CIBA ® DISPEX® -Dispersion Mechanism
Ionic dispersants act by coating the surfaces of inorganic mineral particles as a result of an attraction to the positive charges that develop on particles when in contact with water, a process known as ‘adsorption’. The effect of the adsorption technology is to produce a net negative charge to the particle surface so that the particles are repelled from each other.

When a mineral is dispersed in water using DISPEX® products, this negative attraction reduces the interaction between particles, thus lowering the viscosity of the mineral slurry or paint mill-base. The slurry then remains fluid until quite a high quantity of the mineral has been added (70 - 80% mineral). The addition of DISPEX® gives the slurry better flow properties and it remains stable for longer.

By making the polymer chain more hydrophobic, interaction with minerals such as TiO2 and ZnO is improved, as is the effective water-resistance and gloss of a formulated coating.

Ciba® DISPEX® – Uses
Dispersants such as the DISPEX range are used to supply bulk minerals in a stable slurry form which continues to remain fluid over a period of time. These minerals – such as China clay (or kaolin) which is commonly used in the paper industry in paper coating formulations and as a paper filler, and is also used in the ceramic industry in the slip casting of ceramics – are then used in a wide variety of applications.

Another mineral often supplied in a slurry form is calcium carbonate. Calcium carbonate must normally be ground to a particular particle size in a process greatly assisted by the use of a dispersant. Calcium carbonate is widely used in the paint industry and also for paper production. Numerous other inorganic (and organic) minerals and pigments are also dispersed into water-based slurries for a variety of applications.

Optimum Dosage
Optimum dosage is a function of the actual surface area of the mineral or combination of minerals to be dispersed.  The smaller the particle size, the higher the actual surface area, hence, the larger the area the dispersant has to cover.  By simply measuring the reduction in viscosity as a dispersant is added incrementally to a mineral slurry, a dispersion curve can be plotted and the minimum viscosity shows the optimum dosage level.

For a paint mill-base, the addition of 40% more dispersant is recommended, once the optimum dose has been determined.  This will ensure a safety margin should the particle size distribution of the raw materials vary more than expected.