| In what is probably the first academic research effort of its kind, photopolymer plates and flexographic printing were comprehensively studied.; The DSC data revealed that the elastomeric phase cross-linked on UV exposure because of observed shifts in the glass transition. TEM micrographs of the plates (exposed and unexposed) showed that the thermoplastic phase was swollen by the polymerized acrylate (PAC) and changed morphologically. By systematized NMR spin relaxation studies and swelling experiments with exposed and unexposed samples (of polybutadiene (PB), polystyrene (PS), SBS, acrylate monomer (AC) and an experimental plate C), the effects of the UV exposure were clearly pinpointed.; Several surface energy characterizations based on contact angle measurements were made. It was found that these methods depended greatly upon the specific interactions of the plate and the solvents. By use of the Fowkes acid-base approach, the plate surfaces were found to be predominantly acidic. The surface roughness, a generally neglected factor, was studied qualitatively by SEM and quantitatively by stylus methods. The nature of the surface roughness of the six plates was markedly different.; Apart from static assays such as Shore A2 hardness and Zwick resilience, the plates were tested on the Instron 1350. The plates showed stress hardening to different extents after 10,000 cycles; the plate with the least stress hardening is desired for consistent print quality.; The printability data were statistically analyzed along with plate characteristics and press parameters. The printing nip pressure and the plate surface roughness were found to be the most significant factors in flexo printing. For solids printing, the print quality increased with pressure and plate roughness but the print quality worsened for half-tone dot printing and the dot gain increased. The other factors that mattered were the printing speed, cross-link density of the plates and the non-dispersion component of the plate surface energy.; A model of flexo printing model considered the viscoelastic behavior of the plate and the ink kinematics to estimate the pressure profile and ink thickness in the nip. The predicted pressure compared well with experimentally measured pressure for three plates. (Abstract shortened with permission of author.)... |
