During the production process, it mainly controls the temperature, airflow, agitation, pressure and acid value. In the production process of unsaturated polyester resin, there are mainly the following parts of the temperature to be controlled: the material temperature at the center of the reactor: the material temperature at the wall of the reactor is determined by the steam temperature at the top of the oil temperature fractionation column, often referred to as "distillation head temperature" The temperature of the inlet and outlet water of the device, the temperature of the material in the center of the dilution tank; the temperature of the medium in the jacket of the dilution tank.
The temperature of the central part of the reaction kettle is the temperature of the reactant, but the temperature of the material close to the wall of the kettle is directly affected by the temperature of the medium in the jacket, and its temperature is different from the central part. Under good agitation, the difference is not large. When the agitation is poor, there is a significant temperature difference, the temperature at which the resin is polymerized is not uniform, and local gel may even occur. The temperature of the oil in the jacket should not be too high, otherwise the reactants will heat up too fast, and coking and scaling may occur on the kettle wall.
The control of the steam temperature at the top of the fractionation column, that is, the "head temperature" is also important. In the polyesterification reaction, the temperature should be controlled at about 100 ℃, because there is a large amount of alcohol in the reactant, the alcohol can form an azeotrope with water, at a lower temperature, the alcohol is distilled off, causing the loss of alcohol, up to Less than synthetic requirements. For ordinary resins, the ratio of phthalic anhydride, cis-complex and alcohol is 1:1:2:2, and the alcohol loss is less. For a high content of maleic anhydride or fumaric acid polyester, such as phthalic anhydride, maleic anhydride and the ratio of 1:3:4:4, if the temperature of the top of the fractionation column exceeds 105 ℃, it will cause serious loss of alcohol. Unsaturated polyester is a linear polymer compound with multi-functional groups. It has a recurring ester bond and an unsaturated double bond on its backbone main chain, and has carboxyl groups and hydroxyl groups at both ends of the macromolecular chain.
The double bond on the main chain can undergo copolymerization crosslinking reaction with the vinyl monomer, so that the unsaturated polyester resin changes from soluble and meltable state to insoluble and infusible state. The ester bond on the main chain can undergo a hydrolysis reaction, and an acid or a base can accelerate the reaction. If copolymerized with styrene and cross-linked, the occurrence of hydrolysis reaction can be greatly reduced.
The temperature of each of the above points can be recorded and monitored by a multi-point temperature recorder, and can also be controlled by a computer.