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Stretch wrap films

Inactive Publication Date: 2004-02-17
BERRY PLASTICS CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention provides for a superior stretch wrap film having improved cling, slip, load retention, tear, elongation, and puncture resistance properties. The stretch wrap films are designed for use in cling / slip film applications. The stretch wrap film is advantageously employed in wrapping articles while under tension whereby the film itself is stretched generally between 20 and 400% of its original length.
The multilayer films of the present invention have been found to display unexpectedly superior film properties compared to other film constructions, surprisingly without undue degradation of other important film properties. The incorporation of an internal puncture resistant layer and an internal transverse direction tear resistant layer, using the resins for those layers as set forth herein, has produced an overall film that has superior elongation characteristics. Also, the films of the present invention display enhanced transverse direction tear properties without a concomitant loss of machine direction tear properties.

Problems solved by technology

Generally this loss of toughness is proportional to the amount of stretch imparted to the film as it is overwrapping a load of goods.
However, such load retention films generally have poor puncture characteristics at such stretch conditions.
On the other hand, certain stretch wrap films having superior puncture resistance properties have low load retention properties, thus limiting their use.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

The following example describes the properties of films prepared using a blend of a metallocene-catalyzed polyethylene (PE) resin with a linear low density polyethylene (LLDPE) resin. These blends can be used to construct the puncture resistant film layer of the multilayer films of the present invention.

Various films were prepared from a resin blend containing a LLDPE resin, Resin A, and a metallocene-catalyzed PE resin, Resin B. The LLDPE resin, Resin A, was a resin having a density of 0.918 g / cm.sup.3, a 3.3 MI, a M.sub.n of 22,000 and a M.sub.w of 77,000. The metallocene-catalyzed PE resin, Resin B, was a hexene co-polymer polyethylene having a 3.3 MI, 0.918 g / cm.sup.3 density, a M.sub.n of 26,000 and a M.sub.w of 73,000. The resins were blended together and melted to form a homogeneous blend, and then extruded into a cast film having a thickness of about 0.8 mils. The film was then tested for various properties as set forth in Table 1.1.

The films were also tested for performance...

example 2

Experiments were conducted to analyze the properties of a film containing a layer of a metallocene-catalyzed polyethylene (PE) resin between slip and cling outer film layers. Films were constructed having a three layer construction, ABC, where the films were constructed with an outer slip layer, layer A, constructed from the resins set forth in Table 2.1. The LLDPE1 resin was a polyethylene hexene copolymer resin having a MI of 4 and a density of 0.941 g / cm.sup.3, the LLDPE2 resin was a polyethylene hexene copolymer resin having a MI of 2 and a density of 0.941 g / cm.sup.3, and the PP resin was a polypropylene hexene copolymer resin having a melt flow rate of 4 and a density of 0.90 g / cm.sup.3. The outer cling layer, layer C, was constructed from a polyethylene methyl acrylate (EMA; 28% methyl acrylate) copolymer resin having a MI of 5 and a density of 0.908 g / cm.sup.3. The inner core layer, layer B, was constructed from a metallocene-catalyzed LLDPE resin with a MI of 2.5 and a dens...

example 3

Experiments were conducted to analyze the properties of films utilizing a layer of a strain hardening resin possessing superior transverse direction tear properties along with a layer of a metallocene-catalyzed PE resin. This film construction can be used as the interior core of a multilayer film of the present invention, with the inclusion of an outer slip and an outer cling layer to complete the inventive film construction. Three films were prepared having a BCB film construction where the outer B layers were constructed with the metallocene-catalyzed PE resin used in Example 1, and the C core layer was a 2.0 MI LDPE resin, having a density of 0.921 g / cm.sup.3. The two resins were coextruded with the overall B resin content set forth in Table 3.1, that content being essentially evenly split between both outside film layers. The films were then tested for various properties as set forth in Table 3.1.

The films were also tested for performance in a stretch wrap tester as in Example 1...

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Abstract

The present invention provides for improved polyolefin cling / slip stretch wrap films having superior load retention, elongation, tear resistance and puncture resistance properties and for the methods of using those stretch wrap films. The stretch wrap films are preferably constructed in a multilayer fashion having an outside cling layer, an outside slip layer, at least one inside puncture resistant layer comprising a metallocene-catalyzed polyethylene resin, and at least one inside transverse direction tear resistant layer.

Description

FIELD OF THE INVENTIONThe present invention is directed to stretch wrap films and methods for their use. In particular, the present invention is directed to stretch wrap films having a cling surface and an opposite slip surface and having superior puncture resistance, high elongation to break, high force to stretch the film, and overall strength.BACKGROUND OF THE INVENTIONThe use of thermoplastic stretch wrap films for the overwrap packaging of goods, and in particular, the unitizing of palleted loads is a commercially significant application of polymer film, including generically, polyethylene. Overwrapping a plurality of articles to provide a unitized load can be achieved by a variety of techniques. In one procedure, the load to be wrapped is positioned on a platform, or turntable, which is made to rotate and in so doing, to take up stretch wrap film supplied from a continuous roll. Braking tension is applied to the film roll so that the film is continuously subjected to a stretch...

Claims

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Application Information

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IPC IPC(8): B32B27/32
CPCB32B27/32Y10T428/2839Y10T428/2495Y10T428/2861Y10T428/2848Y10T428/2878Y10T428/31909Y10T428/31928Y10T428/31913
Inventor EICHBAUER, GEORGE N.
Owner BERRY PLASTICS CORP
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