Polyester film, resin current collector, resin current collector for bipolar battery, electrode for bipolar battery, power storage element, secondary battery, electric vehicle, and electric flying body

Abstract

The present invention addresses the problem of providing a polyester film having excellent electrical conductivity, uniform electrical conductivity in the film plane in the thickness direction, and small decrease in electrical conductivity due to processing, and a resin current collector for a bipolar battery having small variation in battery characteristics. The problem is solved by forming a polyester film satisfying (1)-(3) below. (1) The volume resistivity at 23 DEG C and 65% RH is 1.0 * 100 [Omega] cm or more and less than 1.0 * 108 [Omega] cm. (2) The film thickness is 1 [mu] m or more and less than 500 [mu] m. And (3) a polyester resin layer (P1 layer) containing 1.0-30% by mass (inclusive) of conductive particles, the conductive particles being a carbon material.

Description

Technical Field

[0001] The present invention relates to a polyester film, a resin current collector, a resin current collector for a bipolar battery, an electrode for a bipolar battery, a storage element, a secondary battery, an electric vehicle, and an electric flying vehicle. Background Art

[0002] Polyester resins are used in various industrial fields due to their excellent processability. Furthermore, products processed from these polyester resins into films (polyester films) play an important role in today's daily lives, including industrial applications, optical products, packaging, and magnetic recording tapes.

[0003] In recent years, there has been a pressing need to reduce carbon dioxide emissions in order to protect the environment. In the automotive industry, there are high hopes for reducing carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and intensive research is underway into the development of secondary batteries for driving electric motors, a key to their practical application. Secondary batteries include lithium-ion batteries, which offer high energy density and high output density, as well as next-generation batteries such as lithium-ion batteries using metallic lithium anodes, all-solid-state batteries, and air batteries. Furthermore, in addition to automobiles, the development of next-generation mobile devices such as drones, flying cars, and flying communication base stations is also underway, creating a pressing need for lightweight, high-energy-density secondary batteries.

[0004] Metal foil (metal collector foil) has traditionally been used as a current collector in secondary batteries such as lithium-ion batteries. Recently, resin film current collectors, made of resin films, have been proposed as an alternative to metal foil. Resin film current collectors are lighter than metal foil and are expected to increase the battery's output per unit weight.

[0005] In addition, in recent years, the development of bipolar lithium-ion batteries as small and high-output lithium-ion batteries has been prevalent. Unlike previous lithium-ion batteries that extract the current generated in the battery cell from the electrode tabs installed at the ends of the collector foil and connect multiple battery cells, in bipolar lithium-ion batteries, multiple power generation units are stacked on each other via the collector foil arranged on the outermost layer, forming a structure in which current flows in the thickness direction of the collector foil. By adopting the above structure, the electrode terminals, wiring, and outer casings for protecting the battery cells present in existing batteries can be reduced, and the battery size can be greatly reduced. In addition, by making the current flowing in the surface direction of the collector foil further flow in the thickness direction of the collector foil, the resistance to the flowing current can be reduced, and the battery output can be increased.

[0006] On the other hand, in order to produce a thin film current collector foil for bipolar batteries, it is necessary to impart conductivity in the thickness direction.

[0007] For example, Patent Documents 1 to 3 disclose resin current collector materials containing polyolefin resin or imide group-containing resin as a main component and containing a high concentration of conductive filler, and resin current collectors having the resin current collector materials, for bipolar resin current collectors.

[0008] Prior art literature

[0009] Patent Document 1: International Publication No. 2011 / 092938

[0010] Patent Document 2: Japanese Patent Application Publication No. 2019-179732

[0011] Patent Document 3: International Publication No. 2015 / 005116 Summary of the Invention

[0012] Problems to be solved by the invention

[0013] However, patent documents 1 to 3 disclose resin collectors using polyolefin films or imide-containing resins. Based on these, resin collectors using polyester films are produced from the perspectives of heat resistance and dimensional stability. When used as collectors for secondary batteries, the current values ​​generated in the battery cells are excellent. On the other hand, the conductivity within the surface of the polyester film is uneven, or when tension or bending is applied to produce the collector, the conductivity sometimes decreases, indicating that there is a problem of performance deviation in the produced battery cells.

[0014] An object of the present invention is to provide a polyester film having excellent conductivity, uniform conductivity in the thickness direction of the film surface, and little reduction in conductivity due to processing, and a resin current collector for a bipolar battery having little variation in battery characteristics.

[0015] Means for solving problems

[0016] In order to solve the above problems, the preferred technical solution of the present invention adopts the following technical structure.

[0017] [I] A polyester film that satisfies the following (1) to (3).

[0018] (1) Volume resistivity at 23°C and 65% RH is 1.0×10 0 Ωcm or more and less than 1.0×10 8 Ωcm.

[0019] (2) The film thickness is 1 μm or more and less than 500 μm.

[0020] (3) A polyester resin layer (P1 layer) containing 1.0% by mass or more and 30% by mass or less of conductive particles, wherein the conductive particles are carbon materials.

[0021] [II] A polyester film that satisfies the following (1') to (3').

[0022] (1′) The film thickness is 1 μm or more and less than 500 μm.

[0023] (2′) A polyester resin layer (P1 layer) containing 1.0% by mass or more and 30% by mass or less of conductive particles.

[0024] (3′) The P1 layer contains conductive particles C1′ having an aspect ratio of 1 or greater and less than 5, and conductive particles C2′ having an aspect ratio of 5 or greater.

[0025] [III] The polyester film according to [II], wherein the P1 layer satisfies the following (4) to (6).

[0026] (4) The conductive particles contained in the P1 layer are carbon materials.

[0027] (5) The P1 layer contains 0.01% by mass or more and 10% by mass or less of a compound having an ether bond in its main chain.

[0028] (6) The P1 layer contains at least two or more polyester resins having different melting points.

[0029] [IV] The polyester film according to [III], satisfying the following (7).

[0030] (7) The P1 layer is the outermost layer of at least one side of the polyester film, and the P1 layer is composed of a layer mainly composed of a polyester resin (resin α) containing a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms, or a polyester resin (resin β) containing a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms.

[0031] [V] The polyester film according to any one of [I] to [IV],

[0032] The conductive particles are carbon materials, and the volume-based average dispersion diameter of the carbon materials contained in the polyester film is 0.15 μm or more and 0.90 μm or less, and the number of dispersed particles is 1.5 particles / μm. 2 More than 5.0 / μm 2 the following.

[0033] [VI] The polyester film according to any one of [I] to [V],

[0034] The conductive particles are a carbon material, and contain 80% by mass or more of one or more selected from Ketjen black, carbon nanotubes, and acetylene black in total based on 100% by mass of the carbon material.

[0035] [VII] The polyester film according to any one of [I] to [VI],

[0036] The P1 layer contains at least two types of conductive particles, namely, conductive particles C1' having an aspect ratio of greater than 1 and less than 5, and conductive particles C2' having an aspect ratio of greater than 5. The ratio of the area occupied by the conductive particles C1' in the P1 layer (SC1') to the area occupied by the conductive particles C2' (SC2') calculated by the following method is greater than 0.5 times and less than 5 times.

[0037] <Method for measuring the area occupied by each conductive particle>

[0038] The following analysis was performed using image analysis software (Image-Pro Plus Version 4.0 for Windows (registered trademark) manufactured by Planetron Co., Ltd.) on a cross-sectional image (image dimensions: 18.5 μm vertically × 25 μm horizontally) obtained at a magnification of 5000 times using a scanning electron microscope (JSM-6700 manufactured by JEOL Ltd.).

[0039] (i) Image analysis conditions

[0040] After reading the cross-sectional image using the software, perform 8-bit grayscale processing by executing the "Grayscale 8" command under the "Convert" menu. Next, set the horizontal width of the read image to 25 μm using the "Spatial Correction" command under the "Correction" menu. Then, perform binarization using the "Binarization" command under the "Process" menu.

[0041] (Binarization conditions)

[0042] ・Select "3×3"

[0043] ・Threshold setting: Use the value obtained by clicking the auto-detect button located on the right side of the numeric input field once.

[0044] ・Preview conditions: The base part is shown in white and the detection particles are shown in black

[0045] After binarization, open the "Count / Size" command screen under the "Measurement" menu, set the following particle detection and analysis conditions, and execute "Count" to analyze the detected particles.

[0046] (Particle detection conditions)

[0047] ・Brightness range selection: Select "Automatically extract dark objects"

[0048] ・Select "Measurement object"

[0049] (Object extraction option conditions)

[0050] ・4 links / 8 links: Select 4 links

[0051] ・Only "Preselection" and "Hole Filling" are selected

[0052] ・Smoothing: 0

[0053] ・Exclude on boundaries: Select "All boundaries".

[0054] (Particle analysis conditions)

[0055] Based on the obtained image, use the "Count / Size" command on the screen to calculate the aspect ratio (Aspect value) and area (Area value) of each conductive particle in the obtained image.

[0056] For five different fields of view, a population histogram was created with the obtained aspect ratio as the horizontal axis, with intervals set at 0.5 in the interval between 1 and 10, and at 10 for the interval between 1 and 10. In the population histogram, if a local maximum value existed in the region where the aspect ratio was 1 or greater and less than 5, the minimum value of the interval showing this local maximum value (for example, if a local maximum value existed in the interval between 2 and 2.5 or less, 2 was used as the local maximum value) was used as the aspect ratio of the conductive particles (conductive particles C1') present in the region where the aspect ratio was 1 or greater and less than 5. If multiple local maximum peaks existed in the region where the aspect ratio was 1 or greater and less than 5, the weighted average value obtained using the values ​​on the vertical axis of these local maximum peaks was used as the aspect ratio of the conductive particles (conductive particles C1') present in the region where the aspect ratio was 1 or greater and less than 5.

[0057] Similarly, when there is a maximum value in a region with an aspect ratio of 5 or greater, the maximum value is used as the aspect ratio of the conductive particles (conductive particles C2') present in the region with an aspect ratio of 5 or greater. When there are multiple maximum peaks in a region with an aspect ratio of 5 or greater, the weighted average value obtained using their vertical axis values ​​is used as the aspect ratio of the conductive particles (conductive particles C2') present in the region with an aspect ratio of 5 or greater.

[0058] For each of the five different fields of view, the aspect ratios of the conductive particles present in the region with an aspect ratio greater than 1 and less than 5 (conductive particles C1') and the conductive particles present in the region with an aspect ratio greater than 5 (conductive particles C2') were calculated, and the average value of the five fields of view in each region was taken as the aspect ratio of the conductive particles C1' and the conductive particles C2' in the polyester film.

[0059] The total area (SC1') of the conductive particles (conductive particles C1') present in regions with an aspect ratio of 1 or greater and less than 5, as confirmed by the number histogram, is calculated. Next, the total area (SC2') of the conductive particles (conductive particles C2') present in regions with an aspect ratio of 5 or greater is calculated, and the value obtained by dividing SC1' by SC2' is defined as the ratio of the area (SC1') occupied by the conductive particles C1' to the area (SC2') occupied by the conductive particles C2' in the P1 layer of the sample.

[0060] [VIII] The polyester film according to any one of [I] to [VII],

[0061] The P1 layer contains at least two types of carbon materials, namely, a carbon material C1 having an aspect ratio of greater than 1 and less than 5, and a carbon material C2 having an aspect ratio of greater than 5, and the ratio of the area occupied by the carbon material C1 in the P1 layer (SC1) to the area occupied by the carbon material C2 (SC2) calculated using the following method is greater than 0.5 times and less than 5 times.

[0062] <Method for measuring the area occupied by each carbon material>

[0063] The following analysis was performed using image analysis software (Image-Pro Plus Version 4.0 for Windows (registered trademark) manufactured by Planetron Co., Ltd.) on a cross-sectional image (image dimensions: 18.5 μm vertically × 25 μm horizontally) obtained at a magnification of 5000 times using a scanning electron microscope (JSM-6700 manufactured by JEOL Ltd.).

[0064] (i) Image analysis conditions

[0065] After reading the cross-sectional image using the software, perform 8-bit grayscale processing by executing the "Grayscale 8" command under the "Convert" menu. Next, set the horizontal width of the read image to 25 μm using the "Spatial Correction" command under the "Correction" menu. Then, perform binarization using the "Binarization" command under the "Process" menu.

[0066] (Binarization conditions)

[0067] ・Select "3×3"

[0068] ・Threshold setting: Use the value obtained by clicking the auto-detect button located on the right side of the numeric input field once.

[0069] ・Preview conditions: The base part is shown in white and the detection particles are shown in black

[0070] After binarization, open the "Count / Size" command screen under the "Measurement" menu, set the following particle detection and analysis conditions, and execute "Count" to analyze the detected particles.

[0071] (Particle detection conditions)

[0072] ・Brightness range selection: Select "Automatically extract dark objects"

[0073] ・Select "Measurement object"

[0074] (Object extraction option conditions)

[0075] ・4 links / 8 links: Select 4 links

[0076] ・Only "Preselection" and "Hole Filling" are selected

[0077] ・Smoothing: 0

[0078] ・Exclude on boundaries: Select "All boundaries".

[0079] (Particle analysis conditions)

[0080] Based on the obtained image, use the "Count / Size" command on the screen to calculate the aspect ratio (Aspect value) and area (Area value) of each conductive particle in the obtained image.

[0081] For five different fields of view, a count histogram was created, with the obtained aspect ratio as the horizontal axis, with bins set every 0.5 in the range of 1 to 10, and every 10 in the range of 10 to 10. In the count histogram, if a local maximum value existed in the region with an aspect ratio of 1 to 5, the minimum value of the bin showing that local maximum value (for example, if a local maximum value existed in the range of 2 to 2.5, 2 was used as the local maximum value) was used as the aspect ratio of the carbon material (carbon material C1) present in the region with an aspect ratio of 1 to 5. If multiple local maximum peaks existed in the region with an aspect ratio of 1 to 5, the weighted average value obtained using their vertical axis values ​​was used as the aspect ratio of the carbon material (carbon material C1) present in the region with an aspect ratio of 1 to 5.

[0082] Similarly, when there is a maximum value in a region with an aspect ratio of 5 or more, the maximum value is used as the aspect ratio of the carbon material (carbon material C2) present in the region with an aspect ratio of 5 or more. When there are multiple maximum peaks in a region with an aspect ratio of 5 or more, the weighted average value obtained using their vertical axis values ​​is used as the aspect ratio of the carbon material (carbon material C2) present in the region with an aspect ratio of 5 or more.

[0083] For each of the five different fields of view, the aspect ratios of the carbon material (carbon material C1) present in the region with an aspect ratio greater than 1 and less than 5 and the carbon material (carbon material C2) present in the region with an aspect ratio greater than 5 were calculated, and the average value of the five fields of view in each region was taken as the aspect ratio of the carbon material C1 and the carbon material C2 in the polyester film.

[0084] The total area (SC1) of the carbon material (carbon material C1) present in regions with an aspect ratio of 1 or greater and less than 5, as confirmed by the number histogram, is calculated. Next, the total area (SC2) of the carbon material (carbon material C2) present in regions with an aspect ratio of 5 or greater is calculated, and the value obtained by dividing SC1 by SC2 is defined as the ratio of the area (SC1) occupied by the carbon material C1 to the area (SC2) occupied by the carbon material C2 in the P1 layer of the sample.

[0085] [IX] The polyester film according to any one of [I] to [VIII],

[0086] The P1 layer contains at least two polyester resins having different melting points.

[0087] [X] The polyester film according to any one of [I] to [III],

[0088] The P1 layer mainly contains a polyester resin (resin α) containing a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms, or a polyester resin (resin β) containing a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms.

[0089] [XI] The polyester film according to any one of [I] to [X],

[0090] The conductive particles are carbon materials, and a polyester resin layer (P2 layer) having a lower carbon material content than the P1 layer is provided on at least one side of the P1 layer as the outermost layer of the polyester film. When the carbon material content in the P1 layer is set to M P1 (mass %), the content of the carbon material in the P2 layer is set to M P2 (mass %), satisfying M P1 -M P2 ≥0.1.

[0091] [XII] The polyester film according to [XI],

[0092] The P2 layer mainly contains a polyester resin (resin α) containing a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms, or a polyester resin (resin β) containing a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms.

[0093] [XIII] The polyester film according to any one of [I] to [XII],

[0094] The P1 layer contains 0.01% by mass or more and 10% by mass or less of a compound having an ether bond in its main chain.

[0095] [XIV] The polyester film according to any one of [I] to [XIII], which is uniaxially oriented or biaxially oriented.

[0096] [XV] The polyester film according to any one of [I] to [XIV],

[0097] The breaking strength in at least one of the longitudinal direction and the width direction within the film plane is 60 MPa or more and 300 MPa or less.

[0098] [XVI] A laminated polyester film comprising at least a layer composed of a metal and / or a metal-based compound, the polyester film according to any one of [I] to [XV], and a layer composed of a metal and / or a metal-based compound in this order.

[0099] [XVII] The laminated polyester film according to [XVI], satisfying the following (8).

[0100] (8) The outermost layers on both sides of the polyester film are the P1 layers, and layers composed of metal and / or metal-based compounds are provided on both sides of the P1 layer.

[0101] [XVIII] The laminated polyester film according to [XVI] or [XVII],

[0102] The layer composed of the metal and / or the metal-based compound on one surface contains the aluminum element, and the layer composed of the metal and / or the metal-based compound on the opposite surface contains the copper element.

[0103] [XIX] The laminated polyester film according to [XVIII],

[0104] The layer composed of the metal and / or metal-based compound containing the copper element is in contact with a layer mainly composed of a polyester resin (resin α) containing a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms, or a polyester resin (resin β) containing a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms.

[0105] [XX] The laminated polyester film according to any one of [XVI] to [XIX],

[0106] The adhesion between the polyester film surface and the layer composed of metal and / or metal-based compound is 2 N / 15 mm or more on both surfaces.

[0107] [XXI] The laminated polyester film according to any one of [XVI] to [XX],

[0108] The volume resistivity of the laminated polyester film in the through-direction is 1.0×10 0 Ωcm or more and 1.0×10 7 Ωcm or less.

[0109] [XXII] A resin current collector comprising the polyester film described in any one of [I] to [XV], or the laminated polyester film described in any one of [XVI] to [XXI].

[0110] [XXIII] A resin current collector for a bipolar battery according to [XXII].

[0111] [XXIV] A bipolar battery electrode comprising the bipolar battery resin current collector described in [XXIII],

[0112] The resin current collector for a bipolar battery comprises, as at least one surface layer of a polyester film, a surface layer mainly composed of a polyester resin (resin α) comprising a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms, or a polyester resin (resin β) comprising a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms.

[0113] The bipolar battery electrode includes a negative electrode active material layer on the surface layer side of the bipolar battery resin current collector and a positive electrode active material layer on the side opposite to the surface layer.

[0114] [XXV] An electric storage device comprising the bipolar battery resin current collector described in [XXIII] or the bipolar battery electrode described in [XXIV].

[0115] [XXVI] An electric storage device comprising at least two bipolar battery electrodes according to [XXIV],

[0116] The energy storage element has a structure in which at least the bipolar battery resin collector, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer, and the bipolar battery resin collector are repeatedly stacked in this order.

[0117] The resin current collector for a bipolar battery has, as at least one surface layer of a polyester film, a surface layer mainly composed of the polyester resin (resin α) comprising a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms, or the polyester resin (resin β) comprising a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms.

[0118] A negative electrode active material layer is provided on the surface layer side.

[0119] [XXVII] A secondary battery comprising the energy storage element described in [XXV] or [XXVI].

[0120] [XXVIII] An electric vehicle equipped with the secondary battery described in [XXVII].

[0121] [XXIV] An electric flying object equipped with the secondary battery described in [XXVII].

[0122] Effects of the Invention

[0123] The present invention can provide a polyester film having excellent conductivity, uniform conductivity in the thickness direction of the film surface, and little reduction in conductivity due to processing, and a resin current collector for a bipolar battery having little variation in battery characteristics. DETAILED DESCRIPTION

[0124] Hereinafter, the present invention will be described in detail.

[0125] A preferred technical solution of the present invention is a polyester film that satisfies the following (1) to (3).

[0126] (1) Volume resistivity at 23°C and 65% RH is 1.0×10 0 Ωcm or more and less than 1.0×10 8 Ωcm.

[0127] (2) The film thickness is 1 μm or more and less than 500 μm.

[0128] (3) A polyester resin layer (P1 layer) containing 1.0% by mass or more and 30% by mass or less of conductive particles, wherein the conductive particles are carbon materials.

[0129] In addition, another preferred embodiment of the present invention is a polyester film that satisfies the following (1′) to (3′).

[0130] (1′) The film thickness is 1 μm or more and less than 500 μm.

[0131] (2′) A polyester resin layer (P1 layer) containing 1.0% by mass or more and 30% by mass or less of conductive particles.

[0132] (3′) The P1 layer contains conductive particles C1′ having an aspect ratio of 1 or greater and less than 5, and conductive particles C2′ having an aspect ratio of 5 or greater.

[0133] By adopting the present technical solution, a polyester film can be obtained which has good volume resistivity in the thickness direction of the film, excellent conductivity, and uniform conductivity in the thickness direction within the film surface.

[0134] (Mylar)

[0135] The polyester film referred to in the present invention refers to a film containing polyester resin as a main component. The main component here means a component that contains more than 50% by mass in 100% by mass of all components of the object.

[0136] The polyester resin referred to in the present invention is formed by polycondensation of a dicarboxylic acid component and a diol component. In this specification, a component refers to the smallest unit obtainable by hydrolyzing a polyester. Furthermore, in this application, a polyester resin formed by polycondensation of a dicarboxylic acid component and a diol component may sometimes be referred to as a polyester resin containing a dicarboxylic acid component and a diol component.

[0137] Examples of the diol constituent components constituting the polyester resin include aliphatic diols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; and alicyclic diols such as 1,4-cyclohexanedimethanol, 1,3-cyclobutane dimethanol, 2,2,4,4-tetramethyl-1,3-cyclobutane dimethanol, and spirodiol; and products in which a plurality of the above diol components are linked together.

[0138] Examples of the dicarboxylic acid constituent component constituting the polyester resin include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, and 4,4'-diphenyletherdicarboxylic acid.

[0139] Examples of polyester resins containing a dicarboxylic acid component and a diol component include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polycyclohexanedimethanol terephthalate (PCT), and polyethylene naphthalate (PEN). In these polyester resins, isophthalic acid or naphthalene dicarboxylic acid, which are part of the dicarboxylic acid component of the polyester, and 1,3-butanediol, 1,4-cyclohexanedimethanol, or 2,2,4,4-tetramethyl-1,3-cyclobutane dimethanol, which are part of the diol component, may be copolymerized, as long as the effects of the present invention are not impaired.

[0140] (Biaxially oriented polyester film)

[0141] From the perspective of improving the film's mechanical strength and thermal dimensional stability, the polyester film of the present invention is more preferably biaxially oriented. Biaxial orientation herein refers to a pattern exhibiting biaxial orientation in wide-angle X-ray diffraction. Biaxially oriented polyester films are generally obtained by stretching an unstretched thermoplastic resin film in the film-forming axis (hereinafter sometimes referred to as the longitudinal direction) and the width direction of the film, followed by heat treatment to complete the orientation and crystallization.

[0142] The polyester film of the present invention preferably has a volume resistivity of 1.0×10 0 Ωcm or more and less than 1.0×10 8 Ωcm.

[0143] Volume resistivity is a value that reflects the conductivity in the thickness direction of the film and is independent of the film thickness. By making the volume resistivity of the polyester film of the present invention less than 1.0×10 8 Ωcm, excellent conductivity, when used as a resin collector for bipolar batteries, can increase the current value flowing in the battery, can show sufficient battery performance. In addition, by making the volume resistivity of the polyester film of the present invention less than 1.0×10 8 Ωcm, a conductive path can be fully formed in the thickness direction. When the polyester film of the present invention is processed as a battery component, even when it is deformed by stretching or bending, a significant decrease in conductivity can be suppressed. The volume resistivity at 23°C and 65% RH is more preferably 1.0×10 7 Ωcm or less, more preferably 1.0×10 6 Ωcm or less.

[0144] The volume resistivity of the polyester film of the present invention at 23°C and 65%RH is 1.0×10 0 When the electrostatic application method is used to produce a cast film in the film casting process described later, an unstretched film without wrinkles or uneven thickness caused by uneven application can be obtained. This can suppress the occurrence of surface defects in the case of providing a layer composed of a metal and / or a metal compound described later (hereinafter referred to as an M layer) due to wrinkles or uneven thickness of the polyester film after film formation. When the polyester film is assembled as a resin current collector in a storage element, a decrease in current value or an increase in deviation can be suppressed.

[0145] The electrostatic application method is a method of charging the polyester resin layer, making it close to the metal casting roller and cooling it to obtain an unstretched sheet. If the volume resistivity of the polyester film is low, the charge generated by the charging will flow out to the side of the casting roller, and sometimes the close adhesion with the casting roller will be reduced, resulting in uneven application.

[0146] The volume resistivity of the polyester film of the present invention at 23°C and 65%RH is more preferably 1.0×10 1 Ωcm or more, more preferably 1.5×10 2 Ωcm or more, particularly preferably 1.0×10 2 Ωcm or more.

[0147] The polyester film of the present invention preferably has a film thickness of 1 μm or more and less than 500 μm as determined by the method described below.

[0148] By making the film thickness 1 μm or more, the occurrence of cracks based on the P1 layer described later during film formation can be suppressed, and the film forming properties can be improved. In addition, even when the tensile strength becomes high and deformation occurs during processing as a battery component, a significant decrease in conductivity can be suppressed. The film thickness is more preferably 2 μm or more, further preferably 3 μm or more, and most preferably 4 μm or more. In addition, by making the film thickness less than 500 μm, the increase in battery size can be minimized when assembled as a resin collector for a bipolar battery. The film thickness is more preferably 300 μm or less, particularly preferably 150 μm or less, and most preferably 80 μm or less.

[0149] In addition, when the thickness of the polyester film of the present invention is 80 μm or less, the polyester film of the present invention is a uniaxially oriented or biaxially oriented polyester film. In particular, from the viewpoint of improving the strength of the film and suppressing a significant decrease in conductivity even when deformed during processing as a battery component, a biaxially oriented polyester film is a more preferred form.

[0150] (P1 layer: a polyester resin layer containing 1.0% by mass or more and 30% by mass or less of conductive particles)

[0151] The polyester film of the present invention preferably includes a polyester resin layer (P1 layer) containing 1.0% by mass or more and 30% by mass or less of conductive particles.

[0152] By having the P1 layer containing 1.0 mass % or more and 30 mass % or less of conductive particles, the volume resistivity of the film can be controlled within a preferred range, and good conductivity can be exhibited in the thickness direction of the polyester film.

[0153] The conductive particles preferably contain one or more selected from metal particles, metal oxide particles, conductive resin particles, and carbon materials. The conductive particles more preferably contain a carbon material, and further preferably are a carbon material.

[0154] Examples of metal particles used as conductive particles include particles containing one element selected from gold, silver, copper, tin, nickel, indium, aluminum, and iron as a main component, and metal particles of stainless steel, nickel-indium alloy, and the like.

[0155] Examples of metal oxide particles used as conductive particles include tin oxide, zinc oxide, and zinc oxide. Similarly, inorganic particles such as aluminum oxide, calcium carbonate, mica, talc, and glass, having a coating layer composed of the metals listed above for the metal particles and the metal oxides listed above for the metal oxides, may also be used.

[0156] Examples of the conductive resin particles used as the conductive particles include resins having a conjugated double bond structure in the main chain skeleton, such as polyacetylene, polyparaphenylene, polyfluorene, and polyparaphenylenevinylene; thiophene-based resins such as polyethylenedioxythiophene (PEDOT) / polystyrenesulfonic acid (PSS), polythiophene, and polythienylvinylene; polyaniline; and polypyrrole.

[0157] The carbon material is a graphite structure (sp) that is generally referred to as the G band in Raman spectroscopy. 2 Key) 1580cm -1 near and from the diamond structure commonly known as the D band (sp 3 Key) 1350cm -1 Materials where peaks are observed nearby.

[0158] By increasing the amount of conductive particles in the P1 layer to 1.0% by mass or greater, the volume resistivity can be reduced, improving the conductivity of the film. Furthermore, the conductivity throughout the thickness direction can be made uniform. The concentration of the conductive particles in the P1 layer is more preferably 1.5% by mass or greater, and even more preferably 2.0% by mass or greater.

[0159] By limiting the amount of conductive particles contained in the P1 layer to 30% by mass or less, the polyester film of the present invention can be prevented from experiencing discharging disturbances during the film-forming process. Furthermore, during stretching, the formation of cracks originating from the conductive particles or of microscopic air layers (hereinafter sometimes referred to as voids) can be prevented, thereby suppressing film breakage during stretching. This suppression of the formation of numerous voids also allows for uniform conductivity throughout the thickness direction. Furthermore, limiting the amount of conductive particles contained in the P1 layer to 30% by mass or less can prevent a significant decrease in the film's mechanical strength. This prevents significant degradation of conductivity even when subjected to deformation during processing as a battery component. Furthermore, when the polyester film of the present invention is mounted as a current collector on a battery cell, microscopic deformation caused by thermal deformation or external stress associated with battery charging and discharging can be prevented from causing breakage in the polyester film and resulting in a decrease in battery performance. The amount of conductive particles contained in the P1 layer is more preferably 20% by mass or less, even more preferably 15% by mass or less, particularly preferably 10% by mass or less, and most preferably 5% by mass or less.

[0160] The above-mentioned carbon material preferably contains a total of 80% by mass or more of one or more carbon nanotubes selected from the group consisting of furnace black, acetylene black, single-layer carbon nanotubes, multi-layer carbon nanotubes, and thin-layer carbon nanotubes, carbon fibers, graphene, Ketjen black, fibrous carbon, fullerene, and graphite in 100% by mass of the above-mentioned carbon material. From the viewpoint of imparting conductivity by a small amount of addition, the above-mentioned carbon material preferably contains a total of 80% by mass or more and 100% by mass or less of one or more carbon nanotubes selected from Ketjen black, carbon nanotubes, and acetylene black in 100% by mass of the above-mentioned carbon material.

[0161] The polyester film of the present invention preferably comprises at least two types of conductive particles in the P1 layer: conductive particles C1' having an aspect ratio of 1 or greater and less than 5, and conductive particles C2' having an aspect ratio of 5 or greater. The method for determining the aspect ratio of the conductive particles contained in the P1 layer will be described later. The aspect ratio can be determined using the same measurement method regardless of whether the conductive particles are metal particles, metal oxide particles, conductive resin particles, or carbon materials.

[0162] By including at least two types of conductive particles, conductive particles C1' with an aspect ratio of 1 or greater and less than 5, and conductive particles C2' with an aspect ratio of 5 or greater, the P1 layer can achieve a film with a preferred volume resistivity range, even with a reduced amount, compared to when either type of conductive particle is included alone. Furthermore, a sufficient conductive path is formed in the thickness direction, and when the polyester film of the present invention is processed as a battery component, even when subjected to deformation such as stretching or bending, a significant decrease in conductivity can be suppressed. Furthermore, since the conductive particle content can be reduced, the film's mechanical strength can be improved.

[0163] The ability to suppress a significant decrease in conductivity even when subjected to deformation such as stretching or bending can be explained as follows. Conductive particles with an aspect ratio of 5 or more have high conductivity in the long axis direction of the conductive particles and have the function of transmitting electrons over long distances. On the other hand, when subjected to deformation such as stretching or bending, if the spacing between the conductive particles is widened, the connection points are easily cut off. Conductive particles with an aspect ratio of 1 or more and less than 5 are smaller in size than conductive particles with an aspect ratio of 5 or more and are approximately spherical in shape. In the case of containing at least two conductive particles with different aspect ratios in the above-mentioned P1 layer, when subjected to deformation such as stretching or bending, the conductive particles with an aspect ratio of 1 or more and less than 5 enter between the cut-off conductive paths of the conductive particles with an aspect ratio of 5 or more, thereby suppressing the cutting of the conductive paths.

[0164] Furthermore, since the P1 layer contains at least two types of conductive particles, namely, conductive particles C1' having an aspect ratio of 1 or greater and less than 5, and conductive particles C2' having an aspect ratio of 5 or greater, the polyester film of the present invention can suppress a decrease in conductivity when heated. This is because the polyester film of the present invention increases the mobility of the resin molecular chains under high temperature conditions. Therefore, even if the dispersion state of the conductive particles contained therein changes, the conductive particles having an aspect ratio of 1 or greater and less than 5 can enter between the disconnected conductive paths of the conductive particles having an aspect ratio of 5 or greater, thereby suppressing the disconnection of the conductive paths. Therefore, a storage element using the polyester film of the present invention as a resin current collector for a bipolar battery can suppress a decrease in current value even when the temperature rises during operation.

[0165] From the same viewpoint as above, the polyester film of the present invention preferably has the P1 layer containing at least two carbon materials: a carbon material C1 having an aspect ratio of 1 or more and less than 5, and a carbon material C2 having an aspect ratio of 5 or more.

[0166] Here, the carbon material C1 having an aspect ratio of greater than 1 and less than 5 is preferably one or more selected from furnace black, acetylene black, Ketjen black and fullerene. From the viewpoint of excellent conductivity, the carbon material C1 having an aspect ratio of greater than 1 and less than 5 is more preferably acetylene black and / or Ketjen black.

[0167] In addition, the carbon material C2 with an aspect ratio of 5 or more is preferably one or more selected from single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon fibers and graphene, and more preferably one selected from single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon fibers.

[0168] In the polyester film of the present invention, the ratio of the area occupied by the carbon material C1 (SC1) in the P1 layer to the area occupied by the carbon material C2 (SC2) determined by the following method is preferably 0.5 times or more and 5 times or less, and the ratio is preferably 0.5 times or more and 5.0 times or less.

[0169] <Method for measuring the area occupied by each carbon material>

[0170] The following analysis was performed using image analysis software (Image-Pro Plus Version 4.0 for Windows (registered trademark) manufactured by Planetron Co., Ltd.) on a cross-sectional image (image dimensions: 18.5 μm vertically × 25 μm horizontally) obtained at a magnification of 5000 times using a scanning electron microscope (JSM-6700 manufactured by JEOL Ltd.).

[0171] (i) Image analysis conditions

[0172] After reading the cross-sectional image using the software, perform 8-bit grayscale processing by executing the "Grayscale 8" command under the "Convert" menu. Next, set the horizontal width of the read image to 25 μm using the "Spatial Correction" command under the "Correction" menu. Then, perform binarization using the "Binarization" command under the "Process" menu.

[0173] (Binarization conditions)

[0174] ・Select "3×3"

[0175] ・Threshold setting: Use the value obtained by clicking the auto-detect button located on the right side of the numeric input field once.

[0176] ・Preview conditions: The base part is shown in white and the detection particles are shown in black

[0177] After binarization, open the "Count / Size" command screen under the "Measurement" menu, set the following particle detection and analysis conditions, and execute "Count" to analyze the detected particles.

[0178] (Particle detection conditions)

[0179] ・Brightness range selection: Select "Automatically extract dark objects"

[0180] ・Select "Measurement object"

[0181] (Object extraction option conditions)

[0182] ・4 links / 8 links: Select 4 links

[0183] ・Only "Preselection" and "Hole Filling" are selected

[0184] ・Smoothing: 0

[0185] ・Exclude on boundaries: Select "All boundaries".

[0186] (Particle analysis conditions)

[0187] Based on the obtained image, use the "Count / Size" command screen to calculate the aspect ratio (Aspect value) and area (Area value) of each conductive particle in the obtained image.

[0188] For five different fields of view, a count histogram was created, with the obtained aspect ratio as the horizontal axis, with bins set every 0.5 in the range of 1 to 10, and every 10 in the range of 10 to 10. In the count histogram, if a local maximum value existed in the region with an aspect ratio of 1 to 5, the minimum value of the bin showing that local maximum value (for example, if a local maximum value existed in the range of 2 to 2.5, 2 was used as the local maximum value) was used as the aspect ratio of the carbon material (carbon material C1) present in the region with an aspect ratio of 1 to 5. If multiple local maximum peaks existed in the region with an aspect ratio of 1 to 5, the weighted average value obtained using their vertical axis values ​​was used as the aspect ratio of the carbon material (carbon material C1) present in the region with an aspect ratio of 1 to 5.

[0189] Similarly, when there is a maximum value in a region with an aspect ratio of 5 or more, the maximum value is used as the aspect ratio of the carbon material (carbon material C2) present in the region with an aspect ratio of 5 or more. When there are multiple maximum peaks in a region with an aspect ratio of 5 or more, the weighted average value obtained using their vertical axis values ​​is used as the aspect ratio of the carbon material (carbon material C2) present in the region with an aspect ratio of 5 or more.

[0190] For each of the five different fields of view, the aspect ratios of the carbon material (carbon material C1) present in the region with an aspect ratio greater than 1 and less than 5 and the carbon material (carbon material C2) present in the region with an aspect ratio greater than 5 were calculated, and the average value of the five fields of view in each region was taken as the aspect ratio of the carbon material C1 and the carbon material C2 in the polyester film.

[0191] The total area (SC1) of the carbon material (carbon material C1) present in regions with an aspect ratio of 1 or greater and less than 5, as confirmed by the number histogram, is calculated. Next, the total area (SC2) of the carbon material (carbon material C2) present in regions with an aspect ratio of 5 or greater is calculated, and the ratio of the area (SC2) occupied by the carbon material C2 to the area (SC1) occupied by the carbon material C1 in the P1 layer is obtained. The area ratio can be calculated using the same measurement method regardless of whether the conductive particles are metal particles, metal oxide particles, conductive resin particles, or carbon materials.

[0192] By setting the ratio of the area occupied by the carbon material C2 (SC2) in the P1 layer to 0.5 times or greater relative to the area occupied by the carbon material C1 (SC1), the carbon material C1 with an aspect ratio of 1 or greater but less than 5 can be further embedded between the carbon material C2 with an aspect ratio of 5 or greater, thereby suppressing the disconnection of the conductive path during deformation such as stretching or bending. In particular, this can suppress degradation of the electrical properties of the polyester film after tension-inducing processing such as metallization. Furthermore, by setting the area occupied by the carbon material C1 in the P1 layer to 5 times or less relative to the area occupied by the carbon material C2, electrical conductivity can be achieved without increasing the carbon material content, resulting in a film with excellent mechanical strength that is less prone to stretching even under tension, suppressing the disconnection of the conductive path during deformation such as stretching or bending. The ratio of the area occupied by the carbon material C2 (SC2) in the P1 layer to the area occupied by the carbon material C1 (SC1) is more preferably 1.0 times or greater. The ratio of the area (SC2) occupied by the carbon material C2 to the area (SC1) occupied by the carbon material C1 in the P1 layer is more preferably 4.5 times or less, and further preferably 4.0 times or less.

[0193] In addition, from the same viewpoint as above, the polyester film of the present invention preferably contains at least two types of conductive particles, namely, conductive particles C1' having an aspect ratio of greater than 1 and less than 5 and conductive particles C2' having an aspect ratio of greater than 5, and the area occupied by the conductive particles C1' in the P1 layer calculated by the same method as above is greater than 0.5 times and less than 5 times the area occupied by the conductive particles C2'.

[0194] In the polyester film of the present invention, the conductive particles contained are preferably carbon materials. In the P1 layer, the volume-based average dispersion diameter of the carbon materials contained therein, as determined by the method described below, is 0.15 μm or more and 0.90 μm or less, and the number of dispersed particles is 1.5 particles / μm. 2 More than 5.0 / μm 2Below. A volume-based average dispersion diameter of 0.15 μm or more indicates that the carbon material contained in the P1 layer is appropriately aggregated, and acts as a relay point when electrons are conducted in the thickness direction of the film. This is because, when the carbon material is excessively dispersed and exists as a monomer, the movement of electrons is limited to a linear direction or a planar direction due to the molecular structure of the carbon material, and therefore sometimes the electron conductivity in the thickness direction cannot be improved. On the other hand, when a plurality of carbon materials are moderately irregularly aggregated, the range of electron movement is expanded by three-dimensionally expanding the carbon material, so that electrons can be efficiently transferred between the aggregates of carbon materials present in the polyester film, and the electron conductivity in the thickness direction is improved. The volume-based average dispersion diameter of the carbon material contained in the above-mentioned P1 layer is more preferably 0.20 μm or more.

[0195] Furthermore, by setting the volume-based average dispersion diameter to 0.90 μm or less, film breakage originating from the carbon material can be suppressed during film stretching or application of tensile force. The volume-based average dispersion diameter of carbon materials tends to increase with carbon concentration, and when the carbon material content exceeds 30% by mass, it becomes extremely difficult to achieve a volume-based average dispersion diameter of 0.90 μm or less. A more preferred range for the volume-based average dispersion diameter is 0.80 μm or less.

[0196] In the polyester film of the present invention, the conductive particles contained are preferably carbon materials. In the P1 layer, the number of dispersed carbon materials contained is 1.5 particles / μm as determined by the method described below. 2 More than 5.0 / μm 2 The number of dispersed carbon materials contained in the P1 layer is 1.5 per μm. 2 More than 5.0 / μm 2 The following indicates that a good concentration of carbon materials serving as relay points for the above-mentioned electron conduction exists appropriately in the thin film.

[0197] The volume-based average dispersion diameter of the contained carbon material is 0.15 μm or more and 0.90 μm or less, and the number of dispersed particles is 1.5 particles / μm. 2 More than 5.0 / μm 2 The following means that a sufficient amount of carbon material serving as a relay point for conductivity is present in the film. By doing so, the volume resistivity of the polyester film can be more easily controlled within a preferred range.

[0198] When the polyester film of the present invention is used as a resin current collector for a bipolar battery, from the perspective of suppressing decomposition of the polyester resin due to electrochemical reactions within the battery, the surface layer of the polyester film on the side closest to the negative electrode is preferably composed primarily of a polyester resin (resin α) containing a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms. The polyester resin containing a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms refers to a resin formed by polycondensation of a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms.

[0199] By using a diol component having 3 to 16 carbon atoms, the molecular mobility around the ester bonds, which could potentially serve as decomposition points for the polyester resin, can be reduced. This prevents molecules that decompose ester bonds from surrounding electrolytes, electrolytes, and additives from approaching the ester bonds of the polyester resin. Examples of molecules that decompose ester bonds include water molecules, hydrogen ions, alcohols, and carboxylic acids.

[0200] In particular, when a cyclic diol component having 3 to 16 carbon atoms is used, the steric structure of the diol component becomes larger, further preventing the aforementioned molecules that decompose ester bonds from approaching the ester bonds of the polyester resin. Furthermore, when an aliphatic diol component having 3 to 16 carbon atoms is used, the aliphatic diol components self-aggregate, densely packing the polyester resin molecular chains, thereby suppressing the aforementioned molecules that decompose ester bonds from invading the intermolecular spaces between the polyester resin molecular chains.

[0201] By setting the carbon number of the diol component to 16 or less, the polymerization reaction can proceed without aggregation of the diol components during the polyester polymerization step, allowing the production of a polyester resin with a molecular weight suitable for film production. The carbon number of the diol component is more preferably 12 or less, and even more preferably 9 or less. Particularly preferred polyester resins include polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), and polycyclohexanedimethylene terephthalate (PCT).

[0202] In addition, when the P1 layer contains more than 1.0 mass % and less than 30 mass % of carbon material, and the P1 layer has resin α as a main component, and the diol component with a carbon number of 3 or more and less than 16 is an aliphatic diol with a carbon number of 3 or more, the aliphatic component with a carbon number of 3 or more has a high affinity with the graphite structure and / or diamond structure portion of the carbon material contained in the P1 layer, so that the carbon material with high affinity can be dispersed more evenly.

[0203] When the polyester film of the present invention is used as a resin current collector for a bipolar battery, from the perspective of suppressing decomposition of the polyester resin due to electrochemical reactions within the battery, the surface layer of the polyester film closest to the negative electrode preferably contains as its main component a polyester resin (resin β) containing a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms. Furthermore, the polyester resin containing a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms is a resin obtained by polycondensation of a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms. Furthermore, the surface layer of the polyester film closest to the negative electrode preferably corresponds to the aforementioned P1 layer.

[0204] By using a dicarboxylic acid component having 9 to 16 carbon atoms, the molecular mobility around the ester bonds that could serve as decomposition points of the polyester resin can be reduced. This prevents molecules that decompose ester bonds from surrounding electrolytes, electrolytes, and additives from approaching the ester bonds of the polyester resin.

[0205] In particular, when an aromatic dicarboxylic acid component having 9 to 16 carbon atoms or an aliphatic dicarboxylic acid component having 9 to 16 carbon atoms is used, the dicarboxylic acid components self-aggregate with each other, and the polyester resin molecular chains are densely stacked, which can inhibit the above-mentioned molecules that decompose ester bonds from invading the molecular spaces between the polyester resin molecular chains.

[0206] By limiting the carbon number of the dicarboxylic acid component to 16 or less, the polymerization reaction can proceed without aggregation of the dicarboxylic acid components during the polyester polymerization step, allowing the production of a polyester resin with a molecular weight suitable for film production. The carbon number of the dicarboxylic acid component is more preferably 14 or less. Polyethylene naphthalate (PEN) is a particularly preferred polyester resin.

[0207] That is, when the polyester film of the present invention is used as a resin collector for a bipolar battery, from the viewpoint of suppressing the decomposition of the polyester resin caused by the electrochemical reaction in the battery, it is preferred that the above-mentioned P1 layer is the outermost layer on at least one side of the polyester film, and the above-mentioned P1 layer is composed of a layer having resin α or resin β as the main component.

[0208] From the perspective of reducing the variation in the volume resistivity of the polyester film in the in-plane direction, the P1 layer in the polyester film of the present invention preferably contains at least two polyester resins with different melting points. Here, containing two or more polyester resins with different melting points means that two or more melting heat peaks at different temperatures are simultaneously observed in differential scanning calorimetry (DSC) measurements, described below. This is because heat treatment melts only the polyester resin with the lower melting point, filling the voids (air layers) centered around the conductive particles contained in the P1 layer, thereby suppressing localized increases in the volume resistivity of the polyester film. The heat treatment method, particularly a method in which only the polyester resin with the lower melting point is melted during the heat treatment step during film formation, described below, effectively fills voids, particularly voids associated with stretching. Alternatively, heat treatment can be performed by appropriately heating the already formed film.

[0209] From the same viewpoint as above, the P1 layer in the polyester film of the present invention more preferably contains at least two polyester resins having different melting points.

[0210] When two polyester resins having different melting points are contained, a difference of 10°C or more between the two types of polyester resins is preferred because the voids are easily filled. The difference of 15°C or more between the two types of polyester resins is more preferred, and 20°C or more is even more preferred.

[0211] When the P1 layer in the polyester film of the present invention contains three or more polyester resins with different melting points, it is preferred that the difference in melting point between the polyester resin with the highest melting point and the polyester resin with the second highest melting point among the three or more polyester resins with different melting points is 10°C or more, because this facilitates the effect of filling the above-mentioned gaps.

[0212] When the P1 layer of the present invention contains polyethylene terephthalate having a melting point of 255° C., it is preferred that the P1 layer also contain a polyester resin having a melting point of 235° C. or lower as a polyester resin having a low melting point.

[0213] In particular, the diol component constituting the low-melting-point polyester resin contained in the P1 layer is more preferably an aliphatic diol having 3 or more and 16 carbon atoms. This is because the use of an aliphatic diol having 3 or more carbon atoms as a component of the polyester resin improves its affinity for the graphite structure and / or diamond structure of the carbon material contained in the P1 layer. This increased affinity for the carbon material allows the low-melting-point polyester resin to be evenly dispersed within the polyester film, while the carbon material with a higher affinity can also be evenly dispersed. This, combined with the effect of filling the aforementioned voids, can further reduce the variation in volume resistivity within the film surface.

[0214] The P1 layer of the polyester film of the present invention preferably contains 0.01% by mass or more and 10% by mass or less of a compound having an ether bond in its main chain.

[0215] Compounds with ether bonds in their backbones have a structure where hydrocarbon backbones are connected by neutral, non-polar ether bonds. They have excellent affinity for the surface of less polar carbon materials, and the flexibility derived from the ether bonds allows them to adhere to the surface of the carbon material. This prevents excessive aggregation of the carbon material, allowing it to be dispersed within the film. Consequently, even with low carbon material content, the volume resistivity of the polyester film can be reduced.

[0216] Examples of compounds having ether bonds in the main chain include polyether compounds having linear hydrocarbons such as polyethylene glycol, polytrimethylene glycol, and polytetramethylene glycol, and their modified products, aromatic ether compounds such as polyphenylene ether (PPE), polyetheretherketone (PEEK), and polyetherimide (PEI), and their modified products. 2 bonds) and diamond structure (sp 3 From the viewpoint of improving the affinity of the polyester resin (bond) and the flexibility of the molecule, it is preferred to use a polyether compound having a linear hydrocarbon such as polyethylene glycol, polytrimethylene glycol, or polytetramethylene glycol. In addition, a copolymer of the above-mentioned polyester resin and a polyether compound having a linear hydrocarbon can also be used.

[0217] As a method for incorporating the compound having an ether bond in its main chain into a polyester film, there is a method of mixing a polyester resin with a carbon material or a masterbatch containing the carbon material and forming the film into sheets by melt extrusion. A more preferred method, from the perspective of suppressing agglomeration of the carbon material, is to mix the compound having an ether bond in its main chain into the masterbatch formed by mixing the carbon material with the polyester resin to form the masterbatch, thereby forming a masterbatch containing the compound having an ether bond in its main chain and the carbon material. The masterbatch is then mixed with the polyester resin and formed into sheets by melt extrusion.

[0218] The content of the compound having an ether bond in the main chain contained in the P1 layer is preferably 0.01% by mass or more and 10% by mass or less. By setting the content of the compound having an ether bond in the main chain to 0.01% by mass or more, the effect of suppressing the aggregation of the carbon material can be further achieved. The content of the compound having an ether bond in the main chain contained in the P1 layer is more preferably 0.03% by mass or more, further preferably 0.05% by mass or more, and particularly preferably 0.10% by mass or more.

[0219] Furthermore, by limiting the content of the compound having an ether bond in the main chain to 10% by mass or less, it is possible to suppress excessive suppression of molecular orientation, a decrease in mechanical strength, and film breakage during biaxial stretching of the polyester film. Consequently, the volume resistivity, elongation at break, and breaking strength of the polyester film can all be within preferred ranges.

[0220] The elongation at break of the polyester film of the present invention is preferably 25% or more and 120% or less in at least one of the longitudinal and width directions within the film plane. By setting this elongation at break to 25% or more, when the polyester film of the present invention is incorporated into a storage element as a current collector, the storage element will not expand and deform due to the heat generated by the operation of the storage element, thereby suppressing the degradation of the storage element's performance due to breakage of the assembled polyester film. Furthermore, even when the film is subjected to strong stretching or bending, or deformation during processing as a battery component, the conductive path of the conductive particles is interrupted due to breakage, thereby significantly reducing conductivity. Furthermore, by setting the elongation at break to 120% or less, the crystallinity of the polyester film of the present invention is reduced. Thus, when incorporated into a storage element, the heat generated during charging and discharging of the storage element causes the polyester film to crystallize over time, thereby suppressing breakage due to minor impacts and degradation of battery performance.

[0221] The elongation at break is more preferably 30% or more, further preferably 40% or more, and most preferably 90% or more. Furthermore, the elongation at break is more preferably 110% or less, further preferably 100% or less.

[0222] Regarding the elongation at break of the polyester film of the present invention, when the unwinding direction of the polyester film is defined as the longitudinal direction and the direction rotated 90° in-plane relative to the longitudinal direction is defined as the width direction of the polyester film, it is more preferable that the elongation at break in at least one of the longitudinal direction and the width direction falls within the aforementioned preferred range. Furthermore, it is more preferable that the elongation at break in both the longitudinal direction and the width direction fall within the aforementioned preferred range.

[0223] The breaking strength of the polyester film of the present invention is preferably 60 MPa or more and 300 MPa or less in at least one of the longitudinal and width directions within the film surface. By setting the breaking strength to 60 MPa or more, when the polyester film of the present invention is assembled into a storage element as a current collector, it is possible to suppress the situation where the polyester film breaks when a slight impact is applied during the transportation of the storage element, thereby reducing the performance of the storage element. The breaking strength is more preferably 70 MPa or more, further preferably 75 MPa or more, and most preferably 100 MPa or more. In addition, by setting the breaking strength to 60 MPa or more, in the roll-to-roll metal deposition process of the polyester film of the present invention, or in processes where the film is subjected to high temperature while in contact with the rollers during transportation, it is possible to suppress the situation where a slight thermal deformation occurs under the tension during film transportation, which hinders the formation of conductive paths by the carbon material in the polyester film and increases the volume resistivity. Furthermore, when the polyester film of the present invention is incorporated into a battery element, even when the battery element is subjected to a large impact such as a drop or collision, deformation and breakage of the polyester film can be suppressed, thereby suppressing a significant decrease in battery characteristics or fire of the battery element due to a short circuit.

[0224] Furthermore, by setting the breaking strength to 300 MPa or less, when the polyester film of the present invention is incorporated as a current collector into a storage element, it is possible to suppress the polyester film from breaking during charge and discharge, which in turn reduces the performance of the storage element. This can be explained as follows. While proper crystallization of the polyester film improves the breaking strength, it also reduces the film's resistance to deformation. This is believed to be due to the volumetric changes in the battery components during repeated charge and discharge, which accumulate as deformation damage in the polyester film, inducing breakage of the polyester film.

[0225] With respect to the breaking strength of the polyester film of the present invention, when the unwinding direction of the polyester film is defined as the longitudinal direction and the direction rotated 90° in-plane relative to the longitudinal direction is defined as the width direction of the polyester film, it is more preferred that the breaking strength in at least one of the longitudinal direction and the width direction fall within the aforementioned preferred range. It is more preferred that the breaking strength in both the longitudinal direction and the width direction fall within the aforementioned preferred range.

[0226] The affinity of the carbon material contained in the polyester film of the present invention with the polyester resin and the compound having an ether bond in the main chain can be evaluated using the Hansen Solubility Parameter value described below. The Hansen Solubility Parameter value is a numerical value indicating the ease of mixing of two different materials. By reducing the difference in the Hansen Solubility Parameter values ​​(hereinafter sometimes referred to as ΔHSP value (MPa)) between the carbon material and the polyester resin and the compound having an ether bond in the main chain, the affinity can be evaluated. 1 / 2)), can inhibit the aggregation of carbon materials in the resin, and control the volume resistivity of the polyester film within a preferred range. Preferably, the ΔHSP value of the polyester resin and carbon material contained in the polyester film is 6MPa 1 / 2 The ΔHSP value of the compound having an ether bond in the main chain and the carbon material is 6 MPa. 1 / 2 Here, the Hansen solubility parameter value of the carbon material is not divided by the aspect ratio, but is obtained from the entire carbon material included.

[0227] By making each ΔHSP value 6 MPa 1 / 2 The following can improve the agglomeration suppression and dispersion of the carbon material in the film. The more preferable range of the ΔHSP value is 5 MPa. 1 / 2 Below, particularly preferably 4.5 MPa 1 / 2 the following.

[0228] Furthermore, the ΔHSP value of the polyester resin and the compound having an ether bond in the main chain contained in the P1 layer is preferably 8 MPa. 1 / 2 The polyester resin and the compound having an ether bond in the main chain have a ΔHSP value of 8 MPa. 1 / 2 As a result, aggregation of the carbon material due to aggregation of the compound having an ether bond in the main chain in the polyester resin can be suppressed.

[0229] When the compound having an ether bond in the main chain is a copolymer of multiple compounds, the ΔHSP value of the copolymerized components is multiplied by the content ratio (percentage) of each copolymerized component in the compound, and the sum of the results is used as the ΔHSP value of the copolymerized components.

[0230] (P2 layer: A polyester resin layer containing less carbon material than the P1 layer)

[0231] The polyester film of the present invention preferably comprises: the conductive particles contained in the P1 layer are carbon materials, and a polyester resin layer (P2 layer) having a carbon material content less than that of the P1 layer is provided as the outermost layer of the polyester film on at least one side of the P1 layer. When the carbon material content in the P1 layer is set to M P1 (mass %), the content of the carbon material in the P2 layer is defined as M P2 (mass %), satisfying M P1 -M P2 ≥0.1.

[0232] This is because, in the film casting process using electrostatic application, the casting roll and the P2 layer are in contact with each other during coextrusion to form an unstretched film. This allows the P2 layer, with its high volume resistivity, to prevent the flow of charged charges onto the casting roll, even when the P1 layer has a low volume resistivity, thus suppressing uneven application. Furthermore, in processes such as roll-to-roll metal deposition, where the film is exposed to high temperatures while in contact with the rolls during transport, the enhanced contact with the cooling rolls achieved by the electrostatic application can suppress thermal degradation of the film.

[0233] When the polyester film of the present invention is used as a resin collector for a bipolar battery and the P2 layer is arranged on the negative electrode side, from the viewpoint of suppressing the decomposition of the polyester resin caused by the electrochemical reaction in the battery, the P2 layer preferably has resin α or resin β as the main component for the same reason as described in the above-mentioned item of the P1 layer.

[0234] The laminated structure of the polyester film of the present invention may be a two-layer structure of P2 layer / P1 layer, or a three-layer structure of P2 layer / P1 layer / P2 layer or P1 layer / P2 layer / P1 layer, preferably a two-layer structure of P2 layer / P1 layer or a three-layer structure of P2 layer / P1 layer / P2 layer.

[0235] The content M of the carbon material in the P2 layer P2 (mass %) is preferably 0.1 mass % or more. This is because when the P2 layer and the P1 layer are stacked, with the P1 layer sandwiched between two P2 layers, degradation of the electrical characteristics of the P1 layer can be suppressed.

[0236] The proportion of the above-mentioned P1 layer in the entire polyester film is preferably 55% or more. Here, the proportion of the P1 layer in the entire polyester film refers to the percentage ratio obtained by dividing the thickness of the P1 layer by the thickness of the polyester film. When there are multiple P1 layers in the polyester film, the total thickness of these multiple P1 layers is taken as the thickness of the P1 layer. By making the proportion of the above-mentioned P1 layer in the entire polyester film 55% or more, the conductivity of the polyester film as a whole can be further demonstrated, and when used as a resin collector for a bipolar battery, the characteristics of the bipolar battery can be improved. The proportion of the above-mentioned P1 layer in the entire polyester film is more preferably 65% ​​or more.

[0237] (Method for producing biaxially oriented polyester film)

[0238] Next, a method for producing a biaxially oriented film from the polyester film of the present invention will be described with an example, but the present invention is not limited to the product obtained by this example.

[0239] The polyester film used in the present invention can be obtained by conventional polymerization methods. For example, the polyester film can be obtained by subjecting the aforementioned dicarboxylic acid component or its ester-forming derivative to a transesterification reaction or esterification reaction with the aforementioned diol component or its ester-forming derivative by a known method, followed by melt polymerization. Alternatively, the polyester obtained by melt polymerization can be subjected to solid-phase polymerization at a temperature below the melting point of the polyester, as desired.

[0240] The polyester film of the present invention can be obtained by conventionally known production methods. Specifically, the polyester film of the present invention can be produced by a method (melt casting method) in which dried raw materials are heated and melted in an extruder as needed, extruded from a die onto a cooled casting roll, and processed into a sheet. Alternatively, a method (solution casting method) can be used in which the raw materials are dissolved in a solvent, the solution is extruded from a die onto a support such as a casting roll or endless belt to form a film, and the film is dried to remove the solvent and processed into a sheet.

[0241] When producing a polyester film of two or more layers by melt casting, it is preferable to use a method (coextrusion) in which the raw materials for each layer constituting the biaxially oriented polyester film are melted using an extruder. These raw materials are then laminated in a molten state using a merging device provided between the extruder and the die, introduced into the die, and extruded from the die onto a casting roll whose surface temperature has been cooled to a temperature of 20°C to 60°C, where they are bonded to the roll and processed into a sheet to form an unstretched film. In particular, setting the casting roll temperature to 40°C or higher delays the cooling of the resin, facilitating temporary adhesion to the casting roll. This can sometimes further improve the adhesion of the unstretched film obtained by the electrostatic application method described below to the casting roll.

[0242] As a method for dispersing the carbon material contained in the polyester film of the present invention, when preparing a masterbatch containing the carbon material, it is preferred to use a polyester resin having a high affinity with the carbon material, an ether compound on the main chain, and a diol component composed of an aliphatic group having 3 or more carbon atoms.

[0243] Furthermore, when two or more carbon materials with different aspect ratios are present, it is preferable to prepare masterbatches containing each carbon material separately and then mix them together during polyester film formation. This is because when the carbon material and polyester resin are kneaded to form masterbatches, the kneading temperature required to disperse the carbon material and the shear stress during kneading differ. When multiple materials are kneaded simultaneously to form masterbatches, at least one of the carbon materials may agglomerate during kneading.

[0244] As a method for producing master particles for dispersing the carbon material, kneading using a twin-screw kneader is preferred.

[0245] As a method for bringing the unstretched film into close contact with the casting drum, the following methods can be appropriately selected and used: an electrostatic application method in which the extruded polyester resin is charged using a charging treatment device accompanied by high voltage application to bring it into close contact with the casting drum, a method in which the polyester resin is clamped between the casting drum and a nip roller to bring it into close contact, a method in which wind pressure is applied to press the resin to bring it into close contact with the casting drum, etc. From the viewpoint of achieving uniform close contact in the width direction, the electrostatic application method is preferably used.

[0246] (Sequential biaxial stretching)

[0247] Regarding the stretching conditions when biaxially stretching an unstretched film, when the polyester film of the present invention is primarily composed of a polyester resin, the unstretched film is preferably stretched in the longitudinal direction by a set of rolls heated to 70°C or higher, and then cooled by a set of rolls set to a temperature of 20°C to 50°C. The lower limit of the heated roll temperature during longitudinal stretching is not particularly limited as long as it does not impair the stretchability of the sheet, but it is preferably higher than the glass transition temperature of the polyester resin used. The longitudinal stretch ratio is preferably in the range of 1.4x to 5x, with a more preferred range of 2x to 4x. A longitudinal stretch ratio of 1.4x or higher promotes orientational crystallization, thereby improving film strength. On the other hand, a stretch ratio of 5x or lower can prevent excessive orientational crystallization of the polyester resin associated with stretching, resulting in brittleness and cracking during film formation.

[0248] Next, the process film (uniaxially stretched film) stretched in the longitudinal direction is stretched in a direction perpendicular to the longitudinal direction (the width direction). Preferably, while clamping both ends of the uniaxially stretched film with clips, it is introduced into a tenter and stretched in a direction perpendicular to the longitudinal direction (the width direction) by 1.4 to 5 times in an atmosphere heated to a temperature of 70°C to 160°C.

[0249] The stretched film is then preferably heat-treated to stabilize its internal orientation structure. The thermal history of the film during heat treatment can be confirmed by a small endothermic peak (sometimes referred to as Tmeta) that appears just below the melting point as measured by differential scanning calorimetry (DSC), as described later. As for the tenter setting temperature, when polyester (melting point 255°C) is the main component, the maximum temperature within the tenter is preferably set to 210°C or higher and 245°C or lower. When another thermoplastic resin is the main component, the maximum temperature is preferably set to 45°C or higher and 10°C or lower than the melting point (°C) of the main component resin. A heat treatment temperature of 210°C or higher can improve the dimensional stability of the biaxially oriented polyester film. Furthermore, a heat treatment temperature of 245°C or lower can suppress film breakage associated with melting of the polyester film, thereby achieving high productivity. The more preferable range of the heat treatment temperature is more preferably 220° C. or higher and more preferably 235° C. or lower.

[0250] The temperature range of Tmeta, which represents the thermal history temperature to which the polyester film is subjected during heat treatment, is preferably 200°C to 235°C when the polyester resin is the main component for the reasons described above. A more preferred temperature range of Tmeta is 210°C to 225°C.

[0251] Furthermore, to impart dimensional stability after heat treatment, a relaxation treatment (Relax treatment) may be performed within a range of 1% to 6%. A relaxation treatment of 1% or more can improve the dimensional stability of the biaxially oriented polyester film when used in a high-temperature environment, while a relaxation treatment of 6% or less can continuously apply appropriate tension to the biaxially oriented polyester film, thereby preventing the deterioration of thickness unevenness.

[0252] The stretching ratio is preferably 1.4 times or more and 5 times or less in the longitudinal direction and the width direction, respectively, and the area ratio (stretching ratio in the longitudinal direction × stretching ratio in the width direction) is preferably 2 times or more and 25 times or less, more preferably 9 times or more and 20 times or less. By making the area ratio 2 times or more, the molecular orientation of the obtained biaxially oriented polyester film can be promoted, the durability can be improved, and the deviation of the volume resistivity can be reduced by uniformly dispersing the contained carbon in the in-plane direction. Thus, the deviation of the battery characteristics can be reduced. In addition, by making the area ratio 25 times or less, the occurrence of rupture during stretching can be suppressed. As the lower limit of the area ratio, it is more preferably 4 times or more, and further preferably 5 times or more.

[0253] (M layer: a layer composed of metal and / or metal-based compound)

[0254] The laminated polyester film of the present invention preferably comprises at least a layer composed of a metal and / or a metal-based compound, the polyester film, and a layer composed of a metal and / or a metal-based compound in this order. It is more preferred that layers composed of a metal and / or a metal-based compound (M layer) be provided on both surfaces of the polyester film.

[0255] The method for forming the M layer in the present invention is not particularly limited, and the following methods can be used: methods of forming the M layer by vapor deposition, sputtering, or electroplating under vacuum conditions or reduced pressure conditions with an inert gas such as argon (hereinafter sometimes collectively referred to as vapor deposition methods); methods of laminating a metal foil or a metal compound foil to a polyester film directly or via an adhesive layer; and methods of forming a metal layer by electrochemical reaction using a solution containing a metal salt (electrolytic plating methods, electroless plating methods). Of these, vapor deposition methods are preferred from the perspective of continuously forming the M layer on a film using a polyester film roll.

[0256] The preferred method when using the vacuum evaporation method is: pre-set a polyester roll in the vacuum chamber, make the unrolled film close to the cooling roller, and solidify the heated and vaporized metal and / or metal compound and adhere it to the surface of the polyester film. After setting the M layer, roll it into a film roll again.

[0257] Here, a 9.0×10 -3 Pa or less, or fill with inert gas such as argon and reduce the pressure to 9.0×10 -3 Pa or more and 1×10 -1 The M layer may be formed by continuously performing two or more deposition steps, such as forming a first M layer by sputtering and then forming a second M layer by vacuum deposition.

[0258] Vacuum evaporation methods include induction heating evaporation, resistance heating evaporation, laser beam evaporation, and electron beam evaporation. Among these, electron beam evaporation, laser beam evaporation, and induction heating evaporation are preferred, as they generate a high calorific value from the evaporation source. The calorific value of the evaporation source must be increased to form the desired thickness of the M layer. This requires a sufficiently high substrate surface temperature, but actual measurement is difficult. Therefore, sufficient heat generation can be determined by confirming that the M layer after evaporation has reached the desired thickness.

[0259] However, if the calorific value of the evaporation source is increased to the necessary amount of heat, the temperature of the resin film will rise in the management of the cooling function of the usual vacuum evaporation method. Since thermal damage reduces the mechanical properties of the resin film, the resin film may dissolve. Therefore, in order not to excessively increase the temperature during the evaporation process, it is preferred to perform evaporation while managing the cooling function so that the film can be evenly cooled. Specifically, it is preferred to utilize a cooling mechanism consisting of a metal plate or a metal roller that is fully cooled by a refrigerant to evenly cool the film from the back of the evaporation surface. In order to cool evenly, the resin film must be in close contact with the cooling mechanism without generating a gap. By improving the adhesion, the thermal damage to the surface of the resin film can be reduced, and the mechanical properties of the resin film can be suppressed from being reduced.

[0260] For example, if the metal roller of the cooling mechanism is scratched, the scratched area creates a gap, preventing the resin film from being cooled at the scratched area, and increasing thermal damage to the resin film. Furthermore, if foreign matter enters between the resin film and the metal roller of the cooling mechanism, the foreign matter prevents the resin film from being cooled, further increasing thermal damage. If the heating value of the deposition source is increased to the required level, damage to the metal roller or the intrusion of foreign matter, which is permitted in conventional vacuum deposition methods, becomes a problem, necessitating stricter control of damage to the metal roller and the intrusion of foreign matter.

[0261] When the M layer in the present invention is formed to a desired metal layer thickness, from the viewpoint of productivity, resistance characteristics, grade and quality, it is preferred to form it by one vapor deposition (a set of winding out, vapor deposition and winding is defined as one vapor deposition). For example, thin film vapor deposition can be repeated 20 times to form a 50nm thick aluminum vapor deposition layer by one vapor deposition (the above set is repeated 20 times) to form an aluminum metal layer with a total thickness of 1μm.

[0262] Examples of metal elements constituting the M layer include gold, silver, copper, zinc, lead, nickel, iron, aluminum, titanium, cobalt, manganese, cadmium, and palladium. The M layer may be composed of a single substance of one of the above metal elements, or a layer composed of a metal compound in which the above metal elements are mixed with oxygen, nitrogen, fluorine, carbon, boron, chlorine, sulfur, or phosphorus. The metal element of the M layer provided on the polyester film may be the same or different on both sides.

[0263] When used as a resin current collector for a bipolar battery, the M layers present on both sides of the laminated film preferably have one side containing copper and the other side containing aluminum.

[0264] In the laminated polyester film of the present invention, the laminated structure of the polyester film (P1 layer, P2 layer) and a layer composed of a metal and / or a metal-based compound preferably comprises at least, in this order, a layer composed of a metal and / or a metal-based compound, the polyester film, and a layer composed of a metal and / or a metal-based compound. Specifically, the following structures are exemplified. When the polyester film is a single layer, a structure of M layer / P1 layer / M layer is preferred, or a structure of M layer / P1 layer / M' layer is preferred, with a layer (M' layer) composed of a metal and / or a metal-based compound composed of a different metal element from the M layer.

[0265] When the polyester film has two or more layers, the preferred configuration is M layer / P1 layer / P2 layer / M layer, M layer / P1 layer / P2 layer / M' layer, or M layer / P2 layer / P1 layer / P2 layer / M layer, or M layer / P2 layer / P1 layer / P2 layer / M layer, or M layer / P2 layer / P1 layer / P2 layer / M' layer. Furthermore, when used as a resin current collector for a bipolar battery, the laminated polyester film of the present invention is preferably configured such that the outermost layers on both sides of the polyester film are the P1 layer, and layers composed of a metal and / or a metal-based compound are provided on both sides of the P1 layer, from the perspective of reducing the contact resistance at the interface between the active material layer and the resin current collector and suppressing degradation of battery characteristics.

[0266] Furthermore, to improve adhesion with the M layer, the polyester film (P1 layer or P2 layer) of the present invention may be provided with an anchor layer or primer layer not primarily composed of a polyester resin, within a range that does not compromise the effects of the present invention. The thickness of the anchor layer or primer layer (U layer) not primarily composed of a polyester resin is preferably 0.01 μm to 1.0 μm. By setting the U layer thickness to 0.01 μm or greater, adhesion between the polyester film and the M layer can be further enhanced. Furthermore, by setting the U layer thickness to 1.0 μm or less, when the laminated polyester film of the present invention is used as a resin current collector for a bipolar battery, the size of the assembled bipolar battery can be suppressed.

[0267] The thickness of the M layer of the laminated polyester film of the present invention is not particularly limited, but is preferably 0.1 μm or greater. This is because, when used as a resin current collector, this minimizes degradation of electrical properties due to uneven thickness of the metal layer. The thickness of the M layer is more preferably 0.2 μm or greater, and even more preferably 0.5 μm or greater. Furthermore, a thickness of 5 μm or less is preferred because it can minimize increases in battery weight when used as a resin current collector for batteries. A thickness of 3 μm or less is more preferred.

[0268] The adhesion between the outermost layer of the polyester film and the M layer in the laminated polyester film of the present invention is preferably 2N / 15mm or more on both sides. By making the adhesion between the outermost layer of the polyester film and the M layer in the laminated polyester film be 2N / 15mm or more on both sides, when the laminated polyester film with the M layer is assembled in a storage element as a collector, when the collector is deformed by stress such as impact or heat, it is possible to suppress the interface peeling between the polyester at the end and the M layer, and other battery components invading the interface, thereby reducing the efficiency of the charge and discharge reaction of the storage element and reducing the battery characteristics. More preferably, the adhesion is 2.5N / 15mm or more on both sides, and further preferably 3.5N / 15mm or more.

[0269] The laminated polyester film of the present invention preferably has an M layer on both sides of the polyester film, and the through-direction volume resistivity of the laminated polyester film having the M layer measured by the method described below (hereinafter sometimes referred to as through-direction resistivity) is 1.0×10 0 Ωcm or more and 1.0×10 7 Ωcm or less. By making the through-hole resistivity 1.0×10 0 Ωcm or more, when the laminated polyester film of the present invention is assembled into a storage element as a resin current collector for a bipolar battery, the polyester film can act as a resistor, thereby suppressing thermal runaway and fire from the storage element caused by a short circuit when the storage element is damaged. In addition, by setting the through-hole resistivity to 1.0×10 7 Ωcm or less. When the laminated polyester film of the present invention is incorporated into a bipolar battery resin collector in a bipolar storage device, an increase in the internal resistance of the bipolar storage device and a decrease in battery output can be suppressed. The through-hole resistivity is more preferably in the range of 1.0×10 4 Ωcm or less.

[0270] [Resin current collector]

[0271] The resin current collector of the present invention preferably comprises the aforementioned polyester film and an M layer on both surfaces of the polyester film. By using the aforementioned polyester film having excellent volume resistivity, the resin current collector of the present invention exhibits excellent conductivity in the thickness direction, as measured by through-hole resistivity. Furthermore, the M layer exhibits excellent adhesion to the polyester film. Consequently, the resin current collector is suitable for use as a current collector for bipolar batteries, as described below.

[0272] [Current Collector for Bipolar Batteries]

[0273] The current collector for a bipolar battery of the present invention preferably has a structure in which different M layers are provided on both sides of the polyester film in the above-mentioned current collector structure.

[0274] By using this current collector, which exhibits excellent conductivity in the thickness direction, when incorporated into a bipolar battery, the current value stability, described later, is excellent, and variations in battery characteristics can be suppressed. Furthermore, due to its excellent mechanical properties, a bipolar battery incorporating this current collector exhibits excellent durability against external stresses such as deformation and impact. Furthermore, by controlling the shape of the carbon material contained in the polyester film, stable battery operation can be achieved even in high-temperature environments.

[0275] As the metal element constituting the M layer of the current collector for a bipolar battery of the present invention, when used in a lithium ion battery, it is more preferable that one side is aluminum and the other side is copper.

[0276] The current collector for a bipolar battery of the present invention preferably has a surface layer containing resin α or resin β as a main component as at least one surface layer of the polyester film.

[0277] The surface layer primarily composed of resin α or resin β is effective in suppressing decomposition of the polyester resin due to electrochemical reactions on the negative electrode side of the battery, and is therefore preferably positioned on the negative electrode side. A structure in which the copper-containing M layer is in contact with the layer primarily composed of resin α or resin β is more preferred.

[0278] The bipolar battery current collector of the present invention preferably comprises a surface layer primarily composed of Resin α or Resin β on at least one surface of a polyester film, with the goal of suppressing decomposition of the polyester resin due to electrochemical reactions on the negative electrode side of the battery. Furthermore, a negative electrode active material layer is provided on this surface layer, and a positive electrode active material layer is provided on the side opposite the surface layer comprising the negative electrode active material layer. A more preferred structure comprises, in this order, the negative electrode active material layer, a metal layer primarily composed of copper, and a layer primarily composed of Resin α or Resin β. This structure enables the effects of the bipolar battery current collector of the present invention to be exhibited for a long period of time.

[0279] [Electrical storage element]

[0280] The energy storage element of the present invention is composed of an electrode assembly comprising a positive electrode and a negative electrode. It may also contain an electrolyte, in which case a separator is preferably interposed between the positive and negative electrodes. A preferred example of an energy storage element is one composed of a solid electrolyte that does not contain an electrolyte. Furthermore, a battery case may be provided to house the electrode assembly.

[0281] Examples of such power storage devices include primary batteries, secondary batteries, electric double layer capacitors, and aluminum electrolytic capacitors. In the present invention, these power storage devices refer to secondary batteries.

[0282] Examples of secondary batteries include lithium secondary batteries, lead storage batteries, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-iron storage batteries, silver oxide-zinc storage batteries, manganese dioxide-lithium secondary batteries, lithium cobaltate-carbonate secondary batteries, and vanadium-lithium secondary batteries.

[0283] Among them, secondary batteries are preferred from the viewpoint of long-term use, and lithium secondary batteries that achieve high energy density by using an organic solvent are more preferred.

[0284] As the battery case, for example, an aluminum case, an iron case with nickel plating on the inner surface, a case made of an aluminum laminate film, or the like can be used.

[0285] The shape of the battery case includes a pouch shape, a cylindrical shape, a square shape, a coin shape, etc. Among them, the pouch shape is preferred because it can achieve high energy density and can be freely designed at low cost.

[0286] The positive electrode is formed by laminating a positive electrode material consisting of an active material, a binder resin and a conductive additive on a current collector. As the active material, there can be mentioned layered lithium-containing transition metal oxides such as LiCoO2, LiNiO2, Li(NiCoMn)O2, spinel manganese oxides such as LiMn2O4, and iron compounds such as LiFePO4. As the binder resin, a resin with high oxidation resistance can be used. Specifically, fluorine-containing resins, acrylic resins, styrene-butadiene resins, etc. can be mentioned. As the conductive additive, carbon materials such as carbon black and graphite can be mentioned. As the current collector, metal foil is preferred, and aluminum foil is particularly used.

[0287] The negative electrode is made by laminating a negative electrode material composed of an active material and a binder resin on a current collector. Examples of active materials include carbon materials such as artificial graphite, natural graphite, hard carbon, and soft carbon, lithium alloy materials such as tin and silicon, metal materials such as lithium, and lithium titanate (Li4Ti5O 12 ) etc. As binder resin, fluorine-containing resin, acrylic resin, styrene-butadiene resin etc. can be mentioned. As collector, metal foil is preferred, and copper foil is used more particularly.

[0288] The electric storage element of the present invention preferably uses a resin current collector for a bipolar battery composed of a film having a copper layer provided on one surface and an aluminum layer provided on the opposite surface thereof by vacuum deposition on both surfaces of a polyester film.

[0289] When the energy storage device of the present invention contains an electrolyte, the electrolyte serves as a site for ions to move between the positive electrode and the negative electrode in an electrochemical device such as a secondary battery, and has a structure in which the electrolyte is dissolved in an organic solvent.

[0290] Examples of the electrolyte include LiPF6, LiBF4, and LiClO4. However, from the viewpoint of solubility in organic solvents and ion conductivity, LiPF6 is preferably used.

[0291] Examples of the organic solvent include ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Two or more of these organic solvents may be used in combination.

[0292] Hereinafter, a method for producing a lithium secondary battery preferably used as an electricity storage element will be described.

[0293] As a method for producing a lithium secondary battery, the active material and the conductive auxiliary agent are first dispersed in a binder resin solution, an electrode coating liquid is prepared, the coating liquid is applied to the current collector, and the solvent is dried to obtain a positive electrode and a negative electrode, respectively. The film thickness of the dried coating film is preferably not less than 50 μm and not more than 500 μm. Furthermore, it is preferred to apply pressure to the active material layer formed on the current collector by a method such as roller pressing to densify it and make the current collector thinner.

[0294] A lithium secondary battery separator is placed between the obtained positive and negative electrodes so as to contact the active material layers of each electrode, and then sealed in an outer packaging material such as an aluminum laminate film. After injecting the electrolyte, a negative electrode lead and a safety valve are installed, and the outer packaging material is sealed.

[0295] The lithium secondary battery obtained in this manner has high adhesion to the electrode and excellent battery characteristics, and can be manufactured at low cost.

[0296] [Secondary battery]

[0297] In some cases, multiple storage elements produced using the above-described methods are connected in series to suit the application or required battery capacity of the storage element and used as a secondary battery. In such cases, a secondary battery comprising multiple storage elements connected in series and equipped with voltage management, temperature management, and safety devices is preferred, or a secondary battery comprising multiple storage elements connected in series and multiple modular units housed in a housing connected in series or in parallel, also equipped with voltage management, temperature management, and safety devices, is preferred. A preferred example of a secondary battery is one in which the storage elements are connected with tab leads (current extraction wires) and housed in a resin or metal modular housing.

[0298] Electric vehicles

[0299] Secondary batteries produced by the above-mentioned methods, etc., are preferably used in electric vehicles due to their excellent battery properties and durability. An electric vehicle is a vehicle in which part or all of the driving energy required for driving is supplied by a secondary battery. Examples of electric vehicles include BEVs (Battery Electric Vehicles) equipped only with secondary batteries, HEVs (Hybrid Electric Vehicles) equipped with both fossil fuels such as gasoline and secondary batteries, and PHEVs (Plug-in Hybrid Electric Vehicles). The secondary battery of the present invention can be applied to any application.

[0300] [Electric Flying Vehicle]

[0301] Due to their excellent battery properties and durability, secondary batteries produced using the above methods are preferably used in electric aircraft. Electric aircraft are those whose flight energy is partially or entirely supplied by secondary batteries. Specifically, examples include electric aircraft such as drones, stratospheric communication platforms (HAPS), sky subways, and air taxis. The secondary batteries of the present invention are suitable for any application.

[0302] [Evaluation method of characteristics]

[0303] A. Polymer Properties

[0304] (i) Intrinsic viscosity (IV)

[0305] A sample (polyester resin (raw material) or the polyester film of the present invention) was dissolved in 100 ml of o-chlorophenol (solution concentration C (sample weight / solution volume) = 1.2 g / 100 ml). The viscosity of the solution at 25°C was measured using an Ostwald viscometer. The viscosity of the solvent was also measured in the same manner. Using the obtained solution viscosity and solvent viscosity, [η] was calculated using the following formula (1). The resulting value was used as the intrinsic viscosity (IV) of the entire polyester film.

[0306] ηsp / C=[η]+K[η] 2 ・C ・・・(1)

[0307] (Here, ηsp = (solution viscosity / solvent viscosity) - 1, and K is the Huggins constant (0.343).)

[0308] When insoluble matter such as inorganic particles exists in the solution in which the measurement sample is dissolved, measurement is performed using the following method.

[0309] (1-1) The measurement sample is dissolved in 100 mL of o-chlorophenol to prepare a solution having a concentration higher than 1.2 g / 100 mL. Here, the weight of the measurement sample provided to o-chlorophenol is referred to as the measurement sample weight.

[0310] (1-2) Next, the solution containing the insoluble matter is filtered, and the weight of the insoluble matter and the volume of the filtrate after filtration are measured.

[0311] (1-3) Add o-chlorophenol to the filtrate after filtration to adjust (measurement sample weight (g) - weight of insoluble matter (g)) / (volume of filtrate after filtration (mL) + volume of o-chlorophenol added (mL)) to 1.2 g / 100 mL.

[0312] (For example, when a concentrated solution is prepared with a sample weight of 2.0 g / solution volume of 100 mL, the weight of the insoluble matter when filtering the solution is 0.2 g, and the volume of the filtrate after filtration is 99 mL, an additional 51 mL of o-chlorophenol is added to adjust the solution. ((2.0 g - 0.2 g) / (99 mL + 51 mL) = 1.2 g / 100 mL))

[0313] (1-4) Using the solution obtained in (1-3), the viscosity at 25°C was measured using an Ostwald viscometer. The obtained solution viscosity and solvent viscosity were used to calculate [η] according to the above formula (1), and the obtained value was defined as the intrinsic viscosity (IV). The intrinsic viscosity of the polyester film of the present invention obtained according to the above (1-1) to (1-4) is defined as IV. F (dl / g).

[0314] B. Film thickness

[0315] (i) Polyester film thickness T

[0316] The total thickness of the polyester film was measured at five random locations using a micrometer according to JIS K7130 (1992) A-2 method on ten sheets of film stacked together. The average value was divided by 10 to obtain the polyester film thickness T (μm).

[0317] (ii) Stack thickness (T P1 、T P2 、T M )

[0318] The polyester film of the present invention is cut into a cross section parallel to the width direction of the film using a microtome. After the cross section is subjected to a sputtering treatment using platinum palladium, it is observed using a scanning electron microscope (JSM-6700 manufactured by JEOL Ltd.) at an accelerating voltage of 3 kV and a magnification of 5,000 to 20,000 times to confirm the thickness ratio of the layers (P1 layer, P2 layer) and the metal and / or metal compound layer (M layer) constituting the laminated polyester film. The thickness of each layer (T) is calculated from the obtained lamination ratio and the thickness of all the layers obtained in item (i) above. P1 、T P2 、T M ).

[0319] C. Constituent elements of the M layer

[0320] After the surface of the laminated polyester film of the present invention was subjected to a sputtering treatment using platinum and palladium, identification of metal elements was performed using a scanning electron microscope (JSM-6700, manufactured by JEOL Ltd.) and an energy dispersive X-ray spectrometry (EDX) detector (AZtecLiv Standard UltimMax65, manufactured by Oxford Corporation).

[0321] Measurements were performed at varying acceleration voltages from 0.5 kV to 30 kV, and the detected elements were defined as elements constituting the metal and / or metal compound layer (M layer). Platinum and palladium were excluded, and if only platinum or palladium was detected in measurements at all acceleration voltages, these were defined as elements constituting the metal and / or metal compound layer (M layer).

[0322] D. Carbon Material Dispersion Evaluation

[0323] In the same manner as in item B above, image analysis software (Image-Pro Plus Version 4.0 for "Windows" (registered trademark) manufactured by Planetron Co., Ltd.) was used to perform the following analysis on a cross-sectional image (image internal dimensions: 18.5 μm in the vertical direction × 25 μm in the horizontal direction) obtained using a scanning electron microscope (JEOL Ltd., JSM-6700) at a magnification of 5000 times to determine the volume-based average dispersion diameter and the number of dispersed carbon materials.

[0324] (i) Image analysis conditions

[0325] After reading the cross-sectional image using the software, perform 8-bit grayscale processing by executing the "Grayscale 8" command under the "Convert" menu. Next, set the horizontal width of the read image to 25 μm using the "Spatial Correction" command under the "Correction" menu. Then, perform binarization using the "Binarization" command under the "Process" menu.

[0326] (Binarization conditions)

[0327] ・Select "3×3"

[0328] ・Threshold setting: Use the value obtained by clicking the auto-detect button located on the right side of the numeric input field once.

[0329] ・Preview conditions: The base part is shown in white and the detection particles are shown in black

[0330] After binarization, open the "Count / Size" command screen under the "Measurement" menu, set the following particle detection and analysis conditions, and execute "Count" to analyze the detected particles.

[0331] (Particle detection conditions)

[0332] ・Brightness range selection: Select "Automatically extract dark objects"

[0333] ・Select "Measurement object"

[0334] (Object extraction option conditions)

[0335] ・4 links / 8 links: Select 4 links

[0336] ・Only "Preselection" and "Hole Filling" are selected

[0337] ・Smoothing: 0

[0338] ・Exclude on boundaries: Select "All boundaries".

[0339] (Particle analysis conditions)

[0340] Select the following from the "Measurement" tab in the "Count / Size" command screen.

[0341] ・Count (calibrated)

[0342] ・Diameter (average)

[0343] Here, the term "diameter (average)" refers to an average diameter, which is a value obtained by measuring the diameters passing through the center of gravity of the object to be tested at 2° intervals and averaging the measured diameters.

[0344] (ii) Number of dispersed carbon materials

[0345] The value of "count (corrected)" obtained in the above item (i) is used as the number of carbon materials in the image, and the average value of the value of "count (corrected)" in 5 different fields of view is divided by the measurement field area (18.5 μm in length × 25 μm in width = 462.5 μm). 2 ) is defined as the number of dispersed carbon materials in the sample (number / μm2 ).

[0346] (iii) Volume-based average dispersion diameter of carbon materials

[0347] Using the "diameter (average)" of each particle detected in item (i) above, the volume-based average dispersion diameter is calculated according to the following formula (2). The volume-based average dispersion diameters are calculated for five different fields of view, and the average of these values ​​is used as the volume-based average dispersion diameter R (μm) of the carbon material in the sample.

[0348] R (μm) = (Σ (diameter (average)) 2 × number) / (Σ(diameter (average)) × number)…Formula (2).

[0349] (iv) Aspect ratio of carbon materials

[0350] As in the above item (i), the aspect ratio and area of ​​the carbon material in the obtained image are calculated using the "Count / Size" command on the screen.

[0351] For five different fields of view, a count histogram was created, with the obtained aspect ratio as the horizontal axis, with bins set every 0.5 in the range of 1 to 10, and every 10 in the range of 10 to 10. In the count histogram, if a local maximum value existed in the region with an aspect ratio of 1 to 5, the minimum value of the bin showing that local maximum value (for example, if a local maximum value existed in the range of 2 to 2.5, 2 was used as the local maximum value) was used as the aspect ratio of the carbon material (carbon material C1) present in the region with an aspect ratio of 1 to 5. If multiple local maximum peaks existed in the region with an aspect ratio of 1 to 5, the weighted average value obtained using their vertical axis values ​​was used as the aspect ratio of the carbon material (carbon material C1) present in the region with an aspect ratio of 1 to 5.

[0352] Similarly, when there is a maximum value in a region with an aspect ratio of 5 or more, the maximum value is used as the aspect ratio of the carbon material (carbon material C2) present in the region with an aspect ratio of 5 or more. When there are multiple maximum peaks in a region with an aspect ratio of 5 or more, the weighted average value obtained using their vertical axis values ​​is used as the aspect ratio of the carbon material (carbon material C2) present in the region with an aspect ratio of 5 or more.

[0353] For each of the five different fields of view, the aspect ratios of the carbon material (carbon material C1) present in the region with an aspect ratio greater than 1 and less than 5 and the carbon material (carbon material C2) present in the region with an aspect ratio greater than 5 were calculated, and the average value of the five fields of view in each region was taken as the aspect ratio of the carbon material C1 and the carbon material C2 in the polyester film.

[0354] (v) Ratio of the area occupied by the carbon material C1 (SC1) to the area occupied by the carbon material C2 (SC2)

[0355] The total area (SC1) of the carbon material (carbon material C1) present in regions with an aspect ratio of 1 or greater and less than 5, as confirmed by the number histogram in item (iv) above, is calculated. Next, the total area (SC2) of the carbon material (carbon material C2) present in regions with an aspect ratio of 5 or greater is calculated, and the value obtained by dividing SC1 by SC2 is regarded as the ratio of the area (SC1) occupied by the carbon material C1 to the area (SC2) occupied by the carbon material C2 in the P1 layer of the sample.

[0356] E. Volume Resistivity Measurement

[0357] Ten samples of 10 cm x 10 cm were taken from different locations of the polyester film of the present invention and conditioned for one day at 23° C. and 65% humidity. The volume resistivity was then measured by the following method.

[0358] (i) Resistivity meter measurement

[0359] Measurements were performed using a low resistivity meter (Mitsubishi Chemical, Lorester-GP Series MCP-T360) in volume resistivity mode (unit: Ωcm). The sample film thickness was input into the meter for measurement. All ten samples were measured, and the average value was used as the sample's volume resistivity.

[0360] If the volume resistivity measured using the aforementioned low-resistivity meter exceeds the upper limit, perform manual measurement using a high-resistivity meter (Hirester-UP Series MCP-HT450) according to the following procedure. Place the sample on the included resistance meter and press the included URS probe at 10V for 1 minute. Measure all 10 samples, and the average value is the sample's volume resistivity.

[0361] If the volume resistivity is still outside the upper limit of measurement, change the voltage setting to 500V and 1000V, and use the value obtained under the lowest voltage as the volume resistivity of the sample. Measurements are performed in an environment of 23°C and 65% RH.

[0362] (ii) Evaluation of in-plane deviation of volume resistivity

[0363] The maximum value, minimum value, and average value of the 10 measured values ​​obtained for the 10 samples measured in the above item (i) are used to obtain a value obtained by the following formula (3) as the in-plane variation value of the volume resistivity of the sample.

[0364] (In-plane deviation) = 100 × (maximum value - minimum value) / (average value) ... Formula (3)

[0365] F. DSC measurement

[0366] The polyester film of the present invention or its raw material was measured using a Thermo Plus Evo2 series DSC Vesta manufactured by Rigaku Corporation as a differential scanning calorimeter (DSC). Approximately 5 mg of the sample was placed on an aluminum tray and heated from room temperature to 300°C at a rate of 20°C / minute, where the temperature was maintained for 5 minutes (first run measurement). The temperature of the exothermic peak due to glass transition observed during this time was designated as the glass transition temperature (Tg), and the peak temperature of the endothermic peak due to melting was designated as the melting point (Tm). The average of three measurements was used as the glass transition temperature (Tg) and melting point (Tm) of the sample.

[0367] If the DSC curve of the polyester film of the present invention is difficult to distinguish from the minor endothermic peak Tmeta appearing before the melting point, the following measurement can be performed in addition to the above-mentioned first-run measurement. The temperature is raised to 300°C at a rate of 20°C / minute, held for 5 minutes, then rapidly cooled with liquid nitrogen and again raised to 300°C at a rate of 20°C / minute (second-run measurement). The number and temperature of the melting point peaks are confirmed, and any peaks that disappear from the first-run measurement are considered minor endothermic peaks Tmeta appearing before the melting point and are excluded from the first-run measurement data.

[0368] G. Carbon material content and identification of carbon types

[0369] (i) Addition amount of carbon material

[0370] The P1 or P2 layer of the polyester film of the present invention was placed in 200 ml of hexafluoroisopropanol (HFIP) to dissolve the polyester resin. 200 ml of water was added to the dissolved solution, which was then placed in a centrifuge to allow the particles to settle, and the supernatant was removed. Water was then added to the particles, and washing and centrifugation were repeated twice. The resulting particles were dried and weighed to calculate the particle content (mass %) in each layer. This procedure was repeated for three different locations on the polyester film of the present invention, and the resulting particle content was used as the carbon material content of the sample.

[0371] When the identification analysis in the next item (ii) confirms that there are multiple types of carbon materials, the content concentration of each carbon material is determined using the abundance ratio of the carbon materials observed in the next item (ii).

[0372] (ii) Identification of carbon species

[0373] The carbon material particles obtained in the above 1 were subjected to Raman spectroscopy to observe the graphite structure (sp) generally known as the G band. 2 Key) 1580cm -1 near and from the diamond structure commonly known as the D band (sp 3 Key) 1350cm -1 The carbon material present in the sample is identified based on the peak intensity ratio of the peaks near the sample. This identification is performed by comparing peak intensity data obtained from known Raman spectroscopy databases and commercially available carbon materials. Furthermore, the carbon material obtained in item (i) above is observed using a transmission electron microscope (TEM) at magnifications of 50,000 to 500,000. The observed shape is then combined with the Raman spectroscopy results from the previous item to identify the type of carbon material present in the sample. If multiple carbon materials are observed, the number of each carbon material observed using the TEM is converted into a volume ratio, which is used as the abundance ratio of each carbon material.

[0374] H. Quantitative evaluation of resins and compounds constituting polyester films

[0375] (i) Identification of compounds with ether bonds in the main chain

[0376] The entire polyester film, the P1 layer, and the P2 layer of the present invention were immersed in methanol, the soluble portion was separated by centrifugation, and the supernatant was collected to extract the compounds having ether bonds in the main chain contained in the polyester film. The extract was analyzed by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). The obtained mass spectrum and the nuclear magnetic resonance method ( 1 H-NMR) spectroscopy to identify the structure of the compound.

[0377] Similarly, 50 mg of all layers, P1 layer, or P2 layer of the polyester film of the present invention were weighed, and the compounds having ether bonds in the main chain were extracted with deuterated methanol (Methanol-d4). 0.7 ml of deuterated methanol (Methanol-d4) to which 2.63 mg of octamethylcyclotetrasiloxane (OMTS) was added as an internal standard was added to dissolve the soluble portion, and then centrifuged. The supernatant of the centrifugation was collected and analyzed by nuclear magnetic resonance (NMR). 1The compounds contained in the sample are quantified based on the ratio of the NMR spectrum area of ​​the added internal standard substance to the spectrum area of ​​the extract.

[0378] ( 1 H-NMR measurement conditions)

[0379] Device used: ECA-400 (manufactured by JEOL RESONANCE)

[0380] Measurement method: Single pulse

[0381] Observation frequency: 399.8MHz

[0382] Pulse width: 6.45s (45 pulses)

[0383] Lock solvent: deuterated methanol (Methanol-d4)

[0384] Chemical shift standard: heavy solvent residual protons (3.35 ppm)

[0385] Observation width: about 8000Hz (about -2ppm~18ppm)

[0386] Number of data points: 32768

[0387] Waiting time: 30 seconds

[0388] Cumulative number of times: 128 times

[0389] Measurement temperature: room temperature (21°C)

[0390] Sample rotation speed: 15Hz.

[0391] (ii) Quantitative analysis of resins constituting polyester

[0392] As in (i) above, all layers, the P1 layer, and the P2 layer of the polyester film of the present invention were partially immersed in a mixed solution of equal amounts of 1,1,1,2,2,2-hexafluoro-2-isopropanol (HFIP). The soluble portion was separated by centrifugation, and the supernatant was collected to extract the resin components contained in the polyester film. The extract was analyzed by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). Based on the obtained mass spectrum and the nuclear magnetic resonance method ( 1 H-NMR) spectroscopy to identify the structure of the compound.

[0393] 50 mg of all layers, P1 layer, or P2 layer of the polyester film of the present invention were weighed, and 2.63 mg of octamethylcyclotetrasiloxane (OMTS) was added as an internal standard. 0.7 ml of heavy 1,1,1,2,2,2-hexafluoro-2-isopropanol (HFIP-d2) was added to dissolve the soluble portion, and then centrifuged. The supernatant of the centrifuged solution was collected and analyzed by nuclear magnetic resonance (NMR). 1 The compounds contained in the sample are quantified based on the ratio of the NMR spectrum area of ​​the added internal standard substance to the spectrum area of ​​the extract.

[0394] ( 1 H-NMR measurement conditions)

[0395] Device used: ECA-400 (manufactured by JEOL RESONANCE)

[0396] Measurement method: Single pulse

[0397] Observation frequency: 399.8MHz

[0398] Pulse width: 6.45s (45 pulses)

[0399] Lock solvent: HFIP-d2

[0400] Chemical shift standard: heavy solvent residual protons (4.41 ppm)

[0401] Observation width: about 8000Hz (about -2ppm~18ppm)

[0402] Number of data points: 32768

[0403] Waiting time: 30 seconds

[0404] Cumulative number of times: 128 times

[0405] Measurement temperature: room temperature (21°C)

[0406] Sample rotation speed: 15Hz.

[0407] I. Hansen Solubility Parameters

[0408] The polyester resin or compound having an ether bond in the main chain contained in the polyester film of the present invention was calculated using the attached calculation software of the Hansen Solubility Parameters in Practice (HSPiP) software. Using the Polymer mode of the software, the quaternary repeating structure of the target polymer molecular chain was input, and the calculated Hansen solubility parameters (dispersion force component (dD: MPa)1 / 2 )、Polar component(dP:MPa 1 / 2 ), hydrogen bond component (dH: MPa 1 / 2 )) is used as the value possessed by the polyester resin or the compound having an ether bond in the main chain.

[0409] The compatibility of each polyester resin or compound having an ether bond in the main chain with the carbon material was determined by measuring the dispersion force component (dD: MPa) in the Hansen solubility parameter. 1 / 2 )、Polar component(dP:MPa 1 / 2 ), hydrogen bond component (dH: MPa 1 / 2 ) Use the following formula (4) to calculate the ΔHSP value (MPa 1 / 2 ), used as polyester resin or the compatibility of compounds having ether bonds in the main chain with carbon materials.

[0410] ΔHSP (MPa 1 / 2 ) = {4・(dDc-dDp) 2 + (dPc-dPp) 2 + (dHc-dHp) 2} 1 / 2 Formula (4)

[0411] Here, dDp, dPp, and dHp are Hansen solubility parameter values ​​of polyester resins or compounds having ether bonds in the main chain, and dDc, dPc, and dHc are Hansen solubility parameter values ​​of carbon materials. The following values ​​are used when calculating the ΔHSP value.

[0412] (Hansen Solubility Parameters of Carbon Materials)

[0413] ・Dispersion force component (dD: MPa 1 / 2 ):18.8

[0414] ・Polar component (dP: MPa 1 / 2 ):4.6

[0415] ・Hydrogen bonding component (dH: MPa 1 / 2 ):4.3.

[0416] J. Evaluation of Mechanical Properties of Polyester Film

[0417] Measure the elongation at break and breaking strength of polyester film. With the unwinding direction as the longitudinal direction of the polyester film, cut a rectangular sample 150 mm long and 10 mm wide from the polyester film, with the longitudinal direction as the long side. Using an Instron tensile tester (AMF / RTA-100, manufactured by ORIENTEC) according to the following method specified in ASTM-D882, a tensile test was performed at a rate of 300 mm / min using an Instron tensile testing machine (AMF / RTA-100, manufactured by ORIENTEC). The elongation (elongation at break) and strength (strength at break) at break were measured. Five measurements were performed, and the average values ​​were used as the elongation at break and strength at break in the longitudinal direction of the polyester film.

[0418] Similar to the longitudinal direction measurement, a rectangular shape 150 mm long and 10 mm wide was cut out of the polyester film, with the width direction being the long side, and the elongation at break and breaking strength of the sample were measured. Five measurements were performed, and the average values ​​were used as the elongation at break and breaking strength of the polyester film in the width direction.

[0419] When the longitudinal and width directions of the polyester film are unknown, the elongation at break and the breaking strength are measured in four directions, namely, a specific direction and directions rotated 45°, 90°, and 135° in-plane from the specific direction. The maximum value of the elongation at break and the breaking strength obtained in the four directions is used as the elongation at break and the breaking strength of the polyester film whose longitudinal and width directions are unknown.

[0420] K. Adhesion between M layer and polyester film

[0421] A 15 cm square sample was taken from a laminated polyester film having M layers on both surfaces. The following adhesive coating was applied to the surface of the M layer to form an adhesive layer having a thickness of 2 μm.

[0422] (Adhesive coating)

[0423] ・Binder resin: "DIC Dry" (registered trademark) LX500 (manufactured by DIC Corporation), solid content concentration 60% by mass

[0424] ・Curing agent: "DIC Dry" (registered trademark) KW-75 (manufactured by DIC Corporation), solid content concentration 75% by mass

[0425] ・Solvent: Ethyl acetate

[0426] The above LX500 and KW-75 were mixed at a mass ratio of 10:1 and diluted with ethyl acetate to a solid content of 16% by mass. The mixture was then coated with a Metabar (#10) and dried in an oven heated to 85°C for 30 seconds.

[0427] The laminated polyester film of the present invention, with an adhesive layer formed thereon, was fixed to a 2 mm thick metal plate in the direction in which the adhesive layer was exposed. Next, a 38 μm thick PET film (T60, manufactured by Toray Industries, Ltd.), cut to a size of 150 mm x 300 mm, was used as a release film on the side of the adhesive layer opposite to the M layer. The film was laminated under the following conditions, with its short side overlapping one side of the sample having the adhesive layer. Any areas that developed bubbles or lamination wrinkles during lamination were not used as samples for the adhesion evaluation described below.

[0428] (Lamination conditions)

[0429] ・Laminating roller temperature: room temperature

[0430] ・Laminating roller pressure: 0.35MPa

[0431] ・Conveying speed: 0.5m / min

[0432] The laminated sample was placed in an oven heated to 40°C and aged for 48 hours. The laminated sample was then cut into 15 mm x 300 mm pieces, and the surface opposite to the peeling film was fixed to a metal plate with double-sided tape. The portion of the metal plate to which the sample was attached, where no sample was placed, was fixed to the single-sided chuck of the test device "Tensilon" (registered trademark) RTG-1210. Next, the peeling film was fixed to the other chuck of the device, and a 180° peel test was performed at a test speed of 50 mm / min. The peel test was performed using three different samples, and the average value of the stress obtained was used as the adhesion force between the M layer and the polyester film.

[0433] L. Through-hole resistivity

[0434] A 20 mm square sample of the laminated polyester film of the present invention having an M layer on both surfaces was taken as an evaluation sample. Circular copper electrodes with a diameter of 20 mm and a thickness of 10 mm, equipped with electrode tabs, were clamped from both sides, and a pressure of 0.38 MPa was applied in the thickness direction of the sample. The electrode tabs were connected to a GOM-805 milliohmmeter manufactured by TECHIO Corporation, and the resistance value was read at a DC +6.25 V. The value displayed after 1 minute was then calculated. The obtained resistance value was multiplied by the electrode area (3.14 cm 2), then divide by the sample thickness (cm) to calculate the through-hole resistivity (Ωcm). Perform the same measurement on three different samples to calculate the through-hole resistivity, and take the average value as the through-hole resistivity of the sample.

[0435] [Evaluation method for application characteristics]

[0436] M. Dispensing stability

[0437] In the production process of the polyester film of the present invention, the unstretched film is melt-extruded from a die, cooled on a casting roll using an electrostatic application method, and formed into a sheet. A 10 m unstretched film roll is taken from the obtained unstretched film.

[0438] The thickness of the resulting unstretched film roll was measured every 50 cm in the winding direction. The average of all measured values ​​was taken as the average thickness of the unstretched film, the standard deviation of all measured values ​​was taken as the standard deviation of the thickness of the unstretched film, and the percentage obtained by dividing the standard deviation of the thickness by the average thickness was taken as the thickness unevenness value (%) of the unstretched film. Dispensing stability was evaluated as follows.

[0439] A: The thickness unevenness (%) of the unstretched film is 10 or less.

[0440] B: The thickness unevenness value (%) of the unstretched film is greater than 10 and 15 or less.

[0441] C: The thickness unevenness value (%) of the unstretched film is greater than 15 and 20 or less.

[0442] D: The thickness unevenness of the unstretched film (%) is greater than 20.

[0443] As the evaluation of discharge stability, A to C were preferred, with A being the most excellent.

[0444] N. Film Formability

[0445] The polyester film of the present invention was wound up to 1000 m at a winding speed of 20 m / min or higher. The film formability was evaluated as follows based on the number of film breaks that occurred while the film roll was being taken up.

[0446] A: The film was broken 2 times or less.

[0447] B: The film was broken 3 or more and 4 or less times.

[0448] C: The number of times the film was broken was 5 or more and 6 or less.

[0449] D: The film was broken 7 times or more.

[0450] As the evaluation of thin film forming properties, A to C were preferred, with A being the most excellent.

[0451] O. Evaluation of electrical properties and process suitability

[0452] (i) Electrical conductivity evaluation

[0453] The polyester film of the present invention was evaluated according to the above-mentioned "E. Volume Resistivity Measurement" and the evaluation was performed as follows.

[0454] AA: Volume resistivity is 1.0×10 0 Ωcm or more and less than 1.0×10 4 Ωcm.

[0455] A: Volume resistivity is 1.0×10 4 Ωcm or more and less than 1.0×10 6 Ωcm.

[0456] B: Volume resistivity is 1.0×10 6 Ωcm or more and less than 1.0×10 7 Ωcm.

[0457] C: Volume resistivity is 1.0×10 7 Ωcm or more and less than 1.0×10 8 Ωcm.

[0458] D: Volume resistivity is 1.0×10 8 Ωcm or more.

[0459] As for the conductivity evaluation, AA to C are preferred, and AA is the most excellent.

[0460] (ii) Evaluation of conductivity after stretching

[0461] The polyester film of the present invention is cut into 10 sheets of 10 cm x 10 cm. The two ends of the cut sample are clamped with two metal plates with rubber to fix the sample. At this time, the distance between the metal plates fixing the two ends, that is, the exposed part of the polyester film, is 50 mm. Then, using an Instron tensile testing machine (AMF / RTA-100 manufactured by Orientec), the metal plate fixing the cut sample is fixed to the chuck part of the device, and a tensile test is performed to deform the polyester film by 2%. Specifically, the initial sample length of the rubber-attached metal plate is set to 50 mm, and the tensile test is performed at a tensile speed of 300 mm / min until the sample length is extended by 1 mm. Then, the volume resistivity of the stretched part is measured in the same manner as in the above "E. Volume resistivity measurement". Using the obtained volume resistivity R1 (Ωcm) and the volume resistivity R0 (Ωcm) obtained in the above item (i), the following evaluation is performed using the increase rate of the volume resistivity obtained by the following formula (5).

[0462] Volume resistivity increase rate (%) = 100 × (R1 - R0) / R0 ... Formula (5)

[0463] A: The increase rate of volume resistivity is 30% or less.

[0464] B: The increase rate of volume resistivity exceeds 30% and is 50% or less.

[0465] C: The increase rate of volume resistivity exceeds 50% and is 100% or less.

[0466] D: The increase rate of volume resistivity exceeds 100%.

[0467] As the evaluation of conductivity after stretching, A to C are preferred, with A being the most excellent.

[0468] (iii) Evaluation of conductivity after bending

[0469] The polyester film of the present invention was cut into ten 10 cm x 10 cm sheets. The 10 cm x 10 cm sample was wrapped around a 3 cm diameter, 15 cm long SUS cylinder with a 300 g load applied from both ends. The wrapped sample was placed in an oven heated to 50°C for 1 hour for heat treatment.

[0470] After heat treatment, the sample was removed from the cylinder and the volume resistivity of the central portion of the sample was measured in the same manner as described in "E. Volume Resistivity Measurement" above. The following evaluation was performed using the volume resistivity R2 (Ωcm) obtained and the volume resistivity R0 (Ωcm) obtained in (i) above, along with the rate of increase in volume resistivity calculated using the following formula (6).

[0471] Volume resistivity increase rate (%) = 100 × (R2 - R0) / R0 ... Formula (6)

[0472] A: The increase rate of volume resistivity is 30% or less.

[0473] B: The increase rate of volume resistivity exceeds 30% and is 50% or less.

[0474] C: The increase rate of volume resistivity exceeds 50% and is 100% or less.

[0475] D: The increase rate of volume resistivity exceeds 100%.

[0476] As the evaluation of conductivity after bending, A to C are preferred, with A being the most excellent.

[0477] P. Bipolar Battery Evaluation

[0478] (i) Preparation of resin current collectors for bipolar batteries

[0479] A resin current collector for a bipolar battery is produced by vacuum vapor deposition on both surfaces of the polyester film of the present invention to produce a film having a copper layer provided on one surface and an aluminum layer provided on the opposite surface.

[0480] Specifically, a roll of the polyester film of the present invention is placed in a roll vacuum deposition apparatus (ULVAC EWC-060), and an aluminum ingot is heated by induction heating deposition using a carbon crucible, thereby forming an aluminum metal layer by vacuum deposition. The conveying speed and output conditions are adjusted during vacuum deposition to achieve a predetermined thickness for the aluminum metal layer. Next, the roll of polyester film with the aluminum metal layer provided on one side is again placed in a roll vacuum deposition apparatus (ULVAC EWC-060), and a copper ingot is heated by induction heating deposition using a carbon crucible on the surface of the polyester film opposite to the aluminum metal layer, thereby forming a copper metal layer by vacuum deposition. The conveying speed and output conditions are adjusted during vacuum deposition to achieve a predetermined thickness for the copper metal layer.

[0481] (ii) Positive electrode active material, negative electrode active material

[0482] Positive electrode active material slurry was prepared by mixing 85% by mass of LiMn2O4 as a positive electrode active material, 5% by mass of acetylene black as a conductive additive, 10% by mass of polyvinylidene fluoride (PVDF) as a binder, and appropriate amounts of N-methyl-2-pyrrolidone (NMP) as a slurry viscosity adjustment solvent.

[0483] Furthermore, as a positive electrode disposed at the end of a bipolar battery, the positive electrode active material slurry was applied onto a 30 μm thick aluminum foil and cured by thermal polymerization in the same manner to produce a terminal positive electrode having a positive electrode formed on aluminum.

[0484] 90 parts by mass of hard carbon as a negative electrode active material, 5 parts by mass of acetylene black as a conductive additive, 10 parts by mass of PVDF as a binder, and an appropriate amount of NMP as a slurry viscosity adjusting solvent were mixed to prepare a negative electrode active material slurry.

[0485] Furthermore, as a negative electrode to be disposed at the end of a bipolar battery, the negative electrode slurry was applied onto a 30 μm copper foil and cured by thermal polymerization in the same manner to produce a terminal negative electrode having a negative electrode formed on the copper foil.

[0486] (iii) Fabrication of battery evaluation unit

[0487] <Positive electrode-resin current collector assembly>

[0488] The positive electrode active material slurry was applied on the aluminum layer surface of the laminated polyester film having the metal layer using a doctor blade, and the coating of the positive electrode active material slurry was pressed to a current collector film thickness of 30 μm.

[0489] <Production of Electrolytic Layer>

[0490] PEO (polyethylene oxide) (64.5% by mass) as an ion conductive polymer and Li(C2F5SO2)2N (35.5% by mass) as a supporting salt were prepared, and acetonitrile was used as a viscosity adjusting solvent to prepare an electrolyte slurry.

[0491] The electrolyte slurry was injected between glass plates with a gap of 50 μm and dried to prepare an electrolyte layer of 40 μm.

[0492] <Fabrication of a Bipolar Battery Evaluation Cell>

[0493] The final positive electrode, negative electrode, final negative electrode, electrolyte layer, and positive electrode-current collector assembly were cut into 120 mm x 70 mm pieces. The final positive electrode, negative electrode, positive electrode-current collector assembly, and electrolyte layer were stacked twice in this order, and finally the final negative electrode was bonded to create a three-layer bipolar battery.

[0494] An Al sheet and a Ni sheet were welded to the terminal positive electrode and the terminal negative electrode, respectively, and the resulting battery was sealed in an aluminum laminate under high reduced pressure to complete a bipolar battery evaluation cell.

[0495] (iv) Measurement of current value during charge and discharge

[0496] The bipolar battery evaluation unit was charged and discharged to a voltage of 10 mV (Li + / Li), and measure the current value generated at this time.

[0497] (v) Current value stability

[0498] Ten bipolar battery evaluation cells were prepared by sampling from ten different locations of a laminated polyester film having metal layers on both sides according to the above-mentioned procedures (i) to (iii).

[0499] Next, charge and discharge operations were performed according to (iv) above, and the current flowing through each of the 10 bipolar battery evaluation cells was recorded. The average current value obtained was used to evaluate the current stability based on the change in current value relative to the average value during charge and discharge operations.

[0500] AA: The current value is not halved relative to the average value.

[0501] A: The current value is halved relative to the average value once or less.

[0502] B: The current value was halved relative to the average value 2 or more times and 3 or less times.

[0503] C: The current value was halved relative to the average value 4 or more times and 5 or less times.

[0504] D: The current value was halved relative to the average value six or more times, or the current value was zero one or more times.

[0505] As for current value stability, AA~C are good, among which AA is the best.

[0506] (vi) Battery characteristic deviation

[0507] The current values ​​during charge and discharge performed in (v) above were evaluated as follows, using the average value of 10 current values ​​and the difference between the maximum and minimum values ​​of the 10 current values ​​to determine the deviation as the battery characteristic deviation using the following formula (7).

[0508] (Battery characteristic deviation) = 100 × (maximum value - minimum value) / (average value) ... Formula (7)

[0509] AA: Battery characteristic variation is 8% or less.

[0510] A: The battery characteristic deviation is greater than 8% and less than 10%.

[0511] B: The battery characteristic deviation is greater than 10% and less than 20%.

[0512] C: The battery characteristic deviation is greater than 20% and less than 30%.

[0513] D: The battery characteristics deviation is greater than 30%.

[0514] As for the variation in battery characteristics, AA to C are good, with AA being the best.

[0515] (viii) Battery high temperature stability

[0516] Ten bipolar battery evaluation cells were prepared by sampling from 10 different locations of a laminated polyester film having metal layers on both sides according to the above-mentioned procedures (i) to (iii).

[0517] Next, charge and discharge were performed according to the procedure (iv) above, and the current flowing through each of the ten bipolar battery evaluation cells was recorded. The ten bipolar battery evaluation cells were then heated from 25°C to 70°C in a constant temperature oven with air circulation at a rate of 5°C / minute. Heating was continued for 30 minutes, and then charge and discharge were performed according to the procedure (iv) above, with the current flowing through each of the ten bipolar battery evaluation cells recorded.

[0518] The following evaluation was performed based on the reduction (%) of the current value before and after the heat treatment.

[0519] A: The reduction in current value after heat treatment is 20% or less.

[0520] B: The reduction in the current value after the heat treatment is more than 20% and less than 40%.

[0521] C: The reduction in the current value after the heat treatment is greater than 40% and less than 50%.

[0522] D: The reduction in current value after heat treatment is greater than 50%.

[0523] As for the high temperature stability of the battery, A~C are good, among which A is the best.

[0524] (ix) Battery heating deformation durability

[0525] Ten bipolar battery evaluation cells were prepared by sampling from ten different locations of a laminated polyester film having metal layers on both sides according to the above-mentioned procedures (i) to (iii).

[0526] Next, according to the heating test described in JIS 8715-2 (2019), ten fully charged bipolar battery evaluation cells were heated from 25°C to 85°C at a rate of 5°C / minute in a constant temperature chamber with air circulation. After being held at 85°C for 3 hours, the cells were removed from the constant temperature chamber and evaluated under the following conditions.

[0527] A: Less than 1 in 10 units caught fire or ruptured.

[0528] B: Two or more and three or less of ten cells caught fire or ruptured.

[0529] C: 4 or more and 5 or less of 10 cells caught fire or ruptured.

[0530] D: Six or more units out of ten caught fire or ruptured.

[0531] As for the battery heat deformation durability, A to C are good, among which A is the most excellent.

[0532] (x) Battery impact durability

[0533] Ten bipolar battery evaluation cells were prepared by sampling from ten different locations of a laminated polyester film having metal layers on both sides according to the above-mentioned procedures (i) to (iii).

[0534] Next, according to the impact test described in JIS 8715-2 (2019), ten bipolar battery evaluation cells were discharged to 50% of their rated capacity and placed on a flat concrete slab. A SUS316 round bar with a diameter of 15.8 mm, longer than the maximum dimension of the bipolar battery evaluation cell, was placed across the center of the cell. A 9.1 kg weight was dropped onto the bar from a height of 610 mm. The ten bipolar battery evaluation cells were evaluated under the following conditions.

[0535] A: Less than 1 in 10 units caught fire or ruptured.

[0536] B: Two or more and three or less of ten cells caught fire or ruptured.

[0537] C: 4 or more and 5 or less of 10 cells caught fire or ruptured.

[0538] D: Six or more units out of ten caught fire or ruptured.

[0539] As for battery impact durability, A to C are good, with A being the most excellent.

[0540] Example

[0541] Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited to these.

[0542] (Method for producing polyester resin)

[0543] [Manufacturing of Polyester-1]

[0544] 1.9 mol of ethylene glycol was added to 1 mol of dimethyl terephthalate, and 0.05 parts by mass of magnesium acetate tetrahydrate and 0.015 parts by mass of phosphoric acid were added to 100 parts by mass of dimethyl terephthalate, and heated transesterification was performed. Subsequently, 0.025 parts by mass of antimony trioxide was added, and the temperature was raised and polycondensation was performed under high reduced pressure to obtain polyethylene terephthalate (with a ΔHSP value of 5.7 MPa relative to the carbon material) that was substantially free of particles. 1 / 2 ) are particles of polyester-1. The melt-polymerized polyester-1 obtained has a glass transition temperature of 81°C, a melting point of 255°C, and an intrinsic viscosity of 0.70 dl / g.

[0545] [Production of Polyester-2]

[0546] 1.9 mol of 1,4-butanediol was added to 1 mol of a dicarboxylic acid component composed of 0.90 mol of dimethyl terephthalate (DMT) and 0.10 mol of dimethyl isophthalate. Furthermore, 0.05 parts by mass of magnesium acetate tetrahydrate and 0.015 parts by mass of phosphoric acid were added to 100 parts by mass of the dicarboxylic acid component, and heated transesterification was performed. Subsequently, 0.025 parts by mass of antimony trioxide was added, and the temperature was raised. Polycondensation was carried out under a highly reduced pressure to obtain polybutylene terephthalate copolymerized with 10 mol% of the isophthalic acid component, which was substantially free of particles (ΔHSP value with carbon material: 4.9 MPa). 1 / 2 ) are particles of polyester-2. The melt-polymerized polyester-2 obtained has a melting point of 208°C and an intrinsic viscosity of 0.80 dl / g.

[0547] [Production of Polyester-3]

[0548] 1.9 mol of cyclohexanedimethanol was added to 1 mol of a dicarboxylic acid component composed of 0.95 mol of dimethyl terephthalate (DMT) and 0.05 mol of dimethyl isophthalate. Furthermore, 0.05 mol of magnesium acetate tetrahydrate and 0.015 mol of phosphoric acid were added to 100 mol of the dicarboxylic acid component, and heated transesterification was performed. Subsequently, 0.025 mol of antimony trioxide was added, and the temperature was raised. Polycondensation was carried out under a highly reduced pressure to obtain polycyclohexanedimethanol terephthalate copolymerized with 5 mol% of the isophthalic acid component (ΔHSP value with carbon material: 4.8 MPa) that was substantially particle-free. 1 / 2 ) that is, polyester-3 particles. The resulting melt-polymerized polyester-3 had a glass transition temperature of 92°C, a melting point of 280°C, and an intrinsic viscosity of 0.95 dl / g.

[0549] [Manufacturing of Polyester-4]

[0550] By adjusting the polymerization time of the above-mentioned [Production of Polyester-3], a polycyclohexylene dimethylene terephthalate copolymerized with 5 mol% of an isophthalic acid component (ΔHSP value with carbon material: 4.8 MPa) was obtained. 1 / 2 ) that is, particles of polyester-4. The resulting melt-polymerized polyester-4 had a glass transition temperature of 88°C, a melting point of 280°C, and an intrinsic viscosity of 0.75 dl / g.

[0551] [Manufacturing of Polyester-5]

[0552] 1.9 mol of ethylene glycol was added to 1 mol of dimethyl 2,6-naphthalate, and 0.05 parts by mass of magnesium acetate tetrahydrate and 0.015 parts by mass of phosphoric acid were added to 100 parts by mass of dimethyl terephthalate, and heated transesterification was performed. 0.025 parts by mass of antimony trioxide was then added, and the temperature was raised and polycondensation was performed under high reduced pressure to obtain polyethylene naphthalate (with a ΔHSP value of 5.2 MPa) that was substantially free of particles. 1 / 2 ) are particles of polyester-5. Polyester-5 has a glass transition temperature of 118°C, a melting point of 265°C, and an intrinsic viscosity of 0.70 dl / g.

[0553] (Compounds having ether bonds in the main chain)

[0554] [Polyether compound-1]

[0555] Polyethylene glycol with a molecular weight of 4000 (ΔHSP value with carbon material: 2.6 MPa) 1 / 2 ) as the polyether compound-1.

[0556] [Polyether compound-2]

[0557] Using polybutylene terephthalate (PBT, with carbon material ΔHSP value: 4.9MPa 1 / 2 ) was replaced by polytetramethylene ether glycol (PTMG, ΔHSP value with carbon material: 3.8 MPa) 1 / 2 ) with a structure of a PBT / PTMG copolymer elastomer having a melting point of 180°C as the polyether compound-2 (with a ΔHSP value of the carbon material: 4.1 MPa 1 / 2 ).

[0558] (Method for producing carbon material masterbatch)

[0559] [Production of Carbon-1]

[0560] Polyester-2 and Ketjen black (aspect ratio of 1.2) were kneaded and extruded using a twin-screw kneader set to stepwise increase the temperature at 230-270°C to obtain a masterbatch containing 10% by mass of Ketjen black, namely Carbon-1.

[0561] [Production of Carbon-2]

[0562] The polyester-2 and carbon nanotubes (aspect ratio of 250) were kneaded and extruded using a biaxial kneader set to gradually increase the temperature at 230-270°C to obtain master batches of carbon-2 containing 10% by mass of carbon nanotubes.

[0563] [Production of Carbon-3]

[0564] The polyester-1 and Ketjen black (aspect ratio of 1.2) were kneaded and extruded using a twin-screw kneader set to stepwise increase the temperature at 270-285°C to obtain a masterbatch containing 50% by mass of Ketjen black, namely Carbon-3.

[0565] [Production of Carbon-4]

[0566] The polyester-2, carbon nanotubes (aspect ratio of 250), and polyether compound-1 were mixed and extruded using a twin-screw kneader set to gradually increase the temperature between 230°C and 270°C to obtain a masterbatch, carbon-4, containing 10% by mass of carbon nanotubes and 1.0% by mass of polyether compound-1.

[0567] [Manufacturing of Carbon-5]

[0568] The polyester-3 and carbon nanotubes (aspect ratio of 250) were kneaded and extruded using a biaxial kneader set to stepwise increase the temperature at 230-270°C to obtain master batches of carbon-5 containing 10% by mass of carbon nanotubes.

[0569] [Production of Carbon-6]

[0570] The polyester-2, carbon nanotubes (aspect ratio of 250), and polyether compound-1 were mixed and extruded using a twin-screw kneader set to gradually increase the temperature between 230°C and 270°C to obtain a masterbatch of carbon-6 containing 10% by mass of carbon nanotubes and 2.0% by mass of polyether compound-1.

[0571] [Production of Carbon-7]

[0572] The polyester-5 and carbon nanotubes (aspect ratio of 250) were kneaded and extruded using a biaxial kneader set to stepwise increase the temperature at 230-270°C to obtain master batches of carbon-7 containing 10% by mass of carbon nanotubes.

[0573] (Example 1)

[0574] Polyester-1, polyester-2, and carbon-1 were dried under reduced pressure at 180°C for 2 hours and 30 minutes, respectively, at 150°C. The resins were then mixed to the final ratios shown in the table. The mixtures were then fed into an extruder for melt extrusion. After filtration, the mixtures were electrostatically cast through a T-die onto a cooled casting drum maintained at 50°C and cooled to solidify. The resulting polyester films had a thickness of 300 μm as shown in the table. The properties of the resulting films are shown in the table.

[0575] Metal layers M and M' were deposited on both sides of the resulting polyester film by vacuum deposition, with the metal layer thicknesses as listed in the table, to produce a laminated polyester film with metal layers. By adjusting the metal types as listed in the table, a resin current collector for a bipolar battery was produced. As described in the "Bipolar Battery Evaluation" section above, the laminated polyester film with metal layers was assembled as a resin current collector into a bipolar battery evaluation cell, and bipolar battery evaluation was performed.

[0576] (Examples 2 to 4)

[0577] A polyester film was obtained in the same manner as in Example 1, except that the type and concentration of the carbon material and the concentration of polyester-2 were changed as described in the table. In Example 3, carbon-2 was used as the carbon material masterbatch for carbon nanotubes. The evaluation results are shown in the table.

[0578] (Example 5)

[0579] A polyester film was obtained in the same manner as in Example 1 except that Carbon-3 was used as the masterbatch and Polyester-2 was not contained as the low-melting-point polyester component as described in the table. The evaluation results are shown in the table.

[0580] (Example 6)

[0581] A polyester film was produced in the same manner as in Example 1, except that the extruder discharge rate was adjusted and biaxial stretching was performed according to the stretching conditions described in the table. Specifically, the film was first guided in the longitudinal direction onto a set of stretching rolls heated to 60°C to 120°C and stretched to a ratio of 3.0. The uniaxially stretched film was then introduced into a tenter, preheated to 90°C, stretched to a ratio of 3.5 in the width direction at a temperature of 100°C to 130°C, heat treated at 230°C while maintaining a fixed length, and relaxed by 4% in the width direction to produce a biaxially oriented polyester film having a thickness of 3 μm. The evaluation results are shown in the table.

[0582] (Examples 7 and 15)

[0583] A polyester film was produced in the same manner as in Example 1, except that the extruder discharge rate was adjusted and a P2 layer having the composition and configuration described in the table was laminated in addition to the P1 layer. Polyester-3 was dried under reduced pressure at 180°C for 2.5 hours before use. Carbon-2 was used for the P1 layer, and Carbon-5 was used for the P2 layer. The evaluation results are shown in the table.

[0584] (Examples 8-10)

[0585] A polyester film having a thickness of 50 μm was obtained in the same manner as in Example 6, except that the discharge rate from the extruder was adjusted, the type and concentration of the carbon material and the concentration of polyester-2 were changed as indicated in the table, and the stretch ratio was changed as indicated in the table. Carbon-1 and Carbon-2 were used. The evaluation results are shown in the table.

[0586] (Example 11)

[0587] A polyester film having a thickness of 50 μm was obtained in the same manner as in Example 6 except that the discharge rate from the extruder was adjusted, Carbon-1 was used as the carbon material masterbatch, Carbon-4 was used as the masterbatch containing carbon nanotubes and polyether compound-1 as a dispersant, the type and concentration of the carbon material contained, and the concentration of Polyester-2 were varied as described in the table, and the stretch ratio was varied as described in the table. The evaluation results are shown in the table.

[0588] (Examples 12 to 14)

[0589] In Examples 12 and 14, polyester films with a thickness of 300 μm were produced in the same manner as in Example 1, except that the type and concentration of the carbon material, and the concentrations of polyester-1, polyester-2, and polyester-4 were changed as described in the table. Carbon-1 and Carbon-2 were used. In Example 13, the type and concentration of the carbon material, and the content of polyether compound-2 were adjusted to the concentrations described in the table. Polyester-4, polyester-2, carbon material masterbatches (Carbon-1 and Carbon-2), and polyether compound-2 were mixed and fed to the extruder. A polyester film with a thickness of 300 μm was produced in the same manner as in Example 1, except that the type and concentration of the carbon material, and the content of polyether compound-2 were adjusted to the concentrations described in the table. The evaluation results are shown in the table.

[0590] (Example 16)

[0591] In Example 16, the extruder discharge rate was adjusted, a P2 layer having the composition and structure described in the table was laminated in addition to the P1 layer, and biaxial stretching was performed according to the stretching conditions described in the table. A polyester film having a thickness of 35 μm after biaxial stretching was obtained in the same manner as in Example 6. Carbon-1 and Carbon-6 were used to form the P1 layer, and Carbon-5 was used to form the P2 layer. The evaluation results are shown in the table.

[0592] (Examples 17 and 18)

[0593] In Examples 17 and 18, the main resin for the P2 layer was polyester-5, which contains a dicarboxylic acid component with 12 carbon atoms and has a lower ΔHSP value than polyester-1 and a higher ΔHSP value than polyester-4. Example 17 employed the same two-layer structure of P1 layer / P2 layer as in Example 16, while Example 18 employed a three-layer structure of P2 layer / P1 layer / P2 layer. Biaxially stretched polyester films with a thickness of 35 μm were obtained in the same manner as in Example 16. Carbon-1 and Carbon-6 were used for the P1 layer, and Carbon-7 was used for the P2 layer. The evaluation results are shown in the table.

[0594] (Comparative Examples 1 and 2)

[0595] A polyester film was obtained in the same manner as in Example 1, except that the type and concentration of the carbon material and the concentration of polyester-2 were changed as described in the table. The evaluation results are shown in the table. In Comparative Example 1, Carbon-1 was used, and in Comparative Example 2, Carbon-3 was used.

[0596] (Comparative Example 3)

[0597] The extruder discharge rate was adjusted. Furthermore, the type and concentration of the carbon material, as well as the concentrations of polyester-2 and polyether compound-1, were varied as described in the table. The raw materials for the carbon material-containing P1 layer and the carbon material-free P2 layer were combined in a 249-layer multi-manifold feedblock and alternately laminated at a stacking ratio of 1.0. The resulting melt-alternating laminate was then wound onto a cooled casting drum maintained at 50°C using an electrostatic casting method through a T-die and cooled to solidify, producing the 800μm-thick laminated polyester film described in the table. Carbon-1, 2, and 5 were used in the P1 layer. The evaluation results are shown in the table.

[0598] Table 1

[0599]

[0600] Table 2

[0601]

[0602] Table 3

[0603]

[0604] Table 4-1

[0605]

[0606] Table 4-2

[0607]

[0608] Table 5-1

[0609]

[0610] Table 5-2

[0611]

[0612] Table 6-1

[0613]

[0614] Table 6-2

[0615]

[0616] Table 7-1

[0617]

[0618] Table 7-2

[0619]

[0620] Table 8

[0621]

[0622] Table 9

[0623]

Claims

1. A polyester film that satisfies the following (1) to (3), (1) Volume resistivity at 23°C and 65% RH is 1.0×10 0 Ωcm or more and less than 1.0×10 8 Ωcm, (2) The film thickness is 1 μm or more and less than 500 μm, (3) A polyester resin layer (P1 layer) containing 1.0% by mass or more and 30% by mass or less of conductive particles, wherein the conductive particles are carbon materials.

2. A polyester film that satisfies the following (1') to (3'), (1') The film thickness is 1 μm or more and less than 500 μm, (2′) a polyester resin layer containing 1.0% by mass or more and 30% by mass or less of conductive particles, namely, a P1 layer, (3′) The P1 layer contains conductive particles C1′ having an aspect ratio of 1 or greater and less than 5, and conductive particles C2′ having an aspect ratio of 5 or greater.

3. The polyester film according to claim 2, wherein the P1 layer satisfies the following (4) to (6): (4) The conductive particles contained in the P1 layer are carbon materials, (5) The P1 layer contains 0.01% by mass or more and 10% by mass or less of a compound having an ether bond in its main chain, (6) The P1 layer contains at least two or more polyester resins having different melting points.

4. The polyester film according to claim 3, which satisfies the following (7), (7) The P1 layer is the outermost layer of at least one side of the polyester film, and the P1 layer is composed of a layer having resin α or resin β as a main component, wherein the resin α is a polyester resin containing a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms, and the resin β is a polyester resin containing a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms.

5. The polyester film according to claim 1 or 2, The conductive particles are carbon materials, and the volume-based average dispersion diameter of the carbon materials contained in the polyester film is 0.15 μm or more and 0.90 μm or less, and the number of dispersed particles is 1.5 particles / μm. 2 More than 5.0 / μm 2 the following.

6. The polyester film according to claim 1 or 2, The conductive particles are a carbon material, and contain 80% by mass or more of one or more selected from Ketjen black, carbon nanotubes, and acetylene black in total based on 100% by mass of the carbon material.

7. The polyester film according to claim 1 or 2, The P1 layer contains at least two types of conductive particles, namely, conductive particles C1' having an aspect ratio of 1 or greater and less than 5, and conductive particles C2' having an aspect ratio of 5 or greater, and a ratio of an area SC1' occupied by the conductive particles C1' in the P1 layer to an area SC2' occupied by the conductive particles C2', calculated using the following method, is 0.5 times or greater and 5 times or less. Method for measuring the area occupied by each conductive particle: The following analysis was performed on a cross-sectional image with a size of 18.5 μm in the vertical direction and 25 μm in the horizontal direction, obtained at a magnification of 5000 times using a scanning electron microscope, using image analysis software manufactured by Planetron Co., Ltd. and registered trademark Image-Pro Plus Version 4.0 for "Windows". The scanning electron microscope was a JSM-6700 manufactured by JEOL Ltd. (i) Image analysis conditions After reading the cross-sectional image using the software, perform 8-bit grayscale processing by executing the "Grayscale 8" command under the "Conversion" menu. Then, set the horizontal width of the read image to 25 μm using the "Spatial Correction" command under the "Correction" menu. Then, perform binarization processing using the "Binarization" command under the "Processing" menu. Binarization conditions ・Select "3×3" ・Threshold setting: Use the value obtained by clicking the auto-detect button located on the right side of the numeric input field once. ・Preview conditions: The base part is shown in white and the detection particles are shown in black After binarization, open the "Count / Size" command screen under the "Measurement" menu, set the following particle detection and analysis conditions, and analyze the detected particles by executing "Count". Particle detection conditions ・Brightness range selection: Select "Automatically extract dark objects" ・Select "Measurement object" Object extraction option conditions ・4 links / 8 links: Select 4 links ・Only "Preselection" and "Hole Filling" are selected ・Smoothing: 0 ・Exclude borders: Select "All borders" Particle analysis conditions Based on the image obtained, use the "Count / Size" command to calculate the aspect ratio (Aspect value) and area (Area value) of each conductive particle in the image. For 5 different fields of view, the obtained aspect ratio is used as the horizontal axis, and intervals are set every 0.5 in the interval of 1 to 10, and every 10 when the aspect ratio is above 10, to make a number histogram. In the number histogram, when there is a local maximum value in the area where the aspect ratio is above 1 and less than 5, the minimum value of the interval showing the local maximum value is used as the aspect ratio of the conductive particle, i.e., the conductive particle C1', which exists in the area where the aspect ratio is above 1 and less than 5. For example, when the local maximum value is in the interval of 2 to 2.5, 2 is used as the local maximum value. When there are multiple local maximum peaks in the area where the aspect ratio is above 1 and less than 5, the weighted average value obtained by using their vertical axis values ​​is used as the aspect ratio of the conductive particle, i.e., the conductive particle C1', which exists in the area where the aspect ratio is above 1 and less than 5. Similarly, when a maximum value exists in a region with an aspect ratio of 5 or more, the maximum value is used as the aspect ratio of the conductive particle C2' existing in the region with an aspect ratio of 5 or more. When multiple maximum peaks exist in a region with an aspect ratio of 5 or more, the weighted average value obtained using their vertical axis values ​​is used as the aspect ratio of the conductive particle C2' existing in the region with an aspect ratio of 5 or more. For each of the five different fields of view, the aspect ratio of the conductive particles C1' present in the region with an aspect ratio of 1 or greater and less than 5, and the aspect ratio of the conductive particles C2' present in the region with an aspect ratio of 5 or greater, was calculated. The average value of the five fields of view in each region was used as the aspect ratio of the conductive particles C1' to the conductive particles C2' in the polyester film. The total area SC1' of the conductive particles, i.e., the conductive particles C1', existing in the region with an aspect ratio greater than 1 and less than 5 as confirmed by the number histogram is calculated, and then the total area SC2' of the conductive particles, i.e., the conductive particles C2', existing in the region with an aspect ratio greater than 5 is calculated. The value obtained by dividing the SC1' by the SC2' is regarded as the ratio of the area SC1' occupied by the conductive particles C1' in the P1 layer of the sample to the area SC2' occupied by the conductive particles C2'.

8. The polyester film according to claim 1 or 2, The P1 layer contains at least two carbon materials, a carbon material C1 having an aspect ratio of 1 or greater and less than 5, and a carbon material C2 having an aspect ratio of 5 or greater, wherein a ratio of an area SC1 occupied by the carbon material C1 in the P1 layer to an area SC2 occupied by the carbon material C2, calculated using the following method, is 0.5 times or greater and 5 times or less. Method for determining the area occupied by each carbon material: The following analysis was performed on a cross-sectional image with a size of 18.5 μm in the vertical direction and 25 μm in the horizontal direction, obtained at a magnification of 5000 times using a scanning electron microscope, using image analysis software manufactured by Planetron Co., Ltd. and registered trademark Image-Pro Plus Version 4.0 for "Windows". The scanning electron microscope was a JSM-6700 manufactured by JEOL Ltd. (i) Image analysis conditions After reading the cross-sectional image using the software, perform 8-bit grayscale processing by executing the "Grayscale 8" command under the "Conversion" menu. Then, set the horizontal width of the read image to 25 μm using the "Spatial Correction" command under the "Correction" menu. Then, perform binarization processing using the "Binarization" command under the "Processing" menu. Binarization conditions ・Select "3×3" ・Threshold setting: Use the value obtained by clicking the auto-detect button located on the right side of the numeric input field once. ・Preview conditions: The base part is shown in white and the detection particles are shown in black After binarization, open the "Count / Size" command screen under the "Measurement" menu, set the following particle detection and analysis conditions, and analyze the detected particles by executing "Count". Particle detection conditions ・Brightness range selection: Select "Automatically extract dark objects" ・Select "Measurement object" Object extraction option conditions ・4 links / 8 links: Select 4 links ・Only "Preselection" and "Hole Filling" are selected ・Smoothing: 0 ・Exclude borders: Select "All borders" Particle analysis conditions Based on the obtained image, use the "Count / Size" command to calculate the aspect ratio (Aspect value) and area (Area value) in the screen to calculate the aspect ratio and area of ​​each carbon material in the obtained image. For 5 different fields of view, with the obtained aspect ratio as the horizontal axis, intervals are set every 0.5 in the interval of 1 or more and 10 or every 10 when the aspect ratio is greater than 10, and a number histogram is produced. In the number histogram, when a maximum value exists in the region where the aspect ratio is greater than 1 and less than 5, the minimum value of the interval showing the maximum value is used as the aspect ratio of the carbon material, i.e., carbon material C1, existing in the region where the aspect ratio is greater than 1 and less than 5. For example, when a maximum value exists in the interval of 2 or more and 2.5 or less, 2 is used as the maximum value. When multiple maximum peaks exist in the region where the aspect ratio is greater than 1 and less than 5, the weighted average value obtained using their vertical axis values ​​is used as the aspect ratio of the carbon material, i.e., carbon material C1, existing in the region where the aspect ratio is greater than 1 and less than 5. Similarly, when a maximum value exists in a region with an aspect ratio of 5 or more, the maximum value is used as the aspect ratio of the carbon material present in the region with an aspect ratio of 5 or more, that is, the carbon material C2. When multiple maximum peaks exist in a region with an aspect ratio of 5 or more, the weighted average value obtained using their vertical axis values ​​is used as the aspect ratio of the carbon material present in the region with an aspect ratio of 5 or more, that is, the carbon material C2. For each of the five different viewing fields, the aspect ratios of the carbon material C1 present in the region with an aspect ratio of 1 or greater and less than 5, and the carbon material C2 present in the region with an aspect ratio of 5 or greater, were calculated. The average value of the five viewing fields in each region was taken as the aspect ratio of the carbon material C1 to the carbon material C2 in the polyester film. The total area SC1 of the carbon material present in the region with an aspect ratio greater than 1 and less than 5 confirmed by the number histogram, i.e., the carbon material C1, is calculated, and then the total area SC2 of the carbon material present in the region with an aspect ratio greater than 5, i.e., the carbon material C2, is calculated. The value obtained by dividing the SC1 by the SC2 is regarded as the ratio of the area SC1 occupied by the carbon material C1 in the P1 layer of the sample to the area SC2 occupied by the carbon material C2.

9. The polyester film according to claim 1 or 2, The P1 layer contains at least two polyester resins having different melting points.

10. The polyester film according to claim 1 or 2, The P1 layer contains resin α or resin β as a main component. Resin α is a polyester resin containing a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms. Resin β is a polyester resin containing a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms.

11. The polyester film according to claim 1 or 2, The conductive particles are carbon materials, and a polyester resin layer with a lower carbon material content than the P1 layer is provided on at least one side of the P1 layer, that is, a P2 layer as the outermost layer of the polyester film. When the carbon material content in the P1 layer is set to M P1 The unit is mass %, and the content of the carbon material in the P2 layer is set to M P2 When the unit is mass%, M P1 -M P2 ≥0.

1.

12. The polyester film according to claim 11, The P2 layer has resin α or resin β as a main component, the resin α is a polyester resin containing a dicarboxylic acid component and a diol component with a carbon number of 3 or more and 16 or less, and the resin β is a polyester resin containing a diol component and a dicarboxylic acid component with a carbon number of 9 or more and 16 or less.

13. The polyester film according to claim 1 or 2, The P1 layer contains 0.01% by mass or more and 10% by mass or less of a compound having an ether bond in its main chain. The polyester film according to claim 1 or 2, which is uniaxially oriented or biaxially oriented.

15. The polyester film according to claim 1 or 2, The breaking strength in at least one of the longitudinal direction and the width direction within the film plane is 60 MPa or more and 300 MPa or less.

16. A laminated polyester film comprising at least a layer composed of a metal and / or a metal-based compound, the polyester film according to claim 1, and a layer composed of a metal and / or a metal-based compound in this order.

17. A laminated polyester film, satisfying the following (8), (8) A laminated polyester film comprising at least a layer composed of a metal and / or a metal compound, the polyester film according to claim 4, and a layer composed of a metal and / or a metal compound, wherein the outermost layers on both sides of the polyester film are the P1 layers, and layers composed of a metal and / or a metal compound are provided on both side surfaces of the P1 layer.

18. The laminated polyester film according to claim 16 or 17, The layer composed of the metal and / or the metal-based compound on one surface contains the aluminum element, and the layer composed of the metal and / or the metal-based compound on the opposite surface contains the copper element.

19. The laminated polyester film according to claim 18, The layer composed of metal and / or metal-based compound containing copper element is in contact with a layer mainly composed of resin α or resin β, wherein the resin α is a polyester resin containing a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms, and the resin β is a polyester resin containing a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms.

20. A laminated polyester film, The polyester film according to claim 1 or 2 has a layer composed of metal and / or metal compound on both surfaces, and the adhesion between the polyester film surface and the layer composed of metal and / or metal compound is 2N / 15mm or more on both surfaces.

21. A laminated polyester film, The polyester film according to claim 1 or 2 has a layer composed of a metal and / or a metal compound on both surfaces thereof, and the volume resistivity in the through-direction of the laminated polyester film is 1.0×10 0 Ωcm or more and 1.0×10 7 Ωcm or less.

22. A resin current collector composed of the polyester film according to claim 1 or 2.

23. A resin current collector for a bipolar battery, comprising the polyester film according to claim 1 or 2.

24. A bipolar battery electrode comprising a bipolar battery resin current collector comprising the polyester film according to claim 1 or 2, The resin current collector for a bipolar battery has a surface layer composed mainly of resin α or resin β as at least one surface layer of a polyester film, wherein resin α is a polyester resin comprising a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms, and resin β is a polyester resin comprising a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms. The bipolar battery electrode includes a negative electrode active material layer on the surface layer side of the bipolar battery resin current collector and a positive electrode active material layer on the side opposite to the surface layer. 25 . An electric storage device comprising the resin current collector for a bipolar battery according to claim 23 .

26. An electric storage device comprising at least two bipolar battery electrodes according to claim 24, The energy storage element has a structure in which at least the bipolar battery resin collector, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer, and the bipolar battery resin collector are repeatedly stacked in this order. The resin current collector for a bipolar battery has a surface layer composed mainly of resin α or resin β as at least one surface layer of a polyester film, wherein resin α is a polyester resin comprising a dicarboxylic acid component and a diol component having 3 to 16 carbon atoms, and resin β is a polyester resin comprising a diol component and a dicarboxylic acid component having 9 to 16 carbon atoms. A negative electrode active material layer is provided on the surface layer side. 27 . A secondary battery comprising the electric storage element according to claim 25 .

28. An electric vehicle equipped with the secondary battery according to claim 27.

29. An electric flying object equipped with the secondary battery according to claim 27.

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