Analysis on the ink transfer mechanism in R2R application

Abstract

Ink transfer process from the printing roll to the web was investigated using a Computational Fluid Dynamics (CFD) technique for the roll-to-roll (R2R) printing application. A parametric study was conducted to identify the effects of fluid parameters such as viscosity, surface tension and contact angle. To make the present analysis more relevant to the real printing system, a three-dimensional computational configuration for the commercial software was set up using the information obtained from the typical R2R system. Simplified onedimensional semi-analytic model based on Reynolds equation was compared with the CFD results to assess the validity of the results. Pressure distribution states that 1-D analysis is reasonably good in capturing the flow physics. The 3-D simulation with VOF (Volume of Fluid) shows that viscosity is the most important parameter. Moreover, the larger surface tension resulted in smaller amount of ink transfer.

A numerical study of the ink transfer process for roll-to-roll printing applications

“…The presence of reduced viscosity, in turn, is thought to lead to the occurrence of a reduced line width in the calculation as well as in the observed discontinuity of the measurement data shown in Figure 9. In fact, the improvement obtained through the Carreau model seems to be reasonable considering our previous results under the Newtonian assumption, [17][18][19] which shows that the characteristics of the ink transfer process significantly vary with the magnitude of the viscosity. Since the simulation results with these two different cavity shapes compared favorably with the measurement data, it was assumed that the present numerical methodology with the Carreau model was reasonably able to capture important physical features of the ink transfer process.…”

“…Noting our earlier results, [17][18][19] which primarily showed that a larger viscosity tends to produce better quality in terms of the transferred ink shape and that the contact angle played a much less significant role than the viscosity, one of the most effective ways of improving the printing quality has to do with controlling the fluid properties at the step of ink formulation instead of modifying the pattern shape. Another obstacle for complete analysis is the complication resulting from the tension and elasticity of the web: deflection of the web may cause unexpected defects in the case of very thin lines.…”

“…However, a recent study 20 reported that the time for the combined drying and curing processes could be successfully reduced by a factor of as large as 5. Therefore, higher web, handling speeds of up to 30 mpm (¼0.5 m/s) compared to the speeds chosen in previous studies, [17][18][19] was considered in this study. Obviously, a relatively higher speed shortens the convection time-scale, thus increasing the importance of the inertial effect relative to that of viscous action.…”

“…For the purpose of development and proper validation of the numerical methodology at the first stage, this study aims to establish the effects of the various roll patterns shown in Figure 2 in terms of the shape of the transferred ink, which is a very important task for improving the printing quality. 17 Considering recent progress in reducing the time required for curing and drying processes, 20 the web handling speed used in earlier studies [17][18][19] was raised by a factor of up to 5 in this study. This significant increase in the web moving speed is expected to deteriorate the printing quality due to the enhanced effect of convection.…”

“…They successfully illustrated the role of surface wettability and cavity size of their model. In more recent studies by Lee and Na 17,18 and Kim and Na, 19 the geometry of gravure printing, which is one of the most popular R2R printing methods, was considered for direct relevance to real applications. Kim and Na 19 showed that the characteristics of the transferred ink strongly depend on the magnitude of the viscosity under the assumption of Newtonian fluid.…”