Name the stage. A paper-machine EO/PO antifoam is not a decorative-paint defoamer, even when both products are called defoamers.
Stage decides the additive
Pigment dispersants and grind resins foam under the impeller. A persistent defoamer is useful there and dangerous later if it concentrates at the surface of a low-shear letdown. Letdown defoamers are chosen to knock foam from the latex surfactant without leaving a crater.
Esteem’s paper-defoamer range should stay in the mill. Coatings need a defoamer screened in the resin you sell. Tell the lab which stage failed.
How to read a crater
A crater with a gelled center is often incompatible defoamer or a hydrophobic particle. A pinhole field is often microfoam and a degassing question. Photograph the film before the next sample, because the words “foam” and “crater” get used for both.
Tinting adds surfactant from the colorant. A base that was quiet can foam after the dispenser. Include that if the complaint is in the store, not the plant.
| Stage | Foam type | Wrong sample |
|---|---|---|
| Grind | Macrofoam, volume loss | A letdown-only defoamer |
| Letdown | Latex surfactant foam | A heavy grind defoamer |
| Dry film pinholes | Microfoam | More pot defoamer only |
| Paper mill | Liquor foam | Any of the paint defoamers |
Two different foams
Grind foam is air beaten into a thick mill base by a disperser. The film is viscous, so bubbles do not rise and a strong hydrophobic defoamer is needed to rupture them under shear. Let-down foam is air folded in while latex, thickener, and water are added. The continuous phase is thinner and richer in the latex emulsifier, which stabilises microfoam.
One defoamer chemistry rarely sits at the optimum for both. A very strong mineral-oil or silicone defoamer can clear the grind and then crater the finished film. A mild defoamer that is safe in the let-down can leave the grind full of air, and that air becomes pinholes after drying.
Compatibility is the crater mechanism
Craters form when a defoamer droplet is large enough, or hydrophobic enough, to cause local de-wetting as the film forms. Emulsifying the defoamer more finely reduces craters and can also reduce knockdown, because the droplet no longer enters the bubble film. The working window is between those two failures.
Latex surfactants make this window move. A styrene-acrylic rich in nonionic emulsifier can solubilise a defoamer that worked in a vinyl-acrylic. The defoamer disappears into micelles and the foam returns. That is a compatibility failure, not a dose failure, until the dose is so high that craters start.
How to split the addition
Put the stronger defoamer in the grind at the lowest level that clears air under the disperser. Put a more compatible defoamer in the let-down for microfoam and application foam. Test brush-out or drawdown for craters after overnight ageing, because a defoamer can look fine and then float.
Record the latex, the dispersant, and whether a universal colorant is added. Colorants reintroduce foam and surfactant. A panel without tint is not the panel the customer ships.
How to Specify with Esteem
- Split the complaint: millbase volume, letdown foam, or craters in the dry film.
- Name the resin system: latex, alkyd emulsion, or solvent-borne.
- State if silicone is banned because of recoat.
- Do not send a pulp antifoam into a tint base.
- Check cratering on a sealed chart, not only foam height in the pot.
Paper defoamers stay on the paper hub. Coating air-release is discussed in the defoamer versus degassing comparison and paint and coating chemicals.