ink sample and place it in front of the deepest end of the groove of the fineness plate. Hold the scraper to make it perpendicular to the board surface and perpendicular to the groove edge, and scrape the ink through the entire groove area at one time with a stable and rapid action, forming a layer of ink film that transitions from thick to thin. After scraping, the location of the concentrated particle stripes in the ink film should be observed at a perspective of about 30 degrees under a standard light source within three seconds. Read the scale value corresponding to this position, which is the fineness result of the sample. Three parallel measurements are usually taken to average the two results that are consistent or close.
Influencing factors
Fineness detection results are directly related to the application performance of the ink. Excessive fineness indicates that the pigment is not fully dispersed, which may lead to problems such as false dots, pasting plates, and poor gloss during printing. There are various factors affecting the test results, including the hardness and particle size of the pigment itself, the wetting ability of the binder to the pigment, the efficiency and duration of the grinding process, as well as the ambient temperature during testing and the consistency of the operation technique. The test results should be comprehensively judged based on the ink type and application field.
Technical standards
The ink fineness detection method has been included in a number of domestic and foreign standards, which have uniformly stipulated the specifications of the fineness plate, scraper parameters, operating environment, observation conditions, etc., to ensure the reliability and comparability of the test results. Following standards is fundamental to effective quality control.
| Standard system | Standard numbering example |
| Chinese national standards | GB/T 13217.3 |
| American Society for Testing and Materials standards | ASTM D1316 |
| International Organization for Standardization Standards | ISO 1524 |
| Japanese industrial standards | JIS K5701 |
Epilogue
As a basic and effective physical test method, ink fineness plate detection provides key data for evaluating the dispersion quality of pigments. Correctly understanding its principles, strictly standardizing operations, and comprehensively analyzing it in combination with other performance tests are of great significance for optimizing ink formulations, improving production processes, and ensuring the quality of final prints. With the advancement of testing technology, this method will continue to complement modern instrumental analysis methods and continue to serve the quality control system of the ink industry.
References
National Ink Standardization Technical Committee. Ink fineness inspection method. GB/T 13217.3-2008.
American Society for Testing and Materials. Standard Test Method for Fineness of Grind of Printing Inks by the NPIRI Grindometer. ASTM D1316-20.
International Organization for Standardization. Paints, varnishes and printing inks — Determination of fineness of grind. ISO 1524:2020.