Polymer blends for producing bidirectionally oriented polymer films

Abstract

The present invention relates to a polymer blend for producing a bidirectionally oriented polymer film, said blend comprising: A) from 55% to 98% by weight of a first polyethylene component having a density in the range of from 0.948 to 0.960 g / cm3, a melt index MIF in the range of from 30 to 100 g / 10 min, and a melt flow ratio MIF / MIP in the range of from 15 to 35; and B) from 2% to 45% by weight of a second polyethylene component having a density in the range of from 0.949 to 0.965 g / cm3 and a melt index MIF in the range of from 5 to 30 g / 10 min.

Description

Technical Field

[0001] This disclosure relates to a polymer blend, its use, a method for producing a bidirectional polymer film, and a bidirectional polymer film. Background Technology

[0002] Polymer films are widely used in industrial manufacturing processes and non-industrial sectors for delivering goods to consumer markets in both wholesale and retail formats.

[0003] Currently, films composed of vinyl thermoplastic polymers dominate certain market applications, such as the market for household disposable products, garbage bags, and inner lining bags; outer packaging films and bags for laundry and dry cleaning items; and transport and takeaway bags for retail sales of non-perishable goods. In other aspects of the consumer goods delivery market, vinyl polymer films are only marginally competitive (if any) with other more expensive polymer films, such as plasticized PVC films and / or polypropylene films, such as in the heat shrink packaging film market for contour-fitting packaging of various items (especially perishable items such as cuts of meat, poultry, and fish). However, for other applications, such as packaging structures for agricultural products and grains, dry foods, and snacks, vinyl polymer films are competitive in certain cases.

[0004] Due to their valuable mechanical and optical properties, bidirectional oriented polymer films are increasingly in demand for packaging applications.

[0005] Examples of oriented polyethylene films are disclosed in WO9722470.

[0006] However, to achieve optimal performance, bidirectionally oriented polymer films typically have a multilayer structure containing layers of different polymer materials, such as polypropylene, polyethylene, polyethylene terephthalate, polyamide, and ethylene polyvinyl alcohol.

[0007] Such complex structures require complex processing in membrane fabrication and are difficult to meet current sustainability and recyclability requirements.

[0008] Polyethylene, especially high-density polyethylene (HDPE), is an attractive candidate material for the preparation of bidirectional oriented membranes with low complexity in terms of composition and structure.

[0009] In fact, HDPE can achieve high mechanical properties because it can be oriented to a relatively high draw ratio.

[0010] Furthermore, with proper processing, HDPE can acquire valuable optical properties.

[0011] However, due to processing difficulties, the application of HDPE in the preparation of bidirectional oriented films is severely limited, often resulting in insufficient final performance.

[0012] The purpose of this disclosure is to provide a polymer blend, its use, a method for producing a bidirectionally oriented polymer film, and a bidirectionally oriented polymer film that at least partially overcomes the disadvantages of the prior art and is simple and inexpensive to implement. Summary of the Invention

[0013] Therefore, this disclosure provides a polymer blend comprising:

[0014] A) 55% to 98% by weight, preferably 65% ​​to 98% by weight, more preferably 80% to 95% by weight, and most preferably 85% to 95% by weight of a first polyethylene component, wherein the density of the first polyethylene component is 0.948 to 0.960 g / cm³. ³ The melt flow index (MIF) is 35 to 100 g / 10 min, and the melt flow ratio (MIF / MIP) is 15 to 30 (specifically, up to 25); and

[0015] B) 2% to 45% by weight, preferably 2% to 35% by weight, more preferably 5% to 20% by weight, and most preferably 5% to 15% by weight of a second polyethylene component, wherein the density of the second polyethylene component is 0.949 to 0.965 g / cm³. ³ And the melt flow index (MIF) is 5 to 30 g / 10 min;

[0016] The weight percentages of the first polyethylene component and the second polyethylene component are relative to the total weight of the first polyethylene component.

[0017] Experiments have shown that the polymer blends of the present invention provide bidirectional oriented polymer films with unexpectedly good optical properties (especially haze and gloss) and mechanical properties (especially tensile strength). Detailed Implementation

[0018] In this paper: MIF represents the melt flow index measured at 190°C and 21.6 kg load; MIP represents the melt flow index measured at 190°C and 5 kg load; MIE represents the melt flow index measured at 190°C and 2.16 kg load.

[0019] The first polyethylene component A) and the second polyethylene component B) can be selected from ethylene homopolymers and ethylene copolymers, and mixtures thereof, containing α-olefin monomer units (preferably up to 10% by weight). Examples of the α-olefin monomer units are monomer units having 3 to 8 carbon atoms, particularly propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-pentene. 1-Butene and 1-hexene are preferred.

[0020] The homopolymers and copolymers can be obtained by polymerization processes in the presence of a coordination catalyst. These processes and the homopolymers and copolymers obtained therefrom are extensively described in the art.

[0021] In particular, polymerization processes can be carried out in the presence of Ziegler-Natta catalysts or single-point catalysts.

[0022] As is well known, Ziegler-Natta catalysts comprise reaction products of organometallic compounds from Groups 1, 2, or 13 of the periodic table with transition metal compounds from Groups 4 to 10 (new numbering system) of the periodic table. Specifically, the transition metal compound can be selected from compounds of Ti, V, Zr, Cr, and Hf, and is preferably supported on MgCl2.

[0023] Particularly preferred catalysts include reaction products of organometallic compounds of Group 1, Group 2 or Group 13 of the periodic table and solid catalyst components including Ti compounds supported on MgCl2.

[0024] The preferred organometallic compound is an organoaluminum compound.

[0025] Single-point catalysts are well known in the art and are typically selected from metallocene single-point catalysts and non-metallocene single-point catalysts.

[0026] Examples of metallocene single-point catalysts are zirconium and hafnium, such as cyclopentadienyl or indene complexes of zirconium or hafnium, like bis(cyclopentadienyl)zirconium dichloride; bis(indene)zirconium dichloride or bis(indene)hafnium dichloride.

[0027] An example of a nonmetallocene single-site catalyst is an iron complex preferably having a tripentate ligand.

[0028] Particularly suitable tridentate ligands are 2,6-bis[1-(phenylimino)ethyl]pyridine, and preferably the corresponding compounds in which both phenyl groups are substituted at the ortho position with halogen or tertiary alkyl substituents.

[0029] Specific examples are 2,6-bis[1-(2-tert-butylphenylimino)ethyl]pyridine iron(II) dichloride; 2,6-bis[1-(2-tert-butyl-6-chlorophenylimino)ethyl]pyridine iron(II) dichloride or 2,6-bis[1-(2,4-dichlorophenylimino)ethyl]pyridine iron(II) dichloride.

[0030] The metallocene single-site catalyst and the non-metallocene single-site catalyst can also be used in combination.

[0031] Preferably, the unit-point catalyst reacts with an activating compound (co-catalyst), a preferred example of which is an aluminum oxane, such as monomethylaluminoxane (MAO).

[0032] The polymerization reaction can be continuous or intermittent, carried out in the presence of the catalyst, according to known techniques, and in the liquid phase, in the presence or absence of an inert diluent, or in the gas phase or by liquid-gas mixing techniques.

[0033] Reaction time, pressure, and temperature are not critical compared to the polymerization step; however, a temperature of 50 to 100°C is optimal. Pressure can be atmospheric pressure or higher.

[0034] Molecular weight adjustment is achieved by using known modifiers, particularly hydrogen.

[0035] Typically, the term "copolymer" is intended to also include polymers containing more than one comonomer, such as terpolymers.

[0036] All of the ethylene homopolymers and copolymers described are commercially available. Specific commercial polymers suitable for producing these polymer blends are described in the examples.

[0037] Advantageously, but not necessarily, the tensile modulus of the first polyethylene component on the compression-molded sheet is at least 650 MPa (particularly, at least 800 MPa; more particularly, at least 850 MPa). According to some non-limiting embodiments, the tensile modulus of the first polyethylene component on the compression-molded sheet is up to 1300 MPa (particularly, up to 1200 MPa; more particularly, up to 1100 MPa).

[0038] Advantageously, but not necessarily, the second polyethylene component has a tensile modulus of up to 2000 MPa on the compression molding sheet (more specifically, up to 1800 MPa).

[0039] According to some non-limiting embodiments, the tensile modulus of the second polyethylene component on the compression molding sheet is at least 500 MPa (in particular, at least 600 MPa; more particularly, at least 800 MPa).

[0040] Advantageously, but not necessarily, the weight-average molecular weight Mw of the second polyethylene component is equal to or less than 170,000 g / mol (in particular, equal to or less than 160,000 g / mol).

[0041] In some non-limiting cases, the Mw of the second polyethylene component is equal to or greater than 90,000 g / mol (in particular, equal to or greater than 100,000 g / mol).

[0042] According to a particularly preferred but non-limiting embodiment, the Mw / Mn ratio of the second polyethylene component is equal to or less than 18.0 (specifically, equal to or less than 15.0).

[0043] In some non-limiting cases, the Mw / Mn ratio of the second polyethylene component is equal to or greater than 5.0 (in particular, equal to or greater than 6.0).

[0044] According to some non-limiting embodiments, the number average molecular weight Mn of the second polyethylene component is equal to or greater than 9000 g / mol (particularly equal to or greater than 10000 g / mol); particularly, equal to or less than 25000 g / mol (more particularly, equal to or less than 22000 g / mol).

[0045] According to some non-limiting embodiments, the z-average molecular weight Mz of the second polyethylene component is less than 800,000 g / mol (particularly equal to or less than 750,000 g / mol); particularly, equal to or greater than 200,000 g / mol (more particularly, equal to or greater than 250,000 g / mol).

[0046] Advantageously, but not necessarily, the mass-average molecular weight Mw of the first polyethylene component is equal to or greater than 175,000 g / mol (in particular, equal to or greater than 185,000 g / mol).

[0047] In some non-limiting cases, the Mw of the first polyethylene component is equal to or less than 250,000 g / mol (specifically, equal to or less than 210,000 g / mol).

[0048] Advantageously but not necessarily, the Mw / Mn ratio of the first polyethylene component is equal to or greater than 20.0 (in particular, equal to or greater than 22.0; more particularly, equal to or greater than 24.0).

[0049] In some non-limiting cases, the Mw / Mn ratio of the first polyethylene component is equal to or less than 35 (in particular, equal to or less than 30).

[0050] According to some non-limiting embodiments, the z-average molecular weight Mz of the first polyethylene component is equal to or greater than 800,000 g / mol (particularly equal to or greater than 900,000 g / mol); particularly equal to or less than 150,000 g / mol (more particularly equal to or less than 120,000 g / mol).

[0051] According to some non-limiting embodiments, the number average molecular weight Mn of the first polyethylene component is equal to or less than 9000 g / mol (in particular, equal to or less than 8000 g / mol); in particular, equal to or greater than 4000 g / mol (more particularly, equal to or greater than 6000 g / mol).

[0052] In all cases, Mw, Mn, and Mz were determined by gel permeation chromatography (GPC).

[0053] Experiments have shown that bidirectionally oriented polymer films with particularly good optical and mechanical properties can be obtained by using a second polyethylene component with relatively low Mw (and / or Mz) and / or Mw / Mn (see above).

[0054] Advantageously, but not necessarily, the density of the first polyethylene component is 0.950 to 0.960 g / cm³. ³ Alternatively or additionally, the density of the second polyethylene component is 0.952 to 0.960 g / cm³. ³ .

[0055] Advantageously, but not necessarily, the melt index (MIF) of the first polyethylene component is 40 to 80 g / 10 min, more preferably 45 to 80 g / 10 min.

[0056] Advantageously, but not necessarily, the melt index (MIP) of the first polyethylene component is 1.2 to 6.0 g / 10 min.

[0057] Advantageously, but not necessarily, the melt index (MIF) of the second polyethylene component is 5 to 28 g / 10 min, more preferably 10 to 25 g / 10 min.

[0058] Alternatively or additionally, the melt index (MIE) of the second polyethylene component is 0.1 to 3 g / min, more preferably 0.5 to 2 g / 10 min.

[0059] Advantageously, but not necessarily, the MIF / MIP of the second polyethylene component is 5 to 14, more preferably 5 to 12.

[0060] This polymer blend may also contain conventional additives.

[0061] Examples of these additives are heat stabilizers, antioxidants, UV absorbers, light stabilizers, metal deactivators, peroxide-degrading compounds, and basic co-stabilizers, typically added in amounts from 0.01% to 10% by weight of the total weight of the polymer blend, preferably from 0.1% to 5% by weight.

[0062] In another embodiment, this document provides a process for producing the aforementioned polymer blend. The process includes a combination step during which the components are combined by melting and mixing the first polyethylene component and the second polyethylene component, and the mixing is carried out in a mixing apparatus at a temperature typically between 160 and 250°C.

[0063] Any known device and technique can be used for this purpose.

[0064] The melt mixing apparatus useful in this paper is, in particular, an extruder or kneader, with a twin-screw extruder being especially preferred. These components can also be premixed at room temperature in the mixing apparatus.

[0065] In another embodiment, this document provides the use of the polymer blends described above for the production of bidirectional oriented polymer films.

[0066] According to some embodiments, the use includes a stretching step during which the polymer blend film is stretched in a first and second direction that intersect (particularly perpendicular) each other.

[0067] Specifically, the polymer blend film is stretched in the first direction at a stretch ratio of 3:1 to 9:1. Alternatively, the polymer blend film is stretched in the second direction at a stretch ratio of 3:1 to 7:1.

[0068] In some non-limiting cases, the thickness of the primary film before stretching is at least 0.3 mm (particularly, at least 0.5 mm), and the thickness of the biaxially oriented polymer film is less than 250 μm (particularly, less than 100 μm; more particularly, less than 50 μm).

[0069] In all cases, the preferred lower limit for thickness is 10 μm.

[0070] In another embodiment, this document provides a method for producing a biaxially oriented polymer film, the method comprising the stretching step disclosed above. Specifically, the polymer blend and the biaxially oriented polymer film are also disclosed above.

[0071] More precisely, but not necessarily, single-layer or multi-layer bidirectional oriented films can be prepared using known processes.

[0072] Specifically, they can be prepared using a tenter frame process. In this process, the polymer is extruded directly into cooling rollers in the form of a film, and then the film is passed through stretching units by rollers that move at a faster speed than the polymer is extruded. This orients the film in the longitudinal direction (MD).

[0073] The membrane extrusion is carried out using known techniques, preferably at a temperature of 180 to 300°C.

[0074] During the orientation stage in this stretching unit, the preferred main operating conditions are:

[0075] - Preheating temperature: 120 to 130°C;

[0076] - Warm-up time: 60 to 100 seconds;

[0077] -Stretching speed: 30 to 60 mm / second;

[0078] -Stretch rate: 50 to 70% / second;

[0079] - Draw ratio: 3:1 to 9:1.

[0080] The film is then fed into a tenter frame for transverse orientation. In the tenter frame, the film is maintained at a preheated temperature and clamped along each edge by grips attached to moving chains. These moving chains move outward to stretch the film in the transverse direction (TD). After stretching, the film undergoes heat setting to maintain its orientation before being rolled up.

[0081] During this stage, the preferred main operating conditions are:

[0082] -Stretch rate: 30% / second to 60% / second;

[0083] - Stretch ratio: 3:1 to 7:1.

[0084] This biaxially oriented membrane can also be conveniently produced using a double-bubble method. This method involves extruding the polymer components constituting the layers through an annular groove to produce a primary tubular membrane with concentric layers (when the membrane is multilayered). The primary membrane is then calibrated and rapidly cooled, followed by heating and orientation in both the longitudinal and transverse directions by compressed air inflation (TD) and increasing the speed of the take-up rollers (MD). The biaxially oriented membrane is then rapidly cooled to fix its molecular orientation. Annealing and shrinkage stabilization (if applicable) can be performed using a separate oven.

[0085] In all of the aforementioned processes, heating can be achieved by using, for example, an IR lamp or hot air or other heating elements (such as a resistance heater).

[0086] Biaxial orientation provides balanced mechanical properties. Biaxial film stretching significantly improves the tensile strength, flexibility, and toughness of the film. Orientation also enables the film to be used in heat-shrinkable applications.

[0087] Patent application WO9722470 also discloses a method for manufacturing oriented films.

[0088] In another embodiment, this document provides a bidirectionally oriented polymer membrane comprising or composed of polymer blends as disclosed above.

[0089] According to some non-limiting embodiments, the thickness of the bidirectional oriented polymer film is equal to or less than 250 μm (in particular, equal to or less than 100 μm; more particularly, equal to or less than 50 μm), with a preferred lower limit of 10 μm in all cases.

[0090] Specifically, the bidirectional polymer film was obtained using the method previously described.

[0091] Preferably, the bidirectional oriented polymer film has one or more of the following properties:

[0092] - Haze level is 2% to 20%; more preferably, 3% to 12%;

[0093] - Gloss of the film (at 45°C): 45 to 100 GU; preferably, 60 to 90 GU;

[0094] - Tensile modulus MD: 700 to 1600 MPa;

[0095] - Tensile modulus TD: 800 to 2500 MPa;

[0096] - Fracture strength MD: 100 to 250 MPa;

[0097] - Fracture strength TD: 180 to 350 MPa;

[0098] - Elongation at break (MD): 40% to 200%;

[0099] -Elongation at break (TD): 20% to 100%.

[0100] Example

[0101] The practices and advantages of the various embodiments, compositions, and methods provided herein are disclosed in the following examples. These examples are merely illustrative and are not intended to limit the scope of the appended claims in any way.

[0102] The following analytical methods are used to characterize polymer compositions.

[0103] Melt Flow Index

[0104] The determination was performed at 190°C and under the specified load, according to ISO 1133-1 2012-03.

[0105] density

[0106] Determined by immersion method at 23°C according to ISO 1183-1:2012.

[0107] Tensile modulus, yield strength and breaking strength, as well as yield elongation and breaking elongation

[0108] Determined according to ISO 527-2:2012 (for compression-formed sheets) and ASTM D882-18 (for films, TD and MD).

[0109] gloss

[0110] Determined according to ASTM D-2457-13.

[0111] Haze

[0112] Determined according to ASTM D-1003-13.

[0113] membrane shrinkage

[0114] According to ASTM D1204-14 (2020), the test was performed after placing the sample in air at 120°C for 5 minutes.

[0115] Molecular weight distribution determination

[0116] The average values ​​of Mw, Mn, and Mz, and the resulting Mw / Mn ratio, were determined by high-temperature gel permeation chromatography using the methods described in ISO 16014-1, ISO 16014-2, and ISO 16014-4, published in 2003. Details according to the mentioned ISO standards are as follows: solvent 1,2,4-trichlorobenzene (TCB); apparatus and solution temperature 145°C; and a PolymerChar (Valencia, Paterna 46980, Spain) IR-4 infrared detector compatible with TCB as the concentration detector. A WATERS Alliance 2000 system was used, equipped with the following pre-column SHODEX UT-G and separation columns SHODEX UT 806 M (3 columns) and SHODEX UT 807 (Showa Denko Europe GmbH, Konrad-Zuse-Platz 4, 81829 Muenchen, Germany) connected in tandem.

[0117] The solvent was vacuum distilled under nitrogen and stabilized with 0.025 wt% 2,6-di-tert-butyl-4-methylphenol. The flow rate used was 1 ml / min, the injection volume was 500 μl, and the polymer concentration was in the range of 0.01% < concentration < 0.05% w / w. Molecular weight calibration was established using monodisperse polystyrene (PS) standards in the range of 580 g / mol to 11,600,000 g / mol from Polymer Laboratories (now Agilent Technologies, Herrenberger Str. 130, 71034 Boeblingen, Germany), with hexadecane also used.

[0118] The calibration curve was then adapted to polyethylene (PE) using a general calibration method (Benoit H., Rempp P., and Grubisic Z., *Journal of Polymer Science, Phys. Ed.*, 5, 753 (1967)). The Mark-Houwing parameters used here are as follows: for PS, k PS = 0.000121 dl / g, α PS = 0.706, and for PE, k PE = 0.000406 dl / g, α PE = 0.725, effective in TCB at 135℃. Data logging, calibration, and calculations were performed using NTGPC_Control_V6.02.03 and NTGPC_V6.4.24 (hs GmbH, Hauptstraße 36, D-55437 Ober-Hilbersheim, Germany), respectively.

[0119] Comonomer content

[0120] According to ASTM D 6248 98, the comonomer content was determined by IR using a Tensor 27 FT-IR spectrometer from Bruker. The Tensor 27 FT-IR spectrometer was calibrated with a stoichiometric model used to determine the ethyl side chain in PE (when 1-butene is used as a comonomer) and the butyl side chain in PE (when 1-hexene is used as a comonomer).

[0121] Example 1 and Comparative Example 1

[0122] This example discloses the production of a sample of a bidirectional oriented polymer membrane and the properties of the resulting membrane.

[0123] The following commercially available starting materials sold by LyondellBasell Industries were used.

[0124] Component A): Hostalen GD 9555 (GD9555)

[0125] -MIP: 3.0g / 10min;

[0126] -MIF: 63g / 10min;

[0127] -MIF / MIP: 21;

[0128] - Density: 0.953 g / cm³ 3 ;

[0129] -Tensive modulus: Compression-formed sheet: 1050MPa;

[0130] - Yield tensile stress: Compression-formed plate: 25MPa;

[0131] - Yield tensile strain: Compression-formed plate: 10%.

[0132] Component B): Luflexen hyPE 56P FA (hyPE)

[0133] -MIE: 0.77g / 10min;

[0134] -MIF: 20.80g / 10min;

[0135] -MIP: 2.18g / 10min;

[0136] -MIF / MIP: 9.5;

[0137] - Density: 0.955 g / cm³ 3 ;

[0138] -Tensive modulus: Compression-formed sheet: 1220MPa;

[0139] The molecular weights are shown in Table 1 below.

[0140] Table 1

[0141]

[0142] Samples of bidirectional oriented polymer films having the following polymer blends were produced (percentages are by weight relative to the total weight of the polymer blends).

[0143] Example 1: 90% GD9555 + 10% hyPE;

[0144] - Comparative Example 1: 100% GD9555.

[0145] The following procedure was used to obtain the bidirectional polymer film.

[0146] A primary membrane with a thickness of 1 mm was prepared using the Leonard production line with the following characteristics under the following conditions:

[0147] - Extruder diameter: 40mm, L / D 27;

[0148] - Fixed displacement gear pump;

[0149] - Flat die, die lip width 200mm, die lip gap 1mm;

[0150] - Melting temperature: 240℃;

[0151] - 3 cooling rollers, 160mm in diameter, roller temperature 45°C;

[0152] - Membrane cutting unit.

[0153] 93x93mm specimens were cut from the primary membrane. These specimens were then oriented using a Brueckner KARO IV tensile element under the following conditions:

[0154] - Preheating temperature: 126°C;

[0155] Heating time: 80 seconds;

[0156] -Stretch rate: 64% / second;

[0157] - Stretching speed: 45mm / second;

[0158] -Stretch area: 70x70mm (outside the fixture);

[0159] - Stretch ratio: MD 6:1; TD 5:1;

[0160] - Final thickness: 23μm.

[0161] The bidirectional polymer film produced has the properties shown in Table 2 below.

[0162] Table 2

[0163]

[0164]

[0165] MD stands for "longitudinal direction". In other words, it means that the measurement is taken in the extrusion direction.

[0166] TD stands for "lateral direction". In other words, it means that the measurement is performed in a direction that is substantially perpendicular to the extrusion direction.

Claims

1. A polymer blend comprising: A) 55 to 98 wt%, preferably 65 to 98 wt%, more preferably 80 to 95 wt%, most preferably 85 to 95 wt% of a first polyethylene component having a density of 0.948 to 0.960 g / cm3 ³ a melt flow ratio MIF / MIP of 15 to 30 (in particular up to 25); and B) from 2 wt% to 45 wt%, preferably from 2 wt% to 35 wt%, more preferably from 5 wt% to 20 wt%, most preferably from 5 wt% to 15 wt%, of a second polyethylene component having a density of from 0.949 to 0.965 g / cm ³ and a melt index MIF of from 5 to 30 g / 10 min; wherein the weight % of the first polyethylene component A) and the second polyethylene component B) are relative to the total weight of A) and B); MIF is the melt index measured according to ISO 1133-1 2012-03 at 190 °C, 21.6 kg load; MIP is the melt index measured according to ISO 1133-1 2012-03 at 190 °C, 5 kg load.

2. The polymer blend according to claim 1, wherein the Mw / Mn of the first polyethylene component A) is equal to or higher than 20.0, preferably equal to or higher than 22.0, more preferably equal to or higher than 24.0, wherein Mw is the weight average molecular weight and Mn is the number average molecular weight, both measured by gel permeation chromatography (GPC).

3. The polymer blend according to claim 1 or 2, wherein the Mw / Mn of the second polyethylene component B) is equal to or lower than 18.0, preferably equal to or lower than 15.

0.

4. The polymer blend according to claim 1 or 2, wherein the z-average molecular weight Mz of the first polyethylene component A) is equal to or higher than 800000 g / mol, preferably equal to or higher than 900000 g / mol, the z-average molecular weight Mz being measured by gel permeation chromatography (GPC).

5. The polymer blend according to claim 1 or 2, wherein the z-average molecular weight Mz of the second polyethylene component B) is lower than 800000 g / mol, preferably equal to or lower than 750000 g / mol.

6. The polymer blend according to claim 1 or 2, wherein the tensile modulus of the first polyethylene component A) on a compression molded plaque is at least 650 MPa.

7. The polymer blend according to claim 1 or 2, wherein the melt index MIE of the second polyethylene component B) is from 0.1 to 3 g / min; wherein MIE is the melt index measured according to ISO 1133-1 2012-03 at 190 °C, 2.16 kg load.

8. The polymer blend according to claim 1 or 2, wherein the MIF / MIP of the second polyethylene component B) is from 5 to 14, preferably from 5 to 12.

9. A method for producing a biaxially oriented polymer film, the method comprising a stretching step during which a primary film comprising the polymer blend according to any one of claims 1 to 8 is stretched along two directions that cross each other, to obtain the biaxially oriented polymer film.

10. The method according to claim 9, wherein the thickness of the primary film is at least 0.3 mm.

11. A biaxially oriented polymer film consisting of or comprising the polymer blend according to any one of claims 1 to 8.

12. The biaxially oriented polymer film according to claim 11, having a thickness equal to or less than 250 pm.

13. The bidirectional oriented polymer film according to claim 11 or 12, which is stretched in the machine direction (MD) at a stretch ratio of 3: 1 to 9: 1 and in the transverse direction (TD) at a stretch ratio of 3: 1 to 7: 1.

Images