Blown film with integral profiles
View Patent ↗A system and method for extruding film with a thickened profile section. In some embodiments, the film forms bags with integral zipper profiles. Plastic film is extruded to form a tube. During extrusion, cooling jets direct cooling gases toward the thickened profile section below the frost line to preferentially cool the thickened profile sections. In some embodiments, warm air is drawn out of the tube interior through hot air intakes located below the frost line. In certain embodiments, the film is extruded at a higher rate of speed than conventional processes. Likewise, the extruded film tube is expanded at a lower blow up ratio than conventional processes in certain preferred embodiments. In some embodiments, the extrusion system includes an air flow surface oriented relative to the film tube to define an air flow gap of substantially uniform thickness.
1. A method for manufacturing a blown plastic film having integral profiles using an extruder, the method comprising:
extruding a tube of polyethylene-based resin including at least two thickened profile sections extending continuously in the direction of extrusion along a surface of the tube; and
cooling each thickened profile section by directing a jet of cooling gas toward each thickened profile section;
wherein the extruded tube defines a bubble extending from an extrusion die head at a bottom of the bubble to a film collector at a top of the bubble.
2. The method of claim 1 wherein the step of extruding the tube comprises extruding the tube to have a blow up ratio of less than 3.
3. The method of claim 1 wherein the step of extruding the tube comprises extruding the tube to have a blow up ratio of less than 2.
4. The method of claim 1 wherein the step of extruding the tube comprises extruding the tube to have a blow up ratio of less than 1.
5. The method of claim 1 wherein the step of cooling comprises directing the jets of cooling gas to impact the thickened profile sections at a point below a frost line of the bubble.
6. The method of claim 1 wherein the cooling is performed by a cooling cone which comprises cooling jets for directing the jet of cooling gas toward each thickened profile section.
7. The method of claim 6 wherein the cooling jets are located in a common horizontal plane.
8. The method of claim 6 wherein the cooling cone side walls flare outwardly from top to bottom at an angle between about 15° and about 30°.
9. The method of claim 1 further comprising removing hot air from an interior of the bubble through at least one hot air intake.
10. The method of claim 9 wherein the at least one hot air intake and the cooling jets are located in a side wall of a cooling cone, the hot air intake being located at a narrower location of the cooling cone than the jets.
11. The method of claim 9 wherein the at least one hot air intake is located below the frost line.
12. The method of claim 1 wherein the frost line is at least about 13 inches above the extrusion die head.
13. The method of claim 1 wherein the extrusion speed is at least about 100 feet/minute.
14. The method of claim 1 wherein the step of cooling comprises directing a jet of cooling gas out of radially oriented cooling nozzles toward each thickened profile section.
15. An extrusion system comprising:
an extruder configured to extrude a plastic material in an extrusion direction;
an extrusion die defining an extrusion passage having a least one thin segment and at least one thick segment, the extrusion die being operatively connected to the extruder to receive the plastic material therefrom such that the extruded plastic material passes through the extrusion passage, the extrusion passage being configured to shape the plastic material into a film tube having a thickened profile section aligned with the thick segment of the extrusion passage; and
a freezing control device positioned relative to the extrusion die to be received in an interior of the film tube as the film tube is being extruded, the freezing control device comprising a cooling jet configured to deliver the cooling gas toward the thickened profile section of the film tube as the film tube is being extruded and thereby preferentially cool the thickened profile section.
16. The extrusion system of claim 15 wherein the freezing control device further comprises an air flow surface shaped and arranged to be oriented substantially parallel to the film tube as the film tube is being extruded to define an air flow gap between the air flow surface and the film tube of substantially uniform thickness.
17. The extrusion system of claim 16 wherein the cooling jet is arranged to discharge cooling gas in a direction oriented substantially perpendicular to the film tube.
18. The extrusion system of claim 16 wherein the freezing control device further comprises a hot air intake configured to remove hot air from the air flow gap.
19. The extrusion system of claim 16 wherein the air flow surface is substantially conical.
20. The extrusion system of claim 16 wherein the air flow surface flares outwardly from top to bottom.
21. The method of claim 1 wherein the polyethylene-based resin comprises a material selected from the group consisting of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), metallocene linear low density polyethylene (m-LLDPE), and blends thereof.