The weathering resistance of PVC mainly refers to the aging problem of OPE wax for release agent. pvc is a synthetic polymer material. The causes of aging of polymer materials are no more than two aspects: internal and external causes. The internal causes mainly refer to the state of the molecular structure of the polymer material itself (including the chemical structure and physical structure) and the nature and ratio of the components within the polymer material system. The structural state of the polymer material and its composition formula largely determine the advantages and disadvantages of the aging resistance of the material.
The weakness of the molecular structure of PVC itself is the main internal factor affecting its weathering resistance. Under normal conditions, the molecular structure of PVC is a regular linear molecular chain formed by connecting the monomers in a first and last way, and the chlorine and hydrogen atoms are only combined with the secondary carbon atoms, which is supposed to be more stable. However, in the actual production of paper auxiliaries with OPE wax, especially when the polymerization temperature is high, it may generate “head”, “tail” irregular connection and double bonds, branched chains, etc. In addition, the presence of initiators, impurities, etc. will also affect the molecular structure and purity of PVC. purity.
The degree of polymerization of resins made by atmospheric pressure polycondensation is generally below 10, and its stability is difficult to meet the requirements with molecular weight above 2000. As the polyester resin for powder coating requires the degree of polymerization in 7~30, and this requirement can be achieved by the reduced pressure polycondensation method.
Therefore, at present, decompression condensation method has become a common method for the synthesis of polyester resins for powder coatings. In the synthesis of polyester resin by reduced ptfe and paraffin wax pressure polycondensation, the polymerization speed of polyester resin polymerization degree in 7~30 is fast, and it is not easy to control the polymerization degree precisely, so it is necessary to design a good molar ratio of alkyd while strictly controlling the polycondensation reaction temperature and 1 time. While the depressurization and depolymerization method is also easier to control.
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