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Handbook of Solvents - George Wypych - ChemTech - Ventech!

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386 Seung Su Kim, Jae Chun Hyun<br />

7.3 DRYING OF COATED FILM<br />

Seung Su Kim<br />

SKC Co., Ltd., Chon-an City, Korea<br />

Jae Chun Hyun<br />

Department <strong>of</strong> Chemical Engineering, Korea University, Seoul, Korea<br />

7.3.1 INTRODUCTION<br />

Thin film coating and drying technology are the key technologies for manufacturing diverse<br />

kinds <strong>of</strong> functional films, such as photographic films, adhesives, image media, magnetic<br />

media and recently lithium battery coating. Coating applied to a substrate as a liquid need<br />

some degree <strong>of</strong> solidification in order to be final products. The degree <strong>of</strong> solidification can<br />

be low in the case <strong>of</strong> pressure-sensitive adhesives (PSA) and it ranges to high in the case <strong>of</strong><br />

dense metal-oxides. 48 The final structure and properties <strong>of</strong> coating are greatly influenced by<br />

the drying conditions. 21 Poorly chosen operating conditions <strong>of</strong> drying cause unwanted internal<br />

gradients, 6,7 phase separations, 29,35,36 colloidal transformations that lead to the wrong<br />

microstructure, 43,51,56 inappropriate non-uniformities, and stress-related defects. 12-15,21,22<br />

Here we address a subject <strong>of</strong> solvent removal, or drying, which is a part <strong>of</strong> solidification<br />

processes.<br />

Typically a formulation <strong>of</strong> coating solution is consisted <strong>of</strong> pigments, binders (polymer<br />

resins) and solvents. The solvents are used to solubilize the coating formulation and to give<br />

the coating solution(or dispersion) the rheology necessary for the application. The coating<br />

solution is deposited onto a substrate or web at the coating station and is dried by passing<br />

through a series <strong>of</strong> separate ovens (zones). A substrate can be an impermeable material such<br />

as plastic film and permeable in the case <strong>of</strong> paper coating. The dryer is consisted <strong>of</strong> ovens<br />

Figure 7.3.1. An example <strong>of</strong> industrial coating and drying apparatus. A coated liquid is deposited onto a substrate<br />

which is unwound from a supply roll at the coating station and passes through the three separate ovens(dryer)<br />

where the temperature and velocity <strong>of</strong> air is controlled independently. Finally dried coated substrate is taken up by<br />

a take-up roll.

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