Stretched film made of ultrahigh-molecular-weight polyethylene and method for producing stretched film made of polyolefin

Abstract

Provided are: a stretched film made of ultrahigh-molecular-weight polyethylene, the stretched film including ultrahigh-molecular-weight polyethylene having a weight-average molecular weight, as estimated from a molecular-weight distribution curve of the contained polyethylenes obtained by gel permeation chromatography, of 500,000 or higher in an amount of 90 mass% or larger with respect to the whole mass of the stretched film made of ultrahigh-molecular-weight polyethylene, and having a tensile rupture strength of 300 MPa or higher and an elongation at rupture of 7% or higher; and a method for producing a stretched film made of a polyolefin.

Description

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

[0001] The present disclosure relates to a method for producing an oriented ultra-high molecular weight polyethylene film and an oriented polyolefin film.

[0002] Conventionally, methods for synthesizing polyolefins by polymerizing olefin monomers include the slurry method, the gas-phase method, and the solution method (see, for example, "Polyethylene Technology Reader," edited by Matsuura Kazuo and Mikami Naotaka, published by the Industrial Research Institute, 2001). The slurry method is a method of polymerizing olefins by blowing a monomer gas into a solvent containing a catalyst while stirring the solvent, resulting in the precipitation of polyolefins in the solvent. The slurry method typically produces polyolefins as powder. The gas-phase method is a method of polymerizing olefins by introducing catalyst particles into a polymerization vessel containing monomer gas, resulting in the formation of polyolefins around the catalyst particles. The gas-phase method, like the slurry method, produces powdery polyolefins. The solution method is a method of polymerizing olefins by reacting olefins at high temperatures using a solvent containing a catalyst, resulting in the olefin polymerization proceeding with the polyolefin dissolved in the solvent.

[0003] In recent years, oriented films made of ultra-high molecular weight polyethylene have been developed for a variety of applications. Ultra-high molecular weight polyethylene, the raw material for oriented films made of ultra-high molecular weight polyethylene, is usually synthesized using the aforementioned slurry method. For example, the solution method has the limitation that it is difficult to increase the molecular weight of polyethylene because the viscosity of the solution increases when polyethylene is dissolved in a solvent. In contrast, the slurry method is free from such limitations and is effective in that the molecular weight of polyethylene can be increased by extending the reaction time.

[0004] Generally, stretched films of ultra-high molecular weight polyethylene have been produced by a method that includes at least a step of synthesizing powdered ultra-high molecular weight polyethylene by a slurry method, and a step of forming the synthesized powdered ultra-high molecular weight polyethylene into a sheet and then stretching the sheet. Examples of such methods include the "gel film stretching method" (see P. Smith, PJ Lemstra, Colloid & Polymer Science, 1980, 258, 891-894), in which a polymer powder is dissolved in a solvent at a concentration of about 1% by mass, the solvent is evaporated by a casting method to form a film, and the resulting sheet-like film is stretched below the melting point; the "single crystal mat stretching method" (see T. Kanamoto, A. Tsuruta, K. Tanaka, M. Takeda, R.S. Porter, Macromolecules 1988, 21, 470-477), in which a polymer powder is compression-molded below the melting point to form a film, and the resulting sheet-like film is stretched below the melting point; and the "polymerization powder stretching method" (see T. Kanamoto, T. Ohama, K. Tanaka, and a "melt stretching method" in which a polymer powder is compression-molded at or above its melting point to form a film, and the resulting sheet-like film is stretched at or above its melting point (see M. Nakae, H. Uehara, T. Kanamoto, A.E. Zachariades, R.S. Porter, Macromolecules 2000, 33, 2632-2641).

[0005] In contrast, a method for producing an ultra-high molecular weight polyethylene sheet with fewer steps by directly forming a film during the synthesis of ultra-high molecular weight polyethylene has also been reported (see, for example, "P. Smith, H. Chanzy, B. Rotzinger, Journal of Materials Science, 1987, 22, 523-531."). In the method described in "P. Smith, H. Chanzy, B. Rotzinger, Journal of Materials Science, 1987, 22, 523-531," a heptane solution of vanadium chloride (IV) as a metal catalyst is applied to glass to produce glass with vanadium chloride (III) crystals attached to the surface. Next, a heptane solution of triisobutylaluminum as a promoter is contacted with the surface of the produced glass, and ethylene gas is then sprayed onto the surface to form an ultra-high molecular weight polyethylene sheet on the glass surface.

[0006] However, "P. Smith, PJ Lemstra, Colloid & Polymer Science, 1980, 258, 891-894.", "T. Kanamoto, A. Tsuruta, K. Tanaka, M. Takeda, RS Porter, Macromolecules 1988, 21, 470-477.", "T. Kanamoto, T. Ohama, K. Tanaka, M. Takeda, RS Porter, Polymer 1987, 28, 1517-1520.'' and ``M. Nakae, H. Uehara, T. Kanamoto, AE Zachariades, RS Porter, Macromolecules 2000, 33, 2632-2641." can produce an ultra-high molecular weight polyethylene stretched film with high breaking strength, but it has the disadvantage of requiring a process of forming a raw sheet between the process of synthesizing the ultra-high molecular weight polyethylene raw material and the process of stretching the film, making the manufacturing process more complicated.

[0007] The sheet formed by the method described in "P. Smith, H. Chanzy, B. Rotzinger, Journal of Materials Science, 1987, 22, 523-531" can be stretched to obtain the following polymers: "P. Smith, PJ Lemstra, Colloid & Polymer Science, 1980, 258, 891-894"; "T. Kanamoto, A. Tsuruta, K. Tanaka, M. Takeda, R.S. Porter, Macromolecules, 1988, 21, 470-477"; "T. Kanamoto, T. Ohama, K. Tanaka, M. Takeda, R.S. Porter, Polymer, 1987, 28, 1517-1520"; and "M. Nakae, H. Uehara, T. Kanamoto, A.E. Zachariades, R.S. Porter, Macromolecules, 2000, 33, 167-170." This method can produce an ultra-high molecular weight polyethylene stretched film with high mechanical strength without undergoing the process of forming a raw sheet, which was essential in the method described in "J. Appl. Phys. Lett. 2632-2641." However, although the obtained ultra-high molecular weight polyethylene stretched film has excellent tensile strength at break, its breaking elongation is low at 3.5% to 4.5%.This breaking elongation value is similar to the breaking elongation values ​​of stretched ultra-high molecular weight polyethylene films obtained by the methods described in "P. Smith, P.J. Lemstra, Colloid & Polymer Science, 1980, 258, 891-894," "T. Kanamoto, A. Tsuruta, K. Tanaka, M. Takeda, R.S. Porter, Macromolecules, 1988, 21, 470-477," "T. Kanamoto, T. Ohama, K. Tanaka, M. Takeda, R.S. Porter, Polymer, 1987, 28, 1517-1520," and "M. Nakae, H. Uehara, T. Kanamoto, A.E. Zachariades, R.S. Porter, Macromolecules, 2000, 33, 2632-2641." Therefore, it cannot be said that the tenacity (so-called toughness) of the film is sufficient. When a film has a small breaking elongation, its toughness (also called "breaking energy"), which is defined by the area under the stress-strain curve, also becomes small. Therefore, for applications that require not only high strength but also the ability to absorb a large amount of energy before breaking, such as protective films used in precision instruments and packaging films used for food, a larger breaking elongation is preferable for the same tensile breaking strength. For these reasons, there is a demand for the development of new methods for producing stretched ultra-high molecular weight polyethylene films and stretched polyolefin films that can replace conventional methods.

[0008] The present disclosure has been made in consideration of the above circumstances. One embodiment of the present disclosure aims to provide a stretched ultra-high molecular weight polyethylene film that has high tensile strength at break and large elongation at break. Another embodiment of the present disclosure aims to provide a method for producing a stretched polyolefin film that can efficiently produce a stretched polyolefin film.

[0009] Specific means for solving the above problems include the following aspects. <1> A stretched ultra-high molecular weight polyethylene film, containing 90 mass% or more of ultra-high molecular weight polyethylene, based on the total mass of the stretched ultra-high molecular weight polyethylene, having a weight-average molecular weight of 500,000 or more estimated from a molecular weight distribution curve of the contained polyethylene obtained by gel permeation chromatography measurement, and having a tensile strength at break of 300 MPa or more and an elongation at break of 7% or more. <2> The stretched ultra-high molecular weight polyethylene film according to <1>, in which the molecular weight distribution index of the ultra-high molecular weight polyethylene is 5 or less. <3> The stretched ultra-high molecular weight polyethylene film according to <1> or <2>, having a tensile modulus of elasticity less than 35 times the tensile strength at break. <4> The stretched film made of ultra-high molecular weight polyethylene according to any one of <1> to <3>, which has a melting peak at 141°C or higher in measurement with a differential scanning calorimeter, and the area of ​​the melting peak accounts for 90% or more of the total area of ​​all melting peaks of the stretched film made of ultra-high molecular weight polyethylene.

[0010] <5> A method for producing a stretched 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 container whose inner wall surface has been coated with the organic solvent containing the metal catalyst; and Step C: stretching the polyolefin sheet synthesized on the inner wall surface of the container, wherein in Step A, the organic solvent containing the metal catalyst is applied to the inner wall surface of the container by moving the container. <6> A method for producing a stretched polyolefin film according to <5>, wherein in Step A, the organic solvent containing the metal catalyst is applied to the inner wall surface of the container by rotating the container. <7> The method for producing a stretched polyolefin film according to <5> or <6>, wherein the metal catalyst is 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. <8> The method for producing a stretched polyolefin film according to any one of <5> to <7>, wherein the organic solvent containing the metal catalyst further contains a co-catalyst. <9> The method for producing a stretched polyolefin film according to <8>, wherein the co-catalyst is 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. <10> The method for producing a stretched polyolefin film according to any one of <5> to <9>, wherein the step C is a step of multistage stretching the sheet, and includes a stage C1 of contacting the sheet with a heater and stretching the sheet by intermittently or continuously moving the contact portion between the sheet and the heater.<11> The method for producing a stretched polyolefin film according to <10>, wherein the temperature of the heater is 30°C or higher and lower than the melting point of the sheet. <12> The method for producing a stretched polyolefin film according to <10> or <11>, wherein the step C includes a step C2 in which the sheet stretched in step C1 is further stretched. <13> The method for producing a stretched polyolefin film according to <12>, wherein in step C2, the sheet stretched in step C1 is stretched at a temperature not higher than 30°C higher than the melting point of the sheet.

[0011] According to one embodiment of the present disclosure, there is provided a stretched ultra-high molecular weight polyethylene film having high tensile strength at break and large elongation at break. According to another embodiment of the present disclosure, there is provided a method for producing a stretched polyolefin film, which can efficiently produce a stretched polyolefin film.

[0012] 1 shows DSC curves of oriented polyethylene film 1 obtained in Production Example 1, oriented polyethylene film 2 obtained in Production Example 2, polyethylene sheet 3 obtained in Production Example 3, oriented polyethylene film 4 obtained in Production Example 4, oriented polyethylene film 5 obtained in Production Example 5, and oriented polyethylene film 6 obtained in Production Example 6. FIG. 2 shows WAXD images of oriented polyethylene film 1 obtained in Production Example 1, oriented polyethylene film 2 obtained in Production Example 2, and polyethylene sheet 3 obtained in Production Example 3. FIG. 3 is a graph showing the azimuthal angle profiles of oriented polyethylene film 1 obtained in Production Example 1 and oriented polyethylene film 2 obtained in Production Example 2.

[0013] The following provides a detailed description of the methods for producing an oriented ultra-high molecular weight polyethylene film and an oriented polyolefin film according to the present disclosure. 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.

[0014] 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.

[0015] 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 stretched film and a polyolefin stretched film, if multiple substances corresponding to each component are present in the film-forming coating liquid, the amount refers to the total amount of the multiple components present in the film-forming coating liquid, unless otherwise specified.

[0016] In the present disclosure, a combination of two or more preferred aspects is a more preferred aspect.

[0017] 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.

[0018] [Stretched Ultra-High Molecular Weight Polyethylene Film] The stretched ultra-high molecular weight polyethylene film according to the present disclosure contains 90 mass% or more of ultra-high molecular weight polyethylene, based on the total mass of the stretched ultra-high molecular weight polyethylene film, having a weight-average molecular weight (Mw) of 500,000 or more as estimated from a molecular weight distribution curve of the polyethylene contained obtained by gel permeation chromatography (GPC) measurement, and has a tensile breaking strength of 300 MPa or more and a breaking elongation of 7% or more. The stretched ultra-high molecular weight polyethylene film according to the present disclosure has a high tensile breaking strength and a large breaking elongation. Specifically, the stretched ultra-high molecular weight polyethylene film according to the present disclosure exhibits a high breaking elongation of 7% or more despite its high tensile breaking strength of 300 MPa or more.

[0019] The stretched ultra-high molecular weight polyethylene film according to the present disclosure contains ultra-high molecular weight polyethylene having a weight-average molecular weight (Mw) of 500,000 or more. The ultra-high molecular weight polyethylene having a weight-average molecular weight of 500,000 or more contained in the stretched ultra-high molecular weight polyethylene film according to the present disclosure may be one type or two or more types. The content of ultra-high molecular weight polyethylene having a weight-average molecular weight (Mw) of 500,000 or more in the stretched ultra-high molecular weight polyethylene film according to the present disclosure is 90% by mass or more, preferably 92% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more, relative to the total mass of the stretched ultra-high molecular weight polyethylene film, and may be, for example, 100% by mass.

[0020] In the stretched ultra-high molecular weight polyethylene film according to the present disclosure, the weight-average molecular weight (Mw) of the ultra-high molecular weight polyethylene contained in an amount of 90% by mass or more is 500,000 or more, and may be, for example, 800,000 or more, 1,000,000 or more, or 1,200,000 or more. In the stretched ultra-high molecular weight polyethylene film according to the present disclosure, the weight-average molecular weight (Mw) of the ultra-high molecular weight polyethylene contained in an amount of 90% by mass or more 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 an embodiment, the weight-average molecular weight (Mw) of the ultra-high molecular weight polyethylene contained in an amount of 90% by mass or more in the stretched ultra-high molecular weight polyethylene film according to the present disclosure may be 500,000 or more and 15,000,000 or less, 500,000 or more and 10,000,000 or less, 500,000 or more and 6,000,000 or less, or 500,000 or more and 3,000,000 or less.

[0021] In the stretched ultra-high molecular weight polyethylene film according to the present disclosure, the molecular weight distribution index of the ultra-high molecular weight polyethylene contained in an amount of 90% by mass or more is not particularly limited, and may be, for example, 1 to 20, 1 to 10, 1 to 7, or 1 to 5. 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). The closer the molecular weight distribution index value is to 1, the more uniform the molecular chain length of the ultra-high molecular weight polyethylene. 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 narrow. In general, the narrower the molecular weight distribution of polyolefins (including polyethylene), i.e., the smaller the molecular weight distribution index (Mw / Mn), the higher the breaking strength of the polyolefin film.

[0022] 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 polyethylene contained therein obtained by gel permeation chromatography (GPC) measurement. Specifically, the GPC measurement is performed under the following conditions:

[0023] -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: 160°C Sample concentration: 0.1 mg / mL to 1.0 mg / mL (solvent: 1,2,4-trichlorobenzene)

[0024] The stretched ultra-high molecular weight polyethylene film according to the present disclosure may contain, as necessary, components other than the ultra-high molecular weight polyethylene having a weight-average molecular weight of 500,000 or more (so-called other components) within the scope 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).

[0025] The stretched ultra-high molecular weight polyethylene film according to the present disclosure is characterized by high tensile breaking strength. The tensile breaking strength of the stretched ultra-high molecular weight polyethylene film according to the present disclosure is 300 MPa or more, preferably 500 MPa or more, more preferably 700 MPa or more, and even more preferably 1000 MPa or more. The upper limit of the tensile breaking strength of the stretched ultra-high molecular weight polyethylene film according to the present disclosure is not particularly limited, and may be, for example, 5000 MPa or less, 3000 MPa or less, 2000 MPa or less, or 1500 MPa or less. In one embodiment, the tensile breaking strength of the stretched ultra-high molecular weight polyethylene film according to the present disclosure may be 300 MPa or more and 5000 MPa or less, 300 MPa or more and 3000 MPa or more, 500 MPa or more and 2000 MPa or less, or 700 MPa or more and 1500 MPa or less. The stretched ultra-high molecular weight polyethylene film according to the present disclosure has a tensile breaking strength of 300 MPa or more, and can therefore be suitably applied to films used in various industries, such as protective films and packaging films (e.g., food packaging films).

[0026] The stretched ultra-high molecular weight polyethylene film according to the present disclosure is characterized by a large breaking elongation. The breaking elongation of the stretched ultra-high molecular weight polyethylene film according to the present disclosure is 7% or more, preferably 8% or more, more preferably 9% or more, and even more preferably 10% or more. The upper limit of the breaking elongation of the stretched ultra-high molecular weight polyethylene film according to the present disclosure is not particularly limited, and may be, for example, 30% or less, 25% or less, 20% or less, or 15% or less. In one embodiment, the breaking elongation of the stretched ultra-high molecular weight polyethylene film according to the present disclosure may be 7% or more and 30% or less, 7% or more and 25% or less, 7% or more and 20% or less, or 7% or more and 15% or less. Because the stretched ultra-high molecular weight polyethylene film according to the present disclosure has a breaking elongation of 7% or more, it can be preferably used for films that are required not only to have high strength but also to absorb a large amount of energy before breaking, such as protective films used in precision instruments and packaging films used for food.

[0027] In the present disclosure, the tensile breaking strength and breaking elongation of a stretched ultra-high molecular weight polyethylene film are determined by the following measurement method. A stretched ultra-high molecular weight polyethylene film is cut into a 30 mm (length) x 2 mm (width) test piece. A tensile test is performed on the test piece 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 piece are fixed to graph paper using double-sided tape so that the length of the tensile test portion (so-called initial length) is 10 mm. Further, double-sided tape is placed on both ends of the sample piece, and the graph side of another graph paper is placed on top of that to sandwich the sample piece. The test piece is stretched in the longitudinal direction, and the maximum stress on the recorded stress chart is divided by the cross-sectional area of ​​the test piece to determine the tensile breaking strength. The breaking elongation (unit: %) is determined by dividing the strain (unit: mm) at which the maximum stress is applied by the initial length of 10 mm. The cross-sectional area of ​​the test piece in this method is determined by setting the true density of polyethylene in the ultra-high molecular weight polyethylene stretched film to 1 g / cm ３The cross-sectional area of ​​the test specimen is calculated by dividing the mass of the test specimen by the length of the test specimen. Specifically, the cross-sectional area of ​​the test specimen is calculated using the following formula: ２ " = "mass of test piece (mg)" / "length of test piece (mm)" As the 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.

[0028] In the present disclosure, the tenacity (so-called toughness) of a stretched ultra-high molecular weight polyethylene film is defined by the area of ​​the stress chart obtained in the above-mentioned tensile test (so-called area under the stress-strain curve) (unit: MPa·%). The toughness of the stretched ultra-high molecular weight polyethylene film according to the present disclosure is, for example, preferably 500 MPa·% or more, more preferably 1,000 MPa·% or more, even more preferably 2,000 MPa·% or more, and particularly preferably 3,000 MPa·% or more. The upper limit of the toughness of the stretched ultra-high molecular weight polyethylene film according to the present disclosure is not particularly limited, and may be, for example, 500,000 MPa·% or less, 300,000 MPa·% or less, or 100,000 MPa·% or less. In an embodiment, the toughness of the stretched ultra-high molecular weight polyethylene film according to the present disclosure may be 500 MPa·% or more and 500,000 MPa·% or less, 1,000 MPa·% or more and 500,000 MPa·% or less, 5,000 MPa·% or more and 300,000 MPa·% or less, or 10,000 MPa·% or more and 100,000 MPa·% or less.

[0029] The tensile modulus of the stretched ultra-high molecular weight polyethylene film according to the present disclosure is preferably less than 35 times the tensile breaking strength, more preferably 30 times or less the tensile breaking strength, and even more preferably 25 times or less the tensile breaking strength. For example, the tensile modulus, which is an index of rigidity, of conventional ultra-high molecular weight polyethylene gel-stretched films, single-crystal matte-stretched films, polymer powder-stretched films, and melt-stretched films increases upon stretching, exhibiting values ​​of approximately 40 to 100 times the tensile breaking strength, whereas the tensile modulus of the stretched ultra-high molecular weight polyethylene film according to the present disclosure can exhibit a value of less than 35 times the tensile breaking strength. The lower limit of the ratio of the tensile modulus to the tensile breaking strength of the stretched ultra-high molecular weight polyethylene film according to the present disclosure is not particularly limited, and is, for example, 10 times or more. In one embodiment, the tensile modulus of the stretched ultra-high molecular weight polyethylene film according to the present disclosure may be 10 to less than 35 times, 10 to 30 times, or 10 to 25 times the tensile breaking strength. When applied to a protective film and / or packaging film, an oriented ultra-high molecular weight polyethylene film having a tensile modulus less than 35 times the tensile breaking strength retains flexibility that allows it to deform along the shape of the object to be protected and / or packaged, so that no gaps are formed between the film and these objects, thereby enabling the purpose of protection and / or packaging to be suitably achieved.

[0030] In the present disclosure, the tensile modulus of a stretched ultra-high molecular weight polyethylene film is determined by the following measurement method. A stretched ultra-high molecular weight polyethylene film is cut into a size of 30 mm (length) x 2 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 double-sided tape so that the length of the tensile test portion (i.e., the initial length) is 10 mm. Further, double-sided tape is placed on both ends of the specimen, and the graph side of another graph paper is placed on top of the tape to sandwich the specimen. The specimen is stretched in the longitudinal direction, and the tensile modulus is determined from the slope of the recorded stress chart up to a strain of 0.5%. Specifically, when the stress at 0% strain is set to 0 MPa and the stress chart up to 0.5% strain is a straight line, the tensile modulus corresponds to 200 times the stress (unit: MPa) at 0.5% strain. As the 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.

[0031] The stretched ultra-high molecular weight polyethylene film according to the present disclosure may have only one melting peak or may have two or more melting peaks. The number of melting peaks of the stretched ultra-high molecular weight polyethylene film according to the present disclosure can be confirmed from a differential scanning calorimetric curve (DSC curve) obtained by measurement using a differential scanning calorimeter.

[0032] The stretched ultra-high molecular weight polyethylene film according to the present disclosure preferably has a melting peak at 141°C or higher when measured with a differential scanning calorimeter, and the area of ​​the melting peak (the total area when there are two or more melting peaks) accounts for 90% or more of the total area of ​​all melting peaks possessed by the stretched ultra-high molecular weight polyethylene film. The fact that the stretched ultra-high molecular weight polyethylene film according to the present disclosure has a melting peak at 141°C or higher when measured with a differential scanning calorimeter means that the film contains extended chain crystals. The higher the ratio of the area of ​​the melting peak at 141°C or higher to the total area of ​​all melting peaks, the higher the proportion of extended chain crystals forming the stretched ultra-high molecular weight polyethylene film according to the present disclosure. The stretched ultra-high molecular weight polyethylene film according to the present disclosure preferably has a ratio of the area of ​​the melting peak at 141°C or higher to the total area of ​​all melting peaks possessed by the stretched ultra-high molecular weight polyethylene film of 95% or higher, more preferably 98% or higher, and may be, for example, 100%.

[0033] In the present disclosure, a "melting peak at 141°C or higher" refers to a melting peak whose peak temperature is 141°C or higher, and is defined as a "melting peak at 141°C or higher" even if the base of the peak extending to the low temperature side is 141°C or lower, as long as it is a single peak. On the other hand, a melting peak having a peak below 141°C (including a shoulder peak present at the shoulder of the main peak) is not included in the "melting peak at 141°C or higher."

[0034] In the present disclosure, the melting peak temperature and area of ​​a stretched ultra-high molecular weight polyethylene film are determined from the DSC curve obtained by measuring using a differential scanning calorimeter in a nitrogen atmosphere, heating from 30°C to 200°C at a heating rate of 10°C / min. The melting peak temperature is the temperature at the apex of the melting peak. The melting peak area is calculated by peak separation in the DSC profile. 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 an ultra-high molecular weight polyethylene 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 to this.

[0035] For peak separation of a DSC profile, the method described in "M. Nakae, H. Uehara, T. Kanamoto, A.E. Zachariades, R.S. Porter, Macromolecules 2000, 33, 2632-2641" can be suitably used. Specifically, Origin 8.1 (trade name) manufactured by LightStone Corporation is used as software, and two or three endothermic peaks are separated using a function system combining an extreme function and a Lorentz function.

[0036] The endothermic peak area of ​​the obtained DSC profile represents the heat of fusion (J / g). In the case of polyethylene, the heat of fusion of a completely crystalline polyethylene is known to be 290 J / g, and the ratio (%) obtained by dividing the measured heat of fusion by the heat of fusion of a completely crystalline polyethylene can be evaluated as the degree of crystallinity. The stretched ultra-high molecular weight polyethylene film according to the present disclosure has a high degree of crystallinity due to the inclusion of many melting peaks caused by extended chain crystals. It is known that the greater the content of extended chain crystals in an ultra-high molecular weight polyethylene stretched film, the greater the heat of fusion and the higher the degree of crystallinity. The crystallinity of the stretched ultra-high molecular weight polyethylene film according to the present disclosure is preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more.

[0037] The crystalline orientation degree of the stretched ultra-high molecular weight polyethylene film according to the present disclosure is preferably 99% or less, more preferably 98% or less, and even more preferably 97.5% or less. Stretched ultra-high molecular weight polyethylene films with a crystalline orientation degree of 99% or less have excellent flexibility and are suitable for use as protective films and packaging films. The lower limit of the crystalline orientation degree of the stretched ultra-high molecular weight polyethylene film according to the present disclosure is not particularly limited, and may be, for example, 50% or more, 70% or more, or 90% or more. The crystalline orientation degree of the stretched ultra-high molecular weight polyethylene film according to the present disclosure is estimated from the orthorhombic (110) reflection intensity of a diffraction image (so-called two-dimensional image) obtained by vertically incident X-rays on the sheet surface. The degree of crystal orientation is calculated from the full-width at half maximum (FWHM) of the peak in the azimuth angle profile obtained by scanning the orthorhombic (110) reflection of the diffraction pattern in the azimuth angle direction, according to the following formula. For details, please refer to the literature (Y. Ono, M. Kakiage, T. Yamanobe, Y. Yukawa, Y. Higuchi, H. Kamiya, K. Arai, H. Uehara, Polymer, 2011, Vol. 52, pp. 1172-1179). If the azimuth angle profile is flat and no peak is observed, the degree of crystal orientation is considered to be 0%. Crystalline orientation degree (%) = {(180° - FWHM [°]) / 180°} × 100 In an embodiment, the crystal orientation degree of the stretched ultra-high molecular weight polyethylene film according to the present disclosure may be 50% or more and 99% or less, 70% or more and 99% or less, 90% or more and 99% or less, 95% or more and 99% or less, or 97% or more and 98% or less.

[0038] The average thickness of the stretched ultra-high molecular weight polyethylene film according to the present disclosure is not particularly limited, and is preferably, for example, 0.1 μm to 200 μm.

[0039] In the present disclosure, the average film thickness of a stretched polyolefin film (including a stretched polyethylene film) is an average film thickness determined by the following measurement method. The average film thickness of a polyolefin sheet (including a polyethylene sheet) is also determined by the same measurement method. The arithmetic mean of film thicknesses measured at six randomly selected locations in the thickness direction of the stretched polyolefin film is determined, and the obtained value is taken as the average film thickness of the stretched polyolefin film. A thickness gauge is used to measure the film thickness of a stretched 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.

[0040] The stretched ultra-high molecular weight polyethylene film according to the present disclosure can be produced, for example, by the method for producing a stretched polyolefin film according to the present disclosure described below. The method for producing a stretched polyolefin film according to the present disclosure is one of the preferred methods for efficiently producing the stretched ultra-high molecular weight polyethylene film according to the present disclosure.

[0041] The weight-average molecular weight and molecular weight distribution of the polyethylene contained in the stretched ultra-high molecular weight polyethylene film according to the present disclosure can be controlled, for example, by selecting ethylene as the olefin monomer 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) in the method for producing a stretched polyolefin film according to the present disclosure described below. The tensile breaking strength, breaking elongation, and tensile modulus of the stretched ultra-high molecular weight polyethylene film according to the present disclosure can be controlled, for example, by adjusting the stretching conditions in step C1 (e.g., temperature of the heater, stretching ratio, and stretching speed) and the stretching conditions in step C2 (e.g., stretching temperature, stretching ratio, and stretching speed) in the method for producing a stretched polyolefin film according to the present disclosure described below. Specifically, the breaking strength can be increased by setting the stretching temperature in step C2 to a temperature (e.g., 140°C) just below the melting point (e.g., 141.6°C) of the stretched film obtained in step C1. On the other hand, if the stretching temperature in step C2 is set to a temperature (e.g., 130°C) somewhat lower than the melting point (e.g., 141.6°C) of the stretched film obtained in step C1, the breaking elongation can be increased. Also, if the stretching speed in step C2 is increased (e.g., to about 20 mm / min), the ratio of the breaking elongation to the tensile modulus can be reduced, and it tends to be easier to obtain a stretched film that is high in strength, flexibility, and toughness.

[0042] [Method for producing stretched polyolefin film] The method for producing a stretched polyolefin film according to the present disclosure (hereinafter also referred to as the "production method according to the present disclosure") comprises step A of applying an organic solvent containing a metal catalyst to the inner wall surface of a container, 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 step C of stretching the polyolefin sheet synthesized on the inner wall surface of the container, wherein in step A, the container is moved to apply the organic solvent containing the metal catalyst to the inner wall surface of the container. According to the production method according to the present disclosure, a stretched polyolefin film can be produced efficiently.

[0043] 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. The formed polyolefin film has a structure with minimal entanglement of molecular chains. Therefore, when the polyolefin sheet obtained in step B is stretched in step C, many "extended chain crystals" are formed, in which the polyolefin molecular chains are fully extended and crystallized. In a typical stretched film made of ultra-high molecular weight polyethylene, the more extended chain crystals formed, the higher the tensile strength at break, but conversely, the lower the elongation at break. In contrast, the stretched polyolefin film obtained by the production method according to the present disclosure has both high tensile strength at break and large elongation at break. As a result, the tensile modulus also tends to be low. For example, in ultra-high molecular weight polyethylene gel-stretched films, single crystal matte-stretched films, polymer powder-stretched films, and melt-stretched films, the tensile modulus, which is an indicator of rigidity, is about 40 to 100 times the tensile breaking strength, whereas in the polyolefin-stretched films obtained by the production method of the present disclosure, the tensile modulus is only about 20 times the tensile breaking strength.

[0044] The present inventors speculate that the reason for this is as follows. When the present inventors conducted a tensile test on an ultra-high molecular weight polyethylene stretched film obtained by the production method of the present disclosure, they observed that the stretched film did not break perpendicular to the tensile direction, but rather split and fibrillated parallel to the tensile direction. This suggests that the high breaking elongation may be due to delamination between extended chain crystals in the polyolefin stretched film (including the ultra-high molecular weight polyethylene stretched film) obtained by the production method of the present disclosure. Normally, when fibrillation occurs in a stretched film, the individual fibrils break apart, reducing the breaking strength of the stretched film. However, in the production method of the present disclosure, a polyolefin sheet with a narrow molecular weight distribution is obtained by steps A and B, and therefore a polyolefin stretched film with a highly uniform extended chain crystal structure is formed by step C. As a result, the stretched ultra-high molecular weight polyethylene film obtained by the production method of the present disclosure is thought to maintain high breaking strength while maintaining high breaking elongation due to the formation of a highly uniform extended chain crystal structure, which allows fibrils to break in a concentrated manner. On the other hand, the low tensile modulus of the stretched ultra-high molecular weight polyethylene film obtained by the production method of the present disclosure is presumably due to lower molecular orientation than that of stretched ultra-high molecular weight polyethylene films obtained by conventional gel film stretching, single crystal mat stretching, polymer powder stretching, and melt stretching methods, when compared at the same stretch ratio. It is generally known that the tensile modulus of a stretched polyolefin film correlates with molecular orientation. Conventional stretched ultra-high molecular weight polyethylene films are made from ultra-high molecular weight polyethylene synthesized with a Ziegler catalyst, which has a large molecular weight distribution index, and contain a large amount of low-molecular weight polyethylene components. Similar to the swelling solvent, these low-molecular weight polyethylene components promote molecular chain slippage of the high-molecular weight components. Therefore, when a large amount of low molecular weight polyethylene components is contained, the molecular chains of the ultra-high molecular weight polyethylene become highly oriented.For example, when the metal catalyst used in step A is a metallocene complex, the amount of low-molecular-weight polyethylene component contained in the synthesized polyolefin is reduced, and therefore, it is thought that the molecular orientation at the same draw ratio is reduced and the tensile modulus tends to remain at a value of about 20 times the tensile breaking strength.

[0045] For reference, examples of the tensile breaking strength, tensile modulus, and ratio of tensile breaking strength to tensile modulus of conventional ultra-high molecular weight polyethylene stretched films (gel stretched film, single crystal matte stretched film, polymer powder stretched film, and melt stretched film) are shown below. Gel-stretched film [film obtained by the gel film stretching method described in P. Smith, PJ Lemstra, Colloid & Polymer Science, 1980, 258, 891-894]: tensile breaking strength (3.0 GPa), tensile modulus (108 GPa), ratio of tensile modulus to tensile breaking strength (36 times); single-crystal matte-stretched film [film obtained by the single-crystal matte-stretching method described in T. Kanamoto, A. Tsuruta, K. Tanaka, M. Takeda, RS Porter, Macromolecules 1988, 21, 470-477]: tensile breaking strength (3.0 GPa), tensile modulus (220 GPa), ratio of tensile modulus to tensile breaking strength (73 times); polymer powder-stretched film [T. Kanamoto, T. Ohama, K. Tanaka, M. Takeda, RS Porter, Polymer 1987, 28, 1517-1520.]: tensile breaking strength (1.5 GPa), tensile modulus (80 GPa), ratio of tensile modulus to tensile breaking strength (53 times). Melt-stretched film [film obtained by the melt-stretching method described in M. Nakae, H. Uehara, T. Kanamoto, A.E. Zachariades, R.S. Porter, Macromolecules 2000, 33, 2632-2641.]: tensile breaking strength (0.95 GPa), tensile modulus (55 GPa), ratio of tensile modulus to tensile breaking strength (58 times).

[0046] <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."

[0047] The sheet-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 that the breaking strength of the finally obtained stretched polyolefin film tends to be higher.

[0048] 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.

[0049] 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.

[0050] The film-forming coating liquid may contain only one type of metal catalyst, or may contain two or more types.

[0051] 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.

[0052] 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.

[0053] The viscosity of the organic solvent is not particularly limited, but is preferably, for example, 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, the film-forming coating liquid tends to be more effectively applied to the inner wall surface of the container.

[0054] 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.

[0055] 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.

[0056] The film-forming coating liquid may contain only one type of organic solvent, or may contain two or more types of organic solvents.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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, a co-catalyst has a high viscosity itself, and therefore can also function as a so-called thickener. Therefore, when a 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, allowing the film-forming coating solution to be applied smoothly to the inner wall surface of a container, thereby enabling more efficient production of a polyolefin film. From this perspective, the co-catalyst is preferably a solid co-catalyst that easily increases the viscosity of the film-forming coating solution. An example of a solid co-catalyst is methylaluminoxane (MAO).

[0061] When the film-forming coating liquid further contains a co-catalyst, it may contain only one type of co-catalyst or may contain two or more types of co-catalysts.

[0062] 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.

[0063] 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).

[0064] The viscosity of the film-forming coating liquid is not particularly limited, but is preferably, for example, 0.1 mPa·s or more and 10,000 mPa·s or less, more preferably 0.4 mPa·s or more and 10,000 mPa·s or less, and even more preferably 0.4 mPa·s or more and 1,000 mPa·s or less. 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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. Improved wettability of the inner wall surface of the container with the coating liquid for film formation allows for better production of a polyolefin film.

[0071] 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.

[0072] 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 a container through the film-forming coating liquid, a method of immersing a container in the film-forming coating liquid, a method of supplying the film-forming coating liquid to a rotating container, or the like.

[0073] 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 as the rotation axis. 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.

[0074] 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.

[0075] 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.

[0076] <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%.

[0077] 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, and particularly preferably ethylene.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] <Step C> Step C is a step of stretching the polyolefin sheet synthesized on the inner wall surface of the container in step B. The sheet stretching in step C may be carried out in one stage or in two or more stages. The term "multistage" refers to a combination of multiple stages with different stretching conditions such as stretching temperature and stretching speed.

[0083] When the sheet is stretched in step C in one stage, step C may be, for example, a step of tensile stretching the polyolefin sheet synthesized in step B, from the viewpoint of forming a larger number of extended chain crystals and obtaining a polyolefin film with higher mechanical strength. Furthermore, when the sheet is stretched in step C in one stage, the stretching method is not particularly limited as long as it can form extended chain crystals, and roll stretching, press stretching, etc. can be used. The stretching method may be, for example, a roll stretching method such as a roll-to-roll method that utilizes the difference in peripheral speed between two rolls. Furthermore, when the sheet is stretched by tensile stretching, the 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 in that it can more efficiently form extended chain crystals and it is easier to align the molecular chain direction of the extended chain crystals.

[0084] In step C, for example, from the viewpoint of further increasing the proportion of extended chain crystals formed, it is preferable to tensile stretch the polyolefin sheet synthesized in step B while heating it to a temperature not higher than 30°C higher than the melting point of the sheet. The heating temperature of the sheet is, for example, more preferably not higher than 20°C higher than the melting point, even more preferably not higher than 10°C higher than the melting point, and particularly preferably not higher than the melting point. The lower limit of the heating temperature of the sheet is not particularly limited, but is preferably, for example, room temperature (i.e., 25°C) or higher, and may be, for example, 30°C or higher.

[0085] The stretching speed when the sheet is stretched in one stage in step C is not particularly limited, but is preferably 1 mm / min or more, more preferably 2 mm / min or more, and even more preferably 5 mm / min or more, from the viewpoint of crystallizing the stretched molecular chains without relaxing them, for example. Furthermore, the stretching speed is preferably 1000 mm / min or less, more preferably 700 mm / min or less, even more preferably 500 mm / min or less, particularly preferably 300 mm / min or less, and most preferably 200 mm / min or less, from the viewpoint of easily obtaining a uniform stretched film, for example. In one embodiment, when the sheet is stretched in one stage in step C, the stretching speed may be 1 mm / min to 1000 mm / min, 1 mm / min to 700 mm / min, 1 mm / min to 500 mm / min, 2 mm / min to 300 mm / min, or 5 mm / min to 200 mm / min.

[0086] When the sheet is stretched in one stage in step C, the stretch ratio is, for example, preferably 1.1 times or more, more preferably 1.5 times or more, even more preferably 2 times or more, and particularly preferably 5 times or more, from the viewpoint of further increasing the proportion of extended chain crystals formed. Furthermore, the stretch ratio is, for example, preferably 100 times or less, more preferably 50 times or less, even more preferably 30 times or less, and particularly preferably 20 times or less, from the viewpoint of obtaining a uniform stretch ratio throughout the polyolefin sheet. In one embodiment, the stretch ratio when the sheet is stretched in one stage in step C may be 1.1 times to 100 times, 1.5 times to 50 times, 2 times to 30 times, 2 times to 20 times, or 5 times to 20 times.

[0087] In step C, the stretched sheet may be cooled. The cooling method is not particularly limited, but may include cooling in air or water. The cooling temperature is not particularly limited, and may be, for example, room temperature (i.e., 25°C).

[0088] (Step C1) Step C is, for example, a step of multistage stretching the sheet from the viewpoint of forming extended chain crystals more uniformly and obtaining a stretched polyolefin film having higher mechanical strength, and may include Step C1 of contacting the sheet with a heating body and stretching the sheet by intermittently or continuously moving the contact portion between the sheet and the heating body.

[0089] In step C1, the sheet is brought into contact with a heating element, and the contact portion between the sheet and the heating element is moved to stretch the sheet. That is, in step C1, the heating position of the sheet is moved to stretch the sheet. The contact portion between the sheet and the heating element may be moved by alternately repeating a process of stretching the sheet in a contact state and a process of moving the sheet in a non-stretched state, or may be moved continuously while maintaining the contact state. The heating element is not particularly limited as long as it can heat the sheet by contact with the sheet. Examples of heating elements include a heating roll, a heating plate, and a heating rod. For example, from the viewpoint of being able to employ a roll-to-roll method or other roll-stretching method, the heating element is preferably a heating roll. In step C1, for example, from the viewpoint of more uniformly forming extended chain crystals and obtaining a polyolefin stretched film with higher mechanical strength, a rolling method using two heating rolls may be employed.

[0090] Step C1 is preferably a step of performing solid-state stretching. The stretching temperature in step C1, in other words, the temperature of the heater, is preferably lower than the melting point of the sheet. When the temperature of the heater is lower than the melting point of the sheet, the mechanical strength of the finally obtained stretched polyolefin film tends to be further improved. The lower limit of the temperature of the heater is preferably room temperature (i.e., 25°C) or higher (e.g., 30°C or higher), and more preferably higher than the crystal dispersion temperature of the sheet. The temperature of the heater may be room temperature (i.e., 25°C) or higher and lower than the melting point of the sheet, for example, 30°C or higher and lower than the melting point of the sheet, or higher than the crystal dispersion temperature of the sheet and lower than the melting point of the sheet.

[0091] The "crystal dispersion temperature" is the temperature at which molecular chains in the crystalline region begin to move when the temperature is increased, and is defined as the tan δ peak temperature attributable to the crystalline region when solid viscoelasticity is measured during the temperature increase process, or the temperature at which the temperature change in the crystal reflection peak position due to the expansion of the crystal lattice becomes significant when wide-angle X-ray diffraction is measured during the temperature increase process. It is known that the crystal dispersion temperature for polyethylene is about 60°C, and for polypropylene, the crystal dispersion temperature is about 90°C.

[0092] The stretching speed in step C1 is preferably 1 mm / min or more, more preferably 2 mm / min or more, and even more preferably 5 mm / min or more, from the viewpoint of crystallizing the stretched molecular chains without relaxing them. The stretching speed in step C1 is preferably 1000 mm / min or less, more preferably 700 mm / min or less, even more preferably 500 mm / min or less, particularly preferably 300 mm / min or less, and most preferably 200 mm / min or less, from the viewpoint of easily obtaining a uniform stretched film. In one embodiment, the stretching speed in step C1 may be 1 mm / min to 1000 mm / min, 1 mm / min to 700 mm / min, 1 mm / min to 500 mm / min, 2 mm / min to 300 mm / min, or 5 mm / min to 200 mm / min.

[0093] The draw ratio in step C1 is, for example, preferably 1.1 times or more, more preferably 1.5 times or more, even more preferably 2 times or more, and particularly preferably 5 times or more, from the viewpoint of further increasing the proportion of extended chain crystals formed. Furthermore, the draw ratio in step C1 is, for example, preferably 100 times or less, more preferably 50 times or less, even more preferably 30 times or less, and particularly preferably 20 times or less, from the viewpoint of obtaining a uniform draw ratio throughout the entire polyolefin sheet synthesized in step B. In one embodiment, the draw ratio in step C1 may be 1.1 times to 100 times, 1.5 times to 50 times, 2 times to 30 times, 2 times to 20 times, or 5 times to 20 times.

[0094] In step C1, the stretched sheet may be cooled. The cooling method is not particularly limited, but may include cooling in air or water. The cooling temperature is not particularly limited, and may be, for example, room temperature (i.e., 25°C).

[0095] (Step C2) From the viewpoint of further enhancing the orientation of molecular chains, for example, the process C preferably includes Step C2 of tensile stretching the sheet stretched in Step C1.

[0096] In step C2, for example, from the viewpoint of further increasing the proportion of extended chain crystals formed, it is preferable to tensile stretch the sheet stretched in step C1 while heating it to a temperature not higher than 30°C higher than the melting point of the sheet. The heating temperature of the sheet is, for example, more preferably not higher than 20°C higher than the melting point, and even more preferably not higher than 10°C higher than the melting point. The lower limit of the heating temperature of the sheet is not particularly limited, but is preferably, for example, room temperature (i.e., 25°C) or higher (e.g., 30°C or higher), and more preferably the same as the stretching temperature in step C1 (so-called temperature of the heater; the same applies hereinafter) or a temperature higher than the stretching temperature in step C1.

[0097] If the crystals contained in the sheet stretched in step C1 are mainly extended-chain crystals, the temperature at which the sheet stretched in step C1 can be stretched will be higher than the melting point of the extended-chain crystals. From this perspective, the upper limit of the stretching temperature in step C2 (the so-called sheet heating temperature; the same applies hereinafter) is preferably 30°C higher than the melting point of the sheet stretched in step C1. The lower limit of the stretching temperature in step C2 is preferably room temperature (i.e., 25°C) or higher, and may be, for example, 30°C or higher, or may be higher than the crystal dispersion temperature.

[0098] The stretching speed in step C2 is preferably 1 mm / min or more, more preferably 2 mm / min or more, and even more preferably 5 mm / min or more, from the viewpoint of crystallizing the stretched molecular chains without relaxing them. Furthermore, the stretching speed in step C2 is preferably 1000 mm / min or less, more preferably 700 mm / min or less, and even more preferably 500 mm / min or less, from the viewpoint of obtaining a highly uniform stretched film. In one embodiment, the stretching speed in step C2 may be 1 mm / min to 500 mm / min, 2 mm / min to 300 mm / min, or 5 mm / min to 200 mm / min.

[0099] The draw ratio in step C2 is preferably 1.1 times or more, more preferably 1.5 times or more, and even more preferably 2.0 times or more, from the viewpoint of increasing the proportion of extended chain crystals formed. Furthermore, the draw ratio in step C2 is preferably 100 times or less, more preferably 50 times or less, even more preferably 30 times or less, and particularly preferably 20 times or less, from the viewpoint of obtaining a uniform draw ratio throughout the entire polyolefin sheet synthesized in step B. In one embodiment, the draw ratio in step C2 may be 1.1 times to 100 times, 1.1 times to 50 times, 1.1 times to 30 times, 1.1 times to 20 times, or 1.5 times to 20 times.

[0100] In step C2, 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, and C. 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 can be 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 Stretched Polyolefin Film- The stretched polyolefin film obtained by the production method according to the present disclosure has an average thickness of, for example, 0.1 μm to 200 μm. According to the production method according to the present disclosure, the average thickness of the stretched polyolefin film can be, for example, 5 μm or more, 10 μm or more, or 20 μm or more.

[0107] The following examples will further explain the ultra-high molecular weight polyethylene stretched film and the method for producing a polyolefin stretched 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 stretched film and the method for producing a polyolefin stretched film according to the present disclosure should not be construed as being limited by the specific examples shown below.

[0108] [Production of oriented polyethylene film or polyethylene sheet] <Production Example 1> A 96 mL capacity glass pressure-resistant container (model number: HPG-96-3, shape: cylindrical, inner wall surface area: approximately 150 cm) was placed in a container. ２To a pressure-resistant vessel (manufactured by Taiatsu Glass Industry Co., Ltd.) under a nitrogen atmosphere, 0.00014 g (0.00058 mmol) of bis(cyclopentadienyl)titanium(IV) dichloride (metal catalyst) and 0.28 mL of toluene (organic solvent) were added, followed by the addition of 0.420 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) onto the inner wall surface of the pressure-resistant vessel [Step A].

[0109] 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.

[0110] 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 120 minutes to polymerize the ethylene, thereby synthesizing polyethylene on the inner wall surface of the pressure vessel [Step B].

[0111] 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].

[0112] 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].

[0113] 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].

[0114] Next, the washed polyethylene sheet was air-dried [drying step].

[0115] The polyethylene sheet obtained in this manner was a rectangular sheet measuring 15 cm x 8 cm and having an area of ​​120 cm. ２ The film had a weight of 1.08 g and a melting point of 137.8°C. The melting point was measured by the same method as that for measuring the melting peak temperature described above in the section on stretched films made of ultra-high molecular weight polyethylene. The same applies to Production Examples 2 and 18 below.

[0116] Next, the polyethylene sheet was stretched using an electric hot roller (model number: IMC-110F-B, manufactured by Imoto Machinery Co., Ltd.). Specifically, the polyethylene sheet was cut into a size of 70 mm x 3 mm, and both ends of the polyethylene sheet were fixed to graph paper using double-sided tape so that the stretched portion was 50 mm. Further, double-sided tape was placed on both ends of the polyethylene sheet, and the graph side of another graph paper was placed on top of that, thereby sandwiching the polyethylene sheet. The end of the polyethylene sheet was brought into contact with a roll heated to 130°C, and while shifting the contact point between the polyethylene sheet and the roll, the polyethylene film was uniformly uniaxially stretched to a stretch ratio of 16.6 at a stretching speed of 10 mm / min, and then cooled to room temperature (i.e., 25°C) to obtain a first stretched product [Step C1 of Process C]. The melting peak temperature of the obtained first stretched product was measured by the same method as explained in the section on the stretched film made of ultra-high molecular weight polyethylene, and was found to be 141.6°C.

[0117] Next, the first stretched product was stretched using a Tensilon universal testing machine (model number: RTC-1325A, manufactured by A&D Manufacturing Co., Ltd.). Specifically, the first stretched product was cut into a size of 50 mm x 2 mm, and both ends of the first stretched product were fixed to graph paper using an adhesive for difficult-to-bond materials (trade name: Cemedine PPX, manufactured by Cemedine Co., Ltd.) so that the stretched portion was 30 mm. Further, adhesive was placed on both ends of the first stretched product, and the graph side of another graph paper was placed on top of that to sandwich the first stretched product. The first stretched product was tensile stretched at 130°C under conditions of a stretching rate of 10 mm / min and a stretch ratio of 2.3 times, and then cooled to room temperature (i.e., 25°C). The total stretch ratio (stretch ratio in stage C1 x stretch ratio in stage C2) was 38.2 times. In this manner, a stretched polyethylene film 1 was obtained [Step C2 of Process C].

[0118] <Production Example 2> A polyethylene sheet was obtained by carrying out the same operations as in steps A and B in Production Example 1. The melting point of the obtained polyethylene sheet was 137.8°C. Next, a first stretched product was obtained by carrying out the same operation as in step C1 of step C in Production Example 1. The obtained first stretched product was designated polyethylene stretched film 2.

[0119] <Production Example 3> A polyethylene sheet was obtained by carrying out the same operations as in steps A and B in Production Example 1. The obtained polyethylene sheet was designated as polyethylene sheet 3.

[0120] <Production Example 4> A stretched polyethylene film 4 was obtained in the same manner as in Production Example 1, except that in step C2 of process C in Production Example 1, the stretching temperature was changed to 135°C.

[0121] <Production Example 5> A stretched polyethylene film 5 was obtained in the same manner as in Production Example 1, except that in step C2 of process C in Production Example 1, the stretching temperature was changed to 140°C.

[0122] <Production Example 6> A stretched polyethylene film 6 was obtained in the same manner as in Production Example 1, except that in step C2 of process C in Production Example 1, the stretching temperature was changed to 145°C.

[0123] <Production Example 7> Stretched polyethylene film 7 was obtained in the same manner as in Production Example 4, except that in step C2 of process C in Production Example 4, the stretching speed was changed to 20 mm / min.

[0124] <Production Example 8> A stretched polyethylene film 8 was obtained in the same manner as in Production Example 5, except that in step C2 of process C in Production Example 5, the stretching speed was changed to 20 mm / min.

[0125] <Production Example 9> A stretched polyethylene film 9 was obtained in the same manner as in Production Example 4, except that in step C2 of process C in Production Example 6, the stretching speed was changed to 20 mm / min.

[0126] <Production Example 10> A stretched polyethylene film 10 was obtained by carrying out the same operations as in Production Example 1, except that in step C2 of process C in Production Example 1, the stretching speed was changed to 30 mm / min.

[0127] <Production Example 11> A polyethylene stretched film 11 was obtained by carrying out the same operations as in Production Example 4, except that in step C2 of process C in Production Example 4, the stretching speed was changed to 30 mm / min.

[0128] <Production Example 12> A polyethylene stretched film 12 was obtained in the same manner as in Production Example 5, except that in step C2 of process C in Production Example 5, the stretching speed was changed to 30 mm / min.

[0129] <Production Example 13> A polyethylene stretched film 13 was obtained in the same manner as in Production Example 6, except that in step C2 of process C in Production Example 6, the stretching speed was changed to 30 mm / min.

[0130] <Production Example 14> A stretched polyethylene film 15 was obtained by performing the same operation as in Production Example 5, except that in step C1 of process C in Production Example 5, the stretching temperature was changed to 90°C and the stretching ratio was changed to 8.7 times.

[0131] <Production Example 15> A polyethylene stretched film 15 was obtained by performing the same operation as in Production Example 5, except that in step C1 of process C in Production Example 5, the stretching temperature was changed to 110°C and the stretching ratio was changed to 13.8 times.

[0132] <Production Example 16> The same operation as in Production Example 2 was carried out, except that in step C1 of process C in Production Example 2, the stretching temperature was changed to 140°C. As a result, the polyethylene sheet broke during stretching. The broken fragment was designated as stretched polyethylene film 16.

[0133] Production Example 17 The same operations as in Production Example 4 were carried out, except that in step C1 of process C in Production Example 4, the stretching ratio was changed to 18 times and in step C2, the stretching speed was changed to 40 mm / min, to obtain a stretched polyethylene film 17. The peak melting temperature of the first stretched product obtained in step C1 was measured by the same method as described above in the section on stretched films made of ultra-high molecular weight polyethylene, and was found to be 142.0°C.

[0134] <Production Example 18> A polyethylene sheet was obtained by carrying out the same operations as in steps A and B in Production Example 1, except that in step A in Production Example 1, the composition of the film-forming coating solution added to the pressure-resistant container was changed; specifically, the weight of bis(cyclopentadienyl)titanium(IV) dichloride [metal catalyst] was changed to 0.0013 g (0.0050 mmol), the volume of toluene [organic solvent] was changed to 2.1 mL, and the volume of a toluene solution of methylaluminoxane [co-catalyst] [trade name: TMAO-212, manufactured by Tosoh Finechem Co., Ltd.] was changed to 0.90 mL (Al: 2.5 mmol). The melting point of the obtained polyethylene sheet was 139.8°C. Next, the polyethylene sheet was stretched using a Tensilon universal testing machine [model number: RTC-1325A, manufactured by A&D Manufacturing Co., Ltd.]. Specifically, a polyethylene sheet was cut into a size of 50 mm x 2 mm, and both ends of the polyethylene sheet were fixed to graph paper using an adhesive for difficult-to-bond materials (trade name: Cemedine PPX, manufactured by Cemedine Co., Ltd.) so that the stretched portion was 30 mm. Further adhesive was placed on both ends of the polyethylene sheet, and the graph side of another graph paper was placed on top of that, sandwiching the polyethylene sheet between them. The polyethylene sheet was tensile-stretched at 100°C under conditions of a stretching rate of 20 mm / min and a stretching ratio of 20 times, and then cooled to room temperature (i.e., 25°C) to obtain a stretched polyethylene film 18 [Step C]. In Table 2, the values ​​of the stretching temperature, stretching rate, and stretching ratio in Step C are listed in the column of Step C2.

[0135] <Production Example 19> A polyethylene sheet was obtained by carrying out the same operations as in steps A and B in Production Example 18. The obtained polyethylene sheet was designated as polyethylene sheet 19.

[0136] [Measurements and Evaluations] 1. Measurements Using a Differential Scanning Calorimeter Stretched Polyethylene Films 1, 2, and 4 to 18, and polyethylene sheets 3 and 19 were measured using a differential scanning calorimeter. A heat flux type single furnace DSC 4000 (trade name) manufactured by PerkinElmer Japan Co., Ltd. was used as the differential scanning calorimeter. Approximately 2 mg of polyethylene film was sealed in an aluminum pan and heated from 30°C to 180°C at a heating rate of 10°C / min under 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 peak temperature. The melting peak temperatures of Stretched Polyethylene Films 1, 2, and 4 to 10, and polyethylene sheet 3 are shown in Table 1, and the melting peak temperatures of Stretched Polyethylene Films 11 to 15, 17, and 18, and polyethylene sheet 19 are shown in Table 2. The melting peak area was determined from the obtained DSC curve, and the heat of fusion (unit: J / g) was calculated from this melting peak area. The temperature and heat were calibrated using indium and tin as standard substances. The calculated heat of fusion was divided by the heat of fusion of perfectly crystalline polyethylene (290 J / g) to calculate the crystallinity. The heats of fusion and crystallinity of Stretched Polyethylene Films 1, 2, and 4-10 and Polyethylene Sheet 3 are shown in Table 1, and the heats of fusion and crystallinity of Stretched Polyethylene Films 11-15, 17, and 18 and Polyethylene Sheet 19 are shown in Table 2. The DSC curves of Stretched Polyethylene Films 1, 2, and 4-6 and Polyethylene Sheet 3 are shown in Figure 1.

[0137] 2. Tensile Breaking Strength, Elongation at Break, and Tensile Modulus The tensile breaking strength, elongation at break, and tensile modulus were measured for polyethylene stretched films 1, 2, 4 to 15, 17, and 18, and polyethylene sheets 3 and 19. The stretched polyethylene films and polyethylene sheets were cut into test pieces measuring 20 mm (length) x 5 mm (width). 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 at an ambient temperature of 25°C and a stretching rate of 10 mm / min. Both ends of the test piece were fixed to graph paper using double-sided tape so that the length of the test portion (the so-called initial length) was 10 mm. Further double-sided tape was placed on both ends of the sample piece, and the graph side of another graph paper was placed on top of that to sandwich the sample piece. The test piece was pulled in the length direction, and the maximum stress recorded on the stress chart was divided by the cross-sectional area of ​​the test piece to obtain the tensile strength. The cross-sectional area of ​​the test piece was determined based on the true density of polyethylene in the polyethylene film and polyethylene sheet being 1 g / cm. ３ The cross-sectional area of ​​the test specimen was calculated by dividing the mass of the test specimen by the length of the test specimen. Specifically, the cross-sectional area of ​​the test specimen was calculated using the following formula: ２ ) = "mass of test piece (mg)" / "length of test piece (mm)"

[0138] The strain (unit: mm) at the maximum stress was divided by the initial length of 10 mm to obtain the breaking elongation (%). Ink marks were made on both ends of the test piece (both ends of the 10 mm test portion), and it was checked whether the sample had come off the handle (chuck portion) held between graph paper, but no sample came off the chuck.

[0139] Furthermore, the tensile modulus was calculated from the slope of the recorded stress chart up to a strain of 0.5%. Specifically, when the stress at 0% strain is taken as 0 MPa and the stress chart is linear up to a strain of 0.5%, the tensile modulus corresponds to 200 times the stress (unit: MPa) at 0.5% strain. The tensile breaking strength, breaking elongation, and tensile modulus of Stretched Polyethylene Films 1, 2, and 4 to 10, and Polyethylene Sheet 3 are shown in Table 1, and the tensile breaking strength, breaking elongation, and tensile modulus of Stretched Polyethylene Films 11 to 15, 17, and 18, and Polyethylene Sheet 19 are shown in Table 2.

[0140] 3. Molecular Weight Measurement The weight average molecular weight (Mw) and number average molecular weight (Mn) of the polyethylene sheets obtained in each of Production Examples 1 to 19 were measured. The molecular weight distribution index (Mw / Mn) was calculated from the measured weight average molecular weight (Mw) and number average molecular weight (Mn). 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 at 150°C using 1,2,4-trichlorobenzene as an eluent. Specifically, the GPC measurement was carried out under the following conditions. The weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution index (Mw / Mn) are shown in Tables 1 and 2.

[0141] -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)

[0142] 4. Crystalline Orientation Degree The crystal orientation degrees were determined for Stretched Polyethylene Films 1, 2, 4 to 15, 17, and 18, and for Polyethylene Sheets 3 and 19. Using an X-ray measurement device [a combination of an X-ray generator (model number: MicroMaX007 / HF) manufactured by Rigaku Corporation, an image intensifier (model number: V7739) manufactured by Hamamatsu Photonics K.K., and a CCD camera (model number: C4742-98) manufactured by Hamamatsu Photonics K.K.], X-rays were irradiated perpendicularly onto the surfaces of the stretched polyethylene film and the polyethylene sheet to obtain WAXD (Wide Angle X-ray Diffraction) images (two-dimensional diffraction images). The crystalline orientation of the stretched polyethylene film and polyethylene sheet was calculated from the full-width at half maximum (FWHM) of the peak of the azimuth angle profile obtained by scanning the orthorhombic (110) reflection intensity of the obtained diffraction image in the azimuth angle direction, according to the following formula. When the azimuth angle profile was flat and no peak was observed, the orientation degree was recorded as 0.0%. The results are shown in Tables 1 and 2. WAXD images of stretched polyethylene film 1, stretched polyethylene film 2, and polyethylene sheet 3 obtained during the measurement are shown in Figure 2. The azimuth angle profiles of stretched polyethylene film 1 and stretched polyethylene film 2 are shown in Figure 3. Crystal orientation degree (%) = {(180° - FWHM [°]) / 180°} x 100

[0143]

[0144]

[0145] Tables 1 and 2 show mechanical property data (tensile strength at break, elongation at break, toughness, tensile modulus, and ratio of tensile modulus to tensile strength at break) of the ultra-high molecular weight polyethylene stretched film and polyethylene sheet, DSC measurement data (melting peak temperature, heat of fusion, crystallinity, and ratio of the area of ​​the melting peak at 140°C or higher to the total area of ​​all melting peaks), and measurement results of the degree of crystalline orientation. In Tables 1 and 2, "-" means that there is no applicable data.

[0146] As shown in Tables 1 and 2, polyethylene stretched films 1, 2, 4 to 15, 17, and 18 contained 90 mass% or more of ultra-high molecular weight polyethylene having a weight-average molecular weight of 500,000 or more, based on the total mass of the stretched ultra-high molecular weight polyethylene film, and had tensile breaking strengths of 300 MPa or more and breaking elongations of 7% or more, and were confirmed to correspond to the stretched ultra-high molecular weight polyethylene films of the present disclosure. On the other hand, polyethylene sheets 3 and 19 had breaking elongations of 7% or more but tensile breaking strengths of less than 300 MPa, and were confirmed not to correspond to the stretched ultra-high molecular weight polyethylene films of the present disclosure. Furthermore, polyethylene stretched film 16 broke during stretching in step C1 of process C.

[0147] As shown in Table 1 and Figure 1, it was confirmed that polyethylene stretched films 1, 2, and 4 to 10 all had melting peaks at 140°C or higher, and the area of ​​the melting peaks accounted for 90% or more of the total area of ​​all melting peaks of the ultra-high molecular weight polyethylene stretched film. On the other hand, it was confirmed that polyethylene sheet 3 did not have a melting peak at 141°C or higher. Furthermore, as shown in Table 1 and Figure 3, polyethylene stretched films 1 and 2 all exhibited low crystalline orientation degrees of 98% or less. The crystalline orientation degree of polyethylene sheet 3 was 0.0%.

[0148] From the above, it was revealed that the stretched ultra-high molecular weight polyethylene films according to the present disclosure, namely, Stretched Polyethylene Films 1, 2, 4 to 15, 17, and 18, had high tensile strength at break and also large elongation at break. These results demonstrate that the stretched ultra-high molecular weight polyethylene films according to the present disclosure are suitable for use as, for example, protective films, which is one of the industrial applications of ultra-high molecular weight polyethylene films.

[0149] The disclosure of Japanese Patent Application No. 2023-196254, filed on November 17, 2023, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described 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. A stretched ultra-high molecular weight polyethylene film, which contains 90 mass% or more of ultra-high molecular weight polyethylene having a weight average molecular weight of 500,000 or more, based on the total mass of the stretched ultra-high molecular weight polyethylene film, as estimated from the molecular weight distribution curve of the contained polyethylene obtained by gel permeation chromatography measurement, and has a tensile breaking strength of 300 MPa or more and a breaking elongation of 7% or more.

2. The ultra-high molecular weight polyethylene stretched film according to claim 1, wherein the molecular weight distribution index of the ultra-high molecular weight polyethylene is 5 or less.

3. The ultra-high molecular weight polyethylene stretched film according to claim 1, having a tensile modulus less than 35 times the tensile breaking strength.

4. A stretched film made of ultra-high molecular weight polyethylene according to claim 1 or 2, which has a melting peak at 141°C or higher when measured by a differential scanning calorimeter, and the area of ​​said melting peak accounts for 90% or more of the total area of ​​all melting peaks possessed by the stretched film made of ultra-high molecular weight polyethylene.

5. A method for producing a stretched polyolefin film, comprising: step A of applying an organic solvent containing a metal catalyst to the inner wall surface of a container; step B of 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 applied with the organic solvent containing a metal catalyst; and step C of stretching the polyolefin sheet synthesized on the inner wall surface of the container, wherein in step A, the organic solvent containing a metal catalyst is applied to the inner wall surface of the container by moving the container.

6. A method for producing a polyolefin stretched film as described in claim 5, wherein in step A, the organic solvent containing the metal catalyst is applied to the inner wall surface of the container by rotating the container.

7. A method for producing a stretched polyolefin film as described in claim 5 or 6, wherein the metal catalyst is 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.

8. The method for producing a polyolefin stretched film according to claim 5 or 6, wherein the organic solvent containing the metal catalyst further contains a co-catalyst.

9. The method for producing a stretched polyolefin film according to claim 8, wherein the co-catalyst is at least one selected from the group consisting of alkylaluminoxanes, 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.

10. A method for producing a polyolefin stretched film as described in claim 5 or claim 6, wherein process C is a process for multi-stage stretching of the sheet, and includes step C1 of contacting the sheet with a heating body and intermittently or continuously moving the contact area between the sheet and the heating body to stretch the sheet.

11. The method for producing a stretched polyolefin film according to claim 10, wherein the temperature of the heater is 30° C. or higher and lower than the melting point of the sheet.

12. The method for producing a polyolefin stretched film according to claim 10, wherein the process C includes a step C2 of further tensile stretching the sheet stretched in the step C1.

13. The method for producing a polyolefin stretched film according to claim 12, wherein in step C2, the sheet stretched in step C1 is tensile stretched at a temperature not higher than 30° C. higher than the melting point of the sheet.

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