Patent ID: 7935293

Claim:
An injection molding method using a forming mold provided with a cavity which is filled with a resin material to obtain a resin molded article and a resin inlet through which the resin material is introduced into the cavity, wherein a plurality of gas inlets through which a gas is introduced are formed on a rear molding surface of the cavity for molding a rear surface of the resin molded article, and the gas is introduced into an area between the rear molding surface and the resin material inside the cavity, the injection molding method comprising the steps of: introducing the resin material into the cavity from the resin inlet; and pressing the resin material against a front molding surface of the cavity for molding a front surface of the resin molded article by introducing the gas to the gas inlets when the cavity is filled with the resin material, wherein a gas inlet positioned close to the resin inlet starts an introduction of the gas earlier than a gas inlet positioned far from the resin inlet, wherein the resin molded article includes an elongated plate and a standing wall extending from a rear surface of the elongated plate, the elongated plate includes a plurality of elongated body components, a longitudinal direction of each of the body components extends in a longitudinal direction of the elongated plate, the cavity includes a body cavity for molding the elongated plate and a standing wall cavity for molding the standing wall, the body cavity is formed with a plurality of elongated closed spaces which are areas surrounded by the standing wall cavity, the closed spaces include an intermediate closed space arranged between a central closed space and a distal closed space, a longitudinal direction of each of the closed spaces extends in the longitudinal direction of the plate, a passageway length of the resin material from the resin inlet increases in an order of the central closed space, the intermediate closed space and the distal closed space, a plurality of the gas inlets are provided corresponding to portions of the rear molding surface in the plurality of closed spaces, the resin material is introduced into the cavity from the resin inlet, and flows of the resin material into the cavity including the central closed space, the intermediate closed space and the distal closed space from the corresponding resin inlets converge at ends of the cavity in a right-left direction, when an inside of each of the closed spaces is filled with the resin material, a gas inlet provided in the closed space positioned close to the resin inlet starts an introduction of the gas earlier than a gas inlet provided in the closed space positioned far from the resin inlet, and introduction of the gas through the gas inlets is started after an inside of at least one of the closed spaces is filled with the resin material and before a whole of the cavity is filled with the resin material.