Polyesters are produced by polycondensation of polybasic acids and polyols. Polyesters are generally classified into saturated polyesters and unsaturated polyesters depending on whether the polyacid is saturated or not. For products such as fumaric acid or maleic anhydride, polycondensation with polyols is called unsaturated polyester. Saturated polyesters, unsaturated polyesters, and alkyd resins are polymer compounds with a polyester chain as the main chain. They are all linear molecules, R and R' represent the parent of acid and alcohol, respectively. Second, the difference between them is in addition to the fish R, R', but also on the side chain and end group. The difference between them is mainly in the side chains and end groups. The terminal groups of saturated polyesters are reactive hydroxyl or carboxyl groups. Saturated polyesters can be classified into three types: solvent-based coatings, water-based coatings, and powder coatings, depending on the type of coating they are configured with. According to its composition, it can be divided into hydroxyl-terminated polyesters and carboxyl-terminated polyesters. 1, hydroxyl polyester resin In the reaction of a polybasic acid and a polyhydric alcohol, when the polyhydric alcohol is present in excess, the ends of the products resulting from the condensation reaction are hydroxyl groups. As a result, the reaction must stop. Currently, in the industry, special hydroxyl-terminated polyester diols have been produced, mainly for semi-finished products of polyester resins. We can further improve the quality of the polyester diols and introduce new groups through esterification. Hydroxyl-terminated polyesters are used in paints. They can be cross-linked with amino resins as baking-type amino polyester paints. They can also be reacted with isocyanates to produce two-component polyurethane coatings. 2, carboxyl-terminated polyester resin In the reaction, if the carboxyl group is excessive, both ends of the condensation reaction product are carboxyl groups. It can also be obtained by esterification of a polyester diol with a dibasic acid. In order to increase the cross-linking solidification point of the carboxyl group in the molecule, the carboxyl-terminated resin can also participate in the direct condensation synthesis by the trifunctional trimellitic anhydride, so that the molecule contains a carboxyl group. The carboxyl-terminated polyester resin is mostly made of a solvent-free solid resin, which can be cured by a coach with a system such as an epoxy resin, as a polyester, epoxy powder coating material. 3, water dilution polyester resin As mentioned above, a carboxyl-terminated polyester resin containing trimethylene triacetic anhydride is synthesized, or a synthetic hydroxyl-terminated polyester resin containing trimellitic anhydride is synthesized because the molecule always contains a certain amount of carboxyl groups. At this point, the amine can be neutralized with an organic amine to synthesize an ammonium salt, which allows the polymer to "dissolve" in the water, anionically water-soluble polyester resin. At this time, a cross-linking agent such as an amino resin may be added and baked to obtain a paint film with better properties. It is also possible to use 2,2-dihydroxybenzene as a water-dilutable polyester resin instead of trimellitic anhydride, which has better hydrolysis resistance and higher stability in water. 4, high solid low viscosity polyester resin To make solids high, we must make the molecular weight low. General solvent type high solid polyester resins are used for amino group or polyurethane resins, so the number of hydroxyl groups on each molecule must be no less than 2 to be called macromolecules. Therefore, this is related to the molecular weight distribution of the manufacturing process. Coatings made of saturated polyester have many advantages such as high fullness, high gloss, good machinability, good weatherability, gloss retention, color retention, high yellowing, etc., and are widely used in high-grade industries. Paint and coil coating. Want to learn more about buttons: accessible For more details, please pay attention to WeChat public number: NANTONG MASTERPIECE TRADE CO.,LTD , https://www.yuaccessory.com