Radiation-curable systems based on acrylates

A UV-curable acrylate system usually contains four main components prepoly-mer(s), monomer(s), photoinitiator(s), and additives. A fully formulated EB-curable system is not merely a UV system without photoinitiator but the same principles apply and the same raw materials are used. 

Prepolymers. A broad range of acrylated resins (oligomers) are commercially available. The film-forming properties depend on the oligomer system. One of the most common is the acrylated epoxy system. In acrylated urethanes, an isocyanate-functional prepolymer with a polyol backbone can be reacted with a hydroxy-functional monomer (e.g., hydroxyethyl or hydroxypropyl acrylate). Many different resins can be synthesized by varying the polyol backbone, the isocyanate type, and the hydroxy-functional monomer. Polyester acrylates are another example of commercially important prepolymers. Acrylated acrylics have an acrylic backbone with pendant acrylate functionality. 

Selection of the prepolymer is guided by the desired film-forming properties. For example, acrylated epoxy resins typically provide hard, solvent-resistant films with fast cure at relatively low cost. Acrylated urethanes may be chosen for their excellent film flexibility and toughness. Aliphatic urethanes are used in preference to aromatic urethanes for stringent exterior weatherability requirements. The acrylated acrylics offer excellent nonyellowing properties when a soft film can be used. 

Polyester acrylates are used in a wide range of applications from overprinting varnishes to lithographic (offset) inks. 

Monomers. In radiation-curable systems, the solvent is replaced by reactive diluents (monomers) which are incorporated in the network during cross-linking. These monomers have two important functions they reduce the viscosity of the mixture and they strongly influence the physical and chemical properties of the final coating. Monomers can be divided into three groups  

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