Multi-layer finishing shrink film

Abstract

The present invention relates to a multilayer finished shrink film comprising at least three layers wherein the core layer (B) comprises at least (B1) at least 50% by weight, based on the total weight of the core layer (B), of recycled LDPE having a specific linear copolymer of ethylene when at 180 DEG C, and (B2) at least 50% by weight, based on the total weight of the core layer (B), of a specific linear copolymer of ethylene. And a strain hardening factor measured at a strain rate of 3.0 s-1 and a Hungry strain of 2.5. The invention further relates to a method for producing the multilayer film and to the use of the multilayer film in the field of secondary packaging.

Description

Technical Field

[0001] The present invention relates to a multilayer collation shrink film comprising at least three layers, wherein the core layer (B) comprises at least (B1) recycled LDPE in an amount of at least 50 wt. %, based on the total weight of the core layer (B), and (B2) a specific linear copolymer of ethylene, the recycled LDPE having a thermal conductivity of 1.5 to 5.0 when heated at 180° C. at 3.0 s -1 The invention further relates to a method for producing the multilayer film and the use of the multilayer film in the field of secondary packaging. Background Art

[0002] Nowadays, for ecological reasons and to reduce costs, attempts to use polymers obtained from waste materials to manufacture new products are gaining more and more attention and importance. Due to the increasing environmental problems caused by plastics, the focus today is on the recycling of these plastics.

[0003] Secondary packaging, such as collation shrink film, does not require food approval, and a significant amount of recycled material is generated from flexible applications. Due to its original material design, this material's best use is in flexible applications. Therefore, secondary packaging is a perfect application for recycled plastics. However, its use is limited due to the lower performance of recycled materials. However, multilayer collation shrink films containing recycled plastics are also known in the prior art.

[0004] WO 91 / 17886 A1 relates to combining the advantageous high shrinkage but low shrink force of multilayer heat shrinkable films with the use of recycled scrap of such films to provide multilayer heat shrinkable films that retain these advantageous properties. An exemplary film is a core of a blend of a certain linear low density polyethylene and a certain highly branched low density polyethylene sandwiched between two relatively thin outer layers of a propylene / ethylene copolymer, wherein the core also comprises recycled scrap of the multilayer film.

[0005] DE 20 2018 101 226 U1 relates to a packaging for bottles or cans having the following components: 1) an outer packaging for at least partially repackaging the bottle or can, the outer packaging consisting of a heat-shrinkable plastic film, and 2) a handle fastened to the outer packaging by means of a handle attachment, wherein all components of the packaging consist of at least one recyclable plastic and wherein the handle attachment consists of a printable plastic and has an imprint.

[0006] In most multi-layer collation shrink films, it is not possible to use more than 25% recycled material without significantly degrading the mechanical properties. The heterogeneity of contaminants from the original use, collection, and recycling of flexible materials increases the risk of hole formation in ovens (e.g., shrink ovens). Due to this heterogeneity, LDPE is the material most susceptible to hole formation.

[0007] Based on this, one object of the present invention is to provide a multilayer collation shrink film that allows the use of relatively large amounts of recycled LDPE with little or no pore formation. Another object of the present invention is to provide a multilayer collation shrink film that exhibits very good mechanical properties without increasing the film thickness. Furthermore, another object of the present invention is to provide a multilayer collation shrink film that has good optical properties, good shrink behavior, good puncture resistance, and good sealing properties. Summary of the Invention

[0008] The present invention relates to a multilayer collation shrink film comprising an inner surface layer (A), a core layer (B) and an outer layer (C), wherein the core layer (B) is sandwiched between the inner surface layer (A) and the outer layer (C), and the core layer (B) comprises the following components:

[0009] (B1) Recycled LDPE having a relative humidity of 1.5 to 5.0, preferably 1.8 to 4.5, when heated to 3.0s at 180°C. -1 The strain hardening factor when measured at a strain rate of 1000 s and a Hencky strain of 2.5; and

[0010] (B2) linear copolymers of ethylene comprising at least one comonomer chosen from α-olefins having 4 to 10 carbon atoms and having a weight average molecular weight Mw of 150 to 400 kg / mol, preferably 160 to 350 kg / mol and a polydispersity index, i.e. the ratio Mw / Mn, determined by gel permeation chromatography (GPC) according to ISO 16014-4:2003 and ASTM D 6474-12, of 15 to 35, preferably 17 to 32, preferably multimodal, more preferably bimodal;

[0011] wherein the recycled LDPE (B1) has a lower density and a higher melt flow rate MFR2 than the linear copolymer of ethylene (B2), and

[0012] The recycled LDPE (B1) is present in the core layer (B) in an amount of more than 50 wt%, such as 55 to 95 wt%, preferably 60 to 90 wt%, most preferably 65 to 85 wt%, based on the total weight of the core layer (B).

[0013] The invention further relates to a method for producing a multilayer collation shrink film as described above or below, characterized in that the film is produced by a one-step blown film coextrusion process.

[0014] Furthermore, the present invention relates to the use of a multilayer collation shrink film as described above or below for secondary packaging, preferably for bottles and cans, more preferably for bottles and cans in the field of household products, food, healthcare products and beverage products.

[0015] definition:

[0016] In the gist of the present invention, the term "multimodal" may mean multimodal with respect to the molecular weight distribution and thus also includes bimodal polymers. However, as explained in the detailed description of the components, the components may also be multimodal with respect to other properties, such as MFR and / or density.

[0017] Typically, a polymer composition comprising at least two polyethylene fractions, which have been produced under different polymerisation conditions, resulting in different (weight average) molecular weights and molecular weight distributions of the fractions, is referred to as "multimodal". The prefix "multi" relates to the number of different polymer fractions present in the polymer. Thus, for example, the term multimodal polymer includes so-called "bimodal" polymers consisting of two fractions. The form of the molecular weight distribution curve of a multimodal polymer (e.g. LLDPE), i.e. the appearance of a plot of the polymer weight fraction as a function of its molecular weight, will show two or more maxima or at least be significantly broadened compared to the curve for a single fraction.

[0018] Ideally, the molecular weight distribution curve for the multimodal polymers of the present invention will exhibit two distinct maxima. For example, if the polymer is produced in a continuous multi-stage process, utilizing reactors connected in series and using different conditions in each reactor, the polymer fractions produced in the different reactors will each have their own molecular weight distribution and weight average molecular weight. When recording the molecular weight distribution curve for such a polymer, superimposing the individual curves from these fractions onto the molecular weight distribution curve for the entire resulting polymer product will typically produce a curve with two or more distinct maxima.

[0019] In any multimodal polymer, by definition, there is a lower molecular weight component (LMW) and a higher molecular weight component (HMW). The LMW component has a lower molecular weight than the higher molecular weight component. The difference is preferably at least 5000 g / mol.

[0020] In the sense of the present invention, preferably all olefins are α-olefins.

[0021] The meaning of low-density polyethylene (LDPE) is well known and documented in the literature. Although the term LDPE is an abbreviation for low-density polyethylene, the term is understood not to limit the density range but rather encompasses HP polyethylene such as LDPE, which is produced by free radical polymerization in a high-pressure process and has low, medium and higher densities. The term LDPE only describes and distinguishes the properties of HP polyethylene with typical characteristics compared to polyethylene produced in the presence of olefin polymerization catalysts, such as a different branching structure. In addition, the low-density polyethylene (LDPE) homopolymer may be unsaturated.

[0022] In the main points of this invention, "collating shrink film" is a film that is wrapped around the object to be packaged and shrinks to hold the units within the object together. The most common use of these films is to wrap multiple containers (articles), such as bottles or cans that may contain food, beverages, etc. The collation shrink film is wrapped around a number of containers, perhaps a 6-pack of beverages or a 24-pack of food cans, optionally held in a cardboard tray or mat, and shrunk around the containers. The wrapping process typically involves a shrink oven or shrink tunnel, in which the film and the objects covered by the film are briefly heated to allow the collation shrink wrapping to occur. The plastic film then collapses around the multiple containers and holds the units in place.

[0023] For the purposes of this specification and the subsequent claims, the term "recycled LDPE" is used to indicate that the material is recovered from post-consumer waste and / or post-industrial waste. That is, post-consumer waste refers to objects that have completed at least their first use cycle (or life cycle), i.e., have fulfilled their primary purpose; while industrial waste refers to manufacturing waste that does not typically reach consumers. In the gist of the present invention, "recycled LDPE" may also contain up to 30% by weight, preferably up to 25% by weight, more preferably up to 20% by weight, and even more preferably up to 10% by weight, based on the total weight of the corresponding recycled LDPE, of other components (such as, for example, LLDPE, MDPE, HDPE) and / or additives, fillers, and masterbatches.

[0024] Accordingly, the term "virgin" refers to newly produced materials and / or objects, prior to first use and not being recycled. A polymer is a "virgin" polymer if the source of the polymer is not explicitly mentioned.

[0025] The "density" of a material in this specification and claims refers to the density measured according to ISO 1183.

[0026] The "melt flow rate" (=MFR) of a polymer in this specification and claims refers to the MFR determined according to ISO 1133.

[0027] The "melting temperature" of the polymers described in this specification and claims may be measured using a TA Instrument Q200 differential scanning calorimeter (DSC) on 5 to 7 mg samples. The DSC was run according to ISO 11357 / Part 3 / Method C2 in a heating / cooling / heating cycle over a temperature range of 25 to +225°C at a scan rate of 10°C / min. The crystallization temperature (T c ) and crystallization enthalpy (H cryst ) is determined by the cooling step, while the melting temperature (T m ) and heat of fusion (H 熔化 ) is determined by the second heating step. The crystallinity is calculated based on the heat of fusion, assuming that the H of completely crystalline polypropylene is 熔化 The value is 209 J / g (see Brandrup, J., Immergut, EH, eds., Polymer Handbook, 3rd ed., Wiley, New York, 1989; Chapter 3).

[0028] The "weight average molecular weight Mw" and the "number average molecular weight Mn" described in the present specification and claims can be measured by gel permeation chromatography (GPC) according to ISO 16014-4:2003 and ASTM D 6474-12.

[0029] When the term "comprising" is used in this specification and claims, it does not exclude other non-specified elements of major or minor functional importance. For the purposes of the present invention, the term "consisting of" is considered to be a preferred embodiment of the term "comprising". If a group is defined below as comprising at least a certain number of embodiments, this is also to be understood as disclosing a group that preferably consists only of these embodiments.

[0030] Whenever the terms "including" or "having" are used, these terms are meant equivalent to "comprising" as defined above.

[0031] Where an indefinite or definite article is used when referring to a singular noun, for example "a", "an" or "the", this includes a plural of that noun unless something else is specifically stated. DETAILED DESCRIPTION

[0032] Core layer (B)

[0033] The core layer (B) comprises recycled LDPE (B1) and a linear copolymer (B2) of ethylene and one comonomer selected from α-olefins having 4 to 10 carbon atoms.

[0034] The recycled LDPE (B1) is present in the core layer (B) in an amount of more than 50 wt%, such as 55 to 95 wt%, preferably 60 to 90 wt%, most preferably 65 to 85 wt%, based on the total weight of the core layer (B).

[0035] Preferably, the linear copolymer of ethylene (B2) is present in the core layer (B) in an amount of less than 50 wt%, such as 5 to 45 wt%, preferably 10 to 40 wt%, most preferably 15 to 35 wt%, based on the total weight of the core layer (B).

[0036] The core layer (B) may comprise additional polymer components other than the recycled LDPE (B1) and the linear copolymer of ethylene (B2). These additional polymer components are preferably ethylene-based polymers. If present, the additional polymer components are preferably present in an amount of up to 25 wt%, more preferably up to 20 wt%, still more preferably up to 10 wt%.

[0037] The composition forming layer (B) may further contain additives and / or admixtures.

[0038] The additives are preferably selected from the group consisting of slip agents, UV stabilizers, antioxidants, nucleating agents and mixtures thereof, preferably present in an amount ranging from 0 to 5000 ppm, preferably from 10 to 5000 ppm and more preferably from 500 to 3000 ppm, based on the total weight of layer (B).

[0039] The admixtures are preferably selected from the group consisting of pigments, fillers, anti-caking agents and mixtures thereof, preferably, these additives are contained in an amount in the range of 0 to 5 wt.-%, preferably in the range of 0 to 3 wt.-%, more preferably in the range of 0 to 2 wt.-% and most preferably in the range of 0 to 1 wt.-%, based on the total weight of layer (B).

[0040] In one embodiment, the polymer component of the core layer (B) consists of a copolymer of recycled LDPE (B1) and ethylene (B2).

[0041] In said embodiment, the recycled LDPE (B1 ), the linear copolymer of ethylene (B2) and optional additives and admixtures add up to 100 wt.-% of the total weight of the core layer (B).

[0042] Recycled LDPE (B1)

[0043] The recycled LDPE (B1) is preferably derived from post-consumer waste or post-industrial waste, preferably from post-consumer waste.

[0044] Recycled LDPE (B1) may contain up to 20 wt% of components originating from first use. The type and amount of these components influence the physical properties of the recycled LDPE (B1). The properties given below refer to the main components.

[0045] Recycled LDPE (B1) preferably has a viscosity of 915 to 935 kg / m 3 , more preferably 917 to 932 kg / m 3 , most preferably 920 to 930 kg / m 3 density.

[0046] Further, the recycled LDPE (B1) preferably has a melt flow rate MFR2 of 0.1 to 2.0 g / 10 min, more preferably of 0.3 to 1.7 g / 10 min, most preferably of 0.5 to 1.5 g / 10 min.

[0047] Furthermore, the recycled LDPE (B1) preferably has a tensile modulus of 200 to 450 MPa, preferably 225 to 425 MPa, most preferably 250 to 400 MPa.

[0048] Further, the recycled LDPE (B1) preferably has a tensile stress at yield of 6.0 to 15.0 MPa, more preferably 7.5 to 12.5 MPa, most preferably 9.0 to 11.5 MPa.

[0049] Furthermore, the recycled LDPE (B1) preferably has a tensile strain at break of 350 to 1200%, more preferably of 375 to 1100%, most preferably of 400 to 1000%.

[0050] Furthermore, the recycled LDPE (B1) preferably has a flexural modulus of 200 to 500 MPa, more preferably of 225 to 475 MPa, most preferably of 250 to 450 MPa.

[0051] Further, the recycled LDPE (B1) preferably has a viscosity of 40 to 120 kJ / m 2 , more preferably 45 to 110 kJ / m 2 , most preferably 50 to 100 kJ / m 2 Charpy notched impact strength at 23°C.

[0052] Furthermore, the recycled LDPE (B1) preferably has an OD of 5.0 to 20.0 kJ / m 2 , more preferably 6.0 to 18.0 kJ / m 2 , most preferably 7.0 to 16.0 kJ / m 2 The Charpy notched impact strength at -20°C.

[0053] The recycled LDPE (B1) has a relative humidity of 1.5 to 5.0, more preferably 1.8 to 4.5 when heated at 180°C for 3.0s. -1 Strain hardening factor when measured at a strain rate of 1.5 and a Hencky strain of 2.5.

[0054] The recycled LDPE (B1) according to the present invention is characterized by the polymer structure which mainly determines the benefits of the present invention, in particular by the nature of long chain branching (LCB) which can be represented by the strain hardening factor defined as

[0055]

[0056] in

[0057] is the uniaxial extensional viscosity; and

[0058] The Linear Viscoelastic Envelope (LVE) is the time-dependent shear viscosity η within the linear deformation range. + Determination of the linear viscoelastic envelope in tension based on IRIS Rheo Hub 2008 Discrete relaxation time spectra need to be calculated from the storage modulus data (G'(ω)) and the loss modulus data (G"(ω)). Details on this method can be found in the Experimental Section. The strain hardening factor primarily reflects the degree of "dispersion" of the branches relative to the polymer backbone (heterogeneity). Secondarily, the strain hardening factor also provides information about the degree of branching.

[0059] The recycled LDPE (B1) according to the present invention preferably has a relative humidity of 1.5 to 5.0, preferably 1.8 to 4.5 when heated at 3.0 s -1 Strain hardening factor (SHF) when measured at a strain rate of 1000 s and a Hencky strain of 2.5.

[0060] Furthermore, the recycled LDPE (B1) according to the present invention preferably has a carbon monoxide content of 3.6 to 8.0, preferably 3.7 to 7.5, more preferably 3.8 to 7.0 and most preferably 3.9 to 6.5 when heated at 1.0 s. -1 Strain hardening factor (SHF) when measured at a strain rate of 1.5 and a Hencky strain of 2.0.

[0061] It should be understood that the preferred strain hardening factors (SHFs) mentioned above may exist alone or in combination.

[0062] Surprisingly, it has been found that recycled LDPE with a strain hardening factor in the claimed range is particularly suitable for the purpose of the present invention, namely to provide a multilayer collation shrink film which allows the use of larger amounts of recycled LDPE with low or no pore formation and which shows an advantageous balance of properties of very good mechanical properties without increasing the film thickness while having good optical properties, good shrink behavior, good puncture resistance and good sealing properties.

[0063] Recycled LDPE meeting the requirements of recycled LDPE (B1) described above or below is known and can be purchased from suppliers such as Suzhou Jinhui Technology or Plaspulp.

[0064] Linear copolymer of ethylene (B2)

[0065] The linear copolymer of ethylene (B2) is a copolymer of ethylene and at least one comonomer selected from α-olefins having 4 to 10 carbon atoms.

[0066] The at least one comonomer is preferably selected from 1-butene, 1-hexene or 1-octene, more preferably selected from 1-butene or 1-hexene.

[0067] The linear copolymer of ethylene (B2) may contain one or more (such as one to five), preferably one, two or three, more preferably one or two different comonomers selected from α-olefins having 4 to 10 carbon atoms. In this context, "different" means that the α-olefins differ in the amount of their carbon atoms.

[0068] Preferably, the linear copolymer of ethylene (B2) is a copolymer of ethylene and one comonomer selected from α-olefins having 4 to 10 carbon atoms. The term "copolymer of ethylene and one comonomer selected from α-olefins having 4 to 10 carbon atoms" means that the copolymer of ethylene (B2) contains only units derived from ethylene and one comonomer selected from α-olefins having 4 to 10 carbon atoms, preferably from 1-butene, 1-hexene or 1-octene, more preferably from 1-butene or 1-hexene.

[0069] The linear copolymer of ethylene (B2) preferably has a total comonomer content of 0.1 to 15.0 wt%, more preferably 0.15 to 12.5 wt%, still more preferably 0.2 to 10.0 wt%.

[0070] In one embodiment, the linear copolymer of ethylene (B2) is a copolymer of ethylene and 1-butene comonomer units, wherein the 1-butene comonomer units are the only comonomer units present in the linear copolymer of ethylene (B2). In such an embodiment, the linear copolymer of ethylene (B2) preferably has a 1-butene content of 0.1 to 10.0 wt.-%, more preferably 0.15 to 9.0 wt.-%, still more preferably 0.2 to 8.0 wt.-%, based on the total weight of the linear copolymer of ethylene (B2).

[0071] In one embodiment, the linear copolymer of ethylene (B2) is a copolymer of ethylene and 1-hexene comonomer units, wherein the 1-hexene comonomer units are the only comonomer units present in the linear copolymer of ethylene (B2). In such an embodiment, the linear copolymer of ethylene (B2) preferably has a 1-hexene content of 0.1 to 15.0 wt.-%, more preferably 0.15 to 12.5 wt.-%, still more preferably 0.2 to 10.0 wt.-%, based on the total weight of the linear copolymer of ethylene (B2).

[0072] The linear copolymer of ethylene (B2) may be unimodal with respect to the comonomer distribution. This means that the comonomer selected from α-olefins having 4 to 10 carbon atoms, such as 1-butene or 1-hexene, is uniformly distributed in the copolymer of ethylene (B2).

[0073] The linear copolymer of ethylene (B2) may be multimodal with respect to the comonomer distribution.

[0074] This means that the linear copolymer of ethylene (B2) comprises fractions having different comonomer contents.

[0075] In one embodiment, the linear copolymer of ethylene (B2) may comprise an ethylene homopolymer component and a copolymer component of ethylene and one comonomer selected from α-olefins having 4 to 10 carbon atoms, such as 1-butene or 1-hexene.

[0076] In another embodiment, the linear copolymer of ethylene (B2) may comprise two copolymer components of ethylene and one comonomer selected from α-olefins having 4 to 10 carbon atoms, such as 1-butene or 1-hexene, the two copolymer components having different comonomer contents.

[0077] In this context, "linear" means that the copolymer of ethylene (B2) does not comprise any long-chain branches. Thus, the linear copolymer of ethylene (B2) is not an LDPE which has been polymerized in a high-pressure process by free-radical polymerization as known in the art. Instead, the linear copolymer of ethylene (B2) is typically produced in a low-pressure process in the presence of a polymerization catalyst.

[0078] The linear copolymer of ethylene (B2) has a weight average molecular weight Mw of 150 to 400 kg / mol, preferably 160 to 350 kg / mol.

[0079] Further, the linear copolymer of ethylene (B2) preferably has a number average molecular weight Mn of 8 to 12 kg / mol, most preferably 8.5 to 11 kg / mol.

[0080] The linear copolymer of ethylene (B2) has a polydispersity index, ie the ratio Mw / Mn, of 15 to 35, preferably 17 to 32.

[0081] It is preferred that the linear copolymer of ethylene (B2) is multimodal, more preferably bimodal.

[0082] In view of its rather broad molecular weight distribution as shown in the polydispersity index, the linear copolymer of ethylene (B2) is preferably multimodal, more preferably bimodal with respect to the molecular weight distribution.

[0083] The recycled LDPE (B1) has a higher melt flow rate MFR2 than the linear copolymer of ethylene (B2).

[0084] The linear copolymer of ethylene (B2) preferably has a melt flow rate MFR2 of 0.10 to 0.50 g / 10 min, more preferably 0.10 to 0.40 g / 10 min, most preferably 0.12 to 0.30 g / 10 min.

[0085] Further, the linear copolymer of ethylene (B2) preferably has a melt flow rate MFR5 of 0.40 to 1.00 g / 10 min, preferably 0.45 to 0.90 g / 10 min, most preferably 0.50 to 0.80 g / 10 min.

[0086] Furthermore, the linear copolymer of ethylene (B2) preferably has a melt flow rate MFR of 8.0 to 22.0 g / 10 min, more preferably 10.0 to 20.0 g / 10 min, most preferably 11.0 to 19.0 g / 10 min. 21 .

[0087] Furthermore, the linear copolymer of ethylene (B2) preferably has a flow rate ratio FRR of 60 to 150, preferably 70 to 140, most preferably 80 to 120. 21 / 2 , that is, MFR 21 / MFR2 ratio.

[0088] Furthermore, the linear copolymer of ethylene (B2) preferably has a flow rate ratio FRR of 20 to 32, preferably 22 to 30, most preferably 23 to 28. 21 / 5 , that is, MFR21 / MFR5 ratio.

[0089] The recycled LDPE (B1) has a lower density than the linear copolymer of ethylene (B2).

[0090] The linear copolymer of ethylene (B2) preferably has a viscosity of 930 to 945 kg / m 3 , preferably 932 to 942 kg / m 3 , most preferably 933 to 940 kg / m 3 Therefore, the linear copolymers of ethylene (B2) are generally regarded as medium-density copolymers of ethylene.

[0091] The linear copolymer of ethylene (B2) preferably has a melting temperature Tm of 120 to 140°C, more preferably 122 to 138°C, most preferably 125 to 135°C, determined by differential scanning calorimetry (DSC) analysis according to ISO 11357 / part 3 / method C2 in a heating / cooling / heating cycle in a temperature range of 25 to +225°C at a scanning rate of 10°C / min.

[0092] It is preferred that the linear copolymer of ethylene (B2) has a molecular weight of less than 1.2, preferably less than 1.1, most preferably from 0.98 to 1.02 when heated at 180°C for 3.0 s. -1 Strain hardening factor when measured at a strain rate of 1.5 and a Hencky strain of 2.5.

[0093] Surprisingly, it has been found that by carefully choosing the linear copolymer of ethylene (B2) and the recycled LDPE in the core layer (B), the object of the present invention can be met, namely to provide a multilayer collation shrink film which allows the use of relatively large amounts of recycled LDPE with low or no pore formation and which shows an advantageous balance of properties with very good mechanical properties without increasing the film thickness, while having good optical properties, good shrink behavior, good puncture resistance and good sealing properties.

[0094] Linear copolymers of ethylene meeting the requirements of the copolymers of ethylene (B2) described above or below are known and can be purchased from suppliers such as Borouge or Borealis. A suitable copolymer of ethylene is available as FB1350 was purchased commercially.

[0095] Inner surface layer (A)

[0096] The inner surface layer (A) preferably comprises a multimodal copolymer of ethylene and at least one comonomer selected from α-olefins having 4 to 10 carbon atoms (A1 ) and LDPE (A2).

[0097] It is preferred that the multimodal copolymer of ethylene (A1 ) is present in the inner surface layer (A) in an amount of 15 to 90 wt%, preferably 18 to 85 wt%, most preferably 20 to 82 wt%, based on the total weight of the inner surface layer (A).

[0098] It is further preferred that LDPE (A2) is present in the inner surface layer (A) in an amount of 10 to 85 wt%, preferably 15 to 82 wt%, most preferably 18 to 80 wt%, based on the total weight of the inner surface layer (A).

[0099] The inner surface layer (A) may comprise additional polymer components other than the multimodal copolymer of ethylene (A1) and the LDPE (A2). These additional polymer components are preferably ethylene-based polymers. If present, the additional polymer components are preferably present in an amount of up to 20 wt%, more preferably up to 10 wt%.

[0100] The composition forming the inner surface layer (A) may further include additives and / or admixtures.

[0101] The additives are preferably selected from the group consisting of slip agents, UV stabilizers, antioxidants, nucleating agents and mixtures thereof, preferably, these additives are contained in an amount within the range of 0 to 5000 ppm, preferably within the range of 10 to 5000 ppm and more preferably within the range of 500 to 3000 ppm, based on the total weight of the inner surface layer (A).

[0102] The admixtures are preferably selected from the group consisting of pigments, fillers, anti-caking agents and mixtures thereof, preferably, based on the total weight of the inner surface layer (A), the amount of these additives contained is in the range of 0 to 5 wt. %, preferably in the range of 0 to 3 wt. %, more preferably in the range of 0 to 2 wt. % and most preferably in the range of 0 to 1 wt. %.

[0103] In a preferred embodiment the polymer component of the inner surface layer (A) consists of a multimodal copolymer of ethylene (A1) and LDPE (A2).

[0104] In said embodiment, the weight ratio (A1:A2) of the multimodal copolymer of ethylene (A1) to the LDPE (A2) is preferably in the range of 15:85 to 90:10, more preferably in the range of 18:82 to 85:15, most preferably in the range of 20:80 to 82: 18. Further, in said embodiment, the multimodal copolymer of ethylene (A1), the LDPE (A2) and the optional additives and admixtures amount to 100 wt% of the total weight of the inner surface layer (A).

[0105] Outer layer (C)

[0106] The outer layer (C) preferably comprises a multimodal copolymer of ethylene and at least one comonomer chosen from α-olefins having 4 to 10 carbon atoms (C1 ) and LDPE (C2).

[0107] It is preferred that the multimodal copolymer of ethylene (C1 ) is present in the outer layer (C) in an amount of 15 to 90 wt%, preferably 18 to 85 wt%, most preferably 20 to 82 wt%, based on the total weight of the outer layer (C).

[0108] It is further preferred that LDPE (C2) is present in the outer layer (C) in an amount of 10 to 85 wt%, preferably 15 to 82 wt%, most preferably 18 to 80 wt%, based on the total weight of the outer layer (C).

[0109] The outer layer (C) may comprise additional polymer components other than the multimodal copolymer of ethylene (C1) and the LDPE (C2). These additional polymer components are preferably ethylene-based polymers. If present, the additional polymer components are preferably present in an amount of up to 20 wt%, more preferably up to 10 wt%.

[0110] The composition forming the outer layer (C) may further contain additives and / or admixtures.

[0111] The additives are preferably selected from the group consisting of slip agents, UV stabilizers, antioxidants, nucleating agents and mixtures thereof, preferably, these additives are contained in an amount in the range of 0 to 5000 ppm, preferably in the range of 10 to 5000 ppm and more preferably in the range of 500 to 3000 ppm, based on the total weight of the outer layer (C).

[0112] The admixtures are preferably selected from the group consisting of pigments, fillers, anti-caking agents and mixtures thereof, preferably, these additives are contained in an amount in the range of 0 to 5 wt.-%, preferably in the range of 0 to 3 wt.-%, more preferably in the range of 0 to 2 wt.-% and most preferably in the range of 0 to 1 wt.-%, based on the total weight of the outer layer (C).

[0113] In a preferred embodiment the polymer component of the outer layer (C) consists of a multimodal copolymer of ethylene (C1 ) and LDPE (C2).

[0114] In said embodiment, the weight ratio of the multimodal copolymer of ethylene (C1) to LDPE (C2) (C1:C2) is preferably in the range of 15:85 to 90:10, more preferably in the range of 18:82 to 85:15, most preferably in the range of 20:80 to 82:18.

[0115] Further, in said embodiment the multimodal copolymer of ethylene (C1 ), the LDPE (C2) and optional additives and admixtures amount to 100 wt% of the total weight of the outer layer (C).

[0116] In one embodiment, the compositions of the inner surface layer (A) and the outer layer (C) may be different from each other.

[0117] In such embodiments, at least one of components (A1) and (C1) or (A2) and (C2) differ in at least one property.

[0118] However, it is preferred that the properties of components (A1) and (C1) and the properties of components (A2) and (C2) are independently within the same ranges as defined below.

[0119] However, it is preferred that the composition of inner surface layer (A) and outer layer (C) is identical. This means that components (A1) and (C1) are identical, and components (A2) and (C2) are identical. Further, all components of inner surface layer (A) and outer layer (C) are present in the same amount.

[0120] Multimodal copolymer of ethylene (A1) and / or multimodal copolymer of ethylene (C1)

[0121] The following properties preferably apply independently to components (A1) and (C1):

[0122] The multimodal copolymer of ethylene is preferably a copolymer of ethylene and at least one comonomer selected from α-olefins having 4 to 10 carbon atoms.

[0123] The at least one comonomer is preferably selected from 1-butene, 1-hexene and / or 1-octene, more preferably selected from 1-butene and / or 1-hexene.

[0124] In a preferred embodiment the multimodal copolymer of ethylene is a terpolymer of ethylene and two comonomers selected from α-olefins having from 4 to 10 carbon atoms.

[0125] The two comonomers are preferably selected from 1-butene, 1-hexene and 1-octene, more preferably from 1-butene and 1-hexene.

[0126] The term "terpolymer of ethylene and two comonomers selected from α-olefins having 4 to 10 carbon atoms" means that the multimodal copolymer of ethylene (A1) comprises only units derivable from ethylene and two comonomers selected from α-olefins having 4 to 10 carbon atoms, preferably selected from 1-butene, 1-hexene and 1-octene, more preferably selected from 1-butene and 1-hexene.

[0127] The multimodal copolymer of ethylene preferably has a total comonomer content, i.e. a content of comonomer units derivable from 1-butene and / or 1-hexene, of 1.0 to 15.0 wt%, preferably 1.5 to 12.5 wt%, still more preferably 2.0 to 10.0 wt%.

[0128] In one embodiment, the multimodal copolymer of ethylene comprises 1-butene comonomer units. In such an embodiment, the multimodal copolymer of ethylene preferably has a 1-butene content of 0.1 to 5.0 wt%, more preferably 0.2 to 3.5 wt%, still more preferably 0.3 to 2.0 wt%, based on the total weight of the multimodal copolymer of ethylene.

[0129] In one embodiment, the multimodal copolymer of ethylene comprises 1-hexene comonomer units. In such an embodiment, the multimodal copolymer of ethylene preferably has a 1-hexene content of 2.0 to 15.0 wt%, more preferably 2.5 to 12.5 wt%, still more preferably 3.0 to 10.0 wt%, based on the total weight of the multimodal copolymer of ethylene.

[0130] Multimodal copolymers of ethylene may be multimodal with respect to the comonomer distribution.

[0131] This means that the multimodal copolymer of ethylene comprises fractions having different comonomer contents.

[0132] In the case of a copolymer of ethylene and one comonomer selected from α-olefins having from 4 to 10 carbon atoms, such as 1-butene or 1-hexene, in one embodiment the multimodal copolymer of ethylene may comprise an ethylene homopolymer component and a copolymer component of ethylene and one comonomer selected from α-olefins having from 4 to 10 carbon atoms, such as 1-butene or 1-hexene.

[0133] In the case of a copolymer of ethylene and one comonomer selected from α-olefins having from 4 to 10 carbon atoms, such as 1-butene or 1-hexene, in another embodiment the multimodal copolymer of ethylene may comprise two copolymer components of ethylene and one comonomer selected from α-olefins having from 4 to 10 carbon atoms, such as 1-butene or 1-hexene, the two copolymer components having different comonomer contents.

[0134] In the case of a terpolymer of ethylene and two comonomers selected from α-olefins having from 4 to 10 carbon atoms, such as 1-butene and 1-hexene, the multimodal copolymer of ethylene may, in one embodiment, comprise an ethylene homopolymer component, a copolymer component of ethylene and one comonomer selected from α-olefins having from 4 to 10 carbon atoms, such as 1-butene, and a copolymer component of ethylene and another comonomer selected from α-olefins having from 4 to 10 carbon atoms, such as 1-hexene.

[0135] In the case of a terpolymer of ethylene and two comonomers selected from α-olefins having from 4 to 10 carbon atoms, such as 1-butene and 1-hexene, in another embodiment the multimodal copolymer of ethylene may comprise an ethylene homopolymer component and a terpolymer component of ethylene and two comonomers selected from α-olefins having from 4 to 10 carbon atoms, such as 1-butene and 1-hexene.

[0136] In the case of a terpolymer of ethylene and two comonomers selected from α-olefins having from 4 to 10 carbon atoms, such as 1-butene and 1-hexene, in yet another embodiment the multimodal copolymer of ethylene may comprise a copolymer component of ethylene and one comonomer selected from α-olefins having from 4 to 10 carbon atoms, such as 1-butene, and a copolymer component of ethylene and another comonomer selected from α-olefins having from 4 to 10 carbon atoms, such as 1-hexene.

[0137] In a preferred embodiment, the multimodal copolymer of ethylene is a terpolymer of ethylene and two comonomers selected from 1-butene and 1-hexene, the terpolymer having a 1-butene content of 0.1 to 5.0 wt.-%, preferably 0.2 to 3.5 wt.-%, still more preferably 0.3 to 2.0 wt.-% and a 1-hexene content of 2.0 to 14.9 wt.-%, more preferably 2.5 to 12.3 wt.-%, still more preferably 3.0 to 9.7 wt.-%, based on the total weight of the multimodal copolymer of ethylene.

[0138] The multimodal copolymer of ethylene preferably has a viscosity of 920 to 940 kg / m 3 , more preferably 922 to 937 kg / m 3 , most preferably 925 to 935 kg / m 3 density.

[0139] The multimodal copolymer of ethylene is preferably a linear low density polyethylene (LLDPE).

[0140] The multimodal copolymer of ethylene preferably has a melt flow rate MFR2 of 0.5 to 2.0 g / 10 min, more preferably 0.7 to 1.8 g / 10 min, most preferably 1.0 to 1.6 g / 10 min.

[0141] The multimodal copolymer of ethylene preferably has a melting temperature Tm of 115 to 135°C, more preferably 118 to 130°C, most preferably 120 to 128°C, as determined by differential scanning calorimetry (DSC) analysis according to ISO 11357 / part 3 / method C2 in a heating / cooling / heating cycle in the temperature range of 25 to +225°C at a scanning rate of 10°C / min.

[0142] Further, the multimodal copolymer of ethylene preferably has a ratio of weight average molecular weight to number average molecular weight Mw / Mn determined by gel permeation chromatography (GPC) according to ISO 16014-4:2003 and ASTM D 6474-12 of 2.0 to 6.0, preferably 2.5 to 5.5, more preferably 3.0 to 5.0.

[0143] The multimodal copolymer of ethylene is preferably obtainable by polymerization in the presence of a single-site catalyst system. The single-site catalyst system preferably comprises a catalytically active metallocene compound or complex in combination with a cocatalyst. The metallocene compound or complex is also referred to herein as an organometallic compound (C).

[0144] The organometallic compound (C) comprises a transition metal (M) from Groups 3 to 10 of the Periodic Table of the Elements (IUPAC 2007) or an actinide or lanthanide.

[0145] According to the present invention, the term "organometallic compound (C)" includes any metallocene compound of a transition metal that carries at least one organic (coordinating) ligand and exhibits catalytic activity alone or in combination with a cocatalyst. Transition metal compounds are well known in the art and preferably encompass compounds of metals from Groups 3 to 10, for example Groups 3 to 7, or Groups 3 to 6, such as Groups 4 to 6, of the Periodic Table of the Elements (IUPAC 2007), as well as lanthanides or actinides.

[0146] In an embodiment, the organometallic compound (C) has the following formula (I):

[0147] (L) m R n MX q (I)

[0148] in

[0149] "M" is a transition metal (M) of Groups 3 to 10 of the Periodic Table of the Elements (IUPAC 2007),

[0150] Each "X" is independently a monoanionic ligand, such as an ortho-ligand,

[0151] Each "L" is independently an organic ligand coordinated to the transition metal "M",

[0152] "R" is a bridging group connecting the organic ligand (L),

[0153] "m" is 1, 2 or 3, preferably 2,

[0154] "n" is 0, 1 or 2, preferably 1,

[0155] "q" is 1, 2 or 3, preferably 2, and

[0156] m+q equals the valence of the transition metal (M).

[0157] “M” is preferably selected from the group consisting of zirconium (Zr), hafnium (Hf) or titanium (Ti), and more preferably selected from the group consisting of zirconium (Zr) and hafnium (Hf).

[0158] "X" is preferably a halogen, most preferably Cl.

[0159] Most preferably, the organometallic compound (C) is a metallocene complex comprising a transition metal compound as defined above, comprising a cyclopentadienyl, indenyl or fluorenyl ligand as a substituent "L". Further, the ligand "L" may have a substituent such as an alkyl group, an aryl group, an aralkyl group, an alkaryl group, a silyl group, a siloxy group, an alkoxy group or other heteroatom groups. Suitable metallocene catalysts are known in the art and are disclosed, inter alia, in WO-A-95 / 12622, WO-A-96 / 32423, WO-A-97 / 28170, WO-A-98 / 32776, WO-A-99 / 61489, WO-A-03 / 010208, WO-A-03 / 051934, WO-A-03 / 051514, WO-A-2004 / 085499, EP-A-1752462 and EP-A-1739103.

[0160] Most preferably, metallocene catalysts (which refer to catalytically active metallocene complexes as defined above) are used together with cocatalysts (also referred to as activators). Suitable activators are metal alkyl compounds known in the art, especially aluminum alkyl compounds. Especially suitable activators used together with metallocene catalysts are aluminum alkyl compounds, such as methylaluminoxane (MAO), tetraisobutylaluminoxane (TIBAO) or hexaisobutylaluminoxane (HIBAO).

[0161] The multimodal copolymers of ethylene may be produced in any suitable polymerization process known in the art comprising at least one polymerization stage, wherein the polymerization is typically carried out in solution, slurry, bulk or gas phase. Preferably, the multimodal copolymers of ethylene are produced in a multistage polymerization process comprising at least two polymerization zones.

[0162] The first ethylene polymer component is preferably produced in the first polymerization zone, and the second ethylene polymer component is preferably produced in the second polymerization zone.The first polymerization zone and the second polymerization zone can be connected in any order, and promptly the first polymerization zone can be before the second polymerization zone, or the second polymerization zone can be before the first polymerization zone, or alternatively, polymerization zone can be connected in parallel.Yet, preferably operate polymerization zone with cascade mode.Polymerization zone can operate under slurry, solution or gas phase condition or their combination.

[0163] Suitable processes comprising cascaded slurry and gas phase polymerisation stages are disclosed in, inter alia, WO-A-92 / 12182 and WO-A-96 / 18662.

[0164] It is generally preferred to remove the reactants of the preceding polymerization stage from the polymer and then introduce them into the subsequent polymerization stage. This is preferably done when transferring the polymer from one polymerization stage to another.

[0165] The catalyst may be transferred to the polymerization zone by any means known in the art. For example, the catalyst may be suspended in a diluent and maintained as a homogeneous slurry, the catalyst may be mixed with a viscous mixture of grease and oil and the resulting paste fed to the polymerization zone, or the catalyst may be allowed to settle and a portion of the catalyst slurry thus obtained may be introduced into the polymerization zone.

[0166] The polymerization in the first polymerization zone is preferably carried out in a slurry. The polymer particles formed in the polymerization are then suspended in a hydrocarbon fluid together with the catalyst fragmented and dispersed within the particles. The slurry is stirred to transfer the reactants from the fluid to the particles.

[0167] The polymerization is usually carried out in an inert diluent, usually a hydrocarbon diluent such as methane, ethane, propane, n-butane, isobutane, pentane, hexane, heptane, octane, etc., or a mixture thereof. Preferably, the diluent is a low boiling hydrocarbon having 1 to 4 carbon atoms or a mixture of such hydrocarbons, and the preferred diluent is propane.

[0168] The ethylene content of the fluid phase of the slurry may be from 2 to about 50 mol %, preferably from about 2 to about 20 mol % and especially from about 3 to about 12 mol %.

[0169] The temperature in the slurry polymerization is generally from 50 to 115° C., preferably from 60 to 110° C. and in particular from 70 to 100° C. The pressure is from 1 to 150 bar, preferably from 10 to 100 bar.

[0170] The slurry polymerization can be carried out in any known reactor for slurry polymerization.

[0171] The reactor includes a continuous stirred tank reactor and a loop reactor. Particularly preferably, polymerization is carried out in a loop reactor. In such a reactor, the slurry is circulated at high speed along a closed pipeline using a circulation pump. Loop reactors are generally known in the art, and examples are given, for example, in US-A-4582816, US-A-3405109, US-A-3324093, EP-A-479186 and US-A-5391654.

[0172] Sometimes it is advantageous to carry out a slurry polymerization above the critical temperature and pressure of the fluid mixture. Such an operation is described in US-A-5391654. In such an operation, the temperature is generally 80 to 110°C, preferably 85 to 105°C, and the pressure is 30 to 150 bar, preferably 50 to 100 bar.

[0173] The slurry can be withdrawn from the reactor continuously or intermittently. A preferred method of intermittent withdrawal is to use settling legs in which the slurry is allowed to concentrate and then a batch of the concentrated slurry is withdrawn from the reactor. Continuous withdrawal is advantageously combined with a suitable concentration method, such as disclosed in EP-A-1310295 and EP-A-1591460.

[0174] As known in the art, hydrogen can be fed into the reactor to control the molecular weight of the polymer. In addition, one or more comonomers selected from alpha-olefins having 4 to 10 carbon atoms (such as 1-butene and / or 1-hexene) can be added to the reactor, for example, to control the density of the polymer product. The actual amount of such hydrogen and comonomer feed depends on the desired melt index (or molecular weight) and density (or comonomer content) of the catalyst used and the resulting polymer.

[0175] The polymerization in the second polymerization zone is preferably carried out in the gas phase, preferably in a fluidized bed reactor, in a fast fluidized bed reactor or in a settled bed reactor or in any combination of these reactors. The polymerization in the second polymerization zone is more preferably carried out in a fluidized bed gas phase reactor, wherein ethylene is polymerized together with one or more comonomers selected from α-olefins having from 4 to 10 carbon atoms, such as 1-butene and / or 1-hexene, in the presence of a polymerization catalyst and preferably in the presence of the reaction mixture from the first polymerization zone in an upwardly moving gas stream. The reactor typically comprises a fluidized bed comprising growing polymer particles containing the active catalyst above a fluidizing grid.

[0176] The polymer bed is fluidized with the aid of a fluidizing gas comprising the olefin monomer, the final comonomer(s), the final chain growth controller or chain transfer agent (such as hydrogen), and the final inert gas. The fluidizing gas is introduced into an inlet chamber at the bottom of the reactor. One or more of the above components may be added continuously to the fluidizing gas to compensate for losses, particularly those caused by the reaction or product extraction.

[0177] The fluidizing gas is passed through the fluidized bed. The superficial velocity of the fluidizing gas must be higher than the minimum fluidizing velocity of the particles contained in the fluidized bed, otherwise fluidization will not occur. On the other hand, the gas velocity should be lower than the initial velocity of pneumatic transport, otherwise the entire bed will be entrained with the fluidizing gas.

[0178] When the fluidizing gas contacts the bed containing the active catalyst, the reactive components in the gas (such as monomers and chain transfer agents) react in the presence of the catalyst to produce polymer product. At the same time, the gas is heated by the heat of reaction.

[0179] Unreacted fluidizing gas is removed from the top of the reactor and cooled in a heat exchanger to remove the heat of reaction. The gas is cooled to a temperature below that of the bed to prevent the bed from heating up due to the reaction. The gas can be cooled to a temperature that causes some of the gas to condense. When the liquid droplets enter the reaction zone, they vaporize.

[0180] The heat of vaporization then contributes to the removal of the heat of reaction. This operation is known as condensing mode, variations of which are disclosed in particular in WO-A-2007 / 025640, USA-4543399, EP-A-699213 and WO-A-94 / 25495. As disclosed in EP-A-696293, a condensing agent can also be added to the recycle gas stream. The condensing agent is a non-polymerizable component, such as n-pentane, isopentane, n-butane or isobutane, which is at least partially condensed in the cooler.

[0181] The gas is then compressed and recycled to the reactor inlet chamber. Fresh reactants are introduced into the fluidizing gas stream before entering the reactor to compensate for losses due to reaction and product extraction. It is generally known to analyze the composition of the fluidizing gas and introduce gas components to maintain a constant composition. The actual composition is determined by the desired properties of the product and the catalyst used in the polymerization.

[0182] The catalyst can be introduced into the reactor continuously or intermittently in various ways. When the gas phase reactor is part of a reactor cascade, the catalyst is usually dispersed in the polymer particles of the previous polymerization stage. The polymer particles can be introduced into the gas phase reactor as disclosed in EP-A-1415999 and WO-A-00 / 26258. In particular, if the previous reactor is a slurry reactor, it is advantageous to feed the slurry directly into the fluidized bed of the gas phase reactor as disclosed in EP-A-887379, EP-A-887380, EP-A-887381 and EP-A-991684.

[0183] The polymer product can be withdrawn from the gas phase reactor continuously or intermittently. Combinations of these methods can also be used. Continuous withdrawal is particularly disclosed in WO-A-00 / 29452. Intermittent withdrawal is particularly disclosed in US-A-4621952, EP-A-188125, EP-A-250169, and EP-A-579426.

[0184] If desired, antistatic agent(s) (such as water, ketones, aldehydes and alcohols) may also be introduced into the gas phase reactor.The reactor may also include a mechanical stirrer to further promote mixing within the fluidized bed.

[0185] Typically, the fluidised bed polymerisation reactor is operated at a temperature in the range of 50 to 100° C., preferably in the range of 65 to 90° C. The pressure is suitably in the range of 10 to 40 bar, preferably 15 to 30 bar.

[0186] Prior to the polymerization of the first ethylene polymer component and the second ethylene polymer component in the first polymerization zone and the second polymerization zone, a prepolymerization step may be performed. The purpose of the prepolymerization is to polymerize a small amount of polymer onto the catalyst at low temperature and / or low monomer concentration. Prepolymerization can improve the performance of the catalyst in the slurry and / or change the properties of the final polymer.

[0187] The prepolymerization step can be carried out in slurry or gas phase. Preferably, the prepolymerization is carried out in slurry, preferably in a loop reactor. The prepolymerization is then preferably carried out in an inert diluent, preferably a low-boiling hydrocarbon having 1 to 4 carbon atoms or a mixture of such hydrocarbons.

[0188] The temperature in the prepolymerization step is generally from 0 to 90°C, preferably from 20 to 80°C, more preferably from 25 to 70°C.

[0189] The pressure is not critical and is generally from 1 to 150 bar, preferably from 10 to 100 bar.

[0190] The catalyst components are preferably all introduced into the prepolymerization step.

[0191] Preferably, the reaction product of the prepolymerisation step is then introduced into the first polymerisation zone.

[0192] The multimodal copolymer of ethylene obtained by the multistage process can be extruded and pelletized and then blended in pellet form with LDPE (A2) or LDPE (C2).

[0193] It is also possible to blend the multimodal copolymer of ethylene obtained from a multistage process in powder form with LDPE (A2) or LDPE (C2).

[0194] The multimodal copolymer of ethylene is preferably a virgin polymer.

[0195] LDPE(A2) and LDPE(C2)

[0196] The following properties preferably apply independently to components (A2) and (C2):

[0197] Preferably, LDPE has a viscosity of 915 to 935 kg / m 3 , preferably 917 to 932 kg / m 3 , most preferably 920 to 930 kg / m 3 density.

[0198] It is further preferred that the LDPE has a melt flow rate MFR2 of 0.1 to 2.0 g / 10 min, preferably 0.2 to 1.5 g / 10 min, most preferably 0.3 to 1.2 g / 10 min.

[0199] The LDPE preferably comprises virgin LDPE, recycled LDPE or a mixture of virgin LDPE and recycled LDPE.

[0200] In a first embodiment, the LDPE consists of virgin LDPE.

[0201] In a second embodiment, the LDPE consists of recycled LDPE.

[0202] In a third embodiment, the LDPE consists of a mixture of virgin LDPE and recycled LDPE.

[0203] In said third embodiment, the weight ratio of virgin LDPE to recycled LDPE in the mixture is preferably in the range of 5:1 to 1:2, more preferably in the range of 4:1 to 1:1, most preferably in the range of 3:1 to 2:1.

[0204] The virgin LDPE is preferably an ethylene homopolymer.

[0205] The recycled LDPE is preferably the same as the recycled LDPE (B1 ) described above.

[0206] Virgin LDPE meeting the requirements for LDPE described above or below is known and can be purchased from suppliers such as Borouge or Borealis.

[0207] Recycled LDPE meeting the requirements for LDPE described above or below is known and can be purchased from suppliers such as Suzhou Jinhui Technology or Plaspulp.

[0208] Collation shrink film

[0209] The multilayer collation shrink film of the present invention comprises an inner surface layer (A), a core layer (B) and an outer layer (C). Therefore, the core layer (B) is sandwiched between the inner surface layer (A) and the outer layer (C).

[0210] It is preferred that the multilayer collation shrink film comprises at most seven layers, preferably at most five layers, and most preferably consists of three layers.

[0211] Preferably, the film further comprises additional layers, such as a sub-inner surface layer (I1) and / or a sub-outer surface layer (O1), wherein the sub-inner surface layer (I1) is present between the inner surface layer (A) and the core layer (B), and the sub-outer surface layer (O1) is present between the outer surface layer (C) and the core layer (B). Optionally, for a five-layer film or a seven-layer film, the film comprises more than one of any of layers O1, B, I1, A or C.

[0212] For a 3-layer film, it is preferred that the inner surface layer (A) is in adhesive contact with one surface of the core layer (B).

[0213] It is further preferred that the outer layer (C) is in adhesive contact with the other surface of the core layer (B).

[0214] It is particularly preferred that the inner surface layer (A) and the outer layer (C) are in adhesive contact with respective surfaces of the core layer (B).

[0215] In this context, "adhesive contact" means that there are no additional layers between the core layer (B) and the inner surface layer (A) and / or the core layer (B) and the outer layer (C).

[0216] It is preferred that the inner surface layer (A) and the outer layer (C) consist of the same components, and most preferably are identical.

[0217] In this context, "identical" means that the inner surface layer (A) and the outer layer (C) not only consist of the same components (amounts and chemical composition), but also have the same layer thickness, so that the multilayer film is symmetrical.

[0218] The inner surface layer (A) of the multilayer collation shrink film preferably has a thickness in the range of 2 to 25 μm, more preferably in the range of 3 to 23 μm and most preferably in the range of 5 to 20 μm.

[0219] The core layer (B) of the multilayer collation shrink film preferably has a thickness in the range of 10 to 100 μm, more preferably in the range of 15 to 80 μm and most preferably in the range of 20 to 60 μm.

[0220] The outer layer (C) of the multilayer collation shrink film preferably has a thickness in the range of 2 to 25 μm, more preferably in the range of 3 to 23 μm and most preferably in the range of 5 to 20 μm.

[0221] The total film thickness of the multilayer collation shrink film is preferably in the range of 15 to 100 μm, more preferably in the range of 20 to 90 μm and most preferably in the range of 25 to 80 μm.

[0222] The thickness of the core layer (B) in the multilayer collation shrink film is preferably in the range of 40 to 70%, more preferably in the range of 44 to 66%, most preferably in the range of 48 to 62%, based on the total thickness of the multilayer collation shrink film.

[0223] The thickness of the inner surface layer (A) in the multilayer collation shrink film is preferably in the range of 10 to 30%, more preferably in the range of 15 to 28%, most preferably in the range of 19 to 26%, based on the total thickness of the multilayer collation shrink film.

[0224] The thickness of the outer layer (C) in the multilayer collation shrink film is preferably in the range of 10 to 30%, more preferably in the range of 15 to 28%, most preferably in the range of 19 to 26%, based on the total thickness of the multilayer collation shrink film.

[0225] The total amount of recycled LDPE in the multilayer collation shrink film is preferably 25 to 55 wt%, preferably 27 to 53 wt%, most preferably 30 to 50 wt%, based on the total weight of the multilayer collation shrink film.

[0226] The recycled LDPE is present in the core layer (B) and may also be present in the inner surface layer (A) and / or the outer layer (C) as described above and below.

[0227] The multilayer collation shrink film preferably has one or more of the following properties, or all of the following properties:

[0228] 60 to 85%, preferably 65 to 82%, most preferably 70 to 80% longitudinal shrinkage; and / or

[0229] 5 to 25%, preferably 7 to 22%, most preferably 9 to 20% transverse shrinkage; and / or

[0230] 5.0 to 19.0%, preferably 7.0 to 18.0%, most preferably 8.0 to 17.0% haze; and / or

[0231] a gloss at 60° of 70 to 130, preferably 73 to 120, most preferably 75 to 110; and / or

[0232] a longitudinal tensile modulus of 225 to 600 MPa, preferably 240 to 550 MPa, most preferably 250 to 500 MPa; and / or

[0233] a transverse tensile modulus of 250 to 650 MPa, preferably 265 to 600 MPa, most preferably 275 to 550 MPa; and / or

[0234] a longitudinal tensile stress at break of 12.0 to 40.0 MPa, preferably 13.0 to 38.0 MPa, most preferably 14.0 to 36.0 MPa; and / or

[0235] a tensile stress in transverse direction at break of 15.0 to 40.0 MPa, preferably 18.0 to 36.0 MPa, most preferably 20.0 to 32.0 MPa; and / or

[0236] 0.8 to 3.0 J, preferably 0.9 to 2.5 J, most preferably 1.0 to 2.0 J of puncture energy; and / or

[0237] • A seal initiation temperature of 100 to 125°C, preferably 103 to 120°C, most preferably 105 to 115°C.

[0238] Method for producing a multi-layer collation shrink film

[0239] The present invention further relates to a method for producing a multilayer collation shrink film according to the present invention. According to a preferred embodiment, the multilayer collation shrink film is produced by a one-step blown film coextrusion process.

[0240] Application of multi-layer collation shrink film

[0241] The multilayer collation shrink film according to the present invention can be used for secondary packaging, preferably for bottles and cans, more preferably for bottles and cans in the fields of household products, food, health products and beverage products and bottles (also known as wine or milk).

[0242] The invention will now be described with reference to the following non-limiting examples.

[0243] Examples

[0244] 1. Determination method

[0245] Melt flow rate

[0246] The melt flow rate (MFR) is determined according to ISO 1133 and is expressed in g / 10 min. The MFR indicates the flowability, and therefore the processability, of a polymer. The higher the melt flow rate, the lower the viscosity of the polymer.

[0247] The MFR2 of polyethylene is measured at a temperature of 190° C. and a load of 2.16 kg.

[0248] The MFR5 of polyethylene is measured at a temperature of 190° C. and a load of 5 kg.

[0249] MFR of polyethylene 21 It was measured at a temperature of 190°C and a load of 21.6 kg.

[0250] The MFR2 of the high molecular weight ethylene polymer component polymerized in the second polymerization reactor is calculated from the MFR2 of the low molecular weight ethylene polymer component polymerized in the first polymerization reactor and the MFR2 of the base resin as follows:

[0251] LogMFR 最终 = weight % 第一 ×LogMFR 第一 +Weight% 第二 ×LogMFR 第二

[0252] in

[0253] - "Final" refers to "Polyethylene resin"

[0254] - "first" refers to the polymer component produced in the first reactor

[0255] - "Second" refers to the polymer component produced in the second reactor.

[0256] Flow Rate Ratio (FRR) 21 / 2 Calculated as MFR 21 / MFR2 ratio, and flow rate ratio FRR 21 / 5 Calculated as MFR 21 / MFR5 ratio.

[0257] density

[0258] The density of the polymer is measured according to ISO 1183-1:2004 method A on compression molded test specimens prepared according to EN ISO 1872-2 (February 2007) and is expressed in kg / m3 given.

[0259] Comonomer content

[0260] 13 C-NMR spectra were recorded on a Bruker 400 MHz spectrometer at 130° C. from samples dissolved in 1,2,4-trichlorobenzene / benzene-d 6 (90 / 10 w / w). Conversions between weight % and mole % can be performed by calculation.

[0261] DSC analysis

[0262] Melting temperature Tm and crystallization temperature Tc were measured using a TA Instrument Q2000 differential scanning calorimetry (DSC) on 5 to 7 mg samples. The DSC was run according to ISO 11357 / Part 3 / Method C2 in a heating / cooling / heating cycle over a temperature range of 25 to +225°C at a scanning rate of 10°C / min. The crystallization temperature was determined from the cooling step, while the melting temperature (Tm) and the melting enthalpy (Hc) were determined from the cooling step. m ) is determined from the second heating step.

[0263] GPC

[0264] (1) Conventional GPC method

[0265] Unless otherwise stated, conventional GPC methods were used for measurements on ethylene polymers, with the exception of LDPE.

[0266] Average molecular weight (M z 、M w and M n ), molecular weight distribution (MWD) and its polydispersity index PDI = M w / M n Describe the width (where M n is the number average molecular weight, and M w is the weight average molecular weight) is typically determined by gel permeation chromatography (GPC) according to ISO 16014-4:2003 and ASTM D 6474-12 using the following formula:

[0267]

[0268] For a constant elution volume interval ΔV i , where A i and M i and elution volume V, respectively. i Correlate the chromatographic peak slice area and the polyolefin molecular weight (MW), where N equals the number of data points obtained from the chromatogram between the integration limits.

[0269] 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 3x Agilent-PLgel Olexis and 1x Agilent-PLgel Olexis Guard columns) was used. 1,2,4-Trichlorobenzene (TCB) stabilized with 250 mg / L 2,6-di-tert-butyl-4-methyl-phenol was used as the mobile phase. The chromatography system was operated at a column temperature of 160° C., a detector of 160° C., and a constant flow rate of 1 mL / min. 200 μL of sample solution was injected for each analysis. Data were collected using Agilent Cirrus software version 3.3 or PolymerChar GPC-IR control software.

[0270] The column set was calibrated using 19 narrow MWD polystyrene (PS) standards in the range of 0.5 kg / mol to 11 500 kg / mol. The PS standards were dissolved at room temperature for several hours. The conversion of polystyrene peak molecular weight to polyolefin molecular weight was achieved using the Mark-Houwink equation and the following Mark-Houwink constants:

[0271] K PS =19×10 -3 mL / g, α PS =0.655

[0272] K PE =39×10 -3 mL / g, α PE =0.725

[0273] A third-order polynomial fit was used to fit the calibration data.

[0274] All samples were prepared in a concentration range of about 1 mg / ml and dissolved in freshly distilled TCB stabilized with 250 ppm BHT (butylated hydroxytoluene) for PE at 160° C. for 3 (three) hours under continuous gentle shaking under N 2 gas purge.

[0275] (2) GPC viscosity method

[0276] The average molecular weight of LDPE (M z 、M w and M n ), molecular weight distribution (MWD) was measured by GPC-viscosity method using universal calibration. w 、M n), molecular weight distribution (MWD) and its polydispersity index PDI = M w / M n Describe the width (where M n is the number average molecular weight, and M w (weight-average molecular weight) was determined by gel permeation chromatography (GPC) according to ISO 16014-4 2019. A PL 220 (Polymer Laboratories) GPC equipped with an IR4 infrared detector and an online four-capillary bridge viscometer (PL-BV400-HT) was used. 3x Olexis and 1x Olexis Guard columns from Polymer Laboratories were used as stationary phases, and 1,2,4-trichlorobenzene (TCB, stabilized with 250 mg / L of 2,6-di-tert-butyl-4-methylphenol) was used as the mobile phase at 160°C and a constant flow rate of 1 mL / min. 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 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 is 0.094 cm 3 / g determined by NIST1475a.

[0277] The column set was calibrated using universal calibration (according to ISO 16014-2:2019) using at least 15 narrow MWD polystyrene (PS) standards ranging from 0.5 kg / mol to 11,600 kg / mol. The corresponding intrinsic viscosity of the PS standards was calculated from their corresponding concentrations (IR4), the online viscometer signal, and the determined detector constant for polystyrene. For low molecular weight PS with a molar mass below 3,000 g / mol, the initial weighed concentration was used due to end group effects in the IR detector.

[0278] Using the universal calibration method, the molecular weight (M2) of the sample for each chromatographic slice can be calculated using the following correlation:

[0279] logM1[η1]=V R =logM2[η2]

[0280] Where: M1 is the molar mass of PS

[0281] η1 is the intrinsic viscosity of PS

[0282] M2 is the molar mass of the sample

[0283] η2 is the intrinsic viscosity of the sample

[0284] V R To preserve volume

[0285] All data processing and calculations were performed using Cirrus Multi-Offline SEC-Software Version 3.2 (Polymer Laboratories, Varian inc. Company).

[0286] All samples were prepared by dissolving 5.0 to 9.0 mg of polymer in 8 mL (at 160° C.) stabilized TCB (same as mobile phase) at a maximum of 160° C. with gentle shaking for 3 h (for PE).

[0287] Tensile properties

[0288] The tensile properties of the molded specimens were determined on specimens prepared from compression-molded plaques with a specimen thickness of 4 mm. The tensile modulus was determined according to ISO 527-2 / 1A at 1 mm / min and 23°C. To determine the tensile stress at yield, a speed of 50 mm / min was used.

[0289] The tensile modulus in the machine direction (MD) and the tensile modulus in the transverse direction (TD) of the film were measured according to ASTM D882 at a 1% secant modulus with a test speed of 5 mm / min and a gauge length of 50 mm. The tensile stress at break of the film was measured according to ISO 527-3, specimen type 2, with a gauge length of 50 mm and a test speed of 500 mm / min.

[0290] Simple supported beam notched impact strength

[0291] Charpy notched impact strength is measured according to ISO 179 1eA at 23°C and -20°C using a 80×10×4 mm 3 The thermal conductivity is measured on molded bar test specimens prepared by compression molding according to ISO 294-1 or ISO 17855-2 using a melt temperature of 200°C.

[0292] flexural modulus

[0293] The flexural modulus is 80×10×4mm 3 The tensile strength is determined in 3-point bend according to ISO 178 on molded specimens prepared by compression molding according to ISO 294-1 or ISO 17855-2 using a melt temperature of 200°C.

[0294] strain hardening factor

[0295] The strain hardening factor (SHF) was measured at 180°C.

[0296] The strain hardening factor is defined as

[0297]

[0298] in

[0299] is the uniaxial extensional viscosity; and

[0300] The linear viscoelastic envelope (LVE) is the time-dependent shear viscosity η within the linear deformation range. + Determination of the linear viscoelastic envelope in tension based on IRIS Rheo Hub 2008 Discrete relaxation time spectra need to be calculated from the storage modulus data (G'(ω)) and the loss modulus data (G"(ω)). The linear viscoelastic data G'(ω), G"(ω) were determined by frequency sweep measurements at 180°C on an Anton Paar MCR 301 coupled to 25 mm parallel plates.

[0301] The basic calculation principles for determining discrete relaxation spectra are described in Baumgartel M. Winter HH, "Determination of the discrete relaxation and retardation time spectra from dynamic mechanical data," Rheol Acta 28:511519 (1989), which is incorporated by reference in its entirety.

[0302] IRIS Rheo Hub 2008 represents the relaxation time spectrum as the sum of N Maxwell modes

[0303]

[0304] where g i and λ i is the material parameter, G e is the equilibrium modulus.

[0305] The selection of the maximum number of modes N for determining the discrete relaxation spectrum was performed using the option "optimum" in IRIS RheoHub. e Set to zero.

[0306] Used to obtain The nonlinear fitting was performed on the IRIS Rheo Hub 2008 using the Doi-Edwards model.

[0307] Uniaxial extensional viscosity The uniaxial extensional flow measurements were performed on an Anton Paar MCR 501 coupled to a Sentmanat tensile fixture. The temperature for the uniaxial extensional flow measurements was set at 180 °C and the flow rate was applied for 0.3 s. -1 to 10s -1 The stretching rate dε / dt and covers the range of Hencky strain

[0308] ∈=(I-I0) / I0,

[0309] Where I0 is the original length, and I is the actual sample fixed length, ranging from 0.3 to 3.0.

[0310] Special attention was paid to the preparation of samples for extensional flow. The samples were prepared by compression molding at 180°C followed by controlled cooling to room temperature (no forced water or air cooling was used).

[0311] This procedure allows to obtain well-shaped samples without residual stresses.Before performing the uniaxial tensile measurements, the samples are left at the test temperature for a few minutes to ensure thermal stability (set temperature ± 0.1°C).

[0312] Film shrinkage

[0313] The shrinkage is determined in oil according to ISO 14616 and / or ISO 11501.

[0314] A 60 mm x 60 mm film sample was placed in oil (polydimethylsiloxane) at 160°C for 15 seconds. Afterwards, the sample was removed and conditioned at room temperature for 1 hour. Finally, the shrinkage, i.e., the change in dimensions, was measured. The shrinkage value was calculated as follows:

[0315] Shrinkage = (Lo-Lm)*100 / Lo

[0316] Where Lo is the original length (i.e. 60 mm) and Lm is the length measured after heat exposure. If the measured value increases (e.g. in the TD direction), the shrinkage is negative.

[0317] Optical performance

[0318] Haze was measured according to ASTM D 1003 on three-layer collation shrink films prepared as described in the Examples section below.

[0319] Gloss was measured at an angle of 60° on three-layer collation shrink films prepared as described in the Examples section below according to DIN 67530 / ISO 2813. Gloss values were recorded and reported in gloss units (GU).

[0320] Puncture resistance

[0321] Three-layer blown films with a thickness of 60 μm, prepared as described in the Examples section below, were tested for puncture resistance according to ASTM D5748. This test method measures the resistance of a film sample to penetration by a pear-shaped, 19 mm diameter, TFE fluorocarbon-coated probe of specified dimensions at a standard low-rate, single-test speed (250 mm / min). Conducted under standard conditions, the test method applies biaxial stress loading. Film specimens were cut to 150 mm x 150 mm to fit the fixture and conditioned at 23 ± 2°C and 50 ± 5% relative humidity.

[0322] The puncture energy (J) is the energy required until the probe penetrates the test specimen, both of which are measured using a high-precision 500N load cell and a crosshead position sensor.

[0323] Seal Initiation Temperature (SIT)

[0324] In principle, a heat seal is formed by bonding two layers of film (polymer) together in such a way that the surfaces are pressed together in close contact while at least partially melting. This test method also covers the evaluation part after the heat sealing process is carried out. The force required to separate the test strips of film containing the seal is measured using UTM (also used to identify the mode of failure of the specimen). Following ASTM F 2029; ASTM F 88 standards, the preferred film thickness is a test specimen of 30 microns, in which the sealed surface is selected. In the case of PE, after sealing, the sample should be conditioned at 23±2°C and 50±5% relative humidity for at least 24 hours. For the test, a minimum of five specimens should be used for each sealing temperature. The term "seal initiation temperature" (SIT) is designated as "heat seal initiation temperature at 5N", and it refers to the temperature at which a seal is formed that will have a seal strength of 5N after cooling. The heat seal strength is measured at the temperature at which the heat seal is formed immediately after the sealing operation (sealing time of 1.0 second and sealing pressure of 3 bar for films less than 65 microns and sealing time of 1.5 seconds for films 65 microns and greater in thickness) and at a specified time interval (at least 24 hours after the sealing cycle is completed and the seal has cooled to ambient temperature and reached maximum strength).

[0325] 2. Materials used

[0326] FB1350 bimodal ethylene / 1-butene copolymer (MDPE) with a melt flow rate MFR2 of 0.15 g / 10 min.

[0327] MFR5 is 0.60 g / 10 min and density is 935 kg / m 3 , commercially available from Borouge;

[0328] FT5236 tubular LDPE with a melt flow rate MFR2 of 0.75 g / 10 min and a density of 923 kg / m 3 , commercially available from Borouge; contains a slip additive.

[0329] FK2715 multimodal ethylene / 1-butene / 1-hexene terpolymer with a melt flow rate MFR2 of 1.3 g / 10 min and a density of 927 kg / m 3 , commercially available from Borouge;

[0330] 3505MC Enable 3505MC; metallocene-catalyzed ethylene / 1-hexene copolymer with a melt flow rate MFR2 of 0.5 g / 10 min and a density of 935 kg / m 3 , commercially available from ExxonMobil;

[0331] 1327MD Exceed 1327MD; a metallocene-catalyzed ethylene / 1-hexene copolymer with a melt flow rate MFR2 of 1.3 g / 10 min and a density of 927 kg / m 3 , commercially available from ExxonMobil;

[0332] rLDPE1 PCR-LDPE(ML)-A; post-consumer waste LDPE (LDPE+LLDPE content total >80 wt%) with a melt flow rate MFR2 of 1.1 g / 10 min and a density of 925 kg / m 3 , which can be purchased from Suzhou Jinhui Technology.

[0333] 3. Material properties

[0334] rLDPE

[0335] The properties of rLDPE1 were measured on molded specimens and are listed in Table 1 below.

[0336] Table 1: Properties of rLDPE1

[0337] performance rLDPE1 Tensile modulus 309MPa Yield tensile stress 10.6MPa Tensile strain at break 808％ flexural modulus 379MPa Charpy notched impact strength, 23℃ <![CDATA[78.7kJ / m 2 ]]> Charpy notched impact strength, -20℃ <![CDATA[11.3kJ / m 2 ]]>

[0338] strain hardening factor

[0339] The strain hardening factors (SHF) of rLDPE1, FT5236, FB1350, 3505MC and 1327MD were calculated by -1 The SHF results are comparable for grades with not too many long chain branches (when the strain rate is 0.05 s at 180 °C and the strain is 2.5). -1 When measured at a strain rate of 0.5 and a Hencky strain of 2.5, the SHF of all grades was less than 1.2, as shown in Table 2 below. LDPE grades rLDPE1 and FT5236 showed higher SHF due to long chain branching.

[0340] Table 2: Strain hardening factors

[0341] Material SHF rLDPE1 2.02 FT5236 2.90 FB1350 <1.2 3505MC <1.2 1327MD <1.2

[0342] Other features:

[0343] The melt flow rate and GPC data of FK2715, FB1350, 3505MC and 1327MD were measured. The results are shown in Table 3 below.

[0344] Table 3: Melt flow rate and GPC data.

[0345] FK2715 FB1350 3505MC 1327MD <![CDATA[MFR2[g / 10min]]]> 1.30 0.16 0.46 1.34 <![CDATA[MFR5[g / 10min]]]> 3.40 0.67 1.79 3.26 <![CDATA[MFR 21 [g / 10min]]]> 26 17 23.2 20.7 <![CDATA[FRR 21 / 2 ]]> 20 106 50 15.4 <![CDATA[FRR 21 / 5 ]]> 7.6 25.3 12.9 6.3 Mw[kg / mol] 107.7 224.3 103.4 105.5 Mn[kg / mol] 25.0 9.55 20.4 28.8 Mw / Mn 4.3 23.6 5.1 3.7

[0346] 4. Arrange shrink film

[0347] These films are produced on an industrial-scale three-layer extrusion blown film line (Polyrema) using three extruders (extruder main zone temperature setting of 180 to 220°C, die diameter of 180 mm, blow-up ratio (BUR) of 1:3, die gap of 1.8 mm, with internal bubble cooling). Blown films made of polyethylene blends are described herein for each film layer. Any polyethylene blend used in the film layers described above can be produced by any suitable conventional multilayer film extrusion line, preferably at a temperature of 150 to 230°C, more preferably at a temperature of 160 to 225°C. Conventional blown film production technology for this purpose is, in principle, known and available to those skilled in the art. Typically, each film layer is coextruded at a temperature in the range of 160 to 225°C, with a die temperature in the range of 205 to 220°C, and is cooled by blowing air at a temperature of 12 to 16°C to provide a frost line height of 1 to 2 times the die diameter. The blown films were produced on a Polyrema (Reifenhauser blown film line with internal bubble cooling system) with an output of 150 kg / h.

[0348] ABC film layers of Comparative Examples CE-1 and CE-2 and Inventive Examples IE-1 and IE-2 were prepared with a total thickness of 60 to 70 μm, with a thickness distribution of 25% / 50% / 25%. The total rLDPE content of the ABC film layers was approximately 37.5% by weight. The thickness and composition of the sealant layer (C) were identical to those of the inner surface layer (A). The composition of the ABC film layers of the first method is shown in Table 4 below.

[0349] Table 4: Collation shrink film (ABC film layer)

[0350]

[0351]

[0352] The transverse direction (TD) film shrinkage of the films of Examples IE-1, IE-2, CE-1 and CE-2 was measured and compared to the Figure 1 Shown in.

[0353] The films of IE-1 and IE-2 showed a film shrinkage TD of 13 to 16%, while the films of CE-1 and CE-2 showed a film shrinkage TD of 9 to 11%.

[0354] All of these film examples of IE-1, IE-2, CE-1 and CE-2 showed a film shrinkage MD of 75 to 79%, which were comparable to each other.

[0355] The optical properties of Examples IE-1, IE-2, CE-1 and CE-2 were measured and compared to the Figure 2 (Haze) Neutralization Figure 3 (gloss at 60°).

[0356] The films of IE-1 and IE-2 exhibited haze ranging from 12.0 to 12.1%, while the films of CE-1 and CE-2 exhibited haze ranging from 17.7 to 19.7%.

[0357] The films of IE-1 and IE-2 exhibited gloss at 60° of 94 to 98 GU, while the films of CE-1 and CE-2 exhibited gloss at 60° of 86 to 90 GU.

[0358] The tensile properties of Examples IE-1, IE-2, CE-1 and CE-2 were measured and compared to the Figure 4 Shown in.

[0359] The films of IE-1 and IE-2 exhibited a machine direction (MD) tensile modulus of 274 to 295 MPa, while the films of CE-1 and CE-2 exhibited a machine direction (MD) tensile modulus of 282 to 302 MPa.

[0360] The films of IE-1 and IE-2 exhibited a transverse direction (TD) tensile modulus ranging from 289 to 311 MPa, while the films of CE-1 and CE-2 exhibited a transverse direction (TD) tensile modulus ranging from 309 to 355 MPa.

[0361] The films of IE-1 and IE-2 exhibited a tensile stress at break in the machine direction (MD) ranging from 15.5 to 18.2 MPa, while the films of CE-1 and CE-2 exhibited a tensile stress at break in the machine direction (MD) ranging from 14.9 to 15.8 MPa.

[0362] The films of IE-1 and IE-2 exhibited a tensile stress at break in the transverse direction (TD) of 22.8 to 23.1 MPa, while the films of CE-1 and CE-2 exhibited a tensile stress at break in the transverse direction (TD) of 26.1 to 26.3 MPa.

[0363] The puncture energy and SIT of Examples IE-1, IE-2, CE-1 and CE-2 were measured and compared in Figure 5 Shown in.

[0364] The films of IE-1 and IE-2 showed a puncture energy of 1.3 J, while the films of CE-1 and CE-2 showed a puncture energy ranging from 0.9 to 1.2 J.

[0365] The films of IE-1 and IE-2 showed SITs of 110.5 to 111.1 °C, while the films of CE-1 and CE-2 showed SITs of 110.0 to 110.6 °C.

[0366] The films according to the present invention show improved TD shrinkage, comparable mechanical properties and comparable SIT which are generally acceptable on the market, while the films according to the present invention show improved haze and comparable gloss as well as slightly increased puncture energy.

[0367] Thus, the films according to the invention show a good balance of properties of shrinkage, mechanical properties, puncture resistance, sealing properties and optical properties, which surprisingly is not impaired by the presence of up to 40 wt% recycled LDPE.

Claims

1. A multilayer collation shrink film comprising an inner surface layer (A), a core layer (B) and an outer layer (C), wherein the core layer (B) is sandwiched between the inner surface layer (A) and the outer layer (C), and the core layer (B) comprises the following components: (B1) Recycled LDPE having a relative humidity of 1.5 to 5.0, preferably 1.8 to 4.5, when heated to 3.0s at 180°C. -1 The strain hardening factor when measured at a strain rate of 1000 s and a Hencky strain of 2.5; and (B2) linear copolymers of ethylene comprising at least one comonomer chosen from α-olefins having 4 to 10 carbon atoms and having a weight average molecular weight Mw of 150 to 400 kg / mol, preferably 160 to 350 kg / mol and a polydispersity index, i.e. the ratio Mw / Mn, determined by gel permeation chromatography (GPC) according to ISO 16014-4:2003 and ASTM D6474-12, of 15 to 35, preferably 17 to 32, preferably multimodal, more preferably bimodal; wherein the recycled LDPE (B1) has a lower density and a higher melt flow rate MFR2 than the linear copolymer of ethylene (B2), and The recycled LDPE (B1) is present in the core layer (B) in an amount of more than 50 wt%, such as 55 to 95 wt%, preferably 60 to 90 wt%, most preferably 65 to 85 wt%, based on the total weight of the core layer (B).

2. The multilayer collation shrink film according to claim 1 , wherein the linear copolymer of ethylene (B2) is present in the core layer (B) in an amount of less than 50 wt.-%, such as 5 to 45 wt.-%, preferably 10 to 40 wt.-%, more preferably 15 to 35 wt.-%, based on the total weight of the core layer (B).

3. The multilayer collation shrink film according to claim 1 or 2, wherein the linear copolymer of ethylene (B2) is a copolymer of ethylene and 1-butene comonomer units or a copolymer of ethylene and 1-hexene comonomer units, wherein the 1-butene comonomer units or the 1-hexene comonomer units are the only comonomer units present in the linear copolymer of ethylene (B2).

4. The multilayer collation shrink film according to any one of claims 1 to 3, wherein the linear copolymer of ethylene (B2) has one or more of the following properties, or all of the following properties: 930 to 945 kg / m 3 , preferably 932 to 942 kg / m 3 , most preferably 933 to 940 kg / m 3 Density determined according to ISO 1183; a melt flow rate MFR2, measured according to ISO 1133 at a temperature of 190° C. and a load of 2.16 kg, of 0.10 to 0.50 g / 10 min, preferably 0.10 to 0.40 g / 10 min, most preferably 0.12 to 0.30 g / 10 min; a melt flow rate MFR5, measured according to ISO 1133 at a temperature of 190° C. and a load of 5 kg, of 0.40 to 1.00 g / 10 min, preferably 0.45 to 0.90 g / 10 min, most preferably 0.50 to 0.80 g / 10 min; A melt flow rate, MFR, measured according to ISO 1133 at a temperature of 190° C. and a load of 21.6 kg, of 8.0 to 22.0 g / 10 min, preferably 10.0 to 20.0 g / 10 min, most preferably 11.0 to 19.0 g / 10 min 21 ; Flow rate ratio FRR of 60 to 150, preferably 70 to 140, most preferably 80 to 120 21 / 2 , that is, MFR 21 / MFR2 ratio; Flow rate ratio FRR of 20 to 32, preferably 22 to 30, most preferably 23 to 28 21 / 5 , that is, MFR 21 / MFR5 ratio; and / or Less than 1.2, preferably less than 1.1, most preferably 0.98 to 1.02 when at 180°C, at 3.0s -1 Strain hardening factor when measured at a strain rate of 1.5 and a Hencky strain of 2.

5.

5. The multilayer collation shrink film according to any one of claims 1 to 4, wherein the recycled LDPE (B1) originates from post-consumer waste or post-industrial waste, preferably from post-consumer waste.

6. The multilayer collation shrink film according to any one of claims 1 to 5, wherein the recycled LDPE (B1) has one or more of the following properties, or all of the following properties: 915 to 935 kg / m 3 , preferably 917 to 932 kg / m 3 , most preferably 920 to 930 kg / m 3 Density determined according to ISO 1183; a melt flow rate MFR2, measured according to ISO 1133 at a temperature of 190° C. and a load of 2.16 kg, of 0.1 to 2.0 g / 10 min, preferably 0.3 to 1.7 g / 10 min, most preferably 0.5 to 1.5 g / 10 min; a tensile modulus determined according to ISO 527-2 / 1A of 200 to 450 MPa, preferably 225 to 425 MPa, most preferably 250 to 400 MPa; 6.0 to 15.0 MPa, preferably 7.5 to 12.5 MPa, most preferably 9.0 to 11.5 MPa of tensile stress at yield, determined according to ISO 527-2 / 1A; 350 to 1200%, preferably 375 to 1100%, most preferably 400 to 1000% tensile strain at break, determined according to ISO 527-2 / 1A; Flexural modulus determined according to ISO 178 of 200 to 500 MPa, preferably 225 to 475 MPa, most preferably 250 to 450 MPa; 40 to 120 kJ / m 2 , preferably 45 to 110 kJ / m 2 , most preferably 50 to 100 kJ / m 2 Charpy notched impact strength at 23°C, measured according to ISO 1791eA; and / or 5.0 to 20.0 kJ / m 2 , preferably 6.0 to 18.0 kJ / m 2 , most preferably 7.0 to 16.0 kJ / m 2 The Charpy notched impact strength at -20°C is determined according to ISO 1791eA.

7. The multilayer collation shrink film according to any one of claims 1 to 6, wherein both the layer (A) and the layer (C) are in adhesive contact with respective surfaces of the core layer (B), and the multilayer film comprises up to seven layers, and preferably the multilayer film consists of three layers (A), (B) and (C), preferably, wherein the thickness of the core layer (B) in the multilayer collation shrink film is in the range of 40 to 70%, preferably in the range of 44 to 66%, most preferably in the range of 48 to 62%, and the thickness of the layer (A) and the layer (C) in the multilayer collation shrink film are independently in the range of 10 to 30%, preferably in the range of 15 to 28%, most preferably in the range of 19 to 26%, all based on the total thickness of the multilayer collation shrink film.

8. The multilayer collation shrink film according to any one of claims 1 to 7, wherein layer (A) comprises the following components: (A1) a multimodal copolymer of ethylene and at least one comonomer selected from α-olefins having 4 to 10 carbon atoms, said multimodal polymer of ethylene having a mass fraction of 920 to 940 kg / m 3 , preferably 922 to 937 kg / m 3 , most preferably 925 to 935 kg / m 3 a density determined according to ISO 1183 of 0.5 to 2.0 g / 10 min, preferably 0.7 to 1.8 g / 10 min, most preferably 1.0 to 1.6 g / 10 min, determined according to ISO 1133 at a temperature of 190° C. and a load of 2.16 kg; and (A2) LDPE; and Layer (C) comprises the following components: (C1) a multimodal copolymer of ethylene and at least one comonomer selected from α-olefins having 4 to 10 carbon atoms, the multimodal polymer of ethylene having a mass fraction of 920 to 940 kg / m 3 , preferably 922 to 937 kg / m 3 , most preferably 925 to 935 kg / m 3 a density determined according to ISO 1183 of 0.5 to 2.0 g / 10 min, preferably 0.7 to 1.8 g / 10 min, most preferably 1.0 to 1.6 g / 10 min, determined according to ISO 1133 at a temperature of 190° C. and a load of 2.16 kg; and (C2)LDPE.

9. The multilayer collation shrink film according to claim 8, wherein The multimodal copolymer of ethylene (A1) is present in layer (A) in an amount of 15 to 90 wt%, preferably 18 to 85 wt%, most preferably 20 to 82 wt%, and The LDPE (A2) is present in layer (A) in an amount of 10 to 85 wt%, preferably 15 to 82 wt%, most preferably 18 to 80 wt%, Both are based on the total weight of layer (A); and The multimodal copolymer of ethylene (C1) is present in layer (C) in an amount of 15 to 90 wt%, preferably 18 to 85 wt%, most preferably 20 to 82 wt%, and said LDPE (C2) is present in layer (C) in an amount of 10 to 85 wt%, preferably 15 to 82 wt%, most preferably 18 to 80 wt%, Both are based on the total weight of layer (C).

10. The multilayer collation shrink film according to claim 8 or 9, wherein the LDPE (A2) and / or the LDPE (C2) comprises virgin LDPE, recycled LDPE or a mixture of virgin LDPE and recycled LDPE, wherein the weight ratio of virgin LDPE to recycled LDPE in the mixture is preferably in the range of 5:1 to 1:2, more preferably in the range of 4:1 to 1:1, most preferably in the range of 3:1 to 2:1, and / or the LDPE (A2) and / or the LDPE (C2) has a density of 915 to 935 kg / m 3 , preferably 917 to 932 kg / m 3 , most preferably 920 to 930 kg / m 3 A density determined according to ISO 1183 of 0.1 to 2.0 g / 10 min, preferably 0.2 to 1.5 g / 10 min, most preferably 0.3 to 1.2 g / 10 min, determined according to ISO 1133 at a temperature of 190° C. and a load of 2.16 kg.

11. The multilayer collation shrink film according to any one of claims 8 to 10, wherein the multimodal copolymer of ethylene (A1) and / or the multimodal copolymer of ethylene (C1) is a terpolymer of ethylene and two different comonomers selected from α-olefins having 4 to 10 carbon atoms, preferably, the multimodal copolymer of ethylene (A1) and / or the multimodal copolymer of ethylene (C1) is a terpolymer of ethylene, 1-butene comonomer units and 1-hexene comonomer units, wherein the 1-butene comonomer units and the 1-hexene comonomer units are the only comonomer units present in the multimodal copolymer of ethylene (A1) and / or the multimodal copolymer of ethylene (C1), more preferably, the multimodal copolymer of ethylene (A1) and / or the multimodal copolymer of ethylene (C1) comprises a copolymer of ethylene and 1-butene comonomer units and a copolymer of ethylene and 1-hexene comonomer units.

12. The multilayer collation shrink film according to any one of claims 1 to 11, having one or more of the following properties, or all of the following properties: 60 to 85%, preferably 65 to 82%, most preferably 70 to 80% longitudinal shrinkage determined according to ISO 14616 and / or ISO 11501; 5 to 25%, preferably 7 to 22%, most preferably 9 to 20% transverse direction shrinkage determined according to ISO 14616 and / or ISO 11501; 5.0 to 19.0%, preferably 7.0 to 18.0%, most preferably 8.0 to 17.0% haze as measured according to ASTM D 1003; gloss at 60°, measured according to DIN 67530 / ISO 2813, of 70 to 130, preferably 73 to 120, most preferably 75 to 110; a longitudinal tensile modulus determined according to ASTM D882 of 225 to 600 MPa, preferably 240 to 550 MPa, most preferably 250 to 500 MPa; a transverse tensile modulus determined according to ASTM D882 of 250 to 650 MPa, preferably 265 to 600 MPa, most preferably 275 to 550 MPa; a tensile stress at break in the longitudinal direction, determined according to ISO 527-3, of 12.0 to 40.0 MPa, preferably 13.0 to 38.0 MPa, most preferably 14.0 to 36.0 MPa; a tensile stress at break in the transverse direction, determined according to ISO 527-3, of 15.0 to 40.0 MPa, preferably 18.0 to 36.0 MPa, most preferably 20.0 to 32.0 MPa; 0.8 to 3.0 J, preferably 0.9 to 2.5 J, most preferably 1.0 to 2.0 J of puncture energy determined according to ASTM D 5748; and / or • Seal initiation temperature measured according to ASTM F 2029, ASTM F88 of 100 to 125°C, preferably 103 to 120°C, most preferably 105 to 115°C.

13. The multilayer collation shrink film according to any one of claims 1 to 12, wherein the total amount of recycled LDPE in the multilayer collation shrink film is 25 to 55 wt%, preferably 27 to 53 wt%, most preferably 30 to 50 wt%, based on the total weight of the multilayer collation shrink film.

14. A method for producing a multilayer collation shrink film according to any one of claims 1 to 13, characterized in that The films were produced by a one-step blown film coextrusion process.

15. Use of the multilayer collation shrink film according to any one of claims 1 to 14 for secondary packaging, preferably for bottles and cans, more preferably for bottles and cans in the field of household products, food, health products and beverage products.

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