METHOD FOR INJECTION MOLDING MIRROR CABINET BODY

PROBLEM TO BE SOLVED: To provide an injection molding method not to make a sink mark on each surface of rib joining parts of an outside plate 15 and a front side plate 17 on the outside wall of a body 1 of a mirror cabinet made of a polypropylene resin. SOLUTION: A wall thickness of a jointing part T3 to be jointed with an outside plate 15 in a closed mold cavity 23a, the outside plate 15 for a platy rib 18 in a molding region of the front side plate 17 and the platy rib 18, and with the front side plate 17 is made to be 0.29 to 0.46 times the wall thickness T1 of the outside plate 15, or that of the front side plate 17, the outside plate 15 being an object to joint with the jointing part. When a molten polypropylene resin M is filled into a mold cavity 23a on getting the molten polypropylene resin M is cooled to be solidified, a longitudinal area A inside of each of the outside plate 15 and the front side plate 17 is provided with a cavity 24 for preventing a sink mark side from extending to a halfway before the end point along a corner short direction B and C separating from the jointing corner 20, and the platy rib 18 is cooled to be solidified at the state that the inside pressure of each of the outside plate 15 and the front side plate 17 is raised by a compressed gas G. COPYRIGHT: (C)2010,JPO&INPIT