Ciba offers a wide range of products that can be classified in two main groups:

• Low molecular weight dispersants
• High molecular weight dispersants

Both types of dispersants improve the wetting process and result in shorter grinding times. The conventional low molecular weight types are categorized according to their chemical structure as anionic, cationic, electroneutral and non-ionic.

Their effectiveness is determined by the absorption of the polar group onto the pigment surface and the behavior of the non-polar chain in the medium surrounding the particle.

The molecular weight of these products is low, usually between 1000 and 2000 g/mol.  Molecules with only one polar group attach themselves to the pigment surface while their non-polar chains extend into the resin. If the molecules have more than one polar group, they arrange themselves in such a way that the free polar groups form hydrogen bonds and build a physical structure with the pigments. Shear forces are often responsible for breaking down this structure. This principle is called controlled flocculation. It is mainly used for heavily filled systems such as primers and surfacers for industrial and maintenance coatings.  

The polar groups have the strongest affinity for inorganic pigment surfaces, contain positively and negatively charged ions, such as metallic oxides. Unfortunately this type of attachment is not effective with organic pigments, which consist of uncharged covalently bonded carbon, hydrogen, oxygen and nitrogen atoms.

This led to the development of high molecular weight dispersants. These additives are linear or branched molecules with a polyurethane or polyacrylate structure, and have molecular weights between 5000 and 30000 g/mol. These products have pendant anchoring groups, which adsorb onto the surface of the organic pigment particle. Their adsorption mechanism is by:

• Hydrogen bonding
• Dipole-dipole interactions
• London-Van der Waals forces

Adsorption is strong, because the dispersant is bound to numerous sites on the surface at the same time. This same concept makes them effective for inorganic pigments, too.

The remainder of the polymeric backbone is sufficiently large to create an effect called steric stabilization. Permanent deflocculation is achieved with a minimum distance of 200 Å of inter-particle separation.

Our pigment wetting and stabilization concept is also very effective in aqueous systems. When stabilizing pigments in water, normally conventional dispersants are used that build up a charged double layer around the pigment.  This electrostatic repulsion prevents the re-agglomeration of pigments. However, this only works well with single pigments. The stabilizing charge can easily collapse when subjected to external influences such as impurities and other ions, or if other pigments with different zeta potentials are added.

By applying Ciba's high molecular weight dispersants, steric stabilization is achieved, which is far stronger and more effective.  The amount of polymeric dispersant used is very important, since performance depends on optimal saturation by the dispersant of the pigment surface. Our data sheets and pigment list provide excellent guidance for the appropriate use levels.

Ciba offers two different chemical families of high molecular weight dispersants:

• Polyurethanes are the best dispersants for viscosity depression in the mill base. This gives higher pigment loadings, more economical mill base formulations and lower VOCs.
• Polyacrylates show a much wider compatibility in non-polar as well as highly polar systems. They have a higher molecular weight generally which provides effective inter-particle separation.

Both chemical families are suitable for the formulation of pigment concentrates, see “RMPC” section. For your special requirements, please follow our recommendations in the main menu under “Application Field”.