TIPS: Selection and precautions for additives in water-based coatings

Coating additives are an important component of coating products. They can improve the production process, improve product performance, improve coating construction performance, and play a key role in improving the performance of coatings and coating films. As people With the increasing emphasis on environmental protection, water-based coatings have begun to develop rapidly, and water-based coating additives have received more and more attention from people in the industry. So what should we pay attention to when selecting additives for water-based coatings?

wetting and dispersing agent
When solid and liquid come into contact, the original solid-gas interface disappears and a new solid-liquid interface is formed. This phenomenon is called wetting. When a liquid is used to moisten the pigment filler and penetrate it into the agglomerates and aggregates of the pigment filler, if a small amount of surfactant is added to the liquid, the wetting and penetration will be easier. This is the wetting effect. Surfactants that wet or accelerate the wetting of pigment fillers are called wetting agents. The liquid in water-based paint is water.

The surface properties of pigments and fillers, the type and amount of wetting and dispersing agents, and the efficiency of dispersing equipment are the main factors affecting dispersion.

The stability or coagulation of suspended dispersions of pigments and fillers depends on the forces, repulsions and attractions between particles. Repulsive force is the main factor of stability, and attractive force is the main factor of agglomeration.

Defoaming agent
Foam is generated when air enters a liquid containing surfactant under the action of external force, and the surfactant will be directionally arranged at the air-liquid interface. The hydrophobic group faces the air in the bubbles, and the hydrophilic group faces the water, creating a large number of bubbles. There are several reasons why foam occurs in paint.

1: During the production of paint, air will be entrained into the paint due to mechanical stirring;
2: Air brought in during the coating process, such as brush coating, roller coating, high-pressure airless spraying, etc.
3: When mixing two-component paint before construction, stir the mixed air.
4: The object to be painted has many pores, and air bubbles are formed due to the penetration of the paint, such as when painting on porous wood and cement walls.
5: Bubbles generated by chemical reactions, such as polyisocyanate in two-component PU coatings reacting with trace amounts of water to produce carbon dioxide.

Bubbles are inherently unstable, and their destruction requires three processes: redistribution of bubbles, thinning of the film thickness, and rupture of the film. However, for a relatively stable foam system, it will take a long time to achieve natural defoaming through these three processes. Defoaming agents are mostly used in all production. It is generally believed that defoaming agents reduce the local surface tension of the foam liquid film and defoam. Because of the low surface tension of the defoaming agent itself, it always penetrates into the foam system in the form of particles to locally reduce the surface tension of the bubble film. Since liquids with low surface tension always flow toward liquids with high surface tension, the membrane wall gradually becomes thinner and is strongly pulled by the surrounding membrane layers with high surface tension, causing stress imbalance and eventually causing the bubbles to burst.

Currently, there are three general categories of defoaming agents: mineral oil defoaming agents, silicone defoaming agents, and silicone-free polymer defoaming agents.