Aluminum flakes have been used in numerous coating formulations for many years. They are safer than aluminum powders because they have a high surface to weight ratio. In addition, they have been rated as non-hazardous to handle. However, they have not been proven to be effective barrier pigments.
Paints containing aluminum flakes without the inner layer of oxidized aluminum have significantly degraded shear stability. Shear stability can be measured by the difference in lightness values L* before and after shear stress.
An aluminum flake has an inner core of oxidized aluminum that ranges from 5 to 10 nm in thickness. This layer is followed by an alumina support layer that ranges from 50 to 1000 nm. The reflector layer is also a metallic aluminum layer that has a thickness of 10 to 150 nm.
Thin plane-parallel aluminum flakes have improved shear stability and can be used in paints and plastics. Additionally, their mirror-like effects have been enhanced when they are incorporated into coating systems.
Organic encapsulation is commonly employed in the manufacturing of aluminum flakes to provide excellent brightness, dispersion, and outdoor durability. This process also helps to improve handling and application performance. It is especially useful in applications that involve spraying the coating onto a substrate.
Most aluminum flakes are subjected to an encapsulation process to protect the flakes from deterioration. The process can be conducted independently or in combination with silica treatments. Alternatively, additional surface treatment can be selected from chromate or polymer encapsulation with acrylates.