CAST POWER STRETCH FILMS WITH IMPROVED LOAD CONTAINMENT FORCE

Abstract

The present disclosure generally relates to compositions and methods for incorporating higher density metallocene linear low density polyethylene (m-LLDPE) into cast power stretch films. When compared to conventional machine films on a gauge-by-gauge basis, films containing the properly selected m-LLDPE may offer increased load containment force, reduced application force, and comparable elongation and puncture resistance properties.

Claims

1. A cast power stretch film comprised of a higher density m-LLDPE, the cast power stretch film having a total film thickness.

2. The cast power stretch film according to claim 1, wherein the higher density m-LLDPE is blended with resins chosen from the group consisting of polyethylenes, polyethylene copolymers, polypropylenes, and polypropylene copolymers.

3. The cast power stretch film according to claim 1, wherein the film is comprised of a plurality of discrete layers.

4. The cast power stretch film according to claim 3, wherein a discrete layer of the film is comprised of the higher density m-LLDPE.

5. The cast power stretch film according to claim 4, wherein the discrete layer of the film that is comprised of the higher density m-LLDPE has a thickness ranging from 5 to 70 percent of the total film thickness.

6. The cast power stretch film according to claim 5, wherein the discrete layer of the film that is comprised of the higher density m-LLDPE has a thickness of approximately 32 percent of the total film thickness.

7. The cast power stretch film according to claim 1, wherein the higher density m-LLDPE has a melt index ranging from 0.5 to 8.0 (g/10 min. @190° C./2.16 kg).

8. The cast power stretch film according to claim 7, wherein the higher density m-LLDPE has a melt index ranging from 1.0 to 3.0 (g/10 min. @190° C./2.16 kg).

9. The cast power stretch film according to claim 7, wherein the higher density m-LLDPE has a melt index of approximately 2.0 (g/10 min. @ 190° C./2.16 kg).

10. The cast power stretch film according to claim 1, wherein the higher density m-LLDPE has a density ranging from 0.900 g/cm.sup.3 to 0.960 g/cm.sup.3.

11. The cast power stretch film according to claim 10, wherein the higher density m-LLDPE has a density ranging from 0.922 g/cm.sup.3 to 0.940 g/cm.sup.3.

12. The cast power stretch film according to claim 10, wherein the higher density m-LLDPE has a density of approximately 0.925 g/cm.sup.3.

13. The cast power stretch film according to claim 1, wherein the higher density m-LLDPE is comprised of a higher alpha-olefin comonomer.

14. A cast power stretch film comprised of five layers, the film having a total film thickness, wherein a discrete layer is comprised of a higher density m-LLDPE.

15. The cast power stretch film according to claim 14, wherein the higher density m-LLDPE is blended with resins chosen from the group consisting of polyethylenes, polyethylene copolymers, polypropylenes, and polypropylene copolymers.

16. The cast power stretch film according to claim 14, wherein the discrete layer has a thickness ranging from 5 to 70 percent of the total film thickness.

17. The cast power stretch film according to claim 16, wherein the discrete layer has a thickness of approximately 32 percent of the total film thickness.

18. The cast power stretch film according to claim 14, wherein the higher density m-LLDPE has a melt index ranging from 0.5 to 8.0 (g/10 min. @190° C./2.16 kg).

19. The cast power stretch film according to claim 18, wherein the higher density m-LLDPE has a melt index ranging from 1.0 to 3.0 (g/10 min. @190° C./2.16 kg).

20. The cast power stretch film according to claim 18, wherein the higher density m-LLDPE has a melt index of approximately 2.0 (g/10 min. @ 190° C./2.16 kg).

21. The cast power stretch film according to claim 14, wherein the higher density m-LLDPE has a density ranging from 0.900 g/cm.sup.3 to 0.960 g/cm.sup.3.

22. The cast power stretch film according to claim 21, wherein the higher density m-LLDPE has a density ranging from 0.922 g/cm.sup.3 to 0.940 g/cm.sup.3.

23. The cast power stretch film according to claim 21, wherein the higher density m-LLDPE has a density of approximately 0.925 g/cm.sup.3.

24. The cast power stretch film according to claim 14, wherein the higher density m-LLDPE is comprised of a higher alpha-olefin comonomer.

25. The cast power stretch film according to claim 14, wherein the film is comprised of: a layer comprised of ZN-catalyzed LLDPE, with a thickness of approximately 10 percent of the total film thickness; a layer comprised of conventional m-LLDPE, with a thickness of approximately 32 percent of the total film thickness; a layer comprised of ZN-catalyzed LLDPE, with a thickness of approximately 16 percent of the total film thickness; a layer comprised of higher density m-LLDPE, with a thickness of approximately 32 percent of the total film thickness; and a layer comprised of ZN-catalyzed LLDPE, with a thickness of approximately 10 percent of the total film thickness.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The disclosure will be better understood from the following description and the accompanying drawings given as non-limiting examples, and in which:

[0012] FIG. 1 illustrates the load containment force exerted by selected conventional films and an embodiment disclosed herein; and

[0013] FIG. 2 illustrates the resistance to puncture for selected conventional films and an embodiment disclosed herein.

DETAILED DESCRIPTION

[0014] The following detailed description is of the best currently contemplated modes of carrying out the disclosure. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the disclosure, since the scope of the present disclosure is best defined by the appended claims.

[0015] Films containing higher density m-LLDPE may be produced which provide excellent performance with regards to load containment force, ultimate elongation, and puncture resistance. Films with higher density m-LLDPE may provide several advantages over conventional machine films. These advantages may include, but are not limited to: (1) requiring less film on a weight-to-weight basis to achieve the same level of load containment force; (2) applying less force to wrap the load while achieving the same load containment force; (3) significantly reducing load containment decay over time; (4) reducing liability due to product damage from crushing, deformation, or loss of containment; and (5) achieving higher levels of load containment force at lower levels of elongation, resulting in less film stress and fewer film failures.

[0016] Thus, when compared to conventional machine films on a gauge-by-gauge basis, films incorporating a higher density m-LLDPE may improve load containment force while offering comparable ultimate elongation and puncture resistance properties. In addition, the incorporation of a higher density m-LLDPE may significantly reduce load containment decay, or the amount of load containment force that is lost in the first twenty minutes after the load is wrapped. This feature may allow less force to be applied to wrap the load or, if the same amount of force is applied, provide a higher sustainable level of containment.

[0017] Broadly, the current disclosure includes compositions and methods for producing cast power stretch films with improved load containment force. More specifically, according to one aspect of the disclosure, a m-LLDPE having a higher density than that of resins used for conventional machine films may be incorporated into the film. The higher density m-LLDPE may provide for a film with properties, such as ultimate elongation and puncture resistance, which are comparable to those of conventional machine films. In addition, the film may offer increased load containment force and reduced load containment decay, allowing a corresponding reduction in the amount of force that must be applied to wrap a load.

[0018] The film of the present disclosure may be comprised of one layer or multiple layers, and the composition of each layer may vary. Materials that may be used to produce the film layers may include, but are not limited to, m-LLDPE. ZN-catalyzed linear low density polyethylene (LLDPE), polyethylenes, polyethylene copolymers, polyethylene terpolymers, polyethylene blends, polypropylenes, metallocene catalyzed polypropylenes, polypropylene copolymers, and blends thereof.

[0019] An embodiment of the present disclosure may be a film with a discrete layer comprised of a higher density m-LLDPE. The thickness of the discrete layer may vary from 5 to 70 percent of the total film thickness, with a preferred thickness of approximately 32 percent. The melt index of the m-LLDPE selected for the discrete layer may range from 0.5 to 8.0 (g/10 min. @ 190° C./2.16 kg), with a preferred melt index ranging from 1.0 to 3.0 (g/10 min. @ 190° C./2.16 kg). As an alternative, the preferred melt index may be approximately 2.0 (g/10 min. @190° C./2.16 kg). The density of the m-LLDPE selected for the discrete layer may range from 0.900 g/cm.sup.3 to 0.960 g/cm.sup.3, with a preferred melt index ranging from 0.922 g/cm.sup.3 to 0.940 g/cm.sup.3. As an alternative, the preferred density may be approximately 0.925 g/cm.sup.3. The m-LLDPE may also be combined with other resins, including, but not limited to, other polyethylenes, polyethylene copolymers, polypropylenes, and polypropylene copolymers. The discrete layer may be comprised of a polymer produced using a higher alpha-olefin comonomer.

[0020] The remaining layers of the film may be resins comprised of polyethylene, polyethylene copolymers, metallocene catalyzed polypropylenes, polypropylene copolymers, or blends thereof. Depending upon the desired properties of the film, the layers of the film may or may not have the same composition. The melt index of the resin selected for the remaining layers may range from 0.5 to 12 (g/10 min. @ 190° C./2.16 kg), with a preferred melt index ranging from 3 to 5 (g/10 min. @ 190° C./2.16 kg). The density of the resin selected for the remaining layers may range from 0.850 g/cm.sup.3 to 0.960 g/cm.sup.3, with a preferred density of approximately 0.917 g/cm.sup.3.

[0021] Another embodiment of the disclosure may be a five-layer film comprised of the following: a layer comprised of ZN-catalyzed LLDPE, with a thickness of approximately 10 percent of the total film thickness; a layer comprised of conventional m-LLDPE, with a thickness of approximately 32 percent of the total film thickness; a layer comprised of ZN-catalyzed LLDPE, with a thickness of approximately 16 percent of the total film thickness; a layer comprised of higher density m-LLDPE, with a thickness of approximately 32 percent of the total film thickness; and a layer comprised of ZN-catalyzed LLDPE, with a thickness of approximately 10 percent of the total film thickness.

[0022] The layer comprised of higher density m-LLDPE may vary from 5 to 70 percent of the total film thickness, with a preferred thickness of approximately 32 percent. The melt index of the higher density m-LLDPE may range from 0.5 to 8.0 (g/10 min. @190° C./2.15 kg), with a preferred melt index ranging from 1.0 to 3.0 (g/10 min. @ 190° C./2.16 kg). As an alternative, the preferred melt index may be approximately 2.0 (g/10 min. @ 190° C./2.16 kg). The density of the higher density m-LLDPE may range from 0.900 g/cm.sup.3 to 0.960 g/cm.sup.3, with a preferred density ranging from 0.922 g/cm.sup.3 to 0.940 g/cm.sup.3. As an alternative, the preferred density may be approximately 0.925 g/cm.sup.3. The higher density m-LLDPE may also be combined with other resins, including, but not limited to, other polyethylenes, polyethylene copolymers, polypropylenes, and polypropylene copolymers. The discrete layer may be comprised of a polymer produced using a higher alpha-olefin comonomer.

[0023] The remaining layers of the film may be resins comprised of polyethylene, polyethylene copolymers, metallocene catalyzed polypropylenes, polypropylene copolymers, or blends thereof. Depending upon the desired properties of the film, the layers of the film may or may not have the same composition. The melt index of the resin or resins selected for the remaining layers may range from 0.5 to 12 (g/10 min. @ 190° C./2.16 kg), with a preferred melt index ranging from 2 to 5 (g/10 min. @ 190° C./2.16 kg). The density of the resin or resins selected for the remaining layers may range from 0.850 g/cm.sup.3 to 0.960 g/cm.sup.3, with a preferred density of approximately 0.917 g/cm.sup.3.

[0024] As an experiment, selected performance properties of four films containing different resins, including a higher density m-LLDPE, were tested. Each test was run on an 80-gauge five-layer film, using the same production line and the same process conditions. The structure of each film was identical except for one layer, which represented 32 percent of the total film thickness. For Film A, the layer was comprised of Resin A, a conventional ZN-catalyzed solution octene. For Film B, the layer was comprised of Resin B, a conventional ZN-catalyzed gas phase hexene. For Film C, the layer was comprised of Resin C, a conventional metallocene. For Film D, the layer was comprised of Resin D, a higher density m-LLDPE as described in an embodiment of the disclosure. Table 1 describes the density and melt index of each resin:

TABLE-US-00001 Resin A Resin B Resin C Resin D Density 0.926 0.924 0.917 0.925 Melt index 2.0 1.9 4.0 2.0

[0025] The density of each resin was determined in accordance with the methods and procedures of ASTM D792 and is expressed in units of g/cm.sup.3. The melt index for each film was determined in accordance with the methods and procedures of ASTM D1238 and is expressed in units of g/10 min. @ 190° C./2.16 kg.

[0026] Table 2 presents data comparing the results of selected analyses for the four films:

TABLE-US-00002 Film A Film B Film C Film D Load containment force 91 88 82 94 Resistance to puncture 9.5 10.8 14.6 13.5

[0027] The load containment force was determined by pre-stretching the film 270 percent and applying five revolutions of film onto the test cube with a force-to-load of 20 pounds. The values are expressed in units of lbs-force. As shown in Table 2 and FIG. 1, Film D offers higher load containment force than the conventional ZN films (Film A and Film B) or the conventional metallocene film (Film C).

[0028] The resistance to puncture describes the force necessary to pierce or create a hole in the film. The values were generally determined in accordance with the methods and procedures of ASTM 5748 and are expressed in units of lbs-force. As shown in Table 2 and FIG. 2, Film D has the second highest resistance to puncture, after the conventional metallocene film (Film C).

[0029] When comparing the overall performance of the films, Film D offers the highest load containment force. In addition, Film D is much more resistant to punctures than either of the conventional ZN films (Film A and Film B). Although the conventional metallocene film (Film C) is more resistant to punctures than Film D, Film C has the overall lowest load containment force. Therefore, depending upon the desired use of the film, Film D likely offers the best combination of properties.

[0030] As can be seen, the present disclosure provides compositions and methods for producing a cast power stretch film with improved load containment force, reduced application force, and excellent elongation and puncture resistance properties. In particular, the present disclosure relates to the incorporation of higher density m-LLDPE in such films.

[0031] From the foregoing, it will be understood by persons skilled in the art that compositions and methods for producing a cast power stretch film have been provided. While the description contains many specifics, these should not be construed as limitations on the scope of the present disclosure, but rather as an exemplification of the preferred embodiments thereof. The foregoing is considered as illustrative only of the principles of the present disclosure. Further, because numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the present disclosure to the exact methodology shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the present disclosure. Although this disclosure has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and numerous changes in the details of the method may be resorted to without departing from the spirit and scope of the present disclosure.