Meniscus shape experiments in forward roll coating

Abstract

In the present paper, experiments are reported for the measurement of the complete meniscus profile in asymmetric forward roll coating. A thin laser sheet technique is used to recover accurately the shape and position of the interface for an extensive database of operating conditions. Knowledge of the interface profile and position is then used to measure the total flow rate and its distribution on each cylinder. The results provide for the first time validation of numerical predictions for the extended shape of the meniscus. Comparison with existing theoretical and numerical predictions validates both these approaches, but reveals the need to model the whole flow region, including gravity, instead of restricting to the region downstream of the nip separating the rotating cylinders.

An experimental investigation of meniscus roll coating

“…Malone (1992) was the first to employ such techniques to explore the flow in the nip region of a starved fixed-gap forward roll coater and to succeed in unravelling the underlying macroscopic flow structure. Decré, Gailly & Buchlin (1995) used similar techniques to carry out a systematic experimental investigation for the case of asymmetric forward roll coating with the goal of measuring downstream meniscus profiles and location, via a laser sheet technique, together with the total flow rate and its distribution on the rolls. The coating fluid was doped with a fluorescent medium for this purpose.…”

Fluid absorption during forward roll coating of porous webs

“…Pitts and Greiller (1961), Savage (1982), Coyle (1992), Benjamin et al (1994Benjamin et al ( , 1995 and Coyle (1997) studied the flow in a narrow, fixed gap between two rigid rolls. Decre et al (1995) measured the meniscus profiles in asymmetric forward rigid roll coating of Newtonian fluids using laser sheet technique to provide an extensive database of more than 100 meniscus profiles. Gaskell et al (1998) experimentally explored the detailed fluid mechanics of meniscus rigid roll coating of Newtonian fluids in which inlets are starved and flow rates are small.…”

Meniscus Control by a String in a Roll Coating Experiment

“…The predictions with models taking the interface into account never depart much from this[15][16]. Experimental results are less decisive, as Q, values up to 1.52 could recently be attributed to indirect feeding effects[9]. The variation of Q, with the streamwise position of the string jc s tr for Ca\ = Cai = 2.0 and G = 0.0163 are presented infigure 6; the precision on ^-estimate is 0.05.…”

“…It aims at quantitatively understanding the correlation between the position of the string x str , z str in the orthonormal coordinate system defined in figure 1, and the basic coating mechanisms such as the ribbing, total flow rate, partial flow rates on individual cylinders and contact line properties. To this end, a free-surface visualisation technique of the meniscus controlled by a string, al ready developed to measure natural, stable coating meniscus, is presented [9]. A large range of capillary number combinations otherwise displaying ribbing, is cov ered.…”