Powder coating curing reactions can be divided into two types, one is the direct reaction without small molecule release type, such as the reaction of carboxyl groups with epoxy groups, and hydroxyl groups with unblocked isocyanate groups. Polyester / epoxy mixed indoor powder coatings, polyester / TGIC outdoor powder coatings, GMA acrylic resin / DDDA transparent powder coatings, pure epoxy powder coatings, etc., which are widely used in the market, undergo curing reactions during the curing process. No extra small molecules are produced.

Another type of curing reaction releases small molecules, such as polyester / β-hydroxyalkylamide outdoor powder coatings, hydroxypolyester / tetramethoxymethyl glycoluril powder coatings, and hydroxyl / blocked isocyanates (such as Evonik B1530 ) Powder coating system, which releases water, methanol and isocyanate blocking agent respectively during the curing process. The small molecules released by the curing reaction converge into bubbles and are discharged from the coating film. However, due to the increased viscosity of the powder system and the problem of film thickness, some of the small molecules are too late to be released and are wrapped in the coating, resulting in pinholes. Therefore, this type of powder coating not only has native pinholes to be solved, but also small molecular bubbles that are generated and aggregated need to be eliminated. Of course, it is worth mentioning that because the deblocking temperature of the B1530 sealant is relatively high, about 160 ° C, the system has sufficient time and low viscosity to level and release the trapped gas before deblocking. The pinhole problem is not particularly obvious.

Practice has shown that benzoin alone cannot solve this pinhole problem significantly. The elimination of pinholes in such powder coatings requires the use of other defoamers and deaerators in addition to the use of benzoin.