03

The dispersion process

The various processes which occur during pigment dispersion can be divided into the following three steps:

During Step 1, all of the air and moisture at the pigment surface is displaced and then replaced by the binder solution. The binder solution wets the pigment particles and the solid/gaseous interface (pigment/air) is transformed into a solid/liquid interface (pigment/binder solution). To do this, the binder solution must penetrate into the interstitial spaces of the agglomerate.

Step 2 represents the actual dispersing of the pigment. Through mechanical energy (impact and shear forces), the pigment agglomerates are broken up and accordingly reduced to their particle size.

In the concluding Step 3, the pigment dispersion must be stabilized in order to prevent the formation of uncontrolled flocculation. As described later in more detail, suitable measures are used to keep the individual pigment particles at appropriate distances from one another so that they cannot congregate. In most applications the stabilization of the deflocculated state is desirable; in some applications the pigment dispersion can also, however, be stabilized by controlled flocculation (which will be discussed later).

Steps 1 (wetting) and 3 (stabilizing) can be optimized by additives. Wetting additives accelerate the wetting of the pigment agglomerates using the binder. Dispersion additives improve the stabilization of the pigment dispersion. One and the same product can often function as both the wetting and the dispersing additive.

Additives will not help in step 2, the actual dispersion of the pigment agglomerates, even if the term “dispersion” additive would suggest the contrary. Here it is important that the mechanical forces are great enough to break up the agglomerates and that the dwell time of the agglomerates in the sphere of action of these forces is of sufficient length. If the agglomerates are broken up as much as possible, the dispersing additives can then stabilize this state and effectively suppress flocculation.