Have you heard of Flocculation: Sandy Surface in Paints?
- February 6, 2019
- Posted by: MahaChem
- Category: Coating, ST
Have you ever experienced your paint application become "sandy"?
One day, our technical team received a call from an emulsion paint maker. They told us that their high gloss emulsion paint became “sandy” after they added the latex into the mill base. Being “sandy” refers to many particles appeared on the dried paint film. The examples of such phenomenon can be seen as the image shown below. This phenomenon is called “Flocculation” in technical term.
The Causes of Flocculation
Why is flocculation happened after latex was added to the mill base? To answer this question, we have to understand the dispersing and stabilizing mechanism in mill base and also the stabilizing mechanism in latex.
In Mill Base:
- Dispersant and surfactant (wetting agent) help to breakdown the pigment agglomerate into small particles under high speed mixing.
- Dispersant and surfactant adsorbed on the pigment surfaces to keep them apart to prevent pigment particles from stick together to form big particles (flocculation). This is called stabilization of pigment particles.
In Latex, polymer particles are stabilized by surfactants. Below are two scenarios of flocculation when latex is added into the mill base :
- If the latex is lean in surfactant amount, the latex particles will draw the dispersant/surfactant away from the pigment particles in mill base which will cause pigment flocculation.
- If the mill base is lean in dispersant/surfactant amount, the pigment particles will draw the surfactant away from the latex particles which will cause latex flocculation.
The Solution to Flocculation
To avoid this problem, mill base must have slightly excessive dispersant in the formulation. Usually 10% more than the minimum amount should be added in order to prevent flocculation.
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