Why Powder Coating better than painting ?There are four major reasons for considering powder coating over liquid paint:
- To reduce VOC (Volatile Organic Compound) emissions,
- To produce better coatings with improved corrosion protection,
- To reduce production costs,
- To improve Employee safety.
There are two ways to reduce pollution: by installing expensive equipment to treat the pollutants produced; or by eliminating the source of the pollutants. Obviously the second method is more economical. Equipment installed merely to prevent the discharge of pollutants to the environment represents an extra expense which contributes nothing to profitability. Production processes which minimize the production of pollutants at their source are a more positive solution and are less expensive in the long run.
Powder coating eliminates the air and water pollutants produced by solvent paint lines. As a bonus, working conditions are cleaner, healthier and safer.
Nevertheless, although everyone is more aware of emissions problems and anti-pollution laws and regulations are becoming tougher, there are two better reasons for powder coating. As we shall see, powder coatings are superior in quality to solvent-based paint coatings and their cost is competitive.
According to the United States Department of Commerce, the annual loss due to corrosion in this country is ten billion dollars. Powder coatings can help reduce this figure. Coatings formed from dry powders are homogeneous, coherent and free from porosity caused by solvent evaporation. Many experts believe that this is one of the reasons why dry powder coatings exhibit greater corrosion resistance than coatings formed from the same resins in liquid coatings systems. This is further complimented by the user’s selection of predetermined chemicals.
An example of the superior performance of powder coatings over liquid paint systems has been reported by a Canadian manufacturer of steel battery boxes for electric trucks. They found that even the highest quality liquid paint provided protection for only six months. The paint film on the batteries scratched and chipped in service. Battery acid would then penetrate beneath the paint film at these points and attack the otherwise unexposed substrate.
The manufacturer switched to an epoxy powder coating. This coating also gets scratched and chipped during service as batteries are removed for charging and replaced. But, although battery acid attacks the exposed metal, it does not penetrate between the intact film and its substrate. After 18 months there were no signs of deterioration of the epoxy coating or its bond to the substrate.
In order to achieve sufficient thickness to provide the necessary corrosion resistance, most liquid paints must be applied in two passes. Electrostatic spray powder coatings from 1- to 6-mils thick can be applied in one pass. This eliminates the need for two coating booths.
An automotive parts manufacturer had difficulty passing a 96-hour salt spray test with a one-coat liquid paint system. Since converting to an epoxy powder coating, also applied in one pass, the manufacturer gets over 200 hours in the same test. The powder coating also withstands subsequent forming operations.
Powder coatings produce no drips, runs or sags. Edge coverage and coverage inside holes and recesses is excellent. With the electrostatic spray process, the coating powder envelops the part. In addition, the insulating effect of the powder already adhering to the surface limits build-up, thus helping to control coating thickness. Thickness is relatively uniform even on complex shapes.
Powder coatings are cost competitive with liquid paint. In fact, many powder coatings cost less than equivalent coatings formed from liquid paint, because:
- Powders are 100 percent solids.
- Efficient powder recovery provides nearly 100 percent material utilization.
- The coating line can be completely automated and requires very little maintenance.
Electrostatic( powder coating ) spray coating provides other savings, too. ie:
- No solvents, thinners, or chemicals are required at all; not for mixing, not for cleanup.
- In many systems, simple degreasing is sufficient pretreatment. However, iron or zinc phosphate treatment will improve adhesion.
- There are no paint filters, no wash chemicals.
- Cooling or heating of recovery air is not required as clean air is returned to the plant after filtering.
It is no exaggeration to say that the development of the electrostatic powder spray process is a fourth reason for the current powder revolution.
In the electrostatic spray process (Fig. 3) powder is drawn from its container and carried to the spray gun by clean, dry compressed air. Individual particles of powder are electro-statically charged as they pass through the gun. The part to be coated is grounded, and therefore at a lower potential than the charged particles, so an electrostatic field is generated between the tip of the gun and the workpiece. Particles projected from the gun are attracted to the surface of the part and adhere to it until they are fused to the surface and heat cured in the bake oven into a homogeneous coating.
Electrostatic spray can apply powder coatings as thin as 1-mil. As “thin film” refinement continues in the development of powder coatings, lower film build can be expected. The heat retention properties of the part are not a factor. The same thickness can be applied to thin as well as thick sections.