Multi-layer polyethylene film

Abstract

A multi-layer polyethylene film according to the present invention comprises at least three layers, which are a first layer, a second layer, and a third layer in this order, wherein: the softening point of the second layer is higher than the softening point 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 1-3; the temperature indicated by the maximum value of the melting peak as observed in differential scanning calorimetry of the multi-layer polyethylene film is more than 129°C but less than 134°C; and the absolute value of the degree of molecular orientation of the multi-layer polyethylene film is less than 1.07.

Description

Multilayer polyethylene film

[0001] The present invention relates to a multilayer polyethylene film.

[0002] Polyethylene film is used as a packaging material because it is inexpensive and has 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 that are made up of composite materials is to separate the individual materials. However, because the laminates used in packaging materials are given a certain strength, thermal, chemical, or mechanical methods are required to separate the individual materials, and the separated materials also need to be sorted based on differences in specific gravity, spectroscopic properties, etc., which is inefficient.

[0003] In order to recycle packaging materials more efficiently, monomaterialization has been studied, in which a laminate is made of materials of the same type and 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 to be applicable as a packaging material, and also has excellent recyclability, and is characterized by comprising a substrate, an adhesive layer, and a heat-seal layer, the substrate and the heat-seal layer being made of polyethylene, a vapor-deposited film being provided at least either between the substrate and the adhesive layer or between the heat-seal layer and the adhesive layer, and the substrate being made of a stretched film.

[0004] Japanese Patent Application Laid-Open No. 2020-55157

[0005] In developing a mono-material laminate, the inventors conducted research and 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 deposition layers and coating layers. Furthermore, although stretching the polyethylene film could prevent wrinkles from occurring in the polyethylene film, this tended to result in poor adhesion when bonding it to various films such as sealant films.

[0006] Therefore, one aspect of the present invention aims to provide a multilayer polyethylene film that is less likely to wrinkle and has excellent adhesion.

[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 softening point (probe depression temperature) of the second layer is higher than the softening point (probe depression temperature) of the first layer and is higher than the softening point (probe depression temperature) 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 at which the maximum value of the melting peak observed in differential scanning calorimetry of the multilayer polyethylene film appears is higher than 129°C and lower than 134°C, and the absolute value of the degree of molecular orientation of the multilayer polyethylene film is less than 1.07.

[0008] The multilayer polyethylene film has a multilayer structure, and by adjusting the magnitude relationship of the softening points (probe drop temperatures) of the layers and the thickness ratio, and by adjusting the temperature at which the maximum value of the melting peak of the multilayer polyethylene film and the degree of molecular orientation within predetermined ranges, the multilayer polyethylene film is less likely to wrinkle and has excellent adhesion.

[0009] In the multilayer polyethylene film, 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 may each be 1.5 g / 10 min or less, from the viewpoint of being less prone to wrinkles and having better adhesion. １ , MFR ２ , and MFR ３ When this is the case, MFR １ -MFR ２ ≦0.55 g / 10 min, and MFR ３ -MFR ２ Alternatively, the MFR may be ≦0.55 g / 10 min. ２ -MFR １ ≦0.55 g / 10 min, and MFR ２ -MFR ３By 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 tend to be less likely to occur and adhesion tends to be better.

[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 tend to be less likely to occur and adhesion tends to be better.

[0011] According to one aspect of the present invention, a multilayer polyethylene film that is wrinkle-resistant and has excellent adhesion can be provided.

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

[0013] Hereinafter, 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 thickness ratio of each layer may differ from the actual ones. Furthermore, 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 materials, shapes, structures, etc. of the components described below.

[0014] <Multilayer polyethylene film> Figure 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 this order.

[0015] The content of 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, in order to achieve mono-materialization and facilitate resin recycling.

[0016] The temperature at which the melting peak maximum value observed in differential scanning calorimetry of the multilayer polyethylene film 10 is greater than 129°C and less than 134°C. When the melting peak maximum value is greater than 129°C, the multilayer polyethylene film 10 has excellent heat resistance, making the film less susceptible to heat deformation and wrinkles. When the melting peak maximum value is less than 134°C, roughening of the surface of the multilayer polyethylene film 10 can be suppressed, resulting in excellent processability and adhesion when providing a functional layer such as a vapor deposition layer or a coating layer. The temperature at which the melting peak maximum value is observed may be 130°C or higher, 131°C or higher, 132°C or higher, or 132.5°C or higher, from the viewpoint of achieving better heat resistance and less wrinkling of the multilayer polyethylene film 10. The temperature at which the melting peak maximum value is observed may be 133.8°C or lower or 133.5°C or lower, from the viewpoint of further suppressing roughening of the surface of the multilayer polyethylene film 10. When multiple melting peaks are present, the temperature at the maximum value of each melting peak falls within the above range. The temperature at the maximum value of each melting peak means a value measured by the method described in the Examples below.

[0017] The absolute value of the degree of molecular orientation of the multilayer polyethylene film 10 is less than 1.07. When the absolute value of the degree of 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, and achieving excellent adhesion. The absolute value of the degree of molecular orientation may be 1.06 or less, or may be 1 or more, 1.02 or more, or 1.05 or more. From these perspectives, the absolute value of the degree of molecular orientation may be 1 or more but less than 1.07, 1.02 or more but less than 1.07, 1.05 or more but less than 1.07, or 1 to 1.06. The absolute value of the degree of molecular orientation refers to 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. From the viewpoint of realizing a mono-material structure and facilitating resin recycling, 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] Melt flow rate (MFR) of the first polyethylene resin at 190°C and a load of 2.16 kg １ From the viewpoints of improving the heat resistance of the multilayer polyethylene film 10, making it less likely to wrinkle, and improving the adhesion, the MFR of the first polyethylene resin 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. １ From the viewpoint of wrinkles being less likely to occur and adhesion being more excellent, the MFR of the first polyethylene resin may be 0.1 g / 10 min or more, or 0.3 g / 10 min or more. １ may be 0.1 to 5 g / 10 min, 0.3 to 5 g / 10 min, 0.1 to 3 g / 10 min, 0.1 to 1.5 g / 10 min, 0.1 to 1 g / 10 min, or 0.1 to 0.5 g / 10 min. In this specification, the melt flow rate refers to 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, or 0.945 g / cm ３ The density of the first polyethylene resin may be less than 0.92 g / cm from the viewpoint of being less likely to wrinkle and having better adhesion. ３ Above, 0.93g / cm ３ or more, or 0.94 g / cm ３ From these viewpoints, the density of the first polyethylene resin may be 0.92 to 0.95 g / cm ３,0.93~0.947g / cm ３ , or 0.94 g / cm ３ 0.945g / cm or more ３ It may be less than.

[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, reducing wrinkles, and improving adhesion of the multilayer polyethylene film 10. The melting point of the first polyethylene resin may be 110°C or higher, 120°C or higher, or 125°C or higher, from the viewpoints of improving the resistance to wrinkles and improving adhesion. From these viewpoints, the melting point of the first polyethylene resin may be 110 to 145°C, 120 to 140°C, or 125 to 135°C.

[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 to 20,000 or more, or 50,000 or more, from the viewpoint of being less prone to wrinkles and achieving better adhesion. From these viewpoints, the weight average molecular weight Mw of the first polyethylene resin may be 10,000 to 1,000,000, 20,000 to 500,000, or 50,000 to 300,000. In this specification, the weight average molecular weight and the number average molecular weight described below refer to values ​​measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0023] From the viewpoint of being less susceptible to wrinkles and of achieving better adhesion, 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. From these viewpoints, the number average molecular weight Mn of the first polyethylene resin may be 1,000 to 200,000, 2,000 to 100,000, or 4,000 to 50,000.

[0024] From the viewpoint of being less susceptible to wrinkles and of achieving better adhesion, 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. From these viewpoints, the molecular weight distribution Mw / Mn of the first polyethylene resin may be 2 to 100, 3 to 100, 2 to 50, or 2 to 30.

[0025] The first layer 1 may contain a component other than the first polyethylene resin. For example, the first layer 1 may contain a polyethylene resin other than the first polyethylene resin. Examples of the polyethylene resin other than the first polyethylene resin include polyethylene resins that differ from the first polyethylene resin in 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 softening point (probe drop temperature) 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 viewpoints of improving the heat resistance and wrinkle resistance of the multilayer polyethylene film 10, and improving the adhesion. The softening point (probe drop temperature) of the first layer 1 may be 160°C or lower, 155°C or lower, 150°C or lower, or 146°C or lower. From these viewpoints, the softening point (probe drop temperature) of the first layer 1 may be 120 to 160°C, 125 to 155°C, 130 to 150°C, or 133 to 146°C.

[0027] The softening point (probe drop temperature) is a parameter related to localized thermal analysis of materials 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. The cantilever is placed in contact with the surface of a solid sample fixed to a sample stage. When a voltage is applied to the cantilever in contact mode to heat the sample, the sample surface thermally expands, causing the cantilever to rise. Further heating of the cantilever softens the sample surface, significantly changing its hardness. As a result, the cantilever descends and penetrates the sample surface. The point at which the sudden displacement detected at this time begins is the probe drop start point. By converting the voltage to temperature, the softening point (probe drop temperature) can be obtained. This method allows the softening point (probe drop temperature) to be determined locally in the nanoscale region, 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 are also possible with AFMs from other manufacturers if a Nano Thermal Analysis is attached. An example of a cantilever is the AN2-200 manufactured by Anasys Instruments. Cantilevers other than those listed above can also be used, as long as they can sufficiently reflect laser light and allow voltage to be applied.

[0029] The temperature range for measuring the softening point (probe drop temperature) varies depending on the material to be measured, but for example, the starting temperature can be about room temperature, 25° C., and the ending temperature can be about 400° C. In this specification, the temperature range for measuring the softening point (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 for measurements in both tapping mode and contact mode. In AFM, the deflection of the cantilever is sometimes measured 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 preferably 0.2 to 5 V / sec. When the sample surface softens, the tip of the cantilever sinks into the sample and descends. The amount of sinking of the cantilever affects the detection sensitivity of the peak top of the softening curve, and can be set to 3 to 500 nm. From the viewpoint of preventing damage to the cantilever, it is more preferable to set the amount of sinking to 5 to 100 nm.

[0032] In order to calculate the softening point (probe drop temperature), it is necessary to create a calibration curve. In the examples described below, calibration curves were created using polycaprolactone, low-density polyethylene, polypropylene, and polyethylene terephthalate as calibration samples. Details of creating the calibration curve will be described later. The material of the calibration sample is not limited to the above, and it is sufficient to use at least one 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, or somewhere in between. For example, it is also possible to remove polypropylene from the four calibration samples described above and use only three materials, polycaprolactone, low-density polyethylene, and polyethylene terephthalate, as calibration samples.

[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 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 reducing the thickness of the packaging material. From these viewpoints, the thickness of the first layer 1 may be 1 to 50 μm, 2 to 30 μm, 3 to 20 μm, 4 to 10 μm, or 5 to 10 μm.

[0034] <Third Layer> The third layer 3 is a layer containing a third polyethylene resin. From the viewpoint of realizing a mono-material structure and facilitating resin recycling, 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] Melt flow rate (MFR) of the third polyethylene resin at 190°C and a load of 2.16 kg ３ From the viewpoints of improving the heat resistance and wrinkle resistance of the multilayer polyethylene film 10, and improving the adhesion, the MFR of the third polyethylene resin 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. ３ From the viewpoint of wrinkles being less likely to occur and adhesion being more excellent, the MFR of the third polyethylene resin may be 0.1 g / 10 min or more, or 0.3 g / 10 min or more. ３ may be 0.1 to 5 g / 10 min, 0.3 to 5 g / 10 min, 0.1 to 3 g / 10 min, 0.1 to 1.5 g / 10 min, 0.1 to 1 g / 10 min, or 0.1 to 0.5 g / 10 min.

[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 achieving better adhesion. ３ Below, 0.947g / cm ３ or less, or 0.945 g / cm ３From the viewpoint of wrinkles being less likely to occur and adhesion being more excellent, the density of the third polyethylene resin may be less than 0.92 g / cm ３ Above, 0.93g / cm ３ or more, or 0.94 g / cm ３ From these viewpoints, the density of the third polyethylene resin may be 0.92 to 0.95 g / cm ３ ,0.93~0.947g / cm ３ , or 0.94 g / cm ３ 0.945g / cm or more ３ It may be less than.

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

[0038] From the viewpoint of being less susceptible to wrinkles and having better adhesion, 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 to 20,000 or more, or 50,000 or more. From these viewpoints, the weight average molecular weight Mw of the third polyethylene resin may be 10,000 to 1,000,000, 20,000 to 500,000, or 50,000 to 300,000.

[0039] From the viewpoint of being less susceptible to wrinkles and of achieving better adhesion, 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. From these viewpoints, the number average molecular weight Mn of the third polyethylene resin may be 1,000 to 200,000, 2,000 to 100,000, or 4,000 to 50,000.

[0040] From the viewpoint of being less susceptible to wrinkles and of achieving better adhesion, 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. From these viewpoints, the molecular weight distribution Mw / Mn of the third polyethylene resin may be 2 to 100, 3 to 100, 2 to 50, or 2 to 30.

[0041] The third layer 3 may contain a component other than the third polyethylene resin. For example, the third layer 3 may contain a polyethylene resin other than the third polyethylene resin. Examples of the polyethylene resin other than the third polyethylene resin include polyethylene resins that differ from the third polyethylene resin in MFR, density, melting point, molecular weight, etc. The third layer 3 may contain additives such as an antioxidant, a lubricant, an antiblocking agent, and an antistatic agent.

[0042] The softening point (probe drop temperature) 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 viewpoints of improving the heat resistance, wrinkle resistance, and adhesion of the multilayer polyethylene film 10. The softening point (probe drop temperature) of the third layer 3 may be 160°C or lower, 155°C or lower, 150°C or lower, or 146°C or lower, from the viewpoints of improving the wrinkle resistance and adhesion of the multilayer polyethylene film 10. From these viewpoints, the softening point (probe drop temperature) of the third layer 3 may be 120 to 160°C, 125 to 155°C, 130 to 150°C, or 133 to 146°C.

[0043] From the viewpoint of improving processability, 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, and from the viewpoint of reducing the thickness of the packaging material, the thickness of the third layer 3 may be 50 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less. From these viewpoints, the thickness of the third layer 3 may be 1 to 50 μm, 2 to 30 μm, 3 to 20 μm, 4 to 10 μm, or 5 to 10 μm.

[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. 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. From the viewpoint of realizing a mono-material structure and facilitating resin recycling, 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 may be 100% by mass (an embodiment in which the second layer 2 is substantially composed of the second polyethylene resin).

[0046] Melt flow rate (MFR) of the second polyethylene resin at 190°C and a load of 2.16 kg ２ From the viewpoints of improving the heat resistance of the multilayer polyethylene film 10, making it less likely to wrinkle, and improving the adhesion, the MFR of the second polyethylene resin 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. ２ From the viewpoint of wrinkles being less likely to occur and adhesion being more excellent, the MFR 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. ２may be 0.1 to 5 g / 10 min, 0.5 to 5 g / 10 min, 0.8 to 5 g / 10 min, 0.1 to 3 g / 10 min, 0.1 to 2 g / 10 min, 0.1 to 1.5 g / 10 min, or 0.1 to 1 g / 10 min.

[0047] MFR of the second polyethylene resin ２ From the viewpoint of excellent film-forming properties of the multilayer polyethylene film 10, the MFR of the first polyethylene resin is １ and / or the MFR of the third polyethylene resin ３ The MFR of the first polyethylene resin may be smaller than １ and the MFR of the second polyethylene resin ２ Difference from (MFR １ -MFR ２ ) and / or the MFR of the third polyethylene resin ３ and the MFR of the second polyethylene resin ２ Difference from (MFR ３ -MFR ２ From the viewpoint of excellent film-forming properties of the multilayer polyethylene film 10, the MFR may be 0.8 g / 10 min or less, 0.6 g / 10 min or less, or 0.55 g / 10 min or less. １ -MFR ２ and / or MFR ３ -MFR ２ From the viewpoint of wrinkles being less likely to occur and adhesion being more excellent, the MFR may be 0 g / 10 min or more, or may exceed 0 g / 10 min. １ -MFR ２ and / or MFR ３ -MFR ２ may be 0 to 0.8 g / 10 min, 0 to 0.6 g / 10 min, or more than 0 g / 10 min and 0.55 g / 10 min or less.

[0048] MFR of the second polyethylene resin ２ From the viewpoint of excellent film-forming properties of the multilayer polyethylene film 10, the MFR of the first polyethylene resin is １ and / or the MFR of the third polyethylene resin ３ The MFR of the first polyethylene resin may be greater than １and the MFR of the second polyethylene resin ２ the difference (MFR2-MFR1) and / or the MFR of the third polyethylene resin ３ and the MFR of the second polyethylene resin ２ From the viewpoint of excellent film-forming properties of the multilayer polyethylene film 10, the difference between the MFR and the MFR (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. ２ -MFR １ and / or MFR ２ -MFR ３ From the viewpoint of wrinkles being less likely to occur and adhesion being more excellent, the MFR may be 0 g / 10 min or more, or may exceed 0 g / 10 min. ２ -MFR １ and / or MFR ２ -MFR ３ may be 0 to 0.8 g / 10 min, 0 to 0.6 g / 10 min, or more than 0 g / 10 min and 0.55 g / 10 min or less.

[0049] The density of the second polyethylene resin is set to 0.99 g / cm from the viewpoint of being less susceptible to wrinkles and having better adhesion. ３ Below, 0.98g / cm ３ or less, or 0.975 g / cm ３ From the viewpoint of wrinkles being less likely to occur and adhesion being more excellent, the density of the second polyethylene resin may be less than 0.94 g / cm ３ Above, 0.95g / cm ３ or more, or 0.96 g / cm ３ From these viewpoints, the density of the second polyethylene resin may be 0.94 to 0.99 g / cm ３ , 0.95-0.98g / cm ３ , or 0.96 g / cm ３ 0.975g / cm or more ３ It may be less than.

[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 improving the heat resistance, reducing wrinkles, and improving adhesion of the multilayer polyethylene film 10. 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 viewpoints of improving the heat resistance of the multilayer polyethylene film 10. 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 viewpoints of improving the heat resistance of the multilayer polyethylene film 10. From these viewpoints, the melting point of the second polyethylene resin may be 110 to 145°C, 120 to 140°C, or 130 to 135°C.

[0051] From the viewpoint of being less susceptible to wrinkles and having better adhesion, 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 to 20,000 or more, or 50,000 or more. From these viewpoints, the weight average molecular weight Mw of the second polyethylene resin may be 10,000 to 1,000,000, 20,000 to 500,000, or 50,000 to 300,000.

[0052] From the viewpoint of being less susceptible to wrinkles and of achieving better adhesion, 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. From these viewpoints, the number average molecular weight Mn of the second polyethylene resin may be 1,000 to 200,000, 2,000 to 100,000, or 4,000 to 50,000.

[0053] From the viewpoint of being less susceptible to wrinkles and of achieving better adhesion, 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. From these viewpoints, the molecular weight distribution Mw / Mn of the second polyethylene resin may be 2 to 100, 3 to 100, 2 to 50, or 2 to 30.

[0054] The second layer 2 may contain a component other than the second polyethylene resin. For example, the second layer 2 may contain a polyethylene resin other than the second polyethylene resin. Examples of the polyethylene resin other than the second polyethylene resin include polyethylene resins that differ from the second polyethylene resin in 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 softening point (probe drop temperature) of the second layer 2 is higher than that of the first layer 1 and higher than that of the third layer 3. Since the softening point (probe drop temperature) of the second layer 2 is higher than those of the first layer 1 and the third layer 3, the multilayer polyethylene film 10 has excellent heat resistance, and is therefore less susceptible to deformation due to heat and wrinkles. From the viewpoint of achieving even more excellent heat resistance and less susceptibility to wrinkles in the multilayer polyethylene film 10, the softening point (probe drop temperature) 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 reducing the likelihood of wrinkles and improving adhesion, the softening point (probe drop temperature) 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. From these viewpoints, the softening point (probe drop temperature) of the second layer 2 may be 125 to 170° C., 130 to 165° C., 135 to 160° C., 138 to 157° C., 140 to 155° C., or 142 to 155° C.

[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 the 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. From these viewpoints, the thickness of the second layer 2 may be 5 to 80 μm, 8 to 50 μm, 10 to 40 μm, 12 to 30 μm, or 15 to 30 μm.

[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. From the viewpoint of improving processability, 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. From these viewpoints, the thickness of the second layer 2 may be 1.5 to 10 times, 2 to 9 times, or 3 to 8 times 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 this ratio is 1 or more, the multilayer polyethylene film 10 has excellent heat resistance, and therefore the film is less likely to deform due to heat and to wrinkle. When this ratio is 3 or less, roughening of the surface of the multilayer polyethylene film 10 can be suppressed, and therefore the processability and adhesion when providing a functional layer such as a vapor deposition layer or a coating layer can be excellent. From the viewpoints of achieving better heat resistance and less wrinkle formation of the multilayer polyethylene film 10, this ratio may be 1.2 or more, 1.5 or more, or 2 or more. From the viewpoints of easily achieving a smooth surface of the multilayer polyethylene film 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. From these viewpoints, the ratio may be 1 to 2.8, 1 to 2.5, 1 to 2, 1.2 to 3, 1.5 to 3, or 2 to 3.

[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 film can be produced by known methods such as an air-cooled inflation method, a water-cooled inflation method, and 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. The air-cooled inflation method involves installing a mold with an annular lip, known as a ring die or a crosshead die, at the tip of an extruder, and continuously extruding a material into a tubular shape. More specifically, an air hole is installed in the center of a ring die or the like, and compressed air is blown in through the hole to expand the tube. The tube is then cooled while being pulled by rollers known as pinch rolls, and the film is wound up, thereby producing a multilayer polyethylene film (polyethylene laminate film).

[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, to improve printability or lamination suitability during laminate 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 using 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 vapor deposition layer, a coating layer, various functional layers, an adhesive layer, an adhesive resin layer, etc.

[0064] <Packaging> The multilayer polyethylene film and laminate can be used as a packaging material for constituting a packaging. For example, the multilayer polyethylene film (laminate) can be used as a sealing material to make flat bags, three-sided bags, two-sided 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 comprising at least three layers, i.e., a first layer, a second layer, and a third layer, in this order, wherein the softening point of the second layer is higher than that of the first layer and higher than that 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 at the maximum value of the melting peak observed in differential scanning calorimetry of the multilayer polyethylene film is higher than 129°C and lower than 134°C, and 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 rates of the polyethylene resins constituting the first layer, the second layer, and the third layer are all 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 MFR １ , MFR ２ , and MFR ３ When this is the case, MFR １ -MFR ２ ≦0.55 g / 10 min, and MFR ３ -MFR ２[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 each MFR ≦ 0.55 g / 10 min. １ , MFR ２ , and MFR ３ When this is the case, MFR ２ -MFR １ ≦0.55 g / 10 min, and MFR ２ -MFR ３ [5] The multilayer polyethylene film according to [1] or [2], wherein the density of the polyethylene resin constituting the first layer and the third layer is 0.945 g / cm or less. ３ [6] The multilayer polyethylene film according to any one of [1] to [5], wherein the thicknesses of the first layer and the third layer are from 1 μm to 10 μm. [7] The multilayer polyethylene film according to any one of [1] to [6], wherein the thickness of the second layer is from 8 μm to 30 μm. [8] The multilayer polyethylene film according to any one of [1] to [7], wherein the softening points of the first layer and the third layer are from 120°C to 160°C. [9] The multilayer polyethylene film according to any one of [1] to [8], wherein the softening point of the second layer is from 125°C to 170°C.

[10] The multilayer polyethylene film according to any one of [1] to [9], wherein the absolute value of the degree of molecular orientation of the multilayer polyethylene film is 1 or more.

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

[0067] <Polyethylene resin> Resin A: Density 0.941 g / cm ３ , MFR1.30g / 10min ・Resin B: Density 0.962g / cm ３ , MFR0.85g / 10min ・Resin C: Density 0.944g / cm ３ , MFR0.45g / 10min ・Resin D: Density 0.960g / cm３ , MFR1.00g / 10min ・Resin E: Density 0.971g / cm ３ , MFR 1.20 g / 10 min Resin F: Mixture of Resin A and Resin E, Density 0.941 to 0.971 g / cm ３ , MFR 1.20 to 1.30 g / 10 min Resin G: Mixture of Resin A and Resin B, Density 0.941 to 0.962 g / cm ３ , MFR0.85-1.30g / 10min ・Resin H: Density 0.96g / cm ３ Resin I: Density 0.926 g / cm ３ , MFR0.8g / 10min ・Resin J: Density 0.937g / cm ３ , MFR1.8g / 10min

[0068] <Preparation of Multilayer Polyethylene Films> (Examples 1 to 38, Comparative Examples 1 to 15) The resins shown in Tables 1 to 3 constituting the first layer (Layer 1), second layer (Layer 2), and third layer (Layer 3) were each charged into an extruder and melt-kneaded at 190°C. After that, polyethylene resin was introduced through a three-layer die, and multilayer polyethylene films were prepared 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 prepared in each Example and Comparative Example. Next, a sealant film was dry-laminated onto the surface of the metal oxide layer to prepare a laminated film.

[0071] <Softening Point (Probe 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 cross-sectioned in 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 softening point (probe drop temperature) of the multilayer polyethylene film was measured as follows.

[0072] An Oxford Instruments MPF-3D-SA atomic force microscope was used, an Oxford Instruments Ztherm nanothermal microscope was used as the atomic force microscope, and an Anasys Instruments AN2-200 (trade name) cantilever was used. 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 to the sample surface). In this state, the detrend correction function of the instrument was performed in contact mode with a maximum applied voltage of 6 V and a heating rate of 0.5 V / s to correct for changes in the cantilever deflection due to applied voltage. Next, in contact mode, the cantilever was brought into contact with the sample so that the change in deflection between the cantilever and the sample was 0.2 V. While maintaining a constant deflection value, a voltage was applied to the cantilever at a maximum applied voltage of 6 V and a heating rate of 0.5 V / s to heat the sample. 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 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 maximized was converted into 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 softening point (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 vs. temperature was created. Here, the melting point is the melting peak temperature measured using a differential scanning calorimeter (DSC) at a heating rate of 5°C / min. The method for measuring the softening points (probe drop temperatures) of the calibration samples was the same as for measuring the softening points (probe drop temperatures) of the samples described above, except that the maximum applied voltages during Detrend correction and measurement were 3.5 V for polycaprolactone, 5.5 V for low-density polyethylene, 6.5 V for polypropylene, and 7.8 V for polyethylene terephthalate. The relationship between the applied voltage at which the Z displacement was maximized when measuring each calibration sample and the melting point was approximated by a cubic function using the least squares method to create a calibration curve.

[0074] <Melting Peak Temperature> Differential scanning calorimetry was performed on the multilayer polyethylene film in accordance with JIS K7121-1987 using a differential scanning calorimeter (manufactured by Hitachi, Ltd., product name DSC7020) under conditions of 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] <Degree of molecular orientation> The orientation of 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 inspected, and the bubble stability was evaluated based on the following evaluation criteria. The evaluation results are shown in Tables 1 to 3. A: No vibration of the bubbles or wrinkles were observed on the appearance of the formed film. B: Vibration of the bubbles was observed, and slight wrinkles were observed on the formed film. C: Vibration of the bubbles was observed, and wrinkles were observed on the formed film that made it difficult to use as a 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 to 3. A: No wrinkles were observed on the appearance of the multilayer polyethylene film. B: Slight wrinkles were observed on the appearance of the multilayer polyethylene film. C: Many wrinkles were observed on the appearance of the multilayer polyethylene film.

[0078] <Laminate strength> The prepared laminate was cut into 15 mm wide strips and peeled at a peel speed of 300 mm / min and a peel angle of 180° using a Tensilon universal material testing machine (manufactured by A&D Co., Ltd.) in accordance with JIS K6854-2 and ISO8510-2 to measure the laminate strength. The evaluation results are shown in Tables 1 to 3.

[0079]

[0080]

[0081]

[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, namely a first layer, a second layer, and a third layer, in this order, wherein the softening point of the second layer is higher than that of the first layer and is higher than that 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 higher than 129°C and lower than 134°C, and the absolute value of the molecular orientation degree of the multilayer polyethylene film is less than 1.

07.

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 called 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 called 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 The multilayer polyethylene film according to any one of claims 1 to 4, wherein the thickness of the multilayer polyethylene film is less than 1 / 2 mm.

6. The multilayer polyethylene film according to any one of claims 1 to 4, wherein the first layer and the third layer have a thickness of 1 μm or more and 10 μm or less.

7. The multilayer polyethylene film according to any one of claims 1 to 4, wherein the second layer has a thickness of 8 µm or more and 30 µm or less.

8. The multilayer polyethylene film according to any one of claims 1 to 4, wherein the softening points of the first layer and the third layer are 120°C or higher and 160°C or lower.

9. The multilayer polyethylene film according to any one of claims 1 to 4, wherein the softening point of the second layer is 125°C or higher and 170°C or lower.

10. The multilayer polyethylene film according to any one of claims 1 to 4, wherein the absolute value of the degree of molecular orientation of the multilayer polyethylene film is 1 or more.

Images