Coating additives

Water-based coating additives are the core of water-based paint formulations. Due to the significant differences in the physical properties of water and organic solvents (water has high surface tension, evaporates slowly, and is prone to bacterial growth), water-based coatings rely on additives to a far greater extent than oil-based coatings.

To address the specific requirements of water-based systems, the most essential and commonly used water-based coating additives are primarily divided into the following major categories:

1. Rheology and thixotropic modifiers

• Thickeners: Directly determine the paint’s pot life, application thickness, and resistance to sagging.
  • Cellulose-based (HEC): Provide excellent storage stability and prevent separation, but offer only moderate sag resistance.
  • Polyurethane-based (HEUR): Belong to the associative thickener category, providing excellent leveling and reducing brush marks; commonly used in high-end emulsion paints.
  • Alkali-swelling types (ASE/HASE): Cost-effective with strong anti-sagging properties.

2. Interfacial and Dispersion Control Agents

• Wetting Agents: Because the surface tension of water (72.4 mN/m) is much higher than that of organic solvents, it is difficult to wet the substrate. Wetting agents significantly reduce the surface tension of water, allowing the paint to spread evenly on walls, plastics, or metals.
• Dispersants: Water-based pigments are highly prone to agglomeration. Dispersants (such as sodium polyacrylate) adsorb onto the surface of pigment particles. Through electrostatic repulsion or steric hindrance effects, they keep the pigments suspended uniformly in water for an extended period, ensuring no color floating or mottling.
• Defoamers: Water-based coatings contain large amounts of surfactants (which foam easily, much like detergents), leading to the formation of numerous bubbles during mixing and application. Defoamers (typically silicone-based or mineral oil-based) rapidly break existing bubbles and inhibit the formation of new ones, preventing pinholes in the paint film.

3. Film-forming and Protective Additives

Film-forming aids (coalescing agents): Water-based emulsion paints have great difficulty forming a film in winter or at low temperatures. Film-forming aids (such as alcohol esters or Texanol) temporarily soften the emulsion particles, promoting their coalescence to form a continuous paint film, and then evaporate once the film has set.

In-can preservatives (biocides): Water is a breeding ground for bacteria and mold. Preservatives (such as the BIT/MIT system) are used to prevent the paint from developing an odor, spoiling, or separating in the container before it is opened and used.

Dry-film mold and algae inhibitors: These agents take effect after the paint is applied to the wall and dried (e.g., IPBC, OIT). They are specifically designed to address the humid conditions of the rainy season in southern regions, as well as damp environments in bathrooms and on exterior walls, preventing the growth of mold spots on walls.