Waterborne Polyurethane Wood Coating (Clear, Satin Finish)
A waterborne polyurethane dispersion (PUD) coating for interior wood surfaces. This single-component formula provides excellent durability, chemical resistance, and block resistance with low VOC content compliant with EU Directive 2004/42/EC (Category A/i products). The satin finish is achieved through a flatting agent, and the formula includes a coalescent for film formation below 10°C.
Target Application
Interior wood floors, furniture, and joinery — clear satin finish
Key Properties
- Low VOC (<100 g/L)
- Excellent block and mar resistance
- Good water and chemical resistance
- Satin gloss level (30–45 GU at 60°)
Ingredient List
| INGREDIENT | % |
|---|---|
| Waterborne PU Dispersion (35% solids) | 75.0% |
| Deionised Water | 8.0% |
| Propylene Glycol n-Butyl Ether | 2.5% |
| Dipropylene Glycol Monomethyl Ether | 1.5% |
| Wetting & Dispersing Agent | 0.3% |
| Defoamer (non-silicone, waterborne-compatible) | 0.2% |
| Biocide (in-can preservative) | 0.2% |
| INGREDIENT | % |
|---|---|
| Silica Flatting Paste (20% in water) | 8.0% |
| INGREDIENT | % |
|---|---|
| Polyurethane Associative Thickener | 1.0% |
Percentages are by weight unless otherwise noted. “q.s.” = quantity sufficient to reach 100%.
Manufacturing Process
- 1
To the PU dispersion under slow stirring, add deionised water. Mix for 5 minutes.
- 2
Pre-blend coalescent and co-solvent. Add slowly to the dispersion with moderate stirring.
- 3
Add wetting agent and defoamer under stirring. Mix for 10 minutes.
- 4
Pre-disperse silica flatting paste separately with high shear until uniform. Add to main batch under moderate stirring.
- 5
Add rheology modifier slowly, last. Mix until viscosity stabilises (typically 10–15 minutes).
- 6
Add in-can biocide and mix for 5 minutes.
- 7
Measure final viscosity (target: 60–90 KU by Stormer viscometer), pH (target: 7.5–8.5), and gloss.
- 8
Allow to degas overnight before packaging. Perform application testing on wood substrates.
Regulatory Notes
- VOC content must be declared and must comply with EU Directive 2004/42/EC — Category A/i (interior clear coatings): 130 g/L limit for Phase 2
- Biocide: BIT and MIT are regulated under EU Biocidal Products Regulation (BPR) — confirm your supplier's in-can biocide is authorised for product type PT6
- Flatting agent (amorphous silica): check REACH registration; confirm SDS reflects current CLP classification
- SVHC check: verify none of the additives appear on ECHA Candidate List
Formulator Tips
- Aliphatic PU dispersions give better UV stability than aromatic — always specify 'aliphatic' for clear exterior or UV-exposed applications
- The flatting agent settling rate depends on SiO2 particle size — choose grades with D50 3–7 µm for satin applications
- Addition order matters: always add thickener last to avoid localized viscosity spikes that can trap air
- Test block resistance at 50°C / 1kg / 30 minutes on applied films before release
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