Capacitor film, method for producing same, capacitor, and film

Abstract

This capacitor film or film comprises a crystalline dicyclopentadiene ring-opening polymer hydrogenation additive and has a crystal long period in the through direction of no greater than 120 angstroms as determined by small-angle X-ray scattering.

Description

Capacitor film and manufacturing method thereof, capacitor, and film

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

[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 insulation strength retention at high temperatures, metal vapor deposition properties, and formability.

[0003] Therefore, a crystalline polymer containing a hydrogenated dicyclopentadiene ring-opening polymer is prepared, and the heat shrinkage rate when heated at 200°C for 10 minutes is 0.01% or more and 1.0% or less, the plane orientation coefficient is 0.01 or more, and the density is 1.03 × 10 ６ g / m ３ (1.03 g / cm ３ ) or more and a film thickness of 15.0 μm or less has been proposed (see, for example, Patent Document 1). Also, as a biaxially oriented polyester film that can be used to manufacture various molded products, a film having a long period in the edge direction of 7 to 12 (nm) and a peak half-width of 0.1 to 0.8 as determined by small-angle X-ray scattering measurement has been studied (see, for example, Patent Document 2).

[0004] International Publication No. 2019 / 167682 Japanese Patent Application Laid-Open No. 2011-202156

[0005] However, the above-mentioned conventional films have room for further improvement in terms of the dielectric breakdown strength under normal temperature conditions and high temperature conditions.

[0006] Therefore, an object of the present invention is to provide a film for a capacitor that can improve the dielectric breakdown strength at room temperature and at high temperature.

[0007] The present inventors have conducted extensive research to solve the above problems, and have newly discovered that when a capacitor film contains a crystalline hydrogenated dicyclopentadiene ring-opening polymer and the crystalline structure of the polymer is controlled to satisfy specific properties, the dielectric breakdown strength can be increased at both room temperature and high temperature, leading to the completion of the present invention.

[0008] That is, the present invention has an object to advantageously solve the above-mentioned problems, and the capacitor film of the present invention is characterized in that [1] it contains a crystalline hydrogenated dicyclopentadiene ring-opening polymer and has a crystal long period in the through direction measured by small-angle X-ray scattering measurement of 120 angstroms or less. Thus, when the capacitor film contains a crystalline hydrogenated dicyclopentadiene ring-opening polymer and has a crystal long period in the through direction measured by small-angle X-ray scattering measurement of 120 angstroms or less, the dielectric breakdown strength at room temperature and high temperatures can be improved. In this invention, the term "crystalline hydrogenated dicyclopentadiene ring-opening polymer" means "a hydrogenated dicyclopentadiene ring-opening polymer having a melting point Tm (i.e., a hydrogenated dicyclopentadiene ring-opening polymer whose melting point can be observed by differential scanning calorimetry (DSC))." Furthermore, the "crystalline long period in the through direction determined by small-angle X-ray scattering measurement" can be measured by the method described in the examples of this specification.

[0009] [2] The capacitor film of [1] above preferably has a rigid amorphous content of 3% or more. If the capacitor film has a rigid amorphous content of 3% or more, the dielectric breakdown strength, particularly at high temperatures, can be further increased. The "rigid amorphous content" of the capacitor film can be measured by the method described in the Examples of this specification.

[0010] [3] In the capacitor film of the above [1] or [2], it is preferable that the dielectric breakdown strength at 150° C. is 400 kV / mm or more. The "dielectric breakdown strength at 150° C." of the capacitor film is the dielectric breakdown strength of the capacitor film when the thickness is 3 μm, and can be measured by the method described in the examples of this specification.

[0011] [4] In the capacitor film of any of the above [1] to [3], the plane orientation coefficient is preferably 0.010 or more. If the plane orientation coefficient is 0.010 or more, the insulating properties of the capacitor film can be further improved. The "plane orientation coefficient" of the capacitor film can be measured by the method described in the examples of this specification.

[0012] [5] In the capacitor film according to any one of the above [1] to [4], silica particles may be contained as an antiblocking agent.

[0013] The present invention also aims to advantageously solve the above-mentioned problems, and [6] provides a method for producing a capacitor film according to any one of [1] to [5] above, which is characterized by comprising a stretching step of stretching an unstretched film under conditions where the stretching temperature 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, and the areal stretching ratio is 1.5 to 20. This method for producing a capacitor film can efficiently produce a capacitor film with high dielectric breakdown strength at room temperature and high temperature.

[0014] [7] The method for producing a capacitor film according to [6] above preferably further includes a heating step in which the stretched film produced in the stretching step is heated at a temperature of 150°C to 240°C for a heating time of 0.05 to 600 minutes, and a relaxation step in which the stretched film produced in the heating step is relaxed at a relaxation temperature of 150°C to 240°C for a relaxation time of 0.05 to 600 minutes, with a film clamping width reduction rate of more than 0% to 20%. This method for producing a capacitor film that includes these steps can more efficiently produce a capacitor film with high dielectric breakdown strength at room temperature and high temperatures. The "film clamping width reduction rate" refers to the rate at which the film is held apart during the relaxation step.

[0015] Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and provides a capacitor according to [8] the present invention, characterized by including the capacitor film according to any one of [1] to [5] above. Such a capacitor can operate stably at room temperature and at high temperatures.

[0016] The present invention also provides [9] a film containing a crystalline hydrogenated dicyclopentadiene ring-opening polymer, wherein the long crystal period in the through direction as determined by small-angle X-ray scattering measurement is 120 angstroms or less.

[0017] According to the present invention, it is possible to provide a film for a capacitor having high values ​​of dielectric breakdown strength at room temperature and at high temperature.

[0018] 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.

[0019] (Capacitor Film and Film) The film of the present invention contains at least a crystalline hydrogenated dicyclopentadiene ring-opening polymer, and optionally contains other components such as an antiblocking agent. The film of the present invention is particularly suitable as a capacitor film, among various applications. The capacitor film of the present invention contains at least a crystalline hydrogenated dicyclopentadiene ring-opening polymer, and optionally contains other components such as an antiblocking agent.

[0020] <Hydrogenated Crystalline 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] In this specification, 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, more preferably 2,000 to 500,000, and even more preferably 20,000 to 100,000. 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] <Antiblocking Agent> Examples of antiblocking agents added as other components include inorganic fine particles made of inorganic substances such as silica; organic fine particles made of organic substances such as acrylic crosslinked resins and melamine thermosetting resins; and organic-inorganic particles such as fatty acid metal salts such as calcium stearate and silicon-acrylic composite materials. These may be used alone, or two or more may be used in combination at any ratio. Among these, inorganic fine particles such as silica particles and fatty acid metal salts are preferred in terms of slipperiness, with silica particles being particularly preferred. There are no particular restrictions on the number average particle size of the antiblocking agent fine particles, but from the viewpoint of slipperiness, it is preferably 0.01 μm or more, and from the viewpoint of transparency, it is preferably 1.5 μm or less.

[0035] <Other Components> Examples of other components other than the antiblocking agent include antioxidants such as phenol-based 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, azole derivatives (for example, benzoxazole derivatives, benzotriazole derivatives, benzimidazole derivatives, and benzothiazole derivatives), and the like. Examples of the other components include fluorescent brighteners such as benzophenone-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, and benzotriazole-based ultraviolet absorbers; inorganic fillers such as talc, silica (however, different from the silica particles used as the antiblocking agent), calcium carbonate, and glass fiber; colorants; flame retardants; flame retardant auxiliaries; 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 used 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 particularly preferably 2 parts by mass or less, relative to 100 parts by mass of the crystalline hydrogenated dicyclopentadiene ring-opening polymer.

[0037] The capacitor film and film of the present invention can be obtained, for example, by subjecting an unstretched film, described below, obtained by molding a composition containing the hydrogenated product of the crystalline dicyclopentadiene ring-opening polymer by a known molding method to the respective steps (stretching step, heat treatment step, and relaxation treatment step) of the capacitor film manufacturing method described below. The capacitor film will be described in detail below. The various essential or preferred attributes of the capacitor film also apply to the film of the present invention, whose use is not limited to capacitors.

[0038] <Through-direction Crystal Long Period Determined by Small-Angle X-ray Scattering Measurement> The through-direction crystal long period of a capacitor film determined by small-angle X-ray scattering measurement must be 120 angstroms or less. Here, the through-direction crystal long period determined by small-angle X-ray scattering measurement 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 and amorphous portions constituting the lamellar structure are considered as a single repeating unit. The value of the through-direction crystal long period determined by small-angle X-ray scattering measurement is affected by the crystallinity and molecular weight of the polymer. A large value of the "through-direction crystal long period" measured for a crystalline polymer indicates a long distance between lamellar centers in the crystalline polymer's lamellar structure. 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, a low periodicity of the lamellar structure, etc. Therefore, in the present invention, when the "crystalline long period in the through direction" measured for the hydrogenated dicyclopentadiene ring-opening polymer, which is the crystalline polymer constituting the film, is "120 angstroms or less," it is presumed that the degree of crystallinity and the periodicity of the lamellar structure of the hydrogenated dicyclopentadiene ring-opening polymer are appropriately high, and that these structural features act to increase the value of the dielectric breakdown strength under both room temperature and high temperature conditions.

[0039] Furthermore, from the viewpoint of further increasing the dielectric breakdown strength, the value of the crystal long period in the through direction determined by small-angle X-ray scattering measurement is preferably 115 angstroms or less, and more preferably 105 angstroms or less. The lower limit of the value of the crystal long period in the through direction determined by small-angle X-ray scattering measurement is not particularly limited, but can be 80 angstroms or more.

[0040] <Rigid Amorphous Amount> The rigid amorphous amount of the capacitor film is preferably 3% or more, more preferably 10% or more, even more preferably 20% or more, and particularly preferably 30% or more. If the rigid amorphous amount is equal to or greater than the above lower limit, the dielectric breakdown strength of the capacitor film, particularly the dielectric breakdown strength at high temperatures, can be further increased. The upper limit of the rigid amorphous amount of the capacitor film is not particularly limited, but is preferably 50% or less from the viewpoint of processability, etc.

[0041] <Dielectric breakdown strength> The capacitor film of the present invention preferably has a dielectric breakdown strength of 400 kV / mm or more, more preferably 425 kV / mm or more, even more preferably 450 kV / mm or more, and particularly preferably 485 kV / mm or more at 150° C. The upper limit of the dielectric breakdown strength of the capacitor film at 150° C. is not particularly limited, but may be, for example, 600 kV / mm or less.

[0042] <Plane Orientation Coefficient of Capacitor Film> In terms of surface uniformity of the film, the plane orientation coefficient of the capacitor film is preferably 0.010 or more, more preferably 0.011 or more, even more preferably 0.012 or more, and particularly preferably 0.013 or more. In terms of ease of production, it is preferably 0.030 or less, more preferably 0.025 or less, and particularly preferably 0.020 or less. When the plane orientation coefficient of the capacitor film is equal to or greater than the above-mentioned lower limit, the proportion of molecular chains aligned within the plane of the capacitor film increases. Here, when a voltage is applied to the capacitor film, electrons align perpendicular to the direction of voltage application, making it difficult for electrons to flow, thereby improving the insulating properties of the capacitor film. Furthermore, when the plane orientation coefficient of the capacitor film is equal to or greater than the above-mentioned lower limit, the uniformity of the surface (planar shape) of the capacitor film is improved, thereby improving the vapor deposition properties of the capacitor film. The "plane orientation coefficient" can be measured using the method described in the Examples section of this specification.

[0043] <Film Thickness of Capacitor Film> The film thickness of the capacitor film is not particularly limited as long as it is 15.0 μm or less. However, from the viewpoints of improving flexibility, suppressing the occurrence of wrinkles and shifting during molding, and reducing the size of the product, it is preferably 10.0 μm or less, more preferably 8.0 μm or less, particularly preferably 5.0 μm or less, and most preferably 4.0 μm or less. When the film thickness of the capacitor film is 10.0 μm or less, flexibility is improved, wrinkles and shifting during molding can be suppressed, and products using the capacitor film can be reduced in size. The "film thickness" can be measured by the method described in the examples of this specification.

[0044] <Capacitor> The capacitor film of the present invention is optionally subjected to a surface treatment such as corona treatment or plasma treatment, and then cut to a predetermined size for use as a capacitor material. Because the capacitor of the present invention includes the capacitor film of the present invention, it is less likely to short-circuit during operation at room temperature and high temperature, and can operate stably. Examples of capacitors using the capacitor film of the present invention include laminated film capacitors in which capacitor films and metal layers are alternately laminated, and wound film capacitors in which a tape-shaped capacitor film and a metal layer are wrapped around each other. The metal layer is not particularly limited, and a metal layer commonly used in capacitors can be used. The method for manufacturing these capacitors is not particularly limited, and conventionally known methods can be used.

[0045] (Method for Manufacturing Capacitor Film) The method for manufacturing a capacitor film of the present invention (hereinafter sometimes simply referred to as the "manufacturing method") includes at least a stretching step. Furthermore, the manufacturing method of the present invention preferably includes a heating step and a relaxation step following the stretching step, and may include other steps as necessary. In the following description, a "long" film refers to a film having a length of at least 5 times its width, preferably 10 times or more, specifically a film long enough to be wound into a roll for storage or transportation. Furthermore, unless otherwise specified, the directions of elements as "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.

[0046] <Stretching Step> The stretching step is a step of stretching an unstretched film (raw film) at a predetermined stretching temperature and stretch ratio.

[0047] The method for stretching the unstretched film 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).

[0048] 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.

[0049] [Unstretched Film (Original Film)] The unstretched film 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 (original 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.

[0050] [Stretching Temperature] The stretching temperature is not particularly limited, but from the viewpoint 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 equal to or higher than 95°C, more preferably equal to or higher than 100°C, even more preferably equal to or higher than 105°C, and particularly preferably equal to or higher than 110°C. Furthermore, from the viewpoint of efficiently producing a capacitor 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 equal to or lower than 140°C, more preferably equal to or lower than 130°C, and particularly preferably equal to or lower than 125°C. By setting the stretching temperature to be equal to or higher than the glass transition temperature Tg and equal to or lower than the melting point Tm of the hydrogenated dicyclopentadiene ring-opening polymer, it is possible to properly orient the polymer molecules contained in the unstretched film.

[0051] [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 1.5 times or more, more preferably 3.0 times or more, and is preferably 6.0 times or less, more preferably 5.5 times or less, even more preferably 5.0 times or less, and particularly preferably 4.0 times or less, in order to efficiently produce a capacitor film.

[0052] Like the MD stretching ratio, the TD stretching ratio is preferably 1.5 times or more, more preferably 3.0 times or more, and is preferably 6.0 times or less, more preferably 5.5 times or less, even more preferably 5.0 times or less, and particularly preferably 4.0 times or less.

[0053] [Area stretch ratio] In this specification, "area stretch ratio" refers to the product of MD stretch ratio x TD stretch ratio. The resulting product is rounded down to the first decimal place. The areal stretch ratio is preferably 1.5 times or more, more preferably 10.0 times or more, even more preferably 11.0 times or more, even more preferably 13.0 times or more, and particularly preferably 15.0 times or more, in order to efficiently produce a capacitor film with high dielectric breakdown strength. Furthermore, the areal stretch ratio is preferably 20.0 times or less, more preferably 16.0 times or less. If the areal stretch ratio is equal to or less than the above upper limit, film breakage is reduced and the uniformity of the film thickness of the obtained film can be increased, resulting in efficient production of a capacitor film with excellent productivity.

[0054] [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 capacitor 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.

[0055] By subjecting the unstretched film to the above-described stretching treatment, a capacitor film having desired properties can be obtained. Furthermore, by subjecting the unstretched 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 capacitor film.

[0056] <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.

[0057] 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.

[0058] [Heating Temperature] The heating temperature is not particularly limited, but from the viewpoint of improving the value of the dielectric breakdown strength at high temperatures and from the viewpoint of being able to efficiently produce a capacitor film with a small thermal shrinkage rate, 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 being able to efficiently produce a capacitor film with a small thermal shrinkage rate, it is preferably 250°C or lower, more preferably 240°C or lower, and particularly preferably 230°C or lower.

[0059] [Heating Time] The heating time is not particularly limited, but from the viewpoint of improving the value of the dielectric breakdown strength at high temperatures and from the viewpoint of being able to efficiently produce a capacitor film having a small thermal shrinkage rate, it is preferably 3 seconds or more, more preferably 6 seconds or more, even more preferably 12 seconds or more, even more preferably 18 seconds or more, and particularly preferably 24 seconds or more; and from the viewpoint of being able to efficiently produce a capacitor film having a small tan δ, 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] In the heat treatment step, at least two edges of the stretched film are held in a tensile state. This prevents deformation of the stretched film due to thermal shrinkage in the region between the held edges. To prevent deformation over a wide area of ​​the stretched film, it is preferable to hold two opposing edges and keep the region between the held edges in a tensile state. For example, in the case of a rectangular sheet of stretched film, by holding two opposing edges (e.g., long edges or short edges) and keeping the region between the two edges in a tensile state, deformation can be prevented over the entire surface of the sheet. Furthermore, in the case of a long stretched film, by holding two edges (i.e., long edges) at the ends in the width direction and keeping the region between the edges in a tensile state, deformation can be prevented over the entire surface of the long stretched film. A stretched film that is prevented from deformation in this way is less likely to develop wrinkles or other deformations even if stress occurs within the film due to thermal shrinkage.

[0064] In order to more reliably suppress deformation during the heat treatment step, it is preferable to hold as many sides as possible. Therefore, for example, in the case of a sheet of stretched film, it is preferable to hold all sides. Specifically, in the case of a rectangular sheet of stretched film, it is preferable to hold all four sides.

[0065] A holder capable of holding the edges of the stretched film is preferably one that does not come into contact with the stretched film at any portion other than the edges of the stretched film. By using such a holder, a capacitor film with superior smoothness can be obtained. Note that a known gripper can be used as the holder.

[0066] 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.

[0067] <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 ratio for a fixed film width.

[0068] [Relaxation Temperature] The relaxation temperature is not particularly limited, but from the viewpoint of improving the dielectric breakdown strength at high temperatures and efficiently producing a capacitor film with a small thermal shrinkage, it is preferably 150°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, particularly preferably 180°C or higher, and 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 the productivity of the capacitor film.

[0069] [Relaxation Time] The relaxation time is not particularly limited, but from the viewpoint of efficiently producing a capacitor film having a small thermal shrinkage ratio, it is preferably 3 seconds or more, more preferably 0.1 minutes or more, even more preferably 0.2 minutes or more, even more preferably 0.3 minutes or more, and particularly preferably 0.4 minutes or more; and from the viewpoint of efficiently producing a capacitor film having a small tan δ, it 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.

[0070] [Reduction ratio of film fixing width] The reduction ratio of the film fixing width is not particularly limited in either the vertical or horizontal direction, but is preferably more than 0%, more preferably 0.2% or more, even more preferably 0.4% or more, and particularly preferably 0.6% or more, from the viewpoint of efficient production of a capacitor film with a small thermal shrinkage ratio. Also, from the viewpoint of uniformity of the film surface (planar state), it is preferably 20% or less, more preferably 15% or less, even more preferably 13% or less, and particularly preferably 10% or less. Note that the "reduction ratio of film fixing width" refers to the ratio by which the film holding interval is narrowed in the relaxation treatment step.

[0071] 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.

[0072] "Relieving the tension of the heat-stretched film" refers to releasing the heat-stretched film from the tensioned state held by a holding device. The heat-stretched film may be held by a holding device as long as it is not tensioned. When the tension is released in this manner, the heat-stretched film is in a state where it can undergo thermal shrinkage. In the relaxation treatment step, thermal shrinkage of the heat-stretched film is induced, thereby eliminating stress that can occur in the capacitor film during heating. Therefore, the thermal shrinkage of the capacitor film of the present invention in a high-temperature environment can be reduced, resulting in a capacitor film with excellent dimensional stability in a high-temperature environment.

[0073] 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 capacitor film from becoming wavy, wrinkled, or otherwise deformed.

[0074] 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 to prevent deformations such as waving and wrinkling. This can prevent deformations such as waving and wrinkling from occurring in the resulting capacitor film.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] <Other Steps> The other steps are not particularly limited, and for example, the obtained capacitor film may be subjected to a surface treatment.

[0079] 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.

[0080] <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.

[0081] <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.

[0082] <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.

[0083] <Crystalline Long Period in the Through Direction Determined by Small-Angle X-ray Scattering Measurement> A nanoscale X-ray structural evaluation system (Rigaku Corporation, "NanoPIX") was used as the X-ray generator. The mode was two-pinhole high-flux mode, with a CuKα X-ray source, output of 40 kV, 30 mA, pinhole diameters of 1.4 mm to 0.85 mm, a camera length of 1,400 mm, and an exposure time of 600 seconds. A semiconductor detector (Rigaku Corporation, "HyPix-6000") was used as the detector. Using this detector, the scattering intensity I(q) was obtained in the range of 0.0085 to 1.1 angstroms 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 long period d is given by (d = 2π / qmax), where q is the value at which the scattering intensity I is maximized. The lamellar thickness was determined using the method described in Chapter 5, The Semicrystalline State (page 178) of "The Physics of Polymers" by G.R. Strobl (Springer, 2007). Specifically, I(q) was Fourier transformed to obtain the one-dimensional electron density correlation function K(z) relative to the real space z. When zmin is the value at which K(z) is minimized, the line L1 is the linear approximation of K(z) for z < zmin, and L2 is the tangent at K(zmin). The z at the intersection of L1 and L2 is the lamellar thickness zl. Note that the scattering here refers to scattering from the film surface in the "through direction" when X-rays are incident perpendicularly to the film surface.

[0084] <Crystallinity> The long period d and lamellar thickness zl determined by the small-angle X-ray scattering measurement method described above were used to calculate the crystallinity according to the following formula: Crystallinity (%)=zl / d×100

[0085] <Rigid Amorphous Amount> The rigid amorphous amount was measured using temperature-modulated differential scanning calorimetry. A differential scanning calorimeter (Hitachi High-Tech Corporation, "DSC7000X") was used to measure from 30°C to 300°C at a heating rate of 2°C / min, a temperature modulation amplitude of ±3°C, and a temperature modulation frequency of 0.05 Hz. The specific heat difference at the glass transition temperature was determined, and the rigid amorphous amount (%) was calculated according to the following formula using the crystallinity calculated above. Mobile amorphous amount (%) = (specific heat difference) / (specific heat difference of completely amorphous material) × 100. Rigid amorphous amount (%) = 100 - (mobile amorphous amount) - (crystallinity)

[0086] <Plane Orientation Coefficient> The refractive indices (represented as Nx, Ny, and Nz, respectively) in the MD, TD, and ND (thickness) directions were measured using a refractive index measuring device ("AxoScan" manufactured by Axometrics), and the plane orientation coefficient was calculated according to the following formula: ΔP=(Nx+Ny) / 2−Nz

[0087] <Film Thickness (μm) of Capacitor Film> The film thickness (μm) of the obtained capacitor film was measured using a film thickness measuring device (manufactured by Fujiwork Co., Ltd., product name: "HKT-1216").

[0088] <Dielectric Breakdown Strength> The dielectric breakdown strength of the resulting capacitor film (thickness: 3 μm) was measured at 23°C and 150°C according to the plate electrode method specified in JIS C2151:2006. A dielectric breakdown voltage measuring device (Yamayo Test Instruments, YST-243-100RHO) was used, and the dielectric breakdown strength was calculated by dividing the dielectric breakdown voltage by the thickness of the capacitor film. Measurements at 150°C were performed by placing the electrodes and the measurement sample in a hot air oven, holding the oven for 10 minutes, and then starting the voltage increase. Measurements were 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, and the insulating properties of the film were evaluated according to the following criteria. In comprehensively evaluating the insulating properties, the value calculated by calculating the retention rate of the dielectric breakdown strength at 150°C relative to the dielectric breakdown strength at 23°C was also taken into consideration. Capacitor films that receive an A rating according to the following criteria have excellent insulation properties over a wide temperature range and are advantageously resistant to temperature changes. <<Insulation Evaluation Criteria>> A: The dielectric breakdown strength at 23°C is 500 kV / mm or more, and the dielectric breakdown strength at 150°C is 400 kV / mm or more, and the retention rate is 80% or more. B: The above criteria are not met.

[0089] (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.

[0090] (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 set temperature: 270°C to 280°C Die set temperature: 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 (Examples 1 to 5: thickness 45 μm; Example 6: thickness 39 μm; Example 7 to Comparative Example 2: thickness 33 μm) made of the resin and having a width of 155 mm was produced by winding it up on a roll at a speed of 2 m / min. 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

[0091] Example 1 1-1. Stretching Process The long unstretched film obtained in Production Example 2 was cut into a 90 mm x 90 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 direction or width direction of the long unstretched film. The cut unstretched film was then placed in a multi-chamber biaxial stretching birefringence orientation axis measuring device (manufactured by Eto Corporation). This multi-chamber biaxial stretching birefringence orientation axis measuring device has a plurality of clips capable of gripping the four sides of the film and has a structure in which the film can be stretched by moving these clips. Using this multi-chamber biaxial stretching birefringence axis measuring device, the unstretched film was stretched in the MD direction corresponding to the longitudinal direction of the long unstretched film at a stretching ratio of 3.9 times, and then stretched in the TD direction corresponding to the width direction of the long unstretched film at a stretching ratio of 3.9 times (stretching at an areal stretching ratio of 15.2 times) to obtain a stretched film. The operating conditions of the multi-chamber biaxial stretching birefringence axis measuring device are as follows: Stretching speed: 200 mm / min Stretching temperature: 110°C

[0092] <1-2. Heat Treatment Step> The heat-stretched film was attached to the multi-chamber biaxially stretching birefringence orientation axis measurement device by clamping all four sides of the stretched film with the clips of the multi-chamber biaxially stretching birefringence orientation axis measurement device. The stretched film was then placed in a tensioned state by clamping all four sides with the clips. The stretched film was then subjected to a crystallization step in which the hydrogenated ring-opening polymer of dicyclopentadiene contained in the stretched film was crystallized by heat treatment in an oven at 220°C for 5 seconds, thereby obtaining a heat-stretched film. The haze of the resulting heat-stretched film was measured and found to be 0.36%.

[0093] <1-3. Relaxation Treatment Step> The heat-stretched film thus obtained was attached to the multi-chamber biaxially stretched birefringence axis measurement device by clamping the four sides with the clips of the multi-chamber biaxially stretched birefringence axis measurement device. A relaxation treatment step was then performed at 220°C to relax the tension of the heat-stretched film (crystallized film) while maintaining it flat, yielding a capacitor film. In this relaxation treatment step, the clips of the multi-chamber biaxially stretched birefringence axis measurement device were moved in the in-plane direction of the heat-stretched film to reduce the distance between the clips, thereby relaxing the tension of the heat-stretched film. The distance between the clips was reduced by 3% in the longitudinal direction of the heat-stretched film and 3% in the transverse direction of the heat-stretched film over a period of 5 seconds. Various attributes of the capacitor film thus obtained were measured or evaluated using the methods described above.

[0094] Example 2 The same operations, measurements, and evaluations were carried out as in Example 1, except that, instead of mixing 1.1 parts of an antioxidant with 100 parts of a hydrogenated ring-opening polymer of dicyclopentadiene in the "production of an unstretched film," 1.1 parts of an antioxidant and 0.05 parts of an antiblocking agent (silica particles (average particle size 300 nm, manufactured by Nippon Shokubai Co., Ltd., product name: "Seahostar KE-S30")) were mixed with 100 parts of a hydrogenated ring-opening polymer of dicyclopentadiene in the "production of an unstretched film." The results are shown in Table 1.

[0095] Example 3 The same operations, measurements, and evaluations were carried out as in Example 1, except that the temperatures in both "1-2. Heat treatment step" and "1-3. Relaxation treatment step" were changed to 240° C. The results are shown in Table 1.

[0096] Example 4 The same operations, measurements, and evaluations were carried out as in Example 1, except that the temperatures in both "1-2. Heat treatment step" and "1-3. Relaxation treatment step" were changed to 180° C. The results are shown in Table 1.

[0097] Example 5 The same operations, measurements, and evaluations were carried out as in Example 1, except that the temperatures in both "1-2. Heat treatment step" and "1-3. Relaxation treatment step" were changed to 250° C. The results are shown in Table 1.

[0098] (Example 6) The unstretched film used was one prepared to a thickness of 39 μm. The same operations, measurements, and evaluations as in Example 3 were carried out, except that in "1-1. Stretching step", the film was stretched at a stretching ratio of 3.6 times in the MD direction and at a stretching ratio of 3.6 times in the TD direction (stretched at an areal stretching ratio of 13.0 times). The results are shown in Table 1.

[0099] (Example 7) The unstretched film used was one prepared to a thickness of 33 μm. The same operations, measurements, and evaluations were carried out as in Example 1, except that in "1-1. Stretching step", the film was stretched at a stretching ratio of 3.3 times in the MD direction and at a stretching ratio of 3.3 times in the TD direction (stretched at an areal stretching ratio of 10.9 times). The results are shown in Table 1.

[0100] (Example 8) The same operations, measurements, and evaluations were carried out as in Example 7, except that the temperatures in both "1-2. Heat treatment step" and "1-3. Relaxation treatment step" were changed to 180° C. The results are shown in Table 1.

[0101] (Comparative Example 1) An unstretched film prepared to a thickness of 33 μm was used. In "1-1. Stretching step", the film was stretched at a stretch ratio of 3.6 times in the MD direction and at a stretch ratio of 3.6 times in the TD direction (stretched at an areal stretch ratio of 13.0 times), and the temperatures in both "1-2. Heating step" and "1-3. Relaxation step" were changed to 250°C. The same operations, measurements, and evaluations were carried out as in Example 1. The results are shown in Table 1.

[0102] (Comparative Example 2) An unstretched film prepared to a thickness of 33 μm was used. In "1-1. Stretching step", the film was stretched at a stretch ratio of 3.3 in the MD direction and at a stretch ratio of 3.3 in the TD direction (stretched at an areal stretch ratio of 10.9), and the temperatures in both "1-2. Heating step" and "1-3. Relaxation step" were changed to 240° C., but the same operations, measurements, and evaluations were carried out as in Example 1. The results are shown in Table 1.

[0103]

[0104] It can be seen from Table 1 that when a crystalline hydrogenated dicyclopentadiene ring-opening polymer was contained and its crystal structure was controlled to satisfy specific attributes, it was possible to increase the dielectric breakdown strength values ​​at both room temperature and high temperature. On the other hand, it can be seen that in Comparative Examples 1 and 2, in which the crystal long period in the through direction determined by small-angle X-ray scattering measurement exceeded 120 angstroms, it was not possible to increase the dielectric breakdown strength values ​​at room temperature and high temperature in a balanced manner.

[0105] According to the present invention, it is possible to provide a film for a capacitor having high values ​​of dielectric breakdown strength at room temperature and at high temperature.

Claims

1. A film for a capacitor, which contains a crystalline hydrogenated dicyclopentadiene ring-opening polymer, and has a crystal long period in the through direction of 120 angstroms or less as determined by small-angle X-ray scattering measurement.

2. The capacitor film according to claim 1, wherein the amount of rigid amorphous matter is 3% or more.

3. The film for a capacitor according to claim 1, which has a dielectric breakdown strength of 400 kV / mm or more at 150°C.

4. The capacitor film according to claim 1, having a plane orientation coefficient of 0.010 or more.

5. The film for a capacitor according to claim 1, which contains silica particles as an antiblocking agent.

6. A method for producing a capacitor film according to any one of claims 1 to 5, comprising a stretching step of stretching an unstretched film under conditions where the stretching temperature 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, and the areal magnification is 1.5 times or more and 20.0 times or less.

7. A method for producing a film for a capacitor according to claim 6, comprising: a heat treatment process in which the stretched film stretched by the stretching process is heat-treated under conditions of a heating temperature of 150°C or higher and 240°C or lower and a heating time of 0.05 minutes or higher and 600 minutes or lower; and a relaxation process in which the stretched film heated by the heat treatment process is relaxed under conditions of a relaxation temperature of 150°C or higher and 240°C or lower and a relaxation time of 0.05 minutes or higher and 600 minutes or lower, with a reduction rate of the film fixed width being more than 0% and 20% or lower.

8. A capacitor comprising the film for a capacitor according to any one of claims 1 to 5.

9. A film containing a crystalline hydrogenated dicyclopentadiene ring-opening polymer, the film having a crystal long period in the through direction of 120 angstroms or less as determined by small-angle X-ray scattering measurement.

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