The additive is an important part of powder coating. It is to improve the production and construction of powder coating and to improve the performance of the coating film. Although the amount added is much less compared with resin, curing agent, or filler, only about one thousandth to five percent of the total formula, its impact on the performance of powder coating shouldn’t be overlooked.
Powder coating additives mostly evolved from coatings or plastic additives in the form of solids. Although powder coating additives don’t have many varieties as wet paints, the functions and types of additives are increasing with the continuous development of powder coating technology. According to different functions, there are six major types of additives.
Texture agent takes advantage of the difference in surface tension or compatibility between the additive and the molten coating, or influences the melt viscosity and curing speed of the coating, so that the coating eventually produces different styles of texture effects such as sand, wrinkle, hammertone, web pattern, etc.
There are two ways to add texture agent. One is to add with raw material when mixing, the other is to mix with the finished powder. When mixed with the raw material, the recycled powder has a more stable texture effect and the texture is more uniform. While mixed with the finished powder, the texture effect is more obvious but the texture effect of the recycled powder is not stable.
The performance of the texture agent is susceptible to many factors, including the melting viscosity, gelation time, dispersion ability of the production equipment, powder particle size, and curing temperature. So in order to achieve a stable texture effect, the technical indicators of raw materials and the parameters of the production process should be strictly controlled.
The main components of electrical agents are surfactants, nitrogen compounds, fatty acids, and some inorganic substances (metal powder, metal oxides, etc). These kinds of agents are added to the coating to play the following roles:
- Increase the electrical properties of the powder and improve powder coverage
- Reduce the electrostatic shielding effect to improve powder coverage of the film edge.
- Improve the conductivity of the coating film.
Electrical agents are divided into the antistatic agent, electricity increasing agent, and friction electrical agent. Electricity increasing agent is generally used to improve the electrical performance of powder coating. Its dosage is relatively small and can also be used to reduce the surface resistance of the coating film. But the conductive property is not durable, so it’s not suitable for permanent antistatic. An antistatic agent with a relatively large dosage can reduce the volume resistance of the coating, and the antistatic effect is long-lasting. Friction electrical agent is generally nitrogen-containing compounds, which are especially suitable for friction gun spraying.
Small molecules in powder coatings come from the following sources: moisture in raw materials, gases contained in the powder during spraying, volatiles on the substrate surface, and water or other small molecules generated during curing.
As the gelation time of powder coating from melting to losing fluidity is very short, small molecules cannot be discharged in time, which may cause pinholes. The defoaming agent can avoid pinhole defects by reducing the melting viscosity. Or the limited compatibility difference between the defoaming agent and the coating can accelerate the escape of small molecules.
Wax powder as an additive mainly increases the hardness of the coating and improve wear resistance, or prevent mechanical scratches on the surface. According to chemical composition, the wax powder used for powder coating can be divided into polyethylene wax, polypropylene wax, PTFE wax, polyamide wax, etc.
In terms of compatibility and economic effect, polyethylene wax is better and can meet the general requirements of increasing hardness and scratch resistance, thus it is more widely applicable. In terms of enhancing scratch resistance, PTFE wax is the best and also costs the most.
Matting agents can be divided into different types according to matting mechanism, powder coating systems, and the way to add. As for the matting mechanisms, there are physical matting agent and chemical matting agent. For different ways to add, matting agents can be added when mixing with raw materials or added to the finished powder. According to the powder coating systems, there are matting agents for epoxy system and polyester system.
So far, it is hard for the physical matting agent to achieve a 10% gloss level, while the chemical matting agent is easier to achieve. The disadvantage of a chemical matting agent is that it tends to yellowing and the cost is also higher. Physical matting agent is not easy to yellowing and costs less. But the disadvantage is that its storage stability is not very good, and it requires resins with specific features.
Hoyonn Matting Agent can achieve an excellent matte finish on powder coatings. We have 3 types for indoor, outdoor, and HAA powder coating systems. Learn more about this product.
Leveling and Brightening Agents
Leveling agent and brightening agent are the most frequently used additives in powder coatings. They can play the following roles in powder coatings:
- Reduce the melting viscosity of powder coatings, thus increasing the powder fluidity.
- Make the surface tension of the coating more uniform thus reducing the generation of orange peel.
- Reduce the interfacial tension between the molten coating and the substrate (and filler), thus reducing the possibility of shrinkage and obtaining a smoother surface.
More Functional Additives
In addition, other functional additives can give powder coatings or coating film more special functions, such as anti-UV, anti-aging, improved impact resistance, anti-adhesion, flame retardant, anti-bacterial, improved dry powder fluidity, etc.
Related reading: What To Consider When Using Additives In Powder Coatings?