Paint or Powder: the Advantages of Powder Coating
Powder coating was first commercially used in the late 1960’s, although like most innovative ideas, it was slow to start. It has become the fastest growth area in the painting industry, at the expense of the wet paint industry.
Six reasons why powder coating is replacing wet paints
Nearly all wet paint systems require more then one coat, but all wet paint systems take a long time to dry unless stoved. Compared to powder coating, which normally requires one coat only, it can be painted, cured and ready to pack in twenty minutes. The moment it is cool after having been fully cured in an oven, it is as hard as it will ever get, and can be wrapped.
2. Environmentally friendly
It is now important to be seen as environmentally friendly. Powder coating does not rely on the use of solvents. The powder melts to form the liquid coating. It does not generate odours during the curing, and can be used on hot areas like domestic radiators.
On long runs, the powder that is not attracted to the work piece is collected, sieved and passed through the guns again. Many plants are able to achieve 96% efficiency.
4. Anti corrosion
Wet paints can be diluted with as much as 90% solvents. When these solvents evaporate they can leave pores in the paint film. These are weaknesses against moisture permeating through the paint to the surface of the metal. A powder coating is a solid film, offering a more watertight shield. It is for this reason that one coat used to be considered enough, and that it did not need to be as thick as a wet paint film giving the same corrosion protection.
5. Tough finish
The most popular resin used for powder coatings is polyester. This is a long chain molecule, which is both tough and flexible. Powder coatings are generally tougher and harder wearing then wet paints.
6. Easier application
Six examples of why powder coating is often a better finish than liquid paints
1. No runs
Runs are rare, as the molten powder is viscous.
2. No overspray
Spraying a complicated component using a wet paint on a motorbike frame or a balustrade with uprights every 100mm presents problems with overspray. In order to get a wet paint to flow out and look smooth and shiny, the coating has to be applied wet, so that the paint droplets flow into each other. This usually means the gun has to be close to the work piece so that the paint does not dry in the air on its way to the surface. This produces a dry rough finish, like sand paper. On a motorbike frame or a balustrade as the gun is concentrated on the nearest tube, the overspray will ruin the tube previously sprayed. With powder coating, the whole component is sprayed with powdered paint, and only once all the painting has been completed, is it then heated to melt the powder to a liquid. Over spray is then not a problem.
3. Even coating due to wrap around
Again using the motorbike frame or a railing, the advantage of spraying with electro static powder is the wrap around effect. A tube can be sprayed from one side with an intended film thickness of 50 microns, if the guns position is stationary the wrap round will coat the other side to an about 30 microns. This makes the spraying considerably easier and enables a more even coating.
4. Good edge cover
Because of wrap round, edges and difficult areas to see are not missed as they can be with wet spraying.
5. New powders with reduced orange peel
One of the criticisms of powder coating is that it suffers from excess orange peel. All paints suffer from orange peel effect. This is due to the surface tension of the paint whilst in the liquid state. The more viscous the paint, the thicker the coat applied in one coat, the more orange peel. Because up to 90 microns of powder can be applied in one coat, compared to 30 microns of cellulose the orange peel effect can be very noticeable. It can be reduced by by using more expensive powder resins and flowing agents. Powders have improved considerably over the years. They offer a better waterproof film, improved UV stability and flow reducing orange peel.
6. Car industry
The car industry is keen to move to powder because of the above reasons, and because all the painting can be completed in three coats. (Primer, colour and lacquer.) A superb finish that is comparable to multiple coats of wet paint is now available with acrylic polyester hybrid lacquers, these are expensive, but are used on a number of car production lines.