Coating Presentations

Download user presentations that focus on coating applications using FLOW-3D from past users conferences.

2017

Numerical investigation on the influence of the surface tension and the contact angle on the film stability in reverse-roll coating process

Z. Jang, M. Semel, A. Delgado, Lehrstuhl für Strömungsmechanik (LSTM), Friedrich-Alexander-University Erlangen

The reverse-roll-coating (RRC) process is distinguished from other coating process, owing to its versatility of application, speed, and precision (D.J. Coyle, 1990). It is widely used for the finishing of various products such as coated paper and pressure-sensitive-adhesive tape. In this study, the RRC process has a scheme of two counter-rotating cylinders, in whose metering gap an incompressible non-Newtonian fluid is continuously transferred onto the moving substrate. The stability of the coated film, determined by the interplay of the different type of the pressures acting in the metering gap, is, however, only obtainable by the use of numerical or experimental methods. The influence of the surface tension and the contact angle on the stability and the film thickness of coated film is studied by a 2D-numerical simulation with the help of FLOW-3D. A parameter study on an industrial test case is performed for four different surface tensions by three different contact angles. The simulation setup is validated by the help of process data from the industry. It can be concluded that the stability of the coated film is strongly influenced by the change of the surface tension while the influence of the contact angle is negligible.

2016

CFD modelling of narrow strip slot die coating

Julien Bœuf1 and Raed Marwan2
1
Roche Diagnostics GmbH

2Flow Science Japan

Coating of liquid chemistry is one of the central processes of medical test strips production. The most common processes are knife-over-roll coating and slot die coating. The latter is a standard pre-metered process which has been experimentally and theoretically studied for many decades. In the literature one can find many 2D models describing the operating windows for different design and different fluid properties. Those results are relevant for the main applications with large web width, where edges can be neglected or are not relevant for the production. In the case of narrow strip application however, a 3D model is necessary to study edge effects and their influence on operating windows and strip height structure. The present study deals with the 3D modeling of narrow slot die coating using FLOW-3D. Different numerical options were tested and compared. A specific challenge is the modeling of the evolution of the wet film profile after application and before drying. The numerical results are compared to experimental measurements.

2014

3D modeling of narrow strip slot die coating

Julien Bœuf, Roche Diagnostics GmbH

Coating of liquid chemistry is one of the central processes of medical test strips production like coagulation tests. The most common processes are knife-over-roll coating and slot die coating. The latter is a standard pre-metered process which has been experimentally and theoretically studied for many decades. In the literature one can find many 2D models describing the operating windows for different design and different fluid properties. Those results are relevant for the main applications with large web width, where edges can be neglected or are not relevant for the production. In the case of narrow strip application however, a 3D model is basically necessary to study edge effects and their influence on operating windows and strip height structure. The present study deals with the 3D modeling of narrow slot die coating using FLOW-3D. Different numerical options were tested and compared. A specific challenge is the modeling of the pressure boundary conditions at the edge of the fluid bead in case of application of negative pressure at the upstream meniscus.

The onset of air entrainment in pre-metered forward roll processes

Bettina Willinger, Isabell Vogeler, Andreas Olbers, and Antonio Delgado, Institute of Fluid Mechanics, Friedrich-Alexander University of Erlangen-Nuremberg

Roll coating is a common technique for applying thin coating films on continuous substrates, e.g. papers and foils. The product quality of the films is mainly limited by the coating speed. At low speeds a uniform film is formed, but when a critical speed is reached, wetting failure occurs and air can entrain between the coating film and the solid. The air bubbles may create defects on the coating film and have an impact on the product quality. Experimental studies showed that especially the viscosity and the surface tension of the coating fluid are relevant influencing parameters on the critical speed.

The presented study on the onset of air entrainment in pre-metered forward roll coating technique has been performed with two-dimensional time-dependent numerical simulations with Cartesian block-structured mesh in FLOW-3D. Four configurations were tested: The inlet of the flow has been restricted either by a baffle or with two boundary conditions. And the behavior of the entrained air has been modelled either assuming an adiabatic change of state or a constant pressure in the bubbles. A good agreement of the simulation results with experimental data for the critical speeds of air entrainment from the literature can be achieved for both bubble state configurations. Further the influence of the material parameters on the critical speed has been studied.

2013

Coating of thin films using reverse roll process

Bettina Willinger, Sebastian Obermeyer, and Antonio Delgado; Institute of Fluid Mechanics, Friedrich-Alexander University of Erlangen-Nuremberg

For the production of low-cost products like coated papers and foils the use of a stable process technology with high efficiency is of importance. Roll coating is a common technique for applying thin coating films on continuous substrates, which fulfills these requirements. Key advantages are the comparatively simple technology and the possibility of coating thin films using highly viscous fluids especially when using the reverse operation mode. Since roll coating is a self-metered process, the film thicknesses, which are important for industrial process control, depend on several parameters and are hardly predictable. Numerical simulations thus offer possibilities of a deeper process knowledge. The presented study of the flow behavior in reverse roll coating technique has been performed with two-dimensional time dependent numerical simulations with Cartesian block-structured mesh in FLOW-3D. For validation of the used VOF-model, experimental data from literature has been taken. In particular, the impact of viscosity and non-Newtonian behavior on the resulting flows has been studied in detail. The simulations show a significant influence of viscosity on the position of the three phase contact point and thus on the resulting film thickness. Furthermore, it is possible to locate the configuration, i.e., the velocity ratio using a constant geometry, for minimal achievable film thickness. Moreover, the occurrence of cascade instability and its dependency on viscosity can be predicted.

Model of dip coating with concomitant evaporation

Julien Bœuf; Roche Diagnostics GmbH

Dip coating is one of the oldest coating techniques but still widely used. This so-called free-meniscus coating is encountered in many manufacturing operations (casting, ceramics, semi- conductors, optical films…). Also, some complex medical devices like in vivo continuous measurement devices need a treatment to become biocompatible. A specific biocompatible film must be deposited and this can be done by dip coating. Dip coating has been intensively studied for many decades, both experimentally and theoretically. However, the main models concern the steady state of continuous dip coating, which is more specifically relevant for film deposition on a web or on a wire. FLOW-3Dmodels were developed to investigate numerically the transient dip coating of discrete small substrates. In this case, it is of interest to correctly model the “edge effects” for analyzing the influence of process- or fluid parameters on the final thin film homogeneity. In a first step, the model solely describes the deposition of fluid and the profile of the coated wet film. This is sufficient to describe situations with low evaporation rates and high coating speed. In a second step, the model additionally takes into account the evaporation of the solvent. This is relevant in the case of volatile solvent at low coating velocity, for which evaporation overlaps with fluid mechanics during film deposition and influences the dry film profile. This was possible using the Vaporization Residue Model.