Electrostatic spraying requirements for powder coatings

Generally the thickness of less than 35 (or 30) u coating is called a thin layer powder coating, compared with the thickness of the coating is usually 50-70u about half lower, as a thin layer powder coating must have some characteristics.
The first is to have excellent hiding power, to be able to cover the substrate well at a thickness of about 30u, it is necessary to increase the share of color pigments (such as titanium dioxide), to obtain a good leveling when the coating is thin Sex, but also must reduce the paint base ratio (in other words, increase the share of the resin in the formula); because these two points lead to a significant reduction in filler content in the formula, so the powder production costs will increase significantly.

Secondly, the resin suitable for thin-layer powder coatings should have a low melt viscosity, on the one hand, it can fully wet the substrates and pigments, on the other hand, it has good leveling properties. Using this characteristic to analyze polyesters and hybrids Powder coating formulations, the higher the melt viscosity of the poor wettability of the pigment, and therefore not suitable; and polyurethane, acrylic, epoxy powder coating formulations with lower melt viscosity, it is more suitable.

Combining with China's national conditions, acrylic resin and polyurethane resin are still difficult to popularize. Epoxy resin combined with excellent curing agent is a more feasible development path.

The particle size distribution of the powder is also a very important characteristic for thin layer powder coatings. If the maximum thickness is 30u, the maximum particle size of the powder should be less than 60u (approximately 260 mesh), so it is necessary to strengthen the grinding to make the powder finer. But on the other hand, But it will easily produce a higher proportion of ultra-fine powder less than 10u. It is well known that too much ultra-fine powder can cause a series of problems, such as clogging the spray gun, low dusting rate, and agglomeration. Therefore, it is not necessary to achieve an ideal particle size distribution. An easy thing.

Epoxy resin, acrylic resin and urethane resin should consider the contradiction between viscosity and glass transition temperature. It is also a difficult problem to solve. In general, the viscosity of small vitrification temperature will be low; the small viscosity will help the coating flow, However, the low glass transition temperature makes the powder easy to clump and the storage stability is poor. Therefore, on the one hand, the molecular weight distribution should be controlled narrowly; on the other hand, the synthesis formula and production process of these resins should also be adjusted so that the performance of these two aspects can be achieved. Take care of it properly.

Thin-layer powder coating is still in the development stage in China, and the way to go is still very long, but in any case, this is a development direction. Although thin-layer powder coating production cost is high, but the price is high, but ultimately for the user can Saving powder costs about 15-20%.

Heavy Duty Powder Coatings

Heavy-duty anti-corrosion powder coatings have better anti-corrosion ability. Due to the requirement of higher corrosion resistance, novolac epoxy resins are used. Novolac epoxy resins are very different from commonly used bisphenol A series epoxy resins. The molecular structure of novolac resin as the main chain, each molecular chain contains more than three epoxy groups, because its molecules have three functionalities (Bisphenol A series epoxy resin has only two functionalities) When cured, the cured product has a high cross-linking density. Therefore, its heat resistance, mechanical strength, and chemical resistance are superior to those of bisphenol A series epoxy coatings.

At present, it is widely used in foreign countries and is mainly used for the coating of petroleum, natural gas, and chemical pipelines. It can also be applied to the coating of metal parts with heavy corrosion protection requirements in chemical plants. In China, the powder coating of this species is still in its infancy and is used. Not much, but with good prospects for development.