Biaxially oriented polyethylene film

Abstract

To provide a polyethylene film with more suppressed curl generation due to heat. 【Solution means】A biaxially stretched polyethylene film containing a polyethylene resin, wherein (a) the heat shrinkage ratio (MDHS / TDHS) of the longitudinal heat shrinkage rate (MDHS) measured at 100°C based on JIS Z 1712 to the transverse 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), longitudinal direction (Nx), and thickness direction (Nz) measured based on JIS K 7142 is 0.006 or more and 0.035 or less. A biaxially stretched polyethylene film.

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 films 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 releasability, 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, curling due to heat shrinkage occurs, 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 curling 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 prior art, depending on the temperature conditions, curling may occur in the longitudinal direction, and when peeling the protective film from the adherend in the process after heat lamination, the protective film cannot be completely peeled from the adherend and may be conveyed in subsequent processes.

[0006] An object of the present invention is to provide a polyethylene film in which curl generation due to heat is more suppressed.

Means for Solving the Problems

[0007] As a result of intensive studies in view of the above problems, the present inventors have found that a biaxially stretched polyethylene film containing a polyethylene resin, (a) the heat shrinkage ratio (MDHS / TDHS) of the heat shrinkage rate in the machine direction (MDHS) measured at 100 °C based on JIS Z 1712 to the heat shrinkage rate in the transverse direction (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. It has been found that the above problems can be solved with such a biaxially stretched polyethylene film. Based on this finding, the present inventors further conducted research and completed the present invention. That is, the present invention includes the following aspects.

[0008] Item 1. A biaxially stretched polyethylene film containing a polyethylene resin, (a) the heat shrinkage ratio (MDHS / TDHS) of the heat shrinkage rate in the machine direction (MDHS) measured at 100 °C based on JIS Z 1712 to the heat shrinkage rate in the transverse direction (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, biaxially stretched polyethylene film.

[0009] Item 2. The peel strength measured by a 180° peel test on at least one surface is, When the peeling speed is 300 mm / min, it is 1.00 N / 25 mm or more and 4.00 N / 25 mm or less, When the peeling speed is 1000 mm / min, it is 1.60 N / 25 mm or more and 4.00 N / 25 mm or less, and When the peeling speed is 2500 mm / min, it is 2.30 N / 25 mm or more and 4.00 N / 25 mm or less, The biaxially stretched polyethylene film according to claim 1.

[0010] Item 3. The biaxially stretched polyethylene film according to claim 1 or 2, wherein the elastic modulus in the thickness direction at 23 °C measured by the nanoindentation method on at least one surface is 2.00 GPa or less.

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

[0012] Item 5. The biaxially stretched polyethylene film according to any one of claims 1 to 4, wherein the thickness is 10 μm or more and 50 μm or less.

[0013] Item 6. A protective film, a release film, or a packaging film containing the biaxially stretched polyethylene film according to any one of claims 1 to 5.

[0014] Item 7. A laminate containing the biaxially stretched polyethylene film according to any one of claims 1 to 5 and another layer.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a polyethylene film in which the generation of curl due to heat is more suppressed.

Embodiments for Carrying Out the Invention

[0016] In this specification, the expressions "containing" and "including" include the concepts of "containing", "including", "substantially consisting of", and "consisting only 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 described separately, 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 the subjects consisting of any combinations 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".) Hereinafter, this will be described.

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

[0022] As a result of advancing research on curl, the present inventors have found that it is not the numerical value of the heat shrinkage rate (MDHS or TDHS) in the longitudinal or widthwise direction itself that is important, but rather the heat shrinkage ratio (MDHS / TDHS). By adjusting the heat shrinkage ratio to the above range, shrinkage within the film plane is not biased in one direction, and while suppressing curl generation, heat lamination can be suitably performed. Further, when peeling off the film, the film can be peeled off neatly without damaging the appearance of the adherend. In cases outside the above range, wrinkles or bulges occur in the longitudinal or widthwise direction, and curl is likely to occur.

[0023] Further, the present inventors have advanced investigations from another perspective and found that the surface orientation coefficient ΔP is important. By adjusting this to 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 heat shrinkage ratio (MDHS / TDHS) and / or the surface orientation coefficient ΔP to the above range, it is also possible to suppress dipping and poor adhesion under various operating speeds.

[0025] The heat 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 0.40 or more and 1.20 or less, and especially 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 heat shrinkage ratio (MDHS / TDHS) is a value measured according to the method of (4-1) in the examples described below.

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

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

[0029] For the polyethylene film of the present invention, for at least one surface, the peel strength measured by the 180° peel test is 1.00 N / 25 mm or more and 4.00 N / 25 mm or less when the peel rate is 300 mm / min, 1.60 N / 25 mm or more and 4.00 N / 25 mm or less when the peel rate is 1000 mm / min, and 2.30 N / 25 mm or more and 4.00 N / 25 mm or less when the peel rate is 2500 mm / min, from the viewpoints of suppressing dipping, suppressing poor adhesion, etc.

[0030] The peel strength when the peel rate is 300 mm / min is preferably 1.05 N / 25 mm or more and 3.95 N / 25 mm or less, more preferably 1.10 N / 25 mm or more and 3.90 N / 25 mm or less, still more preferably 1.20 N / 25 mm or more and 3.50 N / 25 mm or less, and even more preferably 1.20 N / 25 mm or more and 3.00 N / 25 mm or less, from the viewpoints of suppressing dipping, suppressing poor adhesion, etc.

[0031] When the peeling speed is 1000 mm / min, the peeling force is preferably 1.65 N / 25 mm or more and 3.95 N / 25 mm or less, more preferably 1.70 N / 25 mm or more and 3.90 N / 25 mm or less, still more preferably 1.80 N / 25 mm or more and 3.70 N / 25 mm or less, even more preferably 1.90 N / 25 mm or more and 3.50 N / 25 mm or less, and particularly preferably 1.95 N / 25 mm or more and 3.35 N / 25 mm or less, from the viewpoints of suppressing dipping, suppressing poor adhesion, etc.

[0032] When the peeling speed is 2500 mm / min, the peeling force is preferably 2.35 N / 25 mm or more and 3.90 N / 25 mm or less, more preferably 2.40 N / 25 mm or more and 3.80 N / 25 mm or less, still more preferably 2.40 N / 25 mm or more and 3.40 N / 25 mm or less, and even more preferably 2.40 N / 25 mm or more and 3.15 N / 25 mm or less, from the viewpoints of suppressing dipping, suppressing poor adhesion, etc.

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

[0034] Regarding at least one surface (particularly the surface having the above peeling force) of the polyethylene film of the present invention, the elastic modulus in the thickness direction at 23°C measured by the nanoindentation method is preferably 2.00 GPa or less from the viewpoints of suppressing dipping, suppressing poor adhesion, etc. The elastic modulus is more preferably 0.40 GPa or more and 1.95 GPa or less, still 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 elastic modulus is a value measured according to the method of (4-4) in the examples described below.

[0036] The polyethylene film of the present invention preferably has a melt flow rate (MFR) at 190 °C measured based on JIS K 7210 of 0.8 g / 10 min or more from the viewpoint of suppressing curl generation 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] The MFR is a value measured according to the method of (2-2) in the following examples.

[0038] The polyethylene film of the present invention contains a polyethylene resin. The polyethylene film of the present invention contains a polyethylene resin as a main component. In this specification, containing a polyethylene resin as a main component means containing 50% by mass or more of the polyethylene resin with respect to the entire polyethylene film (when the entire polyethylene film is 100% by mass). The content of the polyethylene resin with respect 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, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 99% by mass or more. The upper limit of the content of the polyethylene resin is, for example, 100% by mass or 99.9% by mass with respect to the entire polyethylene film of the present invention.

[0039] The origin of the polyethylene resin is not particularly limited, and it can be, for example, a resin using a petroleum-derived raw material, or a resin using a plant-derived raw material (so-called biomass plastic).

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

[0041] The weight average molecular weight (Mw) of the polyethylene resin is preferably 200,000 or more and 400,000 or less, and more preferably 210,000 or more and 300,000 or less, from the viewpoints of thickness uniformity, mechanical properties, thermo-mechanical properties, etc.

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

[0043] The molecular weight distribution (Mw / Mn) calculated as the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polyethylene resin is preferably 3 or more and 13 or less, more preferably 3.3 or more and 12 or less, 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 the polyethylene resin at 190 °C and a load of 2.16 kg is not particularly limited, but is preferably 5 g / 10 min or less from the viewpoint of reducing the mechanical load in the film-forming process, and more preferably 0.2 g / 10 min or more and 4 g / 10 min or less from the viewpoint of making the thickness of the polyethylene film of the present invention uniform. Further, 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, from the viewpoint of suppressing the generation of curl due to heat.

[0045] The Z average molecular weight (Mz) of the polyethylene resin is, for example, 500,000 or more and 1,800,000 or less.

[0046] The above average molecular weight and the above molecular weight distribution of the polyethylene resin are values measured according to the method of (2-1) in the examples described later. Further, the above MFR of the polyethylene resin is a value measured according to the method of (2-2) in the examples described later.

[0047] The polyethylene film of the present invention can contain components other than the polyethylene resin as long as the effects of the present invention are not inhibited. Examples of other components can widely 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 scavengers, antifogging agents, hydrolysis inhibitors, and the like. These components can be used alone or in combination of a plurality thereof as necessary. When the polyethylene film of the present invention contains the above-mentioned other components, the content ratio 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 based on the total mass of the polyethylene film.

[0048] The polyethylene film of the present invention is a biaxially stretched film stretched in the biaxial directions of the longitudinal direction (MD direction) and the width direction (MD direction). The polyethylene film of the present invention is particularly preferably a sequential biaxially stretched film from the viewpoint that uniform thickness can be stably obtained and the mechanical strength of the film can be easily adjusted.

[0049] The polyethylene film of the present invention can have a single-layer structure or a multilayer structure. The polyethylene film of the present invention preferably has a single-layer structure. When the polyethylene film of the present invention has a multilayer structure, each layer contains the aforementioned polyethylene resin. In this case, the polyethylene resins contained in each layer may be the same as each other, 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 a desired thickness according to the intended use. From the viewpoint of avoiding film breakage and stably obtaining a uniform thickness, the lower limit of the thickness is preferably 2 μm or more, more preferably 5 μm or more, still 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 in the film-forming process, the upper limit of the thickness is preferably 100 μm or less, more preferably 70 μm or less, still more preferably 50 μm, and even more preferably 30 μm or less. When the polyethylene film of the present invention has the above-mentioned multilayer structure, the thickness of the polyethylene film of the present invention means the total value of the thicknesses of each layer.

[0051] 2. Manufacturing method The method for producing the polyethylene film of the present invention is not particularly limited, and for example, a method similar to that of a known film can be widely adopted. Specifically, for example, the polyethylene film of the present invention can be produced by a production method including a step of obtaining a cast sheet containing a polyethylene resin and performing stretching treatment on the cast sheet in the MD direction and the TD direction. Hereinafter, this method, which is an example, will be described in detail.

[0052] The cast sheet, which is a precursor for stretching, can be obtained using a known method. For example, polyethylene resin pellets, dry-mixed polyethylene resin pellets, or mixed polyethylene resin pellets prepared by pre-melting and kneading are supplied to an extruder, heated and melted, and after removing foreign substances and modified polymers through a filter, they are extruded in a sheet shape from a T-die and cooled and solidified with at least one or more cooling drums to obtain a cast sheet.

[0053] In an extruder, the polyethylene resin is inevitably modified due to thermal degradation and oxidative degradation. From the perspective of suppressing such polymer modification, the resin temperature during melt extrusion is 170°C or higher and 320°C or lower, preferably 200°C or higher and 300°C or lower. In addition, it is possible to suppress degradation by nitrogen substitution in the extruder, screw shape, internal shape of the T-die during casting, addition amount of antioxidant, etc.

[0054] The temperature of the cooling drum is preferably 20°C or higher and 90°C or lower, and more preferably maintained at 40°C or higher and 80°C or lower. As a method of adhering to the casting drum, any method such as an air knife method, a touch roll method, an electrostatic printing method, a water-cooled casting method, etc. may be used, but the air knife method that is easy to adjust when adhering the sheet resin to the cooling drum and can be handled simply is preferred. When using an air knife, the temperature of the blown air (AK air temperature) is preferably 10°C or higher and 90°C or lower, more preferably 20°C or higher and 80°C or lower.

[0055] The cast sheet obtained by adjusting within the above range of the cooling drum temperature and the AK air temperature has suppressed crystallization and a small mechanical load during stretching. As a result, it is considered 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 the cast sheet in two axes in the longitudinal and widthwise directions (MD and TD directions).

[0057] First, the cast sheet is heated to 70°C or higher and 130°C or lower, preferably 80°C or higher and 120°C or lower. The method of heating the cast sheet is not particularly limited, but a method of alternately heating both sides of the cast sheet using a roll group of four or more arranged in the flow direction and simultaneously heating the front and back surfaces of the sheet immediately before stretching in the longitudinal direction is preferred. By setting such a temperature range, the cast sheet does not expand excessively due to heat and can be stretched in the longitudinal direction as described below while maintaining flatness.

[0058] The cast sheet is stretched in the longitudinal direction (MD stretching), and immediately relaxed thereafter 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. Also, 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 planarity and suppresses orientation crystallization, so that the mechanical load can be reduced in the later-described stretching in the transverse direction. Incidentally, the method of stretching and relaxing in the longitudinal direction is not particularly limited, but a method using the peripheral speed difference of two or more roll groups arranged in the flow direction is preferable.

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

[0061] By adjusting within the above range, stretching breakage due to un-stretched residue (remaining) is suppressed, and a polyethylene film with a uniform thickness can be efficiently obtained.

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

[0063] The relaxation rate in the transverse direction (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%. Thereafter, the film temperature when the clips are opened 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 stretching stress remaining in the film after biaxial stretching is uniformly relaxed, and while maintaining flatness, the film has appropriate flexibility. As a result, it is considered that the desired physical properties of the present invention can be easily obtained.

[0065] The film sent out from the tenter is wound into a roll by a winder, and the polyethylene film of the present invention can be obtained. Further, the polyethylene film of the present invention can be surface-treated within a range that does not impair its properties according to the application. Examples of the surface treatment include corona discharge treatment, plasma treatment, flame treatment, etc.

[0066] 3. Use The polyethylene film of the present invention can be applied to various uses. Among them, the polyethylene film of the present invention is particularly suitable as a protective film for electronic components. Further, the polyethylene film of the present invention can also be used for protective films, release films, and packaging films other than the above.

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

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

Example

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

[0070] (1) Preparation of polyethylene resin The polyethylene resins used in the examples and comparative examples are as follows. ·PE1: "TF80" (LLDPE) manufactured by Dow Chemical ·PE2: "SP3010" (LLDPE) manufactured by Prime Polymer ·PE3: "BX202" (LLDPE) manufactured by SABIC ·PE4: "LO4904P" (HDPE) manufactured by LG Chem The physical property values of these polyethylene resins are shown below. The measurement methods are as follows.

[0071]

Table 1

[0072] (2) Physical property measurement of polyethylene resin (2-1) Measurement of various average molecular weights and various molecular weight distributions of polyethylene resin Using SEC (size exclusion chromatography), various average molecular weights and various molecular weight distributions were measured under the following conditions. Apparatus: HLC-8321GPC / HT (Detector: differential refractometer (RI)) (manufactured by Tosoh Corporation) Column: TSKgel guardcolumnH HR (30) HT (7.5 mm I.D. × 7.5 cm) × 1 piece + TSKgel GMH HR -H (20) HT (7.8 mm I.D. × 30 cm) × 3 pieces (manufactured by Tosoh Corporation) Eluent: 1,2,4-trichlorobenzene (for GPC, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) + dibutylhydroxytoluene (0.05%) Flow rate: 1.0 mL / min Detection condition: polarity = (-) Injection volume: 300 μL Column temperature: 140 °C System temperature: 40 °C Sample concentration: 1 mg / mL Pretreatment: The sample was weighed, and a solvent (1,2,4-trichlorobenzene added with 0.1% dibutylhydroxytoluene) was added, and it was shaken and dissolved at 140 °C for 1 hour. Then, it was heated and filtered through a 0.5 μm sintered filter. In addition, no insoluble matter was confirmed in the visual observation of the sample solution. Calibration curve: A calibration curve of a fifth-order approximation curve was created using standard polystyrene manufactured by Tosoh Corporation. Therefore, the obtained value is the polystyrene-equivalent molecular weight. However, the molecular weights of PP1, PP2, and PP3 were converted to the molecular weights of polyethylene 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 the analysis software for the measuring device. Using these values of Mw and Mn, the molecular weight distribution (Mw / Mn) was obtained.

[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 in accordance with Condition M of JIS K 7210 using a melt indexer manufactured by Toyo Seiki Seisaku-sho, Ltd. Specifically, first, a weighed 4 g sample was inserted into a cylinder set at the test temperature (190 °C) and preheated under a load of 2.16 kg for 3.5 minutes. Then, the weight of the sample extruded through the bottom hole in 30 seconds was measured to obtain the MFR (g / 10 min). The above measurement was repeated three times, and the average value was taken as the measured value of MFR.

[0075] (3) Production of biaxially oriented polyethylene film (Example 1) PE1 was supplied to an extruder and melted at a resin temperature of 260 °C. Then, after removing foreign substances, modified polymers, etc. with a filter installed in the middle of the polymer tube, it was extruded using a T-die and wound around a casting drum with a surface temperature maintained at 50 °C to be solidified, thereby producing a cast sheet.

[0076] Also, as a method of adhering to the casting drum, an air knife was used, and the air temperature of the blown air was set at 25 °C.

[0077] The obtained cast sheet was preheated at a temperature of 100 °C, stretched 6 times in the longitudinal direction, then relaxed by 3.5% in the same direction, and immediately returned to room temperature.

[0078] Thereafter, the stretched film was led to a tenter, both ends were gripped with clips at 110 °C and preheated at 165 °C, stretched 7.8 times in the width direction, and then relaxed by 10% in the same direction. Subsequently, after cooling the temperature of the film after biaxial stretching to 60 °C, the clips of the tenter were opened to obtain a biaxially stretched polyethylene film with a thickness of 20 μm.

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

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

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

[0082] (Example 4) A biaxially stretched polyethylene film was obtained in the same manner as in Example 1, except that the film was stretched 8 times in the longitudinal direction and 11 times in the width direction.

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

[0084] (Example 6) A biaxially stretched polyethylene film was obtained in the same manner as in Example 1, except that the film temperature when the clips of the tenter were opened was set to 95°C.

[0085] (Example 7) A biaxially stretched 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 width direction.

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

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

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

[0089] (Comparative Example 2) A biaxially stretched polyethylene film was obtained in the same manner as in Example 1, except that relaxation was applied at 13% in the longitudinal direction and 23% in the width direction, and the film temperature when the clips of the tenter were released was 98°C.

[0090] (Comparative Example 3) A biaxially stretched 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 blown air from the air knife were 70°C.

[0091] (Comparative Example 4) A biaxially stretched polyethylene film was obtained in the same manner as in Example 2, except that relaxation was applied at 13% in the longitudinal direction and 23% in the width direction, and the film temperature when the clips of the tenter were released was 98°C.

[0092] (Comparative Example 5) A biaxially stretched 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 65°C, and the air temperature of the blown air from the air knife was 70°C.

[0093] (4) Physical property measurement of biaxially oriented polyethylene film (4-1) Measurement of heat shrinkage rate and heat shrinkage ratio For the biaxially stretched polyethylene films of the examples and comparative examples, the thermal shrinkage rate in the width direction (TDHS) and the thermal shrinkage rate in the longitudinal direction (MDHS) were measured at 100°C based on 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 a temperature of 100°C ± 3°C in accordance with JIS Z 1712, and the thermal shrinkage ratio was calculated by dividing the value of MDHS by the value of TDHS.

[0094] (4-2) Measurement of refractive index and surface orientation coefficient For the biaxially stretched polyethylene films of the examples and comparative examples, the surface orientation coefficient ΔP was calculated from the refractive indices in the machine direction (Ny), the transverse direction (Nx), and the thickness direction (Nz) measured based on JIS K 7142 by 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 peel strength The peel strength of the biaxially stretched polyethylene films of the examples and comparative examples was measured as follows. (1) On the surface of one of the two sides of the biaxially stretched polyethylene film that is to be bonded to the adherend, an adhesive tape with a width of 50 mm × a length of 150 mm (No. 31B tape manufactured by Nitto Denko Corporation, acrylic-based adhesive) was attached by reciprocating a 2-kg roller twice to obtain a laminate. (2) The obtained laminate was allowed to stand in an environment at a temperature of 70°C and a humidity of 50% for 20 hours, and then cut into a width of 25 mm, which was used as a measurement sample. (3) Using a tensile testing machine (universal tensile testing machine "Technograph TGI-1kN" manufactured by Minebea Co., Ltd.), the measurement sample was subjected to 180° peeling at a constant peeling rate (50 mm / min, 300 mm / min, 1000 mm / min, and 2500 mm / min), and the peeling force at that time was measured. (4) The measurement was carried out with n = 10 for each peeling rate, and the average value was taken as the measurement result.

[0096] (4-4) Measurement of elastic modulus For the surface of the biaxially stretched polyethylene films of the examples and comparative examples that was used for measuring the peel strength in (4-3), the elastic modulus in the thickness direction at 23°C was measured by the nanoindentation method. Specifically, the measurement was carried out as follows.

[0097] Using the dynamic ultra-micro hardness tester "DUH-211S" manufactured by Shimadzu Corporation, the measurement was carried out in accordance with the method specified in ISO 14577 (2002). One drop of "Aron Alpha" (registered trademark) impact-resistant for professional use manufactured by Toagosei Co., Ltd. was applied to the biaxially stretched polyethylene film, and the film was fixed to a dedicated sample fixing table via an instant adhesive. Among the two surfaces of the film, the side to be bonded to the adherend was used as the measurement surface for measurement. A triangular pyramid diamond indenter (Berkovich indenter) with an included angle of 115° between the edges was used for the measurement. The measurement data was processed by dedicated analysis software, and the indentation modulus EIT (GPa) was calculated assuming a Poisson's ratio of 0.44. The measurement was performed with n = 10, and the average value was obtained. The measurement conditions were as follows.

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

[0099] (5) Performance evaluation of biaxially oriented polyethylene film (5-1) Curl evaluation On the surface of the opposite side (air knife side) of the biaxially stretched polyethylene film of the examples and comparative examples that contacted the casting roll, an adhesive tape with a width of 25 mm × a length of 150 mm (No. 31B tape manufactured by Nitto Denko Corporation, acrylic adhesive) was attached by reciprocating a 2 kg roller twice to obtain a laminate. The obtained laminate was placed on a 0.1 mm thick SUS plate with the 31B tape side as the upper surface. It was covered with a 38 μm thick PET film from above, and these were sandwiched between 0.1 mm thick paper and passed through a laminator (LM-A3 manufactured by Aurora Japan Co., Ltd.). The heating temperature confirmed with a thermo label was 75°C.

[0100] After passing through the laminator, the laminate was removed from the paper and SUS plate and cut into a size of 25 mm in width × 25 mm in length. Then, the laminate was left to stand on a flat table with the 31B tape side facing down, and the maximum value among the heights (curls) at which the four corners of the laminate lifted was measured. The measurement was performed with n = 10, the number of measurement samples with a lifted height (curl) exceeding 10 mm was confirmed, and curl evaluation was performed according to the following evaluation criteria.

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

[0102] (5-2) Dipping evaluation On both sides of the biaxially stretched polyethylene film of the examples and comparative examples, an adhesive tape (No. 31B tape manufactured by Nitto Denko Corporation, acrylic adhesive) with a width of 50 mm × a length of 150 mm was attached by reciprocating a 2 kg roller twice to obtain a laminate. The obtained laminate was left to stand in an environment of 70°C and 50% humidity for 20 hours, then cut into a width of 25 mm, and this was used as a measurement sample. Using a tensile testing machine (Universal Tensile Testing Machine "Technograph TGI-1kN" manufactured by Minebea Co., Ltd.), 180° peeling was performed at respective peeling speeds of 50 mm / min, 300 mm / min, 1000 mm / min, and 2500 mm / min, and the occurrence of dipping was confirmed. The measurement was performed with n = 10 for each peeling speed, and the number of measurement samples with dipping was counted. The largest number of occurrences among the results of each peeling speed was adopted as the measurement result, and dipping evaluation was performed according to the following evaluation criteria.

[0103] (Evaluation Criteria) A++: The number of measurement samples with dipping is 0 / 10. A+: The number of measurement samples with dipping is 1 / 10. A: The number of measurement samples with dipping is 2 or more and 4 or less out of 10. B: The number of measurement samples with dipping is 5 out of 10. C: The number of measurement samples with dipping is 6 or more out of 10.

[0104] (5-3) Adhesion failure evaluation Among both sides of the biaxially stretched polyethylene films of the examples and comparative examples, an adhesive tape with a width of 25 mm × a length of 150 mm (No. 31B tape manufactured by Nitto Denko Corporation, acrylic-based adhesive) was attached to the surface on the side to be bonded to the adherend by reciprocating a 2-kg roller twice to obtain a laminate. The obtained laminate was allowed to stand in an environment of a temperature of 70°C and a humidity of 50% for 20 hours, and then this was used as a measurement sample. Using a tensile testing machine (universal tensile testing machine "Technograph TGI-1kN" manufactured by Minebea Co., Ltd.), 180° peeling was performed at respective peeling speeds of 50 mm / min, 300 mm / min, 1000 mm / min, and 2500 mm / min to confirm the occurrence of film lifting. The measurement was performed with n = 10 for each peeling speed, and the number of measurement samples with lifting was counted. Among the results of each peeling speed, the largest number of occurrences was adopted as the measurement result, and the adhesion failure evaluation was performed according to the following evaluation criteria.

[0105] (Evaluation Criteria) A++: The number of measurement samples with lifting is 0 out of 10. A+: The number of measurement samples with lifting is 1 out of 10. A: The number of measurement samples with lifting is 2 or more and 4 or less out of 10. B: The number of measurement samples with lifting is 5 out of 10. C: The number of measurement samples with lifting is 6 or more out of 10.

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

[0107]

Table 2

[0108]

Table 3

Claims

1. A biaxially oriented polyethylene film containing a polyethylene resin, (b) the plane orientation coefficient ΔP calculated from the refractive indices in the width direction (Ny), length direction (Nx), and thickness direction (Nz) according to the formula: plane orientation coefficient ΔP=(Nx+Ny) / 2-Nz, measured in accordance with JIS K 7142, is 0.006 or more and 0.035 or less; Biaxially oriented polyethylene film.

2. (a) A thermal shrinkage ratio (MDHS / TDHS) of a thermal shrinkage ratio in a longitudinal direction (MDHS) measured at 100°C in accordance with JIS Z 1712 to a thermal shrinkage ratio in a transverse direction (TDHS) measured at 100°C in accordance with JIS Z 1712 is 0.35 or more and 2.50 or less, 2. The biaxially oriented polyethylene film according to claim 1.

3. The peel strength measured by a 180° peel test on at least one surface is When the peel speed is 300 mm / min, the peel strength is 1.00 N / 25 mm or more and 4.00 N / 25 mm or less. At a peel speed of 1000 mm / min, the strength is 1.60 N / 25 mm or more and 4.00 N / 25 mm or less, and At a peel speed of 2500 mm / min, the peel strength is 2.30 N / 25 mm or more and 4.00 N / 25 mm or less.

2. The biaxially oriented polyethylene film according to claim 1.

4. 2. The biaxially oriented polyethylene film according to claim 1, wherein the modulus of elasticity in the thickness direction at 23° C. of at least one surface is 2.00 GPa or less as measured by a nanoindentation method.

5. 2. The biaxially oriented polyethylene film according to claim 1, having a melt flow rate (MFR) at 190°C measured in accordance with JIS K 7210 of 0.8 g / 10 min or more.

6. 2. The biaxially oriented polyethylene film according to claim 1, having a thickness of 10 μm or more and 50 μm or less.

7. A protective film, a release film, or a packaging film comprising the biaxially oriented polyethylene film according to any one of claims 1 to 6.

8. A laminate comprising the biaxially oriented polyethylene film according to any one of claims 1 to 6 and another layer.

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