Dispersants are additives that are used to add dispersed solid powder materials to water to form a homogeneous and stable solid-liquid dispersion.
Properties of dispersants
Dispersants are usually polymers containing affinity groups for pigments and long, charged chain segments. Dispersants play a key role in the preparation of aqueous dispersion systems for many powder materials (e.g. pigments, fillers, polishing powders, titanium dioxide, ore powders, resin powders, etc.).
Principle of action of aqueous dispersants
The commercial form of the powder material is flocculated powder particles. It is not a true native particle and in the preparation of aqueous dispersions, these flocculating materials must first be crushed, which is known as flocculation. In solving flocculation problems, the dispersant is usually required to reduce the surface tension of the water and achieve water-to-powder wetting. The total specific surface area of the particles will rapidly increase many times after flocculation breaks down and the energy of the system will also increase (the energy is derived from mechanical energy). In this state, the particles will automatically adsorb surfactants and dispersants from the water to reduce the surface energy of the system.
Demand for dispersants in coatings
Paint in the production and manufacturing process, due to the high surface tension of water, the powder is not easy to wet, the need to add and use of paint dispersant, can improve the gloss and leveling properties of the paint.
During the production process of paint, the colour filler is not easy to wet and disperse difficult in the production process of paint, as the added colour filler will be unevenly dispersed on the surface of the coating film, not easy to wet, easy to produce flocculation problems, affecting the lustre and leveling of the paint film. In the storage process, if the pigments flocculate, the viscosity of the paint will also change significantly. The main function of the dispersant is to disperse and stabilise the pigment to avoid flocculation during storage.
Viscosity-reducing effect of dispersants
In the preparation of waterborne coatings, a grinding process is usually used: pigment concentrates are prepared first and then emulsions are added for blending. Pigment concentrates generally do not contain emulsions (most waterborne emulsions cannot withstand high shear strength) and in this case it is very difficult to prepare concentrates with high pigment concentrations due to the high viscosity. Dispersants also have to have a good viscosity reduction effect.
So the coating formula generally need to add dispersant, so that the pigment filler can be well dispersed pigment filler, the particles are uniform, so that the pigment colouring power and covering power are guaranteed and not affected, and thus the glossy feeling of the paint film, leveling is improved. Easy to use, better construction effect.