Popular science of coatings: the relationship between oil absorption and dispersion of pigments

In the 100g weight of the pigment, add the refined linseed oil drop by drop, and knead it with the ink adjusting knife (scraper) When adding oil for the first time, the pigment still remains loose With the increase of the amount of oil added, the loose particles are connected with each other until the last drop of oil is added, so that all the pigments stick together The oil used in this test is the oil absorption of the pigment The amount of oil absorbed by pigment is related to the degree of dispersion There are two explanations: one is that the amount of oil absorption is related to the gap between pigment particles When the dispersion is increased, the particle I gap is decreased and the oil absorption should be decreased Another view is pigment It is related to the surface phenomenon at the paint interface With the increase of dispersion, the specific surface area of pigment particles increases, so the oil absorption should be increased accordingly When some people study the relationship between the properties of ultramarine, chromium oxide and iron red and their dispersity, they have come to a conclusion: if the particle size distribution of pigments is within a narrow range, the factors that determine their oil absorption are not only the free space between particles, but also the surface phenomenon, but also the white space between particles It also depends on the absorption capacity of the pigment According to the experiment, when the bulk pigment is finely milled, the following changes occur among the pigment particles; because of the damage of the aggregate, the porosity of the particles is reduced, the surface of the particles is flattened, and the specific surface is increased The decrease of porosity and the flattening of surface cause the decrease of oil absorption, but the increase of specific surface should cause the increase of oil absorption If the effect of the reduction of porosity and the flattening of surface roughness is greater than the increase of specific surface, the oil absorption will decrease; otherwise, the oil absorption will increase The results showed that the oil absorption of chromium oxide and ultramarine decreased with the increase of dispersion, but that of iron red increased with the increase of dispersion Following chart