Usually, transparency is obtained by reducing pigment particle size as possible. This is achieved by surrounding the particles as soon as they are formed with a coating, which prevents the growth of crystals. The most common products used for this coating are rosin or rosin derivatives. This is particularly useful for printing ink pigments that are required to have high transparency and it has the added advantage that such pigments are more easily dispersed.

 

Iron oxide pigments can be opaque or transparent. The transparent variety are an important group of inorganic pigments as they are widely used for metallic finishes, where their high level of transparency gives an attractive finish, and their weatherability resistance improves the weatherability of pigments with which they can be combined. This is known as a synergistic effect. Transparent iron oxides depend on the particles being unusually small, and also having a crystal shape.

The dispersion process can influence transparency, as it involves breaking up agglomerates of particles to individual primary particles. However, primary particles are not split up by the dispersion process. All one can do is to make full use of the pigments original particle size. Good dispersion will maximize the transparency of a small particle.

Measurement of transparency

Transparency is simply assessed by applying the coating over a black and white contrast chart and measuring the color difference. The greater the color difference, the higher the transparency.

 

Source from : www.specialchem.com