Solvents and Additives of Polyurethane Coatings
Updated: 2026
Solvents and Additives of Polyurethane Coatings: NCO Compatibility, Carrier Selection and Hardener Grade Matching
Quick Answer: Solvents and additives in polyurethane coatings must be selected to protect NCO reactivity, control viscosity, foam, flow, moisture and UV stability. Dongsen supplies polyisocyanate hardeners and crosslinkers, not finished paints or standalone additive packages; typical Dongsen carriers include PMA, PM, Solvent Naphtha 100, butyl acetate, ethyl acetate and water depending on the grade.
Need help matching a solvent system with a PU hardener?
If you are formulating 2K PU wood coatings, 1K baking coatings, waterborne PU systems, flexible packaging adhesives or shoe-sole adhesives, send us your resin type, solvent package, bake temperature, target hardness/flexibility and application method. Dongsen can recommend a suitable polyisocyanate grade for lab evaluation.
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What are solvents and additives in polyurethane coatings?
Solvents in polyurethane coatings adjust viscosity, resin wetting, flow, application window and film build. Additives support defoaming, leveling, wetting, moisture control, UV stability, slip, matting and other performance needs.
The key difference from many other coating systems is the isocyanate group, or NCO. Solvents and additives used in PU systems should not introduce active water, alcohol, amine or other reactive impurities that consume NCO, release carbon dioxide, raise viscosity, shorten pot life or cause foaming.
Product boundary: Dongsen supplies PU raw materials such as aromatic polyisocyanates, aliphatic polyisocyanates, blocked polyisocyanates, moisture-curing polyisocyanates, waterbased polyisocyanates and polyisocyanates for shoe-sole adhesives. Dongsen crosslinkers can be used to formulate coating or adhesive systems, but Dongsen does not supply finished paint, wall paint, epoxy systems, nitrocellulose, alkyd resin or general additive packages. Dongsen is a Shaoguan, China–based manufacturer specializing in polyisocyanate raw materials for the coatings and adhesives industry.
Which solvent families are safer for NCO-containing PU systems?
PU formulators usually screen solvents by three questions: whether the solvent reacts with NCO, whether it gives enough solvency for the resin and hardener, and whether its evaporation profile matches the application process.
| Solvent family | Typical role in PU systems | Compatibility note | Dongsen carrier reference |
|---|---|---|---|
| Esters | Common solvent family for solventborne PU systems | Useful solvency and evaporation balance; control water content | Butyl acetate / ethyl acetate appears in selected Dongsen ranges |
| Glycol ether esters | Carrier for selected blocked and water-dispersible grades | Often used when compatibility and baking stability are needed | PMA is used in DXB-3370G and water-dispersible blocked grades |
| Glycol ethers | Carrier for selected blocked grades | Check grade-specific compatibility and bake behavior | PM is used in DXB-3270C/D |
| Aromatic hydrocarbons | Cost and evaporation adjustment, usually blended with stronger solvents | Stable toward NCO but limited solvency by itself | Solvent Naphtha 100 is used in DXB-3375C/D/E, DXB-3465C/D and DXTB-65D |
| Water | Medium for water-soluble blocked and water-dispersible systems | Only for grades designed for waterborne use; not for normal solventborne NCO hardeners | Water is used in BI-35/BY-40/HBY water-soluble blocked grades and WD series systems |
| Alcohols / amines / wet raw materials | Usually risk materials in NCO-containing components | May consume NCO, increase viscosity, release CO2 or shorten pot life | Use only after formulation validation |
Takeaway: Esters, PMA, PM, Solvent Naphtha 100 and water can all appear in PU-related systems, but the correct choice depends on the specific polyisocyanate grade. A solvent suitable for a blocked baking crosslinker may be unsuitable for a 2K solventborne wood-coating hardener.
Which common additives need special attention in PU coatings?
Additives are not selected only by their function. In PU coatings, the additive carrier, residual moisture, acidity/basicity and active functional groups can affect NCO stability.
| Additive type | Why it is used | PU formulation risk | Buyer / formulator check |
|---|---|---|---|
| Defoamer | Controls air release during mixing, spraying or rolling | Incompatibility may create craters or haze | Check clarity, recoatability and defoaming in the full PU package |
| Leveling / flow additive | Improves surface flow and reduces orange peel | Overdose may affect intercoat adhesion or gloss | Test with the selected hardener and solvent blend |
| Wetting / dispersing agent | Supports pigment and matting-agent dispersion | Amine-containing or wet materials may affect NCO | Check moisture, amine value and storage stability |
| Moisture scavenger | Reduces water-related foaming and viscosity rise | Wrong choice can change pot life or film performance | Important for moisture-sensitive 2K and moisture-curing systems |
| UV absorber / HALS | Improves light stability in selected clear or exterior systems | More relevant to aliphatic systems than aromatic indoor grades | Use with HDI/IPDI-based systems when yellowing resistance is required |
| Catalyst | Speeds NCO/OH reaction and film development | Can sharply shorten pot life and increase moisture sensitivity | Validate pot life, dry time and storage stability before scale-up |
Takeaway: A PU additive is acceptable only after it is tested in the complete formula. The same defoamer or wetting agent may behave differently with TDI trimer, HDI biuret, HDI trimer, blocked HDI trimer or waterbased polyisocyanate systems.
How do Dongsen hardener grades connect with solvent and carrier selection?
Dongsen grades are not only different by chemistry. They also differ by solids, NCO content, viscosity, free monomer limit, blocked or unblocked structure, water compatibility and carrier system. All values below are typical reference data and subject to the current TDS/COA.
| Dongsen grade | Type | Typical solids | NCO / valid NCO | Viscosity | Carrier / medium | Best-fit formulation direction |
|---|---|---|---|---|---|---|
| HDX-50BA | TDI trimer aromatic polyisocyanate | 51±2% | 7.8±0.5% | 1000±500 cps | Solventborne; confirm exact dilution package by TDS | Fast-drying 2K PU wood and furniture coatings, especially matte systems |
| HDX-960E | TDI trimer aromatic polyisocyanate | 51±2% | 7.2±0.5% | 110±50 cps | Solventborne; confirm exact dilution package by TDS | High-compatibility solventborne 2K wood PU coatings, acrylic-compatible systems |
| HDX-175MPX | HDI biuret aliphatic polyisocyanate | 75±1% | 16.5±0.5% | 210±90 cps | Solventborne | Non-yellowing 2K PU coatings needing flexibility and adhesion |
| HDX-190 | HDI trimer aliphatic polyisocyanate | 90±1% | 19.8±0.5% | 525±75 cps | Solventborne high-solids direction | Non-yellowing systems needing hardness and faster dry |
| DXB-3370G | Solvent-based blocked HDI trimer | 70.0±2.0% | 7.5±0.5% valid NCO | 2000±1000 cps | PMA | Low-temperature 1K baking systems at 80-100°C |
| DXB-3375D | Solvent-based blocked HDI trimer | 75.0±2.0% | 11.2±0.5% valid NCO | 2500±1000 cps | Solvent Naphtha 100 | 1K baking systems at 130-140°C, can & coil and flexible packaging adhesive directions |
| BI-70D | Water-dispersible blocked HDI-based crosslinker | 70% | 7.2±0.5% valid NCO | 4000±1500 cps | PMA | Waterborne 1K baking systems where blocked water-dispersible crosslinker is needed |
| WD-8780 / WD-8980 | Waterbased HDI polyisocyanate | 80.0±2.0% | 15.0±1% | 300±200 cps | Water-dispersible system | Waterborne wood, industrial and selected PU coating systems |
| SA-1007 | Polyisocyanate for 2K PU shoe-sole adhesive | 40±1% | 7.5±0.3% | Approx. 11 cps | Ethyl acetate | Footwear and shoe-sole bonding applications |
Takeaway: DXB-3370G uses PMA and deblocks at 80-100°C, while DXB-3375D uses Solvent Naphtha 100 and deblocks at 130-140°C. That bake-temperature and carrier difference is more useful for buyers than a generic “blocked isocyanate” description.
How should buyers choose a Dongsen grade by application?
| Application need | Solvent / additive focus | Recommended Dongsen direction | Why this direction fits |
|---|---|---|---|
| Fast-drying 2K PU wood coating | Dry ester/ketone solvent package; moisture control; defoamer and leveling validation | HDX-50BA | TDI trimer with 51±2% solids, 7.8±0.5% NCO and fast-drying positioning for wood coatings |
| High-clarity or acrylic-compatible wood PU coating | Solvent compatibility, flow, clarity and low viscosity | HDX-960E or HDX-H77 | HDX-960E has 51±2% solids, 7.2±0.5% NCO and 110±50 cps viscosity for higher compatibility direction |
| Non-yellowing 2K PU system | Aliphatic hardener, UV package, solvent stability | HDX-175MPX, HDX-190 or HDX-100 | HDI biuret supports flexibility/adhesion; HDI trimer supports hardness and faster dry |
| Low-temperature 1K baking coating | Bake profile, blocked NCO release and PMA carrier compatibility | DXB-3370G | Blocked HDI trimer at 70.0±2.0% solids with 80-100°C deblocking range |
| Medium-temperature baking coating / adhesive crosslinking | Solvent Naphtha 100 carrier, bake temperature, storage stability | DXB-3375D | 75.0±2.0% solids, 11.2±0.5% valid NCO and 130-140°C deblocking range |
| Waterborne 2K or water-dispersible PU system | Water compatibility, co-solvent, pH, defoaming and dispersion stability | WD-8780 / WD-8980 | Water-dispersible HDI-based polyisocyanate with 80.0±2.0% solids and 15.0±1% NCO |
| 2K PU shoe-sole adhesive | Ethyl acetate carrier, bonding strength, open time and discoloration control | SA-1003 / SA-1007 / SA-1009 | SA series uses ethyl acetate and is positioned for shoe and footwear bonding |
Takeaway: The buyer should not ask only “which PU hardener is cheapest?” A better starting question pairs the application with the resin and process conditions, so the grade matches dry time, bake temperature and the required hardness, flexibility and yellowing balance.
What should be avoided when using solvents and additives with isocyanate hardeners?
- Do not use wet solvents in solventborne 2K NCO systems. Moisture can react with NCO and generate CO2, causing bubbles, pressure build-up or viscosity rise.
- Do not assume alcohol-containing solvents are safe for unblocked NCO components. Alcohols can react with isocyanate groups.
- Do not copy an additive package across systems without testing. A defoamer that works in a waterborne system may cause haze or craters in a solventborne 2K system.
- Do not choose blocked isocyanates without checking bake temperature. A low-temperature system and a 150°C baking line may require different blocked crosslinkers.
- Do not present Dongsen as a finished-paint supplier. Dongsen supplies raw-material crosslinkers and hardeners for formulators and coating manufacturers.
Which related Dongsen solutions should be considered?
For buyers who are comparing solvent and additive choices, the next step is usually to match the correct crosslinker family. Start from the Dongsen isocyanate hardener category, then choose the relevant product family:
- Solvent-based blocked isocyanates for 1K baking systems where storage stability and controlled deblocking are needed.
- Waterbased isocyanates for waterborne PU systems requiring water-dispersible HDI-based crosslinkers.
- Wood & furniture coatings where fast drying, hardness, matting behavior and solvent release are common buyer concerns.
- Fast-drying PU hardener selection if your main issue is dry speed in wood coatings.
- Blocked polyurethane coating selection if your system depends on baking temperature and latent crosslinking.
Key takeaways for procurement and formulation teams
- Solvent choice in PU coatings is mainly about NCO protection, solvency, evaporation and process fit.
- Alcohols, amines, moisture and wet raw materials can consume NCO and create foaming or pot-life problems.
- Dongsen carriers vary by grade: PMA, PM, Solvent Naphtha 100, BAC, ethyl acetate and water all appear in different product families.
- Blocked isocyanates should be selected by deblocking temperature, not only by solids or NCO content.
- For a tailored grade recommendation, share your application and process details through the inquiry form below, and Dongsen will suggest a grade for testing.
Request a suitable Dongsen grade for your PU system
Share your coating type, resin system, current solvent blend, additive concerns, target performance and estimated order quantity. Dongsen can review the application and recommend a suitable grade for testing.
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Send your solvent, additive or hardener requirement
To help us recommend the correct grade, please include:
- ✅ Coating or adhesive application: wood, automotive refinish, can & coil, flexible packaging, waterborne system or footwear adhesive
- ✅ Resin type and current solvent blend
- ✅ Room-temperature 2K system or 1K baking system, including bake temperature if applicable
- ✅ Target dry time, hardness, flexibility, gloss, yellowing resistance and pot life
- ✅ Required documents: TDS, MSDS, COA, sample or quotation
FAQ: Solvents and additives for PU coatings
Can alcohol solvents be used in polyurethane coatings?
Alcohol solvents should generally be avoided in unblocked NCO-containing components because alcohols can react with isocyanate groups. If an alcohol-containing component is required, validate it in the complete formulation and storage condition.
Why does moisture cause foaming in PU coatings?
Moisture can react with isocyanate groups and generate carbon dioxide, which may cause bubbles, pressure build-up, viscosity increase or gelling. This is why dry solvents and sealed storage are important in solventborne 2K PU systems.
Which Dongsen grade uses PMA as a carrier?
DXB-3370G uses PMA as its standard solvent carrier and has a typical deblocking range of 80-100°C. Water-dispersible blocked grades such as BI-70, BY-70 and HBY-70 series also use PMA.
Which blocked isocyanate should I choose for a 130-140°C baking system?
DXB-3375D is a suitable starting point for a 130-140°C baking system. It is a solvent-based blocked HDI trimer with 75.0±2.0% solids, 11.2±0.5% valid NCO and Solvent Naphtha 100 as the standard carrier.
Does Dongsen sell coating additives or finished polyurethane paint?
No. Dongsen supplies polyisocyanate hardeners and crosslinkers used by coating and adhesive manufacturers. Dongsen does not supply finished paint, wall paint, epoxy systems or standalone additive packages.
What information should I send to get a suitable hardener recommendation?
Send your application, resin type, solvent blend, additive concerns, room-temperature or baking process, bake temperature, target film properties, country and estimated quantity. This helps Dongsen recommend a practical grade for testing.
