Understanding Metallics – the difference between powder and liquid 

Sparkle, shimmer, glitter…the trend for coatings with that extra something isn’t going anywhere. So what do you know about Metallic/Mica effect powders? Joey Roush, IFS bonding expert, explains all… 

To make the powder sparkle, either mica, aluminum flake, or a combination of both can be used. What’s the difference? 

There are two main types of effect pigments used to make metallic or ‘sparkle’ type coatings: aluminum and mica. Mica is a type of mineral that is very thin and flaky. This mineral is then coated with various types of pigments to achieve colors ranging from pearlescent whites to rich coppers, bronzes, and golds. Most of the mica pigments are transparent, which allows the base color to show through – this has a great influence on the overall color. Aluminum flakes, on the other hand, are fully opaque. The higher the loading of aluminum; the greater the silver appearance and the less visible the base color. 

Do you only use mica or aluminum in powder coatings? 

These effect pigments can be added to either liquid or powder coatings, and they look fantastic in both. We use the pigments to create everything from a fine shimmer to a heavier sparkle in a high performance coating. However, there are some differences in what can be achieved.  

Let’s put all our cards on the table - there are some limitations to what can be achieved in powder. The most significant difference between liquid and powder lies in the lower viscosity of the liquid. The lower viscosity allows for a much higher loading of effect pigment to be used while still maintaining favorable application properties. A liquid coating can have up to 25% metallic pigment loading, while most powders can only have around 5-6% loading. The left photo below shows a liquid coating under 20X magnification, while the right is of a similar shade powder. The loading and depth of the liquid is much greater than that which can be achieved in powder. 

Another common practice in liquid is to utilize a multi-coat system. Many times, a solid base coat will be applied, followed by a highly metallic loaded transparent coating over top. This achieves a nice metallic appearance with the characteristic flop of the base coat. Most powder applications are single coat systems, where the opacity and metallic appearance are achieved simultaneously. 

However, with trends moving away from “super sparkle” effect coatings and towards more elegant, subtle effects, high performance powders can deliver the metallic effect you’re looking for -- and without the harsh environmental impact of a liquid coating.  

So how do you make a “sparkle effect” powder? 

There are two ways: dry blending and bonding. 

Dry blending is a quick and simple process where a powder coating and an effect pigment are mixed. This process is very cost effective and can be successfully utilized under certain circumstances. Some of the main benefits include smaller minimum order quantities and quick turnaround times. However, a dry blended product is more susceptible to application issues, depending on the color and loading of the effect pigments. Powder particles and effect pigment particles react differently to the corona field during application and can give a splotchy appearance if unbonded. In fact, some colors cannot be achieved in a dry blend. For example, colors with high effect pigment loading will likely experience ‘spitting’ during application, which is a collection of effect pigment on the spray gun electrode that is transferred to the part. The end result is like it sounds - it will appear as a blemish on the coating. 

The second, and more common, process in architectural powders is bonding.  

Bonding is a more complex process compared to dry blending. During the bonding process, a powder coating is heated using friction in a mixing vessel, to the point where the outside of the powder becomes sticky. The effect pigment then adheres to the powder particle. A properly bonded powder will yield a much more consistent finish as compared to a dry blend. Another benefit is that the powder can also be successfully reclaimed with minimal color shift. Bonding also allows for colors with higher effect pigment loading to be successfully applied. For the architectural market, where both high levels of performance and aesthetics are required, bonded metallics are the sensible option.  

What about a clear coat? With liquid paints, clear coats are always used over top metallic/mica coatings? 

Well, simply put, liquid coatings needed a clear topcoat for protection from scratches and mars, and to meet the AAMA/FGIA performance requirements. Plus, the clear coat helps protect the flakes from degradation - especially at the low films that liquid coatings must be applied. 

With powder coatings, that’s not the case. The scratch and mar resistance of powder is much improved due to its thermosetting properties, and the effect pigments used to conform to the AAMA/FGIA specification have a specialized coating that protects them from degradation. This coating, or protection, of the effect pigment allows the system to meet the AAMA/FGIA performance specifications without the use of a topcoat. 

Ultimately, when it comes to powder coatings, we don’t need – and in fact, we don’t want – to add a clear topcoat over metallics. Adding an unnecessary clear coat over a metallic powder coating will just lead to inter-coat adhesion problems, and our thermosetting powder coatings are tough enough on their own.