Liquid vs Powder - The Pros and Cons

Liquid paint is a mixture composed of non-volatile components (binders, additives, pigments, fillers) and a volatile component (solvent). During the curing process, the solvent begins to evaporate, allowing the remaining paint components to form a dry film.

Powder coating is a dry mixture in which the binder, additives, pigments and fillers are essentially milled to form a fine powder. The primary difference in the composition of these two paint types is the solvent. Solvents are not a component in powder coatings. 

Liquid paint

Liquid paint can be applied in many ways. Job and finish requirements often determine the application type that is most applicable.

• Smaller job requirements tend to utilize brushes, rollers and manual spray guns. In larger scale paint application environments such as manufacturing sectors, automated spray guns and rotary bell devices become more common for the improved speed, consistency and efficiency they offer. Electrostatics are often used in these larger application types to help further increase paint transfer efficiency.
   
• ​​​​​​​Another liquid application method is dipping. In this process, workpieces are submerged in a paint bath. This method is suitable for coating components that are otherwise difficult to coat due to their shape or size.

Powder Coating is most commonly applied through Electrostatic Deposition, which often utilizes spray guns. The workpiece must show electrical conductivity, since the powder adheres to the component by electrostatic (or tribo-static) charging. In special cases, other special application variants are also used:

• Hot Flocking: By heating the substrate, the powder is melted directly on contact and thus adheres to the surface. The powder can be applied either by spray gun or by whirl sintering.
   
• Application of conductive liquid: Creates the conductivity required for powder coating, so that even originally non-conductive substrates, such as plastics, can be coated.

As a result, it is now possible to coat a wide range of non-metallic substrates (plastics, glass, ceramics, etc.).

The curing process for liquid paint takes place once the solvents in the paint have evaporated and the paint has cross linked. This process can take place in an oven or, with certain resins or waterborne paints, can be the result of air drying. Liquid paint solid percentages vary but can range from under 30% to greater than 60%, whereas powder coatings are 100% solids. Solids ratios affect the coverage produced (lower solids equal less theoretical coverage). Liquid finishes often require several coats in order to meet film thickness requirements – resulting in increased processing time.

Powder coating here scores a point with time efficiency. For a high-quality surface, typically only one coat is required with powder coating. After application, the coated parts are placed in the curing oven - here, the powder is melted and cured by means of a chemical hardening reaction. The required curing time depends on the composition of the powder coating and the nature of the workpiece. After cooling, the coating is ready for immediate use.

The usual curing temperatures for powder coatings are in the range of 160-200 °C, which initially limited the types of substrates that could be finished with powder coatings. However, new developments in powder coating technology with significantly lower cure requirements are allowing for greater flexibility in substrate selection. It is already possible to coat wood-based materials such as medium-density fiberboard (MDF) or even individual solid wood pieces.

Due in part to the addition of solvent, which directly influences the flow properties of liquid paints, it is easy to produce a very smooth finish with liquid paints. In addition, liquid paint systems stand out with intensive effects such as metallic effects, since the orientation of the effect pigments can be realized easily during the solvent evaporation process.

Powder coatings have developed rapidly in terms of product diversity for effects. Over the years, various products such as metallics, flip-flops, dormants, pearlescents and many more have been developed and are continuously being improved. With its 3D Metallics, TIGER revolutionized the effect level of powder coatings in 2017, and now creates surfaces with comparable depth and effect to liquid paints. Furthermore, TIGER offers a variety of textured finishes that are unavailable in liquid finishing.

When it comes to durability, powder coatings are ahead of the game. Powder coatings offer high functionality in scratch and impact resistance, deformation resistance and plasticity. This durability can help maintain product integrity during the storage and transportation of finished goods.

Increased film thickness results in better edge coverage for powder coated parts, which, in terms of corrosion protection, makes powder coatings superior to commercially available liquid paint finishes.

When liquid paint cures and the solvent evaporates, vapors known as volatile organic compounds (VOCs) are released into the air. These substances are both a concern for human health and harmful to the environment. Disposing of this paint is also costly, and colour changes in spray guns and rotary bells result in wasted paint and an increased likelihood of colour and appearance defects (due to the introduction of purging solvents). Liquid paint also suffers from a poor reclamation ability when compared to powdered paint. Liquid paint is essentially all spray to waste, as the material that misses the target part cannot be reused.

In powder coating, the degree of material utilization is considerably higher. In modern powder coating booths, up to 100% of the powder that does not reach the target part can be recovered. This is good for both the environment and the budget!