Development and application of HAA weather-resistant powder coatings

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 Weathering resistant powder coating polyester /TGIC type can be made into thick coating film without pores because of no volatile matter in curing reaction, which has good weather resistance and excellent coating appearance.


However, the main disadvantage of polyester /TGIC powder coating is that curing agent TGIC is toxic and irritating to skin, and it is restricted by more and more countries due to the pressure of environmental protection and health situation.  

Polyester /HAA (hydroxyalkylamide) powder coating, which replaces TGIC curing agent, has experienced a tortuous development path for more than ten years. Under the pressure of the mainstream ideas of global health, environmental protection and energy saving, it is gradually maturing, and its market share is increasing year by year, accounting for about 40% of the weather-resistant powder market, close to half of the country. More than half of them are used in Europe, but the polyester /TGIC powder coating system is still dominant in China because of the backward process of environmental protection requirements.  

HAA system has the same outdoor durability as TGIC series powder. After many years of follow-up tests by many companies at home and abroad, it is an inevitable conclusion that HAA has completely or mostly replaced TGIC. Whether it is the increase of HAA users or the decrease of TGIC and PU users, it all originates from caring for human health, reducing pollution to the earth environment and saving energy.  


HAA system powder coating can realize low-temperature curing, non-toxicity, good storage stability, low cost of coating formulation, stronger HAA reaction activity than TGIC, and can be applied to friction gun spraying. Although HAA system has advantages in health and environmental protection, some physical and chemical properties restrict its development.  Hydroxyamide releases small molecular compounds such as water in the process of curing polyester. If the coating is too thick, pinhole will easily appear, and the heat resistance is worse than TGIC system. The surface of high gloss plane powder coating prepared by hydroxyalkylamide is not dense enough, which affects the decoration, and it is often used to produce powder such as sand grain, hammer grain, etc. that does not require smooth appearance. Therefore, it is necessary to focus on research and development to solve the technical problems of pinhole, yellowing and poor acid and rain resistance of thick coating.  

The representative product of HAA curing agent is XL552, whose weak points are flat appearance, yellowing and pinholes, which are also the key issues concerned by powder coating manufacturers, coating application enterprises and powder coating technicians. Through the research and practice in ROYAL Powder Coating Company of Turkey, QM 1260 and SF4510 have completely solved the problems of yellowing, gas baking resistance, hydrolysis resistance and pinhole in thick coating of XL552 by using Primid system improved curing agent products developed by EMS Company of Switzerland.  

Characteristics of the improved HAA curing agent QM1260 mainly solves the problems of yellowing, gas baking resistance and hydrolysis resistance of XL552. The curing agent QM 1260 is a compound containing polyhydroxy and alkyl functional groups, which belongs to HAA and can also replace TGIC as the curing agent of weather-resistant powder coatings. Used for crosslinking hydroxyl-containing polyester resin and polyacrylic resin, polyester powder coatings with no biological mutation, better weather resistance and no toxicity can be prepared, which is mainly attributed to the unique chemical structure of QM1260.

The hydroxyl group of curing agent QM1260 is in β position, which is easily influenced by N atoms and has very high activity. It can be used as a chemical intermediate, and it is easy to react with carboxyl groups, and can still be cured well with carboxyl-containing polyester resin and polyacrylic resin without catalyst.  In addition, the powder coating cured by QM1260 curing agent has better impact resistance and better leveling performance than the powder coating cured by TGIC. At the same time, because HAA has a high melting point, curing agent QM1260 can save energy very effectively, and it can be completely cured at 150℃/20-25min at the lowest. Curing agent QM1260 system powder coating has good triboelectric property, because of its hindered amine structure, which can reduce the spraying voltage, and can also be applied by rubbing spray gun.

Product index: ① Gardner color is less than 0.5; ② The moisture content is less than 1.0%; ③ The melting point range is 100-115℃; ④ The hydroxyl value is 550-650 mg/g.