We would like to acknowledge Jochum Beetsma for sharing his dispersion expertise and validating the page.
The amount of dispersant used in a system is often given as dispersant load.
This is the amount of dispersant polymer (in mg) per square meter of the solid surface of particles. Dispersant load is given in mg/m2.
People often ask what the ideal dispersing loading is for their formula. Indeed, it is an important question for your coatings or inks formulation.
If you feel stuck or tired of searching on your own to solve your dispersion problem, don't forget we are here to help!
What are the signs I am not using the right amount of dispersant?
| Loading is too low
|
When you do not use enough dispersants, you end up with slow and poor dispersion. As a visible sign, you may experience too low gloss, sedimentation, and flocculation to name a few. |
| Loading is too high |
Adding dispersants in excess is not good either. First, it induces extra cost. It can also lead to foaming or worsen the final properties of your coatings or inks (water sensitivity might go up, hardness might go down, etc.). |
As we now understand, dispersant load is an important formulation factor. Let’s see how you can determine how much dispersant you should use, without endless trials and errors.
Here, we assume that your
selection of dispersants is well-suited for your pigments and fillers.
How to determine the theoretical dispersant load?
Solid particles attract each other, and this is precisely what you want to avoid in your final coating.
A quick reminder of how dispersants work
The addition of dispersants in the system aims at bringing a repulsive force. The dispersion force needs to be strong enough to prevent the reagglomeration of particles, called flocculation.
A good dispersant adsorbs strongly on the surface of the solid particles. This happens when specific groups in the dispersant molecules, so-called anchoring groups, can form strong physical bonds with chemical groups that are present on the surface of the particles, the so-called anchor sites.
Anchor Sites: The Place Where the Dispersing Agents Adsorbs on the Particle Surface
What is the optimal dispersant load?
In the case of steric stabilization, the dispersant load is the amount of dispersant needed to cover the surface of the solid particles. No surprise, you need to know your pigment's or filler's specific surface area (m
2/g). If this information does not appear on the product datasheet, contact the pigment or filler producer or one of his distributors.
Step-by-step determination of the theoretical dispersant load
Knowing the specific surface area enables you to calculate the volume of liquid needed to surround the solid particles:
-
The thickness of the tails layer around particles has been widely studied in the literature. We know that we only need a 10 nm thickness to prevent flocculation in coatings and inks.
- The surface area corresponds to: amount of solid particles (g) x specific surface area (m2/g)
When your formula contains a combination of solid particles, the total surface area is the sum of the surface area for each type of particle.
The layer around the particle is made of the coating solvent and x% of polymer tails. The % of polymer should be enough, like 30-40%. With this hypothesis, you can then calculate the amount of polymer needed per gram of pigments or fillers.
Finally, based on the dispersant solid content, you can deduct the amount of additive you should use in your system.
Watch this video tutorial where the calculation is given in more details:
With an electrostatic dispersing agent, dispersant load is more complex to determine than the method presented above. Get in touch with our support team if you need help.
In practice, how to determine the amount of dispersant to use in your coating?
In practice, depending on your chosen stabilization method, you can go straight with the following experiments:
- For dispersants that give electrostatic stabilization:
Take a dispersant load of 0.5 mg/m2 and make a series with dispersant loads of, for example, 0.3, 0.5, 0.8, 1.2, and 1.5 mg/m2.
- For dispersants that give steric stabilization:
Take a dispersant load of 4 mg/m2 and make a series with dispersant loads of, for example, 2, 3, 4, 5, and 6 mg/m2.
If you are unsure about the kind of stabilization provided by your dispersant, ask us for the support!
You can now optimize your dispersant load. It is the sweet spot where you have:
- good dispersion,
- good fineness,
- high color strength,
- low viscosity, and
- good stability of those properties.
Need help optimizing your pigment or filler dispersion?
Despite following these steps, if your pigment dispersion still fails to meet targets, get in touch with our team of material and formulation experts. They will help you analyze what is going wrong and guide you in your optimization work. Wherever possible, we help you source the recommended materials, so you move fast to your lab work.
Submit your case!