Pigment dispersion process in paint toning!

The preparation process of paint is mainly a physical dispersion and mixing process, including ingredients, pre-dispersion, grinding dispersion, blending, toning (color matching), and filter packaging.
The dispersion of pigments is a key step in the preparation of paints.
The advantages and disadvantages of pigment dispersion It directly affects the quality of coatings and production efficiency.

The dispersion of pigments is a key step in the preparation of colored paints.

The dispersion of pigments directly affects the quality and production efficiency of the coatings.

Pigment wetting

The surface of the pigment particles used in the production of paint usually adsorbs water and air, and the gaps between the particles are also filled with air.

Therefore, in the dispersion process of the pigment, the moisture and air on the surface of the pigment are first replaced by the paint, that is, the pigment is wetted by the resin solution or the solution containing the wetting and dispersing agent (ie, the paint).

The lower the viscosity of the paint, the faster the wetting speed of the pigment.

For solvent-based coatings, because the surface tension of the paint is usually less than the surface tension of the pigment, the pigment is easy to wet.
For water-based paints, because the surface tension of water is generally higher than that of organic pigments, it is difficult to wet, so wetting and dispersing agents are needed to speed up the wetting of the pigments.

Grinding and dispersion of pigments

The particle size of the pigment used in the coating is small, and the van der Waals force between the particles can easily make it cluster together.

Therefore, the wetted pigment needs to be pulverized under a certain mechanical external force to make it a Fine particles required by the paint process.

In the coatings industry, this process is usually completed under grinding conditions, where grinding is mainly shear force.

The so-called grinding is not to grind the original particles of the pigment, but to disperse the aggregates of the pigment in the paint.

Pigment stability

After the pigment is dispersed, the surface energy of the pigment particles increases and has a tendency to aggregate with each other.

Therefore, stabilizing the depolymerized pigment particles during the pigment dispersion process is also a very important link, otherwise the coating will re-flocculate during storage and construction, which will reduce the quality of the coating.

In the dispersion system of the paint, the pigment is stabilized mainly through two mechanisms of charge stabilization and three-dimensional protection.

The former method is to add some surfactants or inorganic dispersants, such as polyphosphate or hydroxylamine, etc.
The latter method is to add some long-chain surfactants to the solvent-based coatings, which can form 8-9nm adsorption Floor.

In fact, the three processes of wetting, dispersing, and stabilizing the pigments mentioned above are not completely separate, and sometimes occur simultaneously and alternately.

For the paint dispersion system, wetting is the basis, grinding is for more sufficient wetting, and the stability of the pigment after dispersion is the ultimate goal.