The first experiments with electron beams date from as early as 1920 in the U.S., but the first attempts to cure varnishes with electron beam curing (EBC) were only made in 1960. The essence of EBC is that an electron bundle induces crosslinking in a coating that has been applied, which actually involves radical polymerization as we know it from organic chemistry.
The crosslinking is only possible if the varnish contains double bonds, for example in the form of ethylene, propylene, vinyl or acrylate groups. The last of these are particularly popular for their combination of properties.