A method for injection molding bodies having at least one wall portion externally covered by a label, comprising:
- a) using at least one molding assembly (50) comprising two parts (30 and 40), which are movable with respect to each other, one (30) of said movable parts having a cavity for making said wall portion;
- b) using a label pick-up means (10), a label transfer means (20), and a label depositing means (29), said pick-up means allowing for a label to be picked up in a label feeding area (70), and for said label to be transmitted to said transfer means;
- c) actuating said transfer means by means of a first actuator (90) so that it arrives in alignment with said cavity, and depositing said label inside said cavity by means of said label depositing means;
- d) moving apart said transfer means and said depositing means, moving together the other movable part of the molding assembly so as to form the molding cavity, next closing and locking the movable parts of the mold thus assembled in view of performing the injection of plastic material into the molding cavity;
- characterized in that a machine is used, which comprises:
- A) an indexed rotary platen (60) operating step by step and serving several work stations, on which said molding assembly is mounted;
- B) an injection press, placed at one of the work stations of the rotary platen, the so-called molding station, in such a configuration that when the molding assembly arrives in the closed and locked state at said molding station, said molding assembly is placed by means of a second actuator in alignment with the feeding channels of said injection press, next said molding assembly is pressed and held, typically by means of said second actuator, bearing on said injection press while the plastic injection molding cavity is being filled;
- C) said label transfer means (20), which is placed by said first actuator (90) at a work station, the so-called label depositing station, located upstream of the injection station, said molding assembly being opened at said label depositing station, so that said label can be deposited into said cavity by means of said label depositing means;
- wherein said body to be molded has a substantially planar bottom and a side wall extending according to a surface of revolution having an axis perpendicular to the plane of said bottom and which is covered by a label, wherein:
- a′) said molding assembly (50) comprises a female part or matrix (31) having at least one hollow cavity corresponding to the external shape of said body, and a male part or punch (41) having at least one relief cavity corresponding to the internal side of said body;
- b′) said label transfer means (20) is a mandrel (21) on which said label (5′) is deposited when it is in the horizontal position;
- c′) said label is held on said mandrel by a holding means (23);
- d′) by means of said first actuator (90), said mandrel (21) is introduced into the cavity of the matrix (31) while still holding said label by means of said holding means (23);
- e′) when said mandrel (21) has penetrated into the cavity up to a predetermined depth, said holding means is used as a depositing means (29), by suppressing or reversing the holding action of said holding means;
- wherein a label (5′) is chosen which has a height slightly greater than the height of the side wall of the container so that after the punch and the matrix have been moved together, the second end (8) of the label protrudes from the punch into the molding cavity;
- wherein said body to be molded is a container having a substantially flat bottom and an axially symmetric side wall, and wherein the peripheral part of the cavity (32), near the part (34) designed for forming the connection between said bottom and said axially symmetric side wall has the following shape:
- 1) peripherally, the side wall (35) of the cavity (32) opposite the punch (41) remains substantially axial;
- 2) when the matrix (31) and the punch (41) make contact with one another, the bottom of the cavity (32) of the matrix (31) located in alignment with the side wall is located at a depth greater than the protruding height of the second end (8) of the label (5′), so that said second end (8) does not come into abutment on the bottom (33) of said matrix cavity (32), and during injection, the plastic material injected must flow radially into an annular peripheral area (36) located above the top edge (9) of said second end (8);
- 3) the bottom of the matrix has an annular boss (37) hindering the plastic material flow towards said annular peripheral area (36), the outer edge (38) of said annular boss and the inner edge of said second end (8) being spaced apart from each other by a value which is smaller than the average thickness of the bottom, preferably smaller than half said thickness.