Introduction
Inorganic pigments are typically composed of metal oxides or metal salts and are widely used in industries such as plastics, coatings, construction materials, and rubber. These pigments provide stable coloration and excellent durability for various products.
Inorganic pigments can be divided into two categories:
- Natural inorganic pigments
- Synthetic inorganic pigments
Natural mineral pigments generally have lower purity and darker color, but they are relatively inexpensive. In contrast, synthetic inorganic pigments offer more consistent quality, brighter colors, and stronger covering power.
General Characteristics of Inorganic Pigments
Inorganic pigments have several important advantages:
- Excellent sunlight resistance
- Strong heat resistance
- Good weather resistance
- High solvent resistance
- Strong covering power
However, they also have some limitations:
- Limited color range compared with organic pigments
- Lower coloring strength
- Lower brightness
- Some metal oxides or metal salts may contain toxic elements
Classification of Inorganic Pigments by Color
White Pigments
The most important white pigment is titanium dioxide (TiO₂).
Titanium dioxide is mainly available in two crystal forms:
- Rutile type
- Anatase type
Among these, rutile titanium dioxide provides better weather resistance and durability, making it widely used in outdoor applications such as plastics, coatings, and building materials.
Black Pigments
The most common black pigment is carbon black.
The properties of carbon black used for pigments differ from those used in rubber products. The main quality indicators for pigment-grade carbon black are:
- Blackness
- Color strength
Carbon black not only provides deep coloration but also offers excellent weather resistance and resistance to thermal oxidation.
Red Pigments
The most common red inorganic pigment is iron oxide red.
Iron oxide red has several advantages:
- Good covering power
- Strong coloring ability
- Excellent chemical resistance
- Good color stability
- Good dispersibility
- Low cost
Because of its excellent corrosion resistance, iron oxide red is widely used in floor coatings, marine coatings, and anti-rust paints.
Yellow Pigments
Common inorganic yellow pigments include:
- Lead chrome yellow (lead chromate)
- Zinc chrome yellow (zinc chromate)
- Cadmium yellow (cadmium sulfide)
- Iron oxide yellow (hydrated iron oxide)
Among these pigments:
Lead chrome yellow has strong covering power, bright color, and good dispersibility, but it may darken under sunlight.
Zinc chrome yellow has lighter color and better light resistance but lower covering power.
Cadmium yellow offers excellent heat resistance and bright color but is more expensive and has limited applications.
Because lead chrome yellow and cadmium yellow contain heavy metals, they cannot be used in applications such as:
- Children’s toys
- Educational materials
- Food packaging
Iron oxide yellow is darker in color but provides excellent durability, heat resistance, chemical resistance, and alkali resistance. It is widely used in construction materials and coatings.
Green Pigments
Two common green inorganic pigments are:
- Chromium oxide green
- Composite iron oxide green
Chromium oxide green has excellent light resistance, heat resistance, and chemical stability, although its color is relatively dark and its covering power is moderate.
Blue Pigments
Common inorganic blue pigments include:
- Iron blue
- Cobalt blue
- Ultramarine blue
Among them:
Ultramarine blue is widely used due to its bright color, acid and alkali resistance, and good heat stability.
Iron blue has stronger coloring and covering power than ultramarine blue but slightly lower durability.
Cobalt blue has excellent light and heat resistance but relatively lower coloring power and higher cost, which limits its applications.
With the development of organic pigments such as phthalocyanine blue, the use of iron blue has gradually decreased due to the superior coloring strength of organic pigments.
Brown Pigments
The most common brown inorganic pigment is:
- Iron oxide brown
Iron oxide brown provides good stability and is widely used in construction materials, coatings, and plastics.
Conclusion
Inorganic pigments are widely used in plastics and industrial materials due to their excellent durability, weather resistance, and strong covering power. Although their color range and brightness are more limited compared with organic pigments, their stability and cost-effectiveness make them essential for many applications.
Common inorganic pigments include titanium dioxide, carbon black, iron oxides, chromium oxide pigments, and ultramarine pigments, each offering specific advantages depending on the intended use.
