Polyethylene film structures for safer collation-shrink films and the process thereof, collation-shrink films and the use thereof

Abstract

This invention relates to a layered film structure comprising a core layer C and outer layers E1 and E2, wherein the core layer C comprises a multimodal polyethylene terpolymer (I) having an MFR5 of 0.5 to 5 g / 10 min and a density of 0.928 to 0.940 g / cm³; and wherein the outer layers E1 and / or E2 comprise a multimodal polyethylene terpolymer (II) having an MFR2 of 0.5 to 10 g / 10 min and a density of 0.920 to 0.935 g / cm³. The invention also relates to a process for manufacturing the layered film structure, a bundled shrink film comprising or composed of the layered film structure, and the use of the bundled shrink film for wrapping articles, wherein the layers of the film structure are co-extruded.

Description

[Technical Field]

[0001] This invention relates to a layered membrane structure comprising a core layer and an outer layer, a process for manufacturing the layered membrane structure by co-extrusion of a permeable layer, a collision shrink film comprising the layered membrane structure, and the use of the collision shrink film for wrapping articles. [Previous Technology]

[0002] Cluster shrink film is a membrane structure that wraps around an object to be packaged and shrinks to hold the units within the object together. The basic principle of cluster shrink is to wrap multiple items in a loose membrane "sleeve" and then pass the wrapped items through a heated shrink tunnel / oven to complete the cluster shrink wrap. The membrane folds around multiple items and secures them in place. The most common use of the membrane is to package multiple containers (items), such as bottles or cans that may contain food, beverages, etc. Cluster shrink film wraps around multiple containers and shrinks around them, such as 6 boxes of beverages or 24 food cans, which may optionally be held in a cardboard tray or cardboard mat.

[0003] Currently, as many as 5% to 10% of goods are still wasted during transportation. Using improved bundled shrink film structures to enhance the stability of the packaged goods can reduce manufacturers' losses. Packaging stability is further affected by current challenges and the overall trend towards reducing film thickness.

[0004] Therefore, in order to be suitable for use as a bundled shrink membrane, the membrane structure needs to have a specific combination of properties: First and foremost, the membrane structure must exhibit good shrinkage performance in order to tightly secure the wrapped items. In addition, a suitable membrane structure needs to have good mechanical properties and good tensile properties, such as high rigidity, especially when considering downgauge capacity and packaging stability.

[0005] In addition, in order to provide sufficient packaging stability and to be able to handle the packaging safely, puncture resistance and tear resistance are the most important properties of bundled shrink film.

[0006] At the same time, in order for the packaging to stand out on the shelf, it also needs a good visual appearance, that is, consumers' perception of the selling points.

[0007] Low-density polyethylene (LDPE) currently dominates the bundled film market due to its excellent shrinkage properties, especially transverse (TD) shrinkage properties. However, it is well known that multimodal linear low-density polyethylene (LLDPE) exhibits significant advantages over LDPE when blended with other linear low-density polyethylene and high-density polyethylene components.

[0008] Therefore, the current solution for bundled shrink membranes is a membrane structure that includes LDPE and LLDPE and / or HDPE. LDPE is necessary to provide high shrinkage, while the LLDPE / HDPE component provides a combination of rigidity, toughness and bundling force (also known as cold shrink force).

[0009] For example, WO 2017 / 055174 discloses a bundled shrink film, which is based on a co-extruded film structure comprising two layers, A and B, each made of a specific ethylene copolymer. [Summary of the Invention]

[0010] One object of the present invention is to provide a membrane structure suitable for use as a bundled shrink membrane that meets the above requirements, particularly a membrane structure having improved stability, shrinkage performance, and excellent visual appearance.

[0011] This invention is based on the discovery that such membrane structures for bundled shrink membranes can be provided by membrane structures comprising a core layer and two outer layers, wherein the core layer and at least one outer layer contain a specially selected ethylene terpolymer.

[0012] Therefore, the present invention provides a layered membrane structure comprising or composed of a core layer C and outer layers E1 and E2, wherein the core layer C comprises or is composed of a multimodal polyethylene terpolymer (I), the multimodal polyethylene terpolymer (I) having an MFR5 of 0.5 to 5 g / 10 min and a density of 0.928 to 0.940 g / cm3; and wherein the outer layers E1 and / or E2 comprise or are composed of a multimodal polyethylene terpolymer (II), the multimodal polyethylene terpolymer (II) having an MFR2 of 0.5 to 10 g / 10 min and a density of 0.920 to 0.935 g / cm3.

[0013] The combination of the core layer C and the outer layers E1 and E2, having the above characteristics, achieves the aforementioned objectives. Specifically, this combination allows for improved shrinkage force of the membrane structure, thereby enhancing the packaging stability used as a bundled shrink film, which has better mechanical properties, provides better packaging security (holding bottles together; using the film to support the packaging without breaking), and simultaneously achieves excellent optical properties.

[0014] Due to the improved shrinkage properties and mechanical properties, the thickness of the bundled film can be reduced, especially for low-thickness packaging (<50 micrometers).

[0015] Typically, multimodal ethylene terpolymer (I) is different from multimodal ethylene terpolymer (II).

[0016] Preferably, in the layered membrane structure, the multimodal ethylene terpolymer (I) is bimodal, and the multimodal ethylene terpolymer (I) is a terpolymer comprising or composed of: a) a low molecular weight homopolymer of ethylene; and b) a high molecular weight terpolymer of ethylene, 1-butene, and C6 to C12 α-olefins.

[0017] Alternatively, the multimodal ethylene terpolymer (I) is a terpolymer comprising or composed of: a) a low molecular weight polymer, which is a binary copolymer of ethylene and C4 to C12 α-olefins; and b) a high molecular weight polymer, wherein if the low molecular weight polymer of a) is a binary copolymer of ethylene and C6 to C12 α-olefins, then the high molecular weight polymer is a binary copolymer of ethylene and 1-butene, or the high molecular weight polymer is a terpolymer of ethylene, 1-butene and C6 to C12 α-olefins.

[0018] Such bimodal ethylene terpolymers are disclosed, for example, in WO 03 / 066698. For definitions of these ethylene terpolymers (e.g., the "modality" of the polymer) and methods of manufacture, please refer to WO 03 / 066698. Furthermore, all embodiments and preferred embodiments of such ethylene terpolymers with densities in the range of 0.928 to 0.940 g / cm³ described in WO 03 / 066698 are also preferred embodiments of the ethylene terpolymer (I) of this invention, whether or not explicitly described herein.

[0019] Preferably, the density of the terpolymer (I) is in the range of 0.930 to 0.939 g / cm3.

[0020] Preferably, the C4 to C12 α-olefin of the low molecular weight copolymer portion is selected from the group consisting of 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene and 1-decene.

[0021] Furthermore, preferably, the C6 to C12 α-olefin of the high molecular weight copolymer portion is selected from the group consisting of 1-hexene, 4-methyl-1-pentene, 1-octene and 1-decene.

[0022] Preferably, the terpolymer (I) comprises or consists of: a) a low molecular weight homopolymer of ethylene; and b) a high molecular weight terpolymer of ethylene, 1-butene and C6 to C12 α-olefins, preferably a high molecular weight terpolymer of ethylene, 1-butene and 1-hexene.

[0023] The weight average molecular weight of the terpolymer (I) is preferably between 190,000 and 400,000 g / mol, more preferably between 200,000 and 300,000 g / mol. The weight average molecular weight of the low molecular weight polymer portion is preferably between 4,500 and 55,000 g / mol, more preferably between 5,000 and 50,000 g / mol; and the weight average molecular weight of the high molecular weight polymer portion is preferably between 450,000 and 1,000,000 g / mol, more preferably between 500,000 and 1,000,000 g / mol.

[0024] The melt flow rate MFR5 of the terpolymer (I) is preferably 0.6 to 4 g / 10 min, more preferably 0.7 to 3 g / 10 min.

[0025] The melt flow rate MFR21 of the terpolymer (I) is preferably 10 to 50 g / 10 min, more preferably 15 to 45 g / 10 min.

[0026] The melt index MFR2 of the low molecular weight polymer portion of the terpolymer (I) is preferably 200 to 800 g / 10 min, more preferably 300 to 600 g / 10 min.

[0027] The terpolymer (I) preferably comprises 30 to 60 wt%, more preferably 35 to 50 wt%, most preferably 38 to 45 wt% of a low molecular weight polymer portion, and the remainder preferably comprises a high molecular weight polymer portion.

[0028] The total monomer content in the overall polymer is preferably 1 to 7 mol, more preferably 2 to 6 mol.

[0029] Preferably, in the low molecular weight polymer, the comonomer content is 0 to 2.5 mol%, more preferably 0 to 2 mol%. In the high molecular weight polymer, the comonomer content is preferably 2.5 to 11 mol%, more preferably 3 to 10 mol%.

[0030] In embodiments in which the terpolymer (I) comprises or is composed of a) a low molecular weight homopolymer of ethylene; and b) a high molecular weight terpolymer of ethylene, 1-butene and 1-hexene, preferably, the content of 1-butene in the final polymer is 1.0 to 2.0 wt%, and the content of 1-hexene is 4.0 to 6.0 wt%.

[0031] Preferably, the viscosity η of the terpolymer (I) at 0.05 rad / s is from 10,000 to 65,000 Pa·s, more preferably from 15,000 to 60,000 Pa·s, and most preferably from 20,000 to 55,000 Pa·s.

[0032] The preferred multimodal terpolymer (I) may also be commercially available BorShape™ from Borealis, such as BorShape™FX1001 and BorShape™FX1002.

[0033] FX1001 is a bimodal LLDPE terpolymer. The low molecular weight fraction is a homopolymer of ethylene with an MFR2 of 400 g / 10 min, preferably produced in a circulating reactor. In the high molecular weight fraction, preferably produced in a gas-phase reactor, ethylene is copolymerized with 1-butene and 1-hexene as comonomers. The final resin has a density of 931 kg / m³ and an MFR5 of 0.85 g / 10 min. The low molecular weight fraction / high molecular weight fraction distribution (LMW / HMW) is 39 / 61. The Mw / Mn of FX1001 is about 14 (13 to 15). In the final polymer, the content of 1-butene is 1.5 wt%, and the content of 1-hexene is 5.5 wt%. The viscosity η, measured at 0.05 rad / s, is 52000 (+ / -5000) Pa·s.

[0034] FX1002 is a bimodal MDPE terpolymer. The low molecular weight fraction is a homopolymer of ethylene with an MFR2 of 400 g / 10 min, preferably produced in a circulating reactor. In the high molecular weight fraction, preferably produced in a gas-phase reactor, ethylene is copolymerized with 1-butene and 1-hexene as comonomers. The final resin has a density of 937 kg / m³, an MFR5 of 2 g / 10 min, and an MFR21 of 42 g / 10 min. The low molecular weight fraction / high molecular weight fraction distribution (LMW / HMW) is 43 / 57. The Mw / Mn of FX1002 is about 12 (11 to 13). In the final polymer, the content of 1-butene is 1.5 wt%, and the content of 1-hexene is 4.5 wt%. The viscosity η, measured at 0.05 rad / s, is 23000 (+ / -3000) Pa·s.

[0035] The multimodal ethylene terpolymer (II) of the layered membrane structure of the present invention preferably comprises or is composed of a multimodal polymer of ethylene and at least two different comonomers, wherein the comonomers are selected from α-olefins having 4 to 10 carbon atoms, the multimodal polymer having an MFR21 / MFR2 ratio of 13 to 30, and a MWD of 5 or lower.

[0036] Such multimodal ethylene terpolymers are disclosed, for example, in WO 2016 / 083208. For definitions of these ethylene terpolymers (e.g., the "modality" of the polymer) and methods of manufacture, please refer to WO 2016 / 083208. Furthermore, all embodiments and preferred embodiments of such ethylene terpolymers with densities in the range of 0.910 to 0.935 g / cm³ described in 2016 / 083208 are also preferred embodiments of the ethylene terpolymer (II) of this invention, whether or not explicitly described herein.

[0037] The MFR2 of the multimodal ethylene terpolymer (II) is preferably in the range of 0.5 to 2 g / 10 min, more preferably in the range of 0.8 to 1.6 g / 10 min.

[0038] Preferably, the density of the multimodal ethylene terpolymer (II) is 0.920 to 0.933 g / cm3, more preferably 0.923 to 0.930 g / cm3.

[0039] Preferably, the MFR21 / MFR2 ratio of the multimodal ethylene terpolymer (II) is 15 to 30, more preferably 15 to 25.

[0040] The at least two α-olefin comonomers having 4 to 10 carbon atoms in the multimodal ethylene terpolymer (II) are preferably 1-butene and 1-hexene.

[0041] Preferably, the total amount of comonomers present in the multimodal ethylene terpolymer (II) is 0.5 to 10 mol%, more preferably 1.0 to 8 mol%, more preferably 1.0 to 5 mol%, more preferably 1.5 to 5.0 mol%, and most preferably 1.1 to 3.0 mol%.

[0042] The multimodal ethylene terpolymer (II) is preferably a bimodal terpolymer, which preferably comprises or is composed of an ethylene polymer component (A) and an ethylene polymer component (B).

[0043] Preferably, the MFR2 of the ethylene polymer component (A) is higher than that of the ethylene polymer component (B).

[0044] More preferably, the MFR2 of the ethylene polymer component (A) is 1 to 50 g / 10 min, more preferably 1 to 40 g / 10 min, more preferably 1 to 30 g / 10 min, more preferably 2 to 20 g / 10 min, more preferably 2 to 15 g / 10 min, and even more preferably 2 to 10 g / 10 min.

[0045] Preferably, the ratio of the MFR2 of the ethylene polymer component (A) to the MFR2 of the ethylene polymer component (II) is 2 to 50, more preferably 5 to 40, more preferably 10 to 30, more preferably 10 to 25, and even more preferably 15 to 25.

[0046] Preferably, the ratio of the MFR2 of the ethylene polymer component (A) to the MFR2 of the final multimodal terpolymer is 2 to 10.

[0047] Preferably, the ethylene polymer component (A) contains a comonomer that is different from that of the ethylene polymer component (B).

[0048] Preferably, the amount (mol%) of comonomers in the ethylene polymer component (A) is lower than that in the ethylene polymer component (B). More preferably, the ratio of [the amount (mol%) of α-olefin comonomers having 4 to 10 carbon atoms present in the ethylene polymer component (A)] to [the amount (mol%) of at least two α-olefin comonomers having 4 to 10 carbon atoms in the final multimodal polymer (a) of ethylene] is 0.2 to 0.6, more preferably 0.25 to 0.5.

[0049] Preferably, the α-olefin comonomer having 4 to 10 carbon atoms in the ethylene polymer component (A) is 1-butene, and the α-olefin comonomer having 4 to 10 carbon atoms in the ethylene polymer component (B) is 1-hexene.

[0050] The amount of comonomer in the ethylene polymer component (A) is preferably 0.15 to 1.0 mol.

[0051] Preferably, the amount of comonomer in the ethylene polymer component (B) is 1.5 to 3.5 mol.

[0052] Preferably, the density of the ethylene polymer component (A) is different from the density of the ethylene polymer component (B), and preferably higher than the density of the ethylene polymer component (B).

[0053] The density of the ethylene polymer component (A) is preferably 0.925 to 0.950 g / cm3, more preferably 0.930 to 0.945 g / cm3, and most preferably 0.935 to 0.940 g / cm3.

[0054] Preferably, based on the total amount (100 wt%) of the multimodal terpolymer, the multimodal ethylene terpolymer (II) comprises: an ethylene polymer component (A) having a content of 30 to 70 wt%, more preferably 40 to 60 wt%, more preferably 35 to 50 wt%, more preferably 40 to 50 wt%; and an ethylene polymer component (B) having a content of 70 to 30 wt%, more preferably 60 to 40 wt%, more preferably 50 to 65 wt%, more preferably 50 to 60 wt%.

[0055] Preferably, the multimodal ethylene terpolymer (II) is composed of ethylene polymer component (A) and ethylene polymer component (B) as the only polymer components. Therefore, the distribution between ethylene polymer component (A) and ethylene polymer component (B) is (30 to 70):(70 to 30), more preferably (40 to 60):(60 to 40), more preferably (35 to 50):(65 to 50), and even more preferably (40 to 50):(60 to 50).

[0056] As a preferred option, the multimodal ethylene terpolymer (II) may also be a commercially available AnteoTM with the properties required herein, such as AnteoTMFK2715, available from Borealis or Borouge.

[0057] Preferably, in the layered membrane structure according to the invention, the core layer C contains 30 wt% or more, more preferably 40 wt% or more of the multimodal ethylene terpolymer (I).

[0058] In addition to the multimodal ethylene terpolymer (I), the core layer C may also contain low-density polyethylene (LDPE). LDPE is well known in the art to which this invention pertains and is often manufactured at high pressure in tubular reactors or autoclaves.

[0059] LDPE and its manufacturing process are described, for example, on page 9, line 29 to page 12, line 6 of the referenced WO 2017 / 055174.

[0060] Preferably, if LDPE is present in the core layer, its content is 10 to 60 wt%, more preferably 20 to 50 wt%.

[0061] The density of LDPE used in layer C is preferably 0.900 to 0.940 g / cm3, more preferably 0.910 to 0.930 g / cm3, and most preferably 0.915 to 0.925 g / cm3.

[0062] Preferably, the MFR2 of the LDPE used in layer C is 0.01 to 5 g / 10 min, more preferably 0.05 to 3 g / 10 min, even more preferably 0.1 to 2 g / 10 min, and most preferably 0.15 to 1 g / 10 min.

[0063] In addition, the core layer C may also comprise high-density polyethylene (HDPE). HDPE is also well known in the technical field to which this invention pertains and is frequently manufactured in polymerization processes using catalysts.

[0064] Preferably, if HDPE is present in the core layer, its content is 2.5 to 20 wt%, more preferably 5 to 15 wt%.

[0065] The density of the HDPE used in layer C is preferably 0.950 to 0.970 g / cm3, more preferably 0.955 to 0.965 g / cm3.

[0066] Preferably, the HDPE used in layer C is an ethylene homopolymer.

[0067] Preferably, the MFR2 of the HDPE used in layer C is 0.05 to 10 g / 10 min, more preferably 0.1 to 5 g / 10 min, even more preferably 0.2 to 3 g / 10 min, and most preferably 0.4 to 1.5 g / 10 min.

[0068] In one embodiment, the core layer C is composed of a multimodal ethylene terpolymer (I), LDPE and HDPE as defined herein.

[0069] However, in other embodiments, the core layer C may also be composed of 100 wt% of a multimodal ethylene terpolymer (I), especially if the membrane structure comprises more than 3 layers.

[0070] In any of the embodiments described herein with respect to polymer compositions that can be used for layer E1 and / or layer E2, the outer layers E1 and E2 of the layered film structure of the present invention may be made of the same polymer composition or different polymer compositions. Preferably, E1 and E2 are made of the same polymer composition.

[0071] Preferably, the outer layers E1 and / or E2 contain 60 wt% or more, more preferably 70 wt% or more of the multimodal ethylene terpolymer (II).

[0072] In addition to the multimodal ethylene terpolymer (II), the outer layers E1 and / or E2 may also contain low-density polyethylene (LDPE).

[0073] Preferably, if LDPE is present in the outer E1 and / or E2, its content is 5 to 35 wt%, more preferably 10 to 30 wt%, and even more preferably 15 to 25 wt%.

[0074] The density of LDPE used in layers E1 and / or E2 is preferably 0.905 to 0.945 g / cm3, more preferably 0.915 to 0.935 g / cm3, and most preferably 0.918 to 0.927 g / cm3.

[0075] Preferably, the MFR2 of the LDPE used in layers E1 and / or E2 is 0.05 to 10 g / 10 min, more preferably 0.1 to 5 g / 10 min, even more preferably 0.2 to 3 g / 10 min, and most preferably 0.4 to 1.5 g / 10 min.

[0076] In one embodiment, the outer layers E1 and / or E2 are composed of a multimodal ethylene terpolymer (II) and LDPE as defined herein.

[0077] The layered membrane structure according to the present invention may be composed of a core layer C and outer layers E1 and E2, but it may further include one or more intermediate layers I between the outer layers E1 and / or E2 and the core layer C. For example, the layered membrane structure may be a five-layer membrane structure E1 / I1 / C / I2 / E2.

[0078] If an intermediate layer I is present, it preferably contains or is composed of LDPE.

[0079] The density of the LDPE used in layer I is preferably 0.905 to 0.945 g / cm3, more preferably 0.915 to 0.935 g / cm3, and most preferably 0.918 to 0.927 g / cm3.

[0080] Preferably, the MFR2 of the LDPE used in layer I is 0.05 to 10 g / 10 min, more preferably 0.1 to 5 g / 10 min, even more preferably 0.2 to 3 g / 10 min, and most preferably 0.4 to 1.5 g / 10 min.

[0081] If there is more than one intermediate layer I, they can be made of the same or different materials.

[0082] The thickness of the layered membrane structure of the present invention according to any embodiment described herein is preferably 60 micrometers or less, more preferably 50 micrometers or less.

[0083] The thickness of the core layer C in the layered membrane structure of the present invention is preferably 35 to 75% of the total thickness of the membrane structure, and more preferably 40 to 70% of the total membrane thickness.

[0084] If the membrane structure of the present invention is composed of layer E1, layer C and layer E2, the thickness of the core layer C is preferably 45 to 75% of the total thickness of the membrane structure, and more preferably 50 to 70% of the total membrane thickness.

[0085] If the membrane structure of the present invention is composed of layer E1, layer I1, layer C, layer I2 and layer E2, the thickness of the core layer C is preferably 35 to 65% of the total thickness of the membrane structure, and more preferably 40 to 60% of the total membrane thickness.

[0086] The thickness of outer layer E1 and / or outer layer E2 is preferably 5 to 25% of the total thickness of the membrane structure.

[0087] If the membrane structure of the present invention is composed of layer E1, layer C and layer E2, the thickness of outer layer E1 and / or outer layer E2 is preferably 10 to 25% of the total thickness of the membrane structure, more preferably 15 to 25% of the total membrane thickness.

[0088] If the membrane structure of the present invention is composed of layer E1, layer I1, layer C, layer I2 and layer E2, the thickness of outer layer E1 and / or outer layer E2 is preferably 5 to 20% of the total thickness of the membrane structure, more preferably 7.5 to 15% of the total membrane thickness.

[0089] Based on the total weight of the layered membrane structure, the layered membrane structure of the present invention preferably comprises at least 90 wt%, more preferably at least 95 wt%, and most preferably at least 98 wt% of an ethylene polymer. Preferably, based on the total weight of the layered membrane structure, the layered membrane structure comprises 90 to 100 wt%, more preferably 95 to 100 wt%, and most preferably 98 to 100 wt% of an ethylene polymer. Preferably, the layered membrane structure consists only of one or more ethylene polymers. The ethylene polymer includes: ethylene homopolymers; and / or copolymers of ethylene with propylene and / or any α-olefin having 4 to 10 carbon atoms. In one embodiment, the layered membrane structure does not contain non-olefin polymers, and preferably does not contain non-ethylene polymers.

[0090] Any layer of this layered membrane structure may contain additives, such as stabilizers, processing aids, and / or pigments. Examples of such additives are antioxidants, UV stabilizers, acid scavengers, nucleating agents, anti-caking agents, slip agents, and polymer processing agents (PPA). Additives may be present in the same or different amounts in some layers of the layered membrane structure or in only one layer. For example, the outer layer may contain slip agents and anti-caking agents.

[0091] Typically, each additive may be present in an amount from 0 to 5000 ppm, based on the total weight of the individual layers of the layered membrane structure. Additives are typically available from several suppliers and are included in the composition as a single additive or as a mixture of two or more additives. Such components may typically be present in the one or more layers in an amount from 0 to 5 wt%, based on the weight of the respective layer of the layered membrane structure.

[0092] The longitudinal (machine direction) contraction force of the layered membrane structure of the present invention is preferably 2.0 N or higher, more preferably 2.1 N or higher.

[0093] Furthermore, preferably, the layered film structure of the present invention has a longitudinal shrinkage rate of 75% or higher in oil at 165°C.

[0094] The present invention also relates to a process for manufacturing a layered film structure according to any of the above embodiments, wherein the layers of the film structure are co-extruded.

[0095] The different polymer components in any layer of the film are typically thoroughly mixed before forming the layers, for example using a twin-screw extruder, preferably an anti-rotation extruder. The blend is then converted into a co-extruded film structure. Preferably, the blend is converted into a co-extruded film structure on a blown film production line.

[0096] To manufacture such multilayer films according to the invention, at least two polymer melt streams are typically extruded simultaneously (i.e., co-extruded) through a multi-channel tubular, annular, or circular die to form a tubular structure, which is then inflated, energized, and / or cooled with air (or a mixture of gases) to form a film. The manufacture of blown films is a well-known process.

[0097] Blow co-extrusion can be carried out at temperatures ranging from 160°C to 240°C and cooled by blowing in gas (usually air) at temperatures ranging from 10°C to 50°C to provide a frost line height of 1 to 8 times the die diameter.

[0098] The blow-up ratio (BUR) should generally be in the range of 1.2 to 6, preferably in the range of 1.5 to 4.

[0099] The layered membrane structure of the present invention can also be processed by a stretching step, wherein the membrane is longitudinally stretched (MDO) after it is manufactured. Stretching can be performed using any conventional stretching apparatus well known to those skilled in the art to which this invention pertains, through any conventional technique.

[0100] The present invention also relates to a bundled shrink film comprising or composed of a layered film structure according to any embodiment described herein, and the present invention also relates to the use of said bundled shrink film for wrapping articles.

Implementation Method

[0102] Measurement and Determination Methods

[0103] Unless otherwise defined, the following definitions and determination methods apply to the above general description of the invention and the following embodiments. a) Measurement of melt flow rate (MFR)

[0104] Mel flow rate (MFR) is determined according to ISO 1133 and expressed in g / 10min. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR of polyethylene is determined at 190°C under loads of 2.16 kg (MFR2), 5.00 kg (MFR5), or 21.6 kg (MFR21).

[0105] The quantity of FRR (flow rate ratio) is an indicator of molecular weight distribution and represents the flow rate ratio under different loads. Therefore, FRR21 / 5 represents the value of MFR21 / MFR5. b) Density

[0106] For compression-molded specimens prepared according to EN ISO 1872-2 (February 2007), the density of the polymer shall be measured according to ISO 1183-1:2019 (Method A) and expressed in g / cm3. c) Viscosity

[0107] In dynamic shear measurement conforming to ISO standards 6721-1 and 6721-10, the viscosity η at 0.05 rad / s was measured at 190°C using a parallel plate dynamic frequency sweep. This measurement was performed on an Anton Paar MCR501 stress-controlled rotational rheometer equipped with a 25 mm parallel plate geometry. Measurements were taken on a compression-molded plate using a nitrogen atmosphere and with the strain set within the linear viscoelastic range. Oscillatory shear tests were performed at 190°C using frequencies ranging from 0.01 to 600 rad / s and a gap of 1.3 mm. d) Shrinkage force / shrinkage rate

[0108] The longitudinal and transverse shrinkage properties of the bundled shrink film were tested using Retratech equipment (according to ISO 14616) and an oil bath (according to DIN 55543-4). e) Mechanical properties: tensile modulus

[0109] The TD (transverse) and MD (longitudinal) of the membrane. For the blown membrane of this embodiment, according to ISO 527-3, the longitudinal and transverse tensile moduli of the membrane with a thickness of 25 micrometers or 40 micrometers are determined at a crosshead speed of 1 mm / min. Trouser Tear Method

[0110] Applicable to measurements in the longitudinal (machine direction, MD) and transverse (TD) directions. Tear resistance is measured using the ISO 6383-1 method.

[0111] For a rectangular specimen with a longitudinal slit extending more than half its length, a tensile test is performed on the "trouser legs" formed by the slit. The tear resistance of the test material is calculated using the average force required to completely tear the specimen along its length.

[0112] Test machine: Zwick Z1.0

[0113] Sample: 150 mm long, 50 mm wide, with a narrow 75 mm slit and a thickness of 45 mm.

[0114] Calculate the tear resistance of the specimen [N / mm] according to the formula Ft / d, where:

[0115] Ft is the tearing force of the sample [N], and d is the thickness of the sample [mm]. f) Optical properties

[0116] Gloss, transparency, and haze are determined according to ASTM D2457 (Gloss) and ASTM D1003 (Haze and Transparency) as measures of the film's visual appearance. Therefore, gloss is determined at a 45° angle according to ISO 2813 (ASTM D2457). g) Processability

[0117] Processability is measured by the maximum pressure required to extrude the film structure in the extruder (see Table 3). h) GPC (1) Conventional GPC method

[0118] Unless otherwise stated, GPC standard methods are used to measure ethylene polymers other than LDPE.

[0119] The average molecular weight (Mz, Mw, and Mn), molecular weight distribution (MWD), and their width are generally determined by gel permeation chromatography (GPC) according to ISO 16014-1:2003, ISO 16014-2:2003, ISO 16014-4:2003, and ASTM D 6474-12, using the following formulas, where the molecular weight distribution (MWD) and its width are described by the polydispersity index PDI = Mw / Mn (where Mn is the number average molecular weight and Mw is the weight average molecular weight): (1) (2) (3)

[0120] For a constant elution volume interval ΔVi, where Ai and Mi are the chromatographic peak slice area and the molecular weight (MW) of the polyolefin associated with the elution volume Vi, respectively, and N is equal to the number of data points obtained from the chromatogram between the integral limits.

[0121] A high-temperature GPC instrument equipped with an infrared (IR) detector (IR4 or IR5 from PolymerChar (Valencia, Spain)) or a differential refractometer (RI) (from Agilent Technologies, equipped with three Agilent-PLgel Olexis columns and one Agilent-PLgel Olexis Guard column) was used. 1,2,4-trichlorobenzene (TCB) stabilized with 250 mg / L 2,6-di-tert-butyl-4-methylphenol was used as the mobile phase. The chromatography system was operated at a column temperature of 160 °C, a detector temperature of 160 °C, and a constant flow rate of 1 mL / min. 200 μL of sample solution was injected for each analysis. Data collection was performed using Agilent Cirrus software version 3.3 or PolymerChar GPC-IR control software.

[0122] The column assembly was calibrated using 19 narrow MWD polystyrene (PS) standards ranging from 0.5 kg / mol to 11500 kg / mol. The PS standards were dissolved at room temperature for several hours. The conversion of the peak molecular weight of polystyrene to the molecular weight of polyolefins was performed using the Mark-Howwink equation and the following Mark-Howwink constants: KPS = 19 x 10⁻³ mL / g, αPS = 0.655; KPE = 39 x 10⁻³ mL / g, αPE = 0.725.

[0123] The calibration data were fitted using a third-order polynomial fit.

[0124] All samples were prepared at a concentration of approximately 1 mg / ml and PE was dissolved in freshly distilled TCB stabilized with 250 ppm Irgafos168 at 160°C for 3 (tri) hours with continuous gentle shaking. (2) GPC viscosity method

[0125] The average molecular weight (Mz, Mw, and Mn) and molecular weight distribution (MWD) of LDPE were measured using a universally corrected method via GPC viscosity. The average molecular weight (Mw, Mn), molecular weight distribution (MWD), and their widths were determined according to ISO 16014-4 2019 via gel permeation chromatography (GPC), where the molecular weight distribution (MWD) and its width are described by the polydispersity index PDI = Mw / Mn (where Mn is the number average molecular weight and Mw is the weight average molecular weight). A PL 220 (Polymer Laboratories) GPC equipped with an IR4 infrared detector and an online four-capillary bridge viscometer (PL-BV 400-HT) was used. Three Olexis columns and one Olexis Guard column, purchased from Polymer Laboratories, were used as the stationary phase, and 1,2,4-trichlorobenzene (TCB, stabilized with 250 mg / L 2,6-di-tert-butyl-4-methylphenol) was used as the mobile phase at a constant flow rate of 1 mL / min at 160 °C. 200 μL of sample solution was injected for each analysis. The corresponding detector constant and inter-detector delay volume of the viscometer were determined using a narrow molecular weight distribution PS standard (MWD = 1.01) with a molar mass of 132,900 g / mol and an intrinsic viscosity of 0.4789 dl / g. The detector constant of the IR4 detector was determined using NIST 1475a, with a dn / dc of 0.094 cm³ / g.

[0126] The column assembly was calibrated using at least 15 narrow MWD polystyrene (PS) standards ranging from 0.5 kg / mol to 11600 kg / mol, using a general calibration method (according to ISO 16014-2:2019). The corresponding intrinsic viscosity of the PS standards was calculated from their corresponding concentration (IR4), the online viscometer signal, and the determined polystyrene detector constant. For low molecular weight PS with a molar mass below 3000 g / mol, the initial weight out concentration was used due to the end group effect in the IR detector.

[0127] The molecular weight (M2) of each chromatographic slice using the universal correction method can be calculated by the following formula: logM1[η1] = VR = logM2[η2] Where: M1 is the molar mass of PS, η1 is the intrinsic viscosity of PS, M2 is the molar mass of the sample, η2 is the intrinsic viscosity of the sample, and VR is the retention volume.

[0128] All data processing and calculations were performed using Cirrus Multi-Offline SEC software version 3.2 (Polymer Laboratories a Varian inc. Company).

[0129] All samples were prepared by dissolving 5.0 to 9.0 mg of polymer (at 160°C) in 8 mL of stabilized TCB (same as the mobile phase) under continuous gentle shaking, with a maximum dissolution time of 2.5 hours for PP and a maximum dissolution time of 3 hours for PE. i) Thickness

[0130] Determine the film thickness according to ASTM D6988. j) Comonomer content

[0131] The comonomer content was determined according to the description on pages 31 to 34 of WO2019 / 081611. Example

[0132] Seven layered membrane structures (three according to the examples and four according to the comparative examples) were produced on an Alpine multilayer blown film equipment. All membrane structures were produced under the same processing conditions (BUR 1:3, thickness 45 micrometers, die-gap 1.5 mm, die diameter 300 mm, low neck-height, internal bubble cooling, and cooling air temperature of 22°C). The pressure and temperature process conditions are shown in Table 3.

[0133] The polymers used to manufacture the layered film structures of the embodiments and comparative examples of the present invention are shown in Table 1. Table 1: Resin Name Manufacturer type MFR 190℃ / 2.16 kg (g / 10min) Density (kg / m³) 3 ) Slip aids and anti-caking agents MDPE1 Bimodal terpolymer MDPE 1.3 927 none FX1001 Borealis terpolymer LLDPE 0.85* 931 none FX1002 Borealis terpolymer LLDPE 2* 937 none Supertough 32ST05 Total Metallocene C2 to C6 copolymers 0.5 932 none Enable 4002MC ExxonMobil Metallocene C2 to C6 copolymer MDPE 0.25 940 none Enable 2703CH ExxonMobil Metallocene C2 to C6 copolymers 0.30 927 none Enable 3505CH ExxonMobil Metallocene C2 to C6 copolymer MDPE 0.50 935 none HTA 108 ExxonMobil Homo HDPE 0.7 961 none FT5236 Borealis tubular LDPE 0.75 923 have FT5230 Borealis tubular LDPE 0.75 923 none FB1350 Borealis tubular MDPE 0.6* 935 none FT3200 Borealis tubular LDPE 0.25 920 none * MFR 190℃ / 5 kg As resin "MDPE1", the commercially available product AnteoTMFK2715 (purchased from Borealis or Borouge) was used in all examples.

[0134] The composition and structure of the manufactured layered membranes are shown in Table 2. The thickness of each layer is expressed as a percentage of the total membrane thickness. The total thickness of all membranes produced is 45 micrometers. In Table 2, "E" represents the outer layer, "C" represents the core layer, and "I" represents the intermediate layer. The outer and intermediate layers of the manufactured membranes have the same composition and thickness. Table 2: Examples / Comparative Examples Layered structure Total density (g / cm³) 3 ) Core layer composition: Polymer / Amount wt% Core thickness; density (g / cm³) 3 ) Outer layer composition: Polymer / Amount wt% Outer layer thickness; density (g / cm³) 3 ) The intermediate layer consists of: Intermediate layer thickness; density (g / cm³) 3 ) IE1 E / C / E 0.929 FX1002 FT3200 HTA108 46 44 10 60%; 0.932 MDPE1 FT5236 80 20 20%; 0.926 IE2 E / C / E 0.929 FX1001 FT3200 HTA108 60 30 10 60%; 0.930 MDPE1 FT5236 80 20 20%; 0.926 IE3 E / I / C / I / E 0.931 FX1002 100 50%; 0.937 MDPE1 FT5236 80 20 10%; 0.926 FT5236 15%; 0.923 CE1 E / C / E 0.930 Enable4002MC FT3200 HTA108 44 46 10 60%; 0.933 MDPE1 FT5236 80 20 20%; 0.926 CE2 E / C / E 0.929 Enable2703CH FT3200 HTA108 65 20 15 60%; 0.930 MDPE1 FT5236 80 20 20%; 0.926 CE3 E / C / E 0.929 Supert. 32ST05 FT3200 HTA108 60 30 10 60%; 0.931 MDPE1 FT5236 80 20 20%; 0.926 CE4 E / C / E 0.930 Enable3505CH FT3200 HTA108 60 30 10 60%; 0.933 MDPE1 FT5236 80 20 20%; 0.926

[0135] For simplicity, in all diagrams, only the main core layer components are mentioned in the diagram labels to indicate the laminar membrane.

[0136] The following tests were performed on the manufactured laminar membrane: Shrinkage force / shrinkage rate

[0137] As shown in Figure 1, the shrinkage force of the membrane structure according to the present invention (~2.2 to 2.4 N) is higher than that of the membrane structure of the comparative example (≤1.9 N). The high shrinkage force is beneficial for stronger fixation of articles wrapped in the membrane. At the same time, the longitudinal shrinkage rate (Figure 2) is also on average at a high level (~78% vs. 75%). Mechanical Properties

[0138] The mechanical property data shown in Figure 3 demonstrate that the membrane structure of the present invention also maintains good mechanical properties in other aspects. For example, in terms of TD tear resistance, the strength of IE2 and IE3 is almost twice that of the comparative example. Equally good performance is shown in the TD and MD tensile moduli of the embodiments of the present invention. Optical Properties

[0139] Figure 4 shows excellent optical properties, which remain unchanged as required. The 5-layer version (IE3) has slightly higher haze, but it is still acceptable. Processability

[0140] Referring to Table 3 and Figure 5, the maximum pressure (Ø450 bar) of the embodiments of the present invention is consistently lower than the maximum pressure (Ø480 bar) of the comparative examples. Lower pressure indicates better processability. IE2 is a reasonable exception due to the presence of FX1001, which has lower viscosity, but this is a useful trade-off with the other properties. Table 3: Extruder (melt pressure, bar) name A B C D E F G outer layer Core layer inner layer IE1 319 290 441 447 444 330 309 IE2 312 295 548 542 546 341 319 IE3 320 268 464 436 446 290 317 CE1 343 309 510 448 493 352 326 CE2 347 316 509 512 508 357 332 CE3 345 310 480 481 481 351 327 CE4 342 308 473 456 461 349 325 Extruder (temperature, °C) name A B C D E F G outer layer Core layer inner layer IE1 214 223 238 239 233 222 227 IE2 214 224 258 254 243 222 227 IE3 215 209 239 238 230 212 227 CE1 214 220 240 243 229 222 227 CE2 214 221 241 247 229 222 227 CE3 215 222 231 237 219 222 227 CE4 215 220 239 244 229 222 227 [Simplified Explanation of the Diagram]

[0101] In the following, the present invention will be further described by way of embodiments with reference to the accompanying drawings, in which: Figure 1 shows the shrinkage performance of the tested membrane structure; Figure 2 shows the shrinkage rate of the tested membrane structure in oil; Figure 3 shows the mechanical properties of the tested membrane structure; Figure 4 shows the optical properties of the tested membrane structure; and Figure 5 shows the processability of the components used to produce the membrane structure.

Claims

1. A layered membrane structure for a bundled shrink membrane, comprising a core layer C and outer layers E1 and E2, wherein, The core layer C comprises a multimodal polyethylene terpolymer (I) having a multimodal molecular weight distribution, having an MFR5 of 0.5 to 5 g / 10 min as determined according to ISO 1133 and a density of 0.928 to 0.940 g / cm3, and wherein the outer layers E1 and E2 comprise a multimodal polyethylene terpolymer (II) having a multimodal MFR2 distribution, having an MFR2 of 0.5 to 10 g / 10 min as determined according to ISO 1133 and a density of 0.920 to 0.935 g / cm3, wherein the core layer C is located between the outer layers E1 and E2, and wherein the outer layers E1 and E2 comprise 60 wt% or more of the multimodal polyethylene terpolymer (II).

2. The layered membrane structure as described in claim 1, wherein, The multimodal ethylene terpolymer (I) is bimodal, and the multimodal ethylene terpolymer (I) is a terpolymer comprising: a) a low molecular weight homopolymer of ethylene; and b) a high molecular weight terpolymer of ethylene, 1-butene, and C6 to C12 α-olefins; or the multimodal ethylene terpolymer (I) is a terpolymer comprising: a) a low molecular weight polymer, which is a binary copolymer of ethylene and C4 to C12 α-olefins; and b) a high molecular weight polymer, wherein if the low molecular weight polymer of a) is a binary copolymer of ethylene and C6 to C12 α-olefins, then the high molecular weight polymer is a binary copolymer of ethylene and 1-butene, or the high molecular weight polymer is a terpolymer of ethylene, 1-butene, and C6 to C12 α-olefins.

3. The layered membrane structure as described in claim 1, wherein, The multimodal ethylene terpolymer (II) comprises a multimodal polymer of ethylene and at least two different comonomers selected from α-olefins having 4 to 10 carbon atoms, wherein the MFR21 / MFR2 ratio of the multimodal polymer is 13 to 30 and the MWD is 5 or lower.

4. The layered membrane structure as described in any one of claims 1 to 3, wherein, The membrane structure further includes one or more intermediate layers (I) located between one of the outer layers E1 and / or E2 and the core layer C.

5. The layered membrane structure as described in any one of claims 1 to 3, wherein, The core layer C contains 30 wt% or more of the multimodal ethylene terpolymer (I).

6. The layered membrane structure as described in any one of claims 1 to 3, wherein, The thickness of the membrane structure is 60 micrometers or less.

7. The layered membrane structure as described in any one of claims 1 to 3, wherein, The thickness of the core layer C is 35% to 70% of the total thickness of the membrane structure.

8. The layered membrane structure as described in any one of claims 1 to 3, wherein, The thickness of the outer layers E1 and / or E2 is 10 to 25% of the total thickness of the membrane structure.

9. The layered membrane structure as described in any one of claims 1 to 3, wherein, The outer layers E1 and E2 have the same composition.

10. The layered membrane structure as described in any one of claims 1 to 3, wherein, The membrane structure has a longitudinal shrinkage force of 2.0 N or higher, as determined according to ISO 14616.

11. The layered membrane structure as described in any one of claims 1 to 3, wherein, The membrane structure has a longitudinal shrinkage rate of 75% or higher in oil at 165°C, as determined according to ISO 14616.

12. A process for manufacturing a layered film structure for a bundled shrink film as described in any one of claims 1 to 11, wherein, These layers of the membrane structure are co-extruded.

13. A bundled shrink membrane comprising or composed of a layered membrane structure as described in any one of claims 1 to 11.

14. Use of a bundled shrink film as described in claim 13 for wrapping articles.

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