How to Dry Paint? What Technologies are available?

Since paint is applied in a liquid state there has been the ongoing challenge of reducing the time to get it to a solid state or in other words “Dry”. In order to accelerate this process there have been many techniques used. You will hear terms like drying, hardening, and curing. First we need to clarify each of these terms.

  • Drying  – The paint drying process evaporates all solvents and diluents used in the paint to make it liquid or reduce its viscosity.
  • Hardening  – the hardening of paint when the main polymer of the paint hardens with all other pigments and additives creating a solid coating.
  • Curing  – The paint curing process includes both drying and hardening process. Curing = Drying + Hardening

Paints can be classified by their curing mechanism. This includes:

  • Chemically curing paints – Chemical curing paints represent where the main resin (polymer) is created through chemical reactions (poly reactions) between various compounds, in this type of cure includes both drying and hardening process. Examples: Polyurethane, epoxy, phenolic resins and polysiloxanes.
  • Physical curing paints – Physical curing paints occurs to paints where the main resin is already formed, to cure the paint requires evaporation of the solvent is required. Examples: Nitrocellulose lacquers, acrylic lacquers, chlorinated rubber paints and vinyl paints

All physical or chemical cured paints can accelerate or activate the curing process by applying one of the following techniques:

  • Air – Using ambient air movement to remove solvent vapor allowing for solvents to continue to move out of the paint materials.
  • Heated Air – Using heated air at a certain temperature to accelerate the evaporation of solvents and accelerate the chemical reaction to the main polymer or resin, in other wards the temperature acts as a catalyst which accelerates the drying and hardening process, thereby accelerating the curing process.
    • Combination Spray booth and Oven – Painting booths with hot air recirculating is the most common method to accelerate the curing process regardless of the parts geometry.
    • Oven – Hot air recirculating is the most common method to accelerate the curing process regardless of the parts geometry.
  • Radiation – Radiation curing or infrared technology for increasing the substrate temperature accelerating the paint curing process. Ultraviolet radiation technology activates the chemical reactions necessary to cure the paint.

The main advantage of the radiation curing is the speed to solidify the paint, achieving curing times in order of seconds, as disadvantage this type of curing only can be applied in areas where radiation emitted can see all surfaces, therefore it is typically not used in complex workpieces with different shapes and hidden areas.

Let’s take a look at each from a comparative analysis:

Types of Drying Systems

Performance Parameters Ambient Air Hot Air Hot Air w/ Directional Assist Infared-Short Wave* Infared-Gas Catalytic
Speed 3 5 8 10 10
Accuracy 6 7 10 5 6
Capital Cost 10 8 7 5 3
Operating Cost 10 7 8 6 9

Performance Scale is 1 (Low) – 10 (High)          * Cures what is exposed to radiant waves

In each case, the technology selected has a goal of reducing the drying time of the painted object in order to increase the productive capacity of the operation. The key is to select the correct technology, the best value for an operation to be successful.

 

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