In order to get high quality surface finishing, we always trying to seek for the best equipment as well as its most compatible coatings. Especially for cosmetic and automotive industry, the paint shop is constructed by the most advanced technologies with a variety of intelligent devices. Among all the construction reviews, environment control is the most crucial topic and it will determine if we can receive expected fine rate directly. Environment control is all about temperature and humidity as well as the air cleanness inside workshop. Following we’ll deeply analyze the impact of high temperature and high humidity for coating application.
Impact of high temperature on coating
Different paints have different lifespans, and their lifespan shortens as the temperature rises. The viscosity of two-component paints decreases with increasing temperature. As the temperature rises, the curing time shortens, or even disappears. Higher temperatures also reduce viscosity.
Impact on coating application
High temperature will accelerate the drying of the paint film surface, but the evaporation rate of the internal solvent may not keep up, resulting in the paint film appearing dry on the surface but not completely cured inside, which can easily cause problems such as bubbling and peeling.
Disadvantages of high temperature on coating
- Dry spraying – Rapid solvent evaporation and improper spraying techniques can cause dry spraying.
- Paint mist – Rapid solvent evaporation causes the coating to dry quickly, resulting in paint mist.
- Pinholes – Rapid drying of the paint film causes solvent entrapment and pinholes.
- Poor leveling – Poor leveling of the paint film, resulting in an orange peel-like appearance.
Precautions for construction in high temperature environment
- High temperatures dry quickly on the surface, but internal curing may be delayed. Apply multiple thin coats to prevent solvent buildup.
- After application, protect the paint film from direct sunlight, strong winds, and cracking.
- High temperatures are associated with high humidity. Humidity should not exceed 85% to prevent the paint film from turning white and reducing adhesion.
The impact of high humidity on coating
As we all know, water volatilization is not only affected by temperature but also by the saturation of the air. Therefore, humidity has a significant impact on the film formation of water-based products. For water-based products, the higher the humidity, the more difficult it is for water to evaporate. This causes water to remain on the substrate surface for a longer time, and water reacts more quickly with metals (especially iron), easily forming flash rust or hidden rust, seriously affecting the coating quality.
Therefore, construction should not be done in high humidity environments, such as those with rain, snow, frost, or dew, or dehumidification equipment should be added. Condensation is another form of high humidity. Because the component itself is lower than the ambient temperature, water vapor in the air encounters the cool metal surface. Due to the temperature difference, the water vapor cools on the metal surface and forms water droplets or a water film. Therefore, when painting, the substrate temperature should also be considered to be 3°C above the dew point.
Impact of coating appearance
Whitening: High humidity prevents the moisture in the paint from evaporating quickly, causing condensation on the surface. This condensation then reacts with the paint’s components, causing the coating to whiten. For example, PU and NC paints, which are applied in high humidity environments, are prone to whitening.
Poor leveling: Moisture will affect the leveling performance of the coating, making it unable to level well after construction, resulting in orange peel, sagging and other phenomena, affecting the flatness and smoothness of the coating.
Pinholes and bubbles are generated: In a high humidity environment, the moisture and air in the coating are difficult to be discharged, which easily forms pinholes and bubbles in the coating, reducing the density and corrosion resistance of the coating.
Impact on adhesion
Reduced Adhesion: High humidity causes the substrate surface to absorb large amounts of moisture, changing the surface roughness and chemical properties, and thus impairing the adhesion between the coating and the substrate. For example, coating on damp metal surfaces can easily cause the coating to peel and flake.
Rust: Even after rust removal, metal substrates are susceptible to re-rusting in high humidity, further reducing the coating’s adhesion and durability.
