Low Molecular Weight Dispersants
When dispersing pigments, in particular organic pigments, one frequently encounters problems such as flocculation, insufficient color or transparency, poor rheological qualities or stability. These issues arise along every step of the coatings life cycle from production and storage through to the end-use performance of the film.
The dispersing of solid pigments or fillers into the liquid phase of binder solutions is an important step in paint and coatings production influencing optical properties like gloss and color strength.
Dispersion control additives are used to improve and accelerate the dispersion process and to stabilize the dispersion during storage. For the design and the use of these additives, it is essential to have knowledge about the dispersion process.
Low molecular weight wetting and dispersing agents properties:
- 800 g/mol < Molecular weight < 2,000 g/mol.
- Categorized according to their chemical structure and the nature of their hydrophilic groups (amphoteric, cationic, … etc).
- The interaction of their polar groups with the pigment surface and the behavior of the non-polar chains in the medium determine their effectiveness.
- Only used for stabilizing inorganic pigments and extenders.
Mode of action:
- The polar heads will form hydrogen bonding interactions between different pigment units resulting in a network that enhances the separation of the particles (controlled flocculation).
- This interaction is of great importance in this class of dispersion control additives since the relatively low molecular weight will not give sufficient steric hindrance.
- Inorganic pigments are usually metal oxides which contain positive metal ions and negative oxide ions. These ions are good anchoring points that the anchoring groups that build-up the polar head of the dispersion control additive can attach to (polar interactions).
- Unfortunately this type of charge interaction is not possible with organic or black pigments.