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Stretch wrap films

Inactive Publication Date: 2004-11-23
BERRY PLASTICS CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention sets forth multilayer stretch wrap thermoplastic films that are characterized by having improved cling, tear, elongation, and puncture resistance properties. The stretch wrap films can be used in cling / cling film applications. The stretch wrap film is advantageously employed in wrapping articles while under tension whereby the film itself is stretched generally to at least 2000% of its original length.
The multilayer films of the present invention have been found to display unexpectedly superior films properties compared to other film constructions, surprisingly without undue degradation of other important film properties. The incorporation of the puncture resistant resin in at least one outside cling layer with 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

However, such load retention films generally have only fair or 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 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 in a st...

example 2

Experiments were conducted to analyze the properties of multilayer films constructed with an internal layer of a strain hardening resin possessing superior transverse direction tear properties along with outer film layers constructed with a metallocene-catalyzed polyethylene (PE) resin in comparison to the metallocene resin film, Film 6 of Example 1. The multilayer films represent films similar to the claimed films, however the metallocene-catalyzed PE resins were not blended with a cling additive, such as PIB, for this experiment.

Three films, Films 7-9, 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 2.1, that content being essentially evenly split between both outside film layers. The films were then tested for various pr...

example 3

Multilayer stretch wrap films are made in accordance with the present invention having a B / C / B film construction as described in Example 2. The B film layers are constructed with the same metallocene-catalyzed PE resin stated in Example 2 with the incorporation of about 3 or 4 percent by weight polyisobutylene. The C core film layer is constructed with the same LDPE resin stated in Example 2.

The multilayer films are tested for similar properties as those described in Example 2.

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Abstract

The present invention provides for improved polyolefin stretch wrap films having superior cling force, load retention, tear resistance and puncture resistance properties and for the methods of using those stretch wrap films. The stretch wrap films generally have a thickness of from about 0.4 to about 3 mils, a cling force onto itself of at least 140 g / inch, an F-50 dart drop strength of at least about 150 g / mil. The stretch wrap films are constructed in a multilayer fashion having at least one outside cling polyethylene copolymer layer containing a polyethylene resin preferably produced through metallocene catalyst technology.

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 superior puncture resistance, high elongation to break, high force to stretch the film, high cling force, and overall strength.BACKGROUND OF THE INVENTIONThe use of thermoplastic stretch wrap films for the overwrap packaging of goods, and in particular, the utilizing of palleted loads is a commercially significant application of polymer film, including generically, polyethylene. Overwrapping a plurality of articles to provide a utilized load can be achieved by a variety of techniques. In one procedure, the load to be wrapped is positioned 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. Braking tension is applied to the film roll so that the film is continuously subjected to a stretching, or tensioning, force as it wrap...

Claims

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Application Information

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IPC IPC(8): B32B27/32
CPCB32B27/32Y10T428/28Y10T428/2848Y10T428/2878Y10T428/2861B32B27/08B32B27/18B32B2307/5825B32B2553/00Y10T428/31909Y10T428/31913
Inventor EICHBAUER, GEORGE N.
Owner BERRY PLASTICS CORP
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