Selection of
Powder Coatings (1)
Thermosetting powder coatings are composed of resins, curing agents, pigments, fillers and other additives. The selection of these raw materials is very important because they have a significant impact on the quality of their coatings and film performance.
1. Selection of resin
The structure and performance of resin are the main factors that determine the quality and film performance of
powder coatings, and should have the following basic technical requirements:
(1) The resin for thermosetting
powder coatings must contain active functional groups to ensure the formation of a network structure during baking and film formation.
(2) In the process of powder coating construction, if the decomposition temperature of the resin is very close to the melting temperature, it is very difficult to control the heating temperature. Therefore, the temperature difference between the melting temperature and the decomposition temperature of the resin is required to be large.
(3) The melt viscosity of the resin is required to be low and narrow. When the temperature above the melting point is reached, the viscosity should drop rapidly. In this way, a coating film with better leveling can be obtained after the powder coating is coated on the object to be coated by electrostatic spraying, fluidized bed dipping and other methods.
(4) The coating oversprayed in the powder coating can be recycled and reused. However, some powder particles have been in contact with air for a long time, and because of the influence of moisture and temperature, the physical and chemical stability of the resin is better.
(5) The production of
powder coatings generally adopts mechanical pulverization, which can obtain uniform particle size distribution and particle shape. The resin should choose a higher glass transition temperature and melting point, so that it has better crushability.
(6) The adhesion of
powder coatings depends on resin to play a key role. If the adhesion of the coated object is good, there is no need to apply a primer, and the durability of the coating film is also good. Thermoplastic resins have poor adhesion, so pre-primer is required.
(7) The resin is required to be light in color, transparent and non-toxic.
