Properties / Applications: Bayhydrol UV 2689/1 is used for the formulation of waterborne UV coatings, in particular for plastic applications. The addition of 1.0 to 2.5 weight % photoinitiator relative to binder has proven effective for initiation. We achieved good results with Irgacure® 500, Irgacure® 127, Irgacure® 819 DW (Ciba) and Esacure® KIP 100F (Lamberti). Viscosity is set by the addition of polyurethane thickeners for clear coats or acrylic thickeners for metallic effect coatings. As the dispersion has a relatively high surface tension the formulation should always contain a wetting agent, e.g. BYK® 348 (BYK) to avoid surface defects. Matting agents and additives can be dispersed directly into the formulation using a dissolver. Bayhydrol® UV 2689/1 can be easily matted using common matting agents. The formulation of metallic effect coatings using suitable metallic pigments is also possible. The product can also be combined with Bayhydur® or other hardeners to formulate ”dual cure ” waterborne UV coatings. After evaporation of the water and before UV-cure, the coatings are soft and slightly tacky. Water-free coatings can be cured with suitable UV-curing equipment at a line speed of typically 5 to 10 m/min per 80 W/cm lamp. To achieve the best film properties the coating temperature should be higher than 60°C when entering the UV zone. Care has to be taken if temperature sensitive materials are cured in this way. During UV curing a further temperature increase of 20 to 60°C is possible depending on conditions. UV curing yields surfaces with high hardness, very good mechanical strength and excellent chemical resistance especially against cosmetics. As with any product, use of Bayhydrol UV 2689/1 in a given application must be tested (including but not limited to field testing) in advance by the user to determine suitability.

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