Polyolefin film, production method for stretched polyolefin film, and polyolefin

Abstract

The present invention pertains to: a polyolefin film comprising a polyolefin including a structural unit derived from a six-membered ring olefin monomer that includes a cyclohexane ring having methylene chains bonded to positions 1, 4 thereof, and a structural unit derived from a six-membered ring olefin monomer that includes a cyclohexane ring having a methylene chain bonded to a position other than the positions 1, 4; a production method for a stretched polyolefin film; and a polyolefin.

Description

Polyolefin film, method for producing stretched polyolefin film, and polyolefin

[0001] The present disclosure relates to a polyolefin film, a method for producing a stretched polyolefin film, and a polyolefin.

[0002] Cyclic polyolefins are polymer materials in which a cyclic molecular structure is introduced into the main chain skeleton of polyolefins, and have attracted attention as optical plastics due to their characteristics such as transparency, low birefringence, low moisture absorption, and heat resistance. For example, in recent years, cyclic polyolefins into which a five-membered ring having the structure shown below has been introduced have been put on the market. Many five-membered ring polyolefins having structural units with the structure shown below are amorphous and have good transparency. When a film made of five-membered ring polyolefin is molecularly oriented by stretching, it exhibits polarization performance, and is therefore used as an optical component such as a polarizing plate. In the structure shown below, n represents the number of bonds in the structural units. R １ and R ２ Examples of the alkyl group include alkyl groups.

[0003]

[0004] Most five-membered ring polyolefins are amorphous due to their large molecular chain cross-sectional area, and when formed into a sheet, they have problems with breaking strength and heat resistance.

[0005] Six-membered ring polyolefins, which have a cyclohexane ring structure introduced into the main chain skeleton, are crystalline, but press films made from them have good transparency. In particular, some six-membered ring polyolefins exhibit high melting points of 200°C or higher by controlling the chain length of the alkyl chains connecting the six-membered rings.

[0006] For example, a six-membered ring polyolefin membrane with methylene chains bonded to the 1,4-positions has been proposed (see Non-Patent Document 1), and a method for synthesizing a cyclohexane polymer with methylene chains bonded to the 1,4-positions and the 1,3-positions has been proposed (see Non-Patent Document 2).

[0007] Non-patent document 1: Proceedings of the Society of Fiber Science and Technology (2019), 1, p. 235 Non-patent document 2: Organometallics, Vol. 34, pp. 3007-3011 (2015)

[0008] However, since six-membered ring polyolefins are crystalline, there is a problem that it is difficult to produce a polyolefin film by stretching. According to the studies of the present inventors, the six-membered ring polyolefin films described in Non-Patent Document 1 and Non-Patent Document 2 all have the problem that they are easily broken by stretching, and it is difficult to form a film that is highly transparent and has high strength. Furthermore, although the cyclic polyolefins described in Non-Patent Document 1 and Non-Patent Document 2 have a high melting point and good heat resistance, they have the problem that it is difficult to form a film by stretching and they have low processability.

[0009] The problem to be solved by one embodiment of the present disclosure is to provide a polyolefin film containing a 6-membered ring polyolefin having good heat resistance, strength, and transparency. The problem to be solved by another embodiment of the present disclosure is to provide a method for producing a stretched polyolefin film to obtain a film having good heat resistance, strength, and transparency. The problem to be solved by another embodiment of the present disclosure is to provide a novel polyolefin that is easy to process into a film.

[0010] Specific means for solving the above problems include the following aspects: <1> A polyolefin film made of a polyolefin containing a structural unit derived from a 6-membered ring olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1- and 4-positions, and a structural unit derived from a 6-membered ring olefin monomer containing a cyclohexane ring having a methylene chain bonded to a position other than the 1- and 4-positions. <2> The polyolefin film according to <1>, wherein the methylene chain has a structure represented by the following formula (X):

[0011]

[0012] In the above formula (X), n represents an integer of 2 to 11. <3> The polyolefin film according to <1> or <2>, wherein the structural unit derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to a position other than the 1- and 4-positions is a structural unit derived from a 6-membered cyclic olefin monomer having a methylene chain bonded to the 1- and 2-positions or a structural unit derived from a 6-membered cyclic olefin monomer having a methylene chain bonded to the 1- and 3-positions. <4> The polyolefin film according to any one of <1> to <3>, wherein the structural unit derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to a position other than the 1- and 4-positions is a structural unit derived from a 6-membered cyclic olefin monomer having a methylene chain bonded to the 1- and 2-positions.

[0013] <5> The polyolefin film according to any one of <1> to <4>, wherein the copolymerization ratio of the structural units derived from a 6-membered ring olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1,4-positions and the structural units derived from a 6-membered ring olefin monomer containing a cyclohexane ring having a methylene chain bonded to a position other than the 1,4-positions is in the range of 95:5 to 60:40, calculated on a molar basis. <6> The polyolefin film according to any one of <1> to <5>, wherein the breaking strength measured with a tensile tester is 30 MPa or more and the haze value is 10% or less.

[0014] <7> A method for producing a stretched polyolefin film, comprising: Step A: forming a polyolefin into a film, the polyolefin comprising structural units derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1,4-positions and structural units derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to a site other than the 1,4-positions; and Step B: biaxially stretching the polyolefin film obtained in Step A. <8> A method for producing a stretched polyolefin film according to <7>, wherein the stretching ratio in Step B of biaxial stretching is 1.5 times or more in at least one axis. <9> A method for producing a stretched polyolefin film according to <7> or <8>, wherein the stretching ratio in Step B of biaxial stretching is 1.5 times or more in both axes.

[0015] <10> A polyolefin comprising a structural unit derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1- and 4-positions, and a structural unit derived from a 6-membered cyclic olefin monomer having a methylene chain bonded to the 1- and 2-positions. <11> The polyolefin according to <10>, wherein the copolymerization ratio of the structural unit derived from the 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1- and 4-positions and the structural unit derived from the 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1- and 2-positions is in the range of 95:5 to 60:40, calculated on a molar basis.

[0016] According to one embodiment of the present disclosure, there is provided a polyolefin film containing a six-membered ring polyolefin having good heat resistance, strength, and transparency. According to another embodiment of the present disclosure, there is provided a method for producing a stretched polyolefin film to obtain a film having good heat resistance, strength, and transparency. According to another embodiment of the present disclosure, there is provided a novel polyolefin having good processability into a film.

[0017] FIG. 1 is a model diagram of the bent polyallylcyclohexane (B-P3CH) constituting the polyolefin film of the present disclosure. FIG. 2 is a DSC curve of the sheets of Example 3 and Comparative Example 2. FIG. 3A is a DMA profile of the press sheet of Example 3. FIG. 3B is a DMA profile of the press sheet of Comparative Example 2.

[0018] The polyolefin film, the method for producing a stretched polyolefin film, and the novel polyolefin according to the present disclosure will be described in detail below. The following description of the requirements may be based on a representative embodiment of the present disclosure, but the present disclosure is not limited to such an embodiment and can be implemented with appropriate modifications within the scope of the present disclosure.

[0019] 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.

[0020] In the present disclosure, when referring to the amount of each component in a mixture for forming a polyolefin film or polyolefin, if there are multiple substances corresponding to each component, the total amount of the multiple components present in the film or composition is meant unless otherwise specified. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0021] 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.

[0022] [Polyolefin Film] The polyolefin film according to the present disclosure (hereinafter also referred to as "the film according to the present disclosure") comprises a polyolefin containing a structural unit derived from a 6-membered ring olefin monomer containing a cyclohexane ring having a methylene chain bonded to positions 1 and 4, and a structural unit derived from a 6-membered ring olefin monomer containing a cyclohexane ring having a methylene chain bonded to positions other than positions 1 and 4. The polyolefin film according to the present disclosure has excellent heat resistance, strength, and transparency.

[0023] <Cyclic Polyolefin> The polyolefin film of the present disclosure contains a structural unit derived from a 6-membered ring olefin monomer containing a cyclohexane ring to which a methylene chain is bonded at the 1- and 4-positions (hereinafter also referred to as "structural unit 1"), and a structural unit derived from a 6-membered ring olefin monomer containing a cyclohexane ring to which a methylene chain is bonded at a position other than the 1- and 4-positions (hereinafter also referred to as "structural unit 2").

[0024] The methylene chain preferably has a structure represented by the following formula (X):

[0025]

[0026] In the above formula (X), n represents an integer of 2 to 11. From a certain viewpoint, n is preferably 3 to 6, and more preferably 3 or 5. One embodiment of the structural unit 1 in which the bonding positions of the methylene chain are the 1st and 4th positions is, for example, a structural unit having a structure shown in the following formula (1). In formula (1), a represents the number of bonds in the structural unit and is an integer of 1 or greater. n in formula (1) has the same meaning as n in formula (X), and the preferred range is also the same.

[0027]

[0028] Linear polyallylcyclohexane containing only structural unit 1 in which a linear methylene chain is bonded to a six-membered ring has crystallinity, but is highly transparent, and tends to have a higher glass transition temperature and melting point than the five-membered ring polyolefins described above. Hereinafter, linear polyallylcyclohexane (Linear-P3CH) will also be referred to as "L-P3CH." When the inventors molded a film using L-P3CH and stretched it to a thin film, they found that high stretching ratios, for example, 1.5 times or more, were possible in the uniaxial direction, but biaxial stretching at high stretching ratios of 1.5 times or more was difficult, and examples of tearing were observed. This is thought to be due to the crystal orientation of L-P3CH.

[0029] The film according to the present disclosure contains the bent structural unit 2 in addition to the structural unit 1 described above, thereby enabling stretching at a high ratio while taking advantage of the advantages of transparency, strength, etc. resulting from the high crystallinity of L-P3CH.

[0030] The film according to the present disclosure contains a structural unit (i.e., structural unit 2) derived from a 6-membered olefin monomer containing a cyclohexane ring to which a methylene chain is bonded at positions other than the 1- and 4-positions. Examples of structural unit 2 include structural unit 2-1, which is a structural unit derived from a 6-membered olefin monomer containing a cyclohexane ring to which a methylene chain is bonded at the 1- and 2-positions, and structural unit 2-2, which is a structural unit derived from a 6-membered olefin monomer containing a cyclohexane ring to which a methylene chain is bonded at the 1- and 3-positions. The structure of structural unit 2-1 is represented by formula (2-1) below, and the structure of structural unit 2-2 is represented by formula (2-2) below. In the present disclosure, either or both of structural unit 2-1 and structural unit 2-2 may be referred to as structural unit 2. b in formula (2-1) and c in formula (2-2) represent the number of bonds in the respective structural units and are integers of 1 or greater. n in formula (2-1) and n in formula (2-2) each independently have the same meaning as n in formula (X), and the preferred range is also the same.

[0031]

[0032] From the viewpoint of achieving better transparency and sheet formability for the resulting film, structural unit 2 is preferably structural unit 2-1. That is, the polyolefin used to form the film according to the present disclosure is preferably a copolymer containing structural unit 1 and structural unit 2-1. Furthermore, the copolymerization ratio (in terms of molar ratio) of structural unit 1 to structural unit 2 (at least one of structural unit 2-1 and structural unit 2-2), i.e., at least one of a:b and a:c, is preferably in the range of 95:5 to 60:40, more preferably 90:10 to 70:30, and even more preferably 90:10 to 85:15.

[0033] As a polyalkenylcyclohexane containing a cyclic polyolefin containing structural unit 1, for example, a compound having the following structure is known (D. Takeuchi DOI: 10.1021 / ja2043968 J. Am. Chem. Soc. (2011), Vol. 133, pp. 11106-11109).

[0034] In the above structure, n represents an integer of 2 to 11. m represents the number of bonds between structural units and is an integer of 1 or more.

[0035] A preferred example of the polyolefin constituting the film according to the present disclosure is a polyalkenylcyclohexane copolymer represented by the following formula (Y), which contains structural unit 1 and structural unit 2-1.

[0036]

[0037] In the above formula, a represents the bonding number of structural units 1, b represents the bonding number of structural units 2-1, and each n independently represents an integer of 2 to 10. m represents the degree of polymerization of the copolymer and is an integer of 1 or greater. The ranges of a and b are each selected depending on the intended use of the copolymer. The copolymerization ratio (a:b) of structural units 1 to 2-1, in molar terms, is preferably in the range of 95:5 to 60:40, and more preferably 90:10 to 80:20. From certain viewpoints, n is preferably 3 to 6, and more preferably 3 or 5. Within the above range, a film with good heat resistance, strength, and transparency is likely to be obtained.

[0038] A more preferred example of the polyolefin constituting the film according to the present disclosure is a polyallylcyclohexane copolymer represented by the following formula (Y-2), which contains a structural unit 1 in which n is 3 and a structural unit 2-1 in which n is 3.

[0039]

[0040] In the above formula (Y-2), a, b, and m have the same meanings as in the above formula (Y). In the above formula (Y-2), the number of bonds (n) in the methylene chain in the structure represented by formula (Y) is 3 for both structural unit 1 and structural unit 2-1. The copolymerization ratio (converted into a molar ratio), i.e., a:b, is preferably in the range of 95:5 to 60:40, more preferably 90:10 to 70:30, and even more preferably 90:10 to 85:15. A polyallylcyclohexane [bend-P3CH polyallylcyclohexane] containing, in addition to L-P3CH (structural unit 1), structural unit 2, which is a bent structural unit, is hereinafter also referred to as "B-P3CH."

[0041] The weight average molecular weight (Mw) of B-P3CH is preferably 50,000 or more, more preferably 60,000 or more, and even more preferably 70,000 or more, from the viewpoint of improving the heat resistance and strength of the resulting film. There is no particular upper limit on the weight average molecular weight, but from the viewpoint of ease of processing into a sheet, it can be 200,000 or less. The number average molecular weight (Mn) of B-P3CH is preferably 10,000 or more, preferably 20,000 or more, and even more preferably 30,000 or more, from the viewpoint of improving the heat resistance and strength of the resulting film. In addition, the molecular weight distribution (Mw / Mn) is preferably in the range of 1.000 to 2.000.

[0042] The molecular weight of B-P3CH can be measured by the following method. In the present disclosure, the weight average molecular weight (Mw) and number average molecular weight (Mn) of a polyolefin are values ​​estimated from the molecular weight distribution curve of the polyethylene contained obtained by gel permeation chromatography (GPC) measurement. Specifically, the GPC measurement is performed under the following conditions:

[0043] -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)

[0044] On the other hand, the composition ratio of B-P3CH can be measured by the following method. In the present disclosure, the ratio of L-P3CH (structural unit 1) to structural unit 2, which is a bent structural unit, in a polyolefin is measured by solution NMR measurement. Specifically, the NMR measurement is performed under the following conditions. -Conditions- Apparatus: Fourier transform high-resolution nuclear magnetic resonance apparatus JNM-ECZ500R (manufactured by JEOL Ltd.) Solvent: 1,1,2,2-tetrachloroethane-d2 Measurement temperature: 130°C In the obtained spectrum, the value estimated from the integral ratio of the signals at 41.8 ppm-42.4 ppm to the signals at 38.0 ppm and 38.3 ppm is used as the composition ratio.

[0045] The mechanism by which the film according to the present disclosure exhibits its effectiveness is unclear, but is thought to be as follows. In L-P3CH, the molecular structure is highly linear, so the molecular chains can only align in one direction, whereas B-P3CH has flexibility, allowing the molecular chains to align in various directions. Furthermore, while the crystallinity due to the six-membered ring polyolefin is thought to be equivalent for L-P3CH and B-P3CH, the bent portions of the molecular structure in B-P3CH are not included in the crystals, and the linearly bonded portions are thought to form the crystalline structure. Therefore, it is thought that the inclusion of a bent structure results in some portions that do not crystallize, making it difficult to improve regularity even when the molecular chains are oriented. Therefore, compared to L-P3CH, B-P3CH has better biaxial stretchability due to the influence of the structural unit 2 having a bent structure. Furthermore, it is thought that the molecular chains are distributed throughout the film in a network-like manner through biaxial stretching, resulting in the resulting biaxially stretched polyolefin film exhibiting higher breaking strength compared to L-P3CH. Note that the above mechanism of action is speculative and does not limit the present disclosure.

[0046] The film according to the present disclosure is obtained by molding the polyolefin B-P3CH into a film. The method for molding the film is not particularly limited, and known methods for manufacturing polyolefin films can be applied. Among these, the film is preferably produced by the polyolefin film manufacturing method according to the present disclosure, which will be described later, in which powdered B-P3CH is press-molded using a press to obtain a sheet, which is then stretched to obtain a film. Powdered B-P3CH can be obtained by performing a polymerization reaction using 500 times the amount of monomer relative to the palladium catalyst to obtain a copolymer, and then removing the catalyst with a palladium removal agent.

[0047] The film according to the present disclosure may contain components other than polyolefins (so-called other components) as needed, as long as the effects of the present disclosure are not impaired. Examples of other components include components typically added to polyolefins, such as antioxidants, weathering agents, light stabilizers, UV absorbers, heat stabilizers, antistatic agents, flame retardants, antibacterial agents, antifungal agents, and colorants (e.g., pigments).

[0048] <Preferred Physical Properties of Polyolefin Film> The film according to the present disclosure preferably has a breaking strength of 30 MPa or more as measured with a tensile tester, and a haze value of 10% or less.

[0049] (Preparation of Polyolefin Film for Evaluation) The polyolefin film for evaluation can be obtained by press molding using a tabletop press (manufactured by Tester Sangyo Co., Ltd.). More specifically, the B-P3CH powder is spread on a 125 μm thick spacer prepared by cutting out a polyimide film (UPILEX-125S: product name) manufactured by Ube Industries, Ltd., and a polyimide film is further placed on the spread B-P3CH powder. The spread B-P3CH powder is sandwiched between two polyimide films, and then sandwiched between two stainless steel plates. The sample is pressed at a temperature of 200 ° C. and a pressure of 40 MPa for 5 minutes, and then quenched with ice water to obtain a pressed sheet for evaluation.

[0050] The press sheet obtained above, with an initial inner length of 20 mm x 20 mm, is simultaneously biaxially stretched at equal length and width using a small biaxial stretching machine equipped with an air chuck function to produce a biaxially stretched membrane stretched 3.0 times in both the length and width directions. The small biaxial stretching machine can heat the film by blowing hot air from above and below with a blower. The B-P3CH is held at 100°C for 5 minutes and then biaxially stretched 3.0 times x 3.0 times at a stretching temperature of 100°C and a stretching speed of 20 mm / min to produce a B-P3CH biaxially stretched membrane (polyolefin biaxially stretched film) for evaluation.

[0051] (Measurement of Breaking Strength) Breaking strength is measured by performing a tensile test on the biaxially stretched polyolefin film obtained above at room temperature (25°C) using a Tensilon universal testing machine (RTC-1325A) manufactured by ORINTEC Corporation, as follows. A measurement sample with an initial length of 3 mm and a width of 3 mm is cut out of the biaxially stretched polyolefin film, and a tensile test is performed on the measurement sample. The breaking strength is calculated from the stress value immediately before break in the stress-strain curve recorded at this time and the initial cross-sectional area of ​​the sample. The breaking strength of the film according to the present disclosure is preferably 30 MPa or more, more preferably 40 MPa or more, and even more preferably 50 MPa or more. The above-mentioned preferable breaking strength is equivalent to or greater than the breaking strength of ultra-high molecular weight polyethylene, which is generally referred to as high strength.

[0052] (Haze Value Measurement) The haze value can be measured using an NDH8000 haze meter manufactured by Nippon Denshoku Industries Co., Ltd. The total light transmittance T.T (%), diffuse transmittance Dif (%), and parallel transmittance P.T (%) are measured using the haze meter, and the haze value (Haze) can be calculated as an index of haze according to the following formula: Diffuse transmittance (%): Dif = T.T - P.T Haze value (Haze) (%) = (Dif / T.T) x 100

[0053] The smaller the haze value, the higher the transparency, which is preferable for a sheet. The haze value of the film according to the present disclosure is preferably 10% or less, more preferably 7% or less, and even more preferably 5% or less.

[0054] The crystallinity of the film according to the present disclosure can be confirmed by thermal property measurements using a differential scanning calorimeter (DSC) and dynamic mechanical properties (DMA). The results of the crystallinity analysis of the film according to the present disclosure and the polyolefin sheet that is the precursor of the film are described in detail in the Examples.

[0055] The film according to the present disclosure has the above-described configuration, and therefore has good heat resistance, strength, and transparency, and can be used in a variety of applications. Examples of applications of the film according to the present disclosure include, but are not limited to, polarizing films, protective films, and food packaging films, and the film can be used without particular limitation in applications where heat resistance, strength, and transparency are required.

[0056] Although there are no particular limitations on the method for producing the film according to the present disclosure, it is preferable that the film be produced by the method for producing a stretched polyolefin film described below.

[0057] [Method for producing stretched polyolefin film] The method for producing a stretched polyolefin film according to the present disclosure includes step A of molding a polyolefin into a film, the polyolefin including structural units derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1,4-positions and structural units derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to a position other than the 1,4-positions, and step B of biaxially stretching the polyolefin film obtained in step A. Hereinafter, the method for producing a stretched polyolefin film according to the present disclosure will also be simply referred to as the "production method according to the present disclosure."

[0058] <Step A> Step A in the production method according to the present disclosure is a step of forming a polyolefin into a sheet, the polyolefin comprising: a structural unit derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1,4-positions; and a structural unit derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to a site other than the 1,4-positions. The polyolefin comprising the structural unit derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1,4-positions; and a structural unit derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to a site other than the 1,4-positions, used in step A, is the same as the polyolefin (B-P3CH) used in the film according to the present disclosure described above, and preferred examples are also the same.

[0059] In step A, first, B-P3CH is prepared as a raw material. From the viewpoint of workability, it is preferable to use B-P3CH in powder form.

[0060] Thereafter, the powdered B-P3CH is first formed into a sheet. There are no particular limitations on the method for forming the powdered B-P3CH into a sheet; however, methods such as press molding and roll molding can be applied, with press molding being preferred from the viewpoint of uniformity of the resulting sheet. When forming a powdered raw material into a sheet by press molding or roll molding, the raw material powdered B-P3CH is preferably formed at a temperature above the melting point of B-P3CH, more preferably at 150°C to 220°C. In the present disclosure, the "melting point" of B-P3CH refers to the temperature (°C) at the peak of the DSC curve obtained by measurement using a differential scanning calorimeter (DSC) in which the temperature is increased from 40°C to 250°C at a heating rate of 10°C / min. This may vary depending on the production method and molecular weight of the B-P3CH, but may be in the range of 140°C to 180°C.

[0061] A method for preparing a film by roll-molding the raw material powder B-P3CH is described in JP 2003-165155 A, and the method described therein can also be applied to the present disclosure. When preparing a film by press-molding the raw material powder B-P3CH, the press is preferably performed at a pressure of 0.01 MPa to 100 MPa, and more preferably at a pressure of 0.01 MPa to 50 MPa. During press-molding, the powder B-P3CH may be directly spread over the mold of the press, or the powder B-P3CH may be sandwiched between polyimide films or other spacers.

[0062] The obtained sheet-form B-P3CH is then biaxially stretched to produce a film. From the viewpoint of workability during biaxial stretching, the thickness of the sheet-form B-P3CH is preferably 50 μm to 300 μm, and more preferably 100 μm to 200 μm. In order to obtain a desired thickness for the sheet-form B-P3CH, at least one of press molding and roll molding may be performed multiple times.

[0063] <Step B> Step B in the production method of the present disclosure is a step of biaxially stretching the film-like polyolefin obtained in the above-described step A. Known methods can be used for the biaxial stretching method. The biaxial stretching method may be simultaneous biaxial stretching, in which stretching is performed simultaneously in both the longitudinal and transverse directions, or sequential biaxial stretching, in which stretching is performed sequentially in both the longitudinal and transverse directions. Simultaneous biaxial stretching is preferred from the viewpoint of ease of controlling molecular chains and crystallinity within the desired range. Biaxial stretching is preferably performed while heating the film-like polyolefin in order to enable the formation of a uniformly stretched film. The heating temperature is preferably equal to or higher than the melting point of B-P3CH. If the heating temperature is too high, the sheet may deform, so the upper limit of the heating temperature is preferably equal to or lower than the melting point + 10°C. Specifically, for example, a preferred method is to cut the sheet obtained in step A into a predetermined shape and simultaneously biaxially stretch it in both the longitudinal and transverse directions at the same magnification using a small biaxial stretching machine equipped with an air chuck function. The heating temperature at this time is preferably in the range of 80° C. to 150° C., more preferably in the range of 90° C. to 120° C. Furthermore, when biaxially stretching, a step of preheating the sheet-like polyolefin to, for example, about 80° C. to 120° C. can be carried out. The preheating step enables biaxial stretching to be carried out more efficiently.

[0064] The stretching speed is not particularly limited, but from the viewpoint of crystallizing the stretched molecular chains without relaxing them, it is preferably 1 mm / min or more, more preferably 2 mm / min or more, and even more preferably 5 mm / min or more. Furthermore, from the viewpoint of easily obtaining a uniform stretched film, the stretching speed is preferably 700 mm / min or less, more preferably 500 mm / min or less, even more preferably 300 mm / min or less, particularly preferably 200 mm / min or less, and most preferably 100 mm / min or less. In one embodiment, the sheet stretching speed in step B may be 1 mm / min to 1000 mm / min, 1 mm / min to 700 mm / min, 10 mm / min to 50 mm / min, or 15 mm / min to 30 mm / min.

[0065] The stretching ratio in step B is preferably 1.5 times or more in at least one axis from the viewpoint of the transparency of the obtained film, more preferably 1.8 times or more, even more preferably 2.0 times or more, and particularly preferably 3.0 times or more. Also, the stretching ratio in step B is preferably 1.5 times or more in both axes from the viewpoint of the transparency of the obtained film, more preferably 1.8 times or more, even more preferably 2.0 times or more, and particularly preferably 3.0 times or more. For example, a film having a thickness of about 60 μm can be obtained by stretching a sheet having a thickness of about 100 μm by 3.0 times.

[0066] The ease of stretching the polyolefin sheet compared to, for example, L-P3CH is thought to be due to the lower crystallinity of the raw material polyolefin B-P3CH compared to L-P3CH. In L-P3CH, the molecular structure is highly rigid and linear, so the molecular chains can only align in one direction. Therefore, when stress is applied perpendicular to the molecular chain axis, the crystalline structure cannot be maintained and the sheet breaks, presumably making stretching in at least one direction difficult. On the other hand, the B-P3CH used in the film according to the present disclosure, which has a bent structure, has a less ordered crystalline structure compared to L-P3CH, allowing the molecular chains to align in various directions. Therefore, it is thought that the B-P3CH sheet can be stretched while maintaining its crystalline structure even during biaxial stretching. Therefore, when the B-P3CH sheet is stretched, the molecular orientation becomes more random compared to L-P3CH. Figure 1 shows a model diagram of the bent polyallylcyclohexane (B-P3CH) that constitutes the film according to the present disclosure. The present inventors believe that B-P3CH polyolefin has an amorphous region and a crystalline region, as shown in Figure 1. The enclosed lines indicating the amorphous region and the crystalline region shown in Figure 1 do not necessarily indicate the strict division of each region, but merely conceptually show one embodiment of each region.

[0067] According to the manufacturing method of the present disclosure, by biaxially stretching the polyolefin sheet having a thickness of 150 μm to 200 μm obtained in step A, for example, a film having a thickness of approximately 60 μm is formed at a stretching ratio of 3.0, and a film having a thickness of approximately 40 μm is formed at a stretching ratio of 4.0.

[0068] - Thickness of Polyolefin Sheet and Polyolefin Film - The thickness of the polyolefin sheet and film obtained by the production method according to the present disclosure is an average thickness determined by the following measurement method. The arithmetic mean value of thicknesses measured at six randomly selected locations in the thickness direction of the polyolefin sheet or film is determined, and the obtained value is taken as the thickness of the polyolefin sheet or film. A thickness gauge is used to measure the thickness of the polyolefin sheet or 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.

[0069] According to the production method of the present disclosure, a stretched polyolefin film that is thin, has good transparency, and has high breaking strength can be easily obtained.

[0070] [Polyolefin] The polyolefin according to the present disclosure comprises a structural unit derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1,4-positions, and a structural unit derived from a 6-membered cyclic olefin monomer having a methylene chain bonded to the 1,2-positions. The polyolefin according to the present disclosure is a polymer having a novel structure. In particular, the polyolefin according to the present disclosure preferably has a copolymerization ratio of the structural unit derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1,4-positions and the structural unit derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1,2-positions in a range of 95:5 to 60:40 in terms of moles.

[0071] A preferred embodiment of the polyolefin according to the present disclosure has, for example, a structure represented by the following formula (Y), in which the copolymerization ratio of each constituent unit converted into a molar ratio, i.e., a:b in the following formula (Y), is 90:10 to 85:15. In the following formula (Y), n each independently represents the number of bonds in each methylene chain, and is preferably 2 to 11, and more preferably 3 or 5.

[0072]

[0073] Polyolefins according to the present disclosure can be synthesized, for example, by using a Pd catalyst that does not have bulky substituents around Pd as the Pd catalyst used in the isomerization polymerization reaction of six-membered cyclic polyolefins. It is known that the regioselectivity is controlled by the bulkiness of the Pd complex used in the isomerization polymerization reaction of six-membered cyclic polyolefins. The key reaction in the isomerization polymerization of six-membered cyclic polyolefins is the chain walking reaction. In this reaction, the terminal alkyl metal species undergoes frequent repeated β-hydrogen elimination and reinsertion, and due to steric repulsion between the cyclohexyl group bonded to Pd and the monomer substituent, selective 2,1-insertion into the CH—Pd bond occurs. Utilizing this knowledge, Pd complex 2 shown below in (b) is used in the synthesis of polyolefins according to the present disclosure, instead of Pd complex 1 shown below in (a) used in the synthesis of L-P3CH. Because Pd complex 2 has small bulkiness of the substituents around Pd, trans-1,2-bonds may form during the polymerization reaction. As a result, the bent polyallylcyclohexane (B-P3CH) is obtained as a polyolefin having a highly flexible structure, such as the structure represented by the above formula (Y), which contains a 1,2 bond structure in addition to a 1,4 bond.

[0074]

[0075] The polyolefin according to the present disclosure can be obtained by carrying out a polymerization reaction using the Pd complex 2 shown in (b) above as a Pd catalyst, using a monomer in an amount 500 times that of the Pd catalyst, and then removing the catalyst with a palladium removal agent. The synthesis method and physical properties of the polyolefin according to the present disclosure will be described in detail in the Examples.

[0076] The polyolefin according to the present disclosure has a structure including a bent portion as shown in the above formula (Y), and therefore has good film formability, particularly good stretchability, particularly good biaxial stretchability. Therefore, the polyolefin according to the present disclosure can provide a thin polyolefin film having good heat resistance, strength, and transparency.

[0077] The polyolefin film, the method for producing the polyolefin film, and the novel polyolefin according to the present disclosure will be described in more detail below with reference to the following examples. 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 polyolefin film, the method for producing the polyolefin film, and the novel polyolefin according to the present disclosure should not be construed as being limited by the specific examples shown below.

[0078] First, the method for producing a polyolefin sheet according to the present disclosure will be described with reference to examples.

[0079] [Synthesis of Polyolefins] Example 1 Polyolefin 1 To a 100 mL Schlenk flask under a nitrogen atmosphere were added 0.138 g (0.260 mmol) of a palladium catalyst having the following structure, 0.276 g (0.312 mmol) of sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (cationizing agent), and 65 mL of methylene chloride (organic solvent), followed by the addition of 16.2 g of the raw material allylcyclohexane, which is approximately 500 times the amount of the catalyst. The ambient temperature of the Schlenk flask was maintained at 25° C., and polymerization was carried out for 4 hours to synthesize a polyolefin.

[0080]

[0081] After the polymerization reaction was completed, triethylsilane (a polymerization terminator) was added to terminate the reaction, and the reaction mixture was then poured into methanol to obtain a polyolefin. The obtained polyolefin was dissolved in 1,1,2,2-tetrachloroethane, and diethylammonium diethyldithiocarbamate (a palladium removal agent) was added. The catalyst was removed by reacting at 140°C for 4 hours, and the mixture was then poured into methanol to obtain polyolefin 1. Next, the obtained polyolefin 1 was washed with methanol (a washing liquid) to remove the metal catalyst and palladium removal agent [washing step]. Next, the washed polyolefin 1 was air-dried to obtain powdered polyolefin 1 (11.1 g).

[0082] Example 2 Polyolefin 2 Powdery polyolefin 2 (9.37 g) was obtained in the same manner as in Example 1, except that the amount of the palladium catalyst was changed to 0.107 g (0.163 mmol), the amount of sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate to 0.173 g (0.195 mmol), the amount of methylene chloride to 41 mL, the amount of allylcyclohexane to 10.2 g, and the reaction time to 5 hours.

[0083] Comparative Example 1 Comparative Polyolefin (L-P3CH) Comparative polyolefin (8.80 g) was obtained in the same manner as in Example 1 above, except that the palladium catalyst used in Example 1 was changed to one having the following structure.

[0084]

[0085] The compositional ratios of structural unit 1 (1,4 positions: shown as L-P3CH in the tables below) and structural unit 2 (1,2 positions: shown as B-P3CH in the tables below) of the polyolefins of Example 1, Example 2, and Comparative Example 1, as well as the weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution measured under the conditions below, are shown in Table 1. In the tables below, polyolefin structural unit 1 (1,4 positions) is abbreviated as L-P3CH, and structural unit 2 (1,2 positions) is abbreviated as B-P3CH.

[0086] (Measurement of Molecular Weight) The weight average molecular weight (Mw) and number average molecular weight (Mn) of the polyolefin were estimated from the molecular weight distribution curve of the polyethylene contained obtained by gel permeation chromatography (GPC). Specifically, the GPC measurement was carried out under the following conditions:

[0087] -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)

[0088] (Measurement of Composition Ratio) The composition ratio of the structural unit 1 to the structural unit 2 in the obtained polyolefin was １３ C{ １ 1 H} NMR measurement was performed, and the value estimated from the integral ratio of the signal at 41.8 ppm-42.4 ppm to the signals at 38.0 ppm and 38.3 ppm in the obtained spectrum was used. １３ C{ １ 1H} The NMR measurement was specifically carried out under the following conditions. -Conditions- Apparatus: Fourier transform high-resolution nuclear magnetic resonance apparatus JNM-ECZ500R (manufactured by JEOL Ltd.) Solvent: 1,1,2,2-tetrachloroethane-d2 Measurement temperature: 130°C

[0089]

[0090] [Production of Stretched Polyolefin Film] Using the powdered polyolefin 1 obtained in Example 1, the powdered polyolefin 2 obtained in Example 2, and the powdered comparative polyolefin obtained in Comparative Example 1, a stretched polyolefin film according to the present disclosure was produced according to the following production method.

[0091] Example 3: Production of Stretched Polyolefin Film (1. Production of Press Sheet) 2.0 g of the powdered polyolefin 1 obtained in Example 1 was press-molded using a bench press (manufactured by Tester Sangyo Co., Ltd.) to produce a press sheet. The powdered polyolefin 1 was spread on a 125 μm thick spacer prepared by cutting out a polyimide film (UPILEX-125S: product name) manufactured by Ube Industries, Ltd., and sandwiched between polyimide films, which were then further sandwiched between stainless steel plates. The powder was pressed at a temperature of 200°C and a pressure of 4.5 MPa (cylinder pressure of 40 MPa) for 5 minutes, and then quenched with ice water to obtain a press sheet. (Step A) The film thickness of the press sheet was measured by the following method and found to be 167 μm. The appearance of the press sheet of Example 3 produced using the powdered polyolefin 1 obtained in Example 1 was visually transparent.

[0092] [Method for Measuring Film Thickness] The film thickness at six randomly selected points in the thickness direction of the press sheet was measured using a thickness measuring device (product name: Film Tester, model number: HKT-1216, manufactured by Fuji Work Co., Ltd.) The measured values ​​were arithmetically averaged, and the obtained value was defined as the film thickness of the press sheet of Example 3.

[0093] (2. Preparation of Stretched Polyolefin Film-1) The press sheet of Example 3 obtained above was subjected to simultaneous biaxial stretching at equal length in both the longitudinal and transverse directions using a small biaxial stretching machine equipped with an air chuck function, with the inner side having an initial length of 20 mm x 20 mm, to produce a biaxially stretched film in both the longitudinal and transverse directions. The small biaxial stretching machine can heat the film by blowing hot air from above and below using a blower. B-P3CH was held at 100°C for 5 minutes, and biaxially stretched at a stretching temperature of 100°C and a stretching speed of 20 mm / min. The film was then slowly cooled to room temperature (25°C) to obtain a biaxially stretched polyolefin film. (Step B) Biaxial stretching was performed under the above conditions, and the film was stretched to 3.0x x 3.0x to obtain the polyolefin film of Example 3, which was a 3.0x x 3.0x biaxially stretched film. The film thickness was measured in the same manner as above, and was found to be 66 μm.

[0094] (2. Preparation of Polyolefin Film-2) The press sheet obtained above was biaxially stretched under the same conditions as in "2. Preparation of Polyolefin Film-1" but at a higher stretch ratio. It was stretched to 4.0x x 4.0x without breakage, and a 4.0x x 4.0x biaxially stretched polyolefin film of Example 3 was obtained. The film thickness of the 4.0x x 4.0x biaxially stretched film was also measured in the same manner as above, and was found to be 37 μm.

[0095] Example 4: Production of stretched polyolefin film (1. Production of press sheet) 2.3 g of the powdered polyolefin 2 obtained in Example 2 was press-molded using a bench press (manufactured by Tester Sangyo Co., Ltd.) in the same manner as in Example 3 to produce a press sheet. The film thickness of the press sheet was measured in the same manner as above and found to be 194 μm. The appearance of the press sheet of Example 4 was transparent to the naked eye.

[0096] (2. Preparation of Polyolefin Stretched Film) The press sheet of Example 4 obtained above was subjected to simultaneous biaxial stretching in the same manner as in Example 3, with the inner side having an initial length of 20 mm x 20 mm, in a small biaxial stretching machine equipped with an air chuck function, at equal longitudinal and transverse stretching ratios to produce a biaxially stretched film of 3.0 times in both the longitudinal and transverse directions. That is, when biaxial stretching was performed under the above conditions, it was possible to stretch it up to 3.0 times x 3.0 times without breaking. In this way, a polyolefin film of Example 4, which is a 3.0 times x 3.0 times biaxially stretched film, was obtained. When the film thickness was measured in the same manner as above, it was 61 μm.

[0097] Comparative Example 2: Production of Stretched Polyolefin Film (1. Production of Press Sheet) 1.6 g of the powdered comparative polyolefin obtained in Comparative Example 1 was press-molded using a bench press (manufactured by Tester Sangyo Co., Ltd.) in the same manner as in Example 3 to produce a press sheet of Comparative Example 2. The film thickness of the press sheet of Comparative Example 2 was measured in the same manner as above and was found to be 136 μm. The appearance of the press sheet of Comparative Example 2 was transparent to the naked eye, and no difference in appearance from the press sheets of Examples 2 and 3 could be confirmed.

[0098] (2. Preparation of Polyolefin Film) The press sheet of Comparative Example 2 obtained above was subjected to simultaneous biaxial stretching in the same manner as in Example 3, with the inner side having an initial length of 20 mm x 20 mm, in both the length and width directions at equal magnifications using a small biaxial stretching machine equipped with an air chuck function. The comparative polyolefin of Comparative Example 1 was held at 140°C for 5 minutes, and then biaxially stretched at a stretching temperature of 140°C and a stretching speed of 20 mm / min to produce a biaxially stretched film. The stretching ratio at which uniform biaxial stretching was achieved was up to 1.5 times. Therefore, the polyolefin stretched film of Comparative Example 2 was a 1.5x x 1.5x biaxially stretched film. The film thickness was measured in the same manner as above, and was found to be 106 μm.

[0099] [Evaluation] The following evaluations were carried out on the polyolefin stretched films of Examples 3 and 4 and Comparative Example 2, and their intermediate polyolefin press sheets. In Tables 2 and 3 below, the polyolefin press sheets, which are intermediates obtained from powdered polyolefin, are referred to as "press sheets," and the biaxially stretched films obtained by stretching the press sheets are referred to as "biaxially stretched films," with the stretch ratio (× times) also indicated as "××."

[0100] (1. Haze Value) Haze values ​​were measured using a NDH8000 haze meter manufactured by Nippon Denshoku Industries Co., Ltd. The total light transmittance T.T (%), diffuse transmittance Dif (%), and parallel transmittance P.T (%) were measured using the haze meter, and the haze value (Haze) was calculated as an index of haze according to the following formula: Diffuse transmittance (%): Dif = T.T - P.T Haze value (Haze) (%) = (Dif / T.T) × 100 The results are shown in Table 2 below.

[0101]

[0102] As shown in Table 2, the stretched polyolefin films of Examples 3 and 4 obtained from the powdered polyolefins of Examples 1 and 2 had better stretchability than the stretched polyolefin film of Comparative Example 2. The biaxially stretched films of Examples 3 and 4 all had haze values ​​of 5.0% or less and were films with excellent transparency.

[0103] (2. Breaking Strength) Breaking strength was measured by performing a tensile test on the biaxially stretched polyolefin film obtained above at room temperature (25°C) using a Tensilon universal testing machine (RTC-1325A) manufactured by ORINTEC Corporation, as follows. The tensile test was performed using a measurement sample cut out of the biaxially stretched polyolefin film with an initial length of 3 mm and width of 3 mm, using the tensile tester. The breaking strength was calculated from the stress value just before break in the stress-strain curve recorded at this time and the initial cross-sectional area of ​​the sample. The results are shown in Table 3 below.

[0104]

[0105] As shown in Table 3, the biaxially stretched polyolefin films of Examples 3 and 4 obtained from the powdered polyolefins of Examples 1 and 2 had similar breaking strengths to the biaxially stretched polyolefin film of Comparative Example 2, but had better stretchability. This is presumably due to the moderate amorphous nature of the polyolefin due to the bending structure in the molecules, resulting in good biaxial stretchability. The breaking strengths of the stretched polyolefin films obtained after biaxially stretching the polyolefin press sheets of Examples 3 and 4 were all 30 MPa or higher, a practically acceptable level. The polyolefin constituting the polyolefin film of the present disclosure contains a 6-membered cyclic olefin monomer in the polymer chain, and therefore has a more rigid molecular chain than polyethylene composed solely of methylene chains. Therefore, while the melting point of polyethylene composed solely of methylene chains is around 135°C, a melting point 15°C or higher is observed, as described below. From this, it can be said that the polyolefin film of the present disclosure obtained using a polyolefin containing a six-membered ring olefin monomer in the polymer chain has high heat resistance, regardless of whether it is stretched or not.

[0106] (3. Differential Scanning Calorimetry (DSC) Measurement) Of the films obtained above, the press sheet of Example 3 and the press sheet of Comparative Example 2, which are intermediates of the polyolefin film, were used as the measurement subjects, and DSC measurement was performed to determine the melting peak temperature (Tpm), heat of fusion, and degree of crystallinity. The melting peak temperature (Tpm) was determined from the differential scanning calorimetry curve (DSC curve) obtained by differential scanning calorimetry (DSC). The measurement device was a Perkin-Elmer Pyris 1 differential scanning calorimeter, and the differential scanning calorimetry (DSC) measurement was performed in a nitrogen atmosphere, at a temperature range of 40°C to 250°C, and at a heating rate of 10°C / min. In this case, an aluminum pan was used as the sample pan, and indium and tin were used as standard substances for temperature and calorie correction. The melting behavior was compared based on the results of the DSC measurement. The results are shown in Figure 2. In Figure 2, the graph for Example 3 is shown by a solid line, and the graph for Comparative Example 2 is shown by a dashed line. When observing Figure 2, a comparison of the shapes of the DSC profiles at the melting endothermic peaks of both samples reveals that a sharp melting endothermic peak was observed at 227°C in the sheet of Comparative Example 2, whereas a broad melting endothermic peak was observed between 110°C and 190°C in the sheet of Example 3. This suggests that the sheet of Example 3 does not have a clear melting point like the sheet of Comparative Example 2. The melting points (T ｍ ) and enthalpy of fusion (ΔH ｍ ) are shown in Table 4 below.

[0107]

[0108] According to Table 4, ΔH ｍwas lower for the press sheet of Example 3 than for the press sheet of Comparative Example 2, indicating that the press sheet of Example 3 had lower crystallinity. According to FIG. 2 , in addition to a broad endothermic peak derived from the melting point located near 155°C, an endothermic peak was observed near 55°C for the press sheet of Example 3. For example, it has been reported that when an amorphous polymer such as polystyrene is heated to near its glass transition temperature, an endothermic peak derived from enthalpy relaxation is observed. Therefore, considering that the sheet of Example 3 contains many amorphous regions (amorphous), it was suggested that the peak that appeared at 55°C was due to enthalpy relaxation during the glass transition.

[0109] (4. Dynamic Viscoelasticity (DMA) Measurement) Using a DMA / SDTA861e manufactured by METTLER TOLEDO, temperature dependence was measured in a nitrogen atmosphere at a frequency of 1 Hz, in a temperature range of 40°C to 80°C, at a heating rate of 3°C / min, and in tensile mode. Sample pieces were used, each cut into 5 mm x 25 mm pieces from the press sheet before biaxial stretching. The DMA profile for the press sheet of Example 3 is shown in Figure 3A. Here, E' is the storage modulus, E'' is the loss modulus, and tan δ (= E' / E'') is the loss tangent. In the DMA measurement, the temperature at which tan δ peaks is defined as the glass transition temperature. In Figure 3A and Figure 3B described below, E' (storage modulus) is represented by a solid line, E'' (loss modulus) by a dashed line, and tan δ (loss tangent) by a dashed-dotted line. According to the DMA profile of the sheet of Example 3, E' decreased from around 50°C. Furthermore, a peak in E'' was observed around 55°C, and a corresponding tan δ peak was observed around 60°C. Therefore, since the DMA measurement of the sheet of Example 3 confirmed a glass transition around 60°C, it is believed that the endothermic peak around 55°C observed in the DSC measurement is due to enthalpy relaxation.

[0110] The DMA profile of the press sheet of Comparative Example 2 is shown in Figure 3B. In the sheet of Comparative Example 2, according to the DMA profile, a tan δ peak was observed around 70 ° C., but the change in tan δ was smaller than that of the sheet of Example 3. This is thought to be due to the high crystallinity of the sheet of Comparative Example 2. For this reason, in the sheet of Comparative Example 2, a glass transition occurs around 70 ° C., but it is thought that the enthalpy relaxation peak did not appear because the crystalline amount is greater than that of the sheet of Example 3. From these results, it is thought that the sheet of Example 3, into which a bent structure has been introduced, has a less ordered crystalline structure and is more amorphous than the sheet of Comparative Example 2. Therefore, even when the two samples were stretched, structures with different molecular orientations were obtained, and it is thought that the above assumption that the biaxial stretchability of the sheet of Example 3 was improved due to the amorphous region was supported.

[0111] The disclosure of Japanese Patent Application No. 2024-082864, filed on May 21, 2024, is incorporated herein by reference. All documents, patent applications, and technical standards mentioned in this disclosure 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 polyolefin film made of polyolefin containing a structural unit derived from a 6-membered ring olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1- and 4-positions, and a structural unit derived from a 6-membered ring olefin monomer containing a cyclohexane ring having a methylene chain bonded to a position other than the 1- and 4-positions.

2. The polyolefin film according to claim 1, wherein the methylene chain has a structure represented by the following formula (X): In the formula (X), n represents an integer of 2 to 11.

3. The polyolefin film according to claim 1, wherein the structural unit derived from a 6-membered cyclic olefin monomer containing a cyclohexane ring having a methylene chain bonded to a position other than the 1- and 4-positions is a structural unit derived from a 6-membered cyclic olefin monomer having a methylene chain bonded to the 1- and 2-positions or a structural unit derived from a 6-membered cyclic olefin monomer having a methylene chain bonded to the 1- and 3-positions.

4. A polyolefin film according to claim 1, wherein the structural unit derived from a six-membered ring olefin monomer containing a cyclohexane ring having a methylene chain bonded to a position other than the 1- and 4-positions is a structural unit derived from a six-membered ring olefin monomer having a methylene chain bonded to the 1- and 2-positions.

5. The polyolefin film according to claim 1, wherein the copolymerization ratio of the structural units derived from a 6-membered ring olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1,4-positions and the structural units derived from a 6-membered ring olefin monomer containing a cyclohexane ring having a methylene chain bonded to a position other than the 1,4-positions is in the range of 95:5 to 60:40 on a molar basis.

6. The polyolefin film according to claim 1, which has a breaking strength of 30 MPa or more as measured by a tensile tester and a haze value of 10% or less.

7. A method for producing a stretched polyolefin film, comprising: Step A: forming a polyolefin into a film, the polyolefin containing a structural unit derived from a 6-membered olefin monomer containing a cyclohexane ring having a methylene chain bonded to the 1,4-position and a structural unit derived from a 6-membered olefin monomer containing a cyclohexane ring having a methylene chain bonded to a position other than the 1,4-position; and Step B: biaxially stretching the polyolefin film obtained in Step A.

8. The method for producing a stretched polyolefin film according to claim 7, wherein the stretching ratio in step B of biaxial stretching is 1.5 times or more in at least one axis.

9. The method for producing a stretched polyolefin film according to claim 7, wherein the stretching ratio in step B of biaxial stretching is 1.5 times or more in both axes.

10. A polyolefin comprising a structural unit derived from a six-membered ring olefin monomer containing a cyclohexane ring having methylene chains bonded to the 1- and 4-positions, and a structural unit derived from a six-membered ring olefin monomer having methylene chains bonded to the 1- and 2-positions.

11. The polyolefin according to claim 10, wherein the copolymerization ratio of the structural units derived from a 6-membered ring olefin monomer containing a cyclohexane ring having methylene chains bonded to the 1- and 4-positions and the structural units derived from a 6-membered ring olefin monomer containing a cyclohexane ring having methylene chains bonded to the 1- and 2-positions is in the range of 95:5 to 60:40 on a molar basis.

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