Ultra-high molecular weight polyethylene film and method for producing polyolefin film

Abstract

Disclosed is an ultra-high molecular weight polyethylene film that contains, with respect to the total mass of the ultra-high molecular weight polyethylene film, 50 mass% or more of an ultra-high molecular weight polyethylene which has a weight average molecular weight of more than 500,000 as estimated from the molecular weight distribution curve of polyethylene contained therein, the molecular weight distribution curve being obtained by gel permeation chromatography measurement, and which has a molecular weight distribution index of 4 or less, wherein: the haze value is 30% or less; the nitrogen permeability coefficient is 1 × 10- 12 mol∙m / (m2∙s∙Pa) or less; and the film thickness is 5 µm or more. Also disclosed is a method for producing a polyolefin film.

Description

Ultra-high molecular weight polyethylene film and method for producing polyolefin film

[0001] The present disclosure relates to methods for producing ultra-high molecular weight polyethylene films and polyolefin films.

[0002] Ultra-high molecular weight polyethylene has been put to practical use as high-strength fibers, etc. In recent years, in order to broaden the range of applications of ultra-high molecular weight polyethylene films, attempts have been made to improve the properties of ultra-high molecular weight polyethylene films, and various production methods have been developed.

[0003] For example, Japanese Patent Application Laid-Open No. 2022-045226 discloses a method of forming ultra-high molecular weight polyethylene powder into a film by roll-rolling at a temperature below the melting point of the ultra-high molecular weight polyethylene (the so-called polymerization powder rolling method). According to the method described in Japanese Patent Application Laid-Open No. 2022-045226, a thin ultra-high molecular weight polyethylene film with excellent heat resistance can be obtained. Furthermore, Japanese Patent Application Laid-Open No. 2022-255385 discloses a method of melt-pressing ultra-high molecular weight polyethylene powder into a film, and then melt-biaxially stretching the resulting film (the so-called melt stretching method). According to the method described in Japanese Patent Application Laid-Open No. 2022-255385, an ultra-high molecular weight polyethylene film having a film thickness of less than 1 μm, high visible light transmittance, and high tensile strength at break and tear strength can be obtained. Furthermore, WO 2023 / 047997 discloses a method of biaxially stretching a film obtained by kneading and extruding a plasticizer and ultra-high molecular weight polyethylene, extracting and removing the plasticizer from the film, and then heat-treating the film (so-called thermally induced phase separation method). According to the method described in WO 2023 / 047997, an ultra-high molecular weight polyethylene film having excellent heat resistance, mechanical strength, quality, long-term storage stability, and transparency can be obtained.

[0004] Depending on the application of the ultra-high molecular weight polyethylene film, properties such as transparency and gas barrier properties may be required. In this regard, the film obtained by the manufacturing method described in JP 2022-045226 A cannot achieve high transparency because powder particles remain in the film and the interfaces of the remaining powder particles scatter light. Furthermore, the films obtained by the manufacturing methods described in JP 2022-255385 A and WO 2023 / 047997 A can ensure high transparency by making the film thickness less than 1 μm, but pores are present in the film and exhibit gas permeability.

[0005] The present disclosure has been made in consideration of the above circumstances. One embodiment of the present disclosure aims to solve the problem of providing an ultra-high molecular weight polyethylene film that has high transparency and high gas barrier properties even when the film thickness is large. Another embodiment of the present disclosure aims to solve the problem of providing a method for producing a polyolefin film that can efficiently produce an ultra-high molecular weight polyolefin film that has high transparency and high gas barrier properties even when the film thickness is large.

[0006] Specific means for solving the above problems include the following aspects: <1> An ultra-high molecular weight polyethylene film containing 50 mass% or more of ultra-high molecular weight polyethylene, the weight average molecular weight of which is estimated from a molecular weight distribution curve of the polyethylene contained obtained by gel permeation chromatography measurement and which has a molecular weight distribution index of 4 or less, based on the total mass of the ultra-high molecular weight polyethylene film, and the haze value is 30% or less, and the nitrogen permeability coefficient is 1×10 －１２ mol m / (m ２.s.Pa) or less and a film thickness of 5 μm or more. <2> The ultrahigh molecular weight polyethylene film according to <1>, having a tear strength of 5 N / mm or more. <3> The ultrahigh molecular weight polyethylene film according to <1> or <2>, having a tensile breaking strength of 10 MPa or more. <4> The ultrahigh molecular weight polyethylene film according to any one of <1> to <3>, having a relative dielectric constant of 2.4 or less. <5> A method for producing a polyolefin film, comprising: a step A of applying an organic solvent containing a metal catalyst to the inner wall surface of a container; a step B of synthesizing a polyolefin on the inner wall surface of the container by introducing an olefin monomer into the container whose inner wall surface has been coated with the organic solvent containing the metal catalyst; and a step C of rolling a sheet of the polyolefin synthesized on the inner wall surface of the container. <6> A method for producing a polyolefin film according to <5>, wherein in the step C, a laminate obtained by stacking a plurality of sheets of the polyolefin synthesized on the inner wall surface of the container is rolled. <7> The method for producing a polyolefin film according to <5> or <6>, wherein the surface temperature of the rolled body during rolling is -10°C or higher and lower than the melting point of the sheet. <8> The method for producing a polyolefin film according to any one of <5> to <7>, comprising step D of further tensile stretching the rolled film obtained by rolling in step C. <9> The method for producing a polyolefin film according to <8>, wherein in step D, the rolled film is tensile stretched at a temperature of 0°C or higher and lower than the melting point of the rolled film. <10> The method for producing a polyolefin film according to <8> or <9>, wherein the tensile stretching is uniaxial stretching.

[0007] According to one embodiment of the present disclosure, there is provided an ultra-high molecular weight polyethylene film that has high transparency even when thick and has high gas barrier properties. According to another embodiment of the present disclosure, there is provided a method for producing a polyolefin film that can efficiently produce an ultra-high molecular weight polyolefin film that has high transparency even when thick and has high gas barrier properties.

[0008] The present disclosure provides a detailed description of the manufacturing methods of the ultra-high molecular weight polyethylene film and polyolefin film. The following description of the requirements may be based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments and can be implemented with appropriate modifications within the scope of the present disclosure.

[0009] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples.

[0010] In the present disclosure, when referring to the amount of each component in a film-forming coating liquid used in producing an ultra-high molecular weight polyethylene film or a polyolefin film, if the film-forming coating liquid contains multiple substances corresponding to each component, the amount refers to the total amount of the multiple components present in the film-forming coating liquid, unless otherwise specified.

[0011] In the present disclosure, a combination of two or more preferred aspects is a more preferred aspect.

[0012] In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0013] In this disclosure, the term "lamination" means stacking layers.

[0014] [Ultra-high molecular weight polyethylene film] The ultra-high molecular weight polyethylene film according to the present disclosure contains 50 mass% or more of ultra-high molecular weight polyethylene, based on the total mass of the ultra-high molecular weight polyethylene film, having a weight average molecular weight (Mw) of more than 500,000 and a molecular weight distribution index of 4 or less, as estimated from a molecular weight distribution curve of the contained polyethylene obtained by gel permeation chromatography (GPC) measurement, and has a haze value of 30% or less and a nitrogen permeability coefficient of 1×10 －１２ mol m / (m ２ The ultra-high molecular weight polyethylene film according to the present disclosure has high transparency and high gas barrier properties even when the film is thick. Specifically, the ultra-high molecular weight polyethylene film according to the present disclosure has high transparency with a haze value of 30% or less despite having a thick film thickness of 5 μm or more, and has a nitrogen permeability coefficient of 1×10 －１２ mol m / (m ２ It has high gas barrier properties of less than 1.5 s.Pa.

[0015] The ultra-high molecular weight polyethylene film according to the present disclosure contains 50 mass% or more of ultra-high molecular weight polyethylene having a weight-average molecular weight (Mw) of more than 500,000 and a molecular weight distribution index of 4 or less, relative to the total mass of the ultra-high molecular weight polyethylene film. In the present disclosure, "ultra-high molecular weight polyethylene having a weight-average molecular weight (Mw) of more than 500,000 and a molecular weight distribution index of 4 or less" is also referred to as "specific ultra-high molecular weight polyethylene." The ultra-high molecular weight polyethylene film according to the present disclosure may contain one type of specific ultra-high molecular weight polyethylene alone, or may contain two or more types. The content of the specific ultra-high molecular weight polyethylene in the ultra-high molecular weight polyethylene film according to the present disclosure is 50 mass% or more, preferably 70 mass% or more, more preferably 80 mass% or more, and even more preferably 90 mass% or more, relative to the total mass of the ultra-high molecular weight polyethylene film, and may be, for example, 100 mass%. The content of the specific ultra-high molecular weight polyethylene in the ultra-high molecular weight polyethylene film according to the present disclosure being 50 mass% or more relative to the total mass of the ultra-high molecular weight polyethylene film means that the ultra-high molecular weight polyethylene film according to the present disclosure contains the specific ultra-high molecular weight polyethylene as a main component.

[0016] The weight-average molecular weight (Mw) of the specific ultra-high molecular weight polyethylene exceeds 500,000. The weight-average molecular weight (Mw) of the specific ultra-high molecular weight polyethylene may be, for example, 800,000 or more, 1,000,000 or more, or 1,200,000 or more. The upper limit of the weight-average molecular weight (Mw) of the specific ultra-high molecular weight polyethylene is not particularly limited, and may be, for example, 15,000,000 or less, 10,000,000 or less, 6,000,000 or less, or 3,000,000 or less. In one embodiment, the weight-average molecular weight (Mw) of the specific ultra-high molecular weight polyethylene may be in the range of more than 500,000 to 15,000,000 or less, more than 500,000 to 10,000,000 or less, more than 500,000 to 6,000,000 or less, more than 500,000 to 3,000,000 or less, more than 800,000 to 15,000,000 or less, more than 1,000,000 to 10,000,000 or less, or more than 1,200,000 to 6,000,000 or less.

[0017] The molecular weight distribution index of the specific ultra-high molecular weight polyethylene is 4 or less. The closer the molecular weight distribution index of the ultra-high molecular weight polyethylene is to 1, the more uniform the length of the molecular chains of the ultra-high molecular weight polyethylene. The molecular weight distribution index of the specific ultra-high molecular weight polyethylene may be, for example, in the range of 1 to 4, 1 to 3.5, or 1 to 3. The molecular weight distribution index is a value (Mw / Mn) calculated by dividing the weight average molecular weight (Mw) by the number average molecular weight (Mn). When a metallocene complex is selected as a metal catalyst in the synthesis of polyolefins (including ultra-high molecular weight polyethylene), the molecular weight distribution of the resulting polyolefins (including polyethylene) tends to be narrower, i.e., the molecular weight distribution index (Mw / Mn) tends to be smaller.

[0018] In the present disclosure, the weight average molecular weight (Mw) and number average molecular weight (Mn) of polyolefins (including polyethylene) are values ​​estimated from the molecular weight distribution curve of the polyolefins (including polyethylene) obtained by gel permeation chromatography (GPC). Specifically, the GPC measurement is performed under the following conditions:

[0019] -Conditions- Apparatus: HLC-8121 GPC / HT (detector: RI) [manufactured by Tosoh Corporation] Column: Three connected TSKgel (registered trademark) GMHHR-H(20)HT [7.8 mm I.D. × 30 cm, manufactured by Tosoh Corporation] Eluent: 1,2,4-trichlorobenzene [HPLC grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.] containing 0.05% by mass of dibutylhydroxytoluene (BHT; antioxidant) Flow rate: 1.0 mL / min Detection conditions: polarity = (-) Injection volume: 0.3 mL Column temperature: 160°C Sample concentration: 0.1 mg / mL to 1.0 mg / mL (solvent: 1,2,4-trichlorobenzene)

[0020] The ultra-high molecular weight polyethylene film according to the present disclosure may contain, as necessary, components (so-called other components) other than the ultra-high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 500,000 and a molecular weight distribution index of 4 or less (i.e., specific ultra-high molecular weight polyethylene), within a range that does not impair the effects of the present disclosure. Examples of other components include components that are typically added to polyethylene, such as antioxidants, weathering agents, light stabilizers, ultraviolet absorbers, heat stabilizers, antistatic agents, flame retardants, antibacterial agents, antifungal agents, and colorants (e.g., pigments).

[0021] The ultra-high molecular weight polyethylene film according to the present disclosure is characterized by high transparency. In the present disclosure, the transparency of a film is determined using a haze value as an index. The haze value of the ultra-high molecular weight polyethylene film according to the present disclosure is 30% or less, preferably 25% or less, more preferably 20% or less, even more preferably 10% or less, and particularly preferably 5% or less.

[0022] In the present disclosure, the haze value of an ultra-high molecular weight polyethylene film is measured using a haze meter in accordance with JIS K 7361: 1997. A suitable haze meter that can be used is, for example, a haze meter (model number: NDH800) manufactured by Nippon Denshoku Industries Co., Ltd. However, the haze meter is not limited to this.

[0023] The ultra-high molecular weight polyethylene film according to the present disclosure is characterized by high gas barrier properties. In the present disclosure, the gas barrier properties of a film are determined using the nitrogen permeability coefficient as an index. The nitrogen permeability coefficient of the ultra-high molecular weight polyethylene film according to the present disclosure is 1×10 －１２ mol m / (m ２ s Pa) or less, and －１３ mol m / (m ２ s Pa) or less, and －１３ mol m / (m ２ s Pa) or less, and more preferably 1×10 －１３ mol m / (m ２s Pa) or less, and more preferably 9×10 －１４ mol m / (m ２ The lower limit of the nitrogen permeability coefficient of the ultra-high molecular weight polyethylene film according to the present disclosure is not particularly limited, and is, for example, 1×10 －１５ mol m / (m ２ In one embodiment, the nitrogen permeability coefficient of the ultra-high molecular weight polyethylene film according to the present disclosure may be 1×10 －１５ mol m / (m ２ ・s・Pa) or more 1×10 －１２ mol m / (m ２ s Pa) or less, and may be in the range of 1×10 －１５ mol m / (m ２ ・s・Pa) or more 7×10 －１３ mol m / (m ２ s Pa) or less, and may be in the range of 1×10 －１５ mol m / (m ２ ・s・Pa) or more 5×10 －１３ mol m / (m ２ s Pa) or less, and may be in the range of 1×10 －１５ mol m / (m ２ ・s・Pa) or more 1×10 －１３ mol m / (m ２ .s.Pa) or less.

[0024] In the present disclosure, the nitrogen permeability coefficient of an ultra-high molecular weight polyethylene film is determined by the following measurement method. A circular specimen with a diameter of 30 mm is cut from the ultra-high molecular weight polyethylene film to serve as a test piece. Next, in a 25°C environment, the circular specimen is placed in the measurement cell of a membrane diffusion measurement device connected to a data logger. Nitrogen gas is then introduced into the high-pressure gas reservoir, and the low-pressure side of the cell is evacuated. The high-pressure side valve of the cell is opened to introduce nitrogen gas, and gas permeation measurement is initiated. The voltage change over time is recorded, and the nitrogen permeability coefficient is calculated according to the following equations (1) and (2) [low-pressure side voltage and high-pressure side voltage (1 V = 1.6 KPa)]. A suitable data logger is, for example, a data logger (model number: GL20) manufactured by Graphtec Corporation. A suitable membrane diffusion measurement device is, for example, a membrane diffusion measurement device (model number: K-315N-01) manufactured by Tsukubarika Seiki Co., Ltd. However, the data logger and the membrane diffusion measuring device are not limited to these.

[0025] Q = [V / (R x T x P x A)] x (dp / dt) Formula (1) p = Q x L Formula (2) Q: gas permeability [mol / (m ２ s Pa)] p: gas permeability coefficient [mol m / (m ２ s Pa)] V: Cell low pressure side volume [L] A: Permeation area [m ２ ](π=3.14) T: Test temperature [℃] P: Supply gas differential pressure [Pa] dp / dt: Change in pressure (p) on the low pressure side per unit time (t) [Pa / s] L: Thickness of test piece [m]

[0026] The ultra-high molecular weight polyethylene film according to the present disclosure is characterized by high tear strength. The tear strength of the ultra-high molecular weight polyethylene film according to the present disclosure is, for example, preferably 5 N / mm or more, more preferably 10 N / mm or more, even more preferably 20 N / mm or more, and particularly preferably 30 N / mm or more. The upper limit of the tear strength of the ultra-high molecular weight polyethylene film according to the present disclosure is not particularly limited, and may be, for example, 5000 N / mm or less, 2000 N / mm or less, 1000 N / mm or less, or 500 N / mm or less. In one embodiment, the tear strength of the ultra-high molecular weight polyethylene film according to the present disclosure may be in the range of 5 N / mm or more to 5000 N / mm or less, 10 N / mm or more to 2000 N / mm or less, 20 N / mm or more to 1000 N / mm or less, or 30 N / mm or more to 500 N / mm or less. The ultra-high molecular weight polyethylene film according to the present disclosure has high tear strength and can therefore be used in a variety of applications, such as protective films and packaging films (e.g., food packaging films).

[0027] In the present disclosure, the tear strength of an ultra-high molecular weight polyethylene film is determined by the following measurement method. The ultra-high molecular weight polyethylene film is cut into a size of 35 mm (length) x 35 mm (width) to prepare a test specimen. If roll rolling is used to produce the ultra-high molecular weight polyethylene film, the cutting is performed so that the roll rotation direction is the longitudinal direction of the test specimen. A 15 mm long incision is made in the center of the longitudinal direction of the test specimen, perpendicular to the longitudinal direction (i.e., the width direction). That is, if roll rolling is used to produce the ultra-high molecular weight polyethylene film, the incision is made perpendicular to the roll rotation direction. A Tensilon universal testing machine is used as the measuring device. The two ends of the cut test specimen are gripped with upper and lower chucks, respectively, and pulled vertically (i.e., parallel to the width direction) at a speed of 200 mm / min in an ambient temperature of 25°C. The maximum stress when the remaining 20 mm without the incision is torn is recorded. The tear strength is determined by dividing this maximum stress by the thickness of the test specimen. The thickness of the test piece in this method is measured in the same manner as the thickness of a polyolefin film (including a polyethylene film) described below. As a Tensilon universal testing machine, for example, a Tensilon universal testing machine (model number: RTC-1325A) manufactured by A&D Manufacturing Co., Ltd. can be suitably used. However, the Tensilon universal testing machine is not limited to this.

[0028] The ultra-high molecular weight polyethylene film according to the present disclosure is characterized by high tensile breaking strength. The tensile breaking strength of the ultra-high molecular weight polyethylene film according to the present disclosure is, for example, preferably 10 MPa or more, more preferably 20 MPa or more, even more preferably 30 MPa or more, and particularly preferably 50 MPa or more. The upper limit of the tensile breaking strength of the ultra-high molecular weight polyethylene film according to the present disclosure is not particularly limited and may be, for example, 5000 MPa or less. In one aspect, the tensile breaking strength of the ultra-high molecular weight polyethylene film according to the present disclosure may be in the range of 10 MPa or more to 5000 MPa or less, 20 MPa or more to 5000 MPa or less, 30 MPa or more to 5000 MPa or less, 50 MPa or more to 5000 MPa or less, 100 MPa or more to 5000 MPa or less, 300 MPa or more to 5000 MPa or less, or 500 MPa or more to 5000 MPa or less. The ultra-high molecular weight polyethylene film according to the present disclosure has high tensile strength at break and can therefore be used in a variety of applications, such as protective films and packaging films (e.g., food packaging films).

[0029] In the present disclosure, the tensile breaking strength of an ultra-high molecular weight polyethylene film is determined by the following measurement method. The ultra-high molecular weight polyethylene film is cut into a size of 30 mm (length) x 3 mm (width) to prepare a test specimen. A tensile test is performed on the test specimen using a Tensilon universal testing machine at an ambient temperature of 25°C and a test speed of 10 mm / min. Both ends of the test specimen are fixed to graph paper using Cemedine (registered trademark) PPX so that the length (initial length) of the tensile test portion is 10 mm. Cemedine (registered trademark) PPX is then placed on both ends of the specimen, and the graph side of another graph paper is placed on top of it to sandwich the specimen. The specimen is pulled in the longitudinal direction, and the maximum stress on the recorded stress chart is divided by the cross-sectional area of ​​the specimen to determine the tensile breaking strength. However, if the width of the ultra-high molecular weight polyethylene film is less than 3 mm, the width of the ultra-high molecular weight polyethylene film is used as is. When the ultra-high molecular weight polyethylene film is produced by roll rolling, the cutting is performed so that the roll rotation direction is the length direction of the test piece. When the ultra-high molecular weight polyethylene film is produced by tensile stretching, the cutting is performed so that the tensile stretching direction is the length direction of the test piece. As a Tensilon universal testing machine, for example, a Tensilon universal testing machine (model number: RTC-1325A) manufactured by A&D Co., Ltd. can be suitably used. However, the Tensilon universal testing machine is not limited to this.

[0030] The cross-sectional area of ​​the test piece in this method is calculated using the following formula: "Cross-sectional area of ​​the test piece (mm ２ ) = Width of test piece (mm) × Thickness of test piece (mm) In this method, the thickness of the test piece is measured in the same manner as the film thickness of a polyolefin film (including a polyethylene film) described below.

[0031] The ultra-high molecular weight polyethylene film according to the present disclosure is characterized by a low dielectric constant. The dielectric constant of the ultra-high molecular weight polyethylene film according to the present disclosure is, for example, preferably 2.4 or less, more preferably in the range of 1 to 2.3, even more preferably in the range of 1 to 2.2, and particularly preferably in the range of 1 to 2.0. Because of its low dielectric constant, the ultra-high molecular weight polyethylene film according to the present disclosure is suitable for applications such as insulating film, insulating tape, and wire coating material.

[0032] In the present disclosure, the relative permittivity of an ultra-high molecular weight polyethylene film is determined by the following measurement method. The ultra-high molecular weight polyethylene film is sandwiched between circular electrodes with a diameter of 6 mm, and measurement is performed by an RF voltage-current measurement method (RF-IV method) under measurement conditions of a temperature of 23±2°C, a humidity of 50±10%, a test frequency of 1 MHz to 1 GHz, and a test voltage of 0.5 V. For example, an impedance analyzer (model number: E4991B) manufactured by Keysight Technologies and a dielectric constant test fixture (model number: 16453A) manufactured by Keysight Technologies can be suitably used to measure the relative permittivity. However, the impedance analyzer and the dielectric constant test fixture are not limited to these.

[0033] The thickness of the ultra-high molecular weight polyethylene film according to the present disclosure is 5 μm or more. The thickness of the ultra-high molecular weight polyethylene film according to the present disclosure may be, for example, 10 μm or more, 100 μm or more, 500 μm or more, or 1000 μm or more. The thickness of the ultra-high molecular weight polyethylene film according to the present disclosure may be, for example, 5000 μm or less. In one aspect, the thickness of the ultra-high molecular weight polyethylene film according to the present disclosure may be in the range of 5 μm or more to 5000 μm or less, 10 μm or more to 5000 μm or less, 100 μm or more to 5000 μm or less, 500 μm or more to 5000 μm or less, or 1000 μm or more to 5000 μm or less.

[0034] In the present disclosure, the film thickness of a polyolefin film (including a polyethylene film) is an average film thickness determined by the following measurement method. The film thickness of a polyolefin sheet (including a polyethylene sheet) is also an average film thickness determined by the same measurement method. The arithmetic mean value of film thicknesses measured at six randomly selected points in the thickness direction of the polyolefin film is determined, and the obtained value is taken as the film thickness of the polyolefin film. A thickness gauge is used to measure the film thickness of a polyolefin film. For example, a film tester (model number: HKT-1216) manufactured by Fujiwork Co., Ltd. can be suitably used as the thickness gauge. However, the thickness gauge is not limited to this.

[0035] The ultra-high molecular weight polyethylene film according to the present disclosure can be produced, for example, by the method for producing a polyolefin film according to the present disclosure described below. The method for producing a polyolefin film according to the present disclosure is one of the preferred methods for efficiently producing the ultra-high molecular weight polyethylene film according to the present disclosure.

[0036] The weight average molecular weight and molecular weight distribution index of the polyethylene contained in the ultra-high molecular weight polyethylene film according to the present disclosure can be controlled, for example, by selecting ethylene as the olefin monomer in the method for producing a polyolefin film according to the present disclosure described below and adjusting the polymerization conditions (e.g., polymerization time, pressure of the ethylene monomer introduced, amount of catalyst, amount of co-catalyst, and amount of solvent).

[0037] The haze value of the ultra-high molecular weight polyethylene film according to the present disclosure can be controlled, for example, by adjusting the rolling conditions (e.g., surface temperature of the rolled body and rolling ratio) in step C of the polyolefin film manufacturing method according to the present disclosure described below, and the tensile stretching conditions (e.g., tensile stretching temperature, tensile stretching ratio, and tensile stretching speed) in step D. The haze value of the ultra-high molecular weight polyethylene film according to the present disclosure can be reduced, for example, by setting the surface temperature of the rolled body in step C higher, or by increasing the rolling ratio, within a range that does not exceed the melting point of the polyethylene sheet obtained in step B. The haze value of the ultra-high molecular weight polyethylene film according to the present disclosure can also be reduced, for example, by setting the tensile stretching temperature in step D higher, or by slowing the tensile stretching speed, within a range that does not exceed the melting point of the rolled film obtained in step C.

[0038] The nitrogen permeability coefficient of the ultra-high molecular weight polyethylene film according to the present disclosure can be controlled, for example, by adjusting the rolling conditions (e.g., surface temperature of the rolled body and rolling ratio) in step C of the polyolefin film manufacturing method according to the present disclosure described below, and the tensile stretching conditions (e.g., tensile stretching temperature, tensile stretching ratio, and tensile stretching speed) in step D. The nitrogen permeability coefficient of the ultra-high molecular weight polyethylene film according to the present disclosure can be lowered, for example, by setting the surface temperature of the rolled body in step C higher, provided that the temperature does not exceed the melting point of the polyethylene sheet obtained in step B. The nitrogen permeability coefficient of the ultra-high molecular weight polyethylene film according to the present disclosure can also be lowered, for example, by setting the tensile stretching temperature in step D higher, provided that the temperature does not exceed the melting point of the rolled film obtained in step C, or by slowing the tensile stretching speed.

[0039] The tear strength of the ultra-high molecular weight polyethylene film according to the present disclosure can be controlled, for example, by adjusting the rolling conditions (e.g., surface temperature of the rolled body and rolling ratio) in step C of the polyolefin film manufacturing method according to the present disclosure described below, and the tensile stretching conditions (e.g., tensile stretching temperature, tensile stretching ratio, and tensile stretching speed) in step D. The tear strength of the ultra-high molecular weight polyethylene film according to the present disclosure can be increased, for example, by setting the surface temperature of the rolled body in step C higher or by setting the rolling ratio higher, provided that the temperature does not exceed the melting point of the polyethylene sheet obtained in step B. The tear strength of the ultra-high molecular weight polyethylene film according to the present disclosure can also be increased, for example, by setting the tensile stretching temperature in step D higher or by setting the tensile stretching ratio higher, provided that the temperature does not exceed the melting point of the rolled film obtained in step C.

[0040] The tensile breaking strength of the ultra-high molecular weight polyethylene film according to the present disclosure can be controlled, for example, by adjusting the rolling conditions (e.g., surface temperature of the rolled body and rolling ratio) in step C of the polyolefin film manufacturing method according to the present disclosure described below, and the tensile stretching conditions (e.g., tensile stretching temperature, tensile stretching ratio, and tensile stretching speed) in step D. The tensile breaking strength of the ultra-high molecular weight polyethylene film according to the present disclosure can be increased, for example, by setting the surface temperature of the rolled body in step C higher or by setting the rolling ratio higher, provided that the temperature does not exceed the melting point of the polyethylene sheet obtained in step B. The tensile breaking strength of the ultra-high molecular weight polyethylene film according to the present disclosure can also be increased, for example, by setting the tensile stretching temperature in step D higher or by setting the tensile stretching ratio higher, provided that the temperature does not exceed the melting point of the rolled film obtained in step C.

[0041] The dielectric constant of the ultra-high molecular weight polyethylene film according to the present disclosure can be controlled, for example, by adjusting the rolling conditions (e.g., surface temperature of the rolled body and rolling ratio) in step C of the polyolefin film manufacturing method according to the present disclosure described below, and the tensile stretching conditions (e.g., tensile stretching temperature, tensile stretching ratio, and tensile stretching speed) in step D. The dielectric constant of the ultra-high molecular weight polyethylene film according to the present disclosure can be lowered, for example, by setting the surface temperature of the rolled body in step C higher or increasing the rolling ratio, provided that the temperature does not exceed the melting point of the polyethylene sheet obtained in step B. Furthermore, the dielectric constant of the ultra-high molecular weight polyethylene film according to the present disclosure can be lowered, for example, by setting the tensile stretching temperature in step D higher or increasing the tensile stretching ratio, provided that the temperature does not exceed the melting point of the rolled film obtained in step C.

[0042] [Method for Producing Polyolefin Film] The method for producing a polyolefin film according to the present disclosure (hereinafter also referred to as the "production method according to the present disclosure") comprises the steps of: Step A: applying an organic solvent containing a metal catalyst to the inner wall surface of a container; Step B: synthesizing a polyolefin on the inner wall surface of the container by introducing an olefin monomer into the container whose inner wall surface has been coated with the organic solvent containing the metal catalyst; and Step C: rolling out a sheet of the polyolefin synthesized on the inner wall surface of the container. According to the production method according to the present disclosure, a polyolefin film that has high transparency even when it is thick and has high gas barrier properties can be efficiently produced.

[0043] The inventors of the present application speculate that the reason for this is as follows. In the production method according to the present disclosure, film formation is carried out during the polyolefin synthesis process (i.e., steps A and B) to form a polyolefin film. In the polyolefin synthesis process of steps A and B, the growth and crystallization of the polyolefin molecular chains proceed simultaneously, so the formed polyolefin film has a structure with little entanglement of the molecular chains despite the long molecular chains of the polyolefin, and is highly plastically deformable. Therefore, when the polyolefin sheet obtained by step B is rolled in step C, high shear force is applied to the sheet by rolling, which crushes the irregularities and pores of the sheet, tending to improve the homogeneity of the sheet. From the above, it is believed that the production method according to the present disclosure can produce a polyolefin film that has high transparency and high gas barrier properties even when the film thickness is large.

[0044] <Step A> Step A is a step of applying an organic solvent containing a metal catalyst to the inner wall surface of a container. In the present disclosure, the organic solvent containing a metal catalyst is also referred to as a "film-forming coating liquid."

[0045] The film-forming coating liquid contains a metal catalyst. The type of metal catalyst is not particularly limited. Examples of the metal catalyst include metal complexes such as metallocene complexes, phenoxyimine titanium complexes, phenoxyimine zirconium complexes, phenoxyimine hafnium complexes, cyclopentadienyl quinolyl chromium complexes, diimine palladium complexes, diimine nickel complexes, bisiminopyridine iron complexes, and bisiminopyridine cobalt complexes. The metal catalyst is preferably at least one selected from the group consisting of metallocene complexes, phenoxyimine titanium complexes, phenoxyimine zirconium complexes, phenoxyimine hafnium complexes, cyclopentadienyl quinolyl chromium complexes, diimine palladium complexes, diimine nickel complexes, bisiminopyridine iron complexes, and bisiminopyridine cobalt complexes, more preferably at least one selected from the group consisting of phenoxyimine titanium complexes and metallocene complexes, and even more preferably a metallocene complex. The metallocene complex is a complex having a five-membered conjugated carbon ring containing a metal element. The metal element is not particularly limited, but is preferably, for example, a transition metal element of Group 4 of the periodic table, more preferably hafnium, zirconium, or titanium, and even more preferably titanium. The complex having a five-membered conjugated carbon ring is not particularly limited, but generally, a complex having a substituted or unsubstituted cyclopentadienyl ligand is used. When the metal catalyst is a metallocene complex, the molecular weight distribution of the synthesized polyolefin becomes narrower and the molecular chain length becomes more uniform, so the tensile break strength of the final polyolefin film tends to be higher.

[0046] Examples of metallocene complexes that can be used include hafnocene derivatives, titanocene derivatives, and zirconocene derivatives. The term "derivative" used herein refers to a metallocene having an optional substituent on the carbon of the five-membered conjugated carbon ring. The number of substituents is not important. Also included are those in which two five-membered conjugated carbon rings are linked together via a substituent.

[0047] Specific examples of metallocene complexes include bis(cyclopentadienyl)hafnium(IV) dichloride, bis(cyclopentadienyl)zirconium(IV) dichloride, bis(cyclopentadienyl)titanium(IV) dichloride, bis(propylcyclopentadienyl)hafnium(IV) dichloride, bis(pentamethylcyclopentadienyl)zirconium(IV) dichloride, bis(butylcyclopentadienyl)hafnium(IV) dichloride, [dimethylbis(cyclopentadienyl)silyl]zirconium(IV) dichloride, bis(dodecylcyclopentadienyl)zirconium(IV) dichloride, bis(trimethylsilylcyclopentadienyl)silyl bis(tetrahydroindenyl)zirconium(IV) dichloride, bis(tetrahydroindenyl)zirconium(IV) dichloride, (ethylidene-bisindenyl)zirconium(IV) dichloride, ethylidenebis(tetrahydroindenyl)zirconium(IV) dichloride, bis[3,3-(2-methyl-benzindenyl)]dimethylsilanediylzirconium(IV) dichloride, cyclopentadienyltitanium(IV) trichloride, pentamethylcyclopentadienyltitanium(IV) trichloride, (ethylidene-bisindenyl)titanium(IV) dichloride, and ethylidenebis(tetrahydroindenyl)titanium(IV) dichloride.

[0048] The film-forming coating liquid may contain one type of metal catalyst alone or two or more types.

[0049] The concentration of the metal catalyst in the film-forming coating liquid is not particularly limited, but is preferably, for example, 0.000001 mol / L (liter; the same applies hereinafter) to 0.1 mol / L, more preferably 0.00001 mol / L to 0.01 mol / L, and even more preferably 0.0001 mol / L to 0.005 mol / L.

[0050] The film-forming coating liquid contains an organic solvent. The type of organic solvent is not particularly limited. Examples of the organic solvent include toluene, xylene, hexane, heptane, decalin, methylene chloride, dichloroethane, tetrachloroethane, chlorobenzene, dichlorobenzene, trichlorobenzene, polyethylene glycol, oligoethylene glycol, polydimethylsiloxane, and oligodimethylsiloxane. The organic solvent is preferably at least one selected from toluene and hexane, and more preferably toluene.

[0051] The viscosity of the organic solvent is not particularly limited, but is preferably in the range of 0.1 mPa s or more and less than 100,000 mPa s, more preferably 0.1 mPa s or more and less than 10,000 mPa s, and even more preferably 0.1 mPa s or more and less than 1,000 mPa s. When the viscosity of the organic solvent is within the above range, it tends to be easier to prepare a film-forming coating liquid that can be well applied to the inner wall surface of a container.

[0052] In the present disclosure, the viscosity of an organic solvent refers to the viscosity at 20°C, and is a value measured using a vibration viscometer. As the vibration viscometer, for example, a vibration viscometer (model number: VM-10A) manufactured by Sekonic Corporation can be suitably used. However, the vibration viscometer is not limited to this.

[0053] For example, when the film-forming coating liquid contains a co-catalyst as described below, the organic solvent is preferably dehydrated in order to prevent decomposition of the co-catalyst due to moisture.

[0054] The film-forming coating liquid may contain one kind of organic solvent alone or two or more kinds of organic solvents.

[0055] The content of the organic solvent in the film-forming coating liquid is not particularly limited, but is preferably 60% by mass to 99.99% by mass, more preferably 70% by mass to 99.9% by mass, and even more preferably 80% by mass to 99% by mass, relative to the total mass of the film-forming coating liquid.

[0056] It is preferable that the film-forming coating liquid further contains a co-catalyst. The type of co-catalyst is not particularly limited. Examples of the co-catalyst include alkylaluminoxane, dialkylaluminum chloride, trialkylaluminum / triphenylmethylium tetrakis(pentafluorophenyl)borate, trialkylaluminum / N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, trialkylaluminum / tris(pentafluorophenyl)borane, and sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate. The co-catalyst is preferably at least one selected from the group consisting of alkylaluminoxane, dialkylaluminum chloride, trialkylaluminum / triphenylmethylium tetrakis(pentafluorophenyl)borate, trialkylaluminum / N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, trialkylaluminum / tris(pentafluorophenyl)borane, and sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate, and more preferably alkylaluminoxane.

[0057] The number of carbon atoms in the alkyl moiety of the alkylaluminoxane is not particularly limited, but is preferably 1 to 8, and more preferably 1 to 4. Examples of alkylaluminoxanes include methylaluminoxane, ethylaluminoxane, and isobutylaluminoxane. A preferred alkylaluminoxane is methylaluminoxane (MAO). Examples of commercially available methylaluminoxanes include "TMAO-212 (trade name)" and "MMAO-3A (trade name)" manufactured by Tosoh Finechem Corporation, and "MAO (trade name)" manufactured by Sigma-Aldrich.

[0058] In the present disclosure, the co-catalyst not only functions as a co-catalyst to improve the catalytic activity of the metal catalyst, but also functions to improve the viscosity of the film-forming coating solution. Generally, the co-catalyst has a high viscosity itself, so it can also function as a so-called thickener. Therefore, when the film-forming coating solution contains a co-catalyst, not only the catalytic activity of the metal catalyst is improved, but also the viscosity of the film-forming coating solution is increased, which allows the film-forming coating solution to be applied smoothly to the inner wall surface of the container, tending to more efficiently produce a polyolefin film. From this perspective, a solid co-catalyst that easily increases the viscosity of the film-forming coating solution is preferred. An example of a solid co-catalyst is methylaluminoxane (MAO).

[0059] When the film-forming coating liquid further contains a co-catalyst, it may contain one type of co-catalyst alone or two or more types of co-catalysts.

[0060] When the film-forming coating liquid further contains a co-catalyst, the content of the co-catalyst in the film-forming coating liquid is not particularly limited. For example, when the film-forming coating liquid contains an alkylaluminoxane (preferably methylaluminoxane (MAO)) as a co-catalyst, the content of the co-catalyst in the film-forming coating liquid is preferably an amount such that the content of aluminum in the co-catalyst is 10 to 50,000 times, more preferably 50 to 10,000 times, and even more preferably 100 to 5,000 times, the molar amount of the metal catalyst.

[0061] The film-forming coating liquid preferably comprises a metal catalyst and an organic solvent, wherein the metal catalyst is a metallocene complex and the organic solvent is at least one selected from the group consisting of toluene and hexane; more preferably comprises a metal catalyst, a co-catalyst and an organic solvent, wherein the metal catalyst is a metallocene complex, the organic solvent is at least one selected from the group consisting of toluene and hexane, and the co-catalyst is an alkylaluminoxane; and even more preferably comprises a metal catalyst, a co-catalyst and an organic solvent, wherein the metal catalyst is a metallocene complex, the organic solvent is at least one selected from the group consisting of toluene and hexane, and the co-catalyst is methylaluminoxane (MAO).

[0062] The viscosity of the film-forming coating liquid is not particularly limited, but is preferably in the range of 0.1 mPa·s to 10,000 mPa·s, more preferably in the range of 0.4 mPa·s to 10,000 mPa·s, and even more preferably in the range of 0.4 mPa·s to 1,000 mPa·s. When the viscosity of the film-forming coating liquid is within the above range, the film-forming coating liquid tends to be able to be applied more satisfactorily to the inner wall surface of the container.

[0063] In the present disclosure, the viscosity of the film-forming coating liquid refers to the viscosity at 20°C, and is a value measured using a vibration viscometer. As the vibration viscometer, for example, a vibration viscometer (model number: VM-10A) manufactured by Sekonic Corporation can be suitably used. However, the vibration viscometer is not limited to this.

[0064] The external shape of the container is not particularly limited, and examples thereof include a cylindrical shape (e.g., a cylindrical shape, a rectangular cylindrical shape, etc.), a spherical shape, etc. When the external shape of the container is a cylindrical shape, the shape of the cross section perpendicular to the longitudinal direction of the cylinder may be, for example, a circle, a semicircle, an ellipse, a rectangle, a square, or a trapezoid. The external shape of the container may also be a semi-cylindrical shape.

[0065] The container may have a partially open wall or may be sealed. The container may also be a long hollow tube, which may be spirally wound.

[0066] The shape of the inner wall surface of the container is not particularly limited as long as a film can be formed. The shape of the inner wall surface of the container may be, for example, flat or curved. The shape of the inner wall surface of the container may also be spiral. When at least a portion of the shape of the inner wall surface of the container is spiral, for example, by rotating the container, continuous production of a polyolefin film can be realized.

[0067] The material of the container is not particularly limited. Examples of the material of the container include glass, metal, and resin. Examples of metal include stainless steel (so-called SUS), chrome steel, aluminum, and titanium. Examples of resin include engineering plastics such as fluororesin, polyimide, polyether ether ketone, aramid, polyphenylene sulfide, and polyamide. The container may be made of glass, metal, or resin. Furthermore, the container may be made of two or more materials selected from the group consisting of glass, metal, and resin.

[0068] The inner wall surface of the container may be subjected to a surface treatment such as corona discharge treatment or plasma discharge treatment in order to improve the wettability of the coating liquid for film formation. When the wettability of the coating liquid for film formation to the inner wall surface of the container is improved, a polyolefin film can be produced more satisfactorily.

[0069] The size of the container is not particularly limited and can be appropriately set depending on, for example, the size of the desired polyolefin sheet.

[0070] The method for applying the film-forming coating liquid to the inner wall surface of a container is not particularly limited, and may be, for example, a method of spraying the film-forming coating liquid onto the inner wall surface of a container, a method of allowing the film-forming coating liquid to fall freely onto the inner wall surface of a container, a method of passing the container through the film-forming coating liquid, a method of immersing the container in the film-forming coating liquid, or a method of supplying the film-forming coating liquid to a rotating container.

[0071] From the viewpoint of more uniformly and efficiently applying the film-forming coating liquid to the inner wall surface of the container, it is preferable to apply the film-forming coating liquid to the inner wall surface of the container by moving the container. "Moving the container" may mean changing the attitude of the container, rotating the container, or shaking the container. Changing the attitude of the container, rotating the container, and shaking the container are also preferable from the viewpoint of activating the metal catalyst, and rotating the container is more preferable. When rotating the container, it is preferable to rotate it around the axis of the container. When the film-forming coating liquid is uniformly applied to the inner wall surface of the container, it is possible to form a polyolefin sheet with a uniform film thickness distribution.

[0072] The rotation speed of the container is not particularly limited and may be appropriately set in consideration of, for example, the viscosity (in other words, fluidity) of the film-forming coating liquid, the target film thickness, and production efficiency. The rotation speed of the container may be, for example, 1 rpm (revolutions per minute; the same applies hereinafter) to 1,000 rpm.

[0073] Generally, metal catalysts and co-catalysts are often unstable in air, and therefore, from the viewpoint of the stability of the metal catalyst and co-catalyst, it is preferable to apply the film-forming coating solution to the inner wall surface of the container under a nitrogen atmosphere.

[0074] <Step B> Step B is a step of synthesizing polyolefin on the inner wall surface of a container by introducing an olefin monomer into the inside of a container whose inner wall surface has been coated with a film-forming coating liquid (i.e., an organic solvent containing a metal catalyst). According to Step B, a polyolefin film is formed on the inner wall surface of the container. The proportion of the formed polyolefin film to the total area of ​​the inner wall surface of the container is preferably 80% or more, more preferably 90% or more, and even more preferably 100%.

[0075] The olefin monomer is not particularly limited. Examples of the olefin monomer include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, 4-methyl-1-pentene, cyclopentene, 3-methylcyclopentene, 3-ethylcyclopentene, 4-methylcyclopentene, 4-ethylcyclopentene, norbornene and derivatives thereof, styrene and derivatives thereof, vinylcyclohexane, allylcyclohexane, 4-cyclohexyl-1-butene, 5-cyclohexyl-1-pentene, 6-cyclohexyl-1-hexene, and tert-butylethylene. Here, the term "derivative" refers to a compound having an optional substituent at the 5- and / or 6-position of norbornene, on the benzene ring of styrene, or the like. The olefin monomer is preferably at least one selected from the group consisting of ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, 4-methyl-1-pentene, cyclopentene, norbornene, styrene, vinylcyclohexane, allylcyclohexane, 4-cyclohexyl-1-butene, 5-cyclohexyl-1-pentene, 6-cyclohexyl-1-hexene, and tert-butylethylene, with ethylene being particularly preferred. Furthermore, a mixture of two or more of these olefin monomers may be used, and the mixing ratio may be arbitrary. For example, an ethylene-1-hexene copolymer can be obtained by using a mixed gas of ethylene and 1-hexene as the monomer.

[0076] The olefin monomer introduced into the interior of a vessel whose inner wall surface has been coated with a film-forming coating liquid (i.e., an organic solvent containing a metal catalyst) is preferably in a gaseous or liquid state, and more preferably in a gaseous state. For example, when the olefin monomer is in a gaseous (so-called gas) state, the pressure of the gas introduced into the vessel is not particularly limited, but is preferably, for example, 0.1 MPa to 10 MPa, more preferably 0.2 MPa to 5 MPa, and even more preferably 0.5 MPa to 4 MPa. The gas pressure is a value measured by a pressure gauge connected to the reaction vessel. As the pressure gauge, for example, a pressure gauge manufactured by Taiatsu Glass Industries Co., Ltd. can be suitably used. However, the pressure gauge is not limited thereto.

[0077] The method for introducing the olefin monomer into the container may be, for example, a method of spraying the olefin monomer into the container, or a method of dropping the olefin monomer into the container from the anti-gravity direction of the container.

[0078] When an olefin monomer is introduced into a container whose inner wall surface has been coated with a film-forming coating liquid, a polymerization reaction of the olefin monomer occurs on the inner wall surface of the container, synthesizing a polyolefin. The polymerization time is not particularly limited and can be, for example, 1 minute to 120 minutes. The polymerization time refers to the time from the time the olefin monomer is introduced into the container to the time the pressure inside the container is released. The polymerization temperature is not particularly limited, but is, for example, preferably 0°C to 150°C, more preferably 5°C to 100°C, and even more preferably 10°C to 80°C.

[0079] In step B, a polymerization terminator may be used to terminate the polymerization reaction of the olefin monomer. The polymerization terminator is not particularly limited as long as it is highly reactive with the active terminal. Examples of the polymerization terminator include additives such as methanol, ethanol, and 2-propanol.

[0080] <Step C> Step C is a step of rolling the polyolefin sheet synthesized on the inner wall surface of the container in Step B. In the present disclosure, "rolling" refers to a process of sandwiching a polyolefin sheet between rolling bodies such as metals and applying shear force. In the present disclosure, rolling includes roll rolling, in which a rolled material is sandwiched between rolls rotating at a constant speed in opposite directions and stretched by pressure to reduce its thickness. In addition, rolling in the present disclosure includes press rolling, in which a rolled material is sandwiched between two rolling bodies such as metals and stretched by pressure in opposite directions to reduce its thickness. Furthermore, rolling in the present disclosure includes rubbing rolling, in which a polyolefin sheet is placed on a metal plate and pressure is applied by rubbing another metal member against the polyolefin. Among these rolling methods, roll rolling is more preferable because it can apply a higher shear force.

[0081] In step C, a high shear force is applied to the polyolefin sheet by rolling. The high shear force applied to the polyolefin sheet synthesized in step B collapses the irregularities and pores of the sheet. Therefore, the rolled film obtained in step C has high transparency and gas barrier properties.

[0082] In step C, a laminate obtained by laminating multiple polyolefin sheets synthesized in step B on the inner wall surface of the container may be rolled. When the polyolefin sheets synthesized in step B are laminated and rolled, a polyolefin film in which multiple sheets are integrated can be obtained. This is presumably because polyolefin molecular chains move back and forth across the sheet interface. The polyolefin film in which multiple sheets are integrated has the characteristic of being highly transparent even when it is thick.

[0083] The rolling of the laminate in step C includes a mode in which pre-rolled rolled films are laminated together and then further rolled, and a mode in which a rolled film and a non-rolled polyolefin sheet are laminated together and then further rolled. Furthermore, a roll-to-roll method may be adopted as a method for further roll rolling after roll rolling.

[0084] In step C, the surface temperature of the rolled body during rolling is not particularly limited, but from the viewpoint of further increasing the transparency of the polyolefin film, it is preferably -10 ° C. or higher and lower than the melting point of the polyolefin sheet synthesized on the inner wall surface of the container in step B, more preferably -5 ° C. or higher and not higher than a temperature 5 ° C. lower than the melting point of the polyolefin sheet synthesized on the inner wall surface of the container in step B, even more preferably -1 ° C. or higher and not higher than a temperature 10 ° C. lower than the melting point of the polyolefin sheet synthesized on the inner wall surface of the container in step B, and particularly preferably 0 ° C. or higher and not higher than a temperature 15 ° C. lower than the melting point of the polyolefin sheet synthesized on the inner wall surface of the container in step B. Since the polyolefin sheet synthesized in step B can be rolled to produce a polyolefin film in which multiple sheets are integrated together even when the surface temperature of the rolled body is low, it can be suitably used, for example, as a material for storage bags and packaging bags for refrigerated and frozen foods, in which sheets are bonded and sealed together in a low-temperature environment.

[0085] In the present disclosure, the melting point of the polyolefin sheet is determined from the DSC curve obtained by measuring the polyolefin sheet using a differential scanning calorimeter in a nitrogen atmosphere, where the temperature is increased from 30°C to 200°C at a heating rate of 10°C / min. The melting point is the temperature at the apex of the melting peak. If multiple peaks are present, the peak with the highest temperature is taken as the melting point. Details of the measurement method using a differential scanning calorimeter are as follows. A differential scanning calorimeter is used as the measuring device, and approximately 1.2 mg of the polyolefin sheet is sealed in an aluminum pan and subjected to measurement. The temperature and heat quantity are calibrated using indium and tin as standard materials. A suitable differential scanning calorimeter is, for example, a heat flux type single furnace DSC 4000 (product name) manufactured by PerkinElmer Japan Co., Ltd. However, the differential scanning calorimeter is not limited thereto.

[0086] In step C, the rotation speed of the roll during roll rolling is not particularly limited. For example, from the viewpoint of productivity, the rotation speed of the roll is preferably 0.1 rpm or more, more preferably 0.2 rpm or more, even more preferably 0.5 rpm or more, and particularly preferably 1 rpm or more. Furthermore, for example, from the viewpoint of operability, the rotation speed of the roll is preferably 1000 rpm or less, more preferably 100 rpm or less, even more preferably 50 rpm or less, and particularly preferably 10 rpm or less. In one embodiment, the rotation speed of the roll may be in the range of 0.1 rpm or more to 1000 rpm or less, 0.2 rpm or more to 100 rpm or less, 0.5 rpm or more to 50 rpm or less, or 1 rpm or more to 10 rpm or less.

[0087] In step C, the distance between the rolls when rolling is not particularly limited, and can be set appropriately depending on, for example, the desired thickness of the polyolefin film and the thickness of the sheet to be rolled.

[0088] In step C, the pressing pressure when pressing is not particularly limited. For example, from the viewpoint of being able to apply sufficient shear force to the polyolefin sheet, the pressing pressure is preferably 1 MPa or more, more preferably 5 MPa or more, even more preferably 10 MPa or more, and particularly preferably 50 MPa or more. Furthermore, from the viewpoint of productivity, the pressing pressure is preferably 50,000 MPa or less, more preferably 10,000 MPa or less, even more preferably 5,000 MPa or less, and particularly preferably 2,000 MPa or less. In one embodiment, the pressing pressure may be in the range of 1 MPa or more to 50,000 MPa or less, 5 MPa or more to 10,000 MPa or less, 10 MPa or more to 5,000 MPa or less, or 50 MPa or more to 2,000 MPa or less.

[0089] In step C, the rolling ratio when rolling is not particularly limited. For example, from the viewpoint of being able to increase the transparency of the polyolefin film, the rolling ratio is preferably 1.1 times or more, more preferably 1.5 times or more, even more preferably 2 times or more, and particularly preferably 3 times or more. Furthermore, from the viewpoint of operability, for example, the rolling ratio is preferably 100 times or less, more preferably 50 times or less, even more preferably 20 times or less, and particularly preferably 10 times or less. In one embodiment, the rolling ratio may be in the range of 1.1 times or more and 100 times or less, or may be in the range of 1.5 times or more and 50 times or less, or may be in the range of 2 times or more and 20 times or less, or may be in the range of 3 times or more and 10 times or less.

[0090] In the present disclosure, the "rolling ratio" is calculated from the distance (Lt) between the ink marks on the sheet before rolling, using the distance (Li) between the ink marks on the sheet before rolling as a reference, using the following formula: Rolling ratio = [Lt (mm) / Li (mm)]

[0091] In the case of roll rolling, it refers to the rolling ratio in the direction along the roll direction, and in the case of press rolling, it refers to the average value of the rolling ratio in the longitudinal direction and the rolling ratio in the transverse direction of the rolled film.

[0092] In the manufacturing method according to the present disclosure, step C may be repeated any number of times. In this case, the rolling conditions in step C (rolling method such as roll rolling or press rolling, surface temperature of the rolled body, rolling ratio, etc.) may be the same or different. When roll rolling is repeated, the rolling direction may be changed as desired. For example, by rolling again in a direction perpendicular to the first rolling direction (i.e., a direction rotated 90°), high tear strength can be imparted to the obtained rolled film in both the longitudinal direction (i.e., the first rolling direction) and the transverse direction (i.e., the second rolling direction).

[0093] <Step D> The production method according to the present disclosure preferably includes Step D, in which the rolled film obtained by rolling in Step C is further tensile stretched. Step D tends to form more extended chain crystals, and the breaking strength of the polyolefin film finally obtained is increased.

[0094] The tensile stretching may be, for example, simple uniaxial stretching, biaxial stretching in both the longitudinal and transverse directions, sequential biaxial stretching in which stretching in both the longitudinal and transverse directions is performed sequentially, or width-constrained stretching in which the width is kept constant. However, uniaxial stretching is more preferred because it allows for more efficient formation of extended chain crystals and makes it easier to align the molecular chains of the extended chain crystals.

[0095] In the production method according to the present disclosure, step D may be repeated any number of times. In this case, the tensile stretching conditions in step D (such as tensile stretching temperature, tensile stretching ratio, and tensile stretching speed) may be the same or different.

[0096] In the manufacturing method according to the present disclosure, step C may be performed again after step D. Furthermore, steps C and D may be repeated in any order and any number of times.

[0097] In step D, for example, from the viewpoint of further increasing the proportion of extended chain crystals formed, the rolled film obtained in step C is preferably tensile stretched at a temperature of 0° C. or higher and lower than the melting point of the rolled film, more preferably tensile stretched at a temperature of 25° C. or higher and not higher than 5° C. lower than the melting point of the rolled film, even more preferably tensile stretched at a temperature of 60° C. or higher and not higher than 10° C. lower than the melting point of the rolled film, and particularly preferably tensile stretched at a temperature of 90° C. or higher and not higher than 15° C. lower than the melting point of the rolled film.

[0098] For example, from the viewpoint of productivity, the stretching speed is preferably 0.1 mm / min or more, more preferably 0.5 mm / min or more, even more preferably 1 mm / min or more, and particularly preferably 5 mm / min or more, for a rolled film having a length of 10 mm. Furthermore, from the viewpoint of obtaining a film with higher uniformity, the stretching speed is preferably 1000 mm / min or less, more preferably 500 mm / min or less, even more preferably 100 mm / min or less, and particularly preferably 50 mm / min or less. In one embodiment, the stretching speed may be in the range of 0.1 mm / min to 1000 mm / min, 0.5 mm / min to 500 mm / min, 1 mm / min to 100 mm / min, or 5 mm / min to 50 mm / min, for a rolled film having a length of 10 mm.

[0099] The stretching ratio is preferably 1.1 or more, more preferably 1.5 or more, even more preferably 2 or more, and particularly preferably 3 or more, from the viewpoint of increasing the proportion of extended chain crystals formed. Furthermore, the stretching ratio is preferably 100 or less, more preferably 50 or less, even more preferably 20 or less, and particularly preferably 10 or less, from the viewpoint of obtaining a film with higher uniformity. In one embodiment, the stretching ratio may be in the range of 1.1 to 100, 1.5 to 50, 2 to 20, or 3 to 10.

[0100] In step D, it is desirable to cool the stretched sheet. The cooling means is not particularly limited, but cooling in air or water is preferred. The cooling temperature is not particularly limited, but is preferably room temperature (i.e., 25°C), for example.

[0101] <Other Steps> The production method according to the present disclosure may include steps (so-called other steps) other than the above-described steps A, B, C, and D. Examples of the other steps include a first cleaning step, a peeling step, a second cleaning step, and a drying step. In the production method according to the present disclosure, it is preferable that the first cleaning step, the peeling step, the second cleaning step, and the drying step are all included between step B and step C.

[0102] (First Washing Step) When the film-forming coating liquid contains a co-catalyst, the production method according to the present disclosure preferably includes a first washing step. The first washing step is a step of washing the synthesized polyolefin. In the first washing step, the co-catalyst attached to the polyolefin is removed. The washing liquid is not particularly limited, and examples thereof include hydrochloric acid, methanol, ethanol, 2-propanol, and mixtures thereof. The washing method is not particularly limited, and examples thereof include a method of adding a washing liquid to the inside of a container and then rotating the container to wash the polyolefin.

[0103] (Peeling step) The peeling step is a step of peeling the synthesized polyolefin from the inner wall surface of the container. The polyolefin synthesized in step B forms a film (so-called polyolefin film) on the inner wall surface of the container. In the peeling step, the polyolefin is peeled off as a sheet-like film (so-called polyolefin sheet). The peeling method is not particularly limited, and known peeling methods can be applied.

[0104] (Second Cleaning Step) The second cleaning step is a step of cleaning the peeled polyolefin sheet. In the second cleaning step, for example, the metal catalyst attached to the polyolefin sheet and the cleaning liquid used in the first cleaning step are removed. The cleaning liquid is not particularly limited, and examples thereof include methanol, acetone, toluene, xylene, pentane, hexane, and mixtures thereof. The cleaning method is not particularly limited, and examples thereof include a method of immersing the sheet in the cleaning liquid and a method of spraying the cleaning liquid.

[0105] (Drying step) The drying step is a step of drying the washed polyolefin sheet. In the drying step, the washing liquid adhering to the polyolefin sheet is removed. The drying method is not particularly limited, and known drying methods can be applied. Examples of the drying method include a method of drying by wind (so-called air drying) and a method of drying by heat.

[0106] -Film Thickness of Polyolefin Film- The polyolefin film obtained by the production method according to the present disclosure has a thickness of, for example, 5 μm to 5,000 μm. According to the production method according to the present disclosure, the thickness of the polyolefin film can be 10 μm or more, 100 μm or more, 500 μm or more, or 1,000 μm or more.

[0107] The following examples will further explain the ultra-high molecular weight polyethylene film according to the present disclosure and the method for producing a polyolefin film according to the present disclosure. The materials, amounts used, ratios, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present disclosure. Therefore, the scope of the ultra-high molecular weight polyethylene film according to the present disclosure and the method for producing a polyolefin film according to the present disclosure should not be construed as being limited by the specific examples shown below.

[0108] In the following examples, the thickness of the polyethylene sheet and polyethylene film was measured using a film tester (model number: HKT-1216), a thickness measuring device manufactured by Fujiwork Co., Ltd. Specifically, the arithmetic mean value of the thickness measured at six randomly selected points in the thickness direction of the polyethylene sheet or polyethylene film was calculated, and the obtained value was taken as the thickness of the polyethylene sheet or polyethylene film.

[0109] The melting points of the polyethylene sheet and rolled film were measured using a heat flux type single furnace DSC 4000 (trade name), a differential scanning calorimeter manufactured by PerkinElmer Japan Co., Ltd. Specifically, approximately 2 mg of the polyethylene sheet or rolled film was sealed in an aluminum pan and heated from 30°C to 180°C at a rate of 10°C / min in a nitrogen atmosphere to obtain a DSC curve. The temperature at the apex of the melting peak observed in the obtained DSC curve was taken as the melting point.

[0110] The weight average molecular weight (Mw) and number average molecular weight (Mn) of the polyethylene were estimated from the molecular weight distribution curve of the polyethylene contained obtained by gel permeation chromatography (GPC) measurement under the following conditions. The molecular weight distribution index (Mw / Mn) of the polyethylene was calculated from the obtained weight average molecular weight (Mw) and number average molecular weight (Mn).

[0111] -Conditions- Apparatus: HLC-8121 GPC / HT (detector: RI) [manufactured by Tosoh Corporation] Column: Three connected TSLgel GMHHR-H(20)HT [7.8 mm I.D. × 30 cm, manufactured by Tosoh Corporation] Eluent: 1,2,4-trichlorobenzene [HPLC grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.] containing 0.05% by mass of dibutylhydroxytoluene (BHT; antioxidant) Flow rate: 1.0 mL / min Detection conditions: polarity = (-) Injection volume: 0.3 mL Column temperature: 150°C Sample concentration: 0.1 mg / mL (solvent: 1,2,4-trichlorobenzene)

[0112] [Production of Polyethylene Sheet X] A 96 mL capacity glass pressure-resistant container (model number: HPG-96-3, shape: cylindrical, inner wall area: approximately 150 cm) was prepared. ２To a pressure-resistant vessel (manufactured by Taiatsu Glass Industry Co., Ltd.) under a nitrogen atmosphere, 0.00015 g (0.00058 mmol) of bis(cyclopentadienyl)titanium(IV) dichloride (metal catalyst) and 0.24 mL of toluene (organic solvent) were added, followed by the addition of 0.42 mL (Al: 1.17 mmol) of a toluene solution of methylaluminoxane (co-catalyst) (trade name: TMAO-212, manufactured by Tosoh Finechem Corporation). Next, the pressure-resistant vessel was placed sideways on a rotating stand and rotated at 120 rpm for 10 minutes in an environment with an ambient temperature of 25°C, thereby coating the liquid in the pressure-resistant vessel (organic solvent containing the metal catalyst and co-catalyst; so-called film-forming coating liquid) on the inner wall surface of the pressure-resistant vessel [Step A].

[0113] The viscosity of the film-forming coating liquid at 20° C. was measured using a vibration viscometer (model number: VM-10A) manufactured by Sekonic Corporation and was found to be 0.7 mPs·s.

[0114] Next, ethylene gas (pressure: 2 MPa) was introduced into the pressure vessel by spraying, and the pressure vessel was rotated on a rotating stand for 60 minutes to polymerize the ethylene, thereby synthesizing polyethylene on the inner wall surface of the pressure vessel [Step B].

[0115] After the polymerization reaction was completed, the ethylene gas was released, and ethanol (a polymerization terminator) was added to stop the reaction. Then, a mixed solution of hydrochloric acid and methanol (volume ratio 1:4) (a cleaning solution) was added to the pressure vessel to remove the co-catalyst adhering to the polyethylene [first cleaning step].

[0116] Next, the synthesized polyethylene was peeled off from the inner wall surface of the pressure vessel to obtain a polyethylene film in sheet form (i.e., a polyethylene sheet) [peeling step].

[0117] Next, the peeled polyethylene sheet was washed with methanol (washing liquid) and acetone (washing liquid) to remove the metal catalyst adhering to the polyethylene sheet and the washing liquid used in the first washing step [second washing step].

[0118] Next, the washed polyethylene sheet was air-dried [drying step].

[0119] In this way, a polyethylene sheet X was obtained. The obtained polyethylene sheet X was a rectangular sheet measuring 15 cm x 8 cm and having an area of ​​120 cm. ２ The weight was 1.52 g, the film thickness was 338 μm, and the melting point was 139.8° C.

[0120] The polyethylene sheet X was subjected to the aforementioned gel permeation chromatography (GPC) measurement, and the weight average molecular weight (Mw) estimated from the molecular weight distribution curve of the obtained polyethylene contained therein was 3,080,000, the number average molecular weight (Mn) was 1,040,000, and the molecular weight distribution index was 3.0. This confirmed that the polyethylene contained in the polyethylene sheet X was the ultra-high molecular weight polyethylene of the present disclosure.

[0121] [Production of Polyethylene Sheet Y] A 96 mL capacity glass pressure vessel (model number: HPG-96-3, shape: cylindrical, inner wall area: approximately 150 cm) was prepared. ２ , manufactured by Taiatsu Glass Industry Co., Ltd.] under a nitrogen atmosphere, 0.00024 g (0.00058 mmol) of rac-ethylenebis(indenyl)zirconium(IV) dichloride [metal catalyst] and 0.24 mL of toluene [organic solvent] were added, and then 0.42 mL (Al: 1.17 mmol) of a toluene solution of methylaluminoxane [co-catalyst] [trade name: TMAO-212, manufactured by Tosoh Finechem Co., Ltd.] was added. Next, the pressure-resistant vessel was placed sideways on a rotating stand and rotated at 120 rpm for 10 minutes in an environment with an ambient temperature of 25°C, whereby the liquid in the pressure-resistant vessel [organic solvent containing a metal catalyst and a co-catalyst; so-called sheet-forming coating liquid] was applied to the inner wall surface of the pressure-resistant vessel [Step A].

[0122] Next, ethylene gas (pressure: 1 MPa) was introduced into the pressure vessel by spraying, and the pressure vessel was rotated on a rotating stand for 180 minutes to polymerize the ethylene and synthesize polyethylene on the inner wall surface of the pressure vessel [Step B].

[0123] After the polymerization reaction was completed, the ethylene gas was released, and ethanol (a polymerization terminator) was added to stop the reaction. Then, a mixed solution of hydrochloric acid and methanol (volume ratio 1:4) (a cleaning solution) was added to the pressure vessel to remove the co-catalyst adhering to the polyethylene [first cleaning step].

[0124] Next, the synthesized polyethylene was peeled off from the inner wall surface of the pressure vessel to obtain a polyethylene sheet [peeling step].

[0125] Next, the peeled polyethylene sheet was washed with methanol (washing liquid) and acetone (washing liquid) to remove the metal catalyst adhering to the polyethylene sheet and the washing liquid used in the first washing step [second washing step].

[0126] Next, the washed polyethylene sheet was air-dried [drying step].

[0127] In this way, a polyethylene sheet Y was obtained. The obtained polyethylene sheet Y was a rectangular sheet measuring 15 cm x 8 cm and had an area of ​​120 cm. ２ The weight was 1.66 g, the film thickness was 575 μm, and the melting point was 133.1° C.

[0128] The polyethylene sheet Y was subjected to the above-mentioned gel permeation chromatography (GPC) measurement, and the weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution index (MDA) estimated from the molecular weight distribution curve of the resulting polyethylene were 160,000, 67,000, and 2.4, respectively.

[0129] [Production of Ethylene-1-Hexene Copolymer Sheet Z] A 96 mL glass pressure vessel (model number: HPG-96-3, shape: cylindrical, inner wall area: approximately 150 cm) was placed in a 96 mL glass pressure vessel. ２To the interior of a pressure vessel (manufactured by Taiatsu Glass Industry Co., Ltd.) under a nitrogen atmosphere, 0.00025 g (0.00087 mmol) of bis(cyclopentadienyl)zirconium(IV) dichloride (metal catalyst) and 0.44 mL of toluene (organic solvent) were added, followed by the addition of 0.62 mL (Al: 1.75 mmol) of a toluene solution of methylaluminoxane (co-catalyst) (trade name: TMAO-212, manufactured by Tosoh Finechem Co., Ltd.). Next, the pressure vessel was placed sideways on a rotating stand and rotated at 120 rpm for 10 minutes in an ambient temperature of 25°C, thereby coating the liquid in the pressure vessel (an organic solvent containing a metal catalyst and a co-catalyst; the so-called sheet-forming coating liquid) onto the inner wall surface of the pressure vessel [Step A].

[0130] 1-Hexene (0.2 mL) was added to a 100 mL stainless steel pressure vessel (model number: TVS-1-100, manufactured by Taiatsu Glass Industry Co., Ltd.) under a nitrogen atmosphere, and ethylene gas (pressure: 2 MPa) was introduced thereinto. The vessel was then heated to 75°C to vaporize the 1-hexene. This vessel was connected to a glass pressure vessel containing a catalyst solution at an ambient temperature of 25°C, and a mixed gas of ethylene and 1-hexene was introduced therein by spraying. The glass pressure vessel was then allowed to stand for 120 minutes at an ambient temperature of 25°C, whereby ethylene and 1-hexene were copolymerized to synthesize an ethylene-1-hexene copolymer (also referred to as a "polyethylene copolymer") on the inner wall surface of the pressure vessel [Step B].

[0131] After completion of the polymerization reaction, the ethylene gas was released, and ethanol (a polymerization terminator) was added to stop the reaction. Then, a mixed solution of hydrochloric acid and methanol (volume ratio 1:4) (a cleaning solution) was added to the pressure vessel to remove the co-catalyst adhering to the polyethylene copolymer [first cleaning step].

[0132] Next, the synthesized ethylene / 1-hexene copolymer was peeled off from the inner wall surface of the pressure vessel to obtain an ethylene / 1-hexene copolymer sheet [peeling step].

[0133] Next, the peeled ethylene / 1-hexene copolymer sheet was washed with methanol (washing liquid) and acetone (washing liquid) to remove the metal catalyst adhering to the ethylene / 1-hexene copolymer sheet and the washing liquid used in the first washing step [second washing step].

[0134] Next, the washed ethylene-1-hexene copolymer sheet was air-dried [drying step].

[0135] In this manner, an ethylene / 1-hexene copolymer sheet Z was obtained. The obtained ethylene / 1-hexene copolymer Z was a rectangular sheet measuring 15 cm x 8 cm and having an area of ​​120 cm. ２ The weight was 1.52 g, the film thickness was 163 μm, and the melting point was 126.8° C.

[0136] [Production of Polyethylene Film] <Production Example 1> The polyethylene sheet X obtained above was cut into a size of 10 mm x 10 mm. Next, the cut polyethylene sheet X was introduced between a pair of rolls provided in an electric hot roller (model number: IMC-110F-B, manufactured by Imoto Machinery Co., Ltd.) and roll-rolled under conditions of a roll surface temperature of 25°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm, thereby obtaining a polyethylene film 1 of Production Example 1. The obtained polyethylene film 1 had a size of 45 mm (roll rotation direction) x 10 mm (width direction) and a film thickness of 23 μm. The rolling ratio was 4.5 times.

[0137] <Production Example 2> The polyethylene sheet X obtained above was cut into a size of 10 mm x 10 mm. Next, the cut polyethylene sheet X was introduced between a pair of rolls provided in a rolling mill and rolled under conditions of a roll surface temperature of 60°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm, thereby obtaining a polyethylene film 2 of Production Example 2. The obtained polyethylene film 2 had a size of 50 mm (roll rotation direction) x 10 mm (width direction) and a film thickness of 19 μm. The rolling ratio was 5.0 times.

[0138] <Production Example 3> The polyethylene sheet X obtained above was cut into a size of 10 mm x 10 mm. Next, the cut polyethylene sheet X was introduced between a pair of rolls provided in a rolling mill and roll-rolled under conditions of a roll surface temperature of 100°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm, thereby obtaining a polyethylene film 3 of Production Example 3. The obtained polyethylene film 3 had a size of 70 mm (roll rotation direction) x 10 mm (width direction) and a film thickness of 14 μm. The rolling ratio was 7.0 times.

[0139] <Production Example 4> The polyethylene sheet X obtained above was cut into a size of 10 mm x 10 mm. Next, the cut polyethylene sheet X was introduced between a pair of rolls provided in a rolling mill and roll-rolled under conditions of a roll surface temperature of 8°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm, thereby obtaining a polyethylene film 4 of Production Example 4. The obtained polyethylene film 4 had a size of 35 mm (roll rotation direction) x 10 mm (width direction) and a film thickness of 28 μm. The rolling ratio was 3.5 times.

[0140] <Production Example 5> A rolled film was obtained by the same operation as in Production Example 3 (first roll rolling). The rolling ratio at this time was 8.7 times. Next, this rolled film was cut into a piece of 35 mm (first roll rotation direction) x 35 mm (width direction), and the rolling direction was rotated by 90° (i.e., so that the width direction became the roll rotation direction), followed by a second roll rolling under the same conditions as in Production Example 3. In this way, polyethylene film 5 of Production Example 5 was obtained. The obtained polyethylene film 5 had a size of 35 mm (first roll rotation direction) x 39 mm (width direction) and a film thickness of 18 μm. The rolling ratio was 1.1 times.

[0141] <Production Example 6> The polyethylene sheet X obtained above was cut into a size of 10 mm x 10 mm. Next, the cut polyethylene sheet X was placed on a 20 mm x 20 mm, 2 mm thick stainless steel plate, and another 20 mm x 20 mm, 2 mm thick stainless steel plate was placed on top of that. The entire assembly was placed between the upper and lower press plates of a bench press (manufactured by AS ONE Corporation) heated to 100°C, and a pressure of 297 MPa (cylinder pressure: 50 MPa) was applied to the upper and lower press plates for 1 minute. After unloading, the press-rolled film was removed. In this manner, a polyethylene film 6 of Production Example 6 was obtained. The obtained polyethylene film 6 measured 14 mm (longitudinal direction) x 14 mm (transverse direction) and had a thickness of 53 μm. The rolling ratio was 1.4 times (longitudinal direction) x 1.4 times (transverse direction).

[0142] <Production Example 7> The polyethylene sheet X obtained above was cut into a size of 10 mm x 10 mm. Next, the cut polyethylene sheet X was introduced between a pair of rolls provided in a rolling mill and rolled under conditions of a roll surface temperature of 100°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm to obtain a rolled film [Step C]. The rolling ratio was 7.0 times. The obtained rolled film had a melting point of 145°C. Next, the rolled film was stretched using a Tensilon universal testing machine [model number: RTC-1325A, manufactured by A&D Manufacturing Co., Ltd.]. Specifically, the rolled film was cut into a size of 30 mm x 3 mm, and both ends of the rolled film were fixed to graph paper using an adhesive for difficult-to-bond materials (product name: Cemedine PPX, manufactured by Cemedine Co., Ltd.) so that the stretched portion was 10 mm. Further adhesive was placed on both ends of the rolled film, and the graph side of another graph paper was placed on top of that, sandwiching the rolled film. The rolled film was tensile-stretched at 100°C at a stretching rate of 10 mm / min and then cooled to room temperature (i.e., 25°C) to obtain polyethylene film 7 of Production Example 7 [Step D]. The obtained polyethylene film 7 measured 33 mm (in the tensile stretching direction) x 1.34 mm (in the width direction) and had a film thickness of 9 μm. The tensile stretching ratio was 3.3 times. Therefore, the total stretching ratio (= rolling ratio: 7.0 times x tensile stretching ratio: 3.3 times) was 23.1 times.

[0143] <Production Example 8> A rolled film was obtained by performing the same operation as in step C in Production Example 7. Next, the rolled film was stretched using a Tensilon universal testing machine (model number: RTC-1325A, manufactured by A&D Manufacturing Co., Ltd.). Specifically, the rolled film was cut into a size of 30 mm x 3 mm, and both ends of the rolled film were fixed to graph paper using an adhesive for difficult-to-bond materials (product name: Cemedine PPX, manufactured by Cemedine Co., Ltd.) so that the stretched portion was 10 mm. Further, adhesive was placed on both ends of the rolled film, and the graph side of another graph paper was placed on top of that to sandwich the rolled film. The rolled film was tensile-stretched at 130°C at a stretching rate of 10 mm / min and then cooled to room temperature (i.e., 25°C), yielding polyethylene film 8 of Production Example 8 [Step D]. The resulting polyethylene film 8 had a size of 48 mm (stretching direction) × 1.42 mm (width direction) and a thickness of 10 μm. The stretching ratio was 4.8 times. Therefore, the total stretching ratio (= rolling ratio: 7.0 times × stretching ratio: 4.8 times) was 33.6 times.

[0144] <Production Example 9> A rolled film was obtained by performing the same operation as in step C in Production Example 7. Next, the rolled film was stretched using a Tensilon universal testing machine (model number: RTC-1325A, manufactured by A&D Manufacturing Co., Ltd.). Specifically, the rolled film was cut into a size of 30 mm x 3 mm, and both ends of the rolled film were fixed to graph paper using an adhesive for difficult-to-bond materials (product name: Cemedine PPX, manufactured by Cemedine Co., Ltd.) so that the stretched portion was 10 mm. Further, adhesive was placed on both ends of the rolled film, and the graph side of another graph paper was placed on top of that, sandwiching the rolled film. The rolled film was tensile-stretched at 140°C at a stretching rate of 10 mm / min and then cooled to room temperature (i.e., 25°C), yielding polyethylene film 9 of Production Example 9 [Step D]. The obtained polyethylene film 9 had a size of 79 mm (stretching direction) × 1.05 mm (width direction) and a thickness of 6 μm. The tensile stretching ratio was 7.9 times. Therefore, the total stretching ratio (= rolling ratio: 7.0 times × tensile stretching ratio: 7.9 times) was 55.3 times.

[0145] <Production Example 10> A rolled film was obtained by performing the same operation as in step C in Production Example 7. Next, the rolled film was stretched using a Tensilon universal testing machine (model number: RTC-1325A, manufactured by A&D Manufacturing Co., Ltd.). Specifically, the rolled film was cut into a size of 10 mm x 3 mm, and both ends of the rolled film were fixed to graph paper using an adhesive for difficult-to-bond materials (product name: Cemedine PPX, manufactured by Cemedine Co., Ltd.) so that the stretched portion was 10 mm. Further, adhesive was placed on both ends of the rolled film, and the graph side of another graph paper was placed on top of that, sandwiching the rolled film. The rolled film was tensile-stretched at 145°C at a stretching rate of 10 mm / min and then cooled to room temperature (i.e., 25°C), yielding polyethylene film 10 of Production Example 10 [Step D]. The resulting polyethylene film 10 had a size of 42 mm (stretching direction) × 1.42 mm (width direction) and a thickness of 10 μm. The tensile stretching ratio was 4.2 times. Therefore, the total stretching ratio (= rolling ratio: 7.0 times × tensile stretching ratio: 4.2 times) was 29.4 times.

[0146] <Production Example 11> The polyethylene sheet X obtained above was cut into a size of 10 mm x 10 mm. Next, two of the cut polyethylene sheets X were stacked to form a laminate, which was then introduced between a pair of rolls provided in a rolling mill and roll-rolled under conditions of a roll surface temperature of 25°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm, thereby obtaining a polyethylene film 11 of Production Example 11. The obtained polyethylene film 11 had a size of 50 mm x 10 mm and a film thickness of 47 μm. The rolling ratio was 5.0.

[0147] <Production Example 12> The polyethylene sheet X obtained above was cut into a size of 10 mm x 10 mm. Next, two of the cut polyethylene sheets X were stacked to form a laminate, which was then introduced between a pair of rolls provided in a rolling mill and roll-rolled under conditions of a roll surface temperature of 100°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm, thereby obtaining a polyethylene film 12 of Production Example 12. The obtained polyethylene film 12 had a size of 100 mm x 10 mm and a film thickness of 20 μm. The rolling ratio was 10 times.

[0148] <Production Example 13> The polyethylene sheet X obtained above was cut into a size of 10 mm x 10 mm. Next, two of the cut polyethylene sheets X were stacked to form a laminate, which was then introduced between a pair of rolls provided in a rolling mill and roll-rolled under conditions of a roll surface temperature of 3°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm, thereby obtaining a polyethylene film 13 of Production Example 13. The obtained polyethylene film 13 had a size of 50 mm x 10 mm and a film thickness of 48 μm. The rolling ratio was 5.0.

[0149] <Production Example 14> The same operation as step C in Production Example 7 was performed twice separately to obtain two rolled films. The rolling ratio was 7.0 times. The rolled film obtained above was cut into a size of 30 mm (roll rotation direction) x 10 mm (width). Next, two of the cut rolled films were stacked to form a laminate, which was then introduced between a pair of rolls provided in a rolling mill and roll-rolled under conditions of a roll surface temperature of 100°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm, thereby obtaining a polyethylene film 14 of Production Example 14. The obtained polyethylene film 14 had a size of 36 mm x 10 mm and a film thickness of 32 μm. The rolling ratio was 1.2 times.

[0150] <Production Example 15> The polyethylene sheet X obtained above was cut into a size of 10 mm x 10 mm. Next, the cut polyethylene sheet X was placed on a 20 mm x 20 mm, 2 mm thick stainless steel plate, and another 20 mm x 20 mm, 2 mm thick stainless steel plate was placed on top of that. The entire assembly was placed between the upper and lower press plates of a bench press (manufactured by AS ONE Corporation) at room temperature (25°C). A pressure of 297 MPa (cylinder pressure: 50 MPa) was applied to the upper and lower press plates for 1 minute, and after unloading, the press-rolled film was removed. In this manner, a polyethylene film 15 of Production Example 15 was obtained. The obtained polyethylene film 15 measured 12 mm (longitudinal direction) x 12 mm (transverse direction) and had a thickness of 191 μm. The rolling ratio was 1.2 times (longitudinal direction) x 1.2 times (transverse direction).

[0151] <Production Example 16> The polyethylene sheet X obtained above was cut into a size of 10 mm x 10 mm. Next, the cut polyethylene sheet X was placed on a 20 mm x 20 mm, 2 mm thick stainless steel plate, and another 20 mm x 20 mm, 2 mm thick stainless steel plate was placed on top of that. The entire assembly was placed between the upper and lower press plates of a bench press (manufactured by AS ONE Corporation) heated to 100°C. A pressure of 297 MPa (cylinder pressure: 50 MPa) was applied to the upper and lower press plates for 1 minute, and after unloading, the press-rolled film was removed. In this manner, a polyethylene film 16 of Production Example 16 was obtained. The obtained polyethylene film 16 measured 19 mm (longitudinal direction) x 19 mm (transverse direction) and had a thickness of 122 μm. The rolling ratio was 1.9 (longitudinal direction) x 1.9 (transverse direction).

[0152] <Production Example 17> The polyethylene sheet Y obtained above was cut into a size of 10 mm x 10 mm. Furthermore, the polyethylene sheet X obtained in Production Example 1 was cut into a size of 10 mm x 10 mm. Next, two cut-out polyethylene sheets X and Y were stacked to form a laminate, which was then introduced between a pair of rolls provided in a rolling mill and roll-rolled under conditions of a roll surface temperature of 100°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm, to obtain a polyethylene film 17 of Production Example 17. The obtained polyethylene film 17 had a size of 85 mm x 10 mm and a film thickness of 28 μm. The rolling ratio was 8.5 times.

[0153] <Production Example 18> The ethylene-1-hexene copolymer sheet Z obtained above was cut into a size of 10 mm x 10 mm. The polyethylene sheet X obtained in Production Example 1 was also cut into a size of 10 mm x 10 mm. Next, two cut-out polyethylene sheets X and ethylene-1-hexene copolymer sheets Z were stacked to form a laminate, which was then introduced between a pair of rolls provided in a rolling mill and roll-rolled under conditions of a roll surface temperature of 25°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm, to obtain a polyethylene / ethylene-1-hexene copolymer laminate film 1 of Production Example 18. The resulting polyethylene / ethylene-1-hexene copolymer laminate film 1 had a size of 50 mm x 10 mm and a film thickness of 50 μm. The rolling ratio was 5.0.

[0154] Production Example 19 The ethylene-1-hexene copolymer sheet Z obtained above was cut into a size of 10 mm x 10 mm. The polyethylene sheet X obtained in Production Example 1 was also cut into a size of 10 mm x 10 mm. Next, two cut-out polyethylene sheets X and ethylene-1-hexene copolymer sheets Z were stacked to form a laminate, which was then introduced between a pair of rolls provided in a rolling mill and roll-rolled under conditions of a roll surface temperature of 60°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm, to obtain a polyethylene / ethylene-1-hexene copolymer laminate film 2 of Production Example 19. The resulting polyethylene / ethylene-1-hexene copolymer laminate film 2 had a size of 60 mm x 10 mm and a film thickness of 31 μm. The rolling ratio was 6.0.

[0155] <Production Example 20> The ethylene / 1-hexene copolymer sheet Z obtained above was cut into a size of 10 mm x 10 mm. Next, two of the cut ethylene / 1-hexene copolymer sheets Z were stacked to form a laminate, which was then introduced between a pair of rolls provided in a rolling mill and roll-rolled under conditions of a roll surface temperature of 25°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm, to obtain an ethylene / 1-hexene copolymer film 3 of Production Example 20. The obtained ethylene / 1-hexene copolymer film 3 had a size of 50 mm x 10 mm and a film thickness of 58 μm. The rolling ratio was 5.0.

[0156] <Production Example 21> The ethylene / 1-hexene copolymer sheet Z obtained above was cut into a size of 10 mm x 10 mm. Next, two of the cut ethylene / 1-hexene copolymer sheets Z were stacked to form a laminate, which was then introduced between a pair of rolls provided in a rolling mill and roll-rolled under conditions of a roll surface temperature of 60°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.1 mm, to obtain an ethylene / 1-hexene copolymer film 4 of Production Example 21. The obtained ethylene / 1-hexene copolymer film 4 had a size of 60 mm x 10 mm and a film thickness of 34 μm. The rolling ratio was 6.0.

[0157] Comparative Example 1: A 125 μm thick release polyimide film and a 150 mm diameter x 2 mm thick disc-shaped stainless steel plate (1A) with a rectangular window of 100 mm x 100 mm were placed in that order on the disc-shaped stainless steel plate (1A). Next, approximately 3.0 g of powdered ultra-high molecular weight polyethylene raw material (trade name: Hizex Million 340M, viscosity average molecular weight: 3.3 million, average particle size: 150 μm, manufactured by Mitsui Chemicals, Inc.) was placed in the rectangular window of the disc-shaped stainless steel plate (2). A 125 μm thick release polyimide film and a 150 mm diameter x 2 mm thick disc-shaped stainless steel plate (1B) were placed in that order on the disc-shaped stainless steel plate (1A). The entire assembly was placed between the upper and lower press plates of a bench press (manufactured by Tester Sangyo Co., Ltd.) at room temperature (25°C), and the upper and lower press plates were spaced as close together as possible to avoid stress. The temperature was maintained at 200°C for 5 minutes, and then the heater was turned off and the film was slowly cooled to room temperature (25°C) under reduced pressure while pressed at a pressure of 4.5 MPa (cylinder pressure 60 MPa). The resulting film was then removed. In this manner, a melt-compression molded film made of ultra-high molecular weight polyethylene (also referred to simply as "melt-compression molded film") of Comparative Production Example 1 was obtained. The film thickness of the resulting melt-compression molded film was 0.305 mm.

[0158] - Confirmation of Adhesion of Melt Compression Molded Film - The melt compression molded film obtained above was cut into a size of 10 mm x 10 mm. Next, two of the cut melt compression molded films were stacked to form a laminate, which was then introduced between a pair of rolls equipped in a rolling mill and roll-rolled under conditions of a roll surface temperature of 100°C, a roll rotation speed of 1 rpm, and a roll separation distance of 0.3 mm. However, the two melt compression molded films peeled off and could not be bonded. As described above, it was confirmed that melt compression molded films made of ultra-high molecular weight polyethylene could not be integrated even when laminated and rolled.

[0159] [Evaluation and Results] 1. Tear Strength The tear strength was measured for polyethylene sheet X, polyethylene film 1, polyethylene film 2, polyethylene film 3, polyethylene film 5, and the melt-compression molded film. The specific method is described below. Polyethylene sheet X, polyethylene film 1, polyethylene film 2, polyethylene film 3, polyethylene film 5, and the melt-compression molded film were each cut into a size of 35 mm (length) x 35 mm (width) to prepare test specimens. Polyethylene film 1, polyethylene film 2, polyethylene film 3, and the melt-compression molded film were cut so that the roll rotation direction was the longitudinal direction of the test specimen. A 15 mm long incision was made in the center of the longitudinal direction of the test specimen, perpendicular to the roll rotation direction. A Tensilon universal testing machine was used as the measuring device. The two ends of the separated test piece were gripped with upper and lower chucks, respectively, and pulled in the vertical direction (perpendicular to the roll rotation direction) at a speed of 200 mm / min in an ambient temperature of 25°C. The maximum stress when the remaining 20 mm, which had not been cut, was torn was recorded. The value obtained by dividing this maximum stress by the thickness of the test piece was taken as the tear strength. For polyethylene film 5 that had been rolled multiple times, a cut was made perpendicular to the first roll rotation direction, and the above tear test was performed.

[0160] As a result, the tear strength was 31.3 N / mm for polyethylene sheet X, 31.1 N / mm for polyethylene film 1, 37.2 N / mm for polyethylene film 2, 27.4 N / mm for polyethylene film 3, 46.0 N / mm for polyethylene film 5, and 39.3 N / mm for the melt-compression molded film.

[0161] 2. Tensile Breaking Strength The tensile breaking strength of polyethylene film 3, polyethylene film 7, polyethylene film 8, polyethylene film 9, and polyethylene film 10 was measured. The specific method is described below. Polyethylene film 3 was cut into a size of 30 mm (length) x 3 mm (width) to prepare a test piece. On the other hand, polyethylene film 7, polyethylene film 8, polyethylene film 9, and polyethylene film 10 were each cut into a length of 30 mm, and the width was the same as that of the respective polyethylene films. A Tensilon universal testing machine (model number: RTC-1325A) manufactured by A&D Manufacturing Co., Ltd. was used as the measuring device, and tensile tests were performed in an ambient temperature of 25°C at a stretching rate of 10 mm / min. Both ends of the test piece were fixed on graph paper using Cemedine (registered trademark) PPX so that the length of the test portion (initial length) was 10 mm. Cemedine (registered trademark) PPX was then placed on both ends of the test piece, and the graph side of another graph paper was placed on top of that to sandwich the test piece. The test piece was pulled in the lengthwise direction, and the maximum stress on the recorded stress chart was divided by the cross-sectional area of ​​the test piece to determine the tensile breaking strength. In polyethylene example film 3, the test piece was cut so that the roll rotation direction was the lengthwise direction of the test piece. In polyethylene film 7, polyethylene film 8, polyethylene film 9, and polyethylene film 10, the test piece was cut so that the tensile stretching direction was the lengthwise direction of the test piece. The cross-sectional area of ​​the test piece was calculated using the following formula: "Cross-sectional area of ​​test piece (mm ２ ) = "Width of test piece (mm)" x "Thickness of test piece (mm)"

[0162] As a result, the tensile breaking strength was 96 MPa for polyethylene film 3, 474 MPa for polyethylene film 7, 465 MPa for polyethylene film 8, 904 MPa for polyethylene film 9, and 703 MPa for polyethylene film 10.

[0163] 3. Transparency The transparency of polyethylene film 1, polyethylene film 2, polyethylene film 3, polyethylene film 4, polyethylene film 5, polyethylene film 6, polyethylene film 11, polyethylene film 12, polyethylene film 13, polyethylene film 14, polyethylene film 17, polyethylene / ethylene-1-hexene copolymer laminate film 1, polyethylene / ethylene-1-hexene copolymer laminate film 2, polyethylene / ethylene-1-hexene copolymer laminate film 3, polyethylene / ethylene-1-hexene copolymer laminate film 4, and the melt-compression molded film was evaluated. The transparency was evaluated based on the haze value measured by the following method. The haze value was measured using a haze meter (model NDH800) manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS K 7361:1997. The haze value is measured in the visible light region (360 to 750 nm). A smaller haze value indicates higher transparency.

[0164] As a result, the haze values ​​were 21.11% for polyethylene film 1, 7.51% for polyethylene film 2, 2.62% for polyethylene film 3, 16.99% for polyethylene film 4, 21.96% for polyethylene film 5, 14.12% for polyethylene film 6, 22.56% for polyethylene film 11, 4.37% for polyethylene film 12, and 21.57% for polyethylene film 13. The polyethylene film 14 was 12.05%, the polyethylene film 17 was 3.55%, the polyethylene / ethylene-1-hexene copolymer laminate film 1 was 23.09%, the polyethylene / ethylene-1-hexene copolymer laminate film 2 was 5.56%, the polyethylene / ethylene-1-hexene copolymer laminate film 3 was 20.16%, the polyethylene / ethylene-1-hexene copolymer laminate film 4 was 9.32%, and the melt compression molded film was 40.44%.

[0165] 4. Gas Barrier Properties The gas barrier properties of the polyethylene sheet X, polyethylene film 1, and melt-compression molded film were evaluated. The gas barrier properties were evaluated based on the nitrogen permeability coefficient (p) determined by the following method. The polyethylene sheet, polyethylene film 1, and melt-compression molded film were each cut into a circular shape with a diameter of 30 mm to prepare a test specimen. Next, in a 25°C environment, the circular test specimen was placed in the measurement cell of a membrane diffusion measurement device (model number: K-315N-01, manufactured by Tsukubarika Seiki Co., Ltd.) connected to a data logger (model number: GL20) manufactured by Graphtec Corporation. Nitrogen gas was then introduced into the high-pressure gas reservoir, and the low-pressure side of the cell was evacuated. The high-pressure side valve of the cell was opened to introduce nitrogen gas, and gas permeation measurement was initiated. The time-dependent change in voltage was recorded, and the nitrogen permeability coefficient was calculated according to the following equations (1) and (2) [low-pressure side voltage and high-pressure side voltage (1 V = 1.6 KPa)]. The smaller the nitrogen permeability coefficient, the higher the gas barrier property.

[0166] Q = [V / (R x T x P x A)] x (dp / dt) Formula (1) p = Q x L Formula (2) Q: gas permeability [mol / (m ２ s Pa)] p: gas permeability coefficient [mol m / (m ２ s Pa)] V: Cell low pressure side volume [L] A: Permeation area [m ２ ](π=3.14) T: Test temperature [℃] P: Supply gas differential pressure [Pa] dp / dt: Change in pressure (p) on the low pressure side per unit time (t) [Pa / s] L: Thickness of test piece [m]

[0167] As a result, the nitrogen permeability coefficient of the polyethylene sheet X was 4.02 × 10 －１２ mol m / (m ２ s Pa), and the polyethylene film 1 is 8.45 × 10 －１４ mol m / (m ２ s Pa), and the melt compression molded film has a viscosity of 5.27 × 10 －１５ mol m / (m ２It was confirmed that by rolling a polyethylene sheet, a polyethylene film exhibiting gas barrier properties similar to those of a melt compression molded film can be obtained.

[0168] 5. Relative Dielectric Constant The relative dielectric constants of Polyethylene Film 1, Polyethylene Film 3, Polyethylene Film 12, and the melt-compression molded film were measured. The relative dielectric constants were determined by the following measurement method using an impedance analyzer (model number: E4991B) manufactured by Keysight Technologies and a dielectric constant test fixture (model number: 16453A) manufactured by Keysight Technologies. Each of the above films was sandwiched between circular electrodes with a diameter of 6 mm, and the measurement was performed by RF voltage-current measurement (RF-IV method) under measurement conditions of a temperature of 23±2°C, a humidity of 50±10%, a test frequency of 1 MHz to 1 GHz, and a test voltage of 0.5 V.

[0169] As a result, the dielectric constants of polyethylene film 1 were 2.31 at 1 MHz, 2.30 at 10 MHz, 2.28 at 100 MHz, and 2.26 at 1 GHz. For polyethylene film 3, the dielectric constants were 1.99 at 1 MHz, 1.98 at 10 MHz, 1.98 at 100 MHz, and 1.95 at 1 GHz. For polyethylene film 12, the dielectric constants were 2.12 at 1 MHz, 2.12 at 10 MHz, 2.12 at 100 MHz, and 2.10 at 1 GHz. For the melt-compression molded film of Comparative Production Example 1, the dielectric constants were 2.50 at 1 MHz, 2.50 at 10 MHz, 2.50 at 100 MHz, and 2.51 at 1 GHz. From the above, it was confirmed that the polyethylene film of the present disclosure has a low relative dielectric constant and can be used as insulating tape, insulating sheet, insulating protective outer layer for electric wire coating, etc.

[0170] 6. Adhesion For polyethylene film 11, polyethylene film 12, polyethylene film 13, polyethylene film 14, polyethylene film 15, polyethylene film 16, polyethylene film 17, polyethylene / ethylene-1-hexene copolymer laminate film 1, polyethylene / ethylene-1-hexene copolymer laminate film 2, polyethylene / ethylene-1-hexene copolymer laminate film 3, and polyethylene / ethylene-1-hexene copolymer laminate film 4, the adhesion between the sheets was evaluated. The polyethylene film 11, the polyethylene film 12, the polyethylene film 13, the polyethylene film 17, the polyethylene / ethylene-1-hexene copolymer laminate film 1, the polyethylene / ethylene-1-hexene copolymer laminate film 2, the polyethylene / ethylene-1-hexene copolymer laminate film 3, and the polyethylene / ethylene-1-hexene copolymer laminate film 4 were tested by the method of Evaluation Test 1 described below, the polyethylene film 14 was tested by the method of Evaluation Test 2 described below, and the polyethylene films 15 and 16 were tested by the method of Evaluation Test 3 described below.

[0171] (1) Evaluation Test 1 A laminate of two polyethylene sheets was prepared in the same manner as in each film production example, except that the polyethylene sheet X before rolling was cut to a size of 50 mm (length) x 10 mm (width), and the rolling was stopped midway to keep the edge 10 mm of the sheet unrolled. This prepared laminate was used as a test piece, and the two edge 10 mm of the sheet were fixed with the upper and lower chucks of a Tensilon universal testing machine (model number: RTC-1325A) manufactured by A&D Manufacturing Co., Ltd., and peeled by pulling each in a 180° direction. One of the two laminated polyethylene sheets was peeled 180° in the length direction of the test piece at an ambient temperature of 25°C and a peel rate of 10 mm / min.

[0172] (2) Evaluation Test 2 In the adhesion test of polyethylene film 14, two rolled films obtained by rolling once were cut into a size of 30 mm (roll rotation direction) x 5 mm (width), stacked, and introduced between the rolls. At this time, the rolling was stopped midway to keep 10 mm of the edge of the sheet in an unrolled state. In this state, a laminate of two rolled polyethylene films was prepared in the same manner as in Production Example 14. This prepared laminate was used as a test piece, and 180° peeling was attempted in the same manner as above.

[0173] (3) Evaluation Test 3 In the adhesion test of the polyethylene film 15 and the polyethylene film 16, the polyethylene sheet X was cut into a size of 20 mm (length) × 5 mm (width) and two sheets were stacked together, and only half of the area (10 mm × 5 mm) of the stack was press-bonded to keep 10 mm of the sheet unpressed. In this state, laminates of two polyethylene sheets X were prepared in the same manner as in Production Examples 15 and 16. These prepared laminates were used as test pieces, and 180° peeling was attempted in the same manner as above.

[0174] As a result, it was confirmed that in polyethylene film 11, polyethylene film 12, polyethylene film 13, polyethylene film 14, polyethylene film 15, polyethylene film 16, polyethylene film 17, polyethylene / ethylene-1-hexene copolymer laminate film 1, polyethylene / ethylene-1-hexene copolymer laminate film 2, polyethylene / ethylene-1-hexene copolymer laminate film 3, and polyethylene / ethylene-1-hexene copolymer laminate film 4, no peeling occurred between the laminated sheets, i.e., between the polyethylene sheets, between the rolled films, between the polyethylene sheet and the ethylene-1-hexene copolymer sheet, or between the ethylene-1-hexene copolymer sheets, and that the two polyethylene sheets and / or rolled films were well bonded together to form a single unit.

[0175] The disclosure of Japanese Patent Application No. 2024-082160, filed on May 20, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. An ultra-high molecular weight polyethylene film containing 50% by mass or more of ultra-high molecular weight polyethylene with a weight average molecular weight of more than 500,000 and a molecular weight distribution index of 4 or less, as estimated from the molecular weight distribution curve of the polyethylene contained obtained by gel permeation chromatography measurement, and having a haze value of 30% or less and a nitrogen permeability coefficient of 1 x 10 －１２ mol m / (m ２ .s.Pa) or less and a film thickness of 5 μm or more.

2. The ultra-high molecular weight polyethylene film according to claim 1, having a tear strength of 5 N / mm or more.

3. An ultra-high molecular weight polyethylene film according to claim 1 or 2, having a tensile breaking strength of 10 MPa or more.

4. An ultra-high molecular weight polyethylene film according to claim 1 or 2, having a relative dielectric constant of 2.4 or less.

5. A method for producing a polyolefin film, comprising: step A: applying an organic solvent containing a metal catalyst to the inner wall surface of a container; step B: synthesizing a polyolefin on the inner wall surface of the container by introducing an olefin monomer into the inside of the container whose inner wall surface has been coated with the organic solvent containing the metal catalyst; and step C: rolling out a sheet of the polyolefin synthesized on the inner wall surface of the container.

6. The method for producing a polyolefin film according to claim 5, wherein in step C, a laminate formed by laminating a plurality of sheets of synthesized polyolefin on the inner wall surface of the container is rolled.

7. The method for producing a polyolefin film according to claim 5 or 6, wherein the surface temperature of the rolled body during rolling is −10° C. or higher and lower than the melting point of the sheet.

8. A method for producing a polyolefin film according to claim 5 or 6, further comprising step D of tensile stretching the rolled film obtained by rolling in step C.

9. The method for producing a polyolefin film according to claim 8, wherein in step D, the rolled film is stretched at a temperature of 0°C or higher and lower than the melting point of the rolled film.

10. The method for producing a polyolefin film according to claim 8, wherein the tensile stretching is uniaxial stretching.