State oil length and drier package. An architectural acrylic emulsifier is not an alkyd emulsifier until dry and yellowing are checked.
An oil phase, not a latex seed
Alkyd emulsion manufacture is closer to a resin emulsification than to vinyl acetate polymerization. The HLB pair has to match the alkyd polarity. A polymerization stabilizer chosen for styrene-acrylate will not automatically emulsify a long-oil alkyd, and it may not let the driers work.
Esteem ester emulsifiers, including sorbitan esters, and the ethoxylate range are the two sides of that pair. Ask for both when the brief is a water-borne alkyd rather than an acrylic latex.
Film tests that matter on wood
Through-dry, yellowing in the dark and in light, and early water spotting decide a joinery coating. Emulsion stability at 50 °C is necessary and not sufficient. If the product is a penetrating stain, also look at color uniformity on pine, because excess emulsifier can change uptake.
Keep coalescent and cosolvent written down. They change dry as much as the surfactant and will confuse the sample comparison if they move at the same time.
| Product | Surfactant emphasis | Must-pass test |
|---|---|---|
| Penetrating stain | Lower dose, controlled HLB | Uniform color on wood |
| Alkyd topcoat | Pair that still allows oxidation | Through-dry and water spot |
| Acrylic latex | Polymerization stabilizer | Not a proof for the alkyd |
| Floor polish | High-HLB wax emulsifier | Different film test |
Making the emulsion
A solventborne alkyd is a polyester of fatty acids, polyols, and diacids or anhydrides, dissolved in mineral spirits. An alkyd emulsion puts that polymer in water. The surfactant, often a nonionic ethoxylate plus an anionic, sets droplet size during inversion. Smaller droplets give better gloss and stability and a larger surface for hydrolysis.
Neutralisation of residual acid groups with an amine helps water dispersibility and also sets the pH that drives hydrolysis. There is a window: enough amine to emulsify, not so much that the ester backbone splits on the shelf. The surfactant does not stop hydrolysis. pH and the alkyd design do.
Wood wetting and grain raise
Water raises the grain of wood and can de-wet on oily tropical species or on resinous knots. A wetting agent, separate from the emulsifier that made the alkyd droplet, lowers the contact angle so the first coat penetrates instead of crawling. Too much wetter increases grain raise and water sensitivity of the film.
Open time is short compared with solvent alkyds because water leaves quickly in dry air and slowly in humid air. Surfactant that holds water in the film extends open time slightly and slows hardness. Driers still have to reach the unsaturated fatty acids inside the droplet. A surfactant barrier that is too tight can slow through-dry.
Shelf life is a chemical specification
Measure acid value, pH, and viscosity of the emulsion over the stated shelf life, not only droplet size on day one. A rise in acid value means the alkyd is hydrolysing. Creaming means the emulsifier or the density match is wrong. Grit means inversion shear or pH drifted.
Specify the oil length of the alkyd, the amine used to neutralise, the target pH, and whether the coating is a penetrating stain or a film-forming topcoat. The surfactant level that makes a stable stain can leave a topcoat soft.
How to Specify with Esteem
- Give oil length and solvent left in the alkyd.
- Name the drier metals.
- State the target: stain penetration or a film-forming topcoat.
- Pair a low-HLB ester emulsifier with a higher-HLB ethoxylate rather than using one grade.
- Test through-dry and 24-hour water spot, not emulsion stability alone.
Sorbitan esters and fatty-alcohol ethoxylates are the usual HLB pair to discuss with Esteem ester chemistries and the paint emulsifier range.