Rheological synergists are additives that are used in combination with inorganic rheology additives and significantly enhance their effectiveness - even at low dosages. This results in a more cost-effective formulation overall. The use of synergists also allows a lower dosage of the inorganic component with advantages in terms of the stability of the formulation.
The enhancement of the effect of inorganic rheology additives by synergists is based on the interaction between the surfaces of the particles and the surface affinic groups of the synergist. By acting as a "bridgebuilding agent" between the inorganic particles, a stronger "cohesion" of the network takes place than is possible without synergists. Suitable inorganic rheology additives are organically modified phyllosilicates, mixed minerals or fumed silicas.
In the case of organically modified phyllosilicates or mixed minerals, the liquid synergist is added as a post-additive after dispersion and the reinforcing effect occurs immediately after homogenous distribution in the formulation. Addition of the synergist already during activation of the phyllosilicate is not recommended, as it prevents delamination, which worsens the rheological effect and may make incorporation impossible. Synergists have also proven effective in combination with fumed silica and lead to a reinforcement of their rheological effect. In contrast to the combination with phyllosilicates, the synergist can be used during the dispersion phase of the silica. The advantages are both stabilization of the deagglomerated silica against settling and the reinforcement of the rheological effect. The more uniform spacing between the particles and the interaction of the synergist with the silanol groups of the silica lead to a enhancing effect. Furthermore, there are also special synergists available for amine-curing systems, such as 2-pack epoxy systems, which are added to the hardener component.
A special example of the application of synergists is the so-called "Viscosity Control Technology" (VCT). This is the combination of two additives for use in highly filled 2K epoxy thick film coatings with a high proportion of hydrophilic silica, in which the two additives ideally complement each other. The "Thixbreaker" is used in component A and reduces the usually high viscosity to facilitate the processability of the system. The "Thixbooster" (synergist) is added to the amine component B. When mixing both liquid components, a strong thickening of the system occurs spontaneously and very high film thicknesses can be applied in one working step.