Лако-красочные материалы — производство

There are two major chemical processes used for manufacturing alkyds: the fusion process and the azeotrope process (solvent process). The fusion process is an old method of manufacturing alkyd that involves fusing all components at elevated temperature. An inert gas is continuously purged in the system to avoid oxidation as well as to drive off water of the reaction. Alkyds made by this process are often darker in color. Due to the possibilities of sublima­tion of phthalic anhydride and loss of polyols, this process suffers from poor reproducibility. In the solvent process, poly condensation is carried out in the presence of a small quantity (5 to 10 % of reac­tion mass) of hydrocarbon solvents (normally xylene or toluene) in the reaction mixture. Thus, water of the reaction is carried to the condenser as an azeotrope with the solvent, and upon condensation, being immiscible, water is separated from the solvent and the sol­vent is returned to the reactor. While the process requires complex condensation and separation equipment, most of the alkyds cur­rently manufactured use the solvent process because it reduces the loss of components, allows a lower esterification temperature, gives superior color to the product, and is a faster reaction due to better agitation resulting from viscosity reduction by the solvent. In both processes, the progress of the reaction is monitored by intermittent measurement of viscosity increase and decrease in acid number of samples of the reaction mixture.