What is Ambient Moisture Curing Polyurethane

3rd April 2024

Moisture curing polyurethane coatings, made from excess polyisocyanates and hydroxyl-containing polymers like polyester resins, polyether resins, epoxy resins, hydroxyl acrylic resins, castor oil resins, etc., consist of prepolymers, low water content solvents, pigments, dehydrating agents, additives, and catalysts. They typically have an NCO content of 10% - 15% and an NCO/OH molar ratio of approximately 3 or greater.

1K MCU coatings cure by reacting with moisture in the air, where -NCO groups react with H2O to form amines and carbon dioxide. The amines further react with -NCO groups, forming urethane bonds and urethane methacrylate bonds in the coating. However, a significant amount of -NCO groups remains in the coating. Depending on the curing method, they can be categorized as moisture-curing or latent-curing.

Moisture-curing polyurethane coatings have a broad application range, suitable for temperatures above zero with relative humidity ranging from 30% to 98%. They offer easier application compared to two-component polyurethane coatings and exhibit excellent film-forming properties even under humid conditions. Additionally, they have low substrate preparation requirements, excellent surface tolerance, adhesion to various substrates, and outstanding resistance to abrasion, corrosion, pollution, water, flexibility, and atomic radiation.

The drying time of moisture-curing polyurethane depends on relative humidity and temperature. Therefore, both factors need consideration during coating curing. Lower temperatures result in slower drying due to less moisture in the air, while higher temperatures lead to accelerated reactions with -NCO groups. Hence, environmental conditions should be considered in formulation design.

Doxu are leading manufacturer of Isocyanate Hardeners for 1K/2K coating&adhesive since 1988.  Belows are Doxu 1K Moisture Curing Prepolymers.

Product DXCJ-75 DXC-60S DXC-40W DXCH-80
Type TDI Based TDI Based TDI Based HDI Based
Appearance Colorless to pale yellow transparent viscous liquid Colorless to pale yellow transparent viscous liquid Colorless to pale yellow transparent viscous liquid Colorless to pale yellow transparent viscous liquid
NCO % 7.5±0.5 6.3±0.5 4.2±0.5 9.5±0.5
Solid Content% 75.0±2.0 60±2 40.0±2.0 80±2
Viscosity/ /25℃  (CPS) 2000±500 200-800 12-25 sec (Ford #4) 800±400
Free Monomer % TDI≤0.1 TDI ≤0.1 TDI ≤0.1 HDI≤0.1