Biaxially oriented polyethylene film

Abstract

To provide a polyethylene film in which curling due to heat is more suppressed. [Solution] A biaxially oriented polyethylene film containing polyethylene resin, wherein (a) the thermal shrinkage ratio (MDHS / TDHS) of the thermal shrinkage ratio in the longitudinal direction (MDHS) measured at 100°C according to JIS Z 1712 to the thermal shrinkage ratio in the width direction (TDHS) measured at 100°C according to JIS Z 1712 is 0.35 or more and 2.50 or less, and / or (b) the surface orientation coefficient ΔP calculated from the refractive indices in the width direction (Ny), longitudinal direction (Nx), and thickness direction (Nz), measured according to JIS K 7142, by the formula: surface orientation coefficient ΔP = (Nx + Ny) / 2 - Nz is 0.006 or more and 0.035 or less.

Description

Technical Field

[0001] The present invention relates to a biaxially stretched polyethylene film and the like.

Background Art

[0002] Polyethylene films are excellent in lightness, thermal stability, and mechanical properties, and are widely used as packaging materials and industrial material films. In particular, in recent years, polyethylene films have been widely used in the manufacturing processes of electronic components and printed circuit boards, protective materials used for thermosetting resin members such as fiber-reinforced plastics, release materials, etc., taking advantage of their excellent peelability, and their utility value has been increasing.

[0003] When used as a protective film, heat lamination may be performed to obtain a laminate with other layers. During heat lamination, curl occurs due to heat shrinkage, which reduces the handling property in subsequent processes and lowers the production efficiency. As a conventional technique, a technique for controlling the mechanical strength and heat shrinkage rate of a biaxially stretched polypropylene film within a specific range to suppress film curl while maintaining flexibility and tensile strength has been disclosed (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the conventional technique, depending on the temperature conditions, curl may occur in the longitudinal direction, and when peeling the protective film from the adherent in the process after heat lamination, the protective film cannot be completely peeled from the adherent and may be conveyed in subsequent processes.

[0006] The present invention aims to provide a polyethylene film in which curling due to heat is further suppressed. [Means for solving the problem]

[0007] In view of the above problems, the inventors diligently conducted research and found that a biaxially oriented polyethylene film containing polyethylene resin has the following characteristics: (a) The thermal shrinkage ratio (MDHS / TDHS) of the thermal shrinkage rate in the longitudinal direction (MDHS), measured at 100°C according to JIS Z 1712, to the thermal shrinkage rate in the width direction (TDHS), measured at 100°C according to JIS Z 1712, is 0.35 or more and 2.50 or less; and / or (b) The surface orientation coefficient ΔP, calculated from the refractive indices in the width direction (Ny), longitudinal direction (Nx), and thickness direction (Nz), measured according to JIS K 7142, is 0.006 or more and 0.035 or less;

[0008] Item 1. A biaxially oriented polyethylene film containing polyethylene resin, (a) The thermal shrinkage ratio (MDHS / TDHS) of the thermal shrinkage ratio in the longitudinal direction (MDHS) measured at 100°C according to JIS Z 1712 to the thermal shrinkage ratio in the width direction (TDHS) measured at 100°C according to JIS Z 1712 is 0.35 or more and 2.50 or less, and / or (b) The surface orientation coefficient ΔP, calculated from the refractive indices in the width direction (Ny), length direction (Nx), and thickness direction (Nz) measured in accordance with JIS K 7142, is between 0.006 and 0.035. Biaxially oriented polyethylene film.

[0009] Item 2. The peel force measured in a 180° peel test on at least one surface is At a peeling speed of 300 mm / min, the N / 25 mm is between 1.00 N / 25 mm and 4.00 N / 25 mm. When the peeling speed is 1000 mm / min, the N / 25 mm is between 1.60 N / 25 mm and 4.00 N / 25 mm, and At a peeling speed of 2500 mm / min, the N / 25 mm is between 2.30 N / 25 mm and 4.00 N / 25 mm. The biaxially oriented polyethylene film described in item 1.

[0010] Item 3. The biaxially oriented polyethylene film according to Item 1 or 2, wherein the modulus of elasticity in the thickness direction at 23°C, as measured by nanoindentation on at least one of the surfaces, is 2.00 GPa or less.

[0011] Item 4. A biaxially oriented polyethylene film according to any one of items 1 to 3, wherein the melt flow rate (MFR) at 190°C, measured according to JIS K 7210, is 0.8 g / 10 min or more.

[0012] Item 5. A biaxially oriented polyethylene film according to any of items 1 to 4, having a thickness of 10 μm or more and 50 μm or less.

[0013] Item 6. A protective film, release film, or packaging film comprising a biaxially oriented polyethylene film as described in any of Items 1 to 5.

[0014] Item 7. A laminate comprising a biaxially oriented polyethylene film and other layers as described in any of Items 1 to 5. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a polyethylene film in which curling due to heat is further suppressed. [Modes for carrying out the invention]

[0016] In this specification, the terms “contains” and “includes” include the concepts of “contains,” “includes,” “substantially consist of,” and “consist solely of.”

[0017] In this specification, "~" in a numerical range means "above and below". That is, the notation α~β means α or more and β or less, or β or more and α or less, and includes α and β as a range.

[0018] In this specification, when the upper limit value and the lower limit value are separately described, a range formed by arbitrarily combining the described upper limit value and lower limit value is also disclosed in this specification.

[0019] In identifying the inventions included in the present disclosure, each configuration (properties, structure, functions, etc.) described in each embodiment of the present disclosure may be combined in any manner. That is, the present disclosure includes all themes consisting of any combination of the combinable configurations described in this specification.

[0020] 1. Biaxially oriented polyethylene film In one aspect, the present invention relates to a biaxially stretched polyethylene film containing a polyethylene resin, wherein (a) the heat shrinkage ratio (MDHS / TDHS) of the machine direction heat shrinkage rate (MDHS) measured at 100 °C based on JIS Z 1712 to the transverse direction heat shrinkage rate (TDHS) measured at 100 °C based on JIS Z 1712 is 0.35 or more and 2.50 or less, and / or (b) the surface orientation coefficient ΔP calculated by the formula: surface orientation coefficient ΔP = (Nx + Ny) / 2 - Nz from the refractive indices in the transverse direction (Ny), machine direction (Nx), and thickness direction (Nz) measured based on JIS K 7142 is 0.006 or more and 0.035 or less. (In this specification, it may also be referred to as "the polyethylene film of the present invention".) This will be described below.

[0021] The polyethylene film of the present invention is more suppressed in curl generation due to heat.

[0022] As a result of the inventor's research on curl, it has been found that the numerical value of the thermal shrinkage rate (MDHS or TDHS) in the longitudinal or width direction itself is not important, but the thermal shrinkage ratio (MDHS / TDHS) is important. By adjusting the thermal shrinkage ratio within the above range, the shrinkage in the film plane is not biased in one direction, and while suppressing curl generation, heat lamination can be suitably performed. Also, when peeling off the film, the film can be peeled off neatly without damaging the appearance of the adherent. In cases outside the above range, wrinkles or lifting occur in the longitudinal or width direction, and curl is likely to occur.

[0023] Also, the inventor has advanced the study from another perspective and found that the surface orientation coefficient ΔP is important. By adjusting this within the above range, heat lamination can also be suitably performed while suppressing curl generation.

[0024] When transporting a laminate having a protective film at the operating speed of the processing step and peeling off the protective film at a speed lower than the operating speed, problems such as dipping (slip-stick) occurring and a horizontal stripe pattern being formed on the adhesive surface, and the protective film floating due to poor adhesion may occur. The operating speed can vary depending on the content of the processing and other factors, and it is important to suppress these problems even in such an environment. According to the present invention, by adjusting the thermal shrinkage ratio (MDHS / TDHS) and / or the surface orientation coefficient ΔP within the above range, it is also possible to suppress dipping and poor adhesion under various operating speeds.

[0025] The thermal shrinkage ratio (MDHS / TDHS) is preferably 0.35 or more and 2.20 or less, more preferably 0.35 or more and 2.00 or less, still more preferably 0.37 or more and 2.00 or less, even more preferably 0.37 or more and 1.80 or less, particularly preferably 0.37 or more and 1.50 or less, particularly more preferably 0.37 or more and 1.20 or less, particularly still more preferably from 0.40 or more and 1.20 or less, and particularly preferably 0.42 or more and 1.10 or less, from the viewpoints of suppressing curl generation due to heat, suppressing dipping, suppressing poor adhesion, etc.

[0026] The thermal shrinkage ratio (MDHS / TDHS) is a value measured according to the method of (4-1) in the example described below.

[0027] The surface orientation coefficient ΔP is preferably 0.007 to 0.035, more preferably 0.007 to 0.033, even more preferably 0.007 to 0.031, even more preferably 0.007 to 0.028, particularly preferably 0.007 to 0.025, particularly more preferably 0.007 to 0.022, and especially preferably 0.08 to 0.22, from the viewpoint of suppressing curl generation due to heat, suppressing zipping, and suppressing poor adhesion.

[0028] The surface orientation coefficient ΔP is a value measured according to the method of (4-2) in the example described below.

[0029] The polyethylene film of the present invention preferably has a peel force, measured in a 180° peel test on at least one side, that is 1.00 N / 25 mm to 4.00 N / 25 mm at a peel speed of 300 mm / min, 1.60 N / 25 mm to 4.00 N / 25 mm at a peel speed of 1000 mm / min, and 2.30 N / 25 mm to 4.00 N / 25 mm at a peel speed of 2500 mm / min, from the viewpoint of suppressing zipping and poor adhesion.

[0030] When the peeling speed is 300 mm / min, the peeling force is preferably 1.05 N / 25 mm to 3.95 N / 25 mm, more preferably 1.10 N / 25 mm to 3.90 N / 25 mm, even more preferably 1.20 N / 25 mm to 3.50 N / 25 mm, and even more preferably 1.20 N / 25 mm to 3.00 N / 25 mm, from the viewpoint of suppressing zipping and poor adhesion.

[0031] When the peeling speed is 1000 mm / min, the peeling force is preferably 1.65 N / 25 mm to 3.95 N / 25 mm, more preferably 1.70 N / 25 mm to 3.90 N / 25 mm, even more preferably 1.80 N / 25 mm to 3.70 N / 25 mm, even more preferably 1.90 N / 25 mm to 3.50 N / 25 mm, and especially preferably 1.95 N / 25 mm to 3.35 N / 25 mm, from the viewpoint of suppressing zipping and poor adhesion.

[0032] When the peeling speed is 2500 mm / min, the peeling force is preferably 2.35 N / 25 mm to 3.90 N / 25 mm, more preferably 2.40 N / 25 mm to 3.80 N / 25 mm, even more preferably 2.40 N / 25 mm to 3.40 N / 25 mm, and even more preferably 2.40 N / 25 mm to 3.15 N / 25 mm, from the viewpoint of suppressing zipping and poor adhesion.

[0033] The peeling force is a value measured according to the method of (4-3) in the example described below.

[0034] The polyethylene film of the present invention preferably has an elastic modulus in the thickness direction at 23°C, measured by nanoindentation, of 2.00 GPa or less on at least one surface (particularly the surface having the peeling force described above), from the viewpoint of suppressing zipping and poor adhesion. More preferably, the elastic modulus is 0.40 GPa or more and 1.95 GPa or less, even more preferably 0.50 GPa or more and 1.90 GPa or less, even more preferably 0.55 GPa or more and 1.80 GPa or less, and particularly preferably 0.60 GPa or more and 1.60 GPa or less.

[0035] The modulus of elasticity is a value measured according to the method of (4-4) in the example described below.

[0036] The polyethylene film of the present invention preferably has a melt flow rate (MFR) of 0.8 g / 10 min or more at 190°C, as measured according to JIS K 7210, from the viewpoint of suppressing curling due to heat. The MFR is more preferably 1.2 g / 10 min or more, and even more preferably 1.5 g / 10 min or more.

[0037] MFR is a value measured according to the method of (2-2) in the example described below.

[0038] The polyethylene film of the present invention contains polyethylene resin. The polyethylene film of the present invention contains polyethylene resin as a main component. In this specification, "containing polyethylene resin as a main component" means that the polyethylene film contains 50% by mass or more of polyethylene resin relative to the entire polyethylene film (when the entire polyethylene film is considered to be 100% by mass). The polyethylene resin content relative to the entire polyethylene film of the present invention is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and especially preferably 99% by mass or more. The upper limit of the polyethylene resin content is, for example, 100% by mass and 99.9% by mass relative to the entire polyethylene film of the present invention.

[0039] Polyethylene resin is not particularly limited in its origin; for example, it can be a resin made from petroleum-derived raw materials, or it can be a resin made from plant-derived raw materials (so-called biomass plastic).

[0040] Among polyethylene resins, low-density polyethylene or high-density polyethylene is preferred, and linear low-density polyethylene, so-called LLDPE, is preferred.

[0041] The weight-average molecular weight (Mw) of polyethylene resin is preferably between 200,000 and 400,000, and more preferably between 210,000 and 300,000, from the viewpoint of thickness uniformity, mechanical properties, and thermal-mechanical properties.

[0042] The number-average molecular weight (Mn) of the polyethylene resin is preferably 80,000 or less, and more preferably between 10,000 and 70,000, from the viewpoint of suppressing the elastic modulus after stretching and obtaining a flexible film.

[0043] The molecular weight distribution (Mw / Mn) of polyethylene resin, calculated as the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn), is preferably 3 to 13, and more preferably 3.3 to 12, from the viewpoint of obtaining appropriate resin fluidity during biaxial stretching and efficiently obtaining a film without breakage.

[0044] The melt flow rate (MFR) of polyethylene resin at 190°C and a load of 2.16 kg is not particularly limited, but from the viewpoint of reducing the mechanical load in the film-forming process, it is preferably 5 g / 10 min or less, and from the viewpoint of making the thickness of the polyethylene film of the present invention, it is more preferably 0.2 g / 10 min or more and 4 g / 10 min or less. Furthermore, from the viewpoint of suppressing curling due to heat, the MFR is preferably 0.8 g / 10 min or more, more preferably 1.2 g / 10 min or more, and even more preferably 1.5 g / 10 min or more.

[0045] The average molecular weight (Mz) of polyethylene resin is, for example, between 500,000 and 1,800,000.

[0046] The average molecular weight and molecular weight distribution of the polyethylene resin are values ​​measured according to the method of (2-1) in the example described below. The MFR of the polyethylene resin is a value measured according to the method of (2-2) in the example described below.

[0047] The polyethylene film of the present invention may contain other components besides the polyethylene resin, as long as the effects of the present invention are not hindered. Examples of other components include additives contained in known resin films, such as antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, plasticizers, lubricants, crosslinking agents, flame retardants, antistatic agents, heat resistance improvers, antiblocking agents, inorganic particles, resin particles, chlorine scavenging agents, antifogging agents, hydrolysis inhibitors, and the like. Each of these components may be used individually or in combination as needed. When the polyethylene film of the present invention contains the other components, their content is 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less, relative to the total mass of the polyethylene film.

[0048] The polyethylene film of the present invention is a biaxially oriented film stretched in two axial directions: the longitudinal direction (MD direction) and the width direction (MD direction). The polyethylene film of the present invention is particularly preferably a sequentially biaxially oriented film from the viewpoint of stably achieving uniform thickness and easily adjusting the mechanical strength of the film.

[0049] The polyethylene film of the present invention can have a single-layer structure or a multi-layer structure. A single-layer structure is preferred for the polyethylene film of the present invention. If the polyethylene film of the present invention has a multi-layer structure, each layer contains the aforementioned polyethylene resin. In this case, the polyethylene resins contained in each layer may be the same, or at least one or all of them may be different.

[0050] The thickness of the polyethylene film of the present invention is not particularly limited and can be set to any desired thickness depending on the intended application. From the viewpoint of avoiding film breakage and obtaining a stable and uniform thickness, the lower limit of the thickness is preferably 2 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and even more preferably 15 μm or more. On the other hand, from the viewpoint of suppressing production costs and reducing the mechanical load of the film-forming process, the upper limit of the thickness is preferably 100 μm or less, more preferably 70 μm or less, even more preferably 50 μm or less, and even more preferably 30 μm or less. In the case where the polyethylene film of the present invention has the multilayer structure described above, the thickness of the polyethylene film of the present invention refers to the sum of the thicknesses of each layer.

[0051] 2. Manufacturing method The method for manufacturing the polyethylene film of the present invention is not particularly limited, and a wide range of methods similar to those used for known films can be employed. Specifically, for example, the polyethylene film of the present invention can be manufactured by a manufacturing method that includes the steps of obtaining a cast sheet containing polyethylene resin and stretching the cast sheet in the MD direction and the TD direction. An example of such a method will be described in detail below.

[0052] Cast sheets, which are the stretching precursors, can be obtained using known methods. For example, polyethylene resin pellets, dry-mixed polyethylene resin pellets, or mixed polyethylene resin pellets prepared by pre-melting and kneading can be supplied to an extruder, heated and melted, foreign matter and modified polymers removed through a filter, then extruded into a sheet from a T-die, and cooled and solidified in at least one cooling drum to obtain a cast sheet.

[0053] Inside the extruder, polyethylene resin undergoes some degree of degradation due to thermal and oxidative stress. From the viewpoint of suppressing such polymer degradation, the resin temperature during melt extrusion should be between 170°C and 320°C, preferably between 200°C and 300°C. Furthermore, degradation can be suppressed by adjusting the nitrogen purging inside the extruder, the screw shape, the internal shape of the T-die during casting, and the amount of antioxidant added.

[0054] The temperature of the cooling drum is preferably between 20°C and 90°C, and more preferably maintained between 40°C and 80°C. Any method can be used to bring the sheet resin into contact with the casting drum, such as the air knife method, touch roll method, electrostatic application method, or water-cooled casting method, but the air knife method is preferred because it allows for easy adjustment when bringing the sheet resin into contact with the cooling drum and is easy to handle. When using an air knife, the temperature of the blown air (AK air temperature) is preferably between 10°C and 90°C, more preferably between 20°C and 80°C.

[0055] Cast sheets obtained by adjusting the cooling drum temperature and AK air temperature within the above range exhibit suppressed crystallization and reduced mechanical load during stretching. As a result, it is believed that the desired physical properties of the present invention can be easily obtained.

[0056] The polyethylene film of the present invention can be obtained by stretching a cast sheet in two axes: longitudinal and transverse (MD and TD directions).

[0057] First, the cast sheet is heated to a temperature of 70°C to 130°C, preferably 80°C to 120°C. The method of heating the cast sheet is not particularly limited, but it is preferable to alternately heat both sides of the cast sheet using a group of four or more rolls arranged in the flow direction, and to heat both sides of the sheet simultaneously just before longitudinal stretching. By maintaining this temperature range, the cast sheet does not undergo excessive thermal expansion and can be stretched longitudinally as described later while maintaining its flatness.

[0058] A cast sheet is stretched in the longitudinal direction (MD stretching), and then immediately relaxed to obtain an MD stretched sheet. The stretching ratio in the longitudinal direction (MD ratio) is 3 times or more and 11 times or less, preferably 3.5 times or more and 9 times or less. The relaxation rate (MD relaxation rate) is preferably 12% or less, more preferably 11% or less, and even more preferably 10% or less.

[0059] The MD stretched sheet obtained by adjusting within the above range maintains its flatness and suppresses oriented crystallization, thus reducing the mechanical load during stretching in the width direction, as described later. The method of stretching and relaxing in the longitudinal direction is not particularly limited, but a method that utilizes the difference in peripheral speed of two or more roll groups arranged in the flow direction is preferred.

[0060] Next, the stretched sheet is guided to a tenter and stretched in the width-to-width direction (TD stretching). The temperature for stretching in the width-to-width direction (TD temperature) is 130°C to 190°C, preferably 140°C to 185°C, and more preferably 150°C to 175°C. The stretching ratio in the width-to-width direction (TD ratio) is 4 times to 13 times, preferably 5 times to 12 times, and more preferably 6 times to 11 times.

[0061] By adjusting within the above range, stretching breakage caused by unstretched residue (remaining tension) can be suppressed, and polyethylene film of uniform thickness can be efficiently obtained.

[0062] Finally, the biaxially oriented film is relaxed in the width direction, and then the clips are released at the film temperature described later to obtain the polyethylene film of the present invention.

[0063] The lateral relaxation rate (TD relaxation rate) is 5% or more and less than 23%, preferably 8% or more and less than 22%, and more preferably 9% or more and less than 21%. Subsequently, the film temperature when the clip is released is 50°C or more and less than 98°C, preferably 55°C or more and less than 97°C, and more preferably 60°C or more and less than 96°C.

[0064] By adjusting within the above range, the tensile stress remaining in the film after biaxial stretching is uniformly relieved, maintaining flatness while acquiring appropriate flexibility. As a result, it is believed that the desired physical properties of the present invention can be easily obtained.

[0065] The film fed from the tenter is wound into a roll by a winding machine to obtain the polyethylene film of the present invention. Furthermore, the polyethylene film of the present invention can be surface-treated according to its application, as long as its properties are not impaired. Examples of surface treatments include corona discharge treatment, plasma treatment, and flame treatment.

[0066] 3.Applications The polyethylene film of the present invention can be applied to a variety of uses. In particular, the polyethylene film of the present invention is especially suitable as a protective film for electronic components. Furthermore, the polyethylene film of the present invention can also be used as a protective film, release film, and packaging film other than those mentioned above.

[0067] The polyethylene film of the present invention can be used as a protective film for dry film resists. The type of dry film resist is not particularly limited, and can be broadly applied to known dry film resists, for example. Such a protective film is provided to protect the adhesive layer of the dry film resist. In one embodiment, the dry film resist may be a film laminated in the order of the polyethylene film of the present invention, a resist layer, and a base film (for example, a film containing polyethylene terephthalate (PET)).

[0068] The polyethylene film of the present invention can be used for various applications by arranging other layers on one or both of its surfaces as needed. For example, the polyethylene film of the present invention can be used as a protective film, release film, etc., by arranging a release layer containing a release agent (such as a silicone coating) on ​​one or both of its surfaces as needed. As another example, the polyethylene film of the present invention can be used as a packaging film, etc., by arranging a coating layer (such as a gas barrier layer) on one or both of its surfaces as needed. [Examples]

[0069] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0070] (1) Preparation of polyethylene resin The polyethylene resins used in the examples and comparative examples are as follows: • PE1: Dow Chemical's "TF80" (LLDPE) • PE2: Prime Polymer's "SP3010" (LLDPE) • PE3: SABIC "BX202" (LLDPE) • PE4: LG Chem Co., Ltd. "LO4904P" (HDPE) The physical properties of these polyethylene resins are shown below. The measurement method is as follows.

[0071] [Table 1]

[0072] (2) Measurement of the physical properties of polyethylene resin (2-1) Measurement of various average molecular weights and molecular weight distributions of polyethylene resins Using SEC (size exclusion chromatography), the average molecular weight and molecular weight distribution of various materials were measured under the following conditions. Equipment: HLC-8321GPC / HT (Detector: Differential Refractometer (RI)) (Manufactured by Tosoh Corporation) Column: TSKgel guardcolumnH HR (30)HT(7.5mmI.D.×7.5cm)×1 + TSKgel GMH HR -H(20)HT (7.8mm I.D. x 30cm) x 3 pieces (manufactured by Tosoh Corporation) Eluent: 1,2,4-Trichlorobenzene (for GPC, manufactured by Fujifilm Wako Pure Chemical Industries) + Dibutylhydroxytoluene (0.05%) Flow rate: 1.0mL / min Detection condition: polarization=(-) Injection volume: 300μL Column temperature: 140℃ Temperature: 40°C Sample concentration: 1 mg / mL Pretreatment: The sample was weighed, and dissolved in a solvent (1,2,4-trichlorobenzene with 0.1% dibutylhydroxytoluene added) by shaking at 140°C for 1 hour. The solution was then filtered by heating through a 0.5 μm sintered filter. No insoluble material was observed in any of the sample solutions during visual inspection. Calibration Curve: A calibration curve was created using a fifth-order approximation curve with standard polystyrene manufactured by Tosoh Corporation. Therefore, the obtained values ​​are polystyrene-equivalent molecular weights. However, the molecular weights of PP1, PP2, and PP3 were converted to polyethylene molecular weights using the Q-factor.

[0073] From the obtained calibration curve and SEC chromatogram, the number-average molecular weight (Mn), weight-average molecular weight (Mw), and Z-average molecular weight (Mz) were obtained using analysis software for the measurement device. The molecular weight distribution (Mw / Mn) was then obtained using these Mw and Mn values.

[0074] (2-2) Measurement of Melt Flow Rate (MFR) For each resin, the melt flow rate (MFR) in the form of raw resin pellets was measured using a melt indexer from Toyo Seiki Co., Ltd., in accordance with condition M of JIS K 7210. Specifically, first, a weighed 4g sample was inserted into a cylinder heated to the test temperature (190°C) and preheated for 3.5 minutes under a load of 2.16kg. Then, the weight of the sample extruded from the bottom hole over 30 seconds was measured, and the MFR (g / 10min) was determined. The above measurement was repeated three times, and the average value was taken as the measured MFR.

[0075] (3) Preparation of biaxially oriented polyethylene film (Example 1) PE1 was supplied to an extruder and melted at a resin temperature of 260°C. After removing foreign matter and modified polymer using a filter installed in the middle of the polymer tube, it was extruded using a T-die and solidified by winding it onto a casting drum with a surface temperature maintained at 50°C to produce a cast sheet.

[0076] Furthermore, an air knife was used to ensure close contact with the casting drum, and the temperature of the blown air was set to 25°C.

[0077] The resulting cast sheet was preheated to 100°C, stretched six times in the longitudinal direction, then relaxed by 3.5% in the same direction, and immediately returned to room temperature.

[0078] Subsequently, the stretched film was guided to a tenter, held at both ends with 110°C clips, preheated to 165°C, stretched 7.8 times in the width direction, and then relaxed by 10% in the same direction. After that, the film temperature after biaxial stretching was cooled to 60°C, the tenter clips were released, and a biaxially oriented polyethylene film with a thickness of 20 μm was obtained.

[0079] The film thickness was measured using a micrometer (JIS-B7502) in accordance with JIS-C2330.

[0080] (Example 2) A biaxially oriented polyethylene film was obtained in the same manner as in Example 1, except that the resin supplied to the extruder was PE2.

[0081] (Example 3) A biaxially oriented polyethylene film was obtained in the same manner as in Example 1, except that the resin supplied to the extruder was PE3.

[0082] (Example 4) A biaxially oriented polyethylene film was obtained in the same manner as in Example 1, except that it was stretched eight times in the longitudinal direction and eleven times in the width direction.

[0083] (Example 5) A biaxially oriented polyethylene film was obtained in the same manner as in Example 1, except that the resin was melted at a temperature of 240°C and the surface temperature of the casting drum and the air temperature of the air blown from the air knife were set to 70°C.

[0084] (Example 6) A biaxially oriented polyethylene film was obtained in the same manner as in Example 1, except that the film temperature when the tenter clip was released was set to 95°C.

[0085] (Example 7) A biaxially oriented polyethylene film was obtained in the same manner as in Example 1, except that relaxation was applied by 10% in the longitudinal direction and 20% in the transverse direction.

[0086] (Example 8) A biaxially oriented polyethylene film was obtained in the same manner as in Example 4, except that a 20% relaxation was applied in the width direction and the film temperature when the tenter clips were released was set to 95°C.

[0087] (Example 9) A biaxially oriented polyethylene film was obtained in the same manner as in Example 1, except that the resin supplied to the extruder was PE4.

[0088] (Comparative Example 1) A biaxially oriented polyethylene film was obtained in the same manner as in Example 1, except that the longitudinal relaxation was set to 0% and the film temperature when the tenter clip was released was set to 45°C.

[0089] (Comparative Example 2) A biaxially oriented polyethylene film was obtained in the same manner as in Example 1, except that a relaxation of 13% was applied in the longitudinal direction and 23% in the transverse direction, and the film temperature when the tenter clip was released was set to 98°C.

[0090] (Comparative Example 3) A biaxially oriented polyethylene film was obtained in the same manner as in Example 4, except that the resin was melted at a temperature of 240°C and the surface temperature of the casting drum and the air temperature of the air blown from the air knife were set to 70°C.

[0091] (Comparative Example 4) A biaxially oriented polyethylene film was obtained in the same manner as in Example 2, except that a relaxation of 13% was applied in the longitudinal direction and 23% in the transverse direction, and the film temperature when the tenter clip was released was set to 98°C.

[0092] (Comparative Example 5) A biaxially oriented polyethylene film was obtained in the same manner as in Example 9, except that the resin was melted at a temperature of 245°C, the surface temperature of the casting drum was set to 65°C, and the air temperature of the air blown out by the air knife was set to 70°C.

[0093] (4) Measurement of physical properties of biaxially oriented polyethylene film (4-1) Measurement of thermal shrinkage rate and thermal shrinkage ratio For the biaxially oriented polyethylene films of the examples and comparative examples, the thermal shrinkage coefficient in the width direction (TDHS) and the thermal shrinkage coefficient in the length direction (MDHS) were measured at 100°C according to JIS Z 1712, and the ratio of MDHS to TDHS (thermal shrinkage ratio, MDHS / TDHS) was calculated. Specifically, MDHS and TDHS were measured in an air-circulating constant temperature bath maintained at 100°C ± 3°C in accordance with JIS Z 1712, and the thermal shrinkage ratio was calculated by dividing the MDHS value by the TDHS value.

[0094] (4-2) Measurement of refractive index and surface orientation coefficient For the biaxially oriented polyethylene films of the examples and comparative examples, the surface orientation coefficient ΔP was calculated from the refractive indices in the width direction (Ny), length direction (Nx), and thickness direction (Nz), measured according to JIS K 7142, using the formula: surface orientation coefficient ΔP = (Nx + Ny) / 2 - Nz. The refractive index was measured in accordance with JIS K 7142.

[0095] (4-3) Measurement of peeling force The peel strength of the biaxially oriented polyethylene films of the examples and comparative examples was measured as follows. (1) A laminate was obtained by applying a 50 mm wide x 150 mm long adhesive tape (Nitto Denko Corporation NO.31B tape, acrylic adhesive) to one of the two surfaces of a biaxially oriented polyethylene film, the surface that is to be bonded to the adherend, by passing a 2 kg roller back and forth twice. (2) The obtained laminate was left to stand for 20 hours in an environment of 70°C and 50% humidity, then cut into strips 25 mm wide, which were used as the measurement samples. (3) The sample was subjected to 180° peeling using a tensile testing machine (Minebea Co., Ltd.'s universal tensile testing machine "Technograph TGI-1kN") at constant peeling speeds (50 mm / min, 300 mm / min, 1000 mm / min, and 2500 mm / min), and the peeling force was measured. (4) Measurements were taken for each peeling rate with n=10, and the average value was used as the measurement result.

[0096] (4-4) Measurement of the elastic modulus The elastic modulus in the thickness direction at 23°C was measured by nanoindentation on the surface of the biaxially oriented polyethylene film used for peel force measurement in (4-3) of the examples and comparative examples. Specifically, the measurement was performed as follows.

[0097] Measurements were taken using a Shimadzu Corporation DUH-211S dynamic ultramicrohardness tester in accordance with the method specified in ISO 14577 (2002). One drop of "Aron Alpha" (registered trademark) professional impact-resistant adhesive, manufactured by Toagosei Co., Ltd., was applied to a biaxially oriented polyethylene film. The film was then fixed to a dedicated sample stand using instant adhesive, and the side of the film that would be bonded to the substrate was used as the measurement surface. A triangular pyramidal diamond indenter (Berkovich indenter) with a ridge angle of 115° was used for measurement. The measurement data was processed using dedicated analysis software, and the indentation modulus EIT (GPa) was calculated with a Poisson's ratio of 0.44. Measurements were taken with n=10, and the average value was calculated. The measurement conditions were as follows.

[0098] • Measurement mode: Load-unload test • Maximum load: 0.5mN • Holding time when maximum load is reached: 5 seconds ·Loading speed, unloading speed: 0.02mN / sec.

[0099] (5) Performance evaluation of biaxially oriented polyethylene film (5-1) Carl evaluation A 25mm wide x 150mm long adhesive tape (Nitto Denko Corporation NO.31B tape, acrylic adhesive) was applied to the surface of the biaxially oriented polyethylene film of the examples and comparative examples, on the side opposite to the side in contact with the cast roll (the air knife side), by passing a 2kg roller back and forth twice to obtain a laminate. The obtained laminate was placed on a 0.1mm thick SUS plate with the 31B tape side facing up. A 38μm thick PET film was then used to cover it, and these were sandwiched between 0.1mm thick paper and passed through a laminator (Aurora Japan Co., Ltd. LM-A3). The heating temperature confirmed by a thermolabel was 75°C.

[0100] After passing through the laminator, the laminate was separated from the paper and SUS plate and cut into pieces measuring 25 mm wide x 25 mm long. The laminate was then placed on a flat surface with the 31B tape side down, and the maximum height of the curl at each of the four corners was measured. The measurement was performed with n=10 samples, and the number of samples with a curl height exceeding 10 mm was confirmed. The curl was then evaluated according to the following evaluation criteria.

[0101] (Evaluation Criteria) A: The number of measurement samples that exhibited curl was 0. B: The number of measurement samples that exhibited curl was 1. C: The number of measurement samples that exhibited curl is between 2 and 4. D: The number of measurement samples that exhibited curl is 5 or more.

[0102] (5-2) Zipping evaluation A 50mm wide x 150mm long adhesive tape (Nitto Denko Corporation NO.31B tape, acrylic adhesive) was applied to the surface of the biaxially oriented polyethylene film of the examples and comparative examples that was to be bonded to the adherend, by passing a 2kg roller back and forth twice, thereby obtaining a laminate. The obtained laminate was left to stand for 20 hours in an environment of 70°C and 50% humidity, and then cut into 25mm wide strips to be used as measurement samples. These measurement samples were subjected to 180° peeling at peeling speeds of 50mm / min, 300mm / min, 1000mm / min, and 2500mm / min using a tensile testing machine (Minebea Co., Ltd. universal tensile testing machine "Technograph TGI-1kN") at tensile testing speeds of 50mm / min, 300mm / min, 1000mm / min, and 2500mm / min, and the occurrence of zipping was checked. Measurements were performed with n=10 for each peeling speed, and the number of measurement samples in which zipping occurred was counted. The highest number of occurrences among the results for each peeling speed was adopted as the measurement result, and zipping was evaluated according to the following evaluation criteria.

[0103] (Evaluation Criteria) A++: The number of measurement samples that experienced zipping was 0 out of 10. A+: 1 out of 10 samples showed zipping. A: The number of measurement samples in which zipping occurred was between 2 and 4 out of 10. B: The number of measurement samples that experienced zipping was 5 out of 10. C: The number of measurement samples that experienced zipping was 6 or more out of 10.

[0104] (5-3) Evaluation of poor adhesion For the biaxially oriented polyethylene films of the examples and comparative examples, a 25 mm wide x 150 mm long adhesive tape (Nitto Denko Corporation NO.31B tape, acrylic adhesive) was applied to the surface that would be bonded to the adherend by passing a 2 kg roller back and forth twice, thereby obtaining a laminate. The obtained laminate was left to stand for 20 hours in an environment of 70°C and 50% humidity, and this was used as the measurement sample. The measurement sample was subjected to 180° peeling at peeling speeds of 50 mm / min, 300 mm / min, 1000 mm / min, and 2500 mm / min using a tensile testing machine (Minebea Co., Ltd. universal tensile testing machine "Technograph TGI-1kN") at 180° peeling speeds, and the occurrence of film lifting was checked. Measurements were performed with n=10 for each peeling speed, and the number of measurement samples that showed lifting was counted. The number of lifted samples with the highest number of lifted samples among the results for each peeling speed was adopted as the measurement result, and adhesion failure was evaluated according to the following evaluation criteria.

[0105] (Evaluation Criteria) A++: The number of measurement samples that showed floating was 0 out of 10. A+: The number of measurement samples that showed floating was 1 out of 10. A: The number of measurement samples in which floating occurred was between 2 and 4 out of 10. B: The number of measurement samples that showed floating was 5 out of 10. C: The number of measurement samples that showed floating was 6 or more out of 10.

[0106] (6) Results Table 2 shows the resin composition and manufacturing conditions, and Table 3 shows the physical property measurement results and performance evaluation results.

[0107] [Table 2]

[0108] Table 3

Claims

1. A biaxially oriented polyethylene film containing polyethylene resin, (a) The thermal shrinkage ratio (MDHS / TDHS) of the thermal shrinkage ratio in the longitudinal direction (MDHS) measured at 100°C according to JIS Z 1712 to the thermal shrinkage ratio in the width direction (TDHS) measured at 100°C according to JIS Z 1712 is 0.35 or more and 2.50 or less, and / or (b) The surface orientation coefficient ΔP, calculated from the refractive indices in the width direction (Ny), length direction (Nx), and thickness direction (Nz) measured in accordance with JIS K 7142, is 0.006 or more and 0.035 or less, Biaxially oriented polyethylene film.

2. The peeling force measured in a 180° peel test on at least one side is At a peeling speed of 300 mm / min, the N / 25 mm is between 1.00 N / 25 mm and 4.00 N / 25 mm. When the peeling speed is 1000 mm / min, the N / 25 mm is 1.60 N / 25 mm or more and 4.00 N / 25 mm or less, and At a peeling speed of 2500 mm / min, the value is between 2.30 N / 25 mm and 4.00 N / 25 mm. The biaxially oriented polyethylene film according to claim 1.

3. The biaxially oriented polyethylene film according to claim 1, wherein the elastic modulus in the thickness direction at 23°C, as measured by nanoindentation on at least one of the surfaces, is 2.00 GPa or less.

4. The biaxially oriented polyethylene film according to claim 1, wherein the melt flow rate (MFR) at 190°C, measured according to JIS K 7210, is 0.8 g / 10 min or more.

5. The biaxially oriented polyethylene film according to claim 1, wherein the thickness is 10 μm or more and 50 μm or less.

6. A protective film, release film, or packaging film comprising the biaxially oriented polyethylene film described in any one of claims 1 to 5.

7. A laminate comprising a biaxially oriented polyethylene film and other layers according to any one of claims 1 to 5.

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