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] The present invention relates to a multilayer polyethylene film. [Background technology]

[0002] Polyethylene films are used as packaging materials because they are inexpensive and have excellent flexibility, transparency, moisture resistance, and chemical resistance. In recent years, with the growing demand for a recycling-oriented society, attempts have been made to recycle and reuse packaging materials. One method for reusing packaging materials in which various materials are combined is to separate each material. However, since the laminates used in packaging materials are given a certain strength, thermal, chemical, and mechanical methods are required to separate each material, and each separated material must be sorted based on its specific gravity, spectroscopic difference, etc., which is not efficient.

[0003] In order to recycle packaging materials more efficiently, mono-materialization is being considered, in which a laminate is made of materials of the same type and the laminate is 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 that can be used as a packaging material, and also has excellent recyclability, and is characterized in that the laminate comprises a substrate, an adhesive layer, and a heat seal layer, the substrate and the heat seal layer are made of polyethylene, a vapor deposition film is provided at least one between the substrate and the adhesive layer and between the heat seal layer and the adhesive layer, and the substrate is made of a stretched film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-55157 A Summary of the Invention [Problem to be solved by the invention]

[0005] When the present inventors conducted studies to develop a mono-material laminate, they found that wrinkles were generated in the polyethylene film depending on the type of polyethylene resin constituting each layer of the polyethylene film and the thickness of each layer, which made it difficult to form a functional layer such as a deposition layer or a coating layer. In addition, although the generation of wrinkles in the polyethylene film could be suppressed by stretching the polyethylene film, there was a tendency for the adhesion to be poor when bonding with various films such as a sealant film.

[0006] Therefore, one aspect of the present invention has an object 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, namely a first layer, a second layer, and a third layer, in this order, wherein the probe drop temperature of the second layer is higher than the probe drop temperature of the first layer and is 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 layer and the third layer is 1 to 3, the temperature shown by the maximum value of the melting peak observed in differential scanning calorimetry of the multilayer polyethylene film is more than 129°C and less than 134°C, and the absolute value of the molecular orientation degree of the multilayer polyethylene film is less than 1.07.

[0008] The multilayer polyethylene film has a multilayer structure, and by adjusting the softening point relationship and thickness ratio of each layer and adjusting the temperature at which the maximum value of the melting peak of the multilayer polyethylene film is shown and the degree of molecular orientation within a predetermined range, the multilayer polyethylene film is less likely to wrinkle and has excellent adhesion.

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

[0010] In the multilayer polyethylene film, the density of the polyethylene resin constituting the first layer and the third layer is 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 adhesion tends to be better. Effect of the Invention

[0011] According to one aspect of the present invention, a multilayer polyethylene film which is less prone to wrinkles and has excellent adhesion can be provided. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view of a multilayer polyethylene film according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the drawings are schematic, and for example, the relationship between thickness and planar dimensions, and the ratio of thicknesses of each layer are different from the actual ones. In addition, the embodiments shown below are examples of configurations for embodying the technical idea of ​​the present disclosure, and the technical idea of ​​the present disclosure is not limited to the materials, shapes, structures, etc. of the components described below.

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

[0015] The content of polyethylene resin in the multilayer polyethylene film 10 may be 80 mass% or more, 90 mass% or more, or 95 mass% or more, based on the total amount of the multilayer polyethylene film 10, in order to achieve mono-materialization and facilitate resin recycling.

[0016] The temperature indicated by the maximum value of the melting peak observed in differential scanning calorimetry of the multilayer polyethylene film 10 is more than 129°C and less than 134°C. When the temperature indicated by the maximum value of the melting peak is more than 129°C, the multilayer polyethylene film 10 has excellent heat resistance, so that the film is less likely to be deformed by heat and wrinkles are less likely to occur. When the temperature indicated by the maximum value of the melting peak is less than 134°C, the multilayer polyethylene film 10 can be prevented from becoming rough on its surface, so that the multilayer polyethylene film 10 has excellent processability and excellent adhesion when providing a functional layer such as a deposition layer or a coating layer. The temperature indicated by the maximum value of the melting peak may be 130°C or higher, 131°C or higher, 132°C or higher, or 132.5°C or higher, from the viewpoint of more excellent heat resistance of the multilayer polyethylene film 10 and more unlikely to cause wrinkles. The temperature indicated by the maximum value of the melting peak may be 133.8°C or lower or 133.5°C or lower, from the viewpoint of more suppressing roughness of the surface of the multilayer polyethylene film 10. When multiple melting peaks are present, the temperature indicated by the maximum value of each melting peak is within the above range. The temperature indicated by the maximum value of the melting peak means a value measured by the method described in the Examples below.

[0017] The absolute value of the molecular orientation degree of the multilayer polyethylene film 10 is less than 1.07. When the absolute value of the molecular orientation degree is less than 1.07, crosslinking (high crystallization) of the polyethylene resin on the film surface is suppressed, so that the film has high affinity with functional layers such as vapor deposition layers and coating layers, as well as with adhesives and adhesive resins, and can achieve excellent adhesion. The absolute value of the molecular orientation degree may be 1.06 or less, or may be 1 or more, 1.02 or more, or 1.05 or more. The absolute value of the molecular orientation degree means a value measured by the method described in the Examples below.

[0018] <First Layer> The first layer 1 is a layer containing a 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 may be 100% by mass (an embodiment 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 under 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 viewpoint of better heat resistance and less wrinkles occurring in the multilayer polyethylene film 10, and from the viewpoint of better adhesion. The MFR1 of the first polyethylene resin may be 0.1 g / 10 min or more, or 0.3 g / 10 min or more. In this specification, the melt flow rate means a value measured in accordance with JIS K6921-2.

[0020] The density of the first polyethylene resin is 0.95 g / cm from the viewpoint of suppressing high crystallization of the polyethylene resin and achieving better adhesion. 3 Below, 0.947g / cm 3 or less than 0.945g / cm 3 The density of the first polyethylene resin may be less than 0.92 g / cm 3 More than 0.93g / cm 3 or more than 0.94g / cm 3 It may be more than that.

[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 viewpoints of improving the heat resistance and wrinkle resistance of the multilayer polyethylene film 10, and improving the adhesion. The melting point of the first polyethylene resin may 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, or may be 10,000 or more and 20,000 or more, or 50,000 or more. In this specification, the weight average molecular weight and the number average molecular weight described later refer to values ​​calculated in terms of standard polystyrene 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, or may be 1,000 or more, 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, or may be 2 or more, or 3 or more.

[0025] The first layer 1 may contain a component other than the first polyethylene resin. The first layer 1 may contain, for example, a polyethylene resin other than the first polyethylene resin. Examples of the polyethylene resin other than the first polyethylene resin include polyethylene resins having MFR, density, melting point, molecular weight, etc. different from those of the first polyethylene resin. The first layer 1 may contain additives such as antioxidants, lubricants, antiblocking agents, and antistatic agents.

[0026] The probe drop temperature of the first layer 1 may be 120° C. or more, 125° C. or more, 130° C. or more, or 133° C. or more, from the viewpoints of better heat resistance and less wrinkling of the multilayer polyethylene film 10, and better adhesion. The probe drop temperature of the first layer 1 may be 160° C. or less, 155° C. or less, 150° C. or less, or 146° C. or less. In this specification, the softening point means a value measured by the method described in the examples below.

[0027] The probe drop temperature is a parameter related to the local thermal analysis of a material using a probe, and can be obtained by measuring the rising and falling behavior of the probe. To measure the 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 to heat it, the sample surface thermally expands and the cantilever rises. When the cantilever is further heated, the sample surface softens and its hardness changes significantly. As a result, the cantilever descends and penetrates into the sample surface. The starting point of the sudden displacement detected at this time is the probe drop starting point, and the probe drop temperature can be obtained by converting the voltage into temperature. By this method, the probe drop temperature can be known locally in the nanoscale region and near the surface.

[0028] Examples of AFMs that can be used include the MPF-3D-SA and Ztherm systems manufactured by Oxford Instruments, and the Nano Thermal Analysis series and nanoIR series manufactured by Bruker Japan. Measurements can also be performed with AFMs manufactured by other manufacturers by attaching the Nano Thermal Analysis. Examples of cantilevers that can be used include the AN2-200 manufactured by Anasys Instruments. Cantilevers other than those listed above can be used as long as they can sufficiently reflect laser light and can be applied with voltage.

[0029] The temperature range in the measurement of the probe drop temperature varies depending on the material to be measured, but for example, the start temperature can be about room temperature, 25° C., and the end temperature can be about 400° C. In this specification, the temperature range in the measurement of the probe drop temperature can be from 25° C. to 300° C.

[0030] The spring constant of the cantilever 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 and contact modes. In AFM, the deflection of the cantilever may be detected in units of voltage. In contact mode, the deflection of the cantilever changes before and after contact between the cantilever and the sample. By keeping this change within the range of 0.1 to 3.0 V, it is possible to prevent damage to the sample surface while keeping the cantilever in contact with the sample.

[0031] The temperature rise rate of the cantilever varies depending on the heating mechanism, etc., but may be 0.1 to 10 V / sec, and is preferably 0.2 to 5 V / sec. When the sample surface softens, the tip of the cantilever penetrates into the sample and descends. The amount of penetration of the cantilever 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 set the amount of penetration to 5 to 100 nm.

[0032] In order to calculate the probe drop temperature, it is necessary to create a calibration curve. In the embodiment described later, polycaprolactone, low-density polyethylene, polypropylene, and polyethylene terephthalate were used as calibration samples to create the calibration curve. Details of the creation of the calibration curve will be described later. The material of the calibration sample is not limited to the above, and at least one of the following may be used: a material whose thermal conductivity is not significantly different from that of a general polymer, and whose melting point is near 60°C, near 250°C, and between them. For example, it is also possible to use only three of the above four calibration samples, excluding polypropylene: polycaprolactone, low-density polyethylene, and polyethylene terephthalate.

[0033] From the viewpoint of improving processability, 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 be 50 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less.

[0034] <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, or may be 100% by mass (an embodiment in which the third layer 3 is substantially composed of the third polyethylene resin).

[0035] The melt flow rate MFR3 of the third polyethylene resin at 190°C under 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 of better heat resistance and less wrinkles occurring in the multilayer polyethylene film 10, and better adhesion. 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 from the viewpoint of suppressing high crystallization of the polyethylene resin and providing better adhesion. 3 Below, 0.947g / cm 3 or less than 0.945g / cm 3 The third polyethylene resin may have a density of less than 0.92 g / cm 3 More than 0.93g / cm 3 or more than 0.94g / cm 3 It may be more than that.

[0037] The melting point of the third polyethylene resin may be 145° C. or lower, 140° C. or lower, or 135° C. or lower, from the viewpoints of improving the heat resistance and wrinkle resistance of the multilayer polyethylene film 10, and improving the adhesion. The melting point of the third polyethylene resin may be 110° C. or higher, 120° C. or higher, or 125° C. or higher.

[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, or may be 10,000 or more, 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, or may be 1,000 or more, 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, or may be 2 or more, or 3 or more.

[0041] The third layer 3 may contain a component other than the third polyethylene resin. The third layer 3 may contain, for example, a polyethylene resin other than the third polyethylene resin. Examples of the polyethylene resin other than the third polyethylene resin include polyethylene resins having MFR, density, melting point, molecular weight, etc. different from those of the third polyethylene resin. The third layer 3 may contain additives such as antioxidants, lubricants, antiblocking agents, and antistatic agents.

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

[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 making the packaging material thinner.

[0044] The third layer 3 may have a similar structure to the first layer 1. That is, the multilayer polyethylene film 10 may have a symmetrical structure with respect to the second layer 2. When the multilayer polyethylene film 10 has a symmetrical structure, curling during production of the multilayer polyethylene film 10 can be suppressed, and the multilayer polyethylene film 10 can be produced stably.

[0045] <Second Layer> The second layer 2 is a layer containing a second polyethylene resin. The content of the second polyethylene resin in the second layer 2 may be 80 mass % or more, 90 mass % or more, or 95 mass % or more based on the total amount of the second layer 2, or may be 100 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 under a load of 2.16 kg 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 viewpoints of better heat resistance and less wrinkles occurring in the multilayer polyethylene film 10, and better adhesion. The MFR2 of the second polyethylene resin may be 0.1 g / 10 min or more, 0.5 g / 10 min or more, or 0.8 g / 10 min or more.

[0047] From the viewpoint of excellent film-formability of the multilayer polyethylene film 10, 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 excellent film-formability of 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. MFR1-MFR2 and / or MFR3-MFR2 may be 0 g / 10 min or more, or more than 0 g / 10 min.

[0048] The MFR2 of the second polyethylene resin may be larger than the MFR1 of the first polyethylene resin and / or the MFR3 of the third polyethylene resin, from the viewpoint of excellent film-formability 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 excellent film-formability of the multilayer polyethylene film 10. MFR2-MFR1 and / or MFR2-MFR3 may be 0 g / 10 min or more, or more than 0 g / 10 min.

[0049] The density of the second polyethylene resin is 0.99 g / cm 3 Below, 0.98g / cm 3 or less than 0.975g / cm 3 The density of the second polyethylene resin may be less than 0.94 g / cm 3 More than 0.95g / cm 3 or more than 0.96g / cm 3 It may be more than that.

[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 viewpoints of providing the multilayer polyethylene film 10 with better heat resistance, less prone to wrinkles, and better adhesion. The melting point of the second polyethylene resin may be 110° C. or higher, 120° C. or higher, or 130° C. or higher. From the viewpoint of providing the multilayer polyethylene film 10 with better heat resistance, 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.

[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, or may be 10,000 or more, 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, or may be 1,000 or more, 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, or may be 2 or more, or 3 or more.

[0054] The second layer 2 may contain a component other than the second polyethylene resin. The second layer 2 may contain, for example, a polyethylene resin other than the second polyethylene resin. Examples of the polyethylene resin other than the second polyethylene resin include polyethylene resins having MFR, density, melting point, molecular weight, etc. different from those of the second polyethylene resin. The second layer 2 may contain additives such as antioxidants, lubricants, antiblocking agents, and antistatic agents.

[0055] The probe drop temperature of the second layer 2 is higher than the softening point of the first layer 1 and higher than the softening point of the third layer 3. Since the softening point of the second layer 2 is higher than the softening points of the first layer 1 and the third layer 3, the multilayer polyethylene film 10 has excellent heat resistance, and the film is less likely to deform due to heat and to wrinkle. From the viewpoint of the multilayer polyethylene film 10 having more excellent heat resistance and being less likely to wrinkle, the probe drop temperature of the second layer 2 may be 125°C or more, 130°C or more, 135°C or more, 138°C or more, 140°C or more, or 142°C or more. The probe drop temperature of the second layer 2 may be 170°C or less, 165°C or less, 160°C or less, 157°C or less, or 155°C or less.

[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] From the viewpoint of excellent heat resistance of the multilayer polyethylene film, the thickness of the second layer 2 may be greater than the thickness of the first layer 1 and the thickness of the third layer 3. 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 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 third layer 3.

[0058] The ratio of the thickness of the second layer 2 to the total thickness of the first layer 1 and the third layer 3 is 1 to 3. When the ratio is 1 or more, the multilayer polyethylene film 10 has excellent heat resistance, so that the film is less likely to deform due to heat and wrinkles are less likely to occur. When the ratio is 3 or less, the surface of the multilayer polyethylene film 10 can be prevented from becoming rough, so that the processability and adhesion when providing a functional layer such as a deposition layer or a coating layer are excellent. From the viewpoint of the multilayer polyethylene film 10 having better heat resistance and being less likely to become wrinkled, the ratio may be 1.2 or more, 1.5 or more, or 2 or more. From the viewpoint of the multilayer polyethylene film having a smooth surface and being prevented from becoming rough, the ratio may be 2.8 or less, 2.5 or less, or 2 or less.

[0059] From the viewpoint of excellent transparency, the haze value of the multilayer polyethylene film 10 may be 30% or less, 25% or less, or 20% or less. In this specification, the haze value means a 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, for example, another layer composed of a polyethylene resin other than the polyethylene resins constituting the first layer 1, the second layer 2, and the third layer 3. The multilayer polyethylene film 10 may include adhesive layers composed of an adhesive between each of the first layer 1, the second layer 2, and the third layer 3.

[0061] The method for producing the multilayer polyethylene film 10 is not particularly limited, and the multilayer polyethylene film 10 can be produced by a known method such as an air-cooled inflation method, a water-cooled inflation method, or a T-die casting method. From the viewpoint of versatility, the multilayer polyethylene film 10 is preferably produced by an inflation method, and more preferably by an air-cooled inflation method. In the air-cooled inflation method, a die having an annular lip called a ring die or a crosshead die is installed at the tip of an extruder, and a material is extruded into a tube shape and continuously molded. More specifically, an air hole is installed in the center of the ring die or the like, and compressed air is blown in from here to expand the tube, and the film is cooled while being pulled by a roller called a pinch roll, and then the film is wound up, whereby a polyethylene laminated film can be produced.

[0062] The obtained multilayer polyethylene film 10 may be subjected to a surface modification treatment to improve suitability for subsequent processes, if necessary. For example, in order to improve printability or lamination suitability during lamination use, a surface modification treatment may be performed on the printing surface or the surface that comes into contact with the substrate. 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, and modification treatments by a wet process that forms an easy-adhesion 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 on the multilayer polyethylene film 10. The laminate may include a deposition layer, a coating layer, various functional layers, an adhesive layer, an adhesive resin layer, etc.

[0064] <Package> The multilayer polyethylene film and laminate can be used as a packaging material for constituting a package. For example, the multilayer polyethylene film (laminate) can be used as a sealing material to make flat bags, three-sided bags, palm-shaped bags, gusseted bags, standing pouches, pouches with spouts, pouches with beaks, etc.

[0065] The present invention relates to, for example, the following inventions. [1] A multilayer polyethylene film having at least three layers, a first layer, a second layer, and a third layer, in this order, 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 to 3; The temperature at which the maximum melting peak is observed in differential scanning calorimetry of the multilayer polyethylene film is more than 129°C and less than 134°C, The multilayer polyethylene film has an absolute value of a molecular orientation degree of less than 1.07. [2] The multilayer polyethylene film according to [1], wherein the polyethylene resins constituting the first layer, the second layer, and the third layer all have a melt flow rate of 1.5 g / 10 min or less at 190°C under a load of 2.16 kg. [3] The multilayer polyethylene film according to [1] or [2], wherein MFR1 - MFR2 ≦ 0.55 g / 10 min and MFR3 - MFR2 ≦ 0.55 g / 10 min, where MFR1, MFR2 and MFR3 are melt flow rates at 190°C under a load of 2.16 kg of the polyethylene resins constituting the first layer, the second layer and the third layer, respectively. [4] The multilayer polyethylene film according to [1] or [2], wherein MFR2 - MFR1 ≦ 0.55 g / 10 min and MFR2 - MFR3 ≦ 0.55 g / 10 min, where MFR1, MFR2, and MFR3 are melt flow rates at 190°C under a load of 2.16 kg of the polyethylene resins constituting the first layer, the second layer, and the third layer, respectively. [5] The density of the polyethylene resin constituting the first layer and the third layer is 0.945 g / cm 3 The multilayer polyethylene film according to any one of [1] to [4], wherein EXAMPLES

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

[0067] <Polyethylene resin> ·Resin A: Density 0.941g / cm 3 , MFR1.30g / 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 , MFR1.00g / 10min ·Resin E: Density 0.971g / cm 3 , MFR1.20g / 10min Resin F: A mixture of Resin A and Resin E, density 0.941~0.971g / cm 3 , MFR1.20~1.30g / 10min Resin G: A mixture of Resin A and Resin B, density 0.941~0.962g / cm 3 , MFR0.85~1.30g / 10min ·Resin H: Density 0.96g / cm 3 Less than 1g / 10min, MFR less than 1g / 10min ·Resin I: Density 0.926g / cm 3, MFR 0.8g / 10min ·Resin J: Density 0.937g / cm 3 , MFR1.8g / 10min

[0068] <Preparation of multi-layer polyethylene film> (Examples 1 to 38, Comparative Examples 1 to 15) The resins shown in Tables 1 to 3 constituting the first layer (layer 1), the second layer (layer 2), and the third layer (layer 3) were each fed into an extruder and melt-kneaded at 190°C. After that, polyethylene resin was introduced through a three-layer die, and a multilayer polyethylene film was produced by an air-cooled inflation method.

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

[0070] <Preparation of laminated film> A metal oxide layer was formed by vapor deposition on the surface of the first layer (layer 1) of each multilayer polyethylene film produced in each Example and Comparative Example. Then, a sealant film was dry laminated on 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 the 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, the multilayer polyethylene film was first embedded in a visible light curing resin to obtain a measurement sample. Next, in a -140°C environment, the measurement sample was cut in a cross section 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 as follows.

[0072] An MPF-3D-SA manufactured by Oxford Instruments was prepared as an atomic force microscope, a Ztherm manufactured by Oxford Instruments was used as a nanothermal microscope equipped with the atomic force microscope, and an AN2-200 (trade name) manufactured by Anasys Instruments was used as a cantilever. After measuring the shape of the sample with a 10 μm field of view in AC mode, the cantilever was separated from the sample by 5 to 10 μm in the Z direction (normal direction of the sample surface). In this state, the Detrend correction function of the device was performed in contact mode under the conditions of a maximum applied voltage of 6 V and a heating rate of 0.5 V / s, and the change in the deflection of the cantilever due to the applied voltage was corrected. Next, the cantilever was brought into contact with the sample in contact mode so that the change in deflection before and after contact between the cantilever and the sample was 0.2 V, and the sample was heated by applying a voltage to the cantilever under the conditions of a maximum applied voltage of 6 V and a heating rate of 0.5 V / s while maintaining a constant deflection. The displacement of the cantilever in the Z direction at this time was recorded, and the measurement was stopped when the Z displacement turned from rising to falling and fell 50 nm from the change point. If the Z displacement did not fall 50 nm from the change point and reached the maximum applied voltage, the maximum applied voltage during detrend correction and measurement was increased by 0.5 V 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 10 μm field of view, and the average value of the 10 points was taken as the probe drop temperature.

[0073] A calibration curve was 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 a calibration curve of applied voltage and temperature was created. Here, the melting point is the melting peak temperature measured by a differential scanning calorimeter (DSC) at a heating rate of 5°C / min. The method of measuring the probe drop temperature of the calibration sample was the same as that of the above-mentioned sample, but the maximum applied voltage during Detrend correction and measurement was 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 was maximum when measuring each calibration sample was approximated by a cubic function using the least squares method to create a calibration curve.

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

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

[0076] <Bubble stability> The vibration of the bubbles blown up by the inflation method and the appearance of the formed film were visually observed, and the bubble stability was evaluated based on the following evaluation criteria. The evaluation results are shown in Tables 1 to 3. A: No bubble vibration and no wrinkles were observed on the appearance of the film after film formation. B: Vibration of the bubbles and slight wrinkles on the film after film formation were observed. C: Vibrations were observed in the bubbles and wrinkles were observed in the film after film formation, making it difficult to use the film as a packaging material.

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

[0078] <Lamination strength> The laminate was cut into 15 mm wide strips and measured for laminate strength using a Tensilon universal material testing machine (manufactured by A&D Co., Ltd.) at a peel speed of 300 mm / min and a peel angle of 180° in accordance with JIS K6854-2 and ISO8510-2. 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, 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; the softening point of the first layer and the third layer is 120° C. or higher and 160° C. or lower; a ratio of a thickness of the second layer to a total thickness of the first layer and the third layer is from 1 to 3; The temperature at which the maximum melting peak is observed in differential scanning calorimetry of the multilayer polyethylene film is more than 129° C. and less than 134° C.; The multilayer polyethylene film has an absolute value of a molecular orientation degree of less than 1.

07.

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

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 designated as MFR １ , M.F.R. ２ , and MFR ３ Then, MFR １ -MFR ２ ≦0.55g / 10min and MFR ３ -MFR ２ 2. The multilayer polyethylene film of claim 1, having a modulus of elasticity of ≦0.55 g / 10 min.

4. 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 referred to as MFR. １ , M.F.R. ２ , and MFR ３ Then, MFR ２ -MFR １ ≦0.55g / 10min and MFR ２ -MFR ３ 2. The multilayer polyethylene film of claim 1, having a modulus of elasticity of ≦0.55 g / 10 min.

5. The density of the polyethylene resin constituting the first layer and the third layer is 0.945 g / cm ３ 2. The multilayer polyethylene film of claim 1, wherein the thickness of the multilayer polyethylene film is less than 1 / 2 mm.

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