In the case of photopolymerization which can be initiated by UV-containing light, so-called photoinitiators like e.g. benzoin or benzoin derivatives such as benzoin ethers, benzil and derivatives thereof such as benzil ketals, acrylic diazonium salts, azo initiators such as 2,2???-azobisisobutyronitrile, 2,2???-azobis(2-amidinopropane) hydrochloride or acetophenone derivatives are used.