White black blue red yellow paint cans, close up of red powder and pan out of paint cans.

If you looked at two finished parts that were painted – one with powder and one with liquid, you most likely would not be able to tell the difference. In addition to that, a similarly structured powder coating and liquid coating can share nearly identical performance characteristics (durability, color palette, etc.). What truly sets the two a part?

 

Besides a few obvious properties, the main differences are the surface preparation and the application method.

 

Surface Preparation

 

Powder coatings actually melt before fully curing. In this molten state, the coating adapts to the substrate and spreads. During this process, it is difficult to obtain excellent adhesion, corrosion, and flexibility. In order to ensure those qualities are achieved, an extensive pretreatment process is necessary. Typical pretreatment processes come in three, five, or even seven step procedures.

 

Liquid coatings don’t require nearly the same preparation. This process can be as simple as cleaning, sanding, or blasting the substrate that will be painted.

 

However, when powder and liquid coatings are tested head-to-head with the same pretreatment system, the results can be identical.


Application Method

 

It is obvious that powder and liquid can’t be applied the same way, but it is important to understand the vehicles used to get paint from the container to the part. For liquid coatings, the vehicle is water, solvent, low viscosity resins, and other raw materials. The water and solvents evaporate on the substrate as the coating cures and have no part in the final color or durability of the film.

 

For powder, the paint itself is the vehicle. It is milled down to a specific particle size that will hold an electric charge long enough to land onto a grounded part. To grasp how this works, think about how you can rub a balloon, create a charge, and then stick it to a wall.

 

Once the coatings are applied, how they cure also differs. Liquid can dry in ambient temperatures or the curing process can be accelerated with a low bake (140°F to 180°F). Powder coatings on the other hand need to be baked at approximately 400°F for 30 minutes. This process allows proper melting, flowing, and for the appropriate chemical cross-link reaction to occur. Any “over spray” during a powder coating application can be collected and reused. This process is known as transfer efficiency and is greatly increased in powder application over liquid.

 

Deciding between powder and liquid coatings is a decision that should be made with the help of experts in both industries. Before making a decision you need to consider capital costs, energy consumption, coating prices, and much more. In most circumstances, liquid coatings have a lower total cost because they require less maintenance, but each situation is different.

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