Multilayer stretch cling film

Details Multilayer stretch cling film Multilayer stretch cling film

1999-10-13

2001-07-24

Thibodeau, Paul (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S354000, C428S516000, C428S215000

Reexamination Certificate

active

06265055

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to multi-layer stretch cling films having at least seven individual layers in the film composition offering acceptable cling performance, good balance of strength and good elongation properties.
BACKGROUND OF THE INVENTION
In commercial packaging art, individual articles as well as bundles of articles, including bundles of articles on pallets, are frequently packaged using so called stretch cling film in a stretch wrapping technique. In the stretch wrapping technique, a thin web of film is stretched and applied under tension around the articles to be wrapped or bundled pater wrapping is complete, the film attempts to relax and thus applies a compressive force on the bundled articles prohibiting movement. It is desired that the stretch film have some inherent cling such that it will adhere to itself, and prevent relaxation back to its unstretched state so that the film will not unwrap and cause slippage of the stretched overlaid film layers.
As stated above, stretch wrap films are typically used in wrapping palleted loads of boxes, as well as individual boxes or articles such as furniture and the like. The stretch wrap films of the present invention may be applied various techniques such as by hand or may be applied using a mechanical apparatus specially designed to wrap pallets, for example. In one procedure for using stretch wrap films of the present invention, the load to be wrapped is to be placed upon a platform, or turntable, which is made to rotate and in so doing, to take up stretch wrap film supplied from a continuous roll. Rotational speeds are typically 5 to 50 revolutions per minute. Regardless of the specific wrapping procedure used, at the completion of the wrapping, the stretch wrap film is cut and attached to the underlying layer by cling, tack sealing, adhesive tape, spray adhesives, and the like. When the stretch film of the present invention is applied by hand, the operator typically holds an applicator or wrapping tool that holds the stretch wrap film roll. After the operator completes wrapping, the stretch wrap film is cut.
Mechanical properties that are important in stretch films include, for example, how far the film can be stretched (i.e., stretchability), the film's resistance to stretching, film tensile strength, film puncture resistance, film tear resistance and cling force.
SUMMARY OF THE INVENTION
The present invention is a novel multi-layer stretch film comprising at least 7 layers and having excellent mechanical properties and stretch film performance when compared to stretch films made using fewer than seven layers.
The film comprises two outer, or skin layers that have moderate to high controlled cling and low blocking characteristics, at least five internal layers to assist in producing mechanical strength and stretchability. The resins used in the film composition include polypropylene (PP), ethylene propylene copolymers, low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), metallocene-catalyzed polyethylene (mPE), very low density polyethylene (VLDPE), and/or ultralow density polyethylene (ULDPE). Also, at least two of the resins may be blended to achieve a desired range of physical or mechanical properties of the final film product. The blend ratios may range from 99:1 to 1:99. More preferably, the blend ratios range from 95:5 to 5:95. Even more preferably, the blend ratios range from 90:10 to 10:90.
In one embodiment of the invention, the multi-layer, thermoplastic stretch wrap film of the present invention comprises two outer layers, at least one of which having a cling performance of at least 100 grams/inch. The at least one outer layer is selected from the group consisting of linear low density polyethylene, very low density polyethylene, and ultra low density polyethylene resins, with the resins being homopolymers, copolymers, or terpolymers, of ethylene and alpha-olefins. Each of five inner layers are selected from the group consisting of linear low density polyethylene, very low density polyethylene, ultra low density polyethylene, and metallocene-catalyzed linear low density polyethylene resins, said resins being homopolymers, copolymers, or terpolymers, of ethylene and alpha-olefins.


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