Choosing Hydroxyl Acrylic Resins and Hardeners for 2K Waterborne PU Topcoats

The hardener decides half of a 2K waterborne PU system’s performance, and the hydroxyl resin decides the other half. Monolith’s AH/AC/PU hydroxyl acrylic and polyurethane dispersions are designed to be cured with a water-dispersible isocyanate hardener.

1. Match the hardener’s NCO content to the resin’s OH value

Monolith hydroxyl acrylic dispersions span OH values from 33 (AH210) through 110 (AH233, AH235) up to 129 (AH239, AH252, AH260). Always calculate the NCO:OH ratio from the actual COA, not the datasheet average.

2. Verify emulsification behavior

A good waterborne hardener disperses into AH/AC/PU hydroxyl dispersions by hand-stirring, without high-shear equipment. Poor emulsification shows up as gloss loss and solvent popping.

3. Field-proven hydroxyl resins

• Construction machinery: AH235 / AH239 topcoats over EP137 + EH3510 primer: high gloss and fullness, good weather resistance, high thickness of non-bubble film.
• Rail transit: AH233 / AH252 topcoats over EP141 + EH3510: surface dry slow, hard dry fast, high DOI.
• Petrochemical storage tanks: AH239 over EP137 + EH3513: acid and alkali resistance, aging resistance.
• Containers and wet-on-wet lines: AH239H: high thickness of bubble limit film, high gloss, good chemical resistance.
• Wind turbine blades: PU7502 (solvent-free PUD), AH251, AH221, AH231.

Monolith’s application engineers can validate the hardener-resin pair on your line conditions before you commit to production trials. Request TDS / samples or email martin@monolithchem.com.

All parameters are for reference and based on the COA at the time of shipment.