How moisture scavengers reduce defects in polyurethane coatings
September 7, 2022 | Blog
Polyurethanes are created by reacting a polyol with an isocyanate or a polymeric isocyanate. These coatings are attractive to customers as they enhance durability and energy efficiency in a variety of applications. However, one common issue that arises is moisture absorption by isocyanates in the coating, which can release carbon dioxide (CO2) bubbles. This can result in paint defects such as gloss reduction, haze formation, and foam generation.
With these moisture-related defects in mind, storage stability is critical for polyurethane coatings, adhesives, and sealants. Hot, high-humidity conditions as well as precipitation result in an increase of moisture in an environment. Failing to properly store polyurethane paints can also increase moisture in the coating. A solution is to utilize a moisture scavenger to improve storage stability and eliminate paint defects.
What can be done to prevent moisture-related defects?
Moisture scavengers, like Additive TI and Additive OF, are high-performance additives designed to eliminate moisture in polyurethane systems via different mechanisms. These 100% active additives are low viscosity and help remove unwanted moisture in solvents, fillers, and pigments. They also provide long-term stability for solvent-based 1 and 2-component polyurethane paints, sealants, adhesives, coatings, and casting compounds after exposure to humid atmospheres.
Additive TI and Additive OF help effectively minimize the effects of side reactions during storage. These include CO2 generation and Polyurea formation (gelling effects) in polyisocyanate systems. Additive TI and OF moisture scavenger additives also minimize surface defects (foam, haze, low gloss) in the applied film.
Additive TI: Highly reactive moisture scavenger for short-term dehydration
Additive TI provides excellent short-term dehydration. This moisture scavenger is more effective than other dehydrating methods based on molecular sieves (zeolite) and provides immediate dehydration. Additive TI is colorless and does not cause cloudiness or color issues in polyurethanes. It can be added during the production phase.
Without moisture scavenger With Additive TI
Reduced defects in a PU coating
Additive OF: Easy-to-handle moisture scavenger for long-term dehydration
Additive OF is a solution for long-term dehydration that functions mainly as a package stabilizer. Like Additive TI, this moisture scavenger solution also has an advantage over other dehydrating methods based on molecular sieves (zeolite). This additive chemically converts the water molecules in the coating, not just adsorbs them.
Additive OF is a colorless liquid that does not cause cloudiness or color issues in polyurethane finishes. This solution and its reaction by-products are more sustainable than other reactive moisture scavengers. Additive OF can be added to hydroxyl and isocyanate components but can also be used in the production phase.
Moisture scavenger applications
Additive TI and OF dehydrate pigments and fillers in several applications. The pigments must first be mixed in a solvent along with the calculated amount of the moisture scavenger(s) used. This may widely vary based on the total moisture content.
Complete dehydration can take up to 24 hours. After this time passes, this mixture can be added to the polyol (OF only) or isocyanate (TI and OF) components.
Moisture-cured 1 component polyurethane systems
Both Additive TI and OF can act as storage stabilizers to reduce premature curing in the package (cask). They can be used alone or in combination with one another.
The use of Additive TI in catalyzed prepolymer systems depends on the type of catalyst used. Special amine-based catalysts can also accelerate the reaction between p-toluene sulfonamide and the isocyanate prepolymer which can then influence the NCO/OH ratio. This can result in an incomplete cross-linking reaction.
Additive TI and OF moisture scavengers are both highly efficient solutions for dehydrating pigments, fillers, and solvents within moisture-prone 1 and 2-component polyurethane coatings. This reduces the likelihood of defects like gloss reduction, haze formation, and foam generation. Additive TI is an excellent fast-acting option for short-term dehydration. Additive OF is an ideal package stabilizer for long-term dehydration.
Please visit our moisture scavenger product page for technical data sheets and more information on these products.