Types of Pigment

In today's world, there is a large number of Pigments available. In fact after the advent of Synthetic Pigments there has evolved various classes of pigments that are suited to particular types of Industries.

Metallic Pigments give bright effects, due to this they are widely used and are a very popular category of pigments.

Metallic pigments, can be of two types aluminum and zinc.
Aluminium Pigments:
Glittering silver effects are achieved in the widest variety of different applications by the use of various forms of aluminium pigments. They are further divided into two categories namely leafing grade and non-leafing grade. The aluminum pigments are produced from aluminium that has purity in the range of 99.3-99.97%. The particle has lamellar shape with 0.1-2 um in thickness and diameter of 0.5-200 um. These pigments founds use in automotive topcoats.

Some of the preferred applications of Aluminium Pigments are the following:

• As Reflective paints
• As Corrosion protection coats
• In Marine paints (covering coats)
• Chrome effect paints
• Aerosols
• Roof coatings
• In Heat-proof and highly heat-resistance paints

Zinc Pigments:
The anti-corrosive properties of zinc have been well-known for decades. Zinc pigments represent an almost ideal combination of the active anti-corrosive properties of the metal itself with the protective barrier effect of leaf-shaped pigments.

Zinc Pigments come in two forms of powder and dust. Usually the zinc dust is finer as compared to powder and is spherical in shape. The dust also has a light coating of zinc oxide.

The following table cites some popular Zinc Pigments along with their applications.

Zinc Pigments	Application
Zinc dust	Chemical applications Metallurgical applications
Zinc phosphate	Active ingredient in domestic cleaning products
Zinc oxide	Agricultural applications Rubber industry Brick kilns Ceramics

A few popular pigments have been given below that have very wide uses:

CLC Pigments DPP Pigments Ultramarine Pigments Effect Pigments Pearlescent Fluorescent Pigments Inorganic Pigments Natural Pigments Carbon Black

Organic Pigments Organic vs Inorganic Pigments Mixed Metal Oxide Pigment Phosphorescent Pigment Intermediates Synthetic Iron Oxide Pigments Titanium Dioxide Natural Iron Oxide Pigments

Pigments are used to give color and protect the substrate. To provide color to a material pigment should create an opacity. There is a particular limit to the concentration of pigment particles in a coating determined by the pigment volume concentration (PVC). This is the reason for having pigment particles with a high refractive index.

Based on such refractive index, pigments can be divided into two categories of hiding and extender pigments.

Hiding pigments:
These pigments possess generally refractive index values that are greater than 1.5. Examples: titanium dioxide, zinc oxide, lithophone etc.

Extender pigments:
These pigments have refractive index values that are close to 1.5. Examples: calcium carbonate, silica, alkali and alkaline earth metal silicates etc.

If you are considering pigmentation of a system, that is inherently unstable, for example an unstable binder that is to be pigmented with Titania, the selection of the pigment is then for both coloration and function. While formulating a colored coating, the pigment's role should be as an UV absorber or reflector. Thus blocking UV transmission through the binder, where degradation takes place.

The commercial performance of organic pigments are guided by the following capabilities:

• Coloristic performance
• Durability
• Ecological compatibility
• Tinctorial strength
• Opacity
• Resistance to heat
• Rheological behavior

High performance organic pigments have high color strength, outstanding fastness and weatherability properties. They find usage in specialty applications.