Transparent iron oxide pigments contain very small acicular particles.  The forces of attraction between particles of this size, are high and aggregates formed between the acicular particles are difficult to fully disperse.  Dispersion processes therefore have to be carefully controlled to ensure adequate wetting of particles, disruption of aggregates and subsequent stabilisation of primary particles in the dispersion.

Moisture Content

The first stage of a dispersion process is to wet the pigment surface, then to deagglomerate and deaggregate the primary particles, finally to develop the stability of the dispersion. Trans-Oxide pigments are carefully controlled through the manufacturing process to contain small quantities of surface absorbed moisture to enhance the first stage of dispersion.

Physical For The manufacturing process of Trans-Oxide pigments is controlled to ensure that the degree of agglomeration is high and to reduce the degree of aggregation.

Agglomerates reduce the levels of dust and are readily wet out and dispersed, whereas aggregates are tightly bound clusters of the primary particles and are more difficult to disperse.

Trans-Oxide pigments are available in neutral and acidic grades.  Neutral grades tend to be more easily dispersed and can be used in a wide range of applications whereas the acidic pigments, although more system specific, produce cleaner, higher chroma finishes.

Dispersion Process

For relatively low viscosity systems, a bead mill containing glass, steel or zirconia media is preferred, although ball mills or attritors may also be used.

Where viscous systems are required, for example pastes or concentrates at high pigment loading, then a triple roll mill may be required.

Correct formulation of the system is key to the successful dispersion of Trans-Oxide pigments.

The ideal formulation is also dependent on the dispersion process.

If the formulation fails to provide sufficient binder for the demand of the high surface area of the pigment, then an unstable dispersion or incomplete optimal transparency may result.

If the pigment loading is too low, then low viscosity results and extended grind times become essential   to achieve optimum transparency.  Viscosity of the system being dispersed can be controlled by   increasing or reducing the amount of solvent added prior to the dispersion stage. Any additional solvent   can then be added as a final adjustment.

The dispersion process is enhanced if the temperature is raised above ambient, e.g. 40- 50 degree Celsius, except where safety requires the lower temperature.  Solvent loss should also be considered and minimised.

Recommended Steps to the Dispersion Process

We kindly request you to go through the individual product data sheet and for additional / further details, we will be please to furnish you the desired information / clarification from ushavi@bom5.vsnl.net.in