UV Light Curable PU Systems

PU-based acrylate-terminated polymers have also been introduced for use in UV-cured or electron beam (EB)-cured elastomer coatings. They are usually used in conjunction with di- or trifunctional acrylate resins such as 1,6-hexane diol diacrylate (HDDA) (Fig. 12.8) whose function is to control hardness and flexibility in the final elastomeric lacquer. A series of these special monomers and urethane oligomers is marketed under the trade name Photomer (Harcross Chemicals). 

The primary advantage of such PU elastomers is their freedom from solvent use and hence 100% solids content of their coatings. A typical formulation for UV curing would contain the following  

Typical monomers are of the polymerizable plasticizer type based on functionally active acrylates. A difunctional acrylate (Fig. 12.8) would be used for chain-extension purposes, whilst a trifunctional one (Fig. 12.9) would be primarily used to control crosslink density and hence cure state. Both would have low viscosity, approximately 100 cps, and hence during processing act as plasticizers. 

Benzil dimethyl Ketal (Irgacure 651 Ciba Geigy) 

Note A side reaction can also occur which causes odour problems, e.g. 

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