With the continuous changes in regulations and environmental protection requirements, consumers increasingly demand advanced water-based (WB) low-VOC or non-VOC coating formulations with quality similar to solvent-based (SB) systems. Although water-based coating technology has made significant developments since its introduction decades ago, there is still room for improvement. Particularly challenging is the dispersion of pigments and achieving performance comparable to solvent-based formulations. To meet these challenges, new water-based dispersant technology must enable formulators to develop higher-performance, lower-cost coatings.
Challenges of water-based dispersants:
The dispersant consists of two parts: the pigment/colorant affinity anchor group and the stabilizing chain. In order to achieve the required performance, the dispersant must have a proper structural design and a well-controlled molecular weight distribution, and ensure the proper ratio of anchoring groups to stable chains.
There are two stable mechanisms in water-based systems: space and static electricity. The main stabilizing group in solvent-based dispersions is the steric chain. Due to the limited selection of stable chains in aqueous dispersants, the complexity of the aqueous system is increased. In addition, factors such as electrolyte, pH and other coating/formulation components in the aqueous system will also affect the dispersion and its performance characteristics. Therefore, compared with solvent-based systems, it may be difficult to observe significant differences in performance of water-based systems. For water-based formulations, the chemical components used must be unique in order to achieve a significant performance improvement, and make the coating less precipitate, well dispersed, stable, and at the same time have acceptable coloring characteristics.
Water-based systems may require other complex coatings and formulation components (such as binders, water-soluble co-solvents, surfactants, defoamers, and rheology modifiers) to function effectively. This makes formulation more difficult, because multiple components will introduce more charges, and will also bring compatibility and pigment affinity competition issues to the system, thereby increasing instability. Basically, water-based coating formulations must be stable in the presence of pH, electrolytes, water-soluble components, soluble polymers and colloidal phases.
After the preparation is complete, the coating still needs to be produced. Appropriate choice of dispersant can affect grinding time, rheology, processing stability, particle size, and these are closely related to the time and cost required to produce a batch of coatings. Water-based coatings often require longer grinding time and better control of rheology and dispersion characteristics.
In order to obtain the required performance, it may sometimes need to be further formulated, such as adding adhesives, cosolvents and additives (such as corrosion inhibitors, adhesion promoters, rheology control agents). These will obviously increase the complexity of the system and bring more challenges to the production of coatings.
In-tank stability challenge
When the paint is stored on the shelf, a good dispersant can reduce the production of agglomerates and keep the dispersion stable in a reasonable period of time under environmental and storage conditions. The more agglomerates produced, the more material is wasted, which in turn wastes more time and money.
Effect on coloring and film characteristics
Dispersants play a key role in ensuring excellent coloring properties such as tinting strength, gloss and haze. Even small agglomerates can affect the aesthetics of the paint/coating. In addition, since the water-based dispersant contains hydrophilic groups, it may adversely affect the water resistance and transfer resistance of the coating. Therefore, it is necessary to ensure that the design of the dispersant can minimize this adverse effect while maintaining the coloring performance.