Drying rates of polyamic acid solution film under (i) natural convection and (ii) induced draft drying conditions



Drying rate studies were carried out with polyamic acid solution synthesized in the laboratory in dimethyl acetamide solvent, with a view to determine the process design parameters of a continous polyimide film casting machine. Studies reveal that drying under natural convection condition takes an unduly long time, whereas drying under induced draft/recirculation with partial recycle condition takes only ⅓ the time that of natural convection drying. Another important observation made was that under natural convection drying condition the initial adjustment period was too long and that the drying process was evenly spread over the initial adjustment, constant, and falling rates of the drying periods, whereas under induced draft condition drying mostly took place during the falling rate of drying period. The drying rate data obtained was used for generating the necessary process design, and operating parameters for a continuous polyimide film casting machine.