apparatus and method are described for injection molding of thermoplastic paint cans substantially similar in size and design to the conventional steel one - gallon paint can . the apparatus comprises a cavity element defining the exterior of the container body and a core mold element including a peripheral lip protruding into the interior of the can body at a point below the upper terminus of the top circumference of the container body , thus providing a peripheral upwardly projecting edge . the cavity element includes a plurality of cam elements which move cooperatively on separation of the core and cavity elements . the cam elements grip the ridge of the container and expand it outwardly sufficiently to permit the core element of the mold to be removed from the container without hindrance from the inwardly protruding lip .