It varies from species to species, but basically consists of two steps of polycondensation and blending.
The polycondensation methods are: 1 melt polycondensation method. The polycondensation is directly melted with an acid and an alcohol without adding other components. The water formed by the reaction is separated by a separation column by using a difference in boiling range between the alcohol and the water. This method is simple in equipment, short in production cycle, and widely used. 2 solvent azeotropic dehydration method. Toluene or xylene (solvent) is added during the polycondensation, and the azeotrope of toluene and water is lower than the boiling point of water, and the water formed by the reaction is quickly taken out to promote the polycondensation reaction. The advantage of this method is that the reaction is relatively stable, easy to master, and the color of the product is good, but a set of water refluxing device is needed, the reaction process is toluene, and the polycondensation section is explosion-proof. 3 decompression method.
When the amount of shrinkage in the polycondensation reaches 2/3 to 3/4, it is evacuated until the acid value reaches the required level. 4 pressurization method. Pressurization accelerates the reaction, shortens the reaction cycle, and increases productivity. The blending component is intermixed with wet premixing. Intervention mixing is to mix reactive solid prepolymer, solid crosslinker, glass fiber, catalyst and coloring material to form molding compound; wet premixing is to use styrene as crosslinking agent to make liquid unsaturated polyester and glass. The fiber, the catalyst, the lubricant, the colorant and the like are kneaded in a kneader to form a polyester dough molding compound.
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