The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform

Marcio S Carvalho - One of the best experts on this subject based on the ideXlab platform.

  • Two layer Slot Coating: die configuration and frequency response analysis
    2020
    Co-Authors: Danmer Maza Quinones, Marcio S Carvalho
    Abstract:

    Abstract. Coating uniformity requirements is becoming more severe as new products come into the market. Multi-layerSlot Coating has to be designed not only based on the steady state operation, but also taking into account how the flowresponds to ongoing disturbances, such as flow rate, gap or vacuum pressure oscillations. These disturbances may leadto thickness variation on each deposited liquid layer that may be unacceptable for product performance.This study extends available transient analysis of single layer Slot Coating to determine the amplitude of the oscillationof each individual coated layer obtained by two layer Slot Coating in response to small periodic variation on the Coatinggap, web speed and flow rate as a function of process conditions and frequency of the perturbation. The predictionsare obtained by solving the complete transient Navier-Stokes equations for free surface flows. The results show how thethickness variations on each deposited liquid layer can be minimized by changing the geometry of the die.Keywords: Multilayer Coating, Periodic disturbances, Galerkin/FEM, Transient response, Free surface flow.

  • Transient Slot Coating
    2020
    Co-Authors: Oldrich Joel Romero, Marcio S Carvalho
    Abstract:

    The two-dimensional, transient flow that occurs during the deposition of a Newtonian liquid onto a substrate with a Slot die is examined. The effect of an imposed persistent periodic perturbation on the liquid flow rate in the coated layer thickness is explored at different process conditions and die configurations. The mathematical modeling of the transient Slot Coating flow involves solving an initial boundary value problem in which the location of the free surface is a part of the solution of the problem. The unknown flow domain (physical) is mapped into a fixed domain (computational). The system of equations, with appropriate boundary conditions, for a two-dimensional viscous liquid flow is solved in coupled form by the Galerkin / finite element methods, where the temporal discretization is done by a predictor-corrector algorithm. The set of non-linear algebraic equations for the finite element basis functions is solved by Newton’s method.

  • The instability in two-layer Slot Coating flows
    2020
    Co-Authors: Marcio S Carvalho, Pontifical Catholic, Rio De Janerio
    Abstract:

    The uniformity of the surface that separates the two liquids, the interlayer, plays a crucial role on the final product quality. The interlayer initiates at a point located on the mid die lip, usually called the separation point. In the ideal configuration, it is pinned at the downstream corner of the mid-lip, promoting cross-web uniformity. However, at some operating conditions, it can move upstream, in what is called mid-gap invasion. At these process conditions, the location of the separation point is usually not uniform in the cross web direction, leading to Coating thickness variation. Moreover, the invasion induces microvortices under the mid-lip, mixing the two layers and causing different types of Coating defects. Coating defects can also appear even at flow conditions at which the separation point is pinned at the downstream corner of the mid lip. Because of the small gap between the die and the substrate and the high web speed, the interlayer is subjected to enormous shearing. This may lead to flow instabilities in the interlayer that would ruin the final product quality. Here we study the operating window of dual layer Slot Coating by determining the conditions at which the separating line is pinned and the two layer rectilinear flow under the downstream lip is stable. Methodology and results

  • A computational study of the effect of particle migration on the low-flow limit in Slot Coating of particle suspensions
    Journal of Coatings Technology and Research, 2019
    Co-Authors: I.r. Siqueira, Marcio S Carvalho
    Abstract:

    Slot Coating of particle suspensions is commonly used in the manufacturing of a wide variety of products. An important limit in this process is known as low-flow limit, which refers to the minimum wet film thickness that can be coated at a given substrate velocity. Recent studies have shown that shear-induced particle migration leads to a highly non-uniform particle distribution in the Coating bead, playing an important role in the flow dynamics in Slot Coating of particulate systems. In this work, we extend the previous analyses to investigate the effects of particle migration on the low-flow limit in Slot Coating of particle suspensions at both dilute and concentrated conditions. As a first approximation, the suspension is modeled as a Newtonian liquid with a concentration-dependent viscosity, and shear-induced particle migration is described according to the diffusive flux model. The resulting set of governing equations is solved with a stabilized finite element method coupled with the elliptic mesh generation method for the free-boundary problem. The results show that particle migration changes the liquid viscosity near the downstream meniscus and strongly affects the force balance that sets the critical operating conditions at the low-flow limit. Remarkably, it was found that particle migration enlarges the operating window of the process when the suspensions are compared to a Newtonian liquid with the same bulk properties, especially at high concentrations.

  • Slot Coating flow of particle suspensions: Particle migration in shear sensitive liquids
    Journal of Non-newtonian Fluid Mechanics, 2018
    Co-Authors: R.b. Rebouças, I.r. Siqueira, Marcio S Carvalho
    Abstract:

    Abstract The functionality of several coated products, such as anti-reflection films and flexible electronics, depends on the complex microstructure of the deposited liquid layer. In many of these applications, the Coating liquid is a particle suspension composed by small, solid particles suspended in a viscous liquid medium. Particle suspensions are classified as non-Newtonian fluids, especially at high concentrations. The non-Newtonian behavior of the Coating liquid strongly affects the inner structure of the deposited liquid layer and the operability limits of Slot Coating processes. In this work, we study particle migration and the low-flow limit in Slot Coating flows of particle suspensions. Both shear rate sensitive and non shear rate sensitive suspensions are considered, and shear-induced particle migration is described by the Diffusive Flux Model. The conservation equations are solved together with the elliptic mesh-generation method to compute the position of the free surfaces using a stabilized Finite Element Method. The results show how particle migration and the rheology of the Coating liquid affect the final particle distribution on the deposited liquid film and the process limits in a typical Slot Coating flow.

Hyun Wook Jung - One of the best experts on this subject based on the ideXlab platform.

  • Sensitivity Analysis of Slot Coating Flow using Frequency Response
    2020
    Co-Authors: Hyun Wook Jung, J. C. Hyun
    Abstract:

    Slot Coating process is mainly applied for the manufacture of flat panel displays and long life batteries. In Slot Coating process, as in other Coating process, producing very thin uniform Coating film is a difficult task because of the occurrence of unexpected disturbances that causes defects during Coating operations. The sensitivity of Slot Coating flow has been experimentally and theoretically analyzed in this study using frequency response method. Sinusoidal variations of the wet film thickness with respect to sinusoidal disturbances at flow rate, web speed, Coating gap, bead pressure, etc. have been estimated from both 1D and 2D models. Also, sensitivity results of the wet film thickness and upstream meniscus position on sinusoidal web speed condition have been obtained from Slot Coating experiments and compared with those by simulations.

  • Simulations and Experiments for Flow Behavior and Operability Window in Slot Coating
    2020
    Co-Authors: Hyun Wook Jung
    Abstract:

    Multi-dimensional calculations and experiments in Slot Coating, which is necessarily implemented in IT industries producing flat panel displays, Li-ion secondary batteries, and so on, have been conducted for analyzing flow dynamics and operability Coating windows. Based on the previous theoretical considerations and experimental observations reporting the optimization of the Slot Coating flows (Lee et al., 2011), we would like to further investigate the effect of die lip configuration with different angles of upstream or downstream die lip on the operability windows for Newtonian Coating liquid via two-dimensional finite element method. Also, Coating flow fields predicted by three-dimensional calculations (using CFD software, Fluent) from internal die to external Coating bead regimes have been successfully compared with those by experiments and simple 1-D viscocapillary model.

  • Conformation of single polymer molecule in a Slot Coating flow
    Korea-australia Rheology Journal, 2020
    Co-Authors: Hyun Wook Jung, J. C. Hyun
    Abstract:

    To satisfy good mechanical and optical properties of polymer-coated film products, it will be indispensable to elucidate the molecular orientation of polymer chains within Coating liquids in Coating flows. Using hybridized numerical method between computational fluid dynamics (CFD) and Brownian dynamics (BD) simulations can provide the useful information for the better quality control of coated films. Flexible polymer chains, e.g., λ-DNA molecules here, change their conformation according to the flow strength and the flow type. The molecular conformation within the coated film on the web or substrate is quite different, because the polymer chains experience the complicated flow strength and flow types in flow field. Especially in the Slot Coating flow, these chains are more extended by the extension-like flow field generated in the free surface curvature just beyond the downstream die region. Also, the polymer chain extension beneath the free surface can be affected by the die geometry, e.g., the Coating gap, changing flow field.

  • Effect of upstream meniscus shape on dynamic wetting and operating limits of Newtonian Coating liquids in Slot Coating bead flows
    Journal of Coatings Technology and Research, 2018
    Co-Authors: Hyun Wook Jung
    Abstract:

    The Coating bead flow and operability window for Newtonian Coating liquids are theoretically and experimentally investigated in the Slot Coating process, with a focus on the shape of the upstream meniscus and contact angles. From the flow visualization in the Coating bead region, the contact angles of the upstream meniscus were measured by changing the flow rate and web speed under uniform operating conditions. It was confirmed that the dynamic contact angle is closely related to the capillary number in this process, based on the Hoffman–Voinov–Tanner model. The viscocapillary and two-dimensional Navier–Stokes models using the experimentally observed contact angles accurately predicted the Coating bead dynamics and operability windows for two Newtonian liquids.

  • Operability windows in viscoelastic Slot Coating flows using a simplified viscoelastic-capillary model
    Rheologica Acta, 2017
    Co-Authors: Hyun Wook Jung, J. C. Hyun
    Abstract:

    The viscoelastic-capillary model to predict approximately Coating windows for the stable operations of viscoelastic Coating liquids is derived using a lubrication approximation in Slot Coating processes. Pressure distributions and velocity profiles for viscoelastic liquids based on the Oldroyd-B and Phan-Thien and Tanner (PTT) models are solved in the Coating bead region considering the Couette-Poiseuille flow feature and the pressure jumps at upstream and downstream menisci. Practical operating limits for the uniform Coating of rheologically different liquids that are free from leaking and bead break-up defects are constructed under various conditions, incorporating the position of the upstream meniscus as an important indicator while determining limits. The shift of the uniform operating range shows different patterns for the Oldroyd-B liquid with a constant shear viscosity and the PTT liquid with a shear-thinning nature in comparison with the Newtonian case. The windows predicted by the simplified model are corroborated with experimental observations for one Newtonian and two viscoelastic liquids.

James Q Feng - One of the best experts on this subject based on the ideXlab platform.

  • computational analysis of Slot Coating on a tensioned web
    Aiche Journal, 1998
    Co-Authors: James Q Feng
    Abstract:

    When a web (thin substrate with considerable flexibility) travels through a Coating applicator in free span between the two supporting rollers, the gap between web and Coating applicator is determined primarily by the hydrodynamic stresses in the Coating flow and externally applied tension on the web. The elastohydrodynamic interaction between the tensioned-web deformation and the viscous liquid flow in the Coating bead has not been extensively studied, in spite of its practical importance. A tensioned-web wrapped around a Slot coater was analyzed here by finite-element computations. The externally applied tension on the web typically is much greater than the force due to hydrodynamic stresses. Hence, tension in the web is assumed to be constant in the process direction tangential to the web surface. By neglecting the bending and twisting moments as in the approximation of membrane theory, the shape of the flexible web is determined by a normal stress balance equation, quite similar to that of the free surface of Coating flow with a constant surface tension. In this work, elastohydrodynamic effects in tensioned-web Slot Coating are examined with respect to variations of the liquid feeding rate and externally applied web tension, web wrap angle, and other variables.

J. C. Hyun - One of the best experts on this subject based on the ideXlab platform.

  • Sensitivity Analysis of Slot Coating Flow using Frequency Response
    2020
    Co-Authors: Hyun Wook Jung, J. C. Hyun
    Abstract:

    Slot Coating process is mainly applied for the manufacture of flat panel displays and long life batteries. In Slot Coating process, as in other Coating process, producing very thin uniform Coating film is a difficult task because of the occurrence of unexpected disturbances that causes defects during Coating operations. The sensitivity of Slot Coating flow has been experimentally and theoretically analyzed in this study using frequency response method. Sinusoidal variations of the wet film thickness with respect to sinusoidal disturbances at flow rate, web speed, Coating gap, bead pressure, etc. have been estimated from both 1D and 2D models. Also, sensitivity results of the wet film thickness and upstream meniscus position on sinusoidal web speed condition have been obtained from Slot Coating experiments and compared with those by simulations.

  • Conformation of single polymer molecule in a Slot Coating flow
    Korea-australia Rheology Journal, 2020
    Co-Authors: Hyun Wook Jung, J. C. Hyun
    Abstract:

    To satisfy good mechanical and optical properties of polymer-coated film products, it will be indispensable to elucidate the molecular orientation of polymer chains within Coating liquids in Coating flows. Using hybridized numerical method between computational fluid dynamics (CFD) and Brownian dynamics (BD) simulations can provide the useful information for the better quality control of coated films. Flexible polymer chains, e.g., λ-DNA molecules here, change their conformation according to the flow strength and the flow type. The molecular conformation within the coated film on the web or substrate is quite different, because the polymer chains experience the complicated flow strength and flow types in flow field. Especially in the Slot Coating flow, these chains are more extended by the extension-like flow field generated in the free surface curvature just beyond the downstream die region. Also, the polymer chain extension beneath the free surface can be affected by the die geometry, e.g., the Coating gap, changing flow field.

  • Operability windows in viscoelastic Slot Coating flows using a simplified viscoelastic-capillary model
    Rheologica Acta, 2017
    Co-Authors: Hyun Wook Jung, J. C. Hyun
    Abstract:

    The viscoelastic-capillary model to predict approximately Coating windows for the stable operations of viscoelastic Coating liquids is derived using a lubrication approximation in Slot Coating processes. Pressure distributions and velocity profiles for viscoelastic liquids based on the Oldroyd-B and Phan-Thien and Tanner (PTT) models are solved in the Coating bead region considering the Couette-Poiseuille flow feature and the pressure jumps at upstream and downstream menisci. Practical operating limits for the uniform Coating of rheologically different liquids that are free from leaking and bead break-up defects are constructed under various conditions, incorporating the position of the upstream meniscus as an important indicator while determining limits. The shift of the uniform operating range shows different patterns for the Oldroyd-B liquid with a constant shear viscosity and the PTT liquid with a shear-thinning nature in comparison with the Newtonian case. The windows predicted by the simplified model are corroborated with experimental observations for one Newtonian and two viscoelastic liquids.

  • Effect of shim configuration on internal die flows for non-Newtonian Coating liquids in Slot Coating process
    Korea-Australia Rheology Journal, 2016
    Co-Authors: Hyun Wook Jung, J. C. Hyun
    Abstract:

    In this study, a strategy for designing optimal shim configuration inside a Slot die is suggested to assure the uniform Coating flow distribution of various non-Newtonian shear-thinning liquids at the die exit in a Slot Coating system. Flow patterns of non-Newtonian liquids inside the Slot die, via three-dimensional computations, have been compared using various shim geometries which can adjust the flow region in a Slot manifold. The rather non-uniform (parabolic) velocity distributions of shear-thinning liquids at the die exit under the basic shim condition could be effectively flattened by the modification of shim geometry without the change of die manifold structure. Dimensions of hybrid shims for controlling flow features at edge and center regions within slit channel are positively tuned, according to the shear-thinning level of Coating liquids.

  • Effect of sloped die lip geometry on the operability window in Slot Coating flows using viscocapillary and two-dimensional models
    Journal of Coatings Technology and Research, 2014
    Co-Authors: Hyun Wook Jung, J. C. Hyun
    Abstract:

    As an indicator for determining the operability window in Slot Coating flow, the viscocapillary model considering various configurations of upstream and downstream Slot die lips was tested and compared with Navier–Stokes two-dimensional model. Bead pressure and sloped lip angle conditions for uniform Coating operation demarcated from leaking and bead break-up defects were quantitatively predicted from the position of upstream meniscus from both models. By comparing the results, it is confirmed that the viscocapillary model for many kinds of sloped die lips could predict the operability window accurately. It is also found that there exists vortex or recirculation regimes inside upstream and downstream Coating bead regions, depending on the angles of sloped die lips, even for the stable Coating flow. The flow control by die lip structure will be usefully applied to design the strategy for the reliable and optimal Coating process, including vortex-free windows.

Pingyao Wu - One of the best experts on this subject based on the ideXlab platform.

  • Optical-electronic properties of carbon-nanotubes based transparent conducting films
    Advances in Chemical Engineering and Science, 2013
    Co-Authors: Kuan-ru Chen, Hung-chih Chen, Shu-jiuan Huang, Pingyao Wu
    Abstract:

    Three Coating methods (Slot, dip and blade Coatings) were used separately to coat a well-dispersed single-wall carbonnanotube (SWCNT) solution on polyethylene terephthalate (PET) film, and the resulting optical and electronic properties were measured and compared. It was found that the sheet resistance and the transparency of the SWCNT coated film decreased as the Coating speed increased for dip and blade Coatings, but were independent of the Coating speed for Slot Coating. All three Coating methods were able to produce transparent conductive film with transparency above 85% and sheet resistance close to 1000 ohm/sq. For industrial production, the Slot die Coating method appears to be more suitable in terms of high Coating speed and uniformity of optical and electronic properties.

  • a macroscopic mathematical model for tensioned web Slot Coating
    Polymer Engineering and Science, 2008
    Co-Authors: Pingyao Wu
    Abstract:

    A mathematical model was developed to predict the performance of tensioned-web Slot Coating (TWSC), in particular, the minimum wet thickness. The model was based on the lubrication approximation for the Coating solution flow and a simplified membrane theory for the moving web. The theoretical predictions compared reasonably well with available experimental data. The effects of fluid viscosity, web tension, Coating speed, and wrapping angle on the performance of TWSC were evaluated. An example was presented to illustrate how die lip design could be varied to improve its performance. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers

  • A macroscopic mathematical model for tensioned‐web Slot Coating
    Polymer Engineering and Science, 2008
    Co-Authors: Pingyao Wu
    Abstract:

    A mathematical model was developed to predict the performance of tensioned-web Slot Coating (TWSC), in particular, the minimum wet thickness. The model was based on the lubrication approximation for the Coating solution flow and a simplified membrane theory for the moving web. The theoretical predictions compared reasonably well with available experimental data. The effects of fluid viscosity, web tension, Coating speed, and wrapping angle on the performance of TWSC were evaluated. An example was presented to illustrate how die lip design could be varied to improve its performance. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers

  • experimental study on tensioned web Slot Coating
    Polymer Engineering and Science, 2007
    Co-Authors: Pingyao Wu
    Abstract:

    Tensioned-web Slot Coating (TWSC) technology was developed in the early 1980s and was considered an efficient method for thin liquid film Coating. An experimental study was carried out to investigate the effects of several key parameters on the minimum wet thickness of TWSC. The experiment was performed on a pilot coater with dilute Newtonian poly(vinyl) alcohol (PVA) solutions as test fluids Coating on polyethylene-terephthalate (PET) substrates. It was found that the minimum wet thickness for TWSC was between 0.5 and 1.5 μm, which is much lower than that obtained using conventional Slot die Coating. The minimum wet thickness was proportional to the tension number TN, which is defined as the ratio of fluid viscous force over web tension. Furthermore, on the basis of the experimental data, two additional dimensionless groups: dimensionless pressure PN and dimensionless surface tension LN were found to be relevant to the performance of TWSC. A universal correlation involving these dimensionless groups as well as the die geometry was used to predict the minimum wet thickness of TWSC. POLYM. ENG. SCI., 47:841–851, 2007. © 2007 Society of Plastics Engineers