According to the film-forming substances, powder coatings are mainly divided into two categories: "thermoplastic powder" and "thermosetting powder" coatings. (Other types of powder coatings will not be discussed temporarily)
1. Thermosetting powder coating
Thermosetting powder coating is composed of five parts: thermosetting resin, curing agent, pigment, filler and auxiliary agent. Thermosetting powder coatings also include: epoxy resin, polyester, acrylic resin.
2. Thermoplastic powder coating
Thermoplastic powder coating is composed of five components: thermoplastic resin, pigment, filler, plasticizer and stabilizer. Thermoplastic powder coatings also include: polyethylene, polypropylene, polyester, polyvinyl chloride, chlorinated polyether, polyamide, cellulose, and polyester.
3. The particle size requirements of powder coatings
Generally speaking, the smaller the particle size of the powder, the better the smoothness of the coating during curing; under the same spray thickness, the powder with a smaller particle size is less likely to have particles; the smoother and smoother the appearance of the coating film.
But the powder particle size is too small will also affect the other quality of the coating, for example: when using electrostatic spraying, the main adsorption force is electrostatic force, the charge of the powder is proportional to the square of the particle size of the powder, but too large powder due to gravity, It has fallen off the surface of the workpiece, resulting in a decrease in the powder loading rate. Generally, the powder less than 10μm is basically uncharged; the powder less than 10μm is more likely to form agglomerates and absorb moisture, which affects spraying; in addition, when the powder particle size is less than 10μm, the powder recovery rate will be lower It will be extremely low. Not easy to recycle.
Advantages of powder coatings:
The main reason is that the English does not contain organic solvents, so that organic solvents will not cause pollution to the environment and can also solve the problem of powder waste. Because powder sprayed coatings can be used for secondary use, coatings, if the recycling efficiency of the equipment is high, Then the utilization rate of powder coating can be as high as 99%. In addition to the previous, the efficiency of powder coating is also very high. Only one coating can reach the thickness of a few or even a dozen coatings of solvent-based or water-based coatings, and this coating is not affected by temperature and is automated The degree is usually higher.
Powder coating has obvious advantages, but there are also some small shortcomings.
For example: powder coating requires special spraying equipment, and powder coating manufacturers need to purchase professional equipment; during the production and coating process, it is relatively troublesome to change the color and variety of the coating; powder coatings should only be thickly coated, not thinly coated ; The baking temperature of powder coatings is more than 180 ℃. Except for UV-curable powder coatings, most varieties are not applicable, especially heat-sensitive substrates such as plastic, wood and paper with poor heat resistance.