The settling of the aluminum paste or partial phase separation is not a quality issue; rather, it can have two causes: actual settling of the aluminum particles or condensation of the solvent (or a combination of both).
The absorption of the solvent by the pigment is directly dependent on its surface area. Both size and texture play a role here. Coarse pigments have a smaller surface area than fine pigments. Silver dollar pigments also have a smaller and more uniform surface area than cornflakes of the same fineness. Therefore, coarse silver dollar pigments exhibit the highest tendency to settle.
Large temperature fluctuations during storage and/or transport—very hot during the day, cold at night—cause the solvent to evaporate, condense on the lid, and then drip back onto the paste. This can result in small “puddles” forming on the surface. During transport, depending on road conditions, vibrations of varying intensity may occur, which can cause the paste to compact within the container and the surface to level out. The combination of condensation and vibration can lead to the formation of a solvent layer on the surface, which mimics settling.
The use of plastic liners further intensifies this effect. The paste “sweats” more heavily, and the evaporated solvent cannot return to the paste but remains outside the liner. This can actually lead to a solid-liquid separation. If the entire drum contents are used, no loss of quality is to be expected. If the entire drum contents are not needed at once, a customized solution is recommended. In this case, please contact our Technical Service.
Gold bronze pigments consist of copper or copper-zinc alloys (brass). If the binders or additives used contain acid groups, copper ions can be leached out, causing the gelation effect described above. This effect can be avoided by using coating components with very low acid numbers (guideline: acid number < 10 mg KOH/g). Encapsulated gold bronze pigments, marketed under the name STANDART® Gold Bronze Powder RESIST, are significantly more resistant to gelling effects.
Gold bronze pigments are highly sensitive to temperature. The color can change at temperatures as low as approximately 80°C. Conventional gold bronze pigments can therefore only be used in air-drying coatings. The application should also not be exposed to elevated temperatures (e.g., when creating decorative effects). A significant improvement in color stability is achieved with encapsulated gold bronze pigments, which are available under the name STANDART® Gold Bronze Powder RESIST.
There are three possible causes of gas formation in aqueous metallic coatings:
When incorporating aluminum pigments into water-based coating systems, wetting agents are often used due to water’s poor wetting properties. These can reduce resistance to condensation to varying degrees. Replacing certain surfactants can lead to a significant improvement in this regard.
In addition, additives are used in some stabilized aluminum pigments to suppress gas evolution. These can also reduce resistance to condensation. In such cases, the use of encapsulated aluminum pigments (STAPA® HYDROLAN) or aluminum pigments stabilized with additives is recommended.
Aluminum pigments should ideally be stored in their original, sealed containers at room temperature. In the case of aluminum pastes, the solvent may evaporate, leading to a change in the effect or to agglomeration of the flakes. The optimal storage conditions are 25°C in the original container.
After opening, the containers should be carefully resealed after each use. In addition, it has proven beneficial to plan production batches so that a container is used up as completely as possible. Agglomeration and solvent evaporation are observed more frequently in containers with residual contents.
Product / Product Group – Shelf Life
For leafing aluminum pigments, nonpolar solvents and binders should always be used (e.g., white spirit, solvent naphtha, toluene, xylene, or hydrocarbon resins). All binders used should have the lowest possible acid number (guideline: < 10 mg KOH/g) and contain no functional groups. Moisture in containers or solvents must be strictly avoided, especially during production.
If the product is not stored properly or if there are temperature fluctuations during transport, lubricants from the manufacturing process may accumulate on the surface of the paste and crystallize at lower temperatures. In this case, the entire container should be used up.
As a guideline, a pigment concentration of approximately 5–15% aluminum (by weight, based on the total formulation) can be used. The exact pigment concentration depends on the product’s particle size distribution, the coating parameters, and the desired effect. The coarser the product, the higher the pigment concentration must be to achieve sufficient coverage at the same film thickness.
Yes, but this requires the use of specially stabilized products such as STAPA® HYDROXAL® E. Otherwise, aluminum reacts with water to form hydrogen according to the following chemical equation:
2 Al + 6 H₂O → 2 Al(OH)₃ + 3 H₂
This reaction leads to pressure buildup in the container as well as to a loss or deterioration of the optical properties.
In both cases, it is recommended to first disperse the pigments in a suitable solvent.
For pastes, a weight ratio of 1:1 (paste : solvent) is recommended; for powders, approximately 1:2 (powder : solvent).
It should also be noted that aluminum pastes and powders have a limited shelf life. If the expiration date has been significantly exceeded or the container has been stored improperly, agglomeration may occur, resulting in poor dispersibility.
This appearance can have two causes:
As a general rule, high shear forces should be avoided when processing aluminum pigments.
No, many effect pigments (e.g., pearlescent pigments) cannot be processed directly in the premix without losing their effect. The reason for this is their platelet-like structure: the high shear forces during extrusion can damage the pigments, causing the optical effect to be lost.
However, the dust-free aluminum pellet series Powdersafe is suitable for direct extrusion.
Leafing and non-leafing pigments differ primarily in their orientation within the powder coating, which significantly determines the visual effect.
Leafing pigments (e.g., pigments from the STANDART® PC series) “float” to the surface, where they form a highly reflective layer.
Non-leafing pigments (e.g., STANDART® PCR / PCS / PCU) distribute evenly throughout the powder coating and are completely “embedded.”
In both processes, effect pigments (e.g., metallic and/or pearlescent pigments) are mixed with powder coating base powders. However, the method of incorporation has a decisive influence on the quality, appearance, and processability of the effect powder coating.
Dry-blend powder coatings can exhibit poor color reproducibility as well as a cloudy or uneven appearance.
In the bonding process, the pigment particles adhere firmly to the powder coating particles, preventing segregation. Bonded effect powder coatings thus offer greater process stability, for example during the recycling of overspray.
When using aluminum powder—both in powder coatings and in other applications—important safety considerations must be taken into account. You can find relevant safety information on our website.
ECKART offers several non-leafing aluminum pigment series that differ primarily in their coating technology and, consequently, in their chemical resistance.
The appropriate series is available depending on the application (e.g., outdoor, furniture, facades):
Achieving a true chrome effect with powder coating is only possible to a limited extent. A perfect, mirror-like chrome finish, such as that found on electroplated chrome surfaces, cannot be fully achieved with powder coating.
However, a chrome-like metallic look is possible, for example, using our STANDART® PC 200 pigment in combination with the bonding process.
Defects such as so-called black spots often only become visible when effect pigments—especially fine aluminum pigments—are mixed into the powder coating.
Small defects such as tiny inclusions, gel particles, or impurities, which are not visually noticeable in solid-color powder coatings, become visible due to effect pigments. In these areas, the pigments cannot orient themselves correctly, causing them to appear darker.
The term “gold bronze” generally refers to copper-zinc alloys. These are inherently susceptible to corrosion, which is why even silica-coated gold bronze pigments such as STANDART® RESIST are not suitable for single-coat exterior applications.
However, by combining weather-resistant SYMIC PCE pigments with colored powder coatings, various gold bronze shades—such as rich gold or copper—can be replicated for exterior applications.
Aluminum pigments are shear-sensitive. If shear forces are too high—as can occur during bonding, for example—there is a risk that both the pigments and their protective coating (e.g., made of silica) will be damaged.
STANDART® PCBF was specifically developed for use in the dry-blend process. This pigment preparation is easy to incorporate and, thanks to its special coating technology, offers the advantages of a bonded powder coating.
No – effect pigments do not always need to be bonded. However, depending on the type of pigment, the pigment content, and quality requirements, bonding can be highly beneficial or even necessary.
With STANDART® PCBF, we offer a pigment preparation that allows properties equivalent to those of bonded powder coatings to be achieved even in dry mixtures.
Effect pigments can be used in all standard powder coating systems. However, their stability, appearance, and application properties depend heavily on the specific system.
The selection process follows the same principles as for solid-color powder coatings.
Pearlescent pigments have very little covering power on their own. This must be provided by the base powder itself or by other effect pigments.
Metallic pigments are opaque; however, due to their limited pigmentation depth, it may be advisable to use opaque base powders.
Typical pigmentation levels range from 0.1% to 8%. They depend on the desired effect, the effect pigment used, and the base powder.
In general, all effect pigments can be combined with one another. Even a combination of leafing and non-leafing pigments is often a good idea.
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