Multilayer film suitable for vertical form fill and seal

Abstract

This invention relates to multilayer films suitable for producing packaged materials in vertical fill and seal (VFFS) packaging production lines. The multilayer film comprises: a. a first skin layer and a second skin layer, wherein each of the first and second skin layers independently comprises: ≥30.0 ​​wt% and ≤45.0 wt% of an ethylene polymer relative to the total weight of the skin layers, wherein the density of the ethylene polymer is ≥918 kg / m³ as measured by ASTM D792 (2008). 3 and ≤930kg / m 3 ; ≥55.0 wt% and ≤70.0 wt% of the first ethylene-α-olefin copolymer, wherein the density of the first ethylene-α-olefin copolymer is ≥900 kg / m³ as measured by ASTM D792 (2008). 3 and ≤910kg / m 3 ; and b. a core layer located between the first and second skin layers, wherein the core layer comprises: ≥5.0 wt% and ≤25.0 wt% of an ethylene polymer relative to the total weight of the core layer; ≥25.0 wt% and ≤70.0 wt% of a first ethylene-α-olefin copolymer relative to the total weight of the core layer; and ≥25.0 wt% and ≤50.0 wt% of a second ethylene-α-olefin copolymer, wherein the density of the second ethylene-α-olefin copolymer is ≥850 kg / m³ as measured by ASTM D792 (2008). 3 and ≤900kg / m 3 .

Description

Technical Field

[0001] This invention relates to the field of polyethylene-based multilayer films, which are suitable for use in the production of packaged products in vertical fill and seal (VFFS) production lines. Background Technology

[0002] Vertical Fill and Seal (VFFS) is an automated assembly line product packaging process applicable to a variety of industries, from rubber granule packaging to food and beverage packaging. VFFS is a versatile process suitable for packaging both solid and liquid contents, providing a fast and efficient packaging system while ensuring packaging consistency—each package contains exactly the same amount of product. Typically, VFFS involves rolling flat plastic film into plastic bags, simultaneously filling these bags with the product, and then sealing the filled bags to obtain the final packaged product. However, the plastic bags used in VFFS production lines must have high rigidity (high modulus of elasticity) so that they can resist any tendency to deform after being filled with the product. Preventing deformation is crucial because any excessive deformation will cause the bag to lose its shape, hindering proper sealing and closure after filling, leading to product leakage or damage. Additionally, high rigidity also benefits the transport of the packaged material; the integrity of the packaged material's shape and structure helps prevent damage to the packaged product.

[0003] On the other hand, in some industries, the multilayer films used to form plastic bags on VFFS production lines must meet certain processing characteristics. For example, in the rubber industry, packaging bags made from such multilayer films are widely used for packaging rubber granules. Typically, in mixing equipment, the packaged rubber granules are directly fed into the kneader / mixer without removing the packaging bags. The ability to mix rubber granules without removing the plastic bags can improve the processing efficiency of the mixing machine and reduce operating costs. However, according to industry practitioners, in some cases, the material properties of the plastic bags or multilayer films are incompatible with the rubber melt during the mixing process, causing the plastic bags / films to remain intact as undispersed foreign matter in the rubber melt, resulting in defects in the final rubber product, such as "fisheye" defects. This defect reduces the aesthetics of the final rubber product and may cause the product to not meet customer specifications.

[0004] Therefore, one of the key requirements for the film and the plastic bags formed from it is its compatibility with the rubber melt. In other words, the multilayer film should have a sufficient melting point temperature so that the plastic bag / film can be blended with the rubber melt under mixing conditions, while ensuring that the plastic bags formed on the VFFS production line can be used to package hot rubber granules on the production line.

[0005] European patent EP0742248 B1 describes a film based on an ethylene-α-olefin copolymer suitable for use in rolling rubber bales. US patent 5,120,787 (Drasner) discloses a method for compounding rubber using a bag / seal layer prepared from an ethylene / ethylene acetate (EVA) copolymer, wherein the bag / seal layer is directly compounded with the rubber material. However, this patent disclosure does not specifically describe the requirements for a film suitable for use in VFFS production lines while retaining the desired processing properties. PCT patent PCT / EP2020 / 085419 describes a film suitable for using horizontal filler to wrap rubber bales. However, horizontal filler has less stringent requirements for the elastic modulus than vertical filler seals, and the film described in this PCT application is generally unsuitable for VFFS production lines.

[0006] Therefore, the object of the present invention is to provide a multilayer membrane suitable for use in vertical filler and sealer (VFFS) production lines, the membrane having one or more of the following advantages: (i) high hardness (or high elastic modulus) and mechanical properties; and (ii) suitable compatibility with rubber melts. Summary of the Invention

[0007] Therefore, one or more objectives of the present invention are achieved by a multilayer film comprising:

[0008] a. A first epidermal layer and a second epidermal layer, wherein the first epidermal layer and the second epidermal layer each independently comprise or consist of the following:

[0009] • ≥30.0 ​​wt% and ≤45.0 wt%, preferably ≥35.0 wt% and ≤45.0 wt%, of ethylene polymer relative to the total weight of the epidermis, wherein the density of the ethylene polymer is ≥918 kg / m³ as measured by ASTM D792 (2008). 3 and ≤940kg / m 3 Preferred weight: ≥920kg / m 3 and ≤930kg / m 3 ;

[0010] • A first ethylene-α-olefin copolymer comprising ≥55.0 wt% and ≤70.0 wt%, preferably ≥55.0 wt% and ≤65.0 wt%, wherein the density of the first ethylene-α-olefin copolymer is >900 kg / m³ as measured by ASTM D792 (2008). 3 and ≤915kg / m 3 Preferred weight: ≥905kg / m 3 and ≤910kg / m 3 ;and

[0011] b. A core layer located between the first and second epidermal layers, wherein the core layer comprises or is composed of the following:

[0012] • ≥5.0 wt% and ≤25.0 wt%, preferably ≥5.0 wt% and ≤20.0 wt%, of ethylene polymer relative to the total weight of the core layer;

[0013] • ≥25.0 wt% and ≤70.0 wt%, preferably ≥40.0 wt% and ≤60.0 wt%, of the first ethylene-α-olefin copolymer relative to the total weight of the core layer; and

[0014] • A second ethylene-α-olefin copolymer comprising ≥25.0 wt% and ≤50.0 wt%, preferably ≥25.0 wt% and ≤35.0 wt%, wherein the density of the second ethylene-α-olefin copolymer is ≥850 kg / m³ as measured by ASTM D792 (2008). 3 and ≤900kg / m 3 Preferred weight: ≥860kg / m 3 and ≤890kg / m 3 More preferably ≥865kg / m 3 and ≤885kg / m 3 Even more preferred is ≥865kg / m 3 and ≤875kg / m 3 .

[0015] Advantageously, the multilayer film of the present invention possesses excellent rigidity, making it suitable for use in VFFS packaging production lines. The multilayer film also has a suitable melting point temperature, ensuring compatibility with the polymer or rubber melt during the compounding process, either directly or in the form of packaging bags made from it. Furthermore, the multilayer film exhibits a range of superior mechanical properties, such as tear strength and tensile elongation, making it suitable for packaging products in VFFS production lines and for the transport and storage of packaged goods.

[0016] The term "skin layer" as used in this disclosure refers to the outermost layer of a multilayer film. The term "core" as used in this disclosure refers to the innermost layer of a multilayer film located between two skin layers. The term "rubber material" as used in this disclosure refers to ethylene propylene diene monomer (EPDM) rubber particles.

[0017] For example, the multilayer film may include a suitable proportion of ethylene polymer, a first ethylene-α-olefin copolymer, and a second ethylene-α-olefin copolymer, distributed in the skin layer and core layer of the multilayer film. For example, the multilayer film may include:

[0018] • ≥16.0 wt% and ≤30.0 wt%, preferably ≥20.0 wt% and ≤30.0 wt%, of ethylene polymer relative to the total weight of the multilayer film;

[0019] • ≥50.0 wt% and ≤70.0 wt%, preferably ≥50.0 wt% and ≤60.0 wt%, of a first ethylene-α-olefin copolymer relative to the total weight of the multilayer film; and / or

[0020] • The second ethylene-α-olefin copolymer comprises ≥14.0 wt% and ≤25.0 wt%, preferably ≥20.0 wt% and ≤25.0 wt%, relative to the total weight of the multilayer film.

[0021] In some aspects of the invention, the ethylene polymer has at least the following characteristics:

[0022] • Measured according to ASTM D1238 at 190°C and a 2.16 kg load, the melt flow rate (MFR) is ≥0.1 g / 10 min and ≤5.0 g / 10 min, preferably ≥0.1 g / 10 min and ≤1.0 g / 10 min, more preferably ≥0.1 g / 10 min and ≤0.7 g / 10 min, even more preferably ≥0.2 g / 10 min and ≤0.7 g / 10 min, even more preferably ≥0.2 g / 10 min and ≤0.5 g / 10 min; and / or

[0023] • Measured according to ASTM D3418-15, the melting temperature is ≥105℃ and ≤125℃, preferably ≥110℃ and ≤120℃, wherein differential scanning calorimetry (DSC) is applied. For a 10 mg membrane sample, the first heating and cooling cycle is conducted at temperatures between 23 and 200℃ with a heating and cooling rate of 10℃ / min, using nitrogen purge gas at a flow rate of 50 ± 5 mL / min. The subsequent second heating cycle is identical to the first heating cycle. The ethylene polymer can be, for example, low-density polyethylene (LDPE) or an ethylene polymer prepared by free radical polymerization using high-pressure polymerization, possessing the desired properties such as melt flow rate, density, and melting temperature.

[0024] The first ethylene-α-olefin copolymer preferably has at least one of the following:

[0025] • Melting temperature ≥85℃ and ≤115℃, preferably ≥88℃ and ≤105℃, wherein differential scanning calorimetry (DSC) is used, for a 10 mg membrane sample, the first heating and cooling cycle is at a temperature of 23-200℃ and a heating and cooling rate of 10℃ / min, using nitrogen purge gas at a flow rate of 50±5 mL / min, and the subsequent second heating cycle is the same as the first heating cycle; and / or

[0026] • Measured according to ASTM D1238 at 190°C and 2.16 kg load, the melt flow rate is ≥0.1 g / 10 min and ≤5.0 g / 10 min, preferably ≥0.5 g / 10 min and ≤3.0 g / 10 min, preferably ≥0.8 g / 10 min and ≤2.0 g / 10 min.

[0027] The second ethylene-α-olefin copolymer preferably has at least one of the following:

[0028] Melting temperatures ≥60℃ and ≤85℃, preferably ≥62℃ and ≤65℃, wherein differential scanning calorimetry (DSC) is used. For a 10 mg membrane sample, the first heating and cooling cycle is performed at temperatures between 23-200℃ with heating and cooling rates of 10℃ / min, using nitrogen purge gas at a flow rate of 50±5 mL / min. Subsequent second heating cycles are identical to the first heating cycle; and / or

[0029] Measured according to ASTM D1238 at 190°C and under a 2.16 kg load, the melt flow rate is ≥0.1 g / 10 min and ≤3.0 g / 10 min, preferably ≥0.8 g / 10 min and ≤2.0 g / 10 min.

[0030] The melting temperatures of ethylene polymers, first ethylene-α-olefin copolymers, and second ethylene-α-olefin copolymers can be measured using differential scanning calorimetry (DSC) according to the procedures outlined in ASTM D3418-15. The melting temperature measured using DSC represents the peak melting temperature (T0) observed during the heating / cooling cycle (enthalpy profile) of the DSC measurement. m ).

[0031] In some aspects of the invention, the first ethylene-α-olefin copolymer and the second ethylene-α-olefin copolymer are not identical and have different properties, such as density, melt flow rate, and number of α-olefin-derived units. For example, the first ethylene-α-olefin copolymer may refer to a plastide, while the second ethylene-α-olefin copolymer may refer to an elastomer. The plastide and elastomer copolymers can be distinguished based on the weight of the portion derived from α-olefin units, wherein the plastide has fewer α-olefin-derived units than the elastomer.

[0032] The first ethylene-α-olefin copolymer preferably comprises a portion derived from: (i) ethylene and (ii) a portion derived from one or more α-olefins having 3-12 carbon atoms, relative to the total weight of the first ethylene-α-olefin copolymer, comprising ≥2.0 wt% and ≤25.0 wt%, preferably ≥10.0 wt% and ≤20.0 wt%. The second ethylene-α-olefin copolymer preferably comprises a portion derived from: (i) ethylene and (ii) a portion derived from one or more α-olefins having 3-12 carbon atoms, relative to the total weight of the second ethylene-α-olefin copolymer, comprising ≥30.0 ​​wt% and ≤45.0 wt%, preferably ≥35.0 wt% and ≤40.0 wt%.

[0033] α-olefins having 3-12 carbon atoms can be selected, for example, from 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. α-olefins are preferably selected from 1-hexene or 1-octene. The content of α-olefins can be measured by any suitable technique, for example, on a Bruker Avance 500 spectrometer equipped with a cryogenically cooled probe operating at 125°C. 13 C NMR, in which the sample to be evaluated is dissolved in C2D2Cl4 containing the stabilizer DBPC at 130 °C.

[0034] The skin layer may include, for example, additives present in the layer. Non-limiting examples of such additives include antioxidants, UV stabilizers, slip agents, anti-caking agents, clarifying agents, pigments, masterbatch compositions, and nucleating agents. Preferably, the first skin layer and / or the second skin layer each independently further include one or more additives, present in an amount of ≥1.0 wt% and ≤6.0 wt%, preferably ≥1.5 wt% and ≤5.0 wt%, relative to the total weight of the skin layers.

[0035] A multilayer film may, for example, have at least three layers: two skin layers and a core layer located between the skin layers. In some aspects of the invention, one or more intermediate layers may be disposed between each skin layer and the core layer. Therefore, such a multilayer film may have more than three layers. For example, the intermediate layer may be an adhesive layer or a structural support layer.

[0036] In some aspects of the invention, the multilayer film has a suitable thickness. The thickness of the multilayer film is preferably ≥70 μm and ≤200 μm, more preferably ≥120 μm and ≤185 μm. The multilayer film is intentionally designed to have a suitable ratio of skin layer and core layer. The presence of the core layer relative to the total weight of the multilayer film is preferably ≥65.0 wt% and ≤80.0 wt%, more preferably ≥70.0 wt% and ≤80.0 wt%. The presence of the first skin layer and the second skin layer is preferably independently ≥5.0 wt% and ≤20.0 wt%, more preferably ≥10.0 wt% and ≤15.0 wt%, relative to the total weight of the multilayer film.

[0037] In one aspect of the invention, the inventors have surprisingly discovered that, considering the elastic modulus, tear resistance, tensile elongation, and melting temperature of the multilayer film, the multilayer film achieves a suitable balance between mechanical properties and processability. The multilayer film preferably has the following characteristics:

[0038] • Measured according to ASTM D882, the modulus of elasticity is ≥82.0 MPa and ≤150.0 MPa, preferably ≥95.0 MPa and ≤110.0 MPa; and / or

[0039] • Isothermal hot-stage analysis was performed using an optical microscope according to ISO 17025 (2017), with melting temperatures ≥70°C and ≤110°C, preferably ≥80°C and ≤105°C, wherein temperature scans were performed between ≥85°C and ≤150°C, analysis was performed for 3 minutes at each temperature, and heating and cooling rates were both 10°C / min; and / or

[0040] • Tear resistance along the machine direction (MD) ≥6.0 (g / μm) and ≤15.0 (g / μm), preferably ≥7.0 (g / μm) and ≤10.0 (g / μm), as measured according to ASTM D1922; and / or

[0041] • Yield tensile elongation ≥40.0% and ≤70.0% in the machine direction (MD), as measured by ASTM D882.

[0042] This level of elastic modulus provides suitable stiffness and is particularly suitable for the application of this multilayer film in VFFS packaging production lines. On the other hand, the melting temperature of the multilayer film can be determined using coupled hot-stage analysis and optical microscopy at the temperatures typically used in rubber / polymer compounding processes. Therefore, hot-stage analysis can simulate rubber / polymer compounding conditions, while optical microscopy is used to acquire images of the film sample at specific temperature intervals to visually determine the temperature at which the film sample completely melts, thus determining the film's melting temperature. For example, the film sample can be heated to 85°C, held isothermally at 85°C for 3 minutes, and an image of the film sample can be recorded. Subsequently, the film sample is heated to 90°C and held isothermally at this temperature for 3 minutes to acquire an image of the film sample at 90°C. The same steps can be repeated for temperatures of 95°C, 100°C, 105°C, 110°C, and 150°C, and images of the film sample at each specific temperature can be recorded. Therefore, the melting temperature of the multilayer film refers to the temperature at which the multilayer film essentially melts, leaving no visible film residue traces under an optical microscope. The term "basic" as used herein means that 99 wt% of the membrane sample has been melted, preferably 99.5 wt% of the membrane sample has been melted, and more preferably 100 wt% of the membrane sample has been melted.

[0043] Ethylene polymers and ethylene-α-olefin copolymers can be prepared as described in existing publications, such as the production of LDPE and LLDPE polymers described in Andrew Peacock's (2000; Dekker; ISBN 0824795466) publication "Handbook of Polyethylene," pages 43-66. Ethylene polymers can be prepared using high-pressure polymerization or free radical polymerization. Preferably, ethylene-α-olefin copolymers are prepared using Zeigler-Natta catalysts or metallocene catalysts, employing any of gas-phase fluidized bed polymerization, solution polymerization, or slurry polymerization; more preferably, ethylene-α-olefin copolymers are prepared using gas-phase polymerization with metallocene catalysts. Alternatively, the multilayer films of the present invention can be prepared by blending commercially available polymers in the specific proportions described in this disclosure.

[0044] The multilayer film of the present invention can generally be prepared by any method known in the art. For example, the multilayer film can be prepared by blown film co-extrusion, such as the method disclosed in "Film Extrusion Manual", (TAPPIPRESS, 2005, ISBN 1-59510-075-X, Editor Butler, pages 413-435). For example, in the co-extrusion method, various resins can be melted first in separate extruders and then mixed together in a feed module. The feed module is a series of flow channels that allow the layers to form a homogeneous flow. Leaving the feed module, this multilayer material then flows through an adapter and out of a die. The blown film die can be an annular die. The diameter of the die can range from a few centimeters to more than three meters wide. The molten plastic is pulled upward from the die by a pair of pressure rollers above the die (e.g., from 4 meters to more than 20 meters). Changing the speed of these pressure rollers will change the size (wall thickness) of the film. An air ring can be provided around the die. The air flowing out of the air ring cools the upward-traveling film. An air outlet can be located at the center of the die, through which compressed air is forced into the center of the extruded annular shape, creating a bubble. This causes the extruded annular cross-sectional area to expand at a certain ratio (a multiple of the die diameter). This ratio, called the "blow ratio," can range from, for example, a few percent of the initial diameter to greater than 300%. A pressure roller flattens the bubble into a double-layered film with a width (called "flattening") equal to half the bubble's circumference. This film is then wound or printed, cut into specific shapes, and heat-sealed into bags or other objects.

[0045] For example, a method for preparing a multilayer film may include the following sequential steps:

[0046] • At a temperature not exceeding 40°C, three different polymer compositions are independently mixed in a V-type mixer for about 3-5 minutes, wherein each of the three polymer compositions is suitable for forming a first skin layer, a core layer, and a second skin layer.

[0047] • Each of the formed compositions is introduced independently into the feeder of an extruder capable of independently extruding each composition;

[0048] Optionally, a lubricating additive and an anti-caking additive may be added to the composition suitable for forming the skin layer of the multilayer film of the present invention;

[0049] The above composition was extruded using three co-extrusion production lines to form a uniform extrudate;

[0050] • The extrudate is processed using a conventional screw extruder, followed by the application of a feed splitter to form a molten polymer composition; and

[0051] • Using different types of annular dies, the molten polymer composition is conveyed to the die head section to form a film precursor; and

[0052] • The cooling film precursor forms the multilayer film of the present invention.

[0053] The multilayer film of the present invention provides a suitable balance of performance, which in turn allows the film to be used in a variety of articles for different applications. Articles comprising the multilayer film are preferably selected from packaging bags, agricultural films, or shrink films. The articles are preferably packaging bags suitable for use in vertical fill and seal (VFFS) packaging production lines for rubber granules. In some aspects of the invention, the present invention relates to the use of the multilayer film as a packaging bag suitable for producing packaged materials in a vertical fill and seal (VFFS) packaging production line. In some aspects of the invention, the present invention relates to a method for producing packaged materials in a vertical fill and seal (VFFS) packaging production line, wherein the method comprises the following sequential steps:

[0054] • Provides a packaging bag comprising the multilayer film of the present invention, wherein the packaging bag has a sealed end and an open end, such that the longitudinal axis of the packaging bag passes through the sealed end and the open end axially;

[0055] • Clamp the packaging bag at the sealed end, where the open end and the closed end are coaxial with the longitudinal axis;

[0056] • The material to be packaged is introduced into the packaging bag through the open end until at least part of the packaging bag is filled;

[0057] • The open end of the sealed packaging bag; and

[0058] Remove the clips and obtain the packaged materials.

[0059] The following provides specific embodiments to verify some implementations of the present invention. These embodiments are for illustrative purposes only and are not intended to limit the invention. It should be understood that the embodiments and aspects disclosed herein are not mutually exclusive, and these aspects and embodiments can be combined in any way. Those skilled in the art will readily recognize that some parameters can be changed or adjusted to produce substantially the same results. Example

[0060] Objective: To evaluate the polyethylene-based multilayer membrane prepared according to the embodiments of the present invention. The properties of the membrane of the present invention are compared with those of membranes prepared from other polyethylene compositions (CF1-CF3 membranes) and membranes prepared from ethylene-vinyl acetate (EVA) (CF4).

[0061] Materials used in multilayer films:

[0062] The multilayer film of this invention is prepared from the following materials:

[0063] Table 1

[0064]

[0065] The specific details of the material grade are as follows:

[0066] Table 2

[0067]

[0068] Methods for preparing multilayer films:

[0069] Multilayer films are prepared using the following general steps:

[0070] (a) Three different polymer compositions were independently mixed in a V-type mixer for about 3 minutes at a temperature of about 35°C, wherein each of the three polymer compositions was suitable for forming a first skin layer, a core layer and a second skin layer.

[0071] (b) Subsequently, the formed compositions are independently introduced into the feeder of an extruder capable of independently extruding each composition using three co-extrusion lines;

[0072] (c) The above-mentioned composition thus obtained is extruded using three co-extrusion production lines (extruders A, B, and C) to form a uniform extrudate;

[0073] (d) Adding a lubricating additive and an anti-caking additive to the composition suitable for forming a skin layer in extruders A and C;

[0074] (e) The extrudate thus obtained is further processed using a conventional screw, and then a feed splitter is used to form a molten polymer composition;

[0075] (f) Using different types of annular molds, the molten polymer composition is conveyed to the die head section to form a film precursor; and

[0076] (g) Subsequently, the cooling film precursor forms a multilayer film.

[0077] Specifically, the extrusion conditions applied are summarized below:

[0078] Table 3: Processing conditions of the extruder

[0079] Screw speed (rpm) Melt pressure (bar) Melt temperature (°C) Extruder A (first skin layer) 7 ～104 ～200 Extruder B (core layer) 43 ～140 ～215 Extruder C (Second Skin Layer) 7 ～176 ～201

[0080] Table 4: Extruder Temperature (°C)

[0081] Extruder A (°C) Extruder B (°C) Extruder C (°C) Temperature Zone 1 40-190 40-200 40-190 Temperature Zone 2 195-200 210 195-200 Temperature Zone 3 210 210 210

[0082] Table 5: Extrusion Specifications and Processing

[0083] mold diameter Mold gap Output air ring 200mm 2.5 41kg / h 34％

[0084] The following test procedure was used to evaluate the membrane:

[0085] Melting temperatures of the constituent polymers: The melting temperatures of the ethylene polymer, the first ethylene-α-olefin copolymer, and the second ethylene-α-olefin copolymer were measured using differential scanning calorimetry (DSC) according to the procedure outlined in ASTM D3418-15, as described below:

[0086] • First, weigh the sample using a balance with an accuracy of ±0.01 mg, and use a membrane sample with a mass of 10 mg.

[0087] • Purge the DSC sample cell with nitrogen at a flow rate of 50±5 mL / min, and place samples and empty reference disks of the same size, shape and material in their respective positions;

[0088] • Then, the sample was equilibrated at 23°C for 1 minute, followed by heating to 200°C at a rate of 10°C / min, and the first heating curve was recorded. The sample was then held at 200°C for 2 minutes.

[0089] Subsequently, the sample was cooled at a rate of 10 °C / min, and the cooling curve was recorded. The above steps were repeated to record the second heating curve.

[0090] Melting temperature of multilayer films:

[0091] The melting temperature of the multilayer film was measured by coupling isothermal hot-stage analysis and optical microscopy, following the process steps outlined in ISO 17025 (2017) and at temperature conditions commonly used in rubber / polymer compounding. Analytical samples were ~1.5 mm x 1.5 mm in size. The samples were placed on circular glass slides with a diameter of 1.5 cm. The samples were covered with the same slides and examined using a hot-stage optical microscope (a Leica DMRXP research optical microscope equipped with a Linkam THMS600 heating stage). The samples were heated to 85 °C, held isothermally at 85 °C for 3 minutes, and images of the film samples were recorded. Subsequently, the film samples were heated to 90 °C, held isothermally at this temperature for 3 minutes, and images of the film samples at 90 °C were recorded. The same steps were repeated at various temperatures of 95 °C, 100 °C, 105 °C, 110 °C, and 150 °C, and images of the film samples at each specific temperature were recorded.

[0092] Elastic modulus, yield tensile elongation (TE), and yield tensile strength: measured according to the procedures outlined in ASTM D882.

[0093] Tear resistance: Tear resistance is measured according to the procedures outlined in ASTM D1922.

[0094] Multilayer membrane sample: Analysis of the following membrane structure:

[0095] The membrane 1 (IF1) of the present invention has the polymer distribution shown in the table below:

[0096] Table 6: Membrane (IF1) of the present invention

[0097]

[0098] The membrane 2 (IF2) of the present invention has the polymer distribution shown in the table below:

[0099] Table 7: Membrane (IF2) of the present invention

[0100]

[0101] Comparative membrane 1 (CF1) has the polymer distribution shown in the table below:

[0102] Table 8: Comparison Membrane (CF1)

[0103]

[0104] Comparative membrane 2 (CF2) has the polymer distribution shown in the table below:

[0105] Table 9: Comparison Membrane (CF2)

[0106]

[0107] Comparative membrane 3 (CF3) has the polymer distribution shown in the table below. The membrane structure of membrane CF3 is similar to that described in PCT application PCT / EP2020 / 085419, which describes a membrane suitable for use in horizontally filled rubber packages.

[0108] Table 10: Comparison Membrane (CF3)

[0109]

[0110] Comparative membrane 4 (CF4) is an ethylene-vinyl acetate (EVA) based membrane, which has the polymer distribution shown in the table below:

[0111] Table 11: Comparison Membrane (CF4)

[0112] membrane Thickness (140μm) EVA content (wt%) plastic body Slip aids and anti-caking agents First epidermis 28 94 0 6 Core layer 84 0 97.5 2.5 Second epidermis 28 94 0 6

[0113] The evaluation results of the membranes of the present invention (IF1 and IF2) and the control membranes (CF1-CF4) are as follows:

[0114] Table 12: Performance Parameter Results

[0115]

[0116] As can be seen from the results shown in the table above, the films of the present invention (IF1 and IF2) exhibit a balance of the required melting temperature and elastic modulus compared to the comparative films (CF1-CF4). Specifically, as shown in the films IF1 and IF2 of the present invention, the combination of the ethylene polymer, the first ethylene-α-olefin copolymer, and the second ethylene-α-olefin copolymer has an elastic modulus that is at least 63% higher than that of the comparative films (IF2 compared to CF2), indicating that this film has the stiffness required for VFFS packaging production lines. Surprisingly, the IF1 and IF2 films show melting temperatures suitable for compounding. Optical microscopy analysis revealed no trace amounts of residual film near the melting temperature of the films, and the resulting rubber-based products were free of "fisheye" defects.

[0117] Furthermore, the hardness characteristics of the films IF1 and IF2 of this invention are improved compared to the multilayer film CE3 typically used for horizontal filling. Additionally, the mechanical properties of the films IF1 and IF2 of this invention, such as tear resistance, elongation at break, and tensile strength, are also improved compared to the multilayer film CF4 (EVA-based). For example, the elongation at break of the IF1 film is nearly 46% higher than that of the CF4 film (EVA-based film). These advantageous properties make the films of this invention more durable when packaging and transporting products such as rubber granules or food and beverages.

Claims

1. A multilayer film, comprising: a. A first epidermal layer and a second epidermal layer, wherein the first epidermal layer and the second epidermal layer each independently comprise: Relative to the total weight of the epidermis, ≥30.0 ​​wt% and ≤45.0 wt% of ethylene polymers and ≥55.0 wt% and ≤70.0 wt% of the first ethylene-α-olefin copolymer; and b. A core layer located between the first and second epidermal layers, wherein the core layer comprises: ≥5.0 wt% and ≤25.0 wt% of ethylene polymer relative to the total weight of the core layer; The first ethylene-α-olefin copolymer, ≥25.0 wt% and ≤70.0 wt% relative to the total weight of the core layer; and The second ethylene-α-olefin copolymer comprises ≥25.0 wt% and ≤50.0 wt% relative to the total weight of the core layer; in: The ethylene polymer has a density > 918 kg / m3 3 and < 940 kg / m3 3 as measured according to ASTM D792 (2008). The first ethylene-a-olefin copolymer has a density > 900 kg / m3 3 and < 915 kg / m3 3 ; The density of the second ethylene-α-olefin copolymer, as measured by ASTM D792 (2008), is ≥850 kg / m³. 3 and ≤900kg / m 3 ; The multilayer film comprises, relative to its total weight, ≥20.0 wt% and ≤30.0 wt% of an ethylene polymer; and The multilayer film has: • Measured according to ASTM D882, the elastic modulus is ≥82.0 MPa and ≤150.0 MPa; • Isothermal hot-stage analysis was performed using an optical microscope in accordance with ISO 17025 (2017), with melting temperatures ≥70°C and ≤110°C, and temperature scans were performed between ≥85°C and ≤150°C. The analysis was performed for 3 minutes at each temperature, and the heating and cooling rates were both 10°C / min. Tear resistance ≥6.0 (g / μm) and ≤15.0 (g / μm) along the machine direction (MD), as measured according to ASTM D1922; and • Yield tensile elongation ≥40.0% and ≤70.0% in the machine direction (MD), as measured by ASTM D882.

2. The multilayer film of claim 1, wherein the multilayer film comprises: • ≥50.0 wt% and ≤70.0 wt% of the first ethylene-α-olefin copolymer relative to the total weight of the multilayer film; and • ≥14.0 wt% and ≤25.0 wt% of the second ethylene-α-olefin copolymer relative to the total weight of the multilayer film.

3. The multilayer film of claim 2, wherein the multilayer film comprises: • ≥50.0 wt% and ≤60.0 wt% of the first ethylene-α-olefin copolymer relative to the total weight of the multilayer film; and • ≥20.0 wt% and ≤25.0 wt% of the second ethylene-α-olefin copolymer relative to the total weight of the multilayer film.

4. The multilayer film according to any one of claims 1-3, wherein: The first ethylene-α-olefin copolymer includes portions derived from: (i) ethylene and (ii) portions derived from one or more α-olefins having 3-12 carbon atoms, with a weight of ≥2.0 wt% and ≤25.0 wt% relative to the total weight of the first ethylene-α-olefin copolymer. and The second ethylene-α-olefin copolymer includes portions derived from: (i) ethylene and (ii) portions derived from one or more α-olefins having 3-12 carbon atoms, with a total weight of ≥30.0 ​​wt% and ≤45.0 wt% relative to the total weight of the second ethylene-α-olefin copolymer.

5. The multilayer film of claim 4, wherein one or more α-olefins having 3-12 carbon atoms are selected from 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene.

6. The multilayer film of any one of claims 1-3, wherein the first skin layer and the second skin layer each further independently comprise one or more additives, wherein the one or more additives are present in amounts of ≥1.0 wt% and ≤6.0 wt% relative to the total weight of the respective skin layers.

7. The multilayer film of any one of claims 1-3, wherein the core layer is present in an amount of ≥65.0 wt% and ≤80.0 wt% relative to the total weight of the multilayer film.

8. The multilayer film of any one of claims 1-3, wherein the first skin layer and the second skin layer are each present independently in amounts of ≥5.0 wt% and ≤20.0 wt% respectively, relative to the total weight of the multilayer film.

9. The multilayer film of any one of claims 1-3, wherein the ethylene polymer has at least: • Measured according to ASTM D1238 at 190°C and a 2.16 kg load, the melt flow rate (MFR) is ≥0.1 g / 10 min and ≤5.0 g / 10 min; and • When measured according to the method based on ASTM D3418-15, the melting temperature is ≥105℃ and ≤125℃, where differential scanning calorimetry (DSC) is applied. For a 10mg membrane sample, the first heating and cooling cycle is at a temperature of 23-200℃ and a heating and cooling rate of 10℃ / min, with nitrogen purge gas at a flow rate of 50 ± 5 mL / min. The subsequent second heating cycle is the same as the first heating cycle.

10. The multilayer film of any one of claims 1-3, wherein the first ethylene-α-olefin copolymer has at least: • Melting temperature ≥85℃ and ≤115℃, wherein differential scanning calorimetry (DSC) is used. For a 10mg membrane sample, the first heating and cooling cycle is conducted at temperatures between 23-200℃ with a heating and cooling rate of 10℃ / min, using nitrogen purge gas at a flow rate of 50 ± 5mL / min. The subsequent second heating cycle is the same as the first heating cycle. • Measured according to ASTM D1238 at 190°C and 2.16 kg load, melt flow rate ≥0.1 g / 10 min and ≤5.0 g / 10 min.

11. The multilayer film of any one of claims 1-3, wherein the second ethylene-α-olefin copolymer has at least: • Melting temperature ≥60℃ and ≤85℃, wherein differential scanning calorimetry (DSC) is used. For a 10mg membrane sample, the first heating and cooling cycle is conducted at temperatures between 23-200℃ with a heating and cooling rate of 10℃ / min, using nitrogen purge gas at a flow rate of 50 ± 5 mL / min. The subsequent second heating cycle is the same as the first heating cycle. • Measured according to ASTM D1238 at 190°C and 2.16 kg load, melt flow rate ≥0.1 g / 10 min and ≤3.0 g / 10 min.

12. The multilayer film according to any one of claims 1-3, wherein the multilayer film comprises: • Measured according to ASTM D882, the elastic modulus is ≥95.0 MPa and ≤110.0 MPa; • Isothermal hot-stage analysis was performed using an optical microscope according to ISO 17025 (2017), with melting temperatures ≥80℃ and ≤105℃, and temperature scans were performed between ≥85℃ and ≤150℃. The analysis was performed for 3 minutes at each temperature, and the heating and cooling rates were both 10℃ / min. • Tear resistance ≥7.0 (g / μm) and ≤10.0 (g / μm) along the machine direction (MD), as measured according to ASTM D1922; and • Yield tensile elongation ≥48.4% and ≤70.0% in the machine direction (MD), as measured by ASTM D882.

13. The multilayer film of any one of claims 1-3, wherein the thickness of the multilayer film is ≥70 µm and ≤200 µm.

14. The multilayer film of claim 13, wherein the thickness of the multilayer film is ≥120µm and ≤185µm.

15. An article comprising the multilayer film of any one of claims 1-14, wherein the article is selected from packaging bags, agricultural films or shrink films.

16. The article of claim 15, wherein the article is a packaging bag for a vertical filling and sealing VFFS packaging production line for rubber granules.

17. A method for producing packaged material in a vertically filled and sealed VFFS production line, wherein the method comprises the following sequential steps: • Provide a packaging bag comprising a multilayer film according to any one of claims 1-14, wherein the packaging bag has a sealed end and an open end, such that the longitudinal axis of the packaging bag passes through the sealed end and the open end axially; • Clamp the packaging bag at the sealed end, where the open end and the closed end are coaxial with the longitudinal axis; • The material to be packaged is introduced into the packaging bag through the open end until at least part of the packaging bag is filled; • The open end of the sealed packaging bag; and Remove the clips and obtain the packaged materials.

18. Use of the multilayer film according to any one of claims 1-14, for use as a packaging bag suitable for producing packaged materials in a vertically filled and sealed VFFS packaging production line.

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