Waterborne polyurethane waterproof coatings are favored by manufacturers for their low production cost, non-flammable, non-toxic, non-environmental pollution, and organic solvent-saving advantages. In addition, it retains some excellent properties of traditional solvent-based polyurethane coatings, and has good adhesion to paper, wood, fiberboard, plastic film, metal, glass and leather, etc. Today, let me introduce to you the different types of water-based polyurethane waterproof coatings.
One-component waterborne polyurethane
One-component water-based polyurethane coating is the earliest water-based polyurethane coating, with high elongation at break (up to 800%) and appropriate strength (up to 20MPa), and can be dried at room temperature, but the water resistance and solvent resistance are very high. Poor, hardness, surface gloss and vividness are low. It is a kind of coating with water-based polyurethane resin as the base material and water as the dispersion medium. Because high molecular weight compounds cannot form good and stable aqueous dispersions, traditional one-component waterborne polyurethane coatings are usually of lower molecular weight or low degree of crosslinking.
The current varieties mainly include thermosetting polyurethane coatings and water-based polyurethane coatings containing blocked isocyanates.
Thermosetting Polyurethane Coatings:
Crosslinked polyurethane can increase its solvent resistance and hydrolytic stability. The system composed of polyurethane water dispersion mixed with a small amount of external crosslinking agent during application is called thermosetting waterborne polyurethane coating, also known as externally linked waterborne polyurethane coating.
Waterborne Polyurethane Coatings with Blocked Isoaminoesters:
The film-forming raw material of the coating is composed of a polyisocyanate component and a hydroxyl-containing component. The polyisocyanate is blocked by phenol or other compounds containing monofunctional active hydrogen atoms, so the two parts can be combined without reacting, becoming a one-component coating, and has good storage stability. The early internal crosslinking agents include carbodiimide and methylimide, which can exist stably in polyurethane emulsions. During the drying process of the coating film, due to the volatilization of water and neutralizer, the pH value of the film decreases, and the crosslinking reaction occurs. can be carried out. The use of aziridine compounds as internal cross-linking agents is used in coating systems, which can not only react with carboxyl and hydroxyl groups, but also self-polymerize in acidic environments, and are quite stable in alkaline conditions. At present, Olin Company in the United States uses urethane as an internal crosslinking agent, which can improve the mechanical properties and solvent resistance of one-component waterborne polyurethane coatings, manufacturers of ethylene acrylic acid copolymer.
Room temperature curing waterborne polyurethane coatings:
Heat-activated cross-linking is a stable one-component emulsion formed by mixing a blocked isocyanate emulsion with a polyurethane emulsion. After drying, heat treatment can regenerate the highly reactive NCO groups, which can interact with the active hydrogen groups contained in the polyurethane molecules (such as hydroxyl, amine, urea, polyester) react to form a cross-linked coating.
Two-component waterborne polyurethane coating
In the water-based two-component polyurethane coating, the water is excessive, and the reaction is dominated by the isocyanate group and the hydroxyl group. The reason is that the reaction rate of isocyanide with radicals, water, etc. is lower than the evaporation rate of water. After the water-based two-component polyurethane paint film is formed, the evaporation of water is very fast. Another type of waterborne two-component polyurethane coating composition can be made from water-dispersible polyisocyanate and hydroxyl functional polyurethane dispersion. In water-based two-component polyurethane paint, the type and amount of crosslinking curing agent have a great influence on the performance of the final paint film. The cross-linking mechanism is different from the two-component solvent-based polyurethane coating, but relies on the active hydrogen on the polyurethane dispersion and various cross-linking curing agents for cross-linking and curing. How to make the reaction complete to a greater extent and the two-component reaction more fully , more complete, so as to determine the amount of cross-linking curing agent, which plays a decisive role in the final performance. In waterborne two-pack polyester coatings, the film is formed due to excess water in the reactive two-pack polyurethane composition.
Waterborne Modified Polyurethane Coatings
The most important thing in waterborne modified polyurethane coatings is waterborne polyurethane modified acrylate resin, which combines the toughness and elasticity of polyurethane resin with the good color retention, light stability, hardness and low cost of acrylic acid. The main progress of polyurethane materials is from the original physical mixing modification to chemical modification (called “in situ polymerization”), that is, acrylate is first used as a solvent for synthesizing polyurethane, and then used as a reaction monomer after being dispersed in water. polymerization. This can better improve the performance of the modified material.
At present, the copolymerization modification of polyurethane and polyacrylic acid is also a commonly used modification method. In addition, there are urethane-modified epoxy resins, modified polyethers, and modified alkyd resins in the types of modified materials. Epoxy resin is a kind of thermosetting polymer composite material with good adhesion, corrosion, insulation and high strength.
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