Effect Pigments

Effect Pigments

Effect pigments have broken new ground in color physics technology, especially with regard to industrial-scale research and development for many applications. The color production of effect colorants is predominantly caused by anisotropic processes like single or multiple reflection, interference, or diffraction. These processes are unrealized in absorption colorants. The generic term “effect pigment” is inadequate because colors generated by absorbing colorants are also based on an optical “effect”. However, flake-shaped pigment is an accurate expression for this type of colorants. The generated color impression of effect pigments is extremely depends on the angle. This is a function of both the illumination and the observation direction. Effect pigments result in quite strange color sensations for human color sense because our sense has evolved to perceive only colors from absorption colorations. Practically, effect colorants need more extravagant manufacture methods in comparison to absorption pigments and also a more extensive characterization, measuring techniques, application, and processing.

All types of effect pigments consist of flake-shaped particles with a large range of typical lateral dimensions between 1μm – 1mm. this is more than 10-1000 times larger than that of absorption pigments. The flake thickness has values between 10nm – 1μm. On account of the flake form, the resultant color effect is increasingly distinct with a more uniform morphology and the more the particles are oriented in the binder parallel to the substrate or surface. Like absorption pigments, effect colorants can be of inorganic as well as organic nature. With regard to the processes of color production, they are divided into four groups:

• Metallic pigments
• Pearlescent pigments
• Interference pigments
• Diffraction pigments

Pearl luster pigments are often subsumed to the interference pigment classification. The laws used to describe the optical properties of metallic pigments are essentially geometrical optics. All other sorts of effect pigments are generally described by wave optics.

Metallic pigments consist normally of a metal or an alloy of metals. The typical metallic gloss is increasingly brilliant the more uniformly the flakes are oriented parallel to the boundary surfaces of a coating. The so-called metallic effect is mainly a consequence of the directional and diffuse reflection at the surface and the edges of the flakes.

In contrast, pearlescent pigments consist of two or more layers with a high index of refraction difference. The range of values is between 1.5 – 2.9. the mostly used substrate is mica, but also metals or metal oxides are often applied. The specific pearl luster depends on the permutation of the layers. This luster originates from single or multiple reflections at the layer boundaries followed by interference of the light waves. Differing optical layers are behind the general function of interference pigments. This does not require the use of a mica substrate. An interference pigment subgroup is the optically variable interference pigments. The high ratio of refractive indices, in conjunction with different layer thicknesses, fans out the first or more interference orders in such a way that a variety of interference colors are to observe angle dependence.

The grating structure of diffraction pigments deflects the incoming light. The resulting color effect can be attributed also to the wave nature of light. The substrate consists of a highly reflecting or even ferromagnetic substance. The substance is vapor-coated symmetrically on both sides with several materials known from nanotechnology. The ferromagnetic particles can be oriented with an external magnetic field before the crosslinking of a binder. The produced unusual but often impressive colors require that effect pigments undergo a more subtle and closer examination and handling compared with absorption colorants.

Effect pigments applications:

• Automobile paints
• Industrial paints
• Decorative paints
• Nail paints and varnishes
• Special printing inks