Method of producing a compression-moulded plastic part comprising a neck which is equipped with a dispensing orifice

Compression molding method using continuously moving tools for manufacturing plastic parts having a neck provided with an orifice, comprising the steps of:

• bringing the blank to an appropriate temperature, and then placing the blank in an air gap between at least two moving parts of a compression molding tool and bringing the at least two moving parts towards each other to compress the blank,
• the plastic material of the blank being caused thereby to flow so as to fill cavities in the moving parts until the moving parts stop moving relative to each other, the cavities once brought towards each other defining a volume of the part with a neck,
• constructing the compression tool to produce a molded neck having a top wall that comprises a thinned zone having a contour that delimits a shape of the orifice,
• the compression tool being constructed such that the thinned zone is bounded by a notch having section in a diametric plane passing through the axis of the neck which is oriented along a direction approximately parallel to the axis of the neck, and such that the top wall also comprises a breakoff zone in which a mechanical force can be applied to the top wall with sufficient intensity to break the top wall at the notch, the application zone being distinct from the thinned zone,
• the compression tool further being constructed such that the top wall also includes two zones that can resist the mechanical force, one of the zones being designed to transmit the mechanical force and the other of the zones acting as a support, a protuberance extending from the top wall parallel to the axis of the neck, and
• opening the molding tool by relative displacement of the moving parts, during which a moving part of the molding tool applies a bending force to the protuberance sufficient to cause a break to occur at the notch and detach at a wall of the top wall.