Multilayer polyethylene film

Abstract

To provide a multilayer polyethylene film hard to generate wrinkle, and excellent in adhesion.SOLUTION: A multilayer polyethylene film at least includes three layers of a first layer, a second layer, and a third layer in this order, where a softening point of the second layer is higher than a softening point of the first layer, and higher than a softening point of the third layer, a ratio of a thickness of the second layer to a total thickness of the first layer and the third layer is 1-3, a temperature indicated by a maximum value of a melting peak observed in differential scanning calorimetry of the multilayer polyethylene film is higher than 129°C and lower than 134°C, and an absolute value of a molecular orientation of the multilayer polyethylene film is less than 1.07.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a multilayer polyethylene film. [Background technology]

[0002] Polyethylene film is used as a packaging material because of its excellent flexibility, transparency, moisture resistance, chemical resistance, and low cost. In recent years, with the growing demand for a circular economy, attempts have been made to recycle and reuse packaging materials. One method for reusing packaging materials that are composites of various materials is to separate them back into their individual components. However, because the laminates used in packaging materials are given a certain strength, separating each component requires thermal, chemical, or mechanical methods. Furthermore, the separated components need to be distinguished based on differences in specific gravity, spectroscopic properties, etc., which is not efficient.

[0003] To recycle packaging materials more efficiently, monomaterialization is being considered, in which laminates are constructed from materials of the same type and the laminates are reused as a single material. For example, Patent Document 1 describes a laminate that can realize a packaging material that has sufficient strength, heat resistance and barrier properties suitable for use as a packaging material, and is also highly recyclable, comprising a base material, an adhesive layer and a heat seal layer, wherein the base material and the heat seal layer are made of polyethylene, and a vapor-deposited film is provided between the base material and the adhesive layer, and between the heat seal layer and the adhesive layer, and the base material is made of a stretched film. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-55157 [Overview of the project] [Problems that the invention aims to solve]

[0005] In their investigation into developing monomaterial laminates, the inventors found that depending on the type of polyethylene resin constituting each layer of the polyethylene film and the thickness of each layer, wrinkles could occur in the polyethylene film, making it difficult to form functional layers such as vapor-deposited layers or coating layers. Furthermore, while stretching the polyethylene film could suppress the occurrence of wrinkles, it tended to result in poor adhesion when joining with various films such as sealant films.

[0006] Therefore, one aspect of the present invention aims to provide a multilayer polyethylene film that is less prone to wrinkles and has excellent adhesion. [Means for solving the problem]

[0007] One aspect of the present invention relates to a multilayer polyethylene film comprising at least three layers in this order: a first layer, a second layer, and a third layer, wherein the probe drop temperature of the second layer is higher than the probe drop temperature of the first layer and higher than the softening point of the third layer, the ratio of the thickness of the second layer to the total thickness of the first and third layers is 1 to 3, the temperature at which the maximum value of the melting peak observed in differential scanning calorimetry of the multilayer polyethylene film is greater than 129°C and less than 134°C, and the absolute value of the molecular orientation of the multilayer polyethylene film is less than 1.07.

[0008] The above-mentioned multilayer polyethylene film has a multilayer structure, and by adjusting the relative softening points and thickness ratios of each layer, and by adjusting the temperature indicated by the maximum value of the melting peak of the multilayer polyethylene film and the degree of molecular orientation within a predetermined range, it is less prone to wrinkling and has excellent adhesion.

[0009] In the above multilayer polyethylene film, the melt flow rate of the polyethylene resin constituting the first layer, the second layer, and the third layer at 190°C and a load of 2.16 kg may all be 1.5 g / 10 min or less. Further, in the above multilayer polyethylene film, when the melt flow rates of the polyethylene resins constituting the first layer, the second layer, and the third layer at 190°C and a load of 2.16 kg are MFR1, MFR2, and MFR3, respectively, MFR1 - MFR2 ≤ 0.55 g / 10 min and MFR3 - MFR2 ≤ 0.55 g / 10 min may also be satisfied. Alternatively, MFR2 - MFR1 ≤ 0.55 g / 10 min and MFR2 - MFR3 ≤ 0.55 g / 10 min may also be satisfied. By using a polyethylene resin having a melt flow rate within a specific range as the polyethylene resin constituting each layer of the multilayer polyethylene film, wrinkles are less likely to occur and the adhesion tends to be more excellent.

[0010] In the above multilayer polyethylene film, the density of the polyethylene resin constituting the first layer and the third layer may be less than 0.945 g / cm 3 . By using a polyethylene resin having a density within a specific range as the polyethylene resin constituting the first layer and the third layer of the multilayer polyethylene film, wrinkles are less likely to occur and the adhesion tends to be more excellent.

Advantages of the Invention

[0011] According to one aspect of the present invention, it is possible to provide a multilayer polyethylene film in which wrinkles are less likely to occur and the adhesion is excellent.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a cross-sectional view of a multilayer polyethylene film according to an embodiment of the present invention.

Embodiment for Carrying out the Invention

[0013] Hereinafter, embodiments of the present disclosure will be described in detail while referring to the drawings. Note that the drawings are schematic, and for example, the relationship between the thickness and the planar dimensions, and the ratio of the thicknesses of each layer are different from the actual ones. Further, the embodiments shown below exemplify configurations for embodying the technical idea of the present disclosure, and the technical idea of the present disclosure is not limited to the following in terms of the material, shape, structure, etc. of the components.

[0014] <Multilayer polyethylene film> FIG. 1 is a cross-sectional view of a multilayer polyethylene film according to an embodiment of the present invention. The multilayer polyethylene film 10 includes three layers, a first layer 1, a second layer 2, and a third layer 3, in this order.

[0015] The content of the polyethylene resin in the multilayer polyethylene film 10 may be 80% by mass or more, 90% by mass or more, or 95% by mass or more, based on the total amount of the multilayer polyethylene film 10, from the viewpoint of realizing monomerization and facilitating resin recycling.

[0016] The temperature at which the maximum value of the melting peak observed in differential scanning calorimetry of the multilayer polyethylene film 10 is greater than 129°C and less than 134°C. A temperature above 129°C indicates excellent heat resistance of the multilayer polyethylene film 10, making it less prone to deformation and wrinkle formation due to heat. A temperature below 134°C indicates suppression of surface roughening of the multilayer polyethylene film 10, resulting in superior processability and adhesion when providing functional layers such as vapor-deposited layers or coating layers. From the viewpoint of further improving the heat resistance and reducing wrinkle formation of the multilayer polyethylene film 10, the temperature at which the maximum value of the melting peak is indicated may be 130°C or higher, 131°C or higher, 132°C or higher, or 132.5°C or higher. From the viewpoint of further suppressing surface roughening of the multilayer polyethylene film 10, the temperature at which the maximum value of the melting peak is indicated may be 133.8°C or lower or 133.5°C or lower. If multiple melting peaks are present, the temperature indicated by the maximum value of any of the melting peaks will be within the above range. The temperature indicated by the maximum value of the melting peaks refers to the value measured by the method described in the examples below.

[0017] The absolute value of the molecular orientation of the multilayer polyethylene film 10 is less than 1.07. Because the absolute value of the molecular orientation is less than 1.07, crosslinking (high crystallization) of the polyethylene resin on the film surface is suppressed, resulting in high affinity with functional layers such as vapor-deposited layers and coating layers, as well as adhesives and adhesive resins, thus achieving excellent adhesion. The absolute value of the molecular orientation may be 1.06 or less, or it may be 1 or more, 1.02 or more, or 1.05 or more. The absolute value of the molecular orientation refers to the value measured by the method described in the examples below.

[0018] <First Layer> The first layer 1 is a layer containing the first polyethylene resin. The content of the first polyethylene resin in the first layer 1 may be 80% by mass or more, 90% by mass or more, or 95% by mass or more, based on the total amount of the first layer 1, or it may be 100% by mass (a configuration in which the first layer 1 is substantially composed of the first polyethylene resin).

[0019] The melt flow rate MFR1 of the first polyethylene resin at 190°C and a 2.16 kg load may be 5 g / 10 min or less, 3 g / 10 min or less, 1.5 g / 10 min or less, 1 g / 10 min or less, or 0.5 g / 10 min or less, from the viewpoint of improving the heat resistance of the multilayer polyethylene film 10, reducing the likelihood of wrinkles, and improving adhesion. The MFR1 of the first polyethylene resin may also be 0.1 g / 10 min or more, or 0.3 g / 10 min or more. In this specification, the melt flow rate refers to the value measured in accordance with JIS K6921-2.

[0020] The density of the first polyethylene resin is set to 0.95 g / cm³, from the viewpoint of suppressing high crystallization of the polyethylene resin and improving adhesion. 3 Below, 0.947g / cm 3 The following, or 0.945 g / cm³ 3 It may be less than 0.92 g / cm³. The density of the first polyethylene resin is 0.92 g / cm³. 3 More than 0.93g / cm 3 Above, or 0.94 g / cm³ 3 That's fine too.

[0021] The melting point of the first polyethylene resin may be 145°C or lower, 140°C or lower, or 135°C or lower, from the viewpoint of improving the heat resistance of the multilayer polyethylene film 10, reducing the likelihood of wrinkles, and improving adhesion. The melting point of the first polyethylene resin may also be 110°C or higher, 120°C or higher, or 125°C or higher.

[0022] The weight-average molecular weight Mw of the first polyethylene resin may be 1,000,000 or less, 500,000 or less, or 300,000 or less, and may be 10,000 to 20,000 or more, or 50,000 or more. In this specification, the weight-average molecular weight and the number-average molecular weight described below refer to values ​​on a standard polystyrene basis measured by gel permeation chromatography (GPC).

[0023] The number-average molecular weight Mn of the first polyethylene resin may be 200,000 or less, 100,000 or less, or 50,000 or less, and may also be 1,000 to 2,000 or more, or 4,000 or more.

[0024] The molecular weight distribution Mw / Mn of the first polyethylene resin may be 100 or less, 50 or less, or 30 or less, and may be 2 or more, or 3 or more.

[0025] The first layer 1 may contain components other than the first polyethylene resin. For example, the first layer 1 may contain polyethylene resins other than the first polyethylene resin. Examples of polyethylene resins other than the first polyethylene resin include polyethylene resins that differ from the first polyethylene resin in terms of MFR, density, melting point, molecular weight, etc. The first layer 1 may contain additives such as antioxidants, lubricants, antiblocking agents, and antistatic agents.

[0026] The probe temperature drop of the first layer 1 may be 120°C or higher, 125°C or higher, 130°C or higher, or 133°C or higher, from the viewpoint of improving the heat resistance of the multilayer polyethylene film 10, reducing the likelihood of wrinkles, and improving adhesion. The probe temperature drop of the first layer 1 may also be 160°C or lower, 155°C or lower, 150°C or lower, or 146°C or lower. In this specification, the softening point refers to the value measured by the method described in the examples below.

[0027] Probe drop temperature is a parameter related to the local thermal analysis of a material using a probe, and is obtained by measuring the upward and downward behavior of the probe. To measure probe drop temperature, an atomic force microscope (AFM) equipped with a cantilever (probe) with a heating mechanism and a nanothermal microscope is used. When the cantilever is brought into contact with the surface of a solid sample fixed to a sample stage, and a voltage is applied to the cantilever in contact mode, the sample surface expands thermally, and the cantilever rises. If the cantilever is heated further, the sample surface softens and its hardness changes significantly. As a result, the cantilever descends and sinks into the sample surface. The starting point of the rapid displacement detected at this time is the probe drop start point, and the probe drop temperature can be obtained by converting the voltage into temperature. In this method, the local probe drop temperature in the nanoscale region and near the surface can be determined.

[0028] Suitable AFMs include the MPF-3D-SA and Ztherm systems from Oxford Instruments, and the Nano Thermal Analysis series and nanoIR series from Bruker Japan. Measurements can also be performed with AFMs from other manufacturers by attaching the Nano Thermal Analysis. As for cantilevers, for example, the AN2-200 from Anasis Instruments is an example. Any cantilever that can sufficiently reflect laser light and to which voltage can be applied can be used, other than the cantilevers exemplified above.

[0029] The temperature range for measuring probe drop temperature varies depending on the material being measured, but for example, it can be set as a starting temperature of around 25°C (room temperature) and an ending temperature of around 400°C. In this specification, the temperature range for measuring probe drop temperature can be between 25°C and 300°C.

[0030] The cantilever spring constant may be 0.1 to 3.5 N / m, and is preferably 0.5 to 3.5 N / m in order to perform measurements in both tapping mode and contact mode. In AFM, the amount of cantilever deflection is sometimes detected in units of voltage. In contact mode, the cantilever deflection changes before and after contact between the cantilever and the sample, so by keeping this change within the range of 0.1 to 3.0 V, it is possible to suppress damage to the sample surface while keeping the cantilever in contact with the sample.

[0031] The heating rate of the cantilever varies depending on the heating mechanism, but may be 0.1 to 10 V / second, and preferably 0.2 to 5 V / second. When the sample surface softens, the tip of the cantilever sinks into the sample and descends. The amount of cantilever sinks affects the detection sensitivity of the peak top of the softening curve and can be 3 to 500 nm. From the viewpoint of preventing damage to the cantilever, it is more preferable to have a sinking amount of 5 to 100 nm.

[0032] To calculate the probe drop temperature, it is necessary to create a calibration curve. In the examples described later, polycaprolactone, low-density polyethylene, polypropylene, and polyethylene terephthalate were used as calibration samples to create the calibration curve. Details of how to create the calibration curve will be described later. The materials of the calibration samples are not limited to those mentioned above; any material whose thermal conductivity does not differ significantly from that of a typical polymer, and which has a melting point around 60°C, around 250°C, and in between, should be used. For example, polycaprolactone, low-density polyethylene, and polyethylene terephthalate can be used as calibration samples, excluding polypropylene from the four calibration samples mentioned above.

[0033] The thickness of the first layer 1 may be 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, or 5 μm or more, and may also be 50 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less, from the viewpoint of improving processability.

[0034] <The third layer> The third layer 3 is a layer containing a third polyethylene resin. The content of the third polyethylene resin in the third layer 3 may be 80% by mass or more, 90% by mass or more, or 95% by mass or more, based on the total amount of the third layer 3, and may also be 100% by mass (in the aspect where the third layer 3 consists substantially of the third polyethylene resin).

[0035] The melt flow rate MFR3 of the third polyethylene resin at 190 °C and a load of 2.16 kg may be 5 g / 10 min or less, 3 g / 10 min or less, 1.5 g / 10 min or less, 1 g / 10 min or less, or 0.5 g / 10 min or less, from the viewpoints that the heat resistance of the multilayer polyethylene film 10 is more excellent and wrinkles are less likely to occur, and the adhesion is more excellent. The MFR3 of the third polyethylene resin may be 0.1 g / 10 min or more or 0.3 g / 10 min or more.

[0036] The density of the third polyethylene resin is 0.95 g / cm 3 or less, 0.947 g / cm 3 or less, or 0.945 g / cm 3 or less, from the viewpoint that the high crystallization of the polyethylene resin is suppressed and the adhesion is more excellent. The density of the third polyethylene resin may be 0.92 g / cm 3 or more, 0.93 g / cm 3 or more, or 0.94 g / cm 3 or more.

[0037] The melting point of the third polyethylene resin may be 145 °C or less, 140 °C or less, or 135 °C or less, from the viewpoints that the heat resistance of the multilayer polyethylene film 10 is more excellent and wrinkles are less likely to occur, and the adhesion is more excellent. The melting point of the third polyethylene resin may be 110 °C or more, 120 °C or more, or 125 °C or more.

[0038] The weight-average molecular weight Mw of the third polyethylene resin may be 1,000,000 or less, 500,000 or less, or 300,000 or less, and may also be 10,000 to 20,000 or more, or 50,000 or more.

[0039] The number-average molecular weight Mn of the third polyethylene resin may be 200,000 or less, 100,000 or less, or 50,000 or less, and may also be 1,000 to 2,000 or more, or 4,000 or more.

[0040] The molecular weight distribution Mw / Mn of the third polyethylene resin may be 100 or less, 50 or less, or 30 or less, and may be 2 or more, or 3 or more.

[0041] The third layer 3 may contain components other than the third polyethylene resin. For example, the third layer 3 may contain polyethylene resins other than the third polyethylene resin. Examples of polyethylene resins other than the third polyethylene resin include polyethylene resins that differ from the third polyethylene resin in terms of MFR, density, melting point, molecular weight, etc. The third layer 3 may contain additives such as antioxidants, lubricants, antiblocking agents, and antistatic agents.

[0042] The probe temperature drop of the third layer 3 may be 120°C or higher, 125°C or higher, 130°C or higher, or 133°C or higher, from the viewpoint of improving the heat resistance of the multilayer polyethylene film 10, reducing the likelihood of wrinkles, and improving adhesion. The probe temperature drop of the third layer 3 may also be 160°C or lower, 155°C or lower, 150°C or lower, or 146°C or lower.

[0043] The thickness of the third layer 3 may be 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, or 5 μm or more from the viewpoint of improving processability, and may be 50 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less from the viewpoint of thinning the packaging material.

[0044] The third layer 3 may have the same configuration as the first layer 1. That is, the multilayer polyethylene film 10 may have a symmetrical structure with respect to the second layer 2. Having a symmetrical structure in the multilayer polyethylene film 10 can suppress curling during the manufacturing of the multilayer polyethylene film 10, and enable the stable manufacture of the multilayer polyethylene film 10.

[0045] <Second Layer> The second layer 2 is a layer containing the second polyethylene resin. The content of the second polyethylene resin in the second layer 2 may be 80% by mass or more, 90% by mass or more, or 95% by mass or more, based on the total amount of the second layer 2, or it may be 100% by mass (an embodiment in which the second layer 2 is substantially composed of the second polyethylene resin).

[0046] The melt flow rate (MFR2) of the second polyethylene resin at 190°C and a 2.16 kg load may be 5 g / 10 min or less, 3 g / 10 min or less, 2 g / 10 min or less, 1.5 g / 10 min or less, or 1 g / 10 min or less, from the viewpoint of improving the heat resistance of the multilayer polyethylene film 10, reducing the likelihood of wrinkles, and improving adhesion. The MFR2 of the second polyethylene resin may also be 0.1 g / 10 min or more, 0.5 g / 10 min or more, or 0.8 g / 10 min or more.

[0047] The MFR2 of the second polyethylene resin may be smaller than the MFR1 of the first polyethylene resin and / or the MFR3 of the third polyethylene resin, from the viewpoint of having excellent film-forming properties for the multilayer polyethylene film 10. The difference between the MFR1 of the first polyethylene resin and the MFR2 of the second polyethylene resin (MFR1-MFR2) and / or the difference between the MFR3 of the third polyethylene resin and the MFR2 of the second polyethylene resin (MFR3-MFR2) may be 0.8 g / 10 min or less, 0.6 g / 10 min or less, or 0.55 g / 10 min or less, from the viewpoint of having excellent film-forming properties for the multilayer polyethylene film 10. The MFR1-MFR2 and / or MFR3-MFR2 may be 0 g / 10 min or more, or greater than 0 g / 10 min.

[0048] The MFR2 of the second polyethylene resin may be greater than the MFR1 of the first polyethylene resin and / or the MFR3 of the third polyethylene resin, from the viewpoint of superior film-forming properties of the multilayer polyethylene film 10. The difference between the MFR1 of the first polyethylene resin and the MFR2 of the second polyethylene resin (MFR2-MFR1) and / or the difference between the MFR3 of the third polyethylene resin and the MFR2 of the second polyethylene resin (MFR2-MFR3) may be 0.8 g / 10 min or less, 0.6 g / 10 min or less, or 0.55 g / 10 min or less, from the viewpoint of superior film-forming properties of the multilayer polyethylene film 10. The MFR2-MFR1 and / or MFR2-MFR3 may be 0 g / 10 min or more, or greater than 0 g / 10 min.

[0049] The density of the second polyethylene resin is 0.99 g / cm³. 3 Below, 0.98g / cm 3 The following, or 0.975 g / cm³ 3 It may be less than 0.94 g / cm³. The density of the second polyethylene resin is 0.94 g / cm³. 3 More than 0.95g / cm 3 Above, or 0.96 g / cm³ 3 That's fine too.

[0050] The melting point of the second polyethylene resin may be 145°C or lower, 140°C or lower, or 135°C or lower, from the viewpoint of improving the heat resistance of the multilayer polyethylene film 10, reducing the likelihood of wrinkles, and improving adhesion. The melting point of the second polyethylene resin may be 110°C or higher, 120°C or higher, or 130°C or higher. The melting point of the second polyethylene resin may be higher than the melting point of the first polyethylene resin and / or the melting point of the third polyethylene resin, from the viewpoint of improving the heat resistance of the multilayer polyethylene film 10.

[0051] The weight-average molecular weight Mw of the second polyethylene resin may be 1,000,000 or less, 500,000 or less, or 300,000 or less, and may also be 10,000 to 20,000 or more, or 50,000 or more.

[0052] The number-average molecular weight Mn of the second polyethylene resin may be 200,000 or less, 100,000 or less, or 50,000 or less, and may also be 1,000 to 2,000 or more, or 4,000 or more.

[0053] The molecular weight distribution Mw / Mn of the second polyethylene resin may be 100 or less, 50 or less, or 30 or less, and may be 2 or more, or 3 or more.

[0054] The second layer 2 may contain components other than the second polyethylene resin. For example, the second layer 2 may contain polyethylene resins other than the second polyethylene resin. Examples of polyethylene resins other than the second polyethylene resin include polyethylene resins that differ from the second polyethylene resin in terms of MFR, density, melting point, molecular weight, etc. The second layer 2 may contain additives such as antioxidants, lubricants, antiblocking agents, and antistatic agents.

[0055] The probe temperature drop of the second layer 2 is higher than the softening point of the first layer 1 and also higher than the softening point of the third layer 3. Because the softening point of the second layer 2 is higher than that of the first layer 1 and the third layer 3, the heat resistance of the multilayer polyethylene film 10 is superior, making the film less prone to deformation due to heat and less likely to wrinkle. The probe temperature drop of the second layer 2 may be 125°C or higher, 130°C or higher, 135°C or higher, 138°C or higher, 140°C or higher, or 142°C or higher, from the viewpoint of further improving the heat resistance of the multilayer polyethylene film 10 and making it less prone to wrinkles. The probe temperature drop of the second layer 2 may be 170°C or lower, 165°C or lower, 160°C or lower, 157°C or lower, or 155°C or lower.

[0056] The thickness of the second layer 2 may be 5 μm or more, 8 μm or more, 10 μm or more, 12 μm or more, or 15 μm or more from the viewpoint of heat resistance of the multilayer polyethylene film 10, and may be 80 μm or less, 50 μm or less, 40 μm or less, or 30 μm or less from the viewpoint of improving processability.

[0057] The thickness of the second layer 2 may be greater than the thickness of the first layer 1 and the third layer 3, from the viewpoint of providing excellent heat resistance for the multilayer polyethylene film. The thickness of the second layer 2 may be 1.5 times or more, 2 times or more, or 3 times or more, the thickness of the first layer 1 and / or the thickness of the third layer 3. The thickness of the second layer 2 may be 10 times or less, 9 times or less, or 8 times or less, the thickness of the first layer 1 and / or the thickness of the third layer 3.

[0058] The ratio of the thickness of the second layer 2 to the combined thickness of the first layer 1 and the third layer 3 is 1 to 3. When this ratio is 1 or greater, the heat resistance of the multilayer polyethylene film 10 is excellent, making the film less prone to deformation due to heat and less likely to wrinkle. When this ratio is 3 or less, surface roughness of the multilayer polyethylene film 10 is suppressed, resulting in excellent processability and adhesion when providing functional layers such as vapor-deposited layers or coating layers. From the viewpoint of further improving the heat resistance of the multilayer polyethylene film 10 and making it even less prone to wrinkles, this ratio may be 1.2 or greater, 1.5 or greater, or 2 or greater. From the viewpoint of making the surface of the multilayer polyethylene film smoother and suppressing surface roughness of the multilayer polyethylene film 10, this ratio may be 2.8 or less, 2.5 or less, or 2 or less.

[0059] The haze value of the multilayer polyethylene film 10 may be 30% or less, 25% or less, or 20% or less, from the viewpoint of excellent transparency. In this specification, the haze value refers to the value measured in accordance with JIS K 7136:2000.

[0060] The multilayer polyethylene film 10 may include layers other than the three layers of the first layer 1, the second layer 2, and the third layer 3. The multilayer polyethylene film 10 may further include another layer made of a polyethylene resin other than the polyethylene resin that constitutes the first layer 1, the second layer 2, and the third layer 3. The multilayer polyethylene film 10 may include an adhesive layer made of an adhesive between each of the first layer 1, the second layer 2, and the third layer 3.

[0061] The method for manufacturing the multilayer polyethylene film 10 is not particularly limited and can be manufactured by known methods such as the air-cooled inflation method, the water-cooled inflation method, and the T-die-casting method. From the standpoint of versatility, the multilayer polyethylene film 10 is preferably manufactured by the inflation method, and more preferably by the air-cooled inflation method. In the air-cooled inflation method, a mold with an annular lip called a ring die or crosshead die is installed at the tip of an extruder, and the material is extruded into a tube shape and continuously molded. More specifically, an air hole is installed in the center of the ring die, etc., and compressed air is blown in from here to inflate the tube, and the film is cooled while being pulled by rollers called pinch rolls and wound up, thereby manufacturing a polyethylene laminated film.

[0062] The resulting multilayer polyethylene film 10 may be subjected to surface modification treatments to improve its suitability for subsequent processes, as needed. For example, surface modification treatments may be performed on the printed surface or the surface that comes into contact with the substrate to improve printability or lamination suitability when used in a laminated state. Examples of surface modification treatments include treatments that generate functional groups by oxidizing the film surface, such as corona discharge treatment, plasma treatment, and flame treatment, as well as wet process modification treatments that form an easily adhesive layer by coating.

[0063] When the multilayer polyethylene film 10 is used as a packaging material, it can be used as a laminate in which another layer is further laminated onto the multilayer polyethylene film 10. The laminate may include a vapor-deposited layer, a coating layer, various functional layers, an adhesive layer, an adhesive resin layer, and the like.

[0064] <Package> Multilayer polyethylene films and laminates can be used as packaging materials to constitute packaging. For example, multilayer polyethylene films (laminateds) can be used as a sealing material in flat bags, three-sided bags, gusseted bags, standing pouches, spout pouches, beak pouches, etc.

[0065] This invention relates to, for example, the following inventions. [1] A multilayer polyethylene film comprising at least three layers in this order: a first layer, a second layer, and a third layer, The softening point of the second layer is higher than the softening point of the first layer and also higher than the softening point of the third layer. The ratio of the thickness of the second layer to the combined thickness of the first and third layers is 1 to 3. The temperature at which the maximum value of the melting peak observed in differential scanning calorimetry of the multilayer polyethylene film is greater than 129°C and less than 134°C. A multilayer polyethylene film in which the absolute value of the degree of molecular orientation of the multilayer polyethylene film is less than 1.07. [2] The multilayer polyethylene film according to [1], wherein the melt flow rate of the polyethylene resin constituting the first layer, the second layer, and the third layer at 190°C and a 2.16 kg load is 1.5 g / 10 min or less. [3] The multilayer polyethylene film according to [1] or [2], wherein when the melt flow rates of the polyethylene resin constituting the first layer, the second layer, and the third layer at 190°C and a load of 2.16 kg are MFR1, MFR2, and MFR3, respectively, MFR1-MFR2 ≤ 0.55 g / 10 min and MFR3-MFR2 ≤ 0.55 g / 10 min. [4] The multilayer polyethylene film according to [1] or [2], wherein when the melt flow rates of the polyethylene resin constituting the first layer, the second layer, and the third layer at 190°C and a load of 2.16 kg are MFR1, MFR2, and MFR3, respectively, MFR2-MFR1 ≤ 0.55 g / 10 min and MFR2-MFR3 ≤ 0.55 g / 10 min. [5] The density of the polyethylene resin constituting the first layer and the third layer is 0.945 g / cm³. 3 A multilayer polyethylene film described in any one of [1] to [4], which is less than [1]. [Examples]

[0066] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the following examples.

[0067] <Polyethylene resin> ·Resin A: Density 0.941g / cm 3 MFR 1.30g / 10min ·Resin B: Density 0.962g / cm 3 MFR 0.85g / 10min ·Resin C: Density 0.944g / cm 3 MFR 0.45g / 10min ·Resin D: Density 0.960g / cm 3 MFR 1.00g / 10min ·Resin E: Density 0.971g / cm 3 MFR 1.20g / 10min • Resin F: A mixture of resins A and E, density 0.941~0.971 g / cm³ 3 MFR 1.20~1.30g / 10min • Resin G: A mixture of resin A and resin B, density 0.941~0.962 g / cm³ 3 MFR 0.85~1.30g / 10min ·Resin H: Density 0.96g / cm 3 Less than, MFR less than 1g / 10min ·Resin I: Density 0.926g / cm 3MFR 0.8g / 10min ·Resin J: Density 0.937g / cm 3 MFR 1.8g / 10min

[0068] <Fabrication of multilayer polyethylene film> (Examples 1-38, Comparative Example 1) 、2、4、5、10 ~15) The resins shown in Tables 1 to 3 were used to form the first layer (layer 1), the second layer (layer 2), and the third layer (layer 3). These resins were then introduced into an extruder, melted and kneaded at 190°C, and polyethylene resin was introduced through a three-layer die. A multilayer polyethylene film was then produced by the air-cooled inflation method.

[0069] The multilayer polyethylene film prepared in Comparative Example 2 was stretched in the MD direction to produce a stretched multilayer polyethylene film.

[0070] <Fabrication of laminated films> A metal oxide layer was formed on the surface of the first layer (layer 1) of the multilayer polyethylene film prepared in each example and comparative example by vapor deposition. Next, a sealant film was dry-laminated onto the surface of the metal oxide layer to produce a laminated film.

[0071] <Tip drop temperature> The probe drop temperature (softening point) of each layer of a multilayer polyethylene film was measured using an atomic force microscope equipped with a nanothermal microscope consisting of a cantilever (probe) with a heating mechanism. Specifically, first, the multilayer polyethylene film was embedded in a visible light-curing resin to obtain a sample for measurement. Next, under a -140°C environment, the sample for measurement was cross-cut along a direction parallel to the TD direction using a diamond knife of a cryo-ultramicrotome. After measuring the thickness of each layer from the cross-section of the multilayer polyethylene film, the probe drop temperature of the multilayer polyethylene film was measured in the following manner.

[0072] An Oxford Instruments MPF-3D-SA atomic force microscope was prepared, an Oxford Instruments Ztherm nanothermal microscope was used for the atomic force microscope, and an Anasis Instruments AN2-200 (product name) was used as the cantilever. After measuring the shape of the sample in a 10 μm field of view in AC mode, the cantilever was moved 5 to 10 μm away from the sample in the Z direction (normal direction to the sample surface). In this state, the instrument's Detrend correction function was performed in contact mode under conditions of a maximum applied voltage of 6 V and a heating rate of 0.5 V / s to correct for the change in cantilever deflection due to voltage application. Next, in contact mode, the cantilever was brought into contact with the sample so that the change in Deflection before and after contact between the cantilever and the sample was 0.2V. While maintaining a constant Deflection value, the sample was heated by applying voltage to the cantilever under the conditions of a maximum applied voltage of 6V and a heating rate of 0.5V / s. The displacement of the cantilever in the Z direction was recorded, and the measurement was stopped when the Z displacement changed from rising to falling and dropped 50nm from the point of change. If the Z displacement reached the maximum applied voltage without dropping 50nm from the point of change, the maximum applied voltage during detrend correction and measurement was increased by 0.5V and the measurement was repeated. The applied voltage at which the recorded Z displacement was maximum was converted to temperature. This measurement was performed at 10 points within a 10μm field of view, and the average value of the 10 points was taken as the probe drop temperature.

[0073] Calibration curves were used to convert the applied voltage to temperature. Polycaprolactone (melting point: 60°C), low-density polyethylene (melting point: 112°C), polypropylene (melting point: 166°C), and polyethylene terephthalate (melting point: 255°C) were measured as calibration samples, and calibration curves for applied voltage and temperature were created. Here, the melting point is the peak melting temperature measured by differential scanning calorimeter (DSC) under a heating rate of 5°C / min. The method for measuring the probe drop temperature of the calibration samples was the same as for measuring the probe drop temperature of the samples described above, but the maximum applied voltage during Detrend correction and measurement was set to 3.5V for polycaprolactone, 5.5V for low-density polyethylene, 6.5V for polypropylene, and 7.8V for polyethylene terephthalate. The relationship between the melting point and the applied voltage at which the Z displacement is maximized when measuring each calibration sample was approximated by a cubic function using the least squares method to create a calibration curve and obtain the calibration curve.

[0074] <Melting peak temperature> For multilayer polyethylene films, differential scanning calorimetry was performed using a differential scanning calorimeter (Hitachi, Ltd., product name DSC7020) in accordance with JIS K7121-1987, under conditions of a measurement temperature of 20 to 200°C and a heating rate of 10°C / min. The melting peak temperature was read from the resulting curve. The measurement results are shown in Tables 1 to 3.

[0075] <Molecular orientation degree> Using a microwave molecular orientation meter (Oji Instruments Co., Ltd., product name MOA-5012A), the orientation of molecular chains within a multilayer polyethylene film was measured by rotating the film in a microwave-polarized electric field. The measurement results are shown in Tables 1-3.

[0076] <Bubble Stability> The vibration of the bubbles blown using the inflation method and the appearance of the resulting film were visually inspected, and the bubble stability was evaluated based on the following evaluation criteria. The evaluation results are shown in Tables 1-3. A: No bubble vibrations or wrinkles were observed in the appearance of the film after deposition. B: Vibration was observed in the bubbles, and slight wrinkles were seen in the film after deposition. C: The bubbles exhibited vibration, and the film after deposition showed wrinkles that made it difficult to use as packaging material.

[0077] <Wrinkles> The appearance of the multilayer polyethylene film after vapor deposition was visually inspected, and wrinkles were evaluated based on the following evaluation criteria. The evaluation results are shown in Tables 1-3. A: No wrinkles were observed on the surface of the multilayer polyethylene film. B: Minor wrinkles were observed on the surface of the multilayer polyethylene film. C: Numerous wrinkles were observed on the surface of the multilayer polyethylene film.

[0078] <Lamination Strength> The prepared laminate was cut into 15 mm wide strips and peeled using a Tensilon universal material tester (manufactured by A&D Co., Ltd.) in accordance with JIS K6854-2 and ISO 8510-2, at a peeling speed of 300 mm / min and a peeling angle of 180°, and the laminate strength was measured. The evaluation results are shown in Tables 1 to 3.

[0079] [Table 1]

[0080] [Table 2]

[0081] [Table 3] [Explanation of symbols]

[0082] 1...First layer, 2...Second layer, 3...Third layer, 10...Multilayer polyethylene film.

Claims

1. A multilayer polyethylene film comprising at least three layers in this order: a first layer, a second layer, and a third layer, The softening point of the second layer is higher than the softening point of the first layer and also higher than the softening point of the third layer. The softening point of the third layer is higher than that of the first layer. The softening points of the first layer and the third layer are 120°C or higher and 160°C or lower. The ratio of the thickness of the second layer to the combined thickness of the first and third layers is 1 to 3. The temperature at which the maximum value of the melting peak observed in differential scanning calorimetry of the multilayer polyethylene film is greater than 129°C and less than 134°C. A multilayer polyethylene film wherein the absolute value of the molecular orientation of the multilayer polyethylene film is less than 1.

07.

2. The multilayer polyethylene film according to claim 1, wherein the melt flow rate of the polyethylene resin constituting the first layer, the second layer, and the third layer at 190°C and a 2.16 kg load is 1.5 g / 10 min or less for each.

3. The melt flow rates of the polyethylene resins constituting the first layer, the second layer, and the third layer at 190°C and a load of 2.16 kg are respectively defined as MFR. １ MFR ２ , and MFR ３ In that case, MFR １ - MFR ２ ≤0.55 g / 10 min, and MFR ３ - MFR ２ The multilayer polyethylene film according to claim 1, wherein the density is ≤0.55 g / 10 min.

4. When the melt flow rates of the polyethylene resins constituting the first layer, the second layer, and the third layer at 190°C and a load of 2.16 kg are MFR １ , MFR ２ , and MFR ３ , MFR ２ - MFR １ ≤ 0.55 g / 10 min, and MFR ２ - MFR ３ ≤ 0.55 g / 10 min, the multilayer polyethylene film according to claim 1.

5. The density of the polyethylene resin constituting the first layer and the third layer is 0.945 g / cm³. ３ A multilayer polyethylene film according to claim 1, wherein the value is less than [value missing].

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