Film, method for producing film, and capacitor

Abstract

The film contains a crystalline polymer. In the film, the lamellar orientation degree in the Through direction obtained from small-angle X-ray scattering measurement is 0.75 or more, and the arithmetic mean roughness value of the surface is 0.03 μm or more.

Description

Film, film manufacturing method, and capacitor

[0001] The present invention relates to a film, a method for manufacturing the film, and a capacitor.

[0002] A film capacitor, a type of capacitor, is a device that has a structure in which dielectric films and metal layers are alternately arranged and can store electric charge. The dielectric film of a film capacitor is required to have excellent dielectric breakdown strength, metal vapor deposition properties, and formability. Development of films formed from crystalline resins such as cyclic olefin resins and polypropylene resins has been progressing.

[0003] For example, Patent Documents 1 and 2 discuss films made using a hydrogenated dicyclopentadiene ring-opening polymer. More specifically, Patent Document 1 discusses a technique for heat-treating and stretching an unstretched film having a resin layer made of a crystalline hydrogenated dicyclopentadiene ring-opening polymer under specified conditions. Patent Document 2 specifies various attributes, such as the softening point, heat shrinkage, and static friction coefficient, of a resin film obtained by stretching an unstretched film made using a hydrogenated dicyclopentadiene ring-opening polymer and then heat-treating it. Patent Document 3, for example, discloses a laminated film having a polypropylene resin-containing layer on at least one side of a substrate containing a cyclic olefin resin. Patent Document 4, for example, discloses a film obtained by controlling various attributes, such as the degree of crystalline orientation and heat shrinkage, of the polypropylene film.

[0004] JP 2021-53888 A International Publication No. 2016 / 052303 International Publication No. 2017 / 022706 International Publication No. 2016 / 182003

[0005] However, the above-mentioned conventional films have room for further improvement in dielectric breakdown strength.

[0006] Therefore, an object of the present invention is to provide a film that can improve the value of dielectric breakdown strength.

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems, and have newly discovered that when a film contains a crystalline polymer and has a lamellar orientation degree in the through direction of 0.75 or more and an arithmetic mean roughness value of 0.03 μm or more, as determined by small-angle X-ray scattering measurement, the dielectric breakdown strength can be increased, thereby completing the present invention.

[0008] That is, the present invention aims to advantageously solve the above-mentioned problems, and the film of the present invention is characterized in that [1] it contains a crystalline polymer, and has a lamellar orientation degree in the through direction of 0.75 or more and an arithmetic mean roughness value of the surface of 0.03 μm or more, as obtained by small-angle X-ray scattering measurement. Thus, if the film satisfies the above composition and attributes, the dielectric breakdown strength value can be improved. Note that "small-angle X-ray scattering measurement" of the film can be performed according to the description in the Examples. The lamellar orientation degree in the through direction refers to the degree of orientation of the lamellar structure in the through direction, which is a structure in which polymer chains contained in the crystalline polymer are regularly folded, and can be measured by the method described in the Examples. The arithmetic mean roughness value of the film surface can also be measured by the method described in the Examples.

[0009] [2] The film of [1] above preferably has a thickness of 15 μm or less. The “thickness” of the film can be measured by the method described in the examples of this specification.

[0010] [3] In the film of [1] or [2] above, the static friction coefficient is preferably 0.3 or more and 2.5 or less. The "static friction coefficient" of the film can be measured by the method described in the examples of this specification.

[0011] [4] In any of the films [1] to [3] above, the lamellar long period in the through direction, as determined by small-angle X-ray scattering measurement, is preferably 220 Å or less. The "small-angle X-ray scattering measurement" of the film can be performed as described in the Examples. The "lamellar long period" refers to the distance between the centers of gravity of adjacent lamellar crystal portions.

[0012] [5] In the film of any one of the above [1] to [4], the crystalline polymer is preferably a hydrogenated dicyclopentadiene ring-opening polymer.

[0013] The present invention also aims to advantageously solve the above problems, and provides [6] a capacitor according to the present invention, characterized in that it comprises any one of the films [1] to [5] above.

[0014] The present invention also aims to advantageously solve the above-mentioned problems, and [7] the film manufacturing method of the present invention is a film manufacturing method for manufacturing any of the films described in [1] to [5] above, comprising a pre-crystallization step of heat-treating an unstretched film at a temperature equal to or higher than the glass transition temperature (Tg) of the hydrogenated dicyclopentadiene ring-opening polymer to form a pre-crystallized film, and a pre-crystallization step of heat-treating the pre-crystallized film at a temperature equal to or higher than the glass transition temperature (Tg) of the hydrogenated dicyclopentadiene ring-opening polymer to form a pre-crystallized film. The method includes a stretching step in which the stretched film is stretched at a temperature below Tm and at an areal stretch ratio of 6.0 to 20.0 times; a heat treatment step in which the stretched film stretched in the stretching step is heated at a heating temperature of 150°C to 240°C for a heating time of 600 minutes or less; and a relaxation step in which the stretched film heated in the heat treatment step is relaxed at a relaxation temperature of 150°C to 240°C for a relaxation time of 0.05 to 600 minutes so that a reduction ratio of the film fixing width is 0% to 20%. This film manufacturing method allows for efficient production of films with high dielectric breakdown strength. The "reduction ratio of the film fixing width" refers to the rate at which the film is held apart during the relaxation step.

[0015] Furthermore, the present invention may be as follows. [8] In the film of any of [1] to [4] above, the crystalline polymer preferably contains a crystalline polyolefin resin, specifically, a crystalline hydrogenated dicyclopentadiene ring-opening polymer as the polycycloolefin resin, or a propylene-based resin as the linear polyolefin resin. [9] In any of the films of [1] to [5] and [8] above, the dynamic friction coefficient preferably is 0.3 or more and 2.0 or less.

[10] In any of the films of [1] to [5], [8], and [9] above, the dielectric breakdown strength at 150°C measured on a film with a thickness of 3 μm is preferably 300 kV / mm or more.

[11] In any of the films of [1] to [5] and [8] to

[10] above, the crystallinity preferably is 8% or more.

[12] In the method for producing a film according to [7] above, the MD stretching ratio in the stretching step is preferably 2.0 times or more and 5.0 times or less, and the TD stretching ratio is preferably 2.5 times or more and 6.0 times or less.

[0016] According to the present invention, a film having a high dielectric breakdown strength can be provided.

[0017] The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be implemented with any modifications within the scope of the claims of the present invention and their equivalents. Furthermore, the components disclosed in this specification, as well as the preferred aspects, numerical ranges, and thresholds defining such numerical ranges, can be independently combined with each other in any manner.

[0018] (Film) The film of the present invention is a film containing a crystalline polymer, characterized in that the degree of lamellar orientation in the through direction obtained by small-angle X-ray scattering measurement is 0.75 or more and the arithmetic mean roughness of the surface is 0.03 μm or more. Furthermore, the film contains at least a crystalline polymer and may contain other components as necessary.

[0019] <Crystalline Polymer> The crystalline polymer is not particularly limited, and any polymer can be used. Specifically, the crystalline polymer can be a crystalline polyolefin resin, and particularly, a crystalline hydrogenated dicyclopentadiene ring-opening polymer, which is a polycycloolefin resin, and a propylene-based resin, which is a linear polyolefin resin, can be used.

[0020] <<Crystalline hydrogenated dicyclopentadiene ring-opening polymer>> The crystalline hydrogenated dicyclopentadiene ring-opening polymer is a hydrogenated dicyclopentadiene ring-opening polymer, which can be subjected to a stretching treatment or the like to give a film-like molded product having a melting point.

[0021] The term "crystalline hydrogenated dicyclopentadiene ring-opening polymer" refers to a hydrogenated dicyclopentadiene ring-opening polymer having a melting point Tm (i.e., a melting point that can be observed by differential scanning calorimetry (DSC)). The melting point Tm of the hydrogenated dicyclopentadiene ring-opening polymer is not particularly limited, but is preferably 200°C or higher, more preferably 220°C or higher, even more preferably 230°C or higher, and particularly preferably 250°C or higher, and is preferably 320°C or lower, more preferably 300°C or lower, even more preferably 290°C or lower, and particularly preferably 270°C or lower. Here, the term "dicyclopentadiene ring-opening polymer" refers to a polymer in which the proportion of dicyclopentadiene-derived structural units to all structural units is usually 50% by mass or higher, preferably 70% by mass or higher, more preferably 90% by mass or higher, even more preferably 95% by mass or higher, and particularly preferably 100% by mass. The structural units that the dicyclopentadiene ring-opening polymer can have are not particularly limited as long as they are structural units derived from monomers that are copolymerizable with dicyclopentadienes, and examples thereof include structural units derived from monomers such as norbornenes, cyclic olefins, and dienes.

[0022] An example of the hydrogenated crystalline dicyclopentadiene ring-opening polymer is the hydrogenated ring-opening polymer of syndiotactic dicyclopentadiene described in JP-A-2006-52333. Hereinafter, the "ring-opening polymer of syndiotactic dicyclopentadiene" will be referred to as "polymer (α)," and the "hydrogenated product of polymer (α)" will be referred to as "polymer (β)."

[0023] The glass transition temperature Tg of the crystalline hydrogenated dicyclopentadiene ring-opening polymer is not particularly limited, but is usually preferably 85°C or higher, more preferably 87°C or higher, even more preferably 90°C or higher, and particularly preferably 95°C or higher; and is preferably 170°C or lower, more preferably 150°C or lower, even more preferably 130°C or lower, and particularly preferably 105°C or lower.

[0024] [Polymer (α)] Polymer (α) can be obtained by ring-opening polymerization of dicyclopentadienes. The dicyclopentadienes used include endo and exo stereoisomers. Either the endo or exo isomer can be used as the dicyclopentadienes. Here, as the cyclopentadienes, either the endo or exo isomer may be used alone, or an isomer mixture in which the endo and exo isomers are present in any proportion may be used. In particular, from the viewpoint of improving the crystallinity and heat resistance of polymer (β), it is preferable to increase the proportion of one of the endo or exo stereoisomers, so that either the endo or exo isomer is the main component of the dicyclopentadienes. For example, the proportion of either the endo or exo isomer is preferably more than 50% by mass, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 97% by mass or more. From the viewpoint of ease of synthesis, it is preferable that the proportion of the endo isomer is high.

[0025] The polymer (α) may contain repeating units other than those derived from dicyclopentadiene, as long as they provide a crystalline polymer (β). Such a polymer (α) can be produced by ring-opening copolymerization of dicyclopentadiene and a monomer other than dicyclopentadiene. Examples of the monomer other than dicyclopentadiene include polycyclic norbornene compounds having three or more rings other than dicyclopentadiene, bicyclic norbornene compounds not having a ring structure condensed to the norbornene skeleton, monocyclic olefins, cyclic dienes, and derivatives thereof. When these monomers are used, their amount is typically less than 50% by mass, preferably more than 0% by mass but not more than 20% by mass, and more preferably more than 0% by mass but not more than 10% by mass, based on the total amount of monomers.

[0026] The types and amounts of catalysts and other additives used in producing the polymer (α) may be determined in accordance with, for example, WO 2019 / 167682.

[0027] The crystallinity of polymer (α) can usually be increased by increasing the degree of syndiotactic stereoregularity (ratio of racemo-dyads (meso / racemo ratio)). The ratio of racemo-dyads (degree of syndiotactic stereoregularity) of polymer (α) is not particularly limited, but from the viewpoint of increasing the degree of stereoregularity, it is preferably 51% or more, more preferably 60% or more, particularly preferably 65% ​​or more, and most preferably 70% or more. The ratio of racemo-dyads of polymer (α) can be adjusted by selecting the type of ring-opening polymerization catalyst, for example.

[0028] The weight-average molecular weight (Mw) of the dicyclopentadiene ring-opening polymer is not particularly limited, but is preferably 1,000 to 1,000,000, and more preferably 2,000 to 500,000. By subjecting a ring-opening polymer having such a weight-average molecular weight to a hydrogenation reaction, a polymer (β) with excellent moldability can be obtained. The weight-average molecular weight of the ring-opening polymer can be adjusted by adjusting the amount of molecular weight modifier used during polymerization. The molecular weight distribution (Mw / Mn) of the dicyclopentadiene ring-opening polymer is not particularly limited, but is preferably 1.0 to 4.0, and more preferably 1.5 to 3.5. By subjecting a ring-opening polymer having such a molecular weight distribution to a hydrogenation reaction, a polymer (β) with excellent moldability can be obtained. The molecular weight distribution of the ring-opening polymer can be adjusted by the method of adding monomers and the concentration of monomers during the polymerization reaction. The weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the dicyclopentadiene ring-opening polymer are polystyrene-equivalent values ​​measured by gel permeation chromatography (GPC) using tetrahydrofuran as a developing solvent.

[0029] [Polymer (β)] Polymer (β) can be produced by carrying out a hydrogenation reaction (hydrogenation reaction of carbon-carbon unsaturated bonds) of polymer (α). The hydrogenation reaction of polymer (α) can be carried out, for example, by supplying hydrogen to a reaction system containing polymer (α) in the presence of a hydrogenation catalyst according to a conventional method. In this hydrogenation reaction, if the reaction conditions are appropriately set, the tacticity of the hydrogenated product usually does not change due to the hydrogenation reaction. Such hydrogenation reaction conditions can be, for example, as described in WO 2019 / 167682.

[0030] The hydrogenation rate (proportion of hydrogenated double bonds) in the hydrogenation reaction is not particularly limited, but is preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, particularly preferably 98% or more, and most preferably 99% or more. The higher the hydrogenation rate, the more improved the heat resistance of the polymer (β). Here, the hydrogenation rate of the polymer is determined by the reaction of orthodichlorobenzene-d ４ as a solvent at 145°C, １ It can be calculated by H-NMR measurement.

[0031] In polymer (β), the syndiotactic stereoregularity of polymer (α) subjected to hydrogenation is usually maintained. Therefore, polymer (β) has syndiotactic stereoregularity. The ratio of racemo dyads in polymer (β) (i.e., the ratio of racemo dyads in the repeating units obtained by ring-opening polymerization of dicyclopentadiene to obtain a ring-opened polymer and hydrogenating the ring-opened polymer) is not particularly limited as long as polymer (β) is crystalline, but is preferably 51% or more, more preferably 60% or more, particularly preferably 65% ​​or more, and most preferably 70% or more. The higher the ratio of racemo dyads, i.e., the higher the syndiotactic stereoregularity, the higher the melting point of the hydrogenated dicyclopentadiene ring-opening polymer.

[0032] The ratio of the racemo-dyad of the polymer (α) and the polymer (β) is: １３ The C-NMR spectrum can be measured and quantified based on the spectral data. ３ and orthodichlorobenzene-d ４ Using a mixed solvent of the above, the inverse-gated decoupling method was applied at 200°C. １３ C-NMR measurement was performed to identify orthodichlorobenzene-d ４The ratio of racemo dyads can be determined from the intensity ratio of the signal at 43.35 ppm derived from meso dyads to the signal at 43.43 ppm derived from racemo dyads, using the peak at 127.5 ppm as the reference shift.

[0033] The polymer (β) is crystalline (i.e., it is capable of producing a film-shaped molded product having a melting point). The temperature range of the melting point is not particularly limited, but is usually 260 to 275°C. A polymer (β) having such a melting point has an excellent balance between moldability and heat resistance. The melting point of the polymer (β) can be adjusted by adjusting the degree of syndiotactic stereoregularity (racemo-dyad ratio) or by selecting the type of monomer used. When using the polymer (β), the polymer (β) alone may be used, or other components may be added to the polymer (β).

[0034] <<Propylene-Based Resin>> Examples of propylene-based resins include propylene homopolymers (polypropylene) and copolymers of propylene and other olefins. The propylene-based resins may be used alone or in combination of two or more. The copolymers of propylene and other olefins may be either block copolymers or random copolymers. Examples of olefins copolymerized with propylene include α-olefins such as ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene, and 1-decene.

[0035] <Other Components> The film of the present invention may contain other components in addition to those described above, as necessary. Such other components include antioxidants such as antiblocking agents, phenolic antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants; light stabilizers such as hindered amine-based light stabilizers; waxes such as petroleum waxes, Fischer-Tropsch waxes, and polyalkylene waxes; nucleating agents such as sorbitol-based compounds, metal salts of organic phosphoric acids, metal salts of organic carboxylic acids, kaolin, and talc; diaminostilbene derivatives, coumarin derivatives, and azole derivatives (e.g., benzoxazole derivatives, benzotriazole derivatives, and benzimidazole derivatives); Examples of other components include fluorescent brighteners such as benzothiazole derivatives, benzothiazole derivatives, carbazole derivatives, pyridine derivatives, naphthalic acid derivatives, and imidazolone derivatives; ultraviolet absorbers such as benzophenone-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, and benzotriazole-based ultraviolet absorbers; inorganic fillers such as talc, silica, calcium carbonate, and glass fiber; colorants; flame retardants; flame retardant assistants; antistatic agents; plasticizers; near-infrared absorbers; lubricants; fillers other than antiblocking agents, and polymeric materials other than polymer (β), such as soft polymers. Furthermore, one type of other component may be used alone, or two or more types may be used in combination at any ratio.

[0036] When other components are used, the amount of the other components is not particularly limited as long as it does not impair the effects of the present invention and can be appropriately determined depending on the purpose. The content of the other components is not particularly limited, but is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less, per 100 parts by mass of the crystalline hydrogenated dicyclopentadiene ring-opening polymer. It is particularly preferable that the film of the present invention does not contain the above-mentioned other components, i.e., foreign materials. The film of the present invention has excellent handleability even when it does not contain such foreign materials. The absence of foreign materials in the film can suppress the occurrence of problems associated with foreign materials, for example, when the film of the present invention is used in the production of capacitors. For example, problems associated with foreign materials include reduced risk of contamination of the production equipment due to foreign materials falling off the film and / or reduced risk of foreign matter being introduced into the film.

[0037] The film of the present invention can be obtained, for example, by subjecting an unstretched film, which is obtained by molding a composition containing the above-mentioned crystalline polymer by a known molding method, to the respective steps (pre-crystallization step, stretching step, heat treatment step, and relaxation treatment step) in the film manufacturing method described below. The film properties are described in detail below.

[0038] <Lamellar orientation degree in the through direction> The lamellar orientation degree in the through direction of the film of the present invention, as determined by small-angle X-ray scattering measurement, must be 0.75 or more, preferably 0.76 or more, and more preferably 0.77 or more. Here, with regard to the lamellar orientation degree in the through direction determined by small-angle X-ray scattering measurement, specifically, when the lamellar orientation degree in the through direction is 0.75 or more, the molecular chain axis is roughly parallel to the film surface and oriented in the MD (machine direction) or TD (transverse direction), and the crystalline phase approaches complete orientation (i.e., the amorphous phase also approaches complete orientation), which is considered to result in excellent electrical resistance characteristics, i.e., insulating properties, in the thickness direction of the film (direction perpendicular to the MD and TD directions). The upper limit of the lamellar orientation degree in the Through direction is not particularly limited, but may be 0.90 or less from the viewpoint of handleability and flexibility during the production of capacitor elements, etc. The lamellar orientation degree in the Through direction can be controlled by appropriately controlling the heating temperature and heating time in the pre-crystallization step during film production to appropriately adjust the crystallinity, etc. of the film, and then performing the various subsequent steps. More specifically, the orientation degree value can be controlled to an appropriate value by designing a high areal stretching ratio in the stretching step.

[0039] <Long Lamellar Period in the Through Direction> The long lamellar period in the through direction of the film of the present invention, as determined by small-angle X-ray scattering, is preferably 220 Å or less, more preferably 215 Å or less, even more preferably 210 Å or less, and particularly preferably 205 Å or less. Here, the long lamellar period in the through direction determined by small-angle X-ray scattering is a parameter representing the distance between lamellar centers in the lamellar structure of a crystalline polymer. More specifically, it is the length of one period when the crystalline portion and amorphous portion constituting the lamellar structure are considered as one repeating unit. The value of the long lamellar period in the through direction determined by small-angle X-ray scattering is affected by the crystallinity and orientation of the polymer. A large value of the "long lamellar period in the through direction" measured for a certain crystalline polymer means that the distance between lamellar centers in the lamellar structure of the crystalline polymer is long. In light of the above, this corresponds to a large sum of the thickness of the crystalline portion and the thickness of the amorphous portion. When the "sum of the thickness of the crystalline portion and the thickness of the amorphous portion is large," the cause may be a low degree of crystallinity of the polymer and a low periodicity of the lamellar structure. Therefore, if the value of the "lamellar long period in the Through direction" is large, it is considered that the dielectric breakdown strength, particularly the dielectric breakdown strength at high temperatures, is poor. Therefore, if the lamellar long period in the Through direction is equal to or less than the above upper limit, it is considered that the dielectric breakdown strength value of the film at high temperatures can be increased.

[0040] The lower limit of the lamellar long period in the through direction is not particularly limited, but may be 80 Å or more, or 110 Å or more, or even 130 Å or more, or 150 Å or more.

[0041] The value of the lamellar long period in the Through direction can be controlled by appropriately controlling the heating temperature and heating time in the pre-crystallization step during film production to appropriately adjust the crystallinity of the film, and then performing the subsequent various steps. More specifically, the value of the lamellar long period in the Through direction can be controlled to an appropriate value by increasing the film crystallinity in the pre-crystallization step and adjusting the areal stretching ratio in the stretching step.

[0042] <Arithmetic Mean Roughness of Surface> The arithmetic mean roughness of the surface of the film of the present invention must be 0.03 μm or more, more preferably 0.04 μm or more, preferably 0.15 μm or less, and more preferably 0.10 μm or less. When the arithmetic mean roughness of the film surface is equal to or greater than the above-mentioned lower limit, the film will have moderate slipperiness without being excessively slippery, thereby improving processability during film production and when using such a film to manufacture electrochemical devices such as capacitors. Furthermore, when the arithmetic mean roughness of the film surface is equal to or less than the above-mentioned upper limit, uniform coating can be achieved during surface treatment, such as vapor deposition and functional coating required for capacitor elements. The arithmetic mean roughness of the film surface can be controlled by appropriately controlling the heating temperature and heating time in the pre-crystallization step during film production to appropriately adjust the crystallinity of the film before carrying out the various subsequent steps. More specifically, by controlling the preheating temperature and preheating time in the pre-crystallization step to achieve appropriate crystallization, and then refining the crystals formed in the stretching step, the arithmetic mean roughness value of the film surface can be controlled to an appropriate value.

[0043] <Static Friction Coefficient> The static friction coefficient of the film of the present invention is preferably 0.3 or more, more preferably 0.4 or more, even more preferably 0.5 or more, and preferably 2.5 or less, more preferably 1.5 or less, and even more preferably 1.0 or less. If the static friction coefficient of the film is within the above range, the resistance when unwinding the film from a film roll made of the film of the present invention can be prevented from becoming excessively high or low. This makes the film of the present invention easy to handle when manufacturing electrochemical devices such as capacitors, thereby facilitating the production of highly reliable capacitors. The static friction coefficient of the film can be controlled by appropriately controlling the heating temperature and heating time in the pre-crystallization step during film production to appropriately adjust the film's crystallinity, etc., before carrying out the various subsequent steps. More specifically, the static friction coefficient of the film can be controlled to an appropriate value by increasing the film's crystallinity in the pre-crystallization step and adjusting the stretching areal ratio in the stretching step.

[0044] <Dynamic Friction Coefficient> The dynamic friction coefficient of the film of the present invention is preferably 0.3 or more, more preferably 0.4 or more, even more preferably 0.5 or more, and preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.0 or less. When the dynamic friction coefficient of the film is within the above range, the winding property of the film when wound into a roll during production of the film of the present invention can be improved. This prevents the film from wrinkling and twisting when wound into a roll, and ultimately improves the reliability of the resulting capacitor when an electrochemical device such as a capacitor is manufactured using such a rolled film. The dynamic friction coefficient of the film can be controlled by appropriately controlling the heating temperature and heating time in the pre-crystallization step during film production to appropriately adjust the crystallinity of the film, and then performing the various subsequent steps. More specifically, the dynamic friction coefficient of the film can be controlled to an appropriate value by increasing the film's crystallinity in the pre-crystallization step and adjusting the areal stretching ratio in the stretching step.

[0045] <Film Thickness> The film thickness of the film of the present invention can be appropriately set depending on the application, but is preferably 15 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. When the film thickness is equal to or less than the above upper limit, when a capacitor is formed using the film of the present invention, the capacitor can be made large-capacity and small-sized. The lower limit of the film thickness is not particularly limited, but may be 2 μm or more from the viewpoint of ensuring dielectric breakdown characteristics, mechanical strength, etc. The film thickness can be controlled, for example, by appropriately adjusting the areal stretching ratio in the stretching step in the manufacturing process described below.

[0046] <Dielectric breakdown strength> The film of the present invention preferably has a dielectric breakdown strength of 300 kV / mm or more, more preferably 305 kV / mm or more, measured at 150°C (i.e., high temperature) for a film having a thickness of 3 µm. The upper limit of the dielectric breakdown strength measured at 150°C for a film having a thickness of 3 µm is not particularly limited, but may be, for example, 500 kV / mm or less.

[0047] (Crystallization degree) The film of the present invention preferably has a crystallinity of 8% or more, more preferably 12% or more, and even more preferably 15% or more. An increase in crystallinity means that the surface morphology of the film changes due to crystal growth. Specifically, it is believed that crystals present on the film surface grow, increasing surface roughness. In such films, the sliding interface is in contact at points rather than at a surface, which is thought to improve slipperiness. The upper limit of the film's crystallinity is not particularly limited, but may be, for example, 50% or less, 40% or less, or 30% or less. The crystallinity of the film can be measured according to the density calculation method described in the examples.

[0048] (Capacitor) The film of the present invention is optionally subjected to a surface treatment such as a corona treatment or a plasma treatment, and then cut to a predetermined size and used as a capacitor material. Examples of capacitors using the film include laminated film capacitors in which film and metal layers are alternately laminated, and wound film capacitors in which a tape-like film and a metal layer are wound together. There are no particular limitations on the method for producing these capacitors, and conventionally known methods can be used. The use of the film of the present invention is not limited to capacitors.

[0049] (Film Manufacturing Method) The film manufacturing method of the present invention (hereinafter sometimes simply referred to as the "manufacturing method") includes at least a pre-crystallization step, a stretching step, a heat treatment step, and a relaxation step. Furthermore, the manufacturing method of the present invention may include other steps in addition to the above-mentioned steps, as necessary. In the following description, a "long" film refers to a film having a length five times or more its width, preferably 10 times or more its width, specifically a film long enough to be wound into a roll for storage or transportation. Furthermore, unless otherwise specified, the element directions "parallel," "perpendicular," and "orthogonal" may include an error within a range that does not impair the effects of the present invention, for example, within a range of ±5°. Furthermore, the longitudinal direction of a long film is usually parallel to the film transport direction in the production line. In the following description, the crystalline polymer constituting the film of the present invention is a hydrogenated dicyclopentadiene ring-opening polymer.

[0050] <Pre-crystallization step> In the pre-crystallization step, the unstretched film is heat-treated at a temperature equal to or higher than the glass transition temperature (Tg) of the hydrogenated dicyclopentadiene ring-opening polymer to form a pre-crystallized film. Hereinafter, the temperature "equal to or higher than the glass transition temperature (Tg) + 20°C" in this heat treatment may be referred to as the "pre-heating temperature (Tp)," and the time required for the heat treatment may be referred to as the "pre-heating time (tp)." In this pre-crystallization step, crystallization of the alicyclic crystalline polymer contained in the crystalline resin may proceed.

[0051] The preheating temperature Tp must be equal to or higher than the glass transition temperature Tg of the hydrogenated dicyclopentadiene ring-opening polymer + 20°C, preferably equal to or higher than "Tg + 26°C", and more preferably equal to or higher than "Tg + 31°C". The upper limit of the preheating temperature Tp is not particularly limited, but is usually equal to or lower than "Tg + 60°C", preferably equal to or lower than "Tg + 55°C", and more preferably equal to or lower than "Tg + 50°C". When the preheating temperature Tp is within the above range, the slipperiness of the film obtained by the production method according to this embodiment can be improved, and further, internal haze and coloration can usually be reduced.

[0052] Furthermore, the conditions for the pre-crystallization step are preferably set so as to satisfy the following condition, using the crystallization peak temperature (Tc) of the polymer as a standard. The pre-heating time tp is usually set so that the pre-heating temperature Tp [°C] and the pre-heating time tp [seconds] satisfy the following formula (i). In formula (i), the units of the pre-heating temperature Tp and the crystallization peak temperature Tc of the crystalline resin are "°C", and the unit of the pre-heating time tp is "seconds". 2000≦{Tp-(Tc-15)} ２ ×tp≦30000 (i)

[0053] More specifically, {Tp-(Tc-15)} ２ The parameter represented by ×tp is preferably 2000 or more, more preferably 3000 or more, and is preferably 30000 or less, more preferably 28000 or less, and even more preferably 25000 or less. In the following description, "{Tp-(Tc-15)} ２ The parameter expressed as "×tp" is sometimes referred to as the "preheating parameter." When the preheating parameter is within the above range, the slipperiness of the resin film obtained by the production method according to this embodiment can be improved. Furthermore, when the preheating parameter is equal to or greater than the lower limit of the above range, the crystallization of the hydrogenated dicyclopentadiene ring-opening polymer can be favorably promoted in the pre-crystallization step. Furthermore, when the preheating parameter is equal to or less than the upper limit of the above range, excessive progress of crystallization of the hydrogenated dicyclopentadiene ring-opening polymer can be suppressed.

[0054] The pre-crystallization step can be carried out, for example, by exposing the unstretched film to an atmosphere adjusted to a preheating temperature Tp for a preheating time tp. In this case, the pre-crystallization step can be carried out using a temperature control device, such as an oven, that can adjust the temperature of the atmosphere around the unstretched film. Since unstretched films are generally thin, when the above-mentioned temperature control device is used, the temperature of the unstretched film can usually be the same as the temperature of the atmosphere adjusted by the temperature control device. Therefore, the preheating temperature Tp can be the same as the set temperature of the temperature control device.

[0055] Alternatively, the pre-crystallization step can be carried out, for example, by bringing the unstretched film into contact with a heating section adjusted to a pre-heating temperature Tp for a pre-heating time tp. In this case, the pre-crystallization step can be carried out using a heating device having a heating section, such as a hot plate. When such a heating device is used, the temperature of the unstretched film can usually be the same as the temperature of the heating section. Therefore, the pre-heating temperature Tp can be the same as the set temperature of the heating device.

[0056] In particular, the pre-crystallization step is preferably carried out using an apparatus capable of heating the unstretched film without contact, and specific examples of such an apparatus include an oven and a heating furnace.

[0057] As a preferred specific example, the pre-crystallization step can be carried out using a temperature-adjustable oven. For example, the pre-crystallization step can be carried out by storing an unstretched film in an oven and adjusting the temperature of the oven to satisfy the above-mentioned conditions. As another preferred specific example, the pre-crystallization step can be carried out using an oven having an internal film transport path. For example, the pre-crystallization step can be carried out by transporting an unstretched film through the film transport path of an oven whose temperature is adjusted to satisfy the above-mentioned conditions for a time period that satisfies the above-mentioned conditions.

[0058] The pre-crystallization step is usually carried out so that the unstretched film is not substantially stretched. The term "substantially stretched" means that the unstretched film is stretched to a stretching ratio of 1.1 or more in any direction.

[0059] Furthermore, in the pre-crystallization step, the unstretched film is preferably in a tensed state. The term "tensed state" of the unstretched film refers to a state in which tension is applied to the unstretched film. However, this tensed state does not include a state in which the unstretched film is substantially stretched.

[0060] For example, the unstretched film can be placed in a tensed state by holding a part or the whole of the unstretched film with an appropriate holder.

[0061] The unstretched film used in this step is an unstretched film containing a hydrogenated dicyclopentadiene ring-opening polymer. This unstretched film can be produced by a resin molding method, such as injection molding, extrusion molding, press molding, inflation molding, blow molding, calendar molding, cast molding, or compression molding. Among these, extrusion molding is preferred because it allows for easy thickness control. When producing an unstretched film (raw film) by extrusion molding, the production conditions for the extrusion molding method are as follows: The cylinder temperature (molten resin temperature) is not particularly limited, but is preferably 250°C or higher and 330°C or lower. The cast roll temperature is not particularly limited, but is preferably 45°C or higher and 160°C or lower. The chill roll temperature is not particularly limited, but is preferably 25°C or higher and 150°C or lower. The thickness of the unstretched film is not particularly limited, but is preferably 1 μm or higher and 1 mm or lower.

[0062] <Stretching Step> The stretching step is a step in which the pre-crystallized film obtained in the above-described pre-crystallization step is stretched under temperature conditions of not less than the glass transition temperature Tg of the hydrogenated dicyclopentadiene ring-opening polymer and not more than the melting point Tm of the hydrogenated dicyclopentadiene ring-opening polymer, at an areal stretching ratio of not less than 6.0 and not more than 20.0.

[0063] The stretching method in the stretching step is not particularly limited, and any stretching method can be used. Examples include uniaxial stretching methods such as a method of uniaxially stretching an unstretched film in the longitudinal direction (longitudinal uniaxial stretching method) or a method of uniaxially stretching an unstretched film in the width direction (transverse uniaxial stretching method); biaxial stretching methods such as a simultaneous biaxial stretching method in which an unstretched film is stretched in the longitudinal direction and simultaneously in the width direction, and a sequential biaxial stretching method in which an unstretched film is stretched in one of the longitudinal direction and the width direction and then stretched in the other direction; and a method of stretching an unstretched film in an oblique direction that is neither parallel nor perpendicular to the width direction (oblique stretching method).

[0064] Examples of the longitudinal uniaxial stretching method include a stretching method utilizing the difference in peripheral speed between rolls. Examples of the transverse uniaxial stretching method include a stretching method using a tenter stretching machine. Examples of the simultaneous biaxial stretching method include a stretching method using a tenter stretching machine equipped with a plurality of clips movably arranged along guide rails and capable of fixing the unstretched film, in which the unstretched film is stretched in the longitudinal direction with the clips spaced apart and simultaneously stretched in the width direction by the spread angle of the guide rails. Examples of the sequential biaxial stretching method include a stretching method in which the unstretched film is stretched in the longitudinal direction by utilizing the difference in peripheral speed between rolls, and then both ends of the unstretched film are gripped with clips and stretched in the width direction by the tenter stretching machine. Further, examples of the oblique stretching method include a stretching method in which an unstretched film is continuously stretched in an oblique direction using a tenter stretching machine that can apply a feeding force, a pulling force, or a take-up force at different speeds to the unstretched film in the longitudinal direction or width direction.

[0065] [Stretching Temperature] The stretching temperature is not particularly limited, but from the viewpoints of preventing film breakage during stretching and preventing a decrease in productivity due to clip detachment, it is preferably equal to or higher than the glass transition temperature Tg of the hydrogenated dicyclopentadiene ring-opening polymer, specifically, preferably 100° C. or higher, more preferably 105° C. or higher, even more preferably 110° C. or higher, and particularly preferably 115° C. or higher. Furthermore, from the viewpoint of efficiently producing a film with a small thermal shrinkage rate, it is preferably equal to or lower than the melting point Tm of the hydrogenated dicyclopentadiene ring-opening polymer, specifically, preferably 160° C. or lower, more preferably 150° C. or lower, and particularly preferably 140° C. or lower. By setting the stretching temperature to be equal to or higher than the glass transition temperature Tg and lower than the melting point Tm of the hydrogenated dicyclopentadiene ring-opening polymer, it is possible to appropriately orient the polymer molecules contained in the film.

[0066] [Stretching ratio] The "stretching ratio" includes the stretching ratio in the MD (Machine Direction) direction and the TD (Transverse Direction). Here, the flow direction in which the unstretched film is fed into the stretching device is defined as the MD, and the direction perpendicular to the MD on the film plane is defined as the TD (Transverse Direction). The stretching ratio in the MD direction (hereinafter sometimes referred to as the MD stretching ratio) is the quotient obtained by dividing the MD length after stretching by the MD length before stretching. In other words, the MD stretching ratio = MD length after stretching / MD length before stretching. In this case, the obtained quotient is rounded down to one decimal place. The MD stretching ratio is preferably 2.0 times or more, and is preferably 5.0 times or less, more preferably 4.5 times or less, even more preferably 4.0 times or less, and particularly preferably 3.5 times or less, in order to enable efficient production of the film.

[0067] The TD stretching ratio is preferably 2.5 times or more, more preferably 3.2 times or more, preferably 6.0 times or less, more preferably 5.5 times or less, even more preferably 5.0 times or less, and particularly preferably 4.5 times or less.

[0068] [Stretching areal ratio] In this specification, the "stretching areal ratio" is the product of the MD stretching ratio and the TD stretching ratio. The obtained product is rounded down to the first decimal place. The areal ratio is preferably 6.0 times or more, more preferably 6.4 times or more, from the viewpoint of efficiently producing a film with high dielectric breakdown strength. Furthermore, the areal ratio is preferably 20.0 times or less, more preferably 16.0 times or less, and even more preferably 11.0 times or less. If the stretching areal ratio is equal to or greater than the above lower limit, the dielectric breakdown properties of the obtained film can be further improved. Furthermore, if the stretching areal ratio is equal to or less than the above upper limit, the film breaks less and the uniformity of the film thickness of the obtained film can be improved, resulting in efficient production of a film with excellent productivity.

[0069] [Stretching Speed] The stretching speed is not particularly limited, but is preferably 100 mm / min or more, more preferably 150 mm / min or more, and particularly preferably 200 mm / min or more, from the viewpoint of efficiently producing a film with high dielectric breakdown strength. Furthermore, from the viewpoint of preventing film breakage during stretching and preventing a decrease in productivity due to clip detachment, the stretching speed is preferably 30,000 mm / min or less, more preferably 20,000 mm / min or less, and particularly preferably 5,000 mm / min or less.

[0070] By subjecting the pre-crystallized film to the above-described stretching treatment, a film having desired properties can be obtained. Furthermore, by subjecting the pre-crystallized film to the stretching treatment, the generation of large crystal grains in the heat treatment step (crystallization step) can be suppressed, thereby suppressing whitening caused by the crystal grains and thereby improving the transparency of the film.

[0071] <Heat Treatment Step> The heat treatment step is a step in which the stretched film stretched in the stretching step is heated at a predetermined heating temperature for a predetermined heating time.

[0072] When the stretched film obtained by the stretching treatment is heat-treated, the heating method is not particularly limited, and any known method can be used as appropriate. Examples of the heating method include a method in which the stretched film is fixed to a table and then heated using a heating device such as a heat treatment oven or an infrared heater.

[0073] [Heating Temperature] The heating temperature is not particularly limited, but from the viewpoint of improving the dielectric breakdown strength, particularly the dielectric breakdown strength at high temperatures, it is preferably 150°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, and particularly preferably 180°C or higher. Furthermore, from the viewpoint of enabling efficient production of a film, it is preferably 250°C or lower, more preferably 240°C or lower, and particularly preferably 230°C or lower.

[0074] [Heating Time] The heating time is not particularly limited, but from the viewpoint of improving the dielectric breakdown strength, particularly the dielectric breakdown strength at high temperatures, it is preferably 3 seconds (0.05 minutes) or more, and more preferably 6 seconds (0.1 minutes) or more, and from the viewpoint of efficiently producing a film, it is preferably 600 minutes or less, more preferably 300 minutes or less, even more preferably 200 minutes or less, even more preferably 100 minutes or less, and particularly preferably 30 minutes or less.

[0075] The heating device used in this case is preferably a heating device that can increase the ambient temperature of the stretched film, since contact between the heating device and the stretched film is not required. Specific examples of suitable heating devices include an oven and a heating furnace. After the stretched film is prepared, a heat treatment step is carried out to crystallize the hydrogenated dicyclopentadiene ring-opening polymer contained in the stretched film. In the heat treatment step, at least two sides of the stretched film are held and tensioned while the temperature is kept within a predetermined range, thereby carrying out a crystallization treatment to crystallize the hydrogenated dicyclopentadiene ring-opening polymer.

[0076] Here, the term "tensioned stretched film" refers to a state in which tension is applied to the stretched film. However, this state of tensioned stretched film does not include a state in which the stretched film is substantially further stretched. Furthermore, "substantially further stretched" generally refers to a stretching ratio of 1.1 or more in any direction of the stretched film.

[0077] When holding the stretched film, the stretched film is held by an appropriate holder. The holder may be capable of continuously holding the entire length of the side of the stretched film, or may be capable of holding it intermittently at intervals. For example, the side of the stretched film may be held intermittently by holders arranged at predetermined intervals.

[0078] In the heat treatment step, the stretched film is preferably heated to a temperature (150°C to 250°C) that is equal to or higher than the glass transition temperature Tg of the hydrogenated dicyclopentadiene ring-opening polymer and equal to or lower than the melting point Tm of the hydrogenated dicyclopentadiene ring-opening polymer, while at least two edges of the stretched film are held and tensioned as described above. In a stretched film heated to such a temperature, crystallization of the hydrogenated dicyclopentadiene ring-opening polymer proceeds. Therefore, this heat treatment step results in a heat-stretched film (crystallized film) containing a crystallized hydrogenated dicyclopentadiene ring-opening polymer. Since the heat-stretched film is kept in a tensioned state while preventing deformation, crystallization can proceed without impairing the smoothness of the heat-stretched film.

[0079] <Relaxation Treatment Step> The relaxation treatment step is a step in which the stretched film heated in the heat treatment step is relaxed at a predetermined relaxation temperature for a predetermined relaxation time at a predetermined reduction rate for a fixed film width.

[0080] [Relaxation Temperature] The relaxation temperature is not particularly limited, but from the viewpoint of improving the dielectric breakdown strength, particularly the dielectric breakdown strength at high temperatures, it is preferably 150°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, and particularly preferably 180°C or higher. From the viewpoint of efficient film production, it is preferably 250°C or lower, more preferably 240°C or lower, and particularly preferably 230°C or lower. Furthermore, when the relaxation treatment step is performed immediately after the heat treatment step without cooling, it is preferable that the treatment temperature of the heat-stretched film in the relaxation treatment step be the same as the temperature in the heat treatment step. This can suppress temperature unevenness of the heat-stretched film in the relaxation treatment step and increase film productivity.

[0081] [Relaxation Time] The relaxation time is not particularly limited, but is preferably 3 seconds (0.05 minutes) or more, and more preferably 6 seconds (0.1 minutes) or more, from the viewpoint of enabling efficient production of a film with a small thermal shrinkage rate, and is preferably 600 minutes or less, more preferably 300 minutes or less, even more preferably 200 minutes or less, and particularly preferably 100 minutes or less, from the viewpoint of enabling efficient production of a film.

[0082] [Film Fixing Width Reduction Ratio] Although not particularly limited, in order to efficiently produce a film with a small thermal shrinkage, the film fixing width reduction ratio, at least one of the longitudinal (MD) and transverse (TD) shrinkage ratios, is preferably 0% or more, more preferably 0.2% or more, even more preferably 0.4% or more, and particularly preferably 0.6% or more. Furthermore, although not particularly limited, in order to ensure uniformity of the film surface (surface condition), the film fixing width reduction ratio, at least one of the longitudinal (MD) and transverse (TD) shrinkage ratios, is preferably 20% or less, more preferably 15% or less, even more preferably 13% or less, and particularly preferably 10% or less. The "film fixing width reduction ratio" refers to the ratio by which the film holding interval is narrowed during the relaxation treatment process.

[0083] After the heat treatment step, a relaxation step is carried out to thermally shrink the heat-stretched film obtained in the heat treatment step and remove residual stress. In the relaxation step, the heat-stretched film obtained in the heat treatment step is subjected to a relaxation treatment in a predetermined temperature range to relieve tension in the heat-stretched film while maintaining the film flat.

[0084] "Relieving the tension of the heat-stretched film" refers to releasing the heat-stretched film from a state in which it has been held by a holding device and is under tension; the heat-stretched film may be held by a holding device as long as it is not under tension. When the tension is relieved in this way, the heat-stretched film is in a state in which it can undergo thermal shrinkage. In the relaxation treatment step, thermal shrinkage of the heat-stretched film is caused, thereby eliminating stress that can occur in the film when heated. Therefore, the heat shrinkage of the film of the present invention in a high-temperature environment can be reduced, resulting in a film with excellent dimensional stability in a high-temperature environment.

[0085] The tension of the heat-stretched film may be relaxed all at once, or may be relaxed continuously or stepwise over time, although continuous or stepwise relaxation is preferred to prevent the resulting film from becoming wavy, wrinkled, or otherwise deformed.

[0086] The tension of the heat-stretched film is relaxed while maintaining the heat-stretched film flat. "Maintaining the heat-stretched film flat" means maintaining the heat-stretched film in a planar shape so as to prevent deformation such as waviness and wrinkles from occurring in the heat-stretched film. This can prevent deformation such as waviness and wrinkles from occurring in the resulting film.

[0087] When a sheet of heat-stretched film is subjected to relaxation treatment in the relaxation treatment step as described above, for example, a method can be employed in which the spacing between the held portions is narrowed continuously or stepwise while holding the four sides of the heat-stretched film. In this case, the spacing between the held portions on all four sides of the heat-stretched film may be narrowed simultaneously. Alternatively, the spacing between the held portions on some sides may be narrowed first, and then the spacing between the held portions on other sides may be narrowed. Furthermore, the spacing between the held portions on some sides may be maintained without being narrowed. Alternatively, the spacing between the held portions on some sides may be narrowed continuously or stepwise, and the spacing between the held portions on other sides may be narrowed all at once.

[0088] Furthermore, when a long heat-stretched film is subjected to a relaxation treatment in the relaxation treatment step as described above, for example, a tenter stretching machine may be used, in which the interval between guide rails that can guide the clips is narrowed in the transport direction of the heat-stretched film, or the interval between adjacent clips is narrowed.

[0089] As described above, when the tension of the heat-stretched film is relieved by narrowing the gap between the holding portions while the heat-stretched film is held, the degree to which the gap is narrowed can be set depending on the magnitude of the stress remaining in the heat-stretched film obtained in the heat treatment step. Large stress tends to remain in the heat-stretched film obtained by the heat treatment step. Therefore, it is preferable to narrow the gap between the holding portions to a large extent in order to relieve the tension of the heat-stretched film.

[0090] <Other Steps> The other steps are not particularly limited, and for example, the obtained film may be subjected to a surface treatment.

[0091] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. Furthermore, the operations described below were carried out under conditions of room temperature and normal pressure unless otherwise specified. In the examples and comparative examples, various measurements and evaluations were carried out as follows.

[0092] <Molecular Weight (Weight Average Molecular Weight and Number Average Molecular Weight) of Ring-Opened Polymer of Dicyclopentadiene> A solution containing a ring-opened polymer of dicyclopentadiene was collected to prepare a measurement sample. The molecular weight of the ring-opened polymer of dicyclopentadiene obtained was determined as a polystyrene equivalent value using a gel permeation chromatography (GPC) system HLC-8320 (manufactured by Tosoh Corporation) with an H-type column (manufactured by Tosoh Corporation) at a temperature of 40°C and tetrahydrofuran as a solvent.

[0093] <Glass Transition Temperature and Melting Point of Hydrogenated Dicyclopentadiene Ring-Opening Polymer> The obtained hydrogenated dicyclopentadiene ring-opening polymer was used as a measurement sample. The obtained measurement sample was heated to 320°C under a nitrogen atmosphere and then quenched to room temperature at a cooling rate of -10°C / min using liquid nitrogen. Using a differential scanning calorimeter (DSC), the temperature was increased at a rate of 10°C / min, and the glass transition temperature and melting point of the hydrogenated dicyclopentadiene ring-opening polymer were determined.

[0094] <Racemo-dyad ratio of hydrogenated ring-opening polymer of dicyclopentadiene> The obtained hydrogenated ring-opening polymer of dicyclopentadiene was used as a measurement sample. ４ / 1,2,4-trichlorobenzene (TCB)-d ３ (mixing ratio (mass basis) 1 / 2) was used as a solvent, and the inverse-gated decoupling method was applied at 200°C. １３ C-NMR measurement was performed to determine the ratio of racemo-dyad (meso / racemo ratio). ４ The ratio of racemo dyads was calculated based on the intensity ratio of the signal at 43.35 ppm derived from meso dyads to the signal at 43.43 ppm derived from racemo dyads, with the peak at 127.5 ppm as the reference shift.

[0095] <Small-Angle X-Ray Scattering Measurement> [Long Lamellar Period in the Through Direction] Small-angle X-ray scattering measurements were performed on the films obtained in the Examples and Comparative Examples using a small-angle X-ray scattering device (Rigaku Corporation, "NanoPIX"). The mode was set to two-pinhole high-flux mode, with a CuKα X-ray source, an output of 40 kV, 30 mA, a pinhole of 1.4 mmφ to 0.85 mmφ, a camera length of 1,400 mm, and an exposure time of 900 seconds. A two-dimensional semiconductor detector (Rigaku Corporation, "HyPix-6000") was used as the detector, and scattering intensity I was measured in the range of 0.0085 to 1.5 Å of the scattering vector q. Here, q is given by q = 4π sin θ / λ, where θ is half the scattering angle 2θ, π is the circular constant, and λ is the wavelength of the X-ray. Here, the lamellar long period d in the Through direction is given by d = Lc + a = 2π / qmax, where q is the value at which the scattering intensity I is at its maximum value. Note that, with regard to scattering here, scattering from the film surface when incident from a direction perpendicular to the film surface was defined as scattering in the Through direction. [Lamellar Orientation Degree in the Through Direction] The lamellar orientation degree f in the Through direction was determined by integrating the 2θ range of 0.3° < 2θ < 0.9° from the circular average scattering image obtained from the above measurement based on the azimuthal angle dependency, fitting the peak at 180° or 0° (360°) with a Gaussian function from the relationship diagram between the azimuthal angle and the normalized scattering intensity, and determining the half-width (Δ) of the obtained peak, and then calculating according to the following formula: f = 1 - (Δ / 360°)

[0096] <Crystallization degree> First, the density of the films (sample films) obtained in the examples and comparative examples was measured using a helium gas substitution type dry automatic density meter "AccuPyc 1340" (manufactured by Micromeritics). Approximately 3 g of the sample film was cut into strips with a width of 30 mm or less, rolled into 10 cm pieces, and ３ The sample was placed in a container and maintained at 25°C for measurement. The density was determined from 10 repeated measurements. <Calculation of Crystallinity> The crystallinity x (%) was calculated using the following formula: x = (1 / Da-1 / D) / (1 / Da-1 / Db) x 100. In the formula, x represents the crystallinity. D (g / cm ３) represents the determined density of the sample film. Da is the completely amorphous density (g / cm) of the polymer forming the sample film. ３ ) Db is the perfect crystalline density (g / cm) of the polymer forming the sample film. ３ The following values ​​were used as the completely amorphous density Da and the completely crystalline density Db: Completely amorphous density Da of hydrogenated dicyclopentadiene polymer (COP) = 1.0157 g / cm ３ ・Perfect crystal density Db of hydrogenated dicyclopentadiene polymer (COP) = 1.0857 g / cm ３

[0097] <Film Thickness (μm)> The film thickness (μm) of the films obtained in the examples and comparative examples was measured using a non-contact film thickness measuring device (manufactured by Otsuka Electronics Co., Ltd., product name: "Smart Film Thickness Meter: SM-100").

[0098] <Arithmetic mean roughness value of surface> Three-dimensional surface roughness was measured under the following conditions using a color 3D laser microscope (manufactured by Keyence Corporation, product name "VK-9700"). The sample film was set on the sample stage with the X direction of the visual field measurement being the flow direction (MD) of the film, with the upper surface serving as the measurement surface, and measurements were taken, and the arithmetic mean roughness value (SRa) of the surface was calculated using analysis software. Measurements were taken on both the front and back sides of the film, and the surface with the smallest SRa was designated the evaluation surface. Measurement software: VK-viewer Analysis software: VK-Analyzer Objective lens: 150x Analysis field of view: X direction: 100 μm Y direction: 100 μm Z measurement pitch: 0.01 μm Measurement mode: Transparent body (outermost surface) mode

[0099] <Dielectric Breakdown Strength> The dielectric breakdown strength of the films obtained in the Examples and Comparative Examples (thickness: 3 μm for Examples 1 to 6 and Comparative Examples 2 and 3; thickness: 15 μm for Comparative Examples 1 and 4) was measured at 150°C according to the plate electrode method specified in JIS C2151:2006. The measurement was performed using a dielectric breakdown voltage measuring device (YST-243-100RHO, manufactured by Yamayo Test Instruments Co., Ltd.), and the dielectric breakdown strength was calculated as the average value obtained by dividing the dielectric breakdown voltage by the film thickness. For the measurement at 150°C, the electrodes and the measurement sample were placed in a hot air oven, and after holding for 10 minutes, the pressure increase was started. The measurement was performed in the same manner as above according to the plate electrode method specified in JIS C2151:2006. The measured values ​​are shown in Table 1.

[0100] <Static and dynamic friction coefficients> The films obtained in the examples and comparative examples were cut into 100 mm x 80 mm pieces to obtain test pieces. Next, the films of the predetermined size were fixed on a standard test plate, and the pieces were stacked and set so that the MD directions were parallel. A load of 200 g was placed on the test piece, and using a peel tester, the sliding properties between the test piece film and the fixed film were measured at a peel rate of 100 mm / min in accordance with JIS K 7125, and the static and dynamic friction coefficients were determined and evaluated.

[0101] (Production Example 1: Production of hydrogenated product of ring-opening polymer of dicyclopentadiene) Into a metal pressure-resistant reactor whose interior had been purged with nitrogen, 154.5 parts of cyclohexane as an organic solvent, 42.8 parts (30 parts as dicyclopentadiene) of a cyclohexane solution (70% concentration) of dicyclopentadiene (endo isomer content of 99% or more), which is a dicyclopentadiene, and 1.91 parts of 1-hexene as a molecular weight modifier were added, and the total volume was heated to 53°C. Meanwhile, 0.061 parts of an n-hexane solution (19% concentration) of diethylaluminum ethoxide, an organometallic reducing agent as a ring-opening polymerization catalyst, was added to a solution obtained by dissolving 0.014 parts of a tetrachlorotungsten phenylimide (tetrahydrofuran) complex, which is a metal compound as a ring-opening polymerization catalyst, in 0.70 parts of toluene (organic solvent), and the solution was stirred for 10 minutes to prepare a ring-opening polymerization catalyst solution. This ring-opening polymerization catalyst solution was added to the reactor, and the ring-opening polymerization reaction was carried out at 53 ° C. for 4 hours to obtain a solution containing a dicyclopentadiene ring-opening polymer. 0.037 parts of 1,2-ethanediol was added as a terminator to 200 parts of the obtained solution containing the dicyclopentadiene ring-opening polymer, and the mixture was stirred at 60 ° C. for 1 hour to terminate the polymerization reaction. Thereafter, 1 part of a hydrotalcite-like compound (product name "Kyoward (registered trademark) 2000", manufactured by Kyowa Chemical Industry Co., Ltd.) as an adsorbent was added, heated to 60 ° C., and stirred for 1 hour. 0.4 parts of a filter aid (product name "Radiolite (registered trademark) #1500", manufactured by Showa Chemical Industry Co., Ltd.) was added, and the adsorbent was filtered off using a PP pleated cartridge filter (product name "TCP-HX", manufactured by ADVANTEC Toyo Co., Ltd.) to obtain a solution containing a dicyclopentadiene ring-opening polymer. Using a portion of this solution, the molecular weight of the dicyclopentadiene ring-opening polymer was measured, and the weight average molecular weight (Mw) was 28,100, the number average molecular weight (Mn) was 8,750, and the molecular weight distribution (Mw / Mn) was 3.21. 100 parts of cyclohexane and 0.0043 parts of chlorohydridocarbonyltris(triphenylphosphine)ruthenium were added to 200 parts of the resulting solution containing the dicyclopentadiene ring-opening polymer (polymer content: 30 parts), and a hydrogenation reaction was carried out at a hydrogen pressure of 6 MPa and 180°C for 4 hours. The reaction liquid was a slurry liquid in which solids were precipitated.The reaction mixture was centrifuged to separate the solids from the solution, and the solids were dried under reduced pressure at 60°C for 24 hours to obtain 28.5 parts of a hydrogenated dicyclopentadiene ring-opening polymer. In Table 1, the hydrogenated dicyclopentadiene ring-opening polymer is referred to as "DCPD." The hydrogenation rate of unsaturated bonds in the hydrogenation reaction was 99% or more, and the hydrogenated dicyclopentadiene ring-opening polymer had a glass transition temperature of 98°C and a melting point of 262°C. The racemo-dyad ratio was 89%. The hydrogenation rate of the polymer was calculated using orthodichlorobenzene-d. ４ as a solvent at 145°C, １ Calculated by H-NMR measurement.

[0102] (Production Example 2. Production of Unstretched Film) 100 parts of the hydrogenated product of the ring-opening polymer of dicyclopentadiene obtained in Production Example 1 was mixed with 1.1 parts of an antioxidant (tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane; "Irganox (registered trademark) 1010" manufactured by BASF Japan Ltd.) to obtain a resin that would serve as a material for a film. The resin was fed into a twin-screw extruder ("TEM-37B" manufactured by Toshiba Machine Co., Ltd.) equipped with four die holes with an inner diameter of 3 mm. The resin was molded into a strand-shaped molded body by hot melt extrusion using the twin-screw extruder. The molded body was shredded with a strand cutter to obtain resin pellets. The operating conditions for the twin-screw extruder are shown below. Barrel temperature setting: 270°C to 280°C Die temperature setting: 250°C Screw rotation speed: 145 rpm Feeder rotation speed: 50 rpm Subsequently, the obtained pellets were supplied to a hot melt extrusion film molding machine equipped with a T-die. Using this film molding machine, a long unstretched film having a width of 155 mm (for Examples 1 to 4, 6: thickness 20 μm; for Example 5: thickness 30 μm; for Comparative Examples 1, 3, 4: thickness 15 μm; for Comparative Example 2: thickness 20 μm) made of the above resin was produced by winding it up on a roll at a speed of 2 m / min. This film was a single-layer film. The operating conditions of the film molding machine are shown below. Here, the thickness and length of one side of the unstretched film were adjusted by appropriately adjusting the screw rotation speed. Barrel temperature setting: 280°C to 290°C Die temperature: 270°C Screw rotation speed: 30 rpm

[0103] Example 1 1-1. Pre-crystallization Step The long unstretched film obtained in Production Example 2 was cut into a 120 mm x 120 mm square at an arbitrary position. This cutting was performed so that the sides of the square of the cut unstretched film were parallel to the longitudinal or transverse direction of the long unstretched film. The cut unstretched film was then attached to a three-tank biaxial stretching device (manufactured by Ever Sokki Co., Ltd., product name: "RS-2T"). This attachment was performed by fixing the four sides of the unstretched film with clips of the biaxial stretching device so that the unstretched film was in a tensed state. With the four sides of the unstretched film fixed with clips in this manner, the pre-stretched film was held at a constant preheating temperature Tp = 130°C for a preheating time tp = 30 seconds. 1-2. Stretching Step> Immediately thereafter, the unstretched film was sequentially stretched in the MD and TD directions using the biaxial stretching device at a constant stretching temperature Ts of 120°C for 15 seconds. The stretching ratio in the MD direction was 2.0 (strain rate: 10 mm / sec), and the stretching ratio in the TD direction was 3.2 (strain rate: 10 mm / sec), resulting in an areal stretching ratio of 6.4. This stretching gave a stretched film as the stretched film. <1-3. Heat Treatment Step> Immediately thereafter, a heat treatment step was carried out in which the stretched film obtained above was heated in an oven at 220°C for 0.17 minutes (10 seconds), to give a heat-stretched film. <1-4. Relaxation Step> The heat-stretched film thus obtained was then subjected to a relaxation step in which tension in the heat-stretched film was relaxed while maintaining it flat at 220°C, to give a film. In this relaxation treatment step, the clips of the device were moved in the in-plane direction of the heat-stretched film to reduce the distance between the clips, thereby reducing the tension in the heat-stretched film. The distance between the clips was reduced by 0% in the longitudinal direction of the heat-stretched film and by 5% in the transverse direction over a period of 10 seconds. The various properties of the film thus obtained were measured using the methods described above. The results are shown in Table 1.

[0104] Examples 2 to 4 The same operations and measurements as in Example 1 were carried out, except that the conditions in the "pre-crystallization step" were changed as shown in Table 1. The results are shown in Table 1.

[0105] Example 5 The same operations and measurements as in Example 1 were carried out, except that the conditions in the "pre-crystallization step" and "stretching step" were changed as shown in Table 1. The results are shown in Table 1.

[0106] (Example 6) The same operations and measurements were carried out as in Example 1, except that the "pre-crystallization step" was not carried out. The results are shown in Table 1.

[0107] Comparative Example 1 The unstretched film (thickness: 15 μm) produced in Production Example 2 was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0108] Comparative Examples 2 and 3 The same operations and measurements as in Example 1 were carried out, except that the conditions in the "pre-crystallization step" and "stretching step" were changed as shown in Table 1. The results are shown in Table 1.

[0109] (Comparative Example 4) The unstretched film (thickness: 15 μm) produced in "Production Example 2" was subjected to the "pre-crystallization step" shown in Table 1, and the "heat treatment step" and "relaxation treatment step" similar to those in Example 1. The obtained film was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0110]

[0111] Table 1 shows that the films of Examples 1 to 6, which contained a crystalline polymer, had a lamellar orientation degree in the Through direction of 0.75 or more, and a surface arithmetic mean roughness value of 0.03 μm or more, had high dielectric breakdown strength at 150° C. Furthermore, it can be seen that the films of Comparative Examples 1 and 4, which had no lamellar orientation, and the films of Comparative Examples 2 and 3, which had a low lamellar orientation degree in the Through direction, had poor dielectric breakdown strength at 150° C.

[0112] According to the present invention, a film having a high dielectric breakdown strength can be provided.

Claims

1. A film containing a crystalline polymer, which has a lamellar orientation degree in the through direction of 0.75 or more as determined by small-angle X-ray scattering measurement, and has an arithmetic mean roughness value of the surface of 0.03 μm or more.

2. The film according to claim 1, having a thickness of 15 μm or less.

3. The film according to claim 1, wherein the static friction coefficient is 0.3 or more and 2.5 or less.

4. The film according to claim 1, wherein the lamellar long period in the through direction as determined by small-angle X-ray scattering measurement is 220 Å or less.

5. The film according to claim 1, wherein the crystalline polymer is a hydrogenated dicyclopentadiene ring-opening polymer.

6. A capacitor comprising a film according to any one of claims 1 to 5.

7. A method for producing a film, comprising: a pre-crystallization step of heat-treating an unstretched film at a temperature equal to or higher than the glass transition temperature (Tg) of a hydrogenated dicyclopentadiene ring-opening polymer + 20°C to form a pre-crystallized film; a stretching step of stretching the pre-crystallized film under temperature conditions of equal to or higher than the glass transition temperature (Tg) of the hydrogenated dicyclopentadiene ring-opening polymer and equal to or lower than the melting point (Tm) of the hydrogenated dicyclopentadiene ring-opening polymer, and at an areal stretch ratio of 6.0 to 20.0; a heat treatment step of heat-treating the stretched film stretched in the stretching step at a heating temperature of 150°C to 240°C for a heating time of 600 minutes or less; and a relaxation step of relaxing the stretched film heated in the heat treatment step at a relaxation temperature of 150°C to 240°C for a relaxation time of 0.05 minutes to 600 minutes so that the reduction rate of the fixed film width is 0% to 20%.

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