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Polyurethane acrylates belong to the high-performance UV coatings class. The polymer backbone is polyether, polyester or polycarbonate. By adding isocyanates and hydroxy acrylates at the polymer backbone the resulting polyurethane acrylate binder can be crosslinked via their acryloyl groups. Polyurethane itaconates are an alternative to polyurethane acrylates for UV-curing resins. Itaconic acid is a white, crystalline, monounsaturated dicarboxylic acid and it is commercially produced by fermentation of carbohydrates from raw cane/beet sugar or molasses. It is much less toxic compared to most other monomers used in UV technology. Itaconic acid can be considered as a derivative of methacrylic acid. The price of itaconic acid ranges from 1700 to 2300 € / MT and is thus comparable to that of methacrylic acid (~1800 € / MT). In a recently finished project under the direction of the Johan Heinrich von Thünen-Institut a novel process for biotechnological production of itaconic is being developed that may even reduce the manufacturing costs. The variety of the functional groups of the itaconic acid makes it an extremely versatile interim product. The chemical formula is depicted in Figure 1.
Polyurethane itaconate dispersions were synthesised, preserving the itaconic acid’s carbon double bonds for UV-curing. Application-oriented investigations of UV-curable outdoor and indoor wood coatings were performed and discussed in terms of their physical and chemical parameters. Today high-quality UV coatings require an acrylate component as UV-reactive groups. Acrylate monomers have the potential causing allergic reactions to humans after exposure, which means that appropriate safety precautions have to be taken into consideration when varnishing. Table 1 specifies the LD50-values of acrylic acid and methacrylic acid in comparison to itaconic acid. Due to the low toxicity of itaconic acid, for packaging materials itaconates have a food approval.
Water-based UV coatings even reduce the danger that arises from monomer acrylates. UV technology on an itaconic acid basis takes another step towards employee safety and environmentally friendly coating materials
