The relationship between the mechanical properties of the resin after curing and the composition and structure of the polyester has the following five aspects.
(1) When the molecular weight of the polyester increases, the strength, hardness, and especially the bending strength of the resin after curing increases.
(2) When the number of unsaturated bonds in the molecular chain of polyester increases, the cross-linking point in the resin increases, the stiffness increases after curing, and the wear resistance increases.
(3) The degree of linear growth of the polyester molecular chain during the polycondensation reaction determines the tensile strength of the resin. If both the diol and the dibasic acid do not contain non-aromatic unsaturated bonds, a strict linear type can be obtained. Long-chain molecules that grow; if the reaction product contains a large amount of unsaturated double bonds, cross-linking between the double bonds may occur, the molecular chain may not be linearly grown, and the strength is affected. Therefore, to increase the tensile strength, The polycondensation reaction should be controlled to prevent cross-linking in the reaction and to maximize the esterification reaction.
(4) When the polarity of the polyester molecule increases, the bending strength of the resin after curing increases. The hydroxyl group, carboxyl group, ester bond and ether bond in the molecular chain are all groups which increase the polarity of the resin molecule.
(5) The order of structural arrangement in the molecular chain of polyester increases the tensile strength. In order to obtain an orderly arrangement of structures, including the orderly arrangement of polar groups, the type of dibasic acid and diol can be selected. Minimize; if necessary, use a two-step process for polycondensation.