Patent ID: 7343695

Claim:
A vacuum drying apparatus for placing a substrate coated with coating liquid containing solvent in a vacuum chamber and evaporating the solvent in the coating liquid under reduced pressure, comprising: a vacuum chamber provided with an exhaust port; a vacuum pump connected to the exhaust port of the vacuum chamber through a suction pipe; an alternating current motor for driving the vacuum pump; a frequency converter provided on the input side of the alternating current motor; and a controller for detecting vacuum degree in the vacuum chamber, adjusting the frequency converter by the preset vacuum degree to change an alternating current frequency to be introduced into the alternating current motor, wherein the controller is previously set to: adjust an exhaust rate of the vacuum drying apparatus at high rate until the vacuum degree in the vacuum chamber reaches a pressure level slightly higher than the pressure at which the evaporation rate of the solvent in the coating liquid is rapidly elevated; then, reduce the exhaust rate to low rate, to cause the solvent of the coating liquid to evaporate gradually; and after evaporation of the solvent of the coating liquid, allow the pressure in the vacuum chamber to return to the atmospheric pressure.