PRESTRETCHED BALEWRAP

Abstract

A prestretched polyethylene film having a longitudinal degree of pre-stretching above 70% and a remaining longitudinal elongation capability of at least 300% as determined according to ASTM D882, wherein said film is a coextruded blown film comprising at least one core layer arranged between two exterior layers, wherein the thickness of the film is in the range of 10-30 m, and wherein the film comprises at least 25% by weight of a linear low density polyethylene (LLDPE) substantially free from long chain branching (LCB) produced using a Ziegler Natta catalyst and hexene, heptene or octene as comonomer and having a density of between 910 and 915 kg/m.sup.3. Use of the prestretched polyethylene film as an agricultural balewrap film or silage film, pallet wrapping film, or waste wrap film.

Claims

1. A prestretched polyethylene film having a longitudinal degree of pre-stretching above 70% and a remaining longitudinal elongation capability of at least 300% as determined according to ASTM D882, wherein said film is a coextruded blown film comprising at least one core layer arranged between two exterior layers, wherein the thickness of the film is in the range of 10-30 m, and wherein the film comprises at least 25% by weight of a linear low density polyethylene (LLDPE) substantially free from long chain branching (LCB) produced using a Ziegler Natta catalyst and hexene, heptene or octane as comonomer and having a density of between 910 and 915 kg/m.sup.3.

2. The prestretched polyethylene film according to claim 1, wherein the film comprises at least 35%, by weight of said linear low density polyethylene (LLDPE) substantially free from long chain branching (LCB).

3. The prestretched polyethylene film according to claim 1, wherein the linear low density polyethylene (LLDPE) substantially free from long chain branching (LCB) has a density of between 911 and 913 kg/m.sup.3.

4. The prestretched polyethylene film according to claim 1, wherein the linear low density polyethylene (LLDPE) substantially free from long chain branching (LCB) has a melt flow index in the range of 0.7-1.3 g/10 min, as determined according to ASTM D1238 (190 C., 2.16 kg weight).

5. The prestretched polyethylene film according to claim 1, wherein the linear low density polyethylene (LLDPE) substantially free from long chain branching (LCB) is an LLDPE produced using a Ziegler Natta catalyst and octene as comonomer.

6. The prestretched polyethylene film according to claim 1, said film having a longitudinal degree of prestretching between 70% and 100%, preferably between 70% and 85%.

7. The prestretched polyethylene film according to claim 1, wherein the stress required in order to stretch the prestretched film by 70% in the longitudinal direction is less than 19 MPa, as determined according to ASTM D882.

8. The prestretched polyethylene film according to claim 1, said film having a remaining longitudinal elongation capability of at least 320%, as determined according to ASTM D882.

9. The prestretched polyethylene film according to claim 1, wherein at least one layer comprises in the range of 40-99% by weight of said linear low density polyethylene (LLDPE) substantially free from long chain branching (LCB).

10. The prestretched polyethylene film according to claim 1, wherein the at least one core layer comprises in the range of 40-99% by weight of the linear low density polyethylene (LLDPE) substantially free from long chain branching (LCB).

11. The prestretched polyethylene film according to claim 1, wherein the thickness of the film is in the range of 13-25 m.

12. The prestretched polyethylene film according to claim 1, which is an agricultural balewrap film or silage film.

13. (canceled)

14. (canceled)

15. (canceled)

16. A method of using a prestretched polyethylene film according to claim 1 for baling of agricultural material, comprising: providing a compacted bale of agricultural bulk material, and wrapping the bale with the prestretched polyethylene film.

17. The method of claim 16, wherein the agricultural material is intended to form silage.

18. The method of claim 16, wherein the agricultural material is grass or straw.

19. The method of claim 16, wherein the bale is wrapped with net, twine or film prior to wrapping with the prestretched polyethylene film.

20. The method of claim 16, wherein said wrapping is carried out using a bale wrapper.

21. The method of claim 20, wherein the prestretched polyethylene film is stretched in the bale wrapper prior to being wrapped around the compacted bale.

22. The method of claim 21 wherein the prestretched polyethylene film is stretched by 50-75% in the bale wrapper.

Description

DETAILED DESCRIPTION

[0046] Preferred embodiments of the invention will now be described in more detail. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

[0047] The inventive film comprises at least 25% by weight of linear low density polyethylene (LLDPE) substantially free from long chain branching (LCB) and having a density below 915 kg/m.sup.3.

[0048] The film may be a single layer film or a film comprising more than one layer. A film comprising more than one layer may be called a multi-layer film.

[0049] Preferably, the prestretched polyethylene film according to the present invention is a multi-layer film comprising at least three layers: at least one core layer arranged between two exterior layers.

[0050] The prestretched polyethylene film may comprise from 1 to 5 core layers. In embodiments, where the prestretched polyethylene film comprises more than one core layer, the core layers may have the same composition. Alternatively, the more than one core layers may differ in composition compared to each other. In a preferred embodiment, the film consists of three layers; one core layer arranged between two exterior layers.

[0051] The two exterior layers may have the same or similar composition. Alternatively, the two exterior layers may differ in composition compared to each other.

[0052] The stretch film may be either blown or cast. A blown stretch film has been melted and thereafter air-cooled when blown out. A cast stretch film has been cooled over cooling rollers.

[0053] The at least one core layer may form from 50% to 90%, such as from 70% to 80%, by weight of total weight of the prestretched polyethylene film. In a prestretched polyethylene film comprising one core layer, the one core layer may form from 50% to 90%, such as from 70% to 80% by weight of the total weight of the prestretched polyethylene film. In a prestretched polyethylene film comprising more than one core layer, the total number of core layers may form from 50% to 90%, such as from 70% to 80%, by weight of total weight of the prestretched polyethylene film.

[0054] The two exterior layers may together form from 10% to 50%, such as from 20% to 30% by weight of the total weight of the prestretched polyethylene film. Typically, the exterior layers each forms about 10% by weight of total weight of the prestretched polyethylene film.

[0055] The prestretched polyethylene film may have a total film thickness within the range of from 10 m to 30 m, such as from 15 m to 25 m, such as from 12 m to 20 m, for example about 19 m. The thickness of the two exterior layers may be within the range of from 0.5 m to 10 m, such as from 1 m to 5 m, for example from 2 m to 3 m. The thickness of the at least one core layer may be within the range of from 5 to 28 m, such as from 5 m to 25 m, for example from 10 m to 20 m.

[0056] In an embodiment, the prestretched polyethylene film comprises one core layer. The thickness of the one core layer may be within the range of from 5 to 28 m, such as from 10 m to 25 m, for example from 10 m to 20 m. Alternatively, the prestretched polyethylene film may comprise more than one core layer. The thickness of the total number of core layers may be within the range of from 5 to 28 m, such as from 5 m to 25 m, for example from 10 m to 20 m.

[0057] In an example, a prestretched polyethylene film comprising one core layer and two exterior layers sandwiching the core layer may have a total film thickness of 19 m. The core layer may have a thickness of 14 m and each of the exterior layers has a thickness of 2.5 m.

[0058] The prestretched polyethylene film according to the present invention comprises at least 25% by weight of linear low density polyethylene (LLDPE) substantially free from long chain branching (LOB) and having a density below 915 kg/m.sup.3.

[0059] The portion of the prestretched polyethylene film not made up of the linear low density polyethylene (LLDPE) substantially free from long chain branching (LOB) and having a density below 915 kg/m.sup.3 may comprise other types of LLDPE, LDPE, and other polyolefins and additives commonly used in the manufacture of prestretched polyethylene films. Examples of additional polyolefin components include linear low density polyethylene (LLDPE) having higher density, low density polyethylene (LDPE), and very low density polyethylene (VLDPE), as well as polypropylenes and polybutylenes. Preferably, the portion of the prestretched polyethylene film not made up of the linear low density polyethylene (LLDPE) substantially free from long chain branching (LOB) and having a density below 915 kg/m.sup.3 is substantially made up of higher density LLDPE.

[0060] In a preferred embodiment, the core layer comprises a mixture of LLDPE substantially free from long chain branching (LOB) and having a density below 915 kg/m.sup.3 and higher density LLDPE, wherein the LLDPE mixture has a density below 916 kg/m.sup.3, preferably below 915 kg/m.sup.3, and more preferably below 914 kg/m.sup.3.

[0061] The core layer and the exterior layers may have different composition. At least one of the exterior layers may comprise a polymer such as ethylene vinyl acetate copolymer (EVA) or ethylmethacrylate copolymer (EMA).

[0062] The at least one core layer may preferably comprise from 25 to 95%, preferably from 30 to 95% or from 40 to 95% by weight of the linear low density polyethylene (LLDPE) substantially free from long chain branching (LOB) and having a density below 915 kg/m.sup.3, based on the total weight of the at least one core layer. For instance, the at least one core layer comprise the LLDPE substantially free from long chain branching (LOB) and having a density below 915 kg/m.sup.3, at a content of from 40 to 90% by weight based on the total weight of the core layer, such as from 40 to 70%, 40 to 60%, or 45 to 55% by weight based on the total weight of the core layer.

[0063] The prestretched polyethylene film according to embodiments of the invention comprises two exterior layers. The exterior layers sandwich the at least one core layer, i.e. the core layer is arranged between two exterior layers. By exterior layer is meant a layer forming at least part of a surface of the film.

[0064] The exterior layers may be of identical or similar composition, or may differ in composition. Typically however an exterior layer comprises a thermoplastic polymer, such as a polyolefin, as a base material. Examples of suitable base materials for an exterior layer include polyethylene, especially LLDPE or VLDPE, and ethylene-vinyl acetate co-polymer.

[0065] As described herein, the prestretched polyethylene film according to the invention comprises at least two exterior layers and at least one core layer. Typically, at least one of the two exterior layers has a certain cling. In some embodiments, one exterior layer may have a higher degree of cling than an exterior layer arranged on the opposite side of the core layer.

[0066] In embodiments of the invention, the prestretched polyethylene film may comprise a tackifier. Typically at least one of the exterior layers may comprise a tackifier.

[0067] Conventional tackifiers, known to the person skilled in the art, may be added to the prestretched polyethylene film. Examples of conventional tackifiers include soft polymers and migrating tackifiers. A soft polymer may provide a relatively soft surface which may increase friction, and reduce slip in a direction substantially parallel to the film surface. A migrating tackifier, on the other hand, may provide an adhesive surface that increases the friction in a direction substantially perpendicular to the film surface.

[0068] Examples of suitable soft polymers include ethylene vinyl acetate co-polymer (EVA), ethyl methacrylate co-polymer (EMA) and very low density polyethylene (VLDPE). Hence, in embodiments where an exterior layer comprises EVA, EMA, or VLDPE as a base material, this may provide sufficient cling, such that it may not be necessary to add a further tackifier. Optionally however, a layer comprising a soft polymer may also comprise a migrating tackifier.

[0069] In an example, the cling of at least one of the exterior layers may be achieved by the use of a soft polymer, or a combination of soft polymers, in at least one of the two exterior layers.

[0070] VLDPE may be added to at least one exterior layer in order to provide cling to the at least one exterior layer. In an embodiment, the content of VLDPE may be up to 100% by weight of the at least one exterior layer. For instance, one of the two exterior layers may consist of 100% VLDPE.

[0071] The soft polymer EVA may be used in combination with the migrating tackifier PIB in order to provide cling to at least one exterior layer. For example, PIB may be added to the core layer at a content that is sufficient to allow migration to the exterior surface of at least one of the exterior layers upon saturation of the core layer and the at least one exterior surface. EVA may be comprised in the at least one exterior layer. An advantage of combining a soft polymer, e.g. EVA, and a migrating tackifier, e.g. PIB, in at least one exterior layer is that the cling may be improved due to increased resistance of the exterior layer to forces both substantially parallel as well as substantially perpendicular to the exterior surface of the exterior layer.

[0072] Suitable contents of at least one of a migrating tackifier, a soft polymer and a combination thereof, in the at least one core layer and/or in any or both of the two exterior layers of the prestretched polyethylene film are known to the person skilled in the art.

[0073] A migrating tackifier may migrate within a material, including within a single layer, as well as from one layer to an adjacent layer. In embodiments of the present invention, a migrating tackifier may migrate from any one of the layers of the prestretched polyethylene film (e.g. the core layer) to the film surface of the prestretched polyethylene film (typically the surface of an exterior layer). An example of a migrating tackifier is polyisobutylene (PIB).

[0074] A migrating tackifier may be added to one or more layers of the prestretched polyethylene film, typically including the thickest layer(s) of the prestretched polyethylene film. When the prestretched polyethylene film comprises more than one core layer, the migrating tackifier may be added to one or more, including all, of the core layers. Alternatively, the migrating tackifier may be added to the thickest of the core layers. Upon saturation of the thickest layer(s) with regard to the migrating tackifier, the excess of migrating tackifier may migrate into adjacent layer(s). For example, the migrating tackifier may be initially added to the core layer, and upon saturation of the core layer, the excess of migrating tackifier may migrate into the two exterior layers sandwiching the core layer. Typically, also the exterior layers are saturated with the migrating tackifier, thereby allowing the migrating tackifier to migrate through the exterior layers and accumulate at the exterior surfaces of the exterior layers providing cling.

[0075] The cling of at least one of the exterior layers may be achieved by addition of a migrating tackifier to the at least one core layer. The migrating tackifier will initially be comprised in the core layer, and over time migrate to the exterior layers. The content of migrating tackifier added to the at least one core layer may exceed the content of migrating tackifier required to saturate the at least one core layer with regard to the migrating tackifier.

[0076] The migrating tackifier may be soluble in polyethylene and other polyolefins. Thus, the content required to saturate the at least one core layer may depend on the content of polyethylene and other polyolefins, in which the migrating tackifier is soluble, in the at least one core layer.

[0077] The at least one core layer may comprise migrating tackifier, e.g. in the form of polyisobutylene (PIB), at a content of from 0 to 15% by weight, e.g. from 1 to 15% by weight, such as from 3 to 7% by weight, based on the total weight of the at least one core layer. In an embodiment, the at least one core layer comprises approximately 5% by weight of PIB.

[0078] More specifically, in an embodiment, the prestretched polyethylene film comprises only one core layer. A migrating tackifier, e.g. in the form of PIB, may be present in the core layer at a content of from 0 to 15% by weight, e.g. from 1 to 15% by weight, such as from 3 to 7% by weight, based on the total weight of the one core layer. The one core layer may comprise approximately 5% by weight of PIB.

[0079] In another embodiment, the prestretched polyethylene film comprises more than one core layer, such as two or more core layers arranged adjacent each other. A migrating tackifier, e.g. PIB, may be present in one or more of the core layers at a content of from 0 to 15% by weight, e.g. from 1 to 15% by weight, such as from 3 to 7% by weight based on the total weight of the total number of core layers. The core layers may together comprise approximately 5% by weight of PIB. It is envisaged that when the prestretched polyethylene film comprises multiple core layers, a tackifier could initially be contained in only one of the core layers, or in several or all of the core layers. Typically however, due to the nature and purpose of a migrating tackifier, with time all of the layers may contain the tackifier, even if the tackifier was added only to one of the core layers during manufacture of the multi-layer film.

[0080] By the addition of an additional pigment to the at least one core layer, the color and the opacity of the prestretched polyethylene film may be further varied. The at least one core layer may comprise an additional pigment in a range of from 0 to 10% by weight, e.g. from 1 to 10% by weight, based on the total weight of the at least one core layer. A prestretched polyethylene film for silage, typically comprises from 2 to 5% by weight of an additional pigment in the form of titanium dioxide (TiO.sub.2).

[0081] White pigments provide opacity by scattering visible light. An example of a suitable white additional pigment is titanium dioxide (TiO.sub.2). Colored pigments provide opacity by absorbing light. An example of a suitable colored additional pigment is carbon black (CB).

[0082] Alternatively, an additional pigment may be absent in the prestretched polyethylene film. In such an embodiment, the prestretched polyethylene film can be relatively transparent.

[0083] In some applications, a certain level of opacity may be advantageous with regard to protection against noxious animals, such as vermin, birds, and insects, which may harm either the prestretched polyethylene film or the material being stored inside an arrangement of the prestretched polyethylene film, e.g. a bale of silage. As an example, a certain level of opacity of the prestretched polyethylene film may hinder a bird from observing the material of the bale of silage, thereby hinder the prestretched polyethylene film from being punctured by the beak or claws of the bird. The transparency of the prestretched polyethylene film is usually within the range of from 63 to 73%, such as approximately 70%, measured by the standard ASTM D-1003.

[0084] The prestretched polyethylene film according to embodiments of the invention may comprise a UV stabilizer, contained in at least one layer of the multi-layer film. Conventional UV stabilizer, known to the person skilled in the art, may be added for example to the at least one core layer. A UV stabilizer typically traps free radicals generated in the polyolefin material by UV irradiation, and may thus prevent chain reactions within the polyolefin layer(s) of the prestretched polyethylene film, which would otherwise result in degradation of the polyolefin material.

[0085] In embodiments of the invention, all layers of the prestretched polyethylene film may comprise a UV stabilizer. A good UV stabilization of the film material is desirable in order to avoid that the prestretched polyethylene film degrades during storage time outdoors which typically may be up to a year.

[0086] Examples of suitable UV stabilizers are Chimassorb 944 (BASF, Italy), Tinuvin 622 (BASF, Germany), and Chimassorb 2020 (BASF, Italy). An additional pigment, such as TiO.sub.2 or CB, may also function as a UV stabilizer. The at least one core layer may comprise UV stabilizator in a range of from 0 to 0.6% by weight based on the total weight of the at least one core layer.

[0087] A multilayer prestretched polyethylene film according to embodiments of the invention may be produced by a manufacturing process involving the following steps: [0088] a) providing a first extrudible composition comprising at least 25% by weight of linear low density polyethylene (LLDPE) substantially free from long chain branching (LOB) and having a density below 915 kg/m.sup.3; [0089] b) providing at least one additional extrudible composition comprising at least one polymer; [0090] c) extruding the first composition obtained in step a) to form at least one core layer; [0091] d) extruding the at least one additional extrudible composition to form two exterior layers on opposing sides of the core layer.

[0092] According to embodiments, the linear low density polyethylene (LLDPE) substantially free from long chain branching (LOB) is produced using a Ziegler Natta catalyst and hexene, heptene or octene as comonomer and having a density of between 910 and 915 kg/m.sup.3.

[0093] The first extrudible composition is intended to form a core layer. The first extrudible composition comprising comprising at least 25% by weight of linear low density polyethylene (LLDPE) substantially free from long chain branching (LOB) and having a density below 915 kg/m.sup.3 may be mixed with at least one other polyolefin and optionally at least one additive, e.g. selected form the group consisting of: UV stabilizers, additional pigments, and tackifiers.

[0094] The at least one additional extrudible composition is typically intended to form one of the exterior layers or both exterior layers. The step of providing at least one additional extrudible composition comprising at least one polymer may imply providing a second extrudible composition comprising at least one polymer. Optionally, also a third extrudible composition comprising at least one polymer may be provided. In particular, in embodiments where the exterior layers have different composition, the second extrudible composition is intended to form one of the exterior layers, and the third extrudible composition is intended to form the other one of the exterior layers.

[0095] For example, the second extrudible composition may be provided by mixing a soft polymer with optionally at least one additive selected form the group consisting of: UV stabilizers and tackifiers. The second extrudible composition is typically adapted to provide cling. The third extrudible composition may be provided by mixing a polyolefin, e.g. a polyethylene, with optionally at least one additive selected form the group consisting of: UV stabilizers and tackifiers. The third extrudible composition may be adapted to provide a low friction surface.

[0096] Optionally, a single additional extrudible composition may be provided, which may be adapted to provide cling and/or a low friction surface.

[0097] The step of extruding the first composition obtained in step a) to form at least one core layer may imply that the first composition is extruded to a single core layer or to multiple core layers. Typically, in the case of multiple core layers, the multiple core layers are extruded simultaneously by coextrusion and adhere to each other due to substantially identical chemical properties.

[0098] The step of extruding the at least one additional extrudible composition to form two exterior layers on opposing sides of the core layer may imply extruding the second extrudible composition to form a first exterior layer on a first side of the core layer and extruding the third extrudible composition to form a second exterior layer on a second side of the core layer, wherein the first side of the core layer is arranged opposite to the second side of the core layer.

[0099] Alternatively, the single additional extrudible composition is extruded to form two exterior layers on opposing sides of the core layer.

[0100] The steps of extruding the first extrudible composition to form at least one core layer and the additional extrudible composition to form two exterior layers, respectively, may be performed separately from each other e.g. by monoextrusion, or simultaneously e.g. by coextrusion. Typically, the prestretched polyethylene film is prepared by co-extrusion, using one extruder per layer simultaneously. Monoextrusion and coextrusion are techniques generally known to the person skilled in the art.

[0101] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

EXAMPLES

Preparatory Example 1

Prior Art Balewrap (59% Prestretch)

[0102] A first extrudible composition was prepared. The first extrudible composition comprised LLDPE (Dowlex 2045S) with a density of 918 kg/m.sup.3 at a content of 88.5% by weight, TiO.sub.2 at a content of 6% by weight, a migrating tackifier in the form of PIB (polyisobutylene) at a content of 5% by weight, and a UV stabilizer at a content of 0.5% by weight based on the total weight of the first extrudible composition.

[0103] Two additional extrudible compositions, namely a second extrudible composition and a third extrudible composition, were prepared. The second extrudible composition comprised EVA (Exxon Escorene Ultra FL 00218), at a content of 94.5% by weight, a migrating tackifier in the form of PIB at a content of 5% by weight, and a UV stabilizer at a content of 0.5% by weight based on the total weight of the second extrudible composition. The third extrudible composition comprised polyethylene, i.e. a combination of LLDPE and LDPE, at a content of 99.5% by weight, and a UV stabilizer at a content of 0.5% by weight based on the total weight of the third extrudible composition.

[0104] The extrudible compositions were each mixed separately using blending devices or mixing devices generally known to a person skilled in the art.

[0105] By means of coextrusion, a core layer was formed of the first extrudible composition and two exterior layers sandwiching the core layer were formed of the second extrudible composition and the third extrudible composition, respectively. The coextruded film was blown and subsequently subjected to 59% prestretching. The core layer and the exterior layer together formed a prestretched polyethylene film of a total thickness of 19 m. The second extrudible composition provided cling to the prestretched polyethylene film. The third extrudible composition provided a low friction surface to the prestretched polyethylene film.

[0106] The two exterior layers each formed 10% by weight of the total film. The core layer formed 80% by weight of the total film.

[0107] Several tests were performed to analyze the mechanical properties of the prestretched polyethylene film. The results of the tests are summarized in Table 1.

Preparatory Example 2

Prior Art Balewrap (75% Prestretch)

[0108] A first, second and third extrudible composition were prepared according to Preparatory Example 1.

[0109] By means of coextrusion, a core layer was formed of the first extrudible composition and two exterior layers sandwiching the core layer were formed of the second extrudible composition and the third extrudible composition, respectively. The coextruded film was blown and subsequently subjected to 75% prestretching. The core layer and the exterior layer together formed a prestretched polyethylene film of a total thickness of 19 m. The two exterior layers each formed 10% by weight of the total film. The core layer formed 80% by weight of the total film. Several tests were performed to analyze the mechanical properties of the prestretched polyethylene film. The results of the tests are summarized in Table 1.

Preparatory Example 3

Balewrap with Metallocene LLDPE (75% Prestretch)

[0110] A first, second and third extrudible composition were prepared according to Preparatory Example 1 with the exception that the first extrudible composition comprised a LLDPE mixture of a metallocene LLDPE with a density of 916 kg/m.sup.3 and a melt flow index (MI.sub.2 measured at 190 C. with a 2.16 kg weight) of 1.0 g/10 min at a content of 48% by weight and Dowlex 2045S with a density of 918 kg/m.sup.3 at a content of 40.5% by weight based on the total weight of the first extrudible composition.

[0111] By means of coextrusion, a core layer was formed of the first extrudible composition and two exterior layers sandwiching the core layer were formed of the second extrudible composition and the third extrudible composition, respectively. The coextruded film was blown and subsequently subjected to 75% prestretching. The core layer and the exterior layer together formed a prestretched polyethylene film of a total thickness of 19 m. The two exterior layers each formed 10% by weight of the total film. The core layer formed 80% by weight of the total film. Several tests were performed to analyze the mechanical properties of the prestretched polyethylene film. The results of the tests are summarized in Table 1.

Preparatory Example 4

Balewrap with Metallocene LLDPE (75% Prestretch)

[0112] A first, second and third extrudible composition were prepared according to Preparatory Example 1 with the exception that the first extrudible composition comprised a LLDPE mixture of a metallocene LLDPE with a density of 915 kg/m.sup.3 and a melt flow index (MI.sub.2 measured at 190 C. with a 2.16 kg weight) of 1.0 g/10 min at a content of 48% by weight and Dowlex 2045S with a density of 918 kg/m.sup.3 at a content of 40.5% by weight based on the total weight of the first extrudible composition.

[0113] By means of coextrusion, a core layer was formed of the first extrudible composition and two exterior layers sandwiching the core layer were formed of the second extrudible composition and the third extrudible composition, respectively. The coextruded film was blown and subsequently subjected to 75% prestretching. The core layer and the exterior layer together formed a prestretched polyethylene film of a total thickness of 19 m. The two exterior layers each formed 10% by weight of the total film. The core layer formed 80% by weight of the total film. Several tests were performed to analyze the mechanical properties of the prestretched polyethylene film. The results of the tests are summarized in Table 1.

Preparatory Example 5

Balewrap with High Melt Flow Index (75% Prestretch)

[0114] A first, second and third extrudible composition were prepared according to Preparatory Example 1 with the exception that the first extrudible composition comprised a LLDPE mixture of a metallocene LLDPE with a density of 918 kg/m.sup.3 and a melt flow index (MI.sub.2 measured at 190 C. with a 2.16 kg weight) of 2.3 g/10 min at a content of 48% by weight and Dowlex 2045S with a density of 918 kg/m.sup.3 at a content of 40.5% by weight based on the total weight of the first extrudible composition.

[0115] By means of coextrusion, a core layer was formed of the first extrudible composition and two exterior layers sandwiching the core layer were formed of the second extrudible composition and the third extrudible composition, respectively. The coextruded film was blown and subsequently subjected to 75% prestretching. The core layer and the exterior layer together formed a prestretched polyethylene film of a total thickness of 19 m. The two exterior layers each formed 10% by weight of the total film. The core layer formed 80% by weight of the total film. Several tests were performed to analyze the mechanical properties of the prestretched polyethylene film. The results of the tests are summarized in Table 1.

Preparatory Example 6

Inventive Balewrap with LLDPE Substantially Free from Long Chain Branching (LOB) and Having a Density Below 915 kg/m.SUP.3 .(75% Prestretch)

[0116] A first, second and third extrudible composition were prepared according to Preparatory Example 1 with the exception that the first extrudible composition comprised a LLDPE mixture of an LLDPE substantially free from long chain branching and with a density of 912 kg/m.sup.3 and a melt flow index (MI.sub.2 measured at 190 C. with a 2.16 kg weight) of 1.0 g/10 min at a content of 48% by weight and Dowlex 2045S with a density of 918 kg/m.sup.3 at a content of 40.5% by weight based on the total weight of the first extrudible composition.

[0117] By means of coextrusion, a core layer was formed of the first extrudible composition and two exterior layers sandwiching the core layer were formed of the second extrudible composition and the third extrudible composition, respectively. The coextruded film was blown and subsequently subjected to 75% prestretching. The core layer and the exterior layer together formed a prestretched polyethylene film of a total thickness of 19 m. The two exterior layers each formed 10% by weight of the total film. The core layer formed 80% by weight of the total film. Several tests were performed to analyze the mechanical properties of the prestretched polyethylene film. The results of the tests are summarized in Table 1.

Example

Comparison of Balewrap Produced According to Preparatory Examples 1-6

[0118] Balewrap produced according to Preparatory Examples 1-6 was subjected to tensile testing in a tensile tester (LLOYD instruments, LR5K plus) in accordance with the ASTM D882 standard, wherein a strip of film with a width of 20 mm, clamped between two clamps at a distance of 50 mm from each other is stretched at a rate of 500 mm/min until the film breaks. The results are presented in Table 1. At five strips of the each film were measured, and the elongation capability (elongation at break, machine direction, MD) corresponds to the mean value of the measurements.

[0119] The stress required in order to stretch the prestretched film by 70% in the longitudinal direction was read from the tensile strength graph obtained when measuring the elongation percentage at break in accordance with the ASTM D882 standard as described above. The results are presented in Table 1. At least five strips of the film were measured, and the stress at 70% elongation corresponds to the mean value of the measurements.

TABLE-US-00001 TABLE 1 MD MD Stress Elong. Pre- at at Ex. Co- MI.sub.2 Density Stretch 70% break # mon. [g/10 min] [kg/m.sup.3] Cat. LCB [%] [MPa] [%] 1 Octene 1.0 918 ZN No 59% 17.5 367 2 Octene 1.0 918 ZN No 75% 19.5 298 3 Octene 1.0 916 Met. Yes 75% 21.5 289 4 Octene 1.0 915 Met. Yes 75% 22.5 263 5 Octene 2.3 918 ZN No 75% 19.8 331 6 Octene 1.0 912 ZN No 75% 17.7 340

[0120] Examples 1-2 represent prior art balewrap films. Examples 3-5 represent previous attempts by the inventors to produce improved balewrap films, resulting in films having less suitable properties. Only Example 6 resulted in a more prestretched (75%) film having suitable tensile properties for balewrapping.

[0121] Furthermore, more than 1200 bales were produced on various types of bale wrapping machines under various wrapping conditions using the balewrap produced according to Preparatory Example 6. No problems with tearing of the film were observed. Baling operators executing the bale wrapping tests reported that the balewrap produced according to Preparatory Example 6 was less prone to tearing or breakage even compared to the prior art film of Example 1.

[0122] In conclusion, the inventive prestretched polyethylene film produced according to Preparatory Example 6 exhibited mechanical properties that are highly desirable for use as a balewrap or silage film.