Coalescing agent
- Also known as
- coalescent, coalescing aid
A coalescing agent, or coalescent, is an additive in waterborne latex paints and coatings that softens the polymer particles temporarily so they can fuse into a continuous film as the water evaporates. It lowers the minimum film formation temperature and then leaves the film over time.
What is a coalescing agent?
Latex paint is a dispersion of tiny polymer particles in water. As the paint dries, the water evaporates and the particles pack together. To form a tough, continuous film, the particles must then deform and fuse, or coalesce. Hard polymers, which give durable films, do not coalesce well at room temperature on their own; they dry to a cracked or powdery layer.
A coalescing agent is a slow-evaporating solvent that dissolves into the polymer particles and softens them temporarily, so they can fuse. Afterward, it gradually evaporates from the film, which regains its hardness.
Minimum film formation temperature
The key measure is the minimum film formation temperature (MFFT), the lowest temperature at which a latex forms a continuous film. Coalescents lower the MFFT so paint can be applied in cool conditions while still using polymers hard enough for good durability and block resistance.
Coalescents and VOCs
Because most coalescents are organic solvents that eventually leave the film, they can contribute to volatile organic compound emissions. Regulations limiting VOC content have driven:
- Low-VOC and zero-VOC coalescents, which have very low volatility or remain in the film.
- Softer polymers or polymer blends that need less coalescent.
- Bio-based coalescents.
Other considerations
Coalescent choice affects film hardness development, scrub resistance, odor, freeze-thaw stability and compatibility with other components of the CASE formulation.
Frequently asked questions
The paint can crack, fail to form a continuous film or have poor durability, especially when applied in cool weather.
No. It is a solvent that softens polymer particles. Surfactants serve different roles in paint, such as stabilizing the latex and wetting pigments.
Sources
- Organic Coatings: Science and Technology, 4th edition, F. N. Jones, M. E. Nichols and S. P. Pappas, Wiley, 2017