Blocked shrink bundling film
Multi-layered blocked shrink bundling films include at least one layer that contains a blocking polymer. Materials and methods for forming multi-layered blocked shrink bundling films via a blown film extrusion process are described.
1. A process for making a blocked shrink film, the process comprising the steps of
extruding two or more extrudable materials through a die to form a molten tubular film, wherein at least a first extrudable material comprises a first polyolefin and is configured to form at least a first layer of the molten tubular film, and wherein at least a second extrudable material comprises a blocking polymer and is configured to form at least a second layer of the molten tubular film,
injecting the molten tubular film with air to form a film bubble, wherein an interior surface of the film bubble is provided by the second layer of the molten tubular film,
drawing the film bubble away from the die, and
collapsing the film bubble upon itself, such that a first interior surface of the film bubble adheres to an adjacent second interior surface of the film bubble via blocking, thereby forming the blocked shrink film,
wherein the first polyolefin comprises high density polyethylene, and
wherein the blocking polymer is very low density polyethylene.
2. The process of claim 1 wherein the first polyolefin further comprises low density polyethylene and metallocene polyethylene.
3. The process of claim 1 wherein the second extrudable material further comprises ethylene-vinyl acetate.
4. The process of claim 1 further comprising the step of extruding three or more extrudable materials to form the molten tubular film, wherein at least a third extrudable material comprises a second polyolefin and is configured to form at least a third layer of the molten tubular film, and wherein the third layer is disposed between the first layer and the second layer, wherein the second polyolefin comprises linear low density polyethylene, high density polyethylene, low density polyethylene, and calcium carbonate.
5. The process of claim 1 wherein the drawing of the film bubble occurs in a machine direction and in a direction transverse to the machine direction.
6. The process of claim 1 wherein the collapsing is initiated when the film bubble contacts a collapsing frame.
7. The process of claim 1 further comprising the step of promoting the blocking by increasing a temperature and/or a pressure on a portion of the collapsed film bubble.
8. The process of claim 1 wherein a thickness of a wall of the molten tubular film is between about 0.5 mil and about 1.75 mil, and wherein a thickness of the blocked shrink film is between about 1.0 mil and about 3.5 mil.
9. The process of claim 4 , wherein the molten tubular film has a three-layer structure, and wherein the blocked shrink film has a five-layer structure.
10. The process of claim 1 , wherein the blocked shrink film comprises at least seven layers.
11. The process of claim 1 , wherein the blocked shrink film comprises at least nine layers.
12. A process for making a blocked shrink film, the process comprising the steps of
extruding three or more extrudable materials through a die to form a molten tubular film, wherein at least a first extrudable material comprises low density polyethylene, high density polyethylene, metallocene polyethylene, linear low density polyethylene, or a combination thereof and is configured to form at least a first layer of the molten tubular film, wherein at least a second extrudable material comprises very low density polyethylene, and is configured to form at least a second layer of the molten tubular film, wherein at least a third extrudable material comprises linear low density polyethylene, high density polyethylene, low density polyethylene, calcium carbonate, or a combination thereof and is configured to form at least a third layer of the molten tubular film, and wherein the third layer is disposed between the first layer and the second layer,
injecting the molten tubular film with air to form a film bubble, wherein an interior surface of the film bubble is provided by the second layer of the molten tubular film,
drawing the film bubble away from the die, and
collapsing the film bubble upon itself, such that a first interior surface of the film bubble adheres to an adjacent second interior surface of the film bubble via blocking, thereby forming the blocked shrink film,
wherein at least one of the first or third extrudable materials comprises high density polyethylene.
13. The process of claim 12 , wherein the first extrudable material comprises low density polyethylene and high density polyethylene and the low density polyethylene is present in an amount of between about 30 wt. % and about 95 wt. % and the high density polyethylene is present in an amount of between about 5 wt. % and about 70 wt. % based on total weight of the first extrudable material.
14. The process of claim 12 , wherein the first extrudable material comprises low density polyethylene and linear low density polyethylene and the low density polyethylene is present in an amount of between about 30 wt. % and about 80 wt. % and the linear low density polyethylene is present in an amount of between about 15 wt. % and about 70 wt. % based on total weight of the first extrudable material.
15. The process of claim 12 , wherein the first extrudable material further comprises an antiblock agent, a process aid, or a combination thereof.
16. The process of claim 12 , wherein the third extrudable material comprises low density polyethylene, linear low density polyethylene, and high density polyethylene and the low density polyethylene is present in an amount of between about 20 wt. % and about 80 wt. %, the linear low density polyethylene is present in an amount of between about 5 wt. % and about 65 wt. %, and the high density polyethylene is present in an amount of between about 5 wt. % and about 75 wt. % based on total weight of the third extrudable material.
17. The process of claim 12 wherein the third extrudable material comprises low density polyethylene, linear low density polyethylene, high density polyethylene, and calcium carbonate and the low density polyethylene is present in an amount of between about 20 wt. % and about 80 wt. %, the linear low density polyethylene is present in an amount of between about 5 wt. % and about 65 wt. %, the high density polyethylene is present in an amount of between about 5 wt. % and about 70 wt. %, and the calcium carbonate is present in an amount of between about 5 wt. % and about 25 wt. % based on total weight of the third extrudable material.
18. A process for making a blocked, five-layered shrink film, the process comprising the steps of
extruding three extrudable materials through a die to form a molten tubular film, wherein a first extrudable material comprises low density polyethylene, high density polyethylene, metallocene polyethylene, linear low density polyethylene, or a combination thereof and is configured to form a first layer and a fifth layer of the molten tubular film, wherein a second extrudable material comprises a very low density polyethylene and is configured to form a second layer of the molten tubular film, wherein a third extrudable material comprises linear low density polyethylene, high density polyethylene, low density polyethylene, calcium carbonate, or a combination thereof and is configured to form a third layer and a fourth layer of the molten tubular film, wherein the third layer is disposed between the first layer and the second layer, and wherein the fourth layer is disposed between the second layer and the fifth layer,
injecting air into an interior of the molten tubular film through the die to form a film bubble, wherein an interior surface of the film bubble is provided by the second layer of the molten tubular film,
drawing the film bubble away from the die, thereby imparting orientation to the molten tubular film,
cooling an exterior surface and/or the interior surface of the air bubble with blown air,
collapsing the film bubble upon itself, such that a first interior surface of the film bubble adheres to an adjacent second interior surface of the film bubble via blocking, thereby forming the blocked, five-layered shrink film,
wherein at least one of the first or third extrudable materials comprises high density polyethylene.
19. The process of claim 18 wherein a thickness of a wall of the molten tubular film is between about 0.5 mil and about 1.75 mil, and wherein a thickness of the blocked, five-layered shrink film is between about 1.0 mil and about 3.5 mil.
20. The process of claim 18 , wherein the first layer comprises from about 5% to about 15% by weight of the blocked, five-layered shrink film, the second layer comprises from about 20% to about 40% by weight of the blocked, five-layered shrink film, the third layer comprises from about 10% to about 25% by weight of the blocked, five-layered shrink film, the fourth layer comprises from about 20% to about 40% by weight of the blocked, five-layered shrink film, and the fifth layer comprises from about 5% to about 15% by weight of the blocked, five-layered shrink film.