Water is a highly polar solvent with high surface tension and insufficient wetting properties. Thus, for proper dispersion and stabilization of Pigment Carbon Black in waterborne coatings, the use of wetting and dispersing additives is essential.
The carbon black pigment and polymeric dispersion additive or binder must be compatible. Two ways exist to prepare waterborne coatings:
• A mill base consisting of: polymeric binder as an aqueous dispersion or solution (that is stable against temperature and shear forces), plus wetting agent, defoamer, amine and pigment.
• A mill base without binder consisting of: polymeric additives (instead of the binder), plus defoamer, amine and pigment. The advantage of this system is the high Pigment Carbon Black concentration, improved coloristic properties and universal applicability.
Proper adjustment of the binder pH in both systems is necessary to maximize coating performance.
In waterborne coatings, electrostatic pigment stabilization is important. A mutual repulsion of pigment particles results from equally charged surfaces.
To achieve this, the pigment surface is coated with ionic wetting and dispersing agents, or non-ionic agents with segments of different polarity. The choice of ionic or non-ionic additives depends on the properties of the pigment selected.
Furthermore, in waterborne dispersions, where the binder exists as polymer lattices (binder in micelle), there is almost no interaction between binder and pigment surface, so pigment carbon black dispersion must be assured by wetting and dispersing agents.
In waterborne coatings, use of dispersing additives has always been essential, with concentration typically recommended in the range of 0.5 – 2 mg per m2/g particle surface area.
