Blade Coating Analysis of Newtonian and Non-Newtonian Fluids

Abstract

A coating is the covering which is applied to the object surface and referred to as the substrate usually. The principle for the application of coating may be func- tional or decorative or both. The coating itself may be a completely covering the substrate, an all-overs coating or only covers a part of a substrate. In this thesis, a theoretical analysis for the blade coating process of incompressible Newtonian and non-Newtonian uids, when they are passing through the narrow region between the blade and a moving substrate is presented. The aim of the blade coating phenomenon is to produce the sheet of speci c thickness and nal appearance of the sheet is very important in many industries, such as paper, cellulosic lms, fabric and textile bers, plastic lms, steel and rubber industries for the purpose of production of a sheet with speci c thickness and nishing appearance. Paints and lacquers are such coatings which mostly have twin advantages; one is the protection of the substrate and the other is being the decorative. However, a few artists paints are for the purpose of decoration only, while the paint which are used on large industrial pipes are most likely for the function of preventing corrosion only. The applications of functional coatings include; the change of the properties of substrate surface, such as wetability, adhesion, corrosion resistance or wear resistance. In other cases, for example, when the substrate is a wafer in the semiconductor device fabrication, a completely new property is added by the coating process such as an electrical conductivity or a magnetic response and it forms an important part of the nished product. In blade coating process, the liquid coating is applied to the material which is to xxv be coated under the blade while the distance of the substrate to the blade deter- mines the coating thickness. In order to a ect the coverage, the blade may have di erent pro les and also may be angled. The blade coating process can directly meter the uid to moving web from the pond of the uid to be coated. The blade is xed or it can be exible and act as a spring. The pressure which is developed under the blade determines the precise position of the blade relative to the backup roll and so determines the coating thickness. In order to maintain this process an e ective, the coating of the liquid should be rather viscous. Then the coating is cured or dried to prevent it to be soaked through the fabric. The Lubrication approximation theory (LAT) is outlined along with its calcula- tions for the viscoelastic and viscoplastic materials. The expressions for velocity pro les, pressure gradient, pressure, coating thickness, Power input, shear stresses and load are obtained. The goal of our work is to develop di erent mathematical models to characterize the e ect of various materials on the blade coating process. The calculations of these values are very important and can be used for production purposes in various industries.