Analysis of a gap dryer used to produce polymer films and coatings

The ability to predict the drying behavior of thin films and coatings is of great importance to the coating industry and governs the economical produc tion of various polymeric products. In conventional drying processes, a con tinuous layer of polymer solution is deposited onto a substrate, which is d ried in an oven with forced air convection. Recently, a gap dryer was devel oped that eliminates the need for forced gas flow and provides direct solve nt recovery. A model that incorporates simultaneous heat and mass transfer in the bulk polymer and gas phases and jump conditions across the interface is utilized to describe the drying of a binary polymer-solvent system in a gap dryer: Solvent self-diffusion in the polymer phase is described by fre e-volume theory, and the Flory-Huggins theory is used to describe polymer-s olvent thermodynamics. Simulations indicate the possibility of condensation in the gas phase that carl decrease both drying efficiency and coating qua lity. A method to resolve this problem is proposed, as well as a comparison between the performance of a gap dryer and a conventional convection-oven dryer.