Pigment dispersion is the process of suspending insoluble pigments in a liquid medium, typically water or organic solvent, so that they can be used in inks paints and coatings. Traditionally, pigment dispersion is comprised of three main steps; wetting, deagglomeration, and stabilization. These three steps are outlined in further detail below.
When solid pigments are first added to the liquid medium they are agglomerated and air is entrapped in the surface of the pigment agglomeration. In order for proper wetting to occur the air entrapped in the pigment needs to be replaced with the liquid medium. The use of a wetting agent speeds up the process and ensures complete wetting of the pigment.
Once complete wetting of the pigment particles is achieved, the large agglomerations of pigment must be broken up to reduce the particle size. This is commonly achieved through mechanical shear via the grinding mill. Reduction of the surface tension in the liquid medium allows for faster deagglomeration and a more homogeneous particle size in the dispersion.
Electrostatic dispersants carry an ionic charge. They interact with the surface of the pigment particles to produce like charged surfaces, typically cationic. These like charges on the surface of the pigment particles repel each other and keep the pigment in stable suspension. Changes in pH and addition of ionic material can destabilize particles suspended with electrostatic dispersants.
Steric dispersants consist of molecules with an anchoring head group that is attracted to the pigment particles and tails that are attracted to the liquid phase of the dispersion. The head groups adsorb onto the surface of the pigments and the tails orient themselves outward from the surface. The protruding tails keep the pigment particles separated and suspended. Steric stabilization is incredibly stable at high salt concentrations and over a wide pH range.
Surfactants, or surface active agents, are molecules that reduce the surface tension at the interface between two substances. In the case of wetting and dispersing pigments, a reduction of surface tension between the solid pigment particles and the liquid carrier allows for faster and more efficient wetting and deagglomeration. Additionally, surfactants can adsorb onto the surface of pigment particles and provide steric stabilization of the dispersion. Commercially, there are many types of non-ionic surfactants and anionic surfactants that are used today as wetting agents and dispersants in inks, paints, and coatings. These surfactants are compared below based on performance characteristics.
| Surfactant Type | Reduction of Surface Tension | Foam Tendency
|
Addition Rate
|
|---|---|---|---|
| Alcohol Ethoxylate | Moderate
|
Moderate
|
1-3%
|
| Sulfosuccinate | Good
|
High
|
1-3%
|
| Fluorosurfactants | Excellent
|
Low
|
0.01-0.05%
|
| Polyether Siloxane | Moderate
|
Moderate
|
1-3%
|
| Acetylene Diol | Good
|
Low
|
0.1-1%
|
| Grade | pH
|
Specific Gravity
|
Solids
|
|---|---|---|---|
| Capstone™ FS-30 | 7 - 8.5
|
1.1 g/ml
|
25%
|
| Capstone™ FS-31 | 7 - 8.5
|
1.1 g/ml
|
25%
|
| Capstone™ FS-3100 | 7 - 8.5
|
1.35 - 1.39 g/ml
|
100%
|
| Capstone™ FS-34 | 5.5 - 7.5
|
1.1 g/ml
|
25%
|
| Capstone™ FS-35 | 5.5 - 7.5
|
1.1 g/ml
|
25%
|
PHONE 425.372.9328
We’ve detected that you are located in a different region than the region selected on the website. Would you like to change your region?
Current Region: English - United States
.png)
Hi, let us know if you have any questions as you visit our website.
