Abstract
A change of surface roughness of labeling substrates for flexographic printing was studied. It was found that the composition and structure change of the surface plane of labeling substrates resulted in roughening and smoothening phenomena. Water and solvents appeared to dissolve and removed the furnish additives of substrates; and to redeposit these together with other ingredients of inks during drying in the deep pores under the surface plane, where they could function as geometrical facets. In case of UV ink, the parallel movement of the surface profiles was consistent with, one case, the failure for the liquid polymer to penetrate into the substrate: or another case, the fibrous network was lubricated. This caused differences in ease with which dotted inks spread and the surface becomes smooth as well as tone rendering characteristic on each substrate in printing. Interestingly, the obtained tone rendering quality of printed image could be determined by the RMS surface roughness of substrate together with its printed area. Linear relationship between the slopes of the tone curves and RMS surface roughness was established with the correlation coefficient value at 0.878. Uncoated paper showed the poorest quality whereas polyethylene (PE) substrate gave the best result, particularly at the high light area. The model to determine the quality of tone rendering of printed images was proposed.
