Transparency/Opacity control

Coatings have varying degrees of opacity or transparency depending upon the amount of light transmitted through, or reflected from the surface of the coating.

The choice of the pigment and the degree of its dispersion are major influences on this property. The opaque pigments have a greater tendency to reflect light due to the particle size and refractive index of the pigment.

Figure 2: Drawdowns of ink on a card

As illustrated on the photograph above, hyperdispersants can influence the transparency or opacity of a coating by improving the particle size distribution of the pigment (more uniform and narrower distribution).

Thus, in the case of titanium dioxide, the high refractive index and larger particle size effectively reflects and scatters light of all visible wavelengths. Adding a hyperdispersant will increase the surface area (smaller particle size through less agglomeration) and thus improve opacity.
Equally, with transparent pigments, the hyperdispersant improves the particle size distribution and allows for greater light reflection (increased transparency).