Paints typically provide an aesthetic as well as a protective function. Providing color to paints is an important function which is critical to having a paint that is efficacious in its aesthetic functionality because users not only wish to have a paint coating that protects their surfaces, but a paint coating which is aesthetically appealing.
Colors are commonly imparted to paints through the use of pigments. Pigments are materials that produce color by the reflection or absorption of specific wavelengths of light. In paints, pigments are often inorganic or organic materials which are ground into a fine powder and then dispersed into the paint solution to impart a color onto the paint product. Organic pigments are based on carbon chains and carbon rings. However, they can also contain metallic (inorganic) elements that help stabilize the properties of the organic component. Exemplary organic pigments include: quinacridones, phthalocyanines, perylenes, pyrroles, arylamides, and others. Inorganic pigments, chemical compounds not based on carbon, are usually metals, metal oxides, or mixed metal oxides. Commonly used inorganic paint pigments include metallic pigments which are typically made out of aluminum, but can also be made from copper, bronze, nickel or stainless steel; metal oxides such as iron oxide, manganese oxide, and cobalt oxide; and interference pigments such as metal oxide mica which interact with light to produce an optical effect on the perceived color.
Organic pigments have many benefits, including that they can be made to be very consistent, on a commercial scale, and at a relatively low cost. However, organic pigments may not provide the strongest level of durability because the chemical structure of the pigments may become degraded over time and exposure to the elements, such as rain, air, and sunlight.
Inorganic pigments may also be used to impart color into a paint system. Inorganic pigments have the advantages of being able to withstand the impact of sunlight and chemical exposure in a better way than organic pigments. They also have high opacity and thus provide a relatively high level of hide, and are relatively inexpensive compared to organic pigments. However, inorganic pigments have a low tint strength and thus a large number of pigment particles are required to produce the desired color in a paint composition. In addition, the color from many inorganic pigments is comparatively less vivid and may be perceived by consumers as being less bright or muddier than organic pigments and while many of these limitations can be overcome, the inorganic pigments which provide such effects are cost-prohibitive for large-scale commercial use.
Structurally-produced colors may be provided which overcome many of the hurdles of typical organic pigments because bright, vibrant, durable colors may be delivered. However, structurally-derived colors are limited in their usefulness due to iridescence which often occurs in such pigments. In U.S. Pat. No. 8,323,391 to Banerjee et al., a particular omnidirectional structural pigment for automotive paint is described by providing a particular configuration to a multilayer structure. However, such a structure may not be well suited for use in a paint solution because such color is provided by a film formed on a surface.
An alternative means of delivering structurally-based color is described in Khudiyev, T., Dogan, T. & Bayindir, M. Biomimicry of multifunctional nanostructures in the neck feathers of mallard (Anas platyrhynchos L) drakes. Sci. Rep. 4, 4718 (2014) works by providing an ordered structure of individualized elements that are bundled together. However, using such a methodology is not viable to provide structural colorants for paints due to the color being provided by fibers and the resultant iridescence from this structure.
Thus, there is a need for a method and material that may be used as a structural colorant for use within a paint system that does not exhibit iridescence.