Page 366 - Handbook of Plastics Technologies

PLASTICS ADDITIVES

5.46 CHAPTER 5

FIGURE 5.9 Color sphere.

may be inorganic or organic. In the plastics industry, pigments are commonly used to pro-
duce opaque colors; dyes are used only as specialties where a transparent color is particu-
larly desired.

5.8.3 Major Classes of Colorants in Plastics
5.8.3.1 Inorganics
• Titanium dioxide is used in tremendous tonnage (270 million pounds per year) both as
opaque pigment and as white colorant in plastics. This is 90 percent of the inorganic
pigment usage in the plastics industry.
• Iron oxides (10 million pounds per year) produce a broad range of reds, yellows,
browns, and blacks, which are stable, nontoxic, and low in cost but rather dull in ap-
pearance.
• Cadmiums offer a range of yellow to red colors that are bright, fairly expensive, and
raise health problems.
• Chromiums and molybdenums offer a range of yellow, orange, and green colors that are
attractive but raise health problems.
• Iron blues are attractive and inexpensive.
• Cobalt blues are attractive and expensive.
5.8.3.2 Organic
Carbon black is often listed as the leading “organic” colorant (85 million pounds per year),
but most of this is used for reinforcement, stabilization, conductivity, and other purposes.
Actually, nigrosine dye is a much more effective black colorant.
Generally, the conjugated unsaturation of aromatic carbonyl and nitrogen compounds
produces a wide range of useful colors (Fig. 5.11). For example, carbazoles, perylenes,

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