Properties / Applications: Bayhydur® XP 2655 is a crosslinking agent for waterborne systems from which reliable incorporation and high chemical resistances are required. Despite its relatively low hydrophilia, this hardener can be easily dispersed in the aqueous phase, even at low shear forces such as are typically found in trade applications. Coatings formulated with the product yield films with high gloss and very low haze. The increase in viscosity during mixing that is typical for hydrophilized hardeners, in particular with ionically hydrophilized polyol dispersions, can be controlled by prethinning with water or slight amounts of organic cosolvent. The dispersibility of the product in water is influenced by organic cosolvents, but in different ways. The use of highly hydrophobic or highly hydrophilic cosolvents such as butyl acetate, xylene, butyl glycol acetate, dimethyl formamide or N-methylpyrrolidone generally leads to a coarser dispersion, which may cause turbidity in the coating film depending on the entire system. On the other hand, the use of, for example, methyl ethyl ketone, methoxypropyl acetate, dipropylene glycol dimethyl ether, propylene glycol diacetate or dicarboxylic acid diester mixtures leads to fine-particle dispersions. Because of the balance between moderate hydrophilization and high functionality, waterborne two-component polyurethane coatings formulated with Bayhydur® XP 2655 exhibit fast drying, rapid hardening with high ultimate hardness and excellent chemical resistance of the resultant films. Bayhydur® XP 2655 can also be used as the crosslinking partner for waterborne polyol binders (Bayhydrol®) and as a crosslinker for largely pH-neutral waterborne polymer dispersions such as polyurethane, polyvinyl acetate, polyacrylate and synthetic rubber dispersions. After addition of Bayhydur® XP 2655, the ready-to-use two-component formulation must be used within the pot life. This is not only governed by the polymer content but also by its other constituents (resin, thickener, plasticizer, etc.). With many dispersions, the end of this pot life – usually several hours – is not marked by gelling.

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