Лако-красочные материалы — производство

Most inorganic pigments have surfaces sufficiently polar to have strong adsorption of dispersing agents. On the other hand, many organic pigments and carbon blacks have less polar surfaces, which leads to difficulty in having sufficient coverage of the sur­face by adsorption of the dispersing agent. In addition, they are very small in particle size compared to inorganic pigments and therefore have a very large specific surface area. As a result, they are not adequately stabilized by conventional dispersing agents. The requirement for brighter and more attractive colors in modern coatings has led to increasing use of organic pigments. Therefore, new and more effective types of dispersants have been developed, known as polymeric dispersants or hyperdispersants, which are gaining importance. Compared to conventional dispersants, polymeric dispersants characteristically have much higher MW

and many pigment affinic groups with a specific structure condu­cive for easy adsorption onto pigment surfaces, which gives durable adsorption. Polymeric dispersants consist of functional copolymers that provide effective stabilization of pigment particles against floc­culation by good steric hindrance, resulting from the loops and tails of the high MW polymer chains. For the most efficient steric stabi­lization, it is essential to have a polymer chain that is uncoiled and protrudes from the pigment surface as far as possible. Therefore, the polymeric dispersant must have good compatibility with the binder present in the system. The copolymer structure of hyperdispersants may be of different types (Figure 5.5), according to the distribution of monomers in the polymer chain, such as a statistical copolymer (random copolymer), block copolymer or graft copolymer. Typical dosage levels of polymeric dispersant are higher than those of clas­sical low MW dispersants and are normally calculated based on surface area or oil absorption values of the pigments. They are not restricted to organic pigments, as they are equally effective in inor­ganic pigments too.