The methods used to detect and evaluate the degree of pigment dispersion in industrial production generally include scraper Fineness Meter method, visual dry film method and pigment color development method.
(1) Scraper Fineness Meter method _ to evaluate the degree of dispersion of pigments in coatings in industrial production, the scraper Fineness Meter is usually used to directly measure the most group of pigment particles present in the pigment dispersion. In production, pigments are ground to a specified fineness requirement. The national standard GB1724 stipulates the method of measuring the fineness of paint with a scraper Fineness Meter, and puts forward the technical requirements for the scraper Fineness Meter (also called grinding fineness plate). The polished plate of the scraper Fineness Meter (as shown in Figure 3-9) is made of tool alloy steel (brand Cr12), and there is a long groove (l55mmX12mm) with a slope on the plate. According to different specifications, within 150mrn length It is engraved with equal division scale lines representing different groove depths, the front group roughness Ra is 0.20µm and the division value error is ±0.001mm. The scraper is made of high-quality tool carbon steel (brand T10A), both edges are polished, the length is 60mm, the width is 42m. : m, the roughness of the blade grinding group, is 0.20µm.
Determination method It is advisable to drop a few drops of the sample in the deepest part of the groove of the scraper Fineness Meter to fill the groove structure with a little excess. Hold the spatula with both hands, and place it horizontally on the edge of the sample at the upper end of the Tangguang flat plate. The scraper is in vertical contact with the surface of the polished flat plate. Within 3:s, pull the scraper from the deep part of the groove to the shallow part, so that The sample is full of the groove and there is no sample left on the flat plate. Immediately (no more than 5s) after the scraper is pulled, make the line of sight and the groove plane form an angle of 15°~30°, observe the evenly exposed part of the particles in the groove with the light, and write down Reading (if there are individual particles exposed on other graduation lines, the reading and the adjacent graduation line shall not exceed 3 particles). This method is widely used in solvent-based paint systems. For the determination of pigment paste of latex paint , Apply the emulsion base material "see thin" slurry and then test, otherwise it will be difficult to observe.
(2) Visual inspection of dry film method simply visually inspects the dry film state and is widely used to evaluate the degree of pigment dispersion. Apply a thin layer of slurry or paint on a transparent exposed material (such as a glass plate), and form a film after diluting with water if necessary. After the coating film is dry, compare it with the standard coating film sample. The degree of dispersion of pigments is judged by the degree of detectable defects observed, such as small grains beyond the surface of the coating film and (or) spots that can be identified by projected light are defects caused by poor dispersion of pigments.
(3) Pigment color development method The degree of dispersion of pigments is closely related to the performance of coatings. With the help of some subjective methods to test certain properties of coatings (films), it is also easy to make qualitative judgments on the dispersion state of pigments. If the pigment is not sufficiently dispersed (grinding process is insufficient) or if the paint slurry is prohibited from coagulation caused by the wrong paint operation in the later stage, this ill state can be displayed by the following method, by manually processing a part of the (wet) coating film, and waiting for it to dry Finally, compare the differences in color, tinting strength or hiding power of the treated and untreated coating films to make the difference. Although there is some debate about how manual processing should be done, the following methods are generally used.
① Refers to the grinding method to scrape or spray a latex paint on the non-porous substrate . When the paint film is semi-dry and semi-wet, use your index finger to make a rotary motion on the film within a small range to form a polished circular area. After the paint film is dry, compare the color of the ground circular area and the surrounding unground area to determine the degree of dispersion of the pigment. If there is no obvious color difference between these two areas, it means that the pigment is well dispersed; if there is obvious color difference, there is a problem with the pigment dispersion. If the color in the grinding area is thicker, it means that the color pigment is not well dispersed. If the pigment in the grinding area is lighter, It is the poor dispersion of self-color (or light-color) pigments.
②Brushing and dripping method: Brush a layer of latex paint on the non-porous substrate vigorously. After the paint film is half dry, apply 2~3 full paints on the painted paint film. After the operation, compare the color difference between the paint drop and the surrounding brushed rattan film. The judging rules are similar to finger grinding.
(4) Other methods In fact, any performance of the coating can be related to the degree of pigment dispersion in the coating. Although general optical and rheological properties are commonly used to determine the state of dispersion, many properties are also available, and electrical properties are sometimes used for this purpose. Herbst (H, erbst) used color gray scale, hue, viscosity and gloss to evaluate the degree of dispersion. There are countless research reports on the performance of coatings and the degree of dispersion of pigments, many of which can be found as a method for judging the degree of dispersion of pigments
