Degassing agent is an auxiliary agent that releases volatile substances such as air, moisture, and small molecule compounds generated during the cross-linking and solidification reaction of powder coatings when they melt and form a film. It also compensates for the pinholes of the released small molecule compounds in a timely manner, avoiding the occurrence of small pinholes or pores in the coating film. This type of additive is one of the common additives in powder coatings, and is usually added to powder coating formulations.
The commonly used degassing agent in powder coatings is benzoin. Benzoin is a white or light yellow odorless crystal with a melting point of 133-137 ℃ and a boiling point of 344 ℃. It is slightly soluble in water and ether, and soluble in hot acetone and ethanol; Its disadvantage is that it can easily cause yellowing of the coating at high temperatures. In order to overcome the drawbacks of benzoin, modified benzoin and wax based degassing agents that are not prone to yellowing under baking and curing conditions have been developed.
The results of experiments and production practices indicate that during the cross-linking and curing process of powder coatings, coating varieties that produce small molecule compounds require the addition of degassing agents. It is reasonable to add a degassing agent in general epoxy, epoxy polyester, polyester, and polyurethane powder coatings because powder coatings have problems such as easy moisture absorption during production and use. In epoxy matte and matte powder coatings, it is not easy to produce pinholes and other defects without the addition of defoamers such as benzoin. The reason cannot be explained clearly yet, and it may also be due to the surface of the coating not being as smooth and glossy as high gloss, and some coating defects not being obvious, resulting in a feeling.
At present, benzoin is still a commonly used degassing agent, with a dosage of about 0.5% of the total film-forming material in powder coatings, which can be adjusted appropriately within a certain range according to the variety and composition of powder coatings. In polyester-HAA (hydroxyalkylamide) powder coatings, considering the influence of benzoin on the yellowing of the coating film, its dosage should be controlled at around 0.3% of the total amount of film-forming material, and the usage should be minimized as much as possible. In addition, synthetic wax based smoothing and degassing agents can also be used, with a dosage of about 1% of the total powder coating formula.
In powder coating formulations, defoamers are added to cast iron, cast aluminum, hot-dip galvanized steel plates, and hot-rolled steel plates with sand holes or pinholes on the surface of the coated object (workpiece) during powder coating to prevent the formation of particles or volcanic pits in the coating film. They are additives added to prevent the formation of bubbles in the coating film.
When powder coating is applied to cast iron parts, cast aluminum parts, hot-dip galvanized parts or hot-rolled steel plates with sand holes or pinholes, during the baking and curing process, the powder coating melts and flattens while sealing the sand holes and pinholes on the surface of the coated object. As the temperature of the coated material increases, the air in the sand holes and pinholes of the coated material expands, and the internal pressure also continuously increases. When the internal pressure is slightly greater than the strength of the molten coating, the internal air will burst the coating and form small bubbles to escape. Due to the solidification reaction of powder coating during the film-forming process, the melting viscosity of the coating continuously increases and eventually becomes a solid coating film. Therefore, when the internal pressure in the small bubbles does not reach the energy required to burst the coating film, these small bubbles form particles or granules protruding from the surface of the coating film. When the internal pressure in the small bubble is sufficient to burst the coating, the small bubble will rupture and the air inside will escape into the atmosphere. If the coating at this point has lost its leveling ability and cannot bridge the small air holes that allow air to escape, typical volcanic crater particles or granules will form, becoming a serious problem
If defoamers are added to powder coatings, they can reduce the melt viscosity of the powder coating and also lower the surface tension of the coating. This allows the air in the sand holes and pinholes on the surface of the coated material, which is affected by baking temperature and pressure, to easily burst and flatten the uncured coating film into the atmosphere. At the same time, the gaps in the coating film where bubbles escape can also easily bridge the leveling, preventing the formation of particles and particles in the coating film, or particles with volcanic pits.
Because the defoaming mechanisms of water-based and solvent based coatings are completely different from those of powder coatings, the defoamers used in water-based and solvent based coatings cannot be directly applied to powder coatings. Due to the particularity of powder coatings, there are not as many types of defoamers used in powder coatings as in water-based coatings and solvent based coatings.
Post time: Aug-15-2025