Method and apparatus for pinning the edges of an extruded mass

An edge-pinning group (13) in a machine for extrusion of a plastic film, comprising:

• a first and a second support (18′,18″), each bearing at least one electrode (19), and a first and a second nozzle (20,21),
• wherein the first and the second support and the first and the second nozzle are positioned in the edge-pinning group with respect to an extrusion direction “Y” of the machine, as follows:
• with respect to the extrusion direction “Y”, the first nozzle (21) is positioned upstream of the second nozzle (20), said second nozzle (20) being positioned upstream and in line with the first support (18′), and said second support (18″) being positioned in parallel or downstream of the first support (18′);
• the first nozzle (21) is configured for partially pre-cooling an area (16) of an extruded melt (10) before the extruded melt touches a surface of a rotating cylinder (11), to remove heat;
• the second nozzle (20) is configured for pre-cooling an edge area of the extruded melt (10) affected by an electrostatic discharge of the one or more electrodes (19) positioned on the first support (18′), before the extruded melt comes into contact with the rotating cylinder (11);
• the first support (18′) is configured for electrostatically charging an edge area (15) of the extruded melt (10) cooled by the second nozzle (20) to facilitate an adhesion of the extruded melt to the surface of the rotating cylinder (11) and consequently ensure a desired heat exchange between the extruded melt and the rotating cylinder;
• and
• the second support (18″) is configured for blocking an external edge area (15′) of the extruded melt (10), which is thus caused to adhere to the rotating cylinder (11) avoiding a formation of peduncles.

A machine for extrusion of plastic film (10) comprising:

• an extrusion die (12);
• a rotating cylinder operating as a chill-roll (11);
• and
• at least one edge-pinning group (13),
• wherein said edge-pinning group (13) comprises:
• a first and a second support (18′,18″), each support (18′,18″) bearing at least one electrode (19), and a first and a second nozzle (20,21), and
• wherein the first and the second support and the first and the second nozzle are positioned in the edge-pinning group (13) with respect to an extrusion direction “Y” of the machine and with respect to a surface (R) of the rotating cylinder (11), as follows:
• with respect to the direction “Y”, the first nozzle (21) is positioned upstream of the second nozzle (20), said second nozzle (20) being positioned upstream and in line with the first support (18′), and said second support (18″) being positioned in parallel or downstream of the first support (18′);
• and
• with respect to a centerline of the surface (R) of the rotating cylinder (11), the second support (18″) is positioned externally with respect to the first support (18′), said first support (18′) being positioned parallel to the second nozzle (20), which positioned externally with respect to the first nozzle (21).