Fluidized-bed coating method and fluidized-bed coating apparatus

A fluidized-bed coating method comprising:

• immersing at least part of a workpiece in a powder coating material contained in a fluidized-bed vessel while air is introduced from a bottom of the fluidized-bed vessel at an average air flow rate of 5 mm/min or higher and 20 mm/min or lower per unit area of the bottom so that a floating ratio of the powder coating material is 5% or higher and 20% or lower;
• taking the workpiece out of the powder coating material;
• and
• heating the powder coating material attached to the workpiece,
• wherein when the at least part of the workpiece is immersed in the powder coating material, a surface temperature of an immersed portion of the workpiece decreases by at least 5° C. from a preheating temperature due to conveyance before the immersion and heat conduction to contact particles of the powder coating material during the immersion, and is then maintained in a range of from a softening temperature of the powder coating material to a melting temperature of the powder coating material for at least 5 seconds after the immersion,
• wherein the softening temperature of the powder coating material is a glass transition temperature of the powder coating material and is in a range of 45° C. to 70° C., and the melting temperature of the powder coating material is in a range of 80° C. to 180° C.,
• wherein the powder coating material has a volume average particle diameter D50v of 5 μm or more and 20 μm or less,
• wherein the workpiece is preheated to the preheating temperature before the conveyance and the immersion, and the preheating temperature is set in a range of from a temperature 20° C. higher than the softening temperature of the powder coating material to a temperature 5° C. higher than the melting temperature of the powder coating material.