Too low or too high baking temperature is not conducive to obtaining a low matting effect. Generally, it is recommended that between 170 e – 220 e is ideal. As the structure of the matting agent has a high activity of the ring amidine, so the temperature should not be too high in the extrusion process, too high extrusion temperature will lead to part of the powder pre-crosslinking, affecting the matting effect and leveling. Matting paths are diverse, generally speaking, chemical matting can provide stable reproducibility and good matting effect.
In the use of the matting agent, it must be noted that the addition of excessive matting agent is also inappropriate. The polycarboxylic acid matting agent containing cyclic amidine can provide excellent leveling effect, and also has a good blocking effect on hot water and surfactants. However, the mechanical properties (such as impact properties) are poor as a result of shrinkage of the coating film. Also, due to the presence of cyclic amidine, the tendency of yellowing of the coating film during baking is very serious. In addition, the baking temperature is also an important factor affecting the matting of this system.
The most classic curing agent with two functional groups is the familiar polycarboxylic acid and cyclamidine salt, usually used as pure epoxy and mixed matting curing agent. The mechanism is: the amount of cyclamidine in the curing agent is not enough to completely cure the epoxy resin, only part of the pre-crosslinking wax additive definition , as the temperature continues to rise, the reaction activity of the lower carboxylic acid and epoxy reaction, because of the carboxylic acid multifunctional groups, so the reaction must be accompanied by a strong contraction of molecules. However, this phenomenon is partially offset by the previously pre-crosslinked resin and limits its further mobility. The further cross-linking is not fully compensated by the uniform shrinkage of the coating film.
This eventual shrinkage hindrance therefore leads to uneven shrinkage points on the surface of the coating film, which causes matting. In the hybrid system, in addition to the above reaction, the curing agent in the amine structure also plays a catalytic role in the epoxy and polyester, but the actual reaction mechanism is more complex, the formula must have enough reactants and curing agent reaction, so the polyester in this complex system also plays an extremely important role, its physical and chemical properties have a great impact on the matting effect. In other words, similar polyesters from different manufacturers do not necessarily produce the same matting effect. Therefore, the selection of suitable polyester is very critical, in the mixed system in the amount of matting agent should take into account the amount of epoxy resin consumed by the reaction of the carboxyl end polyester, that is, part of the resin and the carboxyl end polyester cross-linking reaction.
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