PURPOSE: To obtain a coat, which is readily released but prevented from being unnecessarily released during package or transportation, by forming a coat, which requires specified releasing force depending on silicon content selected, on the surface of a structural part.

CONSTITUTION: Fan blade 4, blade fastener 4a, outer frame 8 and oil receiver 17, are integrally molded with a synthetic resin such as a polypropylene resin. Releasable coat 20 is formed by coating their surface with a coating liquid, composed of a synthetic resin, and drying the surface. Said coating liquid is composed of a synthetic resin such as an unmodified polyurethane resin, a solvent, an additive and silicone. Releasing force for coat 20, can be specified in a desired range, depending on the silicon content. From the results of a number of experimental manufactures, it is found that in order to prevent coat 20 from being released during package or transportation, and, to continuously and readily release said coat, without rupture, when required, said leasing force is to be 1W5g for every cm width.