The modification of electrophotographic and mechanical properties of organic photoconductors by ultra-violet irradiation

Experiments have shown that UV treatment has a hardening effect on the surface of a drum-based organic photoconductor (OPC) and improves the retentivity. The dark decay and the photoinduced discharge rates were reduced linearly with the increase of time of UV irradiation. The dark decay rate and photoinduced discharge rates were reduced to 60% and more than 70% of the initial rate, respectively, while there was an increase of the activation energy of the charge transport layer. An initial increase in the residual potential was also observed from 20 to about 70 V. After 40 min of UV irradiation, the residual potential was seen to drop to 50 V again, and at the same time a slight increase of the hardness of the photoreceptor surface was detected from 13 to 16 in Vickers scale (Hv). The phenomena is most likely explained by a photochemical change which reduces the density of charge transport sites, builds up the number of deep traps and changes the molecular distribution. The decrease in charge transport site density and buildup of deep traps reduces the conductivity and hence the dark decay and photoinduced discharge rates. The fragmentation of charge transport molecules may result in a change of activation energy as well as the increase in the residue potential. Moreover, the redistribution of molecules leads to the change in molecular density and hardness.