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Aluminum Pigments or Aluminum Effect Pigments used in coatings generally come from two manufacturing processes: milling and vacuum metallization. Below, we will focus on aluminum pigments made in the milling process.
While there are almost an infinite number of possible visual effects that can be created from milled aluminum effect pigments, these can be broken down into four categories through a combination of two basic factors: behavior and structure. Aluminum pigments exhibit leafing and non-leafing behaviors, where Leafing pigments orient on the surface of the coating film and non-leafing aluminum pigments orient throughout the film leaving a resin layer on the surface.
Milled Aluminum Pigments are so called because their surface appearance under a microscope resembles that of the traditional cornflake breakfast cereal whereas silver-dollar pigments have a much smoother and more reflective surface.
Thus when types based on behavior and structure are combined, the four general categories of aluminum pigments are:
Leafing cornflake aluminum pigments are the oldest technology of aluminum pigments in the marketplace. They are used for various functional and decorative applications in which there exists low surface abrasion and little to no top coat adhesion testing requirement. Because the aluminum flake is literally on the films’ surface, the effects that can be achieved with leafing cornflake aluminum pigments can be visually brilliant and attractive. Some standard applications of Leafing Cornflake pigments include:
Leafing Silver Dollar aluminum pigments are niche products that provide superior brilliance, sparkle and chrome-like appearance when compared to leafing cornflake aluminum pigments. The enhanced brilliance comes from more controlled particle size distributions and a smoother more reflective surface as compared to a cornflake. Most often, leafing silver-dollar aluminum pigments are used in decorative applications where superior brilliance and/or reflectivity compared to leafing cornflake aluminum pigments are needed. Applications may include:
Non-leafing cornflake aluminum pigments are used in a wide variety of applications in which surface-abrasion and inter-coat adhesion are important. The non-leafing cornflake pigments are not as brilliant as the leafing type because they tend to orient throughout the film. This provides a layer of resin between light and the pigment, distorting the brilliance and reflection of the light. Nonetheless, non-leafing cornflake aluminum pigments can produce silver metallic effects in a host of applications including:
Non-leafing Silver Dollar aluminum pigments are likely the most ubiquitous of the various types. The pigments provide superior reflectivity, sparkle, and brilliance to non-leafing cornflake and in some cases leafing cornflake types while also orienting throughout the coating film. Because of the smooth reflective surface and varied achievable effects, the automotive paint and parts industry is the largest user of these pigments. The pigments can be found in coatings formulations for various applications including:
In summary, there is an aluminum effect pigment for any application. The key to determine the best type for each application is to align the application requirement with the pigment performance expectations. By understanding how to pick the proper pigment type and a little trial and error thereafter, almost any imaginable effect can be achieved.