Biaxially oriented multilayer film

Abstract

The present invention relates to a multilayer film comprising: an inner layer system comprising a first surface and a second surface; a first skin layer adhered to the inner layer system at the first surface of the inner layer system; and a second skin layer adhered to the inner layer system at the second surface of the inner layer system; wherein the inner layer system consists of a polymer formulation (A), wherein the polymer formulation (A) comprises: > 60.0 and < 90.0 wt% of a first ethylene-based polymer which is a linear low density polyethylene A (LLDPE A); and > 10.0 and < 40.0 wt% of a high density polyethylene (HDPE) having a density > 940 and < 970 kg / m 3 , preferably > 955 and < 970 kg / m 3 ; measured according to ASTM D792 (2008); and the first and / or second skin layer is a sealing layer comprising a second ethylene-based polymer which is a linear low density polyethylene B (LLDPE B) comprising polymerized moieties derived from ethylene and 1-octene or 1-hexene having a density > 890 and < 915 kg / m 3 , preferably > 900 and < 915 kg / m 3 , measured according to ASTM D792 (2008); preferably, wherein the sealing layer comprises > 70.0 wt% of the second ethylene-based polymer, or wherein the sealing layer consists of the second ethylene-based polymer; wherein the multilayer film is a biaxially oriented film, wherein the biaxial orientation is introduced in solid state. This film allows the production of a sealed package having a sufficiently high seal strength at reduced sealing temperature (also referred to as seal initiation temperature) which at the same time has improved tensile properties, such as an improved tensile modulus in machine and transverse direction and an improved tensile strength in machine and transverse direction, which has proven.

Description

Technical Field

[0001] This invention relates to bidirectionally oriented multilayer films comprising vinyl polymers. The invention also relates to methods for producing such films. Furthermore, the invention relates to the use of such films in packaging applications such as food packaging. Specifically, this invention relates to films requiring certain heat-sealing properties. Background Technology

[0002] Films containing vinyl polymer materials are widely used in a variety of applications. One specific application of such films is food packaging. Applying these films allows for highly hygienic food packaging, contributing to long-term preservation of packaged products, and can be implemented in a very economical manner. Furthermore, these films can be produced with a highly attractive appearance. Examples of vinyl polymers include polyethylene, or PE.

[0003] A special type of film that can be produced from vinyl polymers is a biaxially oriented film, where the orientation is introduced in a solid form; it is also commonly referred to as a two-way oriented film or BO film. BO films are widely used in applications such as food packaging. Such BO films can be produced, for example, by casting extrusion of films stretched sequentially or simultaneously along both the longitudinal (also called longitudinal) and transverse directions. This produces films with high modulus and strength, allowing for smaller film sizes, one of the main driving factors in the packaging industry as it helps reduce packaging weight and material consumption. Furthermore, this type of film can be reliably processed on packaging lines at very high throughput rates.

[0004] An exemplary description of the production of BO film can be found, for example, in WO03 / 059599-A1, which describes a method for producing BO film using a so-called stretching frame, wherein after production by cast extrusion, the film is stretched longitudinally by the operation of various rollers, wherein the rollers apply a stretching force to the cast film due to the selected speed of the cooperating rollers, and the film is subsequently subjected to orientation forces in the transverse direction.

[0005] In many applications of BO film, it is required that the packaging be airtight after the contents to be stored are provided, so as to minimize or even eliminate the permeation of gases or moisture from the environment into the packaging. This is usually achieved by heat-sealing packaging. In this method, the remaining opening of the packaging is subjected to heat energy through direct heat contact or radiation, causing the film surface forming the inner side (and therefore facing the packaged article) to reach a temperature that softens it sufficiently, so that when contact pressure is applied and the temperature is lowered, a thermoplastic seal is formed, sealing the packaged contents away from the environment.

[0006] The temperature needs to be lowered to make the membrane sealing layer soft enough to allow for the production of a seal with sufficient strength. Summary of the Invention

[0007] The present invention achieves this objective through a multilayer film, the multilayer film comprising:

[0008] • An inner layer system comprising a first surface and a second surface;

[0009] • The first skin layer of the inner layer system is bonded to the first surface of the inner layer system; and

[0010] • The second skin layer of the inner layer system is bonded to the second surface of the inner layer system;

[0011] in:

[0012] • The inner layer system comprises a polymer formulation (A) comprising: ≥60.0 and ≤90.0 wt% of a first vinyl polymer, which is linear low-density polyethylene A (LLDPE A); and ≥10.0 and ≤40.0 wt% of high-density polyethylene (HDPE), which has a density of ≥940 and ≤970 kg / m³ as measured by ASTM D792 (2008). 3 Preferred values ​​are ≥955 and ≤970 kg / m³. 3 ;and

[0013] • The first and / or second skin layer is a sealing layer comprising a second vinyl polymer, which is linear low-density polyethylene B (LLDPE B) comprising a polymeric moiety derived from ethylene and 1-octene or 1-hexene, having a density ≥890 and ≤915 kg / m³ as measured by ASTM D792 (2008). 3 Preferred values ​​are ≥900 and ≤915 kg / m³. 3 Preferably, the sealing layer comprises ≥70.0 wt% of a second vinyl polymer, or the sealing layer is composed of a second vinyl polymer;

[0014] The multilayer film is a bidirectionally oriented film, wherein the bidirectional orientation is introduced in the solid state.

[0015] This film allows for the production of sealed packages with sufficiently high sealing strength at a reduced sealing temperature (also known as the sealing initiation temperature), while simultaneously exhibiting improved tensile properties, such as proven improved tensile modulus and tensile strength along both the longitudinal and transverse directions. The film of this invention has been shown to have the required low sealing temperature and can be prepared in a single processing step as a multilayer biaxially stretched film, eliminating the need for a lamination step on the biaxially oriented film for applications requiring sealing layers.

[0016] Furthermore, the membrane of the present invention is essentially composed of polyethylene as the polymer material within the membrane. This is highly advantageous because it makes the membrane particularly suitable for recycling purposes. The membrane can be understood as a "single-material" membrane. In common recycling technologies, attempts are made to separate waste polymer products into multiple streams based on the properties of the polymers constituting the waste. According to the prior art, many multilayer membranes consist of layers and compositions containing polymer products of different properties, and therefore they cannot be considered as single-material products, which reduces the recyclability of the membrane product and may even render them unsuitable for recycling. However, the membrane of the present invention is a single-material product, suitable for processing in recycling processes of various properties, making the membrane particularly suitable for recycling. In the context of the present invention, it should be understood that when referring to the membrane as essentially composed of polyethylene as the polymer material, it means that the membrane contains at least 90 wt% polyethylene material, preferably at least 95 wt%, relative to the total weight of the polymer material in the membrane.

[0017] HDPE densities can be, for example, ≥955 and ≤970 kg / m³. 3 The density of the second vinyl polymer can be, for example, ≥895 and ≤915 kg / m³. 3 Preferably ≥900 and ≤915 kg / m 3 More preferably ≥905 and ≤915 kg / m 3 .

[0018] In some embodiments of the invention, both the first and second skin layers are sealing layers comprising a second vinyl polymer. Particularly preferably, the sealing layer comprises ≥70.0 wt% of the second vinyl polymer. Even more particularly, the sealing layer may be composed of a second vinyl polymer.

[0019] When one of the first or second skin layers is not a sealing layer, the skin layer may, for example, comprise or consist of LLDPE, which comprises a polymeric moiety derived from ethylene and 1-hexene or 1-octene, having a density ≥918 and ≤940 kg / m³ as measured by ASTM D792 (2008). 3 Preferred values ​​are ≥918 and ≤930 kg / m³. 3 More preferably ≥918 and ≤925 kg / m 3 .

[0020] In some specific embodiments of the invention, the melt mass flow rate of the second vinyl polymer, as measured according to ASTM D1238 (2013) at a temperature of 190°C and a load of 2.16 kg, is ≥0.5 and ≤5.0 g / 10 min, preferably ≥0.5 and ≤4.0 g / 10 min, more preferably ≥0.5 and ≤2.5 g / 10 min.

[0021] Relative to its total weight, the fraction of the second vinyl polymer eluted in analytical temperature-elution fractionation (a-TREF) at a temperature ≤30.0°C can, for example, be ≤8.0 wt%, preferably ≤5.0 wt%, more preferably ≤3.0 wt%, even more preferably ≤2.0 wt%, and still even more preferably ≤1.0 wt%. Relative to its total weight, the fraction of the second vinyl polymer eluted in a-TREF at temperatures >30°C and <94.0°C can, for example, be ≥90.0 wt%, preferably ≥95.0 wt%, more preferably ≥97.0 wt%, and even more preferably ≥98.0 wt%. Relative to its total weight, the fraction of the second vinyl polymer eluted in analytical temperature-elution fractionation (a-TREF) at a temperature ≤30.0°C can, for example, be ≤3.0 wt%, and the fraction eluted in a-TREF at temperatures >30°C and <94.0°C can be ≥97.0 wt%. Relative to its total weight, the fraction of the second vinyl polymer eluted at a temperature ≤30.0°C in analytical temperature-elution fractionation (a-TREF) can be, for example, ≤2.0 wt%, and the fraction eluted at temperatures >30°C and <94.0°C in a-TREF can be ≥98.0 wt%.

[0022] The second vinyl polymer may contain, for example, ≥5.0 and ≤20.0 wt%, preferably ≥10.0 and ≤20.0 wt%, more preferably ≥10.0 and ≤15.0 wt% of a portion derived from 1-hexene or 1-octene, relative to its total weight. The second vinyl polymer may also contain, for example, ≥80.0 and ≤95.0 wt% of an ethylene-derived portion relative to its total weight. Preferably, the second vinyl polymer consists of ≥80.0 and ≤95.0 wt% of an ethylene-derived portion and ≥5.0 and ≤20.0 wt% of a portion derived from 1-hexene or 1-octene.

[0023] Application of comonomer content and type 13 C10 NMR was measured on a Bruker Avance 500 spectrometer equipped with a cryogenically cooled probe that operates at 125°C, thereby dissolving the sample in C2D2Cl4 containing DBPC as a stabilizer at 130°C.

[0024] The melt mass flow rate of the high-density polyethylene used in the membrane of the present invention, as measured according to ASTM D1238 (2013) at a temperature of 190°C and a load of 2.16 kg, can be, for example, ≥0.5 and ≤15.0 g / 10 min, preferably ≥0.5 and ≤10.0 g / 10 min.

[0025] Particularly preferred is that the high-density polyethylene is an ethylene homopolymer.

[0026] The inner layer system of the multilayer film of the present invention can, for example, consist of a single layer. Alternatively, the inner layer system can consist of 3, 5, or 7 layers. The inner layer system, relative to its total weight, can, for example, contain ≥20.0 and ≤40.0 wt%, preferably ≥20.0 and ≤35.0 wt%, and even more preferably ≥20.0 and ≤30.0 wt% of HDPE. The inner layer system is preferably composed of a single layer, wherein the single layer contains ≥10.0 wt% and ≤40.0 wt%, preferably ≥20.0 wt% and ≤40.0 wt%, more preferably 20.0 and ≤35.0 wt%, and even more preferably ≥20.0 and ≤30.0 wt% of HDPE.

[0027] The inner layer system may, for example, comprise ≥60.0 and ≤90.0 wt%, preferably ≥60.0 and ≤80.0 wt%, of LLDPE A, which comprises a polymeric moiety derived from ethylene and 1-hexene or 1-octene (preferably 1-hexene), having a density ≥918 and <940 kg / m³ as measured by ASTM D792 (2008). 3 Preferred values ​​are ≥918 and ≤930 kg / m³. 3 More preferably ≥918 and ≤925 kg / m 3 The melt flow rate of LLDPE A used in the inner layer system can be, for example, ≥0.5 and ≤5.0 g / 10 min, preferably ≥1.0 and ≤3.0 g / 10 min.

[0028] Preferably, it is the linear low-density polyethylene A:

[0029] • Density measured according to ASTM D792 (2008) is ≥918 and <940 kg / m³ 3 ;

[0030] • The melt mass flow rate, measured according to ASTM D1238 (2013) at a temperature of 190°C and a load of 2.16 kg, is ≥0.5 and ≤5.0 g / 10 min.

[0031] • The fraction eluted at a temperature ≤30.0 °C relative to the total weight of LLDPE in analytical temperature-eluting fractionation (a-TREF) is ≥3.0 wt%; and / or

[0032] • The fraction eluted in α-TREF at a temperature >94.0 °C relative to the total weight of LLDPE is ≥20.0 wt%.

[0033] The inner layer system may, for example, account for ≥60.0 wt% of the total weight of the multilayer film, preferably ≥70.0 wt%, more preferably ≥80.0 wt%. The first skin layer may, for example, account for ≥5.0 and ≤20.0 wt% of the total weight of the multilayer film, preferably ≥5.0 and ≤15.0 wt%, even more preferably ≥10.0 and ≤15.0 wt%. The second skin layer may, for example, account for ≥5.0 and ≤20.0 wt% of the total weight of the multilayer film, preferably ≥5.0 and ≤15.0 wt%, even more preferably ≥10.0 and ≤15.0 wt%. For example, the first skin layer may account for ≥5.0 and ≤20.0 wt% of the total weight of the multilayer film, preferably ≥5.0 and ≤15.0 wt%, even more preferably ≥10.0 and ≤15.0 wt%, and the second skin layer may account for ≥5.0 and ≤20.0 wt% of the total weight of the multilayer film, preferably ≥5.0 and ≤15.0 wt%, even more preferably ≥10.0 and ≤15.0 wt%.

[0034] The inner layer system may, for example, contain a certain amount of cavitation agent. Suitable cavitation agents may be, for example, inorganic compounds, such as those selected from calcium carbonate, magnesium calcium carbonate, silicates, talc, hydrated alumina, glass, metal or ceramic beads or spheres, and kaolin; or polar polymers, such as polymers selected from those of polybutylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polystyrene, polyacrylate, polyamide, crosslinked polylactic acid, and acrylic resins; or rubber particles. The inner layer system may, for example, contain ≥5.0 and ≤40.0 wt%, preferably ≥5.0 and ≤25.0 wt% of the cavitation agent. Preferably, the inner layer system contains ≤20.0 wt% of the cavitation agent, wherein the cavitation agent is selected from calcium carbonate and polar polymers. The average particle size of the cavitation agent particles may, for example, be 0.1-10 μm.

[0035] The thickness of the multilayer film can be, for example, ≥5μm and ≤200μm, preferably ≥10μm and ≤75μm.

[0036] In some embodiments, the present invention also relates to a method for producing the multilayer film, wherein the method comprises the following steps in sequence:

[0037] (a) Producing an unoriented multilayer film by cast extrusion, the unoriented film comprising:

[0038] • An inner layer system comprising a first surface and a second surface;

[0039] • The first skin layer of the inner layer system is bonded to the first surface of the inner layer system; and

[0040] • The second skin layer of the inner layer system is bonded to the second surface of the inner layer system;

[0041] in:

[0042] The inner layer system comprises a polymer formulation (A) comprising: ≥60.0 and ≤90.0 wt% of a first vinyl polymer, which is linear low-density polyethylene A (LLDPE A); and ≥10.0 and ≤40.0 wt% of high-density polyethylene (HDPE), which has a density of ≥940 and ≤970 kg / m³ as measured by ASTM D792 (2008). 3 Preferred values ​​are ≥955 and ≤970 kg / m³. 3 ;and

[0043] • The first and / or second skin layer is a sealing layer comprising a second vinyl polymer, which is linear low-density polyethylene B (LLDPE B) comprising a polymeric moiety derived from ethylene and 1-hexene or 1-octene, having a density ≥890 and ≤915 kg / m³ as measured by ASTM D792 (2008). 3 Preferably, the sealing layer comprises ≥70.0 wt% of a second vinyl polymer, or the sealing layer is composed of a second vinyl polymer;

[0044] (b) Heating the unoriented film to a temperature >70°C and <T< of the first vinyl polymer. pm T pm Peak melting temperature as measured according to ASTM D3418 (2008);

[0045] (c) Stretch the heated cast film by the following process:

[0046] A tensile force is applied in the longitudinal direction (MD) to stretch the film in the longitudinal direction, and the resulting film is subsequently heated to bring the film temperature to the T value of the first vinyl polymer. pm -25℃ and T pm Between, apply tensile force in the transverse direction (TD) to stretch in the transverse direction; or

[0047] o Apply tensile force simultaneously in the MD and TD directions to stretch in the MD and TD directions;

[0048] (d) Maintain tensile force and temperature to ensure that the TD-direction tension is maintained at >85% of the applied TD-direction tension; and

[0049] (e) Cool the stretched film to obtain a bidirectional oriented film.

[0050] Preferably, the stretch ratio in each of the MD and TD directions is at least 4.5, wherein the stretch ratio is the ratio of the dimensions of the film in a particular direction before and after the orientation step in that direction.

[0051] In one embodiment, the invention also relates to packaging comprising the multilayer film of the invention, wherein the packaging preferably comprises food.

[0052] In some embodiments of the invention, each of the first and second skin layers may contain up to 5.0 wt% of additives, such as anti-caking agents, slip agents, UV stabilizers, antioxidants, and processing aids. In some embodiments, the inner layer system may contain up to 5.0 wt% of additives, such as anti-fogging agents, pigments, and slip agents.

[0053] According to the present invention, analytical temperature-elution fractionation (also known as α-TREF) can be performed using a Polymer Char Crys taf-TREF 300 equipped with a stainless steel column of 15 cm in length and 7.8 mm in inner diameter. The solution used is a solution containing 4 mg / ml of sample prepared in 1,2-dichlorobenzene, which is stabilized at 150°C for 1 hour with 1 g / L Topanol CA (1,1,3-tris(3-tert-butyl-4-hydroxy-6-methylphenyl)butane) and 1 g / L Irgafos168 (tris(2,4-di-tert-butylphenyl)phosphite). Before analysis, the solution can be further stabilized at 95°C for 45 minutes with continuous stirring at 200 rpm. For analysis, the solution is crystallized from 95°C to 30°C using a cooling rate of 0.1°C / min. Elution is performed from 30 to 140°C using a heating rate of 1°C / min. The apparatus can be cleaned at 150°C. The sample injection volume can be 300 μl, and the pump flow rate during elution is 0.5 ml / min. The volume between the column and the detector can be 313 μl. In the context of this invention, the fraction eluted at temperatures ≤30.0 °C can be calculated by subtracting the fraction eluted at >30.0 °C from 100%, so that the sum of the fraction eluted at ≤30.0 °C and the fraction eluted at >30.0 °C is 100.0 wt%.

[0054] Specifically, Polymer Char Crys taf-TREF 300 can be used to perform α-TREF on a solution containing 4 mg / ml of polymer in 1,2-dichlorobenzene, wherein the solution is stabilized at 150°C for 1 hour with 1 g / L 1,1,3-tris(3-tert-butyl-4-hydroxy-6-methylphenyl)butane and 1 g / L tris(2,4-di-tert-butylphenyl)phosphite, and further stabilized at 95°C for 45 minutes with continuous stirring at 200 rpm, wherein the solution is cooled from 95°C to 30°C at a cooling rate of 0.1°C / min before analysis, and eluted from 30°C to 140°C at a heating rate of 1°C / min, and wherein the equipment is cleaned at 150°C.

[0055] The fraction eluted at temperatures ≤30°C can be calculated as follows: subtract the sum of the fraction eluted at >94°C and the fraction eluted at >30°C and ≤94°C from 100%, so that the sum of the fraction eluted at ≤30°C, the fraction eluted at >30°C and ≤94°C, and the fraction eluted at >94°C is 100.0 wt%.

[0056] In the context of this invention, CCDB is determined according to general formula I:

[0057]

[0058] General Formula I

[0059] in:

[0060] T n-2 For quantities calculated according to general formula II:

[0061]

[0062] Formula II

[0063] T z+2 For quantities calculated according to general formula III:

[0064]

[0065] Formula III

[0066] in:

[0067] w(i) represents the sample weight fraction (wt%) relative to the total sample weight in the a-TREF analysis of sample (i) collected at temperature T(i), where T(i) > 30℃. For T(i) > 30℃, the area under the a-TREF curve is normalized to surface area = 1; and

[0068] T(i) is the temperature, expressed in °C, at which sample (i) was collected in the a-TREF analysis.

[0069] In the multilayer film of the present invention, the chemical composition distribution width (CCDB) of the second vinyl polymer can be, for example, ≥5.0 and ≤25.0, preferably ≥5.0 and ≤12.5 or ≥15.0 and ≤25.0.

[0070] In the context of this invention, the bidirectionally oriented film (where both orientations are introduced in a solid state) is preferably not a blown film. In blown films, the orientation is introduced in a molten state. Preferably, the orientation of the film of the present invention is performed at a temperature at least 10°C lower than the melting temperature of the film. Example

[0071] The invention is described below through the following non-limiting embodiments. The following materials are used in the embodiments of the invention:

[0072] HDPE1 High-density polyethylene homopolymer with the properties shown in the table below HDPE2 High-density polyethylene homopolymer with the properties shown in the table below LLDPE1 SABIC LLDPE BX202, linear low-density polyethylene LLDPE2 SABIC SUPEER 8112, linear low-density polyethylene

[0073] The main properties of polyethylene materials are given in the table below.

[0074] Material HDPE1 HDPE2 LLDPE1 LLDPE2 MFR2 0.7 8.0 2.1 1.0 density 961 967 921 912 T pm ]]> 134 134 124 108 <![CDATA[T c ]]> 118 118 111 95 Ethylene unit content 100.0 100.0 89.0 88.1 Comonomer unit content 0.0 0.0 11.0 11.9 Comonomer type 0.0 0.0 C6 C8 <![CDATA[M n ]]> 9 11 18 32 <![CDATA[M w ]]> 105 72 109 95 <![CDATA[M z ]]> 670 324 463 205 <![CDATA[M w / M n ]]> 11.3 6.3 6.0 3.0 <![CDATA[M z / M w ]]> 6.3 4.5 4.2 2.2 <![CDATA[M z / M n ]]> 74 28.4 25.4 6.4 a-TREF<30 0.0 0.0 13.5 0.9 a-TREF 30-94 0.0 0.0 50.9 99.1 a-TREF>94 100.0 100.0 35.6 0.0 CCDB 8.6

[0075] in:

[0076] • MFR2 is the melt mass flow rate measured according to ASTM D1238 (2013) at a temperature of 190°C and a load of 2.16 kg, expressed in g / 10 min;

[0077] • Density measured according to ASTM D792 (2008), in kg / m³ 3 express;

[0078] ·T pm Peak melting temperature, measured by differential scanning calorimetry (DSC) according to ASTM D3418 (2008), is expressed in °C.

[0079] ·T c Crystallization temperature, expressed in °C, is measured by differential scanning calorimetry (DSC) according to ASTM D3418 (2008).

[0080] • Ethylene unit content refers to the weight of ethylene-derived units present in the polymer relative to the total weight of the polymer, expressed in wt%, also known as the amount of ethylene-derived portion;

[0081] • Comonomer content refers to the amount of weight of units derived from the comonomer present in the polymer, expressed in wt%, relative to the total weight of the polymer; it is also called the amount of the portion derived from the comonomer.

[0082] • The type of comonomer refers to the type of comonomer used in the production of the polymer, where C6 is 1-hexene and C8 is 1-octene;

[0083] Application of comonomer content and type 13 C10 NMR measurements were performed on a Bruker Avance 500 spectrometer equipped with a cryogenic probe that operates at 125°C.

[0084] The sample was dissolved at 130°C in C2D2Cl4 containing DBPC as a stabilizer. n M is the number average molecular weight. w The weight-average molecular weight and M z The z-average molecular weight is M.n M w and M z All measurements are expressed in kg / mol and measured according to ASTM D6474 (2012);

[0085] • a-TREF<30 refers to the concentration of a-TREF in wt% at the temperature as described above.

[0086] Polymer fraction eluted at ≤30.0℃, representing the amorphous fraction of the polymer.

[0087] It is calculated by subtracting a-TREF30-94 and a-TREF>94 ​​from 100.0 wt%; a-TREF30-94 refers to the percentage of a-TREF in wt% at temperatures >30.0 and ≤94.

[0088] Polymer fraction eluted at 94.0℃, representing the branched fraction of the polymer;

[0089] • α-TREF>94 ​​refers to the concentration of α-TREF, expressed as wt%, at temperatures >94.0 and <140°C.

[0090] The polymer fraction eluted from the bottom, representing the straight-chain fraction of the polymer;

[0091] • CCDB is the chemical composition distribution width calculated using the method described above.

[0092] α-TREF was performed on a solution containing 4 mg / ml of sample in 1,2-dichlorobenzene using a Polymer Char Crys taf-TREF 300 apparatus. The solution was stabilized for 1 hour at 150°C with 1 g / L Topanol CA (1,1,3-tris(3-tert-butyl-4-hydroxy-6-methylphenyl)butane) and 1 g / L Irgafos 168 (tris(2,4-di-tert-butylphenyl)phosphite). Prior to analysis, the solution was further stabilized at 95°C for 45 minutes with continuous stirring at 200 rpm. For analysis, the solution was crystallized from 95°C to 30°C using a cooling rate of 0.1°C / min. Elution was performed from 30°C to 140°C using a heating rate of 1°C / min. The apparatus was cleaned at 150°C.

[0093] Using the aforementioned polymer, five-layer and three-layer biaxially oriented films are produced. These biaxially oriented films are produced using a cast film production line with a subsequent tenter frame for sequential biaxial orientation.

[0094] For Experiment CE1 (Comparative Example) and E1 and E2 of the present invention, an apparatus comprising five melt extruders was used, wherein extruder A supplies material for the first skin layer A, extruder B supplies material for the first intermediate layer B, extruder C supplies material for the inner layer C, extruder D supplies material for the second intermediate layer D, and extruder E supplies material for the second skin layer E. The extruders were arranged to force molten material through a t-die with a die gap of 3.0 mm, resulting in an arrangement of layers A / B / C / D / E in the obtained cast film. Each extruder was operated to supply them with molten polymer material at a temperature of 240°C. The total throughput was 100 kg / h. The five layers of cast film were cooled to a temperature of 25-50°C on cooling rollers. After cooling, the film was stretched longitudinally through a set of rollers, preheated at 40-100°C to introduce a draw ratio of 5.0 longitudinally, and then annealed at 95°C. The film was then transversely stretched in a stretching oven at a stretch ratio of 10.0. The oven was initially operated at 140°C and ended at 100°C. Layer A was subjected to a stretching of 25 W / min / m. 2 Corona treatment was applied to obtain a biaxially oriented five-layer film with a thickness of 18 μm.

[0095] For embodiment E3 of the invention, an apparatus comprising three melt extruders is used, wherein extruder A supplies material for the first skin layer A, extruder C supplies material for the inner layer C, and extruder E supplies material for the second skin layer E. The extruders are arranged to force the molten material through a t-die, resulting in an A / C / E arrangement in the resulting cast film. Each extruder is operated to supply them with molten polymer material at a temperature of 250°C. The throughput is 135 kg / h. The film is cast along the extruder through the t-die onto cooling rollers to a temperature of 30°C, forming a cast film. The cooled cast film is stretched longitudinally using a set of stretch rollers at a temperature of 88-100°C, and then annealed at 95°C to achieve a longitudinal stretch ratio of 5.5.

[0096] Subsequently, the membrane is heated and stretched to a transverse stretch ratio of 7, and then passed through an oven continuously fed through the oven. The temperature at the oven inlet region is 152°C, decreasing to 110°C towards the oven outlet. Layer A is then subjected to a 25 W / min / m... 2 Corona treatment was applied to obtain a biaxially oriented three-layer film with a thickness of 24 μm.

[0097] The composition of the experimental membranes is shown in the table below. In all examples, the skin layers A and E contain 3.0 wt% of the anti-caking agent CON-X AB 664 and 5.0 wt% of the lubricant CON-X SL 577, both of which are available from Constab Polyolefin Additives GmbH.

[0098]

[0099] The percentage of material composition is related to the specific amount of material, expressed as wt% relative to the total weight of a given layer of material, where layer weight refers to the weight percentage of a given layer relative to the total weight of a given experimental membrane. In the table above, examples E1-E3 are examples of the present invention, and CE1 is a comparative example.

[0100] For the membrane thus obtained, a set of its properties are measured as shown in the table below.

[0101] Example E1 E2 E3 CE1 Haze 6.1 5.9 14.8 12.6 TM-MD 667 768 646 665 TM-TD 1257 1447 855 1617 TS-MD 64 47 86 89 TS-TD 210 247 73 214 EL-MD 294 272 256 246 EL-TD 31 30 112 24

[0102] in:

[0103] • Haze was measured according to ASTM D1003 (2013) and expressed as a percentage.

[0104] •TM is the tensile modulus, measured along the longitudinal (MD) and transverse (TD) direction of the membrane, expressed in MPa, wherein an initial sample length of 250 mm and a test speed of 25 mm / min are applied according to ASTM D882-18, and a preload of 1 N is applied at room temperature as 1% secant modulus measurement.

[0105] •TS is the tensile strength at break, measured in both the longitudinal (MD) and transverse (TD) directions according to ASTM D882-18, expressed in MPa, with an initial sample length of 50 mm and a test speed of 500 mm / min at room temperature;

[0106] •EL is the elongation at break, measured in both the longitudinal (MD) and transverse (TD) directions according to ASTM D882-18, expressed in MPa, with an initial sample length of 50 mm and a test speed of 500 mm / min at room temperature.

[0107] In addition, a series of sealing properties are determined as described below.

[0108] The heat seal strength was measured on a 15 mm wide sample according to ASTM F88 (2015) Application Method A. Finned seals were prepared at different temperatures according to ASTM F2029. Two identical membrane samples were pressed together, with layer E of the first membrane sample in contact with layer E of the second membrane sample. A seal was created by applying a force of 3.0 bar for 1.0 second, wherein the membrane was protected with 25 μm celluloid sheet. The press used to prepare the seal was heated to different temperatures to determine the strength of the seals produced at different temperatures. The seal initiation temperature was determined by varying the press temperature; that is, the lowest temperature at which a seal with a strength of at least 0.5 N / 10 mm was obtained.

[0109] The sealing strength was tested using a tensile testing machine at a test speed of 200 mm / min and a clamping distance of 10 mm. The maximum load was recorded as the sealing strength.

[0110] The following table shows the sealing strength test results of the membranes of the above embodiments sealed at different temperatures.

[0111]

[0112] In this table, SIT represents the seal initiation temperature, which is understood as the minimum temperature at which a seal strength of 0.5 N / 10 mm is obtained. This seal strength is expressed in N / 15 mm width.

[0113] In addition, the thermal bond strength of the membrane was measured. Measurements were taken on a 15 mm wide sample, with layer E to layer E, according to ASTM F1921 Method B. The sealing pressure was 0.3 N / mm². 2 The dwell time is 1.0 second. The delay time is 300 ms and the jig separation rate is 200 mm / s. The thermal bond strength is expressed in N / 15 mm width.

[0114]

Claims

1. A multilayer membrane, said membrane being a single-material membrane comprising at least 90 wt% polyethylene material relative to the total weight of polymer material in the membrane, and said membrane comprising: An inner layer system comprising a first surface and a second surface; The first skin layer of the inner layer system is bonded to the first surface of the inner layer system; and The second skin layer of the inner layer system is bonded to the second surface of the inner layer system; in: The inner layer system comprises a polymer formulation (A) comprising: ≥60.0 and ≤90.0 wt% of a first vinyl polymer, which is linear low-density polyethylene A (LLDPE A); and ≥10.0 and ≤40.0 wt% of high-density polyethylene (HDPE), which has a density of ≥940 and ≤970 kg / m³ as measured by ASTM D792 2008. 3 ;and The first and / or second skin layer is a sealing layer comprising a second vinyl polymer, which is linear low-density polyethylene B (LLDPE B) comprising a polymeric moiety derived from ethylene and 1-octene or 1-hexene, having a density ≥890 and ≤915 kg / m³ as measured by ASTM D792 2008. 3 The sealing layer comprises ≥70.0 wt% of a second vinyl polymer, or the sealing layer is composed of a second vinyl polymer; The multilayer film is a bidirectionally oriented film, wherein the bidirectional orientation is introduced in a solid form.

2. The multilayer film according to claim 1, wherein the linear low-density polyethylene A has: Measured according to ASTM D792 2008, the density is ≥918 and <940 kg / m³. 3 ; According to ASTM D1238 2013, at a temperature of 190°C and a load of 2.16 kg, the melt mass flow rate is ≥0.5 and ≤5.0 g / 10 min. The fraction eluted at temperatures ≤30.0 °C relative to the total weight of LLDPE was ≥3.0 wt% in analytical temperature-eluting fractionation (a-TREF); and / or The fraction eluted in α-TREF at temperatures >94.0 °C relative to the total weight of LLDPE is ≥20.0 wt%.

3. The multilayer film according to any one of claims 1-2, wherein the first and second skin layers are both sealing layers comprising a second vinyl polymer, wherein the sealing layer comprises ≥70.0 wt% of the second vinyl polymer, or wherein the sealing layer is composed of the second vinyl polymer.

4. The multilayer film according to any one of claims 1-2, wherein when one of the first or second skin layers is not a sealing layer, the skin layer comprises or is composed of LLDPE, said LLDPE comprising a polymeric moiety derived from ethylene and 1-hexene or 1-octene, having a density ≥918 and ≤940 kg / m³ as measured by ASTM D792 2008. 3 .

5. The multilayer film according to any one of claims 1-2, wherein the second vinyl polymer has: According to ASTM D1238 2013, at a temperature of 190°C and a load of 2.16 kg, the melt mass flow rate is ≥0.5 and ≤5.0 g / 10 min. The fraction eluted at ≤30.0 °C relative to the total weight of the second vinyl polymer was ≤8.0 wt% in analytical temperature-elution fractionation (a-TREF). The fraction eluted in a-TREF at temperatures >30°C and <94.0°C, relative to the total weight of the second vinyl polymer, is ≥90.0 wt%; and / or Chemical composition distribution width (CCDB) ≥5.0 and ≤25.

0.

6. The multilayer film according to any one of claims 1-2, wherein the melt mass flow rate of the high-density polyethylene is ≥0.5 and ≤10.0 g / 10 min, as measured according to ASTM D1238 2013 at a temperature of 190°C and a load of 2.16 kg.

7. The multilayer film according to any one of claims 1-2, wherein the second vinyl polymer comprises a portion derived from 1-hexene or 1-octene in an amount of ≥5.0 and ≤20.0 wt% relative to its total weight.

8. The multilayer film according to any one of claims 1-2, wherein the second vinyl polymer comprises ≥80.0 and ≤95.0 wt% of an ethylene-derived portion and ≥5.0 and ≤20.0 wt% of a 1-hexene or 1-octene-derived portion.

9. The multilayer film according to any one of claims 1-2, wherein the high-density polyethylene is a homopolymer of ethylene.

10. The multilayer film according to any one of claims 1-2, wherein the inner layer system consists of a single layer, or wherein the inner layer system consists of 3, 5 or 7 layers.

11. The multilayer film according to any one of claims 1-2, wherein the inner layer system comprises ≤20.0 wt% of a cavitating agent, wherein the cavitating agent is selected from calcium carbonate and polar polymers.

12. The multilayer film according to any one of claims 1-2, wherein the thickness of the film is ≥5. m and ≤200 m.

13. The multilayer film according to claim 12, wherein the thickness of the film is ≥10. m and ≤75 m.

14. A method for producing a multilayer film according to any one of claims 1-13, wherein the method comprises the following steps in sequence: (a) Producing an unoriented multilayer film by cast extrusion, said unoriented multilayer film being a single-material film comprising at least 90 wt% polyethylene material relative to the total weight of polymer material in the film, and said unoriented multilayer film comprising: An inner layer system comprising a first surface and a second surface; The first skin layer of the inner layer system is bonded to the first surface of the inner layer system; and The second skin layer of the inner layer system is bonded to the second surface of the inner layer system; in: The inner layer system comprises a polymer formulation (A) comprising: ≥60.0 and ≤90.0 wt% of a first vinyl polymer, which is linear low-density polyethylene A (LLDPE A); and ≥10.0 and ≤40.0 wt% of high-density polyethylene (HDPE), which has a density of ≥940 and ≤970 kg / m³ as measured by ASTM D792 2008. 3 ;and The first and / or second skin layer is a sealing layer comprising a second vinyl polymer, which is linear low-density polyethylene B (LLDPE B) comprising a polymeric moiety derived from ethylene and 1-octene or 1-hexene, having a density ≥890 and ≤915 kg / m³ as measured by ASTM D792 2008. 3 The sealing layer comprises ≥70.0 wt% of a second vinyl polymer, or the sealing layer is composed of a second vinyl polymer; (b) Heating the unoriented multilayer film to a temperature >70°C and <T< of the first vinyl polymer. pm T pm Peak melting temperature as measured according to ASTM D3418 2008; (c) Stretch the heated cast film by the following process: Apply a tensile force along the longitudinal direction (MD) to stretch the film longitudinally, and then heat the resulting film to bring the film temperature to the T value of the first vinyl polymer. pm -25℃ and T pm Meanwhile, a tensile force is applied in the transverse direction (TD) to stretch the material in the transverse direction; or o Apply tensile force simultaneously along MD and TD to stretch along MD and TD; (d) Maintain tensile force and temperature to ensure that the TD-direction tension is maintained at >85% of the applied TD-direction tension; and (e) Cool the stretched film to obtain a bidirectional oriented film.

15. The method of claim 14, wherein the stretch ratios along both the MD and TD directions are at least 4.5, wherein the stretch ratio is the ratio of the dimensions of the film in the respective direction before and after undergoing the orientation step in the particular direction.

16. Packaging comprising the multilayer film according to any one of claims 1-13.

17. The packaging according to claim 16, wherein the packaging is food packaging.

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