Лако-красочные материалы — производство

One of the important classes of organic thickeners used in solvent — based coatings is based on hydrogenated castor oil and its modified amide, ether, and ester derivatives. The hydrogenated castor oil thi­ckener molecule, due to its three-dimensional structure and hydroxyl functionality, can form hydrogen bonds to another thickener molecule or with the solvent. This type of intermolecular association leads to formation of a network by intermolecular association, resulting in increased viscosity. In addition to hydrogen bonds, thixotropy also develops as a result of molecular chain entanglements. Under the influence of shear force, the entangled molecules or hydrogen bonds are disrupted, causing a reduction in viscosity. Hydrogenated castor oilbased thickeners are available in the form of a powder or paste, which has to be dispersed and activated in the coating system to achieve the full thickening effect. This is achieved under the influ­ence of shear forces and heat. Best effectiveness from these thicke­ners is achieved when they are partially dissolved in the coating system. Depending upon the chemical modification, the activation temperature ranges from 35 to 70 °C. Along with their advantages of thixotropic consistency and good flow properties, their main limi­tations are heat sensitivity, solvent dependence and tendency for seeding.

Polyamides

Polyamide thickening agents are available in a variety of chemical compositions depending on combinations of different carboxyls and amines as high MW waxy polymers with terminal amide groups. Their thickening effect in coatings is partly achieved by micelle formation resulting from their hydrophilic and hydrophobic ends, and partly by their association with pigment particles and chain entanglement. Hydrogen bond formation through amide groups also plays a role. A combination of such phenomena typically results in the shear-thinning flow of the coating. Stability and versatility are important merits of such thickeners. They may impair intercoat adhesion in certain systems.