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Coatings Ingredients
The material selection platform
Coatings Ingredients

Using HSP to Select Coalescents and Improve Film Formation

Sander van Loon & Beverley Fricker – Mar 6, 2020

Using HSP to Select Coalescents and Improve Film Formation In dispersion paints, optimal film formation is a crucial factor to achieve coatings with excellent properties and integrity in time. Latex binder systems having a minimum film-formation temperature (MFFT) higher than the temperature at which they will be applied, require the use of a suitable coalescent. By softening the polymer droplets during the crucial period of fusion, it will ensure the film forming process and result in a smooth continuous film[1] upon drying.

Key characteristics of a good coalescing agent are:

  • To be an active solvent for the polymer used.
  • To lower the minimum film-formation temperature (MFFT) of the polymer.
  • To have a lower evaporation rate than water.
  • To have a very low solubility in water.

To learn more about coalescing agents, see Johan Bieleman’s guide on "Role of Coalescing Agents in Coatings".

Texanol is currently the most widely used coalescent for latex paints in the world: despite sometimes not being the most efficient coalescing aid for a given system, it meets all the above requirements and shows a good cost/benefit ratio.

Still with that in mind, coating formulators may still want to replace Texanol when taking into consideration other properties, such as gloss, hardness development, VOC level, odor, greener profile, etc. And finding alternatives is challenging because they have to meet all the listed requirements.

Good news is that with HSP, you can find an efficient route to replace Texanol in your formulations. Let’s discover how!

How Can HSP Identify Good Coalescing Agents?

Dr. Charles Hansen said: “A good coalescent agent can be identified by plotting the HSP of candidate coalescents with those of the polymer and water in a three-dimensional plot and comparing their respective locations. The good coalescent will occupy the boundary area between the solubility envelope of water and polymer.[2]

This extra information allows you to find the right coalescent agent or blend of coalescing agents for your polymer, in addition to the standard criteria (e.g. high boiling point, low VOC, etc.)

Practically Determining the HSP of a Binder

VLCI practically determined the HSP of SETAQUA® 6462 by allnex (a styrene acrylic dispersed in demineralized water) as the first step to finding the best coalescing agent possible. This was achieved by adding 0.1 g of SETAQUA® 6462 to 5 mL of various solvents and solvent blends. These were then visually assessed and ranked from 1 – complete compatibility to 6 – complete incompatibility.

When solvents are combined, the HSP of the resulting blend changes to one that lies between the original solvents, in proportion to the amount of each solvent used. By using sets of solvent blends that cross the boundary of SETAQUA® 6462’s solubility sphere, it is possible to accurately define the outer limit of the sphere. These rankings were entered into the HSPiP software for analysis.

 »  Explore how to select the right coalescent agent for dispersion paints and improve their film formation using Hansen Solubility Parameters.

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