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Powder coatings with crosslinking accelerators
2017-8-31 23:01:19
Powder coatings with crosslinking accelerators
The crosslinking rate of the resin and crosslinking agent can be changed by the crosslinking accelerant of powder coatings, and the crosslinking promoter is often required when the carboxyl polyester resin used in TGIC crosslinking is synthesized.
Due to the polyester resin for end carboxyl polyester resin, crosslinking agent used TGIC for compounds containing epoxy groups, can promote the epoxy groups and carboxyl reaction has a variety of crosslinking promoter, mainly imidazoles, imidazoline, ammonium salt, phosphate salt etc.
The use of crosslinking accelerator can accelerate the reaction activity, which can greatly improve the processing efficiency, reduce the baking temperature and time, and achieve the purpose of saving energy. The crosslinking density and mechanical strength of the coating can also be improved indirectly by adding crosslinked accelerant.
For beta hydroxy alkyl amide, however, the reaction of hydroxyl and carboxyl polycondensation reaction, so the reactions associated with the structure and composition of polyester, usually used TGIC crosslinking promoter on its doesn't work, can reduce polyester resin instead after China's entry into wto and the crosslinking rate of beta hydroxy alkyl amide.
Because in the case of without additives, polyester resin and crosslinking agent of beta hydroxy alkyl amide reaction rate is fast enough, and as the end carboxyl polyester resin of beta hydroxy alkyl amide crosslinking mechanism and different: TGIC TGIC type mainly epoxy groups and end carboxyl of TGIC polyester resin addition reaction of carboxyl, did not produce by-products.
The hydroxy beta hydroxy alkyl amide and end carboxyl polyester carboxyl polycondensation, produce water molecules, so if the crosslinking rate is too fast and reactivity difference is bigger, coating has been part of the crosslinking, may lead to reaction in heating concentration of water molecules into water vapor removal, easy to produce pinhole on the coating.
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However, if the crosslinking rate is more moderate, the melted coating has a smaller viscosity, and the water generated in the pre-reaction can be easily removed and the thickness of the thick film pinhole can be increased. Therefore, the reaction rate of partial auxiliaries to delay resin and crosslinking agent can be added in practice.
In order to further improve the activity of the system, it is necessary to increase the polycondensation reaction of hydroxyl and carboxyl crosslinking promoter, crosslinking temperature can be reduced to 150 ℃ or less, the research work is under way.
The synthesis of a carboxyl ester resin, so it is an acid overdose. However, if all formulations are put into the reaction kettle at one time, the viscosity of the resin is large, the relative molecular weight is wide, the appearance of powder coating is poor, and the impact resistance is poor. If the initial input material for excess alcohol, synthetic end hydroxyl polyester resin after first, then add part polybasic acid, then get the resin molecular weight distribution is narrow, characterized by lower viscosity, in addition with the crosslinking agent crosslinking reaction rate is more appropriate, the final coating with good performance.
Preparation of powder coatings. The preparation of powder coatings used the traditional melt extrusion method, the solid material after weighing the premixed, extruder melt extrusion, cooling, crushing, fine crushing, grading sieve powder coating product.
In the process of pulverizing, it can also be added to the adjuvant to further improve the thickness of the thickness of the coating. The higher the temperature, the shorter the reaction time.
In terms of coating aging, in addition to the sun's ultraviolet light, must also consider the water vapor transmittance, due to the structure of isophthalic acid restricted the molecular motion, so the water vapor transmittance of benzenoid polyester film significantly higher than that of benzenoid between polyester film, so isophthalic acid has good weatherability. Therefore, the influence of different monomers on the resistance of coatings should be considered when designing the formulation of weather-resistant polyester resin.
Copyright: Zhang Jia Gang YaRui Chemical co.,Ltd
Copyright: Zhang Jia Gang YaRui Chemical co.,Ltd
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